Semiconductor device

Abstract

Provided is a novel semiconductor device. Provided is a semiconductor device comprising a first transistor, a second transistor, and a third transistor. The first transistor includes a first gate, a second gate opposing the first gate across a channel formation region of the first transistor, a first source, and a first drain. The second transistor includes a third gate, a second source, and a second drain. The third transistor includes a fourth gate, a third source, and a third drain. One of the first source and the first drain is electrically connected to one of the second source and the second drain, and the other one of the first source and the first drain is electrically connected to one of the third source and the third drain. The first gate is electrically connected to the third gate and the second gate is electrically connected to the other one of the first source and the first drain.

Description

Semiconductor Devices

[0001] One embodiment of the present invention relates to a semiconductor device.

[0002] Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, a driving method, or a manufacturing method. Alternatively, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. More specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification and the like include semiconductor devices, display devices, light-emitting devices, power storage devices, optical devices, imaging devices, lighting devices, arithmetic units, control devices, memory devices, input devices, output devices, input / output devices, signal processing devices, arithmetic processing devices, electronic computers, electronic devices, and driving methods thereof or manufacturing methods thereof.

[0003] In recent years, display devices have been used in a variety of applications. Examples of applications of large display devices include home televisions, digital signage, and public information displays (PIDs). Examples of applications of small display devices include mobile information terminals such as smartphones and tablet devices, as well as wearable devices such as virtual reality (VR) devices and augmented reality (AR) devices. By providing display devices with functions other than display, the display devices are being given enhanced functionality and added value. For example, display devices that function as touch panels have been developed by providing touch sensors to the display devices.

[0004] Furthermore, circuits for driving display devices have been developed, and Patent Document 1 discloses an example of a drive circuit that can be used for a display device.

[0005] JP 2008-122939 A

[0006] An active matrix display device has a drive circuit (sometimes called a gate driver) that selects pixels to which data is written, and a drive circuit (sometimes called a source driver) that supplies data to the selected pixels.

[0007] In order to achieve higher brightness, higher resolution, and larger screens in display devices, the operating voltages of pixel circuits, drive circuits, etc. may be increased. This may increase the voltage between the drain and source of transistors in the pixel circuits, drive circuits, etc. This increases the risk of transistor characteristics deteriorating due to the high voltage between the drain and source. For example, hot carrier degradation is known to occur when hot carriers accelerated by a strong electric field near the drain are injected and accumulated in the gate insulating film, causing changes in transistor characteristics relative to the voltage between the gate and source.

[0008] Therefore, it is desired to devise a method for suppressing the deterioration of transistor characteristics in transistors used in pixel circuits, driver circuits, and the like.

[0009] Furthermore, transistors suitable for high-speed operation must be used to form pixel circuits, driver circuits, etc. In general, it is preferable to use transistors with a large on-state current in order to improve charge / discharge characteristics.

[0010] Furthermore, by reducing the area occupied by a pixel circuit, a driver circuit, etc., it is possible to achieve higher definition and a narrower frame of a display device, etc. Therefore, it is preferable to use a transistor that occupies a small area.

[0011] One way to increase the on-state current of a transistor while reducing its footprint is to shorten its channel length. However, shortening the channel length of a transistor makes it more susceptible to several adverse effects collectively known as short channel effects. For example, the hot carrier degradation mentioned above becomes more pronounced.

[0012] An object of one embodiment of the present invention is to provide a highly reliable semiconductor device, a driver circuit including the semiconductor device, or a display device including the semiconductor device. Another object is to provide a semiconductor device in which deterioration of transistor characteristics can be suppressed, a driver circuit including the semiconductor device, or a display device including the semiconductor device. Another object is to provide a semiconductor device in which hot carrier deterioration can be suppressed, a driver circuit including the semiconductor device, or a display device including the semiconductor device. Another object is to provide a semiconductor device in which the display quality of a display device can be improved, or a driver circuit including the semiconductor device. Another object is to provide a semiconductor device in which the operation speed of a driver circuit can be increased, or a display device including the semiconductor device. Another object is to provide a semiconductor device with reduced power consumption, a driver circuit including the semiconductor device, or a display device including the semiconductor device. Another object is to provide a miniaturized semiconductor device, a driver circuit including the semiconductor device, or a display device including the semiconductor device. Another object is to provide a novel semiconductor device, a driver circuit including the semiconductor device, or a display device including the semiconductor device.

[0013] Note that the above-mentioned problem does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of the above-mentioned problems. Note that problems other than the above-mentioned problem will become apparent from the description of this specification, drawings, claims, etc., and it is possible to extract problems other than the above-mentioned problem from the description of this specification, drawings, claims, etc.

[0014] (1) One aspect of the present invention is a semiconductor device including a first transistor, a second transistor, and a third transistor. The first transistor has a first gate, a second gate facing the first gate across a channel formation region of the first transistor, a first source, and a first drain. The second transistor has a third gate, a second source, and a second drain. The third transistor has a fourth gate, a third source, and a third drain. One of the first source or the first drain is electrically connected to one of the second source or the second drain, and the other of the first source or the first drain is electrically connected to one of the third source or the third drain. The first gate is electrically connected to the third gate, and the second gate is electrically connected to the other of the first source or the first drain.

[0015] (2) In the above (1), the second transistor may have a fifth gate facing the third gate across a channel formation region of the second transistor, and the fifth gate may be electrically connected to the third gate.

[0016] (3) In the above (1) or (2), a first potential may be applied to the other of the second source or the second drain, a second potential higher than the first potential may be applied to the other of the third source or the third drain, a first pulse signal may be applied to the first gate and the third gate, and a second pulse signal having a timing different from that of the first pulse signal may be applied to the fourth gate.

[0017] (4) In the above (1) or (2), the thickness of the gate insulating film of the second gate may be thicker than the thickness of the gate insulating film of the first gate.

[0018] (5) In the above (1) or (2), the channel length of each of the first transistor and the second transistor may be shorter than the channel length of the third transistor.

[0019] (6) In the above (1) or (2), a channel formation region of the first transistor may include an oxide semiconductor.

[0020] (7) One aspect of the present invention is a semiconductor device including a first transistor, a second transistor, and a third transistor. The first transistor has a first gate, a second gate facing the first gate across a channel formation region of the first transistor, a first source, and a first drain. The second transistor has a third gate, a second source, and a second drain. The third transistor has a fourth gate, a third source, and a third drain. One of the first source or the first drain is electrically connected to one of the second source or the second drain, and the other of the second source or the second drain is electrically connected to one of the third source or the third drain. The first gate is electrically connected to the third gate, and the second gate is electrically connected to the other of the first source or the first drain.

[0021] (8) In the above (7), the second transistor may have a fifth gate facing the third gate across a channel formation region of the second transistor, and the fifth gate may be electrically connected to the third gate.

[0022] (9) In addition, in the above (7) or (8), a first potential may be applied to the other of the third source or the third drain, a second potential higher than the first potential may be applied to the other of the first source or the first drain, a first pulse signal may be applied to the first gate and the third gate, and a second pulse signal having a timing different from that of the first pulse signal may be applied to the fourth gate.

[0023] (10) In the above (7) or (8), the thickness of the gate insulating film of the second gate may be thicker than the thickness of the gate insulating film of the first gate.

[0024] (11) In the above (7) or (8), the channel length of each of the first transistor and the second transistor may be shorter than the channel length of the third transistor.

[0025] (12) In the above (7) or (8), a channel formation region of the first transistor may include an oxide semiconductor.

[0026] One embodiment of the present invention can provide a highly reliable semiconductor device, a driver circuit including the semiconductor device, or a display device including the semiconductor device. Alternatively, a semiconductor device in which deterioration of transistor characteristics can be suppressed, a driver circuit including the semiconductor device, or a display device including the semiconductor device can be provided. Alternatively, a semiconductor device in which hot carrier deterioration can be suppressed, a driver circuit including the semiconductor device, or a display device including the semiconductor device can be provided. Alternatively, a semiconductor device in which the display quality of a display device can be improved, or a driver circuit including the semiconductor device can be provided. Alternatively, a semiconductor device in which the operation speed of a driver circuit can be increased, or a display device including the semiconductor device can be provided. Alternatively, a semiconductor device with reduced power consumption, a driver circuit including the semiconductor device, or a display device including the semiconductor device can be provided. Alternatively, a miniaturized semiconductor device, a driver circuit including the semiconductor device, or a display device including the semiconductor device can be provided. Alternatively, a novel semiconductor device, a driver circuit including the semiconductor device, or a display device including the semiconductor device can be provided.

[0027] Note that the above effects do not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of the above effects. Note that effects other than the above effects will become apparent from the description in this specification, drawings, claims, etc., and it is possible to extract effects other than the above effects from the description in this specification, drawings, claims, etc.

[0028] FIG. 1A is a circuit diagram showing a configuration example of a semiconductor device. FIG. 1B is a timing chart showing an operation example of the semiconductor device. FIGS. 2A to 2D are circuit diagrams showing an operation example of the semiconductor device. FIGS. 3A to 3D are circuit diagrams showing a configuration example of a semiconductor device. FIG. 4A is a circuit diagram showing an example of a semiconductor device. FIG. 4B is a timing chart showing an operation example of the semiconductor device. FIGS. 5A to 5D are circuit diagrams showing an operation example of the semiconductor device. FIGS. 6A to 6D are circuit diagrams showing an example of a semiconductor device. FIG. 7A is a circuit diagram showing an example of a semiconductor device. FIG. 7B is a timing chart showing an operation example of the semiconductor device. FIGS. 8A and 8B are circuit diagrams showing an example of a semiconductor device. FIGS. 9A and 9B are circuit diagrams showing an example of a semiconductor device. FIGS. 10A and 10B are circuit diagrams showing an example of a semiconductor device. FIG. 11A is a top view showing an example of a semiconductor device. FIGS. 11B and 11C are cross-sectional views showing an example of a semiconductor device. FIG. 12A is a top view showing an example of a semiconductor device. FIG. 12B is a cross-sectional view showing an example of a semiconductor device. FIG. 13A is a top view showing a configuration example of a semiconductor device. FIGS. 13B and 13C are cross-sectional views showing a configuration example of a semiconductor device. FIG. 14 is a cross-sectional view showing a configuration example of a semiconductor device. FIG. 15 is a cross-sectional view showing a configuration example of a semiconductor device. FIG. 16A is a top view showing a configuration example of a semiconductor device. FIG. 16B is a cross-sectional view showing a configuration example of a semiconductor device. FIGS. 17A and 17B are top views showing a configuration example of a semiconductor device. FIG. 18A is a top view showing a configuration example of a semiconductor device. FIG. 18B is a cross-sectional view showing a configuration example of a semiconductor device. FIG. 19A is a top view showing a configuration example of a semiconductor device. FIG. 19B is a cross-sectional view showing a configuration example of a semiconductor device. FIG. 20A is a top view showing a configuration example of a semiconductor device. FIG. 20B is a cross-sectional view showing a configuration example of a semiconductor device. FIG. 21A is a top view showing a configuration example of a semiconductor device. FIG. 21B is a cross-sectional view showing a configuration example of a semiconductor device. FIG. 22A is a perspective view showing a configuration example of a display device. FIGS. 22B to 22F are top views showing examples of pixel arrays. 23A to 23E are block diagrams showing configuration examples of the display device.24A to 24C and 24E are circuit diagrams showing a configuration example of a semiconductor device. FIG. 24D is a timing chart showing an operation example of the semiconductor device. FIG. 25 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 26 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 27 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 28 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 29 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 30 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 31 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 32 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 33 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 34 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 35 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 36 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 37 is a circuit diagram showing a configuration example of a semiconductor device. FIG. 38 is a cross-sectional view showing a configuration example of a display device. FIGS. 39A and 39B are cross-sectional views showing a configuration example of a display device. FIGS. 40A and 40B are cross-sectional views showing a configuration example of a display device. 41A to 41D are diagrams showing an example of an electronic device. FIGS. 42A to 42F are diagrams showing an example of an electronic device. FIGS. 43A to 43G are diagrams showing an example of an electronic device. FIGS. 44A and 44B are diagrams showing Id-Vg characteristics of a SPICE model of a transistor. FIGS. 45A and 45B are diagrams showing circuit simulation results of a semiconductor device.

[0029] In this specification, a semiconductor device refers to a device that utilizes semiconductor characteristics, such as a circuit including a semiconductor element (e.g., a transistor or a diode), or a device having such a circuit. It also refers to any device that can function by utilizing semiconductor characteristics. For example, an integrated circuit including a semiconductor element, a chip equipped with an integrated circuit, an electronic component in which a chip is housed in a package, or an electronic device equipped with an electronic component are examples of semiconductor devices. Furthermore, for example, a display device, a light-emitting device, a power storage device, an optical device, an imaging device, a lighting device, an arithmetic device, a control device, a memory device, an input device, an output device, an input / output device, a signal processing device, an electronic computer, or an electronic device may be a semiconductor device and may also include a semiconductor device.

[0030] Hereinafter, embodiments will be described with reference to the drawings. However, the embodiments can be implemented in many different ways. Therefore, it will be readily understood by those skilled in the art that various changes in form and details can be made without departing from the spirit and scope of the present invention. Therefore, one aspect of the present invention should not be interpreted as being limited to the description of the embodiments.

[0031] In this specification and the like, the configuration shown in each embodiment can be appropriately combined with the configuration shown in another embodiment to form one aspect of the present invention. Furthermore, when multiple configurations are shown in one embodiment, these configurations can be appropriately combined to form one aspect of the present invention.

[0032] In addition, in the drawings illustrating the embodiments, the same reference numerals may be used in common between different drawings for the same parts or parts having similar functions in the configuration of the invention, thereby omitting repeated description thereof. Furthermore, when the drawings indicate similar functions, for example, the same hatching patterns may be used and no particular reference numerals may be used. Furthermore, in the drawings, for example, in perspective views or top views (also called "plan views"), the illustration of some components may be omitted for ease of understanding. Furthermore, in the drawings, for example, the illustration of some hidden lines may be omitted. Furthermore, in the drawings, for example, the illustration of hatching patterns may be omitted.

[0033] In addition, in the drawings, the size, layer thickness, or area may be exaggerated for clarity. Therefore, the drawings are not limited to, for example, their size or aspect ratio. Note that the drawings are schematic representations of ideal examples and are not limited to, for example, the shapes or values ​​shown in the drawings. For example, in an actual manufacturing process, layers or resist masks may be unintentionally thinned by processes such as etching, but these may not be reflected in the drawings to facilitate understanding. In addition, for example, in actual circuit operation, variations in voltage or current may occur due to noise or timing errors, but these may not be reflected in the drawings to facilitate understanding.

[0034] In addition, in this specification and drawings, components may be classified by function and shown as independent elements. However, it may be difficult to separate components by function, and one element may be involved in multiple functions, or one function may be involved across multiple elements. Therefore, the elements shown in this specification and drawings may not be limited to the descriptions therein and may be rephrased appropriately depending on the situation.

[0035] Furthermore, in this specification and drawings, when the same reference numeral is used for multiple elements, and particularly when it is necessary to distinguish between them, the reference numeral may be accompanied by an identifying symbol such as "A", "b", "_1", "[n]", or "[m, n]". Furthermore, when explaining matters common to multiple elements accompanied by identifying symbols, or when it is not necessary to distinguish between them, the elements may be described without the identifying symbol.

[0036] In this specification and the like, the "conductive state" or "on state" of a transistor refers to, for example, a state in which the source and drain of the transistor are considered to be electrically short-circuited, or a state in which current can flow between the source and drain. For example, a state in which the voltage between the gate and source of an n-channel transistor is higher than the threshold voltage, or a state in which the voltage between the gate and source of a p-channel transistor is lower than the threshold voltage, may be referred to as the "conductive state" or "on state." In addition, the "non-conductive state," "cut-off state," or "off state" of a transistor refers to a state in which the source and drain of the transistor are considered to be electrically cut off. For example, a state in which the voltage between the gate and source of an n-channel transistor is lower than the threshold voltage, or a state in which the voltage between the gate and source of a p-channel transistor is higher than the threshold voltage, may be referred to as the "non-conductive state," "cut-off state," or "off state."

[0037] In this specification, the voltage between the gate and the source (gate-source) may be referred to as the "gate voltage," the voltage between the drain and the source (drain-source) may be referred to as the "drain voltage," and the voltage between the backgate and the source (backgate-source) may be referred to as the "backgate voltage." The current flowing between the drain and the source may be referred to as the "drain current." In an n-channel transistor, terms such as "high gate voltage," "high drain voltage," and "high backgate voltage" may be interchangeable with terms such as "low gate voltage," "low drain voltage," and "low backgate voltage" in a p-channel transistor. In an n-channel transistor, terms such as "low gate voltage," "low drain voltage," and "low backgate voltage" may be interchangeable with terms such as "high gate voltage," "high drain voltage," and "high backgate voltage" in a p-channel transistor.

[0038] In this specification and the like, unless otherwise specified, the "off-state current" of a transistor refers to the drain current when the transistor is in an off state. Note that in this specification and the like, the off-state current and the current flowing between the gate and the source and drain (also referred to as gate leakage current) may also be referred to as leakage current.

[0039] Embodiment 1 A semiconductor device according to one embodiment of the present invention will be described with reference to the drawings. At least a part of the semiconductor device according to one embodiment of the present invention can be used for, for example, a display device. In particular, it can be used for a driver circuit included in the display device.

[0040] <Structural Example 1 of Semiconductor Device> FIG. 1A is a circuit diagram illustrating a structural example of a semiconductor device of one embodiment of the present invention.

[0041] 1A, the semiconductor device 100A includes a switch unit 101A and a switch unit 102A. The switch unit 101A includes a transistor M11 and a transistor M12. The switch unit 102A includes a transistor M13.

[0042] Here, the transistor M11 has two gates (a gate and a back gate) that face each other with a channel formation region therebetween.

[0043] One of the source or the drain of the transistor M11 is electrically connected to one of the source or the drain of the transistor M12. The other of the source or the drain of the transistor M11 is electrically connected to one of the source or the drain of the transistor M13 and the wiring OUT11. The other of the source or the drain of the transistor M12 is electrically connected to the wiring VLS. The other of the source or the drain of the transistor M13 is electrically connected to the wiring VLD. The gate of the transistor M11 is electrically connected to the gate of the transistor M12 and the wiring IN11. The gate of the transistor M13 is electrically connected to the wiring IN12. The backgate of the transistor M11 is electrically connected to the other of the source or the drain of the transistor M11. The one of the source or the drain of the transistor M11 and the one of the source or the drain of the transistor M12 are electrically connected to each other by the wiring NL11.

[0044] In the semiconductor device 100A, the transistors M11, M12, and M13 are either n-channel transistors or p-channel transistors. Here, the description will be given assuming that the transistors M11, M12, and M13 are n-channel transistors, since hot carrier degradation is particularly noticeable in n-channel transistors.

[0045] Here, the threshold voltage of the transistor M11 shifts depending on the back gate voltage. For example, when the back gate voltage is higher than 0 V, the threshold voltage becomes lower (also referred to as a negative shift) compared to when the back gate voltage is 0 V. Also, when the back gate voltage is lower than 0 V, the threshold voltage becomes higher (also referred to as a positive shift) compared to when the back gate voltage is 0 V.

[0046] It is assumed that the transistor M11 is an enhancement type (normally off type) when the back gate voltage is 0 V. The transistors M12 and M13 are each a normally off type, and therefore their threshold voltages are greater than 0 V.

[0047] In one embodiment of the present invention, the transistors M11, M12, and M13 can each be a transistor including a single crystal semiconductor, a polycrystalline semiconductor, a microcrystalline semiconductor, or an amorphous semiconductor in a channel formation region. The semiconductor is not limited to a simple semiconductor whose main component is a single element (e.g., silicon or germanium), but can also be a compound semiconductor (e.g., silicon germanium or gallium arsenide) or an oxide semiconductor. Therefore, the transistors M11, M12, and M13 can each be a transistor including an oxide semiconductor in a channel formation region (OS transistor).

[0048] Note that a configuration example of a transistor that can be applied to each of the transistors M11, M12, and M13 will be described in Embodiment 2 to be described later.

[0049] Here, in a transistor to which a high drain voltage is applied, degradation of the transistor characteristics may occur. For example, in a transistor to which a high drain voltage is applied in the off state, hot carriers may be generated when the transistor is turned on. Therefore, repeated switching of the transistor between the on state and the off state may cause hot carriers to be injected and accumulated in the gate insulating film, resulting in hot carrier degradation that changes the transistor characteristics relative to the gate voltage. Therefore, hot carrier degradation can be suppressed by lowering the drain voltage before the transistor is turned on. In the semiconductor device 100A, the drain voltage can be lowered by the action of the operation example described below.

[0050] [Operation Example 1] Fig. 1B is a timing chart illustrating an operation example of the semiconductor device 100 A. Fig. 2A to Fig. 2D are circuit diagrams illustrating an operation example of the semiconductor device 100 A.

[0051] In the semiconductor device 100A, the wiring VLS and the wiring VLD each function as a power supply line. A potential higher than the potential applied to the wiring VLS is applied to the wiring VLD. For example, a potential VSS (sometimes simply referred to as VSS) is applied to the wiring VLS, and a potential VDD (sometimes simply referred to as VDD) is applied to the wiring VLD. In this case, the difference between VDD and VSS is greater than the threshold voltage of the transistor. VSS may be, for example, a ground potential.

[0052] Note that a signal such as a clock signal or a pulse signal can be applied to at least one of the wiring VLS and the wiring VLD. Thus, at least one of the wiring VLS and the wiring VLD can also function as a signal line.

[0053] The wirings IN11 and IN12 each function as a signal line. Pulse signals are applied to the wirings IN11 and IN12 at different timings.

[0054] Note that, for example, a triangular wave or a sawtooth wave can be applied to at least one of the wiring VLS, the wiring VLD, the wiring IN11, and the wiring IN12. Therefore, the semiconductor device 100A can also be applied to, for example, a pulse width modulation (PWM) circuit.

[0055] In the description of the operation, when the potential changes, a rise time and a fall time may occur due to, for example, a load (parasitic capacitance and parasitic resistance) such as a wiring. Furthermore, even if two different operations are shown to have the same timing, this does not necessarily mean that they are exactly the same timing. For example, even if there is a slight time difference due to signal delay in the wiring, they may be considered to have the same timing.

[0056] Furthermore, in the timing chart, even if each period is shown to have the same length for ease of explanation, the length of each period may be different.

[0057] 1B shows the states of potentials (VDD or VSS) applied to the wirings VLD, VLS, IN11, and IN12 in each period of operation, and also shows changes in the potentials of the wirings OUT11 and NL11.

[0058] 2A to 2D also show the potentials of the wirings VLD, VLS, IN11, IN12, OUT11, and NL11 at each point in time during operation. A symbol indicating a potential (also referred to as a potential symbol), such as "VDD" or "VSS," may be enclosed next to each wiring. An "x" symbol may be attached to a transistor in an off state in which the gate voltage is 0 V or less and no drain current flows. A "△" symbol and a dashed arrow may be attached to a transistor in which a drain current flows even when the gate voltage is 0 V or less.

[0059] It is assumed that immediately before the period T11, VSS is applied to the wiring VLS, the wiring IN11, and the wiring IN12, and VDD is applied to the wiring VLD. Therefore, the transistors M11, M12, and M13 are in an off state. The potentials of the wirings OUT11 and NL11 are also VSS. As a state of the semiconductor device 100A at this time, the potentials of the wirings at time T1a are shown in FIG. 2A. In the following description of the operation, unless otherwise specified, the potentials of the wirings are assumed to be maintained at the potentials of the immediately preceding period.

[0060] In the period T11, VDD is applied to the wiring IN12. Then, the transistor M13 is turned on, and the potential of the wiring OUT11 becomes VDD. Note that for simplicity of explanation, the potential of the wiring OUT11 is described as "VDD," but in reality, it becomes "VDD - the threshold voltage of the transistor M13." Therefore, the potential of the wiring OUT11 may be set to "VDD" by applying "VDD + the threshold voltage of the transistor" to the wiring IN12.

[0061] Here, in the transistor M11, the back gate is electrically connected to the drain, so that the "back gate voltage = drain voltage" and the threshold voltage is shifted downward. At this time, the negative shift occurs to the extent that the drain current flows. Note that in a transistor such as the transistor M11 where the "back gate voltage = drain voltage" is satisfied, the generation of hot carriers may be suppressed, making hot carrier degradation less likely to occur.

[0062] As a result, the drain current of transistor M11 gradually increases the potential of line NL11. If the increase in the potential of line NL11 is "vm," the potential of line NL11 becomes "VSS+vm," the gate voltage of transistor M11 becomes "-vm," and the back gate voltage becomes "VDD-VSS-vm." Therefore, as the potential of line NL11 increases, the gate voltage and back gate voltage of transistor M11 decrease. Furthermore, the decrease in the back gate voltage causes a positive shift in the threshold voltage. As a state of semiconductor device 100A at this time, the potentials of each line at time T1b are shown in FIG. 2B.

[0063] After that, when the potential increase of the wiring NL11 reaches "VM", the transistor M11 turns off and the drain current stops flowing. Then, the potential of the wiring NL11 becomes "VSS+VM", the gate voltage of the transistor M11 becomes "-VM", and the back gate voltage becomes "VDD-VSS-VM". Note that "VM" is assumed to be greater than 0 V and less than "VDD-VSS". Therefore, the potential of the wiring NL11 becomes an intermediate potential between VDD and VSS. As a state of the semiconductor device 100A at this time, the potentials of each wiring at time T1c are shown in FIG. 2C.

[0064] Next, VSS is applied to the wiring IN12. This turns off the transistor M13, and the wiring OUT11 becomes floating. At this time, the drain voltage of the transistor M11 is "VDD-VSS-VM," and the drain voltage of the transistor M12 is "VM." Therefore, the drain voltages of the transistors M11 and M12 each become lower than "VDD-VSS."

[0065] In a period T12, VDD is applied to the wiring IN11. Then, the transistors M11 and M12 are turned on, and the potentials of the wirings NL11 and OUT11 become VSS. As a state of the semiconductor device 100A at this time, the potentials of the wirings at time T1d are shown in FIG. 2D.

[0066] Next, VSS is applied to the wiring IN11, which turns off the transistors M11 and M12, and the wiring OUT11 becomes floating.

[0067] When a transistor is in a state where a high drain voltage is applied and a low gate voltage exceeding the threshold voltage is applied due to a change in at least one of the gate voltage and drain voltage, hot carriers are more likely to be generated. For example, the higher the drain voltage applied immediately before the transistor is turned on, the more likely hot carriers are generated immediately after the transistor is turned on (i.e., immediately after the gate voltage exceeds the threshold voltage).

[0068] According to one embodiment of the present invention, the drain voltages of the transistors M11 and M12 immediately before they are turned on can be reduced by the operation during the period T11. This can suppress hot carrier degradation, thereby improving reliability.

[0069] As described above, one embodiment of the present invention includes two transistors connected in series, such as the switch portion 101A included in the semiconductor device 100A. By electrically connecting the back gate of one of the transistors to the drain, the drain voltage of the transistor can be reduced, thereby suppressing deterioration of the transistor characteristics. In other words, there is no need to add another transistor to reduce the drain voltage of each of the two series-connected transistors. Therefore, reliability can be improved while suppressing an increase in the area occupied by the driver circuit.

[0070] For the above-described operational example to be valid, the condition 0V<“vm”≦“VM”<“VDD-VSS” must be satisfied. Therefore, the amount of threshold voltage shift due to the back-gate voltage of the transistor M11 must be appropriate. For example, the “amount of threshold voltage shift” is proportional to “back-gate capacitance / gate capacitance.” Therefore, for example, in the transistor M11, the back-gate capacitance may be made smaller than the gate capacitance to cause a negative shift so as to satisfy the above condition. For example, the thickness of the back-gate insulating film may be made thicker than the thickness of the gate insulating film. Furthermore, for example, the relative dielectric constant of the back-gate insulating film may be made smaller than the relative dielectric constant of the back-gate insulating film.

[0071] Note that one embodiment of the present invention has a structure in which the transistors M11 and M12 are connected in series. Therefore, for example, a structure that can increase the on-state current of the transistors M11 and M12 may be used. This can increase the on-state current while suppressing hot carrier degradation of the transistors M11 and M12. In other words, the operating speed and reliability of the semiconductor device can be improved.

[0072] For example, the channel length of at least one of the transistors M11 and M12 may be shorter than the channel length of the transistor M13. In addition, in the transistor M11, the back gate voltage may be equal to the drain voltage, which may reduce the likelihood of hot carrier degradation. Therefore, for example, the channel length of the transistor M11 may be shorter than the channel length of the transistor M12.

[0073] For example, the channel width of at least one of the transistors M11 and M12 may be greater than the channel width of the transistor M13. The "channel width / channel length" of at least one of the transistors M11 and M12 may be greater than the "channel width / channel length" of the transistor M13. In the transistor M11, a decrease in the gate voltage in the on-state may reduce the on-state current. That is, the on-state current of the transistor M11 may become rate-limiting. In such a case, for example, the channel width of the transistor M11 may be greater than the channel width of the transistor M12. The "channel width / channel length" of the transistor M11 may be greater than the "channel width / channel length" of the transistor M12. In the transistor M11, a negative shift in the threshold voltage due to the back gate voltage may increase the on-state current. That is, the on-state current of the transistor M12 may become rate-limiting. In such a case, for example, the channel width of the transistor M12 may be greater than the channel width of the transistor M11. Furthermore, the "channel width / channel length" of the transistor M12 may be set larger than the "channel width / channel length" of the transistor M11.

[0074] 3A to 3D each show a modification of the semiconductor device 100 A. The semiconductor device according to one embodiment of the present invention achieves functions and effects by shifting the threshold voltage of the transistor M11 using the back gate voltage, and various configurations are possible within a range in which the functions and effects can be achieved.

[0075] As shown in FIGS. 3A and 3B , each of the transistors M12 and M13 may have a back gate. In this case, for example, as shown in FIG. 3A , the back gate may be electrically connected to the gate. Then, the same potential as that of the gate may be applied to the back gate, thereby increasing the on-state current. Therefore, for example, by increasing the on-state current of the transistor M12, the channel width of the transistor M12 may be made smaller than the channel width of at least one of the transistors M11 and M13. Furthermore, by increasing the on-state current of the transistor M13, the channel width of the transistor M13 may be made smaller than the channel width of at least one of the transistors M11 and M12. This allows for improved reliability while minimizing an increase in the area occupied by the driver circuit.

[0076] Alternatively, for example, as shown in FIG. 3B , the back gate may be electrically connected to the source. This provides the back gate with the same potential as the source, making it difficult for an electric field generated outside the transistor to affect the channel formation region, thereby stabilizing electrical characteristics and improving reliability. Furthermore, in the configuration shown in FIG. 3B , even when the wiring VLS functions as a signal line and the functions of the source and drain of the transistors M11 and M12 are switched, the drain voltages of the transistors M11 and M12 can be reduced. That is, even when the potential of the wiring OUT11 is VSS and the potential of the wiring VLS changes from VSS to VDD, the "back gate voltage = drain voltage" in the transistor M12 can be achieved, thereby reducing the drain voltages of the transistors M11 and M12. This improves reliability.

[0077] Furthermore, although not shown, the threshold voltage may be changed by applying an arbitrary potential to the back gate. For example, a potential higher than VDD may be applied in the on state. This increases the on-state current. Therefore, for example, by increasing the on-state current of the transistor M12, the channel width of the transistor M12 can be made smaller than the channel width of at least one of the transistors M11 and M13. Furthermore, by increasing the on-state current of the transistor M13, the channel width of the transistor M13 can be made smaller than the channel width of at least one of the transistors M11 and M12. This allows for improved reliability while suppressing an increase in the area occupied by the driver circuit.

[0078] Note that when the transistors M12 and M13 have back gates, the back gates can be fabricated simultaneously with the back gate of the transistor M11. In other words, additional steps and masks are not required, and therefore, the back gates can be fabricated without increasing process costs.

[0079] 3C, the back gate of the transistor M11 may be electrically connected to a wiring VLB. In this case, a potential higher than VSS may be applied to the wiring VLB. For example, a potential that makes the back gate voltage higher than 0 V may be applied. Alternatively, for example, a potential equal to or higher than VDD may be applied. The amount of shift in the threshold voltage can be adjusted by the potential applied to the wiring VLB. This, for example, can increase the degree of freedom in designing the film thickness and relative dielectric constant of the back gate insulating film.

[0080] Furthermore, for example, when the transistor M11 is on, the on-state current can be increased by applying a higher potential to the wiring VLB. This allows the channel width of the transistor M11 to be smaller than the channel width of at least one of the transistors M12 and M13. This can improve reliability while suppressing an increase in the area occupied by the driver circuit.

[0081] 3D, a p-channel transistor may be used as the transistor M13. In this case, for example, the transistors M11 and M12 can operate complementarily with the transistor M13. This allows the same potential to be applied to the wirings IN11 and IN12, thereby reducing the circuit size. That is, for example, the wirings IN11 and IN12 may be electrically connected to each other. Furthermore, the gates of the transistors M11, M12, and M13 may be electrically connected to each other.

[0082] As described above, the semiconductor device of one embodiment of the present invention can have various structures. In addition, the semiconductor device is not limited to the above structures, and various structures can be appropriately combined to form a semiconductor device.

[0083] <Structural Example 2 of Semiconductor Device> FIG. 4A is a circuit diagram illustrating another structural example of a semiconductor device of one embodiment of the present invention.

[0084] 4A, the semiconductor device 100B includes a switch unit 101B and a switch unit 102B. The switch unit 101B includes a transistor M21 and a transistor M22. The switch unit 102B includes a transistor M23.

[0085] Here, the transistor M21 has two gates (a gate and a back gate) that face each other with a channel formation region therebetween.

[0086] One of the source or the drain of the transistor M21 is electrically connected to one of the source or the drain of the transistor M22. The other of the source or the drain of the transistor M21 is electrically connected to the wiring VLD. The other of the source or the drain of the transistor M22 is electrically connected to one of the source or the drain of the transistor M23 and the wiring OUT21. The other of the source or the drain of the transistor M23 is electrically connected to the wiring VLS. The gate of the transistor M21 is electrically connected to the gate of the transistor M22 and the wiring IN22. The gate of the transistor M23 is electrically connected to the wiring IN21. The back gate of the transistor M21 is electrically connected to the other of the source or the drain of the transistor M21. Note that one of the source or the drain of the transistor M21 and one of the source or the drain of the transistor M22 are electrically connected to each other by the wiring NL21.

[0087] The semiconductor device 100B is also a modified example of the semiconductor device 100A described above, and therefore, detailed description thereof may be omitted here since the description of the semiconductor device 100A described above can be referred to as appropriate.

[0088] The switch unit 101B corresponds to the switch unit 101A, and the switch unit 102B corresponds to the switch unit 102A. That is, the transistor M21 corresponds to the transistor M11, the transistor M22 corresponds to the transistor M12, and the transistor M23 corresponds to the transistor M13. The wiring IN21 corresponds to the wiring IN11, the wiring IN22 corresponds to the wiring IN12, and the wiring OUT21 corresponds to the wiring OUT11.

[0089] [Operation Example 2] Fig. 4B is a timing chart illustrating an operation example of the semiconductor device 100B. Figs. 5A to 5D are circuit diagrams illustrating an operation example of the semiconductor device 100B.

[0090] 4B shows the states of potentials (VDD or VSS) applied to the wirings VLD, VLS, IN21, and IN22 in each period of operation, and also shows changes in the potentials of the wirings OUT21 and NL21.

[0091] 5A to 5D also show the potentials of the wirings VLD, VLS, IN21, IN22, OUT21, and NL21 at each point in time during operation.

[0092] It is assumed that immediately before the period T21, VSS is applied to the wirings VLD, VLS, IN21, and IN22. Therefore, the transistors M21, M22, and M23 are in an off state. The potentials of the wirings OUT21 and NL21 are VSS. As a state of the semiconductor device 100B at this time, the potentials of the wirings at time T2a are shown in FIG. 5A. In the following description of the operation, unless otherwise specified, the potentials of the wirings are assumed to be maintained at the potentials of the immediately preceding period.

[0093] In a period T21, VDD is applied to the wiring VLD.

[0094] Here, in the transistor M21, when the back gate is electrically connected to the drain, the "back gate voltage = drain voltage" is established, and the threshold voltage is shifted negatively. At this time, the negative shift is assumed to be sufficient to allow the drain current to flow.

[0095] As a result, the drain current of transistor M21 gradually increases the potential of line NL21. If the increase in the potential of line NL21 is "vm," the potential of line NL21 becomes "VSS+vm," the gate voltage of transistor M21 becomes "-vm," and the back gate voltage becomes "VDD-VSS-vm." Therefore, when the potential of line NL21 increases, the gate voltage and back gate voltage of transistor M21 decrease. Furthermore, the decrease in the back gate voltage causes a positive shift in the threshold voltage. As a state of semiconductor device 100B at this time, the potentials of the various lines at time T2b are shown in FIG. 5B.

[0096] After that, when the potential increase of the wiring NL21 reaches "VM", the transistor M21 turns off and the drain current stops flowing. Then, the potential of the wiring NL21 becomes "VSS+VM", the gate voltage of the transistor M21 becomes "-VM", and the back gate voltage becomes "VDD-VSS-VM". Note that "VM" is assumed to be greater than 0 V and less than "VDD-VSS". Therefore, the potential of the wiring NL21 becomes an intermediate potential between VDD and VSS. As a state of the semiconductor device 100B at this time, the potentials of the wirings at time T2c are shown in FIG. 5C.

[0097] In a period T22, VDD is applied to the wiring IN22. Then, the transistors M21 and M22 are turned on, and the potentials of the wirings NL21 and OUT21 become VDD. As a state of the semiconductor device 100B at this time, the potentials of the wirings at time T2d are shown in FIG. 5D.

[0098] Next, VSS is applied to the wiring IN22, which turns off the transistors M21 and M22, and the wiring OUT21 becomes floating.

[0099] Although not shown, after the period T22, VDD is applied to the wiring IN21, so that the transistor M23 is turned on and the potential of the wiring OUT21 becomes VSS.

[0100] According to one aspect of the present invention, the drain voltages of the transistors M21 and M22 immediately before they are turned on can be reduced by the operation during the period T21. This can suppress hot carrier degradation, thereby improving reliability.

[0101] 6A to 6D each show a modification of the semiconductor device 100B. The semiconductor device according to one embodiment of the present invention achieves functions and effects by shifting the threshold voltage of the transistor M21 using the back gate voltage, and various configurations are possible within a range in which the functions and effects can be achieved.

[0102] The modified examples of the semiconductor device 100B shown in each of FIGS. 6A to 6D correspond to modified examples of the semiconductor device 100A shown in each of FIGS. 3A to 3D. Therefore, the above-described descriptions can be referred to as appropriate, and detailed descriptions will be omitted here. That is, for the semiconductor device 100B shown in FIG. 6A, the description of the semiconductor device 100A shown in FIG. 3A can be referred to. Furthermore, for the semiconductor device 100B shown in FIG. 6B, the description of the semiconductor device 100A shown in FIG. 3B can be referred to. Furthermore, for the semiconductor device 100B shown in FIG. 6C, the description of the semiconductor device 100A shown in FIG. 3C can be referred to. Furthermore, for the semiconductor device 100B shown in FIG. 6D, the description of the semiconductor device 100A shown in FIG. 3D can be referred to.

[0103] <Application Example to Driver Circuit> FIG. 7A is a circuit diagram illustrating a configuration example of a driver circuit to which the semiconductor device of one embodiment of the present invention can be applied.

[0104] The drive circuit 110 shown in FIG. 7A includes a transistor M31, a transistor M32, a transistor M33, a transistor M34, a transistor M35, and a transistor M36.

[0105] One of the source or drain of transistor M31 is electrically connected to one of the source or drain of transistor M32 and the gate of transistor M35. One of the source or drain of transistor M33 is electrically connected to one of the source or drain of transistor M34, the gate of transistor M32, and the gate of transistor M35. One of the source or drain of transistor M35 is electrically connected to one of the source or drain of transistor M36 and the wiring OUT31. The other of the source or drain of transistor M31 and the other of the source or drain of transistor M33 are electrically connected to the wiring VLD. The other of the source or drain of transistor M32, the other of the source or drain of transistor M34, and the other of the source or drain of transistor M36 are electrically connected to the wiring VLS. The gates of transistor M31 and transistor M34 are electrically connected to the wiring IN31. The gate of transistor M33 is electrically connected to the wiring IN32. The other of the source and the drain of transistor M35 is electrically connected to wiring CK31. One of the source and the drain of transistor M31, one of the source and the drain of transistor M32, and the gate of transistor M35 are electrically connected to one another by wiring NL31. One of the source and the drain of transistor M33, one of the source and the drain of transistor M34, the gate of transistor M32, and the gate of transistor M36 are electrically connected to one another by wiring NL32.

[0106] A power supply potential is applied to the wiring VLS and the wiring VLD so that the potential of the wiring VLD is higher than the potential of the wiring VLS. Pulse signals with different timings are applied to the wiring IN31 and the wiring IN32. A clock signal is applied to the wiring CK31. A pulse signal is output to the wiring OUT31 in response to these signals.

[0107] FIG. 7B is a timing chart illustrating an example of the operation of the drive circuit 110.

[0108] 7B shows the states of potentials (VDD or VSS) applied to the wirings IN31, IN32, and CK31 during each period of operation, and also shows changes in the potentials of the wirings NL31, NL32, and OUT31.

[0109] It is assumed that immediately before the period T31, VDD is applied to the wiring VLD and VSS is applied to the wiring VLS. Furthermore, VSS is applied to each of the wirings IN31, IN32, and CK31. Therefore, the transistors M31, M33, and M34 are in an off state. The potential of the wiring NL31 is VSS, and the potential of the wiring NL32 is VDD. Therefore, the transistors M32 and M36 are in an on state, and the transistor M35 is in an off state. Therefore, the potential of the wiring OUT31 is VSS. In the following description of the operation, unless otherwise specified, the potential of each wiring is assumed to be maintained at the potential of the immediately preceding period.

[0110] In a period T31, a clock signal is applied to the wiring CK31. At this time, the transistor M35 is off and the transistor M36 is on, so the potential of the wiring OUT31 remains at VSS.

[0111] During period T32, a pulse signal is applied to wiring IN31, and a clock signal is applied to wiring CK31. That is, VDD is applied to wiring IN31, turning on transistors M31 and M34. Then, the potential of wiring NL32 becomes VSS, turning off transistors M32 and M36. Also, the potential of wiring NL31 becomes VDD, turning on transistor M35. Thereafter, VSS is applied to wiring IN31, turning off transistors M31 and M34. Then, the potentials of wiring NL31 and NL32 are maintained, transistor M35 is maintained on, and transistor M36 is maintained off. At this time, the potential of wiring CK31 is applied to wiring OUT31 via transistor M35. That is, a clock signal is applied to wiring OUT31.

[0112] During period T33, a pulse signal is applied to wiring IN32, and a clock signal is applied to wiring CK31. That is, VDD is applied to wiring IN32, turning on transistor M33. Then, the potential of wiring NL32 becomes VDD, turning on transistors M32 and M36. As a result, the potential of wiring NL31 becomes VSS, turning off transistor M35. Thereafter, VSS is applied to wiring IN32, turning off transistor M33. Then, the potentials of wiring NL31 and wiring NL32 are maintained, transistor M35 is maintained in the off state, and transistor M36 is maintained in the on state. At this time, transistor M35 is in the off state and transistor M36 is in the on state, so the potential of wiring OUT31 remains at VSS.

[0113] When the driver circuit 110 performs the above-described operation, in period T31, the transistors M31 and M34 are in the off state and the drain voltage is "VDD-VSS." Therefore, in period T32, when a pulse signal is applied to the wiring IN31 and the transistors M31 and M34 are turned on, hot carriers may be generated. Also, in period T32, the transistors M32 and M33 are in the off state and the drain voltage is "VDD-VSS." Therefore, in period T33, when a pulse signal is applied to the wiring IN32 and the transistors M32 and M33 are turned on, hot carriers may be generated.

[0114] Therefore, by applying at least a part of the semiconductor device 100A and the semiconductor device 100B described above to the drive circuit 110, it is possible to reduce the drain voltage immediately before the transistor turns on, thereby suppressing hot carrier degradation, thereby improving the reliability of the display device to which the drive circuit is applied.

[0115] 8A and 8B are circuit diagrams showing configuration examples in which a switch section 101A and a switch section 101B are applied to a drive circuit 110, respectively.

[0116] 8A includes switch units 101A_1 and 101A_2 instead of transistors M32 and M34. The switch units 101A_1 and 101A_2 correspond to the switch unit 101A. That is, the transistors M32a and M34a correspond to the transistor M11, and the transistors M32b and M34b correspond to the transistor M12.

[0117] In the drive circuit 110A, the drain voltages immediately before the transistors M32a and M32b are turned on can be reduced by the action described in the above-described example of operation of the semiconductor device 100A, and the drain voltages immediately before the transistors M34a and M34b are turned on can be reduced.

[0118] 3A is used, which can suppress the reduction in on-current caused by connecting two transistors in series, and can also suppress a decrease in the operating speed of the drive circuit 110A.

[0119] In the drive circuit 110A, the gate potential of transistor M35 may rise to a potential higher than VDD. Even in such a case, the drain voltages of transistors M32a and M32b can be reduced. This improves the reliability of a display device incorporating the drive circuit 110A. Furthermore, there is no need to provide additional transistors between the gate of transistor M35 and transistors M32a and M32b to suppress the rise in the drain voltages of transistors M32a and M32b. This prevents the drive circuit 110A from occupying an increased area.

[0120] Furthermore, in the drive circuit 110A, VDD may continue to be applied to the gate of transistor M36. Even in such a case, the drain voltages of transistors M34a and M34b can be reduced. This improves the reliability of a display device incorporating the drive circuit 110A.

[0121] In the driving circuit 110A, the switch unit 101B is not applied to the transistors M31 and M33. In the driving circuit 110A, for example, if the potential applied to the wiring VLD is a fixed potential of VDD, the switch unit 101B does not need to be applied to the transistors M31 and M33. This can prevent the area occupied by the driving circuit 110A from increasing. Therefore, the display device using the driving circuit 110A can be made smaller.

[0122] In addition, the driver circuit 110A shows a configuration example in which the switch units 101A and 101B are not applied to the transistors M35 and M36. When the driver circuit 110A is applied to a display device, the wiring OUT31 is electrically connected to the gates of the transistors in each of the pixels. Therefore, a large on-state current is required for the transistors M35 and M36. Therefore, by not applying the switch units 101A and 101B, the reduction in on-state current can be suppressed, thereby improving the operating speed of the driver circuit 110A. Furthermore, the area occupied by the driver circuit 110A can be suppressed. Therefore, a display device using the driver circuit 110A can have a larger screen and higher resolution.

[0123] 8B is a circuit diagram showing a modified example of the drive circuit 110A. The drive circuit 110B shown in FIG. 8B has switch units 101B_1, 101B_2, 101B_3, and 101A_3 instead of transistors M31, M33, M35, and M36. The switch units 101B_1, 101B_2, and 101B_3 correspond to the switch unit 101B, respectively. The switch unit 101A_3 corresponds to the switch unit 101A. That is, the transistors M31a, M33a, and M35a correspond to the transistor M21, the transistors M31b, M33b, and M35b correspond to the transistor M22, the transistor M36a corresponds to the transistor M11, and the transistor M36b corresponds to the transistor M12.

[0124] In the driving circuit 110B, the drain voltage just before each transistor in the driving circuit 110B turns on can be reduced by the action described in the respective operation examples of the semiconductor device 100A and the semiconductor device 100B described above.

[0125] Here, the switch unit 101B shown in FIG. 6A is applied to transistors M31 and M33, and the switch unit 101A shown in FIG. 3A is applied to transistor M36. This suppresses the reduction in on-state current caused by connecting two transistors in series, thereby suppressing a decrease in the operating speed of the driver circuit 110B. Also, the switch unit 101B shown in FIG. 6B is applied to transistor M35. This allows the drain voltage to be reduced even when the source or drain function is switched by a signal applied to wiring CK31. This improves the reliability of a display device incorporating driver circuit 110B.

[0126] In the driver circuit 110B, for example, when the potential applied to the wiring VLD changes from VSS to VDD at power-on or when the wiring VLD functions as a signal line, the drain voltage can be reduced by using the switch unit 101B, thereby improving the reliability of the display device to which the driver circuit 110B is applied.

[0127] In this case, for example, in the switch unit 101B used in the driver circuit 110B, the capacitance between the gate of the transistor M21 and the wiring NL21 may be increased. For example, the parasitic capacitance between the gate and the wiring NL21 may be increased. Alternatively, a capacitive element may be provided between the gate and the wiring NL21. By doing so, when the transistors M21 and M22 are turned off, the potential of the wiring NL21 becomes lower than VDD due to capacitive coupling. In other words, the drain voltages of the transistors M21 and M22 may be reduced in some cases. This may improve the reliability of a display device using the driver circuit 110B.

[0128] 6A may be applied to the transistor M35, thereby suppressing a decrease in on-state current due to the two transistors being connected in series, and suppressing a decrease in the operating speed of the drive circuit 110B.

[0129] Although not shown, in the driver circuit 110B, the wiring VLS electrically connected to the switch portion 101A_3 (here, the wiring VLS_1) and the wiring VLS electrically connected to the switch portion 101A_1 and the switch portion 101A_2 (here, the wiring VLS_2) can be different wirings. In this case, for example, a fixed potential of VSS may be applied to the wiring VLS_2, causing the wiring VLS_1 to function as a signal line. In this case, the switch portion 101A shown in FIG. 3B may be applied to the transistor M36. This allows the drain voltage to be reduced even when the function of the source or drain is switched depending on a signal applied to the wiring VLS_1. This improves the reliability of a display device using the driver circuit 110B.

[0130] Note that the above-described structures of the driver circuit 110A and the driver circuit 110B are just examples. In one embodiment of the present invention, the switch portion 101A, the switch portion 101B, or the like can be applied to at least some of the transistors in the driver circuit 110.

[0131] At least a part of a driver circuit to which the semiconductor device of one embodiment of the present invention is applied can be used in, for example, a display device. The driver circuit can also be used in various devices, such as an input device having a touch sensor and a memory device having memory cells. A structural example of a display device to which the driver circuit can be applied will be described in Embodiment 3 below.

[0132] A driver circuit to which the semiconductor device of one embodiment of the present invention can be applied is not limited to the above-described structure example. The semiconductor device of one embodiment of the present invention can be applied to driver circuits with various structures.

[0133] 9A and 9B are circuit diagrams illustrating configuration examples of driver circuits to which the semiconductor device of one embodiment of the present invention can be applied.

[0134] The drive circuit 116 shown in FIG. 9A includes a transistor M61, a transistor M62, a transistor M63, a transistor M64, a transistor M65, a transistor M66, a transistor M67, a transistor M68, a capacitor C61, a capacitor C62, and a capacitor C63.

[0135] The gate of transistor M61 is electrically connected to one of the source or drain of transistor M63 and one terminal of capacitor C61. The source or drain of transistor M61 is electrically connected to one of the source or drain of transistor M62, one terminal of capacitor C61, and wiring OUT61. The gate of transistor M62 is electrically connected to one of the source or drain of transistor M64, one of the source or drain of transistor M66, and one terminal of capacitor C62. The gate of transistor M64 is electrically connected to the other of the source or drain of transistor M63 and one of the source or drain of transistor M65. The gate of transistor M66 is electrically connected to one of the source or drain of transistor M67, one of the source or drain of transistor M68, and one terminal of capacitor C63. The other of the source or drain of transistor M62, the other of the source or drain of transistor M64, the other of the source or drain of transistor M67, the other of the source or drain of transistor M68, and the other terminal of capacitor C62 are electrically connected to wiring VLS. The other of the source or drain of transistor M61 and the gate of transistor M63 are electrically connected to wiring VLD. One of the source or drain of transistor M65 and the gate of transistor M68 are electrically connected to wiring IN61. The gate of transistor M65, the other of the source or drain of transistor M66, and the other terminal of capacitor C63 are electrically connected to wiring CK61. The gate of transistor M67 is electrically connected to wiring CK62.

[0136] A power supply potential is applied to the wiring VLS and the wiring VLD so that the potential of the wiring VLD is higher than the potential of the wiring VLS. A pulse signal is applied to the wiring IN61. Clock signals of different phases are applied to the wiring CK61 and the wiring CK62. A pulse signal is output to the wiring OUT61 in response to these signals.

[0137] 9B shows a configuration example in which the switch unit 101B shown in FIG. 6A is applied to transistors M61 and M65, the switch unit 101A shown in FIG. 3A is applied to transistors M62, M64, M67, and M68, and the switch unit 101B shown in FIG. 6B is applied to transistor M66. Thus, FIG. 9B shows a configuration in which the switch unit 101B_1 is applied in place of the transistor M61, the switch unit 101A_2 is applied in place of the transistor M62, the switch unit 101A_4 is applied in place of the transistor M64, the switch unit 101B_5 is applied in place of the transistor M65, the switch unit 101B_6 is applied in place of the transistor M66, the switch unit 101A_7 is applied in place of the transistor M67, and the switch unit 101A_8 is applied in place of the transistor M68. That is, transistors M62a, M64a, M67a, and M68a correspond to transistor M11, and transistors M62b, M64b, M67b, and M68b correspond to transistor M12. Furthermore, transistors M61a, M65a, and M66a correspond to transistor M21, and transistors M61b, M65b, and M66b correspond to transistor M22. Note that the configuration shown in FIG. 9B is an example, and switch units 101A and 101B may be applied to at least some of the transistors in drive circuit 116A.

[0138] In the driver circuit 116A, particularly, the transistors M61, M62, and M64 may be applied with a high drain voltage, and therefore the switch units 101A and 101B may be used. The source and drain functions of the transistors M65 and M66 are switched depending on signals applied to the wirings IN61 and CK61. Therefore, the transistors M65 and M66 may have a configuration similar to the switch unit 101B shown in FIG. 6B. By using the switch units 101A and 101B in this manner, the reliability of the driver circuit 116A and a display device using the pixel circuit can be improved.

[0139] Note that by applying the switch unit 101B to the transistor M65, the drain voltage can be reduced, which may eliminate the need for the transistor M63. This prevents an increase in the area occupied by the drive circuit 116A, and allows for the miniaturization of a display device using the drive circuit 116A.

[0140] 10A and 10B are circuit diagrams illustrating a configuration example of a driver circuit to which the semiconductor device of one embodiment of the present invention can be applied.

[0141] The drive circuit 117 shown in FIG. 10A includes a transistor M71, a transistor M72, a transistor M73, a transistor M74, a transistor M75, a transistor M76, a transistor M77, a transistor M78, a capacitor C71, and a capacitor C72.

[0142] The gate of transistor M71 is electrically connected to the gate of transistor M74, one of the source or drain of transistor M75, one of the source or drain of transistor M76, and one terminal of capacitor C71. The one of the source or drain of transistor M71 is electrically connected to one of the source or drain of transistor M72 and wiring OUT71. The gate of transistor M72 is electrically connected to one of the source or drain of transistor M73. The other of the source or drain of transistor M73 is electrically connected to one of the source or drain of transistor M74, the gate of transistor M75, one of the source or drain of transistor M77, one of the source or drain of transistor M78, and one terminal of capacitor C72. The other of the source or drain of transistor M71 and the other terminal of capacitor C71 are electrically connected to wiring VLS_1. The other of the source or the drain of the transistor M74, the other of the source or the drain of the transistor M75, and the other terminal of the capacitor C72 are electrically connected to a wiring VLS. The gate of the transistor M73 and the other of the source or the drain of the transistor M76 are electrically connected to a wiring VLD. The gate of the transistor M77 is electrically connected to a wiring IN71. The gate of the transistor M78 is electrically connected to a wiring IN72. The other of the source or the drain of the transistor M72 is electrically connected to a wiring CK71. The gate of the transistor M76 is electrically connected to a wiring CK72. The other of the source or the drain of the transistor M77 is electrically connected to a wiring SE71. The other of the source or the drain of the transistor M78 is electrically connected to a wiring SE72.

[0143] A power supply potential is applied to the wirings VLS_1, VLS_2, and VLD such that the potential of the wiring VLD is higher than the potential of the wirings VLS_1 and VLS_2. Pulse signals with different timings are applied to the wirings IN71 and IN72. Clock signals with different phases are applied to the wirings CK71 and CK72. Selection signals are applied to the wirings SE71 and SE72. A pulse signal is output to the wiring OUT71 in response to these signals.

[0144] 10B shows a configuration example in which the switch unit 101A shown in FIG. 3A is applied to transistors M71, M74, and M75, the switch unit 101B shown in FIG. 6A is applied to transistors M72 and M76, and the switch unit 101B shown in FIG. 6B is applied to transistors M77 and M78. Thus, FIG. 10B shows a configuration in which the switch unit 101A_1 is applied to the transistor M71, the switch unit 101B_2 is applied to the transistor M72, the switch unit 101A_4 is applied to the transistor M74, the switch unit 101A_5 is applied to the transistor M75, the switch unit 101B_6 is applied to the transistor M76, the switch unit 101B_7 is applied to the transistor M77, and the switch unit 101A_8 is applied to the transistor M78. That is, transistors M71a, M74a, M75a, and M78a correspond to transistor M11, and transistors M71b, M74b, M75b, and M78b correspond to transistor M12. Furthermore, transistors M72a, M76a, and M77a correspond to transistor M21, and transistors M72b, M76b, and M77b correspond to transistor M22. Note that the configuration shown in FIG. 10B is an example, and switch units 101A and 101B may be applied to at least some of the transistors in drive circuit 117A.

[0145] In the driver circuit 117A, particularly, a high drain voltage may be applied to transistors M71, M72, M74, M75, and M76, and therefore switch units 101A and 101B may be used. Furthermore, the source or drain functions of transistors M77 and M78 are switched depending on signals applied to wirings SE71 and SE72. Therefore, a configuration such as switch unit 101B shown in FIG. 6B may be used for transistors M77 and M78. In this way, by using switch units 101A and 101B, the reliability of the driver circuit 117A and a display device using the pixel circuit can be improved.

[0146] Note that by applying the switch units 101A and 101B to the transistors M74, M77, and M78, the drain voltage can be reduced, which may eliminate the need for the transistor M73. This prevents an increase in the area occupied by the drive circuit 117A, and allows for the miniaturization of a display device incorporating the drive circuit 117A.

[0147] One embodiment of the present invention is not limited to the above-described structures, and at least a part of each structure can be combined as appropriate.

[0148] One embodiment of the present invention also includes a structure in which at least one of a gate, a source, and a drain of one or more transistors is not connected to anything or is connected to any wiring. Another embodiment of the present invention also includes a structure in which nothing is input to one or more wirings or a signal or potential is input to one or more wirings.

[0149] Note that the semiconductor device according to one embodiment of the present invention is not limited to the semiconductor device described in this embodiment. At least part of the configuration examples, operation examples, and corresponding drawings described in this embodiment can be appropriately combined with other configuration examples, operation examples, drawings, and embodiments described in this specification.

[0150] In this embodiment, a semiconductor device of one embodiment of the present invention and a transistor included in the semiconductor device will be described with reference to FIGS. 11 to 13. Note that at least part of the transistors described in this embodiment can be applied to the semiconductor device 100A, the semiconductor device 100B, and the like described in Embodiment 1.

[0151] <Configuration Example of Transistor> A semiconductor device according to one embodiment of the present invention will be described. FIG. 11A shows a top view of a semiconductor device 10. FIG. 11B shows a cross-sectional view of a cut surface taken along dashed dotted line A1-A2 in FIG. 11A , and FIG. 11C shows a cross-sectional view of a cut surface taken along dashed dotted line B1-B2. Note that some of the components of the semiconductor device 10 (such as an insulating layer) are omitted in FIG. 11A . As with FIG. 11A , some of the components are also omitted in the top views of the semiconductor device in the following drawings.

[0152] The semiconductor device 10 includes a transistor 300, a transistor 200, a capacitor 350, and an insulating layer 310. The transistor 300, the transistor 200, and the capacitor 350 are provided over a substrate 302. The transistor 300 and the transistor 200 have different structures. The transistor 300, the transistor 200, and the capacitor 350 can be formed using some common steps.

[0153] The transistor 300 includes a conductive layer 304, an insulating layer 306, a semiconductor layer 308, a conductive layer 312a, and a conductive layer 312b. In the transistor 300, the conductive layer 304 functions as a gate electrode, and part of the insulating layer 306 functions as a gate insulating layer. The conductive layer 312a functions as one of a source electrode and a drain electrode, and the conductive layer 312b functions as the other. Each layer constituting the transistor 300 may have a single-layer structure or a stacked-layer structure.

[0154] A conductive layer 312a is provided over a substrate 302, and an insulating layer 310 is provided over the conductive layer 312a. The insulating layer 310 is provided so as to cover the top and side surfaces of the conductive layer 312a. The insulating layer 310 has an opening 341 that reaches the conductive layer 312a in a region overlapping with the conductive layer 312a. It can also be said that the conductive layer 312a is exposed in the opening 341.

[0155] A conductive layer 312b is provided over the insulating layer 310. The conductive layer 312b has a region overlapping with the conductive layer 312a with the insulating layer 310 interposed therebetween. The conductive layer 312b has an opening 343 in the region overlapping with the conductive layer 312a. The opening 343 is provided in a region overlapping with the opening 341.

[0156] The openings 341 and 343 have a columnar shape with a circular or approximately circular upper surface. This configuration allows, for example, miniaturization, high integration, high density, and miniaturization of the semiconductor device. Note that the side surfaces of the openings 341 and 343 are preferably perpendicular to the upper surface of the conductive layer 312 a.

[0157] At least a portion of the semiconductor layer 308 is provided to cover the openings 341 and 343. The semiconductor layer 308 has regions in contact with the top surface and side surfaces of the conductive layer 312b, the side surfaces of the insulating layer 310, and the top surface of the conductive layer 312a. The semiconductor layer 308 is electrically connected to the conductive layer 312a through the openings 341 and 343. The semiconductor layer 308 has a shape that follows the shapes of the top surface and side surfaces of the conductive layer 312b, the side surfaces of the insulating layer 310, and the top surface of the conductive layer 312a. The semiconductor layer 308 has a region that overlaps with the conductive layer 312a with the insulating layer 310 interposed therebetween. It can also be said that the insulating layer 310 has a region sandwiched between the conductive layer 312a and the semiconductor layer 308. That is, it can also be said that a portion of the semiconductor layer 308 is provided inside the openings 341 and 343.

[0158] A region of the semiconductor layer 308 in contact with the conductive layer 312 a functions as one of a source region and a drain region, and a region of the semiconductor layer 308 in contact with the conductive layer 312 b functions as the other. In the semiconductor layer 308, a channel formation region is provided between the source region and the drain region.

[0159] At least a part of the insulating layer 306 is provided to cover the openings 341 and 343. The insulating layer 306 is provided over the semiconductor layer 308, the conductive layer 312b, and the insulating layer 310. The insulating layer 306 has regions in contact with the top surface and side surfaces of the semiconductor layer 308, the top surface and side surfaces of the conductive layer 312b, and the top surface of the insulating layer 310. The insulating layer 306 has a shape that follows the shapes of the top surface and side surfaces of the semiconductor layer 308, the top surface and side surfaces of the conductive layer 312b, and the top surface of the insulating layer 310.

[0160] The conductive layer 304 is provided over the insulating layer 306 and has a region in contact with the top surface of the insulating layer 306. The conductive layer 304 has a region overlapping with the semiconductor layer 308 with the insulating layer 306 interposed therebetween. The conductive layer 304 has a shape that follows the shape of the top surface of the insulating layer 306. Note that the conductive layer 304 may be provided so as to fill the openings 341 and 343.

[0161] The transistor 300 is a so-called top-gate transistor having a gate electrode above the semiconductor layer 308. Furthermore, the bottom surface of the semiconductor layer 308 is in contact with the conductive layers 312a and 312b, which function as a source electrode and a drain electrode, respectively. Therefore, the transistor 300 can be referred to as a top-gate bottom-contact (TGBC) transistor. The source electrode and the drain electrode of the transistor 300 are located at different heights with respect to the surface of the substrate 302, which is a formation surface. Therefore, a drain current flows in the vertical direction (also referred to as the height direction, the depth direction in a top view, or the direction perpendicular to the formation surface (the surface of the substrate 302)). In other words, the channel length direction of the transistor 300 can have a vertical component. Therefore, a transistor such as the transistor 300 of one embodiment of the present invention can be referred to as a vertical transistor, a vertical-channel transistor, a vertical-channel transistor, a vertical field effect transistor (VFET), or the like.

[0162] The channel length of the transistor 300 can be controlled by the thickness of the insulating layer 310 (specifically, the insulating layer 310b) provided between the conductive layer 312a and the conductive layer 312b. Therefore, a transistor having a channel length smaller than the resolution limit of an exposure device used to fabricate the transistor can be fabricated with high precision. Furthermore, the characteristic variation among multiple transistors 300 is also reduced. Therefore, the operation of a semiconductor device including the transistor 300 can be stabilized, and reliability can be improved. Furthermore, the reduced characteristic variation increases the degree of freedom in the circuit design of the semiconductor device, allowing the operating voltage to be reduced. Therefore, the power consumption of the semiconductor device can be reduced.

[0163] In the transistor 300, a source electrode, a semiconductor layer having a channel formation region, and a drain electrode can be provided in an overlapping manner, and therefore the occupied area can be significantly reduced compared to a so-called planar transistor in which a semiconductor layer having a channel formation region is arranged in a planar shape.

[0164] The conductive layers 312a, 312b, and 304 can each function as wirings, and the transistor 300 can be provided in a region where these wirings overlap. That is, in a circuit including the transistor 300 and the wirings, the area occupied by the transistor 300 and the wirings can be reduced. Therefore, the area occupied by the circuit can be reduced, and a small-sized semiconductor device can be obtained.

[0165] The transistor 200 includes a conductive layer 204, a conductive layer 212a, a conductive layer 212b, an insulating layer 306, a semiconductor layer 208, an insulating layer 320, and a conductive layer 202. In the transistor 200, the conductive layer 204 functions as a gate electrode (also referred to as a first gate electrode), and part of the insulating layer 306 functions as a gate insulating layer (also referred to as a first gate insulating layer). The conductive layer 202 functions as a back gate electrode (also referred to as a second gate electrode), and part of the insulating layer 320 functions as a back gate insulating layer (also referred to as a second gate insulating layer). The conductive layer 212a functions as one of a source electrode and a drain electrode, and the conductive layer 212b functions as the other electrode. Each layer constituting the transistor 200 may have a single-layer structure or a stacked-layer structure. Note that the transistor 200 does not necessarily include the conductive layer 202 and the insulating layer 320.

[0166] The entire region of the semiconductor layer 208 that overlaps with the gate electrode with the gate insulating layer interposed therebetween functions as a channel formation region. The semiconductor layer 208 has a pair of regions 208L that sandwich the channel formation region and a pair of regions 208D outside the pair of regions 208L.

[0167] Regions 208L and 208D are regions containing impurity elements. The impurity elements can be one or more of hydrogen, boron, carbon, nitrogen, fluorine, phosphorus, sulfur, arsenic, aluminum, magnesium, silicon, and noble gases. Typical examples of noble gases include helium, neon, argon, krypton, and xenon. It is particularly preferable to use one or more of boron, phosphorus, aluminum, magnesium, and silicon as the impurity elements.

[0168] Using the conductive layer 204, the conductive layer 212a, and the conductive layer 212b as masks, an impurity element is supplied (also referred to as adding or injecting) to the semiconductor layer 208. As a result, a region 208D is formed in a region of the semiconductor layer 208 that does not overlap with any of the conductive layer 204, the conductive layer 212a, the conductive layer 212b, and the insulating layer 306, and a region 208L is formed in a region that does not overlap with any of the conductive layer 204, the conductive layer 212a, and the conductive layer 212b and overlaps with the insulating layer 306.

[0169] In the semiconductor layer 208, a region in contact with the conductive layer 212a and a region 208D adjacent to the conductive layer 212a function as one of a source region and a drain region. In the semiconductor layer 208, a region in contact with the conductive layer 212b and a region 208D adjacent to the conductive layer 212b function as the other of the source region and the drain region.

[0170] The conductive layer 202 is provided over the insulating layer 310, and the insulating layer 320 is provided over the conductive layer 202. The insulating layer 320 is provided so as to cover the top and side surfaces of the conductive layer 202. The insulating layer 320 has a portion that protrudes beyond the end of the conductive layer 202. The end of the insulating layer 320 is in contact with the top surface of the insulating layer 310.

[0171] The semiconductor layer 208 is provided over the insulating layer 320. The semiconductor layer 208 has a region overlapping with the conductive layer 202 with the insulating layer 320 interposed therebetween. The same material as that of the semiconductor layer 308 can be used for the semiconductor layer 208. The semiconductor layer 208 can be formed in the same process as that of the semiconductor layer 308. For example, the semiconductor layer 308 and the semiconductor layer 208 can be formed by forming films that will become the semiconductor layer 308 and the semiconductor layer 208 and processing the films.

[0172] An insulating layer 306 is provided over the semiconductor layer 208. Part of the insulating layer 306 functions as a gate insulating layer of the transistor 300, and the other part functions as a gate insulating layer of the transistor 200. The insulating layer 306 has openings 347a and 347b in a region overlapping with the semiconductor layer 208.

[0173] The conductive layer 204, the conductive layer 212a, and the conductive layer 212b are provided over the insulating layer 306. The conductive layer 204 has a region overlapping with the semiconductor layer 208 with the insulating layer 306 interposed therebetween. The conductive layer 204 has a region overlapping with the conductive layer 202 with the semiconductor layer 208 interposed therebetween. The conductive layer 212a and the conductive layer 212b are provided so as to cover at least a part of the opening 347a and the opening 347b. The conductive layer 212a is electrically connected to the semiconductor layer 208 through the opening 347a, and the conductive layer 212b is electrically connected to the semiconductor layer 208 through the opening 347b. The conductive layer 204, the conductive layer 212a, and the conductive layer 212b can be formed using the same material as the conductive layer 304. The conductive layer 204, the conductive layer 212a, and the conductive layer 212b can be formed in the same process as the conductive layer 304. For example, a film to be the conductive layer 304, the conductive layer 204, the conductive layer 212a, and the conductive layer 212b is formed and then processed to form the conductive layer 304, the conductive layer 204, the conductive layer 212a, and the conductive layer 212b.

[0174] The transistor 200 is a planar transistor in which the semiconductor layer 208 is arranged in a planar shape. The transistor 200 is also a so-called top-gate transistor having a gate electrode above the semiconductor layer 208. For example, by adding an impurity element to the semiconductor layer 208 using the conductive layer 204 functioning as the gate electrode as a mask, regions 208D functioning as source and drain regions can be formed in a self-aligned manner. The transistor 200 can be referred to as a TGSA (Top Gate Self-Aligned) transistor.

[0175] The channel length of the transistor 200 can be controlled by the length of the conductive layer 204. Therefore, the channel length of the transistor 200 is equal to or greater than the resolution limit of an exposure apparatus used to manufacture the transistor. That is, the channel length of the transistor 200 can be made longer than the channel length of the transistor 300. By increasing the channel length, the transistor can have high saturation properties.

[0176] The transistor 300 having a short channel length and the transistor 200 having a long channel length can be formed over the same substrate by sharing some of the steps. For example, by applying the transistor 300 to a transistor that requires a large on-state current and the transistor 200 to a transistor that requires high saturation, a high-performance semiconductor device can be obtained.

[0177] For example, when the semiconductor device of one embodiment of the present invention is applied to a pixel circuit of a display device, the area occupied by the pixel circuit can be reduced, and a high-resolution display device can be obtained.Furthermore, when the semiconductor device of one embodiment of the present invention is applied to a driver circuit of a display device (e.g., one or both of a gate line driver circuit and a source line driver circuit), the area occupied by the driver circuit can be reduced, and a display device with a narrow frame can be obtained.

[0178] The capacitor 350 includes a conductive layer 312b and a conductive layer 202 that function as a pair of electrodes, and an insulating layer 320. The conductive layer 312b functions as the other of the source and drain electrodes of the transistor 300 and also functions as one electrode of the capacitor 350. The conductive layer 202 functions as a backgate electrode of the transistor 200 and also functions as the other electrode of the capacitor 350. A region of the insulating layer 320 sandwiched between the conductive layer 312b and the conductive layer 202 functions as a dielectric of the capacitor 350. By forming the conductive layer 312b and the conductive layer 202 in different processes, the capacitor 350 including these conductive layers as a pair of electrodes can be formed. Furthermore, by forming the conductive layer 312b and the conductive layer 202 in different processes, different materials can be used, thereby widening the range of material selection.

[0179] 11A and the like, an example has been described in which the capacitor 350 is configured with the conductive layer 312b, the conductive layer 202, and the insulating layer 320, but the configuration of the capacitor 350 is not particularly limited. As another example of the configuration of the capacitor 350, for example, the capacitor 350 is configured with the conductive layer 212a (or the conductive layer 212b), the conductive layer 312b, and the insulating layer 306. Also, for example, the capacitor 350 is configured with the conductive layer 202, the conductive layer 312a, and the insulating layer 310. The semiconductor device 10 does not necessarily have to include the capacitor 350. Note that when the capacitor 350 configured with the conductive layer 312b, the conductive layer 202, and the insulating layer 320 is not provided, the conductive layer 312b and the conductive layer 202 may be formed in the same process.

[0180] In Figure 11A and other figures, a configuration is shown in which the other of the source electrode and drain electrode of the transistor 300 is electrically connected to one electrode of the capacitor 350, and the back gate electrode of the transistor 200 is electrically connected to the other electrode of the capacitor 350, but the electrical connection relationship between the transistor 300, the transistor 200, and the capacitor 350 is not particularly limited.

[0181] An insulating layer 395 is provided to cover the transistor 300, the transistor 200, and the capacitor 350. The insulating layer 395 functions as a protective layer for the transistor 300, the transistor 200, and the capacitor 350.

[0182] The semiconductor material used for the semiconductor layer 308 and the semiconductor layer 208 is not particularly limited. For example, a semiconductor made of a single element or a compound semiconductor can be used. Examples of semiconductors made of a single element include silicon and germanium. Examples of compound semiconductors include gallium arsenide and silicon germanium. Other examples of compound semiconductors include organic semiconductors, nitride semiconductors, and oxide semiconductors. Note that these semiconductor materials may contain impurities as dopants.

[0183] The crystallinity of the semiconductor material used for the semiconductor layer 308 and the semiconductor layer 208 is not particularly limited, and any of an amorphous semiconductor, a single crystalline semiconductor, and a semiconductor having crystallinity other than single crystal (a microcrystalline semiconductor, a polycrystalline semiconductor, or a semiconductor having a crystalline region in part) may be used. The use of a single crystalline semiconductor or a crystalline semiconductor is preferable because it can suppress deterioration of transistor characteristics.

[0184] The semiconductor layer 308 and the semiconductor layer 208 can each be made of silicon. Examples of silicon include single crystal silicon, polycrystalline silicon, microcrystalline silicon, and amorphous silicon. Examples of polycrystalline silicon include low temperature polysilicon (LTPS). A transistor using amorphous silicon for its channel formation region can be formed on a large glass substrate and manufactured at low cost. A transistor using polycrystalline silicon for its channel formation region has high field-effect mobility and can operate at high speed. Furthermore, a transistor using microcrystalline silicon for its channel formation region has higher field-effect mobility and can operate at high speed than a transistor using amorphous silicon.

[0185] The semiconductor layer 308 and the semiconductor layer 208 each preferably include a metal oxide (also referred to as an oxide semiconductor) that exhibits semiconductor characteristics.

[0186] The band gap of each of the metal oxides used for the semiconductor layer 308 and the semiconductor layer 208 is preferably 2.0 eV or more, more preferably 2.5 eV or more.

[0187] A transistor including an oxide semiconductor in a channel formation region (OS transistor) has significantly higher field-effect mobility than a transistor using amorphous silicon. Furthermore, the OS transistor has a significantly smaller off-state current. The off-state current of an OS transistor per 1 μm of channel width in a room temperature environment is 1 aA (1×10 −１８ A) Below, 1zA (1×10 −２１ A) or less, or 1 yA (1 x 10 −２４In the case of a Si transistor, the off-state current per 1 μm of channel width in a room temperature environment can be 1 fA (1×10 −１５ A) or more and 1 pA (1 × 10 −１２ A) or less. Therefore, it can be said that the off-state current of an OS transistor is about 10 orders of magnitude smaller than that of a Si transistor. Therefore, for example, when a wiring electrically connected to one of the source and drain of an OS transistor is floating, charge accumulated in the wiring can be held for a long period of time. Therefore, for example, by configuring a memory cell using an OS transistor, data written to the memory cell can be stored for a long period of time.

[0188] Furthermore, the off-state current of an OS transistor hardly increases even in a high-temperature environment. Specifically, the off-state current hardly increases even in an environment of room temperature or higher and 200° C. or lower. The on-state current of an OS transistor is unlikely to decrease even in a high-temperature environment. On the other hand, the on-state current of a Si transistor decreases in a high-temperature environment. That is, the on-state current of an OS transistor is larger than that of a Si transistor in a high-temperature environment. Furthermore, an OS transistor can perform favorable switching operation even in an environment of 125° C. or higher and 150° C. or lower because of its large ratio of on-state current to off-state current. Therefore, a semiconductor device using an OS transistor can operate stably and with high reliability even in a high-temperature environment.

[0189] Furthermore, an OS transistor has a high withstand voltage between the source and the drain (also referred to as drain withstand voltage). Therefore, a semiconductor device including an OS transistor can operate stably and with high reliability even when driven at high voltage.

[0190] 11A to 11C, 12A, and 12B, the detailed structure of the transistor 300 will be described. FIGS. 12A and 12B are enlarged views of the transistor 300 shown in FIGS.

[0191] The insulating layer 310 preferably includes one or more inorganic insulating films. Materials that can be used for the inorganic insulating film include, for example, oxides, nitrides, oxynitrides, and nitride oxides. Examples of oxides include silicon oxide, aluminum oxide, magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide, tantalum oxide, cerium oxide, gallium zinc oxide, and hafnium aluminate. Examples of nitrides include silicon nitride and aluminum nitride. Examples of oxynitrides include silicon oxynitride, aluminum oxynitride, gallium oxynitride, yttrium oxynitride, and hafnium oxynitride. Examples of nitride oxides include silicon nitride oxide and aluminum nitride oxide.

[0192] In this specification and the like, an oxynitride refers to a material having a composition in which oxygen is contained in a larger amount than nitrogen, and a nitride oxide refers to a material having a composition in which nitrogen is contained in a larger amount than oxygen.

[0193] In the transistor 300, the insulating layer 310 has a region in contact with the semiconductor layer 308. When a metal oxide is used for the semiconductor layer 308, at least a part of the region of the insulating layer 310 in contact with the semiconductor layer 308 preferably contains oxygen in order to improve the interfacial characteristics between the semiconductor layer 308 and the insulating layer 310. Specifically, the region of the insulating layer 310 in contact with the channel formation region of the semiconductor layer 308 preferably contains oxygen. One or more of an oxide and an oxynitride can be used in the region of the insulating layer 310 in contact with the channel formation region of the semiconductor layer 308.

[0194] 11B and other drawings show an example in which the insulating layer 310 has an insulating layer 310a, an insulating layer 310b on the insulating layer 310a, and an insulating layer 310c on the insulating layer 310b.

[0195] A region of the semiconductor layer 308 in contact with the insulating layer 310b functions as a channel formation region. The insulating layer 310b preferably contains oxygen and is preferably made of one or more of the above-described oxides and oxynitrides. Specifically, the insulating layer 310b can be made of silicon oxide, silicon oxynitride, or both.

[0196] It is more preferable to use a film that releases oxygen by heating for the insulating layer 310b. When the insulating layer 310b releases oxygen due to heat applied during the manufacturing process of the transistor 300, oxygen can be supplied to the semiconductor layer 308. When oxygen is supplied from the insulating layer 310b to the semiconductor layer 308, particularly to the channel formation region, oxygen vacancies (V Ｏ Therefore, the oxygen vacancies can be repaired and the oxygen vacancies can be reduced, resulting in a highly reliable transistor with favorable electrical characteristics.

[0197] For example, oxygen can be supplied to the insulating layer 310b by heat treatment in an oxygen-containing atmosphere or plasma treatment in an oxygen-containing atmosphere. Alternatively, oxygen may be supplied to the insulating layer 310b by forming an oxide film on the top surface of the insulating layer 310b by a sputtering method in an oxygen-containing atmosphere. Then, the oxide film may be removed.

[0198] It is preferable that hydrogen in the semiconductor layer 308, particularly in the channel formation region, be reduced as much as possible. Hydrogen in the semiconductor layer 308 combines with oxygen vacancies to form defects in which hydrogen enters the oxygen vacancies (V Ｏ Therefore, a material that releases less hydrogen is preferably used as a material surrounding the semiconductor layer 308, for example, as a material used for an insulating layer in contact with the semiconductor layer 308 (for example, the insulating layer 310a, the insulating layer 310b, the insulating layer 310c, and the insulating layer 306).

[0199] The insulating layer 310b is preferably formed by a deposition method such as a sputtering method or a plasma-enhanced chemical vapor deposition (PECVD) method. In particular, by forming the insulating layer 310b by a sputtering method without using hydrogen gas as a deposition gas, a film with an extremely low hydrogen content can be obtained. Therefore, the supply of hydrogen to the channel formation region can be suppressed, and the electrical characteristics of the transistor 300 can be stabilized.

[0200] It is preferable that a substance diffuses easily in the insulating layer 310b. It can also be said that a large diffusion coefficient of the substance in the insulating layer 310b is preferable. In particular, it is preferable that oxygen diffuses easily in the insulating layer 310b. That is, it is preferable that the diffusion coefficient of oxygen in the insulating layer 310b is large. The oxygen contained in the insulating layer 310b diffuses in the insulating layer 310b and is supplied to the semiconductor layer 308 through the interface between the insulating layer 310b and the semiconductor layer 308. By making the insulating layer 310b into which oxygen diffuses easily, the oxygen contained in the insulating layer 310b can be efficiently supplied to the semiconductor layer 308 (particularly, the channel formation region).

[0201] The oxygen diffusion coefficient of the insulating layer 310b at 350°C is 5×10 −１２ cm ２ / sec or more is preferable, and 1×10 −１１ cm ２ / sec or more is preferable, and 5×10 −１１ cm ２ / sec or more is preferable, and 1×10 −１０ cm ２ / sec or more is preferable. This allows oxygen contained in the insulating layer 310b to be efficiently supplied to the semiconductor layer 308. Since a large diffusion coefficient is preferable, no upper limit is particularly set. The diffusion coefficient can be calculated by, for example, thermal desorption spectroscopy (TDS). Alternatively, secondary ion mass spectrometry (SIMS) may also be used.

[0202] Here, by using a material with high conductivity for the semiconductor layer 308, a transistor with high on-state current can be obtained. However, using a material with high conductivity makes it easy for oxygen vacancies to form. If the oxygen vacancies in the channel formation region increase, the threshold voltage of the transistor shifts, and the drain current (hereinafter also referred to as cutoff current) that flows when the gate voltage is 0 V may become large. For example, in an n-channel transistor, a negative shift in the threshold voltage may increase the cutoff current. By providing the insulating layer 310b, oxygen is supplied to at least the region of the semiconductor layer 308 that is in contact with the insulating layer 310b, i.e., the channel formation region, thereby reducing the oxygen vacancies in the channel formation region. This suppresses the shift in threshold voltage, enabling a transistor with both a small cutoff current and a large on-state current to be obtained. Therefore, a semiconductor device with both low power consumption and high performance can be obtained.

[0203] A region of the semiconductor layer 308 in contact with the conductive layer 312a functions as one of a source region and a drain region of the transistor 300, and a region of the semiconductor layer 308 in contact with the conductive layer 312b functions as the other. The source region and the drain region have lower electrical resistance than the channel formation region. The source region and the drain region can also be referred to as a region with a higher carrier concentration or a higher oxygen vacancy density than the channel formation region.

[0204] The insulating layer 310a is provided between the insulating layer 310b and the conductive layer 312a. The insulating layer 310c is provided between the insulating layer 310b and the conductive layer 312b. The insulating layer 310a and the insulating layer 310c preferably emit little impurities (e.g., hydrogen and water) and are less permeable to impurities. This can prevent impurities contained in the insulating layer 310a and the insulating layer 310c from diffusing into the channel formation region. Therefore, a highly reliable transistor can be obtained, exhibiting favorable electrical characteristics.

[0205] The insulating layer 310a and the insulating layer 310c are preferably made of a film that is difficult for oxygen to permeate. This can prevent oxygen contained in the insulating layer 310b from diffusing to the conductive layer 312a through the insulating layer 310a. Similarly, it can prevent oxygen contained in the insulating layer 310b from diffusing to the conductive layer 312b through the insulating layer 310c. This can prevent the electrical resistance of the conductive layer 312a and the conductive layer 312b from increasing. At the same time, since the oxygen contained in the insulating layer 310b is prevented from diffusing to the insulating layer 310a side and the insulating layer 310c side, the amount of oxygen supplied from the insulating layer 310b to the channel formation region increases, and oxygen vacancies in the channel formation region and V Ｏ H can be reduced.

[0206] By using a film through which oxygen does not easily diffuse as each of the insulating layer 310a and the insulating layer 310c, oxygen can be effectively supplied from the insulating layer 310b to the channel formation region. Note that a structure in which one or both of the insulating layer 310a and the insulating layer 310c are not provided may also be used.

[0207] The insulating layer 310a and the insulating layer 310c each preferably contain nitrogen and preferably use one or more of the above-mentioned nitrides and nitride oxides. The insulating layer 310a and the insulating layer 310c can each use, for example, silicon nitride or silicon nitride oxide. Alternatively, one or both of the insulating layer 310a and the insulating layer 310c may use one or more of an oxide and an oxynitride. The insulating layer 310a and the insulating layer 310c can each use, for example, aluminum oxide. Note that the insulating layer 310a may use the same material as the insulating layer 310c, or a different material.

[0208] In this specification and the like, different materials refer to materials in which some or all of the constituent elements are different, or materials in which the constituent elements are the same but the composition is different.

[0209] The thickness T310a of the insulating layer 310a may be, for example, 3 nm or more, 5 nm or more, 10 nm or more, 20 nm or more, 50 nm or more, or 70 nm or more, and may be less than 1 μm, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less, 150 nm or less, or 120 nm or less. The thickness T310a may be the shortest distance between the surface on which the insulating layer 310a is formed (here, the upper surface of the conductive layer 312a) and the lower surface of the insulating layer 310b in a cross-sectional view, as shown in FIG. 12B .

[0210] If the thickness T310a of the insulating layer 310a is large, the amount of impurities released from the insulating layer 310a increases, which may result in an increase in the amount of impurities diffusing into the channel formation region. On the other hand, if the thickness T310a is small, oxygen contained in the insulating layer 310b may diffuse to the conductive layer 312a side through the insulating layer 310a, which may result in a decrease in the amount of oxygen supplied to the channel formation region. By setting the thickness T310a within the above range, oxygen vacancies in the channel formation region and V Ｏ It is possible to reduce H. In addition, it is possible to prevent the conductive layer 312a from being oxidized by oxygen contained in the insulating layer 310b, and to prevent the electrical resistance of the conductive layer 312a from increasing.

[0211] The thickness T310c of the insulating layer 310c may be, for example, 3 nm or more, 5 nm or more, 10 nm or more, 15 nm or more, or 20 nm or more, and may be 1 μm or less, 500 nm or less, 300 nm or less, 200 nm or less, 150 nm or less, 120 nm or less, or 100 nm or less. The thickness T310c may be the shortest distance between the surface on which the insulating layer 310c is formed (here, the upper surface of the insulating layer 310b) and the lower surface of the conductive layer 312b in a cross-sectional view, as shown in FIG.

[0212] If the thickness T310c of the insulating layer 310c is large, the amount of impurities released from the insulating layer 310c increases, which may result in an increase in the amount of impurities diffusing into the channel formation region. On the other hand, if the thickness T310c is small, oxygen contained in the insulating layer 310b may diffuse to the conductive layer 312b side through the insulating layer 310c, which may result in a decrease in the amount of oxygen supplied to the channel formation region. By setting the thickness T310c within the above range, oxygen vacancies in the channel formation region and VＯ It is possible to reduce H. In addition, it is possible to prevent the conductive layer 312b from being oxidized by oxygen contained in the insulating layer 310b, and to prevent the electrical resistance of the conductive layer 312b from increasing.

[0213] At least one of the region of the semiconductor layer 308 in contact with the insulating layer 310a and the region of the semiconductor layer 308 in contact with the insulating layer 310c may have lower electrical resistance than the channel formation region (hereinafter also referred to as a low-resistance region). This region can also be referred to as a region with a higher carrier concentration or a higher oxygen vacancy density than the channel formation region. By using a material that releases impurities (e.g., water and hydrogen) for the insulating layer 310a, the region of the semiconductor layer 308 in contact with the insulating layer 310a can be a low-resistance region. The semiconductor layer 308 can have a low-resistance region between the region in contact with the conductive layer 312a (one of the source region and the drain region) and the channel formation region. Similarly, by using a material that releases impurities for the insulating layer 310c, the region of the semiconductor layer 308 in contact with the insulating layer 310c can be a low-resistance region. The semiconductor layer 308 can have a low-resistance region between the region in contact with the conductive layer 312b (the other of the source region and the drain region) and the channel formation region. The low resistance region can function as a buffer region for alleviating the drain electric field. Note that these low resistance regions may also function as source or drain regions.

[0214] By providing a low-resistance region between the drain region and the channel formation region, a high electric field is less likely to be generated near the drain region, which can suppress the generation of hot carriers and the deterioration of the transistor. For example, when the conductive layer 312a functions as a drain electrode and the conductive layer 312b functions as a source electrode, by making the region of the semiconductor layer 308 in contact with the insulating layer 310a a low-resistance region, a high electric field is less likely to be generated near the drain region, which can suppress the generation of hot carriers and the deterioration of the transistor. When the conductive layer 312a functions as a source electrode and the conductive layer 312b functions as a drain electrode, by making the region of the semiconductor layer 308 in contact with the insulating layer 310c a low-resistance region, a high electric field is less likely to be generated near the drain region, which can suppress the generation of hot carriers and the deterioration of the transistor.

[0215] As described above, if the amount of impurities released from the insulating layer 310 a and the insulating layer 310 c is too large, the impurities may diffuse into the channel formation region. Even when a material that releases impurities is used for the insulating layer 310 a and the insulating layer 310 c, it is preferable that the amount of released impurities is small.

[0216] Note that the insulating layer 310 preferably includes at least the insulating layer 310b. For example, a structure may be adopted in which one or both of the insulating layer 310a and the insulating layer 310c are not included. The insulating layer 310 may have a stacked structure of two layers, four or more layers, or a single layer structure.

[0217] The top surface shape of the openings 341 and 343 is not limited and may be, for example, a circle, an ellipse, a triangle, a quadrangle (including a rectangle, a diamond, and a square), a pentagon, or any other polygonal shape, including shapes with rounded corners. The polygon may be either a concave polygon (a polygon with at least one interior angle exceeding 180 degrees) or a convex polygon (a polygon with all interior angles equal to or less than 180 degrees). As shown in FIG. 11A and other figures, the top surface shape of the openings 341 and 343 is preferably circular. By making the top surface shape of the openings circular, the processing accuracy during the formation of the openings can be improved, allowing for the formation of openings of minute sizes. Note that, in this specification and other figures, "circular" is not limited to a perfect circle.

[0218] By forming the openings 341 and 343 so that their top surfaces have a circular or approximately circular shape, the semiconductor layer 308, the insulating layer 306, and the conductive layer 304 are provided concentrically. This makes the distance between the conductive layer 304 and the semiconductor layer 308 uniform, allowing a gate electric field to be applied uniformly to the semiconductor layer 308.

[0219] In this specification and the like, the top surface shape of the opening 341 refers to the shape of the top surface end portion of the insulating layer 310 on the opening 341 side. Also, the top surface shape of the opening 343 refers to the shape of the bottom surface end portion of the conductive layer 312b on the opening 343 side.

[0220] 11A and other figures, the top shapes of openings 341 and 343 can be the same. In this case, as shown in Figures 11B and 11C and other figures, it is preferable that the height of the bottom surface end of conductive layer 312b on the opening 343 side is the same as the height of the top surface end of insulating layer 310 on the opening 341 side. The bottom surface of conductive layer 312b refers to the surface on the insulating layer 310 side. The top surface of insulating layer 310 refers to the surface on the conductive layer 312b side.

[0221] The top surface shapes of openings 341 and 343 do not have to be the same. Furthermore, when the top surfaces of openings 341 and 343 are circular, openings 341 and 343 may or may not be concentric.

[0222] The channel length and channel width of the transistor 300 will be described with reference to FIGS. 12A and 12B.

[0223] In FIG. 12B , the channel length L300 of the transistor 300 is indicated by a dashed double-headed arrow. The channel length L300 of the transistor 300 corresponds to the length of the side surface of the insulating layer 310b on the opening 341 side in a cross-sectional view. That is, the channel length L300 is determined by the thickness T310b of the insulating layer 310b and the angle θ310 between the side surface of the insulating layer 310b on the opening 341 side and the surface on which the insulating layer 310b is to be formed (here, the upper surface of the insulating layer 310a). Therefore, the channel length L300 can be set to a value smaller than the resolution limit of the exposure equipment, enabling the realization of a fine-sized transistor. Specifically, it is possible to realize a transistor with an extremely small channel length that is difficult to achieve using conventional exposure equipment used in the mass production of flat panel displays (e.g., minimum line widths of approximately 2 μm or 1.5 μm). Furthermore, it is possible to realize a transistor with a channel length of less than 10 nm without using the extremely expensive exposure equipment used in cutting-edge LSI technology.

[0224] The channel length L300 can be, for example, 1 nm or more, 5 nm or more, 7 nm or more, or 10 nm or more, and can be less than 3 μm, 2.5 μm or less, 2 μm or less, 1.5 μm or less, 1.2 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, 200 nm or less, 100 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. For example, the channel length L300 can be 100 nm or more and 1 μm or less.

[0225] By reducing the channel length L300, the on-state current of the transistor 300 can be increased. By using the transistor 300, a circuit capable of high-speed operation can be manufactured. Furthermore, the area occupied by the circuit can be reduced. Therefore, a small-sized semiconductor device can be obtained. For example, when the semiconductor device of one embodiment of the present invention is applied to a large display device or a high-resolution display device, even if the number of wirings is increased, signal delay in each wiring can be reduced, and display unevenness can be suppressed. Furthermore, since the area occupied by the circuit can be reduced, the frame of the display device can be narrowed.

[0226] The channel length L300 can be controlled by adjusting the thickness T310b of the insulating layer 310b and the angle θ310. In Fig. 12B, the thickness T310b of the insulating layer 310b is indicated by a dashed double-headed arrow.

[0227] The thickness T310b of the insulating layer 310b can be, for example, 1 nm or more, 5 nm or more, 7 nm or more, or 10 nm or more, and can be less than 3 μm, 2.5 μm or less, 2 μm or less, 1.5 μm or less, 1.2 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, 200 nm or less, 100 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less.

[0228] The side surface of the insulating layer 310 on the opening 341 side is preferably vertical or tapered. The angle θ310 is preferably 90 degrees or less. By reducing the angle θ310, the coverage of a layer (e.g., the semiconductor layer 308) formed on the insulating layer 310 can be improved. Furthermore, the smaller the angle θ310, the longer the channel length L300 can be, and the larger the angle θ310 (closer to 90 degrees), the shorter the channel length L300 can be.

[0229] The angle θ310 can be, for example, 30 degrees or more, 35 degrees or more, 40 degrees or more, 45 degrees or more, 50 degrees or more, 55 degrees or more, 60 degrees or more, 65 degrees or more, or 70 degrees or more, and can be 90 degrees or less, 85 degrees or less, or 80 degrees or less. The angle θ310 may also be 75 degrees or less, 70 degrees or less, 65 degrees or less, or 60 degrees or less.

[0230] 12B and other drawings show a cross-sectional view in which the side surface of the insulating layer 310 on the opening 341 side has a straight line shape, but one embodiment of the present invention is not limited to this. In a cross-sectional view, the side surface of the insulating layer 310 on the opening 341 side may have a curved line shape, or the side surface may have both a straight line region and a curved line region.

[0231] Here, the conductive layer 312b is preferably not provided inside the opening 341. Specifically, the conductive layer 312b preferably does not have a region in contact with the side surface of the insulating layer 310 on the opening 341 side. If the conductive layer 312b is also provided inside the opening 341, the channel length L300 of the transistor 300 becomes shorter than the length of the side surface of the insulating layer 310b, which may make it difficult to control the channel length L300. Therefore, it is preferable that the top shape of the opening 343 is the same as the top shape of the opening 341, or that the opening 343 encompasses the opening 341 in a top view.

[0232] 12A and 12B, the width D341 of the opening 341 is indicated by a two-dot chain line with a double-headed arrow. FIG. 12A shows an example in which the top surface shape of the opening 341 is circular. In this case, the width D341 corresponds to the diameter of the circle, and the channel width W300 of the transistor 300 is the length of the circumference of the circle. In other words, the channel width W300 is π×D341. In this way, when the top surface shape of the opening 341 is circular, a transistor with a smaller channel width W300 can be realized compared to other shapes.

[0233] If the top surface shape of the opening 341 is other than circular (for example, substantially circular or rectangular with rounded corners), the maximum width of the top surface shape may be set as the width D341, for example.

[0234] The width D341 of the opening 341 may vary in the depth direction. For example, the width D341 of the opening 341 may be an average value of the diameter at the highest point, the diameter at the lowest point, and the diameter at the midpoint between these three diameters of the insulating layer 310b (or the insulating layer 310) in a cross-sectional view. Alternatively, the diameter of the opening 341 may be any of the diameter at the highest point, the diameter at the lowest point, and the diameter at the midpoint between these three diameters of the insulating layer 310b (or the insulating layer 310) in a cross-sectional view.

[0235] When forming the opening 341 using photolithography, the width D341 of the opening 341 is equal to or greater than the resolution limit of the exposure device. When using a conventional exposure device for mass production of flat panel displays, the width D341 can be, for example, 200 nm or more, 300 nm or more, 400 nm or more, or 500 nm or more, and less than 5 μm, 4.5 μm or less, 4 μm or less, 3.5 μm or less, 3 μm or less, 2.5 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less. Alternatively, when using an extremely expensive exposure device used in cutting-edge LSI technology, the width D341 can be, for example, 5 nm or more, 10 nm or more, or 20 nm or more, and less than 100 nm, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less.

[0236] The channel length L300 of the transistor 300 is preferably at least shorter than the channel width W300 of the transistor 300. The channel length L300 of the transistor 300 is 0.1 to 0.99 times, preferably 0.5 to 0.8 times, the channel width W300 of the transistor 300. With such a structure, a transistor with favorable electrical characteristics and high reliability can be realized.

[0237] Note that, when the channel length L300 of the transistor 300 is reduced, the insulating layers 310a and 310c are preferably made of materials that release less hydrogen. When the insulating layers 310a and 310c are made of materials that release even a small amount of hydrogen, their thicknesses are preferably thin. For example, when the channel length L300 is set to 100 nm or less, the thickness T310a of the insulating layer 310a and the thickness T310c of the insulating layer 310c are preferably 1 nm or more, 3 nm or more, or 5 nm or more, and 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, 15 nm or less, or 10 nm or less. This reduces the amount of impurities diffusing into the channel formation region, resulting in a highly reliable transistor that exhibits good electrical characteristics even when the channel length L300 is short.

[0238] Note that although the structure in which the region of the semiconductor layer 308 in contact with the insulating layer 310b functions as a channel formation region has been described as an example here, one embodiment of the present invention is not limited to this. The region of the semiconductor layer 308 in contact with the insulating layer 310a may also function as a channel formation region. Similarly, the region in contact with the insulating layer 310c may also function as a channel formation region.

[0239] 11B and the like illustrate an example in which the semiconductor layer 308, the insulating layer 306, and the conductive layer 304 cover the openings 341 and 343 in the transistor 300; however, one embodiment of the present invention is not limited to this. A step may be formed between the insulating layer 310 and the conductive layer 312a, and the semiconductor layer 308, the insulating layer 306, and the conductive layer 304 may be provided along the step.

[0240] 13A to 13C are enlarged views of the transistor 200 shown in FIGS. 11A to 11C.

[0241] The channel length of the transistor 200 is the length of the region where the semiconductor layer 208 and the conductive layer 204 overlap between the pair of regions 208D. In Figures 13A and 13B, the channel length L200 of the transistor 200 is indicated by a dashed double-headed arrow. The channel length L200 of the transistor 200 is determined by the length of the conductive layer 204 in the channel length direction and is equal to or greater than the resolution limit of an exposure device used to fabricate the transistor. For example, the channel length L200 can be 1.5 μm or greater. By increasing the channel length, the transistor can have high saturation properties.

[0242] The conductive layer 202 functioning as the back gate electrode of the transistor 200 preferably extends beyond the edge of the channel formation region. Specifically, the conductive layer 202 preferably has a portion that protrudes beyond the edge of the conductive layer 204 in the channel length direction.

[0243] For ease of explanation, in this specification, the portion of the semiconductor layer 208 that overlaps with the conductive layer 204 is described as a channel formation region; however, in reality, a channel can also be formed in the portion that overlaps with the conductive layer 202 without overlapping with the conductive layer 204.

[0244] The channel width of the transistor 200 is the width of the region in the direction perpendicular to the channel length direction where the semiconductor layer 208 and the conductive layer 204 overlap. In Figures 13A and 13C, the channel width W200 of the transistor 200 is indicated by a dashed double-headed arrow.

[0245] As described above, the channel length L300 of the transistor 300 can be set to a value smaller than the resolution limit of the exposure tool, and the channel length L200 of the transistor 200 can be set to a value equal to or greater than the resolution limit of the exposure tool. For example, by applying the transistor 300 to a transistor requiring a large on-state current and the transistor 200 to a transistor requiring high saturation, the semiconductor device 10 can be formed with high performance by utilizing the advantages of each transistor. Furthermore, the transistors 300 and 200 can be formed using some common processes. Specifically, the semiconductor layer 308 and the semiconductor layer 208 can be formed in the same process. A part of the insulating layer 306 functions as a gate insulating layer for the transistor 300, and another part of the insulating layer 306 functions as a gate insulating layer for the transistor 200. The conductive layer 304, the conductive layer 204, the conductive layer 212a, and the conductive layer 212b can be formed in the same process. This can improve the productivity of the semiconductor device 10 and reduce manufacturing costs.

[0246] 13A and 13C , the conductive layers 204 and 202 preferably protrude outward beyond the end portions of the semiconductor layer 208 in the channel width direction of the transistor 200. In this case, as shown in Fig. 13C , the entire semiconductor layer 208 in the channel width direction is covered with the conductive layers 204 and 202 via the insulating layers 306 and 320. With this structure, the semiconductor layer 208 can be electrically surrounded by an electric field generated by the pair of gate electrodes.

[0247] Note that the transistor 200 may not include the conductive layer 202 or the insulating layer 320. In other words, the transistor 200 may not include a backgate electrode.

[0248] 14 is a cross-sectional view of a transistor 200A, which is a variation of the transistor 200. The transistor 200A differs from the transistor 200 in that the transistor 200A does not include the conductive layer 202 and the insulating layer 320. This can reduce process costs, for example.

[0249] 13A and 13C show a configuration in which the conductive layer 204 (i.e., the gate electrode) and the conductive layer 202 (i.e., the back gate electrode) are not electrically connected to each other. A constant potential may be applied to one of the gate electrode or the back gate electrode, and a signal for driving the transistor 200 may be applied to the other. In this case, when the transistor 200 is driven by a signal applied to the other of the gate electrode or the back gate electrode, the threshold voltage can be controlled by the potential applied to one of the gate electrode or the back gate electrode.

[0250] The conductive layer 204 and the conductive layer 202 may be electrically connected. By applying the same potential to the gate electrode and the back gate electrode, an electric field for inducing a channel in the semiconductor layer 208 can be effectively applied, thereby increasing the on-state current of the transistor 200. Therefore, the transistor 200 can be miniaturized. For example, openings reaching the conductive layer 202 can be formed in the insulating layer 306 and the insulating layer 320, and the conductive layer 204 can be formed to cover the openings.

[0251] The conductive layer 202 may be electrically connected to the conductive layer 212a or the conductive layer 212b (i.e., the source electrode or the drain electrode). The back gate voltage can be set to 0 V by applying the same potential to the back gate electrode and the source electrode. In addition, the back gate voltage can be set to the same voltage as the drain voltage by applying the same potential to one of the back gate electrode and the drain electrode. For example, an opening reaching the conductive layer 202 can be formed in the insulating layer 320, and the conductive layer 212a or the conductive layer 212b can be formed to cover the opening.

[0252] The insulating layer 320 provided in contact with the top surface and side surfaces of the conductive layer 202 can be formed using the same material as that used for the insulating layer 310 .

[0253] The insulating layer 320 preferably has a layered structure. In Fig. 13B and other figures, the insulating layer 320 has a layered structure of an insulating layer 320a and an insulating layer 320b on the insulating layer 320a. The insulating layer 320a and the insulating layer 320b can each be made of a material that can be used for the insulating layer 310.

[0254] It is more preferable to use a film that releases oxygen when heated for the insulating layer 320b in contact with the channel formation region of the semiconductor layer 208. When the insulating layer 320b releases oxygen due to heat applied during the manufacturing process of the transistor 200, oxygen can be supplied to the semiconductor layer 208, particularly to the channel formation region of the semiconductor layer 208. The oxygen contained in the insulating layer 320b diffuses in the insulating layer 320b and is supplied to the semiconductor layer 208 through the interface between the insulating layer 320b and the semiconductor layer 208. By supplying oxygen from the insulating layer 320b to the semiconductor layer 208, particularly to the channel formation region, oxygen vacancies can be repaired and reduced. Therefore, a transistor exhibiting good electrical characteristics and high reliability can be obtained.

[0255] The oxygen diffusion coefficient of the insulating layer 320b at 350°C is 1×10 −１２ cm ２ / sec or more is preferable, and 5×10 −１２ cm ２ / sec or more is preferable.

[0256] The insulating layer 320b can be made of the same material as the insulating layer 310b. The insulating layer 320b preferably contains oxygen, and can be made of one or more of an oxide and an oxynitride. Specifically, the insulating layer 320b can be made of, for example, silicon oxide or silicon oxynitride.

[0257] Here, compared with the transistor 300 having a short channel length, the transistor 200 having a long channel length has oxygen vacancies in the channel formation region and V Ｏ H has little effect on the electrical characteristics. Therefore, the amount of oxygen supplied from the insulating layer 320b to the semiconductor layer 208 may be smaller than the amount of oxygen supplied from the insulating layer 310b to the semiconductor layer 308. The amount of oxygen released from the insulating layer 320b may be smaller than the amount of oxygen released from the insulating layer 310b.

[0258] The diffusion coefficient of the substance in the insulating layer 310b is preferably larger than that in the insulating layer 320b. In particular, the diffusion coefficient of oxygen in the insulating layer 310b is preferably larger than that in the insulating layer 320b. This allows the transistor 300, even with a short channel length, to exhibit favorable electrical characteristics and be a highly reliable transistor.

[0259] The insulating layer 320a in contact with the conductive layer 202 is preferably made of a material that does not easily diffuse metal elements contained in the conductive layer 202. This can prevent the metal elements contained in the conductive layer 202 from diffusing into the channel formation region of the semiconductor layer 208 through the insulating layer 320.

[0260] The insulating layer 320a is preferably made of a material that can be used for the insulating layer 310a and the insulating layer 310c. The insulating layer 320a preferably contains nitrogen, and one or more of a nitride and a nitride oxide can be used. Specifically, the insulating layer 320a can be made of, for example, silicon nitride. Alternatively, the insulating layer 320a may be made of one or more of an oxide and an oxynitride. The insulating layer 320a can be made of, for example, aluminum oxide. Note that the insulating layer 320a, the insulating layer 310a, and the insulating layer 310c may be made of the same material or different materials.

[0261] The insulating layer 320a preferably releases little impurities (for example, water and hydrogen) from itself, which can prevent impurities contained in the insulating layer 320a from diffusing into the channel formation region of the semiconductor layer 208 through the insulating layer 320b, thereby providing a highly reliable transistor with favorable electrical characteristics.

[0262] Note that although the insulating layer 320 has a two-layer structure here, one embodiment of the present invention is not limited to this. The insulating layer 320 may have a stacked structure of three or more layers or a single-layer structure.

[0263] The insulating layer 320 is preferably provided in at least a region in contact with the channel formation region of the semiconductor layer 208 and so as to cover the top surface and side surfaces of the conductive layer 202. Figure 13B and other figures show a structure in which the semiconductor layer 208 has a portion protruding from the end portion of the insulating layer 320. The semiconductor layer 208 has a region in contact with the side surface of the insulating layer 320. Part of the end portion of the semiconductor layer 208 is in contact with the top surface of the insulating layer 320, and another part is in contact with the top surface of the insulating layer 310. It can also be said that part of the bottom surface of the semiconductor layer 208 is in contact with the top surface of the insulating layer 320, and another part is in contact with the top surface of the insulating layer 310. Alternatively, the insulating layer 320 may be provided in the region where the semiconductor layer 208 is provided, and the entire bottom surface of the semiconductor layer 208 may be in contact with the top surface of the insulating layer 320.

[0264] 13B and the like show an example in which the thickness of the semiconductor layer 208 is uniform regardless of location, but one embodiment of the present invention is not limited to this. The thickness of the semiconductor layer 208 may be different between a region that overlaps with the insulating layer 306 and a region that does not overlap with the insulating layer 306. For example, when forming the openings 347a and 347b, part of the semiconductor layer 208 may be removed, and the thickness of the region of the semiconductor layer 208 that does not overlap with the insulating layer 306 may be thinner than the thickness of the overlapping region. Alternatively, the thickness of the semiconductor layer 208 may be different between a region that overlaps with any of the insulating layer 306, the conductive layer 212a, and the conductive layer 212b and a region that does not overlap with any of these layers. For example, when forming the conductive layers 212a and 212b, part of the semiconductor layer 208 may be removed, and the thickness of the region of the semiconductor layer 208 that does not overlap with any of the insulating layer 306, the conductive layer 212a, and the conductive layer 212b may be thinner than the thickness of the region that overlaps with any of these layers. Alternatively, the thickness may be different between the region of the semiconductor layer 208 overlapping with the insulating layer 306, the region overlapping with any of the insulating layer 306, the conductive layer 212a, and the conductive layer 212b, and the region not overlapping with any of these.

[0265] In the semiconductor layer 208, the region 208D has lower electrical resistance than the channel formation region. The region 208D can also be said to have a higher carrier concentration, a higher oxygen vacancy density, or a higher impurity concentration than the channel formation region.

[0266] Region 208L has electrical resistance that is similar to or lower than that of the channel formation region. Region 208L can also be referred to as a region with a carrier concentration that is similar to or higher than that of the channel formation region, a region with an oxygen vacancy density that is similar to or higher than that of the channel formation region, or a region with an impurity concentration that is similar to or higher than that of the channel formation region. Furthermore, region 208L has electrical resistance that is similar to or higher than that of region 208D. Region 208L can also be referred to as a region with a carrier concentration that is similar to or lower than that of region 208D, a region with an oxygen vacancy density that is similar to or lower than that of the channel formation region, or a region with an impurity concentration that is similar to or lower than that of the channel formation region.

[0267] The region 208L functions as a buffer region for reducing the drain electric field. Since the region 208L does not overlap with the conductive layer 204, a channel is hardly formed in the region 208L even when a gate voltage is applied to the conductive layer 204. The region 208L preferably has a higher carrier concentration than the channel formation region. This allows the region 208L to function as an LDD (lightly doped drain) region. By providing the region 208L functioning as an LDD region between the channel formation region and the region 208D, the transistor 200 can have a high drain breakdown voltage.

[0268] The carrier concentration in the semiconductor layer 208 is preferably lowest in the channel formation region and increases in the order of the region 208L and the region 208D. By providing the region 208L between the channel formation region and the region 208D, the carrier concentration in the channel formation region can be kept extremely low even if impurities such as hydrogen diffuse from the region 208D during the manufacturing process, for example.

[0269] The carrier concentration in the region 208L may not be uniform, and may have a gradient such that the carrier concentration decreases from the region 208D side toward the channel formation region. For example, the hydrogen concentration or the oxygen vacancy concentration in the region 208L or both may have a gradient such that the concentration decreases from the region 208D side toward the channel formation region.

[0270] Furthermore, when the region 208L and the region 208D are formed by adding an impurity element to the semiconductor layer 208, the impurity element may be supplied to the semiconductor layer 308 through the insulating layer 306, using the conductive layer 304 as a mask. As a result, the region 308L is formed in a region of the semiconductor layer 308 that does not overlap with the conductive layer 304. Note that in the transistor 300, a region of the semiconductor layer 308 in contact with the conductive layer 312b functions as a source region or a drain region. The region 308L is formed in a part of the source region or drain region. Note that the concentration of the impurity element in the region 308L may be different from the concentration of the impurity element in the region 208L. Alternatively, the region 308L may not be formed. For example, when the conductive layer 304 extends to cover the end of the semiconductor layer 308, the entire semiconductor layer 308 is masked by the conductive layer 304, and therefore the impurity element is not supplied to the semiconductor layer 308, and the region 308L is not formed.

[0271] 13A and 13B , portions of the ends of the conductive layers 212a and 212b are preferably located inside the openings 347a and 347b. In other words, portions of the ends of the conductive layers 212a and 212b are preferably in contact with the semiconductor layer 208 in the openings 347a and 347b. This allows the region in contact with the conductive layer 212a to be adjacent to one of the pair of regions 208D, and similarly, the region in contact with the conductive layer 212b to be adjacent to the other of the pair of regions 208D.

[0272] Note that the top surface shapes of the openings 347a and 347b are not particularly limited. The top surface shapes of the openings 347a and 347b can be any shape that can be applied to the openings 341 and 343. In Figure 13A and other figures, the top surface shapes of the openings 347a and 347b are rectangular with rounded corners, which differs from the top surface shapes of the openings 341 and 343. However, one embodiment of the present invention is not limited to this. The top surface shapes of the openings 347a and 347b may be the same as the top surface shapes of the openings 341 and 343.

[0273] Although the structure in which the conductive layer 212a and the conductive layer 212b are formed in the same process as the conductive layer 204 is described here, one embodiment of the present invention is not limited to this. The conductive layer 212a and the conductive layer 212b may be formed in a process different from that of the conductive layer 204. For example, the conductive layer 304 and the conductive layer 204 are formed over the insulating layer 306, and an impurity element is supplied to the semiconductor layer 208 using the conductive layer 204 as a mask, thereby forming a source region and a drain region. An insulating layer 395 is formed over the conductive layer 304 and the conductive layer 204, and openings reaching the source region and the drain region are formed in the insulating layer 306 and the insulating layer 395, and the conductive layer 212a and the conductive layer 212b can be formed to cover these openings.

[0274] [Semiconductor Layer 308, Semiconductor Layer 208] Metal oxides that can be used for the semiconductor layer 308 and the semiconductor layer 208 will be specifically described. Examples of metal oxides include indium oxide, gallium oxide, and zinc oxide. The metal oxide preferably contains at least indium or zinc. The metal oxide preferably contains two or three elements selected from indium, element M, and zinc. The element M is a metal element or a metalloid element having a high bond energy with oxygen, for example, a metal element or a metalloid element having a bond energy with oxygen higher than that of indium. Specific examples of the element M include aluminum, gallium, tin, yttrium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zirconium, molybdenum, hafnium, tantalum, tungsten, lanthanum, cerium, neodymium, magnesium, calcium, strontium, barium, boron, silicon, germanium, and antimony. The element M contained in the metal oxide is preferably one or more of the above elements, more preferably one or more selected from aluminum, gallium, tin, and yttrium, and even more preferably one or more of gallium and tin. In this specification and the like, metal elements and metalloid elements may be collectively referred to as "metal elements," and the "metal elements" described in this specification and the like may include metalloid elements.

[0275] The semiconductor layer 308 and the semiconductor layer 208 may each be made of, for example, indium oxide (In oxide), indium zinc oxide (In—Zn oxide), indium tin oxide (In—Sn oxide, or ITO), indium titanium oxide (In—Ti oxide), indium gallium oxide (In—Ga oxide), indium tungsten oxide (In—W oxide, or IWO), indium gallium aluminum oxide (In—Ga—Al oxide), indium gallium tin oxide (In—Ga—Sn oxide), gallium zinc oxide (Ga—Zn oxide, or GZO), aluminum zinc oxide (Al—Zn oxide, Indium aluminum zinc oxide (In-Al-Zn oxide or AZO), indium tin zinc oxide (In-Sn-Zn oxide or ITZO (registered trademark)), indium titanium zinc oxide (In-Ti-Zn oxide), indium gallium zinc oxide (In-Ga-Zn oxide or IGZO), indium gallium tin zinc oxide (In-Ga-Sn-Zn oxide or IGZTO), or indium gallium aluminum zinc oxide (In-Ga-Al-Zn oxide, IGAZO, IGZAO, or IAGZO). Alternatively, silicon-containing indium tin oxide (ITSO), gallium tin oxide (Ga-Sn oxide), or aluminum tin oxide (Al-Sn oxide) can be used. Note that Zn-free materials, such as indium oxide, are preferred because of their high compatibility with Si processes. On the other hand, a material containing Zn is preferable because it can improve crystallinity.

[0276] By increasing the ratio of the number of indium atoms to the total number of atoms of all metal elements contained in the metal oxide, the field-effect mobility of the transistor can be increased, and a transistor with a large on-state current can be realized.

[0277] Note that the metal oxide may contain one or more metal elements with a larger periodic number instead of or in addition to indium. The greater the overlap of the orbitals of the metal elements, the greater the carrier conduction in the metal oxide. Therefore, the presence of a metal element with a larger periodic number may improve the field-effect mobility of a transistor. Examples of metal elements with a larger periodic number include metal elements belonging to the fifth period and the sixth period. Specific examples of such metal elements include yttrium, zirconium, silver, cadmium, tin, antimony, barium, lead, bismuth, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium. Note that lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium are called light rare earth elements.

[0278] The metal oxide may contain one or more nonmetallic elements. The presence of the nonmetallic elements in the metal oxide may increase the carrier concentration or narrow the band gap, thereby increasing the field-effect mobility of the transistor. Examples of nonmetallic elements include carbon, nitrogen, phosphorus, sulfur, selenium, fluorine, chlorine, bromine, and hydrogen.

[0279] By increasing the ratio of the number of zinc atoms to the sum of the numbers of atoms of all metal elements contained in the metal oxide, the metal oxide can be made highly crystalline, and the diffusion of impurities in the metal oxide can be suppressed, thereby suppressing fluctuations in the electrical characteristics of the transistor and improving its reliability.

[0280] By increasing the ratio of the number of atoms of element M to the sum of the numbers of atoms of all metal elements contained in the metal oxide, the formation of oxygen vacancies in the metal oxide can be suppressed. Therefore, carrier generation due to oxygen vacancies can be suppressed, and a transistor with a small off-state current can be obtained. Furthermore, fluctuations in the electrical characteristics of the transistor can be suppressed, thereby improving reliability.

[0281] The electrical characteristics and reliability of a transistor vary depending on the composition of the metal oxide applied to the semiconductor layer 308 and the semiconductor layer 208. Therefore, by varying the composition of the metal oxide depending on the electrical characteristics and reliability required of the transistor, a semiconductor device that has both excellent electrical characteristics and high reliability can be obtained.

[0282] When the metal oxide is an In-M-Zn oxide, the atomic ratio of In in the In-M-Zn oxide is preferably equal to or greater than the atomic ratio of M. Examples of atomic ratios of metal elements in such In-M-Zn oxides include In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=2:1:3, In:M:Zn=3:1:2, In:M:Zn=4:2:3, In:M:Zn=4:2:4.1, In:M:Zn=5:1:3, In:M:Zn=5:1:6, In:M:Zn=5:1:7, In:M:Zn=5:1:8, In: Examples of the composition include In:M:Zn = 6:1:6, In:M:Zn = 10:1:1, In:M:Zn = 10:1:3, In:M:Zn = 10:1:4, In:M:Zn = 10:1:6, In:M:Zn = 10:1:7, In:M:Zn = 10:1:8, In:M:Zn = 5:2:5, In:M:Zn = 10:1:10, In:M:Zn = 20:1:10, In:M:Zn = 40:1:10, and compositions in the vicinity thereof. Note that a composition in the vicinity includes a range of plus or minus 30% of the desired atomic ratio. Increasing the atomic ratio of indium in the metal oxide can increase the on-state current of the transistor or improve the field-effect mobility.

[0283] The atomic ratio of In in the In-M-Zn oxide may be less than the atomic ratio of M. Examples of atomic ratios of metal elements in such In-M-Zn oxide include In:M:Zn=1:3:2, In:M:Zn=1:3:3, In:M:Zn=1:3:4, and compositions close to these. By increasing the proportion of M atoms in the metal oxide, the generation of oxygen vacancies can be suppressed.

[0284] When the element M contains a plurality of metal elements, the total proportion of the number of atoms of the metal elements can be used as the proportion of the number of atoms of the element M.

[0285] In this specification and the like, the ratio of the number of indium atoms to the sum of the numbers of atoms of all contained metal elements may be referred to as the indium content. The same applies to other metal elements.

[0286] Using a material with a high indium content for the semiconductor layer 308 and the semiconductor layer 208 can increase the on-state current or improve the field-effect mobility of the transistor. Furthermore, the presence of the element M can suppress the generation of oxygen vacancies. The content of the element M (the ratio of the number of atoms of the element M to the sum of the numbers of atoms of all the metal elements contained) is preferably 0.1% or more and 3% or less, more preferably 0.1% or more and 2% or less. This allows for a transistor with excellent electrical characteristics. For example, it is preferable to use a metal oxide of In:M:Zn=40:1:10 or similar. The element M is preferably one or more of the above elements, and more preferably one or more selected from aluminum, gallium, tin, and yttrium. Specifically, a metal oxide of In:Sn:Zn=40:1:10 or similar can be used. Alternatively, a metal oxide of In:Al:Zn=40:1:10 or similar can be used.

[0287] Here, if a polycrystalline metal oxide is used for the semiconductor layer 308 and the semiconductor layer 208, the crystal grain boundaries may become recombination centers, trapping carriers and reducing the on-state current of the transistor. When using a metal oxide with a composition that easily forms a polycrystalline structure, it is preferable to include an element that inhibits crystallization. For example, compared to indium tin oxide (ITO), silicon-containing indium tin oxide (ITSO) is less likely to form a polycrystalline structure, and therefore can be used for the semiconductor layer 308 and the semiconductor layer 208. When ITSO is used, the silicon content (the ratio of the number of silicon atoms to the sum of the numbers of atoms of all contained metal elements) is preferably 1% or more and 20% or less, more preferably 3% or more and 20% or less, even more preferably 3% or more and 15% or less, and even more preferably 5% or more and 15% or less. Specifically, metal oxides of In:Sn:Si=45:5:4, In:Sn:Si=95:5:8, and similar metal oxides can be used.

[0288] For example, energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectrometry (XPS), inductively coupled plasma mass spectrometry (ICP-MS), or inductively coupled plasma atomic emission spectrometry (ICP-AES) can be used to analyze the compositions of the semiconductor layer 308 and the semiconductor layer 208. Alternatively, a combination of these techniques may be used for the analysis. For elements with low content, the actual content may differ from the content obtained by analysis due to the influence of analytical accuracy. For example, when the content of element M is low, the content of element M obtained by analysis may be lower than the actual content.

[0289] The metal oxide can be formed by sputtering or atomic layer deposition (ALD). When the metal oxide is formed by sputtering, the composition of the formed metal oxide may differ from the composition of the sputtering target. In particular, the zinc content in the formed metal oxide may decrease to about 50% compared to the sputtering target.

[0290] The semiconductor layer 308 and the semiconductor layer 208 may each have a stacked structure including two or more metal oxide layers. The two or more metal oxide layers included in the semiconductor layer 308 and the semiconductor layer 208 may have the same composition. By using a stacked structure of metal oxide layers having the same composition, for example, the same sputtering target can be used for formation, thereby reducing manufacturing costs.

[0291] The two or more metal oxide layers included in the semiconductor layer 308 and the semiconductor layer 208 may have different compositions. For example, a stacked structure can be used in which a first metal oxide layer has an atomic ratio of In:M:Zn=1:3:4 or a similar composition, and a second metal oxide layer is provided on the first metal oxide layer and has an atomic ratio of In:M:Zn=1:1:1 or a similar composition. Gallium, aluminum, or tin is particularly preferred as the element M. The element M in the first metal oxide layer and the second metal oxide layer may be the same or different from each other. For example, the first metal oxide layer and the second metal oxide layer may be IGZO layers having different compositions.

[0292] For example, a stacked structure can be used that includes a first metal oxide layer having an atomic ratio of In:Zn=4:1 or a composition close thereto, and a second metal oxide layer having an atomic ratio of In:M:Zn=1:1:1 or a composition close thereto that is provided on the first metal oxide layer.

[0293] For example, a stacked structure of any one selected from indium oxide, indium gallium oxide, and IGZO and any one selected from IAZO, IAGZO, and ITZO (registered trademark) may be used.

[0294] In addition, when a stacked structure is formed of a first metal oxide layer having a first metal oxide and a second metal oxide layer having a second metal oxide, and the composition of the first metal oxide is the same as the composition of the second metal oxide, it may be difficult to clearly identify the boundary (interface) between the first metal oxide layer and the second metal oxide layer.

[0295] It is preferable to use a crystalline metal oxide for the semiconductor layer 308 and the semiconductor layer 208. Examples of the structure of a crystalline metal oxide include a c-axis aligned crystal (CAAC) structure, a polycrystalline structure, and a nanocrystalline (nc: nano-crystal) structure. By using a crystalline metal oxide layer, the density of defect states in the semiconductor layer 308 and the semiconductor layer 208 can be reduced, and a highly reliable semiconductor device can be realized.

[0296] By using a metal oxide with high crystallinity for the channel formation region, the density of defect states in the channel formation region can be reduced, while by using a metal oxide with low crystallinity, a transistor capable of passing a large current can be realized.

[0297] When forming a metal oxide by sputtering, the higher the substrate temperature during formation, the more crystalline the metal oxide can be formed. The substrate temperature during formation can be adjusted, for example, by the temperature of the stage on which the substrate is placed during formation. Furthermore, the higher the ratio of the flow rate of oxygen gas to the total film formation gas used for formation (hereinafter also referred to as oxygen flow rate ratio) or the oxygen partial pressure in the processing chamber, the more crystalline the metal oxide can be formed.

[0298] The crystallinity of the semiconductor layer 308 and the semiconductor layer 208 can be analyzed by, for example, an X-ray diffraction (XRD) pattern, a transmission electron microscope (TEM) image, or an electron diffraction (ED) pattern. Alternatively, the analysis may be performed by combining a plurality of these techniques.

[0299] When a metal oxide is used for the semiconductor layer 308 and the semiconductor layer 208, V Ｏ It is preferable to reduce H as much as possible to obtain high-purity intrinsic or substantially high-purity intrinsic. Ｏ To obtain a metal oxide with a sufficiently reduced amount of H, it is important to remove impurities such as water and hydrogen from the metal oxide (sometimes referred to as dehydration or dehydrogenation treatment), and to supply oxygen to the metal oxide to repair oxygen deficiencies. Ｏ Stable electrical characteristics can be imparted by using a metal oxide in which impurities such as H are sufficiently reduced for a channel formation region of a transistor. Note that supplying oxygen to a metal oxide to repair oxygen vacancies may be referred to as oxygen-adding treatment.

[0300] When a metal oxide is used for the semiconductor layer 308 and the semiconductor layer 208, the carrier concentration of the channel formation region is 1×10 １８ cm −３ Preferably, it is 1×10 or less. １７ cm −３ More preferably, it is less than 1×10 １６ cm −３ More preferably, it is less than 1×10 １３ cm −３ More preferably, it is less than 1×10 １２ cm −３ It is more preferable that the carrier concentration in the channel formation region is less than 1×10. −９ cm −３ It can be said that:

[0301] OS transistors have small variations in electrical characteristics due to radiation exposure, i.e., have high radiation resistance, and can therefore be used in environments where radiation may be present. It can also be said that OS transistors have high reliability against radiation. For example, OS transistors can be used in pixel circuits of X-ray flat panel detectors. Furthermore, OS transistors can be used in semiconductor devices used in outer space. Examples of radiation include electromagnetic radiation (e.g., X-rays and gamma rays) and particle radiation (e.g., alpha rays, beta rays, proton rays, and neutron rays).

[0302] The semiconductor layer 308 and the semiconductor layer 208 may each include a layered material that functions as a semiconductor. A layered material is a general term for a group of materials that have a layered crystal structure. A layered crystal structure is a structure in which layers formed by covalent bonds or ionic bonds are stacked via bonds weaker than covalent bonds or ionic bonds, such as van der Waals bonds. A layered material has high electrical conductivity within a unit layer, that is, high two-dimensional electrical conductivity. By using a material that functions as a semiconductor and has high two-dimensional electrical conductivity in the channel formation region, a transistor with a large on-state current can be provided.

[0303] Examples of the layered material include graphene, silicene, and chalcogenides. Chalcogenides are compounds containing chalcogen (an element belonging to Group 16). Examples of chalcogenides include transition metal chalcogenides and Group 13 chalcogenides. Specific examples of transition metal chalcogenides that can be used as the channel formation region of a transistor include molybdenum sulfide (typically MoS ２ ), molybdenum selenide (typically MoSe ２ ), molybdenum telluride (typically MoTe ２ ), tungsten sulfide (typically WS ２ ), tungsten selenide (typically WSe ２ ), tungsten tellurium (typically WTe ２ ), hafnium sulfide (typically HfS ２ ), hafnium selenide (typically HfSe２ ), zirconium sulfide (typically ZrS ２ ), and zirconium selenide (typically ZrSe ２ ) etc.

[0304] [Conductive Layer 312a, Conductive Layer 312b, Conductive Layer 304, Conductive Layer 204, Conductive Layer 212a, Conductive Layer 212b, and Conductive Layer 202] The conductive layers 312a, 312b, 304, 204, 212a, 212b, and 202 may each have a single-layer structure or a stacked structure of two or more layers. Examples of materials that can be used for the conductive layers 312a, 312b, 304, 204, 212a, 212b, and 202 include one or more of chromium, copper, aluminum, gold, silver, zinc, tantalum, titanium, tungsten, manganese, nickel, iron, cobalt, molybdenum, and niobium, as well as alloys containing one or more of the aforementioned metals. A low-resistance conductive material containing one or more of copper, silver, gold, and aluminum can be used for each of the conductive layers 312a, 312b, 304, 204, 212a, 212b, and 202. Copper or aluminum is particularly preferable because of its excellent mass productivity.

[0305] A conductive metal oxide (oxide conductor) can be used for each of the conductive layer 312a, the conductive layer 312b, the conductive layer 304, the conductive layer 204, the conductive layer 212a, the conductive layer 212b, and the conductive layer 202. Examples of oxide conductors (OC) include indium oxide, zinc oxide, In—Sn oxide (ITO), In—Zn oxide, In—W oxide, In—W—Zn oxide, In—Ti oxide, In—Ti—Sn oxide, In—Sn—Si oxide (also referred to as ITO containing silicon or ITSO), zinc oxide to which gallium is added, and In—Ga—Zn oxide. In particular, conductive oxides containing indium are preferable because of their high conductivity.

[0306] When oxygen vacancies are formed in a metal oxide having semiconducting properties and hydrogen is added to the oxygen vacancies, a donor level is formed near the conduction band. As a result, the metal oxide becomes electrically conductive, and the conductivity of the metal oxide increases. The metal oxide that has become electrically conductive can be called an oxide conductor.

[0307] The conductive layer 312a, the conductive layer 312b, the conductive layer 304, the conductive layer 204, the conductive layer 212a, the conductive layer 212b, and the conductive layer 202 may each have a stacked structure of a conductive film containing the oxide conductor (metal oxide) and a conductive film containing a metal or an alloy. By using a conductive film containing a metal or an alloy, wiring resistance can be reduced.

[0308] A Cu-X alloy film (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti) may be applied to each of the conductive layer 312a, the conductive layer 312b, the conductive layer 304, the conductive layer 204, the conductive layer 212a, the conductive layer 212b, and the conductive layer 202. By using a Cu-X alloy film, it can be processed by wet etching, thereby reducing manufacturing costs.

[0309] Note that the conductive layer 312a, the conductive layer 312b, the conductive layer 304, the conductive layer 204, the conductive layer 212a, the conductive layer 212b, and the conductive layer 202 may be formed using the same material or different materials.

[0310] The conductive layer 312a and the conductive layer 312b have a region in contact with the semiconductor layer 308. When a metal oxide is used for the semiconductor layer 308, if a metal that is easily oxidized (e.g., aluminum) is used for the conductive layer 312a and the conductive layer 312b, an insulating oxide (e.g., aluminum oxide) may be formed between the conductive layer 312a and the semiconductor layer 308 and between the conductive layer 312b and the semiconductor layer 308, which may hinder conduction therebetween. Therefore, it is preferable to use a conductive material that is not easily oxidized, a conductive material that maintains low electrical resistance even when oxidized, or a conductive oxide material for the conductive layer 312a and the conductive layer 312b.

[0311] For the conductive layer 312a and the conductive layer 312b, it is preferable to use, for example, titanium, tantalum nitride, titanium nitride, a nitride containing titanium and aluminum, a nitride containing tantalum and aluminum, ruthenium, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, or an oxide containing lanthanum and nickel. These are preferable because they are conductive materials that are resistant to oxidation or materials that maintain low electrical resistance even when oxidized. Note that when the conductive layer 312a has a stacked structure, it is preferable to use a conductive material that is resistant to oxidation for at least the layer in contact with the semiconductor layer 308.

[0312] The conductive layer 312 a and the conductive layer 312 b can each be formed using the above-described oxide conductors, such as indium oxide, zinc oxide, ITO, In—Zn oxide, In—W oxide, In—W—Zn oxide, In—Ti oxide, In—Ti—Sn oxide, In—Sn oxide containing silicon, or zinc oxide doped with gallium.

[0313] The conductive layer 312a and the conductive layer 312b may each be made of a nitride conductor, such as tantalum nitride or titanium nitride.

[0314] Here, in the capacitor 350, the conductive layer 312b is provided over the insulating layer 320b. As described above, the conductive layer 312b is preferably made of a conductive material that is resistant to oxidation, a conductive material that maintains low electrical resistance even when oxidized, or an oxide conductive material. Furthermore, the amount of oxygen released from the insulating layer 320b is smaller than the amount of oxygen released from the insulating layer 310b. Therefore, there is little risk that the conductive layer 312b having a region in contact with the insulating layer 320b will be oxidized and the electrical resistance of the conductive layer 312b will increase.

[0315] The conductive layer 312a, the conductive layer 312b, and the conductive layer 304 may each have a stacked structure. For example, the conductive layer 312a may have a two-layer structure. That is, the conductive layer 312a may have a stacked structure of, for example, a conductive layer 312a_1 (not shown) and a conductive layer 312a_2 (not shown) over the conductive layer 312a_1.

[0316] For the conductive layer 312a_2 having a region in contact with the semiconductor layer 308, a conductive material that is not easily oxidized, a conductive material that maintains low electrical resistance even when oxidized, or an oxide conductive material is preferably used. For materials that can be used for the conductive layer 312a_2, the description of the conductive layer 312a can be referred to.

[0317] The conductive layer 312a_1 does not have a region in contact with the semiconductor layer 308, and therefore the material used is not particularly limited. For example, the conductive layer 312a_1 is preferably made of a material having lower electrical resistivity than the conductive layer 312a_2. This can reduce the electrical resistance of the conductive layer 312a. For example, the conductive layer 312a_2 can be made of In—Sn—Si oxide (ITSO), and the conductive layer 312a_1 can be made of copper or tungsten.

[0318] Note that the thickness of the conductive layer 312a_1 and the thickness of the conductive layer 312a_2 may be the same or different. For example, the conductive layer 312a_1 may be made of a material having a lower electrical resistivity than the conductive layer 312a_2, and the thickness of the conductive layer 312a_1 may be made thicker than the thickness of the conductive layer 312a_2. This can reduce the electrical resistance of the conductive layer 312a.

[0319] The ends of the conductive layer 312a_2 may or may not coincide with the ends of the conductive layer 312a_1. For example, the conductive layer 312a_2 can be provided so as to cover the conductive layer 312a_1. That is, the conductive layer 312a_2 is in contact with the top surface and side surface of the conductive layer 312a_1. It can also be said that the conductive layer 312a_2 has a portion that protrudes beyond the end of the conductive layer 312a_1.

[0320] The above-described configuration of the conductive layer 312a can also be applied to other configuration examples.

[0321] [Insulating Layer 306] The insulating layer 306 may have a single-layer structure or a stacked structure of two or more layers. The insulating layer 306 preferably has one or more inorganic insulating films. Examples of materials that can be used for the inorganic insulating film include oxides, nitrides, oxynitrides, and nitride oxides. The insulating layer 306 can be made of the same materials that can be used for the insulating layer 310.

[0322] The insulating layer 306 has a region in contact with the semiconductor layer 308 and the semiconductor layer 208. When a metal oxide is used for the semiconductor layer 308 and the semiconductor layer 208, it is preferable to use any of the above-described oxides and oxynitrides for at least the films constituting the insulating layer 306 that are in contact with the semiconductor layer 308 and the semiconductor layer 208. It is more preferable to use a film that releases oxygen by heating for the insulating layer 306.

[0323] Specifically, when the insulating layer 306 has a single-layer structure, it is preferable to use an oxide or an oxynitride for the insulating layer 306. Specifically, the insulating layer 306 can be formed using silicon oxide or silicon oxynitride.

[0324] When the insulating layer 306 has a stacked-layer structure, it is preferable that the insulating film in contact with the semiconductor layer 308 and the semiconductor layer 208 contains an oxide or an oxynitride, and the insulating film in contact with the conductive layer 304 and the conductive layer 204 contains a nitride or a nitride oxide. As the oxide or oxynitride, for example, silicon oxide or silicon oxynitride can be used. As the nitride or nitride oxide, silicon nitride or silicon nitride oxide can be used.

[0325] Silicon nitride and silicon nitride oxide have the characteristics of releasing little impurities (for example, water and hydrogen) from themselves and being difficult for oxygen and hydrogen to permeate, and therefore can be used as the insulating layer 306. By suppressing the diffusion of impurities from the insulating layer 306 to the semiconductor layer 308 and the semiconductor layer 208, the electrical characteristics of the transistor can be improved and the reliability can be increased.

[0326] In a miniaturized transistor, a thin gate insulating layer may result in a large gate leakage current. By using a material with a high dielectric constant (also referred to as a high-k material) for the gate insulating layer, a low voltage can be achieved during transistor operation while maintaining a physical film thickness. Examples of high-k materials that can be used for the insulating layer 306 include gallium oxide, hafnium oxide, zirconium oxide, oxides containing aluminum and hafnium, oxynitrides containing aluminum and hafnium, oxides containing silicon and hafnium, oxynitrides containing silicon and hafnium, and nitrides containing silicon and hafnium.

[0327] [Insulating Layer 395] The insulating layer 395, which functions as a protective layer for the transistor 300, the transistor 200, and the capacitor 350, is preferably made of a material through which impurities do not easily diffuse. By providing the insulating layer 395, diffusion of impurities from the outside into the transistor can be effectively suppressed, thereby improving the reliability of the semiconductor device. Examples of impurities include water and hydrogen.

[0328] The insulating layer 395 can be an insulating layer containing an inorganic material or an insulating layer containing an organic material. For example, an inorganic material such as oxide, oxynitride, nitride oxide, or nitride can be used for the insulating layer 395. More specifically, one or more of silicon nitride, silicon nitride oxide, silicon oxynitride, aluminum oxide, aluminum oxynitride, aluminum nitride, hafnium oxide, and hafnium aluminate can be used. For example, one or more of an acrylic resin and a polyimide resin can be used as the organic material. A photosensitive material may be used as the organic material. Two or more of the above insulating films may be stacked. The insulating layer 395 may have a stacked structure of an insulating layer containing an inorganic material and an insulating layer containing an organic material.

[0329] [Substrate 302] There are no significant limitations on the material of the substrate 302, but it must have at least heat resistance sufficient to withstand subsequent heat treatment. The substrate 302 may be, for example, a single-crystal semiconductor substrate made of silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate made of silicon germanium or the like, an SOI substrate, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, or an organic resin substrate. A semiconductor element may also be provided on the substrate 302. The semiconductor substrate and the insulating substrate may have either a circular or rectangular shape.

[0330] A flexible substrate may be used as the substrate 302, and the transistor 300 and the like may be formed directly on the flexible substrate. Alternatively, a peeling layer may be provided between the substrate 302 and the transistor 300 and the like. By providing the peeling layer, after a semiconductor device is partially or entirely completed thereon, it can be separated from the substrate 302 and transferred to another substrate. In this case, the transistor 300 and the like can also be transferred to a substrate with poor heat resistance or a flexible substrate.

[0331] 15 is a cross-sectional view of a transistor 300A that can be used in a semiconductor device according to one embodiment of the present invention. The transistor 300A mainly differs from the transistor 300 shown in FIG. 12 in that it has a back gate. Note that the above description of the transistor 300 can be referred to, and detailed description thereof will be omitted.

[0332] The transistor 300A includes a conductive layer 312a, a conductive layer 303, an insulating layer 307, an insulating layer 310, a semiconductor layer 308, a conductive layer 312b, an insulating layer 306, and a conductive layer 304. Each layer constituting the transistor 300A may have a single-layer structure or a stacked-layer structure.

[0333] The conductive layer 312a is provided over the substrate 302. The conductive layer 312a functions as one of a source electrode and a drain electrode of the transistor 300A.

[0334] The insulating layer 307 is located over the conductive layer 312a and is provided to cover the top and side surfaces of the conductive layer 312a.

[0335] The conductive layer 303 is located on the insulating layer 307. The conductive layer 312a and the conductive layer 303 are electrically insulated from each other by the insulating layer 307. An opening 348 reaching the insulating layer 307 is provided in the conductive layer 303 in a region overlapping with the conductive layer 312a.

[0336] The insulating layer 310 is provided over the insulating layer 307 and the conductive layer 303. The insulating layer 310 is provided to cover the top surface and side surfaces of the conductive layer 303 and the top surface of the insulating layer 307.

[0337] The insulating layer 310 preferably has a stacked structure. Fig. 15 shows an example in which the insulating layer 310 has a stacked structure of an insulating layer 310a, an insulating layer 310b on the insulating layer 310a, and an insulating layer 310c on the insulating layer 310b.

[0338] The insulating layer 310a is located over the insulating layer 307 and the conductive layer 303. The insulating layer 310a is provided so as to cover the top surface and side surfaces of the conductive layer 303. The insulating layer 310a is also provided so as to cover part of the opening 348. The insulating layer 310a is in contact with the insulating layer 307 through the opening 348.

[0339] An insulating layer 310b is provided over the insulating layer 310a, and an insulating layer 310c is provided over the insulating layer 310b. An opening 341 is provided in the insulating layer 307 and the insulating layer 310, reaching the conductive layer 312a.

[0340] The conductive layer 312b is located over the insulating layer 310c. An opening 343 overlapping with the opening 341 is provided in the conductive layer 312b. The conductive layer 312b functions as the other of the source and drain electrodes of the transistor 300A. The conductive layer 312b has a region overlapping with the conductive layer 312a with the insulating layer 307 and the insulating layer 310 interposed therebetween.

[0341] In this specification and the like, the top surface shape of the opening 348 refers to the shape of the top surface end or the shape of the bottom surface end on the opening 348 side of the conductive layer 303. Note that, similar to the openings 341 and 343, there is no limitation on the top surface shape of the opening 348.

[0342] When the top shapes of the openings 341 and 348 are circular, the openings 341 and 348 are preferably concentric. This allows the shortest distance between the semiconductor layer 308 and the conductive layer 303 in a cross-sectional view to be equal on the left and right sides of the opening 341. Furthermore, the openings 341 and 348 may not be concentric.

[0343] The semiconductor layer 308 is in contact with a top surface of the conductive layer 312a, side surfaces of the insulating layer 307, side surfaces of the insulating layer 310, and a top surface and side surfaces of the conductive layer 312b. The semiconductor layer 308 is provided so as to cover the openings 341 and 343. The semiconductor layer 308 is provided in contact with the insulating layer 307, side surfaces of the insulating layer 310 on the opening 341 side, and an end portion of the conductive layer 312b on the opening 343 side (which can also be referred to as a part of the top surface and the side surface on the opening 343 side). The semiconductor layer 308 is in contact with the conductive layer 312a through the openings 341 and 343.

[0344] 15 shows an example in which the end portion of the semiconductor layer 308 is in contact with the top surface of the conductive layer 312b, but one embodiment of the present invention is not limited to this. The semiconductor layer 308 may cover the end portion of the conductive layer 312b and may be in contact with the top surface of the insulating layer 310c.

[0345] The insulating layer 306 is located over the insulating layer 310c, the semiconductor layer 308, and the conductive layer 312b. The insulating layer 306 is provided to cover the openings 341 and 343 with the semiconductor layer 308 interposed therebetween. Part of the insulating layer 306 functions as a gate insulating layer of the transistor 300A.

[0346] The conductive layer 304 is located over the insulating layer 306. The conductive layer 304 overlaps with the semiconductor layer 308 with the insulating layer 306 interposed therebetween. The conductive layer 304 functions as a gate electrode of the transistor.

[0347] In the transistor 300A, the semiconductor layer 308 has a region that overlaps with the conductive layer 304 with the insulating layer 306 interposed therebetween and with the conductive layer 303 with parts of the insulating layer 310 (particularly, the insulating layers 310a and 310b) interposed therebetween. In other words, the semiconductor layer 308 has a region sandwiched between the conductive layer 304 with the insulating layer 306 interposed therebetween and the conductive layer 303 with parts of the insulating layer 310 (particularly, the insulating layers 310a and 310b) interposed therebetween.

[0348] The conductive layer 303 functions as a back gate electrode of the transistor 300A. Part of the insulating layer 310 functions as a back gate insulating layer of the transistor 300A.

[0349] By providing the back gate electrode in the transistor 300A, the potential of the back channel side of the semiconductor layer 308 is fixed, and the saturation property of the transistor 300A can be increased.

[0350] Since the transistor 300A has a back gate electrode, the potential on the back channel side of the semiconductor layer 308 can be fixed, and a shift in the threshold voltage can be suppressed. Here, if the threshold voltage of the transistor shifts, the drain current (hereinafter also referred to as cutoff current) that flows when the gate voltage is 0 V may become large. By suppressing the shift in the threshold voltage of the transistor 300A, the transistor can have a small cutoff current. Note that a small cutoff current is sometimes referred to as a normally-off transistor.

[0351] 15 shows an example in which the semiconductor layer 308, the insulating layer 306, and the conductive layer 304 cover the openings 341 and 343; however, one embodiment of the present invention is not limited to this. A structure may be employed in which a step is formed by the insulating layer 307, the insulating layer 310, the conductive layer 312b, and the conductive layer 312a, and the semiconductor layer 308, the insulating layer 306, and the conductive layer 304 are provided along the step.

[0352] <Application Example to Switch Portion> In one embodiment of the present invention, for example, the transistor 200, the transistor 200A, the transistor 300, the transistor 300A, or the like can be used as appropriate for each transistor included in the semiconductor device 100A, the semiconductor device 100B, or the like described in Embodiment 1. In particular, the transistor 200, the transistor 300A, or the like having a back gate electrode may be used as the transistor M11 included in the switch portion 101A of the semiconductor device 100A, and the back gate electrode may be electrically connected to the drain electrode. Furthermore, the transistor 200, the transistor 300A, or the like having a back gate electrode may be used as the transistor M21 included in the switch portion 101B of the semiconductor device 100B, and the back gate electrode may be electrically connected to the drain electrode.

[0353] Fig. 16A is a top view showing a configuration example in which a transistor 200 and a transistor 200A are used in a switch portion 101A of a semiconductor device 100A. Fig. 16B is a cross-sectional view of a cut surface taken along dashed line C1-C2 shown in Fig. 16A. Note that the above-described descriptions of the transistor 200 and the transistor 200A can be referred to as appropriate, and detailed description thereof may be omitted here.

[0354] 16A and 16B show a semiconductor device 20A that corresponds to the switch section 101A. That is, the semiconductor device 20A has a transistor 200 that corresponds to the transistor M11 and a transistor 200A that corresponds to the transistor M12.

[0355] One of the source and the drain of the transistor 200 is electrically connected to the conductive layer 212_2. The other of the source and the drain of the transistor 200 is electrically connected to the conductive layer 212_1. One of the source and the drain of the transistor 200A is electrically connected to the conductive layer 212_2. The other of the source and the drain of the transistor 200A is electrically connected to the conductive layer 212_3. The gates of the transistors 200 and 200A are electrically connected to the conductive layer 204. The back gate of the transistor 200 is electrically connected to the conductive layer 202_1. The conductive layer 202_1 is electrically connected to the conductive layer 212_1 through an opening 349_1 provided in the insulating layer 306 and the insulating layer 320.

[0356] Here, the semiconductor layer 208_1 included in the transistor 200 and the semiconductor layer 208_2 included in the transistor 200A correspond to the semiconductor layer 208. The conductive layer 202_1 corresponds to the conductive layer 202. The conductive layers 212_1, 212_2, and 212_3 correspond to the conductive layer 212.

[0357] Note that the conductive layer 204 corresponds to the wiring IN11 in the semiconductor device 100A. The conductive layers 212_1 and 202_1 correspond to the wiring OUT11. The conductive layer 212_2 corresponds to the wiring NL11. The conductive layer 212_3 corresponds to the wiring VLS.

[0358] As shown in FIG. 16A, the transistor 200A, the transistor 200, and the opening 349_1 are arranged side by side in the channel length direction of the transistor 200 and the transistor 200A (the horizontal direction in FIG. 16A).

[0359] The conductive layer 202_1 is arranged to detour around one side (upper side in FIG. 16A ) of the transistor 200 in the channel width direction (vertical direction in FIG. 16A ). The conductive layer 204 is arranged to detour around the other side (lower side in FIG. 16A ) of the transistors 200 and 200A in the channel width direction. This arrangement can reduce the area where the conductive layer 202_1 and the conductive layer 204 overlap. This can reduce the parasitic capacitance between the gates of the transistors 200 and 200A and the backgate of the transistor 200. Therefore, for example, when the semiconductor device 20A is used in a driver circuit, the operating speed of the driver circuit can be improved.

[0360] Furthermore, the width of the region of the conductive layer 202_1 bypassing the transistor 200 can be made smaller than the width of the region functioning as the back gate of the transistor 200. This can reduce the area occupied by the semiconductor device 20A. Therefore, a driver circuit using the semiconductor device 20A and a display device using the driver circuit can be miniaturized.

[0361] Furthermore, the width of the conductive layer 204 in the region bypassing the transistor 200 and the transistor 200A can be made smaller than the width of the region functioning as the gate of the transistor 200 and the width of the region functioning as the gate of the transistor 200A. This can reduce the area occupied by the semiconductor device 20A. Therefore, a driver circuit using the semiconductor device 20A and a display device using the driver circuit can be miniaturized.

[0362] 17A is a top view showing a modification of the semiconductor device 20 A. In the semiconductor device 20 A 1 shown in FIG. 17A, the arrangement of the conductive layer 204 is different from that of the semiconductor device 20 A.

[0363] 17A , the conductive layer 204 is arranged to bypass one side (upper side in FIG. 17A ) of the transistor 200 and the transistor 200A in the channel width direction. That is, outside the transistor 200, part of the conductive layer 204 is arranged to overlap part of the conductive layer 202_1. This arrangement can reduce the area occupied by the semiconductor device 20A1. Therefore, it is possible to reduce the size of a driver circuit using the semiconductor device 20A1 and a display device using the driver circuit.

[0364] 17B is a top view showing a modification of the semiconductor device 20 A. In the semiconductor device 20 A2 shown in FIG. 17B, the arrangement of the transistors 200 and 200 A is different from that of the semiconductor device 20 A.

[0365] As shown in FIG. 17B , the transistor 200A, the transistor 200, and the opening 349_1 are arranged side by side in the channel width direction of the transistor 200 and the transistor 200A (the vertical direction in FIG. 17B ). This allows the conductive layer 202_1 to be arranged without bypassing the transistor 200. Furthermore, the conductive layer 204 can be arranged without bypassing the transistor 200 and the transistor 200A. This arrangement reduces the area occupied by the semiconductor device 20A2. Therefore, it is possible to reduce the size of a driver circuit using the semiconductor device 20A2 and a display device using the driver circuit.

[0366] 16A, the length of the conductive layer 212_2 can be made shorter than the length of the conductive layer 212_2 of the semiconductor device 20A2 shown in FIG. 17B. This can reduce the parasitic resistance of the wiring NL11. Therefore, the influence of the parasitic resistance of the wiring NL11 can be reduced, particularly when the drain currents of the transistors 200 and 200A are large.

[0367] 18A and 18B are a top view and a cross-sectional view illustrating a modification of the semiconductor device 20A. The semiconductor device 20B illustrated in FIGS. 18A and 18B differs from the semiconductor device 20A in that the semiconductor device 20B does not include the conductive layer 212_2 and that the transistor 200 and the transistor 200A share a semiconductor layer 208_1 that is provided in a continuous manner. In the semiconductor device 20B, a region in the semiconductor layer 208_1 between the channel formation region of the transistor 200 and the channel formation region of the transistor 200A corresponds to the wiring NL11.

[0368] The semiconductor device 20B does not include the conductive layer 212_2, and therefore the distance between the transistor 200 and the transistor 200A can be made shorter than that of the semiconductor device 20A. This reduces the area occupied by the semiconductor device 20B. Therefore, a driver circuit using the semiconductor device 20B and a display device using the driver circuit can be miniaturized.

[0369] 19A and 19B are a top view and a cross-sectional view illustrating a modification of the semiconductor device 20A, respectively. The semiconductor device 20C illustrated in FIG. 19A and FIG. 19B differs from the semiconductor device 20A in that a transistor 200 having a back gate is used as a transistor corresponding to the transistor M12 and that a conductive layer 202_2 having a region functioning as the back gate is provided.

[0370] The conductive layer 202_2 having a region functioning as the back gate of the transistor 200 corresponding to the transistor M12 is arranged to extend in the channel width direction of the transistor (the up-and-down direction in FIG. 19A ) and is electrically connected to the conductive layer 204 corresponding to the wiring IN11 through an opening 349_2 provided in the insulating layer 306 and the insulating layer 320. That is, the semiconductor device 20C corresponds to the semiconductor device 100A shown in FIG. 3A .

[0371] 20A and 20B are a top view and a cross-sectional view showing a modification of the semiconductor device 20A. The semiconductor device 20D shown in FIGS. 20A and 20B differs from the semiconductor device 20A in that a vertical transistor 300 is used as the transistor corresponding to the transistor M12. Note that the above-described description of the transistor 300 can be referred to as appropriate, and detailed description thereof may be omitted here.

[0372] The conductive layer 204 in the transistor 300 corresponding to the transistor M12 corresponds to the conductive layer 304 of the above-described transistor 300. The conductive layer 312a corresponds to the wiring VLS. The conductive layer 312b is electrically connected to the conductive layer 212_2 corresponding to the wiring NL11 through an opening 349_3 provided in the insulating layer 306.

[0373] The semiconductor device 20D can have a small area and a large on-state current by using the transistor 300. Therefore, the operating speed of a driver circuit including the semiconductor device 20D and a display device including the driver circuit can be improved and the device can be made smaller.

[0374] 21A and 21B are a top view and a cross-sectional view showing a modification of the semiconductor device 20D. The semiconductor device 20E shown in FIGS. 21A and 21B differs from the semiconductor device 20A in that the semiconductor device 20E does not include the conductive layer 212_2 and the conductive layer 312b and that the transistor 200 and the transistor 300 share a semiconductor layer 208_1 that is provided in a continuous manner. Here, the semiconductor layer 208_1 in the transistor 300 that corresponds to the transistor M12 corresponds to the semiconductor layer 308 of the transistor 300 described above. In the semiconductor device 20E, a region in the semiconductor layer 208_1 between the channel formation regions of the transistor 200 and the transistor 300 corresponds to the wiring NL11.

[0375] The semiconductor device 20E does not include the conductive layer 212_2, and therefore the distance between the transistor 200 and the transistor 300 can be shorter than that of the semiconductor device 20D. This reduces the area occupied by the semiconductor device 20E. Therefore, a driver circuit using the semiconductor device 20E and a display device using the driver circuit can be miniaturized.

[0376] Furthermore, the absence of the conductive layer 312b can reduce process costs.

[0377] In the above description, by replacing transistor M11 with transistor M21, transistor M12 with transistor M22, wiring IN11 with wiring IN22, wiring VLS with wiring OUT21, and wiring OUT11 with wiring VLD, each of semiconductor devices 20A to 20E can be applied to switch section 101B.

[0378] Furthermore, in one embodiment of the present invention, semiconductor devices that can be used for each of the switch portion 101A and the switch portion 101B are not limited to the semiconductor devices 20A to 20E, and semiconductor devices in which the respective structures are appropriately combined can also be used.

[0379] The configuration described in this embodiment can be used in appropriate combination with the configuration described in other embodiments. In addition, when a plurality of configuration examples are shown in one embodiment in this specification, these configuration examples can be used in appropriate combination.

[0380] Embodiment 3 In this embodiment, a display device according to one embodiment of the present invention will be described.

[0381] Note that at least part of the semiconductor device 100A, the semiconductor device 100B, and the like described in Embodiment 1 can be applied to a display device of one embodiment of the present invention, a module including the display device, or the like.

[0382] Here, examples of the module having the display device include a module in which a connector such as a flexible printed circuit (FPC) or a tape carrier package (TCP) is attached to the display device, and a module in which an integrated circuit (IC) is mounted by a chip-on-glass (COG) method or a chip-on-film (COF) method.

[0383] <Structural Example of Display Device> FIG. 22A is a perspective view illustrating a structural example of a display device 400 of one embodiment of the present invention.

[0384] The display device 400 has a configuration in which a substrate 411 and a substrate 451 are bonded together. In Fig. 22A, the substrate 411 is indicated by a dashed line.

[0385] The display device 400 includes a display portion 452, a circuit portion 454a, a circuit portion 454b, a connection portion 457, a wiring portion 458, and the like. Fig. 22A shows an example in which an IC 456 and an FPC 459 are mounted on the display device 400. Therefore, the configuration shown in Fig. 22A can also be said to be a display module including the display device 400, an IC, and an FPC.

[0386] The circuit portion 454a includes, for example, a scanning line driver circuit (also referred to as a gate driver or a scan driver), and the circuit portion 454b includes, for example, a signal line driver circuit (also referred to as a source driver or a data driver).

[0387] The wiring portion 458 has a function of supplying signals and power to the display portion 452, the circuit portion 454a, and the circuit portion 454b. The signals and power are input to the wiring portion 458 from the outside of the display device 400 via the FPC 459 or are input to the wiring portion 458 from the IC 456.

[0388] 22A shows an example in which an IC 456 is provided on a substrate 451 by a COG method, a COF method, or the like. For example, an IC including one or both of a scan line driver circuit and a signal line driver circuit can be used as the IC 456. Note that the display device 400 and the display module may not include an IC. Alternatively, the IC may be mounted on an FPC by a COF method or the like.

[0389] Note that a scanning line driver circuit may be formed by one or both of the IC 456 and the circuit portion 454a. In this case, the IC 456 may be referred to as a gate driver IC. Also, a signal line driver circuit may be formed by one or both of the IC 456 and the circuit portion 454b. In this case, the IC 456 may be referred to as a source driver IC.

[0390] The display section 452 is a region in the display device 400 that displays an image, and has a plurality of periodically arranged pixels 455. Fig. 22A shows an enlarged view of one pixel 455.

[0391] The pixel 455 shown in FIG. 22A includes a pixel 453R that emits red (R) light, a pixel 453G that emits green (G) light, and a pixel 453B that emits blue (B) light. A full-color display can be achieved by configuring one pixel 455 with the pixels 453R, 453G, and 453B. The pixels 453R, 453G, and 453B each function as a subpixel. The display device 400 shown in FIG. 22A illustrates an example in which the pixels 453R, 453B, and 453G that function as subpixels are arranged in a stripe array. Note that the number of subpixels that constitute one pixel 455 is not limited to three and may be four or more. For example, the pixel 455 may include four subpixels that emit R, G, B, and white (W) light, respectively. Alternatively, the pixel 455 may include four subpixels that emit R, G, B, and yellow (Y) light, respectively.

[0392] In this specification, elements relating to red light may be identified by the identification symbol "R," elements relating to green light by the identification symbol "G," and elements relating to blue light by the identification symbol "B," and these elements may be described separately. Furthermore, common elements may be described without identifying the elements. For example, when it is necessary to distinguish between multiple pixels 453, they may be referred to as pixel 453R, pixel 453G, or pixel 453B. Furthermore, when it is not necessary to distinguish between pixel 453R, pixel 453G, and pixel 453B, they may be simply referred to as pixel 453.

[0393] Each of the pixels 453R, 453G, and 453B includes a display element and a circuit (pixel circuit) that controls driving of the display element.

[0394] The connection portion 457 is provided outside the display portion 452. The connection portion 457 can be provided along one side or multiple sides of the display portion 452. The number of connection portions 457 may be single or multiple. FIG. 22A shows an example in which the connection portion 457 is provided so as to surround the four sides of the display portion. The connection portion 457 electrically connects the common electrode of the display element and the wiring portion 458, and can supply a potential to the common electrode.

[0395] Here, for example, the semiconductor device of one embodiment of the present invention can be applied to at least part of the display portion 452, the circuit portion 454a, and the circuit portion 454b included in the display device 400.

[0396] For example, the reliability of the display device can be improved by applying at least a part of the semiconductor device 100A or 100B described in Embodiment 1 to one or both of the circuit portion 454a and the circuit portion 454b. Furthermore, by applying a vertical transistor such as the transistor 300 described in Embodiment 2, the area occupied by the driver circuit can be reduced, and a display device with a narrow frame can be obtained.

[0397] Furthermore, for example, by applying a vertical transistor such as the transistor 300 described in Embodiment 2 to a pixel circuit included in the display portion 452, the area occupied by the pixel circuit can be reduced, and a high-resolution display device can be provided. For example, a display device with a resolution of 300 ppi or more, 500 ppi or more, 1000 ppi or more, 2000 ppi or more, or 3000 ppi or more can be provided.

[0398] Note that the display device of one embodiment of the present invention may have a function as a touch panel. For example, various sensing elements (also referred to as sensor elements) that can detect the proximity or contact of a sensed object such as a finger can be applied to the display device.

[0399] Examples of sensor types include a capacitance type, a resistive film type, a surface acoustic wave type, an infrared type, an optical type, and a pressure-sensitive type.

[0400] The capacitance type includes, for example, a surface capacitance type and a projected capacitance type. The projected capacitance type includes, for example, a self-capacitance type and a mutual capacitance type. The mutual capacitance type is preferable because it enables simultaneous multi-point detection.

[0401] Examples of touch panels include out-cell, on-cell, and in-cell types. Note that the in-cell type touch panel has a configuration in which electrodes constituting detection elements are provided on one or both of a substrate supporting a display element (also called a display device) and an opposing substrate.

[0402] 22B to 22F are top views illustrating pixel arrays. In a display device according to one embodiment of the present invention, the pixel array is not particularly limited, and various arrays can be applied. Examples of pixel arrays include a stripe array (see FIG. 22B ), an S-stripe array (see FIG. 22C ), a delta array (see FIG. 22D ), a zigzag array (see FIG. 22E ), and a pentile array (see FIG. 22F ). Other examples include a mosaic array, a diamond array, and a Bayer array.

[0403] 22B to 22F, examples of the top surface shape of each subpixel (pixel 453R, pixel 453G, and pixel 453B) include a triangle, a quadrangle (including a rectangle and a square), a polygon such as a pentagon, shapes with rounded corners of these polygons, an ellipse, and a circle. Here, the top surface shape of each subpixel corresponds to the top surface shape of the display region of the display element included in each subpixel. The top surface shape and size of each subpixel can be determined independently. The arrangements of the pixel 453R, pixel 453G, and pixel 453B may be interchanged as appropriate. The display elements and pixel circuits may have the same arrangement or different arrangements.

[0404] Here, the pentile arrangement is a special pixel arrangement that artificially increases the resolution. Therefore, a stripe arrangement, for example, can be adopted in a display device. In one embodiment of the present invention, a vertical transistor such as the transistor 300 described in Embodiment 2 is used as part or all of the transistors constituting a pixel circuit, thereby enabling the area occupied by the pixel circuit to be reduced. Therefore, the pixel arrangement can be changed from the pentile arrangement to, for example, a stripe arrangement without reducing the resolution of the display device.

[0405] [Display element] Various elements can be used as the display element, for example, a liquid crystal element and a light-emitting element. Other examples include a shutter-type or optical interference-type MEMS (Micro Electro Mechanical Systems) element, or a display element using a microcapsule type, an electrophoresis type, an electrowetting type, or an electronic liquid powder (registered trademark) type. Furthermore, a QLED (Quantum-dot LED) using a light source and color conversion technology using quantum dot materials may also be used.

[0406] Examples of display devices using liquid crystal elements include transmissive liquid crystal display devices, reflective liquid crystal display devices, and semi-transmissive liquid crystal display devices.

[0407] Examples of modes that can be used in display devices using liquid crystal elements include vertical alignment (VA) mode, Fringe Field Switching (FFS) mode, In-Plane-Switching (IPS) mode, Twisted Nematic (TN) mode, Axially Symmetric Aligned Micro-cell (ASM) mode, Optically Compensated Birefringence (OCB) mode, Ferroelectric Liquid Crystal (FLC) mode, Anti-Ferroelectric Liquid Crystal (AFLC) mode, and Electrically Compensated Birefringence (ECB) mode. Examples of the VA mode include a Multi-Domain Vertical Alignment (MVA) mode, a Patterned Vertical Alignment (PVA) mode, and an Advanced Super View (ASV) mode.

[0408] Examples of liquid crystal materials that can be used in liquid crystal elements include thermotropic liquid crystals, low-molecular-weight liquid crystals, polymer liquid crystals, polymer-dispersed liquid crystals (PDLCs), polymer network liquid crystals (PNLCs), ferroelectric liquid crystals, and antiferroelectric liquid crystals. These liquid crystal materials exhibit cholesteric phases, smectic phases, cubic phases, chiral nematic phases, isotropic phases, blue phases, etc., depending on the conditions. Furthermore, either positive-type or negative-type liquid crystals may be used as the liquid crystal material.

[0409] Examples of the light-emitting element include self-luminous light-emitting elements such as LEDs (Light Emitting Diodes), organic EL (Electro Luminescence) elements (also called OLEDs (Organic LEDs)), and semiconductor lasers. Examples of the LED that can be used include mini LEDs and micro LEDs.

[0410] Examples of light-emitting substances that the light-emitting element has include fluorescent substances (fluorescent materials), phosphorescent substances (phosphorescent materials), substances that exhibit thermally activated delayed fluorescence (thermally activated delayed fluorescence: TADF materials), and inorganic compounds (quantum dot materials, etc.).

[0411] The light-emitting element can emit light of infrared, red, green, blue, cyan, magenta, yellow, white, etc. Furthermore, the color purity can be improved by providing the light-emitting element with a microcavity structure.

[0412] One of a pair of electrodes included in the light-emitting element functions as an anode electrode, and the other electrode functions as a cathode electrode.

[0413] In this embodiment, a case where a light-emitting element is used as a display element will be mainly described as an example. In particular, a case where an organic EL element is used as a light-emitting element will be described as an example. Therefore, one embodiment of the present invention is a display device using an organic EL element.

[0414] Note that the display device of one embodiment of the present invention may be any of a top-emission type that emits light in a direction opposite to a substrate on which a light-emitting element is formed, a bottom-emission type that emits light toward a substrate on which a light-emitting element is formed, and a dual-emission type that emits light to both sides.

[0415] Note that, for example, by using a vertical transistor such as the transistor 300 described in Embodiment 2, the area occupied by a pixel circuit can be reduced, and therefore the aperture ratio of a pixel in a bottom-emission display device can be increased. For example, a display device with an aperture ratio of 50% or more, 55% or more, or 60% or more can be realized.

[0416] In this specification and the like, the aperture ratio refers to the ratio of the area of ​​the region through which light is emitted to the area of ​​the pixel.

[0417] <Circuit Configuration Example of Display Device> FIGS. 23A to 23E are block diagrams illustrating circuit configuration examples of a display device of one embodiment of the present invention.

[0418] 23A , display device 460 has a display unit 462, a first drive circuit unit 463, and a second drive circuit unit 464. Display unit 462 has a plurality of pixels 461 arranged in a matrix of m rows and n columns (m and n are each an integer of 2 or greater), for example.

[0419] When at least a part of display device 460 is used in the above-described display device 400, pixel 461 corresponds to pixel 453, display unit 462 corresponds to display unit 452, first drive circuit unit 463 corresponds to circuit unit 454a, and second drive circuit unit 464 corresponds to circuit unit 454b. Each of first drive circuit unit 463 and second drive circuit unit 464 may include at least a part of IC 456.

[0420] 23A , the pixel 461 arranged in the first row and first column is indicated as pixel 461[1,1], the pixel 461 arranged in the first row and nth column is indicated as pixel 461[1,n], the pixel 461 arranged in the mth row and first column is indicated as pixel 461[m,1], and the pixel 461 arranged in the mth row and nth column is indicated as pixel 461[m,n]. Note that the pixel 461 arranged in the uth row and vth column (u is an integer of 1 to m, and v is an integer of 1 to n) may be indicated as pixel 461[u,v].

[0421] The display device 460 also has m wires 465 that are arranged in parallel and whose potentials are controlled by a circuit included in a first drive circuit unit 463. The potential of one wire 465 is applied to n pixels 461 arranged in the row direction. Note that a configuration in which multiple wires are included per wire 465 may be used in accordance with the configuration of the pixel 461. A display device 460A shown in FIG. 23B shows an example configuration in which two wires are included per wire 465.

[0422] The display device 460 also has n wires 466 that are arranged in parallel and whose potentials are controlled by a circuit included in the second drive circuit unit 464. The potential of one wire 466 is applied to m pixels 461 arranged in the column direction. Note that a configuration may be adopted in which one wire 466 includes multiple wires in accordance with the configuration of the pixel 461.

[0423] The pixel 461 has a function of causing a light-emitting element to emit light with emission intensity according to a data potential written to a pixel circuit selected by the potential of a wiring 465 via a wiring 466, for example.

[0424] A specific configuration example of a pixel circuit that can be used for the pixel 461 will be described later. Note that as at least a part of the pixel 461, a semiconductor device 470A described later or the like can be used.

[0425] The circuit included in the first drive circuit unit 463 functions as, for example, a scanning line drive circuit (sometimes called a gate line drive circuit, gate driver, scan driver, or row driver).

[0426] The circuit included in the second driver circuit unit 464 functions as, for example, a signal line driver circuit (which may also be called a source line driver circuit, a source driver, a data driver, or a column driver). In addition, for example, the circuit may have a function of converting image data (image data) displayed on the display device 460 into a data potential (digital-analog conversion).

[0427] Note that the pixel 461 can be configured such that, for example, a current to be passed through a light-emitting element is output to a monitor line. The current output to the monitor line is converted into an analog voltage (current-voltage conversion) or a digital signal (analog-digital conversion) in the second driver circuit unit 464, for example, and can be output to the outside of the display device 460. Using the analog voltage or the digital signal, for example, correction of image data (also referred to as external correction) can be performed outside the display device.

[0428] The following will describe specific configuration examples of each element circuit that can be used in the circuits included in the first drive circuit unit 463 and the second drive circuit unit 464. Note that, for example, a semiconductor device 480 described below can be used as at least a part of the circuits included in the first drive circuit unit 463 and the second drive circuit unit 464.

[0429] One embodiment of the present invention can employ various configurations as modified examples of the display device 460. For example, as shown in Figures 23C to 23E, a configuration can be employed in which a first driver circuit unit 463L and a first driver circuit unit 463R are arranged to face each other with a display unit 462 interposed therebetween.

[0430] 23C shows a configuration example of a display device 460B having m wirings 465L whose potentials are controlled by a circuit included in a first drive circuit unit 463L, and m wirings 465R whose potentials are controlled by a circuit included in a first drive circuit unit 463R. The potentials of one wiring 465L and one wiring 465R are respectively applied to n pixels 461 arranged in the row direction.

[0431] The display device 460C shown in FIG. 23D illustrates an example configuration having m wirings 465 whose potentials are controlled by both a circuit included in a first drive circuit unit 463L and a circuit included in a first drive circuit unit 463R. The potential of one wiring 465 is applied to n pixels 461 arranged in the row direction. This configuration, for example, can reduce the substantial wiring load (parasitic capacitance and parasitic resistance) to one-fourth of the wiring load in the display device 460A shown in FIG. 23B. This allows the display device to achieve, for example, higher speed, higher definition, higher resolution, a narrower frame, and a larger screen.

[0432] 23E shows a display device 460D having m / 2 wirings 465L whose potentials are controlled by a circuit included in a first driver circuit unit 463L and m / 2 wirings 465R whose potentials are controlled by a circuit included in a first driver circuit unit 463R. The potential of one wiring 465L is applied to n pixels 461 arranged in the row direction in odd-numbered rows. The potential of one wiring 465R is applied to n pixels 461 arranged in the row direction in even-numbered rows. This configuration can reduce, for example, the number of stages in the shift register by half. Therefore, for example, the display device can be made faster, more precise, and more highly resolved, with a narrower frame and a larger screen.

[0433] Although not shown, for example, two second drive circuit sections 464 may be arranged to face each other with the display section 462 interposed therebetween.

[0434] Note that one embodiment of the present invention may be a display device 460 having any of the above-described various structures, and may also be provided with a sensor portion overlapping the display portion 462 when viewed from above. The sensor portion can have the function of, for example, a touch sensor, a near-touch sensor, a fingerprint sensor, or the like. These sensors can be, for example, capacitive sensors or optical sensors.

[0435] In the display device 460 provided with a sensor unit, the first drive circuit unit 463 (or the first drive circuit unit 463L and the first drive circuit unit 463R) may include, for example, a circuit having a function of driving the sensor unit. The second drive circuit unit 464 may include, for example, a circuit having a function of outputting a signal detected by the sensor unit to the outside of the display device.

[0436] [Peripheral Driving Circuit] Next, a configuration example of each element circuit that can be used in the peripheral driving circuit of the display device 460 will be described.

[0437] In this specification, the circuits included in the first drive circuit unit 463 and the circuits included in the second drive circuit unit 464 of the display device 460 may be collectively referred to as the "peripheral drive circuit."

[0438] The peripheral driver circuit can be configured using various component circuits. Examples of such component circuits include shift register circuits, flip-flop circuits, latch circuits, buffer circuits, inverter circuits, and level shifter circuits. Other examples include multiplexer circuits, demultiplexer circuits, source follower circuits, source-grounded amplifier circuits, sample-and-hold circuits, and switch circuits (e.g., transmission gates and analog switches). Other examples include current-voltage converter circuits, analog-to-digital converter circuits, digital-to-analog converter circuits, operational amplifier circuits, comparator circuits, pass-transistor logic circuits, encoder circuits, decoder circuits, and gate circuits (e.g., AND circuits, OR circuits, and NOT circuits). Other examples include circuits that combine these circuits. These component circuits can be configured using, for example, transistors and capacitors.

[0439] In one embodiment of the present invention, at least a part of the semiconductor device 100A, the semiconductor device 100B, the driver circuit 110A, the driver circuit 110B, the driver circuit 116A, the driver circuit 117A, and the like described in Embodiment 1 can be used as the peripheral driver circuits (the first driver circuit portion 463 and the second driver circuit portion 464) described in this embodiment. For example, when the driver circuit 110A is used, the driver circuit may be provided in the first driver circuit portion 463, and the wiring OUT31 may be electrically connected to the wiring 465. In this case, the first driver circuit portion 463 includes m driver circuits 110A, and the wiring OUT31 of each driver circuit 110A is electrically connected to n pixels 461 through the wiring 465. Furthermore, when the driver circuit 110B is used, the driver circuit may be provided in the first driver circuit portion 463, and the wiring OUT31 may be electrically connected to the wiring 465. In this case, the first drive circuit unit 463 has m drive circuits 110B, and the wiring OUT31 of each drive circuit 110B is electrically connected to n pixels 461 via wiring 465. Furthermore, for example, when the drive circuit 116A is applied, the drive circuit may be provided in the first drive circuit unit 463, and the wiring OUT61 may be electrically connected to the wiring 465. In this case, the first drive circuit unit 463 has m drive circuits 116A, and the wiring OUT61 of each drive circuit 116A is electrically connected to n pixels 461 via wiring 465. Furthermore, for example, when the drive circuit 117A is applied, the drive circuit may be provided in the first drive circuit unit 463, and the wiring OUT71 may be electrically connected to the wiring 465. In this case, the first drive circuit unit 463 has m drive circuits 117A, and the wiring OUT71 of each drive circuit 117A is electrically connected to n pixels 461 via wiring 465. By applying the drive circuits 110A and 110B in this manner, the reliability of the display device can be improved.

[0440] In one embodiment of the present invention, various transistors can be used as transistors included in the peripheral driver circuit. For example, vertical transistors such as the transistor 300 described in Embodiment 2 can be used as some or all of the transistors included in the peripheral driver circuit.

[0441] By using vertical transistors for some or all of the transistors constituting the peripheral driver circuit, it is possible to reduce the area occupied by, for example, buffer circuits constituting the circuit included in the first driver circuit unit 463. This makes it possible to narrow the frame of the display device. It is also possible to reduce the area occupied by, for example, demultiplexers and source followers constituting the circuit included in the second driver circuit unit 464. This makes it possible to achieve higher resolution and higher definition of the display device.

[0442] Note that some or all of the transistors included in the peripheral driver circuits can be OS transistors, for example. Alternatively, both OS transistors and Si transistors can be used.

[0443] OS transistors have the characteristic of having an extremely small off-state current. Furthermore, they have the characteristic that the off-state current hardly increases even in a high-temperature environment, and the on-state current is not easily reduced. Si transistors have a higher operating speed than OS transistors. Furthermore, for example, by electrically connecting the gate of an n-channel transistor and the gate of a p-channel transistor, a CMOS circuit (e.g., a circuit that operates complementarily, a CMOS logic gate, or a CMOS logic circuit) can be configured.

[0444] Therefore, as transistors included in the peripheral driver circuits, OS transistors and Si transistors can be used as appropriate.

[0445] 24A to 24E are circuit diagrams illustrating configuration examples of a semiconductor device that can be used in a peripheral driver circuit. The semiconductor device can be used, for example, as part of a scanning line driver circuit (such as a circuit included in the first driver circuit portion 463). It can also be used, for example, as part of a shift register.

[0446] The semiconductor device 480 shown in FIG. 24A includes m register portions 481 and m buffer portions 482. The semiconductor device 480 is electrically connected to m wirings GLa and m wirings GLb. The m register portions 481 are electrically connected to each other via m wirings SR. FIG. 24A illustrates a portion of the semiconductor device 480, including register portions 481_u to 481_u+2, buffer portions 482_u to 482_u+2, wirings SR_u-1 to SR_u+4, wirings GLa_u to GLa_u+2, and wirings GLb_u to GLb_u+2. Note that m is an integer equal to or greater than 2. Also, u is an integer equal to or greater than 1 and equal to or less than m.

[0447] FIG. 24B is a circuit diagram illustrating an example configuration of the register unit 481 and the buffer unit 482. FIG. 24C is a circuit block corresponding to the register unit 481 and the buffer unit 482. The register unit 481 can be applied to each of the register units 481_1 to 481_m. The buffer unit 482 can be applied to each of the buffer units 482_1 to 482_m. That is, for example, in the register unit 481_u, the wiring IN81 is electrically connected to the wiring SR_u−1, the wiring IN82 is electrically connected to the wiring SR_u+2, and the wiring OUT81 is electrically connected to the wiring SR_u. Furthermore, for example, in the buffer unit 482_u, the wiring OUT8A is electrically connected to the wiring GLa_u, and the wiring OUT8B is electrically connected to the wiring GLb_u. 24A and 24C , the wirings IN81, IN8A, IN8B, VLD, and VLS are not shown. The same applies to the register units 481_1 to 481_u-1 and the register units 481_u+1 to 481_m. The same applies to the buffer units 482_1 to 482_u-1 and the buffer units 482_u+1 to 482_m.

[0448] That is, in the semiconductor device 480, the wiring OUT81 in the register portion 481_u-1 is electrically connected to the wiring IN81 in the register portion 481_u through the wiring SR_u-1, and the wiring OUT81 in the register portion 481_u is electrically connected to the wiring IN81 in the register portion 481_u+1 through the wiring SR_u. With this configuration, the register portions 481_1 to 481_m are sequentially selected, and a desired potential can be applied to the wiring GLa_u and the wiring GLb_u in the buffer portion 482_u electrically connected to the selected register portion 481_u. Note that in the semiconductor device 480, the potential of the wiring VLS is applied to the wiring GLa_u and the wiring GLb_u in the buffer portion 482_u electrically connected to the unselected register portion 481_u.

[0449] The register unit 481 shown in FIG. 24B includes transistors M81, M82, M83, M84, M85, and M86. The transistor M81 brings the wiring VLD and the wiring NL81 into a conductive state or a non-conductive state depending on the potential of the wiring IN81. The transistor M82 brings the wiring VLD and the wiring NL82 into a conductive state or a non-conductive state depending on the potential of the wiring IN82. The transistor M83 brings the wiring VLS and the wiring NL81 into a conductive state or a non-conductive state depending on the potential of the wiring NL82. The transistor M84 brings the wiring VLS and the wiring NL82 into a conductive state or a non-conductive state depending on the potential of the wiring IN81. The transistor M85 has a function of bringing the wiring IN83 and the wiring OUT81 into a conductive state or a non-conductive state depending on the potential of the wiring NL81. The transistor M86 has a function of bringing the wiring VLS and the wiring OUT81 into a conductive state or a non-conductive state depending on the potential of the wiring NL82.

[0450] 24B includes a transistor M8A, a transistor M8B, a transistor M8C, and a transistor M8D. The transistor M8A brings the wiring IN8A and the wiring OUT8A into a conductive state or a non-conductive state depending on the potential of the wiring NL81. The transistor M8B brings the wiring IN8B and the wiring OUT8B into a conductive state or a non-conductive state depending on the potential of the wiring NL81. The transistor M8C brings the wiring VLS and the wiring OUT8A into a conductive state or a non-conductive state depending on the potential of the wiring NL82. The transistor M8D brings the wiring VLS and the wiring OUT8B into a conductive state or a non-conductive state depending on the potential of the wiring NL82.

[0451] FIG. 24D is a timing chart illustrating an example of the operation of the register unit 481 and the buffer unit 482 shown in FIG. 24B.

[0452] In the following description of the operation, it is assumed that a potential H is applied to the wiring VLD and a potential L is applied to the wiring VLS. It is also assumed that either the potential H or the potential L is applied to each of the wirings IN81, IN82, IN83, IN8A, and IN8B. Note that the potential H is higher than the potential L. For example, it is assumed that the difference between the potential H and the potential L is larger than the threshold voltage of the transistor.

[0453] 24D shows potentials (potential H or potential L) applied to the wirings IN81, IN82, IN83, IN8A, and IN8B in each period (periods T81 to T83) of the operation. The timing chart also shows changes in the potentials of the wirings NL81, NL82, OUT81, OUT8A, and OUT8B.

[0454] In the period T81, a potential L is applied to the wirings IN81 and IN82. The potential of the wiring NL82 is also assumed to be a potential H. Therefore, the potential L is applied to the wiring NL81. At this time, the transistors M85, M8A, and M8B are each in an off state (non-conductive state), and the transistors M86, M8C, and M8D are each in an on state (conductive state). Therefore, the potential L is applied to the wirings OUT81, OUT8A, and OUT8B, regardless of the potentials (potential H or potential L) of the wirings IN83, IN8A, and IN8B. In the following description of the operation, unless otherwise specified, the potential of each wiring is assumed to be maintained at the potential of the previous period.

[0455] In period T82, a potential H is applied to the wiring IN81, causing the potential of the wiring NL82 to become a potential L and the potential of the wiring NL81 to become a potential H. Then, the transistors M85, M8A, and M8B are turned on, and the transistors M86, M8C, and M8D are turned off. Therefore, the potentials (potential H or potential L) of the wirings IN83, IN8A, and IN8B are applied to the wirings OUT81, OUT8A, and OUT8B, respectively, via the transistors M85, M8A, and M8B. Note that even if the potential L is applied to the wiring IN81 after that, the potentials of the wirings NL82 and NL81 are maintained.

[0456] In a period T83, a potential H is applied to the wiring IN82, causing the potential of the wiring NL82 to become the potential H and the potential of the wiring NL81 to become the potential L. Then, the transistors M85, M8A, and M8B are turned off, and the transistors M86, M8C, and M8D are turned on. Therefore, the potential L is applied to the wirings OUT81, OUT8A, and OUT8B, regardless of the potentials (potential H or potential L) of the wirings IN83, IN8A, and IN8B. Note that even if the potential L is applied to the wiring IN82 after that, the potentials of the wirings NL82 and NL81 are maintained.

[0457] 24E is a circuit diagram illustrating a modified example of the register unit 481 and the buffer unit 482. The register unit 481a and the buffer unit 482a shown in FIG. 24E differ from the register unit 481 and the buffer unit 482 in that they include a bootstrap circuit. That is, the register unit 481a includes a transistor M87 and a capacitance C81 in addition to the register unit 481, and the buffer unit 482a includes a transistor M8E, a transistor M8F, a capacitance C8A, and a capacitance C8B in addition to the buffer unit 482. Note that the capacitances C81, C8A, and C8B are sometimes referred to as bootstrap capacitances.

[0458] The gate of the transistor M87 is electrically connected to the wiring VLD. The gate of the transistor M85 is electrically connected to the wiring NL81 via the source and drain of the transistor M87. The gate of the transistor M85 is electrically connected to the wiring OUT81 via the capacitor C81.

[0459] The gate of the transistor M8E is electrically connected to the wiring VLD. The gate of the transistor M8A is electrically connected to the wiring NL81 via the source and drain of the transistor M8E. The gate of the transistor M8A is electrically connected to the wiring OUT8A via a capacitor C8A.

[0460] The gate of the transistor M8F is electrically connected to the wiring VLD. The gate of the transistor M8B is electrically connected to the wiring NL81 via the source and drain of the transistor M8F. The gate of the transistor M8B is electrically connected to the wiring OUT8B via a capacitor C8B.

[0461] In the register unit 481, when the transistor M85 transfers the potential H from the wiring IN83 to the wiring OUT81, a potential drop occurs due to the threshold voltage. Therefore, by employing a bootstrap circuit as in the register unit 481a, the transistor M85 can be maintained in an on state by capacitive coupling due to the bootstrap capacitance. Therefore, the potential H can be transferred to the wiring OUT81 without a potential drop due to the threshold voltage.

[0462] Similarly, in the buffer portion 482, when the transistor M8A transfers the potential H from the wiring IN8A to the wiring OUT8A, a potential drop occurs due to the threshold voltage. Also, when the transistor M8B transfers the potential H from the wiring IN8B to the wiring OUT8B, a potential drop occurs due to the threshold voltage. Therefore, by employing a bootstrap circuit as in the buffer portion 482a, the transistors M8A and M8B can be maintained in an on state due to capacitive coupling by the bootstrap capacitance. Therefore, the potential H can be transferred to the wiring OUT8A and the wiring OUT8B without a potential drop due to the threshold voltage.

[0463] Note that in one embodiment of the present invention, at least part of the semiconductor device 100A, the semiconductor device 100B, and the like described in Embodiment 1 can be applied to the register portion 481, the buffer portion 482, and the like included in the semiconductor device 480. This can improve the reliability of a display device including the semiconductor device.

[0464] [Pixel Circuit] Next, a configuration example of a pixel circuit that can be used for the pixel 461 included in the display device 460 will be described.

[0465] FIG. 25 is a circuit diagram illustrating a configuration example of a semiconductor device that can be used for the pixel 461.

[0466] 25, a semiconductor device 470A includes a pixel circuit 471A and a light-emitting element D51. The pixel circuit 471A includes a transistor M51, a transistor M52, a transistor M53, and a capacitor C51.

[0467] The gate of the transistor M52 is electrically connected to one of the source or drain of the transistor M51 and one terminal of the capacitor C51 via a wiring NL52. The one of the source or drain of the transistor M52 is electrically connected to the other terminal of the capacitor C51, one of the source or drain of the transistor M53, and one terminal (e.g., an anode terminal) of the light-emitting element D51 via a wiring NL51.

[0468] The other of the source and the drain of the transistor M52 is electrically connected to the wiring ANO. The other terminal (e.g., the cathode terminal) of the light-emitting element D51 is electrically connected to the wiring CATHO. The other of the source and the drain of the transistor M51 is electrically connected to the wiring DL. The other of the source and the drain of the transistor M53 is electrically connected to the wiring VL0. The gates of the transistors M51 and M53 are electrically connected to the wiring GLa.

[0469] The light emitting element D51 emits light with a light emitting intensity according to the amount of current flowing through the light emitting element D51. As the light emitting element D51, for example, an organic EL element can be used.

[0470] The transistor M52 can change its drain current depending on the potential applied to its gate. Therefore, in the pixel circuit 471A, the transistor M52 has a function of controlling the amount of current flowing through the light-emitting element D51. In other words, the transistor M52 has a function of controlling the light-emitting intensity of the light-emitting element D51. In this specification and the like, a transistor having a function similar to that of the transistor M52 may be referred to as a "drive transistor."

[0471] The transistor M51 has a function of turning on or off the gate of the transistor M52 and the wiring DL (functioning as a switch). The transistor M53 has a function of turning on or off the source or drain of the transistor M52 and the wiring VL0 (functioning as a switch). The capacitor C51 has a function of holding a potential difference (voltage) between the gate of the transistor M52 and the source or drain of the transistor M52 when the wiring NL52 is floating, for example.

[0472] The wiring GLa may be referred to as, for example, a gate line, a scan line, or a selection line, etc. The wiring DL may be referred to as, for example, a source line, a data line, or a signal line, etc.

[0473] In the semiconductor device 470A, a current flowing through the transistor M52 or a current flowing through the light-emitting element D51 can be output to the wiring VL0 via the transistor M53. Therefore, the wiring VL0 may be referred to as a monitor line.

[0474] In one embodiment of the present invention, various transistors can be used as transistors (transistors M51 to M53) included in the pixel circuit 471A.

[0475] For example, n-channel transistors can be used for some or all of the transistors included in the pixel circuit 471A. Alternatively, for example, p-channel transistors can be used.

[0476] Further, for example, transistors having a back gate can be used for some or all of the transistors included in the pixel circuit 471A.

[0477] 26 is a circuit diagram illustrating a configuration example in which transistors having back gates are used as the transistors (transistors M51 to M53) that constitute the pixel circuit 471A. In each of the transistors M51 to M53, the back gate is electrically connected to the gate. In this way, in a transistor having a back gate, the on-resistance can be reduced by applying the same potential to the back gate as to the gate.

[0478] In a transistor having a back gate, the potential that can be applied to the back gate is not limited to the same potential as that of the gate. For example, applying the same potential as that of the source to the back gate makes it difficult for an electric field generated outside the transistor to affect the channel formation region, thereby stabilizing electrical characteristics and improving reliability. Furthermore, for example, applying an arbitrary potential to the back gate can change the threshold voltage. The potential applied to the back gate is not limited to a fixed potential. The potential applied to the back gate may be the same or different for each transistor.

[0479] Some or all of the transistors included in the pixel circuit 471A can be vertical transistors such as the transistor 300 described in Embodiment 2. Alternatively, a planar transistor such as the transistor 200 described in Embodiment 2 can be used.

[0480] In one embodiment of the present invention, vertical transistors are preferably used as some or all of the transistors included in the pixel circuit 471A, particularly as transistors functioning as switches (the transistors M51 and M53).

[0481] By using a vertical transistor in a pixel circuit, for example, the resolution (also referred to as pixel density) of a display device using the pixel circuit can be increased. Furthermore, for example, the pixel arrangement can be changed from a pentile arrangement to a stripe arrangement without reducing the resolution of the display device. Furthermore, for example, an internal correction circuit as described below can be installed without reducing the resolution of the display device.

[0482] For example, a transistor with high saturation, a transistor with a long channel length, or a planar transistor may be used as the driving transistor (transistor M52).

[0483] In one embodiment of the present invention, an OS transistor with extremely low off-state current may be used as a transistor included in the pixel circuit 471A.

[0484] For example, by using OS transistors as the transistors functioning as switches (the transistors M51 and M53) among the transistors included in the pixel circuit 471A, the charge accumulated in the capacitor C51 can be held for a long period of time.

[0485] Therefore, for example, in a display device using the pixel circuit, when a still image that does not need to be rewritten for each frame is displayed, the image can be continued to be displayed even if the operation of the peripheral driver circuit that drives the pixel circuit is stopped. In this specification, a driving method that stops the operation of the peripheral driver circuit while a still image is displayed is also referred to as "idling stop driving." By performing idling stop driving, it is possible to reduce the power consumption of the display device.

[0486] Note that one embodiment of the present invention is not limited to a structure using an OS transistor as the pixel circuit 471A, and may be a structure using a plurality of types of transistors containing different semiconductor materials. For example, the pixel circuit 471A may be formed using LTPO transistors (that is, both LTPS transistors and OS transistors).

[0487] For example, among the transistors constituting the pixel circuit 471A, OS transistors can be used as transistors functioning as switches (transistors M51 and M53) and an LTPS transistor can be used as a driving transistor (transistor M52). By configuring the pixel circuit 471A using both LTPS transistors and OS transistors, it is possible to reduce the power consumption of a display device using the pixel circuit and improve its driving capability.

[0488] Note that when the pixel circuit 471A is configured using multiple types of transistors containing different semiconductor materials, the transistors may be provided in different layers for each type of transistor. For example, when the pixel circuit 471A is configured using Si transistors and OS transistors, a layer including the Si transistors and a layer including the OS transistors may be stacked. Such a configuration can reduce the area occupied by the pixel circuit 471A.

[0489] In the operation of the semiconductor device 470A, first, a potential H is applied to the wiring GLa, so that a data potential is applied from the wiring DL to the wiring NL52, and a potential is applied from the wiring VL0 to the wiring NL51. That is, a voltage corresponding to the data potential is applied as the gate voltage of the transistor M52.

[0490] Next, when a potential L is applied to the wiring GLa, a current corresponding to the gate voltage applied to the transistor M52 flows through the light-emitting element D51, causing the light-emitting element D51 to emit light with an intensity corresponding to the current amount.

[0491] In one embodiment of the present invention, a semiconductor device that can be used for the pixel 461 is not limited to the structure of the semiconductor device 470A. Modifications of the semiconductor device will be described below.

[0492] 27 is a circuit diagram illustrating a semiconductor device 470B, which is a modified example of the semiconductor device 470A. The semiconductor device 470B has a pixel circuit 471B instead of the pixel circuit 471A. The pixel circuit 471B differs from the pixel circuit 471A in that it has a transistor M54, a transistor M55, a transistor M56, and a capacitor C52 instead of the transistor M53 and the capacitor C51. The pixel circuit 471B has a configuration including an internal correction circuit.

[0493] The gate of transistor M52 is electrically connected to one of the source or drain of transistor M55 and one of the source or drain of transistor M56 via wiring NL52. One of the source or drain of transistor M51 is electrically connected to the other of the source or drain of transistor M56 and one terminal of capacitor C52 via wiring NL53. One of the source or drain of transistor M52 is electrically connected to the other terminal of capacitor C52 and one of the source or drain of transistor M54 via wiring NL51. The other of the source or drain of transistor M54 is electrically connected to one terminal of light-emitting element D51.

[0494] The other of the source and the drain of the transistor M55 is electrically connected to the wiring VL1. The gate of the transistor M55 is electrically connected to the wiring GLa. The gate of the transistor M56 is electrically connected to the wiring GLb. The gate of the transistor M54 is electrically connected to the wiring GLc.

[0495] The transistor M55 has a function of turning on or off the connection between the gate of the transistor M52 and the wiring VL1 (function as a switch). The transistor M56 has a function of turning on or off the connection between the gate of the transistor M52 and one of the source or drain of the transistor M51 (function as a switch). The transistor M54 has a function of turning on or off the connection between one of the source or drain of the transistor M52 and one terminal of the light-emitting element D51 (function as a switch). The capacitor C52 has a function of holding a potential difference (voltage) between one of the source or drain of the transistor M52 and one of the source or drain of the transistor M51 when the wiring NL53 is floating, for example.

[0496] The lines GLb and GLc may be referred to as gate lines, scan lines, or selection lines, for example.

[0497] In the operation of the semiconductor device 470B, first, a potential L is applied to the wiring GLa and the wiring GLb, and a potential H is applied to the wiring GLc. Then, the potential H is applied to the wiring GLa. Next, the potential L is applied to the wiring GLc. Then, the potential L is applied to the wiring GLa. Through this series of operations, a data potential is applied from the wiring DL to the wiring NL53, and a voltage corresponding to the threshold voltage of the transistor M52 is held in the capacitor C52.

[0498] Next, by applying a potential H to the wiring GLb and the wiring GLc, the voltage held in the capacitor C52 is applied as the gate voltage of the transistor M52, and a current corresponding to this voltage flows through the light-emitting element D51. As a result, the light-emitting element D51 emits light with an intensity corresponding to this current. At this time, a voltage independent of the threshold voltage of the transistor M52 is applied as the gate voltage of the transistor M52. Therefore, a current independent of the threshold voltage of the transistor M52 flows through the light-emitting element D51.

[0499] 28 is a circuit diagram illustrating a semiconductor device 470C, which is a modified example of the semiconductor device 470A. The semiconductor device 470C has a pixel circuit 471C instead of the pixel circuit 471A. In addition to the components of the pixel circuit 471A, the pixel circuit 471C further has a transistor M54, a transistor M57, a transistor M58, and a capacitor C53. Also, the pixel circuit 471C differs from the pixel circuit 471A in that the transistor M52 has a back gate. The pixel circuit 471C has a configuration that includes an internal correction circuit different from that of the pixel circuit 471B.

[0500] The gate of transistor M52 is electrically connected to one of the source or drain of transistor M51, one terminal of capacitor C51, and one of the source or drain of transistor M57 via wiring NL52. The back gate of transistor M52 is electrically connected to one terminal of capacitor C53 and one of the source or drain of transistor M58 via wiring NL54. One of the source or drain of transistor M52 is electrically connected to the other terminal of capacitor C51, the other terminal of capacitor C53, the other of the source or drain of transistor M57, one of the source or drain of transistor M53, and one of the source or drain of transistor M54 via wiring NL51. The other of the source or drain of transistor M54 is electrically connected to one terminal of light-emitting element D51.

[0501] The other of the source and the drain of the transistor M58 is electrically connected to the wiring VL2. The gates of the transistors M57 and M58 are electrically connected to the wiring GLb. The gate of the transistor M54 is electrically connected to the wiring GLc.

[0502] The transistor M52 can change its threshold voltage depending on the potential applied to its back gate.

[0503] The transistor M57 functions as a switch to bring the gate of the transistor M52 and either the source or the drain of the transistor M52 into a conductive or non-conductive state. The transistor M58 functions as a switch to bring the back gate of the transistor M52 into a conductive or non-conductive state with the wiring VL2. The transistor M54 functions as a switch to bring either the source or the drain of the transistor M52 into a conductive or non-conductive state with one terminal of the light-emitting element D51. The capacitor C53 holds the potential difference (voltage) between the source or the drain of the transistor M52 and the back gate of the transistor M52 when the wiring NL54 is floating, for example.

[0504] The lines GLb and GLc may be referred to as gate lines, scan lines, or selection lines, for example.

[0505] In the operation of the semiconductor device 470C, first, a potential L is applied to the wiring GLa, and a potential H is applied to the wirings GLb and GLc. Next, the potential L is applied to the wiring GLc. After that, the potential L is applied to the wiring GLb. Through this series of operations, the back-gate voltage that corrects the threshold voltage of the transistor M52 to 0 V is held in the capacitor C53.

[0506] Next, when a potential H is applied to the line GLa, a data potential is applied from the line DL to the line NL52, and a potential is applied from the line VL0 to the line NL51. That is, a voltage according to the data potential is applied as the gate voltage of the transistor M52.

[0507] Next, a potential L is applied to the wiring GLa, and a potential H is applied to the wiring GLc, causing a current amount corresponding to the gate voltage applied to the transistor M52 to flow through the light-emitting element D51. As a result, the light-emitting element D51 emits light with an intensity corresponding to the current amount. At this time, a voltage that corrects the threshold voltage of the transistor M52 to 0 V is applied as the back-gate voltage of the transistor M52. Therefore, a current amount that does not depend on the threshold voltage of the transistor M52 flows through the light-emitting element D51.

[0508] 29 is a circuit diagram illustrating a semiconductor device 470D, which is a modification of the semiconductor device 470C. The semiconductor device 470D has a pixel circuit 471D instead of the pixel circuit 471C. The pixel circuit 471D differs from the pixel circuit 471C in that it does not have the transistor M53.

[0509] In the operation of the semiconductor device 470D, when a data potential is applied from the wiring DL to the wiring NL52, for example, by turning on the transistor M54, the potential of the wiring NL51 may be increased by an amount corresponding to the voltage drop in the light-emitting element D51. The semiconductor device 470D further does not need to include the wiring VL0. This allows the area occupied by the pixel circuit 471D to be reduced.

[0510] 30 is a circuit diagram illustrating a semiconductor device 470E, which is a modification of the semiconductor device 470C. The semiconductor device 470E includes a pixel circuit 471E instead of the pixel circuit 471C. The pixel circuit 471E differs from the pixel circuit 471C in that it does not include the transistor M54. Therefore, one of the source and drain of the transistor M52 is electrically connected to one terminal of the light-emitting element D51.

[0511] During operation of the semiconductor device 470E, when the back-gate voltage that corrects the threshold voltage of the transistor M52 to 0 V is held in the capacitor C53, for example, the same potential as that of the wiring ANO may be applied to the wiring CATHO to prevent current from flowing through the light-emitting element D51. The semiconductor device 470E further does not need to include the wiring GLc. This allows the area occupied by the pixel circuit 471E to be reduced.

[0512] 31 is a circuit diagram illustrating a semiconductor device 470F, which is a modification of the semiconductor device 470B. The semiconductor device 470F has a pixel circuit 471F instead of the pixel circuit 471B. In addition to the pixel circuit 471B, the pixel circuit 471F further has a transistor M59 and a capacitor C54.

[0513] The gate of the transistor M54 is electrically connected to one terminal of the capacitor C54 and one of the source and drain of the transistor M59 via a wiring NL55. The other of the source and drain of the transistor M54 is electrically connected to one terminal of the light-emitting element D51 and the other terminal of the capacitor C54.

[0514] The other of the source and the drain of the transistor M59 is electrically connected to the wiring GLc. The gate of the transistor M59 is electrically connected to the wiring VL3.

[0515] The transistor M59 has a function of turning on or off the gate of the transistor M54 and the wiring GLc (functioning as a switch). The capacitor C54 has a function of holding a potential difference (voltage) between the other of the source or drain of the transistor M54 and the gate of the transistor M54 when, for example, the wiring NL55 is in a floating state.

[0516] During operation of the semiconductor device 470F, when a current corresponding to the gate voltage applied to transistor M52 flows through light-emitting element D51, and the potential of one terminal of light-emitting element D51 (i.e., the other of the source or drain of transistor M54) rises, the potential of wiring NL55 (i.e., the gate of transistor M54) also rises due to capacitive coupling via capacitor C54. This ensures that transistor M54 is turned on. This allows a stable current to be supplied to light-emitting element D51. Note that capacitor C54 is sometimes referred to as a bootstrap capacitance.

[0517] 32 is a circuit diagram illustrating a semiconductor device 470G, which is a modified example of the semiconductor device 470C. The semiconductor device 470G has a pixel circuit 471G instead of the pixel circuit 471C. In addition to the pixel circuit 471C, the pixel circuit 471G further has a transistor M59 and a capacitor C54. In other words, the pixel circuit 471G is configured by combining the internal correction circuit of the pixel circuit 471C with the bootstrap capacitor of the pixel circuit 471F.

[0518] 33 is a circuit diagram illustrating a semiconductor device 470H. The semiconductor device 470H includes a pixel circuit 471H and a liquid crystal element D52. The pixel circuit 471H includes a transistor M51 and a capacitor C55. The pixel circuit 471H includes a transistor M51 and a capacitor C55.

[0519] The gate of the transistor M51 is electrically connected to a wiring GLa. One of the source and the drain of the transistor M51 is electrically connected to one terminal of a capacitor C55 and one terminal of a liquid crystal element D52 via a wiring NL56. The other of the source and the drain of the transistor M51 is electrically connected to a wiring DL. The other terminal of the capacitor C55 is electrically connected to a wiring CS. The other terminal of the liquid crystal element D52 is electrically connected to a wiring COM.

[0520] The liquid crystal element D52 changes its light transmittance in accordance with the potential difference (voltage) between a pair of terminals (between one terminal and the other terminal).

[0521] The transistor M51 has a function of turning on or off the state between one terminal of the capacitor C55 and the wiring DL (a function as a switch). The capacitor C55 has a function of holding a potential difference (voltage) between a pair of terminals of the liquid crystal element D52, for example, when the wiring NL56 is in a floating state.

[0522] 34 is a circuit diagram illustrating a semiconductor device 470J, which is a modified example of the semiconductor device 470A. The semiconductor device 470J has a pixel circuit 471J instead of the pixel circuit 471A. In addition to the pixel circuit 471A, the pixel circuit 471J further has a transistor M5A, a transistor M5B, and a capacitor C5A.

[0523] The gate of the transistor M5B is electrically connected to one of the source and drain of the transistor M5A and one terminal of the capacitor C5A via a wiring NL5A, and the other of the source and drain of the transistor M5B is electrically connected to the gate of the transistor M52, one of the source and drain of the transistor M51, and one terminal of the capacitor C51 via a wiring NL52.

[0524] The other of the source and the drain of the transistor M5A is electrically connected to the wiring DLW. The other of the source and the drain of the transistor M5B is electrically connected to the wiring VLW. The other terminal of the capacitor C5A is electrically connected to the wiring SWEP. The gate of the transistor M51 is electrically connected to the wiring GLb instead of the wiring GLa. The gate of the transistor M53 is electrically connected to the wiring GLc instead of the wiring GLa. The gate of the transistor M5A is electrically connected to the wiring GLa.

[0525] The pixel circuit 471J has a configuration capable of performing PWM control. For example, PWM control can be performed by applying a PWM-controlled data potential from the wiring DLW to the wiring NL5A via the transistor M5A and applying a triangular wave, a sawtooth wave, or the like to the wiring SWEP. Note that, for example, when a micro LED or the like is used as the light-emitting element D51, it is preferable to perform PWM control in order to stabilize the emission wavelength.

[0526] 35 is a circuit diagram showing a modification of the semiconductor device 470B. The semiconductor device 470B1 shown in FIG. 35 has a pixel circuit 471B1 instead of the pixel circuit 471B. The pixel circuit 471B1 is a configuration example in which the switch portion 101A included in the semiconductor device 100A described in Embodiment 1 and the switch portion 101B included in the semiconductor device 100B are applied to the pixel circuit 471B.

[0527] Here, the switch unit 101A shown in FIG. 3A is applied to transistors M54 and M56, the switch unit 101B shown in FIG. 6A is applied to transistor M55, and the switch unit 101A shown in FIG. 3B is applied to transistor M51. Thus, FIG. 35 illustrates a configuration in which the switch unit 101A_1 is applied to transistor M51, the switch unit 101A_4 is applied to transistor M54, the switch unit 101B_5 is applied to transistor M55, and the switch unit 101A_6 is applied to transistor M56. That is, the transistors M51a, M54a, and M56a correspond to the transistor M11, and the transistors M51b, M54b, and M56b correspond to the transistor M12. The transistor M55a corresponds to the transistor M21, and the transistor M55b corresponds to the transistor M22. Note that the configuration shown in FIG. 35 is an example, and the switch section 101A and the switch section 101B can be applied to at least some of the transistors in the pixel circuit 471B1.

[0528] In the pixel circuit 471B1, particularly, the transistors M54 and M55 may be applied with a high drain voltage, and therefore the switch units 101A and 101B may be used. Furthermore, because the transistor M54 is a path for current flowing to the light-emitting element D51, the on-current may be increased. Therefore, the transistor M54 may have a configuration such as the switch unit 101A shown in FIG. 3A. Furthermore, the transistor M54 remains in the on state for a long period of time, and a positive gate bias is continuously applied to it. Therefore, the switch unit 101A shown in FIG. 3B or the switch unit 101A shown in FIG. 1A may be used. Furthermore, the source or drain function of the transistor M51 is switched depending on the data potential applied to the line DL. Therefore, the transistor M51 may have a configuration such as the switch unit 101A shown in FIG. 3B. Furthermore, although not shown, the transistor M52 may have a configuration such as the switch unit 101B shown in FIG. 6B. This may reduce the drain voltage of the transistor M52 and improve saturation. In this manner, by using the switch portion 101A and the switch portion 101B, it is possible to improve the reliability of the pixel circuit 471B1 and the display device using the pixel circuit.

[0529] 36 is a circuit diagram showing a modification of the semiconductor device 470C. The semiconductor device 470C1 shown in Fig. 36 has a pixel circuit 471C1 instead of the pixel circuit 471C. The pixel circuit 471C1 is a configuration example in which the switch portion 101A included in the semiconductor device 100A described in Embodiment 1 and the switch portion 101B included in the semiconductor device 100B described in Embodiment 1 are applied to the pixel circuit 471C.

[0530] 3A is applied to transistors M53, M54, and M57, switch unit 101B shown in FIG. 6A is applied to transistor M58, and switch unit 101A shown in FIG. 3B is applied to transistor M51. Thus, FIG. 36 illustrates a configuration in which switch unit 101A_1 is applied to transistor M51, switch unit 101A_3 is applied to transistor M53, switch unit 101A_4 is applied to transistor M54, switch unit 101A_7 is applied to transistor M57, and switch unit 101B_8 is applied to transistor M58. That is, transistors M51a, M53a, M54a, and M57a each correspond to transistor M11, and transistors M51b, M53b, M54b, and M57b each correspond to transistor M12. 36 is an example, and the switch unit 101A and the switch unit 101B can be applied to at least some of the transistors in the pixel circuit 471C1.

[0531] In the pixel circuit 471C1, particularly, the transistors M53, M54, and M58 may be applied with a high drain voltage, and therefore the switch units 101A and 101B may be used. Furthermore, since the transistor M54 is a path for current flowing to the light-emitting element D51, the on-current may be increased. Therefore, the transistor M54 may have a configuration similar to the switch unit 101A shown in FIG. 3A. Furthermore, since the transistor M53 is also a path for current flowing through the transistor M52 when outputting the current flowing through the semiconductor device 470C1 to the outside, the on-current may be increased. Therefore, the transistor M53 may have a configuration similar to the switch unit 101A shown in FIG. 3A. Furthermore, the transistor M54 remains in the on state for a long period of time, and a positive gate bias is continuously applied to it. Therefore, the switch unit 101A shown in FIG. 3B or the switch unit 101A shown in FIG. 1A may be used. Furthermore, the source or drain function of the transistor M51 is switched depending on the data potential applied to the wiring DL. Therefore, the transistor M51 may have a configuration similar to the switch unit 101A shown in FIG. 3B . Although not shown, the transistor M52 may have a configuration similar to the switch unit 101B shown in FIG. 6B . This may result in a reduction in the drain voltage of the transistor M52 and an increase in saturation. Thus, by using the switch units 101A and 101B, the reliability of the pixel circuit 471C1 and a display device using the pixel circuit can be improved.

[0532] 37 is a circuit diagram showing a modification of the semiconductor device 470J. The semiconductor device 470J1 shown in FIG. 37 has a pixel circuit 471J1 instead of the pixel circuit 471J. The pixel circuit 471J1 is a configuration example in which the switch portion 101A included in the semiconductor device 100A described in Embodiment 1 and the switch portion 101B included in the semiconductor device 100B described in Embodiment 1 are applied to the pixel circuit 471J.

[0533] 3A is applied to the transistors M53 and M5B, and the switch unit 101A shown in FIG. 3B is applied to the transistors M51 and M5A. Thus, FIG. 37 illustrates a configuration in which the switch unit 101A_1 is applied to the transistor M51, the switch unit 101A_3 is applied to the transistor M53, the switch unit 101A_A is applied to the transistor M5A, and the switch unit 101A_B is applied to the transistor M5B. That is, the transistors M51a, M53a, M5Aa, and M5Ba each correspond to the transistor M11, and the transistors M51b, M53b, M5Ab, and M5Bb each correspond to the transistor M12. Note that the configuration shown in FIG. 36 is an example, and in the pixel circuit 471J1, the switch section 101A and the switch section 101B can be applied to at least some of the transistors.

[0534] In the pixel circuit 471J1, a high drain voltage may be applied particularly to the transistors M53 and M5B, so the switch unit 101A may be applied. Furthermore, the gate voltage of the transistor M5B gradually increases due to a triangular wave or sawtooth wave applied to the wiring SWEP, so the switch unit 101A may be applied particularly to the transistor M5B. Furthermore, the transistor M53 also serves as a current path when the current flowing through the transistor M52 is output to the outside of the semiconductor device 470J1, so the on-state current may be increased. Therefore, the transistor M53 may have a configuration similar to the switch unit 101A shown in FIG. 3A. Furthermore, the function of the source or drain of the transistor M51 is switched depending on the data potential applied to the wiring DL. Therefore, the transistor M51 may have a configuration similar to the switch unit 101A shown in FIG. 3B. Furthermore, the function of the source or drain of the transistor M5A is switched depending on the data potential applied to the wiring DLW. Therefore, the transistor M5A may have a configuration similar to the switch unit 101A shown in FIG. 3B. Although not shown, the transistor M52 may have a configuration similar to the switch unit 101B shown in FIG. 6B . This may reduce the drain voltage of the transistor M52 and improve saturation. In this way, by using the switch units 101A and 101B, the reliability of the pixel circuit 471J1 and the display device using this pixel circuit can be improved.

[0535] Note that in one embodiment of the present invention, a semiconductor device that can be used for the pixel 461 is not limited to the above-described structure, and a semiconductor device in which the respective structures are combined as appropriate can be used.

[0536] <Example of Cross-Sectional Structure of Display Device> FIG. 38 is a cross-sectional view illustrating an example of a cross-sectional structure of a display device of one embodiment of the present invention.

[0537] 38 , the structures shown in the regions 490a, 490b, and 490c can be used in the display device 400. For example, the structure shown in the region 490a can be used in a region where the pixel 453 is provided. The structure shown in the region 490b can be used in a region where the circuit portion 454a, the circuit portion 454b, and the like are provided. The structure shown in the region 490c can be used in a region where the FPC 459 is provided.

[0538] The display device 490 has a substrate 351 and a substrate 352. An adhesive layer 342 is provided between the substrates 351 and 352. The substrate 352 faces the substrate 351 via the adhesive layer 342. Note that the region 490c does not have the substrate 352 or the adhesive layer 342.

[0539] An insulating layer 382 is provided on the substrate 352 side of the substrate 351. On the insulating layer 382, ​​a transistor, a light-emitting element, and the like are provided.

[0540] Here, as an example, a structure is shown in which the transistor 300 described in Embodiment 2 is provided in the region 490a, and the transistor 200 described in Embodiment 2 is provided in the region 490b. A conductive layer 384 is provided in the region 490c. The conductive layer 384 can be formed in the same process as the conductive layer 204 and the conductive layer 304.

[0541] An insulating layer 235 is provided to cover the transistor 200 and the transistor 300 .

[0542] In region 490a, a pixel electrode 311 is provided so as to cover a portion of the insulating layer 235 and to have a region in contact with the insulating layer 306, the insulating layer 395, and the conductive layer 312b through an opening provided in the insulating layer 235.

[0543] An insulating layer 237 is provided so as to cover the insulating layer 235 and the pixel electrode 311. The insulating layer 237 has an opening that reaches the pixel electrode 311 in a region overlapping with the pixel electrode 311.

[0544] An EL layer 313 is provided so as to cover the insulating layer 237 and the pixel electrode 311. A common electrode 315 is provided so as to cover the EL layer 313. A protective layer 331 is provided so as to cover the common electrode 315.

[0545] In an opening provided in the insulating layer 237, the pixel electrode 311 functions as one electrode of the light-emitting element 330, the common electrode 315 functions as the other electrode, and the EL layer 313 has a function of emitting light.

[0546] A light-shielding layer 317 is provided on the substrate 352 on the substrate 351 side.

[0547] In region 490a, an opening is provided in light-shielding layer 317 so as to have an area overlapping with light-emitting element 330. Therefore, light emitted by light-emitting element 330 is emitted to the outside of display device 490 through the opening provided in light-shielding layer 317. In Fig. 38, this state is represented by a dashed arrow and the word "Light."

[0548] In the region 490c, the conductive layer 386 is provided so as to cover part of the insulating layer 235 and to have a region in contact with the insulating layer 395 and the conductive layer 384 through an opening provided in the insulating layer 235.

[0549] An FPC 459 is provided with a connection layer 388 interposed therebetween so as to have a region overlapping with the conductive layer 386 .

[0550] The conductive layer 384 is electrically connected to the FPC 459 via the conductive layer 386 and the connection layer 388 .

[0551] The connection layer 388 may be, for example, an anisotropic conductive film (ACF) or an anisotropic conductive paste (ACP).

[0552] <Structure Examples of Light-Emitting Element> In one embodiment of the present invention, light-emitting elements with various structures can be used as light-emitting elements included in a display device.

[0553] 39A, 39B, 40A, and 40B are cross-sectional views illustrating light-emitting elements with various configurations.

[0554] 39A has light-emitting elements 330R, 330G, and 330B between substrates 351 and 352. Light-emitting element 330R is a display element included in a pixel that emits red light, light-emitting element 330G is a display element included in a pixel that emits green light, and light-emitting element 330B is a display element included in a pixel that emits blue light. When describing matters common to light-emitting element 330R, light-emitting element 330G, and light-emitting element 330B, the elements may be simply referred to as light-emitting element 330.

[0555] 39A omits some of the configuration between the substrate 351 and the light-emitting element 330 and the configuration between the substrate 352 and the light-emitting element 330. The display device 490A includes, between the substrate 351 and the light-emitting element 330, for example, a transistor that constitutes a pixel circuit and an insulating layer 235 that is provided to cover the transistor.

[0556] The display device 490A employs an SBS (Side By Side) structure, which allows the materials and configuration to be optimized for each light-emitting element, increasing the degree of freedom in the selection of materials and configurations, and facilitating the improvement of light emission intensity and reliability.

[0557] The display device 490A is a top-emission type. In the top-emission type, a transistor or the like can be arranged to overlap with a light-emitting region of a light-emitting element, and therefore the aperture ratio of a pixel can be increased compared to a bottom-emission type.

[0558] On the insulating layer 235, a light emitting element 330R, a light emitting element 330G, and a light emitting element 330B are provided.

[0559] The light-emitting element 330R has a pixel electrode 311R on the insulating layer 235, an EL layer 313R on the pixel electrode 311R, and a common electrode 315 on the EL layer 313R. The light-emitting element 330R shown in Fig. 39A emits red (R) light. The EL layer 313R has a light-emitting layer that emits red light.

[0560] The light-emitting element 330G has a pixel electrode 311G on the insulating layer 235, an EL layer 313G on the pixel electrode 311G, and a common electrode 315 on the EL layer 313G. The light-emitting element 330G shown in Fig. 39A emits green (G) light. The EL layer 313G has a light-emitting layer that emits green light.

[0561] The light-emitting element 330B has a pixel electrode 311B on the insulating layer 235, an EL layer 313B on the pixel electrode 311B, and a common electrode 315 on the EL layer 313B. The light-emitting element 330B shown in Fig. 39A emits blue (B) light. The EL layer 313B has a light-emitting layer that emits blue light.

[0562] 39A, the EL layers 313R, 313G, and 313B are all shown with the same thickness, but this is not limited to this. The thicknesses of the EL layers 313R, 313G, and 313B may be different. For example, it is preferable to set the thicknesses of the EL layers 313R, 313G, and 313B so that the optical path length increases the intensity of the light emitted by each layer. This allows for a microcavity structure to be realized, and the color purity of the light emitted from each light-emitting element to be increased.

[0563] The pixel electrode 311R is electrically connected to a transistor (not shown) included in a pixel circuit corresponding to the light-emitting element 330R through openings provided in the insulating layer 306, the insulating layer 395, and the insulating layer 235. The pixel electrode 311G is electrically connected to a transistor (not shown) included in a pixel circuit corresponding to the light-emitting element 330G. The pixel electrode 311B is electrically connected to a transistor (not shown) included in a pixel circuit corresponding to the light-emitting element 330B.

[0564] Ends of the pixel electrode 311R, the pixel electrode 311G, and the pixel electrode 311B are covered with an insulating layer 237. The insulating layer 237 functions as a partition wall. The insulating layer 237 can be formed into a single layer structure or a stacked layer structure using one or both of an inorganic insulating material and an organic insulating material. For example, the material that can be used for the insulating layer 395 and the material that can be used for the insulating layer 235 can be used for the insulating layer 237. The insulating layer 237 can electrically insulate the pixel electrode and the common electrode. Furthermore, the insulating layer 237 can electrically insulate adjacent light-emitting elements from each other.

[0565] The common electrode 315 is a continuous film provided in common to the light-emitting elements 330R, 330G, and 330B. The common electrode 315 shared by the plurality of light-emitting elements is electrically connected to a conductive layer formed of the same material and in the same process as the pixel electrodes 311R, 311G, and 311B in a region where no light-emitting element is provided.

[0566] In the display device of one embodiment of the present invention, a conductive film that transmits visible light is preferably used for the electrode from which light is extracted, and a conductive film that reflects visible light is preferably used for the electrode from which light is not extracted, out of the pixel electrode and the common electrode.

[0567] A conductive film that transmits visible light may also be used for the electrode on the side from which light is not extracted. In this case, it is preferable to place the electrode between the reflective layer and the EL layer. In other words, the light emitted from the EL layer may be reflected by the reflective layer and extracted from the display device.

[0568] Materials for forming the pair of electrodes of the light-emitting element can include metals, alloys, electrically conductive compounds, and mixtures thereof. Specific examples of such materials include metals such as aluminum, magnesium, titanium, chromium, manganese, iron, cobalt, nickel, copper, gallium, zinc, indium, tin, molybdenum, tantalum, tungsten, palladium, gold, platinum, silver, yttrium, and neodymium, as well as alloys containing these metals in combination. Examples of such materials include indium tin oxide (In-Sn oxide or ITO), In-Si-Sn oxide (ITSO), indium zinc oxide (In-Zn oxide), and In-W-Zn oxide. Examples of such materials include aluminum alloys, such as an alloy of aluminum, nickel, and lanthanum (Al-Ni-La), and silver alloys, such as an alloy of silver and magnesium and an alloy of silver, palladium, and copper (Ag-Pd-Cu or APC). Other examples of the material include elements belonging to Group 1 or 2 of the periodic table (e.g., lithium, cesium, calcium, and strontium) that are not exemplified above, rare earth metals such as europium and ytterbium, alloys containing appropriate combinations of these, and graphene.

[0569] The light-emitting element preferably has a micro-optical resonator (microcavity) structure. Therefore, one electrode of the light-emitting element is preferably an electrode that is transparent and reflective to visible light (semi-transmissive / semi-reflective electrode), and the other electrode is preferably an electrode that is reflective to visible light (reflective electrode). By having the light-emitting element have a microcavity structure, light emitted from the light-emitting layer can be resonated between both electrodes, thereby intensifying the light emitted from the light-emitting element.

[0570] The light transmittance of the transparent electrode is 40% or more. For example, it is preferable to use an electrode having a visible light (light with a wavelength of 400 nm or more and less than 750 nm) transmittance of 40% or more for the transparent electrode of the light-emitting element. The visible light reflectance of the semi-transmissive / semi-reflective electrode is 10% or more and 95% or less, preferably 30% or more and 80% or less. The visible light reflectance of the reflective electrode is 40% or more and less than 100%, preferably 70% or more and less than 100%. Furthermore, the resistivity of these electrodes is 1×10 −２ Preferably, it is Ωcm or less.

[0571] The EL layer 313R, the EL layer 313G, and the EL layer 313B are each provided in an island shape. In FIG. 39A , the ends of adjacent EL layers 313R and 313G overlap, and the ends of adjacent EL layers 313G and 313B overlap. Although not shown, the ends of adjacent EL layers 313R and 313B overlap. When forming island-shaped EL layers using a metal mask (or a fine metal mask), the ends of adjacent EL layers may overlap as shown in FIG. 39A , but this is not limited to this. That is, adjacent EL layers may not overlap but may be spaced apart. Furthermore, the display device may have both overlapping portions between adjacent EL layers and portions between adjacent EL layers that do not overlap but are spaced apart.

[0572] Each of the EL layers 313R, 313G, and 313B includes at least a light-emitting layer. The light-emitting layer includes one or more light-emitting substances. As the light-emitting substance, a substance that emits light of a color such as blue, purple, blue-purple, green, yellow-green, yellow, orange, or red can be used as appropriate. Furthermore, a substance that emits near-infrared light can also be used as the light-emitting substance.

[0573] The light-emitting material may include a fluorescent material, a phosphorescent material, a TADF material, and a quantum dot material.

[0574] The light-emitting layer may contain one or more organic compounds (such as a host material and an assist material) in addition to a light-emitting substance (guest material). As the one or more organic compounds, one or both of a substance with high hole-transporting properties (hole-transporting material) and a substance with high electron-transporting properties (electron-transporting material) may be used. Furthermore, as the one or more organic compounds, a bipolar substance (a substance with high electron-transporting properties and high hole-transporting properties) or a TADF material may be used.

[0575] The light-emitting layer preferably includes, for example, a phosphorescent material and a hole-transporting material and an electron-transporting material, which are a combination that easily forms an exciplex. This configuration allows efficient emission using Exciplex-Triple Energy Transfer (ExTET), which is energy transfer from the exciplex to the light-emitting material (phosphorescent material). By selecting a combination that forms an exciplex that emits light that overlaps with the wavelength of the lowest-energy absorption band of the light-emitting material, the energy transfer becomes smooth and light emission can be achieved efficiently. This configuration allows the light-emitting element to simultaneously achieve high efficiency, low-voltage operation, and a long life.

[0576] In addition to the light-emitting layer, the EL layer may include one or more of a layer containing a substance with high hole-injecting properties (hole-injecting layer), a layer containing a hole-transporting material (hole-transporting layer), a layer containing a substance with high electron-blocking properties (electron-blocking layer), a layer containing a substance with high electron-injecting properties (electron-injecting layer), a layer containing an electron-transporting material (electron-transporting layer), and a layer containing a substance with high hole-blocking properties (hole-blocking layer).In addition, the EL layer may include one or both of a bipolar substance and a TADF material.

[0577] The light-emitting element can be made of either a low-molecular-weight compound or a high-molecular-weight compound, and may contain an inorganic compound. Each of the layers constituting the light-emitting element can be formed by a method such as a vapor deposition method (including a vacuum vapor deposition method), a transfer method, a printing method, an inkjet method, or a coating method.

[0578] The light-emitting element may have a single structure (a structure having only one light-emitting unit) or a tandem structure (a structure having multiple light-emitting units). The light-emitting unit has at least one light-emitting layer. The tandem structure is a structure in which multiple light-emitting units are connected in series via a charge-generating layer. When a voltage is applied between a pair of electrodes, the charge-generating layer injects electrons into one of the two light-emitting units and holes into the other. The tandem structure allows the light-emitting element to emit light with high luminous intensity. Furthermore, the tandem structure can reduce the current required to achieve the same luminous intensity compared to a single structure, thereby improving reliability. The tandem structure can also be called a stacked structure.

[0579] In Figure 39A, when light-emitting elements with a tandem structure are used, it is preferable that the EL layer 313R has a structure having multiple light-emitting units that emit red light, the EL layer 313G has a structure having multiple light-emitting units that emit green light, and the EL layer 313B has a structure having multiple light-emitting units that emit blue light.

[0580] A protective layer 331 is provided on the light-emitting elements 330R, 330G, and 330B. The protective layer 331 and the substrate 352 are bonded via an adhesive layer 342. A light-shielding layer 317 is provided on the substrate 352. For example, a solid sealing structure or a hollow sealing structure can be applied to seal the light-emitting elements. In FIG. 39A , the space between the substrates 352 and 351 is filled with the adhesive layer 342, thereby applying a solid sealing structure. Alternatively, a hollow sealing structure may be applied in which the space is filled with an inert gas (such as nitrogen or argon). In this case, the adhesive layer 342 may be provided so as not to overlap the light-emitting elements. Alternatively, the space may be filled with a resin different from the frame-shaped adhesive layer 342.

[0581] By providing the protective layer 331 on the light-emitting elements 330R, 330G, and 330B, the reliability of the light-emitting elements can be improved.

[0582] The protective layer 331 may have a single layer structure or a stacked structure of two or more layers. The conductivity of the protective layer 331 does not matter. The protective layer 331 can be formed using at least one of an insulating film, a semiconductor film, and a conductive film.

[0583] The protective layer 331 has an inorganic film, which can prevent oxidation of the common electrode 315 and prevent impurities (such as moisture and oxygen) from entering the light-emitting element, thereby suppressing deterioration of the light-emitting element and improving the reliability of the display device.

[0584] An inorganic insulating film can be used for the protective layer 331. Examples of materials that can be used for the inorganic insulating film include oxides, nitrides, oxynitrides, and nitride oxides. Specific examples of these inorganic insulating films are as described above. In particular, the protective layer 331 preferably contains a nitride or a nitride oxide, and more preferably contains a nitride.

[0585] The protective layer 331 may be an inorganic film containing ITO, In—Zn oxide, Ga—Zn oxide, Al—Zn oxide, IGZO, or the like. The inorganic film preferably has high resistance, specifically, preferably has higher resistance than the common electrode 315. The inorganic film may further contain nitrogen.

[0586] When light emitted from the light-emitting element is extracted through the protective layer 331, it is preferable that the protective layer 331 has high transparency to visible light. For example, ITO, IGZO, and aluminum oxide are preferable because they are inorganic materials that have high transparency to visible light.

[0587] For example, a stacked structure of an aluminum oxide film and a silicon nitride film on the aluminum oxide film, or a stacked structure of an aluminum oxide film and an IGZO film on the aluminum oxide film can be used as the protective layer 331. By using such a stacked structure, impurities (such as water and oxygen) can be prevented from entering the EL layer side.

[0588] Furthermore, the protective layer 331 may have an organic film. For example, the protective layer 331 may have both an organic film and an inorganic film. Examples of organic films that can be used for the protective layer 331 include the organic insulating films that can be used for the insulating layer 235.

[0589] The display device 490A is a top-emission type. Light emitted from the light-emitting elements is emitted toward the substrate 352. The substrate 352 is preferably made of a material that is highly transparent to visible light. The pixel electrodes 311R, 311G, and 311B contain a material that reflects visible light, and the counter electrode (common electrode 315) contains a material that transmits visible light.

[0590] A light-shielding layer 317 is preferably provided on the surface of the substrate 352 facing the substrate 351. The light-shielding layer 317 can be provided between adjacent light-emitting elements.

[0591] A colored layer such as a color filter may be provided on the surface of the substrate 352 on the substrate 351 side or on the protective layer 331. When a color filter is provided over the light-emitting element, the color purity of light emitted from the pixel can be increased.

[0592] The colored layer is a colored layer that selectively transmits light in a specific wavelength range and absorbs light in other wavelength ranges. For example, a red (R) color filter that transmits light in the red wavelength range, a green (G) color filter that transmits light in the green wavelength range, and a blue (B) color filter that transmits light in the blue wavelength range can be used. Each colored layer can be made of one or more of a metal material, a resin material, a pigment, and a dye. The colored layers are formed at desired positions by a printing method, an inkjet method, an etching method using photolithography, or the like.

[0593] Various optical members can be arranged on the outside of the substrate 352 (the surface opposite to the substrate 351). Examples of optical members include a polarizing plate, a retardation plate, a light diffusion layer (such as a diffusion film), an anti-reflection layer, and a light-collecting film. In addition, a surface protection layer such as an anti-static film that suppresses the adhesion of dust, a water-repellent film that makes it difficult for dirt to adhere, a hard coat film that suppresses the occurrence of scratches during use, and an impact absorbing layer may be arranged on the outside of the substrate 352. For example, a glass layer or a silica layer (SiO ｘ The surface protection layer can be preferably formed of a material such as DLC (diamond-like carbon), aluminum oxide (AlO ｘ ), polyester-based materials, or polycarbonate-based materials may also be used. Note that it is preferable to use a material with high transmittance to visible light for the surface protection layer. It is also preferable to use a material with high hardness for the surface protection layer.

[0594] The substrate 351 and the substrate 352 can be made of glass, quartz, ceramics, sapphire, resin, metal, alloy, semiconductor, or the like. A material that transmits light is used for the substrate on the side from which light from the light-emitting element is extracted. Using a flexible material for the substrate 351 and the substrate 352 increases the flexibility of the display device, making it possible to realize a flexible display (for example, a bendable display, a foldable display, a rollable display, a slidable display, or a stretchable display). Furthermore, a polarizing plate may be used for at least one of the substrates 351 and 352.

[0595] The substrates 351 and 352 may each be made of polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), polyacrylonitrile resin, acrylic resin, polyimide resin, polymethyl methacrylate resin, polycarbonate (PC) resin, polyethersulfone (PES) resin, polyamide resin (nylon, aramid, etc.), polysiloxane resin, cycloolefin resin, polystyrene resin, polyamideimide resin, polyurethane resin, polyvinyl chloride resin, polyvinylidene chloride resin, polypropylene resin, polytetrafluoroethylene (PTFE) resin, ABS resin, cellulose nanofiber, etc. At least one of the substrates 351 and 352 may be made of glass having a thickness sufficient to provide flexibility.

[0596] When a circularly polarizing plate is superimposed on a display device, it is preferable that the display device has a substrate with high optical isotropy. A substrate with high optical isotropy has low birefringence (it can also be said that the amount of birefringence is small). Examples of films with high optical isotropy include triacetyl cellulose (TAC, also called cellulose triacetate) films, cycloolefin polymer (COP) films, cycloolefin copolymer (COC) films, and acrylic films.

[0597] The adhesive layer 342 can be made of various curable adhesives, such as photo-curable adhesives (e.g., ultraviolet curable), reactive curable adhesives, thermosetting adhesives, and anaerobic adhesives. Examples of such adhesives include epoxy resin, acrylic resin, silicone resin, phenolic resin, polyimide resin, imide resin, PVC (polyvinyl chloride) resin, PVB (polyvinyl butyral) resin, and EVA (ethylene vinyl acetate) resin. Materials with low moisture permeability, such as epoxy resin, are particularly preferred. Two-component resins may also be used. Adhesive sheets may also be used.

[0598] In one embodiment of the present invention, a light-emitting element can be fabricated by a vacuum process such as a vapor deposition method, or a solution process such as a spin coating method or an inkjet method. Examples of vapor deposition methods include physical vapor deposition (PVD) methods such as sputtering, ion plating, ion beam deposition, molecular beam deposition, and vacuum deposition, and chemical vapor deposition (CVD). In particular, functional layers included in the EL layer (e.g., hole injection layer, hole transport layer, hole blocking layer, light-emitting layer, electron blocking layer, electron transport layer, electron injection layer, charge generation layer, etc.) can be formed by a vapor deposition method (e.g., vacuum deposition), a coating method (e.g., dip coating, die coating, bar coating, spin coating, spray coating), a printing method (e.g., inkjet printing, screen printing (stencil printing), offset printing (lithographic printing), flexography (relief printing), gravure printing, or microcontact printing).

[0599] [Configuration Example 2] A display device 490B shown in Figure 39B includes a light-emitting element 330R, a light-emitting element 330G, a light-emitting element 330B, a colored layer 332R that transmits red light, a colored layer 332G that transmits green light, and a colored layer 332B that transmits blue light. The display device 490B differs from the display device 490A mainly in that a light-emitting element having a common EL layer 313 and a colored layer (such as a color filter) are used for each sub-pixel of each color. Note that descriptions of parts that are the same as those of the display devices described above may be omitted.

[0600] The light emitting element 330R has a pixel electrode 311R, an EL layer 313 on the pixel electrode 311R, and a common electrode 315 on the EL layer 313. The light emitted from the light emitting element 330R is extracted as red light to the outside of the display device 490B via the colored layer 332R.

[0601] The light emitting element 330G has a pixel electrode 311G, an EL layer 313 on the pixel electrode 311G, and a common electrode 315 on the EL layer 313. Light emitted from the light emitting element 330G is extracted as green light to the outside of the display device 490B via a colored layer 332G.

[0602] The lig...

Claims

A first transistor, a second transistor, and a third transistor, the first transistor has a first gate, a second gate facing the first gate across a channel formation region of the first transistor, a first source, and a first drain; the second transistor has a third gate, a second source, and a second drain; the third transistor has a fourth gate, a third source, and a third drain; one of the first source or the first drain is electrically connected to one of the second source or the second drain; the other of the first source or the first drain is electrically connected to one of the third source or the third drain; the first gate is electrically connected to the third gate; the second gate is electrically connected to the other of the first source or the first drain; Semiconductor device. 　 In claim 1, the second transistor has a fifth gate facing the third gate across a channel formation region of the second transistor; the fifth gate is electrically connected to the third gate; Semiconductor device. 　 In claim 1 or 2, a first potential is applied to the other of the second source or the second drain; a second potential higher than the first potential is applied to the other of the third source or the third drain; a first pulse signal is applied to the first gate and the third gate; A second pulse signal having a timing different from that of the first pulse signal is applied to the fourth gate. Semiconductor device. 　 In claim 1 or 2, a thickness of a gate insulating film of the second gate is thicker than a thickness of a gate insulating film of the first gate; Semiconductor device. 　 In claim 1 or 2, a channel length of each of the first transistor and the second transistor is shorter than a channel length of the third transistor; Semiconductor device. 　 In claim 1 or 2, a channel formation region of the first transistor includes an oxide semiconductor; Semiconductor device. 　 A first transistor, a second transistor, and a third transistor, the first transistor has a first gate, a second gate facing the first gate across a channel formation region of the first transistor, a first source, and a first drain; the second transistor has a third gate, a second source, and a second drain; the third transistor has a fourth gate, a third source, and a third drain; one of the first source or the first drain is electrically connected to one of the second source or the second drain; the other of the second source or the second drain is electrically connected to one of the third source or the third drain; the first gate is electrically connected to the third gate; the second gate is electrically connected to the other of the first source or the first drain; Semiconductor device. 　 In claim 7, the second transistor has a fifth gate facing the third gate across a channel formation region of the second transistor; the fifth gate is electrically connected to the third gate; Semiconductor device. 　 In claim 7 or claim 8, a first potential is applied to the other of the third source or the third drain; a second potential higher than the first potential is applied to the other of the first source or the first drain; a first pulse signal is applied to the first gate and the third gate; A second pulse signal having a timing different from that of the first pulse signal is applied to the fourth gate. Semiconductor device. 　 In claim 7 or claim 8, a thickness of a gate insulating film of the second gate is thicker than a thickness of a gate insulating film of the first gate; Semiconductor device. 　 In claim 7 or claim 8, a channel length of each of the first transistor and the second transistor is shorter than a channel length of the third transistor; Semiconductor device. 　 In claim 7 or claim 8, a channel formation region of the first transistor includes an oxide semiconductor; Semiconductor device.

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