Indication device

Abstract

To provide a display device with high luminance.SOLUTION: A pixel includes a light-emitting device, a first transistor, a second transistor, a third transistor, a fourth transistor, a first capacitor element, and a second capacitor element. One electrode of the light-emitting device is electrically connected to one of the source and the drain of the first transistor. The gate of the first transistor is electrically connected to one electrode of the first capacitor element and one of the source and the drain of the second transistor. The other of the source and the drain of the first transistor is electrically connected to one electrode of the second capacitor element. The one electrode of the second capacitor element is electrically connected to a first wire with a function of supplying a first potential. The other electrode of the second capacitor element is electrically connected to the other electrode of the first capacitor element, one of the source and the drain of the third transistor, and one of the source and the drain of the fourth transistor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the present invention relates to a display device.

[0002] Note that one embodiment of the present invention is not limited to the above technical field. 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, memory devices, electronic devices, lighting devices, input devices, input / output devices, driving methods thereof, and manufacturing methods thereof. A semiconductor device refers to any device that can function by utilizing semiconductor characteristics. [Background technology]

[0003] As a semiconductor material applicable to transistors, oxide semiconductors using metal oxides have attracted attention. For example, Patent Document 1 discloses a semiconductor device in which a plurality of oxide semiconductor layers are stacked, and an oxide semiconductor layer serving as a channel contains indium and gallium, and the proportion of indium is made higher than the proportion of gallium, thereby increasing the field-effect mobility (sometimes simply referred to as mobility, μFE, or μ).

[0004] Metal oxides that can be used for semiconductor layers can be formed by sputtering or the like, and therefore can be used for transistors that constitute large display devices. Furthermore, since it is possible to use a part of the production equipment for transistors that use polycrystalline silicon or amorphous silicon by modifying it, capital investment can be reduced. Furthermore, transistors that use metal oxides have higher field-effect mobility than transistors that use amorphous silicon, and therefore, high-performance display devices equipped with driver circuits can be realized.

[0005] Incidentally, wearable display devices and stationary display devices are becoming popular as display devices for Augmented Reality (AR) or Virtual Reality (VR). Examples of wearable display devices include head-mounted displays (HMDs) and eyeglass-type display devices. Examples of stationary display devices include head-up displays (HUDs).

[0006] In electronic devices having an imaging device such as a digital camera, a viewfinder is used to check an image to be captured before capturing the image. Furthermore, an electronic viewfinder is used as the viewfinder. The electronic viewfinder is provided with a display unit, and an image obtained by an imaging device can be displayed on the display unit. For example, Patent Document 2 discloses an electronic viewfinder that can provide good visibility from the center to the periphery of the image. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-7399 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-42569 Summary of the Invention [Problem to be solved by the invention]

[0008] In display devices such as HMDs, where the display unit is close to the user, the user can easily see the pixels, resulting in a strong sense of graininess, which can diminish the immersive and realistic feel of AR or VR. For this reason, HMDs are desired to have high-resolution display devices with fine pixels that prevent the user from seeing the pixels. The pixel density of the display device is preferably, for example, 1000 ppi or higher, more preferably 5000 ppi or higher, and even more preferably 7000 ppi or higher. Furthermore, in AR applications, since images of a virtual space are superimposed on real space, a display device with high brightness is desired, especially when the usage environment is bright.

[0009] In view of the above, an object of one embodiment of the present invention is to provide a display device with high definition. Another object of one embodiment of the present invention is to provide a display device with high luminance. Another object of one embodiment of the present invention is to provide a display device with low power consumption. Another object of one embodiment of the present invention is to provide a display device with a narrow frame. Another object of one embodiment of the present invention is to provide a small-sized display device. Another object of one embodiment of the present invention is to provide a novel display device.

[0010] Note that the description of these problems does not preclude the existence of other problems. Note that one embodiment of the present invention does not necessarily solve all of these problems. Note that problems other than these can be extracted from the description of the specification, drawings, claims, etc. [Means for solving the problem]

[0011] One embodiment of the present invention is a display device including a pixel portion having a plurality of pixels, a first wiring, a second wiring, a third wiring, and a fourth wiring. The pixel includes a light-emitting device, a first transistor, a second transistor, a third transistor, a fourth transistor, a first capacitor, and a second capacitor. One electrode of the light-emitting device is electrically connected to one of a source or a drain of the first transistor. A gate of the first transistor is electrically connected to one electrode of the first capacitor and one of a source or a drain of the second transistor. The other of the source or the drain of the first transistor is electrically connected to one electrode of the second capacitor. One electrode of the second capacitor is electrically connected to a first wiring that supplies a first potential. The other electrode of the second capacitor is electrically connected to the other electrode of the first capacitor, one of a source or a drain of the third transistor, and one of a source or a drain of the fourth transistor. The gate of the second transistor and the gate of the fourth transistor are electrically connected to a second wiring, the gate of the third transistor is electrically connected to a third wiring, and the other of the source or the drain of the second transistor and the other of the source or the drain of the third transistor are electrically connected to a fourth wiring.

[0012] In the above-described display device, the first transistor preferably has a back gate, and the back gate is preferably electrically connected to one of a source and a drain of the first transistor.

[0013] In the above-described display device, the first transistor preferably has a back gate, and the back gate is preferably electrically connected to the gate of the first transistor.

[0014] The above-described display device preferably further includes a fifth transistor, and one of the source and the drain of the fifth transistor is electrically connected to one electrode of the light-emitting device.

[0015] In the display device described above, the other electrode of the light-emitting device is preferably electrically connected to a fifth wiring having a function of supplying a second potential, and the second potential is preferably lower than the first potential.

[0016] In the above display device, the light emitting device is preferably an organic light emitting diode.

[0017] The display device preferably includes a first driver circuit portion that overlaps with the pixel portion and is preferably electrically connected to a fourth wiring.

[0018] The display device preferably includes a first layer and a second layer on the first layer. The first layer preferably includes a first driver circuit unit and a second driver circuit unit. The second layer preferably includes a pixel unit. The second driver circuit unit is preferably electrically connected to the second wiring and the third wiring.

[0019] In the display device, the first, second, third, and fourth transistors each preferably have a metal oxide in a channel formation region, and the metal oxide preferably contains indium, zinc, and an element M (one or more of aluminum, titanium, gallium, germanium, yttrium, zirconium, lanthanum, cerium, tin, neodymium, and hafnium).

[0020] One embodiment of the present invention is an electronic device including the above-described display device and a camera. [Effects of the Invention]

[0021] According to one embodiment of the present invention, a display device with high definition can be provided. Alternatively, according to one embodiment of the present invention, a display device with high luminance can be provided. Alternatively, according to one embodiment of the present invention, a display device with low power consumption can be provided. Alternatively, according to one embodiment of the present invention, a display device with a narrow frame can be provided. Alternatively, according to one embodiment of the present invention, a small-sized display device can be provided. Alternatively, according to one embodiment of the present invention, a novel display device can be provided.

[0022] Note that the description of these effects does not preclude the existence of other effects. Note that one embodiment of the present invention does not necessarily have all of these effects. Note that effects other than these can be extracted from the description in the specification, drawings, claims, etc. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a circuit diagram showing an example of the configuration of a pixel. [Figure 2] FIG. 2 is a timing chart illustrating the operation of the pixel circuit. [Figure 3] 3A and 3B are circuit diagrams showing examples of pixel configurations. [Figure 4] FIG. 4 is a circuit diagram showing an example of the configuration of a pixel. [Figure 5] FIG. 5 is a circuit diagram showing an example of the configuration of a pixel. [Figure 6] FIG. 6 is a circuit diagram showing an example of the configuration of a pixel. [Figure 7] FIG. 7 is a timing chart illustrating the operation of the pixel circuit. [Figure 8] 8A and 8B are diagrams showing examples of pixel layouts. [Figure 9] FIG. 9 is a diagram showing an example of a pixel layout. [Figure 10] FIG. 10 is a schematic diagram showing an example of the configuration of a pixel. [Figure 11] 11A and 11B are schematic diagrams showing examples of pixel configurations. [Figure 12] FIG. 12 is a block diagram showing an example of the configuration of a display device. [Figure 13] 13A and 13B are schematic and block diagrams showing an example of the configuration of a display device. [Figure 14] 14A and 14B are schematic and block diagrams showing an example of the configuration of a display device. [Figure 15] FIG. 15 is a cross-sectional view showing an example of the configuration of a display device. [Figure 16] FIG. 16 is a cross-sectional view showing an example of the configuration of a display device. [Figure 17] FIG. 17 is a cross-sectional view showing an example of the configuration of a display device. [Figure 18] FIG. 18 is a cross-sectional view showing an example of the configuration of a display device. [Figure 19] FIG. 19 is a cross-sectional view showing an example of the configuration of a display device. [Figure 20] 20A, 20B, 20C, 20D, and 20E are diagrams showing configuration examples of light-emitting devices. [Figure 21] 21A is a top view illustrating an example of the structure of a transistor, and FIGS. 21B and 21C are cross-sectional views illustrating an example of the structure of a transistor. [Figure 22] 22A is a top view illustrating an example of the structure of a transistor, and FIGS. 22B and 22C are cross-sectional views illustrating an example of the structure of a transistor. [Figure 23] 23A is a top view illustrating an example of the structure of a transistor, and FIGS. 23B and 23C are cross-sectional views illustrating an example of the structure of a transistor. [Figure 24] Fig. 24A is a diagram explaining the classification of IGZO crystal structures, Fig. 24B is a diagram explaining the XRD spectrum of a CAAC-IGZO film, and Fig. 24C is a diagram explaining the electron microbeam diffraction pattern of a CAAC-IGZO film. [Figure 25] 25A, 25B, 25C, 25D, and 25E are perspective views showing examples of electronic devices. [Figure 26] 26A, 26B, 26C, 26D, 26E, 26F, and 26G are perspective views showing examples of electronic devices. [Figure 27]FIG. 27 is a diagram illustrating the simulation results. [Figure 28] FIG. 28 is a diagram illustrating the simulation results. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments will be described with reference to the drawings. However, it will be readily understood by those skilled in the art that the embodiments can be implemented in many different ways and that various changes in form and details can be made without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the following description of the embodiments.

[0025] In each figure described in this specification, the size of each component, the thickness of a layer, or the area may be exaggerated for clarity.

[0026] The ordinal numbers "first," "second," and "third" used in this specification are used to avoid confusion of components and are not intended to limit the number.

[0027] In this specification, terms indicating arrangement such as "above" and "below" are used for convenience in describing the positional relationship between components with reference to the drawings. Furthermore, the positional relationship between components changes as appropriate depending on the direction in which each component is depicted. Therefore, the terms are not limited to those described in the specification, and can be rephrased appropriately depending on the situation.

[0028] In this specification and the like, the functions of the source and drain of a transistor may be interchanged when the polarity of the transistor or the direction of current flow during circuit operation changes, etc. Therefore, the terms source and drain can be used interchangeably.

[0029] In this specification, terms such as "electrode," "wiring," and "terminal" do not limit the functionality of these components. For example, an "electrode" may be used as part of a "wiring," and vice versa. Furthermore, the terms "electrode" and "wiring" include cases where multiple "electrodes" or "wirings" are integrally formed. Furthermore, for example, a "terminal" may be used as part of a "wiring" or "electrode," and vice versa. Furthermore, the term "terminal" includes cases where multiple "electrodes," "wirings," "terminals," etc. are integrally formed. Therefore, for example, an "electrode" can be part of a "wiring" or "terminal," and a "terminal" can be part of a "wiring" or "electrode." Furthermore, terms such as "electrode," "wiring," and "terminal" may be replaced with terms such as "region" depending on the circumstances.

[0030] In this specification, the term "resistor" may refer to a resistor whose resistance is determined by the length of the wiring. Alternatively, the resistor may be formed by connecting a conductor having a different resistance from the conductor used in the wiring via a contact. Alternatively, the resistance may be determined by doping impurities into a semiconductor.

[0031] In this specification, "electrically connected" includes both direct connection and connection via "something that has some kind of electrical effect." Here, "something that has some kind of electrical effect" is not particularly limited as long as it allows for the exchange of electrical signals between the connected objects. Therefore, even when the expression "electrically connected" is used, in an actual circuit, there may be no physical connection and only an extending wiring. Furthermore, even when the expression "directly connected" is used, it includes cases where wiring is formed between different conductors via contacts. Note that the wiring may be formed between different conductors that contain one or more of the same elements or different elements.

[0032] In this specification and the like, the terms "film" and "layer" are interchangeable. For example, the terms "conductive layer" and "insulating layer" may be interchangeable with the terms "conductive film" and "insulating film."

[0033] In this specification, unless otherwise specified, the off-state current refers to the drain current when a transistor is in an off state (also called a non-conducting state or a cut-off state). Unless otherwise specified, the off-state current refers to the drain current when a transistor is in an off state (also called a non-conducting state or a cut-off state) when a voltage V between the gate and source of an n-channel transistor is applied. gs is the threshold voltage V th (For p-channel transistors, V th This refers to a state of being (higher than)

[0034] In the drawings, sizes, layer thicknesses, or regions may be exaggerated for clarity. Therefore, they are not necessarily limited to the scale. The drawings are schematic and are not limited to the shapes or values ​​shown in the drawings. For example, in actual manufacturing processes, layers, resist masks, etc. may unintentionally lose volume due to etching or other processes. However, this may not be reflected in the drawings to facilitate understanding. In addition, in the drawings, the same symbols are used for identical parts or parts with similar functions, materials, etc., across different drawings, and repeated explanations may be omitted. When referring to similar functions, materials, etc., the same hatch pattern may be used, and no particular symbols may be used.

[0035] In this specification and the like, the term "metal oxide" refers to an oxide of a metal in a broad sense. Metal oxides are classified into oxide insulators, oxide conductors (including transparent oxide conductors), oxide semiconductors (also referred to as "oxide semiconductors" or simply as "OSs"). For example, when a metal oxide is used in the active layer of a transistor, the metal oxide may be referred to as an oxide semiconductor. In other words, an OS transistor can be rephrased as a transistor including an oxide or an oxide semiconductor.

[0036] (Embodiment 1) In this embodiment, a display device which is one embodiment of the present invention will be described.

[0037] One embodiment of the present invention is a display device having pixels. The pixels have a function of generating a voltage higher than a voltage corresponding to image data supplied from a source driver. Each pixel is provided with a storage node, and first data can be stored in the storage node. Second data is further supplied to each pixel, and the first data is added to the second data by capacitive coupling. Then, data obtained by adding the first data to the second data can be supplied to a light-emitting device. Alternatively, the first data can be added by capacitive coupling after the second data is written to the storage node.

[0038] The same image data can be used as the first data and the second data. In this case, the pixels of the display device generate a voltage higher than the voltage corresponding to the image data supplied from the source driver and supply the voltage to the drive transistor that controls the amount of current flowing through the light-emitting device. This allows the current flowing through the light-emitting device to be increased, resulting in a display device with high brightness.

[0039] For example, a display device according to one embodiment of the present invention can be suitably used as a display device for AR, which requires high luminance. Furthermore, the output voltage of a source driver can be reduced, resulting in a display device with low power consumption. Furthermore, a high-voltage output driver can be eliminated, and a general-purpose driver IC or the like can be used. Alternatively, a light-emitting device that is difficult to operate even with a high-voltage output driver can be operated.

[0040] In this specification and the like, generating a voltage higher than the supplied voltage may be referred to as boosting.

[0041] A display device according to one embodiment of the present invention can use, for example, image data as first data and correction data as second data. In this case, the display device can display a corrected image. The correction can upconvert the image. Alternatively, a part or the entire image in the display area can be corrected to display a high dynamic range (HDR) image.

[0042] A display device according to one embodiment of the present invention can display arbitrary images in a superimposed manner by using different image data as the first data and the second data, for example.

[0043] A display device according to one embodiment of the present invention includes a pixel portion having a plurality of pixels and a region where a source driver overlaps. By including a region where the pixel portion and the source driver overlap, the area of ​​a frame, which is a region where no pixels are provided, can be reduced. Therefore, a display device with a narrow frame can be obtained. Furthermore, by narrowing the frame of the display device, a small display device can be obtained.

[0044] In this specification, a pixel refers to, for example, one element whose brightness can be controlled. Therefore, as an example, one pixel refers to one color element, and the brightness is expressed by that one color element. Therefore, in the case of a color display device consisting of R (red), G (green), and B (blue) color elements, the minimum unit of an image is composed of three pixels: an R pixel, a G pixel, and a B pixel. In this case, each of the RGB pixels is called a sub-pixel, and the RGB sub-pixels are sometimes collectively called a pixel.

[0045] <Pixel configuration example 1> 1 shows a structural example of a pixel 10 that can be used in a display device of one embodiment of the present invention. The pixel 10 includes a light-emitting device 114, a transistor 101, a transistor 102, a transistor 103, a transistor 104, a capacitor 111, and a capacitor 112.

[0046] One electrode of the light-emitting device 114 is electrically connected to one of the source and drain of the transistor 101. The gate of the transistor 101 is electrically connected to one of the source and drain of the transistor 102. The other of the source and drain of the transistor 101 is electrically connected to one electrode of the capacitor 112. The other electrode of the capacitor 112 is electrically connected to the other electrode of the capacitor 111. The other electrode of the capacitor 112 is electrically connected to one of the source and drain of the transistor 103. The other electrode of the capacitor 112 is electrically connected to one of the source and drain of the transistor 104.

[0047] In the pixel 10 shown in FIG. 1, a capacitor 111 and a capacitor 112 are connected in series, and the gate of the transistor 101 functioning as a driving transistor is electrically connected to the other of the source and the drain via these capacitors.

[0048] Examples of the light-emitting device 114 include self-luminous light-emitting devices such as light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), quantum-dot light-emitting diodes (QLEDs) that use quantum dots in the light-emitting layer, and semiconductor lasers. Also usable are shutter-type or optical interference-type MEMS (Micro Electro Mechanical Systems) elements, and elements that employ a microcapsule system, electrophoresis system, electrowetting system, or electronic liquid powder (registered trademark) system.

[0049] Here, a wiring to which the gate of the transistor 101, one of the source or drain of the transistor 102, and one electrode of the capacitor 111 are connected is referred to as a node ND1. The current flowing through the light-emitting device 114 can be controlled by the potential of the node ND1, thereby controlling the light emission luminance of the light-emitting device 114. A wiring to which one of the source or drain of the transistor 103, one of the source or drain of the transistor 104, the other electrode of the capacitor 111, and the other electrode of the capacitor 112 are connected is referred to as a node ND2.

[0050] The transistor 101 functions as a drive transistor that controls the amount of current flowing through the light-emitting device 114. The transistors 102 and 103 function as selection transistors that select a pixel. The transistor 104 functions as a switch that writes a specific potential (reference potential) "Vref" that drives the pixel 10 to the pixel.

[0051] A gate of the transistor 102 is electrically connected to a wiring 121. A gate of the transistor 104 is electrically connected to a wiring 121. A gate of the transistor 103 is electrically connected to a wiring 122. The other of the source and the drain of the transistor 102 is electrically connected to a wiring 131. The other of the source and the drain of the transistor 103 is electrically connected to the wiring 131.

[0052] One electrode of the capacitor 112 is electrically connected to a wiring 128. The wiring 128 preferably has a function of supplying a specific potential. By electrically connecting one electrode of the capacitor 112 to the wiring 128, the potential of the one electrode of the capacitor 112 can be fixed to a specific potential supplied from the wiring 128, and a boost operation can be performed stably. The other electrode of the light-emitting device 114 is electrically connected to a wiring 129. The wiring 128 and the wiring 129 can each function as a wiring to which a power supply potential is applied (power supply line). For example, the wiring 128 can function as a high-potential power supply line that supplies a higher potential than the wiring 129. The wiring 129 can also function as a low-potential power supply line that supplies a lower potential than the wiring 128.

[0053] The wirings 121 and 122 function as scan lines for controlling the operations of the transistors 102, 103, and 104. Scan signals applied to the scan lines are signals for controlling the conductive or non-conductive state (on or off) of selection transistors (transistors 102, 103, and 104) that function as switches in the pixel 10. The wiring 131 functions as a data line for supplying first data and second data. The wiring 127 functions to supply a specific potential (reference potential) "Vref" for driving the pixel 10.

[0054] The node ND1 is a storage node, and when the transistor 102 is turned on, the first data supplied to the wiring 131 can be written to the node ND1. When the transistor 102 is turned off, the first data written to the node ND1 can be held.

[0055] The node ND2 is a storage node, and the second data supplied to the wiring 131 can be written to the node ND2 by turning on the transistor 103. The second data supplied to the wiring 127 can be written to the node ND2 by turning on the transistor 104. The second data written to the node ND2 can be held by turning off the transistors 103 and 104.

[0056] It is preferable to use a transistor with extremely low off-state current for at least one of the transistors 101, 102, 103, and 104. In particular, by using transistors with extremely low off-state current for the transistors 102, 103, and 104, the potentials of the nodes ND1 and ND2 can be held for a long time. For example, a transistor using a metal oxide in a channel formation region (hereinafter referred to as an OS transistor) can be preferably used as such a transistor.

[0057] It is more preferable to use OS transistors for all of the transistors 101, 102, 103, and 104. Alternatively, OS transistors may be used for transistors (not shown) other than the transistors 101, 102, 103, and 104. When the transistors operate within an allowable leakage current range, a transistor having silicon in a channel formation region (hereinafter, referred to as a Si transistor) may be used. Alternatively, an OS transistor and a Si transistor may be used in combination. Examples of the Si transistor include a transistor having amorphous silicon and a transistor having crystalline silicon (microcrystalline silicon, low-temperature polysilicon, or single-crystal silicon). Although the transistors shown in FIG. 1 are all n-channel transistors, p-channel transistors may also be used.

[0058] A metal oxide having an energy gap of 2 eV or more, preferably 2.2 eV or more, and more preferably 2.5 eV or more can be used as a semiconductor material for an OS transistor. A typical example is an oxide semiconductor containing indium, such as a C-Axis Aligned Crystalline Oxide Semiconductor (CAAC-OS) or a Cloud-Aligned Composite Oxide Semiconductor (CAC-OS), which will be described later. CAAC-OS has a stable crystal structure and is suitable for transistors requiring high reliability. Furthermore, CAC-OS exhibits high mobility and is therefore suitable for transistors operating at high speed.

[0059] Because the energy gap of the semiconductor layer of an OS transistor is large, the off-state current per 1 μm of channel width is several yA / μm (y is 10 -24 ) can exhibit extremely small off-state current. Furthermore, OS transistors have characteristics different from Si transistors, such as the absence of impact ionization, avalanche breakdown, and short-channel effects, making them suitable for the formation of highly reliable circuits. Furthermore, OS transistors are less susceptible to variations in electrical characteristics due to non-uniformity in crystallinity, which is a problem with Si transistors.

[0060] The semiconductor layer of the OS transistor can be, for example, a film represented by an In-M-Zn oxide containing indium, zinc, and the element M (M is one or more of aluminum, titanium, gallium, germanium, yttrium, zirconium, lanthanum, cerium, tin, neodymium, and hafnium).

[0061] When the oxide semiconductor constituting the semiconductor layer is an In-M-Zn-based oxide, the atomic ratio of the metal elements in a sputtering target used to deposit the In-M-Zn oxide preferably satisfies In≧M and Zn≧M. Preferred atomic ratios of the metal elements in such sputtering targets are In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, 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:M:Zn=10:1:3, In:M:Zn=10:1:6, In:M:Zn=10:1:8, and the like. The atomic ratio of the semiconductor layer to be formed varies within ±40% of the atomic ratio of the metal elements contained in the sputtering target.

[0062] The semiconductor layer is made of an oxide semiconductor with a low carrier concentration. For example, the semiconductor layer has a carrier concentration of 1×10 17 / cm 3 Less than 1 × 10 15 / cm 3 or less, more preferably 1 × 10 13 / cm 3 Less than 1×10, more preferably 11 / cm 3 or less, more preferably 1 × 10 10 / cm 3 Less than 1 x 10 -9 / cm 3 An oxide semiconductor having a carrier concentration above this level can be used. Such an oxide semiconductor is called a high-purity intrinsic or substantially high-purity intrinsic oxide semiconductor. The oxide semiconductor has a low density of defect states and stable characteristics.

[0063] Note that the present invention is not limited to these, and an appropriate composition may be used depending on the required semiconductor characteristics and electrical characteristics (field-effect mobility, threshold voltage, etc.) of the transistor. In order to obtain the required semiconductor characteristics of the transistor, it is preferable to appropriately set the carrier concentration, impurity concentration, defect density, atomic ratio of metal element to oxygen, interatomic distance, density, and the like of the semiconductor layer.

[0064] If silicon or carbon, which is one of the group 14 elements, is contained in the oxide semiconductor that constitutes the semiconductor layer, oxygen vacancies increase, resulting in n-type conductivity. For this reason, the concentration of silicon or carbon in the semiconductor layer (concentration obtained by secondary ion mass spectrometry) is set to 2×10 18 atoms / cm 3 Less than or equal to 2 x 10 17 atoms / cm 3 The following applies.

[0065] Alkali metals and alkaline earth metals may generate carriers when they bond with components contained in an oxide semiconductor, which may increase the off-state current of a transistor. Therefore, the concentration of alkali metals or alkaline earth metals in the semiconductor layer (concentration obtained by secondary ion mass spectrometry) is set to 1×10 18 atoms / cm 3 Less than or equal to 2 x 10 16 atoms / cm 3 Do the following:

[0066] When nitrogen is contained in the oxide semiconductor that constitutes the semiconductor layer, electrons that become carriers are generated in the oxide semiconductor, increasing the carrier concentration and making it more likely to become n-type. As a result, transistors using oxide semiconductors that contain nitrogen tend to have normally-on characteristics. For this reason, the nitrogen concentration in the semiconductor layer (concentration obtained by secondary ion mass spectrometry) is 5×10 18 atoms / cm 3 It is preferable to do the following:

[0067] When hydrogen is contained in an oxide semiconductor constituting a semiconductor layer, it reacts with oxygen bonded to metal atoms in the oxide semiconductor to form water, which may form oxygen vacancies in the oxide semiconductor. When oxygen vacancies are present in the channel formation region of an oxide semiconductor, the transistor may exhibit normally-on characteristics. Furthermore, defects in which hydrogen enters the oxygen vacancies may function as donors and generate electrons, which serve as carriers. Furthermore, some of the hydrogen may bond with oxygen bonded to metal atoms to generate electrons, which serve as carriers. Therefore, a transistor using an oxide semiconductor containing a large amount of hydrogen is likely to exhibit normally-on characteristics.

[0068] A defect in which hydrogen is introduced into an oxygen vacancy can function as a donor in an oxide semiconductor. However, it is difficult to quantitatively evaluate such defects. Therefore, oxide semiconductors are sometimes evaluated using carrier concentration instead of donor concentration. Therefore, in this specification and the like, a carrier concentration assuming a state in which no electric field is applied may be used as a parameter of an oxide semiconductor instead of donor concentration. In other words, the "carrier concentration" described in this specification and the like may be rephrased as "donor concentration."

[0069] Therefore, it is preferable that the hydrogen concentration in the oxide semiconductor be reduced as much as possible. Specifically, the hydrogen concentration in the oxide semiconductor measured by secondary ion mass spectrometry (SIMS) is 1×10 20 atoms / cm 3 Less than 1 x 10 19 atoms / cm 3 less than 5 × 10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 When an oxide semiconductor in which impurities such as hydrogen are sufficiently reduced is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0070] Oxide semiconductors (metal oxides) are classified into single-crystal oxide semiconductors and other non-single-crystal oxide semiconductors. Examples of non-single-crystal oxide semiconductors include CAAC-OS, polycrystalline oxide semiconductors, nanocrystalline oxide semiconductors (nc-OS), amorphous-like oxide semiconductors (a-like OS), and amorphous oxide semiconductors. Among non-single-crystal structures, the amorphous structure has the highest density of defect states, and the CAAC-OS has the lowest density of defect states.

[0071] An amorphous oxide semiconductor film has, for example, a disordered atomic arrangement and does not contain any crystalline components, or has, for example, a completely amorphous structure and does not contain any crystalline parts.

[0072] The semiconductor layer may be a mixed film having two or more of an amorphous structure region, a microcrystalline structure region, a polycrystalline structure region, a CAAC-OS region, and a single-crystal structure region. The mixed film may have a single layer structure or a multilayer structure including two or more of the above-mentioned regions.

[0073] The structure of a CAC-OS, which is one mode of a non-single-crystal semiconductor layer, will be described below.

[0074] CAC-OS is a material in which, for example, elements constituting an oxide semiconductor are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 2 nm, or in the vicinity thereof. Note that hereinafter, a state in which one or more metal elements are unevenly distributed in an oxide semiconductor and regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 2 nm, or in the vicinity thereof, is also referred to as a mosaic or patch state.

[0075] The oxide semiconductor preferably contains at least indium, particularly indium and zinc, and may further contain one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like.

[0076] For example, CAC-OS in In-Ga-Zn oxide (In-Ga-Zn oxide among CAC-OS may be particularly referred to as CAC-IGZO) is an indium oxide (hereinafter referred to as InO X1 (X1 is a real number greater than 0) or indium zinc oxide (hereinafter referred to as In X2 Zn Y2 O Z2 (X2, Y2, and Z2 are real numbers greater than 0.) and gallium oxide (hereinafter referred to as GaO X3 (X3 is a real number greater than 0) or gallium zinc oxide (Ga X4 Zn Y4 O Z4 (X4, Y4, and Z4 are real numbers greater than 0).) The material is separated into mosaics, and the mosaic InO X1 , or In X2 Zn Y2 O Z2 However, the structure is such that the particles are uniformly distributed in the film (hereinafter also referred to as a cloud-like structure).

[0077] In other words, CAC-OS is X3 The region where In is the main component and X2 Zn Y2 O Z2 , or InO X1 In this specification, for example, when the atomic ratio of In to element M in the first region is greater than the atomic ratio of In to element M in the second region, the first region is said to have a higher In concentration than the second region.

[0078] IGZO is a common name and may refer to a compound made of In, Ga, Zn, and O. A typical example is InGaO3(ZnO). m1 (m1 is a natural number), or In (1+x0) Ga (1-x0) O3(ZnO) m0 (-1≦x0≦1, m0 is an arbitrary number).

[0079] The crystalline compound has a single crystal structure, a polycrystalline structure, or a CAAC structure, where multiple IGZO nanocrystals are aligned along the c-axis and connected without being aligned in the ab-plane.

[0080] On the other hand, CAC-OS refers to the material structure of an oxide semiconductor. CAC-OS is a material structure containing In, Ga, Zn, and O, in which some regions observed as nanoparticles mainly composed of Ga and some regions observed as nanoparticles mainly composed of In are randomly dispersed in a mosaic pattern. Therefore, the crystal structure is a secondary element in CAC-OS.

[0081] Note that CAC-OS does not include a stacked structure of two or more films with different compositions, such as a two-layer structure consisting of a film mainly containing In and a film mainly containing Ga.

[0082] In addition, GaO X3 The region where In is the main component and X2 Zn Y2 O Z2 , or InO X1 In some cases, a clear boundary between the region where the main component is the chromatic aberration and the region where the chromatic aberration is the main component may not be observed.

[0083] When one or more elements selected from aluminum, yttrium, copper, vanadium, beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium are contained instead of gallium, the CAC-OS has a structure in which some regions observed to be nanoparticles containing the metal element as the main component and some regions observed to be nanoparticles containing In as the main component are randomly dispersed in a mosaic pattern.

[0084] The CAC-OS can be formed, for example, by a sputtering method without heating the substrate. When the CAC-OS is formed by a sputtering method, one or more of an inert gas (typically argon), oxygen gas, and nitrogen gas may be used as the deposition gas. The lower the flow rate of oxygen gas relative to the total flow rate of deposition gas during deposition, the better. For example, the flow rate of oxygen gas is preferably 0% or more and less than 30%, and more preferably 0% or more and 10% or less.

[0085] CAC-OS has the characteristic that no clear peaks are observed when measured using the θ / 2θ scan by the out-of-plane X-ray diffraction (XRD) method, which indicates that the ab-plane and c-axis orientations of the measured region are not observed.

[0086] In the electron diffraction pattern obtained by irradiating CAC-OS with an electron beam (also called nanobeam electron beam) with a probe diameter of 1 nm, a ring-shaped region of high brightness (ring region) and multiple bright spots are observed in the ring region. Therefore, the electron diffraction pattern indicates that the CAC-OS has a nanocrystal (nc) structure that does not have orientation in the planar and cross-sectional directions.

[0087] For example, in the case of CAC-OS made of In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) revealed that GaO X3 The region where In is the main component and X2 Zn Y2 O Z2 , or InO X1 It can be seen that the region where the main component is the crystalline silicon is unevenly distributed and mixed.

[0088] CAC-OS has a different structure from IGZO compounds, in which metal elements are uniformly distributed, and has different properties from IGZO compounds. X3 The region where In is the main component. X2 Zn Y2 O Z2 , or InO X1 The structure is such that the regions are separated into a mosaic of regions each containing one of the elements as the main component and a region each containing one of the elements as the main component.

[0089] Here, In X2 Zn Y2 O Z2 , or InO X1 The region where is the main component is GaO X3 This is a region with high conductivity compared to regions where the main components are In. X2 Zn Y2 O Z2 , or InO X1 When carriers flow through the region where In is the main component, the conductivity of the oxide semiconductor is exhibited. X2 Zn Y2 O Z2 , or InO X1 When the region mainly composed of is distributed in a cloud-like shape in the oxide semiconductor, a high field-effect mobility (μ) can be achieved.

[0090] On the other hand, GaO X3 The region where the main components are In X2 Zn Y2 O Z2 , or InOX1 This region has higher insulating properties than the region where GaO is the main component. X3 When a region containing the above as a main component is distributed in the oxide semiconductor, leakage current can be suppressed and good switching operation can be achieved.

[0091] Therefore, when CAC-OS is used in a semiconductor device, GaO X3 Insulation due to X2 Zn Y2 O Z2 , or InO X1 The conductivity due to the gate insulating layer and the gate insulating layer work in a complementary manner, resulting in a high on-state current (I on ), and high field-effect mobility (μ) can be achieved.

[0092] Semiconductor elements using CAC-OS have high reliability, making CAC-OS suitable as a constituent material for various semiconductor devices.

[0093] <Pixel operation example 1> An example of the boosting operation of the pixel 10 will be described using the timing chart shown in Fig. 2. Here, the same image data is used as the first data and the second data, and an example of the operation is shown in which a voltage higher than the voltage corresponding to the image data is generated by adding the second data to the first data.

[0094] In the following description, a high potential is represented as "High" and a low potential as "Low." Image data is represented as "Vdata," and a specific potential is represented as "Vref." "Vref" can be, for example, 0 V, GND potential, or a specific reference potential. The potential of the wiring 128 is represented as "Vano." For example, "Vano" is preferably set to a potential at which the transistor 101 operates in the saturation region when the luminance of the light-emitting device 114 is maximized. The potential of the wiring 129 is represented as "Vcath." "Vcath" is preferably set to a potential at which the light-emitting device 114 does not emit light when the potential of the node ND1 is at its lowest potential.

[0095] First, the operation of writing image data “Vdata” as the first data to node ND1 will be described. Note that detailed changes in potential distribution, coupling, or loss due to circuit configuration, operation timing, etc. will not be taken into consideration here.

[0096] At time T1, when the potential of the wiring 121 is set to "High," the potential of the wiring 122 to "Low," the potential of the wiring 131 to "Vdata," and the potential of the wiring 127 to "Vref," the transistors 102 and 104 are turned on, and the potential of the wiring 131 "Vdata" is written to the node ND1, and the potential of the wiring 127 "Vref" is written to the node ND2.

[0097] At this time, if the potential difference across the capacitive element 111 is V1, the potential difference V1 can be expressed by equation (1).

[0098] V1=Vdata-Vref (1)

[0099] Similarly, if the potential difference across the capacitive element 112 is V2, the potential difference V2 can be expressed by equation (2).

[0100] V2=Vano-Vref (2)

[0101] At time T2, the potential of the wiring 121 is set to "low" and the potential of the wiring 122 is set to "low," so that the transistor 102 and the transistor 104 are turned off.

[0102] At this time, the potential V of the node ND1 ND1 The potential V of the node ND2 can be expressed by the following equation (3). ND2 can be expressed by equation (4).

[0103] V ND1 =Vdata-a (3)

[0104] V ND2 =Vref-b (4)

[0105] At this time, the potential difference V1 across the capacitive element 111 can be expressed by equation (5), and the potential difference V2 across the capacitive element 112 can be expressed by equation (6).

[0106] V1=(Vdata-a)-(Vref-b) (5)

[0107] V2=Vano-(Vref-b) (6)

[0108] Note that a is a constant and represents the amount of potential fluctuation due to the influence of feedthrough, charge injection, etc. when the transistor 102 is turned off. b is a constant and represents the amount of potential fluctuation due to the influence of feedthrough, charge injection, etc. when the transistor 104 is turned off.

[0109] Next, the operation of writing image data "Vdata" as second data to the node ND2 and boosting the potential of the node ND1 will be described.

[0110] At time T3, when the potential of the wiring 121 is set to "Low" and the potential of the wiring 122 is set to "High," the transistor 103 is turned on, and the potential of the wiring 131, "Vdata," is written to the node ND2.

[0111] At this time, the potential difference V1 across the capacitive element 111 is maintained at the potential difference V1 shown in equation (5), so the potential V ND1 The potential V of the node ND2 can be expressed by the following equation (7). ND2 can be expressed by equation (8).

[0112] V ND1 =2Vdata-Vref-a+b (7)

[0113] V ND2 =Vdata (8)

[0114] At time T4, when the potential of wiring 121 is set to "Low" and the potential of wiring 122 is set to "Low", transistor 103 becomes non-conductive, the gate-source voltage Vgs of transistor 101 becomes the sum of the voltages held in capacitance elements 111 and 112, and a current corresponding to Vgs flows to light-emitting device 114.

[0115] At this time, the potential V of the node ND1 ND1 The potential V of the node ND2 can be expressed by the following equation (9). ND2 can be expressed by equation (10).

[0116] V ND1 =2Vdata-Vref-a+bc (9)

[0117] V ND2 =Vdata-c (10)

[0118] Note that c is a constant and indicates the amount of change in potential due to the influence of feedthrough, charge injection, and the like when the transistor 103 is turned off.

[0119] In equation (9), if Vref is set to "0V" and constants a, b, and c are set to zero, then V ND1 can be expressed as "2Vdata", and is obtained at a value higher than the potential "Vdata" supplied to the pixel 10. In other words, the voltage can be boosted to a voltage higher than the voltage (Vdata) corresponding to the image data supplied to the pixel 10, and this voltage can be supplied to the transistor 101 functioning as a driving transistor. Therefore, the current flowing through the light-emitting device 114 can be increased, resulting in a display device with high brightness.

[0120] The operation of FIG. 2 can be performed continuously within one horizontal period.

[0121] A display device according to one embodiment of the present invention can generate a high voltage even when a general-purpose driver IC is used. For example, the voltage supplied from the driver IC to drive a light-emitting device can be reduced by about half, thereby reducing the power consumption of the display device. Furthermore, for example, by writing the same image data twice, the current flowing through the light-emitting device can be increased, thereby increasing the luminance of the display.

[0122] By combining such first data and second data, it is possible to perform up-conversion, HDR display, correction of display unevenness inherent to the display device, correction of the threshold voltage of the transistor in the pixel, etc. Alternatively, these can be performed in combination.

[0123] In the up-conversion operation, for example, different correction data is supplied to each of four adjacent pixels (two rows and two columns), and the same image data is also supplied to these pixels. The supplied image data is corrected (converted) to different image data for each pixel, allowing display at each pixel. For example, by inputting data applied to one specific pixel of 4K2K data to specific four pixels of a display device having 8K4K pixels, and inputting different correction data to each of the four pixels, a display with improved resolution can be achieved.

[0124] A display device according to one embodiment of the present invention can correct image data in a broad sense, but can also display different images by superimposing them. For example, a composite image can be displayed by superimposing a first image formed from image data "Vdata" and a second image formed from correction data "Vw." Combining image data and correction data in this manner can not only compositely display different images, but also improve the luminance of the entire displayed image. For example, this can be applied to inserting text or displaying AR images.

[0125] <Pixel configuration example 2> Configurations different from the pixel 10 shown in FIG. 1 are shown in FIGS. 3A, 3B, and 4. FIG.

[0126] As shown in FIG. 3A, each of the transistors 101, 102, 103, and 104 may have a back gate. In particular, the transistor 101, which functions as a driving transistor, preferably has a back gate. FIG. 3A shows a configuration in which the back gate of the transistor 101 is electrically connected to one of the source and the drain, which has the effect of increasing the saturation of the transistor characteristics. Also, the back gate of each of the transistors 102, 103, and 104 is electrically connected to the gate (sometimes referred to as the front gate), which has the effect of increasing the on-state current.

[0127] 3B, the back gate and the front gate of the transistor 101 may be electrically connected to each other. Such a structure has the effect of increasing the on-state current of the transistor 101.

[0128] As shown in Fig. 4, the back gate may be electrically connected to a wiring that can supply a constant potential to control the threshold voltage of the transistor. Note that although Fig. 3A, Fig. 3B, and Fig. 4 show a configuration in which a back gate is provided for all transistors, some transistors may not be provided with a back gate.

[0129] <Pixel configuration example 3> FIG. 5 shows a configuration different from that of pixel 10 shown in FIG. 3A.

[0130] The pixel 10 shown in FIG. 5 differs from the pixel 10 shown in FIG. 3A in that a transistor 105 is included. One of the source and the drain of the transistor 105 is electrically connected to one electrode of the light-emitting device 114. The other of the source and the drain of the transistor 105 is electrically connected to a wiring 143. A gate of the transistor 105 is electrically connected to a wiring 141. The wiring 141 functions as a scan line for controlling the operation of the transistor 105.

[0131] The transistor 105 can have a function of resetting the potential of one electrode of the light-emitting device 114 to the potential of the wiring 143. By resetting the potential of one electrode of the light-emitting device 114, the transistor 105 has a function of suppressing problems such as unintended current flowing through the light-emitting device 114.

[0132] The transistor 105 can be electrically connected to a circuit (not shown) having a function of monitoring current through the wiring 141. In this case, a current that flows when a predetermined potential is applied to the gate of the transistor 101 is passed through the circuit through the transistor 105 and the wiring 141, thereby enabling monitoring of the electrical characteristics of the transistor 101. Variations in the threshold voltage and mobility of the transistor 101 can be calculated from the current flowing through the circuit, and data for correcting the threshold voltage is provided to the transistor 101, thereby enabling a display device with reduced display unevenness.

[0133] The transistor 105 may have a back gate. Figure 5 shows a configuration in which the back gate of the transistor 105 is electrically connected to the gate (front gate). Note that the back gate of the transistor 105 may be electrically connected to one of the source and the drain. Alternatively, the transistor 105 may not have a back gate.

[0134] <Pixel configuration example 4> FIG. 6 shows a configuration different from that of the pixel 10 shown in FIG.

[0135] 6, p-channel transistors are used as the transistors 101, 102, 103, and 104. The connection relationships between the light-emitting device 114, the transistors, the capacitors, and the wirings can be seen in the description of the pixel 10 shown in FIG. 1, and therefore detailed description thereof will be omitted.

[0136] <Pixel operation example 2> An example of the boosting operation of the pixel 10A shown in Fig. 6 will be described using the timing chart shown in Fig. 7. "Vref" can be a high potential. For example, "Vref" can be the same potential as the potential "Vano" of the wiring 128.

[0137] First, the operation of writing image data “Vdata” as the first data to node ND1 will be described. Note that detailed changes in potential distribution, coupling, or loss due to circuit configuration, operation timing, etc. will not be taken into consideration here.

[0138] At time T11, when the potential of the wiring 121 is set to "Low," the potential of the wiring 122 to "High," the potential of the wiring 131 to "Vdata," and the potential of the wiring 127 to "Vref," the transistors 102 and 104 are turned on, and the potential of the wiring 131 "Vdata" is written to the node ND1, and the potential of the wiring 127 "Vref" is written to the node ND2.

[0139] At this time, the potential difference V1 across the capacitive element 111 can be expressed by equation (11). The potential difference V2 across the capacitive element 112 can be expressed by equation (12).

[0140] V1=Vref-Vdata (11)

[0141] V2=Vref-Vano (12)

[0142] At time T12, the potential of the wiring 121 is set to "High" and the potential of the wiring 122 is set to "High," so that the transistor 102 and the transistor 104 are turned off.

[0143] At this time, the potential V of the node ND1 ND1 The potential V of the node ND2 can be expressed by the following equation (13). ND2 can be expressed by equation (14).

[0144] V ND1 =Vdata+a (13)

[0145] V ND2 =Vref+b (14)

[0146] At this time, the potential difference V1 across the capacitive element 111 can be expressed by equation (15). The potential difference V2 across the capacitive element 112 can be expressed by equation (16).

[0147] V1=(Vref+b)-(Vdata+a) (15)

[0148] V2=(Vref+b)-Vano (16)

[0149] Next, the operation of writing image data "Vdata" as second data to the node ND2 and boosting the potential of the node ND1 will be described.

[0150] At time T13, when the potential of the wiring 121 is set to "High" and the potential of the wiring 122 is set to "Low," the transistor 103 is turned on, and the potential of the wiring 131, "Vdata," is written to the node ND2.

[0151] At this time, the potential difference across the capacitive element 111 is maintained at the potential difference V1 shown in equation (15), so the potential V ND1 can be expressed by equation (17). The potential V of the node ND2 ND2 can be shown by equation (18).

[0152] V ND1 =2Vdata-Vref+ab (17)

[0153] V ND2 =Vdata (18)

[0154] At time T14, when the potential of wiring 121 is set to "High" and the potential of wiring 122 is set to "High," transistor 103 becomes non-conductive, the gate-source voltage Vgs of transistor 101 becomes the sum of the voltages held in capacitance elements 111 and 112, and a current corresponding to Vgs flows to light-emitting device 114.

[0155] At this time, the potential V of the node ND1 ND1 The potential V of the node ND2 can be expressed by the following equation (19): ND2 can be expressed by equation (20).

[0156] V ND1 =2Vdata-Vref+a-b+c (19)

[0157] V ND2 =Vdata+c (20)

[0158] As described above, the pixel 10A can boost a voltage higher than the voltage (Vdata) corresponding to the supplied image data and supply the boosted voltage to the transistor 101 functioning as a driving transistor. This allows a larger current to flow through the light-emitting device 114, resulting in a display device with higher brightness.

[0159] <Pixel layout example> An example of the layout of the pixel 10 will be described below.

[0160] An example of the layout of the pixel 10 shown in FIG. 3A is shown in FIG. 8A.

[0161] Fig. 8A shows a transistor 101, a transistor 102, a transistor 103, a transistor 104, a capacitor 111, a capacitor 112, a wiring 121, a wiring 122, a wiring 131, a wiring 127, and a wiring 128. Fig. 8B shows a circuit diagram corresponding to the layout shown in Fig. 8A. Note that in Figs. 8A and 8B, the light-emitting device 114 and the wiring 129 are omitted for clarity.

[0162] 9 shows a configuration in which a pixel electrode 53 is provided in addition to the configuration of FIG. 8A. The pixel electrode 53 is electrically connected to the light-emitting device 114. The light-emitting device 114 can be provided on the pixel electrode 53.

[0163] 9, the pixel electrode 53 is provided so as to overlap with a part of the elements and wirings that constitute the pixel 10, such as the transistor 101 and the capacitor element 111. This configuration is particularly effective when a top-emission light-emitting device is used. By arranging the transistor 101 and the like below the pixel electrode 53 in this way, a large aperture ratio can be achieved even if the area occupied by the pixel 10 is reduced.

[0164] 9, it is preferable that the pixel electrode 53 does not overlap with the wiring 131 that functions as a signal line. If the pixel electrode 53 and the wiring 131 do not overlap, it is possible to prevent a change in the potential of the wiring 131 from affecting the potential of the pixel electrode 53. If it is necessary to arrange the pixel electrode 53 so as to overlap with the wiring 131, the ratio of the area of ​​the overlap to the area of ​​the pixel electrode 53 may be 10% or less, preferably 5% or less.

[0165] <Example of sub-pixel configuration> 10, 11A, and 11B show structural examples of subpixels that can be used in the display device of one embodiment of the present invention.

[0166] 10 shows an example in which a pixel 10 includes a sub-pixel 10R that emits red light, a sub-pixel 10G that emits green light, and a sub-pixel 10B that emits blue light, and these three sub-pixels constitute one pixel 10. In addition to the sub-pixels (two pixels 10) arranged in a matrix of two rows and three columns, Fig. 10 also shows wiring 121, wiring 122, and wiring 131. The wiring 121 and wiring 122 may each have an area overlapping with the pixel electrode 53.

[0167] Subpixel 10R has a pixel electrode 53a, and the display region 51a of subpixel 10R is located inside pixel electrode 53a. Subpixel 10G has a pixel electrode 53b, and the display region 51b of subpixel 10G is located inside pixel electrode 53b. Subpixel 10B has a pixel electrode 53c, and the display region 51c of subpixel 10B is located inside pixel electrode 53c. Note that while FIG. 10 shows an example in which pixel electrode 53a, pixel electrode 53b, and pixel electrode 53c have the same area, they may each have a different area. Furthermore, display region 51a, display region 51b, and display region 51c may each have a different area.

[0168] 10 shows an example in which the positions of sub-pixels of the same color are shifted in the extension direction of the wiring 121 and the wiring 122. In other words, in the pixel 10, the sub-pixels of the same color are arranged in a zigzag pattern in the extension direction of the wiring 121 and the wiring 122.

[0169] 10 shows an example in which the sub-pixels emit light in a combination of three colors: red (R), green (G), and blue (B), but the combination and number of colors are not limited to this. The sub-pixels may emit light in a combination of four colors: red (R), green (G), blue (B), and white (W), or four colors: red (R), green (G), blue (B), and yellow (Y). The color elements applied to the sub-pixels are not limited to the above, and may also be combined with cyan (C) and magenta (M), etc.

[0170] 11A shows an example in which the subpixels 10R, 10G, and 10B are aligned in the extension direction of the wiring 121 and 122. The pixel 10 shown in FIG.

[0171] 11B shows an example in which sub-pixels are arranged in a stripe pattern, and the positions of sub-pixels of the same color are shifted in the extension direction of the wiring 121 and the wiring 122. In other words, in the pixel 10, sub-pixels of the same color are arranged in a zigzag pattern in the extension direction of the wiring 121 and the wiring 122.

[0172] In this specification, the blue wavelength range is from 400 nm to less than 490 nm, and blue light emission has at least one emission spectrum peak in this wavelength range. The green wavelength range is from 490 nm to less than 580 nm, and green light emission has at least one emission spectrum peak in this wavelength range. The red wavelength range is from 580 nm to 680 nm, and red light emission has at least one emission spectrum peak in this wavelength range.

[0173] <Display device configuration example 1> A display device according to one embodiment of the present invention will be described in detail below.

[0174] 12 is a block diagram showing a configuration example of the display device 100. The display device 100 includes a pixel portion 150 having a plurality of pixels 10, a driver circuit portion 130, a driver circuit portion 140a, a driver circuit portion 140b, a wiring 121, a wiring 122, and a wiring 131.

[0175] The pixel unit 150 has a plurality of pixels 10, and the pixels 10 can be arranged in a matrix. The driver circuit unit 130 is electrically connected to the pixels 10 via wirings 121. The driver circuit unit 130 is also electrically connected to the pixels 10 via wirings 122. The driver circuit unit 130 functions as a gate line driver circuit (also referred to as a gate driver). The plurality of pixels 10 are each supplied with a signal via the wirings 121 and 122 from the driver circuit unit 130, and driving is controlled. The driver circuit unit 140a is electrically connected to the pixels 10 via wirings 131. The driver circuit unit 140b is electrically connected via wirings 131 to pixels 10 different from the pixels 10 electrically connected to the driver circuit unit 140a. The driver circuit unit 140a and the driver circuit unit 140b each function as a source line driver circuit (also referred to as a source driver). The driving of each of the plurality of pixels 10 is controlled by receiving a signal from the driving circuit unit 140a or the driving circuit unit 140b via the wiring 131. Fig. 12 shows an example in which the pixels 10 in odd-numbered columns are electrically connected to the driving circuit unit 140a, and the pixels 10 in even-numbered columns are electrically connected to the driving circuit unit 140b.

[0176] The display device according to one embodiment of the present invention includes a plurality of driver circuit units that function as source drivers, so that even a display device with a large number of pixels can operate at high speed. The display device according to one embodiment of the present invention can be suitably used for a high-resolution display device with a resolution of 1000 ppi or more, 2000 ppi or more, or 5000 ppi or more, for example.

[0177] 12 shows an example in which two driver circuit portions, 140a and 140b, are provided as the driver circuit portions functioning as source drivers, but one embodiment of the present invention is not limited to this. Three or more driver circuit portions functioning as source drivers may be provided. Alternatively, one driver circuit portion functioning as the source driver may be provided.

[0178] FIG. 13A is a schematic diagram illustrating a configuration example of a display device 100. The display device 100 has a stacked structure of a first layer 20 and a second layer 30 on the first layer 20. Although FIG. 13A illustrates a configuration in which the second layer 30 is provided on the first layer 20, one embodiment of the present invention is not limited to this. The first layer 20 may be provided on the second layer 30. One or more interlayer insulating layers and wiring layers may be provided between the first layer 20 and the second layer 30. Furthermore, there may be a plurality of interlayer insulating layers and wiring layers provided between the first layer 20 and the second layer 30.

[0179] The first layer 20 includes a driving circuit section 140a and a driving circuit section 140b. The second layer 30 includes a driving circuit section 130 and a pixel section 150.

[0180] An example of the configuration of the first layer 20 and the second layer 30 shown in FIG. 13A is shown in FIG. 13B. In FIG. 13B, the positional relationship between the first layer 20 and the second layer 30 is indicated by open circles and dashed lines, and in a plan view, the open circles of the first layer 20 and the open circles of the second layer 30, which are connected by the dashed line, overlap. Note that similar notations are used in other figures. Note that, for clarity, wiring other than wiring 121, wiring 122, and wiring 131 is omitted in FIG. 13B.

[0181] In the display device 100, it is preferable that the driver circuit units 140a and 140b provided in the first layer 20 each have an area overlapping with the pixel unit 150. By stacking the pixel unit 150, the driver circuit units 140a and 140b so that they have an overlapping area, the area of ​​the frame, which is an area where the pixel unit 150 is not provided, can be reduced. This makes it possible to narrow the frame of the display device 100. Furthermore, by narrowing the frame of the display device 100, the display device 100 can be made smaller.

[0182] 13B shows an example in which the first layer 20 and the second layer 30 are approximately the same size, but the scope of the present invention is not limited to this. The first layer 20 and the second layer 30 may be different sizes. For example, the first layer 20 may be larger than the second layer 30. Alternatively, the first layer 20 may be smaller than the second layer 30.

[0183] After forming the first layer 20, the second layer 30 can be formed on the first layer 20 to manufacture the display device 100. By forming the second layer 30 on the first layer 20, it is possible to improve the alignment accuracy between the first layer 20 and the second layer 30. Therefore, it is possible to improve the productivity of the display device 100.

[0184] The display device 100 may be fabricated by forming the first layer 20 and the second layer 30, respectively, and then bonding the first layer 20 and the second layer 30 together. When fabricating the display device 100 by bonding the first layer 20 and the second layer 30 together, the first layer 20 and the second layer 30 may have different sizes. Therefore, the first layer 20 and the second layer 30 can be formed without being affected by each other's sizes. For example, the display device 100 may be fabricated by forming a plurality of first layers 20 on a substrate on which the first layer 20 is to be formed, dividing the first layers 20 into individual first layers 20, and then bonding the second layers 30 together. Similarly, the display device 100 may be fabricated by forming a plurality of second layers 30 on a substrate on which the second layer 30 is to be formed, dividing the second layers 30 into individual second layers 30, and then bonding the first layers 20 together. That is, the productivity of the first layer 20 and the second layer 30 can be increased, and the productivity of the display device 100 can also be increased.

[0185] <Configuration example 2 of the display device> 14A and 14B show examples of a configuration different from that of the display device 100 shown in Figures 13A and 13B. The display device 100 shown in Figures 14A and 14B differs from the display device 100 shown in Figures 13A and 13B mainly in that the first layer 20 includes a driving circuit unit 130. By providing the driving circuit unit 130 in the same first layer 20 as the driving circuit units 140a and 140b, the driving circuit unit 130 can be manufactured using a common manufacturing process, thereby improving productivity.

[0186] 14B shows an example in which the pixel portion 150 does not have a region overlapping with the driver circuit portion 130; however, one embodiment of the present invention is not limited to this. The pixel portion 150 may have a region overlapping with the driver circuit portion 130. Alternatively, the pixel portion 150 may have a region overlapping with all of the driver circuit portion 130, the driver circuit portion 140a, and the driver circuit portion 140b. With such a structure, the frame of the display device 100 can be narrowed. Furthermore, narrowing the frame of the display device 100 allows the display device 100 to be made smaller.

[0187] <Example 1 of cross-sectional configuration of display device> 15 is a cross-sectional view showing a configuration example of the display device 100. The display device 100 has a substrate 701 and a substrate 705, and the substrate 701 and the substrate 705 are attached to each other with a sealant 712.

[0188] A single crystal semiconductor substrate such as a single crystal silicon substrate can be used as the substrate 701. Note that the substrate 701 may be a semiconductor substrate other than a single crystal semiconductor substrate.

[0189] The transistor 441 and the transistor 601 are provided over a substrate 701. The transistor 441 and the transistor 601 can be transistors provided in the first layer 20. For example, in the display device 100 shown in FIGS. 13A and 13B, the transistor 441 and the transistor 601 can be transistors provided in the driver circuit portion 140a or 140b. For example, in the display device 100 shown in FIGS. 14A and 14B, the transistor 441 and the transistor 601 can be transistors provided in the driver circuit portion 130, the driver circuit portion 140a, or the driver circuit portion 140b.

[0190] The transistor 441 includes a conductor 443 functioning as a gate electrode, an insulator 445 functioning as a gate insulator, and a part of the substrate 701, and includes a semiconductor region 447 including a channel formation region, a low-resistance region 449a functioning as one of a source region and a drain region, and a low-resistance region 449b functioning as the other of the source region and the drain region. The transistor 441 may be either a p-channel type or an n-channel type.

[0191] The transistor 441 is electrically isolated from other transistors by an element isolation layer 403. Fig. 15 shows a case where the transistor 441 and the transistor 601 are electrically isolated by the element isolation layer 403. The element isolation layer 403 can be formed by a LOCOS (LOCal Oxidation of Silicon) method, an STI (Shallow Trench Isolation) method, or the like.

[0192] 15 has a convex semiconductor region 447. A conductor 443 is provided to cover the side surface and the top surface of the semiconductor region 447 with an insulator 445 interposed therebetween. Note that the conductor 443 covering the side surface of the semiconductor region 447 is not shown in FIG. A material that adjusts the work function can be used for the conductor 443.

[0193] A transistor having a convex semiconductor region, such as the transistor 441, can be called a fin transistor because it utilizes the convex portion of a semiconductor substrate. Note that an insulator that is in contact with the top of the convex portion and functions as a mask for forming the convex portion may be provided. Although FIG. 15 shows a configuration in which the convex portion is formed by processing a part of the substrate 701, a semiconductor having a convex portion may be formed by processing an SOI substrate.

[0194] 15 is just an example, and is not limited to this configuration, and may have an appropriate configuration depending on the circuit configuration, the operation method of the circuit, etc. For example, the transistor 441 may be a planar transistor.

[0195] The transistor 601 can have a structure similar to that of the transistor 441 .

[0196] In addition to the element isolation layer 403, the transistor 441, and the transistor 601, an insulator 405, an insulator 407, an insulator 409, and an insulator 411 are provided over the substrate 701. A conductor 451 is embedded in the insulator 405, the insulator 407, the insulator 409, and the insulator 411. Here, the height of the top surface of the conductor 451 and the height of the top surface of the insulator 411 can be made approximately the same.

[0197] An insulator 413 and an insulator 415 are provided on the conductor 451 and the insulator 411. A conductor 457 is embedded in the insulator 413 and the insulator 415. Here, the height of the top surface of the conductor 457 and the height of the top surface of the insulator 415 can be made approximately the same.

[0198] An insulator 417 and an insulator 419 are provided on the conductor 457 and the insulator 415. Furthermore, a conductor 459 is embedded in the insulator 417 and the insulator 419. Here, the height of the top surface of the conductor 459 and the height of the top surface of the insulator 419 can be made approximately the same.

[0199] An insulator 421 and an insulator 214 are provided on the conductor 459 and the insulator 419. A conductor 453 is embedded in the insulator 421 and the insulator 214. Here, the height of the top surface of the conductor 453 and the height of the top surface of the insulator 214 can be made approximately the same.

[0200] An insulator 216 is provided on the conductor 453 and the insulator 214. A conductor 455 is embedded in the insulator 216. Here, the height of the top surface of the conductor 455 and the height of the top surface of the insulator 216 can be made approximately the same.

[0201] Insulators 222, 224, 254, 244, 280, 274, and 281 are provided on conductor 455 and insulator 216. Conductor 305 is embedded in insulators 222, 224, 254, 244, 280, 274, and 281. Here, the height of the top surface of conductor 305 and the height of the top surface of insulator 281 can be made approximately the same.

[0202] An insulator 361 is provided on the conductor 305 and on the insulator 281. The conductor 317 and the conductor 337 are embedded in the insulator 361. Here, the height of the upper surface of the conductor 337 and the height of the upper surface of the insulator 361 can be made approximately the same.

[0203] An insulator 363 is provided on the conductor 337 and on the insulator 361. The conductors 347, 353, 355, and 357 are embedded in the insulator 363. Here, the height of the top surfaces of the conductors 353, 355, and 357 can be made approximately the same as the height of the top surface of the insulator 363.

[0204] Connection electrodes 760 are provided on the conductors 353, 355, 357, and insulator 363. An anisotropic conductor 780 is provided so as to be electrically connected to the connection electrodes 760, and an FPC (Flexible Printed Circuit) 716 is provided so as to be electrically connected to the anisotropic conductor 780. Various signals and the like are supplied to the display device 100 from outside the display device 100 via the FPC 716.

[0205] 15 , the low-resistance region 449b serving as the other of the source region and the drain region of the transistor 441 is electrically connected to the FPC 716 through the conductor 451, the conductor 457, the conductor 459, the conductor 453, the conductor 455, the conductor 305, the conductor 317, the conductor 337, the conductor 347, the conductor 353, the conductor 355, the conductor 357, the connection electrode 760, and the anisotropic conductor 780. Here, although FIG. 15 shows three conductors, the conductor 353, the conductor 355, and the conductor 357, as conductors having a function of electrically connecting the connection electrode 760 and the conductor 347, one embodiment of the present invention is not limited thereto. The number of conductors having a function of electrically connecting the connection electrode 760 and the conductor 347 may be one, two, or four or more. By providing a plurality of conductors that function to electrically connect the connection electrode 760 and the conductor 347, the contact resistance can be reduced.

[0206] A transistor 750 is provided over the insulator 214. The transistor 750 can be a transistor provided in the second layer 30. For example, in the display device 100 illustrated in FIGS. 13A, 13B, 14A, and 14B, the transistor 750 can be a transistor provided in the pixel portion 150. An OS transistor can be preferably used as the transistor 750. An OS transistor has an extremely low off-state current. Therefore, the retention time of an image signal or the like can be extended, thereby reducing the frequency of a refresh operation. Therefore, the power consumption of the display device 100 can be reduced.

[0207] Conductor 301a and conductor 301b are embedded in insulator 254, insulator 244, insulator 280, insulator 274, and insulator 281. Conductor 301a is electrically connected to one of the source and drain of transistor 750, and conductor 301b is electrically connected to the other of the source and drain of transistor 750. Here, the height of the top surfaces of conductor 301a and conductor 301b and the height of the top surface of insulator 281 can be made approximately the same.

[0208] The conductor 311, the conductor 313, the conductor 331, the capacitor 790, the conductor 333, and the conductor 335 are embedded in the insulator 361. The conductor 311 and the conductor 313 are electrically connected to the transistor 750 and function as wirings. The conductor 333 and the conductor 335 are electrically connected to the capacitor 790. Here, the height of the top surfaces of the conductor 331, the conductor 333, and the conductor 335 can be made approximately the same as the height of the top surface of the insulator 361.

[0209] Conductor 341, conductor 343, and conductor 351 are embedded in insulator 363. Here, the height of the top surface of conductor 351 and the height of the top surface of insulator 363 can be made approximately the same.

[0210] The insulators 405, 407, 409, 411, 413, 415, 417, 419, 421, 214, 280, 274, 281, 361, and 363 function as interlayer films and may also function as planarizing films that cover uneven shapes below them. For example, the top surface of the insulator 363 may be planarized by planarization treatment using chemical mechanical polishing (CMP) or the like to improve flatness.

[0211] For example, in the display device 100 shown in FIGS. 13 and 14, the capacitor 790 can be the capacitor 111 or the capacitor 112 provided in the pixel portion 150.

[0212] 15, the capacitor 790 has a lower electrode 321 and an upper electrode 325. An insulator 323 is provided between the lower electrode 321 and the upper electrode 325. That is, the capacitor 790 has a layered structure in which the insulator 323, which functions as a dielectric, is sandwiched between a pair of electrodes. Note that although an example in which the capacitor 790 is provided over the insulator 281 is shown in FIG. 15, the capacitor 790 may be provided over an insulator different from the insulator 281.

[0213] FIG. 15 shows an example in which conductors 301a, 301b, and 305 are formed in the same layer. It also shows an example in which conductors 311, 313, 317, and the lower electrode 321 are formed in the same layer. It also shows an example in which conductors 331, 333, 335, and 337 are formed in the same layer. It also shows an example in which conductors 341, 343, and 347 are formed in the same layer. It also shows an example in which conductors 351, 353, 355, and 357 are formed in the same layer. Forming multiple conductors in the same layer can simplify the manufacturing process of the display device 100, thereby reducing the manufacturing cost of the display device 100. These conductors may be formed in different layers and may be made of different types of materials.

[0214] 15 includes a light-emitting device 782. The light-emitting device 782 includes a conductor 772, an EL layer 786, and a conductor 788. The EL layer 786 includes an organic compound or an inorganic compound such as quantum dots.

[0215] Materials that can be used for the organic compounds include fluorescent materials and phosphorescent materials, etc. Materials that can be used for the quantum dots include colloidal quantum dot materials, alloy quantum dot materials, core-shell quantum dot materials, and core quantum dot materials.

[0216] The conductor 772 is electrically connected to the other of the source and the drain of the transistor 750 through the conductors 351, 341, 331, 313, and 301b. The conductor 772 is formed over the insulator 363 and functions as a pixel electrode.

[0217] A material that transmits or reflects visible light can be used for the conductor 772. For example, an oxide material containing indium, zinc, tin, or the like can be used as the light-transmitting material. For example, a material containing aluminum, silver, or the like can be used as the reflective material.

[0218] Although not shown in FIG. 15, the display device 100 can be provided with optical members (optical substrates) such as a polarizing member, a phase difference member, an anti-reflection member, and the like.

[0219] A light-shielding layer 738 and an insulator 734 in contact with the light-shielding layer 738 are provided on the substrate 705 side. The light-shielding layer 738 has a function of blocking light emitted from an adjacent region. Alternatively, the light-shielding layer 738 has a function of blocking external light from reaching the transistor 750 and the like.

[0220] 15, an insulator 730 is provided over an insulator 363. Here, the insulator 730 can be configured to cover part of a conductor 772. The light-emitting device 782 includes a light-transmitting conductor 788 and can be a top-emission light-emitting device. Note that the light-emitting device 782 may have a bottom-emission structure in which light is emitted to the conductor 772 side, or a dual-emission structure in which light is emitted to both the conductor 772 and the conductor 788.

[0221] The light-shielding layer 738 is provided to have a region overlapping with the insulator 730. The light-shielding layer 738 is covered with the insulator 734. The space between the light-emitting device 782 and the insulator 734 is filled with the sealing layer 732.

[0222] Furthermore, structure 778 is disposed between insulator 730 and EL layer 786. Structure 778 is also disposed between insulator 730 and insulator 734.

[0223] FIG. 16 shows a modified example of the display device 100 shown in FIG. 15 . The display device 100 shown in FIG. 16 differs from the display device 100 shown in FIG. 15 in that a colored layer 736 is provided. The colored layer 736 is provided so as to have an area overlapping with the light-emitting device 782. By providing the colored layer 736, the color purity of the light extracted from the light-emitting device 782 can be improved. This allows the display device 100 to display a high-quality image. Furthermore, since, for example, all of the light-emitting devices 782 of the display device 100 can be light-emitting devices that emit white light, it is not necessary to form the EL layer 786 by different colors, and the display device 100 can have high definition.

[0224] The light-emitting device 782 may have a micro-optical resonator (microcavity) structure. This allows light of a predetermined color (e.g., RGB) to be extracted without providing a colored layer, and the display device 100 can perform color display. By not providing a colored layer, it is possible to suppress light absorption by the colored layer. This allows the display device 100 to display high-brightness images and reduce the power consumption of the display device 100. Note that even when the EL layer 786 is formed in an island shape for each pixel or in a striped shape for each pixel column, i.e., formed by coloring, it is possible to configure the display device 100 without providing a colored layer.

[0225] 15 and 16 show a structure in which the transistors 441 and 601 are provided so that channel formation regions are formed inside the substrate 701 and the OS transistors are stacked over the transistors 441 and 601; however, one embodiment of the present invention is not limited to this. A modification of FIG. 16 is shown in FIG. 17. The display device 100 shown in FIG. 17 is mainly different from the display device 100 shown in FIG. 16 in that OS transistors 602 and 603 are provided instead of the transistors 441 and 601. Furthermore, an OS transistor can be used as the transistor 750. That is, the display device 100 shown in FIG. 17 has a stack of OS transistors.

[0226] An insulator 613 and an insulator 614 are provided over a substrate 701, and a transistor 602 and a transistor 603 are provided over the insulator 614. Note that a transistor or the like may be provided between the substrate 701 and the insulator 613. For example, a transistor having a structure similar to that of the transistor 441 and the transistor 601 shown in FIG. 16 may be provided between the substrate 701 and the insulator 613.

[0227] The transistors 602 and 603 can be transistors provided in the first layer 20. For example, in the display device 100 shown in FIGS. 13A and 13B, the transistors 602 and 603 can be transistors provided in the driver circuit portion 140a or 140b. For example, in the display device 100 shown in FIGS. 14A and 14B, the transistors 602 and 603 can be transistors provided in the driver circuit portion 130, the driver circuit portion 140a, or the driver circuit portion 140b.

[0228] The transistor 602 and the transistor 603 can have a structure similar to that of the transistor 750. Note that the transistor 602 and the transistor 603 may be OS transistors having a structure different from that of the transistor 750.

[0229] In addition to the transistor 602 and the transistor 603, insulators 616, 622, 624, 654, 644, 680, 674, and 681 are provided over the insulator 614. The conductor 461 is embedded in the insulator 654, the insulator 644, the insulator 680, the insulator 674, and the insulator 681. Here, the height of the top surface of the conductor 461 can be made approximately the same as the height of the top surface of the insulator 681.

[0230] An insulator 501 is provided on the conductor 461 and the insulator 681. The conductor 463 is embedded in the insulator 501. Here, the height of the top surface of the conductor 463 and the height of the top surface of the insulator 501 can be made approximately the same.

[0231] An insulator 503 is provided on the conductor 463 and on the insulator 501. A conductor 465 is embedded in the insulator 503. Here, the height of the top surface of the conductor 465 and the height of the top surface of the insulator 503 can be made approximately the same.

[0232] An insulator 505 is provided on the conductor 465 and on the insulator 503. A conductor 467 is embedded in the insulator 505. Here, the height of the top surface of the conductor 467 and the height of the top surface of the insulator 505 can be made approximately the same.

[0233] An insulator 507 is provided on the conductor 467 and on the insulator 505. A conductor 469 is embedded in the insulator 507. Here, the height of the top surface of the conductor 469 and the height of the top surface of the insulator 507 can be made approximately the same.

[0234] An insulator 509 is provided on the conductor 469 and the insulator 507. A conductor 471 is embedded in the insulator 509. Here, the height of the top surface of the conductor 471 and the height of the top surface of the insulator 509 can be made approximately the same.

[0235] An insulator 421 and an insulator 214 are provided on the conductor 471 and the insulator 509. A conductor 453 is embedded in the insulator 421 and the insulator 214. Here, the height of the top surface of the conductor 453 and the height of the top surface of the insulator 214 can be made approximately the same.

[0236] As shown in Figure 17, one of the source and drain of transistor 602 is electrically connected to FPC 716 via conductor 461, conductor 463, conductor 465, conductor 467, conductor 469, conductor 471, conductor 453, conductor 455, conductor 305, conductor 317, conductor 337, conductor 347, conductor 353, conductor 355, conductor 357, connection electrode 760, and anisotropic conductor 780.

[0237] Insulator 613, insulator 614, insulator 680, insulator 674, insulator 681, insulator 501, insulator 503, insulator 505, insulator 507, and insulator 509 function as interlayer films and may also function as planarizing films that cover the uneven shapes underneath.

[0238] 17, the display device 100 can have a narrower frame and be smaller in size, and all of the transistors included in the display device 100 can be OS transistors. This allows, for example, the transistors provided in the first layer 20 and the transistors provided in the second layer 30 to be manufactured using the same device. This reduces the manufacturing cost of the display device 100, and the display device 100 can be manufactured at a low price.

[0239] <Example 2 of cross-sectional configuration of display device> 18 is a cross-sectional view illustrating a configuration example of the display device 100. The display device 100 differs from the display device 100 illustrated in FIG. 16 mainly in that a layer including a transistor 800 is provided between a layer including a transistor 750 and a layer including a transistor 601 and a transistor 441.

[0240] 13A and other drawings, the first layer 20 may have a stacked structure of a first circuit layer and a second circuit layer on the first circuit layer. For example, the transistor 601 and the transistor 441 may be transistors provided in the first circuit layer. The transistor 800 may be a transistor provided in the second circuit layer. The transistor 750 may be a transistor provided in the second layer 30.

[0241] An insulator 821 and an insulator 814 are provided on the conductor 459 and the insulator 419. A conductor 853 is embedded in the insulator 821 and the insulator 814. Here, the height of the top surface of the conductor 853 and the height of the top surface of the insulator 814 can be made approximately the same.

[0242] An insulator 816 is provided on the conductor 853 and the insulator 814. A conductor 855 is embedded in the insulator 816. Here, the height of the top surface of the conductor 855 and the height of the top surface of the insulator 816 can be made approximately the same.

[0243] Insulators 822, 824, 854, 844, 880, 874, and 881 are provided on the conductor 855 and the insulator 816. The conductor 805 is embedded in the insulators 822, 824, 854, 844, 880, 874, and 881. Here, the height of the top surface of the conductor 805 and the height of the top surface of the insulator 881 can be made approximately the same.

[0244] An insulator 421 and an insulator 214 are provided over the conductor 817 and the insulator 881 .

[0245] As shown in Figure 18, the low resistance region 449b, which functions as the other of the source region or drain region of the transistor 441, is electrically connected to the FPC 716 via conductor 451, conductor 457, conductor 459, conductor 853, conductor 855, conductor 805, conductor 817, conductor 453, conductor 455, conductor 305, conductor 317, conductor 337, conductor 347, conductor 353, conductor 355, conductor 357, connection electrode 760, and anisotropic conductor 780.

[0246] A transistor 800 is provided over the insulator 814. The transistor 800 may be provided in the second layer 30. For example, in the display device 100 shown in FIGS. 13A and 13B, the transistor 800 may be provided in the driver circuit portion 140a or 140b. For example, in the display device 100 shown in FIGS. 14A and 14B, the transistor 800 may be provided in the driver circuit portion 130, the driver circuit portion 140a, or the driver circuit portion 140b. The transistor 800 is preferably an OS transistor.

[0247] Conductor 801a and conductor 801b are embedded in insulator 854, insulator 844, insulator 880, insulator 874, and insulator 881. Conductor 801a is electrically connected to one of the source and drain of transistor 800, and conductor 801b is electrically connected to the other of the source and drain of transistor 800. Here, the height of the top surfaces of conductor 801a and conductor 801b and the height of the top surface of insulator 881 can be made approximately the same.

[0248] The transistor 750 can be a transistor provided in the second layer 30. For example, in the display device 100 illustrated in FIGS. 13A, 13B, 14A, and 14B, the transistor 750 can be a transistor provided in the pixel portion 150. The transistor 750 is preferably an OS transistor.

[0249] Note that an OS transistor or the like may be provided between a layer including the transistor 441, the transistor 601, and the like and a layer including the transistor 800 and the like. An OS transistor or the like may be provided between a layer including the transistor 800 and the like and a layer including the transistor 750 and the like. An OS transistor or the like may be provided above the layer including the transistor 750 and the like.

[0250] Insulator 405, insulator 407, insulator 409, insulator 411, insulator 413, insulator 415, insulator 417, insulator 419, insulator 821, insulator 814, insulator 880, insulator 874, insulator 881, insulator 421, insulator 214, insulator 280, insulator 274, insulator 281, insulator 361, and insulator 363 function as interlayer films and may also function as planarizing films that cover the uneven shapes below each other.

[0251] 18 shows an example in which a conductor 801a, a conductor 801b, and a conductor 805 are formed in the same layer. Also shown is an example in which a conductor 811, a conductor 813, and a conductor 817 are formed in the same layer.

[0252] 18 shows a structure in which the transistors 441 and 601 are provided so that channel formation regions are formed inside the substrate 701 and the OS transistors are stacked over the transistors 441 and 601, but one embodiment of the present invention is not limited to this. A modification of FIG. 18 is shown in FIG. 19. The display device 100 shown in FIG. 19 differs from the display device 100 shown in FIG. 18 in that OS transistors 602 and 603 are included instead of the transistors 441 and 601. That is, the display device 100 shown in FIG. 19 has three stacked layers of OS transistors.

[0253] An OS transistor or the like may be provided between a layer including the transistors 602 and 603 and the like and a layer including the transistor 800 and the like. An OS transistor or the like may be provided between a layer including the transistor 800 and the like and a layer including the transistor 750 or the transistor 750 and the like. An OS transistor or the like may be provided above the layer including the transistor 750 and the like.

[0254] For example, transistors 602 and 603 may be transistors provided in the first circuit layer, transistor 800 may be a transistor provided in the second circuit layer, and transistor 750 may be a transistor provided in the second layer 30.

[0255] An insulator 821 and an insulator 814 are provided on the conductor 471 and the insulator 509. A conductor 853 is embedded in the insulator 821 and the insulator 814. Here, the height of the top surface of the conductor 853 and the height of the top surface of the insulator 814 can be made approximately the same.

[0256] As shown in Figure 19, one of the source and drain of transistor 602 is electrically connected to FPC 716 via conductor 461, conductor 463, conductor 465, conductor 467, conductor 469, conductor 471, conductor 853, conductor 855, conductor 805, conductor 817, conductor 453, conductor 455, conductor 305, conductor 317, conductor 337, conductor 347, conductor 353, conductor 355, conductor 357, connection electrode 760, and anisotropic conductor 780.

[0257] 19 , the display device 100 can have a narrower frame and be smaller in size, and all of the transistors included in the display device 100 can be OS transistors. This eliminates the need to manufacture different types of transistors, thereby reducing the manufacturing cost of the display device 100 and making the display device 100 more affordable.

[0258] <Example of light-emitting device configuration> An example of the light-emitting device 572 is an EL element that utilizes electroluminescence. The EL element has a layer containing a light-emitting compound between a pair of electrodes (hereinafter also referred to as an EL layer). When a potential difference greater than the threshold voltage of the EL element is generated between the pair of electrodes, holes are injected into the EL layer from the anode side, and electrons are injected from the cathode side. The injected electrons and holes recombine in the EL layer, causing the light-emitting substance contained in the EL layer to emit light.

[0259] EL elements are classified according to whether the light-emitting material is an organic compound or an inorganic compound, and the former are generally called organic EL elements, and the latter are generally called inorganic EL elements.

[0260] When a voltage is applied to an organic EL element, electrons are injected from one electrode and holes are injected from the other electrode into the EL layer. These carriers (electrons and holes) then recombine, causing the light-emitting organic compound to form an excited state, which emits light when the excited state returns to the ground state. Due to this mechanism, such light-emitting devices are called current-excited light-emitting devices.

[0261] In this specification, the voltage supplied to a display element such as a light-emitting device or a liquid crystal element refers to the difference between the potential applied to one electrode of the display element and the potential applied to the other electrode of the display element.

[0262] In addition to the light-emitting compound, the EL layer may contain a substance with high hole-injection properties, a substance with high hole-transport properties, a hole-blocking material, a substance with high electron-transport properties, a substance with high electron-injection properties, a bipolar substance (a substance with high electron-transport properties and high hole-transport properties), or the like.

[0263] The EL layer can be formed by a method such as a vapor deposition method (including a vacuum deposition method), a transfer method, a printing method, an inkjet method, or a coating method.

[0264] Inorganic EL elements are classified into dispersion-type inorganic EL elements and thin-film inorganic EL elements based on their device configuration. Dispersion-type inorganic EL elements have an emitting layer in which particles of emitting material are dispersed in a binder, and their emission mechanism is donor-acceptor recombination emission, which utilizes donor and acceptor levels. Thin-film inorganic EL elements have a structure in which an emitting layer is sandwiched between dielectric layers, which are then sandwiched between electrodes, and their emission mechanism is localized emission, which utilizes inner-shell electron transitions of metal ions.

[0265] A light-emitting device only needs to have at least one of a pair of electrodes transparent to extract light. A transistor and a light-emitting device are formed on a substrate, and light-emitting devices can be of a top-emission structure in which light is extracted from the surface opposite the substrate, a bottom-emission structure in which light is extracted from the surface facing the substrate, or a dual-emission structure in which light is extracted from both surfaces. Any of these emission structures can be used.

[0266] 20A to 20E are diagrams showing a structural example of a light-emitting device 572. Fig. 20A shows a structure (single structure) in which an EL layer 786 is sandwiched between a conductor 772 and a conductor 788. As described above, the EL layer 786 includes a light-emitting material, such as an organic compound.

[0267] Fig. 20B is a diagram showing the laminated structure of the EL layer 786. In the light-emitting device 572 having the structure shown in Fig. 20B, the conductor 772 functions as an anode, and the conductor 788 functions as a cathode.

[0268] The EL layer 786 has a structure in which a hole injection layer 721, a hole transport layer 722, a light-emitting layer 723, an electron transport layer 724, and an electron injection layer 725 are sequentially stacked on a conductor 772. Note that when the conductor 772 functions as a cathode and the conductor 788 functions as an anode, the stacking order is reversed.

[0269] The light-emitting layer 723 includes a light-emitting material or a combination of materials, and can have a structure that can emit fluorescent light or phosphorescent light of a desired emission color. The light-emitting layer 723 may have a stacked structure that emits light of different colors. In this case, different materials may be used as light-emitting substances and other substances in the stacked light-emitting layers.

[0270] In the light-emitting device 572, for example, by using the conductor 772 shown in Figure 20B as a reflective electrode and the conductor 788 as a semi-transparent and semi-reflective electrode, and forming a micro-optical resonator (microcavity) structure, the light emitted from the light-emitting layer 723 included in the EL layer 786 can be resonated between the two electrodes, and the light emitted through the conductor 788 can be intensified.

[0271] When the conductor 772 of the light-emitting device 572 is a reflective electrode having a laminated structure of a reflective conductive material and a light-transmitting conductive material (transparent conductive film), optical adjustment can be performed by controlling the film thickness of the transparent conductive film. Specifically, it is preferable to adjust the inter-electrode distance between the conductor 772 and the conductor 788 to be approximately mλ / 2 (where m is a natural number) for the wavelength λ of light obtained from the light-emitting layer 723.

[0272] In order to amplify the desired light (wavelength: λ) obtained from the light-emitting layer 723, it is preferable to adjust the optical distance from the conductor 772 to the region (light-emitting region) in the light-emitting layer where the desired light is obtained and the optical distance from the conductor 788 to the region (light-emitting region) in the light-emitting layer 723 where the desired light is obtained to be approximately (2m'+1)λ / 4 (where m' is a natural number). Note that the light-emitting region here refers to the recombination region of holes and electrons in the light-emitting layer 723.

[0273] By performing such optical adjustment, the spectrum of the specific monochromatic light obtained from the light-emitting layer 723 can be narrowed, and light with good color purity can be obtained.

[0274] In the above case, however, the optical distance between the conductor 772 and the conductor 788 can be strictly defined as the total thickness from the reflective region of the conductor 772 to the reflective region of the conductor 788. However, since it is difficult to precisely determine the reflective regions of the conductors 772 and 788, the above-described effect can be sufficiently achieved by assuming that any position on the conductors 772 and 788 is the reflective region. Furthermore, the optical distance between the conductor 772 and the light-emitting layer from which the desired light is obtained can be strictly defined as the optical distance between the reflective region of the conductor 772 and the light-emitting region of the light-emitting layer from which the desired light is obtained. However, since it is difficult to precisely determine the reflective region of the conductor 772 and the light-emitting region of the light-emitting layer from which the desired light is obtained, the above-described effect can be sufficiently achieved by assuming that any position on the conductor 772 is the reflective region and that any position on the light-emitting layer from which the desired light is obtained is the light-emitting region.

[0275] The light-emitting device 572 shown in FIG. 20B has a microcavity structure, so it can extract light of different wavelengths (monochromatic light) even if it has the same EL layer. This eliminates the need for separate coloring (e.g., RGB) to obtain different emitted colors. This makes it easy to achieve high definition. It can also be combined with a colored layer. Furthermore, it is possible to increase the luminous intensity of a specific wavelength in the front direction, thereby reducing power consumption.

[0276] 20B does not necessarily have a microcavity structure. In this case, light-emitting layer 723 may be configured to emit white light, and a colored layer may be provided to extract light of a predetermined color (e.g., RGB). Furthermore, when forming EL layer 786, by applying different colors to obtain different emitted colors, light of a predetermined color may be extracted without providing a colored layer.

[0277] At least one of the conductor 772 and the conductor 788 can be a light-transmitting electrode (transparent electrode, semi-transmitting / semi-reflective electrode, etc.). When the light-transmitting electrode is a transparent electrode, the visible light transmittance of the transparent electrode is 40% or more. In addition, in the case of a semi-transmitting / semi-reflective electrode, the visible light reflectance of the semi-transmitting / semi-reflective electrode is 20% or more and 80% or less, preferably 40% or more and 70% or less. In addition, the resistivity of these electrodes is 1×10 -2 Ωcm or less is preferable.

[0278] When the conductor 772 or the conductor 788 is a reflective electrode (reflective electrode), the reflectance of the reflective electrode for visible light is set to 40% or more and 100% or less, preferably 70% or more and 100% or less. The resistivity of this electrode is set to 1×10 -2 Ωcm or less is preferable.

[0279] The light-emitting device 572 may have a configuration shown in FIG. 20C. FIG. 20C shows a light-emitting device 572 having a stacked structure (tandem structure) in which two EL layers (EL layer 786a and EL layer 786b) are provided between a conductor 772 and a conductor 788, and a charge generation layer 792 is provided between the EL layer 786a and the EL layer 786b. By providing the light-emitting device 572 with a tandem structure, the current efficiency and external quantum efficiency of the light-emitting device 572 can be improved. This allows the display device 100 to display images with high brightness. Furthermore, the power consumption of the display device 100 can be reduced. Here, the EL layer 786a and the EL layer 786b can have the same configuration as the EL layer 786 shown in FIG. 20B.

[0280] The charge generation layer 792 has a function of injecting electrons into one of the EL layers 786a and 786b and injecting holes into the other when a voltage is supplied between the conductor 772 and the conductor 788. Therefore, when a voltage is supplied so that the potential of the conductor 772 is higher than the potential of the conductor 788, electrons are injected from the charge generation layer 792 into the EL layer 786a and holes are injected from the charge generation layer 792 into the EL layer 786b.

[0281] Note that, in terms of light extraction efficiency, the charge generation layer 792 preferably transmits visible light (specifically, the visible light transmittance of the charge generation layer 792 is 40% or more). The conductivity of the charge generation layer 792 may be lower than the conductivity of the conductor 772 or the conductivity of the conductor 788.

[0282] The light-emitting device 572 may have a configuration shown in FIG. 20D . FIG. 20D shows a light-emitting device 572 having a tandem structure in which three EL layers (EL layer 786a, EL layer 786b, and EL layer 786c) are provided between the conductor 772 and the conductor 788, and a charge generation layer 792 is provided between the EL layer 786a and the EL layer 786b and between the EL layer 786b and the EL layer 786c. Here, the EL layer 786a, the EL layer 786b, and the EL layer 786c may have a configuration similar to that of the EL layer 786 shown in FIG. 20B . By configuring the light-emitting device 572 as shown in FIG. 20D , the current efficiency and external quantum efficiency of the light-emitting device 572 can be further improved. Therefore, the display device 100 can display images with even higher brightness. Furthermore, the power consumption of the display device 100 can be further reduced.

[0283] The light-emitting device 572 may have a configuration shown in FIG. 20E. FIG. 20E shows a light-emitting device 572 having a tandem structure in which n EL layers (EL layer 786(1) to EL layer 786(n)) are provided between a conductor 772 and a conductor 788, and a charge generation layer 792 is provided between each of the EL layers 786. Here, the EL layers 786(1) to EL layer 786(n) can have the same configuration as the EL layer 786 shown in FIG. 20B. Note that FIG. 20E shows the EL layer 786(1), the EL layer 786(m), and the EL layer 786(n) among the EL layers 786. Here, m is an integer equal to or greater than 2 and less than n, and n is an integer equal to or greater than m. The larger the value of n, the more the current efficiency and external quantum efficiency of the light-emitting device 572 can be improved. Therefore, a brighter image can be displayed on the display device 100. Furthermore, the power consumption of the display device 100 can be reduced.

[0284] The constituent materials that can be used for the light-emitting device 572 will now be described.

[0285] [Conductor 772 and Conductor 788] The conductors 772 and 788 can be formed from any combination of the following materials, as long as they function as anodes and cathodes. For example, metals, alloys, electrically conductive compounds, and mixtures thereof can be used. Specific examples include In-Sn oxide (ITO), In-Si-Sn oxide (ITSO), In-Zn oxide, and In-W-Zn oxide. Other metals that can be used include aluminum (Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn), indium (In), tin (Sn), molybdenum (Mo), tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium (Y), and neodymium (Nd), as well as alloys containing any combination of these metals. Other examples that can be used include elements belonging to Group 1 or 2 of the periodic table (e.g., lithium (Li), cesium (Cs), calcium (Ca), and strontium (Sr)) that are not listed above, rare earth metals such as europium (Eu) and ytterbium (Yb), and alloys containing appropriate combinations of these, as well as graphene.

[0286] [Hole injection layer 721 and hole transport layer 722] The hole-injection layer 721 is a layer that injects holes from the conductor 772, which is an anode, or the charge-generation layer 792 into the EL layer 786 and contains a material with high hole-injection properties. Here, the EL layer 786 includes an EL layer 786a, an EL layer 786b, an EL layer 786c, and EL layers 786(1) to 786(n).

[0287] Examples of materials with high hole injection properties include transition metal oxides such as molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, and manganese oxide. In addition, phthalocyanine compounds, aromatic amine compounds, polymers, and the like can also be used.

[0288] A composite material containing a hole-transporting material and an acceptor material (electron-accepting material) can also be used as a material with high hole-injection properties. In this case, electrons are extracted from the hole-transporting material by the acceptor material, generating holes in the hole-injection layer 721, and the holes are injected into the light-emitting layer 723 via the hole-transporting layer 722. Note that the hole-injection layer 721 may be formed as a single layer made of a composite material containing a hole-transporting material and an acceptor material (electron-accepting material), or may be formed by laminating the hole-transporting material and the acceptor material (electron-accepting material) as separate layers.

[0289] The hole-transporting layer 722 is a layer that transports holes injected from the conductor 772 by the hole-injecting layer 721 to the light-emitting layer 723. The hole-transporting layer 722 is a layer containing a hole-transporting material. It is particularly preferable to use a hole-transporting material used for the hole-transporting layer 722 that has a HOMO level that is the same as or close to that of the hole-injecting layer 721.

[0290] As an acceptor material used for the hole-injection layer 721, an oxide of a metal belonging to Groups 4 to 8 of the periodic table can be used. Specific examples include molybdenum oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, tungsten oxide, manganese oxide, and rhenium oxide. Among them, molybdenum oxide is particularly preferable because it is stable in the air, has low hygroscopicity, and is easy to handle. Other organic acceptors that can be used include quinodimethane derivatives, chloranil derivatives, and hexaazatriphenylene derivatives.

[0291] The hole transporting material used in the hole injection layer 721 and the hole transporting layer 722 is 10 -6 cm 2 A substance having a hole mobility of 1 / Vs or more is preferred. Note that other substances can be used as long as they have a higher hole transporting property than an electron transporting property.

[0292] The hole transporting material is preferably a π-electron rich heteroaromatic compound (for example, a carbazole derivative or an indole derivative) or an aromatic amine compound.

[0293] However, the hole transport material is not limited to the above, and one or a combination of various known materials can be used as the hole transport material for the hole injection layer 721 and the hole transport layer 722. The hole transport layer 722 may each be formed from a plurality of layers. That is, for example, a first hole transport layer and a second hole transport layer may be stacked.

[0294] [Light-emitting layer 723] The light-emitting layer 723 is a layer containing a light-emitting substance. Note that, 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 is appropriately used. Here, as shown in FIGS. 20C, 20D, and 20E, when the light-emitting device 572 has multiple EL layers, a structure that emits different light colors (e.g., white light emission obtained by combining complementary light colors) can be achieved by using different light-emitting substances for the light-emitting layers 723 provided in the EL layers 786a and 786b. For example, when the light-emitting device 572 has the structure shown in FIG. 20C, the light-emitting layer 723 provided in the EL layer 786a and the light-emitting layer 723 provided in the EL layer 786b may use different light-emitting substances, thereby making the light-emitting color of the EL layer 786a and the light-emitting layer 786b different. Note that one light-emitting layer may have a stacked structure containing different light-emitting substances.

[0295] The light-emitting layer 723 may contain one or more organic compounds (host materials, assist materials) in addition to a light-emitting substance (guest material). As the one or more organic compounds, one or both of a hole-transporting material and an electron-transporting material can be used.

[0296] There is no particular limitation on the light-emitting substance that can be used for the light-emitting layer 723, and a light-emitting substance that converts singlet excitation energy into light emission in the visible light region or a light-emitting substance that converts triplet excitation energy into light emission in the visible light region can be used. Note that examples of the light-emitting substance include the following:

[0297] Examples of luminescent substances that convert singlet excitation energy into luminescence include fluorescent substances (fluorescent materials), such as pyrene derivatives, anthracene derivatives, triphenylene derivatives, fluorene derivatives, carbazole derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, dibenzoquinoxaline derivatives, quinoxaline derivatives, pyridine derivatives, pyrimidine derivatives, phenanthrene derivatives, naphthalene derivatives, etc. Pyrene derivatives are particularly preferred because of their high luminescence quantum yield.

[0298] Examples of luminescent materials that convert triplet excitation energy into luminescence include phosphorescent materials and thermally activated delayed fluorescence (TADF) materials.

[0299] Examples of phosphorescent materials include organometallic complexes, metal complexes (platinum complexes), rare earth metal complexes, etc. These materials emit different luminescent colors (emission peaks), so they can be appropriately selected and used as needed.

[0300] The blue light-emitting substance may have a photoluminescence peak wavelength of 430 nm or more and 470 nm or less, more preferably 430 nm or more and 460 nm or less. The green light-emitting substance may have a photoluminescence peak wavelength of 500 nm or more and 540 nm or less, more preferably 500 nm or more and 530 nm or less. The red light-emitting substance may have a photoluminescence peak wavelength of 610 nm or more and 680 nm or less, more preferably 620 nm or more and 680 nm or less. Photoluminescence measurement may be performed using either a solution or a thin film.

[0301] By using such a compound in combination with the microcavity effect, the above-mentioned chromaticity can be more easily achieved. In this case, the film thickness of the semi-transmissive / semi-reflective electrode (metal thin film portion) required to obtain the microcavity effect is preferably 20 nm or more and 40 nm or less, and more preferably greater than 25 nm and 40 nm or less. However, if the film thickness exceeds 40 nm, there is a possibility that the efficiency will decrease.

[0302] One or more substances having a larger energy gap than that of the light-emitting substance (guest material) may be selected and used as the organic compound (host material, assist material) used in the light-emitting layer 723. Note that the above-described hole-transporting material and the later-described electron-transporting material can also be used as the host material or the assisting material, respectively.

[0303] When the light-emitting substance is a fluorescent material, the host material is preferably an organic compound having a high energy level in a singlet excited state and a low energy level in a triplet excited state, such as an anthracene derivative or a tetracene derivative.

[0304] When the light-emitting substance is a phosphorescent material, an organic compound having a triplet excitation energy greater than the triplet excitation energy (energy difference between the ground state and the triplet excited state) of the light-emitting substance may be selected as the host material. In this case, in addition to zinc or aluminum-based metal complexes, oxadiazole derivatives, triazole derivatives, benzimidazole derivatives, quinoxaline derivatives, dibenzoquinoxaline derivatives, dibenzothiophene derivatives, dibenzofuran derivatives, pyrimidine derivatives, triazine derivatives, pyridine derivatives, bipyridine derivatives, phenanthroline derivatives, aromatic amines, carbazole derivatives, etc. may be used.

[0305] When a plurality of organic compounds are used in the light-emitting layer 723, it is preferable to use a compound that forms an exciplex mixed with a light-emitting substance. In this case, various organic compounds can be used in appropriate combination. However, in order to efficiently form an exciplex, it is particularly preferable to combine a compound that easily accepts holes (hole-transporting material) with a compound that easily accepts electrons (electron-transporting material). Note that the materials shown in this embodiment can be used as specific examples of the hole-transporting material and the electron-transporting material.

[0306] TADF materials are materials that can upconvert a triplet excited state to a singlet excited state with a small amount of thermal energy (reverse intersystem crossing), and efficiently emit light (fluorescence) from the singlet excited state. The conditions for efficiently obtaining thermally activated delayed fluorescence include an energy difference between the triplet excited level and the singlet excited level of 0 eV or more and 0.2 eV or less, preferably 0 eV or more and 0.1 eV or less. The delayed fluorescence in TADF materials refers to light emission that has a spectrum similar to that of normal fluorescence, but has a significantly long lifetime. The lifetime is approximately 10 -6 seconds or more, preferably 10 -3 More than a second.

[0307] Examples of TADF materials include fullerenes and their derivatives, acridine derivatives such as proflavine, eosin, etc. Also included are metal-containing porphyrins containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd).

[0308] In addition, a heterocyclic compound having a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring can be used. Note that a substance in which a π-electron-rich heteroaromatic ring and a π-electron-deficient heteroaromatic ring are directly bonded is particularly preferable because the donor property of the π-electron-rich heteroaromatic ring and the acceptor property of the π-electron-deficient heteroaromatic ring are both strengthened, and the energy difference between the singlet excited state and the triplet excited state is reduced.

[0309] When using a TADF material, it can also be used in combination with other organic compounds.

[0310] [Electron transport layer 724] The electron transport layer 724 is a layer that transports electrons injected from the conductor 788 by the electron injection layer 725 to the light-emitting layer 723. Note that the electron transport layer 724 is a layer containing an electron-transporting material. The electron-transporting material used for the electron transport layer 724 has a concentration of 1×10 -6 cm 2 A substance having an electron mobility of 1 / Vs or more is preferred. Note that other substances can be used as long as they have a higher electron transporting property than a hole transporting property.

[0311] Examples of electron transporting materials include metal complexes having a quinoline ligand, a benzoquinoline ligand, an oxazole ligand, or a thiazole ligand, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, pyridine derivatives, bipyridine derivatives, etc. In addition, π-electron-deficient heteroaromatic compounds such as nitrogen-containing heteroaromatic compounds can also be used.

[0312] The electron transporting layer 724 may have not only a single layer structure but also a stacked structure of two or more layers made of the above substances.

[0313] [Electron injection layer 725] The electron injection layer 725 is a layer containing a substance with high electron injection properties. The electron injection layer 725 may contain lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF), lithium oxide (LiO x ) or an alkaline earth metal, or a compound thereof, can be used. Also, a rare earth metal compound such as erbium fluoride (ErF3) can be used. Furthermore, an electride can be used for the electron injection layer 725. For example, a substance in which electrons are highly concentrated in a mixed oxide of calcium and aluminum can be used as the electride. Note that the above-mentioned substance constituting the electron transport layer 724 can also be used.

[0314] The electron injection layer 725 may be formed using a composite material obtained by mixing an organic compound and an electron donor (donor). Such a composite material has excellent electron injection and electron transport properties because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material that is excellent in transporting the generated electrons. Specifically, the electron transport materials (metal complexes, heteroaromatic compounds, etc.) used in the electron transport layer 724 described above can be used. The electron donor may be any substance that exhibits electron donating properties to the organic compound. Specifically, alkali metals, alkaline earth metals, and rare earth metals are preferred, such as lithium, cesium, magnesium, calcium, erbium, and ytterbium. Alkali metal oxides and alkaline earth metal oxides are also preferred, such as lithium oxide, calcium oxide, and barium oxide. A Lewis base such as magnesium oxide can also be used. Organic compounds such as tetrathiafulvalene (TTF) can also be used.

[0315] [Charge generation layer 792] When a voltage is applied between the conductor 772 and the conductor 788, the charge generation layer 792 injects electrons into the EL layer 786 closest to the conductor 772 and holes into the EL layer 786 opposite the conductor 788, of the two EL layers 786 in contact with the charge generation layer 792. For example, in the light-emitting device 572 shown in FIG. 20C , the charge generation layer 792 injects electrons into the EL layer 786a and holes into the EL layer 786b. The charge generation layer 792 may be configured with an electron acceptor added to a hole-transporting material or with an electron donor added to an electron-transporting material. Alternatively, both of these configurations may be stacked. Forming the charge generation layer 792 using the above-described material can suppress an increase in the driving voltage of the display device 100 when EL layers are stacked.

[0316] When the charge generation layer 792 has a structure in which an electron acceptor is added to a hole-transporting material, examples of the electron acceptor include 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ) and chloranil. Examples of the electron acceptor include oxides of metals belonging to Groups 4 to 8 of the periodic table. Specific examples include vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide.

[0317] When the charge generation layer 792 has a structure in which an electron donor is added to an electron transporting material, the electron donor can be an alkali metal, an alkaline earth metal, a rare earth metal, or a metal belonging to Groups 2 and 13 of the periodic table, or an oxide or carbonate thereof. Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or the like is preferably used. Alternatively, an organic compound such as tetrathianaphthacene can be used as the electron donor.

[0318] The light-emitting device 572 can be fabricated using a vacuum process such as vapor deposition, or a solution process such as spin coating or inkjet printing. When using a vapor deposition method, physical vapor deposition (PVD) methods such as sputtering, ion plating, ion beam deposition, molecular beam deposition, and vacuum deposition, or chemical vapor deposition (CVD) methods can be used. In particular, the functional layers (hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer) and charge generation layer included in the EL layer of the light-emitting device can be formed by a vapor deposition method (vacuum deposition, etc.), a coating method (dip coating, die coating, bar coating, spin coating, spray coating, etc.), a printing method (inkjet printing, screen (stencil printing), offset (lithographic printing), flexography (relief printing), gravure printing, microcontact printing, etc.), or the like.

[0319] The functional layers (hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer) and charge generation layer constituting the EL layer of the light-emitting device described in this embodiment are not limited to the materials described above. Other materials may be used in combination as long as they fulfill the functions of each layer. Examples of usable materials include high molecular weight compounds (oligomers, dendrimers, polymers, etc.), medium molecular weight compounds (compounds between low molecular weight and high molecular weight: molecular weight 400 to 4000), and inorganic compounds (quantum dot materials, etc.). Examples of usable quantum dot materials include colloidal quantum dot materials, alloy quantum dot materials, core-shell quantum dot materials, and core quantum dot materials.

[0320] At least a part of the configuration examples exemplified in this embodiment and the corresponding drawings can be implemented by appropriately combining with other configuration examples or drawings.

[0321] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification.

[0322] (Embodiment 2) In this embodiment, a transistor that can be used in a display device that is one embodiment of the present invention will be described.

[0323] <Transistor configuration example 1> 21A, 21B, and 21C are a top view and a cross-sectional view of a transistor 200A that can be used in a display device of one embodiment of the present invention and the periphery of the transistor 200A. The transistor 200A can be used in the display device of one embodiment of the present invention.

[0324] FIG. 21A is a top view of the transistor 200A. Also, FIGS. 21B and 21C are cross-sectional views of the transistor 200A. Here, FIG. 21B is a cross-sectional view of the portion indicated by the dashed-dotted line A1-A2 in FIG. 21A, and is also a cross-sectional view of the transistor 200A in the channel length direction. Also, FIG. 21C is a cross-sectional view of the portion indicated by the dashed-dotted line A3-A4 in FIG. 21A, and is also a cross-sectional view of the transistor 200A in the channel width direction. Note that in the top view of FIG. 21A, some elements are omitted for clarity.

[0325] As shown in FIG. 21 , the transistor 200A includes a metal oxide 230a disposed on a substrate (not shown), a metal oxide 230b disposed on the metal oxide 230a, a conductor 242a and a conductor 242b disposed spaced apart from each other on the metal oxide 230b, an insulator 280 disposed on the conductors 242a and 242b and having an opening formed between the conductors 242a and 242b, a conductor 260 disposed in the opening, an insulator 250 disposed among the metal oxide 230b, the conductors 242a, 242b, and the insulator 280, and the conductor 260, and a metal oxide 230c disposed among the metal oxide 230b, the conductors 242a, 242b, the insulator 280, and the insulator 250. 21B and 21C, it is preferable that the top surface of the conductor 260 substantially coincides with the top surfaces of the insulators 250, 254, metal oxide 230c, and 280. Note that, hereinafter, the metal oxides 230a, 230b, and 230c may be collectively referred to as metal oxides 230. Furthermore, the conductors 242a and 242b may be collectively referred to as conductors 242.

[0326] 21, the side surfaces of the conductors 242a and 242b facing the conductor 260 have a substantially vertical shape. Note that the transistor 200A shown in FIG. 21 is not limited to this, and the angle formed between the side surface and the bottom surface of the conductors 242a and 242b may be 10° or more and 80° or less, preferably 30° or more and 60° or less. Furthermore, the opposing side surfaces of the conductors 242a and 242b may have multiple surfaces.

[0327] 21, it is preferable that an insulator 254 be disposed between the insulator 224, the metal oxide 230a, the metal oxide 230b, the conductor 242a, the conductor 242b, and the metal oxide 230c and the insulator 280. Here, it is preferable that the insulator 254 be in contact with the side surface of the metal oxide 230c, the top and side surfaces of the conductor 242a, the top and side surfaces of the conductor 242b, the side surfaces of the metal oxide 230a and the metal oxide 230b, and the top surface of the insulator 224, as shown in FIGS.

[0328] Although the transistor 200A has been described as having a three-layer structure of the metal oxide 230a, the metal oxide 230b, and the metal oxide 230c in and around a region where a channel is formed (hereinafter also referred to as a channel formation region), the present invention is not limited to this. For example, a two-layer structure of the metal oxide 230b and the metal oxide 230c or a stacked structure of four or more layers may be provided. Furthermore, the transistor 200A has been described as having a two-layer structure of the conductor 260, but the present invention is not limited to this. For example, the conductor 260 may have a single-layer structure or a stacked structure of three or more layers. Furthermore, each of the metal oxide 230a, the metal oxide 230b, and the metal oxide 230c may have a stacked structure of two or more layers.

[0329] For example, when metal oxide 230c has a layered structure consisting of a first metal oxide and a second metal oxide on the first metal oxide, it is preferable that the first metal oxide has a composition similar to that of metal oxide 230b, and the second metal oxide has a composition similar to that of metal oxide 230a.

[0330] Here, the conductor 260 functions as the gate electrode of the transistor, and the conductors 242a and 242b function as the source and drain electrodes, respectively. As described above, the conductor 260 is formed so as to be embedded in the opening of the insulator 280 and in the region sandwiched between the conductors 242a and 242b. Here, the arrangement of the conductors 260, 242a, and 242b is selected in a self-aligned manner with respect to the opening of the insulator 280. That is, in the transistor 200A, the gate electrode can be positioned between the source and drain electrodes in a self-aligned manner. Therefore, the conductor 260 can be formed without providing an alignment margin, thereby reducing the area occupied by the transistor 200A. This allows for a high-resolution display device. Furthermore, the display device can have a narrow frame.

[0331] As shown in FIG. 21, the conductor 260 preferably has a conductor 260a provided inside the insulator 250 and a conductor 260b provided so as to be embedded inside the conductor 260a.

[0332] The transistor 200A preferably includes an insulator 214 disposed on a substrate (not shown), an insulator 216 disposed on the insulator 214, a conductor 205 disposed so as to be embedded in the insulator 216, an insulator 222 disposed on the insulator 216 and the conductor 205, and an insulator 224 disposed on the insulator 222. A metal oxide 230a is preferably disposed on the insulator 224.

[0333] An insulator 274 functioning as an interlayer film and an insulator 281 are preferably disposed over the transistor 200A. Here, the insulator 274 is preferably disposed in contact with the top surfaces of the conductor 260, the insulator 250, the insulator 254, the metal oxide 230c, and the insulator 280.

[0334] It is preferable that the insulators 222, 254, and 274 have a function of suppressing the diffusion of at least one of hydrogen (e.g., hydrogen atoms, hydrogen molecules, etc.). For example, it is preferable that the insulators 222, 254, and 274 have lower hydrogen permeability than the insulators 224, 250, and 280. It is also preferable that the insulators 222 and 254 have a function of suppressing the diffusion of at least one of oxygen (e.g., oxygen atoms, oxygen molecules, etc.). For example, it is preferable that the insulators 222 and 254 have lower oxygen permeability than the insulators 224, 250, and 280.

[0335] Here, the insulator 224, the metal oxide 230, and the insulator 250 are separated by the insulators 280 and 281, and the insulators 254 and 274. Therefore, impurities such as hydrogen contained in the insulators 280 and 281 and excess oxygen can be prevented from being mixed into the insulators 224, the metal oxide 230a, the metal oxide 230b, and the insulator 250.

[0336] It is preferable that a conductor 240 (conductor 240a and conductor 240b) electrically connected to the transistor 200A and functioning as a plug is provided. Note that an insulator 241 (insulator 241a and insulator 241b) is provided in contact with the side surface of the conductor 240 functioning as a plug. That is, the insulator 241 is provided in contact with the inner wall of the opening of the insulators 254, 280, 274, and 281. Alternatively, a first conductor of the conductor 240 may be provided in contact with the side surface of the insulator 241, and a second conductor of the conductor 240 may be provided further inward. Here, the height of the top surface of the conductor 240 and the height of the insulator 281 can be made approximately the same. Note that, in the transistor 200A, a configuration in which the first conductor of the conductor 240 and the second conductor of the conductor 240 are stacked is shown, but the present invention is not limited to this. For example, the conductor 240 may be configured to have a single layer or a laminated structure of three or more layers. When the structure has a laminated structure, it may be distinguished by assigning an ordinal number to the order of formation.

[0337] In the transistor 200A, a metal oxide that functions as an oxide semiconductor (hereinafter also referred to as an oxide semiconductor) is preferably used for the metal oxide 230 (metal oxide 230a, metal oxide 230b, and metal oxide 230c) including the channel formation region. For example, a metal oxide having a band gap of 2 eV or more, preferably 2.5 eV or more, is preferably used for the channel formation region of the metal oxide 230.

[0338] The metal oxide preferably contains at least indium (In) or zinc (Zn). In particular, it is preferable that it contains indium (In) and zinc (Zn). Furthermore, it is preferable that it contains an element M in addition to these. The element M can be one or more of aluminum (Al), gallium (Ga), yttrium (Y), tin (Sn), boron (B), titanium (Ti), iron (Fe), nickel (Ni), germanium (Ge), zirconium (Zr), molybdenum (Mo), lanthanum (La), cerium (Ce), neodymium (Nd), hafnium (Hf), tantalum (Ta), tungsten (W), magnesium (Mg), or cobalt (Co). In particular, it is preferable that the element M is one or more of aluminum (Al), gallium (Ga), yttrium (Y), or tin (Sn). Furthermore, it is more preferable that the element M contains either or both of Ga and Sn.

[0339] 21B, the film thickness of the metal oxide 230b in the region that does not overlap with the conductor 242 may be thinner than the film thickness of the region that overlaps with the conductor 242. This is formed by removing a portion of the upper surface of the metal oxide 230b when forming the conductors 242a and 242b. When a conductive film that will become the conductor 242 is formed on the upper surface of the metal oxide 230b, a low-resistance region may be formed near the interface with the conductive film. In this way, by removing the low-resistance region located between the conductors 242a and 242b on the upper surface of the metal oxide 230b, it is possible to prevent a channel from being formed in that region.

[0340] According to one embodiment of the present invention, a display device having high definition and a small transistor can be provided. Alternatively, a display device having high luminance and a transistor with high on-state current can be provided. Alternatively, a display device having high-speed operation and a transistor with stable electrical characteristics can be provided. Alternatively, a display device having low power consumption and a transistor with low off-state current can be provided.

[0341] The detailed structure of the transistor 200A that can be used in the display device of one embodiment of the present invention will be described.

[0342] The conductor 205 is arranged so as to have an overlapping region with the metal oxide 230 and the conductor 260. The conductor 205 is preferably embedded in the insulator 216. Here, it is preferable to improve the flatness of the upper surface of the conductor 205. For example, the average surface roughness (Ra) of the upper surface of the conductor 205 may be 1 nm or less, preferably 0.5 nm or less, and more preferably 0.3 nm or less. This improves the flatness of the insulator 224 formed on the conductor 205, and improves the crystallinity of the metal oxide 230b and the metal oxide 230c.

[0343] Here, the conductor 260 may function as a first gate (also referred to as a top gate) electrode. The conductor 205 may function as a second gate (also referred to as a bottom gate) electrode. In this case, the potential applied to the conductor 205 may be changed independently of the potential applied to the conductor 260, thereby controlling the V th In particular, applying a negative potential to conductor 205 can control the V th It is possible to make the off-state current smaller by making the potential greater than 0 V. Therefore, applying a negative potential to the conductor 205 can make the drain current smaller when the potential applied to the conductor 260 is 0 V than when no potential is applied.

[0344] The conductor 205 is preferably provided to be larger than the channel formation region of the metal oxide 230. In particular, as shown in Fig. 21C, the conductor 205 preferably extends also in a region outside the end portion intersecting with the channel width direction of the metal oxide 230. In other words, the conductor 205 and the conductor 260 preferably overlap with each other with an insulator interposed therebetween on the outside of the side surface of the metal oxide 230 in the channel width direction.

[0345] With the above structure, the channel formation region of the metal oxide 230 can be electrically surrounded by the electric field of the conductor 260 that functions as a first gate electrode and the electric field of the conductor 205 that functions as a second gate electrode.

[0346] 21C, the conductor 205 is extended to function as wiring. However, the present invention is not limited to this, and a conductor that functions as wiring may be provided below the conductor 205.

[0347] It is preferable to use a conductive material containing tungsten, copper, or aluminum as a main component for the conductor 205. Although the conductor 205 is illustrated as a single layer, it may have a multilayer structure, for example, a multilayer structure of titanium or titanium nitride and the above-mentioned conductive material.

[0348] A conductor having a function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), copper atoms, etc. (the impurities are less likely to permeate) may be used below the conductor 205. Alternatively, it is preferable to use a conductor having a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.) (the oxygen is less likely to permeate). Note that in this specification, the function of suppressing the diffusion of impurities or oxygen refers to the function of suppressing the diffusion of any one or all of the impurities or oxygen.

[0349] By using a conductor having a function of suppressing oxygen diffusion under the conductor 205, it is possible to suppress oxidation of the conductor 205 and decrease in conductivity. As the conductor having a function of suppressing oxygen diffusion, it is preferable to use, for example, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like. Therefore, the first conductor of the conductor 205 may be a single layer or a multilayer of the above-mentioned conductive material.

[0350] The insulator 214 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the transistor 200A from the substrate side. Therefore, the insulator 214 is preferably made of an insulating material that has a function of preventing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), and copper atoms (i.e., the impurities are less likely to permeate through the material). Alternatively, the insulator 214 is preferably made of an insulating material that has a function of preventing the diffusion of at least one of oxygen (e.g., oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate through the material).

[0351] For example, it is preferable to use aluminum oxide, silicon nitride, or the like as the insulator 214. This can prevent impurities such as water or hydrogen from diffusing from the substrate side of the insulator 214 to the transistor 200A side. Alternatively, it can prevent oxygen contained in the insulator 224 or the like from diffusing toward the substrate side of the insulator 214.

[0352] The insulators 216, 280, and 281, which function as interlayer films, preferably have a lower dielectric constant than the insulator 214. Using a material with a low dielectric constant as the interlayer film can reduce parasitic capacitance between wirings. For example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine has been added, silicon oxide to which carbon has been added, silicon oxide to which carbon and nitrogen have been added, silicon oxide having vacancies, or the like can be used as appropriate for the insulators 216, 280, and 281.

[0353] The insulators 222 and 224 function as gate insulators.

[0354] Here, the insulator 224 in contact with the metal oxide 230 preferably releases oxygen upon heating. In this specification, oxygen released upon heating is sometimes referred to as excess oxygen. For example, the insulator 224 may be made of silicon oxide, silicon oxynitride, or the like, as appropriate. By providing an insulator containing oxygen in contact with the metal oxide 230, oxygen vacancies in the metal oxide 230 can be reduced, and the reliability of the transistor 200A can be improved.

[0355] Specifically, it is preferable to use an oxide material from which a portion of oxygen is released by heating as the insulator 224. The oxide material from which oxygen is released by heating is an oxide material from which the amount of released oxygen converted into oxygen atoms is 1.0×10 in TDS (Thermal Desorption Spectroscopy) analysis. 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 or more, or 3.0 x 10 20 atoms / cm 3 The oxide film is one having the above properties. The surface temperature of the film during the TDS analysis is preferably in the range of 100°C or higher and 700°C or lower, or 100°C or higher and 400°C or lower.

[0356] 21C, the thickness of the region of insulator 224 that does not overlap with insulator 254 and metal oxide 230b may be thinner than the thickness of the other region. It is preferable that the thickness of the region of insulator 224 that does not overlap with insulator 254 and metal oxide 230b is a thickness that allows sufficient diffusion of the oxygen.

[0357] Similar to the insulator 214, etc., the insulator 222 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the transistor 200A from the substrate side. For example, the insulator 222 preferably has lower hydrogen permeability than the insulator 224. By surrounding the insulator 224, the metal oxide 230, the insulator 250, etc. with the insulators 222, 254, and 274, it is possible to prevent impurities such as water or hydrogen from entering the transistor 200A from the outside.

[0358] Furthermore, the insulator 222 preferably has a function of suppressing the diffusion of at least one of oxygen (e.g., oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate). For example, the insulator 222 preferably has lower oxygen permeability than the insulator 224. The insulator 222 preferably has a function of suppressing the diffusion of oxygen and impurities, which can reduce the diffusion of oxygen contained in the metal oxide 230 toward the substrate side. Furthermore, the insulator 222 can suppress the reaction of the conductor 205 with the insulator 224 and the oxygen contained in the metal oxide 230.

[0359] The insulator 222 may be an insulator containing an oxide of one or both of aluminum and hafnium, which are insulating materials. Aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate) is preferably used as the insulator containing an oxide of one or both of aluminum and hafnium. When the insulator 222 is formed using such a material, the insulator 222 functions as a layer that suppresses oxygen release from the metal oxide 230 and the intrusion of impurities such as hydrogen into the metal oxide 230 from the periphery of the transistor 200A.

[0360] Alternatively, for example, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide may be added to these insulators. Alternatively, these insulators may be nitrided. Silicon oxide, silicon oxynitride, or silicon nitride may be stacked on the above insulators.

[0361] The insulator 222 may be a single layer or a multilayer of an insulator containing a so-called high-k material, such as aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). As transistors become smaller and more highly integrated, thinning of the gate insulator can cause problems such as leakage current. Using a high-k material for the insulator that functions as the gate insulator allows for a reduction in the gate potential during transistor operation while maintaining the physical film thickness.

[0362] The insulator 222 and the insulator 224 may have a stacked structure of two or more layers. In this case, the stacked structure is not limited to the stacked structure made of the same material, and may be a stacked structure made of different materials. For example, an insulator similar to the insulator 224 may be provided below the insulator 222.

[0363] The metal oxide 230 includes a metal oxide 230a, a metal oxide 230b on the metal oxide 230a, and a metal oxide 230c on the metal oxide 230b. By providing the metal oxide 230a below the metal oxide 230b, it is possible to suppress the diffusion of impurities from structures formed below the metal oxide 230a to the metal oxide 230b. Furthermore, by providing the metal oxide 230c on the metal oxide 230b, it is possible to suppress the diffusion of impurities from structures formed above the metal oxide 230c to the metal oxide 230b.

[0364] The metal oxide 230 preferably has a stacked structure of multiple oxide layers with different atomic ratios of each metal atom. For example, when the metal oxide 230 contains at least indium (In) and the element M, the ratio of the number of atoms of the element M contained in the metal oxide 230a to the number of atoms of all elements constituting the metal oxide 230a is preferably higher than the ratio of the number of atoms of the element M contained in the metal oxide 230b to the number of atoms of all elements constituting the metal oxide 230b. Furthermore, the atomic ratio of the element M contained in the metal oxide 230a to In is preferably higher than the atomic ratio of the element M contained in the metal oxide 230b to In. Here, the metal oxide 230c can be any metal oxide that can be used for the metal oxide 230a or the metal oxide 230b.

[0365] The energy of the conduction band minimum of the metal oxide 230a and the metal oxide 230c is preferably higher than the energy of the conduction band minimum of the metal oxide 230b. In other words, the electron affinity of the metal oxide 230a and the metal oxide 230c is preferably lower than the electron affinity of the metal oxide 230b. In this case, the metal oxide 230c is preferably a metal oxide that can be used for the metal oxide 230a. Specifically, the ratio of the number of atoms of the element M contained in the metal oxide 230c to the number of atoms of all elements constituting the metal oxide 230c is preferably higher than the ratio of the number of atoms of the element M contained in the metal oxide 230b to the number of atoms of all elements constituting the metal oxide 230b. Furthermore, the atomic ratio of the element M contained in the metal oxide 230c to In is preferably higher than the atomic ratio of the element M contained in the metal oxide 230b to In.

[0366] Here, the energy level of the conduction band minimum changes smoothly at the junction between the metal oxide 230a, the metal oxide 230b, and the metal oxide 230c. In other words, the energy level of the conduction band minimum at the junction between the metal oxide 230a, the metal oxide 230b, and the metal oxide 230c changes continuously or can be said to be a continuous junction. To achieve this, it is advisable to reduce the defect level density of the mixed layer formed at the interface between the metal oxide 230a and the metal oxide 230b and the interface between the metal oxide 230b and the metal oxide 230c.

[0367] Specifically, the metal oxide 230a and the metal oxide 230b, and the metal oxide 230b and the metal oxide 230c, may have a common element other than oxygen (as a main component), thereby forming a mixed layer with a low density of defect states. For example, when the metal oxide 230b is an In-Ga-Zn oxide, the metal oxide 230a and the metal oxide 230c may be made of an In-Ga-Zn oxide, a Ga-Zn oxide, gallium oxide, or the like. The metal oxide 230c may also have a stacked structure. For example, a stacked structure of an In-Ga-Zn oxide and a Ga-Zn oxide on the In-Ga-Zn oxide, or a stacked structure of an In-Ga-Zn oxide and a gallium oxide on the In-Ga-Zn oxide, may be used. In other words, the metal oxide 230c may have a stacked structure of an In-Ga-Zn oxide and an oxide that does not contain In.

[0368] Specifically, the metal oxide 230a may have an atomic ratio of In:Ga:Zn=1:3:4 or 1:1:0.5. The metal oxide 230b may have an atomic ratio of In:Ga:Zn=4:2:3 or 3:1:2. The metal oxide 230c may have an atomic ratio of In:Ga:Zn=1:3:4, In:Ga:Zn=4:2:3, Ga:Zn=2:1, or Ga:Zn=2:5. Specific examples of the metal oxide 230c having a layered structure include a layered structure of In:Ga:Zn=4:2:3 [atomic ratio] and Ga:Zn=2:1 [atomic ratio], a layered structure of In:Ga:Zn=4:2:3 [atomic ratio] and Ga:Zn=2:5 [atomic ratio], and a layered structure of In:Ga:Zn=4:2:3 [atomic ratio] and gallium oxide.

[0369] In this case, the main carrier path is the metal oxide 230b. By configuring the metal oxide 230a and the metal oxide 230c as described above, the defect state density at the interface between the metal oxide 230a and the metal oxide 230b and at the interface between the metal oxide 230b and the metal oxide 230c can be reduced. This reduces the effect of interface scattering on carrier conduction, allowing the transistor 200A to achieve a high on-state current and high frequency characteristics. Note that, when the metal oxide 230c has a stacked structure, in addition to the effect of reducing the defect state density at the interface between the metal oxide 230b and the metal oxide 230c, it is expected to suppress the diffusion of constituent elements of the metal oxide 230c toward the insulator 250. More specifically, by configuring the metal oxide 230c as a stacked structure and positioning an oxide that does not contain In above the stacked structure, it is possible to suppress the diffusion of In toward the insulator 250. Because the insulator 250 functions as a gate insulator, the diffusion of In leads to poor transistor characteristics. Therefore, by forming the metal oxide 230c into a laminated structure, it is possible to provide a highly reliable display device.

[0370] Conductors 242 (conductors 242a and 242b) functioning as a source electrode and a drain electrode are provided on the metal oxide 230b. Conductor 242 is preferably made of a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, or lanthanum, or an alloy containing any of the above metal elements, or an alloy combining any of the above metal elements. For example, tantalum nitride, titanium nitride, tungsten, a nitride containing titanium and aluminum, a nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, or an oxide containing lanthanum and nickel is preferably used. In addition, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are preferred because they are conductive materials that are resistant to oxidation or materials that maintain conductivity even when they absorb oxygen.

[0371] By providing the conductor 242 so as to be in contact with the metal oxide 230, the oxygen concentration may decrease in the vicinity of the conductor 242 of the metal oxide 230. Furthermore, a metal compound layer containing the metal contained in the conductor 242 and components of the metal oxide 230 may be formed in the vicinity of the conductor 242 of the metal oxide 230. In such a case, the carrier density increases in the region of the metal oxide 230 in the vicinity of the conductor 242, and this region becomes a low-resistance region.

[0372] Here, the region between the conductor 242a and the conductor 242b is formed so as to overlap the opening of the insulator 280. This allows the conductor 260 to be disposed in a self-aligned manner between the conductor 242a and the conductor 242b.

[0373] The insulator 250 functions as a gate insulator. The insulator 250 is preferably disposed in contact with the upper surface of the metal oxide 230c. The insulator 250 can be made of silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide doped with fluorine, silicon oxide doped with carbon, silicon oxide doped with carbon and nitrogen, or silicon oxide having vacancies. Silicon oxide and silicon oxynitride are particularly preferred because they are stable against heat.

[0374] The insulator 250 preferably has a reduced concentration of impurities such as water or hydrogen, similar to the insulator 224. The thickness of the insulator 250 is preferably 1 nm or more and 20 nm or less.

[0375] A metal oxide may be provided between the insulator 250 and the conductor 260. The metal oxide preferably suppresses oxygen diffusion from the insulator 250 to the conductor 260. This makes it possible to suppress oxidation of the conductor 260 due to oxygen in the insulator 250.

[0376] The metal oxide may function as part of the gate insulator. Therefore, when silicon oxide, silicon oxynitride, or the like is used for the insulator 250, it is preferable to use a metal oxide that is a high-k material with a high dielectric constant. By forming the gate insulator into a stacked structure of the insulator 250 and the metal oxide, it is possible to achieve a stacked structure that is thermally stable and has a high dielectric constant. Therefore, it is possible to reduce the gate potential applied during transistor operation while maintaining the physical thickness of the gate insulator. In addition, it is possible to reduce the equivalent oxide thickness (EOT) of the insulator that functions as the gate insulator.

[0377] Specifically, it is possible to use a metal oxide containing one or more selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, etc. In particular, it is preferable to use an insulator containing an oxide of either or both of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate).

[0378] Although the conductor 260 is shown as having a two-layer structure in FIG. 21, it may have a single-layer structure or a laminated structure of three or more layers.

[0379] The conductor 260a is preferably made of a conductor having a function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), copper atoms, etc. Alternatively, it is preferable to use a conductive material having a function of suppressing the diffusion of at least one of oxygen (for example, oxygen atoms, oxygen molecules, etc.).

[0380] The conductor 260a has a function of suppressing oxygen diffusion, which can suppress a decrease in conductivity due to oxidation of the conductor 260b caused by oxygen contained in the insulator 250. As a conductive material having a function of suppressing oxygen diffusion, it is preferable to use, for example, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like.

[0381] The conductor 260b is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. Furthermore, since the conductor 260 also functions as wiring, it is preferable to use a conductor with high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. Furthermore, the conductor 260b may have a layered structure, such as a layered structure of titanium or titanium nitride and the above-mentioned conductive material.

[0382] 21A and 21C, in a region of the metal oxide 230b that does not overlap with the conductor 242, in other words, in the channel formation region of the metal oxide 230, the conductor 260 is arranged to cover the side surface of the metal oxide 230. This makes it easier for the electric field of the conductor 260, which functions as the first gate electrode, to act on the side surface of the metal oxide 230. This increases the on-current of the transistor 200A and improves the frequency characteristics.

[0383] Like the insulator 214, the insulator 254 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the transistor 200A from the insulator 280 side. For example, the insulator 254 preferably has lower hydrogen permeability than the insulator 224. Furthermore, as shown in FIGS. 21B and 21C , the insulator 254 preferably contacts the side surface of the metal oxide 230c, the top and side surfaces of the conductor 242a, the top and side surfaces of the conductor 242b, the side surfaces of the metal oxide 230a and the metal oxide 230b, and the top surface of the insulator 224. This configuration can prevent hydrogen contained in the insulator 280 from entering the metal oxide 230 from the top or side surfaces of the conductor 242a, the conductor 242b, the metal oxide 230a, the metal oxide 230b, and the insulator 224.

[0384] Furthermore, it is preferable that the insulator 254 has a function of suppressing at least one diffusion of oxygen (e.g., oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate). For example, it is preferable that the insulator 254 has lower oxygen permeability than the insulator 280 or the insulator 224.

[0385] The insulator 254 is preferably formed by sputtering. By forming the insulator 254 by sputtering in an oxygen-containing atmosphere, oxygen can be added to the insulator 224 near the region where the insulator 254 is in contact with the insulator 254. This allows oxygen to be supplied from this region to the metal oxide 230 through the insulator 224. The insulator 254 has a function of suppressing upward oxygen diffusion, thereby preventing oxygen from diffusing from the metal oxide 230 to the insulator 280. The insulator 222 has a function of suppressing downward oxygen diffusion, thereby preventing oxygen from diffusing from the metal oxide 230 toward the substrate. In this way, oxygen is supplied to the channel formation region of the metal oxide 230. This reduces oxygen vacancies in the metal oxide 230 and suppresses the transistor from becoming normally on.

[0386] For example, an insulator containing an oxide of one or both of aluminum and hafnium may be formed as the insulator 254. Note that as the insulator containing an oxide of one or both of aluminum and hafnium, it is preferable to use aluminum oxide, hafnium oxide, an oxide containing aluminum and hafnium (hafnium aluminate), or the like.

[0387] The insulator 224, the insulator 250, and the metal oxide 230 are covered with the insulator 254, which has a barrier property against hydrogen, and the insulator 280 is separated from the insulator 224, the metal oxide 230, and the insulator 250 by the insulator 254. This makes it possible to prevent impurities such as hydrogen from penetrating from the outside of the transistor 200A, thereby providing the transistor 200A with good electrical characteristics and reliability.

[0388] The insulator 280 is provided over the insulator 224, the metal oxide 230, and the conductor 242 with the insulator 254 interposed therebetween. For example, the insulator 280 preferably includes silicon oxide, silicon oxynitride, silicon nitride oxide, silicon oxide doped with fluorine, silicon oxide doped with carbon, silicon oxide doped with carbon and nitrogen, silicon oxide having vacancies, or the like. Silicon oxide and silicon oxynitride are particularly preferred because they are thermally stable. Materials such as silicon oxide, silicon oxynitride, and silicon oxide having vacancies are particularly preferred because they can easily form a region containing oxygen that is released by heating.

[0389] It is preferable that the concentration of impurities such as water or hydrogen is reduced in the insulator 280. The top surface of the insulator 280 may be flattened.

[0390] Similar to the insulator 214, the insulator 274 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the insulator 280 from above. As the insulator 274, for example, an insulator that can be used for the insulator 214, the insulator 254, etc. may be used.

[0391] An insulator 281 functioning as an interlayer film is preferably provided over the insulator 274. Like the insulator 224 and the like, the insulator 281 preferably has a reduced concentration of impurities such as water or hydrogen.

[0392] The conductor 240a and the conductor 240b are arranged in openings formed in the insulator 281, the insulator 274, the insulator 280, and the insulator 254. The conductor 240a and the conductor 240b are arranged opposite each other with the conductor 260 interposed therebetween. The height of the upper surfaces of the conductor 240a and the conductor 240b may be flush with the upper surface of the insulator 281.

[0393] Note that insulator 241a is provided in contact with the inner walls of the openings of insulators 281, 274, 280, and 254, and a first conductor of conductor 240a is formed in contact with the side surface of insulator 241a. Conductor 242a is located on at least a portion of the bottom of the openings, and conductor 240a is in contact with conductor 242a. Similarly, insulator 241b is provided in contact with the inner walls of the openings of insulators 281, 274, 280, and 254, and a first conductor of conductor 240b is formed in contact with the side surface of insulator 241b. Conductor 242b is located on at least a portion of the bottom of the openings, and conductor 240b is in contact with conductor 242b.

[0394] The conductors 240a and 240b are preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductors 240a and 240b may have a layered structure.

[0395] When the conductor 240 has a layered structure, it is preferable to use the above-mentioned conductors that have the function of suppressing the diffusion of impurities such as water or hydrogen for the conductors in contact with the metal oxide 230a, the metal oxide 230b, the conductor 242, the insulator 254, the insulator 280, the insulator 274, and the insulator 281. For example, it is preferable to use tantalum, tantalum nitride, titanium, titanium nitride, ruthenium, or ruthenium oxide. Furthermore, the conductive material that has the function of suppressing the diffusion of impurities such as water or hydrogen may be used in a single layer or a layered structure. Using such a conductive material can prevent oxygen added to the insulator 280 from being absorbed by the conductors 240a and 240b. Furthermore, it is possible to suppress impurities such as water or hydrogen from layers above the insulator 281 from being mixed into the metal oxide 230 through the conductors 240a and 240b.

[0396] The insulators 241a and 241b may be, for example, insulators that can be used for the insulator 254. The insulators 241a and 241b are provided in contact with the insulator 254, and therefore can prevent impurities such as water or hydrogen from the insulator 280 from being mixed into the metal oxide 230 through the conductors 240a and 240b. Furthermore, oxygen contained in the insulator 280 can be prevented from being absorbed by the conductors 240a and 240b.

[0397] Although not shown, a conductor functioning as wiring may be disposed in contact with the upper surface of the conductor 240a and the upper surface of the conductor 240b. The conductor functioning as wiring is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductor may also have a layered structure, for example, a layered structure of titanium or titanium nitride and the above-mentioned conductive material. The conductor may be formed so as to be embedded in an opening provided in an insulator.

[0398] <Transistor configuration example 2> 22A, 22B, and 22C are a top view and a cross-sectional view of a transistor 200B that can be used in a display device of one embodiment of the present invention and the periphery of the transistor 200B. The transistor 200B is a variation of the transistor 200A.

[0399] FIG. 22A is a top view of the transistor 200B. Also, FIGS. 22B and 22C are cross-sectional views of the transistor 200B. Here, FIG. 22B is a cross-sectional view of the portion indicated by the dashed-dotted line B1-B2 in FIG. 22A, and is also a cross-sectional view of the transistor 200B in the channel length direction. Also, FIG. 22C is a cross-sectional view of the portion indicated by the dashed-dotted line B3-B4 in FIG. 22A, and is also a cross-sectional view of the transistor 200B in the channel width direction. Note that in the top view of FIG. 22A, some elements are omitted for clarity.

[0400] In the transistor 200B, the conductor 242a and the conductor 242b have regions overlapping with the metal oxide 230c, the insulator 250, and the conductor 260. This enables the transistor 200B to have a high on-state current. Furthermore, the transistor 200B can be easily controlled.

[0401] The conductor 260 functioning as the gate electrode includes a conductor 260a and a conductor 260b on the conductor 260a. The conductor 260a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms. Alternatively, the conductor 260a is preferably made of a conductive material that has the function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.).

[0402] The conductor 260a has the function of suppressing oxygen diffusion, which improves the material selectivity of the conductor 260b. In other words, the presence of the conductor 260a suppresses oxidation of the conductor 260b, preventing a decrease in conductivity.

[0403] It is preferable to provide the insulator 254 so as to cover the top surface and side surfaces of the conductor 260, the side surfaces of the insulator 250, and the side surfaces of the metal oxide 230c. Note that the insulator 254 is preferably made of an insulating material that has a function of suppressing the diffusion of impurities such as water or hydrogen, and oxygen.

[0404] Providing the insulator 254 can suppress oxidation of the conductor 260. Furthermore, including the insulator 254 can suppress diffusion of impurities such as water and hydrogen contained in the insulator 280 into the transistor 200B.

[0405] <Transistor configuration example 3> 23A, 23B, and 23C are a top view and a cross-sectional view of a transistor 200C that can be used in a display device of one embodiment of the present invention and the periphery of the transistor 200C. The transistor 200C is a variation of the transistor 200A.

[0406] FIG. 23A is a top view of the transistor 200C. Also, FIGS. 23B and 23C are cross-sectional views of the transistor 200C. Here, FIG. 23B is a cross-sectional view of the portion indicated by the dashed-dotted line C1-C2 in FIG. 23A, and is also a cross-sectional view of the transistor 200C in the channel length direction. Also, FIG. 23C is a cross-sectional view of the portion indicated by the dashed-dotted line C3-C4 in FIG. 23A, and is also a cross-sectional view of the transistor 200C in the channel width direction. Note that in the top view of FIG. 23A, some elements are omitted for clarity.

[0407] The transistor 200C includes an insulator 250 over the metal oxide 230c and a metal oxide 252 over the insulator 250. The transistor 200C also includes a conductor 260 over the metal oxide 252 and an insulator 270 over the conductor 260. The transistor 200C also includes an insulator 271 over the insulator 270.

[0408] The metal oxide 252 preferably has a function of suppressing oxygen diffusion. By providing the metal oxide 252, which suppresses oxygen diffusion, between the insulator 250 and the conductor 260, the diffusion of oxygen into the conductor 260 is suppressed. In other words, it is possible to suppress a decrease in the amount of oxygen supplied to the metal oxide 230. It is also possible to suppress oxidation of the conductor 260 by oxygen.

[0409] The metal oxide 252 may function as a part of the gate electrode. For example, an oxide semiconductor that can be used as the metal oxide 230 can be used as the metal oxide 252. In this case, by forming the conductor 260 by a sputtering method, the electrical resistance value of the metal oxide 252 can be reduced to make it a conductor. This can be called an OC (Oxide Conductor) electrode.

[0410] The metal oxide 252 may function as part of the gate insulator. Therefore, when silicon oxide or silicon oxynitride is used for the insulator 250, it is preferable to use a metal oxide, which is a high-k material with a high dielectric constant, for the metal oxide 252. This layered structure can be thermally stable and have a high dielectric constant. Therefore, it is possible to reduce the gate potential applied during transistor operation while maintaining the physical film thickness. In addition, it is possible to reduce the equivalent oxide thickness (EOT) of the insulating layer that functions as the gate insulator.

[0411] Although the metal oxide 252 in the transistor 200C is shown as a single layer, it may have a stacked structure of two or more layers. For example, a metal oxide functioning as part of the gate electrode and a metal oxide functioning as part of the gate insulator may be stacked.

[0412] When the metal oxide 252 functions as a gate electrode, the on-state current of the transistor 200C can be improved without weakening the influence of the electric field from the conductor 260. Alternatively, when the metal oxide 252 functions as a gate insulator, the physical thickness of the insulator 250 and the metal oxide 252 can maintain a distance between the conductor 260 and the metal oxide 230, thereby suppressing leakage current between the conductor 260 and the metal oxide 230. Therefore, by providing a stacked structure of the insulator 250 and the metal oxide 252, the physical distance between the conductor 260 and the metal oxide 230 and the electric field strength applied from the conductor 260 to the metal oxide 230 can be easily adjusted.

[0413] Specifically, the metal oxide 252 may be a low-resistance oxide semiconductor that can be used for the metal oxide 230. Alternatively, a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like may be used.

[0414] In particular, it is preferable to use an insulating layer containing an oxide of either or both of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate). Hafnium aluminate is particularly preferable because it has higher heat resistance than hafnium oxide film and is therefore less likely to crystallize during heat treatment in a later step. Note that the metal oxide 252 is not an essential component. It may be appropriately designed depending on the desired transistor characteristics.

[0415] The insulator 270 may be made of an insulating material that has the function of suppressing the permeation of impurities such as water or hydrogen, and oxygen. For example, it is preferable to use aluminum oxide or hafnium oxide. This can suppress the conductor 260 from being oxidized by oxygen from above the insulator 270. It can also suppress impurities such as water or hydrogen from above the insulator 270 from being mixed into the metal oxide 230 via the conductor 260 and the insulator 250.

[0416] The insulator 271 functions as a hard mask. By providing the insulator 271, when processing the conductor 260, the side surface of the conductor 260 can be approximately vertical, specifically, the angle between the side surface of the conductor 260 and the substrate surface can be set to 75 degrees or more and 100 degrees or less, preferably 80 degrees or more and 95 degrees or less.

[0417] Note that the insulator 271 may also function as a barrier layer by using an insulating material that has a function of suppressing permeation of impurities such as water or hydrogen and oxygen. In that case, the insulator 270 is not necessary.

[0418] By using the insulator 271 as a hard mask to selectively remove portions of the insulator 270, the conductor 260, the metal oxide 252, the insulator 250, and the metal oxide 230c, their side surfaces can be made approximately coincident and a portion of the surface of the metal oxide 230b can be exposed.

[0419] The transistor 200C has a region 243a and a region 243b on a portion of the exposed surface of the metal oxide 230b, where one of the regions 243a and 243b functions as a source region, and the other of the regions 243a and 243b functions as a drain region.

[0420] The regions 243a and 243b can be formed by introducing impurity elements such as phosphorus or boron into the exposed surface of the metal oxide 230b using, for example, ion implantation, ion doping, plasma immersion ion implantation, plasma treatment, etc. In this embodiment and the like, the term "impurity elements" refers to elements other than the main component elements.

[0421] It is also possible to form regions 243a and 243b by forming a metal film after exposing a portion of the surface of metal oxide 230b and then performing a heat treatment, thereby diffusing elements contained in the metal film into metal oxide 230b.

[0422] The region of the metal oxide 230b into which the impurity element has been introduced has a reduced electrical resistivity, and therefore the region 243a and the region 243b are sometimes referred to as an "impurity region" or a "low-resistance region."

[0423] By using the insulator 271 and / or the conductor 260 as a mask, the regions 243a and 243b can be formed in a self-aligned manner. Therefore, the regions 243a and / or 243b do not overlap with the conductor 260, and parasitic capacitance can be reduced. In addition, an offset region is not formed between the channel formation region and the source / drain region (region 243a or region 243b). By forming the regions 243a and 243b in a self-aligned manner, it is possible to achieve an increase in on-current, a decrease in threshold voltage, an improvement in operating frequency, and the like.

[0424] The transistor 200C includes an insulator 272 on the side surfaces of the insulator 271, the insulator 270, the conductor 260, the metal oxide 252, the insulator 250, and the metal oxide 230c. The insulator 272 is preferably an insulator with a low dielectric constant. For example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine has been added, silicon oxide to which carbon has been added, silicon oxide to which carbon and nitrogen have been added, silicon oxide having vacancies, or a resin is preferable. In particular, using silicon oxide, silicon oxynitride, silicon nitride oxide, or silicon oxide having vacancies for the insulator 272 is preferable because it allows for easy formation of an excess oxygen region in the insulator 272 in a later step. Silicon oxide and silicon oxynitride are also preferable because they are thermally stable. The insulator 272 preferably has a function of diffusing oxygen.

[0425] To further reduce the off-state current, an offset region may be provided between the channel formation region and the source / drain region. The offset region is a region with high electrical resistivity, into which the impurity element described above is not introduced. The offset region can be formed by introducing the impurity element described above after forming the insulator 272. In this case, the insulator 272 also functions as a mask, similar to the insulator 271. Therefore, the impurity element is not introduced into the region of the metal oxide 230b that overlaps with the insulator 272, and the electrical resistivity of the region can be kept high.

[0426] The transistor 200C includes an insulator 272 and an insulator 254 over the metal oxide 230. The insulator 254 is preferably formed by a sputtering method. By using a sputtering method, an insulator with few impurities such as water or hydrogen can be formed.

[0427] Note that an oxide film formed by a sputtering method may extract hydrogen from the structure to be deposited. Therefore, the insulator 254 absorbs hydrogen and water from the metal oxide 230 and the insulator 272, thereby reducing the hydrogen concentrations in the metal oxide 230 and the insulator 272.

[0428] <Transistor constituent materials> The constituent materials that can be used for the transistor will be described.

[0429] 〔substrate〕 The substrate on which the transistor 200A, the transistor 200B, or the transistor 200C is formed may be, for example, an insulating substrate, a semiconductor substrate, or a conductive substrate. Examples of insulating substrates include glass substrates, quartz substrates, sapphire substrates, stabilized zirconia substrates (e.g., yttria-stabilized zirconia substrates), and resin substrates. Examples of semiconductor substrates include semiconductor substrates such as silicon and germanium, and compound semiconductor substrates made of silicon carbide, silicon germanium, gallium arsenide, indium phosphide, zinc oxide, and gallium oxide. Examples of semiconductor substrates include those having an insulating region within the semiconductor substrate, such as an SOI (Silicon-On-Insulator) substrate. Examples of conductive substrates include graphite substrates, metal substrates, alloy substrates, and conductive resin substrates. Other examples include substrates having a metal nitride or a metal oxide. Examples of other substrates include an insulating substrate with a conductor or semiconductor provided thereon, a semiconductor substrate with a conductor or insulator provided thereon, and a conductive substrate with a semiconductor or insulator provided thereon. Alternatively, a substrate having elements provided thereon may be used, such as a capacitor element, a resistor element, a switch element, a light-emitting device, a memory element, and the like.

[0430] [Insulator] Examples of insulators include oxides, nitrides, oxynitrides, nitride oxides, metal oxides, metal oxynitrides, and metal nitride oxides, which have insulating properties.

[0431] For example, as transistors become more miniaturized and highly integrated, thinner gate insulators can cause problems such as leakage current. Using a high-k material for the gate insulator allows for lower voltage operation of the transistor while maintaining the physical film thickness. On the other hand, using a material with a low dielectric constant for the interlayer insulator can reduce the parasitic capacitance between wiring. Therefore, it is best to select materials based on the insulator's function.

[0432] Examples of insulators with a high relative dielectric constant 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.

[0433] Examples of insulators with a low dielectric constant include silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide with fluorine added, silicon oxide with carbon added, silicon oxide with carbon and nitrogen added, silicon oxide with voids, or resin.

[0434] The electrical characteristics of a transistor including an oxide semiconductor can be stabilized by surrounding it with an insulator (such as the insulator 214, the insulator 222, the insulator 254, or the insulator 274) that has a function of suppressing the permeation of impurities such as hydrogen and oxygen. Examples of insulators that have a function of suppressing the permeation of impurities such as hydrogen and oxygen include, for example, a single-layer or stacked insulator containing boron, carbon, nitrogen, oxygen, fluorine, magnesium, aluminum, silicon, phosphorus, chlorine, argon, gallium, germanium, yttrium, zirconium, lanthanum, neodymium, hafnium, or tantalum. Specifically, examples of insulators that have a function of suppressing the permeation of impurities such as hydrogen and oxygen include metal oxides such as aluminum oxide, magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide; and metal nitrides such as aluminum nitride, aluminum titanium nitride, titanium nitride, silicon nitride oxide, and silicon nitride.

[0435] The insulator functioning as the gate insulator is preferably an insulator having a region containing oxygen that is released by heating. For example, by using a structure in which silicon oxide or silicon oxynitride having a region containing oxygen that is released by heating is in contact with the metal oxide 230, oxygen vacancies in the metal oxide 230 can be compensated for.

[0436] 〔conductor〕 As the conductor, it is preferable to use a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, lanthanum, etc., or an alloy containing the above metal element as a component, or an alloy combining the above metal elements. For example, it is preferable to use tantalum nitride, titanium nitride, tungsten, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, oxides containing lanthanum and nickel, etc. Furthermore, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are preferred because they are conductive materials that are resistant to oxidation or maintain conductivity even when absorbing oxygen. Furthermore, semiconductors with high electrical conductivity, such as polycrystalline silicon containing impurity elements such as phosphorus, and silicides such as nickel silicide may also be used.

[0437] A plurality of conductors formed from the above materials may be stacked. For example, a stacked structure may be formed by combining the above-mentioned material containing a metal element and a conductive material containing oxygen. A stacked structure may also be formed by combining the above-mentioned material containing a metal element and a conductive material containing nitrogen. A stacked structure may also be formed by combining the above-mentioned material containing a metal element, a conductive material containing oxygen, and a conductive material containing nitrogen.

[0438] When a metal oxide is used for the channel formation region of a transistor, a conductor functioning as a gate electrode preferably has a stacked structure of a combination of a material containing the metal element and a conductive material containing oxygen. In this case, the conductive material containing oxygen is preferably provided on the channel formation region side. By providing the conductive material containing oxygen on the channel formation region side, oxygen released from the conductive material is easily supplied to the channel formation region.

[0439] In particular, as a conductor functioning as a gate electrode, it is preferable to use a conductive material containing oxygen and a metal element contained in the metal oxide in which the channel is formed. Alternatively, a conductive material containing the above-mentioned metal element and nitrogen may be used. For example, a conductive material containing nitrogen, such as titanium nitride or tantalum nitride, may be used. Alternatively, indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or indium tin oxide doped with silicon may be used. Furthermore, indium gallium zinc oxide containing nitrogen may be used. By using such a material, hydrogen contained in the metal oxide in which the channel is formed may be captured. Alternatively, hydrogen introduced from an external insulator or the like may be captured.

[0440] At least a part of the configuration examples exemplified in this embodiment and the corresponding drawings can be implemented by appropriately combining with other configuration examples or drawings.

[0441] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification.

[0442] (Embodiment 3) In this embodiment, a metal oxide (hereinafter also referred to as an oxide semiconductor) that can be used for the OS transistor described in the above embodiment will be described.

[0443] <Classification of crystal structures> First, classification of crystal structures in oxide semiconductors will be described with reference to Fig. 24A, which is a diagram illustrating classification of crystal structures of oxide semiconductors, typically IGZO (a metal oxide containing In, Ga, and Zn).

[0444] As shown in FIG. 24A, oxide semiconductors are broadly classified into "amorphous," "crystalline," and "crystal." "Amorphous" includes completely amorphous. "Crystalline" includes c-axis-aligned crystalline (CAAC), nanocrystalline (nc), and cloud-aligned composite (CAC). The "Crystalline" classification excludes single crystal, polycrystal, and completely amorphous. "Crystalline" includes single crystal and polycrystal.

[0445] The structure within the bold frame in Figure 24A is an intermediate state between "Amorphous" and "Crystal" and belongs to a new boundary region (New crystalline phase). In other words, this structure can be described as a structure that is completely different from the energetically unstable "Amorphous" and "Crystal."

[0446] The crystalline structure of a film or substrate can be evaluated using X-ray diffraction (XRD) spectroscopy. Figure 24B shows the XRD spectrum obtained by GIXD (Grazing-Incidence XRD) measurement of a CAAC-IGZO film classified as "Crystalline." The GIXD method is also known as the thin-film method or the Seemann-Bohlin method. Hereinafter, the XRD spectrum obtained by GIXD measurement shown in Figure 24B will be simply referred to as the XRD spectrum. The composition of the CAAC-IGZO film shown in Figure 24B is approximately In:Ga:Zn = 4:2:3 [atomic ratio]. The thickness of the CAAC-IGZO film shown in Figure 24B is 500 nm.

[0447] As shown in Figure 24B, a clear peak indicating crystallinity is detected in the XRD spectrum of the CAAC-IGZO film. Specifically, a peak indicating c-axis orientation is detected near 2θ = 31° in the XRD spectrum of the CAAC-IGZO film. As shown in Figure 24B, the peak near 2θ = 31° is asymmetric with respect to the angle at which the peak intensity is detected.

[0448] The crystalline structure of a film or substrate can be evaluated by a diffraction pattern (also called a nanobeam electron diffraction pattern) observed by nanobeam electron diffraction (NBED). The diffraction pattern of a CAAC-IGZO film is shown in Figure 24C. Figure 24C shows a diffraction pattern observed by NBED, in which an electron beam is incident parallel to the substrate. The composition of the CAAC-IGZO film shown in Figure 24C is approximately In:Ga:Zn = 4:2:3 [atomic ratio]. In nanobeam electron diffraction, electron diffraction is performed using a probe diameter of 1 nm.

[0449] As shown in FIG. 24C, multiple spots indicating c-axis orientation are observed in the diffraction pattern of the CAAC-IGZO film.

[0450] [Structure of oxide semiconductor] Note that oxide semiconductors may be classified differently from those shown in FIG. 24A when focusing on their crystal structures. For example, oxide semiconductors are divided into single-crystal oxide semiconductors and other non-single-crystal oxide semiconductors. Examples of non-single-crystal oxide semiconductors include the above-mentioned CAAC-OS and nc-OS. Non-single-crystal oxide semiconductors include polycrystalline oxide semiconductors, amorphous-like oxide semiconductors (a-like OSs), amorphous oxide semiconductors, and the like.

[0451] Here, the above-mentioned CAAC-OS, nc-OS, and a-like OS will be described in detail.

[0452] [CAAC-OS] CAAC-OS is an oxide semiconductor having multiple crystalline regions, each with its c-axis aligned in a specific direction. The specific direction can be the thickness direction of the CAAC-OS film, the normal direction to the surface on which the CAAC-OS film is formed, or the normal direction to the surface of the CAAC-OS film. A crystalline region is a region with periodic atomic arrangement. Considering an atomic arrangement as a lattice arrangement, a crystalline region can also be a region with a uniform lattice arrangement. Furthermore, CAAC-OS has a region where multiple crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a location where the lattice orientation changes between a region with a uniform lattice arrangement and a region with a different uniform lattice arrangement in the region where multiple crystalline regions are connected. In other words, CAAC-OS is an oxide semiconductor with a c-axis aligned but no clear orientation in the ab-plane direction.

[0453] Each of the multiple crystalline regions is composed of one or more minute crystals (crystals with a maximum diameter of less than 10 nm). When a crystalline region is composed of one minute crystal, the maximum diameter of the crystalline region is less than 10 nm. When a crystalline region is composed of many minute crystals, the size of the crystalline region may be several tens of nm.

[0454] In an In-M-Zn oxide (wherein element M is one or more elements selected from aluminum, gallium, yttrium, tin, titanium, etc.), the CAAC-OS tends to have a layered crystal structure (also referred to as a layered structure) in which a layer containing indium (In) and oxygen (hereinafter referred to as an In layer) and a layer containing element M, zinc (Zn), and oxygen (hereinafter referred to as an (M, Zn) layer) are stacked. Note that indium and element M are mutually substituted. Therefore, the (M, Zn) layer may contain indium. Furthermore, the In layer may contain element M. Furthermore, the In layer may contain Zn. The layered structure is observed as a lattice image in a high-resolution TEM image, for example.

[0455] When the CAAC-OS film is subjected to structural analysis using, for example, an XRD apparatus, a peak indicating c-axis orientation is detected at or near 2θ=31° in out-of-plane XRD measurement using θ / 2θ scan. Note that the position of the peak indicating c-axis orientation (2θ value) may vary depending on the type and composition of the metallic elements constituting the CAAC-OS.

[0456] For example, in the electron diffraction pattern of a CAAC-OS film, multiple bright spots are observed, and the spots are observed at positions that are point-symmetric with respect to the spot of the incident electron beam that has passed through the sample (also called the direct spot).

[0457] When the crystalline region is observed from the specific direction, the lattice arrangement in the crystalline region is basically a hexagonal lattice, but the unit cell is not necessarily a regular hexagon and may be non-regular hexagonal. The distortion may also have a pentagonal, heptagonal, or other lattice arrangement. In the CAAC-OS, no clear grain boundaries can be identified even near the distortion. This indicates that the formation of grain boundaries is suppressed by the distortion of the lattice arrangement. This is thought to be because the CAAC-OS can tolerate distortion due to the lack of close-packed oxygen atom arrangement in the ab-plane direction and the change in interatomic bond distance caused by metal atom substitution.

[0458] A crystal structure with clear grain boundaries is called polycrystalline. Grain boundaries act as recombination centers, trapping carriers and potentially causing a decrease in the on-state current and field-effect mobility of a transistor. Therefore, CAAC-OS, which lacks clear grain boundaries, is one of the crystalline oxides with a crystal structure suitable for use in the semiconductor layer of a transistor. Zn is preferred for use in CAAC-OS. For example, In-Zn oxide and In-Ga-Zn oxide are suitable because they can suppress the generation of grain boundaries more effectively than In oxide.

[0459] CAAC-OS is an oxide semiconductor with high crystallinity and no clear grain boundaries. Therefore, it can be said that the CAAC-OS is less susceptible to a decrease in electron mobility due to grain boundaries. Furthermore, since the crystallinity of an oxide semiconductor can be reduced by the inclusion of impurities or the generation of defects, the CAAC-OS can also be said to be an oxide semiconductor with few impurities and defects (such as oxygen vacancies). Therefore, oxide semiconductors with CAAC-OS have stable physical properties. Therefore, oxide semiconductors with CAAC-OS are heat-resistant and highly reliable. Furthermore, the CAAC-OS is stable even under high temperatures (so-called thermal budget) during the manufacturing process. Therefore, using a CAAC-OS for an OS transistor can increase the flexibility of the manufacturing process.

[0460] [nc-OS] The nc-OS has periodic atomic arrangement in a microscopic region (e.g., a region of 1 nm to 10 nm, particularly a region of 1 nm to 3 nm). In other words, the nc-OS has microcrystalline structures. The size of the microcrystalline structures is, for example, 1 nm to 10 nm, particularly 1 nm to 3 nm, and therefore these microcrystalline structures are also called nanocrystalline structures. Furthermore, the nc-OS exhibits no regularity in the crystal orientation between different nanocrystalline structures. Therefore, the entire film lacks orientation. Therefore, depending on the analytical method, the nc-OS may be indistinguishable from an a-like OS or an amorphous oxide semiconductor. For example, when a structural analysis of an nc-OS film is performed using an XRD system, no peaks indicating crystallinity are detected in out-of-plane XRD measurements using θ / 2θ scanning. Furthermore, when an nc-OS film is subjected to electron diffraction (also known as selected-area electron diffraction) using an electron beam with a probe diameter larger than that of nanocrystalline structures (e.g., 50 nm or larger), a halo-like diffraction pattern is observed. On the other hand, when electron diffraction (also called nanobeam electron diffraction) is performed on an nc-OS film using an electron beam with a probe diameter close to or smaller than the size of the nanocrystals (for example, 1 nm to 30 nm), an electron diffraction pattern can be obtained in which multiple spots are observed within a ring-shaped region centered on the direct spot.

[0461] [a-like OS] The a-like OS is an oxide semiconductor having a structure between the nc-OS and the amorphous oxide semiconductor. The a-like OS has a pore or low-density region. That is, the a-like OS has lower crystallinity than the nc-OS and CAAC-OS. Furthermore, the a-like OS has a higher hydrogen concentration in the film than the nc-OS and CAAC-OS.

[0462] [Configuration of oxide semiconductor] Next, the above-mentioned CAC-OS will be described in detail, which relates to the material composition.

[0463] [CAC-OS] CAC-OS is a material structure in which elements constituting a metal oxide are unevenly distributed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof. Note that, hereinafter, a metal oxide in which one or more metal elements are unevenly distributed and the regions containing the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or in the vicinity thereof, is also referred to as a mosaic or patch state.

[0464] Furthermore, CAC-OS has a mosaic structure in which the material is separated into first and second regions, and the first regions are distributed throughout the film (hereinafter also referred to as a cloud structure). That is, CAC-OS is a composite metal oxide having a structure in which the first and second regions are mixed.

[0465] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are denoted as [In], [Ga], and [Zn], respectively. For example, in the CAC-OS in the In-Ga-Zn oxide, the first region is a region where [In] is larger than [In] in the composition of the CAC-OS film. The second region is a region where [Ga] is larger than [Ga] in the composition of the CAC-OS film. Alternatively, for example, the first region is a region where [In] is larger than [In] in the second region and [Ga] is smaller than [Ga] in the second region. The second region is a region where [Ga] is larger than [Ga] in the first region and [In] is smaller than [In] in the first region.

[0466] Specifically, the first region is a region whose main component is indium oxide, indium zinc oxide, or the like. The second region is a region whose main component is gallium oxide, gallium zinc oxide, or the like. In other words, the first region can be rephrased as a region whose main component is In. The second region can be rephrased as a region whose main component is Ga.

[0467] It should be noted that there are cases where a clear boundary between the first region and the second region cannot be observed.

[0468] For example, in the case of CAC-OS in In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) confirms that the CAC-OS has a structure in which a region mainly composed of In (first region) and a region mainly composed of Ga (second region) are unevenly distributed and mixed.

[0469] When CAC-OS is used in a transistor, the conductivity due to the first region and the insulating property due to the second region act in a complementary manner, thereby providing the CAC-OS with a switching function (the ability to turn on and off). In other words, CAC-OS has a conductive function in part of the material and an insulating function in part of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, both functions can be maximized. Therefore, by using CAC-OS in a transistor, a high on-current (I on ), high field-effect mobility (μ), and good switching behavior can be achieved.

[0470] Oxide semiconductors have a variety of structures, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, a CAC-OS, an nc-OS, and a CAAC-OS.

[0471] <Transistors containing oxide semiconductors> Next, a case where the oxide semiconductor is used in a transistor will be described.

[0472] By using the oxide semiconductor for a transistor, a transistor with high field-effect mobility and high reliability can be realized.

[0473] For the transistor, an oxide semiconductor with a low carrier concentration is preferably used. For example, the carrier concentration of the oxide semiconductor is 1×10 17 cm -3 Less than 1 × 10 15 cm -3 or less, more preferably 1 × 10 13 cm -3 Less than 1×10, more preferably 11 cm -3 or less, more preferably 1 × 10 10 cm -3 Less than 1 x 10 -9 cm-3 The above is the case. Note that in order to reduce the carrier concentration of an oxide semiconductor film, the impurity concentration in the oxide semiconductor film may be reduced to reduce the density of defect states. In this specification and the like, a semiconductor having a low impurity concentration and a low density of defect states is referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor. Note that an oxide semiconductor having a low carrier concentration may also be referred to as a highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor.

[0474] A highly purified intrinsic or substantially highly purified intrinsic oxide semiconductor film has a low density of defect states, and therefore, the density of trap states may also be low.

[0475] Charges trapped in the trap states of an oxide semiconductor take a long time to dissipate and may behave like fixed charges. Therefore, a transistor in which a channel formation region is formed in an oxide semiconductor with a high density of trap states may have unstable electrical characteristics.

[0476] Therefore, in order to stabilize the electrical characteristics of a transistor, it is effective to reduce the impurity concentration in the oxide semiconductor. Furthermore, in order to reduce the impurity concentration in the oxide semiconductor, it is preferable to also reduce the impurity concentration in the adjacent film. Impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

[0477] <Impurities> Here, the influence of each impurity in an oxide semiconductor will be described.

[0478] When an oxide semiconductor contains silicon or carbon, which is one of the Group 14 elements, defect levels are formed in the oxide semiconductor. Therefore, the concentrations of silicon or carbon in the oxide semiconductor and those near the interface with the oxide semiconductor (concentrations obtained by SIMS) are calculated as follows: 18 atoms / cm 3 Less than or equal to 2 x 10 17 atoms / cm 3 The following applies.

[0479] When an oxide semiconductor contains an alkali metal or alkaline earth metal, defect levels may be formed and carriers may be generated. Therefore, a transistor using an oxide semiconductor containing an alkali metal or alkaline earth metal is likely to have normally-on characteristics. For this reason, when the concentration of the alkali metal or alkaline earth metal in the oxide semiconductor obtained by SIMS is 1×10 18 atoms / cm 3 Less than or equal to 2 x 10 16 atoms / cm 3 Do the following:

[0480] When nitrogen is contained in an oxide semiconductor, electrons serving as carriers are generated, the carrier concentration increases, and the semiconductor is likely to become n-type. As a result, a transistor using an oxide semiconductor containing nitrogen as a semiconductor tends to have normally-on characteristics. Alternatively, when nitrogen is contained in an oxide semiconductor, trap states may be formed. As a result, the electrical characteristics of the transistor may become unstable. For this reason, the nitrogen concentration in the oxide semiconductor obtained by SIMS is set to 5×10 19 atoms / cm 3 Less than 5 x 10 18 atoms / cm 3 Less than or equal to 1×10 18 atoms / cm 3 Less than 5 × 10, more preferably 17 atoms / cm 3 Do the following:

[0481] Hydrogen contained in an oxide semiconductor reacts with oxygen bonded to a metal atom to form water, which may form an oxygen vacancy. When hydrogen enters the oxygen vacancy, electrons serving as carriers may be generated. Furthermore, some of the hydrogen may bond with oxygen bonded to a metal atom to generate electrons serving as carriers. Therefore, a transistor using an oxide semiconductor containing hydrogen is likely to have normally-on characteristics. For this reason, it is preferable to reduce the amount of hydrogen in the oxide semiconductor as much as possible. Specifically, when the hydrogen concentration in an oxide semiconductor obtained by SIMS is 1×10 20atoms / cm 3 Less than 1 x 10 19 atoms / cm 3 less than 5 × 10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 Make it less than.

[0482] When an oxide semiconductor with sufficiently reduced impurities is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0483] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification.

[0484] (Fourth embodiment) In this embodiment, an electronic device including a display device according to one embodiment of the present invention will be described.

[0485] Fig. 25A is a diagram showing the appearance of camera 8000 with viewfinder 8100 attached. Camera 8000 is provided with an imaging device. Camera 8000 may be, for example, a digital camera. Note that in Fig. 25A, camera 8000 and viewfinder 8100 are separate electronic devices that are detachable, but a viewfinder equipped with a display device may be built into housing 8001 of camera 8000.

[0486] The camera 8000 includes a housing 8001, a display unit 8002, operation buttons 8003, a shutter button 8004, etc. The camera 8000 also has a detachable lens 8006 attached thereto.

[0487] Here, the camera 8000 is configured such that the lens 8006 can be removed from the housing 8001 and replaced, but the lens 8006 and the housing may be integrated.

[0488] The camera 8000 can capture an image by pressing a shutter button 8004. The display portion 8002 also has a function as a touch panel, and an image can be captured by touching the display portion 8002.

[0489] The housing 8001 of the camera 8000 has a mount with electrodes, and can be connected to a finder 8100 as well as a strobe device and the like.

[0490] The finder 8100 includes a housing 8101, a display portion 8102, a button 8103, and the like. The finder 8100 can be an electronic viewfinder.

[0491] The housing 8101 has a mount that engages with the mount of the camera 8000, and the viewfinder 8100 can be attached to the camera 8000. The mount also has electrodes, and images received from the camera 8000 can be displayed on the display portion 8102 via the electrodes.

[0492] The button 8103 functions as a power button, and the display of the display unit 8102 can be switched on and off by the button 8103.

[0493] The display device of one embodiment of the present invention can be applied to the display portion 8002 of the camera 8000 and the display portion 8102 of the finder 8100. The display device of one embodiment of the present invention has extremely high resolution. Therefore, even if the display portion 8002 or the display portion 8102 is close to a user, the pixels are not visible to the user, and a more realistic image can be displayed on the display portion 8002 or the display portion 8102. In particular, an image displayed on the display portion 8102 provided in the finder 8100 is viewed by bringing the user's eye close to the eyepiece of the finder 8100, so the distance between the user and the display portion 8102 is very short. Therefore, it is particularly preferable to apply the display device of one embodiment of the present invention to the display portion 8102. Note that when the display device of one embodiment of the present invention is applied to the display portion 8102, the resolution of an image that can be displayed on the display portion 8102 can be 4K, 5K, or more.

[0494] Note that the resolution of an image that can be captured by an imaging device provided in the camera 8000 is preferably equal to or higher than the resolution of an image that can be displayed on the display unit 8002 or the display unit 8102. For example, if an image with a 4K resolution can be displayed on the display unit 8102, the camera 8000 is preferably provided with an imaging device that can capture an image with a resolution of 4K or higher. Furthermore, for example, if an image with a 5K resolution can be displayed on the display unit 8102, the camera 8000 is preferably provided with an imaging device that can capture an image with a resolution of 5K or higher.

[0495] FIG. 25B is a diagram showing the appearance of the head mounted display 8200.

[0496] The head-mounted display 8200 includes a mounting portion 8201, a lens 8202, a main body 8203, a display portion 8204, and a cable 8205. The mounting portion 8201 has a built-in battery 8206.

[0497] A cable 8205 supplies power from a battery 8206 to the main body 8203. The main body 8203 is equipped with a wireless receiver or the like, and can display an image corresponding to received image data or the like on a display portion 8204. In addition, a camera provided in the main body 8203 captures the movements of the user's eyeballs and eyelids, and calculates the coordinates of the user's line of sight based on the information, thereby allowing the user's line of sight to be used as an input means.

[0498] The wearing unit 8201 may be provided with a plurality of electrodes at positions that come into contact with the user. The main body 8203 may have a function of recognizing the user's line of sight by detecting a current flowing through the electrodes in accordance with the movement of the user's eyeballs. The main body 8203 may also have a function of monitoring the user's pulse by detecting the current flowing through the electrodes. The wearing unit 8201 may also have various sensors such as a temperature sensor, a pressure sensor, and an acceleration sensor, and may have a function of displaying the user's biological information on the display unit 8204. The wearing unit 8201 may also detect the movement of the user's head, etc., and change the image displayed on the display unit 8204 in accordance with the movement.

[0499] The display device of one embodiment of the present invention can be applied to the display portion 8204. This narrows the frame of the head-mounted display 8200, and high-quality images can be displayed on the display portion 8204, resulting in highly realistic images.

[0500] 25C, 25D, and 25E are diagrams showing the appearance of a head mounted display 8300. The head mounted display 8300 includes a housing 8301, a display unit 8302, a band-shaped fixture 8304, and a pair of lenses 8305.

[0501] A user can view the display on the display portion 8302 through the lens 8305. Note that it is preferable to arrange the display portion 8302 in a curved manner. By arranging the display portion 8302 in a curved manner, a user can feel a high sense of presence. Note that although the configuration in which one display portion 8302 is provided has been illustrated in this embodiment, the present invention is not limited thereto, and for example, a configuration in which two display portions 8302 are provided may be used. In this case, if one display portion is arranged at one eye of the user, three-dimensional display using parallax or the like can be performed.

[0502] Note that the display device of one embodiment of the present invention can be applied to the display portion 8302. The display device of one embodiment of the present invention has extremely high resolution; therefore, even when an image is enlarged using the lens 8305 as in FIG. 25E, pixels are not visible to a user, and a more realistic image can be displayed.

[0503] Next, an example of an electronic device different from the electronic device shown in FIGS. 25A to 25E is shown in FIGS. 26A to 26G.

[0504] The electronic device shown in Figures 26A to 26G has a housing 9000, a display unit 9001, a speaker 9003, operation keys 9005 (including a power switch or an operation switch), a connection terminal 9006, a sensor 9007 (including a function to measure force, displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, power, radiation, flow rate, humidity, gradient, vibration, odor, or infrared rays), a microphone 9008, etc.

[0505] The electronic devices shown in FIGS. 26A to 26G have various functions. For example, they may have a function to display various information (still images, videos, text images, etc.) on a display unit, a touch panel function, a function to display a calendar, date, or time, a function to control processing using various software (programs), a wireless communication function, a function to connect to various computer networks using the wireless communication function, a function to send or receive various data using the wireless communication function, a function to read programs or data recorded on a recording medium and display them on a display unit, etc. Note that the functions that the electronic devices shown in FIGS. 26A to 26G can have are not limited to these, and they may have various other functions. Also, although not shown in FIGS. 26A to 26G, the electronic devices may be configured to have multiple display units. Furthermore, the electronic devices may be equipped with a camera or the like to capture still images, capture videos, save the captured images on a recording medium (external or built-in to the camera), display the captured images on a display unit, etc.

[0506] The electronic device shown in FIGS. 26A to 26G will be described in detail below.

[0507] 26A is a perspective view showing a television device 9100. The television device 9100 can incorporate a display unit 9001 with a large screen, for example, 50 inches or more, or 100 inches or more.

[0508] The display device of one embodiment of the present invention can be applied to a display portion 9001 of a television set 9100. This narrows the frame of the television set 9100, and high-quality images can be displayed on the display portion 9001, resulting in highly realistic images.

[0509] FIG. 26B is a perspective view showing a mobile information terminal 9101. The mobile information terminal 9101 has one or more functions selected from, for example, a telephone, a notebook, an information viewing device, and the like. Specifically, it can be used as a smartphone. The mobile information terminal 9101 may also be provided with a speaker 9003, a connection terminal 9006, a sensor 9007, and the like. The mobile information terminal 9101 can display characters and images on multiple surfaces thereof. For example, three operation buttons 9050 (also referred to as operation icons or simply icons) can be displayed on one surface of the display unit 9001. Information 9051, indicated by a dashed rectangle, can be displayed on the other surface of the display unit 9001. Examples of the information 9051 include a display notifying of an incoming email, SNS (social networking service), or phone call; the title of the email or SNS; the name of the sender of the email or SNS; the date and time; the remaining battery level; and the strength of antenna reception. Alternatively, instead of the information 9051, an operation button 9050 or the like may be displayed at the position where the information 9051 is displayed.

[0510] The display device of one embodiment of the present invention can be applied to a display portion 9001 included in a portable information terminal 9101. This allows the portable information terminal 9101 to be miniaturized, and high-quality images can be displayed on the display portion 9001, resulting in highly realistic images.

[0511] FIG. 26C is a perspective view showing mobile information terminal 9102. Mobile information terminal 9102 has a function of displaying information on three or more sides of display unit 9001. Here, an example is shown in which information 9052, information 9053, and information 9054 are displayed on different sides. For example, a user of mobile information terminal 9102 can check the display (information 9053 in this case) while carrying mobile information terminal 9102 in a breast pocket of clothes. Specifically, the telephone number or name of the caller of an incoming call is displayed in a position that can be observed from above mobile information terminal 9102. The user can check the display and decide whether or not to answer the call without taking mobile information terminal 9102 out of their pocket.

[0512] The display device of one embodiment of the present invention can be applied to a display portion 9001 of a portable information terminal 9102. This allows the portable information terminal 9101 to be miniaturized, and high-quality images can be displayed on the display portion 9001, resulting in highly realistic images.

[0513] FIG. 26D is a perspective view showing a wristwatch-type mobile information terminal 9200. The mobile information terminal 9200 can execute various applications, such as mobile phone calls, e-mail, document browsing and creation, music playback, Internet communication, and computer games. The display surface of the display unit 9001 is curved, allowing display along the curved display surface. The mobile information terminal 9200 can also perform short-range wireless communication according to a communication standard. For example, hands-free conversations can be performed by intercommunicating with a wirelessly enabled headset. The mobile information terminal 9200 also has a connection terminal 9006, allowing direct data exchange with another information terminal via a connector. Charging can also be performed via the connection terminal 9006. Charging may be performed by wireless power supply without using the connection terminal 9006.

[0514] The display device of one embodiment of the present invention can be applied to a display portion 9001 included in a portable information terminal 9200. This allows the frame of the portable information terminal 9200 to be narrowed, and high-quality images can be displayed on the display portion 9001, resulting in highly realistic images.

[0515] 26E, 26F, and 26G are perspective views showing a foldable mobile information terminal 9201. Also, FIG. 26E is a perspective view of the mobile information terminal 9201 in an unfolded state, FIG. 26F is a perspective view of the mobile information terminal 9201 in a state in which it is changing from the unfolded state to the folded state, and FIG. 26G is a perspective view of the mobile information terminal 9201 in a folded state. The mobile information terminal 9201 is highly portable in a folded state, and is highly viewable in an unfolded state due to its seamless, wide display area. A display unit 9001 of the mobile information terminal 9201 is supported by three housings 9000 connected by hinges 9055. By bending the two housings 9000 via the hinges 9055, the mobile information terminal 9201 can be reversibly transformed from an unfolded state to a folded state. For example, the portable information terminal 9201 can be bent with a curvature radius of 1 mm or more and 150 mm or less.

[0516] The display device of one embodiment of the present invention can be applied to a display portion 9001 included in a portable information terminal 9201. This allows the frame of the portable information terminal 9201 to be narrowed, and high-quality images can be displayed on the display portion 9001, resulting in highly realistic images.

[0517] At least a part of the configuration examples exemplified in this embodiment and the corresponding drawings can be implemented by appropriately combining with other configuration examples or drawings.

[0518] This embodiment mode can be implemented by appropriately combining at least a part thereof with other embodiment modes described in this specification. [Example]

[0519] In this example, a circuit simulation was used to confirm the boosting operation in the pixel circuit configuration shown in FIG. 1 using the timing chart shown in FIG.

[0520] In the simulation, the transistors 101 and 102 were OS transistors with a channel length of 200 μm and a channel width of 60 μm. The transistors 103 and 104 were OS transistors with a channel length of 60 μm and a channel width of 60 μm. The capacitances of the capacitors 111 and 112 were each 7.26 fF. The voltages applied to the wirings 121 and 122 were set to High and Low, respectively, as 5 V and 0 V. The simulation was performed for the wiring 131 with "Vdata" set to 0.5 V, 1.0 V, 1.5 V, 2.0 V, 2.5 V, 3.0 V, 3.5 V, and 4.0 V. The circuit simulation software used was SmartSpice by Silvaco. The wiring 127 had a "Vref" of 0.5 V, the wiring 128 had a "Vano" of 8.0 V, and the wiring 129 had a "Vcath" of -1.5 V.

[0521] The simulation results are shown in Fig. 27. In Fig. 27, the horizontal axis represents time according to the timing chart, and the vertical axis represents the potential V ND1 Also, the potential V of the node ND1 ND1 The ideal values ​​and simulation results are shown in Table 1.

[0522] In addition, the potential V shown in Table 1 ND1 The ideal value of represents the value obtained by setting the constants a, b, and c in the above-mentioned equation (9) to zero.

[0523] [Table 1]

[0524] As shown in FIG. 27 and Table 1, the potential V of the node ND1 obtained by the simulation ND1It was confirmed that the values ​​were equivalent to the ideal values. The difference from the ideal values ​​is thought to be due to the influence of feedthrough, charge injection, or the like when the transistors 102, 103, and 104, which are represented by constants a, b, and c, are turned off. It was found that the display device according to one embodiment of the present invention can boost a voltage higher than the voltage corresponding to image data supplied to the pixel 10 and supply the boosted voltage to the transistor 101, which functions as a driving transistor. Therefore, it was found that the current flowing through the light-emitting device 114 can be increased. [Example]

[0525] This example shows the results of a simulation performed under conditions different from those of Example 1. See FIG. 1 for the circuit configuration and FIG. 2 for the timing chart.

[0526] In the simulation, the transistors 101 and 102 were OS transistors with a channel length of 200 μm and a channel width of 60 μm. The transistors 103 and 104 were OS transistors with a channel length of 60 μm and a channel width of 60 μm. The capacitances of the capacitors 111 and 112 were each 7.26 fF. The voltages applied to the wirings 121 and 122 were set to High and Low, respectively, as 5 V and 0 V. The simulation was performed with "Vdata" of the wiring 131 set to 4.3 V, "Vref" of the wiring 127 set to 1.1 V, "Vano" of the wiring 128 set to 8.0 V, and "Vcath" of the wiring 129 set to -1.5 V. SPICE was used as the circuit simulation software.

[0527] The simulation results are shown in Fig. 28. In Fig. 28, the horizontal axis represents time according to the timing chart, and the vertical axis represents the potential V of the wiring 121, the wiring 122, the wiring 131, the node ND1, and the node ND2.

[0528] As shown in FIG. 28, it was confirmed that the potential V of the node ND1 obtained by the simulation was 6.1 V, which was higher than the given potential (the potential of the wiring 131). [Explanation of symbols]

[0529] 10: pixel, 10A: pixel, 10B: sub-pixel, 10G: sub-pixel, 10R: sub-pixel, 20: first layer, 30: second layer, 51a: display area, 51b: display area, 51c: display area, 53: pixel electrode, 53a: pixel electrode, 53b: pixel electrode, 53c: pixel electrode, 100: display device, 101: transistor, 102: transistor, 103: transistor, 104: transistor, 105: transistor, 111: capacitor, 112: capacitor, 114: light-emitting device, 121: wiring, 122: wiring, 127: wiring, 128: wiring, 129: wiring, 130: driver driving circuit section, 131: wiring, 140a: driving circuit section, 140b: driving circuit section, 141: wiring, 143: wiring, 150: pixel section, 200A: transistor, 200B: transistor, 200C: transistor, 205: conductor, 214: insulator, 216: insulator, 222: insulator, 224: insulator, 230a: metal oxide, 230b: metal oxide, 230c: metal oxide, 230: metal oxide, 240a: conductor, 240b: conductor, 240: conductor, 241a: insulator, 241b: insulator, 241: insulator, 242a: conductor, 242b: conductor, 242: Conductor, 243a: region, 243b: region, 244: insulator, 250: insulator, 252: metal oxide, 254: insulator, 260a: conductor, 260b: conductor, 260: conductor, 270: insulator, 271: insulator, 272: insulator, 274: insulator, 280: insulator, 281: insulator, 301a: conductor, 301b: conductor, 305: conductor, 311: conductor, 313: conductor, 317: conductor, 321: lower electrode, 323: insulator, 325: upper electrode, 331: conductor, 333: conductor, 335: conductor, 337: conductor, 341: conductor, 343: Conductor, 347: Conductor, 351: Conductor, 353: Conductor, 355: Conductor, 357: Conductor, 361: Insulator, 363: Insulator, 403: Element isolation layer, 405: Insulator, 407: Insulator, 409: Insulator, 411: Insulator, 413: Insulator, 415: Insulator, 417: Insulator, 419: Insulator, 421: Insulator, 441: Transistor, 443: Conductor, 445: Insulator, 447: Semiconductor region, 449a: Low resistance region, 449b: Low resistance region, 451: Conductor, 453: Conductor, 455: Conductor, 457: Conductor, 459: Conductor, 461: Conductor,463: conductor, 465: conductor, 467: conductor, 469: conductor, 471: conductor, 501: insulator, 503: insulator, 505: insulator, 507: insulator, 509: insulator, 572: light-emitting device, 601: transistor, 602: transistor, 603: transistor, 613: insulator, 614: insulator, 616: insulator, 622: insulator, 624: insulator, 644: insulator, 654: insulator, 674: insulator, 680: insulator, 681: insulator, 701: substrate, 705: substrate, 712: sealing material, 716: FPC, 721: hole injection layer, 722: Hole transport layer, 723: light emitting layer, 724: electron transport layer, 725: electron injection layer, 730: insulator, 732: sealing layer, 734: insulator, 736: colored layer, 738: light blocking layer, 750: transistor, 760: connection electrode, 772: conductor, 778: structure, 780: anisotropic conductor, 782: light emitting device, 786a: EL layer, 786b: EL layer, 786c: EL layer, 786: EL layer, 788: conductor, 790: capacitance element, 792: charge generation layer, 800: transistor, 801a: conductor, 801b: conductor, 805: conductor, 811: conductor, 813: conductor, 81 4: Insulator, 816: Insulator, 817: Conductor, 821: Insulator, 822: Insulator, 824: Insulator, 844: Insulator, 853: Conductor, 854: Insulator, 855: Conductor, 874: Insulator, 880: Insulator, 881: Insulator, 8000: Camera, 8001: Housing, 8002: Display, 8003: Operation buttons, 8004: Shutter button, 8006: Lens, 8100: Viewfinder, 8101: Housing, 8102: Display, 8103: Button, 8200: Head-mounted display, 8201: Mounting part, 8202: Lens, 8203: Main body, 8204 : Display unit, 8205: Cable, 8206: Battery, 8300: Head mounted display, 8301: Housing, 8302: Display unit, 8304: Fixing device, 8305: Lens, 9000: Housing, 9001: Display unit, 9003: Speaker, 9005: Operation key, 9006: Connection terminal, 9007: Sensor, 9008: Microphone, 9050: Operation button, 9051: Information, 9052: Information, 9053: Information, 9054: Information, 9055: Hinge, 9100: Television device, 9101: Portable information terminal, 9102: Portable information terminal, 9200: Portable information terminal,9201: Portable information terminals,

Claims

[Claim 1] a first wiring, a second wiring, a third wiring, a fourth wiring, a light emitting device, a first transistor, a second transistor, a third transistor, a fourth transistor, a first capacitance element, and a second capacitance element; one electrode of the light-emitting device is electrically connected to one of the source and drain of the first transistor; a gate of the first transistor is electrically connected to one electrode of the first capacitor element and one of the source and drain of the second transistor; the other of the source and the drain of the first transistor is electrically connected to one electrode of the second capacitor element; one electrode of the second capacitor is electrically connected to the first wiring having a function of supplying a first potential; the other electrode of the second capacitor is electrically connected to the other electrode of the first capacitor, one of the source and the drain of the third transistor, and one of the source and the drain of the fourth transistor; a gate of the second transistor electrically connected to the second wiring; a gate of the fourth transistor is electrically connected to the second wiring; a gate of the third transistor electrically connected to the third wiring; the other of the source and the drain of the second transistor is electrically connected to the fourth wiring; the other of the source and the drain of the third transistor is electrically connected to the fourth wiring; the other of the source and the drain of the fourth transistor is electrically connected to a fifth wiring; A display device, wherein the first wiring, the second wiring, and the third wiring extend in a first direction when viewed from above.

Images