Semiconductor device and driving method thereof

Abstract

Provided is a semiconductor device with a small circuit size. The semiconductor device has first and second circuits. The first circuit has first to nth (n being an integer of 2 or greater) transistors, and the second circuit has (n+1)th to 2nth transistors. The first to nth transistors are connected in parallel, and the (n+1)th to 2nth transistors are connected in series. The first and the second circuits are supplied with first to nth signals. The first circuit has the function of outputting a first potential if all of the first to the nth signals have a potential less than or equal to a first reference potential, and outputting a second potential if at least one of the first to the nth signals has a potential greater than the first reference potential. The second circuit has the function of outputting a third potential if all of the first to the nth signals have a potential greater than a second reference potential, and has the function of outputting the first potential if at least one of the first to the nth signals has a potential less than or equal to the second reference potential.

Description

[Technical field]

[0001] One embodiment of the present invention relates to a semiconductor device and a driving method thereof.

[0002] Note that one embodiment of the present invention is not limited to the above technical field. The technical field of the invention disclosed in this specification relates to an object, a method, or a manufacturing method. Alternatively, one embodiment of the present invention relates to a process, a machine, a manufacture, or a composition of matter. Therefore, examples of the technical field of one embodiment of the present invention disclosed in this specification more specifically include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a power storage device, an imaging device, a memory device, a signal processing device, a processor, an electronic device, a system, a driving method thereof, a manufacturing method thereof, or an inspection method thereof.

[0003] In this specification and the like, the term "semiconductor device" refers to any device that can function by utilizing semiconductor characteristics. Display devices (liquid crystal display devices, light-emitting display devices, etc.), projection devices, lighting devices, electro-optical devices, power storage devices, memory devices, semiconductor circuits, imaging devices, signal processing devices, transmitting / receiving devices, wireless sensors, sensor devices, etc. may be said to include semiconductor devices. [Background technology]

[0004] Semiconductor devices having a function of detecting a potential level have been developed. For example, Patent Document 1 discloses a semiconductor device that detects a potential level of a signal line by using a potential level detection circuit having a comparator. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2007-26670 Summary of the Invention [Problem to be solved by the invention]

[0006] If a comparator is used to detect the potential level, particularly when there are many signals to detect the potential level, many comparators are required, which increases the circuit scale of the semiconductor circuit, leading to an increase in the size of the semiconductor device and an increase in the power consumption of the semiconductor device.

[0007] Moreover, in order to improve characteristics such as gain and input voltage range, a comparator is generally configured with a complementary metal oxide semiconductor (CMOS). That is, the comparator is configured with both an n-channel transistor and a p-channel transistor. Here, for example, a transistor having a metal oxide in a region where a channel is formed (hereinafter also referred to as a channel formation region) (hereinafter also referred to as an OS transistor) is an n-channel transistor. Therefore, if a comparator is configured with only OS transistors, for example, the characteristics of the comparator are significantly degraded.

[0008] Therefore, an object of one embodiment of the present invention is to provide a semiconductor device with a small circuit scale. Another object is to provide a semiconductor device including transistors of the same conductivity type. Another object is to provide a small-sized semiconductor device. Another object is to provide a semiconductor device with low power consumption. Another object is to provide a semiconductor device that can be manufactured by a simple method. Another object is to provide a low-cost semiconductor device. Another object is to provide a semiconductor device that can output a signal with high accuracy. Another object is to provide a semiconductor device that can be operated at high temperature. Another object is to provide a highly reliable semiconductor device. Another object is to provide a novel semiconductor device.

[0009] Another object of the present invention is to provide a method for driving a semiconductor device with a small circuit scale. Another object of the present invention is to provide a method for driving a semiconductor device including transistors of the same polarity. Another object of the present invention is to provide a method for driving a small-sized semiconductor device. Another object of the present invention is to provide a method for driving a semiconductor device with low power consumption. Another object of the present invention is to provide a method for driving a semiconductor device that can be manufactured by a simple method. Another object of the present invention is to provide a method for driving a low-cost semiconductor device. Another object of the present invention is to provide a method for driving a semiconductor device that can output a signal with high accuracy. Another object of the present invention is to provide a method for driving a semiconductor device that can be operated at high temperatures. Another object of the present invention is to provide a method for driving a semiconductor device with high reliability. Another object of the present invention is to provide a novel method for driving a semiconductor 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 will become apparent from the description of the specification, drawings, claims, etc., and it is possible to extract problems other than these from the description of the specification, drawings, claims, etc. [Means for solving the problem]

[0011] One embodiment of the present invention includes a first circuit and a second circuit. The first circuit includes 1st to nth (n is an integer of 2 or more) transistors. The second circuit includes n+1th to 2nth transistors. One of the sources or the drains of the 1st to nth transistors are electrically connected to each other. The other of the sources or the drains of the 1st to nth transistors are electrically connected to each other. The sources and the drains of the n+1th to 2nth transistors are connected in series to each other. The 1st to nth signals are supplied to the first circuit and the second circuit. The circuit has a function of outputting a first potential when any of the potentials of the first to nth signals is equal to or lower than a first reference potential, the first circuit has a function of outputting a second potential when at least one of the potentials of the first to nth signals is higher than the first reference potential, the second circuit has a function of outputting a third potential when any of the potentials of the first to nth signals is higher than a second reference potential, and the second circuit has a function of outputting a first potential when at least one of the potentials of the first to nth signals is lower than a second reference potential.

[0012] Alternatively, in the above aspect, the second potential may be a potential corresponding to the first reference potential, and the third potential may be a potential corresponding to the second reference potential.

[0013] Alternatively, in the above embodiment, the first to 2n-th transistors may be n-channel transistors.

[0014] Alternatively, in the above aspect, the second reference potential may be lower than the first reference potential.

[0015] Alternatively, in the above aspect, the second potential and the third potential may be lower than the first potential.

[0016] Alternatively, in the above embodiment, the first to 2n-th transistors may have a metal oxide in a channel formation region.

[0017] Alternatively, in the above aspect, a semiconductor device may have a 2n+1th transistor and a 2n+2th transistor, one of the source or drain of the 2n+1th transistor being electrically connected to a first circuit, one of the source or drain of the 2n+2th transistor being electrically connected to a second circuit, a second potential being supplied to the other of the source or drain of the 2n+1th transistor, and a third potential being supplied to the other of the source or drain of the 2n+2th transistor.

[0018] Alternatively, in the above aspect, a transistor may be provided that has a 2n+3th transistor and a 2n+4th transistor, one of the source or drain of the 2n+3th transistor being electrically connected to a first circuit, one of the source or drain of the 2n+4th transistor being electrically connected to a second circuit, and a first potential may be supplied to the other of the source or drain of the 2n+3th transistor and the other of the source or drain of the 2n+4th transistor.

[0019] Alternatively, one embodiment of the present invention includes a first circuit and a second circuit, the first circuit includes 1st to nth (n is an integer of 2 or more) transistors, the second circuit includes n+1th to 2nth transistors, the 1st to 2nth transistors have backgates, one of sources or drains of the 1st to nth transistors are electrically connected to each other, the other of the sources or drains of the 1st to nth transistors are electrically connected to each other, the sources and drains of the n+1th to 2nth transistors are connected in series to each other, the 1st to nth signals are supplied to the first circuit and the second circuit, and the 1st to nth transistors have backgates. a first potential is supplied to the back gates of the n+1 to 2n transistors, a second potential is supplied to the back gates of the n+1 to 2n transistors, the first circuit has a function of outputting a third potential when any of the potentials of the first to n signals is lower than a first reference potential, the first circuit has a function of outputting a fourth potential when at least one of the potentials of the first to n signals is higher than the first reference potential, the second circuit has a function of outputting the fourth potential when any of the potentials of the first to n signals is higher than a second reference potential, and the second circuit has a function of outputting the third potential when at least one of the potentials of the first to n signals is lower than a second reference potential.

[0020] Alternatively, in the above embodiment, the first to 2n-th transistors may be n-channel transistors, and the second potential may be higher than the first potential.

[0021] Alternatively, in the above aspect, the fourth potential may be lower than the third potential.

[0022] Alternatively, in the above embodiment, the first to 2n-th transistors may have a metal oxide in a channel formation region.

[0023] Alternatively, in the above aspect, a semiconductor device may have a 2n+1th transistor and a 2n+2th transistor, one of the source or drain of the 2n+1th transistor being electrically connected to a first circuit, one of the source or drain of the 2n+2th transistor being electrically connected to a second circuit, and a fourth potential being supplied to the other of the source or drain of the 2n+1th transistor and the other of the source or drain of the 2n+2th transistor.

[0024] Alternatively, in the above aspect, there may be a 2n+3th transistor and a 2n+4th transistor, one of the source or drain of the 2n+3th transistor being electrically connected to a first circuit, one of the source or drain of the 2n+4th transistor being electrically connected to a second circuit, and a third potential being supplied to the other of the source or drain of the 2n+3th transistor and the other of the source or drain of the 2n+4th transistor.

[0025] Alternatively, one embodiment of the present invention includes a first circuit including 1st to nth transistors (n is an integer of 2 or more), a second circuit including n+1th to 2nth transistors, and a 2n+1th transistor, a 2n+2th transistor, a 2n+3th transistor, and a 2n+4th transistor, in which one of a source or a drain of the 1st to nth transistors is electrically connected to each other, one of a source or a drain of the 1st to nth transistors is electrically connected to each other, one of a source or a drain of the n+1th to 2nth transistors is connected in series to each other, one of a source or a drain of the 2n+1th transistor is electrically connected to the first circuit, one of a source or a drain of the 2n+2th transistor is electrically connected to the second circuit, one of a source or a drain of the 2n+3th transistor is electrically connected to the first circuit, and one of a source or a drain of the 2n+4th transistor is electrically connected to the second circuit. a first potential is supplied to the other of the source or drain of the 2n+3 transistor and the other of the source or drain of the 2n+4 transistor; a second potential is supplied to the other of the source or drain of the 2n+4 transistor; and a third potential is supplied to the other of the source or drain of the 2n+4 transistor; and in a first period, the 2n+1 transistor and the 2n+2 transistor are turned on and the 2n+3 transistor and the 2n+4 transistor are turned off.

[0026] Alternatively, in the above embodiment, the first to 2n-th transistors may be n-channel transistors.

[0027] Alternatively, in the above aspect, the third potential may be lower than the second potential.

[0028] Alternatively, in the above aspect, the second potential and the third potential may be lower than the first potential.

[0029] Alternatively, one embodiment of the present invention includes a first circuit including 1st to nth transistors (n is an integer of 2 or more), a second circuit including n+1th to 2nth transistors, and a 2n+1th transistor, a 2n+2th transistor, a 2n+3th transistor, and a 2n+4th transistor, in which the 1st to 2nth transistors have backgates, one of a source or a drain of the 1st to nth transistors is electrically connected to each other, and the other of the source or the drain of the 1st to nth transistors is electrically connected to each other. a driving method for a semiconductor device in which the n+1-th to 2n-th transistors are electrically connected to each other, the sources and drains of the n+1-th to 2n-th transistors are connected in series with each other, one of the source or the drain of the 2n+1-th transistor is electrically connected to a first circuit, one of the source or the drain of the 2n+2-th transistor is electrically connected to a second circuit, one of the source or the drain of the 2n+3-th transistor is electrically connected to the first circuit, and one of the source or the drain of the 2n+4-th transistor is electrically connected to the second circuit. Thus, the first circuit and the second circuit are supplied with first to n-th signals, the i-th signal is supplied to the gates of the i-th (i is 1 to n) transistor and the n+i-th transistor, a first potential is supplied to the back gates of the first to n-th transistors, a second potential is supplied to the back gates of the n+1-th to 2n-th transistors, a third potential is supplied to the other of the source or drain of the 2n+1-th transistor and the other of the source or drain of the 2n+2-th transistor, and a third potential is supplied to the 2n+3-th transistor. a fourth potential is supplied to the other of the source or drain of the 2n+4th transistor and the other of the source or drain of the 2n+1th transistor and the 2n+2th transistor are turned on and the 2n+3th transistor and the 2n+4th transistor are turned off in a first period, and the 2n+1th transistor and the 2n+2th transistor are turned off and the 2n+3th transistor and the 2n+4th transistor are turned on in a second period.

[0030] Alternatively, in the above embodiment, the first to 2n-th transistors may be n-channel transistors, and the second potential may be higher than the first potential.

[0031] Alternatively, in the above aspect, the fourth potential may be lower than the third potential. Effect of the Invention

[0032] According to one embodiment of the present invention, a semiconductor device with a small circuit scale can be provided. Or a semiconductor device including transistors of the same conductivity type can be provided. Or a small-sized semiconductor device can be provided. Or a semiconductor device with low power consumption can be provided. Or a semiconductor device that can be manufactured by a simple method can be provided. Or a low-cost semiconductor device can be provided. Or a semiconductor device that can output a signal with high accuracy can be provided. Or a semiconductor device that can be operated at high temperature can be provided. Or a highly reliable semiconductor device can be provided. Or a novel semiconductor device can be provided.

[0033] Alternatively, a method for driving a semiconductor device with a small circuit scale can be provided. Alternatively, a method for driving a semiconductor device constituted by transistors of the same polarity can be provided. Alternatively, a method for driving a small-sized semiconductor device can be provided. Alternatively, a method for driving a semiconductor device with low power consumption can be provided. Alternatively, a method for driving a semiconductor device that can be manufactured by a simple method can be provided. Alternatively, a method for driving a low-cost semiconductor device can be provided. Alternatively, a method for driving a semiconductor device that can output a signal with high accuracy can be provided. Alternatively, a method for driving a semiconductor device that can be operated at high temperatures can be provided. Alternatively, a method for driving a highly reliable semiconductor device can be provided. Alternatively, a novel method for driving a semiconductor device can be provided.

[0034] 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 need to have all of these effects. Note that effects other than these will become apparent from the description of the specification, drawings, claims, etc., and it is possible to extract effects other than these from the description of the specification, drawings, claims, etc. [Brief description of the drawings]

[0035] FIG. 1 is a circuit diagram illustrating an example of the configuration of a semiconductor device. FIG. 2 is a timing chart illustrating an example of a method for driving a semiconductor device. FIG. 3 is a circuit diagram illustrating an example of a method for driving the semiconductor device. FIG. 4 is a circuit diagram illustrating an example of a method for driving the semiconductor device. FIG. 5 is a circuit diagram illustrating an example of a method for driving the semiconductor device. FIG. 6 is a circuit diagram illustrating an example of a method for driving a semiconductor device. FIG. 7 is a circuit diagram illustrating an example of a method for driving a semiconductor device. FIG. 8 is a circuit diagram illustrating an example of a method for driving a semiconductor device. FIG. 9 is a circuit diagram illustrating an example of a method for driving a semiconductor device. FIG. 10 is a circuit diagram illustrating a configuration example of a semiconductor device. FIG. 11 is a circuit diagram illustrating a configuration example of a semiconductor device. Fig. 12A is a circuit diagram illustrating a configuration example of a semiconductor device, and Fig. 12B and Fig. 12C are circuit diagrams illustrating an example of a method for driving the semiconductor device. Fig. 13A is a circuit diagram illustrating an example of the configuration of a pixel included in an imaging device, and Fig. 13B is a timing chart illustrating an example of a method for driving the imaging device. FIG. 14 is a block diagram illustrating an example of the configuration of an imaging device. 15A to 15C are diagrams showing configuration examples of transistors. 16A to 16C are diagrams showing configuration examples of transistors. 17A to 17C are diagrams showing configuration examples of transistors. 18A to 18C are diagrams showing configuration examples of transistors. Fig. 19A is a diagram for explaining the classification of IGZO crystal structures, Fig. 19B is a diagram for explaining the XRD spectrum of a CAAC-IGZO film, and Fig. 19C is a diagram for explaining the ultrafine electron beam diffraction pattern of a CAAC-IGZO film. 20A to 20D are cross-sectional views for explaining configuration examples of an imaging device. 21A to 21F are diagrams illustrating an electronic device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The embodiments will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that the form and details of the present invention can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention is not interpreted as being limited to the description of the embodiments shown below. In the configuration of the invention described below, the same reference numerals are used in common between different drawings for the same parts or parts having similar functions, and repeated explanations are omitted.

[0037] In addition, the position, size, range, etc. of each component shown in the drawings, etc. may not represent the actual position, size, range, etc. in order to facilitate understanding of the invention. Therefore, the disclosed invention is not necessarily limited to the position, size, range, etc. disclosed in the drawings, etc. For example, in an actual manufacturing process, a resist mask, etc. may be unintentionally eroded by a process such as etching, but this may not be reflected in the drawings in order to facilitate understanding.

[0038] In addition, in top views (also called "plan views"), perspective views, and the like, illustration of some components may be omitted in order to make the drawings easier to understand.

[0039] In addition, the terms "electrode" and "wiring" used in this specification and the like 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" also include cases where multiple "electrodes" or "wirings" are formed integrally.

[0040] In this specification and the like, the resistance value of a "resistor" may be determined by the length of the wiring, or by connecting a conductive layer having a different resistivity from the conductive layer used in the wiring, or by doping a semiconductor with an impurity.

[0041] In addition, in this specification and the like, a "terminal" in an electric circuit refers to a portion where a current or voltage is input or output, and a signal is received or transmitted. Therefore, a part of a wiring or an electrode may function as a terminal.

[0042] In this specification, the terms "above" and "below" do not limit the positional relationship of components to being directly above or below and in direct contact with each other. For example, the expression "electrode B on insulating layer A" does not require that electrode B be formed in direct contact with insulating layer A, and does not exclude the inclusion of other components between insulating layer A and electrode B.

[0043] In addition, the functions of the source and drain are interchangeable depending on the driving conditions, etc., when transistors of different polarities are used, or when the direction of current changes during circuit driving, etc., so it is difficult to determine which is the source and which is the drain. For this reason, in this specification, etc., the terms source and drain can be used interchangeably.

[0044] In addition, in this specification, "electrically connected" includes a direct connection and a connection via "something having some electrical action". Here, "something having some electrical action" is not particularly limited as long as it allows the transmission and reception of electrical signals between the connection objects. Therefore, even when it is expressed as "electrically connected", in the actual circuit, there may be no physical connection part and only wiring extending. In addition, even when it is expressed as "direct connection", it includes a case where different conductive layers are connected via a contact. Note that in the wiring, there are cases where different conductive layers contain one or more of the same elements and cases where they contain different elements.

[0045] In this specification and elsewhere, when referring to counting values ​​and measurement values, terms such as "same," "equal," "uniform," etc. are used, they are intended to include an error of plus or minus 20% unless otherwise expressly stated.

[0046] In addition, in this specification and the like, when an etching process is performed after forming a resist mask, the resist mask is removed after the etching process is completed, unless otherwise specified.

[0047] Furthermore, voltage often refers to the potential difference between a certain potential and a reference potential (for example, a ground potential or a source potential). Therefore, voltage and potential can often be interchanged. In this specification and the like, unless otherwise specified, voltage and potential can be interchanged.

[0048] In addition, even when written as "semiconductor", if the conductivity is sufficiently low, it has the characteristics of an "insulator". Therefore, it is also possible to use "semiconductor" in place of "insulator". In this case, the boundary between "semiconductor" and "insulator" is ambiguous, and it is difficult to strictly distinguish between the two. Therefore, "semiconductor" and "insulator" described in this specification and the like may be read as interchangeable in some cases.

[0049] Furthermore, even when written as "semiconductor", if the conductivity is sufficiently high, it has the characteristics of a "conductor". Therefore, it is also possible to use "semiconductor" in place of "conductor". In this case, the boundary between "semiconductor" and "conductor" is ambiguous, and it is difficult to strictly distinguish between the two. Therefore, "semiconductor" and "conductor" described in this specification and the like may be interchangeable in some cases.

[0050] In addition, ordinal numbers such as "first" and "second" in this specification are used to avoid confusion of components, and do not indicate any order or ranking, such as a process order or a stacking order. Even if a term does not have an ordinal number in this specification, an ordinal number may be added in the claims to avoid confusion of components. Even if a term has an ordinal number in this specification, a different ordinal number may be added in the claims. Even if a term has an ordinal number in this specification, the ordinal number may be omitted in the claims.

[0051] In this specification, the "on state" of a transistor refers to a state in which the source and drain of the transistor can be regarded as being electrically short-circuited (also referred to as a "conductive state"). The "off state" of a transistor refers to a state in which the source and drain of the transistor can be regarded as being electrically disconnected (also referred to as a "non-conductive state").

[0052] In this specification, the term "on-state current" may refer to a current that flows between a source and a drain when a transistor is on, and the term "off-state current" may refer to a current that flows between a source and a drain when a transistor is off.

[0053] In this specification and the like, a gate refers to a gate electrode and a part or the whole of a gate wiring. A gate wiring refers to a wiring for electrically connecting a gate electrode of at least one transistor to another electrode or another wiring.

[0054] In this specification and the like, a source refers to a source region, a source electrode, and a part or all of a source wiring. A source region refers to a region of a semiconductor having a resistivity equal to or lower than a certain value. A source electrode refers to a conductive layer that is connected to a source region. A source wiring refers to a wiring for electrically connecting a source electrode of at least one transistor to another electrode or another wiring.

[0055] In this specification and the like, a drain refers to a part or all of a drain region, a drain electrode, and a drain wiring. A drain region refers to a region of a semiconductor having a resistivity equal to or lower than a certain value. A drain electrode refers to a conductive layer that is connected to a drain region. A drain wiring refers to a wiring for electrically connecting a drain electrode of at least one transistor to another electrode or another wiring.

[0056] 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 OS), and the like. For example, when a metal oxide is used as a semiconductor for 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 having a metal oxide or an oxide semiconductor.

[0057] In this specification and the like, metal oxides containing nitrogen may also be collectively referred to as metal oxides. Furthermore, metal oxides containing nitrogen may also be referred to as metal oxynitrides.

[0058] (Embodiment 1) In this embodiment, a structural example of a semiconductor device according to one embodiment of the present invention and an example of a driving method thereof will be described with reference to the drawings. However, the present invention is not limited to the structural examples described in this embodiment. In addition, each structural example can be used in appropriate combination.

[0059] <Configuration example of semiconductor device_1> 1 is a diagram showing a configuration example of a semiconductor device 10 which is a semiconductor device of one embodiment of the present invention. The semiconductor device 10 includes a circuit 20, a circuit 30, a transistor 22, a transistor 23, a transistor 32, a transistor 33, a capacitor 24, and a capacitor 34. Note that the capacitor 24 and the capacitor 34 are not essential. The circuit 20 includes transistors 21[1] to 21[n] (n is an integer of 2 or more), and the circuit 30 includes transistors 31[1] to 31[n].

[0060] One of the source or drain of the transistor 23 is electrically connected to one of the source or drain of the transistors 21[1] to 21[n]. That is, one of the sources or drains of the transistors 21[1] to 21[n] are electrically connected to each other. In addition, the other of the source or drain of the transistors 21[1] to 21[n] is electrically connected to one of the source or drain of the transistor 22 and one electrode of the capacitor 24. That is, the other of the source or drain of the transistors 21[1] to 21[n] is electrically connected to each other. From the above, it can be said that the transistors 21[1] to 21[n] are connected in parallel.

[0061] One of the source or drain of the transistor 33 is electrically connected to one of the source or drain of the transistor 31[1]. The other of the source or drain of the transistor 31[1] is electrically connected to one of the source or drain of the transistor 31[2]. In this manner, the other of the source or drain of the transistor 31[k] (k is an integer of 1 to n-1) is electrically connected to one of the source or drain of the transistor 31[k+1]. From the above, it can be said that the transistors 31[1] to 31[n] are connected in series. Here, the other of the source or drain of the transistor 31[n] is electrically connected to one of the source or drain of the transistor 32 and one electrode of the capacitor 34.

[0062] A node to which the other of the sources or drains of the transistors 21[1] to 21[n], one of the sources or drains of the transistor 22, and one electrode of the capacitor 24 are electrically connected is referred to as a node N1. A node to which the other of the source or drain of the transistor 31[n], one of the sources or drains of the transistor 32, and one electrode of the capacitor 34 are electrically connected is referred to as a node N2.

[0063] The gates of the transistors 21[1] to 21[n] and the gates of the transistors 31[1] to 31[n] are electrically connected to a transmission path 11. Signals IN[1] to IN[n] are input to the transmission path 11. The signals IN[1] to IN[n] input to the transmission path 11 are supplied to the transistors 21[1] to 21[n] and the transistors 31[1] to 31[n]. Specifically, the signal IN[i] is supplied to the gates of the transistors 21[i] (i is an integer between 1 and n) and the gates of the transistors 31[i].

[0064] A signal OUT1 can be output from the node N1, and a signal OUT2 can be output from the node N2.

[0065] A signal PRE can be supplied to the gate of the transistor 22 and the gate of the transistor 32. The signal PRE has a function of controlling the on / off of the transistor 22 and the transistor 32. The transistor 22 and the transistor 32 function as switches that are switched on and off by the signal PRE.

[0066] A signal EVA can be supplied to the gates of the transistor 23 and the transistor 33. The signal EVA has a function of controlling the on / off of the transistor 23 and the transistor 33. The transistor 23 and the transistor 33 have a function as a switch that is switched on and off by the signal EVA.

[0067] The capacitor 24 has a function of holding the potential of the node N1, and the capacitor 34 has a function of holding the potential of the node N2.

[0068] Furthermore, by providing the capacitor 24, it is possible to suppress a change in the potential of the signal OUT1 due to a parasitic capacitance or the like between the gate of the transistor 22 and one of the source or drain of the transistor 22 when the transistor 22 is switched from an on state to an off state. Specifically, it is possible to suppress a change in the potential of the signal OUT1 in conjunction with a change in the potential of the gate of the transistor 22 due to the parasitic capacitance or the like when the transistor 22 is switched from an on state to an off state. Furthermore, by providing the capacitor 34, it is possible to suppress a change in the potential of the signal OUT2 in conjunction with a change in the potential of the gate of the transistor 32 due to the parasitic capacitance or the like when the transistor 32 is switched from an on state to an off state. Specifically, it is possible to suppress a change in the potential of the signal OUT2 in conjunction with a change in the potential of the gate of the transistor 32 due to the parasitic capacitance or the like when the transistor 32 is switched from an on state to an off state.

[0069] A potential VC is supplied to the other of the source or drain of transistor 22 and the other of the source or drain of transistor 32. A potential VDET1 is supplied to the other of the source or drain of transistor 23 and the other electrode of capacitor 24. A potential VDET2 is supplied to the other of the source or drain of transistor 33 and the other electrode of capacitor 34.

[0070] Although the details will be described later, the transistors 21[1] to 21[n], the transistor 22, the transistor 23, the transistors 31[1] to 31[n], the transistor 32, and the transistor 33 can all have the same polarity. For example, the transistors 21[1] to 21[n], the transistor 22, the transistor 23, the transistors 31[1] to 31[n], the transistor 32, and the transistor 33 can be n-channel transistors.

[0071] It is preferable to use transistors with extremely low off-state current for the transistors 21[1] to 21[n], the transistor 22, the transistors 31[1] to 31[n], and the transistor 32. As a result, the potential of the node N1 can be held for an extremely long period of time. In addition, the potential of the node N2 can be held for an extremely long period of time. As a result, the circuit 20 can continue to output the signal OUT1 with high accuracy, and the circuit 30 can continue to output the signal OUT2 with high accuracy, as will be described in detail later.

[0072] An example of a transistor with extremely low off-state current is an OS transistor. Specifically, the off-state current per 1 μm of channel width at room temperature is 1×10 -20 Less than A, preferably 1×10 -22 A, more preferably less than 1×10 -24 It can be less than A.

[0073] Furthermore, OS transistors have superior electrical characteristics in a high-temperature environment compared to transistors having silicon in a channel formation region (hereinafter also referred to as Si transistors). By using OS transistors as the transistors included in the semiconductor device 10, a semiconductor device with stable operation and high reliability even in a high-temperature environment can be realized. In particular, by using OS transistors as all of the transistors 21[1] to 21[n], the transistors 22, the transistors 23, the transistors 31[1] to 31[n], the transistors 32, and the transistors 33, the semiconductor device 10 can have stable operation and high reliability even in a high-temperature environment.

[0074] Note that Si transistors may be used as the transistors 21[1] to 21[n], the transistor 22, the transistor 23, the transistors 31[1] to 31[n], the transistor 32, and the transistor 33. Examples of Si transistors include transistors having amorphous silicon, transistors having crystalline silicon (typically, low-temperature polysilicon), and transistors having single crystal silicon. For example, when transistors having single crystal silicon are used as the transistors 21[1] to 21[n], the transistor 22, the transistor 23, the transistors 31[1] to 31[n], the transistor 32, and the transistor 33, the on-current of these transistors can be increased. Thus, the semiconductor device 10 can be driven at high speed.

[0075] The semiconductor device 10, which will be described in detail later, can detect whether an event has occurred in a circuit that generates the signals IN[1] to IN[n]. For example, if the first reference potential is higher than the second reference potential, the semiconductor device 10 can detect that at least one of the potentials of the signals IN[1] to IN[n] is higher than the first reference potential and is equal to or lower than the second reference potential. Alternatively, the semiconductor device 10 can detect that all of the potentials of the signals IN[1] to IN[n] are higher than the second reference potential and are equal to or lower than the first reference potential. For example, if at least one of the potentials of the signals IN[1] to IN[n] is higher than the first reference potential or is equal to or lower than the second reference potential, it can be determined that an event has occurred in the circuit that generates the signals IN[1] to IN[n]. Here, the detection result by the semiconductor device 10 can be output as the signals OUT1 and OUT2.

[0076] <An example of a method for driving a semiconductor device> Next, an example of a method for driving the semiconductor device 10 will be described. Fig. 2 is a timing chart showing an example of a method for driving the semiconductor device 10 having the configuration shown in Fig. 1. In Fig. 2, "H" indicates high potential, and "L" indicates low potential. Note that similar notations are used in other timing charts. Also, Fig. 2 does not take into account fluctuations in potential due to wiring resistance, resistance between the drain and source of a transistor, and the like. The same is true for other timing charts, etc.

[0077] 2, an example of a method for driving the semiconductor device 10 is shown divided into periods T11[1] to T11[7] and periods T12[1] to T12[7]. An example of a method for driving the semiconductor device 10 in the periods T12[1] to T12[7] is also shown in FIGS. 3 to 9.

[0078] In the following description, it is assumed that the threshold voltages of transistors 21[1] to 21[n] and transistors 31[1] to 31[n] are all equal at "Vth."

[0079] In the following, an example of a method for driving the semiconductor device 10 will be described on the assumption that the transistors 21[1] to 21[n], the transistor 22, the transistor 23, the transistors 31[1] to 31[n], the transistor 32, and the transistor 33 are all n-channel transistors. Even if all or some of the transistors 21[1] to 21[n], the transistor 22, the transistor 23, the transistors 31[1] to 31[n], the transistor 32, and the transistor 33 are p-channel transistors, the following description can be referred to by appropriately replacing the magnitude relationship of potentials, for example.

[0080] The potential VC is higher than the potential VDET1 and the potential VDET2. The potential VDET1 is higher than the potential VDET2. In other words, the relationship "VC>VDET1>VDET2" is established.

[0081] In a period T11[1], the signal PRE is set to a high potential. This causes the transistor 22 and the transistor 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0082] In a period T12[1], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0083] In the period T12[1], the potentials of the signals IN[1] to IN[n] are higher than the potential "VDET2+Vth" and lower than the potential "VDET1+Vth". If the difference between the gate potential and the source potential of a transistor is higher than the threshold voltage of the transistor, a current flows between the drain and source of the transistor. On the other hand, if the difference between the gate potential and the source potential of a transistor is lower than the threshold voltage of the transistor, no current flows between the drain and source of the transistor.

[0084] When the transistor 23 is turned on, the potential of one of the source and drain of the transistors 21[1] to 21[n] is set to a potential VDET1. Here, the potential of the other of the source and drain of the transistors 21[1] to 21[n] is set to a potential VC. When the transistor 33 is turned on, the potential of one of the source and drain of the transistor 31[1] is set to a potential VDET2. Here, the potential of the other of the source and drain of the transistor 31[n] is set to a potential VC.

[0085] As described above, the transistors 21[1] to 21[n] and the transistors 31[1] to 31[n] are n-channel transistors, and the potential VC is higher than the potentials VDET1 and VDET2. The transistors 31[1] to 31[n] are connected in series. Therefore, one of the source or the drain of the transistors 21[1] to 21[n] and the transistors 31[1] to 31[n] is a source, and the other of the source or the drain of the transistors 21[1] to 21[n] and the transistors 31[1] to 31[n] is a drain.

[0086] As a result, in the period T12[1], the difference between the gate potential and the source potential of the transistors 21[1] to 21[n] is equal to or less than the threshold voltage Vth. Therefore, no current flows between the drain and the source of any of the transistors 21[1] to 21[n]. Therefore, the potential of the node N1 remains at the potential VC, and the potential of the signal OUT1 becomes the potential VC.

[0087] On the other hand, the difference between the potential of the gate and the potential of the source of the transistors 31[1] to 31[n] is higher than the threshold voltage Vth. Therefore, a current flows between the drain and the source of the transistor 33 from the node N2 through the transistors 31[1] to 31[n]. Therefore, the potential of the node N2 changes to the potential VDET2, and the potential of the signal OUT2 becomes the potential VDET2.

[0088] 3 is a circuit diagram showing the state of the semiconductor device 10 at time T12[1]. In FIG. 3, a transistor that cannot pass a current between the drain and the source is indicated by a cross. Specifically, a transistor in which the difference between the potential of the gate and the potential of the source is equal to or less than the threshold voltage is indicated by a cross. On the other hand, a transistor in which a current can pass between the drain and the source is not indicated by a cross. Specifically, a transistor in which the difference between the potential of the gate and the potential of the source is higher than the threshold voltage is not indicated by a cross. Also, a current is indicated by an arrow. Similar notations may be used in other figures.

[0089] In a period T11[2], the signal PRE is set to a high potential. This causes the transistors 22 and 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0090] In a period T12[2], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0091] In the period T12[2], the potential of the signal IN[n] is higher than the potential "VDET1+Vth". Also, the potentials of the signals IN[1] to IN[n-1] are higher than the potential "VDET2+Vth" and lower than the potential "VDET1+Vth". Since the potential of the signal IN[n] is higher than the potential "VDET1+Vth", the difference between the potential of the gate and the potential of the source of the transistor 21[n] becomes higher than the threshold voltage Vth. As described above, the transistors 21[1] to 21[n] are connected in parallel. As a result, a current flows between the drain and the source of the transistor 23 from the node N1 through the transistor 21[n]. Therefore, the potential of the node N1 changes to the potential VDET1, and the potential of the signal OUT1 becomes the potential VDET1.

[0092] As in the period T12[1], the difference between the potential of the gate and the potential of the source of the transistors 31[1] to 31[n] is higher than the threshold voltage Vth. Therefore, a current flows between the drain and the source of the transistor 33 from the node N2 through the transistors 31[1] to 31[n]. Therefore, as in the period T12[1], the potential of the node N2 changes to the potential VDET2, and the potential of the signal OUT2 becomes the potential VDET2.

[0093] 4 is a circuit diagram showing the state of the semiconductor device 10 during a period T12[2]. In FIG. 4, the potential of the signal OUT1 during the period T12[2] is different from the potential of the signal OUT1 during the period T12[1], as shown by encircling the signal OUT1 with a dashed line.

[0094] In a period T11[3], the signal PRE is set to a high potential. This causes the transistors 22 and 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0095] In a period T12[3], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0096] In the period T12[3], the potential of the signal IN[n] is equal to or lower than the potential "VDET2+Vth". Also, the potentials of the signals IN[1] to IN[n-1] are higher than the potential "VDET2+Vth" and equal to or lower than the potential "VDET1+Vth". Since the potential of the signal IN[n] is equal to or lower than the potential "VDET2+Vth", the difference between the potential of the gate and the potential of the source of the transistor 31[n] is equal to or lower than the threshold voltage Vth. As described above, the transistors 31[1] to 31[n] are connected in series. As a result, no current flows from the node N2 to the transistor 33, the potential of the node N2 remains at the potential VC, and the potential of the signal OUT2 becomes the potential VC.

[0097] As in the period T12[1], the difference between the gate potential and the source potential of the transistors 21[1] to 21[n] is equal to or less than the threshold voltage Vth. Therefore, no current flows between the drain and the source of any of the transistors 21[1] to 21[n]. Therefore, as in the period T12[1], the potential of the node N1 remains at the potential VC, and the potential of the signal OUT1 becomes the potential VC.

[0098] 5 is a circuit diagram showing the state of the semiconductor device 10 during a period T12[3]. In FIG. 5, the potential of the signal OUT2 during the period T12[3] is different from the potential of the signal OUT2 during the period T12[1], as shown by encircling the signal OUT2 with a dashed line.

[0099] In a period T11[4], the signal PRE is set to a high potential. This causes the transistors 22 and 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0100] In a period T12[4], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0101] In the period T12[4], similarly to the period T12[1], the potentials of the signals IN[1] to IN[n] are higher than the potential "VDET2+Vth" and lower than or equal to the potential "VDET1+Vth." In this case, similarly to the period T12[1], the potential of the signal OUT1 is the potential VC, and the potential of the signal OUT2 is the potential VDET2.

[0102] 6 is a circuit diagram showing the state of the semiconductor device 10 at time T12[4]. FIG 6 shows the same state as FIG 3.

[0103] In a period T11[5], the signal PRE is set to a high potential. This causes the transistors 22 and 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0104] In a period T12[5], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0105] In the period T12[5], the potential of the signal IN[1] is higher than the potential "VDET1+Vth". Also, the potentials of the signals IN[2] to IN[n] are higher than the potential "VDET2+Vth" and lower than the potential "VDET1+Vth". Since the potential of the signal IN[1] is higher than the potential "VDET1+Vth", the difference between the potential of the gate and the potential of the source of the transistor 21[1] becomes higher than the threshold voltage Vth. As described above, the transistors 21[1] to 21[n] are connected in parallel. As a result, a current flows between the drain and the source of the transistor 23 from the node N1 through the transistor 21[1]. Therefore, the potential of the node N1 changes to the potential VDET1, and the potential of the signal OUT1 becomes the potential VDET1.

[0106] As in the period T12[4], the difference between the gate potential and the source potential of the transistors 31[1] to 31[n] is higher than the threshold voltage Vth. Therefore, a current flows between the drain and the source of the transistor 33 from the node N2 through the transistors 31[1] to 31[n]. Therefore, as in the period T12[4], the potential of the node N2 changes to the potential VDET2, and the potential of the signal OUT2 becomes the potential VDET2.

[0107] 7 is a circuit diagram showing the state of the semiconductor device 10 during a period T12[5]. In FIG 7, the potential of the signal OUT1 during the period T12[5] is different from the potential of the signal OUT1 during the period T12[4], as shown by encircling the signal OUT1 with a dashed line.

[0108] In a period T11[6], the signal PRE is set to a high potential. This causes the transistors 22 and 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0109] In a period T12[6], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0110] In the period T12[6], the potential of the signal IN[1] is equal to or lower than the potential "VDET2+Vth". Also, the potentials of the signals IN[2] to IN[n] are higher than the potential "VDET2+Vth" and equal to or lower than the potential "VDET1+Vth". Since the potential of the signal IN[1] is equal to or lower than the potential "VDET2+Vth", the difference between the potential of the gate and the potential of the source of the transistor 31[1] is equal to or lower than the threshold voltage Vth. As described above, the transistors 31[1] to 31[n] are connected in series. As a result, no current flows from the node N2 to the transistor 33, the potential of the node N2 remains at the potential VC, and the potential of the signal OUT2 becomes the potential VC.

[0111] As in the period T12[4], the difference between the gate potential and the source potential of the transistors 21[1] to 21[n] is equal to or less than the threshold voltage Vth. Therefore, no current flows between the drain and the source of any of the transistors 21[1] to 21[n]. Therefore, as in the period T12[4], the potential of the node N1 remains at the potential VC, and the potential of the signal OUT1 becomes the potential VC.

[0112] 8 is a circuit diagram showing the state of the semiconductor device 10 during a period T12[6]. In FIG. 8, the potential of the signal OUT2 during the period T12[6] is different from the potential of the signal OUT2 during the period T12[4], as shown by encircling the signal OUT2 with a dashed line.

[0113] In a period T11[7], the signal PRE is set to a high potential. This causes the transistors 22 and 32 to be turned on. When the transistor 22 is turned on, the potential of the node N1 becomes the potential VC. Also, when the transistor 32 is turned on, the potential of the node N2 becomes the potential VC.

[0114] In a period T12[7], the signal PRE is set to a low potential, which turns off the transistors 22 and 32. The signal EVA is set to a high potential, which turns on the transistors 23 and 33.

[0115] In the period T12[7], the potential of the signal IN[n] is higher than the potential "VDET1+Vth" and the potential of the signal IN[1] is lower than the potential "VDET2+Vth". In addition, the potentials of the signals IN[2] to IN[n-1] are higher than the potential "VDET2+Vth" and lower than the potential "VDET1+Vth". Since the potential of the signal IN[n] is higher than the potential "VDET1+Vth", the difference between the potential of the gate and the potential of the source of the transistor 21[n] becomes higher than the threshold voltage Vth. As described above, the transistors 21[1] to 21[n] are connected in parallel. As a result, a current flows between the drain and the source of the transistor 23 from the node N1 through the transistor 21[n]. Therefore, the potential of the node N1 changes to the potential VDET1, and the potential of the signal OUT1 becomes the potential VDET1.

[0116] In addition, since the potential of the signal IN[1] is equal to or lower than the potential "VDET2+Vth", the difference between the potential of the gate and the potential of the source of the transistor 31[1] is equal to or lower than the threshold voltage Vth. As described above, the transistors 31[1] to 31[n] are connected in series. As a result, no current flows from the node N2 to the transistor 33, the potential of the node N2 remains at the potential VC, and the potential of the signal OUT2 becomes the potential VC.

[0117] 9 is a circuit diagram showing the state of the semiconductor device 10 in the period T12[7]. In FIG. 9, the potential of the signal OUT1 in the period T12[7] is different from the potential of the signal OUT1 in the periods T12[1] and T12[4], as shown by surrounding the signal OUT1 with a dashed line. Also, the potential of the signal OUT2 in the period T12[7] is different from the potential of the signal OUT2 in the periods T12[1] and T12[4], as shown by surrounding the signal OUT2 with a dashed line.

[0118] From the above, the circuit 20 can be said to have a function of detecting whether at least one of the potentials of the signals IN[1] to IN[n] is higher than the potential "VDEF1+Vth" or whether all of the signals IN[1] to IN[n] are lower than the potential "VDEF1+Vth" and outputting the detection result as the signal OUT1. Therefore, if the potential "VDEF1+Vth" is the reference potential VREF1, the circuit 20 can be said to have a function of detecting whether at least one of the potentials of the signals IN[1] to IN[n] is higher than the reference potential VREF1 or whether all of the signals IN[1] to IN[n] are lower than the reference potential VREF1. Here, since the potential VDET1 can be expressed as the potential "VREF1-Vth", it can be said that the potential VDET1 is a potential corresponding to the reference potential VREF1.

[0119] The circuit 30 can be said to have a function of detecting whether at least one of the potentials of the signals IN[1] to IN[n] is equal to or lower than the potential "VDEF2+Vth" or whether all of the signals IN[1] to IN[n] are higher than the potential "VDEF2+Vth" and outputting the detection result as the signal OUT2. Therefore, when the potential "VDEF2+Vth" is the reference potential VREF2, the circuit 30 can be said to have a function of detecting whether at least one of the potentials of the signals IN[1] to IN[n] is equal to or lower than the reference potential VREF2 or whether all of the signals IN[1] to IN[n] are higher than the reference potential VREF2. Here, since the potential VDET2 can be expressed as the potential "VREF2-Vth", it can be said that the potential VDET2 is a potential corresponding to the reference potential VREF2.

[0120] As described above, the potential VDET1 is higher than the potential VDET2. The threshold voltages of the transistors 21[1] to 21[n] and the transistors 31[1] to 31[n] are all equal to "Vth." Therefore, the reference potential VREF1 is higher than the reference potential VREF2.

[0121] From the above, the semiconductor device 10 can detect that at least one of the potentials of the signals IN[1] to IN[n] is higher than the reference potential VREF1 and is equal to or lower than the reference potential VREF2. Alternatively, it can detect that all of the potentials of the signals IN[1] to IN[n] are higher than the reference potential VREF2 and are equal to or lower than the reference potential VREF1. This makes it possible to detect, for example, whether an event has occurred in a circuit that generates the signals IN[1] to IN[n]. For example, if at least one of the potentials of the signals IN[1] to IN[n] is higher than the reference potential VREF1 or is equal to or lower than the reference potential VREF2, it can be determined that an event has occurred in the circuit that generates the signals IN[1] to IN[n].

[0122] The detection results can be output as signals OUT1 and OUT2. Specifically, in the period T11, the transistors 22 and 32 are turned on, and the transistors 23 and 33 are turned off, so that the potential of the node N1 and the potential of the node N2 are set to potential VC. Next, in the period T12, the transistors 22 and 32 are turned off, and the transistors 23 and 33 are turned on, so that the semiconductor device 10 can output signals of potentials corresponding to the potentials of the signals IN[1] to IN[n] as the signals OUT1 and OUT2. For example, when the potential of the signal OUT1 is potential VC and the potential of the signal OUT2 is potential VDET2, it can be determined that no event has occurred in the circuit generating the signals IN[1] to IN[n], and when the potentials are other than the potentials, it can be determined that an event has occurred. Note that the potentials of the nodes N1 and N2 are set to potential VC in the period T11, and then the signals OUT1 and OUT2 are output in the period T12, so that it can be said that precharging is performed in the period T11. It can also be said that the potential VC is a precharge potential.

[0123] From the above, it can be said that the semiconductor device 10 has a function of detecting the potential levels of the signals IN[1] to IN[n]. Here, as shown in FIG. 1, the semiconductor device 10 does not include a comparator. As described above, if a comparator is to be provided with the function of detecting the potential levels of the signals IN[1] to IN[n], many comparators are required, particularly when n is large. On the other hand, in the semiconductor device 10, an increase in n can be accommodated by simply increasing the number of transistors 21 and the number of transistors 31. For example, n can be increased by 1 by simply increasing the number of transistors 21 and the number of transistors 31. As described above, even if n increases, a significant increase in the circuit scale of the semiconductor device can be suppressed. Therefore, according to one embodiment of the present invention, the circuit scale of the semiconductor device can be reduced. As a result, the semiconductor device can be miniaturized and the power consumption of the semiconductor device can be reduced.

[0124] Moreover, as described above, when the comparator is configured with transistors of the same polarity, the characteristics of the comparator are significantly degraded. On the other hand, even if all the transistors in the semiconductor device 10 are transistors of the same polarity, the characteristics of the semiconductor device 10 do not change significantly compared to when the semiconductor device 10 is configured with CMOS. Therefore, all the transistors in the semiconductor device 10 can be transistors of the same polarity. For example, the transistors 21[1] to 21[n], the transistors 22, the transistors 23, the transistors 31[1] to 31[n], the transistors 32, and the transistors 33 can all be n-channel transistors. By configuring all the transistors in the semiconductor device 10 as transistors of the same polarity, it is not necessary to separately manufacture n-channel transistors and p-channel transistors. This allows the semiconductor device 10 to be manufactured by a simple method. Therefore, the manufacturing cost of the semiconductor device 10 can be reduced, and the semiconductor device 10 can be manufactured at a low price.

[0125] Further, since all the transistors included in the semiconductor device 10 can be n-channel transistors, all the transistors included in the semiconductor device 10 can be OS transistors. As described above, OS transistors have a feature of having an extremely low off-state current. Therefore, for example, by using OS transistors as all the transistors included in the semiconductor device 10, when the potential of the node N1 does not become the potential VDET1 in the period T12, the potential of the node N1 can be held at the potential VC for a long period of time. When the potential of the node N2 does not become the potential VDET2 in the period T12, the potential of the node N2 can be held at the potential VC for a long period of time. As described above, even if the period T12 is extended, the circuit 20 can continue to output the signal OUT1 with high accuracy, and the circuit 30 can continue to output the signal OUT2 with high accuracy.

[0126] <Example of semiconductor device configuration_2> Fig. 10 is a diagram showing a configuration example of a semiconductor device 10, which is a modified example of the configuration shown in Fig. 1. The semiconductor device 10 shown in Fig. 10 differs from the semiconductor device 10 shown in Fig. 1 in that the transistors 21[1] to 21[n], the transistors 22, the transistors 23, the transistors 31[1] to 31[n], the transistors 32, and the transistors 33 each have a backgate in addition to a gate.

[0127] In this specification and the like, the term "gate" may refer to a front gate. Note that the terms "gate" and "back gate" may be used interchangeably. In addition, when a transistor has a gate and a back gate, one of the gate or the back gate may be referred to as a first gate, and the other of the gate or the back gate may be referred to as a second gate.

[0128] A potential VBG1 can be supplied to the back gates of the transistors 21[1] to 21[n]. A potential VBG2 can be supplied to the back gates of the transistors 31[1] to 31[n].

[0129] By controlling the potential of the back gate of a transistor, the threshold voltage of the transistor can be controlled. Specifically, in an n-channel transistor, the higher the potential of the back gate, the smaller the threshold voltage can be. Thus, even if the potential of the other of the source or drain of the transistor 23 and the potential of the other of the source or drain of the transistor 33 are the same potential, the reference potential VREF1 and the reference potential VREF2 can be made different from each other. Specifically, the reference potential VREF1 can be made higher than the reference potential VREF2 by making the potential VBG1 lower than the potential VBG2.

[0130] In FIG. 10, the potential of the other of the source or drain of the transistor 23 and the other of the source or drain of the transistor 33 is a potential VDET. Here, the threshold voltage of the transistors 21[1] to 21[n] when a potential VBG1 is supplied to the back gates of the transistors 21[1] to 21[n] is Vth1. The threshold voltage of the transistors 31[1] to 31[n] when a potential VBG2 is supplied to the back gates of the transistors 31[1] to 31[n] is Vth2. In this case, the reference potential VREF1 is a potential "VDET+Vth1", and the reference potential VREF2 is a potential "VDET+Vth2". By making the threshold voltage Vth1 higher than the threshold voltage Vth2, the reference potential VREF1 can be made higher than the reference potential VREF2.

[0131] The backgate of the transistor 22 is electrically connected to the gate of the transistor 22. The backgate of the transistor 23 is electrically connected to the gate of the transistor 23. The backgate of the transistor 32 is electrically connected to the gate of the transistor 32. The backgate of the transistor 33 is electrically connected to the gate of the transistor 33. By electrically connecting the gate and backgate of a transistor functioning as a switch in this manner, the on-state current of the transistor can be increased. This allows the semiconductor device 10 to be driven at high speed. Note that even if the transistors 21[1] to 21[n] and the transistors 31[1] to 31[n] do not have backgates, the transistors 22, 23, 32, and 33 may each have a backgate. Alternatively, the backgate and the gate may not be electrically connected, and the potential of the backgate and the potential of the gate may be controlled separately.

[0132] An example of a method of driving the semiconductor device 10 shown in FIG. 10 can be understood by referring to the explanations in FIGS. 2 to 9, by replacing the potentials VDET1 and VDET2 with the potential VDET, setting the reference potential VREF1 to the potential "VDET+Vth1", and setting the reference potential VREF2 to the potential "VDET+Vth2".

[0133] Fig. 11 is a diagram showing a configuration example of the semiconductor device 10, which is a modified example of the configuration shown in Fig. 10. The semiconductor device 10 shown in Fig. 11 differs from the semiconductor device 10 shown in Fig. 10 in that potentials supplied to the backgates of the transistors 21[1] to 21[n] are individually controlled and potentials supplied to the backgates of the transistors 31[1] to 31[n] are individually controlled.

[0134] 11, the potential of the other of the source or drain of the transistor 23 and the potential of the other of the source or drain of the transistor 33 can be set to the same potential (for example, potential VDET), and also the variations in threshold voltages among the transistors 21[1] to 21[n] and among the transistors 31[1] to 31[n] can be corrected. Therefore, the semiconductor device 10 shown in FIG 11 can detect the potential levels of the signals IN[1] to IN[n] with high accuracy.

[0135] <Example of configuration of signal IN generation circuit> Next, generation of signals IN[1] to IN[n] will be described. Signals IN[1] to IN[n] can be signals corresponding to signals output by pixels of an imaging device, for example. FIG. 12A is a diagram showing a configuration example of a circuit having a function of generating signal IN[i]. FIG. 12A shows a pixel circuit 50 and a circuit 40. Also, a specific configuration example of the circuit 40 is shown. The circuit 40 has a capacitor 41 and a transistor 42.

[0136] The pixel circuit 50 has a function of outputting a signal OUTPX. The signal OUTPX can be a signal representing imaging data acquired by the pixel circuit 50. The signal OUTPX is supplied to one electrode of a capacitor 41. The other electrode of the capacitor 41 and one of the source or drain of a transistor 42 are electrically connected at a node N3. A signal IN[i] is output from the node N3. A potential VR is supplied to the other of the source or drain of the transistor 42. A signal RES is supplied to the gate of the transistor 42. The signal RES has a function of controlling the on / off of the transistor 42. The transistor 42 has a function as a switch that is switched on and off by the signal RES.

[0137] An example of a method for driving the circuit 40 will be described below with reference to Fig. 12B1 and Fig. 12B2. Fig. 12B1 shows the state of the circuit 40 in a period T01, and Fig. 12B2 shows the state of the circuit 40 in a period T02. In Fig. 12B1 and Fig. 12B2, transistors in an off state are indicated with a cross. On the other hand, transistors in an on state are not indicated with a cross.

[0138] First, in a period T01, as shown in FIG. 12B1, the transistor 42 is turned on. As a result, the potential of the signal IN[i] becomes the potential VR regardless of the potential of the signal OUTPX. In other words, the potential of the signal IN[i] can be said to be reset to the potential VR. Therefore, the transistor 42 can be said to be a reset transistor, and the signal RES can be said to be a reset signal. Note that the potential of the signal OUTPX in the period T01 is set to the potential VD1.

[0139] Next, in a period T02, as shown in FIG. 12B2, the transistor 42 is turned off. As a result, the node N3 is put into a floating state, and the potential of the node N3 electrically connected to the other electrode of the capacitor 41 fluctuates in response to the fluctuation of the potential of the signal OUTPX supplied to one electrode of the capacitor 41. Therefore, the potential of the signal IN[i] fluctuates in response to the fluctuation of the potential of the signal OUTPX. In FIG. 12B2, the potential of the signal OUTPX fluctuates from the potential VD1 to the potential VD2 in the period T02. Note that in FIG. 12B2, the signal OUTPX is surrounded by a dashed line to show that the potential of the signal OUTPX in the period T02 is different from the potential of the signal OUTPX in the period T01. Also, the signal IN[i] is surrounded by a dashed line to show that the potential of the signal IN[i] in the period T02 is different from the potential of the signal IN[i] in the period T01.

[0140] Here, if the capacitance of the capacitor 41 is sufficiently large compared with the parasitic capacitance of the node N3, such as the gate capacitance of the transistor 42, the capacitive coupling coefficient of the node N3 can be regarded as 1. If the capacitive coupling coefficient of the node N3 is 1, then when the transistor 42 is in the off state, the fluctuation range of the potential of the signal IN[i] becomes equal to the fluctuation range of the potential of the signal OUTPX. As described above, in the period T02, if the potential of the signal OUTPX fluctuates from the potential VD1 to the potential VD2 and the capacitive coupling coefficient of the node N3 is 1, the potential of the signal IN[i] becomes the potential "VR+VD2-VD1".

[0141] The potential VR is set to be equal to or higher than the reference potential VREF2 and equal to or lower than the reference potential VREF1. For example, the potential VR is set to be a potential "(VREF1+VREF2) / 2". Then, after the period T02, the operation in the period T11 shown in FIG. 2 and the like and the operation in the period T12 are performed. This allows the semiconductor device 10 to detect that at least one of the potentials of the signals IN[1] to IN[n] is higher than the reference potential VREF1 and is equal to or lower than the reference potential VREF2. Alternatively, it can detect that all of the potentials of the signals IN[1] to IN[n] are higher than the reference potential VREF2 and are equal to or lower than the reference potential VREF1. Therefore, it can be detected in the period T12 whether or not there is a signal among the signals IN[1] to IN[n] whose potential has changed by a specified value or more in the period T02.

[0142] <Pixel circuit configuration example> Fig. 13A is a diagram showing an example of the configuration of a pixel circuit 50. For ease of explanation, Fig. 13A also shows a circuit 40 having the configuration shown in Fig. 12A.

[0143] The pixel circuit 50 includes a photoelectric conversion device 60 , a transistor 61 , a transistor 62 , a transistor 63 , a transistor 64 , and a capacitor 66 .

[0144] In the following description, the transistor 42 and the transistors 61 to 64 are all n-channel transistors. Even if the transistor 42 and all or some of the transistors 61 to 64 are p-channel transistors, the following description can be referred to by appropriately replacing the magnitude relationship of potentials, for example.

[0145] One electrode of the photoelectric conversion device 60 is electrically connected to one of the source and drain of the transistor 61. In Fig. 13A, one electrode of the photoelectric conversion device 60 is an anode, and the other electrode of the photoelectric conversion device 60 is a cathode.

[0146] The other of the source and the drain of the transistor 61 is electrically connected to the gate of the transistor 62. The gate of the transistor 62 is electrically connected to one of the source and the drain of the transistor 64. The one of the source and the drain of the transistor 64 is electrically connected to one electrode of the capacitor 66. The one of the source and the drain of the transistor 62 is electrically connected to one of the source and the drain of the transistor 63.

[0147] A node to which one electrode of the photoelectric conversion device 60 and one of the source and drain of the transistor 61 are electrically connected is referred to as a node NA. A node to which the other of the source and drain of the transistor 61, the gate of the transistor 62, one of the source and drain of the transistor 64, and one electrode of the capacitor 66 are electrically connected is referred to as a node FD. Note that if the gate capacitance or the like of the transistor 62 is sufficiently large so that the capacitance of the node FD can be sufficiently secured without the capacitor 66, the capacitor 66 does not need to be provided.

[0148] A signal TX is supplied to the gate of the transistor 61. A signal SEL is supplied to the gate of the transistor 63. A signal RESPX is supplied to the gate of the transistor 64. A signal OUTPX is output from the other of the source or drain of the transistor 63.

[0149] As shown in FIG. 13A, when one electrode of the photoelectric conversion device 60 is an anode and the other electrode of the photoelectric conversion device 60 is a cathode, the other electrode of the photoelectric conversion device 60 and the other of the source or drain of the transistor 62 can be supplied with a potential VDD. On the other hand, the other of the source or drain of the transistor 64 and the other electrode of the capacitor 66 can be supplied with a potential VSS. Here, the potential VDD can be a high potential, and the potential VSS can be a low potential. Note that, when one electrode of the photoelectric conversion device 60 is a cathode and the other electrode of the photoelectric conversion device 60 is an anode, the potential VDD can be supplied to the other of the source or drain of the transistor 62 and the other of the source or drain of the transistor 64. In addition, the potential VSS can be supplied to the other electrode of the photoelectric conversion device 60 and the other electrode of the capacitor 66.

[0150] The other of the source or drain of the transistor 63 is electrically connected to one of the source or drain of the transistor 69. A potential VSS can be supplied to the other of the source or drain of the transistor 69. A potential Vbias can be supplied to the gate of the transistor 69. The potential Vbias is a potential that causes the transistor 69 to function as a current source. For example, the potential Vbias is a potential that causes the transistor 69 to operate in a saturation region. The potential Vbias can be called a bias potential, and the transistor 69 can be called a bias transistor.

[0151] Fig. 13B is a timing chart for explaining an example of a method for driving the pixel circuit 50 and the circuit 40 having the configuration shown in Fig. 13A. Fig. 13B shows the operation of a period T01 shown in Fig. 12B1 and the operation of a period T02 shown in Fig. 12B2. Here, in Fig. 13B, the period T01 is divided into periods 71_1 to 75_1, and the period T02 is divided into periods 71_2 to 75_2.

[0152] First, an example of the operation in the period T01 will be described. In the period 71_1, the potentials of the signals TX, RESPX, and RES are set to high potential, and the potential of the signal SEL is set to low potential. As a result, the transistors 61, 64, and 42 are turned on, and the transistor 63 is turned off. When the transistor 64 is turned on, the potential of the node FD becomes the potential VSS. Furthermore, when the transistor 61 and the transistor 64 are turned on, the potential of the node NA also becomes the potential VSS. Furthermore, when the transistor 42 is turned on, the potential of the signal IN[i] becomes the potential VR. Here, the potential VR is set to be equal to or higher than the reference potential VREF2 and equal to or lower than the reference potential VREF1.

[0153] In a period 72_1, the potentials of the signal TX and the signal RESPX are set to low, which turns off the transistor 61 and the transistor 64. When the photoelectric conversion device 60 is irradiated with light in this state, charges according to the illuminance of the light are accumulated in the node NA.

[0154] In a period 73_1, the potential of the signal TX is set to a high potential, which turns on the transistor 61 and transfers the charge accumulated in the node NA to the node FD, thereby increasing the potential of the node FD.

[0155] In the period 74_1, the potential of the signal TX is set to low, which turns off the transistor 61 and ends the transfer of charge from the node NA to the node FD. In this manner, the pixel circuit 50 can obtain image data.

[0156] In the period 75_1, the potential of the signal SEL is set to a high potential. This turns on the transistor 63, and the imaging data acquired by the pixel circuit 50 is read out as the signal OUTPX. Specifically, the potential of the signal OUTPX becomes a potential corresponding to the potential of the node FD. In FIG. 13B, the potential of the signal OUTPX becomes the potential VD1. Note that, since the transistor 42 is in the on state, the potential of the signal IN[i] becomes the potential VR regardless of the level of the potential VD1. This is an example of the operation of the pixel circuit 50 and the circuit 40 configured as shown in FIG. 13A in the period T01.

[0157] 13B, the signal RES is set to a high potential in the period 71_1, but the signal RES may be set to a high potential at any time up to the start of the period 75_1. In other words, the signal RES may be switched from a low potential to a high potential at any time between the periods 71_1 and 74_1.

[0158] Next, an example of the operation in the period T02 will be described. The potentials of the signals TX, SEL, and RESPX in the periods 71_2 to 75_2 are the same as those in the periods 71_1 to 75_1. In addition, the potential of the signal RES is switched from high to low during the periods 71_2 to 74_2. As a result, the signal OUTPX of the potential VD2 is output from the pixel circuit 50 during the period 75_2. As a result, the imaging data acquired by the pixel circuit 50 during the periods 71_2 to 74_2 is read out from the pixel circuit 50 during the period 75_2.

[0159] Here, in the period 75_2, since the signal RES is at a low potential, the transistor 42 is in an off state. Therefore, if the capacitive coupling coefficient of the node N3 is 1, the potential of the signal IN[i] is the potential "VR+VD2-VD1." This is an example of the operation of the pixel circuit 50 and the circuit 40 configured as shown in FIG. 13A in the period T02.

[0160] As described above, after the period T02, the operation in the period T11 and the operation in the period T12 shown in Fig. 2 and the like are performed. In the case shown in Fig. 13B, the potential of the signal IN[i] at the end of the period T02 is higher than the reference potential VREF1. Therefore, in the period T12, the semiconductor device 10 outputs the potential VDET1 as the signal OUT1.

[0161] Here, the pixel circuit 50 acquires and reads out imaging data in a period T01, and acquires and reads out imaging data again in a period T02. Therefore, the periods T01 and T02 can be said to be one frame period each. If the period T01 is a first frame period and the period T02 is a second frame period, the semiconductor device 10 can detect whether or not the difference between imaging data acquired by an imaging device having the pixel circuit 50 in the first frame period and imaging data acquired in the second frame period is equal to or greater than a specified value.

[0162] <Configuration example of imaging device> 14 is a block diagram showing a configuration example of an imaging device 80 that is an imaging device having a semiconductor device 10, a circuit 40, and a pixel circuit 50. In addition to the semiconductor device 10 and the circuit 40, the imaging device 80 has a pixel section 81, a gate driver circuit 82, a data driver circuit 83, and a transistor 69. In the pixel section 81, pixel circuits 50 are arranged in a matrix shape with m rows and n columns (m and n are integers of 1 or more). In this specification and the like, for example, the pixel circuit 50 in the h-th row and the i-th column (h is an integer of 1 or more and m or less, and i is an integer of 1 or more and n or less) is referred to as a pixel circuit 50[h, i].

[0163] In this specification and the like, an imaging device including a semiconductor device according to one embodiment of the present invention may be referred to as an imaging device according to one embodiment of the present invention. For example, an imaging device 80 includes a semiconductor device 10 which is a semiconductor device according to one embodiment of the present invention, and therefore can be referred to as an imaging device according to one embodiment of the present invention.

[0164] The gate driver circuit 82 has a function of generating a signal SEL. Here, the same signal SEL can be supplied to the pixel circuits 50 in the same row. In this specification, for example, the signal SEL supplied to the pixel circuits 50 in the h-th row is referred to as a signal SEL[h]. The gate driver circuit 82 may have a function of generating a signal RESPX. The gate driver circuit 82 may also have a function of generating a signal TX.

[0165] The data driver circuit 83 has a function of outputting imaging data read out from the pixel circuits 50 to the outside of the imaging device 80. Specifically, the data driver circuit 83 has a function of outputting imaging data to the outside of the imaging device 80 based on a signal OUTPX output from the pixel circuits 50. Here, the data driver circuit 83 can read out imaging data for each column of the pixel circuits 50. In this specification and the like, for example, a signal OUTPX output from a pixel circuit 50 in the i-th column is referred to as a signal OUTPX[i].

[0166] The transistor 69 and the circuit 40 can be provided for each column of the pixel circuits 50. Therefore, the imaging device 80 can be provided with, for example, the same number of transistors 69 and circuits 40 as the number of columns of the pixel circuits 50. Therefore, the imaging device 80 can be provided with, for example, n transistors 69 and circuits 40. In this specification, for example, the transistor 69 electrically connected to the pixel circuit 50 in the i-th column is referred to as a transistor 69[i]. Also, for example, the circuit 40 to which the signal OUTPX[i] is supplied is referred to as a circuit 40[i]. Here, for example, the signal IN[i] is output from the circuit 40[i]. The signals IN[1] to IN[n] can be supplied to the semiconductor device 10.

[0167] 14, the semiconductor device 10 can detect whether or not there is a signal OUTPX having a potential higher than the reference potential VREF1 or a signal OUTPX having a potential equal to or lower than the reference potential VREF2 among the signals OUTPX[1] to OUTPX[n] output from the pixel circuits 50[h,1] to 50[h,n]. Therefore, by driving the pixel circuits 50 and the circuit 40 by the method shown in FIG. 13B, etc., the semiconductor device 10 can detect whether or not there is a pixel circuit 50 for which the difference between the imaging data acquired in the first frame period and the imaging data acquired in the second frame period is equal to or greater than a specified value for each row of the pixel circuits 50. For example, it can detect whether or not there is a pixel circuit 50 for which the difference between the imaging data acquired in the first frame period and the imaging data acquired in the second frame period is equal to or greater than a specified value among the pixel circuits 50[h,1] to 50[h,n]. For example, if there is a pixel circuit 50 in which the difference between the imaging data acquired in the first frame period and the imaging data acquired in the second frame period is equal to or greater than a specified value, it can be said that an event has occurred in the second frame period.

[0168] The configurations, structures, methods, and the like described in this embodiment can be used in appropriate combination with the configurations, structures, methods, and the like described in other embodiments.

[0169] (Embodiment 2) In this embodiment mode, a structural example of a transistor that can be applied to the semiconductor device described in the above embodiment mode will be described with reference to the drawings.

[0170] <Transistor configuration example_1> 15A, 15B, and 15C are diagrams showing a configuration example of a transistor 500 which is a transistor applicable to the semiconductor device described in the above embodiment. FIG. 15A is a top view of the transistor 500. FIG. 15B is a cross-sectional view of a portion indicated by a dashed line L1-L2 in FIG. 15A, and is also a cross-sectional view of the transistor 500 in the channel length direction. FIG. 15C is a cross-sectional view of a portion indicated by a dashed line W1-W2 in FIG. 15A, and is also a cross-sectional view of the transistor 500 in the channel width direction. Note that in the top view of FIG. 15A, some elements are omitted for clarity.

[0171] As shown in Figures 15A to 15C, the transistor 500 has an insulating layer 524 arranged on a substrate (not shown), an oxide 530a arranged on the insulating layer 524, an oxide 530b arranged on the oxide 530a, conductive layers 542a and 542b arranged apart from each other on the oxide 530b, an insulating layer 580 arranged on the conductive layers 542a and 542b and having an opening formed therein overlapping between the conductive layers 542a and 542b, an insulating layer 545 arranged on the bottom and side surfaces of the opening, and a conductive layer 560 arranged on the formation surface of the insulating layer 545.

[0172] 15B and 15C, an insulating layer 544 is preferably disposed between the oxide 530a, the oxide 530b, the conductive layer 542a, and the conductive layer 542b and the insulating layer 580. As shown in FIGS. 15B and 15C, the conductive layer 560 preferably has a conductive layer 560a provided inside the insulating layer 545 and a conductive layer 560b provided so as to be embedded inside the conductive layer 560a. As shown in FIGS. 15B and 15C, an insulating layer 574 is preferably disposed on the insulating layer 580, the conductive layer 560, and the insulating layer 545.

[0173] In this specification and the like, oxide 530a and oxide 530b may be collectively referred to as oxide 530.

[0174] Note that, in the transistor 500, a two-layer structure of the oxide 530a and the oxide 530b is illustrated in the region where a channel is formed and in the vicinity thereof, but the present invention is not limited to this structure. For example, a single layer of the oxide 530b or a stacked structure of three or more layers may be used.

[0175] Although the conductive layer 560 in the transistor 500 has a two-layer structure, the present invention is not limited to this. For example, the conductive layer 560 may have a single-layer structure or a stacked structure of three or more layers.

[0176] Here, the conductive layer 560 functions as a gate electrode of the transistor 500. The conductive layer 542a functions as one of a source electrode and a drain electrode of the transistor 500, and the conductive layer 542b functions as the other of the source electrode and the drain electrode of the transistor 500. As described above, the conductive layer 560 is formed so as to be embedded in an opening of the insulating layer 580 formed in a region sandwiched between the conductive layer 542a and the conductive layer 542b. The conductive layer 560, the conductive layer 542a, and the conductive layer 542b are arranged in a self-aligned manner with respect to the opening of the insulating layer 580. That is, in the transistor 500, the gate electrode can be arranged in a self-aligned manner between the source electrode and the drain electrode. Therefore, the conductive layer 560 can be formed without providing a margin for alignment, and therefore the area occupied by the transistor 500 can be reduced. This allows miniaturization and high integration of the semiconductor device.

[0177] Here, in miniaturizing a semiconductor device, it is required to shorten the gate length. On the other hand, it is necessary to prevent the conductivity of the conductive layer 560 from decreasing. If the thickness of the conductive layer 560 is increased in order to prevent the conductivity of the conductive layer 560 from decreasing, the conductive layer 560 may have a shape with a high aspect ratio. As described above, in the transistor 500, the conductive layer 560 is provided so as to be embedded in the opening of the insulating layer 580. This allows the transistor 500 to be formed without the conductive layer 560 collapsing during the process, even if the conductive layer 560 has a shape with a high aspect ratio.

[0178] Furthermore, since the conductive layer 560 is formed in a self-aligned manner in the region between the conductive layer 542a and the conductive layer 542b, the conductive layer 560 does not have a region overlapping with the conductive layer 542a or the conductive layer 542b. This makes it possible to reduce parasitic capacitance formed between the conductive layer 560 and the conductive layer 542a and between the conductive layer 560 and the conductive layer 542b, and thus makes it possible to improve the switching speed and frequency characteristics of the transistor 500.

[0179] In the transistor 500, a metal oxide functioning as an oxide semiconductor is used for the oxide 530 including the channel formation region. Note that the oxide semiconductor preferably contains at least one of In and Zn. For example, a metal oxide such as In-M-Zn oxide (wherein the element M is one or more elements selected from aluminum, gallium, yttrium, copper, vanadium, beryllium, boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.) may be used for the oxide 530.

[0180] The metal oxide functioning as an oxide semiconductor may be formed by a sputtering method or an ALD (Atomic Layer Deposition) method. Note that the metal oxide functioning as an oxide semiconductor will be described in detail in another embodiment.

[0181] The metal oxide that functions as a channel formation region in the oxide 530 preferably has a band gap of 2 eV or more, and more preferably has a band gap of 2.5 eV or more. In this manner, by using a metal oxide with a wide band gap, the off-state current of the transistor can be reduced.

[0182] The oxide 530 has the oxide 530a below the oxide 530b, and thus can suppress the diffusion of impurities from components formed below the oxide 530a to the oxide 530b.

[0183] The oxide 530 preferably has a laminated structure of a plurality of oxide layers having different atomic ratios of metal atoms. Specifically, the atomic ratio of element M among the constituent elements in the metal oxide used for the oxide 530a is preferably larger than the atomic ratio of element M among the constituent elements in the metal oxide used for the oxide 530b. In addition, the atomic ratio of element M to In in the metal oxide used for the oxide 530a is preferably larger than the atomic ratio of element M to In in the metal oxide used for the oxide 530b. In addition, the atomic ratio of In to element M in the metal oxide used for the oxide 530b is preferably larger than the atomic ratio of In to element M in the metal oxide used for the oxide 530a.

[0184] In addition, it is preferable that the energy of the conduction band minimum of the oxide 530a is higher than that of the oxide 530b, or, in other words, it is preferable that the electron affinity of the oxide 530a is smaller than that of the oxide 530b.

[0185] Here, at the junction between the oxide 530a and the oxide 530b, the energy level of the conduction band minimum changes gradually. In other words, it can be said that the energy level of the conduction band minimum at the junction between the oxide 530a and the oxide 530b changes continuously or is a continuous junction. To achieve this, it is preferable to reduce the defect level density of the mixed layer formed at the interface between the oxide 530a and the oxide 530b.

[0186] Specifically, the oxide 530a and the oxide 530b have a common element other than oxygen (as a main component), so that a mixed layer with a low density of defect states can be formed. For example, when the oxide 530b is an In-Ga-Zn oxide, the oxide 530a may be an In-Ga-Zn oxide, a Ga-Zn oxide, or a gallium oxide.

[0187] At this time, the main carrier path is the oxide 530b. By configuring the oxide 530a as described above, the defect state density at the interface between the oxide 530a and the oxide 530b can be reduced. Therefore, the effect of interface scattering on carrier conduction is reduced, and the transistor 500 can obtain a high on-state current.

[0188] As shown in FIGS. 15B and 15C , the insulating layer 524 can be provided to have a region in contact with the oxide 530. When the insulating layer 524 has a region in contact with the oxide 530, it is preferable to use an insulator containing more oxygen than the oxygen that satisfies the stoichiometric composition as the insulating layer 524. The oxygen is easily released from the film by heating. In this specification and the like, oxygen released by heating may be referred to as "excess oxygen." In other words, it is preferable that the insulating layer 524 has a region containing excess oxygen (also referred to as an "excess oxygen region"). By providing such an insulating layer containing excess oxygen in contact with the oxide 530, oxygen deficiencies (V O When hydrogen enters an oxygen vacancy in the oxide 530, the defect (hereinafter, V OH.) may function as a donor and generate electrons as carriers. Some of the hydrogen may bond with oxygen that is bonded to a metal atom to generate electrons as carriers. Therefore, a transistor using an oxide semiconductor containing a large amount of hydrogen is likely to have normally-on characteristics. Furthermore, hydrogen in an oxide semiconductor is easily moved by stress such as heat or an electric field. Therefore, if an oxide semiconductor contains a large amount of hydrogen, the reliability of the transistor may be deteriorated. In one embodiment of the present invention, V in the oxide 530 O It is preferable to reduce H as much as possible to obtain high-purity intrinsic or substantially high-purity intrinsic. O In order to obtain an oxide semiconductor in which H is sufficiently reduced, it is important to remove impurities such as moisture and hydrogen from the oxide semiconductor (also referred to as "dehydration" or "dehydrogenation treatment") and to supply oxygen to the oxide semiconductor to compensate for oxygen vacancies (also referred to as "oxygenation treatment"). O When an oxide semiconductor in which impurities such as H are sufficiently reduced is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0189] In this specification and the like, an oxide semiconductor having a low impurity concentration and a low density of defect states is referred to as a high-purity intrinsic or substantially high-purity intrinsic oxide semiconductor. Note that an oxide semiconductor having a low carrier concentration may be referred to as a high-purity intrinsic or substantially high-purity intrinsic oxide semiconductor.

[0190] Specifically, it is preferable to use an oxide material from which some oxygen is released by heating as an insulator having an excess oxygen region. An 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 18 atoms / cm 3 More than 1.0×10 19 atoms / cm 3 More preferably, 2.0×10 19 atoms / cm 3 or more than 3.0 x 10 20 atoms / cm 3The oxide film is one having the above-mentioned 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.

[0191] In addition, the oxide 530 may be brought into contact with the insulator having the excess oxygen region and subjected to one or more of heat treatment, microwave treatment, and RF treatment. By carrying out such treatment, water or hydrogen in the oxide 530 can be removed. For example, a reaction occurs in the oxide 530 that breaks the bond of VoH, in other words, "V O The hydrogen can be dehydrogenated by the reaction "H → Vo + H". Some of the hydrogen generated at this time may combine with oxygen and be removed as HO from the oxide 530 or the insulating layer near the oxide 530. Some of the hydrogen may be gettered to the conductive layer 542a or the conductive layer 542b.

[0192] In addition, the microwave treatment is preferably performed using, for example, a device having a power source that generates high-density plasma or a device having a power source that applies RF to the substrate side. For example, high-density oxygen radicals can be generated by using a gas containing oxygen and high-density plasma. Then, by applying RF to the substrate side, the oxygen radicals generated by the high-density plasma can be efficiently introduced into the oxide 530 or the insulating layer near the oxide 530. In addition, the pressure of the microwave treatment may be set to 133 Pa or more, preferably 200 Pa or more, and more preferably 400 Pa or more. In addition, for example, oxygen and argon are used as gases to be introduced into the microwave treatment device, and the oxygen flow rate ratio (O2 / (O2+Ar)) is 50% or less, preferably 10% or more and 30% or less.

[0193] In addition, in a manufacturing process of the transistor 500, heat treatment is preferably performed with the surface of the oxide 530 exposed. The heat treatment may be performed at a temperature of, for example, 100° C. or higher and 450° C. or lower, more preferably 350° C. or higher and 400° C. or lower. Note that the heat treatment is performed in an atmosphere of nitrogen gas or an inert gas, or an atmosphere containing an oxidizing gas at 10 ppm or higher, 1% or higher, or 10% or higher. For example, the heat treatment is preferably performed in an oxygen atmosphere. In this way, oxygen is supplied to the oxide 530 to reduce oxygen deficiencies (V O ) can be reduced. The heat treatment may be performed under reduced pressure. Alternatively, the heat treatment may be performed in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas in order to compensate for the desorbed oxygen after the heat treatment in a nitrogen gas or inert gas atmosphere. Alternatively, the heat treatment may be performed in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas in order to compensate for the desorbed oxygen. Alternatively, the heat treatment may be performed in an atmosphere containing 10 ppm or more, 1% or more, or 10% or more of an oxidizing gas in succession to a heat treatment in a nitrogen gas or inert gas atmosphere.

[0194] By subjecting the oxide 530 to oxygen addition treatment, the oxygen vacancies in the oxide 530 can be repaired by the supplied oxygen. In other words, the reaction "Vo+O→null" can be promoted. Furthermore, the hydrogen remaining in the oxide 530 reacts with the supplied oxygen, and the hydrogen can be removed as H2O (dehydrated). As a result, the hydrogen remaining in the oxide 530 recombines with the oxygen vacancies to form V O The formation of H can be suppressed.

[0195] A conductive layer 542a and a conductive layer 542b functioning as a source electrode and a drain electrode are provided over the oxide 530b. For the conductive layer 542a and the conductive layer 542b, 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, and lanthanum, an alloy containing the above metal element, an alloy combining the above metal elements, or the like is preferably used. 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, an oxide containing lanthanum and nickel, or the like 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 conductive materials that are difficult to oxidize, or materials that maintain conductivity even when oxygen is absorbed, and are therefore preferable.Furthermore, metal nitride films such as tantalum nitride are preferable because they have barrier properties against hydrogen or oxygen.

[0196] 15, the conductive layer 542a and the conductive layer 542b have a single-layer structure, but may have a stacked structure of two or more layers. For example, a tantalum nitride film and a tungsten film may be stacked. Alternatively, a titanium film and an aluminum film may be stacked. Alternatively, a two-layer structure in which an aluminum film is stacked over a tungsten film, a two-layer structure in which a copper film is stacked over a copper-magnesium-aluminum alloy film, a two-layer structure in which a copper film is stacked over a titanium film, or a two-layer structure in which a copper film is stacked over a tungsten film may be used.

[0197] In addition, there are three-layer structures in which a titanium film or titanium nitride film is laminated on the titanium film or titanium nitride film, an aluminum film or copper film is laminated on the titanium film or titanium nitride film, and a titanium film or titanium nitride film is further formed thereon, and a three-layer structure in which a molybdenum film or molybdenum nitride film is laminated on the molybdenum film or molybdenum nitride film, an aluminum film or copper film is laminated on the molybdenum film or molybdenum nitride film, and a molybdenum film or molybdenum nitride film is further formed thereon, etc. Note that a transparent conductive material containing indium oxide, tin oxide, or zinc oxide may be used.

[0198] 15B, a region 543a may be formed as a low-resistance region at the interface of the oxide 530 with the conductive layer 542a and in its vicinity. A region 543b may be formed as a low-resistance region at the interface of the oxide 530 with the conductive layer 542b and in its vicinity. In this case, the region 543a functions as one of the source region and the drain region, and the region 543b functions as the other of the source region and the drain region. A channel formation region is formed in a region sandwiched between the regions 543a and 543b.

[0199] By providing the conductive layers 542a and 542b in contact with the oxide 530, the oxygen concentrations in the regions 543a and 543b may be reduced. A metal compound layer containing a metal contained in the conductive layer 542a and a component of the oxide 530 may be formed in the region 543a. A metal compound layer containing a metal contained in the conductive layer 542b and a component of the oxide 530 may be formed in the region 543b. In such a case, the carrier density in the regions 543a and 543b is increased, and the electrical resistance in the regions 543a and 543b is reduced.

[0200] The insulating layer 544 is provided to cover the conductive layers 542a and 542b and has a function of suppressing oxidation of the conductive layers 542a and 542b. In this case, the insulating layer 544 may be provided to cover the side surfaces of the oxide 530 and to be in contact with the insulating layer 524.

[0201] The insulating layer 544 can be made of a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, neodymium, lanthanum, magnesium, etc. Alternatively, the insulating layer 544 can be made of silicon nitride oxide, silicon nitride, or the like.

[0202] In particular, it is preferable to use aluminum oxide or hafnium oxide, which is an insulator containing an oxide of either or both of aluminum and hafnium, as the insulating layer 544. Alternatively, it is preferable to use an oxide containing aluminum and hafnium (hafnium aluminate), or the like. In particular, hafnium aluminate has higher heat resistance than a hafnium oxide film. Therefore, it is preferable because it is less likely to crystallize in a heat treatment in a later step. Note that when the conductive layer 542a and the conductive layer 542b are made of a material having oxidation resistance or a material whose conductivity does not decrease significantly even if it absorbs oxygen, the insulating layer 544 is not an essential component. It may be designed appropriately depending on the desired transistor characteristics.

[0203] The insulating layer 544 can suppress diffusion of impurities such as water and hydrogen contained in the insulating layer 580 into the oxide 530b. In addition, the conductive layer 560 can be prevented from being oxidized by excess oxygen contained in the insulating layer 580.

[0204] The insulating layer 545 functions as a gate insulating film for the conductive layer 560. Like the insulating layer 524, the insulating layer 545 is preferably formed using an insulator that contains excess oxygen and releases oxygen by heating.

[0205] Specifically, silicon oxide having excess oxygen, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine is added, silicon oxide to which carbon is added, silicon oxide to which carbon and nitrogen are added, and silicon oxide having vacancies can be used. In particular, silicon oxide and silicon oxynitride are preferable because they are stable against heat.

[0206] In this specification, silicon oxynitride refers to a material whose composition contains more oxygen than nitrogen, silicon nitride oxide refers to a material whose composition contains more nitrogen than oxygen, aluminum oxynitride refers to a material whose composition contains more oxygen than nitrogen, and aluminum nitride oxide refers to a material whose composition contains more nitrogen than oxygen.

[0207] By providing an insulator containing excess oxygen as the insulating layer 545, oxygen can be effectively supplied from the insulating layer 545 to a channel formation region of the oxide 530b. The concentration of impurities such as water or hydrogen in the insulating layer 545 is preferably reduced. The thickness of the insulating layer 545 is preferably 1 nm to 20 nm.

[0208] Furthermore, in order to efficiently supply excess oxygen contained in the insulating layer 545 to the oxide 530, a metal oxide may be provided between the insulating layer 545 and the conductive layer 560. The metal oxide preferably has a composition that suppresses oxygen diffusion from the insulating layer 545 to the conductive layer 560. By providing a metal oxide that suppresses oxygen diffusion between the insulating layer 545 and the conductive layer 560, the diffusion of excess oxygen from the insulating layer 545 to the conductive layer 560 is suppressed. That is, a decrease in the amount of excess oxygen supplied to the oxide 530 can be suppressed. Furthermore, oxidation of the conductive layer 560 due to the excess oxygen can be suppressed.

[0209] Note that the insulating layer 545 may have a stacked structure. As transistors are miniaturized and highly integrated, problems such as leakage current may occur due to a thinner gate insulating film. For this reason, by forming the insulating layer that functions as the gate insulating film into a stacked structure of a high-k material and a thermally stable material, the gate potential when the transistor is driven can be reduced while maintaining the physical film thickness.

[0210] Although the conductive layer 560 functioning as the first gate electrode is shown as having a two-layer structure in FIGS. 15B and 15C, it may have a single-layer structure or a stacked structure of three or more layers.

[0211] The conductive layer 560a is preferably made of a conductive material having a function of suppressing diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (N2O, NO, NO2, etc.), and copper atoms. Alternatively, a conductive material having a function of suppressing diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.) is preferably used. Since the conductive layer 560a has a function of suppressing diffusion of oxygen, it is possible to suppress a decrease in conductivity due to oxidation of the conductive layer 560b caused by oxygen contained in the insulating layer 545. As a conductive material having a function of suppressing diffusion of oxygen, for example, tantalum, tantalum nitride, ruthenium, ruthenium oxide, or the like is preferably used. In addition, an oxide semiconductor applicable to the oxide 530 can be used as the conductive layer 560a. In that case, the conductive layer 560b is formed by a sputtering method, whereby the electrical resistance value of the conductive layer 560a can be reduced. This can be called an OC (Oxide Conductor) electrode.

[0212] The conductive layer 560b is preferably formed using a conductive material containing tungsten, copper, or aluminum as a main component. Since the conductive layer 560b also functions as a wiring, it is preferable to use a conductor with low electrical resistance. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. The conductive layer 560b may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above conductive material.

[0213] The insulating layer 580 can be provided over the conductive layer 542a and the conductive layer 542b with the insulating layer 544 interposed therebetween. The insulating layer 580 preferably has an excess oxygen region. For example, the insulating layer 580 preferably has 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 voids, a resin, or the like. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In addition, silicon oxide and silicon oxide having voids are preferable because they allow the formation of excess oxygen regions easily in a later step.

[0214] The insulating layer 580 preferably has an excess oxygen region. By providing the insulating layer 580 from which oxygen is released by heating, oxygen in the insulating layer 580 can be efficiently supplied to the oxide 530. Note that the concentration of impurities such as water or hydrogen in the insulating layer 580 is preferably reduced.

[0215] The insulating layer 574 is preferably provided to have a region in contact with a top surface of the insulating layer 580, a top surface of the conductive layer 560, and a top surface of the insulating layer 545. By forming the insulating layer 574 by a sputtering method, excess oxygen regions can be provided in the insulating layer 545 and the insulating layer 580. Thus, oxygen can be supplied from the excess oxygen region to the oxide 530.

[0216] For example, the insulating layer 574 can be made of a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like.

[0217] In particular, aluminum oxide has high barrier properties and can suppress the diffusion of hydrogen and nitrogen even in a thin film of 0.5 nm to 3.0 nm. Therefore, aluminum oxide formed by sputtering can function as a barrier film against impurities such as hydrogen as well as an oxygen source.

[0218] An insulating layer 581 functioning as an interlayer film is preferably provided over the insulating layer 574. The insulating layer 581 preferably has a reduced concentration of impurities such as water or hydrogen.

[0219] Further, the conductive layer 540a and the conductive layer 540b are placed in openings formed in the insulating layer 581, the insulating layer 574, the insulating layer 580, and the insulating layer 544. The conductive layer 540a and the conductive layer 540b are provided opposite to each other with the conductive layer 560 interposed therebetween.

[0220] Examples of the substrate that can be used in the semiconductor device according to one embodiment of the present invention include an insulating substrate, a semiconductor substrate, or a conductive substrate. Examples of the insulating substrate include a glass substrate, a quartz substrate, a sapphire substrate, a stabilized zirconia substrate (such as an yttria-stabilized zirconia substrate), a resin substrate, and the like. Examples of the semiconductor substrate include a semiconductor substrate made of silicon or germanium, or a compound semiconductor substrate made of gallium nitride, silicon carbide, silicon germanium, gallium arsenide, indium phosphide, zinc oxide, or gallium oxide. Examples of the semiconductor substrate include a semiconductor substrate having an insulating region inside the semiconductor substrate, such as an SOI (Silicon On Insulator) substrate. Examples of the conductive substrate include a graphite substrate, a metal substrate, an alloy substrate, a conductive resin substrate, and the like. Examples of the conductive substrate include a substrate having a metal nitride, a substrate having a metal oxide, and the like. Examples of the conductive substrate include a substrate in which a conductor or a semiconductor is provided on an insulating substrate, a substrate in which a conductor or an insulator is provided on a semiconductor substrate, and a substrate in which a semiconductor or an insulator is provided on a conductive substrate.

[0221] <Transistor configuration example 2> 16A, 16B, and 16C are diagrams showing a configuration example of a transistor 500A, which is a modified example of the transistor 500. FIG. 16A is a top view of the transistor 500A. FIG. 16B is a cross-sectional view of a portion indicated by a dashed line L3-L4 in FIG. 16A, and is also a cross-sectional view of the transistor 500A in the channel length direction. FIG. 16C is a cross-sectional view of a portion indicated by a dashed line W3-W4 in FIG. 16A, and is also a cross-sectional view of the transistor 500A in the channel width direction. Note that in the top view of FIG. 16A, some elements are omitted for clarity.

[0222] The transistor 500A differs from the transistor 500 in that insulating layers 514, 516, 520, and 522 are provided between a substrate (not shown) and an insulating layer 524, and a conductive layer 503 is disposed so as to be embedded in the insulating layer 514 and the insulating layer 516. Here, the insulating layer 520 is disposed on the insulating layer 516 and the conductive layer 503, the insulating layer 522 is disposed on the insulating layer 520, and the insulating layer 524 is disposed on the insulating layer 522.

[0223] The conductive layer 503 functions as a backgate electrode. The conductive layer 503 is arranged to have a region overlapping with the oxide 530 and the conductive layer 560. In this manner, when a potential is supplied to the conductive layer 560 and the conductive layer 503, an electric field generated from the conductive layer 560 and an electric field generated from the conductive layer 503 are connected to each other, so that a channel formation region formed in the oxide 530 can be electrically surrounded.

[0224] In this specification, etc., a structure of a transistor in which a channel formation region is electrically surrounded by the electric field of a pair of gate electrodes (a first gate electrode and a second gate electrode) is called a surrounded channel (s-channel) structure. In addition, in this specification, etc., the s-channel structure has a feature that the side and periphery of the oxide 530 in contact with the conductive layer 542a and the conductive layer 542b functioning as a source electrode and a drain electrode are I-type like the channel formation region. In addition, the side and periphery of the oxide 530 in contact with the conductive layer 542a and the conductive layer 542b are in contact with the insulating layer 544, so that they can be I-type like the channel formation region. In this specification, etc., the I-type can be treated as the same as high purity intrinsic. In addition, the s-channel structure disclosed in this specification, etc. is different from the fin type structure and the planar type structure. By adopting the s-channel structure, it is possible to obtain a transistor that is more resistant to the short channel effect, in other words, a transistor in which the short channel effect is less likely to occur.

[0225] The conductive layer 503 can have a structure including a conductive layer 503a and a conductive layer 503b. The conductive layer 503a is formed in contact with the inner walls of the openings of the insulating layer 514 and the insulating layer 516, and the conductive layer 503b is formed further inside. Note that in this embodiment, the conductive layer 503 has a structure in which the conductive layer 503a and the conductive layer 503b are stacked, but one embodiment of the present invention is not limited thereto. For example, the conductive layer 503 may have a single layer structure or a stacked structure of three or more layers.

[0226] Here, the conductive layer 503a is preferably made of a conductive material having a function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (the impurities are less likely to permeate through the conductive material). Alternatively, it is preferably made of a conductive material having a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, and the like) (the oxygen is less likely to permeate through the conductive material). 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 the oxygen.

[0227] For example, the conductive layer 503a has a function of suppressing diffusion of oxygen, so that the conductive layer 503b can be prevented from being oxidized and the conductivity from being reduced.

[0228] In addition, in the case where the conductive layer 503 also functions as a wiring, the conductive layer 503b is preferably formed using a conductive material having high conductivity, which is mainly composed of tungsten, copper, or aluminum.

[0229] In the transistor 500A, the insulating layers 520, 522, and 524 function as gate insulating films for the conductive layer 503. As described above, the insulating layer 545 also functions as a gate insulating film. Thus, the insulating layer 545 can be referred to as a first gate insulating film, and the insulating layers 520, 522, and 524 can be referred to as a second gate insulating film.

[0230] As described above, the insulating layer 524 can have an excess oxygen region. In this case, it is preferable that the insulating layer 522 has a function of suppressing diffusion of oxygen (for example, oxygen atoms, oxygen molecules, or the like) (i.e., the insulating layer 522 is less likely to transmit the oxygen).

[0231] The insulating layer 522 has a function of suppressing diffusion of oxygen and impurities, which can suppress diffusion of oxygen contained in the oxide 530 toward the insulating layer 520. In addition, the conductive layer 503 can be suppressed from reacting with oxygen contained in the insulating layer 524 or the oxide 530.

[0232] The insulating layer 522 is preferably made of a single layer or a multilayer of an insulator containing a so-called high-k material, such as aluminum oxide, hafnium oxide, oxide containing aluminum and hafnium (hafnium aluminate), tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). As transistors become smaller and more highly integrated, problems such as leakage current may occur due to the thinning of the gate insulating film. By using a high-k material as the insulator that functions as the gate insulating film, it is possible to reduce the gate potential when the transistor is driven while maintaining the physical film thickness.

[0233] In particular, it is preferable to use an insulator containing an oxide of one or both of aluminum and hafnium, which are insulating materials having a function of suppressing the diffusion of impurities and oxygen (the oxygen is unlikely to permeate through them). As an 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. When the insulating layer 522 is formed using such a material, the insulating layer 522 functions as a layer that suppresses the release of oxygen from the oxide 530 and the intrusion of impurities such as hydrogen into the oxide 530 from the periphery of the transistor 500.

[0234] 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.

[0235] In addition, it is preferable that the insulating layer 520 is thermally stable. For example, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In addition, by combining a high-k material insulator with silicon oxide or silicon oxynitride, it is possible to obtain the insulating layer 520 having a laminated structure that is thermally stable and has a high relative dielectric constant.

[0236] 16B and 16C, insulating layers 520, 522, and 524 are illustrated as the second gate insulating film having a three-layer stack structure, but the second gate insulating film may have a single layer, two layers, or four or more layers. In this case, the second gate insulating film is not limited to a stack structure made of the same material, and may have a stack structure made of different materials.

[0237] <Transistor configuration example_3> 17A, 17B, and 17C are diagrams showing a configuration example of a transistor 500B, which is a modified example of the transistor 500A. FIG. 17A is a top view of the transistor 500B. FIG. 17B is a cross-sectional view of a portion indicated by a dashed line L5-L6 in FIG. 17A, and is also a cross-sectional view of the transistor 500B in the channel length direction. FIG. 17C is a cross-sectional view of a portion indicated by a dashed line W5-W6 in FIG. 17A, and is also a cross-sectional view of the transistor 500B in the channel width direction. Note that in the top view of FIG. 17A, some elements are omitted for clarity.

[0238] The transistor 500B differs from the transistor 500A in that it includes an insulating layer 552, an insulating layer 513, and an insulating layer 404. The transistor 500B also differs from the transistor 500A in that the insulating layer 552 is provided in contact with a side surface of the conductive layer 540a and the insulating layer 552 is provided in contact with a side surface of the conductive layer 540b. The transistor 500B also differs from the transistor 500A in that the insulating layer 520 is not provided.

[0239] In the transistor 500B, an insulating layer 513 is provided over a substrate (not shown).

[0240] In the transistor 500B, the insulating layer 514, the insulating layer 516, the insulating layer 522, the insulating layer 524, the insulating layer 544, the insulating layer 580, and the insulating layer 574 are patterned, and the insulating layer 404 covers them. That is, the insulating layer 404 contacts the upper surface of the insulating layer 574, the side of the insulating layer 574, the side of the insulating layer 580, the side of the insulating layer 544, the side of the insulating layer 524, the side of the insulating layer 522, the side of the insulating layer 516, the side of the insulating layer 514, and the upper surface of the insulating layer 513. As a result, the oxide 530 and the like are isolated from the outside by the insulating layer 404 and the insulating layer 513.

[0241] The insulating layer 513 and the insulating layer 404 preferably have a high function of suppressing diffusion of hydrogen (for example, at least one of hydrogen atoms, hydrogen molecules, and the like) or water molecules. For example, the insulating layer 513 and the insulating layer 404 are preferably made of silicon nitride or silicon nitride oxide, which are materials with high hydrogen barrier properties. This can suppress diffusion of hydrogen and the like into the oxide 530, thereby suppressing deterioration in the characteristics of the transistor 500B. Therefore, the reliability of the semiconductor device of one embodiment of the present invention can be improved.

[0242] The insulating layer 552 is provided to have a region in contact with the insulating layer 581, the insulating layer 404, the insulating layer 574, the insulating layer 580, and the insulating layer 544. The insulating layer 552 preferably has a function of suppressing diffusion of hydrogen or water molecules. For example, the insulating layer 552 is preferably formed using an insulator having a high hydrogen barrier property, such as silicon nitride, aluminum oxide, or silicon nitride oxide. In particular, silicon nitride is preferably used as the insulating layer 552 because it has a high hydrogen barrier property. By using a material having a high hydrogen barrier property for the insulating layer 552, impurities such as water or hydrogen can be suppressed from diffusing from the insulating layer 580 or the like to the oxide 530 through the conductive layer 540a or the conductive layer 540b. Furthermore, oxygen contained in the insulating layer 580 can be suppressed from being absorbed by the conductive layer 540a and the conductive layer 540b. As described above, the reliability of the semiconductor device of one embodiment of the present invention can be improved.

[0243] <Transistor configuration example_4> 18A, 18B, and 18C are diagrams showing a configuration example of a transistor 500C, which is a modified example of the transistor 500. FIG. 18A is a top view of the transistor 500C. FIG. 18B is a cross-sectional view of a portion indicated by a dashed line L7-L8 in FIG. 18A, and is also a cross-sectional view of the transistor 500C in the channel length direction. FIG. 18C is a cross-sectional view of a portion indicated by a dashed line W7-W8 in FIG. 18A, and is also a cross-sectional view of the transistor 500C in the channel width direction. Note that in the top view of FIG. 18A, some elements are omitted for clarity.

[0244] The conductive layer 560 functioning as the first gate electrode includes a conductive layer 560a and a conductive layer 560b over the conductive layer 560a. The conductive layer 560a is preferably made of a conductive material having a function of suppressing diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms. Alternatively, the conductive layer 560 is preferably made of a conductive material having a function of suppressing diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, and the like).

[0245] Since the conductive layer 560a has a function of suppressing oxygen diffusion, even if the conductive layer 560b is made of a material that is easily oxidized, the conductive layer 560b can be suppressed from being oxidized, and thus a decrease in the conductivity of the conductive layer 560 can be suppressed.

[0246] In addition, an insulating layer 544 is preferably provided so as to cover a top surface and side surfaces of the conductive layer 560 and a side surface of the insulating layer 545. Note that the insulating layer 544 may be formed using an insulating material having a function of suppressing diffusion of impurities such as water or hydrogen and oxygen. For example, aluminum oxide, hafnium oxide, or the like is preferably used. In addition, for example, a metal oxide such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, or tantalum oxide, silicon nitride oxide, silicon nitride, or the like may be used.

[0247] The insulating layer 544 can suppress oxidation of the conductive layer 560. Furthermore, the insulating layer 544 can suppress diffusion of impurities such as water and hydrogen contained in the insulating layer 580 into the transistor 500C.

[0248] In the transistor 500C, a part of the conductive layer 542a and a part of the conductive layer 542b overlap with the conductive layer 560, so that the parasitic capacitance is likely to be larger than that of the transistor 500. Thus, the driving frequency of the transistor 500C tends to be lower than that of the transistor 500. However, the productivity of the transistor 500C is higher than that of the transistor 500 because a step of forming an opening in the insulating layer 580 or the like and filling the conductive layer 560 and the insulating layer 545 or the like is not required.

[0249] The configurations, structures, methods, and the like described in this embodiment can be used in appropriate combination with the configurations, structures, methods, and the like described in other embodiments.

[0250] (Embodiment 3) In this embodiment, an oxide semiconductor, which is a type of metal oxide, will be described.

[0251] The metal oxide preferably contains at least indium or zinc. In particular, it is preferable that the metal oxide contains indium and zinc. In addition to these, it is preferable that the metal oxide contains aluminum, gallium, yttrium, tin, etc. Furthermore, the metal oxide may contain one or more elements selected from boron, silicon, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, cobalt, etc.

[0252] <Classification of crystal structures> First, classification of crystal structures in oxide semiconductors will be described with reference to Fig. 19A. Fig. 19A is a diagram for explaining classification of crystal structures of oxide semiconductors, typically IGZO (metal oxide containing In, Ga, and Zn).

[0253] As shown in FIG. 19A, 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). "Crystalline" excludes single crystal, poly crystal, and completely amorphous. "Crystalline" includes single crystal and poly crystal.

[0254] The structure in the bold frame shown in Fig. 19A is an intermediate state between "Amorphous" and "Crystal" and belongs to a new boundary region (New crystalline phase). In other words, this structure is completely different from the energetically unstable "Amorphous" and "Crystal".

[0255] The crystal structure of the film or substrate can be evaluated using an X-ray diffraction (XRD) spectrum. FIG. 19B shows an XRD spectrum obtained by GIXD (Grazing-Incidence XRD) measurement of the CAAC-IGZO film classified as "Crystalline". The GIXD method is also called the thin film method or the Seemann-Bohlin method. Hereinafter, the XRD spectrum obtained by the GIXD measurement shown in FIG. 19B will be simply referred to as the XRD spectrum. The vertical axis of FIG. 19B is the intensity, and the horizontal axis is 2θ. The composition of the CAAC-IGZO film shown in FIG. 19B is in the vicinity of In:Ga:Zn=4:2:3 [atomic ratio]. The thickness of the CAAC-IGZO film shown in FIG. 19B is 500 nm.

[0256] As shown in Figure 19B, 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. Note that, as shown in Figure 19B, the peak near 2θ=31° is asymmetric with respect to the angle at which the peak intensity is detected.

[0257] The crystal structure of the 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 the CAAC-IGZO film is shown in FIG. 19C. FIG. 19C is a diffraction pattern observed by NBED, which causes an electron beam to be incident parallel to the substrate. The composition of the CAAC-IGZO film shown in FIG. 19C is approximately In:Ga:Zn=4:2:3 [atomic ratio]. In the nanobeam electron diffraction method, electron diffraction is performed with a probe diameter of 1 nm.

[0258] As shown in FIG. 19C, multiple spots indicating c-axis orientation are observed in the diffraction pattern of the CAAC-IGZO film.

[0259] <<Structure of oxide semiconductor>> In addition, when focusing on the crystal structure, oxide semiconductors may be classified differently from that shown in FIG. 19A. 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. In addition, non-single-crystal oxide semiconductors include polycrystalline oxide semiconductors, amorphous-like oxide semiconductors (a-like OS), amorphous oxide semiconductors, and the like.

[0260] Here, the above-mentioned CAAC-OS, nc-OS, and a-like OS will be described in detail.

[0261] [CAAC-OS] CAAC-OS is an oxide semiconductor having a plurality of crystalline regions, each of which has a c-axis aligned in a specific direction. The specific direction is the thickness direction of the CAAC-OS film, the normal direction of the surface on which the CAAC-OS film is formed, or the normal direction of the surface of the CAAC-OS film. The crystalline region is a region having periodic atomic arrangement. If the atomic arrangement is considered as a lattice arrangement, the crystalline region is also a region with a uniform lattice arrangement. CAAC-OS has a region in which a plurality of crystalline regions are connected in the ab-plane direction, and the region may have distortion. The distortion refers to a portion in which the direction of the lattice arrangement changes between a region with a uniform lattice arrangement and another region with a uniform lattice arrangement in the region in which a plurality of crystalline regions are connected. In other words, CAAC-OS is an oxide semiconductor having a c-axis aligned and no clear orientation in the ab-plane direction.

[0262] 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 about several tens of nm.

[0263] In addition, 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, In layer) and a layer containing element M, zinc (Zn), and oxygen (hereinafter, (M, Zn) layer) are stacked. Note that indium and element M are mutually substituted. Thus, the (M, Zn) layer may contain indium. Also, the In layer may contain element M. Note that the In layer may contain Zn. The layered structure is observed as a lattice image in a high-resolution TEM image, for example.

[0264] When the CAAC-OS film is subjected to structural analysis using, for example, an XRD device, 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, composition, etc. of the metal elements constituting the CAAC-OS.

[0265] For example, a plurality of bright points (spots) are observed in the electron diffraction pattern of the CAAC-OS film, and the two spots are observed at positions symmetrical to each other with respect to the spot of the incident electron beam that has passed through the sample (also called the direct spot).

[0266] When the crystal region is observed from the specific direction, the lattice arrangement in the crystal region is based on a hexagonal lattice, but the unit lattice is not necessarily a regular hexagon, and may be a non-regular hexagon. The above distortion may have a lattice arrangement of a pentagon, heptagon, or the like. In addition, in the CAAC-OS, no clear grain boundary can be confirmed even in the vicinity of the distortion. That is, it can be seen that the formation of grain boundaries is suppressed by the distortion of the lattice arrangement. This is considered to be because the CAAC-OS can tolerate distortion due to the fact that the arrangement of oxygen atoms is not dense in the ab-plane direction, or the bond distance between atoms changes due to the substitution of metal atoms.

[0267] A crystal structure in which clear grain boundaries are observed is called polycrystal. The grain boundaries are likely to become recombination centers and capture carriers, causing a decrease in the on-current of a transistor and a decrease in field effect mobility. Therefore, CAAC-OS in which clear grain boundaries are not observed is one of the crystalline oxides having a crystal structure suitable for a semiconductor of a transistor. In order to form a CAAC-OS, a structure containing Zn is preferable. For example, In-Zn oxide and In-Ga-Zn oxide are suitable because they can suppress the occurrence of grain boundaries more than In oxide.

[0268] The CAAC-OS is an oxide semiconductor with high crystallinity and no clear crystal grain boundaries. Therefore, it can be said that the CAAC-OS is less susceptible to a decrease in electron mobility due to crystal grain boundaries. In addition, since the crystallinity of an oxide semiconductor can be decreased by the inclusion of impurities or the generation of defects, the CAAC-OS can be said to be an oxide semiconductor with few impurities and defects (oxygen vacancies, etc.). Therefore, the physical properties of an oxide semiconductor having the CAAC-OS are stable. Therefore, an oxide semiconductor having the CAAC-OS is resistant to heat and has high reliability. In addition, the CAAC-OS is stable against high temperatures (so-called thermal budget) in the manufacturing process. Therefore, the use of the CAAC-OS in an OS transistor can increase the degree of freedom in the manufacturing process.

[0269] [nc-OS] The nc-OS has periodic atomic arrangement in a minute region (for example, a region of 1 nm to 10 nm, particularly a region of 1 nm to 3 nm). In other words, the nc-OS has minute crystals. Note that the size of the minute crystals is, for example, 1 nm to 10 nm, particularly 1 nm to 3 nm, and therefore the minute crystals are also called nanocrystals. In addition, the nc-OS does not show regularity in crystal orientation between different nanocrystals. Therefore, no orientation is seen in the entire film. Therefore, the nc-OS may be indistinguishable from an a-like OS and an amorphous oxide semiconductor depending on the analysis method. For example, when a structure analysis is performed on an nc-OS film using an XRD device, no peak indicating crystallinity is detected in out-of-plane XRD measurement using θ / 2θ scan. In addition, when an nc-OS film is subjected to electron diffraction (also called selected area electron diffraction) using an electron beam with a probe diameter larger than that of nanocrystals (for example, 50 nm or more), a diffraction pattern like a halo 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 (e.g., 1 nm to 30 nm) that is close to the size of a nanocrystal or smaller than the nanocrystal, an electron diffraction pattern in which multiple spots are observed within a ring-shaped region centered on the direct spot may be obtained.

[0270] [a-like OS] The a-like OS is an oxide semiconductor having a structure between the nc-OS and an amorphous oxide semiconductor. The a-like OS has a void or low-density region. That is, the a-like OS has lower crystallinity than the nc-OS and CAAC-OS. Moreover, the a-like OS has a higher hydrogen concentration in the film than the nc-OS and CAAC-OS.

[0271] <<Oxide semiconductor structure>> Next, the above-mentioned CAC-OS will be described in detail, with reference to its material composition.

[0272] [CAC-OS] CAC-OS is, for example, a material 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 the vicinity thereof. In the following, a state in which one or more metal elements are unevenly distributed in a metal oxide and the regions having the metal elements are mixed in a size range of 0.5 nm to 10 nm, preferably 1 nm to 3 nm, or the vicinity thereof, is also referred to as a mosaic or patch state.

[0273] Furthermore, CAC-OS is a composite metal oxide in which the material is separated into a first region and a second region, forming a mosaic structure, and the first region is distributed throughout the film (hereinafter, also referred to as a cloud structure). In other words, CAC-OS is a composite metal oxide in which the first region and the second region are mixed together.

[0274] Here, the atomic ratios of In, Ga, and Zn to the metal elements constituting the CAC-OS in the In-Ga-Zn oxide are represented 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. Also, 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. Also, 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.

[0275] Specifically, the first region is a region mainly composed of indium oxide, indium zinc oxide, etc., and the second region is a region mainly composed of gallium oxide, gallium zinc oxide, etc. In other words, the first region can be rephrased as a region mainly composed of In, and the second region can be rephrased as a region mainly composed of Ga.

[0276] In addition, there are cases where a clear boundary between the first region and the second region cannot be observed.

[0277] For example, in the case of a CAC-OS of an In-Ga-Zn oxide, EDX mapping obtained using EDX (Energy Dispersive X-ray spectroscopy) has confirmed 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.

[0278] 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, giving the CAC-OS a switching function (On / Off function). In other words, CAC-OS has a conductive function in part of the material and an insulating function in other parts of the material, and the material as a whole functions as a semiconductor. By separating the conductive function from the insulating function, it is possible to maximize both functions. Therefore, by using CAC-OS in a transistor, it is possible to achieve a high on-current (I on ), high field effect mobility (μ), and good switching operation can be achieved.

[0279] Oxide semiconductors have a variety of structures and have 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.

[0280] <Transistor Having Oxide Semiconductor> Next, the case where the oxide semiconductor is used for a transistor will be described.

[0281] By using the oxide semiconductor for a transistor, a transistor with high field-effect mobility and high reliability can be realized.

[0282] For the transistor, an oxide semiconductor having a low carrier concentration is preferably used. For example, the carrier concentration of the oxide semiconductor is 1×10 17 cm -3 Less than or equal to 1×10 15 cm -3 Less than 1×10, more preferably 13 cm -3 Less than or equal to 1×10 11 cm -3 Less than 1×10, more preferably 10 cm -3 Less than 1 x 10 -9 cm-3 Note that in order to reduce the carrier concentration in the oxide semiconductor film, the impurity concentration in the oxide semiconductor film may be reduced to reduce the density of defect states.

[0283] Furthermore, 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 might also be low.

[0284] In addition, charges trapped in the trap states of an oxide semiconductor take a long time to disappear and may behave as if they are 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.

[0285] Therefore, in order to stabilize the electrical characteristics of a transistor, it is effective to reduce the impurity concentration in the oxide semiconductor. In order to reduce the impurity concentration in the oxide semiconductor, it is preferable to also reduce the impurity concentration in a nearby film. Examples of impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

[0286] <Impurities> Here, the influence of each impurity in an oxide semiconductor will be described.

[0287] When an oxide semiconductor contains silicon or carbon, which is one of the Group 14 elements, defect levels are formed in the oxide semiconductor. For this reason, the concentration of silicon or carbon in the oxide semiconductor and the concentration of silicon or carbon near the interface with the oxide semiconductor (concentration obtained by secondary ion mass spectrometry (SIMS)) are set to 2×10 18 atoms / cm 3 Less than or equal to 2 x 10 17 atoms / cm 3 The following applies.

[0288] In addition, when an oxide semiconductor contains an alkali metal or an alkaline earth metal, defect states may be formed and carriers may be generated. Therefore, a transistor using an oxide semiconductor containing an alkali metal or an alkaline earth metal is likely to have normally-on characteristics. For this reason, when the concentration of an alkali metal or an alkaline earth metal in an oxide semiconductor obtained by SIMS is 1×10 18 atoms / cm 3 Less than or equal to 2 x 10 16 atoms / cm 3 To the following:

[0289] Furthermore, 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 is likely 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 an 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 To the following:

[0290] Furthermore, 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. In addition, 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 hydrogen in the oxide semiconductor as much as possible. Specifically, when the hydrogen concentration in an oxide semiconductor measured 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.

[0291] When an oxide semiconductor in which impurities are sufficiently reduced is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0292] The configurations, structures, methods, and the like described in this embodiment can be used in appropriate combination with the configurations, structures, methods, and the like described in other embodiments.

[0293] (Embodiment 4) In this embodiment, a structural example of an imaging device to which the semiconductor device of one embodiment of the present invention can be applied will be described with reference to drawings.

[0294] 20A is a cross-sectional view illustrating a configuration example of an imaging device to which the semiconductor device of one embodiment of the present invention can be applied. Specifically, a cross-sectional configuration example of a photoelectric conversion device 60, a transistor 61, and a transistor 64, which are components of the pixel circuit 50 illustrated in FIG. 13A, is illustrated. In FIG. 20A, the pixel circuit 50 has a stacked structure of a layer 561 and a layer 562.

[0295] The layer 561 includes a photoelectric conversion device 60. The photoelectric conversion device 60 may be a laminate of a layer 565a, a layer 565b, and a layer 565c. The layer 565b includes a region 536 for electrically connecting the wiring provided in the layer 562 to the layer 565c. For example, the region 536 may include a p + It can be a mold region.

[0296] The photoelectric conversion device 60 shown in FIG. 20A is a pn junction photodiode. For example, + a layer 565b of an n-type semiconductor, and a layer 565c of an n-type semiconductor.+ Alternatively, layer 565a may be an n-type semiconductor. + a layer 565b is a p-type semiconductor, and a layer 565c is a p-type semiconductor. + Alternatively, the layer 565b may be an i-type semiconductor, which may be a pin junction photodiode.

[0297] The pn junction photodiode or pin junction photodiode can be formed using single crystal silicon. The pin junction photodiode can also be formed using a thin film of amorphous silicon, microcrystalline silicon, polycrystalline silicon, or the like.

[0298] A Si transistor is provided in layer 562. The Si transistor shown in Fig. 20A is a fin type having a channel formation region in a silicon substrate 540, and a cross section in the channel width direction is shown in Fig. 20B. The Si transistor may be a planar type as shown in Fig. 20C.

[0299] 20D, it may be a transistor having a silicon thin-film semiconductor layer 555. The semiconductor layer 555 may be, for example, single crystal silicon (SOI (Silicon on Insulator)) formed on an insulating layer 546 on a silicon substrate 540.

[0300] FIG. 20A shows a configuration example in which electrical connection between elements of layer 561 and elements of layer 562 is achieved by a bonding technique.

[0301] The layer 561 includes an insulating layer 542, a conductive layer 533, and a conductive layer 534. The conductive layer 533 and the conductive layer 534 have regions buried in the insulating layer 542. The conductive layer 533 is electrically connected to a layer 565a. The conductive layer 534 is electrically connected to a region 536. Furthermore, the surfaces of the insulating layer 542, the conductive layer 533, and the conductive layer 534 are planarized so that they are all at the same height.

[0302] The layer 562 includes an insulating layer 541, a conductive layer 531, and a conductive layer 532. The conductive layer 531 and the conductive layer 532 have a region buried in the insulating layer 541. The conductive layer 531 is electrically connected to the source or drain of the transistor 61. The surfaces of the insulating layer 541, the conductive layer 531, and the conductive layer 532 are planarized so that they are all at the same height.

[0303] Here, the conductive layers 531 and 533 preferably contain the same metal element as a main component. The conductive layers 532 and 534 preferably contain the same metal element as a main component. The insulating layers 541 and 542 preferably contain the same component as a main component.

[0304] For example, Cu, Al, Sn, Zn, W, Ag, Pt, Au, or the like can be used for the conductive layers 531, 532, 533, and 534. In view of ease of bonding, it is preferable to use Cu, Al, W, or Au. Furthermore, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, titanium nitride, or the like can be used for the insulating layers 541 and 542.

[0305] That is, the same metal material as described above is preferably used for each of the combination of the conductive layer 531 and the conductive layer 533 and the combination of the conductive layer 532 and the conductive layer 534. The same insulating material as described above is preferably used for each of the insulating layer 541 and the insulating layer 542. With this structure, the layer 561 and the layer 562 can be bonded to each other at a boundary therebetween.

[0306] This bonding can provide electrical connection between the combination of the conductive layer 531 and the conductive layer 533 and the combination of the conductive layer 532 and the conductive layer 534. In addition, the insulating layer 541 and the insulating layer 542 can be connected to each other with sufficient mechanical strength.

[0307] To bond metal layers together, a surface activation bonding method can be used, in which oxide films and adsorbed layers of impurities on the surfaces are removed by a sputtering process or the like, and cleaned and activated surfaces are brought into contact with each other to bond them. Alternatively, a diffusion bonding method can be used, in which surfaces are bonded together using a combination of temperature and pressure. In either case, bonding occurs at the atomic level, so a bond that is excellent not only electrically but also mechanically can be obtained.

[0308] In addition, for bonding insulating layers, a hydrophilic bonding method can be used in which high flatness is obtained by polishing, etc., and then surfaces that have been hydrophilically treated with oxygen plasma, etc. are brought into contact with each other to form a temporary bond, and then the final bond is performed by dehydrating them through heat treatment. Hydrophilic bonding also produces bonds at the atomic level, so mechanically excellent bonds can be obtained.

[0309] When the layer 561 and the layer 562 are bonded to each other, an insulating layer and a metal layer are mixed on the bonding surfaces of the layers, and therefore, for example, a surface activated bonding method and a hydrophilic bonding method may be combined.

[0310] For example, a method of cleaning the surface after polishing, subjecting the surface of the metal layer to an anti-oxidation treatment, and then subjecting it to a hydrophilic treatment and bonding can be used. The surface of the metal layer may be made of a resistant metal such as Au and then subjected to a hydrophilic treatment. Note that bonding methods other than the above-mentioned methods may also be used.

[0311] The configurations, structures, methods, and the like described in this embodiment can be used in appropriate combination with the configurations, structures, methods, and the like described in other embodiments.

[0312] (Embodiment 5) In this embodiment, examples of electronic devices in which a semiconductor device of one embodiment of the present invention can be used will be described.

[0313] Examples of electronic devices in which the semiconductor device of one embodiment of the present invention can be used include display devices, personal computers, image storage devices or image playback devices equipped with a recording medium, mobile phones, game machines including portable types, portable data terminals, electronic book terminals, video cameras, cameras such as digital still cameras, goggle-type displays (head-mounted displays), navigation systems, audio playback devices (car audio, digital audio players, etc.), copiers, facsimiles, printers, printer-combined machines, automated teller machines (ATMs), vending machines, etc. Specific examples of these electronic devices are shown in FIGS.

[0314] 21A shows an example of a mobile phone 910, which includes a housing 911, a display unit 912, operation buttons 913, an external connection port 914, a speaker 915, a socket 916, a camera 917, an earphone socket 918, and the like. The mobile phone 910 can be provided with a touch sensor on the display unit 912. Any operation such as making a call or inputting characters can be performed by touching the display unit 912 with a finger or a stylus. In addition, various removable storage devices such as a memory card such as an SD card, a USB memory, and an SSD (Solid State Drive) can be inserted into the socket 916.

[0315] The semiconductor device of one embodiment of the present invention can be applied to the mobile phone 910. For example, an imaging device including the semiconductor device of one embodiment of the present invention can be applied to an element for acquiring imaging data by the mobile phone 910, such as a camera 917. This allows the mobile phone 910 to be miniaturized.

[0316] 21B shows an example of a portable data terminal 920, which includes a housing 921, a display unit 922, a speaker 923, and a camera 924. Information can be input and output using a touch panel function of the display unit 922. Characters and the like can be recognized from an image acquired by the camera 924, and the characters can be output as voice by the speaker 923.

[0317] The semiconductor device of one embodiment of the present invention can be applied to the portable data terminal 920. For example, an imaging device including the semiconductor device of one embodiment of the present invention can be applied to an element for acquiring imaging data by the portable data terminal 920, such as the camera 924. This allows the portable data terminal 920 to be miniaturized.

[0318] 21C shows an example of a surveillance camera 960, which includes a mounting fixture 961, a housing 962, a lens 963, and the like. The surveillance camera 960 can be attached to a wall, a ceiling, or the like using the mounting fixture 961. Note that the term "surveillance camera" is a common name and does not limit the use. For example, a device having a function as a surveillance camera is also called a camera or a video camera.

[0319] The semiconductor device of one embodiment of the present invention can be applied to the surveillance camera 960. For example, an imaging device including the semiconductor device of one embodiment of the present invention can be applied to an element for acquiring imaging data by the surveillance camera 960. This allows the surveillance camera 960 to be miniaturized.

[0320] 21D shows an example of a video camera 940, which has a first housing 941, a second housing 942, a display unit 943, operation keys 944, a lens 945, a connection unit 946, a speaker 947, a microphone 948, etc. The operation keys 944 and the lens 945 can be provided in the first housing 941, and the display unit 943 can be provided in the second housing 942.

[0321] The semiconductor device of one embodiment of the present invention can be applied to the video camera 940. For example, an imaging device including the semiconductor device of one embodiment of the present invention can be applied to an element for acquiring imaging data by the video camera 940. This allows the video camera 940 to be miniaturized.

[0322] 21E illustrates an example of a digital camera 950, which includes a housing 951, a shutter button 952, a light-emitting portion 953, a lens 954, and the like. The semiconductor device of one embodiment of the present invention can be applied to the digital camera 950. For example, an imaging device including the semiconductor device of one embodiment of the present invention can be applied to an element for acquiring imaging data by the digital camera 950. This allows the digital camera 950 to be miniaturized.

[0323] 21F shows an example of a wristwatch-type information terminal 930, which includes a housing / wristband 931, a display unit 932, operation buttons 933, an external connection port 934, a camera 935, and the like. The display unit 932 is provided with a touch panel for operating the information terminal 930. The housing / wristband 931 and the display unit 932 are flexible and have excellent wearability on the body.

[0324] The semiconductor device of one embodiment of the present invention can be applied to the information terminal 930. For example, an imaging device including the semiconductor device of one embodiment of the present invention can be applied to an element for acquiring imaging data by the information terminal 930, such as a camera 935. This allows the information terminal 930 to be miniaturized.

[0325] The configurations, structures, methods, and the like described in this embodiment can be used in appropriate combination with the configurations, structures, methods, and the like described in other embodiments. [Explanation of symbols]

[0326] 10: semiconductor device, 11: transmission path, 20: circuit, 21: transistor, 22: transistor, 23: transistor, 24: capacitor, 30: circuit, 31: transistor, 32: transistor, 33: transistor, 34: capacitor, 40: circuit, 41: capacitor, 42: transistor, 50: pixel circuit, 60: photoelectric conversion device, 61: transistor, 62: transistor, 63: transistor, 64: transistor, 66: capacitor, 69: transistor, 71: period, 72: period, 73: period, 74: period, 75: period, 80: imaging device, 81 : pixel portion, 82: gate driver circuit, 83: data driver circuit, 404: insulating layer, 500: transistor, 500A: transistor, 500B: transistor, 500C: transistor, 503: conductive layer, 503a: conductive layer, 503b: conductive layer, 513: insulating layer, 514: insulating layer, 516: insulating layer, 520: insulating layer, 522: insulating layer, 524: insulating layer, 530: oxide, 530a: oxide, 530b: oxide, 531: conductive layer, 532: conductive layer, 533: conductive layer, 534: conductive layer, 536: region, 540: silicon substrate, 540a: conductive layer, 540b: Conductive layer, 541: insulating layer, 542: insulating layer, 542a: conductive layer, 542b: conductive layer, 543a: region, 543b: region, 544: insulating layer, 545: insulating layer, 546: insulating layer, 552: insulating layer, 555: semiconductor layer, 560: conductive layer, 560a: conductive layer, 560b: conductive layer, 561: layer, 562: layer, 565a: layer, 565b: layer, 565c: layer, 574: insulating layer, 580: insulating layer, 581: insulating layer, 910: mobile phone, 911: housing, 912: display unit, 913: operation button, 914: external connection port, 915: speaker, 916: socket, 917: camera, 918: earphone jack, 920: portable data terminal, 921: housing, 922: display unit, 923: speaker, 924: camera, 930: information terminal, 931: housing and wristband, 932: display unit, 933: operation button, 934: external connection port, 935: camera, 940: video camera, 941: housing, 942: housing, 943: display unit, 944: operation key, 945: lens, 946: connection unit, 947: speaker, 948: microphone, 950: digital camera, 951: housing, 952: shutter button, 953: light emitting unit, 954: lens, 960: surveillance camera,961: Mounting fixture, 962: Housing, 963: Lens,

Claims

1. A first circuit and a second circuit, the first circuit includes first to n-th transistors (n is an integer of 2 or more); the second circuit includes n+1 to 2n transistors; Either the sources or the drains of the first to n-th transistors are electrically connected to each other; the other of the sources or the drains of the first to n-th transistors are electrically connected to each other; the (n+1)th to (2n)th transistors are connected in series with each other, a first signal to an n-th signal are supplied to each of the first circuit and the second circuit; the first circuit has a function of outputting a first potential when any of the potentials of the first to n-th signals is equal to or lower than a first reference potential; the first circuit has a function of outputting a second potential when at least one of the potentials of the first to n-th signals is higher than the first reference potential; the second circuit has a function of outputting a third potential when any of the potentials of the first to n-th signals is higher than a second reference potential; The second circuit has a function of outputting the first potential when at least one of the potentials of the first to n-th signals is equal to or lower than the second reference potential.

2. In claim 1, the second potential is a potential corresponding to the first reference potential, The third potential is a potential corresponding to the second reference potential.

3. In claim 1 or 2, The first to n-th transistors and the (n+1) to 2n-th transistors are all n-channel transistors.

4. In claim 3, The second reference potential is lower than the first reference potential.

5. In claim 3 or 4, The second potential and the third potential are lower than the first potential.

6. In any one of claims 3 to 5, The first to n-th transistors and the (n+1) to 2n-th transistors all have a metal oxide in a channel formation region.

7. In any one of claims 1 to 6, a (2n+1)th transistor and a (2n+2)th transistor; one of a source and a drain of the 2nd n+1th transistor is electrically connected to the first circuit; one of a source and a drain of the 2nd n+2th transistor is electrically connected to the second circuit; the second potential is supplied to the other of the source or the drain of the 2n+1th transistor; the third potential is supplied to the other of the source and the drain of the 2n+2th transistor.

8. In any one of claims 1 to 7, a (2n+3)th transistor and a (2n+4)th transistor; one of a source and a drain of the 2nd n+3th transistor is electrically connected to the first circuit; one of a source and a drain of the 2nd n+4th transistor is electrically connected to the second circuit; the first potential is supplied to the other of the source or the drain of the 2n+3th transistor and the other of the source or the drain of the 2n+4th transistor.

9. a first circuit having first to n-th transistors (n is an integer of 2 or more); a second circuit having n+1-th to 2n-th transistors; and a 2n+1th transistor, a 2n+2th transistor, a 2n+3th transistor, and a 2n+4th transistor; Either the sources or the drains of the first to n-th transistors are electrically connected to each other; the other of the sources or the drains of the first to n-th transistors are electrically connected to each other; the (n+1)th to (2n)th transistors are connected in series with each other, one of a source and a drain of the 2nd n+1th transistor is electrically connected to the first circuit; one of a source and a drain of the 2nd n+2th transistor is electrically connected to the second circuit; one of a source and a drain of the 2nd n+3th transistor is electrically connected to the first circuit; A method for driving a semiconductor device, in which one of a source or a drain of the 2n+4th transistor is electrically connected to the second circuit, comprising the steps of: a first signal to an n-th signal are supplied to each of the first circuit and the second circuit; an i-th signal among the first to n-th signals is supplied to a gate of an i-th transistor (i is 1 to n) included in the first to n-th transistors and an n+i-th transistor included in the n+1 to 2n transistors; a first potential is supplied to the other of the source or the drain of the 2n+1th transistor and the other of the source or the drain of the 2n+2th transistor; a second potential is supplied to the other of the source or the drain of the 2nd n+3th transistor; a third potential is supplied to the other of the source or the drain of the 2nd n+4th transistor; In a first period, the 2n+1 transistor and the 2n+2 transistor are in an on state, and the 2n+3 transistor and the 2n+4 transistor are in an off state; A method for driving a semiconductor device, wherein the 2n+1 transistor and the 2n+2 transistor are turned off and the 2n+3 transistor and the 2n+4 transistor are turned on in a second period.

10. In claim 9, A method for driving a semiconductor device, in which the first to n-th transistors and the (n+1) to 2n-th transistors are all n-channel transistors.

11. In claim 10, A method for driving a semiconductor device, wherein the third potential is lower than the second potential.

12. In claim 10 or 11, A method for driving a semiconductor device, wherein the second potential and the third potential are lower than the first potential.

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