Power storage device

Abstract

To provide a novel oscillator, amplifier circuit, inverter circuit, amplifier circuit, battery control circuit, battery protection circuit, power storage device, semiconductor device, electric appliance, etc.SOLUTION: A semiconductor device includes an oscillator including a first transistor including a metal oxide, and second to fifth transistors. When the first transistor is turned on, a first potential is applied to a gate of the second transistor and a gate of the third transistor. When the first transistor is turned off, the first potential is kept. The oscillator applies a first signal according to the first potential to a first circuit, and the first circuit performs at least one of rectification and amplification on the first signal. The second transistor and the fourth transistor are connected in series and the third transistor and the fifth transistor are connected in series. A source or a drain of the third transistor is electrically connected to a gate of the fourth transistor, and a source or a drain of the fourth transistor is electrically connected to a gate of the third transistor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] 1. Field of the Invention One embodiment of the present invention relates to a semiconductor device and a method for operating the semiconductor device. 2. Description of the Related Art One embodiment of the present invention relates to a battery control circuit, a battery protection circuit, a power storage device, and an electric device.

[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, more specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a display device, a light-emitting device, a power storage device, an imaging device, a storage device, a driving method thereof, or a manufacturing method thereof. [Background technology]

[0003] Oscillators are widely used in various devices such as wireless communication devices, etc. Patent Document 1 shows an example of a negative impedance circuit used in an oscillator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-324953 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one embodiment of the present invention is to provide a novel oscillator, a novel amplifier circuit, a novel inverter circuit, a novel amplifier circuit, a novel battery control circuit, a novel battery protection circuit, a power storage device, a semiconductor device, an electric device, etc. Alternatively, an object of one embodiment of the present invention is to provide an oscillator, an inverter circuit, an amplifier circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, an electric device, etc., which have a novel structure and can reduce power consumption.

[0006] The problems of one embodiment of the present invention are not limited to the problems listed above. The problems listed above do not preclude the existence of other problems. The other problems are problems not mentioned in this section, which will be described below. Problems not mentioned in this section can be derived by a person skilled in the art from the description in the specification or drawings, and can be appropriately extracted from these descriptions. One embodiment of the present invention solves at least one of the problems listed above and / or other problems. [Means for solving the problem]

[0007] One embodiment of the present invention includes a first transistor, an oscillator, a first wiring, a second wiring, and a first circuit. The oscillator is electrically connected to each of the first wiring, the second wiring, and the first circuit. The first transistor includes a metal oxide including indium or zinc in a channel formation region. The oscillator includes a second transistor, a third transistor, a fourth transistor, a fifth transistor, and a first capacitor. A gate of the second transistor and a gate of the third transistor are electrically connected to one of a source and a drain of the first transistor. One of the source and the drain of the second transistor is electrically connected to the source of the fourth transistor. one of the source and drain of the third transistor is electrically connected to one of the source and drain of the fifth transistor and the other electrode of the first capacitor; one of the source and drain of the third transistor is electrically connected to one of the source and drain of the fifth transistor and the other electrode of the first capacitor; the other of the source and drain of the fourth transistor is electrically connected to the gate of the fifth transistor; the other of the source and drain of the fifth transistor is electrically connected to the first circuit and the gate of the fourth transistor; and a first wiring is electrically connected to the other of the source and drain of the second transistor and the other of the source and drain of the third transistor.

[0008] Also, in the above configuration, the first circuit has at least one of an inverter and a buffer, and an input terminal, the gate of the fourth transistor is electrically connected to the input terminal, and the first circuit is a semiconductor device having a function of at least one of shaping and amplifying a signal provided to the input terminal.

[0009] In the above structure, the second to fifth transistors preferably include a metal oxide containing indium or zinc in a channel formation region.

[0010] In the above structure, it is preferable that the semiconductor device has a second capacitor, one electrode of the second capacitor being electrically connected to one of the source and drain of the first transistor, and the other electrode of the second capacitor being electrically connected to the first wiring.

[0011] In addition, in the above configuration, it is preferable that the first circuit has a second wiring, and the first circuit has two or more transistors connected in series between the first wiring and the second wiring, one of the two or more transistors in the first circuit has one of a source and a drain electrically connected to the first wiring and a gate electrically connected to one of the source and drain of the first transistor, and a low potential signal is applied to the first wiring and a high potential signal is applied to the second wiring.

[0012] In addition, in the above configuration, it is preferable that the first wiring is electrically connected to one of the source and drain of the sixth transistor, the other of the source and drain of the sixth transistor is electrically connected to one of the source and drain of the seventh transistor, the other of the source and drain of the seventh transistor is electrically connected to one electrode of the resistor element, the other electrode of the resistor element is electrically connected to a second wiring, and the other of the source and drain of the first transistor is electrically connected to the source or drain of the seventh transistor, and that at least one of the sixth transistor and the seventh transistor is turned off during a period in which the first potential is held, and that a function of blocking a current flowing between the first wiring and the second wiring is provided, and a low potential signal is provided to the first wiring and a high potential signal is provided to the second wiring.

[0013] In addition, in the above configuration, it is preferable that the first circuit has n transistors (n is a natural number of 2 or more), the n transistors in the first circuit are connected in series between a first wiring and a second wiring, and that the source or drain of one of two adjacent transistors in the first circuit is electrically connected to the source or drain of the other transistor, and that the gate of the fourth transistor is electrically connected to at least one gate of the n transistors in the first circuit.

[0014] In the above configuration, it is preferable that the first circuit has n transistors (n is a natural number of 2 or more), the n transistors in the first circuit are connected in series between a first wiring and a second wiring, a source or drain of the (m-1)th transistor (m is a natural number of 3 or more and n or less) among the n transistors in the first circuit is electrically connected to a source or drain of the (m-2)th transistor, one of the source and drain of the first transistor among the n transistors in the first circuit is electrically connected to the first wiring and the other is electrically connected to the source or drain of the second transistor, one of the source and drain of the nth transistor among the n transistors in the first circuit is electrically connected to the second wiring and the other is electrically connected to the source or drain of the (n-1)th transistor, and a gate of the fourth transistor is electrically connected to at least one gate of the n transistors in the first circuit.

[0015] Alternatively, one embodiment of the present invention is a power storage device including the above-described semiconductor device, a comparator, and an eighth transistor, in which one of a non-inverting input terminal and an inverting input terminal of the comparator is electrically connected to a positive electrode of a secondary battery and the other is electrically connected to one of a source and a drain of the eighth transistor, the eighth transistor has a metal oxide containing indium or zinc in a channel formation region, and has a function of applying a first potential to the other of the non-inverting input terminal and the inverting input terminal by turning on the eighth transistor and holding the first potential by turning off the eighth transistor, the comparator has a function of outputting an output signal in response to a comparison result between a potential of the positive electrode and a second potential, and the oscillator has a function of blocking current between the first wiring and the second wiring in response to the output signal.

[0016] Alternatively, one embodiment of the present invention includes an oscillator, a first transistor, and a first circuit, in which the first transistor has a metal oxide containing indium or zinc in a channel formation region, the oscillator includes a second transistor, a third transistor, a fourth transistor, a fifth transistor, and a first capacitor, the first circuit has an input terminal, a gate of the second transistor and a gate of the third transistor are electrically connected to one of a source and a drain of the first transistor, one of a source and a drain of the second transistor is electrically connected to one of a source and a drain of the fourth transistor and to one electrode of the first capacitor, and one of a source and a drain of the third transistor is electrically connected to one of a source and a drain of the fifth transistor and the other electrode of the first capacitor. , the other of the source and drain of the fourth transistor is electrically connected to a gate of a fifth transistor, and the other of the source and drain of the fifth transistor is electrically connected to an input terminal of a first circuit and to the gate of the fourth transistor, the method comprising: a first step of turning on the first transistor and applying a first potential to the gate of the second transistor and the gate of the third transistor; a second step of an oscillator applying a first signal corresponding to the first potential to the input terminal of the first circuit; a third step of turning off the first transistor and holding the first potential applied to the gate of the second transistor and the gate of the third transistor; and a fourth step of the first circuit performing at least one of shaping and amplifying the first signal.

[0017] In addition, in the above configuration, it is preferable that the semiconductor device has a first wiring, a second wiring, a resistor, a sixth transistor, and a seventh transistor, the first wiring is electrically connected to one of the source and drain of the sixth transistor, the other of the source and drain of the sixth transistor is electrically connected to one of the source and drain of the seventh transistor, the other of the source and drain of the seventh transistor is electrically connected to one electrode of the resistor element, and the other electrode of the resistor element is electrically connected to the second wiring, and the other of the source and drain of the first transistor is electrically connected to the source or drain of the seventh transistor, and in the first step, a low potential signal is applied to the first wiring and a high potential signal is applied to the second wiring, and in the third step, after the first transistor is turned off, at least one of the sixth transistor and the seventh transistor is turned off, and the current flowing between the first wiring and the second wiring is blocked.

[0018] In the above structure, it is preferable that the semiconductor device has a second capacitor, one electrode of the second capacitor being electrically connected to one of the source and drain of the first transistor, and the other electrode of the second capacitor being electrically connected to the first wiring.

[0019] In the above structure, the first circuit preferably has at least one of an inverter and a buffer.

[0020] In the above structure, the second to fifth transistors preferably include a metal oxide containing indium or zinc in a channel formation region.

[0021] Alternatively, one embodiment of the present invention includes an oscillator, a first transistor, a first circuit, a second circuit, and a first wiring, in which the first transistor has a metal oxide containing indium or zinc in a channel formation region, the oscillator includes a second transistor, a third transistor, a fourth transistor, a fifth transistor, and a first capacitor, the first circuit has an input terminal, and the first wiring includes one of a source and a drain of the second transistor, one of a source and a drain of the third transistor, a gate of the second transistor and a gate of the third transistor are electrically connected to one of a source and a drain of the first transistor, the other of the source and the drain of the second transistor is electrically connected to one of a source and a drain of the fourth transistor and one electrode of the first capacitance element, the other of the source and the drain of the third transistor is electrically connected to one of a source and a drain of the fifth transistor and the other electrode of the first capacitance element, the other of the source and drain of the fifth transistor is electrically connected to a gate of a fifth transistor, the other of the source and drain of the fifth transistor is electrically connected to a first circuit and to a gate of a fourth transistor, the second circuit is electrically connected to a positive electrode of a secondary battery, a first step of applying a first potential to the second circuit, a second step of holding the first potential, a third step of the second circuit outputting a second signal, a fourth step of the second circuit applying a low potential signal to the first wiring, a fifth step of turning on the oscillator and applying a second potential to the gate of the second transistor and the gate of the third transistor; a sixth step of the oscillator applying a second signal corresponding to the second potential to an input terminal of the first circuit; a seventh step of turning off the first transistor and holding the second potential applied to the gate of the second transistor and the gate of the third transistor; and an eighth step of the first circuit at least one of shaping and amplifying the second signal.

[0022] In addition, in the above configuration, it is preferable that the semiconductor device has a second wiring, a resistor, a sixth transistor, and a seventh transistor, the first wiring is electrically connected to one of the source and drain of the sixth transistor, the other of the source and drain of the sixth transistor is electrically connected to one of the source and drain of the seventh transistor, the other of the source and drain of the seventh transistor is electrically connected to one electrode of the resistor element, and the other electrode of the resistor element is electrically connected to the second wiring, and the other of the source and drain of the first transistor is electrically connected to the source or drain of the seventh transistor, and in the seventh step, after turning off the first transistor, at least one of the sixth transistor and the seventh transistor is turned off to cut off the current flowing between the first wiring and the second wiring.

[0023] In the above structure, it is preferable that the semiconductor device has a second capacitor, one electrode of the second capacitor being electrically connected to one of the source and drain of the first transistor, and the other electrode of the second capacitor being electrically connected to the first wiring.

[0024] In the above structure, the first circuit preferably has at least one of an inverter and a buffer.

[0025] In the above structure, the second to fifth transistors preferably include a metal oxide containing indium or zinc in a channel formation region. Effect of the Invention

[0026] One embodiment of the present invention can provide a novel oscillator, a novel amplifier circuit, a novel inverter circuit, a novel amplifier circuit, a novel battery control circuit, a novel battery protection circuit, a power storage device, a semiconductor device, an electric device, etc. Furthermore, one embodiment of the present invention can provide an oscillator, an inverter circuit, an amplifier circuit, a battery control circuit, a battery protection circuit, a power storage device, a semiconductor device, an electric device, etc., each having a novel structure that enables reduction in power consumption.

[0027] The effects of one embodiment of the present invention are not limited to the effects listed above. The effects listed above do not preclude the existence of other effects. The other effects are described below and are not mentioned in this section. The effects not mentioned in this section can be derived by a person skilled in the art from the description in the specification or drawings, and can be appropriately extracted from these descriptions. One embodiment of the present invention has at least one of the effects listed above and / or other effects. Therefore, one embodiment of the present invention may not have the effects listed above in some cases. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a circuit diagram showing an example of the configuration of a semiconductor device. [Diagram 2] FIG. 2 is a circuit diagram showing a configuration example of the semiconductor device. [Diagram 3] Fig. 3A is a diagram showing an example of a circuit configuration; Fig. 3B is a diagram showing an example of a circuit configuration; Fig. 3C is a diagram showing an example of a circuit configuration; and Fig. 3D is a diagram showing an example of a circuit configuration. [Figure 4] Fig. 4A is a diagram showing an example of a circuit configuration. Fig. 4B is a diagram showing an example of a circuit configuration. Fig. 4C is a diagram showing an example of a circuit configuration. Fig. 4D is a diagram showing an example of a circuit configuration. Fig. 4E is a diagram showing an example of a circuit configuration. [Diagram 5] FIG. 5 is a timing chart illustrating an example of the operation of the semiconductor device. [Figure 6] Fig. 6A is a circuit diagram showing a configuration example of a semiconductor device, and Fig. 6B is a circuit diagram showing a configuration example of a semiconductor device. [Figure 7] 7A and 7B are circuit diagrams showing examples of the configuration of an amplifier circuit. [Figure 8] Fig. 8A is a circuit diagram showing an example of a secondary battery and a semiconductor device, and Fig. 8B is a diagram for explaining an example of the operation of the semiconductor device. [Figure 9] FIG. 9 is a cross-sectional view showing a configuration example of a semiconductor device. [Figure 10]10A, 10B, and 10C are cross-sectional views illustrating examples of the structure of a transistor. [Figure 11] 11A is a top view illustrating an example of a transistor structure, FIG 11B is a cross-sectional view illustrating an example of a transistor structure, and FIG 11C is a cross-sectional view illustrating an example of a transistor structure. [Figure 12] 12A is a top view illustrating an example of a transistor structure, FIG 12B is a cross-sectional view illustrating an example of a transistor structure, and FIG 12C is a cross-sectional view illustrating an example of a transistor structure. [Figure 13] 13A is a top view illustrating an example of a transistor structure, FIG 13B is a cross-sectional view illustrating an example of a transistor structure, and FIG 13C is a cross-sectional view illustrating an example of a transistor structure. [Figure 14] 14A is a top view illustrating an example of a transistor structure, FIG 14B is a cross-sectional view illustrating an example of a transistor structure, and FIG 14C is a cross-sectional view illustrating an example of a transistor structure. [Figure 15] 15A is a top view illustrating an example of a transistor structure, FIG 15B is a cross-sectional view illustrating an example of a transistor structure, and FIG 15C is a cross-sectional view illustrating an example of a transistor structure. [Figure 16] 16A is a top view illustrating an example of a transistor structure, FIG 16B is a cross-sectional view illustrating an example of a transistor structure, and FIG 16C is a cross-sectional view illustrating an example of a transistor structure. [Figure 17] FIG. 17 is a cross-sectional view showing a configuration example of a semiconductor device. [Figure 18] FIG. 18 is a cross-sectional view showing a configuration example of a semiconductor device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, the embodiments will be described with reference to the drawings. However, it will be easily understood by those skilled in the art that the embodiments can be implemented in many different ways, and that the modes and details can be changed in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the following embodiments.

[0030] In this specification, the ordinal numbers "first," "second," and "third" are used to avoid confusion of components. Therefore, they do not limit the number of components. Furthermore, they do not limit the order of the components. For example, a component referred to as "first" in one embodiment of this specification may be a component referred to as "second" in another embodiment or in the claims. For example, a component referred to as "first" in one embodiment of this specification may be omitted in another embodiment or in the claims.

[0031] In the drawings, the same elements or elements having similar functions, elements made of the same material, or elements formed at the same time may be given the same reference numerals, and repeated description thereof may be omitted.

[0032] 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.

[0033] 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.

[0034] 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" include cases where multiple "electrodes" or "wirings" are formed integrally.

[0035] In addition, in this specification, a "terminal" may refer to, for example, a wiring or an electrode connected to a wiring. In addition, in this specification, a part of a "wiring" may be called a "terminal".

[0036] 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 cases in which other components are included between insulating layer A and electrode B.

[0037] In addition, the functions of the source and drain are interchangeable depending on the operating conditions, such as when transistors of different polarities are used or when the direction of current changes during circuit operation, so it is difficult to determine which is the source and which is the drain. For this reason, in this specification, the terms source and drain can be used interchangeably.

[0038] In addition, in this specification, "electrically connected" includes a direct connection and a connection via "something having some electrical action." Here, the "something having some electrical action" is not particularly limited as long as it allows the transmission and reception of electrical signals between the connected objects. Therefore, even when it is expressed as "electrically connected," in the actual circuit, there may be no physical connection and only wiring extending therethrough.

[0039] In this specification and elsewhere, "parallel" refers to, for example, a state in which two straight lines are arranged at an angle of -10° or more and 10° or less. This therefore includes cases in which the angle is -5° or more and 5° or less. Furthermore, "perpendicular" and "orthogonal" refer to, for example, a state in which two straight lines are arranged at an angle of 80° or more and 100° or less. This therefore includes cases in which the angle is 85° or more and 95° or less.

[0040] 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.

[0041] In addition, in this specification, 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.

[0042] Furthermore, voltage often refers to the potential difference between a certain potential and a reference potential (for example, ground potential or source potential). Therefore, "voltage" and "potential" can often be used interchangeably. In this specification and elsewhere, unless otherwise specified, "voltage" and "potential" can be used interchangeably.

[0043] Even when written as "semiconductor", for example, if the conductivity is sufficiently low, it has the characteristics of an "insulator". Therefore, it is also possible to use "semiconductor" instead 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 may be read as interchangeable.

[0044] 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 may be interchangeable.

[0045] In this specification, the term "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 term "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").

[0046] 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.

[0047] In addition, in this specification, a high potential signal refers to a power supply potential that is higher than a low potential signal. A low potential signal refers to a power supply potential that is lower than a high potential signal. A ground potential can also be used as a high potential signal or a low potential signal. For example, when a high potential signal is the ground potential, a low potential signal is a potential lower than the ground potential, and when a low potential signal is the ground potential, a high potential signal is a potential higher than the ground potential. A high potential signal may also be called a high power supply potential. A low potential signal may also be called a low power supply potential.

[0048] 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.

[0049] In this specification and the like, the source refers to a source region, a source electrode, and a part or all of a source wiring. The source region refers to a region of a semiconductor layer having a resistivity equal to or lower than a certain value. The source electrode refers to a conductive layer connected to the source region. The source wiring refers to a wiring for electrically connecting the source electrode of at least one transistor to another electrode or another wiring.

[0050] In this specification and the like, the drain refers to a part or all of the drain region, the drain electrode, and the drain wiring. The drain region refers to a region of the semiconductor layer whose resistivity is equal to or lower than a certain value. The drain electrode refers to a conductive layer that is connected to the drain region. The drain wiring refers to a wiring for electrically connecting the drain electrode of at least one transistor to another electrode or another wiring.

[0051] (Embodiment 1) In this embodiment, an example of a semiconductor device of one embodiment of the present invention will be described.

[0052] <Examples of semiconductor devices> 1 includes an oscillator 30, a circuit 31, a circuit 32, a wiring VD1, and a wiring VS1. The wiring VD1 and the wiring VS1 are electrically connected to the oscillator 30, the circuit 31, and the circuit 32, respectively. For example, a high potential signal is applied to the wiring VD1, and a low potential signal is applied to the wiring VS1.

[0053] The oscillator 30 includes a transistor 42, a transistor 43, a transistor 44, a transistor 45, a capacitor 51, and a terminal OU1 and a terminal OU2. The terminal VBI1 of the circuit 32 is electrically connected to the oscillator 30, etc. The terminal VBI1 has a function of providing a signal Sv1 to the oscillator 30, etc.

[0054] One of the source and the drain of the transistor 42 is electrically connected to one of the source and the drain of the transistor 44, one electrode of the capacitor 51, and the node ND1. One of the source and the drain of the transistor 43 is electrically connected to one of the source and the drain of the transistor 45, the other electrode of the capacitor 51, and the node ND2. The other of the source and the drain of the transistor 44 is electrically connected to the gate of the transistor 45, a terminal OU2, and a node ND3. The other of the source and the drain of the transistor 45 is electrically connected to the gate of the transistor 44, the terminal OU1, and a node ND4. The other of the source and the drain of the transistor 42 and the other of the source and the drain of the transistor 43 are electrically connected to a wiring VS1.

[0055] The terminal OU1 is electrically connected to a terminal IN2 that the circuit 31 has.

[0056] The oscillator 30 preferably includes a transistor 54 and a transistor 55. In FIG. 1, one of the source and the drain of the transistor 54 is electrically connected to the gate of the transistor 45. The other of the source and the drain and the gate of the transistor 54 are electrically connected to a wiring VD1. One of the source and the drain of the transistor 55 is electrically connected to the gate of the transistor 44. The other of the source and the drain and the gate of the transistor 55 are electrically connected to the wiring VD1.

[0057] Moreover, resistor elements may be used instead of the transistor 54 and the transistor 55. Alternatively, a plurality of transistors connected in series and having gates electrically connected to each other may be used.

[0058] The oscillator 30 has a function of outputting a signal of a frequency determined according to, for example, the capacitance value of the capacitive element 51, the threshold values ​​of the transistors 44 and 45, the currents flowing through the transistors 44 and 45, and the like, to the terminal OU1, etc.

[0059] Oscillator 30 may be called a Source Coupled Voltage Controlled Oscillator.

[0060] The gates of the transistor 42 and the transistor 43 are electrically connected to a terminal VBI1. The magnitudes of the drain currents of the transistor 42 and the transistor 43 can be controlled by a signal Sv1 provided from the terminal VBI1. Thus, in the oscillator 30, the magnitudes of the transistor 44 and the current flowing through the transistor 44 can be controlled by the signal Sv1.

[0061] Also, the frequency of the oscillator 30 can be adjusted by modifying the signal Sv1.

[0062] The circuit 31 includes an inverter 53. Note that the circuit 31 may include a buffer circuit instead of the inverter. The circuit 31 preferably has a function of shaping, amplifying, and the like a signal applied to the terminal IN2.

[0063] 1 includes an inverter 53, a transistor 61, a terminal IN2, and a terminal OU3. The inverter 53 has a function of outputting a signal input from the terminal IN2 to the terminal OU3.

[0064] A high potential signal is applied from the wiring VD1 to the inverter 53. One of the source and the drain of the transistor 61 is electrically connected to the inverter 53, and the other is electrically connected to the wiring VS1. When the transistor 61 is on, a low potential signal is applied to the inverter 53 from the wiring VS1 via the transistor 61.

[0065] A gate of the transistor 61 is electrically connected to the terminal VBI1. The magnitude of the drain current of the transistor 61 can be controlled by a signal Sv1 provided from the terminal VBI1. Thus, in the circuit 31, the current flowing between the wiring VD1 and the wiring VS1 via the inverter 53 can be controlled by the signal Sv1. Thus, more power than necessary does not flow to the circuit 31, and the power consumption of the circuit 31 can be reduced.

[0066] 1 includes a transistor 41, a terminal VBI1, a terminal SH1, and a terminal EN1. One of a source and a drain of the transistor 41 is electrically connected to the terminal VBI1. The terminal SH1 is electrically connected to a gate of the transistor 41. The circuit 32 preferably includes a capacitor 52. In FIG. 1, one electrode of the capacitor 52 is electrically connected to the terminal SH1 of the transistor 41, and the other electrode is electrically connected to a wiring VS1.

[0067] The circuit 32 will be described in detail later.

[0068] 2, the backgates of the transistors 42, 43, 44, 45, 54, 55, and 61 are electrically connected to the sources or drains of the respective transistors, and the backgate of the transistor 41 is electrically connected to a wiring VS1.

[0069] 2 shows an example in which the back gates of the transistors 42, 43, 44, 45, 54, 55, and 61 are electrically connected to the source or drain, but a desired potential may be applied to the back gates of the transistors and the potential may be fixed. The desired potential may be, for example, the potential of the wiring VS1. Alternatively, the potential applied to the back gate may be one potential selected from several potentials. Alternatively, the potential may be a value that changes with time. Furthermore, the back gate may be electrically connected to a gate that is paired with the back gate with a gate insulator and a semiconductor layer sandwiched therebetween.

[0070] 3A, 3B, 3C, and 3D show examples of specific configurations of the circuit 32. The circuit 32 has a function of outputting and holding a desired potential from the terminal VBI1.

[0071] The circuit 32 shown in FIG. 3A includes a transistor 41, a transistor 46a, a transistor 47a, a capacitor 52, and a resistor RL1. In FIG. 3A, one of a source and a drain of the transistor 41 is electrically connected to a terminal VBI1 and one electrode of the capacitor 52. The other electrode of the capacitor 52 is electrically connected to a wiring VS1. The other of the source and the drain of the transistor 41 is electrically connected to one terminal of the resistor RL1, one of a source and a drain of the transistor 47a, and a gate of the transistor 47a. A terminal SH1 is electrically connected to the gate of the transistor 41. The other terminal of the resistor RL1 is electrically connected to a wiring VD1. The other of the source and the drain of the transistor 47a is electrically connected to one of the source and the drain of the transistor 46a, and the other of the source and the drain of the transistor 46a is electrically connected to a wiring VS1. A terminal EN1 is electrically connected to the gate of the transistor 46a.

[0072] A transistor may be used as the resistive element. The resistive element may be a current source. For example, instead of the resistive element, a current generating circuit may be connected and a current may be supplied from the circuit.

[0073] The circuit 32 shown in Fig. 3B includes a transistor 41, a transistor 46a, a transistor 47a, a capacitor 52, and a resistor RL1. The circuit 32 shown in Fig. 3B differs from Fig. 3A in that a terminal VBI1 is electrically connected to the gate of the transistor 47a, instead of one of the source and the drain of the transistor 41.

[0074] The circuit 32 shown in FIG. 3C includes a transistor 41, a transistor 46b, a transistor 47b, a capacitor 52, and a resistor RL1. In FIG. 3C, one of a source and a drain of the transistor 41 is electrically connected to a terminal VBI1 and one electrode of the capacitor 52. The other electrode of the capacitor 52 is electrically connected to a wiring VS1. The other of the source and the drain of the transistor 41 is electrically connected to one of a source and a drain of the transistor 47b, a gate of the transistor 46b, and one of a source and a drain of the transistor 46b. A terminal SH1 is electrically connected to the gate of the transistor 41. The other of the source and the drain of the transistor 46b is electrically connected to the wiring VS1. The other of the source and the drain of the transistor 47b is connected to one terminal of the resistor RL1. The other terminal of the resistor RL1 is electrically connected to the wiring VD1. A terminal EN1 is electrically connected to the gate of the transistor 47b.

[0075] The circuit 32 shown in FIG. 3D includes a transistor 41, a transistor 46b, a transistor 47b, a capacitor 52, and a resistor RL1. The circuit 32 shown in FIG. 3D is different from the circuit shown in FIG. 3C in that the terminal VBI1 is electrically connected to the gate of the transistor 46b, instead of one of the source and drain of the transistor 41. Note that in FIGS. 3A, 3B, 3C, and 3D, an example is shown in which the backgate of the transistor 41 is electrically connected to the wiring VS1, but the backgate of the transistor 41 may be electrically connected to a terminal that outputs a potential different from that of the wiring VS1. Alternatively, the backgate of the transistor 41 may be electrically connected to one of the source and drain of the transistor 41. Alternatively, the backgate of the transistor may be electrically connected to a pair of gates with a gate insulator and a semiconductor layer sandwiched therebetween.

[0076] The off-state current of the transistor 41 can be extremely low by using a transistor including an oxide semiconductor in a channel formation region (hereinafter referred to as an OS transistor) as the transistor 41. After the transistor 41 is turned on and a suitable potential is applied to the terminal VBI1, the transistor 41 is turned off to be in a floating state and the applied potential is held, whereby a potential can be programmed to the node ND2.

[0077] The OS transistor will be described in detail later.

[0078] A potential that turns on the transistor 41 is applied to the terminal SH1 to turn the transistor 41 on, and a desired potential is applied to the terminal VBI1 as the signal Sv1. Then, a potential that turns off the transistor is applied to the terminal SH1 to turn off the transistor 41, and the potential of the terminal VBI1 is held. By using an OS transistor as the transistor 41, the potential applied from the terminal VBI1 can be held for a long period of time, preferably for one minute or more, more preferably for one hour or more, and even more preferably for ten hours or more.

[0079] After that, a potential that turns off the transistor 46a or the transistor 46b is applied to the terminal EN1, thereby cutting off the current that flows between the wiring VD1 and the wiring VS1 via the resistor element RL1 and the like in the circuit 32. By cutting off the current, the power consumption of the circuit 32 can be significantly reduced.

[0080] At least one of the transistors 46a and 46b is preferably an OS transistor. More specifically, for example, by using an OS transistor as the transistor of the transistor 46a and the transistor 46b whose gate is electrically connected to the terminal EN1, leakage current can be significantly reduced when a current flowing between the wiring VD1 and the wiring VS1 in the circuit 32 is blocked.

[0081] In addition, after applying a potential to the terminal EN1 that turns off the transistor 46a or the transistor 46b, each circuit that provides a signal, power supply, current, etc. to the circuit 32, such as a control circuit, a power supply circuit, a current generating circuit, a voltage generating circuit, a current source, a constant current source, etc., may be turned off. Turning off these circuits can reduce power consumption.

[0082] All of the transistors included in the oscillator 30, the circuit 31, and the circuit 32 included in the semiconductor device shown in Fig. 1 may be OS transistors. All of the transistors included in the oscillator 30, the circuit 31, and the circuit 32 included in the semiconductor device shown in Fig. 1 can be unipolar, for example, n-channel transistors. For example, all of the transistors can be n-channel OS transistors.

[0083] An OS transistor can be provided by stacking it on a layer having a transistor having silicon in a channel formation region (hereinafter referred to as a Si transistor). By using OS transistors as all transistors in the oscillator 30, the circuit 31, and the circuit 32, the oscillator 30, the circuit 31, and the circuit 32 can be stacked on a circuit configured using Si transistors, thereby reducing the circuit area.

[0084] In addition, the oxide semiconductor used in the OS transistor can be formed by a thin film method such as a sputtering method. Therefore, the oxide semiconductor can be easily formed over various substrates such as a glass substrate, and a semiconductor device can be manufactured at low cost in some cases.

[0085] 4A shows a configuration example of the circuit 31. The circuit 31 shown in FIG. 4A includes a transistor 61, a transistor 62, and a circuit 63. A gate of the transistor 61 is electrically connected to a terminal VBI1. One of a source and a drain of the transistor 61 is electrically connected to one of a source and a drain of the transistor 62, and the other is electrically connected to a wiring VS1. The other of the source and drain of the transistor 62 is electrically connected to the circuit 63 and a terminal OU3. A gate of the transistor 62 is electrically connected to a terminal IN2.

[0086] In FIG. 4A, a transistor 61 and a transistor 62 have a backgate, and the backgate of each transistor is electrically connected to the source or drain of the corresponding transistor.

[0087] FIG. 4B illustrates a configuration example of the circuit 31. The circuit 31 illustrated in FIG. 4B includes a transistor 64, a transistor 65, and a capacitor 66 in addition to the configuration of the circuit 31 illustrated in FIG. 4A. The gate of the transistor 61 is electrically connected to a terminal VBI1. One of the source and drain of the transistor 61 is electrically connected to one of the source and drain of the transistor 62, and the other is electrically connected to a wiring VS1. The other of the source and drain of the transistor 62 is electrically connected to a circuit 63, one electrode of the capacitor 66, and a gate of the transistor 65. The other electrode of the capacitor 66 is electrically connected to one of the source and drain of the transistor 64, one of the source and drain of the transistor 65, and a terminal OU3. The gate of the transistor 62 and the gate of the transistor 64 are electrically connected to a terminal IN2. The other of the source and drain of the transistor 64 is electrically connected to a wiring VS1, and the other of the source and drain of the transistor 65 is electrically connected to a wiring VD1.

[0088] 4B, the transistor 64 and the transistor 65 each have a backgate. The backgate of the transistor 64 is electrically connected to, for example, a wiring VS1. The backgate of the transistor 65 is electrically connected to, for example, a terminal OU3.

[0089] 4C, 4D and 4E each show an example of the circuit 63.

[0090] A circuit 63 shown in FIG. 4C includes a transistor 63a. One of a source and a drain of the transistor 63a is electrically connected to a gate of the transistor 63a and a wiring VD1, and the other of the source and drain of the transistor 63a is electrically connected to the other of the source and drain of the transistor 62.

[0091] The circuit 63 shown in Figure 4D has transistors 63a and 63b, and the wiring VD1 is electrically connected to one of the source and drain and the gate of the transistor 63a, the other of the source and drain of the transistor 63a is electrically connected to one of the source and drain and the gate of the transistor 63b, and the other of the source and drain of the transistor 63b is electrically connected to the other of the source and drain of the transistor 62.

[0092] 4E, the circuit 63 may have n transistors (n is an integer of 2 or more). The wiring VD1 is electrically connected to one of the source and drain and the gate of a first transistor (transistor 63a in FIG. 4E), the other of the source and drain of the first transistor is electrically connected to one of the source and drain and the gate of a second transistor (transistor 63b in FIG. 4E), and the other of the source and drain of each of the transistors is electrically connected to one of the source and drain and the gate of a transistor in the next stage. The other of the source and drain of the n-th transistor (transistor 63n in FIG. 4E) is electrically connected to the other of the source and drain of the transistor 62.

[0093] Note that the transistors shown in FIGS. 4C, 4D, and 4E each have a backgate, and each backgate is electrically connected to the source or drain of the corresponding transistor.

[0094] FIG. 5 is a timing chart illustrating an example of the operation of the oscillator 30. In FIG.

[0095] Here, the thresholds of the transistors 54, 55, 44, and 45 are set to a potential Vt. The thresholds of these transistors may vary from one transistor to another, but for the sake of simplicity, it is assumed here that the thresholds of these transistors are the same.

[0096] Consider an example of the operation of oscillator 30 when, at a certain time, one of transistor 44 and transistor 45 is on and the other is off. Here, consider, as an example, the case where transistor 44 is on and transistor 45 is off at time t0.

[0097] At time t0, the transistor 45 is off, and the potential of the node ND4 is, for example, a potential that is lower than the potential VD1 by the threshold value of the transistor 55, that is, a potential (VD1-Vt).

[0098] At time t0, the transistor 44 is on, and the potentials of the nodes ND1 and ND3 are approximately equal. The potentials of the nodes ND1 and ND3 at time t0 are set to a potential V0. The potential V0 is a value lower than the potential (VD1-Vt) by at least the threshold value of the transistor 44, for example, a potential (VD1-2Vt).

[0099] The transistor 45 is off, and the charge of the capacitor 51 leaks to the transistor 43 and the like, so that the potential of the node ND2 gradually decreases over time.

[0100] At time t1, when the potential of the node ND2 falls below a potential lower than the potential of the node ND3 by the threshold value of the transistor 45, that is, below a potential (V0-Vt), the transistor 45 is turned on.

[0101] When the transistor 45 is turned on and becomes conductive, the potential of the node ND4 drops, and in the transistor 44, the gate potential (Vgs) with respect to the source becomes equal to or lower than the potential Vt (Vgs≦Vt), and the transistor 44 is turned off.

[0102] When the transistor 44 is turned off, the potential of the node ND3 rises, for example, from the potential VD1 to a potential lower than the threshold value of the transistor 54, that is, to a potential (VD1-Vt). The potential of the node ND1 also rises together with the potential of the node ND3. After that, the potential of the node ND1 gradually decreases over time due to leakage from the capacitive element 51.

[0103] At time t2, when the potential of the node ND1 falls below the potential of the node ND4 by the threshold value of the transistor 44, the transistor 44 is turned on. When the transistor 44 is turned on, the potentials of the nodes ND1 and ND3 become the potential V0. The transistor 45 is turned off, and the potential of the node ND4 rises to the potential (VD1-Vt). The potential of the node ND2 also rises together with the node ND4, but decreases over time.

[0104] The potential of node ND4 is potential VD1-Vt between time t0 and time t1, and potential V0 between time t1 and time t2, and thereafter alternates between potential VD1-Vt and potential V0, functioning as an oscillator. The length of the time from time t0 to time t1 and the length of the time from time t1 to time t2 are determined by the capacitance value of capacitance element 51, the magnitude of the current flowing through transistors 42 and 43, the threshold values ​​of transistors 54, 55, 44, and 45, etc.

[0105] 6A shows a configuration example of the semiconductor device 21. The semiconductor device 21 shown in FIG. 6A has an amplifier circuit 36 ​​in addition to the components shown in FIG. 1 etc. The amplifier circuit 36 ​​is supplied with the signals output from the terminals OU1 and OU2 of the oscillator 30. The amplifier circuit 36 ​​has a function of generating an amplified signal based on the signals supplied from the terminals OU1 and OU2, and supplying the amplified signal to the terminal IN2 of the circuit 31.

[0106] In addition, in the configuration of the semiconductor device 21 shown in Figures 1, 2, 6A, etc., the circuits 31 may be stacked in two stages in the output section. Figure 6B shows an example of a configuration in which the circuits 31 in the output section in Figure 6A are stacked in two stages.

[0107] 7A and 7B show an example of the amplifier circuit 36. In FIG.

[0108] The amplifier circuit 36 ​​shown in Fig. 7A includes a transistor 71, a transistor 72, a transistor 73, a circuit 63x, and a circuit 63y. The circuit 63 shown in Fig. 4C, Fig. 4D, and Fig. 4E, or the like, can be used as the circuit 63x and the circuit 63y.

[0109] In FIG. 7A, the circuit 63x is disposed between the wiring VD1 and one of the source and drain of the transistor 72 and is electrically connected to each of them. The circuit 63y is disposed between the wiring VD1 and one of the source and drain of the transistor 73 and is electrically connected to each of them. One of the source and drain of the transistor 73 is electrically connected to the terminal IN2. The gate of the transistor 72 is electrically connected to the terminal OU1. The gate of the transistor 73 is electrically connected to the terminal OU2. The backgate of the transistor 72, the other of the source and drain of the transistor 72, the backgate of the transistor 73, and the other of the source and drain of the transistor 73 are electrically connected to one of the source and drain of the transistor 71. The other of the source and drain and the backgate of the transistor 71 are electrically connected to the wiring VS1. The gate of the transistor 71 is electrically connected to the terminal VBI1 of the circuit 32.

[0110] The amplifier circuit 36 ​​shown in FIG. 7A has a function of amplifying the difference between the signal applied to the terminal OU1 and the signal applied to the terminal OU2.

[0111] The amplifier circuit 36 ​​shown in FIG. 7B has a transistor 74, a transistor 75, a transistor 76, and a transistor 77 in addition to the components shown in FIG.

[0112] In Fig. 7A, one of the source and the drain of the transistor 73 is electrically connected to the terminal IN2, but in Fig. 7B, one of the source and the drain of the transistor 73 is electrically connected to the gate of the transistor 77. Also in Fig. 7B, one of the source and the drain of the transistor 72 and the circuit 63x are electrically connected to the gate of the transistor 76.

[0113] One of the source and the drain of the transistor 76 is electrically connected to the wiring VD1, and the other is electrically connected to one of the source and the drain of the transistor 74, the gate of the transistor 74, and the gate of the transistor 75. The other of the source and the drain of the transistor 74 is electrically connected to the backgate of the transistor 74 and the wiring VS1.

[0114] One of the source and the drain of the transistor 77 is electrically connected to the wiring VD1, and the other is electrically connected to one of the source and the drain of the transistor 75 and the terminal IN2. The other of the source and the drain of the transistor 75 is electrically connected to the backgate of the transistor 75 and the wiring VS1.

[0115] By including the amplifier circuit 36 ​​and the circuit 31 described above, the semiconductor device 21 can amplify and shape the signal of a desired frequency generated by the oscillator 30, thereby making it possible to obtain a desirable output signal.

[0116] 8A shows an example in which the semiconductor device of one embodiment of the present invention is applied to a secondary battery. A power storage device can be formed by connecting the semiconductor device of one embodiment of the present invention to a secondary battery.

[0117] 8A shows a secondary battery 121 and a semiconductor device 21 electrically connected to the secondary battery 121. The semiconductor device 21 shown in FIG. 8A includes a circuit 33, a transistor 49, a circuit 32, an oscillator 30, and a circuit 31.

[0118] The circuit 33 includes a comparator 56, a transistor 48, and a capacitance element 57. The comparator 56 has a function of comparing a reference potential with the positive electrode potential of the secondary battery 121 and outputting a signal corresponding to the comparison result. In the example shown in FIG. 8A, the positive electrode of the secondary battery 121 is electrically connected to the non-inverting input terminal of the comparator, and a reference potential is applied to the inverting input terminal of the comparator 56. Note that in the example shown in FIG. 8A, the reference potential is applied to the inverting input terminal, and a potential for comparison with the reference potential is applied to the non-inverting input terminal, but the reference potential may be applied to the non-inverting input terminal, and the potential for comparison may be applied to the inverting input terminal, respectively.

[0119] The reference potential given to the comparator 56 is given from a terminal VT1 via a transistor 48. It is preferable to use an OS transistor as the transistor 48. For example, a high potential signal is given from a terminal SH2 to the gate of the transistor 48 to turn on the transistor 48 and give a suitable potential to the inverting input terminal of the comparator 56, and then a low potential signal is given from the terminal SH2 to the gate of the transistor 48 to turn off the transistor 48, thereby putting it into a floating state and holding the given potential, thereby programming a potential to the inverting input terminal of the comparator 56.

[0120] An output terminal (called a terminal OU4) of the comparator 56 is electrically connected to a gate of the transistor 49. One of the source and drain of the transistor 49 (called a terminal SG1 in FIG. 8A) is electrically connected to the wiring VS1, and the other is electrically connected to the circuit 32, the oscillator 30, and the circuit 31. The transistor 49 has a function of controlling a state in which each circuit is electrically connected to the wiring VS1 and a state in which each circuit is electrically disconnected from the wiring VS1. The transistor 49 is electrically connected to, for example, the transistor 42 and the transistor 43 of the oscillator 30 shown in FIG. 1 and the like, the transistor 61 of the circuit 31, the transistor 46a of the circuit 32 shown in FIG. 3A and the like, the transistor 46b of the circuit 32 shown in FIG. 3C and the like, and the like.

[0121] By providing the circuit 33 with a reference potential for controlling or protecting the secondary battery 121, the semiconductor device 21 can be operated as a circuit for controlling or protecting the secondary battery 121. An example of providing the circuit 33 with a potential for overcharge detection as the reference potential will be described below with reference to the timing chart shown in Fig. 8B. The total current flowing through the circuit 32, the oscillator 30, and the circuit 31 is defined as a current ID1.

[0122] At time t11, the potential of the terminal OU4 is a low potential signal, and the terminal SG1 is in a floating state.

[0123] At time t12, when the positive electrode potential of the secondary battery 121 exceeds the reference potential, that is, when it is determined that the secondary battery 121 is in an overcharged state, the comparator 56 outputs a high potential signal from the terminal OU4. The high potential signal is provided from the comparator 56 to the gate of the transistor 49, and the transistor 49 turns on.

[0124] When transistor 49 is turned on, wiring VS1 becomes conductive with circuit 32, oscillator 30, and circuit 31, the potential of wiring VS1 (a low potential signal in the example shown in Figure 8B) is applied to terminal SG1, a potential from wiring VS1 is applied to each circuit via terminal SG1, and circuit 32, oscillator 30, and circuit 31 become conductive with wiring VS1.

[0125] At time t13, a signal is applied to the terminal EN1, and the transistor 46a or the transistor 47a is turned on in the circuit 32. In addition, a signal is applied to the terminal SH1, the transistor 41 is turned on, and the potential VBI1 is applied from the terminal VBI1 to the oscillator 30, causing a signal of the desired frequency to be output from the terminal OU3.

[0126] At time t14, a signal is applied to the terminal SH1 to turn off the transistor 41. The potential output from the terminal VBI1 is held at a constant value.

[0127] At time t15, a signal is applied to the terminal EN1, and a potential that turns off the transistor 46a or the transistor 47a is applied to the gate of the transistor 46a or the transistor 47a. The current flowing through the circuit 32 is cut off, and the current ID1 decreases.

[0128] At time t16, a low potential signal is output from terminal OU4, cutting off the current flowing through circuit 32, oscillator 30, and circuit 31. Terminal SG1 is set in a floating state.

[0129] The secondary battery can be protected or controlled by, for example, stopping charging or changing the charging conditions by supplying a signal from the terminal OU3 to a circuit that controls charging of the secondary battery. A power storage device of one embodiment of the present invention can be configured by controlling a secondary battery using the semiconductor device of one embodiment of the present invention. The power storage device of one embodiment of the present invention can improve the safety of the secondary battery with low current consumption and can extend the life of the secondary battery. Furthermore, the capacity of the secondary battery can be improved while maintaining a high level of safety in some cases.

[0130] When the transistor 49 is off, the currents between the wiring VS1 and the circuit 32, the oscillator 30, and the circuit 31 are cut off, so that the power consumption in each circuit can be significantly reduced. By using an OS transistor as the transistor 49, the leakage current when the transistor 49 is off can be made extremely small, and the power consumption can be reduced to the minimum.

[0131] In the case of over-discharge detection, for example, a reference potential that is determined to be an over-discharge state may be applied to the non-inverting input terminal, and the positive electrode potential of the secondary battery may be applied to the inverting input terminal. In this case, when the positive electrode potential of the secondary battery becomes lower than the reference potential, a high voltage signal is output from the comparator.

[0132] For example, a circuit having a function of controlling a battery may be mounted on the semiconductor device of one embodiment of the present invention. A power storage device can be configured by mounting a circuit having a function of controlling a battery on the semiconductor device of one embodiment of the present invention and connecting it to a secondary battery. In FIG. 8, a control circuit 38 is provided as a circuit having a function of controlling a battery. A signal is supplied from a terminal OU3 to the control circuit 38. The control circuit 38 may generate signals from terminals SH1, EN1, VT1, SH2, and the like and supply them to each circuit. Alternatively, a control signal may be supplied to a circuit generating these signals.

[0133] The control circuit 38 may be equipped with a circuit having a function of changing the conditions for charging or discharging the battery. The conditions include, for example, current density, upper limit voltage, lower limit voltage, mode switching, and the like. Examples of the modes include a constant current mode and a constant voltage mode. The semiconductor device of one embodiment of the present invention has, for example, a function of protecting the battery. For example, it has a function of stopping charging or discharging the battery. For example, it has a function of discharging the battery upon detection of overcharging. For example, it has a function of detecting an abnormality in the battery and stopping the operation of the battery or changing the conditions of the battery. Examples of stopping the operation of the battery include stopping charging or discharging. Examples of abnormalities in the battery include overcharging, overdischarging, overcurrent during charging, overcurrent during discharging, short circuit, micro-short circuit (described later), deviation from a predetermined range of operating temperature, and the like.

[0134] The control circuit 38 can be configured using, for example, Si transistors. Alternatively, the control circuit 38 may be configured using OS transistors and Si transistors. Alternatively, the control circuit 38 may be configured using OS transistors.

[0135] The semiconductor device of one embodiment of the present invention may also include a temperature sensor, a pressure sensor, an illuminance sensor, a motion sensor, an optical sensor, a humidity sensor, etc. The semiconductor device of one embodiment of the present invention has a function of controlling a battery in response to detection results of these sensors, for example.

[0136] (Embodiment 2) In this embodiment mode, a configuration example of an OS transistor that can be used in the semiconductor device described in the above embodiment mode will be described. Note that the OS transistor is a thin film transistor and can be provided in a stacked structure, so in this embodiment mode, a configuration example of a semiconductor device in which an OS transistor is provided above a Si transistor formed on a single crystal silicon substrate will be described.

[0137] <Example of semiconductor device configuration> 9 includes a transistor 300, a transistor 500, and a capacitor 600. Fig. 10A is a cross-sectional view of the transistor 500 in the channel length direction, Fig. 10B is a cross-sectional view of the transistor 500 in the channel width direction, and Fig. 10C is a cross-sectional view of the transistor 300 in the channel width direction.

[0138] The transistor 500 has an OS transistor in a channel formation region. The transistor 500 has a feature of having an extremely low off-state current.

[0139] 9, the semiconductor device described in this embodiment includes a transistor 300, a transistor 500, and a capacitor 600. The transistor 500 is provided above the transistor 300, and the capacitor 600 is provided above the transistor 300 and the transistor 500.

[0140] The transistor 300 is provided on a substrate 311 and includes a conductor 316, an insulator 315, a semiconductor region 313 formed of a part of the substrate 311, and a low resistance region 314a and a low resistance region 314b functioning as a source region or a drain region.

[0141] 10C, the upper surface and the side surface in the channel width direction of the semiconductor region 313 of the transistor 300 are covered with a conductor 316 via an insulator 315. By forming the transistor 300 as a fin type in this manner, the effective channel width is increased, thereby improving the on-characteristics of the transistor 300. In addition, the contribution of the electric field of the gate electrode can be increased, thereby improving the off-characteristics of the transistor 300.

[0142] The transistor 300 may be either a p-channel type or an n-channel type.

[0143] The region where the channel of the semiconductor region 313 is formed, the region nearby, the low resistance region 314a which becomes the source region or the drain region, and the low resistance region 314b preferably contain a semiconductor such as a silicon-based semiconductor, and preferably contain single crystal silicon. Alternatively, they may be formed of a material containing Ge (germanium), SiGe (silicon germanium), GaAs (gallium arsenide), GaAlAs (gallium aluminum arsenide), or the like. A configuration using silicon in which the effective mass is controlled by applying stress to the crystal lattice and changing the lattice spacing may be used. Alternatively, the transistor 300 may be a HEMT (High Electron Mobility Transistor) by using GaAs and GaAlAs, or the like.

[0144] Low resistance region 314a and low resistance region 314b contain, in addition to the semiconductor material applied to semiconductor region 313, an element that imparts n-type conductivity, such as arsenic or phosphorus, or an element that imparts p-type conductivity, such as boron.

[0145] The conductor 316 functioning as the gate electrode can be made of a conductive material such as a semiconductor material, such as silicon, containing an element that imparts n-type conductivity, such as arsenic or phosphorus, or an element that imparts p-type conductivity, such as boron, a metal material, an alloy material, or a metal oxide material.

[0146] Since the work function is determined by the material of the conductor, the Vth of the transistor can be adjusted by changing the material of the conductor. Specifically, it is preferable to use materials such as titanium nitride and tantalum nitride for the conductor. Furthermore, in order to achieve both electrical conductivity and embeddability, it is preferable to use metal materials such as tungsten and aluminum as a laminate for the conductor, and in particular, it is preferable to use tungsten in terms of heat resistance.

[0147] Note that the transistor 300 illustrated in FIG. 9 is just an example, and the present invention is not limited to this structure. An appropriate transistor may be used depending on the circuit configuration and driving method.

[0148] An insulator 320, an insulator 322, an insulator 324, and an insulator 326 are stacked in this order over the transistor 300.

[0149] As the insulators 320, 322, 324, and 326, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like can be used.

[0150] The insulator 322 may function as a planarizing film that planarizes steps caused by the transistor 300 provided thereunder. For example, the top surface of the insulator 322 may be planarized by a planarization process using a chemical mechanical polishing (CMP) method or the like to improve the planarity.

[0151] The insulator 324 is preferably a film having a barrier property that prevents hydrogen or impurities from diffusing from the substrate 311 or the transistor 300 to a region where the transistor 500 is provided.

[0152] As an example of a film having a barrier property against hydrogen, for example, silicon nitride formed by a CVD method can be used. Here, when hydrogen diffuses into a semiconductor element having an oxide semiconductor such as the transistor 500, the characteristics of the semiconductor element may deteriorate. Therefore, it is preferable to use a film that suppresses the diffusion of hydrogen between the transistor 500 and the transistor 300. Specifically, the film that suppresses the diffusion of hydrogen is a film that releases a small amount of hydrogen.

[0153] The amount of desorption of hydrogen can be analyzed, for example, by using a temperature programmed desorption spectrometry (TDS) method. For example, the amount of desorption of hydrogen from the insulator 324 is calculated as 10×10 per area of ​​the insulator 324 when the surface temperature of the film is in the range of 50° C. to 500° C. in the TDS analysis. 15 atoms / cm 2 Less than or equal to 5×10 15 atoms / cm 2 The following is acceptable.

[0154] The insulator 326 preferably has a lower dielectric constant than the insulator 324. For example, the relative dielectric constant of the insulator 326 is preferably less than 4, and more preferably less than 3. For example, the relative dielectric constant of the insulator 326 is preferably 0.7 times or less, and more preferably 0.6 times or less, the relative dielectric constant of the insulator 324. By using a material with a low relative dielectric constant as the interlayer film, the parasitic capacitance generated between wirings can be reduced.

[0155] Conductors 328 and 330, which connect to the capacitor 600 or the transistor 500, are embedded in the insulators 320, 322, 324, and 326. The conductors 328 and 330 function as plugs or wiring. A plurality of conductors that function as plugs or wiring may be collectively given the same reference numeral. In this specification and the like, the wiring and the plug connected to the wiring may be integral. That is, a part of the conductor may function as the wiring, and a part of the conductor may function as the plug.

[0156] As the material for each plug and wiring (conductor 328, conductor 330, etc.), a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material can be used in a single layer or a laminated layer. It is preferable to use a high melting point material such as tungsten or molybdenum that has both heat resistance and conductivity, and it is preferable to use tungsten. Alternatively, it is preferable to form it from a low resistance conductive material such as aluminum or copper. By using a low resistance conductive material, it is possible to reduce the wiring resistance.

[0157] A wiring layer may be provided over the insulator 326 and the conductor 330. For example, in FIG. 9, an insulator 350, an insulator 352, and an insulator 354 are stacked in this order. A conductor 356 is formed in the insulator 350, the insulator 352, and the insulator 354. The conductor 356 functions as a plug or wiring connected to the transistor 300. Note that the conductor 356 can be provided using a material similar to that of the conductor 328 and the conductor 330.

[0158] Note that, for example, the insulator 350 is preferably an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 356 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 350 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0159] Note that, for example, tantalum nitride or the like may be used as the conductor having a barrier property against hydrogen. By stacking tantalum nitride and tungsten having high conductivity, it is possible to suppress diffusion of hydrogen from the transistor 300 while maintaining the conductivity of the wiring. In this case, a structure in which the tantalum nitride layer having a barrier property against hydrogen is in contact with the insulator 350 having a barrier property against hydrogen is preferable.

[0160] A wiring layer may be provided on the insulator 354 and the conductor 356. For example, in FIG. 9, an insulator 360, an insulator 362, and an insulator 364 are stacked in this order. A conductor 366 is formed in the insulator 360, the insulator 362, and the insulator 364. The conductor 366 functions as a plug or a wiring. The conductor 366 can be provided using a material similar to that of the conductor 328 and the conductor 330.

[0161] Note that, for example, the insulator 360 is preferably an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 366 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 360 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0162] A wiring layer may be provided over the insulator 364 and the conductor 366. For example, in FIG. 9, an insulator 370, an insulator 372, and an insulator 374 are stacked in this order. A conductor 376 is formed in the insulator 370, the insulator 372, and the insulator 374. The conductor 376 functions as a plug or a wiring. The conductor 376 can be provided using a material similar to that of the conductor 328 and the conductor 330.

[0163] Note that, for example, the insulator 370 is preferably an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 376 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 370 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0164] A wiring layer may be provided over the insulator 374 and the conductor 376. For example, in FIG. 9, an insulator 380, an insulator 382, ​​and an insulator 384 are stacked in this order. A conductor 386 is formed in the insulator 380, the insulator 382, ​​and the insulator 384. The conductor 386 functions as a plug or a wiring. The conductor 386 can be provided using a material similar to that of the conductor 328 and the conductor 330.

[0165] Note that, for example, the insulator 380 is preferably an insulator having a barrier property against hydrogen, similar to the insulator 324. The conductor 386 preferably includes a conductor having a barrier property against hydrogen. In particular, a conductor having a barrier property against hydrogen is formed in an opening of the insulator 380 having a barrier property against hydrogen. With this structure, the transistor 300 and the transistor 500 can be separated by a barrier layer, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0166] In the above, a wiring layer including the conductor 356, a wiring layer including the conductor 366, a wiring layer including the conductor 376, and a wiring layer including the conductor 386 have been described, but the semiconductor device of this embodiment is not limited to this. There may be three or fewer wiring layers similar to the wiring layer including the conductor 356, or there may be five or more wiring layers similar to the wiring layer including the conductor 356.

[0167] An insulator 510, an insulator 512, an insulator 514, and an insulator 516 are stacked in this order on the insulator 384. Any of the insulator 510, the insulator 512, the insulator 514, and the insulator 516 is preferably made of a substance that has a barrier property against oxygen or hydrogen.

[0168] For example, the insulator 510 and the insulator 514 are preferably formed using a film having a barrier property that prevents hydrogen or impurities from diffusing from the substrate 311 or a region where the transistor 300 is provided to a region where the transistor 500 is provided. Therefore, a material similar to that of the insulator 324 can be used.

[0169] As an example of a film having a barrier property against hydrogen, silicon nitride formed by a CVD method can be used. Here, when hydrogen diffuses into a semiconductor element having an oxide semiconductor such as the transistor 500, the characteristics of the semiconductor element may deteriorate. Therefore, it is preferable to use a film that suppresses the diffusion of hydrogen between the transistor 500 and the transistor 300. Specifically, the film that suppresses the diffusion of hydrogen is a film that releases a small amount of hydrogen.

[0170] As a film having a barrier property against hydrogen, for example, the insulator 510 and the insulator 514 are preferably made of a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide.

[0171] In particular, aluminum oxide has a high blocking effect of preventing the film from permeating both oxygen and impurities such as hydrogen and moisture, which are factors that cause fluctuations in the electrical characteristics of a transistor. Therefore, aluminum oxide can prevent impurities such as hydrogen and moisture from entering the transistor 500 during and after the transistor manufacturing process. In addition, aluminum oxide can suppress the release of oxygen from the oxide that constitutes the transistor 500. Therefore, aluminum oxide is suitable for use as a protective film for the transistor 500.

[0172] For example, the insulator 512 and the insulator 516 can be formed using a material similar to that of the insulator 320. By using a material with a relatively low dielectric constant as an interlayer film, parasitic capacitance between wirings can be reduced. For example, the insulator 512 and the insulator 516 can be formed using a silicon oxide film, a silicon oxynitride film, or the like.

[0173] A conductor 518, a conductor constituting the transistor 500 (the conductor 503), and the like are embedded in the insulator 510, the insulator 512, the insulator 514, and the insulator 516. Note that the conductor 518 functions as a plug or a wiring connected to the capacitor 600 or the transistor 300. The conductor 518 can be provided using a material similar to that of the conductor 328 and the conductor 330.

[0174] In particular, the insulator 510 and the conductor 518 in the region in contact with the insulator 514 are preferably conductors having barrier properties against oxygen, hydrogen, and water. With this structure, the transistor 300 and the transistor 500 can be separated by a layer having barrier properties against oxygen, hydrogen, and water, and diffusion of hydrogen from the transistor 300 to the transistor 500 can be suppressed.

[0175] Above the insulator 516 is a transistor 500 .

[0176] Figure 9 shows an example in which the conductor 610 of the capacitance element 600 is connected to one of the source and drain of the transistor 500 and the gate of the transistor 300 via a conductor provided in an opening such as the insulator 580, but it is also possible to provide another OS transistor in the same layer as the transistor 500, and to connect the conductor 610 to the gate of the OS transistor via a conductor provided in an opening such as the insulator 580.

[0177] As shown in FIGS. 10A and 10B , a transistor 500 includes an insulator 514 and a conductor 503 disposed so as to be embedded in an insulator 516, an insulator 520 disposed on the insulator 516 and the conductor 503, an insulator 522 disposed on the insulator 520, an insulator 524 disposed on the insulator 522, an oxide 530a disposed on the insulator 524, an oxide 530b disposed on the oxide 530a, conductors 542a, and conductors 542b disposed apart from each other on the oxide 530b. and conductor 542b, an insulator 580 disposed on conductor 542a and conductor 542b and having an opening formed thereon overlapping between conductor 542a and conductor 542b, a conductor 560 disposed in the opening, an insulator 550 disposed among oxide 530b, conductor 542a, conductor 542b, and insulator 580, and conductor 560, and an oxide 530c disposed among oxide 530b, conductor 542a, conductor 542b, and insulator 580, and insulator 550.

[0178] 10A and 10B, it is preferable that an insulator 544 is disposed between the oxide 530a, the oxide 530b, the conductor 542a, and the conductor 542b and the insulator 580. It is preferable that the conductor 560 has a conductor 560a provided inside the insulator 550 and a conductor 560b provided so as to be embedded inside the conductor 560a, as shown in FIG. 10A and 10B. It is preferable that an insulator 574 is disposed on the insulator 580, the conductor 560, and the insulator 550, as shown in FIG. 10A and 10B.

[0179] In the following, the oxide 530a, the oxide 530b, and the oxide 530c may be collectively referred to as the oxide 530. The conductor 542a and the conductor 542b may be collectively referred to as the conductor 542.

[0180] In the transistor 500, a three-layer structure of oxide 530a, oxide 530b, and oxide 530c is shown in the region where a channel is formed and in the vicinity thereof, but the present invention is not limited thereto. For example, a single layer of oxide 530b, a two-layer structure of oxide 530b and oxide 530a, a two-layer structure of oxide 530b and oxide 530c, or a stacked structure of four or more layers may be provided. In addition, in the transistor 500, the conductor 560 is shown as having a two-layer stacked structure, but the present invention is not limited thereto. For example, the conductor 560 may have a single-layer structure or a stacked structure of three or more layers. In addition, the transistor 500 shown in FIG. 9, FIG. 10A, and FIG. 10B is an example, and the present invention is not limited thereto, and an appropriate transistor may be used depending on the circuit configuration and the driving method.

[0181] Here, the conductor 560 functions as a gate electrode of the transistor, and the conductors 542a and 542b function as a source electrode and a drain electrode, respectively. As described above, the conductor 560 is formed so as to be embedded in the opening of the insulator 580 and in the region sandwiched between the conductors 542a and 542b. The arrangement of the conductors 560, 542a, and 542b is selected in a self-aligned manner with respect to the opening of the insulator 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 conductor 560 can be formed without providing a margin for alignment, so that the area occupied by the transistor 500 can be reduced. This allows the semiconductor device to be miniaturized and highly integrated.

[0182] Furthermore, since the conductor 560 is formed in a self-aligned manner in the region between the conductor 542a and the conductor 542b, the conductor 560 does not have a region overlapping with the conductor 542a or the conductor 542b. This can reduce the parasitic capacitance formed between the conductor 560 and the conductor 542a and between the conductor 560 and the conductor 542b. This can improve the switching speed of the transistor 500 and provide high frequency characteristics.

[0183] The conductor 560 may function as a first gate (also referred to as a top gate) electrode. The conductor 503 may function as a second gate (also referred to as a bottom gate) electrode. In this case, the Vth of the transistor 500 can be controlled by changing the potential applied to the conductor 503 independently of the potential applied to the conductor 560. In particular, by applying a negative potential to the conductor 503, the Vth of the transistor 500 can be made higher than 0 V, and the off-current can be reduced. Therefore, applying a negative potential to the conductor 503 can reduce the drain current when the potential applied to the conductor 560 is 0 V, compared to not applying a negative potential.

[0184] The conductor 503 is disposed so as to overlap the oxide 530 and the conductor 560. In this manner, when a potential is applied to the conductor 560 and the conductor 503, an electric field generated from the conductor 560 and an electric field generated from the conductor 503 are connected, and a channel formation region formed in the oxide 530 can be covered. In this specification and the like, a transistor structure in which the channel formation region is electrically surrounded by the electric fields of the first gate electrode and the second gate electrode is called a surrounded channel (S-channel) structure.

[0185] In addition, in this specification, the S-channel structure has a feature that the side and periphery of the oxide 530 in contact with the conductor 542a and the conductor 542b functioning as the source electrode and the drain electrode are I-type like the channel formation region. In addition, the side and periphery of the oxide 530 in contact with the conductor 542a and the conductor 542b are in contact with the insulator 544, so they can be I-type like the channel formation region. In this specification, the I-type can be treated as the same as the high purity intrinsic described later. In addition, the S-channel structure disclosed in this specification 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 that is less likely to cause the short channel effect.

[0186] Moreover, the conductor 503 has a configuration similar to that of the conductor 518, and the conductor 503a is formed in contact with the inner walls of the openings of the insulators 514 and 516, and the conductor 503b is formed further inside.

[0187] The insulators 520, 522, 524, and 550 function as gate insulating films.

[0188] Here, the insulator 524 in contact with the oxide 530 preferably contains more oxygen than the oxygen required for the stoichiometric composition. That is, an excess oxygen region is preferably formed in the insulator 524. By providing such an insulator containing excess oxygen in contact with the oxide 530, oxygen vacancies in the oxide 530 can be reduced and the reliability of the transistor 500 can be improved.

[0189] 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 3.0×10 20 atoms / cm 3 The 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 more and 700° C. or less, or 100° C. or more and 400° C. or less.

[0190] When the insulator 524 has an excess oxygen region, it is preferable that the insulator 522 has a function of suppressing the diffusion of oxygen (eg, oxygen atoms, oxygen molecules, etc.) (the oxygen is less likely to permeate).

[0191] The insulator 522 preferably has a function of suppressing diffusion of oxygen and impurities, so that oxygen contained in the oxide 530 does not diffuse toward the insulator 520. Furthermore, reaction of the conductor 503 with the insulator 524 or oxygen contained in the oxide 530 can be suppressed.

[0192] The insulator 522 is preferably a single layer or a multilayer insulator containing a so-called high-k material, such as aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, lead zirconate titanate (PZT), strontium titanate (SrTiO3), or (Ba,Sr)TiO3 (BST). As transistors become smaller and more highly integrated, problems such as leakage current may occur due to the thinning of the gate insulating film. By using a high-k material for the insulator that functions as the gate insulating film, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0193] 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 insulator 522 is formed using such a material, the insulator 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.

[0194] 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.

[0195] In addition, the insulator 520 is preferably 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 insulator 520 having a thermally stable laminated structure with a high dielectric constant.

[0196] The insulator 520, the insulator 522, and the insulator 524 may have a layered structure of two or more layers. In that case, the layers are not limited to being made of the same material, and may be made of different materials.

[0197] In the transistor 500, it is preferable to use a metal oxide that functions as an oxide semiconductor for the oxide 530 including the channel formation region. 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. Alternatively, In-Ga oxide or In-Zn oxide may be used for the oxide 530.

[0198] In addition, it is preferable to use a metal oxide with a low carrier concentration for the transistor 500. In order to reduce the carrier concentration of the metal oxide, the impurity concentration in the metal oxide may be reduced to reduce the defect state density. In this specification and the like, a low impurity concentration and a low defect state density are referred to as high purity intrinsic or substantially high purity intrinsic. Note that examples of impurities in the metal oxide include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

[0199] In particular, hydrogen contained in metal oxide reacts with oxygen that bonds to metal atoms to form water, which may cause oxygen vacancies in the metal oxide. If oxygen vacancies are present in the channel formation region in the metal oxide, the transistor may have normally-on characteristics. Furthermore, defects in which hydrogen has entered the oxygen vacancies may function as donors and generate electrons that serve as carriers. In addition, some of the hydrogen may bond with oxygen that bonds to metal atoms to generate electrons that serve as carriers. Therefore, transistors using metal oxides that contain a large amount of hydrogen tend to have normally-on characteristics.

[0200] A defect in which hydrogen has entered an oxygen vacancy can function as a donor for a metal oxide. However, it is difficult to quantitatively evaluate the defect. Therefore, in a metal oxide, the carrier concentration may be used instead of the donor concentration. Therefore, in this specification, the carrier concentration assuming a state in which no electric field is applied may be used as a parameter of the metal oxide, instead of the donor concentration. In other words, the "carrier concentration" described in this specification may be rephrased as the "donor concentration".

[0201] Therefore, when a metal oxide is used for the oxide 530, it is preferable that hydrogen in the metal oxide is reduced as much as possible. Specifically, in the metal oxide, the hydrogen concentration obtained by secondary ion mass spectrometry (SIMS) is 1×10 20 atoms / cm 3 Less than 1 x 10 19 atoms / cm 3 less than 5×10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 By using a metal oxide in which impurities such as hydrogen are sufficiently reduced for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0202] In addition, when a metal oxide is used for the oxide 530, the carrier concentration of the metal oxide in the channel formation region is 1×10 18 cm -3 It is preferable that the value is less than 1×10 17 cm -3 More preferably, it is less than 1×10 16 cm -3 More preferably, it is less than 1×10 13 cm -3 More preferably, it is less than 1×10 12 cm -3 The lower limit of the carrier concentration of the metal oxide in the channel formation region is not particularly limited, but is preferably, for example, 1×10 -9 cm -3 It can be said that:

[0203] Furthermore, when a metal oxide is used for the oxide 530, contact between the conductor 542 (conductor 542a and conductor 542b) and the oxide 530 may cause oxygen in the oxide 530 to diffuse into the conductor 542, resulting in the oxidation of the conductor 542. The oxidation of the conductor 542 is likely to result in a decrease in the conductivity of the conductor 542. The diffusion of oxygen in the oxide 530 into the conductor 542 can be rephrased as the conductor 542 absorbing the oxygen in the oxide 530.

[0204] Furthermore, oxygen in the oxide 530 may diffuse into the conductor 542 (conductor 542a and conductor 542b), forming a foreign layer between the conductor 542a and the oxide 530b and between the conductor 542b and the oxide 530b. The foreign layer contains more oxygen than the conductor 542, and is therefore presumed to have insulating properties. In this case, the three-layer structure of the conductor 542, the foreign layer, and the oxide 530b can be regarded as a three-layer structure made of a metal-insulator-semiconductor, and may be called a MIS (Metal-Insulator-Semiconductor) structure or a diode junction structure mainly based on the MIS structure.

[0205] In addition, the above-mentioned different layer is not limited to being formed between the conductor 542 and the oxide 530b. For example, the different layer may be formed between the conductor 542 and the oxide 530c, between the conductor 542 and the oxide 530b, and between the conductor 542 and the oxide 530c.

[0206] The metal oxide that functions as a channel formation region in the oxide 530 preferably has a band gap of 2 eV or more, preferably 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.

[0207] The oxide 530 has the oxide 530a below the oxide 530b, so that the diffusion of impurities from structures formed below the oxide 530a to the oxide 530b can be suppressed. Also, the oxide 530 has the oxide 530c on the oxide 530b, so that the diffusion of impurities from structures formed above the oxide 530c to the oxide 530b can be suppressed.

[0208] The oxide 530 preferably has a laminated structure of a plurality of oxide layers having different atomic ratios of metal atoms. Specifically, in the metal oxide used for the oxide 530a, the atomic ratio of element M among the constituent elements 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, in the metal oxide used for the oxide 530a, the atomic ratio of element M to In is preferably larger than the atomic ratio of element M to In in the metal oxide used for the oxide 530b. In addition, in the metal oxide used for the oxide 530b, the atomic ratio of In to element M is preferably larger than the atomic ratio of In to element M in the metal oxide used for the oxide 530a. In addition, the oxide 530c can use a metal oxide that can be used for the oxide 530a or the oxide 530b.

[0209] In addition, the energy of the conduction band minimum of the oxide 530a and the oxide 530c is preferably higher than that of the oxide 530b, or in other words, the electron affinity of the oxide 530a and the oxide 530c is preferably smaller than that of the oxide 530b.

[0210] Here, the energy level of the conduction band minimum changes gradually at the junction of the oxide 530a, the oxide 530b, and the oxide 530c. In other words, it can be said that the energy level of the conduction band minimum at the junction of the oxide 530a, the oxide 530b, and the oxide 530c 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 and the interface between the oxide 530b and the oxide 530c.

[0211] Specifically, the oxides 530a and 530b, and the oxides 530b and 530c 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 oxides 530a and 530c may be made of an In-Ga-Zn oxide, a Ga-Zn oxide, or a gallium oxide.

[0212] At this time, the main carrier path is the oxide 530b. By configuring the oxide 530a and the oxide 530c as described above, the defect state density at the interface between the oxide 530a and the oxide 530b and at the interface between the oxide 530b and the oxide 530c can be reduced. Therefore, the effect of interface scattering on carrier conduction is reduced, and the transistor 500 can obtain a high on-current.

[0213] Conductors 542 (conductors 542a and 542b) functioning as a source electrode and a drain electrode are provided on the oxide 530b. As the conductor 542, it is preferable to use a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, and lanthanum, an alloy containing the above-mentioned metal elements as a component, or an alloy combining the above-mentioned metal elements. For example, it is preferable to use 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. In addition, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are preferred because they are conductive materials that are difficult to oxidize or materials that maintain their conductivity even when they absorb oxygen.

[0214] 10A, a region 543 (regions 543a and 543b) may be formed as a low-resistance region at the interface between the oxide 530 and the conductor 542 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.

[0215] Providing the conductor 542 so as to be in contact with the oxide 530 may reduce the oxygen concentration in the region 543. Also, a metal compound layer containing a metal contained in the conductor 542 and a component of the oxide 530 may be formed in the region 543. In such a case, the carrier concentration in the region 543 increases, and the region 543 becomes a low-resistance region.

[0216] The insulator 544 is provided to cover the conductor 542 and suppresses oxidation of the conductor 542. In this case, the insulator 544 may be provided to cover the side surface of the oxide 530 and to be in contact with the insulator 524.

[0217] The insulator 544 can be a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like.

[0218] In particular, it is preferable to use aluminum oxide, hafnium oxide, hafnium aluminate, or the like, which is an insulator containing an oxide of either or both of aluminum and hafnium, as the insulator 544. 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 process. Note that, if the conductor 542 is made of a material having oxidation resistance or the conductivity does not decrease significantly even when oxygen is absorbed, the insulator 544 is not an essential component. It may be designed appropriately depending on the desired transistor characteristics.

[0219] The insulator 550 functions as a gate insulating film. The insulator 550 is preferably disposed in contact with the inside (top and side surfaces) of the oxide 530c. The insulator 550 is preferably formed using an insulator that releases oxygen when heated. For example, in a TDS analysis, 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 3.0×10 20 atoms / cm 3 The oxide film is as described above. The surface temperature of the film during the TDS analysis is preferably in the range of 100° C. or more and 700° C. or less.

[0220] 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.

[0221] By providing an insulator that releases oxygen when heated as the insulator 550 in contact with the top surface of the oxide 530c, oxygen can be effectively supplied from the insulator 550 to the channel formation region of the oxide 530b through the oxide 530c. Similarly to the insulator 524, the concentration of impurities such as water or hydrogen in the insulator 550 is preferably reduced. The thickness of the insulator 550 is preferably 1 nm or more and 20 nm or less.

[0222] Furthermore, in order to efficiently supply excess oxygen contained in the insulator 550 to the oxide 530, a metal oxide may be provided between the insulator 550 and the conductor 560. The metal oxide preferably suppresses oxygen diffusion from the insulator 550 to the conductor 560. By providing a metal oxide that suppresses oxygen diffusion, the diffusion of excess oxygen from the insulator 550 to the conductor 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 conductor 560 due to the excess oxygen can be suppressed. As the metal oxide, a material that can be used for the insulator 544 may be used.

[0223] Although the conductor 560 functioning as the first gate electrode is shown as having a two-layer structure in FIGS. 10A and 10B, it may have a single-layer structure or a laminated structure of three or more layers.

[0224] Conductor 560a is preferably made of a conductive material having a function of suppressing the 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, conductive material having a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.) is preferably used. Conductor 560a has a function of suppressing the diffusion of oxygen, so that it is possible to suppress the oxidation of conductor 560b due to oxygen contained in insulator 550, which leads to a decrease in conductivity. As a conductive material having a function of suppressing the diffusion of oxygen, for example, tantalum, tantalum nitride, ruthenium, or ruthenium oxide is preferably used.

[0225] The conductor 560b is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. The conductor 560b also functions as wiring, so it is preferable to use a conductor with high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. The conductor 560b may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above conductive material.

[0226] The insulator 580 is provided on the conductor 542 via the insulator 544. The insulator 580 preferably has an excess oxygen region. For example, the insulator 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, or resin. In particular, silicon oxide and silicon oxynitride are preferable because they are thermally stable. In particular, silicon oxide and silicon oxide having voids are preferable because an excess oxygen region can be easily formed in a later step.

[0227] The insulator 580 preferably has an excess oxygen region. By providing the insulator 580, which releases oxygen when heated, in contact with the oxide 530c, oxygen in the insulator 580 can be efficiently supplied to the oxide 530 through the oxide 530c. Note that the concentration of impurities such as water or hydrogen in the insulator 580 is preferably reduced.

[0228] The opening of insulator 580 is formed to overlap the region between conductor 542a and conductor 542b, so that conductor 560 is formed so as to be embedded in the opening of insulator 580 and the region sandwiched between conductor 542a and conductor 542b.

[0229] In miniaturizing a semiconductor device, it is necessary to shorten the gate length, but it is also necessary to prevent the conductivity of the conductor 560 from decreasing. If the film thickness of the conductor 560 is increased for that purpose, the conductor 560 may have a shape with a high aspect ratio. In this embodiment, the conductor 560 is provided so as to be embedded in the opening of the insulator 580, so that even if the conductor 560 has a shape with a high aspect ratio, the conductor 560 can be formed without collapsing during the process.

[0230] The insulator 574 is preferably provided in contact with the top surface of the insulator 580, the top surface of the conductor 560, and the top surface of the insulator 550. By forming the insulator 574 by a sputtering method, excess oxygen regions can be provided in the insulator 550 and the insulator 580. This allows oxygen to be supplied from the excess oxygen regions into the oxide 530.

[0231] For example, the insulator 574 can be a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like.

[0232] In particular, aluminum oxide has high barrier properties and can suppress the diffusion of hydrogen and nitrogen even in a thin film with a thickness 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.

[0233] An insulator 581 functioning as an interlayer film is preferably provided over the insulator 574. Like the insulator 524, the insulator 581 preferably has a reduced concentration of impurities such as water or hydrogen.

[0234] Conductor 540a and conductor 540b are arranged in openings formed in insulator 581, insulator 574, insulator 580, and insulator 544. Conductor 540a and conductor 540b are provided facing each other with conductor 560 interposed therebetween. Conductor 540a and conductor 540b have the same configuration as conductor 546 and conductor 548, which will be described later.

[0235] An insulator 582 is provided over the insulator 581. The insulator 582 is preferably made of a substance that has a barrier property against oxygen and hydrogen. Therefore, the insulator 582 can be made of a material similar to that of the insulator 514. For example, the insulator 582 is preferably made of a metal oxide such as aluminum oxide, hafnium oxide, or tantalum oxide.

[0236] In particular, aluminum oxide has a high blocking effect of preventing the film from permeating both oxygen and impurities such as hydrogen and moisture, which are factors that cause fluctuations in the electrical characteristics of a transistor. Therefore, aluminum oxide can prevent impurities such as hydrogen and moisture from entering the transistor 500 during and after the transistor manufacturing process. In addition, aluminum oxide can suppress the release of oxygen from the oxide that constitutes the transistor 500. Therefore, aluminum oxide is suitable for use as a protective film for the transistor 500.

[0237] An insulator 586 is provided over the insulator 582. The insulator 586 can be formed using a material similar to that of the insulator 320. By using a material with a relatively low dielectric constant as an interlayer film, parasitic capacitance between wirings can be reduced. For example, a silicon oxide film, a silicon oxynitride film, or the like can be used as the insulator 586.

[0238] In addition, conductors 546, 548, etc. are embedded in insulators 520, 522, 524, 544, 580, 574, 581, 582, and 586.

[0239] The conductor 546 and the conductor 548 function as a plug or a wiring connected to the capacitor 600, the transistor 500, or the transistor 300. The conductor 546 and the conductor 548 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0240] Next, a capacitor 600 is provided above the transistor 500. The capacitor 600 includes a conductor 610, a conductor 620, and an insulator 630.

[0241] A conductor 612 may be provided over the conductor 546 and the conductor 548. The conductor 612 functions as a plug or a wiring connected to the transistor 500. The conductor 610 functions as an electrode of the capacitor 600. Note that the conductor 612 and the conductor 610 can be formed at the same time.

[0242] 9 and the like show an example in which the insulator 630 is used as a dielectric of the capacitor, other insulators may be used as the dielectric of the capacitor. In addition, other conductors or the like may be used as electrodes of the capacitor.

[0243] For example, the insulator 315 may function as a gate insulator of the transistor 300. When the insulator 315 is used as a dielectric of a capacitor, the conductor 316 may be used as one electrode of the capacitor and the low resistance region 314a or the like may be used as the other electrode.

[0244] A metal film containing an element selected from molybdenum, titanium, tantalum, tungsten, aluminum, copper, chromium, neodymium, and scandium, or a metal nitride film containing the above-mentioned element (tantalum nitride film, titanium nitride film, molybdenum nitride film, tungsten nitride film), etc. can be used for the conductor 612 and the conductor 610. Alternatively, a conductive material such as indium tin oxide, indium oxide containing tungsten oxide, indium zinc oxide containing tungsten oxide, indium oxide containing titanium oxide, indium tin oxide containing titanium oxide, indium zinc oxide, or indium tin oxide with added silicon oxide can also be used.

[0245] 9, the conductor 612 and the conductor 610 are shown as having a single-layer structure, but are not limited to this configuration and may have a laminated structure of two or more layers. For example, a conductor having a barrier property and a conductor having high adhesion to the conductor having high conductivity may be formed between a conductor having a barrier property and a conductor having high conductivity.

[0246] The conductor 620 is provided so as to overlap with the conductor 610 with the insulator 630 interposed therebetween. Note that the conductor 620 can be made of a conductive material such as a metal material, an alloy material, or a metal oxide material. It is preferable to use a high melting point material such as tungsten or molybdenum that has both heat resistance and conductivity, and it is particularly preferable to use tungsten. When the conductor 620 is formed simultaneously with other structures such as a conductor, a low resistance metal material such as Cu (copper) or Al (aluminum) may be used.

[0247] An insulator 650 is provided over the conductor 620 and the insulator 630. The insulator 650 can be provided using a material similar to that of the insulator 320. The insulator 650 may also function as a planarizing film that covers the uneven shape underneath.

[0248] By using this structure, in a semiconductor device including a transistor having an oxide semiconductor, a change in electrical characteristics can be suppressed and reliability can be improved. Alternatively, a transistor including an oxide semiconductor with high on-state current can be provided. Alternatively, a transistor including an oxide semiconductor with low off-state current can be provided. Alternatively, a semiconductor device with reduced power consumption can be provided. Alternatively, miniaturization or high integration of a semiconductor device including a transistor having an oxide semiconductor can be achieved.

[0249] <Example of transistor structure> Note that the transistor 500 of the semiconductor device described in this embodiment is not limited to the above structure. Hereinafter, examples of a structure that can be used for the transistor 500 will be described.

[0250] <Transistor structure example 1> A structural example of a transistor 510A will be described with reference to Figures 11A, 11B, and 11C. Figure 11A is a top view of the transistor 510A. Figure 11B is a cross-sectional view of a portion indicated by dashed line L1-L2 in Figure 11A. Figure 11C is a cross-sectional view of a portion indicated by dashed line W1-W2 in Figure 11A. Note that in the top view of Figure 11A, some elements are omitted for clarity.

[0251] 11A, 11B, and 11C show a transistor 510A, and insulators 511, 512, 514, 516, 580, 582, and 584 which function as interlayer films. Also shown are a conductor 546 (conductor 546a and conductor 546b) which is electrically connected to the transistor 510A and functions as a contact plug, and a conductor 503 which functions as a wiring.

[0252] Transistor 510A has a conductor 560 (conductor 560a and conductor 560b) that functions as a first gate electrode, a conductor 505 (conductor 505a and conductor 505b) that functions as a second gate electrode, an insulator 550 that functions as a first gate insulating film, insulators 521, 522, and 524 that function as a second gate insulating film, an oxide 530 (oxide 530a, oxide 530b, and oxide 530c) having a region where a channel is formed, a conductor 542a that functions as one of a source or a drain, a conductor 542b that functions as the other of the source or a drain, and an insulator 574.

[0253] 11, the oxide 530c, the insulator 550, and the conductor 560 are disposed in an opening in the insulator 580 with the insulator 574 interposed therebetween. The oxide 530c, the insulator 550, and the conductor 560 are disposed between the conductor 542a and the conductor 542b.

[0254] The insulators 511 and 512 function as interlayer films.

[0255] As the interlayer film, an insulator such as silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, PZT, SrTiO3, or (Ba,Sr)TiO3 (BST) can be used in a single layer or a laminated layer. 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 laminated on the above insulators.

[0256] For example, the insulator 511 preferably functions as a barrier film that suppresses impurities such as water or hydrogen from entering the transistor 510A from the substrate side. Therefore, the insulator 511 is preferably made of an insulating material that has a function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (through which the above impurities are unlikely to permeate). Alternatively, it is preferable to use an insulating material that has a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, and the like) (through which the above oxygen is unlikely to permeate). Furthermore, for example, aluminum oxide or silicon nitride may be used as the insulator 511. With this configuration, it is possible to suppress the diffusion of impurities such as hydrogen and water from the substrate side to the transistor 510A side through the insulator 511.

[0257] For example, the insulator 512 preferably has a lower dielectric constant than the insulator 511. By using a material with a low dielectric constant as an interlayer film, parasitic capacitance generated between wirings can be reduced.

[0258] The conductor 503 is formed so as to be embedded in the insulator 512. Here, the height of the top surface of the conductor 503 and the height of the top surface of the insulator 512 can be made approximately the same. Note that although the conductor 503 is shown as being a single layer, the present invention is not limited to this. For example, the conductor 503 may be a multilayer film structure having two or more layers. Note that the conductor 503 is preferably made of a highly conductive material containing tungsten, copper, or aluminum as a main component.

[0259] In the transistor 510A, the conductor 560 may function as a first gate (also referred to as a top gate) electrode. The conductor 505 may function as a second gate (also referred to as a bottom gate) electrode. In this case, the threshold voltage of the transistor 510A can be controlled by changing the potential applied to the conductor 505 independently of the potential applied to the conductor 560. In particular, by applying a negative potential to the conductor 505, the threshold voltage of the transistor 510A can be made higher than 0 V, thereby reducing the off-current. Therefore, the drain current when the potential applied to the conductor 560 is 0 V can be made smaller when a negative potential is applied to the conductor 505 than when a negative potential is not applied.

[0260] Furthermore, for example, by overlapping the conductor 505 and the conductor 560, when a potential is applied to the conductor 560 and the conductor 505, the electric field generated from the conductor 560 and the electric field generated from the conductor 505 can be connected and can cover the channel formation region formed in the oxide 530.

[0261] That is, the channel formation region can be electrically surrounded by the electric field of the conductor 560 functioning as the first gate electrode and the electric field of the conductor 505 functioning as the second gate electrode. That is, like the transistor 500 described above, this has an S-channel structure.

[0262] The insulator 514 and the insulator 516 function as an interlayer film, similar to the insulator 511 or the insulator 512. For example, the insulator 514 preferably functions as a barrier film that suppresses impurities such as water or hydrogen from entering the transistor 510A from the substrate side. With this structure, impurities such as hydrogen and water can be suppressed from diffusing from the substrate side to the transistor 510A side through the insulator 514. For example, the insulator 516 preferably has a lower dielectric constant than the insulator 514. By using a material with a low dielectric constant as an interlayer film, parasitic capacitance generated between wirings can be reduced.

[0263] The conductor 505 functioning as the second gate has a conductor 505a formed in contact with the inner walls of the openings of the insulator 514 and the insulator 516, and a conductor 505b formed further inside. Here, the height of the top surfaces of the conductor 505a and the conductor 505b can be made approximately the same as the height of the top surface of the insulator 516. Note that although the transistor 510A shows a structure in which the conductor 505a and the conductor 505b are stacked, the present invention is not limited to this. For example, the conductor 505 may have a single layer or a stacked structure of three or more layers.

[0264] Here, the conductor 505a 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 (through which the above impurities are difficult to permeate). Alternatively, it is preferable to use a conductive material having a function of suppressing the diffusion of oxygen (for example, at least one of oxygen atoms, oxygen molecules, etc.) (through which the above oxygen is difficult to permeate). Note that in this specification and the like, 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 above impurities and oxygen.

[0265] For example, the conductor 505a has a function of suppressing the diffusion of oxygen, so that the conductor 505b can be prevented from being oxidized and causing a decrease in electrical conductivity.

[0266] In addition, when the conductor 505 also functions as a wiring, it is preferable that the conductor 505b is made of a highly conductive material containing tungsten, copper, or aluminum as a main component. In that case, the conductor 503 is not necessarily provided. Although the conductor 505b is illustrated as a single layer, it may have a laminated structure, for example, a laminate of titanium or titanium nitride and the above-mentioned conductive material.

[0267] The insulators 521, 522, and 524 function as a second gate insulating film.

[0268] The insulator 522 preferably has a barrier property. When the insulator 522 has a barrier property, it functions as a layer that prevents impurities such as hydrogen from entering the transistor 510A from the periphery of the transistor 510A.

[0269] The insulator 522 is preferably a single layer or a multilayer insulator containing a so-called high-k material, such as aluminum oxide, hafnium oxide, hafnium aluminate, tantalum oxide, zirconium oxide, PZT, 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 for the insulator that functions as the gate insulating film, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0270] In addition, it is preferable that the insulator 521 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 insulator 521 having a thermally stable laminated structure with a high relative dielectric constant.

[0271] 11 shows a three-layered structure as the second gate insulating film, it may be a single layer or a two or more layered structure. In that case, it is not limited to a stacked structure made of the same material, and may be a stacked structure made of different materials.

[0272] The oxide 530 having a region functioning as a channel formation region includes an oxide 530a, an oxide 530b on the oxide 530a, and an oxide 530c on the oxide 530b. By providing the oxide 530a under the oxide 530b, it is possible to suppress the diffusion of impurities from a structure formed below the oxide 530a to the oxide 530b. By providing the oxide 530c on the oxide 530b, it is possible to suppress the diffusion of impurities from a structure formed above the oxide 530c to the oxide 530b. An oxide semiconductor, which is one of the above-mentioned metal oxides, can be used as the oxide 530.

[0273] Note that the oxide 530c is preferably provided in an opening in the insulator 580 via the insulator 574. When the insulator 574 has a barrier property, diffusion of impurities from the insulator 580 to the oxide 530 can be suppressed.

[0274] One side of the conductor 542 functions as a source electrode, and the other side functions as a drain electrode.

[0275] The conductor 542a and the conductor 542b can be made of a metal such as aluminum, titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum, silver, tantalum, or tungsten, or an alloy containing these as a main component. In particular, a metal nitride film such as tantalum nitride is preferable because it has a barrier property against hydrogen or oxygen and has high oxidation resistance.

[0276] Although a single-layer structure is shown in FIG. 11, a laminated structure of two or more layers may be used. For example, a tantalum nitride film and a tungsten film may be laminated. A titanium film and an aluminum film may be laminated. A two-layer structure in which an aluminum film is laminated on a tungsten film, a two-layer structure in which a copper film is laminated on a copper-magnesium-aluminum alloy film, a two-layer structure in which a copper film is laminated on a titanium film, or a two-layer structure in which a copper film is laminated on a tungsten film may be used.

[0277] In addition, there are three-layer structures in which a titanium film or titanium nitride film is laminated with an aluminum film or copper film 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 with an aluminum film or copper film 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 also be used.

[0278] A barrier layer may be provided over the conductor 542. The barrier layer is preferably formed using a substance having a barrier property against oxygen or hydrogen. With this structure, oxidation of the conductor 542 can be suppressed when the insulator 574 is formed.

[0279] For example, a metal oxide can be used for the barrier layer. In particular, it is preferable to use an insulating film having a barrier property against oxygen and hydrogen, such as aluminum oxide, hafnium oxide, or gallium oxide. Silicon nitride formed by a CVD method may also be used.

[0280] The inclusion of the barrier layer can broaden the range of material choices for the conductor 542. For example, a material that has low oxidation resistance but high conductivity, such as tungsten or aluminum, can be used for the conductor 542. In addition, for example, a conductor that is easy to form or process can be used.

[0281] The insulator 550 functions as a first gate insulating film. The insulator 550 is preferably provided in an opening provided in the insulator 580 with the oxide 530c and the insulator 574 interposed therebetween.

[0282] As transistors become smaller and more highly integrated, problems such as leakage current may occur due to the thinning of the gate insulating film. In that case, the insulator 550 may have a laminated structure, as with the second gate insulating film. By making the insulator functioning as the gate insulating film a laminated structure of a high-k material and a thermally stable material, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness. In addition, a laminated structure that is thermally stable and has a high relative dielectric constant can be obtained.

[0283] The conductor 560 functioning as the first gate electrode has a conductor 560a and a conductor 560b on the conductor 560a. As with the conductor 505a, the conductor 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 conductor 560a is preferably made of a conductive material having a function of suppressing diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, and the like).

[0284] The conductor 560a has a function of suppressing oxygen diffusion, which improves the material selectivity of the conductor 560b. In other words, the presence of the conductor 560a suppresses oxidation of the conductor 560b, thereby preventing a decrease in electrical conductivity.

[0285] As the conductive material having the function of suppressing the diffusion of oxygen, for example, tantalum, tantalum nitride, ruthenium, or ruthenium oxide is preferably used. In addition, an oxide semiconductor that can be used as the oxide 530 can be used as the conductor 560a. In this case, the electric resistance value of the conductor 560a can be reduced by forming the conductor 560b by a sputtering method, thereby making the conductor 560a a conductor. This can be called an OC (Oxide Conductor) electrode.

[0286] The conductor 560b is preferably made of a conductive material containing tungsten, copper, or aluminum as a main component. Since the conductor 560 functions as wiring, it is preferable to use a conductor having high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. The conductor 560b may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above conductive material.

[0287] An insulator 574 is disposed between the insulator 580 and the transistor 510A. The insulator 574 may be an insulating material that has a function of suppressing diffusion of impurities such as water or hydrogen, and oxygen. For example, aluminum oxide or hafnium oxide may be 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, or silicon nitride may be used.

[0288] The insulator 574 can prevent impurities such as water and hydrogen contained in the insulator 580 from diffusing to the oxide 530b through the oxide 530c and the insulator 550. The insulator 574 can also prevent the conductor 560 from being oxidized by excess oxygen contained in the insulator 580.

[0289] Insulator 580, insulator 582, and insulator 584 function as interlayer films.

[0290] Like the insulator 514, the insulator 582 preferably functions as a barrier insulating film that prevents impurities such as water or hydrogen from entering the transistor 510A from the outside.

[0291] Similarly to the insulator 516, the insulators 580 and 584 preferably have a lower dielectric constant than the insulator 582. By using a material with a low dielectric constant as an interlayer film, parasitic capacitance between wirings can be reduced.

[0292] Additionally, transistor 510A may be electrically connected to other structures through plugs or wiring, such as conductor 546 embedded in insulator 580, insulator 582, and insulator 584.

[0293] As the material of the conductor 546, a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material can be used as a single layer or a stacked layer, similar to the conductor 505. For example, it is preferable to use a high-melting point material such as tungsten or molybdenum that has both heat resistance and conductivity. Alternatively, it is preferable to form the conductor 546 from a low-resistance conductive material such as aluminum or copper. By using a low-resistance conductive material, the wiring resistance can be reduced.

[0294] For example, by using a layered structure of tantalum nitride, a conductor having barrier properties against hydrogen and oxygen, and tungsten, which has high conductivity, as the conductor 546, it is possible to suppress the diffusion of impurities from the outside while maintaining the conductivity as a wiring.

[0295] With the above structure, a semiconductor device including a transistor having an oxide semiconductor and high on-state current can be provided. Alternatively, a semiconductor device including a transistor having an oxide semiconductor and low off-state current can be provided. Alternatively, a semiconductor device in which fluctuation in electrical characteristics is suppressed, which has stable electrical characteristics and improved reliability can be provided.

[0296] <Transistor structure example 2> A structural example of a transistor 510B will be described with reference to Figures 12A, 12B, and 12C. Figure 12A is a top view of the transistor 510B. Figure 12B is a cross-sectional view of a portion indicated by dashed dotted line L1-L2 in Figure 12A. Figure 12C is a cross-sectional view of a portion indicated by dashed dotted line W1-W2 in Figure 12A. Note that in the top view of Figure 12A, some elements are omitted for clarity.

[0297] The transistor 510B is a modified example of the transistor 510A. Therefore, in order to avoid repetition of the description, the following description will mainly focus on the differences from the transistor 510A.

[0298] The transistor 510B has a region in which the conductor 542 (the conductor 542a and the conductor 542b) overlaps with the oxide 530c, the insulator 550, and the conductor 560. With this structure, a transistor with high on-state current can be provided. In addition, a transistor with high controllability can be provided.

[0299] The conductor 560 functioning as the first gate electrode has a conductor 560a and a conductor 560b on the conductor 560a. As with the conductor 505a, the conductor 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 conductor 560a is preferably made of a conductive material having a function of suppressing diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, and the like).

[0300] The conductor 560a has a function of suppressing oxygen diffusion, which improves the material selectivity of the conductor 560b. In other words, the presence of the conductor 560a suppresses oxidation of the conductor 560b, thereby preventing a decrease in electrical conductivity.

[0301] It is preferable to provide an insulator 574 so as to cover the top surface and side surface of the conductor 560, the side surface of the insulator 550, and the side surface of the oxide 530c. Note that the insulator 574 may be made of an insulating material having a function of suppressing the diffusion of impurities such as water or hydrogen, and oxygen. For example, it is preferable to use aluminum oxide or hafnium oxide. In addition, for example, metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, or tantalum oxide, silicon nitride oxide, or silicon nitride may also be used.

[0302] Providing the insulator 574 can suppress oxidation of the conductor 560. Furthermore, providing the insulator 574 can suppress diffusion of impurities such as water and hydrogen contained in the insulator 580 to the transistor 510B.

[0303] Furthermore, an insulator 576 (insulator 576a and insulator 576b) having barrier properties may be disposed between the conductor 546 and the insulator 580. Providing the insulator 576 can prevent oxygen in the insulator 580 from reacting with the conductor 546 and oxidizing the conductor 546.

[0304] Furthermore, by providing the insulator 576 having a barrier property, the range of materials that can be selected for the conductor used for the plug or wiring can be expanded. For example, by using a metal material that has a property of absorbing oxygen and has high conductivity for the conductor 546, a semiconductor device with low power consumption can be provided. Specifically, a material that has low oxidation resistance but high conductivity, such as tungsten or aluminum, can be used. Also, for example, a conductor that is easy to form or process can be used.

[0305] <Transistor structure example 3> A structural example of a transistor 510C will be described with reference to Figures 13A, 13B, and 13C. Figure 13A is a top view of the transistor 510C. Figure 13B is a cross-sectional view of a portion indicated by dashed line L1-L2 in Figure 13A. Figure 13C is a cross-sectional view of a portion indicated by dashed line W1-W2 in Figure 13A. Note that in the top view of Figure 13A, some elements are omitted for clarity.

[0306] The transistor 510C is a modified example of the transistor 510A. Therefore, in order to avoid repetition of the description, the following description will mainly focus on the differences from the transistor 510A.

[0307] 13, a conductor 547a is disposed between a conductor 542a and an oxide 530b, and a conductor 547b is disposed between a conductor 542b and an oxide 530b. Here, the conductor 542a (conductor 542b) extends beyond the upper surface of the conductor 547a (conductor 547b) and the side surface on the conductor 560 side, and has a region in contact with the upper surface of the oxide 530b. Here, the conductor 547 may be any conductor that can be used for the conductor 542. Furthermore, the film thickness of the conductor 547 is preferably at least thicker than that of the conductor 542.

[0308] 13 has the above-described structure, the conductor 542 can be closer to the conductor 560 than the transistor 510A. Alternatively, the ends of the conductor 542a and the conductor 542b can overlap with the conductor 560. This can shorten the effective channel length of the transistor 510C, and improve the on-state current and frequency characteristics.

[0309] The conductor 547a (conductor 547b) is preferably provided so as to overlap the conductor 542a (conductor 542b). With this configuration, the conductor 547a (conductor 547b) functions as a stopper in etching to form an opening in which the conductor 546a (conductor 546b) is to be embedded, thereby preventing the oxide 530b from being overetched.

[0310] 13 may have a structure in which an insulator 545 is disposed on and in contact with the insulator 544. The insulator 544 preferably functions as a barrier insulating film that suppresses impurities such as water or hydrogen or excess oxygen from entering the transistor 510C from the insulator 580. The insulator 545 can be any insulator that can be used for the insulator 544. The insulator 544 may be a nitride insulator such as aluminum nitride, aluminum titanium nitride, titanium nitride, silicon nitride, or silicon nitride oxide.

[0311] 11, the transistor 510C shown in FIG. 13 may have a single-layer structure including the conductor 505. In this case, an insulating film to be the insulator 516 is formed on the formed conductor 505, and the upper part of the insulating film is removed by a CMP method or the like until the upper surface of the conductor 505 is exposed. Here, it is preferable to improve the flatness of the upper surface of the conductor 505. For example, the average surface roughness (Ra) of the upper surface of the conductor 505 is set to 1 nm or less, preferably 0.5 nm or less, and more preferably 0.3 nm or less. This can improve the flatness of the insulating layer formed on the conductor 505 and improve the crystallinity of the oxide 530b and the oxide 530c.

[0312] <Transistor structure example 4> A structural example of a transistor 510D will be described with reference to Figures 14A, 14B, and 14C. Figure 14A is a top view of the transistor 510D. Figure 14B is a cross-sectional view of a portion indicated by dashed line L1-L2 in Figure 14A. Figure 14C is a cross-sectional view of a portion indicated by dashed line W1-W2 in Figure 14A. Note that in the top view of Figure 14A, some elements are omitted for clarity.

[0313] The transistor 510D is a variation of the transistor described above, and therefore, in order to avoid repetition of the description, the following description will focus mainly on the differences from the transistor described above.

[0314] 14A to 14C, the conductor 503 is not provided, and the conductor 505 having a function as the second gate also functions as a wiring. An insulator 550 is provided over the oxide 530c, and a metal oxide 552 is provided over the insulator 550. A conductor 560 is provided over the metal oxide 552, and an insulator 570 is provided over the conductor 560. An insulator 571 is provided over the insulator 570.

[0315] The metal oxide 552 preferably has a function of suppressing oxygen diffusion. By providing the metal oxide 552, which suppresses oxygen diffusion, between the insulator 550 and the conductor 560, the diffusion of oxygen to the conductor 560 is suppressed. That is, a decrease in the amount of oxygen supplied to the oxide 530 can be suppressed. In addition, oxidation of the conductor 560 by oxygen can be suppressed.

[0316] Note that the metal oxide 552 may function as a part of the first gate. For example, an oxide semiconductor that can be used as the oxide 530 can be used as the metal oxide 552. In that case, by forming the conductor 560 by a sputtering method, the electric resistance value of the metal oxide 552 can be reduced to form a conductive layer. This can be called an OC electrode.

[0317] Furthermore, the metal oxide 552 may function as a part of the gate insulating film. Therefore, when silicon oxide or silicon oxynitride is used for the insulator 550, it is preferable to use a metal oxide that is a high-k material with a high relative dielectric constant for the metal oxide 552. By using such a stacked structure, a stacked structure that is stable against heat and has a high relative dielectric constant can be obtained. Therefore, it is possible to reduce the gate potential applied during transistor operation while maintaining the physical film thickness. In addition, it is possible to reduce the equivalent oxide thickness (EOT) of the insulating layer that functions as a gate insulating film.

[0318] Although the metal oxide 552 in the transistor 510D is shown as a single layer, it may have a stacked structure of two or more layers. For example, a metal oxide functioning as part of a gate electrode and a metal oxide functioning as part of a gate insulating film may be stacked.

[0319] When the metal oxide 552 functions as a gate electrode, the on-state current of the transistor 510D can be improved without weakening the influence of the electric field from the conductor 560. Alternatively, when the metal oxide 552 functions as a gate insulating film, the physical thickness of the insulator 550 and the metal oxide 552 can maintain a distance between the conductor 560 and the oxide 530, thereby suppressing leakage current between the conductor 560 and the oxide 530. Therefore, by providing a stacked structure of the insulator 550 and the metal oxide 552, the physical distance between the conductor 560 and the oxide 530 and the electric field strength applied from the conductor 560 to the oxide 530 can be easily and appropriately adjusted.

[0320] Specifically, an oxide semiconductor that can be used for the oxide 530 can be reduced in resistance to be used as the metal oxide 552. Alternatively, a metal oxide containing one or more elements selected from hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium, tantalum, nickel, germanium, magnesium, and the like can be used.

[0321] In particular, it is preferable to use aluminum oxide, hafnium oxide, hafnium aluminate, or the like, which is an insulating layer containing an oxide of either or both of aluminum and hafnium. 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 process. Note that the metal oxide 552 is not an essential component. It may be appropriately designed depending on the desired transistor characteristics.

[0322] The insulator 570 may be made of an insulating material that has a function of suppressing the permeation of impurities such as water or hydrogen, and oxygen. For example, it is preferable to use aluminum oxide or hafnium oxide. This can suppress the conductor 560 from being oxidized by oxygen from above the insulator 570. In addition, impurities such as water or hydrogen from above the insulator 570 can be suppressed from being mixed into the oxide 530 through the conductor 560 and the insulator 550.

[0323] The insulator 571 functions as a hard mask. By providing the insulator 571, when the conductor 560 is processed, the side surface of the conductor 560 can be approximately vertical, specifically, the angle between the side surface of the conductor 560 and the substrate surface can be set to 75 degrees or more and 100 degrees or less, preferably 80 degrees or more and 95 degrees or less.

[0324] Note that the insulator 571 may also function as a barrier layer by using an insulating material that has a function of suppressing permeation of impurities such as water or hydrogen and oxygen. In that case, the insulator 570 is not necessarily provided.

[0325] Using insulator 571 as a hard mask, portions of insulator 570, conductor 560, metal oxide 552, insulator 550, and oxide 530c can be selectively removed to roughly align their sides and expose a portion of the surface of oxide 530b.

[0326] Transistor 510D also has regions 531a and 531b on a portion of the exposed oxide 530b surface, with either region 531a or region 531b functioning as a source region and the other functioning as a drain region.

[0327] The formation of the regions 531a and 531b can be achieved by introducing an impurity element such as phosphorus or boron into the exposed surface of the oxide 530b by, for example, ion implantation, ion doping, plasma immersion ion implantation, plasma treatment, etc. In this embodiment and the like, the term "impurity element" refers to an element other than the main component element.

[0328] In addition, after exposing a portion of the surface of oxide 530b, a metal film can be formed and then heat-treated, thereby diffusing elements contained in the metal film into oxide 530b to form regions 531a and 531b.

[0329] The region of the oxide 530b into which the impurity element has been introduced has a reduced electrical resistivity, and therefore the region 531a and the region 531b are sometimes referred to as "impurity region" or "low resistance region."

[0330] By using the insulator 571 and / or the conductor 560 as a mask, the regions 531a and 531b can be formed in a self-aligned manner. Therefore, the regions 531a and / or 531b do not overlap with the conductor 560, and parasitic capacitance can be reduced. In addition, an offset region is not formed between the channel formation region and the source / drain region (region 531a or region 531b). By forming the regions 531a and 531b in a self-aligned manner, it is possible to realize an increase in on-current, a reduction in threshold voltage, an improvement in operating frequency, and the like.

[0331] In order to further reduce the off-state current, an offset region may be provided between the channel formation region and the source / drain region. The offset region is a region having high electrical resistivity, into which the above-described impurity element is not introduced. The offset region can be formed by introducing the above-described impurity element after the formation of the insulator 575. In this case, the insulator 575 also functions as a mask, similar to the insulator 571. Therefore, the impurity element is not introduced into the region of the oxide 530b that overlaps with the insulator 575, and the electrical resistivity of the region can be kept high.

[0332] The transistor 510D also has an insulator 575 on the side surfaces of the insulator 570, the conductor 560, the metal oxide 552, the insulator 550, and the oxide 530c. The insulator 575 is preferably an insulator with a low dielectric constant. For example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide to which fluorine has been added, silicon oxide to which carbon has been added, silicon oxide to which carbon and nitrogen have been added, silicon oxide having voids, or a resin is preferable. In particular, when silicon oxide, silicon oxynitride, silicon nitride oxide, or silicon oxide having voids is used for the insulator 575, it is preferable because an excess oxygen region can be easily formed in the insulator 575 in a later step. Silicon oxide and silicon oxynitride are preferable because they are thermally stable. The insulator 575 also preferably has a function of diffusing oxygen.

[0333] The transistor 510D further includes an insulator 575 and an insulator 574 over the oxide 530. The insulator 574 is preferably formed by a sputtering method. By using a sputtering method, an insulator containing few impurities such as water or hydrogen can be formed. For example, aluminum oxide is preferably used as the insulator 574.

[0334] Note that an oxide film formed by a sputtering method may extract hydrogen from a structure to be deposited. Therefore, the insulator 574 absorbs hydrogen and water from the oxide 530 and the insulator 575, thereby reducing the hydrogen concentrations in the oxide 530 and the insulator 575.

[0335] <Transistor structure example 5> A structural example of a transistor 510E will be described with reference to Figures 15A to 15C. Figure 15A is a top view of the transistor 510E. Figure 15B is a cross-sectional view of a portion indicated by dashed dotted line L1-L2 in Figure 15A. Figure 15C is a cross-sectional view of a portion indicated by dashed dotted line W1-W2 in Figure 15A. Note that in the top view of Figure 15A, some elements are omitted for clarity.

[0336] The transistor 510E is a variation of the transistor described above, and therefore, in order to avoid repetition of description, the following description will focus mainly on the differences from the transistor described above.

[0337] 15A to 15C, the conductor 542 is not provided, and the exposed oxide 530b has a region 531a and a region 531b on a part of the surface. One of the region 531a and the region 531b functions as a source region, and the other functions as a drain region. An insulator 573 is provided between the oxide 530b and the insulator 574.

[0338] 15, a region 531 (region 531a and region 531b) is a region in which the following elements are added to an oxide 530b: The region 531 can be formed by using, for example, a dummy gate.

[0339] Specifically, a dummy gate is provided on the oxide 530b, and the dummy gate is used as a mask to add an element that reduces the resistance of the oxide 530b. That is, the element is added to a region where the oxide 530 does not overlap with the dummy gate, forming a region 531. The element can be added by an ion implantation method in which an ionized source gas is added after being mass-separated, an ion doping method in which an ionized source gas is added without being mass-separated, a plasma immersion ion implantation method, or the like.

[0340] Representative elements that reduce the resistance of the oxide 530 include boron and phosphorus. Hydrogen, carbon, nitrogen, fluorine, sulfur, chlorine, titanium, rare gases, and the like may also be used. Representative examples of rare gases include helium, neon, argon, krypton, and xenon. The concentration of the element may be measured using SIMS or the like.

[0341] In particular, boron and phosphorus are preferable because they allow the use of equipment from manufacturing lines for amorphous silicon or low-temperature polysilicon, and existing facilities can be repurposed, allowing capital investment to be reduced.

[0342] Subsequently, an insulating film to be the insulator 573 and an insulating film to be the insulator 574 may be formed over the oxide 530b and the dummy gate. By stacking the insulating film to be the insulator 573 and the insulating film to be the insulator 574, a region in which the region 531 overlaps with the oxide 530c and the insulator 550 can be provided.

[0343] Specifically, an insulating film to be the insulator 580 is provided on the insulating film to be the insulator 574, and then the insulating film to be the insulator 580 is subjected to CMP processing to remove a part of the insulating film to be the insulator 580, thereby exposing the dummy gate. Then, when removing the dummy gate, it is preferable to also remove a part of the insulator 573 in contact with the dummy gate. Therefore, the insulator 574 and the insulator 573 are exposed on the side surface of the opening provided in the insulator 580, and a part of the region 531 provided in the oxide 530b is exposed on the bottom surface of the opening. Next, an oxide film to be the oxide 530c, an insulating film to be the insulator 550, and a conductive film to be the conductor 560 are sequentially formed in the opening, and then the oxide film to be the oxide 530c, the insulating film to be the insulator 550, and a conductive film to be the conductor 560 are removed by CMP processing or the like until the insulator 580 is exposed, thereby forming the transistor shown in FIG. 15.

[0344] Note that the insulators 573 and 574 are not essential components and may be appropriately designed depending on desired transistor characteristics.

[0345] The transistor shown in FIG. 15 can be an existing device and does not include the conductor 542, which leads to cost reduction.

[0346] <Transistor structure example 6> A structural example of a transistor 510F will be described with reference to Figures 16A to 16C. Figure 16A is a top view of the transistor 510F. Figure 16B is a cross-sectional view of a portion indicated by dashed dotted line L1-L2 in Figure 16A. Figure 16C is a cross-sectional view of a portion indicated by dashed dotted line W1-W2 in Figure 16A. Note that in the top view of Figure 16A, some elements are omitted for clarity.

[0347] The transistor 510F is a modified example of the transistor 510A. Therefore, in order to avoid repetition of the description, the following description will focus mainly on the differences from the above transistor.

[0348] In transistor 510A, a portion of insulator 574 is provided in an opening provided in insulator 580 and is provided so as to cover the side surface of conductor 560. On the other hand, in transistor 510F, an opening is formed by removing a portion of insulator 580 and insulator 574.

[0349] Furthermore, an insulator 576 (insulator 576a and insulator 576b) having barrier properties may be disposed between the conductor 546 and the insulator 580. Providing the insulator 576 can prevent oxygen in the insulator 580 from reacting with the conductor 546 and oxidizing the conductor 546.

[0350] In addition, when an oxide semiconductor is used as the oxide 530, it is preferable to have a stacked structure of a plurality of oxide layers having different atomic ratios of metal atoms. Specifically, in the metal oxide used for the oxide 530a, the atomic ratio of element M among the constituent elements 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, in the metal oxide used for the oxide 530a, the atomic ratio of element M to In is preferably larger than the atomic ratio of element M to In in the metal oxide used for the oxide 530b. In addition, in the metal oxide used for the oxide 530b, the atomic ratio of In to element M is preferably larger than the atomic ratio of In to element M in the metal oxide used for the oxide 530a. In addition, the oxide 530c can be a metal oxide that can be used for the oxide 530a or the oxide 530b.

[0351] The oxide 530a, the oxide 530b, and the oxide 530c are preferably crystalline, and in particular, CAAC-OS is preferably used. Crystalline oxides such as CAAC-OS have few impurities and defects (oxygen vacancies, etc.), and have a dense structure with high crystallinity. This can suppress the source electrode or the drain electrode from extracting oxygen from the oxide 530b. As a result, even when heat treatment is performed, the extraction of oxygen from the oxide 530b can be reduced, and the transistor 510F is stable against high temperatures (so-called thermal budget) in the manufacturing process.

[0352] One or both of the oxide 530a and the oxide 530c may be omitted. The oxide 530 may be a single layer of the oxide 530b. When the oxide 530 is a stack of the oxides 530a, 530b, and 530c, it is preferable that the energy of the conduction band minimum of the oxide 530a and the oxide 530c is higher than the energy of the conduction band minimum of the oxide 530b. In other words, it is preferable that the electron affinity of the oxide 530a and the oxide 530c is smaller than the electron affinity of the oxide 530b. In this case, it is preferable that the oxide 530c is made of a metal oxide that can be used for the oxide 530a. Specifically, it is preferable that the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530c is larger than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. In addition, in the metal oxide used for oxide 530c, the atomic ratio of element M to In is preferably greater than the atomic ratio of element M to In in the metal oxide used for oxide 530b. In addition, in the metal oxide used for oxide 530b, the atomic ratio of In to element M is preferably greater than the atomic ratio of In to element M in the metal oxide used for oxide 530c.

[0353] Here, the energy level of the conduction band minimum changes gradually at the junction of the oxide 530a, the oxide 530b, and the oxide 530c. In other words, it can be said that the energy level of the conduction band minimum at the junction of the oxide 530a, the oxide 530b, and the oxide 530c 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 and the interface between the oxide 530b and the oxide 530c.

[0354] Specifically, the oxide 530a and the oxide 530b, and the oxide 530b and the oxide 530c have a common element other than oxygen (as a main component), so that a mixed layer with a low defect level density can be formed. For example, when the oxide 530b is an In-Ga-Zn oxide, the oxide 530a and the oxide 530c may be made of an In-Ga-Zn oxide, a Ga-Zn oxide, gallium oxide, or the like. The oxide 530c may also have a laminated structure. For example, a laminated structure of an In-Ga-Zn oxide and a Ga-Zn oxide on the In-Ga-Zn oxide, or a laminated structure of an In-Ga-Zn oxide and a gallium oxide on the In-Ga-Zn oxide can be used. In other words, a laminated structure of an In-Ga-Zn oxide and an oxide not containing In may be used as the oxide 530c.

[0355] Specifically, the oxide 530a may be a metal oxide having a composition of In:Ga:Zn=1:3:4 [atomic ratio] or a composition close thereto, or a composition of 1:1:0.5 [atomic ratio] or a composition close thereto. The oxide 530b may be a metal oxide having a composition of In:Ga:Zn=1:1:1 [atomic ratio] or a composition close thereto, In:Ga:Zn=4:2:3 [atomic ratio] or a composition close thereto, In:Ga:Zn=5:1:3 [atomic ratio] or a composition close thereto, or a composition of 10:1:3 [atomic ratio] or a composition close thereto, or an In-Zn oxide. The metal oxide that can be used for the oxide 530a or the oxide 530b may be used. The composition close thereto includes a range of ±30% of the desired atomic ratio.

[0356] In addition, the oxide 530c may have a laminated structure of two or more layers. Specific examples of the laminated structure of the oxide 530c include a lower layer of the oxide 530c made of a metal oxide having an atomic ratio of In:Ga:Zn=5:1:3 or a composition close thereto, or an atomic ratio of 10:1:3 or a composition close thereto, or an In-Zn oxide, and an upper layer of the oxide 530c made of In:Ga:Zn=1:3:4 or a composition close thereto, or a Ga:Zn=2:1 or a composition close thereto, or a Ga:Zn=2:5 or a composition close thereto, or gallium oxide.

[0357] By configuring the oxide 530a and the oxide 530c as described above, the defect level density at the interface between the oxide 530a and the oxide 530b and at the interface between the oxide 530b and the oxide 530c can be reduced. Therefore, the influence of the interface scattering on the carrier conduction is reduced, and the transistor 510F can obtain a high on-current and high frequency characteristics. When the oxide 530c has a stacked structure, in addition to the effect of reducing the defect level density at the interface between the oxide 530b and the oxide 530c, it is expected that the constituent elements of the oxide 530c can be suppressed from diffusing to the insulator 550 side. More specifically, the oxide 530c has a stacked structure, and an oxide that does not contain In is positioned above the stacked structure, so that In that may diffuse to the insulator 550 side can be suppressed. Since the insulator 550 functions as a gate insulator, when In diffuses, the transistor characteristics become poor. Therefore, by configuring the oxide 530c as a stacked structure, it is possible to provide a display device with high reliability.

[0358] The oxide 530 is preferably a metal oxide that functions as an oxide semiconductor. For example, a metal oxide that serves as a channel formation region of the oxide 530 has a band gap of 2 eV or more, preferably 2.5 eV or more. By using a metal oxide with a wide band gap in this manner, the off-state current of the transistor can be reduced. By using such a transistor, a semiconductor device with low power consumption can be provided.

[0359] <Configuration Example 2 of Semiconductor Device> Fig. 17 shows an example of the semiconductor device shown in Fig. 9 having a conductor 692 on an insulator 650. The conductor 692 is formed to cover one surface of the semiconductor device. Although not shown in Fig. 17, the conductor 692 may have an opening. Furthermore, a conductor electrically connected to a conductor below the insulator 650 may be provided in the opening.

[0360] A metal can be used as the conductor 692. A metal nitride or metal oxide having electrical conductivity may also be used. For example, titanium, titanium nitride, titanium oxide, or the like can be used as the conductor 692. The conductor 692 has a function of blocking or weakening electromagnetic waves from the outside more than the semiconductor device. The conductor 692 also has a function of diffusing and dissipating static electricity or preventing localization of electric charge. By providing the conductor 692, the operation of the semiconductor device can be further stabilized.

[0361] 18 shows an example in which an insulator 693 is provided between an insulator 650 and a conductor 692. For example, a structure in which a fibrous body is impregnated with an organic resin can be used as the insulator 693. For example, glass fiber may be used as the fibrous body. Also, for example, brominated epoxy resin may be used as the organic resin.

[0362] Note that this embodiment mode can be implemented in appropriate combination with other embodiment modes described in this specification.

[0363] (Embodiment 3) In this embodiment, a structure of a metal oxide that can be used for the OS transistor described in the above embodiment will be described.

[0364] <<Metal oxides>> It is preferable to use a metal oxide that functions as an oxide semiconductor as the oxide 530. Hereinafter, metal oxides that can be used as the oxide 530 according to the present invention will be described.

[0365] 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 indium and zinc, it is preferable that the metal oxide contains gallium, yttrium, tin, etc. In addition, it may contain one or more elements selected from boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, etc.

[0366] Here, the case where the metal oxide is an In-M-Zn oxide having indium, element M, and zinc is considered. The element M is one or more elements selected from aluminum, gallium, yttrium, and tin. Other elements applicable to the element M include boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like. As the element M, a combination of a plurality of the above elements may be used in some cases.

[0367] 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.

[0368] [Metal oxide structures] Oxide semiconductors (metal oxides) are classified into single-crystal oxide semiconductors and other non-single-crystal oxide semiconductors, such as CAAC-OS, polycrystalline oxide semiconductors, nanocrystalline oxide semiconductors (nc-OS), amorphous-like oxide semiconductors (a-like OS), and amorphous oxide semiconductors.

[0369] CAAC-OS has a c-axis orientation and a distorted crystal structure in which multiple nanocrystals are connected in the ab-plane direction. The distortion refers to a portion where the lattice orientation changes between a region with a uniform lattice arrangement and a region with a different uniform lattice arrangement in the region where multiple nanocrystals are connected.

[0370] Nanocrystals are basically hexagonal, but may be non-regular hexagonal. In addition, the lattice arrangement may be pentagonal or heptagonal due to the distortion. It is difficult to confirm clear grain boundaries in CAAC-OS even near the distortion. In other words, it is found that the formation of grain boundaries is suppressed by the distortion of the lattice arrangement. This is because CAAC-OS can tolerate distortion due to the lack of dense arrangement of oxygen atoms in the ab-plane direction and the change in the bond distance between atoms due to the substitution of metal elements.

[0371] CAAC-OS also tends to have a layered crystal structure (also referred to as a layered structure) in which a layer containing indium and oxygen (hereinafter, In layer) and a layer containing element M, zinc, and oxygen (hereinafter, (M, Zn) layer) are stacked. Note that indium and element M can be substituted for each other, and when element M in an (M, Zn) layer is substituted for indium, it can also be expressed as an (In, M, Zn) layer. When indium in an In layer is substituted for element M, it can also be expressed as an (In, M) layer.

[0372] CAAC-OS is a metal oxide with high crystallinity. On the other hand, it is difficult to confirm clear crystal boundaries in CAAC-OS, so it can be said that the decrease in electron mobility caused by crystal boundaries is unlikely to occur. In addition, since the crystallinity of metal oxides can be decreased by the inclusion of impurities or the generation of defects, CAAC-OS can be said to be a metal oxide with few impurities and defects (oxygen vacancies, etc.). Therefore, metal oxides with CAAC-OS have stable physical properties. As a result, metal oxides with CAAC-OS are resistant to heat and highly reliable.

[0373] The nc-OS has periodic atomic arrangement in a microscopic region (for example, a region of 1 nm to 10 nm, particularly a region of 1 nm to 3 nm). In addition, the nc-OS does not show regularity in the crystal orientation between different nanocrystals. Therefore, no orientation is seen throughout the film. Therefore, depending on the analysis method, the nc-OS may be indistinguishable from an a-like OS or an amorphous oxide semiconductor.

[0374] In-Ga-Zn oxide (hereinafter referred to as IGZO), a type of metal oxide containing indium, gallium, and zinc, may have a stable structure when made into the above-mentioned nanocrystals. In particular, since IGZO tends to have difficulty in crystal growth in the atmosphere, it may be structurally more stable when made into small crystals (for example, the above-mentioned nanocrystals) rather than large crystals (here, crystals of several mm or several cm).

[0375] The a-like OS is a metal oxide having a structure between the nc-OS and an amorphous oxide semiconductor. The a-like OS has a pore or low-density region. That is, the a-like OS has lower crystallinity than the nc-OS and CAAC-OS.

[0376] Oxide semiconductors (metal oxides) have a variety of structures and each structure has 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, an nc-OS, and a CAAC-OS.

[0377] [impurities] Here, the influence of each impurity in the metal oxide will be described.

[0378] When impurities are mixed into an oxide semiconductor, defect states or oxygen vacancies may be formed. Therefore, when impurities are mixed into a channel formation region of an oxide semiconductor, the electrical characteristics of a transistor using the oxide semiconductor are likely to fluctuate, and the reliability may be reduced. Furthermore, when oxygen vacancies are included in the channel formation region, the transistor is likely to have normally-on characteristics.

[0379] The defect levels may include trap levels. Charges trapped in the trap levels of metal oxides take a long time to disappear, and may behave as if they were fixed charges. Therefore, a transistor having a channel formation region made of a metal oxide with a high density of trap levels may have unstable electrical characteristics.

[0380] Furthermore, when impurities are present in a channel formation region of an oxide semiconductor, the crystallinity of the channel formation region may be reduced, or the crystallinity of an oxide provided in contact with the channel formation region may be reduced. When the crystallinity of the channel formation region is low, the stability or reliability of the transistor tends to be degraded. When the crystallinity of an oxide provided in contact with the channel formation region is low, an interface state may be formed, which may degrade the stability or reliability of the transistor.

[0381] Therefore, in order to improve the stability or reliability of a transistor, it is effective to reduce the concentration of impurities in the channel formation region of the oxide semiconductor and in its vicinity. Examples of impurities include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

[0382] Specifically, the concentration of the impurities in the channel formation region of the oxide semiconductor and its vicinity, which is obtained by SIMS, is set to 1×10 18 atoms / cm 3Less than or equal to 2 x 10 16 atoms / cm 3 or less. Alternatively, the concentration of the impurity in the channel formation region of the oxide semiconductor and its vicinity, which is obtained by elemental analysis using EDX, is set to 1.0 atomic % or less. Note that when an oxide containing element M is used as the oxide semiconductor, the concentration ratio of the impurity to element M in the channel formation region of the oxide semiconductor and its vicinity is set to less than 0.10, preferably less than 0.05. Here, the concentration of element M used in calculating the concentration ratio may be the concentration in the same region as the region where the concentration of the impurity is calculated, or may be the concentration in the oxide semiconductor.

[0383] Furthermore, since a metal oxide with a reduced impurity concentration has a low defect state density, the trap state density may also be low.

[0384] In addition, when hydrogen enters an oxygen vacancy in a metal oxide, the oxygen vacancy and hydrogen combine to form V O May form H. V O H can act as a donor, generating carrier electrons, and some of the hydrogen can combine with oxygen, which in turn combines with metal atoms, generating carrier electrons.

[0385] Therefore, a transistor using an oxide semiconductor containing a large amount of hydrogen is likely to have normally-on characteristics. In addition, hydrogen in an oxide semiconductor is easily moved by stress such as heat or an electric field, and therefore, when an oxide semiconductor contains a large amount of hydrogen, the reliability of the transistor may be deteriorated.

[0386] That is, V in metal oxide O It is preferable to reduce H as much as possible and make it high-purity intrinsic or substantially high-purity intrinsic. O In order to obtain an oxide semiconductor with sufficiently reduced H, it is important to remove impurities such as moisture and hydrogen from the oxide semiconductor (sometimes referred to as dehydration or dehydrogenation treatment) and to supply oxygen to the oxide semiconductor to compensate for oxygen vacancies (sometimes referred to as oxygen addition treatment).O By using an oxide semiconductor in which impurities such as H are sufficiently reduced for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0387] In addition, it is preferable to use an oxide semiconductor with a low carrier concentration for the transistor. In order to reduce the carrier concentration of an oxide semiconductor, the impurity concentration in the oxide semiconductor may be reduced to reduce the density of defect states. In this specification and the like, a semiconductor having a low impurity concentration and a low density of defect states is referred to as being highly pure intrinsic or substantially highly pure intrinsic. Examples of impurities in an oxide semiconductor include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, silicon, and the like.

[0388] In particular, hydrogen contained in an oxide semiconductor reacts with oxygen bonded to metal atoms to form water, which may form oxygen vacancies in the oxide semiconductor. When oxygen vacancies are present in a channel formation region in an oxide semiconductor, the transistor may have normally-on characteristics. Furthermore, defects in which hydrogen has entered the oxygen vacancies may function as donors and generate electrons that serve as carriers. In addition, some of the hydrogen may bond to oxygen that is bonded to metal atoms to generate electrons that serve as carriers. Therefore, a transistor using an oxide semiconductor that contains a large amount of hydrogen is likely to have normally-on characteristics.

[0389] A defect in which hydrogen has entered an oxygen vacancy (V O H) can function as a donor for an oxide semiconductor. However, it is difficult to quantitatively evaluate the defects. Thus, in an oxide semiconductor, evaluation may be performed using the carrier concentration instead of the donor concentration. Thus, in this specification and the like, as a parameter of an oxide semiconductor, the carrier concentration assuming a state in which no electric field is applied may be used instead of the donor concentration. In other words, the "carrier concentration" described in this specification and the like may be rephrased as the "donor concentration".

[0390] Therefore, it is preferable to reduce hydrogen in the oxide semiconductor as much as possible. 20 atoms / cm 3 Less than 1 x 10 19 atoms / cm 3 less than 5×10 18 atoms / cm 3 less than 1×10 18 atoms / cm 3 When an oxide semiconductor in which impurities such as hydrogen are sufficiently reduced is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0391] The carrier concentration of the oxide semiconductor in the channel formation region is 1×10 18 cm -3 It is preferable that the value is less than 1×10 17 cm -3 More preferably, it is less than 1×10 16 cm -3 More preferably, it is less than 1×10 13 cm -3 More preferably, it is less than 1×10 12 cm -3 The lower limit of the carrier concentration of the oxide semiconductor in the channel formation region is not particularly limited, but is preferably, for example, 1×10 -9 cm -3 It can be said that:

[0392] According to one embodiment of the present invention, a semiconductor device with high reliability can be provided. According to one embodiment of the present invention, a semiconductor device with good electrical characteristics can be provided. According to one embodiment of the present invention, a semiconductor device with large on-state current can be provided. According to one embodiment of the present invention, a semiconductor device that can be miniaturized or highly integrated can be provided. Another object of one embodiment of the present invention is to provide a semiconductor device with low power consumption.

[0393] <<Other semiconductor materials>> The semiconductor material that can be used for the oxide 530 is not limited to the above-mentioned metal oxides. A semiconductor material having a band gap (a semiconductor material that is not a zero-gap semiconductor) may be used for the oxide 530. For example, a semiconductor of a single element such as silicon, a compound semiconductor such as gallium arsenide, or a layered material (also called an atomic layer material, a two-dimensional material, or the like) that functions as a semiconductor is preferably used for the semiconductor material. In particular, a layered material that functions as a semiconductor is preferably used for the semiconductor material.

[0394] Here, in this specification and the like, the layered material is a general term for a group of materials having a layered crystal structure. The layered crystal structure is a structure in which layers formed by covalent bonds or ionic bonds are stacked via bonds weaker than covalent bonds or ionic bonds, such as van der Waals forces. The layered material has high electrical conductivity within a unit layer, that is, high two-dimensional electrical conductivity. By using a material that functions as a semiconductor and has high two-dimensional electrical conductivity in the channel formation region, a transistor with a large on-current can be provided.

[0395] Layered materials include graphene, silicene, and chalcogenides. Chalcogenides are compounds that contain chalcogen. Chalcogen is a general term for elements in group 16, including oxygen, sulfur, selenium, tellurium, polonium, and livermorium. Chalcogenides include transition metal chalcogenides and group 13 chalcogenides.

[0396] It is preferable to use, for example, a transition metal chalcogenide that functions as a semiconductor as the oxide 530. Specific examples of transition metal chalcogenides that can be used as the oxide 530 include molybdenum sulfide (representatively MoS2), molybdenum selenide (representatively MoSe2), molybdenum tellurium (representatively MoTe2), tungsten sulfide (representatively WS2), tungsten selenide (representatively WSe2), tungsten tellurium (representatively WTe2), hafnium sulfide (representatively HfS2), hafnium selenide (representatively HfSe2), zirconium sulfide (representatively ZrS2), and zirconium selenide (representatively ZrSe2).

[0397] Note that this embodiment mode can be implemented in appropriate combination with other embodiment modes described in this specification. [Explanation of symbols]

[0398] EN1: terminal, ID1: current, IN2: terminal, ND1: node, ND2: node, ND3: node, ND4: node, OU1: terminal, OU2: terminal, OU3: terminal, OU4: terminal, RL1: resistor, SG1: terminal, SH1: terminal, SH2: terminal, Sv1: signal, VBI1: terminal, VD1: wiring, VS1: wiring, VT1: terminal, 21: semiconductor device, 30: oscillator, 31: circuit, 32: circuit, 33: circuit, 36: amplifier circuit, 38: control circuit, 41: transistor, 42: transistor, 43: transistor, 44: transistor, 45: transistor, 4 6a: transistor, 46b: transistor, 47a: transistor, 47b: transistor, 48: transistor, 49: transistor, 51: capacitance element, 52: capacitance element, 53: inverter, 54: transistor, 55: transistor, 56: comparator, 57: capacitance element, 61: transistor, 62: transistor, 63: circuit, 63a: transistor, 63b: transistor, 63n: transistor, 63x: circuit, 63y: circuit, 64: transistor, 65: transistor, 66: capacitance element, 71: transistor, 72: transistor, 73 : transistor, 74: transistor, 75: transistor, 76: transistor, 77: transistor, 121: secondary battery, 300: transistor, 311: substrate, 313: semiconductor region, 314a: low resistance region, 314b: low resistance region, 315: insulator, 316: conductor, 320: insulator, 322: insulator, 324: insulator, 326: insulator, 328: conductor, 330: conductor, 350: insulator, 352: insulator, 354: insulator, 356: conductor, 360: insulator, 362: insulator, 364: insulator, 366: conductor, 370: insulator, 372: insulator body, 374: insulator, 376: conductor, 380: insulator, 382: insulator, 384: insulator, 386: conductor, 500: transistor, 503: conductor, 503a: conductor, 503b: conductor, 505: conductor, 505a: conductor, 505b: conductor, 510: insulator, 510A: transistor, 510B: transistor, 510C: transistor, 510D: transistor, 510E: transistor, 510F: transistor, 511: insulator, 512: insulator, 514: insulator, 516: insulator, 518: conductor, 520: insulator, 521: insulator,522: insulator, 524: insulator, 530: oxide, 530a: oxide, 530b: oxide, 530c: oxide, 531: region, 531a: region, 531b: region, 540a: conductor, 540b: conductor, 542: conductor, 542a: conductor, 542b: conductor, 543: region, 543a: region, 543b: region, 544: insulator, 545: insulator, 546: conductor, 546a: conductor, 546b: conductor, 547: conductor, 547a: conductor, 547b: conductor, 548: conductor , 550: insulator, 552: metal oxide, 560: conductor, 560a: conductor, 560b: conductor, 570: insulator, 571: insulator, 573: insulator, 574: insulator, 575: insulator, 576: insulator, 576a: insulator, 576b: insulator, 580: insulator, 581: insulator, 582: insulator, 584: insulator, 586: insulator, 600: capacitance element, 610: conductor, 612: conductor, 620: conductor, 630: insulator, 650: insulator, 692: conductor, 693: insulator,

Claims

1. a first transistor, a second transistor, an oscillator, a first wiring, a second wiring, a first circuit, a secondary battery, and a comparator; the oscillator is electrically connected to each of the first wiring, the second wiring, and the first circuit; the first and second transistors each have a metal oxide containing at least one of indium and zinc in a channel formation region; the second transistor has a first gate and a second gate; the oscillator includes a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, and a first capacitive element; a gate of the third transistor and a gate of the fourth transistor are electrically connected to one of the source and the drain of the first transistor; one of a source and a drain of the third transistor is electrically connected to one of a source and a drain of the fifth transistor and to one electrode of the first capacitance element; one of a source and a drain of the fourth transistor is electrically connected to one of a source and a drain of the sixth transistor and the other electrode of the first capacitance element; the other of the source and the drain of the fifth transistor is electrically connected to a gate of the sixth transistor; the other of the source and the drain of the sixth transistor is electrically connected to the first circuit and to the gate of the fifth transistor; the first wiring is electrically connected to the other of the source and the drain of the third transistor and the other of the source and the drain of the fourth transistor; one of a non-inverting input terminal and an inverting input terminal of the comparator is electrically connected to a positive electrode of the secondary battery, and the other is electrically connected to one of a source and a drain of the second transistor; one of a first gate and a second gate of the second transistor is electrically connected to the first wiring; a first potential is applied to the other of the non-inverting input terminal and the inverting input terminal by turning on the second transistor, and the first potential is held at the other of the non-inverting input terminal and the inverting input terminal by turning off the second transistor; the comparator has a function of outputting an output signal according to a comparison result between the potential of the positive electrode and the first potential, The oscillator has a function of cutting off a current between the first wiring and the second wiring in response to the output signal.

2. In claim 1, the first circuit has at least one of an inverter and a buffer, and an input terminal; a gate of the fifth transistor electrically connected to the input terminal; The first circuit is a power storage device having a function of at least one of shaping and amplifying a signal provided to the input terminal.

3. In claim 1 or 2, The third to sixth transistors are power storage devices each including a metal oxide containing at least one of indium and zinc in a channel formation region.

4. In any one of claims 1 to 3, A second capacitance element is provided. one electrode of the second capacitance element is electrically connected to one of the source and drain of the first transistor; the other electrode of the second capacitor is electrically connected to the first wiring;

5. In any one of claims 1 to 4, a resistor element, a seventh transistor, and an eighth transistor; the first wiring is electrically connected to one of the source and the drain of the sixth transistor; the other of the source and the drain of the seventh transistor is electrically connected to one of the source and the drain of the eighth transistor; the other of the source and the drain of the eighth transistor is electrically connected to one electrode of the resistance element; The other electrode of the resistor element is electrically connected to the second wiring, the other of the source and the drain of the first transistor is electrically connected to the source or the drain of the eighth transistor; A low potential signal is applied to the first wiring, A power storage device to which a high potential signal is applied to the second wiring.

6. In any one of claims 1 to 5, the first circuit has n transistors (n is a natural number equal to or greater than 2); the n transistors of the first circuit are connected in series between the first wiring and the second wiring, The n number of transistors included in the first circuit are such that, in two adjacent transistors, a source or a drain of one transistor is electrically connected to a source or a drain of the other transistor, a gate of the fifth transistor is electrically connected to a gate of at least one of the n transistors included in the first circuit;

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