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] BACKGROUND OF THE INVENTION 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 memory 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] Japanese Patent Application Laid-Open No. 2006-324953 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. with a novel structure that enables reduction in 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 extracted as appropriate 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 the first wiring, the second wiring, and the first circuit. The first transistor includes 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. Gates of the second transistor and 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; 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] In addition, 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 addition, in the above structure, it is preferable that the semiconductor device has a second capacitor, one electrode of which is electrically connected to one of the source and drain of the first transistor, and the other electrode of which is electrically connected to the first wiring.

[0011] In addition, in the above structure, 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 the 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, the transistor includes 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, the other electrode of the resistor 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 during a period in which the first potential is maintained, at least one of the sixth transistor and the seventh transistor is turned off to block current flowing between the first wiring and the second wiring, and it is preferable that a low potential signal is applied to the first wiring and a high potential signal is applied to the second wiring.

[0013] Furthermore, 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 the gate of at least one of the n transistors in the first circuit.

[0014] Furthermore, 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 included in the first circuit are connected in series between a first wiring and a second wiring, the 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 included in the first circuit is electrically connected to the source or drain of the (m-2)th transistor, one of the source and drain of the first transistor among the n transistors included 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 included 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 the gate of the fourth transistor is electrically connected to the gate of at least one of the n transistors included in the first circuit.

[0015] Alternatively, one embodiment of the present invention is a power storage device including the semiconductor device described above, a comparator, and an eighth transistor. 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 terminal 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. The eighth transistor 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 maintaining the first potential by turning off the eighth transistor. The comparator has a function of outputting an output signal in accordance with a result of comparison between a potential of the positive electrode and a second potential. The oscillator has a function of blocking current between a first wiring and a second wiring in accordance with the output signal.

[0016] Alternatively, one embodiment of the present invention includes an oscillator, a first transistor, and a first circuit. The first transistor has a channel formation region formed of a metal oxide containing indium or zinc. 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 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 capacitor. One of the source and the drain of the third transistor is electrically connected to one of the source and the 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 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 maintaining 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 shaping and amplifying the first signal.

[0017] Furthermore, 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, and the other electrode of the resistor 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, in a 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 a third step, after turning off the first transistor, at least one of the sixth transistor and the seventh transistor is turned off, thereby cutting off the current flowing between the first wiring and the second wiring.

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

[0019] In the above structure, the first circuit preferably includes 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. The first transistor has a channel formation region formed of a metal oxide containing indium or zinc. 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. The first wiring is connected to one of a source and a drain of the second transistor and 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 capacitor; 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 capacitor; The other of the source and drain of the fifth 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, the second circuit is electrically connected to the positive electrode of the secondary battery, and the first step is to apply a first potential to the second circuit, a second step is to hold the first potential, a third step is to output a second signal from the second circuit, a fourth step is to apply a low potential signal to the first wiring from the second circuit, and 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 using the oscillator to apply 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 maintaining the second potential applied to the gate of the second transistor and the gate of the third transistor; and an eighth step of using the first circuit to at least one of shape and amplify the second signal.

[0022] Furthermore, 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, and the other electrode of the resistor 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, thereby cutting off the current flowing between the first wiring and the second wiring.

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

[0024] In the above structure, the first circuit preferably includes 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. [Effects 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. with 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. 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 extracted as appropriate 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 explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a circuit diagram showing an example of the configuration of a semiconductor device. [Figure 2] FIG. 2 is a circuit diagram showing an example of the configuration of a semiconductor device. [Figure 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. [Figure 5] FIG. 5 is a timing chart illustrating an example of the operation of the semiconductor device. [Figure 6] 6A and 6B are circuit diagrams showing examples of the configuration 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 illustrating an example of the operation of the semiconductor device. [Figure 9] FIG. 9 is a cross-sectional view showing an example of the configuration 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, 11B, and 11C are top views, cross-sectional views, and cross-sectional views illustrating examples of the structure of a transistor. [Figure 12] 12A is a top view illustrating an example of the structure of a transistor, FIG. 12B is a cross-sectional view illustrating an example of the structure of a transistor, and FIG. 12C is a cross-sectional view illustrating an example of the structure of a transistor. [Figure 13] 13A is a top view illustrating an example of the structure of a transistor, FIG. 13B is a cross-sectional view illustrating an example of the structure of a transistor, and FIG. 13C is a cross-sectional view illustrating an example of the structure of a transistor. [Figure 14] 14A is a top view illustrating an example of the structure of a transistor, FIG. 14B is a cross-sectional view illustrating an example of the structure of a transistor, and FIG. 14C is a cross-sectional view illustrating an example of the structure of a transistor. [Figure 15] 15A is a top view illustrating an example of the structure of a transistor, FIG. 15B is a cross-sectional view illustrating an example of the structure of a transistor, and FIG. 15C is a cross-sectional view illustrating an example of the structure of a transistor. [Figure 16] 16A is a top view illustrating an example of the structure of a transistor, FIG. 16B is a cross-sectional view illustrating an example of the structure of a transistor, and FIG. 16C is a cross-sectional view illustrating an example of the structure of a transistor. [Figure 17] FIG. 17 is a cross-sectional view showing an example of the configuration of a semiconductor device. [Figure 18] FIG. 18 is a cross-sectional view showing an example of the configuration of a semiconductor device. DETAILED DESCRIPTION OF THE INVENTION

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

[0030] In this specification, the ordinal numbers "first," "second," and "third" are used to avoid confusion between 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 explanations thereof may be omitted.

[0032] Furthermore, 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, some components may be omitted to make the drawings easier to understand.

[0034] Furthermore, the terms "electrode" and "wiring" used in this specification and elsewhere do not limit the functionality of these components. For example, an "electrode" may be used as part of a "wiring," and vice versa. Furthermore, the terms "electrode" and "wiring" also include cases where multiple "electrodes" or "wirings" are integrally formed.

[0035] Furthermore, in this specification etc., the term "terminal" may refer to, for example, a wiring or an electrode connected to a wiring. Furthermore, in this specification etc., 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 being 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 where 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 operating conditions, such as when transistors of different polarities are used or when the direction of current changes during circuit operation, making it difficult to define which is the source and which is the drain. For this reason, the terms source and drain can be used interchangeably in this specification.

[0038] Furthermore, in this specification, "electrically connected" includes both direct connection and connection via "something that has some kind of electrical effect." Here, "something that has some kind of electrical effect" is not particularly limited as long as it allows electrical signals to be transmitted and received between the connected objects. Therefore, even when the expression "electrically connected" is used, in an actual circuit, there may be no physical connection and only wiring may be extended.

[0039] Furthermore, 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. Therefore, it also 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. Therefore, it also 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," or "uniform" are used, they are considered to include an error of plus or minus 20%, unless otherwise specified.

[0041] In addition, in this specification, when etching is performed after forming a resist mask, the resist mask is removed after the etching 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] It should be noted that even when written as "semiconductor," if the conductivity is sufficiently low, it will have the properties of an "insulator." Therefore, it is also possible to use "semiconductor" instead of "insulator." In this case, the boundary between "semiconductor" and "insulator" is vague, and it is difficult to strictly distinguish between the two. Therefore, "semiconductor" and "insulator" described in this specification may be read interchangeably.

[0044] Furthermore, even when written as "semiconductor," if the conductivity is sufficiently high, it will have the properties of a "conductor." Therefore, it is also possible to use "semiconductor" instead of "conductor." In this case, the boundary between "semiconductor" and "conductor" is vague, and it is difficult to strictly distinguish between the two. Therefore, "semiconductor" and "conductor" described in this specification may be read interchangeably.

[0045] In this specification and the like, the "on state" of a transistor refers to a state in which the source and drain of the transistor are considered to be electrically short-circuited (also referred to as a "conductive state"). The "off state" of a transistor refers to a state in which the source and drain of the transistor are considered to be 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 the source and drain of a transistor when the transistor is on, and the term "off-state current" may refer to a current that flows between the source and drain of a transistor when the transistor is off.

[0047] Furthermore, 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. Ground potential can also be used as a high potential signal or a low potential signal. For example, if a high potential signal is ground potential, a low potential signal is lower than ground potential, and if a low potential signal is ground potential, a high potential signal is higher than 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 all of a gate wiring, and a gate wiring refers to a wiring for electrically connecting the gate electrode of at least one transistor to another electrode or another wiring.

[0049] In this specification, the term "source" refers to a source region, a source electrode, and part or all of a source wiring. The term "source region" refers to a region of a semiconductor layer whose resistivity is equal to or less than a certain value. The term "source electrode" refers to a conductive layer connected to the source region. The term "source wiring" refers to wiring that electrically connects the source electrode of at least one transistor to another electrode or wiring.

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

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

[0052] <Example of semiconductor device> 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 capacitive element 51, and terminals OU1 and OU2. The circuit 32 includes a terminal VBI1 electrically connected to the oscillator 30 and the like. The terminal VBI1 has a function of providing a signal Sv1 to the oscillator 30 and the like.

[0054] One of the source and drain of the transistor 42 is electrically connected to one of the source and drain of the transistor 44, one electrode of the capacitor 51, and a node ND1. One of the source and drain of the transistor 43 is electrically connected to one of the source and drain of the transistor 45, the other electrode of the capacitor 51, and a node ND2. The other of the source and 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 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 drain of the transistor 42 and the other of the source and 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 of the transistor 54 and the gate 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 of the transistor 55 and the gate are electrically connected to a wiring VD1.

[0057] Resistors may be used instead of the transistors 54 and 55. Alternatively, a plurality of transistors may be used that are connected in series and have their gates electrically connected to each other.

[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, etc. to the terminal OU1, etc.

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

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

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

[0062] The circuit 31 includes an inverter 53. The circuit 31 may include a buffer circuit instead of the inverter. The circuit 31 preferably has a function of shaping, amplifying, etc. 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] The 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. Therefore, 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. Therefore, more power than necessary does not flow in 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 gate of the transistor 41 is electrically connected to the terminal SH1. 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 back gates of the transistors 42, 43, 44, 45, 54, 55, and 61 are electrically connected to the source or drain of each transistor, and the back gate of the transistor 41 is electrically connected to a wiring VS1.

[0069] In the semiconductor device 21 shown in FIG. 2, the back gates of the transistors 42, 43, 44, 45, 54, 55, and 61 are electrically connected to the source or drain, respectively. However, a desired potential may be applied to the back gates of the transistors and fixed at that potential. 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 over time. Furthermore, the back gate may be electrically connected to a pair of gates 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 the source and 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 drain of the transistor 41 is electrically connected to one terminal of the resistor RL1, one of the source and drain of the transistor 47a, and the gate of the transistor 47a. The gate of the transistor 41 is electrically connected to a terminal SH1. The other terminal of the resistor RL1 is electrically connected to a wiring VD1. The other of the source and drain of the transistor 47a is electrically connected to one of the source and drain of the transistor 46a, and the other of the source and drain of the transistor 46a is electrically connected to a wiring VS1. The gate of the transistor 46a is electrically connected to a terminal EN1.

[0072] A transistor may be used as the resistive element. Alternatively, 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] 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 the circuit shown in FIG. 3A in that a terminal VBI1 is electrically connected to the gate of the transistor 47a, rather than to 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 the source and 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 drain of the transistor 41 is electrically connected to one of the source and drain of the transistor 47b, the gate of the transistor 46b, and one of the source and drain of the transistor 46b. The gate of the transistor 41 is electrically connected to a terminal SH1. The other of the source and drain of the transistor 46b is electrically connected to a wiring VS1. The other of the source and 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 a wiring VD1. The gate of the transistor 47b is electrically connected to a terminal EN1.

[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 differs from the circuit shown in FIG. 3C in that the terminal VBI1 is electrically connected to the gate of the transistor 46b, rather than to one of the source and drain of the transistor 41. Note that although FIGS. 3A, 3B, 3C, and 3D illustrate an example in which the back gate of the transistor 41 is electrically connected to the wiring VS1, the back gate of the transistor 41 may be electrically connected to a terminal that outputs a potential different from that of the wiring VS1. Alternatively, the back gate of the transistor 41 may be electrically connected to one of the source and drain of the transistor 41. Alternatively, the back gate 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 turning on the transistor 41 and applying a suitable potential to the terminal VBI1, the transistor 41 is turned off to put the terminal VBI1 in a floating state and maintain the applied potential, 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 on the transistor 41, 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] Thereafter, 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] An OS transistor is preferably used for at least one of the transistors 46a and 46b. More specifically, for example, by using an OS transistor as the transistor 46a or 46b whose gate is electrically connected to the terminal EN1, leakage current can be significantly reduced when current flowing between the wiring VD1 and the wiring VS1 in the circuit 32 is blocked.

[0081] After applying a potential to the terminal EN1 that turns off the transistor 46a or the transistor 46b, the circuits that provide signals, power supplies, currents, 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] 1, all of the transistors included in the oscillator 30, the circuit 31, and the circuit 32 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 its 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, an oxide semiconductor used in an OS transistor can be formed by a thin film method such as a sputtering method. Therefore, the oxide semiconductor can be easily formed on 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 a 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 the 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, the transistor 61 and the transistor 62 have back gates, and the back gates of the respective transistors are electrically connected to the source or drain of the respective transistors.

[0087] FIG. 4B shows a configuration example of a circuit 31. The circuit 31 shown in FIG. 4B includes a transistor 64, a transistor 65, and a capacitor 66 in addition to the configuration of the circuit 31 shown 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 a 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 gates of the transistors 62 and 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 back gate. The back gate of the transistor 64 is electrically connected to, for example, a wiring VS1. The back gate 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] 4C includes a transistor 63a. One of the source and the drain of the transistor 63a is electrically connected to the gate of the transistor 63a and the wiring VD1, and the other is electrically connected to the other of the source and the 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 of the transistor 63a and the gate, the other of the source and drain of the transistor 63a is electrically connected to one of the source and drain of the transistor 63b and the gate, 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 include n transistors (n is an integer greater than or equal to 2). 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). The other of the source and drain of each transistor is electrically connected to one of the source and drain and the gate of the 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 have back gates, and each back gate 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 threshold voltages of transistors 54, 55, 44, and 45 are set to potential Vt. The threshold voltages of these transistors may vary from transistor to transistor, but for simplicity, it is assumed here that the threshold voltages 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 the case where, at time t0, transistor 44 is on and transistor 45 is off.

[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 designated as potential V0. The potential V0 is lower than the potential (VD1-Vt) by at least the threshold value of the transistor 44, for example, 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, the potential (Vgs) of the gate with respect to the source of the transistor 44 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 by the threshold value of the transistor 54, i.e., to a potential (VD1-Vt). The potential of the node ND1 also rises together with the potential of the node ND3. Thereafter, due to leakage from the capacitor 51, the potential of the node ND1 gradually decreases over time.

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

[0104] The potential of node ND4 is potential VD1-Vt between time t0 and time t1, 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 capacitive 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 an example of the configuration 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] 1, 2, 6A, etc., the output section may have two stacked circuits 31. Fig. 6B shows an example of a configuration in which the output section has two stacked circuits 31 in Fig. 6A.

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

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

[0109] In FIG. 7A, the circuit 63x is arranged between the wiring VD1 and one of the source and drain of the transistor 72 and is electrically connected to the wiring VD1. The circuit 63y is arranged between the wiring VD1 and one of the source and drain of the transistor 73 and is electrically connected to the wiring VD1. 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 back gate of the transistor 72, the other of the source and drain of the transistor 72, the back gate of the transistor 73, and the other of the source and drain of the transistor 73 are electrically connected to the one of the source and drain of the transistor 71. The other of the source and drain and the back gate 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 includes a transistor 74, a transistor 75, a transistor 76, and a transistor 77 in addition to the components shown in FIG.

[0112] 7A, one of the source and the drain of the transistor 73 is electrically connected to the terminal IN2, but in FIG. 7B, it 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 back gate 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 back gate 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 the desired frequency generated by the oscillator 30, thereby obtaining 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 capacitor 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 the 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 to be compared 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 to be compared may be applied to the inverting input terminal.

[0119] The reference potential applied to the comparator 56 is applied 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 applied from a terminal SH2 to the gate of the transistor 48 to turn on the transistor 48 and apply a suitable potential to the inverting input terminal of the comparator 56. After that, a low-potential signal is applied from the terminal SH2 to the gate of the transistor 48 to turn off the transistor 48, thereby setting it in a floating state and maintaining the applied potential, thereby programming a potential to the inverting input terminal of the comparator 56.

[0120] An output terminal (referred to as a terminal OU4) of the comparator 56 is electrically connected to the gate of the transistor 49. One of the source and drain of the transistor 49 (referred to as 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 whether each circuit is electrically connected to the wiring VS1 or not. 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, oscillator 30, and circuit 31 is defined as 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 applied from the comparator 56 to the gate of the transistor 49, turning the transistor 49 on.

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

[0125] At time t13, a signal is applied to terminal EN1, turning on transistor 46a or transistor 47a in circuit 32. Also, a signal is applied to terminal SH1, turning on transistor 41, and applying potential VBI1 from terminal VBI1 to oscillator 30, causing a signal of the desired frequency to be output from 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 maintained 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 to a floating state.

[0129] The secondary battery can be protected or controlled by, for example, stopping charging or changing 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 high safety.

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

[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 falls below the reference potential, a high voltage signal is output from the comparator.

[0132] A semiconductor device of one embodiment of the present invention may include, for example, a circuit having a function of controlling a battery. A power storage device can be configured by including a circuit having a function of controlling a battery in a 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 from a terminal OU3 is supplied to the control circuit 38. The control circuit 38 may also generate signals from terminals SH1, EN1, VT1, SH2, and the like and supply them to the respective circuits. Alternatively, a control signal may be supplied to a circuit that generates these signals.

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

[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 accordance with the detection results of these sensors, for example.

[0136] (Embodiment 2) In this embodiment, a structural example of an OS transistor that can be used in the semiconductor device described in the above embodiment will be described. Note that the OS transistor is a thin film transistor and can be provided in a stacked structure. Therefore, in this embodiment, a structural 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] <Configuration example of semiconductor device> 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, and 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 transistors 300 and 500.

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

[0141] 10C , the upper surface and the side surfaces 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 way, the effective channel width is increased, thereby improving the on-state characteristics of the transistor 300. Furthermore, the contribution of the electric field of the gate electrode can be increased, thereby improving the off-state 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 that serves as the source region or 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 also be used. Alternatively, the transistor 300 may be a HEMT (High Electron Mobility Transistor) by using GaAs and GaAlAs, or the like.

[0144] The low resistance region 314a and the low resistance region 314b contain, in addition to the semiconductor material applied to the 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, metal material, alloy material, or metal oxide 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.

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

[0147] Note that the transistor 300 shown in FIG. 9 is just an example, and the structure is not limited to this, and 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] The insulators 320, 322, 324, and 326 can be made of, for example, silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, aluminum oxynitride, aluminum nitride oxide, aluminum nitride, or the like.

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

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

[0153] The amount of desorbed hydrogen can be analyzed using, for example, thermal desorption spectroscopy (TDS analysis). For example, the amount of desorbed 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 TDS analysis. 15 atoms / cm 2 Less than or equal to 5 x 10 15 atoms / cm 2 The following is fine.

[0154] It is preferable that the insulator 326 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. Furthermore, 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 that occurs 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 denoted by the same reference numeral. In this specification and the like, a wiring and a plug connected to the wiring may be integral. That is, a portion of a conductor may function as a wiring, and a portion of a conductor may function as a plug.

[0156] The materials for each plug and wiring (such as the conductor 328 and the conductor 330) can be a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material, and can be used in a single layer or a laminated layer. High-melting-point materials such as tungsten and molybdenum, which have both heat resistance and conductivity, are preferably used, and tungsten is preferred. Alternatively, they are preferably formed from a low-resistance conductive material such as aluminum or copper. The use of a low-resistance conductive material can 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 formed using a material similar to that of the conductor 328 and the conductor 330.

[0158] Note that, for example, the insulator 350 preferably uses 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 is preferably used as the conductor having a barrier property against hydrogen. Stacking tantalum nitride and highly conductive tungsten can 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 over 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 the same material as the conductors 328 and 330.

[0161] Note that, for example, the insulator 360 preferably uses 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 formed using the same material as the conductors 328 and 330.

[0163] Note that, for example, the insulator 370 preferably uses 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 formed using a material similar to that of the conductor 328 and the conductor 330.

[0165] Note that, for example, the insulator 380 preferably uses 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] Although the above describes 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, the semiconductor device according to 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 and hydrogen.

[0168] For example, the insulator 510 and the insulator 514 are preferably films having barrier properties that prevent hydrogen and 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] An example of a film having a barrier property against hydrogen is silicon nitride formed by a CVD method. Here, hydrogen diffusion into a semiconductor element having an oxide semiconductor, such as the transistor 500, may degrade the characteristics of the semiconductor element. Therefore, it is preferable to use a film that suppresses hydrogen diffusion between the transistor 500 and the transistor 300. Specifically, the film that suppresses hydrogen diffusion is a film that releases a small amount of hydrogen.

[0170] As a film having a barrier property against hydrogen, for example, the insulators 510 and 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 against both oxygen and impurities such as hydrogen and moisture, which can 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. Furthermore, 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. Using a material with a relatively low dielectric constant as an interlayer film can reduce parasitic capacitance between wirings. 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 insulators 510, 512, 514, and 516. The conductor 518 functions as a plug or wiring connected to the capacitor 600 or the transistor 300. The conductor 518 can be formed using a material similar to that of the conductor 328 and the conductor 330.

[0174] In particular, the conductor 518 in the region in contact with the insulator 510 and the insulator 514 is preferably a conductor having a barrier property against oxygen, hydrogen, and water. With this structure, the transistor 300 and the transistor 500 can be separated by a layer having a barrier property 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 the transistor 500 .

[0176] Figure 9 shows an example in which the conductor 610 of the capacitor 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. However, another OS transistor may be provided in the same layer as the transistor 500, and the conductor 610 may be connected 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, the transistor 500 includes a conductor 503 disposed so as to be embedded in an insulator 514 and 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 disposed apart from each other on the oxide 530b, and 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, insulator 580, and insulator 550.

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

[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] Although the transistor 500 has a three-layer structure of oxides 530a, 530b, and 530c in and around the channel formation region, the present invention is not limited to this structure. For example, the transistor may have a single layer of oxide 530b, a two-layer structure of oxides 530b and 530a, a two-layer structure of oxides 530b and 530c, or a stacked structure of four or more layers. Although the transistor 500 has a two-layer structure, the present invention is not limited to this structure. For example, the conductor 560 may have a single-layer structure or a stacked structure of three or more layers. The transistor 500 shown in FIGS. 9, 10A, and 10B is merely an example, and the transistor may have any structure suitable for the circuit configuration and driving method.

[0181] Here, the conductor 560 functions as the gate electrode of the transistor, and the conductors 542a and 542b function as the source and drain electrodes, 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 positioned between the source and drain electrodes in a self-aligned manner. Therefore, the conductor 560 can be formed without providing a margin for alignment, thereby reducing the area occupied by the transistor 500. This allows for miniaturization and high integration of semiconductor devices.

[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 that overlaps with the conductor 542a or the conductor 542b. This reduces the parasitic capacitance formed between the conductor 560 and the conductor 542a and between the conductor 560 and the conductor 542b. This improves the switching speed of the transistor 500 and enables it to have 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, applying a negative potential to the conductor 503 can increase the Vth of the transistor 500 above 0 V and reduce the off-state current. 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 to the conductor 503.

[0184] The conductor 503 is arranged to overlap the oxide 530 and the conductor 560. In this way, when a potential is applied to the conductor 560 and the conductor 503, the electric field generated from the conductor 560 and the electric field generated from the conductor 503 are connected, and the 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] Furthermore, in this specification, the S-channel structure is characterized in that the side surfaces and peripheries of the oxide 530 in contact with the conductors 542a and 542b, which function as source and drain electrodes, are I-type, just like the channel formation region. Furthermore, the side surfaces and peripheries of the oxide 530 in contact with the conductors 542a and 542b are in contact with the insulator 544, so they can be I-type, just like the channel formation region. Note that in this specification, I-type can be treated as the same as high-purity intrinsic oxide, as described later. The S-channel structure disclosed in this specification differs from the fin structure and planar structure. The S-channel structure enhances resistance to the short-channel effect, in other words, makes it possible to create a transistor that is less susceptible to the short-channel effect.

[0186] Conductor 503 has the same configuration as conductor 518, with conductor 503a being formed in contact with the inner walls of the openings of insulators 514 and 516, and conductor 503b being 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 a portion of oxygen is released by heating as an insulator having an excess oxygen region. The oxide material from which oxygen is released by heating is an oxide material from which the amount of released oxygen converted to oxygen atoms is 1.0 × 10 in TDS (Thermal Desorption Spectroscopy) analysis. 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 or more, or 3.0 x 10 20 atoms / cm 3 The oxide film is one having the above properties. The surface temperature of the film during the TDS analysis is preferably in the range of 100°C or higher and 700°C or lower, or 100°C or higher and 400°C or lower.

[0190] When the insulator 524 has an excess oxygen region, the insulator 522 preferably has a function of suppressing the diffusion of oxygen (for example, oxygen atoms, oxygen molecules, etc.) (preferably making the oxygen less permeable).

[0191] The insulator 522 preferably has a function of suppressing diffusion of oxygen and impurities, which prevents oxygen contained in the oxide 530 from diffusing toward the insulator 520. Furthermore, reaction of the conductor 503 with oxygen contained in the insulator 524 or the oxide 530 can be suppressed.

[0192] The insulator 522 is preferably a single-layer or multi-layer 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, thinner gate insulating films can cause problems such as leakage current. Using a high-k material for the insulator that functions as the gate insulating film makes it possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0193] In particular, an insulator containing an oxide of one or both of aluminum and hafnium, which is an insulating material that has the function of suppressing the diffusion of impurities and oxygen (i.e., is difficult for oxygen to permeate), is preferably used. Aluminum oxide, hafnium oxide, or an oxide containing aluminum and hafnium (hafnium aluminate) is preferably used as the insulator containing an oxide of one or both of aluminum and hafnium. When the insulator 522 is formed using such a material, the insulator 522 functions as a layer that suppresses oxygen release 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] Furthermore, it is preferable that the insulator 520 be thermally stable. For example, silicon oxide and silicon oxynitride are suitable because they are thermally stable. Furthermore, by combining a high-k insulator with silicon oxide or silicon oxynitride, it is possible to obtain the insulator 520 having a thermally stable layered structure with a high dielectric constant.

[0196] The insulators 520, 522, and 524 may each have a stacked structure of two or more layers. In this case, the stacked structures are not limited to those made of the same material, and may be those made of different materials.

[0197] In the transistor 500, a metal oxide functioning as an oxide semiconductor is preferably used 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, an In-Ga oxide or an In-Zn oxide may be used for the oxide 530.

[0198] Furthermore, it is preferable to use a metal oxide with a low carrier concentration for the transistor 500. To lower the carrier concentration of a metal oxide, the impurity concentration in the metal oxide should be lowered to lower the density of defect states. In this specification and the like, a low impurity concentration and a low density of defect states are referred to as high-purity intrinsic or substantially high-purity intrinsic. Examples of impurities in metal oxides include hydrogen, nitrogen, alkali metals, alkaline earth metals, iron, nickel, and silicon.

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

[0200] Defects in which hydrogen has entered oxygen vacancies can function as donors in metal oxides. However, it is difficult to quantitatively evaluate such defects. Therefore, metal oxides are sometimes evaluated using carrier concentration rather than donor concentration. Therefore, in this specification and the like, the carrier concentration assuming a state in which no electric field is applied may be used as a parameter of metal oxides, rather than donor concentration. In other words, the "carrier concentration" described in this specification and the like may sometimes be rephrased as "donor concentration."

[0201] Therefore, when a metal oxide is used for the oxide 530, it is preferable that the 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 set to 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] 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 Preferably, it is 1×10 or less. 17 cm -3 More preferably, it is less than 1×10 16 cm -3 More preferably, it is less than 1×10 13 cm -3 More preferably, it is less than 1×10 12 cm -3 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 diffuses into the conductor 542 (conductor 542a and conductor 542b), which may form a heterogeneous layer between the conductor 542a and the oxide 530b and between the conductor 542b and the oxide 530b. Since the heterogeneous layer contains more oxygen than the conductor 542, it is presumed that the heterogeneous layer has insulating properties. In this case, the three-layer structure of the conductor 542, the heterogeneous layer, and the oxide 530b can be regarded as a three-layer structure consisting of a metal, an insulator, and a semiconductor, and may be called a metal-insulator-semiconductor (MIS) structure or a diode junction structure mainly based on the MIS structure.

[0205] It should be noted that the above-mentioned different layer is not limited to being formed between the conductor 542 and the oxide 530b, and 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. 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, which can prevent impurities from diffusing from structures formed below the oxide 530a to the oxide 530b. Also, the oxide 530 has the oxide 530c on the oxide 530b, which can prevent impurities from diffusing from structures formed above the oxide 530c to the oxide 530b.

[0208] The oxide 530 preferably has a stacked structure of multiple oxide layers with different atomic ratios of the metal atoms. Specifically, the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530a is preferably greater than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. The atomic ratio of the element M to In in the metal oxide used for the oxide 530a is preferably greater than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. The atomic ratio of In to M in the metal oxide used for the oxide 530b is preferably greater than the atomic ratio of In to M in the metal oxide used for the oxide 530a. The oxide 530c can be the same metal oxide as that used for the oxide 530a or the oxide 530b.

[0209] The oxides 530a and 530c preferably have a conduction band minimum energy higher than that of the oxide 530b, and the oxides 530a and 530c preferably have a lower electron affinity than that of the oxide 530b.

[0210] Here, the energy level of the conduction band minimum changes smoothly at the junction between the oxides 530a, 530b, and 530c. In other words, the energy level of the conduction band minimum at the junction between the oxides 530a, 530b, and 530c changes continuously or forms a continuous junction. To achieve this, it is preferable to reduce the defect level density of the mixed layers formed at the interface between the oxides 530a and 530b and at the interface between the oxides 530b and 530c.

[0211] Specifically, when the oxides 530a and 530b, and the oxides 530b and 530c, contain a common element other than oxygen as a main component, 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] In this case, the oxide 530b serves as the main carrier path. 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. This reduces the effect of interface scattering on carrier conduction, allowing the transistor 500 to obtain a high on-state current.

[0213] Conductor 542 (conductor 542a and conductor 542b) functioning as a source electrode and a drain electrode are provided on oxide 530b. Conductor 542 is preferably made of a metal element selected from aluminum, chromium, copper, silver, gold, platinum, tantalum, nickel, titanium, molybdenum, tungsten, hafnium, vanadium, niobium, manganese, magnesium, zirconium, beryllium, indium, ruthenium, iridium, strontium, or lanthanum, or an alloy containing any of the above metal elements or an alloy combining any of the above metal elements. For example, tantalum nitride, titanium nitride, tungsten, a nitride containing titanium and aluminum, a nitride containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide containing strontium and ruthenium, or an oxide containing lanthanum and nickel is preferably used. In addition, tantalum nitride, titanium nitride, nitrides containing titanium and aluminum, nitrides containing tantalum and aluminum, ruthenium oxide, ruthenium nitride, oxides containing strontium and ruthenium, and oxides containing lanthanum and nickel are preferred because they are conductive materials that are resistant to oxidation or materials that maintain 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 and near the interface between the oxide 530 and the conductor 542. In this case, the region 543a functions as one of a source region and a 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 the 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 the metal contained in the conductor 542 and components 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, or the like.

[0218] In particular, it is preferable to use, as the insulator 544, an insulator containing an oxide of either or both of aluminum and hafnium, such as aluminum oxide, hafnium oxide, or hafnium aluminate. Hafnium aluminate is particularly preferable because it has higher heat resistance than hafnium oxide film. Therefore, it is less likely to crystallize during heat treatment in a later process. Note that if the conductor 542 is made of a material that is resistant to oxidation or does not significantly decrease in conductivity even when it absorbs oxygen, the insulator 544 is not an essential component. It can 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 TDS analysis, the amount of released oxygen converted into oxygen atoms is 1.0×10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 or more, or 3.0 x 10 20 atoms / cm 3 The oxide film is as described above. The surface temperature of the film during the TDS analysis is preferably in the range of 100°C or higher and 700°C or lower.

[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 the insulator 550, which releases oxygen upon heating, 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 insulator 550 preferably has a low concentration of impurities such as water or hydrogen. The thickness of the insulator 550 is preferably 1 nm to 20 nm.

[0222] Furthermore, a metal oxide may be provided between the insulator 550 and the conductor 560 to efficiently supply excess oxygen contained in the insulator 550 to the oxide 530. 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. In other words, a decrease in the amount of excess oxygen supplied to the oxide 530 can be suppressed. Furthermore, oxidation of the conductor 560 due to excess oxygen can be suppressed. As the metal oxide, a material that can be used for the insulator 544 may be used.

[0223] The conductor 560 functioning as the first gate electrode is shown as a two-layer structure in FIGS. 10A and 10B, but may be a single-layer structure or a stacked structure of three or more layers.

[0224] Conductor 560a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (NO, NO, NO, etc.), and copper atoms. Alternatively, conductive material that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) is preferably used. Conductor 560a has the function of suppressing the diffusion of oxygen, which can suppress the oxidation of conductor 560b due to oxygen contained in insulator 550, thereby preventing a decrease in conductivity. As a conductive material that has the 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. Because the conductor 560b also functions as wiring, it is preferable to use a conductor with high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. The conductor 560b may have a layered structure, such as a layered structure of titanium or titanium nitride and the above-mentioned conductive material.

[0226] The insulator 580 is provided on the conductor 542 with the insulator 544 interposed therebetween. The insulator 580 preferably has an excess oxygen region. For example, the insulator 580 preferably includes silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, silicon oxide doped with fluorine, silicon oxide doped with carbon, silicon oxide doped with carbon and nitrogen, silicon oxide having voids, or a resin. Silicon oxide and silicon oxynitride are particularly preferred because they are thermally stable. Silicon oxide and silicon oxide having voids are particularly preferred because they allow for easy formation of an excess oxygen region in a later step.

[0227] The insulator 580 preferably has an excess oxygen region. By providing the insulator 580, from which oxygen is released by heating, 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 the insulator 580 is formed to overlap the region between the conductor 542a and the conductor 542b, so that the conductor 560 is formed to be embedded in the opening of the insulator 580 and the region sandwiched between the conductor 542a and the conductor 542b.

[0229] When miniaturizing semiconductor devices, 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 to achieve this, 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. Therefore, 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 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 when it is a thin film with a thickness of 0.5 nm to 3.0 nm. Therefore, aluminum oxide formed by sputtering can function as both an oxygen source and a barrier film against impurities such as hydrogen.

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

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

[0236] In particular, aluminum oxide has a high blocking effect against both oxygen and impurities such as hydrogen and moisture, which can 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. Furthermore, 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. Using a material with a relatively low dielectric constant as an interlayer film can reduce parasitic capacitance between wirings. For example, a silicon oxide film, a silicon oxynitride film, or the like can be used as the insulator 586.

[0238] Furthermore, 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 that connects 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] Subsequently, 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 other drawings show an example in which the insulator 630 is used as the dielectric of the capacitor, but other insulators may be used as the dielectric of the capacitor. Also, other conductors may be used as the 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 any of the above elements (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 silicon oxide added can also be used.

[0245] 9, the conductor 612 and the conductor 610 are shown as single-layer structures, but are not limited to this configuration and may be a stacked structure of two or more layers. For example, a conductor having barrier properties and a conductor having high adhesion to the conductor having high conductivity may be formed between a conductor having barrier properties 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 tungsten is particularly preferable. Furthermore, 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) can 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 using a transistor including an oxide semiconductor, fluctuations 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 using a transistor including 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. Structural examples that can be used for the transistor 500 are described below.

[0250] <Transistor structure example 1> An example structure of a transistor 510A will be described using Figures 11A, 11B, and 11C. Figure 11A is a top view of the transistor 510A. Figure 11B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 11A. Figure 11C is a cross-sectional view of the portion indicated by the dashed-dotted 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) that has 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] The interlayer film can be a single layer or a stack of insulators such as silicon oxide, silicon oxynitride, silicon nitride oxide, aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide, PZT, SrTiO3, or (Ba,Sr)TiO3 (BST). Alternatively, these insulators may contain, for example, aluminum oxide, bismuth oxide, germanium oxide, niobium oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium oxide, or zirconium oxide. Alternatively, these insulators may be nitrided. Silicon oxide, silicon oxynitride, or silicon nitride may be stacked on the above insulators.

[0256] For example, the insulator 511 preferably functions as a barrier film that prevents 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 preventing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (i.e., the impurities are less likely to permeate through the insulator). Alternatively, the insulator 511 is preferably made of an insulating material that has a function of preventing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate through the insulator). Furthermore, for example, aluminum oxide or silicon nitride may be used as the insulator 511. This structure can prevent impurities such as hydrogen and water from diffusing from the substrate side toward the transistor 510A 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 occurring 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 having a single layer structure, the present invention is not limited to this. For example, the conductor 503 may have a multilayer film structure of 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, applying a negative potential to the conductor 505 can increase the threshold voltage of the transistor 510A above 0 V, thereby reducing the off-state current. Therefore, applying a negative potential to the conductor 505 can reduce the drain current when the potential applied to the conductor 560 is 0 V, compared to 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, which means that the transistor has an S-channel structure, similar to the transistor 500 described above.

[0262] The insulators 514 and 516 function as interlayer films, similar to the insulator 511 or 512. For example, the insulator 514 preferably functions as a barrier film that prevents impurities such as water or hydrogen from entering the transistor 510A from the substrate side. This structure can prevent impurities such as hydrogen or water from diffusing from the substrate side toward the transistor 510A through the insulator 514. Furthermore, for example, the insulator 516 preferably has a lower dielectric constant than the insulator 514. Using a material with a low dielectric constant as an interlayer film can reduce parasitic capacitance between wirings.

[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 has 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 structure or a stacked structure of three or more layers.

[0264] Here, the conductor 505a is preferably made of a conductive material that has the function of suppressing the diffusion of impurities such as hydrogen atoms, hydrogen molecules, water molecules, and copper atoms (i.e., the impurities are less likely to permeate through it). Alternatively, it is preferably made of a conductive material that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms, oxygen molecules, etc.) (i.e., the oxygen is less likely to permeate through it). 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 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 its conductivity from decreasing.

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

[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 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, thinner gate insulating films can cause problems such as leakage current. Using a high-k material for the insulator that functions as the gate insulating film makes it possible to reduce the gate potential during transistor operation while maintaining the physical film thickness.

[0270] Furthermore, it is preferable that the insulator 521 be thermally stable. For example, silicon oxide and silicon oxynitride are suitable because they are thermally stable. Furthermore, by combining a high-k insulator with silicon oxide or silicon oxynitride, it is possible to obtain the insulator 521 having a thermally stable layered structure with a high dielectric constant.

[0271] 11 shows a three-layer stacked structure as the second gate insulating film, it may be a single layer or a stacked structure of two or more layers. In this 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. Having the oxide 530a below the oxide 530b can suppress impurity diffusion from structures formed below the oxide 530a to the oxide 530b. Having the oxide 530c on the oxide 530b can suppress impurity diffusion from structures formed above the oxide 530c to the oxide 530b. The oxide 530 can be made of an oxide semiconductor, which is one of the above-described metal oxides.

[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, it can prevent impurities from the insulator 580 from diffusing into the oxide 530.

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

[0275] The conductors 542a and 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 any of these as its main component. In particular, a metal nitride film such as tantalum nitride is preferable because it has barrier properties against hydrogen or oxygen and is highly resistant to oxidation.

[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. Alternatively, a titanium film and an aluminum film may be laminated. Alternatively, 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] Other examples include a three-layer structure in which a titanium film or titanium nitride film is laminated on the titanium film or titanium nitride film, an aluminum film or copper film is laminated on the titanium film or titanium nitride film, and a titanium film or titanium nitride film is further formed thereon, and a three-layer structure in which a molybdenum film or molybdenum nitride film is laminated on the molybdenum film or molybdenum nitride film, an aluminum film or copper film is laminated on the molybdenum film or molybdenum nitride film, and a molybdenum film or molybdenum nitride film is further formed thereon. 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 that has 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] The barrier layer can be made of, for example, a metal oxide. In particular, it is preferable to use an insulating film that has barrier properties against oxygen and hydrogen, such as aluminum oxide, hafnium oxide, or gallium oxide. Silicon nitride formed by CVD may also be used.

[0280] The presence of the barrier layer can broaden the range of material options for the conductor 542. For example, materials with low oxidation resistance but high conductivity, such as tungsten or aluminum, can be used for the conductor 542. Also, 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 the opening in the insulator 580 with the oxide 530c and the insulator 574 interposed therebetween.

[0282] As transistors become more miniaturized and highly integrated, thinning of the gate insulating film can cause problems such as leakage current. In this case, the insulator 550 may have a stacked structure, similar to the second gate insulating film. By using a stacked structure of a high-k material and a thermally stable material for the insulator functioning as the gate insulating film, it is possible to reduce the gate potential during transistor operation while maintaining the physical film thickness. Furthermore, a stacked structure that is thermally stable and has a high dielectric constant can be achieved.

[0283] The conductor 560 functioning as the first gate electrode includes 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 that has the function of suppressing the 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 that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms and oxygen molecules).

[0284] The conductor 560a has the 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, preventing a decrease in conductivity.

[0285] As a conductive material capable of suppressing oxygen diffusion, for example, tantalum, tantalum nitride, ruthenium, or ruthenium oxide is preferably used. Furthermore, an oxide semiconductor that can be used as the oxide 530 can be used as the conductor 560a. In this case, by forming the conductor 560b by a sputtering method, the electrical resistance of the conductor 560a can be reduced, making it 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. Furthermore, since the conductor 560 functions as wiring, it is preferable to use a conductor with high conductivity. For example, a conductive material containing tungsten, copper, or aluminum as a main component can be used. Furthermore, the conductor 560b may have a layered structure, for example, a layered structure of titanium or titanium nitride and the above-mentioned conductive material.

[0287] An insulator 574 is disposed between the insulator 580 and the transistor 510A. The insulator 574 is preferably 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 is preferably used. Other examples of the insulator include metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and tantalum oxide, silicon nitride oxide, and silicon nitride.

[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] Insulators 580, 582, and 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 interconnects such as conductor 546 embedded in insulator 580, insulator 582, and insulator 584.

[0293] Similarly to the conductor 505, the conductor 546 can be made of a conductive material such as a metal material, an alloy material, a metal nitride material, or a metal oxide material, either in a single layer or a stacked layer. For example, it is preferable to use a high-melting-point material such as tungsten or molybdenum, which 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. The use of a low-resistance conductive material can reduce wiring resistance.

[0294] For example, by using a layered structure of tantalum nitride, a conductor that has 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 fluctuations in electrical characteristics are suppressed, which has stable electrical characteristics and improved reliability can be provided.

[0296] <Transistor structure example 2> An example structure of a transistor 510B will be described using Figures 12A, 12B, and 12C. Figure 12A is a top view of the transistor 510B. Figure 12B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 12A. Figure 12C is a cross-sectional view of the portion indicated by the 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, and therefore, to avoid repetition of explanation, the differences from the transistor 510A will be mainly described.

[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 and high controllability can be provided.

[0299] The conductor 560 functioning as the first gate electrode includes 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 that has the function of suppressing the 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 that has the function of suppressing the diffusion of oxygen (e.g., at least one of oxygen atoms and oxygen molecules).

[0300] The conductor 560a has the 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, preventing a decrease in conductivity.

[0301] Furthermore, it is preferable to provide an insulator 574 so as to cover the top surface and side surfaces of the conductor 560, the side surfaces of the insulator 550, and the side surfaces of the oxide 530c. Note that the insulator 574 is preferably made of an insulating material that has 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. Other examples that can be used include metal oxides such as magnesium oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, and tantalum oxide, silicon nitride oxide, and silicon nitride.

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

[0303] Furthermore, an insulator 576 (insulators 576a and 576b) having barrier properties may be disposed between the conductor 546 and the insulator 580. By providing the insulator 576, it is possible to prevent oxygen in the insulator 580 from reacting with the conductor 546 and oxidizing the conductor 546.

[0304] Furthermore, by providing the insulator 576 with barrier properties, the range of materials that can be used for the plugs and wirings can be expanded. For example, by using a metal material that has oxygen absorption properties and 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. Furthermore, for example, a conductor that is easy to form or process can be used.

[0305] <Transistor structure example 3> An example structure of a transistor 510C will be described using Figures 13A, 13B, and 13C. Figure 13A is a top view of the transistor 510C. Figure 13B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 13A. Figure 13C is a cross-sectional view of the portion indicated by the dashed-dotted 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, and therefore, to avoid repetition of explanation, the differences from the transistor 510A will be mainly described.

[0307] 13, a conductor 547a is disposed between the conductor 542a and the oxide 530b, and a conductor 547b is disposed between the conductor 542b and the oxide 530b. The conductor 542a (conductor 542b) extends beyond the top surface of the conductor 547a (conductor 547b) and the side surface on the conductor 560 side, and has a region in contact with the top surface of the oxide 530b. The conductor 547 may be any conductor that can be used for the conductor 542. Furthermore, the 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 in the transistor 510A. Alternatively, the ends of the conductors 542a and 542b can overlap with the conductor 560. This shortens the effective channel length of the transistor 510C, thereby improving the on-state current and frequency characteristics.

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

[0310] 13 may have a structure in which an insulator 545 is provided on and in contact with the insulator 544. The insulator 544 preferably functions as a barrier insulating film that prevents 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, for example, a nitride insulator such as aluminum nitride, aluminum titanium nitride, titanium nitride, silicon nitride, or silicon nitride oxide.

[0311] Unlike the transistor 510A shown in FIG. 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 CMP or the like until the top surface of the conductor 505 is exposed. Here, it is preferable to improve the flatness of the top surface of the conductor 505. For example, the average surface roughness (Ra) of the top 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 improves the flatness of the insulating layer formed on the conductor 505 and improves the crystallinity of the oxide 530b and the oxide 530c.

[0312] <Transistor structure example 4> An example structure of a transistor 510D will be described using Figures 14A, 14B, and 14C. Figure 14A is a top view of the transistor 510D. Figure 14B is a cross-sectional view of the portion indicated by the dashed-dotted line L1-L2 in Figure 14A. Figure 14C is a cross-sectional view of the portion indicated by the dashed-dotted 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, to avoid repetition of the description, the differences from the transistor described above will be mainly described.

[0314] 14A to 14C, the conductor 503 is not provided, and the conductor 505, which functions as the second gate, also functions as a wiring. Furthermore, an insulator 550 is provided over the oxide 530c, and a metal oxide 552 is provided over the insulator 550. Furthermore, a conductor 560 is provided over the metal oxide 552, and an insulator 570 is provided over the conductor 560. Furthermore, 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 into the conductor 560 is suppressed. That is, a decrease in the amount of oxygen supplied to the oxide 530 can be suppressed. Furthermore, oxidation of the conductor 560 by oxygen can be suppressed.

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

[0317] The metal oxide 552 may also function as 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, which is a high-k material with a high dielectric constant, for the metal oxide 552. This layered structure can be thermally stable and have a high dielectric constant. Therefore, it is possible to reduce the gate potential applied during transistor operation while maintaining the physical film thickness. Furthermore, 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 the gate electrode and a metal oxide functioning as part of the 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 adjusted as needed.

[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 an insulating layer containing oxides of either or both aluminum and hafnium, such as aluminum oxide, hafnium oxide, or hafnium aluminate. Hafnium aluminate is particularly preferable because it has higher heat resistance than hafnium oxide and is therefore less likely to crystallize during heat treatment in a later step. Note that the metal oxide 552 is not an essential component. It can be designed appropriately depending on the desired transistor characteristics.

[0322] The insulator 570 is preferably made of an insulating material that has the function of suppressing the permeation of impurities such as water or hydrogen, and oxygen. For example, aluminum oxide or hafnium oxide is preferably used. This can suppress oxidation of the conductor 560 by oxygen from above the insulator 570. Furthermore, impurities such as water or hydrogen from above the insulator 570 can be prevented 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 perpendicular, specifically, the angle between the side surface of the conductor 560 and the surface of the substrate can be 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 necessary.

[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 one of regions 531a or 531b functioning as the source region and the other as the drain region.

[0327] The regions 531a and 531b can be formed by introducing impurity elements such as phosphorus or boron into the exposed surface of the oxide 530b by, for example, ion implantation, ion doping, plasma immersion ion implantation, or plasma treatment. Note that in this embodiment and other examples, the term "impurity elements" refers to elements other than the main component elements.

[0328] Alternatively, a metal film can be formed after exposing a portion of the surface of oxide 530b, followed by heat treatment to diffuse elements contained in the metal film into oxide 530b, thereby forming 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 an "impurity region" or a "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, reducing parasitic capacitance. Furthermore, no offset region is 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 achieve an increase in on-current, a reduction in threshold voltage, an improvement in operating frequency, and the like.

[0331] To further reduce the off-state current, an offset region may be provided between the channel formation region and the source / drain region. The offset region is a region with high electrical resistivity, into which the impurity element described above is not introduced. The offset region can be formed by introducing the impurity element described above after forming the insulator 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 maintained high.

[0332] The transistor 510D also includes 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 vacancies, or a resin is preferable. In particular, using silicon oxide, silicon oxynitride, silicon nitride oxide, or silicon oxide having vacancies for the insulator 575 is preferable because it allows for easy formation of an excess oxygen region in the insulator 575 in a later step. Silicon oxide and silicon oxynitride are also preferable because they are thermally stable. The insulator 575 preferably has a function of diffusing oxygen.

[0333] The transistor 510D also includes an insulator 574 over the insulator 575 and the oxide 530. The insulator 574 is preferably formed by a sputtering method. By using a sputtering method, an insulator with few impurities such as water or hydrogen can be formed. 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 the 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 FIGS. 15A to 15C. FIG. 15A is a top view of the transistor 510E. FIG. 15B is a cross-sectional view of a portion indicated by dashed dotted line L1-L2 in FIG. 15A. FIG. 15C is a cross-sectional view of a portion indicated by dashed dotted line W1-W2 in FIG. 15A. Note that in the top view of FIG. 15A, some elements are omitted for clarity.

[0336] The transistor 510E is a modified example of the transistor described above, and therefore, to avoid repetition of the description, the differences from the transistor described above will be mainly described.

[0337] 15A to 15C, the conductor 542 is not provided, and the exposed oxide 530b has regions 531a and 531b on a portion of its surface. One of the regions 531a and 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, the region 531 (region 531a and region 531b) is a region in which the following elements are added to the oxide 530b: The region 531 can be formed by using a dummy gate, for example.

[0339] Specifically, a dummy gate is provided on the oxide 530b, and an element that reduces the resistance of the oxide 530b is added using the dummy gate as a mask. That is, the element is added to a region of the oxide 530b that does not overlap with the dummy gate, forming a region 531. The element can be added by ion implantation, which adds an ionized source gas after mass separation, ion doping, which adds an ionized source gas without mass separation, plasma immersion ion implantation, 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, and rare gases 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] Boron and phosphorus are particularly preferred because they allow the use of equipment from manufacturing lines for amorphous silicon or low-temperature polysilicon, and existing facilities can be repurposed, thereby reducing capital investment.

[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 can be formed in which the region 531 overlaps with the oxide 530c and the insulator 550.

[0343] Specifically, an insulating film to be the insulator 580 is formed on the insulating film to be the insulator 574, and then CMP processing is performed on the insulating film to be the insulator 580 to remove a portion of the insulating film to be the insulator 580 and expose the dummy gate. Subsequently, when removing the dummy gate, a portion of the insulator 573 in contact with the dummy gate may also be removed. Therefore, the insulators 574 and 573 are exposed on the side surfaces of the opening formed in the insulator 580, and a portion of the region 531 formed 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. Then, by CMP or the like, the oxide film to be the oxide 530c, the insulating film to be the insulator 550, and the 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 contributes to cost reduction.

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

[0347] The transistor 510F is a modified example of the transistor 510A, and therefore, to avoid repetition of the description, the differences from the above transistor will be mainly described.

[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 (insulators 576a and 576b) having barrier properties may be disposed between the conductor 546 and the insulator 580. By providing the insulator 576, it is possible to prevent oxygen in the insulator 580 from reacting with the conductor 546 and oxidizing the conductor 546.

[0350] When an oxide semiconductor is used for the oxide 530, the oxide 530 preferably has a stacked structure of multiple oxide layers with different atomic ratios of metal atoms. Specifically, the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530a is preferably larger than the atomic ratio of the element M among the constituent elements in the metal oxide used for the oxide 530b. The atomic ratio of the element M to In in the metal oxide used for the oxide 530a is preferably larger than the atomic ratio of the element M to In in the metal oxide used for the oxide 530b. The atomic ratio of In to M in the metal oxide used for the oxide 530b is preferably larger than the atomic ratio of In to M in the metal oxide used for the oxide 530a. The oxide 530c can be the same metal oxide as can be used for the oxide 530a or the oxide 530b.

[0351] The oxide 530a, the oxide 530b, and the oxide 530c preferably have crystallinity, and CAAC-OS is particularly preferable. Crystalline oxides such as CAAC-OS have few impurities and defects (such as oxygen vacancies), and have a highly crystalline and dense structure. This can prevent the source or drain electrode from extracting oxygen from the oxide 530b. This can reduce the extraction of oxygen from the oxide 530b even during heat treatment, making the transistor 510F stable against high temperatures (so-called thermal budget) during the manufacturing process.

[0352] One or both of the oxides 530a and 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, the conduction band minimum energies of the oxides 530a and 530c are preferably higher than the conduction band minimum energy of the oxide 530b. In other words, the electron affinity of the oxides 530a and 530c is preferably lower than the electron affinity of the oxide 530b. In this case, the oxide 530c is preferably a metal oxide that can be used for the oxide 530a. Specifically, the atomic ratio of the element M among the constituent elements of the metal oxide used for the oxide 530c is preferably higher than the atomic ratio of the element M among the constituent elements of the metal oxide used for the oxide 530b. In addition, the atomic ratio of the element M to In in the metal oxide used for oxide 530c is preferably greater than the atomic ratio of the element M to In in the metal oxide used for oxide 530b. In addition, the atomic ratio of In to M in the metal oxide used for oxide 530b is preferably greater than the atomic ratio of In to M in the metal oxide used for oxide 530c.

[0353] Here, the energy level of the conduction band minimum changes smoothly at the junction between the oxides 530a, 530b, and 530c. In other words, the energy level of the conduction band minimum at the junction between the oxides 530a, 530b, and 530c changes continuously or forms a continuous junction. To achieve this, it is preferable to reduce the defect level density of the mixed layers formed at the interface between the oxides 530a and 530b and at the interface between the oxides 530b and 530c.

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

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

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

[0357] The oxide 530a and the oxide 530c have the above-described structure, which reduces 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. This reduces the effect of interface scattering on carrier conduction, allowing the transistor 510F to achieve a high on-state current and high frequency characteristics. Note that, when the oxide 530c has a layered structure, in addition to the effect of reducing the defect state density at the interface between the oxide 530b and the oxide 530c, it is expected to suppress the diffusion of constituent elements of the oxide 530c toward the insulator 550. More specifically, the oxide 530c has a layered structure, and an oxide not containing In is positioned above the layered structure, which suppresses In diffusion toward the insulator 550. Because the insulator 550 functions as a gate insulator, diffusion of In leads to poor transistor characteristics. Therefore, by using the oxide 530c as a layered structure, a highly reliable display device can be provided.

[0358] The oxide 530 is preferably a metal oxide that functions as an oxide semiconductor. For example, a metal oxide having a band gap of 2 eV or more, preferably 2.5 eV or more, is preferably used as the metal oxide that forms the channel formation region of the oxide 530. By using a metal oxide with such a wide band gap, 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> 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. Alternatively, a metal nitride or metal oxide having conductivity may 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 external electromagnetic waves more than the semiconductor device. The conductor 692 also has a function of diffusing and dissipating static electricity or preventing localization of 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 can be used as the fibrous body. Furthermore, for example, brominated epoxy resin can 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. Metal oxides that can be used as the oxide 530 according to the present invention will be described below.

[0365] The metal oxide preferably contains at least indium or zinc. It is particularly preferable that it contains indium and zinc. It is also preferable that it contains gallium, yttrium, tin, or the like in addition to indium and zinc. It may also contain one or more elements selected from boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, magnesium, and the like.

[0366] Here, we consider a case where the metal oxide is an In-M-Zn oxide containing indium, element M, and zinc. The element M is one or more elements selected from aluminum, gallium, yttrium, and tin. Other elements that can be used for element M include boron, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, and magnesium. The element M may be a combination of two or more of the above elements.

[0367] In this specification and the like, nitrogen-containing metal oxides may also be collectively referred to as metal oxides. Nitrogen-containing metal oxides may also be referred to as metal oxynitrides.

[0368] [Metal oxide structures] Oxide semiconductors (metal oxides) are classified into single-crystal oxide semiconductors and 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 distorted crystal structure refers to the change in the lattice orientation between regions with a uniform lattice arrangement and regions with a different uniform lattice arrangement in the regions where multiple nanocrystals are connected.

[0370] Nanocrystals are basically hexagonal, but not necessarily regular hexagons; they can also have non-regular hexagonal shapes. Furthermore, the lattice arrangement of CAAC-OS can be pentagonal, heptagonal, or other shapes due to distortion. It is difficult to identify clear grain boundaries in CAAC-OS, even near the distortion. This indicates 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 close-packed arrangement of oxygen atoms in the ab-plane direction and the change in interatomic bond distance caused by 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 referred to as an In layer) and a layer containing the element M, zinc, and oxygen (hereinafter referred to as an (M,Zn) layer) are stacked. Note that indium and the element M are mutually substituted, and when the element M in an (M,Zn) layer is substituted with indium, it can also be expressed as an (In,M,Zn) layer. When the indium in an In layer is substituted with the element M, it can also be expressed as an (In,M) layer.

[0372] CAAC-OS is a metal oxide with high crystallinity. Because it is difficult to identify clear grain boundaries in CAAC-OS, it is unlikely that the electron mobility will decrease due to grain boundaries. Furthermore, because the crystallinity of metal oxides can be reduced by the incorporation of impurities or the generation of defects, CAAC-OS can be considered a metal oxide with few impurities or defects (such as oxygen vacancies). Therefore, metal oxides with CAAC-OS have stable physical properties. Therefore, metal oxides with CAAC-OS are heat-resistant and highly reliable.

[0373] The nc-OS has periodic atomic arrangement in a small region (for example, a region of 1 nm to 10 nm, particularly a region of 1 nm to 3 nm). Furthermore, the nc-OS exhibits no regularity in the crystal orientation between different nanocrystals. Therefore, no orientation is observed throughout the film. Therefore, depending on the analytical 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, can sometimes have a stable structure when made into the above-mentioned nanocrystals. In particular, since IGZO tends to have difficulty growing crystals in the atmosphere, it may be structurally more stable to make it into smaller crystals (for example, the above-mentioned nanocrystals) than larger crystals (here, crystals of a few millimeters or a few centimeters).

[0375] The a-like OS is a metal oxide having a structure between the nc-OS and the amorphous oxide semiconductor. The a-like OS has pores or low-density regions. 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, each with different characteristics. The oxide semiconductor of one embodiment of the present invention may include two or more of an amorphous oxide semiconductor, a polycrystalline oxide semiconductor, an a-like OS, 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 present 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 like 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, the presence of impurities in the channel formation region of the oxide semiconductor may reduce the crystallinity of the channel formation region or the crystallinity of an oxide provided in contact with the channel formation region. The low crystallinity of the channel formation region tends to reduce the stability or reliability of the transistor. Furthermore, the low crystallinity of the oxide provided in contact with the channel formation region may form an interface state, which may reduce 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 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 measured by SIMS in the channel formation region of the oxide semiconductor and its vicinity 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, as determined 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, metal oxides with reduced impurity concentrations have a low defect state density, and therefore may also have a low trap state density.

[0384] In addition, when hydrogen enters an oxygen vacancy in a metal oxide, the oxygen vacancy and hydrogen bond to form V O May form H. V O H acts as a donor and can generate carrier electrons. Also, some of the hydrogen can bond with oxygen that bonds 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. Furthermore, since hydrogen in an oxide semiconductor is easily moved by stress such as heat or an electric field, the reliability of the transistor may be reduced if the oxide semiconductor contains a large amount of hydrogen.

[0386] That is, V in metal oxides O It is preferable to reduce H as much as possible to obtain high-purity intrinsic or substantially high-purity intrinsic V. O To obtain an oxide semiconductor with a sufficiently reduced amount of 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 fill oxygen vacancies (sometimes referred to as oxygen addition treatment).O When an oxide semiconductor in which impurities such as H are sufficiently reduced is used for a channel formation region of a transistor, stable electrical characteristics can be obtained.

[0387] In addition, it is preferable to use an oxide semiconductor with a low carrier concentration for the transistor. 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, and silicon.

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

[0389] A defect where hydrogen has entered an oxygen vacancy (V O H) can function as a donor in an oxide semiconductor. However, it is difficult to quantitatively evaluate such defects. Therefore, in an oxide semiconductor, evaluation is sometimes performed using the carrier concentration rather than the donor concentration. Therefore, in this specification and the like, the carrier concentration assuming a state in which no electric field is applied may be used as a parameter of an oxide semiconductor, rather than 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 the hydrogen concentration 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 Preferably, it is 1×10 or less. 17 cm -3 More preferably, it is less than 1×10 16 cm -3 More preferably, it is less than 1×10 13 cm -3 More preferably, it is less than 1×10 12 cm -3 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 another embodiment of the present invention, a semiconductor device with excellent electrical characteristics can be provided. According to another embodiment of the present invention, a semiconductor device with high on-state current can be provided. According to another 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 also be used for the oxide 530. For example, a semiconductor of a simple element such as silicon, a compound semiconductor such as gallium arsenide, or a layered material (also called an atomic layer material or a two-dimensional material) that functions as a semiconductor is preferably used as the semiconductor material. In particular, a layered material that functions as a semiconductor is preferably used as the semiconductor material.

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

[0395] Layered materials include graphene, silicene, and chalcogenides. Chalcogenides are compounds containing chalcogen. Chalcogen is a general term for elements in Group 16, including oxygen, sulfur, selenium, tellurium, polonium, and livermorium. Chalcogenides also 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 (typically MoS2), molybdenum selenide (typically MoSe2), molybdenum tellurium (typically MoTe2), tungsten sulfide (typically WS2), tungsten selenide (typically WSe2), tungsten tellurium (typically WTe2), hafnium sulfide (typically HfS2), hafnium selenide (typically HfSe2), zirconium sulfide (typically ZrS2), and zirconium selenide (typically 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: capacitor, 52: capacitor, 53: inverter, 54: transistor, 55: transistor, 56: comparator, 57: capacitor, 61: transistor, 62: transistor, 63: circuit, 63a: transistor, 63b: transistor, 63n: transistor, 63x: circuit, 63y: circuit, 64: transistor, 65: transistor, 66: capacitor, 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 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: capacitor 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 the 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 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 maintained 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 applied to the input terminal.

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

4. In any one of claims 1 to 3, a second capacitance element; one electrode of the second capacitance element is electrically connected to one of the source and the 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 seventh 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 high potential signal is applied to the second wiring of the power storage device.

6. In any one of claims 1 to 5, the first circuit has n transistors (n is a natural number of 2 or more); the n transistors included in 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, for 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 electrically connected to a gate of at least one of the n transistors included in the first circuit;

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