Semiconductor device and electronic device

A semiconductor device including a register controller and a processor which includes a register is provided. The register includes a first circuit and a second circuit which includes a plurality of memory portions. The first circuit and the plurality of memory portions can store data by an arithmetic process of the processor. Which of the plurality of memory portions the data is stored in depends on a routine by which the data is processed. The register controller switches the routine in response to an interrupt signal. The register controller can make any one of the plurality of memory portions which corresponds to the routine store the data in the first circuit every time the routine is switched. The register controller can make data stored in any one of the plurality of memory portions which corresponds to the routine be stored in the first circuit every time the routine is switched.

BACKGROUND OF THE INVENTION

1. Field of the Invention

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

2. Description of the Related Art

The technical development of a semiconductor device that can hold charges corresponding to data by using a transistor including an oxide semiconductor in its channel formation region (OS transistor) and a transistor including silicon in its channel formation region (Si transistor) in combination has been progressing. Such a semiconductor device consumes less power than a static RAM (SRAM) and therefore usage as a processor or the like has been actively developed (e.g., see Patent Document 1).

REFERENCE

Patent Document

SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide a novel semiconductor device or the like.

Another object of one embodiment of the present invention is to provide a semiconductor device or the like that has a novel structure and is excellent in data processing efficiency. Another object of one embodiment of the present invention is to provide a semiconductor device or the like that has a novel structure and is excellent in low power consumption.

Note that objects of one embodiment of the present invention are not limited to the aforementioned objects. The objects described above do not disturb the existence of other objects. The other objects are the ones that are not described above and will be described below. The other objects will be apparent from and can be derived from the description of the specification, the drawings, and the like by those skilled in the art. One embodiment of the present invention solves at least one of the aforementioned objects and the other objects.

One embodiment of the present invention is a semiconductor device which includes a register controller and a processor including a register. The register includes a first circuit and a second circuit. The first circuit has a function of storing data obtained by an arithmetic process of the processor. The second circuit includes a plurality of memory portions. The plurality of memory portions have a function of storing data obtained by an arithmetic process of the processor. Which of the plurality of memory portions the data is stored in depends on a routine by which the data is processed. The register controller has a function of making any one of the plurality of memory portions which corresponds to the routine store the data in the first circuit every time the routine is switched. The register controller has a function of making data stored in any one of the plurality of memory portions which corresponds to the routine be stored in the first circuit every time the routine is switched.

In the above embodiment of the present invention, each of the plurality of memory portions preferably includes a first transistor and a second transistor, a gate of the second transistor is preferably electrically connected to a source or a drain of the first transistor, and the memory portion preferably has a function of holding charges corresponding to data in the gate of the second transistor when the first transistor is in an off state.

In the above embodiment of the present invention, the first transistor preferably includes an oxide semiconductor in its channel formation region, and the oxide semiconductor preferably includes In, Ga, and Zn.

One embodiment of the present invention is an electronic device including the above-described semiconductor device and a display device or a speaker.

Note that other embodiments of the present invention will be described in Embodiments 1 to 7 and the drawings.

With one embodiment of the present invention, a semiconductor device or the like with a novel structure can be provided.

With one embodiment of the present invention, a semiconductor device or the like that has a novel structure and is excellent in data processing efficiency can be provided. With one embodiment of the present invention, a semiconductor device or the like that has a novel structure and is excellent in low power consumption can be provided.

DETAILED DESCRIPTION OF THE INVENTION

Note that one embodiment of the present invention includes, in its category, semiconductor devices in which power gating is performed, such as an integrated circuit, an RF tag, and a semiconductor display device. The integrated circuits include, in its category, large scale integrated circuits (LSIs) including a microprocessor, an image processing circuit, a digital signal processor (DSP), and a microcontroller, and programmable logic devices (PLDs) such as a field programmable gate array (FPGA) and a complex PLD (CPLD). The semiconductor display device includes the following in its category: liquid crystal display devices, light-emitting devices in which a light-emitting element typified by an organic light-emitting diode (OLED) is provided in each pixel, electronic paper, digital micromirror devices (DMDs), plasma display panels (PDPs), field emission displays (FEDs), and other semiconductor display devices.

In the drawings, the size, the layer thickness, or the region is exaggerated for clarity in some cases. Therefore, embodiments of the present invention are not limited to such a scale. Note that the drawings are schematic views showing ideal examples, and embodiments of the present invention are not limited to shapes or values shown in the drawings. For example, the following can be included: variation in signal, voltage, or current due to noise or difference in timing.

In this specification and the like, a transistor is an element having at least three terminals: a gate, a drain, and a source. The transistor includes a channel region between the drain (a drain terminal, a drain region, or a drain electrode) and the source (a source terminal, a source region, or a source electrode) and current can flow through the drain, the channel region, and the source.

Here, since the source and the drain of the transistor change depending on the structure, the operating condition, and the like of the transistor, it is difficult to define which is a source or a drain. Thus, a portion that functions as a source or a portion that functions as a drain is not referred to as a source or a drain in some cases. Instead, one of the source and the drain might be referred to as a first electrode, and the other of the source and the drain might be referred to as a second electrode.

Note that in this specification, ordinal numbers such as “first”, “second”, and “third” are used in order to avoid confusion among components, and thus do not limit the number of the components.

In this specification, the expression “A and B are connected” means the case where A and B are electrically connected to each other in addition to the case where A and B are directly connected to each other. Here, the expression “A and B are electrically connected” means the case where electric signals can be transmitted and received between A and B when an object having any electric action exists between A and B.

Note that, for example, the case where a source (or a first terminal or the like) of a transistor is electrically connected to X through (or not through) Z1and a drain (or a second terminal or the like) of the transistor is electrically connected to Y through (or not through) Z2, or the case where a source (or a first terminal or the like) of a transistor is directly connected to one part of Z1and another part of Z1is directly connected to X while a drain (or a second terminal or the like) of the transistor is directly connected to one part of Z2and another part of Z2is directly connected to Y, can be expressed by using any of the following expressions.

Other examples of the expressions include, “a source (or a first terminal or the like) of a transistor is electrically connected to X through at least a first connection path, the first connection path does not include a second connection path, the second connection path is a path between the source (or the first terminal or the like) of the transistor and a drain (or a second terminal or the like) of the transistor, Z1is on the first connection path, the drain (or the second terminal or the like) of the transistor is electrically connected to Y through at least a third connection path, the third connection path does not include the second connection path, and Z2is on the third connection path”. It is also possible to use the expression “a source (or a first terminal or the like) of a transistor is electrically connected to X through at least Z1on a first connection path, the first connection path does not include a second connection path, the second connection path includes a connection path through the transistor, a drain (or a second terminal or the like) of the transistor is electrically connected to Y through at least Z2on a third connection path, and the third connection path does not include the second connection path”. Still another example of the expression is “a source (or a first terminal or the like) of a transistor is electrically connected to X through at least Z1on a first electrical path, the first electrical path does not include a second electrical path, the second electrical path is an electrical path from the source (or the first terminal or the like) of the transistor to a drain (or a second terminal or the like) of the transistor, the drain (or the second terminal or the like) of the transistor is electrically connected to Y through at least Z2on a third electrical path, the third electrical path does not include a fourth electrical path, and the fourth electrical path is an electrical path from the drain (or the second terminal or the like) of the transistor to the source (or the first terminal or the like) of the transistor”. When the connection path in a circuit structure is defined by an expression similar to the above examples, a source (or a first terminal or the like) and a drain (or a second terminal or the like) of a transistor can be distinguished from each other to specify the technical scope.

Note that these expressions are examples and the expression is not limited to these examples. Here, X, Y, Z1, and Z2each denote an object (e.g., a device, an element, a circuit, a wiring, an electrode, a terminal, a conductive film, and a layer).

Note that in this specification, terms for describing arrangement, such as “over” and “under”, are used for convenience to describe the positional relation between components with reference to drawings. Further, the positional relation between components is changed as appropriate in accordance with a direction in which each component is described. Thus, the positional relation is not limited to that described with a term used in this specification and can be explained with another term as appropriate depending on the situation.

The positional relation of circuit blocks in a block diagram is specified for description. Even when a block diagram shows that different functions are achieved by different circuit blocks, one circuit block may be actually configured to achieve the different functions. Functions of circuit blocks in a diagram are specified for description, and even when a diagram shows one circuit block performing given processing, a plurality of circuit blocks may be actually provided to perform the processing.

In this embodiment, configuration examples of a semiconductor device are described.

FIG. 1is a block diagram illustrating a configuration example of a semiconductor device. InFIG. 1, a semiconductor device100includes a processor10and a register controller11. The processor10includes a register12. The register12includes a memory circuit13and a memory circuit14. The memory circuit14includes a plurality of memory portions14_1to14_n(n is a natural number of 2 or more).

The memory circuit13is a circuit having a function of temporarily storing data that is processed by the processor10. In some cases, the memory circuit13is simply referred to as a circuit. Specific examples of the memory circuit13include a flip-flop, an SRAM, and the like. The data that is processed by the processor10includes not only data obtained by arithmetic but also program execution data. Here, the program execution data includes an address (the value of a program counter (PC)), a status flag, and the like.

The memory circuit14is a circuit that can temporarily store the data stored in the memory circuit13, into which the data is saved (stored or backed up) and from which the data is loaded (restored or recovered). Data saving or loading between the memory circuit13and the memory circuit14is controlled in accordance with a signal output from the register controller11.

The data stored in the memory circuit14is stored in the plurality of memory portions14_1to14_n. The plurality of memory portions14_1to14_nsave the data stored in the memory circuit13in accordance with the routine. Saving of the data is performed with signals Sv_1to Sv_n supplied from the register controller11. The signals Sv_1to Sv_n are output in response to an interrupt signal (also referred to as an interrupt control signal and described as “Interrupt” in the drawing) supplied to the register controller11. The interrupt signal switches the routine. In order that in-process data in the processor10is temporarily saved from the memory circuit13into the memory circuit14, the signals Sv_1to Sv_n corresponding to the routine are output.

For example, in the case where the data processed by a first routine is stored in the memory circuit13, the memory portion14_1is configured to be selected as the memory portion for saving the data into the memory circuit14. In the case where the data processed by a second routine is stored in the memory circuit13, the memory portion14_2is configured to be selected as the memory portion for saving the data into the memory circuit14.

The data saved into the plurality of memory portions14_1to14_nare loaded into the memory circuit13in accordance with the routine that is to execute an instruction in the processor10. Loading of the data is performed with signals Ld_1to Ld_n supplied from the register controller11. The signals Ld_1to Ld_n are output in response to the interrupt signal (described as “Interrupt” in the drawing) supplied to the register controller11. The interrupt signal switches the routine. To load the data for the routine switched in the processor10, the signals Ld_1to Ld_n corresponding to the routine are output.

For example, in the case where the first routine is processed in the processor10, the memory portion14_1is configured to be selected and the data is loaded into the memory circuit13. In the case where the second routine is processed in the processor10, the memory portion14_2is configured to be selected and the data is loaded into the memory circuit13.

By the structure of performing saving or loading between the memory circuit13and the plurality of memory portions14_1to14_nin accordance with the routine executed in the processor10, a plurality of routines can interrupt in response to the interrupt signal in data processing of the processor10. When another routine interrupts, data is saved from the memory circuit13into the memory circuit14or loaded from the memory circuit14into the memory circuit13; thus, although in-process routine is suspended to execute a different routine by priority, the routine executed immediately before the interrupt can be restarted. Since the data for restarting the interrupted routine is stored inside the processor10, no access to a stack region of an external memory such as an SRAM or a DRAM is required for data saving or loading. Therefore, even when a process of switching from a current routine to a different routine is performed by an interrupt, the data saving or loading process due to the switching can be performed efficiently without causing a lag of memory access or the like.

The processor10is a circuit having a function of executing a program written in computer language. The processor10includes an arithmetic portion and a control portion. The processor10may be a single-core processor or a multi-core processor such as a dual-core processor or a many-core processor.

The register controller11is a circuit having a function of outputting signals for performing saving or loading between the memory circuit13and the plurality of memory portions14_1to14_nin response to the interrupt signal. The signals for saving or loading the data are the signals Sv_1to Sv_n and the signals Ld_1to Ld_n. Each of the signals is controlled so as to correspond to the routine switched by the interrupt signal. Accordingly, every time the routine is switched, the register controller11can make any one of the plurality of memory portions14_1to14_nthat corresponds to the routine store the data in the memory circuit13. Furthermore, every time the routine is switched, the register controller11can make the data stored in any one of the plurality of memory portions14_1to14_nthat corresponds to the routine be stored in the memory circuit13.

The register12is a circuit for storing data processed in the processor10and includes the memory circuit13and the memory circuit14. The register12is a circuit for storing data in the processor10and, for example, a circuit used in a register file, a pipeline register, or the like.

Although one register12is provided in the semiconductor device100in the configuration inFIG. 1, another configuration may also be employed. For example, the semiconductor device100may include a plurality of registers. In the semiconductor device100illustrated inFIG. 2, a processor10_A includes a plurality of registers12_1to12_N (N is a natural number of 2 or more). Note that the register controller11outputs the signals Sv_1to Sv_n and the signals Ld_1to Ld_n to each of the plurality of registers12_1to12_N so that data saving or loading between the memory circuit13and the plurality of memory portions14_1to14_ncan be controlled in each of the plurality of registers12_1to12_N. The configuration ofFIG. 2enables the plurality of registers12_1to12_N to independently perform data processing with interrupts of a plurality of routines.

Although one processor10is provided in the semiconductor device100in the configuration ofFIG. 1, another configuration may also be employed. For example, a plurality of processors may be provided in the semiconductor device100.

The memory circuit13is a circuit having a function of storing data obtained by an arithmetic process of the processor10. The memory circuit13is preferably a memory circuit that can write and read data at high speed. For example, a flip-flop or an SRAM which is formed of a combination of a transmission gate, a transistor, an inverter, a logic circuit such as a NAND, or the like that includes a Si transistor can be used.

The flip-flop or SRAM that is used as the memory circuit13is preferably a circuit having a function of statically holding a potential corresponding to the input data. Furthermore, the memory circuit13preferably has a function of controlling data writing and reading in accordance with a clock signal, and for example has a master-slave circuit configuration. Moreover, the memory circuit13preferably has a function of initializing a held potential with a reset signal.

The memory circuit14and the plurality of memory portions14_1to14_nincluded in the memory circuit14are circuits having a function of storing data obtained by an arithmetic process of the processor10. Since the plurality of memory portions14_1to14_nneed to retain data for a certain period, they preferably consume low power for data retention.

FIG. 3illustrates a configuration example of the memory circuit13and the plurality of memory portions14_1to14_nincluded in the register12. In addition,FIG. 3illustrates a specific circuit configuration that can be applied to the plurality of memory portions14_1to14_n. Data is supplied to a terminal D of the memory circuit13and data is output from a terminal Q of the memory circuit13. In addition, the memory circuit13is connected to each of the plurality of memory portions14_1to14_n. To the plurality of memory portions14_1to14_n, a corresponding one of the signals Sv_1to Sv_n and a corresponding one of the signals Ld_1to Ld_n are supplied.

The plurality of memory portions14_1to14_nhave the same circuit configuration. For example, the memory portion14_1includes a transistor15, a capacitor16, a transistor17, and a transistor18.

One of a source and a drain of the transistor15is connected to a node for storing data (memory node) included in the memory circuit13. The other of the source and the drain of the transistor15is connected to a gate of the transistor17. A gate of the transistor15is connected to a wiring to which the signal Sv_1is supplied.

One electrode of the capacitor16is connected to the gate of the transistor17. The other electrode of the capacitor16is connected to a wiring to which a reference potential is supplied, for example, a ground line. The other electrode of the capacitor16may be connected to another wiring such as a wiring to which a power supply potential is supplied.

One of a source and a drain of the transistor17is connected to a wiring to which a reference potential is supplied, for example, a ground line. The other of the source and the drain of the transistor17is connected to one of a source and a drain of the transistor18. The gate of the transistor17is connected to the other of the source and the drain of the transistor15. In the following description, a node to which the gate of the transistor17is connected is referred to as a node ND.

The one of the source and the drain of the transistor18is connected to the other of the source and the drain of the transistor17. The other of the source and the drain of the transistor18is connected to a memory node included in the memory circuit13. A gate of the transistor18is connected to a wiring to which the signal Ld_1is supplied. Note that the memory node of the memory circuit13to which the other of the source and the drain of the transistor18is connected is preferably different from the memory node to which the one of the source and the drain of the transistor15is connected. In this case, the memory nodes preferably hold different logic data from each other.

The operation of the memory portion14_1is briefly described. In the following description, the transistors15,17, and18are assumed to be n-channel transistors. When they are p-channel transistors, the supplied signals have opposite polarities.

First, an operation of saving a potential corresponding to data in the memory circuit13(data potential) into the memory portion14_1is described.

The signal Sv_1is set at H level to bring the transistor15in an on state, which makes the potential of the memory node included in the memory circuit13equal to the potential of the node ND.

Next, the signal Sv_1is set at L level to bring the transistor15in an off state. Charges corresponding to the data potential are held in the node ND. The transistor15preferably has a low current flowing between the source and the drain in an off state (low off-state current).

By the above-described operation, the operation of saving the data potential of the memory circuit13into the memory portion14_1is completed.

Note that the transistor with low off-state current is preferably an OS transistor. An oxide semiconductor that can be used in the OS transistor preferably includes In, Ga, and Zn. In some circuit diagrams, “OS” is written beside a circuit symbol of the transistor15to clearly show that the transistor15is an OS transistor.

Next, an operation of loading the data potential held in the memory portion14_1into the memory circuit13is described.

First, the memory node of the memory circuit13is precharged. In the example described here, the memory node is precharged at H level.

Then, the signal Ld_1is set at H level to bring the transistor18in an on state. At this time, the transistor17is either in an on state or an off state depending on the charges corresponding to the data potential held in the node ND.

For example, in the case where the data potential held in the node ND is at H level, the transistor17is in an on state. In this case, the potential of the ground line, which is a reference potential, i.e., an L level potential, is loaded into the memory node through the transistors17and18. The memory node into which the potential of the ground line is loaded is different from the node into which the data potential is saved, and the original data can be loaded.

For example, in the case where the data potential held in the node ND is at L level, the transistor17is in an off state. In this case, the memory node of the memory circuit13remains at the precharge potential, i.e., the H level potential, and the H level potential is loaded into the memory node.

Through the above-described operation, the operation of loading the data potential of the memory circuit13into the memory circuit13is completed.

FIGS. 4A to 4Dillustrate circuit configurations that can be applied to the memory portions14_1to14_nillustrated inFIG. 3.

As in a memory portion14_A illustrated inFIG. 4A, OS transistors or Si transistors can be used as the transistors17and18. Alternatively, as in a memory portion14_B illustrated inFIG. 4B, only OS transistors can be used as the transistors17and18.

In the case where not the ground potential but a power supply potential VDD is supplied at the time of loading, p-channel transistors can be used as in a memory portion14_C illustrated inFIG. 4C. In the case where the same path of charges is used for both saving and loading, a memory portion14_D illustrated inFIG. 4Dcan be employed.

In the circuit configurations illustrated inFIG. 3andFIGS. 4A and 4B, a back gate may be added to the transistor15. By applying a negative potential to the back gate to positively shift the threshold voltage of the transistor15, the off-state current of the transistor15can be kept low. By applying a positive potential to the back gate to negatively shift the threshold voltage of the transistor15, the on-state current of the transistor15can be increased.

Although the structures of the transistors15,17, and18are not particularly limited, a top-gate structure or a bottom-gate structure can be employed, for example.

The circuit configurations of the plurality of memory portions14_1to14_nhaving a function of storing data obtained by the arithmetic process of the processor10are not limited to those illustrated inFIG. 3andFIGS. 4A and 4B. For example, the plurality of memory portions14_1to14_nmay include a phase-change RAM (PRAM), a phase-change memory (PCM), a resistive RAM (ReRAM), a magnetoresistive RAM (MRAM), or the like. For the MRAM, a magnetic tunnel junction element (also referred to as an MTJ element) can be used, for example.

Next, examples of the operation of the semiconductor device100illustrated inFIG. 1will be described with reference to schematic diagrams ofFIGS. 5A and 5B.

In the examples of the operation of the semiconductor device100inFIGS. 5A and 5B, the plurality of routines are first to third routines and the program processing is interrupted by an interrupt signal so that a different routine can be executed. In the following description, the first routine is a main routine, the second routine is a subroutine A, and the third routine is a subroutine B.

First,FIG. 5Ais explained.FIG. 5Ashows an operation in which the subroutine A interrupts and then the subroutine B interrupts during the program processing of the main routine.

As shown inFIG. 5A, first, instructions are executed in order in the register12to execute the program processing of the main routine (expressed by a solid arrow in the drawing). Then, an interrupt signal interrupts the main routine, so that the subroutine A is preferentially executed (expressed by a dotted arrow in the drawing). Because of the interruption of the main routine, data including program execution data which is stored in the memory circuit13is saved. The data stored in the memory circuit13is saved into the memory portion14_1by supplying the signal Sv_1from the register controller11to the memory portion14_1.

Then, instructions are executed in order in the register12to execute the program processing of the subroutine A (expressed by a solid arrow in the drawing). Then, an interrupt signal interrupts the subroutine A, so that the subroutine B is preferentially executed (expressed by a dotted arrow in the drawing). Because of the interruption of the subroutine A, data including program execution data which is stored in the memory circuit13is saved. The data stored in the memory circuit13is saved into the memory portion142by supplying the signal Sv_2from the register controller11to the memory portion14_2.

Next, to execute the program processing of the subroutine B, instructions are executed in order in the register12(expressed by a solid arrow in the drawing). When the program processing of the subroutine B is finished, the interrupted subroutine A is restarted (expressed by a dotted arrow in the drawing). To restart the subroutine A, the data including the program execution data is loaded into the memory circuit13. The data stored in the memory portion14_2is loaded into the memory circuit13by supplying the signal Ld_2from the register controller11to the memory portion14_2.

Next, to execute the interrupted program processing of the subroutine A, instructions are executed in order in the register12(expressed by a solid arrow in the drawing). When the program processing of the subroutine A is finished, the interrupted main routine is restarted (expressed by a dotted arrow in the drawing). To restart the main routine, the data including the program execution data is loaded into the memory circuit13. The data stored in the memory portion14_1is loaded into the memory circuit13by supplying the signal Ld_1from the register controller11to the memory portion14_1.

AlthoughFIG. 5Ashows a structure for saving data of the interrupted routine and loading the data of the restarting routine, another structure may be employed as well.FIG. 5Bshows another structure of the operation.FIG. 5Bshows the operation in which the subroutine A interrupts and then the subroutine B interrupts during the program processing of the main routine in the same manner as that ofFIG. 5Aexcept that data for executing program processing of the routine is saved into each of the memory portions14_1to14_3in advance. In this structure, a stack region of an external memory such as an SRAM or a DRAM is first accessed to save the data in advance; thus, by performing saving or loading at the input timing of the interrupt signal, the routine can be switched and the program processing can be executed. In this manner, more efficient data processing can be achieved.

The switching of the routine by the interrupt signal shown inFIG. 5Bis described below. To avoid repeated description, the interruption and restart of the main routine and the subroutine are described here.

InFIG. 5B, when the main routine is interrupted by an interrupt signal during the execution of the program processing of the main routine, saving of the data including the program execution data stored in the memory circuit13and loading of the data including the program execution data into the memory circuit13for executing the subroutine A are performed. To save the data stored in the memory circuit13into the memory portion14_1, the register controller11supplies the signal Sv_1to the memory portion14_1. In addition, to load the data stored in the memory portion142into the memory circuit13, the register controller11supplies the signal Ld_2to the memory portion142.

As described above with reference toFIGS. 5A and 5B, the semiconductor device of one embodiment of the present invention can restart the program processing using the interrupted data even when the subroutine A and the subroutine B interrupt during the program processing of the main routine. Since the data for restarting the interrupted routine is stored inside the processor10, no access to a stack region of an external memory such as an SRAM or a DRAM is required for data saving or loading. Therefore, even when a process of switching from a current routine to a different routine is performed by an interrupt, the data saving or loading process due to the switching can be performed efficiently without causing a lag of memory access or the like.

Next, a specific circuit configuration of the memory circuit13and the plurality of memory portions14_1to14_nis illustrated inFIG. 6.FIG. 6illustrates the memory portions14_1and14_2as the plurality of memory portions14_1to14_n.

The memory circuit13illustrated inFIG. 6as an example has a master-slave flip-flop circuit configuration. The memory circuit13includes inverters21and22, transmission gates23to27, and NANDs31to34. A signal RSTB is supplied to the NANDs31and34; when the signal RSTB is at H level, the NANDs function as inverters and when the signal RSTB is at L level, the NANDs have high impedance. Note that the NANDs32and33can be replaced by inverters. Furthermore, a clock signal CLK or a signal LE is supplied to the transmission gates23to27.FIG. 6can be referred to for the connection relation between circuits.

In the drawing, nodes MD and MDB are included as memory nodes in the memory circuit13. The nodes MD and MDB hold different logic data from each other. For example, if one of the data is Data, the other is Data_B.

Since the memory portions14_1and14_2have the same circuit configuration as that inFIG. 3, the description thereof is omitted. Note that a node to which the gate of the transistor17included in the memory portion14_1is connected is referred to as a node ND_1, and a node to which the gate of the transistor17included in the memory portion14_2is connected is referred to as a node ND_2.

FIG. 7is a timing chart of a data saving operation in the circuit illustrated inFIG. 6. As an example, an operation of saving data from the memory circuit13into the memory portion14_1is shown inFIG. 7. The timing chart ofFIG. 7shows a change of a signal at the node MDB, which is the memory node, and changes of the signal RSTB, the signal LE, a signal CLKin, the signal Sv_1, the signal Ld_1, and the potential of the node ND_1.

Note that the signal CLKin is a signal for generating the clock signal CLK and an inverted clock signal CLKB.FIG. 8Aillustrates an example of a circuit configuration for generating the clock signal CLK and the inverted clock signal CLKB using the signal CLKin. InFIG. 8A, inverters41and42are used to generate the signals.

In addition, the signal LE is a signal for bringing the node MD in a floating state at the time of loading data.FIG. 8Billustrates an example of a circuit configuration for generating the signal LE using the signals Ld_1and Ld_2. InFIG. 8B, a NOR43is used to generate the signal. The signal LEB that is an inverted signal of the signal LE can be generated using an inverter44as illustrated inFIG. 8C.

At Time t1in the timing chart ofFIG. 7, waveforms and signal states in a normal operation are shown. In the normal operation, data is supplied to the terminal D in the memory circuit and the memory circuit outputs data from the terminal Q in accordance with the input of the clock signal CLK. Data_B is stored at the node MDB. In addition, the signal RSTB and the signal LE are both at H level. The signal Sv_1and the signal Ld_1are both at L level. A L level potential is held at the node ND_1in an initial state.

Next, at Time t2, waveforms and signal states at the time of saving data are shown. The clock signal CLK is fixed and the signal Sv_1is set to H level. In the example illustrated inFIG. 7, the clock signal CLK is fixed at L level and the signal Sv_1is set to H level. The voltage amplitude of the signal Sv_1is preferably set larger than that of the signal Ld_1; with this structure, the potential that is supplied to the node ND_1and based on Data_B can be prevented from being decreased by the threshold voltage of the transistor15.

Then, at Time t3, waveforms and signal states in a normal operation again are shown. In the normal operation, data is supplied to the terminal D in the memory circuit and the memory circuit outputs data from the terminal Q in accordance with the input of the clock signal CLK. At the node ND_1, the potential corresponding to Data_B, which is saved at Time t2, is held. In addition, the signal RSTB and the signal LE are both at H level. The signal Sv_1and the signal Ld_1are both at L level.

By keeping the L level of the signal Sv_1after Time t3, charges corresponding to the data potential supplied to the node ND_1at Time t2can be kept.

The timing chart for the operation of saving data in the circuit illustrated inFIG. 6has been described so far.

Next,FIG. 9is a timing chart of a data loading operation in the circuit illustrated inFIG. 6. As an example, an operation of loading data from the memory portion14_1into the memory circuit13is shown inFIG. 9. The timing chart ofFIG. 9shows a change of a signal at the node MD, which is the memory node, and changes of the signal RSTB, the signal LE, a signal CLKin, the signal Sv_1, the signal Ld_1, and the potential of the node ND_1.

At Time t4in the timing chart ofFIG. 9, waveforms and signal states in a normal operation are shown. In the normal operation, data is supplied to the terminal D in the memory circuit and the memory circuit outputs data from the terminal Q in accordance with the input of the clock signal CLK. DataA is stored at the node MD. In addition, the signal RSTB and the signal LE are both at H level. The signal Sv_1and the signal Ld_1are both at L level. A potential corresponding to Data_B, which is saved at Time t2inFIG. 7, is held at the node ND_1.

Then, at Time t5, the state in which a precharge operation is performed for data loading is shown. In the precharge operation, the signal CLKin is set at H level, the signal RSTB is set at L level, and the node MD is set at H level.

Next, at Time t6, the state for loading data is shown. In the data loading operation, the signal LE is set at L level to bring the node MD into a floating state, and the signal Ld_1is set at H level. The on/off states of the transistors17and18are determined, and the potential of the node MD becomes Data (LOAD) which is the logically inverted data of the data at the node ND_1.

Next, at Time t7, the signal RSTB is set at H level and the signal Ld_1is set at L level. At Time t8, the signal LE is set at H level to perform a normal operation again.

The timing chart for the operation of loading data in the circuit illustrated inFIG. 6has been described so far.

Note that although a plurality of operations are described as being performed at the same time inFIG. 9(e.g., setting the signal LE at L level and the signal Ld_1at H level at the same time at Time t6), they may be performed at different times. For example, as shown inFIG. 10, they may be performed at Time t6and Time t6′. Furthermore, setting the signal RSTB at H level and setting the signal Ld_1at L level may be performed at different times (e.g., Time t7and Time t7′). Moreover, setting the signal LE at H level and supplying the signal CLKin may be performed at different times (e.g., Time t8and Time t8′).

In the semiconductor device100described in this embodiment, as described above, by the structure of performing saving or loading between the memory circuit13and the plurality of memory portions14_1to14_nin accordance with the routine executed in the processor10, a plurality of routines can interrupt in response to the interrupt signal in data processing in the processor10. When another routine interrupts, data is saved from the memory circuit13into the memory circuit14or loaded from the memory circuit14into the memory circuit13; thus, although in-process routine is suspended to execute a different routine by priority, the routine executed immediately before the interrupt can be restarted. Since the data for restarting the interrupted routine is stored inside the processor10, no access to a stack region of an external memory such as an SRAM or a DRAM is required for data saving or loading. Therefore, even when a process of switching from a current routine to a different routine is performed by an interrupt, the data saving or loading process due to the switching can be performed efficiently without causing a lag of memory access or the like.

The structure described above in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

In this embodiment, a circuit configuration example which is different from that of the memory circuit13and the memory portions14_1and14_2described in Embodiment 1 with reference toFIG. 6will be described.

FIG. 11illustrates a circuit configuration including a memory circuit13xand memory portions14x_1and14x_2, which is the circuit configuration different from that of the memory circuit13and the memory portions14_1and14_2described in Embodiment 1 with reference toFIG. 6. The memory circuit13xincludes inverters51to56, transmission gates57and58, a NAND59, and transistors60to64. The signal RSTB is supplied to the NAND59. In addition, a clock signal CLK is supplied to the transmission gates57and58. A clock signal CLK is supplied to the transistors60and61. A signal LEB is supplied to the transistor62. A signal LRST is supplied to the transistors63and64.FIG. 11can be referred to for the connection relation between circuits.

In the drawing, nodes MD and MDB are included as memory nodes in the memory circuit13x. The nodes MD and MDB hold different logic data from each other. For example, if one of the data is Data, the other is Data_B. Note that the signal LRST is a signal for initializing the nodes MD and MDB. The initialization is performed by setting the nodes MD and MDB at a ground potential or the same potential to each other.

The memory portions14x_1and14x_2each include transistors65and66and capacitors67and68. A signal SL_1and a signal SL_2are supplied to gates of the transistors65and66. The signal SL_1and the signal SL_2are signals for saving or loading data between the memory circuit13xand the plurality of memory portions14x_1to14x_n, and function as the signals Sv_1to Sv_n and the signals Ld_1to Ld_n described in Embodiment 1.FIG. 11can be referred to for the connection relation between circuits. Note that nodes to which one of a source and a drain of the transistor65and one of a source and a drain of the transistor66in the memory portion14x_1are connected are referred to as a node NR_1and a node NRB_1.

Note that the signal CLKin is the same as the signal CLKin described in Embodiment 1, that is, the signal for generating the clock signal CLK and the inverted clock signal CLKB as illustrated inFIG. 8A.

Note that the transistors65and66preferably have low off-state current. The transistors with low off-state current are preferably OS transistors. In some circuit diagrams, “OS” is written beside circuit symbols of the transistors65and66to clearly show that the transistors65and66are OS transistors.

FIG. 12is a timing chart of a data saving operation in the circuit illustrated inFIG. 11. As an example, an operation of saving data from the memory circuit13xinto the memory portion14x_1is shown inFIG. 12. The timing chart ofFIG. 12shows a change of a signal at the node MD(MDB), which is the memory node, and changes of the signal RSTB, the signal LEB, the signal CLKin, the signal SL_1, the signal LRST, and the potential of the node NR_1(NRB_1).

At Time T1in the timing chart ofFIG. 12, waveforms and signal states in a normal operation are shown. In the normal operation, data is supplied to the terminal D in the memory circuit and the memory circuit outputs data from the terminal Q and a terminal QB in accordance with the input of the clock signal CLK. Data is stored at the node MD. In addition, the signal RSTB is at H level, and the signal LEB is at L level. The signal SL_1is at L level. The signal LRST is at L level. A L level potential is held at the node NR_1in an initial state.

Next, at Time T2, waveforms and signal states at the time of saving data are shown. The clock signal CLK is fixed at H level or L level, and the signal SL_1is set to H level. The voltage amplitude of the signal SL_1is preferably set larger than those of the other signals; with this structure, the potentials that are supplied to the node NR_1and NRB_1and based on Data and Data_B can be prevented from being decreased by the threshold voltages of the transistors65and66.

Then, at Time T3, waveforms and signal states in a normal operation again are shown. In the normal operation, data is supplied to the terminal D in the memory circuit and the memory circuit outputs data from the terminal Q and the terminal QB in accordance with the input of the clock signal CLK. At the nodes NR_1and NRB_1, the potentials corresponding to Data and Data_B, which are saved at Time T2, are held. In addition, the signal RSTB is at H level, and the signal LEB is at L level. The signal SL_1is at L level. The signal LRST is at L level.

By keeping the L level of the signal SL_1after Time T3, charges corresponding to the data potential supplied to the nodes NR_1and NRB_1at Time T2can be kept.

The timing chart for the operation of saving data in the circuit illustrated inFIG. 11has been described so far.

Next,FIG. 13is a timing chart of a data loading operation in the circuit illustrated inFIG. 11. As an example, an operation of loading data from the memory portion14x_1into the memory circuit13xis shown inFIG. 13. The timing chart ofFIG. 13shows a change of a signal at the node MD(MDB), which is the memory node, and changes of the signal RSTB, the signal LEB, the signal CLKin, the signal SL_1, the signal LRST, and the potential of the node NR_1(NRB_1).

At Time T4in the timing chart ofFIG. 13, waveforms and signal states at the time of performing a normal operation are shown. In the normal operation, data is supplied to the terminal D in the memory circuit and the memory circuit outputs data from the terminal Q and the terminal QB in accordance with the input of the clock signal CLK. DataA is stored at the node MD. In addition, the signal RSTB is at H level, and the signal LEB is at L level. The signal SL_1is at L level. The signal LRST is at L level. A potential corresponding to Data, which is saved at Time T2inFIG. 12, is held at the node NR_1.

Next, at Time T5, the signal CLKin is set at L level. At Time T6, the signal LEB is set at H level. The transistors60and61are brought into an off state, so that the supply of power supply voltage to the inverters53and54is stopped. Thus, the nodes MD and MDB are brought into a floating state.

Then, at Time T7, the signal LRST is set at H level. At Time T8, the signal LRST is set at L level. The transistors63and64are brought into an on state and then into an off state. The potentials of the nodes MD and MDB both become a ground potential.

Next, at Time T9and T10, data is loaded. In the data loading operation, the signal SL_1is set at H level and then set at L level. The transistors65and66are brought into an on state and then into an off state. Thus, charges transfer between the node MD and the node NR_1and between the node MDB and the node NRB_1. One of the node NR_1and the node NRB_1holds charges corresponding to the H level potential, and the other holds charges corresponding to the L level potential. Consequently, a potential difference between the node MD and the node MDB is generated. In the state where this difference is generated, the signal LEB is set at L level at Time T11. The supply of the power supply voltage to the inverters53and54is restarted, and data is loaded into the nodes MD and MDB. At Time T12, the signal LE is set at H level to perform a normal operation again.

The timing chart for the operation of loading data in the circuit illustrated inFIG. 11has been described so far.

AlthoughFIG. 11shows a circuit configuration in which both the nodes MD and MDB are set at a ground potential by the initialization operation, another structure may be employed as well. For example, a configuration in which the initialization operation is performed by setting the both nodes at the same potential may be employed. An example of the circuit configuration in which the nodes MD and MDB are set at the same potential is illustrated inFIG. 14. A memory circuit13yillustrated inFIG. 14includes a transistor69for making the nodes MD and MDB at the same potential. The signal LRST is supplied to a gate of the transistor69, and data saving and loading can be performed by the operation described with reference toFIG. 12andFIG. 13.

As described above, in the memory circuit13and the memory portions14_1and14_2described in this embodiment, in the same manner as that of the structure described in Embodiment 1, even when a process of switching from a current routine to a different routine is performed by an interrupt, the data saving or loading process due to the switching can be performed efficiently without causing a lag of memory access or the like.

The structure described above in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

In this embodiment, an example of application modes of the semiconductor device will be described.

An example of the configuration of the semiconductor device of one embodiment of the present invention is illustrated inFIG. 15. A semiconductor device100A illustrated inFIG. 15includes a register controller101, a processor102, a cache109, a bus interface110, and a debug interface111. Furthermore, the processor102includes a control unit103, a program counter (PC)104, a pipeline register105, a pipeline register106, an arithmetic logic unit (ALU)107, and a register file108. The semiconductor device of one embodiment of the present invention can be used in the pipeline register105, the pipeline register106, the register file108, and a register, a flip-flop, or the like included in another circuit.

The control unit103has functions of decoding and executing instructions contained in a program such as inputted applications by controlling the overall operations of the register controller101, the PC104, the pipeline registers105and106, the ALU107, the register file108, the cache109, the bus interface110, and the debug interface111.

The ALU107has a function of performing a variety of arithmetic processes such as four arithmetic processes and logic operations.

The control unit103includes a main memory having a function of storing a program such as an application including a plurality of instructions which are executed in the control unit103, and data used for the arithmetic process performed by the ALU107.

The cache109has a function of temporarily storing frequently used data. The PC104is a register having a function of storing an address of an instruction to be executed next. The pipeline register105has a function of temporarily storing frequently used instructions of instructions (programs) used in the control unit103. Although not illustrated inFIG. 15, the semiconductor device100includes a cache controller for controlling the operation of the cache109.

The register file108includes a plurality of registers including a general purpose register and can save data which is read out from the main memory of the control unit103, data which is obtained during the arithmetic processes in the ALU107, data which is obtained as a result of the arithmetic processes in the ALU107, and the like.

The pipeline register106has a function of temporarily storing data obtained during arithmetic processes performed by the ALU107, data obtained as a result of the arithmetic processes by the ALU107, or the like. The pipeline register106may have a function of temporarily storing a program such as an application.

The bus interface110functions as a path for data between the semiconductor device100A and devices outside the semiconductor device. The debug interface111functions as a path of a signal for inputting an instruction to control debugging to the semiconductor device100A. The bus interface110and the debug interface111are each provided with a register.

The register controller101is a circuit having a function of outputting signals for performing saving or loading between the memory circuit13and the plurality of memory portions14_1to14_nincluded in the pipeline register105, the pipeline register106, the register file108, and the like, in response to an interrupt signal. The signals for saving or loading the data are the signals Sv_1to Sv_n and the signals Ld_1to Ld_n, which are described in detail in Embodiment 1 and not described here.

An example of the flow of the data saving or loading operation between the memory circuit13and the plurality of memory portions14_1to14_nin the semiconductor device100A having the above-described structure will be described.

First, an interrupt signal is supplied to the register controller101. The register controller101saves the data stored in the memory circuit13into any of the plurality of memory portions14_1to14_nthat corresponds to the routine that is under execution of the program processing. Then, if necessary, program processing of the routine that is given a higher priority by the interrupt operation is executed. At this time, if necessary, data in the corresponding memory portion among the plurality of memory portions14_1to14_nmay be loaded into the memory circuit13. After the completion of the higher-priority routine, the data for the previous routine is loaded to execute program processing.

Since the data for restarting the interrupted routine is stored inside the processor102, no access to a stack region of an external memory such as an SRAM or a DRAM is required for data saving or loading. Therefore, even when a process of switching from a current routine to a different routine is performed by an interrupt, the data saving or loading process due to the switching can be performed efficiently without causing a lag of memory access or the like.

The structure described above in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

In this embodiment, an example of a cross-sectional structure of transistors included in a semiconductor device will be described.

FIG. 16illustrates an example of a cross-sectional structure of a semiconductor device.FIG. 16exemplifies cross-sectional structures of the transistors15,17, and18and the capacitor16illustrated inFIG. 4Ain Embodiment 1.

InFIG. 16, the transistor15having a channel formation region in an oxide semiconductor film and the capacitor16are formed over the n-channel transistors17and18each having a channel formation region in a single crystal silicon substrate.

The transistors17and18may each have a channel formation region in a semiconductor film or a semiconductor substrate of silicon, germanium, or the like in an amorphous, microcrystalline, polycrystalline, or single crystal state. Alternatively, the transistors17and18may each have the channel formation region in an oxide semiconductor film or an oxide semiconductor substrate. In the case where channel formation regions of all the transistors are included in an oxide semiconductor film or an oxide semiconductor substrate, the transistor15is not necessarily stacked over the transistors17and18, and all the transistors may be formed in the same layer.

In the case where the transistors17and18are formed using a thin silicon film, any of the following can be used: amorphous silicon formed by sputtering or vapor phase growth such as plasma CVD; polycrystalline silicon obtained by crystallization of amorphous silicon by treatment such as laser annealing; single crystal silicon obtained by separation of a surface portion of a single crystal silicon wafer by implantation of hydrogen ions or the like into the silicon wafer; and the like.

A semiconductor substrate400where the transistors17and18are formed can be, for example, a silicon substrate, a germanium substrate, or a silicon germanium substrate. InFIG. 16, a single crystal silicon substrate is used as the semiconductor substrate400.

The transistors17and18are electrically isolated from each other by an element isolation method. As the element isolation method, a local oxidation of silicon (LOCOS) method, a shallow trench isolation (STI) method, or the like can be employed. InFIG. 16, an example in which the trench isolation method is used to electrically isolate the transistors17and18is shown. Specifically, in the example illustrated inFIG. 16, to electrically isolate the transistors17and18, after trenches are formed in the semiconductor substrate400by etching or the like, element separation regions401are formed by embedding an insulating material such as silicon oxide in the trenches.

An insulating film411is provided over the transistors17and18. Openings are formed in the insulating film411. In the openings, a plurality of conductive films412each connected to any of the sources and drains of the transistors17and18and a conductive film429connected to a conductive film428B that is in the same layer as a gate428A of the transistor18are provided over the insulating film411.

An insulating film414is provided over the insulating film411. An insulating film415having an effect of blocking diffusion of oxygen, hydrogen, and water is provided over the insulating film414. As the insulating film415has higher density and becomes denser or has a fewer dangling bonds and becomes more chemically stable, the insulating film415has a higher blocking effect. The insulating film415that has the effect of blocking diffusion of oxygen, hydrogen, and water can be formed using a film formed of aluminum oxide, aluminum oxynitride, gallium oxide, gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide, hafnium oxynitride, or the like, for example. The insulating film415having an effect of blocking diffusion of hydrogen and water can be formed using a film formed of silicon nitride, silicon nitride oxide, or the like, for example.

An insulating film416is provided over the insulating film415, and the transistor15is provided over the insulating film416.

The transistor15includes an oxide semiconductor film420over the insulating film416; a conductive film421and a conductive film422that are connected to the oxide semiconductor film420and serve as a source and a drain; an insulating film423over the oxide semiconductor film420and the conductive films421and422; and a conductive film424overlapping with the oxide semiconductor film420with the insulating film423positioned therebetween. An opening is provided in the insulating films414to416. In the opening, the conductive film422is connected to the conductive film412that is over the insulating film411and is connected to the conductive film429.

An insulating film427is provided over the conductive film422. A conductive film425is provided over the insulating film427to overlap with the conductive film422. A portion in which the conductive film422, the insulating film427, and the conductive film425overlap with one another serves as the capacitor16.

An insulating film426is provided over the transistors15and the capacitor16.

The structure described above in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

In this embodiment, an example of a transistor that can be used in the semiconductor device of one embodiment of the present invention will be described. In particular, an example of the transistor15described with reference toFIG. 16will be described in this embodiment. Since the transistor15having a channel formation region in an oxide semiconductor film has a low off-state current, it can retain charges corresponding to data for a long time.

FIGS. 17A to 17Cillustrate a structure example of the transistor15having a channel formation region in an oxide semiconductor film.FIG. 17Ais a top view of the transistor15. Note that insulating films are not illustrated inFIG. 17Ain order to clarify the layout of the transistor15.FIG. 17Bis a cross-sectional view along the dashed-dotted line A1-A2in the top view ofFIG. 17A.FIG. 17Cis a cross-sectional view along the dashed-dotted line A3-A4in the top view ofFIG. 17A.

As illustrated inFIGS. 17A to 17C, the transistor15includes an oxide semiconductor film82aand an oxide semiconductor film82bthat are stacked in this order over an insulating film81; a conductive film83and a conductive film84that are electrically connected to the oxide semiconductor film82band function as a source electrode and a drain electrode; an oxide semiconductor film82cover the oxide semiconductor film82b, the conductive film83, and the conductive film84; an insulating film85that functions as an insulating film and is located over the oxide semiconductor film82c; and a conductive film86that functions as a gate electrode, lies over the insulating film85, and overlaps with the oxide semiconductor films82ato82c.

FIGS. 18A to 18Cillustrate another specific example of the structure of the transistor15.FIG. 18Ais a top view of the transistor15. Note that insulating films are not illustrated inFIG. 18Ain order to clarify the layout of the transistor15.FIG. 18Bis a cross-sectional view along the dashed-dotted line A1-A2in the top view ofFIG. 18A.FIG. 18Cis a cross-sectional view along the dashed-dotted line A3-A4in the top view ofFIG. 18A.

As illustrated inFIGS. 18A to 18C, the transistor15includes the oxide semiconductor films82ato82cthat are stacked in this order over the insulating film81; the conductive films83and84that are electrically connected to the oxide semiconductor film82cand function as a source electrode and a drain electrode; the insulating film85that functions as an insulating film and is located over the oxide semiconductor film82c, the conductive film83, and the conductive film84; and the conductive film86that functions as a gate electrode, is over the insulating film85, and overlaps with the oxide semiconductor films82ato82c.

FIGS. 21A to 21Cillustrate another specific example of the structure of the transistor15.FIG. 21Ais a top view of the transistor15. Note that insulating films are not illustrated inFIG. 21Ain order to clarify the layout of the transistor15.FIG. 21Bis a cross-sectional view along the dashed-dotted line A1-A2in the top view ofFIG. 21A.FIG. 21Cis a cross-sectional view along the dashed-dotted line A3-A4in the top view ofFIG. 21A.

As illustrated inFIGS. 21A to 21C, the transistor15includes the oxide semiconductor films82ato82cthat are stacked in this order over the insulating film81; the conductive films83,84,89, and90that are electrically connected to the oxide semiconductor film82cand function as a source electrode and a drain electrode; the insulating film85that functions as an insulating film and is located over the oxide semiconductor film82c, the conductive film83, and the conductive film84; and the conductive film86that functions as a gate electrode, is over the insulating film85, and overlaps with the oxide semiconductor films82ato82c.

The layers89and90are layers having a function of not forming a Schottky barrier with the oxide semiconductor films82ato82cand the like. For example, these layers are layers of a transparent conductor, an oxide semiconductor, a nitride semiconductor, or an oxynitride semiconductor. More specifically, the layers89and90may be formed using a layer containing indium, tin, and oxygen, a layer containing indium and zinc, a layer containing indium, tungsten, and zinc, a layer containing tin and zinc, a layer containing zinc and gallium, a layer containing zinc and aluminum, a layer containing zinc and fluorine, a layer containing zinc and boron, a layer containing tin and antimony, a layer containing tin and fluorine, a layer containing titanium and niobium, or the like. Alternatively, any of these layers may contain hydrogen, carbon, nitrogen, silicon, germanium, or argon. With the structure including the layers89and90, on-state characteristics of the transistor can be improved.

FIGS. 17A to 17CandFIGS. 18A to 18Ceach illustrate the structure example of the transistor15in which the oxide semiconductor films82ato82care stacked. However, the structure of the oxide semiconductor film included in the transistor15is not limited to a stacked-layer structure including a plurality of oxide semiconductor films and may be a single-layer structure.

In the case where the transistor15includes the oxide semiconductor films82ato82cstacked in this order, each of the oxide semiconductor films82aand82cis an oxide film that contains at least one of metal elements contained in the oxide semiconductor film82band in which the conduction band minimum is closer to the vacuum level than that in the oxide semiconductor film82bis by higher than or equal to 0.05 eV, 0.07 eV, 0.1 eV, or 0.15 eV and lower than or equal to 2 eV, 1 eV, 0.5 eV, or 0.4 eV. The oxide semiconductor film82bpreferably contains at least indium because carrier mobility is increased.

In the case where the transistor15includes the semiconductor films with the above structure, when an electric field is applied to the semiconductor films by applying voltage to the gate electrode, a channel region is formed in the oxide semiconductor film82b, which has the lowest conduction band minimum among the semiconductor films. That is, the oxide semiconductor film82cprovided between the oxide semiconductor film82band the insulating film85makes it possible to form the channel region in the oxide semiconductor film82b, which is separated from the insulating film85.

Since the oxide semiconductor film82ccontains at least one of the metal elements contained in the oxide semiconductor film82b, interface scattering is less likely to occur at the interface between the oxide semiconductor film82band the oxide semiconductor film82c. Thus, the movement of carriers is less likely to be inhibited at the interface, which results in an increase in the field-effect mobility of the transistor15.

In the case where gallium oxide is used for the oxide semiconductor film82c, indium in the oxide semiconductor film82bcan be prevented from being diffused into the insulating film85; thus, the leakage current of the transistor15can be reduced.

When an interface level is formed at the interface between the oxide semiconductor film82band the oxide semiconductor film82a, a channel region is formed also in the vicinity of the interface, which causes a change in the threshold voltage of the transistor15. However, since the oxide semiconductor film82acontains at least one of the metal elements contained in the oxide semiconductor film82b, an interface level is less likely to be formed at the interface between the oxide semiconductor film82band the oxide semiconductor film82a. Accordingly, the above structure allows reducing of variations in the electrical characteristics of the transistor15, such as the threshold voltage.

Further, it is preferable that a plurality of oxide semiconductor films be stacked so that an interface level due to an impurity existing between the oxide semiconductor films, which inhibits carrier flow, is not formed at the interface between the oxide semiconductor films. This is because when an impurity exists between the stacked oxide semiconductor films, the continuity of the conduction band minimum between the oxide semiconductor films is lost, and carriers are trapped or disappear by recombination in the vicinity of the interface. By reducing an impurity existing between the films, a continuous junction (here, in particular, a U-shape well structure whose conduction band minimum is changed continuously between the films) is formed more easily than the case of merely stacking a plurality of oxide semiconductor films which contain at least one metal in common as a main component.

In order to form such a continuous junction, the films need to be stacked successively without being exposed to the air by using a multi-chamber deposition system (sputtering apparatus) provided with a load lock chamber. Each chamber of the sputtering apparatus is preferably evacuated to a high vacuum (to approximately 5×10−7Pa to 1×10−4Pa) by an adsorption vacuum pump such as a cryopump so that water and the like acting as impurities for the oxide semiconductor are removed as much as possible. Alternatively, a turbo molecular pump and a cold trap are preferably used in combination to prevent backflow of gas into the chamber through an evacuation system.

To obtain a highly purified intrinsic oxide semiconductor, not only high vacuum evacuation of the chambers but also high purification of a gas used in the sputtering is important. When an oxygen gas or an argon gas used as the above gas has a dew point of −40° C. or lower, preferably −80° C. or lower, further preferably −100° C. or lower and is highly purified, moisture and the like can be prevented from entering the oxide semiconductor film as much as possible. Specifically, in the case where the oxide semiconductor film82bis an In-M-Zn oxide film (M is Ga, Y, Zr, La, Ce, or Nd) and a target having the atomic ratio of metal elements of In:M:Zn=x1:y1:z1is used for forming the oxide semiconductor film82b, x1/y1is preferably greater than or equal to ⅓ and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6, and z1/y1is preferably greater than or equal to ⅓ and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6. Note that when z1/y1is greater than or equal to 1 and less than or equal to 6, a CAAC-OS film to be described later as the oxide semiconductor film82bis easily formed. Typical examples of the atomic ratio of the metal elements of the target are In:M:Zn=1:1:1 and In:M:Zn=3:1:2.

Specifically, in the case where the oxide semiconductor films82aand82ccontain an In-M-Zn oxide (M is Ga, Y, Zr, La, Ce, or Nd), it is preferable that x2/y2<x1/y1be satisfied and z2/y2be greater than or equal to ⅓ and less than or equal to 6, further preferably greater than or equal to 1 and less than or equal to 6 when the atomic ratio of metal elements of In to M and Zn in a target for forming the oxide semiconductor films82aand82cis x2:y2:z2. Note that when z2/y2is greater than or equal to 1 and less than or equal to 6, CAAC-OS films as the oxide semiconductor films82aand82care easily formed. Typical examples of the atomic ratio of metal elements of In to M and Zn in the target include 1:3:2, 1:3:4, 1:3:6, and 1:3:8.

The oxide semiconductor films82aand82ceach have a thickness greater than or equal to 3 nm and less than or equal to 100 nm, preferably greater than or equal to 3 nm and less than or equal to 50 nm. The thickness of the oxide semiconductor film82bis greater than or equal to 3 nm and less than or equal to 200 nm, preferably greater than or equal to 3 nm and less than or equal to 100 nm, further preferably greater than or equal to 3 nm and less than or equal to 50 nm.

The three oxide semiconductor films (the oxide semiconductor films82ato82c) can be either amorphous or crystalline. However, when the oxide semiconductor film82bwhere a channel region is formed is crystalline, the transistor15can have stable electrical characteristics; therefore, the oxide semiconductor film82bis preferably crystalline.

Note that a channel formation region refers to a region of the semiconductor film of the transistor15that overlaps with the gate electrode and is located between the source electrode and the drain electrode. A channel region refers to a region through which current mainly flows in the channel formation region.

For example, when an In—Ga—Zn oxide film formed by a sputtering method is used as each of the oxide semiconductor films82aand82c, the oxide semiconductor films82aand82ccan be deposited with the use of an In—Ga—Zn oxide target containing In, Ga, and Zn in an atomic ratio of 1:3:2. The deposition conditions can be as follows: an argon gas (flow rate: 30 sccm) and an oxygen gas (flow rate: 15 sccm) are used as the deposition gas; the pressure is 0.4 Pa; the substrate temperature is 200° C.; and the DC power is 0.5 kW.

Further, in the case where the oxide semiconductor film82bis a CAAC-OS film, the oxide semiconductor film82bis preferably deposited with use of a polycrystalline target including an In—Ga—Zn oxide (In:Ga:Zn=1:1:1 in an atomic ratio). The deposition conditions can be as follows: an argon gas (flow rate: 30 sccm) and an oxygen gas (flow rate: 15 sccm) are used as the deposition gas; the pressure is 0.4 Pa; the substrate temperature is 300° C.; and the DC power is 0.5 kW.

There are few carrier generation sources in a highly purified oxide semiconductor (purified oxide semiconductor) obtained by reduction of impurities such as moisture and hydrogen serving as electron donors (donors) and reduction of oxygen vacancies; therefore, the highly purified oxide semiconductor can be an intrinsic (i-type) semiconductor or a substantially i-type semiconductor. For this reason, a transistor having a channel formation region in a highly purified oxide semiconductor film has extremely small off-state current and high reliability. Thus, a transistor having a channel formation region in the oxide semiconductor film easily has an electrical characteristic of positive threshold voltage (also referred to as a normally-off characteristic).

Specifically, various experiments can prove small off-state current of a transistor having a channel formation region in a highly purified oxide semiconductor. For example, even when an element has a channel width of 1×106μm and a channel length of 10 μm, off-state current can be less than or equal to the measurement limit of a semiconductor parameter analyzer, i.e., less than or equal to 1×10−13A, at voltage (drain voltage) between the source electrode and the drain electrode of 1 V to 10 V. In that case, it can be seen that off-state current normalized on the channel width of the transistor is lower than or equal to 100 zA/μm. In addition, a capacitor and a transistor are connected to each other and the off-state current is measured with a circuit in which charge flowing into or from the capacitor is controlled by the transistor. In the measurement, a highly-purified oxide semiconductor film was used for a channel formation region of the transistor, and the off-state current of the transistor was measured from a change in the amount of charge in the capacitor per unit hour. As a result, it was found that, in the case where the voltage between the source electrode and the drain electrode of the transistor is 3 V, a lower off-state current of several tens of yA/μm is obtained. Accordingly, the off-state current of the transistor in which the purified oxide semiconductor film is used as a channel formation region is considerably lower than that of a transistor in which silicon having crystallinity is used.

In the case where an oxide semiconductor film is used as the semiconductor film, at least indium (In) or zinc (Zn) is preferably included as an oxide semiconductor. As a stabilizer for reducing variation in electrical characteristics of a transistor using the oxide semiconductor, gallium (Ga) is preferably additionally contained. Tin (Sn) is preferably contained as a stabilizer. Hafnium (Hf) is preferably contained as a stabilizer. Aluminum (Al) is preferably contained as a stabilizer. Zirconium (Zr) is preferably contained as a stabilizer.

Among the oxide semiconductors, unlike silicon carbide, gallium nitride, or gallium oxide, an In—Ga—Zn oxide, an In—Sn—Zn oxide, or the like has an advantage of high mass productivity because a transistor with favorable electrical characteristics can be formed by sputtering or a wet process. Further, unlike silicon carbide, gallium nitride, or gallium oxide, with the use of the In—Ga—Zn oxide, a transistor with favorable electrical characteristics can be formed over a glass substrate. Further, a larger substrate can be used.

Note that, for example, an In—Ga—Zn oxide means an oxide containing In, Ga, and Zn and there is no particular limitation on the ratio of In:Ga:Zn. Further, the In—Ga—Zn oxide may contain a metal element other than In, Ga, and Zn. The In—Ga—Zn oxide has sufficiently high resistance when no electric field is applied thereto, so that off-state current can be sufficiently reduced. Further, the In—Ga—Zn oxide has high mobility.

For example, with an In—Sn—Zn oxide, high mobility can be realized relatively easily. However, even with an In—Ga—Zn oxide, mobility can be increased by reducing the defect density in the bulk.

Furthermore, in the transistor15, a metal in the source electrode and the drain electrode might extract oxygen from the oxide semiconductor film depending on a conductive material used for the source electrode and the drain electrode. In this case, regions of the oxide semiconductor film in contact with the source electrode and the drain electrode become n-type regions due to the formation of oxygen vacancies. The n-type regions serve as a source region and a drain region, resulting in a decrease in the contact resistance between the oxide semiconductor film and the source electrode and between the oxide semiconductor film and the drain electrode. Accordingly, the formation of the n-type regions increases the mobility and on-state current of the transistor15, achieving the high-speed operation of a semiconductor device using the transistor15.

Note that the extraction of oxygen by a metal in the source electrode and the drain electrode is probably caused when the source electrode and the drain electrode are formed by a sputtering method or the like or when heat treatment is performed after the formation of the source electrode and the drain electrode. The n-type regions are more likely to be formed by forming the source electrode and the drain electrode with the use of a conductive material that is easily bonded to oxygen. Examples of such a conductive material include Al, Cr, Cu, Ta, Ti, Mo, and W.

Furthermore, in the case where the semiconductor film including the stacked oxide semiconductor films is used in the transistor15, the regions having n-type conductivity preferably extend to the oxide semiconductor film82bserving as a channel region in order that the mobility and on-state current of the transistor15can be further increased and the semiconductor device can operate at higher speed.

The insulating film81preferably has a function of supplying part of oxygen to the oxide semiconductor films82ato82cby heating. It is preferable that the number of defects in the insulating film81be small, and typically the spin density of g=2.001 due to a dangling bond of silicon be lower than or equal to 1×1018spins/cm3. The spin density is measured by ESR spectroscopy.

The insulating film81, which has a function of supplying part of the oxygen to the oxide semiconductor films82ato82cby heating, is preferably an oxide. Examples of the oxide include aluminum oxide, magnesium oxide, silicon oxide, silicon oxynitride, silicon nitride oxide, gallium oxide, germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide. The insulating film81can be formed by a plasma chemical vapor deposition (CVD) method, a sputtering method, or the like.

Note that in this specification, oxynitride contains more oxygen than nitrogen, and nitride oxide contains more nitrogen than oxygen.

Note that in the transistor15illustrated inFIGS. 17A to 17CandFIGS. 18A to 18C, the conductive film86overlaps with end portions of the oxide semiconductor film82bincluding a channel region that do not overlap with the conductive films83and84, i.e., end portions of the oxide semiconductor film82bthat are in a region different from a region where the conductive films83and84are located. When the end portions of the oxide semiconductor film82bare exposed to plasma by etching for forming the end portions, chlorine radical, fluorine radical, or the like generated from an etching gas is easily bonded to a metal element contained in the oxide semiconductor. For this reason, in the end portions of the oxide semiconductor film, oxygen bonded to the metal element is easily eliminated, so that an oxygen vacancy is easily formed; thus, the oxide semiconductor film easily has n-type conductivity. However, an electric field applied to the end portions can be adjusted by controlling the potentials of the conductive film86because the end portions of the oxide semiconductor film82bthat do not overlap with the conductive films83and84overlap with the conductive film86in the transistor15illustrated inFIGS. 17A to 17CandFIGS. 18A to 18C. Consequently, the flow of current between the conductive films83and84through the end portions of the oxide semiconductor film82bcan be controlled by the potential supplied to the conductive film86. Such a structure of the transistor15is referred to as a surrounded channel (s-channel) structure.

With the s-channel structure, specifically, when a potential at which the transistor15is turned off is supplied to the conductive film86, the amount of off-state current that flows between the conductive films83and84through the end portions of the oxide semiconductor film82bcan be reduced. For this reason, in the transistor15, even when the distance between the conductive films83and84at the end portions of the oxide semiconductor film82bis reduced as a result of reducing the channel length to obtain high on-state current, the transistor15can have low off-state current. Consequently, with the short channel length, the transistor15can have high on-state current when in an on state and low off-state current when in an off state.

With the s-channel structure, specifically, when a potential at which the transistor15is turned on is supplied to the conductive film86, the amount of current that flows between the conductive films83and84through the end portions of the oxide semiconductor film82bcan be increased. The current contributes to an increase in the field-effect mobility and an increase in on-state current of the transistor15. When the end portions of the oxide semiconductor film82boverlap with the conductive film86, carriers flow in a wide region of the oxide semiconductor film82bas well as in a region in the vicinity of the interface between the oxide semiconductor film82band the insulating film85, which results in an increase in carrier mobility the transistor15. As a result, the on-state current of the transistor15is increased, and the field-effect mobility is increased to greater than or equal to 10 cm2/V·s or to greater than or equal to 20 cm2/V·s, for example. Note that here, the field-effect mobility is not an approximate value of the mobility as the physical property of the oxide semiconductor film but is an index of current drive capability and the apparent field-effect mobility of a saturation region of the transistor.

A structure of the oxide semiconductor film is described below.

An oxide semiconductor film is classified roughly into a single-crystal oxide semiconductor film and a non-single-crystal oxide semiconductor film. The non-single-crystal oxide semiconductor film includes any of an amorphous oxide semiconductor film, a microcrystalline oxide semiconductor film, a polycrystalline oxide semiconductor film, a c-axis aligned crystalline oxide semiconductor (CAAC-OS) film, and the like.

The amorphous oxide semiconductor film has disordered atomic arrangement and no crystalline component. A typical example thereof is an oxide semiconductor film in which no crystal part exists even in a microscopic region, and the whole of the film is amorphous.

The microcrystalline oxide semiconductor film includes a microcrystal (also referred to as nanocrystal) with a size greater than or equal to 1 nm and less than 10 nm, for example. Thus, the microcrystalline oxide semiconductor film has a higher degree of atomic order than the amorphous oxide semiconductor film. Hence, the density of defect states of the microcrystalline oxide semiconductor film is lower than that of the amorphous oxide semiconductor film.

The CAAC-OS film is one of oxide semiconductor films including a plurality of crystal parts, and most of the crystal parts each fit inside a cube whose one side is less than 100 nm. Thus, there is a case where a crystal part included in the CAAC-OS film fits inside a cube whose one side is less than 10 nm, less than 5 nm, or less than 3 nm. The density of defect states of the CAAC-OS film is lower than that of the microcrystalline oxide semiconductor film. In a transmission electron microscope (TEM) image of the CAAC-OS film, a boundary between crystal parts, that is, a grain boundary is not clearly observed. Thus, in the CAAC-OS film, a reduction in electron mobility due to the grain boundary is less likely to occur.

In the cross-sectional TEM image of the CAAC-OS film observed in a direction substantially parallel to the sample surface, metal atoms arranged in a layered manner are seen in the crystal parts. Each metal atom layer has a shape that reflects a surface over which the CAAC-OS film is formed (hereinafter, a surface over which the CAAC-OS film is formed is referred to as a formation surface) or a top surface of the CAAC-OS film, and is arranged parallel to the formation surface or the top surface of the CAAC-OS film.

From the results of the cross-sectional TEM observation and the plan-view TEM observation, alignment is found in the crystal parts in the CAAC-OS film.

Further, the degree of crystallinity in the CAAC-OS film is not necessarily uniform. For example, in the case where crystal growth leading to the CAAC-OS film occurs from the vicinity of the top surface of the film, the degree of crystallinity in the vicinity of the top surface is higher than that in the vicinity of the formation surface in some cases. Further, when an impurity is added to the CAAC-OS film, the degree of crystallinity in a region to which the impurity is added is changed, and the degree of crystallinity in the CAAC-OS film varies depending on regions.

In a transistor including the CAAC-OS film, a change in electrical characteristics due to irradiation with visible light or ultraviolet light is small. Thus, the transistor has high reliability.

Note that an oxide semiconductor film may be a stacked film including two or more kinds of an amorphous oxide semiconductor film, a microcrystalline oxide semiconductor film, and a CAAC-OS film, for example.

For the deposition of the CAAC-OS film, the following conditions are preferably used.

By reducing the amount of impurities entering the CAAC-OS film during the deposition, the crystal state can be prevented from being broken by the impurities. For example, the concentration of impurities (e.g., hydrogen, water, carbon dioxide, and nitrogen) that exist in the treatment chamber may be reduced. Furthermore, the concentration of impurities in a deposition gas may be reduced. Specifically, a deposition gas whose dew point is −80° C. or lower, preferably −100° C. or lower is used.

By increasing the substrate heating temperature during the deposition, migration of a sputtered particle is likely to occur after the sputtered particle reaches a substrate surface. Specifically, the substrate heating temperature during the deposition is higher than or equal to 100° C. and lower than or equal to 740° C., preferably higher than or equal to 200° C. and lower than or equal to 500° C. By increasing the substrate heating temperature during the deposition, when the flat-plate-like or pellet-like sputtered particle reaches the substrate, migration occurs on the substrate surface, so that a flat plane of the sputtered particles is attached to the substrate.

Furthermore, it is preferable that the proportion of oxygen in the deposition gas be increased and the power be optimized in order to reduce plasma damage at the deposition. The proportion of oxygen in the deposition gas is higher than or equal to 30 vol %, preferably 100 vol %.

As an example of the target, an In—Ga—Zn oxide target is described below.

The In—Ga—Zn oxide target, which is polycrystalline, is made in the following manner: InOXpowder, GaOYpowder, and ZnOZpowder are mixed in a predetermined molar ratio, pressure is applied to the mixture, and heat treatment is performed at a temperature of higher than or equal to 1000° C. and lower than or equal to 1500° C. Note that X, Y, and Z are each a given positive number. Here, the predetermined molar ratio of InOXpowder to GaOYpowder and ZnOZpowder is, for example, 2:2:1, 8:4:3, 3:1:1, 1:1:1, 4:2:3, 4:2:4.1, or 3:1:2. The kinds of powder and the molar ratio for mixing powder may be determined as appropriate depending on the desired target.

An alkali metal is not an element included in an oxide semiconductor and thus is an impurity. Also, alkaline earth metal is an impurity in the case where the alkaline earth metal is not a component of the oxide semiconductor. Alkali metal, in particular, Na becomes Na+when an insulating film in contact with the oxide semiconductor film is an oxide and Na diffuses into the insulating film. Further, in the oxide semiconductor film, Na cuts or enters a bond between metal and oxygen that are included in the oxide semiconductor. As a result, for example, degradation of electrical characteristics of a transistor, such as a normally-on state of the transistor due to shift of the threshold voltage in the negative direction or reduction in mobility, occurs. In addition, variations in electrical characteristics also occur. Specifically, the Na concentration according to secondary ion mass spectrometry is reduced to preferably less than or equal to 5×1016/cm3, further preferably less than or equal to 1×1016/cm3, still further preferably less than or equal to 1×1015/cm3. In a similar manner, the measurement value of Li concentration is preferably less than or equal to 5×1015/cm3, further preferably less than or equal to 1×1015/cm3. In a similar manner, the measurement value of K concentration is preferably less than or equal to 5×1015/cm3, further preferably less than or equal to 1×1015/cm3.

In the case where a metal oxide containing indium is used, silicon or carbon having higher bond energy with oxygen than indium might cut the bond between indium and oxygen, so that an oxygen vacancy is formed. Accordingly, when silicon or carbon is contained in the oxide semiconductor film, the electrical characteristics of the transistor are likely to deteriorate as in the case of using an alkali metal or an alkaline earth metal. Thus, the concentration of silicon and the concentration of carbon in the oxide semiconductor film are preferably low. Specifically, the carbon concentration or the silicon concentration measured by secondary ion mass spectrometry is preferably less than or equal to 1×1018/cm3. In that case, the deterioration of the electrical characteristics of the transistor can be prevented, so that the reliability of the semiconductor device can be improved.

The structure described above in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

In this embodiment, an example of a chip including the semiconductor device of one embodiment of the present invention and an example of a module of an electronic device are described.

FIG. 19Ais a perspective view illustrating a cross-sectional structure of a package using a lead frame interposer.

In the package illustrated inFIG. 19A, a chip751corresponding to the semiconductor device of one embodiment of the present invention is connected to a terminal752over an interposer750by a wire bonding method. The terminal752is placed on a surface of the interposer750on which the chip751is mounted. The chip751can be sealed by a mold resin753, in which case the chip751is sealed so that part of each of the terminals752is exposed.

FIG. 19Billustrates the structure of a module of an electronic device in which the package is mounted on a circuit board.

In the module of a mobile phone illustrated inFIG. 19B, a package802and a battery804are mounted on a printed wiring board801. In addition, the printed wiring board801is mounted on a panel800including a display element by an FPC803.

The structure described above in this embodiment can be combined as appropriate with any of the structures described in the other embodiments.

The semiconductor device of one embodiment of the present invention can be used for display devices, personal computers, and image reproducing devices provided with recording media (typically, devices that reproduce the content of recording media such as digital versatile discs (DVDs) and have displays for displaying the reproduced images). Other examples of electronic devices that can include the semiconductor device of one embodiment of the present invention are mobile phones, game machines including portable game machines, portable information terminals, e-book readers, cameras such as video cameras and digital still cameras, goggle-type displays (head mounted displays), navigation systems, audio reproducing devices (e.g., car audio systems and digital audio players), copiers, facsimiles, printers, multifunction printers, automated teller machines (ATM), and vending machines. Specific examples of these electronic devices are illustrated inFIGS. 20A to 20F.

FIG. 20Aillustrates a portable game machine, which includes a housing5001, a housing5002, a display portion5003, a display portion5004, a microphone5005, speakers5006, a control key5007, a stylus5008, and the like. The semiconductor device of one embodiment of the present invention can be used for a variety of integrated circuits included in the portable game machine. Note that although the portable game machine inFIG. 20Ahas the two display portions5003and5004, the number of display portions included in the portable game machine is not limited thereto.

FIG. 20Billustrates a portable information terminal, which includes a first housing5601, a second housing5602, a first display portion5603, a second display portion5604, a joint5605, an operation key5606, and the like. The first display portion5603is provided in the first housing5601, and the second display portion5604is provided in the second housing5602. The first housing5601and the second housing5602are connected to each other with the joint5605, and the angle between the first housing5601and the second housing5602can be changed with the joint5605. An image on the first display portion5603may be switched depending on the angle between the first housing5601and the second housing5602at the joint5605. The semiconductor device of one embodiment of the present invention can be used for a variety of integrated circuits included in the portable information terminal. A display device with a position input function may be used as at least one of the first display portion5603and the second display portion5604. Note that the position input function can be added by providing a touch panel in a display device. Alternatively, the position input function can be added by provision of a photoelectric conversion element called a photosensor in a pixel area of a display device.

FIG. 20Cillustrates a notebook personal computer, which includes a housing5401, a display portion5402, a keyboard5403, a pointing device5404, and the like. The semiconductor device of one embodiment of the present invention can be used for a variety of integrated circuits included in the notebook personal computer.

FIG. 20Dillustrates an electric refrigerator-freezer, which includes a housing5301, a door for a refrigerator5302, a door for a freezer5303, and the like. The semiconductor device of one embodiment of the present invention can be used for a variety of integrated circuits included in the electric refrigerator-freezer.

FIG. 20Eillustrates a video camera, which includes a first housing5801, a second housing5802, a display portion5803, operation keys5804, a lens5805, a joint5806, and the like. The operation keys5804and the lens5805are provided for the first housing5801, and the display portion5803is provided for the second housing5802. The semiconductor device of one embodiment of the present invention can be used for a variety of integrated circuits included in the video camera. The first housing5801and the second housing5802are connected to each other with the joint5806, and the angle between the first housing5801and the second housing5802can be changed with the joint5806. Images displayed on the display portion5803may be switched in accordance with the angle at the joint5806between the first housing5801and the second housing5802.

FIG. 20Fillustrates a motor vehicle, which includes a car body5101, wheels5102, a dashboard5103, lights5104, and the like. The semiconductor device of one embodiment of the present invention can be used for a variety of integrated circuits included in the motor vehicle.

This application is based on Japanese Patent Application serial no. 2014-122062 filed with Japan Patent Office on Jun. 13, 2014, the entire contents of which are hereby incorporated by reference.