JP4689181B2 - Semiconductor device, CPU, image processing circuit, and electronic apparatus - Google Patents

Description

  The present invention relates to a semiconductor device, and more particularly to a semiconductor device composed of a thin film semiconductor element and an electronic apparatus including the semiconductor device. The present invention also relates to a method for driving a semiconductor device.

  In recent years, with the advance of communication technology, mobile phones have become widespread. In the future, transmission of moving images and transmission of more information are expected. On the other hand, personal computers are also being produced with mobile-friendly products due to their light weight. A large number of information terminals called PDAs that have begun in electronic notebooks are also being produced and spread. In such portable information devices, many semiconductor devices such as a CPU (Central Processing Unit) are used.

  There are various types of semiconductor devices. As an example, a block diagram of a CPU is shown in FIG. A CPU 1001 shown here includes a timing control circuit 1002, an instruction analysis decoder 1003, a register array 1004, an address logic buffer circuit 1005, a data bus interface 1006, an ALU 1007, an instruction register 1008, and the like.

  Here, each circuit will be briefly described. The timing control circuit receives an external command, converts it into information for internal use, and sends it to other blocks. In addition, instructions such as reading and writing of memory data are given to the outside in accordance with internal operations. The instruction analysis decoder 1003 has a role of converting an external instruction into an internal instruction. The register array 1004 is a volatile memory that temporarily stores data. The address logic buffer circuit 1005 is a circuit for designating an address of the external memory. The data bus interface 1006 is a circuit that inputs / outputs data to / from an external memory or a device such as a printer. The ALU 1007 is a circuit that performs an operation. The instruction register 1008 is a circuit for temporarily storing instructions. The CPU is configured by such a combination of circuits.

  In recent years, semiconductor devices such as CPUs using an insulator instead of a silicon substrate have appeared. Such a semiconductor device is called SOI (Silicon On Insulator) and has been developed. By using the substrate as an insulator, parasitic capacitance between the transistor and the substrate can be reduced, and high speed and low power can be achieved. In particular, it is used for portable electronic devices to reduce power consumption. In an electronic device using a semiconductor device that consumes a large amount of power, there are problems that a required battery becomes large and a cooling fan is required, and the electronic device itself becomes large.

  Therefore, there is a device that provides a composite semiconductor device having a structure in which a wiring board and a package are bonded so that high thermal conductivity and low elasticity are simultaneously satisfied.

Japanese Patent Laid-Open No. 7-74282

  FIG. 11 shows an example of a two-stage inverter circuit of a semiconductor device using a conventional silicon substrate. In this example, the inverter circuit includes Pch transistors 1102 and 1104 and Nch transistors 1101 and 1103.

  FIG. 12 shows an example of a two-stage inverter circuit of a semiconductor device using an SOI substrate. In this example, the inverter circuit includes Pch transistors 1202 and 1204 and Nch transistors 1201 and 1203.

As described above, SOI is a very effective means for power saving of portable electronic devices, but the following problems remain.
FIG. 13 is a graph showing the relationship between the drain current and gate voltage of an N-type MOS transistor. Ideally, when the gate voltage Vg is positive, the drain current Id is sufficiently large. When the gate voltage Vg is 0 or less, the drain current Id is preferably 0. Actually, however, a drain current Id flows as much as IL even when the gate voltage Vg is 0 as shown by a curve 1301. Although the current of each transistor is not large, in the present LSI, millions of transistors are provided, and when these leakage currents are combined, it is never small. Such a leakage current has been a cause of increasing power consumption of the semiconductor device during standby.

  This leakage current can be reduced by adding a small amount of impurities to the channel region of the transistor and shifting the curve shown in FIG. 13 to the right. However, in that case, the current when Vg is positive also decreases, and there is a problem that the frequency characteristics of the circuit are deteriorated.

  In the circuit shown in FIG. 11, in a conventional semiconductor device using a silicon substrate, the semiconductor region in contact with the lower side of the channel is connected to GND or a power source, and a fixed potential is applied. Therefore, the Id-Vg curve is fixed, and the above-described problem occurs. In the circuit shown in FIG. 12, in the semiconductor device using the SOI substrate, the semiconductor region in contact with the lower side of the channel is either floating or does not exist. Therefore, the Id-Vg curve is fixed, and the above-described problem occurs.

  In view of the above problems, an object of the present invention is to provide a semiconductor device with low power consumption due to leakage current, a driving method thereof, and an electronic apparatus using the semiconductor device.

  In order to solve the above problems, the present invention provides a gate electrode on each side of a semiconductor thin film constituting a transistor, a logic signal is applied to the first gate electrode, and a threshold control signal is applied to the second gate electrode. In addition, a semiconductor device in which the threshold value of a transistor included in the semiconductor device is variable depending on the potential of a second gate electrode and a driving method thereof are provided. Then, a semiconductor device provided with a plurality of logic circuits including such a back gated transistor and a driving method thereof are provided. That is, the power consumption due to leakage current becomes a problem when there are many periods in which the state change of the transistor is small. Such a state is often in the standby mode. On the other hand, during the period when the circuit is operating frequently, the power consumption is determined by the on-state characteristics of the transistor, and the leakage current can be ignored. Such a mode is an active mode.

  The distinction between the standby mode and the active mode is controlled by detection means (for example, a program) that controls the threshold control circuit, and the threshold value of the transistor can be changed by using the detection means and the threshold control circuit. . Accordingly, since the threshold value of the transistor can be set high during standby, power consumption due to leakage current can be reduced.

  The present invention includes a logic circuit including a thin film transistor on an insulating surface, and detection means for detecting an operation frequency of the logic circuit and outputting the detection result to a threshold control circuit. A first gate electrode to which a signal is input and a second gate electrode to which a threshold control signal is input from the threshold control circuit, and the source of the thin film transistor is generated by the threshold control signal The amount of current flowing between the electrode and the drain electrode is controlled. A semiconductor thin film is provided on the second gate electrode, and the first gate electrode is provided on the semiconductor thin film.

  The present invention relates to a logic circuit including a thin film transistor on an insulating surface, and a memory in which a program for detecting the operation frequency of the logic circuit and outputting the detection result to a threshold control circuit is recorded. The thin film transistor includes a first gate electrode to which a logic signal is input, and a second gate electrode to which a threshold control signal is input from the threshold control circuit. The amount of current flowing between the source electrode and the drain electrode of the thin film transistor is controlled by a threshold control signal.

  The semiconductor device is a CPU or an image processing circuit.

  The present invention includes a logic circuit including a thin film transistor on an insulating surface, and detection means for detecting an operation frequency of the logic circuit and outputting the detection result to a threshold control circuit. When the mode or active mode is determined and the detection means determines the standby mode, the threshold control circuit outputs the threshold control signal for increasing the threshold of the thin film transistor to the logic circuit. It is characterized by that.

  As described above, in the present invention, the threshold value of the transistor can be set high during standby, and the leakage current can be reduced. As a result, the battery can be miniaturized, and an electronic device that is small, lightweight, and has low power consumption can be realized.

  In the present invention, power consumption during standby is reduced by providing a back gate in a transistor and controlling the back gate voltage by a detection unit (a storage medium on which a program is recorded). As a result, the battery can be made small, and an electronic device with a small volume can be realized. A reduction in size, weight and thickness are achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of this embodiment mode.

  FIG. 1 shows a semiconductor device using the present invention. There are various types of semiconductor devices. As an example, a block diagram of a CPU is shown in FIG. The CPU 101 shown here includes a timing control circuit 102, an instruction analysis decoder 103, a register array 104, an address logic buffer circuit 105, a data bus interface 106, an ALU 107, an instruction register 108, and the like. The above is the same as the conventional example, but the threshold value control circuit 109 is added in the block diagram of FIG. The threshold control circuit supplies threshold control signals to other logic circuits.

  This threshold control signal is sent to a transistor that varies the threshold. FIG. 2 will be described using an example of a two-stage inverter circuit. In this example, the inverter circuit is composed of Pch transistors 202 and 204 and Nch transistors 201 and 203. What is different from the prior art is that a transistor with a back gate having gate electrodes on both sides of the channel is used in the present invention. A logic signal is applied to the first gate electrode and a threshold control is applied to the second gate electrode. The signal is to be added. The threshold control signal is supplied via the Pch threshold control line and the Nch threshold control line.

  FIG. 3 shows Id-Vg characteristics of a transistor having first and second gate electrodes. Although three types of curves 301 to 303 are shown in FIG. 3, the curve 302 is a curve when a positive fixed voltage is applied to the second gate electrode. In such a case, the curve shifts to the left and more current flows. A curve 301 is a case where a voltage of 0 is applied to the second gate electrode. Such a case is the same as the conventional example. A curve 303 is a curve when a negative voltage is applied to the second gate electrode. In such a case, the curve shifts to the right, current becomes difficult to flow, and leakage current is also reduced. Thus, by providing the inverter circuit with a threshold control function and shifting the Id-Vg curve, the leakage current can be reduced.

  Next, the operation method will be described with reference to FIG. The semiconductor device of the present invention is equipped with detection means (for example, a program, a storage medium on which the program is recorded, and software) for controlling the threshold value of the transistor. This detection means calls a program for detecting the operation frequency of the semiconductor device (logic circuit) and threshold control data from a memory inside or outside the semiconductor device when the detection exceeds a certain level, and activates the threshold control circuit. It consists of a program that runs.

  The operation frequency detection program counts how many times an instruction in a certain time is used, and can detect the operation frequency according to the count number. That is, the number of times of use within a predetermined time is set, and if the number of times of detection within that period is less than a certain value, the first mode is determined, and if it exceeds a certain value, the second mode is determined. Of course, the determination method is not limited to this. Here, if the first mode is the standby mode and the second mode is the activation mode, the determination can be made during standby and during activation, and the threshold value is controlled accordingly.

  In this way, the threshold control circuit is provided inside the semiconductor device, and the detection unit detects the mode of the semiconductor device and controls the threshold control circuit, so that the power consumption of the semiconductor device is adjusted to the situation. It can be kept low.

  The semiconductor device of this embodiment can be used as a CPU, an image processing device, or the like.

Example 1
FIG. 5 shows a cross-sectional view of a thin film transistor constituting the semiconductor device of the present invention. The manufacturing process will be described below. A base film 502 is formed over the insulating substrate 501 to form second gate electrodes 503 and 504. Next, a gate insulating film 505 for the second gate electrode is formed, and further semiconductor thin film regions 506 and 507 are formed. Next, first gate electrode gate insulating films 508 and 509 are formed, and first gate electrodes 510 and 511 are formed. After adding P-type impurities and N-type impurities to form source / drain regions, an interlayer film 512 is formed, contact holes are opened, and source / drain electrodes 513, 514, 515 are formed. In this way, a transistor with a back gate can be formed.
The present invention is not limited to this embodiment. Adaptation is possible even with other shapes and other manufacturing processes.

(Example 2)
FIG. 6 shows an embodiment of the threshold control circuit. This embodiment is used when there are a plurality of circuits to be subjected to threshold control in a semiconductor device and it is desired to control them independently. The threshold control circuit according to the present embodiment includes memory circuits 603, 606, and 609 for storing control data from a data bus, A / D conversion circuits 602, 605, and 608 for converting the stored data into analog voltages, and analog voltages. The buffer circuit 601, 604, 607 outputs the buffer. The output voltage of the buffer circuit is connected to the second gate electrode of each circuit via a threshold control line to control the threshold value of the transistor. In this embodiment, a plurality of threshold control circuits are provided in order to control a plurality of circuits independently. However, the present invention is not limited to this and one threshold control circuit may be provided.

  (Example 3)

  A specific method of driving the threshold control circuit will be described with reference to FIG. FIG. 7 includes an address comparator 701, an address memory 702, a counter 703, a reset signal generation circuit 704, a discrimination circuit 705, a discrimination reference value memory 706, and a threshold value control circuit 707. An address bus is connected to the address comparator, and address data is input. In addition, address data stored in the address memory is input. The two data are compared, and if they match, a signal indicating the match is output to the counter 703.

The counter 703 counts the output of the address comparator 701. At this time, a reset signal is periodically input from the reset signal generation circuit 704. If the reset signal is input once every 0.01 seconds, for example, the counter 703 counts how many times the data in the address memory 702 and the data on the address bus match in 0.01 seconds. This time is not limited to 0.01 seconds, and may be another time.
The discrimination circuit 705 compares the output of the counter 703 with the data of the discrimination reference value memory 706, and controls the threshold value so as to lower the threshold when the value of the discrimination reference value memory 706 exceeds the value of the output of the counter 703. The circuit 707 is operated. Further, when the output value of the counter 703 falls below the value of the discrimination reference value memory 706, the threshold value control circuit 707 is operated so as to increase the threshold value.

  In FIG. 7, the address memory 702 and the discrimination reference value memory 706 may be a fixed memory such as a mask ROM, a rewritable nonvolatile memory such as an EEPROM, or a volatile memory such as an SRAM as necessary. The data may be stored.

  FIG. 8 shows a circuit diagram of the address comparator 701. Although FIG. 8 shows a 4-bit example for simplification, it is not limited to 4 bits. Values for each bit of the address bus 802 and address memory 801 are input to EXORs 803 to 806, and outputs of EXORs 803 to 806 are input to NOR 807. In FIG. 8, a latch circuit 808 is inserted into the output of the NOR 807. This is to prevent glitches and the like at the time of operation switching. The data after switching is latched by the latch pulse.

  As the counter 703, a known counter with a reset terminal may be used. The reset signal generation circuit 704 may divide a fixed frequency signal such as a clock signal by a necessary number. The discrimination circuit 705 subtracts the value of the discrimination reference value memory 706 from the output of the counter 703 and operates the threshold value control circuit 707 when the difference changes from plus to 0 and from minus to 0. good. Further, the threshold value control circuit 707 may be operated when the difference changes from 0 to minus and when the difference changes from 0 to plus.

Example 4
The semiconductor device of the present invention can be used for various electronic devices. Hereinafter, electronic devices incorporating the semiconductor device of the present invention will be described.

  As such an electronic device, a video camera, a digital camera, a head mounted display (goggles type display), a game machine, a car navigation system, a personal computer, a personal digital assistant (mobile computer, mobile phone, electronic book, etc.), and the like can be given. . An example of them is shown in FIG.

  FIG. 9A illustrates a digital camera, which includes a main body 9101, a display portion 9102, an image receiving portion 9103, operation keys 9104, an external connection port 9105, a shutter 9106, and the like. By using the semiconductor device of the present invention for a camera control circuit, an image processing circuit, or the like, a small digital camera with low power consumption can be obtained.

  FIG. 9B illustrates a laptop computer, which includes a main body 9201, a housing 9202, a display portion 9203, a keyboard 9204, an external connection port 9205, a pointing mouse 9206, and the like. By using the semiconductor device of the present invention for a CPU or the like, a small notebook computer with low power consumption can be obtained.

  FIG. 9C illustrates a portable information terminal, which includes a main body 9301, a display portion 9302, a switch 9303, operation keys 9304, an infrared port 9305, and the like. By using the semiconductor device of the present invention for a CPU, an image processing circuit, or the like, a portable information terminal with a small size and low power consumption can be obtained.

  FIG. 9D illustrates an image reproducing device (specifically, a DVD reproducing device) including a recording medium, which includes a main body 9401, a housing 9402, a recording medium (CD, LD, DVD, or the like) reading unit 9405, and an operation switch 9406. , A display portion a9403, a display portion b9404, and the like. The display unit a mainly displays image information, and the display unit b mainly displays character information. However, by using the semiconductor device of the present invention for an image processing circuit of an image reproducing device including a recording medium, the display unit a is small and low in size. An image reproducing device with power consumption can be obtained. Note that the present invention can be used for a CD playback device, a game machine, or the like as an image playback device provided with a recording medium.

  FIG. 9E illustrates a foldable portable display device, which includes a main body 9501, a display portion 9502, and the like. By mounting a CPU using the present invention on the main body 9501, a portable display device with a small size and low power consumption can be obtained.

  FIG. 9F illustrates a video camera. A main body 9601 includes a display portion 9602, a housing 9603, an external connection port 9604, a remote control receiving portion 9605, an image receiving portion 9606, a battery 9607, an audio input portion 9608, an eyepiece portion 9609, Operation keys 9610 and the like are included. By using the semiconductor device of the present invention for an image processing circuit or the like, a video camera with a small size and low power consumption can be obtained.

  FIG. 9G illustrates a cellular phone. A main body 9701 includes a housing 9702, a display portion 9703, an audio input portion 9704, an antenna 9705, operation keys 9706, an external connection port 9707, and the like. By using the semiconductor device of the present invention for a CPU or the like, a small mobile phone with low power consumption can be obtained.

  As described above, the application range of the present invention is extremely wide and can be applied to electronic devices in various fields. In addition, the electronic apparatus of this example can be realized by using a configuration formed by any combination of the embodiment mode and Examples 1 and 2.

FIG. 11 illustrates a semiconductor device of the present invention. 6 is an inverter circuit of the semiconductor device of the present invention. The drain current characteristic of the transistor used for the semiconductor device of this invention. Detection means used in the semiconductor device of the present invention. Sectional drawing of the semiconductor device of this invention. The threshold control circuit of the present invention. 3A and 3B illustrate a method for driving a threshold control circuit of the present invention. The circuit diagram of the address comparator used for this invention. Electronic equipment using the semiconductor device of the present invention. The figure which shows the conventional semiconductor device. An inverter circuit of a conventional semiconductor device. An inverter circuit of a conventional semiconductor device. Drain current characteristics of transistors used in conventional semiconductor devices.

Claims (7)

A logic circuit having a transistor;
A counter that counts the number of times the data stored in the first memory matches the data input from the address bus;
When the output value of the counter exceeds the value of the data stored in the second memory, the threshold value of the transistor is lowered, and the output value of the counter is the data stored in the second memory. And a control circuit for raising a threshold value of the transistor when the value is lower than the value of. In claim 1,
The DOO transistor has a first gate, a second gate, a semiconductor device characterized by having a semiconductor film sandwiched between the second gate and the first gate. In claim 2,
By signal is input to the second gate of the transistor from the previous SL control circuit, a semiconductor device characterized by the amount of current flowing between the source and drain of the bets transistor is controlled. In claim 2 or claim 3 ,
It said semiconductor film is provided over the second gate,
Wherein a Tei Rukoto the first gate is provided on the semiconductor film. It claims 1 to CPU, characterized by comprising the semiconductor device according to any one of claims 4. The image processing circuit characterized by comprising the semiconductor device according to any one of claims 1 to 4. An electronic apparatus comprising the semiconductor device according to any one of claims 1 to 4 .

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