JP2004319999A - Semiconductor device, cpu, image processing circuit and electronic apparatus, and driving method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device in which power consumption is low at the time of waiting. <P>SOLUTION: In the semiconductor device and its driving method, gate electrodes are provided on opposite sides of a semiconductor thin film constituting a transistor, a logic signal is applied to a first gate electrode and a threshold level control signal is applied to a second gate electrode, and the threshold level of a transistor constituting the semiconductor device is varied depending on the potential of the second gate electrode. In the semiconductor device and its driving method, the semiconductor device has a plurality of logic circuits each comprising such a transistor with a back gate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  2. Description of the Related Art In recent years, with the progress of communication technology, mobile phones have become popular. In the future, transmission of moving images and more information transmission are expected. On the other hand, as for personal computers, mobile-friendly products have been produced due to their light weight. A large number of information terminals called PDA, which began with electronic notebooks, are also being produced and are becoming popular. Many semiconductor devices such as a CPU (Central Processing Unit) are used in such portable information devices.

  Although there are various types of semiconductor devices, a block diagram of a CPU is shown in FIG. 10 as an example. The 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 instruction, converts it into information for internal use, and sends it out to another block. In addition, instructions such as reading and writing of memory data are given to the outside according to the internal operation. 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 that specifies an address of an external memory. The data bus interface 1006 is a circuit for transferring data into and out of 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 an instruction. The CPU is configured by a combination of such 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 an SOI (Silicon On Insulator) and is under development. When the substrate is an insulator, the parasitic capacitance between the transistor and the substrate can be reduced, and high speed and low power can be achieved. In particular, they are used in portable electronic devices to reduce power consumption. An electronic device using a semiconductor device with large power consumption has problems such as an increase in required battery and a need for a cooling fan, and a problem that 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 as to simultaneously satisfy high thermal conductivity and low elasticity.

JP-A-7-74282

  FIG. 11 shows an example of a two-stage inverter circuit of a conventional semiconductor device using a 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 saving power of portable electronic devices, but the following problems remain.
FIG. 13 is a graph showing the relationship between the drain current and the gate voltage of an N-type MOS transistor. Ideally, in a region where the gate voltage Vg is positive, the drain current Id is sufficiently large, and when the gate voltage Vg is 0 or less, it is desirable that the drain current Id be 0. However, actually, as shown by the curve 1301, even if the gate voltage Vg is 0, a leakage current of only IL flows in the drain current Id. Although the current of each transistor is not large, the current LSI has millions of transistors, and the sum of their leakage currents does not become small. Such a leakage current has increased the power consumption of the semiconductor device during standby.

  It is possible to reduce this leakage current 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, there is a problem that the current when Vg is positive also decreases, and the frequency characteristics of the circuit deteriorate.

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

  In view of the above problems, it is an object of the present invention to provide a semiconductor device which consumes less power due to leakage current, a driving method thereof, and an electronic device using the same.

  In order to solve the above problems, the present invention provides a gate electrode on each side of a semiconductor thin film forming a transistor, a logic signal on a first gate electrode, and a threshold control signal on a second gate electrode. In addition, a semiconductor device in which a threshold value of a transistor included in a semiconductor device is made variable by a potential of a second gate electrode and a driving method thereof are provided. In addition, a semiconductor device provided with a plurality of logic circuits including a transistor with a back gate in a semiconductor device and a driving method thereof are provided. That is, 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 common in the standby mode. On the other hand, during a period in which the circuit operates frequently, power consumption is determined by the ON characteristics of the transistor, and leakage current can be ignored. Such a mode is an active mode.

  Such a distinction between the standby mode and the active mode is controlled by detection means (for example, a program) for controlling the threshold control circuit, and the threshold value of the transistor can be changed by using the detection means and the threshold control circuit. . Therefore, the threshold value of the transistor can be set high during standby, so that 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 a detection unit that detects an operation frequency of the logic circuit and outputs a 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. 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 provides a logic circuit including a thin film transistor on an insulating surface, and a storage storing a program for functioning as detection means for detecting an operation frequency of the logic circuit and outputting a detection result to a threshold control circuit. Medium, the thin film transistor has 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.

  Further, 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 a detection unit that detects an operation frequency of the logic circuit and outputs a detection result to a threshold control circuit, wherein the detection unit is in a standby state. When 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 the following.

  As described above, according to 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 reduced in size, and a small and lightweight electronic device with low power consumption can be realized.

  According to 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). Thus, the size of the battery can be reduced and an electronic device with a small volume can be realized. A reduction in size, weight, and thickness is realized.

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

  FIG. 1 shows a semiconductor device using the present invention. Although there are various types of semiconductor devices, a block diagram of a CPU is shown in FIG. 1 as an example. 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 a threshold value control circuit 109 is added in the block diagram of FIG. This threshold control circuit supplies a threshold control signal to another logic circuit.

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

  FIG. 3 shows the Id-Vg characteristics of the transistor having the 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, making it difficult for the current to flow and reducing the leakage current. As described above, by providing the threshold value control function in the inverter circuit and shifting the Id-Vg curve, it is possible to reduce the leakage current.

  Next, the operation method will be described with reference to FIG. The semiconductor device of the present invention includes detection means (for example, a program, a storage medium storing the program, and software) for controlling the threshold value of the transistor. The detection means calls a program for detecting the operation frequency of the semiconductor device (logic circuit) and, when the detection exceeds a certain level, data for threshold control from an internal or external memory of the semiconductor device, and activates the threshold control circuit. It consists of a program to be operated.

  The operation frequency detection program counts how many times a certain instruction is used during a certain period of time, and can detect the operation frequency according to the count number. That is, the number of times of use within a certain period of time is set, and if the number of times of detection within that period is equal to or less than a certain value, the mode is determined to be the first mode. 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, it is possible to judge at the time of standby and at the time of activation, and the threshold value is controlled accordingly.

  In this way, the threshold control circuit is provided inside the semiconductor device, and the mode of the semiconductor device is detected by the detection means, and the threshold control circuit is controlled, so that the power consumption of the semiconductor device is adjusted according to the situation. It can be kept low.

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

(Example 1)
FIG. 5 is a sectional view of a thin film transistor constituting a semiconductor device of the present invention. The manufacturing process will be described below. A base film 502 is formed over an insulating substrate 501, and second gate electrodes 503 and 504 are formed. 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 a P-type impurity and an N-type impurity to form source / drain regions, an interlayer film 512 is formed, contact holes are opened, and source / drain electrodes 513, 514, 515 are formed. Thus, a transistor with a back gate can be formed.
The present invention is not limited to this embodiment. Adaptation is possible even after passing through 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 value 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. It is configured by buffer circuits 601, 604, and 607 that output buffers. The output voltage of the buffer circuit is connected to the second gate electrode of each circuit via a threshold control line, and controls the threshold of the transistor. In this embodiment, a plurality of threshold value control circuits are provided to independently control a plurality of circuits, but the number of threshold value control circuits is not limited to this, and may be one.

  (Example 3)

  A method for driving the threshold control circuit will be specifically 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 control circuit 707. An address bus is connected to the address comparator, and address data is input. Further, address data stored in the address memory is input. The two data are compared, and when 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. Assuming that the reset signal is input, for example, once every 0.01 second, 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 second. This time is not limited to 0.01 second, 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 when the value of the output of the counter 703 exceeds the value of the discrimination reference value memory 706, the threshold value is controlled so as to lower the threshold value. The circuit 707 is operated. When the value of the output of the counter 703 falls below the value of the discrimination reference value memory 706, the threshold control circuit 707 operates to increase the threshold.

  In FIG. 7, an address memory 702 and a determination reference value memory 706 may be fixed memories such as a mask ROM, rewritable nonvolatile memories such as an EEPROM, or volatile memories such as an SRAM as needed. What stored data may be used.

  FIG. 8 shows a circuit diagram of the address comparator 701. FIG. 8 shows an example of 4 bits for simplification, but is not limited to 4 bits. Values for each bit of the address bus 802 and the address memory 801 are input to EXORs 803 to 806, and outputs of the EXORs 803 to 806 are input to a NOR 807. In FIG. 8, the latch circuit 808 is inserted in the output of the NOR 807, but this is necessary to prevent glitches or the like at the time of operation switching, and may be omitted. The data after the 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 required 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 control circuit 707 when the difference becomes 0 from plus and 0 when the difference becomes 0 from minus. good. Further, the threshold control circuit 707 may be operated at the time when the difference goes from 0 to minus, or at the time when the difference goes 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.

  Examples of such electronic devices include a video camera, a digital camera, a head-mounted display (goggle-type display), a game machine, a car navigation, a personal computer, a portable information terminal (a mobile computer, a mobile phone, an electronic book, and the like). . One example 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 in a camera control circuit, an image processing circuit, and the like, a small digital camera with low power consumption can be obtained.

  FIG. 9B illustrates a notebook computer including 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-sized notebook personal 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, and the like, a small and low-power-consumption portable information terminal can be obtained.

  FIG. 9D illustrates an image reproducing device (specifically, a DVD reproducing device) provided with 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 in an image processing circuit or the like of an image reproducing apparatus provided with a recording medium, the display unit a is small and low in size. An image reproducing apparatus with low power consumption can be obtained. Note that the present invention can be applied to a CD playback device, a game machine, and 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 or the like using the present invention in the main body 9501, a small, low-power portable display device 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, a sound input portion 9608, an eyepiece portion 9609, An operation key 9610 and the like are included. When the semiconductor device of the present invention is used for an image processing circuit or the like, a small and low power consumption video camera can be obtained.

  FIG. 9G illustrates a mobile phone. A main body 9701 includes a housing 9702, a display portion 9703, a sound 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 and low-power-consumption mobile phone can be obtained.

  As described above, the applicable range of the present invention is extremely wide, and can be applied to electronic devices in all fields. Further, the electronic apparatus of this embodiment can be realized by using a configuration formed by any combination of the embodiment mode and Embodiments 1 and 2.

FIG. 2 illustrates a semiconductor device of the present invention. 4 shows an inverter circuit of the semiconductor device of the present invention. 13 shows drain current characteristics of a transistor used in the semiconductor device of the present invention. Detection means used for the semiconductor device of the present invention. FIG. 3 is a cross-sectional view of a semiconductor device of the present invention. 3 shows a threshold control circuit according to the present invention. FIG. 4 illustrates a method for driving a threshold control circuit of the present invention. FIG. 2 is a circuit diagram of an address comparator used in the present invention. Electronic equipment using the semiconductor device of the present invention. FIG. 14 illustrates a conventional semiconductor device. Conventional inverter circuit of semiconductor device. Conventional inverter circuit of semiconductor device. Drain current characteristics of a transistor used in a conventional semiconductor device.

Claims (14)

A logic circuit comprising a thin film transistor on an insulating surface;
Detecting means for detecting the operation frequency of the logic circuit, and outputting the detection result to a threshold control circuit,
The semiconductor device, wherein the thin film transistor has 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. A logic circuit comprising a thin film transistor on an insulating surface;
Detecting means for detecting the operation frequency of the logic circuit, and outputting the detection result to a threshold control circuit,
The thin film transistor has 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,
A semiconductor device, wherein an amount of current flowing between a source electrode and a drain electrode of the thin film transistor is controlled by the threshold control signal. A logic circuit comprising a thin film transistor on an insulating surface;
Detecting the operation frequency of the logic circuit, has a storage medium recording a program for functioning as a detection means to output the detection result to the threshold control circuit,
The semiconductor device, wherein the thin film transistor has 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. A logic circuit comprising a thin film transistor on an insulating surface;
Detecting the operation frequency of the logic circuit, has a storage medium recording a program for functioning as a detection means to output the detection result to the threshold control circuit,
The thin film transistor has 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,
A semiconductor device, wherein an amount of current flowing between a source electrode and a drain electrode of the thin film transistor is controlled by the threshold control signal.   5. The semiconductor device according to claim 1, wherein a semiconductor thin film is provided on the second gate electrode, and the first gate electrode is provided on the semiconductor thin film. 6. A substrate having an insulating surface;
A logic circuit having a thin film transistor on the substrate,
Detection means electrically connected to the logic circuit, for detecting an operation frequency of the logic circuit;
A semiconductor device, comprising: a threshold control circuit electrically connected to the detection means. A substrate having an insulating surface;
A logic circuit having a thin film transistor on the substrate,
An address comparator electrically connected to the logic circuit;
A counter electrically connected to the address comparator;
A determination circuit electrically connected to the counter,
A semiconductor device, comprising: a threshold control circuit electrically connected to the determination circuit. A substrate having an insulating surface;
A logic circuit having a thin film transistor on the substrate,
Detection means electrically connected to the logic circuit, for detecting an operation frequency of the logic circuit;
A threshold control circuit electrically connected to the detection means;
Has,
The thin film transistor has a plurality of gate electrodes,
The semiconductor device according to claim 1, wherein the threshold control circuit is electrically connected to at least one of the plurality of gate electrodes. A substrate having an insulating surface;
A logic circuit having a thin film transistor on the substrate,
An address comparator electrically connected to the logic circuit;
A counter electrically connected to the address comparator;
A determination circuit electrically connected to the counter,
A threshold control circuit electrically connected to the determination circuit;
Has,
The thin film transistor has a plurality of gate electrodes,
A semiconductor device, wherein the threshold control circuit is electrically connected to at least one of the plurality of gate electrodes;   A CPU comprising the semiconductor device according to claim 1.   An image processing circuit comprising the semiconductor device according to claim 1.   An electronic apparatus comprising the semiconductor device according to claim 1. A logic circuit comprising a thin film transistor on an insulating surface;
Detecting means for detecting the operation frequency of the logic circuit, and outputting the detection result to a threshold control circuit,
The detecting means determines the first mode or the second mode,
The method of driving a semiconductor device, wherein the threshold value control circuit outputs a threshold value control signal according to the first or second mode to the logic circuit. A logic circuit comprising a thin film transistor on an insulating surface;
Detecting means for detecting the operation frequency of the logic circuit, and outputting the detection result to a threshold control circuit,
The detecting means determines a standby mode or an active mode,
When the detecting 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. Drive method.

Images