JP2012054512A - Storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a storage device capable of suppressing the output error of an output signal caused by leakage of an electric charge, and a display device including the storage device.SOLUTION: A storage device comprises: a photoelectric conversion element for converting an optical signal into an electric signal; a transistor electrically connected to the photoelectric conversion element and including an oxide semiconductor film in a channel formation region; and a holding capacitor electrically connected to the transistor and generating an output voltage by accumulating the electric signal. A display device comprising the storage device is also provided.

Description

One embodiment of the disclosed invention relates to a memory device and a driving method thereof.

In recent years, a semiconductor optical memory device capable of writing an optical signal capable of carrying a large amount of information at high speed has been desired.

As one of such semiconductor optical memory devices, a semiconductor optical memory device having a light detection array having a plurality of photodetectors is known (see Patent Document 1).

JP 2002-141548 A

In the storage device disclosed in Patent Document 1, when the leakage current of the elements that constitute the circuit that controls the photodetector is large, an output signal may be erroneously output due to leakage of electric charge.

In view of the above, an object of one embodiment of the disclosed invention is to obtain a memory device in which erroneous output of an output signal due to charge leakage can be suppressed.

Another object of one embodiment of the disclosed invention is to obtain a display device using a memory device that can suppress an erroneous output of an output signal due to charge leakage.

One embodiment of the disclosed invention includes a photoelectric conversion element that converts an optical signal into an electrical signal, a transistor that is electrically connected to the photoelectric conversion element and includes an oxide semiconductor film in a channel formation region, and an electrical connection to the transistor. And a storage capacitor that generates an output voltage by accumulating the electrical signal.

One embodiment of the disclosed invention includes a photoelectric conversion element that converts an optical signal into an electric signal, a first transistor that is electrically connected to the photoelectric conversion element and includes an oxide semiconductor film in a channel formation region, The second transistor is electrically connected to the first transistor and includes an oxide semiconductor film in a channel formation region, and the electric signal is accumulated in the gate-source capacitance of the second transistor. A memory device comprising: a buffer circuit that generates an output voltage; a first transistor; and a third transistor that is electrically connected to the buffer circuit and includes an oxide semiconductor film in a channel formation region .

One embodiment of the disclosed invention includes a photoelectric conversion element that converts an optical signal into an electric signal, a first transistor that is electrically connected to the photoelectric conversion element and includes an oxide semiconductor film in a channel formation region, The second transistor is electrically connected to the first transistor and includes an oxide semiconductor film in a channel formation region, and the electric signal is accumulated in the gate-source capacitance of the second transistor. A buffer circuit that generates an output voltage; a third transistor that is electrically connected to the first transistor and the buffer circuit and includes an oxide semiconductor film in a channel formation region; the first transistor; the buffer circuit; A storage capacitor that is electrically connected to the third transistor and generates the output voltage by accumulating the electric signal. A storage device according to claim.

One embodiment of the disclosed invention includes a transistor including an oxide semiconductor film in a channel formation region, a photoelectric conversion element that is electrically connected to the transistor and converts an optical signal into an electric signal, and the photoelectric conversion element And a storage capacitor that generates an output voltage by accumulating the electrical signal.

One embodiment of the disclosed invention includes a first transistor including an oxide semiconductor film in a channel formation region, a photoelectric conversion element that is electrically connected to the first transistor and converts an optical signal into an electrical signal; By being electrically connected to the photoelectric conversion element and configured by a second transistor having an oxide semiconductor film in a channel formation region, the electric signal is accumulated in the capacitance between the gate and the source of the second transistor, The present invention relates to a memory device including: a buffer circuit that generates an output voltage; and a third transistor that is electrically connected to the photoelectric conversion element and the buffer circuit and includes an oxide semiconductor film in a channel formation region.

One embodiment of the disclosed invention includes a first transistor including an oxide semiconductor film in a channel formation region, a photoelectric conversion element that is electrically connected to the first transistor and converts an optical signal into an electrical signal; By being electrically connected to the photoelectric conversion element and configured by a second transistor having an oxide semiconductor film in a channel formation region, the electric signal is accumulated in the capacitance between the gate and the source of the second transistor, A buffer circuit that generates an output voltage; a third transistor that is electrically connected to the photoelectric conversion element and the buffer circuit and includes an oxide semiconductor film in a channel formation region; the photoelectric conversion element, the buffer circuit, and a third transistor; And a storage capacitor that is electrically connected to the transistor and generates the output voltage by accumulating the electric signal. On.

In one embodiment of the disclosed invention, the drain current of the transistor is 1 × 10 ⁻¹³ A or less.

In one embodiment of the disclosed invention, the drain current of each of the first transistor, the second transistor, and the third transistor is 1 × 10 ⁻¹³ A or less.

According to one embodiment of the disclosed invention, a memory device in which erroneous output of an output signal due to charge leakage can be suppressed can be obtained.

According to one embodiment of the disclosed invention, a display device using a memory device that can suppress erroneous output of an output signal due to charge leakage can be obtained.

The circuit diagram of a memory | storage device. The circuit diagram of a memory | storage device. FIG. 14 is a cross-sectional view of an oxide semiconductor transistor. 8A and 8B illustrate a method for driving a memory device. 8A and 8B illustrate a method for driving a memory device. 8A and 8B illustrate a method for driving a memory device. 8A and 8B illustrate a method for driving a memory device. 4A and 4B illustrate a driving method of a display device. 4A and 4B illustrate a driving method of a display device. 4A and 4B illustrate a driving method of a display device. The circuit diagram of an inverter. The circuit diagram of a memory cell. The circuit diagram of a memory cell. FIG. 9 illustrates a memory device.

Hereinafter, embodiments of the invention disclosed in this specification will be described with reference to the drawings. However, the invention disclosed in this specification can be implemented in many different modes, and various changes can be made in form and details without departing from the spirit and scope of the invention disclosed in this specification. It will be readily understood by those skilled in the art. Therefore, the present invention is not construed as being limited to the description of this embodiment mode. Note that in the drawings described below, the same portions or portions having similar functions are denoted by the same reference numerals, and repetitive description thereof is omitted.

[Embodiment 1]

<Storage Device and Operation Method shown in FIG. 1A>
A memory device illustrated in FIG. 1A includes a photodiode 101, a transistor 102, a terminal 103, a terminal 104, and a storage capacitor 105.

One terminal of the photodiode 101 is electrically connected to the high potential voltage V _DD . The other terminal of the photodiode 101 is electrically connected to one of a source and a drain of the transistor 102.

One of a source and a drain of the transistor 102 is electrically connected to the other terminal of the photodiode 101. The other of the source and the drain of the transistor 102 is electrically connected to the terminal 104 and one terminal of the storage capacitor 105. A gate of the transistor 102 is electrically connected to the terminal 103.

One terminal of the storage capacitor 105 is electrically connected to the other of the source and the drain of the transistor 102. The other terminal of the storage capacitor 105 is grounded.

In this embodiment, a transistor including an oxide semiconductor film in a channel formation region (hereinafter referred to as an “oxide semiconductor transistor”) is used as the transistor 102. An oxide semiconductor film transistor is so small that leakage current can be regarded as zero.

When an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 102, erroneous output of an output signal due to charge leakage can be suppressed.

Note that in this specification, leakage current (also referred to as off-state current) is an n-channel transistor in which a threshold voltage Vth is positive, and when an arbitrary gate voltage is applied within a range of 0 V or less at room temperature, This refers to the current flowing between the source and drain. In the transistor including an oxide semiconductor film disclosed in this specification, even when the channel width is 10 mm, the drain current is 1 × 10 5 when the drain voltage is 1 V and 10 V and the gate voltage is 0 V or less. ^-13 A or less. Therefore, it can be said that a transistor including an oxide semiconductor film disclosed in this specification is small enough to have zero leakage current.

Note that in the oxide semiconductor film of this specification, the concentration of sodium (Na) measured by secondary ion mass spectrometry (SIMS) is 5 × 10 ¹⁶ cm ⁻³ or less, preferably 1 × 10 ¹⁶ cm ⁻³ or less, more preferably 1 × 10 ¹⁵ cm ⁻³ or less is suitable. In the oxide semiconductor film of this specification, the concentration of lithium (Li) measured by SIMS is 5 × 10 ¹⁵ cm ⁻³ or less, preferably 1 × 10 ¹⁵ cm ⁻³ or less. In the oxide semiconductor film of this specification, the concentration of potassium (K) measured by SIMS is 5 × 10 ¹⁵ cm ⁻³ or less, preferably 1 × 10 ¹⁵ cm ⁻³ or less.

When the concentration of alkali metal such as sodium (Na), lithium (Li), or potassium (K) and alkaline earth metal in the oxide semiconductor film is high, transistor characteristics are deteriorated and transistor characteristics are varied. There is a fear. Therefore, in order to suppress deterioration in transistor characteristics and variation in transistor characteristics, the alkali metal and the alkaline earth metal in the oxide semiconductor film are preferably in the above-described concentration range.

In particular, when the insulating film in contact with the oxide semiconductor film is an oxide insulating film, sodium (Na) diffuses into the insulating film and becomes sodium ions (Na ⁺ ). In addition, sodium (Na) may break a bond between metal and oxygen in the oxide semiconductor film or may break into the bond.

When sodium (Na) becomes sodium ions (Na ⁺ ) in the insulating film, sodium (Na) breaks the bond between metal and oxygen in the oxide semiconductor film, or sodium (Na) is an oxide semiconductor. In the film, interrupting during bonding may cause deterioration of transistor characteristics (for example, normalization (shift of threshold value to negative), mobility decrease, etc.). Further, such behavior of sodium (Na) also causes variations in transistor characteristics.

The above-described deterioration in transistor characteristics and variation in transistor characteristics are particularly noticeable when the concentration of hydrogen in the oxide semiconductor film is sufficiently low. Therefore, when the concentration of hydrogen in the oxide semiconductor film is 5 × 10 ¹⁹ cm ⁻³ or less, particularly 5 × 10 ¹⁸ cm ⁻³ or less, the alkali metal concentration is preferably set to the above value. It is.

The following oxide semiconductor thin films are used as the oxide semiconductor films in this specification.

Examples of the oxide semiconductor include ternary metal oxides such as In—Ga—Zn—O, In—Sn—Zn—O, In—Al—Zn—O, Sn—Ga—Zn—O, Al-Ga-Zn-O-based, Sn-Al-Zn-O-based, quaternary metal oxides In-Sn-Ga-Zn-O-based, and binary metal oxides In-Zn -O, Sn-Zn-O, Al-Zn-O, Zn-Mg-O, Sn-Mg-O, In-Ga-O, In-Mg-O, In-O An oxide semiconductor such as a Sn-O system, a Zn-O system, or the like can be used.

The oxide semiconductor may contain Si. Further, these oxide semiconductors may be amorphous or crystalline. Alternatively, it may be a non-single crystal or a single crystal.

Note that in this specification, a ternary metal oxide refers to a metal oxide containing three metal elements in addition to oxygen (O). Similarly, a quaternary metal oxide is a metal oxide containing four metal elements in addition to oxygen (O), and a binary metal oxide is two metal elements in addition to oxygen (O). A metal oxide containing

Alternatively, a thin film represented by InMO ₃ (ZnO) _m (m> 0) can be used as the oxide semiconductor film. Here, M is one or more metal elements selected from Ga, Al, Mn, and Co. For example, M includes Ga, Ga and Al, Ga and Mn, or Ga and Co.

3A to 3D are cross-sectional views of oxide semiconductor transistors that can be used as the transistor 102. FIG.

A transistor 300 illustrated in FIG. 3A is a bottom-gate transistor. The transistor 300 includes a gate electrode 302 formed over a substrate 301, a gate insulating film 303 over the gate electrode 302, and an oxide semiconductor film which overlaps with the gate electrode 302 over the gate insulating film 303 and functions as a channel formation region. 304, a channel protective film 305 which overlaps with the gate electrode 302 over the oxide semiconductor film 304, and a conductive film 306 and a conductive film 307 which are formed over the oxide semiconductor film 304. Further, the transistor 300 may include an insulating film 308 formed over the oxide semiconductor film 304 as its component. The transistor 300 can be said to be a top contact transistor because the conductive film 306 and the conductive film 307 which are source and drain electrodes are in contact with each other on the top surface of the oxide semiconductor film 304 which is a channel formation region.

In the case where the transistor 300 is used as the transistor 102, one of the source and the drain of the transistor 102 is one of the conductive film 306 and the conductive film 307 of the transistor 300. The other of the source and the drain of the transistor 102 is the other of the conductive film 306 and the conductive film 307 of the transistor 300. Further, the gate of the transistor 102 is the gate electrode 302 of the transistor 310.

FIG. 3B illustrates a transistor 310 having a structure different from that of the transistor 300.

A transistor 310 illustrated in FIG. 3B is a bottom-gate transistor. The transistor 310 overlaps with the gate electrode 311 formed over the substrate 301, the gate insulating film 312 over the gate electrode 311, the conductive film 313 and the conductive film 314 over the gate insulating film 312, and the gate electrode 311. The oxide semiconductor film 315 functions as a formation region. Further, the transistor 310 may include an insulating film 316 formed over the oxide semiconductor film 315 as its component. The transistor 310 can be said to be a bottom-contact transistor because the conductive film 313 and the conductive film 314 which are source and drain electrodes are in contact with the lower surface of the oxide semiconductor film 315 which is a channel formation region.

In the case where the transistor 310 is used as the transistor 102, one of the source and the drain of the transistor 102 is one of the conductive film 313 and the conductive film 314 of the transistor 310. The other of the source and the drain of the transistor 102 is the other of the conductive film 313 and the conductive film 314 of the transistor 310. Further, the gate of the transistor 102 is the gate electrode 311 of the transistor 310.

FIG. 3C illustrates a transistor 320 having a structure different from that of the transistor 300.

A transistor 320 illustrated in FIG. 3C includes an insulating film 321, an oxide semiconductor film 322 functioning as a channel formation region, a conductive film 323 and a conductive film 324 that serve as a source electrode and a drain electrode, a gate insulating film over a substrate 301. 325 and a gate electrode 326. The conductive films 323 and 324 are provided in contact with and electrically connected to the conductive films 327 and 328, respectively. The transistor 320 can be said to be a top-contact transistor because the conductive film 327 and the conductive film 328 which are source and drain electrodes are in contact with each other on the top surface of the oxide semiconductor film 322 which is a channel formation region.

In the case where the transistor 320 is used as the transistor 102, one of the source and the drain of the transistor 102 is one of the conductive film 323 and the conductive film 324 of the transistor 320. The other of the source and the drain of the transistor 102 is the other of the conductive film 323 and the conductive film 324 of the transistor 320. Further, the gate of the transistor 102 is the gate electrode 326 of the transistor 320.

FIG. 3D illustrates a transistor 330 having a structure different from that of the transistor 300.

A transistor 330 illustrated in FIG. 3D is a top-gate transistor. The transistor 330 includes a conductive film 331 and a conductive film 332 which are formed over the substrate 301, an oxide semiconductor film 333 which is formed over the conductive films 331 and 332 and functions as a channel formation region, and the oxide semiconductor film 333. The upper gate insulating film 334 and the gate electrode 335 which overlaps with the oxide semiconductor film 333 over the gate insulating film 334 are included. Further, the transistor 330 may include an insulating film 336 formed over the gate electrode 335 as its component. The transistor 330 can be said to be a bottom-contact transistor because the conductive film 331 and the conductive film 332 which are source and drain electrodes are in contact with the lower surface of the oxide semiconductor film 333 which is a channel formation region.

In the case where the transistor 330 is used as the transistor 102, one of the source and the drain of the transistor 102 is one of the conductive film 331 and the conductive film 332 of the transistor 330. The other of the source and the drain of the transistor 102 is the other of the conductive film 331 and the conductive film 332 of the transistor 330. Further, the gate of the transistor 102 is the gate electrode 335 of the transistor 330.

Note that a circuit for electrically separating the terminal 104 from the transistor 102 and the storage capacitor 105 may be provided. Accordingly, the photodiode 101, the transistor 102, and the storage capacitor 105 can be hardly affected by a device electrically connected to the terminal 104.

A method for driving the memory device illustrated in FIG. 1A is described below.

A voltage V ₁ is applied to the terminal 104 so that the other of the source and the drain of the transistor 102 and one terminal of the storage capacitor 105 have a ground voltage (GND). Note that when the other of the source and the drain of the transistor 102 and one terminal of the storage capacitor 105 are already at the ground voltage, the voltage V ₁ may not be applied to the terminal 104. Note the source and the drain of the other transistor 102, and as one terminal is the ground voltage of the storage capacitor 105, the step of applying voltages V ₁ to the terminal 104 and the first step.

Then, by applying a voltage _{V 2} to the terminal 103 applies a voltage _{V 2} to the gate of the transistor 102. By applying a voltage V ₂ to the gate of the transistor 102, the source and the drain of the transistor 102 are made conductive. Thus, the transistor 102 is electrically connected to the photodiode 101 in which the high potential voltage V _DD is applied to one terminal. Note that the step of applying the voltage V ₂ to the terminal 103 in order to make the source and the drain of the transistor 102 conductive is a second step.

Next, after a predetermined time, application of the voltage V ₂ to the terminal 103 is stopped, and application of the voltage V ₂ to the gate of the transistor 102 is stopped. By stopping the application of voltage V ₂ to the gate of the transistor 102 and between the source and the drain of the transistor 102 non-conductive. Thereby, the connection between the power supply voltage VDD and the photodiode 101 is cut off. Note that a step of stopping application of the voltage V ₂ to the terminal 103 is a third step in order to make the source and drain of the transistor 102 non-conductive.

When light enters the photodiode 101, the incident optical signal is photoelectrically converted by the photodiode 101. The charge generated by the photoelectric conversion is accumulated in the storage capacitor 105, so that the voltage V _H1 is generated. The voltage V _H1 can be detected from the terminal 104.

In this embodiment, an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 102, so that an erroneous output of an output signal due to charge leakage can be suppressed.

A process in which light enters the photodiode 101 is a fourth process.

On the other hand, when light does not enter the photodiode 101, a voltage V _L1 (where the voltage V _L1 is a ground voltage) is output from the terminal 104.

Note that in this embodiment, an example in which an n-channel transistor is used as the transistor 102 has been described. Note that the transistor 102 is not limited to an n-channel transistor and may be a p-channel transistor.

In the case where the transistor 102 is a p-channel transistor, a voltage is applied to the gate of the transistor 102, or a voltage obtained by subtracting a threshold voltage from the source voltage of the transistor 102 is smaller than the gate voltage of the transistor 102. A non-conducting state is established between the source and the drain. When no voltage is applied to the gate of the transistor 102, or when the voltage obtained by subtracting the threshold voltage from the source voltage of the transistor 102 is higher than the gate voltage of the transistor 102, the source and the drain are brought into conduction.

Therefore, in the above steps, when the transistor 102 is turned on, no voltage is applied to the gate, or the voltage obtained by subtracting the threshold voltage from the source voltage of the transistor 102 is higher than the gate voltage of the transistor 102. Like that. When the transistor 102 is turned off, a voltage is applied to the gate, or a voltage obtained by subtracting the threshold voltage from the source voltage of the transistor 102 is made lower than the gate voltage of the transistor 102.

As described above, a memory device that records the irradiated optical signal can be obtained through the first to fourth steps.

The storage device can be used as a ROM (Read Only Memory).

In order to use the memory device obtained as described above as a rewritable memory device (for example, a RAM (Random Access Memory)), the first to fourth steps may be repeated.

<Storage Device and Operation Method shown in FIG. 1B>
The memory device illustrated in FIG. 1B includes a photodiode 111, a transistor 112, a terminal 113, a buffer circuit 114, a terminal 115, a transistor 116, and a terminal 117.

One terminal of the photodiode 111 is electrically connected to the high potential voltage V _DD . The other terminal of the photodiode 111 is electrically connected to one of a source and a drain of the transistor 112.

One of a source and a drain of the transistor 112 is electrically connected to the other of the photodiode 111. The other of the source and the drain of the transistor 112 is electrically connected to the input terminal of the buffer circuit 114 and one of the source and the drain of the transistor 116. A gate of the transistor 112 is electrically connected to the terminal 113.

An input terminal of the buffer circuit 114 is electrically connected to the other of the source and the drain of the transistor 112 and one of the source and the drain of the transistor 116. The output terminal of the buffer circuit 114 is electrically connected to the terminal 115.

As the buffer circuit 114 in this embodiment, a waveform adjustment circuit, an inverter, or the like can be used. In this embodiment, as an example of the circuit configuration of the buffer circuit 114, a case where the inverter 165 illustrated in FIGS. 11A to 11B is used will be described.

FIG. 11A illustrates the inverter 165, the terminal 115 electrically connected to the output terminal of the inverter 165, and the terminal 161 electrically connected to the input terminal of the inverter 165.

FIG. 11B is a circuit diagram in the case where the inverter 165 includes the transistor 162 and the transistor 163.

One of a source and a drain of the transistor 162 is electrically connected to the high potential voltage V _DD and the gate of the transistor 162. The other of the source and the drain of the transistor 162 is electrically connected to the terminal 115 and one of the source and the drain of the transistor 163. A gate of the transistor 162 is electrically connected to one of a source and a drain of the transistor 162 and the high potential voltage V _DD .

One of a source and a drain of the transistor 163 is electrically connected to the other of the source and the drain of the transistor 162 and the terminal 115. The other of the source and the drain of the transistor 163 is grounded. A gate of the transistor 163 is electrically connected to the terminal 161.

As described above, the inverter 165 can be used as the buffer circuit 114.

One of a source and a drain of the transistor 116 is electrically connected to the other of the source and the drain of the transistor 112 and an input terminal of the buffer circuit 114. The other of the source and the drain of the transistor 116 is grounded. A gate of the transistor 116 is electrically connected to the terminal 117.

In this embodiment, oxide semiconductor transistors are used as transistors included in the transistor 112, the transistor 116, and the inverter 165.

Note that as the transistor 112, the transistor 116, and the transistor 162 and the transistor 163 included in the inverter 165 used as the buffer circuit 114, the transistor 300 illustrated in FIG. 3A and the transistor 300 illustrated in FIG. 3B are oxide semiconductor transistors. The transistor 310, the transistor 320 illustrated in FIG. 3C, and the transistor 330 illustrated in FIG. 3D can be used.

In the case where the transistor 300 is used as the transistor 112, the transistor 116, the transistor 162, and the transistor 163, one of the source or the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the conductive film 306 or the conductive of the transistor 300. One of the membranes 307. The other of the source and the drain of each of the transistors 112, 116, 162, and 163 is the other of the conductive film 306 or the conductive film 307 of the transistor 300. Further, the gates of the transistors 112, 116, 162, and 163 are the gate electrode 302 of the transistor 310.

In the case where the transistor 310 is used as the transistor 112, the transistor 116, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the conductive film 313 or the conductive of the transistor 310. One of the membranes 314. The other of the source and the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the other of the conductive film 313 or the conductive film 314 of the transistor 310. Further, the gates of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 are the gate electrode 311 of the transistor 310.

In the case where the transistor 320 is used as the transistor 112, the transistor 116, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the conductive film 323 or the conductive of the transistor 320. One of the membranes 324. The other of the source and the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the other of the conductive film 323 and the conductive film 324 of the transistor 320. Further, the gates of the transistors 112, 116, 162, and 163 are the gate electrode 326 of the transistor 320.

In the case where the transistor 330 is used as each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the conductive film 331 of the transistor 330 or One of the conductive films 332. The other of the source and the drain of each of the transistor 112, the transistor 116, the transistor 162, and the transistor 163 is the other of the conductive film 331 and the conductive film 332 of the transistor 330. Further, the gates of the transistors 112, 116, 162, and 163 are the gate electrode 335 of the transistor 330.

As described above, when an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 112 and the transistor 116, erroneous output of an output signal due to charge leakage can be suppressed.

In this embodiment, the gate-source capacitance of the transistors (transistors 162 and 163) included in the inverter 165 used as the buffer circuit 114 is used as a storage capacitor. As the transistor 162 and the transistor 163 included in the inverter 165, by using an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0, a storage capacitor which does not substantially lose stored charge can be obtained.

Note that a circuit for electrically separating the buffer circuit 114 from the transistor 112 and the transistor 116 may be provided. Accordingly, the photodiode 111, the transistor 112, and the transistor 116 can be hardly affected by a device electrically connected to the terminal 115.

A method for driving the memory device illustrated in FIG. 1B is described below.

By applying a voltage _{V 3} to the terminal 117 applies a voltage _{V 3} to the gate 116 of the transistor. By applying a voltage V _3, to conduct between the source and the drain of the transistor 116. As a result, the state where the input terminal of the buffer circuit 114 is set to the ground voltage and the input terminal of the buffer circuit 114 is set to the floating voltage is eliminated. Note that a step of applying the voltage V ₃ to the terminal 117 in order to make the source and the drain of the transistor 116 conductive is a fifth step.

Then, a voltage _{V 4} is applied to the terminal 113 applies a voltage _{V 4} to the gates of the 112 of the transistor. By applying a voltage V ₄ to 112 of the gate of the transistor, causing conduction between the source and the drain of the transistor 112. Accordingly, the transistor 111 is electrically connected to the photodiode 111 in which the high potential voltage V _DD is applied to one terminal. Note that a step of applying the voltage V ₄ to the terminal 113 in order to make the source and the drain of the transistor 112 conductive is a sixth step.

Next, the application of the voltage V ₃ to the terminal 117 is stopped, and the application of the voltage V ₃ to the gate of the transistor 116 is stopped. By stopping the application of voltage V ₃ to the gate of the transistor 116 and between the source and the drain of the transistor 116 non-conductive. Note that a step of stopping application of the voltage V ₃ to the terminal 117 is a seventh step in order to make the source and drain of the transistor 116 non-conductive.

Next, after a predetermined time, the application of the voltage V ₄ to the terminal 113 is stopped, and the application of the voltage V ₄ to the gate of the transistor 112 is stopped. By stopping the application of voltage V ₃ to the gate of the transistor 116 and between the source and the drain of the transistor 112 non-conductive. Thereby, the connection between the power supply voltage VDD and the photodiode 111 is cut off. Note that the step of stopping the application of the voltage V ₄ to the terminal 113 is an eighth step in order to make the source and the drain of the transistor 112 non-conductive.

When light enters the photodiode 111, the incident optical signal is photoelectrically converted by the photodiode 111. The charge generated by the photoelectric conversion is accumulated in the gate-source capacitance of the oxide semiconductor transistor (the transistor 162 and the transistor 163) included in the inverter 165 used in the buffer circuit 114, whereby the voltage V _H2 is generated. The voltage V _H2 can be detected from the terminal 115.

In this embodiment, an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 112 and the transistor 116, so that an erroneous output of an output signal due to charge leakage can be suppressed.

As described above, the optical signal applied to the photodiode 111 can be recorded.

Note that a step in which light enters the photodiode 111 is a ninth step.

On the other hand, when light does not enter the photodiode 111, the output is stored, and the voltage V _DD is output from the terminal 115.

Note that in this embodiment, an example in which n-channel transistors are used as the transistor 112 and the transistor 116 has been described. Note that the transistors 112 and 116 are not limited to n-channel transistors and may be p-channel transistors.

As a driving method in the case where the transistors 112 and 116 are p-channel transistors, the driving method in the case where the transistor 102 is a p-channel transistor is used.

As described above, the memory device that records the irradiated optical signal can be obtained by the fifth to ninth steps.

The storage device can be used as a ROM (Read Only Memory).

In order to use the storage device obtained as described above as a rewritable storage device (for example, a RAM (Random Access Memory)), the fifth to ninth steps may be repeated.

<Storage Device and Driving Method shown in FIG. 1C>
The memory device illustrated in FIG. 1C includes a photodiode 121, a transistor 122, a terminal 123, a buffer circuit 124, a terminal 125, a storage capacitor 126, a transistor 127, and a terminal 128.

One terminal of the photodiode 121 is electrically connected to the high potential voltage V _DD . The other terminal of the photodiode 121 is electrically connected to one of a source and a drain of the transistor 122.

One of a source and a drain of the transistor 122 is electrically connected to the other of the photodiodes 121. The other of the source and the drain of the transistor 122 is electrically connected to the input terminal of the buffer circuit 124, one terminal of the storage capacitor 126, and one of the source and the drain of the transistor 127. A gate of the transistor 122 is electrically connected to the terminal 123.

An input terminal of the buffer circuit 124 is electrically connected to the other of the source and the drain of the transistor 122, one terminal of the storage capacitor 126, and one of the source and the drain of the transistor 127. The output terminal of the buffer circuit 124 is electrically connected to the terminal 125.

As the buffer circuit 124 in this embodiment, a waveform adjustment circuit, an inverter, or the like can be used. In this embodiment, an inverter 165 illustrated in FIGS. 11A to 11B is used as an example of a circuit configuration of the buffer circuit 124.

One terminal of the storage capacitor 126 is electrically connected to the other of the source and the drain of the transistor 122, the input terminal of the buffer circuit 124, and one of the source and the drain of the transistor 127. The other terminal of the storage capacitor 126 is electrically connected to the other of the source and the drain of the transistor 127 and is grounded.

One of a source and a drain of the transistor 127 is electrically connected to the other of the source and the drain of the transistor 122, an input terminal of the buffer circuit 124, and one terminal of the storage capacitor 126. The other of the source and the drain of the transistor 116 is electrically connected to the storage capacitor 126 and grounded. A gate of the transistor 127 is electrically connected to the terminal 128.

Note that as the transistor 162 and the transistor 163 included in the inverter 165 used as the transistor 122, the transistor 127, and the buffer circuit 124, the transistor 300 illustrated in FIG. 3A and the transistor 310 illustrated in FIG. The transistor 320 illustrated in FIG. 3C and the transistor 330 illustrated in FIG. 3D can be used.

In the case where the transistor 300 is used as the transistor 122, the transistor 127, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the conductive film 306 or the conductive film of the transistor 300. One of the membranes 307. The other of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the other of the conductive film 306 or the conductive film 307 of the transistor 300. Further, the gates of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 are the gate electrode 302 of the transistor 310.

In the case where the transistor 310 is used as the transistor 122, the transistor 127, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the conductive film 313 or the conductive of the transistor 310. One of the membranes 314. The other of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the other of the conductive film 313 or the conductive film 314 of the transistor 310. Further, the gates of the transistors 122, 127, 162, and 163 are the gate electrode 311 of the transistor 310.

In the case where the transistor 320 is used as the transistor 122, the transistor 127, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the conductive film 323 or the conductive film of the transistor 320. One of the membranes 324. The other of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the other of the conductive film 323 and the conductive film 324 of the transistor 320. Further, the gates of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 are the gate electrode 326 of the transistor 320.

In the case where the transistor 330 is used as the transistor 122, the transistor 127, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the conductive film 331 or the conductive of the transistor 330 One of the membranes 332. The other of the source and the drain of each of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 is the other of the conductive film 331 and the conductive film 332 of the transistor 330. Further, the gates of the transistor 122, the transistor 127, the transistor 162, and the transistor 163 are the gate electrode 335 of the transistor 330.

When an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 122 and the transistor 127, an erroneous output of an output signal due to charge leakage can be suppressed.

In this embodiment, the gate-source capacitance of the transistor (the transistor 162 and the transistor 163) included in the inverter 165 used as the buffer circuit 124 and the storage capacitor 126 are used as the storage capacitor. As the transistor 162 and the transistor 163 included in the inverter 165, by using an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0, a storage capacitor which does not substantially lose stored charge can be obtained.

Note that a circuit for electrically separating the buffer circuit 124 from the transistor 122, the transistor 127, and the storage capacitor 126 may be provided. Accordingly, the photodiode 121, the transistor 122, the storage capacitor 126, and the transistor 127 can be hardly affected by a device that is electrically connected to the terminal 125.

A driving method of the memory device illustrated in FIG. 1C is similar to the driving method of the device illustrated in FIG. A method for driving the memory device illustrated in FIG. 1C is the same as the method for driving the memory device illustrated in FIG. 1B. The photodiode 111, the transistor 112, the terminal 113, the buffer circuit 114, the terminal 115, the transistor 116, The terminals 117 may be replaced with photodiodes 121, transistors 122, terminals 123, buffer circuits 124, terminals 125, transistors 127, and terminals 128, respectively. The charge generated by the photoelectric conversion is accumulated in the gate-source capacitance of the oxide semiconductor transistor (transistor 162 and transistor 163) included in the inverter 165 used in the buffer circuit 124 and the storage capacitor 126, whereby the voltage V _H2 is generated.

In this embodiment, an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 122 and the transistor 127, so that an erroneous output of an output signal due to charge leakage can be suppressed.

As described above, the optical signal applied to the photodiode 121 can be recorded.

Note that in this embodiment, an example in which n-channel transistors are used as the transistor 122 and the transistor 127 has been described. Note that the transistor 122 and the transistor 127 are not limited to n-channel transistors, and may be p-channel transistors.

As a driving method in the case where the transistor 122 and the transistor 127 are p-channel transistors, the driving method in the case where the transistor 102 is a p-channel transistor is used.

As described above, a storage device that records the irradiated optical signal can be obtained.

The storage device can be used as a ROM (Read Only Memory).

In order to use the storage device obtained as described above as a rewritable storage device (for example, a RAM (Random Access Memory)), the fifth to ninth steps may be repeated.

2A to 2C illustrate an example of a storage device that functions as an accumulation memory (a memory that counts accumulation).

<Storage device shown in FIG. 2A and driving method thereof>
A memory device illustrated in FIG. 2A includes a photodiode 131, a transistor 132, a terminal 133, a terminal 134, and a storage capacitor 135.

One of a source and a drain of the transistor 132 is electrically connected to the high potential voltage V _DD . The other of the source and the drain of the transistor 132 is electrically connected to one terminal of the photodiode 131. A gate of the transistor 132 is electrically connected to the terminal 133.

One terminal of the photodiode 131 is electrically connected to the other of the source and the drain of the transistor 132. The other terminal of the photodiode 131 is electrically connected to the terminal 134 and one terminal of the storage capacitor 135.

One terminal of the storage capacitor 135 is electrically connected to the other terminal of the photodiode 131 and the terminal 134. The other terminal of the storage capacitor 135 is grounded.

As the oxide semiconductor transistor included in the transistor 132, the transistor 300 illustrated in FIG. 3A, the transistor 310 illustrated in FIG. 3B, the transistor 320 illustrated in FIG. 3C, and the transistor illustrated in FIG. 330 can be used.

In the case where the transistor 300 is used as the transistor 132, one of the source and the drain of the transistor 132 is one of the conductive film 306 and the conductive film 307 of the transistor 300. The other of the source and the drain of the transistor 132 is the other of the conductive film 306 and the conductive film 307 of the transistor 300. Further, the gate of the transistor 132 is the gate electrode 302 of the transistor 310.

In the case where the transistor 310 is used as the transistor 132, one of the source and the drain of the transistor 132 is one of the conductive film 313 and the conductive film 314 of the transistor 310. The other of the source and the drain of the transistor 132 is the other of the conductive film 313 and the conductive film 314 of the transistor 310. Further, the gate of the transistor 132 is the gate electrode 311 of the transistor 310.

In the case where the transistor 320 is used as the transistor 132, one of the source and the drain of the transistor 132 is one of the conductive film 323 and the conductive film 324 of the transistor 320. The other of the source and the drain of the transistor 132 is the other of the conductive film 323 and the conductive film 324 of the transistor 320. Further, the gate of the transistor 132 is the gate electrode 326 of the transistor 320.

In the case where the transistor 330 is used as the transistor 132, one of the source and the drain of the transistor 132 is one of the conductive film 331 and the conductive film 332 of the transistor 330. The other of the source and the drain of the transistor 132 is the other of the conductive film 331 and the conductive film 332 of the transistor 330. Further, the gate of the transistor 132 is the gate electrode 335 of the transistor 330.

When an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 132, erroneous output of an output signal due to charge leakage can be suppressed.

A method for driving the memory device illustrated in FIG. 2A is described below.

The other terminal of the photodiode 131, and as one terminal is the ground voltage of the storage capacitor 135, and applies the voltage V ₅ to the terminal 134. Note that when the other terminal of the photodiode 131 and one terminal of the storage capacitor 135 are already at the ground voltage, the voltage V ₅ may not be applied to the terminal 134. Note the other terminal of the photodiode 131, and as one terminal is the ground voltage of the storage capacitor 135, the step of applying a voltage V ₅ to the terminal 134 and the tenth step.

Then, by applying a voltage _{V 6} to the terminal 133 applies a voltage _{V 6} to the gate of the transistor 132. By applying a voltage V ₆ to the gate of the transistor 132, the source and the drain of the transistor 132 are made conductive. Thereby, the high potential voltage V _DD is applied to one terminal of the photodiode 131. Note that the step of applying the voltage V ₆ to the terminal 133 in order to make the source and drain of the transistor 132 conductive is an eleventh step.

Next, after a certain time, application of the voltage V ₆ to the terminal 133 is stopped, and application of the voltage V ₆ to the gate of the transistor 132 is stopped. By stopping the application of voltage V ₆ to the gate of the transistor 132 and between the source and the drain of the transistor 132 non-conductive. As a result, the connection between the power supply voltage VDD and the photodiode 131 is cut off. Note that for non-conductive state between the source and the drain of the transistor 132, the step of stopping the application of voltage V ₆ to the terminal 133 and the twelfth step.

When light enters the photodiode 131, the incident optical signal is photoelectrically converted by the photodiode 131. The charge generated by the photoelectric conversion is accumulated in the storage capacitor 135, so that the voltage V _H3 is generated. The voltage V _H3 can be detected from the terminal 134.

In this embodiment, an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 132, so that an erroneous output of an output signal due to charge leakage can be suppressed.

As described above, the optical signal applied to the photodiode 131 can be recorded.

A process in which light enters the photodiode 131 is a thirteenth process.

On the other hand, when light does not enter the photodiode 131, a voltage V _L2 (where the voltage V _L2 is a ground voltage) is output from the terminal 134.

Further, when the voltage V ₆ is always applied to the gate of the transistor 132 via the terminal 133, the voltage V _H3 is accumulated in the storage capacitor 135 every time light is irradiated. Thus, a storage device that accumulates and stores the irradiated optical signals can be obtained.

Note that in this embodiment, an example in which an n-channel transistor is used as the transistor 132 has been described. Note that the transistor 132 is not limited to an n-channel transistor, and may be a p-channel transistor.

As a driving method in the case where the transistor 132 is a p-channel transistor, the driving method in the case where the transistor 102 is a p-channel transistor is used.

Through the tenth to thirteenth steps, a storage device that records the irradiated optical signal can be obtained.

The storage device can be used as a ROM (Read Only Memory).

Note that when the transistor 132 is formed using an oxide semiconductor transistor in which a leakage current between a source and a drain is extremely small, power consumption during standby can be reduced.

<Storage Device and Driving Method shown in FIG. 2B>
The memory device illustrated in FIG. 2B includes a photodiode 141, a transistor 142, a terminal 143, a buffer circuit 144, a terminal 145, a transistor 146, and a terminal 147.

One of a source and a drain of the transistor 142 is electrically connected to the high potential voltage V _DD . The other of the source and the drain of the transistor 142 is electrically connected to one of the photodiodes 141. A gate of the transistor 142 is electrically connected to the terminal 143.

One terminal of the photodiode 141 is electrically connected to the other of the source and the drain of the transistor 142. The other terminal of the photodiode 141 is electrically connected to the input terminal of the buffer circuit 144 and one of the source and the drain of the transistor 146.

An input terminal of the buffer circuit 144 is electrically connected to the other terminal of the photodiode 141 and one of a source and a drain of the transistor 146. The output terminal of the buffer circuit 144 is electrically connected to the terminal 145. In this embodiment, an inverter 165 illustrated in FIGS. 11A to 11B is used as an example of a circuit configuration of the buffer circuit 144.

One of a source and a drain of the transistor 146 is electrically connected to an input terminal of the buffer circuit 144 and the other terminal of the photodiode 141. The other of the source and the drain of the transistor 146 is grounded.

Note that as the transistor 162 and the transistor 163 included in the inverter 165 used as the transistor 142, the transistor 146, and the buffer circuit 144, an oxide semiconductor transistor, the transistor 300 illustrated in FIG. 3A and the transistor illustrated in FIG. 310, the transistor 320 illustrated in FIG. 3C, and the transistor 330 illustrated in FIG. 3D can be used.

In the case where the transistor 300 is used as the transistor 142, the transistor 146, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the conductive film 306 or the conductive film of the transistor 300. One of the membranes 307. The other of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the other of the conductive film 306 and the conductive film 307 of the transistor 300. Further, the gates of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 are the gate electrode 302 of the transistor 310.

In the case where the transistor 310 is used as the transistor 142, the transistor 146, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the conductive film 313 or the conductive of the transistor 310. One of the membranes 314. The other of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the other of the conductive film 313 or the conductive film 314 of the transistor 310. Further, the gates of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 are the gate electrode 311 of the transistor 310.

In the case where the transistor 320 is used as the transistor 142, the transistor 146, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the conductive film 323 or the conductive of the transistor 320. One of the membranes 324. The other of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the other of the conductive film 323 and the conductive film 324 of the transistor 320. Further, the gates of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 are the gate electrode 326 of the transistor 320.

In the case where the transistor 330 is used as the transistor 142, the transistor 146, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the conductive film 331 or the conductive of the transistor 330 One of the membranes 332. The other of the source and the drain of each of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 is the other of the conductive film 331 and the conductive film 332 of the transistor 330. Further, the gates of the transistor 142, the transistor 146, the transistor 162, and the transistor 163 are the gate electrode 335 of the transistor 330.

When an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 142 and the transistor 146, erroneous output of an output signal due to charge leakage can be suppressed.

In this embodiment, a gate-source capacitor used as a transistor (a transistor 162 and a transistor 163) included in the inverter 165 used as the buffer circuit 144 is used as a storage capacitor. By using an oxide semiconductor transistor having a leak current as small as 0 that can be regarded as zero as the transistor (transistor 162 and transistor 163) included in the inverter 165 used as the buffer circuit 144, a storage capacitor that does not substantially lose stored charge can be obtained. it can.

A method for driving the memory device illustrated in FIG. 2B is described below.

By applying a voltage _{V 7} to the terminal 147 applies a voltage _{V 7} to the gate of the transistor 146. By applying the voltage V ₇ to the gate of the transistor 146, the source and the drain of the transistor 146 are made conductive. Thus, the state where the input terminal of the buffer circuit 144 is set to the ground voltage and the input terminal of the buffer circuit 144 is the floating voltage is eliminated. Note that a step of applying the voltage V ₇ to the terminal 147 in order to make the source and the drain of the transistor 146 conductive is a fourteenth step.

Next, a voltage V ₈ is applied to the terminal 143 to cause conduction between the source and the drain of the transistor 142. Thereby, the high potential voltage V _DD is applied to one terminal of the photodiode 141. Note that for conducting between the source and the drain of the transistor 142, the step of applying a voltage V ₈ to the terminal 143 and the fifteenth step.

Next, the application of the voltage V ₇ to the terminal 147 is stopped, and the application of the voltage V ₇ to the gate of the transistor 146 is stopped. By stopping the application of voltage V ₇ to the gate of the transistor 146 and between the source and the drain of the transistor 146 non-conductive. Note that the step of stopping application of the voltage V ₇ to the terminal 147 is a sixteenth step in order to make the source and drain of the transistor 146 non-conductive.

Next, after a certain time, the application of the voltage V ₈ to the terminal 143 is stopped, and the application of the voltage V ₈ to the gate of the transistor 142 is stopped. By stopping the application of voltage V ₈ to the gate of the transistor 142 and between the source and the drain of the transistor 142 non-conductive. Thereby, the connection between the high potential voltage V _DD and the photodiode 141 is cut off. Note to the between the source and the drain of the transistor 142 non-conductive, the step of stopping the application of the voltage V ₈ to the terminal 143 and the 17 step.

When light enters the photodiode 141, the incident optical signal is photoelectrically converted by the photodiode 141. The electric charge generated by the photoelectric conversion is accumulated in the gate-source capacitance of the oxide semiconductor transistors (transistors 162 and 163) included in the inverter 165 used in the buffer circuit 144, whereby the voltage V _H4 is generated. The voltage V _H4 can be detected from the terminal 145.

In this embodiment, an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 142 and the transistor 146, so that an erroneous output of an output signal due to charge leakage can be suppressed.

As described above, the optical signal applied to the photodiode 141 can be recorded.

Note that in this embodiment, an example in which n-channel transistors are used as the transistor 142 and the transistor 146 has been described. Note that the transistors 142 and 146 are not limited to n-channel transistors and may be p-channel transistors.

As a driving method in the case where the transistors 142 and 146 are p-channel transistors, the driving method in the case where the transistor 102 is a p-channel transistor is used.
The process in which light enters the photodiode 141 is referred to as a seventeenth process.

On the other hand, when light does not enter the photodiode 141, the output is stored and the voltage V _DD is output from the terminal 145.

In addition, when the voltage V ₈ is always applied to the gate of the transistor 142 through the terminal 143, the voltage V _H4 is applied to the oxide semiconductor transistor (the transistor 162 and the transistor 162 and the inverter 165 used for the buffer circuit 144 each time light is irradiated. It is stored in the capacitance between the gate and source of the transistor 163). Thus, a storage device that accumulates and stores the irradiated optical signals can be obtained.

Through the fourteenth to seventeenth steps, a storage device that records the irradiated optical signal can be obtained.

The storage device can be used as a ROM (Read Only Memory).

Note that when the transistor 142 is formed using an oxide semiconductor transistor in which a leakage current between a source and a drain is extremely small, power consumption during standby can be reduced.

<Storage Device and Driving Method shown in FIG. 2C>
The memory device illustrated in FIG. 2C includes a photodiode 151, a transistor 152, a terminal 153, a buffer circuit 154, a terminal 155, a storage capacitor 156, a transistor 157, and a terminal 158.

One of a source and a drain of the transistor 152 is electrically connected to the high potential voltage V _DD . The other of the source and the drain of the transistor 152 is electrically connected to one of the photodiodes 151. A gate of the transistor 152 is electrically connected to the terminal 143.

One terminal of the photodiode 151 is electrically connected to the other of the source and the drain of the transistor 152. The other terminal of the photodiode 151 is electrically connected to the input terminal of the buffer circuit 154, one terminal of the storage capacitor 156, and one of the source and the drain of the transistor 157.

An input terminal of the buffer circuit 154 is electrically connected to the other terminal of the photodiode 151, one terminal of the storage capacitor 156, and one of a source and a drain of the transistor 157. The output terminal of the buffer circuit 154 is electrically connected to the terminal 155. As an example of the circuit configuration of the buffer circuit 154, an inverter 165 illustrated in FIGS. 11A to 11B is used.

One terminal of the storage capacitor 156 is electrically connected to the other terminal of the photodiode 151, the input terminal of the buffer circuit 154, and one of the source and the drain of the transistor 157. The other terminal of the storage capacitor 156 is electrically connected to the other of the source and the drain of the transistor 157 and is grounded.

One of a source and a drain of the transistor 157 is electrically connected to the other terminal of the photodiode 151, an input terminal of the buffer circuit 154, and one terminal of the storage capacitor 156. The other of the source and the drain of the transistor 157 is electrically connected to the other terminal of the storage capacitor 135 and is grounded.

Note that as the transistor 162 and the transistor 163 of the inverter 165 included in the transistor 152, the transistor 157, and the buffer circuit 154, the transistor 300 illustrated in FIG. 3A and the transistor 310 illustrated in FIG. The transistor 320 illustrated in FIG. 3C and the transistor 330 illustrated in FIG. 3D can be used.

In the case where the transistor 300 is used as the transistor 152, the transistor 157, the transistor 162, and the transistor 163, one of the source or the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the conductive film 306 or the conductive film of the transistor 300. One of the membranes 307. The other of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the other of the conductive film 306 or the conductive film 307 of the transistor 300. Further, the gates of the transistors 152, 157, 162, and 163 are the gate electrode 302 of the transistor 310.

In the case where the transistor 310 is used as the transistor 152, the transistor 157, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the conductive film 313 or the conductive of the transistor 310 One of the membranes 314. The other of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the other of the conductive film 313 or the conductive film 314 of the transistor 310. Further, the gates of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 are the gate electrode 311 of the transistor 310.

In the case where the transistor 320 is used as the transistor 152, the transistor 157, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the conductive film 323 or the conductive film of the transistor 320. One of the membranes 324. The other of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the other of the conductive film 323 and the conductive film 324 of the transistor 320. Further, the gates of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 are the gate electrode 326 of the transistor 320.

In the case where the transistor 330 is used as the transistor 152, the transistor 157, the transistor 162, and the transistor 163, one of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the conductive film 331 of the transistor 330 or conductive One of the membranes 332. The other of the source and the drain of each of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 is the other of the conductive film 331 and the conductive film 332 of the transistor 330. Further, the gates of the transistor 152, the transistor 157, the transistor 162, and the transistor 163 are the gate electrode 335 of the transistor 330.

When an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 152 and the transistor 157, erroneous output of an output signal due to charge leakage can be suppressed.

In this embodiment, the gate-source capacitance of the transistor (the transistor 162 and the transistor 163) included in the inverter 165 used in the buffer circuit 154 and the storage capacitor 156 are used as the storage capacitor. By using an oxide semiconductor transistor having a leak current as small as 0 that can be regarded as zero as the transistors (transistor 162 and transistor 163) included in the inverter 165 used in the buffer circuit 154, a storage capacitor that does not substantially lose stored charge can be obtained. it can.

A method for driving the memory device illustrated in FIG. 2C is similar to the method for driving the memory device illustrated in FIG. 2C is the same as the method for driving the memory device illustrated in FIG. 2B, except that the photodiode 141, the transistor 142, the terminal 143, the buffer circuit 144, the terminal 145, the transistor 146, The terminal 147 may be replaced with a photodiode 151, a transistor 152, a terminal 153, a buffer circuit 154, a terminal 155, a transistor 157, and a terminal 158, respectively. The charge generated by the photoelectric conversion is accumulated in the gate-source capacitance of the transistor (transistor 162 and transistor 163) included in the inverter 165 used in the buffer circuit 154 and the storage capacitor 156, so that the voltage V _H4 is generated. .

In this embodiment, an oxide semiconductor transistor whose leakage current is small enough to be regarded as 0 is used as the transistor 152 and the transistor 157, so that an erroneous output of an output signal due to charge leakage can be suppressed.

As described above, the optical signal applied to the photodiode 151 can be recorded.

Note that in this embodiment, an example in which n-channel transistors are used as the transistor 152 and the transistor 157 has been described. Note that the transistors 152 and 157 are not limited to n-channel transistors and may be p-channel transistors.

As a driving method in the case where the transistors 152 and 157 are p-channel transistors, the driving method in the case where the transistor 102 is a p-channel transistor is used.

Further, when the voltage V ₆ is always applied to the gate of the transistor 152 through the terminal 153, the oxide semiconductor transistor (the transistor 162 and the transistor 162) constitutes the inverter 165 that uses the voltage V _H4 for the buffer circuit 154 each time light is irradiated. 163) and the storage capacitor 156. Thus, a storage device that accumulates and stores the irradiated optical signals can be obtained.

As described above, a storage device that records the irradiated optical signal can be obtained.

The storage device can be used as a ROM (Read Only Memory).

Note that when the transistor 152 is formed using an oxide semiconductor transistor in which the leakage current between the source and the drain is extremely small, power consumption during standby can be reduced.

<Storage device and driving method thereof>
The memory device and the driving method thereof illustrated in FIGS. 1A to 1C and FIGS. 2A to 2C are described below.

The storage device of this embodiment includes a sensor substrate 211 and a light source 212. The sensor substrate 211 is irradiated with the optical signal 213 from the light source 212, and the irradiated optical signal 213 is recorded on the sensor substrate 211 (see FIG. 4A). The optical signal 213 from the light source 212 may be applied to the entire sensor substrate 211 or may be applied locally.

The sensor substrate 211 includes a row decoder 215, a column decoder 214, and a memory cell 216. The memory cell 216 includes m rows × n columns of memory cells 216 _{11 to} 216 _mn (see FIG. 4B). An arbitrary memory cell located in the i-th row and the j-th column among the memory cells 216 is referred to as a memory cell 216 _ij . The memory cell 216 _ij is configured using any of the memory devices illustrated in FIGS. 1A and 2A.

An example in which the memory cell 216 _ij is formed using the memory device described in FIG. 1A is illustrated in FIG.

In the memory cell 216 _ij illustrated in FIG. 12, the terminal 103 is electrically connected to the selection line 171 through a wiring 173. The selection line 171 is electrically connected to the row decoder 215. The row decoder 215 applies the voltage V ₂ to the terminal 103 through the selection line 171 and the wiring 173.

The terminal 104 is electrically connected to the signal line 172 through a wiring 174. The signal line 172 is electrically connected to the column decoder 214. The column decoder 214 applies the voltage V ₁ to the terminal 104 through the signal line 172 and the wiring 174. The column decoder 214 outputs a voltage V _H1 generated by photoelectric conversion of the optical signal. When the optical signal does not enter the photodiode 101, the voltage V _L1 that is the ground voltage is output to the column decoder 214.

In the memory cell 216 _ij illustrated in FIG. 12, the memory device illustrated in FIG. 2A can be used instead of the memory device illustrated in FIG. In the case of using the memory device illustrated in FIG. 2A in the memory cell 216 _ij illustrated in FIG. 12, the wiring 173 may be connected to the terminal 133 and the wiring 174 may be connected to the terminal 134.

FIG. 14 illustrates a structure of the sensor substrate 211 in the case where the memory device illustrated in FIGS. 1B, 1C, 2B, and 2C is used.

A sensor substrate 211 illustrated in FIG. 14 includes a row decoder 215, a column decoder 214, a row decoder 219, and a memory cell 216. The memory cell 216 has m rows × n columns of memory cells 216 _{11 to} 216 _mn . An arbitrary memory cell located in the i-th row and the j-th column among the memory cells 216 is referred to as a memory cell 216 _ij . The memory cell 216 _ij is configured using any of the memory devices illustrated in FIGS. 1B, 1C, 2B, and 2C.

FIG. 13 shows an example in which the memory cell 216 _ij is formed using the memory device described with reference to FIG.

In the memory cell 216 _ij illustrated in FIG. 13, the terminal 113 is electrically connected to the selection line 171 through a wiring 173. The selection line 171 is electrically connected to the row decoder 215. The row decoder 215 applies the voltage V ₄ to the terminal 113 through the selection line 171 and the wiring 173.

The terminal 115 is electrically connected to the signal line 172 through a wiring 174. The signal line 172 is electrically connected to the column decoder 214. Further, the voltage V _H2 generated by photoelectric conversion of the optical signal is output from the terminal 115 to the column decoder 214 via the signal line 172 and the wiring 174. When the optical signal is not incident on the photodiode 101, the voltage V _DD is output to the column decoder 214.

The terminal 117 is electrically connected to the reset line 176 through a wiring 175. The reset line 176 is electrically connected to the row decoder 219. The row decoder 219 applies the voltage V ₃ to the terminal 117 through the reset line 176 and the wiring 175.

In the memory cell 216 _ij illustrated in FIG. 13, the memory device illustrated in FIGS. 1C, 2B, and 2C can be used instead of the memory device illustrated in FIG. .

When the memory device illustrated in FIG. 1C is used in the memory cell 216 _ij illustrated in FIG. 13, the wiring 173 is connected to the terminal 123, the wiring 174 is connected to the terminal 125, and the wiring 175 is connected to the terminal 128. Good.

When the memory device illustrated in FIG. 2B is used in the memory cell 216 _ij illustrated in FIG. 13, the wiring 173 is connected to the terminal 143, the wiring 174 is connected to the terminal 145, and the wiring 175 is connected to the terminal 147. Good.

When the memory device illustrated in FIG. 2C is used in the memory cell 216 _ij illustrated in FIG. 13, the wiring 173 is connected to the terminal 153, the wiring 174 is connected to the terminal 155, and the wiring 175 is connected to the terminal 158. Good.

The row decoder 215 and the column decoder 214 have a function of selectively writing to and reading from the memory cell 216.

A method for driving the memory device of this embodiment is described below with reference to a sensor substrate illustrated in FIG.

First, the optical signal 213 ₁₁ is irradiated (see FIG. 5A), the memory cell 216 ₁₁ is turned on, and the optical signal 213 ₁₁ is recorded in the memory cell 216 ₁₁ (see FIG. 5B). That is, the voltage V _H generated by photoelectric conversion of the irradiated optical signal 213 ₁₁ is maintained in the capacity in the memory cell 216 ₁₁ .

At this time, the memory cells 216 _ij other than the memory cell 216 ₁₁ are turned off, and the optical signal 213 ₁₁ is not recorded in the memory cells 216 _ij other than the memory cell 216 ₁₁ .

Next, an optical signal 213 ₁₂ having information different from the optical signal 213 ₁₁ is irradiated (see FIG. 6A), the memory cell 216 ₁₂ is turned on, and the optical signal 213 ₁₂ is recorded in the memory cell 216 ₁₂ (see FIG. 6A). (See FIG. 6B).

The process of irradiating the optical signal 213 (optical signal 213 ₁₁ to optical signal 213 _mn ) described above is repeated (see FIG. 7A), and the optical signal 213 is recorded in all the memory cells 216 ₁₁ to 216 _mn . (See FIG. 7B). Note that different optical information can be recorded in each of the memory cells 216 ₁₁ to 216 _mn .

The storage device of this embodiment can be configured by only the light source 212 that emits the optical signal 213 and the sensor substrate 211 that records the light source 212.

On the other hand, when recording information on a conventional optical disk (eg, DVD), a head for outputting information by light, a jig for rotating the optical disk at high speed, a prism for selecting and operating light, and a half A mirror, lens, etc. are required.

Therefore, the storage device of the present embodiment can be configured with fewer parts than a conventional optical disk. Therefore, the storage device of this embodiment is preferable in that the production cost can be reduced as compared with the conventional optical disc of the related art.

As described above, according to this embodiment, a memory device that can suppress an erroneous output of an output signal due to charge leakage can be obtained.

[Embodiment 2]
In this embodiment, a display device using the device described in Embodiment 1 is described.

The display device with a sensor in this embodiment includes a light source 212 and a display 221 with a sensor. The light source 212 of the present embodiment is the same as the light source 212 of the first embodiment.

The sensor-equipped display 221 can record the optical signal 213 emitted from the light source 212 as information, and can reproduce the information itself.

Examples of the display included in the sensor-equipped display 221 include a liquid crystal display and an EL display.

A driving method of the display device with a sensor according to the present embodiment will be described below.

First, an optical signal 213 is emitted from the light source 212, and the emitted optical signal 213 is recorded on the sensor-equipped display 221 (see FIG. 8A). Note that the description in Embodiment Mode 1 is used for the step of recording the optical signal 213 emitted from the light source 212. The sensor-equipped display 221 of this embodiment includes the row decoder 215, the column decoder 214, and the memory cell 216 described in Embodiment 1.

In the display device of this embodiment mode, first, an optical signal 213 is emitted from a light source 212. Next, the irradiated optical signal 213 is recorded on the sensor-equipped display 221. Thereafter, the display included in the sensor-equipped display 221 outputs an image 222 based on information from the irradiated optical signal 213.

In the display device with a sensor illustrated in FIG. 8B, the display 221 with a sensor outputs a video 222 from the display included in the display 221 with the sensor while the light signal 213 is emitted from the light source 212.

At this time, when the information already recorded by the sensor-equipped display 221 and the information newly obtained from the light source 212 to the sensor-equipped display 221 are the same, new information can be recorded on the sensor-equipped display 221. On the other hand, when the information already recorded by the sensor-equipped display 221 is different from the information newly obtained from the light source 212 to the sensor-equipped display 221, new information cannot be recorded on the sensor-equipped display 221.

Therefore, normally, after recording desired information, the display with sensor 221 is controlled not to record information.

FIG. 9A shows a case where the information already recorded on the sensor-equipped display 221 and the information included in the optical signal 217 emitted from the light source 212 are different in the sensor-equipped display device of this embodiment. Yes.

If the information already recorded on the sensor-equipped display 221 is different from the information contained in the optical signal 217 emitted from the light source 212, the information newly obtained from the light source 212 is not recorded, and the sensor-equipped display 221 has already been recorded. According to the recorded information, the video 222 is output from the display included in the sensor-equipped display 221.

Therefore, normally, after recording desired information, the display with sensor 221 is controlled not to record information.

FIG. 9B shows an image from the display included in the sensor-equipped display 221 according to the information already recorded by the sensor-equipped display 221 even when information is not obtained from the light source 212 in the sensor-equipped display device of this embodiment. 222 is output.

FIG. 10 shows that in the display device with a sensor according to the present embodiment, even when there is no light source 212, the video 222 is output from the display included in the sensor-equipped display 221 according to the information already recorded by the sensor-equipped display 221. ing.

Note that in the display device with a sensor of this embodiment mode, an optical signal such as visible light, ultraviolet light, infrared light, or X-ray can be used as the optical signal 213 emitted from the light source 212.

As described above, according to this embodiment, a display device using a memory device that can suppress erroneous output of an output signal due to charge leakage can be obtained.

101 Photodiode 102 Transistor 103 Terminal 104 Terminal 105 Storage Capacitor 111 Photodiode 112 Transistor 113 Terminal 114 Buffer Circuit 115 Terminal 116 Transistor 117 Terminal 121 Photodiode 122 Transistor 123 Terminal 124 Buffer Circuit 125 Terminal 126 Storage Capacitor 127 Transistor 128 Terminal 131 Photodiode 132 transistor 133 terminal 134 terminal 135 holding capacitor 141 photodiode 142 transistor 143 terminal 144 buffer circuit 145 terminal 146 transistor 147 terminal 151 photodiode 152 transistor 153 terminal 154 buffer circuit 155 terminal 156 holding capacitor 157 transistor 158 terminal 161 terminal 162 transistor 163 Transistor 165 inverter 171 selection line 172 signal line 173 wiring 174 wiring 175 wiring 176 reset line 211 sensor substrate 212 light source 213 optical signal 214 column decoder 215 row decoder 216 memory cell 217 optical signal 219 row decoder 221 display 222 video 300 transistor 301 substrate 302 Gate electrode 303 Gate insulating film 304 Oxide semiconductor film 305 Channel protective film 306 Conductive film 307 Conductive film 308 Insulating film 310 Transistor 311 Gate electrode 312 Gate insulating film 313 Conductive film 315 Conductive film 315 Oxide semiconductor film 316 Insulating film 320 Transistor 321 Insulating film 322 oxide semiconductor film 323 conductive film 324 conductive film 325 gate insulating film 326 gate electrode 327 conductive film 328 conductive film 330 transistor 331 Conductive film 332 conductive film 333 oxide semiconductor film 334 gate insulating film 335 gate electrode 336 insulating film 213 ₁₁ optical signal 213 ₁₂ optical signal 213 _mn optical signal 216 ₁₁ memory cell 216 ₁₂ memory cell 216 _ij memory cell 216 _mn memory cell

JP 62-299340 A

Claims (10)

A photoelectric conversion element that converts an optical signal into an electrical signal;
A transistor electrically connected to the photoelectric conversion element and having an oxide semiconductor film in a channel formation region;
A storage capacitor electrically connected to the transistor and generating an output voltage by accumulating the electrical signal;
A storage device comprising: In claim 1,
The drain current of the transistor is 1 × 10 ⁻¹³ A or less. A photoelectric conversion element that converts an optical signal into an electrical signal;
A first transistor electrically connected to the photoelectric conversion element and having an oxide semiconductor film in a channel formation region;
The second transistor is electrically connected to the first transistor and includes an oxide semiconductor film in a channel formation region, and the electric signal is accumulated in the gate-source capacitance of the second transistor. A buffer circuit for generating an output voltage;
A third transistor electrically connected to the first transistor and the buffer circuit and having an oxide semiconductor film in a channel formation region;
A storage device comprising: A photoelectric conversion element that converts an optical signal into an electrical signal;
A first transistor electrically connected to the photoelectric conversion element and having an oxide semiconductor film in a channel formation region;
The second transistor is electrically connected to the first transistor and includes an oxide semiconductor film in a channel formation region, and the electric signal is accumulated in the gate-source capacitance of the second transistor. A buffer circuit for generating an output voltage;
A third transistor electrically connected to the first transistor and the buffer circuit and having an oxide semiconductor film in a channel formation region;
A storage capacitor that is electrically connected to the first transistor, the buffer circuit, and the third transistor and generates the output voltage by storing the electrical signal;
A storage device comprising: In claim 3 or claim 4,
A drain current of each of the first transistor, the second transistor, and the third transistor is 1 × 10 ⁻¹³ A or less. A transistor including an oxide semiconductor film in a channel formation region;
A photoelectric conversion element that is electrically connected to the transistor and converts an optical signal into an electrical signal;
A storage capacitor electrically connected to the photoelectric conversion element and generating an output voltage by accumulating the electrical signal;
A storage device comprising: In claim 6,
The drain current of the transistor is 1 × 10 ⁻¹³ A or less. A first transistor having an oxide semiconductor film in a channel formation region;
A photoelectric conversion element that is electrically connected to the first transistor and converts an optical signal into an electrical signal;
By being electrically connected to the photoelectric conversion element and configured by a second transistor having an oxide semiconductor film in a channel formation region, the electric signal is accumulated in a gate-source capacitance of the second transistor, A buffer circuit for generating an output voltage;
A third transistor electrically connected to the photoelectric conversion element and the buffer circuit and having an oxide semiconductor film in a channel formation region;
A storage device comprising: A first transistor having an oxide semiconductor film in a channel formation region;
A photoelectric conversion element that is electrically connected to the first transistor and converts an optical signal into an electrical signal;
By being electrically connected to the photoelectric conversion element and configured by a second transistor having an oxide semiconductor film in a channel formation region, the electric signal is accumulated in a gate-source capacitance of the second transistor, A buffer circuit for generating an output voltage;
A third transistor electrically connected to the photoelectric conversion element and the buffer circuit and having an oxide semiconductor film in a channel formation region;
A storage capacitor that is electrically connected to the photoelectric conversion element, the buffer circuit, and a third transistor and accumulates the electrical signal to generate the output voltage;
A storage device comprising: In claim 8 or claim 9,
A drain current of each of the first transistor, the second transistor, and the third transistor is 1 × 10 ⁻¹³ A or less.

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