JPH06215593A - Optical storage - Google Patents

Abstract

PURPOSE:To obtain an image sensor, an optical sensor, an optical switch and an image pickup device, etc., capable of storing information over a long term by using an optical storage cell not erasing even when optical information is stored in a nonvolatile memory and read out, and power source is turned off. CONSTITUTION:A frash memory transistor 3 having a floating gate 4 and a photoconductive cell 2 consisting of CdS, CdSe, etc., are combined. Then, the optical storage cells 2 directly storing the optical information in the frash memory transistor 3 by using the resistance change of the photoconductive cell 2 by light are arranged in matrix.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an optical storage device. More specifically, the present invention relates to an optical storage device capable of nondestructive read-out, which can hold optical information by a single element by an image sensor, an optical sensor, an optical switch, or the like.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor device for converting optical information into an electric signal and storing and holding it, for example, Japanese Patent Laid-Open No. 2-26
There is known a so-called MOS image sensor, which is disclosed in Japanese Patent Publication No. 076, in which a photodiode is combined with a MOS transistor and electric charges are charged until it is read. On the other hand, there is known a CCD image sensor that moves electric charges as a shift register, as disclosed in JP-A-2-68798. Further, when a single photoelectric device is used, it is usually used as an optical switch or the like that is energized at all times and is used sporadically.

[0003]

Both the conventional MOS type image sensor and CCD type image sensor store the electric charge generated by light irradiation as a charge until the electric charge is read out. However, as in the case where the DRAM capacitor needs to be refreshed, the image sensor also has a problem that charge leakage occurs over time.

On the other hand, in a single photoelectric device used for an optical switch or the like, since the information is available only when light is irradiated, it is necessary to immediately transfer and store it in a memory such as a DRAM.

As described above, in any of the conventional devices, the light information is lost when the power is turned off, and it is necessary to transfer the information to an SRAM or a floppy disk for storage.

The present invention solves such a problem, provides a non-destructive readable non-volatile optical information storage device such as an image sensor and an optical sensor, and further provides an imaging device using the same. To aim.

[0007]

According to another aspect of the present invention, there is provided an optical memory device, wherein one terminal of a photoconductive cell is connected to a gate electrode of a flash memory transistor, and one terminal of the photoconductive cell is grounded. And a high resistance portion is connected between them to form an optical storage cell, the optical storage cells are arranged in a matrix, and the other terminals of the photoconductive cells of the optical storage cells arranged horizontally or vertically are connected. The source electrodes of the transistors of the optical storage cells arranged vertically or horizontally are connected to form the first word line to form the first bit lines of the optical storage cells arranged horizontally or vertically. The drain electrode of the transistor is connected to form a second bit line.

Further, in the optical storage device according to the second aspect of the present invention, one terminal of the photoconductive cell is connected to the source electrode of the flash memory transistor, and the one terminal of the photoconductive cell is connected to the ground. A high resistance portion is connected to form an optical storage cell, the optical storage cells are arranged in a matrix, and the gate electrodes of the transistors of the optical storage cells arranged horizontally or vertically are connected to form a first word line. And the other terminals of the photoconductive cells of the optical storage cells arranged vertically or horizontally are connected to form a first bit line, and the drain electrodes of the transistors of the optical storage cells arranged horizontally or vertically Are connected to form a second bit line.

Further, the image pickup device according to the present invention is constructed by combining the above optical storage device with a camera.

[0010]

In the optical storage device according to the present invention, one terminal of the photoconductive cell is connected to the flash memory transistor, and the high resistance portion is connected between the connected portion and the ground to form the optical storage cell. Since the optical storage cells are assembled in a matrix, each cell can be selectively written and read, and the optical information can be immediately stored directly in the nonvolatile flash memory transistor.

That is, at the time of writing, a voltage is directly applied to either the gate electrode or the source electrode of the flash memory transistor via the photoconductive cell and the other is directly applied to the gate electrode or the source electrode. It becomes a voltage, and writing is performed. In other cells, no voltage is applied to either the gate electrode or the source electrode, and writing is not performed regardless of whether light is irradiated or not. On the other hand, at the time of reading, in the case of a memory device in which the photoconductive cell is connected to the gate electrode, if voltage is applied to the electrode of the photoconductive cell without applying light and then voltage is applied to the source electrode, floating occurs. It is turned on and off in response to electron injection into the gate, and the states "1" and "0" can be read. In the case of a memory device in which the photoconductive cell is connected to the source electrode, a voltage is applied to the electrode of the photoconductive cell and the gate electrode without irradiating the light, and the current between the source and the drain is detected to detect the memory. "1", "0"
Can be read. In other cells, only a specific cell can be read by applying no voltage to the gate electrode or the source electrode.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical storage device of the present invention will be described below with reference to the accompanying drawings. 1 is an equivalent circuit diagram showing an embodiment of an optical storage cell of the present invention, FIG. 2 is an equivalent circuit diagram showing an embodiment of an optical storage device in which the optical storage cells of FIG. 1 are arranged in a matrix, and FIG. FIG. 4 is an equivalent circuit diagram showing another embodiment of the optical storage device of the present invention, FIG. 4 is a conceptual explanatory diagram when the optical storage device of the present invention is applied to an image pickup device, and FIG. 5 is an image pickup device of the optical storage device of the present invention. FIG. 6 is an explanatory view showing an example of how to move the image when it is used in FIG. 6, and FIG. 6 is an explanatory view showing another example of how to move the image.

In FIG. 1, reference numeral 1 is an optical storage device, and a photoconductive cell 2 is connected to a gate electrode 4a of a flash memory transistor 3. Reference numeral 6 denotes a source and 7 denotes a drain. The gate electrode 4a is connected to the ground E via the high resistance portion R. The high resistance portion R is provided for writing and reading without changing the voltage applied to the electrode 2a of the photoconductive cell 2.

In such an optical storage device 1, the photoconductive cell 2 has a characteristic of showing an electric resistance of about 1 MΩ when irradiated with light and about 1 GΩ when not irradiated with light, and the high resistance portion R is about 350 MΩ. . In that case, when a voltage of about 12 V is applied to the electrode 2a of the photoconductive cell 2 and the drain electrode 7a is connected to the ground E, the photoconductive cell 2 of the control gate 4 is connected.
The electric potential of the connection point 4a with is about 12V at the time of light irradiation,
It becomes approximately 3V when not irradiated. Then, when a voltage of 3 to 8 V is applied to the source electrode 6a during the light irradiation, electrons are injected into the floating gate. That is, data is written. If the predetermined voltage is not applied to the electrode 2a of the photoconductive cell 2, the potential of the connection point 4a is connected to the ground E through the high resistance portion R, and therefore becomes 0V, so that the light is not irradiated. No change occurs in the contents of the flash memory transistor 3 regardless of the irradiation, and no writing is done.

On the other hand, when the source electrode 6a is not irradiated with light, 3
By applying a voltage of about V and reading the current between the source and the drain, the memory state can be read by turning the current on and off. That is, when electrons are injected into the floating gate, the threshold voltage becomes high, and the current does not flow and it is turned off. On the other hand, if electrons have not been injected (if not written), a channel is created and a current flows, turning on. As a result, it is possible to read the states of "1" and "0" indicating the presence or absence of storage.

When the written data is erased, a voltage of 5V is applied to the drain electrode 7a and a negative voltage of -7V is applied to the electrode 2a of the photoconductive cell, so that electrons in the floating gate are generated. The data disappears by being pulled out.

An optical storage device can be constructed by arranging optical storage cells that function as described above in a matrix. FIG. 2 shows four parts of an optical storage device in which the optical storage cells are arranged in a matrix. In FIG. 2, the electrode 2 of the photoconductive cell 2 of each optical storage cell arranged in the lateral direction is shown.
first word lines a _1, a ₂ ‥‥‥ a _n is formed by connecting a, first bit line by connecting the source of the flash memory transistor of each optical storage cells arranged in the longitudinal direction b _1,
b ₂ ‥‥‥ b _n it is formed, and the second bit line d _1, d ₂ ‥‥‥ d _n by connecting the drain electrode of the flash memory transistor of each optical storage cells arranged in the lateral direction is formed There is. The first word line in the horizontal direction and the first word line in the vertical direction
The same applies to the bit lines in the vertical and horizontal directions. Further, the other end of the high resistance portion R connected to the connection point between the photoconductive cell and the gate electrode of the flash memory transistor is connected to the ground E to form an optical storage device.

Writing in this optical storage device will be described first. To write only the cell Q ₁ is, 12V to the first word line a _1, a 3V is applied to the first bit line b _1, the other first word lines a _2, a ₃ ‥‥‥ a _n and the first bit lines b ₂ , b _3, ..., B _n are connected to ground and set to 0V. With this configuration, when light is irradiated, the resistance value of the photoconductive cell changes from about 1 GΩ to about 1 MΩ. At this time, since 12V is applied to the _first word line a ₁ in the cell Q ₁ , the resistance value of the photoconductive cell is reduced, and thus the electrode of almost 12V is directly applied to the gate voltage of the flash memory cell. Will be. That is, the resistance value of the high resistance portion R is about 350 MΩ, the resistance value of the photoconductive cell when light is irradiated is about 1 MΩ, and a voltage of about 12 V is applied to the high resistance portion R. . Therefore, about 12V is applied to the gate electrode of the flash memory transistor, and since 3V is applied to the source by the first bit line b ₁ , a current flows between the source and the drain,
Electrons are injected into the floating gate side for writing. On the other hand, the resistance value of the photoconductive cell does not decrease unless it is irradiated with light, and only a voltage of about 3 V is applied to the gate electrode, so that writing is not performed. Therefore, the presence or absence of optical information can be stored.

On the other hand, in the cell Q ₂ , 12 V is applied to the _first word line a ₁ , and when the light is irradiated, the resistance value of the photoconductive cell is lowered and a voltage of about 12 V is applied to the gate electrode. Applied, but the first bit line b ₂ is 0V
Therefore, no current flows between the source and the drain, and writing is not performed.

In the cells Q ₃ and Q ₄ , the word line a ₂ is 0.
Since the voltage is V, no voltage is applied to the gate electrode and writing is not performed regardless of whether or not light is irradiated.

Next, reading will be described. Cell Q
_In order to read ₁ , the first word line a ₁ is read as 12
V, 3V is applied to the first bit line b ₁ , other word lines a ₂ ... A _n , first bit lines b ₂ ... B _n , second bit lines d ₁ , d ₂ Connect all d _n to earth E. When the current between the source and the drain is detected without light irradiation in this configuration, since light is not irradiated, the resistance value of the photoconductive cell is about 1 MΩ and about 3 V is applied to the gate electrode. As a result, if electrons are injected into the flash memory, the threshold voltage becomes high, and current does not flow between the source and drain, and it turns off.
When electrons are not injected (writing is not performed), a current flows and the device is turned on, so that "1" or "0" can be discriminated.

Next, erasing will be described. When erasing connects the first word line a _1, a ₂ ‥‥‥ a _n to the ground E, 12V is applied to the second bit line _{d 1, d 2 ‥‥‥ d n} , all the cells It is performed by the batch erasing method.

FIG. 3 shows an optical memory cell according to another embodiment of the present invention.
Shows a part of an optical storage device in which
Has been. In this example, the photoconductive cell is a flash memory.
A photoconductive cell connected to the source electrode of a molybdenum transistor
The other terminal of the
A high resistance portion R is connected between the optical storage cell
Q₁, Q₂, Q₃, Q_FourIs configured. This photoconductive
The resistance of the cell during light irradiation and non-light irradiation was the same as in the above-mentioned example.
Similarly, about 1 MΩ and about 1 GΩ, the resistance of the high resistance part is about 350 M
Ω. The optical storage cells are arranged in a matrix.
Of the memory transistor of each optical memory cell arranged in the lateral direction.
The first word line a by connecting the gate electrodes₁, A₂‥‥‥‥
a_nAre formed, and the photoconductive cell of each optical memory cell arranged in the vertical direction is formed.
The first bit line b₁, B₂‥‥‥ b
_nIs formed and the memory transistor of each optical storage cell arranged in the lateral direction is formed.
Second bit line connecting the drain electrodes of the transistors
d₁, D ₂‥‥‥ d_nFormed, memory transistor
High resistance connected to the connection point of the photoconductive cell and the source electrode of the
The other terminal of the section R is connected to the ground to form an optical storage device.
Has been. The horizontal cell connection of the first word line and the
Interchange with the vertical cell connection of 1 bit line
To connect the vertical cells to the first word line, horizontal cells
The same applies to the first bit line by connecting the source electrodes of
is there.

Writing in this optical storage device will be described first. In order to write only to the cell Q ₁ , 12V is applied to the _first word line a ₁ , 4V is applied to the _first bit line b ₁ , and the other first word lines a ₂ ... _n, the first bit line b ₂ ‥‥‥ b _n, the second bit line d _1, d ₂ ‥
By connecting d _n to ground, only cell Q ₁ is written when light is irradiated. That is, when light is irradiated, the resistance of the photoconductive cell is reduced to about 1 MΩ, and the high resistance portion is about 350 MΩ, so that 4 V is applied to the source electrode C of the memory transistor. Since 12 V is applied to the gate electrode, a current flows between the source and the drain, and electrons are injected into the gate electrode side with a high voltage, that is, the floating gate side, to perform writing. When one light is not irradiated, the resistance value of the photoconductive cell 2 is about 1 GΩ, the source electrode C is about 1 V, and the current between the source and the drain is small. Not done.

Further, since the first bit line b ₂ is 0V in the cell Q ₂ , writing is not performed regardless of whether light is irradiated or not, and in the cells Q ₃ and Q ₄ , the gate electrode is 0V.
Therefore, similarly, writing is not performed regardless of whether light is irradiated or not.

Next, reading will be described. Cell Q ₁
In order to read the data, first, 3V is applied to the _first word line a ₁ , 4V is applied to the _first bit line b ₁ , and the other first
Of the word lines a ₂ ... a _n and the other first bit lines b ₂ ...
... b _n and the second bit lines d ₁ , d ₂ ... d _n are connected to ground. That is, if 3V is applied as the gate voltage, but electrons are injected into the floating gate and writing is performed,
The injected electrons increase the threshold voltage, turning off between the source and drain. On the other hand, if writing is not performed, a channel is formed and turned on. Therefore, if the drain side is connected to a sense amplifier or the like and the current value is measured, it turns off if writing has been performed and turns on if writing has not been performed, so the state of "1" or "0" can be determined. .

On the other hand, in the cell Q ₂ , 3V is applied to the gate electrode of the memory transistor, but the first bit line b ₂ is 0V and the source electrode is also 0V.
_{In 3} and Q ₄ , the first word line a ₂ is 0 V and the gate electrode is 0 V, and in either case, no current flows between the source and the drain regardless of the presence or absence of memory, and reading cannot be performed.

Next, erasing will be described. When erasing connects the first word line a _1, a ₂ ‥‥‥ a _n to the ground, by the 12V is applied to the second bit line d _1, d ₂ ‥‥‥ d _n, Electrons are extracted from the floating gate of each cell, and all cells are collectively erased.

Next, an image pickup device using the optical storage device according to the present invention will be described. FIG. 4 is a schematic view of the camera, in which the camera is represented by a convex lens 11 and an optical storage device is arranged at the focal position of the convex lens 11. By controlling the voltage of the word line and the bit line of each optical storage cell of the optical storage device to record the optical information in each cell, an optical storage device in which the optical information is stored is formed as in a photograph. The shutter is controlled by the time applied to the corresponding image storage device.
This information can be read out by controlling the voltage applied to the word line and bit line of each cell by the above-mentioned read-out means, without any particular processing such as development.
It can be reproduced immediately.

The optical storage device for storing this optical information does not pick up images for each individual product, but as shown in FIG. 5, for example, each of the optical storage devices 12a, 12b, ... 6
By forming a total of 24 pieces and sequentially moving them as shown by arrow A in FIG. 5, it is possible to continuously record optical information. Further, as another method of changing the image by changing the optical storage device one after another, as shown in FIG. 6, a method of arranging the optical storage device on the circumference and moving the optical storage device as shown by an arrow A while rotating. Can be done at.

[0031]

According to the present invention, the photoconductive cell and the flash memory transistor are connected to each other, and the high resistance portion is connected between the connection portion and the ground to form the optical storage cell. Arrange memory cells in a matrix,
Since the matrix is formed by connecting the horizontal lines and the vertical lines, the optical information can be immediately stored in the flash memory transistor and can be used as an image sensor or an optical sensor that is not erased even if it is read many times.

Furthermore, since the photoconductive cell can be used to form the flash memory cell only with a thin layer film, it can be easily formed in a small area and high integration can be achieved. As a result, the resolution can be improved and it can be conveniently used as an imaging device.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of an embodiment of a cell of an optical storage device of the present invention.

FIG. 2 is an equivalent circuit diagram in which optical storage cells, which are an example of an optical storage device of the present invention, are arranged in a matrix.

FIG. 3 is an equivalent circuit diagram in which optical storage cells that are another embodiment of the optical storage device of the present invention are arranged in a matrix.

FIG. 4 is a conceptual explanatory diagram when the optical storage device of the present invention is applied to an imaging device.

FIG. 5 is a diagram illustrating an example of how to move an image when the optical storage device of the present invention is used in an imaging device.

FIG. 6 is a diagram illustrating another example of how to move an image when the optical storage device of the present invention is used in an imaging device.

[Explanation of symbols]

 1 Optical Storage Device 2 Photoconductive Cell 2a Photoconductive Cell Electrode 3 Flash Memory Transistor 4a Gate Electrode 6a Source Electrode 7a Drain Electrode R High Resistance Part

Claims (4)

[Claims] 1. A flash memory transistor has a gate electrode to which one terminal of a photoconductive cell is connected, and a high resistance portion is connected between one terminal of the photoconductive cell and ground to form an optical memory cell. , The optical memory cells are arranged in a matrix, and the other terminals of the photoconductive cells of the optical memory cells arranged horizontally or vertically are connected to form a first word line, which is arranged vertically or horizontally. The source electrodes of the transistors of the optical storage cells are connected to form a first bit line, and the drain electrodes of the transistors of the optical storage cells arranged horizontally or vertically are connected to form a second bit line. Optical storage device. 2. A flash memory transistor source electrode is connected to one terminal of a photoconductive cell, and a high resistance portion is connected between one terminal of the photoconductive cell and ground to form an optical memory cell. The optical storage cells are arranged in a matrix, and the gate electrodes of the transistors of the optical storage cells arranged horizontally or vertically are connected to form a first word line, and the optical storage cells are arranged vertically or horizontally. The other terminals of the photoconductive cells of the cells are connected to form a first bit line, and the drain electrodes of the transistors of the optical storage cells arranged in the horizontal or vertical direction are connected to form a second bit line. Optical storage device. 3. An image pickup device comprising a combination of the optical storage device according to claim 1 and a camera. 4. An image pickup device comprising a combination of the optical storage device according to claim 2 and a camera.