JP3150438B2 - Optical storage device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical storage device. More specifically, the present invention relates to an optical storage device in which light information can be held by a single element using an image sensor, an optical sensor, an optical switch, or the like, and in which nondestructive reading is possible.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor device which converts optical information into an electric signal and stores and holds the same, for example, Japanese Patent Laid-Open No. 2-26
There is known a so-called MOS image sensor, as disclosed in Japanese Patent Application Publication No. 076, in which a MOS transistor is combined with a photodiode and charged until it is read. On the other hand, a CCD image sensor that moves charges as a shift register as disclosed in Japanese Patent Application Laid-Open No. 2-68798 is known. further,
When a single photoelectric device is used, it is usually used as an optical switch which is always energized and used only once.

[0003]

Both the conventional MOS type image sensor and the CCD type image sensor store charges generated by light irradiation as charges until the charges are read out. However, D
Just as the RAM capacitor needs to be refreshed, the image sensor also has a problem that electric charge leaks over time.

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

[0005] As described above, in the conventional devices, the light information is lost when the power is turned off, and must be transferred to an SRAM or a floppy for preservation.

An object of the present invention is to solve such a problem and to provide a nonvolatile optical information storage device for storing optical information, and to provide a configuration of an optical storage device whose manufacture is easy and a manufacturing method thereof. And

[0007]

An optical storage device according to the present invention comprises:
A flash memory cell formed on a semiconductor substrate, and a photoconductive cell formed on a transparent substrate, wherein a surface on the flash memory cell side formed on the semiconductor substrate and a surface on the photoconductive cell side of the transparent substrate Are attached via an electrode film.

An electrode film may be formed on one main surface of the transparent substrate, and a spiral photoconductive cell may be formed on another portion.

According to the method of manufacturing an optical storage device of the present invention, (a) forming an electrode film and a photoconductive cell on one main surface of a transparent substrate;
(B) forming a flash memory cell on one main surface side of the semiconductor substrate by providing an electrode film on the surface; and (c) adhering the electrode film of the semiconductor substrate and the electrode film of the transparent substrate. I have.

[0010]

In the optical storage device of the present invention, the photoconductive cell formed on the transparent substrate is attached to the flash memory cell formed on the semiconductor substrate and is also electrically connected. If a voltage is applied to the electrode of the photoconductive cell and the gate electrode or the source electrode of the flash memory cell, and the light is irradiated with the drain electrode connected to the ground, the light is irradiated from the transparent substrate side. The optical information can be written into the memory cell.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical storage device according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an equivalent circuit diagram showing an embodiment of the optical storage device of the present invention, FIG. 2 is a sectional view showing an embodiment of the structure of the optical storage device of FIG. 1, and FIG. FIG. 4 is a schematic plan view showing one embodiment of the configuration on the glass substrate in the optical storage device of the present invention.

In FIG. 1, reference numeral 1 denotes an optical storage device, in which a photoconductive cell 2 is connected to a control gate electrode 4a of a flash memory cell 3. 5 is a floating gate, 6 is a source, and 7 is a drain. The control gate electrode 4a is connected to the ground E via the high resistance portion 8. The high resistance portion 8 is an electrode of the photoconductive cell 2
This is provided for writing and reading without changing the voltage applied to 2a.

In the optical storage device 1, the photoconductive cell 2 has a characteristic of exhibiting 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 8 has a characteristic of about 350 MΩ. . In this case, when a voltage of about 12 V is applied to the electrode 2a of the photoconductive cell 2 and the electrode 7a of the drain 7 is connected to the ground E, the potential of the connection point 4a between the control gate 4 and the photoconductive cell 2 becomes It is about 12 V, and about 3 V when not irradiated. If a voltage of 3 to 8 V is applied to the source electrode 6a during the light irradiation,
Thereby, electrons are injected into the floating gate 5. That is, data is written. If a predetermined voltage is not applied to the electrode 2a of the photoconductive cell 2, the potential of the connection point 4a is changed to the ground E via the high resistance portion 8.
, The voltage becomes 0 V, no change occurs in the contents of the flash memory cell 3 irrespective of irradiation or non-irradiation of light, and no writing is performed. On the other hand, when a voltage of about 3 V is applied to the source electrode 6a at the time of non-irradiation of light and a current between the source and the drain is read, electrons are injected into the floating gate.
If electrons have not been injected (if writing has not been performed), no current flows and the switch is OFF, so that the states of “1” and “0” can be read.

When erasing the written data, a voltage of 5 V is applied to the drain electrode 7a and a negative voltage of -7 V is applied to the electrode 2a of the photoconductive cell. Data is lost by being pulled out to the substrate.

The optical storage device 1 that functions as described above can have a structure whose cross section is shown in FIG. Hereinafter, a method for manufacturing the optical storage device 1 will be described with reference to FIG. To facilitate understanding, the same reference numerals as in FIG. 1 are used for the same components as those in the circuit diagram of FIG.

First, ITO or ZnO _{2 serving as} an electrode 2a of the photoconductive cell 2 is formed on one main surface of a transparent substrate 16 such as a glass substrate.
And a thin film of a photoconductive material such as CdS or CdSe for forming the photoconductive cell 2 is formed thereon, and an electrode film 17 of Al-Si or the like is further formed thereon.
To form As a specific example, an ITO film or the like is formed to a thickness of 0.3 to 2 μm by a vapor deposition method or a sputtering method. Subsequently, a photoconductive material is applied by a sputtering method or the like to a thickness of 0.3 to 2 μm. This thickness is in the length direction between the two electrodes and directly affects the resistance value of the photoconductive cell 2.
If it doubles, the resistance value also triples. Although the resistance value is inversely proportional to the area, the area is formed to a size of 1 to 10 ⁴ μm ² from the size of the memory cell and the minimum size that can detect light.

Next, a nonvolatile memory transistor having a floating gate is formed on a semiconductor substrate.
This memory transistor is formed by a normal process. That is, the field insulating film 9 is formed on the semiconductor substrate 11, and the control gate layer 4 is formed on the surface of the semiconductor region surrounded by the field insulating film 9 via the gate insulating film 10, the floating gate layer 5, and the insulating film 12. And
After patterning, a drain region 7 and a source region 6 are formed in the semiconductor region. When the source region 6 is formed, a low-concentration impurity region is formed widely in advance, so that a low-concentration impurity region 6b is formed around the source region 6, so that electrons can be easily injected into the floating gate. I have. Further, an interlayer insulating film 13 is formed, and drain, gate, and source electrode films 7a, 4a, and 6a are formed of a high-resistance portion (not shown) or Al-Si through a contact hole. The gate electrode film 4a is exposed, and the drain and source electrode films 7a and 6a are further covered with a protective film 14,
A memory cell section is formed.

After that, the gate electrode film 4a side of this memory cell portion and the electrode film 17 side of the transparent substrate on which the above-mentioned transparent conductive film, photoconductive cell and electrode film are formed are overlapped at about 400 ° C.
By heating for about 30 minutes.
Are welded to form the optical storage device of the present invention. Since the transparent substrate 16 is bonded to form the photoconductive cell and the electrode film on a flat surface, the transparent substrate 16 can be formed easily and with an accurate film thickness. Further, since the element area may be within the range of the flash memory cell, high integration is possible. Then, ZnO, TiO ₂
By simply forming the ultraviolet shielding film 18 made of, for example, the ultraviolet shielding film 18, the disappearance of the memory contents and the malfunction of the flash memory cell can be prevented.

Here, the photoconductive cell 2 is composed of CdS, CdS
It is made of Se, CdTe, ZnS, or the like, and is formed by a sputtering method or the like. The control gate layer 4 and the floating gate layer 5 are formed of polysilicon or the like, and the electrode films are formed of Al-Si, Al, or the like. Each of the insulating films 10, 12, 13, and 14 is made of Si.
O ₂ is formed from a like, particularly an insulating film 12 between the control gate layer 4 and the floating gate layer 5 from the viewpoint of efficient traps, SiO both sides the Si ₃ N ₄ layers
_The ONO preferably has a three-layer structure sandwiched between _two layers. However, a structure having only one layer of the oxide film or two layers of the oxide film and the nitride film may be employed. FIG. 3 shows an equivalent circuit diagram of another embodiment of the optical storage device of the present invention. In the optical storage device 21 of this embodiment, the photoconductive cell 22 is connected to the source electrode 24a of the flash memory cell 23, and the electrode 24a is connected to the ground E via the high resistance portion 25. In the figure, 26 is a control gate, 27 is a floating gate, and 28 is a drain.

The optical storage device 21 is also the optical storage device 1 (FIG. 1).
Similarly, the photoconductive cell 22 has about 1M when irradiated with light.
Ω, electric resistance of about 1 GΩ when not illuminated.
Has an electrical resistance of about 350 MΩ.

Therefore, about 4% is applied to the electrode 22a of the photoconductive cell.
When a voltage of V is applied and the drain electrode 28a is connected to the ground E, the voltage of the source electrode 24a, that is, the connection point between the photoconductive cell 22 and the source 24 becomes about 4 V during light irradiation and about 1 V during non-light irradiation. . In that state, the control gate electrode 26a
By applying a voltage of about 12 V to the photoconductive cell 22 and irradiating the photoconductive cell 22 with electrons, electrons are injected from the source region 24 into the floating gate 27, and information is written. Unless a predetermined voltage is applied to both the photoconductive cell electrode 22a and the control gate electrode 26a, no change occurs in the contents of the flash memory cell 23 irrespective of light irradiation or non-irradiation, and therefore no writing is performed. .

On the other hand, when the light is not irradiated, a voltage of 3 V is applied to the control gate electrode 24a, a voltage of 4V is applied to the photoconductive cell electrode 22a, and the current of the drain region 28 is detected. "0",
"1" can be determined. When erasing the written data, as in the previous embodiment, 5 V is applied to the drain electrode 28a and -7 is applied to the control gate electrode 26a.
By applying V, electrons in the floating gate 27 are extracted.

The power consumption of the optical storage device 21 is reduced because the applied voltage at the time of writing information may be low.

The optical storage device 21 functioning as described above is also similar to the optical storage device 1 of the above embodiment in that a glass substrate on which a transparent conductive film or a photoconductive cell is formed is attached to a memory cell formed on a semiconductor substrate. The photoconductive cell can be easily formed with an accurate film thickness. However, in this embodiment, since the electrode film of the photoconductive cell is connected to the source electrode of the memory cell, it is connected to the lower side of the memory cell (the memory cell is formed higher because the gate electrode side is stacked. Is). Therefore, a protruding portion is formed on the glass substrate side, and a photoconductive cell must be formed at that portion, or the source electrode needs to be pulled out to the same height as the gate electrode and adhered.

In the embodiment (FIG. 2), the transparent substrate 16
A transparent conductive film is formed on the entire main surface of the photoconductive cell 2 and the photoconductive cell 2 is formed on the entire upper surface thereof. However, since the resistance value of the photoconductive cell is inversely proportional to the area and proportional to the thickness, the shape can be appropriately changed.
For example, as shown in a plan view of another shape of the photoconductive cell in FIG. 4, a conductive film 42 to be an electrode is formed on a part of a glass substrate 41 and connected to the conductive film 42 to form a photoconductive cell. The cell 43 may be formed in a spiral shape. In such a configuration,
Since the conductive film 42 and the photoconductive cell do not overlap, there is no need to use a transparent conductive film, and a general Al electrode or the like can be used. Further, the resistance value of the photoconductive cell 43 can be freely adjusted by changing the length and film thickness of the spiral.

In each of the above embodiments, an example of a glass substrate has been described. However, the present invention is not limited to glass, and any other transparent substrate, such as plastic, which can transmit light may be used.

[0027]

According to the present invention, an optical storage device capable of immediately storing light information in a flash memory by a single element is formed in a photoconductive cell portion formed on a transparent substrate side and a semiconductor substrate. Because it is formed by sticking the memory cell portion that was formed, it can be easily formed,
The thickness of the photoconductive cell can be accurately formed, and the resistance value can be freely adjusted.

Further, since the photoconductive cell is protected by the transparent substrate, light can be detected accurately, and accurate storage without errors can be performed.

[Brief description of the drawings]

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

FIG. 2 is an explanatory sectional view showing one embodiment of the structure of the optical storage device of the present invention.

FIG. 3 is an equivalent circuit diagram showing another embodiment of the optical storage device of the present invention.

FIG. 4 is a schematic plan view showing one embodiment of a configuration of a photoconductive cell on a glass substrate in the optical storage device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical storage device 2 Photoconductive cell 3 Flash memory cell 4 Control gate 5 Floating gate 6 Source 7 Drain 8 High resistance part 16 Transparent substrate 17 Electrode film 21 Optical storage device 22 Photoconductive cell 23 Flash memory cell 24 Source 25 High resistance part 26 Control gate 27 Floating gate 28 Drain 41 Glass substrate 43 Photoconductive cell

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ identification code FI H01L 29/792 (58) Investigated field (Int.Cl. ⁷ , DB name) H01L 21/8247 G11C 11/42 H01L 27/115 H01L 29/788 H01L 29/792

Claims (3)

(57) [Claims] 1. A flash memory cell formed on a semiconductor substrate, and a photoconductive cell formed on a transparent substrate, wherein the surface of the flash memory cell side formed on the semiconductor substrate and light emitted from the transparent substrate are formed. An optical storage device, wherein a surface on the side of a conductive cell is attached via an electrode film. 2. The photoconductive cell formed on the transparent substrate is formed in a spiral shape.
An optical storage device according to claim 1 . (A) forming an electrode film and a photoconductive cell on one principal surface of a transparent substrate; and (b) forming a flash memory cell on the one principal surface side of the semiconductor substrate by providing an electrode film on the surface. And (c) adhering the electrode film of the semiconductor substrate and the electrode film of the transparent substrate.