JPS6140143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reading device that converts a written, typed, or printed manuscript into a time-series electrical signal.

Currently, various devices are used for photoelectric conversion of printed characters, pictures, etc. Among these, many reading devices using highly integrated photodiode array CCD photosensors have been adopted, but these are not compact because they are equipped with a reduced optical system. Figure 1 is a schematic diagram of its configuration.
2 is an integrated photosensor; 2 is a document; 3 is an optical lens that forms an image of the document 2 on the photosensor 1;

Since these conventional photosensors are made of silicon single crystal, there are restrictions in terms of materials, uniformity of properties, manufacturing costs, etc., and it is difficult to make large-sized ones, such as those with the width of an A4 size manuscript. difficult.

Weimer (PKWEIMER: RCA) is Proc
IEEE vol.52 (1964) p. 1479, “Integrated
Circuits Incorporating Thin−Film Active and
In the paper titled ``Passive Element'', he describes a 30-stage one-dimensional image sensor that combines a photodiode using a CdS photoconductive thin film and a MOS-FET switch using a CdS thin film.
Since this image sensor can be made only by vacuum deposition, it can be easily made even in large sizes such as the width of an A4 document.

An example of the structure is shown in FIGS. 2 and 3. this is,
Transparent conductive film 5B provided on transparent glass substrate 4
consists of a lower electrode 5 covered with a metal thin film 5A to make it opaque leaving only a light image entrance window, a photoconductor layer 6, and upper divided electrodes 7-1, 7-2... The image is input from the back side of the substrate 4. The laminated portion of the lower electrode 5, photoconductor 6, and upper divided electrode 7 is formed into pixel-sized light receiving portions 8-1, 8-2...
Configure... Each upper divided electrode 7-1, 7-2...
... is connected at one end to the switch 9, as shown in FIG.

In Figure 4, 9-1, 9-2......, 10-
1, 10-2 are first and second stage FET switches, 11 is a constant voltage power supply, 12 is a signal amplifier, 1
3 and 14 are shift registers, and 15 is a frequency divider.

First, each FET switch is turned on to charge the diodes 8-1, 8-2, etc. in the light receiving section, and then the switch is turned off and a light image is irradiated onto this diode array. Each diode responds to the amount of light it receives. discharge. Next, shift registers 13 and 14
Depending on the FET switch 9-1, 9-2......,
By controlling the diodes 10-1, 10-2, the diodes 8-1, 8-2, . . . are sequentially connected to the power source 11 and recharged. By detecting the charging current flowing at this time with the amplifier 12, the amount of light received by each diode is converted into an electrical signal. The device described above is of the storage type and is known, and is suitable for high-speed reading.

In the conventional reading device described above, a light image passes through a transparent substrate and is formed on the light receiving section. Efficiency decreases.

(2) It is necessary to use optical glass with low distortion as the substrate, which is expensive.

There are drawbacks such as. In order to improve this, it is necessary to apply antireflection treatment to the surface, which increases the manufacturing process and increases the cost. Also, a transparent electrode 5B is placed on the substrate 4.
Two etching processes are required to create the opaque metal thin film 5A, and etching becomes particularly difficult when SnO ₂ is used as the transparent electrode material.

In order to eliminate the above-mentioned drawbacks, it is conceivable to sequentially stack a divided electrode 17, a photoconductor thin film 18, and a transparent electrode 19 on a substrate 16 as shown in FIGS. 5 and 6. However, SnO ₂ , In ₂ O ₃ , or a composite film of these, which are commonly used as materials for the transparent electrode formed on the top layer in FIG. On the other hand, the photoconductor formed under the photoconductor is sensitive to high temperatures and may deteriorate (crystallize and become conductive) at the high temperatures used to produce the transparent conductive film. In severe cases, it may evaporate. For this reason, in the configuration shown in FIG. 6, it is absolutely necessary to first create a transparent conductive film, but such a method for forming a laminated film does not yet exist. Therefore, the laminated film structure shown in FIG. 6 cannot be realized, and the arrangement of the light receiving portions of conventional reading devices of this type has been limited to those shown in FIGS. 2 and 3. In order to realize the electrode arrangement shown in Figures 5 and 6, it was proposed to use an extremely thin vapor-deposited film of gold or the like as a transparent electrode, but in this case, it was difficult to control the film thickness, and the photoconductive thin film was difficult to control. It had drawbacks such as not being able to cover differences in level and would break, making it impossible to put it into practical use.

Therefore, an object of the present invention is to provide a light-receiving element having _a structure in which a light _- transmitting electrode is attached after a photoconductive film is formed _.
The object of the present invention is to provide a light-receiving element that is easy to manufacture and has excellent characteristics by using a transparent thin film.

Another object of the present invention is to provide a simple and highly efficient light-receiving element in which incident light does not pass through a glass substrate, an antireflection film is unnecessary, and there is no absorption by the glass substrate.

FIG. 7 is a perspective view of a reading device in which the light receiving element of the present invention is formed on the same substrate as the switch groups 9-1, 9-2, . . . shown in FIG. 4. below,
The manufacturing process of the light receiving element of the present invention will be explained with reference to FIG. The substrate 16 is made of an insulator such as glass or ceramic, and has a smooth surface. Of course, the substrate does not need to be transparent. The conductor patterns 17, 33-1, 33-2 on the substrate 16 are formed of a base metal.
It is made by patterning a multilayer thin film of Au superimposed on Cr using chemical etching. In the figure, part A is the lower electrode of the light receiving element, and part B is the source or drain electrode of the thin film transistor (FET switch). , 33-1, 33-2 are portions to which matrix wiring C is applied.

A photoconductor 18 (for example, Se-Te-
As, CdSe, etc.) are applied to a thickness of 0.5 to 2 μm by vacuum evaporation at a temperature of about 80°C. Furthermore, a transparent electrode 19 was placed on top of it using a magnetron-type low-temperature sputtering device using a target with a composition ratio of In ₂ O ₃ and SnO ₂ of 9:1, and an argon gas pressure of 5×.
10 ^-3 Torr, oxygen partial pressure 10 ^-4 Torr. Appropriate sputtering time is about 100 seconds and film formation rate is about 200 Å/min. The sheet resistance of the transparent thin film 19 formed under these conditions is about 100Ω and the transmittance is 75% or more.

In this case, the temperature of the substrate 16 is approximately 20°C higher than the room temperature at the end of sputtering, and there is no possibility of crystallizing or thermally damaging the photoconductive thin film 18 that has been applied previously. Katta. Further, there was almost no damage to the photoconductive thin film due to collisions of electrons and spatter particles, and no deterioration in the performance of the light receiving element was observed at all.

Next, a field effect semiconductor 30 (for example, CdS, CdSe, etc.) is applied to the part B by vacuum evaporation.
Can be attached to a thickness of μm. 0.01~0.5μ on top of that
m insulator material 31 (e.g. SiO, CaF ₂ ,
(SiO ₂ , Al ₂ O _3, etc.) is applied by vacuum evaporation or sputtering.

Furthermore, a gate electrode 32 is deposited using a mask so that a plurality of pairs of sources and drains can be controlled simultaneously. In the case of FIG. 7, since two thin film transistors are turned ON and OFF simultaneously, H-type gate electrodes 32-1 and 32-2 are formed. The characteristics of a thin film transistor are controlled by the semiconductor material; in the case of CdSe, when the gate voltage is positive with respect to the source-drain voltage, the source-drain becomes conductive, that is, the transistor is in an ON state.

The part C, that is, the matrix wiring part is the lead line D- of the drain electrode of the thin film transistor.
At the point where 1, D-2...... is made into a matrix,
D-1 and D-3 are connected to conductor 33-1, and D-2 and D
-4 are commonly connected to the conducting wire 33-2. This is a method in which when the number of arrays is n×m and n pixels are arranged in m blocks, the i-th pixel of each block is commonly connected.As is well known, the number of pixels in the array is It is not limited to a number.

As is clear, the device of FIG. 7 corresponds to the part enclosed by the dashed line in the reading circuit shown in FIG. Connections from this portion to an external circuit can be made by known means such as wire bonding using thin conductor wires.

The thin film type photodetector array fabricated by the above procedure can be used with a known reading device (for example, Japanese Patent Application
−146588, etc.). In other words, if the image of the original is formed onto the photodetector array using a one-to-one imaging optical system such as a self-occurring lens, a resolution matching the feeding speed of the original can be obtained using a method similar to the known storage type reading method. Then, each line can be converted into a time-series signal and read out. When this signal is input to a suitable known electrical signal input type hard copy device, the same image as the original input to the reading device is obtained as a hard copy.

In addition, in the manufacturing process of the light-receiving element of the present invention described above with reference to FIG. 90%
In addition to In ₂ O ₃ -10% SnO, SnO ₂ to which 5 to 10% of Sb ₂ O ₅ is added, SnO ₂ , In ₂ O ₃ alone, etc. can be used.

The thin film type light receiving element array implemented by the present inventors has the arrangement shown in FIG.
A commercially available MOS-FET was used instead. The conductor pattern 17 on the substrate 16 is made of a 700 Å thick Au layer on a 800 Å thick base metal Cr, the array pitch is 250 μm, the conductor width is 200 μm, and the number of arrays is 40.
It's a book. Se95%-As5% semiconductor was evaporated to a thickness of 0.9 μm through a metal plate mask so that it was deposited only on the light-receiving area corresponding to part A in FIG. A photoconductor of 20% Te-5% As is deposited to a thickness of 0.3 μm.

The base material thus obtained is covered with a metal plate such that the light receiving area of one pixel is 200 μm x 200 μm, and then placed in a sputtering device. The sputtering device consists of a magnetron-type cathode that avoids electron bombardment of the photoconductor, which prevents the Se-Te-As-based amorphous photoconductor from being thermally degraded. . Targets are In ₂ O ₃ and SnO ₂
The composition ratio is 9:1, and sputtering is performed for 120 seconds under the conditions of argon gas pressure of 5×10 ^-3 Torr and oxygen partial pressure of 1×10 ^-4 Torr.

The transparent electrode 19 obtained under the above conditions has a thickness of 900 mm.
Å, transmittance 75%, sheet resistance 150Ω. The scanning circuit when assembled into the configuration shown in Figure 4 is:
Composed of a shift register and MOS-FET, the 40 pixels were divided into 5 blocks of 8 pixels each, and wired in a matrix scanning manner. An ultrasonic bonder made of thin Al wire was used to connect the light receiving element to the external circuit.

The light-receiving element of the present invention produced as described above is incorporated into a known reading device equipped with a 1:1 imaging optical system using a self-occurring lens, and operated.
When the output was displayed on a storage-type CRT, the displayed image closely matched the input image.

As is clear from the above description, according to the present invention, since the transparent electrode 19 formed by a magnetron type low-temperature sputtering method is used, there is no need to heat the substrate to a high temperature during formation, and the transparent electrode can be used as a photoconductor. After the thin film is formed, it can be formed on top of it. As a result, the following excellent effects can be obtained.

(1) The light image only passes through the transparent electrode 19 and is focused on the light-receiving part, and does not pass through thick glass, so light loss due to reflection and absorption is reduced and conversion efficiency is improved. This will reduce image distortion.

(2) Since the substrate can be opaque, the range of material selection is expanded, allowing the use of ceramics, etc.
Therefore, thin film wiring becomes easy and more precise and fine patterns can be obtained.

(3) Anti-reflection treatment of the substrate is not required, and pattern formation of the divided electrodes 17 on the substrate can be achieved by one etching process, thus simplifying the manufacturing process and reducing costs.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional document reading device configured with a reduction optical system, FIG. 2 is a plan view of a known thin film type light receiving element, FIG. 3 is a cross-sectional view thereof, and FIG. A block diagram showing an example of an applicable reading circuit,
FIG. 5 is a plan view of one embodiment of the present invention, FIG. 6 is a sectional view thereof, and FIG. 7 is a schematic perspective view of an embodiment in which the light receiving element of the present invention is formed on the same substrate as the switch element of FIG. 4. It is. 8... Light receiving element, 16... Substrate, 17... Divided electrode, 18... Photoconductor thin film, 19... Transparent electrode.

Claims (1)

[Scope of Claims] 1. A light-receiving element constructed by laminating a split electrode, a photoconductor thin film, and a light-transmitting electrode on an insulating substrate in this order, with the light-transmitting electrode underneath. 1. A light-receiving element characterized in that it is formed by low-temperature sputtering that does not alter the quality of the formed photoconductor thin film. 2 The material of the transparent electrode is In ₂ O ₃ , SnO ₂ , In ₂ O ₃ −
The light-receiving element according to claim 1, wherein the light-receiving element is one selected from the group consisting of _{SnO2 and SnO2} - _Sb2O5 .