JPS5884457A - Long thin film reading device - Google Patents

Abstract

PURPOSE:To offer a reading device with fast photo-response speed, less dispersion of sensibilities among elements, long-period stability and easy manufacture method thereof. CONSTITUTION:The reading element 9 is constituted of the lower metallic electrode 5 formed on an insulating substrate 8, an amorphous Si layer 6 provided on said lower metallic electrode and the upper clear electrode 7 provided on the amorphous Si layer. The lower metallic electrode is arranged in a plurality to correspond to reading bits. For the material of the lower metallic electrode, Cr-An (double layer), Ni, Al, Cr, Pt, Pd, Mc, Ti, etc. are available. For the formation of the amorphous Si layer, a homogeneous film is formed be a method of plasma CVD, sputter, evaporation, etc., and thereat non-doped one or one formed into an I type layer by doping small amount of hydrogen and a P type layer with doped B and other III group element of a periodic table is appropriate. For the upper transparent electrode 7, an ITO film (In2O3+SnO2) is used, and the ratio between In2O3 and SnO2 is suitably selected. The thickness of this ITO film is suitable in approx. 500-2,000Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel image reading device for use in facsimile machines, printers, and other apparatuses that read fine images and perform information processing.

More specifically, a uniform thin film of amorphous silicon is used as a photoconductor, and electrodes 1 are sandwiched on both sides of the photoconductor.
The present invention relates to a reading device having one structure.

Conventionally, reading devices used in facsimile machines, printers, etc. are CCD, photodiode array, etc.
Semiconductor image sensors such as OS photodiode arrays have become widely used.

Since these image sensors usually use a reduction optical system, lenses and the like are required, resulting in a long optical path length (resulting in a major problem in reducing wrinkles in the device).

On the other hand, a one-shot thin film reading device having the same dimensions as the original width has been proposed. This device is called a planar type device, and as shown in FIG. 1, a photoconductive layer 2 is provided on a substrate 1 and a pair of electrodes δ and 4 are used to form an device corresponding to one bit. A plurality of these elements are formed in a row, and photocurrent corresponding to light irradiation of these element portions is sequentially measured and read.

In this element, there is a limit of about 10 μ of the needle when the electrode ink and 4 are brought extremely close to each other. For example, in the case of a decomposition level of 8 lines/WWL, the time required for one line of A4 width is about 20@Sec, and this speed f is not enough to cope with the reading speed of fast faxes, printers, etc. It was inadequate.

In addition, the chalcogen glass-based photoconductors used in these reading elements, such as 5e-As-Te, undergo crystallization near 80°C, resulting in poor long-term stability.
In addition, in the case of a composite system, since the composition is complex, it is difficult to control the components during manufacturing, which affects the characteristics of the light receiving element. Ratsuki L] It was a big cause.

In addition, in recent years, p-1-n type amorphous silicon has been used for solar cell applications, but these are, for example, disclosed in Japanese Patent Application Laid-open No. Sho Fs6-2784 and shown in V1 above a transparent electrode. The order of p −i −n “epm,
It has a complex structure in which a 1 m long, n-type amorphous silicon film is formed and then covered with a metal electrode, and due to the difficulty in controlling the film formation of the amorphous silicon layer, there is a large A-luck in performance. Furthermore, in order to prevent current leakage between pits, it is necessary to completely separate each pit consisting of an upper electrode, a photoconductive layer, and a lower electrode. Manufacturing was troublesome as it required a large number of steps.

Is this pln? 1 exists because the dark resistance of the n-type semiconductor of the photoconductor formed is as low as 10@4 to 10' Ωa, and each pit is not completely separated (7) and a current flows between the pits.

Therefore, the present invention eliminates the above-mentioned drawbacks of conventional reading devices, and provides a new reading device that has a high optical response speed, has little variation in sensitivity between elements, is stable over a long period of time, and is easy to manufacture. The purpose is to help people.

- A film is formed, but at this time, one layer is undoped or one layer is doped with a small amount of hydrogen.
For the thickness, use Q, 6μ寞~5μ凰, In2o
The ratio of II and 5rKh is selected appropriately. Also, ITO with
Appropriate film thickness is about 500 to 2,000A! be. This layer uniformly covers all the amorphous silicon layers used as the light receiving element.The lower metal electrode and the amorphous silicon layer form a sandwich structure light receiving element or light receiving element. form a group.

In this case, it goes without saying that an amorphous silicon layer is provided to prevent direct contact between the lead wire connected to the lower metal electrode and the upper transparent electrode.

In the sandwich structure described above, it is also possible to use a reverse arrangement of the metal electrode and the transparent electrode.

Next, operations g and 5 of the present invention will be explained.

An equivalent circuit and driving principle when using the light receiving element described above will be explained using FIG. 6. The light receiving element 9 shown in FIG. 2 is connected to the condenser 110 (10-1...
...1O-n) and diode 11 (11-1...
. . 1l-n) can be expressed in parallel circuit 1 equivalently as follows: 1. ? Wear.

Here, the capacitor 10 has a capacitance f formed by the lower metal electrode 6, the amorphous silicon layer 6, and the upper transparent electrode 7. This capacitance also includes the line capacitance generated by the lead wire force. Diode 11 (11-1...
. . 1l-n) indicates an amorphous silicon layer. Illustrated capacitor 10 and diode 11
Each reading element corresponds to one bit in one line, and each reading element is provided for one line, and the original to be read or the object to be read is scanned while crossing the reading elements provided for one line. and read.

As shown in FIG. 6, when the shift register 12 switches the switching element 16 (for example, 0MO8) in the order of 16=1 to 1!1-n, the reading element x no 1 (10, 1
1)' is grounded via the operational amplifier 14. At this time, the opposite side of the reading element (10? 11) is connected to the Noquious power source 15 via the upper transparent electrode. At the scanning start point 1, the reading element (10,11)L'
Since there is no charge in S, the current from the noise power supply flows through the switches 16-1 to 16-1 to the operational amplifier 14.
``I?'' is observed, but this is canceled as a signal.

When entering a line that requires reading, for example, if there is a white 1 document corresponding to 10-1, the amorphous silicon layer becomes conductive, and as a result, a current flows from the noise power supply 16 and charges 10. The charging current at this time is detected by the operational amplifier 14.

Next, when the shift register 12 switches 1s-2, if 10-2 corresponds to the black of the original, the amorphous silicon layer in this part is insulating, so the charge charged in the previous cycle remains. Therefore, no charging current flows and no current signal is generated in the operational amplifier. One line is scanned in this way (and the next line is scanned in the same way).

Next, the effects of the present invention will be explained.

It has been found that the use of the reading element of the present invention described above has the following outstanding effects.

Since the reading element of the present invention has a simple configuration as described above, it is possible to avoid the variation in the signal current between bits compared to the conventional 11.
As shown in FIG. 5, it was possible to keep the value from 0% or more to within ±5%.

This made it easy to set the threshold hold level and measure the stability of the signal.

Also, the manufacturing process has become much easier because it is only necessary to deposit the amorphous silicon layer and the ITO layer in sequence. It is possible to produce benefits in terms of cost.

In addition, the applied voltage and output voltage Rq# characteristics of the reading element of the present invention are determined as follows.
As shown in the figure, it can be driven at a low voltage f of 0 to -10V, as can be easily solved from this graph.

Also, what is particularly noteworthy is that when the bias voltage Ov is applied, the contrast ratio is 5000 to 12000 degrees, which is significantly higher than the 50 to 100 of the conventional p-1-21 structure photodetector! be. The high rise and fall at this time are excellent compared to 111 eK. Regarding the light sensitivity, the reading element of the present invention is 10 pm/1 m
(100μm1X100μia) and conventional s・-〒
・A value nearly twice that of 1 was obtained.

In addition, amorphous silicon ASLL using the developed IjIK
・Very advantageous in manufacturing! be.

The reading element of the present invention obtained as described above has a pitch of 8/1
I was able to read an A4 width (210fi) with less than 10ffls.

The present invention will be described in detail below using Examples.

<Example 1> A glass substrate or a glazed ceramic substrate fi is used as the substrate.

A lower electrode of approximately 3000 ACrf is formed by electron beam evaporation, and predetermined notch turning is formed by 7 otolithography. (Crt was used in Example 1, but since it is used as the lower electrode material, τ1 *
Mo e N 1-cr T A l e A u *
(Pt, etc.) Next, an amorphous silicon film of about 1 and 4 times is formed by glow discharge of silane gas. In this case, the conditions are: substrate temperature (〒s) - 200~3
00C1 discharge pressure (p) = 0.2 to I Torr, distance between electrode plates (d) = 20 to 50 ■, 1tFA power (P) =
10-100W, gas flow rate (r) = 10-50SCCJ
SIH4), and the film was deposited for about 1 hr't'. Furthermore, ITO (In, 08.8nO,) was added as the upper transparent electrode.
DCC sphutter using reactive gas of 0s (Os partial pressure 1.5X10-Torr) It was formed using a metal mask with a noise voltage of about 1500 mu 5 V. As a result of a reading test using this device in the circuit shown in %b,
I was able to read speed 1 below 10111g/11ne (A4 original).

Regarding heat resistance, it was confirmed that the sensor's characteristics were not degraded by heat treatment up to 600 degrees Celsius, making it a very thermally stable reading element.

<Example 2> 10 ppmd of B as an amorphous silicon photoconductive layer
In the case of 0%, it was possible to obtain results with almost no change in characteristics compared to the case of t, which was formed using only one layer.

Gas is 8 using 100ppmBB100pp pace)
Drop deposition was carried out under the same conditions as in Example 1 with a gas composition of 1H4/llm=1 for about 2 hours.

<Example 6> Cr-Au was used as the lower metal electrode 5, and ITO (10 mol% In2o8+ 90 mol% 81
Using α0 to put Cr on the glass substrate 8 at ~500A, mu uv~80
A metal electrode film is grown by electron beam evaporation at a substrate temperature of 250°C. Subsequently, Au and Cr are etched using photolithography to form a predetermined metal electrode.

Next, a glow discharge 1 amorphous silicon layer is deposited to a thickness of 1 μm. The conditions for making the l'M amorphous silicon film are as follows: 81H4if gas mixed with a small amount of hydrogen is used, and R1? A power 20-50W.

Gas flow rate 2D~508CCM, pressure 0.4~0.6
Torr, substrate temperature 200-31] 0" C1 electrode plate distance 40-30 minutes to 1 hour. Subsequently, the ITO of the upper transparent electrode 7 is heated to about 15
00mm film is deposited. The creation conditions are Nowa 170-2
00W, oxygen partial pressure t5×10 Tart, total pressure (oxygen+alnon) 4×10''''5 Tarry% for about 10 minutes.

FIG. 7 shows the I-V% characteristics of the sensor produced in this manner. The bright and dark currents at 07:00 are light receiving area 100μ x
6.6×10 μm (100 μm) per 100μ weight, respectively
per lux), 6.0×10 mm, and the contrast ratio is 1
It was t000″1%.

From this, it became clear that Ov no 9 Ias, that is, No 9 Iasu no 1, is a fist that is sufficiently effective.

<Example 4> Using AI for the lower metal electrode, e-turn the electrode.

After patterning, the metal surface oxide film layer is baked once in an electrode baking oven to grow a thermal oxide film at 20 A@degrees. On top of that, amorphous silicon is deposited to approximately 1 μm using the glow discharge method.
Electrodeposit it to form a photoconductive layer. This amorphous silicon is non-doped type 1 or all or N a
Weak p containing a trace amount (10 to 1000 ppm) of F'-y
There is only one layer of m. Alternatively, an amorphous silicon film may be fabricated by a reactive Kustarling method. Further, as a transparent electrode, ITO (indium oxide film) or In5O11+8m is placed on top of this as a transparent electrode.
The O 2 oxide film layer that is deposited and serves as a negative and negative bias application electrode serves as a blocking layer against hole injection from the AI electrode, and has the effect of suppressing dark current, resulting in a high contrast ratio.

□-- A on the 9th FB where the axis effect appears! Shows the difference between the presence and absence of an oxidized layer.Is the driving noise during actual reading -5V? However, at this time, it is possible to increase the contrast ratio by several to several tens of times by adding an AI oxide film layer.

For example, when Alt' is used as a metal electrode, results obtained are 1 without an oxide film (brightness ratio<1000), whereas results obtained with an oxide film are obtained (brightness ratio≧2000).

In another embodiment, a structure is adopted in which KCr is used instead of AI as the lower electrode. In the case of Cr, the flatness of the metal surface is higher than that of AI (the surface condition of the amorphous silicon film deposited on Cr is also good, f there are fewer defective bits,
The dark current of the structure f using a Cr oxide film is even lower than that of the structure A) and higher than the brightness ratio (brightness ratio', gooo).

The oxide film layer in the above-mentioned example is created by direct thermal oxidation of the lower metal electrode or by using l111111 oxidation such as anodic oxidation, but it is also possible to use natural oxidation or various oxidizing agents. There is a heated argument.

That is, in the four-pronged metal electrode 1, by providing an oxide film layer on the optical surface of the lower metal electrode, hole injection from the lower metal electrode can be prevented and a high contrast ratio can be obtained.

The above embodiment will be described in detail in 1%.The present invention has a plurality of metal electrodes which are provided on an insulating substrate and divided into pits, and which are formed in a flat plate shape on the plurality of metal electrodes. The method is characterized by comprising an amorphous silicon layer, and a transparent electrode formed in a flat plate shape on the amorphous silicon layer at a position facing the plurality of divided metal electrodes.

Further, by making the amorphous silicon layer 1 m long or a P-type layer, the dark resistance can be increased.

Furthermore, the thickness of the amorphous silicon conductive layer can be increased, resulting in an increase in the response speed of the reader.

Historically, by oxidizing the surface of the multiple lower electrodes, especially Cr or the lower metal electrode, in contact with the amorphous silicon, the dark resistance can be kept low because the interface with the amorphous silicon acts as a hole blocking layer.
Wear.

[Brief explanation of the drawing]

Figure 91 is a schematic diagram showing a conventional Zolenar type reading element, Figure IN2 is a cross-sectional view of the reading element of the present invention, and Figure 3.
Figures a = d are Figure 1 showing various arrangement configurations of the lower metal electrode, Figure 4 is Figure 1 showing the WRMiL element of the present invention viewed from the upper transparent electrode side, and Figure 5 is the bright state and A graph showing the photocurrent in the dark is available. [Figure 8 is a diagram showing the characteristics of A/with and without an oxide layer. (Symbols in the figure) 5, + 1 substrate, 2 photoconductive layer. 3 electrodes (1) 4 electrodes (2) 5 Lower metal electrode 6 Amorphous silicon 7 Upper transparent electrode 8 (Insulating) substrate 9 Light receiving element 10 "Condenser 11 / Iode 12 Shift register switching element" 5
14 Operational amplifier 15 Noisy power supply] (c) (d) 8th
I! ! ! Mains voltage (V) Continued from page 1 Inside the Ebina factory of Tsukus Co., Ltd. Inside the Ebina factory of Tsukus Co., Ltd.

Claims (1)

[Claims] 1) A plurality of metal electrodes provided on an insulating substrate and divided into pits, an amorphous silicon layer formed in a flat plate shape on the plurality of metal electrodes, and an amorphous silicon layer formed on the amorphous silicon layer. A long thin film reading device comprising a transparent electrode formed in a flat plate shape at a position facing the plurality of divided metal electrodes. 2) A transparent electrode formed in a flat plate facing the metal electrode is placed at the position of the plurality of metal electrodes divided into each pit, and a plurality of transparent electrodes divided into each pit are placed at the position of the transparent electrode formed in the flat plate shape. 6) The amorphous silicon layer is an i-type or a P multilayer. The elongated thin film reading device according to the range 1 JIJ or item 2.