JPS60147158A - Close-contact image sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a long contact type image sensor of the same size as the width of a document, using an amorphous silicon thin film in the photoelectric conversion element portion, and particularly relates to a long contact type image sensor that uses an amorphous silicon thin film in the photoelectric conversion element portion. The present invention relates to a contact type image sensor that has improved optical response characteristics and can be used in high-speed reading devices such as high-speed facunmills and intelligent copiers.

<Prior Art> One-dimensional image sensors are known for use in reading documents in facsimiles, intelligent copiers, and the like. Conventionally, this type of light-receiving sensor uses a -dimensional solid-state image device (COD or MOS type), and obtains a corresponding image information signal by vertically exposing and reducing an original image. This -dimensional solid-state image device is manufactured using IC technology and is approximately 30 cm in size, and an optical system with a long optical path length must be used to guide the reflected light from the original to the light receiving section. However, it is difficult to miniaturize the device. Furthermore, such an apparatus requires complicated adjustment of the optical system, and also causes problems such as a decrease in the amount of light at the periphery of the screen and a deterioration in resolution.

In order to improve these problems, a so-called contact type image element has been devised, which uses a long image element with a length equal to the width of the document and forms a close image using a fiber lens array. Such a contact type image element requires a large photoelectric conversion section, and requires the formation of a uniform photoelectric conversion film over a large area. Currently, Cd8/CdSe film, Se-A5-Te is used to make long one-dimensional image elements.
system amorphous thin film.

Amorphous Si thin films, etc. have been proposed, but their light response speed is insufficient, or their photosensitivity and contrast ratio are insufficient.
The reading time per line is limited, which is not necessarily sufficient for high-speed reading devices, and there are problems in practical use.

<Object of the Invention> The present invention has been made in view of various problems of conventional contact type image sensors. An object of the present invention is to provide a contact image sensor that has high-speed photoresponsiveness and has significantly improved characteristics required for an image sensor, such as contrast ratio and photosensitivity.

<Example> Fig. 1 is a plan view showing the basic structure of a contact type image sensor according to the present invention.
As shown in the figure.

The photoelectric conversion element is composed of a flat common electrode 2 provided on a transparent substrate 1, a semiconductor layer 3, and individual electrodes 4 processed into stripes. One of the electrodes 2.4 above needs to be a transparent electrode, but the positions of the common electrode 2 and the individual electrodes 4 may be reversed, and in some cases, the substrate 1 needs to be transparent. Nor. The other end of the individual electrode 4 is connected to a semiconductor layer 5 which is separated from the photoelectric conversion semiconductor layer 3 and serves as a blocking diode for preventing deterioration. The other end of the semiconductor layer 5 is connected to an IJ source electrode 6 for scanning the individual electrodes 4. The matrix electrode 6 is formed of a metal film on the substrate 1, and is divided into groups corresponding to the number of individual electrodes 4 belonging to the common electrode 2, and the matrix corresponding to the divided group is The electrodes are connected in common.

For example, a glass substrate can be used as the light-transmitting substrate 1, and if light-transmitting properties are not required, a heat-transmitting organic film typified by polyimide resin or a ceramic substrate is used. As a transparent electrode, indium oxide (I n203), tin oxide, (SnOz), or indium tin oxide (ITO) can be used.If translucency is not required, At+Cu+Cr+A
u + P t + In + In Sn alloy.

A metal electrode such as In-Ga alloy or Ni-Cr alloy is used. The semiconductor layer 3 is made of amorphous hydrogenated silicon and has a pin diode structure.

The equivalent circuit and scanning circuit are shown in FIGS. 3(a) and 3(b).

FIG. 3(a) is an equivalent circuit diagram of a method that does not use a blocking diode to prevent crosstalk, and requires switching elements 7 corresponding to the number of pixels. On the other hand, FIG. 3(b) shows a switching element 8118 using the matrix type switch system shown in FIG.
2 is an equivalent circuit diagram of an image sensor in which the number of pixels is reduced by 2. The image sensor according to this example can scan using either method, but in the following explanation, a matrix type switch method will be adopted. In this switch method, a real-time readout method is used since the use of an accumulation type signal readout method requires a long readout time and is disadvantageous for high-speed reading. By employing matrix wiring, the number of switching elements (8+, 82) can be significantly reduced. As the switching elements 81 and 82, for example, C-MO
S) By using a transistor and connecting each gate to a shift register and sequentially performing a switching operation, each pixel outputs a signal current according to the amount of light it receives, and image information can be read.

Figure 4 shows the voltage-current characteristics of the contact image sensor with the above structure, Figure 5 shows the illuminance dependence of the output current, and Figure 6 shows the reverse bias voltage dependence of the optical response speed. The compatibility as an element will be explained. Song m in Figure 4
Curve A shows the characteristics in the bright area of 60 lux, and curve B shows the characteristics in the dark area.As is clear from both lines, this image sensor has a voltage of 5V.
It is possible to drive at the following low potentials, and the contrast ratio (static characteristics)
shows an extremely large value of ~104. As shown in Figures 5 and 6, it exhibits high sensitivity and good γ-characteristics, as well as excellent photoresponsiveness.
0%) and falling (90%) response time t
When on+toff is defined as shown in FIG. 7, both of these response times exhibit extremely fast responses of 50 .mu.sec or less, exhibiting extremely favorable characteristics as an element for high-speed reading.

The photoelectric conversion film 3 of the above image sensor is made of amorphous hydrogenated silyran, so it tends to have a specific volume resistance of the p-layer or n-layer, which may cause leakage between pixels, so it is necessary. A shape in which the p layer or n layer is divided into patterns having the same shape as the individual electrodes 4 is preferable. At this time, the effect of the etching process on the device characteristics is small.

Note that the p or n layer on the light irradiation side needs to be a thin layer of 50 to 100 OA in order to minimize optical loss in this layer, and the i layer must be made to eliminate defects such as pinholes to prevent current flow. 05μm or more or more 10μm to eliminate rounding 9
Below, the film thickness is preferably about 1 to 3 μm, and 10
A specific resistance value of 7 Ω·m or more, preferably about 10 8 Ω·m is required.

Hereinafter, details of the present invention based on the above basic structure will be explained in Example 7.
show.

[Example 2] A 60×150-Pyrex glass was used as the substrate 1. On this, At was deposited to a thickness of about 200 OA, and the common electrode 2 and lower layer wiring 6 for IJ node wiring were formed using a photolithography process. Form a pattern. In order to form a photodiode and a blocking diode, 50% of p-type amorphous silicon was deposited using the plasma CVD method.
After OA deposition, I-type and N-type amorphous silicon films are deposited to a thickness of 2 μm and 100 Å, respectively, to form a semiconductor layer 3.5. The amorphous silicon thin films 3 and 5 thus formed are etched by a normal dry etching process using CF4. Processed into stripes based on the density of the fight. Note that the conditions for forming the amorphous silicon film are as follows. The substrate temperature is 2501:,
Discharge pressure 0. aTorrs high frequency power 100W (8
0 mW/crl), the p-type amorphous silicon layer was made by diluting a mixed gas of B2H6 and SiH4 with a volume ratio of 500 ppm to about 10% with H2, and the i-type was made by diluting 5iHa to 30% with H2. Mixed gas, and n-type is PH3
A mixed gas having a volume ratio of 110,000 ppm and SiH4 is diluted to about 20% and decomposed by glow discharge. Next, a SiCh film (approximately 200 OA) 9 is formed on this semiconductor layer and matrix wiring portion by plasma CVD, and through holes 10 and 11 are etched as shown in FIGS. 1 and 2.

It goes without saying that in addition to the 5iOz insulating film, for example, 5j3N4 can also be used. Furthermore, on this insulating film 9,
ITO (Inz03SnO2 (5
X)) is evaporated to about 100 OA by RF sputtering, and At is evaporated to about 300 OA to the upper layer wiring of the matrix wiring portion. At the same time, At is further vapor-deposited on the ITO in the blocking diode portion 5 to form a light-shielding film 12. The ITO film 4 has the same stripe shape as the n-layer, with 8 lines/w, and the matrix wiring part 6 is also etched into a predetermined pattern 7, resulting in 1024 pixels (1 pixel: 10
A photoelectric conversion section consisting of 0x100μ2) is created. Each terminal was connected to a drive circuit as shown in FIG. 3(b) above, and image signals were read out from RL in real time. This embodiment enables high-speed reading of 1 ms/line or higher.

[Example 3] An element structure is used in which the direction of light irradiation is opposite to that of Example 2. First, on the Pyrex glass substrate 1, about 10%
0OA of 5nOz, At was vapor-deposited on the main I/lithography wiring part, and etched into a predetermined pattern.
A common electrode 2 and a lower wiring section 6 were formed. Note that it is desirable to form in advance a light-shielding film on the substrate for blocking light from the blocking diode and limiting the image exposure width.

If the light shielding film is a metal thin film (Cr, At, etc.), it goes without saying that an insulating film such as Sioz must be formed thereon by sputter deposition or the like.

P type for light receiving part and blocking diode part.

Approximately 80 I-type and N-type amorphous silicon layers.

The conditions for forming a zero amorphous silicon film with a film thickness of 3 μm and 300 A are almost the same as in Example 2. In this case as well, after etching only the n layer into stripes, a polyimide photoresist film is formed (approximately 1 μm thick) and A
x, form a through hole like a tube. This photoresist is used as an interlayer insulating layer without being peeled off. The individual electrodes 4 and the upper layer of the matrix wiring are formed and patterned by At vapor deposition on this, thereby forming a photoelectric conversion section having a pixel density of 8/. When each terminal was connected to the drive circuit as shown in Figure 3(b) and the sensor characteristics were evaluated, the diode characteristics were almost the same as in Example 2, and the signal variation between pixels was within ±5%. It was stable and good characteristics were obtained.

[Example 4] Almost the same sensor structure as Example 2, but photoelectric? The amorphous silicon layer of the conversion section is completely separated for each pixel. When the leakage current between the pixels of this image sensor was compared with that of Examples 2 and 3, it was confirmed that the leakage current was weak and had no adverse effect regardless of the structure of either Example. In this way, the p-layer has a specific resistance value of 100
- If it is about α or more, there is no need to divide according to the pixel density, and if only at least n layers, which have low resistance, are divided, there will be no horizontal flow of images, and it is possible to create an excellent image element.

〔effect〕

As described above, according to the present invention, a long image element with a simple element structure can be easily manufactured. Furthermore, high-speed reading elements with excellent sensitivity and responsiveness can be manufactured with good mass productivity.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the basic structure of an embodiment according to the present invention;
Fig. 2 is a 1-1 sectional view of the same, Fig. 3 (a) is an equivalent circuit diagram of the same embodiment, Fig. 3 (b) is another equivalent circuit diagram of the same embodiment,
FIG. 4 is a voltage-current characteristic diagram of the same example. FIG. 5 is a surface illuminance-output current characteristic diagram of the same example. FIG. 6 is an applied voltage-light response speed characteristic diagram of the same example. 7 is a diagram illustrating the definition of response time ton+toff in FIG. 6. FIG.

Claims (4)

[Claims] (1) In a processor in which image reading elements that convert optical information into electrical signals according to the light intensity are arranged on a support substrate, a photoelectric conversion film having a pin structure and a photoelectric conversion film on each surface of the photoelectric conversion film are provided. A contact image sensor comprising a flat common electrode formed and individual electrodes corresponding to image reading elements, wherein at least one of the common electrode and the individual electrode is made of a transparent electrode. (2) The photoelectric conversion film is made of amorphous V silicon.
2. The contact image sensor according to claim 1, comprising a -1-n diode structure, reverse biased by an electrode, outputting a signal current corresponding to the amount of incident light, and obtaining image information. (3) In the photoelectric conversion film, only the semiconductor layer in contact with the individual electrodes in the pin stacked structure is divided into almost the same shape as the individual electrodes, and the other semiconductor layers are integrally formed. A contact type image sensor according to claim 1 or 2. (4) The photoelectric conversion film is sequentially arranged on the substrate side electrodes such as p and itn.
Claim 1, characterized in that the n-layer is formed of a semiconductor layer consisting of a shape, has a specific resistance value of 1060 m or less, and a film thickness of 50 A to 1000 A, and is divided into the same shape as the individual electrodes. Close-contact image sensor 0 according to item or item 2