JPS601865A - Close contact type image sensor - Google Patents

Abstract

PURPOSE:To enable to reproduce fresh image by forming to reduce the interelectrode distance of photoconductive element arrays from the center to the end, thereby maintaining the resistance value distribution of the photoconductive film over the entire portion substantially constant. CONSTITUTION:The distance L between the electrodes 13 is formed so that the distance Lc of the centers is considerably larger than the distance Le at the end part. The values of the distances Lc, Le and the variations of them are calculated by measuring the bright sheet resistance of the photoconductive film 12 and the deformation of the value of the W by experiments. The beat phenomenon of the bright resistance distribution due to side etching of the width of the electrode is cancelled, the conversion to binary value can be facilitated, and fresh image can be reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a contact image sensor, and more particularly, to a contact image sensor, which compensates for undulations in the resistivity distribution of a photoconductive film over all bits of the distance between electrodes of a photoconductive element array. The present invention relates to the structure of a contact type image sensor element formed in a tapered shape.

(2) Background of the Technology A conventional close-contact type document reading device has the configuration shown in FIG. 3 represents a light-receiving element array (referred to as a large-sized image sensor or contact type image sensor, Is), and a light guiding system using Irradiated by light source 1, the scattered light (reflected light) corresponding to the black and white of the original is transmitted to the light guide thread (
The light is guided to a light-receiving element array (Is) 3 by SLA) 2, an erect, life-size real image is formed on Is, the light corresponding to black and white is converted into a photocurrent, and the original is read by this photoelectric conversion.

The configuration of the image sensor described above is shown in FIG. 2, in which the sides marked with symbols G and S represent the group side and select side, respectively, t is time, and E is the rectangular wave voltage that drives the photoconductive film. shows. The contact type (large size) image sensor shown in Figure 2 has 1728 elements if the A4 width resolution is 8 lines/mm.
It is made of 125 μm pinhole.

One of the elements constituting one bit of the image sensor is the third
This is shown in the plan view and cross-sectional view of Figures (al and (bl). In the figure, 11 is the substrate, 12 is the photoconductive film, and 13 is the extraction electrode. The area surrounded by the dotted line in the figure is the area occupied by 1 bit. In Fig. 3fa), L is the distance between the electrodes, and W is the distance between the electrodes.
indicates the electrode width.

The manufacturing of such an element can be explained with reference to FIG. 4 and subsequent figures, which are exaggerated and schematically created for explanation (note that although the scales in FIG. 4 and subsequent figures are different, the same parts as those already illustrated are given the same reference numerals. ), cadmium selenide (CdSe) or cadmium sulfide (CdS) on the substrate 11
A photoconductive film 12 is formed. Note that fat and (bl) in the same figure are a plan view and a cross-sectional view of one board.

Next, a metal film 13a forming the electrode 13 is formed by vapor deposition as shown in the plan view and cross-sectional view of FIG. 5(a) and [bl.

The metal film 13a is then patterned by mesa etching so that individual electrodes I3 can be formed separately - the electrodes thus formed are partially shown on an enlarged scale in FIG. As explained with reference to FIG. 2, 1728 peelable electrodes are made in a large image sensor.

(3) Prior art and problems The document reading device described above utilizes the change in the resistance value of the photoconductive film for photoelectric conversion, and the form factor L/W (L is the distance between the electrodes, W
Generally, the electrode width (see FIG. 3) is formed to have the same value over all bits.

However, since the substrate 11 of the image sensor is long, it is extremely difficult to form a film so that all the photoconductive films have the same bright resistivity. A so-called undulation occurs in which the ratio is large at the edges (periphery) and small at the center. It is the seventh
The horizontal axis represents the position on the substrate, and the vertical axis represents the bright sheet resistance ρS of the photoconductive film.According to the prior art, the bright sheet resistance of the photoconductive film is the curve A. It changed as shown in. Note that C on the horizontal axis indicates the center portion of the substrate.

Furthermore, reflecting the large size of the substrate, the pattern etching that determines the electrode width W cannot be strictly uniform, and the amount of side etching (lateral etching) in the patterning described above is small at the center and small at the edges. The portions are large;
The element width, that is, the electrode width W is formed to be large at the center portion and small at the end portions.

Due to the above-mentioned factors, the resulting bright resistance distribution exhibits a large undulation that is high at the edges and low at the center, and the margin width of the level setting that determines binarization is There is a problem in that the area is significantly narrowed, making it difficult to reproduce clear images.

(4) Purpose of the Invention In view of the above-mentioned conventional problems, the present invention provides a contact type image sensor in which the resistance value distribution of the conventional image sensor array is small at the center and highly undulating at the edges (periphery). It is an object of the present invention to provide a contact type image sensor in which elements are formed so that the resistance value distribution is substantially constant over the entire portion of the image sensor and clear image reproduction is possible.

(5) Structure and object of the invention According to the present invention, an image sensor made of a photoconductive film is provided, and the distance between the electrodes of the photoconductive element array is decreased over all bits from the center to the end. This is achieved by providing a contact type image sensor that is formed into a tapered shape to compensate for the waviness of the resistivity distribution of the photoconductive film.

(6) Examples of the invention Embodiments of the present invention will be explained in detail below with reference to the drawings.

The inventors of the present invention have found that, in a conventional contact image sensor, (1) the distribution of bright resistivity is small in the center part and large in the edge (periphery) part, and (2) in electrode formation by etching, the electrode width W is in the central part. We focused on the fact that the resistance value distribution of the image sensor array is small in the center and large at the edges, reflecting the effect of side etching, and that the resistance value distribution of the image sensor array is small in the center and large in the edges. In order to correct the above-mentioned waviness distribution, we considered changing the distance between the electrodes of the contact type image sensor element over all bits, that is, for all electrodes.

Is bright resistance distribution +<p 1 in a contact image sensor?
It is expressed as p=ρs−L/W. Here, it has already been explained that the width W of the electrode is formed to be large at the center part and small at the end part as a result of side etching. Conventionally, the value of L was kept constant, so W
However, in the present invention, the value of L is changed so that it is small at the center and small at the edges, so that ρs/W is small at the center and small at the edges (periphery). This is to offset the waviness phenomenon that becomes large in some areas.

In order to do this, the electrodes 13 should be arranged so that, as shown in the plan view of FIG. to form. Thus, when the outline of both end portions of the electrode is observed as a whole, it appears that the electrode has a tapered shape in which the width is maximum at the center portion and decreases toward both end portions.

How to set this Taber shape, that is, what value to take and how to change the interelectrode distance LC% L(l) is determined by experimentally measuring the deformation of the values of ρS and W.

(7) Effects of the Invention As explained in detail above, according to the present invention, in a contact type image sensor, changes in the resistivity of the photoconductive film and changes in the electrode width due to side etching are taken into account, and based on the results, By setting the distance between the electrodes to be large at the center and small at the edges, it is possible to keep the brightness resistance distribution almost constant over all bits, making binarization easier and achieving clear image reproduction. It becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the document reading device, Fig. 2 is a diagram showing the structure of a contact type image sensor, and Fig. 3 is a plan view of elements constituting one bit of the image sensor in Fig. 2. Cross-sectional views, +a+ and (b) in FIGS. 4 and 5 are a plan view and a cross-sectional view of the same device in the process of manufacturing the device shown in FIG. 3, and FIG. Figure 7 is a diagram showing the resistivity distribution of the photoconductive film of the device in Figure 6;
The figure is a plan view of an embodiment of the invention. LL - one substrate, 12 - photoconductive film, 13 - electrode Fig. 5 (Q) ( 1 Fig. 6: b) 1 13 13

Claims (1)

[Claims] In an image sensor made of a photoconductive film, the distance between the electrodes of the photoconductive element array is formed into a shape that tapers gradually from the center toward the edges over all bits, and the resistivity distribution of the photoconductive film is undulated. A close-contact image sensor that compensates for