JPS6348858A - Optical sensor array - Google Patents

Abstract

PURPOSE:To improve the resolution of a close contact type image sensor, in an optical sensor array using a semiconductor thin film having a P-I-N structure, by setting the resistivity of a P layer or an N layer on the side of discrete electrodes to be a specified value or more, thereby reducing leakage between the neighboring discrete electrodes. CONSTITUTION:Discrete electrodes 21, 22... comprising transparent conducting films are formed on a glass plate 1. An insulating film 5 is formed so as to cover the lead wire part of the discrete electrodes. An a-Si layer 3 and a common electrodes 4 are formed thereon. The insulating film 5 is formed as follows: an inorganic thin film comprising a resin such as polyimide or silicon nitride, silicon oxide and the like is formed, and thereafter patterning is performed by a photolithography method. The structure of the a-Si layer 3 comprises three P-I-N layers. The resistivity of the doped layer (in this case, the P layer 31) on the side of the discrete electrodes is controlled at 10<5> OMEGA.cm or more. Thus, a leaking current, which flows between the discrete electrode and a common electrode through the N layer, can be largely reduced. Therefore, dark current can be decreased and the S/N ratio can be improved.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention is a photoelectric conversion system consisting of three semiconductor thin films of p, l, and n layers, and a photoelectric conversion layer having a common electrode on one side and independent individual electrodes on the other side. , relates to an optical sensor array in which elements are arranged in a line. Such a sensor array is used in a contact image sensor for facsimile and the like.

[Prior art and its problems]

BACKGROUND ART Contact type image sensors for facsimiles are being developed in order to make facsimiles smaller and cheaper, and to reduce errors in signal reading due to optical aberrations. Conventionally, this sensor has been made using elements such as CCDs, but development is moving toward sensors using thin film semiconductors that can be made larger in area. FIG. 2 is a schematic diagram of the implementation of the contact type image sensor unit. The unit is composed of a light emitting diode array 11, a gradient index lens array 12, and a photosensor array 13. Characters or images on the original 14 are imaged with equal dimensions on the photoelectric conversion element 15 of the sensor array through the gradient index lens 12, and converted into a time-series signal by the driving IC 16. FIG. 1 shows a photoelectric conversion unit, and FIG. 1 fat is a plan perspective view in FIG. . Individual portions i21, 22, . The end of the i-pole 4 is connected to the extraction electrode portion 41.One side of the individual electrodes 21 to 25 is formed as a fine lead wire, and is connected to a drive IC consisting of an analog switch and an amplifier (not shown). In this way, a single photoelectric conversion element is formed between each of the individual quantities 8i 21 to 25 and the common electrode 4. The a-3i layer 3 consists of two layers 31.1 layer 32.3 of the n layer 33.
It is made up of layers. Conventionally, it has been said that since a-5i has a higher resistance than single crystal S1, there is no need to separate each pixel. However, when we actually tried making a prototype, we found that the separation between pixels was poor, leading to a drop in resolution. The decrease in resolution between pixels is mainly due to the current generated on the individual electrode 21 flowing through the two layers 31 to the adjacent individual electrode 2.
The difference was that the result leaked to 2nd. In order to avoid the above problems, there is a method of dividing the A-5i layer into photolithography using the soy method, etc., but although the desired resolution can be obtained, it not only increases the number of steps but also reduces the yield due to short circuits on the etched surface. is kept low.

[Purpose of the invention]

The present invention provides p-1-n formed commonly in each photoelectric conversion element.
It is an object of the present invention to provide a photosensor array in which leakage through a semiconductor thin film of a structure is prevented without dividing the semiconductor thin film into elements.

[Key points of the invention]

In the present invention, by setting the resistivity of the layer of one conductivity type adjacent to the individual electrodes to 105Ω·1 or more among the semiconductor thin films constituting the photoelectric conversion layer of the p-1-n structure, the distance between the adjacent individual electrodes is improved. The above objective is achieved by suppressing leakage current.

[Embodiments of the invention]

a-5i is usually formed by high frequency glow discharge in 5iHe gas. That is, when the p-layer is formed using a known technique, a hydrocarbon gas such as C*Hz (acetylene) is added in addition to BzHh (diborane) gas in order to further widen the optical gap and improve sensitivity. Also, when generating the n layer, PI! ! (phosphine) gas is added. p layer or n
In order to change the resistivity of 1li, the concentration of these doping gases, BzHi or PHs, can be changed. Figure 3 shows MTF (Modulation Transfer Funcsilane), a parameter representing the resolution of the image sensor, and its axis in the gas when pJ1 is generated.
This shows the relationship with concentration. Note that the gas concentration of C12 is 5%. As the boronic concentration increases, the resistivity of the second layer 31 decreases, and as mentioned above, leakage current increases and resolution decreases. By the way, MTF means that if the signal current when photoelectrically converting the stripe pattern shown in Fig. 4 fat becomes as shown in Fig. 4, then the signal tf
It is obtained from the maximum value of L, 1.1111, and the minimum value f elm using the following equation. (I□, +1.5, 1) Generally, image sensors for facsimile have MTF>50
% is requested. Therefore, from FIG. 3, the BAH concentration must be 0.1% or less. By the way, the resistivity of the p-layer when the BIH concentration is 0.1% is approximately lXl0'Ω, and when it is 1% it is approximately lXl0'Ω.
・It is prepared. From the above experimental facts, p-! In the a-5t photosensor array with the -n structure, the resistivity of the pN or n layer adjacent to the individual electrodes must be 10 5 Ω·1 or more. Furthermore, for the above-mentioned reason, leakage between individual electrodes depends only on the resistivity of the p-layer or n-layer, and does not depend on the composition or type of dopant. Alternatively, in order to obtain the desired high abrasive resistance in the n-layer formed from SiH* and PH3, it is necessary to further lower the concentration of B, H, or PH than in the above example. However, by doing so, a good bond cannot be obtained and is unstable. Therefore, it is desirable that the layer adjacent to the individual ITS be made of amorphous silicon carbide (a-5iC) by adding a hydrocarbon gas such as methane or acetylene to the reaction gas. FIG. 5 shows another structure according to the invention. The same figure (a) shows a plane perspective view, and (b) shows a cross-sectional view of the c-c' plane in (Ill).Individual electrodes 21, 22, . is formed, and an insulating film 5 is formed thereon so as to cover the lead wire portions of the individual electrodes.A-Stn layer and a common snow scraper 4 are formed thereon.This insulating film 5 is made of polyimide or the like. This is done by forming an inorganic thin film of resin, silicon nitride, silicon oxide, etc., and then patterning it using photolithography.The structure of a-3i1i3 is the same as the previous example, with <p-1-n3 layers, and individual Dope l on the electrode side (
In this case, the resistivity of the second layer 31) is controlled to 10 SΩ·1 or more. A feature of this embodiment is that an insulating film is inserted between the individual electrodes and the a-3tN, thereby making it possible to significantly reduce the leakage current flowing between the individual electrodes and the common 1i electrode through the n-layer. Therefore, dark current can be reduced and the S/N ratio can be improved.

【Effect of the invention】

According to the present invention, in an optical sensor array using a semiconductor thin film with a p-1-n structure, in order to increase the resistivity of the p layer or nM on the individual electrode side to 105Ω·1 or more, it is possible to We were able to reduce leakage and improve the resolution of the contact type image sensor. In particular, by using a-5IC as the layer that increases resistivity, a good bond can be formed,
No deterioration of characteristics occurs.

[Brief explanation of the drawing]

FIG. 1 shows a photoelectric conversion unit of an example of a photosensor array to which the present invention is implemented, where fat is a plan view, (bl), and tel (al) are cross-sections on the A-A' and B-8' planes, respectively. Figure 2 is a schematic side view of the implementation of a contact type image sensor equipped with a photosensor array, and Figure 3 is an MT of the image sensor.
Relationship diagram between F and BJ and concentration during phi generation, Figure 4 is M
Figure 5, which is an explanatory diagram of the definition of TF, shows the structure of the photoelectric conversion unit that is different from Figure 1, (al is a plan view, (b) is c of fat
-c' plane sectional view. 1 glass plate, 21.22.23.24.25: individual electrode, 3: a-5i layer, 31: pF! , 32: n
Layer, 33: nJi, ] Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1) A photoelectric conversion element consisting of three semiconductor thin films of p, i, and n layers and having a common electrode on one side and independent individual electrodes on the other side of the photoelectric conversion element. 1. An optical sensor array characterized in that a layer of one conductivity type of a semiconductor thin film adjacent to an individual electrode has a resistivity of 10^5 Ω·cm or more. 2) In the array according to claim 1, the layer of one conductivity type of the semiconductor thin film, which is adjacent to the individual electrode and has a resistivity of 10^5 Ω·cm or more, is mainly composed of amorphous silicon carbide. An optical sensor array characterized by: