JPS6233480A - Photosensor array - Google Patents

Abstract

PURPOSE:To restrain the leakage current between the adjacent individual electrodes or between the individual electrode and a common electrode by determining the resistivities of both P-layer and N-layer of the semiconductor thin film composing a photoelectric conversion layer of P-I-N structure 10<5>OMEGA.cm or more. CONSTITUTION:When a concentration of boron increases, a resistivity of a P-layer 31 declines and a leakage current increases to lower the resolution, so that a concentration of B2H6 is needed to be 0.1% or under. The resistivity of the P-layer at the time of B2H6 concentration 0.1% is about 1X10<5>OMEGA.cm and in case of 1%, it is about 1X10<4>OMEGA.cm. When a concentration of phosphorus increases, a resistivity of an N-layer 33 declines and a leakage current between an individual electrode and a common electrode increases. Accordingly, in the a-Si photosensor array of P-I-N structure, the resistivities of both P-layer and N-layer are needed to be 10<5>OMEGA.cm or more. The leakage between the individual electrodes and that between the individual electrode and the common electrode depend only on the resistivity of the P-layer or N-layer, respectively and does not depend on the composition of layers, e.g., the kind of a semiconductor or a dopant.

Description

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

The present invention relates to a photosensor array in which photoelectric conversion elements are arranged in a line, each consisting of a p+'+n three-layer semiconductor thin film and having independent individual electrodes on the other side of a photoelectric conversion layer having a common electrode on the negative side. Such a sensor array is used in a contact type 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 a CCD, but development is moving toward a sensor using a III-semiconductor 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 light emitting diode array 11, ifl
A gradient index lens array 12 and a light sensor 13
It consists of 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 2, and converted into a time-series signal by the driving IC 16. Fig. 1 shows the photoelectric conversion section, Fig. 1 ta+ is a plane perspective view, Fig. 1 (bl and (C) are respectively AA' plane of Fig. 1 (al), and a cross-sectional view at the B-8 layer plane. Individual electrodes 21, 22, . . . made of a transparent conductive film are formed on a glass plate l, an amorphous silicon (a-5i) layer 3 is formed thereon, and a common electrode 4 is further formed thereon. The end of the common electrode 4 is connected to the extraction electrode portion 41. Also, one side of each of the individual electrodes 21 to 25 is formed as a fine lead wire, and is connected to a driving 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 electrodes 21 to 25 and the common electrode 3. The a-3t layer 3 has the l! Conventionally, it has been said that because a-Si has a higher resistance than single-crystal Si, there is no need to separate each pixel. However, when we actually prototyped it, we found that the resolution between pixels was Not only did the resolution degrade badly, but the dark current was large, making it impossible to obtain the desired S/N ratio.First of all, the decrease in resolution between pixels is mainly caused by individual electrodes, such as 21
This is the result of the current generated above leaking to the adjacent individual electrode 22 through the 9-layer 3 structure, and the reason for the large dark current is mainly due to the nN33 It turned out that this was the result of a leak through. In order to avoid the above problems, there is a method of dividing the A-3T layer by photolithography, etc., but although the desired resolution and S/N can be obtained, it not only increases the number of steps but also causes short circuits on the etched surface. As a result, the yield 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 that prevents leakage through a semiconductor thin film of a structure without dividing the semiconductor thin film into elements.

[Key points of the invention]

The present invention prevents leakage between adjacent individual electrodes or between individual electrodes and a common electrode by having resistivities of both the p layer and n layer of the semiconductor thin film constituting the photoelectric conversion layer of the pin structure being 10'Ω·1 or more. Achieve the above objectives by suppressing the current.

[Embodiments of the invention]

a-5t is usually formed by high frequency glow discharge in SiH* gas. That is, when forming the p-layer using a known technique, BtHb (diborane) gas is used, and C and H are used to further widen the optical gap and improve sensitivity. Add a hydrocarbon gas such as (acetylene). Also, n
PH5 (phosphine) gas is added during layer formation. p
To change the resistivity of the layer or n-layer, the concentration of these doping gases, B, H, or PH, can be changed. Figure 3 shows MTF (Modulation Transfer), a parameter that represents the resolution of the image sensor.
function) and BtHh in the gas during the formation of the p layer.
This shows the relationship with concentration. As the boronic concentration increases, the resistivity of the nine layers 31 decreases, and as described above, leakage current increases and resolution decreases. By the way, MTF is the signal current when photoelectrically converting the stripe pattern shown in Figure 4 (al).
If it becomes as follows, the maximum value of the signal current is 1 wa
x and minimum value! ■It is obtained from in using the following formula. (I sax + I 5in) Generally, the image sensor for facsimile is M “l”
F>50% is required. Therefore, from Fig. 3, 8.
The H6 concentration needs to be 0.1% or less. By the way, when the B*Hi concentration is 0.1%, the resistivity of the p layer is approximately 1.
×10SΩ・At 1%, it is approximately lXl0' Ω・
It is a country. On the other hand, Figure 5 shows the PH, concentration, and applied voltage of 5V during n-layer formation.
0 as the phosphorus concentration increases.
The resistivity of the layer 33 decreases, and for the reasons mentioned above, the individual electrodes
Leakage current between common electrodes increases. As a result, as shown in the figure, the II current in the dark increases significantly,
The S/N ratio, ie the ratio of the current during illumination to the current in the dark, decreases. Generally, the S/N ratio of an image sensor is required to be 1 digit or more, preferably 2 digits or more, and therefore the PHs s degree is 0.0
5% or less is desirable; by the way, the PHs concentration is 0.05%.
The resistivity of the p-layer when
When , the resistivity is approximately 5 x 10''Ω.From the above experimental facts, in the a-3i optical sensor array with p-1-n structure, the resistivity of both the p layer and the n layer is 10'Ω.
- (2) or more is required. Further, for the above-mentioned reasons, leakage between individual electrodes and leakage between individual electrodes and common electrode each depends only on the resistivity of the p layer 1 nN, and does not depend on the composition of each layer, such as the semiconductor or dopant fl.

【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, the resistivity of both the p layer and the n layer sandwiching the i layer is set to 10'Ω·1 or more, so that adjacent individual electrodes By reducing the leakage between the individual electrodes and the common electrode, we were able to improve the resolution and S/N ratio of the contact-type image sensor.

[Brief explanation of drawings]

FIG. 1 shows a photoelectric conversion unit of an example of a photosensor array to which the present invention is implemented, and fal is a plan view (mountain). fcl is a cross-sectional view of plane A-A' and plane B-B' of (5), Fig. 2 is a schematic side view of the implementation of a contact type image sensor equipped with a photosensor array, and Fig. 3 is a MT of the image sensor.
Relationship diagram between F and B, H & concentration during p layer formation, Figure 4 is M
FIG. 5, which is an explanatory diagram of the definition of TF, is a relationship diagram between the output current of the image sensor and the PH and concentration at the time of n-layer formation. 1 glass plate, 21.21.23.24.25: individual electrode, 3: a-st layer, 31: phi, 32: layer, 33: n layer, 4: common electrode. Ward 2 $3511

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 the p-layer and n-layer of the semiconductor thin film each have a resistivity of 10^5 Ω·cm or more. 2) The optical sensor array according to claim 1, wherein the semiconductor thin film is made of amorphous silicon.