JP2671901B2 - Image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding an image sensor used in a document reading section of a facsimile, an image input terminal device, etc., a transparent image sensor is provided for the purpose of increasing output and improving S / N when elements are miniaturized. In an image sensor in which a photoconductive material is formed on a substrate, and a common electrode and an individual electrode are formed on the substrate so as to face each other, a Pin structure using amorphous silicon on the substrate facing the common electrode and the individual electrode, or A photodiode having a Schottky structure is provided, and an insulating layer is provided between the photodiode and the photoconductive material.

[Industrial applications]

The present invention relates to an image sensor used in a document reading unit such as a facsimile and an image input terminal device.

The contact type image sensor using amorphous silicon has been required to be downsized and high-definition with the spread of facsimiles. However, a structure that does not decrease the output and S / N due to the high-definition is required. ing.

[Conventional technology]

There are two types of conventional image sensor elements, a storage type using a diode and a photoconductive type using a counter electrode. The former one using a diode has a drawback that the output is small and thus it is necessary to make it read by a storage type with a dedicated IC, and the photoconductive type one has a drawback that its output is determined by the material used. In particular, in the case of a photoconductive type using amorphous silicon, there is a drawback that the output is small compared to CdSSe, but the output is small. Therefore, an image sensor having a structure as shown in FIG. 4 has been proposed (Japanese Patent Application No. 62-60161). This is the fourth
As shown in the figure, the transparent gate electrode 2 is formed on the transparent substrate 1.
Is provided, the insulating film 3 and the amorphous silicon layer 4 are provided thereon, and the source electrode 5 and the drain electrode 6 are provided on the amorphous silicon layer 4 at a distance from each other. It is designed to emit light. Then, the photoconductive current generated in the amorphous silicon layer 4 of the light receiving portion is controlled by the gate electrode 2 through the insulating film 3 to utilize the high speed property of amorphous silicon, and further, the conductance control between the source and the drain by the gate potential is used. Then, the absolute value of the current value can be increased as compared with the conventional photoconductive type using amorphous silicon.

[Problems to be solved by the invention]

The conventional backside amorphous silicon image sensor described above has a drawback that the output can be increased but the S / N is lowered.

In view of the above problems, it is an object of the present invention to provide an image sensor capable of increasing output and improving S / N regardless of miniaturization of elements.

[Means for solving the problem]

The purpose is to form the photoconductive material 17 of the transparent substrate 10,
In an image sensor in which a common electrode 20 and an individual electrode 21 are formed to face each other, a photodiode having a pin structure or a Schottky structure using amorphous silicon on the substrate 10 facing the common electrode 20 and the individual electrode 21. Achieved by an image sensor characterized in that 15 is provided at a position where light also hits a part of the photoconductive substance 17, and an insulating layer 16 is provided between the photodiode 15 and the photoconductive substance 17. To be done.

(Operation)

When a constant voltage is applied between the common electrode 20 and the individual electrode 21 and light is radiated from the substrate 10 side, a gate voltage is generated due to the current characteristics of the photodiode 15 provided on the substrate, and a common voltage is produced by the electrolytic effect. The current between the electrode 20 and the individual electrode 21 is increased as compared with the case without a photodiode, and the dark current when light is not emitted is the same as that without a photodiode, so that the output can be increased and the S / N can be improved. Become.

〔Example〕

FIG. 1 is a view showing an embodiment of the present invention, wherein a is a plan view, and b is a cross-sectional view taken along line bb of FIG.

In this embodiment, as shown in the figure, a transparent ITO electrode 11 having a thickness of 1000Å is provided on a transparent substrate 10 such as glass, and an n-type amorphous silicon (thickness 100Å) 12 and an i-type amorphous silicon ( A pin type photo diode (or Schottky diode) 15 consisting of a p-type amorphous silicon (thickness: 80 Å) 13 and a p-type amorphous silicon (thickness: 80 Å) 14 is provided. An insulating film 16 used and an amorphous silicon film 17 having a thickness of 3000 Å are provided, and n-type amorphous silicon is formed on the insulating film 16.
A common electrode 20 made of 18 and Cr or Ti 19 and an individual electrode 21 facing the common electrode 20 and separated by a gap are provided. The photodiode 15 is arranged so as to be located directly below the gap between the common electrode 20 and the individual electrode 21.

The operation of the present embodiment configured as described above will be described with reference to FIG. Fig. 2 shows both electrodes 20 and 2 when a voltage of 2V is applied between the common electrode 20 and the individual electrode 21 to change the potential on the insulating film side.
The current between 1 is shown by curve A when light is irradiated from the substrate side, and by curve B when light is not irradiated. In this embodiment, when light is emitted from the substrate side, the photodiode 15
Generates an electromotive force of 0.75 V, and the addition of the electric field effect causes a current to flow between the common electrode 20 and the individual electrode 21 at the position indicated by the white circle in curve a. The dark output when no light is emitted is Voc
Since it is at = 0, the operating range is as shown by B, which is S compared to the case without a photodiode (indicated by a black circle and range A).
(Bright current) / N (dark current) increases, and the absolute value of the output also increases.

The common electrode 20 and the individual electrode 21 may be comb-shaped electrodes as shown in FIG. 3, and in this case, a sufficiently large output can be obtained even if the element is miniaturized as compared with the conventional photoconductive sensor. Since the S / N is also improved, high definition and colorization are possible.

〔The invention's effect〕

As described above, according to the present invention, by providing the photodiode under the gap between the common electrode and the individual electrode of the photoconductive image sensor, the output can be increased and the S / N can be improved.

[Brief description of the drawings]

 FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the embodiment of the present invention, FIG. 3 is a diagram showing another electrode of the embodiment of the present invention, and FIG. The figure shows a conventional image sensor. In the figure, 10 is a substrate, 11 is a transparent electrode, 15 is a pin type photodiode, 16 is an insulating film, 17 is an amorphous silicon film, 20 is a common electrode, and 21 is an individual electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 62-145866 (JP, A) JP 60-143626 (JP, A) JP 62-250676 (JP, A) JP 50- 106595 (JP, A) JP 59-167075 (JP, A) Actually developed 62-60052 (JP, U)

Claims (1)

(57) [Claims] 1. A photoconductive material (17) is formed on a transparent substrate (10), and a common electrode (20) and an individual electrode (21) are formed thereon.
In the image sensor formed to face each other, a photodiode (15) having a pin structure or a Schottky structure using amorphous silicon is formed on the substrate (10) facing the common electrode (20) and the individual electrode (21). The photoconductive material (17) is provided at a position where it also illuminates a part of the photoconductive material (17), and an insulating layer (16) is provided between the photodiode (15) and the photoconductive material (17). Image sensor.