JPH01201970A - Image sensor - Google Patents

Abstract

PURPOSE:To enable the output of an image sensor to be increased and enable S/N thereof to be improved by providing a photodiode under the gap between a common electrode of a photo-conductive image sensor and a discrete electrode thereof. CONSTITUTION:In an image sensor where a photo-conductive material 17 is formed on a transparent substrate 10, and a common electrode 20 and a discrete electrode 21 are formed facing each other thereon, a photodiode 15 of a pin structure or Schottky structure using amorphous silicon is provided on the substrate 10 facing the common electrode 20 and the discrete electrode 21, furthermore an insulating layer 16 is disposed between a photodiode 15 and a photo-conductive material 17. And a constant voltage is applied between the common electrode 20 and the discrete electrode 21. When light is radiated from the substrate 10, a gate voltage caused by the current characteristics of the photodiode 15 provided on the substrate is generated. Its electric field effect causes the current between the common electrode 20 and the discrete electrode 21 to increase than when a photodiode is not used. As the dark current when light does not radiate is the same as when a photodiode is not used, output thereof can be increased, and S/N thereof can also be improved.

Description

[Detailed Description of the Invention] [Summary] Regarding image sensors used in document reading sections of facsimile machines, image input terminal devices, etc., the aim is to increase the output and improve the S/N when the elements are miniaturized. In an image sensor in which a photoconductive material is formed on a substrate, and a common electrode and individual electrodes are formed facing each other thereon, a pin structure using amorphous silicon or a pin structure is formed on the substrate facing the common electrode and individual electrodes. A photodiode having a Schottky structure is provided, and an insulating layer is provided between the photodiode and a photoconductive material.

[Industrial application field]

The present invention relates to an image sensor used in a document reading section of a facsimile machine, an image input terminal device, etc.

Close-contact image sensors using amorphous silicon have become smaller with the spread of facsimiles.

Although the demand for higher definition is increasing, there is a need for a structure that does not reduce output and S/N due to higher definition.

[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 type, which uses a diode, has a small output, so it must be read as a storage type using a dedicated IC, and the photoconductive type has the disadvantage that its output is determined by the material used. In particular, in the case of a photoconductive type using amorphous silicon, the response is better than that of Cd5Se, but the output is small. For this reason, an image sensor having a configuration as shown in FIG. 4 has been proposed (Japanese Patent Application No. 60161/1986).

As shown in FIG. 4, a transparent gate electrode 2 is provided on a transparent substrate 1, an insulating film 3 and an amorphous silicon layer 4 are provided on the transparent substrate 1, and a source electrode is provided on the amorphous silicon layer 4. 5 and a drain electrode 6 are provided apart from each other so that light is incident from the back surface of the substrate 1 during use. The photoconductive current generated in the amorphous silicon layer 4 of the light receiving part is controlled by the gate electrode 2 via the insulating film 3, thereby utilizing the high speed of amorphous silicon, and further utilizing the conductance control between the source and drain using the gate potential. This makes it possible to increase the absolute value of current compared to the conventional photoconductive type using amorphous silicon.

[One Problem to be Solved by the Invention] The conventional back-side amorphous silicon image sensor described above has the drawback that although it is possible to increase the output, the S/N ratio decreases.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an image sensor that can increase output and improve S/N despite miniaturization of elements.

(Means for solving the problem of nakedness) The above object is to provide an image sensor in which a photoconductive material 17 is formed on a transparent substrate 10, and a common electrode 20 and individual electrodes 21 are formed facing each other on the transparent substrate 10. A photodiode 15 having a pin structure or a Schottky structure using amorphous silicon is provided on the substrate 10 facing the common electrode 20 and the individual electrodes 21, and an insulating layer 16 is provided between the photodiode 15 and the photoconductive material 17. This is achieved by an image sensor characterized in that it is provided.

(Function) When a constant voltage is applied between the common electrode 20 and the individual electrodes 21 and light is irradiated from the substrate 10 side, a gate voltage is generated due to the current characteristics of the photodiode 15 provided on the substrate. Due to the electric field effect, the current between the common electrode 20 and the individual electrodes 21 is increased compared to the case without the photodiode, and the dark current when no light is irradiated is the same as without the photodiode, so the output is increased and the S/N is reduced. Improvement is possible.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention, in which a is a plan view;
b is a cross-sectional view taken along line bb in figure a.

In this embodiment, a transparent electrode 11 made of ITO with a thickness of 1000 nm is provided on a transparent substrate 10 made of glass or the like, and an n-type amorphous silicon (with a thickness of 1
00 people) 12 and 1 type amorphous silicon (thickness 100
(0 Å or less) 13 and p-type amorphous silicon (thickness 80
A pin-type photodiode (or Schottky diode) 15 consisting of a photodiode 14 is provided, and an insulating film 16 made of silicon nitride with a thickness of 3000 nm and an amorphous silicon film 16 with a thickness of 3000 nm are further provided to cover the photodiode 15. A film 17 is provided, on which are provided a common electrode 20 made of n-type amorphous silicon 18 and Cr or Ti 19, and individual electrodes 21 facing the common electrode 20 with a gap therebetween.

Note that the photodiode 15 is arranged so as to be located directly below the gap between the common electrode 20 and the individual electrodes 21.

The operation of this embodiment configured in this manner will be explained with reference to FIG. 2. Figure 2 shows 2V between the common electrode 20 and the individual electrodes 21.
The current between the picture electrodes 20 and 21 when applying a voltage of There is.

In this embodiment, when light is irradiated from the substrate side, the photodiode 15 generates an electromotive force of 0.75V, and due to the addition of the electric field effect, there is a gap between the common electrode 20 and the individual electrodes 21 as shown by the white circle mark of curve A. Position current flows. Since the dark output when no light is irradiated is Voc = 0, its operating range is B
Compared to the case without a photodiode (indicated by the black circle and range A), S (bright current)/N (dark current) increases,
Moreover, the absolute value of the output also increases.

Note that the common electrode 20 and the individual electrodes 21 can also be made into comb-shaped electrodes as shown in FIG. Since the S/N ratio is also improved, higher definition and colorization are possible.

[Effects of the Invention] As explained above, according to the present invention, by providing a photodiode under the gap between the common electrode and the individual electrodes of a photoconductive image sensor, it is possible to increase the output and improve the S/N. becomes.

[Brief explanation of the drawing]

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 in 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, 1 is an amorphous silicon film, 20 is a common electrode, and 21 is an individual electrode. l''I Hecobehetoohmic (IO2) open current [V-2v] Figure 2 for explaining the operation of the embodiment of the present invention Figure 2 Diagram showing other electrodes of the embodiment of the present invention

Claims (1)

[Claims] 1. A photoconductive material (17) is formed on a transparent substrate (10), and a common electrode (20) and individual electrodes (21) are formed on it.
In the image sensor, the substrate (20) facing the common electrode (20) and the individual electrode (21)
10) A photodiode (15) having a pin structure or Schottky structure using amorphous silicon is provided thereon, and an insulating layer (16) is provided between the photodiode (15) and the photoconductive material (17). An image sensor featuring: