JPS62269358A - image sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Increasing the bright current and dark current levels of an image sensor,
As a method for facilitating signal detection, an image sensor is provided in which an amorphous silicon nitride layer and an amorphous silicon layer are formed on an insulating substrate, and a coplanar electrode is provided on the amorphous silicon layer.

[Industrial application field]

The present invention relates to an image sensor configuration with increased bright current level and dark current level.

Image sensors are widely used as information input systems in facsimile machines, optical character readers (abbreviated as OCR), optical symbol readers (abbreviated as OMR), and the like.

Here, in an image sensor, a photoelectric element is formed using a photoelectric material such as amorphous silicon (hereinafter abbreviated as a-8l) or cadmium selenide (CdSe), and a large number of these photoelectric elements are arranged in rows. An image sensor is formed.

To use it, a light-emitting diode (LED) is used to illuminate the original, and a SELFOC lens is used to form an image at the same magnification of the light reflected from the original, which is then received by a photoelectric element and converted into an electrical signal. ing.

That is, the image sensor horizontally scans a fed document, and sequentially transmits electric signals corresponding to black and white of the document detected by each photoelectric element to a shift register to perform information processing.

The present invention relates to an improvement of a coplanar image sensor →J' in which the photoelectric element is made of a-5i.

(Prior Art) FIG. 2(A) is a plan view of a conventional coplanar image sensor, and FIG. 2(B) is a sectional view taken along the line x-x'.

The traditional structure here is glass or ceramic.

An A-5I layer 2 is formed on one insulating substrate I made of a metal such as chromium (Cr) by a method such as a plasma CVD method (chemical vapor deposition method), and a common electrode made of a metal such as chromium (Cr) is formed on the a-5i layer 2. 3 and a large number of gate electrodes 4 made of a transparent conductive film are patterned, thereby forming a large number of photoelectric elements.

Here, since the common electrode 3 and the gate electrode 4 are both made of metal films, a barrier is formed at the interface with the a-5i layer 2, but from the common electrode 3 to the a-5i layer 2. Since the voltage is applied so that the current direction is in the forward direction, the voltage drop at this interface can be ignored.
For this reason, the common electrode 3 is also called an ohmic electrode.

- On the other hand, a voltage is applied to the gate electrode 4 in the opposite direction, and a small reverse current (dark current) flows. The reverse current increases (bright current).

Here, the number of gate electrodes 4 constituting a unit photoelectric element is 10
Although the pattern is formed to a size of approximately 0 μm square,
Conventional current values are bright current or about to-" A, and dark current is about 10-" A, and the bright/dark current ratio can obtain a three-digit value. It was accompanied by major limitations.

[Problem that the invention seeks to solve]

As described above, although the conventional coplanar image sensor can obtain a brightness/dark current ratio of about three digits, it is not easy to form a detection circuit because the absolute value of the current is low.

Therefore, the challenge is to increase the absolute values of the bright current and dark current and to facilitate the design of the detection circuit.

[Means to Solve Problem C] The above problem is solved by the coplanar type in which a common electrode made of a metal film and individual electrodes made of a transparent conductive film are provided on a thin amorphous silicon layer formed on an insulating substrate. This problem can be solved by forming the amorphous silicon thin layer on an amorphous silicon nitride thin film in the image sensor.

[Effect]

In the image sensor of the present invention having a coplanar structure, the reason why the absolute values of bright current and dark current are low is that the resistance of the a-5i layer 2 between the gate electrode 4 and the common electrode 3 is high.

Therefore, as a method to increase the absolute value of the current without changing the shape of the shot barrier, an amorphous silicon nitride (a-5iN) layer is provided under the a-5i layer, and a current can easily pass through this interface. By providing a channel, the absolute value of the current can be increased.

That is, if an a-5iN layer is provided on an insulating substrate and an a-5i layer is provided on top of it as in the conventional method, defects that generate holes, such as dangling Si atoms, may occur in the a-5iN layer. There is a dangling bond, which makes it easier for electrons to gather in the a-Si layer at the boundary, creating a so-called channel and lowering the resistance.

This results in a decrease in series resistance and an increase in bright current value and dark current value compared to the prior art.

〔Example〕

FIG. 1(A) is a plan view of an image sensor embodying the present invention, and FIG. 1(B) is a sectional view taken along line xx'.

The method of manufacturing this image sensor will be explained as follows.

A layer 6 of a-5iN (accurately a-3ix N1-X: H) is deposited on a glass substrate 5 having a thickness of l x m using plasma C.
It is formed to a thickness of about 3000 mm using the VD method, and then a-5i (accurately a-5i: II) is evaporated to a thickness of about 3000 mm using the same method using a metal mask. An A-31 layer 7 having a length of 230 mm and a width of 60 mm was formed.

Next, a common electrode 3 with a width of 1 W and a length of 216 mm was made by vapor depositing Cr to a thickness of approximately 1000 mm on top of this, and indium oxide (InzO:+) and tin oxide (Sn) were similarly deposited.
02) (abbreviated as ITO) at 700-1000
A gate electrode 4 of 100 μm square is formed by mask vapor deposition to the thickness of a person.
was formed into a pattern.

When we measured the bright current and dark current of each photoelectric element of the image sensor made in this way, the bright current was about 10-7A, and the dark current was about 10-''A, which is about 3 orders of magnitude higher than conventional methods. I was able to face the situation.

C. Effects of the Invention] As described below, by implementing the present invention, it has become possible to adjust the bright current value and the dark current value, and the design of the detection circuit has become easier.

[Brief explanation of the drawing]

FIG. 1 is a plan view and a sectional view of an image sensor according to the present invention, and FIG. 2 is a plan view and a sectional view of a conventional image sensor. In the figure, 1.5 is an insulating substrate, 2 and 7 are a-3i layers, 3 is a common electrode, 4 is a gate electrode, and 6 is an a-3iN layer.

Claims (1)

[Scope of Claim] A coplanar image sensor comprising a common electrode made of a metal film and a gate electrode made of a transparent conductive film on an amorphous silicon thin layer formed on an insulating substrate, comprising the steps of: An image sensor characterized in that the thin layer is formed on an amorphous silicon nitride thin layer.