JPS62295470A - Photosensor - Google Patents

Abstract

PURPOSE:To produce many signal currents at bright time in a simple structure by sequentially laminating integrally an N-type a-Si, I-type a-Si and metal oxide transparent electrodes on an electrode to form a photoconductive element, and setting the bias points of the elements in a predetermined sequential current range. CONSTITUTION:An N-type amorphous silicon (a-Si) 2, an I-type a-Si 3 and a metal oxide transparent electrode 4 are sequentially laminated integrally on a conductive substrate 1 which is also used as an electrode to form a photoconductive element, and the bias point of the element is set to a predetermined sequential current range. In a photosensor, a potential barrier is formed in a boundary between the a-Si 3 and the electrode 4, and there is a remarkable difference between the rising voltage and the inclination after rising. Accordingly, when a bias voltage VB of suitable amplitude is set forwardly (in a positive current range), the difference of current values at bright and dark times become large and the current value at the bright time is remarkably increased.

Description

Detailed Description of the Invention a. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical sensor used in an image sensor or the like, and particularly to an optical sensor using a photoconductive element.

[Conventional technology]

Optical sensor elements used in image sensors and the like include photoconductive elements and photodiodes. In general, photoconductive elements have drawbacks such as a slower response speed than photodiodes and a smaller contrast ratio (the ratio of the signal in a bright state when exposed to light to the signal in a dark state when not exposed to light). However, on the other hand, it has features such as high sensitivity (large signal amount in bright state) and simple element structure, so it is used in various fields.

The above photoconductive element can be used as a one-dimensional or two-dimensional optical sensor element.
When a three-dimensional matrix circuit is configured and matrix drive is performed, there is no function to block reverse current, so a rectifier is connected in series to each photoconductive element to block reverse current and reduce electrical loss talk. It is necessary to prevent it.

For this reason, conventional methods have been used to connect a rectifying element to the optical sensor element, but there are two methods: connecting the rectifying element placed on the side of the optical sensor element with electrical wiring, and connecting the rectifying element to the optical sensor element. There is a method of stacking rectifying elements via electrodes.

[The problem that the invention aims to solve]

In the method of connecting the optical sensor element and the rectifying element by electrical wiring, it is difficult to construct a two-dimensional matrix, and even in the case of a one-dimensional matrix, it occupies a large space, resulting in space problems. Ta.

Furthermore, when stacking rectifier elements via electrodes, many steps are required, such as forming electrodes made of different materials and patterning them, resulting in problems such as a high defect rate and variations in characteristics. Ta.

Therefore, an object of the present invention is to provide an optical sensor that uses a laminated structure, which is advantageous in that it occupies a small space, and that solves the problems associated with intervening electrodes in this case.

[Means for solving problems]

As shown in FIG. 1, the optical sensor of the present invention consists of a conductive substrate 1 which also serves as an electrode, an n-type amorphous silicon (abbreviated as a-5i) 2, an i-type layer 3i3, and a transparent metal oxide layer. A photoconductive element is constructed by sequentially laminating and integrating electrodes 4, and the bias point of the photoconductive element is set in a predetermined forward current range.

[Effect]

The optical sensor described above has a potential barrier formed at the interface between the i-type layer 5i3 and the transparent electrode 4, and exhibits an IV characteristic as shown in FIG. Curve a in the figure is the characteristic in bright and dark conditions, and curve a in the same figure is the characteristic in dark conditions. It can be seen that these curves a and b have a remarkable difference in the rising voltage and the slope after rising.

Therefore, if a bias voltage VB of an appropriate magnitude is set in the forward direction (positive current region), the difference between the current value between bright and dark times will become large, and the current value between bright and dark times will become very large.
A value 100 times or more can be obtained when applying a reverse bias voltage, which is normally used with this type of photodiode.

Furthermore, since the current during reverse bias is very small, there is an effect of blocking reverse current.

〔Example〕

An n-type 0) a-Si2, an i-type a-3i3, and a transparent electrode 4 were formed on a mirror-polished nickel substrate 1 by glow discharge decomposition. The conditions for glow discharge decomposition were that the substrate temperature was 250''C, the gas pressure was 1 Torr, and other conditions were set as shown in Table 1.

The transparent electrode 4 in Table 1 was formed of I 2 To (SnO□ or 5 wt % indium tin oxide) by a vapor deposition method.

In this case, the bright current at +1v bias in the forward direction when irradiated with 565 nm light 1001x is 100 ttA/
mm2, and the contrast ratio was 3o. Further, the current value at the time of -1■ bias in the reverse direction is 0.171 A/mm2, which is effective in sufficiently blocking current in the reverse direction.

Note that by microcrystalizing the n-type layer, the bright current can be increased to 20
The voltage was 0 μA/mm2, and a large bright signal was obtained.

If an insulating material is used as the substrate, an electrode 1' is formed on the substrate 5 as shown in FIG.
Form the same layers as in the figure. When a transparent insulating material such as glass is used as the substrate 5, the substrate 5 may be provided on the metal oxide transparent electrode 4 side as shown in FIG.

〔effect〕

As explained above, according to the present invention, with a very simple structure, it is possible to obtain a large amount of bright and dark signal current, increase the brightness ratio, and prevent currents in the opposite direction. can.

Therefore, not only a one-dimensional image sensor but also a two-dimensional image sensor can be constructed, and furthermore, it is possible to significantly reduce the number of steps, reduce the defective rate, and reduce variations in characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment, FIG. 2 is a 1--■ characteristic diagram same as above, and FIGS. 3 and 4 are sectional views of other embodiments.

Claims (3)

[Claims] (1) A photoconductive element is constructed by laminating and integrating an n-type a-Si, an i-type a-Si, and a metal oxide transparent electrode on an electrode, and the bias point of the photoconductive element is set in a predetermined forward direction. An optical sensor characterized by being set in a current range. (2) The optical sensor according to claim 1, wherein the metal oxide transparent electrode is indium tin oxide. (3) The optical sensor according to claim 1 or 2, wherein n-type a-Si is microcrystallized.