JP2658078B2 - Manufacturing method of optical sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical sensor used in an image input unit of an OA device such as a facsimile machine or an optical disk.

Conventional technology In recent years, with the aim of reducing the size of the image information input section of facsimile machines and various OA equipment and improving image distortion, a contact type line sensor with the same size as the document width has been developed, and an image reading device using this has been used At present, there is a strong demand for improvement in performance, that is, improvement in speed and quality.

An optical sensor mainly composed of CdS, CdSe or a solid solution CdS-CdSe is characterized by a large photocurrent. For this reason, a contact-type line sensor using this sensor makes it easy to design peripheral circuits. On the other hand, the optical sensor is slow response to light irradiation of the photocurrent J _p, moreover there are two drawbacks of poor proportionality for L (reflected light intensity from i.e. original) irradiation light intensity. That, gamma value of Ki was a J _p .alpha.L ^gamma in the latter as long as 2~3msec the sensor surface strength 100lux during rise time tau _r and fall time tau _d is normally used for J _p in the former is 50 It is as small as 0.6-0.75 at 100lux.

Problems to be Solved by the Invention As described above, when the rise time and the fall time of the photocurrent of the sensor are long, the reading scanning speed of the line sensor using this sensor is limited to 4 to 5 ms / line. When the γ value is small, the photocurrent generated according to the light intensity on the sensor surface, that is, the output signal value is proportional when γ = 1.0 as shown in FIG. It turns out that the proportionality is very poor. Therefore, extra circuit processing is required to reproduce the halftone.

In the case of a photoconductive sensor in which CdS, CdSe or a solid solution CdS-CdSe is activated and heat-treated in CdCl ₂ vapor, increasing the γ value is realized by, for example, increasing the concentration of Cu as an impurity. However, at the same time, the fall time τ _d of the photocurrent decreases, but the rise time τ _r increases,
There is a major drawback in that the optical response speed as a whole decreases and the photocurrent _Jp also decreases.

Means the present invention for solving the problem is to not reduce the photocurrent J _p faster optical response speed, moreover there is provided a method of increasing the γ value. In other words, CdS, CdSe or solid solution
Forming a semiconductor thin film made of CdS-CdSe, the thin film was exposed to the vapor of CdCl ₂ at a high temperature, a small amount of C after photoelectrically activated
This is a manufacturing method in which a counter electrode is provided on the semiconductor thin film after u is deposited and subjected to a heat treatment, so that the photocurrent is not significantly reduced, the photoresponse speed is remarkably increased, and the γ value is increased.

According to the method of the present invention, the CdS-based photoconductive sensor does not lose its large photocurrent value, and its photoresponse speed can be significantly increased, and its γ value can be increased. Although the photocurrent is almost proportional to the fall time τ _d , the reason that the photocurrent does not decrease even if the fall time is shortened is that the photocarrier (electron) in the semiconductor thin film is reduced by the method of the present invention. This is because the mobility of ()) increases.

Examples Hereinafter, examples of the present invention will be described using CdS _0.6 Se _0.4 as an example. Glass substrate (Corning Co. # 7059.230 × 25 × 1.
2mm ³ ) Deposit a 4000mm thick CdS _0.6 Se _0.4 deposited film on the surface and apply photolithography to form islands (90 × 35
1728 bits are arranged at a rate of 8 bits / mm in 0 μm ² ). After heating this island-shaped CdS _0.6 Se _0.4 film at 500 ° C. in saturated vapor of CdCl ₂ to photoelectrically activate it to form a photoconductor film,
0.005 to 0.1 mol% of C with respect to the CdS _0.6 Se _0.4 film as the base material
deposit u. If the Cu content is less than 0.005 mol%, the effect is small, and if it is more than 0.1 mol%, the rising characteristics are poor. Cu
The substrate temperature during vapor deposition is between room temperature and 400 ° C. Substrate temperature 400
If the temperature exceeds ℃, characteristics are likely to vary, which is not preferable.
Then, in an atmosphere containing neutral or small amounts of oxygen, 150-2
Heat at 50 ° C. When heated in this case 250 ° C. or higher abruptly J _p is characteristic is deteriorated less. Thereafter, a counter electrode (NiCr / Au deposited film), that is, a common electrode and an individual electrode are formed on each of the island-shaped films. The gap between the opposing electrodes is 60 μm. After that, heat treatment at 150 to 400 ° C. in an atmosphere further containing neutral or a small amount of oxygen is more effective for slightly controlling characteristics and improving stability.
After that, a protective film such as silicon resin or polyimide is formed to complete the line sensor. Heat treatment such as drying of the protective film may be replaced with the above heat treatment (150 to 400 ° C.). The characteristics of one bit of these line sensors are examined, and the results when the substrate temperature during Cu deposition and the heat treatment temperature after electrode formation are both 150 ° C. are summarized in Table 1. Normal CdS for comparison
A sensor in which a _0.6 Se _0.4 : Cu (0.01 to 0.1 mol%) vapor-deposited film was formed after the activation heat treatment as described above was examined.
The characteristics are applied voltage DC10V. Light irradiation is green LED light (570n
m, 100 lux) at 1 Hz (0.5 sec each).
Response time was photocurrent J _p rise time is the time until up to 50% of the saturation value from 0 τ _r, J _p is the fall time of the time down to 50% from saturation value tau _d. Γ is 50 to 10
It is the average value between 0lux.

In this way, the fall time τ _d can be reduced to about 0.5 msec and the γ can be increased to 0.70 or more, and in many cases to 0.80 or more, while the photocurrent is kept as large as several μA or more. On the other hand, the rise time τ _{r of the} photocurrent does not increase even when τ _d decreases unlike the case of the normal sensor, and when actually used as a line sensor, the reflected light (at least 3% ) Becomes bias light, which constantly irradiates the sensor, so that it effectively becomes extremely small. The effect is shown in Table 2. There is almost no change in other characteristics (J _p , γ _d , γ) due to the bias light irradiation of this degree.

In the present embodiment, CdS _0.6 Se _0.4 is taken as an example, but the same effect can be obtained with CdS, CdSe or a solid solution CdS-CdSe having another composition ratio.

Effects of the Invention According to the present invention, it is possible to realize an optical sensor having an extremely high optical response speed and a large γ value while maintaining a large photocurrent value. As a result, a high-speed image reading apparatus excellent in halftone reproduction can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between photocurrent and light intensity in an optical sensor.

Continuation of the front page (56) References JP-A-61-24285 (JP, A) JP-A-58-172232 (JP, A) JP-A-60-142579 (JP, A)

Claims (5)

(57) [Claims] CdS, CdSe or solid solution Cd on an insulating substrate.
A semiconductor thin film made of S-CdSe is formed,
A method for producing an optical sensor, comprising: exposing to dCl ₂ vapor to photoelectrically activate, depositing a small amount of Cu, performing a heat treatment thereafter, and providing a counter electrode on the semiconductor thin film. 2. The method for manufacturing an optical sensor according to claim 1, wherein the substrate temperature at the time of depositing Cu is from room temperature to 400 ° C. 3. The method according to claim 1, wherein the heat treatment condition after the Cu deposition and before the electrode formation is 80 to 250 ° C. in an atmosphere containing a neutral or a small amount of oxygen. Manufacturing method of optical sensor. 4. The method for manufacturing an optical sensor according to claim 1, wherein after the electrodes are formed, a heat treatment is performed at 150 to 400 ° C. in an atmosphere containing a neutral or a small amount of oxygen. 5. The method according to claim 1, wherein the amount of the deposited Cu is 0.00
2. The method for manufacturing an optical sensor according to claim 1, wherein the content is 5 to 0.1 mol%.