JPS6148270A - Image sensor and its manufacture - Google Patents

Abstract

PURPOSE:To read the picture of intermediate tone display by using a liquid crystal extinction filter cell so as to adjust independently the quantity of photodetection of each sensor element and obtain a uniform output to all sensor elements. CONSTITUTION:A liquid crystal cell array substrate 5 is placed between a light sensor array substrate 2 and a conductor light system fiber lens array 4. The light irradiated from a light emitting diode array 3 and reflected on an original face 6 is subject to adjustment of the sensor detecting quantity by the liquid crystal array substrate 5 so that the signal output of the light sensor array 1 is uniformed. A white original is used to adjust the quantity of light detection for the sensor element to obtain a signal output distribution of all sensor elements and the minimum output is stored in a memory 10. Finally, a part of amorphous silicon thin film resistor on the liquid crystal cell substrate 5 provided one to one corresponding to each sensor element is evaporated by the laser beam and trimming is applied until the output is coincident with the minimum signal output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image sensor that outputs a uniform signal and a method for manufacturing the same.

[Conventional technology]

In recent years, with the progress of office automation, it has been desired to make facsimile machines smaller.

The biggest obstacle to miniaturizing such devices is the size of the photoelectric conversion system in the image reading section.

It's hard. Conventional fi-axis photoelectric conversion devices (hereinafter referred to as image sensors) are MOS type and CCD.
Semiconductor ICs such as molds have been used. However, the size of the IC chip in this semiconductor image sensor is small, about several tens of layers, so in order to read, for example, a 202-width A4-size document, an optical system is required to reduce the document image to a few tens of square meters wide. and the final optical path length (40 to 60 - in case of A4 size)
) has been considered a bottleneck in downsizing devices. As a solution to this problem, an image sensor called a contact image sensor is attracting attention and development is underway. This is a large image sensor with a large number of tiny photoelectric conversion elements arranged one-dimensionally in the same dimension as the width of the document, and because it is used in close contact with the document, a lens with a long optical path length is used to reduce the document image. Since the system does not need to be used, the device can be significantly miniaturized.

As a basic unit structure of such a contact type image sensor, a structure as shown in Fig. 7 is conventionally known (International Electron Device Meeting Technical Digest) I'EDM'82
, page 329). In the figure, 1 is an optical sensor array;
2 is an optical sensor array substrate, 3 is a light emitting diode array for illumination, and 4 is a light guide fiber lens array. For example, an amorphous silicon sensor is used as the optical sensor array 1, and in the case of an A4 size sensor with 8 elements, each sensor element has a light receiving area of 100 μm square.
28 pieces - lined up in a row. The light-emitting diode array 8 for document illumination is an array of high-intensity green light-emitting diodes arranged at intervals of 2 to 3 meters and integrated with a condenser lens. Using such a solid-state light source improves the reliability of the device. The light guiding system fiber lens array 4 is an equivalent optical system for imaging without reduction, and uses a convergent fiber lens array matched to the emission wavelength of the light emitting diode. By adopting the above configuration, the distance between the document surface and the sensor surface can be set to 20 terms or less, and the apparatus can be significantly miniaturized.

[Problem that the invention seeks to solve]

By the way, as a characteristic of an image sensor, it is desirable that the signal outputs between each element be uniform.

However, in large devices such as contact type image sensors, signal output varies due to various causes described below. FIG. 8 shows an equivalent circuit of a contact type image sensor to explain variations in signal output.

Variations in signal output are caused by (1) variations in the amount of light 12 incident on each sensor element caused by the distribution of light emission intensity of the light emitting diode array, (2) variations in the characteristics of the optical sensor array 1 (such as uneven light-receiving area of each sensor element, etc.) ), (31 This is caused by fluctuations in the wiring capacitance Cs13 from each sensor element to the signal detection circuit, etc.

FIG. 9 is an example of the signal output distribution of all the elements of the image sensor. This is a signal output distribution when a white original is used, and the variation is ±12%, which is large by ib, and almost matches the illuminance distribution of a light emitting diode array.

A more detailed look reveals that the influence of variations in wiring capacitance is also superimposed. When only binary signals of black and white are handled, this degree of variation in signal output is acceptable. However, when reading halftone images, this variation in signal output is a fatal drawback. A conceivable way to overcome this drawback is to electrically process the signal outputs of the image sensors to make the outputs uniform. However, in order to do this, it is necessary to install a special correction circuit on the output side of the sensor array, for example, a correction circuit consisting of memory, comparators, and amplifiers in a number corresponding to the number of sensor elements, which increases the cost considerably. It becomes a factor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a contact-type image sensor and a method for manufacturing the same, in which signal outputs can be made uniform with a simple configuration.

[Failure to solve the problem]

The present invention aims to obtain a uniform signal output from the entire image sensor by introducing a simple means that can independently adjust the amount of light received by each sensor element constituting the image sensor. As a means for adjusting the amount of received light, an array of liquid crystal cells is used as a dark filter, and the amount of light attenuation of each liquid crystal cell is determined by trimming a resistor for adjusting the liquid crystal drive voltage using a laser beam trimmer, etc., and adjusting the voltage applied to the liquid crystal cell. Adjustments are made by adding or subtracting.

FIG. 1 shows an example of the structure of the contact type image sensor of the present invention. In the figure, reference numeral 5 denotes a liquid crystal cell array substrate, which is installed between the optical sensor array substrate 2 and the light guide fiber lens array 4. The light emitted from the light emitting diode array 3 and reflected by the document surface 6 is transmitted to the liquid crystal cell array substrate 5, and the amount of light received by the sensor is adjusted so that the signal output from the photosensor array l becomes uniform. 2 and 8 show a liquid crystal cell array substrate and its equivalent circuit. 7 is a liquid crystal cell, and 8 is a resistor for adjusting the driving voltage of the liquid crystal cell.

Since the on/off characteristics of the liquid crystal cell exhibit a gentle characteristic with respect to the applied driving voltage, it is possible to finely adjust the amount of light. 8
The liquid crystal cell drive voltage adjustment resistor is formed directly on the glass substrate of the liquid crystal cell using, for example, an amorphous silicon thin film resistor.

[Effect]

The amount of light received by the sensor element is adjusted as follows.

First, a white original is used to obtain the signal output distribution of all sensor elements. Next, the minimum output of this signal output is stored in memory. Finally, a part of the amorphous silicon thin film resistor on the liquid crystal cell substrate provided in one-to-one correspondence with each sensor element is evaporated and scattered by a laser beam, so that the signal output of that sensor element becomes the minimum signal stored earlier. Trim until it matches the output.

Naturally, trimming is performed using a white original while outputting a signal. In consideration of productivity, it is desirable that the trimming time per element be within several hundred m5eC. Examples of the present invention are shown below.

[Example 1] The optical sensor element (1 in Fig. 1) is made of a ceramic substrate (1
The light-receiving area of the amorphous silicon Schottky diode formed above 2) in the figure is 100 μm×100 μm. The element density is 8 elements, the total number of elements is 1728, and the document reading width is A4 size. As a light source for document illumination, 92 GaP light emitting diodes with a peak wavelength of 570 nm, 2
．． Two integrated light-emitting diode arrays arranged linearly at a pitch of 5 m and rod-shaped condensing lenses were used (first
8) in the figure.

Is the illuminance of the original surface 2500J? It is x. Since the convergent fiber lens array (4 in FIG. 1) of the light guide system is made of Tl-based material, the aperture angle is large at 25 degrees, and the imaging distance is short at 17 degrees.

The light transmission rate of this lens array is approximately 0. It is O85. As the liquid crystal cell of the liquid crystal cell array substrate (5 in FIG. 1), a guest-host two-layer liquid crystal cell was used, which did not require the use of a polarizing plate in order to obtain a high light transmittance. The liquid crystal material used was nematic liquid crystal, and the guest dye used was a blue-green merocyanine dye. The area of one liquid crystal cell is 110 μm x 110 μm, and it is arranged so as to overlap one-on-one with the optical sensor element, and the cell density is 8 cells, making the total number of cells 1728.

The applied voltage for driving the liquid crystal cell was kept constant at 5V.

The light transmittance when the applied voltage is Ov and 5V is 20% and 90%, respectively. The amount of light received by the sensor element is adjusted by reducing the applied driving voltage.

A phosphorus-doped amorphous silicon thin film (specific resistance: 10Ω) was used as the liquid crystal drive voltage adjusting resistor (8 in FIGS. 2 and 8) provided in series with each liquid crystal cell. The area of this amorphous silicon thin film is 100 μm
x100μm and the thickness is the resistance value of the liquid crystal cell (approximately 10'10
) and amorphous silicon thin film are approximately 10:1.
It was set to 1000 so that A YAG laser with an output of 5 W was used as a laser for trimming the resistance of this amorphous silicon thin film, and a part of the amorphous silicon thin film was evaporated and scattered by the laser beam to change the area of the thin film 6 and increase the resistance. As the resistance increases, the voltage applied to the liquid crystal cell decreases, resulting in a decrease in light transmittance.

FIG. 4(a) shows the signal output distribution of all sensor elements when the voltage applied to all liquid crystal cells is 5 V, that is, when a white original of the contact type image sensor is used before adjustment.

The variation was approximately ±12%. The output at point A, the minimum value of the output distribution, was stored in a memory, and the amount of light attenuation of the liquid crystal cells of all other elements was adjusted using the laser trimming device shown in FIG. The amount of light attenuation is adjusted by comparing the minimum signal output at point A stored in the memory 10 with the signal output of each element using the converter 9 in FIG. Then, the amorphous silicon thin film resistor was trimmed using a YAG laser 11. In consideration of the response speed of the liquid crystal cell, the trimming time per element was set to 800 m5ec. Therefore 1728
It took about 9 minutes to adjust all the elements.

FIG. 4(b) shows the signal output distribution of all the sensor elements when a white original is used in the image sensor after all the elements have been adjusted. The variation was reduced to approximately ±0.4%. As a result of the above, it has become possible to read images with halftone display, which was impossible with conventional contact-type image sensors.
Gradation signal output can now be obtained.

[Example 2] The optical sensor element is an amorphous silicon Mis W sensor (1 in FIG. 6) formed on a transparent glass substrate, and the light-receiving area is 100μyyx100μm, and the light-receiving surface is on the glass substrate side. Element density and total number of elements are as in Example 1
The same is true for . On the other side of this glass substrate, a TTO transparent electrode for driving a liquid crystal cell and an amorphous silicon thin film resistor for adjusting a liquid crystal driving voltage are formed. Each TT
The O transparent electrodes are arranged in one-to-one correspondence with the optical sensor elements, and the area is the same as in the first embodiment.

This transparent glass substrate with an optical sensor element was used as a sealing plate on one side of a liquid crystal cell, and liquid crystal was sealed therein to integrate the optical sensor array 1 and the liquid crystal cell array 7. FIG. 6 shows a cross section of this optical sensor liquid crystal cell array substrate. In the figure, 1 is an optical sensor, 7 is a liquid crystal cell, and 8 is a thin film resistor.

Using this optical sensor liquid crystal array substrate, a contact type image sensor unit was assembled using two light emitting diode plates and a focusing fiber lens array in the same manner as in Example 1.

Further, in the same manner as in Example 1, a laser trimming device was used to adjust the signal outputs of all the elements to be uniform. As a result, in this example, the distance between the optical sensor element and the liquid crystal cell is shortened by the thickness of the glass substrate (in this case 1.2111), so stray light is reduced and the variation in signal output distribution is reduced to ±0.2%. Diminished.

〔Effect of the invention〕

The present invention uses a liquid crystal neutral density filter cell to independently adjust the amount of light received by each sensor element in a close-contact image sensor that makes it possible to significantly reduce the size of facsimile machines and the like. Uniform signal output can be obtained.

As a result, it becomes possible to read halftone images, which has been difficult with conventional contact type image sensors.

Further, since the amount of light received for this purpose is adjusted by laser trimming of the resistor, which is a quick method suitable for automation, productivity is not impaired at all.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration and one embodiment of the image sensor of the present invention, FIG. 2 is a detailed perspective view of the liquid crystal cell array substrate in FIG. 1, FIG. 8 is its equivalent circuit diagram, and FIG. A signal output distribution diagram showing the effects of the invention, FIG. 5 is a block diagram of an apparatus for manufacturing the image sensor of the invention, FIG. 6 is a side view showing another preferred embodiment of the invention, and FIG. FIG. 8 is a block diagram of a conventional image sensor. FIG. 8 is a diagram for explaining problems of the conventional image sensor. FIG. 9 is a signal output distribution diagram of the conventional image sensor. DESCRIPTION OF SYMBOLS 1... Optical sensor array, 2... Optical sensor array board, 3... Light emitting diode array, 4... Fiber lens □ array, 5... Liquid crystal cell array board, 6...
・・Manuscript, 7・Liquid crystal cell, 8・Thin film resistor, 9・
...Memory, 10...Comparator, 11...YA
G laser, 12... incident light.

Claims (3)

[Claims] (1) Light reduction consisting of an optical sensor array substrate consisting of a number of optical sensors arranged one-dimensionally, and an array of liquid crystal cells arranged in one-to-one correspondence with the light-receiving surface of each element of the optical sensor array. An image sensor comprising a filter substrate, a light emitting diode array for illumination, and a condensing fiber lens array that images light emitted from the light emitting diode array and reflected on the document surface onto the photosensor surface. (2) A large number of optical sensor arrays arranged one-dimensionally on one side of a transparent insulating substrate, and one-to-one correspondence with the light-receiving surfaces of each element of the optical sensor array on the other side of the insulating substrate. An optical sensor liquid crystal cell array substrate consisting of an array of liquid crystal neutral density filter cells arranged, a light emitting diode array for illumination, and a light condenser that focuses light emitted from the light emitting diode array and reflected by the document surface onto the optical sensor surface. An image sensor comprising a flexible fiber lens array. (3) A number of one-dimensionally arranged optical sensor arrays, a liquid crystal neutral density filter cell array provided on the front surface of the optical sensor array on the light-receiving surface side, a light emitting diode array for illumination, and a focusing fiber lens array. a step of obtaining the signal output distribution of all elements of the image sensor for a white document, a step of storing the minimum signal output in the output distribution in a memory, and a step of obtaining the signal output of the image sensor and the signal of each sensor element for the white document. A method for manufacturing an image sensor, comprising the step of adjusting the amount of light attenuation of the liquid crystal dark filter cell until the output becomes equal.