JPS6363265A - Contact type image sensor and its manufacture - Google Patents

Abstract

PURPOSE:To align signal outputs with a simple constitution by inserting a filter including a PLZT array substrate that arrays PLZT optical shutter cells between a light converging fiber lens array and an optical sensor array substrate. CONSTITUTION:An image sensor includes a light emitting diode array 3 for lighting an original surface 6, the light converging fiber lens array 4 receiving light that comes from the light emitting diode array 3 and that is refected on the original surface 6, and an optical sensor array substrate 2 arranged on the image forming surface of the light converting fiber lens array 4. The filter including the PLZT array substrate in which plural PLZT optical shutter cells having one vs one correspondence with the light receiving surfaces of respective optical sensor elements on the optical sensor array substrate 5 are arrayed is inserted between the light converging fiber lens array 4 and the optical sensor array substrate. Since the on and off characteristics of the PLZT cell is smooth with respect to an impressed voltage, the quantity of light can be finely adjusted. Thus, by using the filter made of the PLZT optical shutter cell 7, the light receiving quantity of each optical sensor element can be independently adjusted, and uniform signal outputs can be obtained from all the optical sensor elements.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an image sensor and a manufacturing method thereof.

[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. Conventional facsimile photoelectric conversion devices (hereinafter referred to as image sensors) have used semiconductor ICs such as MOS type and CCD type. However, in this semiconductor image sensor, the size of the IC chip is small, about several meters plus one meter, and therefore, for example, 20cm
To read an A4 document with a width of m, an optical system is required to reduce the document image to a width of several meters, and the optical path length (A
Securing a width of 40 to 60 cm in the case of 4-size paper has been regarded as a bottleneck in downsizing the device. 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 document width, 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, the structure shown in Fig. 7 is conventionally known (International Electron Device Meeting Technical Digest (IEDM82)).
, p. 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. In the case of an A4 size sensor with 8 elements/mn, which sensor element has a light receiving area of 100 μm square?
28 pieces - lined up in a row. The light emitting diode array 3 for document illumination is an array of high-intensity green light emitting diodes arranged at intervals of 2 to 3 m+1 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 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 2 Oram or less, and the device can be significantly miniaturized.

[Problem that the invention seeks to solve]

By the way, as a characteristic of the image sensor, it is desirable that the signal output between each element be the same. 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 for explaining variations in signal output. Variations in signal output are caused by (1) variations in the amount of light 12 incident on each photosensor element 1' caused by the emission intensity distribution of the light-emitting diode array, (2) variations in the characteristics of the photosensor array 1 (light received by each photosensor element). (3) variation in the wiring capacitance Cs13 from each photosensor element to the signal detection circuit, etc.

FIG. 9 is a characteristic diagram showing 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 quite large at ±12%, which 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, this requires a special correction circuit, e.g. memory, on the output side of the optical sensor array.
It becomes necessary to install correction circuits consisting of comparators and amplifiers in a number corresponding to the number of optical sensor elements, which becomes a significant cost increase 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.

[Means for solving problems]

The contact image sensor of the present invention includes a light-emitting diode array for illuminating a document surface, a light-concentrating fiber lens array that receives reflected light emitted from the light-emitting diode array and reflected on the document surface, and a light-condensing fiber lens array that receives light emitted from the light-emitting diode array and reflected on the document surface. and a photosensor array substrate disposed on the imaging plane of the image sensor, each photosensor element of the photosensor array substrate is disposed between the light-condensing fiber lens array and the photosensor array substrate. PLZT with PLZT optical shutter cells arranged in an array in one-to-one correspondence with the light-receiving surface of
A filter including an array substrate is inserted.

The contact image sensor manufacturing method of the present invention includes: a light-emitting diode array for illuminating a document surface; a light-concentrating fiber lens array that receives reflected light emitted from the light-emitting diode array and reflected on the document surface; A photosensor array substrate disposed on the image forming surface of the lens array, and a light-receiving surface of each photosensor element of the photosensor array substrate between the light-condensing fiber lens array and the photosensor array substrate. A process of temporarily assembling a contact image sensor formed by inserting a filter including a PLZT array substrate in which corresponding PLZT optical shutter cells are arranged in an array, and determining the signal output distribution of the optical sensor array substrate with respect to a white original. a step of measuring, a step of storing the minimum signal output value in the signal output distribution in a memory, and a step of adjusting the voltage applied to each of the PLZT optical shutter cells to set the signal output of each of the photosensor elements to the white document to the minimum value. and a step of matching the signal output value.

[Effect]

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 of the photosensor elements constituting the photosensor array. As a means for adjusting the amount of received light, an array of PLZT optical shutter cells is used as a neutral density filter, and the amount of attenuation of each PLZT optical shutter cell is determined by trimming the PLZT optical shutter cell driving voltage and adjustment resistor using, for example, a laser beam trimmer. , PLZ
Adjustment is performed by adjusting the voltage applied to the T-light shutter cell.

PLZT is lanthanum-doped lead titanium zirconate (
PbTiO3-PbZrO3) is a transparent ferroelectric ceramic. When an electric field is applied, it exhibits birefringence and rotates the plane of polarization of incident light. Therefore, by placing two polarizing plates on the incident light side and the transmitted light side, sandwiching the PLZT array substrate, and applying an electric field along the surface of the PLZT array substrate, an optical shutter can be created as shown in Figure 2. It can be used as The amount of light received by the optical sensor element is adjusted as follows. First, a white original is used to obtain the signal output distribution of all optical sensor elements.The minimum output value of this signal output is stored in a memory. Finally, a part of the thin film resistor made of amorphous silicon on the PLZT array substrate provided in one-to-one correspondence with each optical sensor element is evaporated and scattered by a laser beam, and the signal output of the optical sensor element is first Trim until it matches the minimum signal output value stored in . 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 + m5 ec.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing the structure of an embodiment of the contact type image sensor of the present invention.

This embodiment includes a light-emitting diode array 3 for illuminating the document surface 6, a light-condensing fiber that receives reflected light emitted from the light-emitting diode array 3 and reflected by the document surface 6, an iber lens array 3, and a light-condensing fiber. In an image sensor including a photosensor array substrate 2 disposed on the imaging plane of a lens array 4, each photosensor of the photosensor array substrate is disposed between the light-condensing fiber lens array 4 and the photosensor array substrate. A filter including a PLZT array substrate in which PLZT optical shutter cells are arranged in an array in one-to-one correspondence with the light-receiving surface of the element is inserted.

The optical sensor array 1 is a one-dimensional array of optical sensor elements made of amorphous silicon Schottky junction diodes formed on an optical sensor array substrate 2 made of glass and having a light receiving area of 100 μm x 100 μm, with an element density of 8. The total number of elements is 1728, and the document reading width is A4.
Judgment. As a light source for document illumination, the peak wavelength is 570.
Two light emitting diode arrays 3 were used in which 92 nm GaP light emitting diodes were linearly arranged at a pitch of 2.5+im and a bar-shaped condenser lens was integrated with a light emitting diode row. The illuminance of the original surface is 2500 fx. Since the condensing fiber lens array 4 of the light guiding system is made of TV-based material, the aperture angle is large at 25° and the imaging distance is short at 17 mm. The light transmission rate of this focusing fiber lens array 4 is about 0.035.

As the PLZT array substrate 5, in order to obtain a high light transmittance, a substrate with a composition ratio of Zr/Ti of 65/35 and doped with 9% La is used, and the front and back surfaces are arranged so that the substrate thickness is 1 rxta. Both were thoroughly mirror polished. 1 P
The LZT cells have an area of 110 μm×110 μm, and are arranged so as to overlap one-on-one with the optical sensor elements, and the cell density is 8 cells/m − and the total number of cells is 1728 cells. FIG. 3 shows a perspective view of the electrode structure of the PLZT array substrate, which has an interdigital structure to increase the optical shutter effect. The applied voltage for driving the PLZT cell was kept constant at 150 μm. When the applied voltage is 0 and 150, the light transmittance is 2% and 70%, respectively. By reducing the applied driving voltage, the amount of light received by the photosensor element is adjusted. As a cell drive voltage adjustment resistor provided in series with each PLZT cell, a thin film resistor 8 made of phosphorus-doped amorphous silicon (specific resistance 106 Ω-1) was used. The area of this amorphous silicon thin film resistor is lOOμm×10
At 0μm, the thickness is the resistance value of PLZT self (approximately 1013Ω
) and the resistance value of the amorphous silicon thin film resistor 8 is approximately 1.
The number of participants was set at 1,000 so that the ratio was 0:1. This thin film resistor 8 is formed on the same ceramic substrate as the PLZT optical shutter cell.

Furthermore, since the on/off characteristics of the PLZT cell exhibit a gentle characteristic with respect to the applied voltage, delicate adjustment of the amount of light is possible.

Next, an embodiment of a method for manufacturing a contact type image sensor of the present invention will be described.

This embodiment includes a light emitting diode array 3 for illuminating the document surface 6, and a condensing fiber lens array 4 that receives reflected light emitted from the light emitting diode array 3 and reflected by the document surface 6.
and a photosensor array substrate 2 disposed on the imaging plane of the light-condensing fiber lens array 4; and between the light-concentrating fiber lens array 4 and the photosensor array substrate 2, each light of the photosensor array substrate 2 is P in one-to-one correspondence with the light-receiving surface of the sensor element
a step of temporarily assembling a contact image sensor formed by inserting a filter including a PLZT array substrate 5 in which LZT optical shutter cells are arranged in an array; a step of measuring the signal output distribution of the optical sensor array substrate with respect to a white original; A step of storing the minimum signal output value in the signal output distribution in a memory, and a step of adjusting the voltage applied to each PLZT optical shutter cell to adjust the signal output of each optical sensor element for a white document to the above-mentioned minimum signal output value. Contains.

The voltage applied to the PLZT optical shutter cell can be adjusted using the PLZT.
This is done by trimming the thin film resistor 8 connected in series with the cell. That is, using a YAG laser with an output of 5 W, a part of one amorphous silicon film was evaporated and scattered by laser light to change the area of the thin film and increase the resistance. As the resistance increases, the voltage applied to the PLZT cell decreases, resulting in a decrease in light transmission.

The curve in Figure 5 (a> is the voltage applied to all PLZT cells of 1
50 is a characteristic curve showing the signal output distribution of all optical sensor elements when a white original of the contact type image sensor before adjustment is used. The variation was approximately ±12%. The output value at point A, the minimum value of the output distribution, was stored in a memory, and the amount of light attenuation of the P L Z T cell corresponding to all the light sensor elements of the pond was adjusted using the laser trimming device shown in FIG. To adjust the amount of light attenuation, the comparator 9 shown in FIG. Trimming was performed by reflecting the output light of the YAG laser 11 on the reflecting mirror 15 and applying it to the amorphous silicon thin film resistor 8 until it became the same as the signal output value. PLZT
Since the optical response speed of the cell is sufficiently high, the trimming time per element can be within 30 m5ec. Therefore, adjustment of all 1728 elements was completed in 51 seconds.

Curve (b) in FIG. 5 is a characteristic curve showing the signal output distribution of the all-photo sensor element when a white document is used in a contact type image sensor for which the output adjustment of the all-photo sensor element has been completed. The variation is reduced to approximately ±0.6%. 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, and it has become possible to actually obtain a 64'Pa tone signal output.

〔Effect of the invention〕

The present invention is a close-contact image sensor that enables drastic downsizing of facsimile machines, etc., by using a filter consisting of a PLZT optical shutter cell to independently adjust the amount of light received by each optical sensor element. Uniform signal output can be obtained for each element. As a result, it becomes possible to read half-tone images, which was difficult to do 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 the drawing]

FIG. 1 is a perspective view showing the structure of an embodiment of the contact type image sensor of the present invention, and FIG.
3 is a perspective view of the PLZT array substrate, FIG. 4 is an equivalent circuit diagram of the PLZT array substrate, and FIG. 5 is a diagram of the optical sensor array substrate for explaining the present invention in detail. 6 is a block diagram of a laser trimming device for manufacturing the contact type image sensor of the present invention; FIG. 7 is a perspective view showing the configuration of a conventional contact type image sensor; FIG. 8 is a characteristic diagram showing the signal output distribution. The figure is an equivalent circuit diagram to explain the problems of conventional contact type image sensors.
The figure is a characteristic diagram showing the signal output distribution of a conventional contact type image sensor. DESCRIPTION OF SYMBOLS 1... Optical sensor array, Plan... Optical sensor array board, 3... Light emitting diode array, 4... Light condensing fiber lens array, 5... PLZT array board, 6...
... Original surface, 7... PLZT cell, 8... Thin film resistor, 9... Memory, 10... Comparator, 11.
... YAG laser, 12... Incident light, 13... Wiring capacitance, 14... Polarizing plate, 15... Reflecting mirror. Take a break! Fig. 4 Kakuko/Dazzle Fly Lance 7t- Fig. 2 Fig. 3 Chrysanthemum Fig. 4 Fig. M6 Fig. 8 Fig. 7 Fig. 4

Claims (2)

[Claims] (1) A light-emitting diode array for illuminating the document surface, a light-condensing fiber lens array that receives reflected light emitted from the light-emitting diode array and reflected by the document surface, and an imaging surface of the light-condensing fiber lens array. In a contact type image sensor comprising a photosensor array substrate, a pair of light receiving surfaces of each photosensor element of the photosensor array substrate is provided between the light-condensing fiber lens array and the photosensor array substrate. What is claimed is: 1. A close-contact image sensor comprising a filter including a PLZT array substrate in which PLZT optical shutter cells corresponding to PLZT light shutter cells arranged in an array are inserted. (2) a light-emitting diode array for illuminating the document surface; a light-concentrating fiber lens array that receives reflected light emitted from the light-emitting diode array and reflected on the document surface; and an imaging surface of the light-condensing fiber lens array. A PLZT optical shutter cell is provided between the disposed optical sensor array substrate, the light-condensing fiber lens array, and the optical sensor array substrate, and corresponds one-to-one to the light receiving surface of each optical sensor element of the optical sensor array substrate. A step of temporarily assembling a contact type image sensor formed by inserting a filter including a PLZT array substrate arranged in an array, a step of measuring a signal output distribution of the optical sensor array substrate with respect to a white original, and a step of measuring the signal output distribution of the optical sensor array substrate with respect to a white document. a step of storing the minimum signal output value of each P in a memory;
A method for manufacturing a contact image sensor, comprising the step of adjusting the voltage applied to the LZT optical shutter cell to adjust the signal output of each of the optical sensor elements for a white document to the minimum signal output value.