JPH0591419A - Image sensor - Google Patents

Abstract

PURPOSE:To extremely reduce the number of defective picture elements by defining the output obtained by adding together the optical charge of two or more photosensors continuous to each other as the optical charge of a single picture element. CONSTITUTION:N pairs of photodiodes 1 and 2 are arranged in a one- dimensional form on a base board. The anode sides of these photodiodes are earthed to a common line together with the cathode sides connected to the terminal of an external reading IC 3 respectively. All photodiodes are previously checked and the positions of the defective photodiodes, the output variance of the optical charge, etc., are stored in a memory 5 connected to an arithmetic unit 4. When the photodiodes 1 and 2 serving as the output of a single picture element work normally, the output variance of the IC 3 is corrected by the unit 4 based on the information on the memory 5. These corrected outputs are added together and outputted as the picture element information. If both photodiodes 1 and 2 are defective, the output of another photodiode is amplified double and outputted through the unit 4 as the picture element information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor which can be integrated and produced on the same substrate and can detect one-dimensional or two-dimensional image information. The image sensor eliminates loss of image information due to defects and the like.

[0002]

2. Description of the Related Art Conventionally, there has been known an image sensor in which a photodiode array is formed on a large area substrate such as a glass substrate using amorphous silicon as a raw material. The image sensor using this photodiode array is 30 cm long.
Amorphous silicon photodiodes are arranged in a line at a pitch of 100 to 200 μm on a glass substrate of a certain size, and are configured so that the photocharge of each photodiode is output from an external drive circuit. Has been put into practical use.

[0003]

However, such an image sensor has only one photodiode per pixel, and therefore, if this photodiode is defective, the image information of this pixel portion will be lost. Therefore, there is a problem that normal image information cannot be captured.

[0004]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems. The present invention is an image sensor in which a large number of photosensors are arrayed in a one-dimensional or two-dimensional direction on the same substrate. In this image sensor, the output obtained by adding the photocharges of two or more photosensors is used as the photocharge of one pixel. Further, in the present invention, a switch element for reading out photocharges, which is provided on the substrate adjacent to the photosensor and is connected to the photosensor, can be provided for each photosensor.

In the present invention, when the photocharge output from one photosensor cannot be taken out of the photocharge from the photosensor constituting the pixel due to a defect in the photosensor or the switch element, the photosensor of the one part is not output. In order to correct the photocharge of (1), it is preferable to amplify the photocharge from the photosensor that constitutes the defective pixel.

In this amplification, when the photocharge output from m photosensors out of n photosensors outputting the photocharge from one pixel is defective, the photocharge output from that pixel is n / (n-).
m).

It is preferable that the m photosensor circuits having this defective portion are completely disconnected from the photocharge output circuit.

The photo sensor and the switch element are usually made of an amorphous material. In particular, when an X-ray image is detected in combination with a scintillator that converts X-rays into visible light, a photosensor made of an amorphous material is used to efficiently photoelectrically convert the light from the scintillator.

[0009]

As described above, according to the present invention, the output obtained by adding the photocharges of two or more adjacent photosensors is used as the photocharge of one pixel. Therefore, the photocharge from a part of the photosensor in one pixel is used. Even if it is not possible to take out, the photocharges of other photosensors can be taken out, or they can be increased and corrected, so that the image information of the pixel is not lost.

[0010]

Embodiments of the one-dimensional image sensor and the two-dimensional image sensor according to the present invention will be described below. Example 1 (One-dimensional image sensor) Fig. 1 shows an equivalent circuit diagram of the one-dimensional image sensor. Figure 1
In, a set of two photodiodes, the photodiode (1) and the photodiode (2), is arranged N-dimensionally one-dimensionally on the substrate (not shown). The anode side of these photodiodes is grounded to a common line, and the cathode side is connected to the terminals of an external read IC (3).
In advance, all the photodiodes have been checked, and the position of the defective die, the variation in the output of the photocharge, and the like are recorded in the memory (5) connected to the arithmetic unit (4). When the photodiode (1) that outputs one pixel and the photodiode (2) operate normally, the output of the read IC (3) varies depending on the information in the memory (5) in the arithmetic unit (4). After being corrected, they are added and output as pixel information. On the other hand, when one of the photodiode (1) and the photodiode (2) is defective, the output of the defective photodiode is ignored by the information from the memory (5), and the output of the other photodiode is corrected for variation, It is amplified twice and output from the arithmetic unit (4) as pixel information.

In the first embodiment, two photodiodes are assigned to obtain the information of one pixel, but three or more photodiodes may be assigned to one pixel. Example 1
If the defect rate of the photodiode, which is the photosensor, is 1%, the probability that the photodiodes (1) and (2) will be defective at the same time is (0.01) ² , which can be reduced to 0.01%. Therefore, the yield of manufacturing the image sensor can be improved.

Embodiment 2 (two-dimensional image sensor) FIG. 2 shows an equivalent circuit diagram of the two-dimensional image sensor. Figure 2
In, a set of two photodiodes (A) and (B) is arranged in a plane of N columns and M rows. Readout thin film transistors (hereinafter referred to as TFTs) (A) and (B), which are respectively connected to the cathodes of the photodiodes (A) and (B), are provided adjacent to each other, and light of the photodiodes (A) and (B) is provided. The electric charge is output by switching operation.

The gate lines G _{A1 to} G _AM are the gate addresses of the TFT-A, and the gate lines G _{B1 to} G _BM are the TFT-A.
The gate address of B is shown. Drain line D ₁ ~ D
_{N + 1} is a line for reading out the photocharges stored in the photodiode. The charge from the photodiode A is D _{1 to DN.}
And the charge from the photodiode B is D ₂ ~
Taken from D _{N + 1} . The symbol "com" is a terminal for setting the potential on the cathode side of the photodiode, and is a common electrode for all the photodiodes.

The operation will be described. Now consider pixel (1,1). This pixel is composed of photodiodes A and B. Now apply + 5V to com. And D _{1 to} D
_{N + 1} is grounded. Light enters each photodiode,
It is photoelectrically converted inside the photodiode. The generated photocurrent (photoelectric charge) raises the anode potential of the photodiode. This anode potential is proportional to the light quantity of the photodiode. In this state, a voltage is applied to G _A1 to turn on the TFT-A. Then, the photocharges accumulated in the anode of the photodiode are taken out to the drain line D ₁ through the TFT-A. Similarly pixel (2, 1)
The electric charge of the photodiode A is taken out to D ₂ , and the electric charge of the pixel (N, 1) is taken out to D _N. After the charge reading of the photodiode A is completed, a voltage is applied to the gate line G _B1 to turn on the TFT-B and read the charge of the photodiode B. This photocharge is read out to the lines D _{2 to} D _{N + 1} . In this way, the outputs of the photodiodes A and B included in the same pixel are read at different timings, so the extracted light output is stored in an external memory, and these two outputs are added together and then the light of the pixel is added. Output.

In this structure, even if one of the photodiode and the TFT is defective, if the defective element is checked in advance, the output from the defective element is ignored, and the normal element output is doubled. Image information having no defect can be obtained by considering it as a pixel signal.

Further, when the defective element is short-circuited or the like, it may cause a problem such as saturation of the read circuit itself. Therefore, it is better to cut the wiring portion to the defective element with a laser beam or the like. There are cases.

It should be noted that the image sensor shown in this embodiment is an image sensor using a photodiode made of amorphous silicon and a TFT made of amorphous silicon or polycrystalline silicon as a main material. Area (several cm
It is designed to detect images above the corner.

It is also possible to form a scintillator (main material CsI or the like) for converting X-rays into visible light on the image sensor to detect an X-ray image. This X
Since the line image sensor does not have a lens for condensing X-rays, a large area is required, and therefore it is necessary to fabricate a large-area and large-capacity photosensor on the same substrate. The present invention can significantly improve the manufacturing yield, which is the most problematic factor when manufacturing such an X-ray image sensor, so that an inexpensive X-ray image sensor can be realized.

[0019]

As described above, according to the present invention, by providing a plurality of photodiodes for outputting the signal of each pixel, ignoring the output from the defective element among them, and using the normal element output as the image output, a defect is caused. The number of pixels can be drastically reduced. Therefore, the image sensor of the present invention has a high manufacturing yield and can be manufactured at low cost.

By combining the present invention with a scintillator, an inexpensive and defect-free X-ray image sensor can be manufactured.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a one-dimensional image sensor according to the present invention.

FIG. 2 is an equivalent circuit diagram of a two-dimensional image sensor according to the present invention.

[Explanation of symbols]

(1), (2) Photodiode (3) Readout IC (4) Computing device (5) Memory (A), (B) Photodiode TFT A, TFT B Thin film transistor G _{A1 to} G _AM , G _{B1 to} G _BM Gate address D _{1 to} D _{N + 1} Photoelectric charge readout line com Cathode terminal

Claims (6)

[Claims] 1. In an image sensor in which a large number of photosensors are arranged in a one-dimensional or two-dimensional direction on the same substrate, the output obtained by adding the photocharges of two or more adjacent photosensors is defined as the photocharge of one pixel. An image sensor characterized by the above. 2. The image sensor according to claim 1, wherein each photosensor is provided with a switch element provided on the substrate adjacent to the photosensor and connected to the photosensor for reading out photocharges. 3. One of the photocharges from the photosensors constituting a pixel due to a defect in the photosensor or the switch element, etc.
When the output of the photocharge from the photosensor of part is not available, the photocharge from the photosensor constituting the defective pixel is amplified in order to correct the photocharge from the photosensor of part 1. The image sensor according to Item 1 or 2. 4. The image sensor according to claim 3, wherein a circuit having a defective portion such as the photosensor or the switch element is disconnected from the output circuit of the photocharge of the pixel. 5. The image sensor according to claim 1, wherein the photo sensor and / or the switch element are made of an amorphous material. 6. An X-ray image is detected in combination with a scintillator for converting X-rays into visible light.
The image sensor according to any one of 1.