JPH05130510A - Image sensor - Google Patents

Abstract

PURPOSE:To increase an photoelectric current and to reduce the influence of a noise in a driving circuit, etc., by using a phototransistor as a photo sensor. CONSTITUTION:A gate electrode 2 is formed on a glass substrate 1, and amorphous material Si3N4-3 and amorphous material Si-4 are filmed on the electrode, and Cr film is formed on the film. A source electrode 5 and a drain electrode 6 are formed by patterning the Cr film. thence, a TFT element B is formed on the substrate 1 by patterning amorphous material Si. Thence, H-type amorphous material Si-7 is filmed, and P-type amorphous material Si-8 and N-type amorphous material Si-9 are filmed sequentially on the Si-7. Also, non-doped amorphous material Si can be interposed among the layers of Si-7, Si-8, and Si-9. Transparent conductive film 10 is patterned by generating on such NPN structure, and furthermore, the phototransistor A is formed on the electrode 5 by patternizing the NPN structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor capable of being integrated on the same substrate and capable of detecting one-dimensional or two-dimensional image information, and more particularly to a scintillator for converting X-rays into visible light. And an image sensor suitable for detecting an X-ray image.

[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, the sensitivity of such an image sensor is not always sufficient. In particular, an X-ray image sensor configured to detect an X-ray image by providing a scintillator for converting X-rays into visible light on a photodiode array made of amorphous silicon needs to detect weak light. Improving the sensitivity of is an important issue. In particular, when obtaining an X-ray image of a human body in the medical field, it is necessary to further increase the sensitivity of the image sensor in order to reduce the amount of X-ray exposure to the human body.

[0004]

The present invention has been made to solve the above-mentioned problems, and the present invention is 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 image sensor is characterized in that the photosensor comprises a phototransistor. It is usually preferable to use an amorphous semiconductor material for the phototransistor.

Further, according to the present invention, a switch element for reading out photocharges, which is provided on the substrate adjacent to the phototransistor and is connected to the phototransistor, can be provided for each phototransistor.

Furthermore, the present invention relates to the image sensor and X
X-ray images can be detected in combination with a scintillator that converts rays into visible light. In this case, the phototransistor can be efficiently photoelectrically converted by forming the phototransistor with an amorphous material.

[0007]

In the present invention, since the phototransistor is used in the photosensor, the photocharge generated in the phototransistor can be amplified, so that the photocurrent becomes large and the influence of noise in the drive circuit connected to the phototransistor is increased. Can be made smaller.

[0008]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a sectional view showing one pixel of the image sensor of the present invention, showing a phototransistor in which a photodiode and a transistor are integrated, and a TFT (thin film transistor) element which is a switch element connected to the photodiode.
A method of forming a large number of such phototransistors and TFT elements in the two-dimensional direction on the glass substrate 1 will be described.

First, the Cr gate electrode 2 of the TFT B is formed on the glass substrate 1. Amorphous Si3 N4 3 and amorphous Si4 are formed thereon by a plasma CVD method, and a Cr film is formed thereon. The source electrode 5 and the drain electrode 6 of the TFTB are formed by patterning this Cr film. Thereafter, by patterning the amorphous Si, the TFT element B as a switch element is formed on the glass substrate 1.

Next, N-type amorphous Si7 is formed by plasma CVD method, and then P-type amorphous Si8 and N-type amorphous Si9 are sequentially formed. This Si7, P-type amorphous Si
8, non-doped amorphous Si between N-type amorphous Si9 layers
May be interposed. The transparent conductive film 10 is formed on the NPN structure by a sputtering method and patterned.
After that, the NPN structure is patterned to form the phototransistor A on the source electrode 5 of the TFTB.

Further, an insulating protective film 11 made of polyimide or the like is formed and a contact hole 13 for connection with the transparent conductive film 10 is formed.
After forming, the electrode 12 such as aluminum is vapor-deposited and patterned.

FIG. 2 shows an equivalent circuit of FIG. Phototransistor A is represented by photodiode C and transistor D. The image light L enters the photodiode C and is photoelectrically converted to generate photocharge. This charge becomes a photocurrent at the base of the transistor D, and this photocurrent is current-amplified by the transistor D and taken out from its emitter. This amplified photocurrent flows to the source electrode 5 of the TFT provided in the same pixel and is stored in the capacitance associated with the source electrode 5. When a voltage is applied to the gate electrode 2 in this state, the TFT is turned on and an image signal can be taken out to the drain electrode side.

FIG. 3 shows an equivalent circuit in which pixels are arranged two-dimensionally. A sensor with M rows and N columns is shown. G ₁ ~G _M is a gate line which addresses each row, TFT is ON for all the pixels voltage G ₁ is connected to the applied G ₁
And the drain line D connected to the drain of each TFT
The light output of each pixel is taken out from _{1 to DN} . When the reading on the G ₁ line is completed, the voltage is sequentially applied to the gate line, such as G ₂ , to read the image information. In this way, a two-dimensional image can be obtained.

FIG. 4 shows an example of forming an X-ray image sensor for detecting an X-ray image combined with a scintillator.
Although details are omitted in FIG. 4, a scintillator F having CsI as a main constituent element is provided on the image sensor E similar to that shown in FIG. The X-ray image incident from the upper portion of the scintillator F is converted into visible light by the scintillator, reaches the image sensor E, and the X-ray image can be read out as image information of an electric signal.

Although silicon (Si) is exemplified as the amorphous semiconductor material in the phototransistor in the embodiments of the present invention, the present invention is not limited to this, and a compound semiconductor material such as CdTe may also be used. Can be used.

Although CsI has been exemplified as the scintillator here, the scintillator is not limited to this and, for example, CaWO ₄ , Gd ₂
O ₂ S, ZnS, BaSO ₄ , BaFCl, Y ₂ O
A scintillator containing ₂ S, LaOBr or the like as a main component may be used.

[0018]

According to the present invention, since the photosensor is an image sensor composed of a phototransistor, the photoelectrically converted current is immediately amplified. Therefore, the switch noise of the TFT and the thermal noise due to the capacitance existing parasitic on the drain line occur. The output of the image sensor is larger than that of the image sensor.
The N ratio can be improved and the sensitivity can be improved.

X for medical use in combination with a scintillator
When the X-ray image sensor is formed, the amount of X-ray exposure to the human body can be reduced, and the power can be exerted in X-ray diagnosis without side effects.

[Brief description of drawings]

FIG. 1 is a schematic view of a partial cross-sectional structure showing an embodiment of the present invention.

2 is an equivalent circuit of FIG.

FIG. 3 is an equivalent circuit of the two-dimensional image sensor of the present invention.

FIG. 4 is a schematic diagram of a partial cross-sectional structure of an X-ray image sensor according to the present invention.

[Explanation of symbols]

A Phototransistor B TFT 1 Glass substrate 2 Gate electrode 3 Amorphous SiN ₄ 4 Amorphous Si 5 Source electrode 6 Drain electrode 7 N-type amorphous Si 8 P-type amorphous Si 9 N-type amorphous Si 10 Transparent conductive film 11 Insulation protection film 12 Electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G21K 4/00 Z 8805-2G H01L 27/146 31/10 H04N 5/32 8838-5C

Claims (4)

[Claims] 1. An image sensor in which a plurality of photosensors are arrayed in a one-dimensional or two-dimensional direction on the same substrate,
An image sensor, wherein the photosensor comprises a phototransistor. 2. The image sensor according to claim 1, wherein the phototransistor is made of an amorphous semiconductor material. 3. The photo-charge reading switch element, which is provided on the substrate adjacent to the phototransistor and is connected to the phototransistor, is provided for each phototransistor. Image sensor described. 4. The image sensor according to claim 1, wherein an X-ray image is detected in combination with a scintillator that converts X-rays into visible light.