JPH0467350B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thin film solid state X-ray sensor, particularly an X-ray
This invention relates to a thin-film solid-state X-ray sensor for use in CT scanners. More specifically, the present invention comprises forming in this order a phosphor layer, a transparent electrode layer, a photoconductor thin film having spectral sensitivity to the wavelength of fluorescence emitted by the phosphor in the phosphor layer, and an upper metal electrode. The present invention relates to a thin-film solid-state X-ray sensor constructed from the obtained laminate.

A conventional X-ray photograph is an image obtained by simply projecting a three-dimensional image onto a two-dimensional plane. On the other hand, X-ray
A CT scanner uses a computer to process a one-dimensional projected image of an object obtained by irradiating a narrow X-ray beam from each direction to reconstruct cross-sectional images of the object.

This makes it possible to distinguish slight differences in X-ray absorption in the subject's soft tissues, and provide extremely clear images of cerebral aneurysms, cerebral hemorrhages, and the like.

For this reason, the position of the X-ray CT scanner as a medical diagnostic device is increasingly improving.

As is well known, an X-ray CT scanner requires an X-ray sensor that can detect X-rays that have passed through an object with high sensitivity and high performance. Therefore, X-ray
In order to improve the performance of CT equipment, various types of
Line sensors have been developed, and some of them have been put into practical use.

FIG. 1 is an overview diagram showing the principle of an X-ray CT scanner.

In the figure, 10 is the subject, 11 is the X-ray tube, 1
1A is a collimator for directing generated X-rays toward the subject 10; 12 is an X-ray beam irradiated to the subject 10; 13 is an X-ray beam transmitted through the subject 10; 14 is an X-ray for detecting the transmitted X-rays 13. It is a line sensor.

Further, 15 is a collimator for defining the direction of X-ray incidence on the X-ray sensor 14, 16 is an amplification device for amplifying the detection output of the X-ray sensor 14, and 17
18 is a computer that receives the amplified detection output and executes predetermined image processing;
This is a video monitor that displays a cross-sectional image of.

As is clear from the figure, the X-ray tube 11 and the X-ray sensor 14 are placed facing each other on both sides of the subject 10, and while the pencil beam-shaped X-ray beam 12 is irradiated to the subject 10, the sensor 14,
Move by combining linear movement and rotation.

After X-ray absorption data is obtained from all directions of the subject 10 in this manner, a cross-sectional image can be displayed on the video monitor 18 by performing predetermined processing on the computer 17. In this case, as the X-ray sensor 14, a NaI (Tl) scintillator detector with high detection efficiency is widely used.

However, this method has the disadvantage that it takes a long time to take one shot, about 5 minutes. To improve this, attempts have been made to shorten the imaging time by using a fan beam instead of a pencil beam or by fixing the detector and rotating the X-ray tube at high speed.

As mentioned above, when the detector is fixedly arranged, attempts have been made to use a semiconductor sensor as the X-ray sensor instead of using a scintillation detector.

This is because in this case, the X-ray sensor is fixedly placed around the subject, which requires high-density mounting, but with a scintillation detector that combines a scintillator and a photomultiplier tube, This is because it becomes large, making it unsuitable for high-density packaging.

It is also possible to use a detector that combines a scintillator and a silicon photodiode. However, in this case, it is necessary to add a new low-noise amplification circuit to detect weak signals. Therefore, in practice, it is not possible to carry out sufficiently high-density packaging.

Another approach is to detect X-rays without a scintillator. In other words, silicon (Si),
Diodes using semiconductor crystals such as cadmium tellurium (CdTe) are also being considered.

JP-A No. 49-78493 discloses that a phosphor layer that generates electromagnetic waves upon receiving X-rays, a transparent electrode, a transparent insulating layer, and a photoconductor layer are laminated, and the photoconductor layer is further spaced apart. A photoelectrostatic conversion element for X-rays is disclosed in which the other electrode is placed facing each other. Paper as a recording medium can be inserted into the space. In this photoelectrostatic conversion element for X-rays, the photoconductor generates electron-hole pairs due to electromagnetic waves generated from the phosphor layer upon receiving X-rays, and an electrostatic latent image is formed on the recording medium. be done.
An X-ray photograph is obtained by developing this electrostatic latent image.

Although the photoelectrostatic conversion element for X-rays has been made thinner than previous X-ray photographic devices,
There was a problem in that the sensitivity of the photoconductor layer to the light emitted from the phosphor layer was insufficient. Another problem was that no measures were taken to prevent deterioration of the phosphor layer. Due to these problems, this type of sensor has not yet been put into practical use.

The present invention has been made in view of the above circumstances, and its purpose is to provide a thin-film solid-state X-ray sensor that can be mounted at high density.

Another object of the present invention is to provide a thin-film solid-state X-ray sensor that is easily miniaturized, has high sensitivity, and has a long life.

Still another object of the present invention is to provide a thin-film solid-state X-ray sensor whose shape can be freely processed.

To achieve the above object, the present invention includes laminating a light-shielding upper electrode, an H-doped amorphous silicon photoconductor layer, a transparent electrode layer, and a phosphor layer in the above order, and The first feature is that the interface between the photoconductor layer and the transparent electrode layer is doped with a P-type impurity, and the first feature is that a transparent insulating layer is arranged between the transparent electrode layer and the phosphor layer. Second
It has the characteristics of Furthermore, a third feature is that a blocking layer is disposed between the P-type impurity-doped silicon photoconductor layer and the transparent electrode layer.

The present invention will be explained in detail below with reference to the drawings. FIG. 2 is a sectional view of one embodiment of the present invention.

In FIG. 2, 6 is a light-shielding support, 5 is a phosphor layer formed on the support 6, and 4 is a transparent electrode layer laminated thereon. 2 is a photoconductor layer formed on the transparent electrode layer 4, and 1 is a light-shielding upper electrode laminated on the photoconductor layer 2.

In addition, in FIG. 2, it is desirable that one of the upper electrode 1 and the transparent electrode layer 4 be a divided electrode. Further, it is desirable that the spectral sensitivity (peak position) of the photoconductor layer 2 corresponds to the wavelength (the peak position thereof) of the light emitted from the phosphor layer 5.

For example, when GdO ₂ S:Tb is used as a phosphor, the peak of the emission spectrum is around 550 nm. Therefore, the photoconductor layer 2 in this case is
It is advantageous to use H-doped amorphous silicon Si:H, which has a peak spectral sensitivity at a wavelength of 550 nm. In addition, as a phosphor,
[ZnCd]S:Ag, ZnS:Ag, etc. can be used.

As the transparent electrode layer 4, any conductive material that sufficiently transmits fluorescence can be used. Among these, oxide semiconductor films such as In ₂ O ₃ /SnO ₂ (ITO) film, In ₂ O ₃ film, and SnO ₂ film are preferred from the viewpoint of ease of production.

The upper electrode 1 (1) transmits X-rays well;
(2) It is necessary that the photoconductive layer has the property of not transmitting light in the wavelength range in which it has spectral sensitivity.

The property (1) above is necessary to increase the X-ray detection efficiency of the sensor, and the property (2) above is necessary to reduce the dark current of the sensor (current flowing through the sensor when not irradiated with X-rays). It is.

The upper electrode 1 used in the present invention includes Cr, Al, Ni,
It can be composed of any one of An or an alloy thereof.

The photoconductor layer 2 of the present invention is an i-type amorphous silicon layer doped with hydrogen, and the interface between the silicon layer and the transparent electrode layer 4 contains a periodic group III element, preferably B. An amorphous silicon (P type) layer doped with is suitable. In addition,
In the latter case, the thickness of the P-type layer may be between 0.05 and 1.0 μm;
Particularly desirable is 0.1 μm to 1.0 μm. The thickness of the entire photoconductor layer is preferably 1 μm to 10 μm.

During operation, most of the X-ray beam 13 incident from the upper electrode 1 passes through the photoconductor layer 2 and the transparent electrode layer 4 and reaches the lowermost phosphor layer 5. As is well known, the phosphor layer 5
interacts with and generates fluorescence. The generated fluorescence passes through the transparent electrode layer 4 and reaches the photoconductor layer 2. The photoconductor layer 2 absorbs the fluorescence and generates electron-hole pairs therein.

Therefore, by applying an electric field (not shown) between the upper electrode 1 and the transparent electrode layer 4, the photocurrent can be extracted to the outside.

In this case, by dividing either the upper electrode 1 or the transparent electrode layer 4 as described above, it becomes possible to detect each segment, thereby improving the resolution.

Further, as a method of making the upper electrode 1 light-shielding, it is possible to form a metal electrode to a certain degree of thickness, that is, to a thickness that allows X-rays to pass through and visible light to pass through.

As is clear, the electrical signal obtained from the sensor array in which a large number of sensors having the above configuration are arranged indicates the distribution of the X-ray absorbance of the subject 10. Therefore, according to known methods,
If this is processed by a computer, a tomographic image of the subject can be obtained.

As mentioned above, hydrogen-doped amorphous silicon Si:H is used as the photoconductor layer 2,
It has been found that when a P-type amorphous silicon layer is interposed at the interface with the transparent electrode layer 4, the photosensitivity of that portion is improved, and therefore the photosensitivity of the photoconductive layer as a whole is also improved.

Furthermore, if a light reflecting layer (not shown) is provided between the support 6 and the phosphor layer 5 so that all the light emitted from the phosphor layer 5 is directed toward the photoconductor layer 2,
X-ray detection sensitivity can be further improved.

Furthermore, with the configuration of the present invention, it is easy to obtain a pattern of 8 lines/mm, that is, a resolution, for the divided upper electrode 1 or the transparent electrode layer 4. Therefore, according to the present invention, a significant improvement in resolution can be realized compared to the conventional method, in which the resolution was approximately 2 mm per pixel.

In addition, although the example in which the X-rays 13 are incident from the upper electrode 1 side has been described above, it is clear that, on the contrary, the X-rays 13 may be incident from the support body 6 side.

FIG. 3 is a cross-sectional view of another embodiment of the invention. In this figure, the same reference numerals as in FIG. 2 represent the same or equivalent parts.

As is clear from the comparison with FIG. 2, this embodiment is different from the embodiment of FIG. 2 in that a transparent insulating layer 45 is provided between the phosphor layer 5 and the transparent electrode layer 4, and the transparent electrode layer A partial region 2A of the photoconductor (Si:H) layer 2 in contact with the photoconductor 4 is made into a P type.

The insulating layer 45 is useful for preventing direct contact between the transparent electrode layer 4 and the phosphor layer 5 to prevent deterioration of the phosphor layer 5, and the P-type layer 2A has high photosensitivity. This helps improve the photosensitivity of the photoconductor layer 2 as a whole.

Specifically, this embodiment can have the following configuration.

Support 6... Aluminum thin plate Phosphor layer 5... GdO ₂ :Tb Transparent insulating layer 45
...SiO ₂ , Si ₃ N _4, etc. (thickness: 100 Å to 3 μm) Transparent electrode layer 4: 800 Å thick In ₂ O ₃ divided by lift-off method.

P-type photoconductor layer 2A...By the plasma CVD method,
B-doped amorphous silicon Si:H
A layer is deposited (thickness is 0.2μm).

Photoconductor layer 2...Amorphous silicon Si:H layer is deposited by plasma CVD method (thickness is
3 μm).

Upper electrode 1: Cr thin film (thickness: 5000 Å) attached by electron beam evaporation.

FIG. 4 is a sectional view of yet another embodiment of the invention. In this figure, the same reference numerals as in FIG. 3 represent the same or equivalent parts.

As is clear from the comparison with FIG. 3, this embodiment is different from the embodiment of FIG. 3 in that a blocking layer 23 is further added between the transparent electrode layer 4 and the P-type photoconductor layer 2A. It was formed.

As the blocking layer 23, Si ₃ N ₄ or the like is suitable. The Si ₃ N ₄ layer can be formed by plasma CVD, and may have a thickness of about 300 Å.

The insertion of this blocking layer 23 makes it possible to further reduce the dark current (current flowing through the sensor when no X-rays are irradiated) without increasing the attenuation of the photocurrent. Therefore, it is possible to obtain good X-ray sensitivity and a good S/N ratio.

With the configuration of the present invention described above, it is easy to obtain a pattern of 8 lines/mm as the divided upper electrode 1 or transparent electrode layer 4, that is, a resolution. Therefore, according to the present invention, a significant improvement in resolution can be realized compared to the conventional method, in which the resolution was approximately 2 mm per pixel.

In addition, although the example in which the X-rays 13 are incident from the upper electrode 1 side has been described above, it is clear that, on the contrary, the X-rays 13 may be incident from the support body 6 side.

As can be easily understood from the above explanation, in the present invention, the P-doped region provided in the portion of the photoconductor layer 2 that is in contact with the transparent electrode layer 4, and the A blocking layer 23 inserted between, a transparent insulating layer 45 inserted between the transparent electrode layer 4 and the phosphor layer 5, and a light reflecting layer inserted between the phosphor layer 5 and the light-shielding support 6. etc.,
Any of these can be optionally inserted or not inserted.

Also, the blocking layer 23 may be inserted between the upper electrode 1 and the photoconductor layer 2. moreover,
The support 6 can be omitted if the upper electrode 1 is also used as a support and the phosphor layer 2, transparent electrode layer 4, phosphor layer 5, etc. are sequentially laminated thereon.

As is clear from the above description, according to the present invention, the following effects can be obtained.

(a) It is possible to provide a compact thin-film solid-state X-ray sensor that can be easily fabricated using existing thin-film technology and can be mounted at high density.

(b) By doping the interface between the H-doped amorphous silicon photoconductor layer and the transparent electrode layer with P-type impurities, a thin-film solid X with high photosensitivity is created.
Line sensor can be provided.

(c) By disposing a transparent insulating layer between the transparent electrode layer and the phosphor layer, a thin-film solid-state X-ray sensor with high performance in preventing deterioration of the phosphor layer can be provided.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the principle of an X-ray CT scanner.
FIG. 2 is a sectional view of one embodiment of the invention, FIG. 3 is a sectional view of another embodiment of the invention, and FIG. 4 is a sectional view of still another embodiment of the invention. 1... Upper electrode, 2, 2A... Photoconductor layer, 4
... Transparent electrode layer, 5 ... Phosphor layer, 6 ... Light-shielding support, 23 ... Blocking layer, 45 ... Transparent insulating layer.

Claims (1)

[Scope of Claims] 1. A light-shielding upper electrode, an H-doped amorphous silicon photoconductor layer, a transparent electrode layer, and a phosphor layer are laminated in the above order, and the photoconductor A thin film type solid-state X-ray, characterized in that the interface between the layer and the transparent electrode layer is doped with a P-type impurity, and the X-ray is made incident from either side of the upper electrode and the phosphor layer. sensor. 2. The thin-film solid-state X-ray sensor according to claim 1, wherein either the upper electrode or the transparent electrode is a split electrode. 3 A light-shielding upper electrode, an H-doped amorphous silicon photoconductor layer, a transparent electrode layer, a transparent insulating layer, and a phosphor layer are laminated in the above order, and the photoconductor layer A thin-film solid-state X-ray sensor, characterized in that the interface with the transparent electrode layer is doped with a P-type impurity, and X-rays are incident from either side of the upper electrode and the phosphor layer. . 4. The thin film solid state X-ray sensor according to claim 3, wherein either the upper electrode or the transparent electrode is a split electrode. 5. A light-shielding upper electrode, an H-doped amorphous silicon photoconductor layer, a blocking layer,
A transparent electrode layer, a transparent insulating layer, and a phosphor layer are laminated in the above order, and an interface between the photoconductor layer and the transparent electrode layer is doped with a P-type impurity,
A thin-film solid-state X-ray sensor, characterized in that it is configured to allow X-rays to enter from either side of the upper electrode or the phosphor layer. 6. The thin-film solid-state X-ray sensor according to claim 5, wherein either the upper electrode or the transparent electrode is a split electrode.