JPH0690318B2 - Solid X-ray image converter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state X-ray image converter, and more particularly to a solid-state X-ray image converter having a thin film laminate and excellent in resolution.

(Prior Art) The principle of so-called optical amplifier, which is a combination of an EL layer and a photoconductive layer, has been known for a long time, and many researchers have also studied an X-ray image converter applying this to an X-ray region. It has been partially commercialized. These X-ray image converters have a sensitivity almost 100 times higher than fluorescent intensifying screens, and have a simple structure and are inexpensive, so they are used in applications where it is not necessary to use expensive devices such as image intensifiers. Has been. In this type of X-ray image conversion device, the portion excluding the electrode portion was formed by dispersing a powdery material in an organic binder and applying the same by screen printing or the like.

(Problems to be Solved by the Invention) The distributed X-ray image conversion device described above has the following drawbacks.

(1) The resolution is greatly influenced by the size and dispersion state of the powder particles, and a thick film thickness is required, so there is no problem in observing with the naked eye, but when enlarging or shooting with a TV camera The resolution is poor.

(2) Since the binder deteriorates due to the heat generated by the irradiation of X-rays, there is a limit to continuous use for a long time.

(3) Since the types of phosphors that can be used are limited, it is difficult to obtain the desired characteristics.

The above drawbacks do not cause much problems for the purpose of observing with the naked eye, but due to the progress of peripheral technologies such as the development of the solid-state imaging device and the development of the image processing technology by the computer in recent years, the solution of the above drawbacks is strongly desired. It became so. In addition, as a matter of course when irradiating the human body with X-rays,
It is desired to further reduce the dose, that is, to increase the sensitivity.

The present invention has been made under the circumstances as described above, shows high resolution, can withstand continuous use, and has high sensitivity and high quality even when combined with a television camera or image processing. An object of the present invention is to provide a solid-state X-ray image conversion device capable of obtaining an image and a manufacturing method thereof.

(Means for Solving the Problems) The present inventor has conducted extensive studies to achieve the above-mentioned object, and as a result, the above-mentioned conventional X-ray image conversion apparatus has a drawback that it is a dispersion type using a powdery material. It was found to be due to something. That is, according to the conventional dispersive X-ray image converter, the resolution is remarkably hindered due to the thick film thickness in the fluorescent layer and the scattering by the powder particles, and the unevenness of brightness is caused by the local nonuniformity of the film thickness. Further, it is necessary to use a binder having a high dielectric constant in order to fill the voids between the powder particles and flow a sufficient current, but the use of such a binder causes the above-mentioned defect (2). Become. Also in the photoconductive layer, the powdery property greatly affects the image quality. Unfortunately, the larger the particles, the higher the sensitivity.

The present invention has been made based on such findings.

That is, the solid-state X-ray image conversion device of the present invention includes, on a transparent substrate, thin films of a first electrode layer, a fluorescent layer, an opaque layer, a photoconductive layer, and a second electrode layer formed of a transparent conductive film. Are sequentially laminated, and an AC voltage is applied between the first electrode layer and the second electrode layer to directly convert an X-ray image incident on the photoconductive layer into a visible light ray or a near infrared ray image.

In the solid-state X-ray image conversion device of the present invention, an insulating layer is provided between the first electrode and the fluorescent layer and / or between the fluorescent layer and the non-translucent layer to improve the life and stabilize the manufacturing. Is preferably provided. In this case, in order to avoid the reaction between the fluorescent layer and the opaque layer and the insulating layer, the insulating layers can be used in a multi-layered manner. Furthermore, it is preferable to have a structure in which the light opaque layer is sandwiched between two insulating layers. This is to avoid a chemical reaction between the non-translucent layer and the adjacent layer. As the insulating layer, one made of a metal oxide or a metal salt can be used. Preferred metal oxides or salts are Al, G
It is a salt of one or more of a, Si, Zr, Ti, Ta, Nb, rare earths and alkaline earth metals, or a salt.

As the fluorescent layer, a II-VI group compound such as an alkaline earth metal, Zn, or Cd and one or more compounds of O, S, Se, or Te is used as a matrix, and a rare earth element, Halogen element, Mn, Cu, Ag, Au, Pb, P, and
It is possible to use the one using at least one kind of As as an activator. The thickness of the fluorescent layer is preferably 0.5 to 1.0 μm.

As the opaque layer, C, Ge, Si, GaAs, InP, InAs, Si
At least one of C and Cu, Pb, Ag or Bi sulfide
Seeds can be used.

As the photoconductive layer, Zn or Cd and O, S, Se, or
It is possible to use at least one kind of semiconductor in which one or more kinds of II-VI group compounds composed of Te are used as a base material and at least one kind of Cu, Ag, F, Cl, Br and I is added to the base material. . The thickness of the photoconductive layer is preferably 2 to 5 μm.

(Operation) In the solid-state X-ray image conversion device of the present invention, all are configured by laminating thin films. Therefore, it becomes possible to eliminate all the drawbacks of the conventional dispersion type X-ray image conversion device which is formed by dispersing a powdery material in an organic binder and applying it by screen printing or the like. .

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a solid-state X-ray image conversion apparatus which is an embodiment of the present invention. As shown in FIG. 1, the solid-state X-ray image converter is configured by laminating multiple thin films on a glass substrate 1. Note that the glass substrate may be colored black in order to prevent a decrease in contrast due to external light. A transparent electrode 2 made of ITO (indium tin oxide) is formed on one surface of the glass substrate 1 by sputtering.

A first insulating layer 3 made of barium titanate is formed on the transparent electrode 2. On the first insulating layer 3, the first insulating layer 3 and the second insulating layer 5 are sandwiched between 0.
A fluorescent layer 4 having a film thickness of 5 to 1.0 μm is provided. As the fluorescent layer 4, an efficient fluorescent material having a peak wavelength suitable for each purpose is selected, although it varies depending on whether the image is observed with the naked eye or is monitored by a television camera or a sensor. In this example, ZnS: TbF ₃ was used. The second insulating layer 5 is made of barium titanate like the first insulating layer 3. The first insulating layer 3, the fluorescent layer 4, and the second insulating layer 5 were all formed by sputtering. The laminated body including the first insulating layer 3, the fluorescent layer 4, and the second insulating layer 5 is hereinafter referred to as a light emitting layer.

An opaque layer 6 is formed on the second insulating layer 5. The opaque layer 6 has a positive feedback from the fluorescent layer 4 to the photoconductive layer,
This is for preventing the image from being lost. As the opaque layer 6, a black conductor, semiconductor, dielectric or the like can be used, and carbon is used in this embodiment.
The impedance of the opaque layer 6 has a great influence on brightness and resolution.

A photoconductive layer 7 made of CdSe: CuCl is provided on the opaque layer 6. The photoconductive layer 7 was also formed by the sputtering method.

A second electrode made of Al is formed on the photoconductive layer 7 by vacuum vapor deposition.

Next, the operation of the solid-state X-ray image conversion device described above will be described.

First, an AC voltage of 400 to 500 V is applied between the transparent electrode 2 and the second electrode. In the state where X-rays are not applied, the photoconductive layer 7 exhibits a high resistance of several MΩ, so most of the applied voltage is consumed by the photoconductive layer 7, and a sufficient voltage is applied to the phosphor layer 4 for light emission. Therefore, the phosphor layer 4 does not emit light.

When X-rays are irradiated in this state and the X-ray dose is gradually increased, the resistance of the photoconductive layer 7 decreases, and the voltage distribution ratio determined by this resistance and the capacitance of the light emitting layer gradually emits light. The voltage is applied to the light emitting layer by increasing the voltage toward the layer side. Then, when the voltage applied to the light emitting layer exceeds the light emission start voltage, the light emission luminance rapidly increases. Since the emission brightness is proportional to the intensity of X-rays, the X-rays are directly converted into a visible light image.

The above operation is performed by using an equivalent circuit as shown in FIG.
It can be explained as follows.

That is, the photoconductive layer is equivalent to the variable resistor 11 whose resistance changes by irradiation with X-rays, the opaque layer is equivalent to the resistor 12, and the light emitting layer is equivalent to the lossy capacitor 13. The film thickness of each layer is directly correlated with the value of resistance and capacitance, and therefore, the unevenness of the film thickness appears as the unevenness of brightness. However, in the conventional layered structure formed of a powdery material, the thickness of the fluorescent layer is several tens of μm and the thickness of the photoconductive layer is several hundreds of μm, and it is practically impossible to eliminate the unevenness of the film thickness. .

On the other hand, in the present invention, the fluorescent layer is 0.5 to 1.0 μm.
m, the photoconductive layer has a thin film structure of 2 to 5 μm, the film thickness is uniform, and the light emitted from the fluorescent layer is not scattered by particles, so that the resolution is much higher than that of the conventional one. . That is, according to the conventional distributed X-ray image conversion device formed of a powdery material, the spatial resolution is 1.25, while according to the X-ray image conversion device of the present embodiment, the spatial resolution is extremely 8.0. It showed a high value.

Further, while the image obtained by the conventional distributed X-ray image conversion device is rough and bleeding, the X-ray image conversion device of the present embodiment has a uniform and even contour. A clear and easy-to-see image was obtained.

Furthermore, the brightness characteristics and contrast (represented by the slope of the brightness curve) of the X-ray image conversion apparatus of this embodiment are as shown by the curve a in FIG. It can be seen that it is considerably improved compared to (curve b). The vertical axis of FIG. 3 is represented on a logarithmic scale. In the test for obtaining the brightness characteristics,
The power supply voltage was set to a brightness of 0.1 ft-L when the X-ray intensity was 0 in order to improve the rising characteristics at a weak X-ray dose, and was set to 1 kHz440V in this example and 1 kHz440V in the conventional example.

In the above embodiments, sputtering was used for film formation, but the present invention is not limited to this, and various techniques used for thin film formation such as vapor deposition, electron beam vapor deposition, MBE, or CVD can be used.

(Effects) As described above, according to the X-ray image conversion apparatus of the present invention, since the entire film structure is formed by laminating thin films, the powdery material is dispersed in the organic binder, Compared with the conventional distributed X-ray image conversion device that is formed by applying
It has become possible to dramatically improve brightness and resolution.

[Brief description of drawings]

FIG. 1 is a sectional view of an X-ray image conversion apparatus according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of the X-ray image conversion apparatus shown in FIG. 1, and FIG. X according to one embodiment of
It is a characteristic view which shows the brightness characteristic of a line image converter in comparison with the conventional distributed X-ray image converter. 1 ... glass substrate, 2 ... transparent electrode, 3,5 ... insulating layer,
4 ... fluorescent layer, 6 ... opaque layer, 7 ... photoconductive layer, 8 ...
…electrode.

Claims (7)

[Claims] 1. A thin film of a first electrode layer, a fluorescent layer, an opaque layer, a photoconductive layer, and a second electrode layer made of a transparent conductive film, which are sequentially laminated on a transparent substrate. A solid-state X-ray image converter for converting an X-ray image incident on the photoconductive layer directly into a visible light image or a near infrared light image by applying an AC voltage between the first electrode layer and the second electrode layer. 2. The solid according to claim 1, wherein a thin film insulating layer is provided between the first electrode and the fluorescent layer and / or between the fluorescent layer and the opaque layer. X-ray image converter. 3. The solid-state X-ray image conversion device according to claim 1, wherein the opaque layer is sandwiched between two thin film insulating layers. 4. The insulating layer comprises Al, Ga, Si, Zr, Ti, Ta,
The solid-state X-ray image conversion device according to claim 2 or 3, comprising an oxide or salt of at least one metal selected from Nb, rare earths and alkaline earth metals. 5. The fluorescent layer comprises, as a base material, one or more kinds of II-VI group compounds composed of alkaline earth metal, Zn or Cd and O, S, Se or Te. Rare earth elements, halogen elements, Mn, Cu, Ag, Au, Pb, P, and As
The solid-state X-ray image conversion device according to claim 1, wherein at least one of the above is used as an activator. 6. The opaque layer is made of C, Ge, Si, GaAs, In.
The solid-state X-ray image conversion device according to claim 1, comprising at least one of P, InAs, SiC, and a sulfide of Cu, Pb, Ag, or Bi. 7. The photoconductive layer comprises Zn or Cd, O, S,
One or two II-VI group compounds consisting of Se or Te
Species or more as a base, Cu, Ag, F, Cl, Br and I
The solid-state X-ray image conversion device according to claim 1, comprising at least one kind of semiconductor to which at least one kind is added.