JP2731220B2 - Image conversion element and X-ray image detection method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image conversion element and an X-ray image detection method using the same, and particularly to a single crystal plate having both an electro-optic effect and a photoconductive effect, Conversion of incoherent images to coherent images, spatial frequency filtering,
The present invention relates to an improvement of an image conversion element for performing an optical logic operation and the like, and an X-ray image detection method for recording X-rays having image information and reading image information by light using such an image conversion element.

(Background Art) Conventionally, bismuth silicon oxide (BSO: Bi ₁₂ Si
Image conversion devices such as O ₂₀ ) have a function of converting an incoherent image into a coherent image. Therefore, various researches have been made on the device for two-dimensional image processing using light. In addition, various applications to spatial frequency filtering, optical logic operation, and the like have been studied.

As a typical example of such an image conversion element, a PSO utilizing the longitudinal primary electro-optic effect of a BSO single crystal is used.
ROM element (Pockels readout optical
Modulators) are known. In addition, as shown in FIG. 1, this PROM element is basically provided with an insulating layer 12 of polyparaxylene or the like on both surfaces of a BSO single crystal (wafer) 11, and further formed thereon of indium oxide or the like. The structure is such that a transparent electrode 13 is provided.

Incidentally, a write operation using such a PROM element is normally performed as follows. First, with a predetermined voltage applied to both surfaces of the BSO crystal 11,
When a two-dimensional image is formed on the surface of the BSO crystal 11, B
Due to the photoconductive effect of the SO crystal, a carrier charge is generated in the crystal according to the intensity of the input light, and the voltage applied to the crystal screen decreases due to the carrier charge. The corresponding voltage distribution is recorded in the crystal.

Next, the reading operation of the image recorded in this manner is performed by BS
This is performed by utilizing the birefringence generated by the voltage applied to the O crystal 11. That is, BS
The O crystal 11 has a different refractive index for linearly polarized light in two directions (X direction and Y direction) parallel to the wafer surface and orthogonal to each other. Thus, for example, as shown in Figure 2, via a polarizer 21, X-axis direction and the Y-axis direction of the bisecting direction of the linearly polarized light from the respective intensity: allowed to light having a I _i to BSO crystal 11 Due to the birefringence of the BSO crystal, the incident linearly polarized light locally becomes elliptically polarized light (Pockels effect) according to the local voltage: V between the two surfaces of the crystal. Therefore, on the output side, an analyzer orthogonal to the incident polarization direction
By placing 22, the input light image recorded as the intensity distribution of the coherent light according to the voltage distribution on the surface of the BSO crystal 11 can be read. The output light intensity: I ₀ at this time is represented by the following equation: Indicated by Where V is the local voltage, V
π is a half-wave voltage.

Note that, in such writing and reading operations, generally,
Blue light near 440 nm, which is the wavelength with the highest sensitivity to the PROM element, is used as the writing light for the input image, and red or infrared light with low sensitivity is used as the reading light for the image. I have. The erasure of the image recorded on the BSO crystal 11 is performed by releasing the voltage application and irradiating the entire surface of the BSO crystal with strong blue light.

Now, in the above operation, the insulating layer of the PROM element
Although the transparent electrode 12 and the transparent electrode 13 are indispensable, conventionally, such an insulating layer 12 is clearly deviated from JP-A-54-48262 or JP-A-57-49916. As described above, polyparaxylene or polystyrene as an organic insulator or mica as an inorganic insulator is used, and as the transparent electrode 13, indium oxide (In ₂ O ₃ ) or the like is used.

However, when polyparaxylene is used as the insulating layer 12, the polyparaxylene has a low melting point (30
0 ° C or lower), which deteriorates when heated to about 100 ° C. In order to attach In ₂ O ₃ as a transparent electrode with low resistance and high transparency, BSO with polyparaxylene attached Strict adjustment of Ar and oxygen pressure while cooling the single crystal,
It is necessary to adopt the DC sputtering method, which requires the application of a spatial magnetic field and the control of the sputtering power,
It is very difficult to optimize all of these conditions, and because polyparaxylene is easily degraded by humidity,
There are inherent problems such as the necessity of putting in an airtight container and enclosing in dry nitrogen gas.

Further, when polystyrene is used for the insulating layer 12, there is an inherent problem that the withstand voltage is insufficient and the mechanical strength of the insulating layer is small, so that the life of the element is short. Further, when mica is used as the insulating layer 12,
Since mica is a birefringent material, there is a phase difference in linearly polarized light in both birefringence due to the electro-optic effect of the BSO crystal 11 and birefringence of mica. The ratio with the applied voltage, that is, the contrast ratio of the image is reduced, the mica has pinholes, etc., causing dielectric breakdown, and it is difficult to control the layer thickness of the mica. Element half-wave voltage: V
There is a problem that π varies.

On the other hand, a technique using X-rays as writing light for an input image of a PROM element is known [M. Graser, Jr. et.al., App.
l.Phys.Lett. "34 (8) 15.April 1979]. This technique employs the same element configuration as that of FIG. 1 except that X-rays are used as the writing light, and the image reading method after recording the image information is also the same. Also, in this X-ray image detection technology, since the organic insulating material such as polyparaxylene or polystyrene or the inorganic insulating material such as mica is used as the insulating layer of the element, the same problem as described above occurs. is there.

(Solution Problem) Here, the present invention has been made in view of such circumstances, and a problem to be solved is a contrast ratio which is one of the characteristic indexes of an image conversion element (PROM element). And to secure stable insulation. Another object of the present invention is to provide an element structure capable of easily controlling the thickness of the insulating layer and maintaining the half-wave voltage: Vπ advantageously constant. Still another object of the present invention is to provide an X-ray image detecting method using such an image conversion device.

(Solution) In order to solve the above-described problems, the present invention provides a single crystal plate having an electro-optic effect and a photoconductive effect, and borosilicate glass or borosilicate glass provided on at least one surface of the single crystal plate. The gist of the present invention is an image conversion element comprising an insulating layer made of quartz glass and a transparent electrode for applying an electric field to the insulating layer and the single crystal plate.

In an X-ray image detecting method using such an image conversion element, an X-ray is irradiated onto a predetermined test object to obtain an X-ray having image information to be recorded. A method of irradiating the conversion element and recording image information, irradiating the image conversion element with a predetermined readout light, and reading the recorded image information,
Will be adopted.

The present invention also provides a single crystal plate having an electro-optic effect and a photoconductive effect, a conductive layer provided on one surface of the single crystal plate, which transmits X-rays but reflects readout light, An insulating layer made of glass provided on the other surface of the single crystal plate,
Provided on a surface of the insulating layer opposite to the single crystal plate side,
An X-ray image conversion device, comprising a transparent electrode that applies an electric field to the insulating layer and the single crystal plate by applying a voltage between the conductive layer and the single crystal plate. .

When detecting an X-ray image using such an X-ray image conversion element, first, an X-ray is irradiated onto a predetermined test object to obtain an X-ray having image information to be recorded. After irradiating the X-ray onto the conductive layer side surface of the X-ray image conversion element and recording image information on the X-ray image conversion element, the X-ray image conversion element is on the side opposite to the X-ray irradiation surface. A method of irradiating a predetermined readout light to the surface and reading out the recorded image information will be adopted.

In such an image conversion device or an X-ray image conversion device, the transparent electrode for applying an electric field to the insulating layer and the single crystal plate is advantageously provided with a transparent electrode layer on a predetermined transparent plate. An anti-reflection film is formed on the surface of the transparent electrode plate opposite to the surface on which the transparent electrode layer is provided. Further, as a single crystal plate having an electro-optical effect and a photoconductive effect, a single crystal plate made of bismuth silicon oxide (BSO: Bi ₁₂ SiO ₂₀ ) or bismuth germanium oxide (BGO: Bi ₁₂ GeO ₂₀ ) is used. The insulating layer made of borosilicate glass or quartz glass is advantageously used.

(Specific Configuration) By the way, preferable specific examples of such an image conversion element or an X-ray image conversion element according to the present invention are shown in FIGS. 3 and 4. FIG.

First, in the specific example of FIG. 3, reference numeral 31 denotes a single crystal plate having an electro-optical effect and a photoconductive effect, such as bismuth silicon oxide (Bi ₁₂ SiO ₂₀ ) and bismuth germanium oxide (Bi ₁₂ GeO ₂₀ ). It is made of a known single crystal material. In addition, this single crystal plate 31 is generally
A material having a thickness of about 10 μm to 5 mm, both surfaces of which are polished according to a known appropriate method, is used.

Glass insulating layers 32, 32 having a predetermined thickness are formed on both surfaces of such a single crystal plate 31, respectively. The glass insulating layer 32 is formed by (a) a method of attaching optically polished glass to be a glass insulating layer to the surface of the single crystal plate 31 with an optical adhesive, and (b) a material for providing the glass insulating layer. Screen printing on the surface of the single crystal plate 31, (c) by dipping or spin coating,
A method of coating the surface of the single crystal plate 31 with a metal alkoxide that provides a glass insulating layer, (d) a method of attaching an elongated thin glass (glass insulating layer) to the surface of the single crystal plate 31 with an optical adhesive, and (e). ) A method by vapor deposition and sputtering or the like is appropriately adopted. In addition, as a glass material constituting the insulating layer 32, quartz glass, borosilicate glass, soda glass, lead glass, or the like is used. Particularly, in reducing the half-wave voltage, glass having a large dielectric constant is advantageous. It is usually used and has a relative dielectric constant of 3.
Five or more glasses are preferably used. Further, the thickness of the glass insulating layer 32 is appropriately set, but is generally about 5 μm to 500 μm. Further, it is desirable to increase the withstand voltage. To this end, it is desirable that the thickness of the glass is large, but it is desirable that the half-wave voltage of the element is small. It is better to reduce the thickness of the layer 32. As the optical adhesive used for forming the glass insulating layer 32, a known adhesive such as a silicone adhesive, an acrylic adhesive, or an epoxy adhesive is used.

Further, on each outer surface of the glass insulating layers 32, 32 formed on both surfaces of the single crystal plate 31, transparent electrodes 33, 3 made of a known transparent conductive material such as indium oxide are provided.
3, and a predetermined electric field is applied to the single crystal plate 31 and the glass insulating layers 32, 32 by applying a voltage from an external power supply 34 to the transparent electrodes 33, 33. I am getting it. The voltage applied by the power supply 34 is about 0 to 30 KV.

Incidentally, the formation of the transparent electrode 33 for applying an electric field to the single crystal plate 31 and the insulating layer 32 includes (a) a method of directly forming a target transparent electrode on the surface of the glass insulating layer 32,
(B) A transparent electrode plate formed by providing a transparent electrode layer on a predetermined transparent plate such as glass, using an optical adhesive as described above,
A method of pasting on the glass insulating layer 32 or the like is appropriately adopted. In the specific example of FIG. 3, the transparent electrode 33 is formed by the latter method. That is, the transparent electrode 33 is formed in a layer on one surface of the base glass 35, and the transparent electrode layer 33
And the glass insulating layer 32 are adhered with an optical adhesive to form an integral structure. It is preferable that the substrate glass 35 serving as the base of such a transparent electrode plate has a surface accuracy of a wavelength of writing light or reading light: λ or less. This is because the coherent image is not distorted. Further, it is desirable that a transparent antireflection film 36 be provided on the surface of the transparent electrode plate (base glass 35) on which the reading light is incident. This antireflection film 36 is made of, for example, SiO ₂
And a multilayer film of TiO _{2 and} the like.

In an apparatus for writing and reading an image using such an image conversion element, as shown in FIG. 3, a polarizer 38 is arranged on the incident side of a reading / writing light 37, The read / write light 37 is guided to the image conversion element through the element 38, and the read / write light 37 output from the image conversion element is extracted through the analyzer 39.

By the way, the operation procedure of the image conversion using the image conversion element is performed, for example, as follows. First, a predetermined static voltage is applied from an external power supply 34 between the transparent electrodes 33, 33, whereby a spatially uniform electric field is applied to the single crystal plate 31. In this state, the writing operation is performed by inputting blue light or an X-ray image as the writing light 37. Carrier charge is generated according to the amount of incident light, and the generated carrier charge moves to the crystal end face by Coulomb force due to an external electric field, but further movement is prevented by the insulating layer 32, and the carrier charge is accumulated there. Is done. This means that the information on the intensity distribution of the writing light has been replaced by the information on the density of the polarized carrier charges. The polarized carrier charge creates an electric field in the direction opposite to the external electric field. The total electric field applied to the crystal 31 is the sum of the external electric field and the electric field due to the carrier charge. Therefore, the electric field in the crystal 31 is smaller as the carrier charge density is higher.
Finally, the information of the written image is replaced with the electric field distribution in the crystal 31.

In order to read the information written in the element in this manner, light having no photoconductive effect as the reading light 37 for the image conversion element, and thus not destroying the written information,
For example, it is made to enter using red light. Polarizer 38
Is converted into elliptically polarized light according to the electric field distribution in the crystal 31 and passes through the crystal 31. Then, the light passes through the analyzer 39 arranged in the cross state and is output as an image having an intensity distribution. In this state, a negative image is output for the original image. Further, as another method for reading, unlike the above-described method, the external electric field applied by the power supply 34 is set to 0 at the time of reading, so that the electric field in the crystal 31 is only generated by carrier charges. . By making the reading light 37 such as red light incident in this state, a positive image is output with respect to the original image.

The information written in the image conversion element is erased by short-circuiting the transparent electrodes 33 and irradiating strong blue light, and the carrier charges polarized by such irradiation are regenerated. Combine and return to the original state.

The image conversion element used in the X-ray detector may have a configuration as shown in FIG. 3 or a reflection type configuration as shown in FIG.

In the image conversion device for an X-ray detector shown in FIG. 4, reference numeral 41 denotes a single crystal plate, on one surface of which a glass insulating layer 42 is formed. A transparent electrode plate provided with a transparent electrode 43 on one surface of 45 and an antireflection film 46 on the other surface is integrally adhered with an optical adhesive. On the other surface of single crystal plate 41, metal film 47 is formed to a predetermined thickness. The material of the metal film 47 is gold,
There are silver, platinum, aluminum, beryllium metal and other conductive materials having excellent X-ray transmittance. Also, such a metal film 47
Will generally be about 1 μm or less. This is because when the film thickness is large, the X-rays 48 for writing are hardly transmitted, and the exposure amount decreases. Then, a predetermined voltage can be applied between the metal film 47 and the transparent electrode 43 by the external power supply 44.

Then, the reading light 49 for reading is made incident on the image conversion element from the side provided with the transparent electrode 43 through the polarizing beam splitter 50, and the light reflected by the metal film 47 is again reflected by the polarizing beam splitter 50. It is to be taken out through.

An X-ray detector using the X-ray image conversion device shown in FIG. 4 is schematically shown in FIG. There, X-rays are emitted from the X-ray source 52 to the inspection object 51, thereby forming X-rays having image information to be recorded. Is irradiated on the surface on the formation side of. Thus, the X-ray image is written on the single crystal plate (41) of the image conversion element 53 as described above. On the other hand, in the reading, the reading light emitted from the reading irradiation light source 54 passes through the polarizer 55 and passes through the half mirror.
After passing through 59, the light was made incident on the surface of the image conversion element 53 opposite to the X-ray irradiation surface, in other words, the surface on the side where the transparent electrode (43) was formed, and recorded on the image conversion element 53. The image information is read out, reflected by the half mirror 59, and analyzed by the analyzer.
The light is received by the CCD camera 57 through 56. And this C
The information received by the CD camera 57 is processed by the image analysis device 60 and appears as an image on the monitor 58, so that necessary inspection information of the inspection object 51 is extracted.

It should be noted that the present invention is by no means limited to the above specific description and preferred embodiments, and various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that the present invention includes those of the embodiments.

(Examples) Hereinafter, in order to clarify the present invention more specifically, some examples of the present invention will be described. However, the present invention is not limited to the description of such examples. It goes without saying that it is not done.

Example 1 Four sides of a 15 mm square, 300 μm thick, double-side polished BSO crystal wafer were polished on both sides with a silicon-based adhesive to a 18 mm square, 10 μm thick, double-sided soda. By bonding glass, lead glass, borosilicate glass, or quartz glass wafers respectively, and further bonding a glass plate with a transparent electrode provided with a transparent electrode made of an ITO film on both surfaces, an image as shown in FIG. 3 is obtained. Four conversion elements were produced. Note that an antireflection film made of a dielectric multilayer film for a reading light source (He-Ne laser wavelength: 633 nm) was applied to the surface of the glass plate with a transparent electrode on the side where the writing / reading light was incident.

Then, writing and reading of an image were performed using the obtained image conversion element. As a writing light source,
Ar ion laser (wavelength: 488nm) light, mesh pattern or direct light as object, and 5mW H as readout light
e-Ne laser (wavelength: 633 nm) converted into a parallel light beam,
Furthermore, a photomultimeter is used for quantitative measurement of output light intensity.
Each was used, and when observing the image, it was projected on a screen.

When the power supply voltage was increased to near 6000 V where a sufficient readout image could be obtained, dielectric breakdown occurred for the element using soda glass or lead glass, but for the element using borosilicate glass or quartz glass as the insulating layer, No dielectric breakdown occurred.

In addition, in order to investigate the dielectric breakdown of the devices manufactured by increasing the number of devices manufactured and changing the glass as the insulating layer in various ways, a voltage application test of 100 cycles at a power supply voltage of 5000 V (ON state for 5 minutes, OFF state) (Repeated for 5 minutes), the results shown in the following table were obtained.

In addition, in order to compare characteristics with an element using borosilicate glass or quartz glass that did not cause dielectric breakdown, mica was used for the insulating layer, and the contrast ratio was the same as that of an image conversion element manufactured by the same method as above. As a result of the measurement, when the mica was used for the insulating layer, the ratio was 1000: 1, but when the borosilicate glass or the quartz glass was used for the insulating layer, it was as large as 4000: 1. Indicated.

Example 2 An Al thin film was formed to a thickness of 200 mm on one surface of each of four BSO crystal wafers having a shape of 15 mm square and a thickness of 300 μm that had been subjected to double-side polishing by vapor deposition. On the other side (back side) of the BSO crystal wafer, soda glass, lead glass, borosilicate glass or quartz glass polished on both sides with a size of 18 mm square and a thickness of 10 μm using a silicon-based adhesive is used. Are bonded together, and a glass with a transparent electrode provided with a transparent electrode made of an ITO film is bonded to the surface of the glass wafer as an insulating layer, thereby producing four X-ray image conversion elements having a configuration as shown in FIG. did. An antireflection film (dielectric multilayer film) for a reading light source (He-Ne laser wavelength: 633 nm) is provided on the surface (outer surface) of the glass plate with a transparent electrode.

Then, using this X-ray image conversion element, an X-ray detector as shown in FIG. 5 was produced. The X-ray image conversion element was arranged so that the surface on which the Al thin film was formed was irradiated with X-rays. As an X-ray source, a tungsten tube was used. The tube voltage was 40 KV, the tube current was 5 mA, and the test object was 5 to 1 mm.
Irradiation was performed for 0 seconds, and image information was recorded on the X-ray image conversion element.
After this recording, a readout beam of 5 mW He-Ne laser (wavelength: 633 nm) was used as a parallel beam, and a photomultimeter was used for quantitative measurement of output light intensity.
When observing the image, I captured it with a CCD camera and imaged it on a monitor.

When the power supply voltage was increased to about 3000 V where a sufficient readout image was obtained, dielectric breakdown occurred in the element using soda glass or lead glass, but in the element using borosilicate glass or quartz glass as the insulating layer, No dielectric breakdown occurred.

In addition, in order to compare characteristics with an element using borosilicate glass or quartz glass as an insulating layer which did not cause dielectric breakdown, mica was used for the insulating layer, and an X-ray image conversion element manufactured by the same method as described above was used. As a result of measuring the ratio under the same conditions, the ratio was 1000: 1 for the device using mica for the insulating layer, but was 4000: 1 for the device using borosilicate glass or quartz glass for the insulating layer. Get bigger,
It showed a remarkable effect.

Furthermore, the resolution of the X-ray image is 5 to 15 lp / mm,
It was found to be better than 0.2-0.3 lp / mm of the imaging intensifier camera used for the line detector.

(Effects of the Invention) As is clear from the above description, in the image conversion device and the X-ray image conversion device according to the present invention, the improvement of the contrast ratio, which is one of the characteristic indices, can be effectively achieved. Since glass is used as the insulating layer,
Since the manufacture of the element becomes extremely easy, stable insulating properties can be ensured, the thickness of the insulating layer can be easily controlled, and the insulating layer can be formed with a uniform thickness. Numerous effects such as the voltage: Vπ can be effectively kept constant can be achieved, and image detection by X-rays using such an image conversion element can be advantageously achieved.

[Brief description of the drawings]

FIG. 1 is a schematic illustration of a conventional image conversion device, and FIG. 2 is a schematic illustration of a conventional image conversion device using such an image conversion device. FIG. 3 is an explanatory cross-sectional view showing an example of the image conversion element according to the present invention, and FIG.
FIG. 5 is an explanatory sectional view showing an example of an image conversion element for an X-ray detector according to the present invention, and FIG. 5 is an explanatory view showing an arrangement form of an X-ray detector using the element shown in FIG. 31, 41: Single crystal plate 32, 42: Glass insulating layer 33, 43: Transparent electrode 34, 44: Power supply, 35, 45: Base glass 36, 46: Anti-reflection film 37: Read / write light, 38: Polarizer 39: analyzer, 47: metal film 48: X-ray, 49: readout light 50: polarizing beam splitter 51: inspection object, 52: X-ray source 53: image conversion element, 54: irradiation light source 55: polarizer, 56 : Analyzer 57: CCD camera, 58: Monitor 59: Half mirror, 60: Image analyzer

Claims (6)

(57) [Claims] 1. A single crystal plate having an electro-optic effect and a photoconductive effect, an insulating layer made of borosilicate glass or quartz glass provided on at least one surface of the single crystal plate, the insulating layer and the single crystal An image conversion element comprising: a plate and a transparent electrode for applying an electric field to the plate. 2. A single crystal plate having an electro-optical effect and a photoconductive effect, an insulating layer made of borosilicate glass or quartz glass provided on at least one surface of the single crystal plate, and the insulating layer and the single crystal And a transparent electrode plate provided with a transparent electrode layer on a predetermined transparent plate body for applying an electric field to the plate. 3. An image conversion device according to claim 1, wherein the object is irradiated with X-rays to obtain X-rays having image information to be recorded. An X-ray image detecting method, comprising: irradiating the image conversion device with image data; and irradiating the image conversion element with predetermined readout light to read the recorded image information. 4. A single crystal plate having an electro-optic effect and a photoconductive effect, a conductive layer provided on one surface of the single crystal plate, which transmits X-rays but reflects readout light, An insulating layer made of borosilicate glass or quartz glass provided on the other surface of the crystal plate, and a voltage applied between the conductive layer and the insulating layer provided on a surface of the insulating layer opposite to the single crystal plate. An X-ray image conversion device comprising: a transparent electrode for applying an electric field to the insulating layer and the single crystal plate by applying a voltage. 5. A single crystal plate having an electro-optic effect and a photoconductive effect, a conductive layer provided on one surface of the single crystal plate for transmitting X-rays but reflecting readout light, An insulating layer made of borosilicate glass or quartz glass provided on the other surface of the crystal plate, and a voltage applied between the conductive layer and the insulating layer provided on a surface of the insulating layer opposite to the single crystal plate. An X-ray image conversion device comprising: a transparent electrode plate provided with a transparent electrode layer on a predetermined transparent plate body, wherein an electric field is applied to the insulating layer and the single crystal plate by applying an electric field. 6. The X-ray image according to claim 4, wherein the X-ray is irradiated on the object to be inspected to obtain X-rays having image information to be recorded. After irradiating the surface on the conductive layer side of the conversion element and recording the image information, the surface of the X-ray image conversion element opposite to the X-ray irradiation surface is irradiated with predetermined readout light. An X-ray image detecting method for reading the recorded image information.