JP4171564B2 - Photoelectric surface forming evaporation source and X-ray image tube manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocathode forming evaporation source for forming a photocathode such as an X-ray image tube and a method for manufacturing an X-ray image tube using the photocathode forming evaporation source.
[0002]
[Prior art]
An X-ray image tube is an electron tube that converts an X-ray image transmitted through a subject into a visible light image. An input unit for converting X-rays into electrons is provided at one end of the vacuum envelope, and electrons are emitted at the other end. An output unit is provided for converting to. The input unit of the X-ray image tube is composed of an input substrate, a fluorescent screen, a photocathode, and the like formed on the input substrate. The photocathode is formed by a method of forming a phosphor screen on the input substrate, evaporating the photoelectric material from the evaporation source, and depositing the photoelectric material on the phosphor screen.
[0003]
In this case, the evaporation source for evaporating the photoelectric material has a structure in which a mass of antimony (Sb) of the photoelectric material is fused to a refractory metal boat, or Sb of the photoelectric material on a linear or planar filament. A structure in which a film is applied is used (see Japanese Patent Laid-Open No. 4-209443).
[0004]
By the way, when forming a photocathode using an evaporation source, one method is to arrange a plurality of evaporation sources in an X-ray image tube. In this method, Sb is heated by passing an electric current through a filament constituting the evaporation source. At this time, Sb evaporates in a vacuum by heating and is deposited on the input substrate surface of the X-ray image tube to form an Sb thin film for the photocathode.
[0005]
Another method for forming the photocathode is to insert an evaporation source from the outside into the X-ray image tube. In this method, an evaporation source inserted in the image tube is arranged on the tube axis or the like to heat Sb. Also in this case, Sb evaporated by heating is deposited on the substrate surface, and an Sb thin film for the photocathode is formed on the substrate.
[0006]
The Sb thin film deposited on the substrate surface by the above-described method is then formed with a compound such as an alkali metal to form a photocathode. Such a method for forming a photocathode is not limited to an X-ray image tube but is also used to form a photocathode such as an image pickup tube or a phototube.
[0007]
[Problems to be solved by the invention]
In the method of arranging a plurality of evaporation sources in the X-ray image tube, it is difficult to manufacture an evaporation source having a uniform structure, and the amount of photoelectric material such as Sb tends to be non-uniform. Variation occurs. As a result, the evaporation rate of the photoelectric material varies depending on the evaporation source, and unevenness in the film thickness of Sb or the like deposited on the input surface occurs.
[0008]
Further, the filament of the evaporation source has a planar or linear structure (see Japanese Patent Laid-Open No. 4-209443). In the planar filament, the temperature of the portion supporting the filament in the tube of the X-ray image tube is lowered, the evaporation rate of the portion is lowered, and the film thickness is uneven. In the case of a planar filament, a thin metal film is usually used in order to increase the resistance value. Therefore, when it is installed in a pipe or when it is thermally expanded by heating, deflection and twist are likely to occur. Further, the filament is deformed by the film stress of the deposited Sb film, and the film thickness of Sb deposited on the substrate surface is uneven. Even in the case of a linear filament, deflection and twist are likely to occur when it is thermally expanded by heating. Further, the filament is deformed by the film stress of the deposited Sb film, and the film thickness of Sb deposited on the substrate surface is uneven.
[0009]
As a method of inserting an evaporation source from the outside into an X-ray image tube, a structure in which an Sb lump is fused to a refractory metal boat is generally used as the evaporation source. With this structure, it is difficult to reduce the variation in the shape of the Sb block, and the film thickness distribution of the Sb layer deposited on the substrate surface is likely to vary. Further, Sb has directivity when evaporated. Therefore, in order to form a uniform Sb layer thin film, the directivity of evaporation must be considered, the position where the evaporation source is inserted is limited, and the design of the electrode structure is restricted.
[0010]
As described above, the conventional photocathode-forming evaporation source and the X-ray image tube manufacturing method tend to cause unevenness in the film thickness distribution of the photoelectric material such as Sb deposited on the substrate surface, and the brightness of the X-ray image tube. There is a problem that the uniformity of.
[0011]
The present invention solves the above-described drawbacks, makes the film thickness distribution of the photoelectric material constituting the photoelectric surface uniform, and improves the luminance uniformity of the X-ray image tube, and the X-ray image tube evaporation source and X-ray image tube It aims at providing the manufacturing method of.
[0012]
[Means for Solving the Invention]
The present invention provides a photocathode-forming evaporation source comprising a heating body that generates heat and a photoelectric material that is evaporated by the heat of the heating body to form a photocathode. However , it is characterized in that it is formed in a spherical shape by a set of curves that are symmetric with respect to an axis passing through the center and does not have a flat portion , and a photoelectric material is deposited on the predetermined region.
[0013]
Further, in the X-ray image tube manufacturing method of the present invention, at least a predetermined region of the surface is symmetrical with respect to an axis passing through the center thereof, and is formed into a spherical shape by a set of curves having no flat portion . And the 1st process which arrange | positions the evaporation source which has a heating body part with which the photoelectric material was apply | coated to the said predetermined area | region on the tube axis | shaft in the vacuum envelope which comprises an X-ray image tube, The said heating body part And a second step of depositing the photoelectric material on the input substrate of the X-ray image tube.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention will be described with reference to FIG. 1 by taking the case where an evaporation source is inserted from the outside as an example. Reference numeral 11 denotes a vacuum envelope constituting an X-ray image tube. An input unit 12 is provided at one end of the vacuum envelope 11 and an output unit 13 is provided at the other end. A focusing electrode 14 is disposed between the input unit 12 and the output unit 13, and an anode 15 is disposed near the output unit 14.
[0015]
The input unit 12 includes, for example, a spherical input substrate 12a, an input phosphor screen 12b formed on the input substrate 12a, an input photocathode 12c formed on the input phosphor screen 12b, and the like. The output unit 13 includes a flat output substrate 13a, an output phosphor screen 13b formed on the output substrate 13a, and the like. An introduction port 16 is provided on the side surface of the vacuum envelope 11.
[0016]
In the X-ray image tube having the above-described configuration, when the input photocathode 12c is formed on the input substrate 12a, first, the evaporation source 17 is inserted into the vacuum envelope 11 through the introduction port 16. The evaporation source 17 is supported at the tip of the introduction rod 18, and is disposed, for example, on the tube axis m of the X-ray image tube and near the center of the radius of curvature of the spherical input substrate 12a. The evaporation source 17 is composed of a spherical heating body 17a and an Sb layer 17b deposited on the upper half surface of the heating body 17a, for example.
[0017]
Next, the heating body 17a of the evaporation source 17 inserted into the vacuum envelope 11 is heated to evaporate the Sb layer 17b attached to the heating body 17a. At this time, the evaporated Sb is vapor-deposited on the input fluorescent screen 12b of the input substrate 12a, for example, and an Sb thin film for the photocathode is formed.
[0018]
Next, when the deposition of the Sb thin film is completed, the evaporation source 17 is taken out of the vacuum envelope 11. Thereafter, the introduction port 16 is chipped off so that the inside of the vacuum envelope 11 can be kept in a vacuum.
[0019]
According to the above configuration, the upper half surface of the evaporation source 17 positioned on the input substrate 12a side, for example, is formed in a spherical shape symmetrical to the tube axis m, for example, in accordance with the surface shape of the input substrate 12a. Therefore, the Sb thin film is uniformly deposited on the input substrate 12a to form a uniform thickness.
[0020]
Here, the evaporation source 17 will be described with reference to FIG. In FIG. 2, parts corresponding to those in FIG.
[0021]
The heating body 17a constituting the evaporation source 17 is formed of, for example, a ceramic heater, and the surface thereof is formed of a set of curves, for example, a spherical surface having no flat portion. A resistance wire 22 that generates heat by an electric current is embedded in the heating body 17a. Current terminals 22a and 22b are connected to both ends of the resistance wire 22, and the current terminals 22a and 22b are drawn to the outside. Then, when a part of the surface of the heating body 17a formed on the spherical surface, for example, as shown in FIG. 1, the evaporation source 17 is arranged in the vacuum envelope 11, the upper half located on the input substrate 12a side is formed. The Sb layer 17b is deposited by sputtering or the like.
[0022]
In addition, if the Sb layer 17b deposited on the heating body 17a evaporates and is deposited on the input substrate 12a, and the Sb layer 17b remains on the surface of the heating body 17a, discharge or dust is generated. Therefore, the thickness of the Sb layer 17b is set to a thickness necessary for the formation of the photocathode, for example, 100 μm or less, and the Sb layer 17b does not remain on the heating body 17a when the deposition of the Sb thin film is completed on the input substrate 12a surface. I am doing so.
[0023]
According to the configuration described above, the surface of the evaporation source 17 is formed in the same spherical shape as the shape of the input substrate 12a, and in the vicinity of the center of curvature of the spherical input substrate 12a on the tube axis of the X-ray image tube. Has been placed. Therefore, the photoelectric material evaporated from the evaporation source 17 is uniformly deposited on the input substrate 12a, and the film thickness distribution of the Sb thin film constituting the photoelectric surface is made uniform.
[0024]
Moreover, in said embodiment, the whole surface of the heating body 17a is a spherical surface. However, when the evaporation source 17 is disposed in the vacuum envelope 11, only a part of the upper half or the upper half, for example, located on the input substrate 12a side is formed into a spherical surface, and the Sb layer 17b is formed on the spherical portion. It is also possible to make a structure with a coating.
[0025]
Next, another embodiment of the present invention will be described with reference to FIG. 3 by taking as an example a case where a plurality of evaporation sources are arranged in an X-ray image tube. In FIG. 3, parts corresponding to those in FIG.
[0026]
A plurality of evaporation sources 17 (two evaporation sources 171 and 172 are shown in the figure) are located at a position where the input substrate 12a can be seen in the vacuum envelope 11, for example, outside the anode 15. For example, they are arranged at equal intervals on one circumference.
[0027]
By the way, when a plurality of evaporation sources, for example, reference numerals 171 and 172 are arranged in the vacuum envelope 11, the plurality of evaporation sources 171 and 172 are arranged at positions displaced from the tube axis m. Therefore, the input substrate 12a is wide on one side and narrow on the other side with respect to the axes n1 and n2 parallel to the tube axis m passing through the evaporation sources 171 and 172, and the distance from the evaporation sources 171 and 172 is also small. Varies by location. Thus, the input substrate 12a is asymmetric with respect to the axes n1 and n2 of the respective evaporation sources 171 and 172.
[0028]
In this case, the predetermined region of the heating body to which the Sb layer is deposited is formed as a set of curves in consideration of the shape of the input substrate 12a viewed from each of the evaporation sources 171 and 172, the distance to the input substrate 12a, and the like. For example, they are formed asymmetrically with respect to the axes n1 and n2 passing through the central portion.
[0029]
Here, the evaporation source 17 in which the surface of the heating portion is formed asymmetrically with respect to the axis will be described with reference to FIG. When the surface of the heating element 17a is arranged in a vacuum envelope as shown in FIG. 3, at least a part of the surface located on the input substrate 12a side is constituted by a set of curves, and the center thereof. Is formed asymmetrically with respect to an axis n passing through. For example, the apex 41 of the surface of the heating body 17a located closest to the input substrate 12a side is shifted from the axis n to one side. And the Sb layer 17b is adhere | attached on the surface of the heating body 17a.
[0030]
When the heating body 17a having the above-described configuration is disposed in the vacuum envelope as shown in FIG. 3, for example, the apex 41 portion is positioned outside the axes n1 and n2 of the evaporation sources 171 and 172, respectively. Thus, the area of the portion of the surface of the heating body 17a that is inclined toward the side where the input substrate 12a can be seen is increased.
[0031]
In the case of the configuration described above, among the heating elements constituting the evaporation source 17, at least the surface of the predetermined region to which the Sb layer is deposited is configured by a set of curves, and the shape of the surface of the predetermined region is determined by the evaporation source. 17 is set according to the shape of the input board 12a viewed from 17 and the distance to the surface of the input board 12a. Therefore, the Sb thin film is uniformly deposited on the input substrate 12a to form a film having a uniform thickness.
[0032]
Here, FIG. 5 and FIG. 6 show examples of the film thickness distribution when the Sb thin film is formed on the input substrate. 5 and 6, the vertical axis indicates the radial distance (mm) with the center on the input substrate as the origin, and the vertical axis indicates the film thickness (%) when the film thickness at the center of the input substrate is 100%. ing. θ represents a rotation angle around the tube axis.
[0033]
FIG. 5 shows a case where the evaporation source is arranged near the center of the radius of curvature of the input substrate surface as shown in FIG. 1, and the evaporation source is a refractory metal wire that generates heat by energization in a spherical ceramic having a diameter of 8 mm. And an Sb layer is deposited by sputtering on the upper half surface of the input substrate surface.
[0034]
FIG. 6 shows a case where a conventional evaporation source is used, and the evaporation source has a structure in which an Sb layer is deposited on a donut-shaped filament.
[0035]
As can be seen by comparing FIG. 5 and FIG. 6, the thickness distribution of the Sb thin film is uniform in the radial direction and the rotational direction in the invention (FIG. 5) compared to the conventional evaporation source (FIG. 6). Yes. Therefore, according to the configuration of the invention, it is possible to obtain an X-ray image tube in which the uniformity of the luminance of the output image is improved and the diagnostic region is enlarged.
[0036]
In the above embodiment, a ceramic heater is used as the heating body. However, the heating element uses a plate material such as refractory metal such as Mo, Ta, W, Ni, Fe, and stainless steel, and at least a part of the surface is formed into a curved surface consisting of a set of curves by pressing or the like. A structure in which a photoelectric material is deposited on the surface of one part can also be used. In the case of this structure, a current is directly applied to the heating body to evaporate Sb deposited on the surface.
[0037]
In the above embodiment, the Sb layer is directly formed on the surface of the heating body. However, in order to prevent the reaction between the heating body and Sb or to improve the adhesion of the Sb layer, an intermediate layer such as Pt is formed on the heating body, and the Sb layer is deposited on the intermediate layer. It can also be made.
[0038]
As described above, according to the configuration of the present invention, at least the surface of the region where the Sb layer is to be deposited is formed by a set of curves in the heating element portion constituting the evaporation source. In this case, the surface of the heating body in the region where the Sb layer is deposited can be formed in an arbitrary shape so that the film thickness distribution of the Sb thin film formed on the input substrate is made uniform according to the position where the evaporation source is arranged. . For this reason, an evaporation source in which the film thickness distribution of the Sb thin film becomes uniform can be obtained.
[0039]
In addition, since the heating body surface is formed in accordance with the position where the evaporation source is disposed, the degree of freedom in the position where the evaporation source is disposed is increased, and the electrode structure supporting the evaporation source is less restricted. .
[0040]
In addition, a structure having a certain thickness can be easily realized by using a heating element portion of the evaporation source as a hemisphere or a sphere. Therefore, the mechanical strength is increased, deformation due to film stress or thermal expansion is prevented, and unevenness of the film thickness distribution due to deformation, twisting, or deflection of the evaporation source is prevented.
[0041]
In each of the above-described embodiments, a description is given of a structure in which the input substrate is separately provided in the vacuum envelope. However, the present invention can also be applied to a structure in which the input portion is formed directly on the front surface portion of the vacuum envelope.
[0042]
【The invention's effect】
According to the present invention, it is possible to realize a photocathode evaporation source and an X-ray image tube in which the film thickness distribution of the thin film constituting the photocathode is made uniform and the luminance uniformity is improved.
[Brief description of the drawings]
FIG. 1 is a schematic structural diagram for explaining an embodiment of the present invention.
FIG. 2 is a schematic structural diagram for explaining an example of an evaporation source used in an embodiment of the present invention.
FIG. 3 is a schematic structural diagram for explaining another embodiment of the present invention.
FIG. 4 is a schematic structural diagram for explaining an example of an evaporation source used in another embodiment of the present invention.
FIG. 5 is a diagram showing a film thickness distribution of an Sb thin film when the evaporation source of the present invention is used.
FIG. 6 is a diagram showing a film thickness distribution of an Sb thin film when a conventional evaporation source is used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Vacuum envelope 12 ... Input part 12a ... Input board 12b ... Input fluorescent screen 12c ... Input photoelectric surface 13 ... Output part 13a ... Output board 13b ... Output fluorescent screen 14 ... Focusing electrode 15 ... Anode 16 ... Inlet 17 ... Evaporation source 17a ... heating element 17b ... Sb layer 18 ... introduction rod m ... tube axis

Claims (6)

In a photocathode-forming evaporation source comprising a heating body that generates heat and a photoelectric material that evaporates with the heat of the heating body to form a photocathode, a predetermined region of at least a part of the surface of the heating body has its center An evaporation source for forming a photocathode characterized in that it is formed in a spherical shape by a set of curves that are symmetrical with respect to an axis passing through and does not have a flat portion , and a photoconductive material is deposited on the predetermined region. The evaporation source for forming a photocathode according to claim 1 , wherein the photoelectric material is deposited on the surface of the heating body via an intermediate layer made of a material different from the photoelectric material . The photoelectron-forming evaporation source according to claim 1 , wherein the photoelectric material is antimony (Sb) and the film thickness is 100 μm or less . The evaporation source for photocathode formation according to claim 1, wherein a metal wire that generates heat when energized is embedded in the heating body . The evaporation source for photocathode formation according to claim 1 , wherein the heating body is composed of a metal resistor that generates heat when energized . A heating process in which at least a part of a predetermined region of the surface is formed in a spherical shape by a set of curves that are symmetrical with respect to an axis passing through the center and does not have a flat portion, and a photoelectric material is deposited on the predetermined region A first step of disposing an evaporation source having a body part on a tube axis in a vacuum envelope constituting an X-ray image tube; heating the heating body part; A method for producing an X-ray image tube comprising a second step of evaporating a photoelectric material.

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