JPH0161221B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photoconductive image pickup tube for television cameras, and mainly enables live imaging with essentially higher image quality (high resolution, low afterimage, uniformity of image quality, and high signal-to-noise ratio) than the current standard television system. The aim is to improve production yields and extend the lifespan of high-quality image pickup tubes. Conventionally, as shown in the cross section of FIG. 1, the electron gun section of a photoconductive image pickup tube for television has been constructed using an electron radioactive material such as barium oxide or strontium oxide on a sleeve 11 whose base metal is nickel or the like. The cathode electron emitting surface 1 coated with No. 12 is heated by a heater 2 consisting of a fine tungsten wire coated with an alumina insulator.
Thermal electrons generated from the cathode are once crossed over and formed into a thin bundle by the electric field created by the electrode 3a, which is negatively biased with respect to the cathode, and the electrodes 3b and 3c, which are positively biased with respect to the cathode. After passing through the beam restriction hole 5 provided through the electrode 3c and forming the required electron beam shape 4, the electron beam impinges on the target 8 under the action of the focusing section 6 and the deflection section 7. It has been assembled like this. Usually, the electrodes 3b and 3c are assembled to form an integrated electrode, and the electrode 3c is usually made of a nickel plate with a thickness of, for example, 0.04 mm, and the aperture 5 is formed by electroforming, and its diameter is They were usually about the same thickness as a board or even thicker. The other electrodes 3a and 3b have been made of stainless steel, which is less likely to adversely affect the degree of vacuum, is relatively easy to mold and assemble, and is non-magnetic and inexpensive. Now, a high-definition television system that essentially exceeds the conventional standard television picture quality standards, such as 1125 horizontal scanning lines and a field frequency of 60
Hz, video frequency bandwidth of 60 MHz, the image pickup tube uses an electron beam to scan the target in order to prevent S/N from deteriorating even if it has a wide signal range, and to reduce image retention. requires more current, e.g., more than twice, than that of conventional standard image pickup tubes. Furthermore, in order to achieve essentially low afterimages, the velocity dispersion of electrons within the beam must be smaller than the twist in the crossover type, for example, 1/2 or less. Furthermore,
In order to achieve high resolution, it is desirable that the diameter of the electron beam be smaller, for example, 1/4 or less, and that the beam divergence angle immediately after passing through the beam restriction hole 5 be close to zero. In order to form such a high-density electron beam with low spread and small electron velocity dispersion, it is necessary to create a double electron beam that does not cross over, as proposed by the applicants in JP-A-154043-1983. It was necessary to have a polar-operating laminar flow electron gun. The configuration of this electron gun will be schematically explained with reference to FIG. Reference numerals 1 and 2 in FIG. 2 are a cathode electron emitting surface and a heating heater, respectively. A control electrode 3a disposed very close to the front surface of the cathode is integrated with an aperture plate 3c, and is accelerated at a positive voltage of, for example, 20V with respect to the cathode in order to extract electrons from the electron emitting surface in parallel without crossover. The electrode 3b is kept positive at 300V, for example. For example, a small hole 5 is provided in the center of the apertured plate 3c to limit the electron beam and maintain high resolution.
They are provided with a diameter of 0.01mm to 0.02mm. With this diameter, the area of the pore 5 is approximately 1/10 of the electron beam limiting aperture area of the crossover electron gun mentioned above, and the distance between the cathode and the control electrode is also designed to be 1/2 or less. In conventional laminar flow electron guns, the material used to construct these electrodes was mainly stainless steel, as in previous crossover types. The reason why this laminar flow type electron pure is functionally superior to the crossover type is that electrons are extracted from the electron emitting surface in a parallel laminar flow without crossover. In order to keep the scanning electron beam density higher than that of the crossover type, the use of impregnated cathodes, for example blocks of barium-impregnated porous tungsten, which can withstand high electron radiation loads, known as cathode electron emitters, This had to be provided in a sleeve made of tantalum or molybdenum. The above-described laminar flow extraction of thermionic electrons and the use of an impregnated cathode have caused the following drawbacks in the construction of conventional electron guns mainly made of stainless steel. The first of these drawbacks is that most of the thermoelectrons generated from the cathode radiation surface during pure electron operation are positively biased by the control electrode, that is, the beam limiting aperture plate, which is placed parallel to and very close to the radiation surface. Because of this, it hits this part and causes abnormal heating. If overheating occurs in an electrode material such as stainless steel, the composition of the electrode material changes, some or all of the constituent materials evaporate, and these evaporated materials then spatter onto the cathode emitting surface at close range. This surface is damaged, and the restriction hole 5 of the perforated plate often expands due to missing surrounding metal. The second drawback arises from the use of an impregnated type cathode electron emitter. Compared to previous oxide-coated electron emitters, impregnated electron emitters require degassing of the electron gun during cathode activation treatment or prior to activation treatment in order to obtain good electron emission ability. Requires higher temperature when heating. For example, the temperature of the impregnated type is 200℃ to 300℃ higher. As a result, the control electrode and the apertured plate in close proximity to the cathode surface were overheated, and the aforementioned undesirable phenomenon often occurred. In order to suppress these undesirable phenomena, a high melting point metal thin plate such as tantalum, molybdenum, or platinum may be used as the material of the beam limiting aperture plate 3c, which is most likely to be hit by radiated thermionic electrons. If the material is different from that of the control electrode 3a, there is a great possibility that the perforated plate 3c will be thermally deformed and come into contact with the cathode, or that uncontrollable characteristic fluctuations will occur. For example, stainless steel electrode 3a thickness 0.18mm
When a 0.03 mm thick platinum perforated plate 3c is welded on top, the central part of the platinum perforated plate 3c becomes a cathode radiation surface due to heating during cathode activation or heating due to thermionic bombardment during electron gun operation. The platinum plate 3c swelled toward the side 1 and came into contact with the cathode, and when it was dismantled for inspection, it was found that the platinum plate 3c had often been deformed due to the thermal history. Therefore, in the present invention, an impregnated radiator is used for the cathode in a bipolar operating laminar flow electron gun of a photoconductive image pickup tube that forms an electron beam and scans a signal accumulation target at low speed. an apertured plate having a beam-limiting aperture for forming the electron beam; and at least a part of a control electrode component formed integrally with the apertured plate or fixed to the apertured plate. , made of the same single high melting point metal tantalum or molybdenum, eliminating the above-mentioned drawbacks that often occur during the operation of the image pickup tube or when producing the image tube exhaust for cathode activation and electrode degassing, making it suitable for high-quality use. We have improved the production yield and extended the lifespan of image pickup tubes. Tantalum or molybdenum was chosen as the electrode material because, as shown in Table 1, it has a high melting point, is a single substance, is non-magnetic, has better thermal conductivity than conventional stainless steel, and is suitable as a material for vacuum tubes. Depends on what you're doing.

[Table] Example 1 is carried out as follows, but since the electrode configuration of this example is exactly the same as that in FIG. 2, it will be explained using the same figure. The control electrode 3a is made of a tantalum plate having a thickness of 0.1 mm to 0.5 mm, and is formed by press molding with a hole having a diameter of, for example, 0.5 mm in the center. The lower and upper limits of the electrode thickness respectively correspond to the strength limit of the electrode structure and the possible limit of press molding at a normal technical level. The aperture plate 3c made of thin tantalum and having the beam-limiting aperture 5 is formed by laser drilling.
Suitable for making holes with a diameter of 0.01mm to 0.03mm
The control electrode 3a has a thickness of 0.02 mm to 0.05 mm.
Welded to the cathode side of the Embodiment 2 will be explained with reference to FIG. 3, where 3a is a member press-molded from a tantalum plate having a thickness of 0.1 mm to 0.5 mm, as in the previous example. This member is further press-formed to make only the center part thinner, or etched to make only the center part thinner, so that the thickness of that part 3c is suitable for laser drilling, and then a laser hole is made in the center. A beam limiting aperture 5 is formed by drilling. Still another embodiment 3 is shown in FIG. In the figure, 3d is a cup-shaped electrode made of a material such as ordinary stainless steel for direct air use, and this has a large hole at the bottom. A flat plate 3a having a thickness of, for example, 0.3 mm is attached using ruthenium solder 9a, and these two members 3a and 3d form a control electrode structure. For example, an opening with a diameter of 0.5 mm is provided in the center of 3a. In order to close this hole, a hole plate 3c made of molybdenum and having a thickness of, for example, 0.03 mm and a beam limiting hole 5 of 0.01 mm to 0.03 mm in the center is connected to the electrode 3a using, for example, ruthenium solder 9b. Attach to. Another example 4 is shown in FIG. 3d is the same as shown in FIG. 3a is a perforated plate 3c having a thickness of, for example, about 0.03 mm, which is suitable for laser drilling by etching or cutting the central portion. 3a is fixed to 3d by, for example, ruthenium solder 9a to form a control electrode structure. Furthermore, a modification of the third embodiment (FIG. 4) is shown in FIG. Instead of the cup-shaped electrode 3d in FIG. 4, a cup-shaped electrode 3d made of the same stainless steel material and a plate-shaped electrode 3 made of stainless steel with a large opening are provided.
d′, sandwich the molybdenum flat electrode 3a between them as shown in the figure, and place the molybdenum plate electrode 3a at the location 10 indicated by the dashed-dotted line.
The ruthenium solder 9a shown in FIG. 4 can be omitted. This method can also be applied to Example 4. By fabricating an image pickup tube in which the electron gun has a control electrode structure made of tantalum or molybdenum material as described in the above embodiments, a bipolar operation laminar flow electron gun with an impregnated radiator in the cathode can be used to achieve cathode activity. There are no accidents such as the control electrode receiving undesirable overheating during the electron gun electrode degassing process or prior to that, resulting in evaporation of its constituent materials and damage to the cathode emission surface. has improved significantly. Further, when such an image pickup tube is operated, the control electrode does not become abnormally heated even by the bombardment of radiated thermoelectrons, and the life of the tube is improved. As is clear from the above description, by implementing the present invention, a laminar flow electron gun, which does not have electron crossover and uses an impregnated radiator for the cathode, as proposed in JP-A-154043, can be realized. Television systems that require essentially higher image quality than previous standards, such as the number of horizontal scanning lines, are being developed to improve production yields and extend the lifespan of image pickup tubes.
1125 lines, field frequency 60Hz, video frequency band
It has become possible to put into practical use a high-quality image pickup tube that is compatible with the 60MHz system and enables live imaging. Furthermore, this invention has the effect of enabling good characteristics without causing any adverse effects when applied to image pickup tubes used in the current standard television system or other different television systems. It can also be applied to cases other than impregnated cathodes, if necessary.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a conventional crossover type electron gun, FIG. 2 is a sectional view showing the configuration of a conventional dual-pole laminar flow type electron gun and the present invention, and FIGS. FIG. 3 is a cross-sectional view showing an example of the configuration of an electron gun in the inventive image pickup tube. 1 is a cathode electron emitting surface, 2 is a heater, 3a is a control electrode, 3b is an accelerating electrode, 3c is a beam limiting aperture plate, 4 is a shaped electron beam, 5 is a beam limiting aperture, 6 is an electron of the image pickup tube Focusing part, 7 is deflection part, 8
1 is a target, 11 is a cathode sleeve, and 12 is an electron emitting material.

Claims (1)

[Claims] 1. In a bipolar operating laminar flow electron gun of a photoconductive type image pickup tube that uses an impregnated emitter as a cathode and forms an electron beam to scan a signal accumulation target at low speed,
an aperture plate disposed close to the cathode radiation surface and having a beam-limiting aperture for forming the electron beam; and a control electrode component integrally molded with the aperture plate or fixed to the aperture plate. 1. An image pickup tube characterized in that at least a portion of the tube is made of the same single high melting point metal tantalum or molybdenum.