MXPA97009182A - Category of electronic tube - Google Patents

Abstract

The present invention relates to an electronic tube cathode comprising a base (1) formed mainly of nickel, an alloy layer (4) disposed on the base (1) and including nickel and tungsten having a smaller grain size than that of the base, and a layer of electron-emitting material (5) deposited on the alloy layer, and including an oxide (6) of an alkaline earth metal containing at least barium, and rare earth metal oxide (7). ) from 0.01 to 25 percent by weight and containing at least one scandium oxide and yttrium oxide. The cathode has improved life characteristics, compared to the prior art, even if operated at a current density of 3 A / cm 2 or m

Description

CÁTODO DE TUBO ELECTRÓNICO BACKGROUND OF THE INVENTION The present invention relates to an improvement of an electron tube cathode used for a cathode ray tube for television, or the like, and in particular to an electron tube cathode having a layer of electron emitting material containing an oxide of rare earth metal, or a heat-resistant oxide, as a substitute for rare earth metal oxide. Figure 9 shows an electron tube cathode used in the cathode ray tube or in the television image camera tube, described for example in Japanese Patent Publication Kokoku No. S64-5417. In the drawing, the reference number 111 denotes a base formed mainly of nickel and containing a small amount of silicon (Si), magnesium (Mg) or similar reducing element. The reference numeral 112 denotes a cathode sleeve formed of nichrome (registered trademark) or the like. The reference numeral 115 denotes a layer of electron-emitting material deposited on the upper surface of the base 111 and containing as its main constituent, an aralinothermal metal oxide 121 containing at least barium (Ba), and additionally strontium (Sr. ) and / or calcium (Ca), and containing a rare earth metal oxide 122 such as a scandium oxide of 0.1 to 20% by weight. The reference numeral 113 denotes a heater placed in the base 111. The heater 113 heats the layer of electron emitting material 115 to emit thermoeye electrons. With the electron tube cathode of the above configuration, the manner of depositing the layer of electron-emitting material 115 on the base 111 will be described below. First a ternary carbonate of barium, strontium and calcium and a predetermined amount of scandium oxide are mixed together with a binder and a solvent, to form a suspension. The suspension is sprayed on the base 111 to a thickness of approximately 80 μm, and subsequently heated by the heater 113 during the evacuation process of the cathode ray tube. The alkaline earth metal carbonate is converted to an alkaline earth metal oxide. Part of the araline-earth metal oxide is reduced and activated to have a semiconductor property, so that the layer of electron-emitting material 115 consists of a mixture of alkaline earth metal oxide 121 and the rare earth metal oxide 122 is formed on the base 111.

In the activation step, part of the alkaline earth metal oxide reacts in the following manner. That is, the silicon, magnesium and similar reducing elements contained in the base 111 move towards the interface between the alkaline earth metal oxide 121 and the base 111 by diffusion, and react with the alkaline earth metal oxide. For example, if the alkaline earth metal oxide is barium oxide, the following reactions (1) and (2) take place: 2BaO + (1/2) Si = Ba + (1/2) Ba2SiO4. . (1) BaO + Mg = Ba + MgO. . (2) As a result of these reactions, part of the alkaline earth metal oxide 121 deposited on the base 111 is reduced, to become a deficient semiconductor of oxygen, so as to facilitate the emission of electrons. If rare earth metal oxide is not contained in the layer of electron-emitting material operation with a current density of 0.5 to 0.8 A / cm2) at a cathode temperature of 700 to 800 ° C is possible. If the oxide of rare earth metal is contained in the layer of electron-emitting material, the operation with a real density of 1.32 to 2.64 A / cm ^ is possible. Generally, the electron yield of the oxide cathodes depends on the amount of excessive Ba in the oxide. If the rare earth metal oxide is not contained, excessive Ba sufficient for a high current operation may not be supplied, and the current density at which the cathode is operable is small. That is to say, magnesium oxide (MgO) or barium silicate (Ba2Si? 4) which is a by-product generated at the time of the previous reaction, and called as an intermediate layer is formed, being concentrated over nickel grain interfaces in the base 111 or the interface between the base 111 and the layer of electron-emitting material 115, so that the speed of the reactions is expressed by the formulas (1) and (2) above is controlled by the rate of magnesium diffusion and the silicon in the intermediate layer and the excessive Ba supply is insufficient. If the rare earth metal oxide is contained in the layer of electron-emitting material, the operation is as follows. The following description is made by taking scandium oxide (SC2O3) as an example. During the operation of the cathode, at the interface between the base 111 and the layer of electron-emitting material, part of the reducing agent that has been moved by diffusion through the base 111 reacts with the scandium oxide (SC2O3) of the described by the following formula (3) and a small amount of metallic scandium is generated, and part of the metallic scandium forms a solid solution with the nickel in the base 111 and a part is retained in the interfaces. (1/2) Sc2O3 + (3/2) Mg = Sc + (3/2) MgO. . (3) The metallic scandium generated by the reaction of the formula (3) decomposes the aforementioned intermediate layer formed on the base 111 or at the nickel grain interfaces in the base 111 in the manner described by the following formula (4) ), so that the excessive Ba supply is improved and the rare earth metal oxide in the electron emitting material layer restricts the evaporation of the excessive Ba, with the result that the operation is possible at a more current density high that if the rare earth metal oxide was not contained. (1/2) Ba2Si04 + (4/3) Sc = Ba + (1/2) Si + (2/3) Sc203. . (4) Japanese Patent Publication Kokai No. S52-91358 discloses a direct heated cathode having a base formed of a nickel alloy containing a high melting metal such as W or Mo which increases the metallic strength, and a reducing agent such as Mg, Al, Si or Zr, and a layer of Ni-W, or Ni-Mo alloy coated on the base surface where an electron-emitting material layer is to be deposited. With an electron tube cathode formed in the manner described above, the rare earth metal oxide improves the supply of excessive Ba, although the rate of supply of the excessive Ba is controlled by the diffusion rate of the reducing agent in the nickel in the base , and the life characteristics at a high current density operation of 2 A / cm 2 or more is substantially low. The last of these mentioned above provides an improvement over thermal deformation which is an inherent problem for the directly heated cathode which emits thermoelectrons from the layer of electron emitting material, using the heat generated by the current through the base itself, by coating the base with a layer of an alloy such as Ni-W or Ni-Mo. However, it does not allow operation at a high current density. With respect to those problems, the assignee of the present application already described in Japanese Patent Application No. H2-56855 (Japanese Patent Application Kokai No. H3-257735) that it is possible to improve the life characteristics with the operation at a high current density of 2 A / cm2 by diffusion into the base of a metallic layer provided between the base and the layer of electron-emitting material. Figure 10 shows the configuration of said cathode.

BRIEF DESCRIPTION OF THE INVENTION The present invention has been made in an attempt to further improve the life characteristics with the operation at a high current density and provides an improvement with respect to the life characteristics with the operation at a high current density of 3 A / cm2. or more, defining the state of distribution of the metallic layer within the base formed mainly of nickel, or on the surface of the base. According to the invention, an electronic tube cathode is provided comprising: a base formed primarily of nickel and including at least one type of reducing agent; an alloy layer placed on the base or as a surface layer of the base, and which includes at least one metal selected from the group consisting of tungsten, molybdenum and tantalum and nickel; and a layer of electron-emitting material formed on the alloy layer and including an alkaline earth metal oxide containing at least barium and a rare earth metal oxide of 0.01 to 25% by weight. Preferably the concentration of at least one metal selected from the group consisting of tungsten, molybdenum and tantalum in the alloy layer is greater towards the layer of electron-emitting material. Preferably the alloy layer is formed of grains, and the grains are smaller than the grains that form the base. Preferably, the thickness of the alloy layer is not less than 1 μm. According to another aspect of the invention, there is provided an electronic tube cathode comprising: a base formed primarily of nickel and including at least one type of reducing agent; a film placed on at least part of the surface of the base and including at least one metal selected from the group consisting of tungsten, molybdenum and tantalum, and a layer of electron-emitting material formed on said film and which it includes an oxide of an alkaline-iron metal containing at least barium and a rare earth metal oxide of 0.01 to 25% by weight. It can be arranged in this manner that the film comprises a mixture film placed on the base and including at least one metal selected from the group consisting of tungsten, molybdenum and tantalum, as well as nickel, or a multiple layer film which includes one or more films of individual material of at least one metal, and a film of individual nickel material. Alternatively, the film may comprise a metal layer on part of the surface of the base, and including at least one metal selected from the group consisting of tungsten, molybdenum and tantalum. Preferably, the film is formed substantially in the center of the base and covers from 12 to 80% of the surface area of the base. It can be arranged that the film comprises a metal layer disposed over part of the base surface and that includes at least one metal selected from the group consisting of molybdenum and tantalum and the thickness of the metal layer is from 0.1 to 1.8 μm . According to another aspect of the invention, there is provided an electronic tube cathode comprising: a base formed primarily of nickel, and including at least one type of reducing agent. an alloy layer placed on the base or as a surface layer of the base, and which includes at least one metal selected from the group consists of tungsten, molybdenum and tantalum, as well as nickel, the concentration of at least one metal selected from the group consisting of tungsten, molybdenum, and tantalum in the alloy layer being higher towards the layer of electron-emitting material, and a layer of electron-emitting material formed on the alloy layer and which includes minus one oxide selected from the group consisting of those of aluminum, titanium, silicon, magnesium, chromium, zirconium, hafnium, indium and tin from 0.01 to 20 percent by weight. With the above arrangement, in addition to the reducing agent in the base, the alloy layer contributes to the excessive Ba supply and the alloy layer serves to ensure the stable supply of the reducing agent at the interface. Accordingly, it is possible to provide an electron tube cathode that can operate at high current density 3 A / cm2 which was difficult to achieve with the prior art oxide cathodes, and to realize a cathode ray tube with a high brightness and high definition. Furthermore, compared to the prior art, the only increment is the step of forming the metal layer, such as tungsten, as an alloy layer and a layer can be formed in such a way as to reduce the residual stress. Accordingly, a cathode ray tube with improved precision can be obtained at a low cost.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of an electronic tube cathode according to the embodiment 1 of the invention; Figure 2 is a characteristic diagram showing the relationship between the emission current ratio after a certain time (4,000 hours) of use and the current density of an electronic tube cathode according to the embodiment 1 of the invention; Figure 3 is a diagram showing the relationship between the ratio of emission current after a certain time (4,000 hours) of use and the thickness of tungsten film of an electron tube cathode according to Modality 1 of the invention; Figure 4 is a schematic sectional view showing the distribution of tungsten in an electron tube cathode according to Modality 1 of the invention; Figure 5 (a) and Figure 5 (b) are schematic sectional views of an electronic tube cathode according to Modality 1 of the invention, showing the grains forming the respective layers; Figure 6 (a) and Figure 6 (b) are schematic section views of an electronic tube cathode according to Modality 1 of the invention, showing the grains forming the respective layers and showing the changes with the advance of the heat treatment Figure 7 (a) to Figure 7 (c) are diagrams showing patterns of the tungsten film formed during the manufacture of an electron tube cathode according to mode 3; Figure 7 (d) is a schematic sectional view of a base and a sleeve; Figure 8 is a diagram showing the variation of the cut-off voltage ratio with the time exhibiting the effect of Mode 5 according to the invention; Figure 9 is a sectional view showing the configuration of an electronic tube cathode in the prior art; and Figure 10 is a sectional view showing the configuration of another electronic tube cathode in the prior art.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Modality 1 An embodiment of the invention will now be described with reference to Figure 1. In the drawing, the reference number 4 denotes an alloy layer formed on the upper surface of a base 1 and containing the nickel and at least one Metal consisting of tungsten, molybdenum and tantalum. The reference number 5 denotes a layer of electron-emitting material deposited on the layer of alloy 4 and containing an alkaline earth metal oxide 6 as a main component containing at least barium (Ba) and additionally strontium (Sr) and / or calcium (Ca), and containing a rare earth metal oxide 7 such as scavenge oxide, yttrium oxide or europium oxide of 0.01 to 25% by weight. The base 1, a sleeve 2, and a heater 3 are identical for the base 111, the sleeve 112 and the heater 113 shown and described in relation to Figure 9. An example of the method of manufacturing an electronic cathode tube configured as described above will now be described. First, a Ni 1 base containing a small amount of Si and Mg is welded to a cathode sleeve 2 and the cathode base unit is then placed in an electronic beam and tungsten evaporation apparatus (W), by example, it is deposited by heating evaporation of the electron beam deposited in a vacuum atmosphere of 10 ~ 5 to 10"**. The cathode base unit is then heated, for example, in a nitrogen atmosphere to 800 to 1100 C. This is to remove impurities such as oxygen that remains inside or on the surface of the metal layer and to cause the concretion of the metal layer or the recrystallization of the metal layer or the diffusion of the metal layer inside the metal layer. the base 1. In this method, the layer of electron-emitting material 5 is formed on the cathode base unit with the alloy layer 4 formed therein, as in the prior art example. character eristic cathode life of electronic tube, ie the ratio of the emission current (with respect to the initial value), in relation to the current density used, according to the modality, manufactured in the manner described above and mounted on a cathode ray tube for an ordinary television , with the cathode ray tube being finished by standard evacuation, with the cathode of electronic tube being used in the operation at a current density of 2 to 4 A / cm2. The life characteristics are shown in comparison with an example of the prior art. A film W of a thickness of 0.7 μm was formed, and heated to 1,000 ° C in a hydrogen atmosphere. Since the layer of electron-emitting material 5, an alkaline earth metal oxide 6 containing scandium oxide of 5 percent by weight was used both for the present embodiment and for the example of the prior art, for the purpose of comparison. As will be seen from Figure 2, the samples according to the present embodiment exhibit a substantially lower emission deterioration during their life compared to the example of the prior art. Figure 3 shows the life characteristics, that is, the ratio of emitter current (with respect to the initial value), of the cathode of electronic tube used in the operation to a density of 2 A / cm2, for different thicknesses of the film, the cathode is mounted on a cathode root tube. From the results shown it is seen that the life characteristics were improved if the film W was of a thickness of 0.1 to 1.6 μm, and a significant improvement was obtained if the film W was 0.3 to 1.1 μm thick. This is due to an optimum composition of the nickel and tungsten which is carried out with this thickness and the effect described above is obtained in a stable manner due to the reduction in the size of the grains of the alloy layer. Figure 4 shows in cross-section the configuration of a cathode having a film W of 0.7 μm, after the operation of 4,000 hours, and the intensity of the X-rays corresponding to the concentration of tungsten with respect to the depth, which represents the depth of the tungsten in the base, obtained by the use of an X-ray microanalyzer. The thickness d in the alloy layer indicates the depth of a part where the intensity is not less than 5% of the maximum intensity. In the drawing, the thickness d of the alloy layer and the depth of the part where the grains are small are shown to be identical, for simplicity of illustration. In many real cases, the layer with small grains within the alloy layer is only in a part of the alloy layer deeper than the depth d, and the grain size gradually approaches the grain size in the nickel base with the depth of increase. If d is not less than 1 μm, the substantial increase in life, compared to the example of the prior art, was observed as shown in Figure 3. The thickness region d is a layer of nickel and tungsten alloy, and may be in the form of at least one solid solution, eutectic (eutectic mixture), and compound (intermetallic compound). Figure 5 shows in cross-section the configuration of the cathode immediately after the formation of the metal layer, in (a), and after the heating step, in (b). Schematically illustrates the configuration as seen through a microscope. After heating, the nickel-tungsten alloy layer extends to the depth d shown in Figure 4, and the grains forming this layer are smaller in average size (the grains are finer) than the grains that form the base. Figure 6 schematically shows in cross-section the configuration of the cathode used for the life test, which is mounted on the cathode ray tube, as described in relation to Figure 2. In Figure 6, (a) shows the cathode which corresponds to (b) in Figure 5, that is, after the heating stage. Figure 6 (b) shows the cathode after the test of Figure 2, that is, having undergone heating cycles. Due to the heating cycles experienced, the distribution of tungsten proceeds to a deeper part, and the thickness of the layer with the fine grains of nickel and tungsten alloy increases. That is, the thickness d1 before the heating cycles increases to a thickness d2. The thickness of the part where the tungsten is present reaches from 10 to 20 μm, and such distribution has been found to contribute substantially to improving the life characteristics. When d1 was less than 1 μm, there was not enough improvement in the observed life characteristics. The improvement in life characteristics was obtained due to the distribution of tungsten or the small grains of the nickel-tungsten alloy layer, which have the following function. First, the principle is explained in detail. In the cathode embodiment of the invention, the fine-grained alloy layer is formed on the surface of, or as a surface layer of the nickel base, and Mg or Si, which are reducing agents diffuse through the Grain interfaces in the alloy layer and react with BaO at the interface between the alloy layer and the electron emitting material layer to form excess Ba. Part of W in the alloy layer contributes to the generation of excess Ba ep according to the formula (5) set out below. Therefore, in the initial activation stage, in which the diffusion of Mg and Si, which are reducing agents, is insufficient, the reduction by W of the side of the electron-emitting material that contributes. After activation, Mg and Si, which have a greater reducing performance and have moved sufficiently towards the interface between the alloy layer and the electron-emitting layer, play an important role in the generation of excess Ba. Consequently, the intermediate layer is generated in the vicinity of the external surface of the fine grains of the alloy layer, although since the grains of the alloy layer are fine, the scale of diffusion of Mg and Si is not controlled by the intermediate layer. Part of the intermediate layer is decomposed by the action of rare earth metal oxide, such as scandium oxide, as in the prior art. However, if the rare earth metal oxide which is simply mixed by dispersion in the layer of electron emitting material as in the prior art example, the effect of decomposing the intermediate layer, originates from the reaction between the scandium oxide and the reducing agent, and is therefore restricted by the solid phase reaction limit, and the current operating density is limited within 2 A / cm 2. According to the invention, the sufficient supply of excess Ba is ensured and the reduction of the consumption of the layer of electron-emitting material according to a high current density due to the improvement in conductivity, and the effect of restricting evaporation of excess Ba by the rare earth metal oxide, such as scandium oxide, in the layer of electron emitting material, are also obtained. As a result of the combination of these effects, a high operating current density of 3 A / cm2 can be achieved. 2BaO + (1/3) W = Ba + (1/3) Ba WO3 ... (5) In addition, W has a smaller reduction property than Si and Mg which are reducing agents of base 1, although it is distributed over Ni grains or inside the grains, so that the reaction with the scandium oxide in the emission of Electron occurs relatively easily and contributes to the generation of Sc that has the effect of breaking down the intermediate layer. In the previous mode, W is used for the metallic layer. It is desirable that the metallic layer 4 have a reducing property that is not greater than at least one of the reducing agents in base 1, and has a reducing property greater than Ni. The reason is that if the reducing property of the metallic layer is less than Ni, the effect of supplying Ba in excess is small, whereas if it is greater than the reductive property of the reducing agent in base 1, the reaction to supply Ba In excess, it occurs mainly at the interface between the metal layer and the electron-emitting metal layer 5, the effect of supplying excess Ba by the reducing agent in the base 1 becomes smaller, and the contribution by the oxide of Scandio to the decomposition of the intermediate layer becomes smaller. The material for the metal layer depends on the reducing agent in the base 1, although in at least one of W, Mo, Ta and the like can be selected. The material for the metallic layer can alternatively be formed of an alloy consisting of a metal, such as W, Mo or Ta, which has a reducing property of no more than at least one of the reducing agents in base 1 and more than Ni, and a metal, such as Ni, which has a reducing property no greater than Ni. In this case, also if the thickness of the film is equal to what was explained in relation to W, an alloy layer having fine grains can be formed, and similar effects can be obtained. The base 1 having a metallic layer of W, for example, is subjected to heat treatment at a maximum temperature of 800 to 1100 ° C, in vacuum or in a reducing atmosphere. By this heat treatment, it is possible to control the metal layer so that it is distributed mainly over the Ni grain in the base 1 or inside the grains, and the diffusion of the reducing agents in the base 1 within the layer of emitter material Electron 6 can be properly maintained. By distributing the coexisting layer of nickel and tungsten over the surface of the base, that is, by distributing the tungsten to a thickness of 1 μm or more, and making the grain size of the coexisting layer smaller than that of the base, the operation at a high current density of 3 A / cm2 or more and improvement in life characteristics have been achieved.

Modality 2 In Modality 1, electron beam evaporation deposition is used to deposit the tungsten that constitutes the metallic layer. Any other method, such as crackling, evaporation-deposition of ion beam CVD (chemical vapor deposition), electrodeposition, ion implantation, or the like, can be used, while a metal layer of at least one of tungsten, molybdenum and tantalum can be used. form.

Mode 3 In the method described in relation to the above embodiments, a metal layer is formed on the base. A blend film containing at least one metal selected from the group consisting of tungsten, molybdenum and tantalum, as well as nickel, or a multiple layer film containing one or more films of the above-mentioned individual material At least one metal and a single nickel material film can be formed using the methods described in connection with Modes 1 and 2. In this case, the residual stress can be relieved. The generation of tension during the manufacture of the cathode can be reduced, and the accuracy can be improved.

Modality 4 In the above modalities, the tungsten constitutes the metallic layer is simply deposited by evaporation. It is not necessary that the tungsten be uniformly formed. If the tungsten distribution defined above can be done by heat treatment, the distribution immediately after the deposition can be so that the tungsten is only formed in part of the base surface. For this purpose, the evaporative deposition or the like described in relation to Modalities 1 and 2 can be used. If a mask or similar is used at the time of deposition of the metal layer, the patterned layers as shown in Figure 7 (a) to Figure 7 (c) can be obtained.

Figure 7 (a) shows a case where the layer is in the form of a disc occupying only the central part of the surface of the base. Figure 7 (b) shows a case where the layer is formed of a matrix of square segments provided with a separation of 400 μm, the length of each section is 200 μm. Figure 7 (c) shows a case where the layer is formed from a matrix of small disc-shaped segments provided at a 400 μm spacing, the diameter of each small disc-shaped segment being 200 μm. In this case, the residual tension in the tungsten layer can be reduced, compared to the case of a uniform layer, and a cathode with a lower tension and greater precision can be formed. In particular, if the diameter of the circular opening (or the length of a shorter side of a rectangular opening) of a first grid (which is placed at the top, as seen in Figure 1, is separated from the cathode, it has a function of limiting the electron emission area of the cathode, and is usually in the form of a metal plate having a circular aperture, or a rectangular aperture) is not greater than 0.5 mm, the variation of the cut-off voltage mentioned above, results from the residual stress, leading to deterioration in the properties of glass and color balance. Figure 8 shows the effect of patterned layers. In the drawing, "WITH ENTIONAL" means the conventional cathode having scandium oxide dispersed in the layer of electron-emitting material at a concentration of 5%. "COMPLETE SURFACE" means the cathode with a film having a thickness of 0.7 μm, and formed through the surface of the base. "SEGMENT" means the cathode with a layer W having a thickness of 0.5 μm, and a pattern shown in Figure 7 (b), the layer is formed of a matrix of square segments provided at a distance of 400 μm, the length on each side is 200 μm. The effect of reduction in residual stress is important. In particular, if the patterned layer covers from 12 to 80% of the central part of the surface part of the base (with the diameter indicated as "BASE DIAMETER" in Figure 7 (d), the reduction in residual stress If the thickness of the layer is 0.1 to 1.8 μm, the tension can be relieved.If the thickness of the layer is from 0.3 to 0.9 μm, the improvement in stress relief and in the life characteristics are Both are important In the above embodiment, W is formed on a part of the base surface A layer of at least one metal selected from the group consisting of tungsten, molybdenum and tantalum can be used. relating to Modality 3, a blend film containing at least one metal selected from the group consisting of tungsten, molybdenum and tantalum, as well as nickel, or a multiple layer film containing one or more individual material films of the before men At least one metal and a film of individual nickel material can be formed on part of the base surface.

Modality 5 In the above embodiment, the rare earth metal oxide is dispersed in the layer of electron-emitting material. Instead of a rare earth metal oxide, the layer of electron-emitting material can be formed of an alkaline earth metal oxide containing at least barium, and at least one oxide selected from the group consisting of those of ( A1), titanium (Ti), silicon (Si), magnesium (Mg), chromium (Cr), zirconium (Zr), hafnium (Hf), indium (In), and tin (Sn) from 0.01 to 20 percent by weight, and even a high current density can be achieved due to the effects of the aforementioned alloy layer, although the effect is smaller than if the rare earth metal oxide were used. In this case, there is no advantage in terms of cost. An electronic tube cathode that modalizes the invention can be used in a cathode ray tube of television, or a tube takes television picture views. By using it in a cathode ray tube for a projection television or on large sized television, and having its operation at a high current, a high brightness can be achieved. In particular, it is useful to achieve high brightness in a cathode ray tube for high definition television. Also, using the cathode ray tube on an exhibition monitor and operating it at a high current density, the area from which the extracted current is reduced, and the definition of the cathode ray tube can be improved.

Claims (9)

1. An electronic tube cathode, characterized in that it comprises: a base formed mainly of nickel, and including at least one type of reducing agent; an alloy layer placed on the base or as a surface layer of the base and including at least one metal selected from the group consisting of tungsten, molybdenum and tantalum and nickel; and a layer of electron-emitting material formed on the alloy layer, and including an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide of 0.01 to 25 weight percent.

2. The electron tube cathode according to claim 1, characterized in that the concentration of at least one metal selected from the group consisting of tungsten, moiibdene and tantalum in such alloy layer is greater towards the electron emitting material layer. .

3. The electronic tube cathode according to claim 1 or 2, characterized in that the alloy layer is formed of grains, and the grains are smaller than the grains forming the base.

4. The cathode of electronic tube, according to any of claims 1 to 3, characterized in that the thickness of the alloy layer is not less than 1 μm.

5. An electron tube cathode, characterized in that it comprises: a base formed mainly of nickel, and including at least one type of reducing agent; a film disposed on at least part of the surface of the base, and including at least one metal selected from a group consisting of tungsten, molybdenum and tantalum; and a layer of electron-emitting material formed on the film and including an alkaline earth metal oxide containing at least barium, and a rare earth metal oxide of 0.01 to 25 weight percent.

6. The cathode of electronic tube according to claim 5, characterized in that the film comprises a film of mixture placed on the base and) which includes at least one metal selected from the group consisting of tungsten, molybdenum and tantalum, as well as nickel, or a multiple layer film including one or more films of individual material of such or at least one metal, and a single nickel material film.

7. The electronic tube cathode according to claim 5, characterized in that the film is formed substantially in the center of the base and covers from 12 to 80% of the surface area of the base.

8. The cathode of electronic tube according to claim 5 or 7, characterized in that the film comprises a metal layer; and the thickness of the metal layer is 0.1 to 1.8 μm.

9. The cathode of electronic tube, characterized in that it comprises: a base formed mainly of nickel, and including at least one type of reducing agent; an alloy layer placed on the base or as a surface layer of the base and including at least one metal selected from a group consisting of tungsten, molybdenum and tantalum, as well as nickel; the concentration of at least one metal selected from the group consisting of tungsten, molybdenum and tantalum in such alloy layer, is greater towards the electron emitting material layer; and a layer of electron-emitting material formed on the alloy layer and including at least one oxide selected from a group consisting of those of aluminum, titanium, silicon, magnesium, chromium, zirconium, hafnium, indium, and tin from 0.01 to 20 percent by weight.