JP2718389B2 - Cathode for electron tube - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode for an electron tube used for a cathode ray tube for a TV, and more particularly to an improvement in an electron emitting material layer. This application is based on Japanese Patent Application No. 2-4.
This is a divisional application whose original application is No. 088884 (filing date: December 28, 1990). Japanese Patent Application No. 2-408888 is a Japanese Patent Application No. 60-160851 (filing date: July 19, 1985).
This is a divisional application whose original application is). 2. Description of the Related Art FIG. 2 shows a cathode used in a conventional cathode ray tube or image pickup tube for TV.
Is a bottomed cylindrical base composed mainly of nickel containing a trace amount of a reducing element such as silicon (Si) and magnesium (Mg), and 2 is coated on the bottom upper surface of the base and contains at least barium (Ba). , And strontium (Sr)
And / or an electron emitting material layer 3 made of an alkaline earth metal oxide containing calcium (Ca), and a heater 3 disposed in the base 1 to emit thermoelectrons from the electron emitting material layer 2 by heating. It is to make it. In the thus configured cathode for an electron tube, the deposition of the electron emitting material layer 2 on the substrate 1 is performed as follows. First, alkaline earth metals (Ba,
A suspension made of a carbonate of Sr, Ca) is applied to the substrate 1 and heated by the heater 3 during the evacuation step. At this time, the alkaline earth carbonate is converted to an alkaline earth metal oxide. After that, a part of the alkaline earth metal oxide is reduced and activated so as to have semiconducting properties, thereby covering the substrate 1 with the electron emitting material layer 2 composed of the alkaline earth metal oxide. It is something that is dressed. [0004] In this activation step, part of the alkaline earth metal oxide is reacted as follows.
In other words, reducing elements such as silicon and magnesium contained in the base 1 move to the interface between the alkaline earth metal oxide and the base 1 by diffusion and react with the alkaline earth metal oxide. For example, if barium oxide (BaO) is used as an alkaline earth oxide, it reacts as in the formulas (1) and (2). BaO + 1 / 2Si = Ba + 1 / 2SiO ₂ (1) BaO + Mg = Ba + MgO (2) As a result of this reaction, a part of the alkaline earth metal oxide formed on the substrate 1 is reduced. As a result, the semiconductor becomes an oxygen-deficient semiconductor, and electron emission of 0.5 to 0.8 A / cm ² can be obtained at an operating temperature of 700 to 800 ° C. at the cathode temperature. However, in the electron tube cathode formed in this manner, a current density of 0.5 to 0.8 A / cm ² or more in electron emission cannot be taken out. The reasons are as follows. That is, when a part of the alkaline earth metal oxide is subjected to a reduction reaction, SiO ₂ , MgO or BaO is formed at the interface between the substrate 1 and the alkaline earth metal oxide as is clear from the above formulas (1) and (2). A composite oxide layer (intermediate layer) of SiO ₂ is formed, and this intermediate layer acts as a high-resistance layer to obstruct the flow of electric current. It has been considered that the diffusion to the surface side of the substrate is prevented and sufficient barium (Ba) is not generated. A conventional cathode for an electron tube has the same structure as that shown in FIG. 2 described in Japanese Patent Application Laid-Open No. Sho 59-20941. In order to reduce the thickness, prevent the reducing agent from becoming turbid during its life, and prevent the strength of the substrate 1 from decreasing, lanthanum is added to the base 1.
In the figure, the components dispersed and contained in the form of aNi ₅ and La ₂ O ₃ are shown. In the cathode for an electron tube constructed as described above, the nickel crystal grain boundary near the interface between the substrate 1 and the electron-emitting material layer 2, particularly the surface near the surface of the substrate 1, is in operation. Since the above-mentioned intermediate layer segregates at a position about 10 μm inside the electron emitting material layer 2 from the above interface, current flow and diffusion of the reducing element to the surface side of the electron emitting material layer 2 are hindered. There is a problem that sufficient electron emission characteristics cannot be obtained. In the case of the latter, LaNi is used when producing the base 1 mainly composed of nickel.
₅ and La ₂ O ₃ , LaN
variations in the content status of i ₅ and LO ₂ O ₃ is was easy to occur. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned point, and it is an object of the present invention to concentrate an intermediate layer made of a complex oxide near an interface between a substrate and an electron emitting material layer under a high current density. It is an object of the present invention to obtain a cathode for an electron tube which prevents emission, has stable emission characteristics for a long time, and has high productivity and reliability. A cathode for an electron tube according to the present invention comprises, as a main component, an alkaline earth metal oxide containing at least barium, and contains 0.3 to 20% by weight of a rare earth metal oxide. The electron emitting material layer containing nickel is a main component and is formed on a substrate containing a reducing element. The cathode used for a television is used as the cathode for an electron tube. Furthermore, the cathode for an electron tube according to the present invention,
An electron emitting material layer containing 0.3 to 20% by weight of a rare earth metal oxide is formed on a substrate containing nickel as a main component and a reducing element containing at least one of silicon and magnesium. It is a thing. In the present invention, 0.3 to 20% by weight of the rare earth metal oxide contained in the electron emitting material layer is activated during the formation of the electron emitting material layer on the substrate. When the alkaline earth metal carbonate is decomposed, or when barium oxide undergoes a dissociation reaction during operation as a cathode, it prevents the base from oxidizing and is contained in the base in the electron emitting material layer. The diffusion of the reduced element is appropriately controlled to prevent the intermediate layer composed of the composite oxide of the reducing element from being formed intensively near the interface between the substrate and the electron emitting material layer, and It is to be dispersed in the emitting material layer. Embodiment 1 An embodiment of the present invention will be described below with reference to FIG. In the drawing, reference numeral 2 denotes an alkaline earth metal oxide 11 which is adhered to the bottom upper surface of the base 1 and contains at least barium, and additionally contains strontium and / or calcium, and is 0.1 to 20% by weight scandium oxide. , An electron emitting material layer containing a rare earth metal oxide 12 such as yttrium oxide. Next, a method of applying the electron emitting material layer 2 to the substrate 1 in the thus configured cathode for an electron tube will be described. First, barium, strontium and calcium ternary carbonate are mixed with scandium oxide powder. Alternatively, a desired weight% (weight% assuming that all of the ternary carbonate becomes an oxide) is added and mixed with the yttrium oxide powder to prepare a suspension. This suspension is applied by spraying to a thickness of about 80 microns on a substrate 1 mainly containing nickel,
Then, like the conventional one, through the decomposition process of carbonate to oxide and the activation process of reducing part of the oxide,
The electron-emitting material layer 2 is applied to the substrate 1. The rare earth metal oxide contained in the electron emissive material layer 2 to be deposited in such a way _{(Sc 2 0 3, Y 2} O
₃ ) Various cathodes for electron tubes with various contents were prepared.
Diode vacuum tubes were prepared using this cathode for electron tubes, life tests were performed at various current densities, and changes in the emission current were examined. The results shown in FIGS. 3 and 4 were obtained. FIG. 3 shows electrons containing 5% by weight of Sc ₂ O ₃ when operated at 3.1 times (2.05 A / cm ² ) the current density of 0.66 A / cm ² as a conventional cathode for television. Lifetime characteristics of an electron tube cathode having an emissive material layer 2 and an electron tube cathode having an electron emissive material layer 2 containing 12% by weight of Y ₂ O _{3 and} electron emission containing no rare earth metal oxide 7 shows a relationship with a conventional life characteristic having a material layer 2. As is clear from FIG. 3, the embodiment of the present invention containing a rare earth metal oxide has less emission degradation at high current density operation than the conventional one. FIG. 4 shows a rare earth metal oxide Sc
₂ 0 ₃ and Y ₂ O ₃ electron emitting substance layer 2 current density 0.66 in the electron tube cathode for having the addition ratio variously changed were the
A / cm ² (1), current density doubled, 3.1
The relationship between the current density and the ratio of the emission current at 6000 hours to the initial emission current was shown by performing a life test under the conditions of 2 times and 4 times. As can be seen from FIG. 4, the rare earth metal oxides Sc ₂ O ₃ , Y
_When the addition ratio of ₂ O ₃ is 0.1% by weight or more, there is an effect of preventing the emission from lowering under high current density operation.
This effect becomes significant when the content is 0.3% by weight or more. Although not shown, this effect was confirmed up to an addition rate of Sc ₂ O ₃ and Y ₂ O ₃ of 20 wt%. Next, the addition ratio of Sc ₂ O ₃ , a rare earth metal oxide, was set to 0.1, 1, ₅ , 10, ₂
Electron emitting material layer 2 changed to six kinds of 0 and 25% by weight
Were assembled into TV cathode-ray tubes, and after a predetermined process, TV cathode-ray tubes were prepared. FIG. 5 is a graph showing the measurement results of the initial electron emission current characteristics. The vertical axis represents the maximum cathode current, and the horizontal axis represents the addition ratio of scandium oxide. As is apparent from FIG. 5, when the addition ratio of scandium oxide exceeds 20 wt%, the initial electron emission current decreases significantly. That is, when the addition ratio of Sc ₂ 0 ₃ and Y ₂ O ₃ is these rare earth metal oxides exceeds 20 wt%, stable removal of not performed newly extended aging when Emitsushiyon current after a manufacturing process Was difficult and not practical. Therefore, the content of the rare earth metal oxide in the electron emitting material layer 2 needs to be in the range of 0.1 to 20% by weight. In particular, the above effect was remarkable in the range of 0.3 to 15% by weight. In order to investigate the effect of the rare earth metal oxide contained in the electron emitting material layer 2 in detail, after measuring the emission current for 6000 hours in the experimental results of FIG. The cross section of the cathode for an electron tube having the electron emitting material layer 2 containing Sc ₂ O ₃ was analyzed by an electron beam X-ray microanalyzer (EPMA), and as a result, the results shown in FIGS. 6 and 7 were obtained. FIG. 6 shows the experimental results of a conventional cathode for an electron tube having the electron emitting material layer 2 containing no rare earth metal oxide. As is clear from FIG. Si and Mg, which are reducing agents contained in the substrate 1, are segregated near the interface with the emissive material layer 2, and this segregation state is closer to the substrate 1 than the interface between the substrate 1 and the electron emissive material layer 2. An electron emissive material layer 2 at a depth of about 5 μm and from the interface
The peaks of the reducing agents Si and Mg were simultaneously observed at a position of about 3 to 5 μm from Si, and the maximum peak of Si was observed at a position of about 13 μm from the above interface to the electron emitting material layer 2 side. Although not shown, the presence of a Ba peak was also confirmed at the same position as the Mg and Si peaks in the electron emitting material. Since the peaks of Si, Mg and Ba almost coincide with the peaks of oxygen, it is considered that these metals exist as oxides or composite oxides. Further, the presence of a small amount of Si in the substrate 1 was confirmed. Thus, in the conventional product operated at a high current density,
In the vicinity of the interface between the substrate 1 and the electron-emitting material layer 2, SiO ₂ , MgO and their composite oxide layers are formed at the crystal grain boundaries in the substrate 1.
It can be seen that a composite oxide layer of BaO, MgO, and SiO ₂ is formed at the position. Si mentioned above
The O ₂ · MgO layer and the BaO · SiO ₂ layer suppress the diffusion speed of Si and Mg, which are reducing agents, from the inside of the substrate 1 into the electron emitting material layer 2 and, because of high insulation, inhibit the flow of current. Eventually, it will cause wear due to dielectric breakdown in the electron emitting material. [0020] In contrast, in the electron tube cathode for having an electron emissive material layer 2 containing the Sc ₂ 0 ₃ is a rare earth metal oxide is present embodiment, the substrate as shown the experimental results in FIG. 7 1, the reducing agents contained in Si, M
g are dispersed on average, and the peaks of these reducing agents do not exist at all near the interface between the substrate 1 and the electron emitting material layer 2 as in the conventional example shown in FIG. . This is considered to be due to the following reasons. That is, when the alkaline earth metal carbonate is decomposed into an oxide at the time of activation, or when BaO is used during operation of the electron tube cathode.
It is considered that the rare earth metal oxide prevents oxidation of the base 1 when such a case causes a dissociation reaction. For example, it is considered that the rare earth metal oxide prevents oxidation of the substrate 1. For example,
Reaction when the rare earth metal oxide is scandium oxide (Sc ₂ 0 ₃₎ is made of a manner of the following formula (4) (6). Embedded image Accordingly, as is apparent from the above formulas (3) and (5), in the electron tube cathode having the electron emitting material layer 2 containing no rare earth metal oxide, the base 1 and the electron are already in the early stage of the life. Nickel oxide formed at the interface with the radioactive material layer 2 and Si and Mg as reducing agents in the base 1
Reacts to form SiO ₂ .MgO ₂ in the outermost layer at the interface and in the grain boundaries in the vicinity thereof. Therefore, the diffusion of the reducing agents Si and Mg into the electron emitting material layer 2 is limited by the SiO ₂ .MgO oxide layer, and
The second site (location) is formed near the oxide layer. Therefore, particularly when operating at a high current density, the reactions (1) and (2) are vigorously carried out, and the oxide SiO ₂ .MgO due to the reducing agent is generated in a concentrated manner in the vicinity of the oxide layer. As the reactions of (1) and (2) proceed, the diffusion of the reducing elements Si and Mg into the electron-emitting material is further suppressed, and the emission is significantly reduced. On the other hand, in the cathode for an electron tube having the electron emitting material layer 2 containing the rare earth metal oxide according to the embodiment of the present invention, the rare earth metal oxide in the electron emitting material layer 2 is made of nickel of the base 1. Since the oxidation reaction is prevented, the reducing elements Si and Mg do not form an oxide layer at or near the crystal grain boundaries in the base 1, but easily diffuse into the electron emitting material layer, and (1) (2) The reaction site (2) is formed at the grain boundary in the electron emitting material layer 2, and the reaction site is located at a more dispersed place than in the conventional example. Further, since the rare earth metal oxide in the electron emitting material layer 2 moderately controls the diffusion of the reducing element into the electron emitting material layer, it is stable and good even after operation under a high current density for a long time. High emission characteristics can be maintained. Therefore, the addition of less than 0.1% by weight of the rare earth metal oxide is insufficient in the effect of suppressing the formation of the SiO ₂ .MgO oxide layer in the vicinity of the grain boundary of the substrate 1, resulting in a decrease in emission characteristics. start. When the rare earth metal oxide is added in an amount of 0.3% by weight or more, the effect of maintaining good emission characteristics becomes remarkable. On the other hand, if it is added in an amount of more than 20% by weight, the function of suppressing the diffusion of the reducing element in the electron-emitting substance becomes large, and long-term aging is required for stable extraction of the emission current. When the rare earth metal oxide is added in the range of 0.1 to 20% by weight, a solid solution phenomenon of the rare earth metal in the substrate 1 is confirmed, and after operating for 6000 hours (current density of 2.05 A). / Cm ² ), there was no peeling phenomenon of the electron emitting material layer 2 from the substrate 1. Incidentally, the occurrence frequency of the peeling phenomenon in the conventional cathode for an electron tube having the electron emitting material layer 2 containing no rare earth metal oxide was 30%. [0028] In the above embodiment, although there have been described what with Sc ₂ 0 ₃ and Y ₂ O ₃ as the rare earth metal oxides obtained a similar effect in other rare earth metal oxides, in particular the effect was pronounced in _{sc 2 0 3, Y 2 O} 3, Ce 2 0 3. As described above, according to the present invention, the cathode can be manufactured under substantially the same manufacturing conditions as the conventional one, and the dispersion state of the rare earth metal oxide can be relatively easily controlled. As described above, the present invention provides an electron-emitting material layer mainly composed of an alkaline earth metal oxide containing at least barium, which is adhered to a substrate containing a reducing element. Contains 0.3 to 20% by weight of a rare earth metal oxide, so that the rare earth metal oxide is 2 to 4 times as large as the conventional one in which the rare earth metal oxide is not contained in the electron emitting material layer.
That is, 1.32 A / cm ² (= 0.66 × 2) to 2.64
It has a long life under an operation of a high current density of A / cm ² (= 0.66 × 4), and has the effect of obtaining an inexpensive and highly reliable electron tube cathode with few restrictions on production. . Further, when used as a cathode for a television, since it can be used at the same operating temperature as a conventional oxide cathode, there is no new influence on thermal deformation of a cathode component in a cathode ray tube for a TV.
Therefore, a highly reliable cathode can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a conventional cathode for an electron tube. FIG. 3 is a characteristic diagram showing a relationship between a life test time and an emission current. FIG. 4 is a characteristic diagram showing a relationship between a current density and an emission current ratio. 5 is a characteristic diagram showing the relationship between the oxide scandium c arm content and maximum cathode current. FIG. 6 is a characteristic diagram showing a result obtained by measuring a cross section of the semiconductor laser shown in FIG. 2 after an emission current measurement for 6000 hours by EPMA. FIG. 7 is a characteristic diagram showing the result of measurement of FIG. 1 in the same manner as in FIG. [Description of Signs] 1 Base 2 Electron emitting material layer

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kinjiro Sano               1 Baba Zujo, Nagaokakyo-shi, Kyoto Mitsubishi Electric               Kiki Co., Ltd. in Kyoto Works (72) Inventor Tomoichi Kamada               1 Baba Zujo, Nagaokakyo-shi, Kyoto Mitsubishi Electric               Kiki Co., Ltd. in Kyoto Works                (56) References JP-A-56-45542 (JP, A)                 JP-A-49-12758 (JP, A)                 JP-B 64-5417 (JP, B2)                 Tokiko Hei 7-75140 (JP, B2)                 US Patent 1794298 (US, A)

Claims (1)

(57) [Claims] Electron emission containing, as a main component, an alkaline earth metal oxide containing at least barium on a substrate containing a reducing element and containing 0.3 to 20% by weight of a rare earth metal oxide. A cathode for an electron tube, wherein a material layer is formed by deposition. 2. The electron emitting material layer is 1.32 A / cm ^{2 to} 2.64 A
The cathode for an electron tube according to claim 1, wherein the cathode is used for a television cathode operated under a current density in the range of / cm ² . 3. If the reducing element is low in silicon or magnesium
The cathode for an electron tube according to claim 1, wherein at least one of the cathodes is included.