JPS6394530A - Filamentary hot cathode - Google Patents

Abstract

PURPOSE:To increase initial emission current and eliminate a drop of emission current after long operation by providing a specific electron emitting substance including a rare earth metal oxide on a heat resistant metal. CONSTITUTION:Electron emitting substance consisting of a mixture of 0.2-20 weight percent of a rare earth metal oxide and a remaining part, an alkaline earth metal oxide including at least barium oxide, is provided on a kind of heat resistant metal of which main component is selected from tungsten, molybdenum or tantalum. A part of the rare earth metal oxide in the electron emitting substance reacts with the heat resistant metal generating excess Ba as a result, so that the electron emitting substance is fully activated. Accordingly, initial emission current is increased and a drop of emission current after long operation is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a linear hot cathode used in vacuum tubes, CRTs, fluorescent display tubes, etc.

[Conventional technology]

FIG. 2 is a sectional view showing a conventional flat panel display device disclosed in, for example, Japanese Patent Laid-Open No. 60-84744, in which hot cathodes are arranged in a matrix and electrons are emitted by heating with electricity. In the figure, (1) is an insulating substrate made of a glass plate, a ceramic plate, etc., and (2) is a locking part provided on this substrate (1) for locking the cathode wire (3). It consists of protrusions or ribs, and its material is usually metal. The cathode wire (3) is a heat-resistant metal wire such as a tungsten wire with a diameter of about 10 μm, and a cathode (4b) holding an oxide electron emitting substance is formed on the surface of the wire. Above the cathode wire (3), there is provided a grid electrode (7) in which a through hole (8) is provided corresponding to each cathode (4b), and above this grid electrode (7), each cathode is further provided. An anode coated with phosphor (9) is provided at a position corresponding to (4b).

Next, the operation will be explained. When power is supplied from a power source (not shown) to both ends of the cathode wire (3) and heated to approximately 700°C, electron emission is obtained from the surface of the cathode (4b), and positive radiation is generated in the grid Wj (7) and the anode cry. By applying the electrode, the electron beam excites the phosphor (9) and reaches the anode α■.The control 1FIl electrode (6) is an electrode for controlling the emission of the electron beam, and is usually a negative Electron emission from the cathode can be stopped by applying a voltage of . Therefore, by applying a positive pulse electrode to the control electrode (6), emission of the electron beam can be controlled.

Here, ternary carbonate of barium, strontium, and calcium [(Ba, S rp Ca) COJ is added to the 1ljE electrode (4b) by electrodeposition or coating on the surface of the cathode wire (3) made of tungsten wire. ) is retained and thermally decomposed in the step of evacuating the inside of the display device container, and the carbonate is converted into oxides [(Ba, Sr, Ca)
Can be changed to O.J. Then, the tungsten of the cathode wire (3) converts into BaoItil and generates excess Ba on the metal, and this excess Ba forms a so-called n-type semiconductor structure.
It lowers the work function of the cathode (4b) surface and contributes to emission p.

[Problem that the invention seeks to solve]

Conventional linear hot cathodes suffer from a large drop in emissions due to the influence of impure gases. There were problems such as a low initial emission current due to the release of impurity gas, and a large amount of Ba consumed after long-term operation, resulting in a large drop in the emission current.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a linear hot cathode which has a high initial emission current and which exhibits a small drop in emission current after long-term operation.

[Means for solving problems]

The linear hot cathode according to this invention has zero
．． It holds an electron emitting material consisting of a mixture of 2 to 20% by weight of a rare earth metal oxide and the balance being a mixture of an alkaline earth metal oxide containing at least barium oxide.

[Effect]

The linear hot cathode of this invention has a high initial emission current because the rare earth metal oxide in the electron emitting material sufficiently activates the electron emitting material, and has the effect of suppressing the action of impurities on the cathode surface. , the emission drop after long-term operation is reduced.

〔Example〕

FIG. 1 is an enlarged view showing the main parts of a display device using a linear hot cathode according to an embodiment of the present invention. In this embodiment, the structure other than the cathode (4a) is the same as the conventional one shown in FIG.

First, electrodeposition solutions with various 5c2 (CO3) contents were prepared, and based on the same electrodeposition method as before, each electrodeposition solution was prepared with an electron-emitting material layer at the same thickness (8μ) as before. Cathode (4
&) and heated in the exhaust process of the display device to form (Ba, S r, Ca)GO, -3c,
Display devices having various cathodes (4a) in which (C03)3 was replaced with (Ba, Sr, Ca)O-3c, OJ were created.

The pulse emission current value was measured when the filament Ti flow was kept constant during the 2-hour operating time of this display device, and the results are shown in FIG.

In this figure, the horizontal axis is B a O-S r O-Ca
It shows the mixing ratio (wt%) of ScUO in O-8C10J, and the vertical axis shows the pulse emission current value of the conventional product at 100%.
The relative current value when As is clear from the figure, when the S c and OJ combined ratio is 0.2% by weight or more, the emission current tends to increase significantly, and especially when the mixture ratio is 1% or more, a high emission current is obtained. Incidentally, if the above-mentioned mixing ratio exceeds 20% by weight, the electron emitting substance will be desorbed from the cathode wire (3), which poses a practical problem.

Next, based on the present invention, a cathode containing an electron emitting material containing 0.5% by weight of Sc and a conventional cathode (Ba, Sr).

Two types of display devices were created, each having a cathode holding an electron-emitting substance made of Ca)O. All conditions were the same except for the cathode. The phosphor layer contains a phosphor for low-speed electron beams (Zn
O: Zn) was used, and the pattern had a diameter of 4. A pattern with several Omm circular patterns was used.

Regarding the two types, the conventional product and the example, the filament voltage,
The brightness of the phosphor layer was measured by lighting five lamps each under the same anode voltage and grid voltage conditions, and the relative value of the average value (the average brightness of the conventional product for 2 hours of operation was 100
) is plotted in Figure 4. In addition, in parallel with the brightness measurement, the pulse emission current value was measured at each operating time under the same conditions as the pulse emission current shown in Figure 3, and the relative value of the average value (compared to the conventional product for 2 hours of operation) was measured. The average brightness was set as 100) and was also plotted in FIG. The initial brightness of the above example after two hours of operation was 18% higher than that of the conventional product. As is clear from this figure, the example has excellent characteristics in both brightness and emission current over a long period of 1000 hours from the initial stage of operation. In particular, compared to the conventional product, which exhibits large reductions in brightness and pulse emission current after 100 hours of operation, the effects of the embodiment are remarkable. When the phosphor layer was analyzed using an X-ray microanalyzer after 1000 hours of operation, a larger amount of Ba was detected in the conventional product compared to the example, so the immersion characteristics of the example reflect the presence of Ba during operation. This is probably due to less wear and tear. In this way, since the initial brightness is high (and the residual brightness after operation is also high), the display device can be used even in bright places.

Although the cause of such remarkable effects of the present invention is not clear, it is thought to be as follows.

In the conventional cathode, Ba reduced by the reaction with tungsten of the cathode wire (3) moves to the cathode surface by diffusion or the like and is adsorbed on the surfaces of Bad, SrO, and CaO, reducing the work function of the surface. On the other hand, in the cathode according to the present invention, Ba adsorbed on 5020.3 is considered to have the effect of increasing emissions for some reason and the effect of suppressing Ba consumption during operation.

Although the effects of the present invention have been explained using Sc03 as an example, the above effects can also be obtained with rare earth metal oxides other than Sc00J.

Further, the cotton-like heat-resistant metal is not limited to tungsten, and similar effects can be obtained even when the main component is Mo, Ta, Pt, etc. The shape of the cathode is not limited to the linear shape as in the embodiment, but any linear cathode shape such as a plate shape, a coil shape, a spiral shape, etc. can achieve the above-mentioned effects. It is clear that the above effects contribute to higher performance of fluorescent display tubes, CRTs using linear hot cathodes, electronic telescopes, and fluorescent lamps. In addition, when increasing the current value flowing through the cathode wire (3) to achieve high brightness, it has a particularly remarkable effect on improving life characteristics.

〔Effect of the invention〕

As explained above, the cathode of the present invention has a large initial emission current and is excellent in maintaining the emission current during operation, so it is effective in realizing higher brightness of display devices and higher performance of electron tube devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a display device implementing the present invention;
Fig. 2 is a cross-sectional view showing a conventional display device, Fig. 3 is a characteristic diagram showing the relationship between the mixing ratio of ScU03 and pulse emission current, and Fig. 4 is an operating time, brightness, and pulse emission current of the display device. FIG. (1) is an insulating substrate, (2) is a cathode wire, (4&)
is a cathode, (9) is a phosphor layer, and QO) is an anode. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] It is characterized by holding an electron-emitting material consisting of a mixture of 0.2 to 20% by weight of rare earth metal oxide and alkaline earth metal oxide containing at least barium oxide on the surface of the linear heat-resistant metal. linear hot cathode.