JPS61253736A - Method for manufacturing lanthanum hexaboride thin film cathode - Google Patents

Abstract

PURPOSE:To facilitate, for example, low voltage pulse activation in gas discharge display, by forming a coat having strong tolerance to ion impact with a comparably simple low work-load method of vapor-depositing hexaboric lantern under vacuum from its material on a heated substrate. CONSTITUTION:A hexaboric lantern (LaB6) thin coat partly containing amorphous LaB6 layer is formed with LaB6 material on a substrate heated from a room temperature up to 500 deg.C by the electron beam impact vapor-deposit method. In this process, a metal easy to react with boric compounds can be employed as the substrate, since the substrate temperature is low. A high quality coat containing less oxide film or impurities can be formed by employing LaB6 crystal body grown from sintered body as a material, and amorphous phase LaB6 can be included in LaB6 by letting the substrate temperature lower than 500 deg.C. Therefore, not only obtaining mechanical improvement of a vapor- deposited coat, but also this method allows to employ low cost substrates from soda glass series.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention uses lanthanum hexaboride (LaBs), which is known to have excellent electron emission properties, as a bulk material.
) The present invention relates to a method for manufacturing an electron-emitting cathode using a thin film.

[Background of the Invention] Conventionally, the LaB thin film used for the cathode has been required to be single-phase in terms of X-ray diffraction. Therefore, thin films of LaB can be formed by plasma spraying LaB powder in an inert gas stream (Television Society Technical Report FD-572, 1981), or by thick film printing method using LaB powder together with organic solvents. (Japanese Patent Laid-Open No. 55-62647) or when depositing by electron beam impact evaporation, the substrate temperature is raised to a high temperature of 500"C or higher.

This required a technology to form a crystalline film (Japanese Patent Publication No. 56-17780).

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to deposit a film with low work and high ion bombardment resistance on a substrate by a relatively simple method, thereby facilitating low-voltage driving of, for example, gas discharge display pulses.

[Summary of the invention]

Lanthanum hexaboride (LaB) has a conductivity of 8X at room temperature.
Since it has a good value of 10-"Ω1 and a low work function of 2.6 eV, it has already been used as a high-brightness electron beam source material for the hot cathodes of various electron microscopes. L a B containing a part of the amorphous layer was formed by electron beam impact evaporation at a temperature between room temperature and 500°C.
, to form a thin film. Furthermore, in the case of the present invention, since the substrate temperature is low, there is an advantage that metals that easily react with boride can also be used for the substrate.

[Embodiments of the invention]

The effects of the present invention will be explained below using five examples.

Example 1 A thin film of LaB was prepared by electron beam impact evaporation. First, when commercially available LaB and a sintered body (density about 90%) were used as raw materials, the gas contained in the sintered body raw material was released as it was heated, and the vacuum during vapor deposition ranged from 10-'' Torr to 1.
The pressure decreased to 0-4 Torr, and a transparent oxide was formed in the deposited film. It was also found that impurities in the raw material for the sintered body are likely to be mixed into the deposited film. This is because the melting point of ordinary impurities is lower than that of LaB (2700° C.), so they evaporate preferentially. On the other hand, when a sintered body raw material is zone-melted using an infrared heating device and a single crystal with a 100> orientation is used as a deposition raw material, a high-quality film is produced without gas generation or impurity release from the raw material. Table 1 shows the concentration of impurities contained in the raw material and the deposited film when vapor deposition was performed using a sintered body and a grown crystal as the vapor deposition raw material using emission spectrometry (unit: ppm). The results are shown below.The advantage of using a crystalline material as a vapor deposition raw material is clear.

Example 2 A LaB thin film was prepared by electron beam impact evaporation using a <100> oriented LaB1+ single crystal as a deposition raw material. Table 2 uses a fused quartz plate as the substrate, and the substrate temperature is room temperature and 20℃.
0℃, 400℃, 500℃.

These are the results of examining the structure of a LaB thin film with a thickness of approximately 1 μm obtained by changing the temperature to 700° C. using an X-ray diffraction method. In order to obtain a single phase of LaB in X-ray diffraction, it is necessary to raise the substrate temperature to 500° C. or higher. However, when considering the practical application of LaB and thin films, such as gas discharge display panels, it is economically impossible to use a fused silica plate as the base substrate because it is too expensive. Soda glass type must be used. From this point of view, a mixed film of LaB and amorphous was deposited to a thickness of approximately 1 μm on soda glass at a substrate temperature of 500'C or lower. As a result, the mechanical strength of the deposited film was unexpectedly high, probably because it was a mixture of LaB and amorphous materials. In addition, by overlapping a mask with a predetermined shape on the substrate during vapor deposition, a pitch of 0.2 wm and a line width of 0.
A large number of cathode rays with a length of about 1 m can be obtained. on the other hand,
A large number of N1 anode wires with a pitch of 0.2''I and a line width of 0.03 mm were formed on transparent soda glass by a thick film printing method. A vacuum space was formed in which cathode rays and anode rays were perpendicular to each other and faced each other, and Ne-Ar (0.4%) gas was introduced into the space to investigate the effect on the discharge sustaining voltage. The experimental results are shown in Figure 1. For comparison, the conventional Ni cathode-N
In the case of i anode, 1 is also shown.

It can be seen that in the case of LaB cathode 2, the discharge sustaining voltage is lowered by nearly 100 V than in the case of Ni cathode, and the fluctuation with respect to gas partial pressure changes is also small. Further, in the case of the present invention, the change in discharge current when operated at a constant voltage was 175 or less compared to the conventional Ni thick film cathode. This shows that the low work function and high ion bombardment resistance of L a B can be well exhibited even if the deposited film contains a portion of the amorphous phase.

Example 3 In the gas discharge display panel described in Example 2, the conventional N
i A powder cathode was coated with a thin film of LaB containing an amorphous phase of the present invention, and the discharge sustaining voltage was measured. As a result, performance exactly the same as in the case of FIG. 1 was obtained.

〔Effect of the invention〕

As clarified by the above examples, according to the present invention, by preferably using L a B a crystal grown from a sintered body as a raw material, a high quality film with less oxide film and impurities can be formed. , and by lowering the substrate temperature to 500°C or less, an amorphous phase can be mixed in the LaB phase, and in addition to mechanically improving the deposited film, an inexpensive soda glass system can also be used for the substrate. Therefore, its industrial value is extremely high when applied to gas discharge display panels.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between discharge sustaining voltage and gas pressure in a gas discharge display panel. 1...Relationship between discharge sustaining voltage and gas pressure of Ni cathode-Ni anode, 2...Relationship between discharge sustaining voltage and gas pressure of L a B, cathode-Ni anode.

Claims (1)

[Claims] 1. Using lanthanum hexaboride as a raw material, heating the substrate in the range from room temperature to 500°C, and depositing lanthanum hexaboride in a vacuum of 10^-^4 Torr or less by electron beam impact evaporation. A method for producing a lanthanum hexaboride thin film cathode.