JPH04286825A - Thermoelectron emitting element - Google Patents

Abstract

PURPOSE:To make a thermoelectron emission section extremely small into a simple structure by laminating a heater to heat the thermoelectron emission section, and providing a thin film thereon to form the thermoelectron emission section. CONSTITUTION:When voltage is applied to a copper supporting layer 2 on both sides of each filament 6, the center Ta filament layer 6 is heated. Radiation heat is generated to heat an upper Ta electron emission board 7 and a W base metal 8 as well as a low work function material 9. At this time, the low work function material, (Ba, Sr, Ca) Co3 is activated by heat and formed into oxide. The W base metal 8 reduces the oxide of the material 9 to cover the surface of the emission section 7 with Ba, Sr, Ca, lower at a work function valve than that of position shown by W. As a result, electrons are easily emitted from the electron emission section 7. In such a structure, with the emission section 7 continuously put over thin film heaters and separated therefrom in space, the emission section 7 is arranged at fine precise picthes to eliminate the need for alignment to the heaters bacause the emission section 7 is a continuous thin plate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermionic emission device, and more particularly to a thermionic emission device having a structure in which a heater for heating a thermionic emission material is made into a thin film.

0002

2. Description of the Related Art Conventionally, a structure as shown in FIG. 6 is typical of a thermionic emitting device that heats a thermionic material through space. To explain this structure in order, there is a cup 62 on the inside upper part of a sleeve 61 with a diameter of 1 to 2 mm, a thermionic emission material 63 is provided in this,
It consists of a porous substrate 64 and an impregnating agent 65. A heater 66 for heating the cup 62 is placed below the cup 62 with a space therebetween. The general materials of these components are Ta for the sleeve 61, Ta for the cup 62, W sintered body for the porous base 64, and B for the impregnating agent 65.
aO, Al2O3, CaO, and the heater 66 is coated with alumina.

A thermionic emission device having such a structure is called an impregnated cathode and is classified as a thermionic source. In operation of such a thermionic source, electric power is first supplied from the outside to the impregnated cathode heater 66 placed in a vacuum. By heating the heater 66, the thermionic emission material 63 in the cup 62 is heated, and the impregnating agent 65 therein is reduced by the W porous substrate 64, reaches the surface, and covers the surface. It is thought that the thermionic electrons excited by the heating of the heater 66 have energy higher than the work function value of the impregnating agent 65 and emit electrons by jumping out from the surface of the thermionic emission material 63 into the vacuum. . The above are examples of conventional thermionic emission devices.

On the other hand, in recent years, there has been active research into arranging multiple electron sources on a plane and applying them to lithography apparatuses as multi-electron beams, and research into electron sources for flat displays. These multi-electron beams generally require a pitch for arranging electron sources of several hundred micrometers or less.

However, when trying to apply the electron-emitting device shown in the conventional example to the above-mentioned requirements, there were the following drawbacks. ■． Because the element size is large, φ1 mm to φ2 mm,
It is not possible to reduce the pitch of the emitting parts even if they are arranged in a multi-layered manner. ■． Because the elements are independent, mechanical alignment is required when trying to arrange them in multiple places on a plane, and when the number is large (for example, 500 x 1,500 elements)
, high precision alignment is very difficult. ■． Because the emission part is large, if you try to narrow down the emission spot, you have to place an electron optical lens above it.

[0006]

Problems to be Solved by the Invention In view of the problems of the prior art described above, the objects of the present invention are: (1). ■.Multi-array of thermionic sources is possible. It is an object of the present invention to provide a thermionic emission device that can improve the precision of positioning and the like by applying thin film manufacturing technology.

[0007]

[Means and operations for solving the problem] The above problem is solved by providing a thermionic emission device having the following configuration. and the heater section is constituted by a thin film heater formed by a thin film process, secondly,
This is achieved by a thermionic emission element in which two or more thin film heaters are arranged on a plane with a spatial interval between them for a continuous thermionic emission part.

That is, the present invention provides a method for forming a portion corresponding to a heater of a thermionic emission device by a film forming method used in IC manufacturing, etc.
By using thin film heaters made into thin films using photolithography and etching technology, it is possible to provide a plurality of thin film heaters on a plane at a narrow pitch (for example, 300 μm).

[0009] By providing a thermionic emission section above such a thin film heater with a space in between, it is possible to fabricate a thermionic emission element in a thin shape and with high density.

0010

[Examples] The present invention will be specifically explained below with reference to Examples.

Embodiment 1 FIG. 1 is an embodiment that best expresses the features of the present invention. In the figure, 1 is a substrate of a thin film filament section, and 2 is a filament support supporting the thin film filament. Layer 3 is a filament layer having a thin film filament 6, 4 is a first electron-emitting part support layer, and 5 is a second electron-emitting part support layer. Further, 7 is an electron emission part substrate, 8
9 is the base metal of the electron emitting portion, and 9 is the low work function material of the electron emitting portion. Hereinafter, 7, 8, and 9 will be collectively referred to as the electron emission part 1.
It is called 0.

In the configuration of this embodiment, the heater 66 in the conventional thermionic emission device corresponds to the thin film filament 6. Further, the first and second electron-emitting part support layers are
This corresponds to a spacer for separating the electron emitting section 10 from the filament 6 by a certain distance. Further, the electron emission part substrate 7,
The base metal 8 of the electron emitting portion and the low work function material 9 of the electron emitting portion correspond to the electron emitting portion including the cup 62 of the conventional example.

A method of manufacturing the heater section and electron emitting section support layer of this embodiment is shown in FIGS. 2 and 3, which show cross sections AA and BB in FIG. 1. As an example, a case where the pitch of a plurality of thermionic emission elements (thin film filaments) is set to 300 μm will be explained while showing dimensions suitable for this. First, as shown in FIG. 1, the element dimensions are L=200 μm, w=20 μm, t=2 μm, and the width of the filament layer 200 μm for the filament 6.

[0014] Furthermore, the method for manufacturing the thin film filament part is as follows:
As will be described below, a particular feature is that the first and second electron-emitting part support layers are integrally formed. The following description will be made according to the manufacturing process diagrams shown in FIGS. 2 and 3. First, as shown in FIGS. 2 and 3(a), on a thin film filament substrate, a Cu layer with a thickness of 8 μm was formed as the filament support layer 2, a Ta layer was formed with a thickness of 2 μm as the filament layer 3, and a first electron emitting portion was formed. A 2 μm thick Cu layer is formed as the support layer 4, and a 4 μm thick SiO2 layer is formed as the second electron emitting part support layer 5.

Next, a resist 11 having an electron-emitting part support layer pattern is formed (FIGS. 2 and 3(b)). For this example,
It becomes a circular pattern. Thereafter, using this resist as a mask, dry etching is performed to remove the SiO2 layer of the second electron-emitting part support layer 5 and the C of the first electron-emitting part support layer 4.
Etch the u layer halfway (FIGS. 2 and 3(c)).

Next, as shown in FIGS. 2 and 3(d), a resist 12 having a filament pattern is formed. In this example, the pattern is a filament layer 3 with filaments 6. Thereafter, using this resist as a mask, the remaining Cu layer of the first electron-emitting part support layer 4, the Ta layer of the filament layer 3, and the Cu layer of the filament support layer 2 are etched by dry etching (see FIGS. 2 and 3). e
)). Thereafter, the Cu layer of the filament support layer 2 is wet-etched to form a gap below the filament 6 (FIGS. 2 and 3(f)), thereby completing the hollow thin film filament portion and the electron emission portion support layer.

[0017] The dry etching method in the above manufacturing process is as follows:
This is possible by using the ion milling method. Also,
Wet etching of the filament support layer requires an etching solution such that the selection ratio of other materials to the material of the filament support layer is 1/n. A mixture of chloric acid and water is suitable.

[0018] In this way, it is possible to fabricate a plurality of thin film hollow filaments on the same substrate. Furthermore, the second electron-emitting part support layer 5 having the plurality of filaments
A thermionic emission device can be completed by placing a thin plate, which is the electron emitting portion 10, prepared in a separate process, on top of the structure. Note that the size of the thin plate serving as the electron emitting portion may be wide enough to cover all of the plurality of filaments on the substrate.

An example of the structure of the electron emitting section 10 is as follows. Tantalum (
Ta) Using a 50 μm thin plate, a 0.5 μm tungsten (W) thin film (e.g., vapor deposited film) is applied to the electron emission part base metal 8.
m, and a low work function material 9 (Ba, Sr
, Ca) CO3 ternary carbonates are provided.

The thermionic emission device thus produced emits electrons as follows. After the thermionic emission device having the above structure is used as a thermionic emission device, each filament 6 is
When a voltage is applied to the filament support layers 2 at both ends located at , the central filament is heated. Then,
The radiant heat heats the upper electron-emitting substrate 7, base metal 8, and low work function material 9. At this time, (Ba, Sr, Ca)CO3, which is a low work function material, is activated by heat and becomes an oxide. The base metal tungsten (W) reduces the oxide of the low work function material, and the surface of the electron emitting part is made of barium (Ba), strontium (Sr), which have a lower work function value than tungsten (W), etc. Covered by calcium (Ca). In this state, among the electrons in the electron emitting part excited by heating the filament, those having energy higher than the work function value of the material covering the surface are emitted into space. The above is an example of a thermionic emission element in which a plurality of thin film filaments (heaters) are arranged on a plane and are spatially spaced (separated) from the thermionic emission part.

As explained above, by spatially separating continuous electron emitting sections on a plurality of thin film heaters, (1). 2. The pitch of the electron emitting parts can be arranged with high precision, with a pitch of several hundred micrometers or less. Since the electron emitting section is a continuous thin plate, there are advantages such as no need for positioning with respect to each heater.

Embodiment 2 In this embodiment, the shape of the electron emission part substrate 7 of the electron emission part 10 is changed from a flat thin plate as shown in FIG. 1 to a thin plate with continuous waveforms as shown in FIG. It can also be made into a chevron-shaped thin plate as shown in FIG. 4(b).

In this way, by using a thin plate with unevenness for the electron-emitting part substrate, (1). Warping of the thin plate due to stress when the base metal 8 is deposited on the electron-emitting part substrate 7 is alleviated; (2). ■．The unevenness of the thin plate absorbs the thermal stress during filament heating and prevents the thin plate from deforming. This improves the mechanical strength of the thin plate, making it easier to handle during assembly.

Embodiment 3 In this embodiment, an electron-emitting substrate 7 with unevenness as shown in FIG. do. In this case, the structure of the filament part is as shown in FIG. 5 without the first electron-emitting part support layer 4 and the second electron-emitting part support layer 5 in FIG. 1.

With such a configuration, the electron emitting section needs to be aligned in the direction according to the pitch of both ends of the filament.
.

[0026]

Effects of the Invention As explained above, by making the heater that heats the thermionic emission part into a thin film and providing a thin film that becomes a continuous thermionic emission part thereon, (1). It is possible to provide a plurality of thermionic emission parts regularly on a plane at minute pitches of several hundred μm or less according to the pitch of the heater formed by a thin film process. ■． Since the thermionic emission section is provided with a continuous thin plate extending over a plurality of heaters, the structure is simple and no mechanical alignment is required. ■． Since the heater is made using a thin film process, several hundred
A heater with a size of ~ several μm can be manufactured, and the electron emission spot can be made small. There are other effects.

[Brief explanation of the drawing]

FIG. 1 shows a configuration diagram of a thermionic emission device embodying the present invention.

2 shows a manufacturing process diagram of a thin film filament section taken along the line AA in FIG. 1; FIG.

FIG. 3 shows a manufacturing process diagram of a thin film filament section taken along the line BB in FIG. 1;

FIG. 4 shows another embodiment of the electron emitting section.

FIG. 5 shows another embodiment of the invention.

FIG. 6 shows a configuration diagram of a conventional impregnated thermionic emission device.

[Explanation of symbols]

1 Board 2 Filament support layer 3 Filament layer 4 First electron emitting part support layer 5 Second electron emission part support layer 6 Filament 7　Electron emission part substrate 8 Base metal 9. Low work function material 10　Electron emission part 11 Resist 12 Resist 61 Sleeve 62 cups 63 Thermionic emission material 64 Porous substrate 65 Impregnating agent 66 Heater

Claims (2)

[Claims] Claim 1: There is a spatial interval between the thermionic emission part and the heater part that excites thermionic electrons, and the heater part is composed of a thin film heater formed by a thin film process. A thermionic emission device. 2. A thermionic emission device characterized in that two or more thin film heaters are arranged on a plane with a spatial interval in relation to a continuous thermionic emission part.