RU2486625C2 - Method to manufacture multi-tip field-emission cathodes - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: in order to form a periodic circuit from micro-tips at surface of monolithic carbon substrate the method of grouped micro-tipping in low-temperature plasma of HF charge in oxygen or in mix of oxygen and inert gas media is used as micro/nano-sized treatment.

EFFECT: increase of density for field-emission current due to formation of micro-tip carbon structure.

Description

The invention relates to a technology for manufacturing carbon multi-axis field emission cathodes used in vacuum electronic devices with efficient cold electron sources.

A technical solution is known [1], which describes the material and method of manufacturing a multi-tip cathode from a composite nanodiamond film material by deposition of a vapor of carbon-containing substances on a substrate in a nonequilibrium plasma of a microwave gas discharge. The technical solution EP 1361592 A1 (H01J 1/30, 12/12/2003) is also known, which presents a method for manufacturing an electron source consisting of a substrate and a composite made from a paste with carbon nanotubes. However, such structures in the above technical solutions have several disadvantages, namely: when using these structures it is impossible to achieve reproducibility of the geometric parameters of the microstructure, stability of emission properties, carbon films obtained from hydrocarbon vapors have low adhesion, therefore, they peel off from the substrate at operating electric field strengths . The proposed technical solution allows to eliminate all of the above disadvantages. This technical solution allows to increase the stability of field emission cathodes, to increase the durability and reliability of electrovacuum devices.

The objective of the invention is to obtain a monolithic, equally high, matrix microstructure with improved reproducibility of emission characteristics. The technical result is achieved by the fact that when performing the proposed sequence of technological processes, a monolithic carbon structure is created with a given height of micro-sized columns, which, in turn, are subjected to group micro-, nanoscale sharpening in a low-temperature plasma of an RF discharge in oxygen or in an oxygen-inert gas environment , and receive a periodic matrix of equal height tips of monolithic carbon.

Figure 1 - technological route of manufacturing a periodic multi-edge structure:

a - polishing the carbon surface to grade 14;

b - activation of the glassy carbon surface before applying the photoresist using low-temperature plasma;

c - applying a film of photoresist and carrying out the process of precision photolithography;

g - the formation of a photoresist mask on the surface of glassy carbon;

d - applying a film of transition metals to a surface not protected by photoresist;

e - thermochemical treatment of a carbon plate in a hydrogen medium and the formation of microprotrusions;

g - removal of metal film residues in a mixture of acids HCl, H ₂ SO ₄ ;

h - sharpening of carbon cylindrical microprotrusions in a low-temperature plasma of an RF discharge in oxygen or in an oxygen-inert gas environment;

figure 2 - elements of the profile of the microprotrusion to the plasma-chemical microzarrhea (a), after microzarrhea (b); figure 3 - microphotographs of the surface of the carbon microstructure before the plasma-chemical microzaostrination (a) and after microzaostrination (b).

The essence of the invention lies in the fact that for the manufacture of field-emission cathodes in the form of a periodic multi-tip structure on the surface of a carbon plate as a micro-, nanoscale treatment, a group micro-sharpening method is used in a low-temperature RF discharge plasma in oxygen or in a mixture of oxygen and inert gas media.

Cylindrical microprotrusions are formed by etching the surface of a carbon substrate with a transition metal film. Previously, the surface of the carbon plate is machined to prepare the surface and activate it before applying the mask from the photoresist (figa and 1b). The grinding process is carried out using fine micropowder, and then polished, where as a result of these treatments, the material is removed from the surface of the carbon plate 0.015 ÷ 0.03 mm (Fig. 1a). After that, the activation of the surface of the carbon plate is carried out before applying the photoresist using low-temperature plasma (figb). The application of photoresist on a carbon polished surface is carried out by centrifugation (pigv). In order to obtain circle-shaped bases periodically located on the surface from a photoresist, the processes of exposure and manifestation of the photoresist are carried out sequentially. The choice of a photomask depends on the requirements for the period of the resulting matrix microstructure and the base area of the cylindrical microprotrusion (Fig.1d).

A transition metal film is applied to the resulting photoresist pattern to further etch the metal film in the periodic bases of the carbon structure free of photoresist (Fig. 1e). As a result of etching, the intensive dissolution of carbon atoms in the metal film and the subsequent diffusion of carbon atoms through the structure of the metal film without the formation of a chemical compound on the surface and the interaction of carbon atoms with a gaseous medium (Fig. 1e) occur. Then, the remnants of the film of transition metals in the mixture of acids are removed (Fig.1g). In order to increase the electrostatic field strength at the vertices of the formed periodic carbon structure with a given height of micro-sized columns, this structure is subjected to group micro-, nanoscale sharpening in a low-temperature RF discharge plasma in oxygen or oxygen-inert gas media to produce carbon micropoints (Fig. 1z) .

Figure 2 presents the profile elements of the plasma-chemical sharpening of the protrusions.

Figure 2 introduced the following notation:

h is the height of the microprotrusion; s is the distance between the microprotrusions; d is the diameter of the base of the microprotrusion; α is the average angle at the apex of the conical microprotrusion; l is the lattice period of the microstructure.

On the top of a cylindrical microprotrusion, the surface is polished and therefore has a less developed microrelief, in contrast to the lateral surface of the microprotrusion. It is known [2] that surface irregularities increase the likelihood of interaction of surface carbon atoms with chemically active particles, since the bond energy of a group of carbon atoms on the surface weakens during a highly developed relief; therefore, it is expected that the component of the point velocity directed perpendicular to the surface will reach its maximum value on the circular boundaries of the flat end and lateral cylindrical surfaces of the protrusions.

The end of the process of plasma-chemical sharpening of the carbon microstructure is determined on the basis of changes in the properties of the polished surface of cylindrical microprotrusions.

The geometric conditions of the process of group plasma-chemical sharpening while maintaining a constant height of the protrusions are:

$$\alpha \le arctg\frac{0.5d}{h};\text{h}\approx \text{const; s}\approx \text{l / 2}\text{.}$$

The periodic carbon structure before and after the plasma-chemical microzarrhea is shown in FIG. 3.

Information sources

1. Patent RU 2309480 C2. Material and method for manufacturing a multi-edge field emission cathode (H01J 1/30, 02/10/2007).

2. Sheshin EP Surface structure and field emission properties of carbon materials - M .: MIPT, 2001, 287 p.

Claims (1)

A method of manufacturing field emission cathodes in the form of a periodic multi-tip structure, characterized in that it includes cleaning and polishing the surface of a monolithic carbon plate, creating micro-, nanoscale disks surrounded by a transition metal group with a catalytic film using photolithography, and thermochemical etching of the carbon plate in a hydrogen medium to form columnar structures, which are then subjected to group micro-, nanoscale sharpening in a low-temperature plasma of an rf discharge in acid hydrogen or in oxygen-inert gas environments.

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