Bonded cathode and electrode structure with layered insulation, and method of manufacture
AssigneeThe United States of America as represented by the Secretary of the Army
InventorsDavid W. Oliver, Casmir R. Trzaskos
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Abstract
The variety of technologies that have been applied in the development of a onded grid cathode are described. These include chemical vapor deposition of tungsten, molybdenum, iridium, BM, and Si.sub.3 N.sub.4 on both sides of a sintered tungsten cathode disk. Zirconium and titanium getters have been used to eliminate nitrogen evolution problems. Films of Si.sub.3 N.sub.4 have been added to the insulation to prevent calcium and barium diffusion into the layer and maintain adequate resistivity and breakdown strength. Plasma etching was introduced as a method of removing Si.sub.3 N.sub.4 from the cathode pores.
Claims19
A bonded grid-cathode structure comprising:
- a tungsten cathode having an emission impregnant;
- a grid of a refractory metal;
- an insulator bonded to the cathode and to the grid, with openings through the grid and insulator to the cathode surface, wherein said insulator comprises a principal boron nitride (BN) layer and a relatively thin diffusion barrier of silicon nitride (Si.sub.3 N.sub.4) bonded between the cathode and the BN layer to counteract the effects of diffusion of said impregnant into the insulator.
A unitary heater, cathode, and control grid structure for an electron discharge device which comprises a circular disk of porous refractory metal having two spaced parallel outer surfaces and a peripheral edge, an inorganic insulating layer which comprises a principal layer of BN covering the surfaces of said disk, and a film of refractory metal overlying substantially all of said insulating layer, the film on one surface having a gridlike configuration, the film on the other surface having a configuration of a heating coil, said disk containing thermionic emissive material, and the insulating layer on said one surface having openings extending into the porous disk corresponding to the openings in the gridlike configuration of said film, whereby when the film on the other surface is heated, electrons are directed through said openings in the insulating layer and the film on said one surface,
- the improvement comprising a relatively thin layer of Si.sub.3 N.sub.4 as a diffusion barrier between said disk and said insulating layer.
A bonded grid-cathode structure comprising:
- a cathode,
- a grid of a refractory metal,
- an insulator principally of boron nitride bonded to the cathode and to the grid,
- with openings through the grid and insulator, in which said insulator comprises a thin layer of BN bonded to the cathode as a stress reliever, a thin layer of Si.sub.3 N.sub.4 which acts as a diffusion barrier, a principal layer of BN, and a thin layer of Si.sub.3 N.sub.4 which improves the adhesion between the metal grid and the insulating structure.
The method of forming a unitary heater, cathode, and control grid structure for an electron discharge device which comprises:
- coating a disk of porous refractory metal with an inorganic insulating layer which includes a principal layer of BN,
- overcoating the insulating layer with a film of refractory metal,
- forming a grid pattern in the film on one side of the disk,
- forming openings in the film and insulating layer corresponding to the pattern,
- forming a heater on the other side of the disk, the disk being impregnant with thermionic emissive material,
- the improvement wherein said insulating layer is formed with a diffusion barrier of Si.sub.3 N.sub.4 to counteract diffusion of said thermionic emissive material into the insulating layer.
The method of making a bonded grid on a cathode, comprising the steps of:
- (a) forming an insulator layer on said cathode,
- (b) forming a metal layer for the grid, on the insulating layer,
- (c) forming a photo-resist layer on the metal layer,
- (d) exposing the photo-resist layer with means to form a grid pattern, followed by a developing process which selectively moves part of the photo-resist layer to expose openings of said grid pattern,
- (e) removing the metal layer in said openings,
- (f) using air blasting with an abrasive powder to remove the insulator layer in said openings, with the photo-resist on the metal layer acting as a mask;
- the improvement wherein step (a) comprises using chemical vapor deposition to:
- deposit a thin layer of BN which acts as a stress reliever,
- deposit a thin layer of Si.sub.3 N.sub.4 which acts as a diffusion barrier,
- deposit BN for the principal layer,
- deposit a thin layer of Si.sub.3 N.sub.4 which serves to improve the adhesion between the metallic grid film and the insulating structure.
Dependencies are inferred from the claim text.