Bonded cathode and electrode structure with layered insulation, and method of manufacture

Claim 2

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 3 N 4 ) bonded between the cathode and the BN layer to counteract the effects of diffusion of said impregnant into the insulator.

Claim 3

A bonded grid-cathode structure as claimed in claim 1, further including a relatively thin layer of silicon nitride bonded between the principal BN layer and the grid.

Claim 4

A bonded grid-cathode structure as claimed in claim 2, further including a relatively thin layer of BN bonded between the Si 3 N 4 diffusion barrier and the cathode surface for stress relief, and wherein said cathode includes an iridium coating.

Claim 5

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 3 N 4 as a diffusion barrier between said disk and said insulating layer.

Claim 6

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 3 N 4 as a diffusion barrier between said disk and said insulating layer.

Claim 7

The structure of claim 4, further including a relatively thin layer of Si 3 N 4 between the principal layer of BN and said film of refractory metal.

Claim 8

The structure of claim 4, wherein said porous refractory metal of the disk is tungsten, the disk further having a coating of iridium directly on the porous tungsten at least on the surface with the gridlike configuration, a relatively thin layer of BN for stress relief between the iridium coating and the Si 3 N 4 diffusion barrier.

Claim 9

The structure of claim 6, wherein said film of refractory metal is selected from the group comprising tungsten, tungsten carbide, molybdenum, molybdenum carbide and zirconium; and further including a relatively thin layer of Si 3 N 4 between the principal layer of BN and the film of refractory metal.

Claim 10

The structure of claim 7, wherein said gridlike configuration comprises holes through the metal film and the insulating layer down to the iridium coating.

Claim 11

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 3 N 4 which acts as a diffusion barrier, a principal layer of BN, and a thin layer of Si 3 N 4 which improves the adhesion between the metal grid and the insulating structure.

Claim 12

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 3 N 4 which acts as a diffusion barrier, a principal layer of BN, and a thin layer of Si 3 N 4 which improves the adhesion between the metal grid and the insulating structure.

Claim 15

The method of claim 10, further including a layer of Si 3 N 4 formed between the BN layer and the film of refractory metal.

Claim 16

The method of claim 11, further including forming a relatively thin layer of BN between said disk and said diffusion barrier.

Claim 19

The method as claimed in claim 13, wherein said step (b) comprises forming said grid from the group of metals comprising W and Mo, using chemical vapor deposition from the metal carbonyl.

Claim 20

The method as claimed in claim 14, including the further step after step (f) of removing the remainder of the photo-resist by heating the cathode grid structure to approximately 400 degrees C. in a low pressure hydrogen atmosphere, whereby the photo-resist evaporates leaving no residue.

Claim 21

The method as claimed in claim 15, further including steps before and after the step of removing the photo-resist of subjecting the cathode to ultrasonic cleaning in ethanol to remove particles of the abrasive powder which might be imbedded in the cathode surface.

Claim 22

The method as claimed in claim 16, wherein said abrasive powder is Al 2 O 3 .

Claim 23

The method as claimed in claim 17, following the second ultrasonic cleaning in ethanol, further including the step of etching with ionized freon gas to remove any Si 3 N 4 insulation remaining in the grid openings or lodged in the pores of the cathode.

Claim 24

The method as claimed in claim 18, further including a final step of firing the unit in hydrogen to remove surface contaminants and aid in reactivation of the cathode, and ensuring complete removal of fluorides.