Erosion lithography to abrade a pattern onto a substrate

DETAILED DESCRIPTION FIG.
1 shows a cross section of a prior art bonded heater-cathode-grid structure for use in the microwave power-amplifier tube disclosed in U.
S.
Pat.
No.
3,638,062 by J.
E.
Beggs.
It embodies a cathode disk (twin-grooved around its edge, boron nitride (BN) insulation, and tungsten (W) film grid and heater electrodes.
This control unit can be efficiently heated, can withstand large voltages between grid and cathode, and has a high grid dissipation capacity.
It is operated in the tube near 1050 degrees C.
The cathode disk used in this assembly can be an impregnated type such as a Philips Type B or a Semicon Type S.
The impregnant is removed from the outer surfaces prior to the BN deposition so as to prevent a direct reaction with the chemical vapors.
This cleaning precedure also permits the BN insulation to become mechanically locked in the open pores of the tungsten surface.
Chemical vapor deposition processes are used to deposit BN and W layers onto the cathode.
The completed structure is made by opening holes in the tungsten and BN layers.
Other forms of the tube and of the bonded heater-cathode-grid structure are shown in U.
S.
Pat.
Nos.
3,599,031 and 3,694,260 by J.
E.
Beggs.
These patents show the structure and the method of manufacture, and include a discussion of alternate materials which may be used.
The three Beggs patents are incorporated herein and made a part hereof by reference.
In FIG.
1, the tungsten cathode 1 has open pores 2, an emission impregnant and an emission surface 3.
An insulating layer 4 of BN is formed on all sides by chemical vapor deposition.
The portion of the insulating layer in and adjacent the lower groove is removed to provide a cathode contact region 5.
A tungsten film is formed over the insulating layer, and perforations are formed by providing a mask and using a blast gun to erode through the insulating layer to form a control grid 6.
The tungsten film extends to the upper groove to provide a grid contact region 7.
A heater 8 is formed in the tungsten film on the opposite face, with heater contact regions 9