MICROWAVE VACUUM TUBE DEVICE EMPLOYING GRID-MODULATED COLD CATHODE SOURCE HAVING NANOTUBE EMITTERS

摘要

An improved gridded microwave tube is provided, the tube containing a cold cathode, an anode, and a grid located between the anode and cathode. In one embodiment, the cold cathode has a refractory metal substrate and carbon nanotube emitters, the emitters having a diameter of 1 to 300 nm and a length of 0.05 to 100 .mu.m. The grid-cathode spacing is 1 to 100 .mu.m, the grid contains apertures having a maximum dimension of 0.5 to 100 .mu.m, and the grid thickness is 0.5 to 100 .mu.m. Emission from the cathode directly onto the grid material itself, which undesirably heats the grid, is reduced by either (a) the presence of a shadow mask between the grid and the emitters or (b) selective formation of the emitters in locations that correspond to the grid apertures. The microwave tube operates at a frequency of greater than 0.5 GHz, advantageously greater than 2 GHz.