A progress report on the Livermore Miniature Vacuum Tube Project

The design and building of micron-sized vacuum diodes and triodes using the sacrificial layer process is discussed. The devices use silicon field emitters etched into the surface of a silicon wafer. The field emitters are then buried in layers of glass and conductive polysilicon to produce the grid and anode. The last step is to remove the glass layers, leaving the free-standing anode and grid with 1-2- mu m separations. Vacuum microelectronics are expected to be hard to more than 10/sup 17/ neutrons/cm/sup 2/ and 10/sup 8/ rad(Si) of gammas without sustaining permanent damage. This is three to four orders of magnitude greater than the radiation levels that comparable silicon devices can withstand. Upset is expected to be on the order of 10/sup 11/ rad(Si)/s, compared to 10/sup 8/ rad(Si)/s for silicon devices. Vacuum microelectronics should also be able to withstand in excess of 775 K, compared to a maximum of 650 K for the best silicon devices. Current work involves enhancing the sharpness of the field emitters, so that they can operate at lower voltages. Recent application of an oxidation sharpening method has created tips with a radius of curvature on the tip of less than 10 AA.<>