Perspectives and limitations of vacuum microtubes

Abstract

The edge or blade type emitter is the basic element of design for vacuum microtubes presented in this article. Several devices are tested which consist of vertical and horizontal structures with two (diode), three (triode), and four (tetrode) electrodes. The experimental results show some correlation with Fowler–Nordheim (FN) theory. In cases where emission occurs, but FN theory is not followed, the results indicate limitations in the ability to model, and to account for those factors which control emission. The cold emission from the grid (gate) electrode, and the phenomena of ‘‘forming’’ a metal surface are also discussed. The difficulty in controlling cold emission makes these devices inflexible. One can conclude from analyzing the experimental results presented in this paper, as well as similar results obtained from other research, that cold emission devices have a number of drawbacks and limitations regardless of the design of the emitter. To mitigate these drawbacks and limitations, a new design for a vacuum microtube is presented which operates on the basis of photoemission, and offers an alternate control mechanism for more stable emission.