Experimental Study of Electron-Beam Driven Semiconductor Devices for Use in a Digital Memory

A novel method of electronic storage is proposed, in which an electron beam would be used to drive active and passive semiconductor devices to perform the functions of a digital memory, including those of nondestructive read-out and reset. Principally to ascertain what speeds and output signals might be currently obtained if the storage method were implemented, an experimental study was made of the response to a bombarding electron beam of commercial “four-layer” and surface-barrier diodes which could function in the proposed store respectively as storage diodes and read-out diodes. Data presented on the Shockley Laboratories’ silicon 4N20D “four-layer” diode give the reduction of firing voltage caused by the bombardment as a function of beam current and bombardment duration. It is found that a beam current as weak as 0.2 µamp can fire a diode in 1/5 µsec. Three types of germanium surface-barrier diodes were studied for maximum speed of response to the bombarding beam current pulse and for charge multiplication. The “fastest” unit tested was a Philco 2N502 transistor modified for beam access to the base region by removal of the emitter dot. This unit could be bombarded to produce a 50 nsec pulse of 0.4 v peak across a 1000-ohm load. In the light of these data and of circuit and semiconductor device theory, a preliminary discussion is presented of the feasibility of a store providing a read-in rate of 5 megapulses/sec, a read-out rate of 15 megapulses/sec and a read-out signal ratio of stored ones to stored zeroes of 50 to 1.