Cavity Sensing of Cryoelectric Memory Planes

Abstract

Continuous film cryoelectric memory planes can be sensed by means of a superconducting line or a normally conducting sense plane located beneath the memory film. These types of sensing, known as line sensing and cavity sensing, respectively, have certain attributes and limitations which are discussed in detail. An expression for the sense voltage output is derived based on the change of the thermodynamic free energy of the memory during the read cycle. With this expression the sense outputs for line sensing and cavity sensing are calculated and compared with experiment. The signal outputs from cavities are compared with simple line sensing. Structured cavities, i.e., arrangements wherein the sense plane is multiply connected are discussed. It is shown that at cold temperatures (T≈3.0°K) and thick memory films (a>5000 Å), useful sense signal outputs can be obtained for cavities large enough to be used in practical computer memories. However, for large sense signals (Vs>1 mV) some form of line sensing or structured cavity will be necessary.