The "Persistor"-A Superconducting Memory Element

The basic components of a Persistor memory element are a superconducting inductor in parallel with a switch element which is normally superconducting, but which becomes resistive when the current exceeds a critical value. When a suitable current pulse is applied to a Persistor memory element, a persistent circulating current is stored. A second pulse in the same direction as the first makes no change, but a pulse in the opposite direction reverses the circulating current and produces a voltage across the element. By mutual inductance coupling to two or more driving circuits, these memory elements can be made to operate in matrices similar to those employed with ferromagnetic cores. Persistor memory elements utilizing lead inductors and thin tin or indium films have performed typical memory unit functions for pulses of 15-mμsec duration and a repetition rate of 15 mc. Performance at higher speeds is possible. The limiting speed is determined by the thickness of the thin film switch element and can be made as fast as is useful for the other parts of the associated circuits. The elements are well suited to compact printed circuit production, with densities of a million per cubic foot possible.