Single flux quantum storage devices and sensing means therefor

Abstract

An information storage device which stores a single flux quantum without bias is disclosed. The device includes a single Josephson tunneling device made from two superconductive materials spaced apart by an insulator wherein a Josephson current density profile J.sub.1 (x) defined by ##EQU1## IS CHARACTERIZED SUCH THAT THE PROFILE HAS A LARGER MAGNITUDE AT THE BOUNDARY PORTIONS OF SAID DEVICE THAN AT THE CENTER. The current density profile is controlled by adjusting either the oxide thicknesses, the work function of the superconductors or by changing the shape of the junction from its usual rectangular cross-section. A sensing arrangement for the above described storage devices is also disclosed. By controlling the damping of the above described structures, the gain characteristics and the vortex characteristics are adjusted to permit coincident selection of a single device. The overall reduction in the magnitude of the Josephson current density profile provides a higher junction resistance with a consequent decrease in damping. This increase in resistance across the tunneling junction unexpectedly extends the switching characteristic from the envelope boundary of all vortex modes to the extent that the application of the same coincident currents permits the unambiguous reading of both positive and zero or negative vortices. Each device during sensing acts as its own sense detector and is capable of switching to the voltage state if a flux quantum is stored. A bit-organized memory array utilizing the devices disclosed is also shown.