Sense junction response in a capacitively coupled josephson memory cell

Abstract

Previously, a capacitively coupled Josephson memory cell was proposed in which an rf‐SQUID device couples capacitively with a single junction. Binary data stored in an rf‐SQUID device can be read through a flux change which generates a pulse signal to be detected. The pulse has a very narrow width, i.e., an order of picoseconds. The current would be different in the time before and after the pulse is applied, which is superimposed by an oscillating current after the application of a pulse. The bias current margin of the memory cell is determined by the way in which a memory is read by using such a pulse. When a memory cell of Josephson junction devices is used, the bias current margin of a sense junction would govern the overall margin of the memory circuit. This bias current margin must be made large for the present study. Therefore, by assuming the read mode of a capacitively coupled memory cell, the response of a single junction has been studied for a very narrow‐width pulse current which varies with fluxons. The minimum pulsewidth and amplitude required to switch a junction and a bias current dependence before and after the pulse is applied are calculated analytically on the basis of the coupling energy reported by Dong and Van Duzer [18]. The relation between a minimum pulse‐width and amplitude and a switching time for a sense junction, which cannot be solved analytically, is calculated by computer simulation. Further, the influence of a sinusoidal current superimposed over a bias current also is studied by computer simulation.