A superconducting millimetre switch with multiple nano-bridges

Abstract

In this paper, we describe the design of a planar superconducting on/off switch comprising a high normal resistance nano-bridge deposited across a slotline transmission line. We present preliminary experimental results measured at 220 GHz range, and we discuss in detail the various parameters that affect the performance of the planar on/off switch, including the optimum thickness required for the nano-bridge to achieve high dynamic range and low transmission loss. The analysis is done by combining the accurate superconducting surface impedance description with rigorous electromagnetic simulations, and comparing the simulated results with the measured performance of a previously fabricated on/off switch fed by a backto- back unilateral finline taper. Finally, we propose an improved method to further increase the dynamic range of the switch, by introducing a multi-bridge design to tune out the residual inductance of the nano-bridges.