Use of super Schottky diodes in a cryogenic radio frequency superconducting quantum interference device readout

Abstract

We describe the fabrication and characterization of super Schottky diodes which are used in the cryogenic part of a 3 GHz radio frequency superconducting quantum interference device (rf SQUID) readout electronics. The diodes were prepared on silicon wafers with an n-doping level of 5×1024 m−3. They exhibited sensitivities of 1500 V−1 at 4.2 K, and a noise equivalent power of 2×10−15 W/√Hz was measured at 2.1 GHz. Using planar niobium 3 GHz rf SQUIDs and a cooled rf amplifier, experiments have been performed to investigate the feasibility of these super Schottky diodes for demodulation of the SQUID rf signal voltage. A simple cryogenic rf SQUID readout, employing two transistors and one super Schottky diode is described and investigated. Flux noise measurements in an open loop have been performed using this readout.