Simulation and Measurement of HTS Josephson Heterodyne Oscillator

J.C. Macfarlane, J. Du, R. Taylor and C.M Pegrum

Abstract—We report continuing investigations into practical applications of the ac Josephson effect as the basis for a voltage-tunable radio-frequency oscillator. We have previously demonstrated experimentally that useful power levels (10s of nW) and linewidths of a few kHz can be achieved in the heterodyne output from a High-Temperature-Superconducting Resistive SQUID (HTS-RSQUID) operating in the frequency range 1 – 50 MHz. Those results were achieved with 2-junction R-SQUIDs incorporating current-biased shunt resistors of a few micro-ohms. We have now modified the fabrication procedures, and adjusted the shunt resistors and bias current values so that higher frequencies can be achieved. The Josephson junctions are of step-edge type, rather than the bi-crystal type used in our earlier work. The step-edge technique permits much more flexibility in the geometrical lay-out and utilises the more cost-effective single-crystal MgO substrates. In the present paper, we report numerical simulations and experimental measurements on these devices in the frequency range up to 2 GHz.

Index Terms— Heterodyne oscillator, Josephson junction, High-Temperature-Superconducting.

Manuscript received 19 August 2008.
This work was supported in part by the CSIRO, Australia, and Mesaplexx Pty Ltd, Australia.
J.C. Macfarlane is an Honorary Research Fellow with the Physics Department, University of Strathclyde, Glasgow G4 0NG, UK; e-mail j.c.macfarlane@strath.ac.uk. Ph: +44 1360 870330.. J. Du is a Principal Research Scientist with CSIRO Materials Science and Engineering, Bradfield Road, Lindfield 2070, Australia. R. Taylor is the Chief Technical Officer with Mesaplexx Pty Ltd, Qld, Australia. C.M. Pegrum is with FieldSolutions, Glasgow G12 9SD, UK and also with the Department of Physics, University of Strathclyde, Glasgow G4 0NG,, UK.

Full Text, PDF