Modeling the Behavior of HTS Terahertz RSQUIDs

Abstract

In previous work we looked in detail at simulations of our HTS Resistive DC SQUIDs (RSQUIDs) using a lumped-component model and neglecting step-edge junction capacitance. These can now be made with junctions that have a high product of critical current and normal resistance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</sub> ) and so the Josephson frequency can be above 1 THz. This calls for a more refined model of the device, which we will present here. The RSQUID series resistor is represented as a distributed combination of resistance and inductance, rather than simply a resistor in series with its self inductance. We now include junction capacitance, as the Stewart-McCumber parameter can be close to unity. We treat the RSQUID loop as a co-planar stripline, rather than as an inductor. We report a range of simulations with these enhancements to the model and comment briefly on the results in relation to potential applications of RSQUIDs as active microwave devices.