PHYSICS AND PERFORMANCE OF HIGH-TEMPERATURE SUPERCONDUCTING VORTEX FLOW TRANSISTORS

The physics and performance of high temperature superconducting vortex flow transistors is analyzed both theoretically and experimentally. V ortex flow transistors based on Josephson vortices are found to be sup erior to those based on Abrikosov vortices with respect to sensitivity , speed and impedance level. For Josephson vortex flow transistors bas ed on single long junctions and parallel arrays of a large number of s hort junctions, expressions for the current gain, the transresistance and the response time are derived as a function of the various device parameters. Our analysis shows that Josephson junctions with high prod ucts of their normal resistance and critical current are required in o rder to obtain large current gain, high transresistance and small resp onse time. Both symmetric and asymmetric Josephson vortex how transist ors based on YBa2Cu3O7-delta bicrystal grain boundary junctions have b een fabricated. Our experimental results agree well with the model pre dictions. Transresistance values of several Omega have been achieved f or devices based on YBa2Cu3O7-delta grain boundary Josephson junctions . The current gain could be increased by using an asymmetric bias curr ent injection. For asymmetric devices a current gain above 20 has been obtained at temperatures below 60 K.