ASYMMETRIC HIGH-TEMPERATURE SUPERCONDUCTING JOSEPHSON VORTEX-FLOW TRANSISTORS WITH HIGH-CURRENT GAIN

We have fabricated Josephson vortex-flow transistors (JVFTs) based on asymmetric parallel arrays of YBa2Cu3O7-delta bicrystal grain boundary junctions. The critical current I-c and the voltage V al fixed bias current I-b were measured as a function of the control current I-ctrl through a control line inductively coupled to the array. For JVFTs with an asymmetric in-line geometry a high current gain g = partial derivative I-c/partial derivative I(ctrl)l ranging between about 20 at 40 K and 14 at 70 K was achieved. This current gain is much higher than that obtained for symmetric devices and results from the self-field effect of the electrode currents. In contrast to the current gain the transresistance r(m) = partial derivative V/partial derivative I-ctrl of the JVFTs could not be enhanced by an asymmetric device structure. The current-voltage characteristics of the asymmetric JVFTs show pronounced step-like structures caused by the self-field of the electrode currents. (C) 1995 American Institute of Physics.