High speed components based on high-Tc superconducting grain boundary junctions

Övrigt konferensbidrag, 1996

Artificial grain boundary junctions of both bi-crystal and step edge configurations have been characterized at high frequency using Fiske type resonances as well as flux flow induced steps in the current-voltage curve. A dielectric behavior of the barrier with sufficiently low microwave losses to allow resonances is indicated. Deduced values of the barrier thickness, the penetration depth, and surface microwave losses agree with those from other measurements. Long grain boundary junctions, as well as parallel arrays of shorter junctions, have been used in Josephson Flux Flow Transistors (J-FFT). Asymmetrically coupled devices give considerable current gain at low temperature. Grain boundary junctions have also been employed in simple Rapid Single Flux Quantum (RSFQ) circuits to demonstrate functions like flip flop, voltage divider and voltage doubler. A single superconducting layer technology implies small inductances formed as narrow slits in the deposited film. A tri-layer technology is superior but puts demands on insulation and strip cross-overs. Presently available high-Tc junctions are not sufficiently reproducible to allow large scale integrated circuits. Another limitation is the limited performance (for example given by the junction IcRn product) of present junctions at 77 K