Abstract
One of the first demonstrated low power applications of high-Tc superconductivity was the DC-SQUID making use of natural grain boundaries as Josephson junctions1/3. That was (and still is) a difficulty in high current applications turned out to be a benefit in the early stages of the research in high-Tc superconducting electronics: grain boundaries in polycrystalline thin films of YBa2Cu307−x (in short YBC0) work as Josephson junctions with superconductor/normal metal/superconductor (SNS) like behavior4. Based on these early investigations two main directions are currently followed in the Josephson junction and SQUID research, (i) the preparation of artificial grain boundaries on bicrystals5 and on edges in the substrate6, and (ii) the development of SNS-like junctions with thin film sandwiches of YBCO/normal metal7 or semiconductor/YBCO8/10. Up to now the best performance at 77 K has been demonstrated for a DC-SQUID with artificial grain boundary junctions on SrTiO3 bicrystals11. It offers relative low noise and a periodic voltage modulation by an external magnetic field at temperatures up to 87 K. However, bicrystal fabrication, control of the critical current and the normal resistance, and reproducibility pose a serious problem.
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