High-T_c-based Josephson-junctions and SQUIDs by mechanically induced growth disorder

Abstract
We have developped a simple method for the reproducible production of high-T_c based Josephson junctions and SQUIDs. By producing a very weak deformation into the substrate surface by a diamond needle before depostion of the thin high-T_c-film, the film shows a growth disturbance in the region of the deformation with quite interesting features, resulting in a Josephson junction. The substrate deformation is characterized by Atomic Force Microscopy and the film growth over the deformation is examined by Scanning Electron Microscopy. The junctions produced by this method show RSJ-like behaviour in their current-voltage characteristics and Shapiro-steps at all temperatures between 4.2 and 89K, when exposed to microwave power. The I_cR_n-products are variable in a wide range and can be very high for properly chosen film thicknesses. SQUIDs produced by this method show voltage modulations due to dc-flux of up to 12µV peak to peak at 77K for low SQUID-performance parameters β<<1. For β>>1 the modulations are between 3 and 5µV at 77K. Finally the noise in SQUIDs produced by this method is examined. It is shown that the noise power is in the region of that of step edge junctions.