YBA2CU3O7 JOSEPHSON-JUNCTIONS AND DC SQUIDS BY MECHANICALLY INDUCED GROWTH DISORDER

A simple and reproducible method for the fabrication of high-T(c) Jose phson junctions and SQUIDs is presented. A very weak disturbance is pr oduced by pressing a diamond needle onto the substrate surface before film deposition. The junction parameters such as the critical current I(c), the I(c)R(n) product, or beta = 2I(c)L/PHI0 (with L the self-ind uctance of the SQUID loop) are accessible by controlling the film thic kness and can be varied by several orders of magnitude. The junctions usually have critical current densities j(c) in the range of 5 X 10(4) 1 X 10(5) A/cm2 at 77 K and show Shapiro steps when exposed to rf pow er. The current-voltage characteristics are resistively shunted juncti onlike and nonhysteretic. In dc SQUIDs a maximum peak-to-peak voltage response to dc flux of up to 12 muV at 77 K is observed.