Control and reproducibility of c-axis microbridges

Vertical c-axis microbridges, with dimensions comparable to the penetration depth (/spl lambda//sub c/), have been investigated experimentally and theoretically. Josephson-like effects are observed due to coherent motion of vortices across the bridge. Both the on-chip and chip to chip reproducibility has been improved from previous reports by process optimisation. Within an array it is highly dependent on the oxygenation state and the temperature of the sample. Although the spread in parameters within an array of standard junctions is almost good enough to fabricate many circuits of interest, the I/sub c/ is too high and the R/sub n/ too low for many logic applications. In an attempt to reduce the coupling strength, the growth temperature of a region of the material in the microbridge has been varied. Initial results suggest I/sub c/ can be reduced and R/sub n/ increased to a level which, with further optimisation, might be useful for logic applications, while the reproducibility was not adversely affected.