Pulsed Laser Deposition of High TC Superconducting Thin Films

Abstract

AbstractIn this paper we present results of studies of the effect of process variations and substrate surface conditions on the microstructure and electrical properties of laser deposited YBa2Cu3O7‐δ thin films. The principle conclusions are as follows. The film properties of YBa2Cu3O7‐δ are relatively constant over a large range of substrate temperatures (620C‐720C) and oxygen pressures (150‐800 mT). There are small compositional variations with substrate temperature similar to, but much smaller than, those seen in reactively sputtered films. The best films were grown at 670C in 400mT of oxygen and have a zero resistance Tc of 89K and Jc > 1x106A/cm2 at 77K. There are, however, variations in the Tc, Jc, and orientation of films grown on MgO under similar deposition conditions. These variations reflect differences in the nucleation and growth process of YBa2Cu3O7‐δ on MgO which can arise from subtle changes in substrate surface properties. In particular, while the films are predominantly oriented with c axis perpendicular and a,b axes in the plane of the substrate along the MgO[100] direction, there are variable amounts of grains whose in‐plane orientations are at large angles to the MgO [100] direction, leading to large angle grain boundaries in some films. These large angle grain boundaries are correlated with the presence of Josephson weak links in some small constrictions for films on MgO.