Microstructural study of yttria stabilized zirconia buffered sapphire for YBa₂Cu₃O_7-δ thin films

Abstract

Yttria stabilized zirconia (YSZ) buffer layers were grown by rf-magnetron sputtering on the r (1102) plane of sapphire for YBa₂Cu₃O_7-δ (YBCO) thin film deposition. Microstructural changes of YSZ buffer layers grown using different sputtering conditions (5, 10, and 20 mTorr; Ar/O₂ gas mix ratio of 9:1 and 1:1) were monitored by atomic force microscopy (AFM). Films grown using a lower oxygen partial pressure (5 mTorr) and a higher Ar/O₂ ratio (9:1) showed smooth surface morphology and the average surface roughness increased with an increase in oxygen partial pressure. YBCO films in situ grown by pulsed laser deposition on sapphire with a YSZ buffer layer deposited using optimized sputtering parameters (5 mTorr gas pressure, 9:1 Ar/O₂ ratio) yielded the highest critical density, J_c4.5×10⁶ A cm^-2 at 77 K. An excellent correlation between microstructure and J_c has been found and AFM has proved to be important for the study of the microstructure of films.