Off-axis pulsed laser deposited YBa₂Cu₃O_7-δ thin films for device applications

YBa₂Cu₃O_7-δ (YBCO) thin films deposited by off-axis pulsed laser deposition could be used for fabricating multilayer devices. Growing YBCO films with high critical current density and high T_c (T_c is around 90 K and J_c is above 10⁷ A/cm² at 77 K), there was a tendency that the surface morphology of YBCO films is rough. This causes problems in fabricating multilayer devices that require a smooth surface. In this work, we have developed two-step procedures of growing YBCO thin films with high critical current and a smooth surface for multilayer device applications. In the two-step procedure, we first grew YBCO film with higher T_c (T_c is around 90 K, but usually the surface is with defects like holes), next we planarized the film by growing the film with lower T_c (T_c is around 83 K and the surface is smooth). YBCO films deposited at low temperatures have critical current densities (J_c) around 10⁶ A/cm² at 77 K in zero magnetic field. These films are almost free from laser droplets and outgrowth-free surface. In two-step procedures, we could grow films with a smooth surface and high critical current density. Methods for growing smooth surfaces in two-step procedures will be presented.