Microstructure of YBCO and YBCO/SrTiO 3 /YBCO PLD Thin Films on Sapphire for Microwave Applications

A large-area pulsed laser deposition process for high-quality YBa2Cu3O7−δ (YBCO) thin films on both sides of R-plane sapphire substrates with CeO2 buffer layer is used routinely to optimize planar microwave filters for satellite and mobile communication systems. With the experience of more than 700 double-sided 3-inch diam. YBCO:Ag films a high degree of reproducibility of jc values above 3.5 MA/cm2 and of state of the art R5 values is reached. TEM cross sections of the large-area and double-sided PLD-YBCO:Ag thin films on R-plane sapphire with CeO2 buffer layers show typical defects like stress modulation, stacking faults, a-axis oriented grains, precipitates and interdiffusion layers. YBCO films on SrTiO3 / YBCO* / CeO2 film systems on R-plane sapphire wafers have more growth defects compared to bare CeO2 buffers on sapphire but show as microwave resonators encouraging electrical tunability.