Microstructure of byco and ybco/SrTiO_3 ybco pld thin films on sapphire for microwave applications

摘要

A large-area pulsed laser deposition process for high-quality YBa_2Cu_3O_(7- #delta#) (YBCO) thin films on both sides of R-plane sapphire substrates with CeO_2 buffer layer is used routinely to optimize planar microwave filters for staellite 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 J_c values above 3.5 MA/cm~2 and of state of the art R_s values is reached. TEM cross sections of the large-area and double-sided PLD-YBCO:Ag thin films on R-plane sapphire with CeO_2 buffer layers show typical defects like stress modulation, stacking faluts, a-axis oriented grains, precipitates and interdiffusion layers. YBCO films on SrTiO_3/YBCO~*/CeO_2 film systems on R-plane sapphire wafers have more growth defects compared to bare CeO_2 buffers on sapphire but show as microwave resonators encouraging electrical tunability.