Large-area YBa2Cu3O7−δ thin films on sapphire for microwave applications

Abstract
We have deposited YBa2Cu3O7−δ(YBCO) films with low microwave surface resistance (Rs) on 5‐cm‐diam, oxide‐buffered sapphire substrates by planar magnetron sputtering. MgO buffer layers are used on M‐plane (101̄0) sapphire, and R‐plane (11̄02) sapphire is buffered by CeO2. Rs values of 450–620 μΩ at 77 K and 10 GHz were measured across an entire 5‐cm diam YBCO film on M‐plane sapphire. For YBCO on R‐plane sapphire, Rs values at 77 K and 10 GHz were 950 μΩ for a 5‐cm‐diam wafer and 700 μΩ for 1×1 cm2 samples.