Ex situ Ohmic contacts on thin film YBa2Cu3O7−x

We report on ex situ fabrication of gold contacts onto patterned YBa2Cu3O7−x films. Gold seed layers were blanket sputtered onto photoresist defined over the patterned films. In a second photo process, openings were aligned to the original pads and 8-μm-thick contacts were electroplated. The two layers of photoresist and sputtered gold were removed leaving defined contacts. We obtained specific contact resistance of 2.6×10−7 Ω cm2 on post-annealed samples at 79 K. Microwave filters with contacts showed 4.2 dB loss at 9 GHz and 77 K, while comparable filters in copper showed 18 dB loss.