Surface impedance measurements on sputtered YBa2Cu3O7 − δ films and first experimental results on a high-TC patch antenna

We have prepared thin films of YBa2Cu3O7 − δ in situ by dc sputtering at an oxygen pressure of 3.8 mbar and a substrate temperature of 700 °C on SrTiO3 and LaAlO3. For our best film on SrTiO3 an effective surface resistance of (48 ± 5) mΩ at 77 K and 87 GHz was achieved. From these data, the measured temperature dependence of the penetration depth, and the film thickness of (190 ± 8)nm an intrinsic value of (12 ± 4) mΩ was determined. Similar good results were obtained with films on LaAlO3. Moreover, we have found by Rutherford backscattering that the film thickness varies only 8% over 1 × 1 cm2. Therefore, such films are appropriate for planar microwave devices. As a first application a miniaturized high-Tc patch antenna, operating at 2.4 GHz, was built from two patterned films on LaAlO3. From the measured quality factor of 800 at 77K an efficiency of about 0.9 was estimated in comparison to 0.25 for high purity copper at the same temperature.