YBCO thin film DC SQUID on a sapphire substrate

We report the fabrication and operation of YBCO thin film DC SQUIDs on Sapphire substrates. The film are prepared by the sequential deposition of Cu, Y 2O 3, BaF 2, with post annealing, and are about 1μm thick. The film are patterned by a conventional photolithographic method on the Cu layer, before the deposition of Y 2O 3 and BaF 2. The critical temperature of the devices is higher than 80 K, and the product of their estimated inductances with the corresponding critical currents is much larger than Φ 0. The SQUIDs have been measured in the resistive mode by a DC technique, with an external magnetic field applied by a small coil. We observed modulation of the voltage on the SQUIDs with the applied flux of the order of 20 μV, with an hysteretic behaviour of the V−Φ curves.