Integrated High-Temperature Superconductor Radio-Frequency Superconducting Quantum Interference Device Covered with Superconducting Thin Films in Flip-Chip Configuration

We developed integrated high-temperature superconductor (HTS) rf superconducting quantum interference devices (SQUIDs) with various hole shapes on bicrystal SrTiO3 substrates. Single-layer YBa2Cu3O7-x thin-film technology and bicrystal Josephson junctions were employed to take advantage of a simple fabrication process. The HTS rf SQUID with a hole of 800×50 µm2 had the lowest inductance and showed the best noise characteristics among the tested SQUIDs. The 1/f noise profile of the HTS rf SQUID, which was covered with HTS thin films on the grain boundary and/or the slit of the SQUID in a flip-chip configuration, was dramatically improved in a frequency range of less than 100 Hz.