High Tc SQUID with a Single Layer Flux Transformer on Sapphire

We have fabricated a HoBa2Cu3O7-y SQUID magnetometer with a single layer flux transformer on a sapphire substrate. It consists of a small SQUID chip (2mm by 2mm) on a SrTi03 substrate and a large single layer flux transformer (17mm by 17mm) on a sapphire substrate. The transformer is mounted on the SQUID by a flip-chip method. We use a sapphire substrate and a large area HoBa2Cu3O7-y excimer laser deposition technique to reduce the cost. Effective area of the bare SQUID is 0.04mm2, and that of the SQUID with the flux transformer is 0.16mm2. The magnetic field resolution is 130fTHz-1/2 at 10Hz.