Characteristics of YBCO SQUIDs with step-edge and biepitaxial grain boundaries

Some characteristics of YBCO SQUIDs with step-edge and biepitaxial grain boundaries were investigated. V-I curves of the step-edge SQUIDs can be described by the RSJ-like model with a linear relationship between the critical current I/sub c/ and temperature T, whereas the typical I/sub c/-T curve for the biepitaxial SQUIDs concaved upward at temperatures near the critical temperature. The V-I curves of both kinds of the step-edge and the biepitaxial SQUIDs under microwave irradiation revealed integral Shapiro steps. Furthermore, the voltages of the step-edge SQUIDs were well modulated by the applied magnetic field. And also, the typical Fraunhofer diffraction of the I/sub c/-/spl Phi/ curve was observed for the single junction in the step-edge SQUIDs. On the other hand, the magnetic field modulated voltage oscillation was also found for the biepitaxial SQUIDs. All the details will be discussed in this report.