Simultaneous optimization of the linear and nonlinear microwave response of YBCO films and devices

We present results of a systematic study of the effect of film deposition temperature on both the linear and nonlinear response of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films and devices at microwave frequencies. Measurements of the unpatterned films show that samples grown by pulsed laser deposition at a lower substrate temperature (740/spl deg/C) display a smaller low-temperature residual surface resistance compared to films grown at a higher substrate temperature (780/spl deg/C). However, the same films which display low residual surface resistance also show increased nonlinear effects (measured by third harmonic generation) at all temperatures. Analysis of these results suggests that the increased defects present in the films grown at the lower deposition temperature are responsible for both the lower surface resistance and the higher third harmonic generation observed in these samples. We discuss the consequences of these results for the simultaneous optimization of both linear and nonlinear microwave properties of HTS thin films and devices.