Particle-induced modification of thin film YBa/sub 2/Cu/sub 3/O/sub 7- delta / transport properties and microwave device performance

The authors examine the modification of the microwave surface resistance (R/sub s/), the critical current (J/sub c/), and the critical temperature (T/sub c/) resulting from 2-MeV H/sup +/ and 12-MeV Si/sup 4+/ irradiation of high-quality thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / on LaAlO/sub 3/ substrates. For both ions, the change in T/sub c/ (R=0) and J/sub c/ (77 K and 4.2 K) was roughly linear with fluence. The change in these properties with fluence was quantitatively similar once corrected for differences in the rate of energy loss to atomic displacements. R/sub s/ was also measured as a function of temperature for the same films at 36 GHz using the cylindrical cavity end-wall replacement technique. High quality c-axis oriented films exhibited sharp transitions in R/sub s/ near T/sub c/, followed by a relatively temperature-independent R/sub s/ with a value of approximately 6 m Omega at 20 K. For irradiation with H/sup +/ and Si/sup 4+/ ions, the sharp transition in R/sub s/ was shifted to lower temperatures, although below the transition temperature R/sub s/(T) was unchanged. The loaded quality factor, or Q, of a 5.3-GHz ring resonator, patterned from a 500-nm film on MgO substrate, was measured as a function of temperature for 2-MeV H/sup +/ irradiation. While Q(T) was observed to decrease as a function of fluence, Q(T/T/sub c/) was invariant, as expected from the insensitivity of R/sub s/ to particle fluence below approximately 0.9 T/sub c/.