Particle-induced modification of thin film YBa2Cu3 O7-δ transport properties and microwave device performance

The authors examine the modification of the microwave surface resistance (R_s), the critical current (J_c), and the critical temperature (T_c) resulting from 2-MeV H⁺ and 12-MeV Si⁴⁺ irradiation of high-quality thin films of YBa₂Cu₃O_7-δ on <100> LaAlO₃ substrates. For both ions, the change in T_c (R=0) and J_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_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_s near T_c, followed by a relatively temperature-independent R_s with a value of ~6 mΩ at 20 K. For irradiation with H⁺ and Si ⁴⁺ ions, the sharp transition in R_s was shifted to lower temperatures, although below the transition temperature R_s (T) was unchanged. The loaded quality factor, or Q, of a 5.3-GHz ring resonator, patterned from a 500-nm film on <100> MgO substrate, was measured as a function of temperature for 2-MeV H⁺ irradiation. While Q(T) was observed to decrease as a function of fluence, Q(T/T_c) was invariant, as expected from the insensitivity of R_s to particle fluence below ~0.9 T_c