Surface Impedance Measurements of YBa2Cu3O7−x Thin Films in Stripline Resonators
Microwave surface impedance of thin films of YBa2Cu3O7−x deposited by a single-target off-axis magnetron sputtering technique was measured as a function of temperature, frequency and if magnetic field, Hrf using a stripline resonator. The measurements included determination of the penetration depth λ, equal to 0.167 µm the best film. The surface resistance Rs was measured over a frequency range of 0.4 to 20 GHz; the temperature range was 4.2 K to Tc, and the Hrf ranged from 0 to 225 Oe. The Rs at 4.2 K and 1.5 GHz is 4.5 × 10−6 Ω. We observed that Rs(Hrf) depends upon the conditions under which the films were deposited. Films deposited at low temperature show a linear dependence on Hrf and those deposited at high temperature show a weak dependence upon on Hrf. All films show a rapid rise in Rs at high values of Hrf.The shape of Rs(Hrf) is similar to that of Nb and NbN films measured in the same stripline geometry. We propose that Rs(Hrf) is related to the grain structure of the films. We have measured intermodulation products in these resonators. Films showing weak dependence of Rs on Hrf demonstrate smaller intermodulation effects. We discuss the implications for microwave device applications.
KeywordsPenetration Depth Weak Dependence Surface Impedance Surface Resistance Center Conductor
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