Effect of Carrier Doping on Nonlinear Distortion of Signals by Superconducting Films
Dr. Stephen Remillard, Hope College
High temperature superconductors are used in high frequency electronic devices. However, superconductor performance is limited by it’s distortion of signals under the influence of electric current. Measurements of non-linear distortion made on Tl2Ba2CaCu2O8-x (TBCCO-2212) wafers reveals dependence on carrier doping x, with grain boundaries contributing more significantly in under-doped films (x>0.1) as compared to those optimally doped (x=.1). The doping level was tuned by annealing the TBCCO-2212 thin films in a reducing nitrogen atmosphere at temperatures ranging from 250oC to 400oC. The microwave current dependent surface impedance of both pre- and post-annealed films was measured using a sapphire dielectric resonator. With the critical temperature being used as the indicator of carrier density, it was found that under-doped samples have larger nonlinear grain boundary losses as indicated by a weaker variation of surface reactance with surface resistance, revealing the preparation conditions for optimal wafer performance.
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