Microwave Quenching in DC-biased Coplanar Waveguide Based on $YBa_2Cu_3O_{7-\delta}$ Thin Film

Abstract

In this paper, we report on the results of features in the discovered effect of a strong change in the microwave losses (quenching) in HTS-based coplanar waveguide (CPW) at certain values of the input power $P_{in}$ and direct current (DC) $I_{dc}$. Two waveguides were studied: CPW-150 and CPW-75, fabricated of epitaxial 150 nm and 75 nm YBCO films. The insertion loss of CPW, $IL = 10 lg (P_{out} / P_{in})$, was measured versus both the operating temperature and the bias DC current $I_{dc}$ when a fixed level of the input X-band pulsed MW signal $P_{in}$ was applied. Here $P_{out}$ is the power measured at the CPW output. A pulse duration ${\tau}_i$ was 5 ${\mu}s$ with pulse repetition period T = 40 ${\mu}s$. Experiments showed a noticeable difference in specific values of $I^*= I_{dc}$ corresponding to the $P_{in}$ dependent quenching phenomenon in CPW-150 and CPW-75. With a weak input signal the difference in behavior of CPWs is anticipated, i.e., quenching occurs at a lower current for thinner film. For $P_{in}>1W$ the situation is opposite, i.e., quenching for CPW-150 takes place at a lower $I^*$. This is explained by stronger microwave heating of CPW-150.