Process development and characteristics of YBCO thin film for radio frequency tranmission wire preparation

Low-temperature interconnection technology, especially radio frequency signal transmission in the 40–4.2 K temperature range, is currently a focus of development. In this temperature range, the transmission line needs to have as little insertion loss and heat leakage as possible. A processing method of preparing coplanar waveguide flexible transmission lines by mechanically cold exfoliating superconducting tape thin films is introduced in this work. Especially YBCO thin films deposited through MOD are more easily exfoliate directly at room temperature. The superconducting transition temperature width of YBCO thin film after exfoliating processing is 0.79 K. Although it is increased by 0.3 K compared with the transition temperature width of the strip, the critical current density at 77 K and 0 T is 7.7 × 10<sup>5</sup> A/cm<sup>2</sup>, which is more than 75% of the critical current density of the strip. The exfoliated YBCO thin film is fabricated into a 12-cm-long and 1-cm-wide PI-YBCO-PI three-layer structure transmission line, and the heat leak value is measured to be 0.238 mW in a temperature range from 40 K to 4.2 K. Five signal channels are prepared on a 1cmwide YBCO thin film, and the simulation shows that the crosstalk between adjacent signal channels is < –40 dB, the insertion loss at 9 GHz is < –2 dB, and the heat leak value of each signal channel is 47.6 μW. Compared with the metal transmission lines currently used in this temperature range, the heat leakage is reduced by at least 5 times.