Proximity-Coupled Al/Au Bilayer Kinetic Inductance Detectors

Abstract : This paper mainly discusses the fabrication and characterization of proximity-coupled Al/Au bilayer kinetic inductance detectors (KIDs). The proximity effect is used to optimize the critical temperature of the superconducting film and to increase the kinetic inductance fraction of the film. An Al/Au bilayer with thickness equal to 30 nm and 10 nm, respectively, is evaporated on a silicon substrate. The KIDs are cooled down to about 90 mK in an adiabatic demagnetization refrigerator. The measured average internal quality factor of the resonances is around 27,000. The critical temperature is 0.8 K, and the kinetic inductance is estimated to be about 2 pH/□. The minimum detectable frequency of the chip is estimated to be about 60 GHz. The critical temperature can be further tuned by optimizing the thickness of the aluminum and gold films. The proximity-coupled Al/Au KIDs represent an appealing detector technology for photon detection at frequencies below 90 GHz.