Development of Al-Nb Hybrid Lumped-Element Kinetic Inductance Detectors for Infrared Photon Detection

direct detection experiment with gallium arsenide (GaAs) as a cryogenic scintillator is proposed to search for dark matter in the mass range below 1 GeV . To detect scintillation photons with high sensitivity, we are developing Lumped Element Kinetic Inductance Detectors (LE-KIDs). We report the first fabrication of the aluminum-niobium LE-KIDs and measurements of their basic properties. We designed LE-KIDs by conducting electro-magnetic simulations, and fabricated them via photolithography. We evaluated the fabricated LE-KIDs at 100 mK and detected 36 resonances out of 39 designed resonances. The resonance frequencies are roughly located at the target locations to an accuracy of 0.1 GHz , and the simulation effectively reproduced the temperature dependence of the resonance frequency. We demonstrated an optical measurement of the LE-KIDs by using an LED with wavelength that matches that of the scintillation photon from GaAs, which can operate at 100 mK .