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Register a new userLow microwave loss in deposited Si and Ge thin-film dielectrics at single-photon power and low temperatures
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Our study shows that deposited Ge and Si dielectric thin-films can exhibit low microwave losses at near single-photon powers and sub-Kelvin temperatures ($approx$40 mK). This low loss enables their use in a wide range of devices, including low-loss coplanar, microstrip, and stripline resonators, as well as layers for device isolation, inter-wiring dielectrics, and passivation in microwave and Josephson junction circuit fabrication. We use coplanar microwave resonator structures with narrow trace widths of 2-16 $mu textrm{m}$ to maximize the sensitivity of loss tangent measurements to the interface and properties of the deposited dielectrics, rather than to optimize the quality factor. In this configuration, thermally-evaporated $approx 1 mu textrm{m}$ thick amorphous germanium (a-Ge) films deposited on Si (100) have a single photon loss tangent of $1-2times10^{-6}$ and, $9 mu textrm{m}$-thick chemical vapor deposited (CVD) homoepitaxial Si has a single photon loss tangent of $0.6-2times 10^{-5}$. Interface contamination limits the loss in these devices.
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Dielectric measurements on insulating materials at cryogenic temperatures can be challenging, depending on the frequency and temperature ranges of interest. We present a technique to study the dielectric properties of bulk dielectrics at GHz frequencies. A superconducting coplanar Nb resonator is deposited directly on the material of interest, and this resonator is then probed in distant-flip-chip geometry with a microwave feedline on a separate chip. Evaluating several harmonics of the resonator gives access to various probing frequencies, in the present studies up to 20 GHz. We demonstrate the technique on three different materials (MgO, LaAlO3, and TiO2), at temperatures between 1.4 K and 7 K.
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