Microwave probing of bulk dielectrics using superconducting coplanar resonators in distant-flip-chip geometry

Abstract

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, LaAlO 3 , and TiO 2 ), at temperatures between 1.4 K and 7 K.

Kinetic planar resonators from strongly disordered ultra-thin MoC superconducting films investigated by transmission line spectroscopy

“…The temperature dependence of the resonances was fitted by numerically calculated complex conductivity of disordered superconductor 1 with finite Γ. The obtained Γ parameters relate reasonably to the ones expected from STS measurements, showing that this theory could be utilized to describe the electrodynamic response of highly disordered superconductors, and vice versa: this non-contact method could be used to estimate the Γ and T c of highly disordered films, avoiding the nontrivial calibration procedure required in similar spectroscopic techniques 36 , or the requirement of structuring special resonators on the films 37 . Moreover, the understanding of the nature of these resonances can help eliminate them in the required bandwidth by smart design, as for example in Ref.…”

Characterization of harmonic modes and parasitic resonances in multi-mode superconducting coplanar resonators

“…The distance between both chips is ≈ 50 µm, and the coupling arm of the resonator on the flip-chip and the copper feedline face each other. 62 The dielectric constant of TiO 2 , between 110 and 260 depending on crystallographic direction, [63][64][65] is rather high, and thus harmonic and parasitic modes incorporating the TiO 2 can occur at comparably low frequencies.…”