Abstract
Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal–air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate–air interface, thereby improving the quality factor.
Highlights
We differentiate four dielectric regions from which we can extract a loss tangent: the metal–substrate (MS) interface, the substrate–air (SA) interface, the metal–air (MA) interface, and the silicon (Si) substrate
While each dielectric region contributes significantly to loss in titanium nitride (TiN) devices, the metal–air interface dominates the loss in the Al devices
By measuring the intrinsic quality factor, Qi, of a set of four specific resonator geometries with a distinct distribution of participation values, we numerically solved for the loss factor of each dielectric region,[10] which we convert to a loss tangent using a reasonable set of assumptions about the dielectric constant and layer thickness.[20]
Summary
We differentiate four dielectric regions from which we can extract a loss tangent (see Fig. 1): the metal–substrate (MS) interface, the substrate–air (SA) interface, the metal–air (MA) interface, and the silicon (Si) substrate. We use the surface-loss extraction (SLE) process, outlined in Ref. 10, to model the dielectric regions of TiN and Al superconducting resonators and calculate the loss tangents of these regions based on the measured quality factors.
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