Low Loss Superconducting Titanium Nitride Coplanar Waveguide Resonators

TL;DR

This study investigates how the crystalline orientation of sputtered TiN films affects the quality factors of coplanar waveguide resonators at millikelvin temperatures, revealing that (200)-oriented TiN yields higher quality factors.

Contribution

It demonstrates that (200)-oriented TiN films, achieved through specific growth conditions, significantly improve the internal quality factors of superconducting resonators compared to (111)-oriented films.

Findings

(200)-TiN orientation correlates with higher Q_i (>10^7) at high power.

(111)-TiN orientation results in lower Q_i (~10^5).

Growth conditions and buffer layers influence TiN orientation and resonator quality.

Abstract

Thin films of TiN were sputter-deposited onto Si and sapphire wafers with and without SiN buffer layers. The films were fabricated into RF coplanar waveguide resonators, and internal quality factor measurements were taken at millikelvin temperatures in both the many photon and single photon limits, i.e. high and low power regimes, respectively. At high power, internal quality factors ($Q_i$'s) higher than $10^7$ were measured for TiN with predominantly a (200)-TiN orientation. Films that showed significant (111)-TiN texture invariably had much lower $Q_i$'s, on the order of $10^5$. Our studies show that the (200)-TiN is favored for growth at high temperature on either bare Si or SiN buffer layers. However, growth on bare sapphire or Si(100) at low temperature resulted in primarily a (111)-TiN orientation. Ellipsometry and Auger measurements indicate that the (200)-TiN growth on the bare Si substrates is correlated with the formation of a thin, $\approx 2$ nm, layer of SiN during the pre-deposition procedure. In the single photon regime, $Q_i$ of these films exceeded $8\times10^5$, while thicker SiN buffer layers led to reduced $Q_i$'s at low power.