Extraction and Modeling of TLS Losses in TiN Qubits*

Predictive modeling of microwave loss due to dielectric two-level-systems allows for design optimization and targeted fabrication-process development to improve the performance of transmon qubits. We have previously used isotropically-trenched TiN and Al resonators to extract TLS-loss characteristics of material interfaces and the Si substrate [1, 2]. Applying this knowledge to the design and modeling of TiN qubits is complicated by the additional processing needed to fabricate high-quality Josephson junctions, which can induce additional defects at the various surfaces and interfaces. In this talk, we discuss the iterative process development that reduced the effect of these additional fabrication steps. With the resulting improved process, we determined the surface-loss contributions in TiN resonators and constructed a predictive loss model for co-fabricated TiN transmon qubits.
[1] Woods, Phys. Rev. Appl. 12, 014012 (2019)
[2] Melville, Appl. Phys. Lett. 117, 124004 (2020)