Loss Tangent of Ta Resonators as a Function of TaN Seed Layer Optimization

Transmon qubits have emerged as a forefront technology in quantum information science (QIS) supported by broadly accessible fabrication techniques. The current leading material for transmon fabrication, alpha-tantalum, requires metal deposition at high temperatures or a seed layer for lower deposition temperatures. In this study, we fabricated coplanar waveguides (CPWs) representing the readout resonator of a transmon qubit. While most transmons begin fabrication as metal films on wafers, we pursued a different route with device patterns initially trenched in the substrate followed by metal deposition and chemical mechanical planarization (CMP). Metal deposition followed a damascene process where TaN was deposited by ALD or PVD followed by sputtered Ta. We investigated loss in these devices as a function of seed layer deposition method and thickness. The etched trenches provided an increased surface area for the seed layer interface with tantalum thus enhancing our sensitivity to deposition parameters. We present the preliminary results of this ongoing research.