Microwave loss in amorphous silicon for coherent superconducting technologies

Efforts to design superconducting quantum technologies have generated an interest in understanding the materials mechanisms responsible for microwave photon loss in coherent devices. While a desire for long coherence times has driven many groups to pursue devices fabricated on crystalline substrates, close study of loss in deposited dielectrics has also played an important role in the development of the field. Recent efforts at 3D integration suggest that a more complete understanding of the relationship between loss and defectivity in amorphous films is still needed. We discuss current microstructural models of defectivity in amorphous silicon (a-Si), a material commonly used in the semiconductor and solar industries, and relate these concepts to microwave photon loss in superconducting resonators fabricated on a-Si films deposited under growth conditions targeting low defect incorporation. Experimental data from cryogenic quality factor measurements will be presented and coupled to structural information derived via TEM and other materials spectroscopies.