Effect of metal annealing on the Q-factor of metal- coated fused silica micro shell resonators

This paper reports on the effect of annealing thin metal films coated on high-Q fused silica shell resonators. While the ring-down time of some resonators improves with annealing, others degrade. Investigations include the effect of annealing on metal film stress, roughness, and elemental composition, as well as the effect of film thickness and roughness on quality factor. Increased tensile stress and film roughness are observed after annealing; it is suspected that these changes are due to formation of intermetallic grain boundaries that result in film densification and the formation of hillocks. Increasing film thickness reduces Q, though it is unlikely due to thermoelastic damping. Surface roughness tends to increase with film thickness, but does not appear to have a direct correlation with Q.