Improving the mechanical quality factor of ultra-low-loss silicon resonators

In its as-fabricated state, a silicon mechanical resonator with a very high quality factor at liquid helium temperatures is found to have two energy loss mechanisms which can be removed with a 3 h anneal at 300 degrees C. Because of the silicon wafer processing history, these mechanisms are likely introduced during the resonator fabrication process. One energy loss mechanism contributes to the overall background damping over the entire measured temperature range, 400 mK <= T <= 300 K, at a level of Delta Q(-1) approximate to 3 x 10(-9), and gradually reappears after aging on the order of 100 d timescales. The second energy loss mechanism is a broad peak, Delta Q(-1) approximate to 2 x 10(-8), centered near 100 K. This peak does not re-appear upon aging and is tentatively attributed to the tetrafluoromethane reactive ion etch step, despite the fact that the silicon resonator is protected with silicon nitride and photoresist during the process.