Quality factor enhancement in micromechanical resonators at cryogenic temperatures

Quality factors as high as 362,768 have been measured for 61-MHz polysilicon wine-glass disk micromechanical resonators operated at cryogenic temperatures down to 5K. The measured results not only represent a ~2.5times increase in Q over the room temperature value, equivalent to a nearly 10-dB improvement in phase noise; but also provide some limited insight into the intrinsic material damping and other loss mechanisms that dominate over certain temperature ranges. In particular, a measured Q versus temperature curve verifies a peaking point for phonon-phonon interaction losses at a temperature around 150K. In addition, measurement versus theory for resonators with different support designs suggests that anchor losses probably still dominate the Q's of the resonators over the entire measured temperature range, implying that improved anchor isolating designs are needed if the true intrinsic material Q's of polysilicon are to be measured at cryogenic temperatures.