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.