Ultrahigh Q-frequency product for optomechanical disk resonators with a mechanical shield

We report on optomechanical GaAs disk resonators with ultrahigh quality factor-frequency product Q × f. Disks standing on a simple pedestal exhibit GHz mechanical breathing modes attaining a Q × f of 10 ¹³ measured under vacuum at cryogenic temperature. Clamping losses are found to be the dominant source of dissipation. An improved disk resonator geometry integrating a shield within the pedestal is then proposed, and its working principles and performances are investigated by numerical simulations. For dimensions compatible with fabrication constraints, the clamping-loss- limited Q reaches 10⁷-10⁹ corresponding to Q × f equals 10¹⁶-10¹⁸. This shielded pedestal approach applies to any heterostructure presenting an acoustic mismatch.