Integrated tuning fork nanocavity optomechanical transducers with high $f_{M}Q_{M}$ product and stress-engineered frequency tuning

摘要

Cavity optomechanical systems are being widely developed for precision forceand displacement measurements. For nanomechanical transducers, there is usuallya trade-off between the frequency ($f_{M}$) and quality factor ($Q_{M}$), whichlimits temporal resolution and sensitivity. Here, we present a monolithiccavity optomechanical transducer supporting both high $f_{M}$ and high $Q_{M}$.By replacing the common doubly-clamped, Si$_3$N$_4$ nanobeam with a tuning forkgeometry, we demonstrate devices with the fundamental $f_{M}\approx29$ MHz and$Q_{M}\approx2.2$$\times10^5$, corresponding to an $f_{M}Q_{M}$ product of6.35$\times10^{12}$ Hz, comparable to the highest values previouslydemonstrated for room temperature operation. This high $f_{M}Q_{M}$ product ispartly achieved by engineering the stress of the tuning fork to be 3 times theresidual film stress through clamp design, which results in an increase of$f_{M}$ up to 1.5 times. Simulations reveal that the tuning fork designsimultaneously reduces the clamping, thermoelastic dissipation, and intrinsicmaterial damping contributions to mechanical loss. This work may findapplication when both high temporal and force resolution are important, such asin compact sensors for atomic force microscopy.