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

TL;DR

This paper introduces a monolithic cavity optomechanical transducer with a tuning fork design that achieves high mechanical frequency and quality factor, enhancing sensitivity and temporal resolution for precision measurements at room temperature.

Contribution

The study presents a novel tuning fork nanocavity design that simultaneously boosts frequency and quality factor, surpassing previous room temperature performance limits.

Findings

Achieved a fundamental frequency of ~29 MHz and Q factor of ~2.2×10^5.

Realized an fQ product of 6.35×10^{12} Hz, comparable to top room temperature values.

Stress engineering and clamp design improve mechanical performance and reduce dissipation.

Abstract

Cavity optomechanical systems are being widely developed for precision force and displacement measurements. For nanomechanical transducers, there is usually a trade-off between the frequency ($f_{M}$) and quality factor ($Q_{M}$), which limits temporal resolution and sensitivity. Here, we present a monolithic cavity 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 fork geometry, 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 of 6.35$\times10^{12}$ Hz, comparable to the highest values previously demonstrated for room temperature operation. This high $f_{M}Q_{M}$ product is partly achieved by engineering the stress of the tuning fork to be 3 times the residual film stress through clamp design, which results in an increase of $f_{M}$ up to 1.5 times. Simulations reveal that the tuning fork design simultaneously reduces the clamping, thermoelastic dissipation, and intrinsic material damping contributions to mechanical loss. This work may find application when both high temporal and force resolution are important, such as in compact sensors for atomic force microscopy.