Sail membranes for optomechanical accelerometry

Strained membrane resonators are a standard platform for force sensing, but achieving the combination of low resonance frequency and high Q-mass product—which is critical for high-sensitivity accelerometry—remains a challenge. The authors sought to overcome the limitations of traditional square membrane geometries by designing a new class of "sail-like" trampoline resonators that optimize the trade-off between mass, frequency, and mechanical dissipation.

The researchers utilized Bayesian optimization to explore a multidimensional design space for silicon nitride (Si3N4) membranes. By varying parameters such as pad width, tether width, and fillet radii, they identified geometries that concentrate stress in the clamps to enhance the quality factor (Q) while simultaneously increasing the effective mass to lower the fundamental frequency. They fabricated these optimized "sail" membranes using photolithography and a two-stage wet-etching process, then integrated them with a nanoribbon to create a monolithic cavity optomechanical accelerometer.

The optimized sail membranes achieved fundamental resonance frequencies below 10 kHz and Q-factors up to 10^7, resulting in a Q-mass product of approximately 10 g. This performance represents an order-of-magnitude reduction in frequency compared to conventional designs while preserving high Q. The integrated accelerometer demonstrated a room-temperature thermal noise of 40 ng/sqrt(Hz) and a displacement imprecision of 10^-14 m/sqrt(Hz), sufficient to resolve ambient vibrations at the micro-g level. The authors suggest that these devices are well-suited for future applications in fundamental physics, such as dark matter searches and distributed quantum sensing.

This work provides a scalable, chip-integrated solution for high-sensitivity acceleration sensing. By using machine-learning-guided design to push the limits of dissipation dilution, the authors have opened a new regime for optomechanical sensors that could eventually surpass the sensitivity of current commercial devices, offering a path toward portable, high-precision instruments for both practical vibrometry and exotic physics experiments.