Precision optomechanical accelerometer via hybrid test mass integration

TL;DR

This paper introduces a hybrid test mass integration method for on-chip accelerometers, significantly enhancing sensitivity by bonding a dense platinum sphere to a silicon nitride membrane, achieving record peak sensitivity.

Contribution

It presents a novel pick-and-place bonding technique to increase test mass in on-chip accelerometers, improving sensitivity beyond previous limits.

Findings

Achieved a quality factor of 1900 in air with 95 mg test mass.

Demonstrated a peak sensitivity of 5.5 nG/√Hz at 117 Hz.

Reported the best peak sensitivity for chip-integrated test mass accelerometers.

Abstract

Accelerometers offer motion sensing capabilities across a wide range of areas, enabling navigational awareness in consumer goods and defense applications, and playing a key role in monitoring and control systems. To date, on-chip accelerometers have largely utilized a single device layer or substrate as a test mass. This constrains the test mass to the dimensions and density of the device layer or substrate, ultimately limiting the sensitivity of the device. We demonstrate a new approach which utilizes a pick-and-place bonding technique to increase the test mass of an on-chip accelerometer. By bonding a high-density platinum sphere to a nanomechanical silicon nitride trampoline membrane, we achieve a quality factor of 1900 in air with 95 mg test mass, corresponding to a thermomechanical noise limited acceleration sensitivity of $0.8\,\mathrm{n}g/\sqrt{\mathrm{Hz}}$. We optically probe the device's response to applied accelerations with increasing level of acoustic and vibration isolation, measuring a peak sensitivity of $5.5\,\mathrm{n}g/\sqrt{\mathrm{Hz}}$ at 117 Hz in air, limited by environmental vibrations. This represents the best peak sensitivity reported using a chip-integrated test mass.