Strained Nanoribbons Enhance Torque and Weak Force Detection Sensitivity

Strained silicon nitride nanoribbons, optimised via Bayesian optimisation, demonstrate enhanced torsional motion with dissipation dilution factors exceeding 100 million and –frequency products exceeding 1 Hz at room temperature. Devices exhibit thermal torque sensitivity at 10⁻¹⁴ Nm/√Hz and angular displacement spectral density of 10⁻⁹ rad/√Hz, alongside ease of fabrication and high thermal conductivity.

The pursuit of highly sensitive mechanical sensors continues to drive innovation in nanoscale fabrication. Researchers are now demonstrating enhanced performance in torsional nanomechanical resonators by optimising device geometry to minimise energy loss. A team led by A. D. Hyatt, A. R. Agrawal, C. M. Pluchar, C. A. Condos, and D. J. Wilson, all from the Wyant College of Optical Sciences at the University of Arizona, detail their work in ‘Ultrahigh-Q Torsional Nanomechanics through Bayesian Optimization’. They report achieving quality factors exceeding 100 million and corresponding frequency products exceeding 1 Hz at room temperature, utilising Bayesian optimisation to design silicon nitride nanoribbons with significantly reduced bending loss.

Optimised Nanoribbon Design for Enhanced Torque Sensitivity

Recent research details substantial progress in high-performance nanomechanical resonator design and fabrication, achieving quality factors exceeding 100 million and frequency-quality products surpassing 1 Hz at room temperature. This optimisation directly addresses limitations imposed by bending loss in strained nanomechanical resonators, specifically mitigating the impact of mode curvature at clamping points. Researchers engineered nanoribbon geometries to maximise dissipation dilution of the fundamental torsion mode, enabling sensitive detection of weak forces and advancing optomechanical experiments.

The study centres on strained nanoribbons, which leverage a phenomenon termed dissipation dilution to amplify torque and improve optomechanical measurements. Bending loss, arising from the curvature of the resonator’s vibrational mode at its fixed ends, traditionally limits performance. To overcome this, scientists employed Bayesian optimisation – a probabilistic method for optimising complex functions – to design nanoribbons that maximise dissipation dilution. Dissipation dilution refers to the spreading of vibrational energy across multiple modes, reducing energy loss from the primary mode of interest.

Researchers successfully applied this optimisation process to the design of centimetre-scale silicon nitride (Si₃N₄) nanoribbons. Silicon nitride was chosen for its high strength, low intrinsic loss, and compatibility with established microfabrication techniques. The resulting devices exhibit quality factors exceeding 100 million and a frequency-times-quality factor product surpassing 1 Hz at room temperature, demonstrating exceptional performance. The optimised design minimises energy dissipation, allowing the resonator to sustain oscillations for longer and detect weaker signals.

The fabricated nanoribbons achieve a thermal torque sensitivity at the level of N⋅m/rad, and a zero-point angular displacement spectral density of rad/s, indicating a high degree of precision. These values represent a considerable improvement over existing technologies.

Importantly, the design facilitates straightforward fabrication, maintains high thermal conductivity, and allows for substantial mass-loading without compromising the quality factor, making it a practical and versatile solution. The fabrication process utilises established microfabrication techniques, ensuring scalability and reproducibility, while the high thermal conductivity efficiently dissipates heat, preventing thermal drift and maintaining stable performance.

The success of this design isn’t solely about minimising loss; it’s also about maximising the resonator’s ability to detect subtle forces, pushing the boundaries of sensitivity in nanomechanical systems.

These characteristics position the optimised nanoribbons as promising candidates for a wide range of applications, encompassing both fundamental investigations into weak forces and the development of sensitive applied technologies. Researchers envision utilising these resonators for diverse applications, including searching for dark matter, developing highly sensitive accelerometers and gyroscopes, and conducting novel optomechanical experiments.

The combination of optimised design, material properties, and fabrication simplicity positions these nanoribbons as a promising platform for future weak force detection technologies. Future work will focus on exploring the limits of this design approach with smaller geometries and different materials, further enhancing the performance and expanding the range of applications. Investigating the integration of these resonators with superconducting circuits could further enhance their performance and unlock new possibilities for quantum sensing and information processing. The demonstrated success of Bayesian optimisation in this context also highlights its potential as a powerful tool for the design of advanced nanomechanical systems across various disciplines.

This work establishes a new benchmark in nanomechanical sensing. The study’s findings have significant implications for various fields, including fundamental physics, materials science, and engineering, opening new avenues for research and innovation.