An ultra-low-loss micromechanical torsion balance leveraging nanoscale dissipation dilution

C. Condos, J. Pratt
NIST/University of Arizona, District of Columbia, United States

Poster stand number: W144

Keywords: gravimetry, accelerometer, gyro, torsion balance

Torsion balances play a pivotal role in a diversity of precision measurements. Recent efforts to reduce their dimensions to the micron scale have enabled a new class of chip-scale sensors that grant access to phenomena at the boundary of gravitational and quantum physics. We have fashioned a micromechanical torsion balance by suspending a silicon mass from a tensile-strained silicon nitride (Si3N4) nanoribbon. Stress in the nanoribbon produces a lossless torsion constant that dilutes the loss produces by elastic deformation, yielding quality factors greater than 10^6 for the 10 Hz fundamental torsional mode of 0.1 mg prototype devices, corresponding to an unprecedented (for this form factor) thermal torque sensitivity of 100 zNm/rt(Hz). We also present a simple theory that successfully predicts the Q of our devices and describes the contributions of elastic, tensile, and gravitational restoring torques to the total torsional stiffness, appealing to well-known results from macroscopic torsion balances. Our ultra-low-loss micromechanical torsion balance is easy to fabricate, lends itself to integration with on-chip light sources, waveguides, patterned electrodes for detection and actuation schemes, and can be fabricated into arrays, hinting at a powerful new platform for the quantum limited detection of forces below a femtonewton.