Ultralow Loss Torsion Micropendula for Chipscale Gravimetry

We explore a new class of chipscale torsion pendula formed by Si3N4 nanoribbon suspensions. Owing to their unique heirarchy of gravitational, tensile, and elastic stiffness, the devices exhibit damping rates of ∼10μHz and parametric gravity sensitivities near that of an ideal pendulum. The suspension nonlinearity can also be used to cancel the pendulum nonlinearity, paving the way toward fully isochronous, high Q pendulum gravimeters. As a demonstration, we study a 0.1 mg, 32 Hz micropendulum with a damping rate of 16μHz, a thermal acceleration sensitivity of 2×10-9g0/Hz(g0=9.8m/s2), and a parametric gravity sensitivity of 5Hz/g0. We record Allan deviations as low as 2.5μHz at 100 seconds, corresponding to a bias stability of 5×10-7g0. We also demonstrate a 100-fold cancellation of the pendulum nonlinearity. In addition to inertial sensing, our devices are well suited to proposed searches for new physics exploiting low-loss micro- to milligram-scale mechanical oscillators.