Process-agnostic design approaches to increase the performance of resonant sensors

Resonant sensors are widely used, especially in microsystems, for their high sensitivity, dynamic range, and resolution. In a typical resonant sensor, the measurand is converted to an axial force on a resonating beam, affecting its effective stiffness and consequently causing a shift in its resonance frequency. For a given operating frequency, it is desired to maximize the sensitivity of the resonance frequency to this axial force. In this paper, we propose new structural designs that significantly improve the sensitivity of resonant sensors to axial force. Our approach relies on structural modifications to resonant beams, including their boundary conditions, and hence, is amiable for implementation in different microfabrication processes. We present a mathematical model which is confirmed through simulations. Test devices were fabricated and used to validate the design principles. Our experimental findings indicate a sensitivity improvement of over four-fold for the test devices compared to the standard clamped-clamped beam structure. Without any modification to a fabrication process, the design principles presented in this work can be utilized to improve the performance of most micro- and nano-device designs that rely on conventional resonant beam force sensors.