Ultrahigh-Dynamic-Range Resonant MEMS Load Cells for Micromechanical Test Frames

This paper presents a resonant double-ended tuning fork (DETF) force sensor with an experimentally demonstrated resolution of 7 nN and a compressive load range of 0.08 N, exceeding a dynamic range of 140 dB (100 parts per billion). The resonator has a scale factor of 216 kHz/N, a Q -factor exceeding 60 000 at 3-mtorr ambient pressure, and a zero-load resonant frequency of 47.6 kHz. The resonator is kept at resonance via a phase-locked loop composed of discrete elements. The sensor is implemented with a silicon-on-glass process with a 100-μm -thick <;111>; silicon structural layer. The sensor and the complete readout circuit are fully embedded in a compact 65 mm × 52 mm printed circuit board (PCB). The out-of-plane parasitic modes of the DETF are also investigated with finite-element simulations and laser Doppler vibrometry experiments, and are verified to be outside of the device working range. The PCB is mounted on a microstage and coupled with an off-the-shelf displacement actuator to realize an economical, versatile, and robust micromechanical test frame with unprecedented combination of force and displacement resolution and range.