Nanostrain Resolution Strain Sensing by Monocrystalline 3C-SiC on SOI Electrostatic MEMS Resonators

The paper reports on the fabrication and characterization of flexural resonators designed for resonant strain sensing and manufactured using 2 ?m thick monocrystalline 3C-SiC layers grown on Silicon-On-Insulator substrates. The resonators are designed with Double-Ended-Tuning Fork geometry and actuated electrostatically using lateral electrodes fixed on the sides of the resonator tines, through coupling gaps with average width of 1.03 ?m. They show excellent performance in vacuum environment with Q-factor around 30,000 and 18 dB high resonance peaks measured in open loop with DC bias voltage of 20 V. The closed-loop operation of the resonators with an external transimpedance amplifier feedback circuit is demonstrated and the stability of the resulting MEMS oscillator is analyzed using a microcontroller-based digital readout to measure its oscillation frequency. The results of the Allan deviation tests on the MEMS oscillator indicate a relative frequency stability better than 10-7 on a measurement time of 280 ms. The results of strain sensitivity experiments in vacuum performed after adhesive attachment of the resonator chip on Al are also reported, indicating a sensitivity of 41.7 Hz/ ? and a resolution of about 0.82 n for the same measurement time. [2019-0183].