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

Abstract

The paper reports on the fabrication and characterization of flexural resonators designed for resonant strain sensing and manufactured using 2 $\mu \text{m}$ 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 $\mu \text{m}$ . 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/ $\mu \varepsilon $ and a resolution of about 0.82 $\text{n}\varepsilon $ for the same measurement time. [2019-0183]