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We present poly-SiC coating and subsequent operation of a Si-based double-ended tuning fork (DETF) resonant strain sensor fabricated in the Bosch commercial foundry process. The coating is applied post release and, hence, has minimal impact on the front end of the microfabrication process. The deposition thickness of nanometer-thin SiC coating was optimized to provide enhanced corrosion resistance to silicon MEMS without compromising the electrical and mechanical performance of the original device. The coated DETF achieves a strain resolution of 0.2 µ in a 10 Hz to 20 kHz bandwidth, which is comparable to the uncoated device. The coated DETF is locally heated with an IR lamp and is shown to operate up to 190°C in air with a temperature sensitivity of -7.6 Hz/°C. The devices are also dipped in KOH at 80°C for 5 minutes without etching the structures, confirming the poly-SiC coating provides a sufficient chemical barrier to the underlying silicon. The results demonstrate that SiC-coated poly-Si devices are an effective bridge between poly-Si and full poly-SiC films for applications requiring a high level of corrosion resistance and moderate operating temperatures (up to 200°C) without compromising the performance characteristics of the original poly-Si device.

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A novel bending plate capacitive strain gauge is designed, fabricated, and tested to measure strain in the range of 1 to 1000 με. This silicon-based strain sensor uses a unique structural design to increase the on-axis gain through the use of a bending beam structure while attenuating signals due to cross-axis strain. A differential capacitive measurement is used to improve the output, reduce the parasitic capacitance, and eliminate the capacitance measurement error due to temperature. The device is fabricated using silicon-on-insulator (SOI) technology. Experimental results exhibit an on-axis sensitivity of 50 aF/με and attenuation of the cross-axis sensitivity to shear strain to less than 10 percent of the applied shear strain. A detailed mechanical analysis of the suspension and deflection-amplifying bent-beam capacitor will be presented. Furthermore, the capacitive plate analytical model is compared to finite element simulations and verified with experimental results. In addition, a noise assessment of the device shows the electronics noise dominates the Brownian noise.