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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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We present the fabrication and testing of a silicon carbide balanced mass double-ended tuning fork that survives harsh environments without compromising the device strain sensitivity and resolution bandwidth. The device features a material stack that survives corrosive environments and enables high-temperature operation. To perform hightemperature testing, a specialized setup was constructed that allows the tuning fork to be characterized using traditional silicon electronics. The tuning fork has been operated at 600°C in the presence of dry steam for short durations. This tuning fork has also been tested to 64,000 G using a hard-launch, soft-catch shock implemented with a light gas gun. However, the device still has a strain sensitivity of 66 Hz/ ⑀ and strain resolution of 0.045 ⑀ in a 10-kHz bandwidth. As such, this balanced-mass double-ended tuning fork can be used to create a variety of different sensors including strain gauges, accelerometers, gyroscopes, and pressure transducers. Given the adaptable fabrication process flow, this device could be useful to microelectromechanical systems ͑MEMS͒ designers creating sensors for a variety of different applications.