Low-Power Temperature-Stable Encapsulated MEMS Silicon Resonators


"[it is desired to have] a Watch to keep Time exactly: But, by reason of the Motion of a Ship, the Variation of Heat and Cold, Wet and Dry, and the difference of Gravity in different Latitudes, such a Watch hath not yet been made."

Sir Isaac Newton, report to the House of Commons, 1714


- Thermal Isolation of MEMS Resonators

- High Precision MEMS Digital Temperature Sensor

- Shape Optimization of Micro-Structures

CMOS compatible MEMS resonators are becoming an interesting and viable technology as a replacement for quartz crystals for timing and frequency reference applications. Oven controlled silicon  and quartz resonators are used to generate high precision frequency references suitable for high-end industry and military standards. In this method, the resonator is held at a fixed temperature to compensate for the temperature dependence of the resonator frequency. The extent to which the resonator is heated depends on the difference between the set-point and the ambient temperature. For an ovenized resonator required to operate within a temperature range of -40C to 85C, the heating has to cover the range of 125C. Due to the large volume of a conventional quartz crystal resonators, which can be up to 1000 mm3, the power consumption is up to 10W with a warm-up time of approximately 30 minutes. MEMS technology offers miniaturization to sub-mm scales which can provide substantial power reduction.

This research describes a miniature thermal isolation design which achieves a small thermal time constant with low power consumption, and a unique self-temperature sensing technique of resonators to achieve our ultimate goal of low-power temperature-stable resonators. To further increase the thermal isolation and temperature-stability of the resonator while maintaining a mechanically stiff structure, an optimum resonant structure needs to be designed.

 


Supported by the DARPA HERMIT Program


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