CMOS Compatible Wafer-Scale Encapsulation MEMS Resonators

A unique MEMS encapsulation process on the use of epipolysilicon as a packaging and sealing layer is demonstrated. This process provides a very clean and stable environment for MEMS, is compatible with CMOS integration, and can be carried out in a conventional CMOS facility with standard tools. Silicon resonators fabricated inside the ‘epi-seal’ encapsulation showed quality factors over 10,000 and commercial level long-term stability (ppm level drift for over 1 year of operation). In addition, several modifications and improvements, such as Si-SiO₂ composite resonators for reduced temperature coefficient of frequency and thermal isolated anchors for direct temperature control were successfully added to this process for improvements in resonator stability over temperature.