I. Introduction
Frequency sources and high quality filters are essential building blocks for both analog and digital electronics, and communication systems. They are becoming more and more ubiquitous every day with growing applications that require further reduction in size, weight and power consumption, driving toward unprecedented scaling and integration of frequency sources and filters. Integration of micro-electro-mechanical (MEM) resonators with CMOS have been studied extensively and several approaches have been proposed [1]–[3], with the most notable including MEMS-first, MEMS-last and CMOS-MEMS technologies. However, these techniques require extensive post-processing, and complicated protection techniques for various parts of the chip at different stages of the fabrication process. Furthermore, the resulting MEMS devices always have exposed moving surfaces, requiring hermetic sealing together with specialized and costly packaging to avoid device performance degradation with time and to shield them from the surrounding environment [4]–[6].