MEMS resonators are widely used in applications such as communications, inertial sensing, and navigation.
Traditional MEMS resonators are freely suspended or released and operated under vacuum/air to ensure free boundary conditions for acoustic reflection. However, when a resonator is fully encapsulated and surrounded by solid material the lack of perfect acoustic reflections at the boundary as well as energy losses to the surrounding medium result in a much reduced quality factor as well as output signal. To maintain a high quality factor for unreleased resonators, Phononic crystals (PnCs) and Acoustic Bragg reflectors (ABRs) can be used as confinement structures and trap specific frequencies within the cavity.
Integration of MEMS resonators with CMOS to form a single chip allows operation at GHz-frequencies, while reducing size, weight, and power consumption of the overall system. This technology is a method for creating acoustic localization structures, such as PnCs and ABRs, to surround a MEMS resonator and form an acoustic cavity. PnCs are structures with periodic variations in space in their mechanical properties, which lead to the existence of frequency bandgaps. ABRs are composed of periodic layers which are usually two or more materials alternatively located in space. By applying ABRs on the side of unreleased resonator, it is possible to reestablish the desired free or fixed boundary condition. In CMOS technology, such material combinations are effectively created using metal layers, vias, and the dielectric used to electrically isolate neighboring metal layers which naturally surrounds the vias.
- Fully CMOS compatible, requires no packaging or post-processing
- Increases quality factor
- Reduces power consumption