VHF CMOS-MEMS resonator monolithically integrated in a standard 0.35μm CMOS technology

This paper focuses on the design, fabrication and characterization of polysilicon microresonators monolithically integrated in a CMOS standard technology (AMS 0.35 mum). The design is focused in on-plane flexural clamped-clamped beams to attain frequencies in the VHF range. Resonators are fabricated using two polysilicon layers separated by a thin silicon oxide layer. Polysilicon layers are used indistinctively for electrodes and resonator structure whereas 40 nm-thick silicon oxide layer defines the gap between resonator and electrodes. A maskless post-CMOS process is needed for releasing the movable structures. A monolithically integrated CMOS circuitry along with the resonator is implemented to increase its capacitive read-out signal. The characterization of the resonators has been done by two-terminal measurements by means of a network analyzer both in air and in vacuum, and complemented by mixing measurements. A Qxf product of 2times10¹¹ MHz in vacuum is achieved.