CMOS-MEMS post processing compatible capacitively transduced GeSi resonators

This paper reports on the fabrication, simulation and characterization of post processing compatible poly GeSi MEM resonators. The resonators are fabricated, following a two masks process flow, using 1.5 μm thick low stress, highly conductive in-situ boron doped LPCVD poly Ge_0.7Si_0.3 structural layers. All the process steps are kept below 450°C to potentially avoid CMOS degradation, a prime concern for post processing compatible MEMS. A narrow gap of ~40 nm is achieved using a sacrificial gap oxide layer between the vibrating structure and the electrodes. The GeSi resonators, square plate and circular disk, are excited in their respective Lamé and Wine glass modes exhibiting the resonance peaks at 47.9 MHz and 72.77 MHz, respectively, with the quality factor around 200,000 in air, the highest reported till date for post processing compatible capacitively transduced resonators.