Selective polysilicon deposition for frequency tuning of MEMS resonators

A post-fabrication process was developed to tune the frequency of a set of comb-drive resonators by selectively adding polysilicon to their rotors. Selective deposition was performed by electrically heating the resonators in a silane environment using the same input voltage but varying process times. The resonant frequency of individual devices increased 0.7 to 2%, from an average initial resonant frequency of 86.6 kHz. A correlation between the change in frequency and the location of the newly deposited material was found and verified in a finite element simulation. The data show the percent change in frequency is also dependent on thermal history and initial material properties. This work describes the trends in a new MEMS resonators frequency tuning method.