A 10MHz piezoresistive MEMS resonator with high Q

A novel bulk mode MEMS resonator is presented where mechanical motion is detected using the piezoresistive properties of Si. The piezoresistive readout allows for a high transduction efficiency. The transconductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> obtained in this manner can be many times higher than the admittance Ym obtained in MEMS resonators that use capacitive read-out. By means of a small signal model it is shown that the transconductance is insensitive to geometric scaling, which allows for the realization of miniature high frequency MEMS resonators and oscillators without performance reduction. The piezoresistive detection method is experimentally validated using a 10MHz bulk acoustic mode resonator processed on SOI. Even for a transduction gap as large as 1.3 mum, it is shown that the transconductance can be as high as 90 muS combined with a Q-factor of 125.000.