Differential piezoresistive sensing in a bulk-mode micromechanical resonator

A report is presented on a differential piezoresistive sensing approach for transducing the motional response of bulk-mode micromechanical resonators. High-frequency bulk-mode micoresonators have inherently high stiffness and demonstrate limited range of motion, which in turn presents challenges for the capacitive sensing method in the presence of large parasitic feedthrough. A differential piezoresistive sensing approach is implemented in this Letter to substantially reject the effects of parasitic capacitive feedthrough, leaving the response recovered directly from the measurement. With differential pick-up, a 33 dB drop of feedthrough has been achieved and a resonant peak magnitude of 14 dB is obtained for a drain current of 1 mA, which is shown to be approximately 20 times higher than that obtained for the conventional piezoresistive sensing scheme. This method also enables a low DC voltage for capacitively driving the bulk-mode resonator. As an example, a resonant peak magnitude of 5 dB is demonstrated using 3.55 mA drain current and 5 V DC driving voltage.