Piezoresistive Transduction in a Double-Ended Tuning Fork SOI MEMS Resonator for Enhanced Linear Electrical Performance

It has been demonstrated that the piezoresistive effect in silicon can be useful for boosting electromechanical transduction in Micro Electro Mechanical Systems (MEMS) resonators. Piezoresistive sensing has been applied to a number of different extensional mode resonator topologies. In comparison, flexural modes are more compliant and of greater interest for mechanical sensing applications. To adopt piezoresistive sensing, flexural-mode resonators require patterning and doping to define piezoresistors at given locations. In this paper, we report a MEMS flexural-mode double-ended tuning fork (DETF) resonator that employs piezoresistive readout using the whole beam as the piezoresistive strain gauge. We show that the boundary conditions of the DETF allow for linear piezoresistive readout at the fundamental resonant frequency. In our device characterization results, we show that a bias current of 10 mA increases the transduction by 22 dB over the capacitive readout. We also model the coupling between beam deformations and the resulting changes in piezoresistivity.