Analysis of Mode-Split Operation in MEMS Based on Piezoresistive Nanogauges

Microelectromechanical system (MEMS) sensors based on nanoscale piezoresistive sensing elements (nanogauges) can have mechanical modes either related only to micrometric springs or related also to nanogauge constraints. Due to the different impact that fabrication process imperfections have on these two kinds of modes, their correlation can be poorer from part to part than in sensors based on capacitive readout. In this context, this paper compares the correlation between two modes in MEMS with and without nanogauges. Experiments show a ± 30% relative variation in the modes difference over 26 samples of the former type, which is more than 3.5 times more than what observed on similar structures with no nanogauges. A theoretical model identifies the sources of this fluctuation (local etching and height nonuniformities), and predicts the behavior and improvements using different springs design.