A New Design Strategy for Innovative MEMS xz-Biaxial Accelerometers

Micro-electro-mechanical systems (MEMS) accelerometers are entering high-end applications, thanks to their improved performance and low costs. Biaxial sensors able to measure two in-plane components of the external acceleration by exploiting a single proof-mass have been recently proposed and optimized both mechanically and electronically in order to minimize cross-axis sensitivity, while preserving a good symmetry between the two axes and high performance. To the author's best knowledge, only a very few commercial high-performance
xz
- or
yz
-biaxial MEMS accelerometers are available so far. In this work, we propose an innovative design strategy for
xz
-biaxial MEMS capacitive accelerometers immune from electrostatic nonlinearities and pull-in instabilities usually related to out-of-plane readout schemes. In particular, thanks to the proposed motion conversion mechanism realizable through the Thelma-double fabrication process of STMicroelectronics, we predict a sensitivity bigger than 30 fF/g on both axes, a cross-axis sensitivity smaller than 0.04% and a nonlinearity lower than 1% at 50 g.