Differential Fringe-Field MEMS Accelerometer

A new differential microelectromechanical systems accelerometer based on fringe-field sensing is presented. The basic working principle relies on the generation of fringe electric fields in the volume in between and over two biased coplanar interconnections; a grounded suspended micromachined mass, moving in this fringe volume, differently intercepts the electric field lines for different positions, giving rise to capacitance changes between the interconnections, used as electrodes. The capacitance variation can be then transformed into a voltage signal using standard capacitive readout techniques. The design exploits a new geometry, a technological scaling, and for the first time, a differential configuration to reach a measured sensitivity of 2.7 fF/g in the tested range of ±2 g of external acceleration. With respect to parallel-plate configurations, the device is immune from in-plane pull-in instability as the suspended mass does not face fixed parts biased at different voltages.