Piezoresistive accelerometer with overload protection and low cross-sensitivity

Abstract

Abstract A piezoresistive silicon bridge-type accelerometer is described. The application of a standard bipolar process allows the mechanical structure to be realized by anisotropic wet etching in KOH with an electrochemical etchstop at selectively diffused n-type layers. A novel glass-bonding technology offers complete encapsulation of the sensor with silicon top and bottom caps, including wafer-level assembly and simultaneous overload protection. Optimization of the mechanical structure by finite-element modelling (FEM) with respect to the resonance frequency results in the application of transverse piezoresistors with excellent cross-sensitivity compensation. The sensor features a sensitivity of 40 μV/N g with a non-linearity of less than 0.5% up to 350 g, first resonance frequency of about 5 kHz, and cross-sensitivity in lateral directions of less than 0.2% with an overall chip size of 3.7 × 3.7 × 1.0 mm3.