Out-of-plane dual flexure MEMS piezoresistive accelerometer with low cross axis sensitivity
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Accelerometers are one of the widely explored microsensors with many transduction mechanisms. One of the primary concerns with piezoresistive microaccelerometers is their cross axis sensitivity. The main reason for cross axis response is the mechanical offset between the flexures and the center of mass of the proofmass. Cross axis sensitivity is generally minimized electronically using bridge configurations of piezoresistors or by depositing high density materials like gold over the proofmass to balance the mechanical structure. Here a novel non planar dual flexure geometry has been proposed which make the effective beam center of mass to align with that of the proof mass and thereby achieve low cross axis sensitivity by the mechanical design itself. The hybrid integration of electronic compensation with the mechanical compensation realizes a high performance accelerometer with ultralow cross axis sensitivity. Four piezoresistors placed on one flexure are configured such that the output voltage will be maximum for prime axis input while the bridge is balanced for the inputs along remaining two axes. The analytical model of the proposed structure, and the finite element analysis results are discussed. The device exhibits a very low cross axis sensitivity of 0.006% in Y direction and 0.005% in X direction while maintaining high prime axis sensitivity of 2.28 mV/g. The device also shows very low non linearity (1%) over a range of 100 g acceleration and a resonant frequency of 1.7 kHz.