Induced Stress Enhancement Using U-shaped Arms in a 3-axis Piezoresistive MEMS Accelerometer

This paper presents a demonstration of the superiority in overall sensitivity of a U-shaped attachment structure used in the design of a 3-axis piezoresistive micromachined accelerometer. This is accomplished through a detailed comparison of generated maximum stress values in different similar designs reported in the literature. All these structures are composed of a seismic mass attached to the substrate with four arms. The structure uses four U-shaped arms with a short fragment located in their middle. The analysis on the U-shaped structure shows that maximum values of induced stress under acceleration in the axes are higher than those given by other structures used in the comparison study. This stress values enhancement is more pronounced for accelerations on the z-axis. Simulated structures used in the comparison study give maximum z-axis stress values of 0.5 MPa and 0.09 MPa while the U-shaped structure's value is 4.25 MPa. In addition, the Ax and Ay accelerations induce in our structure two different paths for maximum stress offering added sensitivity.