4.5 Article

Stress Relaxation Mechanism With a Ring-Shaped Beam for a Piezoresistive Three-Axis Accelerometer

Journal

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS
Volume 22, Issue 2, Pages 386-394

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JMEMS.2012.2227139

Keywords

Accelerometers; microelectromechanical systems; piezoresistance; plastic packaging

Funding

  1. Hitachi Metals, Ltd. Torex Semiconductor Ltd.

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A novel stress-relaxation structure with a ring-shaped beam for ensuring stability in a piezoresistive three-axis accelerometer assembled using wafer-level encapsulation and resin-mold packaging is proposed and evaluated in this paper. The reduction of the unstable increase in sensitivity due to buckling against three stress sources, i.e., the thermal stress in device fabrication, wafer bonding, and resin molding, was evaluated by both computer simulation and experiments on test samples. The measured increase in sensitivity due to stress during wafer bonding and resin molding was kept at 1.26 times using the ring-shaped beam, compared with 7.64 times when using a conventional straight beam. In addition, the standard deviation in the sensitivity of resin-molded samples was kept at 0.04 mV/G using the ring-shaped beam, compared with 2.19 mV/G using the straight beam. The sensitivity variation against the temperature change was also kept small and linear; thus, the effect of the ring-shaped beam was confirmed.

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