High Shock-Resistant Design for Wafer-Level-Packaged Three-Axis Accelerometer With Ring-Shaped Beam

A novel high shock-resistant beam design for a piezoresistive three-axis accelerometer with a distinctive ring-shaped beam structure introduced for relaxing assembling stresses is discussed. Through simulations modeling shock tests, the transient responses of a sensor device having a mass suspended with four beams and encapsulated using a wafer-level-packaging process were analyzed in detail. The beams are negatively affected by large axial tensile stress originating from a high-frequency vibration mode, and rapid stress increases just after the crashing of the mass into the encapsulation caps. Thus, the ring beam should be designed to simultaneously reduce the maximum stress for shock resistance and increase flexibility for stress relaxation against axial tensile load. A noticeable shock resistance against a peak acceleration of 20 000 G was achieved without sacrificing the stress-relaxation effect of the ring by applying an optimized ring design and minimizing the gap between the mass and cap to soften the crash.