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This paper presents the design and results of shock experiments conducted to demonstrate the advantages of two novel shock-protection technologies: 1) nonlinear spring shock stops and 2) soft coating shock stops. Both technologies basically employ the conventional idea of hard shock stops to decouple device design from shock-protection design but are specialized to reduce impact force, which is one of the drawbacks of hard stops. In addition, they enable wafer-level and batch fabrication processes compatible with microfabrication techniques. We designed test devices to reflect the effect of impact force and fabricated them using silicon microbeams (nonlinear springs) or Parylene coating (soft coating). After conducting multiple shock tests (up to 2500 g), we demonstrate that the shock-survival rates of test devices are considerably improved in both our novel technologies (nonlinear spring: 88%, soft coating: 94%) compared to conventional hard stops (4%). Moreover, we demonstrated that shock protection is improved by optimizing the design of shock springs. Finally, we analyzed dynamics of flexible beams and identified a new device-fracture mechanism induced by impact force, which is different from conventionally known mechanisms.
Date of Publication: Aug. 2011