Tension-torsion-bending combined loading test technique for the reliability of MEMS structures

In this paper, tension-torsion-bending combined loading test technique for microscale single crystal silicon beam specimens is described. We have designed and developed two types of the multi-deformation loading test apparatuses to investigate the deformation-mode and specimen-size dependencies on the fracture strength. The comparisons among the strength data under different deformation-modes and different sizes were made using the Weibull statistics. Both of the size effect and the deformation-mode effect were apparently found when all the strength data were calculated based on the assumption that the specimens had ideal flat sidewalls. Stress concentration factors (SCFs) in each specimen were estimated using scanning electron microscopy observation and finite element analysis. After re-calculation of all the strength data in consideration of the SCFs, the Weibull distribution showed no deformation-mode effect though size effect still remained.