Abstract: Single-crystal silicon structures in silicon-based micro-electro-mechanical systems are usually exposed to cyclic stresses, which, consequently, may fail easily because of mechanical fatigue. There’s a great gradient in the fatigue lifetime of the single crystal silicon micro-structures, thus rendering it hard to make out how the phosphorus impurities affect the fatigue properties by comparing the fatigue lifetime of specimens with different doping concentrations. This research aims at solving this problem. A specially designed micro-structure that can simultaneously experiment on four beams is presented. A simple bending test device is presented, which satisfies the requirement for test precision and is economically built. The bending fatigue life for six groups of specimens with different phosphorus doping concentrations is tested at room temperature. A kind of fatigue failure probability prediction model deducted from Paris formula is introduced. The C and n in Paris formula are obtained with the model. The C decreases approximately 3 orders, while the n increases only a little, indicating that C changes dominantly. Therefore, the defect propagation velocity decreases as the phosphorus doping concentration increases. Research on this topic therefore shows some practical significance for the reliability design of silicon-based micro-electro-mechanical systems.

Key words: bending fatigue lifetime, micro-electro-mechanical systems, Paris formula, phosphorus doping, single crystal silicon micro-beam