Fatigue Experiments on Single Crystal Silicon in an Oxygen-Free Environment

The fatigue lifetime of single crystal silicon (SCS) was characterized in an environment free of oxygen, humidity, and organics. Long-term (> 10¹⁰ Hz) fatigue experiments performed with smooth-walled SCS devices showed no signs of fatigue damage up to 7.5 GPa. In contrast, experiments using SCS devices with a silicon dioxide (SiO₂) coating and rough sidewalls due to scalloping from deep reactive ion etching exhibited fatigue drift at 2.7 GPa and suffered from short-term (<; 10¹⁰ Hz) fatigue failure at stress levels >3 GPa. In these SCS-SiO₂ experiments, the initiation of fracture occurs in the SiO₂ layer. It is concluded that fatigue in this case is likely attributed to a subcritical cracking mechanism; not reaction-layer nor dislocation related. A cross-comparison with other works from literature is developed to show that packaging a pristine device in an inert environment is necessary in order to operate devices at high-stress levels.