Optimization of the geometry of a MEMS testing device for SiO₂ – polysilicon interface characterization

Microelectromechanical systems (MEMS) are small-scale devices that combine mechanical and electrical components made through micro-fabrication techniques. These devices have revolutionized numerous technological applications, owing to their miniaturization and versatile functionalities. However, the reliability of MEMS devices remains of critical concern, especially when operating in harsh conditions like high temperature and humidity. The unknown behavior of the structural parts under cyclic loading conditions, possibly affected by microfabrication defects, poses in fact challenges in ensuring their long-term performance. This research focuses on addressing the reliability problem by investigating the fatigue-induced delamination in polysilicon-based MEMS structures, specifically at the interface between SiO₂ and polysilicon. Dedicated test structure based on piezoelectric actuation and sensing for close loop operation have been designed, aiming to maximize the stress in regions susceptible to delamination. By carefully designing the test structure, a localized stress concentration is induced to facilitate the said delamination and help understanding the underlying failure mechanism. The optimization has been performed by taking advantage of finite element analyses, allowing a comprehensive analysis of the mechanical response of the polysilicon MEMS structures under cyclic loads.