Fracture Properties of MEMS/NEMS Thin Films

Abstract

Thin film mechanical property evaluation has become increasingly important for micro devices. To assure the reliability of the devices and to predict the lifetime, fracture properties of thin films need to be investigated. Microtensile testing is a powerful technique to characterize the mechanical and fracture properties of microscale thin films. But the specimen preparation always causes a difficulty. The bulge test, as a relatively simple, fast, and precise method, is extended to the determination of the fracture properties of thin films, such as bending stiffness and prestress of the membrane material, the Young’s modulus, and fracture strength of single layer film and bilayer films. An accurate model describing load-deflection response is applied on thin films made of silicon nitride, silicon carbide, and composite diaphragms of silicon nitride grown on top of thermal silicon oxide films. Fracture reference stresses were computed according to the Weibull model for brittle fracture by integrating the membrane stress over the edge, surface, and volume of the samples, corresponding respectively to the assumption of dominant edge, surface, and volume flaws. This method is very efficient and able to quantify fracture parameters of single and multilayer films.