Effects of residual stresses on cracking and delamination risks of an avionics MEMS pressure sensor
Silicon based pressure sensors often take advantage of piezo-resistive gages which are normally embedded by multiple silicon oxide and silicon nitride layers where gold lines form a Wheatstone bridge. As a result of manufacturing - stepwise deposition of multiple layers - significant layer residual stresses in the GPa range occur in tension and compression. Especially in avionics MEMS applications such stresses determine the major risks for cracking and delamination. To overcome the related reliability issues the authors performed experiments and nonlinear FEM-simulations. Basic information about the residual stresses in the gage stack were captured by a Focused Ion Beam (FIB) trench technique combined with digital image correlation. These results enriched the data base for finite element studies with the ABAQUSTM. Especially delamination risks were investigated by a surface based cohesive contact approach which simulates the initiation and propagation of damage and cracking within and underneath the gage layer. The cracking risk is investigated by means of an Extended Finite Element Method (XFEM). Both, crack initiation location as well as crack path are results of XFEM simulations. Several design variations have been investigated and compared to give insights to potential crack initiation sites and to evaluate the risk of fracture during processing.