Thermal stress concentration points and stress mutations in nano-multilayer film structures

Abstract In the multilayer film-substrate system, the buckling, delamination and cracking of the film caused by the thermal stress concentration point and the stress mutation are the main factors leading to the failure of the corresponding device function. In this paper, we studied the multilayer film system composed of the substrate and the three-layer film. The thermal stress distribution inside the structure was calculated by the finite element method (FEM). It was observed that there was a large thermal stress difference between the layers. This is mainly due to the mismatch of thermal expansion coefficient (CTE) between materials. Different materials have different degrees of change with the external environment temperature, and the layers are squeezed. In particular, there are obvious thermal stress concentration points at the corners of the base layer and the transition layer, which is due to the sudden change of the shape at the geometric section of the structure, resulting in a sudden increase in local stress. In order to solve this problem, we have chamfered the substrate and added an intermediate layer between the substrate and the transition layer to analyze whether the difference between the thermal stress concentration point and the thermal stress can be reduced or eliminated, and the service life of the multilayer structure can be extended. The conclusion shows that chamfering and increasing the intermediate layer can reduce the stress mutation and weaken the thermal stress concentration point, which can effectively improve the interlayer bonding strength.