An analysis of thermal stresses in a multilayer thin film printhead

Abstract

A general formula for the analysis of thermal stresses and radii of curvature of multilayer structures is given. The stresses and bending curvature in a SiO2/Si/SiO2/HfB2/Si3N4/SiC multilayer thin film printhead are calculated using this formula. It is found that processing and substrate temperatures have a strong influence on the sign and magnitude of thermal stress in each layer and on the bending curvature at each processing step. On the basis of temperature profiles in the printhead during an operating cycle, stresses in the layers as a function of time are calculated. There exist large compressive stresses in the resistor (HfB2) and the top overcoat (SiC) when the device temperature peaks near 400°C. Effects of thermal stress and elastic strain energy on device fabrication and integrity are also considered. Thus, a carbide layer thinner than 1.5 μm is recommended to avoid film fracture, whereas a substrate temperature of 220°C is suggested for the deposition of the resistor to prevent delamination. © 1991.