Thermal stress analyses of multilayered films on substrates and cantilever beams for micro sensors and actuators

Thermal stress-induced damage in multilayered films formed on substrates and cantilever beams is a major reliability issue for the fabrication and application of micro sensors and actuators. Using closed-form predictive solutions for thermal stresses in multilayered systems, specific results are calculated for the thermal stresses in PZT/Pt/Ti/SiO₂/Si ₃N₄/SiO₂ film layers on Si substrates and PZT/Pt/Ti/SiO₂ film layers on Si₃N₄ cantilever beams. When the thickness of the film layer is negligible compared to the substrate, thermal stresses in each film layer are controlled by the thermomechanical mismatch between the individual film layer and the substrate, and the modification of thermal stresses in each film layer by the presence of other film layers is insignificant. On the other hand, when the thickness of the film layer is not negligible compared to the cantilever beam, thermal stresses in each film layer can be controlled by adjusting the properties and thickness of each layer. The closed-form solutions provide guidelines for designing multilayered systems with improved reliability.