Thin films for micromechanical sensors

Abstract

Thin films compatible with integrated circuit and batch processing technologies are utilized in the fabrication of cost-effective, high performance integrated micromechanical sensors. These films are used as structural layers, sacrificial layers, passivation layers, oxidation barriers, masking layers, and for electrical interconnection in the formation of microminiature pressure sensors, accelerometers, and force sensors. Low-pressure chemical vapor deposition (LPCVD) polysilicon, LPCVD silicon nitride, and thin films of single crystal silicon are examples of structural layers. Highly controlled surface preparation, deposition conditions, and post-deposition temperature cycles are required to achieve uniform mechanical and thermal properties, low defect density and high stability. Young’s modulus, Poisson’s ratio, and internal stress are the most important properties to control for micromechanical devices. These properties become increasingly significant as multiple thin film or composite microstructures become important. Control and repeatability of these properties are essential in the design, fabrication and successful performance of micromechanical sensors and microstructures.