Chapter 24 - Surface Micromachining

Abstract

Surface Micromachining is so-called because instead of crystal silicon substrate as a functioning material this new technology uses thin film layers deposited on the substrate surface as functioning material. This chapter explains the different types of surface micromachining processes. It details the polycrystalline silicon-based micromachining in a very detailed way with the help of photographs. Integrations concepts are viewed in a very effective manner. Monolithic integration is a very good choice for evaluation of capacitive surface-micromachined sensors, given their low base capacitance values and more supported by shrink tendencies aggressively targeting the size of the sensor core. Monolithic integration is a potential option to be considered not mainly for cost but for performance arguments. This lesson explains the role of metallic thin films in MEMS. It explains the different properties of metals in MEMS applications in a very effective way, which includes electrical conductivity, low-temperature processing, etc. This chapter throws some light on silicononinsulator (SOI)-wafer-based surface micromachining technologies, which are available as MEMS foundry technologies. The main advantage is that the moveable structures are made from a single crystalline device layer hence have excellent, well-defined mechanical properties and high reliability. The SOI-wafer-based surface micromachining technology has been developed for capacitive inertial sensors. To improve the electrical behavior of these types of device, refilled insulation trenches are processed prior to the fabrication of the mechanical structures.