Bulk and surface micromachined MEMS in thin film SOI technology

Silicon-on-insulator (SOI) technology is emerging as a major contender for heterogeneous microsystems applications. In this work, we demonstrate the advantages of SOI technology for building thin film sensors on membranes as well as three-dimensional (3D) surface micromachined sensors and actuators. The flatness and robustness of the thin membrane as well as the self-assembling of 3D microstructures rely on the chemical release of the microstructures and on the control of the residual stresses building up in multilayered structures undergoing a complete thermal process. The deflection of multilayered structures made of both elastic and plastic thin films results from the thermal expansion coefficient mismatches between the layers and from the plastic flow of a metallic layer. The proposed CMOS-compatible fabrication processes were successfully applied to suspended sensors on thin dielectric membranes such as gas-composition, gas-flow and pressure sensors and to 3D self-assembled microstructures such as thermal and flow sensors.