Three-dimensional self-assembled sensors in thin-film SOI technology

A complementary metal-oxide-semiconductor (CMOS)-compatible one-mask process for the design and fabrication of three-dimensional (3-D) mieroelectromechanical systems (MEMS) sensors in thin-film silicon-on-insulator (SOI) technology is presented. The process relies on the control of the internal stresses in multilayered structures originating from thermal expansion mismatch between layers as well as on the control of the plastic yielding of a metallic layer. In contrast with techniques presented in the literature for the fabrication of 3-D MEMS, this process requires fabrication steps and machines fully compatible with a classical CMOS process and available in standard CMOS foundries. Preliminary characterization results of 3-D thermal and flow sensors based on capacitive sensing demonstrate the potential of this concept.