Integrated MEMS in Conventional CMOS

This paper provides an overview of fabrication and design of CMOS-based microelectromechanical systems with emphasis on inertial sensor and data storage applications. High-aspect-ratio (4.4:1) microstructures can be fabricated using conventional CMOS processing followed by a sequence of maskless dry-etching steps. The CMOS dielectric and metallization layers, normally used for electrical interconnect, serve a dual function as a composite metal/dielectric structural material. Reactive-ion etching produces near vertical sidewalls, enabling micromechanical beam widths and gap spacings down to 1.2 μm. The process is tailored for design of lateral electrostatic actuators as well as capacitive position and motion sensors. Tight integration of the microstructures with CMOS provides an opportunity to make low-noise sensor interface circuitry, and to include the signal processing needed to manage arrayed sensor-and-actuator systems-on-a-chip. Novel actuator and sensor topologies can be designed by embedding multiple isolated conductors into the microstructures. An additional post-CMOS processing sequence produces platinum tips on the movable microstructures. These tips are being explored for use in probe-based data storage and tunneling sensor applications.