Laminated high-aspect-ratio microstructures in a conventional CMOS process

Electrostatically actuated microstructures with high-aspect-ratio laminated-beam suspensions have been fabricated using conventional CMOS processing followed by a sequence of maskless dry-etching steps. Laminated structures are etched out of the CMOS silicon oxide, silicon nitride, and aluminum layers. The key to the process is use of the CMOS metallization as an etch-resistant mask to define the microstructures. A minimum beam width and gap of 1.2 /spl mu/m and maximum beam thickness of 4.8 /spl mu/m are fabricated in a 0.8 /spl mu/m 3-metal CMOS process available through MOSIS. Structural features will scale in size as the CMOS technology improves. An effective Young's modulus of 63 GPa is extracted from resonant frequency measurements. Cantilevered structures slightly curl up with a radius of curvature of about 4.2 mm. Multi-conductor electrostatic micromechanisms, such as self-actuating springs and nested comb-drive lateral resonators, are successfully produced. Self-actuating springs are self-aligned multi-conductor electrostatic microactuators that are insensitive to curl. The resonance amplitude is 1 /spl mu/m for an 107 /spl mu/m-wide/spl times/109 /spl mu/m-long spring with an applied 11 V ac signal. Finite-element simulation using the extracted value for Young's modulus predicts the resonant frequency of the springs to within 6% of the measured values.