Damping in CMOS-MEMS Resonator

  Jay Brotz

Gary Fedder
Cantilever resonator

Free-free resonator
Micromechanical resonators are being explored for use as filters and mixer/filters in RF receivers. Selective amplification around their resonant frequency leads to a bandpass filter characteristic. Resonant structures in the CMOS-MEMS process are made of a composite stack of metaland dielectric layers directly from the back-end-of-line CMOS flow. The metal routing in the microstructures allows independent design of electrostatic actuation and capacitive sensing. On-chip amplification of the capacitance can detect the high-impedance motional signal from the structureefficiently. The focus of this project is to study the sources of damping in single CMOS-MEMS resonators. The loss sources are air damping, vibrational loss through the anchor, thermoelastic damping (cyclic heat loss) and internal friction. Understanding these sources will help improve future filter designs to by increasing and stabilizing bandwidth selectivity and out-of-band rejection. Test resonators are fabricated by a CMOS foundry, post-processed, and their performance is measured experimentally at atmospheric pressure down to microTorr levels.



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