Fabrication and design rules for CMOS microstructures with sub-micron gaps

  Fang Chen

Gary Fedder
FIB image of a single two-metal-layer CMOS cantilever resonator after being released. The two gaps are measured to be 0.32μm and 0.25μm respectively. The metal-4 layer was pulled back 2μm from the gap edge.

Mixing/filtering results for a cantilever resonator with 544.2kHz resonant frequency under vacuum condition. RF amplitude is 2V; LO amplitude is1V; Pressure = 1 Torr; Carrier frequencies fLO are 10MHz, 20MHz, 30MHz, 50MHz, 100MHz, 200MHz.

Project Highlights

With my expertise in focused-ion beam (FIB) processing, and micro, nanofabrication, I am studying methods to reduce the critical gap dimensions in CMOS post-fabrication. Sidewall polymers are deposited during the dielectric etching, caused by the interaction of the top aluminum layer with the reactive-ion etch. It has been shown that with proper top metal design rules, mechanical structures with <0.3um gaps can be released. I have also demonstrated by reducing the exposed top metal layer to the plasma, the polymerization can be reduced. It has also been shown that with FIB "microsurgery", mechanical structures stuck due to polymerization may be freed. The freed resonators have been tested and function as RF mixers. The mixing RF frequency has been demonstrated from 10MHz up to 1.5GHz. Currently, I and others in the group are studying methods to reduce mixing feedthrough in order to extend the mixing RF to 10GHz range.



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