Fully single crystal silicon resonators with deep-submicron dry-etched transducer gaps

This paper reports on fully single crystal silicon (SCS) micromechanical resonators with deep-submicron vertical capacitive gaps. The microresonators are fabricated on low resistivity silicon-on-insulator (SOI) substrates and have SCS resonating structure and transducers. The deep-submicron high aspect-ratio transducer gaps are created through a novel processing technique that uses low-cost micron-resolution optical lithography. The mask features defining the width of the transducer gaps are created in a self-aligned manner by the thickness of a deposited sacrificial polysilicon layer, and the gaps are dry-etched using the Bosch process. High aspect ratio (∼20:1) trenches with width as small as 130 nm have been obtained using the Bosch process. Single crystal silicon capacitive beam resonators with frequencies up to 16 MHz and transducer gaps as small as 200 nm have been successfully fabricated and characterized.