The HARPSS process for fabrication of nano-precision silicon electromechanical resonators

In this paper, radio frequency (RF) ultra-stiff electromechanical resonators are introduced and compared with their ultra-light counterparts. RF ultra-stiff resonators with dimensions in the low end of the micrometer scale can yield UHF frequencies (0.33 GHz) by operating at their higher order flexural modes. However, electrostatic actuation and capacitive sensing of ultra-stiff resonators will require nanoscale airgaps. The HARPSS (high aspect-ratio combined poly and single crystal silicon MEMS technology) fabrication process presented in this paper is an all-silicon process that is capable of producing capacitive silicon resonators (poly and single-crystalline) with lateral gap spacing as small as 10 nm between the resonating structure and the silicon electrodes, without the need for nano-lithography.