Nanometer scale gaps for capacitive transduction improvement on RF-MEMS resonators

In this work, we describe a simple 3-mask fabrication process, that allows us to prototype thick silicon lateral bulk acoustical resonators with nanometer scale transducing gaps. The vibrating parts of the MEMS resonator are fabricated on crystalline silicon, and the electrodes for lateral electrostatically excitation and detection are made with deposited polysilicon. The process is specially optimized to prevent overlapping of the polysilicon electrodes with crystalline moving parts, in order to avoid the excitation of vertical vibrating modes. Structures consisting on well known circular and ellipsoidal shape resonators have been designed using FEM simulations and fabricated in order to test the fabrication process. Detailed SEM images of some of the fabricated test structures, as well as the electrical characterization of their frequency response are reported. (c) 2007 Elsevier B.V. All rights reserved.