Poly-sige High Frequency Resonators Based on Lithographic Definition of Nano-gap Lateral Transducers

In this paper, we describe a new approach for fabrication of micromechanical resonators for radio-frequency communication applications. The proposed process provides ultra-narrow lateral gaps using lithographically-defined sacrificial Ge blades. By using Germanium as a sacrificial material, we eliminate the need for HF etching to release mechanical structures and thereby simplify the integration of these devices with CMOS electronics. Polycrystalline silicon-germanium (poly-SiGe) is used as the structural material in order to keep the thermal budget low (maximum temperature 425°C), so as to be compatible with CMOS metallization stacks. Resonators with frequencies up to 200MHz and Q ranging from 3,500 to 14,000 are demonstrated. Index terms – MEMS, resonator, silicon-germanium