Ge-blade damascene process for post-CMOS integration of nano-mechanical resonators

A process is demonstrated for fabrication of high-frequency mechanical resonators applicable for on-chip radio-frequency communication. This Ge-blade damascene process (GBDP) provides ultranarrow lateral gaps using lithographically defined sacrificial Ge blades (high-aspect-ratio Ge features). The use of Ge as the sacrificial material eliminates the need for a hydrogen fluoride etch process to release the mechanical structures, and, hence, simplifies the integration of microelectromechanical (MEMS) with CMOS circuitry. 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. A 24-MHz double-ended tuning fork resonator was successfully fabricated using the GBDP.