Monolithically integrated MEMS resonators and oscillators in standard IC technology

Abstract

Frequency sources and high quality filters based on mechanical resonators are essential building blocks for communication systems as well as analog and digital electronics. Driven by the continuous demand for reduction in power, size and overall cost, monolithic integration of mechanical resonators in standard integrated circuit (IC) technology has been the focus of multiple research efforts. Micro-Electro-Mechanical (MEM) resonators offer an ultimate solution, with 100x higher quality factors and 10⁴x smaller footprint, when compared to on-chip LC tank circuits. A new class of truly solid-state, monolithically integrated, GHz-frequencies CMOS-MEMS resonators is presented. No post-processing or special packaging of any kind is required beyond the standard CMOS process. Resonant body transistor (RBT) is constructed by using active field-effect-transistor (FET) sensing. A phononic crystal (PnC) implemented in the CMOS back-end-of-line (BEOL) layers along with the bulk wafer are used to create a phononic waveguide. The latter confines acoustic vibrations in the CMOS front-end-of-line (FEOL) layers. Operator-theoretic analysis for these waveguides is presented in explicit analogy to quantum mechanics and photonic waveguides; with a study of perturbation theory, coupled-mode theory and adiabatic theorem. Superior energy confinement is achieved, allowing record high Q ~ 14, 800 and fo - Q ~ 4.85 x 10¹³ for CMOS-RBTs at 3 GHz. Simulation, modeling, optimization, proto- typing and testing of these resonators is presented. RBTs in FinFET technologies are also exploerd, for resonance frequencies up to 33 GHz. The thesis also explores the integration of Lamb-mode resonators in standard GaN monolithic-microwave-IC (MMIC) process. The first monolithic 1GHz MEMS-based oscillator in standard GaN MMIC technology is demonstrated, together with monolithic lattice and ladder filters. This allows for complete RF front-ends in GaN MMIC technology.