This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. JOURNAL OF MICROELECTROMECHANICAL SYSTEMS 1 Theory and Design of Phononic Crystals for Unreleased CMOS-MEMS Re

Abstract — Resonant body transistors (RBTs) are solid state, actively sensed microelectromechanical systems (MEMS) resonators that can be implemented in commercial CMOS tech-nologies. With small footprint, high- Q, and scalability to giga-hertz frequencies, they form basic building blocks for radio fre-quency (RF) front-ends and timing applications. Toward the goal of seamless CMOS integration, this paper presents the design and implementation of phononic crystals (PnCs) in the back-end-of-line (BEOL) of commercial CMOS technologies with bandgaps in the gigahertz frequencies to be used for enhanced acousti-cal confinement in CMOS-RBTs. Lithographically defined PnC dimensions allow for bandgap engineering, providing flexibility in resonator design, and allowing for multiple frequencies on a single chip. The theoretical basis for analyzing generic PnCs is presented, with focus on the special case of implementing PnCs i