Integrated Electrostatically- and Piezoelectrically-Transduced Contour-Mode MEMS Resonator on Silicon-on-Insulator (SOI) Wafer

Due to the recent rapid growth in personal mobile communication devices (smartphones, PDA\u27s, tablets, etc.), the wireless market is always looking for new ways to further miniaturize the RF front-ends while reducing the cost and power consumption. For many years, wireless transceivers and subsystems have been relying on high quality factor (Q) passives (e.g., quartz crystal, ceramics) to implement oscillators, filters, and other key RF front-end circuitry elements. However, these off-chip discrete components occupy large chip area and require power-demanding interfacing circuits. As a result, a great deal of research effort has been devoted to the development of micromechanical resonators that are much more amenable to direct integration with integrated circuit (IC). Over the past few years, vibrating RF MEMS (Micro-Electrical-Mechanical-System) resonator technology has emerged as a viable solution, most notably, the film bulk acoustic resonator (FBAR) and surface acoustic wave (SAW) resonator, which have already been successfully implemented into commercial products. Undoubtedly, micromechanical resonators such as FBAR\u27s can perform as well as if not better than its bulky conventional counterparts and facilitate the miniaturization and power reduction of conventional RF systems. However, in some cases when multi-frequency functionality on a single-chip is needed, FBAR simply won\u27t deliver. To address this dilemma, contour-mode MEMS resonators have been developed and regarded as the most viable on-chip high-Q alternative. Unlike FBAR, contour-mode resonators use lateral dimensions to define its resonating frequencies, thus allowing for single-chip multi-frequency functionality. However, there is still room for improvement with respect to lowering the motional resistance of these devices to allow matching to 50 Ω electronics, while retaining low power consumption, small size, and simpler manufacturing process. This dissertation presents the design, fabrication, characterization and experimental analysis of two types of micro-mechanical resonators. Piezoelectrically- and electrostatically-transduced micromechanical resonators will both be shown. Both types of resonator will be fabricated in the same micro-fabrication run, which makes the comparison between the two much more impartial. The impacts of substrate\u27s resistivity over the device performances will also be studied. Among the most significant results, this dissertation also presents several ideas that are enabled by the use of silicon-on-insulator (SOI) wafer. A novel single-mask fabrication process that can produce capacitive resonator with nano-meter gap is demonstrated. The concept of dual-transduced micro-mechanical resonator is introduced by combining both piezoelectric and capacitive based resonators. Finally, frequency tuning of MEMS resonator are explored and detailed in this work as well