Defense-Abu Saleh Imtiaz
August 7, 2014
Title: Piezoelectric micro-resonators on Si for inductor free embedded (on-chip) power converters in PV powered autonomous micro-systems
Microelectromechanical systems (MEMS) resonators on Si have the potential to replace the discrete passive components in a power converter. The main intention of this dissertation is to present a ring-shaped aluminum nitride (AlN) piezoelectric micro-resonator that can be used as an energy-transferring device to replace inductors/capacitors in low power resonant converters for biomedical applications in Autonomous Microsystems. The zero voltage switching (ZVS) condition for a series resonant converter incorporating the proposed MEMS resonator has been presented analytically and verified through experiment. This ZVS condition can be found in terms of the equivalent circuit parameters of the resonator. To the best of my knowledge, a ZVS model for thin film devices has not yet been reported in the literature. A CMOS-compatible fabrication process has been proposed and implemented. In addition, the fabricated devices have been characterized and experimental results are included. The first contour mode AlN MEMS resonator with moderately low resonant frequency and motional resistance is reported in this dissertation with measured resonant frequency and motional resistance of 87.28 MHz and 36.728 Ω respectively.
First part of this dissertation discusses the feasibility of PV powered autonomous micro-system. The reliability, efficiency and controllability of PV power systems can be increased by embedding the components of a typical power converter on the same Si substrate of a PV cell. In order to achieve more insight of the macro or surface electronics, a novel fabrication process along with experimental results have been presented in this dissertation demonstrating the integration of PV cells and major components needed to build a power converter on the same substrate/wafer. Because of the cell level power conversion, PV panels constructed from these cells are likely to be immune to partial shading and hot-spot effects. The effect of light exposure on converter switches has been analyzed to understand the converter behavior at various illumination levels. Simulation and experimental results have been provided to support this analysis. In addition to the process-related challenges and issues, this work explains the justification of this integration by achieving higher reliability, portability and complete modular construction for PV-based energy harvesting units for autonomous micro-systems.