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Title: Analysis and design of SOI MEMS step up voltage converters
Author: Gleeson, Rachel
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2013
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Energy harvesting systems are becoming an increasingly popular area for research as they present themselves as a clean, renewable source of energy. There are currently some key design issues facing the development of these energy harvesting systems. In particular, these harvesters often produce relatively low voltages compared to the requirements of the intended application. For example, scientific apparatus aboard orbital satellites require relatively high voltage levels for operation (kV) but are powered from solar panels providing substantially lower output voltages (24 V). In contrast, for low power energy harvesting, such as micro scale vibration energy harvesters, a harvested voltage level of ≈0.5V is often required to power a low power sensor circuit which requires 2-5V. Voltage multiplication is commonly achieved using charge pump multiplier circuits. However, these circuits are quite limited in both the range of multiplication (per unit area) and the maximum voltage level. This work aims to take advantage of a noticeable gap in the research field and is specifically targeted towards energy harvesting application areas. This thesis presents a comprehensive analysis of novel bi-stable and resonant MEMS voltage step-up converters. The operation is based on isolating the charge of a mechanically variable capacitor and varying the gap between the electrodes by an appropriate method of actuation force. As the electrode gap varies, so does the voltage level across the electrodes. In the case of the bi-stable devices, electrostatic actuation is employed while the resonant devices rely on ambient vibration force. These have been specifically designed for integration with static and vibration energy harvesters respectively. Prototype devices were fabricated using a dicing-free Silicon-on-Insulator (SOI) process developed at the Southampton Nanofabrication Centre. For the bi-stable device, a maximum output voltage of 35.7V was measured, using a 100MΩ load resistance, from a 24V input voltage. Further improvements in the design of the MEMS variable capacitor can be made in order to increase the capacitance level of the devices while reducing the parasitic fringing capacitance. Optimisation of the MEMS device would enable the output to reach a level near the theoretical maximum limit set at 120V.
Supervisor: Kraft, Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering