Design and analysis of an SOI MEMS voltage step-up converter

This paper presents a comprehensive analysis of a MEMS voltage step-up converter for energy harvesting and other low-power applications. The step-up operation is based on isolating the charge of a mechanically variable capacitor and varying the gap between the electrodes by an appropriate method of providing an actuation force. A bi-stable device is discussed and was specifically designed for static energy harvesting. This device features a separate electrostatic actuator element to manipulate the variable capacitor electrodes. Prototypes were then fabricated using a dicing-free silicon-on-insulator process. The devices have been arbitrarily designed to produce an output voltage which is five times the magnitude of the input (M = 5). Due to leakage currents, it was necessary to cascade the MEMS capacitors in parallel to obtain a higher capacitance level. Parasitic fringing capacitances have a substantial impact on the overall capacitance value of the MEMS device and so the measured multiplication level of the devices is limited to M = 2.125. With four devices in parallel, a maximum output voltage of 35.4 V was obtained for a 24 V input was measured. However, a maximum output voltage of ≈60 V is achievable if the capacitance value was further increased by connecting more devices in parallel or if or the load resistance was increased beyond 1 GΩ. (paper)