Converter circuit design, semiconductor device selection and analysis of parasitics for micropower electrostatic generators

For various medical monitoring and sensing applications it is desirable to power the electronics by scavenging energy from any locally available source. An electrostatic motion-driven generator for low-frequency (human body) motion has been developed by the authors using microelecromechanical system technology. The prototype generates pulses of 250 V on a 10-pF capacitor. This paper examines the design of a circuit and semiconductor devices to convert this energy to a low voltage. Because of the very small charge involved, the effects of leakage and parasitic stored charge are important. Converters for this application using silicon-on-insulator metal-oxide-semiconductor field-effect transistors and insulated gate bipolar transistors are compared using physics-based finite-element simulation. The overall effectiveness of the generation process is shown to be composed of several terms which are functions of system parameters such as generator flight time, semiconductor device area, and circuit inductance. It is shown that device area is a compromise between leakage current, charge storage, and on-state voltage. It can, for a given generator and inductance, be optimized to provide the maximum energy yield. Parasitic series inductance is shown to be of little importance to the circuit efficiency; however, parasitic capacitance has a significant influence.