MEMS-based and switched-capacitor approaches for miniature power supply applications

This paper summarizes work towards creating mm-scale power converters using high-frequency CMOS as well as MEMS and micro-machined passives. Reducing the converter size is largely motivated by creating power supplies for micro-robotic platforms (with millimeter and milligram scales) without negatively impacting robotic system functionality. MEMS power passives are first presented where thin-film piezoelectric transformers and resonators are shown as an electromechanical approach to achieve ultra-miniature passives at the chip scale. Piezoelectric transformers fabricated with thin-film lead zirconate titanate (PZT) on silicon are measured and show similar to 60% efficiencies with 240 and 75 Omega loads. These transformers have resonant frequencies ranging between 14 and 20 MHz. Work towards creating transmission lines fabricated with air-core inductors and ferroelectric capacitors is also presented. Finally, a fullyintegrated bi-directional converter in CMOS is shown driving mm-scale robotic wings made with PZT. The converter's maximum efficiency is 77% at similar to 800 mu W load with 9V output and demonstrates >3x voltage boost in 0.13-mu m triple-well CMOS.