Microfabricated Air-Core Toroidal Inductor in Very High-Frequency Power Converters

Miniaturization of power supplies is required for future intelligent electronic systems, e.g., Internet-of-Things devices. Inductors play an essential role, and they are by far the most bulky and expensive components in power supplies. This paper presents a miniaturized microelectromechanical system (MEMS) inductor and its performance in a very highfrequency (VHF) power converter. The MEMS inductor is a silicon-embedded air-core toroidal inductor, and it is constructed with through-silicon vias, suspended copper windings, silicon fixtures, and a silicon support die. The air-core inductors outperform the silicon-core inductors with higher quality factor at higher frequency. This is verified by small-signal measurements. A 20-turn air-core inductor achieved an inductance of 44.6 nH and a quality factor of 13.3 at 33 MHz, while a siliconcore inductor with the same geometry has a quality factor of 9 at 20 MHz. A dc-dc class-E boost converter is designed and implemented using the fabricated MEMS air-core inductor and a high-performance 65-V gallium nitride field-effect transistor. The VHF converter achieved a peak efficiency of 78% at an input voltage of 6.5 VDC. The MEMS inductor can carry 1-A root-mean-square ac current at 33 MHz and delivers 10.5 W to the output.