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

• Published in: IEEE journal of emerging and selected topics in power electronics Vol. 6; no. 2; pp. 604 - 613
• Main Authors: Thanh Le, Hoa, Nour, Yasser, Han, Anpan, Jensen, Flemming, Ouyang, Ziwei, Knott, Arnold
• Format: Journal Article
• Language: English
• Published: IEEE 01.06.2018
• Subjects: DC–DC power converters; Fabrication; Fixtures; gallium nitride; inductor; Inductors; microelectromechanical systems (MEMSs); Micromechanical devices; Silicon; Through-silicon vias; Windings; zero voltage switching (ZVS)
• ISSN: 2168-6777; 2168-6785
• DOI: 10.1109/JESTPE.2018.2798927

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 high-frequency (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 silicon-core 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 <inline-formula> <tex-math notation="LaTeX">\text{V}_{\mathrm {DC}} </tex-math></inline-formula>. The MEMS inductor can carry 1-A root-mean-square ac current at 33 MHz and delivers 10.5 W to the output.