3-D Microtransformers for DC–DC On-Chip Power Conversion

We address the miniaturization of power converters by introducing novel 3-D microtransformers with magnetic core for low-megahertz frequency applications. The core is fabricated by lamination and microstructuring of Metglas 2714A magnetic alloy. The solenoids of the microtransformers are wound around the core using a ball-wedge wirebonder. The wirebonding process is fast, allowing the fabrication of solenoids with up to 40 turns in 10 s. The fabricated devices yield the high inductance per unit volume of 2.95 μH/mm³ and energy per unit volume of 133 nJ/mm³ at the frequency of 1 MHz. The power efficiency of 64-76% is measured for different turns ratio with coupling factors as high as 98%. To demonstrate the applicability of our passive components, two PWM controllers were selected to implement an isolated and a nonisolated switch-mode power supply. The isolated converter operates with overall efficiency of 55% and maximum output power of 136 mW; then, we experimentally demonstrate how we increased this efficiency to 71% and output power to 408 mW. The nonisolated converter can deliver an overall efficiency of 81% with a maximum output power of 515 mW. Finally, we benchmarked the results to underline the potential of the technology for power on-chip applications.