High-Efficiency Silicon-Embedded Coreless Coupled Inductors for Power Supply on Chip Applications

In this paper, high-efficiency silicon-embedded coreless coupled inductors are demonstrated for power supply on chip applications. The embedded coupled inductors have two interleaved thick inductor coils embedded in the bottom layer of the Si substrate and four copper vias formed in the top substrate layer. The embedded coupled inductors can be stacked underneath the active circuitry for compact on-chip integration, while small resistances can be achieved with the thick embedded coils, which lead to high efficiency. As a demonstration, embedded coupled inductors with a small area of 0.5 mm² were designed and fabricated according to the on-chip dc-dc converter with the highest reported efficiency. The fabricated embedded coupled inductors show a much higher efficiency of 93% compared to the 84% efficiency of the originally used on-substrate coupled inductors, allowing the total converter loss to be reduced by 38% and the converter efficiency to be improved from 78% to 85%.