Novel silicon-embedded coreless coupled inductors for high efficiency on-chip DC-DC conversion

In this paper, novel silicon-embedded coreless coupled inductors are proposed and demonstrated for high efficiency on-chip dc-dc conversion. Two interleaved thick inductor coils are embedded in the bottom layer of the Si substrate, providing small dc resistances; while only 4 vias are opened in the top substrate layer, leaving most of the top substrate surface for other converter components. The 0.5 mm2 coupled inductors fabricated show coil dc resistance of 0.11 Ω, coil ac resistance of 0.44 Ω, and coil ac inductance of 3.2 nH at 170 MHz with a coupling factor of 0.73 and a mutual resistance of 0.30 Ω. For 1.2 V to 0.9V, 0.19 A, 170 MHz on-chip dc-dc conversion, a high efficiency of 94% is achieved by the silicon-embedded coreless coupled inductors, leading to a converter loss reduction of 44% and a converter efficiency increase from 78% to 86% compared to the prior art. © 2011 IEEE