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 0.9 V, 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.