On-chip Coupled Power Inductor for Switching Power Converters

This paper proposes a design of an on-chip coupled power inductor (OCPI) structure which consists of a layer of ferrite core material and another layer of coupled spiral windings on a silicon substrate. The flux cancellation effect of the two inversely coupled windings significantly reduces the net fluxes in the ferrite layer, which helps increasing the saturation current of the power inductor. An ANSYS (R)/Maxwell (R) 3-D physical model of a 5.6mmx5.6mm two-phase OCPI is developed and simulation results are obtained. Simulation results show that the saturation current (7A/phase) of the OCPI is twice the saturation current (3.5A) of the non-coupled power inductor with the same inductance density. Based on a 3.3V/1.5V 4MHz two-phase buck converter, the equivalent steady state inductance and transient inductance of the OCPI are calculated to be equal to 78.1nH and 22.2nH, respectively.