Micro fabricated power inductors on silicon

The aim of this paper is to present a new design for an integrated power inductor on silicon. After a choice between different topologies already known, we present the dimensioning of this component. The inductor is designed to work in a DC/DC synchronous buck converter for a portable application (P=1 W, Vout=1.5 V, Vin=3.3 V, F=500 kHz). To reach a high integration level, the manufacturing technologies used for the inductor fabrication should be compatible with the active part implementation of the converter on the same silicon chip. Thus, only one process can be used for iron and copper deposit: electro-deposition. That is why only conductive materials can be used. The chosen inductor topology is based on the spiral structure which consists of copper windings sandwiched between two NiFe layers shielding the magnetic flux induced from the inductor windings. Considering the operating frequency and the NiFe characteristics (resistivity and permeability), eddy currents appear in the magnetic material. New design is developed to limit these eddy currents in the magnetic material by laminating the NiFe. To perform the chosen inductor topology, simulations are presented, using a 3D finite element analysis method (FEA). Simulations show that the inductor has the right value calculated i.e. 1.2 /spl mu/H. The induction repartition in the laminated material is the sign of eddy currents reduction. These results combination shows the validity of our choice for this inductor topology.