A FULLY INTEGRATED PLANAR TOROIDAL INDUCTOR WITH A MICROMACHINED NICKEL IRON MAGNETIC BAR

A fully integrated toroidal inductor is realized on a silicon wafer by using a multilevel metalization technique to fabricate a wrapped coil wound around a micromachined bar of high-permeability magnetic material. In particular, efforts are made to minimize the coil resistance by using thick conductor lines and electroplated vias. In this structure, a 30 mum thick nickel-iron permalloy magnetic core is wrapped with 40 mum thick multilevel copper conductor lines, constructing a conventional toroidal inductor in planar shape. A closed magnetic circuit (i.e., toroidal) in this inductive component is adopted, where magnetic core bar and wrapped conductor lines are tightly interlinked, so that leakage flux and electromagnetic interference are minimized. For an inductor size of 4 mm x 1 mm x 130 mum thickness having 33 turns of multilevel coils, the achieved inductance is approximately 0.4-0.1 muH at 1 kHz-1 MHz, corresponding to a core permeability of approximately 800. The measured dc resistance of the conductor lines is approximately 0.3 OMEGA. Since this inductive component shows favorable magnetic characteristics as well as electrical properties, it is potentially very useful as a basic inductive component in applications for magnetic microsensors, microactuators, and micromagnetic power devices such as a dc/dc converter.