Characteristics and analysis of a thin film inductor with closed magnetic circuit structure

A spiral inductor with closed magnetic circuit was fabricated by an RF sputtering machine and photolithography techniques. The inductance was twice as large as that of a reference sandwiched inductor. The authors analyzed the frequency characteristics of the proposed inductor from three points of view: inner current distribution, flux distribution, and eddy current in the magnetic film. The calculated results agree with the measured ones. It is demonstrated that the current distribution inside the inductors is mostly limited to within the area of the conductor up to several hundred megahertz. The frequency characteristics are influenced by the eddy current loss in the Permalloy film and the stray capacitance between the inductor and the ground plane. The permeability of the Permalloy film is less than that of its as-deposited state, but the closed magnetic circuit structure helps to reduce the influence of the demagnetizing field.<
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