Improvement of high-frequency characteristics of FeCoHfO/AlOx multilayered films

High-permeability magnetic films can enhance the inductance of thin-film inductors in dc–dc converters. The FeCoHfO/AlOx multilayered films were fabricated by dc reactive magnetron co-sputtering. Inserting the AlOx layers can decrease the anisotropic field of the FeCoHfO magnetic films, which was beneficial to raise the permeability of the FeCoHfO/AlOx multilayered films. With this optimum configuration of a nine-layer structure [FeCoHfO (133 nm)/AlOx (10 nm)]9, low anisotropic field (HK = 65 Oe) and high permeability (permeability over 170 at 30–50 MHz) were obtained. The permeability increased nearly six times from 30 (M1) to 175 (M9). The permeability was evidently improved by the employment multilayered coating.