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.