Increase of $Q$ -Factor of RF Magnetic Thin Film Inductor by Introducing Slit-Patterned Magnetic Thin Film and Multiline-Conductor Spiral Coil

In order to increase Q -factor of radio-frequency (RF) magnetic thin film inductor integrated in chip-size-package RF-ICs, two schemes have been investigated experimentally. For suppressing the in-plane eddy current of the magnetic thin film, a slit-patterned structure was introduced, and it was found that the slit-patterned magnetic thin film is very effective for increasing Q-factor. On the other hand, for suppressing alternating current (ac) copper loss, a multiline-conductor spiral coil was introduced, and it was found that the multiline coil is effective for improving decrease of inductance at high frequencies. By introducing the two schemes, a maximum Q-factor of 18 at 1.5 GHz was obtained in a spiral inductor with a bottom slit-patterned CoFeSiO/SiO₂ granular multilayer film and triple-line-conductor spiral coil.