Double spiral inductors using CoFeSiO/SiO₂ multilayer granular films with very narrow ferromagnetic resonance bandwidth

Abstract

  In order to realize the integrated magnetic thin film devices, RF inductors have been fabricated using CoFeSiO/SiO₂ multilayer granular film and copper spiral coil. Multilayer granular magnetic films which consist of alternate stacks of nano-sized granular and insulator layers exhibit very sharp ferromagnetic resonant (FMR) peak. Granular and insulator layers of 6 nm and 1 nm are suitable for obtaining a very narrow FMR linewidth. High-resolution transmission electron microscopy (HR-TEM) observation revealed a well-defined multilayer granular structure and a homogeneous CoFe grain size, which seem to be necessary for realizing a very narrow FMR linewidth. There is no thermal deterioration in frequency dependence of permeability of CoFeSiO/SiO₂ films at the temperature range below 350°C. The fabricated inductor had a size of about 670 × 670 μm², including a 3μm thick copper spiral coil, and a magnetic film with three different thicknesses of 100 nm, 200 nm and 500 nm. The slit patterned magnetic film and the division of conductor line are appeared to be useful for reducing a loss resistance of fabricated inductors.