Integrated X-Band Inductor with a Nanoferrite Film Core

The performance of an on-chip X-band (8-12 GHz) inductor, integrated with a partially-inverted zinc ferrite (piZF) film, is presented. The ferrite-core inductor is realized in three steps - first, fabrication of an uncoated spiral inductor via a 130 nm Si-CMOS process in a foundry, followed by passivation removal around the coil by reactive ion etching (RIE), and finally, deposition of piZF directly on the coil by microwave-assisted solution-based processing. The resulting piZF film covers the inductor coil conformally and exhibits high saturation magnetization (M_S=130 emu/cm³ and very low coercivity (H_C < 15 Oe) at room temperature. The ferromagnetic resonance frequency (f_FMR) of piZF was determined by the coplanar-waveguide ferromagnetic-resonance technique to be ∼sim30 GHz, well above the frequency of targeted X-band applications. The inductance-density and Q-factor of the piZF-coated inductor are enhanced by 13% and 25% to 450 nH/mm² and 5.8, respectively, at 10 GHz. This is the first report of an on-chip ferrite-core RF inductor operating above 6 GHz.