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 (MS= 130 emu/cm3) and very low coercivity (HCFMR) of piZF was determined by the coplanarwaveguide ferromagnetic-resonance technique to be ~30 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/mm2and 5.8, respectively, at 10 GHz. This is the first report of an on-chip ferrite-core RF inductor operating above 6 GHz.