Stacked-spiral RF inductors with vertical nanoparticle magnetic core for radio-frequency integrated circuits in CMOS

A new concept of stacked-spiral inductor with vertical near-closed-circuit nanoparticles-magnetic-core in CMOS is reported. Nanoparticle-embedded magnetic medium is designed, modeled, prepared and characterized, which achieves significantly increased operation frequency to multiple-GHz for RF inductor applications. New inductor prototypes with vertically integrated nanoparticle-magnetic-cores are fabricated in a foundry 0.18 μm CMOS backend process featuring six aluminum metal interconnects (6-Al). Measurement shows significantly improved inductance (L) and quality factor (Q) up to 2.5 GHz. An areal inductance density of 825 nH/mm2, or a +52% increase, is obtained, which is promising for making super compact inductors in RF SoC. Limiting factors and improvement methods for the prototype's Q-factor (Qmax = 3.4 @ 3.2 GHz) are discussed.