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Magnetic Nano Particles and Thin Films for High Frequency Micro Inductors


The size and performance of integrated circuits have been following Moore’s law to continuously shrink and progress over the past decades while on-chip inductors have seen little advancements. This work proposes several unique approaches in the integrated magnetic cores for high frequency micro inductor developments, including: (1) spherical-shape, anti-oxidizing magnetic nanoparticle composites; (2) sputtered magnetic thin films with magnetization-induced anisotropy; and (3) rectangular-shape magnetic particles with geometry-induced anisotropy. Theoretical and simulation studies have been conducted with experimental demonstrations to validate these concepts.

Chemical syntheses of spherical-shape magnetic FeNi3 particles of 100 nm in diameter, with and without a thin passivation SiO2 coating have been investigated. After the integration with micro inductors by a CMOS-compatible process, it is found that the inductance values have increased 20-45% up to 2 GHz for micro inductors after adding the magnetic nanoparticle composites. The quality factors have degraded slightly mainly due to the magnetic losses from large coercivity at about 100 Oe despite of the reduction of eddy current losses in the magnetic nanoparticle composites.

The control of magnetization-induced anisotropy of magnetic thin films by using different magnitudes of sputtering deposition power under an external magnetic field has been studied and characterized. By reducing the sputtering power from 1000 to 150 Watts, the sputtered CoZrTaB thin films have smaller grain size and higher in-plane anisotropy and higher FMR frequency from 1.48 to 2.17 GHz. After the integration the magnetic thin films with stripline inductors, 2.5-3.5 times higher inductances and 2.5-3 times higher Q-factors than those of air-core inductors have been accomplished.

Magnetically aligned, rectangular plate-like structures have been demonstrated for geometry-induced nano magnets in micro inductors. These magnets have been analyzed in theories and simulations with experimental validations to have advantages of particles in low eddy current losses and thin films in magnetic anisotropy for high FMR. After the integration with micro inductors under an external magnetic field, the roll-off frequencies in inductance of micro inductors have reached 4.2 GHz with 10% increase in inductance.

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