Advanced Soft Magnetic Materials for Magnetic Recording Heads and Integrated Inductors
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Advanced Soft Magnetic Materials for Magnetic Recording Heads and Integrated Inductors N. X. Sun1, A. M. Crawford, and S. X. Wang Dept. of Materials Science and Engineering, Stanford University, Stanford, CA 94305-4045 1 Presently at IBM Storage Technology Division, San Jose, CA 95193 ABSTRACT High performance magnetic heads, inductors and transformers, indispensable to information technology encompassing from information storage, portable power delivery, to wireless communication, require soft magnetic films with low coercivities, high permeability, and large ferromagnetic resonance frequencies. The Fe-Co-N-based films have a ferromagnetic resonance frequency of >1 GHz at zerobias field, showing great promise for applications in write heads and integrated inductors in a frequency range of >1 GHz. Magnetization dynamics measurements at sub-nanosecond scale have been performed on Fe-Co-N high saturation soft magnetic films with Permalloy nanolayer seeds having a saturation magnetization of 24 kG. The high frequency behavior appears to be affected by magnetic anisotropy dispersion. One of the biggest challenges facing integration of magnetic material onto silicon is the compatibility of magnetics with standard silicon processing techniques. Integrated inductors were realized using ground planes of Co-Ta-Zr (ρ=100µΩ-cm). The magnetic properties of CoTa-Zr showed no change even after undergoing high temperature processing. Inductors with 1µm Co-Ta-Zr produced inductance values up to 60% higher than the air core inductors at frequencies up to 1.4 GHz. INTRODUCTION Soft magnetic films with low coercivity and high permeability are critical building blocks in numerous electromagnetic devices such as magnetic recording heads, integrated inductors (microinductors), integrated transformers, magnetic sensors, and micromachined motors. However, a lack of soft magnetic materials with a high saturation magnetization (>20 kG) and a large permeability roll-off frequency (>1 GHz) often becomes the bottleneck in these applications, particularly in magnetic hard disk drives. The arrival of the information age is made possible by faster and faster microprocessors, networks, and magnetic hard disk drives. It is anticipated that the data rate of hard disk drives will be >1 Gb/s (1 Gb = 1 billion bits) soon. A data rate of 2 Gb/s corresponds to recording frequencies of ~1 GHz, which exceeds the ferromagnetic resonance (FMR) frequency of most magnetic materials. In addition to the rapid increase in data rate, magnetic information storage technology is approaching the perceived superparamagnetic limit at which the stored bits become thermally unstable [1]. To ensure the stability of recorded information for 10 years will require the stability ratio of magnetic medium, KuV/kBT, to be 60-70 [2], where Ku is the anisotropy energy density, V is the magnetic switching volume, kB is the Boltzmann constant, and T is the absolute temperature. The estimated maximum areal bit density of conventional longitudinal magnetic recording [3] ranges from 40 t
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