Bruno Marchon

Structural stability of hydrogenated amorphous carbon overcoats used in heat-assisted magnetic recording investigated by rapid thermal annealing

Ultrathin amorphous carbon (a-C) films are extensively used as protective overcoats of magnetic recording media. Increasing demands for even higher storage densities have necessitated the development of new storage technologies, such as heat-assisted magnetic recording (HAMR), which uses laser-assisted heating to record data on high-stability media that can store single bits in extremely small areas (∼1 Tbit/in.2). Because HAMR relies on locally changing the coercivity of the magnetic medium by raising the temperature above the Curie temperature for data to be stored by the magnetic write field, it raises a concern about the structural stability of the ultrathin a-C film. In this study, rapid thermal annealing (RTA) experiments were performed to examine the thermal stability of ultrathin hydrogenated amorphous carbon (a-C:H) films deposited by plasma-enhanced chemical vapor deposition. Structural changes in the a-C:H films caused by RTA were investigated by x-ray photoelectron spectroscopy, Raman spectros...

Complete characterization by Raman spectroscopy of the structural properties of thin hydrogenated diamond-like carbon films exposed to rapid thermal annealing

We have demonstrated that multi-wavelength Raman and photoluminescence spectroscopies are sufficient to completely characterize the structural properties of ultra-thin hydrogenated diamond-like carbon (DLC:H) films subjected to rapid thermal annealing (RTA, 1 s up to 659 °C) and to resolve the structural differences between films grown by plasma-enhanced chemical vapor deposition, facing target sputtering and filtered cathodic vacuum arc with minute variations in values of mass density, hydrogen content, and sp3 fraction. In order to distinguish unequivocally between films prepared with different density, thickness, and RTA treatment, a new method for analysis of Raman spectra was invented. This newly developed analysis method consisted of plotting the position of the Raman G band of carbon versus its full width at half maximum. Moreover, we studied the passivation of non-radiative recombination centers during RTA by performing measurements of the increase in photoluminescence in conjunction with the analysis of DLC:H networks simulated by molecular dynamics. The results show that dangling bond passivation is primarily a consequence of thermally-induced sp2 clustering rather than hydrogen diffusion in the film.

Carbon Overcoat Oxidation in Heat-Assisted Magnetic Recording

Due to the ever increasing demand for higher storage capacity in disk drives, novel techniques to read and write information, such as heat-assisted magnetic recording are being developed. However, the recording temperatures impact not only the media but also the carbon overcoat that is used to protect both the media and writing head. In this paper, we discuss the effect of thermal annealing on the rate of carbon erosion on overcoats deposited using two different techniques, viz. filtered-cathodic arc and plasma-enhanced chemical vapor deposition.

Head–Disk Interface Materials Issues in Heat-Assisted Magnetic Recording

In this paper, some issues concerning the reliability of heat-assisted magnetic recording (HAMR) media are highlighted. The large roughness of the grain structure originates from a surface energy mismatch between the FePt grains and the graphene-like segregant material. A simple roughness model, based on interfacial energies, is proposed that can quantitatively predict media grain structure and roughness. The thermal behavior of the disk lubricant is reviewed both experimentally as well as theoretically using molecular dynamics (MD) and density functional theory (DFT). The lubricant film can be subjected to evaporation and oxidation, both of which follow an Arrhenius reaction rate. MD also predicts that the disk carbon overcoat can undergo structural changes under thermal transient exposure in the nanosecond time frame, and Raman imaging performed on a disk zone that was HAMR written shows small but unequivocal changes, consistent with an increase in carbon sp2 cluster size.

A multidentate lubricant for use in hard disk drives at sub-nanometer thickness

We describe a second generation of multidentate lubricant structures for use on a magnetic media in a hard disk drive. Building on earlier work where a perfluoropolyether (PFPE) chain with hydroxyl bonding moieties were placed in the middle of the chain as well as on chain ends, creating a structure with two PFPE sub-units for enhanced tribological performance under very low head-disk spacing, this paper focuses on a PFPE chain composed of three, even shorter PFPE sub-units. Experimental data focusing on surface characterization of sub-nanometer thickness films, as well as tribological performance, are presented that confirm the high confinement level achieved with the lubricant structure. Molecular dynamics calculations are also discussed, that are consistent with a molecular film of high stiffness, leading to a denser, more compact structure. This approach could pave the way to achieving the sub-nanometer head-disk clearance level, presumed necessary for storage densities exceeding the terabit per squar...

Thermal Aspects and Static/Dynamic Protrusion Behaviors in Heat-Assisted Magnetic Recording

The pressure of increasing the areal density of magnetic storage media demands the leap to new storage technologies. Among the prime candidates, available is heat-assisted magnetic recording technology. Among many aspects available in this paper, we will focus on newly introduced thermal aspects and protrusions due to additional heat sources in the recording head and recording media. As needed with the existing head protrusions such as thermal flying height control and writer pole tip protrusion, we will present the data, which is based on thermomechanical modeling and experiments during flying and static conditions. The ongoing debate of comparing flying versus nonflying conditions remains a critical issue but needs to be accepted as an imperfect but valuable way of exploring the new protrusion effects. We will address the important issue of the differences between the pure thermal and the associated mechanical time constants.

Low surface energy and corrosion resistant ultrathin TiSiC disk overcoat

Ultra-thin films of titanium silicon carbide (TiSiC) were deposited by magnetron sputtering (using Ti2SiC3 targets) to form protection overcoats (OCs) onto magnetic recording media of hard disk drives. The chemico-physical properties (composition, optical constants, electrical resistivity, mass density, and surface energy) of titanium silicon nitride (TiSiN) films were measured and correlated to their OC performances in terms of protection against Si oxidation, Co corrosion, and Co diffusion. Performances of TiSiC OCs were compared to those of silicon carbide (SiC), silicon nitride (SiN), and TiSiN OCs. It was found that Ti incorporation into SiC and SiN considerably densifies the films, reduces their surface energy, and renders them more metallic. 25 A thick TiSiC OC forms stable protecting barriers than can sustain hydrolysis conditions without growth of surface silicon oxide or cobalt diffusion or oxidation in the underlying recording magnetic medium. Overall, TiSiC OCs outperformed TiSiN, SiC, and SiN...

Surface chemistry of NiP plated substrates

Circumferential texture grooves polished into NiP plated AlMg substrates promote magnetic crystal anisotropy in longitudinal recording media. Freshly textured or washed NiP is a chemically reactive surface, and combines with atmospheric moisture and carbon dioxide to form Ni carbonates. These adventitious products alter the surface morphology and interfere with magnetic domain growth.

Dynamic Friction Study on Voltage Assisted Overcoat Wearing Head-Disk Interface

Voltage assisted wear at the head and the disk interface is investigated with the motive of understanding the head overcoat wear processes. In this work, we report the quantitative analysis of voltage assisted wear on head carbon overcoat at high sliding speed interfaces. We found that voltage assisted TFC head wear acts asymmetrically at the interface with positive voltage leading to high wear. We quantitatively analyzed the interface using a strain gauge based friction measurement.Copyright

Overcoat Wear and Dynamic Friction Study at the Head-Disk Interface

The dynamic friction and wear at the head and the disk interface is investigated with the motive of understanding the head overcoat wear process associated with physical contact between the head and the disk. In this work, the results from systematic experiments under overpush conditions are presented. Various regimes of head wear are identified based on the individual wear rate of the participating overcoat layers. A strain gauge based friction measurement is used to extract the friction coefficient and the adhering shear strength between the head and the disk.Copyright