Vedantham Raman

Microstructure and properties of ultrathin amorphous silicon nitride protective coating

The effect of N content on the structure and properties of rf reactively sputtered amorphous silicon nitride (a-SiNx) has been studied by Rutherford backscattering spectrometry, x-ray reflectivity, ellipsometry, and nano-indentation. The N content in the film increased with the N2 concentration in the sputtering gas until the Si3N4 stoichiometry was reached. The hardness of a-SiNx increased with density, which in turn increased with the N content. The maximum hardness of 25 GPa and density of 3.2 g/cm3 were attained at the stoichiometric Si3N4 composition. With the application of a protective overcoat for magnetic disks in mind, thin a-SiNx films were deposited on CoPtCr media to examine their coverage, pinhole density, and wear resistance. According to x-ray photoelectron spectroscopy, the minimum thickness of a-SiNx required to protect the CoPtCr alloy from oxidation was 10 A, which was 10 A thinner than that of the reference amorphous nitrogenated carbon (a-CNx). A statistic model showed this lower thi...

Investigation of phoshpazene additive for magnetic recording lubrication

The addition of X-IP to the Fomblin Z-Dol disk lubricant is found to improve the contact start-stop (CSS) durability of hydrogenated carbon overcoated disks. Two-angle electron spectroscopy for chemical analysis (ESCA), contact angle measurements, spin-off measurements, and degradation studies on powdered AlCl/sub 3/ and Al/sub 2/O/sub 3/ are used to show that X-IP improves lubrication by perfluoropolyethers on magnetic disks by chemically interacting with disk and slider surfaces so as to block sites for lubricant degradation, to lower surface energies, and to increase lubricant mobility.

Perfluoropolyethers with Dialkylamine End Groups: Ultrastable Lubricant for Magnetic Disk Application

It has been shown earlier that addition of X1P (partially fluorinated hexaphenoxy cyclotriphosphazene) to the lubricant Z-DOL markedly increases the durability of the magnetic disk system. Its efficacy has been attributed to the strong nucleophilic property of the triphosphazene ring. It follows that perfluoropolyethers terminated with nucleophilic end groups should exhibit a durability comparable to that of the Z-DOL/X1P mixture. To this end perfluoropolyethers with dialkylamine end groups were conceived and synthesized as better alternatives to Z-DOL or to the Z-DOL/X1P mixed system. Examination of the newly synthesized lubricant revealed that (1) perfluoropolyethers with dialkylamine end groups are resistant to the degradation process catalyzed by Lewis acid (e.g., aluminum oxide), (2) disks lubricated with these lubes have durability significantly better than those lubricated with Z-DOL, (3) in the drive system with disks lubricated with these lubes, the issue of the silicon oxide formation from siloxane contaminant is effectively contained (owing to the absence of degraded lube), and (4) the HDI system with disks lubricated with these lubes performs well even in the most aggressive atmospheric condition, i.e., nitrogen with 0% relative humidity.

Degradation of Disk Lubricant: Ramification in Disk Drives and Direct Detection by TOF-SIMS

The degradation of Z-dol catalyzed by Lewis acid centers on the slider surface leads to chain scission forming one type of fragment terminated with a fluorocarbonyl end-group and the other with a trifluoromethoxy end-group. The former, in contact with humid air, converts to a fluorinated carboxylic acid Z-COOH. Z-COOH is an excellent scavenger for alkali or alkaline earth metal ions. Z-COO-M+ thus formed is a strong surfactant, and, in a humid environment, forms microdroplets embodying water in the core. Metal ions thus scavenged on a disk surface can be readily detected by TOF-SIMS, and the microdroplets by optical microscopy in the dark-field mode. The presence of fragments having a trifluoromethoxy end-group on the disk surface can also be established by TOM-SIMS. A careful intensity analysis of peaks due to anions having a trifluoromethoxy end-group permits a semi-quantitative assessment of the extent of degradation. The study has also shown that degradation is caused by such production processes as tape-polishing and by such disk drive operations as the head flying over a single track or over a band in a seek-mode.

Tribology Of Laser Textured Disks With Thin Overcoat

The adoption of dual zone texturing on magnetic disks allows the flying height of the head to be reduced over the data zone compared to a fully textured disk. Laser texture offers a technique far precise topography control and the placement of the landing zone. In this study the effects of the clearance between the head and the disk, and the presence or absence of overcoat on the air bearing surface on contact start-stop performance are evaluated. The wear mechanism of the laser bump by the head was investigated with in situ monitors and followed by surface analysis. Acceptable durability and stiction performance for contact start-stop operation is feasible with a few nm of clearance.

Vapor lubrication of thin film disks

A novel solvent-free coating process is described whereby hysteretic surface adsorption is used to provide uniform coatings of liquid perfluoropolyether lubricants onto thin film disks. The essence of the coating process is to place disks and lubricant in a closed atmosphere over at 170/spl deg/C for one hour. It is observed that the resultant lubricant thickness on the disk surface is near 10 /spl Aring/ and that the resultant lubricant thickness on the disk surface is only weakly dependent upon the coating oven exposure time and temperature. The contact stop/start performance of the disks is equivalent to those lubricated by dipping. >

Environment dependent stiction and durability in hydrogenated carbon overcoated thin film disks

Contact start/stop tests conducted on hydrogenated carbon overcoated thin film disks to examine the influence of test environment on stiction and durability are discussed. Improved mechanical performance was observed for tests performed in nitrogen and argon and sharply reduced durabilities for tests in oxygen-containing environments. Tests at higher humidities do not lead to improvements in disk durability. The sensitivity to the test environment appears to be dependent on the slider material. >

Stress relaxation and stability of sputtered carbon thin films

Stress measurements were performed on sputtered carbon films deposited on Si substrates in the temperature range from room temperature to 350 °C. Both hydrogenated and nonhydrogenated carbon films, ∼100 nm in thickness, were investigated. The stress relaxation kinetics were investigated for films tested in air and in the presence of an inert environment. The experimental data show distinct differences for tests performed in these two environments. Microscopic examination revealed that films tested in air show local loss of carbon following a thermal cycle whereas the films tested in argon show good stability and remain well adhered to the substrate

Hydrocarbon Transfer in Disk Drives

In hard disk drives, oils used in the spindle motor or the actuator assembly are likely to be potential sources of hydrocarbon contaminants. Transfer to, and accumulation of such contaminants on the head would adversely affect its flyability. It was reported earlier that such transfer occurs more readily, the lower the vapor pressure of the contaminant is, and the lower the temperature of the ambiance is. The present study confirmed these findings. It is shown that the transfer is mediated by the disk surface area of high surface energy (openings of the carbon overcoat). Via an airflow transport process, droplets of the contaminant hydrocarbon are formed at such sites, and evolve in size till they are collected by the slider of the head.Copyright

Investigations of Fly Height Changes Due to Small Particles using Capacitance Measurements

Laser texturing has been introduced recently on high performance magnetic rigid discs to optimize trobological performance. while supporting low glide. However, during take-off and landing, system resonances (i.e., slider body. AE sensor, etc.) excited by the periodic laser bump array can cause enormous AE readout, even in the absence of contact, leading sometimes to erroneous glide testing results. In this paper, the dynamics of a slider flying over laser texture will be analyzed in the framework of a joint timdfrequency analysis (spectrogram). It will be shown that the input excitation by the regular laser bump array remains strong. even up to the loth harmonics. When these input excitations intercept system resonances, a strong AE signal is observed. Individual and combined effects of head, laser texture characteristics, and AE (PZT) sensors on glide methodology will be discussed. novel. non-periodic texture patterns will be described, such as pseudo-random and spiral-line laser texture. Techniques for generating them will be discussed briefly, and spectrogram analysis will demonstrate that, as predicted, the pseudo-random texture shows a dramatic reduction in input excitation. while the spiral-line laser texture removes them completely.