Tom E. Karis

TEK Data Systems

The hysteresis properties of a magnetic recording disk drive rotary actuator servo were measured for bearings lubricated with three different types of grease. The three types of grease tested were: 1) mineral oil with a polyurea thickener, 2) polyol ester oil with a polyurea thickener, and 3) perfluorinated polyether (PFPE) oil with a polytetrafluo...

Magnetic recording disk carbon overcoats are lubricated with nanometer thick films of perfluoropolyether lubricant. It is well-known that lubricant thickness redistribution takes place due to air shear stress oscillation at air bearing resonant frequencies and also due to shear stress oscillation induced by disk topography waves on test tracks. We...

Magnetic recording disk carbon overcoats are lubricated with nanometer-thick films of perfluoropolyether lubricant. It is well-known that lubricant thickness redistribution takes place due to air shear stress oscillation at air bearing resonant frequencies and also due to shear stress oscillation induced by disk topography waves on test tracks. We...

A system and associated methods are described for preparing a magnetic disk for installation within a disk drive system. For example, a polyfunctional lubricant may be mixed with a chemical agent to esterify the polyfunctional lubricant and cap hydroxyl groups of the polyfunctional lubricant. The magnetic disk may then be dip coated with the polyfu...

The development of an ester oil formulation with antistatic additives and a novel approach to evaporation control were described. A series RC equivalent circuit model was derived to relate the dielectric properties of the oil with the motor voltage and peak discharge current. The influence of motor voltage and electric energy stored in the bearing...

A pentarythritol tetraester oil was formulated with different proportions of primary antioxidant dioctyldiphenylamine and secondary anti-oxidant zinc dialkyldithiocarbamate with and without 1 wt % of tricresyl phosphate for high performance magnetic recording disk drives. Corrosion inhibitors were tested to help prevent metal dissolution. The most...

The mechanisms and effectiveness of corrosion protection provided by thin ion-beam carbon coatings on Cu, Fe, Mn and Co are discussed. A thin (# 10 Å) layer of protective carbon is produced on metal surfaces by ion-beam dissociation of adventitious or intentional hydrocarbon adsorbates. Below 200°C, oxidation is strongly inhibited, as is corrosion...

Nanoimprint lithography is a low cost method which produces trillions of nanostructures on a substrate. One application of this technology is patterned magnetic media where a single imprint on a disk can create a masking layer with more than a trillion nanostructures. Several challenges exist to imprinting bit patterned media (BPM) at a density gre...

The development of liquid crystalline mixtures with short electro-optic switching times has made possible an array of new products, including hand-held televisions and lap-top computers with flat panel displays. Whereas the switching times for materials with long switching times has been correlated with their steady shear viscosities, this is not t...

A novel region of tribological interaction is explored by inducing near contact between the magnetic recording slider and disk. In this study, we performed frictional measurements over a wide range of subambient air pressure and disk rotation rate. Since the slider is supported over the disk by an air bearing, it has been found that cycling from am...

Frictional hysteresis loops are measured with a pico-slider on typical desktop media to illustrate the bridged state with a chemisorbed perfluoropolyether lubricant. Our new molecular adhesion model calculates the mean spacing and bridge stiffness from the experimental friction force, surface topography, and dispersive surface energy. An increase i...

In an earlier report, flyability failures due to siloxanes were investigated comparing disks with either Z-Dol or X-1P lubricant. On the Z-Dol disk, the head-disk interface failed at 47 h (h) and the slider accumulated silicon oxide smears, whereas the X-1P disk did not fail (truncated at 300 h) and the slider remained clean. The contrasting perfor...

The spreading behavior of non-polar polymers in the nanometer thickness range is revisited. By incorporating a distance of closest approach d0 corresponding to the unbonded atom-atom distance, to the classical London slab-slab interaction energy, we demonstrate that the spreading profiles of a non-polar perfluoropolyether molecule perfectly obeys a...

This paper discusses a new class of lubricants for disk application, designed for ultra-low magnetic spacing. By tying down the middle of the long perfluoropolyether (PFPE) Fomblin chain to the overcoat surface with additional functional groups, one can achieve the very low clearance needed for the future, sub-5 nm flying height head-disk interface...

Needle-like crystalline nanostructures were formed on the surface of a lubricated experimental thin-film media during exposure to elevated temperature and humidity. Clusters of nodules were formed on unlubricated media during the same exposure. Both the needles and nodules were identified as cobalt oxalate by Micro-Raman spectroscopy. A chemical me...

Vapor corrosion inhibitor can improve the reliability of heads and disks in a hard disk drive by forming a protective film over exposed metal. Diffusion channels from a source and to a drain are designed to control the steady state relative partial pressure of the desirable species below saturation. Extended accelerated life tests and repeated cond...

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 i...

Humidity effects in magnetic recording are reviewed. We highlight the progress made toward quantifying water adsorption on lubricated overcoats, leading up to the present understanding of humidity effects on magnetic recording tribology. Recently, it was found that moisture is also absorbed by hygroscopic atmospheric contaminants to form liquid nan...

This article critically reviews the fundamental scientific tools, as well as constructs cohesive schemes for potential applications, relevant to the molecularly-thin liquid film technology. Our focus is to understand the nanoscale dynamic behavior of thin lubricant films, relevant to the emerging field of nanotechnology, especially for achieving du...

The surface chemical evolution of NiP-coated AlMag disk substrate was analyzed using contact angle, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy techniques. Its effect on magnetic film structure and orientation ratio was also studied. It was also shown that slow nickel carbonate surface growth under ambient con...

Inhibition of oil oxidation is the key to long life of synthetic lubricants operating in thermal stress and boundary lubrication environments. A first order reaction model has been employed to derive kinetic parameters from the heating rate dependence of the combustion temperature in the non-isothermal pressure DSC (NIPDSC) test by Adhvaryu et al....

As magnetic recording slider size and flying height evolve to smaller dimensions, previously insignificant levels of contamination begin to play a role in slider media tribology. This article describes a new type of contamination. Liquid nanodroplets on disks originate with electrostatic deposition of hygroscopic ultrafine particles, also referred...

A model is presented that calculates the equilibrium lubricant thickness on a slider, resulting from a steady state where net inflow from disk evaporation equals net outflow from evaporation back to the disk, and flow to the slider back end from air shear. Based on experimental vapor pressure and viscosity data, and using surface viscosity enhancem...

Yield stress, and small- and large- amplitude oscillatory shear measurements were performed on greases in a cone-plate fixture. Below the yield point, the grease behavior mimics that of a lightly crosslinked polymer. In large-amplitude oscillations that exceed the yield stress, harmonic distortion appears in the stress waveform. The elastic compone...

Water adsorption isotherms were measured with two different types of perfluoropolyether lubricants, Zdol 4000 and Ztetraol 2000, on thin film magnetic recording disks. The adsorption isotherm provides the average water film thickness (areal density) as a function of relative humidity. The water film thickness was measured while varying the relative...

Large amplitude oscillatory experiments were performed using a cone-and-plate geometry with two different greases. Odd harmonics of the resultant stress waveforms are used for obtaining the material parameters. The procedure for calculating the crossover shear rate, the first and second region viscosity, and an apparent yield stress from harmonic a...

The magnetic recording industry is projected to continue growing into the foreseeable future. This growth is fueled by increasing data storage density through advances in channel and read/write head integration, tracking servo mechanisms, higher speed spindle motors, chemical integration, and nanotribology. The rotation rate is approaching 20,000 r...

Perfluoropolyethers (PFPEs) are vital lubricants in the aerospace and magnetic recording industry, and they have potential applications in micro-electromechanical and optoelectronic devices. Precise control of their physical properties requires analytical tools, such as nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography...

Large amplitude oscillatory shear experiments, as an alternative measurement technique for nonlinear rheology, were performed using a cone-plate rheometer with a solder paste. We found that odd harmonics appear in the stress waveform. A two-segment, piecewise linear model was introduced to analyze the experimental observation. The procedure for cal...

 Sudden change in the linear stress-strain relationship has long been known to produce interesting discontinuities in the flow properties of polymer melts, concentrated particle suspensions, and gels as the shear rate amplitude is increased. The non-linear effect produces stress harmonics, which contain information about the material properties tha...

Even though the flying height is approaching molecular dimensions, it is expected to decrease as the areal recording density is increased. This study employs a new low-velocity test to obtain ultralow flying height with sustained intermittent asperity contacts and random seek accessing in a region near the middle diameter of the disk. Sensitive sur...

The magnetic recording industry predominantly uses Zdol to lubricate the carbon overcoat of magnetic recording disks. Zdol comprises a perfluoropolyether chain terminated with hydroxyl end groups that are capable of reversibly bonding to the carbon overcoat. Contact start/stop (CSS) tests were done to investigate the effects of Zdol lubricant bondi...

Since many of the newer disk drive products incorporate load/unload to avoid starting and stopping on the disk surface, a new low-velocity accelerated life test was developed to simulate the tribology at ultra-low flying height with asperity contacts. Surface chemical analysis of the tested regions detects lubricant removal by desorption, and fragm...

As the rotation rate of magnetic recording disks increases over the next few years, lubricant spin-off from the disk surface may be significant. Lubricant thickness was measured as a function of spin time at 10000 rpm on typical carbon overcoated magnetic recording disks initially lubricated with 10–135 of perfluoropolyether Zdol. The viscosity of...

Surface chemical analysis of in-contact tested regions detects lubricant removal by desorption and fragments with carboxyl end groups on the overcoat. Formation of a carboxylic acid-amine complex and metal carboxylates is proposed to explain the observed changes in the water adsorption isotherm on the tested regions

Two properties that delimit the useful temperature range of synthetic lubricating oils are the vapor pressure and viscosity. This study investigates the ability of fluid theory to model these two properties for diesters with different diacid chain length and alcohol branching, triesters consisting of triglycerides and a trimethylol propane ester, a...

Disk drives experience a wide range of temperature and humidity during storage and operation. Humidity influences media tribology through the effects of adsorbed water on the interaction of Zdol lubricant hydroxyl end groups with the carbon overcoat. We measured the effects of Zdol 4000 thickness and chemisorption on the water adsorption isotherm a...

Synthetic oils have come into widespread use due to their inherent stability, consistent physical properties, and reproducible composition. As ever increasing demands are being placed on oil performance in magnetic recording disk drives by increasing rotation rates up to 10,000 rpm, it is important to know the ultimate limitations of these function...

Perfluoropolyethers (PFPEs) are widely used as lubricants on magnetic recording media. The mobility of the PFPE on the protective carbon overcoat of the media is widely accepted to be intimately coupled to the resulting tribological performance. The flow properties of molecularly thin films of nonpolar PFPEZ and polar PFPE Zdol fractions on solid s...

The one-dimensional diffusion equation is solved numerically to calculate the spreading profile of a molecularly-thin liquid on a solid surface. The thickness-dependent diffusion coefficient of the liquid is derived from the thickness dependence of the dispersive and polar surface free energies. Changes in the gradient and curvature of the total fr...

The thermal bending of the magnetic recording head gimbal assembly is modeled with elastic theory. The bending arises from the thermal expansion coefficient difference between the ceramic slider and the stainless-steel suspension which are bonded together with an adhesive. The system is modeled as a trilayer composite beam. Displacement compatibili...

In the magnetic recording head gimbal assembly, the ceramic slider is attached to the stainless-steel flexure of the suspension by a thin layer of adhesive. The mismatch of the thermal expansion coefficients between the stainless steel and the ceramic causes thermal bending, or crown sensitivity, as a result of temperature variation. Crown sensitiv...

The temperature excursions inside a magnetic recording disk drive can be as much as 20 to 60°C. When subjected to these temperature changes, thermal expansion coefficient mismatch between the ceramic slider and the stainless steel suspension causes bending. This thermal bending is mediated by the viscoelastic properties of the polymeric adhesive at...

The tribology of several perfluoropolyether (PFPE) lubricants was studied using a pin on disk (POD) test. During the POD test, PFPE is incrementally removed from the track with each sliding cycle. The number cycles to failure, NF, is detected as a sudden increase in the friction coefficient. Molecular theory for polymer melt rheology was employed t...

The hysteresis properties of a magnetic recording disk drive rotary actuator servo were measured for bearings lubricated with three different types of grease. The three types of grease tested were: (1) mineral oil with a polyurea thickener, (2) trimellitate oil with a polyurea thickener, and (3) perfluorinated polyether (PFPE) oil with a polytetraf...

We investigated a new lubricant made using ion beam assisted deposition of fluorinated monomers. The fluorocarbon film is referred to as ion beam lubricant, IBL. Typical thin film media deposition was followed by deposition of the IBL. The IBL provided an acceptable number of start/stop cycles without mechanical wear, but the stiction became too hi...

A methylene dihydropyridine with a high ground-state dipole moment was investigated to explore the possibility of using it to form an organic monomeric glass “electret” film. Measurements were done in a specially designed test cell. An electric field was applied to a 100-μm-thick film of dihydropyridine while cooling from a melt. The cell potential...

Fluorocarbon films were deposited on carbon overcoated magnetic recording media from monomers using an ion beam apparatus. The films were characterized using sensitive surface analytical and spectroscopic methods. These include nuclear magnetic resonance spectroscopy, dielectric spectroscopy, infrared spectroscopy, x-ray photoelectron spectroscopy,...

Perfluoropolyether (PFPE) films for lubrication of thin film magnetic recording media are made progressively thinner and their physical properties are increasingly dominated by molecular interactions with the carbon overcoat. Surface potential measurement is one of a few techniques to study the interaction of ultrathin films with surfaces. A scanni...

Solid fluorocarbon films were deposited on carbon overcoated magnetic recording media. The films were made by direct ion beam deposition of fluorocarbon monomers. This paper presents ellipsometric measurements on films over a range of thickness from 0.5 to 12.5 nm. Film thickness was measured using ellipsometry, and the chemical composition was stu...

A Kelvin probe apparatus was developed to profile surface potential. Measurements were performed on unlubricated and lubricated carbon overcoated thin film magnetic recording media. The surface potential on perfluoropolyether-lubricated media was more negative than that on the unlubricated carbon overcoat. Sliding, start/slop, and low-flying tests...

Two different microrheological characterization techniques for the microstructure of complex fluids (i.e. rheomagnetic and rheooptic measurements) were adopted to study the microstructural state of magnetic particle suspensions. These two techniques measure the dispersion state of various single-domain magnetic particles (rodlike γ-Fe2O3 or CrO2 an...

Continuous improvements in printer resolution place greater demands on toner performance. As the pel size becomes smaller, the requirements for edge definition and the elimination of hot offset increasingly become limiting factors in determining print quality. Edge definition, resolution, and offset can be addressed to some extent by improved charg...

The spreading characteristics of thin polymeric liquid films of perfluoropolyalkylethers (PFPEs) Fomblin Z15 and Fomblin Zdol (hydroxyl terminated PFPE) on silica surfaces have been measured by scanning microellipsometry (SME). We estimated the surface diffusion coefficients and propose a modified diffusion equation to interpret the spreading pheno...

A new technology for printing three-dimensional solid objects from computer-generated images is described. The technology is based on extrusion of a thermoplastic polymer melt as small fibers that bond to form the solid object. This technology is referred to as thermoplastic melt extrusion rapid prototyping (RP). Polymer materials for thermoplastic...

The rheological characterization of a wide variety of materials used in computer hardware is described. The materials and applications presented include liquid crystal polymers for components, solder paste for surface mounting of integrated circuits, screen printable polyimide for dielectric patterns, new photosensitive polyimide to reduce processi...

Dibenzoyl N-alkyl ethylene diamine compounds were prepared and characterized to explore the effects of rotational isomerism and hydrogen bonding on organic monomeric glass formation. The compounds were R1CONHCH2CH2N(R)COR1 with R = −CH3 or −CH2CH3 and R1 = phenyl, 4-nitrophenyl, or 3,5-dinitrophenyl. Rotation takes place about the amide bonds, and...

Surface diffusion of perfluoropolyalkylether (PFPE) Fomblin Z15 and Fomblin Zdol (hydroxyl terminated PFPE) on silicon wafers was investigated over the temperature range of 25 to 50C using scanning microellipsometry. Zdol exhibits a much lower mobility and a distinctly different thickness profile as compared to Z15. The activation energy for surfac...

Glass formation from the melt of organic monomers was studied for a variety of different organic molecular structures with Tg near ambient temperature. Crystallization is suppressed by one or more of the molecular properties, hydrogen bonding, interlocking, dipolar, and hydrogen bonding, combined with hindered rotational isomerism. Examples of mate...

Linear viscoelastic dynamic theological measurements were performed on symmetric diblock copolymers of deuterated polystyrene and poly(n-butyl methacrylate), denoted P(d-S-b-nBMA). Isothermal frequency sweep data were time-temperature superposed. A transition from a disordered to ordered morphology was found with increasing temperature as a functio...

State of the art techniques for measuring magneto optic disks birefringence are reviewed. As an illustration of one technique, we measured the birefringence of different magneto optic disk substrates by ellipsometry. The retardation data was fitted to an analytical expression as a function of the different indices of refraction. The variation of bi...

Polycarbonate substrates are the industry standard for optical storage. Optical anisotropy is frozen into the substrate as polymer orientation during mold flow and thermal stress during cooling. The substrate optical anisotropy degrades the readback of the data [carrier‐to‐noise ratio (CNR)] by increasing the noise level on Kerr rotation measuremen...

DIBLOCK copolymers, comprised of two distinct homopolymers covalently bonded together at one end, undergo a transition on cooling from a state in which the segments of the blocks are homogeneously mixed to one in which they are segregated locally1,2. This microphase separation is driven by the enthalpy of unfavourable interactions between segments....

The dynamics of dewetting were investigated for thin films of poly(ethylenepropylene) (PEP), on polystyrene (PS) and poly(methyl methacrylate) (PMMA) substrates. Dewetting was induced by immersing the films in aliphatic alcohols, thereby changing the equilibrium contact angle of the PEP film from zero to some very high value. Contact angles of 180...

The dynamics of dewetting were investigated for thin films of poly(ethylenepropylene) (PEP), on polystyrene (PS) and poly(methyl methacrylate) (PMMA) substrates. Dewetting was induced by immersing the films in aliphatic alcohols, thereby changing the equilibrium contact angle of the PEP film from zero to some very high value. Contact angles of 180°...

A variety of techniques have recently been published for measuring the bulk average values of the MO disk substrate birefringence(1-4). Interpretation of the bulk average birefringence data has been explored in great detail(5). Birefringence in polycarbonate, PC, magneto-optical, MO, disk substrates arises from a combination of frozen-in polymer ch...

Future disk files will operate at lower flying height, thus increasing the possibility of asperity contacts. Conventional tests include sliding (pin-on-disk or slider-on-disk), flying (flyability tests), or contact start/stop modes of operation. A novel accelerated water test (NAWT) was developed to produce intermittent asperity contacts. The NAWT...

Single-domain magnetic particles are the essential ingredient of magnetic tapes, particulate recording disks and magnetic stripes. The particles are single-domain γ-Fe2O3, CrO2 or barium ferrite, and non-magnetic α-Fe2O3 mixture. Each of these particles has intrinsic coercivity, which should be matched with the magnetic field strength of the writin...

Mechanical scission of two typical perfluoropolyethers was investigated: Y, a copolymer of CF(CF3)CF2O, CF2O, and CF(CF3)O, and Z, a copolymer of (CF2)nO, with n = 1,2,3,4. Undiluted polymers were subjected to prolonged shearing in a media mill with ZrO2 particles. A chemical extraction of the polar ZrO2 particles was carried out to collect adsorbe...

The current trend in the magnetic storage industry is the reduction of the slider size and the height at which the slider flies over a rigid disk. Lower flying heights are achieved by miniaturizing sliders and reducing the normal load. In this paper, force scaling criteria are determined for 3370 and 3370K sliders that are dynamically loaded or ope...

Measurement of magnetic particle flow orientation properties is of considerable practical and fundamental interest as it relates to the particulate recording tape and disk manufacturing industry. For production of high‐quality magnetic tapes and disks, the suspension must be well dispersed. Previous study focused on rodlike single‐domain magnetic p...

The melt rheology of a new liquid crystalline copolyester Vectra E from Hoechst‐Celanese Corp. was investigated. A Rheometrics mechanical spectrometer was used to characterize the change in melt rheology produced by annealing below the melting temperature with dynamic, step shear rate, and step strain tests. The coupled relaxation model was employe...

The use of a rheomagnetic instrument which provides an indirect measure of the dispersion quality of a magnetic ink suspension used for coating application in the manufacture of magnetic recording disks is described. The instrument was designed, tested, and put on a pilot line to study the relationship between the dispersion quality measurement and...

A technique, called rheomagnetic measurement, for studying the concentration and orientation of magnetic particles through inductance measurement is presented. The particles are oriented in a predominantly extensional flow field, and, because they are magnetic, their orientation can be detected with a weak magnetic sensing field. Because flocs of m...

Lubrication of particulate magnetic recording media improves their mechanical durability in sliding and flying by several orders of magnitude compared with unlubricated media. Lubricant removal, degradation, and recovery were studied using microslit scanning Fourier transform infrared spectroscopy and microspot scanning X-ray photoelectron spectros...

A new rheomagnetic measurement for studying the orientation of magnetic particles in suspension is presented. The apparatus, constructed on the basis of our previous theoretical development and Gedanken experiment on the magnetic particle suspension, is described in detail. The magnetic particles are rod-like γ-Fe2O3 such as those employed in magne...

The volumetric information storage density of rigid disk drives continues to increase through decreases in the slider-disk separation (i.e., the flying height). Reductions in slider-disk separations are achieved primarily through smoother surfaces on the magnetic media. The limiting factor in decreasing the slider-disk separation is the interaction...

An aqueous sol-gel procedure to obtain fine Y–Ba–Cu particles with an approximately 1-2-3 stoichiometric ratio is described. This involves precipitating an aqueous solution of the oxides in HC1 by neutralization with Ba(OH)2, and precipitation of BaCO3 from solution with CO2. A novel treatment with H2O2 decreased the weight loss while sintering. Th...

A description is given of the use of a rheomagnetic instrument which provides an indirect measurement of the dispersion quality of a magnetic ink suspension used for coating application in the manufacture of magnetic disks. The instrument was designed, tested, and put on a pilot line to characterize the relationships between the dispersion quality...

Rheomagnetic measurement, a technique for studying the concentration and the orientation of the magnetic particles through inductance measurement, is described. The method may complement conventional techniques. Compared to conventional techniques, the rheomagnetic method is uniquely suitable for process control during the early stages of slurry pr...

The production of particulate magnetic disks or tapes requires consistent and uniform magnetic characteristics over the entire disk or tape to have as few defects as possible. To achieve this goal, the magnetic particle suspension used to coat the disk must be well dispersed. This article describes the use of a rheomagnetic instrument that provides...

Process changes aimed at improving printer engine performance must take into consideration not only the process variables (such as nip temperature and pressure and process time to), but also the melt rheological variables (such as the characteristic time scale of the toner Tc). The melt rheology relevant to the electrophotographic toner fusing proc...

A rheomagnetic measurement (RM) device which is suitable for online characterization of both the concentration and dispersion quality of magnetic suspensions during the early stages of slurry production is presented. New results on the measurement and interpretation of the RM data for the plate-like particles used in perpendicular recording are pre...

Preparation of blends of the homopolymers of 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) has been investigated via compression molding at temperatures up to 460°C and pressures up to 8 kpsi. It has been found that 1:1 mixtures of finely divided powders of the homopolymers when compression molded under these conditions can trans...

Tribological studies of friction and wear were performed on carbon overcoated thin‐film magnetic recording media with pin‐on‐disk tests. Scanning microellipsometry was employed to measure the wear of carbon overcoats on rigid magnetic media. Severe wear produced after the carbon film wore through was measured by mechanical profilometry. The wear ra...

A magnetic recording ink formulation consists of mixed solvents, a polymeric binder, and magnetic pigment. This is coated onto a disk or tape substrate and cured. In the process, the solvent evaporates, and the binders polymerize, embedding the pigment to form the magnetic film. For quality control of the process, it is important to maintain the co...

Although the particulate magnetic recording industry is mature, there still remains an unsolved problem of dispersion quality, which plagues any coating process involving unstable particle suspensions. We re-examine this issue in light of our recently developed concept for dispersion quality measurement. That is, the particles are oriented in a flo...