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This paper is an attempt to review some historical trends in thin film disk lubricant technology, and the associated requirements in terms of overall reliability, as we inexorably approach the subnanometer clearance mark. We will mainly focus on the physical attributes of the lubricant, and more particularly on the slider-induced effects on lubricant dynamics. Design attributes for subnanometer clearance will be discussed in this historical context, as qualitative to semiquantitative models have emerged that allow such extrapolation. Index Terms--Clearance, head-disk interface, lubrication.

A simulation method in which grooves are virtually distributed on the slider air bearing instead of on the grooved medium surface has been developed and used to investigate the performance of sliders flying over the surface of a discrete-track medium. The simulated flying height loss due to a discrete-track medium coincides well with the measured data, whereas the average-estimation method overestimates flying height loss. Among the characteristics of a slider flying over the surface of a discrete-track medium that were studied are the flying attitude, the effect of groove parameters on flying profile, and the flying height losses due to manufacturing variation and altitude. The results indicate that when a slider is flying over the surface of a discrete-track medium, it will have a higher 3[sigma] of flying height, be more sensitive to altitude, and will have a greater flying height loss. [DOI: 10.1115/1.2768069] Keywords: discrete track medium, air bearing slider, head-disk interface, flying height

Micromagnetic simulations of perpendicular recording in hard disk storage media have been performed with model media of variable microstructural disorder. Simulations indicate that increasing disorder, either due to size and shape distribution or due to disordered packing, decreases signal and increases noise. The mechanism observed in the model is that, in a disordered microstructure, there is a distribution of magnetostatic and exchange coupling between grains that acts to create clusters of grains that act collectively. These clusters increase the auto-correlation function of the spatial distribution of magnetization that is a measure of the magnetic feature size. Consequently, the transition width between recorded bits increases and the position variation of the transition locations (jitter) increases, so that signal-to-noise ratio (SNR) falls. The results suggest that microstructurally ordered media will exhibit higher performance, and that such effects may ultimately demand the use of self-assembled or patterned media with regular packing and very narrow size distribution. Index Terms--Magnetic disk recording, micromagnetic modeling, perpendicular recording, recording media.

In the design of a magnetic recording disk file, pitch moment exerted by the flexure on the slider is usually treated as a product of flexure pitch static attitude and pitch-stiffness ([k.sub.p]), both measured in the absence of preload (gram-load). However a slider operates in the presence of preload, which permits a large dimple friction to exist. We shall show by elementary, beam theory that the pitch moment due to dimple friction is appreciable. The lever-arm of dimple friction is proportional to the bow height, and is independent of the slope of the flexure. To minimize the pitch moment associated with dimple friction, hence improving fly-height distribution, the flexure must bow toward the disk. These results are confirmed by optical fly-height tests. [DOI: 10.1115/1.2345394] Keywords: flexure stiffness, dimple fiction, pitch moment, pitch stiffness

This paper reviews a major disk-drive product development effort in IBM during the 1950s, one that was originally based on perpendicular recording. The goal of the project, identified as the Advanced Disk File (ADF), was to develop the successor to the first disk drive, the Random Access Method of Accounting and Control (RAMAC) 350. The ADF eventually became the IBM 1301, the first disk drive to use a flying head per surface. Whereas the RAMAC used longitudinal recording, the ADF project chose perpendicular recording as the mainstream recording technology for magnetic disk data storage and continued on this path for a period of five years. A crisis arose in the later stages of prototype testing due to unacceptable failure rates; one decision made was to change the recording method from perpendicular back to longitudinal. The reasons for the original selection of perpendicular and the subsequent return to longitudinal recording are described and address technology, product, and business issues. General observations on factors influencing the choices made and the final outcome are offered as well as the long-term impact of these events on the disk-drive industry. Index Terms--Disk-drive product design, IBM 1301, perpendicular recording, RAMAC.

An ellipsometry-based direct visualization method for molecularly thin lubricant films on magnetic disks is presented. The visualization of molecularly thin film is useful in investigating the replenishment and retention characteristics of thin lubricant films. Ellipsometric information of a sample surface is converted into a dark-bright contrast image that is then directly visualized with a charge coupled device camera. By combining optical and digital image processing techniques, weak contrasts can be enhanced and noise intensity reduced. The authors' method can provide direct visualization of thin lubricant films in the order of 1 nm. Index Terms--Digital image processing, ellipsometry, lubricant film, microscope.

Ultrathin carbon nitride (C[N.sub.x]) overcoats were grown using pulsed dc magnetron sputtering. Substrates were mounted on a holder that allowed 45[degrees] tilt angle and rotation at different speeds. Effects of sputter gas composition, target power, substrate bias, substrate tilt, and rotation on film growth and properties were explored. Atomic force microscopy scans over large sampling areas show that thin C[N.sub.x] films obtained at--100 V substrate bias with 45[degrees] substrate tilt and 20 r/min rotation have root-mean-square roughness almost four times lower than those prepared without substrate tilt and rotation. Several percent of helium in an Ar-5%[N.sub.2] sputter gas was found to improve surface roughness of these coatings. These 1-nm-thick ultrasmooth coatings reduced corrosion damage compared with coatings of the same thickness grown without substrate tilt and rotation. This improved performance appears to be directly related to the growth of smoother and denser coatings synthesized under the present conditions. Index Terms--Coatings, corrosion, hard disks, sputtering.

The thickness of carbon overcoats has been reduced to 30 [Angstrom] or less to achieve high areal density in magnetic media. Presently, technologies such as ion beam deposition and plasma enhanced chemical vapor deposition (PECVD) produce thin carbon overcoats with a high fraction of [sp.sup.3] bonding. These hard and dense overcoats exhibit good wear durability and corrosion resistance. This paper discusses processing, characterization, and tribological and corrosion performance of ultrathin overcoats (30 [Angstrom] or less) produced by PECVD. The physical and chemical properties of the carbon overcoat affect the carbon-lubricant bonding, which subsequently determines the head--disk interaction. Since optimal properties of the carbon vary at the lubricant and magnetic layer interfaces, an interfacial functionality approach is needed for the design of thin overcoats. Functionalized carbon overcoat is a design that consists of a PECVD carbon layer with a sputtered functional layer on top. Characterization and tribological performance and comparison of functionalized carbon overcoat with PECVD carbon is also presented. Index Terms--Carbon overcoat, characterization, ion beam, magnetic disks, precursors, processing, thin, tribology.

The static spacing loss of slider-disk interface is investigated through careful characterization of disk shape for disks of different form factors with different peak-to-valley flatness values. Measured radial profiles are normalized and found to be confined within a relatively narrow region. The representation of these shapes is reduced to a simple set of quadratic equations. Static flyability models associated with the disk radial slope (crown effect) and radial curvature (camber effect) are presented. Spacing loss is calculated for a negative pressure pico-slider and a positive pressure catamaran nano-slider. Results show that slider geometries and crown/camber sensitivity, as well as disk flatness and shape, all affect static slider-disk spacing loss. The analysis is focused on the effect of disk shape on the static spacing loss and its relationship to slider design. Index Terms--Disk drive, disk shape, flatness, flyability.

The general characteristics of the bouncing vibrations of a IDOF contact slider model over the surface of a harmonic wavy disk were studied both by computer simulation and theoretical analysis. The necessary design conditions for a contact slider and the surface of a disk were discussed in terms of perfect contact sliding and wear durability. It was found that the bouncing vibrations change with the amount of wariness amplitude A([f.sub.r]) at the contact resonant frequency [f.sub.r] (= (1/2[phi]) [square root of [k.sub.c]/m]) relative to static penetration depth [Delta], or [f.sub.r]. relative to limiting critical frequency [f.sub.cl], above which the downward acceleration of the surface of a disk is larger than that of a slider due to slider load. When the contact stiffness is large enough so that [Delta] < A ([f.sub.r]) (f.sub.cl] < ([f.sub.r]), the slider bounces with a large amplitude similar to an elastic impact in a wide frequency range. When the contact stiffness is small enough so that [Delta] > A([f.sub.r]) ([f.sub.cl] > [f.sub.r]), bouncing vibrations occur near the contact resonance, similar to the resonance of a nonlinear soft spring system. Here, the bouncing vibration can be completely eliminated by increasing the contact damping ratio and decreasing the slider mass and the wariness amplitude.

The design of laser zone texture on NiP/Aluminum substrates to create below-25 nm-glide-height media is described in this paper. A range of laser parameters such as beam size, pulse energy, and temporal pulse width of a pulsed Nd-YV[O.sub.4] laser are explored to reveal their relationship to the resulting bump topography. Depending on where the head contact is formed, four major categories of bump shapes are found to exist. The single-crater bump shape was selected to conduct the low glide texture design. Stiction and glide performance are shown to be in agreement with theoretical predictions, which constitute our major design guidelines. It is clearly demonstrated that with proper texture design below-25 nm-glide-height media with low stiction and minimal wear are readily achievable even in the landing zone with laser texture.

To counteract the performance degradation in magnetic disks, it is proposed to develop an evolutionary storage system that is evolving over time. The frequent data is clustered and moved to a flash memory. A large disk trace, collected from real systems, has been used. The experimental results showed that the performance speedup due to the disk reorganization is 4.0. Index Terms--Data transfer rate, flash memory, hybrid disk, magnetic disk, zoned bit recording.

A coarse-grained molecular dynamics simulation of the spreading of monolayer lubricant films on magnetic disks is presented. The simulated diffusion coefficient for various coverages of the bonded molecules was in good agreement with that obtained by an experiment using the half-dip method. The simulated relation between the coverage and bonding ratio was also in good agreement with the experimental one. Index Terms--Diffusion coefficient, head disk interface, molecular dynamics simulation, monolayer lubricant film.

The current design of magnetic-disk head sliders needs an extra margin of flying height for manufacturing tolerance or environmental variation. To reduce this margin, we have developed active-head sliders. These sliders carry an unimorph piezoelectric microactuator, and their flying height can be controlled. After simulating the piezoelectric deflection of the actuator and flying characteristics of air-bearing surfaces, we designed two types of active-head sliders (five-pad type and four-pad type) and fabricated them by silicon microelectromechanical systems (MEMS) processing. In tests, the sliders flew over a glass disk, and the observed stroke of the actuator (30 nm/5 V) was considered large enough to control the flying height. The large area at the rear end of the four-pad-type slider structure is sufficient to carry conventional read/write heads. Moreover, the slider fabrication process will not destroy the heads. We, thus, conclude that the active-head sliders can be applied for practical use easily, and their flying height will be significantly lower than that of conventional disk head sliders. Index Terms--Actuator, flying height, magnetic head slider, MEMS.

Island-type texture was fabricated on two types of picosliders using plasma sputtering and ion beam etching. Laser-Doppler interferometry was used to investigate the vibrations of the textured and untextured sliders in near contact situations. Lubricant redistribution on the disk surface caused by slider/disk interactions was investigated using scanning ellipsometry [surface reflectance analyzer (SRA)]. The results show that texture on the slider surfaces reduces in-plane and out-of-plane slider vibrations. Textured sliders were found to cause less lubricant depletion on the disk surface than untextured sliders. Index Terms--Lubricant redistribution, near contact, slider dynamics, slider surface texture.

A key parameter in the design of magnetic disk drives is the start-up motor torque needed to guarantee a spin-up. We present a detailed discussion of a method to measure motor start torque in the drive and to relate it to head-disk stiction. Our method involves controlling the total current applied to the motor during start attempts, and using externally mounted magnetic field sensors to detect disk rotation. In this way we are able to determine the torque required to cause the heads to break-free of the disks. Index Terms - stiction, magnetic field sensor, hall-sensors, motor torque'

In this paper, we propose a new concept and fabrication process for magnetic disks with embedded servo patterns, named ESPAR. A servo pattern for phase detection consisting of straight lines is formed by photolithography. The disk has a flat and smooth surface for proximity recording. Servo layer thickness and recording layer thickness can be designed independently. We fabricated the disk and demonstrated the demodulation of the servo signal.

A sealed, compact, and low power CO2 pulsed laser is used to melt a focused microscopic area on an alternative glass ceramic substrate. By precisely controlling the laser power, pulse duration, pulse rate, and the disk movement, a well-defined array of bumps can be produced on the alternative substrate. The laser bump formation on the alternative substrate shows a positive-extending volume without any negative-extending volume. TEM electron diffraction shows a phase change from polycrystalline to amorphous in the melted area. In addition to the stress release, the domed bump formation could be due to the volume expansion of newly formed amorphous phase. The CSS test results show that the supersmooth glass ceramic disk stiction can be reduced by one order of magnitude by applying laser zone texture. The transition zone width between laser texture and data zones can also be made as small as a few milli-inches to increase the recording area.

The idea of zone carbon (ZC) is to use a thicker carbon overcoat in the landing zone and a thinner carbon in the data zone. In this study, we demonstrated the use of a zone carbon scheme to improve recording performance while maintaining the durability of the thin film disk.

Discrepancies in the stiction and wear regimes of thin film magnetic disks result in defective contact start stop (CSS) data that evaluate the mechanical properties of the disks. The CSS simulations are grouped into five stiction and wear regimes and are associated with the physical characteristics of the head and disk interface. Static coefficient of friction values become regime- and lubricant thickness-dependent after CSS testing.

A novel MEMS-based electrostatic actuator design is proposed for recording head fly height control below 10 nm. Different from prior work on MEMS-based electrostatic microactuators designed for magnetic hard disk drives (HDD), the proposed microactuator is fabricated monolithically with a conventional head/slider design. The actuator is micromachined into the same side as the head element on a slider with a modified CMOS-MEMS process. It has an extremely small size, light weight and a very simple structure. The head is suspended and actuated up and down by the actuator during recording process to maintain a constant fly height. A desired range and precision of actuation is achieved under control voltages of less than 30 V. A mechanical resonant frequency of over 100 kHz is obtained. Index Terms--Fly height, MEMS electrostatic actuator, microfabrication, slider.

The thermal asperity of the tunneling magnetoresistive (TMR) head was studied using Zip-type flexible media, and compared with that of the anisotropic magnetoresistive (AMR) head. The examined head had a shielded structure with the TMR element close to the air bearing surface. Nevertheless, it generated relatively small thermal asperity even when the mechanical spacing between the head and medium was less than 20 nm, at which large and frequent thermal asperity was observed when the AMR head was used. Such relatively small thermal asperity of the TMR head is attributed mainly to the small low-temperature coefficient of the electric resistivity of the TMR element. Index Terms--Flexible disk, removable disk drive, thermal asperity, tunneling magnetoresistive head.

There is a drive toward achieving much higher track density in magnetic recording. Increase in track density will produce more interaction/crosstalk between adjacent tracks. The simulated variation of bit error rate (BER) as a result of increased inter-track interference (ITI) using a Viterbi Detector is presented in this paper. Results show that for a given BER and signal-to-noise ratio (SNR), different levels of ITI can be tolerated depending on the code. Calculations suggest 2-Dimensional modulation codes designed for a channel experiencing ITI can result in up to 23% gain in areal density. Index Terms--2-dimensional code, Inter-track interference.

This paper presents authors' considerations on anti-particle design and a type of slider air bearing surface (ABS) design with anti-surface borne particle function for load/unload based head--disk systems. The ABS is designed in such a way that the leading edge of ABS is wedge-shaped. The relationship between the ABS wall angle and the energy loss factor when a particle collides with a slider is discussed, aiming to avoid particles being stuck at ABS wall edge. The flying characteristics and load/unload performances of the slider are studied. The proposed ABS design is of good flying characteristics, satisfying load/unload performances, plus anti-contamination function. Index Terms--Air bearing surface, contamination, head/disk interface.

A novel technique for incorporating rapid thermal annealing into media sputter fabrication has facilitated the production of flyable media samples. Discs are fabricated with standard processing techniques to control physical grain size and crystallite texture. A CrMn caplayer ranging in thickness between 0.5 and 5 nm is subsequently deposited to provide the Mn-diffusant necessary to achieve post-treatment exchange decoupling. While still in-situ and before application of protective overcoats, the discs are exposed to temperatures between 200 [degrees] C and 350 [degrees] C compatible with most media production processes. A threefold increase in coercive force (peak reaching ~3800 Oe) and 10 dB improvement in medium signal-to-noise ratio is observed for the optimized process. Index Terms--Boron magnetic alloys, intergranular exchange coupling, post-deposition annealing, SMNR.

A new decoupled track-seeking controller for a dual-stage servo system of a magnetic disk drive has been developed. The controller is applied to the dual-stage system with a push-pull piezoelectric (PZT) micro-actuator and enables high-speed one-track seeking and short-span track seeking. A one-track seeking controller was designed in three steps: 1) a voice coil motor (VCM) feedforward controller was designed to prevent overshoot in response of VCM actuator; 2) a feedforward loop from the VCM reference signal to the PZT actuator was designed in order to de-couple the dual-stage actuator system; 3) a feedforward controller for the PZT actuator was designed such that an output PES (position error signal) only follows a PES reference signal. In the design of the short-span seeking controller, the PZT actuator's stroke limit was considered. Simulations and experiments show that the proposed dual-stage track-seeking controller performs better than the conventional single VCM servo. Index Terms--Decoupled seeking control, dual-stage actuator, magnetic disk drive, motion control.

We have developed a piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. We installed the microactuator in one of Fujitsu's 3.5-inch commercial drives for evaluation of the servo system of dual-stage actuator. The dual-stage actuator system achieved the nonrepeatable position error (NRPE) 3[Sigma] values of 0.036 [micro]m. The dual-stage servo system reduced the NRPE by 35% compared with the conventional single actuator system even in HDD's which has a high rotational speed of 10 000 rpm. Index Terms--Dual-stage actuator, magnetic disk drives, microactuator, piezoelectric actuator, shear mode.

Soft-particle intrusion tests were carried out on load/unload drives. These tests show that to prevent particles intruding into a head/disk interface (HDI) the HDI must be designed with a minimum step height of the slider leading edge. Adhesion of particles to slider rail surface results in slider-disk contact. Even a light intrusion of particles into the leading edge step leads to a decrease both in flying height and the pitch of the slider. Index Terms--Soft particles, head/disk interface, load/unload drives, contamination.

Some Co-Cr-Ta-Mo perpendicular magnetic recording disks with different Mo content ([C.sub.Mo]) ranging from 13 to 5.1 at.% were fabricated by ion beam sputtering prepared. Magnetic properties, crystal structure and recording characteristics of those media were investigated. The disks with [C.sub.Mo] of 0 to 3.5 at.% exhibited almost the same output values, however the media noise was decreased with increasing [C.sub.Mo]. The disks with [C.sub.Mo] of 3.5 at.% exhibited the highest S/[N.sub.m] of which value 3.2 dB higher S/[N.sub.m] than that of the disks without Mo at a wavelength of 0.34 [micro] m. Index Terms--perpendicular magnetic recording, Co-Cr-Ta, Mo, low noise media additive element