Magnetic Recording Slider Research Articles

Substrate tilting effect on structure of tetrahedral amorphous carbon films by Raman spectroscopy

Raman spectra at visible and ultraviolet excitation of tetrahedral amorphous carbon (ta-C) films have been studied as a function of oblique angles of substrates while keeping the energy of incident particles stable. The substrate angle is varied from 0 to 60°. The spectra show that the films contain less sp 3 content and more ordered sp 2 clustering as the substrate tilting angle increases from 0 to 60° for thicker films of 70 nm, and also a decrease of sp 3 content for thinner films of 2 nm from 0 to 45°. Raman data indicates the substrate tilting can dramatically lower internal stress while having less influence on hardness because hardness is related to sp 3 content, but internal stress is related to not only sp 3 content but the order of sp 2 cluster. And this is also consistent with the measurement of hardness and internal stress for thicker films of 70 nm. The implications of these results on the mechanisms proposed for the film formation were discussed. It can provide a way for film application in magnetic recording slider that requires less internal stress and suitable hardness.

Effect of Intermolecular Forces on the Dynamic Response of a Slider

A single-degree-of-freedom spring-mass-damper model has been developed to simulate the dynamic response of a typical magnetic recording slider under the effect of intermolecular forces. Thornton and Bogy (2003, IEEE Trans. Magn., 39(5), pp. 2420–2422) have previously reported that the slider “snaps” to the surface of the disk, below a certain “critical” flying height, due to the intermolecular forces. We have studied impulse response of the model to show that the slider can snap even at flying heights greater than the critical flying height and that the occurrance of snapping also depends on the magnitude of the applied impulse.

The Use of System Identification Methods to Evaluate the Effects of Slider-Disk Contacts and Disk Micro-Waviness on the Flying Height Modulations

System identification methods have been used to study the response of a magnetic recording slider during contact with a scratch on the disk surface. In addition, the slider response was studied taking into account the effect of disk micro-waviness at various disk rotational speeds. The simulated slider response was compared with the measured slider dynamic behavior. Very good agreement was found between simulated and measured data. The flying height modulation of the slider, due to disk micro-waviness, was found to depend on disk velocity.

Investigation of tribological and read-write performance of textured sliders

Texturing of magnetic recording sliders is a promising way to improve the tribological performance of the head/disk interface. However, texturing of sliders may cause deterioration of the read-write performance and care must be taken during texturing to prevent damage of the read-write element. In this study, texturing of sliders was performed after positioning a mica mask over the read-write element for protection from the plasma. After texturing, the tribological and read-write performance of the slider was evaluated and compared with the tribological and magnetic performance of the same slider prior to texturing. The results show that no degradation of the read-write element occurred and that the tribological performance of the slider after texturing was better than before texturing.

Nano-hardness testing with ultrasonic excitation

Accelerated wear of the head/disk interface is investigated using nano-indentation measurements of carbon coated magnetic recording sliders in the presence of ultrasonic excitation. The effect of ultrasonic vibrations on the indentation characteristics and fatigue of carbon coated magnetic recording sliders is studied and the effect of vibration amplitude and frequency is investigated. Significant changes are observed in the type of surface damage that occurs if indentation measurements are performed in the presence of ultrasonic excitation. The dependence of film breakthrough on film thickness during ultrasonic excitation is investigated.

Microtribodynamics of pseudo-contacting head-disk interfaces intended for 1 Tbit/in/sup 2/

As the distance between the magnetic recording slider and the high-speed rotating disk decreases to few nanometers, it is critical to understand the tribological and dynamic interaction at the head-disk interface (HDI). Such interaction involves surface topography, adhesion, friction, and system dynamic coupling and is termed microtribodynamics. A two degree-of-freedom nonlinear dynamic model that includes realistic roughness, adhesion, and friction, as well as the dynamics of a flying and contacting HDI was developed to characterize a pseudo-contacting HDI, intended for 1 Tbit/in/sup 2/. While a fully flying HDI is intended to avoid contact, a pseudo-contact recording system is designed to fly at few nanometers using an air-bearing and at the same time some features of the air-bearing surface are designed to contact with the rotating disk during operation. The model was favorably compared with flyability measurements, and then applied to a pseudo-contacting interface to investigate adhesion, friction, and contact forces as well as bouncing vibration. Contrasting earlier studies adopting a simple Coulomb friction, the friction model used in this work calculates the friction force at the interface, accounting for roughness and adhesion. It was found that unlike a fully flying HDI, adhesion plays a positive role in attaining pseudo-contact recording by reducing bouncing vibrations.

Liquid Nanodroplets on Thin Film Magnetic Recording Disks©

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 to as cloud condensation nuclei (CCN). On lubricated disks, the CCN equilibrate with atmospheric moisture and become partially overcoated with disk lubricant, which acts as a fluorocarbon surfactant. Dark-field microscopy measured deposition rates of 0.001 to 0.006 #/mm 2 /sec on initially clean disks exposed to ambient air in nonconductive cassettes. Tapping mode atomic force microscopy determined that the sites were deformable nanodroplets 70 to 300 nm in diameter and up to 150 nm high. From AFM profiles, the contact angle of the spherical capped nanodroplets with the disk was between 40 and 90 degrees. Nanodroplet contamination is characterized, and its effect on friction, acoustic emission, and slider smears is demonstrated. A surface chemical thermodynamic model is developed and employed to estimate that the average initial dry nucleus diameter is 110 nm. The estimated size range and composition of the initial nuclei are consistent with those well known in the atmospheric sciences. Nanodroplets were absent from disks that were stored in a CCN-free environment, and the deposition rate was reduced 10× by air ionizer or conductive cassette.

Flying-Height Adjustment Technologies of Magnetic Head Sliders

Two of many parameters that need to be controlled in designing magnetic recording sliders with the desired flying height are manufacturing tolerances and environmental variations. To reduce the effect of these two parameters, we have developed an adjustable flying-height slider. This slider carries a piezoelectric microactuator to control the flying height. After simulating the piezoelectric deflection and its effect on the flying characteristics, we designed an air-bearing and fabricated a slider using silicon micro-electromechanical systems processing. Optical measurements showed that the flying height of the slider changed as electric voltage was applied to the microactuator. The observed stroke of 6 nm/15 V is less than the simulated stroke because of contact between the slider and the disk, but it is still large enough to reduce the effect of the two mentioned parameters.

The effect of slider surface texture on flyability and lubricant migration under near contact conditions

Magnetron sputtering and ion beam sputtering were used to texture the air-bearing surface of magnetic recording sliders. Flying height measurements and Laser-Doppler interferometry were used to compare the ‘flyability’ of textured and untextured sliders. Lubricant redistribution on the disk surface caused by slider/disk interactions was investigated using scanning ellipsometry (Surface Reflectance Analyzer (SRA)). The results show that slider surface texture causes only small changes in the flying height of sliders but reduces slider in-plane and out-of-plane vibrations. Textured sliders were found to cause less lubricant depletion on the disk surface than untextured sliders under ‘near contact’ conditions.

The Effects of Slider Material on the Gasification of Carbon

The influence of alumina and titanium carbide, components of magnetic recording sliders, on the carbon gasification reaction was investigated. Pure alumina and titanium carbide powders were each combined with graphite powder and subjected to thermogravimetric analysis (TGA). The molar ratio ranged from 0 to 20 mol percent; graphite powder was the balance. From the thermogravimetric analysis, the activation energy Ea of the reactions was determined. It was found that the activation energy for carbon gasification reduced slightly for increasing alumina mole percentage. Titanium carbide additions markedly increased the activation energy. This increase indicates a competitive oxidation reaction that forms titanium oxide, as confirmed by X-ray diffraction (XRD). As a result of these observations, titanium oxide was also mixed with graphite powders and analyzed by TGA. Titanium oxide has an activation energy behavior that becomes more complex with increasing mole percentage: the activation energy first increases and then decreases. These data are presented and the oxidation reaction is proposed.

Laser gram load adjust for improved disk drive performance

A new manufacturing technology that enables tight distribution of magnetic recording slider flying heights and lower slider disk spacings is described. The technique uses high intensity laser radiation to increase or decrease the suspension preload on the slider to change the flying height. The technique can he employed for tightening gram load or flying height distributions, contact avoidance or to adjust the magnetic recording capabilities of the disk drive.

Wear and hardness of carbon overcoats on magnetic recording sliders

Wear of diamond-like carbon (DLC) overcoats on magnetic recording sliders during contact start stop (CSS) testing is investigated by monitoring changes in the depths of ion-milled “trenches” on the air bearing surface. In addition, nano-indentation, scratch tests, and Raman spectroscopy were used to characterize the DLC films. The correlation between hardness and scratch resistance of DLC films on Si and Al 20 3–TiC coupons as well as hardness and wear resistance of DLC overcoats on sliders during CSS testing is studied. DLC films that exhibit higher durability in scratch tests are found to also exhibit higher durability in CSS tests.

Silicon carbide—;a potential material for magnetic recording sliders

The feasibility of using silicon carbide as a magnetic recording slider material is investigated using stiction tests with different dwell times, contact start-stop (CSS) tests and drag tests at different temperatures and humidities. The stiction and frictional properties of silicon carbide sliders are compared with standard Al2O3-TiC sliders and it is concluded that their tribological behaviour is superior to that of conventional Al2O3-TiC sliders. The results of this study show that silicon carbide is a promising material for magnetic recording sliders.

Measurement of linear nanometric distances between smooth plane parallel bodies by scattered total internal reflection

Measurement of linear nanometric distances between perfectly smooth plane parallel surfaces by scattering evanescent waves of internally reflected light is shown to be possible if one of the two surfaces is optically disseminative, that is, it either possesses a heterogeneous index of refraction or it is capable of absorbing and re-emitting radiation. Good agreement was obtained between the nominal 100 nm fly height of a magnetic recording slider and the 92 nm fly height measured by scattered total internal reflection. This method is simpler and more informative than interferometry or methods that employ the internally reflected beam.

A new wear measurement technique for pseudo-contact magnetic recording heads

Pseudo-Contact magnetic recording sliders remain in contact with the disk even at operating speeds. The continuous contact can cause wear of the interface that might eventually lead to failure of the drive. In order to evaluate the long term reliability, precise measurements of the slider wear are necessary. In this paper, a new method of measuring the depth and location of wear on the slider is described. Fiduciary marks are created on the slider air-bearing surface using a focused ion beam (FIB). These FIB marks are characterized using an AFM before and after a wear test. The technique allows measurement of wear depths within an accuracy of /spl plusmn/1 nm. Some additional techniques for detecting slider wear are described.

Slider Overcoats for Enhanced Interface Durability in Magnetic Recording Applications

The effects on tribological performance of air bearing surface overcoats on magnetic recording sliders are presented. Both component level and disk drive level testing indicate that significant performance enhancements are afforded by the overcoat, and that both stiction/friction and wear of the head/disk interface are reduced, thus increasing interface durability. The degradation in electrical performance of the heads due to the presence of the overcoat is shown to be consistent with that predicted by the Wallace equation. In addition, it is shown that the performance enhancements of the overcoat are achieved only in the presence of lubricant on the disk surface, suggesting that the overcoat lubricant interaction may be more benign than the interaction of the lubricant with the slider material.

Accelerated Natural Convergence for Pivoted Slider Bearings

A solution technique is discussed which accelerates the convergence of the pivoted slider bearing problem. The technique is based on a fully populated, three-degrees-of-freedom stiffness matrix for the hydrodynamic lubricating film. This matrix is developed using a unique perturbation method which, when used in conjunction with a finite element formulation of the Reynolds equation, yields the bearing stiffnesses in a computationally efficient manner. The resulting natural convergence of this hydrodynamic stiffness approach is examined for a typical rigid disk magnetic recording slider. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994

Mechanism for formation of whiskers on a flying magnetic recording slider

When large amounts of contaminant particles exist in magnetic hard disk drives, whiskers can form at the trailing end of the air bearing of the sliders. Through whisker formation, small particles can accumulate to form a mass comparable to the slider dimensions. Redeposition of these whiskers on the tapers of the slider can lead to a loss of air bearing and head crash. We present a systematic study of the whisker formation mechanism. By injecting fluorescent, spherical polystyrene-latex particles we find that virtually all particles in whiskers are deformed from the original spherical shape. This deformation indicates that particles must pass through the interface before they are collected in the whiskers. Whiskers grow at the tip and not at the base, and form an extension of the air bearing surface. Presence of liquid lubricant on the disk is necessary to form whiskers. The viscosity of the lubricant significantly affects whisker morphology and growth rate. The lower the viscosity, the faster the whisker growth, the shorter the life of the whisker, and the longer and thinner the whisker.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thin film thermocouple sensors for measurement of contact temperatures during slider asperity interaction on magnetic recording disks

Thin-film thermocouple sensors have been fabricated on a magnetic recording slider. Both the sensors and the reference junctions are located on the air bearing surface of the slider. The effective size of the junctions is 4 mu m, and response time is faster than 0.5 mu s. The sensitivity of these thermocouples is measured to be 7 mu V/ degrees C. The thermocouple signals obtained at the slider asperity contacts show a temperature rise of 1-5 degrees C. Incorporating the sensor dimensions and assuming asperities of 0.5 mu m width, the actual temperatures are estimated to be in the range of 90-450 degrees C.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The dynamics of slider bearings during contacts between slider and disk

The dynamics of a “mini-Winchester” magnetic recording slider are studied during contacts with a hard, rotating memory disk using numerical simulation. An on-line solution of the Reynolds equation is used to calculate the air-film pressure, and a “coefficient-of-restitution” model is used to describe intermittent slider/disk contacts. Studies are made to identify system configurations which reduce the possibility of a “head crash” during contact start/stop.