Search

Disk drive spindle motors require accurate speed control and highly efficient drive controllers. Small-volume and high-efficiency converters are of particular interest for portable data storage applications. Quasi-resonant voltage controllers are described in this paper and the experimental results are presented. In contrast to the conventional pulsewidth-modulated voltage controller, this technique reduces the switching loss and enables the controller to operate at very high frequencies. Three types of resonant converters are built and tested for the application. A comparison of performance in terms of losses and voltage regulation is given. Index Terms--Disk drives, reverse rotation, spindle motor, starting scheme, voltage controller.

Here we demonstrate a new approach to bring the disk drive recording head close to the disk media, while achieving tight control of the final head-media separation. The slider in this approach has a miniature Wear-In-Pad (WIP) at its trailing edge, encapsulating the read/write elements. As the slider flies over the disk, the slider overcoat and head recession are quickly worn off, resulting in the bottom of read and write elements clearing the disk roughness by only a few nanometers. We show that the Wear-In-Pad is a viable way to achieve the sub 7 nm head-media separations believed to he necessary for Tb/[in.sup.2] recording. Index Terms--Disk drive tribology, head-disk interface, magnetic spacing, wear.

This article introduces the results of our recent study on the design conditions for a contact and near-contact slider and friction-induced bouncing vibrations in a near-contact regime, based on computer simulations using a simple dynamical model of slider, air-bearing, and disk systems. Basic design conditions for contact sliding are discussed. The contact force and attractive force in asperity contact with a lubricant layer and bulk deformation are calculated numerically. Flying height hysteresis and bouncing vibration of a flying slider that are experimentally observed in nanometer spacing can be obtained by the simulation. Index Terms--Bouncing vibration, contact slider, head-disk interface, near-contact slider.

A new read-channel arrangement for use with d = 1 codes equalizes the input to extended partial response IV (EPR4) for clock recovery, and follows this with a new realization of a fixed delay tree search with decision feedback detector with search depth of two. The detector and a discrete-time phase detector for clock recovery share a five-tap finite-impulse response forward equalizer. Clock recovery from EPR4 is fast, while forward and feedback equalizers need no adaptation of tap weights. The read channel, originally developed for a rate-4/5 X{101} code, is extended to the more efficient rate-6/7 maximum-transition-run (MTR) codes. The detector consists of a conventional decision feedback equalizer, assisted by an error-correction circuit to sense and eliminate the major error events, thus performing as well as tree search with depth of two. With MTR code, the read channel outperforms EPR4 with Viterbi detection by 1 dB. Index Terms--Analog delay line, EPR4, FDTS, fixed delay tree search, MDFE, MTR, partial response, phase detector, timing recovery, Viterbi detection.

Electrostatic force has been proposed for use in fly height reduction and control. The dominant failure mode is electrical discharge at the head-disk interface (HDI) due to field emission. Ballast resistor films have been used for limiting field emission. We applied this idea to the HDI by depositing a thick coating of diamond-like carbon (DLC) on the slider. A typical slider has 25 A of DLC and exhibits breakdown voltage of less than 3 V on product media. When the coating thickness was increased to 430 A, it was sufficient to prevent discharge up to 6 V and allowed approximately 33% clearance reduction without crashing or discharging. The result is in good agreement with fly height modeling, which takes into account the head-disk electrostatic force. Index Terms--Electrostatic, magnetic disk, magnetic head.

As flying height is reduced to less than 10 nm, media morphology, overcoat, and lubricant start to have a significant effect in conditioning the head in the early stage of flying. Typical thermal pole tip protrusion (PTP) in the head writing process will further reduce the head-disk clearance and enhance the media burnishing effect on the trailing edge of the flying head. However, excessive burnishing could further damage the head. A properly designed media surface can burnish the head protrusion to maintain head-disk clearance. To observe the burnishing effects of the media surface, heads with a specially designed silder to increase head-disk interference during flying are used with an in-situ acoustic emission monitoring scheme to study the rate of head protrusion adjustment during proximity flying. Various surface textures, overcoat properties, and lubricant thickness are used to measure the media's burnishing power. It is found that surface microscopic features, especially in the circumferential direction, contribute significantly to the reduction of the media's burnishing power. A semi-analytical wear model and simulation are established to explain the texture effects. The overcoat hardness and lubricant coverage effects are also noted in the wear model and verified by experimental observation. Index Terms--Circumferential roughness, lubricant, pole tip protrusion, wear.

As slider-to-disk spacing becomes smaller than 10 nm, electrostatic and intermolecular forces become increasingly important. Even if the slider and disk are both grounded, a potential difference can exist between them due to the contact potential, which, as we show here, can generate an electrostatic force greater than the van der Waals force. We have developed a method for measuring the contact potential between the slider and disk by monitoring the induced slider motion with a Laser-Doppler-Vibrometer (LDV) and lock-in amplifier while applying ac and dc bias voltages. We find that the first harmonic of the ac driving frequency is minimized when the dc bias voltage cancels the contact potential. We have preformed air bearing modeling of the slider-disk interfaces that also incorporates electrostatic forces. From simulation, we find that the flying height is reduced and the pitch angle increased as the potential difference between the slider and disk is increased. Index Terms--Contact potential, electrostatic, flying height, head disk interface.

Write-induced pole-tip-protrusion (WPTP) and its effect on head-disk interface (HDI) clearance are studied. Drives are placed in a vacuum chamber and the contact altitude is used in this study together with triple harmonic method. It is found that write-induced PTP is a function of the write-signal frequency and the write duration of the head. The magnitude of the WPTP is on the order of nanometers. For a state-of-the-art HDI design with nominal flying height around 10 nm, WPTP can reduce the HDI clearance dramatically. It can cause write modulation and altitude failure. In order to improve the HDI reliability, WPTP mast be taken into account. Index Terms--Altitude sensitivity, head-disk interface clearance, pole-tip-protrusion, triple harmonic method.

We have successfully designed, fabricated, and tested contact recording sliders where most of the suspension load is supported by an air-bearing surface with only a small contact force ( Index Terms--Contact recording, disk drives, head-disk interface.

A magnetic head was thermally analyzed. A high-resolution measurement of the temperature distribution on an air-bearing surface (ABS) both during when a slider is flying and when it is not revealed a 'butterfly'-shaped temperature distribution around the head elements. The distribution is important to accurately understand the head thermal protrusion and to design the head structure. The maximum temperature increase during when the slider was flying was as low as one fourth of that when it was not flying at the same applied write power. The temperature distribution across the head was very narrow when the slider was flying. The temperature increase at the slider body was similar to the flexure when the slider was not flying. Moreover, the temperature increase rate was about 1.46[degrees]C/mW with an applied read power, and it was not large enough to interference the read performance and reliability during normal read operation. Index Terms--Head disk interface, magnetic head, slider, thermal protrusion.

This paper presents experimental investigations of the lubricant ripple formation when the slider flies on the track. We quantified the impact of ripple amplitude on slider flying height modulation (FHM). Comparisons were made between experimental observations and a previous modeling study where rippling was shown to be caused by slider-induced air shear modulation. We confirmed our model predictions and demonstrated conditions under which ripple formation is enhanced or reduced. Index Terms--Laser Doppler Vibrometer (LDV), lubricant ripples, slider dynamics, washboard effect.

In drive testing, pseudorandom data is very often used to avoid biasing results to a particular pattern, e.g., constant frequency. Using the readback signal to measure flying height modulation (FHM) is the most convenient method, but available methods need a special data pattern. In this paper, we present a method that can be used to measure FHM from a pseudurandom readback signal. The method was applied to measure the FHM due to slider-lubricant impact during read. The obtained FHM is a half-sinusoidal-like pulse with about 40 nm amplitude and 4 [micro]s width that is very similar to results measured on spin-stand tests by using a laser Doppler vibrometer (LDV). Index Terms--Flying height modulation measurement, lubricant and slider interaction, magnetic readback signal, magnetic recording drive.

Island-type texture with a height of 4.5 nm was fabricated on pico-sliders with a nominal flying height of 7 nm. The dynamics of the textured and untextured sliders were investigated using laser Doppler vibrometry during contact start/stop. The results showed that the amplitudes of both out-of-plane and in-plane vibrations were reduced as a consequence of the texture on the slider surfaces. Index Terms--Contact start/stop (CSS), slider dynamics, textured slider.

An optimal design technique of both the actuator dynamics and the servo controller is presented. The actuator dynamics are characterized by the time delay created by the unstables zeros of the actuator transfer function. The achievable bandwidth is a simple function of the time delay and the sampling frequency. The feedback controller, including the notch filter, is designed simultaneously. The performance with dynamics variations can also be evaluated by the time delay. It is shown that the variations of the high-frequency modes play an important role in the bandwidth improvement of the dual-stage system. Index Terms--Bode Theorem, dual-stage actuator, H-infinity, pole/zero cancellation, sensitivity function, unstable zeros.

Lubricant characteristics of dual lubricant layers, which consist of a first-lubricant bonded layer and second-lubricant mobile layer, were studied. The interface durability is evaluated by a pin-on-disk test. The spin-migration characteristic is evaluated based on the change in thickness of layers after disk spinning. The mobility is estimated from spreading profiles from the lubricant step. Dual lubricant layers, which consists of Z-dol as a mobile layer and Z-tetraol or AM as a bonded layer, shows high mobility, high interface durability, and low spin-migration performance. It is considered that these characteristics can be attributed to higher interaction between the bonded lubricant and the mobile lubricant due to strong polar end groups of the bonded lubricant. Index Terms--Diffusion coefficient, hard-disk drive (HDD), lubricant layer, mobility, optical surface analyzer (OSA), spin migration, wear durability.

The frictional properties of Zdol on a magnetic disk surface have been studied. The friction experiments indicated that the friction coefficient decreases with an increase in the thickness of the mobile and bonded lube layers. The mobile layer allows the replenishment of the lubricant molecule. On the other hand, the bonded lube layer avoids any solid-solid contact between the glass and diamon-like carbon (DLC) AU: DEFN FOR 'DLC' OK?. For an ultrathin film as thin as a monolayer or less, the bonded ratio is very important for controlling the friction properties. There is an optimum combination of film thickness of the mobile and bonded lube layers to provide the minimum friction. Index Terms--Bonded lube, friction, friction coefficient, hard disk drive (HDD), mobile lube, perfluoropolyether (PFPE), ultra-thin films.

This paper presents a study on the calibration of sub-10-nm fly height of slider by detecting slider response to laser bump with known height. The PZT sensor signal was applied to identify the slider air bearing resonance and slider body resonance. By comparing the signals from these two sources, improper measurement results due to the uncertainty of slider-bump response process can be eliminated. The time--frequency analysis of laser Doppler vibrometer measured slider bump responses also correlates the results. Index Terms--Bump response, calibration, flying height, glide.

Spindle motors with hybrid ceramic bearings are well suited for high revolution per minute disk drives due to their high rigidity and low acoustic emission. The rolling elements are nonconductive [Si.sub.3][N.sub.4] precision ground balls. They allow buildup of a voltage between the rotor and stator of the motor. This voltage also appears across the head-disk interface. If large enough, this voltage will damage the drive. This paper analyzes the charge pump mechanism (hearings) responsible for the voltage build up. It also examines the charge bleed-off path (ferro-fluid seal), which holds down the maximum voltage that can appear. An electrical model is given for the ferro-fluid seal that is dynamically as well as statically correct. This model is verified by comparing it to measured static and dynamic current-voltage curves and to the voltage step response of the seal. By a proper design of the ferro-fluid seal, its conductivity can be held low enough to limit the motor voltages to safe levels. This makes the use of these hybrid ceramic bearings in today's hard disk drives attractive. Index Terms--Ceramic ball bearings, electrical over-stress, electrostatic damage, hard disk drives, magnetic recording, spindle motors.

A complete model of an operational hard disk drive (HDD) subject to shock loads is developed to investigate the response of the head/media interface. The model is a coupled solution of the structural components and the hydrodynamic lubrication between the magnetic recording head and the disk surface. The structural model is a finite element simulation of the HDD using commercially available software. The hydrodynamic lubrication, or air bearing, model is a numerical solution of the Reynolds equation used to solve for pressure and spacing between the head and the disk. Combining the two models gives a complete solution of the head/media interface for an operational HDD. Index Terms--Hard disk drive (HDD), head-disk interface, Reynolds equation, shock response.

This paper presents a nonlinear dynamic analysis of the bead-disk interface for sub- 5 nm flying air bearing sliders. It is found that by including intermolecular forces between the slider and disk, the dynamic stability of the slider is dramatically compromised, it is shown by a bifurcation diagram that a slider can easily be forced into unstable motions. It is also shown that the experimentally observed flying-height hysteresis, intermittent instability, and 'snapping' from stable to unstable proximity can be explained by intermolecular forces. Index Terms--Air bearing, hard disk drive, intermolecular force, nonlinear systems, stability.

A novel focused-ion-beam (FIB) head trimming technique is described. As compared to the conventional approach of a symmetric trim, an asymmetric process, whereby only one side of a write pole is FIB milled to achieve the target width, is demonstrated to be robust and advantageous. We use this technique for both longitudinal and perpendicular HGA-level head trimming, demonstrating excellent recording performance out to areal densities of more than 100 Gb/[in.sup.2]. Index Terms--Disk drives, focused ion beam, magnetic heads, magnetic recording, system analysis and design.

Shakers used in modern head gimbal assembly (HGA) resonance testers need to be linear, repeatable, and with minimal out-of-plane movements up to several tens of kilohertz. The authors investigate the suitability of shear-mode piezo actuators for the task. These compact devices also double up as sensors for HGA dynamics testing. Index Terms--Hard disk drive (HDD), head gimbal assembly (HGA), piezo actuator, resonance frequencies, suspension.

A fundamental study on the temperature and slider displacement of a chip-on-suspension (COS) was performed. The results show that the temperature rise in the IC chip is almost proportional to the heating power and that the slider displacement in the tracking direction is almost proportional to the heating power applied to the chip. It takes several seconds for the temperature rise of the chip to saturate and the response of the slider displacement is less rapid than the temperature rise of the chip. The vibrational characteristics of the slider are not affected by the temperature rise. Index Terms--Hard disk drives, head suspension, heating power, R/W-IC, temperature.

This paper will present some aspects of soft magnetic composite (SMC) material application in electrical machines. The stator cores of the prototype axial field permanent magnet disk motor (PMDM), which is under consideration, are made of wound strip cores. Two types of PMDM stators are analyzed: laminated and SMC material stators. The comparison analysis is based on the production complexity and the magnetic properties and calculated parameters. The magnetic parameters under consideration are the flux densities in various sections of the magnetic circuit and the iron losses in these sections. The values for both types of stators are calculated using finite-element-method (FEM) analysis. The production complexity and the values of the magnetic parameters are in favor of the SMC material stators in relation to the laminated stators. Index Terms--FEM analysis, permanent magnet disk motor, soft magnetic composite material.