Search

Thermal flying-height control (TFC) technology has been used in the last few years in hard disk drives (HDDs) to achieve a lower flying height for higher storage areal density. In this paper a slider with dual thermal protrusions, one produced by the laser used to heat the disk in HAMR and the other one used for TFC, is studied. The flying height modulations (FHM) due to disk waviness and external disturbances are compared for the dual protrusions, single protrusion and no protrusion sliders. The protrusions provide additional force and torque excitation to the slider. The protrusions can be viewed as a passive feedback loop to compensate the disturbance. The gain of the feedback loop depends on the stiffness of the protrusions, which is determined by the protrusions' heights and positions. Thus the complicated air bearing slider system with protrusions is simplified by casting the protrusion perturbation as a feedback loop and this simplified model helps to speed up the optimization of the TFC protrusion height and position. The numerical simulation results show that FHM of the dual protrusion slider is reduced significantly when the TFC protrusion height and location are optimized. External disturbance induced FHM can be suppressed as well. This scheme for dual protrusion optimization and analysis described in the work can benefit HAMR head design because the optimized dual protrusion provides a more consistent flying height and a greater ability to compensate external disturbances.

Reducing the spacing between the magnetic head and the magnetic disk media is of crucial importance in enabling further increased recording density of the magnetic disk drives. The head-disk interface technology explored up to now can be classified into the following two categories: in-fly recording and in-contact recording. Pushing the areal density towards 10 Tb/in2 requires the magnetic spacing down to 3 nm level, which it is difficult for the conventional in-fly or in-contact schemes to achieve so small a magnetic spacing. This paper reports the authors' exploration of lube-surfing recording mechanism-majority of slider surface flying over the disk surface and only the tiny protruded read/write head area surfing on the lubricant surface of the disk. The key factors for achieving such a mechanism include technology to sense slider-lubricant contact, nano-actuator and active contact depth control, advanced slider air-bearing design to make the slider well follow up the disk surface waviness and secure the contact depth, super-smooth slider and disk surfaces, and so on. Results presented in this work suggest that the read head can be a promising transducer for slider-lubricant contact detection. Results also suggest that contact depth control is important for this scheme and it is possible to have stable slider surfing on the lubricant, if the contact depth is within a certain range.

As the head-disk spacing is reduced in order to achieve higher areal density, dynamic stability of the slider is compromised by a variety of proximity interactions. One of the key factors is the disk topography, which provides dynamic excitation to the low-flying sliders and strongly influences the dynamics and stability of the slider. Several experimental and numerical studies have been done on the fly height modulation caused by the disk topography along the track (circumferential) direction. In this paper, we investigate the effect of the disk topography in the circumferential as well as the radial directions and use a new method to measure the 2-D (true) disk topography for disks with three different kinds of roughness and waviness features. We used a dynamic air-bearing simulator to simulate the slider dynamics over the measured topographies. Simulations used 1-D topographies along the track direction as well as the actual 2-D topographies. Comparison of the slider dynamics over the different 1-D disk topographies indicates a strong dependence on the circumferential roughness and waviness features. Further, the comparison of slider dynamics and frequency content over 1-D and the 2-D disk topographies indicates that the radial features, which have not been studied intensively until now, are also very important in determining the actual slider dynamics, as they dictate the variation of the adjacent tracks in the circumferential direction. The simulations with 2-D disk topography are more realistic than the 1-D simulations. Further, the effect of the radial features can be reduced through effective air-bearing system design.

To sustain an ultra-low and stable flying height (FH) is crucial for achieving high areal densities in magnetic recording. Recently, a new method called thermal flying height control (TFC) has been introduced to the latest generations of disk drives for precise control of slider-disk spacing. It is noted that the TFC technique is able to eliminate almost all static FH loss, but is unable to circumvent dynamic FH loss such as flying height modulation (FHM) due to disk waviness. It is therefore advantageous to have both high thermal actuation efficiency and low FHM due to disk waviness characteristics in a TFC slider design. This paper investigates the effects of air bearings on the thermal actuation efficiency and the capability in following disk waviness of the TFC sliders. Air bearing surface (ABS) design strategies for TFC slider are proposed and investigated with simulations. The results show that both excellent thermal actuation efficiency and strong capability in following disk waviness can be achieved through proper arrangements of air bearing pressure distribution on the ABS of TFC sliders.

In order to achieve an areal density of 1 Tb/in2 and beyond, not only the mechanical spacing between the slider and the disk but also the track misregistration (TMR) and the fly height modulation (FHM) should be reduced below current levels. But at reduced mechanical spacing there will be elevated excitation due to slider-disk contacts resulting in increased slider vibrations and head-disk interface (HDI) failures. Thus, there is a need to study the effect of slider-disk topography on the slider dynamics and stability at a higher level of complexity. In this paper, we do so by dividing the slider-disk surface features into three regimes based on the amplitude and the wavelength range of the features. Further, we have also proposed several ways of achieving an optimal slider-disk topography that can help reduce the slider vibrations and increase the stability of the HDI.

This paper presents a simulation study on the coupling effects of air bearing dynamics and suspension vibrations due to slider-disk contact or disk waviness. A simulator is developed to include the interactions between the air bearing, the slider-suspension assembly and slider-disk contact by considering the suspension, slider and air bearing as a whole system. From the simulation, the dynamic motion of read/write head in both flying-height (FH) and off-track directions, even on-track direction, can be obtained. It is helpful to characterize dynamics of head positioning and understand the interactions between the head disk interface (HDI) components. In addition, the effects of contact intensity, surface roughness, skew, and disk waviness on the read/write head positioning in both FH and off-track directions are investigated. The mechanisms of these factors' effects on the dynamic stability of read/write head positioning in both FH and off-track directions are also discussed in the paper.

Molecular dynamics simulation would be well suited to predict the physics of molecularly-thick lubricants on magnetic disk surfaces. The difficulty in defining suitable interatomic potentials, as well as the requirement for large computing power, makes this type of study difficult. Treating the lubricant film in the framework of fluid dynamics has proven a much better way to model its behavior. This paper describes a full numerical model of lubricant moguls and ripples formation using finite difference analysis. We demonstrate that both moguls and ripples result from slider-induced air shear. Ripples tend to form at higher disk speed and narrower slider width, whereas moguls are seen at lower speed and larger slider width. Both moguls and ripples are enhanced for thicker lubricants, higher waviness, and lower flying heights. Ripple instabilities that were predicted earlier using a stability analysis are also quantitatively confirmed using this numerical model.

As technology moves toward 600/spl sim/1000 Gb/in/sup 2/, the mechanical spacing between head-slider and disk media must be further reduced to a level of 3/spl sim/4 nm. Such a reduction of the head-disk spacing will be accompanied by a lot new challenges. One severe challenge is how to reduce the flying height modulation caused by the surface waviness with an amplitude even as small as 0.4/spl sim/2 nm. Shifting slider size from its current pico form-factor to femto form-factor seems to be a promising approach for the reduction of such flying height modulation. However, discussions on the femto slider are still limited to theoretical analysis and computer modeling/simulation until now. This paper reports authors' efforts in the design and fabrication of the femto sliders plus the comparative study of the dynamic performance between the femto and the pico sliders. Results indicate that the femto sliders are of smaller flying height modulation, compared with the pico sliders, if both the femto and the pico sliders are of similar air-bearing surface layout. Investigations also extend to the study of flying performance sensitivity of the femto slider to its possible parameter offsets caused by the manufacturing and integration processes.

The effect of morphology on flying height modulation (FHM) of a sub-10 nm flying air bearing slider was studied for three different disks by experiment and simulation. The experimental measurement methods are discussed and a new single beam laser Doppler vibrometer (LDV) measurement method, which yielded the highest resolution with a 2 /spl mu/m beam spot size, was introduced. Analysis was performed in three different frequency bandwidths-a geometric FHM from 10 to 100 kHz, a dynamically excited FHM from 100 to 500 kHz and the third being negligible compared to the other two bands, above 500 kHz. Transfer function analysis was carried out to investigate the FHM in the lowest frequency band. FHM in the first band was shown to be caused primarily by a phase shift between the sliders' response and the disks' morphology and secondarily by decreasing slider motion with decreasing morphology wavelength, which correlated well with previous work. For two of the disks investigated, the FHM due to the disks' morphology showed air bearing excitation that resulted in an intolerable level of FHM. However, for one of the disks studied, the FHM was as low as the disk morphology for wavelengths of 2 /spl mu/m and less, which was within tolerable limits. It is concluded that when designing a disk for low FHM, it is not sufficient to characterize the quality of a disk by a single number such as roughness or waviness. Proper design and optimization of both the disk and air bearing slider results in FHM that is lower than the disks' morphology.

A Laser Doppler Vibrometer (LDV) was used to measure flying height modulation (FHM) of sliders with sub-10 nm flying-heights (FH). It was found that a precise trigger, averaging, and suitable filtering are the key to successfully measuring FHM by LDV. Also, more accurate results can be obtained from the LDV velocity output as opposed to the displacement output. The FHM's of a 7-nm FH slider flying over three different disks were measured. One of the disks had higher roughness and waviness values (disk A) than the other two (disks E and C). Disks B and C had the same super-smooth substrate but different lubricants and carbon overcoats. It was observed that this slider flew steadily over disk A and disk C, but it could not fly over disk B. The repeatable part of the FHM of the slider flying over disk A and disk C was about 0.45 nm and 0.37 nm (RMS), respectively, in the frequency range between 20 kHz and 300 kHz. Also, for disk C, the dependence of FHM on RPM was investigated, and it was found that at the design condition (7200 RPM) the FHM (peak-to-peak) was minimized for this particular slider/disk system. However, we do need to consider the ratio of FHM to FH. Increasing RPM increases FHM due to the disk surface topography and decreasing air-bearing modal frequencies, but the ratio of FHM to FH stays relatively constant. Decreasing RPM increases FHM due to intermittent contacts and excitation of the air-bearing.

The stringent magnetic spacing requirement of future high-density magnetic disk drives requires new head disk interface scheme. One possible approach is the lube-surfing scheme-where majority of the slider body is flying while the reader/writer (R/W) element is thermally protruded to contact and penetrate the disk lubricant. This scheme, however, has many challenges to overcome to be feasible. One of these challenges is a slider with improved disk waviness-following capability especially for waviness with wavelength less than half the slider length. This paper explores air bearing design strategies to improve the waviness-following performance of a Femto slider. We propose a ?W-shaped? trailing pad slider and investigated the impact of pad layout, etching depth and trailing pad size to the disk waviness-following performance. We have also incorporated a trenched trailing pad structure to reduce air bearing pressure over the R/W element so as to minimize the loss in air bearing pressure during lube contact and to improve the actuation efficiency.

To investigate the role of disk surface waviness on the baseline instability (BLI) of the read-back signals from MR head, we measured the average height of surface waviness with a spatial wavelength of 0.4 to 5.0 mm using a white light interferometer instrument. We used an MR head over four sets of media to measure the baseline instability at OD and at MD. The results show that the baseline instability becomes worse as the surface waviness increases and that the baseline instability is linearly proportional to the surface waviness. The result further shows that the effect of bias current on the baseline instability is amplified on the disk with worse surface waviness. The surface waviness, therefore, can not be overlooked when evaluating the media for a high-performance hard disk drive.

In this study, metal evaporated (ME) tapes with and without diamondlike carbon (DLC) coating were tested for friction, wear, and magnetic performance. Performance of flat DLC ME tape is compared with two non-DEC ME tapes (one being flat and the other with waviness). By using a commercial VCR as a magnetometer and the Wallace equation, changes in the rms head output level were correlated to changes in head-to-tape spacing as tape wear occurred during play/rewind cycling tests. Interface stability and recording performance at a 0.6 /spl mu/m recording wavelength were measured to bit level resolution using a dropout counter. Some pause mode and environmental testing were also performed. Tribological performance and magnetic reliability of ME tape was affected by waviness of the ME tape surface as well as by the presence of a DLC coating. Waviness of one kind of non-DEC ME tape caused poor magnetic performance and localized wear of the tape surface, but loose wear debris could escape contact areas by settling into valleys on the tape surface. In the case of flat non-DLC ME tape, loose wear debris could not escape from contact areas leading to early failure. DLC coating prevented catastrophic abrasive wear and reduction in head-to-tape spacing or intimate contact during cycling tests, but could not significantly improve the durability of ME tape. DLC coating reduces asperity compliance as compared to non-DEC tapes. All ME tapes failed by lateral crack formation (cracks often propagated through coating defects) driven by longitudinal tape tension or flexing of the tape in the transport. In pause mode, DLC coating improved magnetic reliability and tribological performance by preventing the heads from contacting the metallic magnetic layer. Based on this study, a flat tape must be used for magnetic considerations and DLC coating is needed to prevent abrasive wear and intimate contact. Reducing the number of coating defects and optimization of the toughness of magnetic and DLC coatings are key parameters for future ME tapes. At fixed temperature, high relative humidity leads to severe tape instability and high dropout frequency. At high specific humidities, lower temperature leads to severe tape instability and high dropout frequency. Bearing ratio curves for the tapes determine the onset of high friction and tape instability at high humidities.

As the slider's flying height (FH) continues to be reduced in hard disk drives, the flying height modulation (FHM) due to disk morphology and interface instability caused by highly nonlinear attractive forces becomes significant. Based on the concept that the FH of a portion of the slider that carries the read/write element can be adjusted by a piezoelectric actuator located between the slider and suspension and that the FH can be measured by use of the magnetic readback signal, a new 3-degree of freedom analytic model and an observer-based nonlinear compensator are designed to achieve ultralow FH with minimum modulation under short range attractive forces. Numerical simulations show that the FHM due to disk waviness is effectively controlled and reduced.

In the optical drive system, adopting the optical-flying-type head (OFH) flying on a removable plastic disk, the flying stability of the small OFH should be carefully considered to ensure the reliability for the first surface recording. This study gives two simulation results on the flying stability of the OFH: one is the dependence of the flying height and pitch angle variations on the wavelength and amplitude of disk waviness, and the other is the flying stability of the slider and suspension system during the dynamic load/unload process.

This paper describes theoretical analysis of radial vibration of a rigid shaft supported by a ball bearing with form errors. Assuming a small sinusoidal waviness of n-th order on the inner race, outer race or rotating balls, the displacement of the shaft center while rotating is numerically calculated. The frequency and amplitude of the shaft vibration are analyzed by numerical FFT. From consideration of the generating mechanism of the shaft vibration, it is found that the outer race waviness of the order n=jZ+1 (j: integer, Z: total ball number) generates a backward exciting force and vibration with frequency of jZf/sub c/ (f/sub c/: cage speed), while that of n=jZ-1 generates forward ones of the same frequency. The inner race waviness of n=jZ+1 generates a forward exciting force and vibration with frequency of jZ(f/sub r/-f/sub c/)+f/sub r/ (f/sub r/: inner race speed), while that of n=jZ-1 generates backward ones with frequency of jZ(f/sub r/-f/sub c/)-f/sub r/. It is also found that small amplitude vibrations with frequencies jZfc and jZ(f/sub r/-f/sub c/)/spl plusmn/f/sub r/ can be generated by the waviness of the order number different from n=jZ/spl plusmn/1, when the ball number Z is a prime number, e.g. 7. A good qualitative agreement between calculated and experimental Campbell diagrams for shaft vibration is obtained.

Flying height modulation (FHM), caused by disk waviness, is one of the new concerns for 3/spl sim/5 nm spaced extremely high density recording head-disk systems. This paper presents authors' efforts on air-bearing surface (ABS) design of subambient femto sliders so as to further reduce such FHM. Results suggest that slider designs with no side pad or with side pad away from the trailing edge of the slider body will have less amount of FHM. Also sliders with reduced central pad length along the slider direction will be of reduced amount of FHM. A model is proposed to explain the above mentioned observations. The model can also be used as a design guideline in terms of reducing flying height modulation caused by disk waviness.

The effect of substrate micro-waviness and laser bump size were identified to be dominant on the tribology performance of laser zone texture for ultra-low glide avalanche applications. Smaller laser bumps tend to give a lower minimum allowable bump height with acceptable stiction, thus allowing for a laser texture design with a lower glide avalanche height. Remarkably, it was found that lower substrate micro-waviness can further reduce the minimum allowable bump height and result in an even lower glide avalanche laser texture. A proper design based on smaller laser bumps and lower substrate micro-waviness demonstrated that it is feasible to have a laser zone texture with a glide avalanche below 0.5 /spl mu/" for conventional pico sliders.

A commercial Hi-8 VCR was instrumented to measure the friction force between the rotary heads and tape, rms head output and signal dropouts to sub-/spl mu/s durations. Streaming mode experiments at design tension using metal evaporated (ME) and metal particle (MP) tapes were performed in which the tapes were subjected to repeated play/rewind cycling. Long wavelength waviness of the ME tape surface and a large number of sharper asperities on the MP tape surface affected the magnetic and tribological performance of the tapes. The friction force and head output generally increased, and the dropout frequency (number of dropouts/min) generally decreased as the tapes were worn smooth. Head-to-tape spacing and dropout frequency decreased more for MP tape, as compared to ME tape. On the ME tape surface, damage initiated at high points or bumps, which resulted in weakening of the metal coating at these locations. Cracks initiated at these locations grew (driven by longitudinal tension) laterally across the tape width and connected localized damage areas at tape failure after 840 play/rewind cycles. MP tape performance improved gradually through 1000 play/rewind cycles. Based on this study, ME tape is less durable than MP tape, and reduced waviness of the ME tape surface could further improve ME tape performance.

Numerical simulations of dynamic spacing induced by a measured track topography and asperity contact is presented for the IBM MR-head three rail slider. The factored implicit scheme is modified for use with the shaped rail slider. The results show that the dynamic spacing consists of low frequency components and high frequency components that are due to, respectively, the waviness and the roughness of the track topography. When disk runout is considered and asperity contact is at the outer rail, the response depends on the location of the asperity with respect to the runout. However, when the asperity contact is at the center rail the response is similar at all locations on the runout. >

The effect of head/disc imperfections on gas lubricated slider performance is investigated using a numerical simulation. The imperfections considered are warping and chipping/pimpling of the rails and waviness and asperities on the disk. A predictor-corrector numerical marching scheme is employed to obtain the solutions for the system of governing equations which includes the Reynolds equation and the slider equations of motion. The warp length of the slider seem to affect the trailing edge flying height considerably and is more critical at low frequency waviness of the disk. Trailing edge flying height increases with increasing chip radius and decreases with increasing dimple radius for all disk waviness frequencies.

This paper presents a method for measuring the head slider spacing fluctuation induced by wavy deformation in a disk. The author's first experiment reveals that disk wavy deformation, which is considered to appear in building up a magnetic disk drive, shortens working life time. To supply a reliable disk drive, it is necessary to evaluate disk waviness after building up a disk drive. The simple and practical readback signal modulation (RSM) method was investigated here. The second experiments, including the measurement of the spacing loss effect in recording, reveal that spacing fluctuation, measured by the RSM method, is in good agreement with that estimated theoretically from the disk displacement waveform. It becomes possible to evaluate the head slider spacing fluctuation quantitatively after building up a disk drive.