Nano-texturing of magnetic recording sliders via laser ablation

To increase the storage density of hard disk drives, the flying height of the slider needs to be reduced to <10 nm. This requires super-smooth surfaces of the disk and slider. As the roughness decreases, stiction and adhesion are found to increase substantially leading to failures of the head/disk interface. Texturing the slider surface is a well-known approach to this issue. In this study we investigated laser ablation as a potential process for texturing magnetic recording sliders. It was found that straight laser machining caused unwanted re-deposition of material. These deposits could be significantly reduced by using a chemical etching enhanced laser process.     

Intermolecular force and surface roughness models for air bearing simulations for sub-5 nm flying height sliders

When the spacing between the slider and the disk is less than 5 nm, the intermolecular forces between the two solid surfaces can no longer be assumed to be zero. The model proposed by Wu and Bogy (ASME J Trib 124:562–567, 2002) can be view as a flat slider–disk intermolecular force model. The contact distance between the slider and disk needs to be considered in this model when the slider-disk spacing is in the contact regime. To get more accurate intermolecular force effects on the head disk interface, the slider and disk surface roughness need to be considered, when the flying height is comparable to the surface RMS roughness value or when contact occurs. With the intermolecular force model and asperity model implemented in the CML air bearing program, the effect of intermolecular adhesion stress on the slider at low flying height is analyzed in the static flying simulation. It is found that the intermolecular adhesion stress between the slider and the disk has slight effect on the slider-disk interface for a flying slider.     

Performance analysis of an integrated piezoelectric ZnO sensor for detection of head–disk contact

Integrated capability for detection of head–disk contact is desired for magnetic sliders with near-contact flying height. At the same time, fabrication of added features should be compatible with the existing slider micromachining process which is highly specialized and cost sensitive. Aimed at meeting the two requirements, a novel sensor configuration is explored in the present study. The new sensor configuration consists of a piezoelectric zinc oxide (ZnO) thin-film sensor sandwiched in the magnetic slider on its trailing side. Coupled structural and piezoelectric finite-element analysis for a sensor–slider–suspension assembly was performed to investigate the dynamic sensing performance. Output voltages on the millivolt level were obtained under typical head–disk interactions. The second in-plane bending mode of the slider was found to be the major contributor to the output voltage. Parametric study further showed that a thicker ZnO layer generally generated a larger output, while the thickness of the slider overcoat had only minimal effect. Simulation results from harmonic and transient analyses demonstrated that the piezoelectric thin-film ZnO sensor was sufficiently sensitive for detection of head–disk contact.     

Study of the stiction free magnetic recording head with DLC pad

This paper presents the study of the stiction free magnetic recording head which has diamond-like-carbon (DLC) pad for use with laser zone texture disk and smooth disk. The magnetic recording head with DLC pad is one of the potential solutions to extend contact start stop (CSS) technology for further lower head-disk spacing, since it can decrease stiction and friction between magnetic recording head and magnetic recording disk during CSS. The optimization of air bearing surface (ABS) design for improving take off characteristics, the optimization of DLC pad design for improving tipping stability and the result of CSS reliability test under several environments are shown in this paper. It is found that the occurrence of tipping accelerates the wear of DLC pad, the degradation of the lubricant and the wear of carbon overcoat (COC) protective layer on the disk. Finally it is shown that the magnetic recording head, which has optimized ABS and optimized DLC pad, has small coefficients of stiction less than 2.0 and reliable CSS performance at 15 nm flying height (FH) on the laser zone texture disk having low bump height. Tipping and major wear of DLC pads are not observed under several environmental conditions with this optimized design.     

Effect of thermal pole tip protrusion and disk roughness on slider disk contacts

Ultra-high areal density for hard disk drives requires a stable head disk interface at a flying height lower than 8 nm. At such a low flying height, small flying height variations may cause slider/disk contacts. Slider/disk contacts can also occur when a write-current is applied to the write coil since the flying height between slider and disk can be affected by the thermal expansion of the pole tip. In this paper, we investigate the vibration characteristics of sliders during thermally induced contacts using laser Doppler vibrometry. We perform a parametric study of contact events using disks with different surface roughness and lubricant thicknesses, and analyze the slider motion statistically. For a given write current, we observe that the slider vibrations increase with disk roughness and lubricant thickness.     

Friction control by micro-vibration of a magnetic recording head under micro-load

To reduce the risk of a head crash in a hard disk drive by reducing stiction/friction at the head-disk interface, micro-vibration was applied to reduce such friction. This friction control between a head and a disk was investigated by means of a model head. The present study investigated the effect of micro-vibration on friction under micro-load conditions and the influence of surface roughness on friction reduction by micro-vibration. These investigations show that micro-vibration of the model head is effective to reduce friction when a slider contacts a smooth disk.     

Data storage channel equalization using neural networks

Unlike in many communication channels, the read signals in thin-film magnetic recording channels are corrupted by non-Gaussian, data-dependent noise and nonlinear distortions. In this work we use feedforward neural networks-a multilayer perceptron and its simplified variations-to equalize these signals. We demonstrate that they improve the performance of data recovery schemes in comparison with conventional equalizers. The variations of the MLP equalizer are suitable for the low complexity VLSI implementation required in data storage systems. We also present a novel training criterion designed to reduce the probability of error for the recovered digital data. The results were obtained both from experimental data and from a software recording channel simulator using thin-film disk and magnetoresistive head models.     

Analysis of the parameters of “Magnetic Disk-Magnetic Head” pair for magnetic recording

Consideration was given to calculations of the parameters of transition between two opposite-magnetization domains in a thin-film working layer of the hard magnetic disk with regard for the saw-toothed form of transition. The transition parameters were related to the properties of the magnetic disk working layer and the magnetic head characteristics. For various recording densities, the levels of the playback signal and the resolution coefficient were determined.     

Development of an optical flying head for a next-generation magneto-optical recording system

We have developed an optical flying head (OFH) comprising a thin-film coil and a high numerical aperture lens for magneto-optical (MO) disk drives. Experiments have shown successful writing and reading of MO media. The following describes the design and testing of the OFH.     

Active flying-height control slider using MEMS thermal actuator

Today’s head/disk interface design has a wide flying height distribution due to manufacturing tolerances, environmental variations, and write-induced thermal protrusion. To reduce the magnetic spacing loss caused by these effects, we developed an active head slider with a nano-thermal actuator. The magnetic spacing of these sliders can be controlled in situ during drive operations. After simulating the heat transfer in the slider to obtain the thermal deformation of the air-bearing surface, we fabricated a thermal actuator using thin-film processing. An evaluation done using a read/write tester showed a linear reduction in the magnetic height as electric power was applied to the actuator. The actuator’s stroke was 2.5 nm per 50 mW with a time constant of 1 ms. There was no significant impact on the reliability of the read element.     

Ultraviolet irradiation of lubricant and additives thin films to reduce wear to the magnetic head

This paper examined the effects of using 1 nm thickness lubricant thin film combined with additives and deep ultraviolet (UV) irradiation at 185 nm wavelength on the magnetic hard disk to the wear of the magnetic head during contact. Different types and amount of additives were added into the lubricant thin film either with or without deep UV irradiation. A test involved burnishing the magnetic head on the lubricated magnetic hard disk was conducted. The experiment was conducted in a class 100 cleanroom. Contrary to previous studies, the addition of additives into the lubricant film did not lead to a decrease in the amount of wear to the magnetic head. Without deep UV irradiation, the lubricant film combined with additives causes more wear to the magnetic head. The effects of using different percentages of cyclotriphosphazene based additives in perfluoropolyether lubricant were also discussed in this paper. We conclude that deep UV irradiation needed if additives were added when the total lubricant thin film thickness is at 1 nm or below.

     

A numerical investigation of different touchdown patterns of thermal-flying-height-control sliders

In this study we employ a numerical approach to explore the touchdown patterns of a thermal-flying-height-control (TFC) slider. Depending on the roughness of the head disk interface and thickness of the lubricant layer a TFC slider can experience different stages during touchdown. Three different touchdown patterns are shown. With a rougher interface profile the slider smoothly transfers from a flying stage to a sliding stage. With an intermediate smooth interface profile the slider experiences a flying-bouncing-sliding transition. With the smoothest interface the slider goes through a flying-bouncing-surfing-sliding transition. Different stages are characterized by different slider dynamics and slider-disk contact status. The different touchdown dynamic patterns shown here can result in a significant difference in the easiness of successful touchdown detection. The general approach proposed here may also be applied to investigate the effects of other important head disk interface factors, e.g., air bearing surface design, heater, suspension, etc. on the slider’s touchdown dynamic behaviors.     

A flyability and durability dilemma in hard disk drives

A magnetic hard disk drive lubrication dilemma was demonstrated through the touch down, wearability and burnish rate tests. It was found that attempts to improve durability and flyability through changes in lubricant film thicknesses, the addition of additives, changes in lubricant molecular weight and irradiating lubricant with deep UV rays (185 nm) have been futile with loss in either flyability or durability of magnetic hard disk. Three key types of head disk interface testing methods were introduced and the results from each parameter change were shown. The touch down test was used to check the fly height of the magnetic heads. The wearability test was used to check the wear resistance of the magnetic hard disks when in contact with the magnetic heads and the burnish rate test was employed to determine the amount of wear of the magnetic heads when in contact with magnetic hard disks. These three techniques may be used for the feasibility study for any newly designed lubricant or technique to reduce the spacing between the magnetic head and magnetic disk. We demonstrate the capability of the three techniques to discriminate different process treatments. The experiments were conducted in a class 100 cleanroom.     

Effects of disk surface roughness on static flying characteristics of air bearing slider by using a combined method of Reynolds equation and rough disk surface

Reynolds equation was modified with adding the surface roughness parameters to analyze the effects of disk surface roughness on the static flying characteristic of an air bearing slider. However, the modification demands the complicated mathematical expressions and related knowledge of physics and mathematics. In this paper, a combined method of Reynolds equation without introducing the roughness parameters and rough disk surface is proposed to investigate the effects of disk surface roughness on the static flying characteristics of an air bearing slider, it is different from those models of modified Reynolds equation introducing the disk surface roughness used by many researchers. More importantly, this method avoids the complicated numerical calculation resulted from the mathematical expressions including the Peklenik parameter \(\gamma\) and roughness R_a. By using an Ω air bearing slider, we investigated the effects of disk surface roughness on the static flying characteristics of this slider, the results show that the Peklenik parameter \(\gamma\) and roughness R_a have a significant influence on the pressure distribution, the load carrying capacity and the location of the pressure centre.     

Sidewall morphology of electroformed LIGA parts-implications for friction, adhesion, and wear control

LIGA fabricated parts are finding application in a wide variety of micro-mechanical systems. For these systems to operate reliably, friction between contacting sidewall surfaces must be understood and controlled. The roughness of the as-plated sidewall is an important determinate of friction forces at such contacts. LIGA sidewalls were characterized in order to provide a basis for predicting the friction, adhesion, and wear behavior of LIGA micromachines. A variety of unexpected sidewall morphologies were observed during this investigation. Three morphologies were identified: a fine scale roughness, a linear through thickness feature, and a group of larger high aspect ratio features. Each morphology has been associated with a specific aspect of the LIGA manufacturing process. Potential friction, adhesion, and wear management strategies suggested by these features have been discussed. In addition, the asperity behavior in a LIGA sidewall contact has been predicted based on the finest roughness observed.     

Reduction in total surface area by the develpment of microdroplets during dewetting

To meet the demand of an increasing storage density, the lubricant film for the head disk interface (HDI) needs to be thinner and stronger. In recent years, a new head/disk system, such as the contact type, has been proposed. It is reported that PFPE Zdol coated on a magnetic disk is dewetted and microdroplets are formed due to polar interactions. This makes a flying magnetic head unstable, therefore, the physics and chemistry of the dewetting phenomenon are topics of current interest. We investigated the formation and development of microdroplets using an atomic force microscope (AFM) and an optical microscope. First, we observed the disk surface coated with PFPE Zdol by AFM. From the cross section images of the microdroplets, we found that the microdroplets had a shape similar to a sphere. With this finding, we estimated the contact angle of the microdroplets in each image. The results showed that the contact angle of the microdroplet gradually decreased with time, which indicated the existence of a PFPE thin film in the dewetted area. The thickness of the PFPE film in the dewetted area was then measured using an elliposometer. Next, we investigated the variation in the number and the average diameter of the microdroplets during dewetting using images observed by the optical microscope. The total surface area change was also calculated from the observed results, and it was found that the total surface area, namely the sum of the microdroplet surfaces and dewetted area, was reduced by the development of the microdroplets.     

Friction and wear of spindle motor hydrodynamic bearings for information storage systems during startup and shutdown

This paper investigates the friction and wear characteristics of two typical hydrodynamic bearings for hard disk drive (HDD) spindle motors (SPM), i.e., the herringbone groove and multi-taper bearings, during start-up and shut-down transient operation. The friction characteristics are calculated by a lubricated friction model which is an extension of Kogut and Etsion’s dry friction model (a modified version of the CEB model), while the wear characteristics are qualitatively evaluated in non-dimensional form by the semi-analytical wear model proposed by Holm–Archard. The average flow Reynolds equation and the pressure-compliance relationship of elastic–plastic roughness contact are used together to consider the combined effects of partial lubrication and asperity contact occurring during start-up and shut-down. Then, the friction and wear characteristics of the herringbone groove and multi-taper bearings are calculated and compared under the condition of HDD application.     

Machine tool condition monitoring using workpiece surface texture analysis

Tool wear affects the surface roughness dramatically. There is a very close correspondence between the geometrical features imposed on the tool by wear and micro-fracture and the geometry imparted by the tool on to the workpiece surface. Since a machined surface is the negative replica of the shape of the cutting tool, and reflects the volumetric changes in cutting-edge shape, it is more suitable to analyze the machined surface than look at a certain portion of the cutting tool. This paper discusses our work that analyzes images of workpiece surfaces that have been subjected to machining operations and investigates the correlation between tool wear and quantities characterizing machined surfaces. Our results clearly indicate that tool condition monitoring (the distinction between a sharp, semi-dull, or a dull tool) can be successfully accomplished by analyzing surface image data. Received: 9 June 1998 / Accepted: 6 October 1999