Development of flying type head/slider for optical recording technology

Flying-type sliders with the integration of optical components were developed for Near-Field Recording (NFR) and Far-Field Recording (FFR) technologies. The key design issue was the integration of the optical components with the slider. Due to the size of the lenses mounted on it, the slider had to be relatively large, corresponding to the size of a micro-slider. Also, the non-uniform distribution of the slider body density was incorporated in the design. As for the optical disk substrate, a plastic material such as polycarbonate was investigated because of its manufacturing convenience and cost effectiveness. The flying and tribological performance of the prototype optical sliders on various media were assessed. The results showed that the tribological characteristics of the slider/disk interface were sensitive to several factors including the properties of the disk. Adequate flying characteristics of the optical sliders on glass (NFR) and plastic (FFR) disks could be attained by optimizing these parameters.     

Effect of contact conditions during thermo-mechanical contact between a thermal flying height control slider and a disk asperity

A three-dimensional thermo-mechanical model is developed for the transient contact between a thermal flying height control (TFC) slider and a disk asperity. The effect of contact conditions is investigated, including the friction coefficient and the circumferential disk velocity. The damage of the read–write shields due to contacts with disk asperities is studied along with the maximum temperature at the location of the read element. The effect of diameter and material properties of the asperity is also investigated. Strong dependence of deformation and maximum temperature is observed as a function of the diameter and material properties of the asperity.     

On tribological problems in magnetic disk recording technology

Critical tribology problems of the head-disk interface are reviewed. Surface topography of hard disks is discussed along with experimental results concerning the friction and stiction behavior of lubricated carbon coated disks. The effect of environmental conditions on the headdisk interface is analyzed together with current techniques to measure the flying height between slider and disk in the nanometer spacing range. The effect of air bearing design on the tribology of the head disk interface is discussed and a critical evaluation of recently proposed approaches towards contact recording is presented.     

离散磁道式磁盘与磁头动力学接触有限元分析

基于Hertz冲击理论,采用有限元仿真方法,建立了无摩擦条件下离散磁道式磁盘与磁头接触的动力学模型,研究了磁头径向寻道速度固定、法向冲击速度变化时,磁道材料力学特性对磁盘接触力场特性的影响规律,研究结果表明:随弹性模量增大,最大接触面积减小,最大接触力、最大VonMises应力和最大等效塑性应变均增大;屈服强度对力场特性的影响与接触力场Von Mises应力大小有关,只有当磁盘最大Von Mises应力达到磁道材料屈服强度时,屈服强度变化才会影响磁盘的接触力场特性。     

Slider–bump contact and flying height calibration

It is a big challenge to determine ultra-low slider flying height accurately. The standard bump disk method is probably the most reliable and acceptable method so far. One of the key issues to determine slider-flying height with the bump disk method is the complicated slider–bump interaction process and the possible disturbance of the bumps on the slider flying performance. Our knowledge about the slider–bump interaction process is still very limited due to the lack of an effective and powerful experimental technique to study it. In this work, the slider–bump interaction process was studied with a dynamic flying height-attitude (3D) system. The interaction process was also simulated to compare with the experimental observations and to help determine the slider–bump contact points in the experimental observations. The accuracy of flying height (FH) calibration with the bump disk method and the minimum slider–bump interference height required for the testing system used in this study to detect the onset of slider–bump contact were analyzed and discussed. It is proved that the 3D system is a very useful and powerful tool for the application. Many details of the slider–bump interaction process can be revealed with the 3D system. It is found that the calibrated FH is much more accurate than that predicated by the simulations.     

Interface technology of ultra-low flying height and highly stable head–disk interface for perpendicular magnetic recording

This paper reports authors’ efforts in slider and interface technologies with extremely small and very high stability head–disk spacing. The dual shallow step strategy is proposed in the femto form-factor slider design. It is found that the dual shallow step design is very effective in reducing flying height modulation (FHM) caused by disk waviness and enhancing the cooling effects on the read/write elements. A simple geometric model is built to explain the schematic of the improvement in FHM.     

Consideration and compensation for precision optical flying height measurement

It is a big challenge to determine ultra-low slider flying height accurately. The intensity interferometry flying height testing method is widely used to determine slider flying height. However, the intrinsic measurement errors of the method are becoming non-negligible with the decrease in slider flying height. Strategies have to be developed to minimize the errors. To measure flying height with a normal incidence optical flying height tester, a calibration process is required to determine several constants used in flying height calculation. In practice, the calibration is usually done simply by retracting the slider from the disk and measuring the intensity minima and maxima of the interferogram during the retracting process. It has been demonstrated that the single most important source of error in the flying height measurement is associated with errors in the determination of the intensity maxima and minima. In this work, the effects of optical filter, the responding frequency of photodetector, and the lack of the first order intensity minimum on the determination of the intensity maxima and minima are studied. Methodologies to minimize the errors in flying height measurement caused by the above factors are developed.     

The effects of texture height and thickness of amorphous carbon nitride coating of a hard disk slider on the friction and wear of the slider against a disk

In order to minimize the stiction force caused by contact of the extremely smooth surfaces of head sliders and disks in hard disk drives, texture is usually applied on the disk surface. For future contact/near-contact recording, the stiction-induced high friction between slider and disk will become a problem. Texture on the slider/disk interface will still be an expected method to reduce friction. Recently, it was suggested to texture the slider surface. A protective coating is usually required on the textured slider surface to reduce wear of the texture. The results showed that texture on the slider surface was effective in reducing the friction between head sliders and disks. On the other hand, the texture and coating on the slider surface increase the spacing between the read/write element and the magnetic layer of the disk. The necessary and effective texture height and coating thickness are still not clear. In the present research, island-type textures with different heights (3–18 mn) were formed on slider surfaces by ion-beam etching. Amorphous carbon nitride (a-CN_x) coatings of different thicknesses (0–50 nm) were coated on the textured slider surfaces as a protective overcoat. The friction and wear properties of these sliders were evaluated by constant-speed drag tests against hard disks coated with diamond-like carbon (DLC). The results show that 2 nm texture on a slider surface is sufficient for low (0.3–0.5) and stable friction of the slider against the disk in a drag test, and coatings thicker than 5 nm show similar wear resistances of the texture on slider surfaces.     

Effects of flying height deviations on glide height tests for manufacturing hard disks

In this study, theoretical analysis and experiments were carried out to investigate the effects of avalanche-point deviation and the deviation between the calibration and test-flying heights during the glide head calibration in the glide height tests for manufacturing hard disks. To obtain accurate glide height test results and improve the reproducibility of the test, flying height control should be carried out by limiting the acceptable deviation range of the flying heights of the glide heads. When the avalanche-point deviation is zero, the test results using different calibrated rails (or heads) are the same when they are used to detect the same defect. To avoid wrong test results due to avalanche-point deviation, the test-flying height should be the same as the calibration flying height because the difference of the output voltages of any two rails (or heads) is zero in this case. If these two deviations cannot be eliminated completely, the calibration and test-flying heights should be carefully selected because the error still can be minimised depending on the selection of the flying heights.     

Effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives

This paper describes the effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid lubricants behavior are investigated using three types of lubricants, which have different end-groups and molecular weight as a function of lubricant film thickness. The dynamics of a contact slider is mainly monitored using acoustic emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the lubricant film thickness instability occurs as a result of slider–disk contacts, when the lubricant film thickness is thicker than one monolayer. Their unstable lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost same, independent of the end-groups and molecular weight for the lubricants, when the lubricant film thickness is approximately one monolayer. The molecular weight, however, affects the contact slider dynamics, when the lubricant film thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the lubricant increases. When the lubricant film thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile lubricant layer, while the lubricant instability affects the contact slider dynamics. Therefore, it may be concluded that the lubricant film thickness should be designed to be approximately one monolayer thickness region in order to achieve contact recording for future head–disk interface.     

Microwear mechanism of head carbon film during head disk interface sliding contact

Thermomechanical sliding contact of head disk interface (HDI) causes critical wear on the carbon film of a head slider. An improved contact model accounting for both asperity and substrate deformation is applied to analyze the HDI contact behavior, while theories of frictional heat generation and heat transfer are used to investigate the change in HDI temperature. Based on actual HDI design and operation parameters, parametric study of thermomechanical HDI contact has been performed. It was found that severe wear of head carbon film would be significantly attributed to thermal degradation of carbon material during its sliding contact.     

The decomposition mechanisms of a perfluoropolyether at the head/disk interface of hard disk drives

The decomposition mechanisms of a perfluoropolyether (ZDOL) at the head/disk interface under sliding friction conditions were studied using an ultra‐high vacuum tribometer equipped with a mass spectrometer. Chemical bonding theory was applied to analyze the decomposition process. For a carbon coated slider/CN_x disk interface, the primary decomposed fragments are CFO and CF₂O, caused by the friction decomposition and electron bombardment in the mass spectrometer. For an uncoated Al₂O₃–TiC slider/CN_x contact, CF₃ and C₂F₃ fragments appear in addition to CFO and CF₂O, resulting from the catalytic reactions and friction decomposition, indicating that the decomposition mechanism associated with friction leads to the breaking of the main chain of ZDOL and forms CF₂=O, which reacts with Al₂O₃ to produce AlF₃, and the rapid catalytic decomposition of ZDOL on the AlF₃ surface follows. Moreover, the effects of frictional heat, tribocharge, mechanical scission and Lewis acid catalytic action, generated in friction process, on the decomposition of ZDOL are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A theoretical model of slider–disk interaction and AE sensing process for studying interface phenomena and estimating unknown parameters

Theoretical models were developed for comprehensively accounting for the AE sensing process in the measurement of interfaces between different sliders and magnetic rigid disks. The models include tribological factors and system dynamics factors such as contact force, sliding velocity, lubricant thickness, topographic parameters, mechanical parameters, system transfer functions and filter design parameters. The theoretical models agree well with the experimental results conducted for different slider–disk interfaces. The models are also well correlated with extensively published experimental results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal sensor for in situ flying height measurements of optical flying heads

The application of flying head technology in optical recording promises a considerable increase in recording density. It may be used for both far field and near field recording. For dynamic in situ flying height and flight attitude measurements, a prototype of a thermal test head has been developed. It takes advantage of the heat transfer in sub-micrometer air bearings as well as its dependence from the air gap width. Such a test head has a slider with a similar air bearing surface as the recording head, but with thermo-resistive sensors that are energized by Joule's heat and embedded at each of the four corners. The paper describes the head design and the fabrication technology and provides first experimental test results as well.     

Numerical simulation of slider dynamics during slider–disk contact

In this paper, the dynamic behavior of pico slider in contact with the disk was calculated. The analysis model consists of a simplified suspension model, an air bearing model, and a slider–disk contact model. The contact model consists of two elements. One is surface roughness model measured by Atomic Force Microscope (AFM) and the other is micro-waviness model. The dynamic behaviors of the tri-pad slider are calculated at several rotation speeds to investigate slider vibration modes during slider–disk contact. The slider oscillation frequency depends on the rotation speed and it saturates about twice as much as eigen frequency of air bearing pitch mode.     

Effect of environment humidity and temperature on stationary and transient flying responses of air bearing slider

It is well known that the environment humidity and temperature have a significant influence on the flying height of an air bearing slider. However, not many research papers address this topic, especially when the transient flying response is considered. This paper studies the influences of the environment humidity and temperature on both the stationary and transient flying responses of slider by simulation. A slider design for the thermal protrusion application is addressed. The reason for causing the drop of the air bearing pressure is discussed, and the methods for decreasing the drop are proposed. It is observed that the environment humidity and temperature may determine whether the slider is in full flying state or in partial flying/partial dragging state, when the slider is released from a certain height. The reason may be due to the high humidity and temperature which weakens the air bearing. As a result, the air bearing becomes not strong enough to support well the full flying of slider when the influence of the intermolecular force is significant. Slider vibrations for the full flying case and the partial flying/partial dragging case are analyzed in frequency domain, and the slider vibration frequencies are discussed. It shows that the environment temperature and humidity have significant effects on both the stationary and transient flying responses of the slider.     

Effect of relative humidity and disk acceleration on tribocharge build-up at a slider–disk interface

High performance disk drives require high spindle speed. The spindle speed of typical hard disk drives has increased in recent years from 5400 to 15000 rpm and even higher speeds are anticipated in the near future. The increasing disk velocity leads to increasing disk acceleration and slider–disk interaction. As the head-to-disk spacing continues to decrease to facilitate increasing recording densities in disk drives, the slider–disk interaction has become much more severe due to the direct contact of head and disk surfaces in both start/stop and flying cases. The slider–disk interaction in contact-start-stop (CSS) mode is an important source of particle generation and tribocharge. Charge build-up in the slider–disk interface can cause electrostatic discharge (ESD) damage and lubricant decomposition. In turn, ESD can cause severe melting damage to MR or GMR heads. We measured the tribocurrent/voltage build-up generated at increasing disk acceleration. In addition, we examined the effects of relative humidity on the tribocharge build-up. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and that its level was below 250 pA and 0.5 V, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions (75–80%) yielded lower levels of tribovoltage/current. Therefore, a higher tribocharge is expected at a lower disk acceleration and lower relative humidity condition.     

Vibration control of a spinning disk

An active control scheme based on the transfer function model is proposed to suppress the vibration of a disk spinning both in the sub- and super-critical speed ranges. The feedback controller consists of a space-fixed point sensor and a point actuator, which are not on any nodal circle of the freely spinning disk. The point sensor can measure both the displacement and the pitching slope of the spinning disk. In the sub-critical speed range, a controller measuring the displacement information alone works well in suppressing the disk vibration. However, such a controller is not only unable to suppress the disk vibration in the super-critical speed range, it may destabilize the spinning disk instead. In order to control a disk in the super-critical speed range, a controller using both the displacement and slope information is proposed. The range of the control gain parameter which renders the spinning disk asymptotically stable can be determined by a stability analysis. The success of such a controller is demonstrated via numerical simulations.     

Dynamics of transient events at the head/disk interface

Slider/disk contacts of nano and pico sliders are investigated using an acoustic emission sensor and a high bandwidth laser Doppler vibrometer (LDV). The following cases are studied: (a) influence of scratch impact on the airbearing stiffness; (b) influence of lubricant thickness on slider dynamics for single bump impacts; (c) influence of lubricant thickness on slider vertical stick–slip vibrations; (d) dynamics of take-off and landing. Linear time frequency analysis is applied to study simultaneously the impact response of the airbearing and the slider torsional and bending modes. The contact dynamics of single bump impacts is examined as a function of disk velocity and lubricant thickness. Increased slider vibrations are found for thick lubricant films both for sliding contacts as well as for single bump impacts. During the transition from sliding to flying a change of the bending mode frequency is observed.     

摩擦片式电磁离合器的测试及选用

从摩擦片式电磁离合器存在的问题、工作特性、性能测试等方面进行论述,提出了安装及选用摩擦片式电磁离合器应注意的事项。