Dynamic instability of flying head slider and stabilizing design for near-contact magnetic recording

The dynamic instability of a flying head slider is described, and a design guideline is presented for a slider that can stably fly at a height of less than 5 nm. The current use of shrouded Rayleigh step-bearing slider has been a good way to increase air-bearing stiffness and damping while reducing meniscus adhesion and friction forces, but does not have enough ability to achieve a small flying height less than 5 nm. On the basis of meniscus interfacial force theory, I proposed a spherical pad slider that is inherently stable in the near-contact regime and that has high durability against intermittent contact, which is necessary for future high-density magnetic recording. This design concept is being partly realized by thermal flying height control technique.     

Interface solution for writing-induced nano-deformation of slider body

Writing-induced nano-deformation of slider body becomes a big concern when the mechanical spacing between the head and disk is continuously reduced to achieve higher magnetic recording areal density. Reduced head–disk spacing increases the risk of head/disk contact and causes the thermal instability in head–disk interface (HDI). This paper reports authors’ efforts towards exploration of interface solutions for writing-induced instability in ultra-low head–disk spacing magnetic system. Multi-shallow step structure with optimized rail position is analyzed and a new femto slider with such structure is explored. The results of numerical simulation indicate that the multi-shallow step structure is an effective approach in reducing the flying height change caused by the writing-induced nano-deformation of the slider body.     

Sub-mm disk waviness characteristics and slider flying dynamics under thermal FH control

The flying dynamics and flying stability of a slider are the key issues at sub-5 nm flying height (FH) under thermal FH control. The resonant frequencies of current sliders are at 100 kHz level. At present linear disk velocities, the disk waviness at sub-mm level and 10 micron level can excite the resonant modes of the slider and induce FH modulation. This work uses the triple-harmonic method to monitor the dynamic FH signal during the process of thermal FH control. As the FH reduces, the same disk waviness characteristics excite larger dynamic FH modulation.     

Ultra low head–disk spacing measurement using dual beam polarisation interferometry

In this paper, a dual-beam normal incidence polarisation interferometer is proposed to measure the flying height or head–disk spacing. Using this interferometer, the head–disk spacing can be measured both in magnetic real disk condition and in glass disk condition. It has the advantage of both the currently popular intensity interferometry method and the oblique incidence polarisation interferometry method. With this polarisation interferometer, not only the flying height can be measured down to contact without losing accuracy, but the pitch and roll of the head-slider can also be detected dynamically. The optical parameters of the head-slider can also be determined. Design details and experimental study are presented.     

基于多物理场的TFC磁头热传导机理及其影响因素仿真研究

为了利用微尺度热效应的热致飞高控制(TFC)磁头技术实现磁头飞行高度的精确控制,分析了工作状态下TFC滑块在多物理场综合作用下所呈现出来的传热特性及其主要影响因素,考虑了磁头磁盘间超薄气膜的稀薄效应,建立滑块导热、空气轴承表面传热、气膜流动等模型,利用有限元法,对磁头热变形作用机理及热传导特性对滑块动力学特性影响进行了仿真研究,结果表明,建立的传热模型及对雷诺方程的修正适用于求解磁头磁盘界面气膜传热问题和磁头滑块的动力学问题;影响滑块热力学性能的因素主要可以归结为加热器高度、热生成率以及材料的传热系数;空气轴承力及工作表面热变形的双重作用决定了滑块飞行高度的改变.仿真结果为磁头滑块加热器的设计及空气轴承动力学特性分析提供了依据.     

磁头-磁盘接触作用力对磁记录层信息强度影响规律的定量研究

磁存储密度的持续增长会导致磁头-磁盘的间距不断减小, 这样, 极有可能引起磁头-磁盘接触退磁的发生, 从而造成磁记录层存储数据的丢失. 为了明确退磁过程中的相应作用关系, 本文通过磁力显微镜的相位成像原理直接给出了磁盘退磁的定量测量方法. 并且依据此方法, 利用纳米划痕实验研究了磁头-磁盘接触作用力对磁记录层信息强度的影响规律. 结果表明:当磁头-磁盘接触作用力超过临界退磁载荷时, 磁记录层的信息强度与磁头-磁盘接触作用力之间存在减函数关系; 在低接触载荷区域中, 即使磁记录层表面没有划痕产生, 磁盘退磁现象仍旧可能发生; 对于任意磁头-磁盘接触作用力, 磁盘表面的破坏区域总是会大于磁记录层的退磁区域; 当磁头反复划刮磁盘的同一位置时, 磁记录层的表面划痕处将出现弹性安定状态, 对应地, 磁记录层的信息强度会趋近于某一定值.     

Lubricant film flow and depletion characteristics at head/disk storage interface

The characteristics of lubricant film at head/disk interface(HDI) are essential to the stability of hard disk drives. In this study, the theoretical models of the lubricant flow and depletion are deduced based on Navier–Stokes(NS) and continuity equations. The air bearing pressure on the surface of the lubrication film is solved by the modified Reynolds equation based on Fukui and Kaneko(FK) model. Then the lubricant film deformations for a plane slider and double-track slider are obtained. The equation of lubricant film thickness is deduced with the consideration of van der Waals force, the air bearing pressure, the surface tension, and the external stresses. The lubricant depletion under heat source is simulated and the effects of different working conditions including initial thickness, flying height and the speed of the disk on lubricant depletion are discussed. The main factors that cause the lubricant flow and depletion are analyzed and the ways to reduce the film thickness deformation are proposed. The simulation results indicate that the shearing stress is the most important factor that causes the thickness deformation and other terms listed in the equation have little influence. The thickness deformation is dependent on the working parameter, and the thermal condition evaporation is the most important factor.     

Investigation of HDD Ramp Unloading Processes with an Efficient Scheme

Ramp load/unload (L/UL) mechanisms are widely used to rest sliders in hard disk drives (HDDs). Loading/unloading a slider swiftly and smoothly is crucial in a HDD design. A novel, efficient simulation scheme is proposed to investigate the behaviors of a head disk interface (HDI) in ramp unloading processes. A dual scale model is enabled by decoupling the nano-meter scale change of an air bearing and the micro- or milli-meter scale deformation of a suspension. A modified Reynolds equation governing the air bearing was solved numerically. The slider design was characterized with performance functions. Three stages in an unloading process were analyzed with a lumped parameter suspension model. Key parameters for the model were estimated with a comprehensive finite element suspension model. Finally, simulation results are presented for a commercial HDI design.     

Air-lubrication of magnetic disk sliders

Steady-state and dynamic flying of a self-acting magnetic disk slider over a hard disk are considered. Some tasks for computations are formulated and the possibilities of developed numerical codes are illustrated. Numerical results of dynamic flying over a disk surface with an obstacle are in agreement with experimental data.     

On the advanced lapping process in the precision finishing of thin-film magnetic recording heads for rigid disc drives

Precision abrasive finishing is a key technology in the manufacture of thin-film magnetic heads (TFH) for rigid disc drives. The read and write microdevices of the recording heads are fabricated on ceramic substrates (wafers) using thin-film processing technology. After wafer processing, the substrates are sliced to individual bars (containing 46 heads per bar) using a diamond dicing wheel. They are then finished using an advanced lapping process with individual head close-loop control (sensor height control for the control of the material removal as well as for the end point detection). Finally, the bars are diced into individual heads (called sliders) using a diamond dicing wheel. The slider abrasive finishing process critically affects the magnetic, electrical and mechanical performance of the recording heads. This paper presents the results of some experimental studies based on the state-of-the-art abrasive finishing of recording heads, taking into account the critical challenges involved, namely the sensor height control, pole-tip recession (PTR) (metal dishing), alumina recession (AluR) (oxide erosion), trailing-edge profile, polishing uniformity, smearing, surface roughness (scratches) and air-bearing surface (ABS) flatness. The relative advantages of the fixed- versus free-abrasive processes are also discussed. The results of chemical-mechanical fixed-abrasive lapping/nanogrinding to achieve near-zero PTR (to minimize magnetic space loss) and low AluR (to reduce flying height variation) to meet the high areal density head requirements are also presented. PACS 60; 81; 81.20; 81.05.Cy; 81.05.Jc     

Effect of pattern shape on etching wall profile in slider fabrication

The effect of pattern shape on etching wall profile in slider fabrication is studied. The testing results show: (1) the wall profile of round pattern is steeper than that of long rectangular; (2) for round patterns, the smaller the radius is, the steeper the wall profile is; (3) the profile of outer angle is steeper than that of inner angle. The flying height offset caused by wall profile with different shapes can be 8% of total flying height, so it is necessary to consider the effect of pattern shape on etching wall profile in ABS design, especially for ultra low flying height slider.     

Disk clamping distortion and slider crown sensitivity induced flying height variation

The disk clamping distortion and slider crown sensitivity induced flying height (FH) variation is investigated. The experimental results which were measured with in situ method were compared with simulated numerical results. Both results indicate that the disk clamping distortion has significant influence on the FH variation. Crown sensitivity of the sliders is one of the factors that determine the amplitude of the FH variation. Higher crown sensitivity sliders exhibit greater FH variation.     

Strain imaging of a perpendicular recording head in a Hard Disk Drive

Imaging of magnetic-field-induced strains using scanning probe microscopy enables us to observe magnetic domain structures and magnetic force distributions. This method has an ability of observing magnetic structures in deep portions along with surface structures. We observed an air-bearing surface of a perpendicular recording head in a hard disk drive in large areas including the whole yokes, and investigated characteristics of the magnetic poles and layers subjected to magnetic fields produced by writing coil currents. Attractive forces independent of the field directions acted between the upper and lower yokes made by soft material, which generated surface displacements in the ABS. The signals were second-harmonic oscillations for alternating currents without a dc bias, and the amplitude images represented the field distribution. Meanwhile, fixed magnetic charges in both ends of the read sensor, which were produced by the hard-bias film, were subjected to the fields. The fixed charges, which hardly changed by the fields, lead to strains depending on the field directions, and generated specific contrasts of one pair of bright-dark spots in the strain images. In the absence of surface underlayer, the fields by the writing coil broke into the read sensor sandwiched by the shield layers.     

Vibrational response of a moving suspension-slider loading system exciting a rotating flexible disk

To investigate the vibrational response of the magnetic read/write head in hard disk drives this paper models a rotating flexible disk excited by a moving suspension-slider system which is considered to be a mass-dashpot-spring loading system, with the initial unstressed transverse runout integrated into the rotating disk dynamic model. The slider motion on the disk surface is driven by the suspension rotating at a constant speed. By subtracting the steady-state deflection component from the instantaneous deflection response of the rotating disk system, the relative vibration transverse deflection of the slider caused by the motion of the suspension-slider loading system is obtained. The effects of the slider initial and final positions, speed of movement, the disk rotational speed, and the disk mode of the initial transverse runout on the maximum amplitude of the relative vibration deflection are analyzed.     

7.5-MHz data-transfer rate with a planar aperture mounted upon a near-field optical slider

We fabricated a planar aperture-mounted (PAM) slider by use of a focused ion beam to demonstrate fast data acquisition for near-field optical data storage. The aperture (200 nm x 500 nm) was formed upon the Ti-coated air-bearing surface of the slider and was directly illuminated with a laser (lambda = 532 nm) beam spot by use of an objective lens (N.A., 0.55). The light transmitted through the aperture was modulated by a Ti-coated SiO(2) disk with 200- and 400-nm-wide line-and-space (L&S) patterns engraved by electron-beam lithography. The optical throughput of the taperless aperture was greater than 0.02. By use of the PAM slider, 400- and 200-nm L&S signals were detected at linear velocities of 6 and 3 m/s, respectively, corresponding to a data-transfer rate of 7.5 MHz.     

Optical and electronic properties of anisotropic parabolic quantum disks in the presence of tilted magnetic fields

In the present work, the electronic and optical properties of anisotropic parabolic quantum disks are studied in the presence of an applied magnetic field. For this goal, we first obtain the electron energy levels of an anisotropic parabolic quantum disk under axial, tilted, and in-plane magnetic fields. According to the results obtained for the energy levels reveal that there is no degeneracy at zero magnetic field due to symmetry breaking. With increasing the anisotropy, the energy level spacing increases. At a constant anisotropy, the energy levels splitting decreases with increasing tilt angle of magnetic field. The total refractive index changes decrease when the tilt angle of magnetic field and the anisotropy increase. Also, the total absorption coefficients increase as the tilt angle of magnetic field and anisotropy increase.     

基于强度干涉原理的双光路动态测量方法

在近场光存储方案中,头盘间距动态测控技术是近场光存储理论和技术的实用化。根据近场光学头的飞行特点,提出了一种基于光强干涉原理的测量系统,重点介绍了其测量原理和标定方法。采用双光路结构来提高测量分辨率,利用光偏振特性来消除反馈光对信号光的干扰。通过对系统性能的分析和试验表明,动态特性达到了500kHz,测量分辨率高于1nm,可满足系统高精度动态测试的要求。     

激光驾束制导仪中调制盘的设计

介绍了激光驾束制导仪中调制盘的空间编码原理,阐述了调制盘的设计过程,采用单调制盘来缩小驾束制导仪的体积和重量。考虑到制导仪器实际工作的各种因素,设计了调制盘内、外码道的宽度,起止位置和5种频率值。给出了调制盘确定偏航信息的原理,表征导弹位置信息的调制系数和频率的计算方法。针对调制盘两场交接处的误码问题,提出了变角度设计方法,将各频率沿径向方向旋转45°,从而保证了5 ms的场周期,提高了制导精度。     

激光驾束制导仪中调制盘的设计

介绍了激光驾束制导仪中调制盘的空间编码原理,阐述了调制盘的设计过程,采用单调制盘来缩小驾束制导仪的体积和重量。考虑到制导仪器实际工作的各种因素,设计了调制盘内、外码道的宽度,起止位置和5种频率值。给出了调制盘确定偏航信息的原理,表征导弹位置信息的调制系数和频率的计算方法。针对调制盘两场交接处的误码问题,提出了变角度设计方法,将各频率沿径向方向旋转45°,从而保证了5 ms的场周期,提高了制导精度。     

Dynamic stability of rotating flexible disk perturbed by the reciprocating angular movement of suspension-slider system

To simulate the dynamic process of a magnetic head reading/writing data in a hard disk drive, a rotating flexible thin disk perturbed by the reciprocating angular movement of a suspension-slider system is modelled, where the suspension-slider system is considered as a mass-damping-spring loading system. A system dynamic model is formulated as a parametrically excited system, and its dynamic stability is studied by Hill’s method involving harmonic balance. The reciprocating angular movement of the suspension-slider system causes system parametric instability at some angular movement frequencies. The large-amplitude angular movement is especially dangerous, and angular movement frequency must be reduced when the slider works at large radii of the disk. The parametric instability can be avoided or suppressed by operating at: low-frequency and small-amplitude reciprocating angular movement, small mass, large natural frequency and damping of the suspension-slider system, and low-speed rotation of the disk.