Tribological impact of touchdown detection on bit patterned media robustness

Touchdown detection by thermal-flying height control (TFC) has been implemented to calibrate flying height (FH) of magnetic sliders for all hard disk drives. For bit patterned media (BPM) to be successful as a revolutionary technology to further increase recording areal density, it must experience the touchdown process with similar robustness as conventional continuous media. Here we numerically study the tribological impact of TFC touchdown detection on the continuous media and unplanarized BPM by three-dimensional (3D) transient finite-element models with the frictional heating and thermal-elastic-plastic materials included. Our results demonstrate that the continuous media exhibits no plastic deformation due to the TFC touchdown with an over-push as large as 2 nm, whereas the plastic strain of the BPM may reach 3 % at higher sliding velocities, and it exists over a wide range of bulge radius and disk velocity. Such plastic deformation can lead to permanent media damage and data loss. Besides, the temperature rise of the BPM (~27 K) is approximately 1.3 times of that of the continuous media (~21 K), and may have to be considered when designing a robust head-disk interface for BPM. Although planarization may improve slider’s flyability performance, our analysis shows that planarizing BPM with SiO₂ deteriorates the tribological robustness of the media in particular at a high disk velocity probably due to the inhomogeneous composition and mismatch of material properties between the filling material and recording material. Hence extreme caution must be exercised when choosing a filling material.     

Static and dynamic flying characteristics of a slider on bit-patterned media (dynamic responses based on frequency domain analysis)

Recording media with grooves, such as discrete track media (DTM) and bit-patterned media (BPM), are considered to be promising media for achieving ultrahigh recording densities. It is thus important to analyze the static and dynamic characteristics of flying head sliders on DTM and BPM using the molecular gas film lubrication equation and the van der Waals (vdW) equation. In this study, we consider BPM with rectangular bits. We express the disk recess as a Fourier series and determine the quasi-static and time-dependent components. We also develop a perturbation method for small groove depths for calculating static slider attitudes and dynamic responses in the frequency domain. The numerical results predict that the grooves will significantly reduce the quasi-static flying height h ₀. They also predict that for a small groove depth h _groove, flying height decrease Δh ₀ almost agree with the value of uniform disk recess obtained by a Fourier series expansion, which also agrees with empirical results. Dynamic slider characteristics obtained by the frequency domain analysis is useful for sliders suffering from excitations of several tens of kHz such as sliders flying at transition between data zone and servo zone, although the dynamic spacing fluctuation by realistic BPM media is negligible.     

Air bearing dynamic stability on bit patterned media disks

Bit Patterned media (BPM) recording is one of the potential technologies to be used in future disk drives in order to increase the areal density to 5 Tbit/in². But one of the main obstacles for BPM is to achieve dynamic stability of the air bearing slider at the head-disk interface (HDI). In this paper we first use a direct simulation method to check the accuracy of our previously developed Homogenization Reynolds equation solution. After confirming the accuracy it is then implemented to study the slider’s flying attitude on BPM disks. Then we investigate the system’s parameters using a system identification method by simultaneously solving the equations of motion of the slider and the Homogenization Reynolds equation. We observe that the first pitch mode frequency of the air bearing increases with increase of pattern groove area ratio and pattern height. And the stiffness decreases when the pattern groove area ratio or pattern height increases. We conclude that a partially planarized BPM is preferred in order to maintain the dynamic stability of the HDI.     

The flying height analysis of patterned sliders in magnetic hard disk drives

The ultra-low spacing of patterned sliders flying above a rotating disk with smooth surface in a hard disk drive is analyzed for high areal density recording. Three types of pattern (slender, square, and broad) with the same bump area are discussed. The molecular gas film lubrication (MGL) equation and the equations of motion of the patterned slider are solved numerically to obtain the steady flying attitude. The results show that the flying height of the broad patterned slider is the greater than either that of the square patterned slider or the slender patterned slider. In addition, we analyzed the effects of bump height and the bump pitch on the slider attitude, including flying heights, pitch angles, and roll angles, are discussed.The authors express their thanks for the foundation support from National Science Council, NSC 92-2212-E-151 -005, ROC.     

Investigation of thermo-mechanical contact between slider and bit patterned media

Contact between a slider and bit patterned media (BPM) is investigated using finite element analysis. The effect of contact conditions and material properties at the interface between slider and disk on plastic deformation and temperature is studied. In addition, the planarization of bit pattern media on temperature and plastic deformation is investigated for different filler materials. It is found that filler material results in reduction of plastic deformation and temperature.     

Dynamic flying characteristics of an air bearing slider over a disk with grooves and distribution of material properties

Bit-patterned media (BPM) consisting of land parts for read/writing and grooves, which are almost filled with non-magnetic materials to prevent magnetic interference between recording bits, are considered to be promising media for achieving ultrahigh density recording. A flying head slider flying over a BPM disk suffers from variations in both the spacing and van der Waals (vdW) attractive forces, which induce slider vibrations and spacing fluctuations. In the present study, we considered that BPM disks not only have a groove depth distribution, but that they also have a distribution of material properties (e.g., refractive index), which gives rise to a distribution in the vdW force. In the dynamic responses of sliders with small groove depths and a small variation in the refractive index, spacing fluctuations are found to be a superposition of fluctuations due to slider behaviors (1) over a disk with transverse grooves in a uniform material with a uniform refractive index (Case 1) and (2) over a flat disk with a refractive index distribution (Case 2). When the effects of Cases 1 and 2 cancel each other, the spacing fluctuations for the two cases cancel each other, reducing the total spacing fluctuation.     

Planarization of patterned magnetic recording media to enable head flyability

The fabrication and planarization of patterned magnetic recording media is investigated and the flyability of magnetic recording sliders on a patterned and planarized 65 mm glass disk is investigated a small coupon of patterned media with an array of nano pillars of 40 nm diameter and 60 nm height was first fabricated by e-beam lithography and reactive ion etching (RIE) to investigate the planarization process for patterned media. Since read/write flyability tests require a patterned disk rather than a small coupon area, we have prepared a bit patterned glass disks of 65 mm diameter (2.5 in.) using the so-called “Ag ball-up process” in combination with RIE. This “Ag ball-up process” permits the manufacturing of a nano-sized bit patterns on a large area, i.e., on a disk with 65 mm diameter. Planarization of the patterned area was performed with hydrogen silsesquioxane (HSQ) by spin coating. The HSQ layer was back-etched using RIE, resulting in a smooth surface. “Flyability testing” indicates significantly improved flying stability of typical magnetic recording sliders on the planarized glass disks, with the standard deviation of flying height fluctuations on the order of 0.1 nm. The latter value is comparable to that of “smooth” disks.     

Patterned media for future magnetic data storage

One strategy to delay the onset of superparamagnetism and achieve magnetic storage densities approaching 1 Tb/in.² is the use of lithographically patterned magnetic media. While one of the main advantages enjoyed by magnetic recording is low cost due to use of featureless media, there are several advantages that may be realized by patterning the medium in a hard disk drive. The commercial success of patterned media will of course depend on the relative costs and gains. In particular, there are three main types of disk patterning proposed, each requiring a different length scale of patterned feature. Patterning of servo marks for maintaining the head position on-track, the fabrication of discrete tracks, and the fabrication of discrete bits have all been proposed and will be discussed. For discrete bit recording single domain magnetic islands are required, and one approach to fabricating these, by depositing magnetic films onto prepatterned substrates, is described. The switching characteristics of the islands as compared to those of the full film, along with initial recording results are presented.     

Numerical simulation of thermal flying height control sliders in heat-assisted magnetic recording

Heat assisted magnetic recording (HAMR) is one of the most promising techniques to extend the recording density in hard disk drives beyond 1?Tb/in². Although the diameter of the spot on the disk that is heated by the laser beam is very small, on the order of nanometers, high local temperatures on the disk and the heat dissipated in the slider during the light delivery process can cause thermal deformations of both the disk and the slider, thereby affecting the flying characteristics at the head-disk interface. In this paper, a finite element model is developed which incorporates a HAMR optical system into a thermal flying height control (TFC) slider with dual heater/insulator elements to study the effect of heat dissipation in the wave guide on the thermal deformation and flying characteristics of a HAMR-TFC slider. In addition, the power input of the laser and design parameters of the heaters are investigated.     

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.     

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.     

Tri-state dynamic model and adhesive effects on flying-height modulation for ultra-low flying head disk interfaces

Physical spacing between a flying slider and a rotating disk is projected to be 3 nm in order to achieve extremely high areal recording densities of 1 Tb/in². In such ultra-low flying-height regimes, two imminent obstacles that need to be overcome are intermittent head/disk contacts and strong intermolecular adhesive forces at the head/disk interface (HDI). Head/disk contact can cause large vibrations of the recording slider and possibly damage the disk and slider due to large contact forces. Strong adhesive forces disturb the balance of forces in a flying slider by pulling it down onto the disk and increasing the possibility of catastrophic HDI failures by doing so. This paper describes a dynamic model that includes contact and adhesive forces. Specifically, a lumped parameter single degree-of-freedom, three state nonlinear dynamic model representing the normal dynamics of the HDI and asperity-based contact and adhesive models were developed and coupled together to predict the performance of ultra-low flying sliders. The validity of the proposed dynamic model was confirmed in terms of flying-height modulation (FHM) by experimental measurements using ultra-low flying HDIs. It was found that the amplitude and frequency components of the dynamic microwaviness play an important role in slider dynamics. Furthermore, the effect of adhesive force on FHM was investigated and design guidelines for reduced FHM were suggested.This research was supported by a grant from the Information Storage Industry Consortium (INSIC) and the National Science Foundation under grant number CAREER CMS-0227842. Gary Prescott and Thomas Pitchford of Seagate Technology provided the spindle motor and HGA samples. The authors gratefully acknowledge this support.     

基于VR设备中IMU的头部姿态感知算法研究

随着头戴式显示设备的发展,基于虚拟现实(Virtual Reality,VR)的教育培训随之流行开来。在基于VR设备的教育培训中,存在用户与设备间进行交互的场景。在这些场景中,VR设备对使用者头部姿态的感知尤为重要。为了保证较高的姿态解算精度,同时降低系统的计算量,设计了四种基于头戴式惯性测量单元(Inertial Measurement Unit,IMU)的姿态解算方法,并对比了这四种算法的姿态解算精度和运算效率。实验结果表明,相比于其他三种算法,使用四元数微分方程的三阶泰勒展开递推式更新四元数,同时利用间接扩展卡尔曼滤波器融合地磁信息进行修正的姿态解算方法保证了较高的解算精度和较少的运算时间。该基于地磁修正+三阶泰勒展开法的头部姿态感知算法计算所得欧拉角与SBG公司生产的IG-500N型号IMU中提供的姿态角具有1.1×10-2度的总体平均偏差,且该算法使用MATLAB R2013a平台计算14000组数据的耗时为5.1秒。     

Acoustic emission (AE) measurements to determine the dynamic flying characteristics of optical sliders

Flying heads carrying a magnetic coil and a high numerical aperture lens for magneto-optic recording or a solid immersion lens for optical phase change recording, respectively, are promising approaches for increasing the data density. A classic approach to dynamically evaluate the flight attitude of flying heads in data storage is acoustic emission (AE) testing of the head/disk interaction using special glide heads. In our paper we introduce the application of AE test heads for measuring the flying characteristics of optical far field and near field sliders. In comparison to conventional external AE sensors, i.e. sensors mounted somewhere in the drive, these AE elements are directly mounted on the sliders thus yielding a higher pulse shape and a better signal to noise ratio. This set-up allows a clear identification of the head disk contact. To calibrate the sensor a bump disk was fabricated and used for AE measurements.     

On-chip manipulation and trapping of microorganisms using a patterned magnetic pathway

We demonstrate on-chip manipulation and trapping of individual microorganisms at designated positions on a silicon surface within a microfluidic channel. Superparamagnetic beads acted as microorganism carriers. Cyanobacterium Synechocystis sp. PCC 6803 microorganisms were immobilized on amine-functionalized magnetic beads (Dynabead^® M-270 Amine) by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)–N-hydroxysulfosuccinimide coupling chemistry. The magnetic pathway was patterned lithographically such that half-disk Ni₈₀Fe₂₀ (permalloy) 5 μm elements were arranged sequentially for a length of 400 micrometers. An external rotating magnetic field of 10 mT was used to drive a translational force (maximum 70 pN) on the magnetic bead carriers proportional to the product of the field strength and its gradient along the patterned edge. Individual microorganisms immobilized on the magnetic beads (transporting objects) were directionally manipulated using a magnetic rail track, which was able to manipulate particles as a result of asymmetric forces from the curved and flat edges of the pattern on the disk. Transporting objects were then successfully trapped in a magnetic trapping station pathway. The transporting object moves two half-disk lengths in one field rotation, resulting in movement at ~24 μm s^?1 for 1 Hz rotational frequency with 5 μm pattern elements spaced with a 1 μm gap between elements.     

MEMS milliactuator for hard-disk-drive tracking servo

This paper describes the design, fabrication, and operational characteristics of a MEMS milliactuator designed for servo tracking in a hard-disk drive (HDD). The actuator is designed to increase the bandwidth of an HDD tracking servo and pack more recording tracks on a disk. An Invar (low thermal expansion metal) electrode position process was developed to meet the thermal stability requirement. The electroplated Invar's thermal coefficient of expansion is as low as 6.3×10^-6/K, which is almost half of that of pure nickel. For the plating mold pattern definition, a high-aspect-ratio polymer etching technique was developed. A high-aspect-ratio structure line-and-gap definition is required to achieve both a high directional stiffness ratio and electrode efficiency for the actuator. The etching technique described can etch through a thick (<40 μm) polymer layer with an aspect ratio of 16:1 at an etch rate of <2 μm/min. Low-cost/high-volume manufacturing is achievable by this batch fabrication technique. A milliactuator was fabricated and assembled with a suspension and a slider weighted at around 2 mg. The slider was successfully driven by the milliactuator while the slider was flying on a spinning disk. The operational characteristics (frequency response) of the in-flight milliactuator were measured, and the results indicate that the actuator is suitable for high-bandwidth HDD servo-tracking applications     

The effect of write current on thermal flying height control sliders with dual heater/insulator elements

The effect of write induced pole tip protrusion on the magnetic spacing of the head/disk interface has to be taken into consideration as flying heights approach the spacing regime of a few nano-meters. Thermal flying height control (TFC) sliders are presently in common use in hard disk drives to control the flying height at the read/write element during drive operations. In this paper the flying characteristics of TFC sliders with dual heater/insulator elements are investigated. Simulation results are shown for situations where the write current is ??on?? and where the write current is ??off??. The effect of design parameters of two heater/insulator elements is studied to optimize the performance of TFC slider.     

On the complexity of algorithms for the translation of polynomials

Three algorithms for computing the coefficients of translated polynomials are discussed and compared from the point of view of complexity. The two classical translation algorithms based on explicit application of the Taylor expansion theorem and the Ruffini-Horner method, respectively, have complexityO (n ²). A third algorithm based on the fast Fourier transform is shown to have complexityO (n logn). However, when the cost of arithmetic operations is explicitly taken into consideration, the Ruffini-Horner algorithm is one order of magnitude better than the one based on the Taylor expansion and competes quite well with the algorithm based on the fast Fourier transform.     

Parametric simulation of piezoelectric flying height control slider using shear-mode deformation

The piezoelectric flying height control slider has recently been implemented in magnetic recording disk drives to reduce the flying height. This paper performs the electromechanical simulation and air-bearing simulation to investigate the effects of the shear-model deformation on the static flying attitude of PZT slider. The location of PZT sheet and air bearing surface of slider are investigated to achieve a low flying height and robust head-disk interface. The results show that a short distance of the PZT sheet to the trailing edge of the slider can help to achieve a low flying height. A small center-trailing pad of the slider can also help to achieve a low flying height, but cannot prevent the reduction in pitch angle. The depth of the center-trailing pad does not change the reduction ratio of the pitch angle when increasing the drive voltage. A big pitch angle value is needed to avoid the pitch angle falling below zero at a high drive voltage.