Flying Head Slider Research Articles

Investigation of electrostatically tunable adhesion and instability of flying head slider

The interfacial adhesion between microstructures is inevitable in a micro-electro-mechanical system (e.g., hard disk drive (HDD)), which may lead to complicated microtribodynamics problems. This research has investigated the effect of surface potential on the interfacial adhesion and microtribodynamics of the head–disk interface (HDI) in an HDD. A dynamic continuum surface force model, where the electrowetting is considered, is proposed to evaluate the interfacial interaction, and then employed into a two-degree-of-freedom (2DOF) model to theoretically analyze the potential influence mechanism on the microtribodynamics. The results confirm that the elimination of potential can effectively repress the adhesion retention, which is further proved by the measured slider response with a laser Doppler vibrometer (LDV). Moreover, the effect of the potential on the adhesion-induced instability is also analyzed through the phase portrait. It tells that the critical stable flying height can be lowered with the elimination of potential.

Analytical Investigation of Touchdown Characteristics of Flying Head Slider for Quasi-Contact Recording

Analytical Investigation of Touchdown Characteristics of Flying Head Slider for Quasi-Contact Recording

Numerical analysis of microwaviness-excited vibrations of a flying head slider at touchdown

The dynamics and stability of a flying head slider at proximity to and touchdown on a magnetic recording disk are attracting considerable research attention, because it is necessary to reduce the head clearance from the lubricant film to ~ 0.5 nm to achieve a higher recording density. As a succeeding study continuing the theoretical investigation of slider dynamics at touchdown, this study theoretically analyzes further details of the different behaviors of a practically applied head slider. The experimental touchdown behaviors at inner, middle, and outer radius positions in a commercially available hard disk drive are introduced. From the improved theoretical analyses, it is determined that different behaviors result from differences in air-bearing stiffness at the inner, middle, and outer radius positions. Moreover, it is found that the first half of the period for which a loss-of-contact signal is obtained corresponds to a light asperity contact state between the head and disk surfaces, whereas the latter half of this period corresponds to a flying state. It is thought that the former light asperity contact state can be well lubricated even at a high bond ratio, and that the light contact state can be used for future contact recording.

Analysis of Microwaviness-Excited Vibrations of a Flying Head Slider in Proximity and Asperity Contact Regimes

The vibration characteristics of a thermal fly-height control (TFC) head slider in the proximity and asperity contact regimes attract much attention, because the head–disk spacing (HDS) must be less than 1 nm in order to increase the recording density in hard disk drives. This paper presents a numerical analysis of the microwaviness (MW)-excited vibrations in the flying head slider during the touchdown (TD) process. We first formulate the total force applied to the TFC head slider as a function of the HDS, based on rough-surface adhesion contact models and an air-bearing force model. Then, the MW-excited vibrations of a single-degree-of-freedom (DOF) slider model at TD are simulated by the Runge–Kutta method. It is found that, when the MW amplitude is less than the spacing range of static instability in the total force, the slider jumps to a contact state from a near-contact or mobile-lubricant-contact state. It then jumps to a flying state even when the head surface is protruded further by increasing the TFC power. When the MW amplitude is relatively large, a drastically large spacing variation that contains a wide range of frequency components below 100 kHz appears in the static unstable region. These calculated results can clarify the mechanisms behind a few peculiar experimental phenomena reported in the past.

ヘッドスライダの近接・接触時におけるディスク微小うねり励起振動の解析

ヘッドスライダの近接・接触時におけるディスク微小うねり励起振動の解析

浮動ヘッドスライダの接触過程におけるディスク微小うねり励振振動の解析

Vibration characteristics of a flying head slider in hard disk drives at touchdown attract strong interest because head‒disk spacing must be decreased to less than 1 nm in order to increase recording density. This study first evaluates head‒disk interfacial force based on rough surface adhesion contact models and a simple air-bearing force model. Then, microwavinessexcited vibration of single-degree-of-freedom slider model at touchdown was numerically simulated in more detail than the previous study. It was found that the slider exhibits a MW-excited vibration having low frequency components of less than 100 kHz at touchdown and shifts to severe contact state near the boundary of static instability onset. When a small static unstable region is generated by decreasing air-bearing stiffness ratio, the occurrence of the low frequency spacing variation is interrupted by temporal flying state (loss of contact). When the static unstable region further increases by decreasing air-bearing stiffness ratio, the spacing variation with low frequencies can appear only at the beginning of contact and immediately jumps to a light contact state and then shifts to a perfect flying state during a long input power range and eventually jumps to a heavy contact state. These calculated results seem to correspond to the actual slider dynamic behaviors at touchdown in the inner, outer and middle diameter regions. The possibility of surfing recording is discussed from the analytical and experimental evidences.

A-2-2 境界面温度を考慮した浮動ヘッドの分子気体潤滑解析 : 周囲気体と温度を考慮した静特性

A new type of flying head slider mechanisms whose air bearing surface (ABS) or disk surface has local temperature distributions such as thermal fly-height control (TFC) and heat assisted magnetic recording (HAMR) have been proposed in order to increase the recording density. Moreover, recently, He-enclosed HDDs have been researched and developed to achieve high performance, because Helium has smaller windage loss and higher heat conductivity than air. Thus, it is becoming increasingly important to analyze the flying characteristics of head sliders over a running disk using the thermo-molecular gas-film lubrication (t-MGL) equation. In this paper, we numerically calculated the static lubrication characteristics for Air/He as working fluid. We also calculated the flying characteristics for various sliders.

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.

7AM2-D-3 液体メニスカス架橋の破断による液体移着特性(基板の表面粗さの影響)(7AM2-D センサと計測)

In recent magnetic storage systems, the spacing between the flying head and the disk has been dramatically decreased to less than 5 nm for realizing ultra-high density recording. Liquid lubricant on the disk is transferred to the flying head slider (pick-up) due to the intermittent contact between the slider and the disk or due to the condensation of the lubricant vapor. The small amount of the lubricant picked-up to the flying head slider will affect the flying characteristics and the read/write performance. In this study, characteristics of liquid transfer due to the breakage of a liquid meniscus bridge are investigated experimentally and theoretically. In particular, the effects of surface roughness on liquid transfer characteristics have been investigated.

Theoretical Model for Lubricant Pickup Considering Disjoining Pressure of Nanometer Thick Film

In recent magnetic storage systems, the spacing between the flying head and the disk has been drastically decreased to less than 5 nm in order to realize ultrahigh density recording. Lubricant on the disk is picked up to the flying head slider as a result of the intermittent contact between the slider and the disk, or due to condensation of the lubricant vapor. We propose a model for the breakage of a liquid meniscus bridge based on the mass conservation of a liquid droplet and derive the volume fraction of the lubricant pickup. In this study, the basic characteristics of lubricant pickup caused by the breakage of a liquid meniscus bridge are investigated theoretically considering the disjoining pressure for a nanometer thick film. The balanced equation for the Laplace pressure and the disjoining pressure is introduced to obtain the liquid meniscus bridge shape and to determine the breakage point of the liquid meniscus bridge. The effects of the radius of curvature of a sphere surface, the receding contact angle, and the thickness of the ultrathin liquid film are discussed.

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.

Lubricant transfer caused by breakage of liquid meniscus bridge

In recent magnetic storage systems, the spacing between the flying head and the disk has been decreased remarkably to less than 5 nm in order to realize ultra-high density recording. Lubricant on the disk is picked up by the flying head slider as a result of intermittent contact between the slider and the disk, or due to condensation of the lubricant vapor. In the present study, the basic characteristics of lubricant transfer (lubricant pick-up) caused by the breakage of a liquid meniscus bridge are investigated experimentally and theoretically. An experimental method by which to measure the volume fraction of the lubricant pick-up has been established. The theoretical results obtained from a simple model proposed by the authors showed good agreement with the experimental results. The validity of the theoretical model was verified based on the experimental results.

Theoretical Model for Lubricant Pick-Up (Breakage of Liquid Meniscus Bridge Due to Elongation in Bridged Direction)

In recent magnetic storage systems, the spacing between the flying head and the disk has been drastically decreased to less than 5 nm in order to realize ultra-high density recording. Lubricant on the disk is picked up on the flying head slider as a result of the intermittent contact between the slider and the disk, or due to condensation of the lubricant vapor. In this study, the basic characteristics of lubricant pick-up caused by the breakage of a liquid meniscus bridge are investigated theoretically. A model for the breakage of a liquid meniscus bridge is proposed and the volume fraction of the lubricant pick-up is derived. The effects of the radius of curvature of a sphere surface and the initial volume of a liquid droplet on the volume fraction of the lubricant pick-up are discussed. The theoretical results obtained from a model that the authors proposed showed good agreement with the experimental results. This model is considered to be useful in the prediction of lubricant pick-up characteristics.

B-2-2 媒質分布を有するディスク面とスライダ間に働くファンデルワールス力の理論解析(B-2 ヘッド・ディスク・インタフェースに作用する相互作用他,口頭発表:ヘッド・ディスク・インターフェイス)

Recording media with grooves such as discrete track media (DTM) and bit-patterned media (BPM) are considered to be some of the most promising media for achieving ultrahigh track densities. Thus, it is becoming increasingly important to analyze the static and dynamic characteristics of flying head sliders over DTM/BPM media using the molecular gas-film lubrication (MGL) equation. In this paper, we established an analysis method of van der Waals forces acting between slider and a disk with distribution of material properties by using Fourier series. The characteristics of the van der Waals forces are quantitatively clarified.

B-2-3 化学修飾したスライダ面を有する浮動ヘッドスライダの開発(B-2 ヘッド・ディスク・インタフェースに作用する相互作用他,口頭発表:ヘッド・ディスク・インターフェイス)

B-2-3 化学修飾したスライダ面を有する浮動ヘッドスライダの開発(B-2 ヘッド・ディスク・インタフェースに作用する相互作用他,口頭発表:ヘッド・ディスク・インターフェイス)

Dynamic Behavior of a Thin Liquid Surface by Repetitively Applied Stress (Numerical Analyses by the Long Wave Equation)

In recent magnetic storage systems, the spacing be- tween the flying head and the disk has been dramati- cally decreased to less than 10 nm for realizing ultra- high density recording. When the flying height is in the same order of the lubricant film thickness, the lubricant deformation will affect the static and dynamic flying char- acteristics of the slider. Therefore, it is very important to investigate the deformation and flow characteristics of the lubricant on the recording disk, especially the dy- namic deformation of the lubricant, which is suffered from the repetitively applied pressure and shear stress by the flying head slider. In this paper, the dynamic behaviors of the ultra-thin liquid (lubricant) surface by the repetitively applied pressure and shear stress under vibrating flying head slider were numerically obtained. The dependence of the liquid surface deformation on the frequency of the stresses, the disjoining pressure and the disk speed were clarified. 1. LONG WAVE EQUATION FOR LIQUID THIN FILM The long-wave equation (1, 2, 3) is derived from the Navier-Stokes equation by applying the lubrication theory and considering the force balance on the liquid- gas interface, the equation is given by 3

A-8 液体超薄膜表面に働く繰り返し応力による表面変形解析 : 線形長波方程式による応答解析(口頭発表:ヘッド・ディスク・インターフェイス)

In recent magnetic storage systems, the spacing between the flying head and the disk has been dramatically decreased to less than 10 nm for realizing ultra-high density recording. Therefore, it is very important to investigate the deformation and flow characteristics of the lubricant on the recording disk, especially the dynamic deformation of the lubricant, which is suffered from the repetitively applied pressure and shear stress by the flying head slider. In this paper, the dynamic behaviors of the ultra-thin liquid (lubricant) surface by repetitively applied gas pressure or shear stress were numerically obtained by frequency domain analysis. The dependence of the liquid surface deformation on the frequency of the stresses and the disk speed were clarified. Transient behaviors to the steady response analysed by time domain analysis were compared with the frequency domain analysis.

A-5 液体メニスカス架橋の破断による潤滑剤ピックアップ特性(口頭発表:ヘッド・ディスク・インターフェイス)

In recent magnetic storage systems, the spacing between the flying head and the disk has been dramatically decreased to less than 10 nm for realizing ultra-high density recording. Lubricant on the disk is picked-up to the flying head slider due to the intermittent contact between the slider and the disk or due to the condensation of the lubricant vapor. The small amount of the lubricant picked-up to the flying head slider will affect the flying characteristics and the read/write performance. In this study, characteristics of the lubricant pick-up due to the breakage of a liquid meniscus bridge are investigated experimentally and theoretically. It was found that the pick-up volume was affected significantly by the difference of the receding contact angles of two solid surfaces. Theoretical results obtained from a model that the authors proposed showed fairly good agreements with experimental results. The present model is considered to be useful for prediction of the lubricant pick-up characteristics.

Numerical Investigation of Bouncing Vibrations of an Air Bearing Slider in Near or Partial Contact

Near or partial contact sliders are designed for the areal recording density of 1 Tbit/in.2 or even higher in hard disk drives. The bouncing vibration of an air bearing-slider in near or partial contact with the disk is numerically analyzed using three different nonlinear slider dynamics models. In these three models, the air bearing with contact is modeled either by using the generalized Reynolds equation modified with the Fukui–Kaneko slip correction and a recent second order slip correction for the contact situation, or using nonlinear springs to represent the air bearing. The contact and adhesion between the slider and the disk are considered either through an elastic contact model and an improved intermolecular adhesion model, respectively, or using an Ono–Yamane multi-asperity contact and adhesion model (2007, “Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region,” ASME J. Tribol., 129, pp. 65–74.). The contact friction is calculated by using Coulomb’s law and the contact force. The simulation results from all of these models show that the slider’s bouncing vibration occurs as a forced vibration caused by the moving microwaviness and roughness on the disk surface. The disk surface microwaviness and roughness, which move into the head disk interface as the disk rotates, excite the bouncing vibration of the partial contact slider. The contact, adhesion, and friction between the slider and the disk do not directly cause a bouncing vibration in the absence of disk microwaviness or roughness.

Erratum: “Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region” [Journal of Tribology, 2007, 129(1), pp. 65–74

Erratum: “Improved Analysis of Unstable Bouncing Vibration and Stabilizing Design of Flying Head Slider in Near-Contact Region” [Journal of Tribology, 2007, 129(1), pp. 65–74