Experimental study of slider dynamics induced by contacts with disk asperities

Vertical vibrations at the slider leading edge exited by a disk asperity were investigated in a drive level system, using laser Doppler vibrometry and acoustic emission (AE) sensors. The flying height change at the leading edge of a thermal flying-height control slider was measured for different power inputs to the heater element. The maximum spacing change at the slider leading edge was found to be about 4 nm for an asperity of 26 nm height and 1.1 μm width. A method was investigated to produce “artificial asperities” on a disk surface using a nano-indentor. The geometry of the “artificial asperities” was characterized using an atomic force microscope. In addition, a spin stand was used to analyze the AE signal of slider vibrations induced by contacts with the “artificial asperities”. First and second pitch modes of the slider were observed.     

Numerical investigation of slider dynamics induced by contacts with disk asperities

A time dependent Reynolds equation simulator combined with a finite element-based transient contact model between a slider and a disk asperity is used to study slider dynamics induced by contacts with disk asperities. The flying height change at the trailing edge of the slider is investigated as a function of asperity height, asperity diameter, and the spacing between the thermal protrusion of a thermal-flying control slider and a disk asperity. The effect of material properties of the disk asperities is studied. Slider vibrations corresponding to the first and the second pitch modes are excited by disk asperities.     

Frictional heating effect on thermal protrusion in head disk interface

The frictional heating effect on the clearance loss in the reader and writer elements of hard disk drive was investigated by conducting a coupled simulation between the air bearing dynamics and the head thermal-mechanics using a frictional heating model. The frictional heating power was obtained through experimentation. In this experiment, the frictional heating power was quantified based on the giant magneto-resistance, which varies with the frictional heating, and the frictional heating induced temperature rise was 15 °C. By matching it with the simulated relationship between the temperature rise and frictional heating power, we found that the frictional heating power was about 3 mW. The simulation results at this power indicated when a touchdown (TD) occurs on the wrap-around shield (WAS), the frictional heating can cause a larger additional protrusion on the writer element, which overestimates the reader topography loss to 0.32 nm, and when the TD point is on leading pole (LP), the frictional heating can cause a larger additional protrusion on the reader element, which underestimates the reader topography loss to 0.2 nm. However, the amount of protrusion caused by frictional heating in the reader and writer elements when TD point in on the WAS and LP is almost the same at only a small difference of 0.052 nm. Finally, we analyzed the frictional heating effect on the clearance in the reader and writer elements. The clearance in the pullback state is not equal to the spacing caused by the TFC pullback power, but the sum of the clearance change caused by the TFC pullback power and the clearance change caused by the frictional heating power, and the clearance change in the reader and writer elements caused by frictional heating are different. Therefore, it is very important to account for the frictional heating effect when designing the reader/writer clearance.     

Contact between a thermal flying height control slider and a disk asperity

Contact between a thermal flying height control slider and an asperity on a disk is investigated using finite element analysis. The finite element model developed accounts for transient elastic–plastic deformation and heat generation due to frictional heating. Plastic deformation and temperature rise of the read/write element are determined as a function of flying height of the slider, location of the read/write element as well as material properties of typical disk asperities. The model shows good agreement with experimental data. Significant plastic deformation and temperature rise were observed in the shield and alumina regions of the slider. Hard and stiff disk asperities, such as alumina asperities, result in more damage to the slider than soft and compliant nickel-phosphorus ones.     

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.     

Visualisation of size-dependent particle deposition in a slider/disk interface

 As contamination will play a significant role in slider-based magneto-optical (MO) data storage systems, a novel experimental technique is proposed to enhance contamination visualisation. This technique is based on using mixtures of different sizes of monodisperse, fluorescent, spherical, polystyrene-latex particles, each size having a different fluorescent colour. Apart from the relatively easy visualisation of size-dependent particle deposition, validation of numerical simulations of particle deposition is also enhanced. The experimental results obtained with the fluorescent particles, which are soft, are compared with results obtained when harder, spherical, silicate particles are used. It is demonstrated that these hard particles are simply embedded in the polycarbonate disk, and cause no significant damage to, or contamination of, the slider. The soft fluorescent particles are not embedded, but smears and scratches on the disk surface are observed. The slider contamination is much more severe with the soft particles than with the hard silica particles, however, also when a hard glass disk is used. This indicates that the MO slider cannot simply be protected from contamination with soft particles by increasing the hardness of the disk. As many soft particles are present in the atmosphere, additional slider features will be needed to reduce slider contamination, and thereby the risk of system malfunction. Future numerical support of the development of such features is believed to be enhanced with the described experimental validation method. Received: 14 February 2002/Accepted: 24 April 2002 The author would like to thank, in random order, Jaap den Toonder, Guus Braun, Frank Penning, Gerard Hoeymans, Bas van Rens, Ferry Zijp, Martin van der Mark, and Geert Koenen, without whom this work would not have been possible.     

Reduction in lubricant pickup by bias voltage between slider and disk surfaces

We studied the effect of bias voltage between slider and disk surfaces to reduce lubricant pickup by the slider. A perfluoropolyether (PFPE) lubricant film, which is coated on the disk surface, has been considered to be charged to a negative voltage by the airflow on the rotational disk surface. Because the PFPE lubricant film is negatively charged, the lubricant pickup should be reduced by a bias voltage with a negative voltage on the slider surface. We confirmed changes in the lubricant pickup in a lubricant pickup test conducted at different bias voltages. A positive voltage of the slider accelerated the lubricant pickup, whereas a negative voltage reduced it.     

Influence of disk curvature on slider attitude under operational shock conditions for a 2.5-in. hard disk drive

Recently, the number of disks in hard disk drives has increased, and the gap between the slider and disk has decreased. These changes make the contact between the ramp and disk easily. External shock and ramp–disk contact can cause change in disk curvature. Such a change in disk curvature affects the air bearing pressure between the slider and disk. However, disk curvature has not been considered in the previous research. Thus, in this study, we investigated the influence of disk curvature on slider dynamics. Disk curvature was calculated from a transient shock analysis, and was then applied to slider dynamic analysis. As a result, disk curvature reduced the shock performance, by decreasing the minimum flying height and increasing the pitch and roll angle of the slider.     

Mechanical stability of the interface between a padded slider and magnetic recording disk

Contact state, friction, and meniscus load between a padded slider and a smooth disk are discrete; friction is determined by the number of pads in contact and the meniscus load acting at each pad. By inducing frictional changes through varying sliding direction, we force the slider from one stable state to another and infer which pads are in contact from the corresponding changes in friction. We find the stability of a given contact state is influenced by friction coefficient, pad location, meniscus load, applied mechanical loads and applied moments. A model is proposed to account for these effects.     

Vibration analysis of a contact slider/gimbal of a flexible disk drive

 To design contact-type gimbal system for a newly developed removable flexible disk drive called Card size flexible disk drive (CFDD) (Shinpuku et al., 2001; Ryoson et al., 2001), the gimbal's vibration characteristics in the disk-rotation direction were measured and simulated using FEM. To determine the relationship between vibration and friction in the head disk interface (HDI), a hard disk was also used. The friction characteristics were inserted into the FEM model based on the results. The gimbal was modified to suppress vibration amplitude to half in both simulation and experiment. Received: 5 July 2001/Accepted: 1 November 2001 Paper presented at the 12th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 28–29 June, 2001.     

Silicon tip sharpening based on thermal oxidation technology

Thermal oxidation at low temperatures (below 1050 °C) is widely used in the microfabrication of sharp silicon tips. However, the influences of the oxidation temperature on morphology of the tips have not been investigated in detail. This work systematically studied the dependence of tip profile on the oxidation temperature. Thermal oxidation were performed in four groups at 900, 950, 1000 and 1050 °C. The results show that a trade-off between the tip aspect ratio and diameter should be taken into account when choosing the oxidation temperature. The optimized oxidation temperature to make tips with small apex, high aspect ratio, and smooth surface is around 1000 °C. The tip with a diameter of 6.3 nm was realized through oxidation at 1000 °C.

     

Experimental study on slider dynamics during touchdown by using thermal flying-height control

To investigate the possibility of further lowering the clearance in head?Cdisk interface systems, slider dynamic behavior during a touchdown sequence with a thermal flying-height control (TFC) function was investigated by using a spinstand-level evaluation utilizing an acoustic emission (AE) sensor and a laser Doppler vibrometer (LDV). Experimental results demonstrated that off-track vibration was easier to excite by head?Cdisk contact at the beginning of head?Cdisk contact. We then confirmed that the amplitude of pitch-mode vibration in the flying-height direction increased and sway-mode vibration in the off-track direction decreased when increasing heater power during the touchdown sequence. Moreover, we found that the peak frequency of pitch-mode vibration shifted to a higher frequency under over-push conditions. Time?Cfrequency domain analysis results showed that the peak shift occurred at several locations during a disk rotation. The mechanism of the peak shift is attributed to the increase in stiffness at the head?Cdisk interface (HDI) due to solid?Csolid contact or mode change occurred in such regions. During the touchdown sequence, the friction force at the HDI continues to increase, even though slider vibration and AE signal decrease when heater power is increased. The friction force at the HDI needs to be decreased to achieve further low-clearance HDI.     

Iteration method for analysis of write-current-induced thermal protrusion

This article presents a detailed iteration method for coupled air bearing and thermal-structure analysis, and introduces a node-to-node schematic for mapping the heat transfer coefficient into the thermal-structure analysis as boundary conditions. A three-dimensional finite element model is developed. The heat transfer coefficient on the air bearing surface of slider is calculated by a quasi-steady heat transfer model and applied to the thermal-structure analysis through the proposed node-to-node mapping schematic. The results show that the iteration process is indispensable for the air-bearing-thermal-structure analysis under high write power, but changeable under low write power. Among iterations, the values and distribution of the heat transfer coefficient vary significantly, especially around the protruding regions. The corresponding thermal protrusion induced by write current and its effects on flying attitude are different and the difference is increased with the heating power. For the application of high heating power and large thermal protrusion, at least a three-time iteration of the heat transfer coefficient is needed.     

The effect of air bearing contour design on thermal pole-tip protrusion

Thermal flying height control has recently been implemented in magnetic recording disk drives to reduce the flying height at the read/write element of magnetic recording sliders. This paper investigates the effect of air bearing contour design on thermal pole-tip protrusion and flying characteristics of magnetic recording sliders. A number of air bearing surface designs are examined to study the relationship between air bearing surface design and efficiency of thermal pole-tip protrusion.     

Simulation of thermal flying height control slider with built-in contact sensor

This work investigates the piezoelectric contact sensor in the thermal flying height control (TFC) slider. A finite element model is built for the thermal flying height control slider with a piezoelectric contact sensor, which is used to detect the contact between the slider and disk. A constant force is applied at the maximum thermal protrusion point of air bearing surface. The simulation results show that the ZnO sensor with shear-mode is more sensitive to contact force than that with transverse-mode. The sensitivity of contact sensor can be increased by reducing the cross-sectional area of sensor, increasing the thickness of sensor, and choosing a short distance of sensor to air bearing surface. In addition, the thermal-stress effects from TFC heater on contact sensor are significantly large and the amplitude of thermal-stress inducing output voltage is orders larger than that induced by contact force. However, by optimizing the distance of sensor to ABS, it is possible to eliminate the thermal-stress effects. Finally, the response time of thermal-stress induced electrical voltage of contact sensor is about 0.3?ms.     

Numerical study on the effects of linear protrusion on flow-induced carriage excitation force in hard disk drives

The positioning accuracy of magnetic heads needs to be improved to increase the recording capacity of hard disk drives. In our previous study, experimental results confirmed that the head-positioning error could be decreased by attaching linear protrusions on the leading edge of the carriage arms. However, the mechanism underlying the phenomenon has not been elucidated. In the present research, we evaluated the effect of leading-edge protrusions on the flow-induced carriage excitation force using computational fluid dynamics (CFD) analysis and the Hilbert–Huang transform (HHT). We prepared two carriage-arm models, with and without linear protrusions, on the leading edges of the arm, and performed the CFD analyses. Subsequently, we conducted a frequency analysis by applying HHT to the simulated disturbance torque time-series of each carriage-arm model and compared the results. Our results show that the leading-edge protrusions decrease the disturbance torque due to the flow fluctuation between the arm and disk and in the wake flow, although the low-frequency disturbance torque due to the pulsatile flow can be deteriorated.

     

Linear protrusion structure on carriage-arm surface for reduction of flow-induced carriage vibration in hard disk drives

One of the major contributors to head positioning errors is carriage vibration in low frequency due to an air flow caused by disk rotation. It is necessary to suppress the disturbance for Hard Disk Drives (HDDs) to have more capacity. We experimentally studied a reduction in the flow-induced carriage vibration using linear protrusion structures by putting wires on carriage arms. This study was carried out using 2.5?inch HDD which has high rotational speed of 10,000?rpm. We measured position error signals (PES) and compared with a conventional carriage. From the experimental results, we found that the linear protrusion structure was effective to reduce the carriage vibration. Leading edge wire configuration and 2 linear protrusion configuration improved average non-repeatable position errors (NRPE) by 6.9% and 6.4%, respectively.