Flying Height Change Research Articles

Effects of Slider Geometry Change on Helium Filled HDD

This paper describes the static characteristics of helium filled hard disk drive for a self-acting two rails flat slider gas bearing. Numerical scheme based on the finite difference with multi-grid multi-level technique were implemented for the ultra-low flying height sliders. The effect of slider geometry change in both crown and camber on flying height have been examined in this research work. The results show that the flying height change is significantly with a few nanometers change in crown and camber. The flying height of helium filled magnetic flat slider head equal to 3.5 nm at trailing edge. The spacing for helium filled hard disk drive is lower than 4 nm when compared with conventional air filled hard disk drive. The increase of slider crown, the flying height increases rapidly but the increase of slider camber, the flying height decreases continuously.

Static and Dynamic Slider Air-Bearing Behavior in Heat-Assisted Magnetic Recording Under Thermal Flying Height Control and Laser System-Induced Protrusion

The air bearing’s response to regions of elevated temperature on its bounding surfaces (the slider and disk) may be an important consideration in the head–disk interface design of heat-assisted magnetic recording (HAMR) systems. We implement the general non-isothermal molecular gas lubrication equation into an iterative static solver and dynamic air-bearing solver to evaluate the effect of localized heating of the air-bearing surface (ABS) due to the near-field transducer (NFT). The heat-dissipating components in our simplified HAMR design are the NFT, laser diode, and thermal flying height control (TFC) heater. We investigate the effect of each HAMR slider component on ABS temperature and thermal deformation and the slider’s flying height. The NFT induces a localized thermal spot and protrusion on the larger TFC bulge, and it is the location of maximum temperature. This ABS temperature profile alters the air-bearing pressure distribution, increasing the pressure at the hot NFT location compared with predictions of an isothermal air-bearing solver, so that the center of the pressure acting on the ABS is slightly closer to the trailing edge, thereby decreasing the pitch angle and increasing the minimum flying height. Other researchers have shown that the NFT’s thermal response time may be much faster than its protrusion response time (Xu et al. in IEEE Trans Magn 48:3280–3283, 2012). The slider’s dynamic response to a time-varying NFT thermal spot on the ABS while the combined TFC and NFT induced thermal protrusion remains constant is investigated with our dynamic air-bearing solver. We simulate the slider’s step response to a suddenly applied ABS temperature profile and a pulsed temperature profile that represents laser-on over data zones and laser-off over servo zones. The sudden (step) or rapid (pulse) increase in ABS temperature induces a sudden or rapid increase in pressure at the NFT location, thereby exciting the air bearing’s first pitch mode. For the slider design and simulation conditions used here, the result of the pitch mode excitation is to alter the position of the center of pressure in the slider’s length direction, thereby changing the pitch moment. In response, the pitch angle and minimum flying height change. The step response decays after approximately 0.15 ms. Because the laser duty cycle is much shorter than this response time, a periodic disturbance is predicted for the center of pressure coordinate, pitch angle, and minimum flying height. The peak-to-peak minimum flying height modulations are relatively small (only up to 0.126 nm); more significantly, the time-averaged minimum flying height increases 0.5 nm for the NFT that reached 208 °C compared to simulations of the isothermal ABS at ambient temperature.

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.

Numerical Simulation of Thermal Flying-Height Control Sliders to Dynamically Minimize Flying Height Variations

Thermal flying-height control (TFC) sliders have been used for active flying height control of hard disk drives. It is of particular interest to investigate if TFC sliders can be used to minimize both repeatable and nonrepeatable flying height variations. To that end, the power input to the heater must be dynamically optimized at each time step in order to minimize changes in flying height. In the current study, a numerical procedure is implemented to simulate the time dependent response of a TFC slider to changes of the heater element power input. The dynamic Reynolds equation and slider equilibrium equations are solved simultaneously to determine the dynamic change in flying height as a function of time. The change of thermal protrusion as a result of the optimized power input to the heater is computed using a TFC slider finite element model. The reduction of flying height variation is studied using past and present flying height histories and optimization of the power input to the heater. It is shown that the dynamic approach can be successfully used to minimize both repeatable and nonrepeatable flying height changes at the hard disk interface.

Air Entrapment in Nanometer-Thick Lubricant Films and its Effect on Slider Flying Height in a Hard Disk Drive

Experimental data are presented, showing that the flying height of a slider in a hard disk drive can be altered by the chemical nature of the molecularly-thin lubricant film on the disk surface. It is suggested that this effect is likely due to entrapment of the air molecules, both nitrogen and oxygen, within the lubricant film, which results in pressurization loss within the air bearing gap, and lower slider flying height. For the two advanced multidentate lubricants reported in this study, the amount of flying height change is almost insignificant for one of them, but amount to about 0.7 nm, i.e. a significant fraction of the magnetic spacing budget for the other. Bulk air solubility data suggest that the magnitude of this effect is diminished for lubricant molecules with a lower density of backbone ether linkages.

Dynamic Flying Height Adjustment in Hard Disk Drives Through Feedforward Control

A dynamic model of the resistance heater element in a thermal flying height control (TFC) slider of a hard disk drive is identified and used for dynamic flying height control. Experimental data obtained on a spin stand and a generalized realization algorithm are used for identification of a discrete-time dynamic model of the thermal actuator. The flying height change is measured in two different ways: using servo burst information written onto the disk surface and using information written in the data sectors only. The resistance change of the thermal actuator based on the input power level is measured. Based on the identified discrete-time model of the heater and using convex optimization techniques, a computational scheme is proposed to obtain optimized feedforward input profiles to the heater element that minimize repeatable flying height variations and enable low flying heights.

Optimal Feed Forward Profiles for Dynamic Flying Height Control in Hard Disk Drives

AbstractA dynamic model of the resistance heater in a thermal flying height control (TFC) slider of a hard disk drive is identified and used for dynamic flying height control. Experimental data obtained on a spin stand and the generalized realization algorithm are used for identification of a discrete-time dynamic model of the resistance heater (thermal actuator). The flying height change is measured using servo burst information written onto the disk surface. Based on the identified discrete-time model of the heater and convex optimization techniques, a computational scheme is proposed to obtain optimized feed forward input profiles to the heater element that minimize repeatable flying height variations and enable low flying heights.

Flying Clearance Distribution With Thermal Flying Height Control in Hard Disk Drives

Flying clearance distribution with thermal flying height control (or thermomechanical actuation) is characterized. Especially, factors contributing to variation in the flying clearance are identified based on the flying height change profiles taken from the burn-in process of hard disk drives and Gage R&R (repeatability and reproducibility) test of touch down repeatability. In addition, the effect of static temperature compensation scheme on the flying clearance distribution is investigated, and the disadvantage of static adaptation to temperature change is identified. In order to avoid early catastrophic head-disk interface failures due to poor static temperature compensation, dynamic clearance adjustment is necessary whenever environmental condition changes. Otherwise, static temperature compensation using the individual temperature sensitivity values of each head needs to be applied.

HDD 액추에이터의 스웨이징성능향상을 위한 베이스플레이트 최적설계

In the manufacturing process of HDD, ball swaging method is commonly used to joint the Head Gimbal Assembly(HGA) with the arm of the actuator. The hub on the HGA is placed into the hole of the actuator arm, and the hub and arm is bonded by the pressure of steel ball. The pressure for plastic deformation on the baseplate causes the undesirable deformation on HGA, such as tilting, flying height change of head. After obtaining the key parameters that have large sensitivity on the swaging process, the optimal shape of baseplate is proposed to increase the static performance during swaging process. Contribution of the proposed design for the swaging performance is verified by contact simulation with elasto-plastic deformation.

Thermal effect on slider flight height in heat assisted magnetic recording

In this paper, the real time thermal effect of the heat assisted magnetic recording (HAMR) on the slider flying height is investigated with HAMR spin stand. In the experiment, a modulated laser beam is used to heat the media and the slider vibration is measured with laser Doppler vibrometer. The slider vibrations at different laser modulation frequencies and different laser powers are investigated and near 0.2nm flying height change is observed. Analysis shows that the main reason to cause the flying height change results from the disk surface thermal distortion caused by thermal expansion.

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.

2102 磁気ヘッド素子突出低減のための熱変形解析(第3報)(要旨講演,情報機器コンピュータメカニクス1)

The rapid increase in the recording density of magnetic disk drives has required decreasing the flying height of magnetic head sliders to approximately 10nm. Under such low flying height conditions, however, the heat generated by the high-frequency current in the writer coils and the rise in the ambient temperature both cause local protrusion of head elements. Such protrusion reduces the flying height below the design value, thus reducing the safety margin for head/disk interference. To analyze this problem, the heat transfer in the head slider, the thermal deformation of the head, and the flying height changes of the slider due to the deformation were numerically simulated. The parameter study showed that short pole and shields cause a smaller ambient-temperature-induced protrusion but a larger write-current-induced protrusion, i.e., a trade-off relationship exists.

Simulation of Thermal Protrusions on Magnetic Head Elements

Under recent low flying height conditions of magnetic head sliders, both the heat generated by the high-frequency current in the write coils and the rise in the ambient temperature cause local protrusion on head elements. Such protrusion reduces the flying height below the design value, thus reducing the safety margin for head/disk interference. To analyze this problem, we numerically simulated the heat transfer in the head slider, the thermal deformation of the head, and the flying height changes of the slider due to the deformation. The typical temperature distribution obtained from the simulation agrees well with reported experimental results. The simulation results show that decreasing the alumina base coat thickness can reduce the magnitude of a protrusion. For write-current-induced protrusions, the reduced flying height is partly compensated by increased air pressure on the air-bearing surface. However, almost the entire magnitude of an ambient-temperature-induced protrusion translates into flying height reduction.

Dynamic in-situ measurements of head-to-disk spacing

The read signal from a magnetoresistive (MR) head is used to measure the dynamic head-to-disk spacing (flying height) inside of an operating disk drive. Changes in flying height modulate both the envelope of the read signal and its mean value. While the envelope is related to the magnetic spacing, the mean value is a function of the thermal spacing. The thermal spacing signal is the result of Joule heating whereby some of the thermal energy generated in the MR head is dissipated into the air film between the head and disk. Changes in head flying height alter the heat transfer and hence the temperature and resistance of the head. The thermal and magnetic signals are separable and give complimentary information about the flying height. To accurately measure flying height changes using the thermal signal when the head is inside a disk drive requires that the signal distortion caused by the head preamplifier and high-pass filter be corrected. The thermal signal, unlike the magnetic signal, is not sensitive to track misregistration making it more accurate for dynamic flying height measurements. In-situ dynamic flying height measurement results using both thermal and magnetic methods are discussed.

Flying height measurement while seeking in hard disk drives

A new technique has been developed to measure flying height changes during a high velocity seek in a fully operational hard disk drive. During a seek, a change in the flying height of the read-write head results from the change in direction and speed of air flow under the air bearing surface (ABS). The application of the Wallace spacing loss formula to peak amplitudes of the magnetic recording signal acquired as the head crosses tracks during the seek forms the basis of the method. The method also requires a means to precisely measure the location along the track at which each track crossing occurs. This additional information is used to remove the variation in the amplitude of the magnetic readback signal which is due to surface roughness and magnetic inhomogeneity of the disk surface and the fact that each seek operation crosses the track in a different circumferential location. Plotting the peak amplitude versus the track crossing location for several thousand seeks provides a profile of the roughness variations of the disk surface over a short length of track. Except for a fixed amplitude offset, the track profile acquired when crossing a particular track from the inner diameter (ID) to the outer diameter (OD) of the disk was the same as that acquired during OD to ID direction. This amplitude offset allows calculation of the difference in fly-height between the three cases of ID/spl rarr/OD seek, OD/spl rarr/ID seek, and track following. This measurement technique can reliably resolve dynamic fly-height changes of 0.05 /spl mu/in. Comparison of the measured data to numerical air bearing simulations will be presented.

Flying height change during seek operation for TPC sliders

The change in the flying height during track seeking is investigated for a TPC slider. A quasi-static approach is used in the numerical simulation of the track seek. We find that at high seek velocities the skew angle effect dominates over the inertia effect. The flying height change is the greatest at the MD. We also found that the deeper etch results in more loss of flying height. Quasi-static measurement is presented. The decrease in the flying height is qualitatively verified through the use of an AE sensor signal in the frequency domain.

Programmable Air Bearing Sliders for Magnetic Storage

This paper introduces a novel approach for low flying sliders. The authors propose a slider with a programmable air bearing that permits it to be flown high or low on demand. This is achieved by changing the shape of the slider body with the use of piezoelectric materials. The design of the slider is presented along with simulation results that indicate a flying height change from 186 to 53 nm with a 80 volt excitation. Experimental data shows a slider changing height in 500 μsec under very stable conditions. The advantages of electrically controlled flying heights are discussed. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 8–10, 1990

Supersmall flying optical head for phase change recording media

A supersmall optically switched laser (OSL) head is proposed. A laser diode attached to an air bearing slider forms a complex cavity together with a recording medium, and its light output is detected by a photodetector placed at the other end of the laser facet. Data signals and track error signals read from the sampled servo marks are successfully detected. The signal amplitude variation caused by the flying height change is much reduced, and the SNR is increased to 36 dB (40 kHz to 20 MHz for a phase change medium) by decreasing the reflectivity of the laser facet facing the medium to <5%.