Thermal Flying Height Control Slider Research Articles

Characterization of slider-lubricant interaction with tribo-current

Lube-surfing recording combined with thermal fly-height control (TFC) technology is considered as a promising head-disk interface (HDI) scheme for further increasing magnetic areal density to 5–10 Tbits/in2. To realize this alternative technology, however, a lot of tricky issues are required to be solved. Among them, how to characterize the flying of slider in the lubricant or light lube-contact by the slider is probably one of the tough but inevitable challenges. In this study, the slider/lubricant/disk contact induced tribo-current is investigated with a modified media-tester in which the TFC slider is electrically isolated with the rest of the tester. The measured tribo-currents versus the heater voltages or the powers to the slider’s heater clearly indicate three different intensity regions of tribo-current, by which the three different contact types, namely, non-contact, lube-contact and solid-contact can be differentiated clearly. This method provides a promising way for accurately studying of lube-surfing recording.

Thermal protrusion induced air bearing frequency variations

The thermal flying height control sliders are widely used in hard disk drives. This paper studies the relationship between the air bearing frequencies and the thermal protrusion values of a thermal flying height control slider by simulation. Simulation results show that the second pitch mode of the slider increases significantly as the thermal protrusion increases. This feature could be used to in situ monitor the thermal protrusion values and the flying heights of the slider. Discussions on all the air bearing frequency modes are given, and the reasons of the frequency variations due to thermal protrusion are explained in details.

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.

Servo signal processing for flying height control in hard disk drives

A novel method of measuring the relative head-medium spacing based on a measurement in the servo sectors is developed and simulated using a read back signal model. The spacing measurement is tested experimentally on a spin stand where the flying height is varied using the resistance heater element in a thermal flying height control slider. In addition, voltage step response measurements were obtained. The data were used to perform system identification and estimate the dynamics of the thermal actuator. The model can potentially be used for thermal flying height control.

Thermal Flying-Height Control Sliders in Air-Helium Gas Mixtures

Filling hard disk drives with air-helium gas mixtures instead of pure helium can balance performance improvement, such as reduced power cost, increased capacity and improved reliability, against manufacturing cost increase. A consistent approach is proposed here to investigate the flying performance of thermal flying height control sliders flying in air-helium gas mixtures. It is found that the smallest power required for a designated flying height appears when the gas mixture is composed of about half helium and half air. The proposed numerical approach can also find application in investigating a slider's flying performance in a humid environment.

Effects of Altitude on Thermal Flying-Height Control Actuation

Thermal flying-height control (TFC) is now a key technology used in hard-disk drives (HDD) as an effective way to push the magnetic spacing to sub-5 nm. Precise control of the TFC sliders’ actuated flying-height (FH) is a major consideration in improving the read/write capability as well as reducing the reliability problem. In this paper, we investigate the response of TFC sliders to altitude changes with a focus on the variation of actuated FH. Numerical and experimental results both indicate an increase in the actuated FH at higher altitudes. Simulations show that the increased TFC protrusion and less air bearing pushback on sliders at higher altitudes contribute to this increase. This study is of practical importance for improving heater and air bearing surface design to reduce the TFC sliders’ sensitivities to altitude changes.

Predicting the flying performance of thermal flying-height control sliders in hard disk drives

Thermal flying-height control (TFC) sliders have been recently used in commercial hard disk drives (HDDs) to increase the HDDs’ capacity. The design of this new class of sliders depends on the numerical prediction of their flying performance, which requires a model for heat flux on the surface of the slider facing the disk. The currently widely used heat flux model is based on a first order slip theory and is believed to lack sufficient accuracy due to its limitation of applicability. This paper implements an improved heat flux model and compares numerical predictions of a TFC slider’s flying performance based on these two models with experiments. It is found that the numerical prediction based on the currently used model has a relative error less than 10% for a state-of-the-art TFC slider. It is suggested that the currently used model might cause large errors for the sliders which do not have a pressure peak near the transducer.

The Effect of Thermal Radiation on Thermal Flying Height Control Sliders

Thermal flying height control (TFC) technology has recently been applied in hard disk drives. In calculating the thermal deformation caused by the resistance heater, radiation as predicted by Plank's blackbody radiation law is usually neglected because of its small magnitude compared to conduction. Recent experimental investigations have shown that Planck's law breaks down in a small gap of nano-scale dimensions and that the heat transfer coefficient at distances on the order of nano-meters can exceed Plank's blackbody radiation by more than three orders of magnitude. This paper investigates numerically the effect of enhanced thermal radiation for thermal flying height control sliders at very small flying heights.

Simulation of Flying Height and Response Time of Thermal Flying Height Control Sliders With Thermal Insulators

Thermal flying height control (TFC) 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 flying height and response time of TFC sliders with single and dual TFC heaters and thermal insulators. Simulation results show that the presence of a thermal insulator has little effect on the response time of thermal protrusions. In addition, the effect of the dimensions of a TFC heater on the flying height and thermal response time is important. For a given heater power, the dual TFC heater design with thermal insulators can provide a very flexible control over flying height and response time of TFC sliders.

Investigation of Flying-Height Stability of Thermal Fly-Height Control Sliders in Lubricant or Solid Contact with Roughness

When the magnetic spacing in hard disk drives is reduced to sub-3 nm, contact between the slider and disk becomes inevitable. Stability analysis is used in this study to investigate the head–disk interface (HDI) stability of thermal fly-height control (TFC) sliders in light contact with the disk lubricant or solid roughness. We implement an improved DMT model with sub-boundary lubrication into the CML air bearing program and analyze the stability of equilibrium states of a TFC slider under different thermal actuations. It is found that stability is lost when the slider penetrates deeper into the lubricant layer, due to a fast growth in the adhesion force, and it is restored when the solid roughness contact develops. In addition, the critical point for the onset of this instability and the range of this instability region is found to vary with lubricant thickness and protrusion surface steepness, while keeping the air bearing design the same.

Optimization of thermal fly-height control slider geometry for Tbit/in2 recording

Magnetic storage advances including thermal fly-height control (TFC) technology were able to reduce the clearance between the read/write elements of the slider and the disk surface to increase the recording density of hard disk drives without compromising the stability of the head–disk interface (HDI). Sliders employing TFC technology are designed for flying recording and can yield clearances of few nanometers. However, it is estimated that TFC technology alone cannot provide the even smaller clearances necessary to achieve Tbit/in2 recording densities primarily due to the presence of instability-inducing vibrations at the HDI. In this work we perform optimization of the geometry of TFC technology sliders to achieve extremely high-density recording. We propose a flyability parameter coupled with a dynamic, contact mechanics-based friction model of the HDI that accounts for TFC geometry and its influence on the HDI dynamics. Optimization results are analyzed and an operating actuation range is identified that can yield Tbit/in2 recording densities with Angstrom-level clearance and minimized vibrations while also accounting for manufacturing and operational tolerances. This allows for light (lubricant) contact or ‘surfing’ recording. The proposed methodology can be used to reduce wear at the interface and investigate the feasibility of contact recoding.

Slider Dynamics in the Lubricant-Contact Regime

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Thermal fly-height control sliders that are capable of subnanometer level actuation are used to investigate the vertical, down-track, and off-track slider dynamics in slider-disk lubricant contact. Slider-lubricant contact introduces significant excitation in all three directions, and the slider dynamics is dependent on the degree of lubricant-contact. The lubricant surface has a significant role in determining the physical clearance and slider fly-height. While slider-lubricant contact may be successfully achieved by carefully controlling the heater power, improved slider designs and associated heater induced protrusion profiles are necessary to successfully mitigate contact induced vibrations and meet the challenges for future hard disk drives. </para>

Investigation of Mechanical Clearance Change with Thermal Flying-height Control Slider at High Altitude

Clearance change between a magnetic head with a thermal flying-height control (TFC) function and a magnetic disk at high altitude was investigated. To clarify the change of head-disk clearance in the case of TFC actuation at high altitude, head-disk clearance change was experimentally evaluated as a function of altitude and head-disk clearance by using a TFC function. The evaluation results show that the head-disk clearance change is larger in the case with TFC actuation at high altitude than that in the case without TFC actuation.

Thermal flying-height control sliders in hard disk drives filled with air-helium gas mixtures

This letter employs established approaches to calculate the physical properties of the air-helium gas mixtures and investigates the thermal flying-height control slider’s flying performance in these environments. It is found that at a fixed heater power, the slider’s flying height first increases and then decreases with the fraction of helium in the gas mixture due to the combined effects of changes in the mean free path, viscosity, and thermal conductivity of the gas mixture with helium content. These findings, together with the proposed approach, are useful for future designs of sliders in air-helium mixtures.

Slider-Disk Contact Characterization Using a Thermal Fly-Height Control Slider

The interaction between the thermal fly height control (TFC) slider and disk is investigated by reader signal with laser Doppler vibrometer and acoustic emission signals used as a reference. When magnetic transition is written on the disk, the first air bearing peak of the reader signal is increased. With increase of the driving voltage to the heater, a frequency shift and harmonics are observed. The lubricant ripples caused by the thermal protrusion induced contact were observed, and the ripples follow the frequency shift with increase of the driving voltage. When the driving voltage to the heater is increased to a state such that higher order harmonics are observed in the frequency spectra, the lubricant is unable to fully recover.

Slider–Lubricant Interaction and Corresponding Tribocurrent

The tribo-current phenomenon is one of the important effects associated with intermittent slider-disk interaction. By the experiment to simulate interaction with a conductive probe and measure the induced current simultaneously using a conductive atomic force microscopy, some critical points, which divide the probe-sample interaction into probe-disk, probe-lubricant, and noncontact, can be observed. Similar phenomena were also observed when flying a thermal flying-height control slider over a specially prepared disk. This proposed technique might be applied to ascertain the dynamic interaction exactly between the slider and the lubricant, which would be the critical issue for accurate studying of ldquofly- and lubricant-contact recordingrdquo approaches in which the slider will be in continuous contact with the lubricant.

Numerical Simulation of a Thermal Flying Height Control Slider With Dual Heater and Insulator Elements

Thermal flying height control (TFC) 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 flying characteristics of a new TFC slider design with two heater and insulator elements. The flying height reduction of the slider is determined as a function of the placement and thermal characteristics of the heater and insulator elements. Simulation results show that for a constant heater power, the dual TFC heater with thermal insulators achieves a larger flying height reduction at the read/write element than the single TFC heater design.

Particle Contamination on a Thermal Flying-Height Control Slider

Particle contamination on a slider in a hard disk drive (HDD) affects the HDD’s reliability. With the introduction of the thermal flying-height control (TFC) slider, the temperature in the head–disk interface (HDI) becomes non-uniform, which induces a temperature-gradient dependent force on particles moving in the HDI. The present article investigates the effect of this force, the so called thermophoretic force, on a particle’s motion in the HDI as well as its effect on particle contamination on the TFC slider. By numerical simulation of the particle’s trajectory together with an analytical analysis, we show that the thermophoretic force is always negligible compared to the Saffman lift force, which points to a direction parallel to the thermophoretic force. We conclude that the current particle contamination simulator without any thermophoretic forces included would not be significantly altered by the inclusion of these forces.

Optimization of micro-thermal actuator for flying height control

In this paper, a three dimensional finite element model of an entire thermal flying height control slider (TFC) with a detailed read/write transducer structure is created. We used the model to perform a thermal-structural coupled field analysis in order to investigate the transient thermal and protrusion response of the TFC slider. Parameter studies are conducted to identify the dominant parameters to reduce the response time of the heat transfer and thermal protrusion of the actuator. The simulation results show that increasing the heat transfer on the air bearing surface (ABS), reducing the distance from the heater to the ABS, reducing the thickness of alumina of the slider body and replacing the slider materials with Si/SiO2 can reduce the response time of the heat transfer and thermal protrusion around the actuator. But the effects of the input power and modifying the thermal properties of the shield materials are very small.

Thermal insulator design for optimizing the efficiency of thermal flying height control sliders

This paper is concerned with the optimization of the location and size of thermal flying height control (TFC) elements in magnetic recording sliders. It investigated the performance of a so-called thermal insulator positioned adjacent to the heater to control the temperature distribution inside the slider. A parametric study of the thermal conductivity, thickness, and location of the thermal insulator was performed to improve the thermal actuation and thermal efficiency. Optimization of the dimensions and properties of a thermal insulator was found to achieve a substantial reduction in the flying height of the read/write elements. In addition, the magnitude of the thermal actuation was found to increase.