Magnetic Recording Slider Research Articles

Temperature-Induced Near-Field Transducer Failure in Heat-Assisted Magnetic Recording

We have studied the reliability of a near-field transducer (NFT) embedded in a magnetic recording slider used for heat-assisted magnetic recording (HAMR) in hard disk drives with a linear velocity of 20 m/s. The NFT head structure and the disk are separated by an air film of 2 nm thickness. In this article, the magnetic write width and amplitude of the written magnetic signal on the disk are used as a “health monitor” for the reliability of the NFT under long-term thermal exposure. The results show that the reliability of the NFT head structure sharply decreases with increasing temperature of the NFT but depends only slightly on the media temperature.

Investigation of Head/Disk Contacts in Helium–Air Gas Mixtures

The shock response of a pico-type magnetic recording slider in different helium–air gas mixtures is investigated numerically. A finite element-based air bearing simulator and a slider/disk contact model including van der Waals and friction forces are coupled to determine the contact characteristics between slider and disk. The minimum flying height and the maximum contact force are studied as a function of helium percentage and disk velocity. The results show that the dynamic performance of the slider is not affected substantially as long as the helium percentage is <50 % but is increasingly more affected if the helium percentage becomes larger than 50 %.

Investigation of Lubricant Transfer between Slider and Disk Using Molecular Dynamics Simulation

A model for lubricant transfer from a rotating magnetic recording disk to a magnetic recording slider is developed using molecular dynamics simulation. The combined effect of disk velocity and local air-bearing pressure changes on lubricant transfer is investigated. The simulation results indicate that local pressure changes in the absence of disk circumferential velocity can cause lubricant redistribution on the disk, while local pressure changes on a moving disk can result in lubricant transfer from the disk to the slider. The amount of lubricant transferred from the disk to the slider and the lubricant buildup on the disk are a function of the local pressure change and disk velocity. The amount of lubricant transferred from the disk to the slider and the height of lubricant buildup on the disk surface decrease with an increase in the number of functional groups of the disk, a decrease in the local pressure change, and a decrease in the disk circumferential velocity.

An X-ray Photoelectron Spectroscopy Investigation of Redeposition from Fluorine-based Plasma Etch on Magnetic Recording Slider Head Substrate

Re-deposition is an etched by-product in the Reactive Ion Etching (RIE) process well known the causing dirty on etching work piece. In this work, we aim to investigate the re-deposition of fluorine-based plasma etch on the Al2O3-TiC substrate. To select the suitable chemical solution for cleaning, it's necessary to know that the chemical bonding of the re-deposition material. Thermodynamic theory is used to predict the potential of re-deposition compounds which should be found in our experiment. The real re-deposition is prepared by the RIE etching system. The morphology of the re-deposition is investigated by scanning electron microscope (SEM). The elemental composition and chemical bonding are characterized by X-ray photoelectron spectroscopy (XPS).Thermodynamic predicts that the re-deposition presented in our experiment should be composed of AlF3(s), TiF4(s), TiF3(s) and TiF2(s). The result showed XPS could detect the prepared re-deposition contained fluorine 31.2 At%, oxygen 23.7 At%, carbon 23.7 At%, aluminium 16.0 At% and titanium 5.4 At%. The chemical bonding; AlF3, AlF6, CF, CO, C2 and TiO2 are formed to be the re-deposition material. The in-coincidence between thermodynamic prediction of forming Ti-F compounds versus Ti-O compound as found in the experiment was able to explain via the oxidation state of atoms; the oxidation state of the sputtered Ti atoms is +4 is suitable to have the reaction with sputtered oxygen atoms (from the substrate) that have an oxidation number +2, forming the TiO2 compound.

Silicon nitride gradient film as the underlayer of ultra-thin tetrahedral amorphous carbon overcoat for magnetic recording slider

There are higher technical requirements for protection overcoat of magnetic recording slider used in high-density storage fields for the future. In this study, silicon nitride (Si-N) composition-gradient films were firstly prepared by nitriding of silicon thin films pre-sputtered on silicon wafers and magnetic recording sliders, using microwave electron cyclotron resonance plasma source. The ultra-thin tetrahedral amorphous carbon films were then deposited on the Si-N films by filtered cathodic vacuum arc method. Compared with amorphous carbon overcoats with conventional silicon underlayers, the overcoats with Si-N underlayers obtained by plasma nitriding especially at the substrate bias of −150 V, can provide better corrosion protection for high-density magnetic recording sliders.

Simulation of the Eddy Current in the Thermal Flying Height Control Slider

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 study numerically investigates the use of AC current to control the temperature and protrusion of the TFC slider. It simulates the eddy current induced by alternating current (AC) applied to TFC heater and its effects on the flying performance of the TFC slider. The results show that the eddy current can be obviously excited in low shield when applying alternating current at the TFC heater. In the investigated TFC slider, the effects of eddy current on temperature rise and thermal protrusion are small. Moreover, the increase in frequency and amplitude of the input alternating current will increase the temperature and thermal protrusion of the slider along with the reduction in flying height. The current amplitude is more efficient than the current frequency to increase the temperature of the slider. Furthermore, the control of frequency and amplitude of alternating current applied to the heater would be necessary to achieve a stable flying height during read/write operation of the TFC slider.

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.

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.

Effect of Impact Conditions and Slider Corner Radius on the Thermal-Mechanical Response During Slider-Disk Contacts

We investigated the transient contact between a magnetic recording slider and a rotating disk using finite-element analysis. We determined the maximum temperature and the maximum plastic strain in the contact region as a function of impact conditions and the corner radius of the impacting slider. We observed a strong dependence of the maximum temperature and the maximum plastic strain on the impact conditions and slider corner radius. We examined the effect of substrate properties for both glass and aluminum disks.

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.

Finite Element Simulation of Static Contact of a Slider with Patterned Media

This investigation presents a finite element simulation of contact between a magnetic recording slider and patterned media. The stress distribution due to contact in patterned media is evaluated. The effects of pad radius and filling materials on the stress distribution are studied.

Planarization of Discrete Track Recording Media to Improve Flyability of Magnetic Recording Sliders

Discrete track recording (DTR) media which consist of discrete tracks are presently considered a new paradigm to achieve ultra-high areal density in hard disk drives (HDDs). However, due to the presence of the grooves, stable flying of magnetic recording sliders over DTR media is a question of great concern. In this study, planarization of DTR media with hydrogen silsesquioxane (HSQ), a nonmagnetic material, is investigated. Scanning electron microscopy (SEM) of planarized disks showed very good ldquogap fillingrdquo properties of HSQ in the groove area during the planarization process. Atomic force microscopy (AFM) measurements indicated that the residual groove depth of planarized DTR media decreases with decreasing rotating speed of the disk during spin-coating. Improved flyability of magnetic recording sliders over DTR media was observed after planarization.

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.

Nano-texturing of magnetic recording sliders via laser ablation

To increase the storage density of hard disk drives, the flying height of the slider needs to be reduced to <10 nm. This requires super-smooth surfaces of the disk and slider. As the roughness decreases, stiction and adhesion are found to increase substantially leading to failures of the head/disk interface. Texturing the slider surface is a well-known approach to this issue. In this study we investigated laser ablation as a potential process for texturing magnetic recording sliders. It was found that straight laser machining caused unwanted re-deposition of material. These deposits could be significantly reduced by using a chemical etching enhanced laser process.

Touch-down and take-off hysteresis of magnetic recording sliders on discrete track media

The touch-down and take-off characteristics of a typical pico-type magnetic recording slider is investigated as a function of pressure level and groove dimensions of discrete track recording (DTR) media. Keeping the ambient pressure constant, we found that the touch-down velocity was higher for DTR disks than for “smooth” disks without discrete tracks. Likewise, the “ambient” touch-down pressure at constant velocity was found to be higher for DTR disks than for smooth media. The hysteresis between touch-down and take-off velocity and touch-down and take-off ambient pressure was found to be larger for DTR media than for smooth media. Start/stop tests on discrete track media were performed to investigate the effect of grooves of discrete track media on the tribology of the head/disk interface.

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.

Dynamics in the Bridged State of a Magnetic Recording Slider

A novel region of tribological interaction is explored by inducing near contact between the magnetic recording slider and disk. In this study, we performed frictional measurements over a wide range of subambient air pressure and disk rotation rate. Since the slider is supported over the disk by an air bearing, it has been found that cycling from ambient to subambient and then back up to ambient pressure over several minutes of time forms a frictional hysteresis loop. The high-friction branch of the loop, referred to as the bridged state, is characterized by an average frictional displacement and resonant vibration of the suspension mount assembly. The bridged state is currently employed for accelerated wear testing of magnetic slider/disk/lubricant systems. Future magnetic recording systems designed to operate at increasingly lower physical spacing will need to take into account these frictional forces which accompany the incipient contact between the lubricated disk and slider with finite surface roughness. A single degree of freedom model is solved to determine the equivalent dynamic friction force on the slider as an impulse series with random impulse frequency and amplitude from the measured frictional displacement in the bridged state. The mean slider-disk spacing in the bridged state is derived from the experimental friction force, the spacing probability density function, and the adhesion stress from the Lifshitz model for dispersion interaction energy.

Analysis of Surface Textured Air Bearing Sliders with Rarefaction Effects

A numerical model is developed to study the effect of texture on air bearing sliders for large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated, and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch, and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.

Different substrate materials effect on structure of ta-C films by Raman spectroscopy for magnetic recording sliders

Raman spectra, using visible (514 nm) and ultraviolet (244 nm) excitation, of tetrahedral amorphous carbon (ta-C) films of thickness of 5 nm have been studied as a function of different substrates materials. These materials are Fe–Co (Fe: 67 at.%, Co: 33 at.%) alloy, Fe–Ni alloy (Fe: 18 at.%, Ni: 82 at.%), Au and Al 2O 3–TiC (Al 2O 3: 64 at.%, TiC: 36 at.%), which are mainly used in magnetic recording sliders. The spectra show that the films deposited on Al 2O 3–TiC contain the highest sp 3 content, with a lower sp 3 content observed in films deposited to Fe–Co and Fe–Ni alloys. The lowest sp 3 content was observed in films on the Au substrate. The results also indicate that the anti-wear performance of ta-C film on different substrates varies as Al 2O 3–TiC (the best) > Fe–Co and Fe–Ni alloy > Au (the worst). Also mechanisms are proposed to explain the effect of substrate material on these thin film properties.

Molecular Adhesion Model for the Bridged State of a Magnetic Recording Slider

Frictional hysteresis loops are measured with a pico-slider on typical desktop media to illustrate the bridged state with a chemisorbed perfluoropolyether lubricant. Our new molecular adhesion model calculates the mean spacing and bridge stiffness from the experimental friction force, surface topography, and dispersive surface energy. An increase in friction force with increasing pressure is consistent with molecular bond orientation by the adhesion stress