Lubricant Pickup Research Articles

Effects of SiO2 Contaminant on Thermo-Mechanical/Chemical Properties and Lubricity of PFPE Lubricants

Using the molecular dynamics (MD) simulations with ReaxFF potential, two different types of PFPE lubricants (Ztetraol and ZTMD) are prepared on a-C film, and SiO2 particles are adsorbed onto the lubricants at room temperature. From the simulation results, it is observed that the adsorbed SiO2 particles increase the stiffness of PFPE lubricants leading to less airshear displacement. Since Ztetraol has higher mobility with lower viscosity than ZTMD, the adsorbed SiO2 particles penetrate deeper into the Ztetraol lubricants. Accordingly, the effect of SiO2 on the airshear displacement is more obvious to Ztetraol than ZTMD. In addition, the adsorbed SiO2 particles increase the friction force and the amount of lubricant pick-up during the sliding contact with a nanosized a-C tip.

TOF-SIMS analysis of perfluoropolyether lubricant smear transferred from disk surface following laser heating

The structural and molecular weight changes of perfluoropolyether lubricant picked up following laser heating in heat-assisted magnetic recording (HAMR) were analyzed using time-of-flight secondary ion mass spectrometry. The molecular weight of the picked up lubricant molecules increase, as the low-molecular-weight molecules decompose owing to laser heating and readily evaporate. The dissociation starts from the end groups of the lubricant molecules at a relatively low heating temperature, and the dissociation of longer hydrocarbon terminal elements occurs with increasing temperature. It is estimated that the decomposition of the ether bond of the main chain also occurs when the temperature further increases. These dissociated lubricant elements are picked up by the pin surface during laser heating. Overall, the results presented herein suggest that the chemical and thermal stability of the hydrocarbon end groups of the lubricants should be improved to reduce the rate of depletion of the lubricant film and lubricant pickup by laser heating in HAMR.

Structural Changes of Perfluoropolyether Lubricant Accumulated on the Pin Surface During Laser Heating

Structural and molecular weight changes to lubricant picked up the following laser heating in heat-assisted magnetic recording (HAMR) were analyzed using time-of-flight secondary ion mass spectroscopy. The average molecular weight of the disk lubricant increased by laser heating at temperatures over 500 °C and that of the picked up lubricant increased at temperatures over 400 °C. The presence of end-group fragments with low molecular weight (CH3O+) increases in both the disk and picked up lubricants, whereas at high temperature the concentration of the end-group component (C3H7O2+) decreases in the disk lubricant and increases in the picked up lubricant. Overall, the results presented herein suggest that the chemical and thermal stability of the terminal ends of lubricants should be improved in order to decrease depletion of the lubricant film and the lubricant pickup by the laser heating in HAMR.

Smear growth on head slider surface from siloxane outgas on heat assisted magnetic recording

In this study, the smear by the lubricant and siloxane pickup at the laser heating in the heat assisted magnetic recording (HAMR) was evaluated using our developed noncontact pin-on-disk test. The smear area on the glass pin surface was measured on the disks with three types of different lubricant films prepared by changing the ultraviolet exposure condition, rinse condition, and lubrication process. The amount of siloxane adsorbed on disk surface relates with the siloxane wettability obtained from the contact angle of siloxane for disk surface and that increased as the siloxane wettability increases. On the other hand, the lubricant pickup increases as the physical and hydrogen bonding fractions increase. Overall, these data suggest that the sufficiently low surface free energy is needed by the lubricant film with only the chemical bonding fraction to reduce the lubricant and siloxane smear at the laser heating of HAMR, because the lubricant fractions of physical and hydrogen bonding increase the lubricant pickup and the much amount of siloxane adsorbs on disks with the large surface free energy.

A Model for Lubricant Transfer from Media to Head During Heat-Assisted Magnetic Recording (HAMR) Writing

One of the challenges in heat-assisted magnetic recording (HAMR) is the creation of write-induced head contamination at the near-field transducer. A possible mechanism for the formation of this contamination is the transfer of lubricant from the disk to the slider (lubricant pickup) due to temperature-driven evaporation/condensation and/or mechanical interactions. Here we develop a continuum model that predicts the head-to-disk lubricant transfer during HAMR writing. The model simultaneously determines the thermocapillary shear stress-driven deformation and evaporation of the lubricant film on the disk, the convection and diffusion of the vapor phase lubricant in the air bearing and the evolution of the condensed lubricant film on the slider. The model also considers molecular interactions between disk–lubricant, slider–lubricant and lubricant–lubricant in terms of disjoining pressure. We investigate the effect of media temperature, head temperature and initial lubricant thickness on the lubricant transfer process. We find that the transfer mechanism is initially largely thermally driven. The rate of slider lubricant accumulation can be significantly reduced by decreasing the media temperature. However, as the amount of lubricant accumulation increases with time, a change in the transfer mechanism occurs from thermally driven to molecular interactions driven. A similar change in transfer mechanism is predicted as the head–disk spacing is reduced. There exists a critical value of head lubricant thickness and a critical head–disk spacing at which dewetting of the disk lubricant begins, leading to enhanced pickup.

Real-Time Observation of Molecularly Thin Lubricant Films on Head Sliders Using Rotating-Compensator-Based Ellipsometric Microscopy

Lubricant transfer or pickup from a disk to a head slider is a crucial issue in designing the head–disk interfaces of hard disk drives (HDDs). A method based on ellipsometric microscopy is presented for observing thin lubricant film on a head slider in real time. The use of rotating-compensator ellipsometry (RCE) results in one order of magnitude higher temporal resolution (0.6 frames/s) and several times higher thickness resolution (0.2 nm) compared to null-ellipsometry-based microscopy, which was recently proposed. RCE-based ellipsometric microscopy will be useful in clarifying the mechanism of lubricant pickup for higher density HDDs.

Measurement of Thickness Distribution of Molecularly Thin Lubricant Films on Head Sliders Using Ellipsometric Microscopy

Lubricant transfer or pickup from a disk to head slider is a crucial issue in designing the head–disk interfaces with a reduced head–disk gap. Observation of lubricant on the slider is difficult with the conventional methods due to their limited lateral resolution. In this paper, nanometer-thick lubricant on a slider was observed by using vertical-objective-based ellipsometric microscopy (VEM). The lubricant thickness was evaluated using a null-ellipsometric method. The thickness measured by VEM agreed fairly well with that by atomic force microscopy. The temporal change in the thickness of a nanometer-thick lubricant film distribution around a read/write element in the slider was successfully observed with a lateral resolution of the order of $1 ~\mu \text{m}$ .

Lubricant Transfer Model at the Head-Disk Interface in Magnetic Storage Considering Lubricant–Lubricant Interaction

Interactions among molecularly thin lubricant–solid and lubricant–vapor interfaces become increasingly strong when the slider approaches closer to the disk (or media) surface, which is desirable for higher storage areal densities. Lubricant transfers from the disk to the slider as the head-media spacing decreases below a critical value, leading to loss of protection for the solid thin films. The present work proposes a new criterion for lubricant pickup to occur by improving the lubricant transfer model via considering interactions between the lubricant films, in addition to lubricant–solid interaction. The effect of lubricant roughness is also included in the proposed model, which is then used to predict critical solid distances as a function of lubricant roughness and average lubricant thickness. It is found that the interaction force between the slider solid and the disk lubricant plays a weaker role than that between the lubricant on the slider and the lubricant on the disk in determining the critical solid distance. The physics for the dependence of the critical clearance on the bonding ratio is explained, and a linear model is developed.

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.

M1105 電場と潤滑剤分子との相互作用による潤滑剤ピックアップ抑制に関する研究(GS8,11,16 機素潤滑設計(1),修士研究発表セッション)

M1105 電場と潤滑剤分子との相互作用による潤滑剤ピックアップ抑制に関する研究(GS8,11,16 機素潤滑設計(1),修士研究発表セッション)

102 ヘッドディスクインタフェース間の電場の潤滑剤ピックアップ特性への影響(GS2-2,21 マイクロデバイス)

102 ヘッドディスクインタフェース間の電場の潤滑剤ピックアップ特性への影響(GS2-2,21 マイクロデバイス)

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.

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.

Boundary Lubricant Film Properties versus Molecular Polarity of Perfluoropolyethers Containing a Pendant Chain

The thin film properties of some novel branched perfluoropolyether (PFPE) boundary lubricants are investigated as a function of molecular polarity and end-group bonding to the underlying carbon film. The PFPE main chain, comprised of n-perfluoroethylene oxide monomer units, is stiffer than the Fomblin Z main chain that is a copolymer of perfluoro-methylene oxide and -ethylene oxide monomer units. Terraced flow and bonding kinetics show decreased lubricant mobility compared to PFPEs based on a Fomblin Z main chain. Lubricant pick-up is reduced for the tetraol adduct due to the larger Hamaker constant and increased intermolecular cohesion.

1305 低浮上HDIにおけるルブピックアップ現象の解析 : UV処理の影響(GS-16 トライボロジー特性(3))

1305 低浮上HDIにおけるルブピックアップ現象の解析 : UV処理の影響(GS-16 トライボロジー特性(3))

Parametric Investigations at the Head-Disk Interface of Thermal Fly-Height Control Sliders in Contact

Accurate touchdown power detection is a prerequisite for read-write head-to-disk spacing calibration and control in current hard disk drives, which use the thermal fly-height control slider technology. The slider air bearing surface and head gimbal assembly design have a significant influence on the touchdown behavior, and this paper reports experimental findings to help understand the touchdown process. The dominant modes/frequencies of excitation at touchdown can be significantly different leading to very different touchdown signatures. The pressure under the slider at touchdown and hence the thermal fly-height control efficiency as well as the propensity for lubricant pickup show correlation with touchdown behavior which may be used as metrics for designing sliders with good touchdown behavior. Experiments are devised to measure friction at the head-disk interface of a thermal fly-height control slider actuated into contact. Parametric investigations on the effect of disk roughness, disk lubricant parameters, and air bearing surface design on the friction at the head-disk interface and slider burnishing/wear are conducted and reported.

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.

Lubricant Pickup of Ultra-Thin PFPE Lubricants With Different Backbone Structures

Lubricant pickups on different perfluoropolyether (PFPE)-lubricant (Z-tetraol, D-4OH, and QA-40) films were compared by using a slider surface analyzing (SSA) tester developed to observe the lubricant thickness mapping on the slider surfaces after the heads slide on the disk surfaces. These lubricants have the same four OH functional end-groups but different backbones. Z-tetraol showed the least lubricant pickup among the four lubricants. D-4OH and QA-40 showed considerable pickup at a large clearance of 30-mW back-off. The pickup volumes of each lubricant disk with a similar mobile lubricant thickness were different, and D-4OH showed the largest pickup volume among these lubricants. An MD simulation was performed to understand the difference in the lubricant pickup of the three types of lubricants. The intermolecular force between the slider and the lubricant molecules was different for these lubricants. This difference in the intermolecular force depended on the dipole-dipole interaction between the end-groups and the slider surface, and the dipole-dipole interaction was affected by the conformation of the lubricant molecules. Therefore, it is estimated that the lubricant pickup phenomenon is influenced by the conformation of the lubricant molecules, and D-4OH with a strong -OH function at the lubricant surface exhibited considerable lubricant pickup.

Lubricant Pickup Under Laser Irradiation

Hard disk lubricants play important roles at head-disk interfaces. Heat assisted magnetic recording (HAMR) is a promising approach for enabling large increases in the storage density of hard disk drives. Under HAMR conditions, lubricated thin films on hard disk surfaces should satisfy all tribological properties. This paper studies the reliability of several types of lubricants on thin-film disks, under HAMR laser irradiation conditions. Through the study and comparison of the lubricants' physical and chemical properties, lubricant pick-up status and composition of the picked-up lubricant, the related tribological properties have been explained and the design and development of new lubricants for HAMR application have been explored.

Effect of Slider Surface Energy on Head Disk Interface Performance

Study of lubricant-coated sliders showed that low slider surface energy increases in stable slider flying and reduces lubricant droplet formation on the disk surface at ultra-narrow clearance. Both component- and drive-level evaluation showed the lubricant pick-up and the flying height it causes were reduced significantly. Furthermore, there was no magnetic spacing increase at the drive-level for the lubricant-coated slider when using contact detection to set the clearance methods.