Effect of Ultra-Thin Liquid Lubricant Films on Dynamics of Nano-Spacing Flying Head Sliders in Hard Disk Drives

2004 ◽  
Vol 126 (3) ◽  
pp. 565-572 ◽  
Author(s):  
Norio Tagawa ◽  
Noritaka Yoshioka ◽  
Atsunobu Mori
Keyword(s):  
Film Thickness ◽  
Hard Disk Drives ◽  
Lubricant Film ◽  
Flying Height ◽  
Air Bearing ◽  
Disk Drives ◽  
Lubricant Film Thickness ◽  
Liquid Lubricant ◽  
Lubricant Films ◽  
Bearing Dynamics

This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of nano-spacing flying head sliders in hard disk drives. The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). The disks with lubricant on one half of disk surface thicker than the other half as well as with uniform thickness lubricant were used to investigate the interactions between the slider and lubricant film experimentally. As a result, it was found that the flying height at which the slider-lubricant contact occurs depends on the lubricant film thickness and it increases as the lubricant film thickness increases. Its flying height is also dependent on the mobile lubricant film thickness under the condition that the total lubricant film thicknesses are the same and the lubricant bonded ratios are different. It increases as the mobile lubricant film thickness increases. The slider-lubricant contact flying height based on the theory for capillary waves is in good agreement with the experimental results. Regard to air bearing dynamics due to the slider-lubricant interactions, it also depends on the mobile lubricant thickness as well as the total lubricant film thickness. However, we should carry out more experimental and theoretical studies in order to confirm and verify these experimental results. In addition, the effect of nonuniform lubricant film thickness on head/disk interface dynamics has been studied. It was found that the lubricant film thickness nonuniformity caused by the slider-lubricant interactions could be observed.

Effects of End-Group Functionality and Molecular Weight of Ultra-Thin Liquid Lubricant Films on Contact Slider Dynamics in Hard Disk Drives

2004 ◽  
Author(s):  
Norio Tagawa ◽  
Yoshiaki Tashiro ◽  
Atsunobu Mori
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
Hard Disk Drives ◽  
Lubricant Film ◽  
Disk Drives ◽  
Lubricant Film Thickness ◽  
Liquid Lubricant ◽  
End Groups ◽  
End Group ◽  
Contact Slider

This paper describes the effect of end-group functionality and molecular weight of ultra-thin liquid lubricant films on contact slider dynamics in hard disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid lubricants behavior are investigated using three kinds of lubricants which have different end-groups and molecular weight as a function of lubricant film thickness. The dynamics of a contact slider is mainly monitored using Acoustic Emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the lubricant film thickness instability due to de-wetting occurs as a result of slider-disk contacts, when the lubricant film thickness is thicker than one monolayer. Their unstable lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost equivalent, independent of the end-groups and molecular weight for the lubricants, when the lubricant film thickness is around one monolayer. The molecular weight, however, affects the contact slider dynamics, when the lubricant film thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the lubricant increases. When the lubricant film thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile lubricant layer, while the lubricant de-wetting instability affects the contact slider dynamics. Therefore, it would be concluded that the lubricant film thickness should be designed to be around one monolayer thickness region in order to achieve contact recording for future head-disk interface.

Depletion of Monolayer Liquid Lubricant Films Induced by Laser Heating in Thermally Assisted Magnetic Recording

2011 ◽  
Author(s):  
Norio Tagawa ◽  
Takao Miki ◽  
Hiroshi Tani
Keyword(s):  
Film Thickness ◽  
Laser Heating ◽  
Temperature Programmed Desorption ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Lubricant Depletion ◽  
Liquid Lubricant ◽  
Lubricant Films ◽  
Temperature Programmed ◽  
Thermally Assisted Magnetic Recording

In this study, the lubricant depletion caused by laser heating was investigated for lubricant films with thicknesses greater than and less than one monolayer. The conventional lubricants Zdol2000 and Ztetrao12000 were used. It was found that the critical temperature at which lubricants start to deplete by laser heating strongly depends on the lubricant film thickness. To analyze the lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested lubricant films. It was found that the lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested lubricant films. It was also found that the depletion mechanism involved the desorption or decomposition of the lubricant molecules that interacted with the diamond-like carbon thin films when the lubricant film thickness was less than one monolayer.

Effects of Molecularly Thin Lubricant Films on Slider Touch-Down and Take-Off Hysteresis Behavior in Hard Disk Drives

2005 ◽  
Author(s):  
Norio Tagawa ◽  
Hiroshi Sendo ◽  
Atsunobu Mori
Keyword(s):  
Molecular Weight ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Lubricant Film ◽  
Disk Drives ◽  
Hysteresis Behavior ◽  
Liquid Lubricant ◽  
Pfpe Lubricant ◽  
Lubricant Films ◽  
The Difference

This paper describes the effects of molecularly thin liquid lubricant films on slider hysteresis phenomena of touch-down and take-off process in hard disk drives. In the experiments, the tested lubricants were conventional Zdol and novel cyclotriphosphazene-terminated PFPE lubricant (A20H lubricant) with different molecular weight. As a result, it is found that the difference between the touch-down velocity and take-off one (hysteresis behavior) for novel A20H lubricant film is larger than that for Zdol. The LDV RMS values for novel lubricant, which indicate the slider bouncing vibration during the slider-lubricant contact, are also larger than that for Zdol. The effects of lubricant film thickness and molecular weight on slider hysteresis behavior as well as slider bouncing vibration are also clarified. In addition, the replenishment performances of test lubricants for depleted tracks due to slider touch down contact are investigated and discussed.

Study of Direct Measuring of Lubricant Condition in Rolling Element Bearings With Microcomputer Technique

1990 ◽  
Vol 112 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Dongchu Zhao
Keyword(s):  
Film Thickness ◽  
Strain Gage ◽  
Lubricant Film ◽  
Rolling Element Bearings ◽  
Main Program ◽  
Test Apparatus ◽  
Lubricant Film Thickness ◽  
Rolling Element ◽  
Lubricant Films ◽  
Flow Charts

A method for measuring the lubricant condition with strain gage in rolling element bearings and the instrument used are introduced. In order to illustrate the method and the instrument, the theory of measuring lubricant films in rolling element bearings using strain technique, test apparatus, microcomputer hardware as well as software, flow charts for the main program and subprograms, are first described in detail. In addition, the lubricant film thickness is measured for several different lubricants and results are compared with theoretical ones. It is demonstrated that using the method and the instrument introduced in this paper, one can measure the lubricant condition inside bearings very accurately.

Depletion of Moleculary Thin Lubricant Under Flying Head in Hard Disk Drives

2007 ◽  
Author(s):  
Kenji Yanagisawa ◽  
Youichi Kawakubo ◽  
Masato Yoshino
Keyword(s):  
Thin Film ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Lubricant Film ◽  
Simulation Program ◽  
Disk Drives ◽  
Lubricant Thickness ◽  
Magnetic Disk ◽  
Lubricant Depletion ◽  
Lubricant Films

In Hard Disk Drives, lubricants are very important materials to reduce head and disk wear. Therefore, it is necessary to know the lubricant depletion under flying heads. Lubricant depletion due to flying heads has been studied experimentally. We developed simulation program to calculate numerically the change in lubricant thickness under a flying head on a thin-film magnetic disk from 10nm thick lubricant film. In recent HDDs, the lubricants thickness has become molecularly thin and polar lubricants have been used. In this paper, we took account of thickness-dependent lubricants diffusion and viscosity in our simulations to calculate a 1.2 nm thick polar lubricant film used in recent HDDs. The simulated results considering the thickness-dependent diffusion and viscosity showed that depletion was small in molecularly thin lubricant films. We considered it necessary to include thickness-dependent diffusion and viscosity in lubricant depletion simulation.

Design and Dynamics of Flying Height Control Slider With Piezoelectric Nanoactuator in Hard Disk Drives

2006 ◽  
Vol 129 (1) ◽  
pp. 161-170 ◽  
Author(s):  
Jia-Yang Juang ◽  
David B. Bogy ◽  
C. Singh Bhatia
Keyword(s):  
Numerical Study ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Areal Density ◽  
Flying Height ◽  
Air Bearing ◽  
Disk Drives ◽  
Adhesion Forces ◽  
Surface Design ◽  
Ultrahigh Density

To achieve the areal density goal in hard disk drives of 1Tbit∕in.2 the minimum physical spacing or flying height (FH) between the read/write element and disk must be reduced to ∼2nm. A brief review of several FH adjustment schemes is first presented and discussed. Previous research showed that the actuation efficiency (defined as the ratio of the FH reduction to the stroke) was low due to the significant air bearing coupling. In this paper, an air bearing surface design, Slider B, for a FH control slider with a piezoelectric nanoactuator is proposed to achieve virtually 100% efficiency and to increase dynamics stability by minimizing the nanoscale adhesion forces. A numerical study was conducted to investigate both the static and dynamic performances of the Slider B, such as uniformity of gap FH with near-zero roll over the entire disk, ultrahigh roll stiffness and damping, low nanoscale adhesion forces, uniform FH track-seeking motion, dynamic load/unload, and FH modulation. Slider B was found to exhibit an overall enhancement in performance, stability, and reliability in ultrahigh density magnetic recording.

The Effect of Thin Lubricant Films on Acoustic Emission Characteristics

2005 ◽  
Author(s):  
Hiroo Taura ◽  
Toshihiko Takaki ◽  
Masahiro Kawaguchi ◽  
Satoru Kaneko ◽  
Takahisa Kato
Keyword(s):  
Acoustic Emission ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Sliding Friction ◽  
Protective Layer ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Lubricant Films ◽  
Circumferential Distribution ◽  
Ae Signals

This paper shows the effect of ultrathin lubricant films between sliding bodies on Acoustic Emission (AE) signals induced by the sliding friction. Experiments were conducted with a ball-on-disk friction tester to measure the friction coefficient, the raw AE signals and the root-mean-squarevalues of the AE signals (the AErms signals). The ball was a glass ball of 5mm diameter. The disk was a magnetic disk used for 2.5 inch HDD with a DLC protective layer on its surface, and was coated with PFPE Z-dol 4000 about 1.5nm thick. The AErms signals kept a low level for some time after the start of the test, and then increased. Its time variation was similar to that of friction coefficient. After the friction test, the circumferential distribution of the lubricant film thickness was measured with an ellipsometer. The distribution demonstrated the reduction of the lubricant film thickness at the circumferential position where the magnitude of AE signals became large. These facts showed that the AE signals correlated well with the lubricant film thickness.

Effects of End Groups on the Spreading Characteristics of Molecularly Thin Liquid Lubricant Films in Hard Disk Drives

2007 ◽  
Vol 43 (9) ◽  
pp. 3705-3709 ◽  
Author(s):  
N. Tagawa ◽  
M. Korenaga ◽  
A. Mori ◽  
N. Kobayashi ◽  
M. Ikegami
Keyword(s):  
Hard Disk Drives ◽  
Hard Disk ◽  
Disk Drives ◽  
Liquid Lubricant ◽  
End Groups ◽  
Lubricant Films
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