Atsunobu Mori

Design and fabrication of MEMS-based active sliders using double-layered composite PZT thin films in hard disk drives

This paper describes MEMS-based active sliders with microactuators. The active sliders that we proposed use PZT thin films as a microactuator and control the slider flying height of less than 10 nm. The design procedure for the active slider is discussed. In addition, novel PZT thin film microactuators are studied, and it is shown that the recently developed PZT thin films have better piezoelectric characteristics than not only conventional sol-gel derived PZT thin films but also sputtered PZT thin films. The micromachining process for the active slider is also developed and the pico-size active slider is fabricated. The technical issues related to the fabrication of MEMS-based active sliders are discussed.

The tribological effect of mechanically produced micro-dents by a micro diamond pyramid on medium carbon steel surfaces in rolling-sliding contact

In order to evaluate the effects of micro-pockets on the lubrication and the pitting durability of medium carbon steel surfaces, in the present paper, using the roller with a small number of micro-dents marked by a diamond pyramid whose total area was, to minimize the effect of work-hardening, set negligibly small compared to the contact area as the follower in a two-roller testing machine, the pitting durability was tested under poor lubrication conditions and/or severe loading levels. The results successfully demonstrate the effect of such micro-pockets on the pitting durability and scuffing resistance of surfaces in rolling-sliding contact.

Effects of Molecularly Thin Liquid Lubricant Films on Slider Hysteresis Behavior in Hard Disk Drives

In order to achieve a magnetic recording density of 1 Tb/in 2 , the spacing is expected to be less than 2-3 nm. However, a critical issue in achieving such an ultralow spacing is the dynamic instability of the head disk interface (HDI). That is, the experimentally observed hysteresis of fly sliders. The phenomenon of slider hysteresis has two features: slider touchdown and slider takeoff The goal of this research is to experimentally clarify the effects of the lubricant bonded ratio as well as the lubricant film thickness on slider hysteresis behavior in detail. It also aims to determine the contributing factors. In this study, the difference in the touchdown and takeoff velocities was monitored by varying the lubricant bonded ratio and lubricant film thickness of the disks. Furthermore, the correlation between the observed phenomenon and the variation in the experimental parameters was investigated. The results showed that the touchdown velocities were almost independent of the lubricant bonded ratio, while the takeoff velocities were greater for a lubricant with a higher bonded ratio. These results were obtained for a constant lubricant film thickness of around one monolayer. Therefore, the slider hysteresis was greater for a lubricant with a higher bonded ratio. With regard to the effect of lubricant film thickness, it was observed that the touchdown and takeoff velocities were greater for thinner lubricants. These results for the effect of lubricant film thickness are very similar to those obtained by Ambekar, Gupta, and Bogy (2005, ASME J. Tribal., 127(3), pp. 530-536). However, the slider hysteresis was greater for thicker lubricants. Considering these experimental results as well as the experimental data for the effect of the surface roughness of a disk on the slider hysteresis obtained by (Tani et al. (2006, J. Appl. Phys. , 99(8), pp. 08N104-1-08N104-3), it was suggested that the variation in the touchdown velocity is due to a variation in the intermolecular forces. Furthermore, it was suggested that the variation in the takeoff velocity is caused by a variation in the friction forces between the slider and disk surface. This occurs because the takeoff velocity was greater for a lubricant with a higher bonded ratio or a thinner lubricant, which only has a small fraction of free mobile lubricant. The results predicted by the simulations are consistent with those observed experimentally. In addition, a design guideline for next-generation HDI, with small touchdown and takeoff velocities, resulting in small slider hysteresis, is discussed in detail in this paper.

Effects of Moving Three-Dimensional Nano-Textured Disk Surfaces on Thin Film Gas Lubrication Characteristics for Flying Head Slider Bearings in Magnetic Disk Storage

This paper describes the effects of moving three-dimensional nano-textured or patterned disk surfaces on thin film gas lubrication characteristics for flying head slider bearings in magnetic disk storage, In order to perform the most realistic simulation of slider flying characteristics over the textured disk surfaces, the direct numerical simulation method is used, instead of using various averaging techniques. Therefore, a deterministic description of the texture is adopted in this study. A dynamic analysis of the slider responses can be carried out, by solving the air bearing equation based on the linearized Boltzmann equation with the equations of motion of the slider under the excitation of the moving texture simultaneously. The sliders dynamic responses to moving spaced bumps disk surfaces, including both the circumferentially and radially ridged disk surfaces, are computed systematically and basic slider dynamics over patterned disk surfaces is investigated, The effects of the texture area ratios (= texture width/texture pitch) in the circumferential and radial directions on the slider spacing dynamic modulations as well as the slider static flying characteristics are also studied. Furthermore, the effects of three kinds of texture patterns on the slider flying characteristics are investigated. Considering those simulation results, the design optimization for the texture pattern that minimizes not only the slider static flying height increase but also spacing dynamic modulations is discussed in order to achieve ultra-high density proximity magnetic recording.

Spreading of Novel Cyclotriphosphazine-Terminated PFPE Films on Carbon Surfaces

Spreading characteristics of novel cyclotriphosphazine-terminated Perfluoropolyether (PFPE) films on carbon surfaces were investigated experimentally by using a scanning micro-ellipsometer. The apparent diffusion coefficients of novel lubricants were also studied in order to evaluate the spreading speed and they were compared with the conventional Zdol. It was found that the mobility of cyclotriphosphazine-terminated PFPE films is lower than that of Zdol. This characteristics is dependent on the interactions between the end groups of the lubricants and carbon surfaces and it is found that the tendency of work of adhesion for the lubricants has a good correlation with the mobility tendency of the lubricants. In addition, the monolayer film thickness of novel lubricant films as well as conventional Zdol was identified, which was extracted using Matano interface method. As a result, the existing conformation of novel cyclotriphosphazine-terminated PFPE film on carbon surfaces could be estimated, based on the monolayer film thickness results.

Spreading characteristics of cyclotriphosphazine-terminated perfluoropolyether films on carbon surfaces

In this paper, we describe the spreading characteristics of novel cyclotriphosphazine-terminated PFPE lubricant films on carbon surfaces are investigated experimentally by scanning micro-ellipsometry.

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

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 groups on the spreading characteristics of molecularly thin liquid lubricant films in hard disk drives

The spreading characteristics of novel alkanolamine-terminated perfluoropolyether (PFPE) films on carbon surfaces were investigated experimentally by using a scanning micro-ellipsometer. The apparent diffusion coefficients of the novel lubricants were studied in order to evaluate the spreading speed and they were compared with the conventional Z-dol, Z-tetraol, and A20H lubricants. It was found that the mobility of a lubricant is lower when the number of OH end groups is higher. It was also found that the mobility of the alkanolamine-terminated PFPE films was lower than that of conventional lubricants with the same number of OH end groups as that of the alkanolamine-terminated lubricants and that the mobility tendency of the lubricants has a good correlation with their viscosity tendency. In addition, the mobility of ZDPA with a dipropylamine end group (no OH end group) has peculiar characteristics. Its mobility is higher than that of Z-dol when the film thickness of the lubricant exceeds that of one monolayer. However, it is lower than that of Z-dol when the film thickness of the lubricant is less than that of one monolayer. This may be due to the unique interaction between the ZDPA amine group and the carbon overcoat.

Effects of functional end-groups on nano-tribology characteristics of ultra-thin liquid lubricant films in hard disk drives

This paper describes the effects of functional end-groups on lubricant redistribution of ultra-thin liquid lubricant films in hard disk drives. In the experiments, the spreading characteristics of ultra-thin liquid lubricant films have been investigated by using the disks with two kinds of lubricants which have different end-groups. In other words, the tested lubricants were conventional Zdol and novel cyclotriphosphazene-terminated PFPE lubricant. It was found that the mobility of novel lubricant film is lower than that of conventional Zdol and these characteristics depend on the interactions between the end-groups of the lubricants and carbon surfaces. The effect of molecularly thin lubricant films on nano-spacing flying head slider hysteresis behavior for touch-down and take-off process has been studied and the dynamic interactions between the slider and the tested lubricants films in near contact regime have been clarified. In addition, the behavior of two kinds of lubricants films for contact sliders also has been investigated. It could be observed that the lubricant film thickness instability occurs as a result of slider-disk contacts for the tested lubricants. Their unstable lubricant behavior depends on the chemical structure of functional end-group. Therefore, it may be concluded that the functional end-groups play a very important role and affect the tribological performance of lubricants in head-disk interface.

Effects of Fluid Inertia Forces on the Performance of a Plane Inclined Sector Pad for an Annular Thrust Bearing Under Laminar Condition

The hydrodynamic wedge of a plane inclined sector pad is analyzed in relation to the lubricant inertia forces under incompressible laminar conditions. Based on the usual assumptions of thin film lubrication theory without the thermal effects, modified Reynolds equations are derived by averaging out all the inertia terms of the Navier-Stokes equations across the film thickness. The equations are linearized with respect to the inertia parameter, and solved numerically for a plane inclined, sectorial configuration. The boundary value of the film pressure at the leading edge is set at the ambient pressure, under the assumption of a negligibly small rampressure thereat. The inertial effects on the static and dynamic performance such as the load carrying capacity, flow rate, frictional torque, position of pressure center, film stiffness, and damping coefficient are discussed, in which the effects of the centrifugal force and those of the other convective inertia forces are compared with each other.