Yoshihiko Miyake

Nanoindentation and FEM study of the effect of internal stress on micro/nano mechanical property of thin CNx films

Abstract Pursuit of ever-increasing storage density has lead to a steady reduction in head-disk separation which requires protective coating as thin and as hard as possible. It has been found that the internal stress affects micro-tribological properties of CN x film. In this study, thin hard CN x overcoats with different internal stress were synthesized by an ion beam assisted deposition method. Nanoindentation was used to evaluate the micro/nano mechanical properties of CN x film. The resultant load–displacement data was analyzed and it was found that the internal stress does affect the elastic modulus and hardness of CN x film according to the magnitude and type of internal stress. A finite element method was used to simulate the nanoindentation process and to examine the dependence of hardness and modulus on internal stress. Experimental results were compared with calculated results.

Scratch–wear resistance of nanoscale super thin carbon nitride overcoat evaluated by AFM with a diamond tip

Abstract Atomic force microscopy (AFM) was used to investigate the scratch–wear resistance of ultrathin superhard carbon nitride overcoats of thickness 1, 2, 4, 6, 8 and 10 nm. When sliding against a diamond tip of radius less than 100 nm in the mode of line scratch, the thin overcoats of thickness 1–4 nm exhibited poor wear resistance, especially at contact pressures larger than 25 GPa, with a wear depth of 4 nm or larger and a specific wear rate up to 0.8×10 −4 mm 3 /nm. Non-contact mode imaging of a scratched surface has shown that a large amount of nanoscale wear debris was formed along the two sides of the scratched grooves, which indicated that the material removal mechanism of such thin overcoats was due to brittle fracture and abrasive wear, both in the nanoscale. In comparison, the overcoats of thickness 6–10 nm exhibited wear resistance with a specific wear rate less than 0.2×10 −4 mm 3 /nm. Instead, the least debris was observed on the scratched surfaces and only shallow grooves were left after scratching. It means that the grooves were formed by both plough and plastic deformation. The micro/nanowear mechanism and thickness effect of coating on scratch resistance were discussed.

Nanometre scale island-type texture with controllable height and area ratio formed by ion-beam etching on hard-disk head sliders

It has been common practice to apply a surface texture to the disk surface in a hard disk drive in order to minimize the stiction force caused by the contact of the extremely smooth surfaces of the head slider and disk. The surface of head sliders is usually made as smooth as possible without any purposely formed texture. In this work, a texture on the hard-disk slider surface was formed by ion-beam etching as a result of the different etching rates among the different phases composing the material of the hard-disk slider. By this method, an island-type texture can be formed on the air-bearing surface of the hard-disk slider. The relation between the texturing condition, the slider material and the shape of the obtained texture is discussed. The texture area ratio was 6-36%, and the diameter of the island was in the range of 0.3-4 µm. The texture area ratio and island diameter could be changed by changing the composition of head slider material. The height of island could be linearly controlled from 3-20 nm with an accuracy of ±1 nm by changing the dose of the ion beam. It is concluded that ion-beam texturing is a promising method for producing texture on the slider surface, with the advantage of simple processing.

The effects of texture height and thickness of amorphous carbon nitride coating of a hard disk slider on the friction and wear of the slider against a disk

In order to minimize the stiction force caused by contact of the extremely smooth surfaces of head sliders and disks in hard disk drives, texture is usually applied on the disk surface. For future contact/near-contact recording, the stiction-induced high friction between slider and disk will become a problem. Texture on the slider/disk interface will still be an expected method to reduce friction. Recently, it was suggested to texture the slider surface. A protective coating is usually required on the textured slider surface to reduce wear of the texture. The results showed that texture on the slider surface was effective in reducing the friction between head sliders and disks. On the other hand, the texture and coating on the slider surface increase the spacing between the read/write element and the magnetic layer of the disk. The necessary and effective texture height and coating thickness are still not clear. In the present research, island-type textures with different heights (3-18 mn) were formed on slider surfaces by ion-beam etching. Amorphous carbon nitride (a-CN x ) coatings of different thicknesses (0-50 nm) were coated on the textured slider surfaces as a protective overcoat. The friction and wear properties of these sliders were evaluated by constant-speed drag tests against hard disks coated with diamond-like carbon (DLC). The results show that 2 nm texture on a slider surface is sufficient for low (0.3-0.5) and stable friction of the slider against the disk in a drag test, and coatings thicker than 5 nm show similar wear resistances of the texture on slider surfaces.

Tribological behavior of thin film rigid disks with regular dot array texture on carbon overcoats

Frictional behavior and contact start/stop (CSS) performance are described for thin film rigid disks with regular dot array texture on carbon overcoats formed by a photo-lithography technique. Both initial friction and friction buildup in CSS tests become smaller with a decrease in apparent area of contact between the slider and disk, while wear depth of carbon overcoats in tests increases. These phenomena agree well with those of concentric circular texture formed by similar process. These results show that the apparent area of contact is the dominant factor for friction and wear, nearly independent of texture arrangement. When the hill height is insufficient, a sudden increase in friction may occur during a CSS test due to wear of the hills. To improve tribological durability, the optimum texture profile should be designed by taking account of the wear rate of overcoats during the operating conditions of magnetic disk drives. >

Micro-tribology of carbon-coated thin-film media with well-defined surface texture

Contact start/stop (CSS) performance is described for thin film media with well-defined surface texture on carbon overcoats. Using a photolithography technique, concentric circular hills with uniform height (ca. 20 nm) are formed on the carbon overcoat to control the apparent area of contact with a slider. This texturing process provides the medium with a flat magnetic layer independent of the texture profile, which would be suitable for high density recording. A decrease in the apparent area of contact results in lower friction buildup during the CSS test, while it causes large wear of the carbon overcoat over the test. Take off velocity of the slider also becomes higher with a decrease in the apparent area of contact, which increases sliding distance prior to take off. Although the smaller apparent area of contact causes greater wear due to an increase in contact pressure and sliding distance between the medium and slider, it effectively limits the increase in the real area of contact, keeping friction low. >

Dependence of microstructure and nanomechanical properties of amorphous carbon nitride thin films on vacuum annealing

Abstract Three kinds of ultrathin amorphous carbon nitride films (α-CNx) with different internal stress were deposited on silicon (111) substrates by an ion beam assisted deposition method. The as-deposited α-CNx was post-annealed to eliminate the internal stress. The microstructure and nanomechanical properties of both as-deposited and annealed α-CNx were studied by using micro Raman spectroscopy, nanoindentation measurement, and nanoscratch test in atomic force microscopy. The Raman spectra of as-deposited and annealed film show that the ratio of intensities of the D band to G band increased after vacuum annealing. Nanoscratch tests showed that the elimination of compressive internal stress due to annealing resulted in reduced scratch resistance, while elimination of tensile internal stress due to annealing resulted in enhanced scratch resistance. Nanoscratch test results were in good agreement with the results of nanoindentation measurement. Experimental results indicate that the effect of internal stress on scratch resistance is stronger than that of microstructure evolution due to post-annealing. Nanoscratch tests show that suitable compressive internal stress is beneficial for enhancement of nanoscratch resistance of the thin α-CNx film.

Friction and wear properties of hard coating materials on textured hard disk sliders

Abstract It has been a common practice to apply a surface texture to disk surface in hard disk drive in order to minimize the stiction force caused by the contact of extremely smooth surfaces of head sliders and disks. The slider surface texture was also suggested recently with the advantage of using smoother disks. The slider surface texture reduced the stiction effect, meanwhile it increased the contact pressure between sliders and disks. The protective coating is required on the textured slider surface to reduce the wear of the texture. In the present research, four kinds of hard coating materials were synthesized by IBAD and evaluated on textured slider surfaces by drag test. The results showed that the a-CNx coating had higher wear resistance than sputtered carbon, TiNx and BNx coatings on textured slider surfaces.

Wear Characteristics of Carbon-Coated Magnetic Rigid Disks With Well-Defined Surface Texture

Wear characteristics are described for carbon-coated magnetic rigid dirks with well-defined surface textures. Concentric circular hills with uniform height (ca. 80 nm) are produced on a dirk surface using a photo-lithography technique, to control the apparent area of contact with a slider. Wear depth on the order of nanometers of the carbon overcoat is evaluated from the decrease in hill height after a drag test. Wear depth increases proportionally with the increase in average contact pressure, which is calculated from the load and apparent area of contact between the disk and slider

Analytical Stability Criteria for Gas-Lubricated Sliders for Magnetic Disk Drive

Stability criteria for gas-lubricated sliders for magnetic disk drives are analyzed using Horis method. Some relations between flotational stability and float factors are discussed. Equations of slider motion for a rigid body slider are expressed using linearized coefficients for gas-lubricated films accounting for second-order slip flow. Stability of the slider is analyzed using the Routh-Hurwitz stability criteria. The calculated results make it clear that some types of sliders become unstable when ambient pressure is reduced, or gas compressibility number is increased. Furthermore, analytical results were confirmed not to conflict with experimental work. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Baltimore, Maryland, October 16–19, 1988