Magnetic disk having ultrathin carbon protective film and...

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Reexamination Certificate

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C428S065100, C428S212000, C428S336000, C428S690000, C428S690000

Reexamination Certificate

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06773784

ABSTRACT:

FIELD OF THE INVENTION
This invention relates, in a magnetic disk having ultrathin carbon protective film 4 nm or less in thickness, to a relation between the protective film property and the lubricant film thickness which can markedly improve the wear resistance of the magnetic disk. Further, it relates, in a magnetic disk apparatus having a mechanism for feeding a lubricant into the apparatus, to a relation between the film property of the protective film of the magnetic disk, the lubricant supplied from the apparatus, and the lubricant film thickness which can impart a high reliability to the magnetic disk apparatus.
BACKGROUND OF THE INVENTION
With recent trend toward higher recording density in magnetic disk apparatuses, the use of thinner protective film is growing in order to narrow the distance between the magnetic head and the magnetic film of the magnetic disk. For protective film of magnetic disks, there has hitherto been used amorphous carbon film or diamond-like carbon (DLC) film. With the tendency of recent years toward the use of thinner film, however, with the object of forming a DLC film more excellent in strength, such processes have been proposed as the chemical vapor deposition (CVD) method, ion beam deposition (IBD) method and filtered cathodic arc method.
In DLC film, there exist in the film carbon bonds of SP
2
and SP
3
structures and bonds of carbon with hydrogen. In particular, the physical property of DLC film varies greatly according to the amount of hydrogen in the film. It is known that, in general, the film hardness becomes maximum at a certain hydrogen amount and the hardness decreases when a more amount of hydrogen is incorporated thereinto because then hydrocarbon structures increase gradually. Accordingly, the optimization of hydrogen amount in DLC film is an important problem in controlling the film property. To deal with the problem, JP-A-6-195694 specifies the atomic ratio of carbon to hydrogen to be not less than 60/40 and not more than 90/10.
Further, JP-A-9-128732 discusses a correlation of film property with hydrogen amount by using the fluorescence intensity ratio of Raman spectrum and specifies the hydrogen amount at 10-37 at %. In these prior examples, since the thickness of protective film is very large, namely not less than 10 nm, the film property evaluation of protective film could be conducted in a simple and easy manner by using FT-IR (Fourier Transform Infrared Spectrometry), Raman spectrometry, etc.
SUMMARY OF THE INVENTION
In the prior techniques, however, the film property evaluation of ultrathin, as 5 nm or less, DLC protective film is difficult to attain, since the film thickness is too small, by such methods of determination as FT-IR or Raman described above because the detection signal becomes too weak. The present inventors have found that even when determination is made with a protective film of increased thickness to cope with the difficulty, an accurate evaluation of film property cannot be attained because the property of the film of increased thickness is not the same as that of a protective film of a thickness used in practice owing to difference in film-forming temperature and film-forming rate. Accordingly, it is intended by the present inventors to establish a proper evaluation method which can determine the film property of ultrathin DLC protective film and to provide a magnetic disk on the basis of the evaluation method.
Up to now, on the protective film of a magnetic disk is coated a fluorine-containing lubricant. The lubricant generally used is one called perfluoropolyether, and the film thickness is about 1-3 nm. However, nothing has hitherto been reported on a relation between protective film and lubricant film, particularly on a relation between the film property of thin protective film and the film thickness of lubricating film. In view of such situations, the present inventors have found an optimum range regarding the relations of these film thicknesses.
The prior technology for feeding a lubricant as a gas into a magnetic disk apparatus comprises providing a lubricant reserver in the head disk assembly. The object of supplying a lubricant is to decrease the spinning off of lubricant due to rotation and heat.
However, in the prior art, no due consideration has been given to the material and adsorption characteristic of a lubricant to be supplied, the material and adsorption characteristic of lubricant film formed on the magnetic disk, and the combination thereof, the combination of the film property of protective film with the material of lubricant to be supplied, and the combination with the film thickness of lubricant film after having been supplied. The present inventors have found that in the prior art methods, even when a lubricant is fed to a magnetic disk or head disk interface, the reliability cannot always be improved.
In the prior art method, further, fouling of the magnetic head cannot always be prevented depending on the lubricant used in supplying, which leads to lowering of reliability. The present inventors have further found that, since no adequate investigation has been made on the congeniality between the film property of thin protective film of a magnetic disk and the lubricant fed from the apparatus, the reliability of a magnetic disk apparatus cannot always be improved depending on the combination thereof.
Particularly, since DLC film generally shows a low adsorption energy of lubricant film unlike amorphous carbon film, due consideration must be given to the relation of lubricant film with protective film. Thus, a lubricant film on DLC film, which has a low adsorption energy, in some cases decreases greatly in its amount during the operation of the apparatus owing to spin-off (scattering of lubricant due to rotation of the magnetic disk) and pick-up by the magnetic head (a phenomenon wherein the lubricant is scratched off by the magnetic head and decreases its amount when the magnetic head and the magnetic disk contact with each other). In such cases, it is important to determine the optimum combination of the lubricant film thickness of the magnetic disk with the film property of protective film.
Presently, the thickness of protective film of magnetic disks is not more than 4-5 nm. In such an ultrathin film, it has become more difficult to secure wear resistance reliability for contact of a magnetic head with a magnetic disk, and it has become difficult to obtain a satisfactory result by optimizing the film property on the basis of hydrogen amount determined by the method of evaluation for DLC protective film as used in prior art techniques. Further, though the previous trend was to pursue high hardness films, in the case of ultrathin film, brittleness to deformation caused by underlayer material, etc., or elasticity to high speed, high friction force contact of a magnetic head with a magnetic disk becomes a problem. As a result, film is required which has both an appropriate hardness and an appropriate elasticity. On the other hand, with the trend toward the use of thin protective film, the contribution of lubricant film pertaining to wear resistance has increased, and importance has been attached to the optimization design of lubricant film suited to protective film.
In view of the above-mentioned problems, the object of this invention is to provide a magnetic disk which is excellent in durability even when the thickness of protective film is small, 4 nm or less, in more particular, to provide, for the purpose of improving the reliability of a magnetic disk apparatus, to provide the optimum combination of the film property of ultrathin protective film 4 nm or less in thickness, the material of lubricant film, and the thickness of lubricant film.
To solve the above-mentioned problems, according to this invention, there is provided a magnetic disk comprising a non-magnetic substrate and, provided thereon, at least a magnetic metal film, a carbon protective film and a fluorine-containing lubricant film, wherein the carbon protective film is a DLC film 4 nm or less in thickness

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