Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-08-14
2004-03-16
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S408000, C428S690000, C427S131000, C427S533000
Reexamination Certificate
active
06706363
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to structure of a magnetic recording medium such as a magnetic disc, and particularly controls surface roughness in a final form by means of technique concerning surface treatment of a overcoat of a magnetic recording medium corresponding to ultra-low floating of a magnetic head.
2. Description of the Related Art
Generally, the magnetic storage device is, as shown in
FIG. 1
, comprised of a magnetic recording medium
1
, a spindle
2
for holding and rotating it, a magnetic head
3
, which performs reading and writing, a servomechanism
4
for positioning the magnetic head, and an electric circuit
5
for driving them, and these are combined together to constitute one magnetic disc drive.
Also, the magnetic recording medium is generally comprised of a metallic undercoat layer, a magnetic layer, a protective layer, and a lubricating film layer on a non-magnetic substrate, and for characteristic properties required for the magnetic recording medium, not only R/W characteristics, but also matters concerning resistance to sliding property and the like such as damages on a surface of the medium by the contact with a magnetic head become important. Particularly, as regards a surface of the substrate, there is generally used a method for preventing the magnetic head from adhering to a magnetic disc by forming a fine groove by circumferential or non-oriented grinding called “texture” due to a machining method using fine abrasive grains.
Also, as other methods, there are a method (method called “depotexture”) in which a similar effect to the texture is obtained by forming a substrate or a magnetic layer with a fine projection on the surface thereof by means of sputtering, and a method (etching texture method) for obtaining the similar effect by, after formation of a overcoat, coating with Teflon particles or the like as masking material, etching the surface by a dry etching method, and machining the surface of the protective layer to form irregularities on the protective layer itself, and the like.
The object of either method is mainly to prevent the magnetic head from sticking onto the magnetic disc, and to confirm reliability by means of contact start stop (hereinafter, referred to as “CS/S”). In recent years, however, in these days in which as particularly the recording density becomes higher, flying height of the magnetic head has reduced less than 10 nm, a lamp load system (method for placing the magnetic head on the magnetic disc after the magnetic disc is kept rotated) has mainly been used in place of the CS/S system, and it has become impossible to represent a durability of a data surface with which the actual magnetic head comes into contact irregularly while floating by means of a conventional evaluation method for CS/S durability, adhesive force and the like.
In the conventional technique, there has been generally used a method for reducing the damage caused by a shock at the time of contact by providing the data surface with a fine groove called “texture” (hereinafter, referred to as TEX) by machining work, and for preventing the magnetic head from sticking using lubricant. According to this method, TEX machining itself means to provide the substrate with surface roughness, and if the surface roughness becomes large, the amount of floating of the magnetic head becomes higher inevitably, and a head take-off height (Hto), which is a minimum height for the magnetic head to float from the surface of the disc, also becomes higher. Therefore, it cannot withstand the use in the extra-low floating area. Further, if the substrate has surface roughness to some extent, it will be emphasized as it is, or more than it to appear on the surface roughness of the under film, the magnetic film, and the protective layer to be laminated naturally on the substrate, and the surface roughness of the magnetic recording medium finally completed will become equal to or higher than that of the substrate. Thus, the surface of the substrate for use is required to be made as flat as possible, and for this reason, the characteristics of resistance to sliding properties to be required for the protective layer and the lubricating film will require to have as much durability as possible. Also in order to solve these problems, such high-hardness, high-strength protective layer as diamond-like carbon film (amorphous hard carbon hydride film)(in the present specification, described as DLC film) is adapted to be required.
For a process for the DLC film, however, the CVD system, PE(Plasma Enhanced)CVD system, IBD(Ion Beam Deposition) system, and others have been used. The DLC film formed by means of these system has features in which the covering rate of the film is very high, the surface is made ultra-flat, and free radicals and the like which connect to a functional group of the lubricant become less. When such a surface is coated with lubricant, the lubricant is difficult to adhere, and is easy to scatter. Also, when the magnetic head comes into contact with the ultra-flat surface, a tangential force at the time of contact becomes great. The flatter the surface becomes, the easier this occurs, which causes the crash.
Further, the protective layer thickness to be required becomes equal to or less than 5 nm as the recording density becomes higher. According to the prior art, in order to enhance the strength of the protective layer, a nitrogen ion has been implanted into the DLC film by means of the ion implantation in Japanese Patent Laid-Open Application No. 1-263912. According to the Laid-Open Application, a nitrogen ion implantation layer is formed on the surface of the DLC film thereby, and the hardness of the film becomes higher toward the surface layer. In this Laid-Open Application, however, as the condition for the ion implantation, the nitrogen ion is accelerated at 5 keV to 60 keV. When accelerated under this condition, it reaches to a depth of about 270 A to 3600 A, very high acceleration is given to the overcoat thickness being 100 to 200 Å, and even though an etching phenomenon occurs before the implantation, it is a phenomenon quite in order. Further, since it is assumed that there is no spacing loss on the surface obtained as described above, and since the nitrogen ion accelerated actually reaches the magnetic layer, it is evident that the magnetic recording characteristics of the magnetic layer will be certainly affected, and it is considered that any increase in error rate due to dropout cannot be expected.
These problems have a similar result even if the method specified in Japanese Patent Laid-Open Application No. 9-219020 is employed, and in a portion as thick as 100 to 200 Å in overcoat thickness, depth of implantation may be controlled by reviewing the implantation condition. Under present circumstances, however, the protective layer thickness is equal to or less than 50 Å, and it becomes difficult by means of these methods. Further, the nitrogen ion entered by implementation bonds to carbon, which is a basic composition of the DLC film, on rare occasion, and is none other than one physically entered.
Therefore, it can be seen that any improvement effects of such adhesive power of lubricant onto the DLC film as described above cannot be expected either. Also, since these methods are unable to control the form of the surface of the DLC film (it has been specified that the form does not change), the tangential force of the magnetic head at the time of contact is steadily rising, and any improvement in the tribological resistance to sliding operation is not wished.
SUMMARY OF THE INVENTION
Thus, in the present invention, there has been proposed a technique and a method for treating only an ultra-surface layer of the DLC film equal to or less than 5 nm with the aim of arbitrarily forming surface roughness on a DLC film, which is an exceedingly thin film of 5 nm or less, at surface roughness Ra of the substrate being 0.4 nm or less with an amount of floating of the magnetic head being 10 nm o
Fujimaki Shigehiko
Honda Yoshinori
Kataoka Hiroyuki
Kokaku Yuuichi
Ono Toshinori
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Resan Stevan A.
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