JPH0729164A - Amorphous carbon substrate for magnetic disk - Google Patents

Abstract

PURPOSE:To obtain an amorphous carbon substrate of which a highly reliable and high performance magnetic disk which facilitates the decrease of the floating height of a head can be composed. CONSTITUTION:The flatness of a whole amorphous carbon substrate is made to be not larger than 10mum and the average surface roughness Ra1 on the center line of the substrate is made to be not larger than 1nm and the surface roughness Ra2 of a region which is brought into contact with a magnetic head at the time of start and stop of a magnetic disk apparatus is made to be not less than 2nm. Therefore, attraction between the magnetic disk surface and the head which is easily produced at the time of stop and start can be avoided and, further, high density recording can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amorphous for a magnetic disk which has been subjected to a zone texture treatment in order to prevent an adsorption phenomenon from occurring between the magnetic head levitating surface and the magnetic disk surface. Regarding carbon substrate.

[0002]

2. Description of the Related Art Conventionally, a Ni-
An Al (aluminum) substrate plated with P (nickel phosphorus) alloy is widely used. However, as the magnetic disk becomes smaller and the recording density becomes higher, the conventional A
The l-board cannot support this. With the miniaturization of magnetic disks, magnetic disks have also been incorporated in portable devices, and new characteristics such as high impact resistance are required for magnetic disk substrates. . Therefore, as a substitute for the Al substrate, new substrates such as tempered glass, ceramics, and amorphous carbon have been developed. In particular, the amorphous carbon substrate is
It is lightweight and has high strength, and is excellent in heat resistance, impact resistance, surface smoothness, and wear resistance affected by surface hardness, and is superior to Al substrates. Therefore, there is a demand for practical use of the amorphous carbon substrate.

By the way, in general, a magnetic disk substrate is subjected to a texture treatment for finely roughening the surface of the substrate after the substrate surface is once smoothed by polishing or the like. this is,
This is to prevent the head from being attracted to the disk surface when the magnetic disk recording / reproducing apparatus is stopped, and to reduce the friction between the magnetic disk surface and the head that occurs when starting and stopping. The conventional amorphous carbon substrate is uniformly textured over the entire substrate surface by a mechanical polishing method such as fixed-abrasive polishing (tape polishing) or free-abrasive polishing and a chemical treatment method such as a surface oxidation method using gaseous oxygen. Has been applied.

[0004]

However, if the substrate surface is subjected to a texture treatment in order to prevent the adsorption of the head to the substrate surface and to reduce the friction between the head and the substrate surface, the surface smoothness of the substrate decreases. Therefore, it is difficult to increase the recording density. In addition, since the surface has fine irregularities, the flying height of the head cannot be lowered, and bit errors easily occur.

The present invention has been made in view of the above problems, and it is possible to prevent the magnetic disk surface and the head from being attracted to each other, realize a high recording density, reduce the flying height of the head, and improve the reliability. It is an object of the present invention to provide an amorphous carbon substrate for a magnetic disk that can obtain a high-performance and high-performance magnetic disk.

[0006]

An amorphous carbon substrate for a magnetic disk according to the present invention has a flatness of the entire substrate of 10 μm or less and an average surface roughness Ra on the center line of the substrate.
₁ is 1 nm or less, and the surface roughness Ra ₂ of the contact area with the head at the time of starting and stopping the magnetic disk device is 2 nm or more.

The flatness means the entire surface of the substrate.
The height difference between the highest position and the lowest position.

[0008]

As described above, the amorphous carbon material has the features of being lightweight and high strength, having a hard surface hardness, and being excellent in heat resistance, impact resistance, surface smoothness, etc. In order to utilize an amorphous material as a magnetic disk substrate, it is necessary to improve the flatness of the entire substrate.

When the substrate is rotated and the head is moved on the substrate surface, the flatness of the entire substrate must be 10 μm or less in order to keep the flying height of the head stable. When the flatness of the entire substrate is poor, the flying height becomes unstable because the entire head moves up and down when the substrate rotates and the head moves on the substrate surface.

Further, in a magnetic disk for recording / reproducing at high density, the surface roughness Ra _{1 of the} substrate needs to be 1 nm or less. The smoothness of the substrate surface greatly affects the flying height of the head and variations in the intensity of the recording / reproducing signal. In order to realize a high recording density, it is necessary to reduce the flying height of the head and reduce the fluctuation of the recording / reproducing signal due to the unevenness of the substrate surface. In order to satisfy these requirements, the surface roughness Ra ₁ of the substrate needs to be 1 nm or less.

On the other hand, the surface roughness Ra over the entire surface of the substrate.
_{When 1 is set} to a high smoothness of 1 nm or less, it is convenient for recording and reproducing signals, but the head is attracted to the disk surface when the magnetic disk device is stopped, or the friction between the head and the disk surface is generated during stop and start. Grows larger. For this reason, not only a large amount of energy is required to drive the disk, but also the head and disk surface may be destroyed. For this reason, the contact area where the head contacts at the time of stopping and starting has the surface roughness Ra ₂ of 2 nm or more. The effective contact area between the head and the disk surface is reduced by exclusively using the area where the surface roughness Ra ₂ is 2 nm or more as the contact area between the head and the disk surface when the magnetic disk device is started and stopped. It is possible to prevent the head from adsorbing to the disk surface when stopped.

In the recording / reproducing area, the average surface roughness Ra ₁ on the center line of the substrate is set to 1 nm or less in order to ensure the smoothness of the substrate. In the present invention, the average surface roughness Ra ₁ on the center line of the substrate is obtained by measuring the surface roughness of the recording / reproducing area excluding the contact area and calculating the average value.

By doing so, it is possible to reduce friction between the head and the disk surface when the magnetic disk is stopped and started, and it is possible to obtain a magnetic disk having a high signal recording density.

[0014]

EXAMPLES Next, examples of the present invention will be described. First, a method for manufacturing the amorphous carbon substrate of this example will be described. The amorphous carbon substrate configured as described above can be manufactured by various methods. Amorphous carbon can be obtained by heat-treating a thermosetting resin, such as a phenol resin, a furan resin, or a polyimide resin, which is a raw material of these materials and has a three-dimensional stitch structure, at 800 to 2700 ° C. in an inert atmosphere. it can. Therefore, by molding these raw material resins into the shape of a magnetic disk and then heat-treating the molded body under the conditions as described above, a disk-shaped amorphous carbon fired body can be obtained.

Next, the fired body is subjected to predetermined end face processing and surface polishing to finish an amorphous carbon disk having a surface roughness Ra ₁ of 1 nm or less. Since the amorphous carbon disk produced in this manner has a high smoothness over the entire surface thereof, a part of the surface is roughened by any of the following methods, so that A crystalline carbon substrate can be obtained.

That is, in the first method, as shown in FIG. 1, an amorphous carbon disk 1 having an entire surface with a surface roughness of 1 nm or less is formed in an atmosphere containing oxygen in an inner peripheral portion thereof. The ring-shaped portion 2 is locally heated by irradiation means such as a microburner, discharge, or infrared rays, and only the heated portion is surface-oxidized to roughen the surface roughness Ra ₂ to 2 nm or more. Amorphous carbon, under controlled conditions,
Since the portion where the processing stress due to polishing remains is selectively oxidized, as shown in FIG. 2, the surface is roughened without causing a step between the smooth polished surface of the disk 1 and the roughened portion 2. Can be faced.

Next, in the second method, while the amorphous carbon disk 1 is being rotated, the polishing tape is brought into contact with the inner peripheral portion 2 of the amorphous carbon disk 1, whereby the surface roughness Ra of only the contact portion 2 is increased. ₂ is roughened to 2 nm or more. On this occasion,
By optimizing the pressure with which the polishing tape is pressed against the substrate and the processing time, it is possible to control the level difference with the smooth polishing surface within a range that does not hinder practical use. Further, even if the tape-polished surface of the portion 2 becomes lower than the smooth surface of the disc 1, as shown in the upper and lower diagrams of FIG. 3, there is smoothness between the smooth polished surface of the disc 1 and the roughened portion 2. The head can be moved without hindrance by connecting the portions having different slopes.

In the third method, a laser beam is focused and irradiated on a part of the inner circumference of the amorphous carbon disk 1 to form a large number of fine holes on the surface of the substrate, which results in surface roughness. Ra _{2 is set} to 2 nm or more. Unlike Al or glass, a carbon material does not melt or soften due to heat.
Therefore, there is no burr or rise in the peripheral portion of the portion 2 irradiated with the laser beam. Therefore, the surface of the portion 2 roughened by the laser light has no step with the smooth polished surface of the disk 1 as shown in FIG.

Thus, the amorphous carbon substrate for a magnetic disk according to the embodiment of the present invention can be manufactured. Since the obtained amorphous carbon substrate has high smoothness in the recording / reproducing area, the recording density of the magnetic disk can be increased and the flying height of the magnetic head can be reduced. Therefore, a high performance magnetic disk can be obtained. On the other hand, the area where the head comes into contact has a surface roughness Ra ₂
Since the surface is roughened to 2 nm or more, head adsorption can be prevented.

Generally, high-density amorphous carbon means that glassy carbon is subjected to an ultra-high temperature HIP (hot isostatic pressing) treatment so that most of the pores are eliminated and the density is 1.80 g /
refers to those as high as cm ³ or more, but what density than that amorphous carbon in the present invention is to HIP treatment by lowering the temperature and pressure in the HIP processing conditions were as less than 1.80 g / cm ³ It also includes amorphous carbon whose properties are close to those of graphite.

Next, the results of actually manufacturing the amorphous carbon substrate for a magnetic disk according to the embodiment of the present invention and comparing the characteristics thereof with the comparative example will be described.

First, a phenol-formaldehyde resin is molded into a magnetic disk shape, and then, in a nitrogen atmosphere, about 1
An amorphous carbon disk was obtained by heat treatment to 500 ° C. Next, this disk was processed into an outer diameter of 65 mm, an inner diameter of 20 mm, and a thickness of 0.635 mm. Then, the surface was polished by a double-sided polishing machine so that the surface roughness Ra ₁ of the amorphous carbon disk was 0.7 nm.

Next, while rotating the disc, an area having an inner peripheral width of about 4 mm was heated by a microburner,
The surface of the carbon substrate was slightly oxidized. By changing the heating time, the surface roughness Ra ₂ of the heat-treated portion is 1.5.
To 8.0 nm. The surface roughness is measured using a non-contact surface roughness meter (TOPO3D; WYKO).
(Manufactured by the company).

Next, the amorphous carbon substrate for each disk manufactured as described above is precisely cleaned, and then a Cr underlayer, a CoNiCr media layer (magnetic film) and a CrNi underlayer are formed on the amorphous carbon substrate. A carbon protective film and a carbon protective film were sequentially formed by vapor deposition, and a lubricant was applied to the surface of the film to prepare a magnetic disk.

As a comparative example, a substrate that has not been textured at all and has been polished and a substrate that has been uniformly textured over the entire surface of the substrate are prepared. Layers etc. were formed.

With respect to the magnetic disks according to Examples 1 to 4 and Comparative Examples 5 to 7, a head adsorption or head crash occurrence status test and a recording / reproduction error test were carried out. The results are shown in Table 1 below.

In Table 1, in Examples 1 to 4 and Comparative Example 5, the surface roughness is roughened by oxidizing only the inner peripheral portion after polishing, and the roughness of the polished surface is the same for all substrates. The surface roughness Ra is 0.7 nm.

In Comparative Example 6, the entire surface was subjected to texture treatment after polishing, and Comparative Example 7 was only polished.

The surface roughness Ra ₂ of the roughened portion of each substrate is shown in Table 1.

[0030]

[Table 1]

As is clear from Table 1, the magnetic disks according to Examples 1 to 4 did not cause head adsorption or head crash. The magnetic disks according to Examples 1 to 4 had excellent recording / reproducing characteristics.

On the other hand, Comparative Example 5 has excellent recording and reproducing characteristics, but has a small surface roughness Ra ₂ of 1.5 nm.
Roughening was insufficient, and head adsorption and head crash occurred. In Comparative Example 6 in which the entire surface was subjected to the texture treatment, head adsorption and head crash did not occur, but the characteristics of recording / reproduction error were deteriorated. Further, in Comparative Example 7 in which the texture treatment was not performed as it was polished, the recording / reproducing error was small, but the head adsorption and the head crash occurred.

[0033]

As described above, according to the present invention, the flatness of the entire substrate is 10 μm or less, the zone texture treatment is applied only to the inner peripheral portion of the substrate surface, and the center line average surface roughness Ra ₁ is In addition to having a smoothness of 1 nm or less, the surface roughness Ra ₂ of the contact area with the head at the time of starting and stopping the magnetic disk device is roughened to 2 nm or more, so that the magnetic disk surface and the head can be prevented from being attracted. A high recording density can be realized, the flying height of the head can be reduced, and a highly reliable and high-performance amorphous carbon substrate for a magnetic disk can be obtained.

Therefore, the amorphous carbon substrate for a magnetic disk according to the present invention is suitable as a substrate for a high performance magnetic disk.

[Brief description of drawings]

FIG. 1 is a plan view showing a zone texture processed portion in an amorphous carbon substrate according to an example of the present invention.

FIG. 2 is a cross-sectional view showing an amorphous carbon substrate according to an embodiment of the present invention, which has been subjected to zone texture treatment by a surface oxidation method such as a microburner, discharge and infrared irradiation.

FIG. 3 is a cross-sectional view showing an amorphous carbon substrate according to an example of the present invention that has been subjected to zone texture processing by tape polishing.

FIG. 4 is a cross-sectional view showing an amorphous carbon substrate according to an example of the present invention that has been subjected to zone texture treatment by laser light irradiation.

[Explanation of symbols] 1; Amorphous carbon disk 2; Part

Claims (1)

[Claims] 1. The flatness of the entire substrate is 10 μm or less, and the average surface roughness Ra ₁ on the center line of the substrate is 1 n.
An amorphous carbon substrate for a magnetic disk having a surface roughness Ra of ₂ nm or more in a contact area with a head when the magnetic disk device is started and stopped.