JPH07230620A - Substrate for magnetic disk and magnetic disk - Google Patents

Abstract

PURPOSE:To obtain a substrate for magnetic disks having an excellent floating characteristic, attraction characteristic and contact start-stop characteristic and a magnetic disk. CONSTITUTION:The surface of the substrate after texturing has roughness of Ra within a range of 20 to 55Angstrom and both of [max. projection height (Rp)/Ra] and [max. valley depth (Rv)/Ra] within a range of 1.0 to 4.2. Further, Pc2 (100Angstrom ) is below 100 pieces and Pc2 (50Angstrom ) is >=100 pieces when the number per roughness curve 0.25m of the projections of the height X (Angstrom ) or above on the bases of the center line of the roughness curve of the texture is defined as Pc2 (XAngstrom ).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk substrate and a magnetic disk having excellent floating characteristics, adsorption characteristics and CSS characteristics.

[0002]

2. Description of the Related Art In recent years, with the development of information processing technology for computers and the like, magnetic recording media such as magnetic disks have been used as external storage devices. Conventionally, as a magnetic recording medium, an aluminum alloy substrate is subjected to alumite treatment or Ni-
A non-magnetic plating treatment such as P plating is applied, followed by coating an underlayer such as Cr, then a magnetic thin film layer of a Co-based alloy, and a carbonaceous protective film. .

As the density of the magnetic recording medium (magnetic disk) increases, the distance between the magnetic disk and the magnetic head, that is, the flying height, is becoming smaller and smaller, and recently, 0.1 μm.
It has become a degree. Regarding the low flying characteristics of the magnetic disk, a correlation with the surface average roughness (Ra) of the substrate after texture processing for forming fine grooves on the substrate surface of the magnetic disk is pointed out, and the surface average roughness is small. By doing so, it is possible to reduce the flying height of the head. However, simply reducing the average surface roughness will increase the coefficient of friction between the magnetic head and the substrate surface, and in extreme cases an adsorption phenomenon will occur, causing the sliding surface to remarkably move due to contact sliding between the two. May be damaged. Furthermore, magnetic disks are being miniaturized in parallel with the increase in capacity and density, and the motors for spindle rotation are becoming smaller and smaller. For this reason, the torque of the motor is insufficient, and the phenomenon that the magnetic head does not fly while being fixed to the magnetic disk surface is likely to occur. In addition, if the average surface roughness is increased to avoid the adsorption phenomenon, it is difficult to reduce the flying height of the head, and the number of abnormal protrusions after texture processing increases, so the head collides with this abnormal protrusion. In this case, similar to the suctioned state, there is a problem that the sliding surfaces of both the head and the disk are significantly damaged.

Therefore, in order to achieve a low flying height of the head while maintaining the surface average roughness that does not cause adsorption, the protrusion portion represented by the maximum protrusion height (Rp) is controlled, and the average surface is controlled. Roughness (Ra) and Rmax (maximum height)
Various substrates have been proposed in which the surface roughness parameter of the texture is defined within a certain range (Japanese Patent Publication No.
765, JP-A-4-212714, JP-A-4-2142
24, JP-A-5-151556, and JP-A-5-543.
74 publication).

[0005]

However, in the substrate described in the above publication, the maximum protrusion height (R
Only p) is controlled, and even if Rp is below a certain value,
Since the optimum Rp value for Ra is not controlled, R
When the value of Rp with respect to a is large, not only is the head impinging on the abnormal protrusion and the low flying height is not achieved, but also the protrusion is damaged due to the collision and C. S. S. (Contact
There is a problem that a head crash occurs in the Start and Stop) test.

Further, the stable flying height of the head (hereinafter referred to as Gri
d Height: G.D. H. Even if it is possible to lower the value of ()), since the valley portion indicated by the maximum valley depth (Rv) is not considered at all, the gap with the head becomes large in the large valley portion, and only that portion has information. Since the reading and writing of data is not performed sufficiently (hereinafter referred to as spacing loss), the disk becomes defective and there is a problem that the effect of lowering the flying height cannot be fully utilized.

[0007]

Means for Solving the Problems As a result of intensive investigations by the present inventors to further improve the levitation characteristics of the above-mentioned magnetic disk, the substrate surface characteristics are improved by applying a texture of a specific shape to the substrate. The inventors have found that the above objects can be achieved and completed the present invention.

That is, the gist of the present invention is that in a magnetic disk substrate formed by subjecting a non-magnetic substrate surface to texturing, the textured substrate surface has an average surface roughness (Ra) of 20 to 55Å. Within the range of, and [maximum protrusion height (Rp) / surface average roughness (R
a)], and [maximum valley depth (Rv) / surface average roughness (R)
a)] has a roughness within the range of 1.0 to 4.2.

The present invention will be described in more detail below.
As the non-magnetic substrate of the magnetic recording medium in the present invention, a disk-shaped substrate generally made of an aluminum alloy is processed to a predetermined thickness, and then the surface is mirror-finished, and then a non-magnetic metal such as Ni-P alloy, Alternatively, a Ni-Cu-P alloy or the like formed as a surface layer having a thickness of about 5 to 20 μm by electroless plating is used.

It is general that the surface layer of the above-mentioned substrate is subjected to polishing and then textured.
Polishing process, for example, sandwich the substrate between the polishing pad impregnated with free abrasive grains on the surface,
Polishing is performed while supplying a polishing liquid such as an aqueous solution of a surfactant, and the polishing is usually performed for about 2 to 5 μm, and the surface thereof has an average surface roughness Ra of 50 Å or less, preferably 30.
Å Make a mirror finish below. As the loose abrasive grains, typically, alumina-based slurry polyplastics 700 and polyplastics 1 are used.
03 (both are registered trademarks of Fujimi Inc.), diamond-based slurry, SiC-based slurry and the like. As a polish pad, typically,
Urethane foams such as Surfin 100 and SurfinXXX-5 (both are registered trademarks of Fujimi Incorporated) are used.

In the present invention, the surface average roughness Ra of the substrate surface is in the range of 20 to 55Å, preferably 25 to 45Å, and [maximum protrusion height (Rp) / Ra] and [maximum valley depth] (Rv) / Ra] are both 1.0 to 4.
2, preferably in the range of 2.0 to 3.8,
Textured. As the texture processing method, for example, tape grinding using a polishing tape carrying alumina abrasive particles or the like, or slurry grinding using free abrasive particles to precisely form fine grooves or irregularities on the surface of the substrate subjected to the polishing processing. Form. Further, it is preferable that the polishing tape is subjected to texture processing while vibrating in the radial direction of the disc to form striations in a cross pattern, and the angle of the striations is 10 to 40 °, more preferably 10 to 40 °. Polishing at 30 ° is preferable from the viewpoint of improving the adsorption property.

Further, in order to remove abnormal protrusions on the substrate surface, a second stage texture may be applied by slurry grinding using loose abrasive grains. In the present invention, the above-mentioned specific substrate surface is formed by performing texture processing by combining conditions such as the grain size of polishing abrasive grains, the number of revolutions of the disk, the tape pressing pressure and the polishing time.

By using the disk-shaped substrate having a specific surface shape according to the present invention, Ra of such an extent that the adsorption phenomenon can be avoided.
By maintaining the Rp / Ra value while maintaining the above value, the abnormal protrusion that obstructs the low flying height of the head is removed, and Rv / R
By defining the a value, it is possible to provide a magnetic recording medium that can eliminate a partial spacing loss between the head and the disk.

In the present invention, further, on the surface of the substrate after the texture processing, protrusions having a height X (Å) or more based on the center line of the roughness curve of the texture per 0.25 mm of the roughness curve are used. When the number is Pc2 (XÅ), Pc2 (100Å) is less than 100, preferably 5
When less than 0 and Pc2 (50Å) is 100 or more, preferably 250 or more, high lubrication characteristics and low flying characteristics required for a magnetic disk can be realized at the same time, and when the head is flying low It is possible to prevent the deterioration of the CSS characteristics in.

The surface shape of the substrate (R
For a, Rp, Rv, Pc2), the definition defined by JIS surface roughness (B0601) is used. By performing recording / reproduction with a magnetic disk manufactured using the magnetic disk substrate of the present invention, the flying height of the head is 0.06 μm or less, particularly preferably 0.
The thickness can be set to 02 μm or less, and the recording density can be remarkably improved.

On the surface of the textured substrate, chromium is formed as an underlayer by sputtering. The thickness of the chromium underlayer is usually 50 to 2000.
It is in the range of Å. As the metal magnetic thin film layer formed on the Cr underlayer of such a substrate, Co--Cr and Co--N are available.
A magnetic thin film layer of a Co-based alloy represented by i, Co-Cr-X, Co-Ni-X, Co-W-X, or the like is preferable. Here, X is Li, Si, Ca, Ti, V, Cr, N
i, As, Y, Zr, Nb, Mo, Ru, Rh, Ag,
Sb, Hf, Ta, W, Re, Os, Ir, Pt, A
u, La, Ce, Pr, Nd, Pm, Sm, and Eu
One or more elements selected from the group consisting of

The metal magnetic thin film layer made of such a Co-based alloy is usually deposited on the underlayer of the substrate by means such as sputtering. The film thickness of the metal magnetic thin film layer is usually in the range of 100 to 1000Å. The protective thin film layer formed on the metal magnetic thin film layer is preferably a carbonaceous film, and the carbonaceous protective thin film layer is usually argon,
In a rare gas atmosphere such as helium or in the presence of a small amount of hydrogen, an amorphous carbon film, a hydrogenated carbon film or the like is deposited by sputtering with carbon as a target. The thickness of the protective thin film layer is usually 50 to 50.
It is set in the range of 0Å. Further, a lubricating film may be further formed on the protective thin film layer in order to reduce the coefficient of friction.

[0018]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. Examples 1 and 2 and Comparative Examples 1 and 2 Ni-
Twelve substrates that had been subjected to P plating treatment and cleaned after mirror polishing were prepared. The surface shape (Ra, Rp) of each substrate was obtained by performing a one-step texture processing by tape grinding on both surfaces of these substrates and then a two-step texture processing by slurry grinding. , Rv,
Three disk substrates each having an average value of Pc2) having four values as shown in Table 2 of Examples 1-2 and Comparative Examples 1-2
One sheet was manufactured. Each surface shape (Ra, Rp, Rv, Pc2)
Was measured under the following conditions.

[0019]

[Table 1] <Surface shape measurement conditions> Surface roughness meter: Rank Taylor Hobson “Taristep” Stylus tip: 0.2 μm square Filter value: 0.33 Hz Measuring length: 0.25 mm Needle pressure: 4 mg Measuring speed : 0.025 mm / s

A Cr underlayer (about 1000 Å) is first formed on this substrate by the sputtering method, and then Co is formed.
A CrTa magnetic film (about 500 Å) is formed. further,
After forming a C protective layer (about 200Å), a lubricant was applied (about 10Å) to manufacture a magnetic disk. With respect to the magnetic disk manufactured in this manner, the stable flying height of the head (GH), the number of surface defects (the number of CMs), the head adsorption characteristic (μ) and the CSS characteristic (μ) were evaluated by the following methods. The results are shown in Table 2.

(1) Stable flying height of head (G.
H. ): Measurement was performed with a commercially available glide tester, and the height at which the head started to collide with one protrusion was defined as the stable flying height of the head. (2) Number of surface defects (number of CM): Measured by a commercially available certifier under the following measurement conditions. The smaller the number of collectable / missing errors (the number of CMs), the better the evaluation.

[0022]

[Table 2] <Measurement conditions> Rotation speed: 5500 rpm Test head Gap width: 5.0 μm Gap length: 0.33 μm Test pitch: 5.0 μm MB (missing bit): 70% or less EB (extra bit): 25% or more The frequency was measured by zone bits.

(3) Head adsorption characteristic (μ): temperature 25
The head and the magnetic disk were left in a static contact state for 1 hour in an atmosphere of 80 ° C. and 80% humidity, and the friction coefficient at the time of start-up was measured. The smaller the value, the smaller the friction and the better the evaluation. (4) CSS characteristics (μ): Using an AlTiC head slider with a load of 5.0 g, the friction coefficient after performing 20,000 CSS cycles was measured. The smaller the value, the better the abrasion resistance. In addition, plots of the relationship between each surface shape of the disk substrate and the characteristics of the obtained magnetic disk are shown in FIGS.
It was shown to.

[0024]

[Table 3]

[0025]

[Table 4] * Figures in parentheses are average values excluding those that have caused HC (head crush) or adsorption.

As is clear from Table 2, the disk of Example 1 satisfying all of the above specific texture shapes,
G. H. It can be seen that good results are shown for all of the number of surface defects, adsorption characteristics and CSS characteristics. From Figure 1, Rp / R
The smaller a is G. H. Is low, 1.0
.About.4.2, preferably 2.0 to 3.8 is shown to be necessary for obtaining good characteristics, and FIG.
The smaller the v / Ra, the smaller the number of CMs, and it is understood that the range of 1.0 to 4.2, preferably 2.0 to 3.8 is necessary to obtain good characteristics.

It can be seen from FIG. 3 that the adsorption property is improved as Ra increases, and that Ra is preferably 20 Å or more, preferably 25 Å or more in order to obtain good properties. From FIG. 4, the adsorption property is improved as the number of Pc2 (50Å) increases, and Pc2 (50Å) is 1
It can be seen that 00 or more, preferably 250 or more are necessary to obtain good characteristics.

As shown in FIG. 5, the larger the number of Pc2 (100Å) is, the more the adsorption characteristic is improved. However, if the number is too large, head crush occurs, and in order to obtain good characteristics without causing head crush, Pc2 (100Å) is 1
It can be seen that the number is less than 00, preferably less than 50. From Figure 6, Pc2 (100 Å) depends on Ra,
If the number of 2 (100Å) is less than 100,
It can be seen that Ra needs to be 55 Å or less, preferably 45 Å or less.

As described above, as shown in FIGS. 1 to 6, Ra on the substrate surface is 20 to 55Å, and Rp / R at that time is Rp / R.
a and Rv / Ra are both required to obtain good characteristics of the texture shape in the range of 0.1 to 4.2, and the number of Pc2 (100Å) is less than 100 and Pc2 (50Å). It can be seen that the substrate having the number of 100) is 100 or more is preferable in terms of good CSS characteristics.

[0030]

By using the substrate having the textured shape of the present invention, the surface defects due to the spacing loss in the groove having the excellent floating characteristics and the large texture can be eliminated,
Furthermore, while maintaining the adsorption property at a good level, excellent C
Since a magnetic disk having SS characteristics can be provided, it has high industrial utility value.

[Brief description of drawings]

FIG. 1 Stable flying height of head and Pp / of disk surface
It is a figure which shows the relationship with Ra.

FIG. 2 is a diagram showing the relationship between the number of surface defects and Rv / Ra on the disk surface.

FIG. 3 is a diagram showing a relationship between an adsorption characteristic and Ra on a disk surface.

[Fig. 4] CSS characteristics and Pc2 (50Å) on the disk surface
It is a figure which shows the relationship with.

FIG. 5 shows CSS characteristics and Pc2 (100
It is a figure which shows the relationship with Å).

FIG. 6 is a diagram showing the relationship between Pc2 (100Å) and Ra on the disk surface.

Claims (8)

[Claims] 1. A magnetic disk substrate formed by subjecting a surface of a non-magnetic substrate to texturing,
The surface of the substrate after texture processing has an average surface roughness (R
a) is in the range of 20 to 55Å, and [maximum projection height (Rp) / surface average roughness (Ra)] and [maximum valley depth (Rv) / surface average roughness (Ra)] are both 1.0-4.
A magnetic disk substrate having a roughness within the range of 2. 2. The magnetic disk substrate according to claim 1, wherein the average surface roughness (Ra) is in the range of 24 to 45Å. 3. The magnetic disk substrate according to claim 1, wherein the [maximum protrusion height (Rp) / surface average roughness (Ra)] is in the range of 2.0 to 3.8. 4. The magnetic disk substrate according to claim 1, wherein the [maximum valley depth (Rv) / surface average roughness (Ra)] is in the range of 2.0 to 3.8. 5. The number of protrusions having a height X (Å) or more based on the center line of the roughness curve of the texture on the surface of the substrate after the texture processing per Pc2 ( If XÅ), Pc2 (100
5. The magnetic disk substrate according to claim 1, wherein Å) is less than 100, and Pc2 (50Å) is 100 or more. 6. The magnetic disk substrate according to claim 5, wherein the number of Pc2 (100Å) is less than 50. 7. The magnetic disk substrate according to claim 5, wherein the Pc2 (50Å) is 250 or more. 8. A magnetic disk manufactured using the magnetic disk substrate according to claim 1, wherein the flying height of the magnetic head during recording / reproducing is 0.02 μm or less. Magnetic disk.