JPH10320761A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the CSS of a magnetic recording medium by providing the congested part of protrusions in a magnetic recording medium in which protrusions are formed on a substrate, thereby reducing the maximum load applied to each protrusion without increasing a friction factor. SOLUTION: At the congested part of protrusions, 2-10 pieces of protrusions are consecutively formed in a circumferential direction, and the interval D1 between outer end parts of the protrusions and the interval D2 between congested parts are respective defined as 0.1-10 μm and 10-100 μm. When the number of the protrusions is 11 and the interval D2 is 10 μm, a protrusion density is too high to cause the possibility that a head is attracted to the surface of a disk, and when the interval D1 is 0.1 μm, the mutual interference between protrusions each other is caused, and further when the interval D1 is >=10 μm, the head load is not sufficiently dispersed. Furthermore, when the interval D2 is >=100 μm, the interval between protrusions is too wide to affect the flying stability of the head. Then, a protrusion itself is regulated to 1-10 μm in diameter and to 1-30 μm in height to avoid the influence of a weak glide noise being the CSS characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium such as a magnetic disk drive, and more particularly, to improving the sliding durability between a magnetic disk (hereinafter referred to as HD) and a magnetic head. The present invention relates to a magnetic recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art The progress of high-density magnetic recording has been steadily increasing, and the speed of improving the recording density of a hard disk drive (HDD), which was once said to be 10 times in 10 years, has recently been 100 times in 10 years. Voices have also been heard.
HDD is popularly called Winchester style.
The CSS (contact start / stop) method, which basically includes contact sliding between magnetic heads, head floating, and contact sliding, is mainly used.
Although this system is a revolutionary one that has rapidly accelerated the increase in the recording density of HDDs, it has also begun to introduce serious tribological issues. The recent increase in recording density has been accompanied by an increase in disk rotation speed and a proposal for the flying height of the magnetic head, and the demands for sliding durability / stability and smoothness of the HD surface in the CSS method are increasing. It is the present situation.

The key to improving the sliding durability between the magnetic head and the HD lies in the improvement of the material strength and the reduction of the friction coefficient including the lubricating property. Like carbon (DLC) protective film,
Efforts have been made to reduce the coefficient of friction by roughening the HD surface along with various types of applied lubricants. This is called texturing, and is intended to reduce the coefficient of friction by effectively reducing the contact area to increase CSS durability / stability. Roughening is basically forming irregularities having a predetermined range of height difference on the HD surface. This texture processing is an important elemental technology of the HD manufacturing technology.

[0004] The above-mentioned texture technique is, of course, inseparable from the material of the substrate.
In the case of a substrate, a method of forming irregularities by mechanical polishing using polishing powder or the like has been mainly used. For a glass substrate or the like, lithography or an etching technique combining the lithography and the printing technique has been proposed, and some of them have been put to practical use.

[0005] As can be said about texture technology in general,
Efficiency in the process is also a necessary condition along with precise unevenness control, but the two are often in opposition to each other, and in particular, as described above, the increase in the recording density of HDDs is progressing at an amazing speed. Under the circumstances, the conventional technology is not only unable to satisfy a predetermined specification, but also exposes various problems that can no longer be covered by accumulating ideas and improvements. For example, the mechanical polishing method is already near the limit of fine processing control, and fundamental difficulties are encountered not only in the level of unevenness but also in precision control of a texture area which is important in zone texturing and the like. More specifically, there are irregularities (over-polishing, burrs, etc.) that occur at a constant rate and indicate a height difference outside a predetermined range, and blurring of texture boundaries. In addition, although the lithographic method has no problem in terms of precision system, the complexity of the process is inevitable, which is the Achilles' heel in terms of efficiency.

On the other hand, a higher recording capacity and a higher quality of an HDD inevitably include achieving a high degree of cleanliness in an HD manufacturing environment, and removal / removal of various contaminants and dust at a high level.
At present, elimination is the ultimate goal for each process. From this point of view, it is desirable that each step is dry, and there is great expectation for this dry texturing.

[0007] It can be said that an attempt to apply laser light to material processing and measurement started from the beginning of the invention of the laser. However, recent development / development of laser light sources has brought about remarkable improvements in basic characteristics and handling properties, and has shifted from high energy processing to ultra-high energy processing. It forms a wide range of utilization technologies, from fine processing to precision measurement. Laser ablation (erosion) or laser etching, which forms a material by a laser beam or processes a material surface, has been actively studied since the 1980s. Recently attracted interest (eg USP
5062021, JP-A-62-209788, JP-A-3-272018, JP-A-7-182655
JP-A-8-129949). The laser texture technique has an advantage that a crater-like projection can be formed on a substrate at an arbitrary height, interval, and position with good control by laser beam irradiation, and is basically a dry process. JP-A-3-272018 discloses an Nd-YAG laser of Q-switch pulse oscillation (wavelength 1064).
nm, oscillation frequency 12 KHz) and a diameter of 2.5 to 1
Crater-like projections of 00 μm (see FIG. 6) are spaced 12.7 apart.
It is formed on a NiP-plated Al substrate with a thickness of ２５25.4 μm. Further, Japanese Patent Application Laid-Open No. 8-129949 proposes that protrusions having a cross-sectional shape shown in FIG. 7 be formed at a predetermined area ratio and a predetermined height.

[0008]

However, in the laser texture technique, if the heights and the intervals of the projections are set incorrectly, the head is attracted to the disk surface and the CSS characteristics are remarkably deteriorated. Friction occurs between the head and the projection during CSS. Due to this friction, the projections are shaved. The shaving amount of the protrusion increases with an increase in the number of CSSs, and is one of the factors that deteriorate the CSS characteristics. In particular, when the projections are greatly shaved and the head comes into contact with the smooth surface of the substrate (the portion other than the projections), CS
The S characteristic deteriorates remarkably, causing a head crash.

[0009] The shaving of the projection is as follows.
It greatly depends on the load applied to each piece and (B) the coefficient of friction. (A) Since the load applied to each projection by the head is (total load of the head) / (projection density), it is considered that the higher the projection density, the smaller the load. On the other hand, (B) the coefficient of friction tends to increase when the projection density becomes too large. That is, if the projection density is simply increased in order to reduce the amount of protrusion shaving, the friction coefficient increases, and it is actually difficult to reduce the amount of protrusion shaving. Therefore, an object of the present invention is to provide an arrangement of projections capable of reducing the maximum load applied to each projection without increasing the friction coefficient, and to improve the CSS characteristics of the magnetic recording medium. And

[0010]

Means for Solving the Problems In order to solve the above problems, the present inventors have further studied the factors (A) and (B) for shaving the projections. (A) The load that the head exerts on each of the projections becomes the maximum when the substrate rotation speed decreases from the time of READ / WRITE and the head contacts the projection for the first time. This is because the higher the rotation speed, the faster the head speed and the greater the kinetic energy of the head. Also, when the head and the projection make contact for the first time, it is considered that only the Trailing Edge Face (see FIG. 8) having a small head area comes into contact with the projection because the head is in a flying state. (B) Regarding the coefficient of friction, the coefficient of static friction and the coefficient of dynamic friction are generally larger than the coefficient of static friction. Therefore, the coefficient of friction becomes maximum when the disk starts rotating. At the start of the rotation of the substrate, the head is stationary, so that the air bearing surface has a large area (see FIG. 8).
It is considered that the whole is in contact with the protrusion.

As described above, the phenomenon in which the factors (A) and (B) are maximized occurs in different time zones, ie, at the time of rotation and at the start of rotation. Further, in these two phenomena, the number of contacting projections is significantly different. That is, at the time of maximum load, the number of projections that contact is extremely small, and at the time of maximum friction, the number of projections that contact is extremely large.

Therefore, the present inventors have found a method of reducing the maximum load of each projection without increasing the maximum friction amount, and have reached the present invention. In other words, in order to reduce the maximum load, the number of protrusions that come into contact with the head may be increased,
Increasing the overall projection density increases the friction coefficient. However, the present inventors have newly conceived that if the projection density is locally increased, the maximum load can be reduced without increasing the friction coefficient. The present invention is based on this idea, and is characterized in that a magnetic recording medium having a plurality of projections formed on a substrate surface has a dense portion where projections are formed more densely than other portions. Medium.

In the present invention, the dense portion may be formed such that projections are continuously formed in the circumferential direction or may be formed in the radial direction. FIG. 1 shows the former example, and FIG. 2 shows the latter example. As shown in FIG. 3, it may be formed continuously in both the circumferential direction and the radial direction. Further, in the present invention, it is basically important that a dense portion is formed,
As shown in FIG. 4, even if there is a projection between the dense portions, the effect is not affected. 6 and 7 are known as the form of the projection by the laser beam irradiation, and FIGS. 1 to 4 are schematically represented by simple circles. The projection of the present invention is typically in the form shown in FIG. 6, but may be in FIG. 7 or another form.

In the dense portion, two or more and ten or less protrusions are continuously formed, and the outer end interval D1 of the protrusions in the dense portion is 0.1 to 10 μm.
It is preferable that the distance D2 between the dense portions is 10 to 100 μm. The reason why the number of protrusions in the dense portion is 2 or more and 10 or less is that if one is used, the head load is not dispersed, and if it is 11 or more, the protrusion density becomes too high, and the head is attracted to the disk surface. This is because there is a risk of occurrence. The reason why the distance D1 between the outer ends of the projections in the dense portion is 0.1 to 10 μm is that when the distance is less than 0.1 μm, mutual interference between the projections occurs.
This is because the shape of the projections may be deformed. When the thickness exceeds 10 μm, the head load is not dispersed because the interval between the projections is too wide, and the reduction of the maximum load applied to each projection is insufficient. This is because Interval D1
D1 is preferably set to 0.1 to 5.0 μm because the smaller the width of the head, the smaller the maximum load of the head exerted on each head.

The distance D2 between the dense portions is 10 to 100 μm.
The reason why m is that if the diameter is less than 10 μm, the projection density becomes too high and the head is easily attracted to the disk surface. This is because the stability is affected. A preferable value of the interval D2 for reducing the maximum friction coefficient while maintaining the flying stability of the head is 20 to 50 μm. Note that the outer end interval D1 and the interval D2 between the dense portions are defined by FIG.

The size of the projection itself in the present invention is desirably 1 to 10 μm in diameter and 1 to 30 nm in height. If the diameter is less than 1 μm, the strength of the protrusion is weak and the CSS characteristics are weak. If the diameter exceeds 10 μm, the protrusion exerts a large impact on the head, which may affect glide noise. In addition, height 1n
If the diameter is less than m, the projections cannot be identified due to the surface roughness of the substrate. If the area exceeds 30 nm, the projections will collide with the head even when the substrate is rotating at high speed, causing a head crash or the like. .

Further, the average value of the protrusion interval, that is, (D1 +
D2) / 2 is preferably from 1 to 50 μm. 1μ
If it is less than m, the continuous projections overlap, and if it exceeds 50 μm, the interval becomes large, and the maximum friction coefficient increases with the number of CSS. Conversely, glide noise increases. A more preferable average value is 10 to 30.
μm. The substrate of the present invention is typically NiP
A plated Al substrate is used, but other materials,
It may have a structure.

The magnetic recording medium of the present invention can be manufactured by various methods as described below. As a method of forming dense portions of protrusions at intervals as in the present invention, there is a method of changing a repetition frequency of a pulse of a laser beam. The repetition frequency of the laser beam pulse is controlled by an external modulator in the case of a continuous wave laser. As an external modulator, an electro-optic effect modulator (Elect
tro-optic-modulator, EO for short
M) or an acousto-optic modulator (Acoustic-Op)
tic-Modulator (AOM for short) is used.

The EOM is capable of continuously changing the laser output by changing the optical path of an incident continuous wave laser by applying a voltage to an optical crystal and utilizing the electro-optic effect of changing the refractive index of the crystal. it can. The AOM is capable of continuously changing the laser output that passes straight through by introducing ultrasonic waves from the outside into the optical crystal and changing the analysis angle of the incident continuous wave laser light using the optical elasticity effect of the crystal. it can. Any of the modulators can modulate the laser output in the MHz band by a signal input from the outside, and the output modulation can be arbitrarily changed.

If the frequency of the external signal input to the modulator is increased, the interval between the protrusions becomes shorter, and a dense portion can be formed. On the other hand, if the frequency of the external signal is reduced, the distance between the protrusions becomes longer, and the distance between the dense portions can be increased.

While rotating the substrate at a constant peripheral speed, frequency modulation is applied to an externally input signal, whereby two or more
Zero or less projections have a densely formed portion formed continuously, and the outer end interval D1 of the projections in this densely spaced portion is 0.1 to 1
A magnetic recording medium having a thickness of 0 μm and a distance D2 between dense portions of 10 to 100 μm can be manufactured. Furthermore, if the pulse width and the pulse intensity are kept constant, the height of the protrusion formed on the substrate surface can be kept constant. Frequency modulation may be performed in two steps, a high frequency area and a low frequency area.
The frequencies in the high frequency region and the low frequency region do not necessarily have to be constant, and the frequency may change in the high frequency region and the low frequency region. Even when the substrate is rotated at a constant rotation, the magnetic recording medium of the present invention can be manufactured in the same manner as described above.

Since the pulse laser has a built-in EOM or AOM for modulation, a pulse control signal from the laser main body is used instead of a pulse control signal, and a signal is input from the outside. A recording medium can be manufactured.

In an optical system for continuously irradiating a laser beam after passing through a mirror whose reflection angle is changed, the processing position can be controlled by controlling the reflection angle of the mirror. Even if the reflection angle of the mirror is controlled using this characteristic, the magnetic recording medium of the present invention can be manufactured.

Also, a magnetic recording medium of the present invention can be manufactured by preparing a mask having a dense portion where protrusions are formed more densely than other portions, and passing a laser beam through the mask. can do.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

[Examples 1 to 10, Comparative Examples 1 to 4] A laser light external modulator using a continuous oscillation YAG laser (double harmonic mode, wavelength 532 nm, output 5 W) of a semiconductor laser excited by a 5 W output as a continuous oscillation laser light source Has EOM (15n rise)
s, maximum conversion efficiency 85%, laser maximum / minimum ratio Imax /
Imin = 80). A waveform generator was connected to the EOM as an external signal input device. The input waveform to EOM is
The pulse width was used, and the pulse width was 150 ns when obtaining a crater-like projection height of 18 nm, and the pulse width was 120 ns when obtaining a height of 14 nm. The repetition frequency of the pulse wave uses the frequency modulation function of the waveform generator.
In Comparative Examples 1 to 4, only one frequency of 400 or 200 Hz was used without performing frequency modulation. The spot diameter of the laser beam was 5 μm, the NiP-plated Al substrate having a diameter of 95 mm was rotated at a constant speed at the peripheral speed shown in Table 1, and the laser beam was rotated 1 mm in the radial direction.
The laser beam irradiation was performed while moving at / s.

In the first to fifth embodiments, the dense portion is formed by two circumferentially continuous projections, and in the sixth embodiment, the dense portion is formed by four circumferentially continuous protrusions. It consists of. In the seventh embodiment, the dense portion is composed of two protrusions, one of which has a height of 18 nm and the other has a height of 14 nm. Examples 8 to 10
The dense portion is constituted by two projections that are continuous in the circumferential direction. The intervals D1 and D2 of the projections formed by the above laser beam irradiation, and the average thereof ((D1 +
D2) / 2) are also shown in Table 1. In Comparative Examples 1 to 4, the protrusions are formed at regular intervals.

[0027]

[Table 1]

The substrates obtained in Examples 1 to 10 and Comparative Examples 1 to 4 were successively sputtered at a substrate temperature of 200 ° C. by successively sputtering 100 nm of Cr as an underlayer, 20 nm of a CoCrTa alloy as a magnetic layer, and 20 nm of carbon as a protective film. A magnetic recording medium was formed by forming a film and further applying a PFPE (perfluoropolyether) -based lubricant to form a film.

With respect to the obtained magnetic recording medium, CSS1
The amount of shaving of the protrusion after 0000 times was measured, and the CSS characteristics were evaluated. Tables 2 and 3 show the results.
In addition, the amount of shaving of the protrusion was determined by Air Bearing Surfac
The height of the shaved protrusions among the protrusions below e was measured, and the difference between the height of the protrusions and the height of other protrusions was obtained.

[0030]

[Table 2]

[0031]

[Table 3]

As shown in Table 2, Examples 1 to 1 of the present invention
In the magnetic recording medium of No. 0, it was confirmed that the shaving amount of the protrusion was reduced. In particular, the reduction of the shaving amount in Examples 1 to 6 is remarkable. Further, as shown in Table 3, Examples 1 to 1 of the present invention
It was confirmed that the magnetic recording medium of No. 0 also achieved an improvement in CSS characteristics.

Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be implemented in any manner unless the configuration described in the claims is changed. it can. For example, the layers formed on the substrate, the underlying film, the magnetic film, the protective film, the lubricant, and the like are not particularly limited in terms of the material, composition, film forming method, and the like, and may be formed using a known material or a known method. They can be appropriately selected and combined for use.

[0034]

As described above, according to the present invention,
Without increasing the coefficient of friction between the head and the substrate,
The maximum load applied to each piece can be reduced. As a result, shaving of the projections is reduced, and deterioration of CSS characteristics, head crash, and the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a plan view showing one embodiment of the present invention.

FIG. 3 is a plan view showing one embodiment of the present invention.

FIG. 4 is a plan view showing one embodiment of the present invention.

FIG. 5 is a diagram for explaining the interval between protrusions in the present invention.

FIG. 6 is a perspective view showing a crater-like projection formed by laser beam irradiation.

FIG. 7 is a cross-sectional view showing one form of a projection by laser beam irradiation.

FIG. 8 is a perspective view schematically showing a head.

Claims (7)

[Claims] 1. A magnetic recording medium having a plurality of protrusions formed on a substrate surface, wherein a dense portion in which protrusions are formed more densely than other portions is present. 2. The magnetic recording medium according to claim 1, wherein the dense portion has projections formed continuously in a circumferential direction. 3. The magnetic recording medium according to claim 1, wherein the dense portion has projections formed continuously in a radial direction. 4. The magnetic recording medium according to claim 1, wherein the projection is a crater-shaped projection formed by laser beam irradiation. 5. The dense portion is one in which two or more and ten or less protrusions are continuously formed, the outer end interval D1 of the protrusion in the dense portion is 0.1 to 10 μm, and the interval between the dense portions is The magnetic recording medium according to claim 1, wherein D2 is 10 to 100 μm. 6. The distance D1 is 0.1 to 5.0 μm, and the distance D
The magnetic recording medium according to claim 5, wherein 2 is 20 to 50 µm. 7. A method of manufacturing a magnetic recording medium in which projections are formed by irradiating a laser beam to a substrate surface, wherein laser beams having different pulse repetition frequencies are alternately irradiated. .