JPH1139647A - Magnetic recording medium, its production and magnetic storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the bonding force with a lubricant by forming a magnetic layer and a protective film on a substrate, forming the protective film comprising a film containing at least carbon, nitrogen and oxygen and specifying each atomic ratio of nitrogen/carbon and oxygen/nitrogen in the film. SOLUTION: The atomic ratio of nitrogen/carbon in the film of the protective layer is specified to 0.05 to 0.3, and the atomic ratio of oxygen/nitrogen in the surface of the film is specified to 0.5 to 2.0. This magnetic recording medium consists of a magnetic disk substrate 1 of a nonmagnetic substrate and a multilayered film produced by successively depositing a Cr base layer 2, a CoCr magnetic layer 3, a carbon protective layer 4 with addition of nitrogen and oxygen, and a perfluoropolyether lubricant layer 5. In the magnetic recording medium having the structure above described, the surface of the protective film as the interface between the protective layer 4 and the lubricant layer 5 has strong electron withdrawing groups by addition of nitrogen and oxygen having large electronegativity so that the molecular end of the lubricant is firmly bonded to the surface of the protective film. This contributes to the improvement in the durability of the magnetic disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic storage device,
Related to a magnetic recording medium using the same and a method for manufacturing the same,
In particular, the present invention relates to a highly reliable magnetic storage device having a recording density of 2 gigabits per square inch or more, a magnetic recording medium for realizing the same, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A conventionally known protective film for a magnetic disk is made of a material formed by sputtering a graphite-like target, is chemically stable, has a low coefficient of friction, and hardly generates abrasion powder during sliding. It has properties suitable for a protective film, but contains a large amount of graphite-like carbon. For this reason, it is difficult to further increase hardness and wear resistance. On the other hand, measures have been proposed to prevent the formation of a graphite-like structure by adding another element to the above-mentioned protective film made of only carbon, thereby achieving densification. As elements to be added, hydrogen, boron, nitrogen, fluorine, silicon, which are covalently bonded to carbon,
Metals, metal oxides and metal nitrides have been proposed. In particular, a carbon-based protective film to which nitrogen is added has an average energy of multiple bonds of nitrogen and carbon higher than that of carbon and carbon, and has a β-C ₃
N ₄ is expected to have high performance as a protective film, for example, it is predicted that N ₄ will be a material having a hardness as high as that of diamond. To be more specific, Japanese Patent Application Laid-Open No. 5-2
No. 25556 and JP-A-7-320256.

[0003]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. Hei 5-22555
The one described in No. 6 is to improve the durability by strengthening the protective layer by adding nitrogen to a graphite-like material rich in carbon. However, the weight reduction of the magnetic head,
In the current situation of low flying height and thinning of the protective film, the chemical action of the protective film surface and the lubricant is more important than the mechanical strength as a factor governing the durability of the protective film. The surface structure and chemical properties have become more important factors than the inside of the film. Therefore, there is a problem that the durability of the magnetic disk cannot be improved only by increasing the mechanical strength of the protective layer.

On the other hand, Japanese Patent Application Laid-Open No. 7-320256 described above is intended to enhance the bonding force of a lubricant by adding a nitrogen element. Unless the chemical structure of the surface of the protective film corresponding to the interface is optimized, there is a problem that the effect of improving the durability of the magnetic disk is small.

In view of the above, an object of the present invention is to focus on the chemical properties of the surface of the protective film, and focus on a carbon-based protective film to which nitrogen has been added. In providing the chemical composition of

[0006]

In order to achieve the above object, a magnetic recording medium of the present invention has a magnetic layer on a base material and a protective film formed on the magnetic layer, and the protective film has at least carbon. , Nitrogen and oxygen, the atomic ratio of nitrogen / carbon of the coating is 0.05 to 0.3 and the atomic ratio of oxygen / nitrogen on the surface of the coating is 0.5 to 2 .0.

In order to achieve the above object, a magnetic recording medium according to the present invention is a magnetic recording medium in which a magnetic layer and a protective layer formed on the magnetic layer are sequentially laminated on a base material.
The protective layer comprises at least carbon, nitrogen and oxygen, and has a nitro group on the surface.

Further, in order to achieve the above object, a magnetic recording medium according to the present invention is a magnetic recording medium comprising: a magnetic layer on a substrate; and a protective layer formed on the magnetic layer. The layer comprises at least carbon, nitrogen and oxygen,
The center line average roughness Ra of the surface is 1 nm or less. Here, the definition of the center line average roughness conforms to the provisions of the Japanese Industrial Standards (JIS-B0601).

A magnetic storage device for achieving the above object is a magnetic recording medium, a drive unit for driving the magnetic recording medium in a recording direction, a magnetic head including a recording unit and a reproducing unit, and a magnetic recording medium. And a read / write signal processing means for performing a signal input to the magnetic head and reproducing an output signal from the magnetic head. Effect type magnetic head, wherein the magnetic recording medium contains at least carbon, nitrogen and oxygen, the atomic ratio of nitrogen / carbon is 0.05 to 0.3, and the ratio of oxygen / The semiconductor device according to claim 1, further comprising the protective layer having an atomic ratio of nitrogen in a range of 0.5 to 2.0.

[0010] A magnetic storage device for achieving the above object is a magnetic recording medium, a driving unit for driving the magnetic recording medium in a recording direction, a magnetic head comprising a recording unit and a reproducing unit, and a magnetic recording medium. A magnetic storage device comprising: means for moving relative to the magnetic head; and recording and reproduction signal processing means for performing signal input to the magnetic head and reproduction of an output signal from the magnetic head. Is formed on a magnetic head slider having a mass of 1.25 mm ² or less and a mass of 2 mg or less, and the magnetic recording medium contains at least carbon, nitrogen and oxygen, and has a nitrogen / carbon atomic ratio of 0.05 to 0.5. 3 and wherein the protective layer has an atomic ratio of oxygen / nitrogen on the surface of the coating in the range of 0.5 to 2.0.

In order to achieve the above object, a method of manufacturing a magnetic recording medium according to the present invention comprises a step of forming a magnetic layer on the surface of a base material and a step of forming a protective layer comprising at least carbon, nitrogen and oxygen on the surface of the magnetic layer And irradiating the surface of the protective layer with ultraviolet light in the air.

According to another aspect of the present invention, there is provided a method of manufacturing a magnetic recording medium, comprising the steps of: forming a magnetic layer on a surface of a substrate; and forming a protective layer comprising at least carbon, nitrogen and oxygen on the surface of the magnetic layer. And a step of subjecting the surface of the protective layer to a plasma treatment in an oxygen atmosphere.

Next, the above configuration will be functionally described.

In the magnetic recording medium having the above structure, a strong electron-withdrawing group is formed by adding nitrogen and oxygen having a high electronegativity to the surface of the protective film corresponding to the interface between the protective layer and the lubricating layer. Strongly binds to the surface of the protective film. In particular, when a nitro group consisting of nitrogen and oxygen is bonded to an aromatic ring or a conjugated double bond, the transfer of π electrons becomes a stronger electron-withdrawing group, and is further strongly bonded to a lubricant. It contributes to the improvement of performance. Such an electron-withdrawing group formed by nitrogen or oxygen is formed by a reaction with oxygen in the atmosphere. However, by adjusting the film forming method and conditions or performing surface treatment, the atomic ratio of oxygen / nitrogen is adjusted. Is optimized, the bonding force with the lubricant is further strengthened.

For example, surface treatment by oxygen plasma or ultraviolet irradiation is also an effective means for optimizing the chemical composition of the surface. Moreover, if oxygen plasma treatment or UV irradiation is used,
It is also effective in removing organic contamination by reaction with oxygen radicals and ozone, and in reducing unevenness by ashing or photoetching.

However, even when nitrogen and oxygen are contained, depending on the chemical state of the surface, the durability may be deteriorated such that the lubricant molecules are easily decomposed. Therefore, in order to improve the durability of the magnetic disk, it is desirable to optimize the surface element ratio of the protective layer as necessary. The lubricant used is not particularly limited.
Fluoropolymers such as perfluoropolyether and perfluorocarboxylic acid are preferred.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a magnetic recording medium according to the present invention and a method for manufacturing the same will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a magnetic recording medium for a hard disk, which best illustrates the features of the present invention. FIG. 2 is a relationship between the chemical composition of a protective layer and the number of times of sliding in a drag test according to an embodiment of the present invention. FIG. 3 is a Raman spectrum diagram of a protective layer having a nitrogen / carbon atomic ratio of 0.48 formed by sputter deposition under a high gas pressure by a high-frequency magnetron method according to an embodiment of the present invention, and FIG. FIG. 5 is a Raman spectrum diagram of a protective layer having an atomic ratio of nitrogen / carbon of 0.055 formed by sputter deposition under a low gas pressure by a high-frequency magnetron method according to an embodiment of the present invention, and FIG. FIG. 6 is a diagram showing the relationship between the atomic ratios of the samples having a life of 150 k times or more, FIG. An example A surface element ratio representative protecting layer.

FIG. 1 shows the configuration of a typical magnetic recording medium according to an embodiment of the present invention. This magnetic recording medium has a Cr underlayer 2, a magnetic layer 3 made of a CoCr-based alloy, a protective layer 4 containing nitrogen and oxygen in carbon, and a perfluoropolyethyl-based It is composed of a multilayer film in which the lubricating layers 5 are sequentially laminated.

This magnetic recording medium was formed as a sample having different atomic ratios of nitrogen / carbon and oxygen / nitrogen on the surface of the protective layer by sputter deposition of a graphite target in the manner shown in Examples 1 to 3 below. The film thickness was 7 nm in each case.

Further, in each of the examples, oxygen plasma treatment and ultraviolet irradiation in the air were also performed in order to change the atomic ratio of oxygen / nitrogen on the surface of the protective layer. In the oxygen plasma treatment, plasma was generated at a power of 150 W from a high frequency power supply in an atmosphere in which oxygen gas was introduced at 100 mTorr, and the sample was left for 4 minutes. For irradiation with ultraviolet rays, a high-pressure mercury lamp equipped with a reflecting mirror was provided at a position 50 mm from the surface of the sample, and a treatment was performed at a power of 10 kW for 4 minutes. By performing such a surface treatment, the atomic ratio of oxygen / nitrogen on the surface of the protective layer was improved to 1.2 to 2 times that before the treatment.

(Example 1) In this example, a protective layer was formed under the conditions shown in Table 1 by a reactive sputter deposition method using a DC magnetron electrode.

[0023]

Table 1 Reactive sputter deposition conditions using a DC magnetron electrode Condition Gas type Operating pressure Input power 1-1 Ar, N ₂ (N ₂ /Ar=0.05) 8 mTorr 1.5 kW 1-2 Ar, N ₂ (N ₂ / Ar = 0.11) 8 mTorr 1.5 kW 1-3 Ar, N ₂ (N ₂ /Ar=0.25) 8 mTorr 1.5 kW 1-4 Ar, N ₂ (N ₂ /Ar=0.43) 8 mTorr 1.5 kW (Comparative Example 1) A protective layer was formed by the same sputter deposition method using a DC magnetron electrode as in Example 1 under the condition that nitrogen gas was not introduced.

Example 2 In this example, a protective layer was formed under the conditions shown in Table 2 by a reactive sputter deposition method using a high-frequency magnetron electrode. In this embodiment, the operating pressure during film formation was 30 mTorr and 5 mTorr. However, if the operating pressure is 5
When the pressure is set to mTorr, the discharge in the gas phase is insufficient and the discharge does not occur spontaneously.
Set to mTorr.

[0025]

Table 2 Reactive sputter deposition conditions using a high-frequency magnetron electrode Condition Gas type Operating pressure Input power 2-1 Ar, N ₂ (N ₂ /Ar=0.05) 30 mTorr 1.0 kW 2-2 Ar, N ₂ (N ₂ / Ar = 0.11) 30 mTorr 1.0 kW 2-3 Ar, N ₂ (N ₂ /Ar=0.25) 30 mTorr 1.0 kW 2-4 Ar, N ₂ (N ₂ /Ar=0.43) 30 mTorr 1.0 kW 2-5 Ar, N ₂ (N ₂ /Ar=0.05) 5 mTorr 1.0 kW 2-6 Ar, N ₂ (N ₂ /Ar=0.11) 5 mTorr 1.0 kW 2-7 Ar , N ₂ (N ₂ /Ar=0.25) 5 mTorr 1.0 kW 2-8 Ar, N ₂ (N ₂ /Ar=0.43) 5 mTorr 1.0 kW (Embodiment 3) In this embodiment, an asymmetric magnetron electrode is used. The protective layer was formed under the conditions shown in Table 3 by a reactive sputter deposition method using The sputter deposition using the asymmetric magnetron electrode used in the present embodiment is a method of controlling the magnet and the arrangement of the magnetron electrode and using the effect of the magnetic flux spreading between the electrodes to generate plasma, and the ions of several tens mA / cm ² are formed on the substrate. Electric current flowed.

[0026]

Table 3 Reactive sputter deposition conditions using a high-frequency magnetron electrode Condition Gas type Operating pressure Input power 3-1 Ar, N ₂ (N ₂ /Ar=0.05) 8 mTorr 1.5 kW 3-2 Ar, N ₂ (N ₂ / Ar = 0.11) 8 mTorr 1.5 kW 3-3 Ar, N ₂ (N ₂ /Ar=0.25) 8 mTorr 1.5 kW 3-4 Ar, N ₂ (N ₂ /Ar=0.43) 8 mTorr 1.5 kW Table 4 shows the results obtained by measuring the surface element ratios of the representative protective films formed in Examples 1 to 3 by X-ray photoelectron spectroscopy. These values were measured at photoelectron take-out angles of 90 and 30 degrees. The values shown in parentheses are values at an electron extraction angle of 30 degrees, and correspond to the element ratio near the outermost surface.

[0027]

[Table 4]

As a result, the nitrogen concentration of the sample of Example 2 formed at a high gas pressure was the highest and was about 30 at.
% Values. This is because active nitrogen molecules were generated at a high concentration during sputter deposition by high-frequency discharge. In the sample of Example 2, the nitrogen concentration was 15 to 20 at% due to the etching effect of the self-bias generated on the substrate when the operating pressure during film formation was lowered.

Next, a 2 nm thick perfluoropolyethyl-based lubricant was applied to the magnetic disks provided with the protective layers formed in Examples 1 to 3 and Comparative Example 1. afterwards,
The magnetic head was pressed with a load of 3 g in an atmosphere reduced to 0.5 atm, and a high-speed drag test was performed at a rotation speed of 1000 rpm.

FIG. 2 shows the result of summarizing the number of times of sliding until the protective layer is broken by the drag test. from now on,
In the sample in which the atomic ratio of nitrogen / carbon in the protective layer was 0.05 to 0.3, the durability life by drag was remarkably increased.

On the other hand, in the sample in which the atomic ratio of nitrogen / carbon exceeds 0.30, the protective layer was destroyed at the same time as the start of the drag, and immediately crashed. So, nitrogen /
When a Raman spectrum was measured for a sample having a carbon atom ratio exceeding 0.3, emission of fluorescence due to the released nitrogen compound was observed.

FIG. 3 is a Raman spectrum measured with a protective layer having a nitrogen / carbon atomic ratio of 0.48. The background was greatly inclined due to the fluorescence emitted from the free nitrogen compound. This sample was sputter-deposited under a high gas pressure using a high-frequency magnetron electrode, and the life due to drag was extremely short because the continuity of the protective layer was lost due to the presence of a free nitrogen compound.

However, in the sample formed at a low operating pressure even by reactive sputter deposition using a high-frequency magnetron, as shown in FIG. 4, no background gradient due to the fluorescence of the Raman spectrum was observed, and the atomic ratio of nitrogen / carbon was observed. Was less than 0.2. If the operating pressure is lowered even in the high-frequency discharge, a self-bias is generated in the substrate, and the free nitrogen compound is decomposed by ion bombardment during sputter deposition, so that the durability against drag is improved.

In general, when dragging under a low load with a lightweight head for a protective film having a film thickness of 10 nm or less, the main factor controlling the sliding resistance is not the mechanical strength but the chemical strength of the protective film surface and the lubricant. Action. Therefore, it is necessary to pay more attention to the surface structure and chemical properties than to the inside of the protective film. Therefore, increasing the mechanical strength of the protective layer is not enough to improve the durability of the magnetic disk, and it is necessary to optimize the chemical composition of the protective film surface at the interface between the protective layer and the lubricating layer.

FIG. 5 shows the result of plotting the atomic ratio of the sample having a life of 150 k times or more in the drag test of this embodiment. As described above, the drag by the magnetic head has a large effect due to the interaction between the protective layer and the lubricating layer,
In addition to the atomic ratio of nitrogen / carbon in the protective layer, the life also changed due to the difference in the chemical composition of the protective film surface at the interface between the lubricating layer and the protective layer. As a result, the number of drags is 150k
The nitrogen / carbon atomic ratio of the sample over 0.05 times
And the atomic ratio of oxygen / nitrogen on the surface was in the range of 0.5 to 1.0. Another characteristic of the sample having excellent resistance to drag as described above is that the center line average roughness of the untextured surface is extremely smooth at 1 nm or less.

(Embodiment 4) The apparatus shown in FIG.
And a drive unit 7, a recording / reproducing signal processing means 9 for the magnetic head 8, a magnetic recording medium 10, and a drive unit 11 for rotating the magnetic recording medium.
The magnetic head 6 is a composite type head having both an electromagnetic induction type magnetic head for recording and a magnetoresistive magnetic head for reproduction. In this magnetic storage device, the magnetic recording medium of the first, second, and third embodiments of the present invention in which the number of times of drag exceeds 150 k times is incorporated, and the head flying height is 30 nm, the linear recording density is 210 kBPI, and the track density is 9.6 kTPI. When the recording / reproducing evaluation was performed, good recording / reproducing characteristics were obtained for all magnetic recording media with a recording density of 2 gigabits per square inch. The number of bit errors after 50,000 head seek tests from the inner circumference to the outer circumference is 10 bits / surface or less in any magnetic recording medium.
TBF achieved 150,000 hours.

Next, using a magnetic head 12 formed on a magnetic head slider having an air bearing surface rail area of 1.25 square mm or less and a mass of 2 mg or less, a head flying height of 30 nm and a linear recording density of 210 kBPI Recording and reproduction were evaluated at a track density of 9.6 kTPI. In this case as well, the life was 150 in the drag test shown in the examples of the present invention.
2 times per square inch for k or more magnetic recording media
Good recording / reproducing characteristics were obtained at a gigabit recording density. Also, the number of bit errors after 50,000 head seek tests from the inner circumference to the outer circumference is 1 in any magnetic recording medium.
It was less than 0 bits / plane, and 150,000 hours could be achieved with MTBF.

As described above, in the magnetic storage device incorporating the magnetic recording medium in which the number of times of drag exceeds 150 k times in the first, second and third embodiments of the present invention, even if the protective layer is thin and the recording density is high. High reliability was obtained.

[0039]

According to the present invention, since the bonding force of the lubricant can be enhanced by optimizing the chemical composition on the surface of the protective layer composed of carbon, nitrogen and oxygen, the protective layer is thin and has a high recording density. However, a highly reliable magnetic recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a recording medium for a magnetic disk according to an embodiment of the present invention.

FIG. 2 is a measurement diagram showing the life of a magnetic disk due to dragging according to one embodiment of the present invention.

FIG. 3 is a measurement diagram of a Raman spectrum of a protective layer having an atomic ratio of nitrogen / carbon of 0.48.

FIG. 4 shows nitrogen / nitrogen formed by sputter deposition under low gas pressure.
FIG. 4 is a measurement diagram of a Raman spectrum of a protective layer in which the atomic ratio of carbon is 0.15.

FIG. 5 is a diagram showing a relationship between atomic ratios of samples whose life was 150 k times or more in a drag test.

FIG. 6 is a plan view and a cross-sectional view of a magnetic storage device according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Cr-based underlayer, 3 ... CoCr-based magnetic layer,
4 ... Protective layer containing nitrogen and oxygen in carbon, 5 ... Lubricating layer, 6 ...
Magnetic head, 7: magnetic head driving unit, 8: recording / reproducing signal processing system, 9: magnetic recording medium, 10: magnetic recording medium driving unit, 11: base.

Claims (7)

[Claims] 1. A magnetic recording medium having a magnetic layer on a base material and a protective layer formed on the magnetic layer, wherein the protective layer comprises a film containing at least carbon, nitrogen, and oxygen. The atomic ratio of carbon / carbon is 0.05 to 0.3 and the atomic ratio of oxygen / nitrogen on the surface of the coating is 0.5 to 0.3.
2. A magnetic recording medium, which is in the range of 2.0. 2. The magnetic recording medium according to claim 1, wherein
A magnetic recording medium, wherein the protective layer has a nitro group on the surface. 3. The magnetic recording medium according to claim 1, wherein the thickness of the protective layer is 10 nm or less, and the center line average roughness Ra of the surface is 1 nm or less. Magnetic recording medium. 4. A magnetic recording medium, a driving unit for driving the magnetic recording medium in a recording direction, a magnetic head comprising a recording unit and a reproducing unit, means for moving the magnetic head relative to the magnetic recording medium, In a magnetic storage device having recording / reproduction signal processing means for performing signal input to a magnetic head and reproduction of an output signal from the magnetic head, a reproduction unit of the magnetic head is constituted by a magnetoresistive magnetic head, and A magnetic storage device comprising: the magnetic recording medium according to claim 1. 5. A magnetic recording medium, a driving unit for driving the magnetic recording medium in a recording direction, a magnetic head comprising a recording unit and a reproducing unit, means for moving the magnetic head relative to the magnetic recording medium, In a magnetic storage device having recording / reproduction signal processing means for performing signal input to a magnetic head and reproduction of an output signal from the magnetic head, the air bearing surface rail of the magnetic head has an area of 1.25 mm ² or less and a mass of 2 mg. A magnetic storage device formed on the following magnetic head slider, wherein the magnetic recording medium is constituted by the magnetic recording medium according to claim 1. 6. A step of forming a magnetic layer on the surface of a base material, a step of forming a protective layer made of at least carbon, nitrogen and oxygen on the surface of the magnetic layer, and using a plasma on the surface of the protective layer in an oxygen atmosphere. A method for producing a magnetic recording medium, comprising performing a surface treatment. 7. A step of forming a magnetic layer on the surface of a base material, a step of forming a protective layer comprising at least carbon, nitrogen and oxygen on the surface of the magnetic layer, and irradiating the surface of the protective layer with ultraviolet rays in the air. A method for manufacturing a magnetic recording medium.