JP2006277779A - Magnetic recording medium and magnetic recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium, having high durability and high corrosion resistance and to provide a magnetic recording apparatus provided with the magnetic recording medium. <P>SOLUTION: The magnetic recording medium has two protective layers of a lower layer and an upper layer, both in contact with a magnetic layer, the lower protective layer is a silicon nitride film having satisfactory covering properties. By making the upper protective layer a discontinuous film of an amorphous carbon film, having high hardness and film-deposited by FCA method, the magnetic recording medium will have high durability and high corrosion resistance; and the magnetic recording apparatus is provided with the magnetic recording medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium.

  2. Description of the Related Art A hard disk drive, which is one of magnetic recording devices with a floating recording conversion element (head), which is an information recording device, is generally widely used as an external storage device such as a computer or various information terminals.

  The current magnetic disk uses a thin magnetic alloy layer made of a cobalt-based alloy showing good magnetic properties on a hard non-magnetic substrate, but the magnetic alloy layer is durable and corrosion resistant. Therefore, magnetic properties are deteriorated and mechanical or chemical damage is likely to occur due to contact with the head, friction due to sliding, wear, and corrosion due to moisture adsorption. Therefore, at present, durability and corrosion resistance are improved by providing a protective layer on the surface of the magnetic alloy layer and further covering the protective layer with a lubricating layer made of a lubricant.

Various materials such as SiO ₂ and Al ₂ O ₃ are used for the protective layer. Currently, a carbon-based protective layer such as amorphous carbon is used for a magnetic recording medium and a magnetic recording medium in terms of heat resistance, corrosion resistance, and wear resistance. A carbon-based protective layer deposited by sputtering or CVD (chemical vapor deposition) is generally used as a protective layer for the head.

  By the way, in the information-oriented society in recent years, the amount of information handled in every application tends to increase, and accordingly, a further increase in recording density and capacity is demanded for magnetic disks. In order to meet the demand for higher recording density, it is essential to shorten the distance between the recording layer of the magnetic recording medium and the recording / reading portion of the head, so-called magnetic spacing. Magnetic spacing is determined by the protective layer formed on the recording layer of the magnetic recording medium, the flying height of the lubricating layer and the head, and the protective layer of the head. Among these, the protective layer itself on the magnetic recording medium is thinned. It has been needed.

  From the viewpoint of HDI (Head Disk Interface) characteristics, there is an increasing need for a protective layer for magnetic recording media that can ensure sufficient durability even for ultra-thin films of 5 nm or less. Attention has been focused on a filtered cathodic arc (FCA) method capable of forming a protective layer with good durability (see, for example, Non-Patent Document 1). Amorphous carbon produced by the FCA method is often called DLC (diamond-like carbon).

  Amorphous carbon can be produced by the FCA method as follows. FIG. 3 is a schematic diagram of an FCA film forming system for performing the FCA method. Referring to FIG. 3, a carbon source such as graphite is used as a cathode 31, and arc discharge is generated between the anode 32 and the generated carbon ions, electrons, carbon neutral atoms, and carbon neutral particles. Atoms and macro particles are removed by a magnetic filter (filter coil 33, raster coil 34), and only carbon ions and electrons are guided onto the substrate 35, and a DLC layer 36 is formed on the substrate. The ion gun 37 can be used when doping with other elements.

The FCA method makes it easy to increase the sp ³ bond amount, generally called diamond bond, to 50% or more because of its film formation principle, and therefore it is possible to realize hardness and density close to diamond in an amorphous state. However, since the protective layer formed by the FCA method has a large internal stress, it has a drawback that it is easily peeled off from the magnetic layer to be protected.

  Furthermore, although the protective layer formed by the FCA method has a high covering property, the protective layer is inferior in corrosion resistance to the protective layer formed by the conventional method, and it has been found that the tendency is conspicuous when the thin film is formed. Also for this reason, it is considered that the high internal stress of the FCA film is far away. That is, it is presumed that the protective layer is broken due to stress release at the interface between the protective layer and the magnetic layer where corrosion has progressed, and as a result, corrosion on the peeled surface of the protective layer is promoted.

  In addition, although the protective layer formed by the FCA method has a high coverage of the film itself, in the case of a very thin layer of, for example, 4 nm or less, moisture enters the magnetic layer from slight defects such as pinholes, and the magnetic layer The problem of being corroded cannot be ignored.

From the above situation, the amorphous carbon protective layer formed by the FCA method is certainly excellent in mechanical strength, but is difficult to apply immediately from the viewpoint of the protective layer of the magnetic recording medium.

H. Hyodo et al., “IEE TRANSACTIONS ON MAGNETICS”, July 2001, Vol. 37, p. 1789-1791

  An object of the present invention is to solve such problems and to provide a magnetic recording medium excellent in durability and corrosion resistance and a magnetic recording apparatus provided with the magnetic recording medium.

  According to one aspect of the present invention, in a magnetic recording medium in which a magnetic layer, a protective layer, and a lubricating layer are sequentially laminated on a substrate, the protective layer is composed of two layers: a lower layer in contact with the magnetic layer and an upper layer thereover. Thus, a magnetic recording medium in which the upper protective layer is a discontinuous film is provided. According to the present invention, a magnetic recording medium having high durability and high corrosion resistance can be provided by reducing internal stress.

  According to another aspect of the present invention, a magnetic recording apparatus including the magnetic recording medium is also provided.

  According to the present invention, it is possible to provide a highly durable and highly corrosion-resistant magnetic recording medium and a magnetic recording apparatus including the magnetic recording medium by reducing internal stress. For this reason, for example, head crash and magnetic layer corrosion can be prevented, and the recording density and reliability can be remarkably improved. Moreover, it can contribute to making magnetic spacing smaller.

  Embodiments of the present invention will be described below with reference to the drawings, examples and the like. In addition, these figures, Examples, etc. and description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention. In the drawings, the same number indicates the same element. The “recording medium” and “magnetic recording apparatus” according to the present invention are used only for recording (writing) magnetic information, for reproducing (reading) magnetic information, and for both recording and reproducing magnetic information. Is possible.

  Hereinafter, the present invention will be mainly described with respect to a hard disk device. The “magnetic recording medium” according to the present invention is an in-plane medium, SFM (Synthetic Ferri Coupled Media), perpendicular recording medium, patterned medium used in the hard disk device. Any recording medium may be used. The “magnetic recording apparatus” according to the present invention includes all magnetic recording apparatuses using such a magnetic recording medium.

  FIG. 1 is a schematic plan view showing the internal structure of the hard disk device, and FIG. 2 is a schematic cross-sectional view showing the relationship between the head and the magnetic recording medium (cut in a direction perpendicular to the magnetic layer of the magnetic recording medium). Figure).

  As shown in FIG. 1, the hard disk device includes a magnetic recording medium 1 and a head slider 2 having a head, a rotation control mechanism (for example, a spindle motor) 3 of the magnetic recording medium 1, a head positioning mechanism 4, and a recording / reproducing signal processing. A circuit (read / write amplifier, etc.) 5 is a main component.

  As shown in FIG. 2, the head slider 2 is connected to the head positioning mechanism 4 by a suspension 6 and a gimbal 7 for flexibly supporting the head slider 2, and a head 8 is provided at the tip thereof. . A head protective layer 9 and a head lubricating layer 10 are provided on the head slider surface.

  The magnetic recording medium 11 includes a substrate 12, a Cr underlayer 13, a magnetic layer 14, a magnetic recording medium protective layer (also referred to simply as a protective layer in this invention) 15, and a magnetic recording medium lubricating layer (in accordance with the present invention) from the bottom of FIG. Then, it is also referred to as a lubricating layer) 16 or the like. Although other layers such as a seed layer may be provided, they are omitted in this figure. In the case of a hard disk, the thickness of each layer is generally about several nm for the lubricating layer, about 5 nm for the protective layer, about 50 nm for the magnetic layer, and about 10 nm for the Cr underlayer.

  As described above, the present invention provides a magnetic recording medium in which a magnetic layer, a protective layer, and a lubricating layer are sequentially laminated on a substrate. The protective layer has two layers: a lower layer in contact with the magnetic layer and an upper layer on the magnetic layer. The above-mentioned subject is solved by making the upper protective layer into a discontinuous film. That is, the lower protective layer is somewhat inferior in durability, but a film having excellent corrosion resistance is used, and the upper protective layer is a discontinuous film having inferior corrosion resistance, but a film having durability is used. It solves the problem.

  The upper protective layer can reduce the film thickness within a range in which durability can be maintained, but the average film thickness is preferably 2 nm or less from the viewpoint of reducing magnetic spacing. Also, from the viewpoint of durability, the upper protective layer is preferably a hard amorphous carbon-based protective layer, and is particularly optimally formed by the FCA method, which can obtain a film quality with an sp3 / sp2 ratio of 1 or more.

  In this case, the upper protective layer does not need to completely cover the lower protective layer, and the ratio of the constituent elements of the lower protective layer exposed on the outermost surface of the protective layer is the number of atoms with the upper constituent element. The number ratio may be 5% or more and 70% or less. In other words, the coverage of the upper protective layer may be 30% or more and 95% or less. The reason is that an average film thickness of 4 nm or more is required to achieve high coverage of 5% or less with a carbon material, and as a result, magnetic spacing cannot be reduced. On the other hand, if it is 70% or more, the maximum film thickness is 0.5 nm or less, and sufficient durability cannot be maintained. Further, nitrogen or oxygen may be added to the upper protective layer, or surface functional groups may be imparted by plasma treatment or ozone water treatment in order to improve the adhesion of the lubricant applied immediately above. Further, an important characteristic of the upper protective layer is the hardness for maintaining durability. Specifically, a hardness of 20 GPa or more is preferable.

  On the other hand, the lower protective layer is excellent in corrosion resistance, and silicon nitride is suitable in consideration of relatively high hardness. In order to improve the corrosion resistance, an element that improves water repellency by combining with a base material such as hydrogen or fluorine may be added to the lower protective layer. The average film thickness of the lower protective layer can be reduced within a range where the corrosion resistance can be maintained, but the average film thickness is preferably 3 nm or less from the viewpoint of reducing magnetic spacing, and the film thickness of all protective layers including the upper layer is 4 nm or less. Is preferred. At this time, the coverage of the silicon nitride film is 90%, and even when the coverage of the upper protective layer is about 70%, the two-layer structure can ensure sufficient touch resistance.

  As described above, the magnetic recording medium having the protective layer according to the present invention can remarkably improve the recording density and reliability. Therefore, a magnetic recording apparatus having a high recording density and high reliability can be obtained.

  Next, examples and comparative examples of the present invention will be described in detail. Each physical property was measured as follows.

(Clothing rate test)
The coverage ratio of the upper protective layer can be measured by coaxial direct collision ion scattering spectroscopy (CA-ISS, TALIS 9700 manufactured by Shimadzu Corporation). CAICISS is a technique for performing elemental analysis and structural analysis by irradiating a sample with rare gas ions at a low energy of about keV and measuring the energy change of the same particles scattered at 180 degrees. In X-ray photoelectron spectroscopy (XPS), the incident ions cannot penetrate into the film and scatter in the very shallow region of the first and second atomic layers. It is a measurement method that can be analyzed.

(Film hardness)
The film hardness was measured using the nanoindentation method. The nanoindentation method is a method for evaluating mechanical characteristics by measuring a minute deformation when a diamond indenter is pushed into a material using a minute load of about μN and unloaded. Since the amount of indentation can be controlled to about several nanometers, it is suitable for evaluating the characteristics of thin film samples.

(Sliding test)
Evaluation was made by contacting an alumina pin with the finished magnetic recording media of Examples and Comparative Examples at a rotational speed of 600 revolutions / minute (rpm) and sliding until the carbon-based protective layer was broken. The alumina pin had a diameter of 2 mm, and the width of the portion in contact with the magnetic recording medium was about 5 μm. The breakage was detected by changing the frictional force, generating streaks on the surface of the magnetic recording medium, or observing a portion where the protective layer disappeared by observation with an electron microscope.

(Corrosion resistance test)
After the magnetic recording medium finished product is allowed to stand at room temperature for 24 hours, 1 mL of diluted nitric acid is dropped on the surface, and 1 hour later, the diluted nitric acid is sucked out and collected, and elemental analysis by an inductively coupled plasma mass spectrometer (ICP-MS) is performed. Asked to go.

[Example 1]
FIG. 1 shows the relationship between the thickness of the protective layer manufactured by the FCA method and the coverage. In the sample used in the figure, an underlayer and a Co metal layer are laminated on an aluminum alloy substrate by a sputtering method, and an arc current of 60 A, an arc voltage of 30 V, and a cathode coil current of 10 A are obtained using a graphite target as a raw material using an FCA apparatus. Under these conditions, amorphous carbon is used as a protective layer. The thickness of the protective layer of the sample was changed by adjusting the film formation time, and the average film thickness was determined by observing a cross section with TEM.

  The vertical axis of FIG. 4 shows the atomic ratio of carbon, which is a constituent element of the protective layer, and Co, which is the base, on the outermost surface, and 100% is in a state where the protective layer is completely covered (the base exposure is 0% indicates a state where Co is completely exposed. The atomic ratio on the outermost surface was calculated from the spectral ratio of carbon and Co measured by coaxial direct collision ion scattering spectroscopy (CAICISS).

  As can be understood from FIG. 4, the exposure amount of the underlying Co increases from 4 nm or less, and when the average thickness of the protective layer is 1 nm, the exposure ratio reaches 35%.

[Example 2]
FIG. 7 is a schematic cross-sectional view of the magnetic recording medium 11 produced in this example. An underlayer 13 and a magnetic layer 14 were sequentially stacked on the aluminum alloy substrate 12 by sputtering. Subsequently, 2 nm of silicon nitride was formed under the conditions of power 2 kW, nitrogen flow rate 10 sccm, and Ar flow rate 3 sccm, using a silicon target as a raw material, using an RF-sputtering device to form a lower protective layer 15a. Thereafter, an amorphous carbon was formed to a thickness of 1 nm under the conditions of an arc current of 60 A, an arc voltage of 30 V, and a cathode coil current of 10 A using an FCA apparatus and a graphite target as a raw material to form an upper protective layer 15 b.

  Subsequently, on this protective layer, a lubricant solution obtained by diluting Fomblin TETRAOL of Italy-Augmond Inc. with hydrodecafluoropentane to about 0.2% by volume is applied to each sample by a pulling method under the condition of an immersion time of 30 seconds. The lubricating layer 16 was provided by coating to complete the magnetic recording medium.

  As a result of the durability test, the protective layer did not break even when the number of rounds exceeded 500.

As a result of the corrosion resistance test, the elution amount of Co was 0.8 μg / m ² .

[Comparative Example 1]
After laminating up to the magnetic layer by the same method as in Example 1, a film was formed at a rate of 0.1 nm / second under the conditions of an arc current of 60 A, an arc voltage of 30 V, and a cathode coil current of 10 A using a graphite target as a raw material using an FCA apparatus. A carbon-based protective layer having a thickness of 5 nm was formed as a single layer at a rate.

  Subsequently, a lubricating layer was provided in the same manner as in Example 1 to complete the magnetic recording medium.

  As a result of the durability test, the protective layer did not break even when the number of rounds exceeded 500.

Further, as a result of the corrosion resistance test, the elution amount of Co is 1.5 μg / m ² , the Co elution amount is increased as compared with Example 1, and sufficient coverage is not obtained.

[Comparative Example 2]
After laminating up to the magnetic layer by the same method as in the example, a silicon target was used as a raw material by using an RF-sputtering apparatus, and a silicon nitride film having a power of 2 kW, a nitrogen flow rate of 10 sccm and an Ar flow rate of 3 sccm was formed to form a protective layer .

  As a result of the durability test, the protective layer broke before reaching 500 turns.

Furthermore, as a result of the corrosion resistance test, the Co elution amount is 0.7 μg / m ^2, which is comparable in corrosion resistance to that of Example 1. Even with the configuration of the present invention of Example 1, sufficient corrosion resistance can be ensured. did it.

[Example 2]
FIG. 5 shows the results of evaluating the sliding strength using the same sample as in Example 1. Although the sliding strength decreases as the thickness of the protective layer becomes thinner, the upper protective layer formed by the FCA method has 500 turns, in which the single protective layer having a thickness of 4 nm prepared by the conventional method breaks. With the configuration of the protective layer of the present invention, even a film thickness of 1 nm can be achieved.

[Example 3]
FIG. 6 shows the results of evaluating the corrosion resistance using the same sample as in Example 1. The Co elution amount increased from the thickness of the protective layer to 4 nm or less, and reached 8 times the amount eluted with the protective layer of 4 nm prepared by the conventional method at a film thickness of 1 nm. That is, in the single protective layer, the film thickness decreases, the coverage decreases, and the Co elution amount increases accordingly.

  In addition, the invention shown to the following additional remarks can be derived from the content disclosed above.

(Appendix 1)
In a magnetic recording medium in which a magnetic layer, a protective layer and a lubricating layer are sequentially laminated on a substrate,
The protective layer is composed of two layers, a lower layer in contact with the magnetic layer and an upper layer above it.
A magnetic recording medium in which the upper protective layer is a discontinuous film. (1)
(Appendix 2)
The magnetic recording medium according to appendix 1, wherein the upper protective film has a coverage of 30% to 95%. (2)
(Appendix 3)
3. The magnetic recording medium according to appendix 1 or 2, wherein the upper protective layer has a thickness of 0.5 nm to 2 nm. (3)
(Appendix 4)
The magnetic recording medium according to any one of appendices 1 to 3, wherein the upper protective layer has a hardness of 20 GPa or more.

(Appendix 5)
2. The magnetic recording medium according to appendix 1, wherein the lower protective film is a continuous film.

(Appendix 6)
The magnetic recording medium according to appendix 1, wherein the lower protective film has a coverage of 90% or more.

(Supplementary note 7) The magnetic recording medium according to supplementary note 1, wherein the lower protective film is a silicon nitride film.

(Appendix 8)
The magnetic recording medium according to any one of appendices 1 to 7, wherein the upper protective film is amorphous carbon. (4)
(Appendix 9)
The magnetic recording medium according to any one of appendices 1 to 8, wherein a ratio of carbon-carbon bonds in the upper protective film is sp3 / sp2 ≧ 1.

(Appendix 10)
In the method of manufacturing a magnetic recording medium in which a magnetic layer, a protective layer, and a lubricant layer are sequentially laminated on a substrate, the protective layer is composed of two layers: a lower layer that is in contact with the magnetic layer and an upper layer on the magnetic layer. The method of manufacturing a magnetic recording medium, wherein the upper protective layer is formed of a discontinuous film in the in-plane direction.

(Appendix 11)
11. The method of manufacturing a magnetic recording medium according to appendix 10, wherein the upper protective film is formed by a filter cathodic arc method.

(Appendix 12)
The method for manufacturing a magnetic recording medium according to appendix 10, wherein the lower protective film is formed by a sputtering method.

(Appendix 13)
A magnetic recording apparatus comprising the magnetic recording medium according to claim 1. (5)

2 is a schematic plan view showing an internal structure of the hard disk device. FIG. It is a typical cross-sectional view showing the relationship between the head of the hard disk device and the magnetic recording medium. 1 is a schematic diagram of an FCA film forming system for performing an FCA method. It is the graph which showed the relationship of the ratio of the number of atoms of carbon and Co in the outermost surface with respect to the film thickness of the DLC film produced by FCA method. It is the graph which showed the relationship of the sliding strength with respect to the film thickness of the DLC film produced by FCA method. It is the graph which showed the relationship of the corrosion resistance with respect to the film thickness of the DLC film produced by the FCA method. 1 is a schematic cross-sectional view of a magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Head slider 3 Rotation control mechanism 4 Head positioning mechanism 5 Recording / reproducing signal processing circuit 6 Suspension 7 Gimbal 8 Head 9 Head protective layer 10 Head lubricating layer 11 Magnetic recording medium 12 Substrate 13 Cr underlayer 14 Magnetic layer DESCRIPTION OF SYMBOLS 15 Protective layer 15a Lower protective layer 15b Upper protective layer 16 Lubricating layer 31 Cathode 32 Anode 33 Filter coil 34 Raster coil 35 Substrate 36 DLC layer 37 Ion gun

Claims (5)

In a magnetic recording medium in which a magnetic layer, a protective layer and a lubricating layer are sequentially laminated on a substrate,
The protective layer is composed of two layers, a lower layer in contact with the magnetic layer and an upper layer above it.
A magnetic recording medium in which the upper protective layer is a discontinuous film.   The magnetic recording medium according to claim 1, wherein a coverage of the upper protective film is 30% or more and 95% or less.   3. The magnetic recording medium according to claim 1, wherein the upper protective layer has a thickness of 0.5 nm to 2 nm.   2. The magnetic recording medium according to claim 1, wherein the lower protective film is a silicon nitride film. A magnetic recording apparatus comprising the magnetic recording medium according to claim 1.

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