JP3080722B2 - Magnetic recording medium and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbonaceous protective film for a magnetic recording medium having a continuous thin film type magnetic layer and a method for producing the same.

[0002]

2. Description of the Related Art Various continuous thin-film type magnetic recording media having a ferromagnetic thin film as a magnetic layer have been put to practical use. Among them, a hard magnetic disk used in a computer or the like has a ferromagnetic thin film provided on a rigid substrate. As a magnetic head that performs recording and reproduction on a hard type magnetic disk,
Various floating magnetic heads are used.

In such a case, the magnetic disk is damaged by the magnetic head during a contact start / stop (CSS). In order to increase the recording density, there is a strong demand for reducing the flying height of the magnetic head as much as possible, but at this time, the damage of the disk during CSS is further increased.

In order to enhance such durability, it is necessary to provide a solid top coat film on the disk surface. In general, a top coat film using various solid lubricants is applied. Such a top coat film includes a carbon lubrication protective film. For example, Japanese Patent Application Laid-Open No. 2-161612 proposes providing a two-layer carbon sputter topcoat film.

[0005] However, such a carbon sputter topcoat film does not have sufficient lubricity and durability. In the above two-layer structure, the lower layer has excellent durability, and the upper layer has excellent lubricity. Therefore, the production method is also complicated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having excellent friction characteristics and durability.

[0007]

This and other objects are achieved by the present invention which is defined below as (1) to (6). (1) In a magnetic recording medium having a ferromagnetic thin film on a substrate and a carbonaceous protective film on the ferromagnetic thin film, the carbonaceous protective film is formed by a sputtering method. A magnetic recording medium wherein the amount of impurities present as a foreign phase therein is 5% by volume or less and the carbonaceous protective film is substantially in an amorphous state. (2) The magnetic recording medium according to the above (1), wherein the carbonaceous protective film has a thickness of 150 to 500A. (3) The above-mentioned (1), wherein the carbonaceous protective film has an area ratio of sp ³ peak to sp ² peak [sp ³ (area) / sp ² (area)] of 3 or less, as measured by Raman scattering spectrum. The magnetic recording medium according to (2). (4) The magnetic recording medium according to any one of (1) to (3), wherein the ferromagnetic thin film is a continuous thin film of a ferromagnetic metal. (5) In producing a magnetic recording medium having a ferromagnetic thin film on a substrate and a carbonaceous protective film on the ferromagnetic thin film, the carbonaceous protective film is formed by a sputtering method. W /
(F · M) [W is the input power (Joule / sec), F is the flow rate of the sputtering gas, M is the molecular weight of the sputtering gas, and the unit of FM is kg / sec. When defined, and this value is ^{5 × 10 7 ~10 9 Joule /} kg, and method for manufacturing a magnetic recording medium the reaction pressure is less than 5 Pa. (6) The method for producing a magnetic recording medium according to (5), wherein the sputtering gas is at least one of Ar, Kr, and Xe.

[0008]

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

According to the present invention, W / (F · M) value of 5 × 10 ⁷ ~
Sputtering is performed under the conditions of 10 ⁹ Joule / kg and a reaction pressure of 5 Pa or less to form a substantially amorphous carbonaceous protective film on the ferromagnetic thin film.

The present applicant has made various studies on a conventional carbon sputtered film, and found that such a carbon sputtered film contains impurities such as metal carbides in an amount exceeding 5% by volume and about 10% by volume. In addition, it has been confirmed that this is a cause of deteriorating friction characteristics and durability. In addition, for example, in the case of a magnetron sputtering method that is widely used, this impurity is caused by sputtering of a shield ring covering an outer periphery of a target mounting surface in this apparatus, and the shield ring is made of metal such as stainless steel. It is thought to be generated due to something.

However, in the present invention, since the sputtering conditions are regulated as described above, the amount of impurities can be suppressed to 5% by volume or less, and the film quality and film thickness can be reduced to predetermined values. The effects of the invention can be obtained.

Note that Japanese Patent Application Laid-Open No. 2-161612 discloses that
It is disclosed that a carbon sputter top coat film having a layer structure is provided. At this time, the lower layer is a film with excellent durability,
The upper layer has a film quality excellent in lubricity. And
According to the laser Raman spectroscopy, the lower layer is the Raman spectrum of i-carbon and the upper layer is amorphous carbon and i-carbon.
It is said that it is similar to the superimposed carbon.

The carbonaceous protective film of the present invention has lubricating properties and durability with only one layer, and is clearly different from the structure disclosed in the above publication. Further, there is no description about impurities as in the present invention, and there is no suggestion that the impurities deteriorate durability and lubricity. Furthermore, sp ² in the Raman scattering spectrum
No mention is made of the area ratio of the sp ³ peak to the peak.

[0019]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

The magnetic recording medium of the present invention is specifically a hard type magnetic disk. Further, a carbonaceous protective film is provided on the ferromagnetic thin film as the magnetic layer.

<Carbon Protective Film> In the present invention, the carbonaceous protective film provided on the magnetic layer contains carbon, and preferably contains only carbon. The impurity amount in the protective film is 5% by volume or less, preferably 2% by volume or less. The lower limit is about the volume% outside the detection limit.

The impurities in this case are considered to be generated mainly by unnecessary reactions during film formation, and are presumed to be mainly metal carbides. In addition, it is considered that metal nitrides, metal oxides, and the like also exist.

As described above, by setting the amount of impurities in the carbonaceous protective film to 5% by volume or less, a uniform film can be obtained, which functions effectively as a lubricating protective film, and the effects of the present invention can be obtained. Can be On the other hand, when the impurity amount exceeds 5% by volume,
The effect of the present invention is critically reduced, and the lubricity and durability of the film become insufficient. This is because the stress from the head concentrates on impurities which are foreign substances because the film does not become a uniform film, and the film is destroyed therefrom.
This is because most of the metal carbide is hard, and thus damages the head.

Such impurities are present in the film as a foreign phase, and the abundance can be determined by observation with a transmission electron microscope (TEM) or the like. The identification of the compound in the impurities is performed by Auger electron spectroscopy (AES), X
The abundance of each compound can be determined by the line photoelectron spectroscopy (ESCA) or the like.
Etc.

The carbonaceous protective film in the present invention is formed by sputtering using carbon as a target.

The sputtering method in the present invention is not particularly limited, and various known methods can be employed. Usually, a magnetron sputtering method is preferably used because the film forming rate is high, and DC or RF may be used. Further, a hollow cathode enhanced magnetron sputtering method may be used.

In this case, the discharge capacity by the sputter gas (impact gas) is W / (FM) [where W is the input power (Joule / sec), F is the flow rate of the sputter gas, and M is the sputter gas. The unit of FM in the molecular weight is kg / sec. ]
This value is 5 × 10 ⁷ to 10 ⁹ Joule / k
g, preferably 1 × 10 ^{8 to} 6 × 10 ⁸ Joule / kg.

Under such sputtering conditions, the amount of impurities in the film can be suppressed to 5% by volume or less. And the W / (FM) value is 5 × 10 ⁷ Joul
If it is less than e / kg, the carbonaceous film will be chipped. Also, 1
If it exceeds 0 ⁹ Joule / kg, the amount of impurities will exceed 5% by volume.

In the present invention, the sputter gas suppresses generation of impurities and has a high sputtering rate. Therefore, at least one of the inert gases Ar, Kr and Xe is used.
More than one kind may be used, and among them, the use of Ar is advantageous in terms of cost and the like.

Further, the reaction pressure during sputtering is set to 5 Pa or less, and the lower limit at this time is about 0.5 Pa, and preferably 4 to 1 Pa. By reducing the pressure in this manner, the erosion area on the target surface is expanded, and the contamination of the film with impurities is reduced.

In the present invention, the thickness of the carbonaceous protective film is 15
0 to 500A, preferably 200 to 300A. With such a thickness, the effect of the present invention can be obtained. When the film thickness is less than 150A, the function as a protective film decreases, and when it exceeds 500A, the spacing loss increases. Note that the film thickness may be measured by a step meter or the like.

The carbonaceous protective film according to the present invention is substantially in an amorphous state, and can be confirmed from a TEM photograph and a result of X-ray diffraction analysis (XRD).

The area ratio of the sp ³ peak to the sp ² peak in the Raman scattering spectrum measurement [sp ³
(Area) / sp ² (area)] is 3 or less, preferably 2 or less, and particularly preferably 0.5 to 1.6 for practical use. By setting the peak ratio in the above range, sufficient lubricity and durability can be obtained. On the other hand, if the peak ratio exceeds 3, lubricity and durability deteriorate.

Since the carbonaceous protective film of the present invention has good lubricating properties, it can be used only as a surface protective film. In addition to this, it is not necessary to provide a new liquid lubricating layer in order to increase lubricity. Disappears.

A hard type magnetic disk provided with such a carbonaceous protective film will be described.

<Substrate> The substrate used in the magnetic disk of the present invention is not particularly limited as long as it is a non-magnetic rigid material. It is. In this case, it is particularly preferable that the rigid substrate is a rigid substrate made of resin.
Since the durability of the resin substrate is reduced, the effect of the present invention is increased. The rigidity of the substrate means that a flexible substrate for a so-called floppy disk is excluded. Therefore, when the Young's modulus of the substrate is E and the thickness is t, E · t ³ ≧ 1 × 10 ⁷ dyn · cm, and more preferably E · t ³ ≧ 3 × 10 ⁷ dyn · cm. preferable.

The resin used is not particularly limited, and any resin such as a thermoplastic resin, a thermosetting resin, and a radiation-curable resin may be used.

In this case, when the substrate is molded by the casting method, for example, polyurethane, epoxy resin, acrylic resin, polystyrene, polyamide, silicone resin, polyester and modified products thereof can be used.

When molding by the injection method, for example, polyethylene, polypropylene, vinyl chloride resin, vinylidene chloride resin, vinylidene fluoride resin, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylic resin , Polyamide, polycarbonate, polyacetal, polyester, polysulfone, polyoxybenzylene, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylenesulfide, polyphenyleneether, polyphenyleneoxide, polyketonesulfide, polyimide, polyamideimide, polyacryl Uses imides, polyetherimides, polyolefins, amorphous polyolefins and their modified products Kill.

The dimensions of the resin substrate may be selected according to the purpose, but usually the thickness is about 0.8 to 1.9 mm and the diameter is about 60 to
It is about 130 mm.

As described above, as the rigid substrate, for example, metals such as aluminum and aluminum alloy, glass, ceramics and the like can be used. Also,
A base layer may be provided on the substrate. The material of the underlayer is not particularly limited, and various inorganic materials, organic materials,
A metal or an alloy may be used, and a film formation method, a film thickness, and the like may be appropriately selected depending on purposes, applications, and the like.

<Magnetic Layer> A magnetic layer is formed directly or via an intermediate layer on a substrate provided with an underlayer if necessary.

The magnetic layer of the present invention is a ferromagnetic thin film. The material of the thin film may be, for example, at least one selected from Fe, Co and Ni, and may be formed of a continuous thin film of a ferromagnetic metal containing the same, particularly a Co-based continuous thin film.

As a specific example of the composition of the magnetic layer, Co-N
i-alloy, Co-Ni-Cr alloy, Co-Cr alloy, Co
-Cr-B alloy, Co-Cr-Mn alloy, Co-Cr-
Mn-B alloy, Co-Cr-Ta alloy, Co-Cr-S
i-Al alloy, Co-V alloy, Co-Ni-P alloy, C
o-P alloy, Co-Zn-P alloy, Co-Ni-Pt alloy, Co-Pt alloy, Co-Ni-Mn-Re-P alloy and the like. In addition, these alloys, if necessary,
Elements such as O, N, Si, Al, Mn, and Ar may be contained in an amount of about 0.1% by weight or less. In addition, γ-Fe ₂
It may be a ferromagnetic oxide thin film such as O ₃ . The thickness of the magnetic layer is preferably 300 to 1000A. If it is less than 300 A, the output during recording and reproduction is insufficient,
If it exceeds 0A, the output is sufficient, but it is disadvantageous because the recording density is reduced.

A non-magnetic intermediate layer is provided between the underlayer and the magnetic layer, if necessary. For example, if the magnetic layer is made of Co
-Ni, Co-Ni-Cr, Co-Cr, Co-Cr-
Ta, Co-Ni-P, Co-Zn-P, Co-Ni-
When the magnetic layer is made of Mn-Re-P or the like, the provision of the non-magnetic intermediate layer makes it possible to favorably perform epitaxial growth of the magnetic layer and improve magnetic properties. The nonmagnetic intermediate layer may be composed of, for example, a continuous thin film containing at least one selected from Cr and W, in particular, Cr and / or W. In this case, the metal to be used may be a simple substance or an alloy. In the case of an alloy, the metal is preferably contained in an amount of 80% by weight or more.

The thickness of the non-magnetic intermediate layer is 500 to 5000
A is preferred. If it is less than 500 A, the epitaxial growth of the cobalt alloy is not sufficiently performed, so that good magnetic properties cannot be obtained. When it exceeds 5000A, the magnetic properties become
Since it converges to a substantially constant value, it has no meaning in magnetic properties and is disadvantageous in mass production.

The non-magnetic intermediate layer and the magnetic layer are
Respectively, evaporation, sputtering, ion plating, C
The film may be formed by various vapor deposition methods such as VD, and particularly preferably formed by sputtering.

In the present invention, as described above, only the carbonaceous protective film is used, and it is not necessary to intervene another protective film between the magnetic layer and the carbonaceous protective film. May be provided with a protective film such as a plasma polymerized film, and the carbonaceous protective film of the present invention may be further provided on this protective film.

<Medium Structure> In the magnetic recording medium of the present invention, it is preferable to form a groove in the substrate. There are no particular restrictions on the shape, pattern, dimensions, etc. of the groove, but it is preferable to form the groove in the circumferential direction of the disk. The grooves are made to act on the surface of the substrate by applying a polishing tape or the like while rotating the substrate.
Even grooves formed by so-called texture processing formed irregularly in concentric circles, etc., are concentric,
Even if it is a groove formed regularly in a spiral shape, or
Both may be used. The regular grooves can be used as grooves for tracking, and the recording density is improved.

In such a case, the groove dimensions and the groove arrangement interval are such that the groove width is 0.1 to 10 μm, particularly about 0.5 to 2 μm, and the gap between the grooves is 0.1 to 10 μm, especially 0.5 to 10 μm. 2 μm
Degree, groove depth 100-5000A, especially 500-1
It is preferably about 000A.

Since no information is recorded in the groove, the groove becomes a guard band regardless of the position of the magnetic head. For this reason, if grooves are provided on the substrate, the accuracy of tracking servo can be relatively low, and the area of the recording surface used for servo signals can be reduced. Also, crosstalk from adjacent tracks is significantly reduced.

In the case of a continuous thin film type magnetic layer, when grooves having the above dimensions are formed regularly in the circumferential direction of the disk, cracks in the magnetic layer are further prevented, and the orientation in the circumferential direction of the disk is reduced. And the coercive force in the disk circumferential direction is improved.

In the above description, a single-sided recording type magnetic disk has been mainly described, but the present invention may be applied to a double-sided recording type magnetic disk.

<Recording / Reproducing> The magnetic head used in combination with such a magnetic disk medium is a floating magnetic head. As a floating magnetic head, metal-in-
A gap (MIG) type magnetic head or a thin film type magnetic head is preferable.

The MIG type magnetic head is a magnetic head having a soft magnetic thin film having a higher saturation magnetic flux density than at least one of the pair of cores on the surface facing the gap. In the MIG type magnetic head, since a strong magnetic flux can be applied to the magnetic layer from the soft magnetic thin film, effective recording can be performed on the magnetic layer having a high coercive force. Further, in the present invention, a so-called enhanced dual gap length (EDG) type magnetic head, which is one type of MIG type magnetic head, may be used.

The MIG type head may be a monolithic head in which the slider body and the core are integrated, or a composite head in which a ferrite core is embedded in a part of the non-polar slider body. In a monolithic head, the air bearing surface is a core material Mn.
-It is composed of ferrite such as Zn ferrite. Also, the slider of the composite head is generally made of CaTi
O _{3 and the} like.

Further, the slider body of the thin film head is generally formed of Al ₂ O ₃ .TiC or the like.

The flying height of such a flying head can be set to various values by changing the shape of the slider, changing the load on the gimbal or suspension, changing the rotational speed of the magnetic disk, and the like. In the present invention, since a digital signal is usually recorded, saturation recording is performed. In addition, since the saturation recording is performed, overwrite recording is possible.

[0059]

The present invention will be specifically described below with reference to examples.

Example 1 A polycarbonate disk-shaped rigid substrate having an outer diameter of 3.5 inches and a thickness of 1.27 mm was produced by injection molding. Grooves were formed on the substrate surface.

The groove is formed in the circumferential direction of the disk,
The cross section was substantially rectangular, and the dimensions were 0.8 μm in width, 0.8 μm in land width, and 400 to 700 A in depth. On this substrate, using CH ₄ as a source gas, a film thickness of 200 A
The underlayer of the plasma polymerized film was formed. On this underlayer, a Co—Ni—Cr magnetic layer having a thickness of 500 A was formed. The magnetic layer was formed by DC-magnetron sputtering. Sputtering was performed in an Ar atmosphere with an operating pressure of 1 Pa. The target was Co ₇₀ Ni ₂₀ Cr ₁₀
Was used. This is designated as magnetic disk sample No. 1.

In magnetic disk sample No. 1, magnetic disk sample Nos. 2 to No. 2 were similarly formed except that a carbonaceous protective film was formed on the magnetic layer by DC-magnetron sputtering under the conditions shown in Table 1. .7 were prepared.

[0063]

[Table 1]

The magnetic disk samples No. 2 to No.
In 7, most of the impurities are considered to be metal carbides,
It is presumed to be mainly FeC.

According to TEM observation, these impurities are:
It was present as a foreign phase, and its abundance (% by volume) was determined from a TEM photograph image. Among these, sample No. 2 and sample no. TEM photographic images of the carbonaceous protective film No. 4 are shown in FIGS. 1 and 2, respectively. As a result, it was found that almost no impurities were observed in FIG. 1, whereas impurities were present in FIG. In FIG. 2, the portion where impurities exist as a different phase is a portion that looks black and round. The abundance was calculated by calculating the ratio of these black and round portions in the photograph to the whole.

FIGS. 3 and 4 show sample No. 2
And X-ray diffraction photographs of Sample No. 4 are shown. These photographs show that the carbonaceous film is in an amorphous state.

FIGS. 5 and 6 show sample No.
2 shows Raman scattering spectra of Sample No. 2 and Sample No. 4. From this spectrum, for each sample, the sp ² peak and the sp ³ peak were separated, and the area intensity ratio of the sp ³ peak to the sp ² peak was calculated. The results are also shown in Table 1.

The thickness of the carbonaceous protective film was 2
It was set to 50 A and measured with a step meter.

Next, the magnetic disk sample Nos.
For No. 7, the following evaluation was performed using a composite head of a calcium titanate slider.

(1) CSS Characteristics Using a 3.5 "magnetic disk drive manufactured by Plus, CS
One pass of S, rest time 10 seconds → rise time 5 seconds →
The time of steady rotation is defined as 10 seconds → the fall time is 30 seconds, the rotation speed of the disk in the steady state is 3600 rpm,
At the position 22 mm from the center of the disk, the number of passes when the friction coefficient of the disk became 1.0 or more, or when the magnetic layer was damaged was determined.

(2) Coefficient of friction μ (1 rpm) The disk was rotated at 1 rpm, the stress applied to the head was measured, and μ was calculated from this. The load was 15 g.

(3) Change in friction coefficient Δμ (100 rpm) The disk was rotated at 100 rpm, the stress applied to the head was measured, and the friction coefficient was calculated from this. The load was 15 g. Then, based on the friction coefficient at time 0, 3
The rate of change of the friction coefficient after sliding for 0 minutes Δμ (%) was determined.

(4) Coefficient of friction μ (50 ° C., 80% RH) After storage in 50 ° C., 80% RH for one week, the disk was rotated at 1 rpm, the stress applied to the head was measured, and μ was calculated from this. The load was 15 g.

(5) Change in friction coefficient Δμ (1 rpm) A value obtained by dividing the friction coefficient measured at 1 rpm after 10,000 passes of the CSS by the friction coefficient measured at the beginning is obtained. Was calculated. Table 2 shows the results.

[0075]

[Table 2]

From Table 2, the effect of the present invention is clear.

[0077]

According to the present invention, the friction characteristics and the durability are excellent.

[Brief description of the drawings]

FIG. 1 is a drawing substitute photograph showing a particle structure, and is a sample.
It is a TEM photograph image of No. 2 carbonaceous protective film.

FIG. 2 is a drawing substitute photograph showing a particle structure, and is a sample.
It is a TEM photograph image of No. 4 carbonaceous protective film.

FIG. 3 is a drawing substitute photograph showing a particle structure, and is a sample.
5 is an X-ray diffraction photograph of the carbonaceous protective film of No. 2.

FIG. 4 is a drawing substitute photograph showing a particle structure, and is a sample.
6 is an X-ray diffraction photograph of the carbonaceous protective film of No. 4.

FIG. 5 is a graph showing a result of a Raman scattering spectrum of the carbonaceous protective film of Sample No. 2.

FIG. 6 is a graph showing a result of a Raman scattering spectrum of the carbonaceous protective film of Sample No. 4.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Tokuoka 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-2-25570 (JP, A) JP-A-Hei 2-29919 (JP, A) JP-A-64-241124 (JP, A) JP-A-1-298097 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/72 G11B 5/84

Claims (6)

(57) [Claims] 1. A magnetic recording medium having a ferromagnetic thin film on a substrate and a carbonaceous protective film on the ferromagnetic thin film, wherein the carbonaceous protective film is formed by a sputtering method. The amount of impurities existing as a different phase in the protective film is 5
A magnetic recording medium having a volume percent or less and the carbonaceous protective film being substantially in an amorphous state. 2. The carbonaceous protective film has a thickness of 150 to 50.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 0 A. 3. The carbonaceous protective film has an area ratio [sp ³ (area) / sp ² (area)] of an sp ³ peak to an sp ² peak measured by Raman scattering spectrum of 3 or less. Or the magnetic recording medium according to 2. 4. The magnetic recording medium according to claim 1, wherein said ferromagnetic thin film is a continuous thin film of a ferromagnetic metal. 5. When manufacturing a magnetic recording medium having a ferromagnetic thin film on a substrate and a carbonaceous protective film on the ferromagnetic thin film, the carbonaceous protective film is formed by a sputtering method. , The discharge capacity by sputtering gas is W / (F ·
M) [where W is the input power (Joule / sec) and F
Is the flow rate of the sputtering gas, M is the molecular weight of the sputtering gas and F ·
The unit of M is kg / sec. When the reaction pressure is 5 × 10 ⁷ to 10 ⁹ Joule / kg, the reaction pressure is 5 × 10 ⁷ to 10 ⁹ Joule / kg.
A method for producing a magnetic recording medium having a Pa or lower. 6. The method according to claim 5, wherein the sputtering gas is at least one of Ar, Kr, and Xe.