JP2006260745A - Perpendicular magnetic recording medium and magnetic recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high quality perpendicular magnetic recording medium, having the fewer number of bright spots and nearly free from occurrence of peripheral damage, and to provide a magnetic recording device using the same. <P>SOLUTION: The perpendicular magnetic recording medium 1 formed by providing at least a soft magnetic backing layer 3 and a magnetic recording layer composed of a Co alloy containing an oxide sequentially on a non-magnetic substrate 2 is characterized in that the non-magnetic substrate has ≤50 Ωcm resistivity. The magnetic recording device using the perpendicular magnetic recording medium is also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a perpendicular magnetic recording medium and a magnetic recording apparatus using the same.

  The storage capacity of magnetic recording devices is increasing rapidly year by year. Conventionally, a longitudinal magnetic recording method has been adopted for a magnetic disk medium used in a magnetic recording apparatus. However, in this method, in order to increase the surface recording density, the thickness of the magnetic recording layer must be reduced. There was a restriction in principle that it had to be. As the recording density increased, the thickness of the magnetic recording layer became thinner, but at the same time, the problem of thermal fluctuation occurred. Thermal fluctuation is a phenomenon in which the magnetic thin film cannot be kept stable even at room temperature when the magnetic recording layer becomes extremely thin, and is a fatal problem in magnetic recording. there were.

Therefore, in recent years, the perpendicular magnetic recording system has been attracting attention (see, for example, Patent Documents 1 and 2).
In the perpendicular magnetic recording system, the magnetization easy axis of the magnetic recording layer, which is oriented in the in-plane direction in the conventional longitudinal magnetic recording system, is oriented in the direction perpendicular to the surface of the magnetic recording medium, so that at the boundary of the recording bit. Since the demagnetizing field in the vicinity of a certain magnetization transition region becomes smaller, and the recording density becomes higher, the magnetic field becomes more stable and the thermal fluctuation resistance is improved. Therefore, this method is suitable for improving the surface recording density. Further, when a soft magnetic layer is formed between the substrate and the perpendicular magnetic recording layer, it can function as a so-called perpendicular double-layer medium by combining with a single pole head, and high recording ability can be obtained. At this time, the soft magnetic layer plays a role of refluxing the recording magnetic field from the magnetic head, so that the recording / reproducing efficiency can be improved.

Various improvements have also been made in the manufacturing method of perpendicular magnetic recording media, and in recent years, the use of a recording layer material in which an oxide such as SiO ₂ is dispersed in a Co-based alloy material is becoming mainstream. . This is said to be due to the formation of a phase in which an oxide is deposited in the thin film, which creates a structure that surrounds the Co alloy, which is a magnetic material, so as to minimize the magnetization transition region that becomes a noise source. ing.
JP-A-2-61819 Japanese Patent Laid-Open No. 2004-146032

  The above-described conventional technology has made it possible to reduce the medium noise that has been a problem of the perpendicular magnetic recording medium, but on the other hand, this oxide becomes particles in the course of the film forming process and adheres to the medium. A new problem has arisen that it tends to cause defects during magnetic recording. Similarly, when the surface of the medium is tape burnished or when the head is sought, the oxide phase in the magnetic recording layer is the starting point, and it is easy to cause scratch-like defects on the surface of the medium. It has also become clear.

  The present invention has been made in view of the above circumstances, it is possible to significantly reduce the fine particles remaining on the medium surface, a magnetic recording using bright points, the circumferential scratches incidence less high quality perpendicular magnetic recording medium and it The purpose is to provide a device.

  To achieve the above object, the present invention includes at least a soft magnetic backing layer on a nonmagnetic substrate, a sequentially arranged perpendicular magnetic recording medium comprising a magnetic recording layer made of a Co alloy containing oxide, the non-magnetic substrate A perpendicular magnetic recording medium having a resistivity of 50 Ω · cm or less is provided.

  In the perpendicular magnetic recording medium of the present invention, the nonmagnetic substrate preferably has a resistivity of less than 1 Ω · cm.

In the perpendicular magnetic recording medium of the present invention, the nonmagnetic substrate preferably has a resistivity of 1 × 10 ⁻⁴ Ω · cm or less.

  In the perpendicular magnetic recording medium of the present invention, the ODT observation bright spot count is preferably 35 (pieces / sheet) or less.

  In the perpendicular magnetic recording medium of the present invention, the ODT observation bright spot count is preferably 10 (pieces / sheet) or less.

  In the perpendicular magnetic recording medium of the present invention, it is preferable to use silicon as the nonmagnetic substrate material.

  In the perpendicular magnetic recording medium of the present invention, it is also preferable to use graphite carbon as the nonmagnetic substrate material.

  In the perpendicular magnetic recording medium of the present invention, it is preferable to use a disk-shaped substrate having a diameter of 28 mm or less.

  The present invention also provides a magnetic recording apparatus using the above-described perpendicular magnetic recording medium according to the present invention.

  The present invention, as a substrate for a perpendicular magnetic recording medium, the resistance of the non-magnetic substrate has a configuration using the following non-magnetic substrate 50 [Omega · cm, it is possible to significantly reduce the fine particles remaining on the surface of the medium In addition, it is possible to provide a high-quality perpendicular magnetic recording medium with a small number of bright spots and a low incidence of circumferential scratches and a magnetic recording apparatus using the same.

The perpendicular magnetic recording medium of the present invention has a structure in which a soft magnetic layer and a perpendicular magnetic recording layer are sequentially laminated on a nonmagnetic substrate, and the resistivity of the nonmagnetic substrate is 50 Ω · cm or less. To do. The perpendicular magnetic recording layer is a material containing an oxide such as SiO ₂ .
A series of film formation is generally performed by a vacuum film formation method such as a sputtering method. For example, a typical method is a sputtering method. This is done by placing an alloy target in which an oxide is dispersed in a sufficiently evacuated vacuum vessel and performing plasma discharge to form a film. Generally, such an oxide is dispersed in a metal alloy. When the material is deposited by a physical deposition method, arcing is likely to occur due to the influence of local electrical conductivity difference. At this time, the oxide often becomes fine particles and scatters in the vacuum vessel and adheres to the surface of the medium. The fine particles generated in this way are attracted by static electricity generated on the substrate surface, resulting in more magnetic recording defects. In order to prevent the generation of such static electricity, it is effective that the substrate material has a certain conductivity.

  However, in recent magnetic recording apparatuses, particularly small-diameter magnetic recording apparatuses with a small substrate diameter, glass that is an insulator is almost always used as a medium substrate from the viewpoint of impact resistance. It was difficult.

  Therefore, in order to solve these problems, we considered that a substrate with material mechanical performance equivalent to that of glass and having a certain electric conductivity was necessary, and as a result of intensive studies, a general semiconductor by using a substrate material having the following electrical resistivity level, it is possible to dramatically reduce the fine particles remaining on the medium surface during the deposition process, also the generation of surface flaws that originate from it It was found that it can be suppressed. As specific substrate materials, silicon and graphite carbon are suitable. The present invention is effective in a small-diameter magnetic recording apparatus that requires particularly excellent impact resistance.

  In addition, although the cause is not clearly understood, since the adhesion of the fine particles described above is generally more intense near the center of the target in the case of the sputtering method, in this sense as well, the smaller the diameter of the substrate of the present invention. The effect is considered large.

  Currently, 48 mmφ, 27.4 mmφ, 21.6 mmφ, and the like are being put to practical use as small-diameter substrate sizes, but a particularly remarkable effect has been found particularly with substrates having a diameter of 27.4 mmφ or less.

  For silicon material according to claim 2, single crystal material produced in the semiconductor industry, of course, it can suitably be used for quality classified as defective as a semiconductor material because of the defects and the like. However, material mechanical performance and surface roughness must be equivalent. In general, the average surface roughness Ra is about 0.1 nm to 0.2 nm, Young's modulus is 160 to 190 GPa, bending strength is 75 to 90 MPa, and hardness is about 7. Of course, a plurality of substrates may be cut out from one wafer. Particularly for a substrate having a small diameter of 27.4 mmφ or less, the merit of cutting out a plurality of sheets is great. Here, when the substrate diameter is small, high mechanical strength is easily obtained when compared with the same substrate thickness.

  A typical example of the configuration of the perpendicular magnetic recording medium according to the present invention is shown in FIG. The perpendicular magnetic recording medium 1 shown in FIG. 1, on a non-magnetic substrate 2, a soft magnetic backing layer 3, the orientation control layer 7, intermediate layer 8, and sequentially deposited perpendicular magnetic recording layer 9 and a protective layer 10 constituting Has been.

  As the non-magnetic substrate 2, as described above, the resistivity is not more than 50 [Omega · cm materials, e.g., silicon, made of graphite carbon or the like, of smaller diameter, a substrate of particular diameter 27.4mmφ following diameters are used .

  As the soft magnetic backing layer 3, what is generally called a soft magnetic material is used. For example, CoZrNb alloy, FeCo alloy, FeSi alloy and the like. The backing soft magnetic layer 3 guides the magnetic flux from the recording head in the recording / reproducing process of the perpendicular magnetic recording medium 1 and functions to ensure sufficient OW (overwrite) characteristics. The film thickness is usually as thick as about 100 nm, but can be set thinner as long as recording and reproduction can be sufficiently performed.

  Further, the soft magnetic backing layer 3 Other monolayer film, there is also possible to provide a structure having a demagnetizing field coupling disposing the soft magnetic film of two layers sandwiching a thin non-magnetic film such as Ru. In the illustration shown in FIG. 1, the soft magnetic backing layer 3 has a structure in which a first soft magnetic layer 4 and a second soft magnetic layer 6 are disposed with a Ru layer 5 interposed therebetween. The soft magnetic backing layer 3 is easy to form a magnetic domain, and spike-like noise is generated from the magnetic domain. Therefore, the soft magnetic backing layer 3 aims to suppress the generation of a domain wall by providing a demagnetizing-coupled bias magnetic field.

  An intermediate layer 8 is often provided on the soft magnetic backing layer 3. This intermediate layer 8 is for adjusting the crystal structure of the perpendicular magnetic recording layer 9 thereon, and for example, a material having the same dense hexagonal crystal structure as that of the perpendicular magnetic recording layer 9, such as a Ru film, is used. The film thickness is adjusted so as to optimize the recording / reproducing characteristics of the perpendicular magnetic recording layer 9, but is generally about 5 to 20 nm. However, as the film thickness of the intermediate layer 8 is thinner, the distance between the recording / reproducing head and the soft magnetic backing layer 3 is shortened, and it becomes easier to secure OW and at the same time, it becomes easier to set the track width narrower.

The perpendicular magnetic recording layer 9 is a magnetic layer that actually records and reproduces information, and generally has a dense hexagonal crystal structure, and its C axis (002) is perpendicular to the substrate. As the material, various Co-based alloys are used. The present invention is particularly intended for a material having a Co-based alloy as a base material and containing an oxide such as SiO _2. For example, Co— Cr—Pt— (SiO ₂ ), Co—Cr—Pt— (Cr ₂ O ₃ ) and the like. These oxide-containing material thin films have a fine structure in which the magnetic alloy material is surrounded by an oxide precipitation phase, thereby minimizing the magnetization transition region that is a medium noise source and consequently reducing the medium noise. It is believed that.

  The thickness of the perpendicular magnetic recording layer 9 can be arbitrarily set depending on the required output and the like, but is generally about 5 nm to 20 nm. Further, the perpendicular coercive force of the perpendicular magnetic recording layer 9 is often used at about 3000 Oe to 5500 Oe, but is considered to change according to the change in head performance. 1 Oe is about 79 A / m.

  Also, the other than each layer, in order to enhance the performance of the perpendicular magnetic recording medium 1, for example, the bottom of the intermediate layer 8, it is possible to insert the seed layer or the orientation control layer 7 to adjust the further crystal structure. The saturation magnetization Ms of the orientation control layer 7 is preferably 0 to 200 emu / cc. If the Ms of the orientation control layer 7 exceeds 200 emu / cc, the recording / reproducing characteristics of the perpendicular magnetic recording layer 9 tend to deteriorate due to noise generated from the orientation control layer 7. Further, the composition of the orientation control layer 7, it is desirable to decide as the recording and reproducing characteristics of the perpendicular magnetic recording layer 9 is optimized, the optimum composition may be have a magnetization, must in particular have a magnetization There is no. In general, considering the generation of noise, it is considered that the Ms of the orientation control layer 7 should be low.

  Further, a protective layer 10 is generally formed on the perpendicular magnetic recording layer 9. The protective layer 10 is provided for the purpose of preventing corrosion of the perpendicular magnetic recording medium 1 and preventing damage to the medium surface when the magnetic head comes into contact with the medium. As the protective layer 10, a carbon thin film is often used, and in particular, a plasma CVD film having a high film density is often used in recent years. Alternatively, a laminated structure of a CVD carbon film and a sputtering carbon film can also be used. If the film quality of the carbon film is hard and brittle, scratches on the surface of the medium are considered to be more likely to occur, and therefore the conditions for forming the carbon film must be carefully selected.

  The thickness of the protective layer 10 is desirably 1 to 10 nm. Accordingly, the distance between the head and the medium can be reduced, which is suitable for high density recording. Further, a lubricating layer can be provided on the protective layer 10. As the lubricant used in the lubricating layer, conventionally known materials such as perfluoropolyether, fluorinated alcohol, and fluorinated carboxylic acid can be used.

  FIG. 2 is a diagram showing an example of the magnetic recording apparatus according to the present invention. The magnetic recording / reproducing apparatus 11 according to the present example includes a perpendicular magnetic recording medium 1 shown in FIG. 1 and a medium drive for rotating the perpendicular magnetic recording medium 1. Unit 12, a magnetic head 13 for recording / reproducing information on the perpendicular magnetic recording medium 1, a head driving unit 14 for moving the magnetic head 13 relative to the perpendicular magnetic recording medium 1, and a recording / reproducing signal processing system 15 It is prepared for. Reproducing signal processing system 15, de-input from the outside - to send a data to the outside - or send a recording signal to the magnetic head 13 to process the data, processes the reproduction signal from the magnetic head 13 de It can be done.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

[Examples 1-3, Comparative Examples 1-6]
As the non-magnetic substrate, the following two types of substrates were prepared for each 50 sheets.
a) Crystallized glass substrate (diameter 48 mmφ, hole diameter 12 mmφ, thickness 0.508 mm, average surface roughness Ra = 0.5 nm, electrical resistivity infinite).
b) Crystallized glass substrate (diameter 27.4 mmφ, hole diameter 7 mmφ, thickness 0.381 mm).
c) Crystallized glass substrate (diameter 21.6 mmφ, hole diameter 6 mmφ, thickness 0.381 mm).
d) Silicon substrate (diameter 48 mmφ, hole diameter 12 mmφ, thickness 0.508 mm, average surface roughness Ra = 0.5 nm, electrical resistivity 10000 Ω · cm).
e) A silicon substrate (diameter: 27.4 mmφ, hole diameter: 7 mmφ, thickness: 0.381 mm, electric resistivity: 10000 Ω · cm).
f) Silicon substrate (diameter 21.6 mmφ, hole diameter 6 mmφ, thickness 0.381 mm, electrical resistivity 10000 Ω · cm).
g) Silicon substrate (diameter 48 mmφ, hole diameter 12 mmφ, thickness 0.508 mm, electrical resistivity 10 Ω · cm).
h) Silicon substrate (diameter 27.4 mmφ, hole diameter 7 mmφ, thickness 0.381 mm, electrical resistivity 10 Ω · cm).
i) Silicon substrate (diameter 21.6 mmφ, hole diameter 6 mmφ, thickness 0.381 mm, electrical resistivity 10 Ω · cm).

Each of the nine substrates a to i is accommodated in a film forming chamber of a DC magnetron sputtering apparatus (Cnel 1030 manufactured by Anelva), and the film forming chamber is evacuated until the ultimate vacuum is 2 × 10 ⁻⁵ Pa. Thereafter, sputtering and lubrication layer application were sequentially performed as shown in the following steps 1 to 5 in an atmosphere of Ar gas partial pressure of 0.6 Pa.

Step 1: A soft magnetic backing layer made of FeCo was formed on the substrate to a thickness of 100 nm.
Step 2: Subsequently, a Ru intermediate layer was formed to a thickness of 20 nm.
Step 3: Subsequently, a perpendicular magnetic recording layer made of Co—Cr—Pt— (SiO ₂ ) was formed to a thickness of 10 nm.
Step 4: Subsequently, a carbon protective layer was formed to a thickness of 4 nm by using a plasma CVD method.
Step 5: The substrate subjected to sputtering was taken out of the vacuum vessel, and a lubricating layer made of perfluoropolyether was formed on the protective layer by dipping, to obtain a perpendicular magnetic recording medium.

In this way, 50 perpendicular magnetic recording media were produced for each substrate.
Next, in order to compare the number of fine particles adhering to the medium surface, the number of white spots (bright spots) on the surface of all the media was counted using an ODT (Optical Defect Tester) for magnetic disk media, The average value of the number of bright spot counts per medium was defined as the average value of the ODT observation bright spot count number. The ODT observation was performed by counting the number of defects having a diameter of 0.010 microns or more using an RDT3500, an ODT tester manufactured by Hitachi High Technology. When the substrate diameter is 48.0 mm, the observation area is within a radius position of 15 mm to 22 mm, when the substrate diameter is 27.4 mm, within a radius position of 9 mm to 13 mm, and when the substrate diameter is 21.6 mm. In the range of radial positions 8 mm to 10 mm, the entire circumference was 0 ° to 360 °.

  Furthermore, the tape grinding | polishing process of the whole medium surface was performed using the tape burnish apparatus for magnetic disc media. The processing conditions are: used abrasive tape 3M alumina tape, roll load 30 gf (290 mN (relative pressure)), rotation speed 1000 rpm, contact speed 0.3 mm / s. Thereafter, the surface of the medium was observed in detail under a high-intensity lamp and examined for the presence of circumferential flaws caused by tape polishing.

  For each substrate type, the number of media was 50, so the number of media surfaces was 100, and the average number of ODT observation bright spot counts and the number of circumferential flaws were investigated. The results are summarized in Table 1.

  From this result, it has been clarified that the number of bright spots and the circumferential flaw generation rate of the perpendicular magnetic recording medium can be greatly improved by using a silicon substrate having a relatively low electric resistivity. In particular, the effect was more noticeable as the substrate diameter was smaller. Although this mechanism is unknown, it is considered that the effect is clearly increased at a diameter of 26 mmφ or less in this embodiment.

[Examples 4 and 5 and Comparative Example 7]
As nonmagnetic substrates, the following three types of substrates were prepared for each 50 sheets.
a) Crystallized glass substrate (diameter 21.6 mmφ, hole diameter 6 mmφ, thickness 0.381 mm, average surface roughness Ra = 0.5 nm, electrical resistivity infinite).
b) Silicon substrate (size is the same as the glass substrate of a, electric resistivity 3 × 10 ⁻⁶ Ω · cm).
c) Carbon graphite substrate (size is the same as glass of a, electric resistivity 4 × 10 ⁻⁵ Ω · cm).

  A substrate with a smaller size was prepared, and Steps 1 to 5 were performed as in Examples 1 to 3 and Comparative Examples 1 to 6, and 50 perpendicular magnetic recording media were manufactured. With respect to these perpendicular magnetic recording media, as in the case of Examples 1 to 3 and Comparative Examples 1 to 6 described above, the ODT observation bright spot count average value and the number of circumferential flaw occurrence surfaces were examined. The results are summarized in Table 2.

  From this result, the effect of the present invention was clarified even in a substrate having a smaller diameter.

[Example 6]
As shown in Table 3, 50 various substrates each having a resistivity of 48 mm in diameter or 21.6 mm in diameter were prepared. Among them, there are several types of silicon substrates, but each of these silicon substrates has a resistivity changed by adding B as a dopant and adjusting the addition amount. Using these substrates, Steps 1 to 5 were performed in the same manner as in Examples 1 to 3 and Comparative Examples 1 to 6, and 50 perpendicular magnetic recording media were manufactured. With respect to these perpendicular magnetic recording media, as in the case of Examples 1 to 3 and Comparative Examples 1 to 6 described above, the ODT observation bright spot count average value and the number of circumferential flaw occurrence surfaces were examined. The results are summarized in Table 3.

From the above experimental results, the following facts were revealed.
1) When the resistivity of the substrate material exceeds 50 Ω · cm, the number of bright spots attached to the surface of the perpendicular magnetic recording medium during the film forming process increases rapidly. Similarly, the frequency of occurrence of circumferential flaws when the media is subjected to tape burnishing also increases rapidly.
2) Even when the same substrate material is used, it is recognized that the smaller the substrate diameter, the higher the number of bright spots per area and the incidence of circumferential scratches. Therefore, it is considered that the perpendicular magnetic recording medium having a smaller diameter is more susceptible to contamination by fine particles during the film forming process, and the effect of the present invention becomes more remarkable.

It is sectional drawing which shows an example of the perpendicular magnetic recording medium of this invention. It is a block diagram which shows an example of the magnetic recording device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Perpendicular magnetic recording medium, 2 ... Nonmagnetic board | substrate, 3 ... Soft magnetic backing layer, 4 ... 1st soft magnetic layer, 5 ... Ru layer, 6 ... 2nd soft Magnetic layer, 7 ... orientation control layer, 8 ... intermediate layer, 9 ... perpendicular magnetic recording layer, 10 ... protective film, 11 ... magnetic recording / reproducing device, 12 ... medium drive unit , 13 ... magnetic head, 14 ... head drive unit, 15 ... recording / reproduction signal processing system.

Claims (9)

  At least a soft magnetic backing layer on a nonmagnetic substrate, a sequentially arranged perpendicular magnetic recording medium comprising a magnetic recording layer made of a Co alloy containing oxide, the resistivity of the non-magnetic substrate is not more than 50 [Omega · cm A perpendicular magnetic recording medium.   The perpendicular magnetic recording medium according to claim 1, wherein the resistivity of the nonmagnetic substrate is less than 1 Ω · cm. The perpendicular magnetic recording medium according to claim 1, wherein the resistivity of the nonmagnetic substrate is 1 × 10 ⁻⁴ Ω · cm or less.   The perpendicular magnetic recording medium according to any one of claims 1 to 3, wherein the ODT observation bright spot count number is 35 (pieces / sheet) or less.   4. The perpendicular magnetic recording medium according to claim 1, wherein the ODT observation bright spot count number is 10 (pieces / sheet) or less.   2. The perpendicular magnetic recording medium according to claim 1, wherein silicon is used as a nonmagnetic substrate material.   2. The perpendicular magnetic recording medium according to claim 1, wherein graphite carbon is used as the nonmagnetic substrate material.   8. The perpendicular magnetic recording medium according to claim 1, wherein a disk-shaped substrate having a diameter of 28 mm or less is used. A magnetic recording apparatus using the perpendicular magnetic recording medium according to claim 1.

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