JP2010146603A - Magnetic recording medium, magnetic recording and reproducing device, and signal processing method of magnetic recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which is manufactured with a proper yield, by forming a tracking servo pattern with high density as tracking servo information, performing positioning of a magnetic head with accuracy at the center of a magnetic recording track, and forming a resist pattern which is used, when forming a pattern form comprising magnetic layers with high accuracy. <P>SOLUTION: In the magnetic recording medium 50, an annular magnetic recording pattern 51a which includes a magnetic layer separated magnetically on a nonmagnetic substrate is provided, and in a part of the magnetic recording pattern 51a, a tracking servo pattern 33, which is formed by making distances between the center and the side part of the magnetic recording pattern 51a different only at one side, is formed as the tracking servo information. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium used in a hard disk device or the like, a magnetic recording / reproducing apparatus, and a signal processing method for the magnetic recording / reproducing apparatus.

  In recent years, the application range of magnetic recording devices such as hard disk devices has been remarkably increased, and the importance thereof has increased, and the recording density of magnetic recording media used in these devices has been remarkably improved. In particular, since the introduction of MR (magnet resistive) head and PRML technology, the increase in surface recording density has become even more intense. In recent years, GMR (giant magnet resistive) heads and TMR (tunneling magnet resistive) heads have also been introduced. It continues to increase at a rate of about 50% per year. For these magnetic recording media, it is required to achieve higher recording density in the future. For this reason, it is required to increase the coercive force of the magnetic layer, achieve a high signal-to-noise ratio (SNR), and high resolution. ing. In recent years, efforts have been made to increase the surface recording density by increasing the track density as well as improving the linear recording density.

In the latest magnetic recording apparatus, the track density has reached 110 kTPI. However, as the track density is increased, magnetic recording information between adjacent tracks interfere with each other, and the problem that the magnetization transition region in the boundary region becomes a noise source and the SNR is easily lost. This directly leads to a decrease in Bit Error rate, which is an obstacle to improving the recording density.
In order to increase the surface recording density, it is necessary to make the size of each recording bit on the magnetic recording medium finer and ensure as much saturation magnetization and magnetic film thickness as possible for each recording bit. However, when the recording bits are miniaturized, the minimum magnetization volume per bit becomes small, and there arises a problem that the recording data is lost due to magnetization reversal due to thermal fluctuation.

  Also, as the track density is increased, the distance between the tracks becomes closer, and therefore a magnetic recording apparatus is required to have an extremely accurate track servo technology. In order to eliminate the influence from adjacent tracks as much as possible, a method is generally used in which recording is performed widely and playback is performed narrower than during recording. This method can minimize the influence between tracks, but it is difficult to obtain a sufficient reproduction output. Therefore, there is a problem that it is difficult to ensure a sufficient SN ratio (SNR).

  As one of the methods for solving the above-mentioned thermal fluctuation problem and ensuring a sufficient S / N ratio or ensuring a sufficient output, irregularities along the tracks are formed on the surface of the recording medium, and the recording tracks are physically separated. Attempts have been made to increase track density by mechanical or magnetic separation. Such a technique is hereinafter referred to as a discrete track method, and a magnetic recording medium manufactured thereby is referred to as a discrete track medium.

As an example of a discrete track medium, a soft magnetic layer and a ferromagnetic layer are laminated on a nonmagnetic substrate having a plurality of convex portions and a concave portion surrounding each convex portion, and the unevenness reflecting the shape of the nonmagnetic substrate is soft magnetic. There is known a magnetic recording medium in which only a convex portion of a ferromagnetic layer formed on a magnetic layer and a ferromagnetic layer is used as a recording region (see, for example, Patent Document 1).
According to this magnetic recording medium, the occurrence of a domain wall in the soft magnetic layer can be suppressed, so that the influence of thermal fluctuation is difficult to occur, and there is no interference between adjacent signals. Has been.

  Discrete track media are generally formed using a method in which a continuous magnetic layer is formed on a nonmagnetic substrate, a patterned resist layer is formed on the magnetic layer, and the magnetic layer is magnetically separated using this. Has been. In addition, as a method for patterning the resist layer, a photolithography method, a nanoimprint method for transferring a pattern using a stamp to a liquid resist, and the like are used.

  In addition, as a method for manufacturing a discrete track medium, a method of forming a track after forming a magnetic recording medium composed of several thin films, or forming a concavo-convex pattern directly on a substrate surface in advance or on a thin film layer for track formation. There is a method of forming a thin film of a magnetic recording medium after the formation (see, for example, Patent Document 2 and Patent Document 3).

In addition, as a method of manufacturing a discrete magnetic recording medium, by performing ion implantation from outside or laser irradiation, the magnetic characteristics of a desired portion of a continuous magnetic layer on a nonmagnetic substrate can be locally changed. There is also a method for forming a recording track (see, for example, Patent Document 4).
For example, Patent Document 5 discloses a magnetic layer having a region that is not magnetized by ion implantation instead of a gap between lands.
Further, for example, in Patent Document 6, a magnetic layer and an ion buffer layer are formed in this order on a substrate, ions are implanted into the magnetic layer with the ion buffer layer interposed, and heat treatment is performed. A magnetic pattern forming method for modifying the magnetic characteristics of the ion implantation region is disclosed.

Further, for example, in Patent Document 7, the first servo burst area in which the first and second servo burst groups are arranged in two rows and the third servo burst group in the second row are arranged in two rows. An information recording medium in which two servo burst areas are alternately arranged with a data area in between is described.
JP 2004-164692 A JP 2004-178793 A JP 2004-178794 A Japanese Patent Laid-Open No. 5-205257 JP 2006-209952 A JP 2006-309841 A JP 2000-090609 A

  However, in the conventional method of manufacturing a discrete track medium, since the accuracy of the pattern shape made of magnetically separated magnetic layers is insufficient and the yield is low, the yield is improved by forming the pattern shape of the magnetic layer with high accuracy. There was a need to improve. As a main cause of reducing the accuracy of the pattern shape of the magnetic layer, there is a resist pattern shape defect such as a variation in the thickness of the resist pattern used for forming the pattern shape made of the magnetic layer or edge sag.

  Here, the problem of the conventional magnetic recording medium will be described with reference to FIG. FIG. 4 is a plan view for explaining an example of a conventional discrete type magnetic recording medium, and FIG. 4A is a schematic view showing the whole of the discrete type magnetic recording medium, and FIG. FIG. 4 is an enlarged schematic view showing only a partial area of the discrete magnetic recording medium indicated by a rectangle in FIG.

As shown in FIGS. 4A and 4B, the magnetic recording medium 40 shown in FIG. 4 includes a data area 41 and a servo information area 42 on one surface of a disk-shaped substrate. It is. In FIG. 4A, an area indicated by a line extending radially from the center corresponds to the servo information area 42, and an area between the radial lines corresponds to the data area 41.
A data recording pattern 41a made of a magnetic layer constituting the data area 41 constitutes a magnetic recording track, and has an annular regular shape as shown in FIG. 4B.

As shown in FIG. 4B, a burst pattern 43a is formed in the servo information area 42 as burst information for positioning the magnetic head at the center of the magnetic recording track. The burst pattern 43a is composed of a magnetic layer constituting the servo information area 42, and has a fine dot shape provided between adjacent magnetic recording tracks. The burst pattern 43 a is normally provided at 255 locations so as to divide the data area 41 in the radial direction of the magnetic recording medium 40.
In the magnetic recording medium 40 shown in FIG. 4A, when reading / writing data from / to the data recording pattern 41a by a magnetic head (not shown), the magnetic head that moves in the circumferential direction on the surface has a servo information area. At 42, the burst information is read and the track position is finely adjusted.

  However, in the magnetic recording medium 40 shown in FIG. 4, the relative position of the magnetic head with respect to the magnetic recording track when data is read from or written to the data recording pattern 41a by the magnetic head due to vibration or thermal expansion accompanying the rotation of the magnetic recording medium 40. In some cases, the magnetic head is not accurately positioned in the center of the magnetic recording track. For this reason, in the magnetic recording medium 40 shown in FIG. 4, there is a possibility that a reading failure or writing failure of the magnetic recording medium 40 by the magnetic head may occur. In particular, in a magnetic recording medium having a high density in the radial direction of the magnetic recording track, the relative position of the magnetic head with respect to the magnetic recording track tends to be misaligned, so that the magnetic head must be accurately positioned at the center of the magnetic recording track. It had been.

  Further, in the magnetic recording medium 40 shown in FIG. 4, since the data recording pattern 41a and the burst pattern 43a are different in shape as shown in FIG. 4B, the shape of the magnetic layer is the pitch, pattern width, etc. These are complex shapes formed by mixing a plurality of different pattern shapes. For this reason, in the magnetic recording medium 40 shown in FIG. 4, it is difficult to form all the pattern shapes made of the magnetic layer with high accuracy, as will be described below.

  In the manufacturing process of the magnetic recording medium 40 shown in FIG. 4, the causes of the defective shape of the resist pattern used when forming the pattern shape made of the magnetic layer are as follows: resist viscosity, resist curing temperature, curing time, humidity, Various patterning conditions, such as exposure time and exposure intensity, can be mentioned. These patterning conditions are appropriately determined according to the pattern shape of the magnetic layer.

However, in the case where the magnetic layer has a complicated shape in which a plurality of pattern shapes are mixed as in the magnetic recording medium 40 shown in FIG. 4, the optimum patterning conditions for forming the resist pattern are set as the pattern. It has been difficult to optimize so as not to cause variations in accuracy due to different shapes.
Specifically, for example, if the patterning conditions for forming the resist pattern are determined so as to correspond to the pattern shape of the data recording pattern 41a, the pattern shape of the burst pattern 43a becomes incomplete. If the patterning conditions for forming the resist pattern are determined so as to correspond to the pattern shape of the burst pattern 43a, the pattern shape of the data recording pattern 41a becomes incomplete.

  Thus, when the magnetic layer has a complicated shape, the patterning conditions for forming the resist pattern cannot be sufficiently optimized, and the magnetic layer formed on the magnetic recording medium cannot be optimized. It is difficult to form a highly accurate resist pattern that can form all the pattern shapes with sufficiently high accuracy. Therefore, in the conventional magnetic recording medium 40 shown in FIG. 4, it is difficult to form all the pattern shapes made of the magnetic layer with high accuracy.

The present invention has been made in view of such circumstances. The magnetic head can be accurately positioned at the center of the magnetic recording track, and a resist pattern used when forming a pattern shape made of a magnetic layer can be increased. It is an object of the present invention to provide a magnetic recording medium that can be formed with high accuracy and can be manufactured with high yield by using a high-precision resist pattern to form all pattern shapes made of a magnetic layer with high accuracy. .
Another object of the present invention is to provide a magnetic recording / reproducing apparatus that includes the magnetic recording medium of the present invention and that can accurately position the magnetic head at the center of the magnetic recording track and that can be manufactured with high yield.
It is another object of the present invention to provide a signal processing method for a magnetic recording / reproducing apparatus capable of accurately positioning a magnetic head at the center of a magnetic recording track.

In order to improve the shape defect of the resist pattern and form the pattern shape of the magnetic layer with high accuracy, the inventor has intensively studied as described below.
That is, the present inventor paid attention to the shape of the magnetic layer in consideration of the fact that the magnetic layer of the magnetic recording medium has a complicated shape is the main cause of reducing the accuracy of the resist pattern shape. And repeated examination. As a result, the present inventor partially varies the radial width of the magnetic recording pattern as tracking servo information in a part of the magnetically separated annular magnetic recording pattern from which information is read and written. By simplifying the shape of the magnetic layer by forming the tracking servo pattern, it is possible to form a resist pattern used for forming the pattern shape made of the magnetic layer with high accuracy and to increase the tracking servo pattern. The present invention has been conceived by finding that the magnetic head can be formed with high density and the magnetic head can be accurately positioned in the center of the magnetic recording track.

That is, the present invention adopts the following configuration.
(1) An annular magnetic recording pattern comprising a magnetic layer magnetically separated is provided on a nonmagnetic substrate, and the distance between the center and the side of the magnetic recording pattern is set on one side of the magnetic recording pattern. A magnetic recording medium characterized in that a tracking servo pattern that is different from each other is formed as tracking servo information.
(2) The magnetic recording medium according to (1), wherein the tracking servo information includes burst information.
(3) The tracking servo pattern includes an inner pattern in which the distance between the center and the inner part of the magnetic recording pattern is different, and an outer pattern in which the distance between the center and the outer part of the magnetic recording pattern is different. The magnetic recording medium according to (1) or (2), wherein the magnetic recording medium includes:

(4) The tracking servo pattern has a plurality of inner patterns in which the distance between the center and the inner part of the magnetic recording pattern is different, and the adjacent inner pattern is one data in the magnetic recording pattern. The magnetic recording medium according to any one of (1) to (3), wherein the magnetic recording medium is arranged with an interval of at least 100 times the bit length.
(5) The tracking servo pattern has a plurality of outer patterns in which the distance between the center and the outer portion of the magnetic recording pattern is different, and the adjacent outer pattern is one data in the magnetic recording pattern. The magnetic recording medium according to any one of (1) to (3), wherein the magnetic recording medium is arranged with an interval of at least 100 times the bit length.

  (6) A magnetic recording / reproducing apparatus comprising a magnetic recording medium and a magnetic head for recording / reproducing information on / from the magnetic recording medium, wherein the magnetic recording medium is any one of (1) to (5). A magnetic recording / reproducing apparatus which is a magnetic recording medium.

  (7) A signal processing method in the magnetic recording / reproducing apparatus according to (5), wherein a step of causing a magnetic head to read a signal from a magnetic recording pattern of a magnetic recording medium and the signal using a difference in frequency are used. And when tracking servo information is obtained from the signal by separating the signal, the magnetic head is positioned at the center in the radial direction of the magnetic recording pattern according to the frequency of the tracking servo information. A signal processing method for a magnetic recording / reproducing apparatus.

  The magnetic recording medium of the present invention is provided with an annular magnetic recording pattern comprising a magnetic layer magnetically separated on a nonmagnetic substrate, and a part of the magnetic recording pattern includes a center and side portions of the magnetic recording pattern. The tracking servo pattern with different distances on one side is formed as tracking servo information, so a complicated shape is formed as when forming a pattern made of a magnetic layer as servo information in the servo information area. It is not necessary to form the magnetic layer, and the shape of the magnetic layer is simple. Therefore, a highly accurate resist pattern can be formed by optimizing the patterning conditions for forming a resist pattern used when forming a pattern shape made of a magnetic layer. Therefore, in the magnetic recording medium of the present invention, all the pattern shapes formed of the magnetic layer formed on the nonmagnetic substrate can be formed with sufficiently high accuracy using a high-precision resist pattern. As a result, the magnetic recording medium of the present invention can be formed with high yield.

  In the magnetic recording medium of the present invention, a tracking servo pattern in which the distance between the center and the side portion of the magnetic recording pattern is changed on only one side is formed as tracking servo information on a part of the magnetic recording pattern. Therefore, the tracking servo information can be written at a high density by forming the tracking servo pattern at a high density. Therefore, for example, the amount of tracking servo information can be increased as compared with a conventional magnetic recording medium in which a burst pattern of 255 positions is provided in the radial direction of the magnetic recording medium. As a result, when reading / writing information from / to the magnetic recording pattern by the magnetic head, the magnetic head reads the tracking servo information, and the head drive unit of the magnetic recording / reproducing apparatus finely adjusts the relative position of the magnetic head with respect to the magnetic recording track. As a result, the magnetic head can be accurately positioned at the center of the magnetic recording track.

In addition, since the magnetic recording / reproducing apparatus of the present invention includes the magnetic recording medium of the present invention, the magnetic head can be accurately positioned at the center of the magnetic recording track and can be manufactured with high yield.
Further, according to the signal processing method of the magnetic recording / reproducing apparatus of the present invention, the magnetic head can be accurately positioned at the center of the magnetic recording track.

  Next, the magnetic recording medium, the manufacturing method thereof, and the magnetic recording / reproducing apparatus of the present invention will be described in detail with reference to the drawings. In the drawings referred to in the following description, the sizes, thicknesses, dimensions, and the like of the respective parts shown in the drawings may differ from the dimensional relationships of the actual magnetic recording medium and magnetic recording / reproducing apparatus.

<Magnetic recording medium>
First, the magnetic recording medium of the present invention will be described with an example.
FIG. 1 is a plan view for explaining an example of the magnetic recording medium of the present invention, and is an enlarged schematic view showing only a partial region of the magnetic recording medium. In FIG. 1, the upper side is the outside of the magnetic recording medium, and the lower side is the center side (inside) of the magnetic recording medium.
FIG. 2I is a cross-sectional view for explaining the cross-sectional structure of the magnetic recording medium shown in FIG. 1, and is an enlarged schematic view of a part of the magnetic recording medium viewed from the radial direction. In FIG. 2I, only the substrate, the magnetic layer, and the protective film layer are shown for ease of explanation. 2A to 2H are process diagrams for explaining a part of the manufacturing process of the magnetic recording medium shown in FIG. 1, which is the same as the region shown in FIG. It is the expanded sectional view which expanded and showed only the field.

  In the magnetic recording medium 50 shown in FIG. 1 and FIG. 2 (i), a plurality of annular magnetic recording patterns 51 a composed of magnetically separated magnetic layers 2 are provided on a disk-like nonmagnetic substrate 1. Yes. A plurality of magnetic recording patterns 51a are regularly formed concentrically with respect to the rotation center of the disk-shaped magnetic recording medium 50, and constitute a magnetic recording track having a width of about 50 nm (see FIG. In FIG. 1, since a part of the magnetic recording medium is shown enlarged, the magnetic recording pattern 51a looks linear).

As shown in FIG. 2 (i), the magnetic layer 2 has a concave portion 51c and a convex portion 51b, and the magnetic properties of the magnetic layer 2 constituting the concave portion 51c are modified to be non-magnetic. As a result, the adjacent convex portions 51b are magnetically separated. The width of the concave portion 51c is preferably about 10 nm to 100 nm, and the width of the convex portion 51b is preferably about 20 nm to 200 nm. In the present embodiment, the width of the protrusion 51b, which is the width of the magnetic recording pattern 51a, is the width of the magnetic recording track.
Here, the magnetic layer 2 is “magnetically separated” as long as it is magnetically separated at least on the surface of the magnetic layer 2 and may not be separated at the bottom of the magnetic layer 2. .

  As shown in FIG. 1, a tracking servo pattern 33 is provided as part of the magnetic recording pattern 51a as tracking servo information. The tracking servo information in the present embodiment includes burst information. The burst information is information for positioning the magnetic head at the center of the magnetic recording track (the center of the width of the magnetic recording pattern 51a).

As shown in FIG. 1, the tracking servo pattern 33 is provided with a convex portion 33a, so that the distance in the radial direction of the magnetic recording medium 50 between the center and the side portion of the magnetic recording pattern 51a is different only on one side. It will be. The convex portion 33a has a semi-elliptical shape in plan view with the radial direction of the magnetic recording medium 50 as the short axis and the circumferential direction of the magnetic recording medium 50 as the long axis.
The tracking servo pattern 33 is not limited to the example shown in FIG. 1 as long as the distance between the center and the side portion of the magnetic recording pattern 51a is different only on one side. Specifically, the tracking servo pattern 33 may increase the distance between the center and the side of the magnetic recording pattern 51a as in the example shown in FIG. 1, or the center and side of the magnetic recording pattern 51a. The distance to the part may be shortened. Moreover, the shape of the convex part 33a which comprises the tracking servo pattern 33 may be a planar view semicircle shape or planar view polygonal shape, for example.

The tracking servo pattern 33 includes an inner pattern 33b and an outer pattern 33c as shown in FIG.
The inner pattern 33b has a plurality of convex portions 33a provided at equal intervals along the extending direction of the magnetic recording pattern 51a on the inner side of the magnetic recording pattern 51a. The distance in the radial direction of the magnetic recording medium 50 is increased.
The outer pattern 33c has a plurality of convex portions 33a provided at equal intervals along the extending direction of the magnetic recording pattern 51a on the outer side of the magnetic recording pattern 51a. The distance in the radial direction of the magnetic recording medium 50 with respect to the portion is increased.

In the present embodiment, as shown in FIG. 1, since the tracking servo pattern 33 is formed on a part of the magnetic recording pattern 51a, the magnetic head (not shown) is positioned at the center of the magnetic recording track (the magnetic recording pattern 51a). If it is not positioned at the center of the width, when a signal is read from the magnetic recording track (magnetic recording pattern 51a) by the magnetic head, the tracking has a frequency corresponding to the amount of deviation between the magnetic head and the magnetic recording track. A signal including servo information is output. In the present embodiment, the tracking servo pattern 33 includes an inner pattern 33b provided in the circumferential direction of the magnetic recording pattern 51a and an outer pattern 33c provided in the circumferential direction of the magnetic recording pattern 51a. Therefore, the tracking servo information having a frequency corresponding to the amount of deviation between the magnetic head and the magnetic recording track, regardless of whether the relative position of the magnetic head with respect to the magnetic recording track is shifted to the inner side or the outer side of the magnetic recording track. A signal including is output.
However, when the magnetic head is positioned at the center of the magnetic recording track, a signal including tracking servo information is not output even if a signal is read from the magnetic recording pattern 51a by the magnetic head.

Therefore, in the magnetic recording medium 50 of the present embodiment, the magnetic head is positioned at the center of the magnetic recording track depending on whether or not tracking servo information is output by reading a signal from the magnetic recording pattern 51a by the magnetic head. Whether it is detected or not. Furthermore, in the magnetic recording medium 50 of the present embodiment, when tracking servo information is output by reading a signal from the magnetic recording pattern 51a by the magnetic head, the magnetic head depends on the frequency of the tracking servo information. And the magnetic recording track can be detected.
Therefore, the magnetic recording medium 50 according to the present embodiment causes the magnetic head to read tracking servo information when reading / writing information from / to the magnetic recording pattern 51a by the magnetic head, and magnetic recording / reproducing is performed based on the obtained tracking servo information. By causing the head drive unit (not shown) of the apparatus to finely adjust the relative position of the magnetic head with respect to the magnetic recording track, the magnetic head can be positioned at the center of the magnetic recording track.

Further, the inner pattern 33b adjacent in the extending direction of the magnetic recording pattern 51a and the outer pattern 33c adjacent in the extending direction of the magnetic recording pattern 51a are each 1 data bit length in the magnetic recording pattern 51a as shown below. It is preferable that the gaps 36 and 37 (pitch) be 100 times or more and 1000 times or less.
That is, in this embodiment, since the tracking servo pattern 33 is formed on a part of the magnetic recording pattern 51a, information is written by the magnetic head when the magnetic head is not positioned at the center of the magnetic recording track. When a signal is read from the magnetic recording pattern 51a, the output signal includes a write data signal and tracking servo information.

  For example, when information is written on the magnetic recording pattern 51a of the magnetic recording medium 50 by the magnetic head at a frequency of 100 MHz and the magnetic head is not positioned at the center of the magnetic recording track, the magnetic recording pattern 51a is used by the magnetic head. When the signal is read, tracking servo information is mixed with a write data signal output at a frequency of 100 MHz and output as a mixed signal. At this time, if the interval 37 between the inner patterns 33b and the interval 36 between the outer patterns 33c are 100 times or more of one data bit length, the tracking servo information output from the tracking servo pattern 33 is written into the tracking servo information. Depending on the interval (in other words, the interval 37 between the inner patterns 33b and the interval 36 between the outer patterns 33c), the signal is output at a frequency of 1 MHz or less (up to 1/100 the frequency of the write data signal).

  As described above, when the interval 37 between the inner patterns 33b and the interval 36 between the outer patterns 33c is 100 times or more of one data bit length, the frequency of the write data signal and the tracking obtained from the inner pattern 33b and the outer pattern 33c. A large difference of 100 times or more occurs between the servo information and the frequency. Therefore, when the tracking servo information is included in the signal read from the magnetic recording pattern 51a by the magnetic head, the write data signal and the tracking servo are used by using the frequency difference between the writing data signal and the tracking servo information. By separating the mixed signal from the information, tracking servo information can be easily obtained.

  On the other hand, when the interval 37 between the inner patterns 33b and the interval 36 between the outer patterns 33c are less than 100 times the length of one data bit, the difference between the frequency of the write data signal and the frequency of the tracking servo information becomes small. The tracking servo information may be difficult to separate from the mixed signal of the write data signal and the tracking servo information, and the tracking servo information may be canceled by the write data signal.

  When the interval 37 between the inner patterns 33b and the interval 36 between the outer patterns 33c exceeds 1000 times the length of one data bit, the difference between the frequency of the write data signal and the frequency of the tracking servo information increases, but the tracking servo There is a risk that the frequency of information becomes too small, and it becomes difficult to extract the tracking servo information from the mixed signal of the write data signal and the tracking servo information. Further, the followability of the magnetic head based on the tracking servo information may be reduced.

  Here, as a method of separating the mixed signal of the write data signal and the tracking servo information, a method using a low-pass filter and / or a band-pass filter can be used. According to the method using the low-pass filter and / or the band-pass filter, only the tracking servo information can be easily extracted from the mixed signal of the write data signal and the tracking servo information.

  In the present embodiment, the distance between the convex portions 33a constituting the tracking servo pattern 33 is such that the outer side (upper side in FIG. 1) and inner side (lower side in FIG. 1) of the magnetic recording pattern 51a, as shown in FIG. ), And the interval 37 between the inner patterns 33b and the interval 36 between the outer patterns 33c are different. Therefore, in this embodiment, the density of the tracking servo pattern 33 (outer pattern 33c) outside the magnetic recording pattern 51a is different from the density of the tracking servo pattern 33 (inner pattern 33b) inside the magnetic recording pattern 51a. It has become a thing.

  In the present embodiment, the interval 36 between the outer patterns 33c is closer than the interval 37 between the inner patterns 33b, and the density of the outer patterns 33c is higher than the density of the inner patterns 33b. Yes. In this way, by making the density of the tracking servo pattern 33 different between the outside and the inside of the magnetic recording pattern 51a, the relative position of the magnetic head with respect to the magnetic recording track is determined according to the tracking servo information output from the magnetic head. It is possible to easily detect whether the track is shifted to the inside or the outside.

For example, in the tracking servo pattern 33 shown in FIG. 1, if the density of the outer pattern 33c is doubled that of the inner pattern 33b, the magnetic head is magnetically recorded when the magnetic head is shifted to the outer side of the magnetic recording pattern 51a. Tracking servo information having a frequency twice that of the pattern 51a when shifted to the inside of the pattern 51a is output.
Specifically, for example, when the interval 36 between the outer patterns 33c is 100 times the length of one data bit and the interval 37 between the inner patterns 33b is 200 times the length of one data bit, the magnetic head performs magnetic recording. When tracking servo information is output at a frequency of 1 MHz due to the shift to the outside of the pattern 51a, the shift amount between the magnetic head and the magnetic recording track is the same, and the magnetic head is shifted to the inside of the magnetic recording pattern 51a. If so, tracking servo information having a frequency of 0.5 MHz is output.

  Further, in the magnetic recording medium 50 shown in FIG. 1, the magnetic layer 2 is formed on the nonmagnetic substrate 1 and the protective film layer 9 is formed on the magnetic layer 2 as shown in FIG. A lubricating layer (not shown in FIG. 2) is formed on the film layer 9. In this embodiment, the magnetic recording medium provided with the protective film layer and the lubricating layer will be described as an example. However, the protective film layer and the lubricating layer may not be provided.

  The nonmagnetic substrate 1 is made of an Al alloy substrate such as an Al—Mg alloy mainly composed of Al, ordinary soda glass, aluminosilicate glass, crystallized glass, silicon, titanium, ceramics, and various resins. Arbitrary things, such as a board | substrate, can be used. Among these, it is preferable to use a glass substrate such as an Al alloy substrate or crystallized glass or a silicon substrate as the nonmagnetic substrate 1. Moreover, the average surface roughness (Ra) of the nonmagnetic substrate 1 is preferably 1 nm or less, more preferably 0.5 nm or less, and even more preferably 0.1 nm or less.

The magnetic layer 2 is preferably formed from an alloy containing Co as a main component. The magnetic layer 2 may be an in-plane magnetic layer or a perpendicular magnetic layer, but is preferably a perpendicular magnetic layer in order to achieve a higher recording density.
For example, as the magnetic layer 2 for the in-plane magnetic layer, a laminated structure composed of a nonmagnetic CrMo underlayer and a ferromagnetic CoCrPtTa magnetic layer can be used.
Also, for example, as the magnetic layer 2 for the perpendicular magnetic layer, soft magnetic FeCo alloys (FeCoB, FeCoSiB, FeCoZr, FeCoZrB, FeCoZrBCu, etc.), FeTa alloys (FeTaN, FeTaC, etc.), Co alloys (CoTaZr, CoZrNB, CoB) Etc.), an orientation control film such as Pt, Pd, NiCr and NiFeCr provided as necessary, an intermediate film such as Ru provided as necessary, and a 60Co-15Cr-15Pt alloy or 70Co. -5Cr-15Pt-10SiO ₂ alloy can be used as the magnetic layer of the multilayer structure composed of a magnetic film made of.

  The film thickness of the magnetic layer 2 is determined so as to obtain a sufficient head input / output according to the type of magnetic material used for the magnetic layer 2 and the laminated structure. The magnetic layer 2 needs to have a film thickness of a certain degree or more in order to obtain a certain output when reproducing information from the magnetic recording medium 50. However, since various parameters representing the recording / reproducing characteristics of the magnetic recording / reproducing apparatus usually deteriorate as the output increases, it is necessary to set the film thickness of the magnetic layer 2 optimally. Specifically, the thickness of the magnetic layer 2 is preferably 3 nm to 20 nm, and more preferably 5 nm to 15 nm.

As the protective film layer 9, carbonaceous layers such as Diamond Like Carbon, hydrogenated carbon (HxC), nitrogenated carbon (CN), amorphous carbon, silicon carbide (SiC), etc., SiO ₂ , Zr Commonly used protective film layer materials such as ₂ O ₃ and TiN can be used. Further, the protective film layer 9 may be composed of two or more layers.
The thickness of the protective film layer 9 is preferably 10 nm or less. If the thickness of the protective film layer 9 exceeds 10 nm, the distance between the magnetic head and the magnetic layer 2 increases, and there is a risk that sufficient input / output signal strength cannot be obtained.

  Further, it is preferable to form a lubricating layer (not shown) on the protective film layer 9. Examples of the lubricant used for the lubricating layer include a fluorine-based lubricant, a hydrocarbon-based lubricant, and a mixture thereof. The thickness of the lubricating layer is usually 1 to 4 nm.

<Method of manufacturing magnetic recording medium>
Next, as a method for manufacturing the magnetic recording medium of the present invention, the method for manufacturing the magnetic recording medium of this embodiment shown in FIGS. 1A and 2I will be described in detail as an example.
First, as shown in FIG. 2A, a magnetic layer 2 is formed on a disk-like nonmagnetic substrate 1 by sputtering or the like.
Next, as shown in FIG. 2B, a mask layer 3 is formed on the magnetic layer 2. The mask layer 3 can be formed by sputtering or CVD.

The mask layer 3 is made of Ta, W, Ta nitride, W nitride, Si, SiO ₂ , Ta ₂ O ₅ , Re, Mo, Ti, V, Nb, Sn, Ga, Ge, As, and Ni. It is preferable to form with the material containing one or more selected. As the material of the mask layer 3, among the above materials, As, Ge, Sn, and Ga are preferably used, Ni, Ti, V, and Nb are more preferably used, and Mo, Ta, W, and C are used. Most preferred.
By using the mask layer 3 made of the above-mentioned material, the magnetic layer 2 has excellent shielding properties in a process of removing a part of the magnetic layer 2 by ion milling or the like, and the magnetic property of the mask layer 3 is increased. The formation accuracy of the recording pattern 51a can be improved. Furthermore, since the above material can be easily subjected to dry etching (reactive ion etching or reactive ion milling) using a reactive gas such as oxygen gas, the mask layer 3 is formed on the magnetic layer 2. By providing this, it is possible to reduce the residue on the magnetic layer 2 in the step of removing the resist layer described later, and to reduce the contamination of the surface of the magnetic layer 2.

Next, as shown in FIG. 2C, a resist layer 4 is formed on the mask layer 3. The resist layer 4 can be formed by a method of applying a resist on the mask layer 3 by a spin coat method.
The resist layer 4 is preferably made of a resist that is cured by irradiation with radiation. The radiation here is an electromagnetic wave of a broad concept such as heat rays, visible rays, ultraviolet rays, X-rays, gamma rays and the like. Moreover, as a resist hardened | cured by radiation irradiation, the thermosetting resin hardened | cured with a heat ray, the ultraviolet curing resin effective with an ultraviolet-ray, etc. are mentioned, for example. Examples of the ultraviolet curable resin include novolak resins, acrylic esters, and alicyclic epoxies.

  Next, the mask layer 3 and the resist layer 4 are patterned. In order to pattern the mask layer 3 and the resist layer 4, first, as shown in FIG. 2D, the negative pattern of the magnetic recording pattern 51a made of the magnetic layer 2 formed on the nonmagnetic substrate 1 is changed to a resist layer. 4 to form. The negative pattern formed here is a pattern in which a recess is formed in the resist layer 4 in a region corresponding to the separation region (the recess 51c) arranged between the magnetic recording patterns 51a.

  As a method for forming a negative pattern on the resist layer 4, an ordinary photolithography technique may be used. However, using a method for transferring a pattern shape using a stamp 5 for the resist layer 4 is advantageous in terms of work efficiency. To preferred. As a method for transferring the pattern shape to the resist layer 4 using the stamp 5, for example, as shown by the arrow in FIG. 2D, the pattern is formed by pressing the stamp 5 against the resist layer 4 with a predetermined pressure. There is a method of separating the stamp 5 from the resist layer 4 after the transfer.

  As the stamp 5, a pattern which is a concentric (a plurality of annular) patterns with respect to the center and has a shape corresponding to the magnetic recording pattern 51a is used. The material of the stamp 5 is not particularly limited as long as it has the hardness and durability necessary for transferring the pattern shape. For example, glass, Ni, resin, and the like can be preferably used. Specifically, for example, as the stamp 5, a metal plate with a pattern formed using a method such as electron beam drawing can be used.

In the present embodiment, the material used for the resist layer 4 is a material that is cured by radiation irradiation, and the pattern is transferred to the resist layer 4 at the time of transferring the pattern using the stamp 5 to the resist layer 4. After the step, it is preferable to cure the resist layer 4 by irradiating the resist layer 4 with radiation.
By using such a manufacturing method, the shape of the stamp 5 can be accurately transferred to the resist layer 4. Further, in the step of removing a part of the mask layer 3 which will be described later, it is possible to prevent sagging at the edge portion of the mask layer 3 and to remove a part of the magnetic layer 2 shown in FIG. In addition, the shielding property of the mask layer 3 in the process of modifying the magnetic characteristics of the magnetic layer 2 can be improved, and the formation accuracy of the magnetic recording pattern 51a can be improved.

Further, in the step of transferring the pattern using the stamp 5 to the resist layer 4 in the manufacturing method of the present embodiment, the resist layer 4 is pressed against the resist layer 4 while the fluidity of the resist layer 4 is high. Alternatively, the resist layer 4 may be cured by irradiating the resist layer 4 with the stamp 5 pressed, and then the stamp 5 may be separated from the resist layer 4. Such a manufacturing method is preferable because the shape of the stamp 5 can be transferred to the resist layer 4 with higher accuracy.
Further, when such a manufacturing method is used, the shape of the stamp 5 can be accurately transferred to the resist layer 4 and a highly accurate resist pattern can be formed, so that the magnetic characteristics of the magnetic layer 2 described later are modified. In this step, the coercive force and residual magnetization of the magnetic layer 2 can be reduced to the utmost, and it is possible to provide a magnetic recording medium having a high surface recording density without blurring of writing during magnetic recording. .

As a method of irradiating the resist layer 4 with radiation while the stamp 5 is pressed against the resist layer 4, for example, a method of irradiating radiation from the opposite side of the stamp 5, that is, the nonmagnetic substrate 1 side, or a material of the stamp 5 As a stamp material, a material that can transmit radiation is selected, a method of irradiating radiation from the stamp 5 side, a method of irradiating radiation from the side surface of the stamp 5, and a radiation having high conductivity with respect to a solid such as heat rays. Alternatively, a method of irradiating radiation by heat conduction from the nonmagnetic substrate 1 can be used.
In particular, UV curable resin is used as a resist material, and glass or resin having excellent UV transmittance is used as a stamp material, and ultraviolet rays are irradiated from the stamp 5 side in a state where the stamp 5 is pressed against the resist layer 4. Thus, it is preferable to cure the resist layer 4.

  Next, the resist layer 8 remaining after the negative pattern shown in FIG. 2D is formed, and the mask layer 3 in a region corresponding to the concave separation region (concave portion 51c) disposed between the magnetic recording patterns 51a. Remove. As a result, as shown in FIG. 2E, a mask composed of the mask layer 3 remaining in the region to be the convex portion 51b on the magnetic layer 2 and the resist pattern 4a which is the patterned resist layer 4 is formed. Is done.

The resist layer 8 remaining after the negative pattern is formed using the stamp 5 can be removed by dry etching such as reactive ion etching or ion milling.
The thickness of the resist layer 8 remaining after the negative pattern is formed is preferably in the range of 0 to 10 nm. By setting the thickness of the resist layer 8 in the above range, in the step of removing the mask layer 3 in the region corresponding to the concave separation region (recessed portion 51c) of the magnetic recording pattern 51a, the edge portion of the mask layer 3 is sagged. It can be prevented from occurring, and the shielding property of the mask layer 3 in the step of removing a part of the magnetic layer 2 shown in FIG. 2 (f) can be improved, and the formation accuracy of the magnetic recording pattern 51a can be improved.
Further, the mask layer 3 in the region corresponding to the concave separation region (the concave portion 51c) disposed between the magnetic recording patterns 51a can be removed by dry etching such as reactive ion etching or ion milling, for example.

  Next, as shown in FIG. 2 (f), the surface layer portion of the magnetic layer 2 in the region to be a concave separation region (concave portion 51c) disposed between the magnetic recording patterns 51a exposed by removing the mask layer 3 is formed. For example, ion milling is performed with a milling ion 6 at a depth d in the range of 0.1 nm to 15 nm. Here, the depth d for removing a part of the surface layer of the magnetic layer 2 is preferably in the range of 0.1 nm to 15 nm, and more preferably in the range of 1 to 10 nm. If the depth d for removing the surface layer of the magnetic layer 2 is smaller than 0.1 nm, the effect of removing the magnetic layer 2 may not be sufficiently obtained. On the other hand, if the depth d for removing the surface layer of the magnetic layer 2 is greater than 15 nm, the surface smoothness of the magnetic recording medium 50 deteriorates, and the flying characteristics of the magnetic head in the magnetic recording / reproducing apparatus using the magnetic recording medium 50 May be reduced.

  When a part of the surface layer of the magnetic layer 2 is removed before the step of modifying the magnetic characteristics of the magnetic layer 2 exposed by removing the mask layer 3 as in this embodiment, the surface layer of the magnetic layer 2 is removed. The contrast of the magnetic recording pattern 51a becomes clearer and the S / N of the magnetic recording medium 50 can be improved as compared with the case where the magnetic characteristics of the magnetic layer 2 are modified without removing a part thereof. The reason is that by removing a part of the surface layer of the magnetic layer 2, the surface of the magnetic layer 2 exposed by removing the mask layer 3 is cleaned and activated, so that the magnetic characteristics of the magnetic layer 2 are improved. The reactivity of the reactive plasma and reactive ions with the magnetic layer 2 during the modification is improved, and defects such as vacancies are introduced into the surface layer of the magnetic layer 2 to modify the magnetic properties of the magnetic layer 2. This is probably because reactive ions easily enter the magnetic layer 2 through defects in the surface layer.

Next, as shown in FIG. 2 (f), the magnetic layer 2 in the region 7 where the surface layer portion has been removed is exposed to reactive plasma or reactive ions to modify the magnetic properties of the magnetic layer 2. The region in which the magnetic characteristics of the magnetic layer 2 are modified is a region that magnetically separates the plurality of magnetic recording tracks formed of the magnetic recording pattern 51a.
Here, the modification of the magnetic layer 2 for forming the magnetic recording pattern 51a partially changes the magnetic characteristics such as coercive force and residual magnetization of the magnetic layer 2 in order to pattern the magnetic layer 2. Means that. In the present embodiment, by modifying the magnetic layer 2, the coercive force of the magnetic layer 2 is reduced and the residual magnetization is reduced.

Examples of the reactive plasma used when modifying the magnetic properties of the magnetic layer 2 include inductively coupled plasma (ICP) and reactive ion plasma (RIE).
Inductively coupled plasma is a high-temperature plasma obtained by applying a high voltage to a gas to generate plasma and generating Joule heat due to eddy currents by a high-frequency fluctuating magnetic field inside the plasma. Inductively coupled plasma has a high electron density, and can improve the magnetic properties of a magnetic film having a large area with high efficiency compared to the case of using a conventional ion beam.

The reactive ion plasma is a highly reactive plasma in which a reactive gas such as O ₂ , SF ₆ , CHF ₃ , CF ₄ , or CCl ₄ is added to the plasma. By using the reactive ion plasma, the modification of the magnetic properties of the magnetic film 2 can be realized with higher efficiency.
Examples of the reactive ions that modify the magnetic properties of the magnetic layer 2 include the reactive ions existing in the inductively coupled plasma and the reactive ion plasma described above.

  The method for manufacturing a magnetic recording medium of the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, a magnetic layer magnetically separated is formed by modifying a part of the surface layer of the magnetic layer 2, but the magnetic layer is physically processed to form a recess in the magnetic layer. After forming and filling the recess with a nonmagnetic material, a magnetic layer magnetically separated may be formed by a method of smoothing the surface of the magnetic recording medium.

  After modifying the magnetic characteristics of a part of the magnetic layer 2 in this way, the resist pattern 4a and the mask layer 3 provided on the magnetic layer 2 are removed as shown in FIG. The resist pattern 4a and the mask layer 3 are preferably removed using a technique such as dry etching, reactive ion etching, ion milling, or wet etching.

  After removing the resist pattern 4a and the mask layer 3, the magnetic layer 2 is irradiated with an inert gas 11 such as Ar as shown in FIG. It is preferable to remove by etching. Thus, even if the surface of the magnetic layer 2 is roughened by modifying a part of the magnetic characteristics of the magnetic layer 2, the surface of the roughened magnetic layer 2 is removed. be able to.

Next, as shown in FIG. 2 (i), it is preferable to form a protective film layer 9 on the magnetic layer 2. Usually, the protective film layer 9 is formed by sputtering or CVD.
Furthermore, it is preferable to form a lubricating layer (not shown) on the protective film layer 9.
As described above, the discrete magnetic recording medium 40 shown in FIGS. 1 to 3 is manufactured.

The magnetic recording medium 50 of the present embodiment is provided with an annular magnetic recording pattern 51a composed of a magnetic layer 2 magnetically separated on a nonmagnetic substrate 1, and the magnetic recording pattern 51a is part of the magnetic recording pattern 51a. Since the tracking servo pattern 33 in which the distance between the center and the side portion is different only on one side is formed as tracking servo information, a pattern made of a magnetic layer is formed as servo information in the servo information area. As in the case, it is not necessary to form a magnetic layer having a complicated shape, and the shape of the magnetic layer 2 can be simplified.
Therefore, it is possible to optimize the patterning conditions for forming the resist pattern 4a used when forming the pattern shape made of the magnetic layer 2, and to form the resist pattern 4a with high accuracy. Therefore, in the magnetic recording medium 50 of the present embodiment, all the pattern shapes formed of the magnetic layer 2 formed on the nonmagnetic substrate 1 can be formed with sufficiently high accuracy using the high-precision resist pattern 4a. It can be formed with good yield.

  Further, in the magnetic recording medium 50 of the present embodiment, a tracking servo pattern 33 is formed as tracking servo information in a part of the magnetic recording pattern 51a by changing the distance between the center and the side of the magnetic recording pattern 51a only on one side. Thus, the tracking servo information can be written at a high density by forming the tracking servo pattern 33 at a high density without reducing the area where information is read and written on the magnetic recording medium 50. Therefore, for example, the amount of tracking servo information can be increased as compared with a conventional magnetic recording medium in which a burst pattern of 255 locations is provided in the radial direction of the magnetic recording medium, and the magnetic head is placed at the center of the magnetic recording track. Can be positioned accurately.

<Magnetic recording / reproducing device>
Next, an example of the magnetic recording / reproducing apparatus of the present invention will be described.
FIG. 3 is a schematic perspective view showing a hard disk drive as an example of the magnetic recording / reproducing apparatus of the present invention. The hard disk drive shown in FIG. 3 includes a discrete magnetic recording medium 50 shown in FIG. 1, a medium driving unit 34 that drives the magnetic recording medium 50 in the recording direction, a magnetic head 27 that includes a recording unit and a reproducing unit, A head drive unit 28 for moving the magnetic head 27 relative to the magnetic recording medium 50, and a recording / reproducing signal system 29 (recording / reproducing signal processing) for performing signal input to the magnetic head 27 and output signal reproduction from the magnetic head 27 Means).

  In the hard disk drive shown in FIG. 3, when the magnetic head reads / writes information from / to the magnetic recording pattern 51a of the magnetic recording medium 50, the magnetic head 27 reads the tracking servo information, and the obtained tracking servo information is used as needed. The magnetic head is positioned at the center of the magnetic recording track while finely adjusting the relative position of the magnetic head with respect to the magnetic recording track.

Next, as a signal processing method in the hard disk drive shown in FIG. 3, a signal processing method when the magnetic head 27 is positioned at the center in the radial direction of the magnetic recording pattern 51a will be described.
First, the magnetic head 27 is caused to read a signal from the magnetic recording pattern 51 a of the magnetic recording medium 50. Next, the signal read from the magnetic recording pattern 51a by the magnetic head 27 is separated using the difference in frequency by a low-pass filter and / or a band-pass filter. When tracking servo information is obtained from the signal by separating the signal read from the magnetic recording pattern 51a (that is, when the magnetic head is not positioned at the center of the magnetic recording track), the tracking servo information The amount of deviation between the magnetic head 27 and the magnetic recording track is detected according to the frequency, and the magnetic head 27 is moved relative to the magnetic recording medium 50 by the head drive unit 28 based on the detected amount of deviation, and the magnetic head 27 is positioned at the center in the radial direction of the magnetic recording pattern 51a.

Since the hard disk drive shown in FIG. 3 includes the discrete magnetic recording medium 50 shown in FIG. 1, the magnetic head 27 can be accurately positioned in the center of the magnetic recording track and can be manufactured with a high yield. .
Further, according to the signal processing method of the hard disk drive of this embodiment, the magnetic head 27 can be accurately positioned at the center of the magnetic recording track.

Hereinafter, the present invention will be specifically described with reference to examples.
(Example)
First, a disk-shaped hard disk (HD) glass substrate was placed in a vacuum chamber and evacuated to 1.0 × 10 ⁻⁵ Pa or less. As a glass substrate, a _{Li 2 Si 2 O 5, Al} 2 O 3 -K 2 O, Al 2 O 3 -K 2 O, MgO-P 2 O 5, Sb 2 O 3 -ZnO constituents It was made of crystallized glass and had an outer diameter of 65 mm, an inner diameter of 20 mm, and an average surface roughness (Ra) of 2 angstroms.

Using a DC sputtering method, a backing layer made of FeCoB soft magnetic film, an intermediate layer made of Ru, and a magnetic film made of 70Co-5Cr-15Pt-10SiO ₂ alloy are laminated in this order on the glass substrate. A magnetic layer was formed. Subsequently, a sputtering method is used to stack a mask layer made of Ta on the magnetic layer, and a resist is applied on the mask layer by a spin coating method to form a resist layer made of a novolak resin that is an ultraviolet curable resin. did.
The thicknesses of the respective layers were a backing layer 60 nm, an intermediate layer 10 nm, a magnetic film 15 nm, a mask layer 60 nm, and a resist layer 100 nm.

Next, a stamp made of glass having an ultraviolet transmittance of 95% or more on which a pattern corresponding to the magnetic recording pattern of the magnetic recording medium is formed is pressed against the resist layer at a pressure of 1 MPa (about 8.8 kgf / cm ² ). The pattern was transcribed. Subsequently, ultraviolet rays having a wavelength of 250 nm were irradiated from the top of the stamp for 10 seconds to cure the resist layer. Thereafter, the stamp was separated from the resist layer.

Next, the resist layer remaining in the recess after the negative pattern was formed was removed by dry etching. Dry etching conditions were O ₂ gas of 40 sccm, pressure of 0.3 Pa, high-frequency plasma power of 300 W, DC bias of 30 W, and etching time of 10 seconds.
Thereafter, the resist layer was removed, and the mask layer in the region corresponding to the concave separation region disposed between the exposed magnetic recording patterns was removed by dry etching. The dry etching conditions were CF ₄ gas 50 sccm, pressure 0.6 Pa, high frequency plasma power 500 W, DC bias 60 W, and etching time 30 seconds. As a result, a mask composed of a mask layer remaining in a region to be a convex portion on the magnetic layer and a resist pattern which is a patterned resist layer was formed.

Thereafter, the surface layer portion of the magnetic layer exposed by removing the mask layer was removed by ion milling. Ar ions were used for ion milling. The amount of ions in ion milling was 5 × 10 ¹⁶ atoms / cm ² and the acceleration voltage was 20 keV. The depth of the surface layer of the magnetic layer removed by ion milling was 0.1 nm.

Next, the magnetic layer in the region where the surface layer portion was removed was exposed to reactive plasma to modify the magnetic properties of the magnetic layer. For this reactive plasma treatment, an inductively coupled plasma apparatus NE550 manufactured by ULVAC was used. As the gas and conditions used for generating plasma, 90 cc / min of O ₂ was used, the input power for generating plasma was 200 W, the pressure in the apparatus was 0.5 Pa, and the magnetic layer was treated for 300 seconds.

After modifying the magnetic properties of the magnetic layer, the resist pattern and the mask layer provided on the magnetic layer were removed by dry etching to expose the magnetic recording pattern.
The magnetic recording pattern thus obtained has an annular shape having a convex portion width (magnetic recording track width) of 120 nm and a concave portion width of 60 nm, and a part of the magnetic recording pattern includes tracking servo information. A tracking servo pattern having a semi-elliptical convex portion in plan view with a short axis of 20 nm and a long axis of 30 nm was formed with the short axis being the radial direction of the magnetic recording medium and the long axis being the circumferential direction of the magnetic recording medium. The average bit length of the magnetic recording medium is 100 nm, and the interval (pitch) between the outer patterns that widens the distance between the center and the side of the magnetic recording pattern outward is 200 times the data bit length. The interval (pitch) between the inner patterns that widens the distance between the center and the side of the recording pattern inward was 300 times the length of one data bit.

  Note that the magnetic recording medium of this embodiment is used at a rotational speed of about 5000 rpm, and reading and writing of information to and from the magnetic recording medium by the magnetic head is performed at about 100 MHz. Accordingly, tracking servo information obtained from the outer pattern is output at a maximum of about 0.5 MHz, and tracking servo information obtained from the inner pattern is output at a maximum of about 0.3 MHz.

  Thereafter, a protective film layer made of carbon and having a thickness of 5 nm was formed on the exposed surface of the magnetic recording pattern by a CVD method. Subsequently, a lubricant was applied on the protective film layer to form a lubricant layer.

  After that, place the magnetic recording medium in the servo writer, read the tracking servo information into the magnetic head of the servo writer, and fine-tune the relative position of the magnetic head with respect to the magnetic recording track at any time using the obtained tracking servo information. While performing, the magnetic head was positioned at the center of the magnetic recording track, and preamble information (width about 0.5 μm) and address information (width about 1 μm) were written in this order in the magnetic recording pattern.

The magnetic conversion characteristics (SNR and 3T-squash) of the magnetic recording medium manufactured by the above method were measured.
Evaluation of electromagnetic conversion characteristics was performed using a spin stand. As the magnetic head for evaluation, a perpendicular recording head for recording and a TuMR head (Tunneling Magneto Resistive head) for reading were used, and the SNR value and 3T-squash when a 750 kFCI signal was recorded were measured. Here, 3T-squash (three-track squash) means that after recording a signal on the center track, the signal is recorded on both sides of the center, and the signal intensity (ratio of the center track before and after recording the signal on both sides) (%)).

  As a result, the magnetic recording medium manufactured by the above method had an SNR of 13.6 dB and a 3T-squash of 87%, and was excellent in electromagnetic conversion characteristics.

  According to the present invention, it is possible to manufacture a magnetic recording medium having a magnetic recording pattern with a high manufacturing yield.

FIG. 1 is a plan view for explaining an example of the magnetic recording medium of the present invention, and is an enlarged schematic view showing only a partial region of the magnetic recording medium. FIG. 2I is a cross-sectional view for explaining the cross-sectional structure of the magnetic recording medium shown in FIG. 1, and is an enlarged schematic view of a part of the magnetic recording medium viewed from the radial direction. 2A to 2H are process diagrams for explaining a part of the manufacturing process of the magnetic recording medium shown in FIG. 1, which is the same as the region shown in FIG. It is the expanded sectional view which expanded and showed only the field. FIG. 3 is a schematic perspective view showing a hard disk drive as an example of the magnetic recording / reproducing apparatus of the present invention. FIG. 4 is a plan view for explaining an example of a conventional discrete type magnetic recording medium, and FIG. 4A is a schematic view showing the whole of the discrete type magnetic recording medium, and FIG. FIG. 4 is an enlarged schematic view showing only a partial area of the discrete magnetic recording medium indicated by a rectangle in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic substrate, 2 ... Magnetic layer, 3 ... Mask layer, 4 ... Resist layer, 4a ... Resist pattern, 5 ... Stamp, 6 ... Milling ion, 8 ... Resist layer, 9 ... Protective film layer, 11 ... Inactive Gas 27, magnetic head 28 ... head drive unit 29 ... recording / reproducing signal system 34 ... medium drive unit 33 ... tracking servo pattern 33a ... convex 40, 50 ... magnetic recording medium 41 ... data region, 41a ... data recording pattern, 42 ... servo information area, 43a ... burst pattern, 51a ... magnetic recording pattern, 51b ... convex portion, 51c ... concave portion.

Claims (7)

An annular magnetic recording pattern comprising a magnetic layer magnetically separated on a nonmagnetic substrate is provided,
A magnetic recording medium, wherein a tracking servo pattern in which a distance between a center and a side portion of the magnetic recording pattern is changed only on one side is formed as tracking servo information on a part of the magnetic recording pattern.   The magnetic recording medium according to claim 1, wherein the tracking servo information includes burst information.   The tracking servo pattern includes an inner pattern in which the distance between the center and the inner part of the magnetic recording pattern is different, and an outer pattern in which the distance between the center and the outer part of the magnetic recording pattern is different. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic recording medium. The tracking servo pattern has a plurality of inner patterns formed by varying the distance between the center and the inner part of the magnetic recording pattern,
The magnetic recording medium according to claim 1, wherein the adjacent inner patterns are arranged with an interval of 100 times or more of one data bit length in the magnetic recording pattern. The tracking servo pattern has a plurality of outer patterns formed by varying the distance between the center and the outer portion of the magnetic recording pattern,
The magnetic recording medium according to claim 1, wherein the adjacent outer patterns are arranged at an interval of 100 times or more of one data bit length in the magnetic recording pattern. A magnetic recording / reproducing apparatus comprising a magnetic recording medium and a magnetic head for recording / reproducing information on the magnetic recording medium,
A magnetic recording / reproducing apparatus according to claim 1, wherein the magnetic recording medium is the magnetic recording medium according to claim 1. A signal processing method in the magnetic recording / reproducing apparatus according to claim 5,
Causing the magnetic head to read a signal from the magnetic recording pattern of the magnetic recording medium;
Separating the signal using a frequency difference;
When tracking servo information is obtained from the signal by separating the signal, the method includes a step of positioning the magnetic head at the center in the radial direction of the magnetic recording pattern according to the frequency of the tracking servo information. A signal processing method for a magnetic recording / reproducing apparatus.

Images