WO2009084364A1

WO2009084364A1 - Magnetic recording medium and method of manufacturing the same

Info

Publication number: WO2009084364A1
Application number: PCT/JP2008/071911
Authority: WO
Inventors: Masatoshi Sakurai
Original assignee: Kabushiki Kaisha Toshiba
Priority date: 2007-12-27
Filing date: 2008-11-26
Publication date: 2009-07-09
Also published as: JP2009163781A

Abstract

A magnetic recording medium has recording regions including patterns of a magnetic material corresponding to servo signals and recording tracks, non-recording regions including an oxide of the magnetic material formed between the recording regions, and a protective film formed on the surfaces of the recording regions and the non-recording regions, in which the protective film has a larger thickness on the recording regions than on the non-recording regions.

Description

D E S C R I P T I O N

MAGNETIC RECORDING MEDIUM AND METHOD OF MANUFACTURING THE SAME

Technical Field

The present invention relates to a magnetic recording medium and a method of manufacturing the same . Background Art

In order to improve recording density of a magnetic recording medium, a discrete track type magnetic recording medium using discrete tracks is effective in which non-recording regions, where magnetic recording cannot be performed, are formed by removing or modifying the magnetic material between recording tracks on the recording medium and which is capable of suppressing interference in reading from and writing to an adjacent track. As a method of manufacturing a discrete track medium, there has been known a method of patterning a magnetic material deposited on a substrate for the purpose of forming the magnetic material into such a structure that desired servo signals and recording tracks are isolated. For example, there is known a method in which the magnetic material at the portions corresponding to the non-recording regions is removed, and then recesses where the magnetic material has been removed are filled with a filling material to flatten the surface of the medium (Patent documents 1 and 2) . Alternatively, there is known another method in which the magnetic material at the portions corresponding to the non-recording regions is chemically modified to locally deactivate the magnetic material, thereby patterning the magnetic material (Patent document 3).

However, in the discrete track type magnetic recording medium provided by using the above method, there has been a problem that corrosion occurs at interfaces between different materials. The corrosion occurs when a protective film has an incomplete structure. In this case, mainly water in the air enters the medium through the protective layer and along the interfaces to produce unnecessary products by chemical reaction, which spread out to the medium surface to induce corrosion.

In order to prevent the corrosion, it is effective to increase the thickness of the protective film. However, when the thickness of the protective film is increased, the magnetic spacing between the head and the magnetic recording medium becomes larger, leading to degraded read/write properties.

[Patent document 1] Jpn. Pat. Appln. KOKAI Publication No. 2006-31849

[Patent document 2] Jpn. Pat. Appln. KOKAI Publication No. 2006-31852 [Patent document 3] Jpn. Pat. Appln. KOKAI Publication No. 2007-273067

Disclosure of Invention

According to an aspect of the present invention, there is provided a magnetic recording medium comprising: recording regions comprising patterns of a magnetic material corresponding to servo signals and recording tracks; non-recording regions comprising an oxide of the magnetic material formed between the recording regions; and a protective film formed on the surfaces of the recording regions and the non-recording regions, wherein the protective film has a larger thickness on the recording regions than on the non- recording regions. According to another aspect of the present invention, there is provided a method of manufacturing a magnetic recording medium comprising: depositing a magnetic material on a substrate; forming masks on portions of the magnetic material corresponding to recording regions; oxidizing the magnetic material in portions uncovered with the masks to form non-recording regions together with recording regions comprising patterns of the magnetic material isolated by the non- recording regions; removing a part of the masks to leave masks having a reduced thickness on the surfaces of the recording regions; and depositing a protective film on the entire surface to form the protective film in a relatively large thickness on the recording regions and in a relatively small thickness on the non- recording regions.

Brief Description of Drawings FIG. 1 is a schematic plan view of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic view of a servo zone and a data zone.

FIG. 3 is a plan view showing patterns of the servo zone and the data zone.

FIG. 4 is a cross-sectional view of the magnetic recording medium according to an embodiment of the present invention.

FIGS. 5A to 5C are cross-sectional views of magnetic recording media in comparative examples.

FIGS. 6A to 6F are cross-section views showing a method of manufacturing the magnetic recording medium according to the present invention.

FIG. 7 is a block diagram of the magnetic recording apparatus according to an embodiment of the present invention.

Best Mode for Carrying Out the Invention FIG. 1 shows a schematic plan view of a magnetic recording medium (DTR medium) 1 according to the present invention. FIG. 1 shows data zones 2 and servo zones 3. The data zone 2 is a zone in which user data is recorded. The servo zone 3 on the medium surface has a circular arc shape corresponding to a locus drawn when a head slider accesses the medium. The length of the servo zone 3 in the circumferential direction is formed so as to be longer as the radial position is on more outer peripheral side. Although 15 servo zones 3 are illustrated in FIG. 1, 100 or more servo zones 3 are formed in the actual medium.

FIG. 2 is a schematic view of a servo zone and a data zone. FIG. 3 shows patterns of recording regions and non-recording regions in the servo zone and the data zone. As shown in these figures, the data zones 2 are divided into sectors in the circumferential direction by the servo zones 3.

In the data zone 2, recording tracks (discrete tracks) 21 as recording regions are formed at a predetermined track pitch Tp. The user data is recorded in the recording track 21. The recording tracks 21 adjacent to each other in the cross-track direction are separated by a non-recording region 22. The servo zone 3 includes a preamble part 31, an address part 32 and a burst part 33. Patterns of the recording regions and the non-recording regions providing servo signals are formed in the preamble part 31, the address part 32 and the burst part 33 in the servo zone 3. These parts have the following functions .

The preamble part 31 is provided for performing PLL processing for synchronizing a servo signal read clock with respect to the time lag occurring due to the rotational deviation of the medium and AGC processing for properly maintaining signal read amplitude. In the preamble part 31, protruded recording regions which continue radially without being divided in the radius direction and have a substantially circular-arc shape are repeatedly formed in the circumferential direction. The address part 32 has a servo signal recognition code called a servo mark, sector data, and cylinder data, which are formed in Manchester code at the same pitch as the circumferential pitch of the preamble part 31. In particular, since the cylinder data is formed as patterns the data of which changes every servo track, it is converted into a gray code, in which change of the code from the adjacent track is made minimum, and then is recorded in Manchester code so that influence of address read error in seek operation can be reduced. The burst part 33 is an off-track detection region for detecting the off-track amount from the cylinder address in the on-track state, where four types of marks (called A, B, C, and D bursts) having shifted pattern phases in the radial direction are formed. In each of the A, B, C and D bursts, marks are arranged in the circumferential direction at the same pitch as that in the preamble part. The cycle of each burst in the radial direction is in proportion to the cycle of change in the address pattern, in other words, the servo track cycle. Each burst is formed in about 10 cycles in the circumferential direction and is repeatedly formed at twice the servo track cycle in the radial direction.

The shape of the marks in the burst part 33 is designed so as to have a rectangular shape, or, in a strict sense, a parallelogram shape in consideration of the skew angle in the head access; however, the marks are formed in a somewhat rounded shape depending on processing accuracy of a stamper and performance of processing such as transfer formation. The marks may be formed as the non-recording regions or the recording regions. Although a detailed description of the principle of position detection from the burst part 33 is omitted, average amplitude values of read signals from the A, B, C and D bursts are processed to calculate the off-track amount. FIG. 4 shows a cross-sectional view of the DTR medium according to an embodiment of the present invention. In FIG. 4, a soft magnetic underlayer 52 is formed on a substrate 51. Recording regions 55 made of patterned magnetic material comprising ferromagnetic crystals are formed on the soft magnetic underlayer 52 corresponding to servo signals and recording tracks. The ferromagnetic crystals constituting the recording region 55 are magnetized with a write head, and the magnetization is read out with a read head, whereby write and read can be performed. Non-recording regions 56 comprising an oxide of a magnetic material are formed between the recording regions 55. The oxide of the magnetic material constituting the non-recording regions 56 reaches the soft magnetic underlayer 52. The oxide constituting the non-recording regions 56 does not have a magnetic property, making it possible to isolate the adjacent discrete tracks.

In the magnetic recording medium according to the present invention, the protective film 57 has a larger thickness on the recording regions 55 than on the non- recording regions 56. The oxide of the magnetic material constituting the non-recording regions 56 is less reactive with oxygen and water from the air and exhibits excellent corrosion resistance. On the other hand, the magnetic material (ferromagnetic crystal) of the recording regions 55 easily reacts with the air, leading to a corrosion problem. Since the corrosion resistance in the non-recording regions 56 is higher than that in the recording regions 55 as described above, the protective film can be made thinner on the non-recording regions 56 than on the recording regions 55. Reducing the thickness of the protective film on the non-recording regions 56 makes it possible to reduce the flying height of the read/write head, further provides an effect of improving the read/write properties through reduction in the magnetic spacing. Specifically, in a magnetic recording apparatus, since a flying head having read/write elements travels over the medium surface and thus performs read and write continuously, it is preferable that the distance between the read/write elements and the magnetic film, that is, the magnetic spacing is reduced as small as possible for improving the read/write properties. The read/write properties are generally estimated based on the error rate in recorded data, and the error rate becomes higher in proportion to increasing of the magnetic spacing. The magnetic spacing is determined by the head flying height and the thickness of the protective film. Regarding the heads with the same flying height, the magnetic spacing is made larger as the thickness of the protective film of the medium is increased. Therefore, in order to reduce the error rate, it is preferable to reduce the thickness of the protective film as small as possible. However, if the thickness of the protective film is too small, mainly water and oxygen in the air penetrating through the protective film react with the ferromagnetic crystals under the protective film, leading to corrosion. Thus, in the prior art, the protective film has been formed as thin as possible in a range where no corrosion occurs . The magnetic recording medium according to the present invention has a feature that the non-recoding regions 56 are formed of an oxide produced by oxidizing the magnetic material. Since the oxide produced by oxidizing the magnetic material already includes oxygen, it is less reactive with oxygen and water in the air. Although the metal constituting the magnetic material reacts with oxygen to produce oxide and reacts with water to produce hydroxide, metal oxide that has been already oxidized is stable without causing these reactions .

Since the magnetic oxide constituting the non- recording regions in the magnetic recording medium according to the present invention is less likely to induce corrosion based on the above-mentioned reasons, the protective film formed thereon can be made thinner. Specifically, in the medium which is not subjected to DTR process, the protective film capable of bearing the corrosion test is required to have a thickness of 4.5 nm or more. However, the protective film formed on the non-recording regions 56 in the magnetic recording medium according to the present invention can be formed in a thickness of 3.5 nm or less. On the other hand, the protective film on the recording regions 55 is required to have a sufficient thickness for protecting the ferromagnetic crystals constituting the recording regions 55. As described above, in the medium which is not subjected to DTR process, the protective film capable of bearing the corrosion test is required to have a thickness of 4.5 nm or more. Likewise, the protective film formed on the recording regions in the magnetic recording medium according to the present invention is also required to have a thickness of 4.5 nm or more .

In the discrete track type magnetic recording medium of the present invention, as described later, the area ratio between the recording regions and the non-recording regions in the user data zone is 2:1. If the thickness of the protective film on the non- recording regions 56 is small in comparison with the case where the entire medium surface is covered with a thick protective film, the head flying height is reduced in proportion to the area ratio of the non- recording regions and the reduction in thickness of the protective film in the non-recording regions.

Specifically, when the area ratio between the recording regions and the non-recording regions is 2:1, the thickness of the protective film on the non- recording regions is 3.5 nm and the thickness of the protective film on the recording regions is 4.5 nm, for example, the flying height can be reduced by 1/3 nm relative to the case where the entire medium surface is covered with the protective film having a thickness of 4.5 nm. Reduction in the flying height by 1/3 nm makes it possible to lower the error rate.

As described above, according to the magnetic recording medium of the present invention, since the non-recording regions is formed of the oxide of the magnetic material and further the protective film is made thinner on the non-recording regions than on the recording regions, the corrosion resistance in the entire medium surface can be kept as with the case where a thick protective film is formed on the entire medium surface and read and write can be performed with a lower error rate because of the reduction in the thickness of the protective film on the non-recording regions .

Here, FIGS. 5A to 5C show cross-sectional views of DTR media of comparative examples. In the medium of

FIG. 5A, the thin protective film 58 having a thickness of 3.5 nm or less is formed on the entire surface. In the medium of FIG. 5B, the thick protective film 57 having a thickness of 4.5 nm or more is formed on the entire surface. In the medium of FIG. 5C, non- recording regions 59 are not formed of an oxide of the magnetic material but formed of AI2O3, for example, which is filled in recesses formed by removing the magnetic material in the portions corresponding to the non-recording regions. Those media cannot provide the above-mentioned effects of the present invention. Next, a method of manufacturing the magnetic recording medium (DTR medium) according to the present invention is described with reference to FIGS. 6A to 6F. In the figures, although the processing is to be performed only on one side of the substrate, the processing is actually performed on the both sides of the substrate.

As shown in FIG. 6A, a soft magnetic underlayer 52, a magnetic material 53 comprising ferromagnetic crystals, and an etching protective film 54 are deposited on a substrate 51. A resist 60 is applied to the etching protective film 54.

The substrate 51 includes, for example, a glass substrate, aluminum alloy substrate, a ceramic substrate, a carbon substrate, a Si single crystal substrate having an oxide surface, and a substrate obtained by plating these substrates with NiP.

As the soft magnetic underlayer 52, a material containing Fe, Ni, or Co is used. More specifically, the soft magnetic underlayer 52 includes FeCo-based alloy such as FeCo and FeCoV, FeNi-based alloy such as FeNi, FeNiMo, FeNiCr and FeNiSi, FeAl-based alloy and FeSi-based alloy such as FeAl, FeAlSi, FeAlSiCr, FeAlSiTiRu, and FeAlO, FeTa-based alloy such as FeTa, FeTaC, and FeTaN, and FeZr-based alloy such as FeZrN. As the magnetic material 53, for example, a magnetic material comprising a CoCrPt alloy and an oxide and having perpendicular magnetic anisotropy is used. As the oxide, silicon oxide or titanium oxide is particularly suitable.

The etching protective film includes, for example, diamond-like carbon and carbon nitride. The resist 60 is used as a mask material for processing the magnetic material 53 into protrusions and recesses after the patterns of protrusions and recesses are transferred to the resist 60 in the next step of imprinting. As the resist, a material which can be applied and to which patterns of protrusions and recesses can be transferred by imprinting is used. The material of the resist includes, for example, a polymer material, a low-molecular organic material, and a liquid Si resist. In this embodiment, spin-on-glass (SOG) which is a type of the liquid Si resist is used. As shown in FIG. 6B, the patterns of protrusions and recesses are transferred by imprinting. In the transfer process, an imprinting apparatus is used which can transfer the patterns to both sides simultaneously. Imprint stampers (not shown) with desired patterns of protrusions and recesses formed thereon are uniformly impressed against the entire surfaces of the resists (SOG) applied to both sides of the substrate to transfer the patterns of protrusions and recesses to the surfaces of the resists 60. The recesses formed in the resist 60 by the transfer process correspond to the non-recording regions. As shown in FIG. 6C, the etching protective film 54 in the non-recording regions exposed without being masked with the resist 60 is etched. When DLC is used as the etching protective film 54, the etching protective film 54 on the non-recording regions can be removed by etching with oxygen.

As shown in FIG. 6D, the residual resist 60 is removed. It is preferable that the resist 60 made of SOG is etched with a fluorine compound. When a resist made of carbon is used, it is preferable that the resist is subjected to ashing with oxygen.

As shown in FIG. 6E, the exposed magnetic material 53 is subjected to oxidation treatment to form the non- recording regions 56 together with the recording regions 55 isolated by the non-recording regions 56.

Further, the etching protective film (DLC) 54 remained on the recording regions 55 is made thinner through the oxidation treatment so as to leave the etching protective film 54 with a thickness of only about 1 nm. As shown in FIG. 6F, the protective film made of DLC having a thickness of 3.5 nm is further formed on the entire surface. As a result, the protective film 57 has a thickness about 4.5 nm on the recording regions 55 and a thickness of about 3.5 nm on the non- recording regions 56. Thereafter, a lubricant is applied to the protective films 57 and 58, and thus the magnetic recording medium according to the present invention is completed.

Now, a magnetic recording apparatus having the magnetic recording medium according to the present invention will be described. FIG. 7 shows a block diagram of the magnetic recording apparatus according to an embodiment of the present invention. The figure shows a head slider only over a top side of the magnetic recording medium. However, a perpendicular magnetic recording layer having discrete tracks is formed on both sides of the magnetic recording medium. A down head and an up head are provided over the top side and under the bottom side of the magnetic recording medium, respectively. The configuration of the magnetic recording apparatus according to the present invention is basically similar to that of the conventional magnetic recording apparatus except that the former uses the magnetic recording medium according to the present invention.

A disk drive includes a main body portion called a head disk assembly (HDA) 100 and a printed circuit board (PCB) 200.

The head disk assembly (HDA) 100 has a magnetic recording medium (DTR medium) 1, a spindle motor 101 that rotates the magnetic recording medium 1, an actuator arm 103 that moves around a pivot 102, a suspension 104 attached to a tip of the actuator arm 103, a head slider 105 supported by the suspension 104 and including a read head and a write head, a voice coil motor (VCM) 106 that drives the actuator arm 103, and a head amplifier (not shown) that amplifies input signals to and output signals from the head. The head amplifier (HIC) is provided on the actuator arm 103 and connected to the printed circuit board (PCB) 200 via a flexible cable (FPC) 120. Providing the head amplifier (HIC) on the actuator arm 103 as described above enables an effective reduction in noise in head signals. However, the head amplifier (HIC) may be fixed to the HDA main body.

The perpendicular magnetic recording layer is formed on both sides of the magnetic recording medium 1 as described above. On each of the opposite perpendicular magnetic recording layers, the servo zones are formed like circular arcs so as to coincide with the locus along which the head moves. Specifications for the magnetic recording medium satisfy an outer diameter, an inner diameter, and read/write properties which are adapted for the drive. The radius of the circular arc formed by the servo zone is given as the distance from the pivot to the magnetic head element.

Four main system LSIs are mounted on the printed circuit board (PCB) 200. The four main system LSIs include a disk controller (HDC) 210-, a read/write channel IC 220, a MPU 230, and a motor driver IC 240. The MPU 230 is a control section for a driving system and includes ROM, RAM, CPU, and a logic processing section which are required to implement a head positioning control system according to the present embodiment. The logic processing section is an arithmetic processing section composed of a hardware circuit to execute high-speed arithmetic processes. The firmware (FW) for the logic processing section is stored in ROM. MPU controls the drive in accordance with FW.

The disk controller (HDC) 210 is an interface section in the hard disk and exchanges information with an interface between the disk drive and a host system (for example, a personal computer), MPU, the read/write channel IC, and the motor driver IC to control the entire drive.

The read/write channel IC 220 is a head signal processing section composed of a circuit which switches a channel to the head amplifier (HIC) and which processes read/write signals.

The motor driver IC 240 is a driver section for the voice coil motor (VCM) 77 and the spindle motor 72. The motor driver IC 240 controls the spindle motor 72 to a given rotation speed and provides a VCM manipulation variable from MPU 230 to VCM 77 as a current value to drive a head moving mechanism.

Hereinafter, examples of the present invention will be described. Example 1

As a mold for forming patterns, a Ni imprint stamper with a thickness of 0.4 mm was prepared. The Ni imprint stamper was produced to form the signal area having the innermost peripheral radius of 4.7 mm and the outermost peripheral radius of 9.7 mm in which a track pitch was set to 104 nm so that the patterns on the stamper corresponded to FIG. 1. The depth of the recesses on the stamper was set to 50 nm.

A troidal glass disk with a diameter of 48 mm and an inner diameter of 12 mm was used as a substrate. FeCoV was deposited in a thickness of 100 nm as a soft magnetic underlayer. A ferromagnetic layer as a magnetic material having a composition comprising

CoCrPt alloy and SiC>2 was deposited in a thickness of 15 nm. A DLC film as an etching protective film was deposited in a thickness of 30 nm. SOG as a resist was applied by spin coating in a thickness of 50 nm. The above imprint stamper was impressed against the resist applied to the substrate for 1 minute at a normal temperature and at a pressure of 200 MPa under atmospheric pressure, whereby the patterns of protrusions and recesses of the imprint stamper were transferred to the surface of the resist. The depth of the recesses on the resist was equal to the depth of the recesses on the imprint stamper, that is, 50 nm. By performing etching with a CF4 gas, resist residues remained on the bottoms of the recesses of the resist were removed to expose the surface of the DLC protective film in the portions corresponding to the non-recording regions. The resist (SOG) was formed into protrusions in the portions corresponding to the recording regions. By performing etching with oxygen using the resist (SOG) patterns as masks, the DLC protective film located in the recesses was removed completely to the thickness of 30 nm to expose the magnetic material.

By performing etching with a CF4 gas, the resist (SOG) patterns remained on the protrusions were removed. By performing oxidation treatment with oxygen, the magnetic film exposed in the recesses was oxidized so as to lose magnetic property to form the non-recording regions together with the recording regions isolated by the non-recording regions. Subsequently, the etching protective film (DLC) remained on the protrusions was partially etched with oxygen to leave the etching protective film in a thickness of only 1 nm. Thereafter, the protective film made of DLC having a thickness of 3.5 nm was formed on the entire surface. Some samples were taken out at that stage and observed with a cross-sectional TEM. As a result, a crystal lattice was observed in the recording regions, showing that the crystal state was maintained. The thickness of the protective film on the recording regions was 4.5 nm. On the other hand, the crystal lattice was not observed in the non-recording regions. Thus, it was found that an oxide was formed by the oxidation treatment with oxygen, whereby it was made amorphous. The thickness of the protective film on the non-recording regions was 3.5 nm. The surface of the sample was subjected to Kerr measurement. Thus, it was found that the magnetic property was lost by a volume ratio corresponding to the oxide in the non-recording regions in predetermined patterns.

Finally, a lubricant was applied to the protective film to manufacture the DTR medium according to the present invention.

Comparative Example 1

The magnetic recording medium (FIG. 5A) was manufactured by the similar method to Example 1. In this case, however, the etching protective film (DLC) remained on the protrusions was removed using oxygen to the surface of the magnetic material and then the DLC protective film having a thickness of 3.5 nm is deposited.

Comparative Example 2 The magnetic recording medium (FIG. 5B) was manufactured by the similar method to Example 1. In this case, however, the etching protective film (DLC) remained on the protrusions was removed using oxygen to the surface of the magnetic material and then the DLC protective film having a thickness of 4.5 nm is deposited. Comparative Example 3

A troidal glass disk with a diameter of 48 mm and an inner diameter of 12 mm was used as a substrate.

FeCoV was deposited in a thickness of 100 nm as a soft magnetic underlayer. A ferromagnetic layer as a magnetic material having a composition comprising CoCrPt alloy and SiC>2 was deposited in a thickness of 15 nm. A DLC film as an etching protective film was deposited in a thickness of 30 nm. SOG as a resist was applied by spin coating in a thickness of 50 nm.

The above imprint stamper was impressed against the resist applied to the substrate for 1 minute at a normal temperature and at a pressure of 200 MPa under atmospheric pressure, whereby the patterns of protrusions and recesses of the imprint stamper were transferred to the surface of the resist. The depth of the recesses on the resist was equal to the depth of the recesses on the imprint stamper, that is, 50 nm.

By performing etching with a CF4 gas, resist residues remained on the bottoms of the recesses of the resist were removed to expose the surface of the DLC protective film in the portions corresponding to the non-recording regions. The resist (SOG) was formed into protrusions in the portions corresponding to the recording regions. By performing etching with oxygen using the resist (SOG) patterns as masks, the DLC protective film located in the recesses was removed completely to the thickness of 30 nm to expose the magnetic material. By performing etching with a CF4 gas, the resist (SOG) patterns remained on the protrusions were removed.

The magnetic film exposed in the recesses was removed by using Ar ion milling. When the sample was observed with a cross-sectional TEM at that stage, it was confirmed that magnetic patterns with a thickness of 15 nm remained in the recording regions and the magnetic material with a thickness of 15 nm was removed from the non-recording regions. An AI2O3 film with a thickness of 30 nm was sputtered on the entire surface to be filled in the recesses to form the non-recording regions. Unnecessary AI2O3 film on the surfaces of the recording regions was removed by using Ar ion milling. Subsequently, the etching protective films (DLC) remained on the protrusions were partly etched with oxygen to leave the etching protective films with a thickness of 1 nm. Thereafter, the protective film made of DLC with a thickness of 3.5 nm was deposited on the entire surface.

Some samples ware taken out at that stage to perform observation and compositional analysis with a cross-sectional TEM. As a result, a crystal lattice was observed in the recording regions, which means that the crystal state of the magnetic recording layer was maintained. The thickness of the protective film on the recording regions was 4.5 nm. On the other hand, AI2O3 was observed in the non-recording regions. The thickness of the protective film on the non-recording regions was 3.5 nm. Further, micro-cracks were observed between the magnetic patterns in the recording regions and AI2O3 in the non-recording regions. It is considered that, at the time when AI2O3 was filled between the magnetic patterns, the cracks were produced due to poor adhesiveness between the sidewall of the magnetic material of the recording regions and the filling material of AI2O3.

Finally, a lubricant was applied to the protective film to manufacture the DTR medium in Comparative Example 3 .

(Evaluation)

The magnetic recording media in Example 1 and Comparative Examples 1 to 3 were evaluated for corrosion test and bit error rate. The results are shown in Table 1.

Table 1

The corrosion test was performed as follows. Each magnetic recording medium in Example 1 and Comparative Examples 1 to 3 was left for 40 hours under a high temperature and humidity environment of 80°C and 80%, and bright spots occurring due to corrosion on the surface thereof were checked.

There were no bright spots on each medium of Example 1 and Comparative Example 2, showing a good result in the corrosion test. On the other hand, each medium of Comparative Examples 1 and 3 exhibited about one to two bright spots per 1 cm² after the test, showing that these media did not pass the corrosion test. It was found that media of Example 1 and Comparative Example 2 exhibited corrosion resistance because the surface of ferromagnetic crystals in the recording regions was covered with the thick protective film.

On the other hand, in the medium of Comparative Example 1, since the protective film on the surface of ferromagnetic crystals in the recording regions is thin, it is considered that the ferromagnetic crystals reacted with the air to induce corrosion.

In the medium of Comparative Example 3, it is considered that the cause of corrosion is cracks produced between the magnetic patterns of the recording regions and the filling material in the non-recording regions, which were observed with the cross-sectional TEM and presumed to be caused due to degraded adhesiveness. Therefore, it is considered that, in order to improve the adhesiveness with the magnetic material, the oxide prepared by oxidizing the magnetic material is more suitable for forming the non-recording regions rather than a material different from the magnetic material.

The bit error rate was measured as follows. A drive with the media of Example 1 and Comparative Examples 1 to 3 mounted therein was fabricated. Each medium was produced at a track density of 244 kTPI (track pitch of 104 nm) , and recorded at a linear recording density of 1260 kBPI . With respect to each medium, the bit error rate was measured in the intermediate region in the radial direction.

A common perpendicular recording medium was manufactured by depositing a continuous film of a magnetic material on a glass substrate, depositing a DLC protective film with a thickness of 4.5 nm, and applying a lubricant. Then the resultant medium was mounted to the same drive as the above one so as to be evaluated. The width of the write head and the width of the read head, measured from the half-value width of the off-track profile of the error rate at the above recording density, were 116 nm and 80 nm, respectively. When the bit error rate was measured in the intermediate region in the radial direction, it was found to be the power of -7.0. However, with respect to the perpendicular recording medium, when 1000 times of recording were performed for the adjacent track at a track pitch of 104 nm and then the bit error rate was measured for the original track, it was found to be the power of -3.6, showing poor resistance to adjacent recording.

The bit error rates for the drives with the media of Example 1 and Comparative Examples 1 to 3 mounted thereto measured in the intermediate region in the radial direction were found to be the power of -6.3, -6.5, -6.0, and -6.3, respectively. The medium of Comparative Example 1 has a thin protective film and a smaller magnetic spacing than other media, and therefore it is considered that it exhibits a lower bit error rate. However, there is a problem that the medium of Comparative Example 1 is poor in the corrosion resistance.

The medium of Comparative Example 2 has a thick protective film and a larger magnetic spacing than other media, and therefore it is considered that it exhibits a high bit error rate. However, the medium of Comparative Example 2 is good in the corrosion resistance .

In the media of Example 1 and Comparative Example 3, the thickness of the protective film on the non- recording regions is smaller by 1 nm than the thickness of the protective film on the recording regions. In these media, although the bit error rates thereof are somewhat higher than the medium of Comparative Example 1, they are less improved than the medium of Comparative Example 2. On the other hand, the medium of Example 1 in good in the corrosion resistance, but the medium of Comparative Example 3 is poor in the corrosion resistance.

With respect to the drives with the media of Example 1 and Comparative Examples 1 to 3 (with a track pitch of 104 nm) mounted thereto, when 1000 times of recording were performed for the adjacent track at a track pitch of 104 nm and then the bit error rate was measured for the original track, they were found to be the power of -5.0, -5.7, -4.0, and -5.0, respectively. This means that these media exhibited higher adjacent recording resistance than that of the common perpendicular recording medium having the continuous film.

As described above, the discrete track media according to the present invention can exhibit excellent corrosion resistance without degrading read/write properties.

Claims

C L A I M S

1. A magnetic recording medium comprising: recording regions comprising patterns of a magnetic material corresponding to servo signals and recording tracks; non-recording regions comprising an oxide of the magnetic material formed between the recording regions; and a protective film formed on the surfaces of the recording regions and the non-recording regions, wherein the protective film has a larger thickness on the recording regions than on the non-recording regions .

2. The magnetic recording medium according to claim 1, wherein surfaces of the recording regions and surfaces of the non-recording regions are in a substantially same height.

3. The magnetic recording medium according to claim 1, wherein the protective film has a thickness of 3.5 nm or less on the non-recording regions and a thickness of 4.5 nm or more on the recording regions.

4. The magnetic recording medium according to claim 1, wherein the thickness of the protective film on the non-recording regions is smaller by 1 nm or more than the thickness of the protective film onκthe recording regions.

5. A magnetic recording apparatus comprising the magnetic recording medium according to claim 1.

6. A method of manufacturing a magnetic recording medium, comprising: depositing a magnetic material on a substrate; forming masks on portions of the magnetic material corresponding to recording regions; oxidizing the magnetic material in portions uncovered with the masks to form non-recording regions together with recording regions comprising patterns of the magnetic material covered with the masks isolated by the non-recording regions; removing a part of the masks to leave masks having a reduced thickness on the surfaces of the recording regions; and depositing a protective film on the entire surface to form the protective film in a relatively large thickness on the recording regions and in a relatively small thickness on the non-recording regions.