JP2006209844A - Master disk for magnetic transfer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a master disk for magnetic transfer in which occurrence of a sub-pulse which may be mistaken for a regular pulse in reproduced signals can be suppressed when information of a master disk for magnetic transfer is magnetically transferred to a magnetic recording medium. <P>SOLUTION: In a cross section of a track direction of the master disk 3 for magnetic transferred, when a land width of a protruded part upper surface 31D of ruggedness 31 is assumed to L, thickness of a magnetic layer formed on the protruded part upper surface 31D is assumed to Mt, a supplementary angle of an angle formed by a protruded part side plane 31C of ruggedness 31 and the protruded part upper surface 31D is assumed to ϕ, a following relation is satisfied: Mt/L≥1.0; and 70°≤ϕ≤90°. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic transfer master disk, and more particularly, to a magnetic transfer master disk having pattern-like irregularities for transferring a magnetic information pattern such as format information to a magnetic recording medium used in a hard disk device or the like.

  Magnetic disks, which are high-density magnetic recording media used in hard disk devices, flexible disk devices, and the like, are capable of high-speed access and are required to have a larger information recording capacity.

  In order to realize this large capacity, the track width is narrowed, and so-called tracking servo technology for accurately scanning the magnetic head within this narrow track width plays an important role.

  On the magnetic disk, a tracking servo signal, an address information signal, a reproduction clock signal, and the like are recorded at a predetermined interval as a preformat for performing tracking servo.

  As a method for performing this preformat accurately and efficiently in a short time, the applicant of the present invention transfers data to a transfer target disk (hereinafter sometimes referred to as a slave disk) which is a high-density in-plane magnetic recording medium. A magnetic transfer master disk (hereinafter sometimes referred to as a master disk) having a magnetic layer with a concavo-convex pattern corresponding to power information is prepared, and the magnetic layer of the slave disk is initially magnetized in one direction of the track in advance. A magnetic transfer method has been proposed in which a transfer magnetic field substantially opposite to the initial magnetization direction is applied in a state where the initially magnetized slave disk and master disk are in close contact with each other (see, for example, Patent Document 1).

  In this case, pattern-shaped unevenness corresponding to information to be transferred is formed on the substrate of the master disk, and the magnetic layer is continuously formed along the unevenness. A transfer magnetic field is applied in a state where the magnetic layer of the master disk and the magnetic layer of the slave disk are tightly held by a disk holder. As a result, a magnetic pattern corresponding to the information pattern of the master disk is magnetically transferred to the slave disk.

According to this magnetic transfer method, information on the master disk can be statically recorded without changing the relative position of the master disk and the slave disk, and accurate preformat recording is possible. Moreover, the time required for recording is very short.
JP 2001-014667 A

  In recent years, recording media have been increased in density, and preformat signals to be recorded in advance on a slave disk as a magnetic recording medium are required to be very minute signals, and a pattern corresponding to information to be transferred formed on the substrate surface. A master disk for magnetic transfer having a minimum unit of the uneven size of several hundreds of nanometers to several tens of nanometers has become necessary.

  Incidentally, magnetic transfer recording is a technique different from servo write recording, and therefore there are problems peculiar to magnetic transfer recording. One of them is the problem of sub-pulse generation. The sub-pulse is a pulse that may be mistaken for a normal pulse as shown by an arrow in FIG. 11, and is defined herein as a pulse having an AGC (Auto Gain Control) output ratio of 50% or more.

  FIG. 11 shows the reproduction signal output of the slave disk, where the outputs of 0.2 and −0.2 are regular pulses, and 0.1 or −0.1 as indicated by the arrows in the figure. A pulse that exceeds this value and may be mistaken for a regular pulse is a sub-pulse.

  Since a pulsating pulse is generated in the magnetic information signal thus transferred, it becomes difficult to accurately read the preformat recording, and a high-quality reproduction signal cannot be obtained, and the magnetic recording medium of the slave disk As a result, there is a problem that the quality of the product is greatly deteriorated.

  This sub-pulse is generated due to many parameters such as the uneven shape formed on the master disk substrate, the magnetic layer shape, and the external magnetic field. However, the present inventor analyzed various parameters of sub-pulse generation and tried many experiments. As a result, by controlling the uneven shape formed on the substrate and the magnetic layer shape formed along the unevenness, It has been found that the number of subpulses is extremely suppressed.

  The present invention has been made in view of such circumstances, and applies a transfer magnetic field by bringing a magnetic transfer master disk having information to be transferred and a magnetic recording medium to be transferred into close contact with each other. An object of the present invention is to provide a magnetic transfer master disk capable of suppressing the generation of sub-pulses that may be mistaken for regular pulses in the reproduction signal output when magnetically transferring information on the master disk to a magnetic recording medium. To do.

  In order to achieve the above object, the present invention provides a substrate having irregularities in a pattern shape corresponding to information to be transferred to an in-plane magnetic recording medium, and a magnetic material continuously formed on the substrate along the irregularities. A magnetic layer formed on the upper surface of the convex portion, wherein the land width of the upper surface of the convex portion of the concave and convex portions is L in the cross section in the track direction of the master disk for magnetic transfer. Mt / L ≧ 1.0 and 70 ° ≦ φ ≦ 90 ° satisfying the relationship, where Mt is the thickness of Mt and the complementary angle of the angle formed by the convex side surface of the concave and convex is the upper surface of the convex portion It is characterized by.

  According to the present invention, in the master disk for magnetic transfer, the land width on the upper surface of the convex portion of the substrate is L, the thickness of the magnetic layer formed on the upper surface of the convex portion is Mt, and the side surface of the convex portion of the concave portion is convex. When the complementary angle of the angle formed with the upper surface of the part is φ, the relationship of Mt / L ≧ 1.0 and 70 ° ≦ φ ≦ 90 ° is satisfied. When transferred onto the medium, the number of subpulses having an AGC output ratio of 50% or more can be extremely suppressed, and a good magnetization pattern can be formed on the magnetic recording medium. Therefore, a high-quality reproduction signal can be obtained by using this magnetic recording medium.

  As described above, according to the master disk for magnetic transfer according to the present invention, the land width of the upper surface of the convex portion of the substrate is L, the thickness of the magnetic layer formed on the upper surface of the convex portion is Mt, When the complementary angle of the angle between the convex side surface and the convex upper surface is φ, the relationship of Mt / L ≧ 1.0 and 70 ° ≦ φ ≦ 90 ° is satisfied. Magnetic transfer can be satisfactorily performed on a magnetic recording medium for transfer.

  The preferred embodiments of the master disk for magnetic transfer according to the present invention will be described below in detail with reference to the accompanying drawings. In each figure, the same number or symbol is attached to the same member.

  The master disk, which is the master disk for magnetic transfer of the present invention, has irregularities corresponding to information to be transferred on the surface of a disk-shaped substrate, and a magnetic layer is continuously formed along the irregularities. Therefore, the unevenness of the master disk is the unevenness in which the magnetic layer is formed on the unevenness of the substrate, and the convexity of the master disk is the convexity in which the magnetic layer is formed on the convexity of the substrate. That is.

  FIG. 1 is a perspective view showing a part of the master disk, and shows a part of the unevenness of the master disk formed as an uneven pattern corresponding to information to be transferred. As shown in FIG. 1, the irregularities 32 of the master disk 3 are composed of convex portions 32A and concave portions 32B.

  In FIG. 1, an arrow X indicates the circumferential direction (track direction) of the master disk 3, and an arrow Y indicates the radial direction of the master disk 3. P indicates the track width.

  FIG. 2 is a plan view showing the convex portion 32 </ b> A of the master disk 3. FIG. 3 shows a cross section (A-A ′ cross section in FIGS. 1 and 2) in the circumferential direction (track direction) of the irregularities 32 of the master disk 3.

  As shown in FIGS. 2 and 3, the substrate 3 a of the master disk 3 is provided with a concavo-convex 31 including a concavo-convex portion 31 A and a concavo-convex portion 31 B formed as a concavo-convex pattern corresponding to information to be transferred. The magnetic layer 3b is continuously formed along the upper and lower surfaces of the master disk 3 to form the irregularities 32 including the convex portions 32A and the concave portions 32B.

  The convex portion 31A of the master disk 3 is formed in a truncated pyramid shape or a rectangular column shape having a rectangular base that is longer in the radial direction than the circumferential direction (track direction), and the side surface 31C of the convex portion 31A of the substrate 3a is convex. The complementary angle of the angle formed with the upper surface 31D of the portion 31A, that is, the angle formed by the extension line of the side surface 31C of the convex portion 31A and the upper surface 31D of the convex portion 31A in the circumferential direction (track direction) as shown in FIG. φ is 70 ° or more and 90 ° or less (70 ° ≦ φ ≦ 90 °).

  Further, as shown in FIG. 3, the length L (referred to as land width) L of the upper surface 31D of the convex portion 31A and the width of the bottom surface of the concave portion 31B (adjacent to the convex portion 31A) in the cross section in the circumferential direction (track direction). Are generally formed to be equal in length.

  The magnetic layer 3b is formed so that the value obtained by dividing the thickness Mt of the magnetic layer 3b formed on the upper surface 31D of the convex portion 31A by the land width L satisfies 1.0 or more (Mt / L ≧ 1.0). Has been.

  The film thickness of the magnetic layer 3b may be a thin film when the land width L is narrow. However, since the magnetic resistance increases as the land width L increases, the film thickness must be increased to some extent. In the present invention, since the ratio of the thickness Mt of the magnetic layer 3b to the land width L is 1.0 or more (Mt / L ≧ 1.0), good magnetic transfer can be performed and the reproduction signal output of the slave disk can be improved. It is possible to suppress the generation of sub-pulses that may be mistaken for regular pulses.

  As the substrate 3a of the master disk 3, nickel, silicon, quartz, glass, aluminum, ceramics, synthetic resin, or the like is used. In addition, a soft magnetic material is used for the magnetic layer 3b, and Co, Co alloy (CoNi, CoNiZr, CoNbTaZr, etc.), Fe, Fe alloy (FeCo, FeCoNi, FeNiMo, FeAlSi, FeAl, FeTaN), Ni, Ni alloy ( NiFe) and the like are preferable, and FeCo and FeCoNi are particularly preferable.

  A photolithography method, a stamper method, or the like is used to form the unevenness 31 of the substrate 3a of the master disk 3. When using the photolithography method, first, a photoresist is formed on the surface of a glass plate (or quartz plate) having a smooth surface by spin coating or the like.

  Next, irradiate the photoresist with laser light (or electron beam) and expose with a pattern corresponding to the servo signal, then develop the photoresist to remove the exposed portion, and create a master with a concavo-convex shape by the photoresist To do.

  Next, Ni plating (electroforming) is performed on the surface of the master to produce a Ni substrate having a concavo-convex pattern, and then peeled off from the master. This Ni substrate may be used as the master disk 3 as it is, but if necessary, a magnetic layer 3b made of a soft magnetic material is formed on the concavo-convex pattern, and a protective film is coated to form the master disk 3.

  As described above, Ni or Ni alloy or the like can be used as the metal substrate 3a. As plating for producing the substrate 3a, various types such as electroless plating, electroforming, sputtering, and ion plating are available. The metal film forming method can be used.

  As for the size of the convex portion 31A of the substrate 3a, a land width L of about 50 nm to 500 nm is used, and the space S has the same size. Further, the height of the protrusion 31A (depth of the uneven pattern) is about 50 nm to 300 nm.

  Next, the transfer mechanism when the information carried by the master disk 3 is magnetically transferred to the slave disk using the master disk 3 will be described with reference to FIG. As shown in FIG. 4A, the magnetic layer 2c of the slave disk 2 is previously magnetized in one direction. Further, as shown in FIG. 4B, magnetic information is formed on the magnetic layer 3b of the master disk 3 as an uneven magnetic layer pattern.

  The magnetic layer 2c of the slave disk 2 and the magnetic layer 3b of the master disk 3 are brought into close contact with each other, and a transfer magnetic field Hdu is applied. At this time, a magnetic field stronger than the transfer magnetic field Hdu is applied to the surface of the magnetic layer 2c of the slave disk 2 that is not in contact with the magnetic layer 3b of the master disk 3, so that the transfer magnetic field has a holding force of the magnetic layer 2c of the slave disk 2. When Hc is exceeded, the magnetization of that part is reversed.

  On the other hand, in the magnetic layer 2 c of the slave disk 2 in contact with the magnetic layer 3 b of the master disk 3, the transfer magnetic field Hdu is concentrated on the magnetic layer 3 b of the master disk 3. That is, the portion is in a state where the transfer magnetic field is shielded. As a result, since only a magnetic field significantly weaker than the transfer magnetic field Hdu is applied to the magnetic layer 2c of the slave disk 2, the magnetization of the slave disk 2 remains in the initial magnetization direction without being influenced by the transfer magnetic field Hdu. The magnetized state is as shown in (c). As a result, the patterned magnetic information formed on the magnetic layer 3b of the master disk 3 is transferred to the magnetic layer 2c of the slave disk 2 and magnetically recorded.

  Next, examples of the magnetic transfer master disk according to the present invention will be described. First, common items will be described. First, a concavo-convex shape corresponding to a servo signal by a photoresist is formed on a glass master by photolithography. Ni was grown on the surface of the glass master by electroforming to produce a Ni substrate having a concavo-convex pattern, and a magnetic layer 3b made of a soft magnetic material was formed on the concavo-convex pattern.

  The magnetic layer 3b was formed by DC sputtering, and FeCo (70-30 at%) was used as a target material. The cleaning of the substrate 3a and the film formation of the magnetic layer 3b were continuously performed in the same chamber. The deposition conditions for the magnetic layer 3b at this time were as follows: the pressure in the chamber was 0.1 Pa (Ar flow rate was 12 sccm), the DC power was 1.5 kW, and the distance between the substrate 3a and the target was 200 mm.

[Example 1]
In the cross section of the master disk 3 in the circumferential direction (track direction), an angle formed by an extension line of the side surface 31C of the convex portion 31A of the substrate 3a and the upper surface 31D of the convex portion 31A (hereinafter sometimes referred to as a substrate tilt angle). φ was 90 °, the land width L was 50 nm, 100 nm, and 150 nm, respectively, and the thickness Mt of the magnetic layer 3b was changed to 5 types to produce 15 types of master disks 3.

  Next, each master disk 3 was used to transfer information carried by the master disk 3 to the slave disk 2, and the sub-pulse generation rate in the reproduction signal of the slave disk 2 was measured.

  FIG. 5 is a table showing the results, and FIG. 8 is a graphical representation of the results. When the land width L is 50 nm, when the value of the ratio Mt / L of the thickness Mt of the magnetic layer 3b to the land width L is less than 1.0, the sub-pulse generation rate was 40%. Is 1.0, the sub-pulse generation rate is suppressed to 18%.

  Even when the land width L is 100 nm and 150 nm, the sub-pulse generation rate decreases rapidly when the value of Mt / L exceeds 1.0.

[Example 2]
Nine types of master disks 3 were prepared by changing the thickness Mt of the magnetic layer 3b into three types with the substrate tilt angle φ of 80 ° to 85 °, the land width L being 50 nm, 100 nm, and 150 nm, respectively.

  FIG. 6 is a table of FIG. 6 and FIG. 9 is a graph of the results of measuring the occurrence rate of subpulses in the reproduction signal of the slave disk 2 by transferring the information carried by the master disk 3 to the slave disk 2 using each master disk 3. Show.

  In the case of Example 2, as in Example 1, when the value of Mt / L exceeded 1.0, the sub-pulse generation rate decreased rapidly, and the value was 5% or less.

[Example 3]
Nine types of master disks 3 were manufactured by changing the thickness Mt of the magnetic layer 3b into three types with the substrate tilt angle φ of 70 ° to 75 °, the land width L being 50 nm, 100 nm, and 150 nm, respectively.

  FIG. 7 and the graph of FIG. 10 show the results of measuring the sub-pulse generation rate in the reproduction signal of the slave disk 2 by transferring the information carried by the master disk 3 to the slave disk 2 using each master disk 3. Show.

  In the case of Example 3 as well as Example 1 and Example 2, when the value of Mt / L exceeded 1.0, the sub-pulse generation rate decreased rapidly, and the value was 5% or less.

  In the analysis of the results of Example 1, Example 2, and Example 3, the subpulse occurrence rate due to the difference in the substrate tilt angle φ when the value of Mt / L is 1.0 is 90 ° for the substrate tilt angle φ. In this case, the sub-pulse generation rates are 18%, 10%, and 8% according to the land widths L of 50 nm, 100 nm, and 150 nm, respectively, and the land width L = 100 nm or more and less than 10%. Yes.

  Further, when the substrate tilt angle φ is 80 ° to 85 °, the generation rate of sub-pulses is drastically reduced to 5% or less in any land width L when the value of Mt / L is 1.0. Similarly, when the substrate tilt angle φ is 70 ° to 75 °, the sub-pulse generation rate is drastically reduced to 5% or less.

  From the above, the value of the ratio Mt / L of the thickness Mt of the magnetic layer 3b to the land width L is 1.0 or more, and the extension line of the side surface 31C of the convex portion 31A of the substrate 3a and the upper surface 31D of the convex portion 31A are formed. By setting the angle (substrate tilt angle) φ to 70 ° to 90 °, the generation rate of the sub-pulse can be suppressed. The substrate tilt angle φ is more preferably 70 ° to 85 °, and the substrate tilt angle φ is more preferably 80 ° to 85 ° in consideration of the miniaturization of the uneven pattern.

  In the formation of the magnetic layer 3b, the magnetic layer 3b is not formed following the shape of the convex portion 31A of the substrate 3a as it is, but tends to slightly overhang at the upper edge portion of the convex portion 31A of the substrate 3a. Therefore, when the thickness Mt of the magnetic layer 3b is excessively increased, for example, when the value of Mt / L is 1.4 or more, there is a possibility that the adjacent magnetic layers 3b may be in contact with each other.

  As described above, according to the transfer unit of the magnetic transfer apparatus according to the present invention, the land width of the upper surface of the convex portion of the substrate is L, the thickness of the magnetic layer formed on the upper surface of the convex portion is Mt, When the complementary angle of the angle formed by the convex side surface with the convex top surface is φ, the relationship of Mt / L ≧ 1.0 and 70 ° ≦ φ ≦ 90 ° is satisfied. When the information contained in is transferred to a magnetic recording medium, the number of sub-pulses with an AGC output ratio of 50% or more of the reproduction signal can be extremely suppressed, and a good magnetization pattern can be formed on the magnetic recording medium. Therefore, a high-quality reproduction signal can be obtained by using this magnetic recording medium.

Perspective view showing a part of the uneven pattern of the master disk Plan view showing the convex part of the master disk Circumferential cross-sectional view of irregularities on the master disk Conceptual sectional view explaining the mechanism of magnetic transfer Table showing results of Example 1 Table showing results of Example 2 Table showing results of Example 3 Graph showing results of Example 1 Graph showing results of Example 2 Graph showing results of Example 3 Waveform diagram showing sub-pulse of playback output signal

Explanation of symbols

  2 ... Slave disk (in-plane magnetic recording medium), 3 ... Master disk (master disk for magnetic transfer), 3a ... Substrate, 3b ... Magnetic layer, 31 ... Concave / concave, 31C ... Convex side, 31D ... Convex top, L ... land width, Mt ... thickness of magnetic layer, φ ... complementary angle of angle between side surface of convex part and upper surface of convex part

Claims (1)

A magnetic transfer master disk comprising a substrate having a pattern of irregularities corresponding to information to be transferred to an in-plane magnetic recording medium, and a magnetic layer continuously formed on the substrate along the irregularities. There,
In the cross section in the track direction of the master disk for magnetic transfer, the land width on the top surface of the projections and depressions is L, the thickness of the magnetic layer formed on the top surface of the projections is Mt, and the side surfaces of the projections and projections are projections. A master disk for magnetic transfer characterized by satisfying the relationship of Mt / L ≧ 1.0 and 70 ° ≦ φ ≦ 90 °, where φ is the complementary angle of the angle formed with the upper surface.

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