Non-magnetic substrate for magnetic recording media, and method for manufacturing magnetic recording media

Abstract

To provide a highly reliable non-magnetic substrate for magnetic recording media. [Solution] A non-magnetic substrate for a magnetic recording medium, which is identified by inspection of the magnetic recording medium 42 as not having a periodic convex shape on its surface, or being below a standard value, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium by the inspection device 41, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium, which has a magnetic layer formed under heating conditions below a guaranteed temperature, with a thermosensitive resistance element, has a periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and a width of 1 μm or more and 15 μm or less.

Description

Technical Field

[0001] The present disclosure relates to a non-magnetic substrate for a magnetic recording medium and a method for manufacturing a magnetic recording medium.

Background Art

[0002] Magnetic recording and reproducing devices typified by hard disk drives (HDDs) are widely used as external storage devices for information processing devices such as computers. In recent years, they are also used as recording devices for moving images and as large-capacity storage in data centers.

[0003] A magnetic recording medium mounted in an HDD is generally manufactured by sequentially forming an underlayer, a magnetic layer, a protective layer, a lubricating layer, etc. on the surface of a substrate made of an aluminum alloy, a glass substrate, or the like. The manufactured magnetic recording medium is evaluated by a glide inspection, a certification inspection, an HDIs (Head Disk Interface sensor) inspection, etc. A magnetic recording medium that has passed the glide inspection, the certification inspection, and the HDIs inspection is guaranteed to have no defective parts, or the amount of defective parts present is guaranteed to be below a reference value, or the position where the defective part exists is specified and then shipped.

[0004] As a conventional method for evaluating a magnetic recording medium, for example, a method for evaluating the surface characteristics of a magnetic recording medium using a signal caused by a thermal asperity phenomenon due to the contact between a magnetic head having an MR element and protrusions generated on the surface of the magnetic recording medium is disclosed (see Patent Document 1). The thermal asperity phenomenon refers to a phenomenon in which when the MR element provided on the magnetic head comes into contact with protrusions on the surface of the magnetic recording medium, a rapid temperature rise occurs in the read element due to the contact heat, and the electrical resistance value of this read element fluctuates.

[0005] Other conventional evaluation methods for magnetic recording media include, for example, a method in which the surface of the magnetic recording media is scanned using a thermoresistive element, and signals caused by long-period undulations of wavelength 40 μm or longer on the surface of the magnetic recording media are separated from the signal output from the thermoresistive element, and protrusions on the surface of the magnetic recording media are detected from the separated signal (see Patent Document 2). The signals caused by undulations from the thermoresistive element are output by heat transfer mediated by air between the inspection head and the surface of the magnetic recording media. That is, it is presumed that the signals caused by undulations from the thermoresistive element are output when the thermoresistive element and the surface of the magnetic recording media are not in contact. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-105908 [Patent Document 2] Japanese Patent Publication No. 2008-146803 [Overview of the project] [Problems that the invention aims to solve]

[0007] This disclosure aims to provide a highly reliable non-magnetic substrate for magnetic recording media. [Means for solving the problem]

[0008] The means to solve the aforementioned problem are as follows: <1> A non-magnetic substrate for a magnetic recording medium, which is determined by inspection of the magnetic recording medium to not have a non-periodic convex shape on its surface, The magnetic recording medium has a magnetic layer on a non-magnetic substrate, In the inspection of the magnetic recording medium, the non-magnetic substrate for the magnetic recording medium, having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, is characterized in that the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium with an inspection head having a thermosensitive resistance element has a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm, and has a non-periodic convex shape. <2> A non-magnetic substrate for a magnetic recording medium, wherein inspection of the magnetic recording medium reveals that the amount of non-periodic convex shapes on the surface is below a standard value, The magnetic recording medium has a magnetic layer on a non-magnetic substrate, In the inspection of the magnetic recording medium, the non-magnetic substrate for the magnetic recording medium, having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, is characterized in that the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium with an inspection head having a thermosensitive resistance element has a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm, and has a non-periodic convex shape. <3> <1> or <2> A method for manufacturing a magnetic recording medium, characterized by including a magnetic recording medium forming step in which a non-magnetic substrate for magnetic recording media described in [reference] is heated at a temperature below the guaranteed temperature to form a magnetic layer. [Effects of the Invention]

[0009] According to embodiments of this disclosure, a highly reliable non-magnetic substrate for magnetic recording media can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view illustrating the mechanism by which the substrate deforms. [Figure 2] This graph schematically shows the signals output from a thermoresistive element during certification testing and HDIs testing of magnetic recording media. [Figure 3]It is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the magnetic recording medium forming process in the present disclosure. [Figure 4] It is a schematic diagram showing an example of an inspection apparatus for inspecting the magnetic recording medium in the present disclosure. [Figure 5] It is a graph showing an example of an output signal obtained by scanning an inspection head having a thermoresistive element when inspecting the magnetic recording medium in the present disclosure using the inspection apparatus. [Figure 6] It is a schematic perspective view showing an example of a magnetic recording and reproducing apparatus using the magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium of the present disclosure. [Figure 7] It is an example of an AFM observation image of the magnetic recording medium in the embodiment. [Embodiments of the Invention]

[0011] The present inventors have discovered that, in conventional HDIs inspections, among the signals output in a state where the thermoresistive element and the magnetic recording medium are non-contact, there are signals different from those caused by the undulations on the surface of the magnetic recording medium. When analyzing this signal, it was found that the signal has a height comparable to that of the undulations, the width is close to the lower limit value of the undulations, has no periodicity like the undulations, and appears superimposed on the signal caused by the undulations.

[0012] When the present inventors investigated the cause of the generation of this signal, they found that it is due to the deformation of the substrate that occurs in the manufacturing process of the magnetic recording medium, particularly in the film-forming process. The reasons for the occurrence of substrate deformation are diverse, but the main causes are as follows.

[0013] The inevitable impurities contained near the surface of the substrate react with the surrounding substances and expand in volume due to the heating of the substrate during film formation. It is considered that the deformation of the substrate occurs due to the film being pushed up as the volume of the inevitable impurities expands. Note that the inevitable impurities are impurities that are unavoidably mixed in from the raw materials and the manufacturing process. This will be described in detail using FIG. 1.

[0014] [FIG. 1] FIG. 1 is a schematic cross-sectional view for explaining a mechanism by which a substrate is deformed. Specifically, FIG. 1(a) is a schematic cross-sectional view showing an example of the state of the substrate 14 before the thin film 12 is formed, and FIG. 1(b) is a schematic cross-sectional view showing an example of the state of the substrate 14 after the thin film 12 is formed.

[0015] As shown in FIG. 1(a), assume a case where unavoidable impurities 11 are contained near the surface of the substrate 14. Since the surface 10 of the substrate 14 is smoothly polished, the portion containing the unavoidable impurities 11 is flat without a step with respect to the surroundings. When forming the thin film 12 on the surface 10 of the substrate 14, when the substrate 14 is heated, the unavoidable impurities 11 expand in volume according to their own coefficient of thermal expansion, or react with the surrounding substances, or expand in volume by crystallizing. Then, since the thin film 12 is pushed up, convex portions 13 may occur on the surface of the thin film 12. Note that the position of the convex portion 13 and the position where the unavoidable impurities 11 are contained substantially coincide in a plan view of the substrate 14.

[0016] In the example shown in FIG. 1, a case where the unavoidable impurities 11 appear on the surface 10 of the substrate 14 is shown, but the same applies to a case where the unavoidable impurities 11 are present inside the substrate 14 and near the surface 10 of the substrate 14.

[0017] As a result of the inventors' study, factors that the surface of the substrate 14 is deformed secondarily by heating and convex portions 13 are formed on the surface of the magnetic recording medium include, in addition to the inclusion of unavoidable impurities 11, aggregation of additive elements, segregation of additive elements, and processing strain. Specific causative materials include an aluminum alloy substrate, a crystallized glass substrate, an amorphous glass substrate, and a ceramic substrate. Further, as causative materials, in addition to these, there are also plating films applied to the substrate surface, such as an amorphous NiP-based plating film.

[0018] Further investigation by the inventors revealed that the protrusions 13 that appear on the surface of the magnetic recording medium have a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm. Magnetic recording media having such protrusions 13 may not be rejected as defective products in the manufacturing process because the protrusions 13 do not come into contact with the thermoresistive element during glide testing, certify testing, and HDIs testing. This can lead to the following problems (1) to (3).

[0019] (1) Unlike the output signals caused by the undulations, the output signals caused by the protrusions lack periodicity and appear superimposed on the output signals caused by the undulations, thus degrading the electromagnetic conversion characteristics of the magnetic recording medium and making signal processing in HDDs difficult.

[0020] (2) The protrusions may grow significantly even after the product has been manufactured. For example, laser heating in heat-assisted HDDs may cause the protrusions to grow even larger, potentially leading to contact between the magnetic head and the protrusions.

[0021] (3) Since the protrusions are generated during the deposition of magnetic films and the like, strain is introduced into the film, which may cause delamination of the film on magnetic recording media in the future.

[0022] Regarding problem (1), we will explain it in detail using Figure 2.

[0023] [Figure 2] Figure 2 is a schematic graph showing the signals output from a thermoresistive element during HDIs inspection of a magnetic recording medium. Specifically, Figure 2(a) is an example of an output signal from a magnetic recording medium with a period of 170 μm. Figure 2(b) is an example of an output signal from a magnetic recording medium with a period of 50 μm. Figure 2(c) is an example of an output signal from a magnetic recording medium with both a 170 μm period and a 50 μm period. Figure 2(d) is an example of an output signal when a signal 21 from a 10 μm wide protrusion is superimposed on the signal in Figure 2(c). Note that all signals from Figure 2(a) to Figure 2(d) are signals output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to temperature changes caused by heat transfer mediated by air between the inspection head (thermoresistive element) and the surface of the magnetic recording medium.

[0024] In the graph shown in Figure 2, the horizontal axis represents time and corresponds to the surface shape of the magnetic recording medium in the circumferential direction. The vertical axis represents signal intensity, and its absolute value corresponds to the magnitude of the surface relief of the magnetic recording medium.

[0025] Periodic output signals, as shown in Figures 2(a) to 2(c), become easier to filter and remove by identifying their period. Furthermore, periodic output signals often possess specific frequency components, and by designing appropriate bandstop and bandpass filters, noise components can be effectively removed. Additionally, signal processing techniques such as Fourier transforms can be used to separate and remove periodic output components in the frequency domain.

[0026] As shown in Figure 2(d), the non-periodic output signal 21 often lacks specific frequency components, making it difficult to remove. Therefore, signals containing the irregularly appearing output signal 21, as shown in Figure 2(d), make signal processing in HDDs difficult.

[0027] Furthermore, the non-periodic output signal 21 is superimposed on the signal caused by undulation, as shown in Figures 2(a) to 2(c), which can increase the signal intensity and degrade the electromagnetic conversion characteristics of the magnetic recording medium.

[0028] The non-magnetic substrate for magnetic recording media described herein has been proposed in view of the above circumstances and provides a highly reliable non-magnetic substrate for magnetic recording media.

[0029] The details of the present invention are described below.

[0030] (Non-magnetic substrate for magnetic recording media) The first embodiment of the non-magnetic substrate for a magnetic recording medium in this disclosure is a non-magnetic substrate for a magnetic recording medium that is identified by inspection of the magnetic recording medium as not having a periodic convex shape on its surface, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed under heating conditions below a guaranteed temperature with a thermal resistance element has a periodic convex shape with a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm.

[0031] The specific guaranteed temperatures in this disclosure are as follows: For non-magnetic substrates for magnetic recording media used in conventional magnetic recording media, the guaranteed temperature is preferably 300°C and more preferably 400°C. For non-magnetic substrates for magnetic recording media used in heat-assisted magnetic recording media, the guaranteed temperature is preferably 700°C, more preferably 800°C, even more preferably 850°C, and particularly preferably 900°C. For non-magnetic substrates for magnetic recording media used in microwave-assisted magnetic recording media, the guaranteed temperature is preferably 300°C and more preferably 400°C.

[0032] A non-magnetic substrate for a magnetic recording medium as a second embodiment of the present disclosure is a non-magnetic substrate for a magnetic recording medium in which, by inspection of the magnetic recording medium, the amount of non-periodic convex shapes on the surface is identified as being below a reference value, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature with a thermosensitive resistance element has a non-periodic convex shape with a height of 0.1 nm or more and 1.5 nm or less and a width of 1 μm or more and 15 μm or less.

[0033] In this disclosure, the specific reference values ​​for the amount of non-periodic convex shapes present are preferably 1,000, more preferably 500, even more preferably 100, and particularly preferably 0 per facet of a non-magnetic substrate for magnetic recording media.

[0034] The non-magnetic substrate for magnetic recording media as the first embodiment and the non-magnetic substrate for magnetic recording media as the second embodiment in this disclosure may be collectively referred to as "non-magnetic substrate for magnetic recording media". In this disclosure, the "non-magnetic substrate for magnetic recording media having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature" may be referred to as a "magnetic recording media" for convenience.

[0035] The non-magnetic substrate for magnetic recording media of this disclosure may include other components as needed.

[0036] The non-magnetic substrate for magnetic recording media of this disclosure makes it possible to identify non-periodic convex-shaped defects in a magnetic recording media having the non-magnetic substrate. Magnetic recording media in which defects are detected are either removed from the production line, the amount of defects in the magnetic recording media is identified, or the location of the defects in the magnetic recording media is identified. In other words, the non-magnetic substrate for magnetic recording media of this disclosure makes it possible to ship highly reliable and high-quality products because it is guaranteed that magnetic recording media having the non-magnetic substrate are free of defects, or that the amount of defects in the magnetic recording media is below a certain value, or the location of defects in the magnetic recording media is identified.

[0037] According to the non-magnetic substrate for magnetic recording media of this disclosure, by applying a magnetic recording media having the non-magnetic substrate to a magnetic recording and playback device, the generation of noise signals can be suppressed, the electromagnetic conversion characteristics of the magnetic recording media can be improved, and signal processing in the magnetic recording and playback device can be facilitated.

[0038] The non-magnetic substrate for magnetic recording media of this disclosure makes it possible to eliminate magnetic recording media having potentially growing defective portions, or to identify the location of such defective portions, in a magnetic recording and playback device equipped with a magnetic recording media having a non-magnetic substrate for magnetic recording media. Therefore, the risk of film peeling of the magnetic recording media can be reduced, and the location of such risk can be identified, thereby providing a highly reliable magnetic recording and playback device.

[0039] <Method for inspecting magnetic recording media> The inspection method for a magnetic recording medium in this disclosure is a method for identifying that a non-magnetic substrate for a magnetic recording medium does not have aperiodic convex shape on its surface, or for identifying that the amount of aperiodic convex shape on the surface of a non-magnetic substrate for a magnetic recording medium is below a reference value. Specifically, the method identifies defective portions based on output signals obtained by scanning the surface of a non-magnetic substrate for a magnetic recording medium having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature with an inspection head having a thermoresistive element. The inspection method for a magnetic recording medium may include other steps as necessary.

[0040] <<Defective part>> The defective portion has a non-periodic convex shape. This convex shape has a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm.

[0041] The height of the convex shape is 0.1 nm or more and 1.5 nm or less, preferably 0.5 nm or more and 1.0 nm or less. In this specification, "height of the convex shape" refers to the maximum height of the convex shape when viewed from the cross-sectional direction, with respect to the surface of the magnetic recording medium.

[0042] The width of the convex shape is 1 μm or more and 15 μm or less, preferably 5 μm or more and 13 μm or less. In this specification, "width of the convex shape" refers to the maximum length of the convex shape when viewed from the cross-sectional direction in the planar direction of the magnetic recording medium.

[0043] The height and width of the convex shape are defined by the following measurement method. (1) In AFM measurement, the measurement is performed in a quadrilateral region (preferably 50 μm) that includes the entire convex shape and also includes a flat region of at least 10 μm or more around it. (2) Extract the profile of the cross-section of the convex shape that passes through the position of the vertex of the convex shape. (3) A flat region of at least 10 μm or more around the convex shape of the obtained cross-sectional profile is used as the baseline (preferably 15 μm). (4) Using the baseline obtained in (3) as a reference, the length to the vertex of the convex shape of the cross-sectional profile is defined as the "height of the convex shape". (5) Using the baseline obtained in (3) as a reference, the length of the base of the convex shape is defined as the "width of the convex shape".

[0044] As mentioned above, it is preferable that the convex shape is formed during the manufacturing process of the magnetic recording medium.

[0045] <<Target of Inspection>> In the inspection method for magnetic recording media described in this disclosure, the object to be inspected is a non-magnetic substrate for magnetic recording media having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature. There are no restrictions on the type and number of each layer to be stacked, and they can be appropriately selected according to the purpose.

[0046] In this disclosure, the process of forming a non-magnetic substrate for a magnetic recording medium having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature may be referred to as the "magnetic recording medium forming process."

[0047] <<<Magnetic recording medium formation process>>> The magnetic recording medium formation process is a process of forming a magnetic layer on a non-magnetic substrate for magnetic recording media by heating it at a temperature below the guaranteed temperature.

[0048] The magnetic recording medium formation process may include a soft magnetic layer formation process, a base layer formation process, a perpendicular magnetic layer formation process, a protective layer formation process, a liquid lubricant layer formation process, and a varnish process.

[0049] There are no particular limitations on the heating process in the magnetic recording medium formation process, and heating processes used in known film formation methods can be appropriately adopted. Examples include heating processes performed before and after the process of forming a thin film by sputtering (sputtering method), and heating processes for laminates of thin films including a non-magnetic substrate. These heating processes are intended to improve and enhance the crystal structure of the thin film, repair defects, relieve stress, promote diffusion processes, accelerate chemical reactions, improve the adhesion of the thin film, promote surface diffusion, accelerate interfacial reactions, and form specific phases.

[0050] There are no particular restrictions on the magnetic recording medium manufactured by the magnetic recording medium formation process, and it can be appropriately selected according to the purpose. Examples include conventional magnetic recording media, magnetic recording media used in heat-assisted methods, and magnetic recording media used in microwave-assisted methods.

[0051] As an example of a magnetic recording medium manufactured by the magnetic recording medium formation process described in this disclosure, a magnetic recording medium used in a heat-assisted method will be specifically described below with reference to Figure 3.

[0052] This disclosure will be described in detail with reference to the drawings. However, the embodiments shown below are illustrative examples to embody the technical concept of this disclosure and are not limited to those described below, and may be modified as appropriate without departing from the gist of this disclosure.

[0053] Furthermore, the dimensions, materials, shapes, numbers, and relative arrangements of the components described in the embodiments are merely illustrative examples and not intended to limit the scope of this disclosure unless otherwise specified. Note that the size and positional relationships of the components shown in each drawing may be exaggerated for clarity. Also, in the following description, the same name and reference numeral indicate the same or identical components, and detailed explanations are omitted as appropriate. To avoid overly complex drawings, schematic diagrams may be used with some elements omitted, or end views showing only the cross-section may be used as cross-sectional views.

[0054] Furthermore, the following description uses terms to indicate specific directions or positions as needed (e.g., "up," "down," "side," "top surface," "bottom surface," "side," "X," "Y," "Z," and other terms including these terms). However, the use of these terms is solely to facilitate understanding of the invention with reference to the drawings, and the meaning of these terms does not excessively limit the technical scope of the invention. For example, if "top surface" is mentioned, the invention must not always be used in a way that it faces upwards.

[0055] [Figure 3] Figure 3 is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the magnetic recording medium forming process described herein.

[0056] The magnetic recording medium shown in Figure 3 has a soft magnetic layer 2, an underlayer 3, a perpendicular magnetic layer 4, and a protective layer 5 sequentially laminated on both main surfaces of a non-magnetic substrate 1 for magnetic recording media. Although Figure 3 shows a non-magnetic substrate 1 for magnetic recording media with each layer laminated on both sides, the magnetic recording media may also consist of a non-magnetic substrate 1 for magnetic recording media with each layer laminated on only one side.

[0057] The shape of the magnetic recording medium is not particularly limited as long as it can be applied to a magnetic recording and playback device, and can be appropriately selected according to the purpose. For example, a disc shape with a central hole can be used.

[0058] <<<<Soft magnetic layer formation process>>>> The soft magnetic layer formation process of this disclosure is a process of forming a soft magnetic layer 2 on a non-magnetic substrate 1 for a magnetic recording medium.

[0059] -Non-magnetic substrate 1 for magnetic recording media- There are no particular limitations on the non-magnetic substrate 1 for magnetic recording media, and it can be appropriately selected according to the purpose. Examples include metal substrates and non-metallic substrates.

[0060] --Non-metallic substrate-- Examples of non-metallic substrates include those made of non-metallic materials such as glass.

[0061] Examples of glass substrates include SiO2-Al2O3-R2O-based chemically strengthened glass, SiO2-Al2O3-Li2O-based glass ceramics, and SiO2-Al2O3-MgO-TiO2-based glass ceramics. Note that R represents at least one element selected from among the alkali metal elements.

[0062] Among these glass substrates, SiO2-Al2O3-MgO-CaO-Li2O-Na2O-ZrO2-Y2O3-TiO2-As2O3-type chemically strengthened glass, SiO2-Al2O3-Li2O-Na2O-ZrO2-As2O3-type chemically strengthened glass, SiO2-Al2O3-MgO-ZnO-Li2O-P2O5-ZrO2-K2O-Sb2O3-type glass ceramics, SiO2-Al2O3-MgO-CaO-BaO-TiO2-P2O5-As2O3-type glass ceramics, and SiO2-Al2O3-MgO-CaO-SrO-BaO-TiO2-ZrO2-Bi2O3-Sb2O3-type glass ceramics are preferred.

[0063] --Metal substrate-- Examples of metal substrates include those made of metallic materials such as aluminum alloys. An aluminum alloy substrate may contain, for example, additive elements including Mg and Cr, with the remainder being Al, and may also contain unavoidable impurities.

[0064] In aluminum alloy substrates, Mg has the function of improving mechanical strength. There are no particular restrictions on the Mg content, and it can be appropriately selected depending on the purpose, but it is preferable that it be 2% by mass or more and 7% by mass or less of the total weight of the aluminum alloy substrate.

[0065] In aluminum alloy substrates, chromium (Cr) has the function of improving strength at high temperatures and improving extrusion processing. There are no particular restrictions on the Cr content, and it can be appropriately selected depending on the purpose, but it is preferable that it be 0.02% by mass or more and 0.3% by mass or less of the total amount of aluminum alloy substrate.

[0066] In addition to Mg and Cr as additive elements, the aluminum alloy substrate may also contain one or more elements selected from the group consisting of Si, Zn, Mn, Ti, Cr, V, Zr, Mo, and Co.

[0067] Unavoidable impurities include, for example, B and P.

[0068] NiP-based alloy layers may be formed on the surfaces of metal and non-metallic substrates. The NiP-based alloy layers can be formed, for example, by plating and sputtering.

[0069] Among these non-magnetic substrates for magnetic recording media, heat-resistant glass substrates with a softening temperature of 500°C or higher, and aluminum alloy substrates with heat-resistant plating such as NiMoP are preferred, and heat-resistant glass substrates with a softening temperature of 600°C or higher are more preferred.

[0070] There are no particular restrictions on the method for forming the soft magnetic layer 2, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0071] There are no particular restrictions on the sputtering method, and it can be appropriately selected depending on the purpose. Examples include DC (Direct Current) sputtering, DC magnetron sputtering, and RF (Radio Frequency) sputtering.

[0072] When using the sputtering method as the method for forming the soft magnetic layer 2, it is preferable to use a target containing the material for forming the soft magnetic layer.

[0073] Examples of targets containing materials that form a soft magnetic layer include soft magnetic alloys such as FeCo alloys, CoZrNb alloys, and CoTaZr alloys.

[0074] <<<<Underlayer formation process>>>> The underlying layer formation process described herein is a process of forming an underlying layer 3 on a soft magnetic layer 2. The sub-layer formation process may include a first sub-layer formation process in which a first sub-layer is formed on the soft magnetic layer 2, a second sub-layer formation process in which a second sub-layer is formed on the first sub-layer, and a third sub-layer formation process in which a third sub-layer is formed on the second sub-layer.

[0075] There are no particular restrictions on the method for forming the underlayer 3, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0076] When using the sputtering method as the method for forming the base layer 3, it is preferable to use a target that contains the material for forming the base layer.

[0077] In the first sublayer formation process, there are no particular restrictions on the material used to form the first sublayer, and it can be appropriately selected according to the purpose. For example, a Cr alloy in which a bcc alloy mainly composed of Cr is (100) oriented can be used.

[0078] In the second sublayer formation process, there are no particular restrictions on the material used to form the second sublayer, and it can be appropriately selected according to the purpose. For example, a W alloy in which a bcc alloy mainly composed of W is (100) oriented can be used.

[0079] In the third subsoil formation process, there are no particular restrictions on the material used to form the third subsoil; it can be appropriately selected according to the purpose. Examples include NaCl-type compounds. Examples of NaCl-type compounds include MgO.

[0080] It is preferable to include a heating step before and after each of the first, second, and third subsoil formation steps. The heating temperature at this time is preferably 150°C or higher, and more preferably 200°C or higher.

[0081] <<<<Perpendicular magnetic layer formation process>>>> The perpendicular magnetic layer formation process of this disclosure is a process of forming a perpendicular magnetic layer 4 on a base layer 3.

[0082] There are no particular restrictions on the method for forming the perpendicular magnetic layer 4, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0083] When using the sputtering method as the method for forming the perpendicular magnetic layer 4, it is preferable to use a target that contains the material for forming the perpendicular magnetic layer.

[0084] There are no particular limitations on the target material that forms the perpendicular magnetic layer 4, and it can be appropriately selected depending on the purpose. For example, a target containing an alloy having an L10 structure can be used.

[0085] Examples of alloys having an L10 structure include alloys containing Fe or Co and Pt, etc. Specific examples of alloys having an L10 structure include FePt alloys and CoPt alloys.

[0086] From the viewpoint of improving the crystal orientation of the perpendicular magnetic layer 4, the perpendicular magnetic layer formation process preferably includes a heating step in which the non-magnetic substrate 1 for magnetic recording media, the soft magnetic layer 2, the underlayer 3, and the perpendicular magnetic layer 4 are heated in a laminated state. As the heating means at this time, known methods such as halogen lamps, lasers, LEDs, high-frequency waves, and electromagnetic waves such as microwaves can be used.

[0087] If the perpendicular magnetic layer 4 contains an FePt alloy having an L10 structure, it is preferable to heat it to a high temperature of 400°C or higher to order it.

[0088] <<<<Protective layer formation process>>>> The protective layer formation step of this disclosure is a step of forming a protective layer 5 on a perpendicular magnetic layer 4.

[0089] There are no particular restrictions on the method for forming the protective layer 5, and general film deposition methods can be used. Examples include the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes a hydrocarbon source gas with a high-frequency plasma to form a film; the IBD (Ion Beam Deposition) method, which ionizes the source gas with electrons emitted from a filament to form a film; and the FCVA (Filtered Cathodic Vacuum Arc) method, which uses a solid carbon target to form a film without using a source gas.

[0090] It is preferable to include a heating step before the protective layer formation step. The heating temperature at this step is preferably 150°C or higher, and more preferably 200°C or higher.

[0091] <<<<Liquid lubricant layer formation process>>>> The liquid lubricant layer formation step of this disclosure is a step of forming a liquid lubricant layer on the protective layer 5.

[0092] The liquid lubricant layer can be formed by applying a fluorine-based lubricant such as a perfluoropolyether using methods such as the dip method and the spin coating method.

[0093] <<<<<Varnishing Process>>>>> The burnishing process described herein is a process of burnishing the surface of a laminate with an abrasive material. Specifically, it is a process of pressing a tape containing an abrasive material (abrasive tape) against the surface of the laminate and rubbing it.

[0094] The methods for inspecting magnetic recording media in this disclosure may include glide testing, certify testing, and HDIs testing.

[0095] <<Glide Test>> The glide inspection is an inspection for checking the presence or absence of protrusions on the surface of a magnetic recording medium. When recording and reproducing a magnetic recording medium using a magnetic head, if there is a protrusion on the surface of the magnetic recording medium with a height greater than the flying height (the distance between the medium and the magnetic head), the magnetic head may collide with the protrusion, causing damage to the magnetic head or defects in the magnetic recording medium. Therefore, a magnetic recording medium detected to have high protrusions on its surface by the glide inspection is excluded from the manufacturing process as a defective product.

[0096] For a magnetic recording medium that has passed the glide inspection, a certification inspection and an HDIs inspection are performed.

[0097] <<Certification Inspection>> The certification inspection is an inspection for confirming defects and quality of the electromagnetic conversion characteristics of a magnetic recording medium. In the certification inspection, for a magnetic recording medium, after recording a predetermined signal using a magnetic head in the same manner as recording and reproducing in a normal HDD, the signal is reproduced, and the electromagnetic conversion characteristics are evaluated from the obtained reproduced signal.

[0098] <<HDIs Inspection>> The HDIs inspection is an inspection for checking the presence or absence of convex defects and concave defects in a magnetic recording medium. The HDIs inspection evaluates the data read / write performance and the reliability of the magnetic recording medium by checking what convex defects and concave defects exist on the surface of the magnetic recording medium.

[0099] The inspection method for the magnetic recording medium in the present disclosure is preferably performed in combination with the HDIs inspection.

[0100] It is not always necessary to inspect the entire area of the magnetic recording medium in the inspection method for the magnetic recording medium in the present disclosure. As a general convention of the inspection method for the magnetic recording medium, it is considered that the overall characteristics can be sufficiently grasped by evaluating an area including 3% or more, more preferably 5% or more, of the inner circumference, middle circumference, and outer circumference of the magnetic recording medium. Note that the higher the ratio of the area to be evaluated, the higher the accuracy.

[0101] For a 2.5-inch diameter magnetic recording medium, the positions of the inner circumference, middle circumference, and outer circumference at the radial position are approximately 15 mm for the inner circumference, approximately 24 mm for the middle circumference, and approximately 33 mm for the outer circumference.

[0102] For a 3.5-inch diameter magnetic recording medium, the positions of the inner circumference, middle circumference, and outer circumference at the radial position are approximately 20 mm for the inner circumference, approximately 31.5 mm for the middle circumference, and approximately 43 mm for the outer circumference.

[0103] The method for inspecting magnetic recording media described herein can be carried out by an inspection device.

[0104] <<Inspection Equipment>> [Figure 4] Figure 4 is a schematic diagram showing an example of an inspection apparatus for performing the magnetic recording medium inspection method described in this disclosure.

[0105] The inspection device 41 shown in Figure 4 comprises a rotating mechanism 43 for rotating the magnetic recording medium 42, an inspection head 50 positioned opposite the measurement area of ​​the non-magnetic substrate 42 for the magnetic recording medium, and an inspection head drive mechanism 60 for driving the inspection head 50 via a suspension 70.

[0106] The inspection head 50 includes a magnetic writing unit 51 that magnetizes the measurement area without contact, a magnetic reading unit 52 that reads the leakage magnetic field of the measurement area without contact, and an HDI sensor unit.

[0107] The HDI sensor unit functions as a thermosensitive resistance element whose physical properties, such as resistance, change with increasing temperature, and can output signals caused by thermal asperity phenomena.

[0108] Examples of thermoresistive elements that can be used include MR elements that utilize the magnetoresistance (MR) effect, GMR elements that utilize the giant magnetoresistance (GMR) effect, and TMR elements that utilize the tunnel magnetoresistance (TuMR) effect. In this specification, MR elements, GMR elements, and TMR elements may be referred to as "magnetoresistive elements."

[0109] The inspection device 41 may also have a laser heating mechanism 40 for non-contact heating of the measurement area when the magnetic recording medium 42 is used in a heat-assisted manner.

[0110] The inspection head 50 can adjust the height of the thermoresistive element relative to the surface of the magnetic recording medium 42 by changing the rotation speed (movement speed) of the magnetic recording medium 42. Furthermore, the inspection head 50 can also adjust the height of the thermoresistive element relative to the surface of the magnetic recording medium 42 by causing expansion or contraction of the area around the thermoresistive element due to the heat generated by a heater located near the thermoresistive element.

[0111] The inspection device 41 may be used in combination with the certifying inspection and HDIs inspection in the magnetic recording medium formation process, or it may be provided separately from the certifying inspection and HDIs inspection.

[0112] [Figure 5] Figure 5 is a graph showing an example of an output signal obtained by scanning an inspection head having a thermoresistive element when inspecting a magnetic recording medium according to this disclosure using an inspection device. Specifically, Figure 5(a) is an example of a signal in which three convex signals 21 with a width of 10 μm are superimposed on a signal 53 having undulations with a period of 170 μm and undulations with a period of 50 μm. Figure 5(b) is an example of a signal obtained by filtering out the signal 53 having undulations with a period of 170 μm and undulations with a period of 50 μm from the signal in Figure 5(a). Note that both signals shown in Figure 5(a) and Figure 5(b) are signals output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to temperature changes caused by heat transfer between the thermoresistive element and the surface of the magnetic recording medium via air.

[0113] In the graphs shown in Figures 5(a) and 5(b), the horizontal axis represents time and corresponds to the surface shape of the magnetic recording medium in the circumferential direction. The vertical axis represents signal intensity, and its absolute value corresponds to the magnitude of the surface relief. Specifically, the height of the convex shape is indicated by the signal intensity on the vertical axis in Figure 5, and the higher the convex shape, the larger the negative potential. The width of the convex shape is indicated by time on the horizontal axis in Figure 5, and the larger the width of the convex shape, the larger the time interval. The width of the convex shape is calculated from the relative speed of the inspection head on the surface of the magnetic recording medium.

[0114] As shown in Figure 5(a), the undulation signal 53 on the surface of the magnetic recording medium has periodicity, while the convex signal 21 does not. Therefore, it is easy to identify the convex signal 21 from the signals in Figure 5(a).

[0115] Here, of the three convex-shaped signals 21 in Figure 5(a), the leftmost signal 21 has a higher signal strength than signal 53 and is easy to identify, but the rightmost signal 21 is difficult to identify because it is buried in the signal strength of signal 53. Therefore, in order to facilitate the identification of all convex shapes, it is preferable to remove signals caused by undulations on the surface of the magnetic recording medium from the output signal from the thermoresistive element.

[0116] Most of the undulations that appear on the surface of magnetic recording media are caused by undulations on the surface of the non-magnetic substrate used for the magnetic recording media. In other words, undulations on the surface of the non-magnetic substrate for the magnetic recording media are influenced by the thin film surface formed on it, and as a result appear on the surface of the magnetic recording media.

[0117] Since the undulations on the surface of non-magnetic substrates for magnetic recording media mostly have wavelength components of 10 μm to 1 mm, it is preferable to remove periodic signals of 10 μm to 1 mm from the output signal from the thermoresistive element.

[0118] Figure 5(b) shows a signal in which three convex-shaped signals 21 with a width of 10 μm are superimposed on a stable amplitude signal 54. In the signal in Figure 5(b), it is even easier to identify all of the convex-shaped signals 21. This is because signals caused by swells repeat at a constant period, and by identifying this period, filtering and other removal techniques become easier to apply. Also, signals caused by swells often have specific frequency components, and can be effectively removed by designing appropriate bandstop filters and bandpass filters. Furthermore, it is also effective to use signal processing techniques such as Fourier transforms to separate periodic noise components in the frequency domain and effectively remove signals caused by swells.

[0119] As described above, the inspection method for magnetic recording media in this disclosure preferably identifies defective portions having a non-periodic convex shape based on an output signal from which signals caused by undulations on the surface of the magnetic recording media have been removed.

[0120] [Figure 6] Figure 6 is a schematic perspective view showing an example of the structure of the magnetic recording and playback apparatus of this disclosure.

[0121] The magnetic recording and playback device shown in Figure 6 comprises a magnetic recording medium 30, a rotational drive unit (a medium drive unit that drives the magnetic recording medium in the recording direction) 31 that rotates the magnetic recording medium 30, a magnetic head 32 that performs recording and playback operations on the magnetic recording medium 30, a head drive unit (a head moving means that moves the magnetic head relative to the magnetic recording medium) 33 that moves the magnetic head 32 in the radial direction of the magnetic recording medium 30, and a recording and playback signal processing system (a recording and playback signal processing means) 34 for inputting signals to the magnetic head 32 and playing back output signals from the magnetic head 32.

[0122] In the magnetic recording and playback apparatus shown in Figure 6, further improvements in reliability can be achieved by using the magnetic recording medium 30 having the non-magnetic substrate for magnetic recording media of this disclosure.

[0123] (Method of manufacturing magnetic recording media) The method for manufacturing a magnetic recording medium according to this disclosure includes a magnetic recording medium forming step of heating a non-magnetic substrate for a magnetic recording medium at a temperature below a guaranteed temperature to form a magnetic layer, and may include other steps as needed. The magnetic recording medium formation process is the same as described in the above <<<Magnetic Recording Medium Formation Process>>>, so redundant descriptions are omitted. [Examples]

[0124] The following are examples of the present invention, but the scope of the present invention is not limited to these examples.

[0125] A magnetic recording medium with an outer diameter of 3.5 inches, used in a heat-assisted system, was manufactured using the method described below.

[0126] A heat-resistant glass substrate was used as the non-magnetic substrate for the magnetic recording medium.

[0127] Using the sputtering method, a Cr-50at%Ti alloy layer with an average thickness of 100 nm and a Co-27at%Fe-5at%Zr-5at%B alloy layer with an average thickness of 30 nm were sequentially formed. Next, after heating the non-magnetic substrate to 200°C, a Cr layer with an average thickness of 10 nm and an MgO layer with an average thickness of 5 nm were sequentially formed using the sputtering method. Next, after heating the non-magnetic substrate to 400°C, a (Fe-49at%Pt)-40 volume% hexagonal boron nitride layer (magnetic layer) with an average thickness of 13 nm was sequentially formed using the sputtering method. Finally, the non-magnetic substrate was heated to 200°C to form a carbon film with an average thickness of 3 nm as a protective layer.

[0128] The obtained magnetic recording media were subjected to a glide test using a glide tester equipped with a piezoelectric element head. The glide height of the head (the distance between the head and the surface of the magnetic recording media, assuming no surface defects) was set to 10 nm, and the glide test was performed to exclude magnetic recording media with large protrusions on the surface.

[0129] One hundred magnetic recording media that passed glide testing were prepared, and each magnetic recording media was subjected to HDIs testing using an inspection head equipped with a thermoresistive element. Specifically, the glide height (height from the surface of the magnetic recording media to the thermoresistive element) was set to 1.5 nm, and a recording media was considered to have passed if the signal output from the thermoresistive element of the inspection head was 500 mV or higher in absolute value and there were no defects. The track pitch during inspection was set to 20 μm, and the magnetic recording media was evaluated from the inner circumference to the outer circumference. This corresponds to evaluating 5% of the entire area of ​​the magnetic recording media. 96 magnetic recording media passed the test.

[0130] Next, a second HDIs inspection was performed on the 96 magnetic recording media that passed the initial inspection, under modified conditions. Specifically, the glide height remained unchanged, and an 800kHz-10MHz bandpass filter was used to remove signals caused by undulation from the output signal from the thermoresistive element of the inspection head, extracting only signals corresponding to non-periodic convex shapes (height between 0.1nm and 1.5nm, and width between 1μm and 15μm). Among the extracted signals, those without defects of 400mV or more in absolute value were deemed to pass. 91 magnetic recording media passed the initial inspection.

[0131] When the defective areas of the magnetic recording media that failed the second HDIs inspection were observed using an AFM (Atomic Force Microscope), a non-periodic convex shape (with a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm) was observed on the surface of the magnetic recording media. An example of the observed image is shown in Figure 7. The convex part in Figure 7 had a height of 0.68 nm and a width of 13.52 μm. It was determined that all of the convex shapes of the magnetic recording media that failed the second HDIs inspection were caused by bulging of the substrate during film deposition.

[0132] The signal-to-noise ratio (SNR) of magnetic recording media that passed the second HDIs test and those that failed the second HDIs test were compared. SNR was measured using a spin stand tester with a magnetic head equipped with a laser spot heating mechanism. The current supplied to the laser diode was adjusted so that the recording track width (MWW), defined as the half-width of the reproduced signal waveform, was 70 nm, and the SNR was then checked. It was confirmed that the SNR of the passing products improved by an average of 0.3%.

[0133] For magnetic recording media that passed the second HDIs test, a third HDIs test was performed under modified conditions. Specifically, the track pitch was set to 1 μm, and the magnetic recording media was evaluated from the inner to the outer edge. This is equivalent to evaluating the entire area of ​​the magnetic recording media, and all magnetic recording media passed the test.

[0134] As described above, this disclosure has been explained based on specific embodiments, but these embodiments are merely examples, and this disclosure is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, additions, modifications, etc., are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0135] 1...Nonmagnetic substrate 2...Soft magnetic layer 3…base layer 4...Perpendicular magnetic layer 5…Protective layer 30…Magnetic recording media 31…Media drive unit 32… Magnetic head 33... Head drive unit 34…Recording and playback signal processing system

Claims

1. A non-magnetic substrate for a magnetic recording medium, which is determined by inspection of the magnetic recording medium to not have a non-periodic convex shape on its surface, The magnetic recording medium has a magnetic layer on a non-magnetic substrate, In the inspection of the magnetic recording medium, the non-magnetic substrate for the magnetic recording medium, having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, is characterized in that the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium with an inspection head having a thermosensitive resistance element has a height of 0.1 nm or more and 1.5 nm or less, and a width of 1 μm or more and 15 μm or less, and has a non-periodic convex shape.

2. A non-magnetic substrate for a magnetic recording medium, wherein inspection of the magnetic recording medium reveals that the amount of non-periodic convex shapes on the surface is below a standard value, The magnetic recording medium has a magnetic layer on a non-magnetic substrate, In the inspection of the magnetic recording medium, the non-magnetic substrate for the magnetic recording medium, having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, is characterized in that the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium with an inspection head having a thermosensitive resistance element has a height of 0.1 nm or more and 1.5 nm or less, and a width of 1 μm or more and 15 μm or less, and has a non-periodic convex shape.

3. A method for manufacturing a magnetic recording medium, characterized by including a magnetic recording medium forming step of heating a non-magnetic substrate for a magnetic recording medium according to claim 1 or 2 at a temperature below the guaranteed temperature to form a magnetic layer.

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