Magnetic recording disc having high internal stress to reduce disc deflection caused by impact forces and method for use with disc

Abstract

A disk for use in a hard disk drive (HDD) or other magnetic recording device. The disk is configured based on the discovery that internal stress within the disk can make the disk more resistant to impact forces. In one example, a disk is provided having a substrate with a thickness of no more than 0.5 millimeters and an internal stress of no less than 300 megapascals. The relatively higher internal stress within the substrate of the disk is used to reduce the magnitude of deflection of an HDD in which the disk is installed caused by mechanical impact, as compared to other disks of the same thickness but having a relatively smaller internal stress. A multi-disk stack of disks is described. Methods for manufacturing such disks and for rejecting disks that do not meet certain internal stress-based criteria are also described. Substrates are also described.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a magnetic recording disk and a method for manufacturing such a disk, and more particularly to a disk for use in a multi-disk hard disk drive (HDD) recording device. BACKGROUND

[0002] Magnetic storage devices, such as hard disk drive disks (HDDs), are storage devices that store data or information in a magnetic manner. High capacity HDDs often use multiple disks to store data (e.g., multi-disk HDDs). Multi-disk HDDs can employ very thin disks. In HDDs that use such disks, disk deflection due to mechanical shock to the HDD can exceed the gap between the outer edge of the disk and the load-unload ramp of the HDD, causing damage. As it is not possible to easily increase the disk thickness, as the overall size of the HDD needs to conform to certain specifications to fit within a host device or other housing or enclosure (e.g., one inch HDD chassis), other methods or techniques are needed to ensure that the disk is sufficiently rigid to withstand mechanical shock. SUMMARY

[0003] In one aspect, a disk for a magnetic recording device is provided. The disk includes a substrate having a thickness less than or equal to 0.5 millimeters (mm) and an internal stress greater than or equal to 300 MegaPascals (MPa), and a magnetic recording layer on the substrate.

[0004] In another aspect, a disk for a magnetic recording device is provided, wherein the disk includes a substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio, and wherein the predetermined ratio is in a range of 0.96 to 1.44 GigaPascals (GPa) per square millimeter (mm 2 )2. A magnetic recording layer is disposed on the substrate.

[0005] In another aspect, a data storage device is provided. The data storage device includes a plurality of stacked recording disks. Each recording disk includes a substrate having a thickness less than or equal to 0.5 mm and an internal stress greater than or equal to 300 MPa, and a magnetic recording layer configured to store information. The data storage device also includes at least one spacer between each adjacent recording disk of the plurality of stacked recording disks, and a clamping mechanism configured to clamp the plurality of stacked recording disks and the spacer together.

[0006] In yet another aspect, a method for providing a disk for a data storage device for a magnetic recording device is provided. The method includes selecting a substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 to 1.44 GPa / mm2 a predetermined ratio within a range of 0.96 to 1.44 GPa / mm

[0007] In yet another aspect, a substrate for use in a magnetic recording device is provided, the substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio within a range of 0.96 to 1.44 GPa / mm 2 a predetermined ratio within a range of 0.96 to 1.44 GPa / mm BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A top plan view of a disk drive is shown, according to an embodiment of the present disclosure.

[0009] Figure 2 A side view of a slider and disk is shown, according to an embodiment of the present disclosure.

[0010] Figure 3 An exemplary magnetic recording medium in the form of a pre-stressed disk having a substrate formed of an aluminum-magnesium (Al-Mg) alloy is shown, according to an embodiment of the present disclosure.

[0011] Figure 4 An exemplary magnetic recording medium in the form of a pre-stressed disk having a substrate formed of glass is shown, according to an embodiment of the present disclosure.

[0012] Figure 5 A side view of a disk under high internal stress is shown, according to an embodiment of the present disclosure.

[0013] Figure 6 A chart to show outer diameter (OD) disk deflection as a function of internal stress, according to aspects of the present disclosure.

[0014] Figure 7 An exemplary magnetic recording medium in the form of a pre-stressed disk having a thickness and internal stress that meet various thresholds is shown, according to an embodiment of the present disclosure.

[0015] Figure 8 An exemplary method for selecting a suitable disk for clamping in a multi-disk HDD based on internal stress within the disk is shown, according to an embodiment of the present disclosure.

[0016] Figure 9 A cross-sectional view of an exemplary multi-disk magnetic recording structure having a pre-stressed disk stack on a spindle is shown, according to an embodiment of the present disclosure.

[0017] Figure 10 Another exemplary magnetic recording medium in the form of a pre-stressed disk is shown, according to an embodiment of the present disclosure.

[0018] Figure 11Another exemplary magnetic recording medium in the form of a pre-stressed disk is shown in accordance with an embodiment of the present disclosure.

[0019] Figure 12 Yet another exemplary magnetic recording medium in the form of a pre-stressed disk is shown in accordance with an embodiment of the present disclosure.

[0020] Figure 13 Yet another exemplary magnetic recording medium in the form of a pre-stressed disk is shown in accordance with an embodiment of the present disclosure.

[0021] Figure 14 An exemplary method for selecting a suitable disk for clamping in a multi-disk HDD based on internal stress within the disk is shown in accordance with an embodiment of the present disclosure.

[0022] Figure 15 An exemplary multi-disk magnetic recording disk structure with a disk stack in accordance with an embodiment of the present disclosure, where a pair of outer disks have higher internal stress than inner disks in the stack.

[0023] Figure 16 An exemplary substrate for use in a magnetic recording device is shown in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0024] In the following description, specific details are set forth to provide a thorough understanding of various aspects of the disclosure. However, persons having ordinary skill in the art will appreciate that the aspects described herein can be practiced without such specific details. For example, circuits can be shown in block diagrams in order to avoid obscuring aspects of the disclosure. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the aspects of the disclosure.

[0025] Disk stiffness and disk flatness deviation (or disk flatness) can be important properties for magnetic recording disks used in HDDs, and it can be important to provide a disk with a sufficient amount of disk stiffness. A sufficient disk stiffness helps to ensure that the disk does not vibrate too much during operation (e.g., during spin). The higher the disk stiffness, the lower the disk vibration. An acceptable disk flatness means that there are no significant surface shape variations that can adversely affect head fly characteristics. A maximum flatness deviation helps to ensure that there is not too much variation between the highest point of the disk and its lowest point. Too much flatness deviation can cause a slider (e.g., a drive assembly positioned near the disk to access information stored on the disk) to hit a portion of the disk. Thus, in some aspects, an HDD disk should (a) meet a minimum disk stiffness, and (b) the flatness deviation should be below a maximum allowable flatness deviation, at least after the disk has been clamped in the HDD, as in a multi-disk HDD.

[0026] In some applications, multi-platter HDDs can require thin platters, each platter having a thickness of 0.5 millimeter (mm) for a 10D form factor (e.g., 10 platters within a one inch chassis) and even thinner for 11D or 12D form factors. One challenging problem is to reduce platter deflection for thin platters, which occurs when mechanical impact forces act on the drive, such as during hot-swap, or more rarely, in the case of a user dropping the drive. (With hot-swap, some drives within a server chassis are running when one drive is replaced. Thus, any impact to the server during hot-swap applies an impact to the running drives.) As explained above, platter deflection due to mechanical impact can exceed the gap between the outer edge of the platter and the load-unload ramp of the HDD, causing damage and possibly preventing the HDD from running. Thicker platters can have more stiffness than thinner platters, but thicker platters are often not feasible given the form factor constraints, and thus thinner platters (e.g., platters having a thickness < 0.5 mm) can be required. Due to form factor constraints, there is not much space within the HDD to reduce the risk of damage due to platter deflection. Thus, other methods are needed to ensure that the platters are sufficiently stiff.

[0027] Herein, a platter for use in an HDD or other magnetic recording device is described, where the platter is configured based on the discovery that the internal stress within the platter can make the platter more resistant to impact forces. For example, a platter having a higher internal stress will exhibit less deflection in response to the same amount of mechanical impact (e.g., in response to the same G-force that can result if the HDD is dropped by a user).

[0028] In one aspect, a platter for a magnetic recording device is provided, the platter having a substrate having a thickness no greater than 0.5 mm and an internal stress no less than (i.e., greater than or equal to) 300 megaPascals (MPa). The relatively higher internal stress (≥ 300 MPa) within the substrate is used to reduce the magnitude of deflection of an HDD in which the platter is installed caused by mechanical impact, as compared to other platters of the same thickness but having a relatively lower internal stress (< 300 MPa).

[0029] In another aspect, a platter is provided, where the platter includes a substrate having a (T) thickness no greater than (i.e., less than or equal to) a thickness threshold (T 阈值 ) and having an internal stress (S) no less than a stress threshold (S 阈值 ). T 阈值 and S 阈值 are such that S 阈值 divided by (T 阈值 ) 2 equals a predetermined ratio (R). In illustrative examples, R is 1.2 GPa / mm 2 , S 阈值 is 300 MPa, T阈值 not greater than 0.5 mm and an internal stress in the range of 300 MPa to 600 MPa. In the case where R is 1.2 GPa / mm 2 In another example, S 阈值 is 240 MPa and T 阈值 is not greater than 0.45 mm and an internal stress in the range of 240 MPa to 600 MPa. Thus, a thinner disk (e.g., 0.45 mm) can have a lower internal stress than a thicker disk (e.g., 0.5 mm) while still achieving satisfactory stiffness. It should be noted that the ratio (R) is based on stress that is approximately proportional to the square of the thickness, and in other examples, R can be in the range of 0.96 GPa / mm 2 to 1.44 GPa / mm 2 , i.e., 1.2 GPa / mm 2 ± 20%.

[0030] To provide a substrate with a high internal stress (e.g., > 300 MPa for a 0.5 mm disk), the substrate can be formed of glass and then subjected to a temperature of 600 degrees Celsius (C) or higher (e.g., during a deposition process for depositing a magnetic recording layer on the substrate). Alternatively, the substrate can be an aluminum-magnesium (Al-Mg) alloy with a nickel-phosphorus (NiP) coated (plated) layer deposited on the opposing surfaces. By selecting the thickness of the NiP coating, a high internal stress (e.g., > 300 MPa for a 0.5 mm disk) can be achieved within the substrate. It should also be noted that for Al-Mg disks, internal stress can be added during an annealing process after the NiP plating. The annealing temperature can be about 250 °C and the annealing duration is about 10 to 30 minutes. If the disk movement is restricted during the annealing process, the disk expansion can create stress in the disk, and some of the stress can remain after the annealing process.

[0031] Thin disks with high internal stress tend to deform or warp due to their high internal stress. For example, the outer diameter (OD) or perimeter of the disk can bend up or down during layer deposition onto the substrate, resulting in a deformed concave or convex disk. That is, for a given disk thickness (at least for disks less than or equal to 0.5 mm), the OD deviation of the disk from a flat disk profile will likely be greater for a disk with a high internal stress than for a similar disk with a lower internal stress. In some aspects, the thin disks described herein have a high enough internal stress such that the (unclamped) OD deviation of the disk from a flat disk profile is greater than a predetermined flatness deviation threshold, e.g., 20 pm. It should be noted that herein, the term deviation generally refers to the inelastic deformation or warping of the disk, which can occur, for example, due to heat or other factors during layer deposition onto the substrate. The term deflection refers to the dynamic change in shape of the disk caused by mechanical shock to the HDD in which the disk is mounted. Deflection can be temporary and elastic.

[0032] In HDDs, a clamping mechanism can be used to clamp together the outer diameter of a stack of deformed disks (with spacers between adjacent disks in the stack) to secure the disks into the disk stack and also to make the disks flat. The disks described herein can be referred to as pre-stressed disks because the disks already have a relatively high internal stress even before the clamping mechanism is applied to the disks. The disks can also be referred to as pre-warped disks because the high internal stress will cause the (unclamped) disks to warp.

[0033] Internal stress can be added to a thin disk that is initially flat by applying a clamping force to the flat disk (or to a set of disks in a multi-disk HDD). However, if the internal stress within the disk is initially relatively low, then the clamping force will add internal stress, but the disk will likely deform due to the externally applied stress from the clamping mechanism (at least for thin disks, e.g., less than or equal to 0.5 mm), thus resulting in a clamped disk that has poor flatness, which can impede HDD performance. On the other hand, if the internal stress within the disk is initially relatively high (e.g., > 300 MPa for a 0.5 mm disk) and the disk is already deformed, then the clamping mechanism will not significantly increase the internal stress of the disk, but will instead act to flatten the disk while maintaining the disk's rigidity. (It should be noted that thick disks often have sufficient rigidity due to their thickness regardless of their internal stress, and thus the considerations described herein with respect to internal stress can not be a practical concern for thicker disks, e.g., disks having a thickness greater than 0.5 mm and especially greater than 1.0 mm.)

[0034] Thus, in some aspects, a deformed (e.g., concave or convex) disk is intentionally provided where the deformation is due to the disk being thin and pre-stressed. Doing so allows the disk to be flattened when a clamping force is then applied to the disk in a multi-disk HDD, while maintaining its high internal stress. The high internal stress allows the disk to maintain high rigidity (even though the disk is thin) in order to resist OD deflection due to impact forces, but the clamped disk is also flat enough to provide good recording performance.

[0035] Thus, in some aspects, a data storage device is provided that includes a set of stacked recording disks, where each recording disk includes (a) a substrate having a thickness no greater than 0.5 mm and an internal stress no less than 300 MPa and (b) a magnetic recording layer configured to store information. At least one spacer is disposed between each adjacent recording disk in the set of stacked recording disks. A clamping mechanism is configured to clamp together the set of stacked recording disks with the spacers. In this way, a multi-disk HDD can be provided in which the disks are rigid enough to resist OD deflection due to any impacts applied to the HDD, while also providing disks that are flat enough to provide good HDD performance. As explained above, thin disks can initially be deformed due to their high internal stress, but the clamping mechanism flattens the disks while the disks maintain their internal stress to provide satisfactory rigidity. These and other features will be described in detail below.

[0036] Further methods are provided for selecting acceptable disks based at least in part on the internal stress of acceptable disks in HDDs and for rejecting disks that do not meet certain internal stress-based criteria. These methods are also described in detail below.

[0037] An exemplary disk drive having a magnetic recording medium with a pre-stressed disk

[0038] Figure 1 This is a top view schematic diagram of a disk drive 100 configured for magnetic recording according to aspects of this disclosure and comprising a magnetic recording medium 102 with a pre-stressed disk. In an illustrative example, the magnetic recording medium 102 comprises a perpendicular magnetic recording (PMR) medium. However, other recording media may be used in other examples, such as shingled magnetic recording (SMR), heat-assisted magnetic recording (HAMR), or microwave-assisted magnetic recording (MAMR) media. The disk drive 100 may comprise one or more disks / media 102 for storing data. The disks / media 102 reside on a spindle assembly 104 mounted to a drive housing 106. Data may be stored along a track 107 in the magnetic recording layer of the disk 102. Reading and writing of data are accomplished via a head / slide 108 which may have both read and write elements. The write elements are used to change the properties of the magnetic recording layer of the disk 102 and thus write information into the magnetic recording layer. In one embodiment, the recording head 108 may have a magnetoresistive (MR) or giant magnetoresistive (GMR) element (e.g., a tunneling magnetoresistive (TMR) element for reading) and a write pole with a coil that can be powered for writing. In another embodiment, the head 108 may be another type of head, such as an inductive read / write head or a Hall effect head. In operation, a spindle motor (not shown) rotates the spindle assembly 104, and in turn rotates the disk 102 to position the head 108 at a specific location along the desired disk track 107. The position of the head 108 relative to the disk 102 may be controlled by a position control circuitry system 110.

[0039] Figure 2 For the magnetic recording medium 102 comprising a prestressed disk according to aspects of this disclosure Figure 1 A side cross-sectional schematic diagram of selected components of the magnetic recording system. A head / slider 108 is positioned above a medium 102. The head / slider 108 includes write elements and read elements (not shown) positioned along an air-bearing surface (ABS) of the slider (e.g., the bottom surface) for writing information to and reading information from the medium 102, respectively. Figure 1 and 2Specific examples of magnetic recording systems are illustrated. In other examples, embodiments of modified media can be used in other suitable magnetic recording systems (e.g., SMR and MAMR recording systems). For the sake of simplicity, various embodiments are described primarily in the context of exemplary HDD magnetic recording systems.

[0040] Figure 3 An exemplary magnetic recording medium, platform, or structure in the form of a prestressed disk 300 having a substrate 302 formed of an Al-Mg alloy is shown in simplified form. A first magnetic recording layer structure 304 is deposited on one side (e.g., the top side) of the substrate 302 above an intervening NiP coating (electroplating) layer 306. A second magnetic recording layer structure 308 is deposited on the other side (e.g., the bottom side) of the substrate 302 below another intervening NiP coating (electroplating) layer 310. The NiP coating is disposed on the Al-Mg alloy substrate because the Al-Mg alloy substrate is not easily polished. The NiP coating is amorphous and provides a smoother layer to allow the deposition of the magnetic recording layer structure. The NiP coating is also a very hard layer, which is advantageous. In some instances, the magnetic recording layer structure is deposited only on one side of the substrate, and therefore only one NiP coating is provided. The first and second magnetic recording layers (e.g., 304, 308) may comprise, for example, cobalt-platinum (CoPt), iron-platinum (FePt) alloys, and / or combinations thereof. For clarity and simplicity, Figure 3 Only a few of the layers typically contained in a recording medium are shown. Others are shown in the following figures (e.g.) Figure 4 , 7 Simplified views, 10 and 11, are similarly presented with other layers omitted. Further details of the exemplary media structure can be found in U.S. Patent Application No. 17 / 361,272, filed June 28, 2021 and assigned to the assignee of this application, entitled "Heat-Assieted Magnetic Recording Medium with Amorphous Magnetic Grain Bondary Material," which is incorporated herein by reference in its entirety.

[0041] Although not in Figure 3 As illustrated, the magnetic recording layer structure 304 may include a magnetic recording sublayer and a switching control sublayer (ECL). Typically, the sublayer formation can be, for example, 100 to 200 angstroms. Thick magnetic recording layer structure 304. Both the NiP layer and the magnetic recording layer structure are very thin (e.g., on the order of micrometers (μm) or...). Therefore, the thickness of disk 300 is primarily the thickness of the substrate, for example, 0.5 mm or less (and in the range of 0.2 mm to 0.5 mm, for example). In some instances, the NiP thickness is 6 to 10 μm / side and the total disk thickness (e.g., 0.5 mm or 0.34 mm) can be measured as containing NiP. It should be noted that other coatings are also available, which are also very thin and do not significantly add thickness. For example, protective layers comprising carbon, diamond-like crystals, carbon with hydrogen and / or nitrogen doping, and / or combinations thereof can be deposited.

[0042] In some instances, substrate 302 has a diameter (i.e., OD) of approximately 97 mm, a thickness of 0.5 mm, and an internal stress of at least 300 MPa. In other instances, the OD may be 98 mm or 98.1 mm. (Generally, such disks are all referred to as "3.5-inch" disks.) As explained above, the relatively high internal stress (≥300 MPa) within the substrate serves to reduce the magnitude of deflection of the HDD in which the disk is mounted due to mechanical shock compared to other disks of the same thickness but with relatively low internal stress (<300 MPa).

[0043] The prestressed disc 300 can be deformed into a convex or concave shape due to its high internal stress (illustrated in...). Figure 5 The disks (described below) have an unclamped OD deviation exceeding a predetermined flatness deviation threshold (e.g., an exemplary threshold of 20 μm). Once clamped with other disks in a multi-disc stack, the disks are flattened to have an OD deviation below the flatness deviation threshold, for example, to an OD deviation of 15 μm below 20 μm. In some instances, a set of screws is used to apply clamping force to the stack. In one particular instance, six screws are used, each providing a torsional force of 40 Newton-centimeters (cNm) (or 0.04 Nm).

[0044] Thin NiP coatings (electroplated) layers 306 and 310 can be applied to a substrate with a thickness ranging from, for example, 6 μm to 30 μm. By applying the NiP coating to a substrate within this thickness range, the NiP tends to prestress the substrate 302 to achieve the required internal stress of at least 300 MPa for a 0.5 mm thick disk. The thicknesses of the two NiP coatings can be different. The selected amount of internal stress can be achieved by selecting the relative thicknesses of the NiP coatings.

[0045] For disks having NiP coatings (e.g., 306, 310) on opposite sides of the substrate, disk flatness deviation is primarily caused by a stress imbalance that is proportional to the thickness imbalance (or thickness difference) in the coatings. The greater the thickness difference between the coatings, the higher the stress imbalance, and thus the greater the internal stress in the substrate, and the greater the disk flatness deviation in the disk. Conversely, the smaller the thickness difference between the coatings, the lower the stress imbalance, and the lower the disk flatness deviation in the disk. The internal stress in the substrate is determined, at least in part, by the difference in thermal expansion rates (e.g., the difference in coefficient of thermal expansion (CTE)) between the substrate 302 (e.g., Al-Mg material) and the coatings (e.g., NiP) 306 and / or 310. Since the expansion rate of the coatings (e.g., 306, 310) is less than the substrate 302, a compressive stress is generally created in the substrate 302, causing the internal stress to increase. In this way, the amount of internal stress in the substrate can be controlled based on the thickness of the NiP coatings.

[0046] Although Figure 3 The example of the substrate (and thus the disk) being about 0.5 mm is shown, but different embodiments can use different thicknesses for the disk. In some embodiments, the thickness of the disk 300 can be in the range of 0.2 mm and 0.5 mm (e.g., 0.2 mm, 0.38 mm, or 0.5 mm). The Young's modulus (E) value of the substrate can be, for example, in the range of 60 to 100 gigapascals (GPa) (e.g., 68 GPa, 95 GPa, or 60 to 80 GPa). Generally, the stiffness of the disk depends on its thickness, the Young's modulus of the substrate material, the disk diameter, and other factors such as the media manufacturing process. In some embodiments, to have sufficient stiffness, the first coating 306 and the second coating 310 can each have a thickness in the range of about 6 μιη to 30 μιη, but the thickness difference between the two coatings is at least 0.43 μιη for an E of 68 GPa, and the thickness difference between the two coatings is at least 0.60 μιη for an E of 95 GPa. The thickness difference provides a stress imbalance that increases the internal stress of the substrate (and the disk itself) to a level sufficient to raise the stiffness to an acceptable level. It is noted that a thickness imbalance as small as 0.1 μιη can cause a flatness deviation of more than 20 μιη on a 97-0.5 mm disk (i.e., a disk with an OD of 97 mm and a thickness of 0.5 mm).

[0047] Figure 4An exemplary magnetic recording medium, platter, or structure in the form of a pre-stressed disk 400 having a substrate 402 formed of glass is shown in simplified form. A first magnetic recording layer structure 404 is deposited on one side surface (e.g., the top surface) at a temperature of 600°C or higher. A second magnetic recording layer structure 406 is deposited on one side surface (e.g., the bottom surface) at a temperature of 600°C or higher. The substrate 402 has a diameter of about 97 mm, a thickness of 0.5 mm, and an internal stress of at least 300 MPa. By heating the glass substrate to 600°C or higher, heat tends to impart a pre-stress to the glass substrate to the desired internal stress of at least 300 MPa. It is noted that internal stress on the glass substrate can also be created during the sputtering process. Typical sputtering equipment uses a disk carrier with pins to support the disk at the OD periphery so that the data surface is unobstructed during deposition. The support pins tend to stress the disk into a convex or concave shape. Because the deposited layers follow the general contour of the disk surface, the deposited layers have different stress levels. Thus, the disk (once released from its carrier at the end of the process) has internal stress.

[0048] Although Figure 4 not shown in FIG. 4, the magnetic recording layer structure 404 can include magnetic recording sub-layers and ECLs that collectively can be, for example, 100 to 200 A thick. Because the magnetic recording layer structures 404 and 406 are very thin, the thickness of the disk 400 is primarily a function of the thickness of the substrate, i.e., 0.5 mm or less. Other coatings can also be provided that are also very thin and do not add significant thickness. For example, an adhesion layer can be provided between the glass substrate and the magnetic recording layer structure. A NiP coating is typically not used for glass substrates because the glass substrate can be polished to be very smooth, unlike the Al-Mg layer discussed above.

[0049] As with the disk 300, the disk 400 can be formed into a convex or concave shape (shown in FIG. 5A) due to its high internal stress and have an unclamped OD deviation that exceeds a predetermined flatness deviation threshold (e.g., an exemplary threshold of 20 μιη). Once clamped together with other disks in a multi-disk stack, the disk is flattened to have an OD deviation that is below the flatness deviation threshold (e.g., below 20 μιη). Figure 5

[0050] Referring now to Figure 5 the disk (e.g., disk 400) will be further described with reference to HAMR. Figure 4 ​HAMR is a magnetic storage technology for use in storage devices such as HDDs in which a magnetic storage material is temporarily heated during the writing of data, potentially allowing a significant increase in the areal density of data compared to other magnetic storage technologies such as conventional perpendicular magnetic recording (PMR), helium-filled drives, or shingled magnetic recording (SMR). A magnetic storage disk for HAMR, such as disk 400, can have a glass-based substrate on which various magnetic recording layers and other layers are deposited. If the deposition temperature, which can be approximately 600°C, 700°C, or higher depending on the substrate glass material, is close to the glass transition temperature, the viscosity of the glass can decrease exponentially, leading to glass softening. Softening can cause the bulk material to deform due to flatness deviations or "creep." Deformation often imparts a concave or convex shape to the substrate. Deviations from a flat surface can cause variations in the magnetic signals applied to (or obtained from) the disk, particularly servo track signals. This can reduce the track density capability and thus the capacity. Additionally, the OD edge of such a deformed or warped disk is closer to the load / unload ramp in a hard disk drive and can also reduce the impact performance.

[0051] Accordingly, it is desirable that the substrate be sufficiently flat (at least after clamping is applied) so that the magnetic recording layers of the substrate can be well suited for reliable high density data storage. It is noted that flatness is not necessarily a local geometric feature of the disk. The entire disk can have a concave, convex, saddle, or cylindrical shape. Such macroscopic variations can impart undesirable flying trajectories to the head / slider. The gap between the OD edge of the disk and the load / unload ramp can also be compromised and thus reduce the tolerance to impact events in which the OD edge moves due to vibration and hits the ramp material. If this occurs during device operation, the disk edge can generate wear debris and this can trigger head crashes and / or signal erasure. In some aspects, a flatness metric can be determined for a substrate that quantifies the aforementioned flatness deviations. In some examples, it is desirable that the glass-based substrate have a low, and for example, less than 20 pm, flatness metric (at least after clamping). It is noted that surface flatness metrics are well known and can represent a flatness of the surface from a perfectly flat surface, for example, in microns, where a smaller flatness value represents a better or flatter surface and a larger flatness value represents a worse or more jagged or deformed surface.

[0052] Figure 5A deformation of disk 500 is shown, which can be attributed to internal stresses occurring within HAMR glass substrate 502 during high temperature deposition (e.g., at temperatures of 600°C or higher) of magnetic recording layer structures 504 and 506 onto the top and bottom surfaces of substrate 502, respectively. The internal stresses generated within substrate 502 cause disk 500 to have an OD flatness deviation (D), where D can exceed a threshold set, e.g., to 20 pm. In some cases, as illustrated by way of disk 500, the top surface of the disk is deformed into a concave shape. In other cases, as illustrated by way of disk 510, the top surface of the disk is deformed into a convex shape. Other forms (shapes) of deformation can also occur. As explained above, it is generally considered undesirable to have a large (e.g., greater than 20 pm) flatness deviation. However, when using the pre-stressed disks described herein, a higher unclamped flatness deviation (e.g., greater than 20 pm) is not considered problematic, and can in fact be beneficial. Once the disk is clamped together with other disks in a multi-disk stack, the deformed disk is flattened to have an OD deviation below a threshold (e.g., below 20 pm), while retaining its high internal stress and thus stiffness, in order to resist large OD deflections caused by mechanical shock. Furthermore, each individual disk in the stack will likely have a different unclamped deformation, which will tend to average out when stacking many disks (e.g., ten). Thus, in some aspects, a multi-disk stack having at least ten disks is provided, such that the variation in deformation among the disks tends to average out over the disk stack when clamped.

[0053] Figure 6 A graph is shown to illustrate OD disk deflection as a function of internal stress. The horizontal X-axis plots internal stress in MPa, increasing from zero to over 600 MPa. The vertical Y-axis plots OD disk deflection (for a 0.5 mm disk having a 97 mm diameter) in pm / G (i.e., the amount of upward or downward deflection exhibited by the OD of a horizontal disk mounted to a spindle and subjected to one G force). As illustrated in the graph, the amount of deflection decreases with increasing internal stress. Arrow 602 illustrates that the maximum deflection amount generally decreases with increasing internal stress. It should be noted that for at least some disks having low internal stress, a relatively small deflection occurs (as illustrated in the lower left-hand portion of the graph). However, other disks having those internal stress levels exhibit a much larger magnitude of deflection (as illustrated in the upper left-hand portion of the graph). Thus, the practical situation is that disks having low internal stress are not very suitable for use in HDDs, because at least some of the disks having such internal stress levels can exhibit large deflections in response to mechanical shock, which can result in damage to the HDD, as already explained. By selecting and using disks having high internal stress (e.g., greater than 300 MPa for a 0.5 mm disk having a 97 mm diameter), the maximum deflection is generally much lower, and thus the risk of HDD damage is less.

[0054] It should be noted that disks with high internal stress are more suitable for positioning at the bottom or top of the disk stack, rather than in the middle (see discussion below Figure 15 ), because disk deflection is typically larger due to differences in clamping surfaces. In this regard, the bottom disk can be the shaft shoulder of the motor hub, while the top disk is the top clamping disk (rather than a flat spacer). Although the initial internal stress can be lower than 300 MPa, if the clamping twists itself creates a stress that is measurable as flatness change, then its disk deflection can be suppressed. It should also be noted that the flatness of a disk with clamping is least dependent on the initial flatness (without clamping force), at least up to around 20 μιη.

[0055] Figure 7 An exemplary magnetic recording medium, platform, or structure in the form of a pre-stressed disk 700 having a substrate 702 is shown in simplified form, with a first magnetic recording layer structure 704 deposited on one side surface (e.g., top surface), and a second magnetic recording layer structure 706 deposited on the other side surface (e.g., bottom surface). The substrate 702 has a thickness (T) that is no greater than a thickness threshold (T 阈值 ) and an internal stress (S) that is no less than a stress threshold S 阈值 , where S 阈值 / (T 阈值 ) 2 =R, and where R is a predetermined ratio, such as 1.2 GPa / mm 2 . In one example where R is 1.2 GPa / mm 2 , S 阈值 is 300 MPa, T 阈值 is no greater than 0.5 mm, and the internal stress S is in the range of 300 MPa to 600 MPa. In another example where R is also 1.2 GPa / mm 2 , S 阈值 is 240 MPa and T 阈值 is no greater than 0.45 mm, with the internal stress in the range of 240 MPa to 600 MPa (e.g., 240 MPa). Thus, a thinner disk (e.g., 0.45 mm) can have a lower internal stress than a thicker disk (e.g., 0.5 mm), while still achieving satisfactory stiffness. As mentioned above, the ratio (R) is based on stress that is proportional to the square of the thickness.

[0056] Figure 8 A method 800 for selecting suitable disks in a multi-disk HDD for clamping based on internal stress within the disks is shown. At block 805, a system or facility manufactures or selects a set of candidate disks having Al-Mg or glass substrates with magnetic recording structures formed thereon (e.g., the pre-stressed disks 700 described above Figure 3 and 4discs) each having a diameter of 97 mm, where the OD deviation can be greater than a flatness deviation threshold of, for example, 20 pm. As explained above, high internal stress within a thin disc can cause the thin disc to deform or warp, resulting in significant OD deviation. Note that in other examples, the substrate can comprise other suitable materials, such as zinc or glass, aluminum, magnesium, and / or combinations of zinc. Note that the discs can be purchased or otherwise acquired or obtained, and then processed by the system.

[0057] At block 810, the system determines or calculates (or looks up from a database) the internal stress within each of the set of candidate discs. For example, the system can measure the thickness (T) of the candidate disc, which can be, for example, 0.5 mm, and then apply the formula S = R*T 2 or other suitable formula using R = 1.2 GPa / mm 2 or other values in the range of 0.96 GPa / mm 2 to 1.44 GPa / mm 2 (i.e., 1.2 GPa / mm 2 ± 20%) to estimate the internal stress (S) within the candidate disc. In some examples, the system (or an operator controlling or programming the system) selects, chooses, or otherwise determines a particular value of R within the range, so that the formula can then be applied using the particular value of R. Otherwise, a routine experiment, such as based on an analysis of a particular compound within the substrate, can be employed to determine or select a particular value of R within the range. In some examples, the system can look up pre-stored internal stress values for different disc thickness values from a table. Again, if equipped with a suitable device for measuring internal stress, the device can be applied to the candidate disc to measure the stress. Depending on the material, exemplary non-destructive techniques for measuring internal stress include, for example, strain gauge techniques, X-ray diffraction, magneto-elastic techniques, neutron diffraction methods, and ultrasonic methods. One skilled in the art can select among those techniques or other suitable techniques based on the material of the disc.

[0058] At block 815, the system rejects candidate discs having an internal stress less than a stress threshold S 阈值 (e.g., 300 MPa for a 0.5 mm thick disc or 240 MPa for a 0.45 mm thick disc). Note here that while some manufacturing or selection procedures or systems can reject discs having significant OD deviation, because discs that are too warped or deformed are considered useful, the system can reject discs having internal stress less than the stress threshold S Figure 8The system and procedure of the present disclosure do not reject such disks. In fact, a significant OD deviation is another indication that a thin disk has a high internal stress. At block 820, the system stacks ten or more non-rejected disks into a multi-disk configuration with at least one spacer disposed between each adjacent pair of stacked disks. At block 825, the system clamps the stacked disks together using a clamping mechanism (e.g., a set of six screws each providing a clamping torque of 0.04 Nm) to flatten the disks to have an OD deviation that is less than a flatness deviation threshold, while maintaining the internal stress that provides stiffness. As has been explained, a thin disk with a high internal stress can be deformed, but by clamping a stack of such disks together (which will typically have random deformations, e.g., some convex, some concave, etc.), the disks are collectively flattened while maintaining their high internal stress and thus the stiffness associated with that stress.

[0059] Although Figure 8 While the example is shown in which all disks having an internal stress below a threshold are rejected, in other examples such disks can be retained and used as inner disks in a multi-disk stack (e.g., as in Figure 15 Furthermore, in some examples, if the internal stress is determined to be less than 300 MPa, then the flatness of the disk is measured under clamping. If the flatness is between 5 and 20 pm, then the internal stress due to clamping is considered sufficient to increase the stiffness. Thus, disks with a stress less than, for example, 100 MPa can still be used in less critical positions within the disk stack (e.g., middle sections). Top and bottom disks are most affected by g-force, so disks with high internal stress should be used at those positions. See the discussion below of Figure 15 .

[0060] Figure 9 To illustrate a cross-sectional view of a subassembly of a data storage device 900 including a plurality of recording disks (e.g., each including a substrate having a thickness no greater than 0.5 millimeters (mm) and an internal stress no less than (i.e., greater than or equal to) 300 MPa) in accordance with an aspect of the present disclosure. In this example, the media (recording disks) include three recording disks 917-A, 917-B, and 917-C, collectively referred to as recording disks 917, with a magnetic recording layer provided adjacent to respective top and bottom surfaces of the recording disks. In other examples, ten or more disks can be stacked, as explained above.

[0061] The recording disks 917 are stacked and secured to a hub 923 coupled to a spindle shaft 918. In an aspect, the top and bottom surfaces of each of the recording disks 917 can individually be used as an information recording surface, and a slider (e.g., a read / write head) is provided to read and / or write information to / from the recording disks 917. Figure 1 and 2Individual heads on the slider 108 in the middle are used for each surface. In addition, each recording disc 917 can include a NiP plating layer as discussed above, as well as a recording layer structure. The individual discs rotate with the hub 923 and the spindle shaft 918, which can be rotated by a spindle motor 925. In the following description, the spindle motor 925 is described as a rotating shaft type that rotates the spindle shaft 918 according to some aspects, however, a stationary shaft type that does not rotate the spindle shaft 918 can also be used in other aspects.

[0062] The hub 923 can have a cylindrical shape / portion 923a. The recording discs 917 can each have a central hole or opening configured to fit over the cylindrical portion 923a of the hub 923. The hub 923 also includes a perimeter portion 923b and a connecting portion 923c that extends outward from the cylindrical portion 923a. The perimeter portion 923b supports the lowermost recording disc 917-C. A first annular spacer 924-1 is disposed on top of the recording disc 917-C. The recording disc 917-B is on top of the first annular spacer 924-1, and a second annular spacer 924-2 is disposed on top of the recording disc 917-B. The recording disc 917-A is on top of the second annular spacer 924-2. In Figure 9 In the middle, the assembly 900 includes three recording discs 917 and two spacers. In other aspects, the assembly 900 (e.g., a data storage device) can have more or less than three recording discs, and more or less than two spacers, such as ten discs and nine spacers.

[0063] The recording discs 917 can be secured to the hub 923 by a top clamp 921 placed at the top of the hub 923, and thus the recording disc 917-A can be secured by a downward force from the upper portion of the data storage device 900 that is opposite an upward force / supporting force provided by the perimeter portion 923b of the hub 923. The top clamp 921 and the hub 923 can be secured together using one or more screws 922, each providing a torque of 40 cNm, which can also secure the recording disc 917 to the spindle shaft 918. For example, if six screws 922 are used, the screws 922 can be disposed at 60 degree intervals, dividing the 360° angle of the circumference of the recording disc 917 into six portions. As has been explained, during disc manufacturing, the clamping force flattens the disc to reduce distortion created within the thin disc, while the disc maintains its high internal stress in order to maintain the stiffness associated with the high internal stress to minimize OD deflection.

[0064] In some aspects, the hub 923 can be made of stainless steel. However, according to some other aspects, the hub 923 can also be made of aluminum or an aluminum alloy. In an aspect, the top clamp 921 can be made of, for example, stainless steel. The clamping force can be obtained from the tightening force of the screws 922 used to tighten against the clamping portions 917a of the disk 917-A and 917b of the disk 917-C, partially from the peripheral portion 923b, and thereby fix the disks 917 to the hub 923 at the upper and lower portions of the data storage device. The hub 923 is fixed to the spindle shaft 918, which is the rotating shaft of the spindle motor 925. The top clamp 921 is fixed by tightening the screws 922 into the hub 923. As Figure 9 As illustrated in FIG. 1 and described above, annular spacers 924-1 and 924-2, collectively 924, (e.g., made of ceramic material, composite material, polymer, and / or metal alloy) are inserted in the space among the three recording disks 917-A, 917-B, and 917-C.

[0065] The radius of the cylindrical portion 923a of the hub 923 that passes through the center hole of the recording disks 917-A, 917-B, and 917-C can be smaller than the radius of the peripheral portion 923b that holds the recording disk 917-C from the lower portion of the data storage device 900. Likewise, the radius of the screwing location 921a disposed in the top clamp 921 can be smaller than the radius of the peripheral portion 921b that holds the recording disk 917-A from the upper portion of the data storage device 900. The screwing location 921a and the peripheral portion 921b of the top clamp 921 can be integrally formed in a stainless steel part (e.g., the top clamp 921), and the thickness of the connecting portion 921c can be LI. The cylindrical portion 923a and the peripheral portion 923b of the hub 923 can also be integrally formed in a stainless steel part, and the thickness of the connecting portion 923c can be L2.

[0066] Additional Examples and Embodiments

[0067] Figure 10 An exemplary disk 1000 for use in a magnetic recording device is shown. The disk 1000 includes a substrate 1002 having a thickness of no greater than (i.e., less than or equal to) 0.5 mm and an internal stress of no less than (i.e., greater than or equal to) 300 MPa. The disk 1000 also includes a magnetic recording layer 1004 on the substrate. In some examples, additional layers or coatings can be provided, including layers between the substrate and the magnetic recording layer. Additional details of exemplary disks are provided above.

[0068] Figure 11An exemplary disk 1100 for use in a magnetic recording device is shown. Disk 1100 includes a substrate 1102 having a thickness no greater than (i.e., less than or equal to) 0.5 mm and an internal stress no less than (i.e., greater than or equal to) 300 MPa, where the disk has an unclamped OD deviation due to an internal stress greater than a flatness deviation threshold of, for example, 20 μιη. Disk 1100 also includes a magnetic recording layer 1104 on the substrate, which includes a magnetic recording sublayer and an exchange control sublayer (ECL). In some examples, additional layers or coatings can be provided, including layers between the substrate and the magnetic recording layer. Additional details of exemplary disks are provided above.

[0069] Figure 12 An exemplary disk 1200 for use in a magnetic recording device is shown. Disk 1200 includes a substrate 1202 having a thickness no greater than (i.e., less than or equal to) a thickness threshold and having an internal stress no less than (i.e., greater than or equal to) a stress threshold, where the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 GPa / mm 2 to 1.44 GPa / mm 2 (i.e., 1.2 GPa / mm 2 ± 20%). In examples where the thickness threshold is 0.5 mm, the stress threshold is in a range of 300 MPa to 600 MPa. In examples where the thickness threshold is 0.45 mm, the stress threshold is in a range of 240 MPa to 600 MPa. In some examples, additional layers or coatings can be provided, including layers between the substrate and the magnetic recording layer. Additional details of exemplary disks are provided above. Figure 12

[0070] Figure 13 An exemplary disk 1300 for use in a magnetic recording device is shown. Disk 1300 includes a substrate 1302 having a thickness of, for example, 0.5 mm and having an internal stress in a range of 300 MPa to 600 MPa, or having a thickness of, for example, 0.45 mm and having an internal stress in a range of 240 MPa to 600 MPa. In some examples, additional layers or coatings can be provided, including layers between the substrate and the magnetic recording layer. Additional details of exemplary disks are provided above.

[0071] Figure 14 An exemplary method 1400 for providing a disk for use in a magnetic recording device is shown. Method 1400 includes, in block 1405, selecting or providing a substrate having a thickness no greater than (i.e., less than or equal to) a thickness threshold and having an internal stress no less than (i.e., greater than or equal to) a stress threshold, where the thickness threshold and the stress threshold are such that the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 GPa / mm 2 to 1.44 GPa / mm 2 (i.e., 1.2 GPa / mm 2 ​a predetermined ratio (and in the illustrative example, the ratio is 1.2 GPa / mm 2 ). The method also includes, in block 1410, forming (e.g., depositing) a magnetic recording layer on the substrate. In some examples, additional layers or coatings can be formed, including layers between the substrate and the magnetic recording layer. Additional details of the example method are provided above.

[0072] Figure 15 An example disk stack 1500 for use in a magnetic recording device is shown, where some of the disks have different levels of internal stress than other disks. The stack 1500 includes a pair of upper and lower outer disks 1502 and 1504 each having an internal stress greater than or equal to 300 MPa, and a set of inner disks 15061 through 1506 N each having an internal stress less than 300 MPa (e.g., 100 MPa). Each of the disks of the stack 1500 may, for example, have a thickness of 0.5 mm and a diameter of 97 mm. Thus, Figure 15 One or more disks in a stack can have an internal stress less than a stress threshold (e.g., < 300 MPa), while one or more other disks in the same stack can have an internal stress greater than or equal to a stress threshold (e.g., > 300 MPa), as has been explained. In other examples, other stress thresholds are appropriate, such as a threshold of 240 MPa for 0.45 mm disks. As mentioned above, during hot-swap, an impact to the server can impart a shock to a running drive. Top and bottom disks of a multi-platter drive typically deflect more in response to a shock than inner disks. Thus, disks having a higher internal stress (e.g., > 300 MPa) can be used as inner and outer disks (1502 and 1504), while disks having a smaller stress (15061 through 1506 N ) can be used in other disk positions.

[0073] Figure 16 An example substrate 1600 for use in a magnetic recording device is shown. The substrate 1600 has (a) a thickness less than or equal to a thickness threshold and an internal stress greater than or equal to a stress threshold, where the stress threshold divided by the square of the thickness threshold is equal to 0.96 to 1.44 GPa / mm 2The substrate 1600(b) has a thickness less than or equal to 0.5 mm and an internal stress greater than or equal to 300 MPa. In some examples, layers or coatings can be disposed on the substrate, including the magnetic recording layer (or layers) described above, as well as various layers between the substrate and the magnetic recording layer. In some examples, the substrate has an unclamped OD deviation due to an internal stress greater than a flatness deviation threshold, where, for example, the flatness deviation threshold is 20 pm. In some examples, the substrate includes or consists of an Al-Mg alloy, or includes or consists of a glass material that has been subjected to a temperature exceeding 600 °C. Additional details of exemplary substrates are provided above.

[0074] Additional aspects and considerations

[0075] In view of the present disclosure, those skilled in the art will appreciate that, although various exemplary manufacturing methods are discussed herein with reference to magnetic recording disks, the methods, with some modifications or without some modifications, can be used to manufacture other types of recording disks, such as optical recording disks (e.g., compact disks (CDs) and digital versatile disks (DVDs)), or magneto-optical recording disks or ferroelectric data storage devices.

[0076] Various components described in this specification can be described as “comprising” or “made of” certain materials or material compositions. In one aspect, this can mean that the component is made of the particular material. In another aspect, this can mean that the component includes the particular material.

[0077] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation or aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term "aspects" does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term "coupled" is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C can still be considered coupled to one another - even if they do not directly physically touch one another - as through their coupling to object B. It is further noted that the term "on" as used in the context of one component being on another component in this application can be used to mean on and / or in (e.g., on the surface of or embedded in) the other component. Thus, for example, a first component on a second component can mean (1) the first component is on the second component, but not directly touching the second component, (2) the first component is on (e.g., on the surface of or embedded in) the second component, and / or (3) the first component is in the second component (e.g., embedded in the second component). The term "about 'value X'" or "approximately value X" as used in this disclosure shall mean within 10 percent of 'value X.' For example, a value of about 1 or approximately 1 would mean a value in the range of 0.9 to 1.1. Various ranges can be specified, described and / or claimed in this disclosure. Note that any time a range is specified, described and / or claimed in the specification and / or claims, it is intended to encompass the endpoints (in at least one embodiment). In another embodiment, the range can not include the endpoints of the range.

Claims

1. A disk for use in a magnetic recording device, comprising: a substrate having a thickness less than or equal to 0.5 millimeters (mm) and an internal stress greater than or equal to 300 megaPascals (MPa); and a magnetic recording layer disposed on the substrate; and wherein the substrate comprises an aluminum-magnesium (Al-Mg) alloy, and wherein a nickel-phosphorus (NiP) coating is disposed between the substrate and the magnetic recording layer; and wherein the internal stress is added during an annealing process after NiP plating for a disk comprising the aluminum-magnesium (Al-Mg) alloy.

2. The disk of claim 1, wherein the disk has an unclamped outer diameter (OD) deviation due to the internal stress being greater than a flatness deviation threshold.

3. The disk of claim 2, wherein the flatness deviation threshold is 20 micrometers (pm).

4. A data storage device, comprising: a plurality of disks according to claim 2, wherein the plurality of disks are disposed in a stacked configuration, wherein at least one spacer is disposed between each adjacent pair of the disks in the plurality of stacked disks, and wherein the plurality of the disks are clamped together by a clamping mechanism to reduce the OD deviation of each of the disks to less than the flatness deviation threshold.

5. A data storage device, comprising: a plurality of disks according to claim 1, wherein the plurality of disks are disposed in a stacked configuration, and wherein at least one additional disk is provided within the stacked configuration, wherein the additional disk has an internal stress less than 300 MPa.

6. The disk of claim 1, wherein the substrate comprises a glass material that has been subjected to a temperature exceeding 600 degrees Celsius (C).

7. A disk for use in a magnetic recording device, comprising: a substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 to 1.44 gigapascals (GPa) per square millimeter (mm 2 ) and a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 to 1.44 gigapascals (GPa) per square millimeter (mm 2 ). a magnetic recording layer disposed on the substrate; and wherein the substrate comprises an aluminum-magnesium (Al-Mg) alloy, and wherein a first nickel-phosphorus (NiP) coating and a second nickel-phosphorus (NiP) coating are disposed on opposite sides of the substrate, wherein at least one of the first and second NiP layers is disposed between the substrate and the magnetic recording layer; and the internal stress is added during an annealing process after NiP plating for a disk comprising the aluminum-magnesium (Al-Mg) alloy.

8. The disc of claim 7, wherein the predetermined ratio is 1.2 GPa / mm 2 .

9. The disk of claim 8, wherein the stress threshold is 300 MPa and the thickness threshold is 0.5 mm.

10. The disk of claim 9, wherein the internal stress is in a range of 300 MPa to 600 MPa and the thickness is no greater than 0.5 mm.

11. The disk of claim 8, wherein the stress threshold is 240 MPa and the thickness threshold is 0.45 mm.

12. The disk of claim 11, wherein the internal stress is in a range of 240 MPa to 600 MPa and the thickness is no greater than 0.45 mm.

13. The disk of claim 7, wherein the substrate comprises a glass material that has been subjected to a temperature exceeding 600 degrees Celsius (C).

14. A data storage device, comprising: a plurality of disks according to claim 7, wherein the plurality of the disks are disposed in a stacked configuration, wherein at least one spacer is disposed between each adjacent pair of the disks in the plurality of stacked disks, and wherein the plurality of the disks are clamped together by a clamping mechanism to reduce the OD deviation of each of the disks to less than the flatness deviation threshold. wherein at least one spacer is disposed between each adjacent pair of the plurality of stacked disks, and wherein the plurality of the disks are clamped together using a clamping mechanism.

15. A method for providing disks for a magnetic recording device, the method comprising: selecting a substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 to 1.44 gigapascals (GPa) per square millimeter (mm 2 ) and a thickness less than or equal to 0.5 mm; and selecting a substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 to 1.44 gigapascals (GPa) per square millimeter (mm 2 ) and a thickness less than or equal to forming a magnetic recording layer on the substrate; and wherein the substrate comprises an aluminum-magnesium (Al-Mg) alloy, and wherein a nickel-phosphorus (NiP) coating is located between the substrate and the magnetic recording layer; and wherein the internal stress is added during an annealing process after NiP plating for a disk comprising the aluminum-magnesium (Al-Mg) alloy.

16. The method of claim 15, wherein the ratio is 1.2 GPa / mm 2 .

17. The method of claim 15, further comprising: stacking a plurality of the disks, wherein at least one spacer is disposed between each adjacent pair of the plurality of stacked disks, and clamping the plurality of the disks together using a clamping mechanism.

18. The method of claim 15, further comprising: manufacturing a plurality of the disks each having a thickness of 0.5 millimeters (mm); determining an internal stress within each of the plurality of the disks; and rejecting at least one of the plurality of disks having an internal stress less than 300 megapascals (MPa).

19. A substrate for use in a magnetic recording device, the substrate having a thickness less than or equal to a thickness threshold and having an internal stress greater than or equal to a stress threshold, wherein the stress threshold divided by the square of the thickness threshold equals a predetermined ratio in a range of 0.96 to 1.44 gigapascals (GPa) per square millimeter (mm 2 ) ; and wherein the substrate comprises an aluminum-magnesium (Al-Mg) alloy; and wherein the internal stress is added during an annealing process after NiP plating for a disk comprising the aluminum-magnesium (Al-Mg) alloy.

20. The substrate of claim 19, wherein the substrate has an unclamped outer diameter (OD) deviation due to the internal stress being greater than a flatness deviation threshold.

21. The substrate of claim 20, wherein the flatness deviation threshold is 20 micrometers (pm).

22. The substrate of claim 19, wherein the substrate comprises a glass material that has been subjected to a temperature exceeding 600 degrees Celsius (C).

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