Substrate for magnetic disk, magnetic disk, and hard disk drive

Abstract

The present invention relates to a substrate for a magnetic disk, a magnetic disk, and a hard disk drive. A diameter D of a disk-shaped substrate for a magnetic disk is 85 mm or more, a plate thickness T of the substrate is 0.6 mm or less, and a material having a Young's modulus E of 90 GPa or more is used in the substrate.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 201980051118.8 (PCT / JP2019 / 031269), filed on August 7, 2019, entitled "Substrate for Disk and Disk". Technical Field

[0002] This invention relates to a disk substrate, a disk, and a hard disk drive device. Background Technology

[0003] Traditionally, glass substrates or aluminum alloy substrates have been used as substrates for hard disk drives (HDDs). In these substrates, a magnetic film is formed on the main surface of the substrate to create the disk. For HDDs, it is desirable to have few surface defects, unimpeded information reading and writing, and the ability to read and write large amounts of data. Furthermore, in response to the increasing storage capacity requirements of hard disk drives (HDDs), high-density magnetic recording has been achieved.

[0004] For example, there is a known method for manufacturing a glass substrate for a disk: in order to enable unimpeded reading and writing using a magnetic head (DFH head) equipped with a DFH (Dynamic Flying Height) mechanism during high-density magnetic recording, the surface roughness (arithmetic mean roughness Ra) of the glass substrate for the disk is reduced (Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2014 / 051153 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in recent years, the miniaturization of magnetic particles in hard disk drives has reached its limit in the hard disk drive industry, and the rate of increase in recording density is showing signs of decline. On the other hand, due to reasons such as big data analysis, the demand for larger HDD storage capacity is becoming increasingly strong. Therefore, research is underway to increase the number of disks mounted in a single HDD unit. As mentioned above, the storage of large amounts of data typically uses a nominal 3.5-inch HDD.

[0010] When increasing storage capacity by increasing the number of disks assembled into an HDD, it is necessary to reduce the thickness of the disk substrate, which accounts for the majority of the disk's thickness, within the limited space within the HDD. Furthermore, to achieve even greater storage capacity, it is also desirable to increase the disk size.

[0011] This shows that increasing the diameter of the disk substrate and decreasing its thickness reduces its rigidity, making it prone to large vibrations that are sometimes difficult to suppress. For example, due to the vast number of HDDs used in cloud data centers, HDD replacements are frequently performed, often accompanied by failures. It is known that new HDDs fail due to impacts during rack installation, or that the time to failure is shortened. Further detailed investigation reveals that when an HDD is subjected to external impact, damage can occur even before power is supplied, as the disk may not be spinning.

[0012] Vibrations caused by external impacts differ from the steady-state flutter produced by the rotating disk and surrounding airflow, which decays over time. However, if the amplitude of this vibration is large, it can easily come into contact with the LEDs inside the HDD and with adjacent disks. Furthermore, the top disk in a series of disks spaced at intervals sometimes comes into contact with the top surface of the HDD's disk housing. Such contact can sometimes cause the contact area of ​​the disk to break, generating particles. Additionally, particles can sometimes be generated due to friction or shearing. In most cases, the generated particles disperse within the housing and adhere to the large read / write area (main surface) of the disk.

[0013] In this way, by increasing the diameter of the disk substrate and reducing its thickness, vibrations caused by external impacts, which were not previously a problem, and the accompanying particles, become significant. Especially in large disk substrates with a nominal size of 3.5 inches (e.g., 95 mm in diameter) or larger, the particle problem caused by the aforementioned contact due to substrate vibration becomes significant.

[0014] Therefore, the object of the present invention is to provide a substrate for a disk and a disk, wherein even if the diameter of the substrate for a disk is increased and the thickness is reduced, it is possible to suppress the generation of particles due to external impact.

[0015] Methods for solving problems

[0016] One aspect of the present invention is a disk-shaped substrate for a magnetic disk.

[0017] The substrate has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less.

[0018] The substrate uses a material with a Young's modulus E of 90 GPa or higher.

[0019] Preferably, the diameter D is 90 mm or more.

[0020] Preferably, when the inner peripheral end of the substrate is fixed, an impact of 70G is applied to the substrate along the normal direction of the main surface of the substrate for 2 m seconds, the maximum amplitude of the vibration in the thickness direction of the outer peripheral end of the substrate is less than 0.25 mm.

[0021] Another aspect of the invention is a disk-shaped substrate for a magnetic disk.

[0022] The substrate has a diameter D of 85 mm or more and a thickness T of 0.6 mm or less.

[0023] When the inner peripheral end of the substrate is fixed, and an impact of 70G is applied to the substrate along the normal direction of the main surface of the substrate for 2 m seconds, the maximum amplitude of the vibration in the thickness direction of the outer peripheral end of the substrate is less than 0.25 mm.

[0024] Preferably, the diameter D is 90 mm or more.

[0025] Preferably, the substrate is a glass substrate made of glass with a vitrification temperature of 650°C or higher.

[0026] Preferably, the change in flatness of the substrate after heating at 730°C is less than 4 μm compared to the flatness of the substrate before heating.

[0027] Preferably, the substrate has a linear expansion coefficient of 70 × 10⁻⁶. -7 Composed of materials with a density of 1 / K or less.

[0028] Preferably, the Vickers hardness Hv of the substrate is 650 kgf / mm. 2 above.

[0029] Preferably, the Knoop hardness Hk of the substrate is 600 kgf / mm. 2 above.

[0030] Preferably, a chamfered surface is provided at least on the surface at the outer peripheral end of the substrate.

[0031] The ratio of the width W1 of the chamfered surface along the radial direction of the substrate to the radius R of the substrate, W1 / R, is less than 0.0025.

[0032] Preferably, the ratio of twice the width W2 of the chamfered surface along the thickness direction of the substrate to the thickness T (2·W2) / T is 0.4 or less.

[0033] Preferably, the Young's modulus E of the substrate and the thickness T of the substrate are related to E·T. 3 The value is 3–18 GPa·mm 3 .

[0034] Preferably, the Q value of the material is 1500 or less at room temperature and 3000 Hz.

[0035] Preferably, let ρ be the density of the material at room temperature (g / cm³). 3 Let Q be the Q value of the material at room temperature and 3000 Hz; let E be the Young's modulus of the material at room temperature (GPa); and let v be the Poisson's ratio of the material at room temperature, ρ·(1-v) of the material. 2 • The Q / E value is less than 25 g / cm³ 3 / GPa.

[0036] Another aspect of the present invention is a disk having at least a magnetic film on the surface of the aforementioned disk substrate.

[0037] Invention Effects

[0038] Based on the aforementioned disk substrate and disk, even if the diameter of the disk substrate is increased and the thickness is reduced, it is possible to suppress the generation of particles due to external impacts. Attached Figure Description

[0039] Figure 1 This is a diagram showing an example of the external shape of a disk substrate according to one embodiment.

[0040] Figure 2 This is a diagram illustrating an example of vibration of a disk substrate according to one embodiment.

[0041] Figure 3 This figure illustrates an example of the outer periphery of a disk according to one embodiment.

[0042] Symbol Explanation

[0043] 1. Disk baseboard

[0044] 2 inner holes

[0045] 3 Main Surface

[0046] 4 side walls

[0047] 5 chamfered surfaces

[0048] 6 jiao

[0049] 10 disks Detailed Implementation

[0050] The disk substrate of the present invention will now be described in detail. In the following description, a glass substrate for disks will be used, but the disk substrate may also be a non-magnetic metal substrate in addition to a glass substrate.

[0051] In the case of glass substrates, aluminosilicate glass, soda-lime glass, borosilicate glass, etc., can be used as the glass. In particular, considering that chemical strengthening can be performed as needed and that a glass substrate for disks with excellent flatness of the main surface and strength of the substrate can be produced, amorphous aluminosilicate glass can be used appropriately.

[0052] Materials that can be used as metal substrates include, for example, aluminum alloys, titanium alloys, and Si single crystals.

[0053] The disk is manufactured by forming at least a magnetic film on the surface of the substrate for the disk.

[0054] Figure 1 This is a diagram showing the external shape of the disk substrate according to this embodiment. Figure 1 As shown, the disk substrate 1 (hereinafter referred to as substrate 1) in this embodiment is a thin, disc-shaped substrate with an inner hole 2. The disk is manufactured by forming films such as a magnetic film, a base film, and a soft magnetic layer on this substrate 1.

[0055] The size of substrate 1 is not limited as long as the diameter D is 85 mm or more, preferably 90 mm or more. However, substrate 1 can be suitably used, for example, as a disk substrate with a nominal diameter of 3.5 inches. In the case of a disk substrate with a nominal diameter of 3.5 inches, the diameter D (outer diameter) of the disk shape is 85 mm or more, preferably 90 mm or more. Specifically, the nominal value of the outer diameter of the disk shape is 95 mm or 97 mm.

[0056] As described above, the larger the outer diameter of the substrate 1, the larger the amplitude of the disk vibration caused by external impacts, which is different from flutter, and the less likely it is to attenuate. Therefore, the substrate 1 of this embodiment is preferred when used for disks with a nominal size of 3.5 inches or larger.

[0057] In this embodiment, the diameter D of the substrate 1 is 85 mm or more, preferably 90 mm or more, and the thickness T of the substrate 1 is 0.6 mm or less. Furthermore, the substrate 1 uses a material with a Young's modulus E of 90 GPa or more. The substrate 1 has a larger diameter D and a thinner thickness T compared to conventional substrates. This allows for an increase in the number of disks assembled into the HDD, thereby increasing the storage capacity. Because the substrate 1 has a large diameter D and a thin thickness T, the disks easily come into contact with the lamps inside the HDD and with adjacent disks within the HDD due to vibrations of the substrate 1 caused by impacts during HDD installation, as described above. Moreover, the uppermost disk sometimes comes into contact with the top surface of the HDD's disk storage container.

[0058] Furthermore, considering the nominal 3.5-inch HDD dimensions, the upper limit of the diameter D of substrate 1 is, for example, 100 mm. Also, considering the need to suppress arcing when a bias voltage is applied during the film deposition process, the lower limit of the substrate thickness T is, for example, 0.30 mm. The upper limit of Young's modulus E does not need to be specifically set, but for ease of processing, it is, for example, 120 GPa.

[0059] Figure 2 This diagram illustrates an example of vibration of the substrate 1 caused by the impact described above. This vibration differs from the steady-state flutter generated during stable rotation due to the airflow around the rotating disk. The vibration caused by the impact is a vibration resulting from the displacement of the main surface of the substrate 1 in the out-of-plane direction. Especially within an HDD, although the inner peripheral end is fixed to the spindle, the outer peripheral end becomes a free end and displaces in the out-of-plane direction towards the main surface. This out-of-plane displacement vibration (vibration in the thickness direction) contacts the lamp within the HDD, the adjacent disks, and ultimately the top surface of the disk storage container. Such contact sometimes causes the contact portion of the disk to break, generating particles. In most cases, the generated particles disperse within the storage container and adhere to the read / write area of ​​the disk. Therefore, in this embodiment, a material with a Young's modulus of 90 GPa or higher is used in the substrate 1.

[0060] When the substrate 1 is a glass substrate, for example, an amorphous oxide glass with a Young's modulus of 90 GPa or more can be obtained by the following glass composition.

[0061] The composition of this amorphous oxide glass is as follows:

[0062] (Glass 1)

[0063] SiO2 content is 56-80 mol%.

[0064] Li2O was 1–10 mol%.

[0065] B2O3 content is 0-4 mol%.

[0066] The total content of MgO and CaO (MgO + CaO) is 9–40 mol%.

[0067] The specific gravity of glass 1 is 2.75 g / cm³. 3 The following are glass transition temperatures (Tg) above 650℃.

[0068] (Glass 2)

[0069] SiO2 content is 56-80 mol%.

[0070] Li2O was 1–10 mol%.

[0071] B2O3 content is 0-4 mol%.

[0072] The total content of MgO and CaO (MgO + CaO) is 9–40 mol%.

[0073] The molar ratio of the total content of SiO2 and ZrO2 to the content of Al2O3 ((SiO2+ZrO2) / Al2O3) is 2 to 13.

[0074] Glass 2 has a glass transition temperature (Tg) of 650℃ or higher.

[0075] (Glass 3)

[0076] Expressed in mole percent,

[0077] The SiO2 content is 56-65%.

[0078] Al2O3 content is 5%–20%.

[0079] B2O3 content is 0-4%.

[0080] MgO content is 3-28%.

[0081] Li2O content is 1-10%.

[0082] The total content of SiO2 and Al2O3 (SiO2 + Al2O3) is 65-80%.

[0083] The total content of MgO and CaO (MgO+CaO) is 11%–30%.

[0084] The total content of MgO, CaO, SrO, and BaO (MgO+CaO+SrO+BaO) is 12%–30%.

[0085] The sum of MgO content, 0.7×CaO content, Li2O content, TiO2 content, and ZrO2 content (MgO + 0.7CaO + Li2O + TiO2 + ZrO2) is above 16%.

[0086] The sum of the contents of 5×Li₂O, 3×Na₂O, 3×K₂O, 2×B₂O₃, MgO, 2×CaO, 3×SrO, and BaO (5Li₂O + 3Na₂O + 3K₂O + 2B₂O₃ + MgO + 2CaO + 3SrO + BaO) is 32%–58%.

[0087] The sum of the contents of SiO2, Al2O3, B2O3, P2O5, 1.5×Na2O, 1.5×K2O, 2×SrO, 3×BaO, and ZnO (SiO2+Al2O3+B2O3+P2O5+1.5Na2O+1.5K2O+2SrO+3BaO+ZnO) is below 86%, and the sum of the contents of SiO2, Al2O3, B2O3, P2O5, Na2O, K2O, CaO, 2×SrO, and 3×BaO (SiO2+Al2O3+B2O3+P2O5+Na2O+K2O+CaO+2SrO+3BaO) is below 92%.

[0088] The molar ratio of CaO content to MgO content (CaO / MgO) is below 2.5.

[0089] The molar ratio of Na₂O content to Li₂O content (Na₂O / Li₂O) is less than 5.

[0090] The molar ratio of Li₂O content to the total content of MgO and CaO (Li₂O / (MgO+CaO)) is 0.03–0.4.

[0091] The molar ratio of SiO2 content to the total content of Li2O, Na2O, and K2O (SiO2 / (Li2O+Na2O+K2O)) is 4–22.

[0092] The total content of SiO2 and ZrO2 to the molar ratio of Al2O3 ((SiO2+ZrO2) / Al2O3) is 2-10.

[0093] The molar ratio of the total content of TiO2 and Al2O3 to the total content of MgO and CaO ((TiO2+Al2O3) / (MgO+CaO)) is 0.35~2.

[0094] The molar ratio of the total content of MgO and CaO to the total content of MgO, CaO, SrO, and BaO ((MgO+CaO) / (MgO+CaO+SrO+BaO)) is 0.7–1.

[0095] The molar ratio of BaO content to the total content of MgO, CaO, SrO, and BaO (BaO / (MgO+CaO+SrO+BaO)) is less than 0.1.

[0096] The molar ratio of P2O5 content to the total content of B2O3, SiO2, Al2O3, and P2O5 (P2O5 / (B2O3+SiO2+Al2O3+P2O5)) is less than 0.005.

[0097] It has a glass transition temperature of 670℃ or higher and a Young's modulus of 90 GPa or higher.

[0098] Specific gravity below 2.75

[0099] The average linear expansion coefficient at 100–300℃ is 40 × 10⁻⁶. -7 ~70×10 -7 Within the range of / ℃.

[0100] At this time, when the inner peripheral end of the substrate 1 is fixed, and an impact (acceleration) of 70G is applied to the substrate 1 along the normal direction of the main surface of the substrate 1 for 2 m / s, the maximum amplitude of the vibration in the thickness direction of the outer peripheral end of the substrate 1 is preferably 0.25 mm or less. By setting the maximum amplitude to 0.25 mm or less, the aforementioned contact can be prevented. In addition, the above impact test is performed using an AVEX-SM-110-MP type testing machine from AR BROWN Co., Ltd.

[0101] Therefore, in one embodiment of the substrate 1, the diameter D of the substrate 1 is 85 mm or more, preferably 90 mm or more, and the thickness T of the substrate 1 is 0.6 mm or less. When the inner peripheral end of the substrate 1 is fixed, an impact of 70G is applied to the substrate 1 along the normal direction of the main surface of the substrate 1 for 2 m seconds, and the maximum amplitude generated by the vibration in the thickness direction of the outer peripheral end of the substrate 1 is 0.25 mm or less.

[0102] According to one embodiment, the substrate 1 is preferably made of glass with a glass transition temperature (Tg) of 650°C or higher, and more preferably with a glass transition temperature (Tg) of 680°C or higher. A higher glass transition temperature (Tg) results in higher heat resistance, thereby suppressing substrate deformation, such as flatness, that occurs during heat treatment of the substrate 1. From the viewpoint of suppressing thermal deformation during heat treatment when forming magnetic films for disks on the substrate 1, it is preferable to set the glass transition temperature (Tg) to 650°C or higher.

[0103] Specifically, when fabricating a disk by forming a metal film of about 30 nm, including a magnetic film, on substrate 1, the substrate 1 is heated. During this heating process, substrate 1 is prone to deformation due to thermal stress. Therefore, according to one embodiment, the change in flatness between the substrate 1 after heating at 730°C and the flatness of the substrate 1 before heating (flatness after heating - flatness before heating) is preferably 4 μm or less. By limiting the change in flatness in this way, a flat disk can be obtained, thereby reducing minor vibrations of the disk during rotation.

[0104] According to one embodiment, the substrate 1 is preferably made of a material with a linear expansion coefficient of 70 × 10⁻⁶. -7 The material composition is less than 1 / K, and more preferably has a linear expansion coefficient of 60×10.-7 Below 1 / K. The lower limit of the linear expansion coefficient of substrate 1 is, for example, 40 × 10⁻⁶. -7 1 / K. The linear expansion coefficient mentioned here is a linear expansion coefficient calculated based on the difference in thermal expansion between 100°C and 300°C. By using such a linear expansion coefficient, thermal expansion can be suppressed during heat treatment such as forming magnetic films. When the holding member of the film forming apparatus holds the outer peripheral end face (hereinafter referred to as the outer peripheral end face) of the substrate 1, thermal deformation of the substrate 1 around the holding portion can be suppressed. The linear expansion coefficient is, for example, 242 × 10⁻⁶ in conventional aluminum alloy substrates. -7 1 / K, which is 95×10 in conventional glass substrates. -7 The linear expansion coefficient is 51 × 10⁻⁶ or higher than 1 / K, while the linear expansion coefficient of the glass substrate 1 in one embodiment is 51 × 10⁻⁶. -7 1 / K. On the other hand, the lower limit of the linear expansion coefficient of substrate 1 does not need to be specially set. However, if the linear expansion coefficient of substrate 1 is too small, the spindle may expand and contact / press the circular hole of the substrate when the temperature inside the HDD rises, causing the substrate to deform. Therefore, it is further preferable, for example, to set the lower limit of the linear expansion coefficient to 20 × 10⁻⁶. -7 1 / K.

[0105] According to one embodiment, the Vickers hardness Hv of the substrate 1 is preferably 650 kgf / mm. 2 That's all. Furthermore, according to one embodiment, the Knoop hardness Hk of the substrate 1 is preferably 600 kgf / mm². 2 The above describes how increasing the Vickers hardness Hv or Knoop hardness Hk can prevent substrate 1 from breaking and generating particles, even if substrate 1 comes into contact with other substrates 1 or other components due to vibrations caused by external impacts. Furthermore, during the formation of magnetic films, when the holding member of the film-forming apparatus holds the outer peripheral end face, it can prevent a portion of the outer peripheral end face from breaking and generating particles, which then adhere to the main surface of substrate 1. For example, the Vickers hardness Hv is 128 kgf / mm² in aluminum alloy substrates. 2 In the past, the resistance of glass substrates was 620 kgf / mm². 2 In one embodiment, the glass substrate 1 has a strength of 741 kgf / mm². 2 .

[0106] Figure 3 This is an enlarged illustration of an example of the end of a disk. Figure 3 This shows two adjacent disks within an HDD. Figure 3 In the diagram, the thickness of the magnetic film, etc., is overwhelmingly small compared to the thickness of the substrate 1, reaching about tens of nm, so the illustration of the magnetic film, etc. is omitted.

[0107] The substrate 1 has: a pair of main surfaces 3; sidewalls 4 arranged in a direction perpendicular to the pair of main surfaces 3; and a pair of chamfered surfaces 5 disposed between the pair of main surfaces 3 and the sidewalls 4. The sidewalls 4 and the chamfered surfaces 5 are respectively formed at the outer peripheral end and the inner peripheral end of the substrate 1.

[0108] like Figure 3 As shown, disks 10, formed by forming a magnetic film (not shown) or the like on the surface of substrate 1, are arranged adjacent to each other within the HDD. Here, when a disk 10 vibrates along the normal direction of the main surface 3 and comes into contact with an adjacent disk 10, the corner 6, located at the outer peripheral end and serving as the connection point between the main surface 3 and the chamfered surface 5, easily comes into contact. Through this contact, the chamfered surface 5 near the corner 6 is subjected to a large impact.

[0109] It is known that the chamfered surface 5 is formed by grinding with a shaped grinding stone and then polishing the end face with a brush, etc. However, in the case of a substrate made of glass material with a Young's modulus E of 90 GPa or higher, compared with the substrate of glass with a lower Young's modulus in the past, a large number of potential cracks or microcracks exist on the surface of the chamfered surface 5. The reason is not yet clear, but it is speculated that the reason is that, for example, glass with a high Young's modulus is usually hard, so the load during grinding is greater, thus producing deeper cracks than before. Some of these cracks remain as potential cracks or microcracks after grinding. In this state, if the aforementioned corner 6 is impacted through contact with lamp components, etc., the potential cracks or microcracks develop. As a result, sometimes the corner 6 or part of the chamfered surface 5 of the substrate 1 in the disk 10 breaks, generating particles together with the magnetic film on top of it. In such cases, the larger the width W1 described later, the easier it is for the corner 6 or part of the chamfered surface 5 to break. In most cases, particles generated in corner 6 or chamfered surface 5 are scattered within the HDD storage container and adhere to the read / write area of ​​disk 10.

[0110] Therefore, according to one embodiment, in the chamfering process, it is preferable to reduce the machining allowance when forming the chamfered surface 5. When the diameter of the disk 10 is large enough to be 85 mm or more, preferably 90 mm or more, and the plate thickness is thin enough to be 0.600 mm or less, the corner 6 is prone to contact due to vibration. Therefore, it is preferable to reduce the machining allowance when forming the chamfered surface 5 to reduce the number of potential cracks or micro-cracks. In this way, even if the corner 6 of the disk 10 contacts the lamp component or the like due to large vibration, the generation of particles can be suppressed. Here, the machining allowance when forming the chamfered surface 5 refers to the value of the width W1 described later. In addition, sometimes a certain amount of material is removed from the outer periphery to adjust the outer diameter in the early stage of grinding, but according to the research of the inventors of this case, such an initial machining allowance does not affect potential cracks, etc. The reason is presumably that potential cracks caused by the initial machining allowance disappear due to the influence of the final machining allowance. Specifically, the chamfered surface 5 is provided at least on the outer peripheral end face of the substrate 1. At this time, the width W1 of the chamfered surface 5 in the radial direction of the substrate 1 is preferred (refer to Figure 3 The width W1 is 120 μm or less. More preferably, the width W1 is 90 μm or less. By adjusting the processing allowance when forming the chamfered surface 5 to a width W1 of 120 μm or less, even when the diameter of the disk 10 using a high Young's modulus glass substrate is large and the plate thickness is thin, causing the corner 6 to easily come into contact due to vibration, the number of potential cracks or micro-cracks in the chamfered surface 5 can be reduced. Therefore, even if the corner 6 comes into contact, the breakage of the corner 6 or part of the chamfered surface 5 can be suppressed to prevent the generation of particles. In addition, the lower limit of the width W1 is, for example, 20 μm. When the width W1 is less than 20 μm, the chamfered surface 5 is too small, which may cause edge chipping in the substrate manufacturing process or film deposition process after shape processing. Figure 3 As shown, the chamfered surface 5 can have a straight shape in the cross-section cut along the radial direction through the center of the disk 10, or it can have a circular arc or curved shape that bulges outward. In this case, the chamfered surface 5 refers to the portion where the tangent at each location has an angle of inclination of 5 to 85 degrees relative to the side wall surface 4 and the main surface 3. Figure 3 The diagram shows a chamfered surface 5 with a certain tilt angle θ1 relative to the main surface 3.

[0111] According to one embodiment, the width W2 of the chamfered surface 5 in the outer periphery of the substrate 1 along the thickness direction of the substrate 1 is preferably (refer to...). Figure 3 The ratio (2·W2) / T of twice the plate thickness T is 0.4 or less. More preferably, the ratio (2·W2) / T is 0.3 or less. When the ratio (2·W2) / T exceeds 0.4, the sidewall surface 4 becomes too small, and therefore, the outer peripheral end may sometimes break or crack due to the application of the holding or bias voltage FCI20JP6918 when forming the magnetic film, etc.

[0112] Furthermore, according to one embodiment, regarding Young's modulus E GPa and plate thickness T mm, E·T is preferred. 3 The value is 3–18 GPa·mm 3 More preferably, it is 3–16 GPa·mm 3 Especially preferred is 5–15 GPa·mm 3 Through E·T 3 Within this range, the value can suppress contact of the disk 10 caused by vibration. In E·T 3 The value is less than 3 GPa·mm 3 In such cases, vibration can easily cause contact issues with the disk 10. (E.T.) 3 The value exceeds 18 GPa·mm 3 In this case, it is not possible to increase the board thickness in order to ensure the number of disks 10 built into the HDD, so the Young's modulus E is increased. In this case, as the Young's modulus E increases, the substrate 1 tends to harden unnecessarily, and the grinding time of the main surface 3 becomes longer, which is not preferable in terms of the production efficiency of the disk substrate 1.

[0113] Furthermore, according to one embodiment, regarding Young's modulus E GPa and density ρg / cm³... 3 The preferred value for the specific elastic modulus calculated based on E / ρ is 36 GPa·cm. 3 / g or higher. Even with a high Young's modulus, if the density is high, vibrations can sometimes increase due to the weight of the substrate itself. An upper limit for the specific modulus does not need to be specifically set, but from a productivity point of view, it could be set to, for example, 41 GPa·cm. 3 / g.

[0114] When such a substrate 1 is mounted on an HDD, the number of substrate 1 units mounted on the HDD depends on the thickness T of the substrate 1. The thickness of the magnetic film or the like formed on the substrate 1 is several tens of nm, thin enough to be non-negligible relative to the thickness T of the substrate 1. For example, when the thickness T of the substrate 1 is 0.635 mm, more than 9 substrate 1 units can be mounted; when the thickness T of the substrate 1 is 0.5 mm, more than 10 substrate 1 units can be mounted; and when the thickness T of the substrate 1 is 0.38 mm, more than 12 substrate 1 units can be mounted. Thus, the number of substrate 1 units mounted varies depending on the thickness T of the substrate 1.

[0115] Therefore, by reducing the thickness T of the substrate 1 and increasing the number of mounted chips, the storage capacity can be increased. At this time, as described above, in the substrate 1 of this embodiment, even if the thickness T is reduced, it is not easy for contact with other substrates 1 or components to occur due to vibration.

[0116] Furthermore, according to one embodiment, it is preferable that the substrate 1 does not break during an impact test in which the inner peripheral end of the substrate 1 is fixed in a manner that allows for the clamping of the reproduction disk, and an impact of 600G is applied to the substrate 1 for 2 m seconds. Such a substrate 1 will not break even when subjected to a large impact on the HDD, and is therefore preferred from the viewpoint of improving durability. This substrate 1 can be made using, for example, the glass 1 to 3 described above.

[0117] According to one embodiment, the Q value (quality factor) of the substrate 1 material at room temperature (25°C) and 3000 Hz is preferably 1500 or less. The Q value is obtained by dividing the vibrational energy accumulated in the substrate 1 during one cycle by the energy dissipated from the vibrating substrate 1. The smaller the value, the greater the vibration attenuation. Therefore, the smaller the Q value of the material used, the faster the vibration attenuation. As a result, the number of contacts with adjacent substrates 1 or lamps in the HDD can be reduced, and the impact during contact can be mitigated, thus suppressing adverse effects such as particle generation caused by contact. Furthermore, the Q value at room temperature and 3000 Hz is more preferably 1300 or less.

[0118] Furthermore, the Q value at 3000 Hz was obtained as follows. First, a laser Doppler oscillometer (LDV) was used to vibrate a substrate 1 rotating via a spin support. The vibration was measured by contacting the laser with approximately the outer periphery of the substrate 1. The obtained data was appropriately subjected to a Fourier transform to obtain the frequency response function (horizontal axis: frequency (unit: Hz), vertical axis: NRRO (Non-Repeatable Runout) Amplitude (unit: nm)). Next, for each peak observed in the frequency response function, the Q value (=f0 / (f2-f1)) was calculated using the half-peak width method (using frequencies f1, f2 (>f1) corresponding to a value 3 dB lower than the peak value of NRRO and the frequency f0 (resonant frequency) corresponding to that peak value). The obtained measurement results were plotted on an XY plane with frequency on the horizontal axis and Q value on the vertical axis, and an approximate straight line was obtained by performing a linear approximation based on the least squares method. The Q value at 3000Hz is obtained by interpolating the approximate straight line or by interpolating the approximate straight line as needed.

[0119] Furthermore, the substrate 1 used in the evaluation using a laser Doppler vibrator was standardized to have an outer diameter of 95 mm, an inner diameter of 25 mm, and a thickness of 0.635 mm. The substrate rotation speed was measured at 6900 rpm at room temperature, and the measurement position was defined as a radius of 46.5 mm from the center of the substrate (1 mm from the inner edge of the outer perimeter).

[0120] According to one embodiment, let ρ be the density (g / cm³) of the material of substrate 1 at room temperature.3 Let Q be the Q value of the material of substrate 1 at room temperature with a frequency of 3000 Hz, let E be the Young's modulus of the material of substrate 1 at room temperature (GPa), and let v be the Poisson's ratio of the material at room temperature. Preferably, the ρ·(1-v) of the material of substrate 1 is... 2 • The Q / E value is less than 25 g / cm³ 3 / Gpa. The amplitude at the outer periphery of substrate 1 is related to ρ·(1-v). 2 / E / ξ (ξ is the attenuation ratio of the material of substrate 1) is proportional to the attenuation ratio ξ, which is expressed as 1 / (2·Q) (Q is the value of Q). Therefore, the above amplitude is proportional to 2·ρ·(1-v). 2 • Q / E is proportional. Here, the following situation was found: by 2·ρ(1-v) 2 • Q / E is set to less than 25 g / cm³ 3 / Gpa can efficiently reduce the amplitude of vibrations in a specific frequency band, specifically setting the RSS (Root of Sum of Squares) of flutter in the 1000–4000 Hz range to less than 80 nm. The RSS in the 1000–4000 Hz range is specifically the square root of the cumulative squares of the flutter amplitudes from 1000 Hz to 4000 Hz. That is, by using 2·ρ(1-v) 2 • Q / E is set to less than 25 g / cm³ 3 / GPa, capable of reducing RSS in the 1000Hz to 4000Hz region. This is achieved by using 2·ρ(1-v) 2 • Q / E is set to 20g / cm 3 Below / Gpa, the RSS in the 1000Hz to 4000Hz region can be set to below 68nm, which is therefore further preferred.

[0121] Furthermore, the impact of jitter in the frequency band below 1000Hz has gradually decreased with recent advancements in head servo technology. On the other hand, jitter in the frequency band above 4000Hz was already minimal. Therefore, reducing jitter in the 1000–4000Hz frequency band is of great importance.

[0122] The substrate 1 of this embodiment has the following characteristics.

[0123] Such a substrate 1 is manufactured as follows, for example. Here, as an example, the case where a glass substrate is used as substrate 1 is described.

[0124] First, a glass preform, which is the raw material for a plate-shaped disk substrate having a pair of main surfaces, is formed. Next, the glass preform is coarsely ground. Then, the glass preform is shaped and its end faces are ground. Next, the main surfaces of the substrate obtained from the glass preform are finely ground using fixed abrasive grains. Then, a first grinding, chemical strengthening, and a second grinding of the main surfaces are performed. In this embodiment, the substrate is manufactured according to the above process, but it is not necessary to always perform the above processes; the order of these processes can be appropriately changed, or they can be appropriately omitted. For example, the fine grinding, first grinding, and chemical strengthening described above may not be performed. Each process will be described below.

[0125] (a) Forming of glass preform

[0126] In the forming of glass preforms, for example, stamping can be used. By stamping, a circular glass preform can be obtained. Furthermore, it can be manufactured using known manufacturing methods such as the drawing method, the redrawing method, and the melting method. By appropriately shaping the plate-shaped glass preform produced using these known manufacturing methods, a circular substrate that forms the basis of a disk substrate can be obtained.

[0127] (b) Rough grinding

[0128] In rough grinding, the main surfaces on both sides of the glass preform are ground. Free abrasive grains are used as the grinding material. In rough grinding, the glass preform is ground to approximately the target thickness and the flatness of the main surfaces. Furthermore, rough grinding is performed according to the dimensional accuracy or surface roughness of the formed glass preform, and may be omitted depending on the circumstances.

[0129] (c) Shape processing

[0130] Next, shape processing is performed. In shape processing, firstly, after the glass preform is formed, a circular hole and outer periphery are formed using known processing methods, thereby obtaining a disc-shaped substrate with the circular hole (circular hole forming process). Secondly, the end faces of the substrate are chamfered (chamfering process). This forms a sidewall surface 4 perpendicular to the main surface 3 and a chamfered surface 5 inclined relative to the main surface 3 between the sidewall surface 4 and the two main surfaces 3 on both sides. In the chamfering process, the end faces of the substrate can also be ground using a shaping grinding stone, simultaneously forming the sidewall surface 4 and two chamfered surfaces 5.

[0131] (d) End face grinding

[0132] Next, the end faces of the substrate are polished. End face polishing, for example, involves supplying polishing slurry containing free abrasive particles between the polishing brush and the outer peripheral end face (side wall surface 4 and chamfered surface 5) and inner peripheral end face (side wall surface 4 and chamfered surface 5) of the substrate, and moving the polishing brush and the substrate relative to each other to perform polishing. In end face polishing, the inner peripheral end face and the outer peripheral end face of the substrate are the polishing objects, and the inner peripheral end face and the outer peripheral end face are set to a mirror finish.

[0133] (e) Precision grinding

[0134] Next, the main surface of the substrate is precision ground. For example, a double-sided grinding apparatus with a planetary gear mechanism is used to grind the main surface 3 of the substrate. In this case, for example, fixed abrasive grains are set on a fixed plate for grinding. Alternatively, grinding using free abrasive grains can also be performed. In addition, precision grinding may be omitted depending on the situation.

[0135] (f) First grinding

[0136] Next, a first grinding is performed on the main surface 3 of the substrate. The first grinding uses free abrasive grains and a grinding pad attached to a fixed plate. The first grinding removes, for example, any cracks or deformations remaining on the main surface 3 that would have occurred during fine grinding with fixed abrasive grains. In the first grinding, it is possible to prevent excessive depression or protrusion of the shape at the ends of the main surface 3, and to reduce the surface roughness of the main surface 3, for example, the arithmetic mean roughness Ra.

[0137] There are no particular restrictions on the free abrasive grains used in the first grinding stage, but for example, cerium oxide abrasive grains or zirconium oxide abrasive grains can be used. Alternatively, the first grinding stage may be omitted depending on the circumstances.

[0138] (g) Chemical fortification

[0139] According to one embodiment of the substrate 1, chemical strengthening can also be appropriately performed. In the case of chemical strengthening, a chemical strengthening solution can be, for example, a solution obtained by heating potassium nitrate, sodium nitrate, or a mixture thereof. The substrate is then immersed in the chemical strengthening solution, whereby lithium ions or sodium ions in the glass composition of the substrate's surface layer are replaced by sodium ions or potassium ions with relatively larger ionic radii in the chemical strengthening solution, thereby forming a compressive stress layer in the surface portion and strengthening the substrate.

[0140] The timing of chemical strengthening can be appropriately determined, but if grinding is performed after chemical strengthening, foreign matter that has adhered to the surface of the substrate through chemical strengthening can be removed as the surface is smoothed, which is therefore particularly preferred.

[0141] (h) Second grinding (mirror polishing)

[0142] Next, a second polishing process is performed on the chemically strengthened substrate. The second polishing aims to achieve a mirror finish on the main surface 3. In the second polishing, a polishing apparatus with the same structure as the first polishing is used. In the second polishing, the type and size of the free abrasive particles are changed compared to the first polishing, and a material with a soft resin polishing material is used as the polishing pad for mirror polishing. This prevents excessive depression or protrusion of the ends of the main surface 3 and reduces the roughness of the main surface 3. Regarding the roughness of the main surface 3, an arithmetic mean roughness Ra (JIS B 0601 2001) of 0.2 nm or less is preferred.

[0143] Substrate 1 is then obtained by cleaning the substrate.

[0144] (Examples, Comparative Examples, and Prior Examples)

[0145] To examine the effect of substrate 1, various substrates were fabricated (previous examples 1 and 2, comparative examples 1 and 2, and examples 1 to 12, examples 61 to 67, examples 81 to 84, examples 111 to 114, examples 121 to 124).

[0146] The substrate used was either a glass substrate or an aluminum alloy substrate. In the conventional Examples 1 and Comparative Example 1, the substrates used glass 4 with the following composition. The substrates 1 of Examples 1 and 2 used the aforementioned glass 1; the substrates 1 of Examples 3-5 used the aforementioned glass 2; the substrates 1 of Examples 6-10 used the aforementioned glass 3; the substrates 1 of Examples 11 and 12 used amorphous aluminosilicate glasses 5 and 6 with a composition different from glass 1-4 and a Young's modulus E of 100 GPa or higher; and the substrates 1 of Examples 61-67 and Examples 81-84 used the aforementioned glass 3. Furthermore, the substrates 1 of Examples 111-114 used glass 5, and the substrates 1 of Examples 121-124 used glass 6. In addition, no chemical strengthening was performed on any of the substrates.

[0147] Furthermore, the specific elastic modulus of glasses 1-3, 5, and 6 is 36 GPa·cm. 3 / g or more. The specific elastic modulus of glass 4 is less than 36.

[0148] (Glass 4)

[0149] An amorphous glass comprising: SiO2, Al2O3; one or more alkali metal oxides selected from the group consisting of Li2O, Na2O, and K2O; one or more alkaline earth metal oxides selected from the group consisting of MgO, CaO, SrO, and BaO; and one or more oxides selected from the group consisting of ZrO2, HfO2, Nb2O5, Ta2O5, La2O3, Y2O3, and TiO2.

[0150] The SiO2 content is above 50 mol%.

[0151] Al2O3 content is above 3 mol%.

[0152] Furthermore, the combined content of SiO2 and Al2O3 is 70–85 mol%.

[0153] It contains Li₂O and Na₂O, with Li₂O accounting for more than 4.3 mol%.

[0154] The Na₂O content is 5 mol% or higher.

[0155] Furthermore, the combined content of Li₂O and Na₂O is less than 24 mol%.

[0156] The total content of the alkali metal oxide and the alkaline earth metal oxide is 8 mol% or more.

[0157] The molar ratio of the total content of the oxides to the total content of the alkali metal oxides and the alkaline earth metal oxides ((ZrO2+HfO2+Nb2O5+Ta2O5+La2O3+Y2O3+TiO2) / (Li2O+Na2O+K2O+MgO+CaO+SrO+BaO)) is 0.035 or higher.

[0158] Contains MgO and CaO,

[0159] MgO less than 3 mol%.

[0160] The CaO content is less than 4 mol%.

[0161] Furthermore, the molar ratio of MgO to CaO (MgO / CaO) is 0.130 to 0.700.

[0162] The manufactured substrate has an outer diameter of 85mm to 97mm and an inner diameter (circular hole diameter) of 25mm. Regarding the specifications of the chamfered surface, the width W1 along the radial direction is 60μm to 150μm, and the width W2 along the thickness direction is 60μm to 150μm. Specifically, for conventional Examples 1 and 2 with a thickness exceeding 0.6mm, the width W1 along the radial direction of the chamfered surface is set to 150μm, and the width W2 along the thickness direction is set to 150μm. Furthermore, for Comparative Examples 1 and 2, and Examples 1 to 12 with a thickness of 0.6mm or less, the width W1 is set to 100μm, and the width W2 is set to 100μm. The widths W1 and W2 of Examples 61 to 67 and 81 to 84 are shown in Tables 3A to 3D below. Therefore, when the widths W1 and W2 are equal, the tilt angle θ1 (refer to...) Figure 3The angle is 45 degrees. Additionally, during the shaping process, when forming the outer periphery of the substrate, a diamond scribing tool is vertically inserted into the cut, causing the cut to develop to the opposite side. In the subsequent chamfering process, a shaping grinding stone is used to form the chamfered surface.

[0163] (Experiment 1)

[0164] The substrates fabricated in the previous examples 1 and 2, comparative examples 1 and 2, and examples 1 to 12 were mounted on an evaluation device equipped with a high-speed camera to determine the maximum amplitude. In this evaluation device, an external impact (acceleration) of any magnitude can be applied, and the motion (vibration) of the outer peripheral end of the substrate that occurs with it can be captured in animation. Then, by analyzing the animation, the displacement of the outer peripheral end in the normal direction of the main surface can be measured.

[0165] An impact test was conducted using this evaluation device, applying a 70G impact to the substrate at 2 [m sec] along the normal direction of the substrate's main surface. Vibration at the outer peripheral end in the normal direction towards the main surface was measured. The measurement results are presented as follows: Figure 2 The waveform data shown is used to represent this. Based on this waveform data, the maximum displacement in any direction in the normal direction is determined as the maximum amplitude relative to the center of the displacement 0 at the outer periphery of the substrate.

[0166] Furthermore, in actual HDDs, the lamps used in the ramp loading mechanism for assembling the read / write heads are spaced 0.25 mm apart from the two main surfaces when each disk is installed. That is, the gap between the lamps and the disks is the disk thickness + 0.5 mm. In actual HDDs, this gap is designed to remain constant even if the substrate thickness changes. On the other hand, this lamp is not provided in the evaluation device. Therefore, the determination of whether the substrate vibration will cause contact with other components (adjacent substrates, lamps, or the HDD's housing) in the actual HDD is based on the maximum amplitude of the substrate vibration. If the maximum amplitude is less than 0.25 mm, it can be determined that contact with the lamp will not occur. If the maximum amplitude exceeds 0.25 mm, the possibility of contact with other components is extremely high. The maximum amplitude was examined for three substrates, and the average of the maximum amplitudes was used. In the evaluation of this case, the substrates were not rotated and were evaluated in a stationary state.

[0167] Furthermore, the thickness of the magnetic film and the like formed in the dielectric process is less than 100 nm on the main surface, so it can be ignored in practice.

[0168] The evaluation results of the maximum amplitude are shown in Tables 1, 2A, and 2B below.

[0169] The aluminum alloy (“Al alloy”) in Conventional Example 2 and Comparative Example 2 is an Al-Mg alloy with the following composition: Mg: 3.5–5% by mass; Si: 0–0.05%; Fe: 0–0.1%; Cu: 0–0.12%; Mn: 0–0.3%; Cr: 0–0.1%; Zn: 0–0.5%; Ti: 0–0.1%; with the remainder being Al. Furthermore, a Ni-P alloy film (P: 10% by mass, remainder Ni) is formed on the surface of the Al-Mg alloy substrate by electroless plating to cover the entire surface of the substrate. The thickness of the substrate with the plating film refers to the thickness including the film.

[0170] [Table 1]

[0171] Previous Example 1 Previous Example 2 Comparative Example 1 Comparative Example 2 Example 1 Example 2 Material Glass 4 aluminum alloy Glass 4 aluminum alloy Glass 1 Glass 1 Young's modulus E [GPa] 83 71 83 71 95 95 Plate thickness T [mm] 0.635 0.635 0.5 0.5 0.55 0.5 Maximum amplitude [mm] 0.15 0.21 0.29 0.35 0.20 0.24

[0172] According to Table 1, in the conventional Examples 1 and 2 where the plate thickness T exceeds 0.6 mm, even though the Young's modulus is less than 90 GPa, the maximum amplitude is small due to the thick plate thickness T, and the substrate does not come into contact with other components. However, as shown in Comparative Examples 1 and 2, when the plate thickness T is less than 0.6 mm, the maximum amplitude exceeds 0.25 mm, and the possibility of the substrate coming into contact with other components is extremely high. In contrast, in Examples 1 and 2, even though the plate thickness T is less than 0.6 mm, the maximum amplitude is less than 0.25 mm because the Young's modulus is greater than or equal to 90 GPa.

[0173] [Table 2A]

[0174]

[0175] [Table 2B]

[0176]

[0177] Similar to Examples 1 and 2, in Examples 3 to 12, even if the plate thickness T is less than 0.6 mm, the maximum amplitude is less than 0.25 mm because the Young's modulus is greater than 90 GPa.

[0178] Based on the above, according to Tables 1 and 2A, 2B, even if the diameter D of substrate 1 is 85 mm or more and the thickness T of substrate 1 is 0.6 mm or less, and the Young's modulus E of substrate 1 material is 90 GPa or more, the maximum amplitude is 0.25 mm or less. Therefore, substrate 1 will not come into contact with other components due to vibrations caused by external impacts. Thus, particle generation can be suppressed within the HDD.

[0179] (Experiment 2)

[0180] Furthermore, based on the substrate 1 of Examples 6, 8, 11, and 12, the quality of the substrate 1 after impact testing was evaluated using substrate 1 with various modifications to the widths W1 and W2 of the chamfered surface 5 (Examples 61-67, Examples 81-84, Examples 111-114, Examples 121-124).

[0181] Furthermore, the widths W1 and W2 were varied by making various changes to the shape of the grinding stone or the processing conditions when performing chamfering using a shaped grinding stone. Examples 61-67 modified the widths W1 and W2 of the substrate 1 in Example 6; Examples 81-84 modified the widths W1 and W2 of the substrate 1 in Example 8; Examples 111-114 modified the widths W1 and W2 of the substrate 1 in Example 11; and Examples 121-124 modified the widths W1 and W2 of the substrate 1 in Example 12. Therefore, the material, Young's modulus E, plate thickness, and outer diameter of Examples 61-67 are the same as those of Example 6; the material, Young's modulus E, plate thickness, and outer diameter of Examples 81-84 are the same as those of Example 8; the material, Young's modulus E, plate thickness, and outer diameter of Examples 111-114 are the same as those of Example 11; and the material, Young's modulus E, plate thickness, and outer diameter of Examples 121-124 are the same as those of Example 12.

[0182] The quality evaluation of the fabricated substrate 1 was obtained as follows: a commercially available HDD was disassembled, and the substrate 1 and spacer of each embodiment were mounted on a spindle, with a simulated lamp component made of engineering plastic protruding from the substrate surface. A gap of 0.25 mm was left between the lamp component and the substrate. Then, an impact test was conducted in which a 200G impact was applied along the normal direction of the main surface of the substrate 1 for 2 m / s while the substrate 1 was fixed in place. This test was an accelerated test in which the outer peripheral end of the substrate 1 collided with the lamp component several times or more. Afterwards, the particle distribution around the surface of the substrate 1 in contact with the lamp component was observed. In addition, since it is difficult to quantify, a relative evaluation was performed.

[0183] Level 1: Almost no particles

[0184] Level 2: The number of particles is moderate.

[0185] Level 3: A large number of particles

[0186] The evaluation results are shown in Tables 3A to 3D below.

[0187] The smaller the grade value, the better the quality evaluation, with grade 1 representing the highest evaluation.

Claims

1. A disk substrate, which is a disk-shaped disk substrate, characterized in that, The diameter D of the substrate is 90 mm or more and 100 mm or less. The thickness T of the substrate is 0.3 mm or more and 0.6 mm or less. Regarding the Young's modulus E of the substrate and the plate thickness T, the value of E-T 3 is 3 to 18 GPa-mm 3 , The substrate uses a material with a Q value of 1500 or less at room temperature and 3000 Hz.

2. A disk substrate, which is a disk-shaped disk substrate, characterized in that, The diameter D of the substrate is 90 mm or more and 100 mm or less. The thickness T of the substrate is 0.3 mm or more and 0.6 mm or less. Regarding the Young's modulus E of the substrate and the thickness T, E·T 3 The value is 3–18 GPa·mm 3 The substrate uses a material with the following density at room temperature (g / cm³): Let ρ be the density of the material. 3 Let Q be the Q value of the material at room temperature and 3000 Hz; let E be the Young's modulus of the material at room temperature (GPa); and let v be the Poisson's ratio of the material at room temperature, ρ·(1-v) of the material. 2 • The Q / E value is less than 25 g / cm³ 3 / GPa.

3. The substrate for a disk drive according to claim 1 or 2, wherein, When the inner peripheral end of the substrate is fixed, and an impact of 70G is applied to the substrate along the normal direction of the main surface of the substrate for 2 m seconds, the maximum amplitude of the vibration in the thickness direction of the outer peripheral end of the substrate is less than 0.25 mm.

4. The substrate for a disk drive according to claim 1 or 2, wherein, The substrate is a glass substrate made of glass with a vitrification temperature of 650°C or higher.

5. The substrate for a disk drive according to claim 1 or 2, wherein, The change in flatness of the substrate after heating at 730°C compared to the flatness of the substrate before heating is less than 4 μm.

6. The substrate for a disk drive according to claim 1 or 2, wherein, The substrate has a linear expansion coefficient of 70×10⁻⁶. -7 Composed of materials with a density of 1 / K or less.

7. The substrate for a disk drive according to claim 1 or 2, wherein, The Vickers hardness Hv of the substrate is 650 kgf / mm. 2 above.

8. The substrate for a disk drive according to claim 1 or 2, wherein, The Knoop hardness Hk of the substrate is 600 kgf / mm. 2 above.

9. The substrate for a disk drive according to claim 1 or 2, wherein, At least the outer peripheral end face of the substrate is provided with a chamfered surface. The width W1 of the chamfered surface along the radial direction of the substrate is less than 120 μm.

10. The substrate for a disk drive according to claim 1 or 2, wherein, The ratio of twice the width W2 of the chamfered surface along the thickness direction of the substrate to the thickness T (2·W2) / T is 0.4 or less.

11. The substrate for a disk drive according to claim 1 or 2, wherein, The Young's modulus E of the substrate is above 90 GPa and below 120 GPa.

12. A disk having at least a magnetic film on the surface of a disk substrate according to any one of claims 1 to 11.

13. A hard disk drive comprising the disk and read / write head as described in claim 12.

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