TW202106649A - Glass substrate for magnetic recording and method of making - Google Patents

Abstract

A process for preparing a glass substrate for an information recording media is provided. The process can include providing a laminated glass article having at least one outer cladding layer and an inner core layer. A first outer cladding layer can be in contact with and adjacent to a first surface of the inner core layer. A second outer cladding layer, if present, can be contact with and adjacent to a second surface of the inner core layer. The process can include reducing the thickness the at least one cladding layer to obtain a glass substrate having at least one flat surfaces that are suitable for a recording process. A glass substrate prepared according to the process is also provided. A hard disk drive that includes the glass substrate is also provided.

Description

Glass substrate for magnetic recording and manufacturing method thereof

This application claims the priority rights of U.S. Provisional Application No. 62/846,923 filed on May 13, 2019 in accordance with the Patent Law. The content of the U.S. Provisional Application is used as a basis and is incorporated herein by reference in its entirety.

The present invention relates to a glass substrate for magnetic recording and a manufacturing method thereof.

In recent years, the data storage capacity of magnetic devices such as hard disk drives has greatly increased. Heat-assisted magnetic recording (HAMR) is an emerging technology that temporarily heats disk data during the writing process, which makes it more receptive to magnetic effects and allows writing to a smaller area. One of the key recording coatings used for HAMR is a highly ordered granular film with high perpendicular magnetic anisotropy. High perpendicular magnetic anisotropy requires heating the substrate to 600°C or higher to obtain good uniformity of grain size and distribution, as well as good control of the randomness of position, texture, and orientation. The high deposition temperature used for HAMR media coating precludes the use of conventional substrates, such as those made of aluminum. In contrast, glass is the preferred substrate for HAMR coating. Perpendicular magnetic recording technology requires a smooth and flat glass surface.

In various embodiments, a method of preparing a glass substrate for an information recording medium is provided. The method may include providing a laminated glass article having at least one outer cladding layer and an inner core layer. The first outer cladding layer may be in contact with and adjacent to the first surface of the inner core layer. The second outer cladding layer (if present) may be in contact with and adjacent to the second surface of the inner core layer. The method may include reducing the thickness of at least one outer cladding layer to obtain a glass substrate (for example, HAMR) having one or two flat surfaces suitable for recording processes.

In various embodiments, a glass substrate prepared according to the method is provided. In various embodiments, a hard disk drive including a glass substrate is provided.

The above general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the essence and characteristics of the claimed subject matter. The accompanying drawings to be considered are included to provide a further understanding of the features and advantages of the various embodiments disclosed in or made apparent by the following detailed description.

The description of the embodiments is intended to be understood in conjunction with the accompanying drawings, which will be regarded as a part of the entire written description of this disclosure. The drawings are not necessarily drawn to scale, and certain features of various embodiments may be exaggerated on scale or in a certain schematic form for the purpose of clarity and conciseness. In this manual, relative terms such as "horizontal", "vertical", "upward", "downward", "top", "bottom" and their derivatives (for example, "horizontal", "downward", "Upward", etc.) should be interpreted as referring to the orientation shown in the schema described or under discussion at the time. These relative terms are for ease of description, and are generally not intended to require a specific orientation. Terms including "inward" and "outward", "longitudinal" and "transverse" should be interpreted relative to each other or relative to the axis of elongation or the axis or center of rotation as appropriate. With regard to terms such as attachment and coupling, such as "connected" and "interconnected", unless expressly stated otherwise, it refers to the relationship in which structures are directly or indirectly fixed or attached to each other through intermediate structures, and movable or rigid Attachment or relationship, and includes terms such as "direct" connection, fixation, etc. The term "operationally connected" is the attachment, connection, or connection that allows related structures to operate as expected by virtue of the relationship.

The laminated glass article 100 shown in Figure 1A may be formed by a fusion lamination method, such as the method described in US Patent No. 4,214,886, which is incorporated herein by reference in its entirety. As shown in FIG. 2, for example, a laminate fusion stretching apparatus 200 for forming a laminated glass product includes an upper isopipe 202 positioned above the lower isopipe 204. The upper isopipe 202 includes a tank 210 into which the molten glass coating component 206 is fed via a self-melter (not shown). Similarly, the lower isopipe 204 includes a tank 212 into which the molten glass core component 208 is fed via a self-melter (not shown).

When the molten glass core component 208 fills the tank 212, the molten glass core component 208 overflows the tank 212 and flows through the outer forming surfaces 216 and 218 of the lower isopipe 204. The outer forming surfaces 216 and 218 of the lower isopipe 204 converge at the root 220. Therefore, the molten glass core component 208 flowing through the outer forming surfaces 216 and 218 reunites at the root 220 of the lower isopipe 204 to form the glass core layer 102 of the laminated glass product 100.

At the same time, the molten glass coating component 206 overflows the groove 210 formed in the upper isopipe 202 and flows through the outer forming surfaces 222 and 224 of the upper isopipe 202. The molten glass coating component 206 is deflected outwards by the upper isopipe 202, so that the molten glass coating component 206 flows around the lower isopipe 204 and interacts with the molten glass flowing through the outer forming surfaces 216 and 218 of the lower isopipe. The core component 208 contacts, thereby fusing into the glass core component 208 and forming glass cladding layers 104a and 104b around the glass core layer 102 of the laminated glass article 100.

The laminate fusion stretching apparatus 200 produces laminated glass in a manner that provides a substantially uniform thickness of the glass layer in the newly formed laminated glass product 100. Alternatively, the viscosity of the molten glass coating component 206, the inclination angle of the groove 210, and the flow rate can be adjusted to distinguish the thickness of the individual coating layers 104a and 104b independently of each other. For example, in some embodiments, the inclination angle of the groove 210 may be large enough so that the molten glass component flows through one side thereof, and the resulting laminated glass article has a single cladding layer (ie, 104a or 104b) in contact with the core 102 ), as shown in Figure 1C.

The composition of molten glass (such as the chemical composition described in US Patent Application Nos. US 2016/0114564 and US 2018/0312422, which are incorporated herein by reference in their entirety) can be used in the fusion forming method . Other components are also envisaged. The properties of the molten glass composition (for example, liquidus viscosity, temperature, etc.) can be controlled to make it very suitable for fusion forming methods, such as fusion down-drawing methods or fusion lamination methods. Specific examples of the glass composition of the core layer include, for example, Lotus NXT glass (Corning) and the like. Specific examples of the glass composition of the coating layer include, for example, Eagle XG glass (Corning), Gorilla glass (Corning), and the like.

The incidence of surface defects of glass produced using a fusion forming method, such as a pull-up or pull-down fusion method, is generally low. However, the airflow and surface temperature changes near the fusion stretching equipment may cause thickness changes and glass warping. These defects mainly affect the surface of the glass. For laminated glass formed by the fusion stretching method, where the outer cladding is formed at the same time as the inner core, the core will be protected from airflow and surface temperature modulation, and compared with the outer surface of the cladding, the thickness of the core changes and warps Will be reduced. For example, the laminated glass product 100 in Figure 1B has a noticeable surface thickness change on the outer main surface of the cladding layers 104a and 104b, but there is no noticeable thickness change or warpage on the main surface of the inner core layer 102. .

In order to increase the recording density of the hard disk drive, the distance between the magnetic recording head and the surface of the disk (defined as flying height) must be as narrow as possible. In general, the flying height is required to be about 10 nm or less. Therefore, the flatness and smoothness of the glass substrate are important to prevent the head from contacting the magnetic disk and causing head damage. Flatness refers to the total thickness variation (TTV) of the substrate. Generally speaking, a TTV of less than about 1 micron is required. Smoothness or roughness refers to the surface texture, and is quantified by the deviation of the normal vector direction of the real surface from its ideal shape. If the deviation is large, the surface is rough. If the deviation is small, the surface is smooth. The profile (line) roughness parameter (Ra) is usually used to calculate the roughness value. Generally speaking, Ra is required to be less than 0.2 nm.

In some embodiments, the laminated glass article 100 is prepared from a combination of different chemical compositions. In such an embodiment, the glass chemical composition of the cladding layers 104a and 104b has different characteristics compared to the glass chemical composition of the core 102. In some embodiments, the core and cladding glass components have different material hardness, different thermal conductivity, and/or different chemical durability. Thermal conductivity is a calculated value equal to the product of the thermal diffusion coefficient multiplied by the specific heat multiplied by the glass density. The thermal conductivity can be improved by adjusting the core-clad glass composition of the laminated glass product 100. In some embodiments, the glass core 102 includes a composition having a higher thermal conductivity. In some embodiments, an alkali-free glass composition may be used in the cladding layers 104a and 104b to prevent impurities from diffusing from the core when the cladding layer is not completely removed.

Chemical durability or corrosion resistance is measured as the weight loss per surface area (mg/cm ² ) after immersion in a corrosive environment. The weight loss rate is based on the time required to obtain weight loss at a certain temperature. The chemical durability is highly dependent on the test conditions. Other properties, including mechanical and electrical properties, viscosity, refractive index, friction coefficient, strength, impact resistance, scratch resistance, etc., will also depend on the glass composition and the processing of the 100 components of laminated glass products.

As disclosed herein, the laminated glass product 100 in which the core 102 and the cladding layers 104a and 104b are made of different glass compositions is beneficial to the production of flat and smooth substrates for information recording media. For example, in some embodiments, the outer surface, major surface, or both of the cladding layer 104a, 104b (ie, the surface that is not adjacent to the core 102, and the surface that is not the peripheral side) may be treated to remove such Defects of warpage or thickness variation, and other ways to improve the final surface quality. In such embodiments, at least one of the cladding layers may be polished or reduced in material to ensure that the resulting laminated glass substrate (101) has at least one flat and smooth surface for the information recording medium. For example, FIGS. 3A to 3D show various embodiments of a laminated glass substrate 101, which is a laminated glass product 100 after surface treatment of the cladding layers 104a, 104b or both.

As shown in FIG. 3A, for example, in some embodiments, the cladding layer 104b is partially reduced (relative to the outer surface of the cladding layer 104b in the laminated glass product 100). In other embodiments, as shown in FIG. 3B, the cladding layer 104b is completely reduced to the adjacent surface of the core 102. In some embodiments, as shown in FIG. 3C, both the cladding layers 104a and 104b are partially reduced. In some embodiments, as shown in FIG. 3D, at least one cladding layer (104a and/or 104b) is completely reduced to the adjacent surface of the core 102, so that the glass core 102 remains. The symbol 106 in each of FIGS. 3A to 3D refers to a portion of the coating layer of the sandwich product 100, which is removed to produce a laminated glass substrate 101a, 101b, 101c, or 101d.

In some embodiments, the glass composition is selected so that the cladding layers 104a and 104b are relatively softer than the core 102. In some embodiments, the glass composition is selected so that the core 102 is more corrosion resistant (chemically durable) than the cladding layers 104a and 104b. In such embodiments, the glass in the cladding layer is easier to shrink (mechanical, chemical, or both) than the glass in the core 102. Therefore, in some embodiments, since the core glass is harder, more corrosion resistant, or both, the core layer 102 acts as a support stop during the cladding reduction process. In addition, in some embodiments, since the core 102 is protected from airflow and surface temperature modulation by cladding in the lamination fusion method, the core 102 provides a substantially flat and smooth surface with minimal surface defects. In such embodiments, the thickness ratio of the glass composition and the layer is adjusted to precisely control the hardness and elastic properties, thermal conductivity and/or chemical durability of the cladding and core glass components to ensure complete removal After at least one cladding layer, a flat and smooth surface of the glass core 102 appears.

Any suitable process can be used in the coating reduction stage. In some embodiments, for example, a chemical etching process is used to shrink the cladding layers 104a and 104b. In such embodiments, the composition used for the core 102 and the cladding layers 104a and 104b can be precisely controlled to establish differential etch selectivities based on their relative corrosion resistance. In addition, the thickness of the core 102 and the cladding layers 104a and 104b can be adjusted to precisely control the rate of material reduction. In such embodiments, the core 102 acts as a stop during the etching process. For example, the core 102 includes a glass component that is substantially resistant to an etchant, but the glass component constituting the cladding layer(s) is not resistant to the same etchant. After selectively etching away some or all of the glass in the cladding layer, a core glass having a smooth and flat surface for an information recording medium, or a core glass and the remaining cladding are respectively obtained.

In some embodiments, the etching step involves wet chemical methods (e.g., solutions containing acids, bases, fluorides, etc.). In some embodiments, the etching step involves dry chemistry (eg, plasma deposited via chemical vapor deposition).

In some embodiments, acid etching surface treatment is used. The etching process includes contacting one or two external surfaces of the laminated glass product 100 with an acid glass etching medium, which can be easily adjusted according to a specific glass composition and applied to flat surfaces and complex surface geometries. Etching the laminated glass product 100 can change the size or geometric structure of the surface defect, and/or reduce the size and number of the surface defect, while having minimal impact on the overall morphology of the processed surface. In addition, in some embodiments, acid etching has been found to effectively reduce strength variability, even in glasses with a low incidence of surface defects, including pull-ups or pull-downs that are conventionally believed to be substantially free of surface defects (e.g., Fusion stretch) glass sheet. In some embodiments, when the cladding layers 104a and 104b are etched away by acid, the newly obtained surface is polished, smooth, and flat.

Various etchant chemicals, concentrations and treatment times can be used to achieve the ideal surface treatment level. For example, chemicals that can be used in the acid etching process include fluorine-containing aqueous media with at least one active glass etching compound, such as but not limited to HF, HF and one or more of HCl, HNO ₃ and H ₂ SO ₄ , ammonium difluoride, Combinations of sodium difluoride and other suitable compounds. If the concentration of HF is closely controlled, it is advantageous to maintain proper control of the thickness of the removed glass 106 by etching in a solution containing HF. An exemplary method for etching the glass layer is described in International Application No. PCT/US13/43561 filed on May 31, 2013, which is incorporated herein by reference in its entirety.

In some embodiments, a surface etching process of limited duration is required. In particular, the step of contacting the surface of the cladding layer of the laminated glass product 100 with the etching medium may be performed for a period of time, and the period of time does not exceed the effective removal of about 2 to about 80 μm (including all ranges and sub-ranges therebetween) The time required for the watch glass 106. For example, in some embodiments, the step of contacting the surface of the cladding layer of the laminated glass product 100 with the etching medium may be performed for a period of time, which does not exceed the effective removal of about 5 to about 50 μm or about 10 to about 10 μm. The time required for the 30 μm watch glass 106. In other embodiments, for example, about 3 μm, 10 μm, 15 μm, 20 μm, 40 μm, etc. are removed. In any particular case, the actual etching time required to limit glass removal may depend on the composition and temperature of the etching medium and the composition of the cladding layer. For example, in an etching composition containing HF, the etching rate will depend on the silicon dioxide content in the glass composition. In such embodiments, the larger the oxygen to silicon ratio, the slower the etching rate.

In some embodiments, each of the cladding layers 104a and 104b independently has a thickness of about 1 μm to about 100 μm, including all ranges and sub-ranges therebetween. For example, in some embodiments, the thickness is about 3 μm to about 75 μm, or about 5 μm to about 50 μm. In some embodiments, the acid etching process is designed to remove the surface glass not exceeding about 50 μm, the surface glass not exceeding about 30 μm, the surface glass not exceeding 15 μm, the surface glass not exceeding 5 μm, and the surface glass not exceeding about 5 μm. 2 μm surface glass, etc. In some embodiments, the glass cladding of about 20 μm to about 50 μm is removed, including all ranges and sub-ranges therebetween. For example, in some embodiments, about 30 μm to about 50 μm of glass cladding is removed.

In some embodiments, sanding and/or grinding are used to reduce at least one coating layer. In such embodiments, the composition used for the core 102 and the cladding layers 104a and 104b is precisely controlled to establish differential hardness selectivity. A laminated glass with a softer cladding layer and a harder core allows the cladding to be removed faster than the core layer 102. By adjusting the core-clad glass composition and core-clad thickness ratio, the hardness and elastic properties can be precisely controlled. The effect of mechanical polishing depends on the size and hardness of the glass, as well as the hardness and wear resistance of the polishing pad. In some embodiments, the polishing and/or lapping process is combined with chemical polishing (a process called chemical mechanical polishing (CMP)). In such embodiments, the combined process can provide a flat and smooth surface for the information recording medium. Generally speaking, in some embodiments, etching is more preferable than a grinding/grinding process because etching produces an ultra-smooth glass surface without exposing the glass to rough polishing and grinding processes.

Relative to the reduction phase, the material removal rate of 106 depends on certain factors, such as the applied pressure and relative speed, the thickness (106) of the layer to be removed, time, and so on. In tribology, under sliding or abrasive wear conditions, the volume of the reduced material is inversely proportional to the hardness of the material, as shown in the following formula (I), where V is the removed volume, L is the load on the sample, and S is Relative to the sliding distance, H is the hardness of the relevant material, and k _w is the wear coefficient.

In formula (I), the hardness ( H ) of the relevant material refers to the value obtained using standard test protocols (for example, Mohs hardness test, Vicker hardness, impact resistance, micro-indentation).

In some embodiments, the core 102 is composed of a first glass component, and at least one cladding layer (104a and/or 104b) is composed of a second glass component, and the first glass component and the second glass component are different chemical components . In such embodiments, the first glass composition has a first hardness value, and the second glass composition has a second hardness value. In some embodiments, the first hardness value is greater than the second hardness value. For example, in such embodiments, the difference in hardness is about 3% to about 50%, including all ranges and subranges therebetween. For example, in some embodiments, the difference in hardness is at least 3%, at least 5%, at least 10%, or at least 20%. In some embodiments, the first hardness value is about 3% to about 50% greater than the second hardness value. In some embodiments, the first hardness value is about 5%, about 10%, about 15%, about 20%, about 30%, etc., than the second hardness value.

)來計算。熱擴散係數(α) 量測自材料的熱端至其冷端的傳熱速率。雷射閃光分析可用於量測玻璃成分的熱擴散係數。材料的比熱是將材料的一個單位量的溫度提高一個單位溫度所需的能量。可使用示差掃描量熱法(DSC)來量測比熱容(c_p )。Thermal conductivity is a useful design parameter for the heat transfer rate of materials, where low thermal conductivity materials have lower heat transfer rates than high thermal conductivity materials. Thermal conductivity (λ) can be obtained by multiplying the material's thermal diffusivity by its density ( ρ ) and multiplying by its specific heat capacity (

) To calculate. The thermal diffusivity ( α) measures the rate of heat transfer from the hot end of a material to its cold end. Laser flash analysis can be used to measure the thermal diffusivity of glass components. The specific heat of a material is the energy required to increase the temperature of a unit amount of the material by a unit temperature. Differential scanning calorimetry (DSC) can be used to measure the specific heat capacity (c _p ).

In some embodiments, the core 102 is composed of a first glass component, and at least one cladding layer (104a and/or 104b) is composed of a second glass component, and the first glass component and the second glass component are different chemical components . In such embodiments, the first glass composition has a first thermal conductivity, and the second glass composition has a second thermal conductivity. In some embodiments, the value of the first thermal conductivity is greater than the value of the second thermal conductivity. For example, in some embodiments, the thermal conductivity difference is about 3% to about 50%, including all ranges and sub-ranges therebetween. For example, in some embodiments, the thermal conductivity difference is at least 3%, at least 5%, at least 10%, or at least 20%. In some embodiments, the first thermal conductivity value is about 3% to about 50% greater than the second thermal conductivity value. In some embodiments, the first thermal conductivity value is greater than the second thermal conductivity value by about 5%, about 10%, about 15%, about 20%, about 30%, etc.

According to various embodiments described herein, the glass substrate is a magnetic disk configured as a hard disk drive. The glass substrate has an information recording medium suitable for depositing information (for example, a coating or thin film, such as highly ordered L10 FePtX). -Y nanoparticle film) at least one surface. After the recording medium is deposited on the glass substrate, the information is recorded on the medium using a magnetic recording head that is separated from the surface of the magnetic disk by about 10 nm or less (flying height). According to various embodiments described herein, the glass substrate has at least one surface that is substantially flat, with a total thickness variation of less than about 1 to 5 microns, including all ranges and sub-ranges therebetween, which are less than the flying height, and are therefore suitable for Record the manufacturing process.

According to various embodiments described herein, a glass substrate with a suitable surface for recording the process is obtained from a laminated glass article having two cladding layers surrounding the core layer 102. One or both of the cladding layers are partially or completely reduced to obtain a flat surface. When one cladding layer is completely reduced, the core 102 and the opposite cladding layer remain. When the two cladding layers are completely reduced, the core 102 remains. In either case, the reduction of the cladding layer produces a substantially flat surface suitable for the substrate and recording process.

According to various embodiments described herein, a laminated glass article includes at least one cladding layer (104a and/or 104b) and a core layer 102, the at least one cladding layer includes a first glass component, and the core layer 102 includes a second glass Composition, the second glass composition is a different chemical composition from the first glass composition. The first glass component and the second glass component are suitable for the production of laminated glass products through the laminating fusion method, and the first glass component and the second glass component have different material hardness, different thermal conductivity and/or different chemical durability . Therefore, when the laminated glass article is subjected to a reduction process such as acid etching, the thickness of the cladding layer(s) will be reduced at a faster rate than the thickness of the core 102. Laminated glass products are formed by a fusion method that forms an outer cladding layer at the same time as the inner core 102, and the core is protected from airflow and surface temperature modulation that can cause thickness changes and warping by the cladding layer.

According to various embodiments described herein, the core layer 102 will have two opposing main surfaces (a first surface and a second surface), which are substantially flat and suitable for substrate and recording processes. The glass composition of the cladding layers 104a and 104b and the core 102 are selected according to different characteristics such as hardness, thermal conductivity, and chemical durability. In such embodiments, the cladding layers 104a and 104b shrink at a faster rate than the core 102, which results in a glass substrate with two substantially flat surfaces suitable for substrate and recording processes.

The above content is provided for the purpose of illustration, explanation and description of the embodiments of this application. Modifications and adaptations to these embodiments are obvious to those familiar with the art, and can be made without departing from the scope or spirit of the application. All such modifications are intended to be covered by the request below.

Although the subject matter has been described according to exemplary embodiments, it is not limited thereto. On the contrary, the accompanying claims should be interpreted broadly to include other variations and embodiments that can be made by those familiar with the technology.

100: laminated glass products 101a: Laminated glass substrate 101b: Laminated glass substrate 101c: Laminated glass substrate 101d: Laminated glass substrate 102: Core 104a, 104b: cladding layer 106: component symbol 200: Laminated fusion stretching equipment 202: upper isopipe 204: Lower equal pressure pipe 206: Molten glass coating composition 208: Molten glass core composition 210,212: Slot 216, 218, 222, 224: outer forming surface 220: root

Figure 1A schematically depicts a cross-section of a laminated glass article according to some embodiments described herein. Figure 1B schematically depicts the laminated glass product of Figure 1A, in which there is a noticeable surface thickness change on the opposite outer covering surface. Figure 1C schematically depicts a cross-section of a laminated glass product according to some embodiments described herein, wherein there is a noticeable surface thickness change on the outer cladding surface thereof.

Fig. 2 schematically depicts an embodiment of a fusion stretching method for manufacturing the laminated glass product of Fig. 1A.

Figure 3A schematically depicts a cross-section of a laminated glass substrate according to some embodiments described herein. Figure 3B schematically depicts a cross-section of a laminated glass substrate according to some embodiments described herein. Figure 3C schematically depicts a cross-section of a laminated glass substrate according to some embodiments described herein. Figure 3D schematically depicts a cross-section of a laminated glass substrate according to some embodiments described herein.

Domestic deposit information (please note in the order of deposit institution, date and number) no Foreign hosting information (please note in the order of hosting country, institution, date, and number) no

100: laminated glass products

102: Core

104a, 104b: cladding layer

Claims (20)

A method of preparing a glass substrate for an information recording medium includes the following steps: Providing a laminated glass product including a first outer cladding layer and an inner core layer, wherein the first outer cladding layer is in contact with and adjacent to a first surface of the core layer; and A thickness of the first coating layer is reduced to obtain the glass substrate with at least one flat surface. The method according to claim 1, wherein the laminated glass product includes a second outer cladding layer, and the second outer cladding layer is in contact with and adjacent to a second surface of the core layer. The method according to claim 2, wherein the core layer includes a first glass composition, and the first outer cladding layer and the second outer cladding layer include a second glass composition different from the first glass composition . The method according to claim 2, wherein the laminated glass article is prepared using a fusion method. The method of claim 1, wherein the at least one flat surface has a total thickness variation of less than about 1 to 5 microns. The method of claim 1, wherein the first outer cladding layer is reduced so that the at least one flat surface is the first surface of the core layer. The method according to claim 3, wherein a first hardness value of the first glass component is greater than a second hardness value of the second glass component. The method according to claim 7, wherein the first hardness value is about 5% to 10% higher than the second hardness value. The method of claim 1, wherein the laminated glass article is about 0.3 to 1.0 mm thick, and the reduced thickness of the at least one cladding layer is about 30 to 50 microns. The method according to claim 3, wherein a first thermal conductivity value of the first glass component is greater than a second thermal conductivity value of the second glass component. The method of claim 10, wherein the first thermal conductivity value is about 5% to 10% higher than the second thermal conductivity value. The method of claim 3, wherein a first weight loss rate of the first glass component is slower than a second weight loss rate of the second glass component. The method according to claim 1, wherein the reducing step includes grinding, grinding, etching or polishing. The method of claim 12, wherein the reducing step includes an acid etching solution. The method according to claim 1, wherein the at least one flat surface has a roughness parameter Ra of about 0.2 to 1 nm. The method according to claim 1, wherein the at least one flat surface has a roughness parameter Ra less than 0.2 nm. The method according to claim 2, wherein the thickness of each of the first outer cladding layer and the second outer cladding layer is reduced to obtain the glass substrate. A glass substrate prepared according to the method described in claim 1. The glass substrate according to claim 18, wherein the at least one flat surface has a total thickness variation of about 1 to 5 microns. A hard disk drive including the glass substrate according to claim 18.

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