JPH0522288B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magnetic disk used in a magnetic disk device.

(Prior Art and its Problems) Conventionally, magnetic disks have been used with an Al alloy substrate, a magnetic film formed thereon, and a protective film further formed thereon as required. In addition to Al alloys, there have also been reports of laboratory use of ceramic substrates mainly made of glass or aluminum oxide as substrate materials. However, none of them exceeds Al alloy substrates in terms of thermal conductivity, and for this reason, Al alloy substrates have been used in all commercial products. This is because in magnetic disk drives, the servo surface that stores servo information and the data surface that stores data information are generally separated, so if there is a temperature difference between the two, a finite amount of off-track will occur due to thermal expansion. This is because the lower the thermal conductivity of the magnetic disk, the greater the temperature difference between the center and the outer periphery of the magnetic disk, or the larger the difference in temperature between the center and the outer periphery of the magnetic disk, or the larger the difference in temperature between the center and the outer periphery of the magnetic disk, or the larger the difference in temperature between the center and the outer periphery of the magnetic disk. In a magnetic disk device, the temperature difference becomes large for each magnetic disk, and the amount of off-track becomes large due to the difference in thermal expansion, making it impossible to increase the track density.

On the other hand, the Al alloy substrate itself was too soft to withstand wear from the magnetic head, and had the disadvantage of lacking reliability.

(Objective of the Invention) The object of the present invention is to reduce the amount of off-track caused by temperature distribution within a magnetic disk device and to achieve high reliability by using a hard material with high thermal conductivity as the substrate material. Our goal is to provide magnetic disks.

(Structure of the Invention) The magnetic disk of the present invention has a thermal conductivity of 0.05 cal/
It is characterized by having a ceramic substrate with a magnetic field of cm/sec/°C or higher and a magnetic film formed thereon with a coercive force of 300 Oe or higher.

(Detailed Description of Configuration) The present invention will be described below with reference to the drawings.
Fig. 1 shows the configuration of the present invention, and a in Fig. 1 shows the structure of the present invention.
An example is shown in which a magnetic film 2 having a coercive force of 300 Oe or more is formed on a ceramic substrate 1 having a thermal conductivity of 0.05 cal/cm/sec/°C or more. Figure b shows this magnetic film 2.
Figure c shows a magnetic disk on which a protective film 3 is formed, and figure d shows a magnetic disk with a lubricating film 4 on the protective film 3. 4 are shown respectively.

Figure 2 shows another configuration of the present invention, and Figure a shows a gap between a ceramic substrate 1 having a thermal conductivity of 0.05 cal/cm/sec/°C or more and a magnetic film 2 having a coercive force of 300 Oe or more. A magnetic disk with a base film 5 provided thereon,
Figure b shows the configuration of figure a, with a protective film 3 on top of the magnetic film 2.
Figure c shows a magnetic disk with a lubricating film 4 on the protective film 3 in the configuration shown in figure b, and figure d shows a magnetic disk with the lubricating film 4 on the magnetic film 2 in the configuration shown in figure a. A magnetic disk provided with a membrane 4 is shown in each case.

Here, the necessary requirements for the constituent elements of the present invention and an example of typical materials are shown below.

The ceramic substrate 1 has a thermal conductivity of
0.05cal/cm/sec/℃ or more, hardness of 600 or more in terms of Vickers value, surface roughness of 0.05μm or less, pore diameter
It needs to be 0.5 μm or less. In particular, regarding thermal conductivity, for example, in a magnetic disk device consisting of 8 disks with a radius l, if the bottom layer (1st disk) is a servo disk, the temperature difference ΔT with the middle layer (4th to 5th disks) The off-track amount Δl of the outermost track is Δl=α・ΔT・l, where α is the thermal expansion coefficient of the disk substrate.In fact, the thermal conductivity of conventional aluminum alloys is 0.2 cal/cm/sec/°C, and l= At 10 cm, ΔT was 1°C. Using α=25×10 ^-6 /℃ as the thermal expansion coefficient of aluminum alloy, Δl2.5μm
The track density is approximately 1000 TPI (Tracks Per
Inch) becomes difficult to exceed. On the other hand, 0.05cal/
When using a ceramic substrate with cm/sec/℃,
The temperature difference ΔT' was approximately 5°C. α of ceramic substrate can be adjusted by composition and is usually 5×10 ^-6 /℃
Δl≦2.5μm, which is lower than that of conventional aluminum alloys. In order to further reduce Δl, it is necessary to increase the thermal conductivity and reduce the temperature difference ΔT, which is an important point in making the temperature of the entire magnetic disk device uniform. It is. As another means of reducing Δl, it is necessary to reduce the coefficient of thermal expansion α, but α
Even if it becomes zero, as long as the temperature difference ΔT is finite, a difference in thermal expansion will occur in the arm supporting the magnetic head, which is undesirable. Therefore, it is fundamental to increase the thermal conductivity and reduce the temperature difference. If Δl is reduced in this way, it becomes possible to increase the track density by that amount.

As for hardness, a Vickers hardness of 600 or higher is required to withstand contact wear with a magnetic head (conventional aluminum alloys have a Vickers hardness of 100 to 200). Defining the surface roughness and pore diameter is an essential condition for making the characteristics of the magnetic film uniform and ensuring mechanical durability. If the ceramic substrate is prone to pores due to the manufacturing method, a base film 5 may be provided in order to reduce or eliminate the pore diameter. Materials that simultaneously satisfy the above conditions for ceramic substrates are quite limited, but ceramics containing silicon carbide as the main part are suitable;
Silicon carbide ceramics containing 10% by weight, 1.3 to 13% by weight of tungsten silicide, or 5 to 12% by weight of erbium oxide, metal elements (light metal elements, transition metal elements, or rare earth metal elements) themselves or their compounds (oxides, Particularly suitable are silicon carbide ceramics containing 1 to 5% by weight of at least one type of nitride or boride. In addition, in the former type of silicon carbide ceramics containing silicon-tungsten silicide, if the silicon content is less than 5% by weight, dense ceramics cannot be obtained, and if the silicon content exceeds 10% by weight, corrosion resistance, mechanical strength, and polished surface deteriorate. If the content of tungsten silicide is less than 1.3% by weight, there is a problem with oxidation resistance, and if it exceeds 13% by weight, the difference in thermal expansion coefficient with silicon carbide becomes noticeable. This takes into consideration the fact that the oxidation resistance has deteriorated. Furthermore, in the latter type of silicon carbide ceramics containing erbium oxide-metallic elements (or their compounds), dense ceramics were not obtained when the erbium oxide content was less than 5% by weight, and when it exceeded 12% by weight. The transverse rupture strength and impact value decreased; when the content of metal elements or their compounds was less than 1% by weight, no significant improvement in thermal conductivity was observed; and when the content exceeded 5% by weight, the transverse rupture strength and impact value decreased. This takes into account that the impact value has decreased.

The base film 5 may be an oxide or nitride such as aluminum oxide, silicon oxide, silicon nitride, or aluminum nitride formed by vapor deposition, sputtering, or plasma CVD, or a nonmagnetic material such as Cr, Ti, Mo, W, etc. Hard cure metals or alloys mainly composed of these metals, oxide films mainly composed of silicon oxide, aluminum oxide, etc. formed by spin coating and baking, or organic materials such as resist, polyimide, epoxy, etc. A thin film etc. that has been prepared is suitable.

The magnetic film 2 has a long diameter formed by a coating method.
Needle-like or grain-like γ-Fe ₂ O ₃ , Co of 0.5 μm or less
Deposited γ-Fe ₂ O ₃ , Co-doped γ-Fe ₂ O ₃ , or major axis
A thin film with a thickness of several microns or less made of a magnetic powder such as a plate-shaped Ba-ferry of 0.5 μm or less and hardened with a resin together with non-magnetic particles such as SiO ₂ or Al ₂ O ₃ , or Co formed by the plating method. -P alloy, CO-Ni-P alloy,
Co-Ni-Mn-P alloy, Co-Ni-Mn-Re-P
Co-containing thin films of 1.0 μm or less in thickness, such as alloys, γ-Fe ₂ O ₃ formed by vapor deposition or sputtering,
γ-Fe ₂ O ₃ , CoO-Co containing oxides such as Co and Cu
Mixture, Co, Fe nitride, Co-Ni alloy, Co-
Contains Co such as Pt alloy, Co-Cr alloy, Co-P alloy, Co-Re alloy, Co-rare earth alloy, or a mixture of these alloys, as well as other third and fourth elements. A thin film or a thin film of 1.0 μm or less in thickness made of an alloy containing Fe such as FeNd is suitable.

The protective film 3 may be an oxide film with a thickness of 0.1 μm or less mainly composed of silicon oxide or aluminum oxide formed by spin coating, silicon oxide or aluminum oxide formed by evaporation/sputtering or plasma CVD, Oxide film or nitride film with a thickness of 0.1 μm or less, mainly composed of silicon nitride, aluminum nitride, etc., or a single substance or alloy with a thickness of 0.1 μm, mainly composed of non-magnetic metals such as C, Cr, Mo, W, Rh, etc. The following thin films are suitable.

As the lubricant film 4, the well-known lubricant KRYTOX or
A fluorocarbon thin film typified by VYDAX (all trade names of DuPont, USA) is suitable.

Next, specific examples of the present invention will be described.

(Example 1) A product consisting of 70% by weight of silicon carbide powder and 30% by weight of carbon powder was selected at a weight ratio of 10% of cellulose and 4% of tungsten powder, respectively, and wax was added and granulated at a pressure of 1000Kg/ ^cm2. Outer diameter 210mm inner diameter 50
Shaped into a disc shape with a thickness of 2 mm, then placed in a vacuum
Temporary firing was performed at 700℃. 15 g of silicon powder was placed on this calcined body, and the temperature was raised to 1500° C. over 1 hour under a reduced pressure of 0.1 Torr, and then held for 3 hours to perform reaction sintering. The composition of the reaction sintered body thus obtained was 6% by weight of silicon, 5% by weight of tungsten silicide, and the balance was silicon carbide, and the thermal conductivity was 0.14 cal//.
cm/sec/°C, thermal expansion coefficient 4.3×10 ^-6 /°C, Vickers hardness 1.800, and pore diameter 0.5 μm or less. The surface of this sintered body was polished with diamond granules of 0.1 μm to give a finished surface roughness of 0.05 μm or less, which was used as a disk substrate. Next, as a representative coating method, γ-Fe ₂ O ₃ needle-shaped particles with a major diameter of 0.2 μm were deposited on this disk substrate.
Al ₂ O ₃ fine particles with a diameter of 0.2 μm are mixed with a dispersant and an epoxy resin, and the thickness is coated by spin coating.
A 0.7 μm magnetic film was formed to form a magnetic disk. The coercive force Hc of the magnetic film after coating was 350 Oe.

(Example 2) A disk substrate was produced in the same manner as in Example 1. However, the substrate material was changed as follows. Cellulose and wax were added to a silicon carbide powder consisting of 90% by weight, 3% by weight of aluminum oxide powder and 7% by weight of erbium oxide powder as oxides of metal elements, and granulated at a pressure of 1000Kg/ ^cm2. Outer diameter
Shaped into a disc shape of 210mm inner diameter 50mm thickness 2mm,
Next, it was pre-baked at 700°C in vacuum. The temperature of this calcined body was raised to 1500° C. over 1 hour under a reduced pressure of 0.1 Torr, and then the temperature was maintained for 3 hours to perform sintering. The composition of the reaction sintered body thus obtained was 3% by weight of aluminum oxide, 7% by weight of erbium oxide, and the balance was silicon carbide, and the thermal conductivity was 0.28 cal/cm/sec/°C. Expansion coefficient is 4.4
×10 ^-6 /℃, Bitkers hardness is 2000, pore diameter is
It was 0.5 μm or less. The surface of this sintered body is 0.1μm
Polished with diamond granules to a surface roughness of 0.05μm
The following is a finished disk substrate.

Next, Co-coated γ-Fe ₂ O ₃ acicular particles with a major diameter of 0.2 μm were deposited on this disk substrate as a representative coating method.
Mix Al ₂ O ₃ fine particles with a diameter of 0.2 μm with a dispersant and an epoxy resin, and apply the mixture to a thickness of 0.7 μm using a spin coating method.
A magnetic film of KRYTOX is formed on this surface.
was applied as a lubricant, and in this way a magnetic disk was made. The coercive force of this magnetic film was 600 Oe.

(Example 3) The disk substrate used in Example 1 was used. However, before polishing with diamond granules, a 10 μm Al ₂ O ₃ film was formed on the sintered body as a base film by sputtering, and then polished with 0.1 μm diamond granules. As a result, the surface roughness was approximately 0.01 μm, and a disk substrate with excellent surface properties was obtained. On top of this, a 0.15 μm Fe ₃ O ₄ film, representative of a thin magnetic material, is formed using a sputtering method, and then gradually oxidized in the atmosphere at 300°C to convert it into a γ-Fe ₂ O ₃ film, creating a magnetic film and forming a magnetic disk. And so. By adding 3.0% by weight and 1.8% by weight of Cu and Co, respectively, the coercive force of this magnetic film became 600 Oe.

(Example 4) A magnetic film was formed using the same manufacturing process as that used in Example 3, and SiO ₂ was added as a protective film on top of the magnetic film.
was formed to a thickness of 0.05 μm using the sputtering method to form a magnetic disk.

(Example 5) A protective film was formed using the same manufacturing process as in Example 4, and a lubricant was added on top of this.
KRYTOX was applied to create a magnetic disk.

(Example 6) A magnetic film was formed using the same manufacturing process as in Example 3, and a lubricant was added on top of this.
KRYTOX was applied to create a magnetic disk.

(Example 7) The disk substrate used in Example 2 was used. However, before polishing with diamond granules, a 5 μm thick W film was formed on the sintered body as a base film by sputtering.
After this, it was polished with 0.1 μm diamond granules.
As a result, the surface roughness was approximately 0.02 μm, and a disk substrate with excellent surface properties was obtained. Cobalt sulfate, nickel sulfate, sodium hypophosphite, sodium malate, sodium succinate,
The sample was immersed in a plating bath containing sodium malonate and ammonium sulfate, and a magnetic film made of Co--Ni--P alloy was formed by electroless plating to a thickness of 0.05 μm.
A 0.1 μm SiO ₂ film was formed on this by spin coating, and then KRYTOX was applied as a lubricant to form a magnetic disk. The coercive force of this magnetic film was 600 Oe.

(Example 8) Using the disk substrate used in Example 7, 0.5 μm of NiFe alloy (Fe18% by weight) was applied on it, and then
A CoCr alloy (20% by weight of Cr) was formed using a 0.2 μm sputtering method to form a magnetic film and a magnetic disk. CoCr
The coercive force of the film in the direction perpendicular to the disk surface was 300 Oe.

(Example 9) A magnetic film was formed using the same manufacturing process as that used in Example 8, and SiO ₂ was added as a protective film on top of the magnetic film.
was formed to a thickness of 0.05 μm using the sputtering method to form a magnetic disk.

(Example 10) A protective film was formed using the same manufacturing process as in Example 9, and VYDAX was applied as a lubricant to prepare a magnetic disk.

(Example 11) A magnetic film was formed using the same manufacturing process as in Example 8, and VYDAX was applied as a lubricant to prepare a magnetic disk.

(Comparative Example) Al-Mg alloy 5086 was processed into a disk shape with an outer diameter of 210 mm, an inner diameter of 50 mm, and a thickness of 1.9 mm, and the surface roughness was finished to about 0.05 μm using a diamond lathe to obtain a disk substrate. On top of this, a magnetic film similar to that in Example 1 was formed using the same procedure, and KRYTOX was added as a lubricant.
was coated to make a magnetic disk. The coercive force of the magnetic film was 350 Oe as in Example 1.

Select eight magnetic disks each from Examples 1 to 11 and Comparative Example, load them into a magnetic disk device, write a servo pattern on the bottom layer (first disk), and write the servo pattern on the middle layer (fourth to fifth disk). When we measured the amount of positional deviation Δl immediately after turning on the power and after a 30-minute seek test, it was found that Δl<1 μm in all cases using the magnetic disks of Examples 1 to 11, whereas Δl was 1.5 μm in the comparative example. In the contact start step test, the former examples of the present invention had no accidents even after 30,000 passes, while the latter comparative example had a crash accident after 5,000 passes.

(Effects of the invention) As shown in the above examples and comparative examples of the present invention,
Compared to conventional magnetic disks, the present invention has the following advantages: (1) Since ceramics with high thermal conductivity are used, the temperature difference between the magnetic disks is small, which reduces the amount of off-track and enables high track density. .

(2) Since ceramics, which are much harder than conventional ones, is used as the substrate material, it has high durability in contact start/stop tests, and therefore has high long-term reliability.

It has extremely useful features in practice.

Note that such effects of the present invention are not limited to the above-mentioned materials or examples using the materials,
It is clear that any magnetic disk that satisfies the conditions set forth in the claims can be provided.

[Brief explanation of the drawing]

Figure 1 a, b, c and d, and Figure 2 a,
b, c, and d are diagrams showing configuration examples of the present invention, in which 1...ceramic substrate, 2...magnetic film, 3...
. . . protective film, 4 . . . lubricating film, 5 . . . base film.

Claims (1)

[Claims] 1. 5 to 10% by weight of silicon, 1.3 to 1.3% of tungsten silicide
13% by weight, the balance is silicon carbide, and the thermal conductivity is
Ceramic substrate of 0.05cal/cm/sec/℃ or more,
1. A magnetic disk comprising a magnetic film having a coercive force of 300 Oe or more formed thereon. 2. The magnetic disk according to claim 1, wherein a base film is formed between the ceramic substrate and the magnetic film. 3. The magnetic disk according to claim 1, further comprising a protective film on the magnetic film. 4. The magnetic disk according to claim 1, which has a lubricating film on at least its surface. 6. The composition of the ceramic substrate is 5 to 12% by weight of erbium oxide, at least one metal element (light metal element, transition metal element, or rare earth metal element) itself or a compound thereof (oxide, nitride, or boride). 1 to 5% by weight. 5. The magnetic disk according to claim 1, wherein the remaining main portion is made of silicon carbide.