JPH0740350B2 - Magnetic disk substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention uses a partially stabilized zirconia substrate as a support for a magnetic disk to obtain high strength and high toughness characteristics, and a magnetic recording medium of 100 to 400 is formed on this substrate. The present invention relates to a magnetic disk substrate having long-term reliability that does not deteriorate the excellent initial characteristics of the substrate itself even when formed at ° C, and further relates to a magnetic disk substrate that can eliminate void defects.

[Prior Art and Problems] A magnetic disk device plays a central role in information storage in a computer information processing system. However, recently, this magnetic recording tends to have a higher density and a larger capacity. ,
By using thin film technology such as sputtering and plating, the magnetic recording medium is made thinner and the surface accuracy is improved, and the demand is being met.

An aluminum alloy is used for a substrate on which such a magnetic recording medium is formed, and an alumite layer obtained by oxidizing the surface of the substrate is coated with a thickness of about 2 μ. This alumite layer increases the hardness of the substrate surface. However, since the thickness of this hard alumite layer is small and the aluminum alloy and alumite have different thermal expansion coefficients, the substrate is likely to be distorted as the substrate temperature rises.
That is, when a magnetic recording medium is formed on a substrate by sputtering, sputtered particles and electrons collide with the substrate, and the collision energy increases the substrate temperature,
Further, in the case of a magnetic recording medium made of γ-Fe ₂ O ₃ , it is usually heat-treated at 300 ° C. or higher,
As the temperature applied to the substrate rises, the aluminum substrate is likely to be distorted. As a result, when a magnetic recording medium is formed on the aluminum substrate and used for high-density magnetic recording, accurate writing and reading are performed. There was a problem that it was difficult to do.

Further, the magnetic disk device arranges a plurality of magnetic disks on the same rotary shaft and rotates them at a high speed of about 1000 to 3000 rpm to perform read and write data processing. If the substrate is formed of, the substrate itself tends to expand due to centrifugal force, and accurate writing and reading suitable for high-density magnetic recording cannot be performed. Therefore, it is desired to solve such writing error and reading error. Was there.

In addition, since the aluminum alloy magnetic disk substrate usually has 100 or more voids of 2 to 3μ over the entire surface of one side of the substrate even if the surface is anodized, the magnetic disk for high density recording is For the disk device, there is also a problem that accurate writing and reading cannot be performed due to this void defect, and a magnetic disk substrate material with few void defects has been desired.

In addition to the alumite treatment, it has been proposed to subject the surface of an aluminum substrate to a Ni-P undercoat treatment by plating, but the production yield is poor due to void defects and uneven plating, and practical application is difficult.

In order to eliminate all the above-mentioned difficulties, a ceramic disk substrate has been attracting attention. According to this, no distortion occurs in sputtering or heat treatment, and the elongation generated in the substrate itself against the centrifugal force applied to the substrate. Becomes smaller,
Further, a high-density magnetic recording substrate having no void defects on the substrate surface can be used.

Among such ceramic substrates, partially stabilized zirconia, in particular, has high strength and high toughness characteristics, so cracks and damages do not occur easily, and the extremely high reliability required for magnetic disks is sufficiently satisfied. It is what makes me.

However, this partially stabilized zirconia (Partially
Stabilized Zirconia (hereinafter abbreviated as PSZ) 100 to 150 ° C when forming a magnetic recording medium by a thin film forming means such as sputtering in a magnetic disk substrate using a sintered body.
As a result, the tetragonal ZrO ₂ phase (hereinafter abbreviated as t-ZrO ₂ ) in the sintered body becomes a monoclinic ZrO ₂ phase (hereinafter m-
This causes a phase transition to ZrO ₂ (abbreviated as ZrO ₂ ), which causes deterioration of high-strength and high-toughness characteristics, and also poses a problem of impairing initial high reliability. In particular, raising the substrate temperature for sputtering can increase the deposition rate,
In addition, when forming the γ-Fe ₂ O ₃ film, if the heat treatment temperature (300 ° C or higher) after film formation is high, excellent magnetic properties can be obtained, so a PSZ magnetic disk substrate with excellent heat resistance is desired. .

[Object of the Invention]

Therefore, the present invention has been completed in view of the above circumstances, and an object of the present invention is to improve the substrate's original high temperature even when the substrate is heated to a desired temperature when the magnetic recording medium is formed on the PSZ magnetic disk substrate by the thin film forming means. An object of the present invention is to provide a magnetic disk substrate that is reliable for a long period of time without impairing the strength and high toughness characteristics.

Another object of the present invention is to provide a magnetic disk substrate capable of forming a magnetic recording medium having excellent magnetic characteristics on the substrate at a high speed.

Still another object of the present invention is to provide a magnetic disk substrate capable of high density recording due to various characteristics such as super-precision workability of PSZ itself and excellent shape accuracy.

[Means for solving problems]

According to the present invention, Y ₂ O ₃ is contained in the range of 1 to 6 mol% as a stabilizer, is mainly composed of tetragonal ZrO ₂ phase, has an average crystal grain size of 0.15 to 0.5 μm, and has a theoretical density ratio of A magnetic disk substrate is composed of a partially stabilized zirconia sintered body of 95% or more.

Zirconia (ZrO ₂ ) sintered body can be a PSZ sintered body or a stabilized zirconia sintered body depending on the addition amount of sintering aids such as Y ₂ O ₃ , MgO, CaO, CeO ₂ etc. Is known,
According to the present invention, Y ₂ O ₃ is added within the range where a PSZ sintered body can be obtained, and the average crystal grain size of this PSZ sintered body is set to 0.15 to 0.5 μm based on the production method described later, and theoretically. Density ratio 95%
The above is important. When the PSZ sintered body was out of this set range, it was found that when the PSZ sintered body was placed in a temperature atmosphere of 100 to 400 ° C., the phase transition of t-ZrO ₂ in the sintered body gradually changed to m-ZrO ₂ .

It is known that this phase transition proceeds from the surface of the PSZ sintered body to the inside thereof. Therefore, in the examples described later, the amount of m-ZrO _{2 on the} surface of the sintered body was measured by an X-ray diffraction method. , And the degree of phase transition.

In the present invention, it is desirable to specify the amount of Y ₂ O _{3 to be} used in setting the average crystal grain size and the theoretical density ratio as described above, and the amount is set to 1 to 6 mol% as the optimum condition and 2 to 4 mol%.
It was confirmed by various experiments by the present inventor that the effect of the present invention becomes remarkable when it is set to be contained in

Further, in the present invention, PSZ mainly composed of t-ZrO ₂
It is desirable that the sintered body contains 10% by weight or less of m-ZrO ₂ .

That is, m-ZrO ₂ undergoes a phase transformation upon heating of the substrate and changes to t-ZrO ₂ so that it contracts, causing distortion in the magnetic disk substrate, and as a result, when used for high density magnetic recording,
There is a problem that it is difficult to write and read accurately.

As a result of repeated experiments, the present inventors have found that the above problems can be solved by setting the amount of m-ZrO ₂ to 10% by weight or less.

In addition, the PSZ sintered body according to the present invention has a t
It is difficult to separate −ZrO ₂ and cubic (Cubic) ZrO ₂ , but Cubic
It also includes one that can confirm the presence of ZrO _{2 in} a slight amount.

Regarding the amount of m-ZrO ₂ , RC Garvie and PSNicho
lson's J. Amer. Ceram. Soc., vol.55, No.6, P303-305 (197
It was based on the X-ray diffraction measurement method described in 2).

That is, the diffraction peak intensities of m-ZrO ₂ are Im (111), Im (ll
), Cubic ZrO ₂ diffraction peak intensity is Ic (111), t−ZrO ₂
When the diffraction peak intensity of is It (111), As a result, the amount of m-ZrO ₂ (% by weight) was determined. It should be noted that although it (111) was not included in the above paper, it was included in this measurement method. The measuring method was also used in Examples described later.

Thus, the heat-resistant magnetic disk substrate of the present invention can be used as a support for a magnetic disk, and a glaze layer can be formed on this support, or a SiC layer by a thin film forming technique such as CVD, PVD, or a molten salt method, Si. ₃ N ₄ layer, BN layer, AlN layer, Al ₂ O ₃ layer, TiN
Layers, TiC layers, TiCN layers, B ₄ C layers, ZnC layers, and other coating layers can be formed to improve surface roughness and eliminate void defects. Furthermore, a high-density recording medium can be formed on it by a thin film forming means such as plating or sputtering.

Further, if the magnetic disk substrate of the present invention is manufactured by HIP processing, it becomes a disk substrate in which void defects are eliminated,
The recording medium can be directly formed on this substrate.

Next, the manufacturing method of the present invention will be described.

The ZrO ₂ raw material powder used in the present invention has an average particle size of 0.15 μm or less,
It is preferably 0.06 μm or less. Alternatively, zirconium hydroxide or the like may be changed to ZrO ₂ powder upon calcination. When this zirconium hydroxide (ZrO ₂ · xH ₂ O) is used, the primary particles of ZrO ₂ powder become larger as the calcination temperature increases, so the calcination temperature can be changed in the range of 900 to 1050 ℃. Has an average particle size of 0.02 to 0.1μ
m several ZrO ₂ powders are obtained.

The Y ₂ O ₃ powder should have an average particle size of 2 μm or less, preferably 1 μm or less.

Alternatively, Y ₂ O ₃ coprecipitated ZrO ₂ powder to which a predetermined Y ₂ O ₃ is added may be used, and when this powder is used, a mixture in which the Y ₂ O ₃ component and the ZrO ₂ component are more densely and uniformly distributed. Since it is in the state, there is an advantage that the crystal grain size of the sintered body is made uniform.

According to the present invention, Y ₂ O ₃ powder is added to ZrO ₂ powder so that the compounding ratio is 1 to 6 mol%, preferably 2 to 4 mol% in the total amount, and then mixed sufficiently to be uniform. This mixed powder is dried and granulated, and if necessary, pressed into a disk shape, and then pressure-sintered or pressureless-sintered at a temperature of 1500 ° C. or lower, preferably 1250 to 1500 ° C.

It is clear from the examples described later that the average crystal grain size in the sintered body increases as the firing temperature is increased. To keep the average crystal grain size at 0.5 μm or less, the firing temperature is set to 150 μm.
It is important to set below 0 ° C. Further, if the firing temperature is less than 1250 ° C., the bulk density of the sintered body tends to be small, and it becomes difficult to obtain the theoretical density ratio according to the present invention. Further, in order to improve the mechanical strength and the like of the sintered body, it is preferable that the average crystal grain size is as small as possible,
When the average crystal grain size of the sintered body is smaller than 0.15 μm, the sinterability is deteriorated, and there is a limit in obtaining particles having a smaller grain size. Therefore, the lower limit of the average crystal grain size of the sintered body is preferably 0.15 μm.

The magnetic disk substrate of the present invention can also be manufactured by HIP processing.

That is, Y ₂ O ₃ is added to the ZrO ₂ powder as described above and mixed sufficiently so as to be uniform. This mixed powder is dried and granulated to form a disk, and pre-baked. This pre-baking is generally carried out at a temperature of 1250 to 1500 ° C. for 1 to 4 hours. Next, the pre-baked body is HIP processed. Pre-baking is not essential, and the disk-shaped molded body can be sealed and subjected to HIP treatment.

The pre-baked body is installed inside the HIP device, and an inert gas is press-fitted therein and heated. At this time, generally, pressurization of 1500 to 2000 atm and heating to 1250 to 1500 ° C. are effective.

The thus-obtained PSZ magnetic disk substrate is used as a magnetic disk substrate by using polishing processing means such as lapping and polishing.

〔Example〕

 Examples will be described below.

(Example 1) Four types of calcination temperatures of zirconyl hydroxide were set within a temperature range of 900 to 1050 ° C, and four types of primary average particle diameters were 0.02μ.
A zirconia raw material powder having m, 0.05 μm, 0.06 μm, and 0.08 μm was used. Y ₄ O ₃ powder (average particle size 0.9 μm) was added to each of these 4 types of zirconia raw material powder so that the total amount was 3 mol%, and they were sufficiently mixed uniformly, and then dried and granulated, and then the donut was dried. Into a circular disc, and the compact was sintered under the firing conditions shown in Table 1.

With respect to the thus obtained sintered body, the bulk density, the theoretical density ratio, the average crystal grain size, and the amount of m-ZrO _{2 on the} surface of the sintered body were measured by the X-ray diffraction method.

Further, the sintered body was placed in a temperature atmosphere of 250 ° C. for 100 hours to measure the amount of increase in m-ZrO _{2 on the} surface of the sintered body. This 250 ° C. was selected because it is the temperature at which the transformation from t-ZrO ₂ to m-ZrO ₂ is most likely to occur.

The results are shown in Table 1.

As is clear from Table 1, in sample numbers 1, 5, 6, and 7, the average crystal grain size and the theoretical density ratio are within the range of the present invention.
Less m-ZrO ₂ amount of surface of the sintered body, and does not increase m-ZrO ₂ content of almost sintered body surface by heat treatment 250 ° C.,
In particular, it was not generated at all in sample numbers 1 and 5.

However, since the sample Nos. 2, 3, 4, and 8 have theoretical density ratios, and the sample Nos. 9, 10, 11, and 12 have average crystal grain sizes outside the scope of the present invention, the amount of m-ZrO _{2 on the} surface of the sintered body is It can be seen that the amount of m-ZrO _{2 on the} surface of the sintered body is remarkably increased by the heat treatment at 250 ° C.

For sample numbers 3, 4, and 6 with an average crystal grain size of 0.2 μm and sample numbers 1, 7, and 8 with an average crystal grain size of 0.3 μm, the larger the bulk density, the more It can be seen that the amount of m-ZrO ₂ is small.

Further, when the firing temperature and the average crystal grain size are plotted based on the results of this example, the results are as shown in FIG. 1, and the characteristic curve can be expressed as (a). According to this figure,
Generally, the average crystal grain size of the sintered body is determined by the firing temperature, and it is understood that the firing temperature of 1500 ° C. or less is important. From Table 1, when the firing temperature exceeds 1500 ° C., the PS of the present invention is irrelevant regardless of the size of the primary average particle diameter of zirconia powder.
It is also clear that a Z sintered body cannot be obtained.

Furthermore, in the table, it is also understood that, under the same firing conditions, the smaller the average primary particle size of the zirconia powder, the smaller the amount of m-ZrO _{2 and the} more PSZ sintered body that does not undergo phase transition due to heat treatment.

Example 2 Sample Nos. 13 to 21 were obtained by the same method as in Example 1 except that ZrO ₂ powder co-precipitated with Y ₂ O ₃ was used.

As is clear from Table 2, sample numbers 13,14,15,16,17,1
In No. 8, since the average crystal grain size and the theoretical density ratio are within the range of the present invention, there is no amount of m-ZrO _{2 on the} surface of the sintered body,
No m-ZrO ₂ was formed even by the heat treatment of.

However, since the sample Nos. 19, 20, and 21 have the average crystal grain size outside the range of the present invention, the heat treatment at 250 ° C.
It can be seen that −ZrO ₂ is significantly increased.

Further, when the firing temperature and the average crystal grain size are plotted based on the results of this example, the results are as shown in FIG. 2, and the characteristic curve can be expressed as (b). This figure also shows that the average crystal grain size of the sintered body is generally determined by the firing temperature, and that the firing temperature of 1500 ° C. or lower is important.

Furthermore, in the case of Example 1, although the bulk density becomes significantly smaller when the firing temperature is lowered, in this example, although it is related to the particle size of the zirconia particles, the bulk density, that is, the theoretical The density ratio can be improved.

As is clear from the above examples, according to the present invention, it is possible to provide a PSZ sintered body having long-term reliability while maintaining the initial high strength and high toughness characteristics.

(Example 3) ZrO ₂ powder co-precipitated with Y ₂ O ₃ (first average particle diameter 0.15 μm, Y ₂ O ₃ 3 mol
%), An organic binder of a wax emulsion was added, sufficiently mixed, and dried and granulated with a spray dryer. This powder is then hydraulically pressed (pressure 1.5t
on / cm ² ) donut-shaped disc (outer diameter 180 mm, inner diameter 52 mm,
A molded body having a thickness of 4 mm was obtained. This molded body was fired at a temperature of 1300 ° C. for 2 hours to obtain a disc-shaped fired product.

Then, pressurizing with Ar gas (2000 atm) for 1 hour at 1400 ° C for 1 hour
IP processing was performed to obtain a magnetic disk substrate.

When the bulk density, theoretical density ratio and average crystal grain size of this substrate were measured, it was 5.91 g / cm ³ , 98.3%, and <0.2 μm. Then, m-Zr on the surface of the sintered body was measured by X-ray diffraction.
When the amount of O ₂ was measured, it was not detected at all. 25 more
It was not detected at all even after heat treatment at 0 ° C for 100 hours.

Polishing is performed in the order of lapping and polishing, and the final product has an outer diameter of 130 mm, an inner diameter of 40 mm, and a thickness of 1.9 mm. Flatness 3 μm, surface roughness 0.01 Ra, coaxiality 10 μm, parallelism 10
A 5.25-inch magnetic disk substrate with an accuracy of μm was obtained.

The area of the substrate thus obtained was measured using an image analyzer (Luzex 500) and a metallurgical microscope (400x).
As a result of examining the voids over 8.0 × 10 ⁵ μm ² , there were no voids of 0.3 μm or more. Further, the amount of m-ZrO _{2 on the} surface did not exceed 10% by weight even by the above-mentioned polishing treatment.

〔The invention's effect〕

Generally, when forming a magnetic recording medium by sputtering, it is possible to increase the film formation rate by increasing the substrate temperature during sputtering, and the heat treatment temperature after film formation is high when forming the γ-Fe ₂ O ₃ film. The one with better magnetic properties can be obtained, but the Ni-P-primed aluminum substrate is 280 ℃.
This temperature is the limit because it exhibits magnetism, and the heat resistance limit of the alumite-treated substrate is about 350 ° C. at most.
On the other hand, the substrate of the present invention is further excellent in heat resistance, and a magnetic recording medium having excellent magnetic characteristics can be formed by high speed film formation.

Furthermore, since the magnetic disk substrate of the present invention has the effects described below, it is clear that it will be a more desirable substrate.

Since a magnetic disk is required to have a very high degree of reliability, cracks or damage should never occur. According to the substrate of the present invention, when the PSZ sintered body is used, the strength and toughness can be remarkably improved, the characteristics thereof are not deteriorated, and long-term reliability is sufficiently satisfied.

Even if a small amount of magnetism is present in the periphery of the substrate other than the magnetic recording medium, it may cause signal loss or noise, but the substrate of the present invention is non-magnetic and enhances the reliability of the magnetic disk device.

Due to its high rigidity, the substrate itself is less likely to be deformed when it is processed, and even if it is rotated at a high speed of 3000 rpm or more, the elongation generated on the substrate itself due to the centrifugal force applied to the substrate itself is small. If the deformation of the disk during clamping or rotation is large, the head cannot follow the disk surface, which causes signal disturbance or head crash, but this problem is completely eliminated.

The magnetic recording medium tends to become thinner as the recording density becomes higher, and the thickness thereof is generally 0.3 μm or less by plating or sputtering. Even if such a thin film is directly formed on the zirconia substrate, it can withstand CSS (Contact-Start-Stop) up to tens of thousands of times with the head.

It excels in ultra-precision machinability and shape accuracy, and by polishing the substrate surface, a center line average roughness (Ra) of 0.01 μm or less can be achieved, and as a result, it is formed by sputtering or plating. Moreover, even if the magnetic recording medium becomes extremely thin, the surface roughness of the substrate hardly causes unevenness on the surface of the recording medium, which is suitable for high-density magnetic recording.

With respect to the aluminum substrate such as the alumite-treated aluminum substrate which was subjected to the base treatment, the crack generation due to the difference in the thermal expansion coefficient between the alumite layer and the aluminum substrate became a problem, but the magnetic disk substrate of the present invention was found to have Since it is a single material, such a problem does not occur.

Since it is a substrate with excellent corrosion resistance, it can be cleaned using acid or alkali. In addition, since it is a non-conductor, electrochemical corrosion is not generated between the metal magnetic medium and the substrate, noise and signal errors caused by this can be eliminated, and long-term reliability can be improved.

With HIP-treated PSZ substrate, Vickers hardness Hv is 1400 kg / m
Since it has a high hardness of m ^2, it does not require alumite treatment or Ni-P undercoating unlike the aluminum substrate, and it has an average void diameter of 1 μm or less. The magnetic recording medium can be formed to have a thickness of not more than μm, whereby the magnetic recording medium can be directly formed by plating or sputtering, and the manufacturing cost can be reduced.

[Brief description of drawings]

1 and 2 are graphs showing firing temperature dependence characteristics of the average crystal grain size in the magnetic disk substrate of the present invention. A, b …… Characteristic curve of firing temperature dependence of average grain size in partially stabilized zirconia sintered body

Claims (1)

[Claims] 1. A stabilizer containing Y ₂ O ₃ in a range of 1 to 6 mol%, consisting mainly of a tetragonal ZrO ₂ phase, having an average crystal grain size of 0.15 to 0.5 μm and a theoretical density ratio of 95. % Magnetic disk substrate made of partially stabilized zirconia sintered body.