JP2010080013A - Method for evaluating durability of magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating durability of a magnetic disk with which durability of a magnetic disk surface is evaluated conveniently and accurately in accordance with a rigorous requirement with respect to the durability of the magnetic disk surface. <P>SOLUTION: Durability of a film on the magnetic disk surface is evaluated by: mounting the magnetic disk on a magnetic disk device with a magnetic head equipped with a DFH element attached thereto; subjecting the magnetic disk to fixed point floating, in a state of pushing out the DFH element of the magnetic head, and at a certain radial position of the magnetic disk surface; and detecting a point of rupture of the film on the magnetic disk surface. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a durability evaluation method for a protective film of a magnetic disk mounted on a magnetic disk device such as a hard disk drive (HDD).

 Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of an HDD (hard disk drive) using magnetic recording technology continues to increase at an annual rate of about 100%. Recently, an information recording capacity exceeding 160 Gbytes has been required for a 2.5 inch diameter magnetic disk used for HDDs and the like. In order to meet such a requirement, one square inch is required. It is required to realize an information recording density exceeding 250 Gbits per unit. In order to achieve a high recording density in a magnetic disk used for an HDD or the like, it is necessary to refine the magnetic crystal particles constituting the magnetic recording layer for recording information signals and to reduce the layer thickness. It was. However, in the case of magnetic disks of the in-plane magnetic recording method (also called longitudinal magnetic recording method or horizontal magnetic recording method) that have been commercialized conventionally, as a result of the progress of miniaturization of magnetic crystal grains, superparamagnetic phenomenon The thermal stability of the recording signal is impaired, the recording signal disappears, and a thermal fluctuation phenomenon occurs, which has been an impediment to increasing the recording density of the magnetic disk.

 In order to solve this hindrance factor, in recent years, a magnetic recording medium for perpendicular magnetic recording has been proposed. In the case of the perpendicular magnetic recording system, unlike the case of the in-plane magnetic recording system, the easy axis of magnetization of the magnetic recording layer is adjusted to be oriented in the direction perpendicular to the substrate surface. The perpendicular magnetic recording method can suppress the thermal fluctuation phenomenon as compared with the in-plane magnetic recording method, and is suitable for increasing the recording density. As such a perpendicular magnetic recording medium, as described in Japanese Patent Application Laid-Open No. 2002-74648 (Patent Document 1), a soft magnetic underlayer made of a soft magnetic material on a substrate and a perpendicular magnetic material made of a hard magnetic material. A so-called double-layered perpendicular magnetic recording disk having a recording layer is known.

JP 2002-74648 A

By the way, the process up to the shipment of the magnetic disk is completed, packed and shipped to the market through a sequential series of manufacturing processes including a disk substrate manufacturing process, a film forming process, and an inspection process. This inspection process usually includes a glide inspection process and a signal quality inspection process. Through this inspection process, magnetic disk products with stable quality are supplied to the market. Before the glide inspection process, there is usually a process called a tape burnish or a head burnish for removing contamination or dirt existing on the magnetic disk. In conventional magnetic disks for in-plane magnetic recording systems, this burnish could remove contamination and dirt existing on the surface of the magnetic disk without any problems. In this case, the physical durability of the protective film is weak, and it has been found that the surface of the magnetic disk may be damaged (scratched) by the burnish process. If scratches or the like are generated on the surface of the magnetic disk, an abnormal signal is generated, for example, in a glide inspection process, and an accurate inspection cannot be performed. For this reason, it may be difficult to give a high quality assurance to the manufactured magnetic disk.
Therefore, a method that can easily evaluate the durability of the surface of the magnetic disk, such as a carbon-based protective film, is useful.

Recently, information recording density of 250 Gbit / inch ² or more has been required for hard disk drives (HDD). This is related to the fact that HDDs have been installed in mobile phones, navigation systems, digital cameras, etc., in addition to the need for conventional computer storage devices.
In these new applications, the housing space for mounting the HDD is significantly smaller than that of a computer, so it is necessary to downsize the HDD. For this purpose, it is necessary to reduce the diameter of the magnetic disk mounted on the HDD. For example, a 3.5-inch type or 2.5-inch type magnetic disk could be used in a computer application, but in the case of the new application, a smaller diameter, for example, a 0.8-inch type to a 1.8-inch type is used. A small-diameter magnetic disk such as an inch type is used. Even when the diameter of the magnetic disk is reduced in this way, it is necessary to store a certain amount of information capacity, which will increase the speed of information recording.

Also, in order to effectively use the limited disk area, a HDD of LUL (Load Unload) method has been used instead of the conventional CSS (Contact Start and Stop) method. In the LUL method, when the HDD is stopped, the magnetic head is retracted to an inclined table called a ramp located outside the magnetic disk, and during the start-up operation, after the magnetic disk starts to rotate, the magnetic head is moved from the ramp onto the magnetic disk. Slide and fly to record and playback. During the stop operation, the magnetic head is retracted to the ramp outside the magnetic disk, and then the rotation of the magnetic disk is stopped. This series of operations is called LUL operation. Magnetic disks for LUL HDDs do not need to have a contact sliding area (CSS area) with the magnetic head as in the CSS system, and can expand the recording / playback area, which is preferable for high information capacity. is there.

In order to improve the information recording density under such circumstances, it is necessary to reduce the spacing loss as much as possible by reducing the flying height of the magnetic head. In order to achieve an information recording density of 250 gigabits per square inch or more, the flying height of the magnetic head needs to be 10 nm or less. Unlike the CSS method, the LUL method does not require a concave / convex shape for CSS on the magnetic disk surface, and the magnetic disk surface can be extremely smoothed. Therefore, in the magnetic disk for LUL method, the flying height of the magnetic head can be further reduced compared to the CSS method, so that the S / N ratio of the recording signal can be increased and the recording capacity of the magnetic disk device can be increased. There is also an advantage of being able to contribute.

Due to a further drop in the flying height of the magnetic head accompanying the recent introduction of the LUL system, it has become necessary to operate the magnetic disk stably even at an extremely low flying height of 10 nm or less. In particular, as described above, in recent years, the magnetic disk has shifted from the in-plane magnetic recording system to the perpendicular magnetic recording system, and there is a strong demand for an increase in the capacity of the magnetic disk and a decrease in flying height associated therewith.
However, the flying height of the magnetic head changes due to changes in the operating environment temperature of the HDD. Therefore, the temperature of the HDD is detected, and in a low temperature environment, for example, a dynamic flying height (Dynamic Flying Height) that corrects a flying change of the slider by driving a heater coil arranged around the magnetic head to thermally expand the magnetic head. (Hereinafter abbreviated as DFH), a DFH head that employs flying control is known. Such a DFH head is effective in achieving a high information recording density of 250 Gbit / inch ² or more. When such a DFH head is employed, durability of the magnetic disk surface becomes more important.

At present, there are few known effective means for simply evaluating the durability of the magnetic disk surface despite strict requirements for the durability. Of course, even in the present situation, a pin-on that evaluates the durability by applying a constant load (for example, 30 gf) to the disk surface, maintaining the disk rotation speed (for example, 120 rpm) and breaking the film on the magnetic disk surface. Although the test has been conducted, according to the study of the present inventors, it has been found that the durability of the magnetic disk surface may not always be accurately evaluated by the conventional evaluation method based on the pin-on test.

From the above situation, it is clear that if the durability of the manufactured magnetic disk surface such as a protective film can be evaluated easily and accurately, its usefulness is extremely high.
The present invention has been made in view of the above problems, and the object of the present invention is an evaluation method that can easily evaluate the durability of the surface of the magnetic disk, in particular, the strict requirement for the durability of the surface of the magnetic disk. An object of the present invention is to provide a method for evaluating the durability of a magnetic disk, which can accurately evaluate the durability of the magnetic disk surface that can be used.

As a result of intensive studies to solve the above problems, the present inventor has completed the present invention.
That is, the present invention is an invention having the following configuration.
(Structure 1 of the invention)
A magnetic disk is mounted on a magnetic disk device equipped with a magnetic head equipped with a DFH element, and the DFH element of the magnetic head is protruded and floated at a fixed point at a certain radius on the surface of the magnetic disk. A method for evaluating the durability of a magnetic disk, wherein the durability of a film on the surface of a magnetic disk is evaluated by detecting a breaking point.

(Configuration 2)
The method for evaluating the durability of a magnetic disk according to Configuration 1, wherein the durability of the carbon-based protective film formed on the surface of the magnetic disk is evaluated.
(Structure 3 of the invention)
3. The method for evaluating the durability of a magnetic disk according to Configuration 1 or 2, wherein a load applied to the magnetic disk during measurement is in a range of 1 gf to 30 gf.

(Configuration 4)
4. The method for evaluating the durability of a magnetic disk according to any one of Structures 1 to 3, wherein the atmospheric pressure in the magnetic disk device at the time of measurement is within a range of 200 Torr or less.
(Structure 5 of the invention)
5. The method for evaluating the durability of a magnetic disk according to any one of Structures 1 to 4, wherein the rotational speed of the magnetic disk at the time of measurement is within a range of 3000 to 8000 rpm.

According to the present invention, as in Configuration 1, a magnetic disk is mounted on a magnetic disk device equipped with a magnetic head equipped with a DFH element, and a position of a radius on the surface of the magnetic disk in a state where the DFH element of the magnetic head is projected. This is a magnetic disk durability evaluation method for evaluating the durability of the film on the surface of the magnetic disk by detecting a point where the film on the surface of the magnetic disk breaks by floating at a fixed point.
In the present invention, a magnetic disk is mounted on a magnetic disk device equipped with a magnetic head having a DFH element, and durability evaluation measurement is performed. This magnetic disk device is a device on which a magnetic disk to be measured is actually mounted, or has the same structure.

The radial position on the surface of the magnetic disk to be measured varies depending on the size of the disk, and is not particularly limited. For example, in the case of a 65 mm (outer diameter) size disk, about 20 mm to 30 mm, particularly preferably 20 mm from the disk center. A radius position of ˜25 mm is suitable.

Further, the rotational speed of the magnetic disk at the time of measurement preferably corresponds to the rotational speed at the time of actual use of the magnetic disk device on which the magnetic disk is mounted. For example, in the range of 3000 to 8000 rpm in accordance with the recent high speed rotation. It is preferable to be inside.

  The load applied to the magnetic disk during measurement is preferably within a relatively low load range of 1 gf to 30 gf, for example.

Further, the atmospheric pressure in the magnetic disk device at the time of measurement is preferably within a low atmospheric pressure range close to a vacuum state of 200 Torr or less.
Note that the rotational speed of the magnetic disk and the load applied to the magnetic disk at the time of the above measurement are preferably matched with the values at the time of use in the magnetic disk device in which the magnetic disk is actually mounted.

As a method for detecting the point at which the film on the surface of the magnetic disk breaks, for example, an acoustic emission (AE) sensor for detecting the head output is attached to the suspension of the magnetic head or the vicinity thereof, and the output of this sensor is monitored. Can be detected.

  The durability evaluation method according to the present invention particularly affects the durability of the magnetic disk surface, and is suitable for evaluating the durability of the carbon-based protective film formed on the surface of the magnetic disk, which has recently become increasingly demanding for durability. It is.

According to the durability evaluation method of the present invention, the durability of the magnetic disk surface can be easily evaluated. In particular, it is possible to accurately evaluate the durability of the magnetic disk surface so as to meet the recent increasingly demanding requirements for the durability of the magnetic disk surface.

A magnetic disk for durability evaluation according to the present invention is manufactured by forming at least a magnetic layer, a protective layer, etc. on a magnetic disk substrate.
A glass substrate is preferred as the magnetic disk substrate. The glass constituting the glass substrate is preferably amorphous aluminosilicate glass. Such a glass substrate can be finished to a smooth mirror surface by polishing the surface. As such an aluminosilicate glass, SiO ₂ is 58 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 23 wt%, Li ₂ O is 3 wt% to 10 wt%, Na ₂ An aluminosilicate glass containing O as a main component in an amount of 4 wt% or more and 13 wt% or less (however, an aluminosilicate glass containing no phosphorus oxide) can be used. For example, SiO ₂ is 62 wt% to 75 wt%, Al ₂ O ₃ is 5 wt% to 15 wt%, Li ₂ O is 4 wt% to 10 wt%, and Na ₂ O is 4 wt% to 12 wt%. Wt% or less, ZrO ₂ containing 5.5 wt% or more and 15 wt% or less as a main component, and a weight ratio of Na ₂ O / ZrO ₂ of 0.5 or more and 2.0 or less, Al ₂ O ₃ / ZrO _An amorphous aluminosilicate glass containing no phosphorous oxide having a weight ratio of ₂ of 0.4 to 2.5 can be obtained.

It is preferable that the glass substrate for a magnetic disk has a mirror surface having a maximum roughness Rmax of 6 nm or less by at least mirror polishing and cleaning of the glass substrate. Such a mirror state can be realized by performing a mirror polishing process and a cleaning process in this order.

In addition, you may perform a chemical strengthening process after a washing | cleaning process process. As a method of chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range that does not exceed the temperature of the glass transition point, for example, a temperature of 300 degrees Celsius or more and 400 degrees Celsius or less is preferable.

As a material for the magnetic layer formed on the magnetic disk substrate, a hexagonal CoPt ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method for forming the magnetic layer, a method of forming a magnetic layer on a glass substrate by sputtering, for example, DC magnetron sputtering can be used. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a cubic base layer such as a Cr-based alloy, for example, the magnetization easy direction of the magnetic layer can be oriented along the magnetic disk surface. In this case, a magnetic disk of the in-plane magnetic recording system is manufactured. Further, for example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

A protective layer is formed on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. The thickness of the protective layer is preferably 35 angstroms to 80 angstroms. The present invention is particularly suitable for evaluating the durability of a carbon-based protective layer of a magnetic disk.

Further, a lubricating layer may be further formed on the protective layer. The lubricating layer is preferably composed mainly of a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound, particularly a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The film thickness of the lubricating layer is preferably 5 angstroms to 15 angstroms. The lubricating layer can be applied and formed by a dip method.

According to the present invention, an evaluation method capable of simply evaluating the durability of the magnetic disk surface, particularly, accurately evaluating the durability of the magnetic disk surface capable of meeting the strict requirements for the durability of the magnetic disk surface. Thus, it is possible to provide a method for evaluating the durability of a magnetic disk.
Further, by applying the magnetic disk durability evaluation method of the present invention, it is possible to provide a magnetic disk capable of meeting strict requirements for the durability of the magnetic disk surface.

Hereinafter, embodiments of the present invention will be described in detail by way of examples.
In this example, first, a glass substrate made of disk-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.5 mm is obtained from molten glass by direct pressing using an upper die, a lower die, and a barrel die, and this is roughly wrapped. For magnetic disks, the process (rough grinding process), shape processing process, fine lapping process (fine grinding process), end mirror processing process, first polishing process, and second polishing process are performed sequentially, followed by chemical strengthening. A glass substrate was produced. This glass substrate is mirror-polished on both the main surface and the end surface.

As a result of visual inspection and precise inspection of the glass substrate surface after the chemical strengthening and subsequent cleaning, no defects such as protrusions and scratches due to deposits were found on the glass substrate surface. Further, when the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), it had an ultra-smooth surface with Rmax = 2.13 nm and Ra = 0.20 nm. A glass substrate for a magnetic disk was obtained. The glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm.

Next, using a single-wafer sputtering apparatus on the obtained magnetic disk glass substrate 1, a Ti-based adhesion layer, a Fe-based soft magnetic layer, a NiW first underlayer, a Ru second underlayer, A CoCrPt magnetic layer was sequentially formed, and then a carbon-based protective layer was formed by plasma CVD. This magnetic disk is a magnetic disk for perpendicular magnetic recording.

The protective layer was a diamond-like carbon protective layer and was formed by plasma CVD so that the film thickness on the main surface was 45 mm.
The magnetic disk manufactured as described above is hereinafter referred to as a magnetic disk 1.
Hereinafter, a magnetic disk manufactured in the same manner as described above except that the protective layer on the main surface has a thickness of 30 mm is referred to as a magnetic disk 2 hereinafter.

For the magnetic disk 1 and magnetic disk 2 described above, the durability of the carbon protective layer on the surface of the magnetic disk was evaluated according to the method of the present invention.
That is, a magnetic disk is mounted on a magnetic disk device equipped with a magnetic head equipped with a DFH element, and a fixed point is levitated at a certain radius position on the surface of the magnetic disk with the DFH element of the magnetic head protruded. The point at which the membrane breaks is detected. This magnetic disk device has the same structure and method as the magnetic disk device on which the magnetic disks 1 and 2 are actually mounted.
The atmospheric pressure in the apparatus during measurement was 100 Torr, and the suspension load of the magnetic head was set to 5 gf. The disk rotation speed was 5400 rpm.

  Under the above conditions, the head was floated at a fixed point at a position where the disk radius on the surface of the magnetic disk was 22 mm, and the point at which the carbon protective layer broke was monitored. The point at which the carbon protective layer breaks was detected by an AE sensor attached to the head suspension.

  As a result, it has been found that the results are different between the magnetic disk 1 and the magnetic disk 2 manufactured under different film formation conditions (film thicknesses) when forming the carbon protective layer. That is, in the magnetic disk 1, the carbon protective layer is not broken until the number of passes is 59400, and in the magnetic disk 2, the carbon protective layer is broken at 27000 times, and is broken at an earlier stage than the magnetic disk 1. It has been found. Therefore, as will be described below, from the evaluation result, it can be determined that the durability of the surface of the magnetic disk 1 is good.

  As a result of performing a normal glide inspection on a magnetic disk of the same lot as the magnetic disk 1, it was found that the yield of the inspection was 90% or more and was stable. Furthermore, in order to confirm the above evaluation results, the surface state of the magnetic disk 1 was observed with an optical surface analyzer (Candela OSA6100). Scratches and the like were hardly confirmed on the surface of the layer. In addition, the magnetic disk 1, which had good results in durability evaluation, is mounted on a load / unload type magnetic disk device equipped with a magnetic head equipped with a DFH element used for durability evaluation. As a result of repeated loading and unloading operations of the head in a high-temperature and high-humidity environment of 70 ° C. and 80% RH with a flying height of 10 nm, the magnetic disk 1 is loaded 600,000 times Durable against unloading and high reliability was obtained.

  On the other hand, as a result of conducting a normal glide inspection on the magnetic disk of the same lot as the magnetic disk 2, it was found that the inspection yield was as low as 70%. Furthermore, when the surface state of the magnetic disk 2 was observed with an optical surface analyzer (Candela OSA6100), scratches and the like were generated on the surface of the carbon protective layer of the magnetic disk 2 that was broken early in the durability evaluation. Was confirmed. Further, the magnetic disk 2 is mounted on a load / unload type magnetic disk apparatus in the same manner as described above, the flying height when the magnetic head is flying is set to 10 nm, and the environment in the magnetic disk apparatus is set to a high temperature of 70 ° C. and 80% RH. As a result of repeated loading and unloading operations of the head in a humid environment, the magnetic disk 3 fails due to a head crash in less than 600,000 times.

  As a reference example for the evaluation method of the present invention, a certain load (30 gf) is applied to the disk surface, the disk rotation speed is constant (120 rpm), and the durability depends on the time until the film on the magnetic disk surface breaks. As a result of the evaluation of the magnetic disk 1 and the magnetic disk 2 by the pin-on test that is currently being performed, it was determined that both endured up to 4 minutes, which is the pass criterion of the pin-on test, and were good. It was. Therefore, it is difficult to discriminate between the magnetic disk 1 and the magnetic disk 2 in the current pin-on test evaluation.

As described above, according to the method for evaluating the durability of a magnetic disk according to the present invention, the durability of the magnetic disk surface can be evaluated easily and accurately in correspondence with the results of the magnetic disk surface observation and the LUL test described above. In particular, it is possible to perform a durability evaluation that can cope with the severe demands on the durability of the surface of a recent magnetic disk.

Claims (5)

  A magnetic disk is mounted on a magnetic disk apparatus equipped with a magnetic head having a dynamic flying height element, and the magnetic disk surface is levitated at a certain radius on the magnetic disk surface with the dynamic flying height element of the magnetic head protruding. A method for evaluating the durability of a magnetic disk, wherein the durability of a film on the surface of a magnetic disk is evaluated by detecting a point at which the film on the surface breaks.   2. The method for evaluating the durability of a magnetic disk according to claim 1, wherein the durability of the carbon-based protective film formed on the surface of the magnetic disk is evaluated.   3. The method for evaluating the durability of a magnetic disk according to claim 1, wherein a load applied to the magnetic disk during measurement is in a range of 1 gf to 30 gf.   4. The method for evaluating the durability of a magnetic disk according to claim 1, wherein the atmospheric pressure in the magnetic disk device at the time of measurement is within a range of 200 Torr or less. The method of evaluating the durability of a magnetic disk according to any one of claims 1 to 4, wherein the number of rotations of the magnetic disk at the time of measurement is within a range of 3000 to 8000 rpm.