Dynamic magnetic information storage or retrieval – Record medium – Disk
Reexamination Certificate
2003-01-22
2004-11-09
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Record medium
Disk
C360S097010, C360S133000, C428S141000, C508S422000
Reexamination Certificate
active
06816341
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hard disk drive that uses a magnetic recording medium in which at least a magnetic layer and a protective layer are formed on a magnetic disk substrate, and a liquid lubricating agent with a perfluoroether structure is applied to the surface thereof. The present invention also relates to a hard disk drive with a mechanism for supplying a lubricating agent into the device in the form of a gas.
The recording densities in hard disk drives has been steadily increasing at a significant rate. Recently, recording densities of 20 gigabits per square inch (Gbit/inch
2
) have been announced. A requirement for achieving these high densities is to reduce the distance between the magnetic head and the magnetic recording layer of the magnetic disk as much as possible. Currently, this distance must be no more than 20 nm.
To reduce this distance as much as possible, the surface roughness of the magnetic disk must be reduced as much as possible. Therefore, there has been a transition from the contact start/stop (CSS) systems, where the magnetic head is in contact with the magnetic disk when the disk is not spinning and the magnetic head flies up due to air currents when the magnetic disk begins spinning, to load/unload (U/UL) systems, where the magnetic head is retracted away from the magnetic disk (unloaded) when the disk is stopped and is loaded on to the magnetic disk when the magnetic disk begins spinning. In U/UL systems, anti-sliding characteristics can be relaxed somewhat. However, the hard disk drive must be able to withstand impacts from load-on operations as well as sudden irregularities in head orientation that can occur even in normal operations.
Improvements in the protective layer and lubricating layer on magnetic disks are being made in order to minimize frication and damage caused by contact between the head and the magnetic disk. For example, in Japanese laid-open patent publication number Hei 8-319491, a perfluoro polyether with a phosphazene ring group is used in a lubricating agent to improve its properties. In Japanese laid-open patent publication number Hei 10-143836, a polyphenoxy cyclotriphosphazene is mixed with a perfluoro polyether at a weight ratio of 0.01-1. In Japanese laid-open patent publication number 2001-187796, a lubricating agent contains at least 30% perfluoro polyether having a phosophezene ring group. The object of these technologies is to improve wear resistance in magnetic disks, reduce head debris, reduce friction, reduce decomposition of the lubricating agent, or the like.
With regard to decomposition of the lubricating agent, it is believed that hydrogen fluoride (HF) is generated due to thermal decomposition from friction heat or decomposition due to Lewis acid, and that this HF causes a chain reaction that leads to decomposition of the lubricating agent. Japanese laid-open patent publication number Hei 10-143839 states that lubricating agents decompose due to exoelectrons generated by friction between the magnetic head and the magnetic disk.
Lubricating agents are supplied so that splattering of the lubricating agent due to rotation and heat can be reduced. In conventional technologies that supply lubricating agents to hard disk drives in the form of a gas, the lubricating agent supply source is placed within the head disk assembly. This conventional technology did not take into account the material and absorption properties of the supplied lubricating agent, the material and absorption properties of the lubricating layer formed on the magnetic disk, and the combinations of these elements. As a result, some lubricating agents are not able to prevent debris on the magnetic head, thus leading to reduced reliability. Furthermore, with some lubricating agents, corrosive outgas in the hard disk drive could generate a deposit on the magnetic head element that corrodes the metal in the element.
Also, absorption properties of the lubricating agent can vary depending on the type and characteristics of the protective layer of the magnetic disk. With diamond-like carbon (DLC) layers in particular, the absorption of the lubricating agent is less than that of carbon layers formed by sputtering, making it difficult to support the supplied lubricating agent on the magnetic disk and leading to reduced wear prevention.
SUMMARY OF THE INVENTION
When mixing two types of lubricating agents, e.g., a lubricating agent containing phosphazene and another lubricating agent, the combination must at least be evaluated based on compatibility, head debris, friction, and the like.
Magnetic heads used in magnetic disks are generally formed from a reproducing element that uses the Magneto-Resistive effect and a magnetic induction recording element. The recording element is formed from a coil generating a magnetic field and a magnetic pole that induces the magnetic field. The recording element records signals by sending a current of approximately a few dozen mA to the coil. The reproducing element receives a bias current. The reproducing element plays back signals by detecting changes in resistance resulting from the magnetic field. This bias current is between a few and a few dozen mA. Recording and reproducing frequencies increase with the recording density. With a 3.5 inch hard disk drive having a recording density of 20 Gbit/inch
2
, the frequency reaches approximately 300 MHz. When recording at such high frequencies, the recording element generates heat due to electrical resistance and impedance resistance, becoming very hot. The heat that is generated depends on the element structure, but can reach 200-250 degrees Centigrade. Heat generation increases when the recording frequency increases. The reproducing element also generates heat in a similar manner. The layer thickness of the reproducing element is on the order of submicrons, and the track width decreases as the recording density increases. As a result, heat generation increases with higher recording densities.
Friction heat causes the lubricating agent of a magnetic disk to decompose. However, it has not been clearly pointed out that heat from the recording or reproducing element in the head leads to the decomposition of the lubricating agent on the slider surface near the recording/reproducing element of the head, resulting in reduced reliability in the hard disk drive. We have studied the causes of reduced reliability in hard disk drives and have discovered that reduced reliability is caused by decomposition and transfer of the lubricating agent due to heat from the recording and reproducing elements in the head.
This will be described in more detail. Lubricating agent adhered to the slider surface near the recording and reproducing elements is decomposed by heat from the recording or reproducing element. This creates hydrogen fluoride (HF), causing lubricating agent with a higher concentration of HF to be adhered to the magnetic disk surface. The lubricating agent adhered to the magnetic disk surface corrodes the magnetic layer and the like of the magnetic disk. As a result, a protrusion formed on the magnetic disk surface, which undergoes volume expansion due to this corrosion, is adhered. The magnetic disk surface forming the protrusion comes into contact with the magnetic head, leading to wear on the protective layer, the magnetic layer, and the like. In the worst case, this can lead to loss of data recorded on the magnetic layer, resulting in secondary errors in which data recorded on the magnetic layer is erased.
The present invention provides a hard disk drive that overcomes the loss of reliability in hard disk drives caused by these secondary errors.
More specifically, the present invention provides a hard disk drive including: a magnetic disk to which is applied a first lubricating agent formed as:
(where p=0 or an integer of at least 1, q=0 or an integer of at least 1, and X=1-5); a spindle motor spinning the magnetic disk; a magnetic head reading information recorded on the magnetic disk; an arm supporting the magnetic h
Amo Mina
Ito Yutaka
Matsumoto Hiroyuki
Nakakawaji Takayuki
Shoda Mitsuhiro
Antonelli Terry Stout & Kraus LLP
Heinz A. J.
Hitachi , Ltd.
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