WO1994008335A1

WO1994008335A1 - Slider for magnetic recording head having self-lubricating overcoat

Info

Publication number: WO1994008335A1
Application number: PCT/US1993/009461
Authority: WO
Inventors: Naum V. Gitis
Original assignee: Maxtor Corporation
Priority date: 1992-10-06
Filing date: 1993-10-05
Publication date: 1994-04-14
Also published as: AU5298993A

Abstract

A slider body (10) supporting magnetic transducer elements (14) for use in a magnetic recording system with a disk (20) includes at least one primary load-bearing surface (12) which is covered with a film having anti-frictional, self-lubricating properties. The film is composed of an immobile (e.g. solid) lubricant material. Processes for forming the solid lubricant layer on the load-bearing surface (12) of the slider body (10) include heat bonding or vapor phase deposition.

Description

SLIDER FOR MAGNETIC RECORDING HEAD HAVING SELF- LUBRICATING OVERCOAT

FIELD OF THE INVENTION

This invention relates to the fields of magnetic recording and tribology; more particularly, to the tribology of the disk-slider interface and to designs and methods for improving the tribology in near-contact and in-contact recording systems.

BACKGROUND OF THE INVENTION

Conventional magnetic recording heads comprise a rectangular slider body onto which is attached a transducer device along one side of the slider body. Normally, sliders are made of various ceramic materials. For instance, alumina and titanium-carbide are one of the more common slider materials in use today. A great variety of other materials have also been used as well. By way of example, U.S. Patent Nos., 4,709,284 and 4,835,640 disclose the use of a stabilized zirconia as a slider material. A single-crystal material with high thermal conductivity is described in U.S. Patent No. 4,819,091. An alumina and silicon-carbide slider body is described in U.S. Patent No. 4,796,127. A cubic zirconia and carbon slider body is disclosed is U.S. Patent No. 4,734,802. A slider body comprised of titania, calcia and zinc-oxide materials is taught in U.S. Patent No.,4,670,805. U.S. Patent No. 4,660,114 discloses the use of.carbide or nitride or carbonitride and oxide of either zirconia and carbon. Aluminum and titanium nitrides are described in U.S. Patent No. 4,639,803. ln a typical magnetic recording system, the rotation of the rigid magnetic disk causes a transducer or magnetic head to be hydrodynamically lifted above the surface of the recording medium. This hydrodynamic lifting phenomena results from the flow of air produced by the rotating magnetic disk; it is this air flow which causes the head to "fly" above the disk surface. Of course, when the rotation of the magnetic disk slows or stops, the head element is deprived of its buoyancy and it lands on the surface of the disk. Repeated starting and stopping of the magnetic disk causes the recording head to be dragged across the surface of the disk over and over again during the "take-off and "landing" phases of its flight.

Thus, the physical and mechanical nature of a typical disk drive recording system mandates that the magnetic head be able to withstand numerous start/stop sequences. The ability of a head to perform despite the repeated impacts caused during the starting or stopping of the disk is referred to as its contact-start-stop (CSS) resistance property. Note that physical contact between the head and disk can also occur at isolated points during flying when the head is flying at an extremely low flying height (e.g., approximately 0.01 to 0J0 microns high). Obviously, any friction generated at the head/disk interface as a result of repeated starting and stopping of the disk will tend to degrade or eventually destroy the read/write performance of the recording head. In view of the damaging sliding action which takes place during the normal operation of a hard disk drive, one of the primary concerns in the industry has been to find ways to minimize the friction (i.e., increase the lubricity) at the head/disk interface.

One of the problems associated with conventional slider designs is the absence of lubricity on their working surfaces. In other words, the slider surfaces which contact the disk surface are often characterized as having a relatively high coefficient of friction. This translates into an increased wear rate as a consequence of repeated sliding of the head across the magnetic disk. In the past, one way that practitioners have tried to combat the drawbacks of friction and wear associated with conventional sliders has been to coat the surface of the magnetic disk with a liquid lubricant. For example, a magnetic storage medium with a lubricating coating is described in U.S. Patent No. 4,696,845. Typically, the thickness of such liquid lubricant layers is in the range of 10-20 angstroms. The problem, however, with the use of liquid lubricants is that while they overcome the problems of friction and wear, they create a new type of problem; namely, stiction.

Stiction refers to the tendency of the slider body to adhere to the surface of the magnetic disk when the head is in contact with the disk and the disk is stationary. Basically, in this situation the head is stuck to the surface of the disk and can only be removed by the application of a considerable force. Attempts to reduce the stiction problem by altering the viscosity of the liquid lubricant have not yielded completely satisfactory results. An example of this approach is found in U.S. Patent No. 5,097,368, which teaches the use of a high viscosity, non-Newtonian liquid bearing in an information storage system.

Another technique for avoiding the problems of friction and wear at the head-disk interface is to finish the surface on the air-bearing surface of the head to extremely high accuracy and tolerances. By way of example, a process for finishing the surface of a ceramic recording head to enhance sliding is described in an article by Chandrasekar et al. entitled, "Surface Finishing Processes for Magnetic Recording Head

Ceramics," Adv. Info. Storage Syst., Vol. 1 , 1991 , ISSN, pp. 353-354.

One of the drawbacks to this approach, however, is that slider-disk stiction is increased. The current trend in the industry is toward increasing the magnetic signal by lowering the slider flying height. Generally, this means that the separation between the head and disk must be reduced. For instance, very low flying heights on the order of 1 -3 microinches are becoming increasingly common. Reducing the separation between the head and the disk medium, of course, normally results in increased abrasive wear, thereby heightening the risk of catastrophic wear on the head. As an example of this latter effect, in near-contact recording systems micro- spots of real contact can occur between the slider and disk surfaces during steady operating conditions as small amounts of disk lubricant gets worn out or squeezed out whenever the slider surface occasionally touches the disk. As described above, a common approach to this problem has been to increase the lubricity of the disk by means of a liquid lubricant to avoid increased wear. However, as the amount of liquid lubricant on the disk surface increases, so does the stiction problem. On the other hand, thinning or removing the liquid lubricant from the disk surface avoids the stiction problem, but only at the expense of increased wear.

Thus, what is needed is a solution to the problem of frictional wear at the slider/disk interface. As will be seen, the present invention provides a new type of slider body that offers both wear resistance and anti-stiction properties. The invented slider has a working surface (i.e.,. facing the disk) which is coated with an immobile or solid lubricant. This self-lubricating overcoat substantially increases the capacity of the head to experience repeated start and stop operations of the disk.

Other known prior art includes U.S. Patent No. 5,041 ,932 and an article by Saperstein and Lin entitled, "Improved Surface Adhesion and

Coverage of Perfluoropolyether Lubricants Following Far-UV

Irraditation," Langmuir, Vol. 6, No. 9, 1990, pp 1522-1524.

SUMMARY OF THE INVENTION

A slider body for use in a magnetic recording system is disclosed. In one embodiment, the slider body comprises at least one primary load- bearing surface which is covered with a film having anti-frictional properties. Importantly, the film comprises a substantially immobile lubricant material in which the liquid/immobile fraction has been eliminated during either the deposition or bonding processes.

In another embodiment, the slider body itself consists essentially of a self-lubricating material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which:

Figure 1 illustrates a typical slider body and its orientation when used in a magnetic recording system.

Figure 2 is a cross-sectional view of a slider body incorporating one embodiment of the present invention.

Figure 3 is a graph illustrating the performance improvement provided by the present invention.

DETAILED DESCRIPTION

A slider body for use in a magnetic recording system is described. In the following description, numerous specific details are set forth such as material types, temperatures, dimensions, etc., in order to provide a thorough understanding of the present invention. However, it will be obvious to one of skill in the art that the invention may be practiced without these specific details. In other instances well known elements and processing techniques have not been shown in particular detail in order to avoid unnecessarily obscuring the present invention.

Figure 1 illustrates a typical slider body for use in a magnetic recording system. Slider 10 comprises a rectangular body onto which are formed a pair of substantially parallel rails 1 1 disposed along opposite sides of the slider body. Each of the rails 11 includes a surface 12 which functions as the primary load-bearing surface of the slider during normal operation. It is these surfaces 12 which come into contact with the disk 20 during dwelling, starting, and stopping of the drive.

Note that in Figure 1 the load is administered primarily by means of load beam 21 which exerts a downward pressure on slider 10; this downward pressure forces surfaces 12 and disk 20 into contact. Each slider rail 11 is further shown having a magnetic transducer element 14 attached to the side of the slider body. Moreover, at the opposite end of each rail is a beveled edge 15 which assists in the take-off of slider 10 from the surface of disk 20 during spin-up.. As discussed above, the lower slider flying heights which are becoming increasingly common in magnetic recording systems lead to more frequent contact between the slider and disk surface. In conventional systems which utilize a liquid lubricant on the disk surface to avoid increased wear, some portion of this disk lubricant gets worn out or squeezed out. Simply covering the slider or the disk with a prodigious amount of liquid lubricant may help to solve the wear problem, but only at the expense of an increased stiction problem. On the other hand, removing lubricant from the disk-slider interface avoids the stiction problem, but with increased wear on the slider body. To achieve both wear-resistance and anti-stiction properties in a slider, the present invention includes a slider body having a working (i.e. facing the disk) surface which is covered with an immobile or solid lubricant. Use of such a self-lubricating overcoat obviates the need for a liquid or mobile lubricant coating.

Referring now to Figure 2, there is shown a conventional ceramic slider 10 having a pair of rails 11 disposed at opposite sides of the slider body. The load-bearing or working surfaces 12 are shown being covered with a very thin layer of a solid lubricant 24. In the currently preferred embodiment, this lubricant comprises a perfluropolyether of a type which is commercially available under the names Z-Dol or AM2001. In accordance with the present invention, the perfluropolyether lubricant is bonded to the surfaces 12 of the slider body so as to create an intentionally immobile lubricant layer. In one embodiment, the thickness of layer 24 is on the order of 0.5 to 4.0 nm.

It should be understood that the solid lubricant 24 may extend over other portions of the slider body beyond surfaces 12. Another words, the side regions of sliders 11 may also be coated with the solid lubricant layer 24. The central requirement of the present invention, however, is to provide the solid lubricant layer on the working surfaces in order to increase the lubricity of the slider-disk interface. It is observed that including the solid lubricant layer 24 dramatically reduces the wear of slider 10 and increase the number of contact starts/stops which can be performed during the lifetime of the head disk assembly. Numerous different processes exist for bonding lubricant onto the slider body in order to create the solid immobile layer 24. For example, bonding can be performed as a separate operation after lubricant deposition. Such a process would consist of dipping or spraying the slider bodies with a liquid lubricant and then either heating or baking the coated sliders for a period of time sufficient to form lubricant-slider surface bonds. For example, baking slider bodies for one hour at 120 C has proven to be adequate. Alternatively, ultraviolet treatment may be used to bond lubricant to the working surfaces 12 of the slider body. Further removal of the liquid/mobile fraction of the lubricant can be facilitated by rinsing the slider body with a solvent. Solvents such as Freon 113 or FC72 are satisfactory.

Another way that bonding can be performed is during the actual lubricant deposition process itself. For instance, bonding can be performed at the same time as the lubricant deposition by the process of vapor phase deposition. Vapor phase deposition of the lubricant does not form and so does not require the subsequent removal of the liquid/mobile fraction of the lubricant. Another alternative is to deposit specific types of lubricants that form the bonded/solid layers by simple dipping of the slider body into the lubricant material with no additional treatment. For example, Demnum SP can be employed under this approach, with the further removal of the liquid phase being accomplished by means of rinsing with either Freon 1 13 or FC72 as described above.

An alternative embodiment of the present invention comprises a conventional ceramic slider body having a working surface covered with a thin film of anti-frictional, self-lubricated polymer. Ideally, such a polymer would have a bulk body value of Young's modulus less than 1.0

GPa. By way of example, this criteria could be satisfied by a fluorocarbon

PTFE or an ultra-high-molecular weight polyethylene, with or without additives. Yet another alternative is to manufacture the slider body completely out of one of the self lubricating plastics described above. Again, these plastics can be manufactured with or without additives to optimize the performance of the magnetic recording head.

Figure 3 is a graph which illustrates the dramatic improvement in slider performance achieved through the use of the present invention. The graph of Figure 3 plots stiction force in grams versus the number of start/stop cycles of the head-disk system. As can be seen, the performance of a slider used in conjunction with a liquid lubricant on either the slider surface or the disk surface produces a relatively high stiction force up to 50,000 start/stop cycles. At the other extreme a slider used without any lubricant whatsoever has an extremely low stiction force, however fails rapidly due to wear (i.e. less than 20,000 cycles).

In contrast, the solution provided by the present invention illustrates a dramatic reduction in stiction force without increased wear or catastrophic damage resulting from excessive friction. Thus, the invented slider significantly improves the tribology of the disk-slider interface and, in doing so, accommodates lower flying heights in near-contact and in- contact recording systems.

Claims

CLAIMSClaim:

1. A slider body for use in a magnetic recording system consisting essentially of a self-lubricating plastic material.

2. The slider body of claim 1 wherein said plastic material has a value of Young's modulus less than about 5.0 GPa.

3. The slider body of claim 2 wherein said plastic material comprises a fluorocarbon.

4. The slider body of claim 2 wherein said plastic material comprises a high molecular weight polyethylene.

5. The slider body of claim 2 wherein said magnetic recording system includes a magnetic disk having a surface essentially devoid of any mobile lubricant.

6. A magnetic recording head comprising a slider body having a primary load-bearing surface which is covered with a film of an anti- frictional, self-lubricating solid polymer.

7. The magnetic recording head of claim 5 wherein said polymer has a value of Young's modulus less than about 5.0 GPa.

8. The magnetic recording head of claim 7 wherein said polymer comprises a fluorocarbon PTFE.

9. The magnetic recording head of claim 7 wherein said polymer comprises a high molecular weight polyethylene.

10. A recording system including a magnetic head comprising a slider body with a magnetic transducer device disposed on an end surface of said slider body, said body having a bearing surface covered with an immobile lubricant layer which comes into sliding contact with a magnetic disk.

11. The recording system of claim 10 wherein said magnetic disk has a surface essentially devoid of any mobile lubricant.

12. The recording system of claim 10 wherein said lubricant layer comprises a perfluoropolyether.

13. The recording system of claim 12 wherein said lubricant layer is less than about 5.0 nm.

14. The recording system of claim 13 wherein said lubricant layer is between 1.0 to 2.0 nm thick.

15. The method of improving the lubricity at the interface between a magnetic recording head and a magnetic disk, said head having a load-bearing surface which contacts said magnetic disk, said method comprising the steps of: depositing a liquid lubricant onto said bearing surface; bonding said lubricant to said surface to form a solid immobile lubricant layer covering said load-bearing surface.

16. The method according to claim 15 wherein said liquid lubricant comprises a perfluoropolyether.

17. The method according the claim 15 wherein said bonding step is performed by baking said head.

18. The method according to claim 17 wherein said baking step is performed for approximately one hour at 120° C.

19. The method according to claim 17 wherein said bonding step is performed by exposing said head to ultraviolet radiation.

20. The method according to claim 16 comprising the additional step of removing the liquid/mobile fraction of said lubricant from said head.

21. The method according to claim 16 wherein said deposition step comprises a vapor phase deposition of said liquid lubricant.

22. The method according to claim 21 wherein said bonding step is performed concurrently with said deposition step.