WO1995012199A1

WO1995012199A1 - Burnishable head and media for near contact and contact recording

Info

Publication number: WO1995012199A1
Application number: PCT/US1994/012069
Authority: WO
Inventors: Jia-Kuen Jerry Lee; Mong-Ping Audrey Chao
Original assignee: Conner Peripherals, Inc.
Priority date: 1993-10-26
Filing date: 1994-10-20
Publication date: 1995-05-04

Abstract

A disk drive having a head and disk assembly designed to transfer data to and from the disk at very low flying heights, for example 2.5 ν'. Due to factors including shock, disk drive vibration and changes in ambient pressure, the head will occasionally fly below the average flying height during rotation of the disk. At these lower heights, the head may contact asperities protruding from the disk surface. The present invention operates with burnishable disks, such that, during operation of the disk drive and rotation of the storage disk, the repeated contact of the head slider with the higher asperities causes the asperities to be worn down, or burnished. In this way, each of the asperities on the disk surface are reduced to be below the flying height of the head when the head flies at lower than normal flying heights. Thus, the danger of damage to the head and/or disk due to intermittent contact of the head with the otherwise protruding asperities on the disk is removed.

Description

BURNISHABLE HEAD AMD MEDIA FOR NEAR CONTACT AND CONTACT RECORDING

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a data storage device, and more particularly, to a disk drive operating at low flying heights having a head and disk assembly where asperities on the surface of the disk are burnished over time with operation of the disk drive.

Description of the Related Art

Conventional disk drives for use in work stations, personal computers, and portable computers, are required to provide a large amount of data storage within a minimum physical space. In general, disk drives operate by positioning a read/write transducing head over respective tracks on a magnetic recording disk. Positioning of the head over the tracks is accomplished by an actuator coupled to control electronics, which control the positioning of the actuator and the read/write functions of the heads.

Greater demands are being placed on disk drives by (1) the use of multi-user and/or multi-tasking operating systems, (2) work stations which provide an operating environment requiring the transfer of large amounts of data to and from a hard disk and/or large numbers of disk accesses to support large application programs or multiple users, (3) the present popularity of notebook and lap top computers, and (4) the continuing trend toward higher performance microprocessors. All such systems require a hard drive having high-capacity storage capability, while occupying a minimum of space within the host computer. In order to accommodate these demands, there is a need to produce a smaller hard disk drive which at the same time has an increased storage capacity. For such applications, single drive capacities on the order of hundreds of megabytes are common.

An important determinant in the storage capacity of a disk drive is the flying height of the transducing heads above the rotating disk. In conventional Winchester-type hard drives, once the storage disk achieves a certain angular velocity after start-up of the drive, a cushion of circulating air above the surface of the disk forces the head up off the surface of the disk to thereby achieve a flying height. Having very low flying heights offers several advantages, primary among them is that flying the head very close to the disk surface allows for a high data bit density (i.e.. the number of data bits per inch on a data track) . The greatest data bit density would be obtained where the transducing head rides in contact with the storage disk. However, the contact of the transducer and head slider with the disk surface would result in damage to the head and/or disk in an unreasonably short period of time. Thus, there has been an industry wide push to decrease the height at which read/write heads are maintained over the disk surface without actually riding in contact with the disk surface. In the 1960's flying heights were commonly about 100 microinches (μ") . At present, technological advances in read/write heads and disk drive design have allowed the reduction of flying heights to around 4 μ" for commercially viable disk drives.

Magnetic recording disks are conventionally formed by thin film deposition processes, such as either sputtering or plating. In thin film deposition, a layer of magnetic material is deposited on a substrate, on which layer is deposited on a protective outer layer. Some disk designs include deposition of several layers of magnetic and/or nonmagnetic material. The outer protective layer is preferably nonmagnetic and may be formed, for example, from either sputtered carbon or a metal. Sputtering, a common form of thin film deposition, fundamentally involves location of a block of the target material to be deposited on the disk surface in a partial vacuum sealed chamber. The chamber is backfilled with an inert gas, and an electric field is introduced. The electric field accelerates the ions in the gas, causing them to impinge on the target surface. As a result of momentum transfer, atoms of the target material are dislodged from the target surface and randomly deposited on the substrate, forming a film.

After deposition of the layers on the disk, if the surface of the storage disk is too smooth, stiction may become a significant problem during operation of the disk drive. Stiction refers to the sticking of the head slider to the disk while the disk is at rest. This sticking requires a greater motor force to break the head free upon start-up of the drive, and may also cause damage to the head and/or disk and failure of the drive in a short period of time. Stiction may arise from one or more of several causes. First, liquid contaminants, such as lubricants used in the manufacture of the drive components, may inadvertently be left on the components, which liquids settle on the disk surface and cause adhesion between the disk and head when the head is at rest on the disk. Second, outgassing may result in the formation of an adhesive material on the surface of the disk, thereby causing stiction between the head and disk. Third, if the head slider and/or disk are too smooth, there will be a high degree of surface contact between them, and the surfaces will adhere to each other according to the jo- block effect. In order to reduce stiction, the disk substrate is generally textured prior to deposition of the magnetic and protective layers. In texturing, the disk is abraded by, for example, a coarse tape and/or an abrasive slurry. Texturing, as well as other surface defects, results in the formation of microscopic asperities, or peaks or valleys, on the surface of the disk. Polishing of the disk surface may reduce the highest of these asperities. However, even after polishing, peaks and valleys still exist on the disk surface extending as much as approximately 150-250 angstroms (A) above or below the normalized surface height of the disk.

When a head flies over a disk, the flying height does not remain constant, but rather tends to fluctuate slightly above and below the normal flying height. At lower flying heights, a variation in the fly height may cause the head to contact the disk surface. This situation is referred to as intermittent contact. Presently, flying heights have been reduced to the point where intermittent contact with disk surface asperities has become an important consideration in the tribology of the head/disk interface. Prolonged intermittent contact between the head and a surface asperity can cause damage to the head and/or disk, and may cause drive failure in an unreasonably short period of time.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a disk drive with a read/write head flying at very low flying heights.

It is a further object of the present invention to provide a disk drive wherein intermittent contact of the head with asperity peaks formed on the disk surface will not cause damage to the head and/or disk over a prolonged period of use of the disk drive.

It is a still further object of the present invention to burnish, or polish off, the higher asperities so that the burnished asperities do not contact the head during rotation of the disk, thereby preventing damage to the head and/or disk.

It is another object of the present invention to provide disk drive according to the above objects which may operate with conventional inductive or magneto- resistive transducing elements.

These and other objects are accomplished by the present invention which relates to a disk drive having a head and disk assembly designed to transfer data to and from the disk at very low flying heights, for example, 2.5 μ". Due to factors including shock, vibration and changes in ambient pressure, the head will occasionally fly below the average flying height during rotation of the disk. At these lower heights, the head may be below the take-off height of the disk. Take-off height is defined as the height at which the head clears the highest asperity peaks on the disk. As such, the head may intermittently contact these asperity peaks. The present invention operates with bumishable disks, such that, during operation of the disk drive and rotation of the storage disk, the repeated contact of the head slider with the higher asperities causes the asperities to be worn down, or burnished. In this way, each of the asperities on the disk surface are reduced to be below the flying height of the head when the head flies at lower than normal flying heights. Thus, the danger of damage to the head and/or disk due to contact of the head with the otherwise protruding asperities on the disk is removed. At some point, defined as the "line of death", the asperities on the disk have been burnished to the point where all of the protruding asperity peaks have been removed. If the disk surface is burnished beyond the line of death, the surface becomes too smooth, and stiction and wear at the head/disk interface become significant problems. This will result in drive failure in an unreasonably short period of time.

The geometry of the asperities formed on the disk surface is significant to the present invention. Some disks are formed with asperities having geometries which are too broad to be substantially burnished. Conversely, some disks are formed with asperities having very narrow geometries. While disks having narrow asperities are bumishable, they are subject to high wear in a short period of time. Thus, an optimal disk for use in connection with the present invention is one having aperities within a range of geometries such that the asperities are narrow enough so that the higher asperities may be burnished to below the lowest flying height of the head, and yet are wide enough so that the disk will not be subject to wear in an unreasonably short period of time. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be explained with reference to the Figures in which:

FIGURE 1 is a top view of a disk drive according to the present invention;

FIGURE 2a is a magnified view through line 2-2 in Fig. 1;

FIGURE 2b is a magnified view of the head/disk interface of Fig. 2a after further rotation of the disk;

FIGURE 2c is a magnified view of the head/disk interface of Fig. 2a after further rotation of the disk;

FIGURE 2d is a magnified view of the head/disk interface of Fig. 2a after several rotations of the disk;

FIGURE 2e is a magnified view of a burnished disk; FIGURE 3a is a graph of take-off height versus contact start/stop cycles for the landing zone of a disk;

FIGURE 3b is a graph of take-off height versus time for the data carrying portions of a disk;

FIGURES 4a and 4b are magnified views of a surface of a non-bumishable disks with larger geometry asperities; and

FIGURE 5 is a graph of normalized surface height versus bearing area.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The invention will now be described with reference to Figs. 1 - 5, which relate in general to a disk drive including a bumishable storage media and slider to allow read and write operations by a head at a flying height lower than the higher asperities initially located on the surface of the disk. It is understood that the present invention may operate with disk drives of various designs and sizes.

Referring now to Fig. 1 there is shown a disk drive 20 including a storage disk 22 and a read/write head 24. Read/write head 24 includes a transducer 25 mounted to a slider 26. The slider 26 is in turn supported on actuator arm 28. Transducer 25 may be a conventional inductive transducing element, or in an alternative embodiment, may be a magneto-resistive (MR) transducing element. Slider 26 may preferably be formed of conventional materials such as calcium titanate or a titanium carbide/aluminum oxide composition. As is known in the art, slider 26 may be formed of other materials in alternative embodiments. Actuator arm 28 is provided to pivot around pin 30 by voice coil motor 32 in response to control signals received from the printed circuit board (not shown) .

As is known in the art, during operation of the drive

20, disk 22 is rotated by a spin motor (not shown) and actuator 28 pivots read/write head 24 across the surface of the disk so that data is transferred between the read/write head 24 and the disk 22 in a plurality of concentric data tracks. Slider 26 is provided to fly a very small distance, for example 2-4 μ", above the surface of disk 22 as disk 22 rotates.

Disk 22 is preferably formed of a plurality of layers. A substrate, preferably comprised of conventional materials such as aluminum or glass is coated with a magnetic layer and a protective, non- magnetic outer layer. The magnetic layer is preferably comprised of conventional materials including cobalt chromium alloys and cobalt nickel alloys. The non¬ magnetic outer layer may preferably be formed of conventional materials including carbon, or a metal such as rhodium. As is known in the art, the substrate may be formed of various other materials and the magnetic and non-magnetic layers may vary in number and composition and still be within the scope of the invention. The disk 22 may further include a perfluoropolyether lubricant or the like as is known in the art on the upper surface of the disk to reduce wear at the head/disk interface.

As described in the Background of the Invention section, a disk surface will unavoidably include a number of asperities. Causes contributing to the formation of asperities on the disk surface include the type of texturing done to the disk substrate and the presence of debris on the disk substrate which subsequently gets coated over during the deposition of the magnetic and protective layers. Asperities on the disk surface may also be formed by an electrical arc during the deposition process which results in a relatively large molten chunk of target material being deposited on the disk substrate. Fig. 2a is a sectional view through line 2-2 of Fig. 1, magnified on the order of one million times, showing an example of such asperities. While the majority of asperities 34 are small, occasionally a larger asperity 34a forms on the disk surface. Polishing of the disk surface may reduce the highest of these asperities, but even after polishing of the disk surface, an asperity or valley may extend as much as 150-250 angstroms (A) above or below the normalized or mean surface of the disk 22, represented by line 36 in Figs. 2a - 2e. The flying height of the read/write head 24 is preferably about 2 - 4 μ" and optimally about 2.5 μ" above the normalized surface of the disk. At these flying heights, the head will be above the "take-off height" of the disk, which is defined as the height at which the head 24 clears even the highest asperity peaks on the disk surface. However, as the disk rotates, the flying height of the head may vary due to several factors, including shock, disk drive vibration, variation in ambient pressure, the radial position of the head and the skew angle of the head. These factors occasionally cause the head to dip below the average flying height, where it may contact the disk surface and a higher asperity 34a, as shown in Fig. 2b. If this intermittent contact of the transducer 25 and/or slider 26 with the asperity 34a occurs over a prolonged period of time, the head and/or disk may be damaged.

Upon disk contact during lower than average flying heights, the slider 26 generally raises up and slides over the asperity 34a, as shown in Fig. 2c. The force of the slider against only asperity 34a creates a relatively large localized pressure between the slider and the asperity 34a. According to the present invention, the repeated pressure contact of slider 26 with the tip of asperity 34a, as disk 22 rotates, will cause a gradual burnishing or wearing away of the tip of asperity 34a, as shown in Fig. 2d. This process continues until the tip of asperity 34a has been burnished to a height where slider 26 no longer contacts asperity 34a, as shown in Fig. 2e. At this height, potentially damaging contact between a protruding asperity and the transducer 25 and/or slider 26 no longer occurs. It is further understood that burnishing of an asperity 34a may occur as result of the slider 26 shearing off an asperity, as opposed to gradually wearing away the asperity. Shearing of an asperity is more likely to occur where the asperity is formed of brittle material, such as, for example, carbon.

Intermittent contact of the transducer and slider with the protruding asperity peaks was commonly thought to be a significant limitation in the reduction of the flying height of the head over the disk. However, according to the present invention, after an initial period of operation of the disk drive, during which the slider 26 burnishes the disk, substantially all of the protruding asperity peaks will have been removed. Upon burnishing the asperity peaks, intermittent contact of the transducer and slider with the disk surface is greatly reduced or minimized. Thus, by utilizing a bumishable disk 22, the disk drive according to the present invention may operate to commercially acceptable specifications with the transducer 25 and slider 26 flying at very low flying heights, for example, 2 μ". As is further seen in the Figs. 2a - 2c, the slider 26 also includes a number of asperities, and the slider asperities are burnished in the same way and by the same principals as the asperities on the disk.

The disk 22 preferably includes a non-data carrying landing zone 38 (Fig. 1) , where the head is parked during nonoperational periods of the disk drive. In operation, upon spin-down of the disk, the voice coil motor 32 pivots actuator 28 and head 24 over the landing zone 38, where the head is parked. During both spin-up and spin down, there is a period of time where the disk is rotating, but the angular velocity is such that there is insufficient air pressure between the head and disk for the head to fly. Thus, during this period, the slider is in intimate contact with the rotating disk. As result of this intimate contact, the landing zone 38 and the slider 26 will become burnished relatively quickly. In a preferred embodiment of the present invention, as shown in Fig. 3a, the area of the landing zone and the slider may be fully burnished after approximately 100 to 200 contact start/stop cycles of the disk 22. However, as explained hereinafter, depending in part on the type of texturing process used, the geometry of the asperities may be narrow or broad. The geometry of the asperities on the disk will affect the number of spin-up/spin-downs required before the landing zone 38 and the slider 26 will be fully burnished.

The data carrying regions of the disk, outside of the landing zone, become burnished as result of random, intermittent contact of the slider 26 with the disk 22 as the slider flies over the disk. As previously stated, the flying height varies, and intermittent contact of the slider with the disk surface occurs at random intervals. Thus, over a sufficiently long period of time, the slider 26 will randomly contact each of the asperity peaks several times, to thereby burnish each of the asperities down to a height where potentially damaging contact with the slider 26 no longer occurs. As shown in Fig. 3b, the time it takes to fully burnish the disk outside of the landing zone as result of intermittent contact is preferably about two to three hours of disk drive operation. However, as stated above, the geometry of the asperities on the disk and the height at which the head flies will affect the burnishing time for the disk.

As shown in the graphs of Figs. 3a and 3b, each disk will have a critical burnishing height 39. This height is referred to as the "line of death". Burnishing of the disk beyond this height results in the disk becoming too smooth, which could lead to stiction between the head and the disk in the landing zone 38, and read/write errors in the data carrying portions of the disk. The height at which the line of death occurs is primarily determined by the texturing process and surface characteristics of the disk, and is not significantly affected by the height at which the head is provided to fly above the disk surface. The flying height does, however, affect the time it takes to reach the line of death, with lower flying heights causing the disk to be burnished to the line of death more quickly than higher flying heights.

At some height, preferably located above the line of death, the protruding asperity peaks have for the most part been burnished away, and the force of the slider against the disk surface upon intermittent contact is distributed over a relatively large disk surface bearing area. This uniform distribution of the slider contact force prevents localized pressure against any one asperity, which localized pressure is primarily responsible for the burnishing of a protruding asperity. Thus, at this height the disk is fully burnished and substantially no further burnishing of the disk occurs. Once fully burnished, there are still large numbers of smaller peaks and valleys, which prevent stiction between the slider and the disk surface. In a preferred embodiment, the height at which a disk is fully burnished will be above the line of death, but below the lowest flying height of the head 24. Whether or not a disk will be bumishable depends largely on the geometry of the asperities formed on the disk surface. Some disks are formed with asperities which are non-bumishable, such as, for example, disks 22 shown in Figs. 4a and 4b. Non-bumishable disks are those having asperities with relatively large and wide geometries, such as asperity 39. A non-bumishable asperity may have a large but somewhat flat geometry, as shown in Fig. 4a, or it may have a large geometry which has been polished down by a special head slider prior to placement of the disk within the disk drive, such as shown in Fig. 4b. With the non-bumishable asperities 39 of either Figs. 4a or 4b, during an intermittent contact of the slider with the disk surface, the burnishing force of the slider against the asperity 39 is distributed over a relatively large surface bearing area of the wide asperity. Thus, there is insufficient localized pressure on the asperity to significantly burnish the asperity. Other factors, including the wear resistance of the outer protective layer and the presence and quality of a surface lubricant, will also affect the degree to which a disk is bumishable.

Fig. 5 shows a plot 40 and 42 representing a graph of normalized surface height versus the bearing area of bumishable and non-bumishable asperities, respectively. The vertical axis represents disk surface height, with the highest asperity peak on the disk normalized to a height of 1. The other heights on the vertical axis are percentage comparisons to the highest asperity on the disk. The horizontal axis shows bearing area, which is represented as the percentage of the disk surface which would be in contact with a slider at a particular surface height. As can be seen by the graph, as the surface height of the disk gets burnished down, the non-bumishable disk will have a much higher bearing area in contact with the slider as compared to the bumishable disk. For example, at a surface height of 0.8 of the highest asperity peak, the bumishable disk (plot 40) will have approximately .04% of its surface in contact with the slider, while the non-bumishable disk (plot 42) will have approximately .25% of its surface in contact with the slider. These percentages are offered by way of example only, and may vary in different embodiments of the present invention. In contrast to non-bumishable disks, some disks are developed with asperities having very narrow geometries. While these disks are bumishable, they are not preferable for use in connection with the present invention, because they are subject to high wear in a short period of time. High wear of the disk surface may cause read/write errors in the data carrying region of the disk and stiction in the non- data carrying landing zone of the disk. Thus, an optimal disk for use in connection with the present invention is one having asperities within a range of geometries such that the asperities are narrow enough so that the higher asperities may be burnished to below the lowest flying height of the head 24, and yet are wide enough so that the disk will not be subject to wear in an unreasonably short period of time.

Texturing is an important factor in determining the geometry of the asperities formed on the disk surface. As is known in the art, the texturing process may be controlled to produce disks having asperity geometries within the above-mentioned optimal range of geometries. Such disks are manufactured, for example, by Komag, 275 South Hillview Drive, Milpitas, CA 95035. In general, texturing the disk to produce optimally bumishable asperities involves two steps. First, the disk substrate is abraded with a tape having abrasive particles thereon. Next, a slurry comprised of a suspension of free abrasive particles in a liquid is applied to the disk. In a preferred embodiment, the abrasive particles may range in size from about 1 to 10 microns, although it is understood that this range may vary in alternative embodiments. The two step combination of a tape then slurry may be controlled to optimally provide a surface roughness (Ra) for the disk of approximately 15 - 25 A. This texturing process provides a disk having optimal bumishable characteristics.

Although the invention has been described in detail herein, it should be understood that the invention is not limited to the embodiments herein disclosed. Various changes, substitutions and modifications may be made thereto by those skilled in the art without departing from the spirit or scope of the invention as described and defined by the appended claims.

Claims

We Claim:

1. A disk drive, comprising: a housing; at least one storage disk within said housing for storing data, said at least one storage disk including a plurality of asperities protruding above a normalized surface height of said storage disk; transducing means for transferring said data to and from said at least one storage disk; bearing means on which said transducing means is mounted for supporting said transducing means at a low flying height over said at least one storage disk during transfer of said data, said bearing means burnishing at least some asperities of said plurality of asperities due to intermittent contact of said bearing means with said at least some asperities during operation of the disk drive, said burnishing of said at least some asperities removing said at least some asperities to allow said bearing means to fly at said low flying height without damage to said transducing means or said at least one storage disk otherwise occurring as result of prolonged contact between said transducing means and said at least some asperities; actuator means within said housing for positioning said transducing means with respect to said at least one storage disk; and control means for controlling said transfer of data and for controlling the position of said actuator means.

2. A disk drive as recited in claim 1, wherein said low flying height is less than approximately 4 microinches.

3. A disk drive as recited in claim 1, wherein said low flying height is less than approximately 3 microinches.

4. A disk drive as recited in claim 1, wherein said low flying height is less than or equal to approximately 2.5 microinches.

5. A disk drive as recited in claim 1, wherein said low flying height is approximately 2 microinches.

6. A disk drive as recited in claim 1, wherein said transducing means comprises an inductive read/write head.

7. A disk drive as recited in claim 1, wherein said transducing means comprises an magneto-resistive read/write head.

8. A disk drive as recited in claim 1, wherein said bearing means comprises an air-bearing slider.

9. A disk drive as recited in claim 1, wherein said at least some asperities are fully burnished after approximately 2 hours of disk drive operation.

10. A disk drive as recited in claim 1, wherein said bearing means comprises an air-bearing slider.

11. A disk drive as recited in claim 1, wherein said air-bearing slider has asperities which are burnished during disk drive operation.

12. A disk drive for flying at low flying heights, comprising: a housing; at least one storage disk within said housing for storing data, said at least one storage disk including a plurality of asperities protruding above a normalized surface height of said storage disk; a head for transferring said data to and from said at least one storage disk; an air-bearing slider on which said head is mounted for supporting said head at a low flying height over said at least one storage disk during transfer of said data; an actuator for positioning said head with respect to said at least one storage disk; and control circuitry for controlling said transfer of data and for controlling the position of said actuator; wherein damage to said head and said at least one storage disk at said low flying height due to prolonged intermittent contact of said head with asperities protruding from a surface of said at least one storage disk is prevented by said air-bearing slider burnishing away said protruding asperities during operation of said disk drive.

13. A disk drive as recited in claim 12, wherein said low flying height is less than or equal to approximately 2.5 microinches.

14. A disk drive as recited in claim 12, further comprising a landing zone on said at least one storage disk, substantially complete burnishing of said protruding asperities within said landing zone occurring within approximately 200 start-up/spin down cycles of the disk drive.

15. A disk drive as recited in claim 14, wherein burnishing of said protruding asperities outside of said landing zone occurs within approximately 2 hours of disk drive operation.

16. A disk drive as recited in claim 12, wherein said air-bearing slider has asperities which are burnished during disk drive operation.

17. A disk drive as recited in claim 16, wherein the air-bearing slider is comprised of calcium titanate.

18. A disk drive as recited in claim 16, wherein the air-bearing slider is comprised of titanium carbide/aluminum oxide composition.

19. A disk drive as recited in claim 12, wherein said at least one storage disk includes an outer protective layer of deposited carbon.

20. A disk drive as recited in claim 12, wherein said at least one storage disk includes a magnetic layer comprised of a cobalt alloy.

21. A disk drive for flying at low flying heights, comprising: at least one storage disk for storing data, said at least one storage disk including a plurality of asperities protruding above a normalized surface height of said storage disk; a head for transferring said data to and from said at least one storage disk; an air-bearing slider on which said head is mounted for supporting said head at a low flying height over said at least one storage disk during transfer of said data, said flying height varying as said at least one storage disk rotates during operation of the disk drive, such that said air-bearing slider and/or said head intermittently contact said protruding asperities; an actuator for positioning said head with respect to said at least one storage disk; and control circuitry for controlling said transfer of data and for controlling the position of said actuator; wherein said protruding asperities are removed by said air-bearing slider upon intermittent contact of said air-bearing slider with said protruding asperities during a first few hours of operation of said disk drive.

22. A disk drive as recited in claim 21, wherein said low flying height is less than or equal to approximately 2.5 microinches.

23. A disk drive as recited in claim 21, wherein a protruding asperity of said plurality of protruding asperities is gradually worn away due to said intermittent contact with said air-bearing slider.

24. A disk drive as recited in claim 21, wherein a protruding asperity of said plurality of protruding asperities is sheared off due to said intermittent contact with said air-bearing slider.