Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1999-01-20
2001-10-09
Pianalto, Bernhard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S129000, C427S130000, C427S131000, C427S132000, C427S264000, C427S265000, C427S270000, C427S275000, C427S276000, C427S287000, C427S314000, C427S318000, C427S320000, C427S327000, C427S328000, C427S404000, C427S405000, C427S556000, C427S595000, C427S596000
Reexamination Certificate
active
06299947
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to magnetic disks, and in particular to textures formed on magnetic disks that induce a minimum amount of vibration of a read-write head while simultaneously reducing static and dynamic friction between the disk and the read-write head. This invention also relates to methods for texturing magnetic disks.
It is known in the art to manufacture magnetic disks using the following process.
1. A NiP layer
1
is electroless plated onto an Al alloy
2
(FIG.
1
). (NiP layer
1
is hard, and protects the disk during collisions with a read-write head during use.)
2. NiP layer
1
is then polished.
3. NiP layer
1
is textured by forming bumps
3
so that the resulting disk has a rough surface. This texture minimizes static and dynamic friction between a read-write head and the resulting disk during use. The texture can be placed either on the entire disk surface or on only a portion of the disk surface called a contact-start-stop, or “CSS” zone. (The CSS zone is where the read-write head rests against the disk when the disk is not in use.)
4. An undercoat
4
(e.g. NiP or Cr), a magnetic Co alloy
5
, and a protective film
6
(e.g. hydrogenated carbon or zirconia) are then sputtered onto NiP layer
1
in that order.
5. A lubricant layer is applied to protective film
6
.
One technique for texturing the NiP layer is to apply laser pulses thereto to form “ridge-shaped” texture bumps. Such bumps comprise a circular ridge having a depression in the middle. One such laser bump is shown in plan view in FIG.
2
A and in perspective view in FIG.
3
A. Laser texturing is discussed, for example, in U.S. Pat. No. 5,062,021, issued to Ranjan. Laser texture bumps should be large enough to decrease the friction force between the head and disk, and at the same time small enough to allow a low flying and glide height at which no contact occurs between the head and the disk.
There is a general trend in the industry to reduce the height of laser bumps on magnetic disks. This height reduction permits the read-write head to fly closer to the magnetic disk. The size of the laser bump determines its mechanical effect on the head-disk interface. The height and diameter of a laser bump can be independently controlled during texturing. If the bump height is reduced without reducing the bump diameter, the bump will have a larger radius of curvature, which causes a greater head-disk contact area (and therefore increased stiction and friction). Accordingly, when one reduces the bump height (to permit a lower flying height), it is also desirable to reduce the bump diameter (to reduce effective contact area between the head and disk).
When a read-write head takes off and lands on a magnetic disk, mechanical interaction between the head and disk causes the head to vibrate. Such vibrations can be measured with a piezoelectric transducer, which provides an output signal called an acoustic emission (“AE”) signal. In recent years, there has been interest in reducing such vibrations to enhance durability and reliability of the disk drive.
SUMMARY
We have discovered that by modifying the shape of a texture bump on a magnetic disk, we can reduce vibration of a read-write head caused by head-disk mechanical contact. In particular, we have discovered that by making elliptical texture bumps on a magnetic disk, we can reduce such vibrations. We have also discovered that making texture bumps elliptical reduces friction between the read-write head and the disk. In one embodiment, the elliptical bumps have their major axis parallel to the circumferential direction of the disk. The elliptical bumps are typically formed by modifying the shape of the laser beam used to texture the substrate. The elliptical bumps typically comprise an elliptical ridge surrounding a depression.
REFERENCES:
patent: 5062021 (1991-10-01), Ranjan et al.
patent: 5108781 (1992-04-01), Ranjan et al.
patent: 5236763 (1993-08-01), Luthi
patent: 5528922 (1996-06-01), Baumgart et al.
patent: 5631408 (1997-05-01), Baumgart et al.
patent: 6146736 (2000-11-01), Liu et al.
patent: 1-180351 (1996-07-01), None
Patent application 09/216,008, filed Dec. 17, 1998, entitled Continuous Texture Features for a Disk Substrate, filed by Li-Ju Lin et al.
Bhushan, et al., “Roughness-Induced Shear- and Squeeze-Film Effects in Magnetic Recording—Part I: Analysis”, Transactions of the ASME Journal of Tribology, 1988, vol. 117, p. 220-227 (No Month Available).
Frusescu Dan
Salamon David Vigdor
Suzuki Shoji
Thomas Rony
Treves David
Komag, Inc.
Pianalto Bernhard
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