Dynamic magnetic information storage or retrieval – Fluid bearing head support – Disk record
Reexamination Certificate
2000-11-09
2002-11-05
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Fluid bearing head support
Disk record
Reexamination Certificate
active
06477013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to data storage systems, and more particularly to a slider air bearing design and method providing writing of laser field measurement without substantial fly height affect.
2. Description of Related Art
Fixed magnetic disk systems, typically referred to as “hard” disk drives, are now commonplace as the main non-volatile storage in modern personal computers, workstations, and portable computers. Such hard disk drives are now capable of storing gigabyte quantities of digital data, even when implemented in portable computers of the so-called “notebook” class. Many important advances have been made in recent years that have enabled higher data density and thus larger storage capacities of hard disk drives, and that have also enabled much faster access speeds, both in the bandwidth of data communicated to and from the hard disk drive, and also in the access time of specified disk sectors. Advances have also been made that have greatly reduced the size and weight of hard disk drives, particularly as applied to portable computers, have been made over recent years. These advances have resulted in the widespread availability of ultra-light portable computers, yet having state-of-the art capability and performance.
A head/disk assembly typically comprises one or more commonly driven magnetic disks rotatable about a common spindle and cooperating with at least one head actuator for moving a plurality of transducers radially relative to the disks so as to provide for the reading and/or writing of data on selected circular tracks provided on the disks. The magnetic transducer or “head” is suspended in close proximity to a recording medium, e.g., a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator.
During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over a desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force us counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head resides near the trailing end, which tends to fly closer to the recording surface than the leading edge.
The recording medium holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer's ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Fly height stability is determined by proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
One important design factor for fly height is the slider's resistance to changing conditions. If the transducer fly height does not stay constant during changing conditions, data transfer between the transducer and the recording medium may be adversely affected. Fly height is further affected by physical characteristics of the slider such as the shape of the ABS. Optimized rail shaping, for example, can provide enough resistance to changes in air flow.
Hard drive manufactures are starting to incorporate proximity recording type sliders in drives in order to achieve higher storage densities. The proximity recording slider is designed to maintain a small area near the read-write element in constant contact with the disk, and thus enabling smaller bit size and ultimately larger storage densities. This approach to increasing storage density puts considerable amount of strain on controlling wear at the slider-disk interface, because a slight variation in contact load and contact area could greatly affect the drive survivability.
Slider-disk contact results in lubricant depletion and degradation, wear of both surfaces, generation of wear particles, stick-slip, etc. All these phenomena affect reliability of the disk drive, e.g., through jitter, as well as its durability.
To continue the increases being made in data-storage density, drive designs call for lower and lower slider fly height. For a magnetic head slider with an ABS pattern, there are numerous slider-curvature parameters and curvature-adjust techniques (CATs) that are considered important for fly height control and tribology. Crown is the maximum separation of the cylindrical contour along the flying direction from an imaginary plane drawn between the leading and trailing edges of the ABS. Camber has a similar definition and is the separation from an imaginary plane drawn perpendicular to the flying direction between the two side edges of the slider. Twist is the difference of the “diagonal” cylindrical curvatures.
For modern pico sliders, these curvature parameters are typically on the order of several nanometers, while the slider width and length are about 1 mm. The actual curvatures of the ABS are therefore truly minute. However, the variance of the crown is a key factor in slider performance.
Fly-height modeling of common “negative-pressure air bearing” sliders indicates that small changes of a few nanometers in the crown can significantly affect the fly height of the slider. Hence there has been an obvious need to develop and implement a method to finely adjust crown.
One technique involves for adjusting crown is “laser scribing”, which refers to the exposure of the slider surface-typically the back or flex side-to sufficiently intense laser irradiation such that a permanent surface modification is produced. The technique of laser scribing to produce surface-stress change is very desirable because laser scribing is non-contact and fast, and there is no mechanical wear and tear of any contact device like a grinding wheel or a diamond scriber; it is more precise, since the positioning of the focused laser beam can be accurately controlled using galvo mirrors and machine vision; and it is more amenable to an in-situ closed-loop control that terminates the scribing when the target crown or camber is reached.
Preferably, laser scribing is performed on the flex side to induce positive curvature changes at the ABS. This is a significant advantage compared to scribing or modifying the ABS side, since any debris that is not cleaned or washed away is much less offensive at the flex side compared to the ABS side. The use of a high-pulse-repetition-rate laser permits rapid processing of the slider by quickly scanning the spot on the surface to produce the scribe pattern required to provide the desired curvature change.
There are various non-contact optical techniques for in-situ monitoring of slider curvature that provide closed-loop control with laser scribing. Applicable optical monitoring techniques include probe-beam deflection sensing (PDS) techniques-used frequently in atomic force microscopy and photothermal beam-deflection spectroscopy and interferometer imaging.
However, one approach involves the “Writing Of a Laser Field” (WOLF) on suitable areas of the slider ABS surface by telecentric scanning of a probe laser beam and monitoring the directions of the scanning reflected laser beam. This WOLF technique is basically a multi-beam differential PDS technique. As a result, it is insensitive to static tilts of the slider surface, unlike the single-beam PDS method. Compared to interferometry, the WOLF method is much faster-providing a crown measurement in 10 milliseconds rather than a few seconds, as in interferometric techniques. Nonetheless, the WOLF method does not typically provide an absolute measurement of crown or camber and so the WOLF measured values have to be converted to a crow
Kang Soo-Choon
McMaster Mark C.
Zhang Tony Jing
LandOfFree
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