Flying height adjustment for air bearing sliders

Details Flying height adjustment for air bearing sliders Flying height adjustment for air bearing sliders

1999-07-13

2002-02-05

Heinz, A. J. (Department: 2652)

Dynamic magnetic information storage or retrieval

Fluid bearing head support

Disk record

C360S294700

Reexamination Certificate

active

06344949

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to air bearing sliders with flying height adjustment, and in particular to air bearing sliders using ducts and/or surface features for altering the air flow to adjust the flying height.
BACKGROUND OF THE INVENTION
Air bearing sliders utilize a boundary layer of air compressed between the slider's air bearing surface and a moving surface to “fly” over the moving surface. The air bearing surface is shaped such that part of the boundary layer of air carried by the moving surface is compressed and forced to flow underneath the slider. This compressed air flow supports the slider at a flying height above the moving surface by creating a lift force. More complicated air bearing surfaces may have air bearing surfaces with areas which reduce the air pressure at some locations under the slider to produce a force pulling the slider down to the moving surface.
Air bearing sliders are commonly used in the field of magnetic recording for carrying magnetic recording heads at a specific flying height above a magnetic recording medium, typically a disk. It is at the interface between the head and the medium where the critical processes of magnetic recording occur. Maintaining a stable and reliable interface is required to ensure proper functioning of a disk drive. For example, if the spacing between a write head and the magnetic disk is too large, the head's fringing field will be too weak to record data on the disk. Also, the read-back signal registered by a read head (usually, a magnetoresistive head integrated with the write head) will be reduced and data errors may occur. On the other hand, very low head-disk spacing may improve magnetic performance, but can lead to mechanical wear of the head and disk, substantially reducing the lifetime of both.
Under some circumstances it is desirable to change the flying height of the slider holding the magnetic recording head in a disk drive. One primary reason is that the areal density of data can be increased when the recording head is close to the disk surface. That is because magnetic recording is a “near-field” process; in other words, writing by the write head and reading by the read head occur in close proximity to the head's gap. This leads to an exponential dependence of the field on the spacing between the head and disk and, consequently, areal density.
Of course, as areal density of data increases, the tolerances in the head-disk spacing or the flying height must be reduced. This places significant constraints on both head and disk parameters. Since typical disks can be out of flatness by as much as 20-50 &mgr;m and the glider flies at a height of less than 50 nm the compliance of the head and suspension must be sufficient to compensate for this large motion while tracking the disk surface.
The prior art air bearing technology used in disk drives offers a large number of different designs. They were developed to satisfy somewhat different criteria, and over the years they have become more elegant, with improved performance allowing decreased head-disk spacing. Some of the requirements for specific air bearing designs include rapid take-off, close compliance to the disk's surface, stable flying and minimal variation of flying height of the slider at different radial positions on the disk. The last item is important since the relative velocity of the head over the disk can change by as much as a factor of 2 from the inside to the outside diameter of a typical magnetic recording disk. The different velocities alter the air pressure under the slider and result in changes in flying heights than can impact the head's ability to read and write properly. Changes in ambient pressure also affect the flying height. Thus, the flying height in a disk drive operating in a low pressure environment, e.g., on-board an airplane, is different than the flying height in a disk drive operating at standard atmospheric pressure. Finally, with the widespread use of rotary actuators in disk drives, the air bearing must be able to fly in a stable manner over a range of azimuthal orientations (20-25 degrees) of the head with respect to the disk.
Most recent technological advances are pushing disk drives to the limiting case in which the head and disk are in contact during recording. A problem associated with contact recording is that the disk and head are subject to wear. Even though wear rates are minimized through coatings and lubrication, this wear can lead to sufficient damage or degradation through corrosion such that the recording process is no longer functional. It would be desirable to limit the contact to the times when recording is taking place while maintaining a low flying height, e.g., on the order of 5-50 nm at all other times.
The prior art contains a number of proposals for reducing and stabilizing the flying height of the various slider designs. Some solutions involve using piezoelectric actuators for exerting a controllable downward force at the supported end of the load arm on which the slider is mounted.
JP-A-63-228461 describes a slider having a negative pressure generating recess. Control is achieved using a vent hole bored through from the negative pressure pocket to the top surface of the slider, and a piezoelectric flap lying over the top surface of the vent hole. Piezoelectric control of the flap acts like a valve on the vent hole and regulates the negative pressure and hence the flying height. U.S. Pat. No. 5,276,573 to Harada et al. also teaches the use of a vent passing from the air bearing surface of the slider to the top surface. A piezoelectrically or electrostatically controlled valve layer is positioned over the vent at the air bearing surface of the slider to control the air flow through the vent hole and thus control the flying height of the slider. The slider body is made of a ceramic base portion and includes a semiconductive insert portion of silicon or photosensitive glass.
Unfortunately, sliders using vent holes between the air bearing surface and the top surface as taught in JP-A-63-228461 and U.S. Pat. No. 5,276,573 do not solve the problem of flying height adjustment. In particular, mounting a valve on the air bearing surface is very difficult to do. Providing a vent hole in the ceramic body of the slider poses serious manufacturing problems because of the hardness of the ceramic material. Furthermore, with the progressive miniaturization of sliders the mounting of valves on the air bearing surface becomes impracticable. In fact, state of the art patterning techniques used in head manufacture are fundamentally incompatible with the solutions taught in JP-A-63-228461 and U.S. Pat. No. 5,276,573. In addition, valve structures (especially thin ones) at the air bearing surface are more subject to contamination which prevents valve motion.
In view of the above, the present air bearing technology does not offer suitable designs for achieving accurate flying height control. Specifically, the prior art does not teach how to achieve low flying heights and maintain or adjust them to enable near-contact or contact recording. Prior art sliders are also not capable of adjustments for operating parameters and environmental factors affecting the flying height. These include flying velocity as well as variations in pressure and temperature. Finally, the prior art solutions are incompatible with modern head manufacturing techniques.
OBJECTS AND ADVANTAGES OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an air bearing slider designed to allow one to efficiently adjust the flying height. The slider should be capable of maintaining flying heights of a read/write head in the range of 5-50 nm to a high degree of accuracy. In addition, the control mechanism should allow the slider to effectuate flying height adjustments in response to changes in operating parameters as well as fluctuations of environmental factors. Specifically, the air bearing slider with the flying height control in accordance with the invention should perm

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