Patent Application
20120154953
Embodiments of the invention generally relate to the air-bearing surface (ABS) of a read/write head of a hard-disk drive (HDD).
A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. An actuator relies on suspension's force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface.
It is desirable, for a variety of reasons, to maintain a constant or approximately constant distance between the read/write head and the surface of the magnetic-recording disk to ensure proper operation of the read/write head. If the distance between a read/write head and the surface of a magnetic-recording disk fluctuates, then the strength of the magnetic dipole field between the read/write head and the surface of the magnetic-recording disk will also fluctuate, which may cause problems in reading data from or writing data to the magnetic-recording disk.
It is observed that when a hard-disk drive (HDD) changes elevation, the fly height of the head slider may change. For example, when a hard-disk drive is taken from sea level to a high altitude, the fly height of the head slider tends to decrease. If the distance between a read/write head and the surface of a magnetic-recording disk fluctuates, then the strength of the magnetic dipole field between the read/write head and the surface of the magnetic-recording disk will also fluctuate, which may cause problems in reading data from or writing data to the magnetic-recording disk. Therefore, a head slider that is resistant to altitude changes would be desirable. By “resistant to altitude changes,” that is to say, that the fly height of a head slider does not change much in response to a change in altitude as in prior approaches.
In an embodiment, a hard-disk drive includes a head slider that comprises an air bearing surface (ABS). The air bearing surface has, disposed thereon at an air outflow end of the air bearing surface, an electromagnetic transducer. The air bearing surface further comprises a slit feature that is positioned before the electromagnetic transducer in the direction of air flow across the air bearing surface. The physical dimensions of the slit feature are designed to lower an amount of pressure required for a protrusion of the head slider to detect a surface of a magnetic-recording disk.
The air bearing surface may further comprise an optional hollow cavity positioned before the slit feature in the direction of air flow. The size and the shape of the hollow cavity are designed to decrease a change in a fly height of the head slider in response to a change in altitude of the hard-disk drive. Certain embodiments may employ a slit feature in conjunction with the hollow cavity so that certain disadvantages of employing the hollow cavity are mitigated or overcome through use of the slit feature, while still yielding the advantages of using the hollow cavity.
Embodiments discussed in the Summary of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section.
Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
Approaches for an air bearing surface of a read/write head which is more resistant to changes in altitude are presented herein. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein.
Prior to describing the air bearing surface (ABS) of a read/write head according to an embodiment, it may be helpful to understand the context in which the ABS of the read/write head will be employed. With reference to
With further reference to
With further reference to
With reference now to
ABS 300 comprises a transducer 330 in the central portion of outflow end 320. Transducer 330 is a component which converts electrical current into a magnetic field and vice-versa. Transducer 330 is used to read data from and write data to the electromagnetic surface of the disk.
ABS 300 comprises a plurality of features which promote the successful operation of transducer 330. These features may be created by etching into the plurality of layers forming ABS 300. The process of etching to remove portions of the layers of an air bearing surface of a read/write head to create features on the air bearing surface is well known to those in the art.
As shown in
ABS 300 comprises a hollow recess 350. Hollow recess 350 may be formed by etching a hole or hollow cavity through layers 340, 342, and 344 to expose layer 346. Thus, layer 346 forms the bottom of hollow recess 350 in an embodiment. In an embodiment, hollow recess 350 is positioned equidistant from side 360 and side 362. Hollow recess 350 may also be positioned before transducer 330 in the direction of air flow over ABS 300 as depicted in
The use of hollow recess 350 yields the advantage of rendering ABS 300 resistant to changes in altitude. More specifically, the inclusion of hollow recess 350 in ABS 300 results in a smaller reduction in fly height of the read/write head when an increase in altitude is experienced. Hollow recess 350 provides a zone of air in the recess cavity that is less sensitive to changes in the ambient pressure caused by altitude. This results in higher air pressure downstream that increases the touchdown pressure when the extendable protrusion approaches the disk.
In different embodiments, the size and the shape of hollow recess 350 may differ, as long as the dimensions of hollow recess 350 achieve the objective of decreasing a change in a fly height of the head slider in response to a change in altitude of the hard-disk drive. In one particular embodiment, hollow recess 350 has an etch depth between 1.0 microns and 1.37 microns.
However, use of hollow recess 350 has a drawback in that such use also tends to increases touchdown pressure. Touchdown pressure is the pressure asserted against a protrusion of the read/write head that is used to determine the fly height of ABS 300 during a calibration process. An extendable protrusion may be used in a calibration process to detect the fly height of ABS 300. When power is applied to a heater (not shown in
Additionally, use of hollow recess 350 tends to lower the efficiency of the extendable protrusion. The efficiency of the extendable protrusion refers to how fast the extendable protrusion will grow in response to the application of power to the heater. Thus, by lowering the efficiency of the extendable protrusion, the rate of growth of the extendable protrusion is reduced. Lowering the efficiency of the extendable protrusion requires a lower fly height of the ABS 300 to achieve best results.
It is observed that the undesirable effects on increasing touchdown pressure resulting from the use of hollow recess 330 may be offset by the use of slit feature 360 by certain embodiments. Slit feature 360 is a channel etched to expose layer 344. Thus, in an embodiment, slit feature 360 may not be as deep as hollow recess 350. As shown in
The use of slit feature 360 yields the desirable advantage of lowering touchdown pressure on the extendable protrusion. Slit feature 360 is positioned in front of the extendable protrusion to divert air into the channel of slit feature 360 and to prevent the air channel of slit feature from pressurizing the air directly on top of the extendable protrusion. This reduces the touchdown pressure and increases the efficiency of the extendable protrusion.
In different embodiments, the size and the shape of slit feature 360 may differ, as long as wherein the physical dimensions of slit feature 360 achieve the objective of lowering an amount of pressure required for a protrusion of the head slider to detect a surface of the magnetic-recording disk. In a particular embodiment, slit feature 360 may have an etch depth between 0.14 microns and 0.2 microns.
Advantageously, use of slit feature 360 has no impact to the fly height of the read/write head when the read/write head experiences a change in altitude. Consequently, if hollow recess 350 is used in conjunction with slit feature 360, slit feature 360 compensates for the drawback of using hollow recess 350 while still achieving the advantages provided by hollow recess 350.
Further, use of slit feature 360 also tends to improve the efficiency of the extendable protrusion. As a result, use of slit feature 360 supports a higher fly height for the ABS 300 to achieve best results.
Therefore, embodiments of the invention, such as the embodiment depicted in
Note that certain embodiments of the invention (not depicted in
Row 412 illustrates the fly height change due to altitude change between sea level and 10 kft elevation at ID, MD and OD radii.
Row 414 illustrates the efficiency of the extendable protrusion for various embodiments. As evidenced by table 400, embodiments possessing slit feature 360 (embodiments 1 and 3) exhibit lowered touchdown pressure than those embodiments lacking slit feature 360 (control and embodiment 2).
Row 416 illustrates touchdown pressure for various embodiments. As evidenced by table 400, embodiments possessing slit feature 360 (embodiments 1 and 3) exhibit lowered touchdown pressure than those embodiments lacking slit feature 360 (control and embodiment 2).
In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
