Patent Application
20050219747
The present invention relates to perpendicular magnetic recording, and more particularly to a trailing shield design using a trailing shield taper for improved magnetic field strength and field gradient performance.
At the heart of a computer is a magnetic disk drive that includes a magnetic disk, a slider where a magnetic head assembly including write and read heads is mounted, a suspension arm, and an actuator arm. When the magnetic disk rotates, air adjacent to the disk surface moves with it. This allows the slider to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk, where signal fields are written and read by the write and read heads, respectively. The write and read heads are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Typically magnetic disk drives have been longitudinal magnetic recording systems, wherein magnetic data is recorded as magnetic transitions formed longitudinally on a disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.
Data density requirements are fast approaching the physical limits, however. For example, increases data capacity requires decreased bit sizes, which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the magnetic field required to write a bit of data increases proportionally. The ability to produce a magnetic field strong enough to write a bit of data using conventional longitudinal write head technologies is reaching its physical limit.
One means for overcoming this physical limit has been to introduce perpendicular recording. In a perpendicular recording system, bits of data are recorded magnetically perpendicular to the plane of the surface of the disk. The magnetic disk may have a relatively high coercivity material at its surface and a relatively low coercivity material just beneath the surface. A write pole having a small cross section and very high flux emits a strong, concentrated magnetic field perpendicular to the surface of the disk. This magnetic field emitted from the write pole is sufficiently strong to overcome the high coercivity of the surface material and magnetize it in a direction perpendicular to its surface. This flux then flows through the relatively magnetically soft underlayer and returns to the surface of the disk at a location adjacent a return pole of the write element. The return pole of the write element has a cross section that is much larger than that of the write pole so that the flux through the disk at the location of the return pole (as well as the resulting magnetic field between the disk and return pole) is sufficiently spread out to render the flux too week to overcome the coercivity of the disk surface material. In this way, the magnetization imparted by the write pole is not erased by the return pole.
It will be appreciated by those skilled in the art that the high coercivity of the disk surface material can make it difficult to magnetize, especially at increasingly small magnetic grain sizes. It has been found that angling the magnetic field slightly can improve transition sharpness and achieve better media signal to noise ratio. A proposal to achieve this has been to place a trailing shield near the write gap and magnetically connected with the return pole. The shield would in effect attract field emitted from the write pole, thereby angling it slightly.
A challenge encountered with this approach is that some field is lost to the shield, and increasing write field to compensate for this can lead to adjacent track interference due to stay fields. In other word, using a trailing shield to angle the magnetic field emitted from the write pole advantageously decreases the switching field necessary to make the perpendicular magnetic transition, increasing the speed with which data can be written. However, this improvement in switching field comes at the cost of lost magnetic field. This is because some of the field leaks to the shield (in a direction parallel to the disk surface) resulting a weaker field being emitted by the write pole. Therefore, there remains a strong felt need for a mechanism for canting the magnetic field of a perpendicular write pole, while minimizing field loss. In addition, a mechanism for doing so would have to manufacturable in a mass production setting to practicable.
The present invention provides a magnetic write head for perpendicular recording that provides improved write field and write gradient performance. The write head includes a write pole and a trailing shield having a tapered surface. A return pole stitched to the trailing shield is magnetically connected with the write pole at a location away from the ABS surface.
The tapered surface of the trailing shield can be parallel to an adjacent tapered surface of the write pole. The use of a trailing shield in a perpendicular magnetic write head improves write performance, but also leads to lost field leaking from the write head to the shield through the write gap, which can result in reduced write field strength. The tapered surface of the trailing shield alleviates this lost field while retaining the advantage of having a trailing shield present. By tapering a surface of the shield, and preferably adjacent portion of the write pole, any field leaking to the sensor will be canted in a direction toward the ABS. A component of this field vector is in a desired direction perpendicular to the ABS (toward the magnetic medium) and therefore contributes to field strength. Experiments have shown substantial write performance through the use of such a tapered shield.
In order to avoid side writing, which might otherwise contribute to adjacent track interference, the tapered trailing shield can include laterally flared wing portions as well as a taper. These laterally flared wing portions could initiate at a point closer to the ABS than the point of taper initiation.
For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings.
The following description is the best embodiment presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein.
Referring now to
At least one slider 113 is positioned near the magnetic disk 112, each slider 113 supporting one or more magnetic head assemblies 121. As the magnetic disk rotates, the slider 113 is moved radially in and out over the disk surface 122 so that the magnetic head assembly 121 may access different tracks of the magnetic disk where desired data are written. Each slider 113 is attached to an actuator arm 119 by way of a suspension 115. The suspension 115 provides a slight spring force which biases slider 113 against the disk surface 122. Each actuator arm 119 is attached to an actuator means 127. The actuator means 127 as shown in
During operation of the disk storage system, the rotation of the magnetic disk 112 generates an air bearing between the slider 113 and the disk surface 122 which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension 115 and supports the slider 113 off and slightly above the disk surface by a small, substantially constant spacing during normal operation.
The various components of the disk storage system are controlled in operation by control signals generated by control unit 129, such as access control signals and internal clock signals. Typically, the control unit 129 comprises logic control circuits, storage means and a microprocessor. The control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123 and head position and seek control signals on line 128. The control signals on line 128 provide the desired current profiles to optimally move and position slider 113 to the desired data track on disk 112. Write and read signals are communicated to and from write and read heads 121 by way of recording channel 125.
The above description of a typical magnetic disk storage system, and the accompanying illustration of
With reference to
A magnetic shaping layer 208 is formed over the substrate 206 and has an end 210 that is recessed from an air bearing surface (ABS) 212. A non-magnetic, dielectric material 214 fills the space between the end 210 of the shaping layer 208 and the ABS 212. The shaping layer 208, and fill material 214, preferably have coplanar upper surfaces which can be produced by a chemical mechanical polishing process.
With continued reference to
A thin non-magnetic write gap layer 226 is formed over the write pole. The write gap layer 226, can be formed of many non-magnetic materials, such as alumina Al2O3, and in is preferably formed of a layer of alumina and a layer of diamond like carbon, for reasons that will be discussed below.
The tapered trailing shield 202 is formed over the write gap layer 226 in the pole tip region 218 of the write element 200. The trailing shield assumes shape of the write pole 216 over which it is formed, having a tapered shape 204 at its bottom that corresponds with the taper 222 of the write pole 216. In this sense the taper begins at essentially the same distance 224 from the ABS 212.
A magnetic return pole 230 is stitched to the top of the trailing shield 202 and extends back to a back gap region 232, where it magnetically connects with the write pole 208 forming a magnetic yoke 234 therewith. The writer 200 also includes an electrically conductive coil 236, having a plurality of winds 238 (shown in cross section), which pass through the magnetic yoke 234. A non-magnetic, dielectric layer 240 surrounds and insulates the winds 238 of the coil 236.
The presence of the magnetic shield 202 improves the field gradient and improves switching field performance by advantageously canting the write field emitted from the write pole 216. However, previously the presence of a trailing shield has meant a loss of write field. Prior art designs have used trailing shields and write poles adjacent thereto that extend straight back from the ABS with no taper. In other words, the surfaces of the trailing shield and write pole in contact with the write gap were extended perpendicular to the ABS. Field lost between the write pole and shield using such a design could be described as a vector oriented parallel with the ABS and perpendicular to the primarily desired direction of emitted write field. Therefore, no component of this vector of lost field contributes to write field. By providing a taper 228 on the trailing shield, field leaking between the write pole and the trailing shield is angled toward the magnetic medium. A component of this vector then contributes to write field and improves write field strength. Experimentation has shown significant improvement in write field performance through the use of such a tapered trailing shield 202. The tapered surface portion of the trailing shield 202 defines a plane having an angle of preferably less than 90 degrees with respect to the ABS and more preferably and angle of between 60 and 90 degrees with respect to the ABS.
A first layer of magnetic write pole material 506 can then be deposited, such as by electroplating. This layer of write pole material is preferably a very high saturation, low coercivity material, and is preferably formed of laminated layers of a high magnetic saturation material (high Bsat) such as CoFe, NiFe or their alloys with interspersed non-magnetic film such as Cr, Ru, etc. A second layer of write pole material 508 is then deposited on top of the first layer 506. This second layer 508 may be a magnetic material that is more readily removed by reactive ion etching than the first layer 506.
Thereafter a layer of Ta may be deposited, followed by a mask 512, such as photoresist. As illustrated in
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While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Other variation and embodiments falling within the scope of the invention will, no doubt be apparent to those skilled in the art. For example, while the present invention was described with reference to a writer having a Return pole formed above the write pole (ie. trailing), the present invention could also be practiced on a perpendicular write element having a return pole below (ie. leading) the write pole. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
