Patent Application
20080112088
The present invention relates to perpendicular magnetic recording and more particularly to a method for manufacturing a write head for perpendicular magnetic recording that has a trailing shield that avoids magnetic saturation by being efficiently magnetically connected with a magnetic return pole.
The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head has traditionally included a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic transitions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
In order to meet the ever increasing demand for improved data rate and data capacity, researchers have recently been focusing their efforts on the development of perpendicular recording systems. A traditional longitudinal recording system, such as one that incorporates the write head described above, stores data as magnetic bits oriented longitudinally along a track in the plane of the surface of the magnetic disk. This longitudinal data bit is recorded by a fringing field that forms between the pair of magnetic poles separated by a write gap.
A perpendicular recording system, by contrast, records data as magnetizations oriented perpendicular to the plane of the magnetic disk. The magnetic disk has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from the write pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer. The resulting magnetic flux then travels through the soft underlayer, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the write pole when it passes back through the magnetically hard top layer on its way back to the return pole.
One feature of perpendicular recording systems is that the low coercivity underlayer of the magnetic medium is particularly susceptible to stray magnetic fields. Unintended magnetic fields, such as from structures of the write head other than the write pole and even coming from the sides of the write pole itself can inadvertently write to portions of the medium that are outside of the intended trackwidth.
Another feature of perpendicular magnetic systems is that the magnetism of the high coercivity magnetic medium can be difficult to quickly switch. It is desired that the system have a high field gradient at transitions so that the magnetic state of the medium can be quickly switched from one direction to another.
Therefore, there is a need for a magnetic write head for perpendicular recording that can effectively avoid stray magnetic fields from inadvertently writing to the magnetic medium. There is also a need for a write head structure that can increase magnetic field gradient, allowing fast switching of the magnetic medium from one magnetic state to another.
The present invention provides magnetic write head for perpendicular magnetic recording. The write head has a magnetic write pole, a magnetic return pole and a trailing shield. A magnetic pedestal extends from the return pole to toward, but not to the write pole, and first and second magnetic studs connect the trailing shield with the pedestal. The studs are formed at either side of the write pole, although they may be completely beneath (leading) the write pole, and are each separated from the write pole by a lateral distance that is not greater than 5 um. In other words, the studs are separated from one another by a distance of not greater than the width of the leading edge of the write pole plus 10 um.
The magnetic studs may be separated from the write pole by a distance that is 4-5 um, and therefore, may be separated from on anther by a distance that is equal to the width of the leading edge of the write pole plus 8-10 um.
The studs and pedestal magnetically connect the trailing shield with the pedestal in order to keep conduct flux from the trailing shield. Ensuring that the studs maintain this desired maximum spacing from the write pole ensures that the trailing shield will not become saturated, and improves write field gradient and writing performance.
The trailing shield can be either a wrap around shield which has side portions that wrap around the sides of the write pole, or can be a purely trailing shield having a leading edge that does not extend down beyond (in the leading direction) the trailing edge of the write pole.
Because the trailing shield is magnetically connected with the return pole, the trailing shield functions as a second return pole as well as a trailing shield, allowing the write head to function as a cusp head design, enjoying the advantages of a cusp head design without many of the disadvantaged. The write head, therefore, can be considered to have a leading return pole and a trailing return pole (trailing shield) both of which are connected with one another by magnetic structures located entirely at the ABS. Both the leading and trailing return poles are driven by a single magnetomotive force in the form of the write coil disposed between the trailing return pole and the write pole. A write head according to an embodiment of the invention, therefore, provides the efficiency benefits of a cusp head design such as increased flux return path, while avoiding the manufacturing complexity ordinarily associated with such designs.
These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout.
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 which are not to scale.
The following description is of the best embodiments 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 221. As the magnetic disk rotates, slider 113 moves 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 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.
With reference to
With reference now to
With continued reference to
An electrically conductive write coil 317, shown in cross section in
With reference to
As can be seen, the trailing shield 322 is separated from the shield 322 by a non-magnetic shield gap material 323 such as alumina or some other material or combination of materials. The trailing portion of the shield 322 is separated from the trailing edge 328 of the write pole 310 by trailing gap thickness (TG), and is separated from the laterally opposed sides of the write pole by a side gap thickness (SG). The portion of the trailing shield 322 that is adjacent to the trailing edge 328 of the write pole 310 increases the field gradient of the write head. This is accomplished by drawing the write field toward this trailing portion of the trailing shield 322, which cants the write field a desired amount. Therefore, the write field is not perfectly perpendicular, but is canted somewhat in the trailing direction.
The trailing gap thickness TG involves a tradeoff. If the trailing gap TG is to large, field gradient will not be large enough. If the trailing shield gap TG is too small, and unacceptable amount of write field will be lost to the trailing shield, resulting in a weak write field. Therefore, the thickness of the trailing gap TG should be somewhat tightly controlled. The thickness of the side gaps SG is, however, not as critical. The side gaps SG are preferably larger than the trailing gap TG.
A magnetic pedestal 402 extends upward (in the trailing direction) from the return pole 314 toward, but not to, the write pole 310. As can be seen in
With reference to
A magnetic write head having connection studs 404, 406 with the above described desired lateral offset LO have been found to provide a 10 percent improvement in field gradient. In addition, such a structure reduces magnetic saturation of the soft underlayer of the magnetic media as well as reducing magnetic saturation of the trailing shield 322 as well as reducing magnetic saturation of the shield 322 when a stray field is present. Reducing the magnetically soft underlayer (SUL) saturation allows further reduction in SUL thickness in the magnetic medium (not shown), which would reduce the cost of manufacturing the magnetic medium by reducing SUL deposition time. The disk medium uniformity can also be improved when deposited on top of the thinner SUL. In general, the design trend is toward having a proper perpendicular writer combined with thinner SUL medium, when it is possible. The robustness against the external stray field makes the disk drive more reliable when there is an unexpected external field present, thereby avoiding potential write errors.
With reference now to
The above described write head structures 302 and 600 can also be described as a cusp head, because they provide the writing efficiency advantages of a cusp head design but with much greater simplicity and ease of manufacture. A cusp head design is a perpendicular write head design that has magnetic return poles both up-track from the write pole (leading) and down track from the write pole (trailing). The leading and trailing return poles in such designs can be magnetically connected at a back gap structure. In addition to being difficult to manufacture, such designs include the risk that excessive write field will be lost to the relatively large second return pole.
The present design provides the efficiency advantages of such a cusp design without the above described disadvantages. For purposes of illustration, these cusp-design features will be described with reference to
In addition, since the trailing shield 322 is magnetically connected with the return pole 402, the magnetomotive force from the coil 317 also increases the efficiency with which the trailing shield 322 can increase the write field gradient. Maintaining the above described lateral offset distances LO described above, maximizes the efficiency with which the trailing shield effectuates these cusp design advantages. In addition, because the trailing shield is magnetically connected with the return pole 402 only in an area near the ABS, there is much less risk of robbing flux from the write pole than would be the case if a return pole were included that ran alongside the write pole 310 and shaping layer 312 all of the way from the ABS to the back-gap 316. In addition, whereas previous cusp head designs have required multiple coils to drive flux through both of the return poles, the above described design can use a single coil 317 to drive flux through both the return pole 402 and the trailing shield 322.
While various embodiments have been described, it should be understood that they have been presented by way of example only, and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention 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.
