The present invention relates to magnetic data recording and more particularly to a scissor type magnetic sensor having a multi-layer back edge bias structure for providing uniform biasing to both free layers of a scissor type magnetic sensor.
The heart of a computer 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 into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions 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 includes at least one coil, a write pole and one or more return poles. When a current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the write pole, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic disk, thereby recording a bit of data. The write field, then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor or a Tunnel Junction Magnetoresisive (TMR) sensor can be employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the adjacent magnetic media.
As the need for data density increases there is an ever present need to decrease the size of a magnetic read sensor. With regard to linear data density along a data track, this means reducing the gap thickness of a magnetic sensor. Currently used sensors, such as the GMR and TMR sensors discussed above, typically require 4 magnetic layers, 3 ferromagnetic (FM) and 1 antiferromagnetic (AFM) layer, along with additional nonmagnetic layers. Only one of the magnetic layers serves as the active (or free) sensing layer. The remaining “pinning” layers, while necessary, nonetheless consume a large amount of gap thickness. One way to overcome this is to construct a sensor as a “scissor” sensor that uses only two magnetic “free” layers without additional pinning layers, thus potentially reducing gap thickness to a significant degree. However, the use of such a magnetic sensor results in design and manufacturing challenges, such as the challenge of providing uniform biasing to both free layers of the magnetic sensor.
The present invention provides a magnetic sensor that includes a sensor stack, and a magnetic bias structure formed adjacent to the sensor stack, the bias structure having a magnetic moment that varies with location within the bias structure.
The magnetic bias structure can include a first magnetic layer and a second magnetic layer formed over the first magnetic layer, the first magnetic layer having a higher magnetic moment than the second magnetic layer. Alternatively, the magnetic bias structure can include more than two magnetic layers of differing magnetic moments. The magnetic bias structure could also be formed as magnetic layer having a gradient magnetic moment, such as with a higher magnetic moment at its bottom and a lower magnetic moment at its top, and wherein the magnet moment gradually varies between the bottom and top surfaces.
This unique magnetic bias structure can be especially advantageous for use as a back edge magnetic bias structure in a scissor type magnetic sensor. In the formation of such sensors, the lower magnetic free layer tends to be less responsive to magnetic biasing than the upper magnetic free layer. This can be as a result of increased stripe height of the bottom free layer as compared with the upper free layer and also as a result of non-uniform thickness of the non-magnetic, electrically insulating layer formed between the sensor stack and the magnetic bias structure. The unique magnetic bias structure compensates for this to provide an equal effective magnetic biasing for both the first and second magnetic free layers, thereby improving performance of the sensor.
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 121. As the magnetic disk rotates, slider 113 moves in and out over the disk surface 122 so that the magnetic head assembly 121 can 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
The first and second magnetic layers 304, 306 can be constructed of multiple layers of magnetic material. For example, the first magnetic layer 304 can be constructed of: a layer of Ni—Fe; a layer of Co—Hf deposited over the layer of Ni—Fe; a layer of Co—Fe—B deposited over the layer of Co—Hf; and a layer of Co—Fe deposited over the layer of Co—Fe—B. The second magnetic layer 306 can be constructed of: a layer of Co—Fe; a layer of Co—Fe—B deposited over the layer of Co—Fe; a layer of Co—Hf deposited over the layer of Co—Fe—B; and a layer of Ni—Fe deposited over the layer of Co—Hf. The capping layer structure 310 can also be constructed as a multi-layer structure and can include first and second layers of Ru with a layer of Ta sandwiched there-between. The seed layer structure 312 can include a layer of Ta and a layer of Ru formed over the layer of Ta.
The sensor stack 302 is sandwiched between leading and trailing magnetic shields 314, 316, each of which can be constructed of a magnetic material such as Ni—Fe, of a composition having a high magnetic permeability (μ) to provide effective magnetic shielding.
During operation, a sense current or voltage is applied across the sensor stack 302 in a direction perpendicular to the plane of the layers of the sensor stack 302. The shields 314, 316 can be constructed of an electrically conductive material so that they can function as electrical leads for supplying this sense current or voltage across the sensor stack 302. The electrical resistance across the sensor stack 302 depends upon direction of magnetization of the free magnetic layers 304, 306 relative to one another. The closer the magnetizations of the layer 304, 306 are to being parallel to one another the lower the resistance will be, and, conversely, the closer the magnetizations of the layers 304, 306 are to being anti-parallel to one another the higher the resistance will be. Since the orientations of the magnetizations of the layers 304, 306 are free to move in response to an external magnetic field, this change in magnetization direction and resulting change in electrical resistance can be used to detect a magnetic field such as from an adjacent magnetic media (not shown in
With continued reference to
However, the presence of the magnetic field from the magnetization 410 of the bias structure 406 causes the magnetizations 338, 340 rotate so that they are generally orthogonal as shown. However, the magnetizations 338, 340 can respond to a magnetic field by rotating in a scissoring fashion. While the bias layer rotates the magnetizations 338, 340 of the free layers 304, 306 in desired orthogonal directions, the magnetization 410 of the bias layer 406 does not prevent the magnetizations 338, 340 from flipping direction (e.g. magnetization 336 pointing to the right and 338 pointing to the left), which would render the sensor 300 incompatible with the signal processing circuitry and would, therefore, render the sensor 300 useless.
The magnetizations 334, 336 from the layers 322, 324 of the soft side shield structure 318 (
If a standard single layer bias structure were used to form a back edge bias structure for biasing the magnetizations of the free layers 304, 306, this would result in inconsistent biasing, wherein the bottom free layer 304 would receive less effective biasing than the upper free layer 306. This is due to the extra stripe height of the bottom free layer 304 as compared with the upper free layer 306 as well as to the extra spacing between bias structure and the free layer 304 due to the increased thickness of the insulation layer 408.
The bias structure 406 of the present invention overcomes this obstacle by providing a varied magnetic biasing to compensate for these shape induced variations in bias between the free layers 304, 306. As shown in
To this end, both the bottom layer 406a and top layer 406b can be constructed of NiFe, CoFe, CoNiFe, or their alloys with the bottom layer 406a having a higher magnetic moment than the top layer 406b. For example, the bottom layer 406a can be constructed of a Ni—Fe—Co alloy having higher moment than the upper layer 406B. The layers 406a and 406b can have a magnetic moment range of up to 2.2 Tesla. As an example, the bottom layer 406a can have a magnetic moment of 2.2-2.4 Tesla and the top layer 406b can have a magnetic moment of 1.8 to 2.0 Tesla.
In
While the above embodiments describe the bias structure 406 as being formed of discreet layers 406a, 406b, each having a different magnetic moment, the bias structure could also be formed to have a gradient magnetic moment. That is, the bias structure 406 could be formed with a magnetic layer having a magnetic moment that gradually varies so that it has a higher magnetic moment at the bottom and a lower magnetic moment at the top, with the magnetic moment gradually varying from bottom to top. In addition, the bias structure 406 could be formed with discreet layers having different magnetic moments, but with more than two discreet layers.
With reference to
With reference to
Then, with reference to
In another embodiment, as shown in
In order to form a sensor such as that described above with reference to
A planarization process such as chemical mechanical polishing can then be performed, leaving a structure such as that shown in
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 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.
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