MAGNETIC SCISSOR SENSOR WITH CLOSED-LOOP SIDE SHIELD
A scissor type magnetic sensor for magnetic data recording having a flux closure magnetic side shield structure. The magnetic sensor has a magnetic side shield structure that includes a non-magnetic layer within a magnetic material layer, with the non-magnetic layer being removed from the sensor stack so as to define upper and lower magnetic portions of the magnetic structure that are separated from one another at a region away from the sensor stack. The upper and lower magnetic portions are connected with one another in a region near the sensor stack so as to magnetic flux closure structure. The novel magnetic side shield structure provides net neutral magnetization that does not provide an inadvertent biasing to the magnetic free layers of the magnetic sensor.
The present invention relates to magnetic data recording and more particularly to a scissor type magnetic sensor with a magnetic side shield having a magnetic flux closure structure.
BACKGROUNDAt 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 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 current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the coil, 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 media, 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 Magnetoresistive (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 magnetic media.
In the push for ever increasing data density, researchers have searched for ways to decrease gap spacing and also to minimize adjacent track interference of magnetic sensors. Structures such as pinning structures can increase the gap spacing (space between upper and lower magnetic shields) which increases bit length that the read sensor can read. In addition, at tight track pitches, adjacent tracks can alter the magnetization of magnetic free layers resulting in unacceptable signal noise. Therefore, there remains a need for a structure for maximizing data bit density and minimizing adjacent track interference in a magnetic data recording system.
SUMMARYThe present invention provides a magnetic sensor that includes a sensor stack having first and second magnetic free layers separated from one another by a non-magnetic layer. The magnetic sensor also includes a magnetic side shield structure that includes a magnetic structure having upper and lower portions that are separated from one another by a non-magnetic layer in a region recessed from the sensor stack. The non-magnetic layer is removed from the sensor stack so that the upper and lower magnetic portions are magnetically connected with one another in a region near the sensor stack.
The novel side shield structure results in a net-zero magnetization in longitudinal direction that will not inadvertently provide a magnetic biasing to the magnetic free layers of the sensor stack. This side shield structure is particularly advantageous in a scissor type magnetic sensor where an inadvertent side bias will result in shift of the magnetizations of the magnetic free layers from optimal biasing states.
The novel side shield structure can be used in a scissor type magnetic sensor having an in-stack magnetic bias structure for magnetically biasing the magnetizations of the magnetic free layers. In addition, the novel magnetic side shield structure can provide significant advantage in a two-dimensional magnetic recording (TDMR) system, wherein a magnetic head is formed with multiple magnetic sensors for increased data density.
These and other features and advantages of the invention will be apparent upon reading of the following detailed description of the embodiments taken in conjunction with the figures in which like reference numeral 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 the 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 the 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, 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 the slider 113 to the desired data track on the media 112. Write and read signals are communicated to and from write and read heads 121 by way of recording channel 125.
The sensor stack 202 includes first and second magnetic free layers 208, 210 that are anti-parallel coupled across a non-magnetic spacer or barrier layer 212 that is sandwiched between the magnetic free layers 208, 210. The magnetic free layers 208, 210 have magnetizations indicated by arrows 216, 218 that can be more easily understood with reference to
With reference again to
With continued reference to
With reference again to
The use of the novel flux closure provides significant performance advantages over other structures. Previously, magnetic scissor sensors have used a non-magnetic isolation layer between top and bottom shield which has resulted in large side reading/skirt ratio, resulting in cross track performance degradation and Areal Density Capacity (ADC) loss. In addition, such previously used non-magnetic isolation layers lead to a larger physical-magnetic track-width offset, resulting in the need for a smaller physical track-width and resulting in significant manufacturing challenges. In addition, conventional unidirectional side shield structures such as those used in other types of sensors such as tunnel junction sensors (TMR) and giant magnetoresistive sensors (GMR) cannot be used in a scissor type sensor, because of the need for oppositely oriented free layer magnetizations in scissor type magnetic sensors.
The above described flux closure side shield structure results in a non-biasing magnetic structure, which reduces magnetic side reading thereby enabling increased track pitch. In the structure of
In effect then, the closed loop side shield structure 240 provides a non-biasing side shield structure. The closed loop side shield structure 240 is preferably magnetically connected with only one of the upper and lower shield structures 204, 206, but not to both. For example, as can be seen in
Then, with reference to
With reference now to
Then, with reference to
With reference now to
Then, with reference to
Then, a chemical mechanical polishing (CMP) is performed to remove the remaining mask layer 612 followed by a reactive ion etching to remove the CMP stop layer 1302, leaving a structure as shown in
While the sensor described above provides performance advantages in a wide variety of magnetic recording systems by reducing adjacent track interference and increasing effective track pitch, it is especially useful in a two-dimensional magnetic recording system. A two dimensional magnetic recording system increases data density by reading and processing signals from multiple magnetic sensors simultaneously.
One example of such a two dimensional magnetic recording head utilizing a flux closure side shield structure is illustrated with reference to
The first, or bottom, in-stack bias structure 1614 can include a layer of anti-ferromagnetic material 1626, and a layer of magnetic material 1628 that is exchange coupled with the layer of anti-ferromagnetic material 1626. The exchange coupling between the layer of anti-ferromagnetic material 1626 and the magnetic layer 1628 pins the magnetization of the magnetic layer 1628, and this pinned magnetization provides magnetic biasing to the magnetic free layer 1610 to which it is adjacent, by one of various biasing mechanisms discussed above with reference to
The second, or middle, in-stack biasing structure 1616 can include a layer of anti-ferromagnetic material 1630 that is located between and exchange coupled with magnetic layers 1632, 1634, which pins the magnetizations of the magnetic layers 1632, 1634 in the same direction as one another. Each of the magnetic layers 1632, 1634 can be anti-parallel coupled with magnetic layers 1636, 1638 across anti-parallel coupling layers 1640, 1642. The magnetic layers 1636, 1638 provide magnetic biasing to their adjacent magnetic free layers 1608, 1610 by biasing mechanisms described above with reference to
Similarly, the third, or upper, in-stack magnetic bias structure 1618, can include a layer of anti-ferromagnetic material 1644 that is exchange coupled with a layer of magnetic material 1646. The magnetic layer 1646 is anti-parallel coupled with a magnetic layer 1648 across an anti-parallel coupling layer 1650 located there-between. The magnetic layer 1648 provides magnetic biasing for the adjacent magnetic free layer 1608. In this case the magnetic bias structure 1616 can provide magnetic biasing to stabilize both the top and bottom sensors 1604, 1606, while reducing the number of anti-ferromagnetic layers needed, thereby reducing the down track separation between the two sensors 1604, 1606.
With continued reference to
Each of the sensors 1702, 1706, 1708 has magnetic flux-closure side shield structures 1652 as previously described. The secondary magnetic sensors 1706, 1708 may have a shared flux closure side shield 1652 between them.
The use of the secondary magnetic sensors 1706, 1708, which are located at off-track locations help to reduce track pitch and improve signal resolution. Because the secondary sensors 1706, 1708 are located closer to adjacent data tracks than the primary sensor, they pick up more signal from these adjacent tracks. Therefore, this signal from adjacent tracks can be detected and subtracted out from the signal detected by the primary sensor 1702.
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 may also become apparent to those skilled in the art. Thus, the breadth and scope of the inventions 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.
Claims
1. A magnetic sensor, comprising:
- a sensor stack having first and second sides, the sensor stack including first and second magnetic free layers; and
- a magnetic side shield structure, comprising a magnetic structure having an upper portion and a lower portion and a non-magnetic layer disposed between the upper and lower portion, wherein the non-magnetic layer does not extend to the sensor stack so that the upper and lower portions of the magnetic structure are directly connected with one another.
2. The magnetic sensor as in claim 1, wherein the upper and lower portions are physically connected with one another in the region near the sensor stack.
3. The magnetic sensor as in claim 1, wherein the magnetic side shield structure is separated from the sensor stack by a non-magnetic, insulation layer.
4. The magnetic sensor as in claim 1, wherein the magnetic sensor is configured to read a data track having a track width, and wherein the non-magnetic layer of the magnetic side shield structure is separated from the sensor stack by a distance of one to two times the track width.
5. The magnetic sensor as in claim 1, wherein the non-magnetic layer of the magnetic side shield structure comprises Ru.
6. The magnetic sensor as in claim 1, further comprising an in-stack magnetic bias structure for biasing the magnetization of the magnetic free layers.
7. The magnetic sensor as in claim 1, wherein one of the upper and lower portions of the magnetic side shield structure is magnetically connected with an in-stack magnetic bias structure.
8. The magnetic sensor as in claim 1, wherein the sensor stack is between leading and trailing magnetic shields, and wherein the magnetic structure of the magnetic side shield structure is magnetically coupled with only one of the leading and trailing magnetic shields.
9. The magnetic sensor as in claim 1, wherein the magnetic structure of the magnetic side shield structure comprises Ni—Fe.
10. A two dimensional magnetic recording head, comprising:
- a magnetic head having a plurality of magnetic sensors, each magnetic sensor comprising:
- a sensor stack having first and second sides, the sensor stack including first and second magnetic free layers; and
- a magnetic side shield structure, comprising a magnetic structure having an upper portion and a lower portion and a non-magnetic layer disposed between the upper and lower portion, wherein the non-magnetic layer does not extend to the sensor stack so that the upper and lower portions of the magnetic structure are directly connected with one another.
11. The magnetic head as in claim 10, wherein one of the magnetic sensors is a primary magnetic sensor configured to read a data track, and at least one of the plurality of magnetic sensors is a secondary magnetic sensor.
12. The magnetic head as in claim 11, wherein the secondary magnetic sensor is arranged so as to be aligned over the data track to be read by the primary magnetic sensor.
13. The magnetic head as in claim 11, wherein the secondary sensor is laterally offset from the primary magnetic sensor.
14. The magnetic head as in claim 11, wherein the secondary sensor is arranged so as to be aligned with a data track that is adjacent to the data track to be read by the primary magnetic sensor.
15. The magnetic head as in claim 10, wherein the upper and lower portions are physically connected with one another in the region near the sensor stack.
16. The magnetic head as in claim 10, wherein the magnetic side shield structure is separated from the sensor stack by a non-magnetic, insulation layer.
17. The magnetic head as in claim 10, wherein each of the plurality of magnetic sensors is configured to define a track width and wherein the non-magnetic layer of the magnetic side shield structure is separated from the sensor stack by a distance of one to two times the track width.
18. The magnetic head as in claim 10, wherein each magnetic sensor further comprises an in-stack magnetic bias structure for biasing a magnetization of the first and second magnetic free layers.
19. The magnetic head as in claim 10 wherein each magnetic sensor includes a leading shield and a trailing shield, the sensor stack being between the leading shield and trailing shield and wherein the magnetic side shield structure is magnetically connected with only one of the leading shield and trailing shield.
20. A magnetic data recording system, comprising:
- a housing;
- a magnetic media mounted within the housing;
- an actuator;
- a slider connected with the actuator for movement adjacent to a surface of the magnetic media; and
- a magnetic sensor formed on the slider, the magnetic sensor further comprising:
- a sensor stack having first and second sides, the sensor stack including first and second magnetic free layers; and
- a magnetic side shield structure, comprising a magnetic structure having an upper portion and a lower portion and a non-magnetic layer disposed between the upper and lower portion, wherein the non-magnetic layer does not extend to the sensor stack so that the upper and lower portions of the magnetic structure are directly connected with one another.
Type: Application
Filed: Dec 1, 2015
Publication Date: Jun 1, 2017
Inventors: Wenqin Hao (Shenzhen), Quang Le (San Jose, CA), Xiaoyong Liu (San Jose, CA), Suping Song (Fremont, CA), Lei Wang (Fremont, CA)
Application Number: 14/955,878