Magnetoresistive sensor having an Ir seed layer for improved pinned layer robustness

A magnetic sensor having an Ir seed layer for improved pinning robustness and improved sensor performance. The sensor includes an Ir seed layer formed directly beneath and in contact with a layer of antiferromagnetic material (AFM). The Ir seed layer improves the grain structure and smoothness of the above applied layers to significantly improve the performance and pinning robustness of the sensor. The use of the Ir seed layer reduces interlayer magnetic coupling of the layers, reduces surface roughness and increases the temperature at which the pinned layer looses it's pinning (i.e. raises the mean blocking temperature Tc of the pinned layer structure).

FIELD OF THE INVENTION

The present invention relates to magnetic data recording and more particularly to a magnetic read sensor having an Ir seed layer beneath an antiferromagnetic layer of a pinned layer structure for improved pinned layer pinning.

BACKGROUND

At 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 data tracks on the rotating disk. The read and write heads are 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.

As magnetic sensors become smaller in order to accommodate increased data density requirements, various sensor performance characteristics become difficult to maintain. For example, at a very small sensor sizes it is difficult to ensure that the pinned layer will remain sufficiently pinned at elevated temperatures. Heat spikes, such as from head disk contact can temporarily cause the pinned layer to become unpinned, leading to catastrophic failure of the magnetic sensor. In addition, smaller sensors exhibit increased magnetic fluctuations in the pinned layer and the free layer. Smaller sensors require thinner barrier layers, which result in deteriorated free layer magnetic properties as a result of increased interlayer coupling effects. Therefore, there remains a need for a sensor design that can achieve increased magnetic performance, pinned layer and free layer magnetic robustness and reduced free layer magnetic interlayer coupling.

SUMMARY

The present invention provides a magnetic sensor that includes a magnetic free layer structure, a magnetic pinned layer structure and a non-magnetic layer sandwiched between the pinned layer structure and the free layer structure. A layer of antiferromagnetic material is exchange coupled with the magnetic pinned layer structure and a seed layer structure is formed beneath the layer of antiferromagnetic material. The seed layer structure includes a layer of Ir that is in contact with the layer of antiferromagnetic material.

The presence of the Ir seed layer directly beneath the layer of antiferromagnetic material advantageously enhances both the performance of the sensor and the pinning robustness. The Ir seed layer reduces roughness of the above formed layers, thereby reducing interlayer coupling and improving the performance of the sensor as well as increasing the blocking temperature of the pinned layer structure thereby improving pinned layer robustness.

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.

DETAILED DESCRIPTION

Referring now toFIG. 1, there is shown a disk drive100. The disk drive100includes a housing101. At least one rotatable magnetic disk112is supported on a spindle114and rotated by a disk drive motor118. The magnetic recording on each disk may be in the form of annular patterns of concentric data tracks (not shown) on the magnetic disk112.

During operation of the disk storage system, the rotation of the magnetic disk112generates an air bearing between the slider113and the disk surface122, which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of the suspension115and supports the slider113off and slightly above the disk surface by a small, substantially constant spacing during normal operation.

FIG. 2, is a schematic illustration of a magnetic sensor200as seen from the media facing surface. The sensor200includes a sensor stack202that is sandwiched between first and second magnetic shields204,206. The sensor stack includes a magnetic pinned layer structure208, a magnetic free layer structure210and a non-magnetic barrier or spacer layer212sandwiched between the magnetic pinned layer structure208and magnetic free layer structure210. A capping layer214can be formed at the top of the sensor stack202to protect layers such as the free layer210during manufacture.

The sensor200also includes magnetic bias structures228at either side of the sensor stack202. The magnetic bias structures228are constructed of a magnetic material that provides a magnetic bias field for biasing the magnetization of the magnetic free layer210in a direction that is generally parallel with the media facing surface as indicated by arrow230. Each of the magnetic bias structures228is separated from the sensor stack202and from the bottom shield204by a thin, electrically insulating layer232.

The pinned layer structure208can include first and second magnetic layers216,218that are separated from one another by a non-magnetic anti-parallel coupling layer220that is sandwiched there-between. The non-magnetic anti-parallel coupling layer220can be a material such as Ru and has a thickness that causes the magnetic layers216,218to be strongly magnetically anti-parallel coupled with one another.

The first magnetic layer216is exchange coupled with a layer of antiferromagnetic material222. The layer of antiferromagnetic material222can be constructed of IrMn, and is preferably an alloy of Ir and Mn having a face centered cubic (FCC) crystalline structure. More preferably, the layer222is L12 IrMn3. The exchange coupling between the first magnetic layer216and the layer of antiferromagnetic material222causes the magnetization of the first magnetic layer216to be strongly pinned in a direction that is generally perpendicular to the media facing surface as indicated by arrow head symbol234. The exchange coupling between the two magnetic layers216,218causes the magnetization of the second magnetic layer218to be strongly pinned in a second direction that is perpendicular to the media facing surface and anti-parallel with the first direction as indicated by arrow tail symbol236.

The sensor stack202also includes a novel seed layer structure203that includes a first seed layer224, and a second seed layer226formed on and in direct contact with the first seed layer224. The second seed layer226is formed of Ir and is directly beneath and in contact with the layer of antiferromagnetic material222. The first seed layer is preferably an amorphous metal, and more preferably can include a Co based amorphous layer and a layer of Ru formed on the Co based amorphous layer.

FIG. 3shows a view of a magnetic sensor300according to another embodiment. This sensor300includes a sensor stack302having a tri-layer seed layer structure303that includes: a first seed layer304; a second seed layer306formed over the first seed layer304; and a third seed layer308formed over the second seed layer306. The first layer304can be formed on a substrate that can be the magnetic shield204or could be formed on some intermediate layer there-between. The first seed layer304can be constructed of an amorphous metal such as Ta or could include a Co based amorphous layer and a layer of Ru formed there-over. The second seed layer306can be a crystalline magnetic material preferably having a face centered cubic (FCC) crystalline structure. Suitable materials for the second seed layer include Co, Ni, Fe or their alloys having an FCC crystalline structure. The third seed layer308is formed of Ir and is formed between and in direct contact with the second seed layer306and the antiferromagnetic material layer222. The ABS widths of cap214and free layer210are set to be equivalent with track width. The width of the magnetic seed layer306is much wider than the width of the free layer210, so that magnetic seed306works as a magnetic shield just like the bottom magnetic shield layer204. An example of the various layers of the sensor302is described below. The first seed layer304can be Ta and can have a thickness of about 15 Angstrom (A). The second seed layer306can be Ni-15at % Fe and can have a thickness of about 300 (A). The third seed layer308can be Ir and can have a thickness of about 20 (A). The antiferromagnetic material layer222can be an Ir—Mn alloy having a thickness of about 55 (A). The first magnetic layer216can be a Co—Fe alloy having a thickness of about 25 (A). The non-magnetic anti-parallel coupling layer220can be Ru having a thickness of about 4.2 (A). The second magnetic layer218can include: a Co—Fe alloy layer having a thickness of about 5 (A); a Co—Fe—B—Ta alloy layer having a thickness of about 5 (A); a Co—Fe—B alloy layer having a thickness of about 10 (A); and a Co—Fe alloy layer having a thickness of about 5 (A).

FIG. 4shows yet another embodiment having a slightly modified seed layer structure401.FIG. 4shows a sensor400having a sensor stack402that is similar to that ofFIG. 3, except that the third seed layer308is a bi-layer structure that includes a layer of Ru308aand a layer of Ir308bformed over the layer of Ru308a, so that the layer of Ir308bis in direct contact with the antiferromagnetic layer222. As can be seen inFIGS. 3 and 4, the magnetic second seed layer306can be substantially thicker than the other seed layers304,308. However, because this layer306is magnetic, it functions magnetically as a part of the shield204and as such does not contribute to gap thickness. Therefore, the presence of the second seed layer has no negative effect on resolution or linear data density. The third seed layer308can include, for example, a Ru layer308ahaving a thickness of about 5 (A) and an Ir layer308bhaving a thickness of about 15 (A).

FIG. 5illustrates a magnetic sensor500according to yet another possible embodiment. This sensor500includes a sensor stack502having a further modified seed layer structure504. This seed layer structure504includes: a first seed layer304; a second seed layer506formed over the first seed layer304; a third seed layer306formed over the second seed layer506; and a fourth seed layer308formed over the third seed layer306. As can be seen, the seed layer structure504is similar to the seed layer structure303described above with reference toFIG. 3, but with the addition of the seed layer506between the seed layers304and306. The seed layer506can be constructed of a NiFeCr alloy. The presence of this layer506enhances grain size of the layers formed above it. As a more specific example, the seed layer506can be constructed of (Ni80Fe20)60—Cr40(at %) and can have a thickness of about 60 (A).

FIG. 6illustrates still another possible embodiment that includes a sensor600having a sensor stack602with a seed layer structure604. The seed layer structure604is similar to the seed layer structure504ofFIG. 5, except that the fourth seed layer structure308is a bi-layer structure including a first sub-layer308aand a second sub-layer308bformed over the first sub-layer308a. In this embodiment, the fourth seed layer structure308is similar to the seed layer structure308described above with reference toFIG. 4. To that end the first sub-layer308acan be Ru and the second sub-layer308bcan be Ir.

Having an Ir seed layer directly beneath the AFM layer222(FIGS. 2-6), increases the magnetoresistive sensitivity (MR) of the sensor. This increased performance results from improved smoothness of the AFM layer222. The presence of the Ir seed layer, and the resulting smoothness of the AFM layer222, also improves the robustness of the pinned layer structure208by increasing the mean blocking temperature Tc and by also reducing the low temperature thermal noise component (TbD). Since the pinned layer related thermal fluctuation noise (RTN) is caused by low the temperature component of TbD, the presence of the Ir seed layer effectively suppresses RTN. In addition, the presence of the Ir seed layer reduces interlayer coupling, resulting in better free layer magnetics and reduced free layer signal noise. As a result of these benefits, a smaller sensor track-width can be realized.

FIGS. 7 through 13illustrate the performance and robustness benefits provided by the use of an Ir seed layer such as described in the above embodiments.FIG. 7is a graph illustrating the magnetoresistance performance (dR/R) of a magnetic head as a function of seed layer thickness for an Ir seed layer verses a Ru seed layer. Line702shows the MR characteristics for an Ir seed layer for seed layer thicknesses up to 20 Angstroms. Line704shows the MR characteristics for a Ru seed layer for seed layer thicknesses up to 20 Angstroms. As can be seen, MR increases and saturates more rapidly with the use of an Ir seed layer than with the use of a Ru seed layer.

FIG. 8shows the area resistance RA as a function of seed layer thickness for Ir and Ru seed layers. As those skilled in the art will appreciate, a lower area resistance results in increased sensor performance. Line802shows the RA for an Ir seed layer and line804shows the RA for a Ru seed layer. As can be seen, the RA is similar for both materials.

FIG. 9is graph showing Tc as a function of seed layer thickness for Ir and Ru seed layers and a combination Ru/Ir seed layer. The magnetic pined layer208(FIGS. 2-6) is magnetically coupled with the layer of the antiferromagnetic material222(FIGS. 2-6), which is composed of poly-crystals of MnIr alloy. Each MnIr crystal in222has its own local blocking temperature. So, the antiferromagnetic material222has distributed local blocking temperatures. Tc is the mean blocking temperature of the distributed local blocking temperatures. Therefore, a higher Tc means better pinned layer robustness. Line902shows the Tc for an Ir seed layer and includes data points represented as diamonds. Line904shows the Tc for a Ru seed layer, and includes data points represented as circles. In addition, line906represents Tc for a sensor having a combination Ru/Ir seed layer having a layer of Ru and a layer of Ir formed there-over. This line906(which overlaps much of line902) includes data points represented as hollow triangles. As can be seen, the use of the Ir seed layer (line902) has Tc very close to that of the combination Ru/Ir seed layer (line906). As can also be seen, the Tc increases much more rapidly with the use of an Ir seed layer (line902) or combination Ru/Ir seed layer (line906) than with the use of a Ru seed layer alone (line904).

FIG. 10is a graph illustrating low temperature thermal noise (TbD) as a function of seed layer thickness. Line1002shows the TbD for an Ir seed layer and line1004shows the TbD for a Ru seed layer. As can be seen, the thermal noise decreases dramatically with use of an Ir seed layer as compared with the use of a Ru seed layer.

FIG. 11shows the relationship between interlayer coupling (H1) and seed layer thickness for Ir and Ru seed layers. The interlayer coupling (H1) is the magnetic coupling between the magnetic layers of the sensor and is generally undesirable in a magnetoresistive sensor. Line1102shows the interlayer coupling (H1) using an Ir seed layer and line1104shows the interlayer coupling using a Ru seed layer. As can be seen, the interlayer coupling is much lower with the use of an Ir seed layer as compared with a Ru seed layer. This is due to improved smoothness of the layers deposited there-over.

FIG. 12is a graph showing a hysteresis curve for sensors using an Ir versus Ru seed layer. Line1202shows the hysteresis curve for a sensor using a 20 Angstrom thick Ir seed layer and line1204shows the hysteresis curve for a sensor using a 20 Angstrom thick Ru seed layer. As can be seen, the sensor having the Ir seed layer exhibits much better H1and improved squareness as compared to the sensor using the Ru seed layer. As a result, the sensor using the Ir seed layer exhibits better free layer magnetic performance than the sensor using the Ru seed layer.

FIG. 13shows a table illustrating the roughness in nanometers (nm) of various sensor layers when using different seed layer structures. InFIG. 13, rows1302-1314show the various layers of the sensor and columns1316-1320show how the roughness of the various layers varies depending the type of seed layer used. A lower roughness is desirable for various reasons such as decreasing interlayer coupling, improving barrier layer performance and improving free layer performance. Row1302is the substrate, such as a bottom shield. Row1304shows roughness of a Ta seed layer. The thickness of the Ta layer is 15 Angstroms, NiFe 300 Angstroms, MnIr 55 Angstroms and CoFe 25 Angtroms. Row1306shows the roughness of a NiFe seed layer formed over the Ta seed layer. Rows1308and1310show the roughness of Ru and Ir seed layers if present in the sensor. Row1312shows the roughness of an IrMn AFM layer. Row1314shows the roughness of a first CoFe magnetic layer of a pinned layer structure formed over the AFM layer. As can be seen, the roughness of the IrMn and CoFe layers is lowest with the use of an Ir seed layer alone. The roughness increases slightly when using a combination of a Ru seed layer and an Ir seed layer formed over the Ru seed layer, however it is possible that such a combination of Ru and Ir seed layers might be desirable for a possible increase in magnetoresistance signal (MR). The roughness is worse when using no seed layer or when using a Ru seed layer alone without an Ir seed layer.

It can be seen from the above that the use of an Ir seed layer, such as described in various embodiments with reference toFIGS. 2-6, provides many advantages with regard to performance and sensor robustness.FIGS. 7-13illustrate clearly these significant performance and robustness advantages.