Patent Application
20120156390
The present invention relates to magnetoresistive sensors and more particularly to a method for manufacturing a sensor that optimizes hard bias to free layer alignment while also producing a flat shield and optimizing hard bias to shield spacing.
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 a 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 sensor includes a nonmagnetic conductive layer (if the sensor is a GMR sensor) or a thin, nonmagnetic, electrically insulating barrier layer (if the sensor is a TMR sensor) sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. Magnetic shields are positioned above and below the sensor stack and can also serve as first and second electrical leads so that the electrical current travels perpendicularly to the plane of the free layer, spacer layer and pinned layer (current perpendicular to the plane (CPP) mode of operation). The magnetization direction of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetization direction 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.
When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering of the conduction electrons is minimized and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. In a read mode the resistance of the spin valve sensor changes about linearly with 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.
The present invention provides a method for manufacturing a magnetic sensor that result in improved magnetic bias field to the sensor, improved shield to hard bias spacing and a flatter top shield profile. The method includes a multi-angled deposition of the hard bias structure.
After forming the sensor stack, a hard bias seed is first deposited. Then, a first hard bias layer is deposited at an angle of less than 90 degrees relative to horizontal, or more preferably 60-80 degrees or about 70 degrees relative to horizontal. This is a conformal deposition. Then, a second deposition is performed at an angle of about 90 degrees relative to horizontal. This is a notching deposition that results in notches being formed adjacent to the sensor stack. Then, a hard bias capping layer is deposited at an angle of about 55 degrees relative to horizontal. This is a leveling deposition that forms a flat surface on which the top shield can be electroplated.
The hard bias seed layer can be NiTa/CrMo, Ta/Cr, Cr, CrMo and CrTi. The first and second hard bias layers can be constructed of CoPt or CoPtCr, and the hard bias capping layer can be constructed of a layer of Ta and a layer consisting of Cr, Ir, Rh, Ru, NiCr, CrMo or NiTa. These layers can be deposited by ion beam deposition.
The first layer, deposited at an angle that results in a conformal deposition, ensures that the sides of the sensor stack are well coated with hard bias material, with no voids or imperfections being present at the interface between the first hard bias layer and the sensor stack. The second deposition is deposited at an angle that causes the deposited layer to be formed with notches adjacent to the sides of the sensor stack. That is, the level of the hard bias actually drops slightly at the sides of the sensor stack. This ensures that the hard bias does not slope upward at the sensor stack, which would cause loss of bias field to the shield, and would also result in a poorly defined top shield with a non-planar bottom interface. The deposition of the hard bias capping layer is performed at a leveling angle that fills the slight notch formed by the second hard bias layer and provides a very flat surface on which to form the top shield.
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 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
The sensor stack 302 can include a non-magnetic layer 308 that is sandwiched between a magnetic pinned layer structure 310 and a magnetic free layer structure 312. The non-magnetic layer 308 can be an electrically conductive material, if the sensor 300 is a Giant Magnetoresistive (GMR) sensor, and can be a thin electrically insulating material layer if the sensor structure 300 is a Tunnel Junction Sensor (TMR).
The pinned layer structure 310 can include first and second magnetic layers 314, 316 with a non-magnetic, antiparallel coupling layer such as Ru 318 sandwiched between the first and second magnetic layers 314, 318 The first magnetic layer 314 has its magnetization pinned in a first direction perpendicular to the ABS. This pinning is a result of exchange coupling with a layer of antiferromagnetic material 320 such as IrMn. The second magnetic layer 316 has its magnetization pinned in a second direction that is antiparallel with the first direction as a result of antiparallel coupling between the first and second magnetic layers 314, 316 across the antiparallel coupling layer 318.
The magnetic free layer 312 has a magnetization that is biased in a direction that is generally parallel with the ABS, but that is free to move in response to a magnetic field. The biasing of the free layer is provided by a magnetostatic coupling with first and second hard magnetic bias layers 322, 324. One or more seed layers 326 may be provided at the bottom of the sensor stack 302 in order to ensure a desired grain growth of the other layers of the sensor stack 302 deposited thereon. In addition a capping layer such as Ta 328 may be provided at the top of the sensor stack to protect the underlying layers during manufacture. In addition, thin insulation layers 330 is provided at either side of the sensor stack 302 and across at least the bottom lead/shield 304 in order to prevent sense current from being shunted through the magnetic bias layers 322, 324. In addition, the hard bias structures 322 also have flat upper surfaces. A non-magnetic hard bias cap layer 330 is provided at the top of each of the hard bias layers 322, 324 to provide magnetic spacing between the hard bias layers 322, 324 and the shield 306.
As can be seen in
A mask structure 502 is formed over the sensor layers 302. The mask structure can be of various configurations. By way of example, the mask 502 can include a hard mask layer 504 such as Diamond Like Carbon (DLC) formed directly on the top of the sensor layers 302, an image transfer layer 506 formed of a soluble polyimide material such as DURIMIDE® formed over the hard mask 504, and a photoresist mask 512 formed over the image transfer layer 506. The photoresist mask is defined by a photolithographic process, and the image of the photoresist mask is transferred onto the underlying layers 506, 504 by one or more processes such as reactive ion etching and/or ion milling, leaving a structure as shown in cross section in
After the mask 502 has been defined, an ion milling is performed to remove portions of the sensor layers 302 that are not protected by the mask 502, leaving a structure as shown in
A hard bias seed layer 801 is deposited on the insulation layer. This seed layer 801 can be a layer or layers that can include materials such as NiT and/or CrMo. Then, with reference to
With reference now to
As can be seen, this second deposition results in the formation of notches 904 at the corners near the sensor stack 302. This prevents the hard bias layer 902 from curving upward at the sensor stack 302. This, provides a straight line of magnetic field to the sensor stack, preventing the hard bias field from curving upward at the sensor stack 302 (as was the case with the magnetic field 414 of the prior art sensor 402 of
In one approach, an ion milling is performed at a glancing angle (near horizontal) to remove portions of the 802 and 902 from the sides of the remaining image transfer layer 506 to remove excess hard bias layer (refer to as hard bias tip mill). Then, with reference now to
In another approach, the first approach will omit tip mill and proceed with hard-bias cap deposition and then to DLC deposition and follow by NMP and CMP to remove overburden materials and stencils.
Afterward, a RIE step is done to remove both the first and second DLC and to leave the capping layer 328 exposed. An additional seed layer consisting of Ru, Rh, or Ir and NiFe or CoFe, or their alloys are deposited, followed by an electroplating process to form the upper shield 308 over the sensor capping layer 328 and the hard bias capping layer 1002. As can be seen, this process provides an excellent flat surface on which to form the shield 308, resulting in a very flat bottom interface for the shield. This provides a well controlled, uniform, thick magnetic spacing between the hard bias layer and the shield 308 and maximizes magnetic biasing to the free layer 312. The resulting flat bottom of the shield also provides a well controlled gap thickness for defining a small bit length for improved data density.
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.
