Patent Application
20120231296
The present invention relates to magnetic data recording and more particularly to a method for manufacturing magnetoresistive sensor that results in improved sensor definition at very small track-widths.
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 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.
In order to maximize data density it is necessary to minimize the track width of the magnetoresistive sensor. However, as the track width of the sensor decreases, the method used to construct the sensors face challenges that can make accurate definition of the sensor very difficult. Therefore, the remains a need for improved methods for manufacturing sensors at very small dimensions.
The present invention provides a method for manufacturing a magnetic sensor that includes depositing a series of sensor layers and forming a first mask structure over the series of mask layers, the first mask structure having a back edge configured to define a back edge of a sensor. A first ion milling is performed to remove portions of the series of sensor layers that are not protected by the first mask structure to define a back edge of the sensor. Then, a non-magnetic fill material is deposited, the non-magnetic fill material including a material having an ion milling rate that is similar to an ion milling rate of the series of sensor layers. A second mask structure is then formed over the series of sensor layers, the second mask structure having a width configured to define a sensor width and a second ion milling is performed to remove portions of the series of sensor layers not protected by the second mask structure to define a width of the sensor.
The invention uses different dielectric materials during sensor stripe height definition processing. By using dielectric materials that have similar ion mill rates to that of the sensor material, the topography can be minimized to only a few nanometers. This almost planar surface facilitates the CMP assisted liftoff used to remove the track width defining mask structure and the fencing, allowing the mask and fencing to be completely removed without damaging the sensor material or the hard bias material. This also provides a planar hard bias formed next to the sensor track, thereby resulting in a flatter shield. In addition, the fill material must have desired breakdown voltage properties so as not to cause electrical shunting. In order to achieve this, a multi-layer fill can be used that includes a bottom layer having a high breakdown voltage, and which may also include a diffusion barrier, along with an upper layer having the desired ion mill rate.
At sensor stripe height definition processing, after the back edge of the sensor has been defined, instead of using alumina as the complete refill material, the present invention uses a refill material that is a single, bi-layer or tri-layer dielectric material having a first layer with a high breakdown voltage or which may also include diffusion barrier material and a last layer having a similar mill rate to that of the sensor material. At track-width definition processing, since the refill dielectric and the sensor material have almost the same ion mill rate at the desired ion mill angle combination, the ion milled surface will be very planar across the active region of the element and in the field. The subsequent hard bias deposition will hence result in an almost planar surface, and this near planar surface will improve its hard bias magnetic field to the sensor with a reduced asymmetrical effect.
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.
FIG.-1 is a schematic illustration of a disk drive system in which the invention might be embodied;
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 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 sensor stack 302 includes a pinned layer structure 304, a free layer structure 306 and a non-magnetic layer 308 sandwiched between the pinned layer structure 304 and the free layer structure 306. If the sensor 300 is a TMR sensor, then the non-magnetic layer 308 is a thin, non-magnetic, electrically insulating barrier layer. If, on the other hand, the sensor 300 is a GMR sensor, then the layer 308 is a non-magnetic, electrically conductive spacer layer.
The pinned layer structure 308 can be an antiparallel coupled structure that includes first and second magnetic layers 310, 312 separated by a non-magnetic antiparallel coupling layer such as Ru 314. The magnetization of the first magnetic layer 310 is pinned in a direction perpendicular to the air bearing surface by exchange coupling with a layer of antiferromagnetic material 316. A seed layer 318 may be provided at the bottom of the sensor stack 302 in order to initiate a desired grain structure in the above layers, and a capping layer 320 can be provided at the top of the sensor stack 302 to protect the layers of the sensor stack 302 during manufacture. The sensor stack 302 is sandwiched between first and second magnetic shields 322, 324 that are constructed of an electrically conductive magnetic material so that they function as electrical leads as well as magnetic shields.
The free layer 306 has a magnetization that is biased in a direction parallel with the air bearing surface by magneto-static coupling with first and second hard magnetic bias layers 326, 328. The hard bias layers 326, 328 are separated from the sensor stack 302 and from at least one of the lead/shields 322 by thin electrically insulating layers 330, 332, which can be constructed of alumina.
During operation, a sensor current flows through the sensor stack 302 in a direction perpendicular to the planes of the layers of the sensors stack 302, the sense current being provided by the lead/shields 322, 324. The electron spin dependent tunneling of electrons through the barrier layer 308 is affected by the relative orientations of the magnetizations of the free layer 306 and layer 312. The closer these layers 306, 312 are to being parallel, the lower the electrical resistance across the barrier layer 308 will be. Conversely the closer the magnetizations of the layers 306, 312 are to being anti-parallel, the higher the electrical resistance across the barrier layer 308 will be. This change in electrical resistance can then be read as a signal in response to an external magnetic field. As seen in
An ion milling can then be performed to remove portions of the sensor stack 504 that are not protected by the mask structure 506 leaving as sensor stack 504 as shown in
With continued reference to
As mentioned above, the fill layer 904 is chosen to have an ion mill rate that is similar to the ion mill rate of the sensor stack 504. Preferably, the fill layer 904 has a mill rate that is no more than plus or minus 5% that of the sensor stack 504. With this in mind, the fill layer 504 can be TaOx, but could also be SiNx, TiOx, SiNxOy, SiOx or MgO. The fill layer 904 could also be AlOx where X is chosen to make the AlOx have the desired ion mill rate discussed. In addition, the fill layer can be TaOx or SiOxNy single layer (902, 904) for CPP sensor.
A second CMP stop layer 906 is then deposited. Like the CMP stop layer 508, the CMP stop layer 906 is a material that is resistant to chemical mechanical polishing, such as diamond like carbon (DLC). After deposition of the CMP stop layer 906, a chemical mechanical polishing process is then performed to planarize the surface of the layers 904, 902, 510. The CMP removes the bump 908 formed over the sensor stack 504, stopping at the base level of the CMP stop layer 906. The layers 902, 904, 906 are preferably deposited such that the base level of the CMP stop layer 906 is at the same level as the layer 508, which also acts as a CMP stop layer. After the chemical mechanical polishing has been performed, a quick reactive ion etching (RIE) can be performed to remove the remaining portion of layers 906, 508, and second DLC CMP stop layer, leaving a planarized structure such as shown in
With reference now to
With reference to
An ion milling is then performed to remove portions of the sensor stack 504 that are not protected by the mask 1102, leaving a structure as shown in
With reference now to
A second chemical mechanical polishing (CMP) is then performed followed by a quick reactive ion etching to remove the remaining CMP stop layer 1606 and hard mask 1104, leaving a structure such as that shown in
With reference now to
By contrast,
As can be seen, the prior art method causes significant topography after the patterning and milling operation has been performed to define the back edge of the sensor. This makes it very difficult to subsequently pattern and mill the track width of the sensor. This presents a problem, because accurate definition of the track width is critically important to sensor performance. The method of the present invention, as described above with reference to
After the DLC CMP stop layer 908 is deposited, this structure is then planarized, such as by chemical mechanical polishing, as described above with reference to
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.
