Patent Application
20110146061
The present invention relates to magnetoresistive sensors and more particularly to a sensor having manufactured by a process that results in a flat upper shield/lead structure and well defined sensor thickness.
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 a coil and first and second pole piece layers separated by a gap layer at an air bearing surface (ABS) of the write head. Current conducted through the coil induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs, a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for passing an electrical sense current through the sensor. 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 the push to increase data density and sensor performance, researchers have sought to develop magnetoresistive sensors having ever increased sensitivity and reduced size. Manufacturing methods that adequately defined sensors at larger dimensions become inadequate at very small dimensions. For example, prior art manufacturing methods result in a sensor and upper shield that are formed with a notch that, at very small sensor sizes, resulting in unacceptable performance degradation.
The present invention provides a method for manufacturing a magnetoresistive sensor. The method includes providing a substrate and depositing a plurality of sensor layers over the substrate. A thin high density carbon CMP stop layer is deposited over the plurality of sensor layers, and a mask is formed over the thin high density carbon CMP stop layer. The image of the mask structure is transferred onto the thin high density carbon CMP stop layer and an ion milling is performed to remove a portion of the plurality of sensor layers that are not protected by the mask and the thin high density carbon CMP stop layer. A layer of hard magnetic bias material is deposited, and a chemical mechanical polishing process is performed to remove the mask structure. A reactive ion etching is performed to remove the thin high density carbon CMP stop layer.
An optional second layer of thin high density carbon CMP stop material can be deposited after the hard magnetic bias layer has been deposited. Also, a thin insulating layer such as alumina can be deposited prior to depositing the hard magnetic bias material.
Because the CMP top layer (or layers) is very dense and hard, it can be deposited much thin than would be possible with other materials while still being able to withstand the chemical mechanical polishing. This thinness means that after the CMP stop layer has been removed, there will be very little notching above the sensor. This in turn results in a much flatter trialing 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
As can be seen in
The sensor layers 704 are shown as a whole in
With reference again to
Carbon, when formed in a high density, amorphous structure has unique properties. Unlike typical metals or ceramics, it offers better wear resistance and lower coefficient of friction at the same time. A combination of low resistance to wear and low friction is a very attractive attribute as a chemical mechanical polishing (MP) stop layer in that it enables the CMP stop layer 706 to be very thin, while generating less mechanical shear for the areas it is protecting. Amorphous carbon can have a density of between 1.5 and 3.3 g/cc and hardness of 10 to 40 GPa. These can be achieved while also having a coefficient of friction that is only 0.1. In addition; the surface energy of amorphous carbon can be as low as that of TEFLON® with a surface contact angle of 70 to 115 degrees, depending on the process conditions with which it is formed. The high density of amorphous carbon also enables it to protect against chemical penetration of the CMP slurry to prevent chemical attack to the protected structure. All of these properties are favorable to stop Chemical Mechanical Polishing (CMP) both chemically and mechanically where it is not intended while exposing other areas for chemical/mechanical actions for controlled stock removal. These above described properties of high density amorphous carbon allow the CMP stop layer 706 to be very thin, while still withstanding the chemical mechanical polishing.
The CMP process is modified to accommodate the reduction in stop layer thickness without resulting in over-polishing. The CMP process which needs to be aggressive enough to lift-off the photo-resist is segregated into multiple steps with an aggressive step used for liftoff followed by gentle polishing steps for planarization and cleaning. This breaking up of CMP steps helps prevent over-polishing of the CMP stop layer which protects the sensor and hard bias while resulting in a reduced notch height.
With reference now to
With reference now to
Then, with reference to
A chemical mechanical polishing (CMP) is then performed to remove the mask layer 708, leaving a structure such as that shown in
Then, a second magnetic shield 1602 is formed over the sensor layer 704 and hard bias layers 1202. This can be performed by depositing a seed layer, forming an electroplating frame mask, electroplating a magnetic material into an opening in the mask, removing the mask and performing a quick ion milling to remove residual seed material. The above described process, which uses thinner denser CMP stop layers 706, 1204 (
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.
