Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-01-18
2004-06-29
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S125330
Reexamination Certificate
active
06757141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a perpendicular recording write head with a ferromagnetic shaping layer and, more particularly, to such a write head wherein the shaping layer provides a planarized surface for the construction of a probe layer and supplies flux to a probe of the probe layer very close to an air bearing surface (ABS).
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm urges 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 adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of 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 field signals 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.
A write head typically employs ferromagnetic first and second pole pieces which are capable of carrying flux signals for the purpose of writing the magnetic impressions into the track. Each of the first and second pole pieces has a pole tip, a yoke and a back gap with the yoke being located between the pole tip and the back gap. The pole tips are located at the ABS and the back gaps are magnetically connected at a recessed location within the write head. At least one coil layer is embedded in an insulation stack between the yokes of the first and second pole pieces. A nonmagnetic write gap layer is located between the pole tips. Processing circuitry digitally energizes the write coil which induces flux signals into the first and second pole pieces. The flux signals bridge across the write gap layer at the ABS so as to write the aforementioned magnetic impressions or bits into the track of the rotating disk.
The first and second pole pieces are typically fabricated by frame plating. Photoresist is employed to provide the frame and a seed layer is employed to provide a return path for the plating operation. A typical sequence for fabricating a pole piece is to sputter clean the wafer, sputter deposit a seed layer, such as nickel iron, on the wafer, spin a layer of photoresist on the wafer, light-image the photoresist layer through a mask to expose areas of the photoresist that are to be removed (assuming that the photoresist is a positive photoresist), develop the photoresist to remove the light-exposed areas to provide an opening in the photoresist and then plate the pole piece in the opening up to a desired height.
A write head is typically rated by its areal density which is a product of its linear bit density and its track width density. The linear bit density is the number of bits which can be written per linear inch along the track of the rotating magnetic disk and the track width density is the number of tracks that can be written per inch along a radius of the rotating magnetic disk. The linear bit density is quantified as bits per inch (BPI) and the track width density is quantified as tracks per inch (TPI). The linear bit density depends upon the length of the bit along the track and the track width density is dependent upon the width of the second pole tip at the ABS. Efforts over the years to increase the areal density have resulted in computer storage capacities increasing from kilobytes to megabytes to gigabytes.
The magnetic moment of each pole piece is parallel to the ABS and to the major planes of the layers of the write head. When the write current is applied to the coil of the write head the magnetic moment rotates toward or away from the ABS, depending upon whether the write signal is positive or negative. When the magnetic moment is rotated from the parallel position, the aforementioned magnetic flux fringes across the write gap layer between the first and second pole pieces impressing a positive or negative bit in the track of the rotating magnetic disk. As the write current frequency is increased, the linear bit density is also increased. An increase in the linear bit density is desirable in order to increase the aforementioned areal density which provides a computer with increased storage capacity.
There are two types of magnetic write heads. One type is a longitudinal recording write head, which is described hereinabove, and the other type is a perpendicular recording write head. In the longitudinal recording write head the flux induced into the pole pieces by the write coil fringes across the write gap layer into the circular track of the rotating magnetic disk. This causes an orientation of the magnetization in the circular disk to be parallel to the plane of the disk which is referred to as longitudinal recording. The volume of the magnetization in the disk is referred to as a bit cell and the magnetizations in various bit cells are antiparallel so as to record information in digital form. The bit cell has a width representing track width, a length representing linear density and a depth which provides the volume necessary to provide sufficient magnetization to be read by a sensor of the read head. In longitudinal recording magnetic disks this depth is somewhat shallow. The length of the bit cell along the circular track of the disk is determined by the thickness of the write gap layer. A write gap layer is made as thin as practical so as to decrease the length of the bit cell along the track which increases the linear density of the recording. The width of the second pole tip of the longitudinal write head is also made as narrow as possible so as to reduce the track width and thereby increase the track width density. Unfortunately, the reduction in the thickness of the write gap layer and the track width is limited because the bit cell is shallow and there must be sufficient bit cell volume in order to produce sufficient magnetization in the recorded disk to be read by the sensor of the read head.
In a perpendicular recording write head there is no write gap layer. In a perpendicular write head the second pole piece comprises a probe layer wherein the probe layer has a probe with a width that defines the track width of the write head and a wider yoke portion which delivers the flux to the probe. At a recessed end of the probe the yoke flares laterally outwardly to its fall width and thence to a back gap which is magnetically connected to a back gap of the first pole piece. The perpendicular write head records signals into a perpendicular recording magnetic disk which are significantly thicker than a longitudinal recording magnetic disk. In the perpendicular recording magnetic disk a soft magnetic layer underlies a thicker perpendicular recording layer which has a high saturation magnetization M
S
and a high coercivity H
C
. The thicker disk permits a larger bit cell so that the length and the width of the cell can be decreased and still provide sufficient magnetization to be read by the read head. This means that the width and the thickness or height of the probe at the ABS can be reduced to increase the aforementioned TPI and BPI. The magnetization of the bit cell in a perpendicular recording scheme is perpendicular to the plane of the disk as contrasted to parallel to the plane of the disk in the longitudinal recording scheme. The flux from the probe is injected into the perpendicular recording magnetic disk in a direction perpendicular to the plane of the disk, thence parallel to the plane of the disk in the aforementioned soft magnetic underlayer and thence again perpendicular to the plane of the disk into the first pole piece to complete the magnetic circuit. It is now readily appa
Emilio Santini Hugo Alberto
Williams Mason Lamar
Hitachi Global Storage Technologies - Netherlands B.V.
Johnston Ervin F.
Klimowicz William
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