Disc drive reader with reduced off-track pickup

Details Disc drive reader with reduced off-track pickup Disc drive reader with reduced off-track pickup

2000-05-01

2002-08-06

Korzuch, William (Department: 2641)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06430010

ABSTRACT:

TECHNICAL FIELD
The present invention is directed to disc drive heads. Specifically, the present invention is directed to configurations of disc drive readers that reduce the amount of sensed off-track magnetic flux.
BACKGROUND
Disc drives have read and write heads that convert magnetic field lines stored on the disc into electrical signals that are processed to produce computer usable data. The discs have data tracks that are positioned as concentric circles. The read and write heads are positioned over a track by an actuator arm that is driven by a servomechanism. The track contains magnetic field lines whose orientation varies throughout the track. The disc is rotated and the magnetic field lines pass under the read/write head. Magnetic flux emanates from the disc and is sensed by the head.
Data is sequentially read from a track as the disc rotates. Adjacent data tracks rotate by the read head as the current data track rotates directly beneath the head's sensing element. Magnetic flux lines also emanate from adjacent tracks. If the read element in the head is not sufficiently shielded from the adjacent tracks' magnetic flux, the electrical signals generated by the read element may not correctly correspond to the magnetic flux of the current data track. In such a case, the data that results from processing the electrical signal will be invalid. Similarly, when writing data, if the flux emanating from the write head is not contained to the current data track, data contained in the adjacent tracks may become invalid. As the track density increases to provide greater amounts of storage per unit area, the degree of shielding necessary for proper reading and writing of the data must also be increased.
Typically, the read and write portions are joined and have three pole pieces to help shield the read and write processes. A giant magnetoresistive head, known as a spin valve configuration, is shown in
FIG. 2
as an example. The pole pieces,
202
,
208
, and
204
, are positioned sequentially. The middle or shared pole piece
208
is shared between the read and write processes. In the write process, the magnetic flux extends from the top pole piece
202
to the shared middle pole piece
208
. In the read process, the magnetic flux extends from the bottom pole piece
204
across the gap
206
and through the read element
210
to the shared middle pole piece
208
. The magnetic flux originates from magnetic medium
212
that forms the surface of the disc.
Several read elements are available for disc drives. Magnetoresistive (MR) films are one type and are used in the spin valve configuration of FIG.
2
. MR elements have an electrical resistance that is directly related to their magnetic orientation (i.e. the direction of a magnetization vector). When an MR element
210
is exposed to magnetic flux, the magnetic orientation of the MR element changes (i.e. the magnetization vector points in a different direction creating an angle between the rest direction and the resulting vector direction), and its electrical resistance is thereby altered. To read the data, MR elements are driven with a constant electric current and a voltage drop across the element changes as the resistance changes in response to the element being exposed to the magnetic flux. The voltage drop is measured and processed to generate the data values sent to the computer system from the disc drive.
As with all read elements, MR elements must be shielded to prevent reading magnetic flux from tracks adjacent to the current data track.
FIG. 2-2
shows an air bearing slider (ABS) view of the spin valve configuration shown in FIG.
2
. An ABS view is one taken upwardly from the surface of the recording medium into the bottom of the slider. In the prior art, as shown in
FIG. 2-2
which is the ABS view taken along line
2
-
2
of
FIG. 2
, the two pole pieces
208
and
204
that shield the MR element
210
provide a gap, or separation zone that the MR element
210
resides between. In the spin valve configuration of FIGS.
2
and
2
-
2
, the separation distance is increased at the ends of the pole pieces that lie above the adjacent tracks. The separation distance must be increased to permit electrical connectors
214
,
216
and stabilizing magnets
218
,
220
to be placed to the sides of the read element
210
. These electrical connectors and stabilizing magnets have been omitted from FIG.
2
.
In the spin valve configuration, the electrical connectors
214
and
216
are used to supply the biasing current to the GMR (giant magnetoresistive) element and are positioned in the separation zone adjacent to the GMR element. The stabilizing magnets
218
and
220
, also positioned within the separation zone adjacent to the GMR element, are used to create a single domain state. The single domain state occurs when the magnetization vectors are consistent throughout the GMR element. The single domain state provides a more accurate voltage drop due to the magnetic flux from the recording medium. Spin valves utilize about 4 sensor layers in the read element with each layer being about 10-50 Å thick. The sensor layers are made of magnetic material and usually 2 layers are placed together to form a pair. Thus the read element contains 2 pairs, and these are separated from one another by a non-magnetic material that conducts electrical current such as copper.
The GMR element's magnetic orientation vectors are important because flux from the recording medium must increase the voltage drop to represent one binary state or decrease the voltage drop to represent the other binary state. Maintaining the angle between the two vectors at 90 degrees is necessary for proper interpretation of the data state because the angle is related to the voltage by a cosine function. If the angle is too close to 0 degrees, then a change in the angle will always result in the voltage increasing. If the angle is too close to 180 degrees, then a change in the angle will always result in the voltage decreasing. In either case, distinguishing a one from a zero is not possible.
The GMR element will have an inherent magnetic orientation vector on each side of the conductor running through the element when no bias current is applied. The films are made so the vector on one side parallel to the vector on the other side, and the vectors typically are parallel with the longitudinal direction of the element. One magnetic film is permanently oriented by a pinning layer that causes the resulting magnetic orientation vectors to create the necessary angle of 90 degrees relative to one another.
Similar to the spin valve, an anisotropic MR configuration uses a single sensor layer in the read element that is about 100-200 Å thick to produce a usable voltage drop. Anisotropic configurations also utilize side conductors to provide the bias current and stabilizing magnets to create the single domain state. Spin valves produce a greater voltage drop for the same amount of flux from the recording medium than do anisotropic MR configurations. However, some potentially troublesome flux from adjacent tracks will be channeled into the read element by the wider separation zones over the adjacent data tracks in both of these configurations. This stray magnetic flux will interfere with the magnetic flux from the current track and may cause invalid data to result.
Rather than using standard anisotropic magnetoresistive heads or spin valve configurations where the biasing current flows through the length of the read element in a direction parallel to the plane of the recording medium as shown in FIGS.
2
and
2
-
2
, some read heads employ vertical giant magnetoresistive (VGMR) read heads. In vertical giant magnetoresistive heads, the current flows perpendicular to the horizontal plane of the recording medium. Thus, electrical conductors are not needed on the sides of the read element that lie over the adjacent data tracks. Instead, conductors are placed above and in some cases below the read element. The stabilizing magnets are not necessary because MR elem

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