Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-03-18
2001-03-06
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120, C360S325000
Reexamination Certificate
active
06198608
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electromagnetic transducers and magnetoresistive sensors.
BACKGROUND OF THE INVENTION
The employment of magnetoresistive (MR) sensors for reading signals from media is well known. Such sensors read signals from the media by detecting a change in resistance of the sensor due to magnetic fields from the media. Many variations of MR sensors are known, such as anisotropic magnetoresistive (AMR) sensors, dual stripe magnetoresistive (DSMR) sensors, giant magnetoresistive (GMR) sensors, spin valve (SV) sensors and dual spin valve (DSV) sensors.
Common to these sensors is the need to provide bias fields, both to eliminate noise and to facilitate signal readout. A known means for biasing the sensor involves abutting a permanent magnet to ends of the sensor, the magnet preferably forming a contiguous junction across plural sensor layers. Conductive leads, which may be separate from the biasing means, may also adjoin sensor layers along a contiguous junction.
In order to form a contiguous junction, a sensor is usually deposited in layers and then its border defined by masking and ion beam milling or etching (IBE), reactive ion etching (RIE) or the like. Ideally, milling could be performed that directs an ion beam exactly perpendicular to the surface on which the MR sensors are being formed, resulting in blunt sensor ends that terminate at a 90° angle to that surface. Redeposition of materials removed by milling and other complications interfere with this scenario, however, so that such exact etching is not practicable. Moreover, following such a perpendicular IBE the deposition of hard bias and/or conductor layers could blanket the mask, so that etching of the mask would be prevented and the necessary lift-off of these layers would become problematic.
A known means for forming a contiguous junction involves forming an undercut in the mask and rotating the IBE at an angle offset from 90°.
FIG. 1
exemplifies this approach, in which a magnetic shield
20
, insulative layer
22
and sensor
25
has been formed atop a substrate
27
. A bi-layer resist
28
and
29
has been photolithographically patterned atop the layers that are to form the sensor
25
, leaving an undercut
30
closest to the sensor. An IBE is directed at a relatively rotating angle to perpendicular to form a curved border
33
for which part of the insulative layer as well as all of the sensor layers have been removed. Dotted lines
35
and
37
represent directions of the rotating ion beam at opposite phases, and show that etching proceeds less beneath the mask where line
37
impinges but not line
35
. The removal of part of layer
22
is termed overmilling. The undercut
30
allows etchant to remove the mask
28
even after deposition of hard bias and lead layers that cover the mask as well as adjoin the border
33
to form a contiguous junction.
The shallow slope of the resulting contiguous junction has a number of drawbacks. The oblique angle of the border defining the contiguous junction denigrates the bias field provided to the sensor and complicates the sensor domain structures, so that noise is not eliminated. The shallow slope also creates inaccuracy in the width of the sensor, which ideally should match the width of magnetic tracks on the media, called the “track width.” Surprisingly, the length of the contiguous junction regions on both ends of the sensor can be comparable to or even greater than the width of the sensor between the contiguous junction regions, blurring images and causing off-track errors.
The contiguous junction
33
could be made more blunt along the sensor with additional ion milling into the insulative layer
22
, also known as the read gap. Unfortunately this may result in electrical shorting between the shield and the hard bias and lead layers. The insulative layer
22
can be made thicker to allow for this overmilling, but the thickness of that read gap separating the sensor from the shield is a primary determinant of the resolution of the sensor. In other words, the sensor “sees” magnetic fields from the media that pass between the shields, and the closer the shields are to the sensor the more narrow the focus of the sensor. Thus an attempt to create a less oblique contiguous junction to solve the bias and resolution problems can result in other resolution problems and electrical shorting.
SUMMARY OF THE INVENTION
The present invention has a number of advantages, including creation of blunt contiguous junctions for MR heads, improving sensor performance. These advantages are achieved in part with a read gap material that has a substantially slower milling rate than conventional alumina. This slower milling rate allows a blunt contiguous junction to be formed along the sensor without excessive overmilling into the read gap. The read gap may also be formed of plural layers with at least one of the layers having a low milling rate. This can allow the other read gap layer to have complimentary attributes, such as high thermal conductivity, low stress, less pinholes and/or better dielectric properties.
The electromagnetic characteristics of MR sensors having such steeply sloped contiguous junctions are enhanced both in reading signals and reducing noise. The track width of such a sensor can be more accurately formed due to the blunt shape of the contiguous junction, clearing blurred signals and errors from reading adjacent tracks. The sensor can also be made to have a sharper linear bit resolution, due to a thinner, high-integrity read gap. Barkhausen noise can be reduced, as well as signal biasing improved, with blunt contiguous junctions. In sum, MR sensors of the present invention can achieve sharper resolution of both the length and width of magnetic bits, reduced noise, and enhanced signal readout.
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Hong Liubo
Knapp Kenneth E.
Evans Jefferson
Lauer Mark
Read-Rite Corporation
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