MR sensor having end regions with planar sides

A magnetoresistive (MR) sensor having passive end regions separated by a central active region in which an MR sensing element is formed over substantially only the central active region. The MR sensor is defined by forming a resist pattern over both the end regions and the MR sensing element followed by an etching step where the duration of the etching is controlled by the time it takes to remove the exposed end regions' material and not by the time it takes to remove the excess MR material in the center active region. This creates an MR sensor having planar sides along the circumference of the end regions where the planar sides have no thinned edges or shoulders. The MR sensor further has no remnant MR material along the inner planar side of the end regions behind the MR sensor's trackwidth edge and adjacent to the MR sensor's back side.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention relates to a thin film magnetic head having a 
magnetoresistive (MR) read sensor for detecting signals recorded on a 
magnetic recording medium. More particularly, this invention relates to an 
improvement in construction of a low noise longitudinally biased MR read 
sensor. 
2. Description of the Background Art 
The use of a magnetoresistive (MR) sensor (also referred to as "transducer" 
or "head") to read signals recorded on a magnetic recording medium has 
been well established in the field of information storage and is believed 
to be the replacement for inductive read sensors. This is due to the fact 
that the MR read sensor has the following major advantages over the 
inductive read sensor: 
1) the MR sensor's intrinsic noise is much lower than the inductive read 
sensor intrinsic noise thus providing improved signal-to-noise (S/N) 
performance, 
2) the MR sensor senses magnetic flux, not the rate of magnetic flux 
change, which means the magnetic signal recorded on the storage medium can 
be reproduced independently of the speed at which the medium is moving 
with respect to the sensor, and 
3) the MR sensor has bandwidth in gigahertz (gHz) range which allows areal 
storage density well in excess of 1 Gb/inch.sup.2 (1 gigabit per square 
inch). 
MR sensors currently fall into two broad classes: 1) anisotropic 
magnetoresistive (AMR) sensors and 2) giant magnetoresistive (GMR) 
sensors. In the AMR sensors, the resistance of the MR sensing element 
varies as a function of cos.sup.2 .alpha. where .alpha. is the angle 
between the magnetization and the direction of the sense current flowing 
in the sensing element. The sensing element is generally made of 
ferromagnetic material. In the GMR sensor, the resistance of the MR 
sensing element varies as a function of spin-dependent transmission of 
electrons between pinned and free magnetic layers separated by 
non-magnetic layers and the accompanying spin-dependent scattering which 
takes place at the interface of the magnetic and non-magnetic layers. The 
magnetic layers are generally made of ferromagnetic material. GMR sensors 
using only two layers of ferromagnetic material separated by a layer of 
non-magnetic metallic material are generally referred to as spin valve 
(SV) MR sensors. The two layers of ferromagnetic material separated by a 
layer of non-magnetic metallic material are also referred to as "spin 
valve material". 
FIG. 1 is a cross-section of a conventional thin film MR sensor 10, 
comprising magnetic shields 12 and 14, interlayer insulating material 13 
and 15, MR sensor 18, soft magnetic material 16 for transverse biasing of 
the MR sensor, and leads 20 and 22. Leads 20 and 22 further comprise 
conductor materials and magnetic materials where the magnetic materials 
are used to longitudinally bias the MR sensor to eliminate Barkhausen 
noise. 
As the demand for higher capacity storage devices continues to grow, it has 
become increasingly more important to produce MR read sensors small enough 
to read the data recorded in ever decreasing track widths at ever 
increasing recording density. One of the most prevailing solutions for 
meeting these requirements is described in commonly assigned U.S. Pat. No. 
5,079,035 in which the disclosed MR sensor comprises an MR layer extending 
over substantially only a central active region and a hard magnetic bias 
layer provided in each of two passive end regions. Each end region further 
forms an abutting junction with the MR layer to produce longitudinal bias 
in the MR read sensor as shown in FIG. 2A. 
Referring to FIG. 2A, there is shown a cross section of an MR read sensor 
50 comprising an MR layer 62 deposited over substrate 66 and extending 
over substantially only the central active region 64 and a hard magnetic 
bias layer (also referred to as "longitudinal bias layer") 58 in each end 
region 52. Each end region 52 further includes a conductor layer 54 
deposited over each magnetic bias layer 58. Each longitudinal bias layer 
58 forms a contiguous (abutting) junction 60 with MR layer 62 to produce a 
longitudinal bias field in the MR read sensor 50. 
In order to fabricate MR sensor 50 shown in FIG. 2A, a photoresist pattern 
is generally formed over both end regions 52 and MR layer 62. The pattern 
is then developed and the excess MR material is then removed, preferably 
by ion beam milling. Since end regions 52, which consist of both conductor 
material 54 and longitudinal bias material 58, are generally thicker than 
MR layer 62 in the central active region, and since the duration of ion 
beam milling is determined by the time it takes to remove the excess MR 
material, this means that not all of the exposed end regions' material are 
removed during the etching step. This in turn leads to the creation of 
thinned edges (shoulder) around the circumference of the end regions as 
well as leaving remnant MR material behind along a portion of the thinned 
edges and near the back edge of the MR sensor as shown in FIG. 2B. 
FIG. 2B shows a top view of the MR sensor of FIG. 2A after ion beam milling 
and lapping steps comprising lead (magnetic bias and conductor materials) 
70 in each end region 52 and thinned edge 74 along the circumference of 
each lead 70. Each thinned edge 74 further comprises inner thinned region 
76 having a thinned corner region 78. MR sensor 50 further comprises 
trackwidth edge 80 (the trackwidth edge of the MR sensor is the surface, 
also referred to as the air bearing surface (ABS), which is in close 
proximity to the surface of the storage medium and is used for reading 
previously recorded information), back edge 82, and magnetic remnant 
material 84 along the length of inner thinned region 76 and near back edge 
82. 
The presence of the thinned edges around the circumference of the end 
regions as well as the remnant MR material are due to the method by which 
the prior art MR sensor is manufactured which is shown in FIGS. 3A-3F. 
FIG. 3A shows a top view of a step 100 of a process for fabricating an MR 
sensor prior to ion beam milling comprising MR material 120, end regions 
110, and photoresist material 130. FIG. 3B is a cross-section of FIG. 3A 
along the line B-B' which is the region directly behind the active region 
of the MR sensor. FIG. 3C is a cross-section of FIG. 3A along the line 
A-A' which is a part of the active region of the MR sensor. 
FIG. 3D shows a top view of step 112 of the process for fabricating the MR 
sensor after ion milling and photoresist removal steps where the duration 
of the ion beam milling has been determined by the time it would take to 
remove excess MR material. Step 112 comprises MR material 120, end regions 
110, trackwidth edge 170, back edge 172, and thinned edges 140 of end 
regions 110. Each thinned edge 140 further comprises an inner thinned edge 
160 having a thinned corner region 165. FIG. 3E is a cross-section of FIG. 
3D along the line D-D' which is the region directly behind the MR sensor 
active region and FIG. 3F is a cross-section of FIG. 3D along the line 
C-C' which is a part of the active region of the MR sensor. 
Referring back to FIGS. 3A-3F, it can be readily appreciated that the 
removal of the MR material by ion beam milling where the duration of ion 
beam milling is determined by the time it takes to remove excess MR 
material has the following major drawbacks: 
(1) it leaves undesirable thinned edges 140 around the circumference of end 
regions 110, of which inner thinned edges 160 behind trackwidth edge 170 
of the MR sensor and near back edge 172 of the MR sensor are the most 
undesirable one. Indeed, during the ion milling, the end regions can be 
thinned to such an extent that the longitudinal material below the 
conductor layer is reduced in thickness to the point that the magnetic 
properties of the thinned end regions are changed, thus substantially 
impacting the longitudinal bias of the MR sensor; 
(2) the presence of thinned corner regions 165 result in a phenomenon known 
as current crowding which effect the amplitude of the signal read from 
magnetic storage medium; and, 
(3) ion beam milling does not completely remove the excess MR material; 
i.e., the material not covered by the photoresist (stencil) pattern, thus 
allowing a small remnant of MR material 150 to be left behind along the 
length of each inner thinned edge 160. 
A small remnant of MR material 180 is also left behind along the length of 
each outer thinned edge 185. Remnant MR material 150 can substantially 
alter and degrade the magnetic domain activities and increase the MR 
sensor noise, especially if the longitudinal bias material thickness has 
been reduced, thus reducing the signal-to-noise ratio. 
Therefore, there is a great need for an invention that can substantially 
eliminate the longitudinal instability (unstable bias point) caused by the 
thinned edges of the end regions of the MR sensor and by the magnetic 
domain altering behavior and noise producing remnant MR material left 
behind. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to disclose a method for 
producing an MR sensor having an improved longitudinal bias. 
It is another object of the present invention to disclose a method for 
producing an MR sensor having low noise. 
It is yet another object of the present invention to disclose a method for 
producing an MR sensor having passive end regions where the end regions 
have virtually no thinned edges. 
It is still another object of the present invention to disclose a method 
for producing an MR sensor where the small remnant MR material is 
eliminated. 
It is yet another object of the present invention to disclose a method for 
producing an MR sensor where the current crowding phenomenon is 
eliminated. 
Toward this end and in accordance with the present invention, an MR sensor 
is disclosed which comprises passive end regions separated by a central 
active region. A thin MR layer is formed substantially over the central 
active region followed by forming a longitudinal bias and conducting 
materials in each passive end region. (The longitudinal bias and 
conducting materials in each end region are also referred together as lead 
material). The longitudinal bias material forms a contiguous (abutting) 
junction having electrical and magnetic continuity with the MR layer to 
produce a longitudinal bias in the MR sensor. The end regions have planar 
sides and no thinned edges or shoulders which causes the end regions to 
have a substantially uniform thickness t (FIG. 7B). Furthermore, there is 
virtually no remnant MR material along the inner planar sides of the end 
regions and near the back side of the MR sensor. 
The preferred method for making the MR sensor of the present invention 
comprises an ion beam milling step for removing the excess MR material 
where the duration of the ion beam milling step is determined by the time 
it takes to remove the exposed end regions' materials and not by the time 
it takes to remove the excess MR material. This critical change, where the 
duration of the milling step is made dependent upon removal of the excess 
materials in the end regions as opposed to removal of the excess MR 
material in the central region, ensures that the exposed lead materials in 
the end regions, as well as the remnant MR material, are completely 
removed, thus allowing the production of an MR sensor with highly enhanced 
magnetic domain control, low noise, and longitudinal stability.

BEST MODE FOR CARRYING OUT THE INVENTION 
The following description is the best mode presently contemplated for 
carrying out the invention. This description is made for the purpose of 
illustrating the general principles of the present invention and is not 
meant to limit the inventive concepts claimed herein. 
With reference to FIG. 4A, there is shown a top view of step 200 in the 
preferred method of making the MR sensor of the present invention prior to 
ion beam milling which shows MR material 220, end regions 210, and 
photoresist material 230 covering a predefined portion of MR material 220 
and end regions 210. Central region 225 comprises exposed MR material 221 
(the portion not covered by photoresist 230) and unexposed (covered) MR 
material 222 (the portion covered by photoresist 230). End regions 210 
includes exposed (not covered by photoresist 230) conductor and 
longitudinal bias materials 211 and covered conductor and longitudinal 
bias materials 212. FIG. 4B is a cross-section of the materials shown in 
step 200 along the line B-B' which is the region directly behind the 
active region of the MR sensor. FIG. 4C is a cross-section of the 
materials shown in step 200 along the line A-A' which is a part of the 
active region of the MR sensor. 
FIG. 4D shows a top view of step 250 in the preferred method of making the 
MR sensor of the present invention after ion beam milling and photoresist 
removal which shows MR material 220 having track width edge 241 and back 
side 242 in central region 225 and lead material 212 in end regions 210. 
Each end region 210 has planar sides 215, 216, 217, and 218 where the 
planar sides have no thinned edges (or shoulders). FIG. 4E shows a 
cross-section of the materials shown in step 250 along the line D-D' which 
is the region directly behind the active region of the MR sensor. As shown 
in FIG. 4E, sides 215 and 218 are planar sides having no thinned edges or 
shoulders. FIG. 4F shows a cross-section of the materials shown in step 
250 along the line C-C' which is a part of the active region of the MR 
sensor. 
Now with reference to FIGS. 4D, 4E and 4F, it can readily be seen that 
according to the present invention, during the ion beam milling step, the 
ion beam milling is continued until exposed portion 221 of MR material 220 
(the portion not covered by photoresist 230) as well as exposed portion 
211 of end regions 210 (the portion of the end regions not covered by 
photoresist 230) are completely removed. As can be seen, the structure 
shown in FIGS. 4D-4F has planar sides 215, 216, 217, and 218 around the 
circumference of each end region 210 as opposed to thinned edges along the 
circumference of end regions 210. The structure shown in FIGS. 4D-4F also 
does not have remnant MR material along planar sides 215 of each end 
region 210 near the MR sensor's back side 242. Furthermore, back side 242 
of the MR sensor is parallel and self-aligned with inner planar side 216 
of each end region 210, thus preventing current crowding and providing a 
well defined geometry from which the sensor's resistance can be accurately 
calculated. 
With reference to FIGS. 5A-5I, there is shown an example of the preferred 
method of manufacturing the thin film MR head of the present invention. 
The method comprises the steps of depositing upon a suitable substrate 
300, a layer of MR material 305 such as NiFe (FIG. 5A) followed by 
depositing a film of suitable material 310 such as photoresist (FIG. 5B), 
and then patterning, exposing and developing the photoresist material to 
define the active regions of the MR sensor (FIG. 5C). Thereafter, the 
exposed portion of the NiFe is removed by etching (FIG. 5D). Next, the end 
region material 315 is deposited over substrate 300 followed by removing 
the resist over the remaining NiFe (FIG. 5E). The end regions comprise 
conductor material such as tantalum or gold and longitudinal bias 
materials such as NiFe/NiMn or CoPtCr, for example. Next, photoresist 320 
is deposited over the end regions 315 and MR material 305 and patterned 
for defining the MR sensor having a center active region and two passive 
end regions (FIG. 5F). Thereafter, the sensor pattern is defined by ion 
beam milling the exposed portion of MR material 305 and the exposed 
portion of end regions 315. The ion beam milling is continued until the 
exposed portion of the MR material and the exposed portion of the end 
regions not covered by photoresist material 320 are completely etched away 
(FIG. 5G). 
Since the extent of ion beam milling in the present invention is determined 
by the ion milling of the end regions, that means that substrate 300 will 
also be etched away to some extent in the areas where the excess (exposed) 
MR material was located. The etched portions 301 of substrate 300 is 
therefore refilled ("backfill") by either depositing or sputtering 
materials such as alumina 330 over resist 320 and exposed ion milled 
regions (FIG. 5H). Excess Alumina material deposited over photoresist 320 
is then removed as a result of photoresist 320 lift off (FIG. 5I). 
With reference to FIGS. 6A there is shown the measured transfer curve of 
resistance change versus applied transverse field for an MR sensor having 
thinned end regions as well as remnant MR material applying positive and 
negative currents. FIG. 6B depicts the measured transverse curve of 
resistance change versus applied transverse field for the MR sensor of the 
present invention having no thinned end regions and no remnant MR material 
applying positive and negative currents. It can readily be seen that the 
transfer curve (resistance change versus applied transverse filed) of the 
MR sensor of the present invention, as shown in FIG. 6B, is substantially 
noise-free as opposed to the prior art MR sensor of FIG. 6A which is 
substantially noisy. 
With reference to FIGS. 7A and 7B, there is shown a perspective view of the 
MR device of FIG. 3D of the prior art after ion milling and resist removal 
and a perspective view of the MR sensor of FIG. 4D of the present 
invention after ion milling and resist removal, respectively. In 
constructing the MR sensor shown in FIG. 7A, the extent of ion milling for 
removing the excess MR material is determined by the time it takes to 
remove the exposed MR material itself. This means that thinned edges (or 
shoulders) along the circumference of the end regions are created as well 
as a small remnant MR material 150 which are left behind along thinned 
inner edges 160 behind the MR sensor's trackwidth edge 170 and near the 
back edge of the MR sensor. 
Referring to FIGS. 2B and 7A, it is well known in the art that the thinned 
edges (1) causes current crowding which affects the amplitude of the read 
signal because most of the current I flows toward the back edge of the MR 
sensor as opposed to the track width (air bearing) edge of the MR sensor; 
(2) the longitudinal bias material in the thinned edges creates fringing 
field H at the back edge of the MR sensor which affects the linearity and 
the bias point of the MR sensor; and (3) the remnant MR material causes 
the MR sensor to be noisy and it degrades and alters its magnetic domain 
activities. 
In contrast, in constructing the MR sensor of the present invention, shown 
in FIG. 7B, since the extent (i.e., duration) of ion milling is determined 
by the time it take to remove the exposed material in the end regions, 
which are thicker than the thickness of the MR material in the central 
region, there are neither thinned edges along the circumference of the end 
regions nor any remnant MR material along planar inner edges 215. 
Therefore, the MR sensor of the present invention is substantially free of 
current crowding and fringing fields due to the thinned edges and degraded 
magnetic domain activity due to the remnant MR material. 
While the present invention has been particularly shown and fully described 
with reference to the preferred embodiment of the present invention, 
nevertheless, it will be understood by those skilled in the art that 
various modifications may be made without departing from the spirit and 
the scope of the invention. For example, although, the preferred 
embodiment of the present invention was described in terms of an 
anisotropic MR sensor, the invention is equally applicable to a spin valve 
MR sensor. Accordingly, it is to be understood that the invention is not 
to be limited by the specific illustrated embodiments, but only by the 
scope of the appended claims.