Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-11-21
2003-06-17
Nguyen, Hoa T. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06580586
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of thin film magnetic transducers (heads) and to methods for fabricating thin film magnetic transducer with recessed magnetic elements.
BACKGROUND OF THE INVENTION
A typical prior art disk drive system
10
is illustrated in FIG.
1
. In operation the magnetic transducer
11
, usually called a “head” is attached to an arm or actuator
13
and flies above the rotating disk
16
. A voice coil motor (VCM) (not shown) pivots the actuator
13
to position the magnetic transducer
11
over selected circumferential tracks on the disk
16
. The disk
16
is attached to spindle
18
that is rotated by a spindle motor
24
. The disk
16
comprises a substrate
26
on which the magnetic medium
21
is deposited. The magnetic medium
21
is used to record the magnetic transitions written by the magnetic transducer
11
in which information is encoded. A tape based storage system uses a magnetic transducer in essentially the same way as a disk drive, with the moving tape being used in place of the rotating disk
16
.
The magnetic transducer
11
is composed of elements that perform the task of writing magnetic transitions (the write head
23
) and reading the magnetic transitions (the read head
12
) as illustrated in the merged head shown in FIG.
2
. The electrical signals to and from the read and write heads
12
,
23
travel along conductive paths (leads) (not shown) which are attached to or embedded in the actuator
13
. Typically there are two leads each for the read and write heads
12
,
23
.
FIG. 2
is a midline section perpendicular to the air bearing surface of one type of prior art magnetic transducer
11
for use in a disk drive
10
. The components of the read head
12
are the first shield (S
1
), two insulation layers
107
,
109
which surround the magnetoresistive sensor element
105
and the second shield
104
(P
1
/S
2
). The sensor element
105
may include multiple layers of material in addition to the magnetoresistive material as is the case in a spin valve sensor. This type of magnetic transducer
11
is called a “merged head” because the P
1
/S
2
layer
104
serves as a shield for the read head
12
and a pole piece for the write head
23
. The yoke also includes a second pole piece
103
(P
2
) which connects with P
1
/S
2
104
at the “back gap” (BG). The P
2
103
confronts the P
1
104
across the write gap layer
42
to form the write gap
43
at the air bearing surface (ABS). The coil
37
in this particular prior art head is deposited on a layer of resist
106
which is used to define the zero throat height (ZTH) by forming a step on the gap layer
42
.
FIG. 3
is symbolic illustration of a prior art tape storage system
203
which utilizes a tape cartridge
202
. The tape storage system
203
uses a magnetic transducer assembly
211
which is positioned between fixed tape support pins
228
,
229
. The electrical signals to and from the magnetic transducer assembly
211
are processed by channel electronics
231
. The tape cartridge
202
includes reels
220
,
221
on which magnetic tape
222
is stored. The magnetic tape
222
is supported by pins
225
,
227
. In operation the magnetic tape
222
is positioned in contact or near contact to magnetic transducer assembly
211
as the tape is moved in either direction to and from reels
220
,
221
. The magnetic transducer assembly
211
indudes a plurality of magnetic transducers to read and write multiple tracks across the width of the tape simultaneously. Separate magnetic transducers are used for each track.
FIG. 4
is a midline section illustrating of a type of prior art magnetic transducer assembly
211
used in tape storage systems. The transducer assembly
211
includes symmetrical components which allow simultaneous reading and writing. These are illustrated as left transducer
51
A with its closure pieces
71
A and right transducer
51
B with its closure pieces
71
B. The tape
222
moves from left to right as well as right to left. The left transducer
51
A and right transducer
51
B are respectively included in the left module
53
A and the right module
53
B which are supported by the left u-beam
55
A and the right u-beam
55
B.
FIG. 5
is a section of a transducer
51
such as might be used for the left and/or right transducers
51
A,
51
B. The relative sizes are not shown to scale, since the wide range of sizes would make the drawing unclear. The section is taken parallel to the tape bearing surface (not shown). The substrate
61
supports undercoat
63
which is an insulating material such as alumina. The first shield (S
1
)
65
is a magnetically permeable material such as Sendust which has been used in tape heads for many years and is well known in the art. Sendust is a nonductile material. The magnetoresistive sensor element
67
is separated from S
1
65
by the first gap
66
. The second gap
68
separates the magnetoresistive sensor element
67
from the second shield
69
. The magnetoresistive sensor element
67
may be a single layer or multiple layers. The first and second gaps
66
,
68
are typically alumina, as is the overcoat
70
. The second shield
69
may be a ferromagnetic material such as permalloy (80 at. % nickel, 20 at. % iron) which is ductile. The closure piece
71
is placed on top of the overcoat
70
.
FIG. 6
is a section of the prior art transducer
51
taken perpendicular to the tape bearing surface
72
. The prior art lapping process results in the tape bearing surface
72
being substantially planar around the magnetoresistive sensor element
67
with each of the components being essentially flush with the tape bearing surface
72
. A problem with prior art heads which results from the action of the moving magnetic media is that elements such as the magnetoresistive sensor element
67
and the second shield
69
which are made from ductile material can be mechanically distorted by having the surface material pushed and pulled into a nonplanar, drift-like shape.
Thin film deposition processes used to fabricate heads typically create a film which conforms to the surface topography on which it is being deposited. When the thin film structures of differing materials are etched, the resulting surface may be significantly nonplanar. The deposition of a subsequent conformal film leaves the surface in a nonplanar state. A planarization process which is commonly used in both thin film head and semiconductor fabrication is called chemical-mechanical polishing (CMP). Both acidic and basic solutions have been suggested for use in CMP to speed up the rate of material removal. The prior art of fabricating magnetic transducers (heads) has included lapping the surface of the heads to present a smooth surface to the magnetic media. The lapping process is performed on rows of heads which have been cut from the wafer after all of the thin film structures have been formed. Lapping the heads is typically a mechanical process, but use of a slurry with an alkaline pH is suggested by Brar, et al., in U.S. Pat. No. 4,837,923. The purpose is to add an etching action in addition the mechanical abrasion. A pH of nine is said to be preferable. The result is claimed by Brar, et al., to be a smooth surface with the pole tip exposed and flush with the surrounding material.
SUMMARY OF THE INVENTION
Applicant discloses a novel magnetic transducer which has selected elements recessed from the surface of the transducer. The magnetic sensor element is recessed below its surrounding gap material and the second shield (S
2
) is preferably recessed below the level of the gap material. The magnetic sensorelement and the second shield are typically made from ductile material. Recessing the softer and more ductile elements below the surrounding ceramic material, results in superior resistance to physical distortion resulting from the action of the moving magnetic media. Applicant discloses two methods for producing magnetic transducers with recessed elements according to the invention. One method uses a lapping medium which chemically etches the
Knight G. Martin
Nguyen Hoa T.
Watko Julie Anne
LandOfFree
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