Thin-film magnetic recording head using a plated metal gap layer

A first layer of magnetic material is deposited onto a substrate to form a bottom pole of an inductive transducer. A second layer of magnetic material is plated on the first layer of magnetic material within the pole tip region to form a bottom pole extension. A layer of non-magnetic metal is then plated on the bottom pole extension to form the gap. A third layer of magnetic material is then plated on the gap layer to form the top pole extension. In one form of the invention, a mask is employed to define a good zero throat level surface to the pole tip region.

BACKGROUND OF THE INVENTION 
This invention relates to thin film inductive magnetic heads having 
well-defined pole tip structures, and particularly to a process to 
efficiently and accurately manufacture such heads. 
Inductive magnetic heads are used to write data to an adjacent magnetic 
medium. In its most basic form, an inductive head employs a pair of 
opposing poles, separated by a nonmagnetic gap at the pole tip region. A 
current-carrying coil passes between the two poles to induce a magnetic 
flux through the poles. The flux forms a reversible magnetic field across 
and adjacent to the nonmagnetic gap at the pole tip to write data into a 
magnetic layer of the adjacent memory medium. 
Gap materials for inductive heads are non-magnetic materials, and commonly 
include metal oxides and metal nitrides, such as alumina (Al.sub.2 
O.sub.3), silicon dioxide (SiO.sub.2), and silicon nitride (Si.sub.3 
N.sub.4). Metal oxide and nitride insulators are typically formed by a 
sputter-depositing technique, a chemical vapor deposition technique or a 
plasma-enhanced chemical vapor deposition technique; they are not capable 
of formation by plating, such as electroplating or electroless plating. 
However, in the fabrication of an inductive head, it is common to plate 
the poles into place. For example, it was common to plate the bottom pole 
on the substrate, and sputter deposit the alumina material over the bottom 
pole. Typically, the gap layer extended into the back region of the 
transducer and the coils and additional insulation material were formed in 
the back region of the head. The top magnetic pole was then plated over 
the coil and pole tip (gap) regions to complete the head. Thus, 
fabrication of inductive magnetic heads employed both sputter and plating 
techniques to form various layers in the thin-film head. These diverse 
techniques did not pose a problem to the fabrication of the head because 
different geometric configurations of the various layers required changing 
the masks for each layer, making it convenient to also change the process 
type. 
As the need for more efficient inductive heads increases, magnetic flux 
losses need to be minimized to thereby concentrate flux in the region of 
the gap. One technique to minimize flux losses is use of pole extensions 
for the top and/or bottom poles. The gap material is sandwiched between 
the pole extensions so that the gap and pole extensions have identical 
geometric configurations. More particularly, the gap and pole extensions 
have identical widths and depths to define the pole tip region without 
sharp corners in the magnetic path that otherwise create flux leakage. For 
example, Cole et al., in U.S. Pat. No. 5,454,164, describes a write head 
employing pole extensions having identical configurations to define the 
pole tip region. Cole forms a lower pole layer, gap layer, and upper pole 
extension layer in successive steps onto the substrate and ion mills all 
three layers (using a photoresist mask) to a design depth into the lower 
pole to define the zero throat level (depth) of the pole tip region for 
the upper pole extension, gap and lower pole extension. 
While the Cole process is designed to produce a write head having a 
well-defined pole tip region, the process does not perform well in a 
manufacturing environment. A principal difficulty with the Cole approach 
resides in the single-step ion milling process that requires continuous 
milling into and through diverse materials of the magnetic material of the 
upper pole extension, the gap material and the magnetic material of the 
lower pole extension. The different materials have different mill rates, 
making control of the milling process difficult in a manufacturing 
environment. The heads are typically formed on wafers, forming many 
hundreds of heads from each wafer. Variations in layer formation 
techniques in different regions of the wafer often leads to minor 
variations in thicknesses of the layers in different regions and in 
different heads being fabricated. Variation in layer thickness affects the 
milling time of the ion milling process; thicker layers require a longer 
milling time than thinner layers of the same material. Where a buried 
layer, such as Cole's gap layer and lower pole extension, is of a 
different material (and therefore has a different mill rate than a layer 
above), thickness variations of the layers alter the time of beginning of 
milling the buried layer and the time of beginning milling the layer below 
the buried layer. As a result, milling of the buried layers (both the gap 
and the lower pole extension) is inconsistent. Hence, the Cole process is 
not altogether satisfactory in a manufacturing environment. 
Another difficulty resides in the fact that Cole employs a metal oxide gap, 
such as alumina, that can only be deposited by sputter-deposition or vapor 
deposition, and cannot be formed by plating. Therefore, Cole requires 
formation of the bottom poles by plating, and a process change to sputter 
or vapor deposit the gap, and then change again to form the top pole 
extension by plating. Cole's process changes limits Cole's process to 
formation of layers that are without precise geometric configuration, and 
subsequent patterning by etching or milling, as Cole does. 
There is, accordingly, a need for a process of forming an inductive thin 
film write head having well-defined pole tip elements, that avoids process 
changes and milling procedures of buried layers. 
As used herein, the term "gap width" refers to the width of the gap across 
the air bearing surface of the head coincident with the width of the track 
being recorded. "Gap length" refers to the length of the gap along the air 
bearing surface between the poles, along the length of the track being 
recorded. "Gap depth" refers to the depth of the gap from the air bearing 
surface to a point (sometimes called the zero throat level) where both 
poles first confront the gap distal from the air bearing surface. 
BRIEF SUMMARY OF THE INVENTION 
The present invention is directed to a process of forming an inductive 
magnetic transducer for a recording head in which the magnetic material of 
the lower pole extension, a metal gap material, and the magnetic material 
of the top pole extension are plated in a single mask, which is thereafter 
removed leaving a well-defined pole/gap/pole sandwich in the pole tip 
region with a precisely defined surface at the zero throat level, without 
a milling process. 
In one embodiment of the invention, a first layer of magnetic material is 
deposited onto a substrate to form a bottom pole of the transducer. In one 
form, the bottom pole is a shared pole with a magnetoresistive read head 
which forms the substrate on which the pole is formed. Where a 
magnetoresistive head is included, a protective layer is formed over a 
portion of the bottom pole layer in the region of the coil region of the 
inductive head. In either case, this embodiment employs a layer of 
photoresist is formed on the first layer of magnetic material (and on the 
protective layer, if employed) that is patterned to define a mask that 
defines the width and the zero throat level of the pole tip region for the 
transducer, the mask exposing the first layer of magnetic material within 
the pole tip region. Using the mask, a second layer of magnetic material 
is plated on the first layer of magnetic material within the pole tip 
region to form a bottom pole extension, a layer of non-magnetic (low 
permeability) metal is then plated on the bottom pole extension to form 
the gap, and a third layer of magnetic material is then plated on the gap 
layer to form the top pole extension. The photoresist mask is then removed 
leaving the first layer of magnetic material (and protective layer, if 
employed) at the back region of the transducer behind the zero throat 
level of the pole tip region, and the bottom pole extension, gap and top 
pole extension at the pole tip. The mask defines a good surface to the 
pole extensions and gap at the zero throat level. Thereafter, the coil and 
top pole are formed in a conventional manner, with the top pole joining 
the top pole extension in the pole tip region and the bottom pole in the 
back region distal from the pole tip region. 
A second embodiment of the invention avoids the mask. In this second 
embodiment, a first layer of magnetic material is deposited onto a 
substrate to form a bottom pole of the transducer, and a first layer of 
insulating material is deposited onto the first layer of magnetic material 
in the coil region of the transducer behind the pole tip region. A gap 
region is deposited on the first layer of magnetic material within the 
pole tip region and abutting the first layer of insulating material. The 
gap region comprises a second layer of magnetic material to form a bottom 
pole extension, a layer of non-magnetic metal, and a third layer of 
magnetic material to form a top pole extension. A coil region is formed on 
the first layer of insulating material and comprises at least a portion of 
a conductive coil within an insulator. Formation of the coil region leaves 
a portion of the first layer of magnetic material distal from the pole tip 
region exposed. A third layer of magnetic material is formed over the 
exposed portions of the first layer of magnetic material, the gap region 
and the coil region to form a top pole of the transducer.

DETAILED DESCRIPTION 
FIGS. 1-8 illustrate a process of forming a thin-film inductive write head 
according to a first embodiment of the present invention. As shown at 
FIGS. 1-3, a layer 10 of magnetic material, such as permalloy, is formed 
on substrate 12. Layer 10 will form the lower pole piece of the thin-film 
inductive magnetic transducing head being fabricated. In one form of the 
invention, the inductive write transducer may be a part of a read/write 
head employing a magnetoresistive (MR) read head (not shown in FIGS. 1-3). 
In such a case, substrate 12 may be a reader isolation layer formed of a 
metal oxide such as alumina or silicon dioxide, and layer 10 will serve 
the dual function as a shield for the MR head, as well as the bottom pole 
for the inductive head. Thus, layer 10 is known in the trade as a shared 
pole. If desired, a protective layer 14 is formed on the exposed surface 
of magnetic layer 10, and is patterned as to expose the top surface of 
layer 10 in a region that encompasses pole tip region 16 and back gap 
region 18. By way of example, layer 14 may be a metal oxide, such as 
alumina, that is sputter-deposited onto the exposed surface of layer 10 
and etched, using a photoresist mask and etchant, to expose layer 10 at 
the back gap region 18 and pole tip region 16. Layer 14 does not extend 
into pole tip region 16. 
Photoresist mask 20 is formed on the exposed surfaces of layers 10 and 14 
and patterned to expose an upper surface of layer 10 in pole tip region 
16. As shown particularly in FIGS. 1 and 2, mask 20 defines the width and 
depth of pole tip region 16 to the zero throat level 22. Conveniently, 
mask 20 may be a U-shaped mask, defining the pole tip width and depth (to 
zero throat level 22), leaving the upper surface of the remainder of 
protective layer 14 and magnetic layer 10 exposed. 
As shown in FIG. 4, a layer of magnetic material, such as permalloy, is 
plated on the exposed portions of the shared pole on each side of mask 20 
as magnetic layer portions 24 and 24a over layer 10 in pole tip region 16 
and over protective layer 14. Next, a layer of non-magnetic (low 
permeability) metal gap material is plated over layer 24, 24a on each side 
of mask 20 as gap material portions 26 and 26a. The metal of gap layer 26, 
may be any non-magnetic metal, such as lead, gold, lead-nickel alloy, 
nickel-phosphorous alloy, or nickel-chromium alloy. Finally, another layer 
of magnetic material, such as permalloy, is plated over layer 26, 26a on 
each side of mask 20 as magnetic portions 28 and 28a. An important feature 
of the invention resides in the fact that the three layers, 24, 26 and 28 
are self-aligned by a plating technique, such as electroplating or 
electroless plating. 
As illustrated in FIG. 5, mask 20 is removed, as are the portions 24a, 26a 
and 28a of the magnetic layers and gap layer in the back region of the 
head, including over back gap 18, leaving the structure illustrated in 
FIG. 5. Portions 24a, 26a and 28a need only be removed to such a level as 
to assure magnetic connection between top pole 36 and bottom pole 10 at 
back gap 18. Thus, if removal of layers 24a, 26a, and 28a is accomplished 
by an etching process, the etching may occur to a level that either leaves 
a portion of magnetic layer 24a at the back gap, or etches into bottom 
pole 10 at the back gap. More preferably, portions of layers 24a, 26a and 
28a are left in place in region 18 and those portions of layers 26a and 
28a are etched away before forming the top pole. In either case, good 
magnetic connection between the top and bottom poles is assured at the 
back gap to assure a good magnetic circuit. 
Next, and as illustrated particularly in FIGS. 6-8, the insulator and coil 
structure are formed in the back region of the head and comprise layers of 
insulating material 30, 32 encapsulating convolutions 34 of an electric 
coil, with a top magnetic pole 36, preferably formed of permalloy, plated 
over the structure and joined to the exposed surface of top pole extension 
28 in the pole tip region 16, and to the exposed surface of bottom pole 10 
in the back gap region 18. In a first embodiment of the process, the coil 
structure is formed by depositing a layer 30 of insulating material, such 
as metal oxide, onto the exposed surfaces of top pole extension 28, 
protective layer 14 and shared pole 10 between the pole tip region 16 and 
protective layer 14 as shown in FIG. 6. Layer 30 is then ground to a 
planar surface to expose a top surface of top pole extension 28, as shown 
in FIG. 7. This grinding step may also grind away a small amount of top 
pole extension 28 to assure a planar surface to the upper surface of both 
insulation layer 30 and top pole extension 28. As shown in FIG. 7, the 
alternative of leaving a portion of layers 24a, 26a and 28a is 
illustrated. These layers serve to protect lower layers, such as an MR 
transducer, during fabrication of the inductive transducer in much the 
same manner as layer 14. After grinding the structure as illustrated in 
FIG. 7, those portions remaining of layers 26a and 28a are etched away, 
leaving magnetic layer 24a at the back gap region 18. As shown in FIG. 8, 
additional insulation layer(s) 32 encapsulates portions of convolutions 34 
of a coil, and top pole piece 36 is formed over the coil region and the 
bottom pole 10 or magnetic extension layer 24a at region 18. 
After completion of the inductive magnetic head according to the present 
invention, the forward surface is lapped and polished to form an air 
bearing surface defined at 36, thereby establishing a precise depth d to 
the pole tip region. 
As shown in FIG. 8 the MR head which includes an MR element 40 connected by 
contacts 42 to external read circuits (not shown). Typically, a metal 
oxide layer 44, such as alumina, is sandwiched between the MR element 40 
and contacts 42 on one side and a second magnetic shield layer 46 on the 
other. The entire structure may be supported on an insulating substrate 
48. Additionally, the MR head may additionally include a boundary control 
stabilization layer, a permanent magnet stabilization layer and/or 
additional layers of contacts for inductive cancellation and/or low 
circuit resistance. 
The embodiment described in connection with FIGS. 1-8 forms a planar coil 
design wherein the coils are formed starting with the same plane as the 
interface between the top pole piece and the top pole extension. FIGS. 
9-13 illustrate a second embodiment of the invention producing a recessed 
pole design. The structure of FIG. 4 is fabricated as described, except 
that protective layer extends though the back gap region 18. Mask 20 is 
removed, leaving layers 24a, 26a, and 28a. As shown in FIG. 9, a layer 50 
of metal oxide, such as alumina, is deposited over the structure and into 
the region left by mask 20. The structure is ground smooth as shown in 
FIG. 10, and layers 24a, 26a and 28a are removed as described above, 
leaving the structure illustrated in FIG. 11 with the layer 14 of 
protective material extending through the back gap region 14. Next, as 
shown in FIG. 12, layer 14 is etched away at back gap region 18 to expose 
bottom pole 10, and, as shown in FIG. 13, layer(s) 32 of insulation 
encapsulate convolutions 34 of the coil, and top pole piece 36 is formed 
as previously described. Again, the structure is lapped and polished to 
form air bearing surface 38. 
FIG. 14 illustrates a third embodiment of the present invention wherein the 
several layers are formed without mask 20. A layer 102 of metal oxide 
insulating material, such as alumina, is deposited in a pattern over 
common pole 10 in the gap region between pole tip region 16 and back gap 
region 18. A layer of bottom pole extension material 104 is plated on the 
exposed surface of common pole 10 in pole tip region 16, a layer of metal 
gap material 106 is plated on the exposed surface of layer 104, and a 
layer of top pole extension material 108 is plated on the exposed surface 
of layer 106. The coil structure comprising convolutions 110 embedded in 
insulating material 112 is formed over insulating layer 102, and a top 
pole layer 114 is formed over at least a portion of the exposed top pole 
extension 108 within the pole tip region, insulating material 112 within 
the coil region, and common pole 10 within the back gap region. The entire 
structure may be encapsulated in insulating cap 116. The structure 
illustrated in FIG. 14 provides a smooth rear surface to the pole 
extensions and gap, due to the common surface with layer 102. 
One feature of the process of FIG. 14 resides in the fact that the 
insulating layer 102 serves as both the smooth stop for the formation of 
the pole extensions and gap layer in the pole tip region and a protective 
layer for an adjacent MR read transducer (not show in FIG. 14) below the 
write transducer. 
Top pole layer 114 might be wider (across the gap width) than top pole 
extension 108, in which case it is preferred that top pole layer 114 does 
not extend to air bearing surface 36, thereby avoiding sharp corners in 
the magnetic path at the junction between top pole layer 114 and top pole 
extension 108 at or near the air bearing surface. Sharp corners in the 
magnetic circuit tend to promote flux leakage, leading to degraded head 
performance. Alternatively, top pole layer 114 may extend to the air 
bearing surface with a width preferably smaller than the width of 
extension 108. 
The present invention thus provides a highly efficient, repetitive process 
for precise fabrication of the pole tip region of a thin-film inductive 
magnetic head that avoids difficulties associated with ion milling, and 
does not require process alteration during fabrication. Although the 
present invention has been described with reference to preferred 
embodiments, workers skilled in the art will recognize that changes may be 
made in form and detail without departing from the spirit and scope of the 
invention.