Note: Descriptions are shown in the official language in which they were submitted.
20~26~1
9539-21
THIN FILM TRANSDUCER/TRANSFORMER ASSEMBLY
BACKGROUND OF THE INVENTION
This invention relates to thin film transducers of
the type found in small computer disk drives.
Thin film magnetic transducers are known which are
used in disk drives to write data to and read data from
magnetic storage disks. A typical thin film transducer
comprises a pair of pole pieces joined at a first region,
usually termed the back gap region, and spaced at an
opposing region, usually termed the pole tip region. In
between the back gap region and the pole tip region, the
pole pieces diverge in order to accommodate an electrical
coil which is electrically insulated from the pole pieces.
The coil is electrically connected to associated read/write
circuitry. The transducer is typically fabricated on a
relatively thick substrate, usually termed a slid~r, with
the pole tip region terminating at a surface termed the air
bearing surface (ABS). A typical example of such a
transducer is described and illustrated in U.S. Patent No.
4,458,279 and the additional references cited therein, the
disclosures of which are hereby incorporated by reference.
Typically, a pair of such thin film transducers is
fabricated on the slider surface, with each transducer
located at a different end o~ the slider surface adjacent a
lobe defined by a rail extending the entire length of the
slider. Thus, in a given assembly the slider has a pair of
rails running mutually parallel along the length of the
slider and a thin film transducer is associated to the lobe
defined by the associated rail.
The demand for increasing data density on magnetic
media has lead to the requirement for substantially smaller
track widths and transducers with correspondingly smaller
pole tip regions. With decreasing pole tip size, the
20~2611
amplitude of the signal output by the transducer coil is
correspondingly reduced. This is undesirable, since noise
signals increasingly mask the data signals generated by the
coils during a read operation, which leads to erroneous data
retrieval. In the past, attempts have been made to
compensate for this decrease in signal amplitude by adding
more turns to a transducer coil. This solution is less than
desirable, however, since it leads to an increased thickness
of the transducer: in particular, in order to accommodate
more turns, the coil is fabricated in several layers. This
increased thickness of the transducer is highly undesirable
because of a corresponding increase in noise, resistance and
power consumption. Moreover, additional process steps are
required, which increase producton cycle time and decrease
the yield rate, thereby contributing to higher cost per
unit.
SUMMARY OF THE INVENTION
The invention comprises a thin film transducer/
transformer assembly and a method of manufacturing such an
assembly which enables the physical size of the transducer
pole tip to be substantially reduced without sacrificing
reliability in the electrical signal generated by the
transducer.
From an apparatus standpoint the invention
comprises a substrate providing a support surface, a thin
film magnetic transducer formed at a first location of the
support surface, a thin film transformer formed at a second
location of the support surface, and means for providing
electrical coupling between the transducer and the
transformer. The substrate support surface is preferably
provided with a pair of laterally spaced lobes, and the
transducer is formed adjacent one of the lobes while the
transformer is located adjacent the other one of the lobes.
The electrical coupling means preferably comprises a pair of
electrically conductive leads extending between the
transducer and the transformer.
6 :~ 1
The transducer includes an electrically conductive
coil having a pair of ends, and the transformer includes a
coil having a pair of ends and a tap connection between
those ends. The coupling means includes a first conductive
path coupled between one of the transducer coil ends and one
of the transformer coil ends, and a second conductive path
coupled between the other one of the transducer coil ends
and the tap connection of the transformer coil. The output
signals from the transducer/transformer assembly are taken
from the ends of the transformer coil. The transformer coil
serves to boost the amplitude of the signal generated by the
transducer coil, with the amount of amplitude boost being
dependent upon the turns ratio of the two portions of the
transformer coil.
The transformer includes a bottom pole member, a
top pole member forming a closed magnetic path with the
bottom pole member, with the top and bottom pole members
being fabricated of a magnetically permeable material, and
an electrically conductive coil positioned between the top
and bottom pole members, the coil having a pair of ends and
a tap connection between the ends. The bottom pole member
preferably includes first and second end portions and an
intermediate body portion extending therebetween; the top
pole member preferably includes first and second end
portions and an intermediate body portion extending
therebetween and disposed above the intermediate body
portion of the bottom pole member to provide an interior
space for accommodating the coil, and the first and second
end portions of the bottom pole member are coupled to the
first and second end portions of the top pole member,
respectively. The intermediate body portion of the top pole
member preferably includes a downwardly depending central
portion extending to the intermediate body portion of the
bottom pole member, and the transformer coil is preferably
disposed about the central portion of the top pole member.
If one of the transformer pole members is electrically
conductive, the tap connection is electrically coupled to
2~26~1
that electrically conductive pole member; alternatively, the
tap connection includes a separate tap element having an
externally accessible end portion.
The thin film magnetic transducer includes a
bottom pole member having a back gap end and a pole end, a
top pole member having a back gap end and a pole end, the
top and bottom pole members being mutually coupled at the
back gap ends thereof, the pole ends being mutually spaced,
a coil having a plurality of turns passing between the top
and bottom pole members, and means for electrically
insulating the coil from the pole members.
From a method standpoint, the invention comprises
the steps of providing a substrate having a support surface,
forming a thin film magnetic transducer at a first location
of the support surface, forming a ~hin film transformer at a
second location of the support surface, and formin~ an
electrically conductive coupling between the transducer and
the transformer. The thin film magnetic transducer is
preferably constructed by forming a magnetically permeable
bottom pole member with a back gap end and a pole end,
forming an electrically conductive coil over the bottom pole
member and enclosing the back gap end, and forming a top
pole member with a back gap end coupled to the back gap end
of the bottom pole member and a pole end spaced from the
pole end of the bottom pole member.
The transformer is preferably fabricated by
forming a bottom pole member of a magnetically permeable
material, forming a coil structure over the bottom pole
member in mutually spaced fashion, and forming a top pole
member over the coil structure with portions of the top pole
member coupled to corresponding portions of the bottom pole
member to form a closed magnetic path with a leg portion
surrounded by the coil structure. The coil structure is
fa`oricated preferably by forming a first insulating layer
over the bottom pole member, forming a first coil segment
over the first insulating layer, forming a second insulating
layer over the first coil segment, forming a second coil
~2~1 ~
segment over the second insulating layer, and forming a
third insulating layer over the second coil segment. The
embodiment having a separate center tap is fabricated by
preceding the step of forming a second coil segment with the
steps of forming a center tap element over the second
insulating layer, and forming a fourth insulating layer over
the center tap element. During formation of the thin film
transformer, certain portions of the bottom psle member
corresponding to certain portions of the to-be-formed top
pole member are exposed, and the top pole member is formed
by depositing a magnetically permeable material over the
coil structure so that the top pole member, when formed,
includes magnetically permeable material contacting the
exposed corresponding portions of the bottom pole member and
extending between the exposed portions of the bottom pole
member over the coil structure. A plurality of externally
accessible contact pads coupled to the coil structure in a
predetermined fashion are also provided during fabrication
of the transformer.
The thin film transducer/transformer assembly can
be fabricated using standard photolithographic/deposition
techniques of the type used in thin film transducer
processing, with corresponding portions of the transducer
and the transformer being simultaneously fabricated using
appropriate masks. Further, batch processing is preferably
employed so that several transducer/transformer assemblies
are fabricated on the same substrate, followed by separation
into individual assemblies. Thus, each assembly can be
fabricated at relatively low cost using standardized
techniques providing relatively high yields. The inclusion
of the transformer in the electrical circuit between the
transducer and the follow-on electronic circuitry enables a
relatively small transducer to be used for read/write
operations without sacrificing the signal-to-noise ratio due
to the signal amplitude boost afforded by the transformer.
For a fuller understanding of the nature and
advantages of the invention, reference should be had to the
2~261~
ensuing detailed description taken in conjunction with the
accompanying drawings.
B~IEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an isometric representation viewed from
the upstream side of a slider depicting the novel structure
of the invention;
Fig. 2 is an enlarged sectional view illustrating
the thin film transducer taken along lines 2-2 of Fig. l;
Fig. 3 is a perspective view of the thin film
transformer;
Fig. 4 is an exploded view of the transformer;
Fig. 5 is an enlarged sectional view illustrating
the transformer taken along lines 5-5 of Fig. 3; and
Fig. 6 is an electrical diagram showing the
coupling between the transducer and the transformer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to the drawings, Fig. 1 illustrates
the preferred embodiment of the invention. As seen in this
Fig., a thin film magnetic transducer generally designated
with reference numeral 10 and a thin film transformer
generally designated with reference numeral 40 are formed on
a support surface 11 of a slider 12. Slider 12 includes
first and second air bearing rails 13, 14 which are
integrally formed with the slider 12 and which provide air
bearing surfaces for supporting the slider 12 above a moving
magnetic disk (not shown) in a known manner.
As best seen in Fig. 2, thin film transducer 10
includes a first layer of magnetic film material forming a
first magnetic pole piece 15 disposed on surface 11 of
slider substrate 12. First magnetic pole piece 15 is
typically of uniform thickness between at least a pole tip
region 15a and a back gap region 15b. A first layer of non-
magnetic insulating material 16 such as silicon dioxide oralumina is deposited over pole piece 15 and extends from
pole tip region 15a to back gap region 15b.
2~ 2 6 ~ ~
A first layer of electrically conductive material
forming a conductive coil winding 20a is deposited in an
appropriate pattern, such as rectangular, circular or
elliptical, over the layer of insulating material 16. A
second layer of insulating material 22 of sufficient
thickness to cover winding 20a is deposited over insulating
layer 16. A second layer of electrically conductive
material forming a further conductive coil winding 20b is
deposited in a suitable pattern over the layer of insulating
material 22. A third insulating layer 24 covers the second
winding 20b. First and second windings 20a and 20b are
connected to form a two layer continuous coil which loops
around the back gap region 15b to enclose the region 15b.
A second layer of magnetic material forming a
second magnetic pole piece 26 is deposited over first pole
piece 15 in the back gap region 15b, over insulatinq layers
22 and 24 in the regions occupied by conductive windings 20a
and 20b and over insulating layer 16 in the pole tip region
15a. Pole pieces 15 and 26 are separated at the pole tip
region by insulating layer 16 in order to provide a
transducing gap therebetween. One end of first winding 20a
and one end of second winding 20b are electrically coupled
to the first end of separate electrically conductive paths
30, 31 (Fig. 1) in order to electrically connect the coil of
the transducer 10 to the coil in transformer 40, as
descri~ed more fully below.
With reference to Figs. 3-5, transformer 40
includes a bottom magnetic pole or bar 60, an upper magnetic
pole or bar 82 joined to lower bar 60 at the edges and the
center thereof, a pair of electrically conductive coil
seqments 66, 68, an electrically conductive center tap
element 76 and a plurality of electrically insulative
spacers 62, 74, 78 and 80. The lower coil segment 66 is
coupled to a first contact pad 50; the center tap element 76
is coupled to a second contact pad 52; and coil segment 68
is coupled to a third contact pad 54.
~26~1
As best seen in Fig. 5, upper magnetic bar 82 has
a central downwardly depending portion 84 generally
cylindrical in configuration which passes through the
central apertures 70, 72 in coil segments 66, 68, and
through central aperture 77 in center tap element 76.
Central element 84 terminates in a bottom portion 85 which
directly contacts the bottom magnetic bar 60 in order to
provide a closed magnetic path therebetween. Central
portion 84 is electrically insulated from the coil segments
66, 68 and center tap element 76 in the embodiment depicted
in Fig. 5. As can be appreciated by those skilled in the
art, if bottom bar 60 or top bar 82 are fabricated from
material which is not only magnetically permeab~e but also
electrically conductive, center tap element 77 can be
eliminated and the tap provided by establishing an
electrical connection between the inner ends of coil
segments 66, 68 and one or both of the bars 60, 82.
Alternatively, the tap can be taken from some point along
either coil segment 66 or 68 to one or both of the bars 60,
82.
As best shown in Fig. 6, the coil segments 20a,
20b of thin film transducer 10 are electrically connected to
coil segment 66 of transformer 40 via conductive leads 30,
31; while the output connections to the follow-on electronic
circuitry (not shown) are taken from the non-common ends of
coil segments 66 and 68 along conductive paths 31, 33. To
facilitate connection to the external circuitry, enlarged
electrical contact areas 34, ~5 are provided as shown.
As will be appreciated by those skilled in the
art, transformer 40 is used to modify the signals generated
by transducer 10 on conductive paths 30, 31 during a read
operation. More particularly, the voltage level of the
signals from transducer 10 is stepped up or boosted by
transformer 40. The amount of boost in the signal level is
determined by the turns ratio of the coil segments 66, 68.
With the configuration depicted in Fig. 6, the number of
turns Nl on the signal input side is simply the number of
2~26~
turns in coil segment 66, while the number of turns N2 on
the signal output side is the combined value of the number
of turns in coil segment 66 and coil segment 68. These
numerical values can be determined in an empirical fashion
for any given application.
As will be appreciated by those skilled in th~
art, the fabrication of thin film transducer 10 and thin
film transformer 40 can be done simultaneously to form the
transducer/transformer assembly described above. Moreover,
the fabrication of the transducer 10 and transformer 40 is
performed using thin film processing steps which are well
known to those skilled in the art. In particular, substrate
12 is initially provided, after which the bottom pole 15 of
transducer 10 and the bottom pole 60 of transformer 40 are
formed by initial deposition of a suitable magnetically
permeable material such as nickel iron to a prescribed
thickness, followed by selective photomask patterning and
etching. Next, first insulation layers 16 and 62 are formed
by depositing an insulation layer, such as silicon dioxide,
followed by photomask patterning and etching.
Alternatively, a photoresist layer is coated onto the bottom
poles 15, 60 and substrate 12 followed by photomask
patterning and hard bake (solidification). Next, first coil
segments 20a and 66 are fabricated from a suitable
conductive material, such as copper, silver, gold or the
like, by first depositing a thin film seed layer to a
thickness on the order of about 200 ~, followed by
deposition of the conductive material to a suitable
thicknessr photomask patterning, soft bake and plating,
followed by photoresist strip and seed layer etching.
Second insulation layers 22, 74 are next formed, followed by
formation of the center tap lead 76 and insulation layer 78
of transformer 40 (where employed), coil segments 20b, 6B,
insulation layers 24, 80 and top magnetic pole pieces 26,
82. During formation of the insulative layer 22, a suitable
aperture is provided (not shown) to provide electrical
connection between appropriate ends of the coil segments;
2~26~ ~
similarly, during formation of coil segments 66, 68 and
center tap element 76, apertures 70, 72 and 77 are etched to
provide a central opening for accommodating the central
region 84 of top bar 82. In addition, apertures are formed
in insulation layers 74, 78 of transformer 40 in order to
provide ohmic contact between the center tap element 76 and
the inner ends of coil segments 66, 68. After the formation
of the conductive paths 30, 31 and 33, and the contact pads
34, 35, a protective layer such as alumina (not illustrated)
is deposited on the top of the now formed transducer/
transformer assembly.
As will now be apparent, the transducer/
transformer assembly can be fabricated using standard
integrated circuit or thin film transducer batch fabrication
techniques, thus providing great e~onomies of scale so that
the individual assemblies can be produced at a favorably low
cost with relatively high yield. The inclusion of the
transformer 40 in the assembly permits a transducer 10 with
smaller pole tip dimensions to be employed without
sacrificing signal amplitude and thus signal reliability.
For example, for a transducer 10 having a coil segment 20a
with 17 turns and a coil segment 20b of 15 turns, for a
total of 32 turns, the use of a transformer having a turns
ratio of 2:1 has the same effect on signal amplitude as
fabricating a 64 turn transducer coil.
While the above provides a complete and adequate
description of the preferred embodiments of the invention,
various modifications, alternate constructions and
equivalents will occur to those skilled in the art. For
example, although the invention has been disclosed with the
transducer 10 on the left lobe 13 and the transformer 40 on
the right lobe 14 of the slider 12, assemblies in which the
locations of the transducer 10 and transformer 40 are
reversed are envisioned. Therefore, the above should not be
construed as limiting the invention, which is defined by the
appended claims.
