Note: Descriptions are shown in the official language in which they were submitted.
,f~9L3~Z8
ELECTRICAL LAPPING GUIDE FOR CONTROLLING
THE BATCH FABRIcATIoN OF T~IIN FILM M~G~ETIC TRANs-DucERs
BACKGROUND OF THE INVENTION
This invention relates generally to a dynamic magnetic
information storage retrieval apparatus and a method and
apparatus to control the manufacture of magnetic trans-
ducers, and in particular to an electrical lapping guide
structure useful for batch fabricating thin film magnetic
heads.
FIELD OF THE INVENTION
In high speed data processing systems, magnetic disks have
been employed for large memory capacity requirements. Data
is read and written onto the disks from magnetic transducers
commonly called magnetic heads which are positioned over the
disk during the retrieval and storage of data on tracks of
the disks. The requirements for higher data density on
magnetic disks have imposed a requirement to read and write
more data on narrower tracks located on the disk. Further,
the disks have become thinner in order to improve the
coercivity for maintaining the integrity of the data on the
disk. The requirement for a higher data density imposes a
higher flux density generation and sensing capability on the
transducer. In order to achieve maximum efficiency Erom the
transducer or head element, the element or pole pieces are
formed from thin films of a magnetic material~ The pole
SA9-84-025X 1
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34;~8
pieces must have a pole tip h~ight dim~nsion, commonly
called throat height, which must be maintained within a
certain limited tolerance for generating a maximum amount of
electrical signals from a given head. For a further discus-
sion of the necessity to maintain the throat height to acertain distance, reference is made to U.S. Patents
4,190,872 and 4,295,173, both assigned to the assignee of
the present invention.
A method of producing a required throat height includes a
lapping stage in which an abrasive griding surface accu~
rately grinds the pole tips to a desired length. Suitable
techniques for controlling the throat height during the
lapping operation are described in U.S. Patent 3,821,815,
also assigned to the assignee of the present invention. In
this patent, a technique is employed for measuring the
resistance of an element located on the substrate containing
the transducer being lapped to a final throat height. The
resistance element is lapped along one dimension to the same
extent as the transducer pole tips. The resistance of the
element at any given time indicates the amount of material
that has been removed from the element and hence the resis-
tance is an indication of the final throat height of the
transducer being lapped.
A further U.S. Patent 4,014,141, also assigned to the
assignee of the present invention, describes another appara-
tus for controlling the grinding and the lapping of a
magnetic head surface under control of electrical lapping
guides.
SA9-84-025X
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The present invention provides for an i~proved electrical
lapping guide useful, for instance, in one of these systems
described above to control the lapping process such that the
final throat height of thin film magnetic heads can be
accomplished using batch processing techniques.
DESCRIPTION OF THE PRIOR ART
Electrical lapping guides are well known in the processing
OL thin film transducers. Most often the electrical lapping
guide is a flat element resistor having one of the electri-
cal guide resistors located on each end of a row of aplurality of magnetic transducing elements, such as is shown
in the IBM Technical Disclosure Bulletin, Vol. 18, No. 11,
April 1976 at pages 3782-3. Similar electrical lapping
guide elements are disclosed in the IsM Technical Disclosure
15 Bulletins at Vol. 23, No. ~, September 1980 at page 1631 and
Vol. 23, No. 2, July 1980 at page 776. In all of these
articles, an electrical lapping guide is deposited on both
ends of a row of magnetic transducers shown as read elements
or data elements or an array of devices in the articles. As
is disclosed in these articles, as the lapping proceeds, the
resistance between the conductors of the electrical lapping
guides is increased as the material between the conductors
of the guides is removed.~ These articles disclosed one
means of controlling the final throat height of the finished
head and that is by depositing a separate test element to
which the electrical lapping guide is compared in order to
stop the lapping process at the correct throat height.
An object of the present invention, therefore, is to provide
an enhanced electrical lapping guide apparatus useful for
SA9-84-025X 3
~,Z43~Z8
the control of -the grinding and lapping processes to obtain
a precise throat height of the thin film magnetic head.
Another object of the present invention is to provide an
electrical lapping guide that is designed to precisely
control the manufacturing processes such that the throat
height of the completed magnetic head can be held to a
precise length.
A further object of the invention is to provide an electri-
cal lapping guide apparatus that can be monitored during a
lapping operation to produce a precise throat height of thin
film magnetic heads.
Still another object of the present invention is to provide
an enhanced method of making electrical lapping guide
apparatus using the batch processes used to manufacture thin
film magnetic heads.
Electrical lapping guides previously included only junction
connections between conductors and straps. When the junc-
tion connection was broken during the lapping process, the
resistance between the conductors went to infinity because
the electrical connection to the strap was interrupted. The
lapping process could not be controlled further since no
resistance measurement was possible unless a second lapping
guide was provided.
Yet another object of the invention is to provide an elec-
2s trical lapping guide having junctions that provide electri-
cal contact to a strap of higher electrical resistance than
usual in a lapping guide, with the junction bridging a
SA9-84-025X 4
resistive element and producing a change in the elec-trical
conduction when broken that provides an indication of the
lapping progression to determine the throat height of the
magnetic head.
5 SUMMARY OF THE INVENTION
In accordance with the present invention, a resistive elec-
trical lapping guide is deposited on at least one end of a
linear array of magnetic head elements during the deposition
of the head elements on a substrate. The electrical lapping
guide includes a plurality of switching junctions formed
between a section of electrically resistive material and
conductors. The conductors provide electrical interconnec-
tion to e~ternal testing equipment. The interconnection or
switching junction between the conductor and the section of
15 resistive material or strap provides a known switching plane
when the junction is interrupted by the lapping process.
Each switching junction is interrupted to form a change in
the electrical state between the conductors when a known
throat height is reached. Forming the electrical lapping
guide resistor strap and the switching junctions at the same
time that elements of the film transducer are formed, pro-
vides good registry between the throat height measurements
and the actual pole tip dimension of the magnetic head. A
shunt resistor deposited in parallel with the switching
25 junction continues electrical conduction while enhancing
detection of the opening of the switching junction. In a
preferred embodiment the resis-tance of the strap is formed
by one of the layers deposited during the formation of -the
magnetic head and used in the process for building a
magnetic head. The strap resistor is thinner than that used
SA9-84-025X 5
3~Z13
in the prior art electrical lapping guides and therefore is
of a higher resistance than that formally used.
Another object of the present invention, therefore, ls to
provide an electrical lapplng guide for the batch fabrica~
tion of magnetlc heads that includes a plurality of points
at which the electrical current passed through the electri-
cal lapping guide during the processing of the magnetic head
is switched from different paths by interrupting conductor
and strap junction points at several throat height lengths
to provide a precise control of the lapping process by the
electrical guide.
Yet another object, therefore, is to provide an electrical
lapping guide that has a higher resistance between the
conductors than that used by prior art devices.
Still another object is to provide a shunt resistor across
the switching junctions of an electrical lapping guide to
enhance the detection of the change in state of the switch-
ing junction when the contact between the conductor and the ~-
strap is interrupted by lapping through the junction.
Further in accordance with the present invention, a method
is claimed for making electrical lapping guides during the
process of forming at least one batch fabricated magnetic
transducer selecting a special site on a wafer adjacent to
and aligned with the magnetic transducer. A conductive
layer of an electrically conductive material is then
deposited on the substrate at the selected site to form the
strap of a strap-to-junction type electrical lapping guide
and to form a serpentine-shaped length such that one end of
SA9-84-025~ 6
3 L?/~
the length is electrically connected to the strap of conduc~
tive film material. An electrically insulating material is
then deposited onto the first conductive layer at two spaced
apart areas at the selected site. The insulating material
5 is deposited and ormed at the same time and of the same
material that determines the throat height of the
transducer. The insulating material includes vias -to the
conductive material at the guides. The vias are formed at
selected throat height lengths relative to the transducer.
A second layer of an electrically conductive material is
deposited over the vias to form conductors at the spaced
apart areas for electrical measurement of the strap. The
second conductive layer is placed into electrical contact
with a second end of the serpentine-shaped length of first
conductive material.
The resistance of the electrical lapping guide strap resis-
tor is monitored during the lapping of the magnetic head
array to achieve the final head element throat height. ~t a
known throat height which is greater than the final throat
height, the switching junction opens to change electrical
state between the conductors of the electrical lapping
guide. This change in state provides a distinct readily
detectable change in resistance that can be readily sensed
by the test equipment connected to the electrical lapping
guide. Detection of the change of state of the switching
junction provides a known throat height which may be com-
pared with the throat height determined from the resistance
measurement of the strap in the electrical guide. These
changes in state allow the subsequent resistance measure-
ments to be calibrated in light of the interruption of theswitching junction that provided the change in state, to
SA9-84-025X 7
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provide an accurate determin~tion o~ the amount of material
removed in the lapping process and thereby provide an
accurate determination of the throat height of the magnetic
head array that is being lapped. -
Therefore an object of the present invention is to provide a
method that produces a more precise control of the lapping
process used to form a throat height of the magnetic heads
in the array being lapped to a more precise state than
formerly possible.
In prior art devices, when the junction of a strap and
junction electrical lapping guide was broken by the lapping
process, the entire electrical connection to that portion of
the guide was forever interrupted. With the present inven-
tion, when the junction switch is broken by the lapping
process, the electrical conduction continues through the
resistor that bridges the junction switch. Therefore the
electrical lapping guide may have a second junction switch,
or more, bridged by resistors that can provide continued
control of a continuing lapping process.
It is, therefore, another object of the present invention to
provide an electrical lapping guide that includes a resistor
that bridges the junction switches of the guides to permit
continued control of the lapping process of thin film
magnetic transducers.
These and other objects of the present invention will become
apparent to those skilled in the art as the description
proceeds.
SA9-84-025X 8
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BRIEF DESCRIPTION OF Tl-IE DRAWINGS
The various novel features of this invention, along wi~h
foregoing and other objects, as well as the invention itself
both as to its organization and method of operation may be
more fully understood from the following description of
illustrated embodiments when read in conjunction with the
accompanying drawing, wherein:
Fig. 1 is an overall system block diagram illustrating a
lapping system that can be used with the guides according to
the present invention.
Fig. 2 represents one end portion of the substrate being
lapped in Fig. l showing the electrical lapping guide in
more detail according to an embodiment of the present
invention.
Fig. 3 is an enlarged portion of the electrical lapping
guide of Fig. 2 showing the details of the strap and junc-
tion design useful with the present invention.
-
Fig. 4 is a sectional view taken along lines 4-4 of Fig. 3
and showing the detail of the interconnection between the
conductor and the strap at the junction of the electrical
lapping guide.
Fig. 5 is an elec~rical schematic representation of the
electrical lapping guide structure of Fig. 2.
Fig. 6 represents one end portion of the substrate being
lapped in Fig. 1 showing the electrial lapping guide in more
S~9-84-025X 9
~;243~S
detail according to ~ preferred embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED ~BODIMENT
_ .
The present invention is preferably for use in the fabrica-
tion of thin film head assemblies. The transducer portion
of the thin film head is formed by depositing layers of
magnetic material, electrically conductive material and
insulated material to form the well known pole pieces and
magnetic gap necessary for the transducing function with a
magnetic coating formed on a dis~. A plurality of transduc-
ers are deposited onto a wafer which is then cut to form
rows of the transducers with the transducers set in a
side-by-side relationship. Electrical lapping guides are
formed onto the wafer at the same time that the transducers
are deposited. At least one electrical lapping guide is
deposited at each end of the row of transducers. The
electrical lapping guides are used during the lapping
process that determines the throat height of the transduc-
ers. The wafer eventually is formed to become the slider of
the magnetic head. The slider is mounted onto a suspension
system which in turn is mounted to an accessing system for
locating the magnetic head onto tracks formed by the
magnetic heads when writing onto the rotating disk. The
electrical lapping guide of the present invention, there-
fore, controls the lapping of a row of transducers in thebatch fabrication process.
Referring to Fig. 1, there is shown an overall system block
diagram of apparatus that controls the lapping of a portion
SA9-84-025X 10
~'~4~Z~
of a substrate row ~0 h~ving a plurali-ty of transducer
elements 12 with electrical lapping guide systems 14 and 16
located at both ends of the row. As stated previously, this
one row 10 of transducers 12 and electrical lapping yuides
14 and 16 are but one section from the total wafer which
includes a plurality of rows as well as a plurality of
columns of transducer elements. The substrate row 10 is
fastened to a holder 18 and placed against tt~o actuators 20
and 22 which position the substrate into a spaced relation-
ship with a lapping plate 24. The actuators urge thesubstrate row 10 against the lapping plate 24 and control
the amount of pressure placed against the holder 18. The
lapping plate 24 is, as is known to those skilled in the
art, an abrasive surface which through relative motion
affects lapping of the substrate row 10. The substrate row
10 is lapped in order to remove material such that the
throat of the transducers 12 can be precisely located under
control of the electrical lapping guide systems 14 and 16.
The depth of the lapping provided by the lapping plate 24 is
monitored through the two electrical lapping guide systems
14 and 16. The electrical lapping guide systems 14 and 16
are deposited on the substrate at the same time as various
layers of the transducer elements 12, and provide a means of
electrically determining the throat height for the trans- -
ducer elements. The electrical lapping guide systems 14 and
16 are connected to a multiplexer 26. The multiplexer 26
senses the electrical resistance of the separate electrical
lapping guide systems and directs this information to a
meter 28 which can be a standard ohmmeter measuring electri-
cal resistance and also sends this information to a control-
ler 30. The controller 30 in turn controls the two
SA9-84-025X 11
.,'243 ~;Z;~3
actuators 20 and 22 such that the substra~e row 10 can be
kept level by varying the amount of pressure applied by each
actuator at its end of the substrate row.
With electrical lapping guide systems 14 and 16 at each end
of the row, it is possiblc to control the amount of pressure
each end of the substrate rows receive, and thus permit the
actuators 20 and 22 to maintain the substrate row 10 level
with the lapping surface. Thus, by comparing the relative
resistance measurements from each lapping guide system, the
throat heights of each of the plurality of transducers along
the row can be maintained at the same length during lapping.
The resistance measurements provided by the electrical
lapping guide systems 14 and 16 are determined from the
multiplexer 26 and the meter 28. Under control of the
controller 30, each of the resistance measurements provided
by electrical lapping guide systems 14 and 16 may be addres-
sed through the multiplexer 26 and the meter 28. The
results of the measurement is stored in the controller 30
and is utilized as an indication of the throat height
achieved for the transducer elements 12 during the lapping
process. The controller 30 can, by constantly measuring the
resistance of each of the electrical lapping guide systems,
maintain the substrate row 10 level with respect to the
lapping plate 24. Additionally, when a certain throat
height is detected as having been achieved through the
lapping process, the controller 30 may command the actuators
20 and 22 to withdraw the substrate row 10 from the lapping
surface to terminate the lapping process.
In general, the resistances and the switching aspects of
each electrical lapping guide system 14 and 16 is sensed by
S~9-84-025X 12
Z~3~
the controller 30. The controller 30 reacts to any diEfer-
ence in resistance, for instance, bctween -the electrical
lapping guide systems by applying added pressure to the end
of the substrate row with the lower resistance such that
additional material can be removed Erom that end to cause
the resistance oE the electrical lapping guide to be removed
quicker and thereby increase the resistance measured at its
electrical lapping guide as will be discussed later. When a
switching junction is opened during the lapping process, the
controller 30 can react by withdrawing the substrate row 10
from contact with the lapping process. Or the process can
be changed from a rough lap process to a fine lap process
such that more material can be removed for instance at the
beginning of the lap and a further lap used for better
control as the ideal throat height is approached as
indicated hy the electrical lapping guide systems. Examples
of lapping systems that could be adapted to perform the
control of the lapping system as shown in Fig. 1 are dis-
closed in the aforementioned U.S. Patents 3,821,815 and
4,014,141. Each of the electrical lapping guide systems 14
and 16 shown in Fig. 1 are identical. The structure o~ one
of the electrical lapping guide systems 14 and 16 of Fig. 1
is shown more particularly in Fig. 2.
Referring now to Fig. 2, the electrical lapping guide system
16 includes two straps 32 and 34 interconnected to end
conductors 36 and 38 and a centertap conductor ~0 through
vias 42, 44, 46 and 48 formed in insulation layers 50, 52,
54 and S6, respectively. These vias, called junctions or
junction switches for purposes of this invention, are the
controlled points at which the conductors connect electri-
cally with the straps. Each end conductor 36 and 38 is
S~9-8~-025X 13
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connected to one strap 32 or 34, while tl~e center conductor
40 is connected to one end of both straps. A layer of
conductive material forming thin film resis-tors 58, 60, 62
and 64 interconnect the conductive material of the conduc-
tors 36, 38 and 40 and the conductive material of the straps
32 and 34 to effectively bridge the interconnecting junction
switches 42, 44, 46 and 48. Thus for instance, the thin
film resistor 58 bridges the junction switch 42 at the left
hand conductor 36 which is connected through the junction
switch 42 to the right end of the strap 32. Thin film
resistor 60 bridges the junction switch 44 interconnecting
the right end of the strap 32 to the center conductor 40.
The thin film resistor 62 bridges the junction switch 46
connecting the centertap conductor 40 to the right strap 34
while the thin film resistor 64 bridges the junction switch
48 connecting the strap 34 to the right conductor 38. The
conductors 36, 38 and 40 are connected through external
wires to the multiplexer 26 for the sensing of the resis-
tances between the conductors as caused by the thin film
resistors, junction switches, and the straps themselves,
The material forming the strap and the thin film resistors
is preferably made from an electrically conductive material
such that its resistance is as high as possible. The width
of the thin film resistors is much smaller than that of the
straps and therefore the thin film resistors have a much
higher resistance compared to the straps. Since preferably
the layers of the electrical lapping guides are deposited at
the same time as portions of the transducer elements, it is
possible that one of the seed layers used to electrically
activate the substrate for a subsequent electroplating
operation can be used to form both the straps 32 and 34 and
SA9-84-025X 14
.Z~34Z~3
the thin film resistors 58-64. Thus the material coul~ be
nickel-iron sputter depositcd on the substrate in prepara-
tion for an electroplatillg process whlch deposits the
nickel-iron materi~l forming either one of the pole pieces
of the transducer elements. Preferably, according to the
present invention, the strap and thin film resistors are
formed from a chromium layer which is deposited in the
formation of the transducers as an adhesive enhancing layer
or as a layer to better optically define different portions
10 of the transducer. The insulating layers 50, 52, 54 and 56
can be formed at the same time as one of the insulative
layers used in the transducer element. Thus the insulating
layers may be formed from an aluminum oxide which is pre-
ferred as the magnetic gap layer of the transducer. Or the
insulated layer may be any onc of the layers that insulates
the conductive layers of the transducer from the pole
pieces. Thus the insulated layers 50-56 may be ~ormed from
the hard-baked photorcsist formed over the first pole piece
before the conductive la~er is deposited or it can be formed
from the photoresist insulative material that is placed over
the conductor before the second pole piece is deposited.
Each of the insulating la~ers 50-56 include the vias 42-48,
respectively, which is a lack of insulative materials
permitting an electrical connection between the conductors
25 36-40 and the straps 32 and 34.
The conductors 36, 38 and 40 are thcn deposited over the
insulated material in the approximate shape as shown such
that the conductors are electrically insulated from the
straps except through thc vias. These interconnectionS
between the conductor an~ the strap at the vias are called
junctions or junction switchcs wi~h the electrical lapping
SA9-84-025X 15
guide called a str~p-to-junction arrangernent to siynify the
interconnection of the conductors through junctions with the
straps. The conductors 36, 38 and 40 may be forme~ together
with any one of the electrically conductive materials used
in the transducer elements. The conductors are generally
made to have low resistance and therefore are preferably
formed of the nickel-iron material which is electroplated at
the same time that either the first pole piece or the second
pole piece of the transducer elements is formed. Or the
conductive elements may be electroplated copper formed
together with the conductors of the transducer elements or
any of the other electrically conductive layers used in the
formation of the transducer elements. Preferably, the
insulating layers 50-56 are deposited at the same time with
the layer that determines the throat height of the trans-
ducer elements. Since the junctions are deposited at the
same time and in the same process as the layer that deter-
mines the throat height, the junctions can be accurately
placed relative to the transducer elements and thus provide
a precise accurate indication of the throat height length
during the lapping process. Preferably, therefore, the
insulating layers 52-56 are formed together with the first
insulating layer that separates the first pole piece from
the conductors of the transducer elements and the conductors
25 36, 38 and 40 are electroplated at the same time that the
second pole piece of the transducing elements are deposited.
In the embodiment of the invention shown in Fig. 6, the
basic arrangement and the method for making the structure is
substantially the same as that described above in connection
with Fig. 2. However, it has been found that, by making the
length of one of the straps substantially longer than the
SA9-84-025X 16
~4~4Z~3
other strap, a greater precision c~n be ~chieved in the
~inal throat height. The lapping operation always pro~uces
high levels of electrical noise, and the longer strap
improves the precision of the electrical measurements due to
a higher signal to noise ratio.
The embodiment shown in Fig. 6 comprises a right strap 3~',
the length of which is about twice the length of the left
strap 32. For this reason, the resistance of the right
strap 34' is higher, and the ratio of the resistance of
strap 34' to the shunt resistor 64 is higher so that the
influence of shunt resistor 64 is reduced. The right strap
34' is chosen as the longer strap sinc~ the junction switch
46, which is substantially coincident with the throat height
line TH (see Fig. 3), is the most critical, and this
junction switch 46 is connected to right strap 34'. Since
the embodiment of the invention shown in Fig. 6 provides
improved precision of the electrical measurements, this
embodiment is the preferred embodiment.
Further details of the interconnection between the conduc-
tors and the strap can be obtained by referring to Figs. 3
and 4. Figs. 3 and 4 show the details of the right strap of
Fig. 2. Common reference numerals are used throughout this
description. Reference is made to the aforementioned U.S.
Patent 4,190,872 for a further description of the transducer
elements described with the present invention.
As shown in Figs. 3 and 4, the conductive material of the
strap 34, preferably chromium, is deposited onto the wafer
substrate material shown as substrate row 10. The insula-
tion layers 54 and 56 are then placed over at least portions
SA9-84-025X 17
2~
Oe the strap 34. The insulation layers 5~ and 5fi include
the vias 46 and 48 which leave areas of the strap 34
exposed. The vias ~16 and 48 arc very precisely located
relative to the optimum throat height measurernent of the
transducer elements. The conductors 38 and 40 are then
preferably electroplated. The conductors 38 and 40 are
electrically connected to the thin film resistors 62 and 64,
respectively, and to the strap 34 through the vias 46 and
48. The vias 46 and 48 as previously stated, form the
junction switching elements of the electrical lapping guides
of the present invention. A line T~l is shown approximately
level to the top of the junction switch 46. rrhe line ~H can
represent the final throat height desirRd as measured
through the mask set that determincd the junction switch 46
together with the insulation layer that formed the layer
that eventually determines the throat height of the trans-
ducing element. Thus when the junction switch 46 is opened
in the lapping process, the controller 30 can signal the
lapping process to be halted because the final throat height
is reached. The junction switch 46 is essentially opened
because there is no electrical connection from the conductor
40 to the strap 34. The only interconnection is through the
thin film resistor 62. Cpening the junction switch 46 while
lapping away the connecting material causes a jump in
resistance level bec~use the essentially lower resistive
material of the conductor 40 and the strap 34 is removed as
a bridge shorting out the thin film resistor 62. An elec-
trically represented circuit of one of the electrical
lapping guide systems 14 and 16 of the present invention is
shown in Fig. 5.
SA9-84-025X 18
34Z~
Referring to Fig. 5, the reference numerals of the various
resistors and the switches are given the same numeral at
that of the element itself. The representative electrical
configuration shown in Fig. 5 is a direct electrical
replacement for the electrical lapping guide 16 shown in
Fig. 2. The resistance of the various conductors is repre-
sented by reference numerals R36-R40. The thin ~ilm resis-
tors are likewise represented by reference numerals R58-R64.
The straps 32 and 34 shown are variable resistors R32 and
lO R34 to represent that they change in resistance durlng the
lapping process. The junction switches 42-48 in turn are
represented by reference numerals S42-S48 to show the direct
electrical replacement between the switches of Fig. 5 to the
junction switches of Fig. 2. The switches S42-S48 are shown
bridging the thin film resistors R58-R64, respectively.
The operation of the electrical lapping guide system of this
invention will now be described. After the transducer
elements are deposited together with the elements of the
electrical lapping guides onto a wafer, the wafer is cut
such that the substrate row 10 is formed with an electrical
lapping guide systems 14 and 16 at each end of the row of
transducer elements 12 as shown in Fig. 1. The substrate
row 10 is fastened to the holder 18 and then placed in a
lapping system such that the substrate row lO is placed
adJacent to the lapping plate 24 to lap away a portion of
the material on one surface o the substrate row lO. The
lapping is controlled by the electrical lapping guide
systems 14 and 16 such that the correct throat height of the
transducer elements lZ can be achieved. Relative motion
SA9-84-025X 19
" 1;2~3~2~3
between the lap pl~te 2~ and the substra~e row 10 is pro-
vided to start the lapping away of the material. The ~rans~
ducer throat height lengths, the lengths of the pole pieces,
are shortened and the widths of the straps are narrowed
during the lapping process. The resistances of the electri-
cal lapping guide systems are directed to the multiplexer 26
for combination, to the meter 28 for measurement and onto
the controller 30. The controller 30 in turn activates the
actuators 20 and 22 to place the substrate rows 10 against
the lapping plate 24 to start the lapping process. The
controller 30 senses the electrical resistance of each of
the four series parallel electrical circuits ~rom both
electrical lapping guide systems 14 and 16. One electrical
lapping guide system is shown in Fig. 5 and therefore the
controller for the electrical lapping guide system 16 senses
the electrical resistance as measured by the conductor
resistance R36, through the junction switch S42 through the
strap resistance R32, through the second junction switch S44
and through the center tapped conductor resistance R40. The
controller 30 is also measuring the resistance from the
other half of this electrical lapping guide system 16 by
sensing the resistance again throughou~ the center tapped
conductor resistor R40 through the junction switch S46, the
strap resistance R34, the second junction switch S48 and the
right conductor resistance R38. Likewise, the controller 30
is sensing the resistances of the other electrically lapping
guide system 14 located at the opposite end of the substrate
row 10.
The lapping continues with the controller 30 keeping the
resistances of each of the elcctrical lapping guide systems
14 and 16 as equal as possible by adjusting the associated
SA9-84-025X 20
~ 34Z13
actuator 20 and 22 according -to the resistance sensecl. The
lapping continues in this f~shion until it reaches thc point
identified by a line 66 in Fig. 2. At this point, the
junction switch 42 should be opened at approximately the
same time on both ends of the substrate row l0 since the
junction switch 42 represented by switch S42 has been
opened. As shown in Fig. 5, opening the junction switch S42
places the thin film resistor resistance R58 into the series
circuit on the left side of the figure thereby increasing
the resistance of this half of the circuit. This change in
resistance is transmitted to the multiplexer 26 sensed by
the meter 28 and the controller 30. This change can be used
by the controller 30 to signify any one of a plurality of
operations. For instance, a rough lap could take place
until the opening of the junction switch 42 and a change to
a medium or a fine lapping process could be then undertaken.
Or perhaps the pressure applied by the actuators 20 and 22
can be lessened for a slower, more controlled lap. Or the
change in resistance might merely be sensed by the control-
ler 30 as an indication of further things to come. Eachhalf of the electrical resistance circuit shown in Fig. 5
may also be used as a redundant lapping guide. That i5, in
the event one-half of the circuit is inoperative because of
a deposition fault in the formation of the electrical
lapping guide, the other half can be substituted with the
controller 30 adapting accordingly.
If desired and in fact in the preferred process, the lapping
continues until the switching junctions S42-S48 are all
interrupted. The opening of the final switching junction
46, as is shown in Fig. 4, means that the lapping has
reached the line T~l. This could have been determined
SA9-84-025X 21
~%4~4Z~3
previously to be the optim~lm thxoat height length of the
transducer elements. At this time the controller 30 removes
all pressure by the act~lators 20 and 22 -to remove the
substrate row 10 from contac~ with the lap plate 2~. The
holder 18 and the substrate row 10 are removed from the
lapping system. The substrate row 10 is subsequently
removed from the holder 18 and the substrate row is placed
on machinery that forms the rails of the slider for eventual
flying operation relative to a rotating disk. The electri-
cal lapping guide systems 14 and 16 are cut off and dis-
carded from the substrate row and the transducer elements 12
are separated into individual magnetic heads. The indivi-
dual magnetic heads are then bonded to suspension elements
for eventual insertion into a disk file system.
The advantages of the electrical lapping guide system
according to the present invention are many. The electrical
lapping guide can be constructed at the same time that
routine fabrication processes for the thin film magnetic
head are performed. The standard construction processes
such as the photolithographic process, sputtering deposition
and electroplating can be used. The electrical lapping
guide systems can be formed with the same masks used in the
construction of the thin film head thereby insuring accurate
relationship between the transducer elements and the elec-
trical lapping guides. Using the preferred elements in theelectrical lapping guide of the present invention, the
electrical lapping guide can be constructed after the
deposition of the magnetic gap layer. This can be performed
by depositing a very tilin chromium layer of approximately
1000 angstroms, etching the chromium layer to obtain a
pattern such as shown for the straps 32 and 34 and the thin
SA9-84-025X 22
- ~Z434~8
film resistors 58-64 of Fi~. 2. Then the insulating layers
50-56 as shown in Fig. 2 together with the photoresist
insulation layer that is deposited on the first pole piece
to electrically insulate the first pole piece to the conduc-
tor layers of the magnetic transducers can be spun onto thewafer, patterned by the photolithographic process and hard
baked for permanency. The insulating layers 50-56 of the
electrical lapping guides form the junction switches 42-48
for accurate position detection. The conductors 36-40 of
the electrical lapping guides of Fig. 2 are deposited by
electroplating at the same time that the second pole layer
of the transducer is deposited. The second pole piece is
generally made of nickel-iron and serves as the low resis-
tors R36-R38 of the conductors 36-40. The conductors 36-40
interconnect the high resistance strap resistors R32 and 34
and the thin film resistors R58-R64 and the wires connecting
the electrical lapping guide to the multiplexer 26. Again,
reference is made to U.S. Patent 4,190,872 for the identifi-
cation of the different layers used in building a thin film
transducer. Likewise, that patent teaches the importance of
a particular throat height and the method of measurement of
that throat height length.
In practice and referring to FigO 2, it has been demon-
strated that the switching planes for junction switches
42-48 are appropriately located at throat height positions
of 20 microns, 2-1/2 microns, 2 microns and 10 microns,
respectively. The straps 32 and 34 are appropriately thin
film resistance elements R32 and R34, preferably of a
chromium material having a nominal conductivity or sheet
resistance RS. Typically, a rectangular bar of chromium
having a dimension of 500 x 80 micrometers (microns) will
SA9-84-025X 23
3~Z8
suffice for each o~ the straps 32 and 3~. Each of the thin
film resistors 58-64 also preferably of a chromium material,
have line dimensions of ~00 x 10 microns. The thin film
resistors are, of course, deposited on the substrate at the
same time and therefore have the same thickness as the
straps 32 and 34.
During lapping of the substrate row l0, the resistance R32
and R34 of each strap 32 and 34 will follow the equation
RX = RS x X+H + RC (1)
where RX is the actual resistance reading at an un~nown
lapping plane position X; RS is the sheet resistance of the
straps; RC is the contact and lead resistance of appropri-
ately connected conductors 36-40; L is the length of the
strap subject to lapping; H is the strap/junction dimen-
sion. The strap/junction dimension is the distance from theedge of the strap parallel to the edge being lapped, and a
particular junction switching plane; X is the distance from
the lapping surface and a respective junction switch. This
distance (X+H) represents the width of the strap. Once the
final throat height has been achieved, X will be perfectly
aligned with the zero throat height condition. In practice,
the strap to iunction dimension may preferably be l0
microns. By including a strap to junction dimension of this
size, the effects of so-called rat bite on the rear edge of
the strap, incurred during fabrication of the straps,
tending to make the strap resistance non-linear, are
avoided. During lapping, the reduction of the strap width
X+H will result in an increase in resistance measurement RX.
SA9-84-025X 24
~;~43 ~2~
The process carried out by the system of Fig. 1 will now be
explained with respect to the tneasurements of -the equivalent
electrical circuit of Fig. 5.
During a first lapping stage which is preferably a rough
lap, wherein the dimension X is reduced from 70 microns to
20 microns, the measured resistance R32 and R34 of each of
the straps 32 and 34 and the sum of the measured resistances
R32 plus R34, can be shown to be the following:
R32~70 = RS+H L ~ RC1 + RC2 (2)
R34,70 = Rx+H + RC3 + RC2 ~3)
R32+R34,70 = 2 X~H + RC3 + RCl (4)
R32;X = Rx+1OL (5)
The nominal width (W) and length (I,) of the straps are known
to be 80 microns and 500 microns, and H is lO microns.
The first of these three equations contains four (4)
unknowns. By assigning a nominal value to RC3, the second,
third and fourth equations may be solved and a rough value
of the resistivity RS and contact resistances RCl and RC2
are obtained. The position of the lapping plane can then be
determined as X by solving the equation 5 from these assumed
and determined values.
When the first of the junction switches 42 changes state, at
the distance X = 20 microns, i.e., at line 66, the resis-
tance change is detected at the conductors 36 and 40 and
will show a step-wise change indicating that the thin film
SA9-84-025X 25
34;~8
resistor 58 is now in the serles measurement of the resis-
tance of the strap 32. At this known position of the
lapping plane, by adopting the previously dctermined values
of RC1, RC2 and RC3 from the rough lapping stage, valu~s of
H, RS and ~ can be obtained from the following equations:
R32,20 = RS 25 + 80~0 + RCl + RC2 (6)
R34,20 = RS 25l f 80*0 + RC2 +.RC3 (7)
R32+R34,20 = RS 12 -~ 1600 + RC1 + RC3 (8)
where W** is the width of the straps
As the lapping continues, the position of the lapping plane
may be now determined from the following equation, using
these additionally determined levels of H, RS and W, which
represent calibrated parameters obtained by noting the
change in state of the junction switch 42.
R32X = RS ~ + ~ + RCl + RC2 (9)
The opening of the junction switch 48 provides a step-wise
change in the resistance measurement of strap 34. The
opening of the junction switch 48 thus places the thin film
resistor 64 in the series resistance measurement of strap
34.
Vtilizing the previously determined values of H, RS, W, RCl
and RC2, three additional equations as below can be deter-
mined.
SA9-84-025X 26
~Z4~
R32,10 = RS 15 -~ ~* + ~Cl ~ RC2 (10)
R34,10 = RS 1500 + 80*0 .~ ~C2 + RC3 (11)
R32+34,10 = RS 11 + lG00 + RC3 -~ RCl (12)
where W** is the width of the thin film resistors 58-64
Now, during this fine lapping state of rom X=10 microns to
the nominal throat height, established to be approximately 2
microns in this embodiment, it is possible to solve the six
equations ~6), (7), (8), (10), (11) and ~12) resultlng at
the X=10 micron switching point, and X=20 microns switching
point, to determine all the values of the unknowns RCl, RC2,
RC3, W, RS and H. Thus, the resistance R32 and R34 are
fully calibrated during the fine lap stage, and fine lapping
may be achieved by monitoring this resistance level defined
by equation (1) at the controller 30 to determine when the
nominal throat height of 2 microns is achieved.
The remaining junction switches 44 and 46, previously
identified as located at 2 and 2-1/2 microns, can be used to
terminate lapping of the substrate row. The opening of the
junction switches 44 and 46 will produce two additional
step-wise changes in resistance measurements for straps 32
and 34. At this time, controller 30 controls actuators 20
and 22 to terminate lapping. The holder 18 is retracted
moving the substrate row 10 from the lapping plate 2~, to
permit the fine surface polish to commence.
The foregoing embodiment has been described with respect to
the operation of one of the electrical lapping guide systems
16. The remaining lapping guide system 14, shown in Fig. 1,
is similarly constructed and the resistance measurements
SA9-84-025X 27
~Z~3~
made to permit an accuratc de~ermination of the position of
the lapping plane with respect to tlle desired throat heiyht
are the same. Thus, it is possi~le to compare in controller
30 the lapping plane position on each side of the substrate
row 10, permitting leveling thereof. ~s is known by those
skilled in the ar-t, the substrate row 10 may undergo a bow
effect from the stress applied by the lapping plate 24 and
the actuators 20 and 22. This bow effect may move the plane
of pole tips for the transducers 12 in the center closer or
further from those at the outer edge of the substrate row.
As such, the bow effect is taken into effect by establishing
a nominal throat height of 2 microns in accordance with the
preferred embodiment. Thus, although the pole tips of the
outer transducers will lie 2 microns a~ay from a desired
plane as determined by the electrical lapping guides, the
centrally located transducer element will have a pole tip
plane greater than zero.
The principles of the present invention have now been made
clear in an illustrative embodiment. There will be immedi-
ately obvious to those skilled in the art many modifications
of structure, arrangement, proportions, the elements,
materials and components used in the practice of the inven-
tion. For instance, the strap material of the present
invention is preferably chromium but it should be evident
that any electrically conductive material may be used.
Also, only one-half of the electrical lapping guide system
described herein could form the total electrical lapping
guide system. As explained prcviously, each half could form
a redundant systcm if neccssary. One-half of the system
from the center tab conductor to onc of the side conductors
SA9-84-025X 28
1;243~Z~3
is sufficient for controlling the lapping process to accom-
plish the advantages and objects of the present invention.
Various deposition techniques well kno~n in the process for
construction of thin film heads can be used in the deposi-
tion of the electrical lappinq guides. For instance, anytype of vacuum deposition could be used for all of the
layers of the electrical lapping guic~e and electroplating is
not absolutely necessary ~or the construction of the elec-
trical lapping guide according to thc present invention.
The appendant claims are, therefore, intended to cover and
embrace any such modification, within the limits only of the
true spirit and scope of the invention.
SA9-84-025X 29
