CA1249075A - Method and apparatus for controlling the throat height of batch fabricated thin film magnetic transducers - Google Patents
Method and apparatus for controlling the throat height of batch fabricated thin film magnetic transducersInfo
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- CA1249075A CA1249075A CA000528223A CA528223A CA1249075A CA 1249075 A CA1249075 A CA 1249075A CA 000528223 A CA000528223 A CA 000528223A CA 528223 A CA528223 A CA 528223A CA 1249075 A CA1249075 A CA 1249075A
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- lapping
- switching
- resistance
- substrate
- resistor
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Abstract
Abstract of the Disclosure A method for determining the position of a lapped edge of a substrate during lapping of a row of thin film magnetic transducer elements. First and second electrical lapping guide structures are formed on each side of the row of transducer elements. The lapping guide structures include a series of switching junctions, each switching junction paralleled by a resistor. A lapping resistor which provides a change in resistance proportional to the lapping of the row is measured and compared with the position of the lapping plane as determined from each switching junction change of state. Calibration of the resistor versus lapping plane position is effected to permit an accurate determination of the lapped surface from subsequent resistance measurements of the lapping resistor.
Description
METHOD AND APPARATUS FOR CONTROLLING THE THROAT HEIGHT
OF BATCH FABRICATED THIN FILM MAGNETIC TRANSDUCERS
The present invention relates to method~ and apparatus of manufacturing thin film magnetic transducers.
Specifically, a method and apparatus for determining the position of a lapped edge of a substrate during lapping of the transducer pole ~ips to a final throat height is provided.
Thin film transducers for reading maynetic disc struc-tures are batch fabricated through thin film deposition techniques. Typically, transducers are formed in rows and columns on a substrate. The substrate is then cut into a plurality of rows of transducers in a side-by-side relationship with the pole tips of the transducers extending to an edge of the substrate row. In order to achieve a maximum transducing efficiency, the pole tip length must be lapped to a final dimension known as throat height. The final throa~ height for a given thin film transducer must be established within a minimum tolerance in order to provide for transducing e~ficien-cies capable of handling s~ate of the art data recording densities.
Lapping of the pole tip ends which define an air bearing surface is measured by an elec~rical lapping guide (ELG) structure. A lapping ~uide is located on each end of a substrate row at each end of the row o transducers. The E1G is ad]acent to the surface to be lapped and provides electrical signals identifying the position o the lapped surface. The ELG structure will be used to signal the lapping machinery when the lapped surface has progressed to a final throat height position~
Current requirements for throat height control require that flatness of the lapped substrate surface be main-tained. In order to achieve the required flatness and lower the amount of recession of the pole pieces o~ the transducers as a result o the lapping process, the inal .... .. . ..
lapping to the final throat hei~ht is accomplished during a final wash cycleO The wash cycle is fixed to lap for a calculated wash cycle time which produces a very fine ~lapping of the pole tips. The final lapped dis~ance o~
the priQ~ art represents an estimate based on a predeter-mined ~ping time versus lapped distance relationship as curren~ ELG structures do not have sufficient resolution ` to measure the final distance lapped during the fine lap procédure. The present invention provides an ELG struc-ture capable of monitoring lapping during a final finelap cycle as well as during the rouyh lapping stages to achieve final throat height.
Summary of the Invention It is an object of this invention to provide for an accurate monitoring of the position of a lapped edge.
It is ano-ther object of this invention to provide for an accurate monitoring of the throat height of batch fabri-cated thin film magnetic transducers.
It is a more specific object of the invention to measure the position of opposite ends of a lapped edge defining the throat height of batch fabricated thin film magnetic transducers.
These and other objects are derived rom a method and apparatus in accordance with the invention. An electrical lapping guide structure is formed on preferably two (2) opposite ends of a substrate bearing a row of thin film magnetic transducers. The substrate is lapped to a final throat height dimension along one edge.
The position of the lapped edge is monitored at opposite ends with the electrical lapping guide structures.
The electrical lapping guide is formed ~i~h at least one switching junction which changes state during lapping of the substrate~ The switching junction includes a par-allel resistance element. The switching junction has a distinct switching plane which is ~ known distance from the desired ~inal throat height dimension. When the lapped edge coincidcs with ~he switching plane, a distinct stepwise change in resistance is detected across the switching plane.
In a preferred embodiment of the invention, each lapping guide in~ludes a plurality of switching junctions and ,, , , ~
shunt ~èslstance elements formed as a sexies circuit.
Eac~ swi~ching junction of a series is located to have a ! switchi`ng plane a known distance from the final throat height dimension, and different from the remaining switching junctions. The s ries circuit experiences a stepwise change in resistance as the lapping progressesu The lapped substrate edge posi~ion at each of ~he switch-ing planes is therefore detectable at discrete swi~ching planes.
The method of the preferred embodiment further includes depositing a resistance element on the substrate for each lapping guide. The resistance element has a configura-tion which provides a resistance change as lapping progresses. The resistance element resistance change versus lapped distance is determined by comparing each lapping edge position detected by each switching junction state change with the measured resistance element resist-ance. Thus, as the lapping edge approaches the final throat height position, the resistance element character-istic resistance change versus lapping distance charact-2s eristic is accurately known.
-- Each electrical lapping guide provides for position measurements of each end of a lapped edgeO Thus, the level of the lapped edge may be determined and corrective forces applied to the substrate to maintain the lapped edge level with respect to the final throat height dimension of the transducer row.
Description of the Fiqures Figure 1 is a block diagram of apparatus for lapping a substrate edge to a final dimension.
Figure 2 is a plan view of an electrical lapping guide ~or carryin~ out an embodiment of the invention.
Figure 3 is an isometric view of the electrical lapping . guide of Figure 2~
Figure 4 is an electrical schematic demonstrating the operation of the ELG structure of Figures 2 and 3.
, ~ , Figure.-:-5 is a plan view of an electrical lapping guide for carrying out a preferred embodiment of the invention.
Figure 6 is an electrical schematic demonstrating the operation of the ELG structure of Figure 5.
Descr~e~ on of the Preferred Embodiment Referring now to Figure 1, there .is shown an overall block diagram of apparatus for lapping a surface 23 of a substrate row 11 to establish precision throat heights for a plurality of thin film magnetic transducers 30.
The apparatus of Figure 1 includes a lapping fixture 12 for holding the substrate 11 in position over a lapplng plate 20. Lapping plate 20 is an abrasive surface for accurately lapping surface 23 to a final dimension.
The force applied to lapping fixture 12 is derived from first and second pressure actuators 15 and 16. Varying the force applied by the actuators 15 and 16 against substrate 11 controls leveling of the lapped surface 23.
Measurements of the deviations from a level surface are provided by electrical lapping guides 21 and 22. Elec-trical lapping guides 21 and 22 provide signals indica-tive of the distance lapped, identifying the position of the plane of the lapped surface 23 with respect to a desired final transducer dimension. These electrical measurements are applied to a multiplexer 26. Digital ohmeter 25 measures the resistance of each electrical lapping guide 21 and 22 through the multiplexer 26. The resulting resistance measurements determine the position of the lapped suxface 23 with respect to the right and left ends of substrate ll by directing the output of the digital ohmmeter 25 to a controller 27~ The controller 27 in turn activates thc actuators 15 and lG to level the substrate ro~J 11 relative to the lapping plate 2G thereby insuring that the throa~ heights of all of the trans-ducers 30 are at the same lengthv Referring now to Figure 2, there is shown more partic-`ularly ~ plan view of the electrical lapping guide structur`é 21 with respect ~o the lapped surface 23, and the final dimension, identified as the final throat height whera lapping is to cease. It is, of course, understood that t~e left hand electrical lapping guide 22 is the mirror image of the right hand electrical lapping guide 21 and will not therefore be further described.
Adjacent to the thin film transducer 30 is the electrical lapping guide structure 21 which includes an electrical lapping guide resistor 31. As surface 23 is lapped by the lapping plate 20, the resistance value measured between terminals 21a and 21b will vary according to the following relationship:
P ,~
R = t x w (1) where R = resistance of lapping guide resistor 31 p - resi.stivity of the material comprislng resistor 31 Q = the resistor 31 length -- w = the resistor 31 width t = the thickness o~ resistor 31.
Lapping of surface 23 will reduce the width w of resistor 31, increasing the resistance R of resistor 31. Measur-ing this resistance makes it possible to monitor the positional change of lapping surface 23 as it approaches the ~inal throat height.
The electrical lapping guides 21 and 22 axe deposited by thin film deposition techniques during the manufacture of each of the thin film transducers 30. It is assumed that the length R, resistivity and thickness t of the resistor 31 have been controlled during manufactuxe.
Thickness is controlled during the deposition o~ the transducer elernents on the substrate 11. The resistivity is determined by the metallic layer used as the resistor - 31. Chromium is preferred, but any other metal such as nickel-iron of the pole pieces could be used. The length and widt~ of the resistor 31 is determined in the mask used t~--form the resistor 31. The length of the resistor is preferably approximately 500 micrometers. The resis-tivity, thickness and beginning width for the electrical lapping guide resistor are typically of the following dimensions and values:
p = .55 micrometers t - .25 micrometers Q = 500.
For convenience, t x Q of equation (1) may be repre-sented as k, and for the preferred embodiment is equal to 1100.
Adjacent to the electrical lapping guide resistor 31 and part of the electrical lapping guide structure 21 are a plurality of switches 32 through 35. Although four (4) are shown in Figure 2, in the preferred embodiment of the invention, a total of six t6) switches are incorporated on the substrate adjacent an end of each row of thin film transducers 30.
Each of the switches 32 through 35 have a switching junction 32a through 35a, located at a specific distance from the final throat height. The switches are deposited on substrate ll during the deposition of the transducers 30 onto the substrate 11. By depositing switching elements 32 through 35 during the deposition of the thin film transducer 30, the planes at which the switching junctions change state are accurately located with respect to final throat height. Connected in parallel with each switching junction is a single shunt resistance 38 through 41. The shunt resistance 38-41 can be formed at the same time and of the same material as the resistor 31. The switching junctions are serially connected, forming a series circuit between terminals 21a and 21c.
Another embodiment of the electrical lapping guides 21 and 22 is shown in Figure 5, and the principle of operation of this apparatus is the same as that for the embodiment shown in Figure 2. In this embodiment the switches-32 through 35 are deposited in a series electr~-c~l circuit between terminals 21a' and 21c'close to the~`-l~ast thin film magnetic transducer 30 in the row.
The electrical lapping guide resistor 31 is deposited toward the end of the row in an electrical circuit between terminals 21c' and 21b'. Since t:his embodiment is less sensitive to variations in the manufacturing process, the embodiment shown in Figure 5 is the preferred embodiment.
When the lapped surface 23 is coincident with the switch-ing plane 32a of switching junction 32, the switching junction will change state. Preferably, switching junction 32 will change from a conducting to a norl-conducting state, presenting a distinct binary change in resistance rather than a gradual change in resistance as lapping occurs. Thus, the current path between terminals 21a and 21c will necessarily be through shunt resistance 38. At this time, when the digital ohmeter 25, connected to controller 27 of Figure l, measures a step increase in resistance between terminals 21a and 21c, the position of the lapping surface 23 is accurately known with respect to the final throat height. As each switching plane 32a through 35a is accurately known with respect to final throat height, each discontinuity in resistance measure-ments appearing between terminals 21a and 21c provide ~or an accurate check of the lapping surface 23 at various positions with respect to final throat height. Each shunt resistance is located a distance from the final lapping edge to avoid being lapped or severed during lapping.
The measurement of a change in state of each switching junction 32 through 35, as seen by the total resistance appearing between terminals 21a and 21c, may be used to calibrate the electrical lapping guide resistor 31. As - such, the electrical lapping guide resistor 31, when approachin~ the final throat helght, will be accurately calibrated, permitting the lapped surface 23 to be positioned within a nominal throat height of approxi-mately 1 to 2 microns to the desired final throat height.
The chan~e in electrical resistance appearing between tèrmi~als: 21a and 21c can readily be .recognized wi.th referenc~e to Figure 4. Figure 4 electrically represents the pos;ition of each switching junctions 32 through 35 with réspect to the final throat height~ It is clear that as the-lapping surface 23 is lapped away, switches 32 through 35 will, in se~uence, be rendered in an open circuit ccndition. Each open circuit condition which results from lapped surface 23 proyressing toward final throat height, is seen as the addition of resistances 38 through 41 in the series circuit represent~d between terminals 21a and 21c. Of course, during the switching of junctions 32 through 3S, the analog resistance measured between terminals Zla and 21b will be changing in accordance with the above equation.
The change in electrical resistance appearing between terminals 21a', 21b' and 21c' of Figure 5 can be determined by reference to Figure 6. This change in resistance is the same as that described above with reference to Figures 2 and 4 for the corresponding elements.
With the foregoing calculation, it is possible to deter-mine with two ELG structures on opposite sides of the lapped surface, the required force differential to maintain the lapped surface level with respect to the final throat height ~or the transducer array. Addition-ally, an end resistance may be determined for each electrical lapping guide resistor 31 identifying a desired throat height. Lapping may then be terminated on this desired throat height. Thus, the prior art tech-nique of fine lapping during a wash cycle by setting a pre-fixed wash cycle time may ~e avoided as the resistor 31 is sufficiently accurate at this stage in the lapping process and its width close to the end of the lapping process to determine a fi.ne lapping point. Alterna-tively, lappin~ may be terminated when the last of the switches, switch 35, changes state.
A perspective view of the electrical lapping guide structure shown in Figure 2 appears in Figure 3. Figure - 3 demonstrates the relationship between each of the switching junctions 32 through 35, and the final throat height,`~. An insulative magnetic gap layer 30c is deposi~e~ between pole pieces 30a and 30b of transducer 30. A~other layer, not shown, such as a conductive coil layer and other insulation layers 30d are deposited on thé substrate 11 betwPen ~he pole pieces 30a and 30b and form a part of the transducer 30. The insulation layer 30d between the pole pieces 30a and 30b determine the throat height of the transducers. During ~he deposition of the pole pieces 30a and 30b, each half of switching junctions 32-35, including conductor 35c and 35b, for example, are deposited on substrate 11. An insulation layer separates the conductors of the switching junction except at switch contact points 32d-35d. Thus, by depositing the conductor elements and insulation layer of switching junctions 32 through 35, corresponding struc-tural elements of transducer 30, i.e., the pole pieces 30a and 30b and the insulation layer 30d, are deposited on substrate 11. The registry of the corresponding switching planes is defined by the leading edge or the insulation layers that separates the conductors of a switchîng element. Thus the registry of the switching junctions 32-35 with respect to the final th~oat height is maintained. The electrical lapping guide resistor 31 is also deposited on the substrate 11 at the same time , , transducer elements 30 are formed. Thus, during manufac-ture of the transducer array, registry is maintained between the electrical lapping guide components including the contact joints of the switching junctions 32 through 35, and electrical lapping guide resistor 31. The ~resistors 38 through 41 are deposited as a thin film of chromium with a resistance of 100 Ohms. The 100 Ohm chromium resistor appears across the switching junction having a closed circuit resistance of appruximately 1 Ohm. Insulation material is deposited between the conductor elements 35c and 35b to define the switch contact joint 35d. The insulation layer for each of the - switches 3S throuyh 32 is deposited at the same time the insulation layer 30d that determines the throat height TH
is deposited or transducer element 30, thus maintaining ~L~ ~7~;g accurate control over the switching junctions with respect to final throat height. The geometry of the conductor elements of each switching junction arz also maintained congruent with the pole piece 30a, 30b geom-etxy sin~e these elements are all deposited during thesame p~ocess. The commonly formed insulation layer and conduc~o`r geometries improve the overall precision location of switching planes with respect to the flnal throat height.
The electrical lapping guide structure shown in Figure 5 is also fabricated in a manner similar to ~hat de cribed above and shown in Figure 3. As described a~ove, the em~odiment of the ELG shown in Figure 5 is less sensitive to variations in the manufacturing process. It has been found that variations in the thickness of the insulation layers and variations in the thickness of the conductor elements of each switching junction can cause variations from the desired value in the final throat height of the transducer elements 30. It has also been found that variations in thic~ness of the insulation layers and in the conductor elements are more likely to occur near the edge of the substrate 11 than near the center of the substrate 11. The embodiment of Figure 5 places the last of the switching junctions, switch 35 near the last transducer 30 in the row. This is the switching junction which is the final switching control on throat height, and the closer proximity reduces the chance of a substantial difference in thickness of either the insulation layer or the conductor elements between the position of the last transducer 30 and the position of the last switching junction 35. The electrical lapping guide resistor 31 is near the edge of the substrate where it has been found that thickness variations are more likely to occur, but this produces less chance for a signi~icant impact on final throat height accuracy since the resistor 31 is calibrated at relative positions during the lapping operation.
The electrical lapping guide resistor 31 is deposited between two conductors which form terminals 21a and 21b in the Figure 2 embodiment or between two conductors SA98~02~X 10 which form terminals 21bl and 21c' in the Figure 5 embodiment. The electrical lapping guide resistor 31 is also preferably of chromium and is deposited at the same time as resistors 38 through 41 are dPposited on substrate 11.
: ,, By mea~u~ing the relative position oE lapped surface 23 with respect to the right and left ends of substrate 11, it is possible to maintain lapped surfac:e 23 level with respect to final throat height for the entire array of transducers 30 on substrate 11. The controller 27 can be a computer programmed with an algorithm which will determine a force differential for transducers lS and 16 which will correct leveling errors. The force differ-ential is determined as:
R31L ~ Aw ) / K
where R31L is the resistance of the left electrical lapping guide resistor 31 R31R is the resistance of the right electrical lapping guide resistor 31 ~w is the difference in OFFSET distance of each lapping gulde resistor 31.
The offset distance is shown in Figures 2 and 3 as the distance from the rearward edge of resistor 31 to the throat height dimension.
-Continually determining the force differential necessaryto level the lapping surface 23 and applying the differ-ential orce with the actuators 15-16 will achieve a substantially level condition.
The calculated inal throat height resistance of elec-trical lapping guide resistor 31 may be represented by the following:
R3 ~
OFFSET ~ TH
SA939024X ll .. .. .
where the OFFSET distance of each lapping resistor is determined by OFFSET = R31 ~ Ddn, Ddn being the switch~
ing position of a given switching junction~
The computer 27 is programmed to measure the resistance s of eac~ ~eveling resistor of each lapping guide, both left a~d right, and the serial arrangement of six (6) i switching junctions. The parameters of the resistors and switching junctions which are utilized to determine the level condition of lapping surface 23 include the OFFSET
of each leveling resistor, as shown in Figure 3. The OFFSET represents the distance from the desired throat height to the rearward resistor edge, parallel with the lapping surface 23. The distance from the throat to a given detector switching plane, generically described as Ddn, and desired throat height, TH, are utilized to determine the following calculations.
The OFFSET is calculated for each of the leveling resis-tors by utilizing the following formula:
OFFsET = R 1 - Ddn The difference in OFFSETs between the right and left leveling resistors is expressed as:
~w = OFFSETR le~t ~ OFFSETR right ., With the difference in OFFSETs, it is possible to deter-mine a force differential between the actuators 15 and 16, such as to correct for an unlevel lapping surface.
This differential, Fd, previously described is:
Fd = ( K - Aw ) - K
By calculating the force differential in accordance with the above formulation, the computer 27 will set a force differential for the actuators lS and 16, according to the following determination:
. . .
Fd < 0 Left force < Right force Fd = 0 Left force = Right force Fd > 0 Left force ~ Right force This ~orce determination is a subroutine in programming steps ~o~be described, such that computer 27 will provide the ap~ropriate force differentlal to the substrate 11 to correc~ any leveling errors.
As a final basic calculation for the system, a final throat height resistance is determined from the elec-trical lapping guide resistor 31 for each side of the - transducer substrate row according to the previously described relationship:
~C
R31~side) OFFSET (side) TH
In view of the foregoing basic calculations, which provide ~or leveling information, as well as for a final throat height determination, the following programming steps have been incorporated in the computer 27. These programming steps, described in pseudo-code, are useful for electrical lapping guide structures having the six (6~ switching junctions described in the foregoing. Of course, six (6) is not necessary to implement the inven-tion, but is, however, considered preferable. The pseudo-code described is a series of do loops, each beginning from 1 to n where n = number of switching junctions employed in the electrical lapping guide structure~
.
Prior to beginning the lapping process, a number of values are inserted in the computer 27. The irst being the value of the constant K, previously described with respect to equation 1. The distance from the final throat height to each s~itching plane Ddl to Dd6, is inserted in the computer program. The program to be described will, at the user's option, end lapping on a calculated throat height, as inserted in the com~uter program, or on the last change of state of the switching junction closest to the ~inal throat height. In the event that a calculated throat height is to be used as the endpoint for ceasing lapping operations, this calcu-lated throa~ height (TH) is loaded into the computer program~ A wash cycle distance Wc is also inserted in the prog~am. At the end of -the coarse lapping, as is lcnown to those skilled in the art, a wash cycle which affects~-a finer lapping to the lapped surface 23 permits lapping`for a specified distance of Wc.
i An additional subrou~ine will be employed in the program-ming to read the left and right resistance values pro-vided by each electrical lapping guide resistor 31. This subroutine additionally subtracts a leacl resistance before making the measured values available for program execution. A lead resistance constant would normally be included in the subroutine, however, this may also be inputted by the operator with the other parameter values.
The program is configured in three l3) separate ~ortions which will be described in pseudo-code programming format as DO LOOPS.
The first portion comprises a section of the program which will, during lapping to the first of the switching junction, execute the following steps.
Do until first switching junctions activate and level resistor values stored Call read Left & Right R31 values Calc force differential Read level R31 values right and left Fd=R31Left R31Right Equation (1) Call set mechanics If both left and right detectors activate Then Store both level R values in R1ll and Rrn respectively SA9~40~X 14 s I one detector activates Store level R valu~ in Rside Rside - 1.0 (detected side) ~; Rside - 0.0 (undetected side) ~ , Calc force differential `~ Call set mechanics ~
- Do until other detector activates If other detector activates Then Call read Left and Right R values Store other level R value in Rsi.de The result o~ the first portion of the code is to calcu-late a force differential and apply the force differen-tial through the actuators 15 and 16 to the substrate 11.
This force differential is calcu1ated before the first switching junction, referred to as a detector in the pseudo-code, o each side of the substrate changes state by subtracting the resistance levels measured at each si~e of the substrate of each electrical lapping guide resistor 31 and 32. The SET MECHANICS subroutine called to establish this force differential on the actuators 15 and 16.
If correspo~ding switching junctlons on each electrical lapping guide structure change state simultaneously, then the value of each electrical lapping guide resistor, left and right t are stored.
:
: In the event that on.ty one switching junction on one of the electrical lapping guide structures changes state, indicating a non-level condition, the two ELG resistors 31 of each side of the substrate are measured and set to 1 and 0, respectively. The ~orce differential is calcu-lated and the SET MECE~ANICS apply the calculated force ~or the actuators 15 and ~6.
When the seco~d of the switching junctions of th~ oppo-site electrical lappin~ guide structure is found to change s~ate, the le~t and right R31 resistor values are read and stored.
Thus, after a pair of switches on opposite sides of the substrate ln different ELG structures changes state, the S first ~o~tion of the programming is completedO
, ;.
The second portion of the programming below consists of performing a series of calculations when lapping prog-resses from the first pair of switching junctions which have been activated to the third pair to change state.
Do N from 1 to 3 Calc offsets right and left wside = Rsiden Ddn Equation (2) Store offsets in Wsiden Calc ~ offset W W1n Wrn Equation (3) Store offset in ~Wn Do until next detector activates Call read Left & Right R values Calc new force differential Fd = ( - W J ~ K . Equation (4) Call set mechanics End do until next detectors activate If both detectors activate Then ; Store both level R values in Rside ~, .
~ , ., !` ~ Else ~`: If one detector activates Then Store level resistor values in Rside Rside=l.0 (detected side~
Rside~0.0 (undetected side) .. 10 Calc force differential Equation (l) Fd = R3lL ~ R3lR
Do until other side detected Call set mechanics End do until other side detected Read and store other level resistor in Rside End do N from l to 3 Calc & store next offset in Wside E~uation t2) Calc ~ store next ~W in ~Wside Equation (3) The OFFSETs, Wside, for ~he right and let ELG structures Z0 are calcula~ed and stored in a matrix. The differential : offset w is also stored as lapping progresses between the first pair of switching junctions to change state and : the~third pair to change state~ -~ : : As ~apping proceeds from the first pair of switching : 25 junctions:to change state a force differential is calcu-lated based upon equation 4. This force differential is applied through the set mechanics to the actuators 15 and 16 until the:subsequent pair of switching junctions, one in each ELG structure, change state.
In the event that only one switching junction on one side of the substrate ll chan~cs state, a force diferential is calculated as was accomplished earlier until the remaining switching junction of the oth~r electrical lapping guide structure changes state. When both switch-ing junctions have changed state, the two resistors R
are measured and their resistance values stored.
~ he above routine is repeated until the third pair of the switchi~g~junctions changes state.
.
The OFFSETs, Wside, and difference in offsets, Qw, are calculated at the completion of the above steps and stored.
The following steps executed by the computer program of computer 27 occur during ~he lapping of substrate 11 between switching junctions 3 to 6.
Do N from 3 to 6 Find the largest absolute value of QWl to ~Wn and store its real value W1 Check error correction value n ~ Equation (5) w - - - ~wk - Wl~
k=1 n ~ 1 Do until next detector pairs activate Call read level R values Calc force differential Fd= ( K _ W~ - K
CaIl set mechanics SA98402~X 18 If end on calculated throat height Then Find largest offset values for left and rlght and store off , ~ Average offsets , ~
oFrsÉTs = L~ Wside ~ - OFF Equation (6) n-l . . .
Calc final throat resistance Reside = K Equation (7) FFside T
If REside ~ ~side Equation (8 Then Print data `~
Exit program If not in wash cycle : Then 15 If end on calculated throat height '' Then :
Calc wash cycle resistance 'Rw= K Equati~n (9) OFFS ide~Th ~wc :
: : If Rw-Rside < 0 ~ .
Thcn Fix wash cycle in on condition SA984024X l9 7~i Else Calc wash cycle resistance Rw = - K _ Equation (10) OFFside+Dd6 C
-- If Rw-Rside < 0 Then Fix wash cycle in on condition As lapping progresses from the third switching junction pair to change state, the stored differential of~sets Ww are examined and the largest differential o~fset is identified. An average of the offsets determined is computed according to equation ~5). When the next pair of switches on opposite sides of substrate 11 change state, each resistor 31 is measured and a force differen-tial calculated. The force differential is applied through the set mechanics to the actuators 15 and 16.
If the operator o~ computer 27 has entered a calculated throat height at which lapping is to cease, then the computer determines the largest of the previous o~fset values determined, and averages the offset measurements according to equation ~6). The final throat hei~ht resistance is calculated by equation (7~ and compared with the actual measured resistance of each ELG resistor -- 31 of each side of the substrate 11. When the calculated final throat height resis~ance is equal to the actual measured resistance of resistor 31, equation (8) will terminate lapping.
As was mentioned, typically in lapping substrates 11, a final lapping distance is obtained in a wash cycle. The wash cycle will typicall~ lap from approximately 5 - 30 microns within final throat height to a final throat - height measurement. The final throat height measurement indicated as the ideal throat height, may, of course, be set to any distance from this height. In the event a throat height is selectcd other than this final throat height, this nominal throat height is utilized in equa~
tion (9) with the wash cycle lapping distance, Wc, to calculate a final lapping resistance, RW for each ELG
~resistor 31. The wash cycle resistance i5 continuously compared with the measured ELG resistance 31 of each side o subs~rate 11. When the wash cycle resistance equals i . ;
the measured resistance, the wash cycle is efected for final lapping of the su~strate.
In the event that the lapping is not to end on a calcu-lated throat height, but rather is to end on the changing of state of one of the switching junction, the programm-ing steps will calculate a wash cycle resistance RW
according to equation (10). The wash cycle resistance is compared with each measured resistance of resistors 31, and the switching junction on which the lapping is to end is monitored.
The following sequences of steps are executed depending on whether one of the remaining detector pairs is acti-vated, or both.
If one detector activates Then Store level R value in Rside Calc ~ store next offset in W . Equation (2) slde If both offsets stored Then Calc and store next ~W in ~Wn Else If both detectors have activated SA98~1024 X 21 Then S~ore level R values in Rln an n ~ ~; Calc & store next offsets in S ~,Wln and Wrn Equation (2) ~, .. ; :
Calc & store next ~W in ~W Equation (3) End do until next End do from 3 to 6 Print data Exit program These calculations are repeated for each of the remaining detector pairs which are to change state during lapping.
The values of the OFFSETs and differential offsets, ~w, are continuously determined and the wash cycle resistance computed again from averaging the calculated offsets and calculated differential offsets.
Thus, there is described with respect to one program;a method for reducing the resistance information derived from the electrical lappinct guide structure of the - present invention. Those skilled in the art will recog-nize yet other ways of r~ducing these measurements to effectively control leveling and lapping of batch fabri-cated thin film magnetic transducers to a final throat height.
SA98~02~X 22
OF BATCH FABRICATED THIN FILM MAGNETIC TRANSDUCERS
The present invention relates to method~ and apparatus of manufacturing thin film magnetic transducers.
Specifically, a method and apparatus for determining the position of a lapped edge of a substrate during lapping of the transducer pole ~ips to a final throat height is provided.
Thin film transducers for reading maynetic disc struc-tures are batch fabricated through thin film deposition techniques. Typically, transducers are formed in rows and columns on a substrate. The substrate is then cut into a plurality of rows of transducers in a side-by-side relationship with the pole tips of the transducers extending to an edge of the substrate row. In order to achieve a maximum transducing efficiency, the pole tip length must be lapped to a final dimension known as throat height. The final throa~ height for a given thin film transducer must be established within a minimum tolerance in order to provide for transducing e~ficien-cies capable of handling s~ate of the art data recording densities.
Lapping of the pole tip ends which define an air bearing surface is measured by an elec~rical lapping guide (ELG) structure. A lapping ~uide is located on each end of a substrate row at each end of the row o transducers. The E1G is ad]acent to the surface to be lapped and provides electrical signals identifying the position o the lapped surface. The ELG structure will be used to signal the lapping machinery when the lapped surface has progressed to a final throat height position~
Current requirements for throat height control require that flatness of the lapped substrate surface be main-tained. In order to achieve the required flatness and lower the amount of recession of the pole pieces o~ the transducers as a result o the lapping process, the inal .... .. . ..
lapping to the final throat hei~ht is accomplished during a final wash cycleO The wash cycle is fixed to lap for a calculated wash cycle time which produces a very fine ~lapping of the pole tips. The final lapped dis~ance o~
the priQ~ art represents an estimate based on a predeter-mined ~ping time versus lapped distance relationship as curren~ ELG structures do not have sufficient resolution ` to measure the final distance lapped during the fine lap procédure. The present invention provides an ELG struc-ture capable of monitoring lapping during a final finelap cycle as well as during the rouyh lapping stages to achieve final throat height.
Summary of the Invention It is an object of this invention to provide for an accurate monitoring of the position of a lapped edge.
It is ano-ther object of this invention to provide for an accurate monitoring of the throat height of batch fabri-cated thin film magnetic transducers.
It is a more specific object of the invention to measure the position of opposite ends of a lapped edge defining the throat height of batch fabricated thin film magnetic transducers.
These and other objects are derived rom a method and apparatus in accordance with the invention. An electrical lapping guide structure is formed on preferably two (2) opposite ends of a substrate bearing a row of thin film magnetic transducers. The substrate is lapped to a final throat height dimension along one edge.
The position of the lapped edge is monitored at opposite ends with the electrical lapping guide structures.
The electrical lapping guide is formed ~i~h at least one switching junction which changes state during lapping of the substrate~ The switching junction includes a par-allel resistance element. The switching junction has a distinct switching plane which is ~ known distance from the desired ~inal throat height dimension. When the lapped edge coincidcs with ~he switching plane, a distinct stepwise change in resistance is detected across the switching plane.
In a preferred embodiment of the invention, each lapping guide in~ludes a plurality of switching junctions and ,, , , ~
shunt ~èslstance elements formed as a sexies circuit.
Eac~ swi~ching junction of a series is located to have a ! switchi`ng plane a known distance from the final throat height dimension, and different from the remaining switching junctions. The s ries circuit experiences a stepwise change in resistance as the lapping progressesu The lapped substrate edge posi~ion at each of ~he switch-ing planes is therefore detectable at discrete swi~ching planes.
The method of the preferred embodiment further includes depositing a resistance element on the substrate for each lapping guide. The resistance element has a configura-tion which provides a resistance change as lapping progresses. The resistance element resistance change versus lapped distance is determined by comparing each lapping edge position detected by each switching junction state change with the measured resistance element resist-ance. Thus, as the lapping edge approaches the final throat height position, the resistance element character-istic resistance change versus lapping distance charact-2s eristic is accurately known.
-- Each electrical lapping guide provides for position measurements of each end of a lapped edgeO Thus, the level of the lapped edge may be determined and corrective forces applied to the substrate to maintain the lapped edge level with respect to the final throat height dimension of the transducer row.
Description of the Fiqures Figure 1 is a block diagram of apparatus for lapping a substrate edge to a final dimension.
Figure 2 is a plan view of an electrical lapping guide ~or carryin~ out an embodiment of the invention.
Figure 3 is an isometric view of the electrical lapping . guide of Figure 2~
Figure 4 is an electrical schematic demonstrating the operation of the ELG structure of Figures 2 and 3.
, ~ , Figure.-:-5 is a plan view of an electrical lapping guide for carrying out a preferred embodiment of the invention.
Figure 6 is an electrical schematic demonstrating the operation of the ELG structure of Figure 5.
Descr~e~ on of the Preferred Embodiment Referring now to Figure 1, there .is shown an overall block diagram of apparatus for lapping a surface 23 of a substrate row 11 to establish precision throat heights for a plurality of thin film magnetic transducers 30.
The apparatus of Figure 1 includes a lapping fixture 12 for holding the substrate 11 in position over a lapplng plate 20. Lapping plate 20 is an abrasive surface for accurately lapping surface 23 to a final dimension.
The force applied to lapping fixture 12 is derived from first and second pressure actuators 15 and 16. Varying the force applied by the actuators 15 and 16 against substrate 11 controls leveling of the lapped surface 23.
Measurements of the deviations from a level surface are provided by electrical lapping guides 21 and 22. Elec-trical lapping guides 21 and 22 provide signals indica-tive of the distance lapped, identifying the position of the plane of the lapped surface 23 with respect to a desired final transducer dimension. These electrical measurements are applied to a multiplexer 26. Digital ohmeter 25 measures the resistance of each electrical lapping guide 21 and 22 through the multiplexer 26. The resulting resistance measurements determine the position of the lapped suxface 23 with respect to the right and left ends of substrate ll by directing the output of the digital ohmmeter 25 to a controller 27~ The controller 27 in turn activates thc actuators 15 and lG to level the substrate ro~J 11 relative to the lapping plate 2G thereby insuring that the throa~ heights of all of the trans-ducers 30 are at the same lengthv Referring now to Figure 2, there is shown more partic-`ularly ~ plan view of the electrical lapping guide structur`é 21 with respect ~o the lapped surface 23, and the final dimension, identified as the final throat height whera lapping is to cease. It is, of course, understood that t~e left hand electrical lapping guide 22 is the mirror image of the right hand electrical lapping guide 21 and will not therefore be further described.
Adjacent to the thin film transducer 30 is the electrical lapping guide structure 21 which includes an electrical lapping guide resistor 31. As surface 23 is lapped by the lapping plate 20, the resistance value measured between terminals 21a and 21b will vary according to the following relationship:
P ,~
R = t x w (1) where R = resistance of lapping guide resistor 31 p - resi.stivity of the material comprislng resistor 31 Q = the resistor 31 length -- w = the resistor 31 width t = the thickness o~ resistor 31.
Lapping of surface 23 will reduce the width w of resistor 31, increasing the resistance R of resistor 31. Measur-ing this resistance makes it possible to monitor the positional change of lapping surface 23 as it approaches the ~inal throat height.
The electrical lapping guides 21 and 22 axe deposited by thin film deposition techniques during the manufacture of each of the thin film transducers 30. It is assumed that the length R, resistivity and thickness t of the resistor 31 have been controlled during manufactuxe.
Thickness is controlled during the deposition o~ the transducer elernents on the substrate 11. The resistivity is determined by the metallic layer used as the resistor - 31. Chromium is preferred, but any other metal such as nickel-iron of the pole pieces could be used. The length and widt~ of the resistor 31 is determined in the mask used t~--form the resistor 31. The length of the resistor is preferably approximately 500 micrometers. The resis-tivity, thickness and beginning width for the electrical lapping guide resistor are typically of the following dimensions and values:
p = .55 micrometers t - .25 micrometers Q = 500.
For convenience, t x Q of equation (1) may be repre-sented as k, and for the preferred embodiment is equal to 1100.
Adjacent to the electrical lapping guide resistor 31 and part of the electrical lapping guide structure 21 are a plurality of switches 32 through 35. Although four (4) are shown in Figure 2, in the preferred embodiment of the invention, a total of six t6) switches are incorporated on the substrate adjacent an end of each row of thin film transducers 30.
Each of the switches 32 through 35 have a switching junction 32a through 35a, located at a specific distance from the final throat height. The switches are deposited on substrate ll during the deposition of the transducers 30 onto the substrate 11. By depositing switching elements 32 through 35 during the deposition of the thin film transducer 30, the planes at which the switching junctions change state are accurately located with respect to final throat height. Connected in parallel with each switching junction is a single shunt resistance 38 through 41. The shunt resistance 38-41 can be formed at the same time and of the same material as the resistor 31. The switching junctions are serially connected, forming a series circuit between terminals 21a and 21c.
Another embodiment of the electrical lapping guides 21 and 22 is shown in Figure 5, and the principle of operation of this apparatus is the same as that for the embodiment shown in Figure 2. In this embodiment the switches-32 through 35 are deposited in a series electr~-c~l circuit between terminals 21a' and 21c'close to the~`-l~ast thin film magnetic transducer 30 in the row.
The electrical lapping guide resistor 31 is deposited toward the end of the row in an electrical circuit between terminals 21c' and 21b'. Since t:his embodiment is less sensitive to variations in the manufacturing process, the embodiment shown in Figure 5 is the preferred embodiment.
When the lapped surface 23 is coincident with the switch-ing plane 32a of switching junction 32, the switching junction will change state. Preferably, switching junction 32 will change from a conducting to a norl-conducting state, presenting a distinct binary change in resistance rather than a gradual change in resistance as lapping occurs. Thus, the current path between terminals 21a and 21c will necessarily be through shunt resistance 38. At this time, when the digital ohmeter 25, connected to controller 27 of Figure l, measures a step increase in resistance between terminals 21a and 21c, the position of the lapping surface 23 is accurately known with respect to the final throat height. As each switching plane 32a through 35a is accurately known with respect to final throat height, each discontinuity in resistance measure-ments appearing between terminals 21a and 21c provide ~or an accurate check of the lapping surface 23 at various positions with respect to final throat height. Each shunt resistance is located a distance from the final lapping edge to avoid being lapped or severed during lapping.
The measurement of a change in state of each switching junction 32 through 35, as seen by the total resistance appearing between terminals 21a and 21c, may be used to calibrate the electrical lapping guide resistor 31. As - such, the electrical lapping guide resistor 31, when approachin~ the final throat helght, will be accurately calibrated, permitting the lapped surface 23 to be positioned within a nominal throat height of approxi-mately 1 to 2 microns to the desired final throat height.
The chan~e in electrical resistance appearing between tèrmi~als: 21a and 21c can readily be .recognized wi.th referenc~e to Figure 4. Figure 4 electrically represents the pos;ition of each switching junctions 32 through 35 with réspect to the final throat height~ It is clear that as the-lapping surface 23 is lapped away, switches 32 through 35 will, in se~uence, be rendered in an open circuit ccndition. Each open circuit condition which results from lapped surface 23 proyressing toward final throat height, is seen as the addition of resistances 38 through 41 in the series circuit represent~d between terminals 21a and 21c. Of course, during the switching of junctions 32 through 3S, the analog resistance measured between terminals Zla and 21b will be changing in accordance with the above equation.
The change in electrical resistance appearing between terminals 21a', 21b' and 21c' of Figure 5 can be determined by reference to Figure 6. This change in resistance is the same as that described above with reference to Figures 2 and 4 for the corresponding elements.
With the foregoing calculation, it is possible to deter-mine with two ELG structures on opposite sides of the lapped surface, the required force differential to maintain the lapped surface level with respect to the final throat height ~or the transducer array. Addition-ally, an end resistance may be determined for each electrical lapping guide resistor 31 identifying a desired throat height. Lapping may then be terminated on this desired throat height. Thus, the prior art tech-nique of fine lapping during a wash cycle by setting a pre-fixed wash cycle time may ~e avoided as the resistor 31 is sufficiently accurate at this stage in the lapping process and its width close to the end of the lapping process to determine a fi.ne lapping point. Alterna-tively, lappin~ may be terminated when the last of the switches, switch 35, changes state.
A perspective view of the electrical lapping guide structure shown in Figure 2 appears in Figure 3. Figure - 3 demonstrates the relationship between each of the switching junctions 32 through 35, and the final throat height,`~. An insulative magnetic gap layer 30c is deposi~e~ between pole pieces 30a and 30b of transducer 30. A~other layer, not shown, such as a conductive coil layer and other insulation layers 30d are deposited on thé substrate 11 betwPen ~he pole pieces 30a and 30b and form a part of the transducer 30. The insulation layer 30d between the pole pieces 30a and 30b determine the throat height of the transducers. During ~he deposition of the pole pieces 30a and 30b, each half of switching junctions 32-35, including conductor 35c and 35b, for example, are deposited on substrate 11. An insulation layer separates the conductors of the switching junction except at switch contact points 32d-35d. Thus, by depositing the conductor elements and insulation layer of switching junctions 32 through 35, corresponding struc-tural elements of transducer 30, i.e., the pole pieces 30a and 30b and the insulation layer 30d, are deposited on substrate 11. The registry of the corresponding switching planes is defined by the leading edge or the insulation layers that separates the conductors of a switchîng element. Thus the registry of the switching junctions 32-35 with respect to the final th~oat height is maintained. The electrical lapping guide resistor 31 is also deposited on the substrate 11 at the same time , , transducer elements 30 are formed. Thus, during manufac-ture of the transducer array, registry is maintained between the electrical lapping guide components including the contact joints of the switching junctions 32 through 35, and electrical lapping guide resistor 31. The ~resistors 38 through 41 are deposited as a thin film of chromium with a resistance of 100 Ohms. The 100 Ohm chromium resistor appears across the switching junction having a closed circuit resistance of appruximately 1 Ohm. Insulation material is deposited between the conductor elements 35c and 35b to define the switch contact joint 35d. The insulation layer for each of the - switches 3S throuyh 32 is deposited at the same time the insulation layer 30d that determines the throat height TH
is deposited or transducer element 30, thus maintaining ~L~ ~7~;g accurate control over the switching junctions with respect to final throat height. The geometry of the conductor elements of each switching junction arz also maintained congruent with the pole piece 30a, 30b geom-etxy sin~e these elements are all deposited during thesame p~ocess. The commonly formed insulation layer and conduc~o`r geometries improve the overall precision location of switching planes with respect to the flnal throat height.
The electrical lapping guide structure shown in Figure 5 is also fabricated in a manner similar to ~hat de cribed above and shown in Figure 3. As described a~ove, the em~odiment of the ELG shown in Figure 5 is less sensitive to variations in the manufacturing process. It has been found that variations in the thickness of the insulation layers and variations in the thickness of the conductor elements of each switching junction can cause variations from the desired value in the final throat height of the transducer elements 30. It has also been found that variations in thic~ness of the insulation layers and in the conductor elements are more likely to occur near the edge of the substrate 11 than near the center of the substrate 11. The embodiment of Figure 5 places the last of the switching junctions, switch 35 near the last transducer 30 in the row. This is the switching junction which is the final switching control on throat height, and the closer proximity reduces the chance of a substantial difference in thickness of either the insulation layer or the conductor elements between the position of the last transducer 30 and the position of the last switching junction 35. The electrical lapping guide resistor 31 is near the edge of the substrate where it has been found that thickness variations are more likely to occur, but this produces less chance for a signi~icant impact on final throat height accuracy since the resistor 31 is calibrated at relative positions during the lapping operation.
The electrical lapping guide resistor 31 is deposited between two conductors which form terminals 21a and 21b in the Figure 2 embodiment or between two conductors SA98~02~X 10 which form terminals 21bl and 21c' in the Figure 5 embodiment. The electrical lapping guide resistor 31 is also preferably of chromium and is deposited at the same time as resistors 38 through 41 are dPposited on substrate 11.
: ,, By mea~u~ing the relative position oE lapped surface 23 with respect to the right and left ends of substrate 11, it is possible to maintain lapped surfac:e 23 level with respect to final throat height for the entire array of transducers 30 on substrate 11. The controller 27 can be a computer programmed with an algorithm which will determine a force differential for transducers lS and 16 which will correct leveling errors. The force differ-ential is determined as:
R31L ~ Aw ) / K
where R31L is the resistance of the left electrical lapping guide resistor 31 R31R is the resistance of the right electrical lapping guide resistor 31 ~w is the difference in OFFSET distance of each lapping gulde resistor 31.
The offset distance is shown in Figures 2 and 3 as the distance from the rearward edge of resistor 31 to the throat height dimension.
-Continually determining the force differential necessaryto level the lapping surface 23 and applying the differ-ential orce with the actuators 15-16 will achieve a substantially level condition.
The calculated inal throat height resistance of elec-trical lapping guide resistor 31 may be represented by the following:
R3 ~
OFFSET ~ TH
SA939024X ll .. .. .
where the OFFSET distance of each lapping resistor is determined by OFFSET = R31 ~ Ddn, Ddn being the switch~
ing position of a given switching junction~
The computer 27 is programmed to measure the resistance s of eac~ ~eveling resistor of each lapping guide, both left a~d right, and the serial arrangement of six (6) i switching junctions. The parameters of the resistors and switching junctions which are utilized to determine the level condition of lapping surface 23 include the OFFSET
of each leveling resistor, as shown in Figure 3. The OFFSET represents the distance from the desired throat height to the rearward resistor edge, parallel with the lapping surface 23. The distance from the throat to a given detector switching plane, generically described as Ddn, and desired throat height, TH, are utilized to determine the following calculations.
The OFFSET is calculated for each of the leveling resis-tors by utilizing the following formula:
OFFsET = R 1 - Ddn The difference in OFFSETs between the right and left leveling resistors is expressed as:
~w = OFFSETR le~t ~ OFFSETR right ., With the difference in OFFSETs, it is possible to deter-mine a force differential between the actuators 15 and 16, such as to correct for an unlevel lapping surface.
This differential, Fd, previously described is:
Fd = ( K - Aw ) - K
By calculating the force differential in accordance with the above formulation, the computer 27 will set a force differential for the actuators lS and 16, according to the following determination:
. . .
Fd < 0 Left force < Right force Fd = 0 Left force = Right force Fd > 0 Left force ~ Right force This ~orce determination is a subroutine in programming steps ~o~be described, such that computer 27 will provide the ap~ropriate force differentlal to the substrate 11 to correc~ any leveling errors.
As a final basic calculation for the system, a final throat height resistance is determined from the elec-trical lapping guide resistor 31 for each side of the - transducer substrate row according to the previously described relationship:
~C
R31~side) OFFSET (side) TH
In view of the foregoing basic calculations, which provide ~or leveling information, as well as for a final throat height determination, the following programming steps have been incorporated in the computer 27. These programming steps, described in pseudo-code, are useful for electrical lapping guide structures having the six (6~ switching junctions described in the foregoing. Of course, six (6) is not necessary to implement the inven-tion, but is, however, considered preferable. The pseudo-code described is a series of do loops, each beginning from 1 to n where n = number of switching junctions employed in the electrical lapping guide structure~
.
Prior to beginning the lapping process, a number of values are inserted in the computer 27. The irst being the value of the constant K, previously described with respect to equation 1. The distance from the final throat height to each s~itching plane Ddl to Dd6, is inserted in the computer program. The program to be described will, at the user's option, end lapping on a calculated throat height, as inserted in the com~uter program, or on the last change of state of the switching junction closest to the ~inal throat height. In the event that a calculated throat height is to be used as the endpoint for ceasing lapping operations, this calcu-lated throa~ height (TH) is loaded into the computer program~ A wash cycle distance Wc is also inserted in the prog~am. At the end of -the coarse lapping, as is lcnown to those skilled in the art, a wash cycle which affects~-a finer lapping to the lapped surface 23 permits lapping`for a specified distance of Wc.
i An additional subrou~ine will be employed in the program-ming to read the left and right resistance values pro-vided by each electrical lapping guide resistor 31. This subroutine additionally subtracts a leacl resistance before making the measured values available for program execution. A lead resistance constant would normally be included in the subroutine, however, this may also be inputted by the operator with the other parameter values.
The program is configured in three l3) separate ~ortions which will be described in pseudo-code programming format as DO LOOPS.
The first portion comprises a section of the program which will, during lapping to the first of the switching junction, execute the following steps.
Do until first switching junctions activate and level resistor values stored Call read Left & Right R31 values Calc force differential Read level R31 values right and left Fd=R31Left R31Right Equation (1) Call set mechanics If both left and right detectors activate Then Store both level R values in R1ll and Rrn respectively SA9~40~X 14 s I one detector activates Store level R valu~ in Rside Rside - 1.0 (detected side) ~; Rside - 0.0 (undetected side) ~ , Calc force differential `~ Call set mechanics ~
- Do until other detector activates If other detector activates Then Call read Left and Right R values Store other level R value in Rsi.de The result o~ the first portion of the code is to calcu-late a force differential and apply the force differen-tial through the actuators 15 and 16 to the substrate 11.
This force differential is calcu1ated before the first switching junction, referred to as a detector in the pseudo-code, o each side of the substrate changes state by subtracting the resistance levels measured at each si~e of the substrate of each electrical lapping guide resistor 31 and 32. The SET MECHANICS subroutine called to establish this force differential on the actuators 15 and 16.
If correspo~ding switching junctlons on each electrical lapping guide structure change state simultaneously, then the value of each electrical lapping guide resistor, left and right t are stored.
:
: In the event that on.ty one switching junction on one of the electrical lapping guide structures changes state, indicating a non-level condition, the two ELG resistors 31 of each side of the substrate are measured and set to 1 and 0, respectively. The ~orce differential is calcu-lated and the SET MECE~ANICS apply the calculated force ~or the actuators 15 and ~6.
When the seco~d of the switching junctions of th~ oppo-site electrical lappin~ guide structure is found to change s~ate, the le~t and right R31 resistor values are read and stored.
Thus, after a pair of switches on opposite sides of the substrate ln different ELG structures changes state, the S first ~o~tion of the programming is completedO
, ;.
The second portion of the programming below consists of performing a series of calculations when lapping prog-resses from the first pair of switching junctions which have been activated to the third pair to change state.
Do N from 1 to 3 Calc offsets right and left wside = Rsiden Ddn Equation (2) Store offsets in Wsiden Calc ~ offset W W1n Wrn Equation (3) Store offset in ~Wn Do until next detector activates Call read Left & Right R values Calc new force differential Fd = ( - W J ~ K . Equation (4) Call set mechanics End do until next detectors activate If both detectors activate Then ; Store both level R values in Rside ~, .
~ , ., !` ~ Else ~`: If one detector activates Then Store level resistor values in Rside Rside=l.0 (detected side~
Rside~0.0 (undetected side) .. 10 Calc force differential Equation (l) Fd = R3lL ~ R3lR
Do until other side detected Call set mechanics End do until other side detected Read and store other level resistor in Rside End do N from l to 3 Calc & store next offset in Wside E~uation t2) Calc ~ store next ~W in ~Wside Equation (3) The OFFSETs, Wside, for ~he right and let ELG structures Z0 are calcula~ed and stored in a matrix. The differential : offset w is also stored as lapping progresses between the first pair of switching junctions to change state and : the~third pair to change state~ -~ : : As ~apping proceeds from the first pair of switching : 25 junctions:to change state a force differential is calcu-lated based upon equation 4. This force differential is applied through the set mechanics to the actuators 15 and 16 until the:subsequent pair of switching junctions, one in each ELG structure, change state.
In the event that only one switching junction on one side of the substrate ll chan~cs state, a force diferential is calculated as was accomplished earlier until the remaining switching junction of the oth~r electrical lapping guide structure changes state. When both switch-ing junctions have changed state, the two resistors R
are measured and their resistance values stored.
~ he above routine is repeated until the third pair of the switchi~g~junctions changes state.
.
The OFFSETs, Wside, and difference in offsets, Qw, are calculated at the completion of the above steps and stored.
The following steps executed by the computer program of computer 27 occur during ~he lapping of substrate 11 between switching junctions 3 to 6.
Do N from 3 to 6 Find the largest absolute value of QWl to ~Wn and store its real value W1 Check error correction value n ~ Equation (5) w - - - ~wk - Wl~
k=1 n ~ 1 Do until next detector pairs activate Call read level R values Calc force differential Fd= ( K _ W~ - K
CaIl set mechanics SA98402~X 18 If end on calculated throat height Then Find largest offset values for left and rlght and store off , ~ Average offsets , ~
oFrsÉTs = L~ Wside ~ - OFF Equation (6) n-l . . .
Calc final throat resistance Reside = K Equation (7) FFside T
If REside ~ ~side Equation (8 Then Print data `~
Exit program If not in wash cycle : Then 15 If end on calculated throat height '' Then :
Calc wash cycle resistance 'Rw= K Equati~n (9) OFFS ide~Th ~wc :
: : If Rw-Rside < 0 ~ .
Thcn Fix wash cycle in on condition SA984024X l9 7~i Else Calc wash cycle resistance Rw = - K _ Equation (10) OFFside+Dd6 C
-- If Rw-Rside < 0 Then Fix wash cycle in on condition As lapping progresses from the third switching junction pair to change state, the stored differential of~sets Ww are examined and the largest differential o~fset is identified. An average of the offsets determined is computed according to equation ~5). When the next pair of switches on opposite sides of substrate 11 change state, each resistor 31 is measured and a force differen-tial calculated. The force differential is applied through the set mechanics to the actuators 15 and 16.
If the operator o~ computer 27 has entered a calculated throat height at which lapping is to cease, then the computer determines the largest of the previous o~fset values determined, and averages the offset measurements according to equation ~6). The final throat hei~ht resistance is calculated by equation (7~ and compared with the actual measured resistance of each ELG resistor -- 31 of each side of the substrate 11. When the calculated final throat height resis~ance is equal to the actual measured resistance of resistor 31, equation (8) will terminate lapping.
As was mentioned, typically in lapping substrates 11, a final lapping distance is obtained in a wash cycle. The wash cycle will typicall~ lap from approximately 5 - 30 microns within final throat height to a final throat - height measurement. The final throat height measurement indicated as the ideal throat height, may, of course, be set to any distance from this height. In the event a throat height is selectcd other than this final throat height, this nominal throat height is utilized in equa~
tion (9) with the wash cycle lapping distance, Wc, to calculate a final lapping resistance, RW for each ELG
~resistor 31. The wash cycle resistance i5 continuously compared with the measured ELG resistance 31 of each side o subs~rate 11. When the wash cycle resistance equals i . ;
the measured resistance, the wash cycle is efected for final lapping of the su~strate.
In the event that the lapping is not to end on a calcu-lated throat height, but rather is to end on the changing of state of one of the switching junction, the programm-ing steps will calculate a wash cycle resistance RW
according to equation (10). The wash cycle resistance is compared with each measured resistance of resistors 31, and the switching junction on which the lapping is to end is monitored.
The following sequences of steps are executed depending on whether one of the remaining detector pairs is acti-vated, or both.
If one detector activates Then Store level R value in Rside Calc ~ store next offset in W . Equation (2) slde If both offsets stored Then Calc and store next ~W in ~Wn Else If both detectors have activated SA98~1024 X 21 Then S~ore level R values in Rln an n ~ ~; Calc & store next offsets in S ~,Wln and Wrn Equation (2) ~, .. ; :
Calc & store next ~W in ~W Equation (3) End do until next End do from 3 to 6 Print data Exit program These calculations are repeated for each of the remaining detector pairs which are to change state during lapping.
The values of the OFFSETs and differential offsets, ~w, are continuously determined and the wash cycle resistance computed again from averaging the calculated offsets and calculated differential offsets.
Thus, there is described with respect to one program;a method for reducing the resistance information derived from the electrical lappinct guide structure of the - present invention. Those skilled in the art will recog-nize yet other ways of r~ducing these measurements to effectively control leveling and lapping of batch fabri-cated thin film magnetic transducers to a final throat height.
SA98~02~X 22
Claims (10)
1. In a process for batch fabricating thin film transducers, a method for measuring the position of a lapped edge of a substrate supporting said thin film transducers comprising the steps of:
depositing a plurality of switching junctions on said substrate, each of said switching junctions having a distinct switching plane parallel to and a known distance away from a desired position for said lapped edge;
depositing a shunt resistance in parallel with each of said switching junctions and spaced apart from the lapped edge to avoid severing by lapping;
forming a circuit comprising each of said switching junctions connected in a series circuit;
lapping said substrate from an initial edge of said substrate toward said desired position for said lapped edge wherein each of said switching junctions changes from a closed state to an open state when said lapping plane is coincident with said switching junction switching plane whereby said shunt resistance in parallel with said switching junction which changes state is connected into said series circuit; and detecting stepwise changes in said series circuit resistance during lapping of said substrate, each of said changes indicating a change of state of one of said switching junctions thereby identifying the position of said lapped edge to be coincident with said switching plane of said switching junction which changes state.
depositing a plurality of switching junctions on said substrate, each of said switching junctions having a distinct switching plane parallel to and a known distance away from a desired position for said lapped edge;
depositing a shunt resistance in parallel with each of said switching junctions and spaced apart from the lapped edge to avoid severing by lapping;
forming a circuit comprising each of said switching junctions connected in a series circuit;
lapping said substrate from an initial edge of said substrate toward said desired position for said lapped edge wherein each of said switching junctions changes from a closed state to an open state when said lapping plane is coincident with said switching junction switching plane whereby said shunt resistance in parallel with said switching junction which changes state is connected into said series circuit; and detecting stepwise changes in said series circuit resistance during lapping of said substrate, each of said changes indicating a change of state of one of said switching junctions thereby identifying the position of said lapped edge to be coincident with said switching plane of said switching junction which changes state.
2. The method of claim 1 further comprising:
depositing a resistor element on said substrate, said resistor element having a resistance which changes with lapping of said substrate;
measuring the resistance of said resistor each time a switching junction changes state; and determining a lapping edge position versus resistance characteristic for said lapping resistor each time a switching junction changes state, whereby said lapping resistor is recalibrated each time a switching junction changes state.
depositing a resistor element on said substrate, said resistor element having a resistance which changes with lapping of said substrate;
measuring the resistance of said resistor each time a switching junction changes state; and determining a lapping edge position versus resistance characteristic for said lapping resistor each time a switching junction changes state, whereby said lapping resistor is recalibrated each time a switching junction changes state.
3. The method of claim 2 wherein said resistor element is positioned on said substrate between said series circuit and said supported thin film transducers.
4. The method of claim 3 wherein said switching junc-tions are spaced apart on said substrate with the switch-ing junction having a switching plane closest to a final throat height being adjacent said resistor element.
5. In a process for lapping batch produced transducer elements to a final throat height, a method for accu-rately determining the position of a lapping plane with respect to a desired throat height comprising:
depositing on each side of a substrate an electrical lapping guide means, each of said guide means having an electrical resistance proportional to a change in lapping plane position;
forming adjacent each of said electrical lapping guide means a series circuit made from a plurality of switching means, each switching means of a plurality having a distinct switching plane which changes state when said lapping plane is coincident therewith, producing a stepwise change in resistance thereof, each series circuit producing during lapping of said transducer elements discrete resistance changes corresponding to a change in state of one of said switching element means;
measuring the resistance of each lapping guide means and each corresponding series circuit during lapping of said transducer elements; and, determining from a plurality of stepwise changes in resistance of each series circuit and measured guide means resistance levels the position of the lapping plane with respect to each side of said substrate.
depositing on each side of a substrate an electrical lapping guide means, each of said guide means having an electrical resistance proportional to a change in lapping plane position;
forming adjacent each of said electrical lapping guide means a series circuit made from a plurality of switching means, each switching means of a plurality having a distinct switching plane which changes state when said lapping plane is coincident therewith, producing a stepwise change in resistance thereof, each series circuit producing during lapping of said transducer elements discrete resistance changes corresponding to a change in state of one of said switching element means;
measuring the resistance of each lapping guide means and each corresponding series circuit during lapping of said transducer elements; and, determining from a plurality of stepwise changes in resistance of each series circuit and measured guide means resistance levels the position of the lapping plane with respect to each side of said substrate.
6. In a process for batch fabricating thin film trans-ducer elements, wherein said transducer element pole tips are lapped to a final throat height, a method for measur-ing a final throat height during lapping of said trans-ducer elements, comprising:
forming a plurality of switching junctions on a substrate bearing said transducer elements, each of said switching junctions having a switching plane a known distance away from a desired throat height of said pole tips;
forming shunt resistance elements across each of said switching junctions;
forming a series circuit including said switching junc-tions;
forming an electrical lapping resistance on said sub-strate which provides a resistance proportional to the position of said lapped pole tips;
measuring during lapping the resistance of said series circuit and said lapping resistance;
deriving a resistance versus lapping plane position characteristic from said measured lapping resistance and each detected step change in said series circuit resis-tance measurements; and measuring subsequent lapping plane positions by measuring said resistance.
forming a plurality of switching junctions on a substrate bearing said transducer elements, each of said switching junctions having a switching plane a known distance away from a desired throat height of said pole tips;
forming shunt resistance elements across each of said switching junctions;
forming a series circuit including said switching junc-tions;
forming an electrical lapping resistance on said sub-strate which provides a resistance proportional to the position of said lapped pole tips;
measuring during lapping the resistance of said series circuit and said lapping resistance;
deriving a resistance versus lapping plane position characteristic from said measured lapping resistance and each detected step change in said series circuit resis-tance measurements; and measuring subsequent lapping plane positions by measuring said resistance.
7. In a process for batch fabricating thin film magnetic transducers, said transducers formed in a row on a substrate and each having pole tip regions, a method for lapping said pole tip regions to a final throat height comprising:
depositing first and second electrical lapping guide structures on each end of the substrate, said lapping guides including a serial connection of switching junctions, each switching junction having a switching plane a known distance away from a final pole tip plane and terminated with a parallel resistance ;
lapping said substrate along an edge parallel to said pole tip regions;
applying first and second forces to each of said ends of said substrate in a direction perpendicular to said substrate edge, said forces controlling the lapping rate at each end of said substrate;
monitoring the state of each switching junction by measuring the resistance of series connections of switch-ing junctions; and, establishing a force differential between said first and second forces when a switching junction of one of said electrical lapping guide switching junctions changes state, said force differential being in a direction to maintain said substrate edge level.
depositing first and second electrical lapping guide structures on each end of the substrate, said lapping guides including a serial connection of switching junctions, each switching junction having a switching plane a known distance away from a final pole tip plane and terminated with a parallel resistance ;
lapping said substrate along an edge parallel to said pole tip regions;
applying first and second forces to each of said ends of said substrate in a direction perpendicular to said substrate edge, said forces controlling the lapping rate at each end of said substrate;
monitoring the state of each switching junction by measuring the resistance of series connections of switch-ing junctions; and, establishing a force differential between said first and second forces when a switching junction of one of said electrical lapping guide switching junctions changes state, said force differential being in a direction to maintain said substrate edge level.
8. The process of claim 7 further comprising:
depositing an electrical resistor between each series connection of switching junctions and a respective row end, said resistor providing for each lapping guide structure a change in resistance versus distance lapped of said substrate edge;
determining a resistance versus lapping position of said substrate edge characteristic for said resistor after each switching junction changes state;
determining a final resistance value for said resistor corresponding to said final throat height based upon said resistance versus lapping positions of said substrate characteristic; and terminating lapping of said substrate when said resistor resistance is equivalent to said determined final resis-tance value.
depositing an electrical resistor between each series connection of switching junctions and a respective row end, said resistor providing for each lapping guide structure a change in resistance versus distance lapped of said substrate edge;
determining a resistance versus lapping position of said substrate edge characteristic for said resistor after each switching junction changes state;
determining a final resistance value for said resistor corresponding to said final throat height based upon said resistance versus lapping positions of said substrate characteristic; and terminating lapping of said substrate when said resistor resistance is equivalent to said determined final resis-tance value.
9. In apparatus for batch fabricating thin film transducers, said apparatus comprising an electrical lapping guide for measuring the position of a lapped edge of a substrate supporting said thin film transducers said apparatus comprising:
a plurality of switching junctions formed on said substrate, in known spaced relation to said thin film transducers, each of said switching junctions having a distinct switching plane parallel to and a known distance away from a desired position for said lapped edge;
a shunt resistance formed in parallel with each of said switching junctions and spaced apart from the lapped edge to avoid severing by lapping;
an electrical circuit comprising each of said switching junctions connected in a series circuit, said electrical circuit having a first and a second terminal; and a resistor element having two terminals formed on said substrate adjacent to said plurality of switching junctions, said resistor element having a resistance which changes with lapping of said substrate, whereby, upon connection of means for measuring resistance across said first and second terminals, stepwise changes in said series circuit resistance can be detected during lapping of said substrate, each of said changes indicating a change of state of one of said switching junctions thereby identifying the position of said lapped edge to be coincident with said switching plane of said switching junction which changes state, and whereby, upon connection of means for measuring resistance across said two terminals, a lapping edge position versus resistance characteristic can be determined for said resistor element each time a switching junction changes state, whereby said resistor element is recalibrated each time a switching junction changes state.
a plurality of switching junctions formed on said substrate, in known spaced relation to said thin film transducers, each of said switching junctions having a distinct switching plane parallel to and a known distance away from a desired position for said lapped edge;
a shunt resistance formed in parallel with each of said switching junctions and spaced apart from the lapped edge to avoid severing by lapping;
an electrical circuit comprising each of said switching junctions connected in a series circuit, said electrical circuit having a first and a second terminal; and a resistor element having two terminals formed on said substrate adjacent to said plurality of switching junctions, said resistor element having a resistance which changes with lapping of said substrate, whereby, upon connection of means for measuring resistance across said first and second terminals, stepwise changes in said series circuit resistance can be detected during lapping of said substrate, each of said changes indicating a change of state of one of said switching junctions thereby identifying the position of said lapped edge to be coincident with said switching plane of said switching junction which changes state, and whereby, upon connection of means for measuring resistance across said two terminals, a lapping edge position versus resistance characteristic can be determined for said resistor element each time a switching junction changes state, whereby said resistor element is recalibrated each time a switching junction changes state.
10. The apparatus of claim 9 wherein said plurality of switching junctions are closer to said thin film transducers than said resistor element.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000528223A CA1249075A (en) | 1987-01-27 | 1987-01-27 | Method and apparatus for controlling the throat height of batch fabricated thin film magnetic transducers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000528223A CA1249075A (en) | 1987-01-27 | 1987-01-27 | Method and apparatus for controlling the throat height of batch fabricated thin film magnetic transducers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1249075A true CA1249075A (en) | 1989-01-17 |
Family
ID=4134834
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000528223A Expired CA1249075A (en) | 1987-01-27 | 1987-01-27 | Method and apparatus for controlling the throat height of batch fabricated thin film magnetic transducers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1249075A (en) |
-
1987
- 1987-01-27 CA CA000528223A patent/CA1249075A/en not_active Expired
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