CA2115396A1 - Thin film transducer with coil guard segment - Google Patents

Abstract

A thin film transducer has a top pole formed by ion beam milling, a bottom pole and a multi-turn coil inductively coupled to the poles. The multi-turn coil has an outer dummy turn which is electrically disconnected from the remaining coil segments so that the external electrical connection to the outer portion of the coil is made to an inner segment. During fabrication of the top pole, any damage to the previously formed coil by ion beam milling occurs to the dummy turn, rather than the inner segment to which electrical connection is made. A thin film transformer is provided with the same dummy turn structure.

Description

21 1~3~6 THIN FILM TRANSDUCER WITH COILGUARD SEGMENT

BACKGROUND OFTHEINVENTION
This invention relates to the art of thin film transducers of the type used in disk drives.
Thin film magnetic transducers are known which are used in disk drives to write data to and read data from magnetic storage disks. A typical thin film transducer comprises a pair of pole pieces joined at a first region, usually termed the back gap region, and spaced at an opposing region, usually termed the pole tip region. In between the back gap region and the pole tip region, the pole pieces diverge in order to accommodate an electrical coil which is electrically insulated from the pole pieces. The coil is electrioally connected to associated read/write circuitry by means of external conductive leads formed on the adjacent substrate surface. The transducer is typically fabricated using photolithographic techniques on a relatively thick substrate, usually termed a slider, with the pole tip region terminating at a surface termed the air bearing surface (ABS). A typical example of such a transducer is described and illustrated in U.S. Patent No. 4,458,279 and the additional references cited therein, the disclosures of which are hereby incorporated by reference.
Typically, a pair of such thin film transducers is fabricated on the siider surface, with each transducer located at a different end of the slider surface adjacent a lobe defined by a rail extending the entire length of the slider. Thus, in a given assembly the slider has a pair of rails running mutually parallel along the length of the slider and a thin film transducer is associatedto each lobe defined by the associated rail.
The demand for increased data density on magnetic media has led to the requirement for substantially smaller track widths and transducers with correspondingly smaller pole tip regions. With decreasing pole tip size, - 211~3~6 the amplitude of the electrical signal output by the transducer coil is correspondingly reduced. This is undesirable, since noise signals increasingly mask the data signals generated by the coils during a read operation, which leads to erroneous data retrieval. In the past, attempts have been made to 5 compensate for this decrease in signal amplitude by adding more turns to a transducer coil by both narrowing the widths of the individual coil loops and by ~aL.ricaling the coil in two or more layers. An improvement in the signal amplitude has also been afforded by the use of a miniature thin film transformer to boost the electrical signal output from the thin film transducer.In our co-pending patent application serial no. 07/463,567, filed January 11, 1990, entitled Thin Film TransducertTransformer Assembly, now allowed a suitable thin film transformer is described which is formed on one of the two slider lobes in the position normally occupied by one of the thin film transducers in the prior art devices. This thin film transformer includes a 15 bottom pole member, a top pole member forming a closed magnetic path with the bottom pole member, and a coil. The top and bottom pole members are fabricated of a magnetically permeable material. The electrically conductive coil is positioned between the top and bottom pole members, the coil having a pair of ends and a tap connection between the ends. The bottom pole 20 member of the transformer includes first and second end portions and an intermediate body portion extending therebetween. The top pole member includes first and second end portions and an intermediate body portion extending therebetween and disposed above the intermediate body portion of the bottom pole member to provide an interior space for accommodating the 25 coil, and the first and second end portions of the bottom pole member are coupled to the first and second portions of the top pole member, respectively.
The intermediate body portion of the top pole member preferably includes a downwardly depending central portion extending to the intermediate body portion of the bottom pole member, and the transformer coil is preferably 30 disposed about the central portion of the top pole member. In addition to being located on one of the two lobes, the transformer can be positioned 211539~

elsewhere on the same substrate as the thin film transducer, or can be formed as a separate unit. The transformer coil is electrically connected to the transducer coil and to the follow-on electrical circuitry by means of conductiveleads. Like the transducer, the thin film Irans~on"er is fabricated using 5 integrated circuit fabrication techniques.
In the process of forming both the thin film ~,ans~Gr")er and the thin film transducer, after the upper coil layer has been formed an insulator isprovided over this top coil layer. Thereafter, a layer of suitable ferromagneticmaterial which will form the top pole member is deposited over the insulator 10 layer, and a photoresist layer is formed on top of the ferromagnetic layer and exposed with a suitable mask to provide the desired outline of the top pole member. Thereafter, the layer of ferromagnetic material which is not protected by the exposed photoresist is etched away using ion beam milling to provide the final top pole structure. Although the ion beam milling process can be 15 carefully controlled, it frequently occurs that the outermost turn of the top coil layer is damaged during the ion beam milling step due to the relative thinness of the protective insulative layer in the forward region of the coil (i.e., the region of the coil adjacent the pole tip region in the thin film transducer or adjacent one end of the joined top and bottom pole regions for the 20 transformer). This is due to the sloping contour of the insulative layer which results during the fabrication of the multi-layered coil and the insulative layers.
As a consequence of this damage to the outer coil turn, the manufacturing yield of both thin film transducers and thin film transformers is lower than desired.
SUMMARY OF THE INVENTION
The invention comprises an improved coil structure for both thin film transducers and thin film transformers and the method of making same which provides an improved yield and substantial immunity from ion beam 30 milling damage.

- 211S3~

The improved coil structure of the invention is applicable to both a thin film transducer and a thin film transformer. In either application, the normal coil pattern is altered by electrically disconnecting an outer coil segment from the inner coil segments. In one embodiment this is done by 5 disconnecting the outer end of the outermost coil segment from the external lead and making the external lead connection to the adjacent portion of the next segment. In another embodiment, both the outer end of the outermost coil segment and the adjacent portion of the next inner segment are joined and connected to the external lead. In both embodiments, a portion of the 10 outer segment is removed, or not deposited, so that the outer segment cannot be connected to the remaining coil structure, i.e., the outer segment is discontinuous in the inward spiralling direction.
By connecting the external lead to an inner segment of the coil while permitting a substantial portion of the outer se~""e"t to remain, any 15 damage to the coil by means of the ion beam milling process used to form the top pole occurs only to the outer dummy turn coil segment. As a consequence, the manufacturing yield is substantially increased without the need for any significant changes in the overall fabrication process.
For a fuller understanding of the nature and advantages of the 20 invention, reference should be had to the ensuing detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an idealized perspective view from the upstream side of 25 a slider having a thin film transducer and a thin film transformer with the improved coil structure according to the invention;
Fig. 2 is an enlarged sectional view taken along lines 2-2 of Fig. 1 illustrating the thin film transducer;
Fig. 3 is an enlarged sectional view taken along lines 3-3 of Fig. 1 30 illustrating the thin film transformer;

- 211~3~6 Fig. 4 is an electrical diagram showing the coupling between the transducer and a transformer;
Fig. 5 is an enlarged top plan detailed view illustrating the appearance of the combined structure of the top and bottom thin film 5 transducer coils, the external electrical conductors and the top pole;
Fig. 6 is a top plan detail view illustrating the bottom coil winding;
Fig. 7 is a top plan detail view illustrating the top coil winding;
Fig. 8 is an enlarged view of the top coil winding of Fig. 7;
Fig. 9 is a view similar to Fig. 8 illustrating a first embodiment of 10 the invention; and Fig. 10 is a view similar to Fig. 8 illustrating a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to the drawings, Fig. 1 illustrates a thin film magnetic transducer generally designated with reference numeral 10 and a thin film transformer generally designated with reference numeral 40, both formed on the same support surface 11 of a slider 12. Slider 12 includes first and second air bearing rails 13, 14 which are integrally formed with the slider 12 20 and which provide air bearing surfaces for supporting the slider 12 above a moving magnetic disk (not shown) in a known manner.
As best in seen in Fig. 2, thin film transducer 10 includes a first layer of magnetic film material forming a first magnetic pole piece 15 disposed on surface 11 of slider substrate 12. First magnetic pole piece 15 is typically 25 of uniform thickness between at least a pole tip region 15a and a back gap region 15b. A first layer of non-magnetic insulating material 16 such as silicondioxide or alumina is deposited over pole piece 15 and extends from pole tip region 15a to back gap region 15b.
A first layer of electrically conductive material forming a 30 conductive coil winding 20a is deposited in an appropriate pattern, such as the pattern illustrated in Fig. 6, over the insulating material 16. A second layer 2115~6 of insulating material 22 of sufficient thickness to cover winding 20ais deposited over insulating layer 16. A second layer of electrically conductive material forming a further conductive coil winding 20bis deposited in a suitable pattern, such as the pattern illustrated in Fig. 7, over the layer of 5 insulating material 22. A third insulating layer 24 covers the second coil winding 20b. First and second coil winding layers 20a and 20b are connected at their respective centers 21a, 21b (Figs. 6 and 7) to form a two layer continuous coil which loops around the back gap region 15b to enclose the region 15b.
A second layer of magnetic material forming a second magnetic pole piece 26is deposited over first pole piece 15 in the back gap region 15b, over insulating layers 22 and 24 in the regions occupied by conductive coil windings 20a and 20b and over insulating layer 16 in the pole tip region 15a.
Pole pieces 15 and 26 are separated at the pole tip region by insulating layer 16 in order to provide a transducing gap therebetween. One end of first winding 20a and one end of second winding 20b are electrically coupled to the first end of separate electrically conductive paths 30, 31 in order to electrically connect the coil of transducer 10 to the coil in transformer 40, asdescribed more fully below.
As shown in Fig. 1, the coil segments 20a, 20b of thin film transducer 10 are electrically connected to the thin film transformer 40 via conductive leads 30, 31. As best shown in Fig. 3, thin film transformer 40 includes a bottom magnetic pole or bar 60, an upper magnetic pole or bar 62 joined to lower bar 60 at a front end 63 and a rear end 64, a pair of conductive coil windings 66a and 66b, and three insulative layers 67, 68, 69.
Coil windings 66a, 66b are patterned in a manner similar to that already described with respect to coil windings 20a, 20b of thin film transducer 10, and are thus connected at the respective centers thereof. In addition, the central connection between coil windings 66a and 66b is led out from the coil structure and connected to conductive lead 30. Thus, the electrical connections are as illustrated in Fig. 4 wherein upper coil winding 66b has the 2115~96 ends thereof connected to the thin film transducer coil via conductive leads 30,31, while one end of lower coil winding 66a and one end of upper coil winding 66b are connected to conductive leads 31, 33. To facilitate connection to the exter~,al circuitry, enlarged contact areas 34,35 are provided as shown in Fig.
1.
As will be appreciated by those skilled in the art, transformer 40 is used to modify the signals generated by transducer 10 on conductive paths 30,31 during a read operation. More particularly, the voltage level of the signals from transformer 10 is stepped up or boosted by transformer 40. The amount of boost in the signal level is determined by the turns ratio of the coilsegments 66a, 66b. With the configuration depicted in Figure 4, the number of turns N1 on the signal input side is simply the number of turns in coil segment 66b, while the number of turns N2 on the signal output side is the combined value of the number of turns in coil segments 66a and 66b. These numerical values can be determined in an empirical fashion for any given application.
As will be appreciated by those skilled in the art, the fabrication of thin film transducer 10 and thin film transformer 40 can be done either simultaneously to form the combined transducer/transformer assembly described above, or thin film transducer 10 and thin transformer 40 can be fabricated separately for subsequent combination. The fabrication of the transducer 10 and the transformer 40iS performed using conventional thin film processing steps which are well known to those skilled in the art. In particular, substrate 12 is initially provided, after which the bottom pole 15 of transducer 10 and the bottom pole 60 of transformer 40 are formed by initial deposition of a suitable magnetically permeable material such as nickel iron to a prescribed thickness, followed by selective photomask patterning and etching. Next, first insulation layers 16 and 67 are formed by depositing an insulation, such as silicon dioxide, followed by photomask patterning and etching. Alternatively, a photoresist layer is coated onto the bottom poles 15, 60 and substrate 12, followed by photomask patterning and hard bake ~--` 2115396 (solidification). Next, first coil segments 15a and 66a are fabricated f-om a suit~hlQ conductive material, such as copper, silver, gold or the like, by firstdepositing a thin film seed layer to a thickness on the order of about 20ûA, followed by deposition of the conductive material to a suitable thickness, 5 photomask patterning, soft bake and plating, followed by photoresist strip andseed layer etching. Second insulation layers 22, 68 are next formed, followed by formation of coil segments 20b, 66b, insulation layers 24, 69 and top magnetic pole pieces 26, 62. During formation of the insulative layers 22, 68, suitable apertures are provided to facilitate electrical connection between 10 appropriate ends of the coil segments (such as central ends 21a, 21b ~f coil windings 20a, 20b). Similarly, during formation of insulative layer 69 suitable apertures are etched to provide a central opening to facilitate the tap connection between the inner end of coil segment 66b and conductive lead 30.
During formation of the top magnetic pole pieces, 26, 62, a layer of magnetic material is deposited over at least a substantial portion of the coils for the transducer 10 and the transformer 40. The deposited magnetic layer is next covered by a layer of photoresist, and photomask patterning is then formed by conventional techniques to provide a protective photoresist layer in 20 the shape of the transducer upper pole 26 and the transformer upper pole 62.
Thereafter, the excess surrounding layer of magnetic material is removed using ion beam milling. In the course of performing this ion beam milling step, portions of the upper insulative layers 24 and 69 are typically eroded. So long as the erosion does not penetrate into the coil layers no adverse effect occurs.25 However, due to the extremely small dimensions it has been found that the upper coil winding 20b and 66b is subject to damage during ion beam milling.
To understand this phenomenon, it is helpful to examine the structure of the coil windings in more detail. Fig. 6 illustrates the lower coil winding 20a typically found in a thin film transducer. As seen in this Fig., the coil has a 30 unique shape terminating in the central end 21a. Fig. 7 illustrates a prior art -upper coil winding 20b having the central end 21b. Figure 8 illustrates the upper coil winding 20b in an enlarged manner from that shown in Fig. 7. As seen in Fig. 8, coil winding 20b has an outer turn 25b connected at its outer end to conductive lead 30. Outer coil turn 25b proceeds downward as viewed in Fig. 8 towards the front of the transducer 10 structure, to the right across the pole tip region, upp~erwardly towards and past the conductive lead 31 and in an essentialiy circular arc around the back of the coil to the region of the connection with conductive lead 30. The coil path continues in an inward spiral as shown and finally terminates in the central end 21b. The portions of outer turn 25b which have been found empirically to be highly susceptible to ion beam milling damage are the two regions designated with reference numerals 27b, 28b, which are the regions adjacent pole tip region 15a. The reason for this susceptibility to damage seems to be the sloping nature of the outer edges of the upper insulative layer 24 (Fig. 2) which covers the upper coil winding 20b with decreasing thickness of material near the outer edges.
During ion beam milling of the top pole 26, the portion of the insulative layer 6 24 adjacent the outline of the developing upper pole 26 is eventually exposed to the flux of the ion beam. It is has been determined empirically that this leads to a high incidence of ion beam penetration through the outer upper coil winding 20b layer 25b in the regions 27b and 28b. In severe cases, the beam cuts entirely through the outer winding 25b. As a consequence, the continuous path is interrupted and the electrical connection between conductive lead 30 and central end 21b is disturbed (even though the physical connection frequently remains between outer winding 25b and conductive lead 30). Consequently, winding 20b is useless, which causes the transducer 10 to be useless.
Fig. 9 illustrates a first upper coil winding 20b designed to substantially reduce the problem of transducer malfunction due to ion beam erosion or severing of the outer coil winding 25b, and thus to improve the yield of transducers fabricated in accordance with the invention. As seen in Fig. 9, an upper coil winding generally designated with reference numeral 80 ' 21iS396 has a central terminal 81 essentially identical to central terminal 21b of the prior art upper coil 20b shown in Fig. 8, and a discontinuous outer coil winding segment 82. The next innermost segment of winding 80 designated with reference numeral 83 is connected to conductive lead 30 via a transition 5 region 85. In this arrangement, the discontinuous outer segment 82 functions as a "dummy turn" and is deliberately left disconnected'from the electrical conductive path between the conductive lead 30 and the central end 81 of winding 80. The pattern for winding 80 is essentially the same pattern as that used for prior art winding 20b: however, the prior art outer segment 25b is 10 deliberately left unconnected to conductive lead 30 and the semicircular backportion of the prior art outer segment 25b is removed from the pattern to form the generally U-shaped dummy turn 82. With this arrangement, any ion beam milling damage will essentially occur to the outermost dummy turn 82, thereby leaving the coil winding 80 intact with respect to the electrically conductive 15 path between conductor 30 and central terminal 81.
Fig. 10 illustrates an alternate embodiment of the invention in which the conductive lead 30 is connected to both the dummy turn 82 and the next innermost segment 83 via transition region 87. As with the embodiment of Fig. 9, the semicircular shaped back portion of the outer segment of the 20 prior art coil winding 20b is removed to form the outer dummy turn 82.
By providing the electrical connection between the conductive lead 30 and the central terminal 81 via the next innermost segment 83 of the upper coil winding 80, it has been determined that the manufacturing yield is improved substantially. This solution to the problem of ion beam milling 25 damage to the upper coil winding can be implemented at extremely low cost since it merely requires altering the shape of the upper coil winding, which canbe done by providing a suitable modified mask. It should be noted that the improvement afforded by the invention occurs at the expense of removing one of the turns from the transducer coil. However, when used in conjunction with 30 a thin film transformer 40 (or some other suitable signal boosting device), the 2 ~

reduction in signal amplitude from the transformer 10 is easily accon,modated by the signal boost afforded by the transformer 40.
While the above provides a complete and adequate description of the preferred embodiments of the invention, various modifications, alternate 5 constructions and equivalents will occur to those skilled in the art. For example, other patterns for the coils than those shown ih Figures 5-10 can be used without departing from the spirit of the invention. In addition, although the invention has been described with specific reference to the transducer 10 upper coil winding 20b, it is understood that the principles of the invention 10 apply equally to the upper coil winding 66b of the thin film transformer 40. In addition, although the embodiment shown in Fig. 1 employs a transducer on the left lobe 13 of the slider 12 and a transformer on the right lobe 14 of the slider 12, assemblies in which the locations of the transducer 10 and transformer 40 are reversed are envisioned. Further, in some applications the 15 ion beam milling damage may extend inwardly to the next inner segment of the upper coil winding or downwardly into the outer segment of the lower coil winding. In the former case, the connection between external conductor 30 and central terminal 81 can be made by an inner coil segment closer to the center of the coil winding structure, such as the second-most inner segment 20 88 (Fig. ~), third-most inner segment 89, and the like. In the latter case, the lower coil windings 20a, 66a can be modified in the manner described for the upper coil windings 20b, 66b. Similarly, embodiments employing two transducers 10, one on each lobe, and an auxiliary signal booster located adjacent thereto are also envisioned. Therefore, the above should not be 25 construed as limiting the invention, which is defined by the appended claims.

Claims (13)

1. In a thin film conductive device having top and bottom magnetic poles and a multi-turn coil inductively coupled to at least one of saidpoles, said coil having an outer end and a central terminal coupled to externally accessible leads, an outer segment and at least one inner segment, the improvement wherein one of said externally accessible leads is coupled to said inner segment, and one end of said outer segment is disconnected from the coil.

2. The invention of claim 1 wherein said outer segment has an outer end and an inner end, and wherein the end of said outer segment disconnected from the coil comprises the outer end.

3. The invention of claim 1 wherein said outer segment has an outer end and an inner end, and wherein the end of said outer segment disconnected from the coil comprises the inner end.

4. The invention of claim 1 wherein said thin film inductive device comprises a thin film transducer.

5. The invention of claim 1 wherein said thin film inductive device comprises a thin film transformer.

6. The invention of claim 1 wherein said coil comprises an upper winding and a lower winding, and wherein said outer segment and said inner segment are included in said upper winding.

7. The invention of claim 1 wherein said inner segment comprises the coil segment immediately adjacent said outer segment.

8. A method of fabricating a thin film inductive device having top and bottom magnetic poles, and a multi-turn coil inductively coupled to at least one of said poles, said method comprising the steps of:
(a) forming a bottom pole;
(b) forming a multi-turn coil over the bottom pole, the coil having an outer segment and an inner segment, the outer coil segment being disconnected electrically from the inner portion of the coil;
(c) forming a top pole; and (d) providing an external electrical connection to the inner segment.

9. The method of claim 8 wherein said step (d) of providing includes the step of connecting the outer ends of the outer segment and the inner segment together.

10. The method of claim 8 wherein said step (d) of providing includes the step of establishing the external electrical connection to the outer end of the inner coil segment.

11. The method of claim 8 wherein said step (c) of forming a top pole includes the step of providing direct magnetic coupling between first regions of said top and bottom poles and providing a gap between other regions of said top and bottom poles so that said device comprises a thin film transducer.

12. The method of claim 8 wherein said step (c) of forming a top pole includes the steps of providing direct magnetic coupling between first and second portions of said top and bottom poles so that said thin film inductive device comprises a transformer.

13. The method of claim 8 wherein said step (b) of forming a multi-turn coil includes the step of forming a multi-layer coil.