Abstract:
An apparatus and method of making is disclosed for a combination read/write head having improved topography. The disclosed read/write head combines a magnetoresistive (MR) read head with an inductive magnetic write head. The head is planarized at a second shield layer with a planarization layer such that pads and leads connecting the pads to the MR sensor and coil are on a planar surface of the planaritzation layer. This planarization layer allows first and second shield layers to be optimized for the MR sensor to be used and also separates the pads and leads from the substrate. The combination head has first and second shield layers formed on a substrate, the shield layers being separated by a read gap. A magnetoresistive (MR) sensor and MR leads are located in the read gap. The planarization layer is then formed on the substrate, surrounding the first and second shield layers creating a planar surface that is coplanar with a top surface of the second shield layer. A write gap layer is fabricated along with a pole piece. The pole piece being separated by the write gap layer at the ABS and connected to the second shield layer at a back gap that is recessed in the head from the ABS. An insulation layer and coil layer embedded in the insulation layer with the insulation layer and the coil layer being located between the second shield layer and the pole piece. Pads and leads are formed on the planarization layer, with the leads electrically connected to the MR sensor and the coil.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inductive write head combined with a magnetoresistive (MR) read head and, more particularly, to a combined head with improved topography in which pads and leads are planar, thereby eliminating shorts or opens in the structure due to steps. 
     2. Description of the Related Art 
     Typical mass storage devices store information on spinning magnetic disks, the information being recorded by transitions in magnetic flux on the magnetic surface of the disk. In particular, the data is recorded in a plurality of tracks, with each track being a selected radial distance from the center of the disk. A read/write head is positioned in close proximity to the disk surface and is held in place by an arm. Under control of the systems processor unit, the arm can move the read/write head to the appropriate track where data is recorded that it can be read or written. 
     A magnetic disk drive includes a magnetic head in a transducing relationship with a surface of the magnetic disk. When the disk is rotated, the magnetic head is supported on a thin cushion of air. The magnetic head may then be employed for writing information to multiple circular tracks on the surface of the disk, as well as for reading information therefrom. Processing circuitry exchanges signals, representing such information, with the head, provides motor drive signals for rotating the magnetic disk, and provides control signals for moving the head to various tracks. The magnetic head is comprises two components, an inductive write head and a read head. 
     An inductive write head includes a coil layer embedded in an insulation layer between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted through the coil layer produces a magnetic field in the pole pieces. The magnetic field fringes across the gap at the ABS for the purpose of writing the aforementioned data in tracks on the rotating disk or longitudinal tracks on a moving magnetic tape. 
     The second part of the head is the read portion. One type of head is the magnetoresistive (MR) head that utilizes direct magnetic flux sensing as a means of readback. The MR head includes a magnetoresistive sensor that detects magnetic field signals through resistance changes of a magnetoresistive material. In applying MR sensors to magnetic recording, many difficulties must be addressed including magnetic behaviors of the sensors that are appropriate for the recording environment and fabrication of the sensors. 
     For efficient read/write operations, the inductive write head should be placed in close proximity to the MR sensor. One type of read/write head is called a “piggy back” head, where the inductive head and the MR sensor positioned adjacent to each other. For closer placement of the components, a merged head is used. In the merged head, some components of the inductive head are shared with the MR head. Still another type of head places the MR read sensor at the center of the write gap between the pole tips. The problem with this design is intense magnetic field perturbations at every write cycle may aggravate instability problems of the MR sensor. Further, the pole tips are wide at the ABS in order to provide proper shielding for the MR sensor resulting in decreased track width density. 
     During fabrication of these heads, each of the layers is fabricated one on top of the next. The first device to be fabricated is the MR head and then the inductive head is fabricated. The MR head comprises a sensor located between first and second gap layers and the gap layers are located between first and second shield layers. To fabricate the MR head, the first shield layer is formed on a substrate with undercoat therebetween, the first gap layer is fabricated next, the MR sensor is next, next is the second gap layer and finally is the second shield layer. The inductive write head is then fabricated on top of the MR head. Fabrication of the inductive head includes a coil layer located between insulation layers with the insulation layers being between first and second pole piece layers. For the “piggy back” head, the first pole piece layer is formed on top of the second shield layer of the MR head. For a merged head, the second shield layer is the same as the first pole piece layer (performs a double function). 
     One disadvantage of the layered structures described above is the uneven or “stepped” topography resulting from the layering process. Most commonly, each of the layers differ in width, such that as the layers are formed on top of one another, steps form near the edges. As multiple layers are formed, multiple steps may be formed. These steps are a common area of failure causing shorts and opens for the lead layers that connect the MR sensor and coil contact points pads to the outer edge of the head. Another problem is if the diameter of the coil is greater than the previous layers, portions of the coil then are formed on multiple layers or steps, which could lead to shorts or opens in the coil itself. 
     It is desirable to provide a substantially even surface below the inductive coil. This is accomplished by adding material, such as an insulation layer or hard bake resist around the sides of a narrow layer to widen the layer under the coil area. A chemical mechanical polish (CMP) may then be done to eliminate the step and create a planar surface for the next layer. This solution introduces additional steps to the manufacturing process and makes excessive regions of hard bake resist. 
     Another method of planarization is to extend the layers under the coil to form planar surfaces for each subsequent layer. This makes layers that are unnecessarily large and not optimized. Extending the area of the pole pieces increases the risk of shorting between the lower pole piece and the shielding layer of the MR leads in the merged head. Additionally, extending the layers also extends the leads, which then increase lead resistance and the possibility of shorting between the leads and the shield layers. It is desirable to reduce the length and total area of the MR leads. 
     While prior art solutions, as indicated above, have described planar regions under the coil above the second shield layer (S 2 ) of the MR head, the remainder of the head is not planarized. This creates shorts or opens in the leads that connect the pads at the outer edge to the MR sensor and coil contacts. Excessive topography for the leads can result in shorting paths around the outside edges of the hard baked regions. Additionally, these leads and pads are separated from the substrate only by the undercoat increasing the chance of capacitance coupling between the conducting undercoat layer and the leads and pads. 
     From the above it becomes apparent that the prior art combination inductive write head with MR read head results in devices that create pseudo planar surfaces with additional problems or do not provide planarization over the entire head structure. What is needed then is a combination read/write head that planarizes the head to eliminate shorts or opens due to underpass features, S 1  shield or S 2  shield. Ideally, the improved head should reduce the amount of hard baked resist and optimize the width of the shield layers. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a merged magnetoresistive (MR) read head/inductive write head that improves the device topography by creating a planar surface such that the pads and leads are on the same plane. Additionally, the present invention discloses a head in which the shield layers may be optimized to be as small as possible while still shielding the MR sensor without concern for planarizing under the coil layer. To accomplish this, once the shield and sensor layers are formed, a planarizing layer of material is used, to not only planarize the area under the coil, but also to planarize the entire device surface, all the way out to the pads at the outer edge. 
     The unique design of the present invention offers many advantages over the prior art by virtually eliminating any shorts or opens of the leads due to steps. Other advantages of this design are that the separation between the leads and pads and substrate are substantially increased, thereby reducing the capacitance coupling between the conducting undercoat layer and the leads and pads. The first shield layer and the substrate may now be in direct contact (i.e., no undercoat alumina required). Reducing the size of the first shield layer also reduces the hard baked resist area, since the resist does not need to extend past the outer perimeter of the first shield layer, thus increasing the region where the pads can be safely positioned (i.e., the pads should not overlap any underlying hard baked resist). 
     The present magnetic merged MR head comprises a write head portion and a read head portion employing an MR sensor. The sensor is located between first and second gap layers and the gap layers are located between first and second shield layers. In a preferred embodiment, the first shield layer is essentially the same length as the second shield layer, which is shorter than the coil. In other embodiments, the second shield may be optimized to be shorter or longer depending on the minimum shielding requirements of the MR sensor used. To planarize the entire device at the second shield layer (the S 2  layer), a planarizing layer is used. The planarizing layer extends the plane defined by the top surface of the second shield layer to create a structure in which the pads and the leads are coplanar. 
     The write head portion of the merged MR head includes an inductive coil positioned inside of an insulation layer. A portion of the coil along with insulation layer are located between first and second pole piece layers while the remainder of the coil is inside of insulation layer being formed on the planarizing layer. In a preferred embodiment, the first pole piece layer (P 1 ) and the second shield layer (S 2 ) are a common layer The first and second pole piece layers and are magnetically coupled at a back gap and separated by a write gap layer at the ABS. 
     The coil and MR sensor are connected with leads to pads formed on the planarizing layer. The pads connect to the coil and MR sensor with leads. The leads for the MR sensor are connected to the sensor with vias while the leads for the coil is connected to the inner and outer coil tap. 
     A method of manufacture is disclosed on the construction of the combination inductive write head and MR read head. The head is fabricated from numerous layers of material starting with a first shield layer (S 1 ) that has been optimized for the sensor to be used is formed on a substrate. An insulation layer is next with upon which the sensor layer is placed comprising a MR or Giant MR (GMR) with sensor leads attached. An insulation layer is applied to cover the sensor and leads. The second shield layer (S 2 ) /first pole piece layer (P 1 ) is formed on the insulation layer. Because of the desire to planarize the head structure at a level with the top surface of the second shield layer, a planarization layer of material is applied to the substrate up to the top surface of the second shield layer. Chemical mechanical polishing (CMP) may be done make a smooth plane surface. The rest of the inductive head is now formed on the second shield layer/planarization layer including the coil embedded in insulation, the write gap layer and the second pole piece layer (P 2 ). The pads are formed on the plane surface along with the leads connecting the pads to the coils and MR sensor. 
     The nature, objects, and advantages of the invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a planar view of an exemplary magnetic disk drive; 
     FIG. 2 is an end view of a slider with a magnetic head of the disk drive as seen in plane  2 — 2 ; 
     FIG. 3 is an elevation view of the magnetic disk drive wherein multiple disks and magnetic heads are employed; 
     FIG. 4 is an isometric illustration of an exemplary suspension system for supporting the slider and magnetic head; 
     FIG. 5 is an ABS view of the magnetic head taken along plane  5 — 5  of FIG. 2; 
     FIG. 6 is a partial cross-sectional view of the prior art magnetic head as seen in plane  6 — 6  of FIG. 2; 
     FIG. 7 is a enlarged partial ABS view of the slider taken along plane  7 — 7  of FIG. 6 to show the read and write elements of the prior art magnetic head; 
     FIGS. 8 and 9 are views taken along plane  8 — 8  and  9 — 9  of FIG. 6 illustrating the prior art; 
     FIG. 10 is a partial cross-sectional view of the preferred embodiment magnetic head as seen in plane  10 — 10  of FIG. 2; 
     FIG. 11 is a view taken along plane  11 — 11 -of FIG.,  10  illustrating the present invention; 
     FIGS. 12A and 12B are views taken along plane  12 A— 12 A and  12 B— 12 B of FIG. 11 illustrating the present invention; and 
     FIGS. 13A-13D illustrate some of the processing steps to planarized the surface at the second shield layer. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein like reference numerals designate like or similar parts throughout the several views there is illustrated in FIGS. 1-3 a magnetic disk drive  30 . The drive  30  includes a spindle  32  that supports and rotates a magnetic disk  34 . The spindle  32  is rotated by a motor  36  that is controlled by a motor controller  38 . A read/write magnetic head  40  is mounted on a slider  42  that is supported by a suspension  44  and actuator arm  46 . A plurality of disks, sliders and suspensions may be employed in a large capacity direct access storage device (DASD) as shown in FIG.  3 . The suspension  44  and actuator arm  46  position the slider  42  so that the magnetic head  40  is in a transducing relationship with a surface of the magnetic disk  34 . When the disk  34  is rotated by the motor  36  the slider is supported on a thin (typically, 0.05 μm) cushion of air (air bearing) between the surface of the disk  34  and the air bearing surface (ABS)  48 . The magnetic head  40  may then be employed for writing information to multiple circular tracks on the surface of the disk  34 , as well as for reading information therefrom. Processing circuitry  50  exchanges signals, representing such information, with the head  40 , provides motor drive signals for rotating the magnetic disk  34 , and provides control signals for moving the slider to various tracks. In FIG. 4 the slider  42  is shown mounted to the suspension  44 . The components described hereinabove may be mounted on a frame  54  of a housing  55 , as shown in FIG.  3 . 
     FIG. 5 is an ABS view of the slider  42  and the magnetic head  40 . The slider has a center rail  56  that supports the magnetic head  40 , and side rails  58  and  60 . The rails  56 ,  58  and  60  extend from a cross rail  62 . With respect to rotation of the magnetic disk  34 , the cross rail  62  is at a leading edge  64  of the slider and the magnetic head  40  is at a trailing edge  66  of the slider. 
     Prior Art Merged MR Head 
     FIG. 6 is a side cross-sectional elevation view of the merged magnetic head  40  which has a prior art write head portion  70  and a read head portion  71 , the read head portion employing an MR sensor  74 . FIG. 7 is ABS view of FIG.  6 . The sensor  74  is located between first and second gap layers  76  and  78  and the gap layers are located between first and second shield layers  80  and  82 . In response to external magnetic fields, the resistance of the sensor  74  changes. A sense current I S  conducted through the sensor  74  causes these resistance changes to be manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry  50  shown in FIG.  3 . The shielding layers  80  and  82  typically comprise a soft ferromagnetic material such as sendust or NiFe, and are formed by conventional methods such as chemical vapor deposition (CVD) or sputtering or plating. Shield layer  80  is formed on a substrate  72 , being separated by a undercoat  73 . The gap layers  76  and  78  comprise any material suitable for electrically isolating the conductive layers of the read head, e.g., Al 2 O 3 , SiO 2 , etc. 
     The prior art write head portion  70  of the merged MR head includes an inductive coil layer  84  located in insulation layers  86  and  87 . The coil layer  84  and insulation layers  86  are located between first and second pole piece layers  92  and  94 . The first and second pole piece layers  92  and  94  are magnetically coupled at a back gap  96  and have first and second pole tips  98  and  100  which are separated by a write gap layer  102  at the ABS. An overpass conductor  90  provides electrical coupling between a write pad and the inner tap  91  of the inductive coil  84 . The conductor  90  has access to the inner coil tap  91  through a via  89  in the insulation  87 . 
     The coil  84  is provided with two electrical leads, at an inner tap  91  and at an outer tap (not shown). When a write current I in sent through the electrical leads and the coil  84 , the current I produces a flux. The flux provides a substantial magnetomotive potential difference between first pole tip  98  and second pole tip  100  which provides an efficient write process. 
     As shown in FIGS. 2 and 4, first and second terminal pads  104  and  106  connect to leads  112  and  114  on the suspension  44  and third and fourth terminal pads  116  and  118  connect to leads  124  and  126  on the suspension. A wear layer  128  may be employed for protecting the sensitive elements of the magnetic head, as shown in FIGS. 2 and 4. It should be noted that the illustrated magnetic head  40  employs a single layer  82 / 92  to serve a double function as a second shield layer S 2  for the read head and as a first pole piece PI for the write head. A piggyback MR head employs two separate layers for these functions. 
     FIG. 7 shows an ABS view of the read/write head  40 . FIGS. 8 and 9 show cross-sectional views of FIG.  6 . As can be seen, the layers used in forming the head  40  form a bulge with steps near the outer edges. Attempts have been tried to planarize the head  40  above the second shield layer  82  (S 2 ) level so that the layer for the coil  84  is relatively flat. Prior art heads accomplish this planarization by starting with an excessively large first shield layer  80 . As the layers are fabricated, hard bake resist is used to provide build up for the pseudo planarization for the coil  84 . As can be seen in the figure, this also creates steps for the leads  20  at the edge of the head  40  where the leads travel from the head  40  to the pads  21 . This excessive topography for the leads  20  can result in shorting paths around the edges  22  of the hard bake regions and shields. Additionally, the leads and pads are separated from the substrate by only the undercoat  73 . 
     The Invention 
     The merged read/write head  140  of the present invention improves the device topography by creating a planar structure such that the pads  121  and leads  120  are on the same plane. After the shield and sensor layers are formed, a planarizing layer of material is used, to not only planarize the area under the coil, but also planarize the entire device surface, all the way out to the pads at the outer edge. In this unique design, the leads connecting the MR sensor or coil and the pads are parallel to the substrate surface and on a plane defined by the top of the second shield layer S 2  (i.e., all the pads and leads are coplanar). This virtually eliminates any shorts or opens of the leads due to steps. Some of the advantages of this design are that the separation between the pads and substrate are substantially increased, thereby reducing the capacitance coupling between the conducting undercoat layer and the pads. The first shield layer and the substrate may now be in direct contact (i.e., no undercoat alumina required). Reducing the size of the first shield layer thereby reduces the hard baked resist area, since the resist does not need to extend past the outer perimeter of the first shield layer, thus increasing the region where the pads can be safely positioned (i.e., the pads should not overlap any underlying hard baked resist). 
     FIG. 10 is a side cross-sectional elevation view of the head  140  of the present invention which includes a write head portion  170  and a read head portion  171 , the read head portion  171  employing an MR sensor  174 . In response to external magnetic fields, the resistance of the MR sensor  174  changes. A sense current Is conducted through the MR sensor  174  causes these resistance changes to be manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry  50  shown in FIG.  3 . FIG. 11 shows a planar view with portions of the upper layers removed for clarity. FIGS. 12A and 12B show cross-sectional views of FIG.  10 . The sensor  174  is located between first and second gap layers  176  and  178  and the gap layers are located between first and second shield layers  180  and  182 . In the embodiment shown in FIG. 11, the first shield layer  180  is essentially the same length as the second shield layer  182 , which is shorter than coil  184 . In still other embodiments, the shields  180  and  182  may be shorter or longer depending on the minimum shielding requirements of the MR sensor  174  used. To planarize the entire device at the second shield layer  182  (the S 2  layer), a planarizing layer  188  is used. Planarizing layer  188  may be made of Al 2 O 3 . The shielding layers  180 ,  182  typically comprise a soft ferromagnetic material such as sendust or NiFe, and are formed by conventional methods such as chemical vapor deposition (CVD) or sputtering or plating. Shield layer  180  is formed on a substrate  172 , and may be separated by an undercoat  173 . The gap layers  176 ,  178  comprise any material suitable for electrically isolating the conductive layers of the read head, e.g., SiO 2 , etc. 
     The write head portion  170  of the merged MR head  140  includes an inductive coil  184 . The coil  184  is positioned inside of insulation layers  186  and  187 . A portion of the coil  184  along with insulation layer  186  are located between first and second pole piece layers  192  and  194 . The remainder of the coil is inside of insulation layers  186  and  187  being formed on the planarizing layer  188 . The first and second pole piece layers  192  and  194  are magnetically coupled at a back gap  196  and have first and second pole tips  198  and  200  which are separated by a write gap layer  202  at the ABS. An overpass conductor  190  provides electrical coupling between a pad  121  and the inner tap  220  of the inductive coil  184 . The conductor  190  has access to the inner coil tap  220  through a via  189  in the insulation  186 . As shown in FIGS. 2 and 4, first and second terminal pads  104  and  106  connect to leads  112  and  114  on the suspension  44 . Third and fourth terminal pads  116  and  118  connect to leads  124  and  126  on the suspension  44 . Leads  120  and pads  121  are formed on the planar layer. The leads  120  are connected by vias  123  and copper studs  125  to the MR sensor leads  145  and  146 . A wear layer (not shown) may be employed for protecting the sensitive elements of the magnetic head, as shown in FIGS. 2 and 4. It should be noted that the merged MR head  140  employs a single layer  182 / 192  to serve a double function as a second shield layer S 2  for the read head and as a first pole piece P 1  for the write head. A piggyback MR head employs two separate layers for these functions. 
     Method of Making 
     The various layers of the method of making are formed by sputter deposition or plating. Generally, the metallic layers are formed by plating and the non-conductive layers are formed by sputter deposition or forming hard baked photoresist. Sputter deposition is implemented in a vacuum chamber wherein a target of desired material is sputtered to a substrate via a plasma in the chamber because of an applied potential between the target and the substrate. Plating is a wet process wherein the wafer is placed in an electrolyte and a potential is applied between the surface to be plated and a plating material. Metallic ions from the plating material are then deposited on the desired surface. Masking is accomplished by photoresist masks which are spun onto the wafer, imaged with light and then portions to be removed are removed by a developer. Positive photoresist may be employed wherein the area of light imaging is removed by a developer to provide an opening for plating or a negative photoresist (cross-linked photoresist) may be employed where an area not imaged by light is removed by the developer to provide an opening for plating. After the desired layer is deposited the photoresist mask is then stripped by a dissolvent. Layer portions are removed by ion milling which, in essence, is particle bombardment of the layer with ions. It should be understood that these process steps are exemplary and there may be other steps well known in the art for forming the layers. 
     The shields and pole pieces are preferably Permalloy which is Ni 80 Fe 20 . If desired, a higher magnetic moment material may be employed for the second pole piece such as Ni 45 Fe 55 . The insulation layers of the insulation are preferably photoresist, except the first insulation layer and the planarizing layer which are preferably alumina (Al 2 O 3 ). Because of the present inventions unique design of minimizing the shield layers, the amount of photoresist is also minimized. After each photoresist layer is patterned, it is hard baked, such as at a temperature of 200° C., which provides each layer with sloping surfaces at its edges. Optionally, the insulation layers may be another insulation material, such as alumina (Al 2 O 3 ) or silicon dioxide (SiO 2 ). The write gap layer is preferably alumina and formed by sputtering. The pole piece layers are frame plated which comprises patterning with photoresist, plating into the opening in the photoresist and then removing the photoresist. If the pole piece layer is formed on a nonmagnetic layer, such as alumina or baked photoresist, a seedlayer, such as copper or Permalloy, is sputtered on the layer to provide a return path for electroplating. A copper seedlayer is employed before the frame plating of a coil layer, after which the seedlayer is removed by ion milling without any patterning. Accordingly, the ion milling step for removing the seedlayer, after frame plating a coil layer, ion mills all of the surfaces of the wafer upon which rows and columns of heads are normally constructed. A metallic layer is normally constructed by frame plating. Frame plating comprises sputtering a seedlayer on the underlying layer if the underlying layer is electrically non-conductive, spinning a photoresist layer on the underlying layer, light imaging the photoresist layer in areas that are to be opened, developing the exposed regions of the photoresist to provide openings, or an opening, exposing the seedlayer where a metallic layer is to be plated, plating the metallic layer by electroplating, stripping the photoresist layer with a solvent and removing any seedlayer by ion milling. 
     FIGS. 13A-13D illustrated a planarization process for the formation of a planarized surface at the S 2  (second shield) layer. The first shield layer  180  is formed on a substrate  172 . Optionally, a layer of undercoat  173  may be positioned between the first shield layer  180  and the substrate  172 . The first shield layer  180  being sized to shield the MR sensor  174 . A first gap layer  176  is formed on the first shield layer  180  by conventional means. The MR sensor  174  is then formed by subtractive etching or another suitable process, and sensor leads  144  and  145  are formed thereon by methods such as electroplating or sputtering. A second gap layer  178  is then formed over the sensor  174  and leads  144  and  145 . The second shield layer  182  is formed over the second gap layer  178  completing the read portion  171  of the head  140 . Vias  123  are opened to expose the sensor leads. Copper studs  125  are plated into the vias to a thickness greater than the height of the S 2  (second shield  182 ) surface. To planarize the head at the S 2  level, a planarizing layer  188  is applied. Planarizing layer  188  is preferably made from a electrically isolating material, such as Al 2 O 3  and may be fabricated on a single layer (as shown in the figures) or may be separate layers. Once formed, the planarization layer  188  may be planarized by chemical mechanical polishing (CMP) or other suitable means of planarization to form a planar surface. Once planarized, as shown in FIG. 13D, the write portion  170  of the head  140 , along with pads  121  and leads  120  are fabricated on the planar surface. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.