Patent Publication Number: US-6339523-B1

Title: Write head before read head constructed magnetic head with track width and zero throat height defined by first pole tip

Description:
REFERENCE TO RELATED APPLICATION 
     This is a continuation application of application Ser. No. 09/058,521 filed Apr. 10, 1998, now U.S. Pat. No. 6,130,809. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a write head before read head constructed merged magnetic head with the track width and the zero throat height of the write head being defined by a first pole tip and more particularly to a magnetic head wherein a first pole tip of a first pole piece is frame plated on a planarized surface so as to accurately define the track width of the write head with high resolution and wherein planarization after constructing the first pole tip reduces separation between read and write gaps of the magnetic head. 
     2. Description of the Related Art 
     An inductive write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being located 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. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing bits of magnetic field information in tracks on moving media, such as in circular tracks on a rotating magnetic disk or longitudinal tracks on a moving magnetic tape. 
     The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium. Since magnetic flux decays as it travels down the length of the narrow second pole tip, shortening the second pole tip will increase the flux reaching the recording media. Therefore, performance can be optimized by aggressively placing the flare point close to the ABS. 
     Another parameter important in the design of a write head is the location of the zero throat height (ZTH). The zero throat height is the location where the first and second pole pieces first separate from one another after the ABS. ZTH separation is imposed by an insulation layer, typically the first insulation layer in the insulation stack. Flux leakage between the first and second pole pieces is minimized by locating the ZTH as close as possible to the ABS. 
     Unfortunately, the aforementioned design parameters require a tradeoff in the fabrication of the second pole tip. The second pole tip should be well-defined in order to produce well-defined written tracks on the rotating disk. Poor definition of the second pole tip may result in overwriting of adjacent tracks. A well-defined second pole tip should have parallel planar side walls which are perpendicular to the ABS. This definition is difficult to achieve because the second pole tip is typically formed along with the yoke after the formation of the first insulation layer, the coil layer and the second and third insulation layers. Each insulation layer includes a hard-baked photoresist having a sloping front surface. 
     After construction, the first, second and third insulation layers present front sloping surfaces which face the ABS. The ZTH defining layer rises from a plane normal to the ABS at an angle (apex angle) to the plane. After hard baking of the insulation layers and deposition of a metallic seedlayer the sloping surfaces of the insulation layers exhibit a high optical reflectivity. When the second pole tip and yoke are constructed, a thick layer of photoresist is spun on top of the insulation layers and photo patterned to shape the second pole tip, using the conventional photo-lithography technique. In the photo-lithography light imaging step, ultraviolet light is directed vertically through slits in an opaque mask, exposing areas of the photoresist which are to be removed by a subsequent development step. One of the areas to be removed is the area where the second pole piece (pole tip and yoke) is to be formed by plating. Unfortunately, when ultraviolet light strikes the sloping surfaces of the insulation layers in a flaring region of the second pole piece, the ultraviolet light is reflected forward, toward the ABS, into photorresist areas at the sides of the second pole tip region. After development, the side walls of the photoresist extend outwardly from the intended ultraviolet pattern, causing the pole tip plated therein to be poorly formed. This is called “reflective notching”. As stated hereinabove this causes overwriting of adjacent tracks on a rotating disk. It should be evident that, if the flare point is recessed far enough into the head, the effect of reflective notching would be reduced or eliminated since it would occur behind the sloping surfaces. However, this solution produces a long second pole tip which quickly reduces the amount of flux reaching the recording medium. 
     The high profile of the insulation stack causes another problem after the photoresist is spun on a wafer. When the photoresist is spun on a wafer it is substantially planarized across the wafer. The thickness of the resist in the second pole tip region is higher than other regions of the head since the second pole tip is substantially lower on the wafer than the yoke portion of the second pole piece. During the light exposure step the light progressively scatters in the deep photoresist like light in a body of water causing poor resolution during the light exposure step. 
     A scheme for minimizing the reflective notching and poor resolution problems is to construct the second pole piece with bottom and top second pole tips. The bottom second pole tip is constructed before the insulation layers to eliminate the reflective notching problem. After forming the first pole piece layer and the write gap layer, a photoresist layer is spun on the partially completed head. Ultraviolet light from the photo-patterning step is not reflected forward since the photoresist layer does not cover an insulation stack. Further, the photoresist is significantly thinner in the pole tip region so that significantly less light scattering takes place. After plating the bottom second pole tip the photoresist layer is removed and the first insulation layer, the coil layer and the second and third insulation layers are formed. The top second pole tip is then stitched (connected) to the bottom second pole tip and extends from the ABS to the back gap. Since the bottom second pole tip is well-formed, well-formed notches can be made in the first pole piece, as discussed hereinafter. However, with this head, the ZTH is dependent upon the location of the recessed end of the bottom second pole tip. Since the bottom second pole tip has to be long enough to provide a sufficient stitching area, this length may result in undesirable flux leakage between the first and second pole pieces. Since the top second pole tip is typically wider than the bottom second pole tip, the second pole piece has a T-shape at the ABS. The upright portion of the T is the front edge of the bottom second pole tip, and the cross of the T is the front edge of the top second pole tip. A problem with this configuration is that during operation, flux fringes from the outer corners of the top second pole tip to a much wider first pole piece at the ABS, causing adjacent tracks to be overwritten. 
     Once the bottom second pole tip is formed, it is desirable to notch the first pole tip of the first pole piece opposite the first and second corners at the base of the bottom second pole tip so that flux transfer between the pole tips does not stray beyond the track width defined by the bottom second pole tip. Notching provides the first pole piece with a track width that substantially matches the track width of the bottom second pole tip. A prior art process for notching the first pole piece entails ion beam milling the gap layer and the first pole piece, employing the bottom second pole tip as a mask. The gap layer is typically alumina and the first and second pole pieces and pole tips are typically Permalloy (NiFe). The alumina mills more slowly than the Permalloy; thus the top of the bottom second pole tip and a top surface of the first pole piece are milled more quickly than the gap layer. Further, during ion milling, there is much redeposition (redep) of alumina on surfaces of the workpiece. In order to minimize redep, the milling ion beam is typically directed at an angle to a normal through the layers, which performs milling and cleanup simultaneously. The gap layer in the field remote from the first and second corners of the bottom second pole tip is the first to be milled because of a shadowing effect at the first and second corners caused by the bottom second pole tip when the ion beam is angled. In this case, the ion stream will overmill the first pole piece before the gap layer is removed adjacent the first and second corners of the bottom second pole tip in the region where the notching is to take place. After the gap layer is removed above the sites where the notching is to take place, ion milling continues in order to notch the first pole piece. Overmilling of the first pole piece continues to take place in the field beyond the notches, thereby forming surfaces of the first pole piece that slope downwardly from the notches. As is known, such overmilling of the first pole piece can expose leads to the MR sensor, thereby rendering the head inoperative. 
     Even if overmilling of the first pole piece can be controlled, there is potentially a more troublesome problem, namely overmilling the top of the bottom second pole tip when the unwanted portions of the gap layer are milled and notches are formed. In order to compensate for this overmilling, the aspect ratio (ratio of thickness of photoresist to track width of the bottom second pole tip) is increased so that a top portion of the top of the bottom second pole tip can be sacrificed during the milling steps. When the aspect ratio is increased, definition of the bottom second pole tip is degraded because of the thickness of the photoresist, discussed hereinabove, resulting in track overwriting. 
     Another problem with the prior art merged MR head is that the profile of the MR sensor between the first and second gap layers is replicated through the second shield/first pole piece layer to the write gap layer causing the write gap layer to be slightly curved concave toward the MR sensor. When the write head portion of the merged MR head writes data the written data is slightly curved on the written track. When the straight across MR sensor reads this curved data there is progressive signal loss from the center of the data track toward the outer extremities of the data track. 
     All merged magnetic heads have a separation between the read and write gaps. This separation causes misregistration between the read and write gaps when the magnetic head is located at outer tracks on the magnetic disk. In the magnetic disk drive, an actuator swings the magnetic head across the rotating disk to various circular tracks on the disk. At the innermost track the read and write gaps are substantially aligned with one another and there is substantially no misregistration. At the innermost track the read gap follows within the track written by the write gap. However, when the actuator swings the magnetic head to the outermost track the read and write gaps are misaligned with respect to the track. If the write gap is within the track being written the read gap may be partially in the track and partially in an adjacent track. The misregistration increases with an increase in the separation between the read and write gaps. In magnetic heads where the write head is constructed before the read head the profile of the insulation stack of the write head raises the height of the first shield layer of the read head. It would be desirable if this profile could be reduced so that the read and write gaps are closer together. 
     Still another problem with prior art magnetic heads is that heating of high magnetic moment pole tips risks damage to the read sensor of the read head. A high magnetic material is Ni 45 Fe 55  as compared to Ni 80 Fe 20 . Pole tips constructed of high magnetic material are desirable because they will conduct higher flux density without saturating. A still further problem with prior art magnetic heads is the risk of shorting of lead layers in the read head through the first read gap layer to the first shield layer. The first and second read gap layers are purposely very thin so as to narrow the read gap and increase linear bit density reading capability. Pinholes are more likely at steps in the first read gap layer than in flat portions of the first read gap layer. It is desirable that the partially completed magnetic head be planarized before the first read gap layer is constructed so as to reduce the chance of pinholes. The lack of planarity can cause still another problem in the construction of one or more coil layers. If there is a step, such as at a side edge of the first pole piece layer, this will cause reflective notching in adjacent portions of a photoresist layer employed to construct the coil layer. 
     SUMMARY OF THE INVENTION 
     The advantages of the present invention are as follows: (1) substantially eliminate reflective notching and increase resolution of a photoresist pattern for constructing a pole tip that defines the track width of the head, (2) eliminate write gap curvature, (3) lower the insulation stack so that the read and write gaps are closer together, (4) planarize the construction of the partially completed head at various steps so that frame plating of metallic layers is more accurate, (5) high temperature construction of high magnetic moment pole tips without risking damage to the read sensor, (6) construction of a first read gap layer on a planarized first shield layer so as to minimize shorting of the lead layers to the first shield layer and (7) eliminate reflective notching of a photoresist pattern for constructing a coil layer. 
     In the present invention the write head of the merged magnetic head is constructed before the read head. In one embodiment a first pole piece layer is formed on a wafer with front and back upstanding components to form a recess between the components in a yoke region of the head. An insulation material, such as alumina, is deposited over the entire wafer. The wafer is then lapped until tops of the front and back components are exposed leaving a bed of flat alumina therebetween, as well as flat alumina portions adjacent side edges of the first pole piece layer. A first coil can then be frame plated on the flat alumina portions with high resolution. The front and back components are then built up higher by frame plating followed by deposition of alumina and lapping to planarize the construction. A second coil may then be formed on the planar alumina surface. 
     A highly defined front component, which comprises the first pole tip, may then be frame plated on the flat alumina layer with substantially no reflective notching along with a back component which comprises a back gap. Alumina may then be deposited and lapped until top surfaces of the pole tip and the back gap are exposed. After deposition of a gap layer a flat second pole piece/first shield layer is frame plated followed by deposition of another alumina layer and lapping until the partially completed head is planar. Then a first read gap layer, read sensor first and second lead layers and a second read gap layer are formed. The front components, other than the first pole tip, can be at or recessed from the ABS. Further, the first pole tip may be constructed before the second coil layer or on a flat alumina layer after forming the second coil layer. 
     With the present invention the insulation stack can be recessed with respect to the write gap so that the profile of the insulation stack does not contribute to the separation between the read and write gaps. Since the read head is constructed after the write head, high temperatures can be employed in the construction of a high magnetic moment first pole tip without damaging the read sensor. Since the partially completed head is planarized before construction of a coil layer a more highly defined coil layer can be constructed. Another embodiment of the invention is a single coil magnetic head constructed similarly to that described for the double coil magnetic head. 
     An object of the present invention is to substantially eliminate reflective notching and increase resolution of a photoresist pattern for constructing a pole tip that defines the track width of a write head before read head constructed merged magnetic head. 
     Another object is to eliminate write gap curvature. 
     A further object is to lower an insulation stack so that the read and write gaps are closer together. 
     Yet another object is to planarize the construction of a partially completed magnetic head at various steps so that frame plating of metallic layers is more accurate. 
     Still another object is to employ high temperature construction of high magnetic moment pole tips without risking damage to a read sensor. 
     Still a further object is to construct a first read gap layer without steps so as to minimize shorting of first and second lead layers to a first shield layer. 
     Still another object is to eliminate reflective notching of a photoresist pattern for constructing a coil layer. 
     Other objects and attendant advantages of the invention will become apparent upon reading the following description taken together 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 view of the slider and a prior art magnetic head as seen in plane  6 — 6  of FIG. 2; 
     FIG. 7 is a 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; 
     FIG. 8 is a view taken along plane  8 — 8  of FIG. 6 with all material above the second pole piece removed; 
     FIG. 9 is an enlarged front portion of the prior art magnetic head of FIG. 6 to show various details thereof; 
     FIG. 10 is the same as FIG. 9 except a photo-patterning step is illustrated for constructing the second pole tip of the magnetic head; 
     FIG. 11 is a view taken along plane  11 — 11  of FIG. 9; 
     FIG. 12 is a view taken along plane  12 — 12  of FIG. 10; 
     FIG. 13 is an isometric illustration of FIG. 10 without the P 2  photoresist; 
     FIG. 14 is an ABS view of a prior art merged MR head before notching of the first pole piece; 
     FIG. 15 is an ABS view of the merged MR head shown in FIG. 14 after ion milling to form the first pole piece with notches adjacent the second pole tip; 
     FIG. 16 is an isometric illustration of an embodiment of the present invention which has a double coil and a single first pole tip (pole tip design) at an air bearing surface; 
     FIG. 17 is an isometric illustration of the first pole piece and first pole tip of the pole tip design shown in FIG. 16; 
     FIG. 18 is a longitudinal cross-section through the pole tip design employing a double coil; 
     FIG. 19 is a longitudinal cross-sectional view of another embodiment of the pole tip design employing a single coil; 
     FIG. 20 is a schematic ABS illustration of an embodiment of the pole tip design; 
     FIG. 21 is a schematic ABS illustration of another embodiment of the pole tip design; 
     FIG. 22 is an isometric illustration of another embodiment of the magnetic head employing a double coil and top and bottom first pole tips which is referred to as a lip design; 
     FIG. 23 is an isometric illustration of the first pole piece of the embodiment shown in FIG. 22 showing a bottom first pole tip which looks like a lip and a top first pole tip which is a pedestal; 
     FIG. 24 is a longitudinal cross-sectional view through the embodiment shown in FIG. 22; 
     FIG. 25 is a longitudinal cross-sectional view through another embodiment of the lip design showing a single coil layer; 
     FIG. 26 is an ABS illustration of one embodiment of the lip design; 
     FIG. 27 is an ABS illustration of another embodiment of the lip design; 
     FIG. 28 is an ABS illustration of a further embodiment of the lip design; 
     FIG. 29A is a longitudinal cross-sectional view of a first step of plating a bottom layer portion of a first pole piece on a wafer; 
     FIG. 29B is the same as FIG. 29A except front and back components of the first pole piece have been formed; 
     FIG. 29C is the same as FIG. 29B except alumina is deposited on the wafer: 
     FIG. 29D is an ABS illustration taken along plane  29 D— 29 D of FIG. 29C; 
     FIG. 29E is the same as FIG. 29C except the wafer has been lapped so that all surfaces are flush with respect to one another; 
     FIG. 29F is an ABS view taken along plane  29 F— 29 F of FIG. 29E; 
     FIG. 29G is the same as FIG. 29E except a first coil layer has been frame plated on the wafer; 
     FIG. 29H is the same as FIG. 29G except front and back components of the first pole piece have been frame plated; 
     FIG. 29I is the same as FIG. 29H except alumina has been deposited on the wafer; 
     FIG. 29J is an ABS illustration taken along plane  29 J— 29 J of FIG. 29I; 
     FIG. 29K is the same as FIG. 29I except the wafer has been lapped until all surfaces are flush with respect to one another; 
     FIG. 29L is an ABS view taken along plane  29 L— 29 L of FIG. 29K; 
     FIG. 29M is the same as  29 K except a seedlayer has been deposited; 
     FIG. 29N is the same as FIG. 29M except a second coil layer has been frame plated; 
     FIG. 29O is the same as FIG. 29N except a photoresist pattern has been formed; 
     FIG. 29P is a view taken along plane  29 P— 29 P of FIG. 29O; 
     FIG. 29Q is the same as FIG. 29O except a first pole tip and a back gap portion have been frame plated; 
     FIG. 29R is a view taken along plane  29 R— 29 R of FIG. 29Q; 
     FIG. 29S is the same as FIG. 29Q except the photoresist pattern has been removed; 
     FIG. 29T is an ABS view taken along plane  29 T— 29 T of FIG. 29S; 
     FIG. 29U is the same as FIG. 29S except an alumina layer has been deposited; 
     FIG. 29V is an ABS view taken along plane  29 V— 29 V of FIG. 29U; 
     FIG. 29W is the same as FIG. 29U except the wafer has been lapped until all surfaces are flush with respect to one another; 
     FIG. 29X is a view taken along plane  29 X— 29 X of FIG. 29W; 
     FIG. 29Y is the same as FIG. 29W except a write gap layer has been deposited; 
     FIG. 29Z is an ABS view taken along plane  29 Z— 29 Z of FIG. 29Y; 
     FIG.  29 AA is the same as FIG. 29Y except a second pole piece/first shield layer has been frame plated; 
     FIG.  29 AB is an ABS view taken along plane  29 AB— 29 AB of FIG.  29 AA; 
     FIG.  29 AC is the same as FIG.  29 AA except a layer of alumina has been deposited on the wafer; 
     FIG.  29 AD is a view taken along plane  29 AD— 29 AD of FIG.  29 AC; 
     FIG.  29 AE is the same as FIG.  29 AC except the wafer has been lapped until all surfaces are flush with respect to one another; 
     FIG.  29 AF is a view taken along plane  29 AF— 29 AF of FIG.  29 AE; 
     FIG.  29 AG is the same as FIG.  29 AE except a first read gap, a read sensor, first and second lead layers, a second read gap and a second shield layer have been formed; and 
     FIG.  29 AH is an ABS view taken along plane  29 AH— 29 AH of FIG.  29 AG. 
     FIG. 30 is a block diagram of another method of the invention; 
     FIG. 31 is a block diagram of a further method of the invention; 
     FIG. 32 is a block diagram of yet another method of the invention; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Magnetic Disk Drive 
     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  2  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 combined read and 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) a s shown in FIG.  3 . The suspension  44  and actuator arm  46  position the slider  42  so that the magnetic head  4  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 , 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 MR head  40  which has a prior art write head portion  70  and a read head portion  72 , the read head portion employing an MR sensor  74 . FIG. 7 is an 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 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 prior art write head portion of the merged MR head includes a coil layer  84  located between first and second insulation layers  86  and  88 . A third insulation layer  90  may be employed for planarizing the head to eliminate ripples in the second insulation layer caused by the coil layer  84 . The first, second and third insulation layers are referred to in the art as an “insulation stack”. The coil layer  84  and the first, second and third insulation layers  86 ,  88  and  90  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. As shown in FIGS. 2 and 4, first and second solder connections  104  and  106  connect leads from the sensor  74  to leads  112  and  114  on the suspension  44  and third and fourth solder connections  116  and  118  connect leads  120  and  122  from the coil  84  (see FIG. 8) 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,  4 ,  6  and  7 . It should be noted that the merged MR head  40  employs a single layer  82 / 92  to serve a double function as a second shield layer for the read head and as a first pole piece for the write head. A piggyback MR head employs two separate layers for these functions. 
     As shown in FIG. 9, the second pole piece layer  94  has a pole tip region and a yoke region, the merging of these components being defined by a flare point  130  which is the location where the second pole piece layer  74  begins to widen as it recesses in the head. The second pole tip region extends from the ABS to the flare point  130 , and the yoke region extends from the flare point  130  to the back gap  96  (see FIG.  6 ). In FIG. 12 are shown the pole tip region, the yoke region and the flare point  130  as defined by a photoresist mask (P 2  frame). 
     The location of the flare point  130 , shown in FIGS. 9,  12  and  13 , is an important design parameter of the write head. The further the flare point is recessed into the head, the longer the pole tip  100 , which increases magnetic inductance and the likelihood that the pole tip  100  will saturate in response to flux from the coil layer  84 . In the past it has been difficult to locate the flare point closer to the ABS than 10 μm because of a fabrication problem in making the second pole tip. 
     Another important design parameter in making the write head is the location of a zero throat height (ZTH), which is where the first and second pole piece layers  92  and  94  first separate from one another behind the ABS. It is important to locate the ZTH as close as possible to the ABS (typically within about 1 μm) in order to reduce flux loss between the pole pieces before the fields reach the gap layer  102  at the ABS. In the prior art, locating the ZTH close to the ABS contributed to the aforementioned problem of fabricating a well-defined second pole tip  100 . 
     FIG. 10 shows the prior art head of FIG. 9 during the step of constructing the second pole piece  94  (see FIG.  9 ). In FIG. 10 the first, second and third insulation layers  86 ,  88  and  90  are shown with sloping surfaces  132 ,  134  and  136  respectively, which terminate at apexes  138 ,  139  and  140  respectively. As stated hereinabove, the first, second and third insulation layers are hard-baked photoresist which results in the sloping surfaces  132 ,  134  and  136  being highly reflective to light. All of the sloping surfaces  132 ,  134  and  136  face the pole tip region where the second pole tip  100  of the second pole piece  94  is to be formed. As shown in FIG. 10, the second pole piece is formed with a photoresist layer  141  that is spun on top of the partially completed head. The height of the photoresist layer may be as much as 12 μm thick in the pole tip region and is typically approximately 4.5 μm thick above the third insulation layer  90 . Since the flare point  130  of the second pole piece  94  (shown in FIGS. 9,  12  and  13 ) is located on the sloping surfaces of the insulation layers, light directed through a second pole-shaped opening (not shown) in a mask  142  will be reflected from the sloping surfaces forward toward the ABS into areas of the photoresist layer  141  adjacent the pole tip region. This causes the pole tip region to be wider than the opening in the mask  142 . This is referred to as “reflective notching” and is illustrated in FIG.  12 . 
     The photoresist pattern for the second pole piece is shown in FIG. 12 at  94 ′ which comprises the second pole tip pattern  100 ′ and the second pole piece yoke pattern  103 ′. This is referred to as the “P 2  frame”. Reflective notching of the photoresist layer  141  (see FIG. 10) by light reflected at an angle of incidence from the sloping layers of the insulation layers is shown at  144  and  146  in FIG.  12 . When light ray A is directed downwardly during the photo-imaging step of the photoresist, it is reflected at an angle of incidence from the insulation stack into the pole tip region without causing any reflective notching of the second pole tip. However, light ray B from the photo-imaging process is reflected from the sloping surfaces of the insulation layers behind the flare point  130  at an angle of incidence into the photoresist  141  in a side region outside the intended pole tip pattern  100 ′. It is light reflection B and similar light reflections that cause the reflective notching shown in FIG.  12 . 
     When the second pole piece  94  is plated and the photoresist layer  141  is removed the head is complete, as shown in FIG.  9 . However, the pole tip  100  is poorly formed, exhibiting irregular side walls  148  and  150 , as shown in FIG.  11 . Furthermore, photoresist notching results in a second pole tip  100  that has wider areas at the upper pole tip region than at the base of the pole tip (adjacent the write gap). If the irregular second pole tip  100  is used as a milling mask to notch the first pole tip  98 , the wider regions of the second pole tip shadows the milling beam. Thus, the milling process is less effective at removing the first pole tip material directly beneath the side walls of the second pole tip. This results in a poorly formed P 1  notched write head structure due to incomplete notching of the first pole piece  72 . These poorly formed pole tips result in side writing of adjacent tracks. 
     FIG. 14 is an ABS view of a prior art merged magnetic head  150  after a P 2  seedlayer (not shown) has been removed by ion milling. It can be seen that the ion milling has slightly notched the gap layer  102  at  154  and  156 . One method of notching the first pole piece layer  82 / 92  in the prior art is to ion mill through the gap layer into the first pole piece layer as shown in FIG.  15 . This notches the first pole piece layer at  159  and  160 . Notching of the first pole piece layer  82 / 92  is desirable since it minimizes side writing between the second pole tip  100  and the first pole piece  82 / 92 . Unfortunately, the process shown in FIG. 15 results in consumption of a top surface  159  of the second pole tip  100 , as shown by the phantom lines in FIG.  15 . Since ion milling is typically performed at an angle to a normal to the thin film layers, as shown in FIG. 15, the second pole tip  158  shadows the milling of the notching at  159  and  160  approximately 50% of the time while the workpiece is rotated. Consequently, the first pole piece  82 / 92  is overmilled in locations  164  and  166  which extend in the field remote from the notches  159  and  160  respectively. This causes the first pole piece  82 / 92  to have downwardly sloping top surfaces  164  and  166 , as shown in FIG. 15, which undesirably reduces the thickness of the first pole piece  82 / 92  in the field. This can potentially expose sensitive elements beneath the first pole piece  82 / 92  rendering the head inoperative. The gap layer  102  mills more slowly than the Permalloy (NiFe) of the first and second pole pieces which results in more rapid ion milling of the top  159  of the second pole tip  100  and the fields  164  and  166  of the first pole piece  82 / 92  than the gap layer  102 . 
     It can be seen from FIG. 15 that the beginning thickness of the second pole tip layer  100  has to be thicker than the final height of the second pole tip layer at  159  in order to compensate for the top portion of the second pole tip layer consumed by ion milling. This then requires the photoresist mask to be thicker which increases the aforementioned problem of additional light scattering during the light photo-imaging step as the photoresist layer increases in depth. This means that the second pole tip cannot be constructed as narrow because of loss of definition during the photoresist patterning. FIG. 15 also shows the write gap  102  slightly curved due to the profile of the MR sensor being replicated through the second shield first pole tip layer  82 / 92  to the gap layer  102 . Accordingly, it can now be seen that the prior art merged MR head suffers from the disadvantages of reflective notching of the second pole tip, loss of a top portion of the second pole tip upon notching the first pole piece and write gap curvature. These problems are overcome by the inverted merged MR head described hereinbelow. 
     Another problem with the prior art head in FIGS. 14 and 15 is that the write gap  102  has a curvature due to replication of the profile of the MR sensor by the second gap layer  78  and the second shield/first pole piece layer  82 / 92 . As discussed hereinabove, this causes information to be written in a curve across a track which is inaccurately read by the straight MR sensor  74 . 
     The Invention 
     FIGS. 16 and 18 show a first embodiment  200  of the present invention wherein a read head portion of a merged magnetic head is constructed on top of a write head portion. The write head includes first and second pole pieces  202  and  204  (P 1  and P 2 ), respectively, which are separated by a gap layer  206  at the ABS to form a write gap therebetween and are connected at a back gap  208 . An insulation stack  210  is located vertically between the first and second pole pieces and horizontally between the air bearing surface (ABS) and the back gap  208 . First and second coil layers  212  and  214  may be embedded in the insulation stack with the first coil  212  being separated from the first pole piece  202  by a first insulation layer  216 , the first and second coil layers being separated from one another by a second insulation layer  218  and the second coil layer  214  being insulated from the second pole piece  204  by a third insulation layer  220 . During construction of the write head portion, the top surfaces of each of these insulation layers are planarized with respect to top surfaces of front and rear components of the first pole piece, which will be discussed in more detail hereinafter under the method of construction. 
     The first pole piece includes a first pole piece layer  222  which has an intermediate component  224  between front and rear components  226  and  228 . Each of these components has top and bottom surfaces which are substantially flat and define a planar surface. A first pole tip  230  is located on the front component of the first pole piece layer and has a width at the ABS which defines the track width (TW) of the write head, as shown in FIGS. 20 and 21. The first pole tip also has a back wall  232  that defines a zero throat height (ZTH) of the write head where the first and second pole pieces first commence to separate from one another after the ABS. The flare point of the head, which is where the first pole piece layer  222  first commences to widen after the ABS, is shown at  234 . The pole tip region of the head is defined between the ABS and the flare point. As shown in FIG. 18, the write head portion has a yoke region which is located between the pole tip region and the back gap region. The first pole tip  230  is the only pole tip of the first pole piece and is connected to the front component  226 . Accordingly, the head shown in FIGS. 16-21 is referred to as a pole tip design since there is no bottom first pole tip. This is clearly shown in FIG. 17 where only the front portion of the bottom pole piece  202  is illustrated. The first pole tip  230  has a substantially uniform width from its top to its bottom which defines the track width of the head. The first pole tip can be easily constructed by frame plating on a planar surface, which will be discussed in more detail hereinafter, and has a back wall  232  that defines the zero throat height with great accuracy. The frame plating of the first pole tip on a planar surface also eliminates reflective notching and promotes high resolution of the side walls of the first pole tip. The first pole tip  230  can be a high moment magnetic material, such as Ni 45 Fe 55 , since it is constructed separately from the remainder of the first pole piece  202 . This high moment material can be annealed at a high temperature without damage of a read sensor, which is to be described hereinafter. Since the insulation layers of the insulation stack  208  are planarized at each step, the coil layers  212  and  214  can be frame plated without reflective notching with high resolution of their side walls. 
     After planarizing the top insulation layer  220  with the top of the first pole tip  230  the write gap layer  206  is deposited, which extends from the ABS to the back gap  208 . Accordingly, a second pole piece/first shield layer  204  (P 2 /S 1 ) can be a substantially flat layer. This enables the following layers, namely the first and second read gap layers  238  and  240 , a read sensor  242  and first and second lead layers  244  and  245  located between the first and second read gap layers and a second shield layer  246  (S 2 ) to be planar. This is especially important for the first read gap layer  238  since steps in the second pole piece/first shield layer  204  risk pinholes in the first read gap layer, which allow the first and second lead layers  244  and  245  to short to the second pole piece/first shield layer  204 . 
     The preferred material for the insulation layers of the insulation stack  210  and the extensions of these layers beyond side edges of the first pole piece layer  202  is alumina or silicon dioxide in lieu of baked photoresist. The extensions of these layers beyond the side edges  247  and  248  of the first pole piece layer  202 , which are shown hereinafter in the method of making, provide flat surfaces for the construction of the first and second coil layers  212  and  214 . The construction of the first insulation layer  216  (see FIG. 18) fills in the steps caused by the first and second side edges  247  and  248  of the first pole piece layer  202  so as to promote planarization. 
     Another embodiment  250  of the pole tip design is shown in FIG. 19 which employs a single coil layer  252  in lieu of a double coil layer. As in the double coil layer embodiment, the first pole piece  254  includes an intermediate component  256  between front and rear components, the front component being shown at  258 . The front component  258  extends to the ABS and the first pole tip  262  is constructed thereon. The front component  258  and the first pole tip  262  have the same width which defines the track width (TW) of the head. The insulation stack  264  has first, second and third insulation layers  266 ,  268  and  270  with the coil layer  252  on the first insulation layer  266 . The second insulation layer  268  is planarized with the top surface  270  of the front component so that the first pole tip  262  can be constructed with a photoresist frame on a flat surface. 
     FIG. 20 is an ABS illustration of either of the embodiments shown in FIGS. 18 or  19 . FIG. 21 is an alternative embodiment wherein the second pole piece  204  has a bottom second pole tip  272  (P 2 B) and a top second pole tip  274  (P 2 T). The bottom second pole tip  272  has substantially the same width as the first pole tip  230  and is separated therefrom by the write gap layer  206 . This embodiment is referred to in the art as being notched since the bottom second pole tip  272  is the same width as the first pole tip  230 . The purpose of the notched configuration is to slightly increase side writing between the pole pieces which has the effect of writing a guard band of noise on each side of the written track so that when the track is read by the read head a slight misregistration will not cause the read head to read data on an adjacent track. In the construction of the embodiment shown in FIG. 21, the bottom second pole tip  272  can be frame plated after electroplating the write gap of NiP or Pd or Ir followed by the deposition of alumina and lapping to make a planar surface for the construction of the top second pole tip. 
     Another embodiment  300  of the merged magnetic head is shown in FIGS. 22-28. This embodiment differs from the first embodiment in that the front component  302  of the first pole piece  301  has a width at the ABS that is wider than the first pole tip  304 . Accordingly, the front component  302  forms a bottom first pole tip  306  (P 1 B) and the pole tip thereon is a top first pole tip  304  (P 1 T). The top first pole tip  304  defines the track width (TW) of the head, as shown in FIGS. 26-28. Except for the front component  302  defining a bottom first pole tip  306 , the double coil head shown in FIGS. 22 and 24 is the same as the first embodiment shown in FIGS. 16 and 18. FIG. 23 shows more clearly the front portion  302  of the first pole piece  301  wherein the wide expanse of the bottom first pole tip  306  at the ABS appears as a lip. Accordingly, the embodiment  300  is referred to hereinafter as the lip design. The top first pole tip  304  is constructed directly on the top surface of the bottom first pole tip  306  after the top surface  308  of the bottom first pole tip  306  is planarized with the top surface of the second insulation layer  312 . The single coil lip design, shown in FIG. 25, is the same as the single coil pole tip design shown in FIG. 19, except the front component  320  of the first pole piece forms a bottom first pole tip  322  which is wider than the top first pole tip  324 . It should be noted that the lip design in FIGS. 92,  24  and  25  does not have a flare point since the bottom first pole tip  322  is the same width as the first pole piece  324  from the ABS to the back cap  326 . As shown in FIG. 22, insulation of the insulation stack  310  extends beyond side edges  347  and  348  of the first pole piece to planarize the wafer for construction of the coil layers  312  and  314 . 
     FIGS. 26-28 illustrate various configurations for the lip design at the ABS. The illustration in FIG. 26 is representative of the air bearing surfaces of the heads shown in FIGS. 22,  24  and  25 . FIG. 27 is a modification of the illustration shown in FIG. 26 in that the second pole piece layer  360  has first and second upwardly inclined portions  362  and  364  which are connected to elevated first and second flat portions  366  and  368 . The purpose of this construction is to further separate the bottom outside corners  370  and  372  of the second pole piece layer from the wide expanse of the bottom first pole tip  374 . Since high flux densities are concentrated in these corners, this extra distance minimizes flux leakage between the second pole piece layer  360  and the bottom first pole tip  374 . In FIG. 28, the second pole piece  376  is provided with top and bottom second pole tips  378  and  380  in a notched configuration so as to promote a slight amount of side writing, as explained hereinabove with regard to FIG.  21 . 
     Method of Construction 
     An exemplary method of construction of the merged magnetic head  300 , shown in FIGS. 22 and 24, is shown in FIGS.  29 A- 29 AH. In FIG. 29A a bottom flat layer portion  400  of a first pole piece is frame plated on a wafer  401 . In FIG.,  29 B a first front component  402  and a first rear component  404  are frame plated on the layer  400  in a spaced relationship so as to define a recess  406  therebetween. In FIG. 29C alumina is sputter deposited over the entire wafer covering all components of the first portion of the first pole piece layer. FIG. 29D is an ABS illustration of FIG. 29C showing how the alumina fills in the steps at first and second side edges  408  and  410  of the first front component  402 . In FIG. 29E the wafer is chemically mechanically polished (CMP), which causes top surfaces  412 ,  414  and  416  of the alumina layer and top surfaces  418  and  420  of the first front component and the first rear component to be flush with respect to one another. This provides a first insulation layer  422  within the recess and insulation layers  424  and  426  in the field beyond front and rear edges  428  and  430  of the bottom layer portion of the first pole piece layer. FIG. 29F is an ABS view of FIG. 29E showing the alumina to have first and second layers  432  and  434  adjacent first and second side edges  436  and  438  of the bottom portion of the first pole piece so as to planarize the wafer in the field beyond the partially completed magnetic head. 
     In FIG. 29G a first coil layer  440  is frame plated on the first insulation layer employing a photoresist frame (not shown), which is planarized across the wafer. In FIG. 29H a second front component  442  and a second rear component  444  are frame plated on the first front component and the first rear component, respectively, thereby raising the front and back ends of the partially completed first pole piece to form a second recess  450  above the first coil layer  440 . The second front component may have a step  452  for facilitating placement of a second coil, which will be described hereinafter. If desired, the order of the steps in FIGS. 29G and 29H can be reversed which will be discussed in more detail hereinafter. In FIG. 291 alumina is deposited over the entire wafer covering the entire partially completed head. FIG. 29J is an ABS illustration of the partially completed head shown in FIG.  291 . In FIG. 29K the wafer is CMP causing the deposited alumina to form a second insulation layer  454  in an intermediate region of the partially completed head and layer portions  456  and  458  forward and rearward of the head to planarize the entire wafer. FIG. 29L is an ABS illustration of FIG.  29 K. 
     In FIG. 29M a seedlayer  460  is sputter deposited over the entire wafer in preparation for electroplating a second coil. In FIG. 29N a second coil layer  462  has been frame plated on the second insulation layer  454 . In FIG. 290 a photoresist layer  464  has been spun on the wafer and photo-patterned to provide openings  466  and  467  for constructing the top first pole tip and a back gap portion of the first pole piece layer. The seedlayer  460  for the coil layer  462  is removed and a seedlayer  465  is deposited for constructing the top first pole tip. The photoresist layer  464  can be significantly thinner since it does not have to accommodate the profile of an insulation stack. The thinner resist allows more efficient penetration of light during the light exposure step so as to promote high resolution of the side walls  468  and  469  of the opening in the resist and the side walls of the top first pole tip which is to be plated therein, as shown in FIG.  29 P. In FIG. 29Q the top first pole tip  470  and the back gap portion  472  are plated through openings in the photoresist layer. FIG. 29R is an ABS illustration of FIG.  29 Q. In FIG. 29S the photoresist is removed and any remaining seedlayer is also removed by ion milling. FIG. 29T is an ABS illustration of FIG.  29 S. Constructing the top first pole tip by the above-described photoresist patterning scheme results in a superior first pole tip  470  which can be submicron with high 
     In FIG. 29U an alumina layer  474  is deposited on the entire wafer. FIG. 29V is an ABS illustration of FIG.  29 U. In FIG. 29W the entire wafer is CMP causing the alumina to form a third insulation layer  476  above the second coil layer  462  with front and rear layer portions  478  and  480  which are flush with top surfaces of the top first pole tip  470  and the back gap region  472 . FIG. 29X is an ABS illustration of FIG.  29 W. In FIG. 29Y a write gap layer  482  is sputter deposited, which is preferably a full film layer over the entire wafer. This will maintain planarization of the partially completed head with respect to the rest of the wafer. FIG. 29Z is an ABS illustration of FIG.  29 Y. In FIG.  29 AA a second pole piece/first shield layer  484  (P 2 /S 1 ) is frame plated on the gap layer  482  and is flat because of the flatness of the gap layer. FIG.  29 AB is an ABS illustration of FIG.  29 AA. 
     In FIG.  29 AC alumina  485  is once again sputter deposited over the entire wafer. FIG.  29 AD is an ABS illustration of FIG.  29 AC. In FIG.  29 AE the entire wafer is CMP to ensure planarization of the second pole piece/first shield layer  484  for forming a first read gap layer thereon. FIG.  29 AF is an ABS illustration of FIG.  29 AE. Next, the read gap layer  486 , read sensor  488  and first and second leads (not shown) are frame plated on the first read gap layer followed by sputter deposition of a second read gap layer  490  and a second shield layer  492 . FIG.  29 AH is an ABS illustration of FIG.  29 AG. The wafer is now ready for an overcoat layer (not shown) which essentially completes the construction of the merged magnetic head. 
     As stated hereinabove, the steps in regard to the construction of the second coil layer and the first pole tip, shown in FIGS. 29N and 29Q, may be reversed in their order. When these steps are reversed the method would be as shown in FIG.  30 . The seedlayer is still deposited as shown in FIG.  29 M. The next step would be to form the first pole tip  470  and back gap  472  (FIG.  29 Q). Next, the second coil  462  would be formed (FIG. 29N) followed by deposition of the alumina layer over the entire wafer (FIG.  29 V). The wafer is then CMP and the write gap layer  482  is formed, as shown in FIG.  29 Y. 
     FIG. 31 illustrates still another modification of the method. A seedlayer is deposited on the second insulation layer above the first coil, as shown in FIG. 29M, followed by formation of the second coil (FIG.  29 N). Next, front and rear components of the first pole piece are formed followed by deposition of alumina over the entire wafer. After CMP the wafer flat until the top surfaces of the front and rear components are exposed, the first pole tip and back gap can then be formed on the front and rear components respectively. Next, an alumina layer is deposited over the entire wafer followed by lapping. The write gap layer can then be deposited, as shown in FIG.  29 Y. This modified method would enable construction of the first pole tip and the back gap on an entirely flat wafer without the presence of a coil layer. 
     FIG. 32 shows exemplary steps for the construction of the merged magnetic heads shown in FIGS. 19 and 25. The first step is to form a bottom layer of a first pole piece, as shown in FIG. 29A, followed by forming front and rear components of the first pole piece, as shown in FIG.  29 B. Next, alumina is deposited followed by CMP the wafer until the top surfaces of the front and rear components are flush with the alumina layer. A single coil layer is then formed followed by formation of the first pole tip and back gap. Alumina is then again deposited and the wafer lapped until the top surfaces of the first pole tip and the back gap are flush with the alumina layer. The write gap can then be deposited, as shown in FIG.  29 Y. The remainder of the steps for constructing the read head would be as shown in FIGS.  29 AA- 29 AH. It should be noted that the fifth and sixth steps in FIG. 32 could be reversed so that the first pole tip and back gap are formed before the coil layer. Further, the method could be modified by forming second front and second rear components on the first front and first rear components after construction of the coil layer followed by deposition of alumina and lapping to provide a flat surface for the construction of the first pole tip and back gap. 
     The construction of the pole tip design shown in FIGS. 16-21 is similar to the method described hereinabove, except the photoresist patterning for the front portions of the first pole piece layer differ slightly in order to obtain the configurations shown. The construction of the single layer embodiments shown in FIGS. 19 and 25 would employ the method described hereinabove except the construction of the second coil layer is omitted. 
     In some embodiments it may be desirable to employ a high magnetic moment for the first pole tip which may be Ni 45 Fe 55 . It should be noted from FIGS. 29O-29T that a different material can be employed for the top first pole tip than employed for the remainder of the first pole piece. A top first pole tip constructed of Ni 45 Fe 55  can be annealed to improve its properties without damaging the read sensor since it has not yet been constructed. The read sensor can be either a magnetoresistive (MR) sensor or a spin valve sensor which are both well known in the art. In lieu of alumina (Al 2 O 3 ) silicon dioxide (SiO 2 ) may be employed. Alumina or silicon dioxide have greater electrical insulating and thermal insulating properties than hard baked photoresist. While it is preferred that the write gap layer be alumina, it should be understood that it may be a nonmagnetic material, such as copper, which is frame plated or sputter deposited. While frame plating is preferable for all of the metallic layers, it should be understood that these layers could be sputter deposited employing bilayer photoresist techniques which are well known in the art. The alumina layers or silicon dioxide layers are preferably sputter deposited. The read gap layers are preferably alumina and the read sensor is preferably constructed of Permalloy (Ni 80 Fe 20 ). 
     Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.