REFERENCES TO PRIOR APPLICATIONS  
       [0001]     This application is related to co-pending provisional application, reference No. 60/609,017, filed Sep. 9, 2004, entitled NARROW PITCH TAPE HEAD ARRAY USING AN ORTHOGONAL BACKGAP; co-pending provisional application, reference No. 60/609,009, filed Sep. 9, 2004, entitled HEAD DESIGN WITH OVERLAPPING COIL FOR NARROW PITCH TAPE HEAD; and claims benefit of both thereof. Provisional applications Nos. 60/609,017 and 60/609,009 are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to the construction of magnetic media read and write heads. More specifically, the invention relates to the construction of multi-layer tape head arrays having a narrow pitch.  
         [0004]     2. Description of the Related Art  
         [0005]     A typical tape head consists of an array of writers and readers dispositioned across a row fabricated by thin-film wafer technology. The separation between adjacent elements in an array has constraints. Consequently adjacent elements stretch across multiple tracks written in the tape. Read and Write access to all tracks is achieved by indexing the array across the tape.  
         [0006]     One limitation on the separation between elements is to allow space for a wide coil on each write head. The width of the coil is constrained by magnetic requirements on the backgap size, number of turns and state-of-the-art coil photolithography. These limitation impose a separation much wider than the write track width and tape track pitch.  
         [0007]      FIG. 1  is a top view of a typical write head array  100  of the prior art, with insulating layers transparent to aid in viewing relevant details. Tape or other magnetic media contacts the head array at the air bearing surface (ABS)  112 . Write heads  102   a - 102   c  are located at a distance  122  from each other, which is about the width of five tracks in the example shown. Track position is determined by the center of write pole  110  of write head  102 . Track location diagram  114  shows the location of tracks  116   a - 116   c,  which correspond to the write track locations of heads  102   a - 102   c,  respectively. Distance  122  is primarily determined by the width of backgap  106  in combination with the dimensions of coil  104 . Yoke  108  returns the magnetic flux from write gap  110  to backgap  106 .  
         [0008]      FIG. 2  (prior art) is an air bearing surface (ABS) end view of tape head array  100  at section B-B in  FIG. 1 , with insulating layers  212  transparent to aid in viewing relevant details. Write heads  102   a - 102   c  are situated above shield layer  202  and insulating layer  204 , respectively. Bottom pole layer  206  is situated above insulating layer and is common for all writes heads in the array. Bottom pole tip  208  is coupled to bottom pole layer  206 . Upper pole tip  210  is separated from lower pole tip  208  by write gap  110 . Upper pole tip  210  is coupled to yoke  108 .  
         [0009]      FIG. 3  (prior art) is a cross section view through section A-A of  FIG. 2 , with insulating layers transparent to aid in viewing relevant details.  
         [0010]     U.S. Pat. No. 5,452,165 discloses a plurality of thin film magnetic heads which are arranged in a linear array with a spacing D between adjacent heads. The pole pieces of the magnetic heads are positioned in a side by side relationship in contrast to the normal pancake type of magnetic head. The linear array is angled at a skew angle theta with respect to the direction of travel of the magnetic medium. The track pitch is then D sin theta. The track width is substantially equal to the thickness of the pole tips P1T and P2T of the magnetic heads. This thickness can be in the order of 3 microns. With such a pole tip thickness the track pitch of each magnetic head in the linear array can be 3-4 microns. A plurality of narrow data tracks can then be provided with minimum pitch by a corresponding number of magnetic heads. The write signals are simultaneously fed to the heads or the read signals are simultaneously fed to the heads. This allows high data rates to be processed. The invention also provides different azimuth between adjacent heads to minimize cross talk between the tracks caused by track misregistration. Additional magnetic heads can be employed for servo control as needed.  
         [0011]     U.S. Pat. No. 5,546,650 discloses a method of manufacturing a thin-film magnetic head having a write element capable of producing a magnetic flux density sufficient to write the high coercivity magnetic tapes at high track density. The manufacturing process requires a minimum number of lithographic steps, thereby increasing the yield of the multiple track magnetic head module. A trench is cut into the ferrite substrate material and filled with an insulator to produce a more efficient write element. A recess is then formed in the ferrite substrate having a geometry sufficient to hold a deposited thin-film conductive coil below the surface of the ferrite substrate. An insulator is then deposited on the ferrite substrate to form a gap spacer as well as to insulate the conductive thin-film coils from the ferrite substrate. The conductive thin-film coil is then deposited on the ferrite substrate in the recesses. A high-saturation flux density magnetic material is deposited on a planar nonmagnetic closure section and formed into separate magnetic pole pieces for each individual track. The magnetic pole pieces are then insulated from each other to produce a closure section having a planar surface matable with the ferrite substrate. The closure section is attached to the substrate by aligning the metal pole piece on the closure section. The magnetic pole piece is positioned in the front gap and has a width which defines the track width on the magnetic tape. The magnetic pole piece is also positioned to substantially cover the back gap region to increase the flux density existing at the front gap region.  
         [0012]     U.S. Pat. No. 5,982,591 discloses integrated, juxtaposed head units of a magnetic head have transducing gaps directly adjacent a central plane transverse to the longitudinal direction of relative movement of a magnetic recording medium, adjacent transducing gaps being to opposite sides of the central plane. Head units adjoin each other so that a recording channel density of 100% is achieved. In one embodiment a common electrical conductor passes through a plurality of head units to one side of the central plane, and electrical connection tracks extending from a portion of the conductor form inductive transducing elements.  
         [0013]     U.S. Pat. No. 6,650,496 discloses a matrix array of recording heads, wherein each head is independent from another both in terms of its magnetic circuit and excitation conductors. Each individual head has a planar magnetic circuit and an helical coil wrapped around the lower part of the magnetic circuit. The matrix array is collectively fabricated using full thin film technology on non-magnetic substrates. Preferably, the heads are aligned in an oblique lattice with the write gaps aligned along rows and offset by a constant value along columns. Each individual head is connected to the control electronics through interconnects to the backside of the wafer, allowing independent control of the write parameters. The die forming the device is shaped on its edges and top surface to optimize head/medium positioning and minimize wear.  
         [0014]     U.S. Pat. No. 6,687,083 discloses a low profile inductive write head to improve track definition and head efficiency and to reduce overcoat and pole tip protrusion and cracking caused by thermal expansion. A first insulation layer of an insulation stack enclosing the coil layer is formed of an non-magnetic inorganic insulator material such as aluminum oxide, silicon dioxide or titanium dioxide having a thickness of in the range of 0.2-0.3 microns. The thinner first insulation layer results in a significantly reduced slope of the insulation stack which decreases reflective notching during processing of the second pole tip to improve track definition. Improved thermal conduction properties of the inorganic insulator material improves heat sinking of the write coil reducing overcoat and pole tip protrusion and cracking at the pole tip/write gap layer interface.  
         [0015]     U.S. patent application Publication 2002/0135918 A1 discloses a multi-magnetic recording head capable of increasing a magnetic recording density of information recorded on a magnetic recording medium. The multi-magnetic recording head includes a substrate, a pair of first thin film magnetic poles with a specific gap put therebetween, which are stacked over the substrate, and a pair of second thin film magnetic poles with a specific gap put therebetween, which are stacked over the pair of first thin film magnetic poles, wherein the pair of first thin film magnetic poles and the pair of second thin film magnetic poles are offset from each other in the direction nearly perpendicular to the stacking direction.  
         [0016]     U.S. patent application Publication 2004/0066576 A1 discloses a magnetic write head having a vertically laminated back gap structure and method of making the same. The magnetic head is formed with lower and upper pole pieces and a back gap structure which connects the lower and the upper pole pieces in a back gap region. In one illustrative example, the back gap is a vertically laminated structure having alternating layers of magnetic and non-magnetic materials. Each alternating layer is perpendicular to both the lower and the upper pole pieces. This vertically laminated structure significantly reduces the eddy currents in the back gap region at high operating frequencies as the layers are oriented in a direction parallel with the magnetic flux.  
         [0017]     U.S. patent application Publication 2002/0060879 A1 discloses a thin film magnetic head having a plurality of coils is capable of recording with higher density. A magnetic pole section for restricting a track width is formed between a lower core layer and an upper core layer, and two coil layers are tiered between a reference surface and a lower core layer through the intermediary of a coil insulating layer. This allows a magnetic path to be shortened. As a result, narrower tracks and lower inductance can be both achieved, and the narrower tracks combined with faster data transfer enable higher-density recording to be attained.  
         [0018]     Head arrays of the prior art having a relatively large spacing can exhibit a number of disadvantages. One is the possibility of track misregistration (TMR), which is an alignment or registration error from the first track position (i.e.  116   a ) to the last track position (i.e.  116   c ) due to expansion or contraction of the magnetic media. Magnetic media, particularly tape, can expand or contract as a function of temperature or humidity. The magnitude of this error is dependent on the total distance between the first and last head positions in the array, therefore the further the heads are apart, the greater the registration error. Another disadvantage of a widely spaced head array is that data write times can be longer for a given media width and number of tracks. Closely spaced heads produce arrays having more heads per unit media width, and therefore more tracks can be written in parallel, increasing total data rates to the storage media. This may be of considerable importance in computer data back-up applications, where large hard drives need to be backed up on tape media.  
         [0019]     In order to reduce adjacent head to head dimension  122 , some designs in the prior art have used a staggered head positioning, requiring adjacent heads to be located on different levels (when viewed in the ABS view). This construction can result in higher production costs, since proportionately more layers have to be added during fabrication.  
         [0020]     Of value would be an invention that allows a reduction of the spacing between the elements in the array while maintaining the same number of elements. Location of all elements within the same horizontal plane would be desirable to reduce fabrication costs.  
       SUMMARY OF THE INVENTION  
       [0021]     It is an object of the present invention to provide a thin film head array including a first head containing a first upper pole, a first lower pole including a first lower pole tip magnetically coupled to a lower pole layer, and a first write coil disposed between the first upper pole and the first lower pole. A second head contains a second upper pole, a second lower pole having a second lower pole tip magnetically coupled to the lower pole layer, and a second write coil disposed between the second upper pole and the second lower pole. The first head is adjacent to the second head, and a portion of the first write coil overlaps at least a portion of the second write coil.  
         [0022]     It is another object of the present invention to provide a thin film head array including a first head containing a first upper pole containing a first upper pole tip magnetically coupled to a first yoke, a first lower pole containing a first lower pole tip magnetically coupled to a first lower pole layer, a first write coil disposed between the first upper pole and the first lower pole, and a first write gap disposed between the first upper pole tip and the first lower pole tip. A second head contains a second upper pole containing a second upper pole tip magnetically coupled to a second yoke, a second lower pole containing a second lower pole tip magnetically coupled to a second lower pole layer, a second write coil disposed between the second upper pole and the second lower pole, and a second write gap disposed between the second upper pole tip and the second lower pole tip. The first head is adjacent to the second head, a portion of the first write coil overlaps at least a portion of the second write coil, and the first write gap and the second write gap lie approximately in a plane perpendicular to an air bearing surface.  
         [0023]     It is yet another object of the present invention to provide a method for making a thin film head array including providing a substrate having a top surface, depositing a lower pole layer on the top surface of the substrate, depositing a first dielectric layer on a top surface of the lower pole layer, and forming a first coil structure of a first write head on a top surface of the first dielectric layer. The method further includes depositing a plurality of second dielectric layers, the plurality of second dielectric layers enclosing a top surface of the first coil structure. A second coil structure of a second write head is formed on a top surface of the plurality of second dielectric layers. The first write head is adjacent to the second write head, and a portion of the second coil structure overlaps at least a portion of the first coil structure.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:  
         [0025]      FIG. 1  (prior art) is a top view of a typical write tape head array with insulating layers transparent;  
         [0026]      FIG. 2  (prior art) is an air bearing surface (ABS) end view at section B-B in  FIG. 1 , with insulating layers transparent;  
         [0027]      FIG. 3  (prior art) is a cross section view through section A-A of  FIG. 2 , with insulating layers transparent;  
         [0028]      FIG. 4  is a top view of a write head array having overlapping coils, with insulating layers transparent, according to an embodiment of the present invention;  
         [0029]      FIG. 5  is an air bearing surface (ABS) end view at section C-C in  FIG. 4 , with insulating layers transparent, according to an embodiment of the present invention;  
         [0030]      FIG. 6  is a cross section view through section D-D of  FIG. 5 , with insulating layers transparent, according to an embodiment of the present invention;  
         [0031]      FIG. 7  is a cross section view through section E-E of  FIG. 5 , with insulating layers transparent, according to an embodiment of the present invention;  
         [0032]      FIG. 8  is a partial cross section view of an alternative embodiment of the present invention;  
         [0033]      FIGS. 9   a - 9   j  are air bearing surface end views illustrating a method of making a write head array having overlapping coils, according to an embodiment of the present invention; and,  
         [0034]      FIGS. 10   a - 10   c  are air bearing surface end views illustrating an alternative method of making a write head array having overlapping coils, according to an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]      FIGS. 1-3  (prior art) have been discussed in the Background section above.  
         [0036]      FIG. 4  is a top view of a write head array  300  having overlapping coils, with insulating layers transparent to aid in viewing relevant details, according to an embodiment of the present invention. Head array  300  is comprised of individual head structures  302   a - 302   d.  Head structures  302   a  and  302   c  have their coils  304   a  and  304   c  fabricated below coils  304   b  and  304   d  of head structures  302   b  and  302   d.  This allows coil  304   b  to overlap adjacent coils  304   a  and  304   c.  Likewise, coils  304   d  and  304   b  overlap coil  304   c.  Head to head spacing  314  is therefor reduced in comparison to spacing  122  of the prior art. An important feature of the present invention is that write gap  310   a  is coplanar with the write gaps of the other heads in the array  300 , as will be clarified in subsequent figures. This configuration reduces the number of fabrication layers required for the array  300 , reducing the cost of manufacturing. The head array  300  illustrated in  FIG. 4  utilizes conventional backgap and yoke structures (for example,  306   a  and  308   a  of head  302   a ). However, the orthogonal backgap and yoke structures disclosed in co-pending provisional application, reference No. 60/609,017, filed Sep. 9, 2004, entitled NARROW PITCH TAPE HEAD ARRAY USING AN ORTHOGONAL BACKGAP, may also be utilized to produce head arrays of even tighter spacing.  
         [0037]      FIG. 5  is an air bearing surface (ABS) end view at section C-C in  FIG. 4 , with insulating layers  512  transparent to aid in viewing relevant details, according to an embodiment of the present invention. Write heads  302   a - 302   d  are situated above shield layer  502  and insulating layer  504 , respectively. Bottom pole layer  506  is situated above insulating layer  504  and is common for all writes heads in the array. In an alternative embodiment (not shown), bottom pole layer may be separated into discreet, isolated sections for each of heads  302   a - 302   d.  However, it is still desirable that these sections be located in the same plane above layer  504  to simplify construction and reduce fabrication costs. In head  302   a,  bottom pole layer  506  is in contact with bottom pole tip  508   a,  and together comprise the lower pole. Upper pole tip  510   a  is in contact with yoke  308   a,  and together comprise the upper pole. The upper pole tip  510   a  and lower pole tip  508   a  are separated by write gap  310   a,  which is generally filled with a non-magnetic, insulator material. Heads  302   b - d  are constructed in a similar manner. Upper pole tip  510   a,  yoke  308   a,  lower pole tip  508   a,  and lower pole layer  506  may be any suitable magnetic material, preferably one having a high magnetic moment such as Permalloy or other compositions of NiFe, CoFe or CoNiFe alloys, which may contain dopants or other additives known by those of ordinary skill in the art to provide desirable material properties. The specific material compositions of the upper pole tip  510   a,  yoke  308   a,  lower pole tip  508   a,  and lower pole layer  506  may be different, in order to optimize the function of each component. Write gap  310   a  may be composed of alumina or other suitable non-magnetic material. Insulating material  512  may be composed of alumina, silica, baked photo-resist, or layers and combinations of any of the foregoing materials. Details are not shown for clarity.  
         [0038]     Coil structures  304   a,    304   c  of heads  302   a  and  302   c,  respectively, are placed below the coil structures  304   b,    304   d  of adjacent heads  302   b  and  302   d,  respectively. This allows coils of adjacent heads to overlap by dimension  514 , allowing a tighter head to head spacing  314 . Coil structures  304   a - d  are generally made from conductive metals as is well known to those skilled in the art, preferably copper and copper alloys. Notice that write gaps  310   a - 310   d  are located approximately in the same horizontal plane (perpendicular to the ABS), as are the lower poles, which comprise lower pole tips  508   a - d  and lower pole layer  506 . This construction facilitates a lower production cost when compared to prior art processes using staggered head arrays. These staggered head arrays can produce tight head to head spacing, but require the fabrication of a complete head stack for each adjacent head. Thus, a four head array would contain a structure having four times the number of layers as the present invention, thus considerably increasing the cost.  
         [0039]      FIG. 6  is a cross section view through section D-D of  FIG. 5 , with insulating layers transparent to aid in viewing relevant details, according to an embodiment of the present invention This view is taken through the center line axis of write head  302   c,  perpendicular to the air bearing surface (ABS), and shows the position of coil  304   c.  Coil  304   c  is generally placed below the position of write gap  310   c,  although this is not a strict requirement as long as the coil position does not interfere with the coils of adjacent heads.  
         [0040]      FIG. 7  is a cross section view through section E-E of  FIG. 5 , with insulating layers transparent to aid in viewing relevant details, according to an embodiment of the present invention. This view is taken through the center line axis of write head  302   d,  perpendicular to the air bearing surface (ABS), and shows the position of coil  304   d.  Coil  304   d  is generally placed above the position of write gap  310 d, although this is not a strict requirement as long as the coil position does not interfere with the coils of adjacent heads.  
         [0041]      FIG. 8  is a partial cross section view of an alternative embodiment  800  of the present invention. This view is taken through the center line axis of write head  302   d,  perpendicular to the air bearing surface (ABS), and shows an alternative position for coil  304   d,  now labeled  802 . Generally, coil  802  is placed in this embodiment above the upper pole tip  510   d.  Yoke  804  is deposited over insulating layers  512  in an arch to cover coil  802 .  
         [0042]      FIGS. 9   a - 9   j  are air bearing surface end views illustrating a method of making a write head array having overlapping coils, according to an embodiment of the present invention.  
         [0043]     In  FIG. 9   a,  lower pole layer  902  is deposited on a substrate (not shown). As mentioned previously, layer  902  may be a continuous layer (as shown), or optionally a coplanar layer of separated segments (not shown). Layer  902  is generally composed of a magnetic material as previously disclosed, and is deposited according to methods well known in the art.  
         [0044]     In  FIG. 9   b,  a first dielectric layer  904  is deposited upon the top surface of lower pole layer  902 . Layer  904  may be composed of any suitable insulating material, deposited in accordance with known methods. Lower coil structures  906  are then deposited upon dielectric layer  904 . The intermediate steps of photo-resist deposition, imaging, development, coil electroplating, and photo-resist removal shall not be described in detail, and are well known to those skilled in the art. In accordance with the present invention, lower coil structures  906  are placed at locations corresponding to every other write head in the array, as illustrated in  FIGS. 4 and 5  discussed previously.  
         [0045]     In  FIG. 9   c,  lower pole tips  910   a  and  910   b  are deposited directly on the upper surface of lower pole layer  902 . Lower pole tips  910   a  coupled to lower pole layer  902  comprise the lower poles of write head structures having a lower coil structure  906 . Lower pole tips  910   b  coupled to lower pole layer  902  comprise write head structures having an upper coil structure. In  FIG. 9   d,  insulating layer  908  is deposited on the structure as shown in  FIG. 9   e.  CMP (chemical-mechanical-planarization) is used to planarize the structure at the top surface of lower pole tips  910   a,b.  Insulating layer  902  may be any suitable material, including but not limited to silica, alumina, or polymers such as polyamides and photo-resists. Preferably, alumina is used. In  FIG. 9   e,  write gap layer  912  is deposited on the upper surfaces of pole tips  910   a,b.  In  FIG. 9   f,  upper pole tips  914   a,b  are deposited on the upper surface of write gap layer  912 . Upper pole tips  914   a  correspond to write heads having lower coil structures  906 , and upper pole tips  914   b  correspond to write heads having upper coil structures. In  FIG. 9   g,  upper coil insulating layer  916  is deposited on the upper surface of write gap layer  912 . Layer  916  may be any suitable insulating material, deposited in accordance with known methods. In  FIG. 9   h,  upper coil structures  920  are deposited on the upper surface of insulating layer  916 , at locations corresponding to write heads with upper pole tips  914   b.  In accordance with the present invention, upper coil structures  920  overlap the lower coil structures  906  of adjacent heads. In  FIG. 9   i,  insulation layers are placed over coil structures  920  and surface  916 . Any suitable insulation material can be used, preferably alumina. CMP is then utilized to remove insulating films on the top surface of the upper pole tips  914  in preparation for adding the yoke structures. In  FIG. 9   j,  yokes  924  are added to the top surface of upper pole tips to form completed upper poles of the thin film head array.  
         [0046]      FIGS. 10   a - 10   c  are air bearing surface end views illustrating an alternative method of making a write head array having overlapping coils, according to an embodiment of the present invention. This method is utilized to make the heads of  FIG. 8 . The method begins by following the steps outlined in  FIGS. 9   a  through  9   f.  Following step  9   f,  insulating layers are deposited on the upper surface of layer  912 . Any suitable insulation material can be used, preferably alumina. CMP is then utilized to remove any insulation material on the top surface of the upper pole tips and to planarize the structure. In  FIG. 10   b,  coil strucures  1004  are added to the top surface of insulating layer  1002 , and in accordance with the present invention, are placed so that they overlap coils  906  of the adjacent heads. In  FIG. 10   c,  yokes  1006  are added to complete the thin film head structures subsequent to the deposition of an insulation layer (not shown) over the coil structures  1004 .  
         [0047]     The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.
The structure for a closely spaced, coplanar tape head array is disclosed. Narrow pitch is obtained by utilizing an overlapping coil structure, wherein write coils of adjacent heads overlap. The overlap is made possible by placing coils of adjacent heads at different levels within the thin film structure, separated by dielectric insulating layers.