Abstract:
A write pole for a read/write head of a disk drive system has a tapered surface on a leading edge thereof. Preferably, the tapered surface has a taper angle of between 0 and 20 degrees from a plane normal to the ABS. By having a write pole with a taper in this manner, sufficient write fields can be achieved even with thinner write pole tips on the ABS surface. By decreasing the thickness of the write pole tip in this manner while maintaining sufficiently high write fields, the skew profile of a write head can be decreased and areal density increased.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This patent application is a divisional of, and claims priority under 35 U.S.C. §120 to, U.S. patent application Ser. No. 10/993,915, that is entitled “TAPERED WRITE POLE FOR REDUCED SKEW EFFECT”, and it was filed on Nov. 18, 2004, which claims priority from U.S. Provisional Application No. 60/523,556, filed Nov. 20, 2003, entitled “TAPERED WRITE POLE FOR REDUCED SKEW EFFECT”. The entire disclosure od each of these applications is incorporated herein by reference in their entirety herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This application relates to techniques and arrangements for write heads in data storage applications, particularly geometries and processes for achieving geometries of write heads that reduce skew effects.  
       BACKGROUND OF THE INVENTION  
       [0003]     In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on a pivotably-mounted actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.  
         [0004]     During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.  
         [0005]     Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of a magnetoresistive sensor stripe sandwiched between two magnetic shields that may be electrically connected together but are otherwise isolated. A current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.  
         [0006]     The write element typically includes a coil of wire through which current is passed to create a magnetic field that can be directed toward an adjacent portion of the disk by a ferromagnetic member known as a write pole. While it is known that the write element can be arranged to either store data longitudinally or perpendicularly on the disk, most, if not all, commercial disk drives to date have utilized longitudinal recording arrangements. Although perpendicular recording techniques have the potential to allow for higher densities of recorded information, longitudinal recording is used in all current products for historical reasons. An early perpendicular recording technique is disclosed in U.S. Patent No. RE33,949, the contents of which are incorporated herein by reference.  
         [0007]     The &#39;949 patent discloses a perpendicular or vertical write head with a write pole section, downstream shield section, and a pancake coil surrounding the write pole section to generate magnetic flux therein. The shield section is disclosed to have a surface facing toward the media that is many times larger than a similarly-oriented face of the write pole. The media is disclosed to include two layers, an upper layer closer to the head having perpendicular uniaxial. anisotropy and a lower layer having low magnetic reluctance (now known as the Soft Under Layer (SUL)). A high write field can then be produced between the write pole and the SUL to record information in the upper layer of the media. The write flux returns through the SUL to the downstream write shield.  
         [0008]     Due to the pivotable mounting of the actuator arm, the angular alignment of the read/write head to a particular data track on the adjacent storage disk can vary based on the radial position of the data track on a disk. In other words, the angular alignment at a data track near the inner diameter of the media surface on the disk will be different than the angular alignment near the outer diameter of the media surface on the disk. This phenomenon is known as skew or the skew angle, and the profile of such skew angles across the different radial portions of the disk is known as the skew profile. As can be appreciated, depending on design criteria, it is possible for the disk drive system to be designed so that the relative angular alignment is optimal at the outer diameter and the greatest amount of skew angle is achieved at the inner diameter. Conversely, the design could optimize the skew angle at the inner diameter and have the least optimal skew angle at the outer diameter, or the optimal angular alignment could be achieved somewhere in between the inner or outer diameter. In modern disk drive systems, the worst-case skew angle may typically be in a range of 15 to 20 degrees (e.g., 17 degrees).  
         [0009]     It should be understood that a primary difference between longitudinal recording and perpendicular recording is that with longitudinal recording the magnetic field is primarily generated in the write gap between the write pole tip and the return pole tip, while in perpendicular recording the magnetic field is primarily generated in the region between the write pole tip and the soft underlayer in the magnetic media. Thus, with perpendicular recording, the field will be generated in a cross-sectional area that corresponds to the footprint of the write pole tip appearing at the ABS. It can then be appreciated that it is desirable for the footprint of a write pole tip to be minimized. It can also be appreciated that significant skew angles produce a footprint that is skewed relative to the data recording track and creates a portion in the track where some of the data recorded is via side writing from a side edge of the footprint, which is undesirable. In order to reduce this effect, write pole tips for perpendicular recording may typically be trapezoidal in shape rather than rectangular. The side bevel angle on the write pole tip (the extent to which the lateral side of the write pole tip deviates from a 90 degree angle with the leading or trailing edge) determines the amount of bevel of the trapezoidal head. Unfortunately, there are limits to the amount of side bevel in a trapezoidal head that is desirable. Typically, it is not desirable to have a bevel greater than 10 degrees because of the lost cross-sectional area that a bevel creates, which reduces write flux, write field, and eventually areal density.  
         [0010]     It is desirable to design a write head which does not suffer from the above drawbacks. It is against this background and a desire to improve on the prior art that the present invention has been developed.  
       SUMMARY OF THE INVENTION  
       [0011]     In view of the foregoing, a broad objective of the present invention is to provide a read/write head with reduced skew effect.  
         [0012]     In carrying out these and other objectives, features, and advantages of the present invention, a read/write head for a disk drive is described, the head being suitable for recording data in adjacent magnetic recording media, the media including a first layer for recording data and a second layer that is a soft underlayer (SUL) to return magnetic flux to the read/write head. The head includes a read transducer and a write transducer that includes a write pole and a write coil. The write pole has a tapered surface on a side that is generally perpendicular to the direction of relative motion between the read/write head and the adjacent magnetic recording media, the magnitude of the taper being less than 20 degrees.  
         [0013]     The magnitude of the taper may be less than 15 degrees. The magnitude of the taper may be more than 5 degrees. The magnitude of the taper may be between 7 and 13 degrees. The magnitude of the taper may be approximately 10 degrees.  
         [0014]     The write transducer also may include a write shield. The tapered surface may be on an opposite side of the write pole from the write shield. The tapered surface may be on a side of the write pole facing the write shield. The tapered surface may be on a leading side or a trailing side of the write pole.  
         [0015]     The write pole may have a thickness on an ABS side thereof that is less than 300 nanometers from a leading edge to a trailing edge thereof. The tapered surface may be generally planar. The tapered surface may include a series of cascading steps. The write pole may have an ABS and the distance from the ABS to a first step may be equal to or greater than the distance from the ABS to the SUL.  
         [0016]     The invention may also relate to a method for producing a tapered write pole in a read/write head for a disk drive. The method includes providing a substrate; applying a photo resist mask to a portion of the substrate; depositing an insulative material to a portion of the substrate adjacent to the photo resist mask, at least a portion of the insulative material being formed in a ramp; removing the photo resist mask; applying a write pole tip layer on top of the substrate and insulative ramp; planarizing the write pole tip layer and insulative ramp to substantially create a plane; and lapping the entire structure from a direction generally parallel to the plane to create an ABS surface.  
         [0017]     The insulative material may be aluminum oxide. The ramp shape to the insulative layer may be created by sweeping the angle of deposition in depositing the insulative layer. Ion beam deposition may be used. The slope of the ramped insulative layer relative to the substrate may be less than 20 degrees, less than 15 degrees, more than 5 degrees, between 7 and 13 degrees, or approximately 10 degrees.  
         [0018]     The substrate may include a write yoke. The substrate may include other components of a write transducer. The substrate may include other components of a read transducer. The ramp may be generally planar. The ramp may include a series of cascading steps. The disk drive may include a magnetic storage disk adjacent to the head, the disk having an SUL, wherein the distance from the ABS to a first step may be equal to or greater than the distance from the ABS to the SUL.  
         [0019]     The invention may also relate to a method for producing a tapered write pole in a read/write head for a disk drive. The method may include providing a substrate; depositing an insulative material to the substrate, at least a portion of the insulative material forming a ramp; applying a write pole tip layer to the structure so that the write pole tip has a tapered surface corresponding to the ramp; and lapping the entire structure to create an ABS surface.  
         [0020]     Numerous additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the further description that follows.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a side view of portions of a read/write head according to the present invention adjacent to a magnetic storage disk.  
         [0022]      FIG. 2  is a view like  FIG. 1 , showing an alternative embodiment for the read/write head of the present invention.  
         [0023]      FIG. 3  is a side view of a portion of the read/write head during a manufacturing process step.  
         [0024]      FIG. 4  is a view like  FIG. 3  showing the read/write head at a later time in the manufacturing process.  
         [0025]      FIG. 5  is a view like  FIG. 4  showing the read/write head in an even later point in the manufacturing process.  
         [0026]      FIG. 6  is a view similar to  FIG. 1  showing an alternative embodiment of a read/write head of the present invention.  
         [0027]      FIG. 7  is a top view of a disk drive system that utilizes a read/write head of the present invention.  
         [0028]      FIG. 8  is a view like  FIG. 1 , showing another alternative embodiment for the read/write head of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     Reference will now be made to the accompanying drawings, which assist in illustrating the various pertinent features of the present invention. Although the present invention will now be described primarily in conjunction with disk drives, it should be expressly understood that the present invention may be applicable to other applications where magnetic recording of data is required/desired. In this regard, the following description of a disk drive is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention.  
         [0030]      FIG. 7  illustrates one embodiment of a disk drive  10 . The disk drive  10  generally includes a base plate  12  and a cover (not shown) that may be disposed on the base plate  12  to define an enclosed housing or space for the various disk drive components. The disk drive  10  includes one or more data storage disks  14  of any appropriate computer-readable data storage media. Typically, both of the major surfaces of each data storage disk  14  include a plurality of concentrically disposed tracks for data storage purposes. Each disk  14  is mounted on a hub or spindle  16 , Which in turn is rotatably interconnected with the disk drive base plate  12  and/or cover. Multiple data storage disks  14  are typically mounted in vertically spaced and parallel relation on the spindle  16 . Rotation of the disk(s)  14  is provided by a spindle motor  18  that is coupled to the spindle  16  to simultaneously spin the data storage disk(s)  14  at an appropriate rate.  
         [0031]     The disk drive  10  also includes an actuator arm assembly  20  that pivots about a pivot bearing  22 , which in turn is rotatably supported by the base plate  12  and/or cover. The actuator arm assembly  20  includes one or more individual rigid actuator arms  24  that extend out from near the pivot bearing  22 . Multiple actuator arms  24  are typically disposed in vertically spaced relation, with one actuator arm  24  being provided for each major data storage surface of each data storage disk  14  of the disk drive  10 . Other types of actuator arm assembly configurations could be utilized as well, such as an “E” block having one or more rigid actuator arm tips or the like that cantilever from a common structure. In any case, movement of the actuator arm assembly  20  is provided by an actuator arm drive assembly, such as a voice coil motor  26  or the like. The voice coil motor  26  is a magnetic assembly that controls the operation of the actuator arm assembly  20  under the direction of control electronics  28 . Any appropriate actuator arm assembly drive type may be utilized by the disk drive  10 , including a linear drive (for the case where the actuator arm assembly  20  is interconnected with the base plate  12  and/or cover for linear movement versus the illustrated pivoting movement about the pivot bearing  22 ) and other types of rotational drives.  
         [0032]     A load beam or suspension  30  is attached to the free end of each actuator arm  24  and cantilevers therefrom. Typically, the suspension  30  is biased generally toward its corresponding disk  14  by a spring-like force. A slider  32  is disposed at or near the free end of each suspension  30 . What is commonly referred to as the “head” (e.g., transducer) is appropriately mounted on the slider  32  and is used in disk drive read/write operations.  
         [0033]     The head on the slider  32  may utilize various types of read sensor technologies such as anisotropic magnetoresistive (AMR), giant magnetoresistive (GMR), tunneling magnetoresistive (TuMR), other magnetoresistive technologies, or other suitable technologies. AMR is due to the anisotropic magnetoresistive effect with a normalized change in resistance (ΔR/R) of 2-4%. GMR results from spin-dependent scattering mechanisms between two (or more) magnetic layers. The typical use in recording heads is the spin valve device that uses a pinned magnetic layer and a free layer to detect external fields. The normalized change in resistance is typically 8-12%, but can be as large as 15-20% when used with specular capping layers and spin-filter layers. TuMR is similar to GMR, but is due to spin dependent tunneling currents across an isolation layer. The typical embodiment includes a free layer and a pinned layer separated by a insulating layer of Al 2 O 3  with the current flowing perpendicular to the film plane, producing normalized change in resistance of 12-25%. The term magnetoresistive is used in this application to refer to all these types of magnetoresistive sensors and any others in which a variation in resistance of the sensor due to the application of an external magnetic field is detected. The write transducer technology of the head of the present invention is discussed in further detail below.  
         [0034]     The biasing forces exerted by the suspension  30  on its corresponding slider  32  thereby attempt to move the slider  32  in the direction of its corresponding disk  14 . Typically, this biasing force is such that if the slider  32  were positioned over its corresponding disk  14 , without the disk  14  being rotated at a sufficient velocity, the slider  32  would be in contact with the disk  14 .  
         [0035]     The head on the slider  32  is interconnected with the control electronics  28  of the disk drive  10  by a flex cable  34  that is typically mounted on the actuator arm assembly  20 . Signals are exchanged between the head and its corresponding data storage disk  14  for disk drive read/write operations. In this regard, the voice coil motor  26  is utilized to pivot the actuator arm assembly  20  to simultaneously move the slider  32  along a path  36  and “across” the corresponding data storage disk  14  to position the head at the desired/required radial position on the disk  14  (i.e., at the approximate location of the correct track on the data storage disk  14 ) for disk drive read/write operations.  
         [0036]     When the disk drive  10  is not in operation, the actuator arm assembly  20  is pivoted to a “parked position” to dispose each slider  32  generally at or beyond a perimeter of its corresponding data storage disk  14 , but in any case in vertically spaced relation to its corresponding disk  14 . This is commonly referred to in the art as being a dynamic load/unload disk drive configuration. In this regard, the disk drive  10  includes a ramp assembly  38  that is disposed beyond a perimeter of the data storage disk  14  to typically both move the corresponding slider  32  vertically away from its corresponding data storage disk  14  and to also exert somewhat of a retaining force on the actuator arm assembly  20 . Any configuration for the ramp assembly  38  that provides the desired “parking” function may be utilized. The disk drive  10  could also be configured to be of the contact start/stop type, where the actuator arm assembly  20  would pivot in a direction to dispose the slider(s)  32  typically toward an inner, non-data storage region of the corresponding data storage disk  14 . Terminating the rotation of the data storage disk(s)  14  in this type of disk drive configuration would then result in the slider(s)  32  actually establishing contact, with or “landing” on its corresponding data storage disk  14 , and the slider  32  would remain on the disk  14  until disk drive operations are re-initiated.  
         [0037]     The slider  32  of the disk drive  10  may be configured to “fly” on an air bearing during rotation of its corresponding data storage disk(s)  14  at a sufficient velocity. The slider  32  may be disposed at a pitch angle such that its leading edge is disposed further from its corresponding data storage disk  14  than its trailing edge. The head would typically be incorporated on the slider  32  generally toward its trailing edge since this is positioned closest to its corresponding disk  14 . Other pitch angles/orientations could also be utilized for flying the slider  32 .  
         [0038]     As shown in  FIG. 1 , a write head pole region  50  of a read/write head includes a portion of a write pole  52  and possibly a write shield  54 . The present invention is equally applicable to shielded as well as unshielded write pole designs (e.g., monopole designs). The head  50  is positioned so that the write pole  52  and write shield  54  are adjacent to a magnetic storage disk  56  having an SUL. Typically, the disk drive system will be configured so that the magnetic storage disk  56  is moved relative to the write head  50 , although it is possible for the head  50  to be moved relative to the storage disk  56 . Also, most typically the storage disk  56  is moved in a direction from right to left as viewing the arrangement in  FIG. 1 . Thus, a specific portion of the magnetic storage disk  56  would move by the write pole  52  prior to moving by the write shield  54 .  
         [0039]     In referring to components in the head  50 , it is common to refer to one side of a component as being at the leading edge or side of the component if it is on the side of the component that a particular portion of the magnetic storage disk  56  passes by prior to passing other portions of the component. Similarly, it is common to refer to a side of a component on the head  50  that is last passed by a specific portion of the storage disk  56  as the trailing edge or side of the component. Other terminology such as upstream and downstream portions and other alternatives may also be used.  
         [0040]     As can be seen in  FIG. 1 , the write pole  52  has a side facing the magnetic storage disk  56  that is generally planar and parallel to the upper surface of the storage disk  56 . This side of the write pole  52  is referred to as the ABS side  58 . The write pole  52  also has sides generally facing in the direction of the observer when viewing  FIG. 1  and on an opposite side thereof. These lateral sides are not depicted in any detail in  FIG. 1 . The write pole  52  also has a trailing side  62  that generally faces toward the write shield  54 , is generally planar in a region near the ABS side  58 , and is generally perpendicular to the ABS side  58 . The write pole  52  also has a leading side  60  that is generally on an opposite face from the trailing side  62  and thus faces away from the write shield  54 . In this embodiment, the leading side  60  is generally planar in the region near the ABS side and is not precisely perpendicular to the ABS side, but is closer to perpendicular to the ABS side than parallel thereto. Thus, this leading side may be said to be generally perpendicular to the direction of travel. As can be seen in  FIG. 1 , these characteristics cause the write pole  52  to be tapered in the region near the ABS side  58 . The magnitude of this taper can be expressed as the taper angle, which is the angle between a plane perpendicular to the ABS side  58  yet parallel to the trailing side  62  and the plane formed by the leading side  60 . For example, in this embodiment, the taper angle is approximately  10  degrees (although the drawing may not be exactly to scale). The taper angle may also be referred to as a leading edge bevel, which should not be confused with the side bevel inherent in a trapezoidal footprint. Although not shown in  FIG. 1 , the write pole  52  may have a trapezoidal footprint.  
         [0041]     It has been discovered that write poles with non-zero taper angles provide a greater write field for a given pole thickness than do write poles with a zero taper. Further, the dependence of the amplitude of the write field on the taper angle is greater with smaller write pole thicknesses. In this discussion, the write pole thickness refers to the length of the ABS side  58  of the write pole  52  as shown in  FIG. 1 . In other words, it is the length of the ABS side  58  from the trailing side  62  to the leading side  60 . From this discovery, it can be seen that with the use of tapered write poles it is possible to produce a given write field with a write pole of lesser thickness. Reducing the thickness of the write pole reduces the skew effect as it reduces the length of the lateral edge of the footprint at the ABS and the area of the lateral side of the write pole. Thus, it can be seen that through the use of trapezoidal-shaped write poles (in a footprint sense) that are also tapered (as viewed in  FIG. 1 ), the skew profile can be greatly reduced.  
         [0042]     For example, it has been found that with distances of 50 nanometers from the ABS side  58  to the SUL of the magnetic storage disk  56  and pole thicknesses in the range of 250 nanometers that a trapezoidal shaped head having a bevel of 10 degrees that is also tapered with a taper angle of 10 degrees can greatly reduce the skew profile of the head. It has been discovered that this enhanced effect to the write field continues as the taper angle is made greater. However, as the taper angle becomes greater, it may become more difficult to control the pole thickness. This difficulty arises because the amount of lapping back of the head in the manufacturing process is much more critical since the taper and the amount of lapping together determine the pole thickness. For this reason, it has been found that taper angles less than 20 degrees are preferred. More specifically, it is preferred for taper angles to be between 5 and 15 degrees. Even more specifically, it has been found that taper angles between 7 and 13 degrees may work best. As stated above, in this specific embodiment, a taper angle of 10 degrees is used. It should also be understood that only small portions of the write head  50  and of the combined read/write head are shown in  FIG. 1 . In particular, there is a read transducer that is not shown. Further, there are write coils that are not shown as well as the fact that only portions of the write shield  54  and write pole  52  are illustrated. Other arrangements that include having a tapered trailing or leading side on a write pole are considered to fall within the invention described herein.  
         [0043]      FIG. 2  discloses a somewhat similar approach, with the primary difference being that the tapered surface of the write pole is on a trailing side, or a side facing toward the write shield (if the design includes a write shield) rather than away from the write shield.  FIG. 8  shows a similar arrangement to that shown in  FIG. 2 , with the difference being that the side of the write shield facing toward the write pole is similarly tapered so that the two facing sides are parallel. With this arrangement, the write gap between the write pole and the write shields is constant and thus the magnitude of the effective write gap is not made a function of how precisely one can control the lapping process.  
         [0044]     An exemplary process for manufacturing the tapered write pole  52  as part of the write head  50  is illustrated in  FIGS. 3, 4 , and  5 . Of course, several minor and major components of the head  50  have been omitted for ease of illustration and explanation. In  FIG. 5 , a substrate  70  on a wafer is shown with a write yoke  72  having already been deposited thereon. The write yoke  72  has been deposited, encapsulated, and planarized with chemo-mechanical polishing (CMP). A photoresist mask  74  has been placed on top of the write yoke  72  and  FIG. 3  illustrates the ion beam deposition (IBD) of aluminum oxide (Al 2 O 3 ) and a swept or continuously varying deposition angle. As can be seen, this deposition process creates a ramped deposit of Al 2 O 3    76  on the substrate  70 .  
         [0045]     Next, the photoresist mask  74  is lifted off and a write pole tip layer  78  is deposited on top of the write yoke  72  and ramped Al 2 O 3  deposit  76  as is shown in  FIG. 4 . The write pole tip layer  78  can be patterned by ion milling as necessary.  
         [0046]     Next, the write pole tip layer  78  is encapsulated with Al 2 O 3  and CMP is used to planarize it. This yields a structure such as is shown in  FIG. 5 . Lapping is then performed to the ends of a plurality of heads that are in bar form. The lapping generally removes all of the material to the right of the dashed line  84  in  FIG. 5  to define the final ABS or ABS side  58 . As can be appreciated, the resulting structure has a tapered side facing toward the substrate  70 .  
         [0047]     An alternative process is discussed in conjunction with  FIG. 6 .  FIG. 6  shows a write head pole region  90  (of a read/write head) having a write pole  92  and a write shield  94 . The head  90  is adjacent to a magnetic storage disk  96 . As can be seen, the taper in the write pole  92  is illustrated as not being exactly planar in shape. Instead, the taper is achieved by a series of process steps that produce a stepped edge that approximates a taper. The process steps could include additive steps, subtractive steps, or any other suitable methodology. One example of step heights and spacing may be step heights and widths of 20 nanometers. The steps and heights should be selected appropriate to provide the desired effective taper angle of approximately 10 degrees.  
         [0048]     It can also be appreciated that this invention is distinguishable from a somewhat similar disclosure from Hitachi in 2000. M. Mochizuke et al., J. of Magnetism and Magnetic Materials 235, p. 194,  FIG. 8  (2001). In this disclosure, a write pole is produced and then a 45 degree bevel is cut-out at the ABS. Unfortunately, it is very difficult to manufacture a write head in this manner since it is difficult to ion mill the write head at the ABS in an accurate and economical method that has minimal defects.  
         [0049]     The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.