Abstract:
In a T-head design, it is desirable to reduce the side-writing that occurs during the write operation. The side-writing causes the track width to increase and therefore reduces the track density that can be achieved. The side-writing is caused by certain corners of the T-head producing extraneous fluxes over the magnetic disk. The extraneous fluxes write to the magnetic disk, causing the track width to be increased. The present invention recesses part of the T-head from the air bearing surface by a focused ion beam milling, an ion milling, or an etching process. The extraneous fluxes are therefore recessed from the magnetic disk by a shallow distance sufficient to prevent writing to the magnetic disk, but not so great a distance to inhibit the flux carrying capacity of the structure to the actively writing pole tip.

Description:
FIELD OF THE INVENTION 
     The present invention relates to write heads for magnetic disk drives and more particularly to methods of reducing side writing of the write head in magnetic disk drives. 
     DESCRIPTION OF THE RELATED ART 
     Magnetic head disk drive systems have been widely accepted in the computer industry as a cost-effective form of data storage. In a magnetic disk drive system, a magnetic recording medium in the form of a disk rotates at high speed while a magnetic read/write transducer, referred to as a magnetic head, “flies” slightly above the surface of the rotating disk. The magnetic disk is rotated by means of a spindle drive motor. The magnetic head is attached to or formed integrally with a “slider” which is suspended over the disk on a spring-loaded support arm known as the actuator arm. As the magnetic disk rotates at operating speed, the moving air generated by the rotating disk in conjunction with the physical design of the slider lifts the magnetic head, allowing it to glide or “fly” slightly above and over the disk surface on a cushion of air, referred to as an air bearing. The flying height of the magnetic head over the disk surface is typically only a few tens of nanometers or less and is primarily a function of disk rotation, the aerodynamic properties of the slider assembly and the force exerted by the spring-loaded actuator arm. 
     The dimensions of a slider&#39;s transducer can be a substantial factor in defining the number of data tracks that may be written onto a magnetic disk. Specifically, the effective magnetic width of the pole tip region of the magnetic transducer is directly related to the physical width, as well as to other factors such a flying height above the rotating disk, in the case of flying head technology. In turn, the transducer&#39;s magnetic width relates to the width of each track written to the storage medium. If the width of the pole tip region of the transducing member is made relatively smaller, a greater number of tracks can be written in the same recording area. Therefore, the width of the pole tip region of a magnetic transducer is inversely related to track density of the magnetic storage medium. 
     However, the reduction in width of the pole tip also limits the amount of magnetic flux flowing to the pole tip for writing operations. One solution to this problem is to create a pole tip that has a “T” like shape, herein referred to as the T-head. The wider part of the “T” conducts magnetic flux to the bottom of the “T”. This enables sufficient magnetic flux to flow into the pole tip, which is the bottom tip of the “T” like structure, for writing operations. 
     Yet, this T-head configuration has its own problems. The top part of the T-head, which is the horizontal part, has four corners exposed to the air bearing surface, directly over the magnetic disk that is being written. These corners create extraneous magnetic fluxes, which causes side-writing and therefore reduces the track density. 
     A need therefore exists for providing a T-head with significantly reduced side-writing during the write operation of the magnetic transducer. 
     SUMMARY OF THE INVENTION 
     A principle objective of the present invention is to provide a T-head with reduced side-writing and a method for making a T-head with reduced side-writing. 
     In view of the foregoing objects, the present invention provides a T-head design that recesses portions of the T-head to increase the distance between the recessed portion of the T-head and the magnetic disk. This would reduce the side-writing of the T-head. The method for recessing a portion of the T-head is performed in a focused ion beam (FIB) operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention, reference being made to the accompanying drawing, in which like reference numerals indicate like parts and in which: 
     FIG. 1 is a simplified block diagram of a magnetic disk storage system; 
     FIGS. 2A and 2B are cross-sectional views of MR read/inductive write magnetic transducers; 
     FIG. 3 is an illustration showing a plan view of an embodiment of the present invention; 
     FIG. 4 is an illustration showing a side view of an embodiment of the present invention; 
     FIG. 5 is an illustration showing an overall view of an embodiment of the present invention. 
     FIG. 6 is a graph illustrating the effects of side-writing before the recessing of P 3 . 
     FIG. 7 is a graph illustrating the reduction in effects of side-writing after the recessing of P 3 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Although the invention is described as embodied in a magnetic disk storage system, the invention also applies to other magnetic recording systems and applications using a sensor to detect a magnetic field, such as magnetic tape recording systems for example. 
     Referring to prior art FIG. 1, a magnetic disk storage system comprising at least one rotatable magnetic disk  20  is supported on a spindle  22  and rotated by a disk drive motor  24  with at least one slider  26  positioned on the disk  20 . Each slider  26  supports one or more magnetic read/write transducers  28 , typically referred to as read/write heads. The magnetic recording media on each disk is in the form of a thin film on which are recorded an annular pattern of concentric data tracks (not shown) on disk  20 . As the disks rotate, the sliders  26  are moved radially in and out over the disk surface  30  so that the heads  28  may access different portions of the disk where desired data is recorded. Each slider  26  attaches to an actuator arm  32  by means of a suspension  34 . The suspension  34  provides a slight spring force which biases the slider against the disk surface  30 . Each actuator arm  32  attaches to an actuator means  36 . The actuator means as shown in FIG. 1 may be a voice coil motor (VCM), for example. The VCM comprises a coil moveable within a fixed magnetic field. The controller supplies motor current signals to control the direction and acceleration of the coil movements. 
     During operation of the disk storage system, the rotation of the disk  20  generates an air bearing between the slider  26  and the disk surface  30  which exerts an upward force or lift on the slider. The air bearing thus counterbalances the slight spring force of the suspension  34  and supports the slider off and slightly above the disk surface a small, substantially constant spacing during operation. 
     The various components of the disk storage system are controlled in operation by control signals generated by control unit  38 , such as access control signals and internal clock signals. Typically, the control unit  38  comprises logic control circuits, storage means and a microprocessor, for example. The control unit  38  generates control signals to control various system operations such as drive motor control signals on line  40  and head position and seek control signals on line  42 . The position control signals  42  provide the desired current profiles to optimally move and position a selected slider  26  to the desired data track on the associated disk  20 . A recording channel  44  communicates read and write signals to and from the read/write heads  28 . 
     The above description of a typical magnetic disk storage system, and the accompanying illustration of FIG. 1 are for representation purposes only. Disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders. 
     Referring now to prior art FIGS. 2A and 2B, a portion of a giant magnetoresistive (G)MR read/inductive write magnetic head or magnetic head assembly or head  50  is shown in transducing relationship with a rotating magnetic disk  20  such that the head air bearing surface  52  (ABS) is disposed in facing relationship with and slightly above the disk recording surface. Generally, such a magnetic head assembly  50  includes an (G)MR read assembly and an inductive write assembly formed adjacent to one another on a substrate surface. The substrate surface is typically the vertical surface forming the trailing end of the slider  26  carrying the magnetic head. A traditional MR read assembly comprises an anisotropic magnetoresistive (AMR) sensing element  54  fabricated of a ferromagnetic material, such as nickel-iron (NiFe) alloy, for example, which is enclosed by first and second magnetic shield elements  56  and  58 , respectively. In a more advanced giant magnetoresistive (GMR) head, the magnetic sensing element  54  comprises a multilayer magnetic structure, including magnetic bias layers, of the type described in commonly assigned U.S. Pat. No. 4,785,366 or of the type described in commonly assigned U.S. Pat. No. 5,206,590. This multilayer magnetic structure consists of a conducting layer sandwiched by two magnetic layers, one of which has a fixed magnetization. The other magnetic layer&#39;s magnetization is free to change, affected by an external magnetic field. By utilizing the spin direction of electrons transversing these three layers, a giant MR effect is created. The shield elements  56  and  58  are generally made of a highly permeable magnetic material, such as NiFe or Sendust, a trialloy of aluminum-silicon-iron. The magnetic shield elements  56  and  58  minimize or eliminate magnetic interferences from affecting the (G)MR sensing element  54  thereby producing extraneous electrical pulses and improve the resolution of the sensor thereby allowing more closely spaced data patterns to be read. Conductive leads, of tantalum (Ta) or copper (Cu) or other suitable conductive material, attached electrically at the end portions of the (G)MR element  54  couple the (G)MR sensing element to external circuitry to provide a means for sensing the resistance of the (G)MR sensing element. 
     The (G)MR read assembly is formed by well-known vacuum deposition techniques, such as sputter deposition, for example, on the substrate  60 . Layers  62  of insulating material surround and insulate the various elements of the (G)MR assembly from each other. For example, the layers  62  are made from silicon dioxide (SiO.sub.2) or aluminum oxide (Al.sub.2 O.sub.3). 
     The inductive write assembly comprises a lower or first pole piece  64  and an upper or second pole piece  66 . The first and second pole pieces  64 ,  66  are made of a highly permeable magnetic material such as NiFe, for example. The first and second pole pieces  64 ,  66  form a magnetic circuit magnetically connected together at a back gap portion (not shown) with the first and second pole tips  68 ,  69  forming a magnetic gap  70  at the air bearing surface  52 . One or more layers of electrical conductors  72 , generally made of Cu, for example, form a write coil  72  disposed between the first and second pole pieces  64 ,  66 . The write coil  72  also connects to external circuitry via conductive leads. The pole pieces  64 ,  66  and the write coil conductors are fabricated by well-known processes such as electro-plating or sputter deposition, for example. Layers  62  of insulating material electrically insulate the pole pieces from the write coil and the (G)MR read assembly. In addition, a capping layer  62  of insulating and protective material covers the entire assembly. 
     The magnetic head assembly  50  shown in FIG. 2 a  is sometimes referred to as a “piggyback” head. FIG. 2 b  shows an alternate configuration referred to as a “merged” head where the second (G)MR magnetic shield element  58  is merged with the inductive assembly first pole piece  64  to form a single element  74  which performs both functions. 
     FIG. 3 illustrates an embodiment of the present invention. A T-head is shown illustrating the fluxes that occur in the three pole elements. Pole P 1   300  is analogous to the first pole piece  64  in FIG.  2 B and pole P 2   302  is analogous to the second pole piece  66  in FIG.  2 B. Pole P 3   304  is not shown in FIG. 2B but is also referred to as third pole piece. The flux  308  that is created between the P 1   300  and P 2   302  pole tips is used to write data on the magnetic disk. The width of pole tip P 2   306  determines the track width which also directly affects the track density of the magnetic disk. It is desirable to maximize the track density of the magnetic disk and therefore minimize the width of pole tip of pole P 2   302 . However, as pole P 2   302  gets narrower and narrower, there is less and less material to conduct magnetic flux to the tip to create the magnetic flux  308  that writes the disk. 
     To solve this problem, pole P 3   304  is used to assist in conducting magnetic flux to pole P 2   302  for creating the magnetic flux  308  that writes the disk. For the same height in Pole P 2   302  and Pole P 3   304 , if Pole P 3   304  is wider than pole P 2   302 , it can therefore carry more magnetic flux than pole P 2   302 . However, the corners of pole tip P 3  creates extraneous flux  310  that is causing side-writing on the magnetic disk. This side-writing in effect increases the track width of the magnetic transducer and requires greater spacing between tracks to prevent erroneous readings during the read-back operation. 
     The present invention solves this problem by recessing the tip of pole P 3   304  by approximately 5-10 nanometers. This sets the tip pole P 3   304  back from the magnetic disk, thereby significantly reducing the ability of the extraneous magnetic flux  310  to write to the magnetic disk. 
     FIG. 4 shows a side view of the present invention which illustrates clearly that the pole P 3   408  is shallow recessed. A prior art T-head  420  is shown and a T-head  430  of the present invention, with the pole P 3   408  recessed which is also shown. The magnetic flux  400  used for the writing of data is shown between the tips of poles P 1   402  and P 2   404 . The magnetic flux  412  caused by the corners of pole tip P 3   406  is also shown. The extraneous magnetic flux  412  at the corners of pole tip P 3  is causing the side-writing. 
     The present invention shows a T-head  430  with the pole P 3   408  tip shallow recessed from the tip of pole P 2   404 . Because of the increased distance  410  between the extraneous magnetic flux  416  generated by the recessed corners of pole P 3   408  and the magnetic disk (not shown), the extraneous magnetic flux  416  is much less effective in side-writing on the magnetic disk. 
     The present invention minimizes the recess of pole P 3   408  tip to a distance just enough to prevent extraneous flux from writing to the magnetic disk. Through experimental data, it has been found that with a recess of 5 to 10 nanometers, the effects of side-writing can be reduced to a point where the track width is determined by the width of P 2 . Any further recess has produced no significant increase in the reduction of side-writing. However, as the size of T-heads reduce, the minimum amount of recess of pole P 3   408  tip will also decrease. 
     FIG. 5 illustrates a cross section of a write head of the present invention. The pole tips of poles P 1   500 , P 2   502 , and P 3   504  are shown in context of the write head. Pole P 1   500  is on the bottom. Slightly on top of that is pole P 2   502 , which is connected to pole P 3   504 . Pole P 3   504  is connected to P 2   502  in order to assist in conducting magnetic flux to the pole tip of pole P 2   502  to create enough magnetic flux  510  between tips of poles P 2   502  and P 1   500  to write data on the magnetic disk. As the illustration shows, the pole tip P 3  is recessed from the tip of pole P 2   502 . The recess is shown as area  506 . This recess of pole tip P 3  from the tip of pole P 2   502  significantly reduces side-writing. The present invention recesses the pole tip of pole P 3   504  by 5 to 10 nanometers. It has been shown experimentally that recessing by more than 5 to 10 nanometers does not yield any significant increase in the reduction of side-writing compared to recessing only by 5 to 10 nanometers. 
     The ability of the pole P 3  to conduct magnetic flux to pole tip of pole P 2   502  is also inversely related to the amount of recession  506  in the pole tip of pole P 3   504 . As FIG. 5 illustrates, the recess in the pole tip of pole P 3   504  decreases the contact area between poles P 2   502  and P 3   504 . This reduces the effectiveness of pole P 3   504  to conduct magnetic flux to the pole tip of pole P 2   502 . 
     FIG. 6 illustrates a graph showing the effects of side-writing before the recessing of P 3 . The high tails  600  on the leading edge of the track profiles  602  illustrates the side-writing that is caused by the extraneous magnetic fluxes at the corners of pole tip P 3 . 
     FIG. 7 illustrates a graph showing the reduced side-writing after the recessing of pole tips of pole P 3  by 5 to 10 nanometers. The tails  700  on the leading edge of the track profiles  702  are much lower signifying a much reduced side-writing by the corners of pole tips of pole P 3 . 
     The reduction of side-writing by recessing the pole tip P 3  to beyond 5 to 10 nanometers will become less and less significant. Therefore, it is unnecessary to trim pole tip P 3  beyond 10 nanometers. This is in contrast to prior art recessing of the P 3  to 1 micron. The manufacturing throughput of prior art recessing of the P 3  by 1 micron is approximately 5 seconds per write head which translates into approximately 4 hours of focused ion beam milling time of the total wafer handling budget of approximately 8 hours per wafer. In contrast, the present invention has a theoretical manufacturing throughput of approximately 0.002 seconds per write head element which translates into approximately 12 seconds of focused ion beam milling time per wafer reducing the total wafer handling budget to approximately 4 hours. 
     The recessing of the tip of pole P 3  can be performed by other manufacturing processes besides focused ion beam milling (FIB) as indicated above. The advantage of FIB milling is that it does not require pattern masking. Alternative manufacturing processes include ion milling and chemical or reactive ion etching (RIE) processes which require pattern masking but allows batch processing of head rows. 
     A wafer is cut into head rows and each head row is masked using lithography processes, leaving only the tip of pole P 3  exposed on the surface of the head row. Each head row is exposed to ion particle bombardment or reactive etchants to remove the desired amount of material to recess the tip of pole P 3 . The masked areas of the heads are protected from the ion particle bombardment or the reactive etchants and therefore the material beneath the mask is not removed. 
     The shallow recessing of the pole tip of pole P 3  leaves a relatively large area of pole P 3  in contact with the pole P 2 . This large area of contact provides a good conduit between pole P 3  and the P 2  pole tip allowing ample magnetic flux to flow to the P 2  pole tip for writing operations. 
     It will be clear to one skilled in the art that the above embodiment may be altered in many ways without departing from the scope of the invention. Accordingly, the scope of the invention should be determined by the following claims and their legal equivalents.