Abstract:
One or two shield structures is provided for a read head wherein each shield structure has a heat sink layer for dissipating heat from the read sensor and a ferromagnetic layer for shielding signal fields from a rotating magnetic disk other than the signal field being detected by the read head. In a preferred embodiment the heat sink layer employs a gold (Au) film between first and second tantalum (Ta) films and the ferromagnetic layer employs an iron nitride (FeN) film and a nickel iron cobalt (NiFeCo) film. The ferromagnetic layer is located between the heat sink layer and the read sensor. Iron nitride (FeN) has a high magnetization so that it can be relatively thin and yet provide necessary shielding of the read sensor and the nickel iron cobalt (NiFeCo) film as a high uniaxial anisotropy (H K ) which ensures that the magnetic moment of the ferromagnetic layer returns to its original position parallel to the air bearing surface of the read head after being rotated by an external magnetic field. The thinness of the iron nitride (FeN) film locates the heat sink layer close to the read sensor for improved heat dissipation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a shield structure with a heat sink layer for dissipating heat from a read sensor and, more particularly, to a shield structure which has a heat sink layer and a ferromagnetic layer wherein the heat sink layer includes a gold film and the ferromagnetic layer includes iron nitride (FeN) and nickel iron cobalt (NiFeCo) films. 
     2. Description of the Related Art 
     The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are embedded in a slider and have an air bearing surface (ABS) that is exposed for facing the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk so that the read and write heads are positioned for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
     The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack) which are, in turn, sandwiched 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 and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field in the pole pieces which causes flux across the gap at the ABS for the purpose of writing the aforementioned magnetic impression in tracks on the aforementioned rotating disk. 
     The read head includes a read sensor which is located between nonmagnetic nonconductive first and second read gap layers. The first and second read gap layers are located between ferromagnetic first and second shield layers. First and second leads are connected to the sensor for conducting a sense current I S  therethrough and are further connected by additional leads to the processing circuitry. The magnetization of the sensor changes in response to signal fields from tracks on the rotating disk which causes a change in the resistance of the sensor. These resistance changes cause corresponding potential changes in the processing circuitry which are processed as playback signals. 
     The sense current I S  is a major contributor to the generation of heat within the magnetic head. Another heat source is the write coil in the write head. Excessive heat generated within the magnetic head can degrade the magnetics of the ferromagnetic layers in the read sensor as well as causing pole tip protrusion. Pole tip protrusion is caused by heat expansion of the insulation stack which, in turn, causes an alumina overcoat layer to protrude beyond the ABS and destroy the head. Accordingly, the sense current I S  and the write coil current are maintained at appropriate levels so that heat will not degrade performance of the head. It is known, however, that an increase in the sense current I S  results in an increased detection of the signal fields from the rotating disk. An increase in the detected signal equates to increased storage capacity of the magnetic disk drive. 
     The first and second shield layers of the read head are the best candidates for reducing heat generated by the sensor. It is desirable that the materials employed for the first and second shield layers have the best heat conductivity possible for promoting heat dissipation. Constraints on the selection of shield materials, however, are acceptable hardness, sufficient magnetization (M S ) to function as a shield and sufficient magnetic stability so that a magnetic moment of the shield layer fully returns to its easy axis orientation. Hardness is important because of a lapping process which laps the air bearing surface of the magnetic head. The ABS must be precisely lapped so that the sensor is established with a designed stripe height. Lapping is a grinding process which can smear soft materials across the ABS and cause shorting between the sensitive elements of the read sensor to the first and second shield layers. The shields are required to have high magnetization (M S ) so that the shields will readily conduct signal fields from bits (magnetic impressions) on the rotating disk adjacent to the bit being read by the read head. In order to promote magnetic stability it is required that the shield material have a high uniaxial anisotropy (H K ). The easy axis of the magnetic moment of each shield layer is parallel to the ABS and the surface planes of the shield layers. In a merged head, where the second shield layer also serves as a first pole piece layer, the write current rotates the magnetic moment of the second shield/first pole piece layer perpendicular to the ABS during the write function. If the magnetic moment does not return to the original parallel position to the ABS after relaxation of the write current the magnetic moment will magnetically influence the sensor in a different way which will alter the performance of the read head. Accordingly, it is important to consider the hardness of the materials and the magnetics of materials when selecting a material to improve the heat conductivity of the shield layers. 
     Typical materials employed for shield layers are Sendust (FeAlSi) and nickel iron (NiFe). Nickel iron (NiFe) is known to be a better heat sink than Sendust (FeAlSi), however, nickel iron (NiFe) has a tendency to smear across the ABS during the lapping operation. There is strong-felt need for providing shield layers which have heat conductivity, yet will provide the required hardness and magnetic properties mentioned hereinabove. 
     SUMMARY OF THE INVENTION 
     The present invention provides a shield stricture which includes a heat sink layer for dissipating heat and a ferromagnetic layer for satisfying the aforementioned magnetic properties of the shield layer. In a preferred embodiment, the heat sink layer includes a gold (Au) film. Gold (Au) is soft and will smear across the ABS unless properly supported. The gold (Au) film is sandwiched between first and second tantalum (Ta) films which are harder than gold and actually increase the hardness of the gold (Au) film itself. Gold (Au) has approximately four times the heat conductivity of nickel iron (NiFe). In a preferred embodiment the ferromagnetic layer includes an iron nitride (FeN) film and a nickel iron cobalt (NiFeCo) film. Iron nitride (FeN) is harder than Sendust (FeAlSi) or nickel iron (NiFe) which plays an important role in the invention which will be discussed hereinafter. Iron nitride (FeN) also has a high magnetization (M S ) which is approximately twice the magnetization (M S ) of nickel iron cobalt (NiFeCo). This is important so that the shield structure functions as a good magnetic shield for the sensor. On the other hand, nickel iron cobalt (NiFeCo) has a higher uniaxial anisotropy (H K ) than iron nitride (FeN). This ensures that the magnetic moment of the shield layer will return to its original easy axis position parallel to the ABS after being rotated by an external magnetic field. While a single nickel iron cobalt (NiFeCo) film can be employed for a shield structure this would require that the nickel iron cobalt (NiFeCo) film be twice as thick as an iron nitride (FeN) film since the magnetization (M S ) of the nickel iron cobalt (NiFeCo) film is one-half the magnetization (M s ) of an iron nitride (FeN) film. Accordingly, by employing the iron nitride (FeN) film between the heat sink layer and the nickel iron cobalt (NiFeCo) film the shield structure can be made thinner so that the heat sink layer is closer to the sensor for increased heat dissipation. An optional substitution for the nickel iron cobalt (NiFeCo) film is a nickel iron (NiFe) film and alloys thereof. While nickel iron (NiFe) and gold (Au) have a tendency to smear during lapping the tantalum (Ta) films promote the hardness of the gold (Au) film and the iron nitride (FeN) film in the ferromagnetic layer is harder than all of the films which provides support during the lapping process to reduce smearing of the softer films. 
     An object of the present invention is to provide a shield structure which has increased heat conductivity without sacrificing hardness and magnetic properties of the shield structure. 
     Another object is to provide one or more shield structures which enables an increase in the sense current I S  without generating additional heat. 
     A further object is to provide a heat sink shield structure which provides high magnetization and high uniaxial anisotropy with a minimum thickness. 
     Other objects and 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 plan 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 slider taken along plane  5 — 5  of FIG. 2; 
     FIG. 6 is a partial view of the slider and a piggyback magnetic head as seen in plane  6 — 6  of FIG. 2; 
     FIG. 7 is a partial view of the slider and a merged magnetic head as seen in plane  7 — 7  of FIG. 2; 
     FIG. 8 is a partial ABS view of the slider taken along plane  8 — 8  of FIG. 6 to show the read and write elements of the piggyback magnetic head; 
     FIG. 9 is a partial ABS view of the slider taken along plane  9 — 9  of FIG. 7 to show the read and write elements of the merged magnetic head; 
     FIG. 10 is a view taken along plane  10 — 10  of FIGS. 6 or  7  with all material above the coil layer and leads removed; 
     FIG. 11 is an isometric ABS illustration of a prior art read head which employs a spin valve sensor; 
     FIG. 12 is an ABS illustration of a shield structure composed of Sendust; 
     FIG. 13 is the same as FIG. 12 except a heat sink layer composed of gold and tantalum underlies the Sendust film; 
     FIG. 14 is the same as FIG. 13 except the gold film is thicker; 
     FIG. 15 is an ABS illustration of the present invention wherein the shield structure includes a heat sink layer with gold and tantalum and a ferromagnetic layer with films of iron nitride (FeN) and nickel iron cobalt (NiFe Co); 
     FIG. 16 is an ABS illustration of a read head employing a shield structure such as that shown in FIG. 15; and 
     FIG. 17 is a read head wherein each of the first and second shield structures employs a shield structure such as that shown in FIG.  15 . 
    
    
     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, FIGS. 1-3 illustrate a magnetic disk drive  30 . The drive  30  includes a spindle  32  that supports and rotates a magnetic disk  34 . The spindle  32  is rotated by a spindle 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  that is rotatably positioned by an actuator  47 . A plurality of disks, sliders and suspensions may be employed in a large capacity direct access storage device (DASD) as shown in FIG.  3 . The suspension  44  and actuator arm  46  are moved by the actuator  47  to position the slider  42  so that the magnetic head  40  is in a transducing relationship with a surface of the magnetic disk  34 . When the disk  34  is rotated by the spindle 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 spindle motor drive signals for rotating the magnetic disk  34 , and provides control signals to the actuator  47  for moving the slider to various tracks. In FIG. 4 the slider  42  is shown mounted to a suspension  44 . The components described hereinabove may be mounted on a frame  54  of a housing  55 , as shown in FIG.  3 . 
     FIG. 5 is an ABS view of the slider  42  and the magnetic head  40 . The slider has a center rail  56 , which 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. 
     FIG. 6 is a side cross-sectional elevation view of a piggyback magnetic head  40 , which includes a write head portion  70  and a read head portion  72 , the read head portion employing a spin valve sensor  74  of the present invention. FIG. 8 is an ABS view of FIG.  6 . The spin valve sensor  74  is sandwiched between nonmagnetic nonconductive first and second read gap layers  76  and  78 , and the read gap layers are sandwiched between ferromagnetic first and second shield layers  80  and  82 . In response to external magnetic fields, the resistance of the spin valve 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 write head portion  70  of the magnetic head  40  includes a coil layer  84  sandwiched 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 sandwiched between first and second pole piece layers  92  and  94 . The first and second pole piece layers  92  and  94  are magnetically coupled at a back gap  96  and have first and second pole tips  98  and  100  which are separated by a write gap layer  102  at the ABS. An insulation layer  103  is located between the second shield layer  82  and the first pole piece layer  92 . Since the second shield layer  82  and the first pole piece layer  92  are separate layers this head is known as a piggyback head. As shown in FIGS. 2 and 4, first and second solder connections  104  and  106  connect leads from the spin valve 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. 10) to leads  124  and  126  on the suspension. 
     FIGS. 7 and 9 are the same as FIGS. 6 and 8 except the second shield layer  82  and the first pole piece layer  92  are a common layer. This type of head is known as a merged magnetic head. The insulation layer  103  of the piggyback head in FIGS. 6 and 8 is omitted. 
     FIG. 11 is an isometric ABS illustration of a prior art read head  72  which has a spin valve sensor  130 . An antiferromagnetic pinning layer  132 , such as 425 Å of nickel oxide (NiO), may be employed for pinning a magnetic moment of a pinned layer of the spin valve sensor  130  perpendicular to the ABS. First and second hard bias and lead layers  134  and  136  are connected to first and second side edges  138  and  139  of the spin valve sensor. This connection is known in the art as a contiguous junction and is fully described in commonly assigned U. S. Pat. 5,018,037. The first hard bias and lead layers  134  include a first hard bias layer  140  and a first lead layer  142  and the second hard bias and lead layers  136  include a second hard bias layer  144  and a second lead layer  146 . The hard bias layers  140  and  144  cause magnetic flux to extend longitudinally through the spin valve sensor  130  for stabilizing magnetic domains of the free layer. The spin valve sensor  130  and the first and second hard bias and lead layers  134  and  136  are located between nonmagnetic electrically insulative first and second read gap layers  148  and  150 . The first and second read gap layers  148  and  150  are, in turn, located between first and second shield layers  152  and  154 . 
     Various tests were conducted on the examples shown in FIGS. 12-15 to determine the sense current I S  while maintaining the generation of heat constant. The example shown in FIG. 15 is a preferred embodiment of the present invention. FIG. 12 shows a shield structure which employs a 5000 Å thick Sendust (FeAlSi) film  202 . This shield structure is typically employed for the first shield layer. FIG. 13 shows a shield structure  210  which is the same as the shield structure  200  except a heat sink layer  212  underlies the Sendust layer  202 . The heat sink layer includes a 2000 Å gold (Au) film  214  sandwiched between 50 Å thick tantalum (Ta) first and second films  216  and  218 . With the heat sink layer shown in FIG. 13 the shield structure was capable of conducting 5% more sense current I S  than the sense current I S  conducted by the shield structure  200  in FIG.  12 . In FIG. 14 there is shown a shield structure  220  which is the same as the shield structure  210  shown in FIG. 13 except the gold (Au) layer is 5000 Å thick instead of 2000 Å thick. The sense current I S  through the sensor was increased 7.5% over the FIG. 12 embodiment without generating additional heat. 
     The Invention 
     The present shield structure  300  is shown in FIG. 15 which includes the heat sink layer  212  and a ferromagnetic layer  302 . The gold (Au) film  214  is 2000 Å thick and each of the first and second tantalum (Ta) films  216  and  218  is 50 Å thick. The ferromagnetic layer  302  includes a 4000 Å thick iron nitride (FeN) film  304  and a 1000 Å thick nickel iron cobalt (NiFeCo) film  306 . As discussed hereinabove, the iron nitride (FeN) film  304  has high magnetization (M S ) and the nickel iron cobalt (NiFeCo) film  306  has a high uniaxial anisotropy (H K ). The iron nitride (FeN) film  304  provides a high degree of shielding for the sensor while the nickel iron cobalt (NiFeCo) film  306  provides magnetic stability by ensuring that a magnetic moment  310  of the ferromagnetic layer  302  returns to its original orientation parallel to the ABS. 
     FIG. 16 shows an ABS illustration of an exemplary read head  400  which is employed in either a merged or piggyback type of head. The read head  400  has a read sensor  402  which is connected to first and second hard bias and lead layers  404  and  406 . The read sensor  402  and the first and second hard bias and lead layers  404  and  406  are located between nonmagnetic nonconductive first and second read gap layers (G   1   and G2)  408  and  410 . The first and second read gap layers  408  and  410  are located between a first shield structure (S1)  412  and a second shield structure (S2) or second shield/first pole piece layer (S2/P1)  414 . The second shield structure  414  may be a single layer of nickel iron (NiFe). 
     The first shield structure  412  includes a heat sink layer  416  and a ferromagnetic (FM) layer  418  with the ferromagnetic layer  418  being located between the heat sink layer  416  and the first read gap layer  408 . The heat sink layer  416  includes first, second and third films  420 ,  422  and  424  with the second film  422  being located between the first and third films  420  and  424 . The second film  422  is a highly heat conductive film which is thicker than either of the first and second films  420  and  424  and may be composed of gold (Au), silver (Ag) or copper (Cu) with the preferred material being gold (Au). The first and third films  420  and  424  may be composed of tantalum (Ta), titanium (Ti) or chromium (Cr) with the preferred material being tantalum (Ta). The first and third films  420  and  424  are harder than the second film  422 . When the first and third films  420  and  424  are tantalum (Ta) and the second film is gold (Au) the first and third films increase the hardness of the gold (Au) second film  422 . The thickness of the heat sink layer  416  is less than the thickness of the ferromagnetic layer  418 . 
     The ferromagnetic layer  418  is composed of an iron nitride (FeN) based film  426 , with a preferred material being iron nitride (FeN), and a nickel iron (NiFe) based film  428  which is preferably nickel iron cobalt (NiFeCo). The iron nitride (FeN) based film  426  is thicker than the nickel iron (NiFe) based film  428 . The iron nitride (FeN) based film  426  has a higher magnetization (Ms) than the nickel iron (NiFe) based film  428  so that the iron nitride (FeN) based film  426  can be thinner for locating the heat sink layer  416  closer to the sensor  402  for increased heat dissipation. However, the nickel iron cobalt (NiFeCo) film  428  has a high uniaxial anisotropy which ensures that a magnetic moment  430  of the ferromagnetic layer  418  is returned to its initial easy axis orientation parallel to the ABS after being rotated therefrom by an external magnetic field. This is important for assuring a constant magnetic influence on the sensor  402 . The magnetic moment  430  can be either directed from left to right or from right to left. 
     The read head  500  shown in FIG. 17 is the same as the read head  400  shown in FIG. 16 except a second shield structure  502  also includes a heat sink layer  416  and a ferromagnetic layer  418  in the same manner as the first shield structure  412 . This type of read head is typically employed in a piggyback type head since the write head has a separate layer that functions as a first pole piece layer. The head  500  will dissipate more heat than the head  400  since each of the shield structures employs a heat sink layer. 
     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 the accompanying drawings.