Abstract:
A method of making gold (Au) lead layers for a read sensor forms the leads with micro voids which permit the leads to collapse slightly under operating pressures and temperatures to prevent nodule growth of the lead material at the air bearing surface. The method of making permits the use of gold (Au) leads which have high conductivity and high resistance to corrosion, but heretofore have been unacceptable for use in read heads because of nodule growth.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to high operating temperature gold (Au) leads for a read sensor and, more particularly, to gold leads which will not flow out of a read head at the air bearing surface (ABS) when subjected to pressure and various temperatures under operating conditions. 
     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, a slider that has write and read heads, 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 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 an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed 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), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field or the lack thereof writes information in tracks on moving media, such as in circular tracks on a rotating disk. 
     The read head includes a sensor that is located between nonmagnetic electrically insulative first and second read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. 
     The spin valve sensor is characterized by a magnetoresistive (MR) coefficient, also known as giant magnetoresistance (GMR), that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. MR coefficient is dr/R were dr is the change in resistance of the spin valve sensor and R is the resistance of the spin valve sensor before the change. 
     Because of high conductance (low resistance) and resistance to corrosion, gold (Au) is a desirable material for the first and second leads that are connected to the read sensor. Pure gold (Au), when used as conductor leads, however, presents a problem due to nodule formation of the gold at the ABS. This is due to pressure and high temperatures within the head during operating conditions of the read head within a magnetic disk drive. The operating temperatures can vary between 80° C.-120° C. Pressure on the leads increases with an increase in temperature due to expansion of layers adjacent the leads such as the first and second read gap layers and the first and second shield layers which are adjacent the read gap layers. With pressure due to the aforementioned temperatures the gold (Au), which is soft, is squeezed out of the leads at the ABS of the read head causing the aforementioned nodules. The nodules can short the leads to the first and second shield layers or short across edge portions of sensitive elements of the read sensor causing a failure of the read head. Because of the problems with gold (Au) leads have been made from tantalum (Ta) which does not have the nodule problem. Unfortunately, tantalum (Ta) has a significantly higher resistance than gold (Au) which results in increased heating of the read head unless the thickness of the tantalum (Ta) lead layers is increased. Unfortunately, an increase in thickness of the lead layers causes steps adjacent the read sensor which are replicated by subsequent layers all the way to the write gap which can cause the write gap of the write head to be curved. This is known in the art as write gap curvature and causes the write head to write curved magnetic impressions into tracks of a rotating magnetic disk which are then read by sensors that read straight across. This causes a reduction in the read signal which equates to less storage capacity of the magnetic disk drive. 
     SUMMARY OF THE INVENTION 
     I have found a method of forming gold (Au) conductor leads for a read sensor which is resistant against nodule growth by withstanding the pressure at operating temperatures of a disk drive without being extruded in the form of nodules at the ABS. Prior art gold or gold alloy leads are typically sputtered in a sputtering chamber. Within the sputtering chamber are a target of the material to be sputtered, namely the gold or gold alloy, a substrate supporting a wafer upon which the gold leads are to be formed and an ion beam gun which directs an ion beam onto the target for sputtering gold atoms from the target onto the wafer. The sputtering chamber typically has an outlet for drawing a vacuum and an inlet for inserting an inert gas, such as argon (Ar), into the chamber. In the prior art surface planes of the target and the substrate are oriented substantially parallel with respect to one another. In the present invention the surface planes of the target and the substrate are oriented at an angle with respect to one another, such as 20°-40°, which is referred to hereinafter as oblique ion beam sputtering. I have discovered with this scheme that the density of the gold or gold alloy formed on the wafer is less than the natural or elemental density of the gold or gold alloy. This decreased density causes the gold or gold alloy to have a degree of porosity which permits the leads to be compressed or squeezed in place under pressure and operating temperatures of the read head without the material of the leads flowing from the leads to form nodules at the ABS. The gold or gold alloy leads may be entirely porous or there may be alternate gold and porous gold layers forming the leads, as desired. Further, the method may be employed for other lead material such as copper (Cu) or molybdenum (Mo). 
     An object of the present invention is to provide improved lead layers for a read sensor by forming them with an oblique sputter deposition scheme. 
     Another object is provide gold or gold alloy lead layers for a read sensor which have a reduced density as compared to elemental forms of the gold or gold alloy so that the gold or gold alloy lead layers can function at operating conditions without nodule growth at the ABS. 
     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 magnetic head 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 FIG. 6 or  7  with all material above the coil layer and leads removed; 
     FIG. 11 is an isometric ABS illustration of a read head which employs an AP pinned spin valve (SV) sensor; 
     FIG. 12 is a schematic illustration of a prior art ion beam sputtering chamber for forming prior art lead layers wherein surface planes of the substrate and the target are parallel with respect to one another; 
     FIG. 13 is the same as FIG. 11 except the lead layers have a reduced density due to the present method of making the lead layers; 
     FIG. 14 illustrates the present ion beam sputtering chamber which is the same as the sputtering chamber in FIG. 12 except the surface planes of the substrate and the target are at an angle with respect to one another; 
     FIG. 15 is an ABS illustration of a read head showing a second embodiment of the present invention; 
     FIG. 16 is an ABS illustration of the read head showing a third embodiment of the present invention; 
     FIG. 17 is a schematic illustration of an ion beam gun, target and substrate; and 
     FIG. 18 is a view taken along plane  18 — 18  of FIG.  17 . 
    
    
     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 slider  42  has a combined read and write magnetic head  40  and 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 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, as shown in FIG.  3 . 
     FIG. 5 is an ABS view of the slider  42  and the magnetic head  40 . The slider has a center rail  56  that supports the magnetic head  40 , and side rails  58  and  60 . The rails  56 ,  58  and  60  extend from a cross rail  62 . With respect to rotation of the magnetic disk  34 , the cross rail  62  is at a leading edge  64  of the slider and the magnetic head  40  is at a trailing edge  66  of the slider. 
     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 electrically insulative 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. 8) 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 the read head  72  shown in FIG. 6 or  8 . The read head  72  includes the present spin valve sensor  130  which is located on an antiferromagnetic (AFM) pinning layer  132 . A ferromagnetic pinned layer in the spin valve sensor  130 , which is to be described hereinafter, is pinned by the magnetic spins of the pinning layer  132 . The AFM pinning layer is preferably  425  A of nickel oxide (NiO). First and second hard bias and lead layers  134  and  136  are connected to first and second side edges  138  and  140  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. No. 5,018,037 which is incorporated by reference herein. 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 fields to extend longitudinally through the spin valve sensor  130  for stabilizing the magnetic domains therein. The AFM pinning layer  132 , 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 ferromagnetic first and second shield layers  152  and  154 . 
     When the lead layers  142  and  146  are made of gold (Au) there has been a problem of nodule growth at the ABS as shown by the nodules  160 ,  162  and  164  in FIG.  11 . The nodules  160  and  162  show a shorting of the leads  142  and  146  to the second shield layer  154  while the nodule  164  bridges across edges (not shown) of magnetic layers of the spin valve sensor  130 . These nodules destroy the operation of the read head. While gold (Au) is very desirable as a material for conductor leads because of its high conductivity (low resistance) and resistance to corrosion at the ABS, it grows nodules at operating temperatures of the read head, which temperatures can range from 80° C.-120° C. At operating temperatures other layers of the read head, such as the pinning layer  132 , the hard bias layers  140  and  144 , the first and second gap layers  148  and  150  and the first and second shield layers  152  and  154 , exert a pressure on the leads  142  and  146  which cause the leads to be extruded at the ABS like toothpaste from a tube thereby shorting the leads to the shields. For this reason, tantalum (Ta) is typically substituted for gold (Au) in the first and second leads  142  and  146 . Unfortunately, tantalum (Ta) has a resistance more than five times that of gold (Au). In order to carry the sense current and lower the generation of heat, tantalum (Ta) leads have to be made significantly thicker than gold (Au) leads which causes write gap curvature, as discussed hereinabove. 
     The prior art sputtering system  200  for forming the leads  142  and  146  in FIG. 11 is shown in FIG.  12 . The sputtering system  200  includes a chamber  202  which has a valve controlled outlet  204  and a valve control inlet  206 . The outlet  204  is for the purpose of drawing a vacuum in the chamber and the inlet  206  is for the purpose of introducing an inert gas, such as Argon (Ar), into the chamber. Mounted within the chamber is a substrate  208  which supports a wafer  210  upon which layers of the read head are formed, such as the first and second lead layers  142  and  146  in FIG.  11 . Opposite the wafer and substrate is a target  212  composed of the material to be sputter deposited on the wafer  210 . An ion beam gun  214  may be mounted at one end of the chamber  202  for the purpose of directing a beam of ions onto the target  212 . Within the ion beam gun high energy electrons collide with atoms, such as argon (Ar) or xenon (Xe) atoms, knocking out one of the electrons of each atom causing atoms to be ionized with a positive charge. Electrons knocked out of the atoms have high energy which knock out additional electrons from other atoms which creates a plasma within the ion beam gun  214 . Ionized atoms from the ion beam gun strike the target  212  which causes the material of the target to be sputtered and deposited on the wafer  210 . In a prior art sputter system  200  the nominal planes of the substrate  208  and the target  212  are substantially parallel with respect to one another. When the nominal planes are parallel this results in non-oblique sputtering of atoms onto the substrate. 
     The Invention 
     The present invention is illustrated in the read head  300  shown in FIG. 13 which is the same as the read head  72  shown in FIG. 11 except for the lead layers  302  and  304 . Assuming the same elemental material or materials for the lead layers in FIGS. 11 and 13 the lead layers  302  and  304  in FIG. 13 have a reduced density as compared to the density of the lead layers  142  and  146  in FIG.  11 . The reason that the lead layers  302  and  304  are less dense is because of micro voids at the atomic level in the material of the lead layers, as shown at  306 . The lead layers  302  and  304  can be referred to as being porous because of the micro voids  306  at the atomic level even though the lead layers may not be porous to a liquid such as water. The importance of the micro voids  306  is that when the read head  300  is subjected to operating pressures and temperatures the material of the leads  302  and  304  will not be extruded at the ABS to cause nodules, as discussed hereinabove. When the lead layers are subjected to the operating pressures and temperatures the material of the leads  302  and  304  collapses into the voids  306  so as to prevent an extrusion of the lead material at the ABS. This is especially useful for lead layers  302  and  304  which are composed of gold (Au) or gold (Au) alloys. At the operating pressures and temperatures a minute collapse of the gold lead layers into the voids  306  prevents the undesirable extrusion. 
     The present sputtering system  400  for forming the leads  302  and  304  in FIG. 13 is shown in FIG.  14 . The sputtering chamber  400  is the same as the sputtering chamber  300  except for the substrate  402  and the target  404 . The difference is that the nominal planes of the substrate  402  and  404  are oriented at an angle θ with respect to one another instead of being parallel with respect to one another as shown in FIG.  12 . While the angle θ is shown in the plane of the paper, angle θ can be located at any angle within 360° commencing with the plane of the paper and rotated into and out of the paper back to the plane of the paper which will be described in more detail hereinafter. With this arrangement atoms of the material sputtered from the target  404  are deposited on the wafer  406  at an angle to a normal to the nominal surface plane of the substrate. I have found that this oblique sputtering results in the lead layers having a reduced density due to the micro voids  306  in the lead layers shown in FIG.  13 . The preferred angle θ is from 20°-40°. The chamber pressure can be 10 −4  torr and the working gas may be argon (Ar), krypton (Kr) or xenon (Xe). The preferred target material is gold (Au). In another preferred embodiment the target material may be a gold alloy such as gold nickel (AuNi), gold copper (AuCu) or gold tantalum (AuTa). 
     While each of the lead layers  302  and  304  in FIG. 13 comprise, in one embodiment, a single layer, another embodiment of the read head  500  is illustrated in FIG. 15 wherein each of the lead layers  502  and  504  comprise multilayers of the same material, except alternate layers of the same material are less dense or porous according to the present invention. Accordingly, each of the lead layer structures  502  and  504  may include less dense material layers  506  and  508  which are alternately formed with respect to natural density material layers  510  and  512 . In the preferred embodiment the layers  506 ,  508 ,  510  and  512  are composed of gold (Au). Performance of the gold (Au) lead layer structures  502  and  504  can be similar to the lead layers  302  and  304  shown in FIG.  13 . When subjected to operating pressures and temperatures the gold layers  510  and  512  will collapse minutely into the layers  506  and  508  because of the voids  514  in these layers, thereby obviating the aforementioned nodule growth. 
     Still another embodiment  600  of the read head with first and second lead layer structures  602  and  604  is shown in FIG.  16 . Each of the lead layer structures  602  and  604  includes low density metallic layers, such as gold (Au),  606 ,  608   610  with reduced density according to the present invention interleaved with tantalum (Ta) layers  612 ,  614 ,  616  and  618 . The tantalum (Ta) layers which, may be 50 Å thick as compared to 200 Å thick for the gold layers, provide a desired structural support for the gold layers. 
     With the present invention the density of the gold (Au) can be reduced from 19.3 gm/cc for element gold to 15.0 gm/cc. In a preferred embodiment the invention encompasses gold (Au) lead layers with a density from 15.0 gm/cc to 19.0 gm/cc. 
     FIGS. 17 and 18 are schematic diagrams of an ion beam gun  700 , a target  702  of some metal and a substrate  704  to illustrate various angles α and β that a nominal surface plane of the substrate can make with respect to a nominal surface plane of the target in order to achieve a non-parallel relationship therebetween of angle θ described for FIG. 14 for the purpose of achieving oblique sputtering of the metal onto the substrate with a reduced density. Either angle α or β or a combination of the angles results in oblique sputtering (non-normal flux flow) from the center of the target to the center of the substrate. In FIG. 17 the surface plane  706  of the substrate  704  is rotated about an axis perpendicular to the paper with respect to the surface plane  708  of the target and in FIG. 18 the surface plane of the substrate shown in phantom is further rotated by an angle β about an axis perpendicular to the paper with respect to the surface plane  708  of the target. Either the target  702  or the substrate  704  may be maintained stationary while the other is rotated by angles α and/or β to achieve a non-parallel relationship of angle θ therebetween as shown in FIG.  14 . 
     It should be understood that the present invention may be employed for metals other than gold, gold alloy, copper or molybdenum. Further, the sensor  210  may be a spin valve sensor or an AMR sensor, as discussed hereinabove. Further, the first and second leads may overlap the top of various layers of the sensor with a space between the leads for defining the active region of the sensor. This is known in the art as a continuous junction sensor as contrasted to the contiguous junction sensor described hereinabove. Still further, the invention applies to any thin film leads, such as leads connected to the write head of a magnetic head assembly. 
     Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.