Abstract:
A magnetic data storage and retrieval system has a bottom shield, a first half gap positioned on the bottom shield, a sensor layer positioned on the first half gap, a second half gap positioned on the sensor layer; and a top shield positioned on the second half gap. The sensor layer includes a magnetoresistive sensor having sidewalls and a barrier surrounding and in direct contact with the sidewalls of the magnetoresistive sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This Application claims priority from provisional application No. 60/162,612, filed Oct. 28, 1999 for “Edge Barrier to Prevent Spin Valve Sensor Corrosion and Improve Long Term Reliability” of Hong Wang, Robbee L. Grimm, Matthew T. Johnson, John P. Spangler, Craig A. Ballentine, Qing He, Steven C. Riemer and Brian J. Daniels. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to magnetic data storage and retrieval systems. More particularly, the present invention relates to an edge barrier for prevention of spin valve sensor corrosion and improvement of spin valve sensor reliability. 
     A transducing head of a magnetic data storage and retrieval system typically includes a magnetoresistive reader portion for retrieving magnetic data stored on magnetic media. The reader is typically formed of several layers which include a magnetoresistive (MR) sensor positioned between two gap layers, which are in turn positioned between two shield layers. The MR sensor may be any one of a plurality of MR-type sensors, including, but not limited to, AMR, GMR, VGMR, spin valve and spin tunneling sensors. 
     During fabrication of the transducing head, the MR sensor is subjected to many processing steps. Current contacts and biasing layers are commonly deposited adjacent to the MR sensor after the MR sensor is shaped, but before the second half gap is deposited. The formation of the contacts and biasing layers, as well as the patterning of the MR sensor itself, subjects the MR sensor to a harsh environment that may result in corrosion of the MR sensor. This is particularly true of a multi-layered sensor such as a spin valve sensor. Multi-layered sensors generally are formed of multiple materials, several of which very easily corrode. Since an MR sensor relies on the existence of each of its layers to operate properly, corrosion of any of its layers will result in the sensor having a reduced amplitude, a distorted signal output, decreased stability, and/or increased noise. 
     Accordingly, there is therefore a need for a means of preventing corrosion of the sensor in a transducing head. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is an edge barrier of corrosion-resistant material for preventing corrosion of a sensor of a transducing head during fabrication of the transducing head. In a transducing head of a magnetic data storage and retrieval system in accord with the present invention, the transducing head has a bottom shield, a first half gap positioned on the bottom shield, a sensor layer positioned on the first half gap, a second half gap positioned on the sensor layer; and a top shield positioned on the second half gap. 
     The sensor layer includes a magnetoresistive sensor having sidewalls and a barrier surrounding and in direct contact with the sidewalls of the magnetoresistive sensor. An acute angle formed between the sidewalls of the magnetoresistive sensor and the first halfgap preferably is in the range of about 40° to about 90°. The barrier is preferably formed of a corrosion-resistant material such as Ta, TaN, W, Cr, Al 2 O 3 , SiO 2 , or NiFe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a magnetic transducing head. 
     FIG. 2 is a layer diagram of a typical top spin valve sensor. 
     FIG. 3 is a layer diagram of a typical bottom spin valve sensor. 
     FIG. 4 is a graph of potentiodynamic polarization scans (0.5 mV/sec) for typical spin valve materials in a phthalate buffer at 0.01 M and pH of 6. 
     FIGS. 5A-5H are cross-sectional drawings illustrating the formation of a magnetic transducing head in accord with the present invention. 
     FIG. 6 is a graph correlating signal distortion and signal amplitude of prior art transducing heads. 
     FIG. 7 is a graph correlating signal distortion and signal amplitude of transducing heads with the sensor barrier of the present invention. 
     FIG. 8 is a cross sectional TEM image of a prior art transducing head. 
     FIG. 9 is a cross sectional TEM image of a transducing head with the sensor barrier of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a cross-sectional view of magnetic transducing head  10  having substrate  12 , bottom shield  14 , first half gap  16 , sensor  18 , second half gap  20 , and top shield  22 . Sensor  18  is positioned between first half gap  16  and second half gap  20  at an air bearing surface (ABS) of transducing head  10 . First and second half gaps  16  and  18  are positioned between bottom shield  14  and top shield  22 . 
     Bottom and top shields  14  and  22  ensure that sensor  18  reads only the information stored directly beneath it on a specific track of the magnetic medium or disc (not shown in FIG. 1) by absorbing any stray magnetic fields emanating from the adjacent tracks and transitions. First and second half gaps  16  and  20  serve to isolate sensor  18  from bottom and top shields  14  and  22 . Gaps  16  and  20  are typically formed of insulating materials. Sensor  18  may be any type of magnetoresistive (MR) sensor, including, but not limited to, AMR, GMR, VGMR, spin valve and spin tunneling sensors. 
     During fabrication of transducing head  10 , several processing steps occur after the shaping of sensor  18  and before the deposition of second half gap  20 . These processing steps include the deposition of biasing layers and current contacts. During these intermediate processing steps, back edge  24  of sensor  18  is exposed to an environment that may harm sensor  18 , potentially resulting in corrosion of sensor  18 . 
     The likelihood of sensor corrosion during fabrication increases when sensor  18  is a multi-layered sensor such as a spin valve sensor. FIG. 2 is a layer diagram of typical top spin valve  30  having substrate  32 , seed layer  34 , free layer  36 , spacer layer  38 , pinned layer  40  and pinning layer  42 . In spin valve sensor  30 , a magnetization direction of pinned layer  42  is fixed in a predetermined direction, generally normal to an air bearing surface of spin valve  30 , while a magnetization direction of free layer  36  rotates freely in response to external magnetic fields. An easy axis of free layer  36  is typically set normal to the magnetization direction of pinned layer  42 . The resistance of spin valve sensor  30  varies as a function of an angle formed between the magnetization direction of free layer  36  and the magnetization direction of pinned layer  42 . 
     Seed layer  34  is typically deposited on substrate  32  to promote the texture and enhance the grain growth of each of the layers subsequently grown on top of it. The seed layer material is chosen such that its atomic structure, or arrangement, corresponds with the preferred crystallographic and magnetic orientations of top spin valve  30 . Seed layer  34  is typically a thin layer formed of a nonmagnetic material such as Ta, TaN, NiFeCr, or a TaN/NiFeCr bilayer. 
     Free layer  36  is positioned on seed layer  34 . Each of free layer  36  and pinned layer  40  are formed of ferromagnetic materials such as NiFe or CoFe. Additionally, each of free layer  36  and pinned layer  40  may also be formed of multiple layers. As shown in FIG. 2, free layer  36  is a bilayer structure consisting of first ferromagnetic layer  44  formed of NiFe and second ferromagnetic layer  46  formed of CoFe. Similarly, pinned layer  40  is a bilayer structure consisting of first ferromagnetic layer  48  formed of CoFe and second ferromagnetic layer  50  formed of NiFe. Pinned layer  40  may also be a CoFe/Ru/CoFe trilayer structure. 
     Spacer layer  38  separates pinned layer  40  from free layer  36 , and is typically formed of a nonmagnetic material such as copper, or a copper alloy. 
     Pinning layer  42  is exchange coupled to pinned layer  40  to fix the magnetization of pinned layer  40  in a predetermined direction. Pinning layer  42  is typically formed of an antiferromagnetic material such as NiMn, NiMnCr, IrMn, PtMn, PdMn, PdPtMn, CrMnPt, CrMnCu, CrMnPd, NiO or PtRuMn. Pinning layer  42  may be eliminated from spin valve sensor  30  by using self-saturation to pin the magnetization of pinned layer  40 . 
     FIG. 3 is a layer diagram of typical bottom spin valve sensor  60  having substrate  62 , seed layer  64 , pinning layer  66 , pinned layer  68 , spacer layer  70  and free layer  72 . Bottom spin valve sensor  60  differs from top spin valve sensor  30  in the order in which its layers are deposited. In bottom spin valve  60 , pinning layer  66  is positioned on seed layer  64 , while in top spin valve sensor  30 , free layer  36  is positioned on seed layer  34 . 
     Seed layer  64  is deposited on substrate  62 , and is typically formed of a nonmagnetic material such as Ta, TaN, NiFeCr or a TaN/NiFeCr bilayer. 
     Pinning layer  66  is deposited on seed layer  64  and is typically formed of an antiferromagnetic material such as NiMn, NiMnCr, IrMn, PtMn, PdMn, PdPtMn, CrMnPt, CrMnCu, CrMnPd, NiO or PtRuMn. As described in reference to spin valve sensor  30 , pinning layer  66  may be eliminated from spin valve sensor  60  by using self-saturation to pin the magnetization of pinned layer  68 . 
     Pinned layer  68  is typically exchanged coupled with pinning layer  66  to fix the magnetization direction of pinned layer  68 . Each of free layer  72  and pinned layer  68  are formed of either single or multiple layers of ferromagnetic materials such as NiFe or CoFe. As shown in FIG. 3, pinned layer  68  is a bilayer structure consisting of first ferromagnetic layer  74  formed of NiFe and second ferromagnetic layer  76  formed of CoFe. Similarly, free layer  72  is a bilayer structure consisting of first ferromagnetic layer  78  formed of CoFe and second ferromagnetic layer  80  formed of NiFe. Pinned layer  68  may also be a CoFe/Ru/CoFe trilayer structure. 
     Spacer layer  70  separates pinned layer  68  from free layer  72 , and is typically formed of a nonmagnetic material such as copper, or a copper alloy. 
     As described above, multi-layer sensor  18  is particularly vulnerable to corrosion during fabrication of transducing head  10 . Until second half gap  20  is deposited to seal sensor  18 , sensor  18  is exposed to several ashing and/or chemical stripping processes, rinse and dry steps, and vapor condensation from the surrounding environment. It is well established that several of the materials used in forming spin valve sensors, such as those described above for the sensors shown in FIGS. 2 and 3, corrode very easily. Corrosion is likely to occur when two materials with different electrochemical potentials are connected to each other in an electrolytic environment. 
     FIG. 4 is a graph of potentiodynamic polarization scans (0.5 mV/sec) for typical spin valve materials in a phthalate buffer at 0.01 M and pH of 6. In this mild solution, FIG. 4 illustrates that Cu, Co and NiMn are each very vulnerable to corrosion in comparison to NiFe, Ta and Cr. In the harsher environment that those materials are subjected to during fabrication of transducing head  10 , corrosion is highly likely. Since spin valve sensor  18  relies on the existence of each of its layers to operate properly, corrosion of any of those layers will result in a sensor having a reduced amplitude, a distorted signal output, decreased stability, and increased noise. 
     There is therefore a need for a means of preventing corrosion of sensor  18 . The present invention is a barrier that protects sensor  18  during subsequent processing steps from the harsh environment. The barrier is placed around sensor  18  immediately after sensor  18  has been shaped to prevent sensor  18  from corroding due to the harsh environment before second half gap  20  is deposited. Preferably, the barrier is formed of a corrosion-resist material. 
     FIGS. 5A-5H are cross-sectional drawings illustrating a method of forming of magnetic transducing head  90  in accord with the present invention. FIG. 5A is a cross-sectional view of transducing head  90  after bottom shield  92  has been deposited on a substrate (not shown in FIGS.  5 A- 5 H). FIG. 5B shows transducing head  90  after deposition of first half gap  94  on bottom shield  92 . FIG. 5C is a view showing deposition of sensor layer  96  over first half gap  94 . At this stage, sensor layer  96  has not yet been shaped into its final sensor form. Sensor layer  96  may be formed of a plurality of layers to form any of a plurality of MR-type sensors. 
     FIG. 5D is a cross-sectional view of transducing head  90  after photo-resist  98  has been deposited onto a central region of sensor layer  96  to pattern sensor layer  96 . Photo-resist mask or hard mask  98  is defined by lithography. The pattern of photo-resist mask  98  is then transferred to sensor layer  96 , as shown in FIG. 5E, by selectively removing portions of sensor layer  96  not covered by photo-resist mask  98 . The removal of the uncovered portions of sensor layer  96  is preferably implemented by an ion milling technique having a near normal incidence angle so that sidewalls  100  of sensor  96  are as vertical as possible. Preferably, an acute angle formed between sidewalls  100  of sensor  96  and first half gap  94  is in the range of about 40° to about 90°. 
     FIG. 5F illustrates transducing head  90  after barrier material  102  has been deposited over first half gap  94 , sidewalls  100  of sensor  96  and mask  98 . Barrier material  102  is preferably a corrosion-resistant material, such as Ta, TaN, W, Cr, Al 2 O 3 , or SiO 2 . Preferably, barrier material  102  is deposited by isotropic sputter deposition. To ensure a conformal coating of barrier material  102  over sidewalls  100  of sensor  96 , the deposition of barrier material  102  preferably is performed with a low power and a high gas pressure sputter deposition. 
     FIG. 5G is a cross-sectional view of transducing head  90  after removal of excess barrier material  102  over first half gap  94 . Barrier material  102  is left covering sensor  96  to form barrier  104  over sidewalls  100  of sensor  96 . The thickness of barrier material  102  over sidewalls  100  of sensor  96  is preferably in the range of about 5 Angstroms to about 1000 Angstroms. 
     The removal of barrier material  102  is preferably performed using a collimated, or anisotropic, ion milling process having a near vertical incidence angle. The ion mill rate at any given location is inversely proportional to the cosine of the angle between the ion beam and the local tangent of the surface. For an ion beam with a near-normal incidence angle, the mill rate on top of photo-resist mask  98  and on outside edges of first half gap  94  will be high, while the mill rate at sidewalls  100  of sensor  96  will be very low. As a result of the ion mill rate differential, barrier material  102  is left over sidewalls  100  of sensor  96 , while barrier material  102  is cleared nearly everywhere else on sensor  96 , thereby forming barrier  104 . The anisotropic ion milling technique may be any of a plurality of ion milling techniques, such as ion milling, reactive ion milling, chemically assisted ion milling and reactive ion etching. 
     FIG. 5H is a cross-sectional view of transducing head  90  after photo-resist mask  98 , as well as excess barrier material  102  still adhering tb photo-resist mask  98 , has been removed. Mask  98  may be removed by known methods, such as ashing or chemical stripping. After photo resist mask  98  is removed, transducing head  90  is prepared for the deposition of contacts and biasing layers, followed by the deposition of a second half gap over sensor  96 . Finally, a top shield is deposited over the second half gap. As these final steps are well known in the art of transducing head design, they are not illustrated in figures. 
     FIG. 6 is a graph correlating signal distortion and signal amplitude of prior art transducing heads without a sensor barrier, while FIG. 7 is a similar graph of transducing heads with the sensor barrier of the present invention. The sample transducing heads used in generating data for the graphs of both FIG.  6  and FIG. 7, have a top spin valve sensor having a Co/Ru/Co trilayer pinned layer and a NiMn pinning layer. As discussed above, Co and NiMn are both highly sensitive to corrosion. As shown in FIG. 6, there is substantial corrosion of the prior art transducing heads. The correlation in FIG. 7 shows no signs of corrosion when compared to the correlation shown in FIG.  6 . The comparison of FIGS. 6 and 7 shows that the average amplitude of a corrosion-free sensor is 130% higher than that of a corroded sensor and the signal distortion is 25 dB better. 
     FIG. 8 is a cross sectional TEM image of a prior art transducing head. Shown in FIG. 8 are portions of a bottom shield, a first gap (gap  1 ), a spin valve sensor (SV), a second gap (gap  2 ) and a shared pole of the transducing head. The spin valve sensor has a NiMn pinning layer adjacent the second gap. As FIG. 8 illustrates, a substantial portion of the spin valve sensor, particularly the NiMn pinning layer, has corroded during the fabrication of the prior art transducing head. 
     FIG. 9 is a cross sectional TEM image of a transducing head with the sensor barrier of the present invention. Shown in FIG. 9 are portions of a bottom shield, a first gap. a spin valve sensor (SV), a Ta barrier layer, a second gap and a shared pole. As FIG. 9 illustrates, the Ta barrier layer prevents any corrosion of the spin valve sensor. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.