Abstract:
Currently, the shield-to-shield separation of a spin valve head cannot be below about 800 Å, mainly due to sensor-to-lead shorting problems. This problem has now been overcome by a manufacturing method that includes inserting a high permeability, high resistivity, thin film shield on the top or bottom (or both) sides of the spin valve sensor. A permeability greater than about 500 is required together with a resistivity about 5 times greater than that of the free layer and an M r T value for the thin film shield that is 4 times greater than that of the free layer.

Description:
This is a division of patent application Ser. No. 09/696,134, filing date Oct. 26, 2000, now U.S. Pat. No. 6,885,527, Integrated Spin Valve, assigned to the same assignee as the present invention, which is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the general field of magnetic recording with particular reference to improving linear resolution. 
     BACKGROUND OF THE INVENTION 
     The present invention is concerned with the manufacture of the read element in a magnetic disk system. This is a thin slice of material located between two magnetic shields which we will refer to a primary shields. The principle governing operation of the read sensor is the change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance). In particular, most magnetic materials exhibit anisotropic behavior in that they have a preferred direction along which they are most easily magnetized (known as the easy axis). The magneto-resistance effect manifests itself as a decrease in resistivity when the material is magnetized in a direction perpendicular to the easy axis, said decrease being reduced to zero when magnetization is along the easy axis. Thus, any magnetic field that changes the direction of magnetization in a magneto-resistive material can be detected as a change in resistance. 
     It is now known that the magneto-resistance effect can be significantly increased by means of a structure known as a spin valve (SV). The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole. 
     The key elements of a spin valve structure are two magnetic layers separated by a non-magnetic layer. The thickness of the non-magnetic layer is chosen so that the magnetic layers are sufficiently far apart for exchange effects to be negligible (the layers do not influence each other&#39;s magnetic behavior at the atomic level) but are close enough to be within the mean free path of conduction electrons in the material. If, now, these two magnetic layers are magnetized in opposite directions and a current is passed through them along the direction of magnetization, half the electrons in each layer will be subject to increased scattering while half will be unaffected (to a first approximation). Furthermore, only the unaffected electrons will have mean free paths long enough for them to have a high probability of crossing the non magnetic layer. However, once these electron ‘switch sides’, they are immediately subject to increased scattering, thereby becoming unlikely to return to their original side, the overall result being a significant increase in the resistance of the entire structure. 
     In order to make use of the GMR effect, the direction of magnetization of one the layers must be permanently fixed, or pinned. Pinning is achieved by first magnetizing the layer (by depositing and/or annealing it in the presence of a magnetic field) and then permanently maintaining the magnetization by over coating with a layer of antiferromagnetic material. The other layer, by contrast, is a “free layer” whose direction of magnetization can be readily changed by an external field (such as that associated with a bit at the surface of a magnetic disk). 
     Structures in which the pinned layer is at the top are referred to as top spin valves. Similarly, It is also possible to form a ‘bottom spin valve’ structure where the pinned layer is deposited first. Although not directly connected to the GMR effect, an important feature of spin valve structures is a pair of longitudinal bias stripes that are permanently magnetized in a direction parallel to the long dimension of the device. Their purpose is to prevent the formation of multiple magnetic domains in the free layer portion of the GMR sensor, particularly near its ends. 
       FIG. 1  shows a typical structure that embodies the features described above. As noted above, the device is sandwiched between two primary shields  11  and  12 . Currently, the shield-to-shield separation of a spin valve head cannot be below about 800 Å, mainly due to the sensor-to-shield shorting problem. This is pointed to in the figure by arrow  13 . Since improvements in the density of recorded data require that this distance be reduced below 800 Å, there is a need for a structure (and a process for manufacturing it) that is not susceptible to said shorting problem. 
     An application that describes a structure that is related to that disclosed by the present invention was filed on Sep. 30, 1999 as application Ser. No. 09/408,492. Additionally, a routine search of the prior art was performed and the following references of interest were found: 
     In U.S. Pat. No. 5,978,182, Kanai et al. show a SV with a first soft magnetic layer. In U.S. Pat. No. 5,608,593, Kim et al. shows a SV with a non-magnetic (e.g., Cr) under-layer. Takada et al show a stabilizing layer with an under-layer of Cr and a hard magnetic layer in U.S. Pat. No. 5,828,527, while Ohsawa et al. (U.S. Pat. No. 5,777,542), Dykes et al. (U.S. Pat. No. 5,668,688), and Hsiao et al. (U.S. Pat. No. 5,999,379) all show related SV devices with shield layers. 
     SUMMARY OF THE INVENTION 
     It has been an object of the present invention to provide a spin valve structure that is free of internal electrical shorting by maintaining a relatively large shield-to-shield spacing while continuing to obtain very narrow feedback pulse widths. 
     Another object of the invention has been to provide a process for manufacturing said spin valve structure. 
     A further object has been that said structure be given its longitudinal bias through either permanent magnet or exchange magnet means. 
     A still further object has been that said structure be either a top or a bottom spin valve. 
     These objects have been achieved by inserting a high permeability, high resistivity, thin film shield on the top or bottom (or both) sides of the spin valve sensor. A permeability greater than about 500 is required together with a resistivity about 5 times greater than that of the free layer and an M r T value for the thin film shield that is 4 times greater than that of the free layer. Five embodiments of the invention are described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows how a structure made according to earlier teachings is subject to shorting (through the dielectric layer that insulated the shield from the sensor) if made too thin. 
         FIGS. 2 and 3  show bottom spin valve structures with permanent magnet biasing, having a single thin film shield, as taught by the present invention. 
         FIG. 4  shows a bottom spin valve structure with exchange magnet biasing, having a single thin film shield, as taught by the present invention. 
         FIG. 5  shows a top spin valve structure with exchange magnet biasing, having a single thin film shield, as taught by the present invention. 
         FIG. 6  shows a bottom spin valve structure with permanent magnet biasing, having two thin film shields, as taught by the present invention. 
         FIG. 7  compares read back signal pulse shape for structures with and without the thin film shield. 
         FIG. 8  plots voltage against total magnetic moment for structures with and without the thin film shield. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As already noted above, present SV designs cannot have their shield-to-shield spacing thicknesses reduced below about 800 Å because of shorting through the dielectric insulating coverage over the conductor lead. In dual stripe MR structures, it has been observed that if one of the MR stripes is not performing correctly, the signal contribution is dominated by the other MR, so that the read back pulse width, PW 50 , is reduced. PW 50  is the pulse width measured at the 50% of amplitude point (in nanoseconds or nanometers). It is measured at low frequency to avoid interference between adjacent pulses. 
     The present invention solves this problem by the insertion of a high permeability, high resistivity thin film shield on the top or bottom (or both) sides of the spin valve sensor. Examples of materials suitable for the thin film shields include (but are not limited to) nickel-iron-chromium, cobalt-niobium-zirconium, and cobalt-niobium-hafnium. We now describe five embodiments of the present invention. Although each embodiment is described in terms of the process for its manufacture, the structure of each embodiment will become apparent as each manufacturing process is disclosed. The following compositions and thickness ranges are common to all embodiments: 
     
       
         
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 LAYER 
                 COMPOSITION 
                 THICKNESS (Å) 
               
               
                   
               
             
             
               
                 free 
                 Co 90 Fe 10 , Ni 8 Fe 19   
                  5–50 
               
               
                 non-magnetic spacer 
                 Cu 
                 12–22 
               
               
                 pinned 
                 Co 90 Fe 10   
                 10–30 
               
               
                 pinning 
                 Ni 45 Mn 55 , Mn 50 Pt 50   
                  80–200 
               
               
                 dielectric 
                 Al 2 O 3 , AlN 
                 100–200 
               
               
                 Thin film shield 
                 NiFeCr, CoZrNb, 
                  50–400 
               
               
                   
                 CoHfNb, CoZrHf, 
               
               
                   
                 CoFeX (X = Cr, N, Ta, Ti) 
               
               
                 decoupling 
                 TaO, NiCr, NiFeCr 
                 20–50 
               
               
                   
               
             
          
         
       
     
     First Embodiment 
     This process is for manufacturing a top spin valve structure. It begins with the provision the first (lower) of the two primary magnetic shields. This can be seen as layer  15  in  FIG. 2  on which dielectric layer  17  is deposited, followed by the deposition of free layer  21 . This is followed by the deposition of non-magnetic Layer  22  onto which is deposited pinned layer  23 . Next, onto pinned layer  23  there is deposited anti-ferromagnetic layer  24  for use as a pinning layer. This completes formation of the spin valve itself. 
     Now follows a key feature of the invention. On anti-ferromagnetic layer  24 , decoupling layer  25  is deposited, followed by the deposition of thin film shield  26 . The purpose of the decoupling layer is to avoid any exchange coupling of the thin film shield by layer  24 . The thin film shield is a layer of ferromagnetic material having a permeability greater than about 500. It needs to have as high an electrical resistivity as possible within other constraints of the structure. It is required to be at least 5 times more resistive than the free layer. Since the latter is about 25 micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to be preferred. The thickness of the thin film shield should be such that the moment-thickness product (of the thin film shield) is 2–5 times that of the free layer. The presence of this thin film shield allows relatively thicker dielectric layers to be used, thereby reducing or eliminating the chances of shorting, while still being able to obtain very narrow feedback pulse widths (namely PW 50 ). 
     To initiate completion of the structure, trench  29  is formed using conventional patterning and etching. This trench extends through thin film shield  26  down as far as the top surface of dielectric layer  17 . The trench has a sidewall  30  that slopes at an angle of about 20 degrees. Onto this sidewall, as well as the exposed surface of dielectric layer  17 , is selectively deposited layer  27  of a ferromagnetic material (such as CoCrPt) that is suitable for use as a permanent magnet, the direction of permanent magnetization being set by a field that is present during or after deposition of the layer. Layer  27  will serve to provide longitudinal bias to the structure, as discussed earlier. 
     With layer  27  in place, a layer of conductive material  28 , suitable for use as a connecting lead to the structure, is selectively deposited thereon. This is followed by the deposition of second dielectric layer  18  onto which is deposited upper primary magnetic shield  16 . 
     Second Embodiment 
     This process is also for manufacturing a top spin valve structure. Referring now to  FIG. 3 , this embodiment begins with the provision of the first (lower) of the two primary magnetic shields  15  on which dielectric layer  17  is deposited. Now follows a key feature of the invention, namely the deposition of thin film shield  36 . The thin film shield is a layer of high permeability (greater than about 500) ferromagnetic material. It needs to have as high an electrical resistivity as possible within other constraints of the structure. It is required to be at least 5 times more resistive than the free layer. Since the latter is about 25 micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to be preferred. The thickness of the thin film shield should be such that the moment-thickness product (of the thin film shield) is 2–5 times that of the free layer. The presence of this thin film shield allows relatively thicker dielectric layers to be used, thereby reducing or eliminating the chances of shorting, while still being able to obtain very narrow feedback pulse widths. 
     With the thin film shield in place, decoupling layer  25  is laid down followed by the deposition of free layer  21 . This is followed by the deposition of non-magnetic layer  22  onto which is deposited pinned layer  23 . Next, onto pinned layer  23  there is deposited anti-ferromagnetic layer  24  for use as a pinning layer. This completes formation of the spin valve itself. 
     Completion of the structure then continues with the formation of trench  29 , using conventional patterning and etching. This trench extends through layer  24  down as far as the top surface of dielectric layer  17 . The trench has a sidewall  30  that slopes at an angle of about 20 degrees. Onto this sidewall, as well as the exposed surface of dielectric layer  17 , is selectively deposited layer  27  of a ferromagnetic material (such as CoCrPt) that is suitable for use as a permanent magnet, the direction of permanent magnetization being set by a field that is present during deposition of the layer or by later annealing in such a field. Layer  27  will serve to provide longitudinal bias to the structure, as discussed earlier. 
     With layer  27  in place, a layer of conductive material  28 , suitable for use as a connecting lead to the structure, is selectively deposited thereon. This is followed by the deposition of second dielectric layer  18  onto which is deposited upper primary magnetic shield  16 . 
     Third Embodiment 
     This process is also for manufacturing a top spin valve structure. We refer now to  FIG. 4  which begins with the provision of the first (lower) of the two primary magnetic shields  15  onto which is deposited dielectric layer  17 . Then, on a selected area at the surface of layer  17 , a layer of conductive material  47 , suitable for use as a connecting lead to the structure, is deposited. Then, on layer  47  only, layer  48  of a ferromagnetic material suitable for use as an exchange magnet is deposited. This will serve to provide the needed longitudinal bias for the structure, as discussed above. 
     Then, free layer  21  is deposited over the full surface followed by the deposition of non-magnetic layer  22  onto which is deposited pinned layer  23 . Next, onto pinned layer  23  there is deposited anti-ferromagnetic layer  24  for use as a pinning layer. 
     Now follows a key feature of the invention. On anti-ferromagnetic layer  24 , decoupling layer  25  is deposited, followed by the deposition of thin film shield  46 . The purpose of the decoupling layer is to avoid any pinning of the thin film shield by layer  24 . The thin film shield is a layer of high permeability (greater than about 500) ferromagnetic material. It needs to have as high an electrical resistivity as possible within other constraints of the structure. It is required to be at least 5 times more resistive than the free layer. Since the latter is about 25 micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to be preferred. The presence of this thin film shield allows a relatively large shield-to-shield spacing to be maintained (thereby reducing or eliminating the chances of shorting) while still being able to obtain very narrow feedback pulse widths. 
     Since the lead and biasing structure is already in place, all that remains to complete this embodiment is the deposition of second dielectric layer  18  onto which is deposited upper primary magnetic shield  16 . 
     Fourth Embodiment 
     Unlike the previous three embodiments, this process is for manufacturing a bottom spin valve structure. Referring to  FIG. 5 , it begins, as before, with the provision of the first (lower) of the two primary magnetic shields  15  onto which dielectric layer  17  is deposited. A key feature of the invention now follows, namely the deposition of thin film shield  56 . The thin film shield is a layer of high permeability (greater than 500) ferromagnetic material. It needs to have as high an electrical resistivity as possible within other constraints of the structure. It is required to be at least 5 times more resistive than the free layer. Since the latter is about 25 micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to be preferred. The thickness of the thin film shield should be such that the moment-thickness product (of the thin film shield) is 2–5 times that of the free layer. The presence of this thin film shield allows relatively thicker dielectric layers to be used, thereby reducing or eliminating the chances of shorting, while still being able to obtain very narrow feedback pulse widths (namely PW 50 ). 
     With the thin film shield in place, decoupling layer  25  is laid down followed by the deposition of anti-ferromagnetic layer  24 . This is followed by the deposition of pinned layer  23  onto which is deposited non-magnetic layer  22 . Next, onto non-magnetic layer  22  there is deposited free layer  21  which completes formation of the spin valve itself. 
     To initiate completion of the structure, shallow trench  59  is formed using conventional patterning and etching. This trench extends part way through the free layer  21 . On the part of the free layer that lies outside the trench, capping layer  51  of tantalum, tantalum oxide, and alumina, among others, is deposited. Its purpose is to provide protection against oxidation or other forms of contamination. On the part of the free layer that forms the base of the trench, refill layer  52  of the same material as used for the free layer (typically permalloy). 
     Layer  48 , comprising a ferromagnetic material suitable for use as an exchange magnet is then selectively deposited onto the trench base portion of layer  21  where it will provide longitudinal bias to the structure. Then, layer  47  of conductive material suitable for use in connecting leads to the structure is selectively deposited onto exchange magnet layer  48 . To complete this embodiment, second dielectric layer  18  is deposited onto layers  47  and  51  followed by the overall deposition of upper primary magnetic shield  16 . 
     Fifth Embodiment 
     The process of this embodiment is also for manufacturing a top spin valve structure but, unlike the previous four embodiments, it makes use of two thin film shields. While adding slightly to the overall thickness, the two shield structure has the advantage that, since PW 50  is defined by the distance between these two shields, even narrower pulse widths can be obtained. Note also that this scheme is not limited to conventional spin-valve structures. It is also readily applicable to synthetic anti-ferromagnet SVs and Dual-SV applications. 
     Referring now to  FIG. 6 , this embodiment begins with the provision of the first (lower) of the two primary magnetic shields  15  on which dielectric layer  17  is deposited. Now follows a key feature of the invention, namely the deposition of thin film shield  66 . The thin film shield is a layer of high permeability (greater than 500) ferromagnetic material. It needs to have as high an electrical resistivity as possible within other constraints of the structure. It is required to be at least 5 times more resistive than the free layer. Since the latter is about 25 micro-ohm-cm, a value greater than about 125 micro-ohm-cm is to be preferred. The thickness of the thin film shield should be such that the moment-thickness product (of the thin film shield) is 2–5 times that of the free layer. The presence of this thin film shield allows relatively thicker dielectric layers to be used, thereby reducing or eliminating the chances of shorting, while still being able to obtain very narrow feedback pulse widths (namely PW 50 ). 
     With the thin film shield in place, decoupling layer  25  is laid down followed by the deposition of free layer  21 . This is followed by the deposition of non-magnetic layer  22  onto which is deposited pinned layer  23 . Next, onto pinned layer  23  there is deposited anti-ferromagnetic layer  24  for use as a pinning layer. 
     Now follows another key feature of the invention. On anti-ferromagnetic layer  24 , decoupling layer  25  is deposited, followed by the deposition of a second thin film shield  67 . The second thin film shield has the same properties as the first thin film shield. The presence of the thin film shields allows a relatively large shield-to-shield spacing to be maintained (thereby reducing or eliminating the chances of shorting) while still being able to obtain very narrow feedback pulse widths. 
     To initiate completion of the structure, trench  29  is formed using conventional patterning and etching. This trench extends through thin film shield  67  down as far as the top surface of dielectric layer  17 . The trench has a sidewall  30  that slopes at an angle of about 20 degrees. Onto this sidewall, as well as the exposed surface of dielectric layer  17 , is selectively deposited layer  27  of a ferromagnetic material (such as CoCrPt) that is suitable for use as a permanent magnet, the direction of permanent magnetization being set by a field that is present during deposition of the layer or by later annealing in such a field. Layer  27  will serve to provide longitudinal bias to the structure, as discussed earlier. 
     With layer  27  in place, a layer of conductive material  28 , suitable for use as a connecting lead to the structure, is selectively deposited thereon. This is followed by the deposition of second dielectric layer  18  onto which is deposited upper primary magnetic shield  16 . 
     In  FIGS. 7 and 8  we present data that confirms the effectiveness of the present invention.  FIG. 7  illustrates the reduction in PW 50  that the present invention brings about. Shown there are micro-magnetic simulated playback wave-forms. The cases involved are curve  71 , conventional SV head with 800 Å shield-to-shield spacing (dashed), and curve  72  which is for double-sided thin film shields(solid), the free layer being located at the center of the two thin film shields. The spacing between the thin film shields is 300 Å. The total distance between the primary shields is about 1000 Å. The M r T (remnant magnetization×layer thickness=total magnetic moment) of both thin film shields is four times that of the free layer. The resistivity of the thin film shield is assumed to be nine times greater than that of the free layer. Simulation shows that the PW 50  for the conventional SV is about 700 Å while the PW 50  for the thin film shield head is about 550 Å, which is approximately equivalent to a 450 Å shield-to-shield space in the case without the thin film shields. 
     Since the thin film shields are magnetic materials, the fringe field from the shield layers will affect the performance of the free layer and cause instability if they are not properly biased. No additional bias scheme is needed for the continuous thin film shield. For the permanent magnet (PM) abutted scheme ( FIGS. 2 ,  3 , and  6 ), a permanent magnet is placed adjacent to both sides of the thin film shield to provide a horizontal bias along the track width direction, just as the free layer is given its bias. The highly localized PM field removes the magnetic charge at the ends of the thin film shield, while still keep the high permeability property of the shield layers. 
     From the curves shown in  FIG. 7 , the data displayed in TABLE II can be derived: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE II 
               
               
                   
                   
               
               
                   
                   
                   
                 equivalent shield-to- 
               
               
                   
                 structure 
                 PW 50  (Å) 
                 shield spacing 
               
               
                   
                   
               
             
             
               
                   
                 no TF shield 
                 700 
                 800 
               
               
                   
                 with TF shield 
                 550 
                 450 
               
               
                   
                   
               
             
          
         
       
     
     This shows that when the thin film shield disclosed in the present invention is used, the 550 Angstrom PW 50  that is obtained is equivalent to a shield-to-shield spacing of only 450 Angstroms. 
       FIG. 8  shows calculated transfer curves for the double-sided thin film shield for two different PM bias strength presented as voltage vs. total magnetic moment in milli-electromagnetic units. A “kink”  83  appears in the transfer curve where hard bias curve  81  for a field that is not strong enough crosses curve  82  which is for a field of adequate strength. Calculations show that a stability coefficient (M r T) PM /(M r T) TFS  of 1 is sufficient to provide the proper horizontal bias for the thin film shields. 
     Note that since the thin film shield is at least two times thicker than the free layer, the degree of the magnetization rotation in the thin film shield is usually much less than in the free layer. The magnetization in the thin film shield is essentially oriented along the track width direction. The change of the free layer bias level due to the flux from the shield layer is not significant. The effect of current field from the thin film shield layers on the bias is also negligible due to the high resistivity of the shield material. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.