Abstract:
A method of forming a DSMR head comprises the steps of forming a first ferromagnetic (FM) strip on a substrate with a first anti-FM (AFM) pinning layer over a portion of the first ferromagnetic strip, the first AFM pinning layer being composed of a first material. Then perform a first high temperature annealing step. Form a non-magnetic layer over the strip and the pinning layer. Then form a second FM strip on the non-magnetic layer, and form a second AFM pinning layer over a portion of the second FM strip, with a second AFM pinning layer being composed identically of the first material. Perform a second high temperature annealing step on the first and second FM strips and the first and second pinning layers and the intermediate non-magnetic layer in the presence of a second magnetic field antiparallel to the first magnetic field. A head with NiFe FM strips and FeMn or MnPt, etc, AFM layers for both strips is provided.

Description:
This is a division of patent application Ser. No. 09/369,289, now U.S. Pat. No. 6,308,400, filing date Aug. 6, 1999, High Density Recording, Dual Stripe Mr (Dsmr) Head And Method For Achieving Anti-Parallel Exchange Coupling With One Biased Layer Having Low Coercivity, assigned to the same assignee as the present invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to magnetic recording, dual stripe, magnetoresistive (DSMR) read heads and more particularly to methods of forming such read heads. 
     2. Description of Related Art 
     Askar, Magnetic Disk Drive Technology: Heads, Media, Channel, Interfaces And Integration, IEEE Press Inc., (1996) pp. 142-146, describes DSMR sensors and exchange biasing. 
     U.S. Pat. No. 5,262,914 of Chen et al. for “Magnetoresistive Head with Enhanced Exchange Bias Field” describes a MnFe AntiFerro-Magnetic (AFM) bias layer in direct contact with a NiFe MR layer which in turn is in physical contact with an interdiffusion layer composed of a noble metal, with a 240° C., 7 hour annealing process for thermally forming an interface between the AFM layer and the MR layer which produces an exchange bias field to the MR layer. 
     U.S. Pat. No. 5,406,433 of Smith for “Dual Magnetoresistive Head for Reproducing Very Narrow Track Width Short Wavelength Data” describes at Col. 5, line 54 to Col. 6, line 33 longitudinal biasing of MR elements in opposite directions by pinning at the ends of the elements by use of patterned exchange biasing. After an MR element is deposited a patterned exchange layer of FeMn is deposited over the two ends of the first MR element. Either during (1) deposition of the AFM FeMn exchange layer or (2) after annealing, a longitudinal magnetic field is applied to the structure to orient the exchange bias field in the selected longitudinal direction. After formation of a spacer and the second MR element, a second patterned ferrimagnetic (TbCo) exchange layer of a different material from the AFM FeMn layer is deposited over the two ends of the second MR element. A post deposition field in the opposite direction from the first field is applied to the TbCo layer so that there is opposite magnetization in the two MR elements. 
     U.S. Pat. No. 5,561,896 of Voegeli et al. for “Method of Fabricating Magnetoresistive Transducer” teaches a Selective Pulse Interdiffusion (SPI) process during which areas destined to become biasing segments of an MagnetoResistive (MR) head are selectively heated using one or more electrical current pulses of short duration. 
     U.S. Pat. No. 5,684,658 of Shi et al. for “High Track Density Dual Stripe Magnetoresistive (DMSR) Head” shows a DSMR having a first anti-ferromagnetic (AFM) longitudinal biasing layer and a second anti-ferromagnetic (AFM) longitudinal biasing layer that are parallel, in contrast with the present invention as described at Col. 8, lines 20-39. The AFM materials include NiMn, CoCr, CoCrPt, CoCrTa, CoCrNi, CoCrPtNi, CoCrNiTa, etc. 
     U.S. Pat. No. 5,696,654 of Gill et al. for “Dual Element Magnetoresistive Sensor with Anti-Parallel Magnetization Directions for Magnetic State Stability” describes a dual MR element sensor with two MR elements separated by a high resistivity, conductive spacer element. A layer of a hard bias material abutting the track edges of the MR 2  element biases it longitudinally in one direction. The MR 1  layer is biased by a pair of exchange bias layers (NiFe/NiMn or NiFe/NiO) abutting the track edges of the MR 1  strip by exchange coupling in an opposite, i.e. antiparallel longitudinal direction. 
     U.S. Pat. No. 5,859,753 of Ohtsuka et al. for “Spin Valve Magnetoresistive Head with Spun Valves Connected in Series” that includes first and second magnetization pinning layers which are anti-parallel to each other including AFM layers one of which is NiMn that has a high blocking temperature and one of which if FeMn that has a low blocking temperature. At col. 10, lines 10-19”. . . NiMn having a high blocking temperature is formed as the first antiferromagnetic layer . . . on the first magnetization pinning layer . . . at a temperature of 200° to 300° C. The NiMn is grown in a magnetic field H 01  applied in the first direction. Thereafter, . . . FeMn is formed as the second antiferromagnetic layer . . . on the second magnetization spinning layer . . . at a temperature of around 160° C. While applying a magnetic field H 02  in the direction opposite to the first direction, the growth of FeMn is carried out.” At Col. 10, lines 37-60 it is pointed out that an alternative process can employ a step of heating to the higher blocking temperature and application of field H 01  which is followed by a step of heating to the lesser blocking temperature temperature and application of field H 02  can be deferred until after formation of the AFM layers. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention a method is provided for forming a DSMR head including forming a first ferromagnetic (FM) strip on a substrate with a first anti-FM (AFM) pinning layer over a portion of the first ferromagnetic strip, the first AFM pinning layer being composed of a first material. Then perform a first high temperature annealing step. Form a non-magnetic layer over the strip and the pinning layer, and form a second FM strip on the non-magnetic layer. Form a second AFM pinning layer over a portion of the second FM strip, with a second AFM pinning layer being composed identically of the first material. Perform a second high temperature annealing step on the first and second FM strips and the first and second pinning layers and the intermediate non-magnetic layer in the presence of a second magnetic field antiparallel to the first magnetic field. A head with NiFe FM strips and FeMn, or MnPt, etc, AFM layers for both strips is provided. Preferably, the first and second magnetoresistive strips are composed of NiFe, and the first and second antiferromagnetic pinning layers are composed of FeMn or MnPt. Preferably, the first high temperature annealing step is performed at a temperature of about 300° C. for from about 50 minutes to about 5 hours, with an applied external field of about 2000 Oe, the second high temperature annealing step is performed at a temperature of about 250° C. for a duration of about 1 hour, with an applied external field of about 2000 Oe, and a third high temperature annealing step is performed at a temperature of about 250° C. for a duration of about 4 hours, with no applied external field after completion of the second high temperature annealing step. 
     In accordance with another aspect of this invention, a dual stripe, magnetoresistive head comprises a first ferromagnetic strips on a substrate, and a first antiferromagnetic pinning layer over a portion of the first ferro-magnetic stripe, the first antiferromagnetic pinning layer being composed of a first material magnetized in a first direction. There is an intermediate non-magnetic layer over the strips and the pinning layer. A second ferro-magnetic stripe overlies the intermediate non-magnetic layer and there is a second antiferromagnetic pinning layer over a portion of the second ferromagnetic strips, the second antiferromagnetic pinning layer being composed of the first material, the second pinning layer being magnetized in a direction antiparallel to the first magnetic field. Preferably, the first and second magnetoresistive stripes are composed of NiFe, and the first and second antiferromagnetic pinning layers are composed of a material selected from the group consisting of FeMn, MnPt, MnPdPt, and NiMn, wherein Hpin for the first stripe is about 287 Oe and Hc is about 177 Oe and Hpin/Hc is about 1.62, and Hpin for the second stripe is about 227 Oe and He is about 35 Oe and Hpin/Hc is about 6.5. 
     An advantage of this method is that the same antiferromagnetic material with high blocking temperature, e.g. NiMn or MnPt can be used in the applications where the magnetization directions of the two exchange-coupled layers need to be set at various angles between them. 
     The invention teaches an anti-parallel exchange biased DSMR device with two annealing steps to set two exchange bias layers in different directions. 
     Another advantage of this invention is that the third annealing step increases the pinning field of the second MR strip and restores the pinning field of the first MR strip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other aspects and advantages of this invention are explained and described below with reference to the accompanying drawings, in which: 
     FIGS. 1A and 1B show a flow chart of a sequence of steps in accordance with the method of this invention. 
     FIG. 2 is a sectional view of a device manufactured in accordance with the method of FIGS. 1A and 1B. 
     FIG. 3 shows an anti-parallel magnetization structure in a DSMR head (inverted with respect to FIG.  2 ), with two MR stripes each having an MR sensing region and exchange bias regions and leads on the ends. 
     FIG. 4 shows the device of FIG. 3, but in an early stage of manufacture with a magnetization M 1  in the set of exchange pinned regions of the first MR stripe after the first annealing step. 
     FIG. 5 shows the device of FIG. 4, in a later stage of manufacture with the added magnetization in the second set of exchange pinned regions after the second annealing step. 
     FIG. 6 is a graph of Hpin, Hc vs. annealing time showing the effect of the opposing field annealing step on Hpin and Hc and illustrating the effect on the exchange field and coercivity of MR 1 /NiMn, which has been through initial annealing step with an opposing field as in FIG.  1 B. 
     FIG. 7 is a graph of exchange field Hpn and coercivity Hc (Oe) vs. annealing time for annealing a DSMR MR/EB (NiFe/NiMn) device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1A and 1B show a flow chart of a sequence of steps in accordance with the method of this invention. This produces an anti-parallel magnetization or an anti-parallel exchange bias for the MR layers in a DSMR head using the same antiferromagnetic (AFM) material composed of alloys such as Nickel/Manganese (NiMn), Manganese/Platinum (MnPt), etc. The method produces a high density, high data rate Dual-Stripe MagnetoResistive (DSMR) head with an anti-parallel exchange biased DSMR configuration. This method produces a DSMR head with a uniform cross-track bias profile and a higher signal amplitude especially for narrow Track Width (TW) applications. 
     The reason to use the same antiferromagnetic (AFM) materials for both stripes composed of alloys of such as NiMn, MnPt, etc., is that the exchange coupling field is strong and the blocking temperature is high, which are desirable characteristics for longitudinal stability of the DSMR device. 
     This invention provides a fabrication method for providing an antiparallel magnetization state between two magnetoresistive (MR) stripes in a DSMR device while maintaining a large Hex/Hc ratio of one MR stripe. This is needed to allow for a large process window for initialization. 
     FIG. 2 is a sectional view of a device manufactured in accordance with the method of FIGS. 1A and 1B. A substrate SUB is formed of a material such as aluminum oxide (Al 2 O 3 ). 
     On the substrate SUB, an undercoat layer UC is deposited. On the undercoat layer UC is deposited a magnetic shield layer SH 1  formed of the alloys Nickel/Iron (NiFe) or Cobalt/Zirconium/Hafnium/Niobium (CoZrHfNb). 
     A first read dielectric gap layer D 1  is formed over the shield layer SH 1 . Layer D 1  is formed of a material such as aluminum oxide (Al 2 O 3 ). 
     A first magnetoresistive (MR) layer MR 1  composed of NiFe alloy is formed on the surface of the dielectric gap layer D 1 . 
     Exchange bias first antiferromagnetic pinning regions EB 1  are composed of a material selected from the group of nickel manganese (NiMn), manganese palladium platinum (MnPdPt) and manganese platinum (MnPt). 
     U.S. Pat. Nos. 5,406,433 and 5,684,658 illustrate connections of exchange bias (AFM) layers and the leads such as sketch for the AFM Dinning regions EB 1  and EB 2  and the leads L 1  and L 2 . 
     A thin protective layer PL is formed on the surface of the first MR layer MR 1 , preferably composed of an electrically insulating material such as aluminum oxide (Al2/O3), or a highly resistive layer. The thin protective layer PL covers first MR layer MR 1 , leads L 1  and AFM pinning regions EB 1 . 
     A second MR layer MR 1  composed of nickel iron alloy (NiFe) is formed on the surface of the protective layer PL. 
     Exchange bias first antiferromagnetic structures EB 2  is composed of a alloy material selected from the group of nickel/manganese (NiMn), manganese/platinum (MnPt), and manganese/palladium/platinum (MnPdPt). 
     Again, U.S. Pat. Nos. 5,406,433 and 5,684,658 illustrate connections of exchange bias (AFM) layers and the leads such as sketch for the exchange bias (AFM) layers and the leads. 
     A thin dielectric gap layer D 3  is formed on the surface of the layer MR 2 . The thin dielectric layer D 3  covers second MR layer MR 2 , leads L 2  and AFM pinning region EB 2 . 
     On the thin dielectric gap layer D 3  is deposited a magnetic shield layer SH 2  formed of NiFe alloy. 
     FIG. 3 shows an anti-parallel magnetization structure in a DSMR head  10 ′ (which is inverted with respect to FIG.  2 ), with MR stripes MR 1  and MR 2  with MR sensing regions and exchange bias regions EB 1  and EB 2  on the ends. 
     In MR stripe MR 1 , there is a magnetization M 1  in Dinning regions EB 1  in a longitudinal direction at an angle—Θ relative to the horizontal (X) axis and a corresponding magnetization M 1 ′ at the same angle—Θ in the first sensor region SR 1  as in the AFM exchange bias pinning regions EB 1 . 
     In MR stripe MR 2 , there are magnetization M 2  in pinning regions EB 2  in a longitudinal direction at an angle Θ, in the opposite direction relative to the horizontal (X) axis and a corresponding magnetization M 2 ′ at the same angle Θ in the second sensor region SR 2 , as in the pinning regions EB 2 . 
     FIG. 4 shows the device  10 ′ of FIG. 3, but in an early stage of manufacture with a magnetization M 1  in the set of exchange pinned pinning regions EB 1  after the first annealing step. There is magnetization in the sensor region SR 1 . 
     FIG. 5 shows the device  10 ′ of FIG. 4, in a later stage of manufacture with the added magnetization M 2  in the set of exchange pinned pinning regions EB 2  after a second annealing step. 
     Referring to step  10  in FIG.  1 A and to FIG. 2, the process starts with a planar substrate SUB, preferably comprising a silicon wafer. First, an undercoat layer UC, preferably composed of carbon (C) is deposited upon the substrate SUB. 
     Then a shield layer SH 1 , preferably composed of NiFe alloy, is formed above the undercoat layer UC. 
     In step  12 , a first read dielectric gap layer D 1  is formed on the surface of shield layer SH 1 . The read dielectric gap layer D 1  is preferably composed of alumina (Al 2 O 3 ). 
     In step  14 , a ferromagnetic first MR layer MR 1 , preferably composed of NiFe alloy, is deposited on top of a first read dielectric gap, D 1  so that now the structure includes underneath structures of the first shield SH 1 , undercoat layer UC and substrate SUB. 
     In step  16 , a protective layer PL comprising either a thin insulator is then deposited on the top of the first magnetoresistive (MR) layer MR 1 . Such a highly resistive layer is composed of alumina (Al 2 O 3 ). 
     In step  18  the first MR layer MR 1  has a first sensor region longitudinally biased in a first longitudinal bias direction through a patterned first longitudinal magnetic exchange biasing antiferromagnetic layer EB 1  and the combined first conductor lead layer L 1  by a lift-off scheme. The first antiferromagnetic pinning regions EB 1  are composed of a material selected from the group of nickel manganese (NiMn) manganese platinum (MnPt), etc. 
     In step  20 , a second magnetoresistive (MR) layer MR 2  is formed on the surface of the thin protective layer PL. The second magnetoresistive (MR) layer MR 2  is parallel with and separated from the first magnetoresistive (MR) layer MR 1  and layer MR 2  is preferably composed of nickel iron alloy (NiFe), which is the same material as the first magnetoresistive (MR) layer MR 1 . 
     First High Temperature Annealing Step 
     In step  22 , a first high temperature annealing step is used to create a strong exchange biasing in the first magnetoresistive (MR) layer with the presence of the first magnetic field, as shown by the arrows in FIG.  4 . The first high temperature annealing step is performed at a temperature from about 280° C. to about 300° C. for a time from about 50 minutes to about 10 hours, with an applied field from about 500 Oe to about 2,000 Oe, preferably at 300° C. for from 50 minutes to 5 hours and an applied external field of about 2,000 Oe. 
     In step  24 , in the second magnetoresistive (MR) MR 2 , a second sensor region SR 2  of MR 2  formed longitudinally magnetically biased in a second longitudinal bias direction through a patterned second longitudinal magnetic exchange biasing antiferromagnetic layer and the second conductor lead layer by a lift-off scheme. The second antiferromagnetic pinning regions EB 2  are composed of a material selected from the group of nickel/manganese (NiMn) manganese/platinum (MnPt), etc. 
     In step  28 , a thin dielectric layer is deposited to form the gap D 3 , preferably composed of a material such as alumina (Al 2 /O 3 ). 
     In step  30 , the second shield SH 2  is deposited and a write head fabrication process is performed (not shown in FIG.  2 ). 
     Second Annealing Step 
     Referring to FIG. 5, and step  32  in FIG. 1B, to create a strong exchange biasing in the second stripe MR 2 , a second high temperature annealing treatment is applied in the presence of the second magnetic field which is anti-parallel to the first magnetic field which was applied during the first annealing step. The final exchange bias pinning regions EB 1  of first MR stripe MR 1  are set along the first magnetic direction, while the exchange bias pinning regions in the second MR stripe MR 2  set along the second field direction. 
     First Alternative, Second Annealing Step 
     The temperature of the second annealing step can be as high as the annealing e.g., 300° C., but the magnitude of the magnetic field is controlled to be smaller than the residual exchange coupling field at that specific second annealing temperature. In the experiments conducted, the magnetic field is controlled within 50 Oe to 120 Oe range. After the second annealing step, the majority of the exchange of first MR stripe MR 1  is still toward the first magnetic direction. 
     Second Alternative, Second Annealing Step 
     In this alternative, the second high temperature annealing step is applied to create a strong exchange biasing in the second MR stripe MR 2  in the presence of the second magnetic field which is anti-parallel to the first magnetic field during first annealing, shown in FIG.  5 . The temperature of the second annealing step is controlled around 250° C. and with a field in 200-2000 Oe range. 
     In step  34 , after a second field annealing step, a third high temperature annealing step is performed to cure the device by further increasing the pinning field of the second MR stripe MR 2  and providing for the recovery of the the exchange biasing of second MR stripe MR 2  by restoring the pinning field of the first MR stripe MR 1  to a far higher level. The third high temperature annealing step is performed in the absence of a magnetic biasing field, i.e. with no external magnetic field applied at a temperature of about 250° C. to increase the pinning field of the second sensor region SR 2  of the second MR stripe MR 2  and to restore the pinning field of the first sensor region SR 1  of the first MR stripe MR 1 . 
     FIG. 5 illustrates the desired magnetization states of the stripes MR 1  and MR 2  in a DSMR device  10 ′ with an exchange pinned region EB 2  after the second annealing step  32  in FIG. 1B in accordance with this invention. 
     FIG. 6 is a graph of Hpin, Hc vs. Anneal time which shows the effect of the opposing field annealing step on Hpin and Hc and which illustrates the effect on the exchange field and coercivity of MR 1 /NiMn, which has been through an initial annealing step at a temperature of 300° C. for a duration of eight (8) hours in step  22  in FIG. 1A, after annealing at a temperature 300° C. with an opposing field of 100 Oe in step 32 in FIG.  1 B. 
     FIG. 6 clearly shows that the Hpin exchange field of sample #1 reduces from 230 Oe to 180 Oe after 50 min. of an opposing field annealing step, and Hc is reduced from 150 Oe to 60 Oe after 50 min. However, for data (not shown) the exchange field Hpin of sample #2 is at 160 Oe. 
     FIG. 7 is a graph for a DSMR MR/EB (NiFe/NiMn) of an annealing experiment of exchange field Hpn and coercivity Hc (Oe) vs. annealing time (minutes) illustrating that during application of a 300° C./100 Oe field the exchange field strength of the sample #2 increases as the annealing time increases as shown in FIG.  7 . 
     The Hpn in FIG. 7 is for EB 2  and Hpin in FIG. 6 is for EB 1 . 
     The coercivity approaches a maximum of nearly 150 Oe asymptotically near an annealing time of 300 minutes. 
     On the other hand, the exchange field and coercivity of sample #1 is reduced slightly with a longer annealing time. By controlling the annealing time and magnetic field of the second annealing step, the two MR stripes can be set with the desired anti-parallel state as shown in FIG.  3 . The process window of resetting them into the anti-parallel state is wide enough to assure consistency in device performance. 
     Third Annealing Step 
     In the experiments conducted, the magnetic field for second annealing step is 2000 Oe. In the final step, the magnetization of the first exchange bias pinning region EB 1  in the first MR sensor MR 1  sensor is set along the first magnetic direction, while the magnetization in the second exchange bias region EB 2  in the second MR sensor MR 2  is set along the second, opposite field direction, i.e. antiparallel. 
     The coercivity of the exchange bias pinning region EB 2  in the second MR sensor MR 2  is very small which is highly desirable in setting of the antiparallel state of the magnetizations of the two exchange biased MR layers. One example is in the anti-parallel DSMR application. The other example is in an SVMR (Spin Valve MR) application, where the small Coercivity of the pinned layer may be desirable for a head operation. 
     Table I lists the exchange field and coercivity of MR 1 /NiMn and MR 2 /NiMn after different annealing steps. The data in Table I clearly show that the exchange field strength Hpin of the MR 1  declines very sharply from 260 Oe to 6 Oe after exposure for one (1) hour to an opposing field annealing step at 250° C. with an applied field of 2000 Oe. However, after curing the device in a “no field” annealing step at a temperature of about 250° C. for about four (4) hours, the exchange field of MR 1  recovers (increases) back to about 287 Oe. The exchange field strength Hpin of MR 2  after 250° C., 2000 Oe, during a one (1) hour annealing step is about 10 Oe and it is further increased by annealing for four (4) hours with no field at 250° C. to about 227 Oe. It is noted that the final coercivity of the MR 2  is about 35 Oe with a Hpin/Hc ratio of 6.5, which is very desirable in setting the two DSMR sensors into an antiparallel magnetization state. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Hpin and Hc after each annealing step 
               
             
          
           
               
                 ANNEALING STEP 
                 FM (NiFe) 
                   AFM 
                        CONDITIONS         TEMP.  HRS  FIELD   
                 Hpin (Oe) 
                 Hc (Oe) 
                 
                   
                     
                       
                         Hpin 
                         Hc 
                       
                     
                             
                     
                         
                     
                   
                 
               
               
                   
               
             
          
           
               
                 FIRST SENSOR 
               
             
          
           
               
                 ONE 
                 MR1 
                 NiMn 
                  300° C. 
                 5 
                 2000 Oe 
                 260 
                 106 
                 2.45 
               
               
                 TWO 
                 MR1 
                 NiMn 
                 +250° C. 
                 1 
                 2000 Oe 
                  6 
                 213 
                 0.03 
               
               
                 THREE 
                 MR1 
                 NiMn 
                 +250° C. 
                 4 
                 No Field 
                 287 
                 177 
                 1.62 
               
             
          
           
               
                 SECOND SENSOR 
               
             
          
           
               
                 TWO 
                 MR2 
                 NiMn 
                  250° C. 
                 1 
                 2000 Oe 
                  10 
                  20 
                 0.50 
               
               
                 THREE 
                 MR2 
                 NiMn 
                 +250° C. 
                 4 
                 No Field 
                 227 
                  35 
                 6.50 
               
               
                   
               
             
          
         
       
     
     While this invention has been described in terms of the above specific embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims, i.e. that changes can be made in form and detail, without departing from the spirit and scope of the invention. Accordingly, all such changes come within the purview of the present invention and the invention encompasses the subject matter of the claims which follow.