United States Patent [19J
`Dill et al.
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US006023395A
`6,023,395
`[11] Patent Number:
`[45] Date of Patent:
`Feb.8,2000
`
`[54] MAGNETIC TUNNEL JUNCTION
`MAGNETORESISTIVE SENSOR WITH IN(cid:173)
`STACK BIASING
`
`[75]
`
`Inventors: Frederick Hayes Dill, South Salem,
`N.Y.; Robert Edward Fontana, Jr.,
`San Jose, Calif.; Tsann Lin, Saratoga,
`Calif.; Stuart Stephen Papworth
`Parkin, San Jose, Calif.; Ching Hwa
`Tsang, Sunnyvale, Calif.
`
`[73] Assignee: International Business Machines
`Corporation, Armonk, N.Y.
`
`[21]
`
`Appl. No.: 09/087,334
`
`[22]
`
`Filed:
`
`May 29, 1998
`
`[51]
`[52]
`[58]
`
`[56]
`
`Int. Cl.7
`........................................................ GllB 5/39
`U.S. Cl . .............................................................. 360/113
`Field of Search .................... 360/113; 257/421-427;
`365/158, 171, 173
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`3,623,038 11/1971 Franklin et al. .................. 340/174 TF
`5/1991 Krounbi et al. ........................ 360/113
`5,018,037
`2/1995 Nakatani et al. ....................... 360/113
`5,390,061
`5/1995 Kamiguchi et al. .................... 257/421
`5,416,353
`7/1995 Kawano et al. ........................ 365/158
`5,432,734
`5,465,185 11/1995 Heim et al. ............................. 360/113
`6/1996 Fontana et al. ......................... 360/113
`5,528,440
`5,695,864 12/1997 Slonczewski ........................... 428/212
`3/1998 Nakatani et al. ....................... 360/113
`5,726,837
`3/1998 Fontana et al. ......................... 360/133
`5,729,410
`4/1999 Fontana, Jr. et al. ................... 360/113
`5,898,547
`
`FOREIGN PAI'ENT DOCUMENTS
`
`WO 95/10123
`
`4/1995 WIPO .
`
`01HER PUBLICATIONS
`
`M. Julliere, "Tunneling Between Ferromagnetic Films",
`Physics Letters, vol. 54A, No. 3, Sep. 8, 1975, pp. 225-226.
`K. Matsuyama et al., "Fabrication of Microstructured Mag(cid:173)
`netic Tunneling Valve Junction", IEEE Transactions on
`Magnetics, vol. 31, No. 6, Nov. 1995, pp. 3176-3178.
`
`J. S. Moodera et al., "Ferromagnetic-insulator-ferro(cid:173)
`magnetic Tunneling: Spin-dependent Tunneling and Large
`Magnetoresistance in Trilayer Junctions", Symposium on
`Spin Tunneling and Injection Phenomena, Journal of
`Applied Physics, vol. 79, No. 8, Apr. 15, 1996, pp.
`4724-4729.
`
`Primary Examiner-William J. Klimowicz
`AttorneJ\ Agent, or Firm-Thomas R. Berthold
`
`[57]
`
`ABSTRACT
`
`A magnetic tunnel junction (MTJ) magnetoresistive (MR)
`read head has one fixed ferromagnetic layer and one sensing
`ferromagnetic layer on opposite sides of the tunnel barrier
`layer, and with a biasing ferromagnetic layer in the MTJ
`stack of layers that is magnetostatically coupled with the
`sensing ferromagnetic layer to provide either longitudinal
`bias or transverse bias or a combination of longitudinal and
`transverse bias fields to the sensing ferromagnetic layer. The
`magnetic tunnel junction in the MTJ MR head is formed on
`an electrical lead on a substrate and is made up of a stack of
`layers. The layers in the stack are an antiferromagnetic layer,
`a fixed ferromagnetic layer exchange biased with the anti(cid:173)
`ferromagnetic layer so that its magnetic moment cannot
`rotate in the presence of an applied magnetic field, an
`insulating tunnel barrier layer in contact with the fixed
`ferromagnetic layer, a sensing ferromagnetic layer in contact
`with the tunnel barrier layer and whose magnetic moment is
`free to rotate in the presence of an applied magnetic field, a
`biasing ferromagnetic layer that has its magnetic moment
`aligned generally within the plane of the device and a
`nonmagnetic electrically conductive spacer layer separating
`the biasing ferromagnetic layer from the other layers in the
`stack. The self field or demagnetizing field from the biasing
`ferromagnetic layer magnetostatically couples with the
`edges of the sensing ferromagnetic layer to stabilize its
`magnetic moment, and, to linearize the output of the device.
`The electrically conductive spacer layer prevents direct
`ferromagnetic coupling between the biasing ferromagnetic
`layer and the other layers in the stack and allows sense
`current to flow perpendicularly through the layers in the
`MTJ stack.
`
`28 Claims, 7 Drawing Sheets
`
`116
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`TDK Corporation Exhibit 1009 Page 1
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`U.S. Patent
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`Feb.8,2000
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`Sheet 1of7
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`6,023,395
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`24 25 20
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`50
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`16
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`10
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`12
`FIG. 1 (PRIOR ART)
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`20
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`50
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`17
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`19
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`25
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`24
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`FIG. 2 (PRIOR ART)
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`15
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`22
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`14
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`TDK Corporation Exhibit 1009 Page 2
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`U.S. Patent
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`Feb.8,2000
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`Sheet 2 of 7
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`6,023,395
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`G3 G2 G1
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`25
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`(
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`c
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`S2
`P1
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`S1
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`20
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`40
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`MR
`~ ABS
`
`WRITE
`HEAD
`
`FIG. 3 (PRIOR ART)
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`TDK Corporation Exhibit 1009 Page 3
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`U.S. Patent
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`Feb.8,2000
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`Sheet 3 of 7
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`6,023,395
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`151
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`134
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`170
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`118
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`116
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`FIG. 4A
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`TDK Corporation Exhibit 1009 Page 4
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`U.S. Patent
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`Feb.8,2000
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`Sheet 4 of 7
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`6,023,395
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`133
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`G2
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`104
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`170
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`102
`G1
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`TDK Corporation Exhibit 1009 Page 5
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`U.S. Patent
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`Feb.8,2000
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`Sheet 5 of 7
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`6,023,395
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`150
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`151
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`156
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`154
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`FIG. 5A
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`TDK Corporation Exhibit 1009 Page 6
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`U.S. Patent
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`Feb.8,2000
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`Sheet 6 of 7
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`6,023,395
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`150
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`TDK Corporation Exhibit 1009 Page 7
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`

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`U.S. Patent
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`Feb.8,2000
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`Sheet 7 of 7
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`6,023,395
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`G1
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`194
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`195
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`193
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`
`TDK Corporation Exhibit 1009 Page 8
`
`

`
`6,023,395
`
`1
`MAGNETIC TUNNEL JUNCTION
`MAGNETORESISTIVE SENSOR WITH IN(cid:173)
`STACK BIASING
`
`Related Applications
`
`This application is related to application Ser. No. 09/087,
`533 titled "MAGNETIC TUNNEL JUNCTION MEMORY
`CELL WITH IN-STACK BIASING OF THE FREE FER(cid:173)
`ROMAGNETIC LAYER AND MEMORY ARRAY USING
`THE CELL" and application Ser. No. 09/087,322 titled
`"MAGNETIC TUNNEL JUNCTION MAGNETORESIS(cid:173)
`TIVE READ HEAD WITH LONGITUDINAL AND
`TRANSVERSE BIAS", both filed concurrently with this
`application.
`
`TECHNICAL FIELD
`
`This invention relates in general to a magnetic tunnel
`junction (MTJ) magnetoresistive (MR) sensor for sensing
`external magnetic fields, such as a MTJ MR read head for
`reading magnetically-recorded data. More particularly the
`invention relates to a MTJ MR sensor with biasing of the
`magnetic moment of the free or sensing ferromagnetic layer
`in the MTJ provided by an additional in-stack ferromagnetic
`layer.
`
`BACKGROUND OF THE INVENTION
`
`5
`
`25
`
`2
`moment of the first ferromagnetic layer, there are more
`available electronic states than when the magnetic moment
`of the second ferromagnetic layer is aligned antiparallel to
`that of the first ferromagnetic layer. The tunneling probabil-
`ity of the charge carriers is highest when the magnetic
`moments of both layers are parallel, and is lowest when the
`magnetic moments are antiparallel. Thus, the electrical
`resistance of the MTJ depends on both the spin polarization
`of the electrical current and the electronic states in both of
`10 the ferromagnetic layers.
`For a memory cell application one of the ferromagnetic
`layers in the MTJ has its magnetic moment fixed or pinned
`so as to be parallel or antiparallel to the magnetic moment
`of the other free or sensing ferromagnetic layer in the
`15 absence of an applied magnetic field \vithin the cell. For a
`MR field sensor or read head application one of the ferro(cid:173)
`magnetic layers has its magnetic moment fixed or pinned so
`as to be generally perpendicular to the magnetic moment of
`the free or sensing ferromagnetic layer in the absence of an
`20 external magnetic field.
`A MR sensor detects magnetic field signals through the
`resistance changes of a read element, fabricated of a mag(cid:173)
`netic material, as a function of the strength and direction of
`magnetic flux being sensed by the read element. The con(cid:173)
`ventional MR sensor, such as that used as a MR read head
`for reading data in magnetic recording disk drives, operates
`on the basis of the anisotropic magnetoresistive (AMR)
`effect of the bulk magnetic material, which is typically
`permalloy (Ni81Fe19). A component of the read element
`resistance varies as the square of the cosine of the angle
`between the magnetization direction in the read element and
`the direction of sense current through the read element.
`Recorded data can be read from a magnetic medium, such as
`the disk in a disk drive, because the external magnetic is field
`from the recorded magnetic medium (the signal field) causes
`a change in the direction of magnetization in the read
`element, which in turn causes a change in resistance of the
`read element and a corresponding change in the sensed
`current or voltage.
`The use of an MTJ device as a MR read head has been
`described in U.S. Pat. No. 5,390,061. One of the problems
`with such a MR read head, however, lies in developing a
`structure that generates an output signal that is both stable
`45 and linear with the magnetic field strength from the recorded
`medium. If some means is not used to stabilize the sensing
`ferromagnetic layer of the MTJ, i.e., to maintain it in a single
`magnetic domain state, the domain walls of magnetic
`domains will shift positions within the sensing ferromag-
`50 netic layer, causing noise which reduces the signal-to-noise
`ratio. This may give rise to a non-reproducible response of
`the head, when a linear response is required. Similarly the
`response of the MTJ MR read head must be approximately
`symmetric with regard to positive and negative sense fields.
`The problem of maintaining a single magnetic domain
`state is especially difficult in the case of an MTJ MR read
`head because, unlike an AMR sensor, the sense current
`passes perpendicularly through the ferromagnetic layers and
`the tunnel barrier layer, and thus any metallic materials used
`to stabilize the sensing ferromagnetic layer that may come in
`contact with the ferromagnetic layers in the MTJ will short
`circuit the electrical resistance of the MTJ. IBM's U.S. Pat.
`No. 5,729,410 describes a MTJ MR read head with ferro(cid:173)
`magnetic material for longitudinally stabilizing or biasing
`the sensing ferromagnetic layer, wherein the biasing mate(cid:173)
`rial is located outside the MTJ stack and separated from the
`stack by electrically insulating material.
`
`40
`
`30
`
`35
`
`A magnetic tunnel junction (MTJ) device is comprised of
`two ferromagnetic layers separated by a thin insulating
`tunnel barrier layer and is based on the phenomenon of
`spin-polarized electron tunneling. One of the ferromagnetic
`layers has a higher saturation field in one direction of an
`applied magnetic field, typically due to its higher coercivity
`than the other ferromagnetic layer. The insulating tunnel
`barrier layer is thin enough that quantum mechanical tun(cid:173)
`neling occurs between the ferromagnetic layers. The tunnel(cid:173)
`ing phenomenon is electron-spin dependent, making the
`magnetic response of the MTJ a function of the relative
`orientations and spin polarizations of the two ferromagnetic
`layers.
`MTJ devices have been proposed as memory cells for
`solid state memory and as external magnetic field sensors,
`such as MR read sensors or heads for magnetic recording
`systems. The response of the MTJ device is determined by
`measuring the resistance of the MTJ when a sense current is
`passed perpendicularly through the MTJ from one ferro(cid:173)
`magnetic layer to the other. The probability of tunneling of
`charge carriers across the insulating tunnel barrier layer
`depends on the relative alignment of the magnetic moments
`(magnetization directions) of the two ferromagnetic layers.
`The tunneling current is spin polarized, which means that the
`electrical current passing from one of the ferromagnetic
`layers, for example, a ferromagnetic layer whose magnetic
`moment is fixed or prevented from rotation, is predomi(cid:173)
`nantly composed of electrons of one spin type (spin up or 55
`spin down, depending on the orientation of the magnetic
`moment of the ferromagnetic layer). The degree of spin
`polarization of the tunneling current is determined by the
`electronic band structure of the magnetic material compris(cid:173)
`ing the ferromagnetic layer at the interface of the ferromag- 60
`netic layer with the tunnel barrier layer. The first ferromag(cid:173)
`netic layer thus acts as a spin filter. The probability of
`tunneling of the charge carriers depends on the availability
`of electronic states of the same spin polarization as the spin
`polarization of the electrical current in the second ferromag- 65
`netic layer. Usually, when the magnetic moment of the
`second ferromagnetic layer is parallel to the magnetic
`
`TDK Corporation Exhibit 1009 Page 9
`
`

`
`6,023,395
`
`4
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`3
`What is needed is an MTJ device that has a stable and
`linear output and can thus function as an MTJ MR read head
`that provides a linear response to the magnetic fields from
`the recorded medium.
`
`SUMMARY OF THE INVENTION
`
`The invention is an MTJ MR read head with one fixed
`ferromagnetic layer and one sensing ferromagnetic layer on
`opposite sides of the tunnel barrier layer, and with a biasing
`ferromagnetic layer in the MTJ stack of layers that is
`macrnetostatically coupled with the sensing ferromagnetic
`lay~r to provide either longitudinal bias or transverse bias or
`a combination of longitudinal and transverse bias fields to
`the sensing ferromagnetic layer. The magnetic tunnel junc(cid:173)
`tion in the MTJ MR head is formed on an electrical lead on
`a substrate and i5 made up of a stack of layers. The layers in
`the stack are an antiferromagnetic layer, a fixed ferromag(cid:173)
`netic layer exchange biased with the antiferromagnetic layer
`so that its magnetic moment cannot rotate in the presence of
`an applied magnetic field, an insulating tunnel barrier layer
`in contact with the fixed ferromagnetic layer, a sensing
`ferromagnetic layer in contact with the tunnel barrier layer
`and whose magnetic moment is free to rotate in the presence
`of an applied magnetic field, a biasing ferromagnetic layer
`that has its magnetic moment aligned generally within the
`plane of the device and a nonmagnetic electrically conduc(cid:173)
`tive spacer layer separating the biasing ferromagnetic layer
`from the other layers in the stack. The self field or demag(cid:173)
`netizing field from the biasing ferromagnetic layer magne(cid:173)
`tostatically couples v.rith the edges of the sensing ferromag(cid:173)
`netic layer to stabilize its magnetic moment, and, to linearize
`the output of the device. The electrically conductive spacer
`layer prevents direct ferromagnetic coupling between the
`biasing ferromagnetic layer and the other layers in the stack 35
`and allows sense current to flow perpendicularly through the
`lavers in the MTJ stack. The biasing ferromagnetic layer
`m;y be a single relatively high coercivity material, a bilayer
`of a first lower coercivity ferromagnetic film and a second
`higher coercivity ferromagnetic film, or a ferromagnetic film
`interfacially exchange coupled to an antiferromagnetic film.
`For a fuller understanding of the nature and advantages of
`the present invention, reference should be made to the
`following detailed description taken together with the
`accompanying figures.
`
`Prior Art
`Although the MTJ device of the present invention will be
`s described below as embodied as a MR sensor in a magnetic
`recording disk drive, the invention is also applicable to other
`magnetic recording systems, such as magnetic tape record(cid:173)
`incr systems and to other external magnetic field sensors.
`Referring' first to FIG. 1, there is illustrated in sectional
`10 view a schematic of a prior art disk drive of the type using
`a MR sensor. The disk drive comprises a base 10 to which
`are secured a disk drive motor 12 and an actuator 14, and a
`cover 11. The base 10 and cover 11 provide a substantially
`sealed housing for the disk drive. Typically, there is a gasket
`15 13 located between base 10 and cover 11 and a small
`breather port (not shown) for equalizing pressure between
`the interior of the disk drive and the outside environment. A
`magnetic recording disk 16 is connected to drive motor 12
`by means of hub 18 to which it is attached for rotation by the
`20 drive motor 12. A thin lubricant film 50 is maintained on the
`surface of disk 16. A read/write head or transducer 25 is
`formed on the trailing end of a carrier, such as an air-bearing
`slider 20. Transducer 25 is a read/write head comprising an
`inductive write head portion and a MR read head portion, as
`25 will be described with respect to FIG. 3. The slider 20 is
`connected to the actuator 14 by means of a rigid arm 22 and
`a suspension 24. The suspension 24 provides a biasing force
`which urges the slider 20 onto the surface of the recording
`disk 16. During operation of the disk drive, the drive motor
`30 12 rotates the disk 16 at a constant speed, and the actuator
`14, which is typically a linear or rotary voice coil motor
`(VCM), moves the slider 20 generally radially across the
`surface of the disk 16 so that the read/write head 25 may
`access different data tracks on disk 16.
`FIG. 2 is a top view of the interior of the disk drive \vith
`the cover 11 removed, and illustrates in better detail the
`suspension 24 which provides a force to the slider 20 to urge
`it toward the disk 16. The suspension may be a conventional
`type of suspension, such as the well-known Watrous
`40 suspension, as described in IBM's U.S. Pat. No. 4,167,765.
`This type of suspension also provides a gimbaled attachme~t
`of the slider which allows the slider to pitch and roll as it
`rides on the air bearing. The data detected from disk 16 by
`the transducer 25 is processed into a data readback signal by
`45 signal amplification and processing circuitry in the inte(cid:173)
`grated circuit chip 15 located on arm 22. The signals from
`transducer 25 travel via flex cable 17 to chip 15, which sends
`its output signals to the disk drive electronics (not shown)
`via cable 19.
`FIG. 3 is a cross-sectional schematic view of the read/
`write head 25 which includes a MR read head portion and an
`inductive write head portion. The head 25 is lapped to form
`an air-bearing surface (ABS), the ABS being spaced from
`the surface of the rotating disk 16 (FIG. 1) by the air bearing
`55 as discussed above. The read head includes a MR sensor 40
`sandwiched between first and second gap layers Gl and G2
`which are, in turn, sandwiched between first and second
`shield layers Sl and S2. In a conventional disk drive, the MR
`sensor 40 is an AMR sensor. The write head includes a coil
`layer C and insulation layer 12 which are sandwiched
`between insulation lavers I1 and I3 which are, in turn,
`sandwiched between fi~t and second pole pieces Pl and P2.
`A gap layer G3 is sandwiched between the first and second
`pole pieces Pl, P2 at their pole tips adjacent to the ABS for
`65 providing a magnetic gap. During writing, signal current is
`conducted through the coil layer C and flux is induced into
`the first and second pole layers Pl, P2 causing flux to fringe
`
`50
`
`60
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`FIG. 1 is a simplified block diagram of a conventional
`magnetic recording disk drive for use with the MTJ MR read
`head according to the present invention.
`FIG. 2 is a top view of the disk drive of FIG. 1 with the
`cover removed.
`FIG. 3 is a vertical cross-section of a conventional induc(cid:173)
`tive write head/MR read head with the MR read head located
`between shields and adjacent to the inductive write head.
`FIG. 4Ais a cross-sectional view of a first embodiment of
`the MTJ MR read head of the present invention.
`FIG. 4B is a cross-sectional view of a second embodiment
`of the MTJ MR read head of the present invention.
`FIG. 5 is a schematic illustrating the magnetostatic cou(cid:173)
`pling between the biasing ferromagnetic layer and the sens(cid:173)
`ing ferromagnetic layer of the MTJ.
`FIG. 6 is a top view of the MTJ MR read head of FIG. 4
`illustrating the shape of the head and its position relative to
`the air-bearing surface (ABS) of the slider.
`
`TDK Corporation Exhibit 1009 Page 10
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`

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`6,023,395
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`25
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`5
`across the pole tips at the ABS. This flux magnetizes circular
`tracks on the rotating disk 16 during a write operation.
`During a read operation, magnetized regions on the rotating
`disk 16 inject flux into the MR sensor 40 of the read head,
`causing resistance changes in the MR sensor 40. These
`resistance changes are detected by detecting voltage changes
`across the MR sensor 40. The voltage changes are processed
`by the chip lS (FIG. 2) and drive electronics and converted
`into user data. The combined head 2S shown in FIG. 3 is a
`"merged" head in which the second shield layer S2 of the
`read head is employed as a first pole piece Pl for the write
`head. In a piggyback head (not shown), the second shield
`layer S2 and the first pole piece Pl are separate layers.
`The above description of a typical magnetic recording
`disk drive with an AMR read head, and the accompanying
`FIGS. 1-3, are for representation purposes only. Disk drives
`may contain a large number of disks and actuators, and each
`actuator may support a number of sliders. In addition,
`instead of an air-bearing slider, the head carrier may be one
`which maintains the head in contact or near contact v.rith the
`disk, such as in liquid bearing and other contact and near(cid:173)
`contact recording disk drives.
`Preferred Embodiments
`The present invention is a MR read head with a MTJ
`sensor for use in place of the MR sensor 40 in the read/write
`head 2S of FIG. 3.
`Referring first to FIG. 4A, the MTJ MR read head
`includes a bottom electrical lead 102 formed on the gap layer
`Gl substrate, a top electrical lead 104 below gap layer G2,
`and the MTJ 100 formed as a stack of layers between top and
`bottom electrical leads 102, 104 and surrounded by insulat(cid:173)
`ing alumina layer 140.
`The MTJ 100 includes a first electrode multilayer stack
`110, an insulating tunnel barrier layer 120, and a top
`electrode stack 130. Each of the electrodes 110, 130 includes
`a ferromagnetic layer in direct contact with tunnel barrier
`layer 120, i.e., ferromagnetic layers 118 and 132, respec(cid:173)
`tively.
`The base electrode layer stack 110 formed on electrical
`lead 102 includes a seed or "template" layer 112 on the lead
`102, a layer of antiferromagnetic material 116 on the tem(cid:173)
`plate layer 112, and a ''fixed" ferromagnetic layer 118
`formed on and exchange coupled with the underlying anti(cid:173)
`ferromagnetic layer 116. The ferromagnetic layer 118 is
`called the fixed layer because its magnetic moment or
`magnetization direction is prevented from rotation in the
`presence of applied magnetic fields in the desired range of
`interest. The top electrode stack 130 includes a "sensing"
`ferromagnetic layer 132. The sensing ferromagnetic layer
`132 is not exchange coupled to an antiferromagnetic layer,
`and its magnetization direction is thus free to rotate in the 50
`presence of applied magnetic fields in the range of interest.
`The sensing ferromagnetic layer 132 is fabricated so as to
`have its magnetic moment or magnetization direction
`(shown by arrow 133) oriented generally parallel to the ABS
`(FIG. 3) and generally perpendicular to the magnetization 55
`direction of the fixed ferromagnetic layer 118 in the absence
`of an applied magnetic field. The fixed ferromagnetic layer
`118 in electrode stack 110 just beneath the tunnel barrier
`layer 120 has its magnetization direction fixed by interfacial
`exchange coupling with the immediately underlying antifer- 60
`romagnetic layer 116, which also forms part of bottom
`electrode stack 110. The magnetization direction of the fixed
`ferromagnetic layer 118 is oriented generally perpendicular
`to the ABS, i.e., out of or into the paper in FIG. 4 (as shown
`by arrow tail 119).
`Also shown in FIG. 4A as part of top electrode stack 130
`is a biasing ferromagnetic layer lSO to provide bias fields for
`
`6
`stabilizing the magnetization direction of the sensing ferro(cid:173)
`magnetic layer 132, and an electrically conductive nonfer(cid:173)
`romagnetic spacer layer 1S2 separating and isolating the
`biasing layer lSO from the sensing ferromagnetic layer 132
`s and the other layers of the MTJ 100. Finally there is a
`protective or capping layer 134 formed on top on the biasing
`layer lSO. In one embodiment the biasing ferromagnetic
`layer lSO is a "hard" (relatively high coercivity) magnetic
`material, such as a binary alloy of Co and Pt or a ternary
`10 CoPtX alloy where X may be, for example, Cr or Ni, that has
`its magnetic moment (shown by arrow lSl) aligned anti(cid:173)
`parallel to the magnetic moment 133 of the sensing ferro(cid:173)
`magnetic layer 132 in the absence of an applied magnetic
`field. The spacer layer 1S2, which is preferably Cr or a
`15 Cr-V alloy has a thickness sufficient to prevent direct
`ferromagnetic coupling between the biasing layer lSO and
`the sensing ferromagnetic layer 132, but is still thin enough
`to permit magnetostatic coupling (shown by dashed arrows
`170) with the sensing ferromagnetic layer 132. The mini-
`20 mum thickness for the spacer layer 1S2 is approximately 2
`nm. In addition to Cr or Cr-V, other materials that will
`function as the electrically conductive spacer layer are Ta,
`Cu, Pd, Pt, Rh, Ti and titanium nitride (TiN), depending on
`the nature of the biasing layer lSO.
`FIG. SA illustrates the function of the self field or demag-
`netizing field from the biasing layer lSO when the moment
`of the biasing layer lSO is fixed in a direction approximately
`parallel to the ABS (FIG. 3) as indicated by the arrow lSl
`in FIG. SA The arrows 170 indicate the magnetostatic
`30 coupling between the edges 1S4 and 1S6 of the biasing layer
`lSO and the edges 134 and 136 of the sensing layer 132. The
`edges of the layers, such as edges 134, 136 of sensing layer
`132, define the track width (TW) of the sensor. Linear
`operation of the MTJ MR head requires that the sensing
`35 ferromagnetic layer 132 have its magnetic moment aligned
`along the track \vidth direction (arrow 133) and that the fixed
`ferromagnetic layer 118 have its magnetic moment aligned
`generally perpendicular to this direction (arrow 119) in the
`absence of an applied magnetic field. By setting the mag-
`40 netic moment of the biasing ferromagnetic layer lSO to be
`along the track width direction but opposite or antiparallel to
`the magnetic moment of the sensing ferromagnetic layer 132
`the self field from the biasing layer lSO \vill stabilize the
`magnetic moment of the sensing layer 132 at the track width
`45 edges 134 and 136. Thus the biasing layer lSO provides
`longitudinal bias to the sensing ferromagnetic layer 132
`when the moment of the biasing layer lSO is set approxi(cid:173)
`mately parallel to the ABS and antiparallel to the moment of
`the sensing ferromagnetic layer 132.
`In an alternative embodiment illustrated in FIG. SB the
`moment of the biasing layer lSO is set approximately
`orthogonal to the ABS and approximately along the direc(cid:173)
`tion 119 of the magnetic moment of the fixed layer 118. In
`this embodiment the moment of the biasing layer is shown
`by arrow lSl and provides a "transverse" magnetostatic
`coupling field. The arrows 170 in FIG. SB indicate the
`resulting magnetostatic coupling between the edges 1S8 and
`1S9 of the biasing layer lSO and the edges 172 and 174 of
`the sensing layer 132. In order to obtain a symmetric
`response of the MTJ device with regard to positive and
`negative sense fields it is necessary to ensure that in the
`absence of any sense field the magnetic moment of the
`sensing layer 132 is aligned approximately orthogonal to
`that of the fixed layer 118. Typically the magnetic moments
`65 of the sensing layer 132 and the fixed layer 118 are mag(cid:173)
`netically coupled to one another via a number of mecha(cid:173)
`nisms which include the possibility of a ferromagnetic
`
`TDK Corporation Exhibit 1009 Page 11
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`

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`6,023,395
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`7
`coupling field, HF, which may result from roughness of the
`surfaces of the magnetic layers, as well as an antiferromag(cid:173)
`netic coupling field, HD, which results from magnetostatic
`coupling of the edges of the sensing and fixed layers. It is
`important to balance these coupling fields so that the sum of
`the coupling fields in the absence of any sense field is
`approximately zero. In conventional AMR sensors these
`coupling fields may be partially offset by the self-field
`provided by the sense current passing parallel to the layers
`of the sensor. In a MTJ device the current passes perpen(cid:173)
`dicular to the sensor and cannot be used to provide such a
`field. Thus the biasing layer lSO is used to provide a
`transverse bias field which can be used to balance the
`coupling fields, HF and HD. Note that in FIG. SB the
`moment (arrow lSl) of the biasing layer lSO is set in a
`direction approximately antiparallel to the moment 119 of
`the fixed layer 118. Thus the biasing layer lSO will provide
`a magnetostatic coupling field on the sensing layer 32 which
`is approximately in the same direction as any ferromagnetic
`coupling field between the fixed layer 118 and the sensing
`layer 132. By setting the moment of the biasing layer lSO in
`the opposite direction to that shown in FIG. SB the biasing
`layer lSO will provide a magnetostatic coupling field at the
`sensing layer 132 which is along a direction approximately
`opposite to that of any ferromagnetic coupling field between
`the fixed layer 118 and the sensing layer 132. Thus in this
`case the magnetostatic coupling field provided by the bias(cid:173)
`ing layer lSO would compensate to a greater or less extent
`the ferromagnetic coupling field, Hp
`Generally the moment of the biasing layer lSO can be set
`in any direction 8 in the plane of the film lSO where 8 is the
`angle between the direction of the moment of the biasing
`layer and the ABS (see FIG. SB). In FIG. SA 8 is - zero
`degrees and in FIG. SB 8 is set at approximately 90 degrees.
`By setting 8 at an intermediate angle, i.e., neither approxi(cid:173)
`mately parallel nor orthogonal to the ABS, then the biasing
`layer lSO can provide a combination of longitudinal and
`transverse bias. To assure stable longitudinal biasing (8--0°)
`the product M*t of the biasing ferromagnetic layer lSO
`(where M is the magnetic moment per unit area of the
`material in a ferromagnetic layer and t is the thickness of the
`ferromagnetic layer) must be greater than or comparable to
`the M*t of the sensing ferromagnetic layer 132. For
`example, if the sensing ferromagnetic layer 132 is com(cid:173)
`prised of an alloy of Ni and Fe with the composition
`Nicrno-x)-Fe(x) with x being approximately 19 then since its
`magnetic moment per unit area is about twice that of the
`magnetic moment per unit area of a typical hard magnetic
`material suitable for the biasing ferromagnetic layer lSO,
`such as Co75Pt13Cr 12 , the thickness of the biasing ferromag(cid:173)
`netic layer lSO should be at least approximately twice that
`of the sensing ferromagnetic layer 132.
`FIG. 6 is a top view of the MTJ MR head of FIG. 4A with
`the layers above and including the G2 layer removed and the
`top electrical lead 104 shown in dotted lines so that the
`underlying head can be illustrated. The dashed line 161
`represents the ABS and the line to which the layers are
`lapped back after the MTJ MR head is fabricated. The MTJ
`100 is depicted as a stripe having a width TW, appropriate
`to the track width of the recorded data on the disk, and a final
`stripe height SH after lapping. The width of the recorded
`data track is wider than TW.
`Referring again to FIG. 4A, sense current I is directed
`from first electrical lead 102 perpendicularly through the
`antiferromagnetic layer 116, the fixed ferromagnetic layer
`118, the tunnel barrier layer 120, the sensing ferromagnetic
`layer 132, the electrically conductive spacer