Abstract:
A GMR spin valve is provided for reading a magnetic signal from a magnetic recording medium. The spin valve includes a non-magnetic layer such as for example copper, separated by first and second magnetic layers. The spin valve includes a pinned magnetic layer and a free magnetic layer, the resistance of the spin valve changing with the relative angle between the direction of magnetization of free and pinned layers. Extremely smooth surfaces are provided at the interfaces between the non-magnetic layer and the adjacent magnetic layers. This smooth interface greatly enhances the performance and reliability of the spin valve by allowing extremely tight control of the thickness of the non-magnetic layer and by preventing atomic diffusion between the non-magnetic and magnetic layers. This smooth interface is achieved by including a surfactant in the deposition of the non-magnetic layer.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to magnetic disk drives, and more particularly to spin valve—giant magnetoresistive (GMR) thin film read heads. 
     BACKGROUND OF THE INVENTION 
     Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk drive D of the prior art includes: a sealed enclosure  1 ; a disk drive motor  2 ; a magnetic disk  3  supported for rotation by a spindle S 1  of motor  2 ; an actuator  4 ; and an arm  5  attached to a spindle S 2  of actuator  4 . A suspension  6  is coupled at one end to the arm  5 , and at its other end to a read/write head or transducer  7 . The transducer  7  is typically an inductive write element with a sensor read element. As the motor  2  rotates the disk  3 , as indicated by the arrow R, an air bearing is formed under the transducer  7  to lift it slightly off of the surface of the disk  3 . Various magnetic “tracks” of information can be read from the magnetic disk  3  as the actuator  4  is caused to pivot in a short arc as indicated by the arrow P. The design and manufacture of magnetic disk drives is well known to those skilled in the art. 
     The most common type of sensor used in the transducer  7  is the magnetoresistive sensor. A magnetoresistive (MR) sensor is used to detect magnetic field signals by means of changing resistance in a read element. A conventional MR sensor utilizes the anisotropic magnetoresistive (AMR) effect for such detection, where the read element resistance varies in proportion to the square of the cosine of the angle between the magnetization in the read element and the direction of a sense current flowing through the read element. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium causes a change in the direction of magnetization in the read element, thereby causing a corresponding change in resistance of the read element. The change in resistance can be detected to recover the recorded data on the magnetic medium. 
     Another form of magnetetoresistance is known as spin valve magnetoresistance or giant magnetoresistance (GMR). In such a spin valve sensor, two ferromagnetic layers are separated by a non-magnetic layer such as copper. One of the ferromagnetic layers is a “free” layer and the other ferromagnetic layer is a “pinned” layer. This pinning is typically achieved by providing an exchange-coupled anti-ferromagnetic layer adjacent to the pinned layer. 
     More particularly, and with reference to FIG. 1C, a shielded, single-element magnetoresistive head (MRH)  10  includes a first shield  12 , a second shield  14 , and a spin valve sensor  16  disposed within a gap (G) between shields  12  and  14 . An air bearing surface S is defined by the MRH  10 . The spin valve sensor is preferably centered within the gap G to avoid self-biasing effects. Lines of magnetic flux impinging upon the spin valve sensor create a detectable change in resistance. The design and manufacture of magnetoresistive heads, such as MRH  10 , are well known to those skilled in the art. 
     With reference to FIG. 2A, a cross-sectional view taken along line  2 — 2  of FIG. 1C illustrates the structure of the spin valve sensor  16  of the prior art. The spin valve sensor  16  is built upon a substrate  17  and includes: an anti-ferromagnetic layer  24 ; a pinned layer  22 ; a first cobalt enhanced layer  19 ; a thin copper layer  20 ; a second cobalt enhanced layer  23  and a free layer  18 . Ferromagnetic end regions  21  abut the ends of the spin valve sensor  16 . Leads  25 , typically made from gold or another low resistance material, bring the current to the spin valve sensor  16 . A capping layer  27  is provided over the free layer  18  opposite the Co enhanced layer  23 . A current source  29  provides a current I b  which flows through the various layers of the sensor  16 , and signal detection circuitry  31  detects changes in resistance of the sensor  16  as it encounters magnetic fields. 
     The free and pinned layers  18  and  22  are typically made from a soft ferromagnetic material such as Permalloy. As is well known to those skilled in the art, Permalloy is a magnetic material nominally including 80% nickel (Ni) and 20% iron (Fe). While the layer  20  is typically copper, other non-magnetic materials have been used as well. The cobalt enhanced layer can be preferably constructed of Co or more preferably of Co 90 Fe 10 . The AFM layer  24  is used to set the magnetic direction of the pinned layer  22 . 
     With continued reference to FIG. 2A, the spin valve sensor  16  develops a rough interface between the copper layer  20  and the cobalt enhanced layer  23 . This can be understood better with reference to FIG. 2B, wherein the interface is shown at the atomic level. Both the copper layer  20 , shown in solid, and the cobalt enhanced layer  23  have face centered cubic (FCC) crystalline structures. However, as the copper is deposited onto the first cobalt enhanced layer  19 , the copper tends to form in groups or “islands” rather than being deposited layer by layer as would be desired. This leads to a rough copper surface upon which the second must subsequently be deposited. Therefore, the interface  30  between the copper spacer layer and the second cobalt enhanced layer  23  takes on this rough texture as shown in FIG.  2 A. 
     With reference to FIGS. 3A and 3B, the free layer  18  can have a magnetization vector  26  which is free to rotate about an angle α, while the pinned layer  22  is magnetized as indicated by the arrow  28 . Absent the influence of a magnetic field, such as that provided by a magnetic recording medium, the magnetization of the free layer, as represented by arrow  30 , would ideally be perpendicular to the direction of the magnetization  28  of the pinned layer  28 . However, when the free layer is subjected to a magnetic field, represented by arrow  32 , the resulting magnetization  26  of the free layer becomes the sum of the magnetic flux magnetization  32  and the magnetization  30 . It is a property of GMR heads that as the angle α changes, the resistance of the sensor  16  will change. The relationship between the angle α and the resistance of the sensor will be essentially linear in the region of α=0 degrees (i.e. when vector  26  is approximately perpendicular to vector  28 . This can be seen with reference to FIG.  3 B. 
     With reference to FIG. 3C, a GMR read element  10  which does not have an initial angle α which is substantially equal to zero in the absence of any external magnetic field will experience errors when reading data. A typical magnetic recording medium records data as a series of magnetic pulses in the form of waves. The sensor reads these waves and generates a signal having a sensor output, i.e. Track Average Amplitude (TAA). As can be seen with reference to FIG. 3C, a positive magnetic pulse results in an output amplitude TAA 1  followed by an equivalent negative pulse resulting in a sensor output amplitude TAA 2  of the same absolute value. If a read sensor  10  has an initial magnetization angle α of zero then the read sensor will be able to detect these opposite pulses as such. However, if the angle is substantially greater than or less than zero the read sensor will impart an offset error which will cause the sensor to read one of the pulses as being larger than it actually is and the other as being smaller. In such a case, the sensor may not register the smaller pulse and may miss that bit of data. The tendency of read heads to impart such an offset error is termed Track Average Amplitude Asymmetry (TAAA) and is defines as (TAA 1 −TAA 2 )/(TAA 1 +TAA 2 ). A TAAA of less than 15% is generally required for a read head to function properly. 
     With brief reference to  3 A, in order for α to equal 0 in the free state, several magnetic forces acting on a magnetization vector  26  of the free layer  18  must balance to 0. In FIG. 3D, H d  represents a demagnetization vector. Demagnetization can be controlled by adjusting the thickness of the pinned layer  22 . This H d  is offset by an interlayer magnetic coupling field H int  and a current induced magnetic field H i . H i  is controlled by the bias current I b  and is generally set by design considerations external to the head  10  itself. Correct operation of the head  10  requires that the these three magnetic field vectors: H d , H int  and H i  sum to 0. 
     With reference to FIG. 4 H int , is dependent upon the thickness t cu  (FIG.2A) of the copper layer. The thickness of the copper layer is desirably chosen so that H int  will be 0. Furthermore, the sensitivity of the sensor (Δr/r) increases with decreasing copper layer thickness. Therefore, the copper layer is preferably chosen to have a thickness corresponding to node  34  in FIG.  4 . However, as indicated by the steep slope of the curve in region  34 , H int  changes drastically with copper spacer thickness in this region. In fact a single angstrom change in copper layer thickness can have a substantial impact upon H int . Therefore, control of copper layer thickness is critical in the design and production of GMR heads. However, as will be appreciated, any roughness in the interface between the copper layer and adjacent magnetic layers will render such copper layer thickness variable across the surface of the copper layer. 
     Another problem experienced by GMR heads, is that of diffusion at high temperatures. Migration of atoms across the interface between the copper layer and the adjacent magnetic layers results in degradation of performance. This is especially a problem when the sensor is subjected to high temperatures. It has been discovered that roughness of the interface contributes greatly to such diffusion. 
     Therefore, there remains a need for a GMR sensor and a method of manufacturing the same which will allow a smooth interface between the copper layer and adjacent pinned and free magnetic layers. Such a GMR head would achieve the benefit of tighter control of copper layer thickness as well as reduced diffusion of atoms across the interface. 
     SUMMARY OF THE INVENTION 
     The present invention provides a spin valve sensor having improved performance, reliability and durability and a method of manufacturing same. The spin valve includes a copper layer separating first and second magnetic layers disposed adjacent the copper layer. The spin valve achieves the above described beneficial results by maintaining a very smooth interface between the copper layer and the adjacent magnetic layers. An anti-ferromagnetic (AFM) layer fixes the magnetization of a pinned layer. The spin valve also includes a free layer having a magnetization which can move under the influence of an external magnetic field. Changes in relative orientation of magnetizations between the free and pinned layers cause measurable changes in the resistance of the spin valve. 
     By providing improved interfaces between the copper layer and adjacent magnetic layers, the copper layer thickness can be precisely controlled. This results in the ability to precisely control the relative magnetization angles between the free and pinned layers. Furthermore, such a smooth interfaces maximize Δr/r performance. These improved interfaces between the copper and adjacent magnetic layers also act to prevent inter layer diffusion of atoms which would degrade performance of the spin valve, especially at high temperatures, and would decrease the life of the spin valve. 
     More particularly, the spin valve includes a substrate upon which the spin valve is built. This substrate may be, for example, ceramic. The AFM layer is deposited onto the substrate and the pinned layer is subsequently deposited onto the AFM layer. The pinned layer can be preferably constructed of Co or more preferably of Co 90 Fe 10 . 
     An ultra thin layer of lead is deposited onto the pinned. layer. This layer of lead is preferably no more than two or three atoms thick and most preferably is no more than a single atom thick. With the lead deposited onto the pinned layer, a copper layer is then deposited onto the lead. The presence of the lead serves as a surfactant, causing the copper atoms to move to the desired location, growing layer by layer in a face centered cubic structure. As the copper is deposited, the lead rises to remain on the top of the deposited copper layer. The lead continues to migrate as the spin valve is formed, so that when the spin valve is completed, no detectable trace of the lead remains. 
     The layer by layer growth of the copper layer provides a smooth surface on which to deposit a cobalt (Co) enhanced layer. The Co enhanced layer preferably consists of Co 90 Fe 10 . The free magnetic layer is then deposited onto this Co enhanced layer. 
     Thereafter, ferromagnetic end regions are provided at the ends of the spin valve so as to span across the various layers of the spin valve. A pair of leads are also provided to allow a bias current to be fed through the spin valve. 
     The improved interface provided between the copper layer and the adjacent layers allows the copper layer thickness to be tightly controlled, thereby improving sensor performance and reliability. Furthermore, these improved interfaces prevent interlayer diffusion, also as discussed above. 
     These and other advantages of the invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, with like reference numerals designating like elements. 
     FIG. 1A is a partially sectioned, front elevational view of a magnetic disk drive assembly of the prior art; 
     FIG. 1B is a cross section taken along line  1 B— 1 B— of FIG. 1A; 
     FIG. 1C is a perspective view of a prior art shielded vertical magnetoresistive spin valve sensor head; 
     FIG. 2 is a cross sectional view of the prior art spin valve sensor of the prior art and associated substrates, support structures, and circuitry taken along line  2 — 2  of FIG. 1C, shown enlarged; 
     FIG. 2B is a view of area  2 B of FIG. 2A shown rotated 90 degrees clockwise and enlarged to the atomic level; 
     FIG. 3A illustrates the directions of magnetization of free and pinned layers in the spin valve; 
     FIG. 3B is a graph illustrating the relationship between the electrical resistance of the spin valve and the relative directions of magnetization between the free and pinned layers; 
     FIG. 3C is a graph illustrating track average amplitude (TAA) of a spin valve detecting a magnetic data signal over a period of time; 
     FIG. 3D illustrates the balancing of magnetic field vectors in a free layer of a spin valve; 
     FIG. 4 is a graph illustrating the relationship between interlayer magnetizatic coupling (H int ) and copper layer thickness (t cu ); 
     FIG. 5A is a perspective view of a shielded vertical magnetoresistive spin valve sensor head according to the present invention; 
     FIG. 5B is a cross sectional view of the spin valve sensor and associated substrates, support structures, and circuitry taken along line  2 — 2  of FIG. 1C, shown enlarged; 
     FIG. 6 is a view taken from area  6  of FIG. 5B showing the spin valve sensor in an intermediate stage of development and enlarged to the atomic level; 
     FIG. 7 is a view similar to that of FIG. 6 showing the spin valve sensor in another a subsequent, intermediate stage of development; 
     FIG. 8 is a graph showing the spectral intensity exhibited by copper with respect to copper coverage for copper deposited on several types of substrates; and 
     FIG. 9 is process diagram illustrating a method of constructing a spin valve sensor of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A-C,  2 A-B,  3 A-C and  4  were discussed with reference to the prior art. With reference to FIGS. 5A-B, a read head  500  of the present invention includes a GMR spin valve  502  disposed between first and second shields  505  and  506 . The GMR spin valve  502  is built upon a substrate  504  which can be constructed of many suitable materials, for example ceramic. An AFM pinning layer  507  abuts the substrate  504  and also abuts a pinned layer  508 . The pinned layer  508  is constructed of a magnetic material and is preferably constructed of Co 90 Fe 10  or alternatively of Co. However, if layer  508  is made of Ni 80 Fe 20 , a first cobalt enhanced layer  509  must be formed adjacent the pinned layer  508 , opposite the AFM pinning layer  507  and is most preferably constructed of Co 90 Fe 10  or alternatively of Co. A very thin copper spacer layer  510  is formed adjacent the first cobalt enhanced layer  509 . A second cobalt enhanced layer  512 , most preferably constructed of Co 90 Fe 10  or alternatively of Co, abuts the copper layer  510  opposite the first cobalt enhanced layer  509 . While the first and second cobalt enhanced layers  509  and  512  are preferably constructed of Co 90 Fe 10  or of Co, other magnetic material would also be suitable. 
     With continued reference to FIG. 5B, there exists an interface  514  between the first cobalt enhanced layer  509  and the copper layer  510 . Similarly, there exists an interface between the copper layer  510  and the second cobalt enhanced layer  512 . Both of these interfaces are very smooth. These smooth interfaces preferably have a roughness of less than 100 atomic diameters and more preferably less than about 50 atomic layers. Even more preferably each of these interfaces has a roughness which is no greater than a few atomic diameters, and most preferably only one or two atomic diameters. A mechanism for achieving these extremely smooth interfaces will be discussed further below. 
     A free layer  518  adjoins the cobalt enhanced layer  512  opposite the copper layer  510 . While the free layer  518  could be constructed of any suitable magnetic material, it is preferably constructed of an alloy of nickel and iron. More preferably, the free layer  518  is constructed of Ni 80 Fe 20 . A capping layer  520  seals the spin valve  502 . 
     Ferromagnetic end regions  522  abut the ends of the spin valve sensor  502 . Leads  524 , typically made from gold or another low resistance material, bring the current to the spin valve sensor  502 . A current source  526  provides a current I b  to flow through the various layers of the sensor  502 , and signal detection circuitry  528  detects changes in resistance of the sensor  502  as it encounters magnetic fields. 
     With reference to FIG. 6 the construction of the spin valve  502  having smooth interfaces  514  and  516  between the copper layer  510  and the cobalt enhanced layers  509  and  512  will be described. In the preferred embodiment of the invention, the first cobalt enhanced layer  509  consists of Co atoms or more preferably consists of Co 90 Fe 10  wherein Co atoms  530  and Fe atoms  531  are arranged in a FCC structure. On top of the layer  509 , a surfactant layer  532  is deposited. The surfactant is preferably in the form of an ultra thin layer  532  of lead (Pb) atoms  534 . The lead atoms  534  are preferably deposited no more than two or three atomic layers thick and more preferably no more than a single atomic layer thick. Lead atoms residing on top of a Cu(111) surface, for example, are known to form a compact, quasi-hexagonal layer. The term surfactant is used herein to describe a material which affects the surface properties of another material while not necessarily becoming part of the structure of that surface. 
     With continued reference to FIG. 6, the copper layer  510  is then deposited on top of the surfactant layer  532 . Individual copper atoms  536  are indicated as solid circles. The presence of the Pb atoms  534  causes the copper atoms  536  to move to desired locations so that the copper forms a FCC structure and grows layer by layer rather than in islands or individual groups. The mechanism by which this occurs is discussed in an article by J. Camerero et al., entitled  Atomistic Mechanism of Surfactant - Assisted Epitaxial Growth , Physical Review Letters, Volume 81, 850 (1998), which is incorporated herein by reference in its entirety. The above cited article describes the use of a surfactant to generate a smooth interface between materials. Under surfactantassisted epitaxial growth, layer by layer growth occurs while the surfactant efficiently floats at the external surface. The authors state that “the diffusion of Cu atoms to the steps have taken place underneath the compact Pb overlayer,” and conclude that “the main effect of the Pb surfactant is to modify the mechanism of atomic diffusion on the terraces of Cu(111), which now takes place below the surfactant layer and by exchange.” 
     With reference to FIG. 7, as the copper atoms move to the desired locations in the layer by layer growth of the FCC crystalline structure, the Pb atoms  534  migrate away from the first cobalt enhanced layer  509 . This upward migration continues throughout the formation of spin valve  502 . The copper  510  continues to grow atomic layer by atomic layer, thereby maintaining a very smooth surface, so that when the second cobalt enhanced layer  512  is deposited onto the copper layer  510  a very smooth interface will be formed between the layers  510  and  512 . 
     The layer by layer growth of the copper layer  510  is evidenced by FIG. 8 which illustrates the specular intensities of several copper surfaces. Curve (A) shows the periodic oscillations of the specular intensity of layer by layer growth of Cu on Cu(100). This is compared with curve (B) which illustrates the monotonic decrease in specular intensity of Cu on Cu(111) which reveals the three dimension growth of copper as it forms islands or groups. Curve (C), on the other hand shows periodic oscillations in spectral intensity evidencing the layer by layer growth of Cu on the surfactant covered copper of the present invention. 
     With a very smooth interface thus formed at the interfaces  514  and  516 , the thickness of the copper layer can be tightly controlled and remains constant throughout the copper layer. This allows the magnetization of the free layer to be precisely controlled as discussed above. Furthermore, providing such very smooth interfaces prevents diffusion of atoms across the interfaces, thereby extending the life and reliability of the spin valve. With the second cobalt enhanced layer  512  deposited onto the copper layer  510 , the construction of the read head  500  can continue according to the methods of the prior art. As a further benefit of the present invention, research has shown that the Δr/r value for a spin valve  502  is maximized when smooth interfaces  514 ,  516  exist between the copper layer  510  and the adjacent magnetic layers  508 ,  512 . 
     With reference to FIG. 9, a process  900  for constructing the spin valve  502  of the present invention will be described. The process  900  begins with a step  902  of providing a substrate, which can be a ceramic material. This is followed by a step  904  of depositing the AFM layer  507  onto the substrate. The AMF layer can be deposited by plating. Then, in a step  906 , the pinned layer  508  is deposited onto the AFM layer. While the pinned layer can be constructed of many suitable magnetic materials it is preferably constructed of Ni 80 Fe 20 . Then in a step  907 , the first magnetic, or cobalt enhanced, layer  509  is deposited onto the pinned layer  508 . Then in a step  908 , the layer  534  is deposited a single atomic layer thick, onto the first cobalt enhanced layer  509 . Subsequently in a step  909 , the copper  536  is deposited onto the lead  532 . The copper can be deposited by sputtering. As the copper is deposited, the lead migrates above the copper while causing the copper to grow a single layer at a time in a FCC structure. 
     When the desired copper thickness has been reached, the second cobalt enhanced magnetic layer  512  can be deposited in a step  910 . The layer by layer growth of the copper in step  910  provides a very smooth surface on which to deposit the second cobalt enhanced layer  512 , producing the very smooth interface  516  between the copper layer  510  and the second cobalt enhanced layer  512 . Then in a step  912 , the free layer  518  is deposited onto the second cobalt enhanced layer  512 . In a step  914 , the capping layer  520  is provided adjacent the free layer, and in a step  916  the ferromagnetic end regions  522  are provided at either end of the spin valve. Finally in a step  918 , the leads  524  are installed to provide electrical connection to the required circuitry  526  and  528 . 
     It will therefore be apparent that the present invention provides a method for manufacturing a spin valve having smooth interfaces between the copper layer  510  and adjacent magnetic, cobalt enhanced layers  509  and  512 . These smooth interfaces  514  and  516  provide multiple benefits. First, the thickness of the copper layer  510  can be precisely controlled, thereby allowing H int  to be precisely controlled. Second maintaining smooth interfaces  514  and  516  maximizes Δr/r, thereby improving the performance of the spin valve  510 . Finally, the smooth interfaces prevent interlayer diffusion of atoms which would otherwise degrade performance of the spin valve over time, especially at high temperatures. In this way the life, durability and reliability of the spin valve  510  is improved. 
     While this invention has been described in terms of a preferred embodiment, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. It is therefore intended that the following appended claims include all such alternatives modifications, permutations and equivalents as fall within the true spirit and scope of the present invention.