Patent Abstract:
An improved and novel magnetic element and fabrication method. The magnetic element ( 10;30 ) including a bottom pinned ferromagnetic layer ( 12;32 ) and a top pinned ferromagnetic layer ( 20;40 ) fabricated antiparallel to one another. The magnetic element ( 10;30 ) further including a bottom tunnel barrier layer ( 14;34 ), a free ferromagnetic layer ( 16;46  and  48 ) and a top tunnel barrier layer ( 18;38 ) formed between the bottom pinned ferromagnetic layer ( 12;32 ) and the top pinned ferromagnetic layer ( 20;40 ). The structure is defined as including two (2) tunnel barrier layers in which one tunnel barrier layer is normal ( 18 ) and one is reversed ( 14 ), or a structure in which the two tunnel barrier layers are of the same type ( 34; 38 ) with the structure further includes a SAF structure ( 36 ) to allow for consistently changing magnetoresistance ratios across both tunnel barriers. The magnetic element ( 10;30 ) having an improved magnetoresistance ratio and a decrease in voltage dependence.

Full Description:
This application is a division of application Ser. No. 09/532,721, filed Mar. 22, 2000, now U.S. Pat. No. 6,469,926. 
    
    
     This invention was made with Government support under Agreement No. MDA972-96-3-0016 awarded by DARPA. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to magnetic elements for information storage and/or sensing and a fabricating method thereof, and more particularly, to a method of fabricating and thus defining the magnetic element to improve the magnetoresistance ratio. 
     BACKGROUND OF THE INVENTION 
     This application is related to a co-pending application that bears Motorola docket number CR97-133 and U.S. Ser. No. 09/144,686, entitled “MAGNETIC RANDOM ACCESS MEMORY AND FABRICATING METHOD THEREOF,” filed on Aug. 31, 1998, assigned to the same assignee and incorporated herein by this reference, co-pending application that bears Motorola docket number CR 97-158 and U.S. Ser. No. 08/986,764, entitled “PROCESS OF PATTERNING MAGNETIC FILMS” filed on Dec. 8, 1997, assigned to the same assignee and incorporated herein by this reference and issued U.S. Pat. No. 5,768,181, entitled “MAGNETIC DEVICE HAVING MULTI-LAYER WITH INSULATING AND CONDUCTIVE LAYERS”, issued Jun. 16, 1998, assigned to the same assignee and incorporated herein by. 
     Typically, a magnetic element, such as a magnetic memory element, has a structure that includes ferromagnetic layers separated by a non-magnetic layer. Information is stored as directions of magnetization vectors in magnetic layers. Magnetic vectors in one magnetic layer, for instance, are magnetically fixed or pinned, while the magnetization direction of the other magnetic layer is free to switch between the same and opposite directions that are called “parallel” and “anti-parallel” states, respectively. In response to parallel and anti-parallel states, the magnetic memory element represents two different resistances. The resistance has minimum and maximum values when the magnetization vectors of the two magnetic layers point in substantially the same and opposite directions, respectively. Accordingly, a detection of change in resistance allows a device, such as an MRAM device, to provide information stored in the magnetic memory element. The difference between the minimum and maximum resistance values, divided by the minimum resistance is known as the magnetoresistance ratio (MR). 
     An MRAM device integrates magnetic elements, more particularly magnetic memory elements, and other circuits, for example, a control circuit for magnetic memory elements, comparators for detecting states in a magnetic memory element, input/output circuits, etc. These circuits are fabricated in the process of CMOS (complementary metal-oxide semiconductor) technology in order to lower the power consumption of the device. 
     Magnetic elements structurally include very thin layers, some of which are tens of angstroms thick. The manufacturability throughput and performance of the magnetic element is conditioned upon the magnetic structure utilized and its complexity. Accordingly, it is necessary to make a magnetic device in which a simple structure is sought. A magnetic element structure in which including are fewer layers than the standard magnetic element and less targets, is sought. In addition, it is sought to build a device in which a centered R—H(I) loop does not depend on the precise overly for each of the millions to billions of bits. 
     During typical magnetic element fabrication, such as MRAM element fabrication, metal films are grown by sputter deposition, evaporation, or epitaxy techniques. One such magnetic element structure includes a substrate, a base electrode multilayer stack, a synthetic antiferromagnetic (SAF) structure, an insulating tunnel barrier layer, and a top electrode stack. The base electrode layer stack is formed on the substrate and includes a first seed layer deposited on the substrate, a template ferromagnetic layer formed on the seed layer, a layer of an antiferromagnetic material on the template layer and a pinned ferromagnetic layer formed on and exchange coupled with the underlying antiferromagnetic layer. The ferromagnetic layer is called the pinned layer because its magnetic moment (magnetization direction) is prevented from rotation in the presence of an applied magnetic field. The SAF structure includes a pinned ferromagnetic layer, and a fixed ferromagnetic layer, separated by a layer of ruthenium, or the like. The top electrode stack includes a free ferromagnetic layer and a protective layer formed on the free layer. The magnetic moment of the free ferromagnetic layer is not pinned by exchange coupling, and is thus free to rotate in the presence of applied magnetic fields. As described, this type of magnetic element structure includes a very complex arrangement of layers and as such is not amenable to high throughput. 
     An alternative structure includes, a magnetic element material stack which includes three magnetic layers separated by one tunnel barrier and one conductive spacer, such as TaN y . The middle magnetic layer is formed so that it is free to rotate or change direction, while the top and bottom magnetic layers are locked in an antiparallel arrangement or direction due to lowered energy from flux closure at the ends. During operation, the structure will have different resistances depending on which of the two directions the middle magnetic layer points its magnetization. In order to achieve a magnetic element which includes a better signal, or an improved magnetoresistance ratio, it is desirable to includes dual tunnel barrier layers. Yet, it has been found that this structure will fail if a tunnel barrier is utilized in the place of the conductive spacer. 
     Accordingly, it is a purpose of the present invention to provide an improved magnetic element with an improved magnetoresistance ratio. 
     It is another purpose of the present invention to provide an improved magnetic element that includes a higher MR % or signal, and less voltage dependence. 
     It is a still further purpose of the present invention to provide a method of forming a magnetic element with an improved magnetoresistance ratio. 
     It is still a further purpose of the present invention to provide a method of forming a magnetic element with an improved magnetoresistance ratio which is amenable to high throughput manufacturing. 
     SUMMARY OF THE INVENTION 
     These needs and others are substantially met through provision of a magnetic element including a first magnetic layer, comprised of a pinned ferromagnetic material, a second magnetic layer, that is free to rotate, a third magnetic layer, comprised of a pinned ferromagnetic material, and two (2) tunnel barrier layers. The structure is defined as including two (2) tunnel barrier layers in which one tunnel barrier layer is normal and one is reversed, or a structure in which the two tunnel barrier layers are of the same type and the structure further includes a SAF structure to allow for same sign changing magnetoresistance ratios across both tunnel barriers. A spacer layer is generally included when the magnetic element includes the SAF structure. The magnetic element further includes a metal lead. The metal lead, the plurality of magnetic layers, the plurality of tunnel barrier layers, and the spacer layer being formed on a substrate material, such as a dielectric. Additionally disclosed is a method of fabricating the magnetic element with an improved magnetoresistance ratio. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 illustrate in cross-sectional views, first and second embodiments of a magnetic element with an improved magnetoresistance ratio according to the present invention; and 
     FIGS. 3 and 4 illustrate in cross-sectional views, second and third embodiments of a magnetic element with an improved magnetoresistance ratio according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     During the course of this description, like numbers are used to identify like elements according to the different figures that illustrate the invention. FIGS. 1 and 2 illustrate in cross-sectional views a first and second embodiment of a magnetic element according to the present invention. More particularly, illustrated in FIG. 1, is a first embodiment of a fully patterned magnetic element  10 . Magnetic element  10  structurally includes a bottom pinned magnetic layer  12 , a bottom tunnel barrier layer  14 , a free magnetic layer  16 , a top tunnel barrier layer  18 , and a top pinned magnetic layer  20 . Bottom pinned magnetic layer  12 , free magnetic layer  16  and top pinned magnetic layer  20  include ferromagnetic layers. Bottom magnetic layer  12  is formed on a diffusion barrier layer  22  which is formed on a metal lead  24 . Diffusion barrier layer  22  is typically formed of tantalum nitride (TaN), and aids in the thermal stability of magnetic element  10 . Metal lead  24  is typically formed on some type of dielectric material (not shown). 
     Bottom and top pinned ferromagnetic layers  12  and  20  are described as pinned, or fixed, in that their magnetic moment is prevented from rotation in the presence of an applied magnetic field. Ferromagnetic layers  12 ,  16  and  20  are typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co) and each include a top surface  13 ,  17 , and  21 , respectively, and a bottom surface  11 ,  15  and  19 , respectively. Magnetic layer  16  is described as a free ferromagnetic layer. Accordingly, the magnetic moment of free ferromagnetic layer  16  is not fixed, or pinned, by exchange coupling or magneto static coupling through flux closure, and is free to rotate in the presence of an applied magnetic field. Free ferromagnetic layer  16  is formed co-linear with pinned magnetic layers  12  and  20  and of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co). Pinned ferromagnetic layers  12  and  20  are described as having a thickness within a range of 5-5000 Å. Free ferromagnetic layer  16  is described as having a thickness generally less than 500 Å. A second diffusion barrier layer  26  is formed on an uppermost surface  21  of top pinned magnetic layer  20 . A metal lead  28  is formed on a surface of second diffusion barrier layer  26 . 
     In this particular embodiment, bottom tunnel barrier layer  14  is formed of tantalum (Ta) and oxygen (O). More particularly, bottom tunnel barrier layer  14  is formed having a general formula of TaO Y , where 1&lt;Y&lt;2.5. Top tunnel barrier layer  18  is formed of oxidized aluminum (Al), generally having the formula AlO x , where x≦1.5. 
     In this particular embodiment, top tunnel barrier layer  18  is described as being a normal tunnel barrier, such that the magnetic tunnel junction has a maximum resistance (R) for anti-parallel aligned magnetic electrodes, and a minimum resistance (R) for parallel aligned magnetic electrodes. More specifically, when free ferromagnetic layer  16  is aligned parallel with bottom pinned magnetic layer  12  and anti-parallel to top pinned magnetic layer  20 , maximum resistance is achieved. When free ferromagnetic layer  16  is aligned anti-parallel with bottom pinned magnetic layer  12  and aligned parallel with top pinned ferromagnetic layer  20 , minimum resistance is achieved. Bottom tunnel barrier  14  is described as being a reverse tunnel barrier such that the magnetic tunnel junction has a maximum resistance (R) for parallel aligned magnetic electrodes, and a minimum resistance (R) for anti-parallel aligned magnetic electrodes. This type of structure provides for a higher magnetoresistance ratio (MR %) or stronger signal, and less voltage dependence. Typically the MR % decreases as the bias voltage increases. Accordingly, by including dual tunnel barrier layers,  16  and  18 , each will see one-half of the bias voltage, thus reducing the rate of drop in MR % as the bias voltage increases. In addition, only four (4) targets are needed, and no exact overlay is required. During operation, any topological positive coupling of the free magnetic layer  16  from bottom and top are canceled. This type of structure is designed for MRAM applications. During operation of magnetic element  10 , magnetic layers  12  and  20  will point and lock into an anti-parallel orientation due to magnetic flux closure and reduced magnetic energy, especially for smaller dimension memory cells for high density MRAM. Magnetic layer  16  remains free to switch directions, for use in memory devices, such as MRAM applications. Alternatively, in a larger dimension MRAM cell, pinning from an antiferromagnetic layer can be used to pin the bottom  12  and top  20  magnetic layers. 
     Illustrated in FIG. 2, is an alternative embodiment of a fully patterned magnetic element structure, referenced  10 ′, typical for use in read head and magnetic sensor applications. It should be noted that all components of the first embodiment that are similar to components of the second embodiment, are designated with similar numbers, having a prime added to indicate the different embodiment. Similar to the structure described with regard to FIG. 1, this structure includes a bottom pinned magnetic layer  12 ′, a bottom tunnel barrier layer  14 ′, a free magnetic layer  16 ′, a top tunnel barrier layer  18 ′, and a top pinned magnetic layer  20 ′. Bottom pinned magnetic layer  12 ′, free magnetic layer  16 ′ and top pinned magnetic layer  20 ′ include ferromagnetic layers. Bottom magnetic layer  12 ′ is formed on a diffusion barrier layer  22 ′ which is formed on a metal lead  24 ′. Diffusion barrier layer  22 ′ is typically formed of tantalum nitride (TaN), and aids in the thermal stability of magnetic element  10 ′. Metal lead  24 ′ is typically formed on some type of dielectric material (not shown). 
     Bottom and top pinned ferromagnetic layers  12 ′ and  20 ′ are described as pinned, or fixed, in that their magnetic moment is prevented from rotation in the presence of an applied magnetic field. Ferromagnetic layers  12 ′,  16 ′ and  20 ′ are typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co) and each include a top surface  13 ′,  17 ′, and  21 ′, respectively, and a bottom surface  11 ′,  15 ′ and  19 ′, respectively. Magnetic layer  16 ′ is a free ferromagnetic layer. Accordingly, the magnetic moment of free ferromagnetic layer  16 ′ is not fixed, or pinned, by exchange coupling or magnetostatic coupling through flux closure, and is free to rotate in the presence of an applied magnetic field. Free ferromagnetic layer  16 ′ typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co). In contrast to the embodiment described in FIG. 1, in this particular embodiment, free ferromagnetic layer  16 ′ is perpendicularly aligned with respect to pinned ferromagnetic layers  12 ′ and  20 ′. Pinned ferromagnetic layers  12 ′ and  20 ′ are described as having a thickness within a range of 5-5000 Å. Free ferromagnetic layer  16 ′ is described as having a thickness generally less than 500 Å. A second diffusion barrier layer  26 ′ is formed on an uppermost surface  21 ′ of top pinned magnetic layer  20 ′. A metal lead  28 ′ is formed on a surface of second diffusion barrier layer  26 ′. 
     In this particular embodiment, bottom tunnel barrier layer  14 ′ is formed of tantalum (Ta) and oxygen (O). More particularly, bottom tunnel barrier layer  14 ′ is formed having a general formula of TaO Y , where 1&lt;Y&lt;2.5. Top tunnel barrier layer  18 ′ is formed of aluminum, generally having the formula AlO x , where x≦1.5. 
     Similar to the first described embodiment, top tunnel barrier layer  18 ′ is described as being a normal tunnel barrier, such that the magnetic tunnel junction has a maximum resistance (R) for anti-parallel aligned magnetic electrodes, and a minimum resistance (R) for parallel aligned magnetic electrodes. Tunnel barrier layer  14 ′ is described as being a reverse tunnel barrier, as previously described with respect to FIG.  1 . In contrast to the embodiment of FIG. 1, free ferromagnetic layer  16 ′ is perpendicularly aligned with bottom pinned magnetic layer  12 ′ and top pinned magnetic layer  20 ′. This type of structure provides for a higher magnetoresistance ratio (MR %) or stronger signal, and less voltage dependence. Typically the MR % decreases as the bias voltage increases. Similar to the embodiment of FIG. 1, by including dual tunnel barrier layers,  16 ′ and  18 ′, each will see one-half of the bias voltage, thus reducing the rate of drop in MR % as the bias voltage increases. In addition, only four (4) targets are needed, and no exact overlay is required. During operation, any topological positive coupling from bottom and top are canceled. This type of structure is designed for read head and magnetic sensor applications. During operation of magnetic element  10 ′, magnetic layers  12 ′ and  20 ′ will point and lock into an anti-parallel orientation due to magnetic flux closure and reduced magnetic energy for smaller dimension devices. Magnetic layer  16 ′ remains free to rotate perpendicularly to magnetic layers  12 ′ and  20 ′, and thus is suitable for use in read head or magnetic field sensors devices. Alternatively, in a larger dimension MRAM cell, pinning from an antiferromagnetic layer can be used to pin the bottom  12 ′ and top  20 ′ magnetic layers. 
     Referring now to FIG. 3, illustrated in simplified sectional view is a third embodiment of a magnetic element, according to the present invention. More particularly, illustrated is a magnetic element  30  including as a part thereof a synthetic antiferromagnetic (SAF) structure (discussed presently). Magnetic element  30  includes a bottom pinned magnetic layer  32 , a bottom tunnel barrier layer  34 , a SAF structure  36 , a top tunnel barrier layer  38 , and a top pinned magnetic layer  40 . Bottom pinned magnetic layer  32 , SAF structure  36  and top pinned magnetic layer  40  include ferromagnetic layers. Bottom magnetic layer  32  is formed on a diffusion barrier layer  42  which is formed on a metal lead  44 . Diffusion barrier layer  42  is typically formed of tantalum nitride (TaN), and aids in the thermal stability of magnetic element  30 . Metal lead  44  is typically formed on some type of dielectric material (not shown). 
     Bottom and top pinned ferromagnetic layers  32  and  40  are described as pinned, or fixed, in that their magnetic moment is prevented from rotation in the presence of an applied magnetic field. Ferromagnetic layers  32  and  40  are typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co) and each include a top surface  33  and  41 , respectively, and a bottom surface  31  and  39 , respectively. 
     SAF structure  36  includes a bottom free magnetic layer  46 , and a top free magnetic layer  48  formed antiparallel to each other, and co-linearly aligned relative to bottom pinned ferromagnetic layer  32  and top pinned ferromagnetic layer  40  at rest state for this embodiment. Bottom free magnetic layer  46  and top free magnetic layer  48  are separated by an exchange spacer layer  50 , typically formed of a layer of ruthenium (Ru), or the like. Antiparallel alignment between free magnetic layers  46  and  48  is achieved through an exchange spacer layer  50  which induces antiferromagnetic coupling between bottom free magnetic layer  46  and top free magnetic layer  48 , or through end magnetostatic coupling, or other means. 
     Free ferromagnetic layers  46  and  48  and pinned ferromagnetic layer  32  and  40  are typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co). Pinned ferromagnetic layers  32  and  40  are described as having a thickness within a range of 5-5000 Å. Free ferromagnetic layers  46  and  48  are described as each having a thickness generally less than 500 Å. A second diffusion barrier layer  52  is formed on an uppermost surface  41  of top pinned magnetic layer  40 . A metal lead  54  is formed on a surface of second diffusion barrier layer  52 . 
     In this particular embodiment, bottom tunnel barrier layer  34  and top tunnel barrier layer  38  are both formed of oxidized aluminum, generally having the formula AlO x , where x≦1.5. It is disclosed that in this embodiment, which includes SAF structure  36 , bottom tunnel barrier layer  34  and top tunnel barrier layer  38  are of the same type. More particularly, bottom tunnel barrier layer  34  and top tunnel barrier layer  38  are described as being normal tunnel barrier layers, such that the magnetic tunnel junction has a maximum resistance (R) for anti-parallel aligned magnetic electrodes, and a minimum resistance (R) for parallel aligned magnetic electrodes. More specifically, with free ferromagnetic layers  46  and  48  oppositely opposed, when bottom free magnetic layer  46  is anti-parallel to pinned magnetic layer  32  and top free magnetic layer  48  is anti-parallel to pinned magnetic layer  40 , maximum resistance is achieved. When bottom free magnetic layer  46  is parallel to pinned magnetic layer  32  and top free magnetic layer  48  is parallel to pinned magnetic layer  40 , minimum resistance is achieved. This magnetic element including a SAF structure provides for the inclusion of the same type of material for the formation of tunnel barrier layers  34  and  38 , and for a higher magnetoresistance ratio (MR %) or stronger signal, and less voltage dependence. Typically the MR % decreases as the bias voltage increases. Accordingly, by including dual tunnel barrier layers,  34  and  38 , each will see one-half of the bias voltage, thus reducing the rate of drop in MR % as the bias voltage increases. During operation, any topological positive coupling from bottom and top are canceled. This type of structure is designed for MRAM applications. During operation of magnetic element  30 , magnetic layers  32  and  40  will point and lock into an anti-parallel orientation due to magnetic flux closure and reduced magnetic energy for smaller dimension devices. Magnetic layers  46  and  48  will remain free to rotate so that to stay in one of the two co-linear states to magnetic layers  32  and  40 , thus making this structure suitable for use in memory devices, such as MRAM applications. Alternatively, in a larger dimension MRAM cell, pinning from an antiferromagnetic layer can be used to pin the bottom  12 ′ and top  20 ′ magnetic layers. 
     It should be understood that it is anticipated by this disclosure to include SAF structure  36  that is formed between two tunnel barrier layers  34  and  38  as previously disclosed, or alternatively below bottom tunnel barrier layer  34 , or on a surface  39  of top tunnel barrier layer  38 . The inclusion of SAF structure  36  between bottom tunnel barrier layer  34  and top tunnel barrier layer  38  is described with respect to FIG. 3, for ease of disclosure. 
     Referring now to FIG. 4, illustrated in simplified sectional view is a fourth embodiment of a magnetic element, according to the present invention. It should be noted that all components of the third embodiment as illustrated in FIG. 3, that are similar to components of the fourth embodiment, are designated with similar numbers, having a prime added to indicate the different embodiment. Similar to the structure described with regard to FIG. 3, this structure includes a magnetic element  30 ′ including as a part thereof a synthetic antiferromagnetic (SAF) structure. Magnetic element  30 ′ includes a bottom pinned magnetic layer  32 ′, a bottom tunnel barrier layer  34 ′, a SAF structure  36 ′, a top tunnel barrier layer  38 ′, and a top pinned magnetic layer  40 ′. Bottom pinned magnetic layer  32 ′, SAF structure  36 ′ and top pinned magnetic layer  40 ′ include ferromagnetic layers. Bottom magnetic layer  32 ′ is formed on a diffusion barrier layer  42 ′ which is formed on a metal lead  44 ′. Diffusion barrier layer  42 ′ is typically formed of tantalum nitride (TaN), and aids in the thermal stability of magnetic element  30 . Metal lead  44 ′ is typically formed on some type of dielectric material (not shown). 
     Bottom and top pinned ferromagnetic layers  32 ′ and  40 ′ are described as pinned, or fixed, in that their magnetic moment is prevented from rotation in the presence of an applied magnetic field. Ferromagnetic layers  32 ′ and  40 ′ are typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co) and each include a top surface  33 ′ and  41 ′, respectively, and a bottom surface  31 ′ and  39 ′, respectively. 
     SAF structure  36 ′ includes a bottom free magnetic layer  46 ′, and a top free magnetic layer  48 ′ formed antiparallel to each other and perpendicularly aligned relative to bottom pinned ferromagnetic layer  32 ′ and top pinned ferromagnetic layer  40 ′. Bottom free magnetic layer  46 ′ and top free magnetic layer  48 ′ are separated by an exchange spacer layer  50 ′, typically formed of a layer of ruthenium (Ru) or the like. Antiparallel alignment between free magnetic layers  46 ′ and  48 ′ is achieved through an exchange spacer layer  50 ′ which induces antiferromagnetic coupling between bottom free magnetic layer  46 ′ and top free magnetic layer  48 ′, or through end magnetostatic coupling, or other means. 
     Free ferromagnetic layers  46 ′ and  48 ′ and pinned ferromagnetic layer  32 ′ and  40 ′ are typically formed of alloys of one or more of the following: nickel (Ni), iron (Fe), and cobalt (Co). Pinned ferromagnetic layers  32 ′ and  40 ′ are described as having a thickness within a range of 5-5000 Å. Free ferromagnetic layers  46 ′ and  48 ′ are described as each having a thickness generally less than 500 Å. A second diffusion barrier layer  52 ′ is formed on an uppermost surface  41 ′ of top pinned magnetic layer  40 ′. A metal lead  54 ′ is formed on a surface of second diffusion barrier layer  52 ′. 
     In this particular embodiment, bottom tunnel barrier layer  34 ′ and top tunnel barrier layer  38 ′ are formed of an oxidized aluminum, generally having the formula AlO x , where x≦1.5. It is disclosed that in this embodiment, which includes SAF structure  36 ′, bottom tunnel barrier layer  34 ′ and top tunnel barrier layer  38 ′ are of the same type. More particularly, bottom tunnel barrier layer  34 ′ and top tunnel barrier layer  38 ′ are described as being normal tunnel barrier layers, such that the magnetic tunnel junction has a maximum resistance (R) for anti-parallel aligned magnetic electrodes, and a minimum resistance (R) for parallel aligned magnetic electrodes. More specifically, with free ferromagnetic layers  46 ′ and  48 ′ oppositely opposed, when bottom free magnetic layer  46 ′ is rotated to be anti-parallel to pinned magnetic layer  32 ′ and top free magnetic layer  48 ′ is rotated to be anti-parallel to pinned magnetic layer  40 ′, maximum resistance is achieved. When bottom free magnetic layer  46 ′ is rotated to be parallel to pinned magnetic layer  32 ′ and top free magnetic layer  48 ′ is rotated to be parallel to pinned magnetic layer  40 ′, minimum resistance is achieved. This type of structure provides the inclusion of the same type of material for the formation of tunnel barrier layers  34 ′ and  38 ′, and for a higher magnetoresistance ratio (MR %) or stronger signal, and less voltage dependence. Typically the MR % decreases as the bias voltage increases. Accordingly, by including dual tunnel barrier layers,  34 ′ and  38 ′, each will see one-half of the bias voltage, thus reducing the rate of drop in MR % as the bias voltage increases. During operation, any topological positive coupling from bottom and top are canceled. This type of structure is designed for read head and magnetic sensor applications. During operation of magnetic element  30 ′, magnetic layers  32 ′ and  40 ′ will point and lock into an anti-parallel orientation due to magnetic flux closure and reduced magnetic energy. Magnetic layers  46 ′ and  48 ′ will remain free to rotate around the perpendicular direction to magnetic layers  32 ′ and  40 ′ when they detect a magnetic field, thus producing linear voltage change in proportion to the magnetic field it detects, and making this structure suitable for use in magnetic read head devices and magnetic sensors. 
     It should be understood that it is anticipated by this disclosure to include SAF structure  36 ′ that is formed between two tunnel barrier layers  34 ′ and  38 ′ as previously disclosed, or alternatively below bottom tunnel barrier layer  34 ′, or on a surface  39 ′ of top tunnel barrier layer  38 ′. The inclusion of SAF structure  36 ′ between bottom tunnel barrier layer  34 ′ and top tunnel barrier layer  38 ′ is described with respect to FIG. 4, for ease of disclosure. 
     Thus, a magnetic element with an improved magnetoresistance ratio and fabricating method thereof is disclosed in which the magnetoresistance ratio is improved based on the inclusion of dual tunnel barrier layers. As disclosed, this technique can be applied to devices using patterned magnetic elements, such as magnetic sensors, magnetic recording heads, magnetic recording media, or the like. Accordingly, such instances are intended to be covered by this disclosure

Technology Classification (CPC): 7