Abstract:
A magnetic tunneling junction structure for magnetic random access memory is disclosed. A composite structure includes at least a pinning layer, a barrier layer, a ferromagnetic layer and a free layer, and the material of the pinning layer and the free layer are perpendicularly anisotropic ferrimagnetic. As the structures include of several barrier layers, free layers and ferrimagnetic layers, that lower coercivity and high squareness for the hysteresis curves can be obtained, and reduction of the coercivity of the free layer can be achieved.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is based on, and claims priorities from, Taiwan Application Serial Number 95109488, filed Mar. 20, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a kind of magnetic tunneling junction structure for magnetic random access memory, and more particularly to a kind of magnetic tunneling junction structure for magnetic random access memory, which comprises multiple barrier layers and lowers the coercive field of free layers. 
         [0004]    2. Description of Related Art 
         [0005]    The magnetic random access memory (MRAM) is non-violate data storage memory, wherein the magnetic tunneling junction (MTJ) could be the magnetoresistance device for data storage. 
         [0006]    The conventional structure of a magnetic tunneling junction is a usually a sandwich structure like “ferromagnetic layer/barrier layer/ferromagnetic layer” discovered in  1995 . The sandwich structure induces the “tunnel magnetoresistance (TMR)” effect, and the magnetoresistance of TMR at room temperature is greater than the “giant magnetoresistance (GMR)” discovered in 1988. In the last decade, many research institutes made an effort to increase the magnetoresistance at room temperature. It is hoped that practical applications of MRAM will be developed soon. 
         [0007]    There are two conventional methods to raise the value of tunneling magnetoresistance: first, the barrier layer material can be changed into materials like aluminum oxide or magnesium oxide; second, ferromagnetic materials with high spin polarization, such as CoFeB. 
         [0008]    Reference is made to  FIG. 1 , which illustrates the conventional structure of a magnetic tunneling junction for magnetic random access memory. The structure of a magnetic tunneling junction  100  includes a substrate  110 , a lower electrode  120 , a free layer  130 , a ferrimagnetic module  140 , a barrier layer  160  and an upper electrode  170 . 
         [0009]    The ferrimagnetic module  140  includes a lower ferrimagnetic layer  141 , an upper ferrimagnetic layer  142  and a barrier layer  150 . The barrier layer  150  is between the lower ferrimagnetic layer  141  and the upper ferrimagnetic layer  142  to perform tunneling magnetoresistance effect. 
         [0010]    Reference is made to  FIG. 2 , which illustrates a hysteresis curve of the structure of a magnetic tunneling junction  100  between −10,000 and 10,000 Oersted (Oe). The squareness of the structure of the magnetic tunneling junction  100  is not satisfied. Squareness is a ratio of remanent magnetization (M r ) and saturation magnetization (M s ). When the ratio is closer to 1, the squareness is much better. Referring to  FIG. 2 , the squareness of the hysteresis curve is 0.567, and the coercive field of the hysteresis curve is 822.8 Oersted. 
         [0011]    Reference is made to  FIG. 3 , which illustrates a hysteresis curve of the magnetic tunneling junction  100  when a magnetic field between −1,000 and 1,000 Oersted (Oe) is applied. The squareness of the hysteresis curve is 0.6026, and the coercive field of the hysteresis curve is 100 Oersted. 
         [0012]    The disadvantages of the aforementioned structures and methods are: 
         [0013]    1. The coercive field intensity from the free layer in the conventional structure of a magnetic tunneling junction is high, therefore, it requires a more powerful applied magnetic field to drive the magnetic tunneling junction. Hence the power consumption is required higher and the adjacent layers in the structure of the magnetic tunneling junction are affected. 
         [0014]    2. The squareness of the hysteresis curve of the conventional structure for the magnetic tunneling junction is not satisfied. The squareness is an important parameter for memory or switch devices. Squareness could affect the characteristics, for example, the speed for data reads and writes or the response time it takes for the switch to be switched on and switched off. 
         [0015]    The above-mentioned problems happened frequently in the conventional method and the magnetic devices consist of the multi-layer films of various materials. Therefore, the current invention provides the solution for the above-mentioned problems through a magnetic tunneling junction which requires a smaller applied magnetic field and generates a hysteresis curve with a higher squareness. 
       SUMMARY 
       [0016]    In order to solve the above-mentioned and other problems and to achieve the technical advantages of the present invention, the present invention provides a method of measuring anisotropic energy. The method can measure the anisotropic energy from the magnetic structure consisting of multiple materials. 
         [0017]    Therefore, an objective of the present invention is to provide a magnetic tunneling junction structure for a magnetic memory component. The structure could reduce the coercive field of the free layer, and improve the squareness of the hysteresis curve. 
         [0018]    According to the aforementioned objectives of the present invention, a magnetic tunneling junction structure for MRAM is described. The magnetic structure includes multiple barrier layers, ferrimagnetic layers, pinned layers and free layers. The multiple ferrimagnetic layers include horizontal or perpendicular polarized ferrimagnetic layers. Both the pinned layers and free layers contain perpendicular anisotropic magnetizations. The multiple barrier layers of the magnetic structure is disposed between the horizontal polarized ferrimagnetic layers, and it also could be disposed between two free layers. The material of the barrier layer is a nonmagnetic and nonconducting film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
           [0020]      FIG. 1  illustrates an isometric view of the conventional magnetic tunneling junction structure; 
           [0021]      FIG. 2  is a hysteresis curve plot of a magnetic tunneling junction with a conventional structure when a magnetic field between −10,000 and 10,000 Oersted is applied; 
           [0022]      FIG. 3  is a hysteresis curve plot of a magnetic tunneling junction with a conventional structure when a magnetic field between −1,000 and 1,000 Oersted is applied; 
           [0023]      FIG. 4  illustrates an isometric view of a magnetic tunneling junction structure for a preferred embodiment of the present invention; 
           [0024]      FIG. 5  illustrates a hysteresis curve plot of a magnetic tunneling junction with the structure of the present preferred embodiment when a magnetic field between −10,000 and 10,000 Oersted is applied; 
           [0025]      FIG. 6  illustrates a hysteresis curve plot of a magnetic tunneling junction with the structure of the present preferred embodiment when a magnetic field between −1,000 and 1,000 Oersted is applied; 
           [0026]      FIG. 7  illustrates an isometric view of the magnetic tunneling junction structure for the preferred embodiment of the present invention; 
           [0027]      FIG. 8  illustrates a hysteresis curve plot of a magnetic tunneling junction with the structure of the present preferred embodiment when a magnetic field between −10,000 and 10,000 Oersted is applied; and 
           [0028]      FIG. 9  illustrates a hysteresis curve plot of a magnetic tunneling junction with the structure of the present preferred embodiment when a magnetic field between −1,000 and 1,000 Oersted. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    Reference is now made in detail to the present preferred embodiments of the invention, examples are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0030]    While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention is better understood from a consideration of the following description in conjunction with the figures, in which like reference numerals are carried forward. 
         [0031]    Reference is made to  FIG. 4 , which illustrates the magnetic tunneling junction structure of the preferred embodiment of the present invention. A magnetic tunneling junction structure  200  includes a substrate  210 , a lower electrode  220 , a first free layer  231 , a second free layer  232 , a lower ferrimagnetic module  241 , an upper ferrimagnetic module  242 , a first barrier layer  251 , a second barrier layer  252 , a pinned layer  260  and an upper electrode  270 . 
         [0032]    The material of the substrate  210  is an insulator, in this case is silicon (Si). The material of the lower electrode  220  and the upper electrode  270  is metal, in this case is platinum (Pt). The material of the first free layer  231  and the second free layer  232  are selected from ferromagnetic groups with small coercivity, in this case is GdFeCo. The materials of the lower ferrimagnetic module  241  and the upper ferrimagnetic module  242  are horizontally or perpendicularly polarized films. The materials of the first barrier layer  251  and the second barrier layer  252  are aluminum oxide, magnesium oxide or silicon nitride, which are nonmagnetic and nonconducting films. The material of the pinned layer  260  is selected from ferromagnetic groups with large coercivity, in this case is TbFeCo. 
         [0033]    The lower ferrimagnetic module  241  includes a first ferrimagnetic layer  243  and a second ferrimagnetic layer  244 . The first barrier layer  251  is between the first ferrimagnetic layer  243  and the second ferrimagnetic layer  244 , which produces the tunneling magnetoresistance effect. The upper ferrimagnetic module  242  includes a third ferrimagnetic layer  245  and a fourth ferrimagnetic layer  246 . The second barrier layer  252  is disposed between the third ferrimagnetic layer  245  and the fourth ferrimagnetic layer  246 , which also perform tunneling magnetoresistance effect. 
         [0034]    The aforementioned materials use several targets and are deposited by sputter in order to form the structure of the magnetic tunneling junction. 
         [0035]    The lower electrode  220  is disposed on the substrate  210  and the lower electrode  220  through sputtering deposition, and the thickness of the lower electrode  220  is 25 nanometers (nm). The first free layer  231  is disposed on the lower electrode  220  and the first free layer  231 , and the thickness of the first free layer  231  is 50 nanometers (nm). The first ferrimagnetic layer  243  is disposed on the first free layer  231  and the thickness of the first ferromagnetic layer  243  is 2 nanometers (nm). The first barrier layer  251  is disposed on the first ferromagnetic layer  243  and the thickness of the first barrier layer  251  is 1 nanometer (nm). The second ferrimagnetic layer  244  is disposed on the first barrier layer  251  and the thickness of the second ferromagnetic layer  244  is 2 nanometers (nm). The second free layer  232  is disposed on the second ferromagnetic layer  244  and the thickness of the second free layer  232  is 50 nanometers (nm). The third ferrimagnetic layer  245  is disposed on the second free layer  232  and the thickness of the third ferromagnetic layer  245  is 2 nanometers (nm). The second barrier layer  252  is disposed on the third ferromagnetic layer  245  and the thickness of the second barrier layer  252  is 1 nanometer (nm). The fourth ferromagnetic layer  246  is disposed on the second barrier layer  252  and the thickness of the fourth ferromagnetic layer  246  is 2 nanometers (nm). The pinned layer  260  is disposed on the fourth ferromagnetic layer  246  and the thickness of the pinned layer is 35 nanometers (nm). Finally, the upper electrode  270  is disposed on the pinned layer  260  and the thickness of the upper electrode is 25 nanometer (nm). 
         [0036]    Reference is made to  FIG. 5 , which illustrates a hysteresis curve plot of the structure of the magnetic tunneling junction structure  200  when a magnetic field between −10,000 and 10,000 Oersted is applied. Although the squareness of hysteresis curve of the magnetic tunneling junction structure  200  is 0.285, the intensity of the coercive field is very much lower down than coercive field for the magnetic tunneling junction with a conventional structure, the intensity of the coercive field for the current invention is, for example, 260 Oersted. Reference is made to  FIG. 6 , which illustrates a hysteresis curve plot of a magnetic tunneling junction structure  200  when a magnetic field between −1,000 to 1,000 Oersted is applied. In this case, the intensity of the coercive field is 105.5 Oersted. The squareness of the hysteresis curve is 0.501. 
         [0037]    Reference is made to  FIG. 7 , which illustrates the structure of a magnetic tunneling junction  300  of the preferred embodiment of the present invention. The structure of the magnetic tunneling junction  300  includes at least a substrate  310 , a lower electrode  320 , a first free layer  331 , a second free layer  332 , a first barrier layer  341 , a second barrier layer  342 , a ferrimagnetic module  351 , a pinned layer  360  and an upper electrode  370 . 
         [0038]    The material of the substrate  310  is Si or SiN, in this case is Si. The material of the lower electrode  320  and the upper electrode  370  are Pt, Ru, Ta or Ti, in this case is Pt. The material of the first layer  331  and the second free layer  332  are GdFeCo, TbFeCo, DyFeCo or Co/Pt multilayer, in this case is GdFeCo. The materials of the first barrier layer  341  and the second barrier layer  342  are aluminum oxide, magnesium oxide or silicon nitride, which are nonmagnetic and nonconducting films. The material of the ferrimagnetic module  351  is FeCo or FeCoB, in this case is FeCo. The material of the pinned layer  360  is GdFeCo, TbFeCo, DyFeCo or Co/Pt multilayer, in this case is TbFeCo. 
         [0039]    The structure of magnetic tunneling junction is constructed through depositing to from the aforementioned materials using physical vapor deposition (PVD). 
         [0040]    The lower electrode  320  is deposited on the substrate  310  and the lower electrode  320  has a thickness of 25 nanometers (nm). The first free layer  331  is then disposed on the lower electrode  320  and the thickness of the first free layer  331  is 50 nanometers (nm). The first barrier layer  341  is disposed on the first free layer  331 . The second free layer  332  is disposed on the first barrier layer  341  and the second free layer  332 , and the thickness is 50 nanometers (nm). The first ferrimagnetic layer  352  is disposed on the second free layer  332  and the thickness of the first ferromagnetic layer  352  is 2 nanometers (nm). The second barrier layer  342  is disposed on the first ferrimagnetic layer  352 . The second ferrimagnetic layer  353  is disposed on the second barrier layer  342  and the the thickness of second ferromagnetic layer  353  is 2 nanometers (nm). The pinned layer  360  is disposed on the second barrier layer  342  and the thickness of the pinned layer  360  is 35 nanometers (nm). Finally, the upper electrode  370  is disposed on the pinned layer  360  and the thickness of the upper electrode  370  is 25 nanometers (nm). 
         [0041]    Reference is made to  FIG. 8 , which illustrates a hysteresis curve plot of the magnetic tunneling junction  300  when a magnetic field between −10,000 and 10,000 Oersted is applied. The intensity of the coercive field is 67.66 Oersted. The squareness of the hysteresis curve is 0.7766. Reference is made to  FIG. 8 , which illustrates a hysteresis curve plot of the magnetic tunneling junction  300  when a magnetic field between −1,000 and 1,000 Oersted is applied. The intensity of the coercive field is much lower than the conventional structure, normally is larger than 200, in the case of the present invention is 40.66 Oersted. The squareness of the hysteresis curve in the case of the present invention is 0.9855, while the conventional structure can only present the data normally smaller than 0.7. 
         [0042]    The difference between the structure of the magnetic tunneling junction  200  and the structure of the magnetic tunneling junction  300  is that in the  10  structure of the magnetic tunneling junction  300  there are no horizontal polarized ferrimagnetic layers disposed above or beneath the multiple barrier layers of the in the structure of the magnetic tunneling junction  300 . 
         [0043]    According to the composition and the embodiments above, there are many advantages of the present invention over the prior art, such as: 
         [0044]    1. The coercive field of the structure of magnetic tunneling junction with multiple barrier layers is much lower than the coercive field of conventional structures. Hence, the intensity of the applied magnetic field can be reduced, and the power consumption of the magnetic device can be lowered. 
         [0045]    2. The squareness of the hysteresis curve of the structure of the magnetic tunneling junction with multiple barrier layers is much better than the squareness of the hysteresis curve for a magnetic tunneling junction with a conventional structure. Hence, the structure described above is more suitable for a memory device or a switch component. 
         [0046]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.