Abstract:
A high density magnetoresistance memory and a manufacturing method thereof are provided. The magnetoresistance memory includes: a memory cell storing information; a conductive line contacting the memory cell to change the magnetization direction of the memory cell by generating a magnetic field; and at least one flux concentrating island (FCI) located between the conductive line and the memory cell for concentrating flux onto the memory cell. The flux is concentrated onto the memory cell to reduce a required electric current and improve selectivity, thereby forming a high-density and highly integrated memory cell.

Description:
BACKGROUND OF THE INVENTION 
   This application claims the priority of Korean Patent Application No. 2003-35302, filed on Jun. 2, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   1. Field of the Invention 
   The present invention relates to a high density magnetoresistance memory and a manufacturing method thereof, and particularly, to a magnetoresistance memory and a manufacturing method thereof for achieving high selectivity. 
   2. Description of the Related Art 
     FIG. 1  is a view of a conventional magnetic random access memory (MRAM) array. Referring to  FIG. 1 , the conventional MRAM stores information by reversing the magnetization direction of a memory cell  5  located between a digit line  1  and a bit line  3  using a magnetic field generated on the digit line  1  and the bit line  3  to which electric current is applied. However, the magnetic field generated due to the electric current applied to the digit line  1  and the bit line  3  may affect memory cells  7  and  9  located around the memory cell  5  which is at a point where the digit line  1  and the bit line  3  cross each other. Especially, in a memory cell that has gradually become compact and has a high memory density, coercivity of the memory cell increases and a current value required to reverse the magnetization direction also increases. Thus, the magnetic field affects the peripheral cells  7  and  9  beside the memory cell  5  and reverses the magnetization direction, thereby possibly increasing mis-operation of the memory. 
   To solve the above disadvantages of the MRAM,  FIG. 2  shows an example of a conventional magnetoresistance memory having a structure capable of concentrating flux onto a memory cell.  FIG. 2  is a cross-sectional view of an MRAM disclosed in U.S. Pat. No. 5,659,499. 
   Referring to  FIG. 2 , MRAM  35  comprises a substrate  11  and a memory cell  14  in which information is stored as a magnetization vector on the substrate  11 . The memory cell  14  is made of a magnetoresistive (MR) material having a multi-layer structure including an insulating layer between magnetic materials, and having a length  21  (L) designated by an arrow and a width perpendicular to the ground. A column conductive material  12  is used to connect the memory cell  14  of a column shape to another memory cell. A dielectric material  13  is applied on the memory cell  14  and the conductive material  12  so as to insulate them from a conductive material  36  of the digit line. The conductive material  36  of the digit line is arranged to cross the memory cell  14  at a right angle. High-permeability materials  17  and  18  are applied on an upper surface and a side surface of the conductive material  36 , which is on the digit line to change the magnetization direction according to the electric current applied to the digit line conductive material  36  and to focus the magnetic field onto the magnetic material in the memory cell  14 . High-permeability materials  31  and  32  are formed on left and right upper portions of the memory cell  14  as strips to support the flux focusing function of the high-permeability materials  17  and  18 . A distance  37  between the high permeable materials  32  and  33  is formed to be smaller than the width of the memory cell  14 . 
   U.S. Pat. No. 6,174,737 also discloses an improved MRAM and manufacturing method thereof similar to the MRAM structure disclosed in U.S. Pat. No. 5,659,499. However, the conventional conductive layer for focusing the flux is formed as a stripe pattern on an upper portion of the bit line or the digit line to distribute the flux on a portion where the memory cell is not located, and thus, the flux cannot be focused effectively on the desired memory cell. Also, the stripe pattern should be fabricated after forming the memory cell, and therefore, it is not easy to perform the manufacturing processes. 
   SUMMARY OF THE INVENTION 
   The present invention provides a magnetoresistance memory having a flux concentration structure by which the flux can be concentrated effectively onto a memory cell and a manufacturing method of the magnetoresistance memory. 
   According to an aspect of the present invention, there is provided a magnetoresistance memory comprising: a memory cell storing information; a conductive line contacting the memory cell for changing magnetization direction of the memory cell by generating a magnetic field; and at least one flux concentrating island (FCI) located between the conductive line and the memory cell for concentrating flux onto the memory cell. 
   According to another aspect of the present invention, there is provided a method of manufacturing a magnetoresistance memory comprising: forming a memory cell and a conductive line applying an electric current to the memory cell on a substrate; and forming an FCI concentrating flux onto the memory cell between the memory cell and the conductive line. 
   The conductive line may be a bit line or a digit line which is formed to cross the bit line at a right angle while interposing the memory cell between the bit line and the digit line. 
   The conductive line may include a flux concentrating layer (FCL) for concentrating the flux onto the memory cell on a surface which does not contact the memory cell. 
   The FCI and the FCL may be formed using a material having high permeability. 
   The FCI and the FCL may improve selectivity by 5% or more. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a view of a conventional magnetic random access memory (MRAM); 
       FIG. 2  is a cross-sectional view of an MRAM disclosed in U.S. Pat. No. 5,659,499; 
       FIG. 3  is a perspective view of a magnetoresistance memory according to an embodiment of the present invention; 
       FIG. 4A  is a cross-sectional view of a conductive line if there is no flux concentrating island (FCI); 
       FIG. 4B  is a cross-sectional view of a conductive line on which the FCI is disposed; 
       FIG. 4C  is a cross-sectional view of a conductive line on which a flux concentrating layer (FCL) is disposed; 
       FIG. 4D  is a cross-sectional view of a conductive line on which an FCI and an FCL are disposed; and 
       FIGS. 5A through 5D  are views of results of simulations in which an electric current is applied to respective memory cells shown in FIGS.  4 A through  4 D. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  is a perspective view of a magnetoresistance memory according to an embodiment of the present invention. Referring to  FIG. 3 , the magnetoresistance memory  50  comprises: a bit line  53  formed as a stripe on a substrate  57 ; a memory cell  55  disposed on the bit line  53 ; a digit line  51  contacting an upper surface of the memory cell  55  and formed as a stripe so as to cross the bit line  53  at a right angle; a flux concentrating island (FCI) for bit line  56  located adjacent to the bit line  53  that mainly concentrates a magnetic field generated from the bit line  53  onto the memory cell  55 ; and an FCI for digit line  54  located adjacent to the digit line  51  that mainly concentrates a magnetic field generated from the digit line  51  onto the memory cell  55 . At that time, insulating layers are disposed between all components so that the components do not contact each other physically. 
   When the electric current is required to record onto the magnetoresistance memory, a large amount of heat is generated due to the electric current and the heat affects the adjacent cells, and thus, the probability of switching the magnetization direction of undesired magnetoresistance memory cell increases. Also, when the magnetoresistance memory is highly condensed by configuring the memory to be highly integrated, the size of the memory cell becomes smaller and coercivity is increased. Thus, increasing the intensity of the magnetic field required to switch the magnetization direction and increasing the required electric current. 
   In the magnetic memory according to the embodiment of the present invention, the FCI, which is made of a material having high permeability, is formed around the memory cell which is configured to be highly integrated so as to change the path of a magnetic field generated on the bit line  53  and the digit line  51 , thereby concentrating the magnetic field being emitted outward onto a desired memory cell. Thus, a sufficient magnetic field that is able to switch the magnetization direction of the memory cell with a small amount of electric current can be applied only to the desired memory cell. The FCI can be formed variously as a square, a rectangle, or a circle. 
   The magnetoresistance memory of  FIG. 3  is formed of a conductive material of an island shape around the memory cell  53  in order to concentrate the flux, however, a flux concentrating layer (FCL) shown in  FIG. 1  may be further formed on the digit line  51  to improve the flux concentrating effect. However, in a case where the FCL is adopted, it should be noted that a process is added and the processing cost may increase. 
     FIG. 4A  is a cross-sectional view of a conductive line if there is no FCI,  FIG. 4B  is a cross-sectional view of a conductive line on which the FCI is disposed,  FIG. 4C  is a cross-sectional view of a conductive line on which the FCL is disposed, and  FIG. 4D  is a cross-sectional view of a conductive line on which the FCI and the FCL are disposed. Here, the conductive line may be the bit line or the digit line. 
   The conductive line  61  of  FIG. 4A  has a width of 0.6 μm and a height of 0.3 μm, and does not include a flux concentrating configuration, such as the FCI and/or the FCL. Referring to  FIG. 4B , an insulating layer  68   a  is applied to the side surfaces and a lower surface of the conductive line  61 , and the FCIs  66   a  and  66   b  are formed on the left and right lower surfaces of the insulating layer  68   a . The insulating layer  68   a  is deposited to have a width of about 0.1 μm, and the FCIs  66   a  and  66   b  are formed to have a width of about 0.3 μm and a thickness of about 0.04 μm. 
   Regarding the conductive layer  61  of  FIG. 4C , the FCL  62  is applied on the side surfaces and a lower surface of the insulating layer  68   b  instead of the FCIs  66   a  and  66   b  of FIG.  4 B. Herein, the FCL  62  is formed to have a thickness of about 0.04 μm.  FIG. 4D  is a cross-sectional view of the conductive line  61  on which the FCL  62  and the FCIs  66   a  and  66   b  are formed. The thickness of the insulating layer is about 0.1 μm, the FCIs  66   a  and  66   b  are formed to be at the same size as that of FIG.  4 B and the FCL  62  is formed to be of the same size as that of FIG.  4 C. 
     FIGS. 5A through 5D  are views of simulation results of applying an electric current to selected memory cells in the respective cases shown in  FIGS. 4A through 4D . Referring to  FIGS. 5A through 5D , nine memory cells are arranged, and lines of a magnetic force are formed upward from the memory cell located on the right side of the selected memory cell at the center portion and are formed downward from the memory cell located on the left side of the selected memory cell. 
   The gradual increase of the intensities of the magnetic fields of the memory cells in  FIGS. 4A and 4B  can be known from the scroll bars of  FIGS. 5A and 5B  representing the intensities of the magnetic fields. The maximum intensity of the memory cell is about 2612(G) in  FIG. 5A , about 4262(G) in  FIG. 5B , about 5868(G) in  FIG. 5C , and about 7427(G) in FIG.  5 D. The intensity of the magnetic field is noted to be strongest from the simulation results in a case where the FCI according to the present invention and the conventional FCL are used together. 
   Table 1 shows an x-axis, a y-axis, a required current, and the selectivity for respective cases 1, 2, 3, and 4 shown in  FIGS. 4A through 4D . 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
                 
               Required 
                 
             
             
                 
               Hx(0e) 
               Hy(0e) 
               current (mA) 
               Selectivity (%) 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               Case 1 
               20.7 
               22.0 
               8.5 
               178 
             
             
               Case 2 
               21.9 
               27.5 
               7.5 
               192 
             
             
               Case 3 
               31.0 
               45.4 
               4.7 
               182 
             
             
               Case 4 
               31.1 
               53.5 
               4.5 
               196 
             
             
                 
             
           
        
       
     
   
   Here, the required current means the electric current required to reverse the magnetization direction of the memory cell, and the selectivity is defined as Equation 1 shown below, that is, a relational expression between a magnetic field (H x0 , H y0 ) applied to a selected memory cell and a magnetic field (H x1 , H y1 ) applied to an adjacent memory cell. The higher the selectivity is, the higher the concentration of the magnetic field toward the selected memory cell is. 
                         selectivity   =       ⁢     2   /     (           (         (       H   x1     /     H   x0       )     2     +       (       H   y1     /     H   y0       )     2       )     /   2       +                         ⁢         (         (       H   x2     /     H   x0       )     2     +       (       H   y2     /     H   y0       )     2       )     /   2                       [     Equation   ⁢           ⁢   1     ]             
 
   Referring to Table 1, the strongest intensity of a magnetic field (Hx) in an x-axis direction is about 31(0e) in cases 3 and 4, and the strongest intensity of a magnetic field (Hy) in a y-axis direction is about 45(0e) in case 3 and about 53(0e) in case 4. The required current is smallest in cases 3 and 4 amounting to about 4.5 through 4.7. 
   However, the selectivity is largest in cases 2 and 4 ranging from about 192% to 196%. The selectivity of case 2 is improved in that it amounts to about 8% more than the selectivity of case 1, that is, 178%. It is preferable that the selectivity of the magnetoresistance memory is designed to be improved by 5% or more. 
   From the above results, the magnetoresistance memory including the FCI functions more effectively in view of selectivity, and shows the best functionality in views of the intensity of the magnetic field, the required current, and the selectivity in a case where the FCI and the FCL are disposed. Optimal conditions of thickness and width of the FCI can be found through experiments. 
   The magnetic material, which is the same as the magnetoresistance memory cell, can be used as the FCI. Thus, the desired structure can be achieved without increasing the processes by using a mask of the same shape as that of the FCI when the memory cell is etched in the manufacturing process. 
   The magnetoresistance memory according to the present invention includes the flux concentration structure to increase the flux density per unit current applied to the memory cell, thereby, reducing the required current which is needed to switch the magnetization direction of the cell and improving the selectivity so as to manufacture the high density magnetoresistance memory. 
   As described above, the magnetoresistance memory according to the present invention has advantages in that it reduces the required current and improves the selectivity by increasing the flux density per unit current, thereby a high-density and highly integrated structure can be achieved easily. 
   Also, the manufacturing method of the magnetoresistance memory according to the present invention has an advantage in that the FCI can be fabricated by simply changing the mask which is required in the etching process. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.