MRAM memory cell having a weak intrinsic anisotropic storage layer and method of producing the same

Abstract

An MRAM memory cell has a layer system of circular-disk-shaped layers. The memory cell includes two magnetic layers separated by a nonmagnetic intermediate layer. The first magnetic layer or reference layer exhibits hard-magnetic behavior. The second magnetic layer or storage layer exhibits soft-magnetic behavior. Information is stored by the magnetization state of the storage layer. The storage layer has a weak intrinsic anisotropy that defines a magnetic preferred direction. The magnetization direction of the reference layer is parallel to the magnetization direction of a remnant magnetization in the interior of the storage layer. The remnant magnetization occurs as a result of applying an external magnetic field with a field component perpendicular to the preferred direction of the intrinsic anisotropy of the storage layer.

1 . An MRAM memory cell having a layer system of substantially circular-disk-shaped layers, comprising: 
 two magnetic layers separated by a non-magnetic intermediate layer, the first magnetic layer exhibiting hard-magnetic behavior, the second magnetic layer exhibiting soft-magnetic behavior such that information is stored by a magnetization state of the storage layer, the storage layer having a weak intrinsic anisotropy defining a magnetic preferred direction,    wherein magnetization of the reference layer is substantially parallel to a remnant magnetization in the interior of the storage layer, the remnant magnetization occurring as a result of applying an external magnetic field with a field component perpendicular to the preferred direction of the intrinsic anisotropy of the storage layer.    
   
   
       2 . The MRAM memory cell as claimed in  claim 1 , wherein the magnetization of the reference layer is directed at an angle α with respect to the preferred direction of the intrinsic anisotropy of the storage layer, the angle α having a value in the range of 10° to 50°.  
   
   
       3 . The MRAM memory cell as claimed in  claim 1 , wherein the storage layer and/or reference layer are/is constructed from a plurality of individual layers.  
   
   
       4 . The MRAM memory cell as claimed in  claim 3 , wherein magnetization of the individual layers of the storage layer and/or reference layer are coupled by a magnetic coupling selected from the group consisting of magnetic leakage field coupling, antiferromagnetic coupling, and exchange coupling.  
   
   
       5 . The MRAM memory cell as claimed in  claim 3 , wherein the net magnetization of the storage layer and/or reference layer is substantially zero.  
   
   
       6 . The MRAM memory cell as claimed in  claim 1 , wherein the materials of the reference layer and/or storage layer are based on an alloy of the (Co, Ni, Fe) system.  
   
   
       7 . The MRAM memory cell as claimed in  claim 6 , wherein the materials of the storage layer and/or reference layer are amorphous alloys.  
   
   
       8 . A method for producing an MRAM memory cell, comprising: 
 (A) providing a layer system of substantially circular-disk-shaped layers, the layer system having two magnetic layers separated by a nonmagnetic intermediate layer, the first magnetic layer exhibiting hard-magnetic behavior and, the second magnetic layer exhibiting soft-magnetic behavior such that information is stored by a magnetization state of the storage layer, the storage layer having a weak intrinsic anisotropy defining a magnetic preferred direction;    (B) generating a first, substantially homogeneous, external magnetic field during a first elevated-temperature age hardening of the layer system, a direction of the first magnetic field being oriented at an angle α with respect to the preferred direction of the intrinsic anisotropy of the storage layer such that the direction of the first magnetic field is substantially parallel to the magnetization direction of a remnant magnetization in the interior of the storage layer, the remnant magnetization occurring as a result of applying an external magnetic field with a field component perpendicular to the preferred direction of the intrinsic anisotropy of the storage layer; and    (C) first elevated-temperature age hardening the layer system at a temperature below the Curie point of the two magnetic layer systems, a field strength of the first magnetic field being greater than the saturation field strength of the reference layer such that the magnetization of the reference layer is oriented along the field direction of the first magnetic field.    
   
   
       9 . The method as claimed in  claim 8 , wherein the angle α has a value in the range of 10° to 50°.  
   
   
       10 . The method as claimed in  claim 8 , further comprising: 
 (D) generating a second, substantially homogeneous, external magnetic field during a second elevated-temperature age hardening of the layer system, a direction of the second magnetic field being directed in a direction −α with respect to the direction of the first magnetic field; and    (E) second elevated-temperature age hardening of the layer system at a temperature below the Curie point of the two magnetic layer systems, a field strength of the second magnetic field being less than the saturation field strength of the reference layer, such that the magnetization of the reference layer substantially remains unchanged and the preferred direction of the magnetic anisotropy of the storage layer is oriented along the field direction of the second magnetic field.    
   
   
       11 . The method as claimed in  claim 8 , wherein the temperature during the first and/or second elevated-temperature age hardening is in the range of 250° C. to 350° C.  
   
   
       12 . The method as claimed in  claim 8 , wherein the field strength of the first magnetic field has a value in the range of 0.1 to 2 tesla.  
   
   
       13 . The method as claimed in  claim 8 , wherein the field strength of the second magnetic field has a value in the range of 0.001 to 0.1 tesla.  
   
   
       14 . The method as claimed in  claim 8 , wherein the storage layer is formed in intrinsic anisotropic fashion by heat treatment in an external magnetic field.  
   
   
       15 . The method as claimed in  claim 8 , wherein the storage layer is formed in intrinsic anisotropic fashion by oblique ion beam sputtering.  
   
   
       16 . The method as claimed in  claim 8 , wherein the storage layer is formed in intrinsic anisotropic fashion by ion beam sputtering in an external magnetic field.  
   
   
       17 . The method as claimed in  claim 8 , wherein the first temperature and the second temperature are substantially identical.