Ferromagnetic tunnel junction element and method of driving ferromagnetic tunnel junction element

Abstract

In a tunnel junction element having a ferromagnetic free layer, an insulating layer and a ferromagnetic fixed layer, in order to reduce the current necessary for spin-transfer magnetization reversal operation in the tunnel junction element, the ferromagnetic free layer comprises first and second ferromagnetic layers, a nonmagnetic metal layer is provided between these ferromagnetic layers, the nonmagnetic metal layer is such that magnetic coupling is preserved between the first and second ferromagnetic layers, also such that there is no influence on the crystal growth of the first and second ferromagnetic layers, the first ferromagnetic layer and the second ferromagnetic layer are placed such that the first ferromagnetic layer is in contact with the insulating layer, and the second ferromagnetic layer has a smaller magnetization than the first ferromagnetic layer.

What is claimed is: 
     
         1 . A method of operating a ferromagnetic tunnel junction element, the method comprising:
 passing a write current through a ferromagnetic free layer, an insulating layer, and a ferromagnetic fixed layer of the ferromagnetic tunnel junction element, wherein the ferromagnetic free layer and the ferromagnetic fixed layer sandwich the insulating layer;   in response to said passing a write current, reversing a magnetization direction of a first ferromagnetic layer of the ferromagnetic free layer; and   in response to said reversing, reversing a magnetization direction of a second ferromagnetic layer of the ferromagnetic free layer due to ferromagnetically coupling of the second ferromagnetic layer to the first ferromagnetic layer maintaining the magnetization direction of the first ferromagnetic layer parallel with and in a same direction as the magnetization direction of the second ferromagnetic layer.   
     
     
         2 . The method of  claim 1 , wherein said reversing a magnetization direction of a first ferromagnetic layer changes the magnetization direction of the first ferromagnetic layer from a parallel state to an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         3 . The method of  claim 1 , wherein said reversing a magnetization direction of a first ferromagnetic layer changes the magnetization direction of the first ferromagnetic layer from an anti-parallel state to parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         4 . The method of  claim 1 , wherein said passing a write current comprises passing the write current in a first direction from the ferromagnetic fixed layer toward the ferromagnetic free layer. 
     
     
         5 . The method of  claim 4 , wherein said reversing a magnetization direction of a first ferromagnetic layer stores a first logic state by changing, in response to said passing a write current in the first direction, the magnetization direction of the first ferromagnetic layer from an anti-parallel state to a parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         6 . The method of  claim 1 , wherein said passing a write current comprises passing the write current in a second direction from the ferromagnetic free layer toward the ferromagnetic fixed layer. 
     
     
         7 . The method of  claim 6 , wherein said reversing a magnetization direction of a first ferromagnetic layer stores a second logic state by changing, in response to said passing the write current in the second direction, the magnetization direction of the first ferromagnetic layer from a parallel state to an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         8 . The method of  claim 1 , further comprising:
 passing a read current having a smaller magnitude than the write current through the ferromagnetic free layer, the insulating layer, and the ferromagnetic fixed layer of the ferromagnetic tunnel junction element to produce a sense current; and   detecting, based on the sense current, whether the magnetization directions of the first and second ferromagnetic layers of the ferromagnetic free layer have a parallel state or an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer.   
     
     
         9 . A method, comprising:
 applying a write magnetic field to a ferromagnetic tunnel junction element having an insulting layer sandwiched between a ferromagnetic free layer and a ferromagnetic fixed layer;   in response to said magnetic field, reversing a magnetization direction of a first ferromagnetic layer of the ferromagnetic free layer; and   in response to said reversing, reversing a magnetization direction of a second ferromagnetic layer of the ferromagnetic free layer due to ferromagnetically coupling of the second ferromagnetic layer to the first ferromagnetic layer maintaining the magnetization direction of the first ferromagnetic layer parallel and in a same direction as the magnetization direction of the second ferromagnetic layer.   
     
     
         10 . The method of  claim 9 , wherein said reversing a magnetization direction of a first ferromagnetic layer changes the magnetization direction of the first ferromagnetic layer from a parallel state to an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         11 . The method of  claim 9 , wherein said reversing a magnetization direction of a first ferromagnetic layer changes the magnetization direction of the first ferromagnetic layer from an anti-parallel state to parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         12 . The method of  claim 11 , wherein said applying a write magnetic field comprises:
 generating a first magnetic field component of the write magnetic field by passing a first current through a write line associated with the ferromagnetic tunnel junction; and   generating a second magnetic field component of the write magnetic field by passing a second current through a bit line associated with the ferromagnetic tunnel junction.   
     
     
         13 . The method of  claim 12 , wherein said reversing a magnetization direction of a first ferromagnetic layer stores a first logic state by changing, in response to said passing the write magnetic field, the magnetization direction of the first ferromagnetic layer from an anti-parallel state to a parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         14 . The method of  claim 12 , wherein said reversing a magnetization direction of a first ferromagnetic layer stores a second logic state by changing, in response to said passing the write magnetic field, the magnetization direction of the first ferromagnetic layer from a parallel state to an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         15 . The method of  claim 9 , further comprising:
 passing a read current through the ferromagnetic free layer, the insulating layer, and the ferromagnetic fixed layer of the ferromagnetic tunnel junction element to produce a sense current; and   detecting, based on the sense current, whether the magnetization directions of the first and second ferromagnetic layers of the ferromagnetic free layer have a parallel state or an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer.   
     
     
         16 . A method, comprising:
 writing to a ferromagnetic tunnel junction having an insulating layer sandwiched between a ferromagnetic free layer and a ferromagnetic fixed layer, wherein said writing comprises:   reversing a magnetization direction of a first ferromagnetic layer of the ferromagnetic free layer; and   in response to said reversing, reversing a magnetization direction of a second ferromagnetic layer of the ferromagnetic free layer due to ferromagnetically coupling of the second ferromagnetic layer to the first ferromagnetic layer maintaining the magnetization direction of the first ferromagnetic layer parallel with and in a same direction as the magnetization direction of the second ferromagnetic layer.   
     
     
         17 . The method of  claim 16 , wherein said reversing a magnetization direction of a first ferromagnetic layer changes the magnetization direction of the first ferromagnetic layer from a parallel state to an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         18 . The method of  claim 16 , wherein said reversing a magnetization direction of a first ferromagnetic layer changes the magnetization direction of the first ferromagnetic layer from an anti-parallel state to parallel state with respect to a magnetization direction of the ferromagnetic fixed layer. 
     
     
         19 . The method of  claim 16 , further comprising:
 passing a write current in a first direction from the ferromagnetic fixed layer toward the ferromagnetic free layer;   wherein said reversing a magnetization direction of a first ferromagnetic layer stores a first logic state by changing, in response to said passing the write current in the first direction, the magnetization direction of the first ferromagnetic layer from an anti-parallel state to a parallel state with respect to a magnetization direction of the ferromagnetic fixed layer.   
     
     
         20 . The method of  claim 16 , further comprising;
 passing a write current in a second direction from the ferromagnetic free layer toward the ferromagnetic fixed layer;   wherein said reversing a magnetization direction of a first ferromagnetic layer stores a second logic state by changing, in response to said passing the write current in the second direction, the magnetization direction of the first ferromagnetic layer from a parallel state to an anti-parallel state with respect to a magnetization direction of the ferromagnetic fixed layer.