Abstract:
A method for resetting a spin-transfer based random access memory system, the method comprising, inducing a first current through a first conductor, wherein the first current is operative to propagate a magnetic domain wall in a ferromagnetic film layer and the propagation of the magnetic domain wall is further operative to change the direction of a magnetic state of a first free layer magnet, and inducing a second current only through a second conductor, wherein the second current is operative to further propagate the magnetic domain wall in the ferromagnetic film layer and the propagation of the magnetic domain wall is further operative to change the direction of a magnetic state of a second free layer magnet.

Description:
The present application is co-pending with the concurrently filed applications, entitled “SYSTEMS INVOLVING SPIN-TRANSFER MAGNETIC RANDOM ACCESS MEMORY,” and “METHODS INVOLVING RESETTING SPIN-TORQUE MAGNETIC RANDOM ACCESS MEMORY” assigned to the assignee of the present application, the contents of which are incorporated herein by reference in their entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to magnetic random access memory and specifically to methods involving resetting spin-torque based magnetic random access memory. 
   2. Description of Background 
   A dense, diode-selection based memory architecture has recently been demonstrated for a two-terminal memory device based on phase change materials. However, since spin-RAM usually uses bidirectional current for writing the 0 and 1 states, a dense, diode selection-based memory architecture is difficult to implement with spin-RAM since diodes may limit the use of bidirectional current. 
   A method for resetting a spin-RAM that uses bidirectional current is desired. 
   SUMMARY OF THE INVENTION 
   The shortcomings of the prior art are overcome and additional advantages are achieved through an exemplary method for resetting a spin-transfer based random access memory system, the method comprising, inducing a first current through a first conductor, wherein the first current is operative to propagate a magnetic domain wall in a ferromagnetic film layer and the propagation of the magnetic domain wall is further operative to change the direction of a magnetic state of a first free layer magnet, and inducing a second current through a second conductor, wherein the second current is operative to further propagate the magnetic domain wall in the ferromagnetic film layer and the propagation of the magnetic domain wall is further operative to change the direction of a magnetic state of a second free layer magnet. 
   Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other aspects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
       FIG. 1  illustrates a block diagram of an exemplary method for resetting a three terminal spin-RAM device with a domain wall. 
       FIG. 2  illustrates a front partially cut-away view of an example of an embodiment of a spin-torque based magnetic write random access memory system. 
       FIG. 3  illustrates a perspective view the example of the embodiment of the spin-torque based magnetic write random access memory system of  FIG. 2 . 
       FIGS. 4-8  illustrate a side-view of an example of an embodiment of a spin-torque based magnetic write random access memory system and the method described in  FIG. 1 . 
   

   The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Methods involving resetting spin-torque based magnetic write random access memory are provided. Several exemplary embodiments are described. 
   The embodiments of a spin-torque based magnetic write random access memory allow for more robust operation of the memory device with existing materials combination. It further enables the implementation of a high-density version of spin-RAM, based on diode-selection that makes spin-RAM more economical to produce. This improves cost-to-performance characteristics, while retaining the basic advantages of a spin-torque-based RAM. 
     FIG. 2  illustrates a front partially cut-away view of a three-terminal spin-torque based magnetic write random access memory containing three electrical connections, T 1   a , T 2 , and T 3   a  terminals. In the illustrated embodiment, a write portion  100   a  is a pillar-shaped non-linear selection device, such as, for example, P/N junction that includes a p-type doped region  110   a  and an n-type doped region  120   a  (or in reverse order, depending on the direction of write current for the design). The n-type doped region  120   a  electrically contacts a ferromagnetic film layer  200 . The p-type doped region  110   a  electrically contacts a conductor  130   a  that is connected to the T 1   a  terminal. Though the illustrated embodiment shows a P/N junction, any suitable non-linear selection device may be used for the write portion  100   a.    
   A spin-current generating portion  20  includes the ferromagnetic film layer  200 , and a conductance layer  220 . The ferromagnetic film layer  200  is a magnetic, spin-polarizing layer. The conductance layer  220  is a non-magnetic, spin preserving, high conductance layer such as, for example, copper. A tunnel layer (not shown) may be used to separate the ferromagnetic film layer  200  and the conductance layer  220 . Depending on the specifics of materials properties, the tunnel layer may not be necessary. In some materials combinations, it is possible to allow a direct, high quality interface (usually formed during thin film deposition) between the ferromagnetic film layer  200  and the conductance layer  220 . The conductance layer  220  electrically contacts the T 2  terminal. 
   A read portion  400   a  forms the magnetic state detection device group. The read portion  400   a  is a pillar shape on the conductance layer  220 . The read portion  400   a  includes a free layer magnet  410   a  disposed on the conductance layer  220 , a read non-magnetic layer  420   a , and a reference layer  430   a . The read non-magnetic layer  420   a  is a non-magnetic spin-preserving metallic separation layer that may be, for example, a tunnel barrier layer. The reference layer  430   a  electrically contacts the T 3   a  terminal. The read portion  400   a  is disposed on the conductance layer  220   a  with a high quality interface, usually formed during film growth, to allow efficient interaction between the free layer magnet  410   a  and a spin-current (not shown). 
   The reference layer  430   a  is magnetically fixed. A direction of magnetization of the reference layer  430   a  is permanently fixed in the direction indicated by the arrow  402   a . In the illustrated embodiment, the arrow  402   a  points to the left, however, the arrow  402   a  may point to the right in other embodiments. The free layer magnet  410   a  is a nanomagnet having a magnetic state illustrated by the arrow  401   a . The free layer magnet  410   a  serves as a memory element, and the direction of the arrow  401   a  (right or left) indicates two bi-stable memory states of the free layer magnet  410   a .  FIG. 2  also includes a second read portion  400   b  and a second write portion  100   b  that are similar to the read portion  400   a  and write portion  100   a .  FIG. 3  illustrates a perspective view of the three-terminal spin-torque based magnetic write random access memory of  FIG. 2  including a point A  301  and a point B  303  on the conductor  130   a , and a point C  305  and a point D  307  on the conductor  130   b.    
     FIG. 1  illustrates a block diagram of an exemplary method of resetting a spin-torque-based RAM. Referring to block  151 , a first current is induced through a first conductor to create and propagate a magnetic domain wall in a ferromagnetic film layer, changing the state of a first free layer magnet. In block  153 , a second current is induced through a second conductor to further propagate the magnetic domain wall in the ferromagnetic film layer, changing the state of a second free layer magnet. In block  155 , a third current is induced through the first conductor to change the direction of magnetic orientation of the ferromagnetic film layer. In block  157 , a fourth current is induced through the second conductor to further change the direction of magnetic orientation of the ferromagnetic film layer. The method illustrated in  FIG. 1  is shown in detail in  FIGS. 4-8 . 
     FIG. 4  shows an embodiment of a spin-torque-based RAM similar to the embodiment of  FIG. 2 . In  FIG. 4 , the magnetization of the reference layers  430   a  and  430   b  are fixed in the direction indicated by the arrows  402   a  and  402   b . The magnetic orientation of the free layer magnets  410   a  and  410   b , memory elements, are shown by of the arrows  401   a  and  401   b . In the illustrated embodiment the arrows  401   a  and  401   b  point to the left, representing 1 bits. 
   Resetting the spin-torque-based RAM is accomplished by changing the free layer magnets  410   a  and  410   b  from representing 1 bits to 0 bits. To change the free layer magnets  410   a  and  410   b  from representing 1 bits to 0 bits, a magnetic domain wall is created and propagated through the ferromagnetic film layer  200 .  FIG. 4  illustrates a method of creating a magnetic domain wall in the ferromagnetic film layer  200 . As illustrated in block  151  (of  FIG. 1 ), a first current  101   a  is induced along the conductor  130   a  through the point A  301  and the point B  303  (shown in  FIG. 3 ). The conductor  130   a  is orientated at a right angle to the ferromagnetic film layer  200 . The first current  101   a  creates a magnetic flux  103   a  that is effective create a magnetic domain wall  105 . The magnetic domain wall  105  has a magnetic flux  109 . 
   Referring to  FIG. 5 , once the magnetic domain wall  105  is created, the first current  101   a  causes the magnetic domain wall  105  to propagate through the ferromagnetic layer  200  in the right direction. The propagation of the magnetic domain wall  105  and the magnetic flux  109  causes the magnetic orientation of the free layer magnet  410   a  to be changed from representing a 1 bit to a 0 bit. 
   As illustrated in block  153  (of  FIG. 1 ) and shown in  FIG. 6 , a second current  101   b  is induced along the conductor  130   b  through the point C  305  and the point D  307  (shown in  FIG. 3 ). The second current  101   b  results in a magnetic flux  103   b  and the further propagation of the magnetic domain wall  105  along the ferromagnetic film layer  200 . In  FIG. 7  the second current  101   b  has caused the magnetic domain wall  105  to propagate along the ferromagnetic film layer  200  and past the free layer magnet  410   b . The magnetic orientation of the free layer magnet now represents a 0 bit. 
     FIG. 8  illustrates blocks  155  and  157  (of  FIG. 1 ). After the direction of the magnetic state of the free layer magnets  410   a  and  410   b  are changed, the direction of the magnetic orientation of the ferromagnetic film layer  200  may be returned to the first direction shown in  FIG. 2  by arrow  201 . A fourth current  102   a  and a fifth current  102   b  are induced along the conductors  130   a  and  130   b  in a direction opposite to the first current  101   a  and the second current  101   b . The fourth current  102   a  and the fifth current  102   b  create magnetic flux  107   a  and  107   b  that are effective to change the direction of the magnetic orientation of the ferromagnetic film layer  200  to an opposite direction as indicated by the arrow  201 . The fourth current  102   a  and the fifth current  102   b  may be induced at the same time or in a sequence to change the direction of the magnetic orientation of the ferromagnetic film layer  200 . The methods described above may be used to reset the memories of embodiments having any additional number of read portions and write portions similar to read portion  400  and write portion  100 . 
   While the preferred embodiment to the invention has been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.