Spinram

Abstract

Magnetic random-access memory (RAM) cells and arrays are described based on magnetoresistive thin-film structures.

What is claimed is: 
     
       1. A memory, comprising:
 a plurality of first signal lines; 
 a plurality of second signal lines; and 
 a plurality of first thin-film structures exhibiting magnetoresistance, each of the first thin-film structures having a longitudinal axis; 
 a plurality of second thin-film structures exhibiting magnetoresistance, each of the second thin-film structures having a longitudinal axis;  
 wherein the first signal lines, the second signal lines, and the first thin-film structures, and the second thin-film structures form an array of memory cells, each memory cell comprising:
 a portion of a corresponding one of the first thin-film structures; 
 a portion of a corresponding one of the second thin-film structures;  
 a portion of a corresponding one of the first signal lines coinciding with the portion of the corresponding one of the first thin-film structure structures and the portion of the corresponding one of the second thin-film structures and electrically isolated therefrom; 
 a portion of a corresponding one of the second signal lines coinciding with the portion of the corresponding one of the first signal line and lines, the portion of the corresponding one of the first thin-film structure structures, and the portion of the corresponding one of the second thin-film structures, the portion of the corresponding one of the second signal line lines being electrically isolated from the corresponding one of the first signal line and lines, the corresponding one of the first thin-film structure structures, and the corresponding one of the second thin-film structures; and 
 one or morea plurality of keeper elements in direct contact with the portion of the corresponding one of the first thin-film structurestructures and the portion of the corresponding one of the second thin-film structures such that the portion of the corresponding one of the first thin-film structurestructures, the portion of the corresponding one of the second thin-film structures, and the one or more keeper elements form at least part of a fully-closed-flux structure of the memory cell; and 
 
 wherein, for each memory cell, the portion of the corresponding one of the first thin-film structure has an easy axis of magnetization perpendicular to a the longitudinal axis of the corresponding one of the first thin-film structures and in a plane of the portion of the corresponding one of the first thin-film structure structures, and the portion of the corresponding one of the second thin-film structures has an easy axis of magnetization perpendicular to the longitudinal axis of the corresponding one of the second thin-film structures and in a plane of the portion of the corresponding one of the second thin-film structures, and wherein the first and second signal lines are configured to generate magnetizing fields at each memory cell that have components in the planes of the corresponding portions of the corresponding one of the first thin-film structures and the corresponding one of the second thin-film structures that are perpendicular to the longitudinal axis of the portion axes of the corresponding one of the first thin-film structures and the corresponding one of the second thin-film structure structures. 
 
     
     
       2. The memory of  claim 1 , further comprising a plurality of second thin-film structures exhibiting magnetoresistance, each memory cell further comprising a portion of a corresponding one of the second thin-film structures, the portion of the corresponding second thin-film structure for each memory cell coinciding with and being electrically isolated from the corresponding first signal line, the corresponding second signal line, and the corresponding first thin-film structure, and wherein, for each memory cell, the portion of the corresponding second thin-film structure forms part of the fully-closed flux structure. 
     
     
       3. The memory of  claim 1 , wherein the first and second signal lines are configured such that, for each memory cell, a primary direction of current flow in the portion of the corresponding one of the first signal line lines is parallel to a primary direction of current flow in the portion of the corresponding one of the second signal line lines. 
     
     
       4. The memory of  claim 1 , wherein at each memory cell, the portion of the corresponding one of the first thin-film structure structures and the portions of the corresponding one of the first signal lines and the corresponding one of the second signals lines are co-linear. 
     
     
       5. The memory of  claim 4 , wherein each of the first thin-film structures includes sections of non-magnetic conductors between adjacent memory cells. 
     
     
       6. The memory of  claim 1 , wherein each of the first thin-film structure structures includes at least one high-coercivity magnetic layer and at least one low-coercivity magnetic layer. 
     
     
       7. The memory of  claim 6 , wherein each of the first thin-film structure structures includes a pair of low-coercivity magnetic layers. 
     
     
       8. The memory of  claim 7 , wherein each of the first thin-film structure structures includes a first permalloy layer, a first copper layer, a cobalt layer, a second copper layer, and a second permalloy layer. 
     
     
       9. The memory of  claim 6 , wherein each of the first thin-film structure structures comprises a ferromagnetically-coupled superlattice having multiple periods of the high and low-coercivity layers. 
     
     
       10. The memory of  claim 1 , wherein each memory cell is characterized by an aspect ratio of approximately 1 to 1.2. 
     
     
       11. A memory cell comprising:
 a portion of a first thin-film structure, the first thin-film structure having a longitudinal axis; 
 a portion of a second thin-film structure, the second thin-film structure having a longitudinal axis;  
 a first signal line coinciding with the portion of the first thin-film structure and the portion of the second thin-film structure, the first signal line being electrically isolated therefrom; 
 a second signal line coinciding with the first signal line and, the portion of the first thin-film structure, and the portion of the second thin-film structure, the second signal line being electrically isolated from the first signal line and the first thin-film structure; and 
 one or morea plurality of keeper elements in direct contact with the portion of the first thin-film structure and the portion of the second-thin film structure such that the portion of the first thin-film structure, the portion of the second thin-film structure, and the one or more keeper elements form at least part of a fully-closed-flux structure of the memory cell; and 
 wherein, the portion of the first thin-film structure has an easy axis of magnetization perpendicular to a the longitudinal axis of the first thin-film structure and in a plane of the first thin-film structure, wherein the second thin-film structure has an easy axis of magnetization perpendicular to the longitudinal axis of the second thin-film structure and in a plane of the second thin-film structure, and wherein the first and second signal lines are configured to generate magnetizing fields having components in the planes of the first and second thin-film structures that are perpendicular to the longitudinal axis axes of the first and second thin-film structure structures. 
 
     
     
       12. The memory cell of  claim 11 , further comprising a portion of a second thin-film structure coinciding with and electrically isolated from the first signal line, the second signal line, and the first thin-film structure, wherein the portion of the second thin-film structure forms part of the fully-closed flux structure. 
     
     
       13. The memory cell of  claim 11 , wherein the first and second signal lines are configured such that a primary direction of current flow in the first signal line at the memory cells is parallel to a primary direction of current flow in the second signal line at the memory cell. 
     
     
       14. The memory cell of  claim 11 , wherein the portion of the first thin-film structure and the first and second signals lines are co-linear at the memory cell. 
     
     
       15. The memory cell of  claim 14 , wherein the first thin-film structure includes sections of non-magnetic conductors on either side of the memory cell. 
     
     
       16. The memory cell of  claim 11 , wherein the portion of the first thin-film structure includes at least one high-coercivity magnetic layer and at least one low-coercivity magnetic layer. 
     
     
       17. The memory cell of  claim 16 , wherein the portion of the first thin-film structure includes a pair of low-coercivity magnetic layers. 
     
     
       18. The memory cell of  claim 17 , wherein the portion of the first thin-film structure includes a first permalloy layer, a first copper layer, a cobalt layer, a second copper layer, and a second permalloy layer. 
     
     
       19. The memory cell of  claim 16 , wherein the portion of the first thin-film structure comprises a ferromagnetically-coupled superlattice having multiple periods of the high and low-coercivity layers. 
     
     
       20. A memory cell comprising:
 a portion of a first thin-film structure exhibiting giant magnetoresistance, the first thin film structure including a high-coercivity magnetic layer and a corresponding pair of low-coercivity magnetic layers, the first thin-film structure having a longitudinal axis; 
 a first signal line coinciding with the portion of the first thin-film structure and electrically isolated therefrom; 
 a second signal line coinciding with the first signal line and the portion of the first thin-film structure, the second signal line being electrically isolated from the first signal line and the first thin-film structure; 
 a portion of a second thin-film structure coinciding with and electrically isolated from the first signal line, the second signal line, and the first thin-film structure, the second thin-film structure exhibiting giant magnetoresistance and including a high-coercivity magnetic layer and a corresponding pair of low-coercivity magnetic layers, the second thin-film structure having a longitudinal axis oriented in parallel with the longitudinal axis of the first thin-film structure; and 
 one or morea plurality of keeper elements in direct contact with the portion of the first thin-film structure and the portion of the second thin-film structure such that the portion of the first thin-film structure, the portion of the second thin-film structure, and the one or more keeper elements form a fully-closed-flux structure of the memory cell; and 
 wherein, the portion of the first thin-film structure has an easy axis of magnetization perpendicular to a the longitudinal axis of the first thin-film structure and in a plane of the first thin-film structure, the portion of the second thin-film structure has an easy axis of magnetization perpendicular to a the longitudinal axis of the second thin-film structure and in a plane of the second thin-film structure, and wherein the first and second signal lines are configured to conduct currents having a primary direction of current flow parallel to the longitudinal axes of the first and second thin-film structures and to thereby generate magnetizing fields having components in the planes of the first and second thin-film structures that are perpendicular to the longitudinal axes of both the first and second thin-film structures.