Current switched magnetoresistive memory cell

Abstract

A ferromagnetic thin-film based digital memory cell with a memory film of an anisotropic ferromagnetic material and with a source layer positioned on one side thereof so that a majority of conduction electrons passing therefrom have a selected spin orientation to be capable of reorienting the magnetization of the film. A disruption layer is positioned on the other side of the memory film so that conduction electrons spins passing therefrom are substantially random in orientation. The magnitude of currents needed to operate the cell can be reduced using coincident thermal pulses to raise the cell temperature.

What is claimed is: 
     
       1. A ferromagnetic thin-film based digital memory cell, said memory cell comprising:
 a substrate; and 
 a bit structure formed of a plurality of layers provided in a selected sequence between a pair of electrodes in electrical contact therewith at opposite ends of said sequence and supported on said substrate comprising:
 a memory film of an anisotropic ferromagnetic material capable of conducting an electrical current therethrough; 
 a source layer positioned on one side of said memory film capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation; and 
 a disruption layer positioned on another side of said memory film capable of conducting an electrical current therethrough so that conduction electrons spins passing therefrom are substantially random in orientation. 
 
 
     
     
       2. The device of  claim 1  further comprising an electrically insulative intermediate layer provided between said source layer and said memory film. 
     
     
       3. The device of  claim 1  wherein said source layer is a first source layer and said memory film is a first memory film, and further comprises a second memory film of an anisotropic ferromagnetic material positioned on an opposite side of said disruption layer from said first memory film and capable of conducting an electrical current therethrough, and a second source layer positioned on an opposite side of said second memory film from said disruption layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation. 
     
     
       4. The device of  claim 1  wherein a said memory film and said source layer have a length along a selected direction and a width substantially perpendicular thereto that is smaller in extent than said length and have a shaped end portion extending over a portion of said length in which said width gradually reduces to zero at that corresponding end thereof. 
     
     
       5. The device of  claim 1  wherein said source layer is of a ferromagnetic material and further comprising a magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction. 
     
     
       6. The device of  claim 3  further comprising a first electrically insulative intermediate layer provided between said first source layer and said first memory film, and a second electrically insulative intermediate layer provided between said second source layer and said second memory film. 
     
     
       7. The device of  claim 3  further comprising a first electrically insulative intermediate layer provided between said first source layer and said first memory film, and a conductive intermediate layer provided between said second source layer and said second memory film. 
     
     
       8. The device of  claim 3  wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction. 
     
     
       9. The apparatus of  claim 5  wherein said magnetization reference layer comprises an antiferromagnetic layer. 
     
     
       10. The apparatus of  claim 8  wherein said first magnetization reference layer comprises a first antiferromagnetic layer, and said second magnetization reference layer comprises a second antiferromagnetic layer. 
     
     
       11. The apparatus of  claim 9  wherein said magnetization reference layer further comprises a reference ferromagnetic thin-film layer provide between said antiferromagnetic layer and said source layer but separated from said source layer by an antiparallel magnetization directing layer forcing those magnetizations of said reference ferromagnetic thin-film layer and said source layer to be oppositely directed. 
     
     
       12. The apparatus of  claim 10  wherein said first magnetization reference layer farther comprises a first reference ferromagnetic thin-film layer provide between said first antiferromagnetic layer and said first source layer but separated from said first source layer by a first antiparallel magnetization directing layer forcing those magnetizations of said first reference ferromagnetic thin-film layer and said first source layer to be oppositely directed, and a second reference ferromagnetic thin-film layer provide between said second antiferromagnetic layer and said second source layer but separated from said second source layer by a second antiparallel magnetization directing layer forcing those magnetizations of said second reference ferromagnetic thin-film layer and said second source layer to be oppositely directed. 
     
     
       13. The device of  claim 1  wherein said substrate further comprises a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to one of said electrodes. 
     
     
       14. The device of  claim 2  wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       15. The device of  claim 2  wherein said source layer is of a ferromagnetic material and further comprising a magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction. 
     
     
       16. The device of  claim 6  wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction. 
     
     
       17. The device of  claim 6  wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       18. The device of  claim 9  further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell. 
     
     
       19. The device of  claim 10  further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell. 
     
     
       20. The device of  claim 11  wherein said source layer and said reference ferromagnetic thin-film layer are of unequal thicknesses. 
     
     
       21. The device of  claim 12  wherein said first source layer and said first reference ferromagnetic thin-film layer are of unequal thicknesses, and said second source layer and said second reference ferromagnetic thin-film layer are of unequal thicknesses. 
     
     
       22. The device of  claim 15  wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       23. The device of  claim 16  wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       24. The device of  claim 18  wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout. 
     
     
       25. The device of  claim 19  wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said first magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout. 
     
     
       26. A ferromagnetic thin-film based digital memory cell, said memory cell comprising:
 a substrate; and 
 a bit structure formed of a plurality of layers provided in a selected sequence between a pair of electrodes in electrical contact therewith at opposite ends of said sequence and supported on said substrate comprising:
 an electrically insulative intermediate layer; 
 a source layer on one side of said insulative intermediate layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation; 
 a memory film of an anisotropic ferromagnetic material on another side of said insulative intermediate layer capable of conducting an electrical current therethrough; and 
 an antiparallel maintenance layer adjacent to a ferromagnetic material layer together on a side of at least one of said source layer and said memory film across from said intermediate layer. 
 
 
     
     
       27. The device of  claim 26  wherein said substrate further comprises a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to one of said electrodes. 
     
     
       28. The device of  claim 26  wherein said source layer is a first source layer and said memory film is a first memory film, and further comprises a second memory film of an anisotropic ferromagnetic material positioned on an opposite side of said antiparallel maintenance layer from said first memory film and capable of conducting an electrical current therethrough, and a second source layer positioned on an opposite side of said second memory film from said anti-parallel maintenance layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation. 
     
     
       29. The device of  claim 26  wherein a said memory film and said source layer have a length along a selected direction and a width substantially perpendicular thereto that is smaller in extent than said length and have a shaped end portion extending over a portion of said length in which said width gradually reduces to zero at that corresponding end thereof. 
     
     
       30. The device of  claim 26  wherein said source layer is of a ferromagnetic material and further comprising magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction. 
     
     
       31. The device of  claim 26  wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       32. The device of  claim 28  wherein said electrically insulative intermediate layer is a first electrically insulative intermediate layer, and further comprising a second electrically insulative intermediate layer provided between said second source layer and said second memory film. 
     
     
       33. The device of  claim 28  wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction. 
     
     
       34. The apparatus of  claim 30  wherein said magnetization reference layer comprises an antiferromagnetic layer. 
     
     
       35. The device of  claim 30  wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       36. The device of  claim 32  wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       37. The device of  claim 32  wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction. 
     
     
       38. The apparatus of  claim 33  wherein said first magnetization reference layer comprises a first antiferromagnetic layer, and said second magnetization reference layer comprises a second antiferromagnetic layer. 
     
     
       39. The device of  claim 34  further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell. 
     
     
       40. The device of  claim 37  wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       41. The device of  claim 38  further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell. 
     
     
       42. The device of  claim 39  wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout. 
     
     
       43. The device of  claim 41  wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said first magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout. 
     
     
       44. A ferromagnetic thin-film based digital memory cell, said memory cell comprising:
 a substrate; and 
 a bit structure formed of a plurality of layers provided in a selected sequence between a pair of electrodes in electrical contact therewith at opposite ends of said sequence and supported on said substrate comprising:
 an electrically conductive intermediate layer; 
 a source layer on one side of said conductive intermediate layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation; 
 a memory film of an anisotropic ferromagnetic material on another side of said conductive intermediate layer capable of conducting an electrical current therethrough, and 
 an antiparallel maintenance layer adjacent to a ferromagnetic material layer together on a side of at least one of said source layer and said memory film across from said intermediate layer. 
 
 
     
     
       45. The device of  claim 44  wherein said substrate further comprises a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to one of said electrodes. 
     
     
       46. The device of  claim 44  wherein said source layer is a first source layer and said memory film is a first memory film, and further comprises a second memory film of an anisotropic ferromagnetic material positioned on an opposite side of said antiparallel maintenance layer from said first memory film and capable of conducting an electrical current therethrough, and a second source layer positioned on an opposite side of said second memory film from said anti-parallel m aintenance layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation. 
     
     
       47. The device of  claim 44  wherein a said memory film and said source layer have a length along a selected direction and a width substantially perpendicular thereto that is smaller in extent than said length and have a shaped end portion extending over a portion of said length in which said width gradually reduces to zero at that corresponding end thereof. 
     
     
       48. The device of  claim 44  wherein said source layer is of a ferromagnetic material and further comprising magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction. 
     
     
       49. The device of  claim 46  further comprising an electrically insulative intermediate layer provided between said second source layer and said second memory film. 
     
     
       50. The device of  claim 46  wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction. 
     
     
       51. The apparatus of  claim 48  wherein said magnetization reference layer comprises an antiferromagnetic layer. 
     
     
       52. The device of  claim 49  wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       53. The device of  claim 49  wherein said source layer is of a ferromagnetic material and further comprising magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction. 
     
     
       54. The apparatus of  claim 50  wherein said first magnetization reference layer comprises a first antiferromagnetic layer, and said second magnetization reference layer comprises a second antiferromagnetic layer. 
     
     
       55. The device of  claim 51  further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell. 
     
     
       56. The device of  claim 53  wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω-μm 2 . 
     
     
       57. The device of  claim 54  further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell. 
     
     
       58. The device of  claim 55  wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout. 
     
     
       59. The device of  claim 57  wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said first magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout. 
     
     
       60. The device of claim 1, wherein when a write current flows through the bit structure between the pair of electrodes, the electrical current conducted through the memory film is capable of reorienting magnetization of the memory film by spin momentum transfer.  
     
     
       61. The device of claim 60, wherein the source layer is part of a first synthetic antiferromagnet (SAF), wherein the memory film and the disruption layer are part of a second synthetic antiferromagnet (SAF), and wherein the source layer and the memory film are separated by a spacer layer.  
     
     
       62. The device of claim 61, wherein the spacer layer comprises an electrically insulative layer.  
     
     
       63. The device of claim 62, wherein the source layer has a fixed magnetization.  
     
     
       64. The device of claim 63, and further comprising an antiferromagnetic layer in contact with the first SAF.  
     
     
       65. The device of claim 60, wherein the source layer has a fixed magnetization.  
     
     
       66. The device of claim 65, wherein the write current has a current density and polarization that are large enough to switch magnetization direction of the memory film.  
     
     
       67. The device of claim 66, wherein the current density is at least about 10 7  amps/cm 2 .  
     
     
       68. The device of claim 60, wherein the disruption layer is a ruthenium layer.  
     
     
       69. The device of claim 1, wherein the bit structure is configured to allow magnetization of the memory film to change direction due to spin momentum transfer when a write current is passed through the bit structure.  
     
     
       70. The device of claim 69, wherein the source layer is part of a first synthetic antiferromagnet (SAF), wherein the memory film and the disruption layer are part of a second synthetic antiferromagnet (SAF), and wherein the source layer and the memory film are separated by a spacer layer.  
     
     
       71. The device of claim 69, wherein the spacer layer comprises an electrically insulative layer.  
     
     
       72. The device of claim 71, wherein the source layer has a fixed magnetization.  
     
     
       73. The device of claim 72, and further comprising an antiferromagnetic layer in contact with the first SAF.  
     
     
       74. The device of claim 69, wherein the source layer has a fixed magnetization.  
     
     
       75. The device of claim 69, wherein the write current has a current density and polarization that are large enough to switch magnetization direction of the memory film.  
     
     
       76. The device of claim 69, wherein the current density is at least about 10 7  amps/cm 2 .  
     
     
       77. The device of claim 69, wherein the disruption layer is a ruthenium layer.  
     
     
       78. The device of claim 1, wherein the memory film is capable of switching magnetization direction in response to spin momentum transfer from electrons having the selected spin orientation that pass through the memory film.  
     
     
       79. The device of claim 1, wherein magnetization direction of the memory film is changed by spin momentum transfer by electrical current from the source layer passing through the memory film.  
     
     
       80. The device of claim 1, wherein the electrical contacts apply a write current through the bit structure that causes magnetization of the memory film to switch by spin momentum transfer.  
     
     
       81. The device of claim 1, wherein the electrodes apply a write current through the bit structure to affect a direction of magnetization of the memory film.  
     
     
       82. The device of claim 81, wherein the write current has a current density and polarization that are large enough to switch magnetization direction of the memory film.  
     
     
       83. The device of claim 82, wherein the current density is at least about 10 7  amps/cm 2 .  
     
     
       84. The device of claim 26, wherein when a write current flows through the bit structure between the pair of electrodes, the electrical current conducted through the memory film is capable of reorienting magnetization of the memory film by spin momentum transfer.  
     
     
       85. The device of claim 84, wherein the source layer is part of a first synthetic antiferromagnet (SAF), and wherein the memory film and the disruption layer are part of a second synthetic antiferromagnet (SAF).  
     
     
       86. The device of claim 85, wherein the source layer has a fixed magnetization.  
     
     
       87. The device of claim 86, and further comprising an antiferromagnetic layer in contact with the first SAF.  
     
     
       88. The device of claim 84, wherein the source layer has a fixed magnetization.  
     
     
       89. The device of claim 88, wherein the write current has a current density and polarization that are large enough to switch magnetization direction of the memory film.  
     
     
       90. The device of claim 89, wherein the current density is at least about 10 7  amps/cm 2 .  
     
     
       91. The device of claim 84, wherein the disruption layer is a ruthenium layer.  
     
     
       92. The device of claim 26, wherein the bit structure is configured to allow magnetization of the memory film to change direction due to spin momentum transfer when a write current is passed through the bit structure.  
     
     
       93. The device of claim 92, wherein the source layer is part of a first synthetic antiferromagnet (SAF), and wherein the memory film and the disruption layer are part of a second synthetic antiferromagnet (SAF).  
     
     
       94. The device of claim 93, wherein the source layer has a fixed magnetization.  
     
     
       95. The device of claim 94, and further comprising an antiferromagnetic layer in contact with the first SAF.  
     
     
       96. The device of claim 92, wherein the source layer has a fixed magnetization.  
     
     
       97. The device of claim 96, wherein the write current has a current density and polarization that are large enough to switch magnetization direction of the memory film.  
     
     
       98. The device of claim 97, wherein the current density is at least about 10 7  amps/cm 2 .  
     
     
       99. The device of claim 92, wherein the disruption layer is a ruthenium layer.  
     
     
       100. The device of claim 26, wherein the memory film is capable of switching magnetization direction in response to spin momentum transfer from electrons having the selected spin orientation that pass through the memory film.  
     
     
       101. The device of claim 26, wherein magnetization direction of the memory film is changed by spin momentum transfer by electrical current from the source layer passing through the memory film.  
     
     
       102. The device of claim 26, wherein the electrical contacts apply a write current through the bit structure that causes magnetization of the memory film to switch by spin momentum transfer.  
     
     
       103. The device of claim 26, wherein the electrodes apply a write current through the bit structure to affect a direction of magnetization of the memory film.  
     
     
       104. The device of claim 26, wherein the write current has a current density and polarization that are large enough to switch magnetization direction of the memory film.  
     
     
       105. The device of claim 26, wherein the current density is at least about 10 7  amps/cm 2 .