Nanowire magnetic random access memory
View Patent ↗An integrated array of non volatile magnetic memory devices, each having a first magnetic layer ( 10 ) with a fixed magnetization direction; a free magnetic layer ( 20 ) with a changeable magnetization direction; a spacer layer ( 30 ) separating the first magnetic layer and the free magnetic layer, and a switch ( 40 ) for selecting the device, the layers and at least part of the switch being formed as a columnar structure such as a nanowire. The switch is preferably formed integrally with the columnar nano-structure. By incorporating the switch in the columnar structure with the magnetic layers, the device can be made smaller to enable greater integration. This can be applied to magnetic devices using external fields or those using only fields generated in the columnar structure. A write current can be coupled along the columnar structure in a forward or reverse direction to alter the direction of magnetization of the free magnetic layer according to the direction of the current.
1. A magnetic device comprising:
at least one nanotube forming a columnar structure including
a first magnetic layer with a fixed magnetization direction;
a free magnetic layer with a changeable magnetization direction; and
a spacer layer separating the first magnetic layer and the free magnetic layer; and
a selection device for selecting the magnetic device, at least part of the selection device being part of the columnar structure.
2. The magnetic device of claim 1 wherein at least two of the magnetic layers comprise diluted magnetic semiconductor material of one of the at least one nanotube having dopants that respectively form the at least two magnetic layers.
3. The magnetic device of claim 1 , the selection device comprising a switch.
4. The magnetic device of claim 3 , wherein the switch is a transistor.
5. The magnetic device of claim 4 , wherein the at least part of the selection device comprises a channel of a transistor.
6. The magnetic device of claim 5 , having a gate electrode around the channel and separated from the channel by a gate dielectric.
7. The magnetic device of claim 1 , the at least part of the selection device being located at one end of the columnar structure.
8. The magnetic device of claim 1 , having a gate dielectric layer surrounding the columnar structure.
9. The magnetic device of claim 1 , the free magnetic layer being thinner than the first magnetic layer.
10. The magnetic device of claim 1 , the thickness of the spacer layer being arranged such that the free magnetic layer is within a spin flip length of majority carriers of the first magnetic layer.
11. The magnetic device of claim 1 , the columnar structure comprising n-type dopant atoms.
12. The magnetic device of claim 1 , having a second magnetic layer with a fixed magnetization direction in a different direction to that of the first magnetic layer.
13. The magnetic device of claim 1 , arranged as a memory and having circuitry arranged to couple a current along the columnar structure with sufficient spin polarized current density to alter the direction of magnetization of the free magnetic layer.
14. The magnetic device of claim 1 , arranged as a memory and having circuitry to couple a current along the columnar structure in a forward or reverse direction for writing the memory with a value according to the direction of the current.
15. The magnetic device of claim 1 , at least part of the columnar structure being tubular.
16. An integrated memory array having a substrate and an array of the magnetic devices of claim 1 , the columnar structure in each magnetic device being arranged perpendicular to the substrate.
17. The array of claim 16 , having a first select line coupling the switches of the devices in a row of the array, and a second select line for coupling a top or bottom of the columnar structure of magnetic devices in different rows.
18. The magnetic device of claim 1 , the respective layers and a channel region of the selection device being part of a nanotube that forms a semiconducting nanowire extending along a length of the columnar structure and having doped regions that respectively form the channel region and the magnetic layers.
19. The magnetic device of claim 1 , wherein junctions in the columnar structure with each of the first magnetic layer, the free magnetic layer and the spacer layer are homogeneous regions of the at least one nanotube.
20. The magnetic device of claim 1 , wherein junctions in the columnar structure with each of the first magnetic layer, the free magnetic layer and the spacer layer are devoid of heterogeneous regions.
21. The magnetic device of claim 1 , wherein at least two of the first magnetic layer, free magnetic layer, spacer layer and selection device include regions that
are immediately adjacent one another, and
include nanotubes that form part of both of the immediately adjacent regions.
22. The magnetic device of claim 1 , wherein the selection device includes
a channel region in the at least one nanotube between the free magnetic layer and an electrode,
a dielectric material on the channel region, and
a gate separated from the channel region by the dielectric material and configured to apply a bias to the channel region to switch the channel region between conductive states for connecting the free magnetic layer to the electrode.
23. A magnetic memory device comprising:
a column of semiconducting nanowires connected between upper and lower electrodes, the column including
over the lower electrode, a fixed magnetic layer having a fixed magnetization direction,
a free magnetic layer over the fixed magnetic layer and having a magnetization direction that is changeable between the fixed magnetization direction and an opposite magnetization direction that is opposite the fixed magnetization direction, the respective magnetization directions corresponding to logic states,
a spacer layer that separates the fixed and free magnetic layers,
a channel region that connects the free magnetic layer with the upper electrode;
a switch having a gate separated from the channel region by a dielectric material and configured to connect the free magnetic layer to the upper electrode for read and write operations by switching the channel region between conductive states;
a write circuit configured to set the magnetization direction of the free magnetic layer to the fixed magnetization direction by applying a high voltage write current across the electrodes in the fixed magnetization direction, and to set the magnetization direction of the free magnetic layer to the opposite magnetization direction by applying a high voltage write current across the electrodes in a direction that is opposite the fixed magnetization direction; and
a read circuit configured to apply a low read voltage across the electrodes, the column being responsive to the low read voltage by passing a high current level when the free magnetic layer has the fixed magnetization direction, and by passing a low current level when the free magnetic layer has the opposite magnetization direction.