Multi-bit STRAM memory cells
View Patent ↗A multi-bit spin torque magnetic element that has a ferromagnetic pinned layer having a pinned magnetization orientation, a non-magnetic layer, and a ferromagnetic free layer having a magnetization orientation switchable among at least four directions, the at least four directions being defined by a physical shape of the free layer. The magnetic element has at least four distinct resistance states. Magnetic elements with at least eight magnetization directions are also provided.
1. A magnetic element comprising:
a ferromagnetic pinned layer having a pinned magnetization orientation;
a ferromagnetic free layer having a magnetization orientation switchable among at least four directions, the at least four directions defined by a physical shape of the free layer; and
a non-magnetic layer between the pinned layer and the free layer,
wherein the magnetic element is a spin-torque magnetic element that can be written to by a sufficient level of spin polarized current and has at least four distinct resistance states.
2. The magnetic element of claim 1 , wherein the at least four directions are 90 degrees apart.
3. The magnetic element of claim 1 , wherein the at least four directions are not 90 degrees apart.
4. The magnetic element of claim 1 , wherein the physical shape of the free layer has at least four arms, with one of the four directions extending between adjacent arms.
5. The magnetic element of claim 4 , wherein the at least four directions are 90 degrees apart.
6. The magnetic element of claim 4 , wherein the at least four directions are not 90 degrees apart.
7. The magnetic element of claim 4 , wherein the pinned layer magnetization orientation is between two adjacent of the at least four directions.
8. A method of affecting a resistance state of a magnetic element, the method comprising:
providing a magnetic element that comprises
a ferromagnetic pinned layer having a pinned magnetization orientation;
a ferromagnetic free layer having a magnetization orientation switchable among at least four directions, the at least four directions defined by a physical shape of the free layer; and
a non-magnetic layer between the pinned layer and the free layer,
wherein the magnetic element is a spin-torque magnetic element that can be written to by a sufficient level of spin polarized current and has at least four distinct resistance states; and
driving a current through the magnetic element in order to switch the resistance state of the magnetic element.
9. The method of claim 8 , wherein the current is driven from the ferromagnetic pinned layer to the ferromagnetic free layer.
10. The method of claim 9 , wherein the current is at least about 100 microAmps.
11. The method of claim 8 , wherein the current is driven from the ferromagnetic free layer to the ferromagnetic pinned layer.
12. The method of claim 8 further comprising determining the resistance state of the magnetic element by passing a current through the magnetic element.
13. The method of claim 12 , wherein the current for determining the resistance state is less than the current to switch the resistance state.
14. The method of claim 13 , wherein the current for determining the resistance is tens of microAmps.
15. A memory device comprising:
a magnetic element, the magnetic element comprising:
a ferromagnetic pinned layer having a pinned magnetization orientation;
a ferromagnetic free layer having a magnetization orientation switchable among at least four directions by a sufficient level of spin polarized current, the at least four directions defined by a physical shape of the free layer; and
a non-magnetic layer between the pinned layer and the free layer,
wherein the magnetic element is a spin-torque magnetic element and has at least four distinct resistance states;
a bit line; and
a source line,
wherein the magnetic element is electrically connected to the bit line and the source line.
16. The memory device of claim 15 , wherein the at least four directions are 90 degrees apart.
17. The memory device of claim 15 , wherein the at least four directions are not 90 degrees apart.
18. The memory device of claim 15 , wherein the physical shape of the free layer has at least four arms, with one of the four directions extending between adjacent arms.
19. The memory device of claim 18 , wherein the pinned layer magnetization orientation is between two adjacent of the at least four directions.
20. The memory device of claim 15 further comprising a controller electrically connected to the magnetic element and configured to apply current through the magnetic element to switch the resistance state of the magnetic element.