Spin-transfer torque memory self-reference read method

1. A method of self-reference reading a magnetic tunnel junction data cell, comprising:

applying a read voltage across a magnetic tunnel junction data cell and forming a read current, the magnetic tunnel junction data cell having a first resistance state, the read voltage being sufficient to switch the magnetic tunnel junction data cell resistance;

detecting the read current; and

determining the resistance state of the magnetic tunnel junction data cell, wherein

if the read current remains constant during the applying step, then the first resistance state of the magnetic tunnel junction data cell is the resistance state that the read voltage was sufficient to switch the magnetic tunnel junction data cell to, and

if the read current changes during the applying step, then the first resistance state of the magnetic tunnel junction data cell is a second resistance state.

2. A method according to claim 1 , wherein the applying step has a time duration in a range from 0.1 to 50 nanoseconds.

3. A method according to claim 1 , wherein the applying step has a time duration in a range from 0.1 to 25 nanoseconds.

4. A method according to claim 1 , wherein the read voltage is sufficient to switch the magnetic tunnel junction data cell from a high resistance state to a low resistance state, and the first resistance state is the low resistance state and the second resistance state is the high resistance state.

5. A method according to claim 1 , wherein the read voltage is sufficient to switch the magnetic tunnel junction data cell from a low resistance state to a high resistance state, and the first resistance state is the high resistance state and the second resistance state is the low resistance state.

6. A method according to claim 1 , further comprising determining if the read current increases during the applying step, and if the read current increases during the applying step the first resistance state of the magnetic tunnel junction data cell is a high resistance state and the second resistance state is the low resistance state.

7. A method according to claim 6 , further comprising writing back the high resistance state to the magnetic tunnel junction data cell.

8. A method according to claim 1 , further comprising determining if the read current decreases during the applying step, and if the read current decreases during the applying step the first resistance state of the magnetic tunnel junction data cell is a low resistance state and the second resistance state is a high resistance state.

9. A method according to claim 8 , further comprising writing back the low resistance state to the magnetic tunnel junction data cell.

10. A method according to claim 1 , wherein the magnetic tunnel junction data cell is a spin-transfer torque magnetic tunnel junction data cell.

11. A method of self-reference reading a magnetic tunnel junction data cell, comprising:

applying a read current across a magnetic tunnel junction data cell and forming a read voltage, the magnetic tunnel junction data cell having a first resistance state, the read current being sufficient to switch the magnetic tunnel junction data cell resistance;

detecting the read voltage; and

determining if the read voltage remains constant during the applying step, wherein

if the read voltage remains constant during the applying step, then the first resistance state of the magnetic tunnel junction data cell is the resistance state that the read current was sufficient to switch the magnetic tunnel junction data cell to, and

if the read voltage changes during the applying step, then the first resistance state of the magnetic tunnel junction data cell is a second resistance state.

12. A method according to claim 11 , wherein the applying step has a time duration in a range from 0.1 to 50 nanoseconds.

13. A method according to claim 11 , wherein the read current is sufficient to switch the magnetic tunnel junction data cell from a high resistance state to a low resistance state, and the first resistance state is the low resistance state and the second resistance state is the high resistance state.

14. A method according to claim 11 , wherein the read current is sufficient to switch the magnetic tunnel junction data cell from a low resistance state to a high resistance state, and the first resistance state is the high resistance state and the second resistance state is the low resistance state.

15. A method according to claim 11 , further comprising determining if the read voltage decreases during the applying step, and if the read voltage decreases during the applying step the first resistance state of the magnetic tunnel junction data cell is a high resistance state and the second resistance state is a low resistance state.

16. A method according to claim 15 , wherein the read voltage decreases by more than 100 mV.

17. A method according to claim 15 , further comprising writing back the high resistance state to the magnetic tunnel junction data cell.

18. A method according to claim 11 , further comprising determining if the read voltage increases during the applying step, and if the read voltage increases during the applying step the first resistance state of the magnetic tunnel junction data cell is a low resistance state and the second resistance state is the high resistance state.

19. A method according to claim 18 , further comprising writing back the low resistance state to the magnetic tunnel junction data cell.

20. A method according to claim 11 , wherein the magnetic tunnel junction data cell is a spin-transfer torque magnetic tunnel junction data cell.