Apparatuses and methods for bi-directional access of cross-point arrays
The disclosed technology generally relates to apparatuses and methods of operating the same, and more particularly to cross point memory arrays and methods of accessing memory cells in a cross point memory array. In one aspect, an apparatus comprises a memory array. The apparatus further comprises a memory controller configured to cause an access operation, where the access operation includes application of a first bias across a memory cell of the memory array for a selection phase of the access operation and application of a second bias, lower in magnitude than the first bias, across the memory cell for an access phase of the access operation. The memory controller is further configured to cause a direction of current flowing through the memory cell to be reversed between the selection phase and the access phase.
1. An apparatus comprising:
a memory array comprising a memory cell; and
a memory controller configured to cause an access operation, the access operation comprising application of a first bias across the memory cell for a selection phase of the access operation and application of a second bias, lower in magnitude than the first bias, across the memory cell for an access phase of the access operation,
wherein the memory controller is further configured to cause a direction of current flowing through the memory cell to be reversed between the selection phase and the access phase.
2. The apparatus of claim 1 , wherein the memory cell is configured to threshold in response to application of the first bias.
3. The apparatus of claim 2 , wherein the memory controller is further configured to remove the first bias and cause a current flowing through the memory cell to fall below a minimum hold current to release the memory cell from a thresholded condition prior to application of the second bias.
4. The apparatus of claim 3 , wherein the memory controller is configured to apply the second bias after releasing the memory cell within less than about 5 microseconds.
5. The apparatus of claim 1 , wherein the memory controller is further configured to cause a snap-back discharge current to flow through the memory cell, prior to application of the second bias.
6. The apparatus of claim 1 , wherein the first bias has a first polarity and the second bias has a second polarity opposite to the first polarity.
7. The apparatus of claim 6 , wherein the memory cell is further configured to also threshold in response to application of the second bias.
8. The apparatus of claim 1 , wherein the memory array comprises a cross point memory array, and the memory cell comprises a selector element and a storage element electrically arranged in series.
9. The apparatus of claim 8 , wherein at least one of the selector element or the storage element comprises a chalcogenide material.
10. The apparatus of claim 9 , wherein the memory cell has a threshold voltage having a magnitude which depends on a time lapse from the memory cell being released from a previous thresholding event.
11. An apparatus comprising:
a memory array comprising a memory cell; and
a memory controller configured to cause an access operation, the access operation comprising application of a first bias across the memory cell for a selection phase of the access operation, removal of the first bias and application of a second bias subsequent to the first bias across the memory cell for an access phase of the access operation, wherein the second bias has a lower magnitude than the first bias and the first and second biases have opposite polarities.
12. The apparatus of claim 11 , wherein the memory cell is configured to threshold in response to application of the first bias.
13. An apparatus comprising:
a memory array comprising a memory cell; and
a memory controller configured to cause an access operation, the access operation comprising application of a first bias across the memory cell for a selection phase of the access operation, removal of the first bias and application of a second bias across the memory cell for an access phase of the access operation, the first and second biases having opposite polarities,
wherein the apparatus further comprises a deselection circuit configured to couple the memory cell to a first voltage during at least a portion of the selection phase and to couple the memory cell to a second voltage during at least a portion of the access phase.
14. The apparatus of claim 13 , wherein the controller is configured to cause the deselection circuit to switch from coupling the memory cell to the first voltage to coupling the memory cell to the second voltage during the access phase.
15. The apparatus of claim 13 , wherein the controller is configured to cause the deselection circuit to switch from coupling the memory cell to the first voltage to coupling the memory cell to the second voltage during the selection phase.
16. The apparatus of claim 13 , wherein the controller is configured to cause the deselection circuit to switch from coupling the memory cell to the first voltage to coupling the memory cell to the second voltage during the access phase and in response to detection of a snap back event.
17. The apparatus of claim 13 , wherein the controller is further configured to cause a current flowing through the memory cell to fall below a minimum hold current between the application of the first bias and application of the second bias.
18. The apparatus of claim 13 , wherein the deselection circuit comprises a column deselection circuit.
19. The apparatus of claim 13 , wherein the deselection circuit comprises a row deselection circuit.
20. The apparatus of claim 13 , further comprising a processor configured to send an access command to the memory controller, wherein the memory controller is configured to cause the access operation in response to receiving the access command.
21. A method of accessing a memory cell, the method comprising:
applying a first bias across the memory cell for a selection phase of an access operation and applying a second bias, lower in magnitude than the first bias, across the memory cell for an access phase of an access operation; and
reversing a direction of current flow between the selection phase and the access phase.
22. The method of claim 21 , wherein the memory cell thresholds in response to applying the first bias.
23. The method of claim 21 , further comprising releasing the memory cell from a thresholded condition prior to applying the second bias by removing the first bias and causing a current flowing through the memory cell to fall below a minimum hold current.
24. The method of claim 23 , further comprising applying the second bias within less than about 5 microseconds after releasing the memory cell from the thresholded condition.
25. The method of claim 21 , wherein applying the first bias causes a snap-back discharge current to flow through the memory cell.