Reverse set with current limit for non-volatile storage
View Patent ↗A storage system includes a substrate, control circuitry on the substrate, a three dimensional memory array (above the substrate) that includes a plurality of reversible resistance-switching elements, and circuits for limiting the SET current for the reversible resistance-switching elements. The memory cell is SET in a reverse biased fashion.
1. A storage system, comprising:
a reversible resistance-switching memory cell that includes a steering element in series with reversible resistance-switching material;
a current limiting circuit;
a first control line in communication with the reversible resistance-switching memory cell;
a first selection circuit in communication with the first control line, the first selection circuit selectively provides a first signal to the reversible resistance-switching memory cell;
a second control line in communication with the reversible resistance-switching memory cell; and
a second selection circuit in communication with the second control line, the second selection circuit selectively connects the second control line to the current limiting circuit while the first selection circuit provides the first signal to the reversible resistance-switching memory cell to reverse bias the steering element beyond the steering element's reverse break down voltage and set the reversible resistance-switching material to a low resistance state.
2. The storage system of claim 1 , wherein:
the current limiting circuit includes a first node, a current mirror having an output at the first node and a comparator in communication with the first node; and
the first node is in communication with the second control line via the second selection circuit.
3. The storage system of claim 2 , wherein:
current into the first node from the second control line is indicative of current through the reversible resistance-switching memory cell;
the current mirror operates to mirror a reference current;
as current into the first node from the second control line approaches the reference current a voltage at the first node moves toward a reference voltage; and
the comparator compares the voltage at the first node with the reference voltage.
4. The storage system of claim 3 , wherein:
the current limiting circuit includes a switch in communication with and controlled by an output of the comparator to selectively assert a signal on the second control line to deselect the reversible resistance-switching memory cell from being subjected to a condition for setting the reversible resistance-switching memory cell to the low resistance state.
5. The storage system of claim 4 , wherein:
the reversible resistance-switching memory cell is associated with a current limit for an operation that sets the reversible resistance-switching memory cell to the low resistance state; and
the reference current is indicative of the current limit.
6. The storage system of claim 5 , wherein:
the reversible resistance-switching memory cell is non-volatile.
7. The storage system of claim 6 , further comprising:
an additional plurality of memory cells, the reversible resistance-switching memory cell and the additional plurality of memory cells comprise a monolithic three dimensional memory array.
8. The storage system of claim 1 , further comprising:
a read circuit in communication with the reversible resistance-switching memory cell.
9. The storage system of claim 1 , wherein:
the reversible resistance-switching memory cell is non-volatile.
10. The storage system of claim 1 , wherein:
the steering element is forward biased when the reversible resistance-switching material is reset to a high resistance state.
11. The storage system of claim 1 , wherein:
the steering element is a diode.
12. A method for operating a storage system, comprising:
setting a reversible resistance-switching nonvolatile storage memory cell to a low resistance state by reverse biasing the reversible resistance-switching nonvolatile storage memory cell, the reversible resistance-switching nonvolatile storage memory cell includes a steering element in series with reversible resistance-switching material, the reverse biasing the reversible resistance-switching nonvolatile storage memory cell provides a reverse bias to the steering element beyond the steering element's reverse break down voltage and sets the reversible resistance-switching material to the low resistance state; and
limiting current through the reversible resistance-switching nonvolatile storage memory cell using a current limiting circuit while setting the reversible resistance-switching material to the low resistance state.
13. The method of claim 12 , wherein setting the reversible resistance-switching nonvolatile storage memory cell to the low resistance state comprises:
biasing word lines and bit lines for a monolithic three dimensional memory array to a first voltage level, the monolithic three dimensional memory array includes the reversible resistance-switching nonvolatile storage memory cell as well as other reversible resistance-switching storage memory cell;
biasing a selected word line to at least a diode drop higher than the first voltage level; and
connecting a selected bit line to the current limiting circuit with a path to ground.
14. The method of claim 12 , wherein limiting current through the reversible resistance-switching nonvolatile storage memory cell comprises:
operating a current mirror connected to the selected bit line via a first node;
monitoring the voltage at the first node;
comparing the voltage at the first node to a reference voltage; and
applying a save voltage to the selected bit line when the voltage at the first node is at a predetermined level with respect to the reference voltage.
15. The method of claim 14 , wherein limiting current through the reversible resistance-switching nonvolatile storage memory cell further comprises:
disabling a reference current input for the current mirror when the voltage at the first node is at a predetermined level with respect to the reference voltage.
16. The method of claim 14 , wherein:
the current mirror includes a reference current input that is mirrored at an output of the current mirror, the reference current input is equal to a current limit for setting the reversible resistance-switching nonvolatile storage memory cell to the low resistance state.
17. The method of claim 12 , further comprising:
setting the reversible resistance-switching material to a high resistance state by forward biasing the diode.
18. The method of claim 12 , wherein:
the steering element is a diode.
19. A method for programming a reversible resistance-switching memory cell that includes a diode in series with reversible resistance-switching material, the method comprising:
setting the reversible resistance-switching material to a low resistance state including providing a first signal to a first terminal of the reversible resistance-switching memory cell and providing a second signal to a second terminal of the reversible resistance-switching memory cell to cause a current through the diode in a direction that is reverse of easiest current flow through the diode and that operates the diode in reverse break down; and
limiting current through the reversible resistance-switching memory cell, including the diode, using a current limiting circuit while setting the reversible resistance-switching material to the low resistance state.
20. The method of claim 19 , wherein setting the reversible resistance-switching material to the low resistance state comprises:
biasing word lines and bit lines for a monolithic three dimensional memory array to a first voltage level, the monolithic three dimensional memory array includes the reversible resistance-switching nonvolatile storage memory cell as well as other reversible resistance-switching storage memory cells;
biasing a selected word line to at least a diode drop higher than the first voltage level; and
connecting a selected bit line to the current limiting circuit with a path to ground.
21. The method of claim 19 , wherein limiting current through the reversible resistance-switching nonvolatile storage memory cell comprises:
operating a current mirror in communication with the reversible resistance-switching nonvolatile storage memory cell via a first node;
monitoring the voltage at the first node;
comparing the voltage at the first node to a reference voltage; and
asserting a signal on the second control line to deselect the reversible resistance-switching nonvolatile storage memory cell from being subjected to a condition for setting to the low resistance state.
22. The method of claim 21 , wherein limiting current through the reversible resistance-switching nonvolatile storage memory cell further comprises:
disabling the reference current input for the current mirror when the voltage at the first node is at a predetermined level with respect to the reference voltage.
23. A storage system, comprising:
a reversible resistance-switching memory cell that includes a steering element in series with reversible resistance-switching material;
a current limiting circuit;
a first control line in communication with the reversible resistance-switching memory cell;
a first selection circuit in communication with the first control line, the first selection circuit selectively provides a first signal to the reversible resistance-switching memory cell;
a second control line in communication with the reversible resistance-switching memory cell; and
a second selection circuit in communication with the second control line;
the second selection circuit selectively connects the second control line to the current limiting circuit while the first selection circuit provides the first signal to the reversible resistance-switching memory cell in order to reverse bias the steering element, operate the steering element in break down and set the reversible resistance-switching material to a low resistance state.