Non-volatile storage system biasing conditions for standby and first read
Methods for reducing power consumption of a non-volatile storage system and reducing first read latency are described. The non-volatile storage system may include a cross-point memory array. In some embodiments, during a standby mode, the memory array may be biased such that both word lines and bit lines are set to ground. During transition of the memory array from the standby mode to a read mode, a selected word line comb may be set to a read voltage while the unselected word lines and the bit lines remain at ground. During the read mode, memory cells connected to the selected bit lines and the selected word line comb may be sensed while the selected bit lines are biased to a selected bit line voltage equal to or close to ground and the unselected bit lines are left floating after initially being set to ground.
1. A method for operating a non-volatile storage system, comprising:
setting a plurality of word lines associated with a memory array to an unselected voltage, the memory array comprises a cross-point memory array including a plurality of rewriteable non-volatile memory cells;
setting a plurality of bit lines associated with the memory array to the unselected voltage;
determining a selected bit line of the plurality of bit lines and a plurality of unselected bit lines of the plurality of bit lines;
determining a selected word line of the plurality of word lines and a plurality of unselected word lines of the plurality of word lines;
floating the plurality of unselected bit lines subsequent to the setting a plurality of bit lines associated with the memory array to the unselected voltage;
setting the selected bit line to a selected bit line voltage;
setting the selected word line to a read voltage greater than the selected bit line voltage;
determining a state of a memory cell connected to the selected word line and the selected bit line while setting the selected word line to the read voltage and floating the plurality of unselected bit lines; and
outputting the state of the memory cell.
2. The method of claim 1 , wherein:
each memory cell of the plurality of rewriteable non-volatile memory cells includes a reversible resistance-switching element without an isolation element in series with the reversible resistance-switching element.
3. The method of claim 1 , further comprising:
determining if a first period of time has occurred since a last read operation was performed on the memory array; and
placing a plurality of word line drivers connected to the plurality of word lines into a current limited state if the first period of time has occurred since the last read operation was performed on the memory array.
4. The method of claim 3 , wherein:
the first period of time is set based on a temperature associated with the memory array.
5. The method of claim 3 , wherein:
the placing a plurality of word line drivers connected to the plurality of word lines into a current limited state includes placing a current limiting transistor between an on-chip power supply and a local power supply connected to the plurality of word line drivers.
6. The method of claim 1 , further comprising:
determining if a first period of time has occurred since a last read command was received by the non-volatile storage system; and
placing a plurality of bit line drivers connected to the plurality of bit lines into a current limited state if the first period of time has occurred since the last read command was received by the non-volatile storage system.
7. The method of claim 6 , wherein:
the first period of time is set based on a temperature associated with the memory array.
8. The method of claim 6 , wherein:
the selected bit line voltage is the unselected voltage.
9. The method of claim 1 , wherein:
the determining a state of a memory cell includes sensing a current through the memory cell using sensing circuitry when the selected bit line is biased to the selected bit line voltage and the selected word line is biased to the read voltage.
10. The method of claim 9 , wherein:
the sensing circuitry level shifts a voltage of the selected bit line using a PMOS source follower.
11. The method of claim 9 , wherein:
the sensing circuitry includes a pair of cross-coupled NMOS devices, a source of a first NMOS device of the pair is connected to a reference voltage and a source of a second NMOS device of the pair is connected to the selected bit line.
12. The method of claim 1 , wherein:
the plurality of word lines comprises a plurality of word line combs; and
the plurality of bit lines are arranged orthogonal to a semiconductor substrate.
13. The method of claim 1 , wherein:
the memory array comprises a three-dimensional memory array.
14. A non-volatile storage system, comprising:
a memory array, the memory array includes a plurality of word lines and a plurality of bit lines, the memory array comprises a cross-point memory array including a plurality of rewriteable non-volatile memory cells, each memory cell of the plurality of rewriteable non-volatile memory cells includes a reversible resistance-switching element without an isolation element in series with the reversible resistance-switching element; and
one or more managing circuits in communication with the memory array, the one or more managing circuits configured to determine a selected bit line of the plurality of bit lines and a plurality of unselected bit lines of the plurality of bit lines, the one or more managing circuits configured to determine a selected word line of the plurality of word lines, the one or more managing circuits configured to float the plurality of unselected bit lines and set the selected bit line to a selected bit line voltage, the one or more managing circuits configured to set the selected word line to a read voltage greater than the selected bit line voltage, the one or more managing circuits configured to determine a state of a memory cell connected to the selected word line and the selected bit line while the selected word line is set to the read voltage and the plurality of unselected bit lines are floated.
15. The non-volatile storage system of claim 14 , wherein:
the one or more managing circuits configured to determine if a first period of time has occurred since a last read operation was performed on the memory array, the one or more managing circuits configured to set a plurality of word line drivers connected to the plurality of word lines into a current limited state if the first period of time has occurred since the last read operation was performed on the memory array.
16. The non-volatile storage system of claim 14 , wherein:
the one or more managing circuits configured to determine if a first period of time has occurred since a last read command was received by the non-volatile storage system, the one or more managing circuits configured to set a plurality of bit line drivers connected to the plurality of bit lines into a current limited state if the first period of time has occurred since the last read command was received by the non-volatile storage system.
17. The non-volatile storage system of claim 14 , wherein:
the selected bit line voltage is the unselected voltage; and
the memory array comprises a three-dimensional memory array.
18. A method for operating a non-volatile storage system, comprising:
receiving a read command to read data from a memory array, the memory array includes a plurality of word lines and a plurality of bit lines, the memory array comprises a cross-point memory array including a plurality of rewriteable non-volatile memory cells, each memory cell of the plurality of rewriteable non-volatile memory cells includes a reversible resistance-switching element without an isolation element in series with the reversible resistance-switching element;
determining a selected bit line of the plurality of bit lines and a plurality of unselected bit lines of the plurality of bit lines based on the read command;
determining a selected word line of the plurality of word lines and a plurality of unselected word lines of the plurality of word lines based on the read command;
floating the plurality of unselected bit lines;
setting the selected bit line to a selected bit line voltage;
setting the selected word line to a read voltage greater than the selected bit line voltage;
determining a state of a memory cell connected to the selected word line and the selected bit line while setting the selected word line to the read voltage and floating the plurality of unselected bit lines; and
outputting the state of the memory cell.
19. The method of claim 18 , further comprising:
determining if a first period of time has occurred since the read command was received; and
placing a plurality of bit line drivers connected to the plurality of bit lines into a current limited state if the first period of time has occurred since the read command was received.
20. The method of claim 19 , wherein:
the first period of time is set based on a temperature associated with the memory array; and
the memory array comprises a three-dimensional memory array.