Method for sensing negative threshold voltages in non-volatile storage using current sensing
View Patent ↗Current sensing is performed in a non-volatile storage device for a selected non-volatile storage element with a negative threshold voltage. A control gate read voltage is applied to a selected word line of a non-volatile storage element, and source and p-well voltages are applied to a source and a p-well, respectively, associated with the non-volatile storage element. The source and p-well voltages exceed the control gate read voltage so that a positive control gate read voltage can be used. There is no need for a negative charge pump to apply a negative word line voltage even for sensing a negative threshold voltage. A programming condition of the non-volatile storage element is determined by sensing a voltage drop which is tied to a fixed current which flows in a NAND string of the non-volatile storage element.
1. A method for operating a non-volatile storage system, comprising:
applying a first voltage to a selected word line which is associated with at least a first non-volatile storage element, the at least a first non-volatile storage element being provided in a set of non-volatile storage elements;
applying source and p-well voltages to a source and a p-well, respectively, which are associated with the at least a first non-volatile storage element during at least a portion of a time in which the first voltage is applied, the source and p-well voltages exceed the first voltage; and
determining whether the at least a first non-volatile storage element is in a conductive state or a non-conductive state using current sensing while applying the first voltage and the source and p-well voltages.
2. The method of claim 1 , wherein:
during the current sensing, a fixed current flows through the at least a first non-volatile storage element and sinks into the source when the at least a first non-volatile storage element is in the conductive state.
3. The method of claim 1 , wherein:
the using the current sensing comprises determining a voltage drop which is proportional to a fixed current which flows through the at least a first non-volatile storage element and sinks into the source when the at least a first non-volatile storage element is in the conductive state.
4. The method of claim 1 , wherein:
regulating the source and p-well voltages to respective fixed DC levels during the applying of the source and p-well voltages.
5. The method of claim 1 , wherein:
regulating the source and p-well voltages to a common fixed DC level during the applying of the source and p-well voltages.
6. The method of claim 1 , wherein:
the at least a first non-volatile storage element is in a NAND string and the source voltage is applied to a source side of the NAND string.
7. The method of claim 1 , wherein:
the first, source and p-well voltages are positive and the at least a first non-volatile storage element has a negative threshold voltage.
8. The method of claim 1 , wherein the selected word line, the source and the p-well are associated with a plurality of adjacent non-volatile storage elements which include the at least a first non-volatile storage element, the method further comprising:
determining, concurrently, whether the plurality of non-volatile storage elements are in the conductive state or the non-conductive state using current sensing while applying the first voltage and the source and p-well voltages.
9. A method for operating a non-volatile storage system, comprising:
providing a potential of a drain associated with at least a first non-volatile storage element above a potential of a source associated with the at least a first non-volatile storage element;
applying positive voltages to the source and to a p-well associated with the at least a first non-volatile storage element while applying a positive voltage to a word line associated with the at least a first non-volatile storage element, a level of the voltage applied to the word line is less than levels of the voltages applied to the source and p-well;
while applying the voltages to the source, p-well and word line, performing current sensing with respect to a level of a current which flows through the at least a first non-volatile storage element and sinks into the source; and
determining a programming condition of the at least a first non-volatile storage element according to the sensing.
10. The method of claim 9 , wherein:
the current sensing comprises determining a voltage drop which is proportional to the level of the current when the current is fixed.
11. The method of claim 9 , wherein:
the programming condition is defined with respect to a negative threshold voltage.
12. The method of claim 11 , further comprising:
applying different voltages to the source, p-well and word line for performing the current sensing when the negative threshold voltage is at different levels, the voltages applied to the source and p-well exceed the voltage applied to the word line for each different level of the negative threshold voltage.
13. The method of claim 9 , wherein:
the at least a first non-volatile storage element is in a NAND string, the source comprises a source side of the NAND string, and the p-well comprises a p-well of the NAND string.
14. The method of claim 9 , wherein the selected word line, the source and the p-well are associated with a plurality of adjacent non-volatile storage elements which include the at least a first non-volatile storage element, the method further comprising:
determining, concurrently, whether the plurality of non-volatile storage elements are in the conductive state or the non-conductive state using current sensing while applying the first voltage and the source and p-well voltages.
15. A method for operating a non-volatile storage system, comprising:
in a first sensing operation:
applying a first voltage to a control gate of at least a first non-volatile storage element, the at least a first non-volatile storage element being provided in a set of non-volatile storage elements;
applying a source voltage to a source which is associated with the at least a first non-volatile storage element during at least a portion of a time in which the first voltage is applied, the source voltage exceeds the first voltage; and
determining whether the at least a first non-volatile storage element is in a conductive state or a non-conductive state using current sensing while applying the first voltage and the source voltage; and
in a second sensing operation:
applying a second voltage to the control gate of the at least a first non-volatile storage element;
applying the source voltage to the source during at least a portion of a time in which the second voltage is applied; and
determining whether the at least a first non-volatile storage element is in a conductive state or a non-conductive state using current sensing while applying the second voltage and the source voltage.
16. The method of claim 15 , further comprising:
applying a p-well voltage to a p-well which is associated with the at least a first non-volatile storage element during at least a portion of a time in which the first voltage is applied, and during at least a portion of a time in which the second voltage is applied.
17. The method of claim 15 , wherein:
the at least a first non-volatile storage element is in a NAND string, the source comprises a source side of the NAND string, and the p-well comprises a p-well of the NAND string.
18. The method of claim 15 , wherein:
the first and second sensing operations are part of read or verify operations.
19. The method of claim 15 , further comprising:
during the current sensing of the first and second sensing operations, a fixed current flows through the at least a first non-volatile storage element and sinks into the source when the at least a first non-volatile storage element is in the conductive state.