Compensating non-volatile storage using different pass voltages during program-verify and read
First Claim
1. A method for operating non-volatile storage, comprising:
- programming at least one selected storage element in a set of storage elements, including performing a verify operation which involves applying a verify voltage to a control gate of the at least one selected storage element while applying a first pass voltage to respective control gates of unselected storage elements which are connected in series with the at least one selected storage element and which are in an unprogrammed or only partly programmed state;
programming the unselected storage elements; and
reading the at least one selected storage element, including applying a read compare voltage to the control gate of the at least one selected storage element while applying a second pass voltage, lower than the first pass voltage, to the unselected storage elements, the at least one selected storage element and the unselected storage elements are provided in a NAND string.
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Accused Products
Abstract
Optimized verify and read pass voltages are obtained to improve read accuracy in a non-volatile storage device. The optimized voltages account for changes in unselected storage element resistance when the storage elements become programmed. This change in resistance is referred to as a front pattern effect. In one approach, the verify pass voltage is higher than the read pass voltage, and a common verify voltage is applied on the source and drain sides of a selected word line. In other approaches, different verify pass voltages are applied on the source and drain sides of the selected word line. An optimization process can include determining a metric for different sets of verify and read pass voltages. The metric can indicate threshold voltage width, read errors or a decoding time or number of iterations of an ECC decoding engine.
47 Citations
18 Claims
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1. A method for operating non-volatile storage, comprising:
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programming at least one selected storage element in a set of storage elements, including performing a verify operation which involves applying a verify voltage to a control gate of the at least one selected storage element while applying a first pass voltage to respective control gates of unselected storage elements which are connected in series with the at least one selected storage element and which are in an unprogrammed or only partly programmed state; programming the unselected storage elements; and reading the at least one selected storage element, including applying a read compare voltage to the control gate of the at least one selected storage element while applying a second pass voltage, lower than the first pass voltage, to the unselected storage elements, the at least one selected storage element and the unselected storage elements are provided in a NAND string. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for operating non-volatile storage, comprising:
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programming at least one selected storage element in a set of storage elements, including performing a verify operation which involves applying a verify voltage to a control gate of the at least one selected storage element while applying a first pass voltage to respective control gates of unselected storage elements which are connected in series with the at least one selected storage element and which are in a programmed state; reading the at least one selected storage element, including applying a read compare voltage to the control gate of the at least one selected storage element while applying a second pass voltage, lower than the first pass voltage, to the unselected storage elements; and during the verify operation and the reading of the at least one selected storage element, applying a common pass voltage to respective control gates of the unselected storage elements.
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10. A method for operating non-volatile storage, comprising:
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programming a first selected storage element in a NAND string, including performing a verify operation which involves applying a verify voltage to a control gate of the first selected storage element while applying a first common pass voltage to respective control gates of unselected storage elements in the NAND string on source and drain sides of the first selected storage element; subsequently programming a second selected storage element in the NAND string, including performing a verify operation which involves applying a verify voltage to a control gate of the second selected storage element while applying the first common pass voltage to respective control gates of unselected storage elements in the NAND string on source and drain sides of the second selected storage element; reading the first selected storage element, including applying a read compare voltage to the control gate of the first selected storage element while applying a second common pass voltage, lower than the first common pass voltage, to respective control gates of unselected storage elements in the NAND string on source and drain sides of the first selected storage element; and reading the second selected storage element, including applying a read compare voltage to the control gate of the second selected storage element while applying the second common pass voltage to respective control gates of unselected storage elements in the NAND string on source and drain sides of the second selected storage element, the NAND string has n storage elements arranged between a source side select gate and a drain side select gate, the first storage element is within n/4 storage elements of the source side select gate and the second storage element is within n/4 storage elements of the drain side select gate. - View Dependent Claims (11)
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12. A method for operating non-volatile storage, comprising:
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programming at least one selected storage element in a set of storage elements, including performing a verify operation which involves applying a verify voltage to a control gate of the at least one selected storage element while applying a first pass voltage to respective control gates of unselected storage elements which are connected in series with the at least one selected storage element and which are in a programmed state; reading the at least one selected storage element, including applying a read compare voltage to the control gate of the at least one selected storage element while applying a second pass voltage, lower than the first pass voltage, to the unselected storage elements; determining an optimized value for a difference between the first and second pass voltages; and setting the first and second pass voltages based on the optimized difference. - View Dependent Claims (13, 14)
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15. A method for operating non-volatile storage, comprising:
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programming at least one selected storage element in a set of storage elements, including performing a verify operation which involves applying a verify voltage to a control gate of the at least one selected storage element while applying a first pass voltage to respective control gates of unselected storage elements which are connected in series with the at least one selected storage element and which are in a programmed state and while applying a second pass voltage, lower than the first pass voltage, to respective control gates of additional unselected storage elements which are connected in series with the at least one selected storage element and which are in an unprogrammed or only partly programmed state; programming the additional unselected storage elements; and reading the at least one selected storage element, including applying a read compare voltage to the control gate of the at least one selected storage element while applying the second pass voltage to the unselected storage elements and to the additional unselected storage elements. - View Dependent Claims (16, 17)
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18. A non-volatile storage system, comprising:
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a set of storage elements comprising a NAND string, the NAND comprising at least one selected storage element and unselected storage elements which are connected in series with the at least one selected storage element and which are in an unprogrammed or only partly programmed state; and one or more managing circuits, the one or more managing circuits; to program the at least one selected storage element, perform a verify operation which involves applying a verify voltage to a control gate of the at least one selected storage element while applying a first pass voltage to respective control gates of the unselected storage elements; program the unselected storage elements; and to read the at least one selected storage element, apply a read compare voltage to the control gate of the at least one selected storage element while applying a second pass voltage, lower than the first pass voltage, to the unselected storage elements.
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Specification