Mimicking program verify drain resistance in a memory device
First Claim
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1. A method for programming a non-volatile memory device, the method comprising:
- biasing a selected memory cell, in a series string of memory cells coupled between a source line and a bit line, with a program voltage;
biasing the selected memory cell with a program verify voltage during a verify operation; and
adjusting a drain resistance of the selected memory cell, during the verify operation, by biasing unselected memory cells of the series string of memory cells between the selected memory cell and a bit line with a modified Vpass voltage that produces an average drain resistance between the selected memory cell and the bit line that mimics a drain resistance of half of the unselected memory cells being programmed.
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Abstract
A selected word line is biased with a program verify voltage. A predetermined quantity of unselected word lines that are between the selected word line and the bit line are biased with a modified Vpass voltage that is determined in response to a predetermined drain resistance. In one embodiment, the predetermined quantity is all of the word lines. Other embodiments can use smaller quantities. The remaining unselected word lines are biased with a normal Vpass voltage. The modified Vpass changes the resistance of the memory cells, acting as pass-gates during the program verification operation, to mimic a resistance of already programmed memory cells.
56 Citations
20 Claims
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1. A method for programming a non-volatile memory device, the method comprising:
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biasing a selected memory cell, in a series string of memory cells coupled between a source line and a bit line, with a program voltage; biasing the selected memory cell with a program verify voltage during a verify operation; and adjusting a drain resistance of the selected memory cell, during the verify operation, by biasing unselected memory cells of the series string of memory cells between the selected memory cell and a bit line with a modified Vpass voltage that produces an average drain resistance between the selected memory cell and the bit line that mimics a drain resistance of half of the unselected memory cells being programmed. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method for programming a series string of memory cells in a non-volatile memory device, the method comprising:
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biasing a selected memory cell of the series string with a programming voltage; biasing the selected memory cell with a program verify voltage during a program verify operation; and adjusting a drain resistance between the selected memory cell and a bit line of the series string, during the program verify operation, by biasing the unselected memory cells between the selected memory cell and the bit line with a modified Vpass voltage that changes in response to a quantity of memory cells remaining between the selected memory cell and the bit line as the selected memory cell moves upward from a source line of the series string towards the bit line. - View Dependent Claims (9, 10, 11, 12)
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13. A method for programming a series string of non-volatile memory cells between a source line and a bit line, the method comprising:
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biasing a selected memory cell with a program voltage wherein the selected memory cell begins adjacent to the source line and moves upward through the series string to be adjacent to the bit line; and performing a program verify operation on the selected memory cell, after each program voltage, that comprises biasing the selected memory cell with a verify voltage and biasing a subgroup of unselected memory cells between the selected memory cell and the bit line with a modified Vpass voltage that is determined in response to a predetermined drain resistance wherein the subgroup of unselected memory cells is less than a number of memory cells between the selected memory cell and the bit line. - View Dependent Claims (14, 15)
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16. A NAND flash memory device comprising:
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a memory array comprising a plurality of memory cell series string columns each coupled between a source line and a bit line; and a memory control circuit coupled to the memory array and configured to generate a plurality of program pulses for biasing a selected memory cell, control a program verify operation between each program pulse wherein the program verify operation mimics an average drain resistance of a programmed quantity of memory cells between a selected memory cell and the bit line. - View Dependent Claims (17, 18, 19, 20)
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Specification