Selective slow programming convergence in a flash memory device
First Claim
1. A method for selectively slow programming convergence in a memory device comprising an array of memory cells having rows coupled by word lines and columns coupled by bit lines, the method comprising:
- increasing a threshold voltage for each of a plurality of memory cells; and
selectively biasing bit lines coupled to the plurality of memory cells such that a bit line is only biased when the threshold voltage of an associated memory cell reaches a first verify threshold voltage of two verify threshold voltages, the first verify threshold voltage being less than the second verify threshold voltage.
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Abstract
A plurality of memory cells are programmed with incrementally increased programming pulses applied to word lines to which the memory cells are coupled. After each pulse, a verify operation determines the threshold voltage for each cell. When the threshold voltage reaches a pre-verify threshold, only the bit line connected to that particular cell is biased with an intermediate voltage that slows down the change in the Vt of the cell. The other cells continue to be programmed at their normal pace. As the Vt for each cell reaches the pre-verify level, it is biased with the intermediate voltage. All of the bit lines are biased with an inhibit voltage as their threshold voltages reach the verify voltage threshold.
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Citations
24 Claims
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1. A method for selectively slow programming convergence in a memory device comprising an array of memory cells having rows coupled by word lines and columns coupled by bit lines, the method comprising:
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increasing a threshold voltage for each of a plurality of memory cells; and
selectively biasing bit lines coupled to the plurality of memory cells such that a bit line is only biased when the threshold voltage of an associated memory cell reaches a first verify threshold voltage of two verify threshold voltages, the first verify threshold voltage being less than the second verify threshold voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for selectively slow programming convergence in a flash memory device comprising a matrix of memory cells having rows coupled by word lines and columns coupled by bit lines, the method comprising:
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performing a programming operation on each of a plurality of memory cells;
performing a verify operation on each of the plurality of memory cells to determine its respective threshold voltage; and
selectively biasing bit lines coupled to the plurality of memory cells such that a bit line is only biased with a first bit line bias voltage when the threshold voltage of an associated memory cell reaches a first verify threshold voltage of two verify threshold voltages, the first verify threshold voltage being less then the second verify threshold voltage, the first bit line bias voltage being greater than 0V and less than a supply voltage. - View Dependent Claims (10, 11, 12)
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13. A memory device comprising:
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an array of memory cells arranged in rows and columns such that the rows are coupled by word lines and the columns are coupled by bit lines, each memory cell having an associated threshold voltage; and
control circuitry that controls programming of the array of memory cells, the control circuitry adapted to control generation of a plurality of programming pulses to increase the associated threshold voltages of a set of memory cells to be programmed, the control circuitry further adapted to selectively control biasing of only a bit line associated with a memory cell having a threshold voltage that is equal to or greater than a first verify threshold voltage but less than a second verify threshold voltage. - View Dependent Claims (14, 15, 16, 17, 18)
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19. A memory system comprising:
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a processor that generates memory program signals; and
a memory device coupled to the processor that operates in response to the memory program signals, the device comprising;
an array of memory cells arranged in rows and columns such that the rows are coupled by word lines and the columns are coupled by bit lines, each memory cell having an associated threshold voltage; and
control circuitry that controls programming of the array of memory cells, the control circuitry adapted to control generation of a plurality of programming pulses to increase the associated threshold voltages of a set of memory cells to be programmed, the control circuitry further adapted to selectively control biasing of only a bit line associated with a memory cell having a threshold voltage that is equal to or greater than a first verify threshold voltage but less than a second verify threshold voltage.
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20. A method for selectively slow programming convergence in a flash memory device comprising a matrix of memory cells having rows coupled by word lines and columns coupled by bit lines, the method comprising:
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performing a programming operation on each of a set of multilevel memory cells, each memory cell of the set having a threshold voltage distribution, the programming operation comprising a plurality of programming pulses that increase incrementally from a previous pulse and are applied to each word line coupled the set of memory cells, the threshold voltage distribution increasing in response to each programming pulse;
performing a verify operation, after each programming pulse, on each memory cell to determine its respective threshold voltage distribution;
selectively biasing, with a first bias voltage, only each bit line that is associated with a memory cell having maximum voltage in its threshold voltage distribution that is equal to or greater than a pre-verify threshold voltage and less than a verify threshold voltage, the first bias voltage being greater than 0V and less than a supply voltage; and
selectively biasing, with an inhibit voltage, only each bit line that is associated with a memory cell having the maximum voltage in the threshold voltage that is at least equal to the verify threshold voltage. - View Dependent Claims (21, 22, 23, 24)
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Specification