MULTIPLE LEVEL CELL MEMORY DEVICE WITH IMPROVED RELIABILITY
First Claim
Patent Images
1. A series string of memory cells comprising:
- a first end coupled to a transfer line;
a second end coupled to a source; and
a plurality of memory cells coupled between the first end and the second end wherein at least one memory cell closest to the second end is programmed to a different bit density than a majority of the plurality of memory cells.
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Abstract
The reliability of multiple level cells in a memory device should be increased by programming the ends of the series strings of memory cells differently than the remaining quantity of memory cells of the series string. The end cells closest to select gate source and select gate drain transistors can be programmed as single level cells while the remaining cells of the string are programmed as multiple level cells. Another embodiment can program only one or more cells at the source end of the series string as single level cells. Still another embodiment can skip programming of the cells at either only the source end or both the source end and the drain end of the series string.
35 Citations
25 Claims
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1. A series string of memory cells comprising:
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a first end coupled to a transfer line; a second end coupled to a source; and a plurality of memory cells coupled between the first end and the second end wherein at least one memory cell closest to the second end is programmed to a different bit density than a majority of the plurality of memory cells. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A series string of memory cells comprising:
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a first end coupled through a select gate drain transistor to a bit line; a second end coupled through a select gate source transistor to a source line; and a plurality of memory cells coupled between the first end and the second end wherein a first memory cell closest to the select gate source transistor is not used and a remainder of the plurality of memory cells is programmed as multiple level cells. - View Dependent Claims (9, 10, 11, 12)
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13. A memory device comprising:
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control circuitry for controlling operation of the memory device; and a memory array, coupled to the control circuitry, comprising; a plurality of series strings of memory cells, each series string comprising a first end and a second end and a plurality of memory cells between the first and second ends wherein a first subset of the plurality of memory cells is adjacent to the first end and a second subset of the plurality of memory cells is adjacent to the second end and a remaining quantity of memory cells between the first and second subsets are programmed to a higher bit density than the first and second subsets. - View Dependent Claims (14, 15, 16, 17, 18)
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19. A method for programming a memory device, the method comprising:
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programming at a first bit density at least one memory cell, of a series string of memory cells, closest to a source line of the memory device; and programming a remaining quantity of memory cells of the series string of memory cells at a second bit density that is higher than the first bit density. - View Dependent Claims (20, 21, 22, 23)
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24. A memory device comprising;
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control circuitry for controlling operation of the memory device; and a memory array, coupled to the control circuitry, comprising; a plurality of series strings of memory cells, each series string comprising a first end and a second end and a plurality of memory cells between the first and second ends wherein the number of the memory cells is more than 2N and less than 2M wherein (M=N+1), and the controller is configured to control the memory cells on a cell-by-cell basis. - View Dependent Claims (25)
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Specification