Partial string erase scheme in a flash memory device
First Claim
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1. A method for erasing a memory device having a memory array comprising a plurality of memory strings coupled to a source line and fabricated on a substrate, the method comprising:
- biasing with an erase voltage a first predetermined subset of a first memory string; and
biasing with an erase inhibit voltage a second predetermined subset of the first memory string.
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Abstract
A memory block has an increased quantity of memory cells while keeping the erase block the same size. The memory block is broken down into at least two memory sub-blocks. While one sub-block is biased with erase voltages, the other sub-block or shadow block is biased with erase inhibit voltages. For wear leveling purposes, the shadow block only experiences a predetermined quantity of program/erase cycles that is less than the maximum experienced by the normal memory sub-block.
60 Citations
28 Claims
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1. A method for erasing a memory device having a memory array comprising a plurality of memory strings coupled to a source line and fabricated on a substrate, the method comprising:
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biasing with an erase voltage a first predetermined subset of a first memory string; and
biasing with an erase inhibit voltage a second predetermined subset of the first memory string. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for erasing a memory device having a memory array comprising a plurality of memory cell strings each coupled to a source line and fabricated on a substrate, each memory cell string comprising a first subset of memory cells and a second subset of memory cells, the method comprising:
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determining a quantity of program/erase cycles performed on the second subset of memory cells;
preventing further erase operations on the second subset of memory cells if the quantity of program/erase cycles is greater than a predetermined threshold;
biasing the first subset of memory cells with erase voltages; and
biasing the second subset of memory cells with erase inhibit voltages. - View Dependent Claims (10, 11, 12)
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13. A memory device comprising:
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a memory array comprising a plurality of memory cell strings each coupled to a source line and fabricated on a substrate, each memory cell string comprising a first subset of memory cells and a second subset of memory cells; and
memory control circuitry coupled to the memory array, the control circuitry adapted to control program and erase operations of the memory array such that only one of the first or the second subsets of memory cells of each memory cell string is biased for an erase operation at any one time. - View Dependent Claims (14, 15, 16)
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17. A memory device comprising:
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a memory array comprising a plurality of memory blocks each having a source line and fabricated on a substrate, each memory block comprising a first subset memory block and a second subset memory block; and
memory control circuitry coupled to the memory array, the control circuitry adapted to control program and erase operations of the memory array such that only one of the first subset memory block or the second subset memory block is biased for an erase operation at any one time. - View Dependent Claims (18, 19)
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20. An electronic system comprising:
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a processor that generates memory signals; and
a flash memory device, coupled to the processor, that operates in response to the memory signals, the device comprising;
a memory array comprising a plurality of memory cell strings each coupled to a source line and fabricated on a substrate, each memory cell string comprising a first subset of memory cells and a second subset of memory cells; and
memory control circuitry coupled to the memory array, the control circuitry adapted to control program and erase operations of the memory array such that only the first subset of memory cells of each memory cell string is biased for an erase operation. - View Dependent Claims (21, 22)
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23. A method for erasing a memory device having a memory array comprising a plurality of memory cell strings each coupled to a source line and fabricated on a substrate, each memory cell string comprising a first subset of memory cells and a second subset of memory cells, each subset having 32 memory cells, the method comprising:
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determining a quantity of program/erase cycles performed on the second subset of memory cells;
preventing further erase operations on the second subset of memory cells if the quantity of program/erase cycles is greater than a predetermined threshold;
biasing selected word lines of the first subset of memory cells at ground potential and the substrate and source line at a voltage greater than VCC; and
biasing unselected word lines of the second subset of memory cells at a voltage greater than VCC. - View Dependent Claims (24)
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25. A method for erasing a memory device having a memory array comprising a plurality of memory strings coupled to a source line and fabricated on a substrate, the method comprising:
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biasing the substrate and a source line coupled to a first memory string at a voltage greater than VCC;
biasing, with an erase voltage, selected word lines of the first memory string; and
floating unselected word lines of the first memory string. - View Dependent Claims (26, 27, 28)
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Specification