Charge retention for flash memory by manipulating the program data methodology
A method, system and apparatus for determining whether any un-programmed cell is affected by charge disturb by comparing the voltage threshold of the un-programmed cells against a reference voltage. If the voltage threshold for the un-programmed cell exceeds the reference voltage, the failed or defective un-programmed cell will be then be programmed. This will change the defective un-programmed cell to a new programmed value. To account for the location of the failing memory cell, address syndrome bits are used to identify the location of the defective memory cell.
1. A method in a multi-cell memory device, comprising:
reading a voltage threshold of a cell in an un-programmed state from the multi-cell memory device;
programming the cell when the voltage threshold of the cell exceeds a reference voltage; and
writing address syndrome data in association with the programming of the cell.
2. The method of claim 1 wherein a complementary bit of the cell is in a programmed state.
3. The method of claim 1 wherein the reference voltage is greater than a range of voltage thresholds within which the cell is in an un-programmed state.
4. The method of claim 1 further comprising:
determining a range of voltage thresholds within which the cell is in an un-programmed state, which range is used during a read operation to determine whether the cell is in the un-programmed or a programmed state; and
setting the reference voltage to be 200 mv to 400 mv higher than the range of voltage thresholds.
5. The method of claim 1 wherein the reference voltage is proportional to a number of occurrences of un-programmed cells having voltage thresholds exceeding the reference voltage.
6. The method of claim 1 wherein the address syndrome bits are set in conjunction with programming the cell and are used during readout to account for the programming of the cell.
7. The method of claim 1 further comprising:
determining whether a failure occurs in the programming of the cell; and
re-programming the cell on occurrence of the failure.
8. The method of claim 1 further comprising:
marking a location of the cell that exceeds the reference voltage.
9. A flash device comprising:
a plurality of multi-cell memory devices forming a memory array; and
a controller coupled to the plurality of multi-cell memory devices and operative to enable actions including:
reading a voltage threshold of a cell in an un-programmed state from the multi-cell memory device;
programming the cell when the voltage threshold of the cell exceeds a reference voltage; and
writing address syndrome data in association with the programming of the cell.
10. The flash device of claim 9 wherein the flash device is used in a memory card, USB flash drive or a consumer electronics application.
11. The flash device of claim 9 wherein the reference voltage is greater than a range of voltage thresholds within which the cell is in an un-programmed state.
12. The flash device of claim 9 , wherein the controller is further operative to enable actions including:
determining a range of voltage thresholds within which the cell is in an un-programmed state, which range is used during a read operation to determine whether the cell is in the un-programmed or programmed state; and
setting the reference voltage to be 200 mv to 400 mv higher than the range of voltage thresholds.
13. The flash device of claim 9 wherein the reference voltage is proportional to a number of occurrences of un-programmed cells having voltage thresholds exceeding the reference voltage.
14. The flash device of claim 9 wherein the address syndrome bits are set in conjunction with programming the cell and are used during readout to account for the programming of the cell.
15. The flash device of claim 9 , wherein the controller is further operative to enable actions including:
determining whether a failure occurs in the programming of the cell; and
re-programming the cell on occurrence of the failure.
16. The flash device of claim 9 , wherein the controller is further operative to enable actions including:
marking a location of the first un-programmed bit that exceeds the reference voltage.
17. The flash device of claim 9 , wherein the controller includes means for programming multi-cell memory devices.
18. A system for storing information comprising:
a memory array having a plurality of multi-cell memory devices; and
a controller coupled to the memory array and operative to enable actions including:
determining a reference voltage that is greater than a range of voltage thresholds within which a cell is in an un-programmed state, which range is used during a read operation to determine whether the cell is in the un-programmed or programmed state;
reading a voltage threshold of the cell, which cell has been set to be in the un-programmed state;
programming the cell when the voltage threshold of the un-programmed cell exceeds the reference voltage; and
writing address syndrome data in association with the programming of the cell.
19. The system of claim 18 further comprising:
setting the reference voltage to be 200 mv to 400 mv higher than a range of voltage thresholds within which the cell is in an un-programmed state.
20. The system of claim 18 wherein the controller includes a means for programming multi-cell memory devices.