Erase method for a dual bit memory cell
View Patent ↗An erase methodology of flash memory cells in a multi-bit memory array with bits disposed in normal and complimentary locations. An erase verify of bits in the normal locations is performed and if a bit in the normal location fails and if the maximum erase pulse count has not been reached, erase pulses are applied to both the normal bit and the complimentary bit. An erase verify of bits in the complimentary locations is performed and if a bit in the complimentary location fails and if the maximum erase pulse count has not been reached, erase pulses are applied to both the complimentary and the normal bit locations. If the bits pass the erase verify, the bits are subjected to a soft programming verify. If the bits are overerased and if the soft programming pulse count has not been reached a soft programming pulse is applied to the overerased bit.
1. A methodology of erasing flash memory cells in a multi-bit flash memory array with bits in the flash memory cells disposed in normal and complimentary locations, the methodology comprising:
(a) programming all cells in a sector of the multi-bit flash memory array;
(b) setting an address location to an initial setting;
(c) performing an erase verify of a bit in a normal bit location;
(d) if the bit does not verify as erased, determining if a maximum erase pulse count has been reached;
(e) if the maximum erase pulse count has been reached, a failure is indicated and the erase methodology is terminated;
(f) if the maximum pulse count has not been reached applying an erase pulse to the normal and complimentary bit locations;
(g) performing an erase verify of a bit in a complimentary bit location;
(h) if the bit does not verify as erased, determining if the maximum erase pulse count has been reached;
(i) if the maximum erase pulse count has been reached, a failure is indicated and the erase methodology is terminated;
(j) if the maximum pulse count has not been reached applying an erase pulse to complimentary and normal bit locations.
2. The methodology of claim 1 further comprising (k) repeating steps (a)-(j) until the erase verify of the bit in the complimentary bit location in step (g) passes.
3. The methodology of claim 2 further comprising:
(l) determining if a maximum address has been reached;
(m) if the maximum address has been reached, terminating the erase methodology and initiate a soft programming methodology; and
(n) if the maximum address has not been reached, incrementing the address location and repeating steps (c)-(n) until the maximum address has been reached.
4. The methodology of claim 3 , further comprising:
(m) setting the address location to the initial setting;
(n) performing a soft program verify of the bit identified at the address location;
(o) determining if a maximum soft programming pulse count has been reached if the bit fails the soft program verify of step (n);
(p) if the maximum soft programming pulse count has been reached, a failure is indicated and the erase methodology is terminated;
(q) if the maximum pulse count has not been reached applying a soft programming pulse;
(r) repeating steps (n)-(q) until the bit passes the soft program verify at step (n).
5. The methodology of claim 4 further comprising:
(s) determining if the maximum address has been reached;
(t) if the maximum address has not been reached, incrementing the address location and repeating steps (n)-(r) until the maximum address has been reached; and
(u) if the maximum address has been reached, terminating the erase methodology.