Erasing flash memory using adaptive drain and/or gate bias

1. An erase method for a nonvolatile memory device having an array of memory cells, each memory cell being configured to store information corresponding to at least one bit, the method comprising:

initiating an erase operation for a group of bits in the array of memory cells, the erase operation comprising a preliminary erase operation for a first portion of the group of bits;

obtaining a count corresponding to a number of erase pulses utilized to erase the first portion of the group of bits;

determining an adjusted erase bias voltage in response to the count; and

erasing a second portion of the group of bits utilizing the adjusted erase bias voltage.

2. An erase method according to claim 1 , wherein the first portion of the group of bits and the second portion of the group of bits are non-intersecting.

3. An erase method according to claim 1 , wherein the first portion of the group of bits represents less than half of the group of bits.

4. An erase method according to claim 3 , wherein the first portion of the group of bits represents approximately ten percent of the group of bits.

5. An erase method according to claim 1 , wherein obtaining the count is associated with the preliminary erase operation.

6. An erase method according to claim 5 , wherein performing the preliminary erase operation comprises erasing the first portion of the group of bits utilizing a default erase bias voltage.

7. An erase method according to claim 6 , wherein:

the default erase bias voltage is a default drain bias voltage; and

the adjusted erase bias voltage is an adjusted drain bias voltage.

8. An erase method according to claim 7 , wherein determining the adjusted erase bias voltage comprises increasing a baseline drain bias voltage proportionately to the count to obtain the adjusted drain bias voltage.

9. An erase method according to claim 6 , wherein:

the default erase bias voltage is a default gate bias voltage; and

the adjusted erase bias voltage is an adjusted gate bias voltage.

10. An erase method according to claim 9 , wherein determining the adjusted erase bias voltage comprises increasing the absolute value of a baseline negative gate bias voltage proportionately to the count to obtain the adjusted gate bias voltage.

11. An erase method according to claim 1 , further comprising saving the adjusted erase bias voltage for use as a default erase bias voltage during a subsequent preliminary erase operation for the group of bits.

12. An erase method according to claim 1 , wherein the group of bits corresponds to a sector in the array.

13. A nonvolatile memory system comprising:

an array of memory cells, each memory cell being configured to store information corresponding to at least one bit;

a command component coupled to the array of memory cells, the command component being configured to initiate an erase operation for a sector of bits in the array of memory cells, wherein the erase operation comprises a preliminary erase operation for a first portion of the sector;

an erase pulse counter configured to obtain a count corresponding to a number of erase pulses utilized to erase the first portion of the sector;

an erase bias voltage adjustment component configured to determine an adjusted erase bias voltage in response to the count; and

a voltage generator coupled to the array of memory cells, the voltage generator being configured to apply the adjusted erase bias voltage to the array of memory cells to erase a second portion of the sector.

14. A system according to claim 13 , wherein the first portion of the sector and the second portion of the sector are non-intersecting.

15. A system according to claim 13 , wherein:

the command component is configured to perform a preliminary erase operation to erase the first portion of the sector utilizing a default erase bias voltage;

obtaining the count is associated with the preliminary erase operation;

the default erase bias voltage is a default drain bias voltage; and

the adjusted erase bias voltage is an adjusted drain bias voltage.

16. A system according to claim 13 , wherein:

the command component is configured to perform a preliminary erase operation to erase the first portion of the sector utilizing a default erase bias voltage;

obtaining the count is associated with the preliminary erase operation;

the default erase bias voltage is a default gate bias voltage; and

the adjusted erase bias voltage is an adjusted gate bias voltage.

17. An erase method for a nonvolatile memory device having a sector of memory cells, each memory cell being configured to store information corresponding to at least one bit, the method comprising:

establishing a baseline drain bias voltage for the sector;

establishing a baseline negative gate bias voltage for the sector;

erasing a first portion of bits in the sector utilizing a default drain bias voltage;

obtaining a count corresponding to a number of erase pulses utilized to erase the first portion of bits;

increasing the baseline drain bias voltage in response to the count;

generating an adjusted drain bias voltage in response to the increasing step; and

erasing a second portion of bits in the sector utilizing the adjusted drain bias voltage.

18. An erase method according to claim 17 , wherein the increasing step increases the baseline drain bias voltage proportionately to the count.

19. An erase method according to claim 17 , wherein if the count is greater than a maximum drain bias count:

increasing the absolute value of the baseline negative gate bias voltage in response to the count; and

generating an adjusted gate bias voltage in response to the increasing step, wherein erasing the second portion of bits in the sector utilizes the adjusted drain bias voltage and the adjusted gate bias voltage.

20. An erase method according to claim 19 , wherein the increasing step increases the absolute value of the baseline negative gate bias voltage proportionately to the count.