Erase techniques and circuits therefor for non-volatile memory devices
Disclosed herein is a method that comprises applying a first voltage to a memory cell, applying again the first voltage to the memory cell when the memory cell have not been shifted to an erased condition, and applying a second voltage to the memory cell when the memory cell have not still been shifted to an erased condition, the second voltage being higher than the first voltage.
1. A device comprising:
a memory array including a plurality of memory cells;
an erase pulse circuit configured to supply the memory array with a first erase pulse in response to a first control information and with a second erase pulse in response to a second control information, the second erase pulse being higher in voltage level than the first erase pulse; and
a control circuit configured to produce the first control information a first number of plural and programmable times in total in order to bring each of the memory cells of the memory array into an erased state, the control circuit being further configured to produce the first control information at least one more time when at least one of the memory cells has not been brought into the erased state, the control circuit being further configured to produce the second control information when at least one of the memory cells has not still been brought into the erased state irrespective of having been supplied with the first erase pulse twice or more times, wherein the control circuit comprises a content addressable memory that is configured to store the first number and enable a change of the first number by using a fuse line in the content addressable memory.
2. The device of claim 1 , wherein the erase pulse circuit comprises a digital-to-analog converter configured to generate the first and second erase pulses in response respectively to the first and second control information, each of the first and second erase pulses being supplied to a well of the memory array.
3. The device of claim 1 , wherein the content addressable memory is configured to set the first number.
4. The device of claim 1 , wherein the control circuit is further configured to produce the second control information at least one more time when at least one of the memory cells has not still been brought into the erased state irrespective of having been supplied with the second voltage.
5. The device of claim 4 , wherein the erase pulse circuit is further configured to supply the memory array with a third erase pulse in response to third control information, the third erase pulse being higher in voltage level than the second erase pulse.
6. The device of claim 5 , wherein the control circuit produces the third control information after producing the second control information a plurality of times.