According to one embodiment, a memory device includes a controller, and a nonvolatile memory controlled by the controller, the nonvolatile memory executing an erase operation by an algorithm which repeats loops, each loop including an erase step applying an erase pulse to a memory cell and a verify step verifying a threshold voltage of the memory cell after the erase step, an erase-verify-read voltage using the verify step changing in a x-th loop (x is a natural number equal to or larger than 2). The controller is capable of changing a value of x, and indicates the value of x to the nonvolatile memory.

A post over-erase correction (POEC) method with an auto-adjusting verification mechanism and a leakage degree detection function detects g.sub.m degradation or leakage degree of flash cells before or after entering the POEC process. When a preset condition is satisfied, the auto-adjusting verification mechanism of the POEC is switched on to further reduce leakage current. After cycling, the POEC repairs Vt of over-erased cells to a higher level to solve leakage issues. The erase shot count increases due to slower erase speeds after cycling. Therefore, the cycling degree of flash cells is detected by observing the shot number that the erase operation used. When the leakage phenomenon becomes serious, the bit line (BL) leakage current, amount of repaired BLs, and over-erase correction (OEC) shot number will increase during the OEC procedure. Therefore, the leakage degree of flash cells can be detected by inspecting the above data.

An erase voltage compensation mechanism for group erase mode with bit line leakage detection comprises performing a block erase operation by applying an erase voltage. Continue block erasing until bit line leakage is detected upon which the erase voltage is latched and over-erase correction is performed. A compensation voltage value is calculated by finding the difference between an upper bound of a threshold voltage distribution and an erase verify point when the bit line leakage was detected. The latched erase voltage is increased by the compensation voltage to create a compensated voltage. A group erase operation is performed and the group address is incremented by 1 and the compensated voltage value is loaded. Then the group erase operation is performed on the next group. The address is incremented, the compensated voltage is loaded, and the group erase operation is performed until the group is the last group.

A memory controller includes an over-program controller that preprograms and then erases the memory cells such that each of the memory cells has a first threshold voltage level, wherein fast cells are detected among the memory cells according to a threshold voltage less than or equal to a second threshold voltage less than the first threshold voltage, and a processor that generates fast cell information identifying the fast cells among the memory cells and stores the fast cell information in a buffer. The over-program controller controls the over-programming of the fast cells and normal programming of normal cells among the memory cells based on the fast cell information stored in the buffer.

A non-volatile memory device, described herein, comprises: a plurality of memory strings and at least one control circuit in communication with the non-volatile memory cell array. The at least one control circuit is configured to perform, for the plurality of memory strings, one erase-verify iteration in an erase operation including determining whether at least one memory string of the plurality of memory strings passes an erase-verify test. The at least one control circuit is configured to, if the at least one memory string passes the erase-verify test, inhibit the at least one memory string for erase including ramping up, to an erase voltage, of a voltage applied to a gate of a SGD transistor of the at least one memory string and to perform a next erase-verify iteration in the erase operation for remaining memory strings of the plurality of memory strings other than the at least one memory string.

A controller of a memory device may determine that an endurance parameter associated with a wear leveling pool of a memory of the memory device satisfies a threshold. The wear leveling pool includes a plurality of memory blocks of the memory. The controller may divide, based on determining that the endurance parameter satisfies the threshold, the plurality of memory blocks of the wear leveling pool into a first wear leveling pool subset that includes a first subset of the plurality of memory blocks and a second wear leveling pool subset that includes a second subset of the plurality of memory blocks. A first subset of a plurality of data partitions is stored in the first subset of the plurality of memory blocks, and a second subset of the plurality of data partitions is stored in the second subset of the plurality of memory blocks.

A post over-erase correction (POEC) method with an auto-adjusting verification mechanism and a leakage degree detection function detects gm degradation or leakage degree of flash cells before or after entering the POEC process. When a preset condition is satisfied, the auto-adjusting verification mechanism of the POEC is switched on to further reduce leakage current. After cycling, the POEC repairs Vt of over-erased cells to a higher level to solve leakage issues. The erase shot count increases due to slower erase speeds after cycling. Therefore, the cycling degree of flash cells is detected by observing the shot number that the erase operation used. When the leakage phenomenon becomes serious, the bit line (BL) leakage current, amount of repaired BLs, and over-erase correction (OEC) shot number will increase during the OEC procedure. Therefore, the leakage degree of flash cells can be detected by inspecting the above data.

A memory apparatus and method of operation is provided. The apparatus includes a block of memory cells. Each of the memory cells is connected to one of a plurality of word lines and arranged in strings. Each of the memory cells is also configured to retain a threshold voltage corresponding to one of a plurality of data states and be erased in an erase operation. A control circuit is coupled to the word lines and the strings and is configured to identify ones of the strings having a faster relative erase speed compared to others of the strings. During the erase operation, the control circuit raises the threshold voltage of the memory cells associated with the ones of the strings having the faster relative erase speed while not raising the threshold voltage of the memory cells associated with the others of the strings.

According to one embodiment, a semiconductor memory device includes: a first memory cell; a second memory cell; a first word line; a second word line; and a first bit line. The device is configured to execute a first operation, a second operation, and a third operation to write data into the first memory cell. In the first operation, a first voltage is applied to the second word line. In the second operation, after the first operation, a second voltage higher than the first voltage is applied to the second word line. In the third operation, after the second operation, a third voltage higher than the second voltage is applied to the first word line, and a fourth voltage lower than both the second voltage and the third voltage is applied to the second word line.

According to one embodiment, a semiconductor memory device includes: a first memory cell; a second memory cell; a first word line; a second word line; and a first bit line. The device is configured to execute a first operation, a second operation, and a third operation to write data into the first memory cell. In the first operation, a first voltage is applied to the second word line. In the second operation, after the first operation, a second voltage higher than the first voltage is applied to the second word line. In the third operation, after the second operation, a third voltage higher than the second voltage is applied to the first word line, and a fourth voltage lower than both the second voltage and the third voltage is applied to the second word line.