Impact of Program/Erase Cycling Interval on the Transconductance Distribution of NAND Flash Memory Devices

This study comprehensively investigates the impact of the time interval (twait) between program/erase (P/E) cycles on the oxide quality of nand Flash memory devices. It is observed that, at room temperature, P/E cycles with a shorter twait yield a better oxide quality than those with a longer twait. The oxide charge (QT) evolution by distributed P/E cycles can be well described by an analytical equation through the extension of our previous statistical transconductance reduction (Gm,max) method. This equation is characterized by a power of the number of P/E cycles multiplied by an exponential decay term of twait. The former term is related to the QT generation, whereas the latter is related to the QT emission during twait between cycles. This model allows to evaluate the activation energy for both QT generation (EA,G) and recovery (EA,R). EA,G is revealed to be a function of the logarithmic scale of twait, decreasing from 100 to 85 meV for twait varying from 0.1 to 4 s. Moreover, EA,R is approximately 0.4 eV, which is consistent with the value of electron thermal emission from traps in SiO₂.