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 (t(wait)) 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 t(wait) yield a better oxide quality than those with a longer t(wait). The oxide charge (Q(T)) evolution by distributed P/E cycles can be well described by an analytical equation through the extension of our previous statistical transconductance reduction (G(m,max)) method. This equation is characterized by a power of the number of P/E cycles multiplied by an exponential decay term of t(wait). The former term is related to the Q(T) generation, whereas the latter is related to the Q(T) emission during t(wait) between cycles. This model allows to evaluate the activation energy for both QT generation ((EA,G)) and recovery (E-A,E-R). E-A,E-G is revealed to be a function of the logarithmic scale of t(wait), decreasing from 100 to 85meV for t(wait) varying from 0.1 to 4 s. Moreover, E-A,E- R is approximately 0.4 eV, which is consistent with the value of electron thermal emission from traps in SiO2.