Transconductance Distribution in Program/Erase Cycling of NAND Flash Memory Devices: a Statistical Investigation

Abstract

A new method for characterizing the evolution of oxide charge (Q(T)) generation during program/erase (P/E) cycles is developed. The concentration of Q(T) can be separated from the floating gate charge (Q(FG)) by statistically analyzing the distribution of transconductance reduction (Delta G(m,max)) after P/E cycles. The effect of the number and position of discrete Q(T) on the distribution of Delta G(m,max) is studied. The cycling dependence of the Q(T) generation is given by a fractional equation that includes a power of the number of P/E cycles in the denominator. For fewer than 30k cycles, the equation can be simplified as a power-law equation in the number of cycles with a power factor of 0.58. For more than 30k cycles, the Q(T) generation gradually goes to a plateau value Q(0) = 1.5 x 10(20) cm(-3). It is indicated that the Q(T) generation is limited by the concentration of inherent weak bonding points inside SiO2 or the Si/SiO2 interface. The temperature dependence of the Q(T) generation is also provided. The activation energy (EA) of the Q(T) generation is approximately 0.1 eV, which is compatible with the EA value of electron traps creation in SiO2.