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

A new method for characterizing the evolution of oxide charge (QT) generation during program/erase (P/E) cycles is developed. The concentration of QTcan be separated from the floating gate charge (QFG) by statistically analyzing the distribution of transconductance reduction (ΔGm,max) after P/E cycles. The effect of the number and position of discrete QTon the distribution of ΔGm,max is studied. The cycling dependence of the QTgeneration 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 QTgeneration gradually goes to a plateau value Q0= 1.5 × 1020cm-3. It is indicated that the QTgeneration is limited by the concentration of inherent weak bonding points inside SiO2or the Si/SiO2interface. The temperature dependence of the QTgeneration is also provided. The activation energy (EA) of the QTgeneration is approximately 0.1 eV, which is compatible with the EAvalue of electron traps creation in SiO2.