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

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 (QFG) by statistically analyzing the distribution of transconductance reduction (ΔGm,max) after P/E cycles. The effect of the number and position of discrete Q
_T
on the distribution of ΔGm,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 × 10
²⁰
cm
^-3
. It is indicated that the Q
_T
generation is limited by the concentration of inherent weak bonding points inside SiO
₂
or the Si/SiO
₂
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 E
_A
value of electron traps creation in SiO
₂
.