State Dependent Threshold Voltage Shift in Irradiated 64-Layer 3-D NAND Memories

We analyze and model state-dependent total-ionizing-dose (TID)-induced threshold-voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {th}}$ </tex-math></inline-formula>) shift characteristics of a commercial 64-layer 3-D <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nand</small> floating gate (FG) flash memory chip. We find that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {th}}$ </tex-math></inline-formula> shift follows a linear tread with TID for higher <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {th}}$ </tex-math></inline-formula> states, whereas a slightly saturating trend is observed for the lowest programmed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\text {th}}$ </tex-math></inline-formula> state. We provide a model and explanation illustrating the observed trend.