Activation Energies (Ea) of Failure Mechanisms in Advanced NAND Flash Cells for Different Generations and Cycling

The conventional temperature-accelerated lifetime test method of NAND Flash memory does not follow the Arrhenius model, as various failure mechanisms occur concurrently. We completely separated three main failure mechanisms and extracted each activation energy (E-a) value in three generations (A, B, C) of advanced NAND Flash memory. We compared and analyzed each value of E-a of the three main mechanisms with different device generations and cycling times. The results confirmed that each failure mechanism follows the Arrhenius law. The extracted E-a values of the detrapping mechanism were almost the same (E-a similar to 1.0 eV) regardless of the generation or the cycling times because they are determined by the rate of change of the detrapping probability of each trapped electron according to the baking temperature, not the surface area or trap density. However, the E-a value of the trap-assisted tunneling (TAT) mechanism is dependent on the generation and cycling times. Both the dominant trap energy levels and the average distance between the traps in the oxide layer have a strong impact on the E-a value of the TAT mechanism. The interface trap recovery mechanism has very small time-constant (tau), and its activation energy is very small (E-a similar to 0.2 eV).