A new technique for hot carrier reliability evaluations of flash memory cell after long-term program/erase cycles

In this paper, we provide a methodology to evaluate the hot-carrier-induced reliability of flash memory cells after long-term program/erase cycles. First, the gated-diode measurement technique has been employed for determining the lateral distributions of interface state (N_it) and oxide trap charges (Q_ox) under both channel-hot electron (CHE) programming bias and source-side erase-bias stress conditions. A gate current model was then developed by including both the effects of N_it and Q_ox. Degradation of flash memory cell after P/E cycles due to the above oxide damage was studied by monitoring the gate current. For the cells during programming, the oxide damage near the drain will result in a programming time delay and we found that the interface state generation is the dominant mechanism. Furthermore, for the cells after long-term erase using source-side FN erase, the oxide trap charge will dominate the cell performance such as read disturb. In order to reduce the read-disturb, source bias should be kept as low as possible since the larger the applied source erasing bias, the worse the device reliability becomes