An anomalous threshold-voltage (V t ) spread of the program-inhibited cell is investigated for the first time in NAND flash memory. The program disturb characteristics are studied by applying the program-inhibited stress on the Nth cell of the unselected bitline with various string patterns for the 0th to (N-1)th cell, using the global self-boosting method. Distinguishing features of the variance of the number of injected electrons (σ n 2 ) into the floating gate are observed. The variance is proportional to the mean value of injected electrons (n) times 10. The other is proportional to n times 20 and occurs only when the (N-1)th cell is programmed in a high V t level and the other cells are in the erased state. A 3-D TCAD simulation reveals that the former case is attributed to Fowler-Nordheim tunneling from the insufficiently boosting channel, and the latter is explained by hot-electron injection owing to the strong lateral electric field between the Nth and (N-1)th cells.
- Fowler-Nordheim (FN) tunneling
- NAND flash memory
- hot-carrier injection (HCI)
- program disturb