Method for high precision programming nonvolatile memory cells, with optimized programming speed

摘要

A programming method comprises the steps of applying a ramp voltage having a first slope to the gate terminal of a selected memory cell to rapidly bring the threshold voltage of the selected cell to an intermediate value; then applying a ramp voltage having a second slope lower than the first, to end programming to the desired final threshold value with high precision. Thereby, when a high threshold value is to be programmed, programming time is reduced; on the other hand, if a low threshold value is to be programmed, the slower ramp voltage is applied right from the start, to prevent possible overprogramming of the cell.