Method and apparatus for optimizing erase and program times for a non-volatile memory device

摘要

A nonvolatile semiconductor memory device optimizes the time required for erasing or programming a cell by determining an optimal initial programming voltage. The initial programming voltage is relatively low and is fixed in the device during a test mode operation. During a normal erasing or programming operation, a programming signal having the initial programming voltage level is applied to the cell. The programmed state of the cell is then checked. If the cell did not program successfully, the voltage of the programming signal is increased and another programming cycle is executed. The programming cycle is repeated until the cell is programmed properly or a maximum number of programming cycles is reached. To determine the optimal initial programming voltage, an automatic programming operation is performed using a relatively low voltage programming signal. If the time required to complete the programming operation exceeds a target programming time, the voltage of the programming signal is repetitively increased, and the programming operation is repeated until the time required for the programming operation is less than the target time. The optimal initial voltage level of the programming signal is then fixed in the memory device by selectively cutting fuses in a trimming address register in a programming circuit which also includes a loop counter for counting the number of programming cycles during a programming operation and a programming signal generator that varies the voltage of the programming signal responsive to a control signal from the loop counter.