Flash memory with high speed erasing structure using thin oxide semiconductor devices

摘要

A flash memory with a high speed erasing structure includes a bank of flash transistors having a plurality of wordlines, a plurality of bitlines and a sourceline. A wordline decoder is coupled to the wordlines and configured to selectively apply voltages to the wordlines to perform procedures on the flash transistors, where the procedures include a read procedure, an erase procedure and a program procedure. During the erase procedure, the wordline decoder is configured to apply a first increasingly negative voltage in a first voltage range to at least one selected wordline until a first threshold voltage is met, then to apply a second increasingly negative voltage in a second voltage range to the selected wordline and to simultaneously apply a third negative voltage in a third voltage range to at least one deselected wordline. Another embodiment of the invention increases the selected sourceline voltage to achieve a high voltage differential between the gate and source of flash transistors selected to be erased. Advantages of the invention include a fast erasing procedure due to the increased voltage differential applied between the gate and source of flash transistors selected to be erased. Moreover, since the deselected wordlines are also ramped to a negative voltage, stress is reduced on the deselected wordline drivers, thereby increasing the longevity of the flash memory.