Patent ID: 7791934

Claim:
A method for driving a phase change memory device having a phase change resistor and sensing a change in a crystallization state of the phase change resistor according to currents applied to the phase change resistor to store data corresponding to the crystallization state, the method comprising: reading cell data of a selected cell; comparing the cell data with multi-level data to be written to the cell; applying a write voltage corresponding to a threshold voltage to the cell to write a high resistance reset state to the phase change resistor when the cell data is different from the multi-level data; and writing and verifying a set state corresponding to the multi-level data, wherein the writing and verifying step comprises: writing a set state corresponding to the multi-level data to the cell; reading a multi-level cell data stored in the cell; comparing the multi-level data to the multi-level cell data; repeating the writing step, the reading step, and the comparing step; and performing a redundancy operation after the writing step when an n th multi-level data is different from a n th multi-level cell data, wherein the writing and verifying step is repeated until the multi-level data is identical to the multi-level cell data.