Patent ID: 8634235

Claim:
A method for operating an array of phase change memory cells, comprising: writing data by inducing a first resistance state in some of the phase change memory cells in the array which is distinguishable from a second resistance state in others of the phase change memory cells in the array, the first resistance state corresponding to a crystalline phase active region having a first temperature-hardened morphology, and the second resistance state having a higher resistance than the first resistance state and having a minimum resistance greater than a maximum resistance of the first resistance state and corresponding to a crystalline phase active region having a second morphology, wherein said inducing the first resistance state includes applying a current pulse having a first energy content, and including inducing the second resistance state by applying a current pulse having a second energy content, the first energy content being greater than the second energy content; and reading data in a selected phase change memory cell in the array of the phase change memory cells by sensing whether the selected cell has the first resistance state or the second resistance state.