| CPC H10N 70/8613 (2023.02) [H10N 70/231 (2023.02); H10N 70/8413 (2023.02)] | 20 Claims | 

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               1. A memory device, comprising: 
            a phase change layer, configured to store multilevel data; and 
                a heater, comprising heat conducting materials having different resistivities and respectively in contact with the phase change layer, wherein a first heat conducting material of the heat conducting materials is formed in a recess shape, a second heat conducting material of the heat conducting materials is filled in a recess defined by the first heat conducting material, the heat conducting materials are formed of a metal nitride, a metal content in the first heat conducting material is greater than a metal content in the second heat conducting material, and a nitrogen content in the first heat conducting material is less than a nitrogen content in the second heat conducting material. 
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