Memory devices and methods of forming the same

A method of forming a memory device, comprising:

• forming a bottom electrode layer over a substrate;
• forming a phase change material layer over the bottom electrode layer;
• forming an amorphous material layer over the phase change material layer;
• forming a selector material layer over the phase change material layer;
• forming a top electrode material layer over the selector material layer;
• and
• patterning the phase change material layer, the amorphous material layer, the selector material layer and the top electrode material layer, so as to form a memory stack.

A method of forming a memory device, comprising:

• forming a memory stack over a substrate, wherein a method of forming the memory stack comprises:
• forming a bottom electrode over the substrate;
• forming a selector structure over the bottom electrode, wherein the selector structure comprises a first layer and a second layer adjacent to each other, the first layer comprises a composition of the second layer and further comprises a nitrogen element;
• forming a phase change layer over the selector structure;
• and
• forming a top electrode over the phase change layer;
• and
• forming a moisture-resistant spacer on a sidewall of the memory stack.