Non-volatile memory and methods of fabricating the same

A non-volatile memory device, comprising:

• a first electrode layer;
• a second electrode layer;
• a buffer layer disposed between the first electrode and the second electrode;
• and
• a primary memory layer comprising three active layers disposed between the buffer layer and the second electrode, the first active layer is physically connected to the buffer layer and the third active layer is physically connected to the second electrode;
• wherein the first active layer having a high oxygen concentration, the second active layer having a lower oxygen concentration than the first active layer, and the third active layer having a lower oxygen concentration than the second active layer, an oxygen concentration decreasing in stages or gradually in a direction from the first active layer to the third active layer.