Data storage structure for improving memory cell reliability

A memory device comprising:

• a bottom electrode;
• a top electrode overlying the bottom electrode;
• and
• a data storage structure disposed between the bottom electrode and the top electrode, wherein the data storage structure comprises:
• a first data storage layer contacting the bottom electrode and comprising a first material;
• a second data storage layer contacting the first data storage layer and comprising a second material different from the first material;
• a third data storage layer disposed between the second data storage layer and the top electrode, wherein the third data storage layer comprises a third material different from the first material and the second material, wherein the first, second, and third materials respectively comprise a metal oxide;
• and
• wherein respective bandgaps of the first, second, and third data storage layers gradually decrease or increase from the top electrode to the bottom electrode, wherein the top electrode is configured to receive a programming voltage and the bottom electrode is configured to receive a reference voltage.