Semiconductor device structure with multiple resistance variable layers

A semiconductor device structure, comprising:

• a semiconductor substrate;
• a lower electrode over the semiconductor substrate;
• a storage element over the lower electrode, wherein the storage element comprises:
• a first resistance variable region over the lower electrode;
• a second resistance variable region over the first resistance variable region;
• a third resistance variable region over the second resistance variable region, wherein each of the first resistance variable region, the second resistance variable region, and the third resistance variable region is made of an oxide material containing a first element and a second element, a bonding strength between the first element and oxygen is greater than a bonding strength between the second element and oxygen, the second resistance variable region has a greater atomic concentration of the first element than that of the first resistance variable region, and the second resistance variable region has a greater atomic concentration of the first element than that of the third resistance variable region;
• and
• an upper electrode over the storage element.

A semiconductor device structure, comprising:

• a semiconductor substrate;
• a lower electrode over the semiconductor substrate;
• a first oxide layer over the lower electrode;
• a second oxide layer over the first oxide layer;
• a third oxide layer over the second oxide layer, wherein oxygen ions are bonded more tightly in the second oxide layer than those in the first oxide layer, and oxygen ions are bonded more tightly in the second oxide layer than those in the third oxide layer;
• and
• an upper electrode over the third oxide layer.