Nonvolatile memory element, manufacturing method thereof, and nonvolatile semiconductor device incorporating nonvolatile memory element

A nonvolatile memory element comprising:

• a first electrode;
• a second electrode;
• and
• a resistance variable layer which is interposed between the first electrode and the second electrode and is configured to switch a resistance value reversibly in response to electric signals applied between the electrodes;
• the nonvolatile memory element being configured to reversibly switch a resistance value between the first electrode and the second electrode in response to electric signals of different polarities which are applied between the first electrode and the second electrode;
• wherein the resistance variable layer has a multi-layer structure in which a second hafnium oxide layer being electrically conductive and having a composition expressed as HfOx, and a first hafnium oxide layer having a composition expressed as HfOy(x<y) are stacked together.