Piezoelectric actuator unit having a stress relieving layer and method for manufacturing the same

A method for manufacturing the piezoelectric actuator unit which has a multi-layer piezoelectric element having a plurality of piezoelectric layers and a plurality of metal layers which comprise an internal electrode and a stress relieving layer, the piezoelectric layers and the metal layers being stacked one on another, and a case which houses the multi-layer piezoelectric element, the method comprising:

• a process of making the multi-layer piezoelectric element in which the stress relieving layer comprises a plurality of metal particles and voids, the metal particles being scattered so as to be electrically separated from each other by the voids throughout the entire region between two piezoelectric layers adjoining in the direction of stacking;
• and
• a process of forming a peel-off section at least in a part of the interface between the metal particles and the piezoelectric layer that adjoins therewith by applying polarization treatment under the condition that the multi-layer piezoelectric element is housed in the case to separate a part of the plurality of metal particles from the piezoelectric layer.