Image Number 8 for United States Patent #7564173.
An ultrasonic motor piezoelectric actuator element uses a primary longitudinal mode and a secondary bending mode and includes a stacked piezoelectric element in which piezoelectric layers and electrode layers are stacked alternately in such a manner that the electrode layers divide the piezoelectric layers into two approximately equal portions. A piezoelectric inactive region is formed from the surface portion to the center portion in the thickness direction of the stacked piezoelectric element. The migration resistance of the piezoelectric actuator element is improved while suppressing a decrease in displacement so that a short circuit can be prevented and portions generating heat during alternating polarization can be dispersed, whereby reliability is increased. Moreover, the amount of electrode material used can be reduced, whereby cost can be reduced.