LIQUID INJECTION HEAD AND METHOD FOR MANUFACTURING ACTUATOR DEVICE FOR THE LIQUID INJECTION HEAD

PROBLEM TO BE SOLVED: To solve a problem in which stress concentration is apt to occur in a boundary between a displacement portion and a non-displacement portion of a piezoelectric element, causing a failure.SOLUTION: A flow passage forming substrate including predetermined flow passages corresponding a plurality of nozzles is held between a nozzle plate having the nozzles and a vibration plate, and the piezoelectric element is disposed on the surface opposite to the flow passage forming substrate in the vibration plate in conformation to each flow passage. When a predetermined drive signal is given to the piezoelectric element, the piezoelectric element is displaced, and liquid filled in a predetermined flow passage of the flow passage forming substrate, such as ink corresponding to each flow passage, is discharged through the nozzle. When the piezoelectric element is laminated and formed on the vibration plate by semiconductor process, a weight material composed of a metallic member adjacent to the piezoelectric element is formed. Although a site subjected to stress concentration is caused during repeated displacement of the piezoelectric element, the formation of the weight material allows the piezoelectric element to resist the stress concentration.