Piezoelectric element substrate, bonded substrate, liquid discharge head, liquid discharge unit, and liquid discharge apparatus

A bonded substrate, comprising:

• a piezoelectric element substrate including:
• a substrate member;
• a plurality of piezoelectric elements on the substrate member, each of the piezoelectric elements including a first electrode;
• a piezoelectric body, and a second electrode;
• a plurality of wiring patterns in a first region on one side of the substrate member on which the plurality of piezoelectric elements is disposed, the wiring patterns connected to the corresponding piezoelectric elements;
• and
• a bonding pattern occupying a second region different from the first region of the wiring patterns on the one side of the substrate member, the bonding pattern made of a metal layer having a plurality of slots, in which no metal is present, arranged within the metal layer of the bonding pattern;
• and
• another substrate bonded to the bonding pattern of the piezoelectric element substrate directly or via an insulating film.