Liquid discharge head, element substrate and method for manufacturing the same

A liquid discharge head comprising an element substrate, the element substrate including:

• a first substrate including a discharge opening for discharging a liquid;
• a second substrate joined with the first substrate and including a liquid chamber for supplying the liquid to the discharge opening;
• and
• a third substrate joined with the second substrate via an adhesive and including a through hole for supplying the liquid to the liquid chamber,
• wherein the second substrate includes:
• a piezoelectric element disposed on a surface closer to the third substrate, the piezoelectric element being configured to generate energy for discharging the liquid;
• and
• a protective layer covering at least part of the piezoelectric element and including an opening connecting the liquid chamber and the through hole,
• wherein the protective layer includes a first protective layer in contact with the piezoelectric element and a second protective layer covering the first protective layer,
• wherein L3>L1>L2 is satisfied, where L1 is a length of the through hole, L2 is a length of a communication port connecting the through hole and the liquid chamber in the second substrate, and L3 is a length of the opening of the protective layer, on a straight line passing through a center of the through hole when viewed from a direction perpendicular to a surface of the element substrate,
• wherein an inner wall surface of the opening of the protective layer is a substantially flat surface, and
• wherein in the opening of the protective layer, an edge of the first protective layer is covered by the second protective layer.

An element substrate for use in a liquid discharge head, the element substrate comprising:

• a first substrate including a discharge opening for discharging a liquid;
• a second substrate joined with the first substrate and including a liquid chamber for supplying the liquid to the discharge opening;
• and
• a third substrate joined with the second substrate via an adhesive and including a through hole for supplying the liquid to the liquid chamber,
• wherein the second substrate includes:
• a piezoelectric element on a surface closer to the third substrate, the piezoelectric element being configured to generate energy for discharging the liquid;
• and
• a protective layer covering at least part of the piezoelectric element and including an opening connecting the liquid chamber and the through hole,
• wherein the protective layer includes a first protective layer in contact with the piezoelectric element and a second protective layer covering the first protective layer,
• wherein L3>L1>L2 is satisfied, where L1 is a length of the through hole, L2 is a length of a communication port connecting the through hole and the liquid chamber in the second substrate, and L3 is a length of the opening of the protective layer, on a straight line passing through a center of the through hole when viewed from a direction perpendicular to a surface of the element substrate,
• wherein an inner wall surface of the opening of the protective layer is a substantially flat surface, and
• wherein the inner wall surface of the opening of the protective layer is in contact with the adhesive.