Substrate for liquid ejection head, liquid ejection head, and method for manufacturing substrate for liquid ejection head

A liquid ejection head incorporating a substrate, the substrate comprising:

• a heating element configured to generate an energy for ejecting a liquid;
• an electrode pad portion having a wiring layer at a lower layer thereof, electrically connected to the heating element through the wiring layer, and electrically connected to an external component through a bonding material;
• and
• an insulating protection layer, wherein
• the electrode pad portion further has a lower electrode layer and an upper electrode layer,
• the insulating protection layer disposed at a first region overlapping the wiring layer in a film thickness direction has a first opening through which the lower electrode layer and the upper electrode layer are connected, and
• the insulating protection layer disposed at a position including at least a second region overlapping the bonding material in the film thickness direction has a second opening through which the lower electrode layer and the upper electrode layer are connected.

A manufacturing method of a substrate for a liquid ejection head, the substrate including

• a heating element configured to generate an energy for ejecting a liquid,
• an electrode pad portion that having a wiring layer at a lower layer thereof, electrically connected to the heating element through the wiring layer, and electrically connected to an external component through a bonding material,
• an anti-cavitation layer that is formed so as to cover the heating element, and
• an insulating protection layer,
• the method comprising:
• forming the wiring layer at the lower layer in the electrode pad portion;
• forming a lower electrode layer at a region including a first region overlapping the wiring layer in a film thickness direction and a second region overlapping the bonding material in the film thickness direction, the lower electrode layer being made of a same material as at least part of the anti-cavitation layer;
• forming the insulating protection layer such that a first opening through which the lower electrode layer and an upper electrode layer are connected is formed at the first region and a second opening through which the lower electrode layer and the upper electrode layer are connected is formed at the second region;
• forming the upper electrode layer such that the upper electrode layer covers the first opening and the second opening;
• and
• bonding the bonding material to the upper electrode layer.