Liquid ejection head substrate, liquid ejection head, and method of manufacturing liquid ejection head substrate

A liquid ejection head comprising:

• a liquid ejection head substrate including
• a first wiring layer for supplying electric power,
• an insulation layer covering the first wiring layer,
• a resistance heating element formed on a surface of the insulation layer on an opposite side of the first wiring layer and configured to generate thermal energy for ejecting a liquid by the electric power supplied from the first wiring layer,
• a second wiring layer formed at a different portion from the resistance heating element on the surface of the insulation layer on the opposite side of the first wiring layer and electrically connected to the first wiring layer,
• a first protection layer having an insulation property and covering the resistance heating element and the second wiring layer, and
• a second protection layer formed to overlap the first protection layer;
• and
• a channel forming member including an ejection nozzle for ejecting the liquid and configured to form a liquid channel between the channel forming member and the liquid ejection head substrate to communicate with the ejection nozzle, wherein
• the second protection layer includes
• a heating element side electrode portion configured to overlap a portion of the first protection layer covering the resistance heating element, and
• a counter electrode portion located away from the heating element side electrode portion and configured to overlap a portion of the first protection layer covering the second wiring layer.

A method of manufacturing a liquid ejection head substrate comprising:

• forming a first wiring layer for supplying electric power;
• forming an insulation layer covering the first wiring layer;
• forming a resistance heating element on a surface of the insulation layer on an opposite side of the first wiring layer so as to generate thermal energy for ejecting a liquid by the electric power supplied from the first wiring layer;
• forming a second wiring layer at a different portion from the resistance heating element on the surface of the insulation layer on the opposite side of the first wiring layer so as to be electrically connected to the first wiring layer;
• forming a first protection layer having an insulation property and covering the resistance heating element and the second wiring layer;
• and
• forming a second protection layer so as to overlap the first protection layer, wherein
• a heating element side electrode portion configured to overlap a portion of the first protection layer covering the resistance heating element, and a counter electrode portion located away from the heating element side electrode portion and configured to overlap a portion of the first protection layer covering the second wiring layer are formed in the forming a second protection layer.