Electron barrier height measurements at TiN _x / HfO ₂ interfaces in metal-insulator-metal structures using internal photoemission of electrons reveal a significant (≈1 eV, i.e., about 1/3 of the total barrier height) influence of the opposite electrode material, i.e., Hf versus TiN _x . This effect is suggested to be caused by oxygen scavenging from HfO ₂ by the opposite Hf electrode resulting in generation of positive charges in the oxide above the metal electrode surfaces. Such a considerable interface dipole component demonstrates a principle that may be used to tune the barrier.