Embodiments of the present invention are directed to a liquid delivery apparatus. A non-limiting example of the apparatus includes a substrate including a cavity formed in a surface of the substrate. The apparatus can also include a membrane disposed on the surface of the substrate covering an opening of the cavity. The apparatus can also include a hydrophobic layer disposed on the membrane. The apparatus can also include a seal disposed between the membrane and the substrate, wherein the seal surrounds the opening of the cavity. The apparatus can also include an electrode layer coupled to the membrane.
