Patent ID: 7431433

Claim:
An ink jet printhead comprising: a plurality of nozzles, each nozzle defining a nozzle aperture having a central axis; a bubble forming chamber corresponding to each of the nozzles respectively; a plurality of heater elements disposed in each of the bubble forming chambers respectively, each heater element being configured for thermal contact with a bubble forming liquid; such that, heating each heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein, each heater element is suspended between corresponding electrodes so as to be spaced from the central axis, defines a current path substantially around the central axis, and has a bubble nucleation section defined about the central axis, the bubble nucleation section having a smaller cross section than the rest of the heater element so that the temperature of the bubble nucleation section is heated to above said boiling point before the rest of the heater element, and the heater elements and associated electrodes in each bubble forming chamber are arranged so that respective associated electrodes corresponding to each heater element are non-coincident with each other.