Patent ID: 7134744

Claim:
An ink jet printhead comprising: a plurality of nozzles, each nozzle having a nozzle aperture; a bubble forming chamber corresponding to each of the nozzles respectively; at least one heater corresponding to each of the nozzles respectively, each heater having a heater element and a pair of electrodes, the heater element being disposed in the bubble forming chamber, for thermal contact with a bubble forming liquid; such that, heating the 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, the heater element has a double omega shape with a first omega shape extending between the pair of electrodes positioned adjacent each other in a side wall of the bubble forming chamber, the pair of electrodes being separated by a first gap, and a second omega shape is inverted relative to the first and extending between a second gap in the first omega shape, the second gap in the first omega being positioned diametrically opposite the gap between the pair of electrodes, such that the heater element generates the gas bubble substantially symmetrically about an axis extending normal to the plane of the nozzle aperture.