Patent ID: 7510269

Claim:
An ink jet printhead comprising: a plurality of nozzles; a plurality of bubble forming chambers each corresponding to a respective one of the nozzles; and a heater element and a non-heater element disposed in each of the bubble forming chambers to overlay one another with a space therebetween, the heater and non-heater elements being formed of the same heater material and each heater element being connected to corresponding electrodes so as to be in thermal contact with a bubble forming liquid in the respective bubble forming chamber, such that: heating each heater element with said corresponding electrodes 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 has a bubble nucleation section, each bubble nucleation section having a smaller cross section than the remainder of that heater element, and each bubble forming chamber has a circular cross section and each heater element has arcuate sections that are concentric with the circular cross section.