Patent ID: 7465036

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; an ejectable liquid inlet for establishing fluid communication between the nozzle aperture and an ejectable liquid supply, the ejectable liquid inlet and the nozzle aperture being aligned such that they have a common central axis; a heater element disposed in each of the bubble forming chambers respectively, the heater element having two bubble nucleation regions suspended within the bubble forming chamber in a plane parallel to and less than 5 microns from that of the nozzle aperture such that in use, a layer of an ejectable liquid is between the plane of the two bubble nucleation regions and that of the nozzle aperture, the two bubble nucleation regions also being laterally offset from the central axis, the lateral offset of one of the bubble nucleation regions being equal and opposite to the lateral offset of the other bubble nucleation region; 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 the ejectable liquid through the nozzle aperture corresponding to that heater element; wherein, the bubble nucleation regions are spaced from each other such that bubbles nucleated at each will grow until they unite to form the gas bubble that causes the ejection of a drop of ejectable liquid, wherein each heater element is configured such that an actuation energy of less than 500 nanojoules (nJ) is required to be applied to that heater element to heat that heater element sufficiently to form a said bubble in the bubble forming liquid thereby to cause the ejection of a said drop.