Thermal ink jet printhead with bubble nucleation laterally offset from nozzle

A printer system which incorporates a printhead, the printhead comprising:

• a plurality of nozzles, each nozzle having a nozzle aperture;
• 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 bubble forming chamber corresponding to each of the nozzles respectively;
• at least one 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.

A method of ejecting drops of an ejectable liquid from 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;
• at least one 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 the 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;
• the method comprising the steps of:
• heating the heater element to a temperature above the boiling point of the bubble forming liquid to form a gas bubble that causes the ejection of a drop of the ejectable liquid from the nozzle;
• and
• supplying the nozzle with a replacement volume of the ejectable liquid equivalent to the ejected drop;
• 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
• said step of heating the at least one heater element is effected by applying an actuation energy of less than 500 nJ to each such heater element.