Inkjet printhead with symetrical heater and nozzle sharing common plane of symmetry

1. An inkjet printhead comprising:

a nozzle aperture that defines a planar opening, the nozzle aperture has two planes of symmetry that both extend perpendicular to the plane of the opening;

a heater element corresponding to the nozzle aperture wherein during use, the heater element is configured to generate a gas bubble in printing fluid to eject a drop of the printing fluid through the nozzle aperture, the heater element being a suspended beam that has two planes of symmetry; wherein,

at least one of the heater element planes of symmetry is common to one of the nozzle aperture plane of symmetry.

2. An inkjet printhead according to claim 1 wherein both the heater element planes of symmetry extend perpendicular to the plane on the opening defined by the nozzle aperture.

3. An inkjet printhead according to claim 1 wherein the energy to heat the heater element to form the gas bubble is less than the energy to heat a volume of the printing fluid equal to the volume of the drop, from a temperature equal to the ambient temperature to the printing fluid boiling point.

4. An inkjet printhead according to claim 1 further comprising a chamber in which the heater is disposed wherein the chamber has a circular cross section and the heater element is extends diametrically across the chamber.

5. An inkjet printhead according to claim 4 further comprising a plurality of the nozzle apertures, the chamber and the heater elements, and a substrate having a substrate surface, wherein the areal density of the nozzles relative to the substrate surface exceeds 10,000 nozzles per square cm of substrate surface.

6. An inkjet printhead according to claim 1 wherein the heater element has an enclosed geometric shape formed between the ends of the suspended beam.

7. An inkjet printhead according to claim 6 wherein the enclosed geometric shape has a higher resistance than the remainder of the element.

8. An inkjet printhead according to claim 1 being configured to print on a page and to be a pagewidth printhead.

9. An inkjet printhead according to claim 1 wherein the heater element is predominantly formed from titanium nitride.

10. An inkjet printhead according to claim 1 wherein the heater element is configured such that an actuation energy of less than 500 nanojoules (nJ) is required to form the gas bubble in the printing fluid.

11. An inkjet printhead according to claim 1 wherein the gas bubble encircles the heater element.

12. An inkjet printhead according to claim 1 wherein the bubble which each element is configured to form is collapsible and has a point of collapse, and wherein each heater element is configured such that the point of collapse of a bubble formed thereby is spaced from that heater element.

13. An inkjet printhead according to claim 1 comprising a structure that is formed by chemical vapor deposition (CVD), the nozzles being incorporated on the structure.

14. An inkjet printhead according to claim 1 comprising a structure which is less than 10 microns thick, the nozzles being incorporated on the structure.

15. An inkjet printhead according to claim 1 comprising a plurality of said heater elements being disposed within each chamber, the heater elements within each chamber being formed on different respective layers to one another.

16. An inkjet printhead according to claim 1 wherein each heater element is formed of solid material more than 90% of which, by atomic proportion, is constituted by at least one periodic element having an atomic number below 50.

17. An inkjet printhead according to claim 1 wherein each heater element has a mass of less than 10 nanograms.

18. An inkjet printhead according to claim 1 wherein each heater element is substantially covered by a conformal protective coating, the coating of each heater element having been applied substantially to all sides of the heater element simultaneously such that the coating is seamless.