High nozzle density printhead

1. An ink jet printhead comprising:

a substrate with an outer layer defining a nozzle structure having an array of nozzles, each nozzle defining a nozzle aperture, the substrate defining a flow path for an ejectable liquid to each nozzle;

at least one heater element corresponding to each nozzle in the array, each of the heater elements are positioned for heating the ejectable liquid above its boiling point to form a bubble to eject a drop of the ejectable liquid from the corresponding nozzle through the nozzle aperture; wherein,

the thickness of the nozzle structure at the nozzle aperture and in the direction of the ejection of the ejectable liquid is less than 5 microns.

2. An inkjet printhead according to claim 1 being configured to print on a page and to be a page-width printhead.

3. An inkjet printhead according to claim 1 wherein the outer layer is less than 2.5 microns thick.

4. An inkjet printhead according to claim 1 wherein each heater element is in the form of a suspended beam having a pair of planar surfaces on opposite sides of the element, the element being suspended such that each of the planar surfaces is in thermal contact with the ejectable liquid such that the bubble is formed at both of the element surfaces.

5. An inkjet printhead according to claim 1 wherein each of the heater elements is configured such that an actuation energy of less than 500 nanojoules (nJ) is required to be applied to that element to heat that element sufficiently to form said bubble in the ejectable liquid thereby to cause the ejection of said drop.

6. An inkjet printhead according to claim 1 wherein the ejectable liquid is supplied at an ambient temperature, wherein each heater element is configured such that the energy required to be applied thereto to heat said part to cause the ejection of said drop is less than the energy required to heal a volume of said ejectable liquid equal to the volume of the said drop, from a temperature equal to said ambient temperature to said boiling point.

7. An inkjet printhead according to claim 1 wherein the areal density of the nozzles relative to the substrate surface exceeds 10,000 nozzles per square cm of substrate surface.

8. An inkjet printhead according to claim 1 wherein the bubble formed is collapsible and has a point of collapse that is spaced from the heater element.

9. An inkjet printhead according to claim 1 further comprising a plurality of nozzle chambers each corresponding to a respective nozzle, and a plurality of said heater elements being disposed within each chamber, the heater elements within each chamber being formed in different respective layers.

10. 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 element having an atomic number below 50.

11. An inkjet printhead according to claim 1 wherein each heater element includes solid material and has amass of less than 10 nanograms of the solid material of that element to be heated to a temperature above the boiling point of the ejectable liquid thereby to heat said part of the ejectable liquid to a temperature above said boiling point to cause the ejection of said drop.

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