Inkjet printhead with suspended heater element spaced from chamber walls

1. An inkjet printhead comprising:

a substrate defining a plurality of inlet passages;

sidewalls extending from the substrate;

a nozzle plate defining a plurality of nozzle apertures supported by the sidewalls, a plurality of chambers being defined by the nozzle plate, the sidewalls and the substrate; and

a heater element suspended within each of the chambers for heating a liquid in the chamber to form a gas bubble that causes the ejection of a drop of the liquid through the nozzle aperture, the heater element having a planar structure parallel to the plane of the nozzle plate,

wherein a spacing between the heater element and each sidewall of the chamber is between 0.1 microns and 20 microns.

2. An inkjet printhead according to claim 1 wherein the spacing is between 0.2 microns and 10.0 microns.

3. An inkjet printhead according to claim 1 wherein the spacing is between 0.5 microns and 5.0 microns.

4. An inkjet printhead according to claim 1 wherein the spacing is between 1.0 microns and 3.0 microns.

5. An inkjet printhead according to claim 1 wherein the nozzle apertures are arranged in an array extending the width of a page in one dimension.

6. An inkjet printhead according to claim 1 wherein each heater element is in the form of a cantilever beam.

7. An inkjet printhead according to claim 1 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 the gas bubble in the liquid.

8. An inkjet printhead according to claim 1 configured to receive a supply of the liquid at an ambient temperature through the inlet passages, wherein each heater element is configured such that the energy required to be applied thereto to cause the ejection of the drop is less than the energy required to heat a volume of said liquid equal to the volume of the said drop, from a temperature equal to said ambient temperature to boiling point.

9. An inkjet printhead according to claim 1 wherein the density of the nozzle apertures relative to the surface of the nozzle plate exceeds 10,000 nozzles per square cm.

10. An inkjet printhead according to claim 1 wherein each heater element has two opposite sides and is configured such that the gas bubble formed by that heater element is formed at both of said sides of that heater element.

11. An inkjet printhead according to claim 1 wherein the bubble which each heater 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 the bubble formed thereby is spaced from that heater element.

12. An inkjet printhead according to claim 1 wherein the chambers and the nozzle plate is a unitary structure that is formed by chemical vapor deposition (CVD).

13. An inkjet printhead according to claim 12 wherein the nozzle plate is less than 10 microns thick.

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

15. 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.

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

17. 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.