Thermal ink jet with chemical vapor deposited nozzle plate

1. An ink jet printhead comprising:

an elongate substrate;

a plurality of nozzles formed on a surface of the substrate;

at least one nozzle plate spaced apart from the substrate surface, wherein each nozzle comprises:

one nozzle chamber corresponding to each of the nozzles respectively, said nozzle chamber comprising a roof, defined by at least part of the nozzle plate, and walls extending therefrom to the substrate surface, said nozzle chamber having one opening in its roof, said opening defining an ink ejection aperture for the nozzle chamber; and

at least one heater element corresponding to each of the nozzles respectively, said heater element being configured for thermal contact with a bubble forming liquid, to heat at least part of the bubble forming liquid to a temperature above its boiling point to form a gas bubble to eject a drop of the bubble forming liquid through the ink ejection aperture corresponding to that heater element,

wherein said at least one nozzle plate and said walls are fabricated by a process of:

depositing sacrificial material onto the substrate surface and heater element;

defining openings in the sacrificial material for deposition of wall material;

co-forming said at least one nozzle plate and said walls by chemical vapor deposition (CVD) of silicon nitride, silicon oxide or silicon oxi-nitride onto the sacrificial material and into the openings defined in the sacrificial material;

defining the nozzle openings in the nozzle plate; and

removing the sacrificial material.

2. The printhead of claim 1 wherein the bubble forming liquid is in thermal contact with the at least one corresponding heater element, and to support the bubble forming liquid adjacent each nozzle.

3. The printhead of claim 1 being configured to print on a page and to be a page-width printhead.

4. The printhead of claim 1 wherein the CVD is of silicon nitride.

5. The printhead of claim 1 wherein the CVD is of silicon dioxide.

6. The printhead of claim 1 wherein the CVD is of oxi-nitride.

7. The printhead of claim 1 wherein each heater element is in the form of a suspended beam, that is suspended over at least a portion of the bubble forming liquid so as to be in thermal contact therewith.

8. The printhead of 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 a said bubble in the bubble forming liquid thereby to cause the ejection of said drop.

9. The printhead of claim 1 configured to receive a supply of the bubble forming liquid at an ambient temperature, wherein each heater element is configured such that the energy required to be applied thereto to heat said part of the bubble forming liquid to cause the ejection of said drop is less than the energy required to heat 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.

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

11. The printhead of 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 a bubble formed thereby is spaced from that heater element.

12. The printhead of claim 1 , wherein the at least one nozzle plate is less than 10 microns thick.

13. The printhead of claim 1 comprising a plurality of said heater elements disposed within each nozzle chamber, the heater elements within each chamber being formed on different respective layers.

14. The printhead of 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.

15. The printhead of 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 bubble forming liquid thereby to heat at least part of the bubble forming liquid to a temperature above said boiling point to cause the ejection of a said drop.

16. The printhead of 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.

17. The printhead of claim 1 , wherein the areal density of the nozzles relative to the substrate surface exceeds 10,000 nozzles per square cm of substrate surface.