Printhead having polysilsesquioxane coating on ink ejection face

1. A printhead having an ink ejection face, wherein at least part of the ink ejection face is coated with a hydrophobic polymeric material selected from the group consisting of: polysilsesquioxanes.

2. The printhead of claim 1 , wherein said polymeric material is selected from the group consisting of: poly(alkylsilsesquioxanes) and poly(arylsilsesquioxanes).

3. The printhead of claim 1 , wherein said polymeric material is selected from the group consisting of: poly(methylsilsesquioxane) and poly(phenylsilsesquioxane).

4. The printhead of claim 1 , wherein said polymeric material is deposited and hardbaked onto a nozzle plate of the printhead during MEMS printhead fabrication.

5. The printhead of claim 1 comprising a plurality of nozzle assemblies formed on a substrate, each nozzle assembly comprising: a nozzle chamber, a nozzle opening defined in a roof of the nozzle chamber and an actuator for ejecting ink through the nozzle opening.

6. The printhead of claim 5 , wherein the polymeric material is coated on a nozzle plate of the printhead, said nozzle plate being at least partially defined by the roof of each nozzle chamber.

7. The printhead of claim 6 , wherein each roof has a hydrophobic outside surface relative to inside surfaces of each nozzle chamber by virtue of said hydrophobic coating.

8. The printhead of claim 5 , wherein each nozzle chamber comprises a roof and sidewalls comprised of a ceramic material.

9. The printhead of claim 8 , wherein the ceramic material is selected from the group consisting of: silicon nitride, silicon oxide and silicon oxynitride.

10. The printhead of claim 5 , wherein said roof is spaced apart from the substrate, such that sidewalls of each nozzle chamber extend between said nozzle plate and said substrate.

11. The printhead of claim 5 , wherein said actuator is a heater element configured for heating ink in said chamber so as to form a gas bubble, thereby forcing a droplet of ink through said nozzle opening.

12. The printhead of claim 11 , wherein said heater element is suspended in said nozzle chamber.

13. The printhead of claim 5 , wherein said actuator is a thermal bend actuator comprising:

a first active element for connection to drive circuitry; and

a second passive element mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator.

14. The printhead of claim 13 , wherein said thermal bend actuator defines at least part of a roof of each nozzle chamber, whereby actuation of said actuator moves a moving portion of said roof towards a floor of said nozzle chamber.

15. The printhead of claim 14 , wherein said nozzle opening is defined in said moving portion of said roof.

16. The printhead of claim 14 , wherein said nozzle opening is defined in a stationary portion of said roof.

17. The printhead of claim 14 , wherein said polymeric material defines a mechanical seal between said moving portion and a stationary portion of said roof, thereby minimizing ink leakage during actuation of said actuator.