Thermal ink jet printhead with cavitation gap

1. An ink jet printhead comprising:

a plurality of nozzles supported on a substrate; and

at least one respective heater element corresponding to each nozzle, wherein

each heater element is arranged for being in thermal contact with a bubble forming liquid,

each heater element is configured to heat at least part of the bubble forming liquid to a temperature above its boiling point to form therein a collapsible gas bubble having a point of collapse, thereby to cause the ejection of a drop of the ejectable liquid through the nozzle corresponding to that heater element, the heater element generating the gas bubble from an electrical pulse having a duration less than 2 microseconds, and

each heater element is configured such that the point of collapse of a bubble formed thereby is spaced from that heater element; 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 said boiling point thereby to heat said part of the bubble forming liquid to a temperature above said boiling point thereby to cause the ejection of a said drop.

2. The printhead of claim 1 being configured to support the bubble forming liquid in thermal contact with each said heater element and to support the ejectable liquid adjacent each nozzle.

3. The printhead of claim 1 wherein the bubble forming liquid and the ejectable liquid are of a common body of liquid.

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

5. The printhead of claim 1 wherein each heater element is configured such that the point of collapse of a bubble formed thereby is at a position at which there is no solid material forming part of the printhead.

6. The printhead of claim 1 wherein each heater element has parts defining a gap between them and is configured such that the point of collapse of a bubble formed thereby is within the gap corresponding to that heater element.

7. The printhead of claim 1 wherein each heater element is in the form of a suspended beam, arranged for being 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 a said drop.

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

10. The printhead of claim 1 comprising a structure that is formed by chemical vapor deposition (CVD), each nozzle being incorporated on the structure.

11. The printhead of claim 1 comprising a structure that is less than 10 microns thick, the nozzles being incorporated on the structure.

12. The printhead of claim 1 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 on different respective layers to one another.

13. 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.

14. 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.

15. A printer system incorporating a printhead, the printhead comprising:

a plurality of nozzles supported on a substrate; and

at least one respective heater element corresponding to each nozzle, wherein

each heater element is arranged for being in thermal contact with a bubble forming liquid,

each heater element is configured to heat at least part of the bubble forming liquid to a temperature above its boiling point to form therein a collapsible gas bubble having a point of collapse, thereby to cause the ejection of a drop of the ejectable liquid through the nozzle corresponding to that heater element, the heater element generating the gas bubble from an electrical pulse having a duration less than 2 microseconds, and

each heater element is configured such that the point of collapse of a bubble formed thereby is spaced from that heater element; 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 said boiling point thereby to heat said part of the bubble forming liquid to a temperature above said boiling point thereby to cause the ejection of a said drop.

16. The system of claim 15 being configured to support the bubble forming liquid in thermal contact with each said heater element, and to support the ejectable liquid adjacent each nozzle.

17. The system of claim 15 wherein the bubble forming liquid and the ejectable liquid are of a common body of liquid.

18. The system of claim 15 being configured to print on a page and to be a page-width printhead.

19. The system of claim 15 wherein each heater element is configured such that the point of collapse of a bubble formed thereby is at a position at which there is no solid material forming part of the printhead.

20. The system of claim 15 wherein each heater element has parts defining a gap between them and is configured such that the point of collapse of a bubble formed thereby is within the gap corresponding to that heater element.

21. The system of claim 15 wherein each heater element is in the form of a suspended beam, arranged for being suspended over at least a portion of the bubble forming liquid so as to be in thermal contact therewith.

22. The system of claim 15 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 a said drop.

23. The system of claim 15 wherein each heater element has two opposite sides and is configured such that a said gas bubble formed by that heater element is formed at both of said sides of that element.

24. The system of claim 15 comprising a structure that is formed by chemical vapor deposition (CVD), each nozzle being incorporated on the structure.

25. The system of claim 15 comprising a structure that is less than 10 microns thick, the nozzles being incorporated on the structure.

26. The system of claim 15 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 on different respective layers to one another.

27. The system of claim 15 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.

28. The system of claim 15 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.

29. A method of ejecting a drop of an ejectable liquid from a printhead, the printhead comprising a plurality of nozzles supported on the substrate, and at least one respective heater element corresponding to each nozzle, the method comprising the steps of:

energizing at least one heater element corresponding to a nozzle with an electrical pulse so as to heat at least part of a bubble forming liquid which is in thermal contact with the at least one heated heater element to a temperature above the boiling point of the bubble forming liquid;

generating a collapsible gas bubble, having a point of collapse, in the bubble forming liquid by said step of heating, such that the point of collapse is spaced from the at least one heated heater element; and

causing the drop of the ejectable liquid to be ejected through the nozzle corresponding to the at least one heated heater element by said step of generating a gas bubble; wherein,

the electrical pulse has a duration less than 2 microseconds, and

each heater element includes solid material, and the step of heating at least one heater element comprises heating a mass of less than 10 nanograms of the solid material of each such heater element to a temperature above said boiling point.

30. The method of claim 29 comprising before said step of heating the steps of:

disposing the bubble forming liquid in thermal contact with the heater elements; and

disposing the ejectable liquid adjacent the nozzles.

31. The method of claim 29 wherein the bubble forming liquid and the ejectable liquid are of a common body of liquid.

32. The method of claim 29 wherein the step of generating a gas bubble comprises generating the gas bubble such that its point of collapse is at a position at which there is no solid material of the printhead.

33. The method of claim 29 wherein each heater element has parts defining a gap between them and the step of generating a gas bubble comprises generating the gas bubble such that its point of collapse is within the gap corresponding to the heated heater element.

34. The method of claim 29 wherein each said heater element is in the form of a suspended beam, the method further comprising, prior to the step of heating at least one heater element, the step of disposing the bubble forming liquid such that the heater elements are positioned above, and in thermal contact with, at least a portion of the bubble forming liquid.

35. The method of claim 29 wherein said step of heating at least one heater element is effected by applying an actuation energy of less than 500 nJ to each such heater element.

36. The method of claim 29 wherein each heater element has two opposite sides, and wherein, in the step of generating a gas bubble, the bubble is generated at both of said sides of each heater element.

37. The method of claim 29 comprising the step of providing the printhead, including forming a structure by chemical vapor deposition (CVD), the structure incorporating the nozzles thereon.

38. The method of claim 29 comprising the step of providing the printhead including a structure which is less that 10 microns thick and which incorporates said nozzles thereon.

39. The method of claim 29 wherein the printhead has a plurality of nozzle chambers, each chamber corresponding to a respective nozzle, the method further comprising the step of providing the printhead including forming a plurality of said heater elements in each chamber, such that the heater elements in each chamber are formed on different respective layers to one another.

40. The method of claim 29 comprising the step of providing the printhead 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.

41. The method of claim 29 comprising the step of providing the printhead, including applying to each heater element, substantially to all sides thereof simultaneously, a conformal protective coating such that the coating is seamless.