Thermal ink jet printhead with rotatable heater element Number:7,111,926 from the United States Patent and Trademark Office (PTO) owispatent There is disclosed an ink jet printhead that has a plurality of nozzles 3 and a bubble forming chamber 7 corresponding to each nozzle respectively. At least one heater element 10 suspended in each bubble forming chamber 7 to heat a bubble forming liquid 11 to a temperature above its boiling point to form a gas bubble 12 therein. The generation of the bubble 12 causes the ejection of a drop 16 of an ejectable liquid (such as ink) through an ejection aperture 5 in each nozzle 3, to effect printing. The heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element. The heater elements are formed by depositing a thin strip of heater material, usually less than 1 micron thick. Repeated bending of the element can lead to oxidation and embrittlement, especially at small radius bends. This, in turn, leads to cracking and ultimately failure. Heater elements according to this invention are configured so that the thermal expansion is accommodated by the rotation of a section within the plane of lamination.<H rotatable, printhead, Thermal, ink, jet, 7111926.html, Patent, pto, 7111926

Title: Thermal ink jet printhead with rotatable heater element

Abstract: There is disclosed an ink jet printhead that has a plurality of nozzles 3 and a bubble forming chamber 7 corresponding to each nozzle respectively. At least one heater element 10 suspended in each bubble forming chamber 7 to heat a bubble forming liquid 11 to a temperature above its boiling point to form a gas bubble 12 therein. The generation of the bubble 12 causes the ejection of a drop 16 of an ejectable liquid (such as ink) through an ejection aperture 5 in each nozzle 3, to effect printing. The heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element. The heater elements are formed by depositing a thin strip of heater material, usually less than 1 micron thick. Repeated bending of the element can lead to oxidation and embrittlement, especially at small radius bends. This, in turn, leads to cracking and ultimately failure. Heater elements according to this invention are configured so that the thermal expansion is accommodated by the rotation of a section within the plane of lamination.

Patent Number: 7,111,926 Issued on 09/26/2006 to Silverbrook

Inventors: Silverbrook; Kia (Balmain, AU)
Assignee: Silverbrook Research Pty Ltd (Balmain, AU)

Appl. No.: 10/773,193

Filed: February 9, 2004

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10302274	Nov., 2002	6755509

Current U.S. Class: 347/62 ; 347/61

Current International Class: B41J 2/01 (20060101); B41J 2/05 (20060101)

Field of Search: 347/54,55,56,57,58,59,60,61,62

References Cited [Referenced By]

U.S. Patent Documents


4490728	December 1984	Vaught et al.
4827294	May 1989	Hanson
4870433	September 1989	Campbell et al.
4894664	January 1990	Tsung Pan
4965594	October 1990	Komuro
5534898	July 1996	Kashino et al.
5706041	January 1998	Kubby
5841452	November 1998	Silverbrook
5905517	May 1999	Silverbrook
6019457	February 2000	Silverbrook
6340223	January 2002	Hirata
6460961	October 2002	Lee et al.
6543879	April 2003	Feinn et al.
2002/0008732	January 2002	Moon et al.
2004/0160490	August 2004	Silverbrook

Foreign Patent Documents


1211072	Jun., 2002	EP
WO 01/66357	Sep., 2001	WO

Other References

The Fabrication and Reliability Testing of Ti/TiN Heaters, P. Demoor, Proceedings of SPIE, Micromachining and Microfabrication Process Technology V, vol. 3874, pp. 284-294. Please note, this document was provided in copending U.S. Appl. No. 10/303,348. cited by other .
Shamilian, John H., Baird, Henry S., & Wood, Thomas L. "A Retargetable Table Reader", Bell Laboratories, Lucent Tech Inc. Crawfords Corner Rd. Room 2F-217, Holmdel, NJ 07733-1988 USA. cited by other .
Dymetman, M., and Copperman, M., "Intelligent Paper in Electronic Publishing, Artist Imaging, and Digital Typography, Proceedings of EP '98", Mar./Apr. 1998, Springer Verlag LNCS 1375; pp. 392-406. cited by other.

Primary Examiner: Patel; Vip
Assistant Examiner: Choi; Han Samuel

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation-In-Part application of U.S. application Ser. No. 10/302,274 filed on Nov. 23, 2002, now issued U.S. Pat. No. 6,755,509.

Claims

The invention claimed is:

1. An ink jet printhead comprising: a plurality of nozzles; a bubble forming chamber corresponding to each of the nozzles respectively; at least one substantially planar heater element suspended in each of the bubble forming chambers respectively, the heater element configured for thermal contact with a bubble forming liquid; such that, heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein, the heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element.

2. The printhead of claim 1 wherein the heater element extends between electrodes mounted on opposite sides of the bubble forming chamber.

3. The printhead of claim 2 wherein the bubble forming chamber has a circular cross section and the heater element has arcuate sections that are concentric with the circular cross section wherein the rotatable section connects the arcuate sections.

4. The printhead of claim 3 wherein the rotatable section is ring shaped and co-axial with the bubble forming chamber.

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

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

7. The printhead of claim 1 wherein each heater element is predominantly formed from titanium nitride.

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 configured to receive a supply of the ejectable liquid 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 a 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 comprising a substrate having a substrate surface, wherein the areal density of the nozzles relative to the substrate surface exceeds 10,000 nozzles per square cm of substrate surface.

11. 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 heater element.

12. The printhead of claim 1 wherein the bubble which each 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.

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

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

15. 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.

16. 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.

17. 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 said boiling point thereby to heat said part of the bubble forming liquid to a temperature above said boiling point to cause the ejection of a said drop.

18. 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.

19. A printer system which incorporates a printhead, the printhead comprising: a plurality of nozzles; a bubble forming chamber corresponding to each of the nozzles respectively; at least one heater element suspended in each of the bubble forming chambers respectively, the heater element configured for thermal contact with a bubble forming liquid; such that, heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein, the heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element.

20. The system of claim 19 wherein the heater element extends between electrodes mounted on opposite sides of the bubble forming chamber.

21. The system of claim 20 wherein the bubble forming chamber has a circular cross section and the heater element has arcuate sections that are concentric with the circular cross section wherein the rotatable section connects the arcuate sections.

22. The system of claim 21 wherein the rotatable section is ring shaped and co-axial with the bubble forming chamber.

23. The system of claim 19 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.

24. The system of claim 19 wherein the bubble forming liquid and the ejectable liquid are of a common body of liquid.

25. The system of claim 19 being configured to print on a page and to be a page-width printhead.

26. The system of claim 19 wherein each heater element is predominantly formed from titanium nitride.

27. The system of claim 19 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.

28. The system of claim 19, wherein the printhead is configured to receive a supply of the ejectable liquid at an ambient temperature, and wherein each heater element is configured such that the energy required to be applied thereto to heat said part to cause the ejection of a 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.

29. The system of claim 19 comprising a substrate having a substrate surface, wherein the areal density of the nozzles relative to the substrate surface exceeds 10,000 nozzles per square cm of substrate surface.

30. The system of claim 19 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 heater element.

31. The system of claim 19 wherein the bubble which each 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.

32. The system of claim 19 comprising a structure that is formed by chemical vapor deposition (CVD), the nozzles being incorporated on the structure.

33. The system of claim 19 comprising a structure which is less than 10 microns thick, the nozzles being incorporated on the structure.

34. The system of claim 19 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.

35. The system of claim 19 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.

36. The system of claim 19 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 to cause the ejection of a said drop.

37. The system of claim 19 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.

38. A method of ejecting drops of an ejectable liquid from a printhead, the printhead comprising a plurality of nozzles; a bubble forming chamber corresponding to each of the nozzles respectively; at least one substantially planar heater element suspended in each of the bubble forming chambers respectively, the heater element configured for thermal contact with a bubble forming liquid; wherein, the heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element; the method comprising the steps of: heating the heater element to a temperature above the boiling point of the bubble forming liquid to form a gas bubble that causes the ejection of a drop of the ejectable liquid from the nozzle; and supplying the nozzle with a replacement volume of the ejectable liquid equivalent to the ejected drop.

39. The method of claim 38 wherein the heater element extends between electrodes mounted on opposite sides of the bubble forming chamber.

40. The method of claim 39 wherein the bubble forming chamber has a circular cross section and the heater element has arcuate sections that are concentric with the circular cross section wherein the rotatable section connects the arcuate sections.

41. The method of claim 40 wherein the rotatable section is ring shaped and co-axial with the bubble forming chamber.

42. The method of claim 38 wherein the bubble forming liquid and the ejectable liquid are of a common body of liquid.

43. The method of claim 38 wherein the printhead is configured to print on a page and to be a page-width printhead.

44. The method of claim 38 wherein said step of heating the at least one heater element is effected by applying an actuation energy of less than 500nJ to each such heater element.

45. The method of claim 38 wherein prior to the step of heating the at least one heater element, a supply of the ejectable liquid, at an ambient temperature, is fed to the printhead, wherein the step of heating is effected by applying heat energy to the at least one heater element, wherein said applied heat energy is less than the energy required to heat a volume of said ejectable liquid equal to the volume of said drop, from a temperature equal to said ambient temperature to said boiling point.

46. The method of claim 38 wherein the printhead includes a substrate on which said nozzles are disposed, the substrate having a substrate surface and the areal density of the nozzles relative to the substrate surface exceeding 10,000 nozzles per square cm of substrate surface.

47. The method of claim 38 wherein the at least one heater element has two opposing sides and the bubble is generated at both of said sides of each heated heater element.

48. The method of claim 38 wherein the generated bubble is collapsible and has a point of collapse, and is generated such that the point of collapse is spaced from the at least one heater element.

49. The method of claim 38 wherein the printhead has a structure that is less than 10 microns thick and which incorporates said nozzles thereon.

50. The method of claim 38 wherein the nozzles of the printhead are formed by chemical vapor deposition (CVD).

51. The method of claim 38 wherein the printhead has a plurality of nozzle chambers each chamber corresponding to a respective nozzle and a plurality of said heater elements are formed in each of the chambers, such that the heater elements in each chamber are formed on different respective layers to one another.

52. The method of claim 38 wherein the heater elements are 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.

53. The method of claim 38 wherein the heater elements include solid material and wherein 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.

54. The method of claim 38 wherein a conformal protective coating is applied to substantially to all sides of each of the heater elements simultaneously, such that the coating is seamless.

Description

FIELD OF THE INVENTION

The present invention relates to a thermal ink jet printhead, to a printer system incorporating such a printhead, and to a method of ejecting a liquid drop (such as an ink drop) using such a printhead.

BACKGROUND TO THE INVENTION

The present invention involves the ejection of ink drops by way of forming gas or vapor bubbles in a bubble forming liquid. This principle is generally described in U.S. Pat. No. 3,747,120 (Stemme).

There are various known types of thermal ink jet (bubblejet) printhead devices. Two typical devices of this type, one made by Hewlett Packard and the other by Canon, have ink ejection nozzles and chambers for storing ink adjacent the nozzles. Each chamber is covered by a so-called nozzle plate, which is a separately fabricated item and which is mechanically secured to the walls of the chamber. In certain prior art devices, the top plate is made of Kapton.TM. which is a Dupont trade name for a polyimide film, which has been laser-drilled to form the nozzles. These devices also include heater elements in thermal contact with ink that is disposed adjacent the nozzles, for heating the ink thereby forming gas bubbles in the ink. The gas bubbles generate pressures in the ink causing ink drops to be ejected through the nozzles.

It is an object of the present invention to provide a useful alternative to the known printheads, printer systems, or methods of ejecting drops of ink and other related liquids, which have advantages as described herein.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides an ink jet printhead comprising:

a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzles respectively;

at least one substantially planar heater element suspended in each of the bubble forming chambers respectively, the heater element configured for thermal contact with a bubble forming liquid; such that,

heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein,

the heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element.

The heater elements are formed by depositing a thin strip of heater material, usually less than 1 micron thick. The strip is typically more than 2 microns wide and therefore the bending resistance out of the plane of lamination is generally much weaker than the bending resistance in any lateral directions. Repeated bending of the element can lead to oxidation and embrittlement, especially at small radius bends. This, in turn, leads to cracking and ultimately failure. Heater elements according to this invention are configured so that the thermal expansion is accommodated by the rotation of a section within the plane of lamination. This gives the heater element greater longevity and reliability by minimizing bend regions, which are prone to oxidation and cracking.

According to a second aspect, the present invention provides a printer system which incorporates a thermal inkjet printhead, the printhead comprising:

a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzles respectively;

at least one substantially planar heater element suspended in each of the bubble forming chambers respectively, the heater element configured for thermal contact with a bubble forming liquid; such that,

heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein,

the heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element.

According to a third aspect, the present invention provides a method of ejecting drops of an ejectable liquid from a printhead, the printhead comprising a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzles respectively;

at least one substantially planar heater element suspended in each of the bubble forming chambers respectively, the heater element configured for thermal contact with a bubble forming liquid; wherein,

the heater element has a rotatable section configured such that the strain of thermal expansion is relieved by rotation of the rotatable section within the plane of the heater element; the method comprising the steps of:

heating the heater element to a temperature above the boiling point of the bubble forming liquid to form a gas bubble that causes the ejection of a drop of the ejectable liquid from the nozzle; and

supplying the nozzle with a replacement volume of the ejectable liquid equivalent to the ejected drop.

Preferably, the heater element extends between electrodes mounted on opposite sides of the bubble forming chamber. In a further preferred form, the bubble forming chamber has a circular cross section and the heater element has arcuate sections that are concentric with the circular cross section wherein the rotatable section connects the arcuate sections. In a particularly preferred embodiment, the rotatable section is ring shaped and co-axial with the bubble forming chamber.

As will be understood by those skilled in the art, the ejection of a drop of the ejectable liquid as described herein, is caused by the generation of a vapor bubble in a bubble forming liquid, which, in embodiments, is the same body of liquid as the ejectable liquid. The generated bubble causes an increase in pressure in ejectable liquid, which forces the drop through the relevant nozzle. The bubble is generated by Joule heating of a heater element which is in thermal contact with the ink. The electrical pulse applied to the heater is of brief duration, typically less than 2 microseconds. Due to stored heat in the liquid, the bubble expands for a few microseconds after the heater pulse is turned off. As the vapor cools, it recondenses, resulting in bubble collapse. The bubble collapses to a point determined by the dynamic interplay of inertia and surface tension of the ink. In this specification, such a point is referred to as the "collapse point" of the bubble.

Throughout the specification the terms `lateral`, `laterally` and so on will be understood as a reference to a plane extending parallel to the plane of lamination of the various layers within the nozzle structure.

The printhead according to the invention comprises a plurality of nozzles, as well as a chamber and one or more heater elements corresponding to each nozzle. Each portion of the printhead pertaining to a single nozzle, its chamber and its one or more elements, is referred to herein as a "unit cell".

In this specification, where reference is made to parts being in thermal contact with each other, this means that they are positioned relative to each other such that, when one of the parts is heated, it is capable of heating the other part, even though the parts, themselves, might not be in physical contact with each other.

Also, the term "ink" is used to signify any ejectable liquid, and is not limited to conventional inks containing colored dyes. Examples of non-colored inks include fixatives, infra-red absorber inks, functionalized chemicals, adhesives, biological fluids, water and other solvents, and so on. The ink or ejectable liquid also need not necessarily be a strictly a liquid, and may contain a suspension of solid particles or be solid at room temperature and liquid at the ejection temperature.

In this specification, the term "periodic element" refers to an element of a type reflected in the periodic table of elements.

DETAILED DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying representations. The drawings are described as follows.

FIG. 1 is a schematic cross-sectional view through an ink chamber of a unit cell of a printhead according to an embodiment of the invention, at a particular stage of operation.

FIG. 2 is a schematic cross-sectional view through the ink chamber FIG. 1, at another stage of operation.

FIG. 3 is a schematic cross-sectional view through the ink chamber FIG. 1, at yet another stage of operation.

FIG. 4 is a schematic cross-sectional view through the ink chamber FIG. 1, at yet a further stage of operation.

FIG. 5 is a diagrammatic cross-sectional view through a unit cell of a printhead in accordance with the an embodiment of the invention showing the collapse of a vapor bubble.

FIGS. 6, 8, 10, 11, 13, 14, 16, 18, 19, 21, 23, 24, 26, 28 and 30 are schematic perspective views (FIG. 30 being partly cut away) of a unit cell of a printhead in accordance with an embodiment of the invention, at various successive stages in the production process of the printhead.

FIGS. 7, 9, 12, 15, 17, 20, 22, 25, 27, 29 and 31 are each schematic plan views of a mask suitable for use in performing the production stage for the printhead, as represented in the respective immediately preceding figures.

FIG. 32 is a further schematic perspective view of the unit cell of FIG. 30 shown with the nozzle plate omitted.

FIG. 33 is a schematic perspective view, partly cut away, of a unit cell of a printhead according to the invention having another particular embodiment of heater element.

FIG. 34 is a schematic plan view of a mask suitable for use in performing the production stage for the printhead of FIG. 33 for forming the heater element thereof.

FIG. 35 is a schematic perspective view, partly cut away, of a unit cell of a printhead according to the invention having a further particular embodiment of heater element.

FIG. 36 is a schematic plan view of a mask suitable for use in performing the production stage for the printhead of FIG. 35 for forming the heater element thereof.

FIG. 37 is a further schematic perspective view of the unit cell of FIG. 35 shown with the nozzle plate omitted.

FIG. 38 is a schematic perspective view, partly cut away, of a unit cell of a printhead according to the invention having a further particular embodiment of heater element.

FIG. 39 is a schematic plan view of a mask suitable for use in performing the production stage for the printhead of FIG. 38 for forming the heater element thereof.

FIG. 40 is a further schematic perspective view of the unit cell of FIG. 38 shown with the nozzle plate omitted.

FIG. 41 is a schematic section through a nozzle chamber of a printhead according to an embodiment of the invention showing a suspended beam heater element immersed in a bubble forming liquid.

FIG. 42 is schematic section through a nozzle chamber of a printhead according to an embodiment of the invention showing a suspended beam heater element suspended at the top of a body of a bubble forming liquid.

FIG. 43 is a diagrammatic plan view of a unit cell of a printhead according to an embodiment of the invention showing a nozzle.

FIG. 44 is a diagrammatic plan view of a plurality of unit cells of a printhead according to an embodiment of the invention showing a plurality of nozzles.

FIG. 45 is a diagrammatic section through a nozzle chamber not in accordance with the invention showing a heater element embedded in a substrate.

FIG. 46 is a diagrammatic section through a nozzle chamber in accordance with an embodiment of the invention showing a heater element in the form of a suspended beam.

FIG. 47 is a diagrammatic section through a nozzle chamber of a prior art printhead showing a heater element embedded in a substrate.

FIG. 48 is a diagrammatic section through a nozzle chamber in accordance with an embodiment of the invention showing a heater element defining a gap between parts of the element.

FIG. 49 is a diagrammatic section through a nozzle chamber not in accordance with the invention, showing a thick nozzle plate.

FIG. 50 is a diagrammatic section through a nozzle chamber in accordance with an embodiment of the invention showing a thin nozzle plate.

FIG. 51 is a diagrammatic section through a nozzle chamber in accordance with an embodiment of the invention showing two heater elements.

FIG. 52 is a diagrammatic section through a nozzle chamber of a prior art printhead showing two heater elements.

FIG. 53 is a diagrammatic section through a pair of adjacent unit cells of a printhead according to an embodiment of the invention, showing two different nozzles after drops having different volumes have been ejected therethrough.

FIGS. 54 and 55 are diagrammatic sections through a heater element of a prior art printhead.

FIG. 56 is a diagrammatic section through a conformally coated heater element according to an embodiment of the invention.

FIG. 57 is a diagrammatic elevational view of a heater element, connected to electrodes, of a printhead according to an embodiment of the invention.

FIG. 58 is a schematic exploded perspective view of a printhead module of a printhead according to an embodiment of the invention.

FIG. 59 is a schematic perspective view the printhead module of FIG. 58 shown unexploded.

FIG. 60 is a schematic side view, shown partly in section, of the printhead module of FIG. 58.

FIG. 61 is a schematic plan view of the printhead module of FIG. 58.

FIG. 62 is a schematic exploded perspective view of a printhead according to an embodiment of the invention.

FIG. 63 is a schematic further perspective view of the printhead of FIG. 62 shown unexploded.

FIG. 64 is a schematic front view of the printhead of FIG. 62.

FIG. 65 is a schematic rear view of the printhead of FIG. 62.

FIG. 66 is a schematic bottom view of the printhead of FIG. 62.

FIG. 67 is a schematic plan view of the printhead of FIG. 62.

FIG. 68 is a schematic perspective view of the printhead as shown in FIG. 62, but shown unexploded.

FIG. 69 is a schematic longitudinal section through the printhead of FIG. 62.

FIG. 70 is a block diagram of a printer system according to an embodiment of the invention.

FIG. 71 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

FIG. 72 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 71.

FIG. 73 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

FIG. 74 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 73.

FIG. 75 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

FIG. 76 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 75.

FIG. 77 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

FIG. 78 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

FIG. 79 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 78.

FIGS. 80 to 90 are schematic perspective views of the unit cell shown in FIGS. 78 and 79, at various successive stages in the production process of the printhead.

FIGS. 91 and 92 show schematic, partially cut away, schematic perspective views of two variations of the unit cell of FIGS. 78 to 90.

FIG. 93 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

FIG. 94 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.

DETAILED DESCRIPTION

In the description than follows, corresponding reference numerals, or corresponding prefixes of reference numerals (i.e. the parts of the reference numerals appearing before a point mark), which are used in different figures, relate to corresponding parts. Where there are corresponding prefixes and differing suffixes to the reference numerals, these indicate different specific embodiments of corresponding parts.

Overview of the Invention and General Discussion of Operation

With reference to FIGS. 1 to 4, the unit cell 1 of a printhead according to an embodiment of the invention comprises a nozzle plate 2 with nozzles 3 therein, the nozzles having nozzle rims 4, and apertures 5 extending through the nozzle plate. The nozzle plate 2 is plasma etched from a silicon nitride structure which is deposited, by way of chemical vapor deposition (CVD), over a sacrificial material which is subsequently etched.

The printhead also includes, with respect to each nozzle 3, side walls 6 on which the nozzle plate is supported, a chamber 7 defined by the walls and the nozzle plate 2, a multi-layer substrate 8 and an inlet passage 9 extending through the multi-layer substrate to the far side (not shown) of the substrate. A looped, elongate heater element 10 is suspended within the chamber 7, so that the element is in the form of a suspended beam. The printhead as shown is a microelectromechanical system (MEMS) structure, which is formed by a lithographic process which is described in more detail below.

When the printhead is in use, ink 11 from a reservoir (not shown) enters the chamber 7 via the inlet passage 9, so that the chamber fills to the level as shown in FIG. 1. Thereafter, the heater element 10 is heated for somewhat less than 1 micro second, so that the heating is in the form of a thermal pulse. It will be appreciated that the heater element 10 is in thermal contact with the ink 11 in the chamber 7 so that when the element is heated, this causes the generation of vapor bubbles 12 in the ink. Accordingly, the ink 11 constitutes a bubble forming liquid. FIG. 1 shows the formation of a bubble 12 approximately 1 microsecond after generation of the thermal pulse, that is, when the bubble has just nucleated on the heater elements 10. It will be appreciated that, as the heat is applied in the form of a pulse, all the energy necessary to generate the bubble 12 is to be supplied within that short time.

Turning briefly to FIG. 34, there is shown a mask 13 for forming a heater 14 (as shown in FIG. 33) of the printhead (which heater includes the element 10 referred to above), during a lithographic process, as described in more detail below. As the mask 13 is used to form the heater 14, the shape of various of its parts correspond to the shape of the element 10. The mask 13 therefore provides a useful reference by which to identify various parts of the heater 14. The heater 14 has electrodes 15 corresponding to the parts designated 15.34 of the mask 13 and a heater element 10 corresponding to the parts designated 10.34 of the mask. In operation, voltage is applied across the electrodes 15 to cause current to flow through the element 10. The electrodes 15 are much thicker than the element 10 so that most of the electrical resistance is provided by the element. Thus, nearly all of the power consumed in operating the heater 14 is dissipated via the element 10, in creating the thermal pulse referred to above.

When the element 10 is heated as described above, the bubble 12 forms along the length of the element, this bubble appearing, in the cross-sectional view of FIG. 1, as four bubble portions, one for each of the element portions shown in cross section.

The bubble 12, once generated, causes an increase in pressure within the chamber 7, which in turn causes the ejection of a drop 16 of the ink 11 through the nozzle 3. The rim 4 assists in directing the drop 16 as it is ejected, so as to minimize the chance of drop misdirection.

The reason that there is only one nozzle 3 and chamber 7 per inlet passage 9 is so that the pressure wave generated within the chamber, on heating of the element 10 and forming of a bubble 12, does not affect adjacent chambers and their corresponding nozzles.

The advantages of the heater element 10 being suspended rather than being embedded in any solid material, is discussed below.

FIGS. 2 and 3 show the unit cell 1 at two successive later stages of operation of the printhead. It can be seen that the bubble 12 generates further, and hence grows, with the resultant advancement of ink 11 through the nozzle 3. The shape of the bubble 12 as it grows, as shown in FIG. 3, is determined by a combination of the inertial dynamics and the surface tension of the ink 11. The surface tension tends to minimize the surface area of the bubble 12 so that, by the time a certain amount of liquid has evaporated, the bubble is essentially disk-shaped.

The increase in pressure within the chamber 7 not only pushes ink 11 out through the nozzle 3, but also pushes some ink back through the inlet passage 9. However, the inlet passage 9 is approximately 200 to 300 microns in length, and is only approximately 16 microns in diameter. Hence there is a substantial viscous drag. As a result, the predominant effect of the pressure rise in the chamber 7 is to force ink out through the nozzle 3 to eventually form an ejected drop 16, rather than back through the inlet passage 9.

Turning now to FIG. 4, the printhead is shown at a still further successive stage of operation. A neck section 19 forms which shrinks and narrows until the drop 16 ultimately breaks off. The rate at which this neck is narrowed and broken is important to the momentum of the drop 16 necessary to overcome the surface tension of the ink 11. At any instant, the force retarding the ejection of the drop 16 is the surface tension around the circumference of the neck 19 at its narrowest diameter. Reducing the diameter of the neck 19 as quickly as possible, reduces the duration and magnitude of the retarding force applied by the surface tension. Consequently, the drop 16 requires less momentum to escape the surface tension.

As the bubble collapses, the surrounding ink flows toward the collapse point 17. The fluid flow of the ink is greatest in the ink immediately surrounding the bubble 12. By configuring the nozzle so that the collapse point is close to the nozzle aperture (e.g. less than about 50 microns), significantly more ink 11 is drawn from the annular neck 19. The diameter of the neck rapidly reduces, as does the surface tension retarding the ejection of the ink. The neck 19 breaks sooner and more easily thereby allowing the momentum of the ejected drop to be lower. Reduced ink drop momentum means that the input energy to the nozzle can be reduced. This in turn improves the operating efficiency of the printer.

When the drop 16 breaks off, cavitation forces are caused as reflected by the arrows 20, as the bubble 12 collapses to the collapse point 17. It will be noted that there are no solid surfaces in the vicinity of the collapse point 17 on which the cavitation can have an effect.

Manufacturing Process

Relevant parts of the manufacturing process of a printhead according to embodiments of the invention are now described with reference to FIGS. 6 to 29.

Referring to FIG. 6, there is shown a cross-section through a silicon substrate portion 21, being a portion of a Memjet printhead, at an intermediate stage in the production process thereof. This figure relates to that portion of the printhead corresponding to a unit cell 1. The description of the manufacturing process that follows will be in relation to a unit cell 1, although it will be appreciated that the process will be applied to a multitude of adjacent unit cells of which the whole printhead is composed.

FIG. 6 represents the next successive step, during the manufacturing process, after the completion of a standard CMOS fabrication process, including the fabrication of CMOS drive transistors (not shown) in the region 22 in the substrate portion 21, and the completion of standard CMOS interconnect layers 23 and passivation layer 24. Wiring indicated by the dashed lines 25 electrically interconnects the transistors and other drive circuitry (also not shown) and the heater element corresponding to the nozzle.

Guard rings 26 are formed in the metallization of the interconnect layers 23 to prevent ink 11 from diffusing from the region, designated 27, where the nozzle of the unit cell 1 will be formed, through the substrate portion 21 to the region containing the wiring 25, and corroding the CMOS circuitry disposed in the region designated 22.

The first stage after the completion of the CMOS fabrication process consists of etching a portion of the passivation layer 24 to form the passivation recesses 29.

FIG. 8 shows the stage of production after the etching of the interconnect layers 23, to form an opening 30. The opening 30 is to constitute the ink inlet passage to the chamber that will be formed later in the process.

FIG. 10 shows the stage of production after the etching of a hole 31 in the substrate portion 21 at a position where the nozzle 3 is to be formed. Later in the production process, a further hole (indicated by the dashed line 32) will be etched from the other side (not shown) of the substrate portion 21 to join up with the hole 31, to complete the inlet passage to the chamber. Thus, the hole 32 will not have to be etched all the way from the other side of the substrate portion 21 to the level of the interconnect layers 23.

If, instead, the hole 32 were to be etched all the way to the interconnect layers 23, then to avoid the hole 32 being etched so as to destroy the transistors in the region 22, the hole 32 would have to be etched a greater distance away from that region so as to leave a suitable margin (indicated by the arrow 34) for etching inaccuracies. But the etching of the hole 31 from the top of the substrate portion 21, and the resultant shortened depth of the hole 32, means that a lesser margin 34 need be left, and that a substantially higher packing density of nozzles can thus be achieved.

FIG. 11 shows the stage of production after a four micron thick layer 35 of a sacrificial resist has been deposited on the layer 24. This layer 35 fills the hole 31 and now forms part of the structure of the printhead. The resist layer 35 is then exposed with certain patterns (as represented by the mask shown in FIG. 12) to form recesses 36 and a slot 37. This provides for the formation of contacts for the electrodes 15 of the heater element to be formed later in the production process. The slot 37 will provide, later in the process, for the formation of the nozzle walls 6, that will define part of the chamber 7.

FIG. 13 shows the stage of production after the deposition, on the layer 35, of a 0.25 micron thick layer 38 of heater material, which, in the present embodiment, is of titanium nitride.

FIG. 14 shows the stage of production after patterning and etching of the heater layer 38 to form the heater 14, including the heater element 10 and electrodes 15.

FIG. 16 shows the stage of production after another sacrificial resist layer 39, about 1 micron thick, has been added.

FIG. 18 shows the stage of production after a second layer 40 of heater material has been deposited. In a preferred embodiment, this layer 40, like the first heater layer 38, is of 0.25 micron thick titanium nitride.

FIG. 19 then shows this second layer 40 of heater material after it has been etched to form the pattern as shown, indicated by reference numeral 41. In this illustration, this patterned layer does not include a heater layer element 10, and in this sense has no heater functionality. However, this layer of heater material does assist in reducing the resistance of the electrodes 15 of the heater 14 so that, in operation, less energy is consumed by the electrodes which allows greater energy consumption by, and therefore greater effectiveness of, the heater elements 10. In the dual heater embodiment illustrated in FIG. 38, the corresponding layer 40 does contain a heater 14.

FIG. 21 shows the stage of production after a third layer 42, of sacrificial resist, has been deposited. The uppermost level of this layer will constitute the inner surface of the nozzle plate 2 to be formed later. This is also the inner extent of the ejection aperture 5 of the nozzle. The height of this layer 42 must be sufficient to allow for the formation of a bubble 12 in the region designated 43 during operation of the printhead. However, the height of layer 42 determines the mass of ink that the bubble must move in order to eject a droplet. In light of this, the printhead structure of the present invention is designed such that the heater element is much closer to the ejection aperture than in prior art printheads. The mass of ink moved by the bubble is reduced. The generation of a bubble sufficient for the ejection of the desired droplet will require less energy, thereby improving efficiency.

FIG. 23 shows the stage of production after the roof layer 44 has been deposited, that is, the layer which will constitute the nozzle plate 2. Instead of being formed from 100 micron thick polyimide film, the nozzle plate 2 is formed of silicon nitride, just 2 microns thick.

FIG. 24 shows the stage of production after the chemical vapor deposition (CVD) of silicon nitride forming the layer 44, has been partly etched at the position designated 45, so as to form the outside part of the nozzle rim 4, this outside part being designated 4.1

FIG. 26 shows the stage of production after the CVD of silicon nitride has been etched all the way through at 46, to complete the formation of the nozzle rim 4 and to form the ejection aperture 5, and after the CVD silicon nitride has been removed at the position designated 47 where it is not required.

FIG. 28 shows the stage of production after a protective layer 48 of resist has been applied. After this stage, the substrate portion 21 is then ground from its other side (not shown) to reduce the substrate portion from its nominal thickness of about 800 microns to about 200 microns, and then, as foreshadowed above, to etch the hole 32. The hole 32 is etched to a depth such that it meets the hole 31.

Then, the sacrificial resist of each of the resist layers 35, 39, 42 and 48, is removed using oxygen plasma, to form the structure shown in FIG. 30, with walls 6 and nozzle plate 2 which together define the chamber 7 (part of the walls and nozzle plate being shown cut-away). It will be noted that this also serves to remove the resist filling the hole 31 so that this hole, together with the hole 32 (not shown in FIG. 30), define a passage extending from the lower side of the substrate portion 21 to the nozzle 3, this passage serving as the ink inlet passage, generally designated 9, to the chamber 7.

FIG. 32 shows the printhead with the nozzle guard and chamber walls removed to clearly illustrate the vertically stacked arrangement of the heater elements 10 and the electrodes 15.

While the above production process is used to produce the embodiment of the printhead shown in FIG. 30, further printhead embodiments, having different heater structures, are shown in FIG. 33, FIGS. 35 and 37, and FIGS. 38 and 40.

Control of Ink Drop Ejection

Referring once again to FIG. 30, the unit cell 1 shown, as mentioned above, is shown with part of the walls 6 and nozzle plate 2 cut-away, which reveals the interior of the chamber 7. The heater 14 is not shown cut away, so that both halves of the heater element 10 can be seen.

In operation, ink 11 passes through the ink inlet passage 9 (see FIG. 28) to fill the chamber 7. Then a voltage is applied across the electrodes 15 to establish a flow of electric current through the heater element 10. This heats the element 10, as described above in relation to FIG. 1, to form a vapor bubble in the ink within the chamber 7.

The various possible structures for the heater 14, some of which are shown in FIGS. 33, 35 and 37, and 38, can result in there being many variations in the ratio of length to width of the heater elements 10. Such variations (even though the surface area of the elements 10 may be the same) may have significant effects on the electrical resistance of the elements, and therefore on the balance between the voltage and current to achieve a certain power of the element.

Modern drive electronic components tend to require lower drive voltages than earlier versions, with lower resistances of drive transistors in their "on" state. Thus, in such drive transistors, for a given transistor area, there is a tendency to higher current capability and lower voltage tolerance in each process generation.

FIG. 36, referred to above, shows the shape, in plan view, of a mask for forming the heater structure of the embodiment of the printhead shown in FIG. 35. Accordingly, as FIG. 36 represents the shape of the heater element 10 of that embodiment, it is now referred to in discussing that heater element. During operation, current flows vertically into the electrodes 15 (represented by the parts designated 15.36), so that the current flow area of the electrodes is relatively large, which, in turn, results in there being a low electrical resistance. By contrast, the element 10, represented in FIG. 36 by the part designated 10.36, is long and thin, with the width of the element in this embodiment being 1 micron and the thickness being 0.25 microns.

It will be noted that the heater 14 shown in FIG. 33 has a significantly smaller element 10 than the element 10 shown in FIG. 35, and has just a single loop 36. Accordingly, the element 10 of FIG. 33 will have a much lower electrical resistance, and will permit a higher current flow, than the element 10 of FIG. 35. It therefore requires a lower drive voltage to deliver a given energy to the heater 14 in a given time.

In FIG. 38, on the other hand, the embodiment shown includes a heater 14 having two heater elements 10.1 and 10.2 corresponding to the same unit cell 1. One of these elements 10.2 is twice the width as the other element 10.1, with a correspondingly larger surface area. The various paths of the lower element 10.2 are 2 microns in width, while those of the upper element 10.1 are 1 micron in width. Thus the energy applied to ink in the chamber 7 by the lower element 10.2 is twice that applied by the upper element 10.1 at a given drive voltage and pulse duration. This permits a regulating of the size of vapor bubbles and hence of the size of ink drop ejected due to the bubbles.

Assuming that the energy applied to the ink by the upper element 10.1 is X, it will be appreciated that the energy applied by the lower element 10.2 is about 2X, and the energy applied by the two elements together is about 3X. Of course, the energy applied when neither element is operational, is zero. Thus, in effect, two bits of information can be printed with the one nozzle 3.

As the above factors of energy output may not be achieved exactly in practice, some "fine tuning" of the exact sizing of the elements 10.1 and 10.2, or of the drive voltages that are applied to them, may be required.

It will also be noted that the upper element 10.1 is rotated through 180.degree. about a vertical axis relative to the lower element 10.2. This is so that their electrodes 15 are not coincident, allowing independent connection to separate drive circuits.

Features and Advantages of Particular Embodiments

Discussed below, under appropriate headings, are certain specific features of embodiments of the invention, and the advantages of these features. The features are to be considered in relation to all of the drawings pertaining to the present invention unless the context specifically excludes certain drawings, and relates to those drawings specifically referred to.

Suspended Beam Heater

With reference to FIG. 1, and as mentioned above, the heater element 10 is in the form of a suspended beam, and this is suspended over at least a portion (designated 11.1) of the ink 11 (bubble forming liquid). The element 10 is configured in this way rather than forming part of, or being embedded in, a substrate as is the case in existing printhead systems made by various manufacturers such as Hewlett Packard, Canon and Lexmark. This constitutes a significant difference between embodiments of the present invention and the prior ink jet technologies.

The main advantage of this feature is that a higher efficiency can be achieved by avoiding the unnecessary heating of the solid material that surrounds the heater elements 10 (for example the solid material forming the chamber walls 6, and surrounding the inlet passage 9) which takes place in the prior art devices. The heating of such solid material does not contribute to the formation of vapor bubbles 12, so that the heating of such material involves the wastage of energy. The only energy which contributes in any significant sense to the generation of the bubbles 12 is that which is applied directly into the liquid which is to be heated, which liquid is typically the ink 11.

In one preferred embodiment, as illustrated in FIG. 1, the heater element 10 is suspended within the ink 11 (bubble forming liquid), so that this liquid surrounds the element. This is further illustrated in FIG. 41. In another possible embodiment, as illustrated in FIG. 42, the heater element 10 beam is suspended at the surface of the ink (bubble forming liquid) 11, so that this liquid is only below the element rather than surrounding it, and there is air on the upper side of the element. The embodiment described in relation to FIG. 41 is preferred as the bubble 12 will form all around the element 10 unlike in the embodiment described in relation to FIG. 42 where the bubble will only form below the element. Thus the embodiment of FIG. 41 is likely to provide a more efficient operation.

As can be seen in, for example, with reference to FIGS. 30 and 31, the heater element 10 beam is supported only on one side and is free at its opposite side, so that it constitutes a cantilever. This minimises any direct contact with, and hence reduces heat transfer to, the solid material of the nozzle.

Efficiency of the Printhead

The printhead of the present invention has a design that configures the nozzle structure for enhanced efficiency. The heater element 10 and ejection aperture are positioned to minimize the momentum necessary for the ink drop to overcome the surface tension of the ink during ejection from the nozzle. As a result, the distance between the collapse point and the ejection aperture is relatively short. Preferably, the distance between the collapse point and the ejection aperture is less than 50 microns. In a further preferred form, the distance is less than 25 microns, and in some embodiments the distance is less than 10 microns. In a particularly preferred embodiment, the distance is less than 5 microns.

Using this configuration, less than 200 nanojoules (nJ) is required to be applied to the element to heat it sufficiently to form a bubble 12 in the ink 11, so as to eject a drop 16 of ink through a nozzle 3. In one preferred embodiment, the required energy is less that 150 nJ, while in a further embodiment, the energy is less than 100 nJ. In a particularly preferred embodiment the energy required is less than 80 nJ.

It will be appreciated by those skilled in the art that prior art devices generally require over 5 microjoules to heat the element sufficiently to generate a vapor bubble 12 to eject an ink drop 16. Thus, the energy requirements of the present invention are an order of magnitude lower than that of known thermal ink jet systems. This lower energy consumption allows lower operating costs, smaller power supplies, and so on, but also dramatically simplifies printhead cooling, allows higher densities of nozzles 3, and permits printing at higher resolutions.

These advantages of the present invention are especially significant in embodiments where the individual ejected ink drops 16, themselves, constitute the major cooling mechanism of the printhead, as described further below.

Self-Cooling of the Printhead

This feature of the invention provides that the energy applied to a heater element 10 to form a vapor bubble 12 so as to eject a drop 16 of ink 11 is removed from the printhead by a combination of the heat removed by the ejected drop itself, and the ink that is taken into the printhe