EP1871606A1 - Method of hydrophobically coating a printhead - Google Patents

Method of hydrophobically coating a printhead

Info

Publication number
EP1871606A1
EP1871606A1 EP05714351A EP05714351A EP1871606A1 EP 1871606 A1 EP1871606 A1 EP 1871606A1 EP 05714351 A EP05714351 A EP 05714351A EP 05714351 A EP05714351 A EP 05714351A EP 1871606 A1 EP1871606 A1 EP 1871606A1
Authority
EP
European Patent Office
Prior art keywords
printhead
ink
nozzle
hydrophobizing
hydrophobic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05714351A
Other languages
German (de)
French (fr)
Other versions
EP1871606A4 (en
Inventor
Kia Silverbrook Research Pty Ltd Silverbrook
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Silverbrook Research Pty Ltd
Original Assignee
Silverbrook Research Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Silverbrook Research Pty Ltd filed Critical Silverbrook Research Pty Ltd
Publication of EP1871606A1 publication Critical patent/EP1871606A1/en
Publication of EP1871606A4 publication Critical patent/EP1871606A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14016—Structure of bubble jet print heads
    • B41J2/14088—Structure of heating means
    • B41J2/14112—Resistive element
    • B41J2/1412—Shape
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1601—Production of bubble jet print heads
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1606—Coating the nozzle area or the ink chamber
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1626—Manufacturing processes etching
    • B41J2/1628—Manufacturing processes etching dry etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1631—Manufacturing processes photolithography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1637—Manufacturing processes molding
    • B41J2/1639—Manufacturing processes molding sacrificial molding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • B41J2/1642—Manufacturing processes thin film formation thin film formation by CVD [chemical vapor deposition]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • B41J2/1645—Manufacturing processes thin film formation thin film formation by spincoating

Definitions

  • the present invention relates to the field of inkjet printers and, discloses an inkjet printing system using printheads manufactured with microelectro-mechanical systems (MEMS) techniques.
  • MEMS microelectro-mechanical systems
  • Ink Jet printers themselves come in many different types.
  • the utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein US Patent No. 1941001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
  • US Patent 3596275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation.
  • This technique is still utilized by several manufacturers including Elmjet and Scitex (see also US Patent No. 3373437 by Sweet et al)
  • Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in US Patent No. 3946398 (1970) which utilizes a diaphragm mode of operation, by Zolten in US Patent 3683212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in US Patent No.
  • the ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in US Patent 4490728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media.
  • Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
  • a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
  • inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, galium arsenide etc.
  • MEMS micro-electromechanical systems
  • a desirable characteristic of inkjet printheads would be a hydrophobic nozzle (front) face, preferably in combination with hydrophilic nozzle chambers and ink supply channels. This combination is optimal for ink ejection. Moreover, a hydrophobic front face minimizes the propensity for ink to flood across the front face of the printhead. With a hydrophobic front face, the aqueous inkjet ink is less likely to flood sideways out of the nozzle openings and more likely to form spherical, ejectable microdroplets.
  • hydrophobic front faces and hydrophilic ink chambers are desirable, there is a major problem in fabricating such printheads by MEMS techniques.
  • the final stage of MEMS printhead fabrication is typically ashing of photoresist using an oxygen plasma.
  • any organic, hydrophobic material deposited onto the front face will typically be removed by the ashing process to leave a hydrophilic surface. Accordingly, the deposition of hydrophobic material needs to occur after ashing.
  • a problem with post-ashing deposition of hydrophobic materials is that the hydrophobic material will be deposited inside nozzle chambers as well as on the front face of the printhead.
  • the resultant printhead chip has improved surface characteristics, without comprising the surface characteristics of nozzle chambers. It would further be desirable to provide a printhead fabrication process, in which the resultant printhead chip has a hydrophobic front face in combination with hydrophilic nozzle chambers.
  • a printhead comprising a plurality of nozzles formed on a substrate, each nozzle 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, wherein at least part of an ink ejection face of the printhead is hydrophobic relative to the inside surfaces of each nozzle chamber.
  • a method of hydrophobizing an ink ejection face of a printhead whilst avoiding hydrophobizing nozzle chambers and/or ink supply channels, the method comprising the steps of:
  • the printhead is an inkjet printhead.
  • the liquid is an inkjet ink.
  • the step of filling the nozzle chambers is priming the printhead with ink.
  • the deposition of the hydrophobizing material is chemical vapour deposition.
  • the printhead face comprises atoms available for covalent bonding with the hydrophobizing material.
  • the atoms are oxygen or nitrogen atoms.
  • the hydrophobizing compound forms covalent bonds with the printhead face.
  • the hydrophobizing material is a silyl compound comprising a hydrophobic group.
  • the hydrophobizing material is a silyl chloride.
  • the hydrophobizing compound is non-polymerizable in the liquid.
  • the hydrophobizing compound is a silyl monochloride.
  • each roof forms at least part of the ink ejection face of the printhead, each roof having a hydrophobic outside surface relative to the inside surfaces of each nozzle chamber.
  • At least part of the ink ejection face has a contact angle of more than 90° and the inside surfaces of the nozzle chambers have a contact angle of less than 90°.
  • At least part of the ink ejection face has a contact angle of more than 110°.
  • the inside surfaces of the nozzle chambers have a contact angle of less than 70°.
  • each nozzle chamber comprises a roof and sidewalls walls formed from a ceramic material.
  • the ceramic material is selected from silicon nitride, silicon oxide or silicon oxynitride.
  • the roof and sidewalls are formed by a chemical vapour deposition process.
  • the ink ejection face is hydrophobic relative to ink supply channels in the printhead, the ink supply channels being configured to supply ink to each nozzle.
  • the ink ejection face comprises a layer of hydrophobic material, and the inside surfaces of each nozzle chamber lacks a layer of hydrophobic material.
  • the hydrophobic material is covalently bonded to at least part of the ink ejection surface.
  • Fig. 1 is a schematic cross-sectional view through an ink chamber of a unit cell of a printhead according to an embodiment using a bubble forming heater element;
  • 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 an embodiment of the invention showing the collapse of a vapor bubble.
  • Fig. 6 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
  • Fig. 7 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 6.
  • Fig. 8 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
  • Fig. 9 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 8.
  • Fig. 10 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
  • Fig. 11 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 10.
  • Fig. 12 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
  • Fig. 13 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
  • Fig. 14 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 13.
  • Figs. 15 to 25 are schematic perspective views of the unit cell shown in Figures 13 and 14, at various successive stages in the production process of the printhead.
  • Fig. 26 shows partially cut away schematic perspective views of the unit cell of Figure 25.
  • Fig. 27 shows the unit cell of Fig. 25 primed with a fluid.
  • Fig. 28 shows the unit cell of Fig. 27 with a hydrophobic coating on the nozzle plate
  • the unit cell 1 of a printhead 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.
  • CVD chemical vapor deposition
  • 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.
  • MEMS microelectromechanical system
  • ink 11 from a reservoir enters the chamber 7 via the inlet passage 9, so that the chamber fills to the level as shown in Figure 1.
  • the heater element 10 is heated for somewhat less than 1 microsecond, 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.
  • Figure 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.
  • the bubble 12 forms along the length of the element, this bubble appearing, in the cross-sectional view of Figure 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 pressure wave generated within the chamber creates significant stresses in the chamber wall.
  • Forming the chamber from an amorphous ceramic such as silicon nitride, silicon dioxide (glass) or silicon oxynitride gives the chamber walls high strength while avoiding the use of material with a crystal structure. Crystalline defects can act as stress concentration points and therefore potential areas of weakness and ultimately failure.
  • Figures 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 Figure 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.
  • 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 as an ejected drop 16, rather than back through the inlet passage 9.
  • the printhead is shown at a still further successive stage of operation, in which the ink drop 16 that is being ejected is shown during its "necking phase" before the drop breaks off.
  • the bubble 12 has already reached its maximum size and has then begun to collapse towards the point of collapse 17, as reflected in more detail in Figure 21.
  • the collapsing of the bubble 12 towards the point of collapse 17 causes some ink 11 to be drawn from within the nozzle 3 (from the sides 18 of the drop), and some to be drawn from the inlet passage 9, towards the point of collapse. Most of the ink 11 drawn in this manner is drawn from the nozzle 3, forming an annular neck 19 at the base of the drop 16 prior to its breaking off.
  • the drop 16 requires a certain amount of momentum to overcome surface tension forces, in order to break off.
  • the diameter of the neck 19 reduces thereby reducing the amount of total surface tension holding the drop, so that the momentum of the drop as it is ejected out of the nozzle is sufficient to allow the drop to break off.
  • Figures 6 to 29 show further embodiments of unit cells 1 for thermal inkjet printheads, each embodiment having its own particular functional advantages. These advantages will be discussed in detail below, with reference to each individual embodiment. For consistency, the same reference numerals are used in Figures 6 to 29 to indicate corresponding components.
  • the unit cell 1 shown has the chamber 7, ink supply passage 32 and the nozzle rim 4 positioned mid way along the length of the unit cell 1.
  • the drive circuitry 22 is partially on one side of the chamber 7 with the remainder on the opposing side of the chamber.
  • the drive circuitry 22 controls the operation of the heater 14 through vias in the integrated circuit metallisation layers of the interconnect 23.
  • the interconnect 23 has a raised metal layer on its top surface.
  • Passivation layer 24 is formed in top of the interconnect 23 but leaves areas of the raised metal layer exposed. Electrodes 15 of the heater 14 contact the exposed metal areas to supply power to the element 10.
  • the drive circuitry 22 for one unit cell is not on opposing sides of the heater element that it controls. All the drive circuitry 22 for the heater 14 of one unit cell is in a single, undivided area that is offset from the heater. That is, the drive circuitry 22 is partially overlaid by one of the electrodes 15 of the heater 14 that it is controlling, and partially overlaid by one or more of the heater electrodes 15 from adjacent unit cells. In this situation, the center of the drive circuitry 22 is less than 200 microns from the center of the associate nozzle aperture 5. In most Memjet printheads of this type, the offset is less than 100 microns and in many cases less than 50 microns, preferably less than 30 microns.
  • Configuring the nozzle components so that there is significant overlap between the electrodes and the drive circuitry provides a compact design with high nozzle density (nozzles per unit area of the nozzle plate 2). This also improves the efficiency of the printhead by shortening the length of the conductors from the circuitry to the electrodes. The shorter conductors have less resistance and therefore dissipate less energy.
  • the high degree of overlap between the electrodes 15 and the drive circuitry 22 also allows more vias between the heater material and the CMOS metalization layers of the interconnect 23.
  • the passivation layer 24 has an array of vias to establish an electrical connection with the heater 14. More vias lowers the resistance between the heater electrodes 15 and the interconnect layer 23 which reduces power losses.
  • the passivation layer 24 and electrodes 15 may also be provided without vias in order to simplify the fabrication process.
  • the unit cell 1 is the same as that of Figures 6 and 7 apart from the heater element 10.
  • the heater element 10 has a bubble nucleation section 158 with a smaller cross section than the remainder of the element.
  • the bubble nucleation section 158 has a greater resistance and heats to a temperature above the boiling point of the ink before the remainder of the element 10.
  • the gas bubble nucleates at this region and subsequently grows to surround the rest of the element 10.
  • the heater element 10 is configured to accommodate thermal expansion in a specific manner. As heater elements expand, they will deform to relieve the strain. Elements such as that shown in Figures 6 and 7 will bow out of the plane of lamination because its thickness is the thinnest cross sectional dimension and therefore has the least bending resistance. Repeated bending of the element can lead to the formation of cracks, especially at sharp corners, which can ultimately lead to failure.
  • the heater element 10 shown in Figures 8 and 9 is configured so that the thermal expansion is relieved by rotation of the bubble nucleation section 158, and slightly splaying the sections leading to the electrodes 15, in preference to bowing out of the plane of lamination.
  • the geometry of the element is such that miniscule bending within the plane of lamination is sufficient to relieve the strain of thermal expansion, and such bending occurs in preference to bowing. This gives the heater element greater longevity and reliability by minimizing bend regions, which are prone to oxidation and cracking.
  • the heater element 10 used in this unit cell 1 has a serpentine or 'double omega' shape. This configuration keeps the gas bubble centered on the axis of the nozzle.
  • a single omega is a simple geometric shape which is beneficial from a fabrication perspective.
  • the gap 159 between the ends of the heater element means that the heating of the ink in the chamber is slightly asymmetrical. As a result, the gas bubble is slightly skewed to the side opposite the gap 159. This can in turn affect the trajectory of the ejected drop.
  • the double omega shape provides the heater element with the gap 160 to compensate for the gap 159 so that the symmetry and position of the bubble within the chamber is better controlled and the ejected drop trajectory is more reliable.
  • Figure 12 shows a heater element 10 with a single omega shape.
  • the simplicity of this shape has significant advantages during lithographic fabrication. It can be a single current path that is relatively wide and therefore less affected by any inherent inaccuracies in the deposition of the heater material.
  • the inherent inaccuracies of the equipment used to deposit the heater material result in variations in the dimensions of the element. However, these tolerances are fixed values so the resulting variations in the dimensions of a relatively wide component are proportionally less than the variations for a thinner component. It will be appreciated that proportionally large changes of components dimensions will have a greater effect on their intended function.
  • the omega shape directs current flow around the axis of the nozzle aperture 5. This gives good bubble alignment with the aperture for better ejection of drops while ensuring that the bubble collapse point is not on the heater element 10. As discussed above, this avoids problems caused by cavitation.
  • FIG. 13 to 26 another embodiment of the unit cell 1 is shown together with several stages of the etching and deposition fabrication process.
  • the heater element 10 is suspended from opposing sides of the chamber. This allows it to be symmetrical about two planes that intersect along the axis of the nozzle aperture 5. This configuration provides a drop trajectory along the axis of the nozzle aperture 5 while avoiding the cavitation problems discussed above.
  • CMOS processing of a silicon wafer provides a silicon substrate 21 having drive circuitry 22, and an interlayer dielectric ("interconnect") 23.
  • the interconnect 23 comprises four metal layers, which together form a seal ring for the inlet passage 9 to be etched through the interconnect.
  • the top metal layer 26, which forms an upper portion of the seal ring, can be seen in Figure 15.
  • the metal seal ring prevents ink moisture from seeping into the interconnect 23 when the inlet passage 9 is filled with ink.
  • a passivation layer 24 is deposited onto the top metal layer 26 by plasma-enhanced chemical vapour deposition (PECVD). After deposition of the passivation layer 24, it is etched to define a circular recess, which forms parts of the inlet passage 9. At the same as etching the recess, a plurality of vias 50 are also etched, which allow electrical connection through the passivation layer 24 to the top metal layer 26.
  • the etch pattern is defined by a layer of patterned photoresist (not shown), which is removed by O 2 ashing after the etch.
  • a layer of photoresist is spun onto the passivation later 24.
  • the photoresist is exposed and developed to define a circular opening.
  • the dielectric interconnect 23 is etched as far as the silicon substrate 21 using a suitable oxide-etching gas chemistry (e.g. 0 2 /C 4 F 8 ).
  • Etching through the silicon substrate is continued down to about 20 microns to define a front ink hole 52, using a suitable silicon-etching gas chemistry (e.g. 'Bosch etch').
  • a suitable silicon-etching gas chemistry e.g. 'Bosch etch'.
  • the same photoresist mask 51 can be used for both etching steps.
  • Figure 17 shows the unit cell after etching the front ink hole 52 and removal of the photoresist 51.
  • the front ink hole 52 is plugged with photoresist to provide a front plug 53.
  • a layer of photoresist is deposited over the passivation layer 24.
  • This layer of photoresist is exposed and developed to define a first sacrificial scaffold 54 over the front plug 53, and scaffolding tracks 35 around the perimeter of the unit cell.
  • the first sacrificial scaffold 54 is used for subsequent deposition of heater material 38 thereon and is therefore formed with a planar upper surface to avoid any buckling in the heater element (see heater element 10 in Figure 13).
  • the first sacrificial scaffold 54 is UV cured and hardbaked to prevent reflow of the photoresist during subsequent high-temperature deposition onto its upper surface.
  • the first sacrificial scaffold 54 has sloped or angled side faces 55. These angled side faces 55 are formed by adjusting the focusing in the exposure tool (e.g. stepper) when exposing the photoresist.
  • the sloped side faces 55 advantageously allow heater material 38 to be deposited substantially evenly over the first sacrificial scaffold 54.
  • the next stage of fabrication deposits the heater material 38 over the first sacrificial scaffold 54, the passivation layer 24 and the perimeter scaffolding tracks 35.
  • the heater material 38 is typically a monolayer of TiAlN.
  • the heater material 38 may alternatively comprise TiAlN sandwiched between upper and lower passivating materials, such as tantalum or tantalum nitride. Passivating layers on the heater element 10 minimize corrosion of the and improve heater longevity.
  • the heater material 38 is subsequently etched down to the first sacrificial scaffold 54 to define the heater element 10.
  • contact electrodes 15 are defined on either side of the heater element 10.
  • the electrodes 15 are in contact with the top metal layer 26 and so provide electrical connection between the CMOS and the heater element 10.
  • the sloped side faces of the first sacrificial scaffold 54 ensure good electrical connection between the heater element 10 and the electrodes 15, since the heater material is deposited with sufficient thickness around the scaffold 54. Any thin areas of heater material (due to insufficient side face deposition) would increase resistivity and affect heater performance.
  • Adjacent unit cells are electrically insulated from each other by virtue of grooves etched around the perimeter of each unit cell.
  • the grooves are etched at the same time as defining the heater element 10.
  • a second sacrificial scaffold 39 of photoresist is deposited over the heater material.
  • the second sacrificial scaffold 39 is exposed and developed to define sidewalls for the cylindrical nozzle chamber and perimeter sidewalls for each unit cell.
  • the second sacrificial scaffold 39 is also UV cured and hardbaked to prevent any reflow of the photoresist during subsequent high-temperature deposition of the silicon nitride roof material.
  • silicon nitride is deposited onto the second sacrificial scaffold 39 by plasma enhanced chemical vapour deposition.
  • the silicon nitride forms a roof 44 over each unit cell, which is the nozzle plate 2 for a row of nozzles.
  • Chamber sidewalls 6 and unit cell sidewalls 56 are also formed by deposition of silicon nitride.
  • the nozzle rim 4 is etched partially through the roof 44, by placing a suitably patterned photoresist mask over the roof, etching for a controlled period of time and removing the photoresist by ashing.
  • the nozzle aperture 5 is etched through the roof 24 down to the second sacrificial scaffold 39. Again, the etch is performed by placing a suitably patterned photoresist mask over the roof, etching down to the scaffold 39 and removing the photoresist mask.
  • the first and second sacrificial scaffolds of photoresist, together with the front plug 53 are ashed off using an O 2 plasma. Accordingly, fluid connection is made from the ink supply channel 32 through to the nozzle aperture 5.
  • a portion of photoresist, on either side of the nozzle chamber sidewalls 6, remains encapsulated by the roof 44, the unit cell sidewalls 56 and the chamber sidewalls 6.
  • This portion of photoresist is sealed from the O 2 ashing plasma and, therefore, remains intact after fabrication of the printhead.
  • This encapsulated photoresist advantageously provides additional robustness for the printhead by supporting the nozzle plate 2.
  • the printhead has a robust nozzle plate spanning continuously over rows of nozzles, and being supported by solid blocks of hardened photoresist, in addition to support walls.
  • a hydrophobic material may be deposited onto the roof 44 at this stage by, for example, chemical vapour deposition.
  • the whole of the front face of the printhead may be coated with hydrophobic material.
  • predetermined regions of the roof 44 e.g. regions surrounding each nozzle aperture 5
  • die final stage of printhead fabrication involves ashing off the photoresist, which occupies the nozzle chambers. Since hydrophobic coating materials are generally organic in nature, the ashing process will remove the hydrophobic coating on the roof 44 as well as the photoresist 39 in the nozzle chambers. Hence, a hydrophobic coating step at this stage would ultimately have no effect on the hydrophobicity of the roof 44.
  • a hydrophobic material may be deposited onto the roof 44 at this stage by, for example, chemical vapour deposition.
  • the CVD process will deposit the hydrophobic material both onto the roof 44, onto nozzle chamber sidewalls, onto the heater element 10 and inside ink supply channels 32.
  • a hydrophobic coating inside the nozzle chambers and ink supply channels would be highly undesirable in terms of creating a positive ink pressure biased towards the nozzle chambers.
  • a hydrophobic coating on the heater element 10 would be equally undesirable in terms of kogation during printing.
  • FIG. 27 there is shown a process for depositing a hydrophobic material onto the roof 44, which eliminates the aforementioned selectivity problems.
  • die printhead is primed with a liquid, which fills the ink supply channels 32 and nozzle chamber up to the rim 4.
  • the liquid is preferably ink so that the hydrophobic deposition step can be incorporated into the overall printer manufacturing process.
  • the front face of the printhead, including the roof 44 is coated with a hydrophobic material 61 by chemical vapour deposition (see Figure 28).
  • the hydrophobic material 61 cannot be deposited inside the nozzle chamber, because the ink 60 effectively seals the nozzle aperture 5 from the vapour.
  • the ink 60 protects the nozzle chamber and allows selective deposition of the hydrophobic material 61 onto the roof 44.
  • the final printhead has a hydrophobic front face in combination with hydrophilic nozzle chambers and ink supply channels.
  • the choice of hydrophobic material is not critical. Any hydrophobic compound, which can adhere to the roof 44 by either covalent bonding, ionic bonding, chemisorption or adsorption may be used. The choice of hydrophobic material will depend on the material forming the roof 44 and also the liquid used to prime the nozzles.
  • the roof 44 is formed from silicon nitride, silicon oxide or silicon oxynitride.
  • the hydrophobic material is typically a compound, which can form covalent bonds with the oxygen or nitrogen atoms exposed on the surface of the roof.
  • suitable compounds are silyl chlorides (including monochlorides, dichlorides, trichlorides) having at least one hydrophobic group.
  • the hydrophobic group is typically a Ci. 2 oalkyl group, optionally substituted with a plurality of fluorine atoms.
  • the hydrophobic group may be perfluorinated, partially fluorinated or non-fluorinated.
  • hydrophobic compounds include: trimethylsilyl chloride, dimethylsilyl dichloride, methylsilyl trichloride, triethylsilyl chloride, octyldimethylsilyl chloride, perfluorooctyldimethylsilyl chloride, perfluorooctylsilyl trichloride, perfluorooctylchlorosilane etc.
  • the nozzles are primed with an inkjet ink.
  • the hydrophobic material is typically a compound, which does not polymerise in aqueous solution and form a skin across the nozzle aperture 5.
  • non-polymerizable hydrophobic compounds include: trimethylsilyl chloride, triethylsilyl chloride, perfluorooctyldimethylsilyl chloride, perfluorooctylchlorosilane etc.
  • silyl chlorides have been exemplified as hydrophobizing compounds hereinabove, it will be appreciated that the present invention may be used in conjunction with any hydrophobizing compound, which can be deposited by CVD or another suitable deposition process.
  • the invention has been described above with reference to printheads using bubble forming heater elements. However, it is potentially suited to a wide range of printing system including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers high speed pagewidth printers, notebook computers with inbuilt pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic "minilabs", video printers, PHOTO CD (PHOTO CD is a registered trade mark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.
  • PHOTO CD PHOTO CD is a registered trade mark of the Eastman Kodak Company
  • inventions of the invention use an ink jet printer type device. Of course many different devices could be used.
  • thermal ink jet The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy- inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. In conventional thermal inkjet printheads, this leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.
  • piezoelectric inkjet The most significant problem with piezoelectric inkjet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.
  • the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications.
  • new ink jet technologies have been created.
  • the target features include: low power (less than 10 Watts) high resolution capability (1,600 dpi or more) photographic quality output low manufacturing cost small size (pagewidth times minimum cross section) high speed ( ⁇ 2 seconds per page).
  • inkjet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.
  • the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing.
  • the printhead is 100 mm long, with a width which depends upon the ink jet type.
  • the smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square nun.
  • the printheads each contain 19,200 nozzles plus data and control circuitry.
  • Ink is supplied to the back of the printhead by injection molded plastic ink channels.
  • the molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool.
  • Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer.
  • the printhead is connected to the camera circuitry by tape automated bonding.
  • Actuator amplification or modification method (17 types) Actuator motion (19 types) Nozzle refill method (4 types) Method of restricting back-flow through inlet (10 types)
  • Nozzle clearing method (9 types) Nozzle plate construction (9 types) Drop ejection direction (5 types) Ink type (7 types)
  • ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes.
  • Most of the IJOl to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.
  • print technology may be listed more than once in a table, where it shares characteristics with more than one entry. Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

Abstract

A method of hydrophobizing an ink ejection face of a printhead, whilst avoiding hydrophobizing nozzle chambers and/or ink supply channels (32) is provided. The method comprises the steps of (a) filling nozzle chambers on the printhead with a liquid and (b) depositing hydrophobizing material (61) onto the ink ejection face (44) of the printhead. The method advantageously provides selectivity during deposition of the hydrophobizing material by CVD.

Description

METHOD OF HYDROPHOBICALLY COATING A PREVTHEAD
FDELD OF THE INVENTION
The present invention relates to the field of inkjet printers and, discloses an inkjet printing system using printheads manufactured with microelectro-mechanical systems (MEMS) techniques.
CROSS REFERENCES TO RELATED APPLICATIONS
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.
6750901 6750901 6476863 6788336 11/003786 11/003354 11/003616
11/003418 11/003334 11/003600 11/003404 11/003419 11/003700 11/003601
11/003618 11/003615 11/003337 11/003698 11/003420 11/003682 11/003699
CAAO18US 11/003463 11/003701 11/003683 11/003614 11/003702 11/003684
11/003619 11/003617 6623101 6406129 6505916 6457809 6550895
6457812 IJ52NPUS 6428133 10/815625 10/815624 10/815628 10/913375
10/913373 10/913374 10/913372 10/913377 10/913378 10/913380 10/913379
10/913376 10/913381 10/986402 10/407212 10/760272 10/760273 10/760187
10/760182 10/760188 10/760218 10/760217 10/760216 10/760233 10/760246
10/760212 10/760243 10/760201 10/760185 10/760253 10/760255 10/760209
10/760208 10/760194 10/760238 10/760234 10/760235 10/760183 10/760189
10/760262 10/760232 10/760231 10/760200 10/760190 10/760191 10/760227
10/760207 10/760181 10/728804 10/728952 10/728806 10/728834 10/729790 10/728884 10/728970 10/728784 10/728783 10/728925 10/728842 10/728803
10/728780 10/728779 10/773189 10/773204 10/773198 10/773199 6830318
10/773201 10/773191 10/773183 10/773195 10/773196 10/773186 10/773200
10/773185 10/773192 10/773197 10/773203 10/773187 10/773202 10/773188
10/773194 10/773193 10/773184 11/008118 MTB38US MTB39US 10/727181
10/727162 10/727163 10/727245 10/727204 10/727233 10/727280 10/727157
10/727178 10/727210 10/727257 10/727238 10/727251 10/727159 10/727180
10/727179 10/727192 10/727274 10/727164 10/727161 10/727198 10/727158
10/754536 10/754938 10/727227 10/727160 10/934720 PECOlNPUS 6795215
10/296535 09/575109 6805419 6859289 09/607985 6398332 6394573
6622923 6747760 10/189459 10/884881 10/943941 10/949294 10/039866
10/854521 10/854522 10/854488 10/854487 10/854503 10/854504 10/854509
10/854510 10/854496 10/854497 10/854495 10/854498 10/854511 10/854512
10/854525 10/854526 10/854516 10/854508 10/854507 10/854515 10/854506
10/854505 10/854493 10/854494 10/854489 10/854490 10/854492 10/854491
10/854528 10/854523 10/854527 10/854524 10/854520 10/854514 10/854519 PLT036US 10/854499 10/854501 10/854500 10/854502 10/854518 10/854517
10/934628 10/760254 10/760210 10/760202 10/760197 10/760198 10/760249
10/760263 10/760196 10/760247 10/760223 10/760264 10/760244 10/760245
10/760222 10/760248 10/760236 10/760192 10/760203 10/760204 10/760205
10/760206 10/760267 10/760270 10/760259 10/760271 10/760275 10/760274
10/760268 10/760184 10/760195 10/760186 10/760261 10/760258 11/014764
RRB002US 11/014748 11/014747 11/014761 11/014760 11/014757 11/014714
11/014713 RRBOlOUS 11/014724 11/014723 11/014756 11/014736 11/014759
11/014758 11/014725 11/014739 11/014738 11/014737 11/014726 11/014745
11/014712 11/014715 11/014751 11/014735 11/014734 RRB030US 11/014750
11/014749 11/014746 11/014769 11/014729 11/014743 11/014733 RRC005US
11/014755 11/014765 11/014766 11/014740 11/014720 RRCOIlUS 11/014752
11/014744 11/014741 11/014768 RRCO16US 11/014718 11/014717 11/014716
11/014732 11/014742 09/575197 09/575197 09/575195 09/575159 09/575132
09/575130 09/575165 6813039 09/575118 09/575131 09/575116 6816274
09/575139 09/575186 6681045 6728000 09/575145 09/575192 09/575181
09/575193 09/575183 6789194 09/575150 6789191 6644642 6502614
6622999 6669385 6549935 09/575187 6727996 6591884 6439706
6760119 09/575198 6290349 6428155 6785016 09/575174 6822639
6737591 09/575154 09/575129 6830196 6832717 09/575189 09/575170
09/575171 09/575161 09/575123 6825945
Some applications have been listed by docket numbers. These will be replaced when application numbers are known.
BACKGROUND OF THE INVENTION
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, "Non-Impact Printing: Introduction and Historical Perspective", Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207 - 220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein US Patent No. 1941001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
US Patent 3596275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also US Patent No. 3373437 by Sweet et al) Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in US Patent No. 3946398 (1970) which utilizes a diaphragm mode of operation, by Zolten in US Patent 3683212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in US Patent No. 3747120 (1972) discloses a bend mode of piezoelectric operation, Howkins in US Patent No. 4459601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in US 4584590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in US Patent 4490728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
In the construction of any inkjet printing system, there are a considerable number of important factors which must be traded off against one another especially as large scale printheads are constructed, especially those of a pagewidth type. A number of these factors are outlined in the following paragraphs. Firstly, inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, galium arsenide etc. Hence, it is desirable, in any MEMS constructions, to utilize well proven semi-conductor fabrication techniques which do not require any "exotic" processes or materials. Of course, a certain degree of trade off will be undertaken in that if the advantages of using the exotic material far out weighs its disadvantages then it may become desirable to utilize the material anyway. However, if it is possible to achieve the same, or similar, properties using more common materials, the problems of exotic materials can be avoided.
A desirable characteristic of inkjet printheads would be a hydrophobic nozzle (front) face, preferably in combination with hydrophilic nozzle chambers and ink supply channels. This combination is optimal for ink ejection. Moreover, a hydrophobic front face minimizes the propensity for ink to flood across the front face of the printhead. With a hydrophobic front face, the aqueous inkjet ink is less likely to flood sideways out of the nozzle openings and more likely to form spherical, ejectable microdroplets.
However, whilst hydrophobic front faces and hydrophilic ink chambers are desirable, there is a major problem in fabricating such printheads by MEMS techniques. The final stage of MEMS printhead fabrication is typically ashing of photoresist using an oxygen plasma. However, any organic, hydrophobic material deposited onto the front face will typically be removed by the ashing process to leave a hydrophilic surface. Accordingly, the deposition of hydrophobic material needs to occur after ashing. However, a problem with post-ashing deposition of hydrophobic materials is that the hydrophobic material will be deposited inside nozzle chambers as well as on the front face of the printhead. With no photoresist to protect the nozzle chambers, the nozzle chamber walls become hydrophobized, which is highly undesirable in terms of generating a positive ink pressure biased towards the nozzle chambers. This is a conundrum, which has to date not been addressed in printhead fabrication.
Accordingly, it would be desirable to provide a printhead fabrication process, in which the resultant printhead chip has improved surface characteristics, without comprising the surface characteristics of nozzle chambers. It would further be desirable to provide a printhead fabrication process, in which the resultant printhead chip has a hydrophobic front face in combination with hydrophilic nozzle chambers.
SUMMARY OF THE INVENTION
In a first aspect, there is provided a printhead comprising a plurality of nozzles formed on a substrate, each nozzle 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, wherein at least part of an ink ejection face of the printhead is hydrophobic relative to the inside surfaces of each nozzle chamber.
In a second aspect, there is provided a method of hydrophobizing an ink ejection face of a printhead, whilst avoiding hydrophobizing nozzle chambers and/or ink supply channels, the method comprising the steps of:
(a) filling nozzle chambers on the printhead with a liquid; and (b) depositing a hydrophobizing material onto the ink ejection face of the printhead.
Optionally the printhead is an inkjet printhead.
Optionally the liquid is an inkjet ink.
Optionally the step of filling the nozzle chambers is priming the printhead with ink.
Optionally the deposition of the hydrophobizing material is chemical vapour deposition.
Optionally the printhead face comprises atoms available for covalent bonding with the hydrophobizing material.
Optionally the atoms are oxygen or nitrogen atoms.
Optionally the hydrophobizing compound forms covalent bonds with the printhead face. Optionally the hydrophobizing material is a silyl compound comprising a hydrophobic group.
Optionally the hydrophobizing material is a silyl chloride.
Optionally the hydrophobizing compound is non-polymerizable in the liquid.
Optionally the hydrophobizing compound is a silyl monochloride.
Optionally there is provided a printhead obtained by the above method.
Optionally each roof forms at least part of the ink ejection face of the printhead, each roof having a hydrophobic outside surface relative to the inside surfaces of each nozzle chamber.
Optionally at least part of the ink ejection face has a contact angle of more than 90° and the inside surfaces of the nozzle chambers have a contact angle of less than 90°.
Optionally at least part of the ink ejection face has a contact angle of more than 110°.
Optionally the inside surfaces of the nozzle chambers have a contact angle of less than 70°.
Optionally each nozzle chamber comprises a roof and sidewalls walls formed from a ceramic material.
Optionally the ceramic material is selected from silicon nitride, silicon oxide or silicon oxynitride.
Optionally the roof and sidewalls are formed by a chemical vapour deposition process.
Optionally the ink ejection face is hydrophobic relative to ink supply channels in the printhead, the ink supply channels being configured to supply ink to each nozzle.
Optionally the ink ejection face comprises a layer of hydrophobic material, and the inside surfaces of each nozzle chamber lacks a layer of hydrophobic material.
Optionally the hydrophobic material is covalently bonded to at least part of the ink ejection surface.
BRIEF DESCRIPTION OF THE DRAWINGS
Notwithstanding any other forms that may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic cross-sectional view through an ink chamber of a unit cell of a printhead according to an embodiment using a bubble forming heater element;
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; and
Fig. 5 is a diagrammatic cross-sectional view through a unit cell of a printhead in accordance with an embodiment of the invention showing the collapse of a vapor bubble.
Fig. 6 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
Fig. 7 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 6.
Fig. 8 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
Fig. 9 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 8.
Fig. 10 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
Fig. 11 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 10.
Fig. 12 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
Fig. 13 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
Fig. 14 is a schematic, partially cut away, exploded perspective view of the unit cell of Fig. 13.
Figs. 15 to 25 are schematic perspective views of the unit cell shown in Figures 13 and 14, at various successive stages in the production process of the printhead. Fig. 26 shows partially cut away schematic perspective views of the unit cell of Figure 25.
Fig. 27 shows the unit cell of Fig. 25 primed with a fluid.
Fig. 28 shows the unit cell of Fig. 27 with a hydrophobic coating on the nozzle plate
DESCRIPTION OF OPTIONAL EMBODIMENTS
Bubble Forming Heater Element Actuator
With reference to Figures 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 Figure 1. Thereafter, the heater element 10 is heated for somewhat less than 1 microsecond, 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.
Figure 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.
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 Figure 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 pressure wave generated within the chamber creates significant stresses in the chamber wall. Forming the chamber from an amorphous ceramic such as silicon nitride, silicon dioxide (glass) or silicon oxynitride, gives the chamber walls high strength while avoiding the use of material with a crystal structure. Crystalline defects can act as stress concentration points and therefore potential areas of weakness and ultimately failure.
Figures 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 Figure 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 as an ejected drop 16, rather than back through the inlet passage 9.
Turning now to Figure 4, the printhead is shown at a still further successive stage of operation, in which the ink drop 16 that is being ejected is shown during its "necking phase" before the drop breaks off. At this stage, the bubble 12 has already reached its maximum size and has then begun to collapse towards the point of collapse 17, as reflected in more detail in Figure 21.
The collapsing of the bubble 12 towards the point of collapse 17 causes some ink 11 to be drawn from within the nozzle 3 (from the sides 18 of the drop), and some to be drawn from the inlet passage 9, towards the point of collapse. Most of the ink 11 drawn in this manner is drawn from the nozzle 3, forming an annular neck 19 at the base of the drop 16 prior to its breaking off.
The drop 16 requires a certain amount of momentum to overcome surface tension forces, in order to break off. As ink 11 is drawn from the nozzle 3 by the collapse of the bubble 12, the diameter of the neck 19 reduces thereby reducing the amount of total surface tension holding the drop, so that the momentum of the drop as it is ejected out of the nozzle is sufficient to allow the drop to break off.
When the drop 16 breaks off, cavitation forces are caused as reflected by the arrows 20, as the bubble 12 collapses to the point of collapse 17. It will be noted that there are no solid surfaces in the vicinity of the point of collapse 17 on which the cavitation can have an effect. Features and advantages of further embodiments
Figures 6 to 29 show further embodiments of unit cells 1 for thermal inkjet printheads, each embodiment having its own particular functional advantages. These advantages will be discussed in detail below, with reference to each individual embodiment. For consistency, the same reference numerals are used in Figures 6 to 29 to indicate corresponding components.
Referring to Figures 6 and 7, the unit cell 1 shown has the chamber 7, ink supply passage 32 and the nozzle rim 4 positioned mid way along the length of the unit cell 1. As best seen in Figure 7, the drive circuitry 22 is partially on one side of the chamber 7 with the remainder on the opposing side of the chamber. The drive circuitry 22 controls the operation of the heater 14 through vias in the integrated circuit metallisation layers of the interconnect 23. The interconnect 23 has a raised metal layer on its top surface. Passivation layer 24 is formed in top of the interconnect 23 but leaves areas of the raised metal layer exposed. Electrodes 15 of the heater 14 contact the exposed metal areas to supply power to the element 10.
Alternatively, the drive circuitry 22 for one unit cell is not on opposing sides of the heater element that it controls. All the drive circuitry 22 for the heater 14 of one unit cell is in a single, undivided area that is offset from the heater. That is, the drive circuitry 22 is partially overlaid by one of the electrodes 15 of the heater 14 that it is controlling, and partially overlaid by one or more of the heater electrodes 15 from adjacent unit cells. In this situation, the center of the drive circuitry 22 is less than 200 microns from the center of the associate nozzle aperture 5. In most Memjet printheads of this type, the offset is less than 100 microns and in many cases less than 50 microns, preferably less than 30 microns.
Configuring the nozzle components so that there is significant overlap between the electrodes and the drive circuitry provides a compact design with high nozzle density (nozzles per unit area of the nozzle plate 2). This also improves the efficiency of the printhead by shortening the length of the conductors from the circuitry to the electrodes. The shorter conductors have less resistance and therefore dissipate less energy.
The high degree of overlap between the electrodes 15 and the drive circuitry 22 also allows more vias between the heater material and the CMOS metalization layers of the interconnect 23. As best shown in Figures 14 and 15, the passivation layer 24 has an array of vias to establish an electrical connection with the heater 14. More vias lowers the resistance between the heater electrodes 15 and the interconnect layer 23 which reduces power losses. However, the passivation layer 24 and electrodes 15 may also be provided without vias in order to simplify the fabrication process.
In Figures 8 and 9, the unit cell 1 is the same as that of Figures 6 and 7 apart from the heater element 10. The heater element 10 has a bubble nucleation section 158 with a smaller cross section than the remainder of the element. The bubble nucleation section 158 has a greater resistance and heats to a temperature above the boiling point of the ink before the remainder of the element 10. The gas bubble nucleates at this region and subsequently grows to surround the rest of the element 10. By controlling the bubble nucleation and growth, the trajectory of the ejected drop is more predictable.
The heater element 10 is configured to accommodate thermal expansion in a specific manner. As heater elements expand, they will deform to relieve the strain. Elements such as that shown in Figures 6 and 7 will bow out of the plane of lamination because its thickness is the thinnest cross sectional dimension and therefore has the least bending resistance. Repeated bending of the element can lead to the formation of cracks, especially at sharp corners, which can ultimately lead to failure. The heater element 10 shown in Figures 8 and 9 is configured so that the thermal expansion is relieved by rotation of the bubble nucleation section 158, and slightly splaying the sections leading to the electrodes 15, in preference to bowing out of the plane of lamination. The geometry of the element is such that miniscule bending within the plane of lamination is sufficient to relieve the strain of thermal expansion, and such bending occurs in preference to bowing. This gives the heater element greater longevity and reliability by minimizing bend regions, which are prone to oxidation and cracking.
Referring to Figures 10 and 11, the heater element 10 used in this unit cell 1 has a serpentine or 'double omega' shape. This configuration keeps the gas bubble centered on the axis of the nozzle. A single omega is a simple geometric shape which is beneficial from a fabrication perspective. However the gap 159 between the ends of the heater element means that the heating of the ink in the chamber is slightly asymmetrical. As a result, the gas bubble is slightly skewed to the side opposite the gap 159. This can in turn affect the trajectory of the ejected drop. The double omega shape provides the heater element with the gap 160 to compensate for the gap 159 so that the symmetry and position of the bubble within the chamber is better controlled and the ejected drop trajectory is more reliable.
Figure 12 shows a heater element 10 with a single omega shape. As discussed above, the simplicity of this shape has significant advantages during lithographic fabrication. It can be a single current path that is relatively wide and therefore less affected by any inherent inaccuracies in the deposition of the heater material. The inherent inaccuracies of the equipment used to deposit the heater material result in variations in the dimensions of the element. However, these tolerances are fixed values so the resulting variations in the dimensions of a relatively wide component are proportionally less than the variations for a thinner component. It will be appreciated that proportionally large changes of components dimensions will have a greater effect on their intended function.
Therefore the performance characteristics of a relatively wide heater element are more reliable than a thinner one.
The omega shape directs current flow around the axis of the nozzle aperture 5. This gives good bubble alignment with the aperture for better ejection of drops while ensuring that the bubble collapse point is not on the heater element 10. As discussed above, this avoids problems caused by cavitation.
Referring to Figures 13 to 26, another embodiment of the unit cell 1 is shown together with several stages of the etching and deposition fabrication process. In this embodiment, the heater element 10 is suspended from opposing sides of the chamber. This allows it to be symmetrical about two planes that intersect along the axis of the nozzle aperture 5. This configuration provides a drop trajectory along the axis of the nozzle aperture 5 while avoiding the cavitation problems discussed above.
Fabrication Process
In the interests of brevity, the fabrication stages have been shown for the unit cell of Figure 13 only (see Figures 15 to 25). It will be appreciated that the other unit cells will use the same fabrication stages with different masking.
Referring to Figure 15, there is shown the starting point for fabrication of the thermal inkjet nozzle shown in Figure 13. CMOS processing of a silicon wafer provides a silicon substrate 21 having drive circuitry 22, and an interlayer dielectric ("interconnect") 23. The interconnect 23 comprises four metal layers, which together form a seal ring for the inlet passage 9 to be etched through the interconnect. The top metal layer 26, which forms an upper portion of the seal ring, can be seen in Figure 15. The metal seal ring prevents ink moisture from seeping into the interconnect 23 when the inlet passage 9 is filled with ink.
A passivation layer 24 is deposited onto the top metal layer 26 by plasma-enhanced chemical vapour deposition (PECVD). After deposition of the passivation layer 24, it is etched to define a circular recess, which forms parts of the inlet passage 9. At the same as etching the recess, a plurality of vias 50 are also etched, which allow electrical connection through the passivation layer 24 to the top metal layer 26. The etch pattern is defined by a layer of patterned photoresist (not shown), which is removed by O2 ashing after the etch.
Referring to Figure 16, in the next fabrication sequence, a layer of photoresist is spun onto the passivation later 24. The photoresist is exposed and developed to define a circular opening. With the patterned photoresist 51 in place, the dielectric interconnect 23 is etched as far as the silicon substrate 21 using a suitable oxide-etching gas chemistry (e.g. 02/C4F8). Etching through the silicon substrate is continued down to about 20 microns to define a front ink hole 52, using a suitable silicon-etching gas chemistry (e.g. 'Bosch etch'). The same photoresist mask 51 can be used for both etching steps. Figure 17 shows the unit cell after etching the front ink hole 52 and removal of the photoresist 51.
Referring to Figure 18, in the next stage of fabrication, the front ink hole 52 is plugged with photoresist to provide a front plug 53. At the same time, a layer of photoresist is deposited over the passivation layer 24. This layer of photoresist is exposed and developed to define a first sacrificial scaffold 54 over the front plug 53, and scaffolding tracks 35 around the perimeter of the unit cell. The first sacrificial scaffold 54 is used for subsequent deposition of heater material 38 thereon and is therefore formed with a planar upper surface to avoid any buckling in the heater element (see heater element 10 in Figure 13). The first sacrificial scaffold 54 is UV cured and hardbaked to prevent reflow of the photoresist during subsequent high-temperature deposition onto its upper surface. Importantly, the first sacrificial scaffold 54 has sloped or angled side faces 55. These angled side faces 55 are formed by adjusting the focusing in the exposure tool (e.g. stepper) when exposing the photoresist. The sloped side faces 55 advantageously allow heater material 38 to be deposited substantially evenly over the first sacrificial scaffold 54.
Referring to Figure 19, the next stage of fabrication deposits the heater material 38 over the first sacrificial scaffold 54, the passivation layer 24 and the perimeter scaffolding tracks 35. The heater material 38 is typically a monolayer of TiAlN. However, the heater material 38 may alternatively comprise TiAlN sandwiched between upper and lower passivating materials, such as tantalum or tantalum nitride. Passivating layers on the heater element 10 minimize corrosion of the and improve heater longevity.
Referring to Figure 20, the heater material 38 is subsequently etched down to the first sacrificial scaffold 54 to define the heater element 10. At the same time, contact electrodes 15 are defined on either side of the heater element 10. The electrodes 15 are in contact with the top metal layer 26 and so provide electrical connection between the CMOS and the heater element 10. The sloped side faces of the first sacrificial scaffold 54 ensure good electrical connection between the heater element 10 and the electrodes 15, since the heater material is deposited with sufficient thickness around the scaffold 54. Any thin areas of heater material (due to insufficient side face deposition) would increase resistivity and affect heater performance.
Adjacent unit cells are electrically insulated from each other by virtue of grooves etched around the perimeter of each unit cell. The grooves are etched at the same time as defining the heater element 10.
Referring to Figure 21, in the subsequent step a second sacrificial scaffold 39 of photoresist is deposited over the heater material. The second sacrificial scaffold 39 is exposed and developed to define sidewalls for the cylindrical nozzle chamber and perimeter sidewalls for each unit cell. The second sacrificial scaffold 39 is also UV cured and hardbaked to prevent any reflow of the photoresist during subsequent high-temperature deposition of the silicon nitride roof material.
Referring to Figure 22, silicon nitride is deposited onto the second sacrificial scaffold 39 by plasma enhanced chemical vapour deposition. The silicon nitride forms a roof 44 over each unit cell, which is the nozzle plate 2 for a row of nozzles. Chamber sidewalls 6 and unit cell sidewalls 56 are also formed by deposition of silicon nitride.
Referring to Figure 23, the nozzle rim 4 is etched partially through the roof 44, by placing a suitably patterned photoresist mask over the roof, etching for a controlled period of time and removing the photoresist by ashing. Referring to Figure 24, the nozzle aperture 5 is etched through the roof 24 down to the second sacrificial scaffold 39. Again, the etch is performed by placing a suitably patterned photoresist mask over the roof, etching down to the scaffold 39 and removing the photoresist mask.
With the nozzle structure now fully formed on a frontside of the silicon substrate 21 , an ink supply channel
32 is etched from the backside of the substrate 21, which meets with the front plug 53.
Referring to Figure 25, after formation of the ink supply channel 32, the first and second sacrificial scaffolds of photoresist, together with the front plug 53 are ashed off using an O2 plasma. Accordingly, fluid connection is made from the ink supply channel 32 through to the nozzle aperture 5.
It should be noted that a portion of photoresist, on either side of the nozzle chamber sidewalls 6, remains encapsulated by the roof 44, the unit cell sidewalls 56 and the chamber sidewalls 6. This portion of photoresist is sealed from the O2 ashing plasma and, therefore, remains intact after fabrication of the printhead. This encapsulated photoresist advantageously provides additional robustness for the printhead by supporting the nozzle plate 2. Hence, the printhead has a robust nozzle plate spanning continuously over rows of nozzles, and being supported by solid blocks of hardened photoresist, in addition to support walls.
Hydrophobic Coating of Front Face Referring to Figure 24, it can been seen that a hydrophobic material may be deposited onto the roof 44 at this stage by, for example, chemical vapour deposition. The whole of the front face of the printhead may be coated with hydrophobic material. Alternatively, predetermined regions of the roof 44 (e.g. regions surrounding each nozzle aperture 5) may be coated. However, referring to Figure 25, die final stage of printhead fabrication involves ashing off the photoresist, which occupies the nozzle chambers. Since hydrophobic coating materials are generally organic in nature, the ashing process will remove the hydrophobic coating on the roof 44 as well as the photoresist 39 in the nozzle chambers. Hence, a hydrophobic coating step at this stage would ultimately have no effect on the hydrophobicity of the roof 44.
Referring to Figure 25, it can be seen that a hydrophobic material may be deposited onto the roof 44 at this stage by, for example, chemical vapour deposition. However, the CVD process will deposit the hydrophobic material both onto the roof 44, onto nozzle chamber sidewalls, onto the heater element 10 and inside ink supply channels 32. A hydrophobic coating inside the nozzle chambers and ink supply channels would be highly undesirable in terms of creating a positive ink pressure biased towards the nozzle chambers. A hydrophobic coating on the heater element 10 would be equally undesirable in terms of kogation during printing.
Referring to Figure 27, there is shown a process for depositing a hydrophobic material onto the roof 44, which eliminates the aforementioned selectivity problems. Before deposition of the hydrophobic material, die printhead is primed with a liquid, which fills the ink supply channels 32 and nozzle chamber up to the rim 4. The liquid is preferably ink so that the hydrophobic deposition step can be incorporated into the overall printer manufacturing process. Once primed with ink 60, the front face of the printhead, including the roof 44, is coated with a hydrophobic material 61 by chemical vapour deposition (see Figure 28). The hydrophobic material 61 cannot be deposited inside the nozzle chamber, because the ink 60 effectively seals the nozzle aperture 5 from the vapour. Hence, the ink 60 protects the nozzle chamber and allows selective deposition of the hydrophobic material 61 onto the roof 44. Accordingly, the final printhead has a hydrophobic front face in combination with hydrophilic nozzle chambers and ink supply channels. The choice of hydrophobic material is not critical. Any hydrophobic compound, which can adhere to the roof 44 by either covalent bonding, ionic bonding, chemisorption or adsorption may be used. The choice of hydrophobic material will depend on the material forming the roof 44 and also the liquid used to prime the nozzles.
Typically, the roof 44 is formed from silicon nitride, silicon oxide or silicon oxynitride. In this case, the hydrophobic material is typically a compound, which can form covalent bonds with the oxygen or nitrogen atoms exposed on the surface of the roof. Examples of suitable compounds are silyl chlorides (including monochlorides, dichlorides, trichlorides) having at least one hydrophobic group. The hydrophobic group is typically a Ci.2oalkyl group, optionally substituted with a plurality of fluorine atoms. The hydrophobic group may be perfluorinated, partially fluorinated or non-fluorinated. Examples of suitable hydrophobic compounds include: trimethylsilyl chloride, dimethylsilyl dichloride, methylsilyl trichloride, triethylsilyl chloride, octyldimethylsilyl chloride, perfluorooctyldimethylsilyl chloride, perfluorooctylsilyl trichloride, perfluorooctylchlorosilane etc.
Typically, the nozzles are primed with an inkjet ink. In this case, the hydrophobic material is typically a compound, which does not polymerise in aqueous solution and form a skin across the nozzle aperture 5. Examples of non-polymerizable hydrophobic compounds include: trimethylsilyl chloride, triethylsilyl chloride, perfluorooctyldimethylsilyl chloride, perfluorooctylchlorosilane etc. Whilst silyl chlorides have been exemplified as hydrophobizing compounds hereinabove, it will be appreciated that the present invention may be used in conjunction with any hydrophobizing compound, which can be deposited by CVD or another suitable deposition process.
Other Embodiments
The invention has been described above with reference to printheads using bubble forming heater elements. However, it is potentially suited to a wide range of printing system including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers high speed pagewidth printers, notebook computers with inbuilt pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic "minilabs", video printers, PHOTO CD (PHOTO CD is a registered trade mark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.
It will be appreciated by ordinary workers in this field that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive. Ink Jet Technologies
The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used.
The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy- inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. In conventional thermal inkjet printheads, this leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.
The most significant problem with piezoelectric inkjet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.
Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include: low power (less than 10 Watts) high resolution capability (1,600 dpi or more) photographic quality output low manufacturing cost small size (pagewidth times minimum cross section) high speed (< 2 seconds per page).
All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different inkjet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.
The inkjet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.
For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square nun. The printheads each contain 19,200 nozzles plus data and control circuitry.
Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.
Tables of Drop-on-Demand Ink Jets
Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.
The following tables form the axes of an eleven dimensional table of ink jet types. Actuator mechanism (18 types) Basic operation mode (7 types)
Auxiliary mechanism (8 types)
Actuator amplification or modification method (17 types) Actuator motion (19 types) Nozzle refill method (4 types) Method of restricting back-flow through inlet (10 types)
Nozzle clearing method (9 types) Nozzle plate construction (9 types) Drop ejection direction (5 types) Ink type (7 types)
The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJOl to IJ45 above which matches the docket numbers in the table under the heading Cross References to Related Applications.
Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJOl to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.
Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJOl to IJ45 series are also listed in the examples column. In some cases, print technology may be listed more than once in a table, where it shares characteristics with more than one entry. Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.
The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

Claims

1. A method of hydrophobizing an ink ejection face of a printhead, whilst avoiding hydrophobizing nozzle chambers and/or ink supply channels, the method comprising the steps of: (a) filling nozzle chambers on the printhead with a liquid; and
(b) depositing a hydrophobizing material onto the ink ejection face of the printhead.
2. The method of claim 1, wherein the printhead is an inkjet printhead.
3. The method of claim 1 , wherein the liquid is an inkjet ink.
4. The method of claim 1, wherein the step of filling the nozzle chambers is priming the printhead with ink.
5. The method of claim 1, wherein the deposition of the hydrophobizing material is chemical vapour deposition.
6. The method of claim 1, wherein the printhead face comprises atoms available for covalent bonding with the hydrophobizing material.
7. The method of claim 6, wherein the atoms are oxygen or nitrogen atoms.
8. The method of claim 6, wherein the hydrophobizing compound forms covalent bonds with the printhead face.
9. The method of claim 1, wherein the hydrophobizing material is a silyl compound comprising a hydrophobic group.
10. The method of claim 8, wherein the hydrophobizing material is a silyl chloride.
11. The method of claim 9, wherein the hydrophobizing compound is non-polymerizable in the liquid.
12. The method of claim 10, wherein the hydrophobizing compound is a silyl monochloride.
13. A printhead obtained by the method according to claim 1.
14. A printhead comprising a plurality of nozzles formed on a substrate, each nozzle 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, wherein at least part of an ink ejection face of the printhead is hydrophobic relative to the inside surfaces of each nozzle chamber.
15. The printhead of claim 14, wherein each roof forms at least part of the ink ejection face of the printhead, each roof having a hydrophobic outside surface relative to the inside surfaces of each nozzle chamber.
16. The printhead of claim 14, wherein at least part of the ink ejection face has a contact angle of more than 90° and the inside surfaces of the nozzle chambers have a contact angle of less than 90°.
17. The printhead of claim 14, wherein at least part of the ink ejection face has a contact angle of more than 110°.
18. The printhead of claim 14, wherein the inside surfaces of the nozzle chambers have a contact angle of less than 70°.
19. The printhead of claim 14, wherein each nozzle chamber comprises a roof and sidewalls walls formed from a ceramic material.
20. The printhead of claim 19, wherein the ceramic material is selected from silicon nitride, silicon oxide or silicon oxynitride.
21. The printhead of claim 19 , wherein the roof and sidewalls are formed by a chemical vapour deposition process.
22. The printhead of claim 14, wherein the ink ejection face is hydrophobic relative to ink supply channels in the printhead, the ink supply channels being configured to supply ink to each nozzle.
23. The printhead of claim 14, wherein the ink ejection face comprises a layer of hydrophobic material, and the inside surfaces of each nozzle chamber lacks a layer of hydrophobic material.
24. The printhead of claim 14, wherein the hydrophobic material is covalently bonded to at least part of the ink ejection surface.
EP05714351A 2005-04-04 2005-04-04 Method of hydrophobically coating a printhead Withdrawn EP1871606A4 (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/AU2005/000482 WO2006105571A1 (en) 2005-04-04 2005-04-04 Method of hydrophobically coating a printhead

Publications (2)

Publication Number Publication Date
EP1871606A1 true EP1871606A1 (en) 2008-01-02
EP1871606A4 EP1871606A4 (en) 2009-12-30

Family

ID=37072994

Family Applications (1)

Application Number Title Priority Date Filing Date
EP05714351A Withdrawn EP1871606A4 (en) 2005-04-04 2005-04-04 Method of hydrophobically coating a printhead

Country Status (2)

Country Link
EP (1) EP1871606A4 (en)
WO (1) WO2006105571A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SG176493A1 (en) * 2007-03-12 2011-12-29 Silverbrook Res Pty Ltd Method of fabricating printhead having hydrophobic ink ejection face

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4406224A1 (en) * 1993-02-25 1994-09-01 Seiko Epson Corp Nozzle plate and method for the surface treatment thereof
US6126269A (en) * 1993-10-29 2000-10-03 Seiko Epson Corporation Nozzle plate for ink jet printer and method of manufacturing said nozzle plate
EP1043160A1 (en) * 1999-03-17 2000-10-11 Fujitsu Limited Print head with water repellent coating
US6511156B1 (en) * 1997-09-22 2003-01-28 Citizen Watch Co., Ltd. Ink-jet head nozzle plate, its manufacturing method and ink-jet head
EP1386951A1 (en) * 2001-04-02 2004-02-04 Matsushita Electric Industrial Co., Ltd. Water-repellent film and method for preparing the same, and ink-jet head and ink-jet type recording device using the same
EP1428662A2 (en) * 2002-12-05 2004-06-16 Samsung Electronics Co., Ltd. Monolithic ink-jet printhead and method for manufacturing the same
US20040130597A1 (en) * 2001-10-25 2004-07-08 Samsung Electronics Co., Ltd. Monolithic ink-jet printhead and method for manufacturing the same
EP1506869A1 (en) * 2003-08-11 2005-02-16 Brother Kogyo Kabushiki Kaisha Method for producing a nozzle plate and nozzle plate

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3918472A1 (en) * 1989-06-06 1990-12-13 Siemens Ag HYDROPHOBIC AGENTS AND APPLICATION METHOD, ESPECIALLY FOR INK JET PRINT HEADS
EP0882593A1 (en) * 1997-06-05 1998-12-09 Xerox Corporation Method for forming a hydrophobic/hydrophilic front face of an ink jet printhead

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4406224A1 (en) * 1993-02-25 1994-09-01 Seiko Epson Corp Nozzle plate and method for the surface treatment thereof
US6126269A (en) * 1993-10-29 2000-10-03 Seiko Epson Corporation Nozzle plate for ink jet printer and method of manufacturing said nozzle plate
US6511156B1 (en) * 1997-09-22 2003-01-28 Citizen Watch Co., Ltd. Ink-jet head nozzle plate, its manufacturing method and ink-jet head
EP1043160A1 (en) * 1999-03-17 2000-10-11 Fujitsu Limited Print head with water repellent coating
EP1386951A1 (en) * 2001-04-02 2004-02-04 Matsushita Electric Industrial Co., Ltd. Water-repellent film and method for preparing the same, and ink-jet head and ink-jet type recording device using the same
US20040130597A1 (en) * 2001-10-25 2004-07-08 Samsung Electronics Co., Ltd. Monolithic ink-jet printhead and method for manufacturing the same
EP1428662A2 (en) * 2002-12-05 2004-06-16 Samsung Electronics Co., Ltd. Monolithic ink-jet printhead and method for manufacturing the same
EP1506869A1 (en) * 2003-08-11 2005-02-16 Brother Kogyo Kabushiki Kaisha Method for producing a nozzle plate and nozzle plate

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO2006105571A1 *

Also Published As

Publication number Publication date
EP1871606A4 (en) 2009-12-30
WO2006105571A1 (en) 2006-10-12

Similar Documents

Publication Publication Date Title
JP4160250B2 (en) Thermally operated inkjet
US7328976B2 (en) Hydrophobically coated printhead
US7794613B2 (en) Method of fabricating printhead having hydrophobic ink ejection face
EP2129526B1 (en) Metal film protection during printhead fabrication with minimum number of mems processing steps
JP2003521389A5 (en)
US20080225082A1 (en) Printhead having hydrophobic polymer coated on ink ejection face
IL164931A (en) Ink jet printhead chip with predetermined micro-electromechanical systems height
US7976132B2 (en) Printhead having moving roof structure and mechanical seal
US7984975B2 (en) Printhead nozzle cell having photoresist chamber
US20100271430A1 (en) Printhead provided with individual nozzle enclosures
WO2008109910A1 (en) Method of fabricating printhead having hydrophobic ink ejection face
US20010009430A1 (en) Differential thermal ink jet printing mechanism
JP4473314B2 (en) Print head, printer, and method for printing
WO2006105571A1 (en) Method of hydrophobically coating a printhead
AU2005242168B2 (en) Ink jet nozzle with slotted sidewall and moveable vane
EP2349724B1 (en) Inkjet nozzle assembly having moving roof structure and sealing bridge
WO2009039551A1 (en) Method of removing photoresist

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 20071101

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU MC NL PL PT RO SE SI SK TR

DAX Request for extension of the european patent (deleted)
A4 Supplementary search report drawn up and despatched

Effective date: 20091126

17Q First examination report despatched

Effective date: 20111017

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20120228