Patent Grant
7794613
The present invention relates to the field of printers and particularly inkjet printheads. It has been developed primarily to improve print quality and reliability in high resolution printheads.
The following applications have been filed by the Applicant simultaneously with the present application:
The disclosures of these co-pending applications are incorporated herein by reference.
The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.
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 U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 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 U.S. Pat. No. 3,373,437 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 U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal inkjet 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 U.S. Pat. No. 4,490,728. 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 below.
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, gallium 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 ink ejection face (“front face” or “nozzle face”), preferably in combination with hydrophilic nozzle chambers and ink supply channels. Hydrophilic nozzle chambers and ink supply channels provide a capillary action and are therefore optimal for priming and for re-supply of ink to nozzle chambers after each drop ejection. 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. Furthermore, any ink which does flood from nozzle openings is less likely to spread across the face and mix on the front face—they will instead form discrete spherical microdroplets which can be managed more easily by suitable maintenance operations.
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, organic, hydrophobic materials deposited onto the front face are typically removed by the ashing process to leave a hydrophilic surface. Moreover, a problem with post-ashing vapour 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 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 creates significant demands on printhead fabrication.
Accordingly, it would be desirable to provide a printhead fabrication process, in which the resultant printhead 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 has a hydrophobic front face in combination with hydrophilic nozzle chambers.
In a first aspect the present invention provides a method of fabricating a printhead having a hydrophobic ink ejection face, the method comprising the steps of:
(a) providing a partially-fabricated printhead comprising a plurality of nozzle chambers and a relatively hydrophilic nozzle surface, said nozzle surface at least partially defining the ink ejection face;
(b) depositing a layer of relatively hydrophobic polymeric material onto the nozzle surface, said polymeric material being resistant to removal by ashing; and
(c) defining a plurality of nozzle openings in said nozzle surface,
thereby providing a printhead having a relatively hydrophobic ink ejection face,
wherein steps (b) and (c) are performed in any order.
Optionally, step (c) is performed prior to step (b), and the method comprises the further step of defining a corresponding plurality of aligned nozzle openings in said deposited polymeric material.
Optionally, said corresponding plurality of aligned nozzle openings are defined by photopatterning said polymeric material.
Optionally, step (c) is performed after step (b), and said polymeric material is used as a mask for etching said nozzle surface.
Optionally, said polymeric material is photopatterned to define a plurality of nozzle opening regions prior to etching said nozzle surface.
Optionally, (c) is performed after step (b), and step (c) comprises the steps of:
Optionally, said mask is photoresist, and said photoresist is removed by ashing.
Optionally, a same gas chemistry is used to etch said polymeric material and said nozzle surface.
Optionally, said gas chemistry comprises O2 and a fluorine-containing compound.
Optionally, in said partially-fabricated printhead, a roof of each nozzle chamber is supported by a sacrificial photoresist scaffold, said method further comprising the step of removing said photoresist scaffold by ashing.
Optionally, a roof of each nozzle chamber is defined at least partially by said nozzle surface.
Optionally, said nozzle surface is spaced apart from a substrate, such that sidewalls of each nozzle chamber extend between said nozzle surface and said substrate.
Optionally, a roof and sidewalls of each nozzle chamber are comprised of a ceramic material depositable by CVD.
Optionally, said roof and sidewalls are comprised of a material selected from the group comprising: silicon oxide, silicon nitride and silicon oxynitride.
Optionally, said hydrophobic polymeric material forms a passivating surface oxide in an O2 plasma.
Optionally, said hydrophobic polymeric material recovers its hydrophobicity after being subjected to an O2 plasma.
Optionally, said polymeric material is selected from the group comprising: polymerized siloxanes and fluorinated polyolefins.
Optionally, said polymeric material is selected from the group comprising: polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE).
Optionally, at least some of said polymeric material is UV-cured after deposition.
In a further aspect the present invention provides a printhead obtained or obtainable by the method of the present invention.
In a second aspect the present invention provides a printhead having an ink ejection face, wherein at least part of the ink ejection face is coated with a hydrophobic polymeric material selected from the group comprising: polymerized siloxanes and fluorinated polyolefins.
Optionally, said polymeric material is resistant to removal by ashing.
Optionally, said polymeric material forms a passivating surface oxide in an oxygen plasma.
Optionally, said polymeric material recovers its hydrophobicity after being subjected to an oxygen plasma.
Optionally, the polymeric material is selected from the group comprising: polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE).
In a further aspect the present invention provides a printhead comprising a plurality of nozzle assemblies formed on a substrate, each nozzle assembly comprising: a nozzle chamber, a nozzle opening defined in a roof of the nozzle chamber and an actuator for ejecting ink through the nozzle opening,
Optionally, a nozzle surface, having the hydrophobic polymer coated thereon, at least partially defines the ink ejection face.
Optionally, each roof defines at least part of the nozzle surface of the printhead, each roof having a hydrophobic outside surface relative to the inside surfaces of each nozzle chamber by virtue of said hydrophobic coating.
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, each nozzle chamber comprises a roof and sidewalls comprised of a ceramic material.
Optionally, the ceramic material is selected from the group comprising: silicon nitride, silicon oxide and silicon oxynitride.
Optionally, said roof is spaced apart from a substrate, such that sidewalls of each nozzle chamber extend between said nozzle surface and said substrate.
Optionally, the ink ejection face is hydrophobic relative to ink supply channels in the printhead.
Optionally, said actuator is a heater element configured for heating ink in said chamber so as to form a gas bubble, thereby forcing a droplet of ink through said nozzle opening.
Optionally, said heater element is suspended in said nozzle chamber.
Optionally, said actuator is a thermal bend actuator comprising:
Optionally, said thermal bend actuator defines at least part of a roof of each nozzle chamber, whereby actuation of said actuator moves said actuator towards a floor of said nozzle chamber.
Optionally, said nozzle opening is defined in said actuator or in a static portion of said roof.
Optionally, said hydrophobic polymeric material defines a mechanical seal between said actuator and a static portion of said roof, thereby minimizing ink leakage during actuation
Optionally, said hydrophobic polymeric material has a Young's modulus of less than 1000 MPa.
In a third aspect the present invention provides a nozzle assembly for an inkjet printhead, said nozzle assembly comprising:
wherein said mechanical seal comprises a polymeric material selected from the group comprising:
polymerized siloxanes and fluorinated polyolefins.
Optionally, said nozzle opening is defined in said moving portion.
Optionally, said nozzle opening is defined in said static portion.
Optionally, said actuator is a thermal bend actuator comprising:
Optionally, said first and second elements are cantilever beams.
Optionally, said thermal bend actuator defines at least part of the moving portion of said roof, whereby actuation of said actuator moves said actuator towards a floor of said nozzle chamber.
Optionally, the polymeric material has a Young's modulus of less than 1000 MPa.
Optionally, the polymeric material is selected from the group comprising: polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE).
Optionally, said polymeric material is hydrophobic and is resistant to removal by ashing.
Optionally, said polymeric material recovers its hydrophobicity after being subjected to an O2 plasma.
Optionally, the polymeric material is coated on the whole of said roof, such that an ink ejection face of said printhead is hydrophobic.
Optionally, each roof forms at least part of a nozzle surface of the printhead, each roof having a hydrophobic outside surface relative to the inside surfaces of each nozzle chamber by virtue of said polymeric coating.
Optionally, said polymeric coating 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, said polymeric has a contact angle of more than 110°.
Optionally, inside surfaces of said nozzle chamber have a contact angle of less than 70°.
Optionally, said nozzle chamber comprises sidewalls extending between said roof and a substrate, such that said roof is spaced apart from said substrate.
Optionally, said roof and said sidewalls are comprised of a ceramic material depositable by CVD.
Optionally, the ceramic material is selected from the group comprising: silicon nitride, silicon oxide and silicon oxynitride.
Optional embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
The present invention may be used with any type of printhead. The present Applicant has previously described a plethora of inkjet printheads. It is not necessary to describe all such printheads here for an understanding of the present invention. However, the present invention will now be described in connection with a thermal bubble-forming inkjet printhead and a mechanical thermal bend actuated inkjet printhead. Advantages of the present invention will be readily apparent from the discussion that follows.
Thermal Bubble-Forming Inkjet Printhead
Referring to
Each nozzle assembly comprises a nozzle chamber 24 formed by MEMS fabrication techniques on a silicon wafer substrate 2. The nozzle chamber 24 is defined by a roof 21 and sidewalls 22 which extend from the roof 21 to the silicon substrate 2. As shown in
Returning to the details of the nozzle chamber 24, it will be seen that a nozzle opening 26 is defined in a roof of each nozzle chamber 24. Each nozzle opening 26 is generally elliptical and has an associated nozzle rim 25. The nozzle rim 25 assists with drop directionality during printing as well as reducing, at least to some extent, ink flooding from the nozzle opening 26. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29 positioned beneath the nozzle opening 26 and suspended across a pit 8. Current is supplied to the heater element 29 via electrodes 9 connected to drive circuitry in underlying CMOS layers 5 of the substrate 2. When a current is passed through the heater element 29, it rapidly superheats surrounding ink to form a gas bubble, which forces ink through the nozzle opening. By suspending the heater element 29, it is completely immersed in ink when the nozzle chamber 24 is primed. This improves printhead efficiency, because less heat dissipates into the underlying substrate 2 and more input energy is used to generate a bubble.
As seen most clearly in
The MEMS fabrication process for manufacturing such printheads was described in detail in our previously filed U.S. application Ser. No. 11/246,684 filed on Oct. 11, 2005, the contents of which is herein incorporated by reference. The latter stages of this fabrication process are briefly revisited here for the sake of clarity.
In the prior art process, and referring to
Referring to
With all the MEMS nozzle features now fully formed, the next stage removes the SAC1 and SAC2 photoresist layers 10 and 16 by O2 plasma ashing (
Referring to
Finally, and referring to
As already discussed above, this prior art MEMS fabrication process inevitably leaves a hydrophilic ink ejection face by virtue of the nozzle surface 56 being formed of ceramic materials, such as silicon dioxide, silicon nitride, silicon oxynitride, aluminium nitride etc.
Nozzle Etch Followed by Hydrophobic Polymer Coating
As an alternative to the process described above, the nozzle surface 56 has a hydrophobic polymer deposited thereon immediately after the nozzle opening etch (i.e. at the stage represented in
Referring to
After deposition, this layer of polymeric material is photopatterned so as to remove the material deposited within the nozzle openings 26. Photopatterning may comprise exposure of the polymeric layer 100 to UV light, except for those regions within the nozzle openings 26. Accordingly, as shown in
Hydrophobic Polymer Coating Prior to Nozzle Etch with Polymer Used as Etch Mask
As an alternative process, the hydrophobic polymer layer 100 is deposited immediately after the stage represented by
Referring to
The nozzle opening 26 is defined by etching through the roof structure 21, which is typically performed using a gas chemistry comprising O2 and a fluorinated hydrocarbon (e.g. CF4 or C4F8). Hydrophobic polymers, such as PDMS and PFPE, are normally etched under the same conditions. However, since materials such as silicon nitride etch much more rapidly, the roof 21 can be etched selectively using either PDMS or PFPE as an etch mask. By way of comparison, with a gas ratio of 3:1 (CF4:O2), silicon nitride etches at about 240 microns per hour, whereas PDMS etches at about 20 microns per hour. Hence, it will be appreciated that etch selectivity using a PDMS mask is achievable when defining the nozzle opening 26.
Once the roof 21 is etched to define the nozzle opening, the nozzle assembly 24 is as shown in
Hydrophobic Polymer Coating Prior to Nozzle Etch with Additional Photoresist Mask
However, as a further alternative and particularly to accommodate situations where there is insufficient etch selectivity, a layer of photoresist (not shown) may be deposited over the hydrophobic polymer 100 shown in
Subsequent O2 ashing may be used to remove just the top layer of photoresist (to obtain the nozzle assembly shown in
The skilled person will be able to envisage other alternative sequences of MEMS processing steps, in addition to the three alternatives discussed herein. However, it will be appreciated that in identifying hydrophobic polymers capable of withstanding O2 and H2 ashing, the present inventors have provided a viable means for providing a hydrophobic nozzle surface in an inkjet printhead fabrication process.
Thermal Bend Actuator Printhead
Having discussed ways in which a nozzle surface of a printhead may be hydrophobized, it will be appreciated that any type of printhead may be hydrophobized in an analogous manner. However, the present invention realizes particular advantages in connection with the Applicant's previously described printhead comprising thermal bend actuator nozzle assemblies. Accordingly, a discussion of how the present invention may be used in such printheads now follows.
In a thermal bend actuated printhead, a nozzle assembly may comprise a nozzle chamber having a roof portion which moves relative to a floor portion of the chamber. The moveable roof portion is typically actuated to move towards the floor portion by means of a bi-layered thermal bend actuator. Such an actuator may be positioned externally of the nozzle chamber or it may define the moving part of the roof structure.
A moving roof is advantageous, because it lowers the drop ejection energy by only having one face of the moving structure doing work against the viscous ink. However, a problem with such moving roof structures is that it is necessary to seal the ink inside the nozzle chamber during actuation. Typically, the nozzle chamber relies on a fluidic seal, which forms a seal using the surface tension of the ink. However, such seals are imperfect and it would be desirable to form a mechanical seal which avoids relying on surface tension as a means for containing the ink. Such a mechanical seal would need to be sufficiently flexible to accommodate the bending motion of the roof.
A typical nozzle assembly 400 having a moving roof structure was described in our previously filed U.S. application Ser. No. 11/607,976 filed on Dec. 4, 2006 (the contents of which is herein incorporated by reference) and is shown here in
As shown more clearly in
The nozzle assembly 400 is characterized in that the moving portion 409 is defined by a thermal bend actuator 410 having a planar upper active beam 411 and a planar lower passive beam 412. Hence, the actuator 410 typically defines at least 50% of the total area of the roof 404. Correspondingly, the upper active beam 411 typically defines at least 50% of the total area of the roof 404.
As shown in
However, it will of course be appreciated that the active beam 411 may, alternatively, be fused or bonded directly to the passive beam 412 for improved structural rigidity. Such design modifications would be well within the ambit of the skilled person.
The active beam 411 is connected to a pair of contacts 416 (positive and ground) via the Ti bridging layer. The contacts 416 connect with drive circuitry in the CMOS layers.
When it is required to eject a droplet of ink from the nozzle chamber 401, a current flows through the active beam 411 between the two contacts 416. The active beam 411 is rapidly heated by the current and expands relative to the passive beam 412, thereby causing the actuator 410 (which defines the moving portion 409 of the roof 404) to bend downwards towards the substrate 403. Since the gap 460 between the moving portion 409 and a static portion 461 is so small, surface tension can generally be relied up to seal this gap when the moving portion is actuated to move towards the substrate 403.
The movement of the actuator 410 causes ejection of ink from the nozzle opening 408 by a rapid increase of pressure inside the nozzle chamber 401. When current stops flowing, the moving portion 409 of the roof 404 is allowed to return to its quiescent position, which sucks ink from the inlet 406 into the nozzle chamber 401, in readiness for the next ejection.
Turning to
An alternative nozzle assembly 500 shown in
However, in contrast with the nozzle assembly 400, the nozzle opening 508 and rim 515 are not defined by the moving portion of the roof 504. Rather, the nozzle opening 508 and rim 515 are defined in a fixed or static portion 561 of the roof 504 such that the actuator 510 moves independently of the nozzle opening and rim during droplet ejection. An advantage of this arrangement is that it provides more facile control of drop flight direction. Again, the small dimensions of the gap 560, between the moving portion 509 and the static portion 561, is relied up to create a fluidic seal during actuation by using the surface tension of the ink.
The nozzle assemblies 400 and 500, and corresponding printheads, may be constructed using suitable MEMS processes in an analogous manner to those described above. In all cases the roof of the nozzle chamber (moving or otherwise) is formed by deposition of a roof material onto a suitable sacrificial photoresist scaffold.
Referring now to
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.
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