Patent Application
20100128086
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:
CPH015US CPH017US
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.
Various methods, systems and apparatus relating to the present invention are disclosed in the following US Patents/Patent Applications filed by the applicant or assignee of the present 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 U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static inkjet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous inkjet 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 inkjet stream and Fischbeck in U.S. Pat. No. 4,584,590 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 2,007,162 (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.
The present Applicant has described a plethora of inkjet printheads, which are constructed utilizing micro-electromechanical systems (MEMS) techniques. As described in the Applicant's earlier U.S. application Ser. Nos. 11/685,084; 11/763,443; and 11/763,440, the contents of which are incorporated herein by reference, a MEMS inkjet printhead may comprise a nozzle plate having moving portions. Each moving portion typically has a nozzle opening defined therein so that actuation of the moving portion results in ejection of ink from the printhead.
An advantage of this type of printhead is that the energy required to eject a droplet of ink is small compared with, for example, traditional thermal bubble-forming printheads. The Applicant has previously described how specific actuator designs and complementary actuation methods provide highly efficient drop ejection from such printheads (see, for example, U.S. application Ser. Nos. 11/607,976 and 12/239,814, the contents of which are herein incorporated by reference).
However, a problem with ‘moving nozzle’ printheads is that they require a good fluidic seal between the moving portion and the stationary portion of the printhead. Ink should only be ejected through the nozzle opening and should not leak out of seals. If the distance between the moving portion and the stationary portion is small, then surface tension may retain ink inside nozzle chambers. However, the use of ink surface tension as a fluidic seal is problematic and usually cannot provide a reliable seal, especially if the ink inside nozzle chambers experiences pressure surges.
In the Applicant's earlier application Ser. Nos. 11/685,084; 11/763,443; and 11/763,440, there was described a method of fabricating a mechanical seal for moving portions of a nozzle plate. Typically, a flexible layer of polydimethylsiloxane (PDMS) is coated over the nozzle plate, which acts as a sealing membrane between the moving portions and the stationary part of the printhead. Moreover, the layer of PDMS provides a hydrophobic ink ejection surface, which is also highly desirable in terms of printhead fluidics and, ultimately, print quality.
It would be desirable to provide improved mechanical seals for inkjet printheads having moving nozzles. It would be particularly desirable to provide efficacious mechanical seals, which have minimal impact on the overall efficiency of the printhead.
In a first aspect the present invention provides a nozzle assembly for an inkjet printhead, said nozzle assembly comprising:
Optionally, said seal member is comprised of a polymeric material.
Optionally, said polymeric material is comprised of polydimethylsiloxane (PDMS).
Optionally, said seal member is absent from a space between said moving portion and said stationary portion.
Optionally, said seal member has a non-planar profile configured for facilitating movement of said moving portion.
Optionally, said seal member comprises at least one ridge and/or at least one furrow in profile.
Optionally, said seal member comprises a crown portion, said crown portion standing proud of a first end of said seal member connected to said moving portion and a second end of said seal member connected to said stationary portion.
Optionally, said seal member is corrugated.
Optionally, said nozzle opening is defined in said moving portion.
Optionally, said nozzle opening is defined in said stationary 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.
Optionally, the polymeric material is coated on a substantial part of said roof, such that an ink ejection face of said printhead is hydrophobic.
Optionally, each roof forms at least part of a nozzle plate 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 nozzle chamber comprises sidewalls extending between said roof and a substrate, such that said roof is spaced apart from said substrate.
Optionally, said moving portion is configured to move towards said substrate upon actuation of said actuator.
In a further aspect the presenting invention provides an inkjet printhead comprising a plurality of nozzle assemblies, each nozzle assembly comprising:
Optionally, a nozzle plate of said printhead comprises a polymeric coating.
Optionally, said polymeric coating comprises said seal members.
In a second aspect the present invention provides an inkjet printhead comprising:
wherein each seal member is configured as a bridge spanning between its respective moving portion and said stationary portion.
Optionally, a nozzle plate comprises the plurality of moving portions and the stationary portion.
Optionally, said nozzle plate comprises a flexible polymeric coating, said coating comprising said seal members.
Optionally, said polymeric coating is hydrophobic.
Optionally, the polymeric coating is comprised of polydimethylsiloxane (PDMS).
Optionally, said seal member is absent from a space between said moving portion and said stationary portion.
Optionally, said seal member has a non-planar profile configured for facilitating movement of said moving portion.
Optionally, each seal member comprises at least one ridge and/or at least one furrow in profile.
Optionally, each seal member comprises a crown portion, said crown portion standing proud of a first end of said seal member connected to said moving portion and a second end of said seal member connected to said stationary portion.
Optionally, each seal member is corrugated.
In another aspect the present invention provides a printhead comprising a plurality of nozzle assemblies, each nozzle assembly comprising:
Optionally, said nozzle opening is defined in said moving portion.
Optionally, said nozzle opening is defined in said stationary 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.
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 moving portion is configured to move towards said substrate upon actuation of said actuator.
Optionally, said roof and said sidewalls are comprised of a ceramic material depositable by CVD, said ceramic material being selected from the group comprising: silicon nitride, silicon oxide and silicon oxynitride.
In a further aspect the present invention provides an inkjet printer comprising the printhead according to claim 1.
In a third aspect the present invention provides a method of fabricating an inkjet nozzle assembly having a seal member bridging between a moving portion and a stationary portion, said method comprising the steps of:
wherein said seal member is comprised of said flexible material.
Optionally, said flexible material a polymeric material.
Optionally, said flexible material is comprised of polydimethylsiloxane (PDMS).
Optionally, said plug fills said via, such that said seal member is absent from said via.
Optionally, said plug has a head extending out of said via, said head presenting a scaffold surface for deposition of said flexible material.
Optionally, said seal member has a non-planar profile configured for facilitating movement of said moving portion.
Optionally, said seal member comprises at least one ridge and/or at least one furrow in profile.
Optionally, said seal member comprises a crown portion, said crown portion standing proud of a first end of said seal member connected to said moving portion and a second end of said seal member connected to said stationary portion.
Optionally, said seal member is corrugated.
In a further aspect the present invention provides a method further comprising the step of:
Optionally, said nozzle opening is etched through said moving portion.
Optionally, said moving portion comprises a thermal bend actuator.
Optionally, said thermal bend actuator comprises:
Optionally, said flexible material is a hydrophobic material, and wherein said deposition of said flexible material is over a substantial portion of said roof such that said roof is relatively hydrophobic.
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 moving portion is configured to move towards said substrate upon actuation of an actuator.
Optionally, said flexible layer is covered with a sacrificial protective metal layer prior to removal of said plug.
Optionally, said sacrificial protective metal layer is removed after removal of said plug.
Optionally, said plug is removed by exposing said nozzle assembly to an oxidizing plasma.
In a further aspect the present invention provides an inkjet nozzle assembly having a seal member bridging between a moving portion and a stationary portion, wherein said seal member is comprised of a flexible material deposited over a roof of said nozzle assembly.
Optional embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
The starting point for MEMS fabrication is a standard CMOS wafer having CMOS drive circuitry formed in an upper portion of a silicon wafer. At the end of the MEMS fabrication process, this wafer is diced into individual printhead integrated circuits (ICs), with each IC comprising drive circuitry and plurality of nozzle assemblies.
As shown in
The other electrode 3 shown in
In the sequence of steps shown in
As shown in
In
In
In
To form the active beam member 10, a 1.5 micron layer of active beam material is initially deposited by standard PECVD. The beam material is then etched using a standard metal etch to define the active beam member 10. After completion of the metal etch and as shown in
Still referring to
Referring to
A perimeter space or gap 17 around the moving portion 14 of the roof separates the moving portion from a stationary portion 18 of the roof. This gap 17 allows the moving portion 14 to bend into the nozzle chamber 5 and towards the substrate 1 upon actuation of the actuator 15.
Referring to
The use of photopatternable polymers to coat arrays of nozzle assemblies was described extensively in our earlier U.S. application Ser. Nos. 11/685,084 filed on 12 Mar. 2007 and Ser. No. 11/740,925 filed on 27 Apr. 2007, the contents of which are incorporated herein by reference. Typically, the hydrophobic polymer is polydimethylsiloxane (PDMS) or perfluorinated polyethylene (PFPE). Such polymers are particularly advantageous because they are photopatternable, have high hydrophobicity, and low Young's modulus.
As explained in the above-mentioned U.S. Applications, the exact ordering of MEMS fabrication steps, incorporating the hydrophobic polymer, is relatively flexible. For example, it is perfectly feasible to etch the nozzle opening 13 after deposition of the hydrophobic polymer 19, and use the polymer as a mask for the nozzle etch. It will appreciated that variations on the exact ordering of MEMS fabrication steps are well within the ambit of the skilled person, and, moreover, are included within the scope of the present invention.
The hydrophobic polymer layer 19 performs several functions. Firstly, it fills the gap 17 to provide a mechanical seal between the moving portion 14 and stationary portion 18 of the roof 7. Provided that the polymer has a sufficiently low Young's modulus, the actuator can still bend towards the substrate 1, whilst preventing ink from escaping through the gap 17 during actuation. Secondly, the polymer has a high hydrophobicity, which minimizes the propensity for ink to flood out of the relatively hydrophilic nozzle chambers and onto an ink ejection face 21 of the printhead. Thirdly, the polymer functions as a protective layer, which facilitates printhead maintenance.
Finally, and as shown in
Following the ink supply channel etch, the polyimide 6, which filled the nozzle chamber 5, is removed by ashing (either frontside ashing or backside ashing) using, for example, an O2 plasma to provide the nozzle assembly 100.
Although not described above, a metal film (e.g titanium or aluminium) may be used to protect the polymer layer 19 during final stage MEMS processing, as described in our earlier U.S. application Ser. Nos. 11/740,925 and 11/946,840, the contents of which are herein incorporated by reference. Typically, the protective metal film is deposited onto the polymer layer 19 prior to etching the nozzle opening 13. After all etching and oxidative photoresist removal steps (“ashing steps”) have been completed, the protective metal film may be removed using a simple HF or H2O2 rinse.
In the nozzle assembly 100 described above, the polymer layer 19 fills the gap between the moving portion 14 and the stationary portion 18 of the roof 7. Although this provides a good mechanical seal and can be readily manufactured, the configuration of the seal inevitably impacts on the overall performance and efficiency of the nozzle assembly.
Turning to
Referring then to
In
Referring next to
Following formation of the plug 30, the partially-formed nozzle assembly is then coated with a layer 19 of flexible polymeric material. Typically, the polymeric material is polydimethylsiloxane (PDMS). As shown in
A protective aluminium film 31 is subsequently deposited over the PDMS layer 19. The aluminium film 31 protects the PDMS layer 19 from an oxidative plasma used for removal of the polyimide 6 (
Referring now to
Finally, and referring to
The completed nozzle assembly 200 shown in
The seal member 32 has the profile of a bridge, where one end is connected to the moving portion 14 and the other end is connected to the stationary portion 18. Furthermore, the bridge substantially takes the form of a single-arch bridge, having a ridge or crown portion 33 standing proud of each end of the bridge. Of course, the seal member may alternatively take the form of a simple beam bridge spanning between the moving portion 14 and stationary portion 18, depending on the profile of the upper surface of the plug 30.
The seal member 32 has a number of advantages over the embodiment shown in
Of course, other configurations of the seal member 32 are within the ambit of the present invention. For example, as shown in
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.
