Pump action refill ink jet printing mechanism

[0002] The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their U.S. patent application serial numbers (USSN) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.

[0003] Not applicable.

[0004] The present invention relates to ink jet printing and in particular discloses a Pump Action Refill Ink Jet Printer.

[0005] The present invention further relates to the field of drop on demand ink jet printing.

[0006] 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.

[0007] 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.

[0008] 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).

[0009] Ink Jet printers themselves come in many different types. The utilisation of a continuous stream 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.

[0010] 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 utilised by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)

[0011] Piezo-electric ink jet printers are also one form of commonly utilized ink jet printing device. Piezo-electric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilises 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 piezo electric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezo-electric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a Piezo electric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4584590 which discloses a sheer mode type of piezo-electric transducer element.

[0012] 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 U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques 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.

[0013] 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.

[0014] It is an object of the present invention to provide an alternative form of ink jet printing based around ink jet nozzles which utilize a pump action so as to rapidly refill a nozzle chamber for ejection of subsequent ink drops.

[0015] In accordance with a first aspect of the present invention, there is provided an inkjet nozzle chamber having an ink ejection port in one wall of the chamber and an ink supply source interconnected to the chamber. The inkjet nozzle chamber can comprise two actuators the first actuator for ejecting ink from the ink ejection port and a second actuator for pumping ink into the chamber from the ink supply source after the first actuator has caused the ejection of ink from the nozzle chamber. The actuators can utilize thermal bending caused by a conductive heater element encased within a material having a high coefficient of thermal expansion whereby the actuators operate by means of electrical heating by the heater elements. The heater elements can be of serpentine form and concertinaed upon heating so as to allow substantially unhindered expansion of said actuation material during heating. The first actuator is arranged substantially opposite the ink ejection port and both actuators form segments of the nozzle chamber wall opposite the ink ejection port and between the nozzle chamber and the ink supply source. The method for driving the actuators for the ejection of ink from the ink ejection port comprises utilizing the first actuator to eject ink from the ejection port and utilizing the second actuator to pump ink towards the ink ejection port so as to rapidly refill the nozzle chamber around the area of the ink ejection port. The method for driving the actuators can comprise the following steps:

[0016] (a) activating the first actuator to eject ink from the ink ejection port;

[0017] (b) deactivating the first actuator so as to cause a portion of the ejected ink to break off from a main body of ink within the nozzle chamber;

[0018] (c) activation of the second actuator to pump ink towards the ink ejection port so as to rapidly refill the nozzle chamber around the area of the ink ejection port;

[0019] (d) activating the first actuator to eject ink from the ink ejection port while simultaneously deactivating the second actuator so as to return to its quiescent position; or otherwise

[0020] (e) deactivating the second actuator to return to its quiescent position.

[0021] The material of the two actuators having a high coefficient of thermal expansion can comprise substantially polytetrafluoroethylene and the surface of the actuators are treated to make them hydrophilic. Preferably, the heater material embedded in the thermal actuators comprises substantially copper. Further, the actuators are formed by utilization of a sacrificial material layer which is etched away to release the actuators. The inkjet nozzle chamber can be formed from crystallographic etching of a silicon substrate. Further, the thermal actuators are attached to a substrate at one end and the heating of the actuators is primarily near the attached end of the devices. The inkjet nozzle is preferably constructed via fabrication from a silicon wafer utilizing semiconductor fabrication techniques.

[0022] Notwithstanding any other forms which 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 which:

[0023] FIG. 1 is a cross-sectional schematic diagram of the inkjet nozzle chamber in its quiescent state;

[0024] FIG. 2 is a cross-sectional schematic diagram of the inkject nozzle chamber during activation of the first actuator to eject ink;

[0025] FIG. 3 is a cross-sectional schematic diagram of the inkjet nozzle chamber after deactivation of the first actuator;

[0026] FIG. 4 is a cross-sectional schematic diagram of the inkjet nozzle chamber during activation of the second actuator to refill the chamber;

[0027] FIG. 5 is a cross-sectional schematic diagram of the inkjet nozzle chamber after deactivation of the actuator to refill the chamber;

[0028] FIG. 6 is a cross-sectional schematic diagram of the inkjet nozzle chamber during simultaneous activation of the ejection actuator whilst deactivation of the pump actuator;

[0029] FIG. 7 is a top view cross-sectional diagram of the inkjet nozzle chamber; and

[0030] FIG. 8 is an exploded perspective view illustrating the construction of the inkjet nozzle chamber in accordance with the preferred embodiment.

[0031] FIG. 9 provides a legend of the materials indicated in FIGS. 10 to 22; and

[0032] FIG. 10 to FIG. 22 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle.

[0033] In the preferred embodiment, each nozzle chamber having a nozzle ejection portal further includes two thermal actuators. The first thermal actuator is utilized for the ejection of ink from the nozzle chamber while a second thermal actuator is utilized for pumping ink into the nozzle chamber for rapid ejection of subsequent drops.

[0034] Normally, ink chamber refill is a result of surface tension effects of drawing ink into a nozzle chamber. In the preferred embodiment, the nozzle chamber refill is assisted by an actuator which pumps ink into the nozzle chamber so as to allow for a rapid refill of the chamber and therefore a more rapid operation of the nozzle chamber in ejecting ink drops.

[0035] Turning to FIGS. 1-6 which represent various schematic cross sectional views of the operation of a single nozzle chamber, the operation of the preferred embodiment will now be discussed. In FIG. 1, a single nozzle chamber is schematically illustrated in section. The nozzle arrangement 10 includes a nozzle chamber 11 filled with ink and a nozzle ink ejection port 12 having an ink meniscus 13 in a quiescent position. The nozzle chamber 11 is interconnected to an ink reservoir 15 for the supply of ink to the nozzle chamber. Two paddle-type thermal actuators 16, 17 are provided for the control of the ejection of ink from nozzle port 12 and the refilling of chamber 11. Both of the thermal actuators 16, 17 are controlled by means of passing an electrical current through a resistor so as to actuate the actuator. The structure of the thermal actuators 16, 17 will be discussed further herein after. The arrangement of FIG. 1 illustrates the nozzle arrangement when it is in its quiescent or idle position.

[0036] When it is desired to eject a drop of ink via the port 12, the actuator 16 is activated, as shown in FIG. 2. The activation of activator 16 results in it bending downwards forcing the ink within the nozzle chamber out of the port 12, thereby resulting in a rapid growth of the ink meniscus 13. Further, ink flows into the nozzle chamber 11 as indicated by arrow 19.

[0037] The main actuator 16 is then retracted as illustrated in FIG. 3, which results in a collapse of the ink meniscus so as to form ink drop 20. The ink drop 20 eventually breaks off from the main body of ink within the nozzle chamber 11.

[0038] Next, as illustrated in FIG. 4, the actuator 17 is activated so as to cause rapid refill in the area around the nozzle portal 12. The refill comes generally from ink flows 21, 22.

[0039] Next, two alternative procedures are utilized depending on whether the nozzle chamber is to be fired in a next ink ejection cycle or whether no drop is to be fired. The case where no drop is to be fired is illustrated in FIG. 5 and basically comprises the return of actuator 17 to its quiescent position with the nozzle port area refilling by means of surface tension effects drawing ink into the nozzle chamber 11.

[0040] Where it is desired to fire another drop in the next ink drop ejection cycle, the actuator 16 is activated simultaneously which is illustrated in FIG. 6 with the return of the actuator 17 to its quiescent position. This results in more rapid refilling of the nozzle chamber 11 in addition to simultaneous drop ejection from the ejection nozzle 12.

[0041] Hence, it can be seen that the arrangement as illustrated in FIGS. 1 to 6 results in a rapid refilling of the nozzle chamber 11 and therefore the more rapid cycling of ejecting drops from the nozzle chamber 11. This leads to higher speed and improved operation of the preferred embodiment.

[0042] Turning now to FIG. 7, there is a illustrated a sectional perspective view of a single nozzle arrangement 10 of the preferred embodiment. The preferred embodiment can be constructed on a silicon wafer with a large number of nozzles 10 being constructed at any one time. The nozzle chambers can be constructed through back etching a silicon wafer to a boron doped epitaxial layer 30 using the boron doping as an etchant stop. The boron doped layer is then further etched utilising the relevant masks to form the nozzle port 12 and nozzle rim 31. The nozzle chamber proper is formed from a crystallographic etch of the portion of the silicon wafer 32. The silicon wafer can include a two level metal standard CMOS layer 33 which includes the interconnect and drive circuitry for the actuator devices. The CMOS layer 33 is interconnected to the actuators via appropriate vias. On top of the CMOS layer 33 is placed a nitride layer 34. The nitride layer is provided to passivate the lower CMOS layer 33 from any sacrificial etchant which is utilized to etch sacrificial material in construction of the actuators 16, 17. The actuators 16, 17 can be constructed by filling the nozzle chamber 11 with a sacrificial material, such as sacrificial glass and depositing the actuator layers utilizing standard micro-electro-mechanical systems (MEMS) processing techniques.

[0043] On top of the nitride layer 34 is deposited a first PTFE layer 35 followed by a copper layer 36 and a second PTFE layer 37. These layers are utilised with appropriate masks so as to form the actuators 16, 17. The copper layer 36 is formed near the top surface of the corresponding actuators and is in a serpentine shape. Upon passing a current through the copper layer 36, the copper layer is heated. The copper layer 36 is encased in the PTFE layers 35, 37. Plan has a much greater coefficient of thermal expansion than copper (770×10−6) and hence is caused to expand more rapidly than the copper layer 36, such that, upon heating, the copper serpentine shaped layer 36 expands via concertinaing at the same rate as the surrounding teflon layers. Further, the copper layer 36 is formed near the top of each actuator and hence, upon heating of the copper element, the lower PTFE layer 35 remains cooler than the upper PTFE layer 37. This results in a bending of the actuator so as to achieve its actuation effects. The copper layer 36 is interconnected to the lower CMOS layer 34 by means of vias eg 39. Further, the PTFE layers 35/37, which are normally hydrophobic, undergo treatment so as to be hydrophilic. Many suitable treatments exist such as plasma damaging in an ammonia atmosphere. In addition, other materials having considerable properties can be utilized.

[0044] Turning to FIG. 8, there is illustrated an exploded perspective of the various layers of an ink jet nozzle 10 as constructed in accordance with a single nozzle arrangement 10 of the preferred embodiment. The layers include the lower boron layer 30, the silicon and anisotropically etched layer 32, CMOS glass layer 33, nitride passivation layer 34, copper heater layer 36 and PTFE layers 35/37, which are illustrated in one layer but formed with an upper and lower teflon layer embedding copper layer 36.

[0045] One form of detailed manufacturing process which can be used to fabricate monolithic ink jet print heads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

[0046] 1. Using a double sided polished wafer 50 deposit 3 microns of epitaxial silicon heavily doped with boron 30.

[0047] 2. Deposit 10 microns of epitaxial silicon 32, either p-type or n-type, depending upon the CMOS process used.

[0048] 3. Complete a 0.5 micron, one poly, 2 metal CMOS process. The metal layers are copper instead of aluminum, due to high current densities and subsequent high temperature processing. This step is shown in FIG. 10. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 9 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

[0049] 4. Etch the CMOS oxide layers down to silicon or second level metal using Mask 1. This mask defines the nozzle cavity and the bend actuator electrode contact vias 39. This step is shown in FIG. 11.

[0050] 5. Crystallographically etch the exposed silicon using KOH. This etch stops on (111) crystallographic planes 51, and on the boron doped silicon buried layer. This step is shown in FIG. 12.

[0051] 6. Deposit 0.5 microns of low stress PECVD silicon nitride 34 (Si3N4). The nitride acts as an ion diffusion barrier. This step is shown in FIG. 13.

[0052] 7. Deposit a thick sacrificial layer 52 (e.g. low stress glass), filling the nozzle cavity. Planarize the sacrificial layer down to the nitride surface. This step is shown in FIG. 14.

[0053] 8. Deposit 1.5 microns of polytetrafluoroethylene 35 (PTFE).

[0054] 9. Etch the PTFE using Mask 2. This mask defines the contact vias 39 for the heater electrodes.

[0055] 10. Using the same mask, etch down through the nitride and CMOS oxide layers to second level metal. This step is shown in FIG. 15.

[0056] 11. Deposit and pattern 0.5 microns of gold 53 using a lift-off process using Mask 3. This mask defines the heater pattern. This step is shown in FIG. 16.

[0057] 12. Deposit 0.5 microns of PTFE 37.

[0058] 13. Etch both layers of PTFE down to sacrificial glass using Mask 4. This mask defines the gap 54 at the edges of the main actuator paddle and the refill actuator paddle. This step is shown in FIG. 17.

[0059] 14. Mount the wafer on a glass blank 55 and back-etch the wafer using KOH, with no mask. This etch thins the wafer and stops at the buried boron doped silicon layer. This step is shown in FIG. 18.

[0060] 15. Plasma back-etch the boron doped silicon layer to a depth of 1 micron using Mask 5. This mask defines the nozzle rim 31. This step is shown in FIG. 19.

[0061] 16. Plasma back-etch through the boron doped layer using Mask 6. This mask defines the nozzle 12, and the edge of the chips.

[0062] 17. Plasma back-etch nitride up to the glass sacrificial layer through the holes in the boron doped silicon layer. At this stage, the chips are separate, but are still mounted on the glass blank. This step is shown in FIG. 20.

[0063] 18. Strip the adhesive layer to detach the chips from the glass blank.

[0064] 19. Etch the sacrificial glass layer in buffered BF. This step is shown in FIG. 21.

[0065] 20. Mount the print heads in their packaging, which may be a molded plastic former incorporating ink channels which supply different colors of ink to the appropriate regions of the front surface of the wafer.

[0066] 21. Connect the print heads to their interconnect systems.

[0067] 22. Hydrophobize the front surface of the print heads.

[0068] 23. Fill the completed print heads with ink 56 and test them. A filled nozzle is shown in FIG. 22.

[0069] The presently disclosed ink jet printing technology is potentially suited to a wide range of printing systems 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 in-built 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.

[0070] It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the preferred embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

[0071] Ink Jet Technologies

[0072] The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

[0073] 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. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

[0074] The most significant problem with piezoelectric ink jet 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.

[0075] 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:

[0076] low power (less than 10 Watts)

[0077] high resolution capability (1,600 dpi or more)

[0078] photographic quality output

[0079] low manufacturing cost

[0080] small size (pagewidth times minimum cross section)

[0081] high speed (<2 seconds per page).

[0082] All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet 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.

[0083] The ink jet 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.

[0084] 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 mm. The printheads each contain 19,200 nozzles plus data and control circuitry.

[0085] 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.

[0086] Tables of Drop-on-Demand Ink Jets

[0087] The present invention is useful in the field of digital printing, in particular, ink jet printing.

[0088] 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.

[0089] The following tables form the axes of an eleven dimensional table of ink jet types.

[0090] Actuator mechanism (18 types)

[0091] Basic operation mode (7 types)

[0092] Auxiliary mechanism (8 types)

[0093] Actuator amplification or modification method (17 types)

[0094] Actuator motion (19 types)

[0095] Nozzle refill method (4 types)

[0096] Method of restricting back-flow through inlet (10 types)

[0097] Nozzle clearing method (9 types)

[0098] Nozzle plate construction (9 types)

[0099] Drop ejection direction (5 types)

[0100] Ink type (7 types)

[0101] 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 IJ01 to UI45 above which matches the docket numbers in the table under the heading Cross References to Related Applications.

[0102] 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 IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

[0103] 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 IJ01 to IJ45 series are also listed in the examples column. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

[0104] 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.

[0105] The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.