Method of manufacture of a conductive PTFE bend actuator vented ink jet printer

[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 nrght of priority.

[0003] Not applicable.

[0004] The present invention relates to the manufacture of ink jet printheads.

[0005] Many ink jet printing mechanisms are known. Unfortunately, in mass production techniques, the production of ink jet printheads is quite difficult. For example, often, the orifice or nozzle plate is constructed separately from the ink supply and ink ejection mechanism and bonded to the mechanism at a later stage (Hewlett-Packard Journal, Vol. 36 no 5, pp 33-37 (1985)). These separate material processing steps required in handling such precision devices often add a substantial expense in manufacturing.

[0006] Additionally, side shooting ink jet technologies (U.S. Pat. No. 4,899,181) are often used but again, this limits the amount of mass production throughput given any particular capital investment.

[0007] Additionally, more esoteric techniques are also often utilized. These can include electroforming of nickel stage (Hewlett-Packard Journal, Vol. 36 no 5, pp 33-37 (1985)), electro-discharge machining, laser ablation (U.S. Pat. No. 5,208,604), micro-punching, etc.

[0008] The utilization of the above techniques is likely to add substantial expense to the mass production of ink jet printheads and therefore add substantially to their final cost.

[0009] It would therefore be desirable if an efficient system for the mass production of ink jet printheads could be developed.

[0010] It is an object of the present invention to provide an alternative form of inkjet printer having an energy efficient nozzle actuator design which also can be simply constructed.

[0011] In accordance with a first aspect of the present invention, there is provided a method of manufacturing a conductive PTFE bend actuator vented ink jet printhead wherein an array of nozzles are formed on a substrate utilizing planar monolithic deposition, lithographic and etching processes. Preferably, multiple ink jet printheads are formed simultaneously on a single planar substrate such as a silicon wafer.

[0012] The printheads can be formed utilizing standard vlsi/ulsi processing and can include integrated drive electronics formed on the same substrate. The drive electronics preferably are of a CMOS type. In the final construction, ink can be ejected from substantially normal to the substrate.

[0013] 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:

[0014] FIG. 1 is a cut out topside view illustrating two adjoining inkjet nozzle arrangements constructed in accordance with the preferred embodiment;

[0015] FIG. 2 is an exploded perspective view illustrating the construction of a single inkjet nozzle arrangement in accordance with the preferred embodiment;

[0016] FIG. 3 is a sectional view through the nozzle arrangement of FIG. 1;

[0017] FIG. 4 is a sectional view through the line IV-IV′ of FIG. 3;

[0018] FIG. 5 provides a legend of the materials indicated in FIGS. 6 to 19; and

[0019] FIG. 6 to FIG. 19 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle arrangement.

[0020] FIG. 6 shows a wafer for use in a manufacturing process.

[0021] FIG. 7 shows the wafer of FIG. 6 with an etched sacrificial layer to define a venting layer support pillars and anchor.

[0022] FIG. 8 shows the wafer of FIG. 7 with an etched PTFE venting layer.

[0023] FIG. 9 shows the wafer of FIG. 8 with an etched sacrificial layer and etched actuator contact areas.

[0024] FIG. 10 shows the wafer of FIG. 9 with deposited conductive PTFE.

[0025] FIG. 11 shows the wafer of FIG. 10 with the conductive PTFE etched.

[0026] FIG. 12 shows the wafer of FIG. 11 with deposited PTFE to define an actuator paddle.

[0027] FIG. 13 shows the wafer of FIG. 12 with etched sacrificial material to define the nozzle chamber and inlet filter.

[0028] FIG. 14 shows the wafer of FIG. 13 with deposited glass.

[0029] FIG. 15 shows the wafer of FIG. 14 etched to define the nozzle rim.

[0030] FIG. 16 shows the wafer of FIG. 15 etched to define the nozzle and etch access holes.

[0031] FIG. 17 shows the wafer of FIG. 16 back etched to define an ink inlet channel.

[0032] FIG. 18 shows the wafer of FIG. 17 with sacrificial material etched to free the actuators and separate the chips.

[0033] FIG. 19 shows a completed printhead filled with ink.

[0034] In the preferred embodiment, an inkjet nozzle arrangement is provided having a thermally based actuator which is highly energy efficient. The thermal actuator is located within a chamber filled with ink and relies upon the thermal expansion of materials when an electric current is being passed through them to activate the actuator thereby causing the ejection of ink out of a nozzle arrangement provided in the nozzle chamber.

[0035] Turning to the Figures, in FIG. 1, there is illustrated two adjoining inkjet nozzle arrangement 10 constructed in accordance with the preferred embodiment, with FIG. 2 showing an exploded perspective and FIGS. 3 and 4 showing various sectional views. Each nozzle arrangement 10, can be constructed as part of an array of nozzles on a silicon wafer device and can be constructed utilizing semiconductor processing techniques in addition to micro machining and micro fabrication process technology (MEMS) and a full familiarity with these technologies is hereinafter assumed.

[0036] The nozzle arrangement 10 includes an ink ejection port 11 for the ejection of ink from within a nozzle chamber. Ink is supplied via an inlet port 12 which has a grill structure fabricated from a series of posts 14, the grill acting to filter out foreign bodies within the ink supply and also to provide stability to the nozzle arrangement 10. Inside the nozzle chamber is constructed a thermal actuator device 16 which is interconnected to an electric circuit (not shown) which, when thermally actuated, acts as a paddle bending upwards so as to cause the ejection of ink from each ink ejection port 11. A series of etchant holes e.g. 18 are also provided in the top of nozzle chamber 10, the holes 18 being provided for manufacturing purposes only so as to allow a sacrificial etchant to easily etch away the internal portions of the nozzle chamber. The etchant holes 18 are of a sufficiently small diameter so that the resulting surface tension holds the ink within the nozzle chamber such that no ink leaks out via the holes 18.

[0037] The thermal actuator 16 is composed primarily of polytetrafluoroethylene (PTFE) which is a generally hydrophobic material. The top layer of the actuator 16 is treated or coated so as to make it hydrophilic and thereby attract water/ink via inlet port 12. Suitable treatments include plasma exposure in an ammonia atmosphere. The bottom surface remains hydrophobic and repels the water from the bottom surface of the actuator 16. Underneath the actuator 16 is provided a further surface 19 also composed of a hydrophobic material such as PTFE. The surface 19 has a series of holes 20 in it which allow for the flow of air into the nozzle chamber. The diameter of the holes 20 is of such a size so as to restrict the flow of fluid out of the nozzle chamber via surface tension interactions.

[0038] The surface 19 is separated from a lower level 23 by means of a series of spaced apart posts e.g. 22 which can be constructed when constructing the layer 19 utilizing an appropriate mask. The nozzle chamber, but for grill inlet port 12, is walled on its sides by silicon nitride walls e.g. 25,26. An air inlet channel is formed between adjacent nozzle arrangement 10 such that air is free to flow between the walls 25,28. Hence, air is able to flow down channel 29 and along channel 30 and through holes e.g. 20 in accordance with any fluctuating pressure influences.

[0039] The air flow acts to reduce the vacuum on the bottom surface of actuator 16 during operation. As a result, less energy is required for the movement of the actuator 16. In operation, the actuator 16 is thermally actuated so as to move upwards and cause ink ejection. As a result, air flows in along channels 29,30 and through the holes e.g. 20 into the bottom area of actuator 16. Upon deactivation of the actuator 16, the actuator lowers with a corresponding airflow out of port 20 along channel 30 and out of channel 29. Any fluid within nozzle chamber 10 is firstly repelled by the hydrophobic nature of the bottom surface of actuator 16 in addition to the top of the surface 19 which is again hydrophobic. As noted previously the limited size of holes 20 further stops the fluid from passing through the holes 20 as a result of surface tension characteristics.

[0040] A further preferable feature of nozzle chamber 10 is the utilization of the nitride posts 14 to also clamp one end of the surfaces 16 and 19 firmly to bottom surface 23 thereby reducing the likelihood of delaminating during operation.

[0041] In FIG. 2, there is illustrated an exploded perspective view of a single nozzle arrangement 10. The exploded perspective view illustrates the form of construction of each layer of a simple nozzle arrangement 10. The nozzle arrangement 10 can be constructed on a base silicon wafer 34 having a top glass layer 35 which includes the various drive and control circuitry and which, for example, can comprise a two level metal CMOS layer with the various interconnects (not shown). On top of the layer 35 is first laid out a nitride passivation layer 23 of approximately one micron thickness which includes a number of vias (not shown) for the interconnection of the subsequent layers to the CMOS layer 35. The nitride layer is provided primarily to protect lower layers from corrosion or etching, especially where sacrificial etchants are utilized. Next, a one micron PTFE layer 19 is constructed having the aforementioned holes e.g. 20 and posts 22. The structure of the PTFE layer 19 can be formed by first laying down a sacrificial glass layer (not shown) onto which the PTFE layer 19 is deposited. The PTFE layer 19 includes various features, for example, a lower ridge portion 38 in addition to a hole 39 which acts as a via for the subsequent material layers.

[0042] The actuator proper is formed from two PTFE layers 40,41. The lower PTFE layer 40 is made conductive. The PTFE layer 40 can be made conductive utilizing a number of different techniques including:

[0043] (i) Doping the PTFE layer with another material so as to make it conductive.

[0044] (ii) Embedding within the PTFE layer a series of quantum wires constructed from such a material as carbon nano-tubes created in a mesh form. (“Individual single-wall carbon nano-tubes as quantum wires” by Tans et al Nature, Volume 386, Apr. 3, 1997 at pages 474-477). The PTFE layer 40 includes certain cut out portions e.g. 43 so that a complete circuit is formed around the PTFE actuator 40. The cut out portions can be optimised so as to regulate the resistive heating of the layer 40 by means of providing constricted portions so as to thereby increase the heat generated in various “hot spots” as required. A space is provided between the PTFE layer 19 and the PTFE layer 40 through the utilization of an intermediate sacrificial glass layer (not shown).

[0045] On top of the PTFE layer 40 is deposited a second PTFE layer 41 which can be a standard non conductive PTFE layer and can include filling in those areas in the lower PTFE layer e.g. 43 which are not conductive. The top of the PTFE layer is further treated or coated to make it hydrophilic.

[0046] Next, a nitride layer can be deposited to form the nozzle chamber proper. The nitride layer can be formed by first laying down a sacrificial glass layer and etching the glass layer to form walls e.g. 25, 26 and grilled portion e.g. 14. Preferably, the mask utilized results in a first anchor portion 45 which mates with the hole 39 in layer 19 so as to fix the layer 19 to the nitride layer 23. Additionally, the bottom surface of the grill 14 meets with a corresponding step 47 in the PTFE layer 41 so as to clamp the end portion of the PTFE layers 41,40 and 39 to the wafer surface so as to guard against delamination. Next, a top nitride layer 50 can be formed having a number of holes e.g. 18 and nozzle hole 11 around which a rim can be etched through etching of the nitride layer 50. Subsequently, the various sacrificial layers can be etched away so as to release the structure of the thermal actuator.

[0047] Large arrays of inkjet nozzles 10 can be created side by side on a single wafer. The ink can be supplied via ink channels etched through the wafer utilizing a high density low pressure plasma etching system such as that supplied by Surface Technology Systems of the United Kingdom.

[0048] The foregoing describes only one embodiment of the invention and many variations of the embodiment will be obvious for a person skilled in the art of semi conductor, micro mechanical fabrication. Certainly, various other materials can be utilized in the construction of the various layers.

[0049] One form of detailed manufacturing process which can be used to fabricate monolithic ink jet printheads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

[0050] 1. Using a double sided polished wafer 34, complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, 2 metal CMOS process to form layer 35. Relevant features of the wafer at this step are shown in FIG. 6. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 5 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

[0051] 2. Deposit 1 micron of low stress nitride 23. This acts as a barrier to prevent ink diffusion through the silicon dioxide of the chip surface.

[0052] 3. Deposit 2 microns of sacrificial material 60 (e.g. polyimide).

[0053] 4. Etch the sacrificial layer 60 using Mask 1. This mask defines the PTFE venting layer support pillars and anchor point. This step is shown in FIG. 7.

[0054] 5. Deposit 2 microns of PTFE 19.

[0055] 6. Etch the PTFE 19 using Mask 2. This mask defines the edges of the PTFE venting layer, and the holes in this layer. This step is shown in FIG. 8.

[0056] 7. Deposit 3 micron of sacrificial material 61 (e.g. polyimide).

[0057] 8. Etch the sacrificial layer 61 and CMOS passivation layer 23 using Mask 3. This mask defines the actuator contacts. This step is shown in FIG. 9.

[0058] 9. Deposit 1 micron of conductive PTFE 40. Conductive PTFE 40 can be formed by doping the PTFE with a conductive material, such as extremely fine metal or graphitic filaments, or fine metal particles, and so forth. The PTFE 40 should be doped so that the resistance of the PTFE conductive heater is sufficiently low so that the correct amount of power is dissipated by the heater when the drive voltage is applied. However, the conductive material should be a small percentage of the PTFE volume, so that the coefficient of thermal expansion is not significantly reduced. Carbon nanotubes can provide significant conductivity at low concentrations. This step is shown in FIG. 10.

[0059] 10. Etch the conductive PTFE 40 using Mask 4. This mask defines the actuator conductive regions. This step is shown in FIG. 11.

[0060] 11. Deposit 1 micron of PTFE 41.

[0061] 12. Etch the PTFE 41 down to the sacrificial layer 61 using Mask 5. This mask defines the actuator paddle. This step is shown in FIG. 12.

[0062] 13. Wafer probe. All electrical connections are complete at this point, and the chips are not yet separated.

[0063] 14. Plasma process the PTFE to make the top and side surfaces of the paddle hydrophilic. This allows the nozzle chamber to fill by capillarity.

[0064] 15. Deposit 10 microns of sacrificial material 62.

[0065] 16. Etch the sacrificial material 62 down to nitride 23 using Mask 6. This mask defines the nozzle chamber and inlet filter. This step is shown in FIG. 13.

[0066] 17. Deposit 3 microns of PECVD glass 50. This step is shown in FIG. 14.

[0067] 18. Etch to a depth of 1 micron using Mask 7. This mask defines the nozzle rim 63. This step is shown in FIG. 15.

[0068] 19. Etch down to the sacrificial layer 62 using Mask 8. This mask defines the nozzle 11 and the sacrificial etch access holes 18. This step is shown in FIG. 16.

[0069] 20. Back-etch completely through the silicon wafer 34 (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask 9. This mask defines the ink inlets 64 which are etched through the wafer 34. The wafer 34 is also diced by this etch. This step is shown in FIG. 17.

[0070] 21. Back-etch the CMOS oxide layers 35 and subsequently deposited nitride layers 23 through to the sacrificial layer 60 using the back-etched silicon as a mask.

[0071] 22. Etch the sacrificial material 60 and 62. The nozzle chambers are cleared, the actuators freed, and the chips are separated by this etch. This step is shown in FIG. 18.

[0072] 23. Mount the printheads in their packaging, which may be a molded plastic former incorporating ink channels which supply the appropriate color ink to the ink inlets at the back of the wafer.

[0073] 24. Connect the printheads to their interconnect systems. For a low profile connection with minimum disruption of airflow, TAB may be used. Wire bonding may also be used if the printer is to be operated with sufficient clearance to the paper.

[0074] 25. Hydrophobize the front surface of the printheads.

[0075] 26. Fill the completed printheads with ink and test them. A filled nozzle is shown in FIG. 19.

[0076] 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 specific 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.

[0077] 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 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.

[0078] Ink Jet Technologies

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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:

[0083] low power (less than 10 Watts)

[0084] high resolution capability (1,600 dpi or more)

[0085] photographic quality output

[0086] low manufacturing cost

[0087] small size (pagewidth times minimum cross section)

[0088] high speed (<2 seconds per page).

[0089] 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 above under the heading

[0090] Cross References to Related Applications

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Tables of Drop-on-Demand Ink Jets

[0095] The present invention is useful in the field of digital printing, in particular, ink jet printing.

[0096] 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.

[0097] The following tables form the axes of an eleven dimensional table of ink jet types.

[0098] Actuator mechanism (18 types)

[0099] Basic operation mode (7 types)

[0100] Auxiliary mechanism (8 types)

[0101] Actuator amplification or modification method (17 types)

[0102] Actuator motion (19 types)

[0103] Nozzle refill method (4 types)

[0104] Method of restricting back-flow through inlet (10 types)

[0105] Nozzle clearing method (9 types)

[0106] Nozzle plate construction (9 types)

[0107] Drop ejection direction (5 types)

[0108] Ink type (7 types)

[0109] 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 IJ45 which matches the docket numbers in the in the table under the heading Cross References to Related Applications.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.