Method of manufacture of a thermoelastic bend actuator ink jet printer

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

[0003] Not applicable.

[0004] The present invention relates to the manufactured of ink jet printheads and, in particular, discloses a method of manufacture of a thermoelastic bend actuator ink jet printer.

[0005] Many ink jet printing mechanisms are known. Unfortunately, in mass production techniques, the production of ink jet heads 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, pp33-37 (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 utilised. These can include electroforming of nickel stage (Hewlett-Packard Journal, Vol. 36 no 5, pp33-37 (1985)), electro-discharge machining, laser ablation (U.S. Pat. No. 5,208,604), micro-punching, etc.

[0008] The utilisation 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 printing device having a number of advantageous features over and above those mentioned in the prior art.

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

[0012] The printheads can be formed utilising 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 the substrate substantially normal to said substrate.

[0013] In accordance with a further aspect of the present invention, there is provided a method of manufacture of an ink jet printhead arrangement including a series of nozzle chambers, the method comprising the steps of: (a) providing an initial semiconductor wafer having an electrical circuitry layer formed thereon; (b) etching a series of vias in the wafer at predetermined positions interconnecting with the electrical circuitry; (c) depositing and etching a first sacrificial material layer, the etching including etching an actuator anchor area in the first sacrificial material layer located around the vias; (d) depositing and etching a first expansion material layer of a material having a high coefficient of thermal expansion, the etching including etching predetermined vias in the first expansion material layer; (e) depositing and etching a conductive layer on the first expansion material layer, the conductive material layer being conductively interconnected with the electrical circuitry layer via the vias; (f) depositing and etching a second expansion material layer of a material having a high coefficient of thermal expansion, the etching including forming a paddle anchored at the vias from the combination of the first and second expansion material layers and the conductive layer; (g) depositing and etching a second sacrificial material layer, the etching forming a nozzle chamber mould; (h) depositing and etching an inert material layer over the sacrificial material layer so as to form a nozzle chamber around the moveable paddle, the etching including etching a nozzle ejection aperture in the inert material layer; (i) etching an ink supply channel through the wafer; and (j) etching away the sacrificial layers.

[0014] Preferably, the method further includes the step of treating the top of the second expansion layer so as form a hydrophilic surface.

[0015] The step (h) preferably can include etching a series of small holes in the inert material layer.

[0016] The first and second expansion material layers can comprise substantially polytetrafluoroethylene and the inert material layer can comprise substantially glass.

[0017] The ink supply channel can be formed by etching a channel from the back surface of the wafer.

[0018] The steps are preferably also utilized to simultaneously separate the wafer into separate printheads.

[0019] 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 in which:

[0020] FIG. 1 is a schematic cross-sectional view of a single ink jet nozzle constructed in accordance with the preferred embodiment, in its quiescent state;

[0021] FIG. 2 is a cross-sectional schematic diagram of a single ink jet nozzle constructed in accordance with the preferred embodiment, illustrating the activated state;

[0022] FIG. 3 is a schematic cross-sectional diagram of a single ink jet nozzle illustrating the deactivation state;

[0023] FIG. 4 is a schematic cross-sectional diagram of a single ink jet nozzle constructed in accordance with the preferred embodiment, after returning into its quiescent state;

[0024] FIG. 5 is a schematic, cross-sectional perspective diagram of a single ink jet nozzle constructed in accordance with the preferred embodiment;

[0025] FIG. 6 is an exploded perspective view illustrating the construction of a single ink jet nozzle in accordance with the preferred embodiment;

[0026] FIG. 7 provides a legend of the materials indicated in FIGS. 8 to 19;

[0027] FIG. 8 shows a sectional side view of an initial manufacturing step of an ink jet printhead nozzle showing a silicon wafer layer and an electrical circuitry layer;

[0028] FIG. 9 shows a step of depositing and etching a first sacrificial material layer;

[0029] FIG. 10 shows a step of depositing a first permanent material layer;

[0030] FIG. 11 shows a step of depositing and etching a heater material layer;

[0031] FIG. 12 shows a step of depositing and etching a second permanent material layer;

[0032] FIG. 13 shows a step of depositing a second sacrificial material layer and etching both sacrificial material layers;

[0033] FIG. 14 shows a step of depositing a third permanent material layer;

[0034] FIG. 15 shows a step of etching the third permanent material layer;

[0035] FIG. 16 shows a step of further etching the third permanent material layer;

[0036] FIG. 17 shows a step of back etching through the silicon wafer layer;

[0037] FIG. 18 shows a step of etching the first and second sacrificial material layers; and

[0038] FIG. 19 shows a step of filling the completed ink jet printhead with ink.

[0039] In the preferred embodiment, a new form of thermal actuator is utilized for the ejection of drops of ink on demand from an ink nozzle. Turning now to FIGS. 1 to 4, there will be illustrated the basis of operation of the inkjet printing device utilising the actuator. Turning initially to FIG. 1, there is illustrated 1, the quiescent position of a thermal actuator 2 in a nozzle chamber 3 filled with ink and having a nozzle 4 for the ejection of ink. The nozzle 4 has an ink meniscus 5 in a state of surface tension ready for the ejection of ink. The thermal actuator 2 is coated on a first surface 6, facing the chamber 3, with a hydrophilic material. A second surface 7 is coated with a hydrophobic material which causes an air bubble 8 having a meniscus 9 underneath the actuator 2. The air bubble 8 is formed over time by outgassing from the ink within chamber 3 and the meniscus 9 is shown in an equilibrium position between the hydrophobic surface 7 and hydrophilic surface 6. The actuator 2 is fixed at one end 11 to a substrate 12 from which it also derives an electrical connection.

[0040] When it is desired to eject a drop from the nozzle 4, the actuator 2 is activated as shown in FIG. 2, resulting in a movement in direction 14. The movement in direction 14 causes a substantial increase in the pressure of the ink around the nozzle 4. This results in a general expansion of the meniscus 5 and the passing of momentum to the ink so as to form a partial drop 15. Upon movement of the actuator 2 in the direction 14, the ink meniscus 9 collapses generally in the indicated direction 16.

[0041] Subsequently, the thermal actuator 2 is deactivated as illustrated in FIG. 3, resulting in a return of the actuator 2 in the direction generally indicated by the arrow 17. The movement back of the actuator 2 results in a low pressure region being experienced by the ink within the nozzle area 4. The forward momentum of the drop 15 and the low pressure around the nozzle 4 results in the ink drop 15 being broken off from the main body of the ink. The drop 15 continues to the print media as required. The movement of the actuator 2 in the direction 17 further causes ink to flow in the direction 19 around the actuator 2 in addition to causing the meniscus 9 to move as a result of the ink flow 19. Further, ink 20 is sucked into the chamber 3 to replace the ejected ink 15.

[0042] Finally, as illustrated in FIG. 4, the actuator 2 returns to its quiescent with the meniscus 5 also returning to a state of having a slight bulge. The actuator 2 is then in a state for refiring of another drop on demand as required.

[0043] In one form of implementation of an inkjet printer utilizing the method illustrated in FIGS. 1 to 4, standard semi-conductor fabrication techniques are utilized in addition to standard micro-electro-mechanical systems (MEMs) to construct a suitable print device having a plurality of the chambers as illustrated in FIG. 1 with corresponding actuators 2.

[0044] Turning now to FIG. 5, there is illustrated a cross-section through one form of suitable nozzle chamber. One end 11 of the actuator 2 is connected to the substrate 12 and the other end includes a stiff paddle 25 for utilisation in ejecting ink. The actuator itself is constructed from a four layer MEMs processing technique. The layers are as follows:

[0045] 1. A polytetrafluoroethylene (PTFE) lower layer 26. PTFE has a very high coefficient of thermal expansion (approximately 770×10⁻⁶, or around 380 times that of silicon). This layer expands when heated by a heater layer.

[0046] 2. A heater layer 27. A serpentine heater 27 is etched in this layer, which may be formed from nichrome, copper or other suitable material with a resistivity such that the drive voltage for the heater is compatible with the drive transistors utilized. The serpentine heater 27 is arranged to have very little tensile strength in the direction 29 along the length of the actuator 2.

[0047] 3. A PTFE upper layer 30. This layer 30 expands when heated by the heater layer.

[0048] 4. A silicon nitride layer 32. This is a thin layer 32 of high stiffness and low coefficient of thermal expansion. Its purpose is to ensure that the actuator bends, instead of simply elongating as a result of thermal expansion of the PTFE layers. Silicon nitride can be used simply because it is a standard semi-conductor material, and SiO₂cannot easily be used if it is also the sacrificial material used when constructing the device.

[0049] Operation of the ink jet actuator 2 will then be as follows:

[0050] 1. When data signals distributed on the printhead indicate that a particular nozzle is to eject a drop of ink, the drive transistor for that nozzle is turned on. This energises the heater 27 in the paddle for that nozzle. The heater is energised for approximately 2 μs, with the actual duration depending upon the exact design chosen for the actuator nozzle and the inks utilized.

[0051] 2. The heater 27 heats the PTFE layers 26, 30 which expand at a rate many times that of the Si₃N₄layer 32. This expansion causes the actuator 2 to bend, with the PTFE layer 26 being the convex side. The bending of the actuator moves the paddle, pushing ink out of the nozzle. The air bubble 8 (FIG. 1) between the paddle and the substrate, forms due to the hydrophobic nature of the PTFE on the back surface of the paddle. This air bubble reduces the thermal coupling to the hot side of the actuator, achieving a higher temperature with lower power. The cold side of the actuator including SiN layer 32 will still be liquid cooled. The air bubble will also expand slightly when heated, helping to move the paddle. The presence of the air bubble also means that less ink is required to move under the paddle when the actuator is energised. These three factors lead to a lower power consumption of the actuator.

[0052] 3. When the heater current is turned off, as noted previously, the paddle 25 begins to return to its quiescent position. The paddle return ‘sucks’ some of the ink back into the nozzle, causing the ink ligament connecting the ink drop to the ink in the nozzle to thin. The forward velocity of the drop and the backward velocity of the ink in the chamber are resolved by the ink drop breaking off from the ink in the nozzle. The ink drop then continues towards the recording medium.

[0053] 4. The actuator 2 is finally at rest in the quiescent position until the next drop ejection cycle.

[0054] Basic Fabrications Sequence

[0055] One form of printhead fabrication sequence utilizing MEMs technology will now be described. The description assumes that the reader is familiar with surface and micromachining techniques utilized for the construction of MEMs devices, including the latest proceedings in these areas. Turning now to FIG. 7, there is illustrated an exploded perspective view of a single ink jet nozzle as constructed in accordance with the preferred embodiment. The construction of a printhead can proceed as follows:

[0056] 1. Start with a standard single crystal silicon wafer 80 suitable for the desired manufacturing process of the active semiconductor device technology chosen. Here the manufacturing process is assumed to be 0.5μ CMOS.

[0057] 2. Complete fabrication of the CMOS circuitry layer 83, including an oxide layer (not shown) and passivation layer 82 for passivation of the wafer. As the chip will be immersed in water based ink, the passivation layer must be highly impervious. A layer of high density silicon nitride (Si₃N₄) is suitable. Another alternative is diamond-like carbon (DLC).

[0058] 3. Deposit 2μ of phophosilicate glass (PSG). This will be a sacrificial layer which raises the actuator and paddle from the substrate. This thickness is not critical.

[0059] 4. Etch the PSG to leave islands under the actuator positions on which the actuators will be formed.

[0060] 5. Deposit 1.0 μm of polytetrafluoroethylene (PTFE) layer 84. The PTFE may be roughened to promote adhesion. The PTFE may be deposited as a spin-on nanoemulsion. [T. Rosenmayer, H. Wu, “PTFE nanoemulsions as spinon, low dielectric constant materials for ULSI applications”, PP463-468, Advanced Metallisation for Future ULSI, MRS vol. 427,1996].

[0061] 6. Mask and etch via holes through to the top level metal of the CMOS circuitry for connection of a power supply to the actuator (not shown). Suitable etching procedures for PTFE are discussed in “Thermally assisted Ion Beam Etching of polytetrafluoroethylene: A new technique for High Aspect Ratio Etching of MEMS” by Berenschot et al in the Proceedings of the Ninth Annual International Workshop on Micro Electro Mechanical Systems, San Diego, February 1996.

[0062] 7. Deposit the heater material layer 85. This may be Nichrome (an alloy of 80% nickel and 20% chromium) which may be deposited by sputtering. Many other heater materials may be used. The principal requirements are a resistivity which results in a drive voltage which is suitable for the CMOS drive circuitry layer, a melting point above the temperature of subsequent process steps, electromigration resistance, and appropriate mechanical properties.

[0063] 8. Etch the heater material using a mask pattern of the heater and the paddle stiffener.

[0064] 9. Deposit 2.0 μm of PTFE. As with step 5), the PTFE may be spun on as a nanoemulsion, and may be roughened to promote adhesion. (This layer forms part of layer 84 in FIG. 6.)

[0065] 10. Deposit via a mask 0.25 of silicon nitride for the top layer 86 of the actuator, or any of a wide variety of other materials having suitable properties as previously described. The major materials requirements are: a low coefficient of thermal expansion compared to PTFE; a relatively high Young's modulus, does not corrode in water, and a low etch rate in hydrofluoric acid (HF). The last of these requirements is due to the subsequent use of HF to etch the sacrificial glass layers. If a different sacrificial layer is chosen, then this layer should obviously have resistance to the process used to remove the sacrificial material.

[0066] 11. Using the silicon nitride as a mask, etch the PTFE. PTFE can be etched with very high selectivity (>1,000 to one) with ion beam etching. The wafer may be tilted slightly and rotated during etching to prevent the formation of microglass. Both layers of PTFE can be etched simultaneously.

[0067] 12. Deposit 20 μm of SiO₂. This may be deposited as spin-on glass (SOG) and will be used as a sacrificial layer (not shown).

[0068] 13. Etch through the glass layer using a mask defining the nozzle chamber and ink channel walls, e.g. 51, and filter posts, e.g. 52. This etch is through around 20 μm of glass, so should be highly anisotropic to minimise the chip area required. The minimum line width is around 6 μm, so coarse lithography may be used. Overlay alignment error should preferably be less than 0.5 μm. The etched areas are subsequently filled by depositing silicon nitride through the mask.

[0069] 14. Deposit 2 μm of silicon nitride layer 87. This forms the front surface of the printhead. Many other materials could be used. A suitable material should have a relatively high Young's modulus, not corrode in water, and have a low etch rate in hydrofluoric acid (HF). It should also be hydrophilic.

[0070] 15. Mask and etch nozzle rims (not shown). These are 1 μm annular protrusions above the printhead surface around the nozzles, e.g. 4, which help to prevent ink flooding the surface of the printhead. They work in conjunction with the hydrophobising of the printhead front surface.

[0071] 16. Mask and etch the nozzle holes 4. This mask also includes smaller holes, e.g. 47, which are placed to allow the ingress of the etchant for the sacrificial layers. These holes should be small enough so that the ink surface tension ensures that ink is not ejected from the holes when the ink pressure waves from nearby actuated nozzles is at a maximum. Also, the holes should be small enough to ensure that air bubbles are not ingested at times of low ink pressure. These holes are spaced close enough so that etchant can easily remove all of the sacrificial material even though the paddle and actuator are fairly large and flexible. Stiction should not be a problem for this design. This is because the paddle is made from PTFE.

[0072] 17. Etch ink access holes (not shown) through the wafer 80. This can be done as an anisotropic crystallographic silicon etch, or an anisotropic dry etch. A dry etch system capable of high aspect ratio deep silicon trench etching such as the Surface Technology Systems (STS) Advance Silicon Etch (ASE) system is recommended for volume production, as the chip size can be reduced over wet etch. The wet etch is suitable for small volume production where a suitable plasma etch system is not available. Alternatively, but undesirably, ink access can be around the sides of the printhead chips. If ink access is through the wafer higher ink flow is possible, and there is less requirement for high accuracy assembly. If ink access is around the edge of the chip, ink flow is severely limited, and the printhead chips must be carefully assembled onto ink channel chips. This latter process is difficult due to the possibility of damaging the fragile nozzle plate. If plasma etching is used, the chips can be effectively diced at the same time. Separating the chips by plasma etching allows them to be spaced as little as 35 μm apart, increasing the number of chips on a wafer. At this stage, the chips must be handled carefully, as each chip is a beam of silicon 100 mm long by 0.5 mm wide and 0.7 mm thick.

[0073] 18. Mount the printhead chips into printhead carriers. These are mechanical support and ink connection mouldings. The printhead carriers can be moulded from plastic, as the minimum dimensions are 0.5 mm.

[0074] 19. Probe test the printheads and bond the good printheads. Bonding may be by wire bonding or TAB bonding.

[0075] 20. Etch the sacrificial layers. This can be done with an isotropic wet etch, such as buffered HF. This stage is performed after the mounting of the printheads into moulded printhead carriers, and after bonding, as the front surface of the printheads is very fragile after the sacrificial etch has been completed. There should be no direct handling of the printhead chips after the sacrificial etch.

[0076] 21. Hydrophobise the front surface of the printheads.

[0077] 22. Fill with ink and perform final testing on the completed printheads.

[0078] 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:

[0079] 1. Using a double sided polished wafer 80, complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, 2 metal CMOS process 83. Relevant features of the wafer at this step are shown in FIG. 8. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 7 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

[0080] 2. Deposit 1 micron of low stress nitride 82. This acts as a barrier to prevent ink diffusion through the silicon dioxide of the chip surface.

[0081] 3. Deposit 3 micron of sacrificial material 90 (e.g. polyimide).

[0082] 4. Etch the sacrificial layer using Mask 1. This mask defines the actuator anchor point. This step is shown in FIG. 9.

[0083] 5. Deposit 0.5 microns of PTFE91.

[0084] 6. Etch the PTFE, nitride, and CMOS passivation down to second level metal using Mask 2. This mask defines the heater vias 11. This step is shown in FIG. 10.

[0085] 7. Deposit and pattern resist using Mask 3. This mask defines the heater.

[0086] 8. Deposit 0.5 microns of gold 92 (or other heater material with a low Young's modulus) and strip the resist. Steps 7 and 8 form a lift-off process. This step is shown in FIG. 11.

[0087] 9. Deposit 1.5 microns of PTFE93.

[0088] 10. Etch the PTFE down to the sacrificial layer using Mask 4. This mask defines the actuator paddle and the bond pads. This step is shown in FIG. 12.

[0089] 11. Wafer probe. All electrical connections are complete at this point, and the chips are not yet separated.

[0090] 12. Plasma process the PTFE to make the top surface hydrophilic. This allows the nozzle chamber to fill by capillarity, but maintains a hydrophobic layer underneath the paddle, which traps an air bubble. The air bubble reduces the negative pressure on the back of the paddle, and increases the temperature achieved by the heater.

[0091] 13. Deposit 10 microns of sacrificial material 94.

[0092] 14. Etch the sacrificial material down to nitride using Mask 5. This mask defines the nozzle chamber 51 and the nozzle inlet filter 52. This step is shown in FIG. 13.

[0093] 15. Deposit 3 microns of PECVD glass 95. This step is shown in FIG. 14.

[0094] 16. Etch to a depth of 1 micron using Mask 6. This mask defines the nozzle rim 96. This step is shown in FIG. 15.

[0095] 17. Etch down to the sacrificial layer using Mask 7. This mask defines the nozzle 4 and the sacrificial etch access holes 47. This step is shown in FIG. 16.

[0096] 18. Back-etch completely through the silicon wafer (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask 8. This mask defines the ink inlets 98 which are etched through the wafer. The wafer is also diced by this etch. This step is shown in FIG. 17.

[0097] 19. Back-etch the CMOS oxide layers and subsequently deposited nitride layers through to the sacrificial layer using the back-etched silicon as a mask.

[0098] 20. Etch the sacrificial material. The nozzle chambers are cleared, the actuators freed, and the chips are separated by this etch. This step is shown in FIG. 18.

[0099] 21. 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.

[0100] 22. 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.

[0101] 23. Hydrophobize the front surface of the printheads.

[0102] 24. Fill the completed printheads with ink 99 and test them. A filled nozzle is shown in FIG. 19.

[0103] 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.

[0104] 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.

[0105] Ink Jet Technologies

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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:

[0110] low power (less than 10 Watts)

[0111] high resolution capability (1,600 dpi or more)

[0112] photographic quality output

[0113] low manufacturing cost

[0114] small size (pagewidth times minimum cross section)

[0115] high speed (<2 seconds per page).

[0116] 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 list under the heading Cross References to Related Applications.

[0117] 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

[0118] 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 covered in U.S. patent application Ser. No. 09/112,764, 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.

[0119] 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.

[0120] Tables of Drop-on-Demand Ink Jets

[0121] 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.

[0122] The following tables form the axes of an eleven dimensional table of ink jet types.

[0123] Actuator mechanism (18 types)

[0124] Basic operation mode (7 types)

[0125] Auxiliary mechanism (8 types)

[0126] Actuator amplification or modification method (17 types)

[0127] Actuator motion (19 types)

[0128] Nozzle refill method (4 types)

[0129] Method of restricting back-flow through inlet (10 types)

[0130] Nozzle clearing method (9 types)

[0131] Nozzle plate construction (9 types)

[0132] Drop ejection direction (5 types)

[0133] Ink type (7 types)

[0134] 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. Forty-five such inkjet types were filed simultaneously to the present application.

[0135] 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 forty-five examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

[0136] 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 simultaneously filed patent applications by the present applicant are listed by USSN numbers. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

[0137] 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.

[0138] The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.