Method of manufacture of a thermally actuated slotted chamber wall 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 right of priority.

[0003] Not applicable.

[0004] The present invention relates to the field of ink jet printing and, in particular, discloses a method of manufacture of a thermally actuated slotted chamber wall 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. Patent 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)), electrodischarge machining, laser ablation (U.S. Patent 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 print heads 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 print heads could be developed.

[0010] It is an object of the present invention to provide for a method of manufacture of an ink jet printer device which includes a thermally actuated slotted chamber wall ink jet printer.

[0011] In accordance with a first aspect of the present invention, there is provided a method of manufacturing a thermally actuated slotted chamber wall ink jet print head wherein an array of nozzles are formed on a substrate utilizing planar monolithic deposition, lithographic and etching processes.

[0012] Multiple ink jet heads are preferably formed simultaneously on a single planar substrate which can comprise a silicon wafer.

[0013] The print heads are preferably formed utilizing standard vlsi/ulsi processing. The integrated drive electronics are preferably formed on the same substrate. The integrated drive electronics are formed using a CMOS fabrication process.

[0014] Ink can be ejected from the substrate substantially normal to the substrate.

[0015] 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:

[0016] FIG. 1 illustrates a perspective view of an ink jet nozzle arrangement in accordance with the preferred embodiment;

[0017] FIG. 2 illustrates the arrangement of FIG. 1 when the actuator is in an activated position;

[0018] FIG. 3 illustrates an exploded perspective view of the major components of the preferred embodiment;

[0019] FIG. 4 provides a legend of the materials indicated in FIGS. 5 to 16; and

[0020] FIG. 5 to FIG. 16 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle.

[0021] FIG. 5 shows a wafer with a CMOS layer.

[0022] FIG. 6 shows formation of an ink inlet.

[0023] FIG. 7 shows etching to define the nozzle chamber wall and actuator anchor point.

[0024] FIG. 8 shows etched heater material.

[0025] FIG. 9 shows definition of the nozzle chamber wall.

[0026] FIG. 10 shows etched sacrificial material to define the nozzle chamber wall and paddle.

[0027] FIG. 11 shows definition of the nozzle chamber wall.

[0028] FIG. 12 shows etched sacrificial material to define the nozzle rim.

[0029] FIG. 13 shows etched sacrificial material to define the roof of the nozzle chamber and nozzle.

[0030] FIG. 14 shows etched ink inlets.

[0031] FIG. 15 shows etched sacrificial material to free the actuators and to separate into chips.

[0032] FIG. 16 shows a filled nozzle.

[0033] In the preferred embodiment, there is provided an ink jet printing system wherein each nozzle has a nozzle chamber having a slotted side wall through which is formed an actuator mechanism attached to a vane within the nozzle chamber such that the actuator can be activated to move the vane within the nozzle chamber to thereby cause ejection of ink from the nozzle chamber.

[0034] Turning now to the figures, there is illustrated in FIG. 1 an example of an ink jet nozzle arrangement 1 as constructed in accordance with the preferred embodiment. The nozzle arrangement includes a nozzle chamber 2 normally filled with ink and an actuator mechanism 3 for actuating a vane 4 for the ejection of ink from the nozzle chamber 2 via an ink ejection port 5.

[0035] FIG. 1 is a perspective view of the ink jet nozzle arrangement of the preferred embodiment in its idle or quiescent position. FIG. 2 illustrates a perspective view after actuation of the actuator 3.

[0036] The actuator 3 includes two arms 6, 7. The two arms can be formed from titanium di-boride (TiB₂) which has a high Young's modulus and therefore provides a large degree of bending strength. A current is passed along the arms 6, 7 with the arm 7 having a substantially thicker portion along most of its length. The arm 7 is stiff but for in the area of thinned portion 8 and hence the bending moment is concentrated in the area 8. The thinned arm 6 is of a thinner form and is heated by means of resistive heating of a current passing through the arms 6, 7. The arms 6, 7 are interconnected to electrical circuitry via connections 10, 11.

[0037] Upon heating of the arm 6, the aim 6 is expanded with the bending of the arm 7 being concentrated in the area 8. This results in movement of the end of the actuator mechanism 3 which proceeds through a slot in the wall of the nozzle chamber 2. The bending further causes movement of vane 4 so as to increase the pressure of the ink within the nozzle chamber and thereby cause its subsequent ejection from ink ejection nozzle 5. The nozzle chamber 2 is refilled via an ink channel 13 (FIG. 3) formed in the wafer substrate 14. After movement of the vane 4, so as to cause the ejection of ink, the current to arm 6 is turned off which results in a corresponding back movement of the end vane 4. The ink within nozzle chamber 2 is then replenished by means of wafer ink supply channel 13 which is attached to an ink supply formed on the back of wafer 14. The refill can be by means of a surface tension reduction effects of the ink within nozzle chamber 2 across ink ejection port 5.

[0038] FIG. 3 illustrates an exploded perspective view of the components of the ink jet nozzle arrangement.

[0039] Referring now specifically to FIG. 3, the preferred embodiment 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.

[0040] For a general introduction to a micro-electro mechanical system (MEMS) reference is made to standard proceedings in this field including the proceeding of the SPIE (International Society for Optical Engineering) including volumes 2642 and 2882 which contain the proceedings of recent advances and conferences in this field.

[0041] The nozzles can preferably be constructed by constructing a large array of nozzles on a single silicon wafer at a time. The array of nozzles can be divided into multiple print heads, with each print head itself having nozzles grouped into multiple colors to provide for full color image reproduction. The arrangement can be constructed via the utilization of a standard silicon wafer substrate 14 upon which is deposited an electrical circuitry layer 16 which can comprise a standard CMOS circuitry layer. The CMOS layer can include an etched portion defining pit 17. On top of the CMOS layer is initially deposited a protective layer (not shown) which comprise silicon nitride or the like. On top of this layer is deposited a sacrificial material which is initially suitably etched so as to form cavities for the portion of the thermal actuator 3 and bottom portion of the vane 4, in addition to the bottom rim of nozzle chamber 2. These cavities can then be filled with titanium di-boride. Next, a similar process is used to form the glass portions of the actuator. Next, a further layer of sacrificial material is deposited and suitably etched so as to form the rest of the vane 4 in addition to a portion of the nozzle chamber walls to the same height of vane 4.

[0042] Subsequently, a further sacrificial layer is deposited and etched in a suitable manner so as to form the rest of the nozzle chamber 2. The top surface of the nozzle chamber is further etched so as to form the nozzle rim rounding the ejection port 5. Subsequently, the sacrificial material is etched away so as to release the construction of the preferred embodiment. It will be readily evident to those skilled in the art that other MEMS processing steps could be utilized.

[0043] Preferably, the thermal actuator and vane portions 3 and 4 in addition to the nozzle chamber 2 are constructed from titanium di-boride. The utilization of titanium di-boride is standard in the construction of semiconductor systems and, in addition, its material properties, including a high Young's modulus, is utilized to advantage in the construction of the thermal actuator 3.

[0044] Further, preferably the actuator 3 is covered with a hydrophobic material, such as Teflon, so as to prevent any leaking of the liquid out of the slot 19.

[0045] Further, as a final processing step, the ink channel can be etched through the wafer utilizing a high anisotropic silicon wafer etch. 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 a 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 print head 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 print head 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 35μm apart, increasing the number of chips on a wafer.

[0046] 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:

[0047] 1. Using a double sided polished wafer, complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, 2 metal CMOS process. Relevant features of the wafer at this step are shown in FIG. 5. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 4 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

[0048] 2. Etch oxide down to silicon or aluminum using Mask 1. This mask defines the ink inlet, the heater contact vias, and the edges of the print head chips. This step is shown in FIG. 6.

[0049] 3. Deposit 1 micron of sacrificial material 21 (e.g. aluminum)

[0050] 4. Etch the sacrificial layer 21 using Mask 2, defining the nozzle chamber wall and the actuator anchor point. This step is shown in FIG. 7.

[0051] 5. Deposit 1 micron of heater material 22, for example titamnum nitride TiN) or titanium diboride (TiB₂).

[0052] 6. Etch the heater material 22 using Mask 3, which defines the actuator loop and the lowest layer of the nozzle wall. This step is shown in FIG. 8.

[0053] 7. Wafer probe. All electrical connections are complete at this point, bond pads are accessible, and the chips are not yet separated.

[0054] 8. Deposit 1 micron of titanium nitride 23.

[0055] 9. Etch the titanium nitride 23 using Mask 4, which defines the nozzle chamber wall, with the exception of the nozzle chamber actuator slot, and the paddle. This step is shown in FIG. 9.

[0056] 10. Deposit 8 microns of sacrificial material 24.

[0057] 11. Etch the sacrificial material 24 down to titanium nitride 23 using Mask 5. This mask defines the nozzle chamber wall and the paddle. This step is shown in FIG. 10.

[0058] 12. Deposit a 0.5 micron conformal layer of titanium nitride 25 and planarize down to the sacrificial layer using CMP.

[0059] 13. Deposit 1 micron of sacrificial material 26.

[0060] 14. Etch the sacrificial material down 26 to titanium nitride 25 using Mask 6. This mask defines the nozzle chamber wall. This step is shown in FIG. 11.

[0061] 15. Deposit 1 micron of titanium nitride 27.

[0062] 16. Etch to a depth of (approx.) 0.5 micron using Mask 7. This mask defines the nozzle rim 28.

[0063] This step is shown in FIG. 12.

[0064] 17. Etch down to the sacrificial layer 26 using Mask 8. This mask defines the roof of the nozzle chamber 2, and the nozzle itself 5. This step is shown in FIG. 13.

[0065] 18. Back-etch completely through the silicon wafer 14 (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask 9. This mask defines the ink inlets which are etched through the wafer 14. The wafer 14 is also diced by this etch. This step is shown in FIG. 14.

[0066] 19. Etch the sacrificial material 24. The nozzle chambers 2 are cleared, the actuators 3 freed, and the chips are separated by this etch. This step is shown in FIG. 15.

[0067] 20. Mount the print heads 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.

[0068] 21. Connect the print heads 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.

[0069] 22. Hydrophobize the front surface of the print heads.

[0070] 23. Fill the completed print heads with ink 29 and test them. A filled nozzle is shown in FIG. 16.

[0071] The presently disclosed ink jet printing technology is potentially suited to a wide range of printing system 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.

[0072] It would be appreciated by a person skilled in the art that numerous variations and/or modifications any 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.

[0073] 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.

[0074] 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.

[0075] 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 print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.

[0076] 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:

[0077] low power (less than 10 Watts)

[0078] high resolution capability (1,600 dpi or more)

[0079] photographic quality output

[0080] low manufacturing cost

[0081] small size (pagewidth times minimum cross section)

[0082] high speed (<2 seconds per page).

[0083] 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 Cross References to Related Applications.

[0084] 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 For ease of manufacture using standard process equipment, the print head is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the print head is 100 mm long, with a width which depends upon the ink jet type. The smallest print head designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The print heads each contain 19,200 nozzles plus data and control circuitry.

[0085] Ink is supplied to the back of the print head 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 print head is connected to the camera circuitry by tape automated bonding.

[0086] 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.

[0087] The following tables form the axes of an eleven dimensional table of ink jet types.

[0088] Actuator mechanism (18 types)

[0089] Basic operation mode (7 types)

[0090] Auxiliary mechanism (8 types)

[0091] Actuator amplification or modification method (17 types)

[0092] Actuator motion (19 types)

[0093] Nozzle refill method (4 types)

[0094] Method of restricting back-flow through inlet (10 types)

[0095] Nozzle clearing method (9 types)

[0096] Nozzle plate construction (9 types)

[0097] Drop ejection direction (5 types)

[0098] Ink type (7 types)

[0099] 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.

[0100] 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 print heads with characteristics superior to any currently available ink jet technology.

[0101] 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 printer may be listed more than once in a table, where it shares characteristics with more than one entry.

[0102] 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.

[0103] The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.