Method of manufacture of a radial back-curling thermoelastic ink jet printer

[0002] The following co-pending US patent applications, identified by their US patent application serial numbers (USSN), were filed simultaneously to the present application on July 10, 1998, and are hereby incorporated by cross-reference. 091113,060; 09/113,070; 09/113,073; 09/112,748; 09/112,747; 09/112,776; 09/112,750; 09/112,746; 09/112,743; 09/112,742; 09/112,741; 09/112,740; 09/112,739; 09/113,053; 09/112,738; 09/113,067; 09/113,063; 09/113,069; 09/112,744; 09/113,058; 09/112,777; 09/113,224; 09/112,804; 09/112,805; 09/113,072; 09/112,785; 09/112,797; 09/112,796; 09/113,071; 09/112,824; 09/113,090; 09/112,823; 09/113,222; 09/112,786; 09/113,051; 09/112,782; 09/113,056; 09/113,059; 09/113,091; 09/112,753; 09/113,055; 09/113,057; 09/113,054; 09/112,752; 091112,759; 09/112,757; 09/112,758; 09/113,107; 09/112,829; 09/112,792; 09/112,791; 09/112,790; 09/112,789; 09/112,788; 09/112,795; 09/112,749; 09/112,784; 09/112,783; 09/112,763; 09/112,762; 09/112,737; 09/112,761; 09/113,223; 09/112,781; 09/113,052; 09/112,834; 09/113,103; 09/113,101; 09/112,751; 09/112,787; 091112,802; 09/112,803; 09/113,097; 09/113,099; 09/113,084; 09/113,066; 09/112,778; 09/112,779; 09/113,077; 09/113,061; 09/112,818; 09/112,816; 09/112,772; 09/112,819; 09/112,815; 09/113,096; 09/113,068; 09/113,095; 09/112,808; 09/112,809; 09/112,780; 09/113,083; 09/113,121; 09/113,122; 091112,793; 091112,794; 09/113,128; 09/113,127; 09/112,756; 09/112,755; 09/112,754; 09/112,811; 09/112,812; 09/112,813; 09/112,814; 091112,764; 09/112,765; 09/112,767; 09/112,768; 09/112,807; 09/112,806; 09/112,820; 09/112,821; 09/112,822; 09/112,825; 09/112,826; 09/112,827; 09/112,828; 09/113,111; 09/113,108; 09/113,109; 09/113,123; 09/113,114; 09/113,115; 09/113,129; 09/113,124; 09/113,125; 09/113,126; 09/113,119; 09/113,120; 09/113,221; 09/113,116; 09/113,118; 09/113,117; 09/113,113; 09/113,130; 09/113,110; 09/113,112; 09/113,087; 09/113,074; 09/113,089; 09/113,088; 09/112,771; 09/112,769; 09/112,770; 09/112,817; 09/113,076; 09/112,798; 09/112,801; 09/112,800; 09/112,799; 09/113,098; 09/112,833; 09/112,832; 09/112,831; 09/112,830; 09/112,836; 09/112,835; 09/113,102; 09/113,106; 09/113,105; 09/113,104; 09/112,810; 09/112,766; 09/113,085; 09/113,086; 09/113,094; 09/112,760; 09/112,773; 09/112,774; 09/112,775; 09/112,745; 09/113,092; 09/113,100; 09/113,093; 09/113,062; 09/113,064; 09/113,082; 09/113,081; 09/113,080; 09/113,079; 09/113,065; 09/113,078; 09/113,075;

[0003] Not applicable.

[0004] The present invention relates to the field of inkjet printers and discloses an inkjet printing system which includes a bend actuator interconnected into a paddle for the ejection of ink through an ink ejection nozzle. In particular, the present invention includes A Method of Manufacture of a Radial Back-Curling Thermoelastic Ink Jet.

[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 adds 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)), electro-discharge 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 ejection nozzle arrangement suitable for incorporation into an inkjet printhead arrangement for the ejection of ink on demand from a nozzle chamber in an efficient manner. In particular the inkjet printer can comprise a Radial Back-Curling Thermoelastic Ink Jet.

[0011] In accordance with a first aspect of the present invention, there is provided a method of manufacturing a Radial Back-Curling Thermoelastic Ink Jet print head wherein an array of nozzles are formed on a substrate utilising planar monolithic deposition, lithographic and etching processes.

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

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

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

[0015] In accordance with a further aspect of the present invention, there is provided a method of manufacture of an ink jet print head arrangement including a series of nozzle chambers, the method comprising the steps of: (a) utilizing an initial semiconductor wafer having an electrical circuitry layer formed thereon; (b) etching the circuitry layer to define a nozzle cavity area; (c) depositing and etching a first material layer, the first material having a high coefficient of thermal expansion, the etching including etching for vias through the first material layer for electrical interconnection of subsequently deposited layers with the circuitry layer; (d) depositing and etching a conductive material layer on the first material layer, the etching resulting in the conductive material layer forming a heater pattern; (e) depositing and etching a second material layer, the second material layer having a high coefficient of thermal expansion, the etching defining a nozzle chamber rim and a rim at the edge of the nozzle chamber; (f) etching the wafer to define the nozzle chamber; (g) etching an ink supply channel through the wafer in fluid communication with the nozzle chamber.

[0016] The step (f) can comprise performing a crystallographic etch of the wafer utilizing slots created as a result of etching the second material layer.

[0017] The crystallographic etch forms a nozzle chamber having an inverted square pyramid shape. The step (g) can comprise a through wafer etch from a back surface of the wafer.

[0018] The first material layer or the second material layer can comprise substantially polytetrafluoroethylene and the conductive material layer can comprise substantially gold, copper or aluminum.

[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] FIGS. 1-3 are schematic sectional views illustrating the operational principles of the preferred embodiment;

[0021] FIG. 4(a) and FIG. 4(b) are again schematic sections illustrating the operational principles of the thermal actuator device;

[0022] FIG. 5 is a side perspective view, partly in section of a single nozzle arrangement constructed in accordance with the preferred embodiments;

[0023] FIGS. 6-13 illustrate side perspective views partly in section illustrating the manufacturing steps of the preferred embodiments; and

[0024] FIG. 14 illustrates an array of ink jet nozzles formed in accordance with the manufacturing procedures of the preferred embodiment;

[0025] FIG. 15 provides a legend of the materials indicated in FIGS. 16 to 23;

[0026] FIG. 16 to FIG. 23 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle;

[0027] In the preferred embodiment, ink is ejected out of a nozzle chamber via an ink ejection hole as the result of the utilisation of a series of radially placed thermal actuator devices that are arranged around the ink ejection nozzle and are activated so as to compress the ink within the nozzle chamber thereby causing ink ejection.

[0028] Turning now to FIGS. 1, 2 and 3, there will first be illustrated the basic operational principles of the preferred embodiment. FIG. 1 illustrates a single nozzle chamber arrangement 1 when it is in its quiescent state. The arrangement 1 includes a nozzle chamber 2 which is normally filled with ink so as to form a meniscus 3 around an ink ejection nozzle 4. The nozzle chamber 2 is formed within a wafer 5. The nozzle chamber 2 supplied from an ink supply channel 6 which can be etched through the wafer 5 through the utilisation of a highly isotropic plasma etching system. A suitable etcher can be the Advance Silicon Etch (ASE) system available from Surface Technology Systems of the United Kingdom.

[0029] The top of the nozzle chamber arrangement 1 includes a series of radially placed thermoactuator devices e.g. 8, 9. These devices comprise a series of polytetrafluoroethylene (PTFE) actuators having an internal serpentine copper core. Upon heating of the copper core, the surrounding Teflon expands rapidly resulting in a generally downward movement of the actuator 8, 9. Hence, when it is desired to eject ink from the ink ejection nozzle 4, a current is passed through the actuators 8, 9 which results in generally bending downwards as illustrated in FIG. 2. The downward bending movement of actuators 8, 9 results in a substantial increase in pressure within the nozzle chamber 2. The rapid increase in pressure in nozzle chamber 2, in turn results in a rapid expansion of the meniscus 3 as illustrated in FIG. 2.

[0030] The actuators are turned on for a limited time only and subsequently deactivated. A short time later the situation is as illustrated in FIG. 3 with the actuators 8, 9 rapidly returning to their original positions. This results in a general inflow of ink and a necking and breaking of the meniscus 3 resulting in the ejection of a drop 12. The necking and breaking of the meniscus is a consequence of the forward momentum of the ink associated with drop 12 and the backward pressure experienced as a result of the return of the actuators 8, 9 to their original positions. The return of the actuator also results in a general inflow of ink 50 from the supply channel 6 as a result of surface tension effects and, eventually, the state returns to the quiescent position as illustrated in FIG. 1.

[0031] FIGS. 4(a) and 4(b) illustrate the principle of operation of the thermal actuator. The thermal actuator is preferably constructed from a material 14 having a high coefficient of thermal expansion. Embedded within the material 14 is a series of heater elements e.g. 15 which can be a series of conductive elements designed to carry a current. The conductive elements 15 are heated by means of passing a current through the elements with the heating resulting in a general increase in temperature in the area around the heating elements. The increase in temperature causes a corresponding expansion of the PTFE which has a high coefficient of thermal expansion. Hence, as illustrated in FIG. 4(b), the PTFE is bent generally in a downward direction.

[0032] Turning now to FIG. 5, there is illustrated a side perspective view of one nozzle arrangement constructed in accordance with the principles previously outlined. The nozzle chamber 2 can be constructed by means of an isotropic surface etch of the wafer surface 5. The wafer surface 5 can include a CMOS layer 21 including all the required power and drive circuits. Further, a series of leaf or petal type actuators e.g. 8, 9 are provided each having an internal copper core e.g. 17 which winds in a serpentine nature so as to provide for substantially unhindered expansion of the actuator device. The operation of the actuator is similar to that as illustrated in FIG. 4(a) and FIG. 4(b) such that, upon activation, the petals e.g. 8 bend downwardly as previously described. The ink supply channel 6 can be created via a deep silicon back edge of the wafer utilising a plasma etcher or the like. The copper or aluminum coil e.g. 17 can provide a complete circuit around each petal. A central arm 18 which can include both metal and PTFE portions provides the main structural support for the petal arrangement in addition to providing a current trace for the conductive heaters.

[0033] Turning now to FIG. 6 to FIG. 13, there will now be explained one form of manufacturing of a printhead device operational in accordance with the principles of the preferred embodiment. The device is preferably constructed utilising microelectromechanical (MEMS) techniques and can include the following construction techniques:

[0034] As shown initially in FIG. 6, the initial processing starting material is a standard semi-conductor wafer 20 have a complete CMOS level 21 to the first level metal step. The first level metal includes portions eg. 22 which are utilized for providing power to the thermal actuator.

[0035] The first step, as illustrated in FIG. 7, is to etch a nozzle region down to the silicon wafer 20 utilizing an appropriate mask.

[0036] Next, as illustrated in FIG. 8, a 2 micron layer of polytetrafluoroethylene (PTFE) 23 is deposited and etched so as to include vias eg. 24 for interconnecting multiple levels.

[0037] Next, as illustrated in FIG. 9, the second level metal layer is deposited, masked and etched so as to form heater structure 25. The heater structure 25 including via interconnect 26 with the lower aluminum layer.

[0038] Next, as illustrated in FIG. 10, a further 2 micron layer of PTFE is deposited and etched to the depth of 1 micron utilizing a nozzle rim mask so as to form nozzle rim eg. 28 in addition to ink flow guide rails eg. 29 which generally restrain any wicking along the surface of the PTFE layer. The guide rails eg. 29 surround small thin slots and, as such, surface tension effects are a lot higher around these slots which in turn results in minimal outflow of ink during operation.

[0039] Next, as illustrated in FIG. 11, the PTFE is etched utilizing a nozzle and paddle mask so as to define nozzle portion 30 and slots eg. 31 and 32.

[0040] Next, as illustrated in FIG. 12, the wafer is crystal calligraphically etched on the <111 >plane utilizing a standard crystallographic etchant such as KOH. The etching forms chamber 33, directly below the ink ejection nozzle.

[0041] Next, turning to FIG. 13, the ink supply channel 6 can be etched from the back of the wafer utilizing a highly anisotropic etcher such as the STS etcher from Silicon Technology Systems of United Kingdom. Obviously, an array of ink jet nozzles can be formed simultaneously with a portion of an array 36 being illustrated in FIG. 14 with a portion of the printhead being formed simultaneously and diced by the STS etch etching process. The array 36 shown provides for four column printing with each separate column attached to a different color ink supply channel being supplied from the back of the wafer. The bond pads 37 provide for electrical control of the ejection mechanism.

[0042] In this manner, large pagewidth printheads can be formulated so as to provide for a drop on demand ink ejection mechanism.

[0043] 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 along the following steps:

[0044] 1. Using a double sided polished wafer 20, complete a 0.5 micron, one poly, 2 metal CMOS process to form layer 21. This step is shown in FIG. 16. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 15 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

[0045] 2. Etch the CMOS oxide layers down to silicon or second level metal using Mask 1. This mask defines the nozzle cavity and the edge of the chips. This step is shown in FIG. 16.

[0046] 3. Deposit a thin layer (not shown) of a hydrophilic polymer, and treat the surface of this polymer for PTFE adherence.

[0047] 4. Deposit 1.5 microns of polytetrafluoroethylene (PIFE) 60.

[0048] 5. Etch the PIFE and CMOS oxide layers to second level metal using Mask 2. This mask defines the contact vias 24 for the heater electrodes. This step is shown in FIG. 17.

[0049] 6. Deposit and pattern 0.5 microns of gold 61 using a lift-off process using Mask 3. This mask defines the heater pattern. This step is shown in FIG. 18.

[0050] 7. Deposit 1.5 microns of PTFE 62.

[0051] 8. Etch 1 micron of PTFE using Mask 4. This mask defines the nozzle rim 28 and the ink flow guide rails 29 at the edge of the nozzle chamber. This step is shown in FIG. 19.

[0052] 9. Etch both layers of PTFE and the thin hydrophilic layer down to silicon using Mask 5. This mask defines the gap 64 at the edges of the actuator petals, and the edge of the chips. It also forms the mask for the subsequent crystallographic etch. This step is shown in FIG. 20.

[0053] 10. Crystallographically etch the exposed silicon using KOH. This etch stops on <111>crystallographic planes 65, forming an inverted square pyramid with sidewall angles of 54.74 degrees. This step is shown in FIG. 21.

[0054] 11. Back-etch through the silicon wafer (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask 6. This mask defines the ink inlets 6 which are etched through the wafer. The wafer is also diced by this etch. This step is shown in FIG. 22.

[0055] 12. 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.

[0056] 13. 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.

[0057] 14. Fill the completed print heads with ink 66 and test them. A filled nozzle is shown in FIG. 23.

[0058] 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.

[0059] 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 embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

[0060] Ink Jet Technologies

[0061] 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.

[0062] The most significant problem with thermal inkjet 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 inkjet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

[0063] The most significant problem with piezoelectric inkjet 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.

[0064] Ideally, the inkjet 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 inkjet technologies have been created. The target features include:

[0065] low power (less than 10 Watts)

[0066] high resolution capability (1,600 dpi or more)

[0067] photographic quality output

[0068] low manufacturing cost

[0069] small size (pagewidth times minimum cross section)

[0070] high speed (<2 seconds per page).

[0071] All of these features can be met or exceeded by the inkjet systems described below with differing levels of difficulty. Forty-five different inkjet 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 below.

[0072] The inkjet 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

[0073] 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 inkjet 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.

[0074] 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.

[0075] Tables of Drop-on-Demand Ink Jets

[0076] The present invention is useful in the field of digital printing, in particular, ink jet printing. A number of patent applications in this field were filed simultaneously and incorporated by cross reference.

[0077] 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.

[0078] The following tables form the axes of an eleven dimensional table of ink jet types.

[0079] Actuator mechanism (18 types)

[0080] Basic operation mode (7 types)

[0081] Auxiliary mechanism (8 types)

[0082] Actuator amplification or modification method (17 types)

[0083] Actuator motion (19 types)

[0084] Nozzle refill method (4 types)

[0085] Method of restricting back-flow through inlet (10 types)

[0086] Nozzle clearing method (9 types)

[0087] Nozzle plate construction (9 types)

[0088] Drop ejection direction (5 types)

[0089] Ink type (7 types)

[0090] 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 IJ145 which matches the docket numbers in the table under the heading CROSS REFERENCES TO RELATED APPLICATIONS.

[0091] Other ink jet configurations can readily be derived from these 45 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.

[0092] 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.

[0093] 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 Ww printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

[0094] The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.