Abstract:
An inkjet printhead with an array of nozzles arranged in a series of rows, each nozzle having an ejection aperture, a chamber for holding printing fluid and a heater element for generating a vapor bubble in the printing fluid contained by the chamber to eject a drop of the printing fluid through the ejection aperture. The nozzle, the heater element and the chamber are all elongate structures that have a long dimension that exceeds their other dimensions respectively. The respective long dimensions of the nozzle, the heater element and the chambers are parallel and extend normal to the row direction. To increase the nozzle density of the array, each of the nozzle components—the chamber, the ejection aperture and the heater element are configured as elongate structures that are all aligned transverse to the direction of the row. This raises the nozzle pitch, or nozzle per inch (npi), of the row while allowing the chamber volume and therefore drop volume to stay large enough for a suitable color density. It also avoids the need to spread the over a large distance in the paper feed direction (in the case of pagewidth printers) or in the scanning direction (in the case of scanning printheads).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation in part of application Ser. No. 11/246,687 filed 11 Oct. 2005 the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to the field of printing. In particular, the invention concerns an inkjet printhead for high resolution printing.  
       CROSS REFERENCE TO OTHER RELATED APPLICATIONS  
       [0003]     The following applications have been filed by the Applicant simultaneously with this application.  
                                                   MNN022US   MNN023US   MNN024US   MNN026US   MNN027US       MNN028US   MNN029US   MNN030US                  
 
         [0004]     The disclosures of these co-pending applications are incorporated herein by reference. The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.  
         [0005]     The following applications were filed by the Applicant simultaneously with the parent application, application Ser. No. 11/246,687:  
                                                   11/246676   11/246677   11/246678   11/246679   11/246680       11/246681   11/246714   11/246713   11/246689   11/246671       11/246670   11/246669   11/246704   11/246710   11/246688       11/246688   11/246715   11/246718   11/246685   11/246686       11/246703   11/240691   11/246711   11/246690   11/246712       11/246717   11/246769   11/246700   11/246701   11/246702       11/246668   11/246697   11/246698   11/246699   11/246675       11/246684   11/246672   11/246673   11/246683   11/246682       11/246707   11/246706   11/246705   11/246708   11/246693       11/246692   11/246696   11/246695   11/246694   11/246674       11/246667                  
 
         [0006]     The disclosures of these applications are incorporated herein by reference.  
         [0007]     The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.  
                                                           6405055   6628430   7136186   10/920372   7145689   7130075   7081974       7177055   7209257   7161715   7154632   7158258   7148993   7075684       11/635526   11/650545   11/653241   11/653240   11758648   7241005   7108437       6915140   6999206   7136198   7092130   09/517539   6566858   6331946       6246970   6442525   09/517384   09/505951   6374354   7246098   6816968       6757832   6334190   6745331   09/517541   10/203559   7197642   7093139       10/636263   10/636283   10/866608   7210038   10/902833   10/940653   10/942858       11/706329   11/757385   11/758642   7170652   6967750   6995876   7099051       11/107942   7193734   11/209711   11/599336   7095533   6914686   7161709       7099033   11/003786   11/003616   11/003418   11/003334   11/003600   11/003404       11/003419   11/003700   11/003601   11/003618   7229148   11/003337   11/003698       11/003420   6984017   11/003699   11/071473   11748482   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11/607978   11/735961   11/685074   11/696126   11/696144   11/696650   11/763446       10/407212   10/407207   10/683064   10/683041   11766713   11/482980   11/563684       11/482967   11/482966   11/482988   11/482989   11/293832   11/293838   11/293825       11/293841   11/293799   11/293796   11/293797   11/293798   11/124158   11/124196       11/124199   11/124162   11/124202   11/124197   11/124154   11/124198   11/124153       11/124151   11/124160   11/124192   11/124175   11/124163   11/124149   11/124152       11/124173   11/124155   7236271   11/124174   11/124194   11/124164   11/124200       11/124195   11/124166   11/124150   11/124172   11/124165   11/124186   11/124185       11/124184   11/124182   11/124201   11/124171   11/124181   11/124161   11/124156       11/124191   11/124159   11/124176   11/124188   11/124170   11/124187   11/124189       11/124190   11/124180   11/124193   11/124183   11/124178   11/124177   11/124148       11/124168   11/124167   11/124179   11/124169   11/187976   11/188011   11/188014       11/482979   11/735490   11/228540   11/228500   11/228501   11/228530   11/228490       11/228531   11/228504   11/228533   11/228502   11/228507   11/228482   11/228505       11/228497   11/228487   11/228529   11/228484   11/228489   11/228518   11/228536       11/228496   11/228488   11/228506   11/228516   11/228526   11/228539   11/228538       11/228524   11/228523   11/228519   11/228528   11/228527   11/228525   11/228520       11/228498   11/228511   11/228522   111/228515   11/228537   11/228534   11/228491       11/228499   11/228509   11/228492   11/228493   11/228510   11/228508   11/228512       11/228514   11/228494   11/228495   11/228486   11/228481   11/228477   11/228485       11/228483   11/228521   11/228517   11/228532   11/228513   11/228503   11/228480       11/228535   11/228478   11/228479   6087638   6340222   6041600   6299300       6067797   6286935   6044646   6382769   10/868866   6787051   6938990       11/242916   11/242917   11/144799   11/198235   11/766052   7152972   11/592996       6746105   11/763440   11/763442   11/246687   11/246718   11/246685   11/246686       11/246703   11/246691   11/246711   11/246690   11/246712   11/246717   11/246709       11/246700   11/246701   11/246702   11/246668   11/246697   11/246698   11/246699       11/246675   11/246674   11/246667   7156508   7159972   7083271   7165834       7080894   7201469   7090336   7156489   10/760233   10/760246   7083257       10/760243   10/760201   7219980   10/760253   10/760255   10/760209   7118192       10/760194   10/706238   7077505   7198354   7077504   10/760189   7198355       10/760232   10/760231   7152959   7213906   7178901   7222938   7108353       7104629   11/446227   11/454904   11/472345   11/474273   11/478594   11/474279       11/482939   11/482950   11/499709   11/592984   11/601668   11/603824   11/601756       11/601672   11/650546   11/653253   11/706328   11/706299   11/706965   11/737080       11/737041   11/778062   11778566   11782593   11/246684   11/246672   11/246673       11/246683   11/246682   60/939086   10/728804   7128400   7108355   6991322       10/728790   7118197   10/728970   10/728784   10/728783   7077493   6962402       10/728803   7147308   10/728779   7118198   7168790   7172270   7229155       6830318   7195342   7175261   10/773183   7108356   7118202   10/773186       7134744   10/773185   7134743   7182439   7210768   10/773187   7134745       7156484   7118201   7111926   10/773184   7018021   11/060751   11/060805       11/188017   7128402   11/298774   11/329157   11/490041   11/501767   11/499736       11/505935   7229156   11/505846   11/505857   11/505856   11/524908   11/524938       11/524900   11/524912   11/592999   11/592995   11/603825   11/649773   11/650549       11/653237   11/706378   11/706962   11749118   11/754937   11749120   11/744885       11779850   11765439   11/097308   11/097309   11/097335   11/097299   11/097310       11/097213   11/210687   11/097212   7147306   11/545509   11764806   11782595       11/482953   11/482977   11/544778   11/544779   11/764808   11/066161   11/066160       11/066159   11/066158   11/066165   10/727181   10/727162   10/727163   10/727245       7121639   7165824   7152942   10/727157   7181572   7096137   10/727257       10/727238   7188282   10/727159   10/727180   10/727179   10/727192   10/727274       10/727164   10/727161   10/727198   10/727158   10/754536   10/754938   10/727227       10/727160   10/934720   7171323   11/272491   11/474278   11/488853   11/488841       11749750   11749749   10/296522   6795215   7070098   7154638   6805419       6859289   6977751   6398332   6394573   6622923   6747760   6921144       10/884881   7092112   7192106   11/039866   7173739   6986560   7008033       11/148237   7222780   11/248426   11/478599   11/499749   11/738518   11/482981       11/743661   11/743659   11/752900   7195328   7182422   11/650537   11/712540       10/854521   10/854522   10/854488   10/854487   10/854503   10/854504   10/854509       7188928   7093989   10/854497   10/854495   10/854498   10/854511   10/854512       10/854525   10/854526   10/854516   10/854508   10/854507   10/854515   10/854506       10/854505   10/854493   10/854494   10/854489   10/854490   10/854492   10/854491       10/854528   10/854523   10/854527   10/854524   10/854520   10/854514   10/854519       10/854513   10/854499   10/854501   10/854500   7243193   10/854518   10/854517       10/934628   7163345   11/499803   11/601757   11/706295   11/735881   11748483       11749123   11766061   11775135   11772235   11778569   11/014731   11/544764       11/544765   11/544772   11/544773   11/544774   11/544775   11/544776   11/544766       11/544767   11/544771   11/544770   11/544769   11/544777   11/544768   11/544763       11/293804   11/293840   11/293803   11/293833   11/293834   11/293835   11/293836       11/293837   11/293792   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 10/760220   7002664   10/760252   10/760265   7088420       11/446233   11/503083   11/503081   11/516487   11/599312   11/014728   11/014727       7237888   7168654   7201272   6991098   7217051   6944970   10/760215       7108434   10/760257   7210407   7186042   10/760266   6920704   7217049       10/760214   10/760260   7147102   10/760269   10/760199   10/760241   10/962413       10/962427   10/962418   7225739   10/962402   10/962425   10/962428   7191978       10/962426   10/962409   10/962417   10/962403   7163287   10/962522   10/962523       10/962524   10/962410   7195412   7207670   11/282768   7220072   11/474267       11/544547   11/585925   11/593000   11/706298   11/706296   11/706327   11/730760       11/730407   11/730787   11/735977   11/736527   11/753566   11/754359   11/778061       11/765398   11778556   11780470   11/223262   11/223018   11/223114   11/223022       11/223021   11/223020   11/223019   11/014730   7079292   09/575197   7079712       09/575123   6825945   09/575165   6813039   6987506   7038797   6980318       6816274   7102772   09/575186   6681045   6728000   7173722   7088459       09/575181   7068382   7062651   6789194   6789191   6644642   6502614       6622999   6669385   6549935   6987573   6727996   6591884   6439706       6740119   09/575198   6290349   6428155   6785016   6870966   6822639       6737591   7055739   7233320   6830196   6832717   6957768   09/575172       7170499   7106888   7123239                  
 
       BACKGROUND OF THE INVENTION  
       [0008]     The quality of a printed image depends largely on the resolution of the printer. Accordingly, there are ongoing efforts to improve the print resolution of printers. The print resolution strictly depends on the spacing of the printer addressable locations on the media substrate and the drop volume. The spacing between nozzles on the printhead need not be as small as the spacing between addressable locations on the media substrate. The nozzle that prints a dot at one addressable location can be spaced any distance away from the nozzle that prints the dot at the adjacent addressable location. Movement of the printhead relative to the media, or vice versa, or both, will allow the printhead to eject drops at every addressable location regardless of the spacing between the nozzles on the printhead. In the extreme case, the same nozzle can print adjacent drops with the appropriate relative movement between the printhead and the media.  
         [0009]     Excess movement of the media with respect to the printhead will reduce print speeds. Multiple passes of a scanning printhead over a single swathe of the media, or multiple passes of the media past the printhead in the case of pagewidth printhead reduces the page per minute print rate.  
         [0010]     Alternatively, the nozzles can be spaced along the media feed path or in the scan direction so that the addressable locations on the media are smaller than the physical spacing of adjacent nozzles. It will be appreciated that the spacing the nozzles over a large section of the paper path or scan direction is counter to compact design. More importantly, it requires the paper feed to carefully control the media position and precise printer control of nozzle firing times.  
         [0011]     For pagewidth printheads, the large nozzle array emphasizes the problem. Spacing the nozzles over a large section of the paper path requires the nozzle array to have a relatively large area. The nozzle array must, by definition, extend the width of the media. But its dimension in the direction of media feed should be as small as possible. Arrays that extend a relatively long distance in the media feed direction require complex print platens that maintain the spacing between the nozzles and the media surface across the entire array. Some printer designs use a broad vacuum platen opposite the printhead to get the necessary control of the media. In light of these issues, there is a strong motivation to increase the density of nozzles on the printhead (that is, the number of nozzles per unit area) in order to increase the addressable locations of the printer and therefore the print resolution while keeping the width of the array (in the direction of media feed) small.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, the present invention provides a printhead for an inkjet printer, the printhead comprising:  
         [0013]     an array of nozzles arranged in adjacent rows, each nozzle having an ejection aperture and a corresponding actuator for ejecting printing fluid through the ejection aperture, each actuator having electrodes spaced from each other in a direction transverse to the rows; and,  
         [0014]     drive circuitry for transmitting electrical power to the electrodes; wherein,  
         [0015]     the electrodes of the actuators in adjacent rows have opposing polarities such that the actuators in adjacent rows have opposing current flow directions.  
         [0016]     By reversing the polarity of the electrodes in adjacent rows, the punctuations in the power plane of the CMOS can be kept to the outside edges of the adjacent rows. This moves one line of narrow resistive bridges between the punctuations to a position where the electrical current does not flow through them. This eliminates their resistance from the actuators drive circuit. By reducing the resistive losses for actuators remote from the power supply side of the printhead IC, the drop ejection characteristics are consistent across the entire array of nozzles.  
         [0017]     Preferably, the electrodes in each row are offset from its adjacent actuators in a direction transverse to the row such that the electrodes of every second actuator are collinear. In a further preferred form, the offset is less than 40 microns. In a particularly preferred form, the offset is less than 30 microns. Preferably the array of nozzles is fabricated on an elongate wafer substrate extending parallel to the rows of the array, and the drive circuitry is CMOS layers on one surface of the wafer substrate, the CMOS layers being supplied with power and data along a long edge of the wafer substrate. In a further preferred form, the CMOS layers have a top metal layer forming a power plane that carries a positive voltage such that the electrodes having a negative voltage connect to vias formed in holes within the power plane. In another preferred form, the CMOS layers have a drive FET (field effect transistor) for each actuator in a bottom metal layer. Preferably, the CMOS layers have layers of metal less than 0.3 microns thick.  
         [0018]     In some embodiments, the actuators are heater elements for generating a vapor bubble in the printing fluid such that a drop of the printing fluid is ejected from the ejection aperture. Preferably, the heater elements are beams suspended between their respective electrodes such that they are immersed in the printing fluid. Preferably, the ejection apertures are elliptical with the major axis of the ejection aperture parallel to the longitudinal axis of the beam. In another preferred form, the major axes of the ejection apertures in one of the rows are respectively collinear with the major axes of the ejection apertures in the adjacent row such that each of the nozzles in one of the rows is aligned with one of the nozzles in the adjacent row. Preferably, the major axes of adjacent ejection apertures are spaced apart less than 50 microns. In a further preferred form, the major axes of adjacent ejection apertures are spaced apart less than 25 microns. In a particularly preferred form, the major axes of adjacent ejection apertures are spaced apart less than 16 microns.  
         [0019]     In particular embodiments, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. In preferred embodiments, the nozzle pitch is greater than 3000 npi. In a particularly preferred embodiment, the printhead has a print resolution in dots per inch (dpi) that equals the nozzle pitch. In specific embodiments, the printhead is a pagewidth printhead configured for printing A4 sized media. Preferably, the printhead has more than 100,000 of the nozzles.  
         [0000]     Accordingly, the present invention provides an inkjet printhead for a printer that can print onto a substrate at different print resolutions, the inkjet printhead comprising:  
         [0020]     an array of nozzles, each nozzle having an ejection aperture and a corresponding actuator for ejecting printing fluid through the ejection aperture; and,  
         [0021]     a print engine controller for sending print data to the array of nozzles; wherein,  
         [0022]     during use the print engine controller can selectively reduce the print resolution by apportioning print data for a single nozzle between at least two nozzles of the array.  
         [0023]     The invention recognizes that some print jobs do not require the printhead&#39;s best resolution—a lower resolution is completely adequate for the purposes of the document being printed. This is particularly true if the printhead is capable of very high resolutions, say greater than 1200 dpi. By selecting a lower resolution, the print engine controller (PEC) can treat two or more transversely adjacent (but not necessarily contiguous) nozzles as a single virtual nozzle in a printhead with less nozzles. The print data is then shared between the adjacent nozzles—dots required from the virtual nozzle are printed by each the actual nozzles in turn. This serves to extend the operational life of all the nozzles.  
         [0024]     Preferably, the two nozzles are positioned in the array such that they are nearest neighbours in a direction transverse to the movement of the printhead relative to the substrate. Preferably, the PEC shares the print data equally between the two nozzles in the array. In a further preferred form, the two nozzles are spaced at less than 20 micron centres. In a particularly preferred form, the printhead is a pagewidth printhead and the two nozzles are spaced in a direction transverse to the media feed direction at less than 16 micron centres. In a specific embodiments, the two nozzles are spaced in a direction transverse to the media feed direction at less than 8 micron centres. In particular embodiments, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. In preferred embodiments, the nozzle pitch is greater than 3000 npi. In a particularly preferred embodiment, the printhead has a print resolution in dots per inch (dpi) that equals the nozzle pitch. In specific embodiments, the printhead is configured for printing A4 sized media and the printhead has more than 100,000 of the nozzles.  
         [0025]     In some embodiments, the printer operates at an increased print speed when printing at the reduced print resolution. Preferably, the increased print speed is greater than 60 pages per minute. In preferred forms, the PEC halftones the color plane printed by the adjacent nozzles with a dither matrix optimized for the transverse shift of every drop ejected.  
         [0000]     Accordingly, the present invention provides an inkjet printhead comprising:  
         [0026]     an array of nozzles arranged in adjacent rows, each nozzle having an ejection aperture, a chamber for containing printing fluid and a corresponding actuator for ejecting the printing fluid through the ejection aperture, each of the chambers having a respective inlet to refill the printing fluid ejected by the actuator; and,  
         [0027]     a printing fluid supply channel extending parallel to the adjacent rows for supplying printing fluid to the actuator of each nozzle in the array via the respective inlets; wherein,  
         [0028]     the inlets of nozzles in one of the adjacent rows configured for a refill flowrate that differs from the refill flowrate through the inlets of nozzles in another of the adjacent rows.  
         [0029]     The invention configures the nozzle array so that several rows are filled from one side of an ink supply channel. This allows a greater density of nozzles on the printhead surface because the supply channel is not supplying just one row of nozzles along each side. However, the flowrate through the inlets is different for each row so that rows further from the supply channel do not have significantly longer refill times.  
         [0030]     Preferably, the inlets of nozzles in one of the adjacent rows configured for a refill flowrate that differs from the refill flowrate through the inlets of nozzles in another of the adjacent rows such that the chamber refill time is substantially uniform for all the nozzles in the array. In a further preferred form, the inlets of the row closest the supply channel are narrower than the rows further from the supply channel. In some embodiments, there are two adjacent rows of nozzles on either side of the supply channel.  
         [0031]     Preferably, the inlets have flow damping formations. In a particularly preferred form, the flow damping formation is a column positioned such that it creates a flow obstruction, the columns in the inlets of one row creating a different degree of obstruction to the columns is the inlets of the other row. Preferably, the columns create a bubble trap between the column sides and the inlet sidewalls. Preferably, the columns diffuse pressure pulses in the printing fluid to reduce cross talk between the nozzles.  
         [0032]     In some embodiments, the actuators are heater elements for generating a vapor bubble in the printing fluid such that a drop of the printing fluid is ejected from the ejection aperture. Preferably, the heater elements are beams suspended between their respective electrodes such that they are immersed in the printing fluid. Preferably, the ejection apertures are elliptical with the major axis of the ejection aperture parallel to the longitudinal axis of the beam. Preferably, the major axes of adjacent ejection apertures are spaced apart less than 50 microns. In a further preferred form, the major axes of adjacent ejection apertures are spaced apart less than 25 microns. In a particularly preferred form, the major axes of adjacent ejection apertures are spaced apart less than 16 microns.  
         [0033]     In particular embodiments, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. In preferred embodiments, the nozzle pitch is greater than 3000 npi. In a particularly preferred embodiment, the printhead has a print resolution in dots per inch (dpi) that equals the nozzle pitch. In specific embodiments, the printhead is a pagewidth printhead configured for printing A4 sized media. Preferably, the printhead has more than 100,000 of the nozzles.  
         [0000]     Accordingly, the present invention provides an inkjet printhead comprising:  
         [0034]     an array of nozzles arranged in a series of rows, each nozzle having an ejection aperture, a chamber for holding printing fluid and a heater element for generating a vapor bubble in the printing fluid contained by the chamber to eject a drop of the printing fluid through the ejection aperture; wherein,  
         [0035]     the nozzle, the heater element and the chamber are all elongate structures that have a long dimension that exceeds their other dimensions respectively; and,  
         [0036]     the respective long dimensions of the nozzle, the heater element and the chambers are parallel and extend normal to the row direction.  
         [0037]     To increase the nozzle density of the array, each of the nozzle components—the chamber, the ejection aperture and the heater element are configured as elongate structures that are all aligned transverse to the direction of the row. This raises the nozzle pitch, or nozzle per inch (npi), of the row while allowing the chamber volume and therefore drop volume to stay large enough for a suitable color density. It also avoids the need to spread the over a large distance in the paper feed direction (in the case of pagewidth printers) or in the scanning direction (in the case of scanning printheads).  
         [0038]     Preferably each of the rows in the array is offset with respect to it adjacent row such that none of the long dimensions of the nozzles in one row are not collinear with any of the long dimensions of the adjacent row. In a further preferred form the printhead is a pagewidth printhead for printing to a media substrate fed past the printhead in a media feed direction such that the long dimensions of the nozzles are parallel with the media feed direction.  
         [0039]     Preferably the long dimensions of the nozzles in every second are in registration. In a particularly preferred form the ejection apertures for all the nozzles is formed in a planar roof layer that partially defines the chamber, the roof layer having an exterior surface that is flat with the exception of the ejection apertures. In a particularly preferred form, the array of nozzles is formed on an underlying substrate extending parallel to the roof layer and the chamber is partially defined by a sidewall extending between the roof layer and the substrate, the side wall being shaped such that its interior surface is at least partially elliptical. Preferably, the sidewall is elliptical except for an inlet opening for the printing fluid. In a particularly preferred form, the minor axes of the nozzles in one of the rows partially overlaps with the minor axes of the nozzles in the adjacent row with respect to the media feed direction. In a further preferred form, the ejection apertures are elliptical.  
         [0040]     Preferably, the heater elements are beams suspended between their respective electrodes such that, during use, they are immersed in the printing fluid. Preferably, the vapor bubble generated by the heater element is approximately elliptical in a cross section parallel to the ejection aperture.  
         [0041]     In some embodiments, the printhead further comprises a supply channel adjacent the array extending parallel to the rows. In a preferred form, the array of nozzles is a first array of nozzles and a second array of nozzles is formed on the other side of the supply channel, the second array being a mirror image of the first array but offset with respect to the first array such that none of the major axes of the ejection apertures in the first array are collinear with any of the major axes of the second array. Preferably, the major axes of ejection apertures in the first array are offset from the major axes of the ejection apertures in the second array in a direction transverse to the media feed direction by less than 20 microns. In a particularly preferred form, the offset is approximately 8 microns. In some embodiments, the printhead has a nozzle pitch in the direction transverse to the direction of media feed greater than 1600 npi. In a particularly preferred form, the substrate is less than 3 mm wide in the direction of media feed.  
         [0000]     Accordingly, the present invention provides an inkjet printhead comprising:  
         [0042]     an array of nozzles for ejecting drops of printing fluid onto print media when the print media and moved in a print direction relative to the printhead; wherein,  
         [0043]     the nozzles in the array are spaced apart from each other by less than 10 microns in the direction perpendicular to the print direction.  
         [0044]     With nozzles spaced less than 10 microns apart in the direction perpendicular to the print direction, the printhead has a very high ‘true’ print resolution—i.e. the high number of dots per inch is achieved by a high number of nozzles per inch.  
         [0045]     Preferably, the nozzles in the array that are spaced apart from each other by less than 10 microns in the direction perpendicular to the print direction, are also spaced apart from each other in the print direction by less than 150 microns.  
         [0046]     In a further preferred form, the array has more than 700 of the nozzles per square millimeter.  
         [0047]     Preferably, the array of nozzles is supported on a plurality of monolithic wafer substrates, each monolithic wafer substrate supporting more than 10000 of the nozzles. In a further preferred form, each monolithic wafer substrate supports more than 12000 of the nozzles. In a particularly preferred form, the plurality of monolithic wafer substrates are mounted end to end to form a pagewidth printhead for mounting is a printer configured to feed media past the printhead is a media feed direction, the printhead having more than 100000 of the nozzles and extends in a direction transverse to the media feed direction between 200 mm and 330 mm. In some embodiments, the array has more than 140000 of the nozzles.  
         [0048]     Optionally, the printhead further comprises a plurality of actuators for each of the nozzles respectively, the actuators being arranged in adjacent rows, each having electrodes spaced from each other in a direction transverse to the rows for connection to respective drive transistors and a power supply; wherein,  
         [0049]     the electrodes of the actuators in adjacent rows have opposing polarities such that the actuators in adjacent rows have opposing current flow directions. Preferably the electrodes in each row are offset from its adjacent actuators in a direction transverse to the row such that the electrodes of every second actuator are collinear. In particularly preferred embodiments, the droplet ejectors are fabricated on an elongate wafer substrate extending parallel to the rows of the actuators, and power and data supplied along a long edge of the wafer substrate.  
         [0050]     In some embodiments, the printhead has a print engine controller (PEC) for sending print data to the array of nozzles; wherein,  
         [0051]     during use the print engine controller can selectively reduce the print resolution by apportioning print data for a single nozzle between at least two nozzles of the array. Preferably, the two nozzles are positioned in the array such that they are nearest neighbours in a direction transverse to the movement of the printhead relative to a print media substrate. In a particularly preferred form, the PEC shares the print data equally between the two nozzles in the array. Preferably, the two nozzles are spaced at less than 40 micron centers.  
         [0052]     In a particularly preferred form, the printhead is a pagewidth printhead and the two nozzles are spaced in a direction transverse to the media feed direction at less than 16 micron centers. Preferably, the adjacent nozzles are spaced in a direction transverse to the media feed direction at less than 8 micron centers. Preferably, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. In a further preferred form, the nozzle pitch is greater than 3000 npi.  
         [0000]     Accordingly, the present invention provides a printhead integrated circuit for an inkjet printhead, the printhead integrated circuit comprising:  
         [0053]     a monolithic wafer substrate supporting an array of droplet ejectors for ejecting drops of printing fluid onto print media, each drop ejector having a nozzle and an actuator for ejecting a drop of printing fluid through the nozzle; wherein,  
         [0054]     the array has more than 10000 of the droplet ejectors.  
         [0055]     With a large number of droplet ejectors fabricated on a single wafer, the nozzle array has a high nozzle pitch and the printhead has a very high ‘true’ print resolution—i.e. the high number of dots per inch is achieved by a high number of nozzles per inch.  
         [0056]     Preferably, the array has more than 12000 of the droplet ejectors. In a further preferred form, the print media moves in a print direction relative to the printhead and the nozzles in the array are spaced apart from each other by less than 10 microns in the direction perpendicular to the print direction. In a particularly preferred form, the nozzles in the array that are spaced apart from each other by less than 10 microns in the direction perpendicular to the print direction, are also spaced apart from each other in the print direction by less than 150 microns.  
         [0057]     In a preferred embodiment, the array has more than 700 of the droplet ejectors per square millimeter. In a particularly preferred form, the actuators are arranged in adjacent rows, each having electrodes spaced from each other in a direction transverse to the rows for connection to respective drive transistors and a power supply, the electrodes of the actuators in adjacent rows having opposing polarities such that the actuators in adjacent rows have opposing current flow directions. In a still further preferred form, the electrodes in each row are offset from their adjacent actuators in a direction transverse to the row such that the electrodes of every second actuator are collinear.  
         [0058]     In specific embodiments, the monolithic wafer substrate is elongate and extends parallel to the rows of the actuators, such that in use power and data is supplied along a long edge of the wafer substrate. In some forms, the inkjet printhead comprises a plurality of the printhead integrated circuits, and further comprises a print engine controller (PEC) for sending print data to the array of droplet ejectors wherein during use the print engine controller can selectively reduce the print resolution by apportioning print data for a single droplet ejector between at least two droplet ejectors of the array. Preferably, the two nozzles are positioned in the array such that they are nearest neighbours in a direction transverse to the movement of the printhead relative to a print media substrate. In a particularly preferred form, the PEC shares the print data equally between the two nozzles in the array. Optionally, the two nozzles are spaced at less than 40 micron centers. In particularly preferred embodiments, the printhead is a pagewidth printhead and the two nozzles are spaced in a direction transverse to the media feed direction at less than 16 micron centers. In a still further preferred form, the adjacent nozzles are spaced in a direction transverse to the media feed direction at less than 8 micron centers.  
         [0059]     In some embodiments, the inkjet printhead comprises a plurality of the printhead integrated circuits mounted end to end to form a pagewidth printhead for a printer configured to feed media past the printhead is a media feed direction, the printhead having more than 100000 of the nozzles and extends in a direction transverse to the media feed direction between 200 mm and 330 mm. In a further preferred form the array has more than 140000 of the nozzles.  
         [0060]     Preferably, the array of droplet ejectors has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction, and preferably the nozzle pitch is greater than 3000 npi.  
         [0000]     Accordingly, the present invention provides a printhead integrated circuit (IC) for an inkjet printhead, the printhead IC comprising:  
         [0061]     a planar array of droplet ejectors, each having data distribution circuitry, a drive transistor, a printing fluid inlet, an actuator, a chamber and a nozzle, the chamber being configured to hold printing fluid adjacent the nozzle such that during use, the drive transistor activates the actuator to eject a droplet of the printing fluid through the nozzle; wherein,  
         [0062]     the array has more than 700 of the droplet ejectors per square millimeter.  
         [0063]     With a high density of droplet ejectors fabricated on a wafer substrate, the nozzle array has a high nozzle pitch and the printhead has a very high ‘true’ print resolution—i.e. the high number of dots per inch is achieved by a high number of nozzles per inch.  
         [0064]     Preferably, the array ejects drops of printing fluid onto print media when the print media and moved in a print direction relative to the printhead, and the nozzles in the array are spaced apart from each other by less than 10 microns in the direction perpendicular to the print direction. In a further preferred form, the nozzles that are spaced apart from each other by less than 10 microns in the direction perpendicular to the print direction, are also spaced apart from each other in the print direction by less than 150 microns.  
         [0065]     In specific embodiments of the invention, a plurality of the printhead ICs are used in an inkjet printhead, each printhead IC having more than 10000 of the droplet ejectors, and preferably more than 12000 of the nozzle and cells.  
         [0066]     In some embodiments, the printhead ICs are elongate and mounted end to end such that the printhead has more than 100000 of the droplet ejectors and extend in a direction transverse to the media feed direction between 200 mm and 330 mm. In a further preferred form, the printhead has more than 140000 of the droplet ejectors.  
         [0067]     In some preferred forms, the actuators are arranged in adjacent rows, each having electrodes spaced from each other in a direction transverse to the rows for connection to the corresponding drive transistor and a power supply; wherein,  
         [0068]     the electrodes of the actuators in adjacent rows have opposing polarities such that the actuators in adjacent rows have opposing current flow directions.  
         [0069]     Preferably, in these embodiments, the electrodes in each row are offset from its adjacent actuators in a direction transverse to the row such that the electrodes of every second actuator are collinear. In further preferred forms, the elongate wafer substrate extends parallel to the rows of the actuators, and power and data supplied along a long edge of the wafer substrate.  
         [0070]     In specific embodiments, the printhead has a print engine controller (PEC) for sending print data to the array of nozzles; wherein,  
         [0071]     during use the print engine controller can selectively reduce the print resolution by apportioning print data for a single nozzle between at least two nozzles of the array.  
         [0072]     Preferably, the two nozzles are positioned in the array such that they are nearest neighbours in a direction transverse to the movement of the printhead relative to a print media substrate. In a further preferred form, the PEC shares the print data equally between the two nozzles in the array. Preferably, the two nozzles are spaced at less than 40 micron centers. In a particularly preferred form, the printhead is a pagewidth printhead and the two nozzles are spaced in a direction transverse to the media feed direction at less than 16 micron centers. In a still further preferred form, the adjacent nozzles are spaced in a direction transverse to the media feed direction at less than 8 micron centers.  
         [0073]     In some forms, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. Preferably, the nozzle pitch is greater than 3000 npi.  
         [0000]     Accordingly, the present invention provides a pagewidth inkjet printhead comprising:  
         [0074]     an array of droplet ejectors for ejecting drops of printing fluid onto print media fed passed the printhead in a media feed direction, each drop ejector having a nozzle and an actuator for ejecting a drop of printing fluid through the nozzle; wherein,  
         [0075]     the array has more than 100000 of the droplet ejectors and extends in a direction transverse to the media feed direct between 200 mm and 330 mm.  
         [0076]     A pagewidth printhead with a large number of nozzles extending the width of the media provides a high nozzle pitch and a very high ‘true’ print resolution—i.e. the high number of dots per inch is achieved by a high number of nozzles per inch.  
         [0077]     Preferably, the array has more than 140000 of the droplet ejectors. In a further preferred form, the nozzles are spaced apart from each other by less than 10 microns in the direction perpendicular to the media feed direction. In a particularly preferred form, the nozzles that are spaced apart from each other by less than 10 microns in the direction perpendicular to the media feed direction, are also spaced apart from each other in the media feed direction by less than 150 microns.  
         [0078]     In specific embodiments, the array of droplet ejectors is supported on a plurality of monolithic wafer substrates, each monolithic wafer substrate supporting more than 10000 of the droplet ejectors, and preferably more than 12000 of the droplet ejectors. In these embodiments, it is desirable that the array has more than 700 of the droplet ejectors per square millimeter.  
         [0079]     Optionally, the actuators are arranged in adjacent rows, each having electrodes spaced from each other in a direction transverse to the rows for connection to respective drive transistors and a power supply; wherein,  
         [0080]     the electrodes of the actuators in adjacent rows have opposing polarities such that the actuators in adjacent rows have opposing current flow directions. Preferably the electrodes in each row are offset from its adjacent actuators in a direction transverse to the row such that the electrodes of every second actuator are collinear. In particularly preferred embodiments, the droplet ejectors are fabricated on an elongate wafer substrate extending parallel to the rows of the actuators, and power and data supplied along a long edge of the wafer substrate.  
         [0081]     In some embodiments, the printhead has a print engine controller (PEC) for sending print data to the array of nozzles; wherein,  
         [0082]     during use the print engine controller can selectively reduce the print resolution by apportioning print data for a single nozzle between at least two nozzles of the array. Preferably, the two nozzles are positioned in the array such that they are nearest neighbours in a direction transverse to the movement of the printhead relative to a print media substrate. In a particularly preferred form, the PEC shares the print data equally between the two nozzles in the array. Preferably, the two nozzles are spaced at less than 40 micron centers.  
         [0083]     In a particularly preferred form, the printhead is a pagewidth printhead and the two nozzles are spaced in a direction transverse to the media feed direction at less than 16 micron centers. Preferably, the adjacent nozzles are spaced in a direction transverse to the media feed direction at less than 8 micron centers. Preferably, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. In a further preferred form, the nozzle pitch is greater than 3000 npi.  
         [0000]     Accordingly, the present invention provides a printhead integrated circuit for an inkjet printer, the printhead integrated circuit comprising:  
         [0084]     a monolithic wafer substrate supporting an array of droplet ejectors for ejecting drops of printing fluid onto print media, each droplet ejector having nozzle and an actuator for ejecting a drop of printing fluid the nozzle, the array being formed on the monolithic wafer substrate by a succession of photolithographic etching and deposition steps involving a photo-imaging device that exposes an exposure area to light focused to project a pattern onto the monolithic substrate; wherein,  
         [0085]     the array has more than 10000 of the droplet ejectors configured to be encompassed by the exposure area.  
         [0086]     The invention arranges the nozzle array such that the droplet ejector density is very high and the number of exposure steps required is reduced.  
         [0087]     Preferably the exposure area is less than 900 mm 2 . Preferably, the monolithic wafer substrate is encompassed by the exposure area. In a further preferred form the photo-imaging device is a stepper that exposes an entire reticle simultaneously. Optionally, the photo-imaging device is a scanner that scans a narrow band of light across the exposure area to expose the reticle.  
         [0088]     Preferably, the monolithic wafer substrate supports more than 12000 of the droplet ejectors. In these embodiments, it is desirable that the array has more than 700 of the droplet ejectors per square millimeter.  
         [0089]     In some embodiments, the printhead IC is assembled onto a pagewidth printhead with other like printhead ICs, for ejecting drops of printing fluid onto print media fed passed the printhead in a media feed direction, wherein  
         [0090]     the printhead has more than 100000 of the droplet ejectors and extends in a direction transverse to the media feed direct between 200 mm and 330 mm. In a further preferred form, the nozzles are spaced apart from each other by less than 10 microns in the direction perpendicular to the media feed direction. Preferably, the printhead has more than 140000 of the droplet ejectors. In a particularly preferred form, the nozzles that are spaced apart from each other by less than 10 microns in the direction perpendicular to the media feed direction, are also spaced apart from each other in the media feed direction by less than 150 microns.  
         [0091]     Optionally, the actuators are arranged in adjacent rows, each having electrodes spaced from each other in a direction transverse to the rows for connection to respective drive transistors and a power supply; wherein,  
         [0092]     the electrodes of the actuators in adjacent rows have opposing polarities such that the actuators in adjacent rows have opposing current flow directions. Preferably the electrodes in each row are offset from its adjacent actuators in a direction transverse to the row such that the electrodes of every second actuator are collinear. In particularly preferred embodiments, the droplet ejectors are fabricated on an elongate wafer substrate extending parallel to the rows of the actuators, and power and data supplied along a long edge of the wafer substrate.  
         [0093]     In some embodiments, the printhead has a print engine controller (PEC) for sending print data to the array of nozzles; wherein,  
         [0094]     during use the print engine controller can selectively reduce the print resolution by apportioning print data for a single nozzle between at least two nozzles of the array. Preferably, the two nozzles are positioned in the array such that they are nearest neighbours in a direction transverse to the movement of the printhead relative to a print media substrate. In a particularly preferred form, the PEC shares the print data equally between the two nozzles in the array. Preferably, the two nozzles are spaced at less than 40 micron centers.  
         [0095]     In a particularly preferred form, the printhead is a pagewidth printhead and the two nozzles are spaced in a direction transverse to the media feed direction at less than 16 micron centers. Preferably, the adjacent nozzles are spaced in a direction transverse to the media feed direction at less than 8 micron centers. Preferably, the printhead has a nozzle pitch greater than 1600 nozzle per inch (npi) in a direction transverse to a media feed direction. In a further preferred form, the nozzle pitch is greater than 3000 npi. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0096]     Preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:  
         [0097]      FIG. 1A  is a schematic representation of the linking printhead IC construction;  
         [0098]      FIG. 1B  shows a partial plan view of the nozzle array on a printhead IC according to the present invention;  
         [0099]      FIG. 2  is a unit cell of the nozzle array;  
         [0100]      FIG. 3  shows the unit cell replication pattern that makes up the nozzle array;  
         [0101]      FIG. 4  is a schematic cross section through the CMOS layers and heater element of a nozzle;  
         [0102]      FIG. 5A  schematically shows an electrode arrangement with opposing electrode polarities in adjacent actuator rows;  
         [0103]      FIG. 5B  schematically shows an electrode arrangement with typical electrode polarities in adjacent actuator rows;  
         [0104]      FIG. 6  shows the electrode configuration of the printhead IC of  FIG. 1 ;  
         [0105]      FIG. 7  shows a section of the power plane of the CMOS layers;  
         [0106]      FIG. 8  shows the pattern etched into the sacrificial scaffold layer for the roof/side wall layer;  
         [0107]      FIG. 9  shows the exterior surface of the roof layer after the nozzle apertures have been etched;  
         [0108]      FIG. 10  shows the ink supply flow to the nozzles;  
         [0109]      FIG. 11  shows the different inlets to the chambers in different rows;  
         [0110]      FIG. 12  shows the nozzle spacing for one color channel;  
         [0111]      FIG. 13  shows an enlarged view of the nozzle array with matching elliptical chamber and ejection aperture;  
         [0112]      FIG. 14  is a sketch of a photolithographic stepper; and,  
         [0113]      FIGS. 15A  to  15 C schematically illustrate the operation of a photolithographic stepper. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0114]     The printhead IC (integrated circuit) shown in the accompanying drawings is fabricated using the same lithographic etching and deposition steps described in the U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005), the contents of which are incorporated herein by reference. The ordinary worker will understand that the printhead IC shown in the accompanying drawings have a chamber, nozzle and heater electrode configuration that requires the use of exposure masks that differ from those shown in U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005 Figures. However the process steps of forming the suspended beam heater elements, chambers and ejection apertures remains the same. Likewise, the CMOS layers are formed in the same manner as that discussed MNN001US with the exception of the drive FETs. The drive FETs need to be smaller because the higher density of the heater elements.  
         [0000]     Linking Printhead Integrated Circuits  
         [0115]     The Applicant has developed a range of printhead devices that use a series of printhead integrated circuits (ICs) that link together to form a pagewidth printhead. In this way, the printhead IC&#39;s can be assembled into printheads used in applications ranging from wide format printing to cameras and cellphones with inbuilt printers. The printhead IC&#39;s are mounted end-to-end on a support member to form a pagewidth printhead. The support member mounts the printhead IC&#39;s in the printer and also distributes ink to the individual IC&#39;s. An example of this type of printhead is described in U.S. Ser. No. 11/293,820, the disclosure of which is incorporated herein by cross reference.  
         [0116]     It will be appreciated that any reference to the term ‘ink’ is to be interpreted as any printing fluid unless it is clear from the context that it is only a colorant for imaging print media. The printhead IC&#39;s can equally eject invisible inks, adhesives, medicaments or other functionalized fluids.  
         [0117]      FIG. 1A  shows a sketch of a pagewidth printhead  100  with the series of printhead ICs  92  mounted to a support member  94 . The angled sides  96  allow the nozzles from one of the IC&#39;s  92  overlap with those of an adjacent IC in the paper feed direction  8 . Overlapping the nozzles in each IC  92  provides continuous printing across the junction between two IC&#39;s. This avoids any ‘banding’ in the resulting print. Linking individual printhead IC&#39;s in this manner allows printheads of any desired length to be made by simply using different numbers of IC&#39;s.  
         [0118]     The end to end arrangement of the printhead ICs  92  requires the power and data to be supplied to bond pads  98  along the long sides of each printhead IC  92 . These connections, and the control of the linking ICs with a print engine controller (PEC), is described in detail in Ser. No. 11/544,764 (Docket No. PUA001US) filed 10 Oct. 2006.  
         [0000]     3200 dpi Printhead Overview  
         [0119]      FIG. 1B  shows a section of the nozzle array on the Applicants recently developed 3200 dpi printhead. The printhead has ‘true’ 3200 dpi resolution in that the nozzle pitch is 3200 npi rather than a printer with 3200 dpi addressable locations and a nozzle pitch less than 3200 npi. The section shown in  FIG. 1B  shows eight unit cells of the nozzle array with the roof layer removed. For the purposes of illustration, the ejection apertures  2  have been shown in outline. The ‘unit cell’ is the smallest repeating unit of the nozzle array and has two complete droplet ejectors and four halves of the droplet ejectors on either side of the complete ejectors. A single unit cell is shown in  FIG. 2 .  
         [0120]     The nozzle rows extend transverse to the media feed direction  8 . The middle four rows of nozzles are one color channel  4 . Two rows extend either side of the ink supply channel  6 . Ink from the opposing side of the wafer flows to the supply channel  6  through the ink feed conduits  14 . The upper and lower ink supply channels  10  and  12  are separate color channels (although for greater color density they may print the same color ink—eg a CCMMY printhead).  
         [0121]     Rows  20  and  22  above the supply channel  6  are transversely offset with respect to the media feed direction  8 . Below the ink supply channel  6 , rows  24  and  26  are similarly offset along the width of the media. Furthermore, rows  20  and  22 , and rows  24  and  26  are mutually offset with respect to each other. Accordingly, the combined nozzle pitch of rows  20  to  26  transverse to the media feed direction  8  is one quarter the nozzle pitch of any of the individual rows. The nozzle pitch along each row is approximately 32 microns (nominally 31.75 microns) and therefore the combined nozzle pitch for all the rows in one color channel is approximately 8 microns (nominally 7.9375 microns). This equates to a nozzle pitch of 3200 npi and hence the printhead has ‘true’ 3200 dpi resolution.  
         [0000]     Unit Cell  
         [0122]      FIG. 2  is a single unit cell of the nozzle array. Each unit cell has the equivalent of four droplet ejectors (two complete droplet ejectors and four halves of the droplet ejectors on both sides of the complete ejectors). The droplet ejectors are the nozzle, the chamber, drive FET and drive circuitry for a single MEMS fluid ejection device. The ordinary worker will appreciate that the droplet ejectors are often simply referred to as nozzles for convenience but it is understood from the context of use whether this term is a reference to just the ejection aperture of the entire MEMS device.  
         [0123]     The top two nozzle rows  18  are fed from the ink feed conduits  14  via the top ink supply channel  10 . The bottom nozzle rows  16  are a different color channel fed from the supply channel  6 . Each nozzle has an associated chamber  28  and heater element  30  extending between electrodes  34  and  36 . The chambers  28  are elliptical and offset from each other so that their minor axes overlap transverse to the media feed direction. This configuration allows the chamber volume, nozzle area and heater size to be substantially the same as the 1600 dpi printheads shown in the above referenced U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005. Likewise the chamber walls  32  remain 4 microns thick and the area of the contacts  34  and  36  are still 10 microns by 10 microns.  
         [0124]      FIG. 3  shows the unit cell replication pattern that makes up the nozzle array. Each unit cell  38  is translated by its width x across the wafer. The adjacent rows are flipped to a mirror image and translated by half the width: 0.5x=y. As discussed above, this provides a combined nozzle pitch for the rows of one color channel ( 20 ,  22 ,  24  and  26 ) of 0.25x. In the embodiment shown, x=31.75 and y=7.9375. This provides a 3200 dpi resolution without reducing the size of the heaters, chambers or nozzles. Accordingly, when operating at 3200 dpi, the print density is higher than the 1600 dpi printhead of U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005, or the printer can operate at 1600 dpi to extend the life of the nozzles with a good print density. This feature of the printhead is discussed further below.  
         [0000]     Heater Contact Arrangement  
         [0125]     The heater elements  30  and respective contacts  34  and  36  are the same dimensions as the 1600 dpi printhead IC of U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005. However, as there is twice the number of contacts, there is twice the number of FET contacts (negative contacts) that punctuate the ‘power plane’ (the CMOS metal layer carrying the positive voltage). A high density of holes in the power plane creates high resistance through the thin pieces of metal between the holes. This resistance is detrimental to overall printhead efficiency and can reduce the drive pulse to some heaters relative to others.  
         [0126]      FIG. 4  is a schematic section view of the wafer, CMOS drive circuitry  56  and the heater. The drive circuitry  56  for each printhead IC is fabricated on the wafer substrate  48  in the form of several metal layers  40 ,  42 ,  44  and  45  separated by dielectric material  41 ,  43  and  47  through which vias  46  establish the required inter layer connections. The drive circuitry  56  has a drive FET (field effect transistor)  58  for each actuator  30 . The source  54  of the FET  58  is connected to a power plane  40  (a metal layer connected to the position voltage of the power supply) and the drain  52  connects to a ground plane  42  (the metal layer at zero voltage or ground). Also connected to the ground plane  42  and the power plane  40  are the electrodes  34  and  36  or each of the actuators  30 .  
         [0127]     The power plane  40  is typically the uppermost metal layer and the ground plane  42  is the metal layer immediately beneath (separated by a dielectric layer  41 ). The actuators  30 , ink chambers  28  and nozzles  2  are fabricated on top of the power plane metal layer  40 . Holes  46  are etched through this layer so that the negative electrode  34  can connect to the ground plane and an ink passage  14  can extend from the rear of the wafer substrate  48  to the ink chambers  28 . As the nozzle density increases, so to does the density of these holes, or punctuations through the power plane. With a greater density of punctuations through the power plane, the gaps between the punctuations are reduced. The thin bridge of metal layer though these gaps is a point of relatively high electrical resistance. As the power plane is connected to a supply along one side of the printhead IC, the current to actuators on the non-supply side of the printhead IC may have had to pass through a series of these resistive gaps. The increased parasitic resistance to the non-supply side actuators will affect their drive current and ultimately the drop ejection characteristics from those nozzles.  
         [0128]     The printhead uses several measures to address this. Firstly, adjacent rows of actuators have opposite current flow directions. That is, the electrode polarity in one rows is switched in the adjacent row. For the purposes of this aspect of the printhead, two rows of nozzles adjacent the supply channel  16  should be considered as a single row as shown in  FIG. 5A  instead of staggered as shown in the previous figures. The two rows A and B extend longitudinally along the length of the printhead IC. All the negative electrodes  34  are along the outer edges of the two adjacent rows A and B. The power is supplied from one side, say edge  62 , and so the current only passes through one line of thin, resistive metal sections  64  before it flows through the heater elements  30  in both rows. Accordingly, the current flow direction in row A is opposite to the current flow direction in row B.  
         [0129]     The corresponding circuit diagram illustrates the benefit of this configuration. The power supply V+ drops because of the resistance R A  of the thin sections between the negative electrodes  34  of row A. However, the positive electrodes  36  for all the heaters  30  are at the same voltage relative to ground (V A =V B ). The voltage drop across all heaters  30  (resistances R HA  and R HB  respectively) in both rows A and B is uniform. The resistance R B  from the thin bridges  66  between the negative electrodes  34  of row B is eliminated from the circuit for rows A and B.  
         [0130]      FIG. 5B  shows the situation if the polarities of the electrodes in adjacent rows are not opposing. In this case, the line of resistive sections  66  in row B are in the circuit. The supply voltage V+ drops through the resistance R A  to V A —the voltage of the positive electrodes  36  of row A. From there the voltage drops to ground through the resistance R HA  of the row A heaters  30 . However, the voltage V B  at the row B positive electrodes  36  drops from V A  through R B  from the thin section  66  between the row B negative electrodes  34 . Hence the voltage drop though the row B heaters  30  is less than that of row A. This in turn changes the drive pulse and therefore the drop ejection characteristics.  
         [0131]     The second measure used to maintain the integrity of the power plane is staggering adjacent electrodes pairs in each row. Referring to  FIG. 6 , the negative electrode  34  are now staggered such that every second electrode is displaced transversely to the row. The adjacent row of heater contacts  34  and  36  are likewise staggered. This serves to further widen the gaps  64  and  66  between the holes through the power plane  40 . The wider gaps have less electrical resistance and the voltage drop to the heaters remote from the power supply side of the printhead IC is reduced.  FIG. 7  shows a larger section of the power plane  40 . The electrodes  34  in staggered rows  41  and  44  correspond to the color channel feed by supply channel  6 . The staggered rows  42  and  43  relate to one half the nozzles for the color channels on either side—the color fed by supply channel  10  and the color channel fed by supply channel  12 . It will be appreciated that a five color channel printhead IC has nine rows of negative electrodes that can induce resistance for the heaters in the nozzles furthest from the power supply side. Widening the gaps between the negative electrodes greatly reduces the resistance they generate. This promoted more uniform drop ejection characteristics from the entire nozzle array.  
         [0000]     Efficient Fabrication  
         [0132]     The features described above increase the density of nozzles on the wafer. Each individual integrated circuit is about 22 mm long, less than 3 mm wide and can support more than 10000 nozzles. This represents a significant increase on the nozzle numbers (70,400 nozzles per IC) in the Applicants 1600 dpi printhead ICs (see for example U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005). In fact, a true 3200 dpi printhead nozzle array fabricated to the dimensions shown in  FIG. 12 , has 12,800 nozzles.  
         [0133]     The lithographic fabrication of this many nozzles (more than 10,000) is efficient because the entire nozzle array fits within the exposure area of the lithographic stepper or scanner used to expose the reticles (photomasks). A photolithographic stepper is sketched in  FIG. 14 . A light source  102  emits parallel rays of a particular wavelength  104  through the reticle  106  that carries the pattern to be transferred to the integrated circuit  92 . The pattern is focused through a lens  108  to reduce the size of the features and projected onto a wafer stage  110  the carries the integrated circuits  92  for ‘dies’ as they are also known). The area of the wafer stage  110  illuminated by the light  104  is called the exposure area  112 . Unfortunately, the exposure area  112  is limited in size to maintain the accuracy of the projected pattern—whole wafer discs can not be exposed simultaneously. The vast majority of photolithographic steppers have an exposure area  112  less than 30 mm by 30 mm. One major manufacturer, ASML of the Netherlands, makes steppers with an exposure area of 22 mm by 22 mm which is typical of the industry.  
         [0134]     The stepper exposes one die, or a part of a die, and then steps to another, or another part of the same die. Having as many nozzles as possible on a single monolithic substrate is advantageous for compact printhead design and minimizing the assembly of the ICs on a support in precise relation to one another. The invention configures the nozzle array so that more than 10,000 nozzles fit into the exposure area. In fact the entire integrated circuit can fit into the exposure area so that more than 14,000 nozzles are fabricated on a single monolithic substrate without having to step and realign for each pattern.  
         [0135]     The ordinary worker will appreciate that the same applies to fabrication of the nozzle array using a photolithographic scanner. The operation of a scanner is sketched in  FIG. 15A  to  15 C. In a scanner, the light source  102  emits a narrower beam of light  104  that is still wide enough to illuminate the entire width of the reticle  106 . The narrow beam  104  is focused through a smaller lens  108  and projected onto part of the integrated circuit  92  mounted in the exposure area  112 . The reticle  106  and the wafer stage  110  are moved in opposing directions relative to each other so that the reticle&#39;s pattern is scanned across the entire exposure area  112 .  
         [0136]     Clearly, this type of photo-imaging device is also suited to efficient fabrication of printhead ICs with large numbers of nozzles.  
         [0000]     Flat Exterior Nozzle Surface  
         [0137]     As discussed above, the printhead IC is fabricated in accordance with the steps listed in cross referenced U.S. Ser. No. 11/246,687 (Our Docket MNN001US) filed 11 Oct. 2005. Only the exposure mask patterns have been changed to provide the different chamber and heater configurations. As described in MNN001US, the roof layer and the chamber walls are an integral structure—a single Plasma Enhanced Chemical Vapor Deposition (PECVD) of suitable roof and wall material. Suitable roof materials may be silicon nitride, silicon oxide, silicon oxynitride, aluminium nitride etc. The roof and walls are deposited over a scaffold layer of sacrificial photoresist to form an integral structure on the passivation layer of the CMOS.  
         [0138]      FIG. 8  shows the pattern etched into the sacrificial layer  72 . The pattern consists of the chamber walls  32  and columnar features  68  (discussed below which are all of uniform thickness. In the embodiment shown, the thickness of the walls and columns is 4 microns. These structures are relatively thin so when the deposited roof and wall material cools there is little if any depression in the exterior surface of the roof layer  70  (see  FIG. 9 ). Thick features in the etch pattern will hold a relatively large volume of the roof/wall material. When the material cools and contracts, the exterior surface draws inwards to create a depression.  
         [0139]     These depressions leave the exterior surface uneven which can be detrimental to the printhead maintenance. If the printhead is wiped or blotted, paper dust and other contaminants can lodge in the depressions. As shown in  FIG. 9 , the exterior surface of the roof layer  72  is flat and featureless except for the nozzles  2 . Dust and dried ink is more easily removed by wiping or blotting.  
         [0000]     Refill Ink Flow  
         [0140]     Referring to  FIG. 10 , each ink inlet supplies four nozzles except at the longitudinal ends of the array where the inlets supply fewer nozzles. Redundant nozzle inlets  14  are an advantage during initial priming and in the event of air bubble obstruction.  
         [0141]     As shown by the flow lines  74 , the refill flow to the chambers  28  remote from the inlets  14  is longer than the refill flow to the chambers  28  immediately proximate the supply channel  6 . For uniform drop ejection characteristics, it is desirable to have the same ink refill time for each nozzle in the array.  
         [0142]     As shown in  FIG. 11 , the inlets  76  to the proximate chambers are dimensioned differently to the inlets  78  to the remote chambers. Likewise the column features  68  are positioned to provide different levels of flow constriction for the proximate nozzle inlets  76  and the remote nozzle inlets  78 . The dimensions of the inlets and the position of the column can tune the fluidic drag such that the refill times of all the nozzles in the array are uniform. The columns can also be positioned to damp the pressure pulses generated by the vapor bubble in the chamber  28 . Damping pulses moving though the inlet prevents fluidic cross talk between nozzles. Furthermore, the gaps  80  and  82  between the columns  68  and the sides of the inlets  76  and  78  can be effective bubble traps for larger outgassing bubbles entrained in the ink refill flow.  
         [0000]     Extended Nozzle Life  
         [0143]      FIG. 12  shows a section of one color channel in the nozzle array with the dimensions necessary for 3200 dpi resolution. It will be appreciated that ‘true’ 3200 dpi is very high resolution—greater than photographic quality. This resolution is excessive for many print jobs. A resolution of 1600 dpi is usually more than adequate. In view of this, the printhead IC sacrifice resolution by sharing the print data between two adjacent nozzles. In this way the print data that would normally be sent to one nozzle in a 1600 dpi printhead is sent alternately to adjacent nozzles in a 3200 dpi printhead. This mode of operation more than doubles the life of the nozzles and it allows the printer to operate at much higher print speeds. In 3200 dpi mode, the printer prints at 60 ppm (full color A4) and in 1600 dpi mode, the speed approaches 120 ppm.  
         [0144]     An additional benefit of the 1600 dpi mode is the ability to use this printhead IC with print engine controllers (PEC) and flexible printed circuit boards (flex PCBs) that are configured for 1600 dpi resolution only. This makes the printhead IC retro-compatible with the Applicant&#39;s earlier PECs and PCBs.  
         [0145]     As shown in  FIG. 12 , the nozzle  83  is transversely offset from the nozzle  84  by only 7.9375 microns. They are spaced further apart in absolute terms but displacement in the paper feed direction can be accounted for with the timing of nozzle firing sequence. As the 8 microns transverse shift between adjacent nozzles is small, it can be ignored for rendering purposes. However, the shift can be addressed by optimizing the dither matrix if desired.  
         [0000]     Bubble, Chamber and Nozzle Matching  
         [0146]      FIG. 13  is an enlarged view of the nozzle array. The ejection aperture  2  and the chamber walls  32  are both elliptical. Arranging the major axes parallel to the media feed direction allows the high nozzle pitch in the direction transverse to the feed direction while maintaining the necessary chamber volume. Furthermore, arranging the minor axes of the chambers so that they overlap in the transverse direction also improves the nozzle packing density.  
         [0147]     The heaters  30  are a suspended beam extending between their respective electrodes  34  and  36 . The elongate beam heater elements generate a bubble that is substantially elliptical (in a section parallel to the plane of the wafer). Matching the bubble  90 , chamber  28  and the ejection aperture  2  promotes energy efficient drop ejection. Low energy drop ejection is crucial for a ‘self cooling’ printhead.  
         [0000]     Conclusion  
         [0148]     The printhead IC shown in the drawings provides ‘true’ 3200 dpi resolution and the option of significantly higher print speeds at 1600 dpi. The print data sharing at lower resolutions prolongs nozzle life and offers compatibility with existing 1600 dpi print engine controllers and flex PCBs. The uniform thickness chamber wall pattern gives a flat exterior nozzle surface that is less prone to clogging. Also the actuator contact configuration and elongate nozzle structures provide a high nozzle pitch transverse to the media feed direction while keeping the nozzle array thin parallel to the media feed direction.  
         [0149]     The specific embodiments described are in all respects merely illustrative and in no way restrictive on the spirit and scope of the broad inventive concept.