Patent Publication Number: US-2009237447-A1

Title: Inkjet printhead having wiped nozzle guard

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application is a Continuation of U.S. application Ser. No. 11/604,323 filed on Nov. 27, 2006, which is a Continuation of U.S. application Ser. No. 11/172,838 filed on Jul. 5, 2005, which is a Continuation of U.S. application Ser. No. 10/487,823 filed Aug. 12, 2004, now Issued U.S. Pat. No. 6,953,236,which is a National Phase (371) Application of PCT/AU02/01 122 filed on Aug. 21, 2002, which is a Continuation of U.S. application Ser. No. 09/942,547 filed on Aug. 31, 2001, now Issued U.S. Pat. No. 6,412,904, which is a Continuation-in-Part of U.S. application Ser. No. 09/575,147 filed on May 23, 2000, now Issued U.S. Pat. No. 6,390,591 all of which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to digital printers and in particular ink jet printers. 
     BACKGROUND TO THE INVENTION 
     Ink jet printers are a well-known and widely used form of printed media production. Colorants, usually ink, are fed to an array of micro-processor controlled nozzles on a printhead. As the print head passes over the media, colorant is ejected from the array of nozzles to produce the printing on the media substrate. 
     Printer performance depends on factors such as operating cost, print quality, operating speed and ease of use. The mass, frequency and velocity of individual ink drops ejected from the nozzles will affect these performance parameters. 
     Recently, the array of nozzles has been formed using micro electro mechanical systems (MEMS) technology, which have mechanical structures with sub-micron thicknesses. This allows the production of printheads that can rapidly eject ink droplets sized in the picolitre (×10 −12  litre) range. 
     While the microscopic structures of these printheads can provide high speeds and good print quality at relatively low costs, their size makes the nozzles extremely fragile and vulnerable to damage from the slightest contact with fingers, dust or the media substrate. This can make the printheads impractical for many applications where a certain level of robustness is necessary. Furthermore, a damaged nozzle may fail to eject the colorant being fed to it. As colorant builds up and beads on the exterior of the nozzle, the ejection of colorant from surrounding nozzles may be affected and/or the damaged nozzle will simply leak colorant onto the printed substrate. Both situations are detrimental to print quality. 
     To address this, an apertured guard may be fitted over the nozzles to shield them against damaging contact. Ink ejected from the nozzles passes through the apertures on to the paper or other substrate to be printed. However, to effectively protect the nozzles the apertures need to be as small as possible to maximize the restriction against the ingress of foreign matter while still allowing the passage of the ink droplets. Ideally, each nozzle would eject ink through its own individual aperture in the guard. 
     As the apertures in the guard are generally microscopic they can be easily clogged. Therefore, it is often desirable to keep the exterior of the nozzle guard clean especially in environments with relatively high levels of dust and other airborne particulates. This is conveniently achieved using a wiper blade that periodically sweeps across the exterior face of the guard to remove dust or ink residues. However, the residual matter on the wiper often becomes lodged on the exterior rim especially the portion of the rim facing into the wipers&#39; direction of travel. This build up of residue tends not to get removed by the wiper and can soon clog the aperture. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an apertured nozzle guard for an ink jet printer printhead having an array of nozzles for ejecting colorant onto a substrate to be printed; wherein, 
     the nozzle guard is adapted to be positioned on the printhead such that it extends over the exterior of the nozzles to inhibit damaging contact with the nozzles while permitting colorant ejected from the nozzles to pass through the apertures and onto the substrate to be printed; the nozzle guard including: 
     an exterior surface that, when in use, faces the media; 
     the exterior surface being configured for engagement with a wiper blade that periodically sweeps the surface to remove residual matter; wherein, 
     the exterior surface has a recess individually associated with each of the apertures to prevent the wiper blade from engaging the exterior surface immediately adjacent the aperture. 
     In this specification the term “nozzle” is to be understood as an element defining an opening and not the opening itself. 
     Preferably, the exterior surface further includes a deflector ridge in each of the recesses, the deflector ridge positioned to engage the wiper blade before the blade passes over the aperture associated with the recess. In one convenient form, the deflector ridge is arcuate and positioned with respect to the wiping direction to deflect residual material away from the aperture and toward the edge of the recess. 
     The nozzle guard may further include fluid inlet openings for directing fluid over the nozzle array and out through the passages in order to inhibit the build up of foreign particles on the nozzle array. 
     The nozzle guard may include an integrally formed pair of spaced support elements one support element from the pair being arranged at each end of the guard. 
     In this embodiment, the fluid inlet openings may be arranged in one of the support elements. 
     It will be appreciated that, when air is directed through the openings, over the nozzle array and out through the passages, the build up of foreign particles on the nozzle array is inhibited. 
     The fluid inlet openings may be arranged in the support element remote from a bond pad of the nozzle array. 
     To optimize the effectiveness of the wiper blade, the exterior surface is flat except for the recesses and deflector ridges. By forming the guard from silicon, its coefficient of thermal expansion substantially matches that of the nozzle array. This will help to prevent the array of apertures in the guard from falling out of register with the nozzle array. Using silicon also allows the shield to be accurately micro-machined using MEMS techniques. Furthermore, silicon is very strong and substantially non-deformable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Preferred embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  shows a three dimensional, schematic view of a nozzle assembly for an ink jet printhead; 
         FIGS. 2 to 4  show a three dimensional, schematic illustration of an operation of the nozzle assembly of  FIG. 1 ; 
         FIG. 5  shows a three dimensional view of a nozzle array; 
         FIG. 6  shows, on an enlarged scale, part of the array of  FIG. 5 ; 
         FIG. 7  shows a three dimensional view of an ink jet printhead including a nozzle guard; 
         FIG. 7A  shows a partial sectional side view of the ink jet printhead and nozzle guard of  FIG. 7  being cleaned by a wiper blade; 
         FIG. 7B  shows a partial sectional side view of a nozzle guard according to the present invention; 
         FIG. 7C  shows a plan view of the exterior surface of the nozzle guard of  FIG. 7B ; 
         FIGS. 8A to 8R  show three dimensional views of steps in the manufacture of a nozzle assembly of an ink jet printhead; 
         FIGS. 9A to 9R  show sectional side views of the manufacturing steps; 
         FIGS. 10A to 10K  show layouts of masks used in various steps in the manufacturing process; 
         FIGS. 11A to 11C  show three dimensional views of an operation of the nozzle assembly manufactured according to the method of  FIGS. 8 and 9 ; and 
         FIGS. 12A to 12C  show sectional side views of an operation of the nozzle assembly manufactured according to the method of  FIGS. 8 and 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring initially to  FIG. 1  of the drawings, a nozzle assembly, in accordance with the invention is designated generally by the reference numeral  10 . An inkjet printhead has a plurality of nozzle assemblies  10  arranged in an array  14  ( FIGS. 5 and 6 ) on a silicon substrate  16 . The array  14  will be described in greater detail below. 
     The assembly  10  includes a silicon substrate  16  on which a dielectric layer  18  is deposited. A CMOS passivation layer  20  is deposited on the dielectric layer  18 . 
     Each nozzle assembly  10  includes a nozzle  22  defining a nozzle opening  24 , a connecting member in the form of a lever arm  26  and an actuator  28 . The lever arm  26  connects the actuator  28  to the nozzle  22 . 
     As shown in greater detail in  FIGS. 2 to 4 , the nozzle  22  comprises a crown portion  30  with a skirt portion  32  depending from the crown portion  30 . The skirt portion  32  forms part of a peripheral wall of a nozzle chamber  34 . The nozzle opening  24  is in fluid communication with the nozzle chamber  34 . It is to be noted that the nozzle opening  24  is surrounded by a raised rim  36  which “pins” a meniscus  38  ( FIG. 2 ) of a body of ink  40  in the nozzle chamber  34 . 
     An ink inlet aperture  42  (shown most clearly in  FIG. 6  of the drawings) is defined in a floor  46  of the nozzle chamber  34 . The aperture  42  is in fluid communication with an ink inlet channel  48  defined through the substrate  16 . 
     A wall portion  50  bounds the aperture  42  and extends upwardly from the floor portion  46 . The skirt portion  32 , as indicated above, of the nozzle  22  defines a first part of a peripheral wall of the nozzle chamber  34  and the wall portion  50  defines a second part of the peripheral wall of the nozzle chamber  34 . 
     The wall  50  has an inwardly directed lip  52  at its free end which serves as a fluidic seal which inhibits the escape of ink when the nozzle  22  is displaced, as will be described in greater detail below. It will be appreciated that, due to the viscosity of the ink  40  and the small dimensions of the spacing between the lip  52  and the skirt portion  32 , the inwardly directed lip  52  and surface tension function as an effective seal for inhibiting the escape of ink from the nozzle chamber  34 . 
     The actuator  28  is a thermal bend actuator and is connected to an anchor  54  extending upwardly from the substrate  16  or, more particularly from the CMOS passivation layer  20 . The anchor  54  is mounted on conductive pads  56  which form an electrical connection with the actuator  28 . 
     The actuator  28  comprises a first, active beam  58  arranged above a second, passive beam  60 . In a preferred embodiment, both beams  58  and  60  are of, or include, a conductive ceramic material such as titanium nitride (TiN). 
     Both beams  58  and  60  have their first ends anchored to the anchor  54  and their opposed ends connected to the arm  26 . When a current is caused to flow through the active beam  58  thermal expansion of the beam  58  results. As the passive beam  60 , through which there is no current flow, does not expand at the same rate, a bending moment is created causing the arm  26  and, hence, the nozzle  22  to be displaced downwardly towards the substrate  16  as shown in  FIG. 3 . This causes an ejection of ink through the nozzle opening  24  as shown at  62 . When the source of heat is removed from the active beam  58 , i.e. by stopping current flow, the nozzle  22  returns to its quiescent position as shown in  FIG. 4 . When the nozzle  22  returns to its quiescent position, an ink droplet  64  is formed as a result of the breaking of an ink droplet neck as illustrated at  66  in  FIG. 4 . The ink droplet  64  then travels on to the print media such as a sheet of paper. As a result of the formation of the ink droplet  64 , a “negative” meniscus is formed as shown at  68  in  FIG. 4  of the drawings. This “negative” meniscus  68  results in an inflow of ink  40  into the nozzle chamber  34  such that a new meniscus  38  ( FIG. 2 ) is formed in readiness for the next ink drop ejection from the nozzle assembly  10 . 
     Referring now to  FIGS. 5 and 6  of the drawings, the nozzle array  14  is described in greater detail. The array  14  is for a four color printhead. Accordingly, the array  14  includes four groups  70  of nozzle assemblies, one for each color. Each group  70  has its nozzle assemblies  10  arranged in two rows  72  and  74 . One of the groups  70  is shown in greater detail in  FIG. 6 . 
     To facilitate close packing of the nozzle assemblies  10  in the rows  72  and  74 , the nozzle assemblies  10  in the row  74  are offset or staggered with respect to the nozzle assemblies  10  in the row  72 . Also, the nozzle assemblies  10  in the row  72  are spaced apart sufficiently far from each other to enable the lever arms  26  of the nozzle assemblies  10  in the row  74  to pass between adjacent nozzles  22  of the assemblies  10  in the row  72 . It is to be noted that each nozzle assembly  10  is substantially dumbbell shaped so that the nozzles  22  in the row  72  nest between the nozzles  22  and the actuators  28  of adjacent nozzle assemblies  10  in the row  74 . 
     Further, to facilitate close packing of the nozzles  22  in the rows  72  and  74 , each nozzle  22  is substantially hexagonally shaped. 
     It will be appreciated by those skilled in the art that, when the nozzles  22  are displaced towards the substrate  16 , in use, due to the nozzle opening  24  being at a slight angle with respect to the nozzle chamber  34 , ink is ejected slightly off the perpendicular. It is an advantage of the arrangement shown in  FIGS. 5 and 6  of the drawings that the actuators  28  of the nozzle assemblies  10  in the rows  72  and  74  extend in the same direction to one side of the rows  72  and  74 . Hence, the ink ejected from the nozzles  22  in the row  72  and the ink ejected from the nozzles  22  in the row  74  are offset with respect to each other by the same angle resulting in an improved print quality. 
     Also, as shown in  FIG. 5  of the drawings, the substrate  16  has bond pads  76  arranged thereon which provide the electrical connections, via the pads  56 , to the actuators  28  of the nozzle assemblies  10 . These electrical connections are formed via the CMOS layer (not shown). 
     Referring to  FIG. 7 , a nozzle array and a nozzle guard is shown. With reference to the previous drawings, like reference numerals refer to like parts, unless otherwise specified. 
     A nozzle guard  80  is mounted on the silicon substrate  16  of the array  14 . The nozzle guard  80  includes a shield  82  having a plurality of apertures  84  defined therethrough. The apertures  84  are in registration with the nozzle openings  24  of the nozzle assemblies  10  of the array  14  such that, when ink is ejected from any one of the nozzle openings  24 , the ink passes through the associated passage before striking the print media. 
     In environments with relatively high levels of dust or other airborne particulates, the apertures  84  can become clogged. Furthermore, the exterior surface of the nozzle guard  80  can accumulate ink leaked from damaged nozzles. As shown in  FIG. 7A , it is convenient to provide a wiper blade  143  that periodically sweeps the residual material  144  from the exterior surface  142 . Unfortunately, the residual matter  144  on the wiper  143  often becomes lodged on the exterior rim of the aperture  84 , especially the portion of the rim facing into the wipers&#39; direction of travel  145 . The build up this residue  144  tends not to get removed by the wiper  143  and can soon clog the aperture  84 . 
     As shown in  FIG. 7B , the present invention provides recesses in the exterior surface  142  around each of the apertures  84 . The wiper blade  143  now passes over the aperture  84  so the collected residual material  144  does not lodge in the rim. As a further safeguard, each of the recesses  146  is provided with a deflector ridge  147 . As best shown in  FIG. 7C , the deflector ridge  147  engages the wiper blade  143  immediately before it passes over the aperture  84 . The deflector ridge  147  removes some of the residual material  144  on the blade  143  to further reduce the possibility of residual material  144  dropping into the aperture  84 . The deflector ridge  147  is arcuate with faces that are inclined to the direction  145  of the wiper blade  143  to direct the accumulated residual material  144  away from the aperture  84  and toward the edge of the recess  146 . 
     The guard  80  is silicon so that it has the necessary strength and rigidity to protect the nozzle array  14  from damaging contact with paper, dust or the users&#39; fingers. By forming the guard from silicon, its coefficient of thermal expansion substantially matches that of the nozzle array. This aims to prevent the apertures  84  in the shield  82  from falling out of register with the nozzle array  14  as the printhead heats up to its normal operating temperature. Silicon is also well suited to accurate micro-machining using MEMS techniques discussed in greater detail below in relation to the manufacture of the nozzle assemblies  10 . 
     The shield  82  is mounted in spaced relationship relative to the nozzle assemblies  10  by limbs or struts  86 . One of the struts  86  has air inlet openings  88  defined therein. 
     In use, when the array  14  is in operation, air is charged through the inlet openings  88  to be forced through the apertures  84  together with ink traveling through the apertures  84 . 
     The ink is not entrained in the air as the air is charged through the apertures  84  at a different velocity from that of the ink droplets  64 . For example, the ink droplets  64  are ejected from the nozzles  22  at a velocity of approximately 3 m/s. The air is charged through the apertures  84  at a velocity of approximately 1 m/s. 
     The purpose of the air is to maintain the apertures  84  clear of foreign particles. As discussed above, a danger exists that these foreign particles, such as dust particles, could fall onto the nozzle assemblies  10  adversely affecting their operation. With the provision of the air inlet openings  88  in the nozzle guard  80  this problem is ameliorated. Referring now to  FIGS. 8 to 10  of the drawings, a process for manufacturing the nozzle assemblies  10  is described. 
     Starting with the silicon substrate or wafer  16 , the dielectric layer  18  is deposited on a surface of the wafer  16 . The dielectric layer  18  is in the form of approximately 1.5 microns of CVD oxide. Resist is spun on to the layer  18  and the layer  18  is exposed to mask  100  and is subsequently developed. 
     After being developed, the layer  18  is plasma etched down to the silicon layer  16 . The resist is then stripped and the layer  18  is cleaned. This step defines the ink inlet aperture  42 . 
     In  FIG. 8B  of the drawings, approximately 0.8 microns of aluminum  102  is deposited on the layer  18 . Resist is spun on and the aluminum  102  is exposed to mask  104  and developed. The aluminum  102  is plasma etched down to the oxide layer  18 , the resist is stripped and the device is cleaned. This step provides the bond pads and interconnects to the ink jet actuator  28 . This interconnect is to an NMOS drive transistor and a power plane with connections made in the CMOS layer (not shown). 
     Approximately 0.5 microns of PECVD nitride is deposited as the CMOS passivation layer  20 . Resist is spun on and the layer  20  is exposed to mask  106  whereafter it is developed. After development, the nitride is plasma etched down to the aluminum layer  102  and the silicon layer  16  in the region of the inlet aperture  42 . The resist is stripped and the device cleaned. 
     A layer  108  of a sacrificial material is spun on to the layer  20 . The layer  108  is 6 microns of photo-sensitive polyimide or approximately 4 μm of high temperature resist. The layer  108  is softbaked and is then exposed to mask  110  whereafter it is developed. The layer  108  is then hardbaked at 400° C. for one hour where the layer  108  is comprised of polyimide or at greater than 300° C. where the layer  108  is high temperature resist. It is to be noted in the drawings that the pattern-dependent distortion of the polyimide layer  108  caused by shrinkage is taken into account in the design of the mask  110 . 
     In the next step, shown in  FIG. 8E  of the drawings, a second sacrificial layer  112  is applied. The layer  112  is either 2 μm of photo-sensitive polyimide which is spun on or approximately 1.3 μm of high temperature resist. The layer  112  is softbaked and exposed to mask  114 . After exposure to the mask  114 , the layer  112  is developed. In the case of the layer  112  being polyimide, the layer  112  is hardbaked at 400° C. for approximately one hour. Where the layer  112  is resist, it is hardbaked at greater than 300° C. for approximately one hour. 
     A 0.2 micron multi-layer metal layer  116  is then deposited. Part of this layer  116  forms the passive beam  60  of the actuator  28 . 
     The layer  116  is formed by sputtering 1,000 Å of titanium nitride (TiN) at around 300° C. followed by sputtering 50 Å of tantalum nitride (TaN). A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaN and a further 1,000 Å of TiN. Other materials which can be used instead of TiN are TiB 2 , MoSi 2  or (Ti, Al)N. 
     The layer  116  is then exposed to mask  118 , developed and plasma etched down to the layer  112  whereafter resist, applied for the layer  116 , is wet stripped taking care not to remove the cured layers  108  or  112 . 
     A third sacrificial layer  120  is applied by spinning on 4 μm of photo-sensitive polyimide or approximately 2.6 μm high temperature resist. The layer  120  is softbaked whereafter it is exposed to mask  122 . The exposed layer is then developed followed by hard baking. In the case of polyimide, the layer  120  is hardbaked at 400° C. for approximately one hour or at greater than 300° C. where the layer  120  comprises resist. 
     A second multi-layer metal layer  124  is applied to the layer  120 . The constituents of the layer  124  are the same as the layer  116  and are applied in the same manner. It will be appreciated that both layers  116  and  124  are electrically conductive layers. 
     The layer  124  is exposed to mask  126  and is then developed. The layer  124  is plasma etched down to the polyimide or resist layer  120  whereafter resist applied for the layer  124  is wet stripped taking care not to remove the cured layers  108 ,  112  or  120 . It will be noted that the remaining part of the layer  124  defines the active beam  58  of the actuator  28 . 
     A fourth sacrificial layer  128  is applied by spinning on 4 μm of photo-sensitive polyimide or approximately 2.6 μm of high temperature resist. The layer  128  is softbaked, exposed to the mask  130  and is then developed to leave the island portions as shown in  FIG. 9K  of the drawings. The remaining portions of the layer  128  are hardbaked at 400° C. for approximately one hour in the case of polyimide or at greater than 300° C. for resist. 
     As shown in  FIG. 8L  of the drawing a high Young&#39;s modulus dielectric layer  132  is deposited. The layer  132  is constituted by approximately 1 μm of silicon nitride or aluminum oxide. The layer  132  is deposited at a temperature below the hardbaked temperature of the sacrificial layers  108 ,  112 ,  120 ,  128 . The primary characteristics required for this dielectric layer  132  are a high elastic modulus, chemical inertness and good adhesion to TiN. 
     A fifth sacrificial layer  134  is applied by spinning on 2 μm of photo-sensitive polyimide or approximately 1.3 μm of high temperature resist. The layer  134  is softbaked, exposed to mask  136  and developed. The remaining portion of the layer  134  is then hardbaked at 400° C. for one hour in the case of the polyimide or at greater than 300° C. for the resist. 
     The dielectric layer  132  is plasma etched down to the sacrificial layer  128  taking care not to remove any of the sacrificial layer  134 . 
     This step defines the nozzle opening  24 , the lever arm  26  and the anchor  54  of the nozzle assembly  10 . 
     A high Young&#39;s modulus dielectric layer  138  is deposited. This layer  138  is formed by depositing 0.2 μm of silicon nitride or aluminum nitride at a temperature below the hardbaked temperature of the sacrificial layers  108 ,  112 ,  120  and  128 . 
     Then, as shown in  FIG. 8P  of the drawings, the layer  138  is anisotropically plasma etched to a depth of 0.35 microns. This etch is intended to clear the dielectric from all of the surface except the side walls of the dielectric layer  132  and the sacrificial layer  134 . This step creates the nozzle rim  36  around the nozzle opening  24  which “pins” the meniscus of ink, as described above. 
     An ultraviolet (UV) release tape  140  is applied. 4 μm of resist is spun on to a rear of the silicon wafer  16 . The wafer  16  is exposed to mask  142  to back etch the wafer  16  to define the ink inlet channel  48 . The resist is then stripped from the wafer  16 . 
     A further UV release tape (not shown) is applied to a rear of the wafer  16  and the tape  140  is removed. The sacrificial layers  108 ,  112 ,  120 ,  128  and  134  are stripped in oxygen plasma to provide the final nozzle assembly  10  as shown in  FIGS. 8R and 9R  of the drawings. For ease of reference, the reference numerals illustrated in these two drawings are the same as those in  FIG. 1  of the drawings to indicate the relevant parts of the nozzle assembly  10 .  FIGS. 11 and 12  show the operation of the nozzle assembly  10 , manufactured in accordance with the process described above with reference to  FIGS. 8 and 9  and these figures correspond to  FIGS. 2 to 4  of the drawings. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the 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 as illustrative and not restrictive.