Abstract:
A printer includes a microelectromechanical printhead formed upon a wafer by integrated circuit fabrication techniques. The printhead has a plurality of electrically actuated ink ejection assemblies that are include thermal bend actuators responsive to drive signals emanating from electronic drive circuitry formed in a layer of the wafer. Each of the ink ejection assemblies includes a thermal bend actuator that is arranged displace an ink ejection member that extends into an ink chamber of the assembly. An ink ejection port is formed into a roof of the chamber. Upon activation of the thermal bend actuator the ink ejection member disturbs ink within the chamber resulting in the ejection of an ink droplet. A port is formed within a wall of the chamber for ink replenishment.

Description:
[0001]     This is a Continuation (or Continuation-in-Part) of U.S. Ser. No. 10/713,071 filed on Nov. 17, 2003 which is a Continuation of Ser. No. 10/120,347 which is a Continuation-in-Part of Ser. No. 09/112,767 all of which are herein incorporated by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       FIELD OF THE INVENTION  
       [0003]     This invention relates to a micro-electromechanical device. More particularly, this invention relates to a micro-electromechanical device that incorporates a motion-transmitting structure.  
       Reference Patent Applications  
       [0004]     The following patents/patent applications are incorporated by reference.  
                                                   6,227,652   6,213,588   6,213,589   6,231,163   6,247,795       09/113,099   6,244,691   6,257,704   09/112,778   6,220,694       6,257,705   6,247,794   6,234,610   6,247,793   6,264,306       6,241,342   6,247,792   6,264,307   6,254,220   6,234,611       09/112,808   09/112,809   6,239,821   09/113,083   6,247,796       09/113,122   09/112,793   09/112,794   09/113,128   09/113,127       6,227,653   6,234,609   6,238,040   6,188,415   6,227,654       6,209,989   6,247,791   09/112,764   6,217,153   09/112,767       6,243,113   09/112,807   6,247,790   6,260,953   6,267,469       09/425,419   09/425,418   09/425,194   09/425,193   09/422,892       09/422,806   09/425,420   09/422,893   09/693,703   09/693,706       09/693,313   09/693,279   09/693,727   09/693,708   09/575,141       09/113,053   09/855,094   09/854,762   09/854,715   09/854,830       09/854,714   09/854,703   09/855,093   09/854,815   09/854,825       09/864,377   09/864,380   09/900,178   09/864,379   09/864,378       09/864,334   09/864,332   09/864,343   09/864,342   09/866,786       09/874,757   09/900,174   09/900,160   09/900,175   09/900,177       09/900,159   09/900,176   09/922,274   09/922,275   09/922,158       09/922,159   09/922,036   09/922,047   09/922,029   09/922,207       09/922,112   09/922,105   09/942,549   09/942,605   09/942,548       09/942,603   09/942,604                  
 
       BACKGROUND OF THE INVENTION  
       [0005]     As set out in the above referenced applications/patents, the Applicant has spent a substantial amount of time and effort in developing printheads that incorporate micro electro-mechanical system (MEMS)—based components to achieve the ejection of ink necessary for printing.  
         [0006]     As a result of the Applicant&#39;s research and development, the Applicant has been able to develop printheads having one or more printhead chips that together incorporate up to 84 000 nozzle arrangements. The Applicant has also developed suitable processor technology that is capable of controlling operation of such printheads. In particular, the processor technology and the printheads are capable of cooperating to generate resolutions of 1600 dpi and higher in some cases. Examples of suitable processor technology are provided in the above referenced patent applications/patents.  
         [0007]     Common to most of the printhead chips that the Applicant has developed is a component that moves with respect to a substrate to eject ink from a nozzle chamber. This component can be in the form of an ink-ejecting member that is displaceable in a nozzle chamber to eject the ink from the nozzle chamber.  
         [0008]     A particular difficulty that the Applicant has been faced with is to achieve a suitable interface between a prime mover in the form of an actuator and the moving component. This interface is required to permit the moving component to be displaced in the nozzle chamber and to inhibit leakage of ink from the nozzle chamber.  
         [0009]     As set out in the above referenced patents/patent applications, the printhead chip is manufactured using integrated circuit fabrication techniques. This is the usual manner in which MEMS-based devices are fabricated. Such forms of fabrication are subject to constraints since they involve successive deposition and etching techniques. It follows that MEMS-based devices are usually formed in layers and that components having relatively complex shapes are difficult and expensive to fabricate.  
         [0010]     In  FIG. 1 , reference numeral  10  generally indicates part of a nozzle arrangement of a printhead chip. The part  10  shown illustrates an actuator  12  and an ink-ejecting member  14 . The actuator  12  includes an elongate actuator arm  16  that extends from an anchor  18 . The actuator arm  16  is configured so that, when it receives a drive signal, the actuator arm  16  bends towards a substrate  20  as indicated by an arrow  22 . A connecting formation  24  is interposed between the actuator arm  16  and the ink-ejecting member  14 . Thus, when the actuator arm  16  is bent towards the substrate  20 , the ink-ejecting member  14  is displaced in the direction of an arrow  26  to eject ink from the nozzle chamber.  
         [0011]     It would be intuitive simply to use the arrangement  10  together with a suitable sealing structure to achieve effective ink ejection and sealing. The reason for this is that it would appear that the actuator arm  16 , the connecting formation  24  and the ink-ejecting member  14  could be in the form of a unitary structure. However, the Applicant has found that it is not possible to achieve a working configuration as shown by using MEMS-based fabrication techniques. In particular, it has been found by the Applicant that such a unitary structure does not lend itself to such fabrication techniques.  
         [0012]     It follows that the Applicant has been led to conceive the present invention.  
       SUMMARY OF THE INVENTION  
       [0013]     According to a first aspect of the invention, there is provided a micro-electromechanical device that comprises 
        a substrate that incorporates drive circuitry;     an elongate drive member, the drive member being fast with the substrate at a fixed end and incorporating an electrical circuit that is in electrical contact with the drive circuitry to receive an electrical signal from the drive circuitry, the drive member being configured so that a free end is displaced relative to the substrate on receipt of the electrical signal;     a motion-transmitting member that is fast with the free end of the drive member so that the motion-transmitting member is displaced together with the free end; and     a working member that is fast with the motion-transmitting member to be displaced together with the motion-transmitting member to perform work.        
 
         [0018]     The motion-transmitting member may define a first class lever and may have an effort formation that is fast with the free end of the drive member, a load formation that is fast with the working member and a fulcrum formation that is fast with the substrate. The effort and load formations may be pivotal with respect to the fulcrum formation.  
         [0019]     The drive member may be a thermal bend actuator of the type that uses differential thermal expansion to achieve displacement.  
         [0020]     The thermal bend actuator may be of a conductive material that is capable of thermal expansion and may have an active portion and a passive portion. The active portion may define the electrical circuit, in the form of a heating circuit, so that the active portion is heated and expands relative to the passive portion on receipt of the electrical signal to generate displacement of the actuator in one direction and termination of the signal results in cooling contraction of the active portion to generate displacement of the actuator in an opposite direction.  
         [0021]     The conductive material of the actuator may be resiliently flexible to facilitate said displacement of the actuator in the opposite direction.  
         [0022]     The drive member and the working member may be of the same material, while the motion-transmitting member may be of a different material to that of the drive member and the working member.  
         [0023]     The drive member and the working member may both be of titanium nitride.  
         [0024]     According to a second aspect of the invention, there is provided a micro-electromechanical device that comprises 
        a substrate that incorporates drive circuitry;     a plurality of elongate drive members, each drive member being fast with the substrate at a fixed end and incorporating an electrical circuit that is in electrical contact with the drive circuitry to receive an electrical signal from the drive circuitry, the drive member being configured so that a free end is displaced relative to the substrate on receipt of the electrical signal;     a plurality of motion-transmitting members fast with respective free ends of the drive members so that each motion-transmitting member is displaced together with its associated free end; and     a plurality of working members fast with respective motion-transmitting members so that each working member is displaced together with its associated motion-transmitting member to perform work.        
 
         [0029]     According to a third aspect of the invention, there is provided a printhead chip for an inkjet printhead, the printhead chip comprising 
        a substrate; and     a plurality of nozzle arrangements positioned on the substrate, each nozzle arrangement comprising 
            a nozzle chamber structure that defines a nozzle chamber in which ink is received;     an ink-ejecting member that is positioned in the nozzle chamber and is displaceable in the nozzle chamber to eject ink from the nozzle chamber;    
            at least one actuator that is positioned on the substrate, the, or each, actuator having a working portion that is displaceable with respect to the substrate when the actuator receives a driving signal;     a sealing structure that is positioned on the substrate and is interposed between the, or each, actuator and the ink-ejecting member to inhibit a passage of ink between the ink-ejecting member and the actuator; and     a motion-transmitting structure that bridges the sealing structure, the motion-transmitting structure interconnecting the working portion of the actuator and the ink-ejecting member so that displacement of the working portion relative to the substrate is transmitted to the ink-ejecting member.     The invention is now described, by way of example, with reference to the accompanying drawings. The following description is not intended to limit the broad scope of the above summary.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]     In the drawings,  
         [0039]      FIG. 1  shows a schematic side sectioned view of part of a nozzle arrangement of a printhead chip for an inkjet printhead for the purposes of conceptual illustration;  
         [0040]      FIG. 2  shows a schematic side sectioned view of a nozzle arrangement of a first embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead;  
         [0041]      FIG. 3  shows a three dimensional, side sectioned view of a nozzle arrangement of a second embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead; and  
         [0042]      FIG. 4  shows a three dimensional view of the nozzle arrangement of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     In  FIG. 2 , reference numeral  30  generally indicates a nozzle arrangement of a first embodiment of an ink jet printhead chip, in accordance with the invention, for an inkjet printhead.  
         [0044]     The nozzle arrangement  30  is one of a plurality of such nozzle arrangements formed on a silicon wafer substrate  32  to define the printhead chip of the invention. As set out in the background of this specification, a single printhead can contain up to 84 000 such nozzle arrangements. For the purposes of clarity and ease of description, only one nozzle arrangement is described. It is to be appreciated that a person of ordinary skill in the field can readily obtain the printhead chip by simply replicating the nozzle arrangement  30  on the wafer substrate  32 .  
         [0045]     The printhead chip is the product of an integrated circuit fabrication technique. In particular, each nozzle arrangement  30  is the product of a MEMS—based fabrication technique. As is known, such a fabrication technique involves the deposition of functional layers and sacrificial layers of integrated circuit materials. The functional layers are etched to define various moving components and the sacrificial layers are etched away to release the components. As is known, such fabrication techniques generally involve the replication of a large number of similar components on a single wafer that is subsequently diced to separate the various components from each other. This reinforces the submission that a person of ordinary skill in the field can readily obtain the printhead chip of this invention by replicating the nozzle arrangement  30 .  
         [0046]     An electrical drive circuitry layer  34  is positioned on the silicon wafer substrate  32 . The electrical drive circuitry layer  34  includes CMOS drive circuitry. The particular configuration of the CMOS drive circuitry is not important to this description and has therefore been shown schematically in the drawings. Suffice to say that it is connected to a suitable microprocessor and provides electrical current to the nozzle arrangement  30  upon receipt of an enabling signal from said suitable microprocessor. An example of a suitable microprocessor is described in the above referenced patents/patent applications. It follows that this level of detail will not be set out in this specification.  
         [0047]     An ink passivation layer  36  is positioned on the drive circuitry layer  34 . The ink passivation layer  36  can be of any suitable material, such as silicon nitride.  
         [0048]     The nozzle arrangement  30  includes a nozzle chamber structure  38 . The nozzle chamber structure  38  defines a nozzle chamber  40  and has a roof  42  that defines an ink ejection port  44 .  
         [0049]     The nozzle chamber structure  38  includes a pair of opposed sidewalls  46 , a distal end wall  48  and a proximal end wall  50  so that the nozzle chamber  40  is generally rectangular in plan.  
         [0050]     A plurality of ink inlet channels  52  are defined through the silicon wafer substrate  32 , the drive circuitry layer  34  and the ink passivation layer  36 . One ink inlet channel  52  is in fluid communication with each respective nozzle chamber  40 . Further, each ink inlet channel  52  is aligned with each respective ink ejection port  44 .  
         [0051]     The nozzle arrangement  30  includes an ink-ejecting member in the form of a paddle  54 . The paddle  54  is dimensioned to correspond generally with the nozzle chamber  40 . Further, the paddle  54  has a distal end portion  56  that is interposed between an opening  58  of the ink inlet channel  52  and the ink ejection port  44 . The paddle  54  is angularly displaceable within the nozzle chamber  40  so that the distal end portion  56  can move towards and away from the ink ejection port  44 . Thus, when the nozzle chamber  40  is filled with ink  60 , such movement of the paddle  54  results in a fluctuation of ink pressure within the nozzle chamber  40  so that an ink drop  62  is ejected from the ink ejection port  44 . The mechanism of ink drop ejection is fully set out in the above referenced applications and patents. It follows that this detail is not set out in this specification.  
         [0052]     The nozzle arrangement  30  includes an actuator in the form of a thermal bend actuator  64 . This form of actuator is also described in the above referenced applications and patents and is therefore not described in further detail in this specification. Briefly, however, the thermal bend actuator  64  includes an actuator arm  66  that has a fixed end  68  that is fixed to an anchor  70  and a working end  72  that is displaceable towards and away from the substrate  32  upon receipt of a drive signal in the form of a current pulse emanating from the drive circuitry layer  34 .  
         [0053]     The nozzle arrangement  30  includes a sealing structure  78  that is interposed between the working end  72  of the actuator arm  66  and a proximal end portion  76  of the paddle  54 . The actuator arm  66 , the sealing structure  78  and the paddle  54  are the product of a deposition and etching process carried out with a single material. However, the arm  66 , the sealing structure  78  and the paddle  54  are discrete components. This facilitates fabrication of the nozzle arrangement  30 .  
         [0054]     The material can be any of a number of materials used in integrated circuit fabrication processes. However, it is a requirement that the material have a coefficient of thermal expansion that is such that the material is capable of expansion and contraction when heated and subsequently cooled to an extent sufficient to perform work on a MEMS scale. Further, it is preferable that the material be resiliently flexible. The Applicant has found that titanium aluminum nitride (TiAlN) is particularly suited for the task.  
         [0055]     The nozzle arrangement  30  includes a motion-transmitting structure  74  that interconnects the working end  72  of the actuator arm  66  and the proximal end portion  76  of the paddle  54 . The motion-transmitting structure  74  bridges the sealing structure  78  so that the sealing structure  78  is interposed between at least a portion of the motion-transmitting structure  74  and the sealing structure  78 .  
         [0056]     The motion-transmitting structure  74  includes an effort formation  80  that extends from the working end  72  of the actuator arm  66 . The motion-transmitting structure  74  also includes a load formation  82  that extends from the proximal end portion  76  of the paddle  54 . A lever arm formation  84  interconnects the effort and load formations  80 ,  82 . The lever arm formation  84  is pivotally connected between the sidewalls  46  with connectors in the form of opposed flexural connectors  85 . The flexural connectors  85  are configured to experience torsional distortion upon pivotal movement of the lever arm formation  84 . It will therefore be appreciated that, upon reciprocal movement of the working end  72  of the actuator arm  66 , the lever arm formation  84  pivots. This pivotal movement results in the angular displacement of the paddle  54 , as described above, via the load formation  82 .  
         [0057]     The motion-transmitting structure  74  and the roof  42  define a slotted opening  86  that accommodates relative movement of the structure  74  and the roof  42 . The slotted opening  86  is interposed between a pair of ridges  88  that extend from the structure  74  and the roof  42 . The ridges  88  are dimensioned so that, when the nozzle chamber  40  is filled with the ink  60 , a fluidic seal  90  is defined between the ridges  88 . Similarly, the sealing structure  78  and the proximal end portion  76  of the paddle  54  are configured so that a fluidic seal  92  is defined between the proximal end portion  76  and the sealing structure  78 .  
         [0058]     In  FIGS. 3 and 4 , reference numeral  100  generally indicates a nozzle arrangement of an inkjet printhead chip, in accordance with the invention, for an inkjet printhead. With reference to  FIG. 2 , like reference numerals refer to like parts, unless otherwise specified.  
         [0059]     The nozzle arrangement  100  includes nozzle chamber walls  102  positioned on the ink passivation layer  36 . A roof  104  is positioned on the nozzle chamber walls  102  so that the roof  104  and the nozzle chamber walls  102  define a nozzle chamber  106 . The nozzle chamber walls  102  include a distal end wall  108 , a proximal end wall  110  and a pair of opposed sidewalls  112 . An ink ejection port  114  is defined in the roof  104  to be in fluid communication with the nozzle chamber  106 . The roof  104  defines a nozzle rim  116  and a recess  118  positioned about the rim  116  to inhibit ink spread. The walls  102  and the roof  104  are configured so that the nozzle chamber  106  is rectangular in plan.  
         [0060]     A plurality of ink inlet channels  120 , one of which is shown in the drawings, are defined through the substrate  32 , the drive circuitry layer  34  and the ink passivation layer  36 . The ink inlet channel  120  is in fluid communication with the nozzle chamber  106  so that ink can be supplied to the nozzle chamber  106 .  
         [0061]     The nozzle arrangement  100  includes a motion-transmitting structure  122 . The motion-transmitting structure  122  includes an effort formation  124 , a lever arm formation  126  and a load formation  128 . The lever arm formation  126  is interposed between the effort formation  124  and the load formation  128 .  
         [0062]     The nozzle arrangement  100  includes a sealing structure  130  that is fast with the ink passivation layer  36 . In particular, the sealing structure  130  is composite with a primary layer  132  and a secondary layer  134 . The layers  132 ,  134  are configured so that the sealing structure  130  is resiliently deformable to permit pivotal movement of the lever arm formation  126  with respect to the substrate  32 . The layers  132 ,  134  can be of a number of materials that are used in integrated circuit fabrication. The Applicant has found that titanium aluminum nitride (TiAlN) is a suitable material for the layer  132  and that titanium is a suitable material for the layer  134 .  
         [0063]     The load formation  128  defines part of the proximal end wall  110 . The load formation  128  is composite with a primary layer  136  and a secondary layer  138 . As with the sealing structure  130 , the layers  136 ,  138  can be of any of a number of materials that are used in integrated circuit fabrication. However, as set out above, successive deposition and etching steps are used to fabricate the nozzle arrangement  100 . It follows that it is convenient for the layers  136 ,  138  to be of the same material as the layers  132 ,  134 . Thus, the layers  136 ,  138  can be of TiAlN and titanium, respectively.  
         [0064]     The nozzle arrangement  100  includes an ink-ejecting member in the form of an elongate rectangular paddle  140 . The paddle  140  is fixed to the load formation  128  and extends towards the distal end wall  108 . Further, the paddle  140  is dimensioned to correspond generally with the nozzle chamber  106 . It follows that displacement of the paddle  140  towards and away from the ink ejection port  114  with sufficient energy results in the ejection of an ink drop from the ink ejection port. The manner in which drop ejection is achieved is described in detail in the above referenced patents/applications and is therefore not discussed in any detail here.  
         [0065]     To facilitate fabrication, the paddle  140  is of TiAlN. In particular, the paddle  140  is an extension of the layer  136  of the load formation  128  of the motion-transmitting structure  122 .  
         [0066]     The paddle  140  has corrugations  142  to strengthen the paddle  140  against flexure during operation.  
         [0067]     The effort formation  124  is also composite with a primary layer  144  and a secondary layer  146 .  
         [0068]     The layers  144 ,  146  can be of any of a number of materials that are used in integrated circuit fabrication. However, as set out above, successive deposition and etching steps are used to fabricate the nozzle arrangement  100 . It follows that it is convenient for the layers  144 ,  146  to be of the same material as the layers  132 ,  134 . Thus, the layers  144 ,  146  can be of TiAlN and titanium, respectively.  
         [0069]     The nozzle arrangement  100  includes an actuator in the form of a thermal bend actuator  148 . The thermal bend actuator  148  is of a conductive material that is capable of being resistively heated. The conductive material has a coefficient of thermal expansion that is such that, when heated and subsequently cooled, the material is capable of expansion and contraction to an extent sufficient to perform work on a MEMS scale.  
         [0070]     The thermal bend actuator  148  can be any of a number of thermal bend actuators described in the above patents/patent applications. In one example, the thermal bend actuator  148  includes an actuator arm  150  that has an active portion  152  and a passive portion. The active portion  152  has a pair of inner legs  154  and the passive portion is defined by a leg positioned on each side of the pair of inner legs  154 . A bridge portion  156  interconnects the active inner legs  154  and the passive legs. Each leg  154  is fixed to one of a pair of anchor formations in the form of active anchors  158  that extend from the ink passivation layer  36 . Each active anchor  158  is configured so that the legs  154  are electrically connected to the drive circuitry layer  34 .  
         [0071]     Each passive leg is fixed to one of a pair of anchor formations in the form of passive anchors  160  that are electrically isolated from the drive circuitry layer  34 .  
         [0072]     Thus, the legs  154  and the bridge portion  156  are configured so that when a current from the drive circuitry layer  34  is set up in the legs  154 , the actuator arm  150  is subjected to differential heating. In particular, the actuator arm  150  is shaped so that the passive legs are interposed between at least a portion of the legs  154  and the substrate  32 . It will be appreciated that this causes the actuator arm  150  to bend towards the substrate  32 .  
         [0073]     The bridge portion  156  therefore defines a working end of the actuator  148 . In particular, the bridge portion  156  defines the primary layer  144  of the effort formation  124 . Thus, the actuator  148  is of TiAlN. The Applicant has found this material to be well suited for the actuator  148 .  
         [0074]     The lever arm formation  126  is positioned on, and fast with, the secondary layers  134 ,  138 ,  146  of the sealing structure  130 , the load formation  128  and the effort formation  124 , respectively. Thus, reciprocal movement of the actuator  148  towards and away from the substrate  32  is converted into reciprocal angular displacement of the paddle  140  via the motion-transmitting structure  122  to eject ink drops from the ink ejection port  114 .  
         [0075]     Each active anchor  158  and passive anchor is also composite with a primary layer  160  and a secondary layer  162 . The layers  160 ,  162  can be of any of a number of materials that are used in integrated circuit fabrication. However, in order to facilitate fabrication, the layer  160  is of TiAlN and the layer  162  is of titanium.  
         [0076]     A cover formation  164  is positioned on the anchors to extend over and to cover the actuator  148 . Air chamber walls  166  extend between the ink passivation layer  36  and the cover formation  164  so that the cover formation  164  and the air chamber walls  166  define an air chamber  168 . Thus, the actuator  148  and the anchors are positioned in the air chamber  168 .  
         [0077]     The cover formation  164 , the lever arm formation  126  and the roof  104  are in the form of a unitary protective structure  170  to inhibit damage to the nozzle arrangement  100 .  
         [0078]     The protective structure  170  can be one of a number of materials that are used in integrated circuit fabrication. The Applicant has found that silicon dioxide is particularly useful for this task.  
         [0079]     It will be appreciated that it is necessary for the lever arm formation  126  to be displaced relative to the cover formation  164  and the roof  104 . It follows that the cover formation  164  and the lever arm formation  126  are demarcated by a slotted opening  172  in fluid communication with the air chamber  168 . The roof  104  and the lever arm formation  126  are demarcated by a slotted opening  174  in fluid communication with the nozzle chamber  106 .  
         [0080]     The lever arm formation  126  and the roof  104  together define ridges  176  that bound the slotted opening  172 . Thus, when the nozzle chamber  106  is filled with ink, the ridges  176  define a fluidic seal during ink ejection. The ridges  176  serve to inhibit ink spreading by providing suitable adhesion surfaces for a meniscus formed by the ink.  
         [0081]     The slotted openings  172 ,  174  demarcate resiliently flexible connectors in the form of a pair of opposed flexural connectors  178  defined by the protective structure  170 . The flexural connectors  178  are configured to experience torsional deformation in order to accommodate pivotal movement of the lever arm formation  126  during operation of the nozzle arrangement  100 . The silicon dioxide of the protective structure  170  is resiliently flexible on a MEMS scale and is thus suitable for such repetitive distortion.  
         [0082]     It should be noted that the paddle  140 , the sealing structure  130  and the actuator arm  150  are discrete components. This facilitates fabrication of the nozzle arrangement  100  while still retaining the advantages of efficient motion transfer and sealing.