Abstract:
A printer has a plurality of ink ejection devices, each device comprising a substrate that incorporates drive circuitry and defines a fluid inlet channel; a nozzle chamber structure that is positioned on the substrate and defines a nozzle chamber in fluid communication with the fluid inlet channel and a fluid ejection port in fluid communication with the nozzle chamber; a micro-electromechanical actuator that is positioned on the substrate and is electrically connected to the drive circuitry to be displaced relative to the substrate on receipt of an electrical current from the drive circuitry; a fluid ejecting member that is positioned in the nozzle chamber and is connected to the actuator to eject fluid from the ink ejection port on displacement of the actuator; and a covering formation that is positioned on the substrate and is configured to enclose the micro-electromechanical actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a Continuation Application of U.S. application Ser. No. 10/962,394 filed on Oct. 13, 2004, which is a Continuation of U.S. application Ser. No. 10/713,072 filed Nov. 17, 2003, now U.S. Pat. No. 6,824,251, which is a Continuation Application of U.S. application Ser. No. 10/302,556 filed Nov. 23, 2002, issued as U.S. Pat. No. 6,666,543, which is a Continuation Application of U.S. application Ser. No. 10/120,346 filed Apr. 12, 2002, issued as U.S. Pat. No. 6,582,059, which is a Continuation-in-Part Application of U.S. application Ser. No. 09/112,767 filed Jul. 10, 1998, issued as U.S. Pat. No. 6,416,167. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a micro-electromechanical fluid ejecting device. More particularly, this invention relates to a micro-electromechanical fluid ejecting device which incorporates a covering formation for a micro-electromechanical actuator.  
       REFERENCED PATENT APPLICATIONS  
       [0003]     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  
       [0004]     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.  
         [0005]     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.  
         [0006]     The Applicant has overcome substantial difficulties in achieving the necessary ink flow and ink drop separation within the ink jet printheads. A number of printhead chips that the Applicant has developed incorporate nozzle arrangements that each have a nozzle chamber with an ink ejection member positioned in the nozzle chamber. The ink ejection member is then displaceable within the nozzle chamber to eject ink from the nozzle chamber.  
         [0007]     A particular difficulty that the Applicant addresses in the present invention is to do with the delicate nature of the various components that comprise each nozzle arrangement of the printhead chip. In the above referenced matters, the various components are often exposed as a requirement of their function. On the MEMS scale, the various components are well suited for their particular tasks and the Applicant has found them to be suitably robust.  
         [0008]     However, on a macroscopic scale, the various components can easily be damaged by such factors as handling and ingress of microscopic detritus. This microscopic detritus can take the form of paper dust.  
         [0009]     It is therefore desirable that a means be provided whereby the components are protected.  
         [0010]     Applicant has found, however, that it is difficult to fabricate a suitable covering for the components while still achieving a transfer of force to an ink-ejecting component and efficient sealing of a nozzle chamber.  
         [0011]     The Applicant has conceived this invention in order to address these difficulties.  
       SUMMARY OF THE INVENTION  
       [0012]     According to a first aspect of the invention, there is provided a micro-electromechanical fluid ejection device that comprises 
        a substrate that incorporates drive circuitry and defines a fluid inlet channel;     a nozzle chamber structure that is positioned on the substrate and defines a nozzle chamber in fluid communication with the fluid inlet channel and a fluid ejection port in fluid communication with the nozzle chamber;     a micro-electromechanical actuator that is positioned on the substrate and is electrically connected to the drive circuitry to be displaced relative to the substrate on receipt of an electrical current from the drive circuitry;     a fluid ejecting member that is positioned in the nozzle chamber and is connected to the actuator to eject fluid from the ink ejection port on displacement of the actuator; and     a covering formation that is positioned on the substrate and is configured to enclose the micro-electromechanical actuator.        
 
         [0018]     The covering formation may include sidewalls that extend from the substrate and a roof wall that spans the substrate.  
         [0019]     The actuator may be elongate and may have a fixed end that is connected to the substrate so that the actuator can receive an electrical signal from the drive circuitry and a movable end.  
         [0020]     The actuator may be configured so that the movable end is displaced relative to the substrate on receipt of the electrical signal.  
         [0021]     A motion-transmitting structure may be fast with the movable end of the actuator. The motion-transmitting structure may be connected to the fluid ejecting member so that movement of the actuator is translated to the fluid ejecting member. The motion-transmitting structure may define part of the roof wall and may be spaced from a remaining part of the roof wall to allow for movement of the motion-transmitting structure.  
         [0022]     The roof wall may define a cover that spans the walls to cover the elongate actuator, the motion-transmitting structure being shaped so that the cover and the motion-transmitting structure define generally co-planar surfaces that are spaced from, and generally parallel to the substrate. An opening may be defined between the cover and the motion-transmitting surface to facilitate relative displacement of the cover and the motion-transmitting surface.  
         [0023]     The actuator may include at least one elongate actuator arm of a conductive material that is capable of thermal expansion to perform work. The actuator arm may have an active portion that defines a heating circuit that is connected to the drive circuitry layer to be resistively heated on receipt of the electrical signal from the drive circuitry layer and subsequently cooled on termination of the signal, and a passive portion which is insulated from the drive circuitry layer.  
         [0024]     The active and passive portions may be positioned with respect to each other so that the arm experiences differential thermal expansion and contraction reciprocally to displace the movable end of the actuator.  
         [0025]     The motion-transmitting structure may define a lever mechanism and may have a fulcrum formation that is fast with the substrate and pivotal with respect to the substrate and a lever arm formation mounted on the fulcrum formation. An effort formation may be connected between the movable end of the actuator and the lever arm formation and a load formation may be connected between the lever arm formation and the fluid ejecting member.  
         [0026]     The cover and the walls may define a unitary structure with the lever arm formation being connected to the walls with a pair of opposed torsion formations that are configured to twist as the lever formation is displaced.  
         [0027]     According to a second aspect of the invention, there is provides a micro-electromechanical assembly that comprises 
        a substrate that incorporates drive circuitry;     a micro-electromechanical device that is positioned on the substrate and is electrically connected to the drive circuitry to be driven by electrical signals generated by the drive circuitry; and     a covering formation that is positioned on the substrate and is configured to enclose the micro-electromechanical device.        
 
         [0031]     The covering formation may include sidewalls that extend from the substrate and a roof wall that spans the substrate.  
         [0032]     The micro-electromechanical device may include an elongate actuator that has a fixed end that is connected to the substrate so that the actuator can receive an electrical signal from the drive circuitry and a movable end, the actuator being configured so that the movable end is displaced relative to the substrate on receipt of the electrical signal.  
         [0033]     A motion-transmitting structure may be fast with the movable end of the actuator. The motion-transmitting structure may be connected to a working member so that movement of the actuator is translated to the working member. The motion-transmitting structure may define part of the roof wall and may be spaced from a remaining part of the roof wall to allow for movement of the motion-transmitting structure.  
         [0034]     The roof wall may define a cover that spans the walls to cover the elongate actuator. The motion-transmitting structure may be shaped so that the cover and the motion-transmitting structure define generally co-planar surfaces that are spaced from, and generally parallel to the substrate. An opening may be defined between the cover and the motion-transmitting surface to facilitate relative displacement of the cover and the motion-transmitting surface.  
         [0035]     The actuator may include at least one elongate actuator arm of a conductive material that is capable of thermal expansion to perform work. The actuator arm may have an active portion that defines a heating circuit that is connected to the drive circuitry layer to be resistively heated on receipt of the electrical signal from the drive circuitry layer and subsequently cooled on termination of the signal, and a passive portion which is insulated from the drive circuitry layer, the active and passive portions being positioned with respect to each other so that the arm experiences differential thermal expansion and contraction reciprocally to displace the movable end of the actuator.  
         [0036]     The motion-transmitting structure may define a lever mechanism and may have a fulcrum formation that is fast with the substrate and pivotal with respect to the substrate and a lever arm formation mounted on the fulcrum formation. An effort formation may be connected between the movable end of the actuator and the lever arm formation and a load formation may be connected between the lever arm formation and the working member.  
         [0037]     The lever arm formation, the cover and the walls may define a unitary structure with the lever arm formation being connected to the walls with a pair of opposed torsion formations that are configured to twist as the lever formation is displaced.  
         [0038]     The sidewalls may include nozzle chamber walls, the roof wall defining a nozzle chamber together with the nozzle chamber walls and the motion-transmitting structure. The roof wall may define an ejection port in fluid communication with the nozzle chamber, the working member being in the form of a fluid ejection device that is positioned in the nozzle chamber, such that displacement of the working member results in ejection of fluid in the nozzle chamber from the ejection port. The substrate may define a fluid inlet channel in fluid communication with the nozzle chamber to supply the nozzle chamber with fluid.  
         [0039]     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 that is positioned on the substrate, each nozzle arrangement comprising 
            nozzle chamber walls and a roof that define a nozzle chamber with the roof defining an ink ejection port in fluid communication with the nozzle chamber;     an ink-ejecting member that is positioned in the nozzle chamber, the ink-ejecting member being displaceable towards and away from the ink ejection port so that a resultant fluctuation in ink pressure within the nozzle chamber results in an ejection of ink from the ink ejection port;     at least one work-transmitting structure that is displaceable with respect to the substrate and is connected to the ink-ejecting member so that displacement of the work transmitting structure results in displacement of the ink-ejecting member;     an actuator that is connected to the work-transmitting structure, the actuator being capable of displacing the work transmitting structure upon receipt of an electrical drive signal; and    
            air chamber walls and a covering formation that is positioned over the actuator, the air chamber walls and the covering formation defining an air chamber in which the actuator is positioned, the roof, the work transmitting structure and the covering formation together defining a protective structure positioned in a common plane.        
 
         [0047]     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  
       [0048]     In the drawings,  
         [0049]      FIG. 1  shows a sectioned, three dimensional view of a nozzle arrangement of a printhead chip, in accordance with the invention, for an inkjet printhead; and  
         [0050]      FIG. 2  shows a three dimensional view of the nozzle arrangement of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]     In the drawings, reference numeral  10  generally indicates a nozzle arrangement for a first embodiment of an ink jet printhead chip, in accordance with the invention.  
         [0052]     The nozzle arrangement  10  is one of a plurality of such nozzle arrangements formed on a silicon wafer substrate  12  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  10  on the wafer substrate  12 .  
         [0053]     The printhead chip is the product of an integrated circuit fabrication technique. In particular, each nozzle arrangement  10  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  10 .  
         [0054]     An electrical drive circuitry layer  14  is positioned on the silicon wafer substrate  12 . The electrical drive circuitry layer  14  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  10  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.  
         [0055]     An ink passivation layer  16  is positioned on the drive circuitry layer  14 . The ink passivation layer  16  can be of any suitable material, such as silicon nitride.  
         [0056]     The nozzle arrangement  10  includes nozzle chamber walls  18  positioned on the ink passivation layer  16 . A roof  20  is positioned on the nozzle chamber walls  18  so that the roof  20  and the nozzle chamber walls  18  define a nozzle chamber  22 . The nozzle chamber walls  18  include a distal end wall  24 , a proximal end wall  26  and a pair of opposed sidewalls  28 . An ink ejection port  30  is defined in the roof  20  to be in fluid communication with the nozzle chamber  22 . The roof  20  defines a nozzle rim  32  and a recess  34  positioned about the rim  32  to accommodate ink spread.  
         [0057]     The walls  18  and the roof  20  are configured so that the nozzle chamber  22  is rectangular in plan.  
         [0058]     A plurality of ink inlet channels  36 , one of which is shown in the drawings, is defined through the substrate  12 , the drive circuitry layer  14  and the ink passivation layer  16 . The ink inlet channel  36  is in fluid communication with the nozzle chamber  18  so that ink can be supplied to the nozzle chamber  18 .  
         [0059]     The nozzle arrangement  10  includes a work-transmitting structure in the form of a lever mechanism  38 . The lever mechanism  38  includes an effort formation  40 , a fulcrum formation  42  and a load formation  44 . The fulcrum formation  42  is interposed between the effort formation  40  and the load formation  44 .  
         [0060]     The fulcrum formation  42  is fast with the ink passivation layer  16 . In particular, the fulcrum formation  42  is composite with a primary layer  46  and a secondary layer  48 . The layers  46 ,  48  are configured so that the fulcrum formation  42  is resiliently deformable to permit pivotal movement of the fulcrum formation  42  with respect to the substrate  12 . The layers  46 ,  48  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  46  and that titanium is a suitable material for the layer  48 .  
         [0061]     The load formation  44  defines part of the proximal end wall  26 . The load formation  44  is composite with a primary layer  50  and a secondary layer  52 . As with the fulcrum formation  42 , the layers  50 ,  52  can be of any of a number of materials that are used in integrated circuit fabrication. However, as set out above, the nozzle arrangement  10  is fabricated by using successive deposition and etching steps. It follows that it is convenient for the layers  50 ,  52  to be of the same material as the layers  46 ,  48 . Thus, the layers  50 ,  52  can be of TiAlN and titanium, respectively.  
         [0062]     The nozzle arrangement  10  includes an ink-ejecting member in the form of an elongate rectangular paddle  54 . The paddle  54  is fixed to the load formation  44  and extends towards the distal end wall  24 . Further, the paddle  54  is dimensioned to correspond generally with the nozzle chamber  22 . It follows that displacement of the paddle  54  towards and away from the ink ejection port  30  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.  
         [0063]     To facilitate fabrication, the paddle  54  is of TiAlN. In particular, the paddle  54  is an extension of the layer  50  of the load formation  44  of the lever mechanism  38 .  
         [0064]     The paddle  54  has corrugations  56  to strengthen the paddle  54  against flexure during operation.  
         [0065]     The effort formation  40  is also composite with a primary layer  58  and a secondary layer  60 .  
         [0066]     The layers  58 ,  60  can be of any of a number of materials that are used in integrated circuit fabrication. However, as set out above, the nozzle arrangement  10  is fabricated by using successive deposition and etching steps. It follows that it is convenient for the layers  58 ,  60  to be of the same material as the layers  46 ,  48 . Thus, the layers  58 ,  60  can be of TiAlN and titanium, respectively.  
         [0067]     The nozzle arrangement  10  includes an actuator in the form of a thermal bend actuator  62 . The thermal bend actuator  62  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.  
         [0068]     The thermal bend actuator  62  can be any of a number of thermal bend actuators described in the above patents/patent applications. In one example, the thermal bend actuator  62  includes an actuator arm  64  that has an active portion  82  and a passive portion. The active portion  82  has a pair of inner legs  66  and the passive portion is defined by a leg positioned on each side of the pair of inner legs  66 . A bridge portion  68  interconnects the active legs  66  and the passive legs. Each leg  66  is fixed to one of a pair of anchor formations in the form of active anchors  70  that extend from the ink passivation layer  16 . Each active anchor  70  is configured so that the legs  66  are electrically connected to the drive circuitry layer  14 .  
         [0069]     Each passive leg is fixed to one of a pair of anchor formations in the form of passive anchors  88  that are electrically isolated from the drive circuitry layer  14 .  
         [0070]     Thus, the legs  66  and the bridge portion  68  are configured so that when a current from the drive circuitry layer  14  is set up in the legs  66 , the actuator arm  64  is subjected to differential heating. In particular, the actuator arm  64  is shaped so that the passive legs are interposed between at least a portion of the legs  66  and the substrate  12 . It will be appreciated that this causes the actuator arm  64  to bend towards the substrate  12 .  
         [0071]     The bridge portion  68  therefore defines a working end of the actuator  62 . In particular, the bridge portion  68  defines the primary layer  58  of the effort formation  40 . Thus, the actuator  62  is of TiAlN. The Applicant has found this material to be well suited for the actuator  62 .  
         [0072]     The lever mechanism  38  includes a lever arm formation  72  positioned on, and fast with, the secondary layers  48 ,  52 ,  60  of the fulcrum formation  42 , the load formation  44  and the effort formation  40 , respectively. Thus, reciprocal movement of the actuator  62  towards and away from the substrate  12  is converted into reciprocal angular displacement of the paddle  54  via the lever mechanism  38  to eject ink drops from the ink ejection port  30 .  
         [0073]     Each active anchor  70  and passive anchor is also composite with a primary layer  74  and a secondary layer  76 . The layers  74 ,  76  can be of any of a number of materials that are used in integrated circuit fabrication. However, in order to facilitate fabrication, the layer  74  is of TiAlN and the layer  76  is of titanium.  
         [0074]     A cover formation  78  is positioned on the anchors  70 ,  88  to extend over and to cover the actuator  62 . Air chamber walls  90  extend between the ink passivation layer  16  and the cover formation  78  so that the cover formation  78  and the air chamber walls  90  define an air chamber  80 . Thus, the actuator  62  and the anchors are positioned in the air chamber  80 .  
         [0075]     The cover formation  78 , the lever arm formation  72  and the roof  20  are in the form of a unitary protective structure  92  to inhibit damage to the nozzle arrangement  10 .  
         [0076]     The protective structure  92  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.  
         [0077]     It will be appreciated that it is necessary for the lever arm formation  72  to be displaced relative to the cover formation  78  and the roof  20 . It follows that the cover formation  78  and the lever arm formation  72  are demarcated by a slotted opening  94  in fluid communication with the air chamber  80 . The roof  20  and the lever arm formation  72  are demarcated by a slotted opening  96  in fluid communication with the nozzle chamber  22 .  
         [0078]     The lever arm formation  72  and the roof  20  together define ridges  98  that bound the slotted opening  96 . Thus, when the nozzle chamber  22  is filled with ink, the ridges  98  define a fluidic seal during ink ejection. The ridges  98  serve to inhibit ink spreading by providing suitable adhesion surfaces for a meniscus formed by the ink.  
         [0079]     The slotted openings  94 ,  96  demarcate a torsion formation  100  defined by the protective structure  92 . The torsion formation  100  serves to support the lever mechanism  38  in position. Further, the torsion formation  100  is configured to experience twisting deformation in order to accommodate pivotal movement of the lever mechanism  38  during operation of the nozzle arrangement  10 . The silicon dioxide of the protective structure  92  is resiliently flexible on a MEMS scale and is thus suitable for such repetitive distortion.  
         [0080]     Applicant believes that this invention provides a printhead chip that is resistant to damage during handling. The primary reason for this is the provision of the protective structure  92 , which covers the moving components of the nozzle arrangements of the printhead chip. The protective structure  92  is positioned in a common plane. It follows that when a plurality of the nozzle arrangements  10  are positioned together to define the printhead chip, the printhead chip presents a substantially uniform surface that is resistant to damage.