Abstract:
A printhead chip for an inkjet printhead includes a substrate. A plurality of nozzle arrangements is positioned on the substrate. Each nozzle arrangement includes a nozzle chamber structure that is positioned on the substrate and that defines a nozzle chamber from which ink is to be ejected. An ink-ejecting mechanism is operatively arranged with respect to the nozzle chamber structure. The ink-ejecting mechanism includes at least one moving component that is displaceable to generate a pressure pulse within the nozzle chamber to eject ink from the nozzle chamber. An actuator is positioned on the substrate and has at least one working member that is of a material having a coefficient of thermal expansion such that the, or each, working member is capable of substantially rectilinear expansion and contraction when heated and subsequently cooled. An energy transmitting means interconnects the, or each, moving component and the, or each, working member so that energy generated by the, or each, working member as a result of expansion and subsequent contraction of the, or each, working member is transmitted to the, or each, moving component resulting in displacement of the, or each, moving component and generation of said pressure pulse.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. application Ser. No. 10/120,345 filed on Apr. 12, 2002, now issued as U.S. Pat. No. 6,513,908, which is a continuation in part of U.S. application Ser. No. 09/112,767 filed on Jul. 10, 1998, now issued as U.S. Pat. No. 6,416,167, all of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a printhead chip for an inkjet printhead. More particularly, this invention relates to a printhead chip for an inkjet printhead that incorporates pusher actuation in order to achieve ink drop ejection. 
     BACKGROUND OF THE INVENTION 
     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 electromechanical system (MEMS)-based components to achieve the ejection of ink necessary for printing. 
     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. 
     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. 
     As is also clear from the above applications, Applicant has developed a number of ways in which to achieve the ejection of ink from the respective nozzle chambers. A majority of these are based on the selection of a material having a coefficient of thermal expansion that is such that, on a MEMS scale, expansion upon heating and subsequent contraction upon cooling can be harnessed to perform work. The material is formed to define at least part of a thermal actuator that includes a heating circuit. The heating circuit is shaped to be resistively heated when a current passes through the circuit. The current is supplied to the circuit in the form of pulses at a frequency that depends on the printing requirements. The pulses are usually supplied from a CMOS layer positioned on a substrate of the printhead chip. The pulses are shaped and have a magnitude that is also dependent on the printing requirements. The generation and control of the pulses is by way of a suitable microprocessor of the type described in the above referenced applications. 
     On a macroscopic scale, it is counter-intuitive to use the expansion and subsequent contraction of material in order to achieve the performance of work. Applicant submits that the perceived slow rate of expansion and contraction would lead a person of ordinary skill in the field of macroscopic engineering to seek alternative energy sources. 
     On a MEMS scale, however, Applicant has found that expansion and contraction of such a material can be harnessed to perform work. The reason for this is that, on this scale, expansion and contraction are relatively rapid and can transmit relatively high force. 
     There remains an issue of range of movement. While the expansion and contraction are both rapid and forceful, Applicant has found that it would be desirable for a mechanism to be provided whereby such rapidity and force of movement could be amplified at a region where the work is required to eject the ink. 
     A majority of the nozzle arrangements covered by the above applications and patents use differential expansion in the thermal actuator to achieve bending of the thermal actuator. This bending movement is transmitted to an ink-ejecting component that is either rectilinearly or angularly displaced to eject the ink. 
     Applicant has found that it would be desirable for simple rectilinear expansion of a thermal actuator to be transmitted to an ink-ejecting component, since such simple rectilinear expansion on a MEMS scale is relatively efficient. 
     The Applicant has conceived this invention in order to achieve the desired transmission and amplification of motion mentioned above. 
     SUMMARY OF THE INVENTION 
     According to one broad form 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
         a nozzle chamber structure that is positioned on the substrate and that defines a nozzle chamber from which ink is to be ejected;   an ink-ejecting mechanism that is operatively arranged with respect to the nozzle chamber structure, the ink-ejecting mechanism including at least one moving component that is displaceable to generate a pressure pulse within the nozzle chamber to eject ink from the nozzle chamber;   an actuator that is positioned on the substrate and that has at least one working member that is of a material having a coefficient of thermal expansion such that the, or each, working member is capable of substantially rectilinear expansion and contraction when heated and subsequently cooled; and   an energy transmitting means that interconnects the, or each, moving component and the, or each, working member so that energy generated by the, or each, working member as a result of expansion and subsequent contraction of the, or each, working member is transmitted to the, or each, moving component resulting in displacement of the, or each, moving component and generation of said pressure pulse.
 
In another broad form the invention provides 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   a nozzle chamber structure positioned on the substrate and that defines a nozzle chamber from which ink is to be ejected;   an ink-ejecting mechanism operatively arranged with respect to the nozzle chamber structure, the ink-ejecting mechanism including at least one component displaceable within the nozzle chamber to eject ink from the nozzle chamber;   an actuator that is positioned on the substrate and that has at least one portion that is configured to undergo rectilinear expansion or contraction when its temperature changes; and   at least one mechanical interconnection that interconnect the at least one component and the actuator so that expansion or contraction of the at least one portion is transmitted to the at least one component resulting in displacement of the at least one component.
 
The invention is now described, by way of examples, 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 
       In the drawings, 
         FIG. 1  shows a schematic view of a nozzle arrangement of a first embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead; 
         FIG. 2  shows a schematic view of a nozzle arrangement of a second embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead; 
         FIG. 3  shows a schematic view of a nozzle arrangement of a third embodiment of a printhead chip, in accordance with the invention; 
         FIG. 4  shows a schematic view of a nozzle arrangement of a fourth embodiment of a printhead chip, in accordance with the invention; 
         FIG. 5  shows a schematic view of a nozzle arrangement of a fifth embodiment of a printhead chip, in accordance with the invention; 
         FIG. 6  shows a schematic side view showing further detail of the nozzle arrangement of  FIG. 5  in a quiescent condition; 
         FIG. 7  shows a schematic side view of the nozzle arrangement of  FIG. 5  in an operative condition; 
         FIG. 8  shows a schematic plan view of the nozzle arrangement of  FIG. 5 ; and 
         FIG. 9  shows a schematic side view of a nozzle arrangement of a sixth embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , reference numeral  10  generally indicates a nozzle arrangement for a first embodiment of an ink jet printhead chip, in accordance with the invention. 
     The nozzle arrangement  10  is one of a plurality of such nozzle arrangements formed on a silicon wafer substrate  12  ( FIG. 6 ) 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 . 
     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 . 
     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. 
     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. 
     The nozzle arrangement  10  is shown in  FIG. 1  as broadly conceptual. The nozzle arrangement  10  includes an actuator in the form of an electro thermal actuator  18 . The actuator  18  includes an electrical resistive heating circuit  20 . The circuit  20  incorporates a working member in the form of a conductive heating element  22 . The heating element  22  is of a material having a coefficient of thermal expansion that is such that when the material is heated and subsequently cooled, the material is capable of expansion and subsequent contraction to an extent sufficient to perform work on a MEMS—scale. Any of a number of materials used in integrated circuit fabrication could be suitable. Such materials could include gold, copper or titanium. The Applicant has found that titanium aluminum nitride (TiAlN) is particularly suitable for this purpose. 
     Thermal expansion and contraction occurs per unit length of the heating element  22  as is known. The principle behind the nozzle arrangement  10  is to provide the heating element  22  with sufficient length so that the extent of movement when the heating element  22  expands and contracts is sufficient to generate useful energy. Thus, the length of the heating element  22  is a factor that defines a useful energy transmitting means. In particular, the heating element  22  is of a length which is such that the extent of movement is similar to the extent of movement of the components of the nozzle arrangements described in the above referenced patents/patent applications. 
     The heating element  22  is connected to an ink-ejecting mechanism in the form of an ink-ejecting member or piston  24 . The piston  24  is positioned in a nozzle chamber structure  26 . The nozzle chamber structure  26  has nozzle chamber walls  28  and a roof  30 . The roof  30  defines an ink ejection port  32 . 
     The heating element  22  has a fixed end  34  and a working end  36  so that, on expansion and contraction of the heating element  22 , the working end  36  is displaceable, in a rectilinear manner, with respect to the fixed end  34 . This results in reciprocal movement of the piston  24  relative to the roof  30  and subsequent ejection of ink from the ink ejection port  32 . 
     In  FIG. 2 , reference numeral  40  generally indicates a nozzle arrangement of a second embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead. With reference to  FIG. 1 , like reference numerals refer to like parts, unless otherwise specified. 
     Again the nozzle arrangement  40  is shown only conceptually. It is respectfully submitted that a person of ordinary skill in the field of MEMS fabrication could readily fabricate a nozzle arrangement that utilizes the concept illustrated in  FIG. 2 . 
     The nozzle arrangement  40  also includes a heating circuit  42 . However, a heating element  44  of the heating circuit  42  is a convenient length. The nozzle arrangement  40  utilizes a hydraulic principle in order to achieve a useful force transmitting means. In this embodiment, a cross sectional area of the piston  24  and thus the nozzle chamber  26  are a sufficiently high number of orders of magnitude larger than a cross sectional area of the ink ejection port  32 . Thus, a required extent of movement of the piston  24  can be reduced considerably from what would usually be required in the nozzle arrangements described in the above referenced applications, while still achieving drop ejection. 
     In  FIG. 3 , reference numeral  50  generally indicates a nozzle arrangement of a third embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead. With reference to  FIGS. 1 and 2 , like reference numerals refer to like parts, unless otherwise specified. 
     The nozzle arrangement  50  is again shown as broadly conceptual. In particular, the nozzle arrangement  50  illustrates that instead of having the dimensional configurations described in the previous embodiment, a suitable motion amplifying means  52  can be positioned between the heating element  44  and the piston  24 . The motion amplifying means  52  can take a number of different forms. In particular, the motion amplifying means can be in the form of a conventional micro mechanical arrangement such as a gearing system. 
     In  FIG. 4 , reference numeral  60  generally indicates a nozzle arrangement of a fourth embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead. With reference to  FIGS. 1 to 3 , like reference numerals refer to like parts, unless otherwise specified. 
     The nozzle arrangement  60  is shown as broadly conceptual. In this embodiment, a lever mechanism  62  is positioned intermediate the working end  36  of the heating element  44  and the piston  24 . The lever mechanism  62  has an effective effort arm  64  connected to an effective load arm  66  with a fulcrum  68 . It is to be noted that the lever mechanism  62  shown in  FIG. 4  is schematic and that any of a number of micro mechanical systems defining lever mechanisms  62  can be used. 
     The lever mechanism  62  is configured so that the effective load arm  66  is between approximately 20 and 60 times longer than the effective effort arm  64 . In particular, the lever mechanism  62  is configured so that the effective load arm  66  is approximately 40 times longer than the effective effort arm  64 . 
     In  FIGS. 5 to 8 , reference numeral  70  generally indicates a nozzle arrangement of a fifth embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead. With reference to  FIGS. 1 to 4 , like reference numerals refer to like parts, unless otherwise specified. 
     The nozzle arrangement  70  includes nozzle chamber walls in the form of a distal end wall  72 , a proximal end wall  74  and a pair of opposed sidewalls  76 . A roof  78  spans the walls  72 ,  74 ,  76 . The roof  78  and the walls  72 ,  74 ,  76  define a nozzle chamber  80 . The roof  78  defines an ink ejection port  82  in fluid communication with the nozzle chamber  80 . The walls  72 ,  74 ,  76  and the roof  78  are dimensioned so that the nozzle chamber  80  has a rectangular shape when viewed in plan. The ink ejection port  82  is positioned adjacent a distal end  84  of the nozzle chamber  80 . 
     A plurality of ink inlet channels  86  is defined through the substrate  12  and the layers  14 ,  16 . Each ink inlet channel  86  is in fluid communication with a respective nozzle chamber  80 . Further, an opening  88  of each ink inlet channel  86  is aligned with the ink ejection port  82  of its associated nozzle chamber  80 . 
     An anchor formation in the form of a pair of anchors  90  is fast with the substrate  12  on a proximal side of the nozzle chamber  80 . The heating circuit  44  includes an electro thermal expansion actuator  92  that is fast with the anchors  90  and extends towards the proximal end wall  74 . The thermal expansion actuator  92  is of a conductive material and is shaped to define part of the heating circuit  44 . The actuator  92  is of a material that has a coefficient of thermal expansion that is such that, when heated and subsequently cooled, expansion and contraction of the material can be harnessed to perform work on a MEMS scale. An example of a suitable material is TiAlN. In particular, the thermal expansion actuator  92  has a pair of arms  94  that are interconnected by a bridge portion  96 . The actuator  92  has a fixed portion defined by fixed ends  98  of the arms  94  that are fast with respective anchors  90 . 
     Each of the anchors  90  are configured to provide electrical connection between the fixed ends  98  and the electrical drive circuitry layer  14 . In particular, the anchors  90  are configured to provide electrical connection between one fixed end  98  and a negative contact and the other fixed end  98  and a positive contact. The electrical drive circuitry layer  14  is connected to a microprocessor of the type described in the above referenced patents/applications so that electrical current pulses of suitable shape and magnitude can be supplied to the actuator  92 . 
     The bridge portion  96  of the actuator  92  defines a working portion of the actuator  92 . 
     The nozzle arrangement  70  includes a pivot member  100  that is pivotally arranged on the proximal end wall  74 . The bridge portion  96  of the actuator  92  is connected to the pivot member  100  at a position intermediate a pivot point, indicated at  102 , defined by the pivot member  100  and the proximal end wall  74 . It is to be understood that the pivot point  102  can be defined by any number of configurations of the pivot member  100  and the proximal end wall  74 . For this reason, the pivot point  102  is indicated schematically only. In one possible embodiment, the proximal end wall  74  could define the pivot member  100 . In this case, the pivot point  102  would be defined between the proximal end wall  74  and the sidewalls  76 . In particular, this would entail hingedly connecting the proximal end wall  74  to the sidewalls  76 . 
     It will be appreciated that, in any event, the pivot member  100  is to form part of the proximal end wall  74 . Thus, a sealing member  104  is provided intermediate the pivot member  100  and the ink passivation layer  16 . The sealing member  104  is configured to accommodate pivotal movement of the pivot member  100  upon expansion and subsequent contraction of the thermal expansion actuator  92 . 
     The nozzle arrangement  70  includes an ink ejection member in the form of a paddle  106 . The paddle  106  is dimensioned to correspond generally with the nozzle chamber  80 . In particular, the paddle  106  is dimensioned so that an end portion  108  of the paddle  106  is positioned intermediate the ink ejection port  82  and the opening  88  of the ink inlet channel  86 . 
     The paddle  106  and the pivot member  100  are configured so that the paddle  106  is between approximately 20 and 60 times longer than an effective lever arm, indicated at  110 , defined by the paddle  106  and the pivot member  100 . In particular, the paddle  106  can be approximately 40 times longer than the effective lever arm  110 . It should be noted that the lever arm  110  is only shown schematically because of the wide variety of different possible configurations available for defining the lever arm  110 . Further, a ratio of paddle length to lever arm length can vary widely from the 40:1 ratio. This could depend on a number of factors such as driving signal strength and actuator material. For example, in one embodiment, the Applicant has devised the actuator  92  to expand by 50 nanometers while the end portion  108  of the paddle  106  moves through between 1 and 2 microns. 
     It will be appreciated that a maximum extent of movement of the paddle  106  takes place at the end portion  108  of the paddle  106 . Furthermore, this extent of movement is up to 40 times greater than a range of movement of the effective lever arm  110 . It follows that the expansion of the thermal actuator  92  is substantially amplified at the end portion  108 , therefore facilitating the ejection of ink  112  from the ink ejection port  82  as indicated at  114  in  FIG. 7 . When the actuator  92  cools, subsequent contraction of the actuator  92  causes an amplified extent of movement of the end portion  108  back into a quiescent position shown in  FIG. 6 . This results in separation of the ink  114  from the ink  112  to form an ink drop  116 . 
     The paddle  106  includes reinforcing ribs  118  to strengthen the paddle  106 . This is necessary due to the relative length of the paddle  106  and a resultant bending moment exerted on the paddle  106 . 
     It will be appreciated that, in light of the above referenced applications and patents, the nozzle arrangement  70  is suited for fabrication with an integrated circuit fabrication technique. Furthermore, the pivot member  100  and pivot point  102  can be defined by any number of micro mechanical arrangements. For example, a flexible member may be formed intermediate the pivot member  100  and the sidewalls  76  or proximal end wall  74  that is distorted to accommodate pivotal movement of the pivot member  100 . 
     In  FIG. 9 , reference numeral  120  generally indicates a nozzle arrangement of a sixth embodiment of a printhead chip, in accordance with the invention, for an inkjet printhead. With reference to  FIGS. 1 to 8 , like reference numerals refer to like parts, unless otherwise specified. 
     The nozzle arrangement  120  includes a nozzle chamber structure in the form of an active ink-ejecting structure  122 . The active ink-ejecting structure  122  has a roof  124  and walls  126  that extend from the roof  124  towards the substrate  12 . The roof  124  defines an ink ejection port  128 . The roof  124  and the walls  126  together define a nozzle chamber  130 . 
     The walls  126  comprise a proximal end wall  132 , an opposed distal end wall  134  and a pair of opposed sidewalls  136 . The ink ejection port  128  is positioned adjacent the distal end wall  134 , while the opening  88  of the ink inlet channel  86  is positioned adjacent the proximal end wall  132 . 
     The proximal end wall  132  is pivotally mounted on the substrate  12  so that the active ink-ejecting structure  122  is pivotal with respect to the substrate  12 . In particular, the active ink-ejecting structure  122  is pivotal in the direction of an arrow  138  to an extent that is sufficient to facilitate the ejection of ink from the ink ejection port  128 . 
     The roof  124  and the walls  126  are dimensioned so that the nozzle chamber  130  is rectangular and has a length that is more than 3 times a height of the nozzle chamber  130 . This, together with the fact that the ink ejection port  128  and the opening  88  are positioned at opposite ends of the nozzle chamber  130  facilitates the retardation of ink flow from the ink ejection port  128  towards the opening  88  when the structure  122  is pivotally displaced towards the substrate  12 . This flow is referred to as backflow and is highly undesirable. 
     The bridge portion  96  of the actuator  92  is fixed to the proximal end wall  132 . Thus, on heating and subsequent expansion of the actuator  92  in the manner described above, the ink-ejecting structure  122  is pivoted towards the substrate  12 . Upon cooling and subsequent contraction of the actuator  92  in the manner described above, the ink-ejecting structure  122  is pivoted away from the substrate  12 . This reciprocal movement of the ink-ejecting structure  122  results in the ejection of an ink drop from the ink ejection port  128 . 
     The bridge portion  96  is connected to the proximal end wall  132  at a position in which a length of the ink-ejecting structure  122  is up to 40 times greater than a length of an effective lever arm, indicated at  140 . It follows that pivotal movement of the effective lever arm  140  as a result of displacement of the bridge portion  96  upon heating and subsequent cooling of the actuator  92  can be amplified by a factor as high as 40. It has been found by the Applicant that this facilitates efficient ink drop ejection. 
     The nozzle arrangement  120  includes a sealing structure  142  that extends from the ink passivation layer  16 . The walls  126  overlap the sealing structure  142  so that a fluidic seal is defined between the sealing structure  142  and the walls  126  when the nozzle chamber  130  is filled with ink. 
     Applicant believes that this invention provides a means whereby simple thermal expansion and contraction, in a rectilinear manner, can be converted into useful work.