WO2007041747A1 - Printhead with elongate nozzles - Google Patents

Printhead with elongate nozzles Download PDF

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Publication number
WO2007041747A1
WO2007041747A1 PCT/AU2005/001564 AU2005001564W WO2007041747A1 WO 2007041747 A1 WO2007041747 A1 WO 2007041747A1 AU 2005001564 W AU2005001564 W AU 2005001564W WO 2007041747 A1 WO2007041747 A1 WO 2007041747A1
Authority
WO
WIPO (PCT)
Prior art keywords
ink
nozzle
nozzles
inkjet printhead
optionally
Prior art date
Application number
PCT/AU2005/001564
Other languages
French (fr)
Inventor
Matthew Taylor Worsman
Azimi Mehdi
Kia Silverbrook
Original Assignee
Silverbrook Research Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Silverbrook Research Pty Ltd filed Critical Silverbrook Research Pty Ltd
Priority to AU2005337419A priority Critical patent/AU2005337419B2/en
Priority to PCT/AU2005/001564 priority patent/WO2007041747A1/en
Priority to KR1020087011268A priority patent/KR101019281B1/en
Priority to EP05791455.8A priority patent/EP1945458B1/en
Priority to JP2008534809A priority patent/JP4709285B2/en
Publication of WO2007041747A1 publication Critical patent/WO2007041747A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14016—Structure of bubble jet print heads
    • B41J2/14032—Structure of the pressure chamber
    • B41J2/1404—Geometrical characteristics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14016—Structure of bubble jet print heads
    • B41J2/14032—Structure of the pressure chamber
    • B41J2/14056—Plural heating elements per ink chamber
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1601—Production of bubble jet print heads
    • B41J2/1603—Production of bubble jet print heads of the front shooter type
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1626—Manufacturing processes etching
    • B41J2/1628—Manufacturing processes etching dry etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1631—Manufacturing processes photolithography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/1637—Manufacturing processes molding
    • B41J2/1639—Manufacturing processes molding sacrificial molding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • B41J2/1642—Manufacturing processes thin film formation thin film formation by CVD [chemical vapor deposition]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/16—Production of nozzles
    • B41J2/1621—Manufacturing processes
    • B41J2/164—Manufacturing processes thin film formation
    • B41J2/1645—Manufacturing processes thin film formation thin film formation by spincoating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14016—Structure of bubble jet print heads
    • B41J2002/14169—Bubble vented to the ambience
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2/14016—Structure of bubble jet print heads
    • B41J2002/14177—Segmented heater
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2002/14403—Structure thereof only for on-demand ink jet heads including a filter
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
    • B41J2/01—Ink jet
    • B41J2/135—Nozzles
    • B41J2/14—Structure thereof only for on-demand ink jet heads
    • B41J2002/14475—Structure thereof only for on-demand ink jet heads characterised by nozzle shapes or number of orifices per chamber
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2202/00—Embodiments of or processes related to ink-jet or thermal heads
    • B41J2202/01—Embodiments of or processes related to ink-jet heads
    • B41J2202/11—Embodiments of or processes related to ink-jet heads characterised by specific geometrical characteristics

Definitions

  • the present invention relates to the field of micro-electromechanical systems (MEMS) devices and discloses an inkjet printing system using MEMS techniques.
  • MEMS micro-electromechanical systems
  • the present invention involves the ejection of ink drops by way of forming gas or vapor bubbles in a bubble forming liquid. This principle is generally described in US 3, 747,120 (Stemme). Each pixel in the printed image is derived ink drops ejected from one or more ink nozzles. In recent years, inkjet printing has become increasing popular primarily due to its inexpensive and versatile nature. Many different aspects and techniques for inkjet printing are described in detail in the above cross referenced documents.
  • Nozzle packing density or the number of nozzles per square mm of printhead, has a bearing on the print resolution and fabrication costs.
  • individual nozzle structures are configured to reduce the spacing between adjacent nozzles.
  • One such configuration uses an elongated ink chamber and similarly elongated ink ejection actuator to reduce the spacing between adjacent nozzles.
  • ejecting a substantial proportion of the ink in an elongate chamber out of a nozzle involves significant hydraulic losses.
  • the actuator uses more energy to create a pressure pulse in the ink that is sufficient to eject a drop. Therefore, the overall efficiency of the printhead is lower than an actuator in a less elongated chamber.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle, an elongate actuator for ejecting ink through the nozzle; wherein, the nozzle has an elongate shape with its long dimension aligned with that of the elongate actuator.
  • the nozzle shape By elongating the nozzle and aligning it with the actuator, the nozzle shape more closely corresponds with the shape of the pressure pulse that the actuator creates in the ink. This allows the pressure pulse to eject ink through the nozzle more easily.
  • the hydraulic losses are less because the ink being pushed by the pressure pulse is subject to less fluidic drag as it ejects through a nozzle with a similar shape. This, in turn improves the operational efficiency of the printhead.
  • the nozzle is elliptical.
  • the actuator is a thermal actuator with an elongate heater element that generate a vapour bubble to eject in through the nozzle.
  • each ink chamber in the array has a plurality of elongate nozzles aligned with the elongate actuator.
  • each ink chamber in the array has a plurality of elongate nozzles corresponding to a plurality of elongate actuators respectively.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle, an elongate actuator for ejecting ink through the nozzle; wherein, the nozzle has an elongate shape with its long dimension aligned with that of the elongate actuator.
  • the nozzle is elliptical.
  • the actuator is a thermal actuator with an elongate heater element that generate a vapour bubble to eject in through the nozzle.
  • each ink chamber in the array has a plurality of elongate nozzles aligned with the elongate actuator.
  • each ink chamber in the array has a plurality of elongate nozzles corresponding to a plurality of elongate actuators respectively.
  • an inkjet printhead according further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • a trench etched into the drive circuitry extends between the electrodes.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • an inkjet printhead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
  • an inkj et printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
  • each of the ink conduits is in fluid communication with two of the ink inlets.
  • each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
  • the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
  • the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
  • the present invention provides an inkjet printhead comprising: an array of nozzles; a plurality of actuators for ejecting ink through the nozzles such that a bulb of ink attached to a droplet stem forms prior to drop separation when the stem breaks; a plurality of droplet stem anchors positioned between adjacent actuators; wherein during use, the adjacent actuators eject ink simultaneously and the droplet stem anchors combine the ink simultaneously ejected by the adjacent nozzles into a single drop.
  • the adjacent actuators are two thermal actuators ejecting ink through a single oval shaped nozzle.
  • the thermal actuators are both heater elements connected in series for simultaneous actuation and ejection.
  • the two heater elements are part of a single beam of heater material suspended at its ends and at it mid point.
  • the heater elements have a tapered section where electrical resistance is at a maximum such that vapour bubbles initiate at the maximum resistance sections.
  • the heater elements are on opposite sides of the droplet stem anchor so that the trajectory of the ink ejected by one heater element intersects with the trajectory of ink ejected by the other heater element.
  • the heater elements are in adjacent ink chambers with the droplet stem anchor at an adjoining boundary.
  • the heater elements are in a single ink chamber.
  • the ink ejected by the adjacent actuators is in fluid communication prior to actuation.
  • the heater elements are formed from TiAlN.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • an inkjet printhead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
  • an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
  • each of the ink conduits is in fluid communication with two of the ink inlets.
  • each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
  • the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
  • the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having an ink refill aperture, a nozzle and an actuator for ejecting ink through the nozzle; and, a fluid flow rectifying valve at the ink refill aperture for providing less hydraulic resistance to ink flowing into the chamber than ink flowing out of the chamber.
  • the recifying valve is a Tesla valve with a main conduit and a secondary conduit and at least one secondary conduit; wherein during use, ink flow out of the chamber is split into a main flow and a secondary flow such that when ink flows out of the chamber the secondary flow is combined with the main flow so as to constrict the main flow.
  • the Tesla valve has two secondary conduits, on opposite sides of the main conduit.
  • the upstream openings of the secondary conduits are in plane parallel to the flow direction and the downstream openings direct any secondary flow parallel and adjacent to flow from the main conduit downstream opening.
  • downstream openings of the secondary conduits during ink flow out of the chamber are on opposing sides of the main conduit face transversely to the flow direction through the main conduit.
  • an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • a trench etched into the drive circuitry extends between the electrodes.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • an inkjet printhead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
  • an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
  • each of the ink conduits is in fluid communication with two of the ink inlets.
  • each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
  • the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
  • the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle, a droplet stem anchor and an actuator for ejecting ink through the nozzle; wherein during use, the ink ejected from the nozzle is attached to the droplet stem anchor by an ink stem until the stem breaks so that the ejected ink forms a separate drop.
  • the droplet stem anchor is a columnar feature with one proximate the nozzle.
  • the axis of the droplet stem anchor and the central axis of the nozzle are collinear.
  • each ink chamber has two actuators, each actuators having a heater element for generating a vapour bubble to eject ink through the nozzle, and the droplet stem anchor being positioned between the heater elements.
  • the actuator has a plurality of heater elements connected in parallel with a cross bracing structure extending between the heater elements, the cross bracing structure also providing the droplet stem anchor.
  • the actuator has two heater elements in parallel and the cross bracing structure is a single beam with a surface irregularity to locate the droplet stem actuator.
  • an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • a trench etched into the drive circuitry extends between the electrodes.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • an inkjet printhead further comprising an ink conduit between a nozzle plate and an underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
  • an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
  • each of the ink conduits is in fluid communication with two of the ink inlets.
  • each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
  • the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and an actuator for ejecting ink through the nozzle; wherein during use, the actuator initiates a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
  • the actuator is a thermal actuator with heater elements that generate vapour bubbles to eject the ink.
  • the actuator has two parallel current paths with two heater elements connected in series along each current path for initiating the quadrupole pressure pulse.
  • the heater elements include bubble nucleation sections that heat more rapidly than other sections of the current path.
  • the bubble nucleation sections are between sections of the current path with greater thermal inertia.
  • the bubble nucleation sections are tight radius curves in between larger radius curves such that current crowding around the tight radius curves generates more resistive heating than the larger radius curves.
  • the heater elements are suspended within the chamber.
  • the actuator has a cross bracing structure extending between intermediate points on the parallel current paths.
  • the cross bracing structure provides increased thermal inertia where it connects to each current path.
  • the cross bracing structure provides a droplet stem anchor.
  • an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and a thermal actuator for generating vapour bubbles to eject ink through the nozzle; wherein, the thermal actuator has a pair of contacts and at least two parallel current paths between the contacts, each of the current paths having a plurality of heater elements for nucleating a vapour bubble.
  • the heater elements nucleate their respective bubbles simultaneously with every activation of the actuator.
  • the actuator has two parallel current paths with two heater elements connected in series along each current path.
  • the heater elements include bubble nucleation sections that heat more rapidly than other sections of the current path.
  • the bubble nucleation sections are between sections of the current path with greater thermal inertia.
  • the bubble nucleation sections are tight radius curves in between larger radius curves such that current crowding around the tight radius curves generates more resistive heating than the larger radius curves.
  • the heater elements are suspended within the chamber.
  • the thermal actuator has a cross bracing structure extending between intermediate points on the parallel current paths.
  • the cross bracing structure provides increased thermal inertia where it connects to each current path.
  • the cross bracing structure provides a droplet stem anchor.
  • the actuator initiates a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
  • the thermal actuator is formed from TiAlN.
  • an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • a trench etched into the drive circuitry extends between the electrodes.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and a plurality of heater elements for generating vapour bubbles to eject ink through the nozzle, the heater elements being suspended for immersion in the ink; and, a cross bracing structure for maintaining the spacing between the heater elements.
  • the heater elements nucleate their respective bubbles simultaneously with every activation of the actuator.
  • the ink chamber has a pair of contacts with two parallel current paths extending between the contacts, each current path having two of the heater elements connected in series.
  • the heater elements include bubble nucleation sections that heat more rapidly than other sections of the current path.
  • the bubble nucleation sections are between sections of the current path with greater thermal inertia.
  • the cross bracing structure is integrally formed with the hater elements and extends between intermediate points on the parallel current paths.
  • the cross bracing structure provides sections of greater thermal inertia in the current paths.
  • the heater elements initiate a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
  • the thermal elements and the contacts are formed from TiAlN.
  • the cross bracing structure provides a droplet stem anchor.
  • the actuator initiates a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
  • an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • a trench etched into the drive circuitry extends between the electrodes.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ej ects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and an actuator for ejecting ink through the nozzle; wherein, the nozzle has a nozzle rim defining a nozzle aperture and a localized irregularity, on the nozzle rim extending toward the centre of the nozzle aperture.
  • the localized irregularity is a droplet stem anchor positioned so that a droplet stem will attach to it in preference to any other point on the nozzle rim.
  • the localized irregularity is a lateral spur extending into the nozzle aperture from the nozzle rim.
  • the actuator is a thermal actuator with a suspended beam heater element for immersion in the ink.
  • all the spurs in the array are parallel and have the same position relative to the heater element.
  • an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
  • a trench etched into the drive circuitry extends between the electrodes.
  • each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
  • each of the ink chambers have two nozzles.
  • the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
  • the nozzles are elliptical.
  • the major axes of the elliptical nozzles are aligned.
  • the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
  • FET drive field effect transistor
  • the drive voltage of the drive FET is 2.5 Volts.
  • an inkjet pri ⁇ thead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
  • an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
  • each of the ink conduits is in fluid communication with two of the ink inlets.
  • each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
  • the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
  • the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
  • the printhead according to the invention comprises a plurality of nozzles, as well as a chamber and one or more heater elements corresponding to each nozzle.
  • the smallest repeating units of the printhead will have an ink supply inlet feeding ink to one or more chambers.
  • the entire nozzle array is formed by repeating these individual units. Such an individual unit is referred to herein as a "unit cell”.
  • the term "ink” is used to signify any ejectable liquid, and is not limited to conventional inks containing colored dyes.
  • non-colored inks include fixatives, infrared absorber inks, functionalized chemicals, adhesives, biological fluids, medicaments, water and other solvents, and so on.
  • the ink or ejectable liquid also need not necessarily be a strictly a liquid, and may contain a suspension of solid particles.
  • Figure 1 shows a partially fabricated unit cell of the MEMS nozzle array on a printhead according to the present invention, the unit cell being section along A-A of Figure 3;
  • Figure 2 shows a perspective of the partially fabricated unit cell of Figure 1 ;
  • Figure 3 shows the mark associated with the etch of the heater element trench
  • Figure 4 is a sectioned view of the unit cell after the etch of the trench
  • Figure 5 is a perspective view of the unit cell shown in Fig 4;
  • Figure 6 is the mask associated with the deposition of sacrificial photoresist shown in Figure 7;
  • Figure 7 shows the unit cell after the deposition of sacrificial photoresist trench, with partial enlargements of the gaps between the edges of the sacrificial material and the side walls of the trench;
  • Figure 8 is a perspective of the unit cell shown in Fig 7;
  • Figure 9 shows the unit cell following the reflow of the sacrificial photoresist to close the gaps along the side walls of the trench
  • Figure 10 is a perspective of the unit cell shown in Fig 9;
  • Figure 11 is a section view showing the deposition of the heater material layer
  • Figure 12 is a perspective of the unit cell shown in Fig 11 ;
  • Figure 13 is the mask associated with the metal etch of the heater material shown in Figure 14;
  • Figure 14 is a section view showing the metal etch to shape the heater actuators
  • Figure 15 is a perspective of the unit cell shown in Fig 14;
  • Figure 16 is the mask associated with the etch shown in Fig 17;
  • Figure 17 shows the deposition of the photoresist layer and subsequent etch of the ink inlet to the passivation layer on top of the CMOS drive layers;
  • Figure 18 is a perspective of the unit cell shown in Fig 17;
  • Figure 19 shows the oxide etch through the passivation and CMOS layers to the underlying silicon wafer
  • Figure 20 is a perspective of the unit cell shown in Fig 19;
  • Figure 21 is the deep anisotropic etch of the ink inlet into the silicon wafer
  • Figure 22 is a perspective of the unit cell shown in Fig 21 ;
  • Figure 23 is the mask associated with the photoresist etch shown in Fig 24;
  • Figure 24 shows the photoresist etch to form openings for the chamber roof and side walls
  • Figure 25 is a perspective of the unit cell shown in Fig 24;
  • Figure 26 shows the deposition of the side wall and risk material
  • Figure 27 is a perspective of the unit cell shown in Fig. 26;
  • Figure 28 is the mask associated with the nozzle rim etch shown in Fig 29;
  • Figure 29 shows the etch of the roof layer to form the nozzle aperture rim
  • Figure 30 is a perspective of the unit cell shown in Fig 29;
  • Figure 31 is the mask associated with the nozzle aperture etch shown in Fig 32;
  • Figure 32 shows the etch of the roof material to form the elliptical nozzle apertures
  • Figure 33 is a perspective of the unit cell shown in Fig 32;
  • Figure 34 shows the oxygen plasma release etch of the first and second sacrificial layers
  • Figure 35 is a perspective of the unit cell shown in Fig 34;
  • Figure 36 shows the unit cell after the release etch, as well as the opposing side of the wafer
  • Figure 37 is a perspective of the unit cell shown in Fig 36;
  • Figure 38 is the mask associated with the reverse etch shown in Fig. 39;
  • Figure 39 shows the reverse etch of the ink supply channel into the wafer
  • Figure 40 is a perspective of unit cell shown in Fig 39;
  • Figure 41 shows the thinning of the wafer by backside etching
  • Figure 42 is a perspective of the unit cell shown in Fig 41;
  • Figure 43 is a partial perspective of the array of nozzles on the printhead according to the present invention.
  • Figure 44 shows the plan view of a unit cell
  • Figure 45 shows a perspective of the unit cell shown in Fig 44;
  • Figure 46 is schematic plan view of two unit cells with the roof layer removed but certain roof layer features shown in outline only;
  • Figure 47 is schematic plan view of two unit cells with the roof layer removed but the nozzle openings shown in outline only;
  • Figure 48 is a partial schematic plan view of unit cells with ink inlet apertures in the sidewall of the chambers;
  • Figure 49 is schematic plan view of a unit cells with the roof layer removed but the nozzle openings shown in outline only;
  • Figure 50 is a partial plan view of the nozzle plate with stiction reducing formations and a particle of paper dust;
  • Figure 51 is a partial plan view of the nozzle plate with residual ink gutters
  • Figure 52 is a partial section view showing the deposition of SACl photoresist in accordance with prior art techniques used to avoid stringers;
  • Figure 53 is a partial section view showing the deposition of a layer of heater material onto the SACl photoresist scaffold deposited in Figure 52;
  • Figure 54 is a partial schematic plan view of a unit cell with multiple nozzles and actuators in each of the chambers;
  • Figures 55 to 59 are schematic cross sections of the ink chamber shown in Fig 44 at sequential stages of drop ejection;
  • Figure 60 is a schematic perspective of a nozzle with droplet stem anchor as shown in Fig 61;
  • Figure 61 is a plan view of nozzle apertures with centrally disposed droplet stem anchors
  • Figure 62 is schematic plan view of a unit cell with the roof layer removed showing a simple 'theta' heater element
  • Figure 63 shows a theta heater element with a sudden reduction in cross section on the cross bar to locate the droplet stem
  • Figure 64 shows a theta heater element with a formation in cross section on the cross bar to locate the droplet stem
  • Figure 65 shows a dual bar, four kink heater element
  • Figure 66 is schematic plan view of a unit cell with a Tesla valve to rectify the ink flow through the chamber inlets.
  • Figure 67 is a schematic perspective of a nozzle with a spur extending into the nozzle aperture for controlled drop misdirection.
  • Bubble cage 32 bubble retention structure
  • main conduit 110 secondary conduit 112. lateral spur from nozzle rim
  • FIG. 2 is a cutaway perspective view of a nozzle unit cell 1 after the completion of CMOS processing and before MEMS processing.
  • CMOS processing of the wafer four metal layers are deposited onto a silicon wafer 2, with the metal layers being interspersed between interlayer dielectric (ILD) layers.
  • ILD interlayer dielectric
  • the four metal layers are referred to as Ml, M2, M3 and M4 layers and are built up sequentially on the wafer during CMOS processing.
  • Ml, M2, M3 and M4 layers are built up sequentially on the wafer during CMOS processing.
  • each heater element actuator is connected to the CMOS via a pair of electrodes defined in the outermost M4 layer.
  • the M4 CMOS layer is the foundation for subsequent MEMS processing of the wafer.
  • the M4 layer also defines bonding pads along a longitudinal edge of each printhead integrated circuit. These bonding pads (not shown) allow the CMOS to be connected to a microprocessor via wire bonds extending from the bonding pads.
  • Figures 1 and 2 show the aluminium M4 layer 3 having a passivation layer 4 deposited thereon. (Only MEMS features of the M4 layer are shown in these Figures; the main CMOS features of the M4 layer are positioned outside the nozzle unit cell).
  • the M4 layer 3 has a thickness of 1 micron and is itself deposited on a 2 micron layer of CVD oxide 5.
  • the M4 layer 3 has an ink inlet opening 6 and pit openings 7. These openings define the positions of the ink inlet and pits formed subsequently in the MEMS process.
  • bonding pads along a longitudinal edge of each printhead integrated circuit are defined by etching through the passivation layer 4. This etch reveals the M4 layer 3 at the bonding pad positions.
  • the nozzle unit cell 1 is completely masked with photoresist for this step and, hence, is unaffected by the etch.
  • the first stage of MEMS processing etches a pit 8 through the passivation layer 4 and the CVD oxide layer 5.
  • This etch is defined using a layer of photoresist (not shown) exposed by the dark tone pit mask shown in Figure 3.
  • the pit 8 has a depth of 2 microns, as measured from the top of the M4 layer 3.
  • electrodes 9 are defined on either side of the pit by partially revealing the M4 layer 3 through the passivation layer 4.
  • a heater element is suspended across the pit 8 between the electrodes 9.
  • the pit 8 is filled with a first sacrificial layer (“SACl") of photoresist 10.
  • SACl first sacrificial layer
  • a 2 micron layer of high viscosity photoresist is first spun onto the wafer and then exposed using the dark tone mask shown in Figure 6.
  • the SACl photoresist 10 forms a scaffold for subsequent deposition of the heater material across the electrodes 9 on either side of the pit 8. Consequently, it is important the SACl photoresist 10 has a planar upper surface that is flush with the upper surface of the electrodes 9.
  • the SACl photoresist must completely fill the pit 8 to avoid 'stringers' of conductive heater material extending across the pit and shorting out the electrodes 9.
  • the present process deliberately exposes the SACl photoresist 10 inside the perimeter walls of the pit 8 ⁇ e.g. within 0.5 microns) using the mask shown in Figure 6. This ensures a planar upper surface of the SACl photoresist 10 and avoids any spiked regions of photoresist around the perimeter rim of the pit 8.
  • the photoresist After exposure of the SACl photoresist 10, the photoresist is reflowed by heating. Reflowing the photoresist allows it to flow to the walls of the pit 8, filling it exactly.
  • Figures 9 and 10 show the SACl photoresist 10 after reflow.
  • the photoresist has a planar upper surface and meets flush with the upper surface of the M4 layer 3, which forms the electrodes 9.
  • the SACl photoresist 10 is U.V. cured and/or hardbaked to avoid any reflow during the subsequent deposition step of heater material.
  • Figures 11 and 12 show the unit cell after deposition of the 0.5 microns of heater material 11 onto the SACl photoresist 10. Due to the reflow process described above, the heater material 11 is deposited evenly and in a planar layer over the electrodes 9 and the SAC 1 photoresist 10.
  • the heater material may be comprised of any suitable conductive material, such as TiAl, TiN, TiAlN, TiAlSiN etc.
  • a typical heater material deposition process may involve sequential deposition of a 100 A seed layer of TiAl, a 2500 A layer of TiAlN, a further 100 A seed layer of TiAl and finally a further 2500 A layer of TiAlN.
  • the layer of heater material 11 is etched to define the thermal actuator 12.
  • Each actuator 12 has contacts 28 that establish an electrical connection to respective electrodes 9 on either side of the SACl photoresist 10.
  • a heater element 29 spans between its corresponding contacts 28.
  • the heater element 12 is a linear beam spanning between the pair of electrodes 9.
  • the heater element 12 may alternatively adopt other configurations, such as those described in Applicant's US Patent No. 6,755,509, the content of which is herein incorporated by reference.
  • heater element 29 configurations having a central void may be advantageous for minimizing the deleterious effects of cavitation forces on the heater material when a bubble collapses during ink ejection.
  • Other forms of cavitation protection may be adopted such as 'bubble venting' and the use of self passivating materials.
  • an ink inlet for the nozzle is etched through the passivation layer 4, the oxide layer 5 and the silicon wafer 2.
  • each of the metal layers had an ink inlet opening (see, for example, opening 6 in the M4 layer 3 in Figure 1) etched therethrough in preparation for this ink inlet etch.
  • a relatively thick layer of photoresist 13 is spun onto the wafer and exposed using the dark tone mask shown in Figure 16.
  • the thickness of photoresist 13 required will depend on the selectivity of the deep reactive ion etch (DRIE) used to etch the ink inlet. With an ink inlet opening 14 defined in the photoresist 13, the wafer is ready for the subsequent etch steps.
  • DRIE deep reactive ion etch
  • the dielectric layers are etched through to the silicon wafer below. Any standard oxide etch (e.g. O 2 ZC 4 F 8 plasma) may be used.
  • an ink inlet 15 is etched through the silicon wafer 2 to a depth of 25 microns, using the same photoresist mask 13. Any standard anisotropic DRIE, such as the Bosch etch (see US Patent Nos. 6,501,893 and 6,284,148) may be used for this etch. Following etching of the ink inlet 15, the photoresist layer 13 is removed by plasma ashing.
  • the ink inlet 15 is plugged with photoresist and a second sacrificial layer (“SAC2") of photoresist 16 is built up on top of the SACl photoresist 10 and passivation layer 4.
  • SAC2 photoresist 16 will serve as a scaffold for subsequent deposition of roof material, which forms a roof and sidewalls for each nozzle chamber.
  • a ⁇ 6 micron layer of high viscosity photoresist is spun onto the wafer and exposed using the dark tone mask shown in Figure 23.
  • the mask exposes sidewall openings 17 in the SAC2 photoresist 16 corresponding to the positions of chamber sidewalls and sidewalls for an ink conduit.
  • openings 18 and 19 are exposed adjacent the plugged inlet 15 and nozzle chamber entrance respectively.
  • These openings 18 and 19 will be filled with roof material in the subsequent roof deposition step and provide unique advantages in the present nozzle design.
  • the openings 18 filled with roof material act as priming features, which assist in drawing ink from the inlet 15 into each nozzle chamber. This is described in greater detail below.
  • the openings 19 filled with roof material act as filter structures and fluidic cross talk barriers. These help prevent air bubbles from entering the nozzle chambers and diffuses pressure pulses generated by the thermal actuator 12.
  • the next stage deposits 3 microns of roof material 20 onto the S AC2 photoresist 16 by PECVD.
  • the roof material 20 fills the openings 17, 18 and 19 in the SAC2 photoresist 16 to form nozzle chambers 24 having a roof 21 and sidewalls 22.
  • An ink conduit 23 for supplying ink into each nozzle chamber is also formed during deposition of the roof material 20.
  • any priming features and filter structures are formed at the same time.
  • the roof material 20 may be comprised of any suitable material, such as silicon nitride, silicon oxide, silicon oxynitride, aluminium nitride etc.
  • the next stage defines an elliptical nozzle rim 25 in the roof 21 by etching away 2 microns of roof material 20. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone rim mask shown in Figure 28.
  • the elliptical rim 25 comprises two coaxial rim lips 25a and 25b, positioned over their respective thermal actuator 12.
  • the next stage defines an elliptical nozzle aperture 26 in the roof 21 by etching all the way through the remaining roof material 20, which is bounded by the rim 25. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone roof mask shown in Figure 31.
  • the elliptical nozzle aperture 26 is positioned over the thermal actuator 12, as shown in Figure 33.
  • the next stage removes the SACl and SAC2 photoresist layers 10 and 16 by O 2 plasma ashing ( Figures 34 to 35).
  • the thermal actuator 12 is suspended in a single plane over the pit 8.
  • the coplanar deposition of the contacts 28 and the heater element 29 provides an efficient electrical connection with the electrodes 9.
  • Figures 36 and 37 show the entire thickness (150 microns) of the silicon wafer 2 after ashing the SACl and SAC2 photoresist layers 10 and 16.
  • ink supply channels 27 are etched from the backside of the wafer to meet with the ink inlets 15 using a standard anisotropic DRIE. This backside etch is defined using a layer of photoresist (not shown) exposed by the dark tone mask shown in Figure 38.
  • the ink supply channel 27 makes a fluidic connection between the backside of the wafer and the ink inlets 15.
  • Figure 43 shows three adjacent rows of nozzles in a cutaway perspective view of a completed printhead integrated circuit.
  • Each row of nozzles has a respective ink supply channel 27 extending along its length and supplying ink to a plurality of ink inlets 15 in each row.
  • the ink inlets supply ink to the ink conduit 23 for each row, with each nozzle chamber receiving ink from a common ink conduit for that row.
  • the heater element 29 is suspended within the chamber. This ensures that the heater element is immersed in ink when the chamber is primed. Completely immersing the heater element in ink dramatically improves the printhead efficiency.
  • the contacts may be used to support the element at its raised position.
  • the contacts at either end of the heater element can have vertical or inclined sections to connect the respective electrodes on the CMOS drive to the element at an elevated position.
  • heater material deposited on vertical or inclined surfaces is thinner than on horizontal surfaces.
  • the contact portion of the thermal actuator needs to be relatively large. Larger contacts occupy a significant area of the wafer surface and limit the nozzle packing density.
  • the present invention etches a pit or trench 8 between the electrodes 9 to drop the level of the chamber floor.
  • a layer of sacrificial photoresist (SAC) 10 (see Figure 9) is deposited in the trench to provide a scaffold for the heater element.
  • SAC 10 sacrificial photoresist
  • depositing SAC 10 in the trench 8 and simply covering it with a layer of heater material can lead to stringers forming in the gaps 46 between the SAC 10 and the sidewalls 48 of the trench 8 (as previously described in relation to Figure 7).
  • the gaps form because it is difficult to precisely match the mask with the sides of the trench 8.
  • the gaps 46 form between the sides of the pit and the SAC.
  • the heater material layer When the heater material layer is deposited, it fills these gaps to form 'stringers' (as they are known).
  • the stringers remain in the trench 8 after the metal etch (that shapes the heater element) and the release etch (to finally remove the SAC).
  • the stringers can short circuit the heater so that it fails to generate a bubble.
  • the SAC 10 By making the UV mask that exposes the SAC slightly bigger than the trench 8, the SAC 10 will be deposited over the side walls 48 so that no gaps form. Unfortunately, this produces a raised lip 50 around top of the trench.
  • the heater material layer 11 When the heater material layer 11 is deposited (see Figure 53), it is thinner on the vertical or inclined surfaces 52 of the lip 50. After the metal etch and release etch, these thin lip formations 52 remain and cause 'hotspots' because the localized thinning increases resistance. These hotspots affect the operation of the heater and typically reduce heater life.
  • the Applicant has found that refiowing the SAC 10 closes the gaps 46 so that the scaffold between the electrodes 9 is completely flat. This allows the entire thermal actuator 12 to be planar.
  • the unit cell shown has two separate ink chambers 38, each chamber having heater element 29 extending between respective pairs of contacts 28.
  • Ink permeable structures 34 are positioned in the ink refill openings so that ink can enter the chambers, but upon actuation, the structures 34 provide enough hydraulic resistance to reduce any reverse flow or fluidic cross talk to an acceptable level.
  • Ink is fed from the reverse side of the wafer through the ink inlet 15.
  • Priming features 18 extend into the inlet opening so that an ink meniscus does not pin itself to the peripheral edge of the opening and stop the ink flow.
  • Ink from the inlet 15 fills the lateral ink conduit 23 which supplies both chambers 38 of the unit cell.
  • each chamber 38 has two nozzles 25.
  • the heater element 29 actuates (forms a bubble)
  • two drops of ink are ejected; one from each nozzle 25.
  • Each individual drop of ink has less volume than the single drop ejected if the chamber had only one nozzle.
  • each nozzle With every nozzle, there is a degree of misdirection in the ejected drop. Depending on the degree of misdirection, this can be detrimental to print quality.
  • each nozzle ejects drops of smaller volume, and having different misdirections. Several small drops misdirected in different directions are less detrimental to print quality than a single relatively large misdirected drop. The Applicant has found that the eye averages the misdirections of each small drop and effectively 'sees' a dot from a single drop with a significantly less overall misdirection.
  • a multi nozzle chamber can also eject drops more efficiently than a single nozzle chamber.
  • the heater element 29 is an elongate suspended beam of TiAHSf and the bubble it forms is likewise elongated.
  • the pressure pulse created by an elongate bubble will cause ink to eject through a centrally disposed nozzle.
  • some of the energy from the pressure pulse is dissipated in hydraulic losses associated with the mismatch between the geometry of the bubble and that of the nozzle. Spacing several nozzles 25 along the length of the heater element 29 reduces the geometric discrepancy between the bubble shape and the nozzle configuration through which the ink ejects. This in turn reduces hydraulic resistance to ink ejection and thereby improves printhead efficiency.
  • the hydraulic resistance to droplet ejection can be reduced by using an elliptical nozzle.
  • the vapour bubbles generated by the heater elements 29 are elongated.
  • the heater elements are designed to heat uniformly along most of their length so bubble nucleation and growth is likewise substantially uniform along the length.
  • an elliptical nozzle 25 centred over the heater element 29 such that its major axis is parallel with the centre-line of the element the geometry of the bubble roughly corresponds to that of the nozzle.
  • the ink pushed along by the pressure pulse is not changing direction sharply and generating high fluidic drag before ejecting through the nozzle. With less power required for droplet ejection, the printhead is more efficient.
  • the elliptical nozzle is also thinner than a circular nozzle of equivalent aperture area. Hence the spacing between adjacent nozzles is reduced. This helps to increase nozzle pitch and therefore improve print resolution.
  • unit cell has four ink chambers 38.
  • the chambers are defined by the sidewalls 22 and the ink permeable structures 34.
  • Each chamber has its own heater element 29.
  • the heater elements 29 are arranged in pairs that are connected in series. Between each pair is 'cold spot' 54 with lower resistance and or greater heat sinking. This ensures that bubbles do not nucleate at the cold spots 54 and thus the cold spots become the common contact between the outer contacts 28 for each heater element parr.
  • the ink permeable structures 34 allow ink to refill the chambers 38 after drop ejection but baffle the pressure pulse from each heater element 29 to reduce the fluidic cross talk between adjacent chambers. It will be appreciated that this embodiment has many parallels with that shown in Figure 49 discussed above. However, the present embodiment effectively divides the relatively long chambers of Figure 49 into two separate chambers. This further aligns the geometry of the bubble formed by the heater element 29 with the shape of the nozzle 25 to reduce hydraulic losses during drop ejection. This is achieved without reducing the nozzle density but it does add some complexity to the fabrication process.
  • the conduits (ink inlets 15 and supply conduits 23) for distributing ink to every ink chamber in the array can occupy a significant proportion of the wafer area.
  • the unit cell shown has two chambers 38; each chamber has two heater elements 29 and two nozzles 25.
  • the effective reduction in drop misdirection by using multiple nozzles per chamber is discussed above in relation to the embodiment shown in Figure 49.
  • the additional benefits of dividing a single elongate chamber into separate chambers, each with their own actuators, is described above with reference to the embodiment shown in Figure 46.
  • the present embodiment uses multiple nozzles and multiple actuators in each chamber to achieve much of the advantages of the Figure 46 embodiment with a markedly less complicated design. With a simplified design, the overall dimensions of the unit cell are reduced thereby permitting greater nozzle densities.
  • the footprint of the unit cell is 64 ⁇ m long by 16 ⁇ m wide.
  • the ink permeable structure 34 is a single column at the ink refill opening to each chamber 38 instead of three spaced columns as with the Figure 46 embodiment.
  • the single column has a cross section profiled to be less resistive to refill flow, but more resistive to sudden back flow from the actuation pressure pulse.
  • Both heater elements in each chamber can be deposited simultaneously, together with the contacts 28 and the cold spot feature 54.
  • Both chambers 38 are supplied with ink from a common ink inlet 15 and supply conduit 23. These features also allow the footprint to be reduced and they are discussed in more detail below.
  • the priming features 18 have been made integral with one of the chamber sidewalls 22 and a wall ink conduit 23. The dual purpose nature of these features simplifies the fabrication and helps to keep the design compact.
  • actuators are connected in series and therefore fire in unison from the same drive signal to simplify the CMOS drive circuitry.
  • actuators in adjacent nozzles are connected in series within the same drive circuit.
  • the actuators in adjacent chambers could also be connected in parallel.
  • the CMOS drive circuitry would be more complex and the dimensions of the unit cell footprint would increase.
  • combining several actuators and their respective nozzles into a common drive circuit is an efficient implementation both in terms of printhead IC fabrication and nozzles density.
  • Reduction in the unit cell width enables the printhead to have nozzles patterns that previously would have required the nozzle density to be reduced.
  • a lower nozzle density has a corresponding influence on printhead size and/or print quality.
  • the nozzle rows are arranged in pairs with the actuators for each row extending in opposite directions.
  • the rows are staggered with respect to each other so that the printing resolution (dots per inch) is twice the nozzle pitch (nozzles per inch) along each row.
  • the same number of nozzles can be arranged into a single row instead of two staggered and opposing rows without sacrificing any print resolution (d.p.i.).
  • the embodiments shown in the accompanying figures achieve a nozzle pitch of more than 1000 nozzles per inch in each linear row.
  • the print resolution of the printhead is better than photographic (1600 dpi) when two opposing staggered rows are considered, and there is sufficient capacity for nozzle redundancy, dead nozzle compensation and so on which ensures the operation life of the printhead remains satisfactory.
  • the embodiment shown in Figure 54 has a footprint that is 16 ⁇ m wide and therefore the nozzle pitch along one row is about 1600 nozzles per inch. Accordingly, two offset staggered rows yield a resolution of about 3200 d.p.i.
  • the Applicant has focussed on identifying and combining a number of features to reduce the relevant dimensions of structures in the printhead. For example, elliptical nozzles, shifting the ink inlet from the chamber, finer geometry logic and shorter drive FETs (field effect transistors) are features developed by the Applicant to derive some of the embodiments shown. Each contributing feature necessitated a departure from conventional wisdom in the field, such as reducing the FET drive voltage from the widely used traditional 5V to 2.5V in order to decrease transistor length.
  • FIG. 50 shows a portion of the nozzle plate 56. For clarity, the nozzle apertures 26 and the nozzle rims 25 are also shown.
  • the exterior surface of the nozzle plate is patterned with columnar proj ections 58 extending a short distance from the plate surface.
  • the nozzle plate could also be patterned with other surface formations such as closely spaced ridges, corrugations or bumps.
  • Inlet Priming Feature Referring to Figure 47, two unit cells are shown extending in opposite directions to each other.
  • the ink inlet passage 15 supplies ink to the four chambers 38 via the lateral ink conduit 23.
  • ink through micron-scale conduits, such as the ink inlet 15, to individual MEMS nozzles in an inkjet printhead is complicated by factors that do not arise in macro-scale flow.
  • a meniscus can form and, depending on the geometry of the aperture, it can 'pin' itself to the lip of the aperture quite strongly. This can be useful in printheads, such as bleed holes that vent trapped air bubbles but retain the ink, but it can also be problematic if stops ink flow to some chambers.
  • the priming features 18 are columns extending from the interior of the nozzle plate (not shown) to the periphery of the inlet 15. A part of each column 18 is within the periphery so that the surface tension of an ink meniscus at the ink inlet will form at the priming features 18 so as to draw the ink out of the inlet. This 'unpins' the meniscus from that section of the periphery and the flow toward the ink chambers.
  • the priming features 18 can take many forms, as long as they present a surface that extends transverse to the plane of the aperture. Furthermore, the priming feature can be an integral part of other nozzles features as shown in Figure 54.
  • the elongate heater elements 29 extend parallel to the ink distribution conduit 23. Accordingly, the elongate ink chambers 38 are likewise aligned with the ink conduit 23. Sidewall openings 60 connect the chambers 38 to the ink conduit 23. Configuring the ink chambers so that they have side inlets reduces the ink refill times. The inlets are wider and therefore refill flow rates are higher.
  • the sidewall openings 60 have ink permeable structures 34 to keep fluidic cross talk to an acceptable level.
  • the ink refill opening to each chamber 38 has a filter structure 40 to trap air bubbles or other contaminants.
  • Air bubbles and solid contaminants in ink are detrimental to the MEMS nozzle structures.
  • the solid contaminants can obvious clog the nozzle openings, while air bubbles, being highly compressible, can absorb the pressure pulse from the actuator if they get trapped in the ink chamber. This effectively disables the ejection of ink from the affected nozzle.
  • a filter structure 40 in the form of rows of obstructions extending transverse to the flow direction through the opening, each row being spaced such that they are out of registration with the obstructions in an adjacent row with respect to the flow direction, the contaminants are not likely to enter the chamber 38 while the ink refill flow rate is not overly retarded.
  • the rows are offset with respect to each other and the induced turbulence has minimal effect on the nozzle refill rate but the air bubbles or other contaminants follow a relatively tortuous flow path which increases the chance of them being retained by the obstructions 40.
  • the embodiment shown uses two rows of obstructions 40 in the form of columns extending between the wafer substrate and the nozzle plate.
  • FIG 51 the exterior surface of the nozzle 56 is shown for a unit cell such as that shown in Figure 46 described above.
  • the nozzle apertures 26 are positioned directly above the heater elements (not shown) and a series of square-edged ink gutters 44 are formed in the nozzle plate 56 above the ink conduit 23 (see Figure 46).
  • InkJet printers often have maintenance stations that cap the printhead when it's not in use. To remove excess ink from the nozzle plate, the capper can be disengaged so that it peels off the exterior surface of the nozzle plate. This promotes the formation of a meniscus between the capper surface and the exterior of the nozzle plate.
  • the residual ink left in or around a given nozzle aperture may be a different colour than that ejected by the nozzle because the meniscus draws ink over the whole surface of the nozzle plate.
  • the contamination of ink in one nozzle by ink from another nozzle can create visible artefacts in the print.
  • Gutter formations 44 running transverse to the direction that the capper is peeled away from the nozzle plate will remove and retain some of the ink in the meniscus. While the gutters do not collect all the ink in the meniscus, they do significantly reduce the level of nozzle contamination of with different coloured ink. Bubble Trap
  • Air bubbles entrained in the ink are very bad for printhead operation. Air, or rather gas in general, is highly compressible and can absorb the pressure pulse from the actuator. If a trapped bubble simply compresses in response to the actuator, ink will not eject from the nozzle. Trapped bubbles can be purged from the printhead with a forced flow of ink, but the purged ink needs blotting and the forced flow could well introduce fresh bubbles.
  • the embodiment shown in Figure 46 has a bubble trap at the ink inlet 15.
  • the trap is formed by a bubble retention structure 32 and a vent 36 formed in the roof layer.
  • the bubble retention structure is a series of columns 32 spaced around the periphery of the inlet 15.
  • the ink priming features 18 have a dual purpose and conveniently form part of the bubble retaining structure.
  • the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere. By trapping the bubbles at the ink inlets and directing them to a small vent, they are effectively removed from the ink flow without any ink leakage.
  • printheads according to the present invention have at least two ink inlets 15 supplying each chamber 38 via an ink conduit 23 between the nozzle plate and underlying wafer.
  • Droplet Stem Anchors The droplet stem that attaches the ejected ink to the ink in the chamber immediately prior to drop separation, can be a cause of drop misdirection.
  • Figures 55 to 59 show sequential stages of the drop ejection process from a nozzle. In Figure 55, the heater element 29 is rapidly heated and vaporises the ink 64 in immediate contact with its surface to nucleate a bubble 66.
  • the bubble has grown to the point where it vents to atmosphere through the nozzle aperture 26. This is an important mechanism for avoiding cavitation corrosion of the heater element 29. Cavitation corrosion occurs when a bubble collapses back to a single point on the heater element surface. As the bubble reaches the singularity of a collapse point, the surface tension creates severe hydraulic forces that can abrade the heater material. By venting the bubble, there is no collapse point on the heater element.
  • the droplet stem 72 can attach itself to a point 74 on the nozzle rim. As the attachment point 74 is not on the centre- line 76 of the nozzle aperture 26, the ink bulb 70 is deflected 78 away from the centre-line because of the surface tension's tendency to reduce surface area.
  • the stem 52 eventually breaks and the ink drop 80 forms and continues on its trajectory to the print media. However, the misdirection 78 remains for the ink drop 80 as well as any satellite drops 82.
  • the vented bubble has become an extended ink meniscus that helps to draw ink back into the chamber as it contracts to the nozzle aperture 26.
  • Figures 60 - 67 show nozzle designs with droplet stem anchors that positively locate where the droplet stem attaches. Knowing where the stem will attach reduces the misdirection, or in some cases, controls the misdirection so that all nozzles are misdirected in the same direction by roughly the same amount.
  • the droplet stem anchors can also perform secondary functions and these will now be discussed below.
  • the nozzle design shown has two actuators 29 ejecting ink through a single oval shaped nozzle 25.
  • the actuators are both heater elements connected in series for simultaneous actuation and ejection.
  • Both actuators 29 are part of a single beam of heater material such as TiAlN which is suspended at its ends and at it mid point.
  • Both heater elements 29 have a tapered section 86 where electrical resistance is at a maximum. During actuation, the vapour bubbles initiate at these maximum resistance sections or 'hotspots' 86.
  • the ink covering both heater elements 29 is connected by the slots 88.
  • the slots can be dimensioned so that they damp fiuidic cross talk to the extent that the heater elements are in two separate ink chambers, or they can be large enough to that both elements 29 are considered to be in the same chamber 38.
  • the heater elements 29 are positioned relative to the droplet stem anchor 84 so that as the ink ejected by each actuator forms a bulb attached by a stem, the ink surface tension, seeking to occupy the least surface area, will attach the stem to the anchor in preference to any other point on the nozzle rim 25.
  • the hotspots 86 are on diametrically opposed sides of the anchor 84, the bulbs of ink attached to respective droplet stems will be misdirected toward each other. Eventually they meet directly above the anchor and the opposing misdirections cancel each other out, or at least, the resultant misdirection is very small.
  • Figures 62 - 65 show several embodiments of nozzles with quadrupolar actuation.
  • Quadrupolar actuation initiates the pressure pulse at positions in the ink chamber that are symmetrical about two orthogonal axes. As the pulses converge within the chamber, the symmetry about two axes pushes the ink in a direction that is normal to both axes, at least in the ideal case. In reality, slight asymmetries mean the drop direction may be not be exactly normal, but it will typically be much closer than if the pressure pulse initiated from a single point in the chamber.
  • the unit cell shows two nozzles 25 in respective chambers 38, each having a quadrupole thermal actuator 12.
  • each actuator 12 is shaped similar to the Greek letter 'theta' .
  • Each actuator has two semi-circular current paths 90 between the contacts 28.
  • a central bar 94 extends between the mid points of each current path. The entire theta-shaped structure is suspended in the chamber 38 to minimise heat dissipation into the wafer substrate and maximise heater transfer to the ink.
  • the central bar 94 serves multiple purposes. Firstly, it provides the heater element with structural rigidity and bracing. Without it, the cyclical heating and cooling of the semi-circular current paths would cause some buckling into or out of the page of Figure 62. This could be addressed by supporting the semi-circles on the chamber floor, or even by a single support at each mid-point. However, this increases contact with the underlying wafer substrate and therefore increases heat dissipation.
  • the central bar 94 provides resistance to buckling while keeping the heater element suspended within the chamber.
  • the central bar 94 also provides a 'cold spot' 92 at the mid-point of each semi-circle.
  • the thermal mass of the bar provides a small heat sink so the junction between the bar and the semi-circular current path heats to bubble nucleation temperature more slowly than the sections either side of the junction.
  • the contacts 28 act as heat sinks so bubble nucleation is directed to the middle of the arc between the contact and the junction with the central car 94. This ensures that the vapour bubbles nucleate at four positions on the theta shape and that these positions have quadrupole symmetry about two orthogonal axes.
  • the central bar also provides a droplet stem anchor for additional control of misdirection.
  • the central bar 94 has a latch point 96 for locating the base of the droplet stem.
  • the latch point is simply a surface irregularity that the surface tension of the ink can 'pin' itself to. If the central bar 94 is not parallel to the plane of the nozzle aperture 26, or there is some asymmetry in the position of the bubble nucleation sites, the droplet stem may latch to an off centre part of the centre bar 94.
  • a surface irregularity 96 on the central bar 94 tends to snag on the surface tension of the droplet stem and anchor it to the middle of the bar.
  • the surface irregularity 96 can be a sudden reduction in cross section as shown in Figure 63, or a boss such as that shown in Figure 64. In either case, the droplet stem originates from the middle of the central bar 94 and so any misdirection in the drop trajectory is minimised.
  • Dual Bar Four Kink, Heater Element
  • Figure 65 shows another quadrupole thermal actuator 12. Again it has two current paths 90 provided by separate beams extending between the contacts 28. For clarity, the other features of the unit cell have been omitted.
  • the beams 90 are suspended in the chamber 38 to minimise heat dissipation into the wafer substrate and each beam has two tight radius curves or kinks 98, between curves of larger radius 96.
  • the tight radius kinks 98 act as hotspots where the vapour bubbles nucleate. This is because the current flow around the kinks 98 will concentrate towards the radially inner side of the element 102 and away from the outside radius 100. This acts like a localised reduction in cross section which increases the resistance at these points.
  • the difference in current density between the inside edge and the outside edge is much less so the increase in resistance is small compared to that in the tight kinks 98.
  • the tight kinks 98 have a relatively low bending resistance so the longitudinal expansion of the beam 90 during actuation is accommodated without buckling inot or out of the plane of the page. This makes the position of the hotspots in the chamber 38 relatively stable thereby maintaining the quadrupole symmetry and minimising drop misdirection.
  • the unit cell shown in Figure 66 has a rectifying valve 106 at the ink refill aperture 104 to each chamber 38.
  • the particular rectifying valve shown is known as a Tesla valve.
  • a rectifying valve provides less hydraulic resistance to ink flowing into the chamber 38 than ink flowing out of the chamber. This can be used to reduce fluidic cross talk between chambers 38, while not retarding ink refill times ( and therefore print speeds).
  • the heater element 29 is a simple beam suspended in the chamber 38 between the contacts 28. Also for clarity, the nozzle rim has been omitted, however the skilled worker will appreciate that it is centrally disposed over the heater element 29.
  • the chambers 38 could have several nozzles each, as discussed above.
  • the chambers 38 are supplied with ink from the ink inlet 15 via the lateral ink conduit 23.
  • the Tesla valve 106 at each refill aperture 104 has a main conduit 108 between a pair of smaller secondary conduits 110. As ink flows into the chamber 38, there is little resistance to the flow through the main conduit 108 other than fiuidic drag against the walls of the conduit itself.
  • the upstream openings of the secondary conduits 110 do not face into the flow so little of the main flow is diverted into them.
  • the downstream openings direct any flow parallel and adjacent to the flow from the main conduit 108 downstream opening. Therefore, the secondary conduits 110 have negligible impact on ink flow into the chamber 38.
  • the pressure pulse can create a back flow of ink out of the chamber 38 and back into the lateral ink conduit 23.
  • Back flow is detrimental to drop ejection as it uses some of the energy from the pressure pulse.
  • the back flow can also create fiuidic cross talk that affects the ejection characteristics of adjacent chambers.
  • the Tesla valve 106 resists any back flow by using flow from the secondary conduits 110 to constrict flow through the main conduit 108.
  • the upstream openings of the secondary conduits 110 are facing the flow direction. So to is the upstream opening to the main conduit 108.
  • the pressure pulse forces ink along the main and secondary conduits however, the downstream openings of the secondary conduits 110 direct their ink flow across and counter to the main flow direction. These conflicting flows create turbulence and a hydraulic constriction in the main conduit 108.
  • back flow through the main conduit 108 and the secondary conduits 110 is stifled. With a high resistance to back flow, a greater portion of the pressure pulse is used to eject the ink drop through the nozzle and fiuidic cross talk is reduced.
  • Figure 67 is a schematic perspective of a nozzle with controlled drop misdirection. This is a different approach to minimising the drop misdirection as discussed above. By intentionally misdirecting the drops ejected by every nozzle in the array by a controlled amount, the printed image is equivalent to one from a minimised drop misdirection printhead (albeit slightly offset from the nozzle array).
  • this approach uses a droplet stem anchor 74 is positioned so that the droplet stem will attach to it in preference to any other point on the nozzle rim 25 or heater element 29.
  • the anchor can be positioned at a point that will cause a known misdirection that is the same magnitude and direction as every other nozzle in the array.
  • the embodiment shown in Figure 67 provides a droplet stem anchor at the end of a lateral spur 112 extending into the nozzle aperture 26 from the side of the nozzle rim 25.
  • This nozzles uses a simple suspended beam heater element 29 which is easier to deposit and etch than a theta heater (described above), but still controls drop misdirection with a droplet stem anchor.
  • the spur 112 is an obstruction that deflects the drop from the normal trajectory. However, if all the spurs in the nozzle array are parallel and have the same position relative to the heater element, the misdirection across the whole array will be uniform.

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Abstract

An inkjet printhead comprising an array of ink chambers, each having a nozzle (25), an elongate actuator for ejecting ink through the nozzle (25), wherein the nozzle (25) has an elongate shape with its long dimension aligned with that of the elongate actuator.

Description

PRINTHEAD WITH ELONGATE NOZZLES
Field of the Invention The present invention relates to the field of micro-electromechanical systems (MEMS) devices and discloses an inkjet printing system using MEMS techniques.
Cross References to Related Applications Various methods, systems and apparatus relating to the present invention are disclosed in the following US Patents/ Patent Applications filed by the applicant or assignee of the present invention:
09/517539 6566858 09/112762 6331946 6246970 6442525 09/517384
09/505951 6374354 09/517608 09/505147 10/203564 6757832 6334190
6745331 09/517541 10/203559 10/203560 10/636263 10/636283 10/866608
10/902889 10/902833 10/940653 10/942858 10/727181 10/727162 10/727163 10/727245 10/727204 10/727233 10/727280 10/727157 10/727178 10/727210 10/727257 10/727238 10/727251 10/727159 10/727180 10/727179 10/727192
10/727274 10/727164 10/727161 10/727198 10/727158 10/754536 10/754938
10/727227 10/727160 10/934720 11/212,702 10/296522 6795215 10/296535
09/575109 10/296525 09/575110 09/607985 6398332 6394573 6622923
6747760 10/189459 10/884881 10/943941 10/949294 11/039866 11/123011
11/123010 11/144769 11/148237 10/922846 10/922845 10/854521 10/854522
10/854488 10/854487 10/854503 10/854504 10/854509 10/854510 10/854496
10/854497 10/854495 10/854498 10/854511 10/854512 10/854525 10/854526
10/854516 10/854508 10/854507 10/854515 10/854506 10/854505 10/854493
10/854494 10/854489 10/854490 10/854492 10/854491 10/854528 10/854523
10/854527 10/854524 10/854520 10/854514 10/854519 10/854513 10/854499
10/854501 10/854500 10/854502 10/854518 10/854517 10/934628 PLT046US
10/728804 10/728952 10/728806 10/728834 10/729790 10/728884 10/728970
10/728784 10/728783 10/728925 10/728842 10/728803 10/728780 10/728779
10/773189 10/773204 10/773198 10/773199 10/773190 10/773201 10/773191
10/773183 10/773195 10/773196 10/773186 10/773200 10/773185 10/773192
10/773197 10/773203 10/773187 10/773202 10/773188 10/773194 10/773193
10/773184 11/008118 11/060751 11/060805 11/188017 6623101 6406129
6505916 6457809 6550895 6457812 10/296434 6428133 6746105
10/407212 10/407207 10/683064 10/683041 6750901 6476863 6788336
11/097308 11/097309 11/097335 11/097299 11/097310 11/097213 11/210687 11/097212 11/212637 10/760272 10/760273 10/760187 10/760182 10/760188
10/760218 10/760217 10/760216 10/760233 10/760246 10/760212 10/760243
10/760201 10/760185 10/760253 10/760255 10/760209 10/760208 10/760194
10/760238 10/760234 10/760235 10/760183 10/760189 10/760262 10/760232
10/760231 10/760200 10/760190 10/760191 10/760227 10/760207 10/760181
10/815625 10/815624 10/815628 10/913375 10/913373 10/913374 10/913372
10/913377 10/913378 10/913380 10/913379 10/913376 10/913381 10/986402
11/172816 11/172815 11/172814 11/003786 11/003354 11/003616 11/003418
11/003334 11/003600 11/003404 11/003419 11/003700 11/003601 11/003618
11/003615 11/003337 11/003698 11/003420 11/003682 11/003699 11/071473
11/003463 11/003701 11/003683 11/003614 11/003702 11/003684 11/003619
11/003617 10/760254 10/760210 10/760202 10/760197 • 10/760198 10/760249
10/760263 10/760196 10/760247 10/760223 10/760264 10/760244 10/760245
10/760222 10/760248 10/760236 10/760192 10/760203 10/760204 10/760205
10/760206 10/760267 10/760270 10/760259 10/760271 10/760275 10/760274
10/760268 10/760184 10/760195 10/760186 10/760261 10/760258 11/014764
11/014763 11/014748 11/014747 11/014761 11/014760 11/014757 11/014714
11/014713 11/014762 11/014724 11/014723 11/014756 11/014736 11/014759
11/014758 11/014725 11/014739 11/014738 11/014737 11/014726 11/014745
11/014712 11/014715 11/014751 11/014735 11/014734 11/014719 11/014750
11/014749 11/014746 11/014769 11/014729 11/014743 11/014733 11/014754
11/014755 11/014765 11/014766 11/014740 11/014720 11/014753 11/014752
11/014744 11/014741 11/014768 11/014767 11/014718 11/014717 11/014716
11/014732 11/014742 11/097268 11/097185 11/097184 09/575197 09/575195
09/575159 09/575132 09/575123 09/575148 09/575130 09/575165 09/575153
09/575118 09/575131 09/575116 09/575144 09/575139 09/575186 6681045
6728000 09/575145 09/575192 09/575181 09/575193 09/575156 09/575183
6789194 09/575150 6789191 6644642 6502614 6622999 6669385
6549935 09/575187 6727996 6591884 6439706 6760119 09/575198
6290349 6428155 6785016 09/575174 09/575163 6737591 09/575154
09/575129 09/575124 09/575188 09/575189 09/575162 09/575172 09/575170
09/575171 09/575161
The disclosures of these applications and patents are incorporated herein by reference.
Background of the Invention
The present invention involves the ejection of ink drops by way of forming gas or vapor bubbles in a bubble forming liquid. This principle is generally described in US 3, 747,120 (Stemme). Each pixel in the printed image is derived ink drops ejected from one or more ink nozzles. In recent years, inkjet printing has become increasing popular primarily due to its inexpensive and versatile nature. Many different aspects and techniques for inkjet printing are described in detail in the above cross referenced documents.
Nozzle packing density, or the number of nozzles per square mm of printhead, has a bearing on the print resolution and fabrication costs. In view of this, there are ongoing efforts to increase nozzle packing densities. As a result, individual nozzle structures are configured to reduce the spacing between adjacent nozzles. One such configuration uses an elongated ink chamber and similarly elongated ink ejection actuator to reduce the spacing between adjacent nozzles. However, ejecting a substantial proportion of the ink in an elongate chamber out of a nozzle involves significant hydraulic losses. To overcome these losses, the actuator uses more energy to create a pressure pulse in the ink that is sufficient to eject a drop. Therefore, the overall efficiency of the printhead is lower than an actuator in a less elongated chamber.
Summary of the Invention
Accordingly, the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle, an elongate actuator for ejecting ink through the nozzle; wherein, the nozzle has an elongate shape with its long dimension aligned with that of the elongate actuator.
By elongating the nozzle and aligning it with the actuator, the nozzle shape more closely corresponds with the shape of the pressure pulse that the actuator creates in the ink. This allows the pressure pulse to eject ink through the nozzle more easily. The hydraulic losses are less because the ink being pushed by the pressure pulse is subject to less fluidic drag as it ejects through a nozzle with a similar shape. This, in turn improves the operational efficiency of the printhead. Preferably the nozzle is elliptical. In a further preferred form, the actuator is a thermal actuator with an elongate heater element that generate a vapour bubble to eject in through the nozzle. In some embodiments, each ink chamber in the array has a plurality of elongate nozzles aligned with the elongate actuator. Optionally, each ink chamber in the array has a plurality of elongate nozzles corresponding to a plurality of elongate actuators respectively.
In a first aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle, an elongate actuator for ejecting ink through the nozzle; wherein, the nozzle has an elongate shape with its long dimension aligned with that of the elongate actuator. Optionally, the nozzle is elliptical.
Optionally, the actuator is a thermal actuator with an elongate heater element that generate a vapour bubble to eject in through the nozzle.
Optionally, each ink chamber in the array has a plurality of elongate nozzles aligned with the elongate actuator.
Optionally, each ink chamber in the array has a plurality of elongate nozzles corresponding to a plurality of elongate actuators respectively.
In a further aspect there is provided an inkjet printhead according further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes.
Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts. In a further aspect there is provided an inkjet printhead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
In a further aspect there is provided an inkj et printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
Optionally, each of the ink conduits is in fluid communication with two of the ink inlets.
Optionally, each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
Optionally, the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
Optionally, the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
La a second aspect the present invention provides an inkjet printhead comprising: an array of nozzles; a plurality of actuators for ejecting ink through the nozzles such that a bulb of ink attached to a droplet stem forms prior to drop separation when the stem breaks; a plurality of droplet stem anchors positioned between adjacent actuators; wherein during use, the adjacent actuators eject ink simultaneously and the droplet stem anchors combine the ink simultaneously ejected by the adjacent nozzles into a single drop.
Optionally, the adjacent actuators are two thermal actuators ejecting ink through a single oval shaped nozzle.
Optionally, the thermal actuators are both heater elements connected in series for simultaneous actuation and ejection. Optionally, the two heater elements are part of a single beam of heater material suspended at its ends and at it mid point.
Optionally, the heater elements have a tapered section where electrical resistance is at a maximum such that vapour bubbles initiate at the maximum resistance sections.
Optionally, the heater elements are on opposite sides of the droplet stem anchor so that the trajectory of the ink ejected by one heater element intersects with the trajectory of ink ejected by the other heater element.
Optionally, the heater elements are in adjacent ink chambers with the droplet stem anchor at an adjoining boundary.
Optionally, the heater elements are in a single ink chamber.
Optionally, the ink ejected by the adjacent actuators is in fluid communication prior to actuation.
Optionally, the heater elements are formed from TiAlN.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts.
In a further aspect there is provided an inkjet printhead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
In a further aspect there is provided an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers. Optionally, each of the ink conduits is in fluid communication with two of the ink inlets.
Optionally, each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
Optionally, the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
Optionally, the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
In a third aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having an ink refill aperture, a nozzle and an actuator for ejecting ink through the nozzle; and, a fluid flow rectifying valve at the ink refill aperture for providing less hydraulic resistance to ink flowing into the chamber than ink flowing out of the chamber. Optionally, the recifying valve is a Tesla valve with a main conduit and a secondary conduit and at least one secondary conduit; wherein during use, ink flow out of the chamber is split into a main flow and a secondary flow such that when ink flows out of the chamber the secondary flow is combined with the main flow so as to constrict the main flow.
Optionally, the Tesla valve has two secondary conduits, on opposite sides of the main conduit.
Optionally, during use, when ink flows into the chamber, the upstream openings of the secondary conduits are in plane parallel to the flow direction and the downstream openings direct any secondary flow parallel and adjacent to flow from the main conduit downstream opening.
Optionally, the downstream openings of the secondary conduits during ink flow out of the chamber are on opposing sides of the main conduit face transversely to the flow direction through the main conduit.
In a further aspect there is provided an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes.
Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts.
In a further aspect there is provided an inkjet printhead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
In a further aspect there is provided an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
Optionally, each of the ink conduits is in fluid communication with two of the ink inlets.
Optionally, each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere. Optionally, the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
Optionally, the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
In a fourth aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle, a droplet stem anchor and an actuator for ejecting ink through the nozzle; wherein during use, the ink ejected from the nozzle is attached to the droplet stem anchor by an ink stem until the stem breaks so that the ejected ink forms a separate drop.
Optionally, the droplet stem anchor is a columnar feature with one proximate the nozzle.
Optionally, the axis of the droplet stem anchor and the central axis of the nozzle are collinear.
Optionally, each ink chamber has two actuators, each actuators having a heater element for generating a vapour bubble to eject ink through the nozzle, and the droplet stem anchor being positioned between the heater elements.
Optionally, the actuator has a plurality of heater elements connected in parallel with a cross bracing structure extending between the heater elements, the cross bracing structure also providing the droplet stem anchor.
Optionally, the actuator has two heater elements in parallel and the cross bracing structure is a single beam with a surface irregularity to locate the droplet stem actuator.
In a further aspect there is provided an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes.
Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber. Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts.
In a further aspect there is provided an inkjet printhead further comprising an ink conduit between a nozzle plate and an underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
In a further aspect there is provided an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
Optionally, each of the ink conduits is in fluid communication with two of the ink inlets.
Optionally, each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
Optionally, the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
In a fifth aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and an actuator for ejecting ink through the nozzle; wherein during use, the actuator initiates a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
Optionally, the actuator is a thermal actuator with heater elements that generate vapour bubbles to eject the ink.
Optionally, the actuator has two parallel current paths with two heater elements connected in series along each current path for initiating the quadrupole pressure pulse.
Optionally, the heater elements include bubble nucleation sections that heat more rapidly than other sections of the current path.
Optionally, the bubble nucleation sections are between sections of the current path with greater thermal inertia.
Optionally, the bubble nucleation sections are tight radius curves in between larger radius curves such that current crowding around the tight radius curves generates more resistive heating than the larger radius curves.
Optionally, the heater elements are suspended within the chamber.
Optionally, the actuator has a cross bracing structure extending between intermediate points on the parallel current paths.
Optionally, the cross bracing structure provides increased thermal inertia where it connects to each current path.
Optionally, the cross bracing structure provides a droplet stem anchor.
In a further aspect there is provided an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes. Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts.
Optionally, the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
In a sixth aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and a thermal actuator for generating vapour bubbles to eject ink through the nozzle; wherein, the thermal actuator has a pair of contacts and at least two parallel current paths between the contacts, each of the current paths having a plurality of heater elements for nucleating a vapour bubble.
Optionally, the heater elements nucleate their respective bubbles simultaneously with every activation of the actuator.
Optionally, the actuator has two parallel current paths with two heater elements connected in series along each current path.
Optionally, the heater elements include bubble nucleation sections that heat more rapidly than other sections of the current path. Optionally, the bubble nucleation sections are between sections of the current path with greater thermal inertia.
Optionally, the bubble nucleation sections are tight radius curves in between larger radius curves such that current crowding around the tight radius curves generates more resistive heating than the larger radius curves.
Optionally, the heater elements are suspended within the chamber.
Optionally, the thermal actuator has a cross bracing structure extending between intermediate points on the parallel current paths.
Optionally, the cross bracing structure provides increased thermal inertia where it connects to each current path.
Optionally, the cross bracing structure provides a droplet stem anchor.
Optionally, the actuator initiates a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
Optionally, the thermal actuator is formed from TiAlN.
In a further aspect there is provided an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes.
Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element. Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
In a seventh aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and a plurality of heater elements for generating vapour bubbles to eject ink through the nozzle, the heater elements being suspended for immersion in the ink; and, a cross bracing structure for maintaining the spacing between the heater elements.
Optionally, the heater elements nucleate their respective bubbles simultaneously with every activation of the actuator.
Optionally, the ink chamber has a pair of contacts with two parallel current paths extending between the contacts, each current path having two of the heater elements connected in series.
Optionally, the heater elements include bubble nucleation sections that heat more rapidly than other sections of the current path.
Optionally, the bubble nucleation sections are between sections of the current path with greater thermal inertia.
Optionally, the cross bracing structure is integrally formed with the hater elements and extends between intermediate points on the parallel current paths.
Optionally, the cross bracing structure provides sections of greater thermal inertia in the current paths.
Optionally, the heater elements initiate a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
Optionally, the thermal elements and the contacts are formed from TiAlN. Optionally, the cross bracing structure provides a droplet stem anchor.
Optionally, the actuator initiates a quadrupole pressure pulse that is symmetrical about two orthogonal axes parallel to the plane of the nozzle, the orthogonal axes intersecting a mutually orthogonal axis extending through the centre of the nozzle.
In a further aspect there is provided an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes.
Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ej ects ink through all the nozzles of the chamber.
Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts.
In an eighth aspect the present invention provides an inkjet printhead comprising: an array of ink chambers, each having a nozzle and an actuator for ejecting ink through the nozzle; wherein, the nozzle has a nozzle rim defining a nozzle aperture and a localized irregularity, on the nozzle rim extending toward the centre of the nozzle aperture. Optionally, the localized irregularity is a droplet stem anchor positioned so that a droplet stem will attach to it in preference to any other point on the nozzle rim.
Optionally, the localized irregularity is a lateral spur extending into the nozzle aperture from the nozzle rim.
Optionally, the actuator is a thermal actuator with a suspended beam heater element for immersion in the ink.
Optionally, all the spurs in the array are parallel and have the same position relative to the heater element.
In a further aspect there is provided an inkjet printhead further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
Optionally, a trench etched into the drive circuitry extends between the electrodes.
Optionally, each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ejects ink through all the nozzles of the chamber.
Optionally, each of the ink chambers have two nozzles.
Optionally, the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
Optionally, the nozzles are elliptical.
Optionally, the major axes of the elliptical nozzles are aligned.
Optionally, the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
Optionally, the drive voltage of the drive FET is 2.5 Volts. In a further aspect there is provided an inkjet priαthead further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
In a further aspect there is provided an inkjet printhead further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
Optionally, each of the ink conduits is in fluid communication with two of the ink inlets.
Optionally, each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
Optionally, the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
Optionally, the nozzles are arranged in rows such that the nozzle centres are collinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
The printhead according to the invention comprises a plurality of nozzles, as well as a chamber and one or more heater elements corresponding to each nozzle. The smallest repeating units of the printhead will have an ink supply inlet feeding ink to one or more chambers. The entire nozzle array is formed by repeating these individual units. Such an individual unit is referred to herein as a "unit cell".
Also, the term "ink" is used to signify any ejectable liquid, and is not limited to conventional inks containing colored dyes. Examples of non-colored inks include fixatives, infrared absorber inks, functionalized chemicals, adhesives, biological fluids, medicaments, water and other solvents, and so on. The ink or ejectable liquid also need not necessarily be a strictly a liquid, and may contain a suspension of solid particles.
Brief Description of the Drawings
Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a partially fabricated unit cell of the MEMS nozzle array on a printhead according to the present invention, the unit cell being section along A-A of Figure 3;
Figure 2 shows a perspective of the partially fabricated unit cell of Figure 1 ;
Figure 3 shows the mark associated with the etch of the heater element trench;
Figure 4 is a sectioned view of the unit cell after the etch of the trench;
Figure 5 is a perspective view of the unit cell shown in Fig 4;
Figure 6 is the mask associated with the deposition of sacrificial photoresist shown in Figure 7;
Figure 7 shows the unit cell after the deposition of sacrificial photoresist trench, with partial enlargements of the gaps between the edges of the sacrificial material and the side walls of the trench;
Figure 8 is a perspective of the unit cell shown in Fig 7;
Figure 9 shows the unit cell following the reflow of the sacrificial photoresist to close the gaps along the side walls of the trench;
Figure 10 is a perspective of the unit cell shown in Fig 9;
Figure 11 is a section view showing the deposition of the heater material layer;
Figure 12 is a perspective of the unit cell shown in Fig 11 ;
Figure 13 is the mask associated with the metal etch of the heater material shown in Figure 14;
Figure 14 is a section view showing the metal etch to shape the heater actuators;
Figure 15 is a perspective of the unit cell shown in Fig 14;
Figure 16 is the mask associated with the etch shown in Fig 17; Figure 17 shows the deposition of the photoresist layer and subsequent etch of the ink inlet to the passivation layer on top of the CMOS drive layers;
Figure 18 is a perspective of the unit cell shown in Fig 17;
Figure 19 shows the oxide etch through the passivation and CMOS layers to the underlying silicon wafer;
Figure 20 is a perspective of the unit cell shown in Fig 19;
Figure 21 is the deep anisotropic etch of the ink inlet into the silicon wafer;
Figure 22 is a perspective of the unit cell shown in Fig 21 ;
Figure 23 is the mask associated with the photoresist etch shown in Fig 24;
Figure 24 shows the photoresist etch to form openings for the chamber roof and side walls;
Figure 25 is a perspective of the unit cell shown in Fig 24;
Figure 26 shows the deposition of the side wall and risk material;
Figure 27 is a perspective of the unit cell shown in Fig. 26;
Figure 28 is the mask associated with the nozzle rim etch shown in Fig 29;
Figure 29 shows the etch of the roof layer to form the nozzle aperture rim;
Figure 30 is a perspective of the unit cell shown in Fig 29;
Figure 31 is the mask associated with the nozzle aperture etch shown in Fig 32;
Figure 32 shows the etch of the roof material to form the elliptical nozzle apertures;
Figure 33 is a perspective of the unit cell shown in Fig 32;
Figure 34 shows the oxygen plasma release etch of the first and second sacrificial layers; Figure 35 is a perspective of the unit cell shown in Fig 34;
Figure 36 shows the unit cell after the release etch, as well as the opposing side of the wafer;
Figure 37 is a perspective of the unit cell shown in Fig 36;
Figure 38 is the mask associated with the reverse etch shown in Fig. 39;
Figure 39 shows the reverse etch of the ink supply channel into the wafer;
Figure 40 is a perspective of unit cell shown in Fig 39;
Figure 41 shows the thinning of the wafer by backside etching;
Figure 42 is a perspective of the unit cell shown in Fig 41;
Figure 43 is a partial perspective of the array of nozzles on the printhead according to the present invention;
Figure 44 shows the plan view of a unit cell;
Figure 45 shows a perspective of the unit cell shown in Fig 44;
Figure 46 is schematic plan view of two unit cells with the roof layer removed but certain roof layer features shown in outline only;
Figure 47 is schematic plan view of two unit cells with the roof layer removed but the nozzle openings shown in outline only;
Figure 48 is a partial schematic plan view of unit cells with ink inlet apertures in the sidewall of the chambers;
Figure 49 is schematic plan view of a unit cells with the roof layer removed but the nozzle openings shown in outline only; Figure 50 is a partial plan view of the nozzle plate with stiction reducing formations and a particle of paper dust;
Figure 51 is a partial plan view of the nozzle plate with residual ink gutters;
Figure 52 is a partial section view showing the deposition of SACl photoresist in accordance with prior art techniques used to avoid stringers;
Figure 53 is a partial section view showing the deposition of a layer of heater material onto the SACl photoresist scaffold deposited in Figure 52;
Figure 54 is a partial schematic plan view of a unit cell with multiple nozzles and actuators in each of the chambers;
Figures 55 to 59 are schematic cross sections of the ink chamber shown in Fig 44 at sequential stages of drop ejection;
Figure 60 is a schematic perspective of a nozzle with droplet stem anchor as shown in Fig 61;
Figure 61 is a plan view of nozzle apertures with centrally disposed droplet stem anchors;
Figure 62 is schematic plan view of a unit cell with the roof layer removed showing a simple 'theta' heater element;
Figure 63 shows a theta heater element with a sudden reduction in cross section on the cross bar to locate the droplet stem;
Figure 64 shows a theta heater element with a formation in cross section on the cross bar to locate the droplet stem;
Figure 65 shows a dual bar, four kink heater element;
Figure 66 is schematic plan view of a unit cell with a Tesla valve to rectify the ink flow through the chamber inlets; and,
Figure 67 is a schematic perspective of a nozzle with a spur extending into the nozzle aperture for controlled drop misdirection. Detailed Description of the Preferred Embodiments
In the description than follows, corresponding reference numerals relate to corresponding parts. For convenience, the features indicated by each reference numeral are listed below.
1. Nozzle Unit Cell
2. Silicon Wafer
3. Topmost Aluminium Metal Layer in the CMOS metal layers
4. Passivation Layer 5. CVD Oxide Layer
6. Ink Inlet Opening in Topmost Aluminium Metal Layer 3.
7. Pit Opening in Topmost Aluminium Metal Layer 3.
8. Pit
9. Electrodes 10. SACl Photoresist Layer
11. Heater Material (TiAlN)
12. Thermal Actuator
13. Photoresist Layer
14. Ink Inlet Opening Etched Through Photo Resist Layer 15. Ink Inlet Passage
16. SAC2 Photoresist Layer
17. Chamber Side Wall Openings
18. Front Channel Priming Feature
19. Barrier Formation at Ink Inlet 20. Chamber Roof Layer
21. Roof
22. Sidewalls
23. Ink Conduit
24. Nozzle Chambers 25. Elliptical Nozzle Rim 25 (a) Inner Lip 25(b) Outer Lip
26. Nozzle Aperture
27. Ink Supply Channel 28. Contacts
29. Heater Element.
30. Bubble cage 32. bubble retention structure
34. ink permeable structure
36. bleed hole
38. ink chamber
40. dual row filter
42. paper dust
44. ink gutters
46. gap between SACl and trench sidewall
48. trench sidewall
50. raised lip of SACl around edge of trench
52. thinner inclined section of heater material
54. cold spot between series connected heater elements
56. nozzle plate
58. columnar projections
60. sidewall ink opening
62. ink refill opening
64. ink
66. bubble
68. bulging ink meniscus
70. ink bulb
72. droplet stem
74. droplet stem attachment point
76. nozzle centre-line
78. drop misdirection
80. drop
82. satellite drop
84. droplet stem anchor
86. maximum resistance section or 'hotspot'
88. shots either side of droplet stem anchor
90. semi-circular current path
92. 'cold spot'
94. central bar
96. larger radius curve
98. tight radius curve
100. outside edge of tight radius curve
102. inside edge of tight radius curve
104. ink refill aperture 106. rectifying valve (Tesla valve)
108. main conduit 110. secondary conduit 112. lateral spur from nozzle rim
MEMS Manufacturing Process
The MEMS manufacturing process builds up nozzle structures on a silicon wafer after the completion of CMOS processing. Figure 2 is a cutaway perspective view of a nozzle unit cell 1 after the completion of CMOS processing and before MEMS processing.
During CMOS processing of the wafer, four metal layers are deposited onto a silicon wafer 2, with the metal layers being interspersed between interlayer dielectric (ILD) layers. The four metal layers are referred to as Ml, M2, M3 and M4 layers and are built up sequentially on the wafer during CMOS processing. These CMOS layers provide all the drive circuitry and logic for operating the printhead.
In the completed printhead, each heater element actuator is connected to the CMOS via a pair of electrodes defined in the outermost M4 layer. Hence, the M4 CMOS layer is the foundation for subsequent MEMS processing of the wafer. The M4 layer also defines bonding pads along a longitudinal edge of each printhead integrated circuit. These bonding pads (not shown) allow the CMOS to be connected to a microprocessor via wire bonds extending from the bonding pads.
Figures 1 and 2 show the aluminium M4 layer 3 having a passivation layer 4 deposited thereon. (Only MEMS features of the M4 layer are shown in these Figures; the main CMOS features of the M4 layer are positioned outside the nozzle unit cell). The M4 layer 3 has a thickness of 1 micron and is itself deposited on a 2 micron layer of CVD oxide 5. As shown in Figures 1 and 2, the M4 layer 3 has an ink inlet opening 6 and pit openings 7. These openings define the positions of the ink inlet and pits formed subsequently in the MEMS process.
Before MEMS processing of the unit cell 1 begins, bonding pads along a longitudinal edge of each printhead integrated circuit are defined by etching through the passivation layer 4. This etch reveals the M4 layer 3 at the bonding pad positions. The nozzle unit cell 1 is completely masked with photoresist for this step and, hence, is unaffected by the etch.
Turning to Figures 3 to 5, the first stage of MEMS processing etches a pit 8 through the passivation layer 4 and the CVD oxide layer 5. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone pit mask shown in Figure 3. The pit 8 has a depth of 2 microns, as measured from the top of the M4 layer 3. At the same time as etching the pit 8, electrodes 9 are defined on either side of the pit by partially revealing the M4 layer 3 through the passivation layer 4. In the completed nozzle, a heater element is suspended across the pit 8 between the electrodes 9.
In the next step (Figures 6 to 8), the pit 8 is filled with a first sacrificial layer ("SACl") of photoresist 10. A 2 micron layer of high viscosity photoresist is first spun onto the wafer and then exposed using the dark tone mask shown in Figure 6. The SACl photoresist 10 forms a scaffold for subsequent deposition of the heater material across the electrodes 9 on either side of the pit 8. Consequently, it is important the SACl photoresist 10 has a planar upper surface that is flush with the upper surface of the electrodes 9. At the same time, the SACl photoresist must completely fill the pit 8 to avoid 'stringers' of conductive heater material extending across the pit and shorting out the electrodes 9.
Typically, when filling trenches with photoresist, it is necessary to expose the photoresist outside the perimeter of the trench in order to ensure that photoresist fills against the walls of the trench and, therefore, avoid 'stringers' in subsequent deposition steps. However, this technique results in a raised (or spiked) rim of photoresist around the perimeter of the trench. This is undesirable because in a subsequent deposition step, material is deposited unevenly onto the raised rim - vertical or angled surfaces on the rim will receive less deposited material than the horizontal planar surface of the photoresist filling the trench. The result is 'resistance hotspots' in regions where material is thinly deposited.
As shown in Figure 7, the present process deliberately exposes the SACl photoresist 10 inside the perimeter walls of the pit 8 {e.g. within 0.5 microns) using the mask shown in Figure 6. This ensures a planar upper surface of the SACl photoresist 10 and avoids any spiked regions of photoresist around the perimeter rim of the pit 8.
After exposure of the SACl photoresist 10, the photoresist is reflowed by heating. Reflowing the photoresist allows it to flow to the walls of the pit 8, filling it exactly. Figures 9 and 10 show the SACl photoresist 10 after reflow. The photoresist has a planar upper surface and meets flush with the upper surface of the M4 layer 3, which forms the electrodes 9. Following reflow, the SACl photoresist 10 is U.V. cured and/or hardbaked to avoid any reflow during the subsequent deposition step of heater material.
Figures 11 and 12 show the unit cell after deposition of the 0.5 microns of heater material 11 onto the SACl photoresist 10. Due to the reflow process described above, the heater material 11 is deposited evenly and in a planar layer over the electrodes 9 and the SAC 1 photoresist 10. The heater material may be comprised of any suitable conductive material, such as TiAl, TiN, TiAlN, TiAlSiN etc. A typical heater material deposition process may involve sequential deposition of a 100 A seed layer of TiAl, a 2500 A layer of TiAlN, a further 100 A seed layer of TiAl and finally a further 2500 A layer of TiAlN.
Referring to Figures 13 to 15, in the next step, the layer of heater material 11 is etched to define the thermal actuator 12. Each actuator 12 has contacts 28 that establish an electrical connection to respective electrodes 9 on either side of the SACl photoresist 10. A heater element 29 spans between its corresponding contacts 28.
This etch is defined by a layer of photoresist (not shown) exposed using the dark tone mask shown in Figure 13. As shown in Figure 15, the heater element 12 is a linear beam spanning between the pair of electrodes 9. However, the heater element 12 may alternatively adopt other configurations, such as those described in Applicant's US Patent No. 6,755,509, the content of which is herein incorporated by reference. For example, heater element 29 configurations having a central void may be advantageous for minimizing the deleterious effects of cavitation forces on the heater material when a bubble collapses during ink ejection. Other forms of cavitation protection may be adopted such as 'bubble venting' and the use of self passivating materials. These cavitation management techniques are discussed in detail in US patent application (our docket MTCOOlUS).
In the next sequence of steps, an ink inlet for the nozzle is etched through the passivation layer 4, the oxide layer 5 and the silicon wafer 2. During CMOS processing, each of the metal layers had an ink inlet opening (see, for example, opening 6 in the M4 layer 3 in Figure 1) etched therethrough in preparation for this ink inlet etch. These metal layers, together with the interspersed ILD layers, form a seal ring for the ink inlet, preventing ink from seeping into the CMOS layers.
Referring to Figures 16 to 18, a relatively thick layer of photoresist 13 is spun onto the wafer and exposed using the dark tone mask shown in Figure 16. The thickness of photoresist 13 required will depend on the selectivity of the deep reactive ion etch (DRIE) used to etch the ink inlet. With an ink inlet opening 14 defined in the photoresist 13, the wafer is ready for the subsequent etch steps.
In the first etch step (Figures 19 and 20), the dielectric layers (passivation layer 4 and oxide layer 5) are etched through to the silicon wafer below. Any standard oxide etch (e.g. O2ZC4F8 plasma) may be used. In the second etch step (Figures 21 and 22), an ink inlet 15 is etched through the silicon wafer 2 to a depth of 25 microns, using the same photoresist mask 13. Any standard anisotropic DRIE, such as the Bosch etch (see US Patent Nos. 6,501,893 and 6,284,148) may be used for this etch. Following etching of the ink inlet 15, the photoresist layer 13 is removed by plasma ashing.
Ia the next step, the ink inlet 15 is plugged with photoresist and a second sacrificial layer ("SAC2") of photoresist 16 is built up on top of the SACl photoresist 10 and passivation layer 4. The SAC2 photoresist 16 will serve as a scaffold for subsequent deposition of roof material, which forms a roof and sidewalls for each nozzle chamber. Referring to Figures 23 to 25, a ~ 6 micron layer of high viscosity photoresist is spun onto the wafer and exposed using the dark tone mask shown in Figure 23.
As shown in Figures 23 and 25, the mask exposes sidewall openings 17 in the SAC2 photoresist 16 corresponding to the positions of chamber sidewalls and sidewalls for an ink conduit. In addition, openings 18 and 19 are exposed adjacent the plugged inlet 15 and nozzle chamber entrance respectively. These openings 18 and 19 will be filled with roof material in the subsequent roof deposition step and provide unique advantages in the present nozzle design. Specifically, the openings 18 filled with roof material act as priming features, which assist in drawing ink from the inlet 15 into each nozzle chamber. This is described in greater detail below. The openings 19 filled with roof material act as filter structures and fluidic cross talk barriers. These help prevent air bubbles from entering the nozzle chambers and diffuses pressure pulses generated by the thermal actuator 12.
Referring to Figures 26 and 27, the next stage deposits 3 microns of roof material 20 onto the S AC2 photoresist 16 by PECVD. The roof material 20 fills the openings 17, 18 and 19 in the SAC2 photoresist 16 to form nozzle chambers 24 having a roof 21 and sidewalls 22. An ink conduit 23 for supplying ink into each nozzle chamber is also formed during deposition of the roof material 20. In addition, any priming features and filter structures (not shown in Figures 26 and 27) are formed at the same time. The roofs 21, each corresponding to a respective nozzle chamber 24, span across adjacent nozzle chambers in a row to form a continuous nozzle plate. The roof material 20 may be comprised of any suitable material, such as silicon nitride, silicon oxide, silicon oxynitride, aluminium nitride etc.
Referring to Figures 28 to 30, the next stage defines an elliptical nozzle rim 25 in the roof 21 by etching away 2 microns of roof material 20. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone rim mask shown in Figure 28. The elliptical rim 25 comprises two coaxial rim lips 25a and 25b, positioned over their respective thermal actuator 12. Referring to Figures 31 to 33, the next stage defines an elliptical nozzle aperture 26 in the roof 21 by etching all the way through the remaining roof material 20, which is bounded by the rim 25. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone roof mask shown in Figure 31. The elliptical nozzle aperture 26 is positioned over the thermal actuator 12, as shown in Figure 33.
With all the MEMS nozzle features now fully formed, the next stage removes the SACl and SAC2 photoresist layers 10 and 16 by O2 plasma ashing (Figures 34 to 35). After ashing, the thermal actuator 12 is suspended in a single plane over the pit 8. The coplanar deposition of the contacts 28 and the heater element 29 provides an efficient electrical connection with the electrodes 9.
Figures 36 and 37 show the entire thickness (150 microns) of the silicon wafer 2 after ashing the SACl and SAC2 photoresist layers 10 and 16.
Referring to Figures 38 to 40, once frontside MEMS processing of the wafer is completed, ink supply channels 27 are etched from the backside of the wafer to meet with the ink inlets 15 using a standard anisotropic DRIE. This backside etch is defined using a layer of photoresist (not shown) exposed by the dark tone mask shown in Figure 38. The ink supply channel 27 makes a fluidic connection between the backside of the wafer and the ink inlets 15.
Finally, and referring to Figures 41 and 42, the wafer is thinned 135 microns by backside etching. Figure 43 shows three adjacent rows of nozzles in a cutaway perspective view of a completed printhead integrated circuit. Each row of nozzles has a respective ink supply channel 27 extending along its length and supplying ink to a plurality of ink inlets 15 in each row. The ink inlets, in turn, supply ink to the ink conduit 23 for each row, with each nozzle chamber receiving ink from a common ink conduit for that row. Features and Advantages of Particular Embodiments
Discussed below, under appropriate sub-headings, are certain specific features of embodiments of the invention, and the advantages of these features. The features are to be considered in relation to all of the drawings pertaining to the present invention unless the context specifically excludes certain drawings, and relates to those drawings specifically referred to.
Low Loss Electrodes
As shown in Figures 41 and 42, the heater element 29 is suspended within the chamber. This ensures that the heater element is immersed in ink when the chamber is primed. Completely immersing the heater element in ink dramatically improves the printhead efficiency.
Much less heat dissipates into the underlying wafer substrate so more of the input energy is used to generate the bubble that ejects the ink.
To suspend the heater element, the contacts may be used to support the element at its raised position. Essentially, the contacts at either end of the heater element can have vertical or inclined sections to connect the respective electrodes on the CMOS drive to the element at an elevated position. However, heater material deposited on vertical or inclined surfaces is thinner than on horizontal surfaces. To avoid undesirable resistive losses from the thinner sections, the contact portion of the thermal actuator needs to be relatively large. Larger contacts occupy a significant area of the wafer surface and limit the nozzle packing density.
To immerse the heater, the present invention etches a pit or trench 8 between the electrodes 9 to drop the level of the chamber floor. As discussed above, a layer of sacrificial photoresist (SAC) 10 (see Figure 9) is deposited in the trench to provide a scaffold for the heater element. However, depositing SAC 10 in the trench 8 and simply covering it with a layer of heater material, can lead to stringers forming in the gaps 46 between the SAC 10 and the sidewalls 48 of the trench 8 (as previously described in relation to Figure 7). The gaps form because it is difficult to precisely match the mask with the sides of the trench 8. Usually, when the masked photoresist is exposed, the gaps 46 form between the sides of the pit and the SAC. When the heater material layer is deposited, it fills these gaps to form 'stringers' (as they are known). The stringers remain in the trench 8 after the metal etch (that shapes the heater element) and the release etch (to finally remove the SAC). The stringers can short circuit the heater so that it fails to generate a bubble.
Turning now to Figure 52 and 53, the 'traditional' technique for avoiding stringers is illustrated.
By making the UV mask that exposes the SAC slightly bigger than the trench 8, the SAC 10 will be deposited over the side walls 48 so that no gaps form. Unfortunately, this produces a raised lip 50 around top of the trench. When the heater material layer 11 is deposited (see Figure 53), it is thinner on the vertical or inclined surfaces 52 of the lip 50. After the metal etch and release etch, these thin lip formations 52 remain and cause 'hotspots' because the localized thinning increases resistance. These hotspots affect the operation of the heater and typically reduce heater life.
As discussed above, the Applicant has found that refiowing the SAC 10 closes the gaps 46 so that the scaffold between the electrodes 9 is completely flat. This allows the entire thermal actuator 12 to be planar. The planar structure of the thermal actuator, with contacts directly deposited onto the CMOS electrodes 9 and suspended heater element 29, avoids hotspots caused by vertical or inclined surfaces so that the contacts can be much smaller structures without acceptable increases in resistive losses. Low resistive losses preserves the efficient operation of a suspended heater element and the small contact size is convenient for close nozzle packing on the printhead.
Multiple Nozzles for each Chamber
Referring to Figure 49, the unit cell shown has two separate ink chambers 38, each chamber having heater element 29 extending between respective pairs of contacts 28. Ink permeable structures 34 are positioned in the ink refill openings so that ink can enter the chambers, but upon actuation, the structures 34 provide enough hydraulic resistance to reduce any reverse flow or fluidic cross talk to an acceptable level.
Ink is fed from the reverse side of the wafer through the ink inlet 15. Priming features 18 extend into the inlet opening so that an ink meniscus does not pin itself to the peripheral edge of the opening and stop the ink flow. Ink from the inlet 15 fills the lateral ink conduit 23 which supplies both chambers 38 of the unit cell.
Instead of a single nozzle per chamber, each chamber 38 has two nozzles 25. When the heater element 29 actuates (forms a bubble), two drops of ink are ejected; one from each nozzle 25. Each individual drop of ink has less volume than the single drop ejected if the chamber had only one nozzle. By ejecting multiple drops from a single chamber simultaneously improves the print quality.
With every nozzle, there is a degree of misdirection in the ejected drop. Depending on the degree of misdirection, this can be detrimental to print quality. By giving the chamber multiple nozzles, each nozzle ejects drops of smaller volume, and having different misdirections. Several small drops misdirected in different directions are less detrimental to print quality than a single relatively large misdirected drop. The Applicant has found that the eye averages the misdirections of each small drop and effectively 'sees' a dot from a single drop with a significantly less overall misdirection.
A multi nozzle chamber can also eject drops more efficiently than a single nozzle chamber. The heater element 29 is an elongate suspended beam of TiAHSf and the bubble it forms is likewise elongated. The pressure pulse created by an elongate bubble will cause ink to eject through a centrally disposed nozzle. However, some of the energy from the pressure pulse is dissipated in hydraulic losses associated with the mismatch between the geometry of the bubble and that of the nozzle. Spacing several nozzles 25 along the length of the heater element 29 reduces the geometric discrepancy between the bubble shape and the nozzle configuration through which the ink ejects. This in turn reduces hydraulic resistance to ink ejection and thereby improves printhead efficiency.
Elliptical Nozzle
Similarly, the hydraulic resistance to droplet ejection can be reduced by using an elliptical nozzle. As shown in Figure 44, the vapour bubbles generated by the heater elements 29 are elongated. The heater elements are designed to heat uniformly along most of their length so bubble nucleation and growth is likewise substantially uniform along the length. With an elliptical nozzle 25 centred over the heater element 29 such that its major axis is parallel with the centre-line of the element, the geometry of the bubble roughly corresponds to that of the nozzle. Hence the ink pushed along by the pressure pulse is not changing direction sharply and generating high fluidic drag before ejecting through the nozzle. With less power required for droplet ejection, the printhead is more efficient.
The elliptical nozzle is also thinner than a circular nozzle of equivalent aperture area. Hence the spacing between adjacent nozzles is reduced. This helps to increase nozzle pitch and therefore improve print resolution.
Ink Chamber Re-Filled Via Adjacent Ink Chamber
Referring to Figure 46, two opposing unit cells are shown. In this embodiment, unit cell has four ink chambers 38. The chambers are defined by the sidewalls 22 and the ink permeable structures 34. Each chamber has its own heater element 29. The heater elements 29 are arranged in pairs that are connected in series. Between each pair is 'cold spot' 54 with lower resistance and or greater heat sinking. This ensures that bubbles do not nucleate at the cold spots 54 and thus the cold spots become the common contact between the outer contacts 28 for each heater element parr.
The ink permeable structures 34 allow ink to refill the chambers 38 after drop ejection but baffle the pressure pulse from each heater element 29 to reduce the fluidic cross talk between adjacent chambers. It will be appreciated that this embodiment has many parallels with that shown in Figure 49 discussed above. However, the present embodiment effectively divides the relatively long chambers of Figure 49 into two separate chambers. This further aligns the geometry of the bubble formed by the heater element 29 with the shape of the nozzle 25 to reduce hydraulic losses during drop ejection. This is achieved without reducing the nozzle density but it does add some complexity to the fabrication process. The conduits (ink inlets 15 and supply conduits 23) for distributing ink to every ink chamber in the array can occupy a significant proportion of the wafer area. This can be a limiting factor for nozzle density on the printhead. By making some ink chambers part of the ink flow path to other ink chambers, while keeping each chamber sufficiently free of fluidic cross talk, reduces the amount of wafer area lost to ink supply conduits.
Ink Chamber with Multiple Actuators and Respective Nozzles
Referring to Figure 54, the unit cell shown has two chambers 38; each chamber has two heater elements 29 and two nozzles 25. The effective reduction in drop misdirection by using multiple nozzles per chamber is discussed above in relation to the embodiment shown in Figure 49. The additional benefits of dividing a single elongate chamber into separate chambers, each with their own actuators, is described above with reference to the embodiment shown in Figure 46. The present embodiment uses multiple nozzles and multiple actuators in each chamber to achieve much of the advantages of the Figure 46 embodiment with a markedly less complicated design. With a simplified design, the overall dimensions of the unit cell are reduced thereby permitting greater nozzle densities. In the embodiment shown, the footprint of the unit cell is 64μm long by 16μm wide.
The ink permeable structure 34 is a single column at the ink refill opening to each chamber 38 instead of three spaced columns as with the Figure 46 embodiment. The single column has a cross section profiled to be less resistive to refill flow, but more resistive to sudden back flow from the actuation pressure pulse. Both heater elements in each chamber can be deposited simultaneously, together with the contacts 28 and the cold spot feature 54. Both chambers 38 are supplied with ink from a common ink inlet 15 and supply conduit 23. These features also allow the footprint to be reduced and they are discussed in more detail below. The priming features 18 have been made integral with one of the chamber sidewalls 22 and a wall ink conduit 23. The dual purpose nature of these features simplifies the fabrication and helps to keep the design compact.
Multiple Chambers and Multiple Nozzles for each Drive Circuit
In Figure 54, the actuators are connected in series and therefore fire in unison from the same drive signal to simplify the CMOS drive circuitry. In the Figure 46 unit cell, actuators in adjacent nozzles are connected in series within the same drive circuit. Of course, the actuators in adjacent chambers could also be connected in parallel. In contrast, were the actuators in each chamber to be in separate circuits, the CMOS drive circuitry would be more complex and the dimensions of the unit cell footprint would increase. In printhead designs where the drop misdirection is addressed by substituting multiple smaller drops, combining several actuators and their respective nozzles into a common drive circuit is an efficient implementation both in terms of printhead IC fabrication and nozzles density.
High Density Thermal InkJet Printhead
Reduction in the unit cell width enables the printhead to have nozzles patterns that previously would have required the nozzle density to be reduced. Of course, a lower nozzle density has a corresponding influence on printhead size and/or print quality.
Traditionally, the nozzle rows are arranged in pairs with the actuators for each row extending in opposite directions. The rows are staggered with respect to each other so that the printing resolution (dots per inch) is twice the nozzle pitch (nozzles per inch) along each row. By configuring the components of the unit cell such that the overall width of the unit is reduced, the same number of nozzles can be arranged into a single row instead of two staggered and opposing rows without sacrificing any print resolution (d.p.i.). The embodiments shown in the accompanying figures achieve a nozzle pitch of more than 1000 nozzles per inch in each linear row. At this nozzle pitch, the print resolution of the printhead is better than photographic (1600 dpi) when two opposing staggered rows are considered, and there is sufficient capacity for nozzle redundancy, dead nozzle compensation and so on which ensures the operation life of the printhead remains satisfactory. As discussed above, the embodiment shown in Figure 54 has a footprint that is 16μm wide and therefore the nozzle pitch along one row is about 1600 nozzles per inch. Accordingly, two offset staggered rows yield a resolution of about 3200 d.p.i.
With the realisation of the particular benefits associated with a narrower unit cell, the Applicant has focussed on identifying and combining a number of features to reduce the relevant dimensions of structures in the printhead. For example, elliptical nozzles, shifting the ink inlet from the chamber, finer geometry logic and shorter drive FETs (field effect transistors) are features developed by the Applicant to derive some of the embodiments shown. Each contributing feature necessitated a departure from conventional wisdom in the field, such as reducing the FET drive voltage from the widely used traditional 5V to 2.5V in order to decrease transistor length.
Reduced Stiction Printhead Surface
Static friction, or "stiction" as it has become known, allows dust particles to "stick" to nozzle plates and thereby clog nozzles. Figure 50 shows a portion of the nozzle plate 56. For clarity, the nozzle apertures 26 and the nozzle rims 25 are also shown. The exterior surface of the nozzle plate is patterned with columnar proj ections 58 extending a short distance from the plate surface. The nozzle plate could also be patterned with other surface formations such as closely spaced ridges, corrugations or bumps. However, it is easy to create a suitable UV mask for the pattern columnar projections shown, and it is a simple matter to etch the columns into the exterior surface.
By reducing the co-efficient of static friction, there is less likelihood that paper dust or other contaminants will clog the nozzles in the nozzle plate. Patterning the exterior of the nozzle plate with raised formations limits the surface area that dust particles contact. If the particles can only contact the outer extremities of each formation, the friction between the particles and the nozzle plate is minimal so attachment is much less likely. If the particles do attach, they are more likely to be removed by printhead maintenance cycles.
Inlet Priming Feature Referring to Figure 47, two unit cells are shown extending in opposite directions to each other. The ink inlet passage 15 supplies ink to the four chambers 38 via the lateral ink conduit 23.
Distributing ink through micron-scale conduits, such as the ink inlet 15, to individual MEMS nozzles in an inkjet printhead is complicated by factors that do not arise in macro-scale flow. A meniscus can form and, depending on the geometry of the aperture, it can 'pin' itself to the lip of the aperture quite strongly. This can be useful in printheads, such as bleed holes that vent trapped air bubbles but retain the ink, but it can also be problematic if stops ink flow to some chambers.
This will most likely occur when initially priming the printhead with ink. If the ink meniscus pins at the ink inlet opening, the chambers supplied by that inlet will stay unprimed.
To guard against this, two priming features 18 are formed so that they extend through the plane of the inlet aperture 15. The priming features 18 are columns extending from the interior of the nozzle plate (not shown) to the periphery of the inlet 15. A part of each column 18 is within the periphery so that the surface tension of an ink meniscus at the ink inlet will form at the priming features 18 so as to draw the ink out of the inlet. This 'unpins' the meniscus from that section of the periphery and the flow toward the ink chambers. The priming features 18 can take many forms, as long as they present a surface that extends transverse to the plane of the aperture. Furthermore, the priming feature can be an integral part of other nozzles features as shown in Figure 54.
Side Entry Ink Chamber
Referring to Figure 48, several adjacent unit cells are shown. In this embodiment, the elongate heater elements 29 extend parallel to the ink distribution conduit 23. Accordingly, the elongate ink chambers 38 are likewise aligned with the ink conduit 23. Sidewall openings 60 connect the chambers 38 to the ink conduit 23. Configuring the ink chambers so that they have side inlets reduces the ink refill times. The inlets are wider and therefore refill flow rates are higher. The sidewall openings 60 have ink permeable structures 34 to keep fluidic cross talk to an acceptable level.
Inlet Filter for Ink Chamber Referring again to Figure 47, the ink refill opening to each chamber 38 has a filter structure 40 to trap air bubbles or other contaminants. Air bubbles and solid contaminants in ink are detrimental to the MEMS nozzle structures. The solid contaminants can obvious clog the nozzle openings, while air bubbles, being highly compressible, can absorb the pressure pulse from the actuator if they get trapped in the ink chamber. This effectively disables the ejection of ink from the affected nozzle. By providing a filter structure 40 in the form of rows of obstructions extending transverse to the flow direction through the opening, each row being spaced such that they are out of registration with the obstructions in an adjacent row with respect to the flow direction, the contaminants are not likely to enter the chamber 38 while the ink refill flow rate is not overly retarded. The rows are offset with respect to each other and the induced turbulence has minimal effect on the nozzle refill rate but the air bubbles or other contaminants follow a relatively tortuous flow path which increases the chance of them being retained by the obstructions 40. The embodiment shown uses two rows of obstructions 40 in the form of columns extending between the wafer substrate and the nozzle plate. Intercolour Surface Barriers in Multi Colour InkJet Printhead Turning now to Figure 51, the exterior surface of the nozzle 56 is shown for a unit cell such as that shown in Figure 46 described above. The nozzle apertures 26 are positioned directly above the heater elements (not shown) and a series of square-edged ink gutters 44 are formed in the nozzle plate 56 above the ink conduit 23 (see Figure 46). InkJet printers often have maintenance stations that cap the printhead when it's not in use. To remove excess ink from the nozzle plate, the capper can be disengaged so that it peels off the exterior surface of the nozzle plate. This promotes the formation of a meniscus between the capper surface and the exterior of the nozzle plate. Using contact angle hysteresis, which relates to the angle that the surface tension in the meniscus contacts the surface (for more detail, see the Applicant's co-pending USSN (our docket FND007US) incorporated herein by reference), the majority of ink wetting the exterior of the nozzle plate can be collected and drawn along by the meniscus between the capper and nozzle plate. The ink is conveniently deposited as a large bead at the point where the capper fully disengages from the nozzle plate. Unfortunately, some ink remains on the nozzle plate. If the printhead is a multi-colour printhead, the residual ink left in or around a given nozzle aperture, may be a different colour than that ejected by the nozzle because the meniscus draws ink over the whole surface of the nozzle plate. The contamination of ink in one nozzle by ink from another nozzle can create visible artefacts in the print. Gutter formations 44 running transverse to the direction that the capper is peeled away from the nozzle plate will remove and retain some of the ink in the meniscus. While the gutters do not collect all the ink in the meniscus, they do significantly reduce the level of nozzle contamination of with different coloured ink. Bubble Trap
Air bubbles entrained in the ink are very bad for printhead operation. Air, or rather gas in general, is highly compressible and can absorb the pressure pulse from the actuator. If a trapped bubble simply compresses in response to the actuator, ink will not eject from the nozzle. Trapped bubbles can be purged from the printhead with a forced flow of ink, but the purged ink needs blotting and the forced flow could well introduce fresh bubbles.
The embodiment shown in Figure 46 has a bubble trap at the ink inlet 15. The trap is formed by a bubble retention structure 32 and a vent 36 formed in the roof layer. The bubble retention structure is a series of columns 32 spaced around the periphery of the inlet 15. As discussed above, the ink priming features 18 have a dual purpose and conveniently form part of the bubble retaining structure. In use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere. By trapping the bubbles at the ink inlets and directing them to a small vent, they are effectively removed from the ink flow without any ink leakage.
Multiple Ink Inlet Flow Paths
Supplying ink to the nozzles via conduits extending from one side of the wafer to the other allows more of the wafer area (on the ink ejection side) to have nozzles instead of complex ink distribution systems. However, deep etched, micron-scale holes through a wafer are prone to clogging from contaminants or air bubbles. This starves the nozzle(s) supplied by the affected inlet. As best shown in Figure 48, printheads according to the present invention have at least two ink inlets 15 supplying each chamber 38 via an ink conduit 23 between the nozzle plate and underlying wafer.
Introducing an ink conduit 23 that supplies several of the chambers 38, and is in itself supplied by several ink inlets 15, reduces the chance that nozzles will be starved of ink by inlet clogging. If one inlet 15 is clogged, the ink conduit will draw more ink from the other inlets in the wafer. Droplet Stem Anchors The droplet stem that attaches the ejected ink to the ink in the chamber immediately prior to drop separation, can be a cause of drop misdirection. Figures 55 to 59 show sequential stages of the drop ejection process from a nozzle. In Figure 55, the heater element 29 is rapidly heated and vaporises the ink 64 in immediate contact with its surface to nucleate a bubble 66. This causes the ink meniscus 68 across the nozzle aperture 26 to start bulging outwardly. In Figure 56, the bubble 66 continues to grow as the heater element 29 vaporises more of the ink 64 in the chamber 38. This pressure pulse from the growing bubble pushes the ink meniscus further out of the nozzle aperture 26. In Figure 57, the bubble 66 continues to grow and the ejected ink starts to become a bulb 70 connected to the ink 64 in the chamber 38 by a relatively thick droplet stem 72.
In Figure 58, the bubble has grown to the point where it vents to atmosphere through the nozzle aperture 26. This is an important mechanism for avoiding cavitation corrosion of the heater element 29. Cavitation corrosion occurs when a bubble collapses back to a single point on the heater element surface. As the bubble reaches the singularity of a collapse point, the surface tension creates severe hydraulic forces that can abrade the heater material. By venting the bubble, there is no collapse point on the heater element.
As shown in Figure 58, when the bubble vents, the droplet stem 72 can attach itself to a point 74 on the nozzle rim. As the attachment point 74 is not on the centre- line 76 of the nozzle aperture 26, the ink bulb 70 is deflected 78 away from the centre-line because of the surface tension's tendency to reduce surface area.
Referring to Figure 59, the stem 52 eventually breaks and the ink drop 80 forms and continues on its trajectory to the print media. However, the misdirection 78 remains for the ink drop 80 as well as any satellite drops 82. The vented bubble has become an extended ink meniscus that helps to draw ink back into the chamber as it contracts to the nozzle aperture 26.
Figures 60 - 67 show nozzle designs with droplet stem anchors that positively locate where the droplet stem attaches. Knowing where the stem will attach reduces the misdirection, or in some cases, controls the misdirection so that all nozzles are misdirected in the same direction by roughly the same amount. However, the droplet stem anchors can also perform secondary functions and these will now be discussed below.
Combining Ink Ejected from Adjacent Actuators
Referring to Figures 60 and 61, the nozzle design shown has two actuators 29 ejecting ink through a single oval shaped nozzle 25. The actuators are both heater elements connected in series for simultaneous actuation and ejection. Both actuators 29 are part of a single beam of heater material such as TiAlN which is suspended at its ends and at it mid point. Both heater elements 29 have a tapered section 86 where electrical resistance is at a maximum. During actuation, the vapour bubbles initiate at these maximum resistance sections or 'hotspots' 86.
The ink covering both heater elements 29 is connected by the slots 88. The slots can be dimensioned so that they damp fiuidic cross talk to the extent that the heater elements are in two separate ink chambers, or they can be large enough to that both elements 29 are considered to be in the same chamber 38.
The heater elements 29 are positioned relative to the droplet stem anchor 84 so that as the ink ejected by each actuator forms a bulb attached by a stem, the ink surface tension, seeking to occupy the least surface area, will attach the stem to the anchor in preference to any other point on the nozzle rim 25. As the hotspots 86 are on diametrically opposed sides of the anchor 84, the bulbs of ink attached to respective droplet stems will be misdirected toward each other. Eventually they meet directly above the anchor and the opposing misdirections cancel each other out, or at least, the resultant misdirection is very small. Quadrupolar Actuation
Figures 62 - 65 show several embodiments of nozzles with quadrupolar actuation. Quadrupolar actuation initiates the pressure pulse at positions in the ink chamber that are symmetrical about two orthogonal axes. As the pulses converge within the chamber, the symmetry about two axes pushes the ink in a direction that is normal to both axes, at least in the ideal case. In reality, slight asymmetries mean the drop direction may be not be exactly normal, but it will typically be much closer than if the pressure pulse initiated from a single point in the chamber. Referring to Figure 62, the unit cell shows two nozzles 25 in respective chambers 38, each having a quadrupole thermal actuator 12. The heater element portion 29 of each actuator 12 is shaped similar to the Greek letter 'theta' . Each actuator has two semi-circular current paths 90 between the contacts 28. A central bar 94 extends between the mid points of each current path. The entire theta-shaped structure is suspended in the chamber 38 to minimise heat dissipation into the wafer substrate and maximise heater transfer to the ink.
The central bar 94 serves multiple purposes. Firstly, it provides the heater element with structural rigidity and bracing. Without it, the cyclical heating and cooling of the semi-circular current paths would cause some buckling into or out of the page of Figure 62. This could be addressed by supporting the semi-circles on the chamber floor, or even by a single support at each mid-point. However, this increases contact with the underlying wafer substrate and therefore increases heat dissipation. The central bar 94 provides resistance to buckling while keeping the heater element suspended within the chamber.
The central bar 94 also provides a 'cold spot' 92 at the mid-point of each semi-circle. The thermal mass of the bar provides a small heat sink so the junction between the bar and the semi-circular current path heats to bubble nucleation temperature more slowly than the sections either side of the junction. Likewise, the contacts 28 act as heat sinks so bubble nucleation is directed to the middle of the arc between the contact and the junction with the central car 94. This ensures that the vapour bubbles nucleate at four positions on the theta shape and that these positions have quadrupole symmetry about two orthogonal axes. Finally, the central bar also provides a droplet stem anchor for additional control of misdirection. If the position of the central bar 94 below the nozzle 25 is such that the area of the surface tension is minimised if the droplet stem attaches to the bar instead of a point on the nozzle 25, then the drop trajectory will be more closely aligned with the central axis extending normal to the nozzle aperture 26. In Figure 63 and 64, the central bar 94 has a latch point 96 for locating the base of the droplet stem. The latch point is simply a surface irregularity that the surface tension of the ink can 'pin' itself to. If the central bar 94 is not parallel to the plane of the nozzle aperture 26, or there is some asymmetry in the position of the bubble nucleation sites, the droplet stem may latch to an off centre part of the centre bar 94. A surface irregularity 96 on the central bar 94 tends to snag on the surface tension of the droplet stem and anchor it to the middle of the bar. The surface irregularity 96 can be a sudden reduction in cross section as shown in Figure 63, or a boss such as that shown in Figure 64. In either case, the droplet stem originates from the middle of the central bar 94 and so any misdirection in the drop trajectory is minimised. Dual Bar. Four Kink, Heater Element
Figure 65 shows another quadrupole thermal actuator 12. Again it has two current paths 90 provided by separate beams extending between the contacts 28. For clarity, the other features of the unit cell have been omitted.
The beams 90 are suspended in the chamber 38 to minimise heat dissipation into the wafer substrate and each beam has two tight radius curves or kinks 98, between curves of larger radius 96. In this embodiment, the tight radius kinks 98 act as hotspots where the vapour bubbles nucleate. This is because the current flow around the kinks 98 will concentrate towards the radially inner side of the element 102 and away from the outside radius 100. This acts like a localised reduction in cross section which increases the resistance at these points. In the large radius curves 96, the difference in current density between the inside edge and the outside edge is much less so the increase in resistance is small compared to that in the tight kinks 98.
The tight kinks 98 have a relatively low bending resistance so the longitudinal expansion of the beam 90 during actuation is accommodated without buckling inot or out of the plane of the page. This makes the position of the hotspots in the chamber 38 relatively stable thereby maintaining the quadrupole symmetry and minimising drop misdirection.
Rectifying Valve at Ink Chamber Inlet
The unit cell shown in Figure 66 has a rectifying valve 106 at the ink refill aperture 104 to each chamber 38. The particular rectifying valve shown is known as a Tesla valve. A rectifying valve provides less hydraulic resistance to ink flowing into the chamber 38 than ink flowing out of the chamber. This can be used to reduce fluidic cross talk between chambers 38, while not retarding ink refill times ( and therefore print speeds).
For the purposes of this example, the heater element 29 is a simple beam suspended in the chamber 38 between the contacts 28. Also for clarity, the nozzle rim has been omitted, however the skilled worker will appreciate that it is centrally disposed over the heater element 29. Alternatively, the chambers 38 could have several nozzles each, as discussed above. The chambers 38 are supplied with ink from the ink inlet 15 via the lateral ink conduit 23. The Tesla valve 106 at each refill aperture 104 has a main conduit 108 between a pair of smaller secondary conduits 110. As ink flows into the chamber 38, there is little resistance to the flow through the main conduit 108 other than fiuidic drag against the walls of the conduit itself. The upstream openings of the secondary conduits 110 do not face into the flow so little of the main flow is diverted into them. The downstream openings direct any flow parallel and adjacent to the flow from the main conduit 108 downstream opening. Therefore, the secondary conduits 110 have negligible impact on ink flow into the chamber 38.
Upon actuation, the pressure pulse can create a back flow of ink out of the chamber 38 and back into the lateral ink conduit 23. Back flow is detrimental to drop ejection as it uses some of the energy from the pressure pulse. The back flow can also create fiuidic cross talk that affects the ejection characteristics of adjacent chambers.
The Tesla valve 106 resists any back flow by using flow from the secondary conduits 110 to constrict flow through the main conduit 108. During back flow, the upstream openings of the secondary conduits 110 are facing the flow direction. So to is the upstream opening to the main conduit 108. The pressure pulse forces ink along the main and secondary conduits however, the downstream openings of the secondary conduits 110 direct their ink flow across and counter to the main flow direction. These conflicting flows create turbulence and a hydraulic constriction in the main conduit 108. Hence back flow through the main conduit 108 and the secondary conduits 110 is stifled. With a high resistance to back flow, a greater portion of the pressure pulse is used to eject the ink drop through the nozzle and fiuidic cross talk is reduced.
Controlled Drop Misdirection
Figure 67 is a schematic perspective of a nozzle with controlled drop misdirection. This is a different approach to minimising the drop misdirection as discussed above. By intentionally misdirecting the drops ejected by every nozzle in the array by a controlled amount, the printed image is equivalent to one from a minimised drop misdirection printhead (albeit slightly offset from the nozzle array).
As with minimising drop misdirection, this approach uses a droplet stem anchor 74 is positioned so that the droplet stem will attach to it in preference to any other point on the nozzle rim 25 or heater element 29. However, in nozzle designs that do not allow the drop to form symmetrically around the droplet stem anchor, so the drop trajectory is not normal to the plane of the nozzle aperture, the anchor can be positioned at a point that will cause a known misdirection that is the same magnitude and direction as every other nozzle in the array.
The embodiment shown in Figure 67 provides a droplet stem anchor at the end of a lateral spur 112 extending into the nozzle aperture 26 from the side of the nozzle rim 25. This nozzles uses a simple suspended beam heater element 29 which is easier to deposit and etch than a theta heater (described above), but still controls drop misdirection with a droplet stem anchor. It will be appreciated that the spur 112 is an obstruction that deflects the drop from the normal trajectory. However, if all the spurs in the nozzle array are parallel and have the same position relative to the heater element, the misdirection across the whole array will be uniform.
Although the invention is described above with reference to specific embodiments, it will be understood by those skilled in the art that the invention may be embodied in many other forms.

Claims

1. An inkj et printhead comprising: an array of ink chambers, each having a nozzle, an elongate actuator for ejecting ink through the nozzle; wherein, the nozzle has an elongate shape with its long dimension aligned with that of the elongate actuator.
2. An inkjet printhead according to claim 1 wherein the nozzle is elliptical.
3. An inkjet printhead according to claim 1 wherein the actuator is a thermal actuator with an elongate heater element that generate a vapour bubble to eject in through the nozzle.
4. An inkjet printhead according to claim 1 wherein each ink chamber in the array has a plurality of elongate nozzles aligned with the elongate actuator.
5. An inkjet printhead according to claim 1 wherein each ink chamber in the array has a plurality of elongate nozzles corresponding to a plurality of elongate actuators respectively.
6. An inkjet printhead according to claim 1 further comprising drive circuitry for providing actuator drive signals via a pair of electrodes for each actuator respectively, wherein the actuators are thermal actuators, each having an elongate heater element extending between two contacts on the pair of electrodes wherein the thermal actuators are all unitary planar structures.
7. An inkjet printhead according to claim 6 wherein a trench etched into the drive circuitry extends between the electrodes.
8. An inkjet printhead according to claim 1 wherein each of the ink chambers have a plurality of nozzles; wherein during use, the actuator simultaneously ej ects ink through all the nozzles of the chamber.
9. An inkjet printhead according to claim 8 wherein each of the ink chambers have two nozzles.
10. An inkjet printhead according to claim 8 wherein the nozzles in each chamber are arranged in a line parallel to the length of the heater element with the central axes of the nozzles are regularly spaced along the heater element.
11. An inkjet printhead according to claim 8 wherein the nozzles are elliptical.
12. An inkjet printhead according to claim 11 wherein the major axes of the elliptical nozzles are aligned.
13. An inkjet printhead according to claim 5 wherein the drive circuitry has a drive field effect transistor (FET) for each of the thermal actuators, the drive voltage of the drive FET being less than 5 Volts.
14. An inkjet printhead according to claim 13 wherein the drive voltage of the drive FET is 2.5 Volts.
15. An inkjet printhead according to claim 3 further comprising an ink conduit between the nozzle plate and the underlying wafer, the ink conduit being in fluid communication with the openings of a plurality of the ink chambers.
16. An inkj et printhead according to claim 15 further comprising a plurality of ink inlets defined in the wafer substrate; wherein, each of the ink conduits is in fluid communication with at least one of the ink inlets for receiving ink to supply to the ink chambers.
17. An inkjet printhead according to claim 16 wherein each of the ink conduits is in fluid communication with two of the ink inlets.
18. An inkj et printhead according to claim 15 wherein each of the ink inlets has an ink permeable trap and a vent sized so that the surface tension of an ink meniscus across the vent prevents ink leakage; wherein during use, the ink permeable trap directs gas bubbles to the vent where they vent to atmosphere.
19. An inkjet printhead according to claim 15 wherein the ink chambers have an elongate shape such that two of the sidewalls are long relative to the others, and the opening for allowing ink to refill the chamber is in one of the long sidewalls.
20. An inkjet printhead according to claim 1 wherein the nozzles are arranged in rows such that the nozzle centres are coUinear and the nozzle pitch along each row is greater than 1000 nozzles per inch.
PCT/AU2005/001564 2005-10-10 2005-10-10 Printhead with elongate nozzles WO2007041747A1 (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
AU2005337419A AU2005337419B2 (en) 2005-10-10 2005-10-10 Printhead with elongate nozzles
PCT/AU2005/001564 WO2007041747A1 (en) 2005-10-10 2005-10-10 Printhead with elongate nozzles
KR1020087011268A KR101019281B1 (en) 2005-10-10 2005-10-10 Printhead with elongate nozzles
EP05791455.8A EP1945458B1 (en) 2005-10-10 2005-10-10 Printhead with elongate nozzles
JP2008534809A JP4709285B2 (en) 2005-10-10 2005-10-10 Print head with elongated nozzle

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/AU2005/001564 WO2007041747A1 (en) 2005-10-10 2005-10-10 Printhead with elongate nozzles

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WO2007041747A1 true WO2007041747A1 (en) 2007-04-19

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EP (1) EP1945458B1 (en)
JP (1) JP4709285B2 (en)
KR (1) KR101019281B1 (en)
AU (1) AU2005337419B2 (en)
WO (1) WO2007041747A1 (en)

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Also Published As

Publication number Publication date
EP1945458A4 (en) 2011-03-30
JP2009511294A (en) 2009-03-19
AU2005337419A1 (en) 2007-04-19
EP1945458A1 (en) 2008-07-23
AU2005337419B2 (en) 2009-12-10
KR20080061396A (en) 2008-07-02
EP1945458B1 (en) 2014-07-16
JP4709285B2 (en) 2011-06-22
KR101019281B1 (en) 2011-03-07

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