Patent Grant
7661800
The following applications have been filed by the Applicant simultaneously with the present application:
The disclosures of these co-pending applications are incorporated herein by reference.
Various methods, systems and apparatus relating to the present invention are disclosed in the following U.S. Patents/Patent Applications filed by the applicant or assignee of the present invention:
The disclosures of these applications and patents are incorporated herein by reference.
The present invention relates to the field of micro-electromechanical systems (MEMS) devices and discloses an inkjet printing system using MEMS techniques.
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 U.S. Pat. No. 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.
One of the perennial problems with inkjet printing is the control of drop trajectory as it is ejected from the 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.
Accordingly, the present invention provides an inkjet printhead comprising:
Nucleating a plurality of bubbles within each chamber is an effective way to shape the pressure pulse in a way that offers better control of drop trajectory. The heat generated by several heater elements would normally heat the wafer substrate so much that unintentional ink boiling would become an issue. By suspending the heater elements within the chamber interior they are immersed in the ink and much more thermally isolated from the wafer substrate. This addresses the excess heat generation problem but the suspended heater elements can buckle and bend with use. This changes their relative positioning and therefore alters the shape of the pressure pulse they generate. This affects the direction of the ejected drop. A cross bracing structure between the heater elements maintains the spacing between the heater elements and preserves the shape of the pressure pulse.
Preferably, the heater elements nucleate their respective bubbles simultaneously with every activation of the actuator. In a further preferred form, 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. In some forms, the bubble nucleation sections are between sections of the current path with greater thermal inertia. Preferably, 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.
In a specific embodiment, 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. Preferably, the thermal elements and the contacts are formed from TiAlN.
In a first aspect the present invention provides an inkjet printhead comprising:
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,
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,
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,
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 second aspect the present invention provides an inkjet printhead comprising:
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,
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,
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:
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,
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,
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,
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:
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,
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,
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,
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,
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,
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:
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,
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:
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,
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:
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,
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,
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,
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, infra-red 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.
Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
In the description than follows, corresponding reference numerals relate to corresponding parts. For convenience, the features indicated by each reference numeral are listed below.
MEMS Manufacturing Process
The MEMS manufacturing process builds up nozzle structures on a silicon wafer after the completion of CMOS 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 M1, 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.
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
In the next step (
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
After exposure of the SAC1 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.
Referring to
This etch is defined by a layer of photoresist (not shown) exposed using the dark tone mask shown in
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
Referring to
In the first etch step (
In the second etch step (
In 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 SAC1 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
As shown in
Referring to
Referring to
Referring to
With all the MEMS nozzle features now fully formed, the next stage removes the SAC1 and SAC2 photoresist layers 10 and 16 by O2 plasma ashing (
Referring to
Finally, and referring to
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
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
Turning now to
As discussed above, the Applicant has found that reflowing 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
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 TiAlN 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
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
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
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
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
Multiple Chambers and Multiple Nozzles for each Drive Circuit
In
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
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.
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
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
Side Entry Ink Chamber
Referring to
Inlet Filter for Ink Chamber
Referring again to
Intercolour Surface Barriers in Multi Colour Inkjet Printhead
Turning now to
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
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
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.
In
In
As shown in
Referring to
Combining Ink Ejected from Adjacent Actuators
Referring to
The ink covering both heater elements 29 is connected by the slots 88. The slots can be dimensioned so that they damp fluidic 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
Referring to
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
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
Dual Bar, Four Kink, Heater Element
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
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 fluidic 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 fluidic 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 fluidic cross talk is reduced.
Controlled Drop Misdirection
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
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.
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