Hot bending actuator with improved lifespan

Abstract

A thermal bending actuator includes: a thermoplastic beam for connection to a drive circuit system; and a passive beam mechanically cooperating with the thermoplastic beam such that when an electric current passes through the thermoplastic beam, the thermoplastic beam expands relative to the passive beam, thereby causing the actuator to bend. The thermoplastic beam comprises an aluminum alloy. The aluminum alloy comprises: a first metal being aluminum, a second metal, and at least 0.1 at.% of a third metal selected from the group consisting of copper, scandium, tungsten, molybdenum, chromium, titanium, silicon, and magnesium.

Description

Invention Field

[0001] This invention relates to MEMS thermal bending actuators, such as those configured for use in inkjet printheads. The invention was primarily developed to improve the lifespan of thermal bending actuators while maintaining optimal efficiency. Background of the Invention

[0002] The applicant has developed a series of Memjet products as described in, for example, WO 2011 / 143700, WO 2011 / 143699 and WO 2009 / 089567. ® The contents of these three patent applications concerning inkjet printers are incorporated herein by reference. Memjet ® The printer uses a fixed-page-width printhead integrated with a feed mechanism that feeds the print media through the printhead in a single pass. Therefore, Memjet... ® The printer offers significantly higher printing speeds than traditional scanning inkjet printers.

[0003] Inkjet printheads comprise multiple (typically thousands) individual inkjet nozzle assemblies, each supplied with ink. Each nozzle assembly typically includes a nozzle chamber with a nozzle orifice and an actuator for ejecting ink through the orifice. The design space for inkjet nozzle assemblies is vast, with numerous different nozzle assemblies described in patent literature, encompassing various types of actuators and configurations. Inkjet nozzle assemblies used in commercial printheads typically employ thermal bubble forming actuators or piezoelectric actuators. Thermal bubble forming inkjet actuators offer advantages such as low cost, high nozzle density, and the ability to be manufactured using MEMS processes; piezoelectric inkjet actuators, on the other hand, offer compatibility with a wide variety of inks, including non-aqueous and high-viscosity inks.

[0004] While inkjet printing technology has achieved significant commercial success over the past few decades, there remains a need for novel inkjet technologies that can potentially combine the advantages of thermal bubble formation and piezoelectric technologies. The applicant continues research related to such novel inkjet technologies, focusing on developing MEMS thermal bending actuators as a potential new tool for inkjet actuation. The thermal bending actuator utilizes a thermoplastic layer that mechanically cooperates with a passive layer to provide bending motion through thermal expansion of the thermoplastic layer relative to the passive layer. As extensively described in many of the applicant's previous patents, the thermally actuated bending motion of a paddle can be used to provide the necessary mechanical pulses for droplet ejection.

[0005] For example, US 6,623,101 (the contents of which are incorporated herein by reference) describes an inkjet nozzle assembly including a nozzle chamber having a movable top plate defining a nozzle opening. The top plate is connected via an arm to a thermoplastic actuator positioned outside the nozzle chamber, the thermoplastic actuator having an upper thermoplastic beam and a lower passive beam. When an electric current passes through the thermoplastic beam, the movable top plate bends toward the bottom plate of the nozzle chamber, thereby acting as a paddle to increase the pressure within the nozzle chamber and eject ink droplets through the nozzle opening.

[0006] US 7,794,056 (the contents of which are incorporated herein by reference) describes an inkjet nozzle device in which a movable top plate portion of the nozzle chamber incorporates a thermal bending actuator. By incorporating the thermal bending actuator into the movable top plate, greater efficiency is achieved in terms of the energy required for droplet ejection.

[0007] The choice of material for the thermoplastic layer in a hot bending actuator is crucial for both efficiency and lifespan. For example, US 6,428,133 describes the use of TiB2, MoSi2, and TiAlN as suitable thermoplastic materials. More recently, US 7,984,973 (the contents of which are incorporated herein by reference) describes the use of aluminum alloys as thermoplastic materials. Aluminum alloys (such as VAl) offer advantages such as excellent thermoplastic efficiency and the ability to be manufactured using deposition processes available in many plants.

[0008] However, in order for hot bending technology to compete with existing piezoelectric technologies, it needs to have a comparable lifespan and minimize device failures after billions of inkjet cycles. Accordingly, it is desirable to provide a thermoplastic material suitable for use in inkjet nozzle devices, which has an improved lifespan and excellent thermoplastic efficiency compared to known thermoplastic materials. Invention Overview

[0009] In a first aspect, a hot bending actuator is provided, the hot bending actuator comprising:

[0010] A thermoplastic beam for connection to a drive circuit system; and

[0011] A passive beam, which mechanically cooperates with a thermoplastic beam, causes the thermoplastic beam to expand relative to the passive beam when an electric current passes through it, thereby causing the actuator to bend.

[0012] The thermoplastic beam comprises an aluminum alloy, which includes: a first metal, which is aluminum; a second metal; and at least 0.1 at.% of a third metal selected from the group consisting of copper, scandium, tungsten, molybdenum, chromium, titanium, silicon, and magnesium.

[0013] Advantageously, the hot bending actuator according to the first aspect exhibits superior lifespan compared to hot bending actuators that include aluminum alloys but not the third metal. Without wishing to be bound by theory, the inventors understand that the addition of the third metal suppresses electromigration in the thermoplastic beam. This suppression of electromigration is believed to be the reason for the observed significant improvement in lifespan. In addition to copper, metals such as scandium, tungsten, molybdenum, chromium, titanium, and magnesium are also expected to provide comparable lifespan improvements based on their ability to suppress electromigration.

[0014] To avoid any doubt, the first metal, the second metal, and the third metal are not the same as each other.

[0015] Preferably, the second metal is selected from the group consisting of vanadium, titanium, chromium, manganese, cobalt, nickel, and scandium.

[0016] For the avoidance of doubt, the second metal may include one or more of the metals listed above. Similarly, the third metal may include one or more of the metals listed above.

[0017] Preferably, the second metal is vanadium and the third metal is copper.

[0018] Preferably, the amount of aluminum is in the range of 80 to 95 at.%; the amount of the second metal is in the range of 2 to 18 at.%; and the amount of the third metal is in the range of 0.1 to 5 at.%.

[0019] Preferably, the aluminum alloy comprises aluminum, vanadium, and copper. In some embodiments, the aluminum alloy is substantially composed of aluminum, vanadium, and copper, as these three elements constitute at least 90% or at least 95% of the alloy.

[0020] Preferably, the aluminum alloy contains aluminum in an amount ranging from 80 to 95 at.%, or more preferably from 85 to 95 at.%.

[0021] Preferably, the aluminum alloy contains vanadium in the range of 2 to 18 at.%, or preferably in the range of 3 to 15 at.%, or preferably in the range of 7 to 13 at.%. Typically, the amount of vanadium present is at least 5 at.%.

[0022] Preferably, the aluminum alloy contains copper in an amount ranging from 0.1 to 5 at.%, or preferably from 0.15 to 3 at.%, or preferably from 0.2 to 1 at.%. Typically, the amount of copper present is at least 0.1 at.% or at least 0.2 at.%.

[0023] The passive beam can be multi-layered or single-layered. For example, the passive beam may include a first layer and a second layer, each layer comprising a different material (e.g., the first layer comprising silicon nitride and the second layer comprising silicon oxide, as described in US 8,079,668, the contents of which are incorporated herein by reference). Alternatively, the passive layer may be a single-layered material.

[0024] Preferably, the passive beam comprises at least one material selected from the group consisting of silicon oxide and silicon nitride.

[0025] Preferably, the thermoplastic beam is fused or bonded to the passive beam. Typically, the thermoplastic beam material is directly deposited onto the passive beam using MEMS deposition processes (such as CVD, PECVD, etc.).

[0026] Preferably, the passive beam is cantilevered, having a free end and an opposite end connected to a support.

[0027] Preferably, the thermoplastic beam is connected to a pair of electrical terminals located at one end of the passive beam, typically at the anchoring end connected to the support.

[0028] Preferably, the thermoplastic beam includes a plurality of legs interconnected by one or more bends. For example, the thermoplastic beam may have a first leg extending longitudinally from a first electrical terminal and a second leg extending longitudinally and parallel to a second electrical terminal, the first leg and the second leg being connected by a single bend away from the electrical terminal. Alternatively, the thermoplastic beam may have a serpentine configuration, for example, having four parallel legs interconnected by three bends. These and other configurations of the thermoplastic beam will be apparent to those skilled in the art.

[0029] In a second aspect, an inkjet nozzle device is provided, the inkjet nozzle device comprising:

[0030] A nozzle chamber having a nozzle opening and an ink inlet; and

[0031] The thermal bending actuator as described above.

[0032] Preferably, the nozzle chamber includes a base plate and a top plate having a movable portion (e.g., in the form of a paddle), thereby actuating an actuator to move the movable portion toward the base plate.

[0033] Preferably, the moving part includes an actuator.

[0034] Preferably, the nozzle opening is defined in the movable portion, such that the nozzle opening is movable relative to the base plate. Alternatively, the nozzle opening may be defined in the fixed portion of the top plate.

[0035] In some embodiments, the top plate of the nozzle chamber may include a plurality of thermal bending actuators for ejecting ink through the nozzle opening. For example, opposing thermal bending actuators on either side of a nozzle opening may be used to generate increased mechanical pulses for droplet ejection.

[0036] In a third aspect, an inkjet printhead is provided that includes a plurality of inkjet nozzles as described above.

[0037] As used herein, the term "ink" refers to any jettable fluid and may include, for example, conventional CMYK inks (e.g., pigment- and dye-based inks), infrared inks, UV-curable inks, fixatives, 3D printing fluids, polymers, biofluids, functional fluids (e.g., sensing inks, solar inks), etc.

[0038] For the avoidance of doubt, the term "at.%" refers to the amount of metal in an alloy based on the relative atomic number (or molar). For example, an alloy containing V (9.8 at.%), Al (89.9 at.%), and Cu (0.3 at.%) is equivalent to V (17 wt.%), Al (82.5 wt.%), and Cu (0.5 wt.%), as will be readily understood by those skilled in the art. Attached Figure Description

[0039] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0040] Figure 1 It is a schematic plan view of an inkjet nozzle assembly including a thermal bending actuator;

[0041] Figure 2 It is along Figure 1 The cross-section of line 2-2 of the inkjet nozzle assembly shown; and

[0042] Figure 3 It includes multiple Figure 1 A perspective view of a portion of the inkjet printhead of the inkjet nozzle assembly shown. Detailed Implementation

[0043] refer to Figure 1 and Figure 2 The image illustrates an inkjet nozzle assembly 1 according to an embodiment of the invention, which incorporates a pair of opposing thermal bending actuators 3. Methods for manufacturing are described in the applicant's US 2008 / 0309728 and US 2008 / 0225077. Figure 1 and Figure 2 Suitable MEMS processes for nozzle devices of the type shown are described in these two patent applications, the contents of which are incorporated herein by reference.

[0044] The inkjet nozzle assembly 1 is fabricated on a passivation layer 5 of a silicon substrate 7, the passivation layer having a drive circuitry layer 8 for delivering current pulses to a thermally bent actuator 3. The inkjet nozzle assembly 1 includes a nozzle chamber 9 having a nozzle opening 10, a top plate 11, and sidewalls 13 extending between the top plate and the silicon substrate 7. A covering silicon oxide layer 15 deposited on the passivation layer 5 defines the sidewalls 13 of the nozzle chamber. Electrical connector posts 17 (e.g., copper posts), formed by a damascene process as described in US 7,819,503 (the contents of which are incorporated herein by reference), extend through the silicon oxide layer 15 to form an electrical connection to the drive circuitry layer 8 of the silicon substrate 7. Figure 1 As shown, a pair of connector posts 17 (power and ground) are provided at the anchoring end of each overhanging thermal bending actuator 3.

[0045] Each of these hot bending actuators 3 includes a lower passive beam 20 and an upper thermoplastic (“active”) beam 22. Each passive beam 20 is formed by depositing a suitable passive material onto a sacrificial support (not shown), such that the passive beam at least partially defines the top plate 11 of the nozzle chamber 9. Figure 2 In the illustrated embodiment, each passive beam 20 is only a single layer of silicon oxide, but it should be understood that multilayer passive beams as described in US 8,079,668 are within the scope of this invention.

[0046] Each thermoplastic beam 22 is formed by depositing thermoplastic material onto both the passive beam 20 and the exposed upper surface of the connector post 17, thereby creating an electrical connection with the drive circuitry layer 8. The thermoplastic beams 22 are defined by etching the thermoplastic material, each configured as a pair of parallel legs 24 extending from corresponding power and ground terminals 26 (defined by the upper surface of the connector post 17) toward the nozzle opening 10 and interconnected at their respective distal ends by bends 28. The thermoplastic material is typically a vanadium-aluminum-copper alloy, as will be described in more detail below.

[0047] Therefore, as will be understood from the above, each hot bending actuator 3 takes the form of an overhanging paddle, thus forming the moving portion of the top plate 11 of the nozzle chamber 9. During actuation, the thermoplastic beam 22 of each hot bending actuator 3 receives an electrical signal from the drive circuit system 8, which causes the thermoplastic beam to expand relative to the passive beam 20, thereby causing each hot bending actuator to move along the arrow... AThe indicated direction bends downward toward the silicon substrate 7. This bending motion increases the pressure inside the nozzle chamber 9, causing ink droplets to be ejected through the nozzle opening 10. The circular nozzle opening 10 has a semi-circular portion defined in each of these thermal bending actuators 3, allowing the nozzle to move during actuation. After droplet ejection, ink is replenished into the nozzle chamber through a pair of ink inlets 32, which receive ink from ink supply channels (not shown) defined in the silicon substrate.

[0048] like Figure 2 As shown, a polymer layer 30 (e.g., a polyimide layer) is stacked across the entire structure (including the exposed portion of the passive beam and the thermoplastic beam) to protect the thermally bent actuator 3 from the ink and provide thermal insulation. The polymer layer 30 may include a desiccant coating (e.g., a hydrophobic coating and / or an oleophobic coating) to help prevent spillage and promote stable droplet ejection. For clarity, Figure 1 Polymer layer 30 is not shown.

[0049] Figure 3 An example of a page-width inkjet printhead 100 is shown, which incorporates a MEMS inkjet nozzle device 1 as described above.

[0050] Improved thermoplastic materials

[0051] As described in US 7,984,973, aluminum alloys are excellent candidates for use as thermoplastic beams in hot bending actuators, combining relatively high thermal expansion and relatively high modulus of elasticity compared to other known thermoplastic materials. For example, the applicant has already used vanadium-aluminum alloys and titanium-aluminum alloys in the development of inkjet nozzle devices employing hot bending actuation technology.

[0052] However, there remains a need to improve the lifespan of hot bending actuators while maintaining the aforementioned desired properties of aluminum alloys. Following extensive research into materials and device configurations, it has now been found that adding small amounts of copper (e.g., up to about 5 at.%) to aluminum alloys can significantly improve lifespan without compromising performance.

[0053] Table 1 shows the examples used for the above conjunctions. Figure 1 and Figure 2 The properties of the two aluminum alloys used in the inkjet nozzle assembly 1 of the described type are identical in all other respects. One aluminum alloy (“VAl”) comprises 90 at.% Al and 10 at.% V; the other aluminum alloy (“VAlCu”) comprises 89.9 at.% Al, 9.8 at.% V, and 0.3 at.% Cu.

[0054] Table 1: Comparison of VAl and VAlCu as thermoplastic materials

[0055]

[0056] The results in Table 1 clearly demonstrate that adding copper to aluminum alloys unexpectedly improves lifespan. With similar energy input and current density, only 17% of devices with VAl thermoplastic beams remained functional and actuated after approximately 6 billion actuations, while 93% of devices with VAlCu thermoplastic beams remained functional after the same number of actuations. Notably and unexpectedly, the lifespan improved fivefold.

[0057] Furthermore, the two hot bending actuators exhibited very similar performance in terms of hot bending response and maximum speed during free-air oscillation. Therefore, while the addition of copper significantly improved lifespan, the difference in device performance was negligible. Thus, it can be concluded that aluminum alloys containing a small amount of copper are optimal for overall device performance and lifespan.

[0058] Of course, it should be understood that the invention has been described by way of example only, and modifications to the details may be made within the scope of the invention as defined in the appended claims.

Claims

1. A thermal bend actuator comprising: a thermoplastic beam for connection to drive circuitry; and a passive beam mechanically cooperating with the thermoplastic beam such that when an electric current is passed through the thermoplastic beam, the thermoplastic beam expands relative to the passive beam, thereby causing the thermal bend actuator to bend, wherein the thermoplastic beam comprises an aluminium alloy comprising: an amount of aluminium in the range of 80 to 95 at.%; an amount of a second metal in the range of 2 to 18 at.%; and an amount of copper in the range of 0.1 to 5 at.%; wherein the second metal comprises one or more selected from the group consisting of: vanadium, titanium, chromium, manganese, cobalt, nickel, and scandium.

2. The thermal bend actuator of claim 1, wherein, The second metal is vanadium.

3. The thermal bend actuator of claim 1, wherein, The passive beam is multilayered or single layered.

4. The thermal bend actuator of claim 3, wherein, The passive beam comprises at least one material selected from the group consisting of: silicon oxide and silicon nitride.

5. The thermal bend actuator of claim 1, wherein, The thermoplastic beam is fused or bonded to the passive beam.

6. The thermal bend actuator of claim 1, wherein, The passive beam is overhanging.

7. The thermal bend actuator of claim 6, wherein, The thermoplastic beam is connected to a pair of electrical terminals positioned at one end of the passive beam.

8. The thermal bend actuator of claim 7, wherein, The thermoplastic beam comprises a plurality of legs interconnected by one or more turns.

9. An inkjet nozzle device comprising: a nozzle chamber having a nozzle opening and an ink inlet; and a thermal bend actuator according to any one of the preceding claims for ejecting ink through the nozzle opening.

10. The inkjet nozzle device of claim 9, wherein, The nozzle chamber comprises a floor and a roof having a moving part, whereby actuating the thermal bend actuator moves the moving part towards the floor.

11. The inkjet nozzle device of claim 10, wherein, The moving part comprises the thermal bend actuator.

12. The inkjet nozzle device of claim 11, wherein, The nozzle opening is defined in the moving part such that the nozzle opening is movable relative to the floor.

13. The inkjet nozzle device of claim 9, comprising a plurality of the thermal bend actuators for ejecting ink through the nozzle opening.

14. An inkjet printhead comprising a plurality of inkjet nozzle devices according to any one of claims 9 to 13.

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