Thermally flexed actuator with improved lifespan

Abstract

The thermal bending actuator includes a thermoelastic beam for connection to a drive circuit and a passive beam in mechanical cooperation with the thermoelastic beam, such that when a current is passed through the thermoelastic beam, the thermoelastic beam expands relative to the passive beam, thereby causing bending of the actuator. The thermoelastic beam is constructed from an aluminum alloy. The aluminum alloy includes a first metal that is aluminum, a second metal, and at least 0.1 atomic % of a third metal selected from the group consisting of copper, scandium, tungsten, molybdenum, chromium, titanium, silicon, and magnesium.

Description

Technical Field

[0001] The present invention relates to a MEMS thermal bending actuator, such as one configured for use in an inkjet printhead. It was mainly developed to improve the lifespan of the thermal bending actuator while maintaining optimal efficiency.

Background Art

[0002] The applicant has developed a series of Memjet (registered trademark) inkjet printers, such as those described in International Publication No. WO 2011 / 143700, International Publication No. WO 2011 / 143699, and International Publication No. WO 2009 / 089567, the contents of which are incorporated herein by reference. Memjet (registered trademark) printers employ a fixed page width printhead in combination with a feed mechanism that feeds the print medium through the printhead in a single pass. Thus, Memjet (registered trademark) printers achieve a much higher printing speed than conventional scanning inkjet printers.

[0003] An inkjet printhead is composed of a plurality (usually thousands) of individual inkjet nozzle devices each supplied with ink. Each inkjet nozzle device typically includes a nozzle chamber having a nozzle opening and an actuator for ejecting ink through the nozzle opening. The design space for inkjet nozzle devices is vast, and the patent literature describes numerous different nozzle devices, including different types of actuators and different device configurations. Inkjet nozzle devices used in commercially available printheads typically use either a thermal bubble forming actuator or a piezoelectric actuator. Thermal bubble forming inkjet devices have the advantages of low cost and high nozzle density achievable through MEMS manufacturing processes, while piezoelectric inkjet devices have the advantage of being compatible with a wide range of inks, such as non-aqueous inks and high viscosity inks.

[0004] While inkjet printing technology has achieved great commercial success over the past several decades, there is still a need for new inkjet technologies that potentially combine the advantages of thermal bubble formation and piezoelectric technologies. The applicant has been continuously engaged in research on such new inkjet technologies, focusing on MEMS thermal bending actuators as a potentially novel means for inkjet operation. A thermal bending actuator uses a thermoelastic layer that mechanically cooperates with a passive layer to provide bending motion through the thermal expansion of the thermoelastic layer relative to the passive layer. As described in detail in many of the applicant's previous patents, the bending motion of a heat-actuated paddle can be used to provide the mechanical impact necessary for droplet ejection.

[0005] For example, U.S. Patent No. 6,623,101 (the contents of which are incorporated herein by reference) describes an inkjet nozzle device comprising a nozzle chamber with a movable ceiling that defines a nozzle opening. The ceiling is connected via an arm to a thermal bending actuator having an upper thermoelastic beam and a lower passive beam located outside the nozzle chamber. When an electric current is passed through the thermoelastic beam, the movable ceiling bends toward the floor of the nozzle chamber, thereby increasing the pressure inside the nozzle chamber and functioning as a paddle that ejects ink droplets through the nozzle opening.

[0006] U.S. Patent No. 7,794,056 (the contents of which are incorporated herein by reference) describes an inkjet nozzle device in which a thermal bending actuator is incorporated into the movable ceiling portion of the nozzle chamber. By incorporating the thermal bending actuator into the movable ceiling portion, higher efficiency is achieved in terms of the energy required for droplet ejection.

[0007] The selection of materials for the thermoelastic layer of a thermal bending actuator is important not only for efficiency but also for lifespan. For example, U.S. Patent No. 6,428,133 describes the use of TiB2, MoSi2, and TiAlN as suitable thermoelastic materials. More recently, U.S. Patent No. 7,984,973 (the contents of which are incorporated herein by reference) describes the use of aluminum alloys as thermoelastic materials. Aluminum alloys such as VAl have the advantages of excellent thermoelastic efficiency and manufacturability using deposition processes available in many factories.

[0008] However, for thermal bending technology to compete with existing piezoelectric technology, it needs to have a comparable lifespan with minimal device failure after billions of ejection cycles. Therefore, it is desirable to provide a thermoelastic material suitable for use in inkjet nozzle devices that has improved lifespan and superior thermoelastic efficiency compared to known thermoelastic materials. [Overview of the project]

[0009] In the first embodiment, a thermal bending actuator, A thermoelastic beam for connecting to the drive circuit, A passive beam that mechanically cooperates with a thermoelastic beam, wherein when an electric current flows through the thermoelastic beam, the thermoelastic beam expands relative to the passive beam, resulting in bending of the actuator, and the passive beam comprises: A thermoelastic beam is provided, which is made of an aluminum alloy, and the aluminum alloy comprises a first metal which is aluminum, a second metal, and at least 0.1 atomic percent of a third metal selected from the group consisting of copper, scandium, tungsten, molybdenum, chromium, titanium, silicon, and magnesium, and is used as a thermoflex actuator.

[0010] The thermal bending actuator according to the first embodiment has the advantage of having a superior lifespan compared to a thermal bending actuator composed of an aluminum alloy without the third metal. While we do not wish to be bound by theory, the inventors understand that the addition of the third metal suppresses electromigration in the thermoelastic beam. This suppression of electromigration is thought to be the cause of the dramatic improvement in lifespan observed. In addition to copper, metals such as scandium, tungsten, molybdenum, chromium, titanium, and magnesium are also expected to yield similar improvements in lifespan based on their ability to suppress electromigration.

[0011] To avoid misunderstanding, the first, second, and third metals are different from each other.

[0012] Preferably, the second metal is selected from the group consisting of vanadium, titanium, chromium, manganese, cobalt, nickel, and scandium.

[0013] To avoid misunderstanding, the second metal can include one or more of the metals listed above. Similarly, the third metal can include one or more of the metals listed above.

[0014] Preferably, the second metal is vanadium and the third metal is copper.

[0015] Preferably, the amount of aluminum is in the range of 80 to 95 atomic percent, the amount of the second metal is in the range of 2 to 18 atomic percent, and the amount of the third metal is in the range of 0.1 to 5 atomic percent.

[0016] Preferably, the aluminum alloy comprises aluminum, vanadium, and copper. In some embodiments, the aluminum alloy is essentially composed of aluminum, vanadium, and copper, insofar as these three elements form at least 90% or at least 95% of the alloy.

[0017] Preferably, the aluminum alloy contains an amount of aluminum in the range of 80 to 95 atomic percent, or more preferably 85 to 95 atomic percent.

[0018] Preferably, the aluminum alloy contains vanadium in an amount ranging from 2 to 18 atomic percent, or more preferably 3 to 15 atomic percent, or more preferably 7 to 13 atomic percent. Typically, vanadium is present in an amount of at least 5 atomic percent.

[0019] Preferably, the aluminum alloy contains copper in an amount ranging from 0.1 to 5 atomic percent, or more preferably 0.15 to 3 atomic percent, or more preferably 0.2 to 1 atomic percent. Typically, copper is present in an amount of at least 0.1 atomic percent or at least 0.2 atomic percent.

[0020] The passive beam may be multilayered or single-layered. For example, the passive beam may comprise a first layer and a second layer, each composed of a different material (e.g., a first layer of silicon nitride and a second layer of silicon oxide, as described in U.S. Patent No. 8,079,668, the contents of which are incorporated herein by reference). Alternatively, the passive layer may be a single layer of material.

[0021] Preferably, the passive beam comprises at least one material selected from the group consisting of silicon oxide and silicon nitride.

[0022] Preferably, the thermoelastic beam is fused to or bonded to the passive beam. Typically, the thermoelastic beam material is deposited directly onto the passive beam via a MEMS deposition process (e.g., CVD, PECVD, etc.).

[0023] The passive beam is preferably cantilevered and has one free end and the opposite end connected to a support.

[0024] Preferably, the thermoelastic beam is connected to a pair of electrical terminals located at one end of the passive beam (typically a fixed end connected to a support).

[0025] Preferably, the thermoelastic beam includes a plurality of legs interconnected by one or more bends. For example, the thermoelastic beam can have a first leg extending longitudinally from a first electrical terminal and a second leg extending longitudinally parallel to the second electrical terminal, and the first leg and the second leg are connected by one bend distally from the electrical terminals. Alternatively, the thermoelastic beam may have, for example, a meandering configuration in which four parallel legs are interconnected by three bends. These and other configurations of the thermoelastic beam will be readily apparent to those skilled in the art.

[0026] In a second aspect, a nozzle chamber having a nozzle opening and an ink inlet, an inkjet nozzle device is provided that includes a thermo-bending actuator as described above.

[0027] Preferably, the nozzle chamber includes a floor and a ceiling having a movable part (e.g., in the form of a paddle), whereby, upon actuation of the actuator, the movable part moves towards the floor.

[0028] Preferably, the movable part includes an actuator.

[0029] Preferably, the nozzle opening is defined within the movable part such that the nozzle opening is movable relative to the floor. Alternatively, the nozzle opening may be defined within a stationary part of the ceiling.

[0030] In some embodiments, the ceiling of the nozzle chamber can include a plurality of thermo-bending actuators for ejecting ink through the nozzle opening. For example, opposing thermo-bending actuators on either side of one nozzle opening can be used to generate an increased mechanical shock for droplet ejection.

[0031] In a third aspect, an inkjet printhead is provided that includes a plurality of inkjet nozzle devices as described above.

[0032] As used herein, the term "ink" refers to any ejectable fluid, which 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, and functional fluids (e.g., sensor inks, solar inks).

[0033] To avoid misunderstanding, the term "atomic percent" refers to the amount of metal in an alloy based on the relative number (or moles) of atoms. For example, an alloy containing V (9.8 atomic%), Al (89.9 atomic%), and Cu (0.3 atomic%) is equivalent to V (17 wt%), Al (82.5 wt%), and Cu (0.5 wt%), as will be easily understood by those skilled in the art. [Brief explanation of the drawing]

[0034] Herein, embodiments of the present invention will be described merely as examples with reference to the attached drawings.

[0035] [Figure 1] Figure 1 is a schematic plan view of an inkjet nozzle device equipped with a thermal bending actuator. [Figure 2] Figure 2 is a cross-sectional view of the inkjet nozzle device shown in Figure 1, along line 2-2. [Figure 3] Figure 3 is a perspective view of a portion of an inkjet printhead equipped with the multiple inkjet nozzle devices shown in Figure 1. [Modes for carrying out the invention]

[0036] Referring to Figures 1 and 2, an inkjet nozzle device 1 incorporating a pair of opposing thermal bending actuators 3 according to one embodiment of the present invention is shown. Suitable MEMS processes for manufacturing the type of nozzle device shown in Figures 1 and 2 are described in the applicant's U.S. Patent Application Publication No. 2008 / 0309728 and U.S. Patent Application Publication No. 2008 / 0225077, which are incorporated herein by reference.

[0037] The inkjet nozzle device 1 is manufactured on a passivation layer 5 of a silicon substrate 7 having a drive circuit layer 8 for supplying current pulses to a thermal bending actuator 3. The inkjet nozzle device 1 comprises a nozzle chamber 9 having a nozzle opening 10, a ceiling 11, and side walls 13 extending between the ceiling and the silicon substrate 7. A blanket silicon oxide layer 15 deposited on the passivation layer 5 defines the side walls 13 of the nozzle chamber. Electrical connector posts 17 (e.g., copper posts) formed by a damascene process, such as described in U.S. Patent No. 7,819,503 (the contents of which are incorporated herein by reference), extend through the silicon oxide layer 15 and form an electrical connection to the drive circuit layer 8 of the silicon substrate 7. As best shown in Figure 1, a pair of connector posts 17 (power and ground) are provided at the fixed end of each cantilevered thermal bending actuator 3.

[0038] Each of the thermal bending actuators 3 consists of a lower passive beam 20 and an upper thermoelastic ("active") beam 22. Each passive beam 20 is formed by depositing appropriate passive material onto a sacrificial scaffold (not shown) such that the passive beam defines at least partially the ceiling 11 of the nozzle chamber 9. In the embodiment shown in Figure 2, each passive beam 20 is simply a single layer of silicon oxide, but it will be understood that multilayer passive beams, such as those described in U.S. Patent No. 8,079,668, are also within the scope of the present invention.

[0039] Each thermoelastic beam 22 is formed by depositing thermoelastic material on both the passive beam 20 and the exposed upper surface of the connector post 17, thereby forming an electrical connection to the drive circuit layer 8. Etching of the thermoelastic material defines the thermoelastic beams 22, each consisting of a pair of parallel legs 24 that extend from their respective power terminals 26 and ground terminals 26 (defined by the upper surface of the connector post 17) toward the nozzle opening 10 and are interconnected at their distal ends by bends 28. As will be described in more detail below, the thermoelastic material is typically a vanadium-aluminum-copper alloy.

[0040] Therefore, from the above description, it will be understood that each thermal bending actuator 3 takes the form of a cantilevered paddle that forms a movable portion of the ceiling 11 of the nozzle chamber 9. During operation, the thermoelastic beam 22 of each thermal bending actuator 3 receives an electrical signal from the drive circuit 8, which causes the thermoelastic beam to expand relative to the passive beam 20, thereby bending each thermal bending actuator downward toward the silicon substrate 7 in the direction indicated by arrow A. This bending motion increases the pressure inside the nozzle chamber 9, thereby ejecting ink droplets through the nozzle opening 10. The circular nozzle opening 10 has a semicircular portion defined within each thermal bending actuator 3, which moves the nozzle during operation. Following droplet ejection, ink is replenished into the nozzle chamber via a pair of ink inlets 32 that receive ink from an ink supply channel (not shown) defined in the silicon substrate.

[0041] As shown in Figure 2, a polymer layer 30 (e.g., a polyimide layer) is superimposed over the entire structure, including the exposed portions of the passive and thermoelastic beams, to protect the thermal bending actuator 3 from ink and provide insulation. The polymer layer 30 may include a dewetting coating (e.g., a hydrophobic and / or oleophobic coating) to help prevent flooding and promote stable droplet ejection. For clarity, the polymer layer 30 is not shown in Figure 1.

[0042] Figure 3 shows an example of a page-width inkjet print head 100 incorporating the MEMS inkjet nozzle device 1, as described above.

[0043] Improved thermoelastic materials As described in U.S. Patent No. 7,984,973, aluminum alloys are excellent candidates for use as thermoelastic beams in thermoflex actuators, possessing a combination of relatively high thermal expansion and relatively high modulus compared to other known thermoelastic materials. For example, vanadium-aluminum alloys and titanium-aluminum alloys have been used by the applicant in the development of inkjet nozzle devices employing thermoflex actuation technology.

[0044] However, there remains a need to improve the lifespan of thermal bending actuators while maintaining the desirable properties of aluminum alloys mentioned above. Detailed examination of materials and device configurations revealed that adding a small amount of copper (e.g., up to approximately 5 atomic%) to the aluminum alloy dramatically improves lifespan without compromising performance.

[0045] Table 1 shows the performance of two aluminum alloys used as thermoelastic materials in an otherwise identical inkjet nozzle device 1 of the type described above, in relation to Figures 1 and 2. One aluminum alloy ("VAl") consists of 90 atomic% Al and 10 atomic% V, while the other aluminum alloy ("VAlCu") consists of 89.9 atomic% Al, 9.8 atomic% V, and 0.3 atomic% Cu.

[0046] TIFF0007877324000001.tif77170

[0047] The results in Table 1 clearly demonstrate that adding copper to aluminum alloys dramatically improves lifespan. Under similar energy input and current density conditions, only 17% of devices with VAl thermoelastic beams were still operational after approximately 6 billion cycles, compared to 93% of devices with VAlCu thermoelastic beams. This represents a remarkable and astonishing five-fold improvement in lifespan.

[0048] Furthermore, the performance of both thermal flex actuators was very similar in terms of thermal flex response and maximum velocity during free-air vibration. Therefore, while the addition of copper dramatically improved the lifespan, there was little difference in terms of device performance. Thus, it was concluded that an aluminum alloy with a small amount of copper is optimal for overall device performance and lifespan.

[0049] Naturally, the present invention is described merely as an example, and it will be understood that modifications of details are possible within the scope of the invention as defined in the appended claims.

Claims

1. A thermal bending actuator, A thermoelastic beam for connecting to the drive circuit, A passive beam that mechanically cooperates with the thermoelastic beam, wherein when an electric current flows through the thermoelastic beam, the thermoelastic beam expands relative to the passive beam, resulting in bending of the actuator. The thermoelastic beam is made of an aluminum alloy, and the aluminum alloy is Aluminum in an amount ranging from 80 to 95 atomic percent, A second metal in an amount ranging from 2 to 18 atomic percent, It contains copper in an amount ranging from 0.1 to 5 atomic percent, The second metal is vanadium, in the thermal bending actuator.

2. The thermal bending actuator according to claim 1, wherein the passive beam is multilayer or single-layer.

3. The thermal bending actuator according to claim 2, wherein the passive beam comprises at least one material selected from the group consisting of silicon oxide and silicon nitride.

4. The thermal bending actuator according to claim 1, wherein the thermoelastic beam is fused to or joined to the passive beam.

5. The thermal bending actuator according to claim 1, wherein the passive beam is a cantilever beam.

6. The thermal bending actuator according to claim 5, wherein the thermoelastic beam is connected to a pair of electrical terminals located at one end of the passive beam.

7. The thermal bending actuator according to claim 6, wherein the thermoelastic beam comprises a plurality of legs interconnected by one or more curved portions.

8. An inkjet nozzle device, A nozzle chamber having a nozzle opening and an ink inlet, An inkjet nozzle device comprising a thermal bending actuator according to any one of claims 1 to 7 for ejecting ink through the nozzle opening.

9. The inkjet nozzle device according to claim 8, wherein the nozzle chamber comprises a floor portion and a ceiling portion having a movable portion, and thereby, by the operation of the actuator, the movable portion moves toward the floor portion.

10. The inkjet nozzle device according to claim 9, wherein the movable part comprises the actuator.

11. The inkjet nozzle device according to claim 10, wherein the nozzle opening is defined within the movable portion so that the nozzle opening is movable relative to the floor portion.

12. The inkjet nozzle device according to claim 8, further comprising a plurality of thermal bending actuators for ejecting ink through the nozzle opening.

13. An inkjet print head comprising a plurality of inkjet nozzle devices according to any one of claims 8 to 12.

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