KR101356333B1 - Printhead having polysilsesquioxane coating on ink ejection face - Google Patents

Abstract

A printhead having an ink ejection surface coated with a hydrophobic polymer material is disclosed. The polymeric material is composed of polysilsesquioxanes, such as poly (methylsilsesquioxane) or poly (phenylsilsesquioxane). The printhead is compatible with various printhead maintenance tasks that require contact with the ink ejection surface.

Description

Printhead with polysilsesquioxane coating on ink ejection surface {PRINTHEAD HAVING POLYSILSESQUIOXANE COATING ON INK EJECTION FACE}

TECHNICAL FIELD The present invention relates to the field of printers and, more particularly, to inkjet printheads. In high resolution printheads, improvements in print quality and printhead maintenance have been primarily developed.

Many different printing forms have been invented, many of which are currently in use. Known print forms have a variety of methods for marking on print media with suitable marking media. Commonly used printing forms are offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders ), Thermal wax printers, dye sublimation printers, and inkjet printers of both drop on demend and continuous flow types. Each type of printer has its advantages and problems when considering cost, speed, quality, reliability, structure and simplicity of operation.

In recent years, the field of inkjet printing has become increasingly popular, mainly because of its low cost and versatility, in that each individual ink pixel is obtained from one or more ink nozzles.

Many different techniques have been invented in connection with inkjet printing. To explore this area, J Moore's paper, "Non-Impact Printing: Introduction and Historical Perspective", Output Hard Copy Devices See Editors Du Dubeck and S Sherr, pages 207-220 (1988).

Inkjet printers themselves are of many different types. In inkjet printing, the use of continuous ink flow is at least 1929 in that Hansell, US Patent No. 1,941,001, discloses a simple form of continuous stream electrostatic ink jet printing. It seems to date back.

Sweet US Pat. No. 3,596,275 also discloses a continuous inkjet printing process comprising the step of adjusting inkjet flow by a high frequency electro-static field to cause drop separation. have. This technology is still used by several manufacturers, including Elmjet and Scitex (see also US Pat. No. 3,373,437 to Sweet et al.).

Piezoelectric ink jet printers are also a form of inkjet printing apparatus that are commonly used. Piezoelectric systems are described in US Pat. No. 3,946,398 (1970) using diaphragm mode of operation by Kyser et al. To disclose a squeeze mode of operation of piezoelectric crystals. Piezoelectric push of inkjet flow by Zolten at 3,683,212 (1970) and by Stetemme in US Pat. No. 3,747,120 (1972), which initiated the piezoelectric operation of the bend mode. published by Howkins in US Pat. No. 4,459,601, which discloses mode actuation, and by Fischbeck in US Pat. No. 4,584,590, which discloses a piezoelectric transducer element of shear mode type. It is.

In recent years, thermal ink jet printing has become one of the most popular forms of ink jet printing. Inkjet printing techniques include those disclosed by Endo et al. In GB 2007162 (1979) and by Vaught et al. In US Pat. No. 4,490,728. Both of these references allow for the ejection of ink onto an appropriate print medium, through an aperture connected to a confined space, by activation of an electrothermal actuator that causes the generation of bubbles in a constricted space, such as a nozzle. Disclosed inkjet printing techniques. Printing apparatuses using electrothermal actuators are manufactured by manufacturers such as Canon and Hewlett Packard.

As can be seen from the above, many other types of printing techniques are available. It is ideal that printing techniques have many desirable properties. These features include inexpensive configuration and operation, high speed operation, long term safe and continuous operation, and the like. Each technology may have its own advantages and disadvantages in terms of cost, speed, quality, reliability, power usage, simplicity of configuration and operation, durability and consumption.

In the construction of any inkjet printing system, there are many important factors to consider when large printheads, especially printheads in the form of pagewidths, are to be exchanged with one another. Many of these factors are outlined below.

First, inkjet printheads are typically constructed using microelectromechanical system (MEMS) techniques. As such, inkjet printheads tend to rely on standard integrated circuit construction / fabrication techniques that deposit planar layers on a silicon wafer and then etch certain portions of the planar layers. have. Among silicon circuit fabrication techniques, some techniques are more known than others. For example, techniques related to the generation of CMOS circuits

There is a potential to be more readily available than techniques related to the creation of exotic circuits, including ferroelectrics, gallium arsenide and the like. Thus, in some MEMS configurations, it is desirable to make good use of proven semiconductor fabrication techniques that do not require any "special" processes or materials. Of course, if the advantages of using exceptional special materials are more important than its shortcomings, then some degree of trade off will be made, in which case it may be desirable to use those materials anyway. However, if it is possible to achieve the same or similar properties using more general materials, the problems of special materials can be avoided.

Preferred properties of the inkjet printheads will be in combination with a hydrophobic ink discharging surface ("front" or "nozzle face"), preferably with hydrophilic nozzle chambers and ink supply channels. Hydrophilic nozzle chambers and ink supply channels provide capillary action, which is optimal for re-supply and priming of ink into nozzle chambers after each drop ejection. The hydrophobic front minimizes the tendency for ink to flood across the entire printhead front. Along with the hydrophobic front, aqueous inkjet inks are less likely to flood out transversely of the nozzle openings. Also, any ink flooding from the nozzle openings is less likely to spread across the surface and mix on the front surface—instead, the nozzle openings form respective spherical microdroplets that can be more easily handled by appropriate maintenance operations. something to do.

To date, applicants have described the use of PDMS (polydimethylsiloxane) to coat the front surface of a printhead to provide a hydrophobic surface. However, even though PDMS has good hydrophobicity and can be easily incorporated into the printhead MEMS manufacturing process, the PDMS is relatively poor in wear resistance and can be scratched or damaged by the wiper blades used for printhead maintenance (eg See, eg, US Application No. 12 / 014,772, filed Jan. 16, 2008, incorporated herein by reference). It would therefore be desirable to provide a printhead having a hydrophobic ink ejecting surface, which can be easily produced by a MEMS manufacturing process and has excellent wear resistance.

In a first aspect, a printhead having an ink ejection face is provided, wherein at least a portion of the ink ejection face is coated with a hydrophobic polymeric material, wherein the polymeric material is polysilsesquioxanes. ) Printheads according to the present invention have excellent durability and wear resistance that make the printheads compatible in a variety of printhead maintenance operations that require contact (eg, wiping) with the ink ejection surface. In addition, polysilsesquioxanes can be deposited into thin layers (0.5 to 2 microns) by a spin-on process, so they are easily incorporated into MEMS printhead manufacturing processes.

Optionally, polysilsesquioxanes are selected from the group consisting of poly (alkylsilsesquioxane) and poly (arylsilsesquioxane).

Optionally, the polysilsesquioxane is selected from the group consisting of poly (methylsilsesquioxane) and poly (phenylsilsesquioxane).

Optionally, the polymeric material is deposited and hardback onto the nozzle plate of the printhead during MEMS printhead manufacture.

Optionally, the printhead comprises a plurality of nozzle assemblies formed in a substrate, each nozzle assembly comprising a nozzle chamber, a nozzle opening formed in a roof of the nozzle chamber. And an actuator for ejecting ink through the nozzle opening.

Optionally, the polymeric material is coated on the nozzle plate of the printhead, the nozzle plate being formed at least in part by a loop of each nozzle chamber.

Optionally, each loop has a hydrophobic outside surface relative to the inside surface of each nozzle chamber by hydrophobic coating.

Optionally, each nozzle chamber includes a roof and sidewalls made of ceramic material.

Optionally, the ceramic material is selected from the group consisting of silicon nitride, silicon oxide and silicon oxynitride.

Optionally, the loops are spaced apart from the substrate such that sidewalls of each nozzle chamber extend between the nozzle plate and the substrate.

Optionally, the actuator is a heater element configured to forcibly eject an ink droplet through the nozzle opening by heating the ink in the chamber to form a gas bubble.

Optionally, the heater element is suspended in the nozzle chamber.

Optionally, the actuator

A first active element for connecting to drive circuitry; And

A thermal bend actuator comprising a second passive element mechanically cooperating with the first element,

When a current flows through the first element, the first element expands than the second element, causing bending of the actuator.

Optionally, the thermal bend actuator forms at least a portion of the loop of each nozzle chamber, such that operation of the actuator causes the moving portion of the loop to move toward the floor of the nozzle chamber.

Optionally, nozzle openings are formed in the fluctuations of the loop.

Optionally, the nozzle opening is formed in a stationary portion of the loop.

Optionally, the polymeric material forms a mechanical seal between the fluctuations of the loop and the fixture, thereby minimizing ink leakage during operation of the actuator.

In a second aspect, there is provided a printhead having an ink ejection surface, wherein at least a portion of the ink ejection surface is coated with a polymeric material, the polymeric material consisting of polymerized siloxane comprising nanoparticles. . According to a second feature, the nanoparticles impart desirable properties such as durability, wear-resistance, fatigue-resistance, hydrophobicity, hydrophilicity and the like to the polymer coating.

Optionally, the polymeric siloxane is selected from the group consisting of poly (alkylsilsesquioxanes), poly (arylsilsesquioxanes) and polydialkylsiloxanes.

Optionally, the polymeric siloxane is selected from the group consisting of poly (methylsilsesquioxane), poly (phenylsilsesquioxane) and polydimethylsiloxane.

Optionally, the nanoparticles are selected from the group consisting of inorganic nanoparticles and organic nanoparicles.

Optionally, the inorganic nanoparticles are selected from the group consisting of metal oxides, metal carbonates and metal sulfates.

Optionally, the inorganic nanoparticles may be silica, zirconium oxide, titanium oxide, aluminum oxide, calcium carbonate, tin oxide, zinc oxide. zinc oxide, copper oxide, chromium oxide, calcium oxide, tungsten oxide, iron oxide, cobalt oxide and barium sulfate Is selected from the group consisting of

Optionally, the organic nanoparticles may be cross-linked silicone resin particles, cross-linked polyolefin resin particles, cross-linked acryl resin particles, crosslinking Styrene-acryl resin particles, cross-linked polyester particles, polyimide particles, melamine resin particles and carbon Selected from the group consisting of carbon nanotubes.

Optionally, the nanoparticles are included in the polymerized siloxane in amounts ranging from 1 to 70 wt.%.

Optionally, the nanoparticles have an average particle size in the range of 1 to 100 nm.

Optionally, the printhead includes a plurality of nozzle assemblies formed in the substrate, each nozzle assembly including a nozzle chamber, a nozzle opening formed in a loop of the nozzle chamber, and an actuator for ejecting ink through the nozzle opening.

Optionally, the polymeric material is coated on the nozzle plate of the printhead, the nozzle plate being formed at least in part by a loop of each nozzle chamber.

Optionally, each nozzle chamber comprises loops and sidewalls made of a ceramic material selected from the group consisting of silicon nitride, silicon oxide and silicon oxynitride.

Optionally, the loops are spaced apart from the substrate such that sidewalls of each nozzle chamber extend between the nozzle plate and the substrate.

Optionally, the actuator is a heater element configured to forcibly eject ink droplets through the nozzle opening by heating the ink in the chamber to form gas bubbles.

Optionally, the heater element is suspended in the nozzle chamber.

Optionally, the actuator

A first active element for connecting to a drive circuit; And

A thermal bend actuator comprising a second passive element that mechanically cooperates with the first element,

When a current flows through the first element, the first element expands than the second element, causing bending of the actuator.

Optionally, the thermal bend actuator forms at least a portion of the loop of each nozzle chamber, such that operation of the actuator causes the fluctuation of the loop to move toward the floor of the nozzle chamber.

Optionally, nozzle openings are formed in either the fluctuations of the loop or the fastenings of the loop.

Optionally, the polymeric material forms a mechanical seal between the fluctuations of the loop and the fixture, thereby minimizing ink leakage during operation of the actuator.

In a third aspect, an inkjet printhead is provided for ejecting an ejectable fluid, the printhead having an ink ejection surface coated with a polymeric material comprising nanoparticles, the nanoparticles having an ink ejection surface relative to the ink ejection surface. One or more predetermined characteristics, the predetermined characteristics,

Inherent properties of the ejectable fluid;

Printhead maintenance regime associated with the printhead; And

Complement one or more of the types of nozzle actuators.

The present invention according to the third aspect can make the surface characteristics of the ink ejecting surface suitable for the predetermined characteristics of the printer. For example, there may be printers where printhead maintenance is a priority, while other printers may be prioritized for optimal fluid discharge. Alternatively, nanoparticles can be selected to provide a compromise of printer characteristics.

Optionally, the one or more predetermined properties are selected from the group consisting of hydrophilicity, hydrophobicity, abrasion resistance, and fatigue resistance.

Optionally, one or more predetermined properties are imparted by one or more of the surface energy properties of the nanoparticles, the size of the nanoparticles, the amount of nanoparticles, and the durability of the nanoparticles.

Optionally, the nanoparticles are selected from the group consisting of inorganic nanoparticles and organic nanoparticles.

Optionally, the inorganic nanoparticles are from the group consisting of silica, zirconium oxide, titanium oxide, aluminum oxide, calcium carbonate, tin oxide, zinc oxide, copper oxide, chromium oxide, calcium oxide, tungsten oxide, iron oxide, cobalt oxide and barium sulfate Is selected.

Optionally, the organic nanoparticles may be crosslinked silicone resin particles, crosslinked polyolefin resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, melamine resin particles and carbon. Selected from the group consisting of nanotubes.

Optionally, the intrinsic properties of the ejectable fluid are selected from the group consisting of hydrophilicity, hydrophobicity, viscosity, surface tension, and boiling point.

Optionally, the dischargeable fluid is selected from the group consisting of aqueous and non-aqueous fluids.

Optionally, the printhead maintenance scheme is one or more operations selected from the group consisting of printhead capping, printhead wiping, printhead flooding, and non-contact ink removal. It includes.

Optionally, the polymeric material consists of polymeric siloxanes.

Optionally, the polymerization siloxane is selected from the group consisting of poly (alkylsilsesquioxanes), poly (arylsilsesquioxanes) and polydialkylsiloxanes.

Optionally, the polymerization siloxane is selected from the group consisting of poly (methylsilsesquioxane), poly (phenylsilsesquioxane) and polydimethylsiloxane.

Other selectable embodiments of the printhead according to the third feature are similar to selectable embodiments according to the first and second features.

Selectable embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:
1 is a partial perspective view showing the arrangement of the nozzle assembly of the thermal inkjet printhead;
FIG. 2 is a side view of the nozzle assembly unit cell shown in FIG. 1; FIG.
3 is a perspective view of the nozzle assembly shown in FIG. 2, FIG.
4 shows a nozzle assembly partially formed after depositing sidewalls and loop material onto a sacrificial photoresist layer;
5 is a perspective view of the nozzle assembly shown in FIG. 4;
6 is a mask related to the nozzle rim etching shown in FIG.
FIG. 7 shows etching of a roof layer to form a nozzle opening rim,
8 is a perspective view of the nozzle assembly shown in FIG. 7, FIG.
9 is a mask related to the nozzle opening etch shown in FIG. 10,
10 illustrates etching of loop material to form an elliptical nozzle opening,
11 is a perspective view of the nozzle assembly shown in FIG. 10, FIG.
12 shows oxygen plasma ashing of the first and second sacrificial layers,
FIG. 13 is a perspective view of the nozzle assembly shown in FIG. 12; FIG.
FIG. 14 shows the nozzle assembly after the opposing side of the wafer is also ashed;
15 is a perspective view of the nozzle assembly shown in FIG. 14;
FIG. 16 is a mask associated with the backside etch shown in FIG. 17;
FIG. 17 shows a back etch of an ink supply channel into the wafer,
18 is a perspective view of the nozzle assembly shown in FIG. 17;
FIG. 19 shows the nozzle assembly of FIG. 7 after deposition of a hydrophobic polymeric coating,
20 is a perspective view of the nozzle assembly shown in FIG. 19, FIG.
FIG. 21 shows the nozzle assembly of FIG. 19 after deposition of a protective metal film, and
22 shows the nozzle assembly of FIG. 21 after etching through the protective metal thin film, polymer coating and nozzle loop,
23 shows the completed nozzle assembly after backside MEMS processing and removal of photoresist;
24 is a perspective view of the nozzle assembly shown in FIG. 23, FIG.
25 is a cross-sectional side view of another inkjet nozzle assembly partially manufactured after a series of first steps in which nozzle chamber sidewalls are formed;
FIG. 26 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 25;
FIG. 27 is a side cross-sectional view of an inkjet nozzle assembly partially manufactured after a series of second steps in which the nozzle chamber is filled with polyimide; FIG.
FIG. 28 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 27;
FIG. 29 is a cross sectional side view of a partially manufactured inkjet nozzle assembly after a series of third steps in which connector posts are formed to the chamber loop; FIG.
30 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 29;
31 is a cross sectional side view of a partially manufactured inkjet nozzle assembly after a series of fourth steps in which conductive metal plates are formed;
32 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 31;
33 is a sectional side view of a partially manufactured inkjet nozzle assembly after a series of fifth steps in which an active beam member of a thermal bend actuator is formed;
FIG. 34 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 33;
35 is a cross sectional side view of a partially produced inkjet nozzle assembly after a sixth step after coating with a polymer layer, protecting with a metal layer and etching the nozzle opening;
36 is a side cross-sectional view of the completed inkjet nozzle assembly after backside MEMS treatment and removal of photoresist;
FIG. 37 is a cross-sectional perspective view of the inkjet nozzle assembly shown in FIG. 36.

The present invention can be used with any type of printhead. Applicant has previously described many inkjet printheads. It is not necessary to describe all such printheads here in order to facilitate understanding of the present invention. In the following, however, the present invention will be described with reference to a thermal bubble-forming inkjet printhead and a mechanical thermal bend actuated inkjet printhead. Advantages of the present invention will be readily apparent from the following discussion.

Thermal Bubble-Forming Inkjet Printheads

Referring to FIG. 1, a portion of a printhead including a plurality of nozzle assemblies is shown. 2 and 3 show one of these nozzle assemblies in side cross-sectional and partial perspective views.

Each nozzle assembly includes a nozzle chamber 24 formed by MEMS fabrication technology on a silicon wafer substrate 2. The nozzle chamber 24 is formed of a loop 21 and sidewalls 22 extending from the loop 21 to the silicon substrate 2. As shown in FIG. 1, each loop is formed as part of the nozzle surface 56, which spans the discharge surface of the printhead. The nozzle surface 56 and the sidewalls 22 are formed of the same material, which is deposited by PECVD onto the sacrificial scaffold of the photoresist during MEMS fabrication. In general, the nozzle surface 56 and sidewalls 22 are formed of a ceramic material such as silicon dioxide or silicon nitride. These hard materials have excellent properties for printhead robustness, and their inherently hydrophilic nature draws ink into the nozzle chambers 24 by capillary action. It is advantageous to supply. However, the outer surface (ink ejection surface) of the nozzle surface 56 is also hydrophilic, which causes some flooded ink to spread on the surface.

Returning to the detailed configuration of the nozzle chamber 24, it will be seen that a nozzle opening 26 is formed in the loop of each nozzle chamber 24. Each nozzle opening 26 is generally elliptical and has an associated nozzle rim 25. The nozzle rim 25 not only helps drop directionality during printing, but at least to some extent reduces ink flooding from the nozzle opening 26. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29 positioned below the nozzle opening 26 and floating across the pit 8. Current is supplied to the heater element 29 via electrodes 9 connected to the drive circuit in the CMOS layers 5 of the substrate 2 at the bottom. As current flows through the heater element 29, the heater element rapidly overheats the surrounding ink to form gas bubbles, which forcibly eject ink through the nozzle openings. By floating the heater element 29, the heater element is completely submerged in the ink when the nozzle chamber 24 is ready for operation. This improves printhead efficiency because less heat is dissipated to the underlying substrate 2 and more input energy is used to generate bubbles.

As most clearly shown in FIG. 1, the nozzles are arranged in rows, supplying ink to each nozzle lined with longitudinally extending ink supply channels 27. Ink supply channel 27 supplies ink to an ink inlet passage 15 for each nozzle, which passes through an ink conduit 23 in nozzle chamber 24. Ink is supplied to the nozzle opening 26 side.

The MEMS manufacturing process for manufacturing such printheads is disclosed in detail in the inventor's prior US application Ser. No. 11 / 246,684, filed Oct. 11, 2005, the contents of which are incorporated herein by reference. . The later steps of this manufacturing process are briefly reintroduced here for clarity.

4 and 5 show a partially manufactured printhead constituting a nozzle chamber 24 that seals sacrificial photoresist 10 (" SAC1 " and 16 (" SAC2 ")). The SAC1 photoresist 10 is used as a support for the deposition of the heater material forming the floating heater element 29. The SAC2 photoresist 16 is used as a support for the deposition of the side walls 22 and the loop 21 (which forms part of the nozzle surface 56).

In the prior art process, referring to FIGS. 6-8, the next step in MEMS fabrication is to form an elliptical nozzle rim 25 in the loop 21 by etching away the 2 micron loop material 20. This etching is formed using a photoresist layer (not shown) exposed by the dark colored rim mask shown in FIG. The elliptical rim 25 includes two coaxial rim lips 25a, 25b, positioned over their respective thermal actuators 29.

9 to 11, the next step forms an elliptical nozzle aperture 26 in the loop 21 by etching through the remaining loop material completely, which is formed by the rim 25. The boundary is cleared. This etching is formed using a photoresist layer (not shown) exposed by the dark colored roof mask shown in FIG. The elliptical nozzle hole 26 is located above the thermal actuator 29, as shown in FIG. 11.

Now, as all MEMS nozzle features are fully formed, the next step is to remove the SAC1 photoresist layer 10 and SAC2 photoresist layer 16 by O ₂ plasma ashing (FIGS. 12 and 13). . 14 and 15 show the total thickness (150 microns) of the silicon wafer 2 after the SAC1 photoresist layer 10 and the SAC2 photoresist layer 16 are ashed.

16 to 18, once the frontside MEMS processing of the wafer is completed, the ink supply channels 27 may be filled with ink injection passages 15 using standard anisotropic DRIE. Is etched from the back of the wafer to meet This back etch is formed using a photoresist layer (not shown) exposed by the dark colored mask shown in FIG. The ink supply channel 27 forms a fluidic connection between the back side of the wafer and the ink injection passages 15.

Finally, referring to Figures 2 and 3, the wafer is thinned down to about 135 microns by back etching. 1 is a cross-sectional perspective view of a completed printhead integrated circuit showing three adjacent nozzle rows. Each nozzle row has a respective ink supply channel 27 which extends along the longitudinal direction and supplies ink to a plurality of ink injection passages 15 in each row. The ink injection passages, as a result, supply ink to each row of ink conduits 23, and each nozzle chamber receives ink from a common ink conduit of that row.

As already mentioned above, this prior art MEMS manufacturing process is formed of ceramic materials such as silicon dioxide, silicon nitride, silicon oxynitride, aluminum nitride, and the like. Because of the nozzle surface 56, the hydrophilic ink ejection face is inevitably left.

In a preferred process for hydrophobizing the nozzle surface 56 (as disclosed in US 2009/0139961, the contents of which are incorporated herein by reference), the nozzle rim is provided in the steps illustrated in FIGS. 7 and 8. After etching, the wafer is immediately coated with hydrophobic polymer 80.

To provide the partially manufactured printhead shown in FIGS. 19 and 20, a thin layer (about 1 to 2 microns) of hydrophobic polymer 100 is spun onto the wafer and hardened.

Referring now to FIG. 21, a protective metal film (about 100 nm thick) is next deposited on polymer layer 80. The metal thin film is generally composed of titanium or aluminum and protects the hydrophobic polymer 80 from late-stage oxygen ashing conditions. For this reason, the polymer layer 80 is not exposed to aggressive ashing conditions and maintains hydrophobic properties throughout the MEMS treatment step.

FIG. 22 shows the wafer after etching the nozzle opening 26 through the metal thin film 110, the polymer layer 80, and the nozzle loop 21. This etching step uses a conventional patterned photoresist layer (not shown) as a common mask for all nozzle etching steps. In a typical etching sequence, by either standard dry metal-etching (eg BCl ₃ / Cl ₂ ) or wet metal-etching (eg H ₂ O ₂ or HF), The metal thin film 90 is etched first. A second dry etch is then used to etch through the polymer layer 80 and the nozzle loop 21. Generally, the second etching step is dry etching using oxygen and a fluorine based etching gas (eg SF ₆ or CF ₄ ).

Once the nozzle opening 26 is formed as shown in FIG. 22, back MEMS processing steps (eg, etching ink supply channels, thinning the wafer, etc.) and end ashing of the photoresist are shown in FIG. 14. Proceed according to known procedures, similar to the steps described above with respect to 18 to. Final removal of the metal thin film 90 using H ₂ O ₂ or HF rinse produces the finished nozzle assembly shown in FIGS. 23 and 24 having a hydrophobic polymer layer 80. do.

Thermal Bend Actuator Printhead

From the foregoing, it will be appreciated that any type of printhead can be hydrophobized in a similar manner. However, because the polymer layer acts as a mechanical seal between the moving loop portion of the printhead and the fixture, the polymer coating is particularly advantageous for use in Applicants' thermal bend actuator nozzle assemblies. These advantages are disclosed in more detail in Applicant's US Publication No. 2008/0225076, the contents of which are incorporated herein by reference.

25-37 show the procedure of the MEMS manufacturing steps for the inkjet nozzle assembly 100 disclosed in the inventor's prior application US 2008/0309728, the contents of which are incorporated herein by reference. As the finished inkjet nozzle assembly 100 shown in FIGS. 36 and 37 utilizes thermal bend actuation, the fluctuations of the loop bend toward the substrate, causing ink ejection.

The starting point for MEMS fabrication is a standard CMOS wafer with a CMOS drive circuit formed on top of the silicon wafer. At the end of the MEMS fabrication process, the wafer is diced into respective printhead integrated circuits (ICs), each IC including a drive circuit and a plurality of nozzle assemblies.

As shown in FIGS. 25 and 26, the substrate 101 has an electrode 102 formed on top of the substrate. The electrode 102 is one of a pair of adjacent electrodes (positive and earth) for powering the actuator of the inkjet nozzle 100. The electrodes receive power from a CMOS drive circuit (not shown) in the upper layers of the substrate 101.

The other electrode 103 shown in Figs. 25 and 26 is for supplying power to an adjacent ink jet nozzle. Generally, the figures show MEMS manufacturing steps for one nozzle assembly, which is one of a number of nozzle assemblies. The description below focuses on the manufacturing steps for one of these nozzle assemblies. However, it will of course be understood that the steps are being performed simultaneously for all nozzle assemblies being formed on the wafer. If an adjacent nozzle assembly is partially shown in the figures, this may be ignored for the purpose at hand. So all features of the adjacent nozzle assembly and electrode 103 will not be described in detail herein. In fact, for clarity, some MEMS fabrication steps will not be shown in adjacent nozzle assemblies.

In the order of the steps shown in FIGS. 25 and 26, a layer of 8 microns of silicon dioxide is initially deposited on the substrate 101. The depth of silicon dioxide defines the depth of the nozzle chamber 105 for inkjet nozzles. After deposition of the SiO ₂ layer, the SiO ₂ layer is etched to form the walls 104, which will be the sidewalls of the nozzle chamber 105, most clearly shown in FIG. 26.

27 and 28, the nozzle chamber 105 is then filled with a photoresist or polyimide 106, which acts as a sacrificial support for subsequent deposition steps. . Polyimide 106 is spun onto a wafer using standard techniques, UV cured and / or hardbaked, and then SiO ₂ Receive chemical mechanical planarization (CMP) that stops at the top surface of the wall 104.

In FIGS. 29 and 30, the roof member 107 of the nozzle chamber 105 is formed with high conductive connector posts 108 extending down to the electrodes 102. have. Initially, a 1.7 micron layer of SiO ₂ is deposited over the polyimide 106 and the wall 104. This layer of SiO ₂ forms a loop 107 of the nozzle chamber 105. Next, a pair of vias are formed in the wall 104 up to the electrodes 102 using standard anisotropic depth reactive ion etching. This etching exposes the pair of electrodes 102 through respective vias. Next, the vias are filled with a high conductivity metal, such as copper, using electroless plating. The deposited copper pillars 108 are subjected to CMP, stopping on the SiO ₂ loop member 107 to provide a planar structure. It can be seen that the copper connector pillars 108 formed during the electroless copper plating meet each of the electrodes 102 to provide a straight conductive path leading to the loop member 107.

In FIGS. 31 and 32, metal pads 109 are formed by initially depositing a 0.3 micron layer of aluminum over the loop member 107 and the connector posts 108. Any high conductivity metal (eg, aluminum, titanium, etc.) may be used and should be deposited to a thickness of about 0.5 micron or thinner so as not to affect the overall planarity of the nozzle assembly too severely. The metal pads 109 are located over the connector pillars 108 and on the loop member 107 in a predetermined 'bend region' of the thermoelastic active beam member.

33 and 34, a thermoelastic active beam member 110 is formed over the SiO ₂ loop 107. By fusion with the active beam member 110, a portion of the SiO ₂ loop member 107 functions as a lower passive beam member 116 of the mechanical thermal bend actuator, which acts as an active beam ( 110 and passive beam 116. The thermoelastic active beam member 110 may be composed of any suitable thermoelastic material, such as titanium nitride, titanium aluminum nitride, and aluminum alloys. As described in Applicant's prior application US 2008/0129793 (the contents of which are incorporated herein by reference), vanadium-aluminum alloys have large thermal expansion, low density and high Young's modulus. It is a preferred material because it has advantageous properties called Young's modulus.

To form the active beam member 110, a 1.5 micron layer of active beam material is initially deposited by standard PECVD. The beam material is then etched using standard metal etching to form the active beam member 110. After completion of the metal etching, as shown in FIGS. 33 and 34, the active beam member 110 includes a partial nozzle opening 111 and a beam element 112, which at each end have a connector post. Electrically connected to the anode and ground electrode 102 via 108. The planar beam element 112 is bent 180 degrees to extend from the top of the first (anode) connector post and then back to the top of the second (ground) connector post.

With continued reference to FIGS. 33 and 34, the metal pads 109 are positioned to facilitate current flow even in areas of potentially higher resistance. One metal pad 109 is located in the bending area of the beam element 112 and is sandwiched between the active beam member 110 and the passive beam member 116. The other metal pads 109 are located between the top of the connector pillars 108 and the ends of the beam element 112.

Referring to FIG. 35, hydrophobic polymer layer 80 is deposited on a wafer and then covered with a protective metal layer 90 (eg, 100 nm aluminum). After properly masking, the metal layer 90, the polymer layer 80 and the SiO ₂ loop member 107 are then etched to fully form the fluctuations 114 and nozzle openings 113 of the loop. Etching is generally a two step etching process, as described above with respect to FIG. 22.

The fluctuation section 114 includes a thermal bend actuator 115, which itself consists of an active beam member 110 and a passive beam member 116 below. The nozzle opening 113 is formed in the fluctuation portion 114 of the loop such that during operation, the nozzle opening moves with the actuator. As disclosed in US Publication No. 2008/0129793, structures in which the nozzle opening 113 is stationary relative to the variation 114 are also possible and are within the scope of the present invention.

A peripheral space or gap 117 surrounding the fluctuations 114 of the loop separates the fluctuations from the fixing part 118 of the loop. This spacing 117 allows the fluctuation portion 114 to bend toward the substrate 101 into the nozzle chamber 105 during operation of the actuator 115. The hydrophobic polymer layer 80 fills the gap 117 to provide a mechanical seal between the fixture 118 and the fluctuation 114 of the loop 107. During operation, the polymer has a sufficiently low Young's modulus to prevent the ink from leaking through the gap 117 while allowing the actuator to bend towards the substrate 101.

In the final MEMS processing steps, as shown in FIGS. 36 and 37, the ink supply channel 120 is etched through from the back of the substrate to the nozzle chamber 105. Although the ink supply channel 120 is shown aligned with the nozzle opening 113 in FIGS. 36 and 37, it is of course possible that the ink supply channel 120 can be positioned offset from the nozzle opening.

After the ink supply channel etch, to provide the nozzle assembly 100, the polyimide 106 filled in the nozzle chamber 105 is removed by ashing using an oxidizing plasma, and the metal thin film 90 is HF or H ₂ O _2. It is removed by the cleaning liquid.

MSQ Polymer layer containing

Hydrophobic polymer layer 80 has proven to be an important feature of Applicants' printheads. The hydrophobic polymer layer hydrophobicizes the front of the printhead, which not only helps to improve overall print quality, but also printhead maintenance means (e.g. wiper blades) used to maintain the printhead under operational conditions. It also helps to maintain printheads by providing a planar hydrophobic surface for the wiper blade. Of course, for the thermal bend-operated printheads 100 described above, the polymer 80 provides an additional function of mechanically sealing the fluctuations of the nozzle from the body of the printhead.

To date, the applicant has proposed the use of polydimethylsiloxane (PDMS). This material can be easily incorporated into MEMS manufacturing processes and has a Young's modulus and excellent hydrophobicity to enable effective thermal bend operation. PDMS, however, is relatively poor in wear resistance, and can be scratched or damaged, for example, by repeated contact with the wiper blades.

Applicants have found, however, that polysilsesquioxanes still retain all the benefits of PDMS and provide better wear resistance than PDMS. Polysilsesquioxane belong to the general class of known with a polymerized siloxane or silicone polymer, chemical empirical formula (RSiO _{1 .5)} for indicating to n, where R is hydrogen or an organic group (organic group), n is a polymer An integer representing the length of the chain. The organic group is C _{1 - 12} alkyl (alkyl) (for example, methyl (methyl)), C _{1 -10} aryl (arly) (for example, phenyl (phenyl)), or C _{1 - 16} aryl-alkyl (arylalkyl) ( For example, benzyl). The polymer chain can be any length known in the art (eg, n is from 2 to 10,000).

Poly (alkylsilsesquioxanes) and poly (arylsilsesquioxanes), such as poly (methylsilsesquioxane) and poly (phenylsilsesquioxane), may be selected from the polymer layer ( 80 has been shown to have excellent hydrophobicity, durability and wear resistance. For example, printheads coated with MSQ or PSQ can be wiped clean without damage even after the ink and paper fibers have solidified on the printhead for one hour.

Poly (methylsilsesquioxane) is known in the art as methylsilsesquioxane, MSQ, MSSQ, PMSQ and PMSSQ. Poly (phenylsilsesquioxane) is also known in the art as phenylsilsesquioxane, PSQ, PSSQ, PPSQ and PPSSQ. For the sake of brevity, Applicants hereafter refer to poly (methylsilsesquioxane) as MSQ and poly (phenylsilsesquioxane) as PSQ.

MSQ has a low dielectric constant (k = 2.7) and has previously been used as an insulating material. However, the use of MSQ as a hydrophobic coating for MEMS inkjet printheads was previously unknown.

MSQ or PSQ may be incorporated into the printheads as polymer layer 80 by the MEMS fabrication process described above. The MSQ or PSQ solution is spun on a wafer to a thickness of about 0.5 to 5 microns (eg 1 micron) and then provides a durable ink ejection surface for the printhead to enhance adhesion to the nozzle plate. To harden. Curing may include a UV treatment step. For example, a typical hardbaking process may include the following steps.

1. Contact bake at 110 ° C. for 2 minutes immediately after coating

2. Bake contact at 300 ° C. for 6.5 minutes

3. UV exposure (~ 1300mJ) for 130 seconds

4. Oven cure for 1 hour (start at 180 ° C and rise to -4 ° C / min)

Applicant's curing process described above provides MSQ coated or PSQ coated printheads with good durability, but it will be appreciated that the curing can follow any conventional procedure.

Each of the MSQ and PSQ has a Young's modulus of about 3 dB, which is slightly higher than the Young's modulus of PDMS. However, the Applicant has found that thermal bend-operated printheads still work effectively when the polymer layer 80 is composed of MSQ or PSQ despite the higher Young's modulus. In addition, the overall robustness of MSQ and PSQ is generally more important than any negative aspects due to their higher Young's modulus. Of course, in thermal bubble-forming printheads without fluctuations, the Young's modulus of the polymer layer 80 is independent of nozzle operation.

We believe that the use of MSQ or PSQ represents a significant advance in inkjet printhead technology. The hydrophobicization of inkjet printheads, especially inkjet printheads made by MEMS manufacturing processes, has been considered a very important challenge for all industry stakeholders. Applicant has demonstrated that MSQ or PSQ can be incorporated into the MEMS manufacturing process and also provide a hydrophobic ink dispensing surface having excellent durability and wear resistance. Combinations of these desirable features have not previously been accomplished in the art.

Polymer layer containing nanoparticles

As mentioned above, MSQ and PSQ have significant advantages over PDMS in their use as polymer coatings, but there are some cases where PDMS is still chosen as the material. For example, in low-powered thermally bend-actuated printheads, the lower Young's modulus of PDMS may be beneficial to minimize droplet discharge energy. For example, it would be desirable to improve the wear resistance of PDMS without being composed of low Young's modulus.

In other situations, the polymeric coating of the printhead may have properties that are not suitable for the particular fluid ejected from the printhead. It should be noted that thermal bend-operated printheads can eject both aqueous and non-aqueous liquids (eg, polymers for OLED printing), and the inherent properties of the fluid from which the ink ejection surface of the printhead is ejected It may have complementary characteristics. These properties may include, for example, the hydrophilicity, hydrophobicity, viscosity, surface tension and / or boiling point of the fluid.

Alternatively, the ink ejection surface may have properties that complement the particular type of printhead maintenance scheme employed (e.g., printhead capping disclosed in US Application No. 12 / 014,772, incorporated herein by reference). capping / wiping; or printhead flooding / contactless maintenance as disclosed in US Pat. No. 7,401,886, incorporated herein by reference. For example, wear resistance is important in printhead maintenance schemes involving contact with the printhead, but less important in non-contact maintenance schemes.

Alternatively, the ink ejection surface may have properties that complement a particular type of nozzle actuator. For example, fatigue resistance is important in thermal bend actuators in which the polymeric material seals the fluctuations of the nozzle with respect to the body of the printhead. However, in nozzles that do not fluctuate, such as the thermal bubble-forming nozzles described above, fatigue resistance is less important.

It would be highly desirable to be able to 'tune' the properties of the ink ejection surface without fundamentally changing the MEMS manufacturing process. This 'adjustment' may, for example, improve the toughness, wear resistance, fatigue resistance and / or surface energy characteristics of the ink ejection surface. As a trivial example, when printing hydrophobic liquids such as polymers, it would be better for the ink ejection surface to be relatively hydrophilic than hydrophobic (as opposed to printing an aqueous ink).

The usefulness of silicone polymers, including nanoparticles (formerly known as "fillers" in the art), can be used to modify silicone polymers (eg, PDMS, MSQ, PSQ) by changing the nanoparticles contained in the silicone polymer. ) Means that the characteristics of can be adjusted. The use of different nanoparticles will 'adjust' the properties of the ink ejection surface formed from the polymer layer 80 correspondingly.

Of course, the nanoparticles can be of any suitable type, size and shape depending on the particular application. Nanoparticles can include inorganic particles, organic particles, or a combination of both. Some examples of inorganic nanoparticles include metal oxides, metal carbonates and metal sulfates. More specifically, inorganic nanoparticles are, for example, silica (including colloidal silica), zirconium oxide, titanium oxide, aluminum oxide, calcium carbonate, tin oxide, zinc oxide, copper oxide, chromium oxide, calcium oxide, tungsten oxide , Iron oxide, cobalt oxide, barium sulfate, and the like. Some examples of organic nanoparticles include crosslinked silicone resin particles (eg PDMS, MSQ, PSQ), crosslinked polyolefin resin particles (eg polystyrene, polyethylene, polypropylene) And crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, melamine resin particles, carbon nanotubes, and the like.

As used herein, the term "nanoparticle (s)" has an average particle size in the range of 1-1000 nm, typically 1-100 nm, more typically 1-50 nm. Represents particle (s). An average particle diameter of about 20 nm is generally preferred. The particles can be monodisperse or polydisperse.

Nanoparticles may be present in amounts ranging from 1-70 wt%, optionally 5-60 wt%, optionally 10-50 wt%. The amount of nanoparticles present will depend on the essential properties of the polymer film.

Nanoparticles can be incorporated into a polymer by any suitable process, such as a sol-gel process, which is well known to those of ordinary skill in the art. The resulting polymer can be deposited by any suitable process, such as a spin-on process followed by curing.

PDMS polymers comprising silica nanoparticles are known in the art, and such polymers may be used as the polymer layer 80 in the present invention. Silica nanoparticles impart desirable properties such as wear resistance and fatigue resistance for PDMS polymers. Depending on the amount of silica particles present, PDMS may also have a relatively hydrophilic surface that is useful in some applications.

Those skilled in the art will understand that numerous modifications and / or changes may be made in accordance with the invention shown in the specific embodiments without departing from the spirit or scope of the invention as broadly disclosed. Accordingly, the present embodiments are to be considered in all respects as illustrative and not restrictive.

Claims (17)

A printhead comprising a plurality of nozzle assemblies formed on a substrate, the printhead comprising:
Each nozzle assembly
A nozzle chamber;
A nozzle opening formed in a roof of the nozzle chamber; And
A thermal bend actuator forming a moving portion of the loop of each nozzle chamber,
The thermal bend actuator,
A first active element connecting to drive circuitry; And
By including a second passive element mechanically cooperating with the first active element, when a current flows through the first active element, the first active element expands above the second passive element, thereby providing a floor of the nozzle chamber ( bending of the actuator towards the floor,
Hydrophobic polymeric material is coated on the nozzle plate of the printhead, the nozzle plate formed at least in part by a loop of each nozzle chamber,
The hydrophobic polymer material is selected from the group consisting of polysilsesquioxanes. The method of claim 1,
The hydrophobic polymer material is selected from the group consisting of poly (alkylsilsesquioxanes) and poly (arylsilsesquioxanes). The method of claim 1,
And the hydrophobic polymer material is selected from the group consisting of poly (methylsilsesquioxane) and poly (phenylsilsesquioxane). The method of claim 1,
Each loop having a hydrophobic outside surface with respect to the inside surface of each nozzle chamber by a hydrophobic coating. The method of claim 1,
Each nozzle chamber includes a loop and sidewalls made of ceramic material. The method of claim 5,
The ceramic material is selected from the group consisting of silicon nitride, silicon oxide and silicon oxynitride. The method of claim 1,
The loops spaced apart from the substrate such that sidewalls of each nozzle chamber extend between the nozzle plate and the substrate. The method of claim 1,
And the nozzle opening is formed in the fluctuation portion of the loop. The method of claim 1,
And the nozzle opening is formed in a stationary portion of the loop. The method of claim 1,
The polymeric material minimizes ink leakage during operation of the actuator by forming a mechanical seal between the fluctuations of the loop and the fixture. delete delete delete delete delete delete delete

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