CN102470675B - Printhead having polysilsesquioxane coating on ink ejection face - Google Patents

Abstract

The present invention discloses a printhead having an ink ejection face coated with a hydrophobic polymeric material. The polymeric material includes polysilsesquioxanes, such as polymethylsilsesquioxane or polyphenylsilsesquioxane. The printhead is compatible with various printhead maintenance operations that require contact with the ink ejection face.

Description

Printhead with polysilsesquioxane coating on inkjet side

technical field

The present invention relates to the field of printers and in particular to inkjet printheads. It was primarily developed to improve print quality and printhead maintenance for high-resolution printheads.

Background technique

Many different types of printing have been invented and many of them are currently in use. Known printing formats have a variety of methods for printing a print medium with the relevant print medium. Commonly used printing formats include offset printing, laser printing and duplicating devices, dot-matrix impact printers, thermal paper printers, film recorders, thermal wax printers, dye-sublimation printers, and drop-on-demand and continuous-flow inkjet printers. ink printer. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation, and the like.

In recent years, inkjet printing techniques, in which each individual pixel of ink originates from one or more ink nozzles, have become more popular mainly due to their cheapness and versatility.

Many different technologies have been invented for inkjet printing. For a comprehensive understanding of the field, refer to J Moore's article: "Non-Impact Printing: Introduction and Historical Perspective" (non-impact printing: introduction and historical perspective), Output Hard CopyDevices (output hard copy device), edited by R Dubeck and S Sherr , pp. 207-220 (1998).

Inkjet printers present themselves in a variety of types. The utilization of a continuous stream of ink in inkjet printing dates back to at least 1929, where US Patent No. 1941001 to Hansell discloses a simple form of continuous stream electrostatic inkjet printing.

US Patent 3,596,275 to Sweet also discloses a continuous inkjet printing process including a step in which the inkjet flow is conditioned by a high frequency electrostatic field to cause ink drop separation. This technology is still used by several manufacturers, including Elmjet and Scitex (see also US Patent No. 3,373,437 to Sweet et al.).

Piezoelectric inkjet printers are also a form of commonly used inkjet printing devices. In U.S. Patent No. 3,946,398 (1970) to Kyser et al., which employs a diaphragm mode of operation, in U.S. Patent 3,683,212 (1970) to Zolten, which discloses a squeeze mode of operation for a piezoelectric crystal, in U.S. Patent No. 3,683,212 (1970) which discloses a piezoelectric mode of operation for a piezoelectric crystal In U.S. Patent No. 3,747,120 (1972) to Stemme, in U.S. Patent No. 4,459,601 to Howkins disclosing piezoelectric push mode actuation of an inkjet stream, and in Fischbeck disclosing a shear mode type of piezoelectric transducer element Piezoelectric systems are disclosed in US 4584590.

Recently, thermal inkjet printing has become a very popular form of inkjet printing. Inkjet printing techniques include those disclosed in Endo et al., GB 2007162 (1979) and Vaught et al., U.S. Patent 4,490,728. The aforementioned two documents disclose inkjet printing techniques that rely on the actuation of electrothermal actuators that generate air bubbles in compressed spaces such as nozzles, thereby causing ink to flow from openings connected to the confined spaces. The holes jet onto the associated print media. Printing devices employing electrothermal actuators are manufactured by manufacturers such as Canon and Hewlett-Packard.

As can be seen from the foregoing, many different types of printing techniques are available. Ideally, a printing technique should have several desirable attributes. These include inexpensive construction and operation, high-speed operation, safe and continuous long-term operation, and more. Each technology may have its own advantages and disadvantages in terms of cost, speed, quality, reliability, power consumption, simplicity of construction operation, durability, and consumables.

In the construction of any inkjet printing system, a considerable number of important factors must be weighed against one another, especially in the case of constructing large printheads, especially pagewide large printheads. A number of these factors are summarized below.

First, inkjet printheads are typically constructed using micro-electromechanical systems (MEMS) technology. Therefore, they tend to rely on standard integrated circuit construction/manufacturing techniques of depositing a planar layer on a silicon wafer and etching some portion of the planar layer. In the art of silicon circuit fabrication, some techniques are better known than others. For example, techniques associated with creating CMOS circuits are likely to be easier to use than techniques associated with creating exotic circuits including ferroelectrics, gallium arsenide, and the like. Thus, it is desirable to employ well-known semiconductor fabrication techniques that do not require any "exotic" processes or materials in any MEMS configuration. Of course, some trade-offs will be made, as it is desirable to employ exotic materials anyway if the advantages of using the materials far outweigh the disadvantages. However, the problem of exotic materials can be avoided if the same or similar properties can be obtained using more general materials.

A desirable characteristic of an inkjet printhead is a hydrophobic ink ejection face ("front side" or "nozzle face"), preferably in combination with hydrophilic nozzle chambers and ink supply channels. The hydrophilic nozzle chamber and ink supply channel provide capillary action and are thus optimally used for priming and for resupplying ink to the nozzle chamber after each ink drop ejection. The hydrophobic front side minimizes the tendency of ink to flood on the front side of the printhead. With a hydrophobic front, aqueous inkjet is less likely to exit the nozzle opening and flood sideways. Furthermore, any ink overflowing the nozzle openings is less likely to spread on the face and mix on the front side - instead they will form discrete spherical droplets that can be more easily managed with proper maintenance operations.

Heretofore, the applicant has described the use of polydimethylsiloxane (PDMS) to coat the front side of a printhead and provide a hydrophobic surface. However, although PDMS has excellent hydrophobicity and can be easily incorporated into the printhead MEMS fabrication process, it has relatively poor wear resistance and may be scratched or otherwise damaged by wipers used for printhead maintenance ( See, eg, US Application No. 12/014,772, filed January 16, 2008, which is incorporated herein by reference). Therefore, it is desirable to provide a printhead with a hydrophobic inkjet face that can be easily produced by MEMS fabrication processes and has good wear resistance.

Contents of the invention

In a first aspect, there is provided a printhead having an ink-ejecting face, wherein at least a portion of the ink-ejecting face is coated with a hydrophobic polymeric material, the polymeric material comprising polysilsesquioxane. Printheads according to the present invention have excellent durability and wear resistance, making them compatible with various printhead maintenance operations involving contact with the ink ejection face (eg, wiping). Furthermore, polysilsesquioxanes can be deposited as thin layers (0.5 microns to 2 microns) by a spin-coating process that can be easily incorporated into the MEMS printhead manufacturing process.

Optionally, the polysilsesquioxane is selected from the group consisting of polyalkylsilsesquioxanes and polyarylsilsesquioxanes.

Optionally, the polysilsesquioxane is selected from the group consisting of polymethylsilsesquioxane and polyphenylsilsesquioxane.

Optionally, the polymeric material is deposited and hard baked onto the nozzle plate of the printhead during MEMS printhead fabrication.

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

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

Optionally, each top has, by means of said hydrophobic coating, a hydrophobic outer side surface relative to the inner side surface of each nozzle chamber.

Optionally, each nozzle chamber includes a top and side walls of ceramic material.

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

Optionally, the top is spaced apart from the base such that a side wall of each nozzle chamber extends between the nozzle plate and the base.

Optionally, the actuator is a heater element configured to heat ink in the chamber to form bubbles thereby forcing ink drops through the nozzle opening.

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

Optionally, the actuator is a thermal bending actuator comprising:

a first active element for connection to a drive circuit; and

a second passive element that mechanically cooperates with the first element such that when current passes through the first element, the first element expands relative to the second element, causing the The actuator is bent.

Optionally, the thermal bending actuator defines at least a portion of the top of each nozzle chamber, whereby actuation of the actuator moves a movable portion of the top towards the bottom of the nozzle chamber.

Optionally, said nozzle opening is defined in said movable portion of said top.

Optionally, a nozzle opening is defined in a fixed portion of said top.

Optionally, said polymeric material defines a mechanical seal between said movable and fixed parts of said top, thereby minimizing ink leakage during actuation of said actuator.

In a second aspect, there is provided a printhead having an ink-ejecting face, wherein at least a portion of the ink-ejecting face is coated with a polymeric material comprising polysiloxane incorporating nanoparticles. According to a second aspect, the nanoparticles impart desired properties such as durability, abrasion resistance, fatigue resistance, hydrophobicity, hydrophilicity, etc. to the polymeric coating.

Optionally, the polysiloxane is selected from the group consisting of polyalkylsilsesquioxanes, polyarylsilsesquioxanes and polydialkylsilsesquioxanes.

Optionally, the polysiloxane is selected from the group consisting of polymethylsilsesquioxane, polyphenylsilsesquioxane and polydimethylsilsesquioxane.

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

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

Optionally, the inorganic nanoparticles are made of silica, zirconia, titania, alumina, calcium carbonate, tin oxide, zinc oxide, copper oxide, chromium oxide, calcium oxide, tungsten oxide, iron oxide, cobalt oxide and selected from the group consisting of barium sulfate.

Optionally, the organic nanoparticles are selected from cross-linked silicone resin particles, cross-linked polyolefin resin particles, cross-linked propylene resin particles, cross-linked styrene-propylene resin particles, cross-linked polyester particles, polyimide Particles, melamine resin particles and carbon nanotubes are selected from the group.

Optionally, the nanoparticles are incorporated into polysiloxane in an amount ranging from 1% to 70% by weight.

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

Optionally, the printhead includes a plurality of nozzle assemblies formed on a substrate, each nozzle assembly including: a nozzle chamber, a nozzle opening defined in the top of the nozzle chamber, and a ink actuator.

Optionally, a polymeric material coats a nozzle plate of the printhead at least partially defined by the top of each nozzle chamber.

Optionally, each nozzle chamber includes a top and side walls having a ceramic material selected from the group consisting of silicon nitride, silicon oxide and silicon oxynitride.

Optionally, the top is spaced apart from the base such that a side wall of each nozzle chamber extends between the nozzle plate and the base.

Optionally, the actuator is a heater element configured to heat ink in the chamber to form bubbles thereby forcing ink drops through the nozzle opening.

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

Optionally, the actuator is a thermal bending actuator comprising:

a first active element for connection to a drive circuit; and

a second passive element that mechanically cooperates with the first element such that when current passes through the first element, the first element expands relative to the second element, causing the Actuator bends

Optionally, the thermal bending actuator defines at least a portion of the top of each nozzle chamber, whereby actuation of the actuator moves a movable portion of the top towards the bottom of the nozzle chamber.

Optionally, the nozzle opening is defined in either of the movable portion of the top or the fixed portion of the top.

Optionally, said polymeric material defines a mechanical seal between said movable part and said fixed part of said top, thereby minimizing ink leakage during actuation of said actuator.

In a third aspect, there is provided an inkjet printhead for ejecting a jettable fluid, the printhead having an inkjet face coated with a polymeric material incorporating nanoparticles, wherein the nanoparticles incorporate one or more Predetermined properties are imparted to the ink-ejection face, the predetermined properties complementing at least one of the following:

Inherent properties of jettable fluids;

a printhead maintenance mechanism associated with the printhead; and

Type of nozzle actuator.

The present invention according to the third aspect can modulate the surface characteristics of the ink ejection face to predetermined characteristics of the printer. For example, printhead maintenance may be a priority in some printers, while optimal fluid ejection may be a priority in other printers. Alternatively, the nanoparticles can be selected to provide compromised printer properties.

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

Optionally, the 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 the nanoparticles, and the wear resistance of the nanoparticles.

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

Optionally, the inorganic nanoparticles are made of silica, zirconia, titania, alumina, calcium carbonate, tin oxide, zinc oxide, copper oxide, chromium oxide, calcium oxide, tungsten oxide, iron oxide, cobalt oxide and selected from the group consisting of barium sulfate.

Optionally, the organic nanoparticles are selected from cross-linked silicone resin particles, cross-linked polyolefin resin particles, cross-linked propylene resin particles, cross-linked styrene-propylene resin particles, cross-linked polyester particles, polyimide Particles, melamine resin particles and carbon nanotubes are selected from the group.

Optionally, the intrinsic property of the jettable fluid is selected from the group consisting of hydrophilicity, hydrophobicity, viscosity, surface tension and boiling point.

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

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

Optionally, the polymeric material comprises polysiloxane.

Optionally, the polysiloxane is selected from the group consisting of polyalkylsilsesquioxanes, polyarylsilsesquioxanes, and polydialkylsilsesquioxanes.

Optionally, the polysiloxane is selected from the group consisting of polymethylsilsesquioxane, polyphenylsilsesquioxane and polydimethylsilsesquioxane.

Other optional embodiments of the printhead according to the third aspect are the same as those according to the first and second aspects.

Description of drawings

Alternative 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 of a nozzle assembly array of a thermal inkjet printhead;

Figure 2 is a side view of the nozzle assembly unit shown in Figure 1;

Figure 3 is a perspective view of the nozzle assembly shown in Figure 2;

Figure 4 shows the partially formed nozzle assembly after depositing sidewall and top material onto the sacrificial photoresist layer;

Figure 5 is a perspective view of the nozzle assembly shown in Figure 4;

Figure 6 is a mask associated with the nozzle edge etch shown in Figure 7;

Figure 7 shows the etching of the top layer to form the nozzle opening edge;

Figure 8 is a perspective view of the nozzle assembly shown in Figure 7;

Figure 9 is a mask associated with the nozzle opening etch shown in Figure 10;

Figure 10 shows etching of the top material to form an elliptical nozzle opening;

Figure 11 is a perspective view of the nozzle assembly shown in Figure 10;

Figure 12 shows oxygen plasma ashing of first and second sacrificial layers;

Figure 13 is a perspective view of the nozzle assembly shown in Figure 12;

Figure 14 shows the nozzle assembly after ashing, and the opposite side of the wafer;

Figure 15 is a perspective view of the nozzle assembly shown in Figure 14;

Figure 16 is a mask associated with the backside etch shown in Figure 17;

Figure 17 shows backside etching of ink supply channels into the wafer;

Figure 18 is a perspective view of the nozzle assembly shown in Figure 17;

Figure 19 shows the nozzle assembly of Figure 7 after deposition of a hydrophobic polymeric coating;

Figure 20 is a perspective view of the nozzle assembly shown in Figure 19;

FIG. 21 shows the nozzle assembly of FIG. 19 after deposition of a protective metal film; and

Figure 22 shows the nozzle assembly of Figure 21 after etching through the protective metal film, polymeric coating and nozzle top;

Figure 23 shows the completed jetpack assembly after backside MEMS processing and photoresist removal;

Figure 24 is a perspective view of the nozzle assembly shown in Figure 23;

Figure 25 is a side cross-sectional view of a partially fabricated alternative inkjet nozzle assembly following a first sequence of steps in which nozzle chamber sidewalls are formed;

Figure 26 is a perspective view of the partially fabricated inkjet nozzle assembly shown in Figure 25;

27 is a side cross-sectional view of a partially fabricated inkjet nozzle assembly after a second sequence of steps in which the nozzle chambers are filled with polyimide;

Figure 28 is a perspective view of the partially fabricated inkjet nozzle assembly shown in Figure 27;

Figure 29 is a side cross-sectional view of a partially fabricated inkjet nozzle assembly after a third sequence of steps in which connector posts are formed up to the top of the chamber;

Figure 30 is a perspective view of the partially fabricated inkjet nozzle assembly shown in Figure 29;

Figure 31 is a side cross-sectional view of a partially fabricated inkjet nozzle assembly after a fourth sequence of steps in which a conductive metal plate is formed;

Figure 32 is a perspective view of the partially fabricated inkjet nozzle assembly shown in Figure 31;

33 is a side cross-sectional view of a partially fabricated inkjet nozzle assembly following a fifth sequence of steps in which an active beam member of a thermal bending actuator is formed;

Figure 34 is a perspective view of the partially fabricated inkjet nozzle assembly shown in Figure 33;

35 is a side cross-sectional view of a partially fabricated inkjet nozzle assembly after a sixth sequence of steps in which a polymeric layer is applied, shielded with a metal layer, and the nozzle opening is etched;

Figure 36 is a side cross-sectional view of the completed inkjet nozzle assembly after backside MEMS processing and photoresist removal;

37 is a cross-sectional perspective view of the inkjet nozzle assembly shown in FIG. 36 .

Detailed ways

The present invention can be used with any type of printhead. The applicant has previously described a number of inkjet printheads. It is not necessary to describe all of these printheads here for an understanding of the present invention. However, the invention will now be described in connection with thermal bubble forming inkjet printheads and mechanical thermal bend actuated inkjet printheads. The advantages of the present invention will become apparent from the following description.

Thermal bubble formation inkjet printhead

Referring to Figure 1, a portion of a printhead including a plurality of nozzle assemblies is shown. Figures 2 and 3 show one of these nozzle assemblies in side sectional view and in sectional perspective view.

Each nozzle assembly includes a nozzle chamber 24 formed on a silicon wafer substrate 2 by MEMS fabrication techniques. The nozzle chamber 24 is defined by a top 21 and side walls 22 extending from the top 21 to the silicon substrate 2 . As shown in FIG. 1, each top is defined by a portion of the nozzle surface 56 that spans the jetting face of the printhead. The nozzle surface 56 and the sidewall 22 are formed from the same material that is deposited by PECVD onto a sacrificial scaffold of photoresist during MEMS fabrication. Typically, nozzle surface 56 and sidewall 22 are formed of a ceramic material such as silicon dioxide or silicon nitride. These hard materials have excellent properties for robustness of the printhead, and their inherent hydrophilicity is advantageous for supplying ink to the nozzle chambers 24 by capillary action. However, the outer (ink ejection) surface of the nozzle surface 56 is also hydrophilic, which causes any overflow ink to spread across the surface.

Returning to the details of the nozzle chambers 24 , it will be seen that nozzle openings 26 are defined in the top of each nozzle chamber 24 . Each nozzle opening 26 is generally oval and has an associated nozzle lip 25 . The nozzle lip 25 aids in the directionality of the ink drops during printing and reduces ink overflow from the nozzle opening 26 at least to some extent. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29 arranged below the nozzle opening 26 and suspended in the recess 8 . Electric current is supplied to the heater element 29 via an electrode 9 connected to a driving circuit in the lower CMOS layer 5 of the substrate 2 . When current is passed through the heater element 29, it rapidly superheats the surrounding ink to form air bubbles, which forces the ink through the nozzle opening. By suspending the heater element 29, the heater element 29 is fully immersed in ink when the nozzle chamber 24 is activated. This improves the efficiency of the printhead, since less heat is diffused into the underlying substrate 2 and more input energy is used to generate air bubbles.

As best seen in Figure 1, the nozzles are arranged in rows and ink supply channels 27 extending longitudinally along the row supply ink to each nozzle in the row. An ink supply channel 27 delivers ink to the ink inlet passage 15 for each nozzle, which supplies ink into the nozzle chamber 24 from the side of the nozzle opening 26 via the ink conduit 23 .

The MEMS fabrication process for making such a printhead is described in detail in Applicant's previously filed U.S. Application No. 11/246,684, filed October 11, 2005, the entire disclosure of which is incorporated by reference This article. For clarity, reference is made here again to later stages of the fabrication process.

4 and 5 illustrate a partially fabricated printhead including nozzle chamber 24 enclosing sacrificial photoresists 10 ("SAC1") and 16 ("SAC2"). The SAC1 photoresist 10 serves as a scaffold for the deposition of heater material to form suspended heater elements 29 . The SAC2 photoresist 16 serves as a scaffold for the deposition of the sidewalls 22 and the top 21 which defines a portion of the nozzle surface 56 .

In the prior art process, and with reference to FIGS. 6-8 , the next stage of MEMS fabrication defines an elliptical nozzle edge 25 in the top 21 by etching away 2 microns of top material 20 . The etch is defined using a layer of photoresist (not shown) exposed through the dark fringe mask shown in FIG. 6 . The elliptical lip 25 comprises two coaxial lips 25a and 25b which are arranged on their respective thermal actuators 29 .

Referring to FIGS. 9 to 11 , the next stage defines an oval nozzle opening 26 in the top 21 , bounded by a rim 25 , by etching all the way through the remaining top material. The etch is defined using a layer of photoresist (not shown) exposed through the dark top mask shown in FIG. 9 . As shown in FIG. 11 , an oval nozzle opening 26 is provided on a thermal actuator 29 .

With all MEMS nozzle features now fully formed, the next stage removes the SAC1 and SAC2 photoresist layers 10 and 16 by _O2 plasma ashing (FIGS. 12 and 13). Figures 14 and 15 show the total thickness of the silicon wafer 2 (150 microns) after ashing of the SAC1 and SAC2 photoresist layers 10 and 16 .

Referring to Figures 16-18, once the front side MEMS processing of the wafer is complete, the ink supply channel 27 is etched from the back side of the wafer to meet the ink inlet 15 using standard anisotropic DRIE. The backside etch is defined using a layer of photoresist (not shown) exposed through the dark mask shown in FIG. 16 . Ink supply channel 27 forms a fluid connection between the backside of the wafer and ink inlet 15 .

Finally, and referring to Figures 2 and 3, the wafer is thinned to approximately 135 microns by backside etching. Figure 1 shows three adjacent rows of nozzles in a cross-sectional perspective view of a completed printhead integrated circuit. Each row of nozzles has a respective ink supply channel 27 extending along its length and supplying ink to the plurality of ink inlets 15 in each row. The ink inlets in turn supply ink to ink conduits 23 for each row, with each nozzle chamber receiving ink from a common ink conduit for that row.

As already discussed above, this prior art MEMS fabrication process inevitably leaves Lower hydrophilic inkjet side.

In a preferred process for hydrophobizing the nozzle surface 56 (and as described in US2009/0139961, the disclosure of which is incorporated herein by reference), wafers are exposed to the nozzles illustrated in FIGS. 7 and 8 . The hydrophobic polymer 80 is applied immediately after the edge etch stage.

A thin layer (approximately 1 micron to 2 microns) of hydrophobic polymer 100 was spun onto the wafer and hard baked to provide the partially fabricated printhead shown in FIGS. 19 and 20 .

Referring now to FIG. 21 , a protective metal film 90 (approximately 100 nm in thickness) is then deposited onto polymer layer 80 . The metal film is typically composed of titanium or aluminum and protects the hydrophobic polymer 80 from the oxygen ashing conditions of later stages. Thus, the polymer layer 80 is not exposed to aggressive ashing conditions and retains its hydrophobic properties throughout the MEMS process steps.

FIG. 22 shows the wafer after the nozzle openings 26 have been etched through the metal film 110 , the polymer layer 80 and the nozzle top 21 . This etch step utilizes a conventionally patterned photoresist layer (not shown) as a common mask for all nozzle etch steps. In a typical etch sequence, the metal film 90 is first etched by a standard dry metal etch (eg, BCl ₃ /Cl ₂ ) or by a wet metal etch (eg, H ₂ O ₂ or HF). A second dry etch is then used to etch through the polymer layer 80 and the nozzle top 21 . Typically, the second etch step is a dry etch with _O2 and a fluorinated etch gas (eg, _SF6 or _CF4 ).

Once the nozzle openings 26 are defined as shown in FIG. 22, backside MEMS processing steps (e.g., etching ink supply channels, wafer thinning, etc.) can be performed according to known protocols similar to those described above in connection with FIGS. etc.) and subsequent stages of ashing of the photoresist. The final removal of the thin metal film 90 using H ₂ O ₂ or HF cleaning yields the finished nozzle assembly shown in FIGS. 23 and 24 , having the hydrophobic polymer layer 80 .

Thermal Bending Actuator Printheads

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

25-37 illustrate the sequence of the MEMS fabrication process for the inkjet nozzle assembly 100 described in Applicant's earlier US Publication No. 2008/0309728, the contents of which are incorporated herein by reference. The completed inkjet nozzle assembly 100 shown in Figures 36 and 37 employs thermal bending actuation whereby the active portion of the top bends towards the base, causing ink ejection.

The starting point for MEMS fabrication is a standard CMOS wafer with CMOS drive circuitry formed in the upper portion of the silicon wafer. At the end of the MEMS fabrication process, the wafer is diced into individual printhead integrated circuits (ICs), where each IC includes driver circuitry and multiple nozzle assemblies.

As shown in FIGS. 25 and 26 , a substrate 101 has an electrode 102 formed in an upper portion thereof. Electrode 102 is one of a pair of adjacent electrodes (positive and ground) for supplying electrical power to actuators of inkjet nozzle 100 . The electrodes receive power from a CMOS driver circuit (not shown) in the upper layer of the substrate 101 .

Another electrode 103 shown in FIGS. 25 and 26 is used to supply electric power to adjacent inkjet nozzles. In general, the figures illustrate MEMS fabrication steps for a nozzle assembly that is one of an array of nozzle assemblies. The following description focuses on the manufacturing steps for one of these nozzle assemblies. However, it should of course be understood that the corresponding steps for all nozzle assemblies formed on the wafer are performed simultaneously. Although the adjacent nozzle assembly is partially shown in the figures, it can be omitted for this purpose. Accordingly, not all features of the electrode 103 and adjacent nozzle assembly will be described in detail herein. In fact, some MEMS fabrication steps will not be shown in the adjacent nozzle assembly for the benefit of clarity.

In the sequence of steps shown in FIGS. 25 and 26 , an 8 micron layer of silicon dioxide was initially deposited on substrate 101 . The depth of the silica defines the depth of the nozzle chamber 105 for the inkjet nozzle. After the _SiO2 layer is deposited, it is etched to define the walls 104 which will become the side walls of the nozzle chamber 105, shown most clearly in FIG. 26 .

As shown in Figures 27 and 28, the nozzle chamber 105 is then filled with photoresist or polyimide 106, which acts as a sacrificial standoff for subsequent deposition steps. Polyimide 106 is spin-coated onto the wafer using standard techniques, UV curing and/or hard-baking, and then subjected to chemical mechanical planarization (CMP), stopping at the top surface of the SiO ₂ wall 104 .

In FIGS. 29 and 30 , the top member 107 of the nozzle chamber 105 is formed and the highly conductive connector post 108 extends down to the electrode 102 . Initially, a 1.7 micron layer of SiO ₂ is deposited onto polyimide 106 and wall 104 . This SiO ₂ layer defines the top 107 of the nozzle chamber 105 . Next, a pair of via holes down to electrode 102 are formed in wall 104 using standard anisotropic DRIE. The etching exposes the counter electrode 102 through the corresponding via hole. Next, a highly conductive metal, such as copper, is filled into the via holes by electroless plating. The deposited copper pillars 108 are subjected to CMP, stopping on the SiO ₂ top member 107 to provide a planar structure. It can be seen that copper connector posts 108 formed during electroless copper plating meet corresponding electrodes 102 to provide a linear conductive path to top member 107 .

In FIGS. 31 and 32 , metal pads 109 are formed by initially depositing a 0.3 micron layer of aluminum on top member 107 and connector post 108 . Any highly conductive metal (eg, aluminum, titanium, etc.) can be used and should be deposited to a thickness of about 0.5 microns or less so as not to seriously affect the overall planarity of the nozzle assembly. A metal pad 109 is disposed over the connector post 108 and on the top member 107 in a predetermined "bend region" of the thermoelastic active beam member.

In FIGS. 33 and 34 , thermoelastic active beam members 110 are formed on top 107 of SiO ₂ . By means of welding to the active beam member 110 , a portion of the SiO ₂ top member 107 serves as the lower passive beam member 116 of the mechanothermal bending actuator defined by the active beam 110 and the 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 explained in Applicant's earlier U.S. Publication No. 2008/0129793, the contents of which are incorporated herein by reference, aluminum vanadium alloys are preferred materials because of their combination of high thermal and the favorable properties of high Young's modulus.

To form 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 define active beam members 110 . After metal etching is complete and as shown in FIGS. Positive and ground electrodes 102 . A planar beam element 112 extends from the top of the first (positive) connector post and bends approximately 180 degrees to return to the top of the second (ground) connector post.

Still referring to FIGS. 33 and 34 , metal pads 109 are provided to facilitate current flow in potentially high resistive regions. A metal pad 109 is disposed at the bending region of the beam element 112 and is sandwiched between the active beam element 110 and the passive beam element 116 . Another metal pad 109 is provided between the top of the connector post 109 and the end of the beam element 112 .

Referring to Figure 35, a hydrophobic polymer layer 80 is deposited onto the wafer and covered with a protective metal layer 90 (eg, 100 nm aluminum). After appropriate masking, the metal layer 90, polymer layer 80 and SiO ₂ top member 107 are then etched to fully define the nozzle opening 113 and active portion 114 of the top. Etching is typically a two-stage etch process as described above in connection with FIG. 22 .

The active portion 114 includes a thermal bending actuator 115 which itself includes an active beam member 110 and an underlying passive beam member 116 . A nozzle opening 113 is defined in the top movable portion 114 such that the nozzle opening moves with the actuator during actuation. Configurations in which the nozzle opening 113 is fixed relative to the movable portion 114, as described in US Publication No. 2008/0129793, are also possible and within the scope of the present invention.

A peripheral space or gap 117 around the movable portion 114 of the top separates the movable portion from the fixed portion 118 of the top. This gap 117 allows the movable portion 114 to flex into the nozzle chamber 105 and towards the substrate 101 when the actuator 115 is actuated. Hydrophobic polymer layer 80 fills gap 117 to provide a mechanical seal between movable portion 114 and fixed portion 118 of top 107 . The polymer has a Young's modulus low enough to allow the actuator to flex towards the substrate 101 during actuation while preventing ink from escaping through the gap 117 .

In a final MEMS processing step, and as shown in FIGS. 36 and 37 , an ink supply channel 120 is etched from the backside of the substrate 101 through to the nozzle chamber 105 . Although the ink supply channels 120 are shown in alignment with the nozzle openings 113 in FIGS. 36 and 37 , they could of course be arranged offset from the nozzle openings.

After the etching of the ink supply channel, the polyimide 106 filling the nozzle chamber 105 is removed by ashing in oxidative plasma, and the metal thin film 90 is removed by HF or H ₂ O ₂ cleaning to provide the nozzle assembly 100 .

Polymer layer including MSQ

The hydrophobic polymer layer 80 has proven to be an important feature of the Applicant's printhead. Not only does it make the front face of the printhead hydrophobic (which helps improve overall print quality), it also aids printhead maintenance by presenting a planarized hydrophobic surface for printhead maintenance devices (e.g., wipers), which A maintenance device is employed to maintain the printhead in an operable condition. Of course, in the case of the thermally bend-actuated printhead 100 described above, the polymer 80 provides the additional function of mechanically sealing the active portion of the nozzle from the body of the printhead.

Hitherto, the applicant has proposed the use of polydimethylsiloxane (PDMS). The material can be easily incorporated into MEMS fabrication processes, has excellent hydrophobicity and a Young's modulus that allows efficient thermal bending actuation. However, PDMS has relatively poor abrasion resistance and can be scratched or otherwise damaged by repeated contact with, for example, a squeegee brush.

Applicants have now found that polysilsesquioxanes provide abrasion resistance superior to PDMS while still maintaining all the advantages of PDMS. Polysilsesquioxanes belong to the general class of polymers known as polymeric siloxanes or polymeric silicones, and have the empirical formula (RSiO _1.5 ) _n , where R is hydrogen or an organic group and n is the number representing the polymer chain Integer of length. The organic group can be C _1-12 alkyl (eg, methyl), C _1-10 aryl (eg, phenyl) or C _1-16 aralkyl (eg, benzyl). The polymer chains can be of any length known in the art (eg, n is from 2 to 10,000).

Poly(alkylsilsesquioxanes) and polyarylsilsesquioxanes (poly(arylsilsesquioxanes)) (such as poly(methylsilsesquioxanes)) and polyphenylsilsesquioxanes Poly(phenylsilsesquioxanes)) have been shown to have excellent hydrophobicity, durability and abrasion resistance when used as polymer layer 80 in Applicants' printheads. For example, a printhead coated with MSQ or PSQ was able to be wiped clean without damage even after the ink and paper fibers were baked onto the printhead for 1 hour.

Polymethylsilsesquioxane is also known in the art as methylsilsesquioxane, MSQ, MSSQ, PMSQ, and PMSSQ. Polyphenylsilsesquioxane is also known in the art as phenylsilsesquioxane, PSQ, PSSQ, PPSQ, and PPSSQ. For the sake of brevity, applicants will hereinafter refer to polymethylsilsesquioxane as MSQ and polyphenylsilsesquioxane as PSQ.

MSQ has a low dielectric constant (k=2.7) and has been previously used as an insulating material. However, the use of MSQ as a hydrophobic coating for MEMS inkjet printheads was not previously known.

MSQs or PSQs can be incorporated into the printhead as polymer layer 80 by the MEMS fabrication process described above. The MSQ or PSQ solution is spin-coated onto the wafer to a thickness of approximately 0.5 micron to 5 micron (eg, 1 micron) and then hard baked to improve adhesion to the nozzle plate and provide a durable inkjet surface for the printhead. A hard bake may include a UV curing step. For example, a typical hard bake process may include the following steps:

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

2. Contact bake at 300°C for 6.5 minutes

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

4. Oven cure for 1 hour (start at 180°C and ramp up at ~4°C/min)

While Applicants' above-described hardbake process provides MSQ coated or PSQ coated printheads with excellent durability, it should be understood that the hardbake may follow any conventional procedure.

MSQ and PSQ each have a Young's modulus of about 3 GPa, which is slightly larger than that of PDMS. However, applicants have discovered that thermally bend-actuated printheads operate efficiently when polymer layer 80 comprises MSQ or PSQ despite their higher Young's modulus. Furthermore, the overall firmness of MSQ and PSQ generally outweighs any disadvantages caused by their higher Young's modulus. Of course, in a thermal bubble forming printhead where there are no moving parts, the Young's modulus of the polymer layer 80 is not correlated with nozzle actuation.

The inventors believe that the use of MSQ or PSQ represents a major breakthrough in inkjet printhead technology. Hydrophobic inkjet printheads, especially those manufactured by MEMS manufacturing processes, are considered a very significant challenge for all industry players. The applicant has demonstrated that MSQ or PSQ can be incorporated into the MEMS fabrication process and provide a hydrophobic inkjet face with excellent durability and abrasion resistance. This ideal combination of features has not been previously achieved in the art.

Polymer layer containing nanoparticles

As mentioned above, while MSQ and PSQ have significant advantages over PDMS for use as polymer coatings, there are some examples where PDMS is still the material of choice. For example, in low power thermal bend actuated printheads, the low Young's modulus of PDMS can be advantageously used to minimize ink drop ejection energy. It would be desirable to improve the wear resistance properties of eg PDMS apart from its low Young's modulus.

In other cases, the polymer coating of the printhead may have properties that are unsuitable for a particular fluid being ejected from the printhead. It should be noted that thermal bend-actuated printheads can jet both aqueous and non-aqueous liquids (e.g., polymers for printing OLEDs), and that the ink-jet face of the printhead can have properties that complement the intrinsic properties of the jetted fluid. . These properties may include, for example, the hydrophilicity, hydrophobicity, viscosity, surface tension, and/or boiling point of the fluid.

Alternatively, the ink-ejection face may have properties that complement the particular type of printhead maintenance mechanism employed (e.g., a printhead overseal as described in U.S. Application No. 12/014,772, incorporated herein by reference ( capping)/wiping; or printhead flooding/non-contact maintenance as described in US 7,401,886 incorporated herein by reference). For example, abrasion resistance is important for printhead maintenance mechanisms that involve contact with the printhead, but is less important for non-contact maintenance mechanisms.

Optionally, the ink ejection face may have properties that complement a particular type of nozzle actuator. For example, fatigue resistance is important for thermal bend actuators where a polymeric material seals the active portion of the nozzle to the body of the printhead. However, fatigue resistance is less important in inactive nozzles such as the hot bubble forming nozzles described above.

The ability to "modulate" the properties of the jetting face without fundamentally changing the MEMS fabrication process would be highly desirable. This "modulation" can improve, for example, the toughness, abrasion resistance, fatigue resistance and/or surface energy properties of the inkjet face. As a general example, when printing hydrophobic liquids such as polymers, the ink ejection side should preferably be relatively hydrophilic rather than hydrophobic (compared to printing aqueous inks).

The availability of silicone polymers incorporating nanoparticles (sometimes referred to in the art as "fillers") means that the properties of silicone polymers (e.g., PDMS, MSQ, PSQ) can be modified by changing the nanoparticle Particles are adjusted. The use of different nanoparticles will correspondingly "modulate" the properties of the ink-ejection face defined by the polymer layer 80 .

Nanoparticles can, of course, be of any suitable type, size and shape depending on the particular application. Nanoparticles can include inorganic particles, organic particles, or combinations thereof. Some examples of inorganic nanoparticles are metal oxides, metal carbonates and metal sulfates. More specifically, the inorganic nanoparticles can be, for example, silica (including silica gel), zirconia, titania, alumina, calcium carbonate, tin oxide, zinc oxide, copper oxide, chromium oxide, calcium oxide, tungsten oxide, iron oxide , cobalt oxide, barium sulfate, etc. Some examples of organic nanoparticles are cross-linked silicone resin particles (e.g. PDMS, MSQ, PSQ), cross-linked polyolefin resin particles (e.g. polystyrene, polyethylene, polypropylene), cross-linked propylene resin particles, cross-linked benzene Ethylene-propylene resin particles, cross-linked polyester particles, polyimide particles, melamine resin particles, carbon nanotubes, etc.

As used herein, the term "nanoparticle" refers to a particle having an average particle size in the range of 1 nm to 1000 nm, more typically in the range of 1 nm to 100 nm, and more typically in the range of 1 nm to 50 nm . An average particle size of about 20 nm is generally preferred. Particles can be monodisperse or polydisperse.

The nanoparticles may be present in an amount ranging from 1% to 70%, alternatively in an amount ranging from 5% to 60%, alternatively in an amount ranging from 10% to 50% by weight. The amount of nanoparticles present will depend on the desired properties of the polymer film.

Nanoparticles can be incorporated into polymers by any suitable process, such as sol-gel processes, which are well known to those skilled in the art. The resulting polymer can be deposited by any suitable process, such as a spin coating process followed by a hard bake.

PDMS polymers incorporating silica nanoparticles are well known in the art and such polymers may be used as the polymer layer 80 of the present invention. Silica nanoparticles impart desirable wear and fatigue resistance to PDMS polymers. Depending on the amount of silica particles present, PDMS can also have a more hydrophilic surface, which is useful in certain applications.

Those skilled in the art will appreciate that many variations and/or modifications may be made to the invention as shown in the specific examples without departing from the spirit and scope of the invention as broadly described. Therefore, the present embodiment should be considered in all respects as illustrative rather than restrictive.

Claims (10)

1. a printhead with ink ejection face, comprises and is formed on suprabasil a plurality of nozzle assembly, and each nozzle assembly comprises:

Nozzle box;

Be limited to the nozzle opening in the top of described nozzle box; And

The thermal bend actuator of movable part that limits the top of each nozzle box, described thermal bend actuator comprises:

The first active member, described the first active member for being connected of drive circuit; And

The second passive device, described the second passive device cooperates with described the first active member machinery, so that when electric current passes through described the first active member, described the first active member is with respect to described the second passive device expansion, cause described actuator towards the bottom bend of described nozzle box, wherein

Hydrophobic polymeric material is coated on the nozzle plate of described printhead, and described nozzle plate is limited by the described top of each nozzle box at least in part, and wherein, described hydrophobic polymeric material is chosen from the group being comprised of polysilsesquioxane.

2. printhead as claimed in claim 1, wherein, described hydrophobic polymeric material is chosen from the group being comprised of poly-alkyl silsesquioxane and poly-aryl silsesquioxane.

3. printhead as claimed in claim 1, wherein, described hydrophobic polymeric material is chosen from the group being comprised of poly methyl silsesquioxane and polyphenylsilsesquioxane.

4. printhead as claimed in claim 1, wherein, each top has the hydrophobic outer surface with respect to the inner surface of each nozzle box by means of coated hydrophobic polymeric material.

5. printhead as claimed in claim 1, wherein, each nozzle box comprises top and the sidewall with ceramic material.

6. printhead as claimed in claim 5, wherein, described ceramic material is chosen from the group being comprised of silicon nitride, silica and silicon oxynitride.

7. printhead as claimed in claim 1, wherein, described top and described substrate are spaced apart, so that the sidewall of each nozzle box extends between described nozzle plate and described substrate.

8. printhead as claimed in claim 1, wherein, described nozzle opening is limited in the described movable part at described top.

9. printhead as claimed in claim 1, wherein, described nozzle opening is limited in the standing part at described top.

10. printhead as claimed in claim 1, wherein, described polymeric material limits the described movable part at described top and the mechanical seal between standing part, makes thus the ink leakage between described actuator period of energization minimize.