EP2349724B1

EP2349724B1 - Inkjet nozzle assembly having moving roof structure and sealing bridge

Info

Publication number: EP2349724B1
Application number: EP08878343.6A
Authority: EP
Inventors: Gregory John Mcavoy; Kia Silverbrook
Original assignee: Zamtec Ltd
Current assignee: Memjet Technology Ltd
Priority date: 2008-11-26
Filing date: 2008-11-26
Publication date: 2014-05-07
Anticipated expiration: 2028-11-26
Also published as: EP2349724A4; JP2012506782A; WO2010060129A1; KR20110055747A; EP2349724A1; KR101311281B1

Description

Field of the Invention

The present invention relates to the field of printers and particularly inkjet printheads. It has been developed primarily to improve print quality and reliability in high resolution printheads.

Background of the Invention

Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, "Non-Impact Printing: Introduction and Historical Perspective", Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein US Patent No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
US Patent 3,596,275 by Sweet also discloses a process of a continuous inkjet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also US Patent No. 3,373,437 by Sweet et al )
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in US Patent No. 3,946,398 (1970 ) which utilizes a diaphragm mode of operation, by Zolten in US Patent 3,683,212 (1970 ) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in US Patent No. 3,747,120 (1972 ) discloses a bend mode of piezoelectric operation, Howkins in US Patent No. 4,459,601 discloses a piezoelectric push mode actuation of the inkjet stream and Fischbeck in US 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2,007,162 (1979 ) and Vaught et al in US Patent 4,490,728 . Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
The present Applicant has described a plethora of inkjet printheads, which are constructed utilizing micro-electromechanical systems (MEMS) techniques. As described in the Applicant's earlier US Application Nos. 11/685,084 ; 11/763,443 ; and 11/763,440 , a MEMS inkjet printhead may comprise a nozzle plate having moving portions. Each moving portion typically has a nozzle opening defined therein so that actuation of the moving portion results in ejection of ink from the printhead.
An advantage of this type of printhead is that the energy required to eject a droplet of ink is small compared with, for example, traditional thermal bubble-forming printheads. The Applicant has previously described how specific actuator designs and complementary actuation methods provide highly efficient drop ejection from such printheads (see, for example, US Application Nos. 11/607,976 and 12/239,814 ).
However, a problem with 'moving nozzle' printheads is that they require a good fluidic seal between the moving portion and the stationary portion of the printhead. Ink should only be ejected through the nozzle opening and should not leak out of seals. If the distance between the moving portion and the stationary portion is small, then surface tension may retain ink inside nozzle chambers. However, the use of ink surface tension as a fluidic seal is problematic and usually cannot provide a reliable seal, especially if the ink inside nozzle chambers experiences pressure surges.
In the Applicant's earlier Application Nos. 11/685,084 ; 11/763,443 ; and 11/763,440 , there was described a method of fabricating a mechanical seal for moving portions of a nozzle plate. Typically, a flexible layer of polydimethylsiloxane (PDMS) is coated over the nozzle plate, which acts as a sealing membrane between the moving portions and the stationary part of the printhead. Moreover, the layer of PDMS provides a hydrophobic ink ejection surface, which is also highly desirable in terms of printhead fluidics and, ultimately, print quality.
It would be desirable to provide improved mechanical seals for inkjet printheads having moving nozzles. It would be particularly desirable to provide efficacious mechanical scals, which have minimal impact on the overall efficiency of the printhead.
US 2008/225083 relates to a nozzle assembly for an inkjet printhead. The nozzle assembly comprises a nozzle chamber having a roof, the roof having a moving portion moveable relative to a static portion and a nozzle opening defined in the roof, such that movement of the moving portion relative to the static portion causes ejection of ink through the nozzle opening. The nozzle assembly also comprises an actuator for moving the moving portion relative to the static portion, and a mechanical seal interconnecting the moving portion and the static portion. The mechanical seal comprises a polymeric material selected from the group comprising: polymerized siloxanes and fluorinated polyolefins.

Summary of the Invention

In a first aspect the present invention provides a nozzle assembly for an inkjet printhead according to claim 1.
Optionally, said polymeric material is comprised of polydimethylsiloxane (PDMS).
Optionally, said seal member is absent from a space between said moving portion and said stationary portion.
Optionally, said seal member comprises at least one ridge and/or at least one furrow in profile.
Optionally, said seal member comprises a crown portion, said crown portion standing proud of a first end of said seal member connected to said moving portion and a second end of said seal member connected to said stationary portion.
Optionally, said seal member is corrugated.
Optionally, said nozzle opening is defined in said moving portion.
Optionally, said nozzle opening is defined in said stationary portion.
Optionally, said actuator is a thermal bend actuator comprising:

a first active element for connection to drive circuitry; and
a second passive element mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator.

Optionally, said first and second elements are cantilever beams.
Optionally, said thermal bend actuator defines at least part of the moving portion of said roof.
Optionally, the polymeric material is coated on a substantial part of said roof, such that an ink ejection face of said printhead is hydrophobic.

Brief Description of the Drawings

Optional embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a first sequence of steps in which nozzle chamber sidewalls are formed;
Figure 2 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 4;
Figure 3 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a second sequence of steps in which the nozzle chamber is filled with polyimide;
Figure 4 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 3;
Figure 5 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a third sequence of steps in which connector posts are formed up to a chamber roof;
Figure 6 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 5;
Figure 7 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a fourth sequence of steps in which conductive metal plates are formed;
Figure 8 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 7;
Figure 9 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a fifth sequence of steps in which an active beam member of a thermal bend actuator is formed;
Figure 10 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 9;
Figure 11 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a sixth sequence of steps in which a moving roof portion comprising the thermal bend actuator is formed;
Figure 12 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 11;
Figure 13 is a side-sectional view of a partially-fabricated inkjet nozzle assembly after a seventh sequence of steps in which hydrophobic polymer layer is deposited and photopatterned;
Figure 14 is a perspective view of the partially-fabricated inkjet nozzle assembly shown in Figure 13;
Figure 15 is a side-sectional view of an fully formed inkjet nozzle assembly;
Figure 16 is a cutaway perspective view of the inkjet nozzle assembly shown in Figure 15;
Figure 17 is a schematic side-sectional view of the partially-fabricated inkjet nozzle assembly shown in Figures 9 and 10;
Figure 18 is a schematic side-sectional view of the partially-fabricated inkjet nozzle shown in Figure 17 after etching a via to define moving and stationary portions of a chamber roof;
Figure 19 is a schematic side-sectional view of the partially-fabricated inkjet nozzle shown in Figure 18 after filling the via with a plug of photoresist;
Figure 20 is a schematic side-sectional view of the partially-fabricated inkjet nozzle shown in Figure 19 after deposition of a polymer layer and a protective metal layer;
Figure 21 is a schematic side-sectional view of the partially-fabricated inkjet nozzle shown in Figure 20 after etching a nozzle opening;
Figure 22 is a schematic side-sectional view of an inkjet nozzle assembly according to the present invention; and
Figure 23 is a schematic side-sectional view of an alternative seal member.

Detailed Description of Specific Embodiments

Nozzle Assembly with Polymer Filling Space Between Moving Portion and Stationary Portion

Figures 1 to 16 shows a sequence of MEMS fabrication steps for an inkjet nozzle assembly 100 described in our earlier US Application No. 11/763,440 . The completed inkjet nozzle assembly 100 shown in Figures 15 and 16 utilizes thermal bend actuation, whereby a moving portion of a roof bends towards a substrate resulting in ink ejection.
The starting point for MEMS fabrication is a standard CMOS wafer having CMOS drive circuitry formed in an upper portion of a silicon wafer. At the end of the MEMS fabrication process, this wafer is diced into individual printhead integrated circuits (ICs), with each IC comprising drive circuitry and plurality of nozzle assemblies.
As shown in Figures 1 and 2, a substrate 1 has an electrode 2 formed in an upper portion thereof. The electrode 2 is one of a pair of adjacent electrodes (positive and earth) for supplying power to an actuator of the inkjet nozzle 100. The electrodes receive power from CMOS drive circuitry (not shown) in upper layers of the substrate 1.
The other electrode 3 shown in Figures 1 and 2 is for supplying power to an adjacent inkjet nozzle. In general, the drawings shows MEMS fabrication steps for a nozzle assembly, which is one of an array of nozzle assemblies. The following description focuses on fabrication steps for one of these nozzle assemblies. However, it will of course be appreciated that corresponding steps are being performed simultaneously for all nozzle assemblies that are being formed on the wafer. Where an adjacent nozzle assembly is partially shown in the drawings, this can be ignored for the present purposes. Accordingly, the electrode 3 and all features of the adjacent nozzle assembly will not be described in detail herein. Indeed, in the interests of clarity, some MEMS fabrication steps will not be shown on adjacent nozzle assemblies.
In the sequence of steps shown in Figures 1 and 2, an 8 micron layer of silicon dioxide is initially deposited onto the substrate 1. The depth of silicon dioxide defines the depth of a nozzle chamber 5 for the inkjet nozzle. After deposition of the SiO₂ layer, it is etched to define walls 4, which will become sidewalls of the nozzle chamber 5, shown most clearly in Figure 2.
As shown in Figures 3 and 4, the nozzle chamber 5 is then filled with photoresist or polyimide 6, which acts as a sacrificial scaffold for subsequent deposition steps. The polyimide 6 is spun onto the wafer using standard techniques, UV cured and/or hardbaked, and then subjected to chemical mechanical planarization (CMP) stopping at the top surface of the SiO₂ wall 4.
In Figures 5 and 6, a roof member 7 of the nozzle chamber 5 is formed as well as highly conductive connector posts 8 extending down to the electrodes 2. Initially, a 1.7 micron layer of SiO₂ is deposited onto the polyimide 6 and wall 4. This layer of SiO₂ defines a roof 7 of the nozzle chamber 5. Next, a pair of vias are formed in the wall 4 down to the electrodes 2 using a standard anisotropic DRIE. This etch exposes the pair of electrodes 2 through respective vias. Next, the vias are filled with a highly conductive metal, such as copper, using electroless plating. The deposited copper posts 8 are subjected to CMP, stopping on the SiO₂ roof member 7 to provide a planar structure. It can be seen that the copper connector posts 8, formed during the electroless copper plating, meet with respective electrodes 2 to provide a linear conductive path up to the roof member 7.
In Figures 7 and 8, metal pads 9 are formed by initially depositing a 0.3 micron layer of aluminium onto the roof member 7 and connector posts 8. Any highly conductive metal (e.g. aluminium, titanium etc.) may be used and should be deposited with a thickness of about 0.5 microns or less so as not to impact too severely on the overall planarity of the nozzle assembly.
The metal pads 9 are positioned over the connector posts 8 and on the roof member 7 in predetermined 'bend regions' of the thermoelastic active beam member.
In Figures 9 and 10, a thermoelastic active beam member 10 is formed over the SiO₂ roof 7. By virtue of being fused to the active beam member 10, part of the SiO₂ roof member 7 functions as a lower passive beam member 16 of a mechanical thermal bend actuator, which is defined by the active beam 10 and the passive beam 16. The thermoelastic active beam member 10 may be comprised of any suitable thermoelastic material, such as titanium nitride, titanium aluminium nitride and aluminium alloys. As explained in the Applicant's earlier US Application No. 11/607,976 filed on 4 December 2002 , vanadium-aluminium alloys are a preferred material, because they combine the advantageous properties of high thermal expansion, low density and high Young's modulus.
To form the active beam member 10, a 1.5 micron layer of active beam material is initially deposited by standard PECVD. The beam material is then etched using a standard metal etch to define the active beam member 10. After completion of the metal etch and as shown in Figures 9 and 10, the active beam member 10 comprises a partial nozzle opening 11 and a beam element 12, which is electrically connected at each end to positive and ground electrodes 2 via the connector posts 8. The planar beam element 12 extends from a top of a first (positive) connector post and bends around 180 degrees to return to a top of a second (ground) connector post.
Still referring to Figures 9 and 10, the metal pads 9 are positioned to facilitate current flow in regions of potentially higher resistance. One metal pad 9 is positioned at a bend region of the beam element 12, and is sandwiched between the active beam member 10 and the passive beam member 16. The other metal pads 9 are positioned between the top of the connector posts 8 and the ends of the beam element 12.
Referring to Figures 11 and 12, the SiO₂ roof member 7 is then etched to define fully a nozzle opening 13 and a moving portion 14 of the roof. The moving portion 14 comprises a thermal bend actuator 15, which is itself comprised of the active beam member 10 and the underlying passive beam member 16. The nozzle opening 13 is defined in the moving portion 14 of the roof so that the nozzle opening moves with the actuator during actuation. Configurations whereby the nozzle opening 13 is stationary with respect to the moving portion 14, as described in Applicant's US Application No. 11/607,976 are also possible.
A perimeter space or gap 17 around the moving portion 14 of the roof separates the moving portion from a stationary portion 18 of the roof. This gap 17 allows the moving portion 14 to bend into the nozzle chamber 5 and towards the substrate 1 upon actuation of the actuator 15.
Referring to Figures 13 and 14, a layer of photopatternable hydrophobic polymer 19 is then deposited over the entire nozzle assembly, and photopatterned to re-define the nozzle opening 13.
The use of photopatternable polymers to coat arrays of nozzle assemblies was described extensively in our earlier US Application Nos. 11/685,084 filed on 12 March 2007 and 11/740,925 filed on 27 April 2007 . Typically, the hydrophobic polymer is polydimethylsiloxane (PDMS) or perfluorinated polyethylene (PFPE). Such polymers are particularly advantageous because they are photopatternable, have high hydrophobicity, and low Young's modulus.
As explained in the above-mentioned US Applications, the exact ordering of MEMS fabrication steps, incorporating the hydrophobic polymer, is relatively flexible. For example, it is perfectly feasible to etch the nozzle opening 13 after deposition of the hydrophobic polymer 19, and use the polymer as a mask for the nozzle etch. It will appreciated that variations on the exact ordering of MEMS fabrication steps are well within the ambit of the skilled person, and, moreover, are included within the scope of the present invention.
The hydrophobic polymer layer 19 performs several functions. Firstly, it fills the gap 17 to provide a mechanical seal between the moving portion 14 and stationary portion 18 of the roof 7. Provided that the polymer has a sufficiently low Young's modulus, the actuator can still bend towards the substrate 1, whilst preventing ink from escaping through the gap 17 during actuation. Secondly, the polymer has a high hydrophobicity, which minimizes the propensity for ink to flood out of the relatively hydrophilic nozzle chambers and onto an ink ejection face 21 of the printhead. Thirdly, the polymer functions as a protective layer, which facilitates printhead maintenance.
Finally, and as shown in Figures 15 and 16, an ink supply channel 20 is etched through to the nozzle chamber 5 from a backside of the substrate 1. Although the ink supply channel 20 is shown aligned with the nozzle opening 13 in Figure 15 and 16, it could, of course, be positioned offset from the nozzle opening.
Following the ink supply channel etch, the polyimide 6, which filled the nozzle chamber 5, is removed by ashing (either frontside ashing or backside ashing) using, for example, an O₂ plasma to provide the nozzle assembly 100.
Although not described above, a metal film (e.g. titanium or aluminium) may be used to protect the polymer layer 19 during final stage MEMS processing, as described in our earlier US Application Nos. 11/740,925 and 11/946,840 . Typically, the protective metal film is deposited onto the polymer layer 19 prior to etching the nozzle opening 13. After all etching and oxidative photoresist removal steps ("ashing steps") have been completed, the protective metal film may be removed using a simple HF or H₂O₂ rinse.

Nozzle Assembly with Polymer Bridging Space Between Moving Portion and Stationary Portion

In the nozzle assembly 100 described above, the polymer layer 19 fills the gap between the moving portion 14 and the stationary portion 18 of the roof 7. Although this provides a good mechanical seal and can be readily manufactured, the configuration of the seal inevitably impacts on the overall performance and efficiency of the nozzle assembly.
Turning to Figures 17 to 22, there is shown schematically an alternative sequence of fabrication steps, which results in an improved sealing member bridging between the moving portion 14 and stationary portion 18. In the interests of simplicity, the schematic illustrations in Figures 17 to 22 do not show detailed features of the actuator. However, it will be appreciated that Figure 17, which is the starting point for this alternative sequence of fabrication steps, is schematically representative of the partially-formed nozzle assembly shown in Figures 9 and 10. In the interests of clarity, like reference numerals will be used to refer to corresponding features in the nozzle assembly.
Referring then to Figure 17, there is shown a partially-formed nozzle assembly having a nozzle chamber 5 filled with polyimide 6. A roof 7 comprising a thermal bend actuator (not shown in Figure 17) forms a cover over the nozzle chamber 5.
In Figure 18, a via is etched into the roof 7. The via defines the gap 17 between the moving portion 14 and the stationary portion 18 of the roof 7.
Referring next to Figure 19, the gap 17 is filled with a plug 30 of sacrificial material, such as photoresist. The plug 30 serves as a sacrificial scaffold for deposition of a polymeric seal member in a subsequent step. Specifically, an upper surface of the plug 30 defines a profile of the seal member. The configuration of the plug 30 and the profile of its upper surface may be controlled by conventional photolithographic techniques. For example, sloped sidewalls of the plug 30 may be formed by adjusting a focusing parameter during exposure of the photoresist.
Following formation of the plug 30, the partially-formed nozzle assembly is then coated with a layer 19 of flexible polymeric material. Typically, the polymeric material is polydimethylsiloxane (PDMS). As shown in Figure 20, the PDMS layer 19 conforms to the profile of an upper surface of the nozzle assembly.
A protective aluminium film 31 is subsequently deposited over the PDMS layer 19. The aluminium film 31 protects the PDMS layer 19 from an oxidative plasma used for removal of the polyimide 6 (Figure 22).
Referring now to Figure 21, the nozzle opening 13 is then defined by etching through the aluminium film 31, the PDMS layer 19 and the roof 7. This etch may require different etch chemistries at different stages in order to etch through all three layers.
Finally, and referring to Figure 22, the nozzle assembly is subjected to an oxidative plasma (e.g. O₂ plasma), which removes the polyimide 6 and photoresist plug 30. Following oxidative removal of the polyimide 6 and plug 30, the protective aluminium layer 31 is removed by washing in HF or H₂O₂.
The completed nozzle assembly 200 shown in Figure 22 has a seal member 32 bridging across the gap 17 between the moving portion 14 and the stationary portion 18 of the roof 7. Significantly, the seal member 32 does not fill the gap 17 and is, indeed, wholly absent from the space between the moving portion 14 and the stationary portion 18.
The seal member 32 has the profile of a bridge, where one end is connected to the moving portion 14 and the other end is connected to the stationary portion 18. Furthermore, the bridge substantially takes the form of a single-arch bridge, having a ridge or crown portion 33 standing proud of each end of the bridge. Of course, the seal member may alternatively take the form of a simple beam bridge spanning between the moving portion 14 and stationary portion 18, depending on the profile of the upper surface of the plug 30.
The seal member 32 has a number of advantages over the embodiment shown in Figures 15 and 16, where the gap 17 is completely filled with the polymeric material 19. Firstly, by reducing the overall volume of polymer between the moving portion 14 and the stationary portion 18, there is much less impedance to downward motion of the moving portion 14 towards the substrate 1. In addition, the profile of the seal member is specifically adapted to facilitate downward motion of the moving portion 14. Since the seal member 32 takes the form of a flexible bridge, having a length which is longer than the distance between the moving portion 14 and the stationary portion 18, any downward motion of the moving portion 14 during actuation can be readily accommodated by the bridge structure with minimal flexing or extension of the polymer material. Hence, the seal member 32 provides minimal impedance to movement of the moving portion 14, whilst still providing an excellent seal. By minimizing impedance to movement of the moving portion 14, the overall efficiency of the nozzle assembly 200, and printheads comprising such nozzle assemblies, is improved.
Of course, other configurations of the seal member 32 are within the ambit of the present invention. For example, as shown in Figure 23, the seal member 32 may be a corrugated structure 40 having a plurality of ridges 41 and furrows 42. It will be appreciated that the corrugated structure 40 can readily accommodate movement of the moving portion 14
It will be appreciated by ordinary workers in this field that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the scope of the claims. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

A nozzle assembly (200) for an inkjet printhead, said nozzle assembly comprising:
a nozzle chamber (5) comprising a roof (7) having a nozzle opening (13) defined therein, said roof comprising a moving portion (14) moveable relative to a stationary portion (18), such that movement of said moving portion relative to said stationary portion causes ejection of ink through the nozzle opening;

an actuator (15) for moving said moving portion relative to said stationary portion; and

a seal member (32) configured as a bridge spanning between said moving portion and said stationary portion,
characterized in that:
said seal member (32) has a non-planar profile configured for facilitating movement of said moving portion.
The nozzle assembly of claim 1, wherein said seal member (32) is comprised of a polymeric material.
The nozzle assembly of claim 1 or claim 2, wherein said polymeric material is comprised of polydimethylsiloxane (PDMS).
The nozzle assembly of any one of the preceding claims, wherein said seal member (32) is absent from a space between said moving portion (14) and said stationary portion (18).
The nozzle assembly of any one of the preceding claims, wherein said seal member (32) comprises at least one ridge (41) and/or at least one furrow (42) in profile.
The nozzle assembly of any one of the preceding claims, wherein said seal member (32) comprises a crown portion (33), said crown portion standing proud of a first end of said seal member connected to said moving portion (14) and a second end of said seal member connected to said stationary portion (18).
The nozzle assembly of any one of the preceding claims, wherein said seal member (32) is corrugated.
The nozzle assembly of any one of the preceding claims, wherein said nozzle opening (13) is defined in said moving portion (14).
The nozzle assembly of any one of claims 1 to 7, wherein said nozzle opening (13) is defined in said stationary portion (18).
The nozzle assembly of any one of the preceding claims, wherein said actuator (15) is a thermal bend actuator comprising:
a first active element (10) for connection to drive circuitry; and

a second passive element (16) mechanically cooperating with the first element, such that when a current is passed through the first element, the first element expands relative to the second element, resulting in bending of the actuator.
The nozzle assembly of claim 10, wherein said first and second elements are cantilever beams.
The nozzle assembly of claim 10 or claim 11, wherein said thermal bend actuator defines at least part of the moving portion (14) of said roof.
The nozzle assembly of claim 2, wherein the polymeric material is coated on a substantial part of said roof, such that an ink ejection face of said printhead is hydrophobic.
An inkjet printhead comprising a plurality of nozzle assemblies according to any one of the preceding claims.