KR101064043B1 - Method for forming a connection between an electrode and an actuator in an inkjet nozzle assembly - Google Patents

Abstract

A method of forming a connection between an electrode and an actuator in an inkjet nozzle assembly is provided. The method comprises the steps of: (a) providing a substrate having a layer of drive circuit comprising an electrode for connecting to the actuator; (b) forming a wall of insulating material on the electrode; (c) forming a via in at least the wall that exposes the electrode; (d) filling said vias with a conductive material using electroless plating to provide a connector post; (e) forming at least a portion of the actuator on the connector post to provide an electrical connection between the actuator and the electrode; It includes.

Inkjet, Nozzle Assembly, Thermal Bend Actuator, Passive Beam, Active Beam

Description

TECHNICAL FIELD OF FORMING CONNECTION BETWEEN ELECTRODE AND ACTUATOR IN AN INKJET NOZZLE ASSEMBLY}

The present invention relates to inkjet nozzle assemblies and methods of making inkjet nozzle assemblies. The present invention has been developed primarily to reduce electrical losses in powering inkjet actuators.

Applicant has previously described a number of MEMS inkjet nozzles using thermal bend actuation. Thermal bend actuation generally refers to a bend movement caused by thermal expansion of another material through which a current passes through one material. The resulting bending motion can be used to selectively eject ink from the nozzle opening via the movement of a paddle or vane, causing a pressure wave in the nozzle chamber.

Some representative types of thermal bend inkjet nozzles are illustrated in the patents or patent applications listed above, the contents of which are incorporated herein by reference.

Applicant's US Pat. No. 6,416,167 describes an inkjet nozzle having a paddle located in the nozzle chamber and a thermal bend actuator located outside of the nozzle chamber. The actuator takes the form of a lower active beam of conductive material fused to an upper passive beam of non-conductive material (eg silicon dioxide). . The actuator is connected to the paddle via an arm that is received through a slot formed in the wall of the nozzle chamber. As the current passes through the lower active beam, the actuator is bent downward and the paddle moves toward the nozzle opening formed in the roof of the nozzle chamber, whereby ink droplets are ejected. This design has the advantage that the configuration is simplified. The disadvantage of this design is that both sides of the paddle counteract the relatively viscous ink inside the nozzle chamber.

Applicant's US Patent No. 6,260,953, assigned to Applicant, describes an inkjet nozzle wherein the actuator forms a moving roof portion of the nozzle chamber. This actuator takes the form of a serpentine core of a conductive material sealed by a polymer material. In operation, the actuator is bent toward the bottom of the nozzle chamber, increasing the pressure in the chamber and driving the ink droplets out of the nozzle openings formed in the ceiling of the chamber. The nozzle opening is formed in the non-moving portion of the ceiling. The advantage of this design is that only one side of the movable ceiling counteracts the relatively viscous ink inside the nozzle chamber. A disadvantage of this design is that it is difficult to form the actuator with meandering conductive elements sealed by polymer material in the MEMS manufacturing process.

Applicant's US Pat. No. 6,623,101 describes an inkjet nozzle comprising a nozzle chamber having a movable ceiling having a nozzle opening formed therein. The movable ceiling is connected via an arm to a thermal bend actuator located outside of the nozzle chamber. This actuator takes the form of an upper active beam spaced apart from a lower passive beam. By spacing the active beam and the passive beam, the thermal bend efficiency is maximized because the passive beam acts as a heat sink for the active beam. When the current passes through the upper active beam, the movable ceiling with the nozzle opening therein rotates toward the bottom of the nozzle chamber, thereby being injected through the nozzle opening. Since the nozzle opening moves with the ceiling, the flight direction of the ink droplets can be controlled by appropriate shape change of the nozzle rim. The advantage of this design is that only one side of the movable ceiling counteracts the relatively viscous ink inside the nozzle chamber. Another advantage is that the heat loss is minimal by separating the active and passive beam members. The disadvantage of this design is the lack of structural stiffness when separating the active and passive beam elements.

For MEMS inkjet nozzles of all designs, there is a need to minimize electrical losses. It is particularly important to minimize the electrical losses when the design of the nozzles presents an adverse configuration in terms of electrical losses. For example, a relatively long distance between an actuator and a CMOS electrode supplying current to the actuator can further worsen electrical losses. Moreover, curved or tortuous current paths further exacerbate electrical losses.

In general, the actuator material in the inkjet nozzle is selected from materials satisfying several criteria. For mechanical thermal bend actuated nozzles, these criteria include electrical conductivity, coefficient of thermal expansion, Young's module, and the like. For thermally bubbled inkjet nozzles, these criteria include electrical conductivity, oxidation resistance, crack resistance, and the like. Therefore, it will be appreciated that the choice of actuator material is a compromise between various physical properties and does not necessarily have an optimum electrical conductivity. If the actuator material itself has a sub-optimal electrical conductivity, it is particularly important to minimize the electrical losses everywhere in the nozzle assembly.

Finally, any improvement in nozzle design needs to be compatible with standard MEMS manufacturing processes. For example, some materials cause contamination in the manufacturing process and are therefore not compatible with MEMS processing.

From the foregoing, it will be seen that there is a need to improve the design and manufacturability of the inkjet nozzles in order to minimize electrical losses and to provide more efficient ink jetting from the resulting printhead. It is particularly necessary to improve the design and manufacturability of a mechanical thermal bend actuated inkjet nozzle, where electrical losses may be exacerbated by the inherent form of the nozzle design.

Summary of the Invention

In a first aspect, the invention provides a method of forming an electrical connection between an electrode and an actuator in an inkjet nozzle assembly.

(a) providing a substrate having a layer of drive circuit including an electrode for connecting to said actuator;

(b) forming a wall of insulating material on the electrode;

(c) forming a via in at least the wall that exposes the electrode;

(d) filling the vias with conductive material using electroless plating to provide a connector post;

(e) forming at least a portion of the actuator on the connector post to provide an electrical connection between the actuator and the electrode;

It provides a method of forming an electrical connection between the electrode and the actuator in the inkjet nozzle assembly.

Optionally, the distance between the actuator and the electrode is at least 5 microns.

Optionally, the layer of the drive circuit is a CMOS layer of a silicon substrate.

Optionally, the drive circuit comprises a pair of electrodes for each inkjet nozzle assembly, each of which is connected to the actuator with a respective connector post.

Optionally, the wall of insulation material is made of silicon dioxide.

Optionally, the via has sidewalls perpendicular to the face of the substrate.

Optionally, the via has a minimum cross-sectional dimension of at least 1 micron.

Optionally, the conductive material is a metal.

Optionally, the conductive material is copper.

In another aspect, there is provided a method further comprising depositing a catalyst layer on a base of the via prior to the electroless plating.

Optionally, the catalyst is palladium.

Optionally, the conductive material is planarized by chemical mechanical planarization prior to forming the actuator.

Optionally, the actuator is a thermal bend actuator comprising a planar active beam that mechanically interacts with a planar passive beam.

Optionally, the thermal bend actuator at least partially forms a ceiling of the nozzle chamber relative to the inkjet nozzle assembly.

Optionally, the wall of insulating material forms a sidewall of the nozzle chamber.

Optionally, step (e) deposits active beam material over the passive beam material.

Optionally, the active beam member is made of the active beam material and extends from the top of the connector post in a plane perpendicular to the post.

In another form, a first metal pad configured to facilitate current flow from the connector post to the active beam member is deposited on top of the connector post prior to deposition of the active beam material.

Optionally, said planar active beam member comprises a bent or meandering beam element, said beam element on a first end and a second connector post positioned on a first connector post. And a second end positioned at the first and second connector posts adjacent to each other.

In yet another aspect, the invention further comprises depositing a second metal pad positioned on the passive beam material prior to deposition of the active beam material, the second metal pad being positioned to facilitate current flow in the bending region of the beam element. Provide a method.

In a second aspect, the invention provides a printhead integrated circuit comprising a substrate having a plurality of inkjet nozzle assemblies formed on a surface thereof, the substrate having a drive circuit for supplying power to the nozzle assemblies, wherein each nozzle assembly comprises ink. A nozzle chamber accommodating the nozzle opening therein; An actuator for ejecting ink through the nozzle opening; A pair of electrodes positioned on a surface of the substrate and electrically connected to the driving circuit; And a pair of connector posts electrically connecting respective electrodes to the actuators, respectively. Wherein each connector post provides a printhead integrated circuit that extends linearly from each electrode to the actuator.

Optionally, each connector post is perpendicular to the surface of the substrate.

Optionally, the shortest distance between the actuator and the electrodes is at least 5 microns.

Optionally, the minimum cross-sectional area of the connector posts is at least 2 microns.

Optionally, the nozzle assemblies are arranged in a plurality of nozzle rows, the nozzle rows extending longitudinally along the substrate.

Optionally, the distance between adjacent nozzles in one nozzle row is less than 50 microns.

Optionally, the actuator is a thermal bend actuator that includes a planar active beam that mechanically interacts with the planar passive beam.

Optionally, the thermal bend actuator at least partially forms a ceiling of the nozzle chamber and the nozzle opening is formed in the ceiling.

Optionally, the wall of insulating material forms a sidewall of the nozzle chamber.

Optionally, the active beam member is electrically connected to the tops of the connector posts.

Optionally, a portion of the active beam member is located over the top of the connector posts.

In yet another aspect, the invention is configured to facilitate current flow from each connector post to the active beam member, further comprising a first metal pad located between the active beam material and the top of each connector post. Provides a printhead integrated circuit.

Optionally, the active beam member comprises an aluminum alloy; It consists of an active beam material selected from the group consisting of titanium nitride and titanium aluminium nitride.

Optionally, the active beam member is made of a vanadium-aluminum alloy.

Optionally, said planar active beam member comprises a bent or meandering beam element, said beam element having a first end located on a first connector post and a second end located on a second connector post, The first and second connector posts are adjacent to each other.

In still another aspect, the present invention provides a printhead integrated circuit further comprising at least one second metal pad positioned to facilitate current flow in the bending region of the beam element.

In still another aspect, the present invention provides a printhead integrated circuit further comprising an outer surface layer of a hydrophobic polymer on the ceiling.

Optionally, the outer surface layer forms a planar ink ejection face of the printhead integrated circuit, the planar ink ejection surface being spaced apart from the nozzle openings and having no substantial contours.

Optionally, the hydrophobic polymer mechanically seals a gap between the thermal bend actuator and the nozzle chamber.

In still another aspect, the present invention provides a page width inkjet printhead having a printhead integrated circuit including a substrate having a plurality of inkjet nozzle assemblies formed on a surface thereof, the substrate having a driving circuit for supplying power to the nozzle assemblies. Each nozzle assembly comprises: a nozzle chamber for receiving ink and having a nozzle opening formed therein; An actuator for ejecting ink through the nozzle opening; A pair of electrodes positioned on a surface of the substrate and electrically connected to the driving circuit; And a pair of connector posts electrically connecting respective electrodes to the actuators, respectively. Wherein each connector post provides a pagewidth inkjet printhead that extends linearly from each electrode to the actuator.

1 is a side cross-sectional view of a thermal bend actuated inkjet nozzle assembly having a thin tortuous connection between an electrode and an actuator.

FIG. 2 is a cutaway perspective view of the nozzle assembly shown in FIG. 1. FIG.

3 shows a mask for etching silicon oxide walls.

4 is a side cross-sectional view of a partially manufactured inkjet nozzle assembly after the sequence of first steps of forming nozzle chamber sidewalls;

FIG. 5 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 4. FIG.

6 is a side cross-sectional view of an inkjet nozzle assembly partially produced after the sequence of the second step of filling the nozzle chamber with polyimide;

FIG. 7 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 6. FIG.

8 shows a mask for an electrode through etching;

9 is a side cross-sectional view of a partially manufactured inkjet nozzle assembly after the third step sequence of forming connector posts to the chamber ceiling;

FIG. 10 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 9. FIG.

11 shows a mask for etching a metal plate.

12 is a side cross-sectional view of a partially manufactured inkjet nozzle assembly after the sequence of the fourth step of forming the conductive metal plate.

FIG. 13 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 12. FIG.

14 shows a mask for etching an active beam member.

FIG. 15 is a side cross-sectional view of a partially manufactured inkjet nozzle assembly after the sequence of the fifth step of forming the active beam member of the thermal bend actuator. FIG.

FIG. 16 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 15. FIG.

17 shows a mask for etching a silicon oxide ceiling member.

18 is a side cross-sectional view of a partially manufactured inkjet nozzle assembly after the sixth step sequence of forming a movable ceiling including a thermal bend actuator;

FIG. 19 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 18. FIG.

20 shows a mask for patterning a photopatternable hydrophobic polymer.

FIG. 21 is a side cross-sectional view of a partially manufactured inkjet nozzle assembly after the seventh step sequence of depositing and patterning the hydrophobic polymer layer. FIG.

FIG. 22 is a perspective view of the partially manufactured inkjet nozzle assembly shown in FIG. 21. FIG.

FIG. 23 is a perspective view of FIG. 22 with underlying MEMS layers shown in dashed lines; FIG.

Fig. 24 shows a mask for etching a bachside ink supply channel.

25 is a side cross-sectional view of an inkjet nozzle assembly in accordance with the present invention.

FIG. 26 is a cutaway perspective view of the inkjet nozzle assembly shown in FIG. 25. FIG.

Detailed description of the invention

1 and 2 show nozzle assemblies as described in US application Ser. No. 11 / 607,976, attorney docket no. IJ70US, filed December 4, 2002, the contents of which are incorporated by reference. Is incorporated into the specification. The nozzle assembly 400 includes a nozzle chamber 401 formed on a passivated CMOS layer 402 of a silicon substrate 403. The nozzle chamber is formed by the ceiling 404 and sidewall portions 405 extending from the ceiling to the passivated CMOS layer 402. Ink is supplied to the nozzle chamber 401 by the ink inlet 406 in fluid communication with the ink supply channel 407 containing ink from the back side of the silicon substrate. Ink is ejected from the nozzle chamber 401 by the nozzle opening 408 formed in the ceiling 404. The nozzle opening 408 is offset from the ink inlet 406.

As is more clearly shown in FIG. 2, the ceiling 404 has a moving portion 409 that forms a substantial portion of the total ceiling area. Since the nozzle opening 408 and the nozzle edge 415 are formed in the moving part 409, the nozzle opening and the nozzle edge move with the moving part.

The moving part 409 is formed by a thermal bend actuator 410 having a planar upper active beam 411 and a planar lower passive beam 412. The active beam 411 is connected to a pair of electrode contacts 416 (positive and ground). The electrodes 416 are connected with a drive circuit in the CMOS layers.

If it is desired to eject ink droplets from the nozzle chamber 401, current flows through the active beam 411 between the two contacts 416. The active beam 411 is rapidly heated by an electric current to expand with respect to the passive beam 412, whereby the actuator 410 (which forms the moving part 409 of the ceiling part 404) forms the substrate 403. Will be bent downward. This movement of actuator 410 causes ink to be ejected from nozzle opening 408 by a rapid increase in pressure in nozzle chamber 401. When the current flow stops, the moving portion 409 of the ceiling 404 returns to its stop position, which draws ink from the inlet 406 into the nozzle chamber 401 in preparation for the next injection.

In the nozzle design shown in FIGS. 1 and 2, it is advantageous for the actuator 410 to form at least a portion of the ceiling 404 of the nozzle chamber 401. This not only simplifies the overall design and manufacture of the nozzle assembly 400, since only one side of the actuator 410 counteracts the relatively viscous ink, but also provides higher injection efficiency. In contrast, because both sides of the actuator counteract ink in the nozzle chamber, nozzle assemblies having actuator paddles located within the nozzle chamber are less efficient.

However, when the actuator 410 at least partially forms the ceiling of the chamber 401, the distance between the active beam 411 and the electrodes 416 to which the active beam is inevitably relatively long. Moreover, the current path between the electrodes 416 and the active beam 411 is curved in various bends in a relatively thin layer of beam material. The combination of the relatively wide distances between the electrode 416 and the actuator 410, the winding current path and the thickness of the beam material cause significant electrical losses.

To date, MEMS manufacturing of inkjet nozzles has relied primarily on standard plasma-enhanced chemical vapor deposition (PECVD) and mask / etching steps to construct the nozzle structure. The use of PECVD to simultaneously deposit the connection to the electrode 416 and the active beam 411 has advantages from the MEMS manufacturing perspective but inevitably results in a thin meandering connection, which is disadvantageous in terms of current loss. Current loss is further exacerbated when the beam material does not have optimal conductivity. For example, vanadium-aluminum alloys have excellent thermoelastic properties, but have poor electrical conductivity compared to aluminum, for example.

Another disadvantage of PECVD is that a via 418 with sloped sidewalls is required for effective deposition on the sidewalls. Due to the directionality of the plasma it is not possible to deposit material on the vertical sidewalls by PECVD. There are several problems with these inclined sidewalls. First, a photoresist scaffold with sloped sidewalls is required. This is typically accomplished using out of focus photoresist exposure, which inevitably results in some degree of accuracy loss. Secondly, the overall footprint area of the nozzle assembly is increased, thereby reducing the nozzle packing density. This increase in area is significantly worsened when the height of the nozzle chamber is increased.

One attempt to mitigate the problem of current loss in the nozzle assembly 400 is to introduce a highly conductive interlayer layer 417, such as titanium or aluminum, between the electrode contact 416 and the active beam material 411 ( See FIG. 1). This intermediate layer 417 reduces the current loss to some extent, but significant current loss still remains.

Another disadvantage of the nozzle assembly shown in FIGS. 1 and 2 is that the ink jetting surface of the printhead is non-planar due to the electrode vias 418. Non-planarity of the ink jet can also cause structural weaknesses and problems during printhead maintenance.

In light of the above problems, Applicants have developed a new method for manufacturing a mechanical thermal bend inkjet nozzle assembly without resorting to PECVD to form connections from the CMOS contacts to the actuator. As will be described in more detail below, the final inkjet nozzle assembly has minimal electrical loss and the additional structural advantages of planar ink jetting surfaces. While the present invention will be illustrated with reference to a mechanical thermal bend inkjet nozzle assembly, it will be readily appreciated that the present invention may be applied to any type of inkjet nozzle made by MEMS technology.

3 to 26 show a series of MEMS manufacturing steps for the inkjet nozzle assembly shown in FIGS. 25 and 26. The starting point for MEMS fabrication is a standard CMOS wafer with a CMOS drive circuit formed on top of a silicon wafer. At the end of the MEMS fabrication process, the wafer is diced into individual printhead integrated circuits (ICs), each IC comprising a drive circuit and a plurality of nozzle assemblies.

As shown in Figs. 4 and 5, the substrate 1 has an electrode 2 formed at its upper portion. The electrode 2 is one of a pair of adjacent electrodes (positive and earth) for powering the actuator of the inkjet nozzle 100. These electrodes are powered from a CMOS drive circuit (not shown) of the upper layers of the substrate 1.

The other electrode 3 shown in Figs. 4 and 5 is for supplying power to adjacent inkjet nozzles. In general, these figures show the MEMS manufacturing 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 will of course be appreciated that the corresponding steps are executed simultaneously for all the nozzle assemblies formed on the wafer. Although adjacent nozzle assemblies are partially shown in the figures, this may be ignored for this purpose. Therefore, hereinafter, all the features of the adjacent nozzle assembly and the electrode 3 will not be described in detail. Indeed, for clarity, several MEMS manufacturing steps will not be shown for adjacent nozzle assemblies.

3 and 5, the sequence of first MEMS fabrication steps starting from a CMOS wafer is illustrated. First, an 8 micron layer of silicon dioxide is deposited on the substrate 1. The depth of silicon dioxide defines the depth of the nozzle chamber 5 relative to the ink jet nozzle. Depending on the size of the nozzle chamber 5 required, the silicon dioxide layer may have a depth of 4-20 microns, i.e. 6-12 microns. An advantage of the present invention is that silicon dioxide may be used to produce nozzle assemblies having a relatively deep nozzle chamber (eg> 6 microns).

After deposition of the SiO ₂ layer, it is etched to form a wall 4, which becomes the side wall of the nozzle chamber 5, as most clearly shown in FIG. 5. The dark tone mask shown in Fig. 3 is used for the patterned photoresist (not shown) which makes the above etching. For this etching step, any standard anisotropic DRIE (eg, C ₄ F ₈ / O ₂ plasma) suitable for SiO ₂ may be used. Also, SiO ₂ Instead, any depositable insulating material (eg, silicon nitride, silicon nitride oxide, aluminum oxide) may be used. 4 and 5 show the wafer after the sequence of the first SiO ₂ deposition and etching steps.

In the sequence of the second step, the nozzle chamber 5 is filled with a photoresist or polyimide 6 which acts as a sacrificial scaffold for the continuous deposition step. The polyimide 6 is spun onto a wafer using standard techniques, UV cured and / or hardbaked, and then chemical mechanical planarization (CMP) stopping at the top surface of SiO ₂ . Will be processed. 6 and 7 show the nozzle assembly after the sequence of the second step. In preparing for the next deposition step, the top surface of the polyimide 6 and SiO ₂ It is important to ensure that the top surface of the wall 4 is coplanar. In addition, SiO ₂ It is also important to ensure that the top surface of the wall 4 is cleaned after CMP, and a simple clean up etch may be used to ensure this case.

In the sequence of the third step, not only the ceiling 7 of the nozzle chamber 5 but also the highly conductive connector posts 8 which are lowered to the electrodes 2 are formed. First, a 1.7 micron SiO ₂ layer is deposited on the polyimide 6 and on the wall 4. Next, a pair of vias are formed in the wall 4 down to the electrodes 2 using standard anisotropic DRIE. The dark tone mask shown in Fig. 8 is used for a pattern photoresist (not shown) that defines this etching. This etching is anisotropic so high that the via sidewalls are preferably perpendicular to the surface of the substrate 1. This means that any depth of the nozzle chamber may be adjusted without affecting the overall footprint area of the nozzle assembly on the wafer. This etching exposes the pair of electrodes 2 through each via.

Next, the vias are filled with a highly conductive metal such as copper using electroless pating. Copper electroless plating methods are well known in the art and may be integrated directly into fabs. Typically, an electrolyte comprising a copper complex, an aldehyde (eg, formaldehyde) and a hydroxide base deposits a copper coating on the exposed surface of the substrate. Generally, electroless plating is carried out by an ultra thin coating of seed metal (eg palladium) (eg 0.3 micron or less) that catalyzes the plating process. Therefore, electroless plating of vias may proceed by depositing a suitable catalyst seed layer such as palladium by CDV.

In the final step of this third step sequence, the deposited copper is CMP treated to stop at the SiO ₂ ceiling 7 to provide a planar structure. 9 and 10 illustrate a nozzle assembly following this third step sequence. In this figure, it can be seen that the copper connector posts 8 formed during the electroless copper plating encounter each electrode 2 to provide a linear conductive path to the ceiling 7. This conductive path does not include any bends or kinks and has a minimum cross-sectional dimension of at least 1 micron, at least 1.5 microns, at least 2 microns, or at least 3 microns. Thus, the copper connector posts 8 exhibit minimal current loss when powering the actuator of the inkjet nozzle assembly.

In the order of the fourth step, conductive metal pads 9 are formed, which are configured to minimize power loss in any areas with potentially high resistance. These regions are typically at the junction of the thermoelastic element with the connector posts 8 and at any bend of the thermoelastic element. This thermoelastic element is formed in the next step and the function of the metal pads 9 will be readily understood as long as the description of the nozzle assembly is made with the nozzle assemblies fully formed.

The metal pads 9 are formed by first depositing a 0.3 micron layer of aluminum over the ceiling 7 and the connector posts 8. Highly conductive metals (eg, aluminum, titanium, etc.) should be deposited to a thickness of about 0.5 microns or less in order to use any and to not overly affect the overall planarity of the nozzle assembly. Following deposition of the aluminum layer, standard metal etching (eg Cl ₂ / BCl ₃ ) is used to form the metal pads 9. The clear tone mask shown in Fig. 11 is used for a pattern photoresist (not shown) which forms such an etching.

12 and 13 show the nozzle assembly after the sequence of the fourth step, wherein the metal pads 9 are provided with a ceiling 7 in certain 'bend regions' of the thermoelastic active beam member. Formed in the connector posts 8, which are formed continuously. For clarity, metal pads 9 are not shown on the laterally adjacent nozzle assemblies in FIG. 13. However, it will of course be appreciated that all nozzle assemblies in the array are manufactured simultaneously and in accordance with the fabrication steps described herein.

In the sequence of the fifth step illustrated by FIGS. 14-16, SiO ₂ A thermoelastic active beam member 10 is formed on the ceiling 7. By fusion to the active beam member 10, a portion of the SiO ₂ ceiling 7 is formed by the active beam 10 and the passive beam 16 of the lower passive beam member 16 of the mechanical thermal bend actuator. Act as. The thermoelastic active beam member 10 may be made of any suitable thermoelastic material such as titanium nitride, titanium aluminum nitride and aluminum alloy. A vanadium-aluminum alloy is the preferred material, as described in Applicant's co-pending US patent application Ser. No. 11 / 607,976, filed December 4,2002. This is because the alloy combines advantageous properties such as high thermal expansion, low density, and high Young modules.

To form the active beam member 10, a layer of 1.5 micron active beam material is first deposited by standard PECVD. Next, the beam material is etched using standard metal etching to form the active beam member 10. The clear tone mask shown in Fig. 14 is used for a pattern photoresist (not shown) which forms such an etching.

After completion of the metal etching shown in FIGS. 15 and 16, the active beam member 10 includes a partial nozzle opening 11 and a beam element 12, the beam element 12 having a connector at each end thereof. It is electrically connected to the positive and ground electrodes 2 via posts 8. The planar beam element 12 is bent about 180 degrees extending from the top of the first (positive) connector post and back to the top of the second (ground) connector post. Of course, the meandering beam element shape is within the scope of the present invention as described in Applicant's pending US patent application Ser. No. 11 / 607,976.

As most clearly shown in FIGS. 15 and 16, the metal pads 9 are positioned to facilitate current flow in the region of potentially high resistance. One metal pad 9 is located in the bending area of the beam element 12 and is interposed between the active beam member 10 and the passive beam member 16. The other metal pad 9 is located between the top of the connector posts 8 and the end of the beam element 12. It will be appreciated that the metal pads 9 reduce the resistance in this area.

In the sixth step sequence illustrated in FIGS. 17 to 19, the SiO ₂ ceiling 7 is etched to completely form the nozzle opening 13 and the moving portion 14 of the ceiling. The dark tone mask shown in Fig. 17 is used for a pattern photoresist (not shown) which forms such an etching.

As can be seen most clearly in FIGS. 18 and 19, the moving part 14 of the ceiling is formed by this etching and includes a thermal bend actuator 15. This actuator itself consists of an active beam member 10 and a lower active beam member 16. The nozzle opening 13 is formed in the movable portion 14 of the ceiling, so that it moves in accordance with the actuator during driving. Of course, the form in which the nozzle opening 13 is fixed relative to the movable portion 14 is also possible as described in US patent application Ser. No. 11 / 607,976 and is within the scope of the present invention.

A perimeter gap 17 around the moving part 14 of the ceiling separates the moving part and the stationary portion of the ceiling part. This gap 17 causes the moving part 14 to be bent toward the nozzle chamber 5 and towards the substrate 1 when the actuator 15 is driven.

In the order of the seventh step illustrated in FIGS. 20 to 23, the photopatternable hydrophobic polymer 9 is deposited on the entire nozzle assembly and photopatterned to form the nozzle opening 13 again. The dark tone mask shown in FIG. 20 is used to pattern the hydrophobic polymer 9.

The manner in which the photopatternable polymer is used to coat arrays of nozzle assemblies is described in US patent application Ser. No. 11 / 685,084, filed March 12, 2007 and US application filed April 27, 2007. It is described extensively in patent application Ser. No. 11 / 740,925 (agent document number CPH003, CPH006). The contents of the foregoing U.S. patent applications are incorporated herein by reference. Typically, the hydrophobic polymer is polydimethylsiloxane (PDMS) or perfluorinated polyethylene (PFPE). Such polymers are particularly advantageous because they are photopatternable and have high hydrophobicity and low Young modules.

As described in the above-mentioned US patent applications, the exact sequence of MEMS manufacturing steps is relatively flexible by incorporating hydrophobic polymers. For example, it is completely possible to etch the nozzle opening 13 after deposition of the hydrophobic polymer 19 and to use such a polymer as a mask for nozzle etching. It will be appreciated that changes in the exact order of MEMS manufacturing steps are within the scope of the skilled person and are also within the scope of the present invention.

The hydrophobic polymer layer 19 performs several actions. First, it provides a mechanical seal for the peripheral gap 17 around the moving part 14 of the ceiling. The low Young's module of polymer (<1000 MPa) does not significantly inhibit bending of the actuator, but it means preventing ink from escaping through the peripheral gap 17 during operation. Secondly, the polymer has a high hydrophilicity which minimizes the tendency of ink to leak into the inkjet surface 21 of the printhead and the relatively hydrophilic nozzle chamber. Third, the polymer acts as a protective layer to facilitate printhead maintenance.

In the final eighth step sequence illustrated in FIGS. 24 to 26, the ink supply channel 20 is etched through the nozzle chamber 5 from the backside of the substrate 1. The dark tone mask shown in FIG. 24 is used to pattern the backside photoresist (not shown) that forms this etch. In FIGS. 25 and 26, the ink supply channel 20 is shown in alignment with the nozzle opening 13 of, but naturally offset from the nozzle opening as illustrated by the nozzle assembly 400 shown in FIG. 1. offset).

Following etching of the ink supply channel, the nozzle is removed by ashing (either front ashing or back ashing), for example, using an O ₂ plasma, for example, the polyimide 6 filled in the nozzle chamber 5. Form assembly 100.

The final nozzle assembly 100 shown in FIGS. 25 and 26 has several additional advantages over the nozzle assembly 400 shown in FIGS. 1 and 2. Firstly, the nozzle assembly 100 minimizes electrical losses in connection between the active beam 10 of the actuator and the electrodes 2. The copper connector posts 8 are excellent in conductivity. It has its own relatively large cross-sectional dimensions (> 1.5 microns); Intrinsic high conductivity of copper; And the absence of any bending at the time of connection. Thus, copper connector posts 8 minimize power transfer from the drive circuit to the actuator. In contrast, the corresponding connection in the nozzle assembly shown in FIGS. 1 and 2 is relatively thin, meandering and almost formed of the same material as the active beam 411.

Secondly, the connector posts 8 extend perpendicularly from the surface of the substrate 1 such that the height of the nozzle chamber 5 is increased without affecting the overall footprint area of the nozzle assembly 100. In contrast, the nozzle assembly 400 requires an inclined connection between the electrode 416 and the moving beam member 411 so that the connection can be formed by PECVD. This inclination certainly affects the overall footprint area of the nozzle assembly 400, which is particularly disadvantageous when the height of the nozzle chamber 401 is increased (eg to provide improved ink jetting characteristics). . According to the present invention, nozzle assemblies having a relatively large volume of nozzle chambers may be arranged in several rows, for example, with nozzle pitches of less than 50 microns.

Thirdly, the nozzle assembly 100 has a high planar ink jetting surface 21 since there are no pit or vias in the region of the electrodes 2. The planarity of the ink jetting surface is advantageous for printhead maintenance because there is a gentle washable surface of any maintenance device. In addition, there is no risk of the particles being permanently trapped in the electrode vias or any other external structure of the ink ejection surface.

While the invention has been described above by way of example only, it will of course be understood that specific changes may be made within the scope of the invention as described herein.

Claims (20)

A method of forming an electrical connection between an electrode and an actuator in an inkjet nozzle assembly, the method comprising: (a) providing a substrate having a layer of drive circuit including an electrode for connecting to said actuator; (b) forming a wall of insulating material on the electrode; (c) forming a via in at least the wall that exposes the electrode; (d) filling the vias with conductive material using electroless plating to provide a connector post; (e) forming at least a portion of the actuator on the connector post to provide an electrical connection between the actuator and the electrode; A method of forming an electrical connection between an electrode and an actuator in an inkjet nozzle assembly comprising a. The method of claim 1, And the distance between the actuator and the electrode is at least 5 microns. The method of claim 1, And the layer of the drive circuit is a CMOS layer of a silicon substrate. The method of claim 1, And said drive circuit comprises a pair of electrodes for each inkjet nozzle assembly, each of said electrodes being connected to said actuator by respective connector posts. The method of claim 1, And wherein the wall of insulation material is made of silicon dioxide. The method of claim 1, And the via has sidewalls perpendicular to the face of the substrate. The method of claim 1, And wherein said via has a minimum cross-sectional dimension of at least 1 micron. The method of claim 1, And wherein the conductive material is a metal. The method of claim 1, And wherein the conductive material is copper. The method of claim 1, Depositing a catalyst layer on a base of said via prior to said electroless plating. The method of claim 10, And said catalyst is palladium. delete delete delete delete delete delete delete delete delete

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