AU2004202404A1 - An ink jet printhead that incorporates fluidic seals - Google Patents

Description

"AN INKJET PRINTHEAD THAT INCORPORATES FLUIDIC SEALS" FIELD OF THE INVENTION This invention relates to an ink jet printhead. More particularly, the invention relates to an ink jet printhead having a plurality of nozzle assemblies that incorporate fluidic seals.

CO-PENDING APPLICATIONS Various methods, systems and apparatus relating to the present invention are disclosed in the following copending applications tiled by the applicant or assignee of the present invention simultaneously with the present application: PCT/AUOO/005 18, PCT/AUOO/005 19, PCT!AUOO/00520, PCT/AUOO/00521, PCT/AUOO/00522, PCT/AUOO/00523, PCT/AUOO/00524, PCT/AUOO/00525, PCT/AUOO/00526, PCT/AUOO/00527, PCT/AUOO/00528, PCT/AUOO/00529, PCT/AUOO/00530, PCT/AUOO/0053 1, PCT/AUOO/00532, PCT/AUOO/00533, PCT/AUOO/00534, PCTfAUOO/00535, PCT/AUOO/00536, PCT/AUOO/00537, PCT/AUOO/00538, PCT/AUOO/005 39, PCT/AUOO/00540, PCT/AUOO/0054 1, PCT/AUOO/00542, PCT/AUOO/00543, PCT/AUOO/00544, PCT/AUOO/00545, PCT/AUOO/00547, PCT/AUOO/00546, PCT/AUOO/00554, PCT/AUOO/00556, PCT/AUOO/00557, PCT/AUOO/00558, PCT/AUOO/00559, PCT/AUOO/00560, PCT/AUOO/00561, PCT/AUOO/00562, PCT/AU00/00563, PCT/AUOO/00564, PCT/AUOO/00565, PCT/AUOO/00566, PCT/AUOO/00567, PCT/AUOO/00568, PCT/AUOO/00569, PCT/AUOO/005 70, PCT/AUOO/00571, PCT/AUOO/005 72, PCT/AUOO/005 73, PCT/AUOO/005 74, PCT/AUOO/005 75, PCT/AUOO/00576, PCT/AUOO/00577, PCT/AUOO/00578, PCT/AUOO/00579, PCTIAUOOIOO58I, PCT/AUOO/00580, PCT/AUOO/00582, PCT/AUOO/00587, PCT/AUOO/00588, PCT/AUOO/005 89, PCT/AUOO/005 83, PCT/AUOO/00593, PCT/AUOO/00590, PCT/AUOO/00591, PCT/AUOO/00592, PCT/AUOO/00584, PCT/AUOO/00585, PCT/AUOO/00586, PCT/AUOO/00594, PCT/AUOO/00595, PCT/AUOO/00596, PCT/AUOO/00597, PCT/AUOO/00598, PCT/AUOO/005 16, PCT/AUOO/005 17, PCT/AU0O/005 11, PCT/AU00/0050 1, PCT/AUOO/00502, PCT/AUOO/00503, PCT/AUOO/00504, PCT/AUOO/00505, PCT/AUOO/00506, PCT/AUOO/00507, PCT/AUOO/00508, PCT/AUOO/00509, PCT/AUOO/005 10, PCT/AUOO/005 12, PCT/AUOO/0051 3, PCT/AUOO/005 14, PCT/AUOO/005 The disclosures of these co-pending applications are incorporated herein by cross-reference.

BACKGROUND TO THE INVENTION Various types of ink jet nozzle assemblies are known where a displaceable element arranged in a nozzle chamber effects ink ejection through a nozzle opening of the nozzle assembly. In certain of these devices, the moveable element is, itself, an actuator. In other devices, an actuator is arranged externally of the nozzle chamber and is connected via an opening in a wall of the nozzle chamber to the displaceable element. Where the actuator is arranged externally of the displaceable element, a seal needs to be provided to minimnise ink loss through such opening.

In yet other embodiments, the nozzle itself is displaceable for effecting ink ejection. In this case, ink toss around a periphery of the nozzle needs to be minimised.

MJ1 19-AU SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided an inkjet printhead which includes a substrate that defines a plurality of ink inlet channels and incorporates drive circuitry; and a plurality of nozzle assemblies positioned on the substrate, each nozzle assembly defining a nozzle chamber in fluid communication with one of the ink inlet channels and each nozzle assembly including an actuator that is mounted on the substrate and is electrically connected to the drive circuitry to be displaceable with respect to the substrate on receipt of an electrical signal from the drive circuitry; a nozzle that is connected to the actuator and is displaceable relative to the substrate to be displaced by the actuator, the nozzle defining a nozzle opening such that, in use, upon displacement of the nozzle relative to the substrate, ink is ejected from the nozzle chamber through the nozzle opening; and a pair of complementary fluidic seal forming structures positioned on the nozzle and the substrate respectively, the seal forming structures being configured so that, when the nozzle chamber is filled with ink, a meniscus is defined between the seal forming structures to accommodate movement of the nozzle while inhibiting leakage of ink from the nozzle chamber.

Each actuator may be an elongate thermal bend actuator that is connected to the substrate at one end and is configured so that an opposite end is displaceable with respect to the substrate on receipt of said electrical signal.

Each nozzle may include a crown portion and a skirt portion that depends from the crown portion. The crown portion may define the nozzle opening and the skirt portion may define one of the fluidic seal forming structures. The other fluidic seal forming structure may extend from the substrate about one of the ink inlet channels.

Each skirt portion and said other fluidic seal forming structure may define a peripheral wall of the nozzle chamber such that, when the nozzle is displaced towards and away from the substrate, a volume of the nozzle chamber is reduced and subsequently enlarged, resulting in the ejection of a drop of ink from the nozzle chamber.

Each actuator may include an active beam and a second passive beam. At least the active beam may define an electrical heating circuit and may be of a material that expands and contracts when heated and subsequently cooled. The beams may be positioned with respect to each other such that heating and cooling of the active beam results in displacement of the actuator.

The second passive beam may be interposed between the first active beam and the substrate such that heating and subsequent expansion of the active beam results in the actuator being displaced towards the substrate and cooling and subsequent contraction of the active beam results in the actuator being displaced away from the substrate.

The inkjet printhead may include a nozzle guard that is mounted on the substrate. The nozzle guard may include a body member that is spaced from the nozzle assemblies. The body member may define a plurality of passages, each passage corresponding with a respective nozzle opening such that ink ejected from each nozzle opening passes through a corresponding passage.

According to a second aspect of the invention, there is provided an inkjet nozzle assembly which includes a substrate; a nozzle displaceably arranged relative to the substrate, the nozzle defining a nozzle opening such that, in use, upon displacement of the nozzle relative to the substrate, ink is ejected through the opening; and an inhibiting means arranged intermediate the substrate and the nozzle for inhibiting leakage of ink from around the periphery of the nozzle.

In this specification the term "nozzle" is to be understood as an element defining an opening and not the opening itself.

MJ119-AU The nozzle may include a crown portion defining the nozzle opening and a skirt portion depending from the crown portion, the skirt portion, together with the inhibiting means, defining an ink chamber with which the nozzle opening is in fluid communication.

An ink supply channel may be defined through the substrate to be in communication, via an aperture in the substrate, with the chamber, the inhibiting means being arranged about the aperture.

The inhibiting means may be arranged externally of the skirt portion of the nozzle. The inhibiting means may include a radially inwardly directed lip portion or wiper portion extending towards an external surface of the skirt portion of the nozzle.

The inhibiting means may be fabricated by deposition and etching techniques.

The inhibiting means may be of a ceramic material. The inhibiting means may be a conductive ceramic which may be laid down at the same time as other components of the assembly and may include titanium nitride or other materials.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described by way of example with reference to the accompanying diagrammatic drawings in which:- Figure 1 shows a three dimensional, schematic view of a nozzle assembly for an ink jet printhead in accordance with the invention; Figures 2 to 4 show a three dimensional, schematic illustration of an operation of the nozzle assembly of Figure 1; Figure 5 shows a three dimensional view of a nozzle array constituting an ink jet printhead; Figure 6 shows, on an enlarged scale, part of the array of Figure Figure 7 shows a three dimensional view of an ink jet printhead including a nozzle guard; Figures 8a to 8r show three dimensional views of steps in the manufacture of a nozzle assembly of an ink jet printhead; Figures 9a to 9r show sectional side views of the manufacturing steps; Figures 10 Oa to 10k show layouts of masks used in various steps in the manufacturing process; Figures 1 la to 1 Ic show three dimensional views of an operation of the nozzle assembly manufactured according to the method of Figures 8 and 9; and Figures 12a to 12c show sectional side views of an operation of the nozzle assembly manufactured according to the method of Figures 8 and 9.

DETAILED DESCRIPTION OF THE DRAWINGS Referring initially to Figure 1 of the drawings, a nozzle assembly, in accordance with the invention is designated generally by the reference numeral 10. An inkjet printhead has a plurality of nozzle assemblies 10 arranged in an ink array 14 (Figures 5 and 6) on a silicon substrate 16. The array 14 will be described in greater detail below.

The assembly 10 includes a silicon substrate or wafer 16 on which a dielectric layer 18 is deposited. A CMOS passivation layer 20 is deposited on the dielectric layer 18.

Each nozzle assembly 12 includes a nozzle 22 defining a nozzle opening 24, a connecting member in the form of a lever arm 26 and an actuator 28. The lever arm 26 connects the actuator 28 to the nozzle 22.

As shown in greater detail in Figures 2 to 4 of the drawings, the nozzle 22 comprises a crown portion 30 with a skirt portion 32 depending from the crown portion 30. The skirt portion 32 forms part of a peripheral wall of a nozzle chamber 34 (Figures 2 to 4 of the drawings). The nozzle opening 24 is in fluid communication with the nozzle chamber MJ1 19-AU 34. It is to be noted that the nozzle opening 24 is surrounded by a raised rim 36 which "pins" a meniscus 38 (Figure 2) of a body of ink 40 in the nozzle chamber 34.

An ink inlet aperture 42 (shown most clearly in Figure 6 of the drawing) is defined in a floor 46 of the nozzle chamber 34. The aperture 42 is in fluid communication with an ink inlet channel 48 defined through the substrate 16.

A wall portion 50 bounds the aperture 42 and extends upwardly from the floor portion 46. The skirt portion 32, as indicated above, of the nozzle 22 defines a first part of a peripheral wall of the nozzle chamber 34 and the wall portion defines a second part of the peripheral wall of the nozzle chamber 34.

The wall 50 has an inwardly directed lip 52 at its free end which serves as a fluidic seal which inhibits the escape of ink when the nozzle 22 is displaced, as will be described in greater detail below. It will be appreciated that, due to the viscosity of the ink 40 and the small dimensions of the spacing between the lip 52 and the skirt portion 32, the inwardly directed lip 52 and surface tension function as an effective seal for inhibiting the escape of ink from the nozzle chamber 34.

The actuator 28 is a thermal bend actuator and is connected to an anchor 54 extending upwardly from the substrate 16 or, more particularly from the CMOS passivation layer 20. The anchor 54 is mounted on conductive pads 56 which form an electrical connection with the actuator 28.

The actuator 28 comprises a first, active beam 58 arranged above a second, passive beam 60. In a preferred embodiment, both beams 58 and 60 are of, or include, a conductive ceramic material such as titanium nitride (TiN).

Both beams 58 and 60 have their first ends anchored to the anchor 54 and their opposed ends connected to the arm 26. When a current is caused to flow through the active beam 58 thermal expansion of the beam 58 results. As the passive beam 60, through which there is no current flow, does not expand at the same rate, a bending moment is created causing the arm 26 and, hence, the nozzle 22 to be displaced downwardly towards the substrate 16 as shown in Figure 3 of the drawings. This causes an ejection of ink through the nozzle opening 24 as shown at 62 in Figure 3 of the drawings.

When the source of heat is removed from the active beam 58, i.e. by stopping current flow, the nozzle 22 returns to its quiescent position as shown in Figure 4 of the drawings. When the nozzle 22 returns to its quiescent position, an ink droplet 64 is formed as a result of the breaking of an ink droplet neck as illustrated at 66 in Figure 4 of the drawings. The ink droplet 64 then travels on to the print media such as a sheet of paper. As a result of the formation of the ink droplet 64, a "negative" meniscus is formed as shown at 68 in Figure 4 of the drawings. This "negative" meniscus 68 results in an inflow of ink 40 into the nozzle chamber 34 such that a new meniscus 38 (Figure 2) is formed in readiness for the next ink drop ejection from the nozzle assembly Referring now to Figures 5 and 6 of the drawings, the nozzle array 14 is described in greater detail. The array 14 is for a four color printhead. Accordingly, the array 14 includes four groups 70 of nozzle assemblies, one for each color.

Each group 70 has its nozzle assemblies 10 arranged in two rows 72 and 74. One of the groups 70 is shown in greater detail in Figure 6 of the drawings.

To facilitate close packing of the nozzle assemblies 10 in the rows 72 and 74, the nozzle assemblies 10 in the row 74 are offset or staggered with respect to the nozzle assemblies 10 in the row 72. Also, the nozzle assemblies 10 in the row 72 are spaced apart sufficiently far from each other to enable the lever arms 26 of the nozzle assemblies 10 in the row 74 to pass between adjacent nozzles 22 of the assemblies 10 in the row 72. It is to be noted that each nozzle assembly is substantially dumbbell shaped so that the nozzles 22 in the row 72 nest between the nozzles 22 and the actuators 28 of adjacent nozzle assemblies 10 in the row 74.

Further, to facilitate close packing of the nozzles 22 in the rows 72 and 74, each nozzle 22 is substantially hexagonally shaped.

MJ119-AU It will be appreciated by those skilled in the art that, when the nozzles 22 are displaced towards the substrate 16, in use, due to the nozzle opening 24 being at a slight angle with respect to the nozzle chamber 34 ink is ejected slightly off the perpendicular. It is an advantage of the arrangement shown in Figures 5 and 6 of the drawings that the actuators 28 of the nozzle assemblies 10 in the rows 72 and 74 extend in the same direction to one side of the rows 72 and 74. Hence, the ink ejected from the nozzles 22 in the row 72 and the ink ejected from the nozzles 22 in the row 74 are offset with respect to each other by the same angle resulting in an improved print quality.

Also, as shown in Figure 5 of the drawings, the substrate 16 has bond pads 76 arranged thereon which provide the electrical connections, via the pads 56, to the actuators 28 of the nozzle assemblies 10. These electrical connections are formed via the CMOS layer (not shown).

Referring to Figure 7 of the drawings, a development of the invention is shown. With reference to the previous drawings, like reference numerals refer to like parts, unless otherwise specified.

In this development, a nozzle guard 80 is mounted on the substrate 16 of the array 14. The nozzle guard includes a body member 82 having a plurality of passages 84 defined therethrough. The passages 84 are in register with the nozzle openings 24 of the nozzle assemblies 10 of the array 14 such that, when ink is ejected from any one of the nozzle openings 24, the ink passes through the associated passage before striking the print media.

The body member 82 is mounted in spaced relationship relative to the nozzle assemblies 10 by limbs or struts 86.

One of the struts 86 has air inlet openings 88 defined therein.

In use, when the array 14 is in operation, air is charged through the inlet openings 88 to be forced through the passages 84 together with ink travelling through the passages 84.

The ink is not entrained in the air as the air is charged through the passages 84 at a different velocity from that of the ink droplets 64. For example, the ink droplets 64 are ejected from the nozzles 22 at a velocity of approximately 3m/s.

The air is charged through the passages 84 at a velocity of approximately lm/s.

The purpose of the air is to maintain the passages 84 clear of foreign particles. A danger exists that these foreign particles, such as dust particles, could fall onto the nozzle assemblies 10 adversely affecting their operation. With the provision of the air inlet openings 88 in the nozzle guard 80 this problem is, to a large extent, obviated.

Referring now to Figures 8 to 10 of the drawings, a process for manufacturing the nozzle assemblies 10 is described.

Starting with the silicon substrate or wafer 16, the dielectric layer 18 is deposited on a surface of the wafer 16.

The dielectric layer 18 is in the form of approximately 1.5 microns of CVD oxide. Resist is spun on to the layer 18 and the layer 18 is exposed to mask 100 and is subsequently developed.

After being developed, the layer 18 is plasma etched down to the silicon layer 16. The resist is then stripped and the layer 18 is cleaned. This step defines the ink inlet aperture 42.

In Figure 8b of the drawings, approximately 0.8 microns of aluminum 102 is deposited on the layer 18. Resist is spun on and the aluminum 102 is exposed to mask 104 and developed. The aluminum 102 is plasma etched down to the oxide layer 18, the resist is stripped and the device is cleaned. This step provides the bond pads and interconnects to the inkjet actuator 28. This interconnect is to an NMOS drive transistor and a power plane with connections made in the CMOS layer (not shown).

Approximately 0.5 microns of PECVD nitride is deposited as the CMOS passivation layer 20. Resist is spun on and the layer 20 is exposed to mask 106 whereafter it is developed. After development, the nitride is plasma etched down to the aluminum layer 102 and the silicon layer 16 in the region of the inlet aperture 42. The resist is stripped and the device cleaned.

MJ119-AU A layer 108 of a sacrificial material is spun on to the layer 20. The layer 108 is 6 microns of photo-sensitive polyimide or approximately 4 tm of high temperature resist. The layer 108 is softbaked and is then exposed to mask 110 whereafter it is developed. The layer 108 is then hardbaked at 400°C for one hour where the layer 108 is comprised of polyimide or at greater than 300°C where the layer 108 is high temperature resist. It is to be noted in the drawings that the pattern-dependent distortion of the polyimide layer 108 caused by shrinkage is taken into account in the design of the mask 110.

In the next step, shown in Figure 8e of the drawings, a second sacrificial layer 112 is applied. The layer 112 is either 2 tm of photo-sensitive polyimide which is spun on or approximately 1.3 pm of high temperature resist. The layer 112 is softbaked and exposed to mask 114. After exposure to the mask 114, the layer 112 is developed. In the case of the layer 112 being polyimide, the layer 112 is hardbaked at 400°C for approximately one hour. Where the layer 112 is resist, it is hardbaked at greater than 300°C for approximately one hour.

A 0.2 micron multi-layer metal layer 116 is then deposited. Part of this layer 116 forms the passive beam 60 of the actuator 28.

The layer 116 is formed by sputtering 1,000A of titanium nitride (TiN) at around 300°C followed by sputtering 50A of tantalum nitride (TaN). A further 1,000A of TiN is sputtered on followed by 50A of TaN and a further 1,000A of TiN.

Other materials which can be used instead of TiN are TiB,, MoSi, or (Ti, AI)N.

The layer 116 is then exposed to mask 118, developed and plasma etched down to the layer 112 whereafter resist, applied for the layer 116, is wet stripped taking care not to remove the cured layers 108 or 112.

A third sacrificial layer 120 is applied by spinning on 4 jim of photo-sensitive polyimide or approximately 2.6 im high temperature resist. The layer 120 is softbaked whereafter it is exposed to mask 122. The exposed layer is then developed followed by hard baking. In the case of polyimide, the layer 120 is hardbaked at 400°C for approximately one hour or at greater than 300°C where the layer 120 comprises resist.

A second multi-layer metal layer 124 is applied to the layer 120. The constituents of the layer 124 are the same as the layer 116 and are applied in the same manner. It will be appreciated that both layers 116 and 124 are electrically conductive layers.

The layer 124 is exposed to mask 126 and is then developed. The layer 124 is plasma etched down to the polyimide or resist layer 120 whereafter resist applied for the layer 124 is wet stripped taking care not to remove the cured layers 108, 112 or 120. It will be noted that the remaining part of the layer 124 defines the active beam 58 of the actuator 28.

A fourth sacrificial layer 128 is applied by spinning on 4 im of photo-sensitive polyimide or approximately 2.61im of high temperature resist. The layer 128 is softbaked, exposed to the mask 130 and is then developed to leave the island portions as shown in Figure 9k of the drawings. The remaining portions of the layer 128 are hardbaked at 400°C for approximately one hour in the case of polyimide or at greater than 300°C for resist.

As shown in Figure 81 of the drawing a high Young's modulus dielectric layer 132 is deposited. The layer 132 is constituted by approximately 1 im of silicon nitride or aluminum oxide. The layer 132 is deposited at a temperature below the hardbaked temperature of the sacrificial layers 108, 112, 120, 128. The primary characteristics required for this dielectric layer 132 are a high elastic modulus, chemical inertness and good adhesion to TiN.

MJ119-AU A fifth sacrificial layer 134 is applied by spinning on 2im of photo-sensitive polyimide or approximately 1.3tm of high temperature resist. The layer 134 is softbaked, exposed to mask 136 and developed. The remaining portion of the layer 134 is then hardbaked at 400 0 C for one hour in the case of the polyimide or at greater than 300'C for the resist.

The dielectric layer 132 is plasma etched down to the sacrificial layer 128 taking care not to remove any of the sacrificial layer 134.

This step defines the nozzle opening 24, the lever arm 26 and the anchor 54 of the nozzle assembly A high Young's modulus dielectric layer 138 is deposited. This layer 138 is formed by depositing 0.21m of silicon nitride or aluminum nitride at a temperature below the hardbaked temperature of the sacrificial layers 108, 112, 120 and 128.

Then, as shown in Figure 8p of the drawings, the layer 138 is anisotropically plasma etched to a depth of 0.35 microns. This etch is intended to clear the dielectric from all of the surface except the side walls of the dielectric layer 132 and the sacrificial layer 134. This step creates the nozzle rim 36 around the nozzle opening 24 which "pins" the meniscus of ink, as described above.

An ultraviolet (UV) release tape 140 is applied. 4gm of resist is spun on to a rear of the silicon wafer 16. The wafer 16 is exposed to mask 142 to back etch the wafer 16 to define the ink inlet channel 48. The resist is then stripped from the wafer 16.

A further UV release tape (not shown) is applied to a rear of the wafer 16 and the tape 140 is removed. The sacrificial layers 108, 112, 120, 128 and 134 are stripped in oxygen plasma to provide the final nozzle assembly 10 as shown in Figures 8r and 9r of the drawings. For ease of reference, the reference numerals illustrated in these two drawings are the same as those in Figure 1 of the drawings to indicate the relevant parts of the nozzle assembly 10. Figures 11 and 12 show the operation of the nozzle assembly 10, manufactured in accordance with the process described above with reference to Figures 8 and 9 and these figures correspond to Figures 2 to 4 of the drawings.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

M J119-AU

Claims (7)

1. An inkjet printhead which includes a substrate that defines a plurality of ink inlet channels and incorporates drive circuitry; and a plurality of nozzle assemblies positioned on the substrate, each nozzle assembly defining a nozzle chamber in fluid communication with one of the ink inlet channels and each nozzle assembly including an actuator that is mounted on the substrate and is electrically connected to the drive circuitry to be displaceable with respect to the substrate on receipt of an electrical signal from the drive circuitry; a nozzle that is connected to the actuator and is displaceable relative to the substrate to be displaced by the actuator, the nozzle defining a nozzle opening such that, in use, upon displacement of the nozzle relative to the substrate, ink is ejected from the nozzle chamber through the nozzle opening; and a pair of complementary fluidic seal forming structures positioned on the nozzle and the substrate respectively, the seal forming structures being configured so that, when the nozzle chamber is filled with ink, a meniscus is defined between the seal forming structures to accommodate movement of the nozzle while inhibiting leakage of ink from the nozzle chamber.

2. An ink jet printhead as claimed in claim 1, in which each actuator is an elongate thermal bend actuator that is connected to the substrate at one end and is configured so that an opposite end is displaceable with respect to the substrate on receipt of said electrical signal.

3. An ink jet printhead as claimed in claim 2, in which each nozzle includes a crown portion and a skirt portion that depends from the crown portion, the crown portion defining the nozzle opening and the skirt portion defining one of the fluidic seal forming structures, with the other fluidic seal forming structure extending from the substrate about one of the ink inlet channels.

4. An ink jet printhead as claimed in claim 3, in which each skirt portion and said other fluidic seal forming structure define a peripheral wall of the nozzle chamber such that, when the nozzle is displaced towards and away from the substrate, a volume of the nozzle chamber is reduced and subsequently enlarged, resulting in the ejection of a drop of ink from the nozzle chamber.

An inkjet printhead as claimed in any one of claims 2 to 4, in which each actuator includes an active beam and a second passive beam, at least the active beam defining an electrical heating circuit and being of a material that expands and contracts when heated and subsequently cooled, the beams being positioned with respect to each other such that heating and cooling of the active beam results in displacement of the actuator.

6. An inkjet printhead as claimed in claim 5, in which the second passive beam is interposed between the first active beam and the substrate such that heating and subsequent expansion of the active beam results in the actuator being displaced towards the substrate and cooling and subsequent contraction of the active beam results in the actuator being displaced away from the substrate. MJ 119-AU -9-

7. An ink jet printhead as claimed in any one of the preceding claims which includes a nozzle guard that is mounted on the substrate, the nozzle guard including a body member that is spaced from the nozzle assemblies, the body member defining a plurality of passages, each passage corresponding with a respective nozzle opening such that ink ejected from each nozzle opening passes through a corresponding passage. MJ119-AU