Abstract:
A nozzle arrangement is provided for an inkjet printhead. The nozzle arrangement includes a wafer substrate assembly defining an ink inlet channel and a first wall surrounding the ink inlet channel. A thermal actuator includes an anchor extending from the wafer substrate assembly outside of the confines of the first wall, and thermal actuator arms extending from the anchor. A roof structure is operatively mounted to terminate the actuator arms and covers the first wall. The roof structure defines a second wall surrounding the first wall so that the wafer substrate assembly and the roof structure together define a nozzle chamber in which ink from the ink inlet channel can be supplied. The roof structure further defines a rim through which ink in the nozzle chamber can be ejected. Upon thermal actuation of the actuator, the actuator moves the roof structure with respect to the wafer substrate assembly to thereby eject ink in the nozzle chamber through the rim.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is a continuation of U.S. application Ser. No. 10/698,374 filed on Nov. 3, 2003, which is a continuation-in-part of U.S. application Ser. No. 10/160,273 filed on Jun. 4, 2002, now issued as U.S. Pat. No. 6,746,105, which is a continuation of U.S. application Ser. No. 09/112,767 filed on Jul. 10, 1998, now issued as U.S. Pat. No. 6,416,167 all of which are herein incorporated by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates to a nozzle arrangement for a microelectromechnical system (‘MEMS’) inkjet printhead.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the MEMS nozzle arrangement described in U.S. Pat. No. 6,243,113 “Image Creation Method and Appartus”(the contents of which are incorporated herein by cross reference), an ink chamber is provided with an ink inlet and an ink ejection port, which are coaxial. The ink ejection port is provided through thermal actuator that incorporates a paddle mounted to a substrate by a passive anchor and an active anchor. The active anchor includes a resistive element that heats up upon application of a current. This heating causes expansion of the active anchor, whilst the passive anchor is sufficiently shielded from the generated heat that it remains the same length. The change in relative lengths of the anchors is amplified by the geometric position of the anchors with respect to each other, such that the paddle can selectively be displaced with respect to the ink chamber by applying a suitable drive current to the active anchor.  
         [0004]     Upon actuation, the paddle is urged towards the ink chamber, causing an increase in pressure in the ink in the chamber. This in turn causes ink to bulge out of the ink ejection port. When the drive current is removed, the active anchor quickly cools, which in turn causes the paddle to return to its quiescent position. The inertia of the moving ink bulge causes a thinning and breaking of the ink surface adjacent the ink ejection port, such that a droplet of ink continues moving away from the port as the paddle moves back to its quiescent position. As the quiescent position is reached, surface tension of a concave meniscus across the ink ejection port causes ink to be drawn in to refill the ink chamber via the ink inlet. Once the ink chamber is full, the process can be repeated.  
         [0005]     One difficulty with the arrangement described in this nozzle arrangement (and similar systems) is optimising resistance of the ink inlet to ink ingress. If it is too high, then the ink chamber will refill relatively slowly and the rate at which the nozzle can be fired will drop. If the resistance is too low, then the increase in ink pressure within the ink chamber will cause backflow of ink from the chamber to the inlet, thereby hampering ejection efficiency. Two ways in which resistance has been controlled to date is length and diameter of the ink supply inlet.  
       SUMMARY OF INVENTION  
       [0006]     In accordance with the invention, there is provided a nozzle arrangement for an inkjet printhead, the nozzle arrangement including: 
    (a) a nozzle chamber for holding ink;     (b) an actuator in fluid communication with the nozzle chamber, the actuator being moveable with respect to the nozzle chamber upon actuation;     (c) a fluid ejection port in fluid communication with the nozzle chamber for allowing ejection of ink upon movement of an operative portion of the actuator relative to the nozzle chamber during actuation, the fluid ejection port defining an ejection axis generally perpendicular to a plane within which the fluid ejection port is disposed; and     (d) an inlet channel in fluid communication with the nozzle chamber for supplying ink thereto from an ink supply; 
        wherein the inlet channel is positioned for supplying ink to refill the nozzle chamber at a position radially displaced from the ejection axis.    
       
 
         [0012]     Preferably, the inlet channel is orientated such that the ink enters the nozzle chamber along an inlet axis that is substantially parallel to, but displaced from, the ejection axis.  
         [0013]     In a preferred form, the fluid ejection port is formed in a roof portion that at least partially defines the nozzle chamber. The nozzle arrangement is configured such that, upon actuation, an operative portion of the actuator is moved relative to the fluid ejection port, causing the ink to be ejected from the fluid ejection port.  
         [0014]     In a preferred embodiment, at least part of the operative portion of the actuator defines a roof portion that at least partially defines the nozzle chamber. The fluid ejection port is formed in the roof portion. In this embodiment, the nozzle arrangement is configured such that, upon actuation, the roof portion, and thereby the fluid ejection port, are moved relative to the nozzle chamber, thereby causing the ink to be ejected from the fluid ejection port.  
         [0015]     Preferably, the nozzle chamber is refilled with ink via the inlet channel upon return of the actuator to a quiescent position after actuation. More preferably, the nozzle chamber is refilled with ink from the inlet channel due to a reduction in pressure within the nozzle chamber caused by surface tension of a concave ink meniscus across the fluid ejection port after ink ejection.  
         [0016]     In a preferred embodiment, the actuator is a thermal actuator. More preferably, the actuator comprises at least one passive anchor and at least one active anchor, wherein the active anchor is resistively heatable by means of an electric current to cause thermal expansion relative to the passive anchor.  
         [0017]     Preferably, the actuator is moveable within a plane upon actuation, the plane intersecting and being parallel with the ejection axis. More preferably, the actuator is mounted to flex about an anchor point upon actuation. It is particularly preferred that the inlet channel is located in a plane that is parallel to both the inlet channel axis and the ejection axis and which intersects both axes.  
         [0018]     In a preferred embodiment, the nozzle arrangement further includes a raised rib formation disposed on a floor or wall of the nozzle chamber adjacent the inlet channel, for impeding backflow of ink during the actuation. Preferably, the rib formation at least partially encircles the inlet channel. More preferably, the rib formation comprises a collar that encircles the inlet channel. It is particularly preferred in this embodiment that the rib formation comprise a radially inward-extending lip.  
         [0019]     Preferably, the actuator is rotatably moved about a pivot region upon actuation and the inlet channel is disposed closer to the pivot region than to the ejection port.  
         [0020]     Other preferred aspects, features and embodiments of the invention are described in the detailed description below.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0022]      FIG. 1  shows a plan view of an inkjet printhead chip incorporating nozzle arrangements, the nozzle arrangements being in accordance with the invention.  
         [0023]      FIG. 2  shows a three-dimensional sectioned view of one nozzle arrangement of the inkjet printhead chip in an operative condition.  
         [0024]      FIG. 3A  shows a side sectioned view of the nozzle arrangement of  FIG. 2 .  
         [0025]      FIG. 3B  shows a side sectioned view of the circled portion of  FIG. 3A .  
         [0026]      FIG. 4  shows a three-dimensional sectioned view of the nozzle arrangement of  FIG. 2  in a post-ejection quiescent condition.  
         [0027]      FIG. 5A  shows a side sectioned view of the nozzle arrangement of  FIG. 4 .  
         [0028]      FIG. 5B  shows a side sectioned view of the circled portion of  FIG. 5A .  
         [0029]      FIG. 6  shows a plan view of the nozzle arrangement of  FIG. 2 .  
         [0030]      FIG. 7  shows a cut away plan view of the nozzle arrangement of  FIG. 2 .  
         [0031]      FIG. 8  shows a sectioned view through C-C in  FIG. 6  of the nozzle arrangement of  FIG. 2 .  
         [0032]      FIG. 9  shows a three-dimensional sectioned view through A-A in  FIG. 11  of a wafer substrate, a drive circuitry layer and an ink passivation layer for a starting stage in the fabrication of each nozzle arrangement of the printhead chip.  
         [0033]      FIG. 10  shows a sectioned view through B-B in  FIG. 11  of the stage of  FIG. 9 .  
         [0034]      FIG. 11  shows a mask used for patterning the ink passivation (silicon nitride) layer of the CMOS wafer.  
         [0035]      FIG. 12  shows a three-dimensional view through A-A in  FIG. 11  of the stage of  FIG. 9  with a resist layer deposited and patterned on the ink passivation layer.  
         [0036]      FIG. 13  shows a side sectioned view through B-B in  FIG. 11  of the stage of  FIG. 12 .  
         [0037]      FIG. 14  shows a mask used for patterning the resist layer of  FIG. 12 .  
         [0038]      FIG. 15  shows a three-dimensional sectioned view of the stage of  FIG. 12 , with the resist layer removed and the wafer substrate etched to a predetermined depth to define an inlet channel of the nozzle arrangement.  
         [0039]      FIG. 16  shows a side sectioned view of the stage of  FIG. 15 .  
         [0040]      FIG. 17  shows a three-dimensional sectioned view through A-A in  FIG. 16  of the stage of  FIG. 15  with a first sacrificial layer deposited and patterned on the ink passivation layer.  
         [0041]      FIG. 18  shows a side sectioned view through B-B in  FIG. 19  of the stage of  FIG. 17 .  
         [0042]      FIG. 19  shows a mask used for patterning the first sacrificial layer.  
         [0043]      FIG. 20  shows a three-dimensional sectioned view through A-A in  FIG. 22  of the stage of  FIG. 17  with a second sacrificial layer deposited and patterned on the first sacrificial layer.  
         [0044]      FIG. 21  shows a side sectioned view through B-B in  FIG. 22  of the stage of  FIG. 20 .  
         [0045]      FIG. 22  shows a mask used for patterning the second sacrificial layer.  
         [0046]      FIG. 23  shows a three-dimensional view through A-A in  FIG. 25  of the stage of  FIG. 20  after a selective etching of the second sacrificial layer.  
         [0047]      FIG. 24  shows a side sectioned view through B-B in  FIG. 25  of the stage of  FIG. 23 .  
         [0048]      FIG. 25  shows a mask used for the selective etching of the second sacrificial layer.  
         [0049]      FIG. 26  shows a three-dimensional sectioned view of the stage of  FIG. 23  with a first conductive layer deposited on the second sacrificial layer and the ink passivation layer.  
         [0050]      FIG. 27  shows a side sectioned view of the stage of  FIG. 26 .  
         [0051]      FIG. 28  shows a three-dimensional sectioned view through A-A in  FIG. 30  after a selective etching of the first conductive layer.  
         [0052]      FIG. 29  shows a sectioned side view through B-B in  FIG. 30  of the stage of  FIG. 28 .  
         [0053]      FIG. 30  shows a mask used for selectively etching the first conductive layer.  
         [0054]      FIG. 31  shows a three-dimensional sectioned view taken through A-A in  FIG. 33  of a third sacrificial layer deposited and patterned on the first conductive layer.  
         [0055]      FIG. 32  shows a side sectioned view through B-B in  FIG. 33  of the stage of  FIG. 31 .  
         [0056]      FIG. 33  shows a mask used for depositing and patterning the third sacrificial layer.  
         [0057]      FIG. 34  shows a three-dimensional sectioned view of the stage of  FIG. 31  with a second layer of conductive material deposited on the third sacrificial layer.  
         [0058]      FIG. 35  shows a side sectioned view of the stage of  FIG. 34 .  
         [0059]      FIG. 36  shows a three-dimensional sectioned view through A-A of  FIG. 38  of the stage of  FIG. 34  after a selective etching of the second conductive layer.  
         [0060]      FIG. 37  shows a side sectioned view through B-B of  FIG. 38  of the stage of  FIG. 36 .  
         [0061]      FIG. 38  shows a mask used for the selective etching of the second conductive layer.  
         [0062]      FIG. 39  shows a three-dimensional sectioned view of the stage of  FIG. 36  with a dielectric layer deposited on the second conductive layer.  
         [0063]      FIG. 40  shows a side sectioned view of the stage of  FIG. 39 .  
         [0064]      FIG. 41  shows a three-dimensional sectioned view through A-A in  FIG. 43  of the stage of  FIG. 39  after a selective etching of the dielectric layer.  
         [0065]      FIG. 42  shows a side sectioned view through B-B in  FIG. 43  of the stage of  FIG. 41 .  
         [0066]      FIG. 43  shows a mask used in the selective etching of the dielectric layer.  
         [0067]      FIG. 44  shows a three-dimensional sectioned view through A-A in  FIG. 46  of the stage of  FIG. 41  after a further selective etching of the dielectric layer.  
         [0068]      FIG. 45  shows a side sectioned view through B-B in  FIG. 46 .  
         [0069]      FIG. 46  shows a mask used for the further selective etching of the dielectric layer.  
         [0070]      FIG. 47  shows a three-dimensional sectioned view through A-A in  FIG. 49  of the stage of  FIG. 44  with a resist layer deposited on the dielectric layer and subsequent to a preliminary back etching of the wafer substrate.  
         [0071]      FIG. 48  shows a side sectioned view taken through B-B in  FIG. 49  of the stage of  FIG. 47 .  
         [0072]      FIG. 49  shows a mask used for the preliminary back etching of the wafer substrate.  
         [0073]      FIG. 50  shows a three-dimensional sectioned view of the stage of  FIG. 48  subsequent to a secondary back etching of the material of the first sacrificial layer positioned in an inlet and nozzle chamber of the nozzle arrangement.  
         [0074]      FIG. 51  shows a side sectioned view of the stage of  FIG. 50 .  
         [0075]      FIG. 52  shows a sectioned three-dimensional view of the stage of  FIG. 50  with all the sacrificial material and resist material removed.  
         [0076]      FIG. 53  shows a side sectioned view of the stage of  FIG. 52 .  
         [0077]      FIG. 54  shows a simplified side sectioned view of an alternative embodiment of a nozzle arrangement according to the invention, in a quiescent state.  
         [0078]      FIG. 55  shows a side sectioned view of the nozzle arrangement of  FIG. 54 , during actuation. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0079]     In FIGS.  1  to  7 , reference numeral  10  generally indicates a nozzle arrangement for an inkjet printhead chip  12 , part of which is shown in  FIG. 1 .  
         [0080]     The nozzle arrangement  10  is the product of an integrated circuit fabrication technique. In particular, the nozzle arrangement  10  defines a micro-electromechanical system (MEMS).  
         [0081]     In this description, only one nozzle arrangement  10  is described. This is simply for clarity and ease of description. A printhead having one or more printhead chips  12  can incorporate up to 84000 nozzle arrangements  10 . Further, as is clear from  FIG. 1 , the printhead chip  12  is a multiple replication of the nozzle arrangement  10 . It follows that the following detailed description of the nozzle arrangement  10  adequately describes the printhead chip  12 .  
         [0082]     The inkjet printhead chip  12  includes a silicon wafer substrate  14 . 0.35 Micron 1 P4M 12 volt CMOS microprocessing circuitry is positioned on the silicon wafer substrate  14 . The circuitry is shown as a drive circuitry layer  16 .  
         [0083]     A silicon dioxide or glass layer  18  is positioned on the wafer substrate  14 . The layer  18  defines CMOS dielectric layers. CMOS top-level metal defines a pair of aligned aluminum electrode contact layers (not shown) positioned on the silicon dioxide layer  18 . Both the silicon wafer substrate  14  and the silicon dioxide layer  18  are etched to define an ink inlet channel  22  having a circular cross section. A diffusion barrier  24  of CMOS metal  1 , CMOS metal  2 / 3  and CMOS top level metal is positioned in the silicon dioxide layer  18  about the ink inlet channel  22 . The diffusion barrier  24  serves to inhibit hydroxyl ions from diffusing through CMOS oxide layers of the drive circuitry layer  16 .  
         [0084]     A portion of the diffusion barrier  24  extends from the silicon dioxide layer  18 . An ink passivation layer in the form of a layer of silicon nitride  26  is positioned over the aluminum contact layers and the silicon dioxide layer  18 , as well as the diffusion barrier  24 . Each portion of the layer  26  positioned over the contact layers has an opening  28  defined therein to provide access to the drive circuitry layer  16 .  
         [0085]     Each nozzle arrangement  10  has a rectangular, elongate configuration as shown in the drawings.  FIG. 1  shows the manner in which the nozzle arrangements  10  are positioned. Each nozzle arrangement uses an area  40  of the wafer substrate  14  that has a first end  34 , a second end  36  and a pair of opposed sides  38 .  
         [0086]     The printhead chip  12  is configured to generate text and images having a resolution of 1200 dpi (dots per inch). Furthermore, as can be seen in  FIG. 1 , the nozzle arrangements  10  are arranged in an aligned, side-by-side manner in each row so that the ink ejection ports  88  extend rectilinearly along a length of the substrate  14 . It follows that a distance between consecutive ink ejection ports  88  is approximately 21 microns. It can therefore be deduced that a width of each nozzle arrangement  10  is also approximately 21 microns or slightly less, since clearance between consecutive nozzle arrangements  10  should be taken into account. A length of each nozzle arrangement  10  is approximately 84 microns. It follows that, for a column of ink dots on a print medium moving in the direction of an arrow  11  shown in  FIG. 1 , 1770 microns square of chip real estate is required.  
         [0087]     A thermal actuator  30  is electrically connected to both the contact layers at the openings  28 , proximate the first end  34  of the area  40 . The thermal actuator  30  is of titanium aluminum nitride. Further, the thermal actuator  30  has four anchor portions  32  that extend from the silicon nitride layer  26  to a predetermined point spaced from the silicon nitride layer  26 . The anchor portions  32  define a pair of spaced active anchor portions  32 . 1  and a pair of spaced passive anchor portions  32 . 2 . The active anchor portions  32 . 1  are aligned across the area  40 . The passive anchor portions  32 . 2  are also aligned across the area  40 . The passive anchor portions  32 . 2  are positioned inwardly, lengthwise, of the active anchor portions  32 . 1 .  
         [0088]     Each of the active anchor portions  32 . 1  is positioned at respective openings  28 . Further, each active anchor portion  32 . 1  is electrically connected to the drive circuitry layer  16  to define vias  42 . Each via  34  includes a titanium layer  44  and the active anchor portion  32 . 1  sandwiched between a layer  46  of dielectric material in the form of low temperature silicon nitride and the drive circuitry layer  16 .  
         [0089]     Each of the passive anchor portions  32 . 2  is retained in position by being sandwiched between the layer  46  of low temperature silicon nitride and the silicon nitride layer  26 . Generally, the structure of the active anchor portions  32 . 1  and the vias  34  are similar to the structure of the layer  46  in combination with the passive anchor portions  32 . 2 . However, the absence of the openings  28  at the passive anchor portions  32 . 2  ensures that electrical contact between the thermal actuator  30  and the drive circuitry layer  16  is not made. This is enhanced by the fact that silicon nitride is a dielectric material.  
         [0090]     Details of the thermal actuator  30  are shown in FIGS.  6  to  8 . The thermal actuator  30  includes a pair of inner actuator arms  48 . 1  and a pair of outer actuator arms  48 . 2 . Each inner actuator arm  48 . 1  is connected to a free end of a respective active anchor portion  32 . 1 . Similarly, each outer actuator arm  48 . 2  is connected to a free end of a respective passive anchor portion  32 . 2 . The actuator arms  48  extend from the anchor portions  32  in a plane that is generally parallel to a plane of the wafer substrate  14 , towards a longitudinal axis of the ink inlet channel  22 . The actuator arms  48  terminate at a common bridge portion  50 .  
         [0091]     Each inner actuator arm  48 . 1  includes a central planar section  52  that is positioned in a plane parallel to that of the wafer substrate  14 . A pair of opposed intermediate planar sections  54  are connected to respective sides of the central section  52  to extend towards the wafer substrate  14 . A pair of opposed, outer planar sections  56  extend from each of the intermediate sections  54 , parallel to the wafer substrate  14 , at a position intermediate the central section  52  and the wafer substrate  14 .  
         [0092]     Each of the outer actuator arms  48 . 2  has a similar configuration that is simply an inverse of the configuration of the inner actuator arms  48 . 1 . It follows that outer planar sections  58  of each outer actuator arm  48 . 2  are co-planar with the outer sections  56  of the inner actuator arms  48 . 1 . A central planar section  60  of each outer actuator arm  48 . 2  is positioned intermediate the outer planar sections  58  and the wafer substrate  14 .  
         [0093]     The arms  48  and the bridge portion  50  are configured so that, when a predetermined electrical current is applied to the inner actuator arms  48 . 1  the inner actuator arms  48 . 1  are heated to the substantial exclusion of the outer actuator arms  48 . 2 . This heating results in an expansion of the inner actuator arms  48 . 1 , also to the exclusion of the outer actuator arms  48 . 2 . As a result, a differential expansion is set up in the actuator arms  48 . The differential expansion results in the actuator arms  48  bending towards the layer  26  of silicon nitride.  
         [0094]     A nozzle chamber wall  62  of titanium aluminum nitride is positioned on that portion of the layer  26  of silicon nitride that is positioned over the diffusion barrier  24 . The nozzle chamber wall  62  has an inner wall portion  64  and an outer wall portion  66 . The inner wall portion  64  defines part of the ink inlet channel  22 . A radially inwardly directed ledge  68  is positioned on the inner wall portion  64 .  
         [0095]     The outer wall portion  66  is spaced from the inner wall portion  64  and extends past the inner wall portion  64  away from the wafer substrate  14 .  
         [0096]     The nozzle arrangement  10  includes a roof structure  72 . The roof structure  72  has a roof member  74  that is positioned above the nozzle chamber wall  62 . A complementary nozzle chamber wall  76  depends from the roof member  74  towards the wafer substrate  14 . The complementary nozzle chamber wall  76  overlaps the outer wall portion  66 .  
         [0097]     As can be seen in the drawings, the nozzle chamber wall  62  and the complementary nozzle chamber wall  76  together define a nozzle chamber  75 . The nozzle chamber  75  and the ink inlet channel  22  are in fluid communication to be filled with ink  77 , in use.  
         [0098]     The outer wall portion  66  and the complementary nozzle chamber wall  76  define an ink sealing structure  78 . In particular, the outer wall portion  66  includes a radially extending rim  80 . The complementary nozzle chamber wall  76  is configured so that, when the nozzle arrangement  10  is in a quiescent condition, a free edge  82  of the complementary nozzle chamber wall  76  is generally aligned with the rim  80  and spaced from the rim  80 .  
         [0099]     When the nozzle chamber  75  is filled with the ink  77 , an ink meniscus  84  forms between the free edge  82  and the rim  80 . As can be seen in the drawings, the outer wall portion  66  includes a re-entrant section  86 , the rim  80  depending from the re-entrant section  86 .  
         [0100]     As can be seen in  FIG. 5B , when the nozzle arrangement  10  is in a quiescent condition, the meniscus  84  extends from the free edge  82  to an outer edge of the rim  80 . As can be seen in  FIG. 3B , when the nozzle arrangement  10  is in an initial stage of operation, the meniscus  84  extends from the free edge  82  to an inner edge of the rim  80 . The re-entrant section  86  inhibits an inner edge of the meniscus  84  from moving further than the inner edge of the rim  80 . Thus, wetting of a remaining portion of the outer wall portion  66  and subsequent leaking of ink is inhibited.  
         [0101]     It follows that when the nozzle chamber  75  is filled with the ink  77 , the sealing structure  78  defines a fluidic seal.  
         [0102]     An ink ejection port  88  is defined in the roof member  74 . A nozzle rim  90  bounds the ink ejection port  88 . A plurality of radially extending recesses  91  is defined in the roof member  74  about the rim  90 . These serve to contain radial ink flow as a result of ink escaping past the nozzle rim  90 . A rectangular recess  92  is defined in the roof member  74  in communication with the recesses  91 .  
         [0103]     The roof structure  72  includes a mounting formation  94  that is positioned on the bridge portion  50  of the thermal actuator  30 . The mounting formation  94  includes a layer  96  of titanium in contact with the bridge portion  50 . Instead of titanium, any other inert metal, such as tantalum, would be suitable. A layer  98  of silicon nitride is positioned on the layer  96  of titanium and extends away from the mounting formation  94  to define the roof member  74 . The ink sealing structure  78  is also of titanium.  
         [0104]     The nozzle arrangement  10  includes a test switch arrangement  100 . The test switch arrangement  100  includes a pair of titanium aluminum nitride contacts  102  that is connected to test circuitry (not shown) and is positioned at a predetermined distance from the wafer substrate  14 . The roof structure  72  includes an extended portion  104  that is opposed to the mounting formation  94  with respect to the roof member  74 . A titanium bridging member  106  is positioned on the extended portion  104  so that, when the roof structure  72  is displaced to a maximum extent towards the wafer substrate  14 , the titanium bridging member  106  abuts the contacts  102  to close the test switch arrangement  100 . Thus, operation of the nozzle arrangement  100  can be tested.  
         [0105]     In use, a suitable voltage, typically 3V to 12V depending on the resistivity of the TiAlNi and the characteristics of the drive circuitry is set up between the active anchor portions  32 . 1 . This results in a current being generated in the inner actuator arms  48 . 1  and a central portion of the bridge portion  50 . The voltage and the configuration of the inner actuator arms  48 . 1  are such that the current results in the inner actuator arms  48 . 1  heating. As a result of this heat, the titanium aluminum nitride of the inner actuator arms  48 . 1  expands to a greater extent than the titanium aluminum nitride of the outer actuator arms  48 . 2 . This results in the actuator arms  48  bending as shown in  FIG. 3A . Thus, the roof structure  72  tilts towards the wafer substrate  14  so that a portion  108  of the ink  77  is ejected from the ink ejection port  88 .  
         [0106]     A voltage cut-off results in a rapid cooling of the inner actuator arms  48 . 1 . The actuator arms  48 . 1  subsequently contract causing the actuator arms  48 . 1  to straighten. The roof structure  72  returns to an original condition as shown in  FIG. 5 . This return of the roof structure  72  results in the required separation of a drop  110  of the ink  77  from a remainder of the ink  77  within the nozzle chamber  75 .  
         [0107]     The walls  62 ,  76  are dimensioned so that a length of the nozzle chamber  75  is between approximately 4 and 10 times a height of the nozzle chamber  75 . More particularly, the length of the nozzle chamber  75  is approximately seven times a height of the nozzle chamber  75 . It is to be understood that the relationship between the length of the nozzle chamber  75  and the height of the nozzle chamber  75  can vary substantially while still being effective for the purposes of this invention.  
         [0108]     A difficulty to overcome in achieving the required ink ejection pressure was identified by the Applicant as being backflow towards the ink inlet channel  22  along the ink flow path. In order to address this problem, a length of the nozzle chamber  75  is between 3 and 10 times a height of the nozzle chamber  75 , as described above. Thus, while the roof member  74  is displaced towards the substrate  14 , viscous drag within the nozzle chamber  75  retards backflow of ink towards the ink inlet channel  22 , since the ink inlet channel  22  and the ink ejection port  88  are positioned at opposite ends of the nozzle chamber  75 . The fact that the inner wall portion  64  extends towards the roof member  74  also serves to inhibit backflow.  
         [0109]     There is also a requirement that the nozzle chamber  75  be refilled with ink sufficiently rapidly so that a further ink drop can be ejected. It follows that, with such factors as ink viscosity and structural materials taken as constant, the optimal relationship between the length of the nozzle chamber  75  and the height of the nozzle chamber  75  is a function of the required ink ejection pressure and a required maximum refill time. Thus, once these factors are known, it is possible to determine an optimum relationship between the nozzle chamber length and the nozzle chamber height.  
         [0110]     The printhead chip  12  incorporates a plurality of nozzle arrangements  10  as shown in  FIG. 1 . It follows that, by connecting the nozzle arrangements  10  to suitable micro processing circuitry and a suitable control system, printing can be achieved. A detail of the manner in which the nozzle arrangements  10  are connected to such components is described in the above referenced patents/patent applications and is therefore not set out in any detail in this specification. It is to be noted, however, that the inkjet printhead chip  12  is suitable for connection to any micro processing apparatus that is capable of controlling, in a desired manner, a plurality of nozzle arrangements. In particular, since the nozzle arrangements  10  span the print medium, the nozzle arrangements  10  can be controlled in a digital manner. For example, a 1 can be assigned to an active nozzle arrangement  10  while a 0 can be assigned to a quiescent nozzle arrangement  10 , in a dynamic manner.  
         [0111]     In the following paragraphs, the manner of fabrication of the nozzle arrangement  10  is described, by way of example only. It will be appreciated that the following description is for purposes of enablement only and is not intended to limit the broad scope of the preceding summary or the invention as defined in the appended claims.  
         [0112]     In  FIGS. 9 and 10 , reference numeral  112  generally indicates a complete 0.35 micron 1P4M 12 Volt CMOS wafer that is the starting stage for the fabrication of the nozzle arrangement  10 . It is again emphasized that the following description of the fabrication of a single nozzle arrangement  10  is simply for the purposes of convenience. It will be appreciated that the processing techniques and the masks used are configured to carry out the fabrication process, as described below, on a plurality of such nozzle arrangements. However, for the purposes of convenience and ease of description, the fabrication of a single nozzle arrangement  10  is described. Thus, by simply extrapolating the following description, a description of the fabrication process for the inkjet printhead chip  12  can be obtained.  
         [0113]     The CMOS wafer  112  includes a silicon wafer substrate  114 . A layer  116  of silicon dioxide is positioned on the wafer substrate  114  to form CMOS dielectric layers. Successive portions of CMOS metal  1 , CMOS metal  2 / 3  and CMOS top level metal define an aluminum diffusion barrier  118 . The diffusion barrier  118  is positioned in the layer  116  of silicon dioxide with a portion  120  of the barrier  118  extending from the layer  116 . The barrier  118  serves to inhibit hydroxyl ions from diffusing through oxide layers of the layer  116 . The CMOS top level metal defines a pair of aluminum electrode contact layers (not shown) positioned on the layer  116 .  
         [0114]     A layer  124  of CMOS passivation material in the form of silicon nitride is positioned over the layer  116  of silicon dioxide and the portion  120  of the diffusion barrier  118 . The silicon nitride layer  124  is deposited and subsequently patterned with a mask  126  in  FIG. 11 . The silicon nitride layer  124  is the result of the deposition of a resist on the silicon nitride, imaging with the mask  126  and subsequent etching to define a pair of contact openings  128 , an opening  130  for an ink inlet channel to be formed and test switch openings  132 .  
         [0115]     The silicon dioxide layer  116  has a thickness of approximately 5 microns. The layer  124  of silicon nitride has a thickness of approximately 1 micron.  
         [0116]     In FIGS.  12  to  14 , reference numeral  134  generally indicates a further fabrication step on the CMOS wafer  112 . With reference to FIGS.  9  to  11 , like reference numerals refer to like parts, unless otherwise specified.  
         [0117]     The structure  134  shows the etching of the CMOS dielectric layers defined by the layer  116  of silicon dioxide down to bare silicon of the layer  114 .  
         [0118]     Approximately 3 microns of resist material  136  is spun onto the silicon nitride layer  124 . The resist material  136  is a positive resist material. A mask  138  in  FIG. 14  is used for a photolithographic step carried out on the resist material  136 . The photolithographic image that is indicated by the mask  138  is then developed and a soft bake process is carried out on the resist material  136 .  
         [0119]     The photolithographic step is carried out as a 1.0 micron or better stepping process with an alignment of +/−0.25 micron. An etch of approximately 4 microns is carried out on the silicon dioxide layer  116  down to the bare silicon of the silicon wafer substrate  114 .  
         [0120]     In  FIGS. 15 and 16 , reference numeral  140  generally indicates the structure  134  after a deep reactive ion etch (DRIE) is carried out on the silicon wafer substrate  114 .  
         [0121]     The etch is carried out on the bare silicon of the substrate  114  to develop the ink inlet channel  22  further. This is a DRIE to  20  microns (+10/−2 microns). Further in this step, the resist material  136  is stripped and the structure is cleaned with an oxygen plasma cleaning process.  
         [0122]     The etch depth is not a critical issue in this stage. Further, the deep reactive ion etch can be in the form of a DRAM trench etch.  
         [0123]     In FIGS.  17  to  19 , reference numeral  142  generally indicates the structure  140  with a first layer  144  of sacrificial resist material positioned thereon. With reference to the preceding Figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0124]     In this stage, approximately 3.5 microns of the sacrificial resist material  144  is spun on to the front surface of the structure  140 . A mask  148  in  FIG. 19 , is used together with a photolithographic process to pattern the first layer  144  of the sacrificial material.  
         [0125]     The photolithographic process is a 1.0 micron stepping process or better. The mask bias is +0.3 micron and the alignment is +/−0.25 micron.  
         [0126]     The sacrificial material  144  is a positive resist material. The sacrificial material  144  can be in the form of a polyimide.  
         [0127]     Being a positive resist, the first layer  144 , when developed, defines a pair of contact openings  150  which provide access to the aluminum electrode contact layers  122  and a pair of inwardly positioned openings  152  which are aligned with the contact openings  150  and terminate at the layer  124  of silicon nitride. As can be seen in the drawings, a region that was previously etched into the silicon wafer substrate  114  and through the silicon dioxide layer  116  to initiate the ink inlet channel  22  is filled with the sacrificial material  144 . A region  154  above the portion  120  of the diffusion barrier  118  and the layer  124  is cleared of sacrificial material to define a zone for the nozzle chamber  75 . Still further, the sacrificial material  144  defines a pair of test switch openings  156 .  
         [0128]     The sacrificial material  144  is cured with deep ultraviolet radiation. This serves to stabilize the sacrificial material  144  to increase the resistance of the sacrificial material  144  to later etching processes. The sacrificial material  144  shrinks to a thickness of approximately 3 microns.  
         [0129]     In FIGS.  20  to  22 , reference numeral  158  generally indicates the structure  142  with a second layer  160  of sacrificial resist material developed thereon. With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0130]     In this stage, approximately 1.2 microns of the sacrificial resist material  160  in the form of a positive resist material are spun onto the structure  142 . The sacrificial material  160  can be in the form of a polyimide.  
         [0131]     A mask  164  shown in  FIG. 22  is used together with a photolithographic process to pattern the sacrificial material  160 . The photolithographic process is a 1.0 micron stepper or better process.  
         [0132]     Further, the mask bias is +0.2 micron for top features only. The alignment during the photolithographic process is +/−0.25 micron.  
         [0133]     It should be noted that, in the previous stage, a relatively deep hole was filled with resist. The sacrificial material  160  serves to fill in any edges of the deep hole if the sacrificial material  144  has shrunk from an edge of that hole.  
         [0134]     Subsequent development of the sacrificial material  160  results in the structure shown in  FIGS. 20 and 21 . Of particular importance is the fact that the openings  150 ,  152  are extended as a result of the mask  164 . Further, deposition zones  166  are provided for the central planar sections  60  of the outer actuator arms  48 . 2 . It will also be apparent that a further deposition zone  168  is formed for the titanium aluminum nitride nozzle chamber wall  62 . The mask  164  also provides for extension of the test switch openings  156 .  
         [0135]     Once developed, the sacrificial material  160  is cured with deep ultraviolet radiation. This causes the layer  160  to shrink to 1 micron.  
         [0136]     In FIGS.  23  to  25 , reference numeral  170  generally indicates the structure  158  with a third layer  172  of sacrificial resist material positioned thereon. With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0137]     At this stage, approximately 1.2 microns of the sacrificial material  172  are spun onto the structure  158 . The sacrificial material  172  is a positive resist material. The sacrificial material  172  can be in the form of a polyimide.  
         [0138]     A mask  176  in  FIG. 25  is used to carry out a photolithographic imaging process on the sacrificial material  172 .  
         [0139]     The photolithographic process is a 1.0 micron stepper or better process. Further, the mask bias is +0.2 micron for the top features only. The alignment of the mask  176  is +/−0.25 micron. Subsequent development of the sacrificial material  172  results in the structure  170  shown in  FIG. 23  and  FIG. 24 .  
         [0140]     During this step, the layers  144 ,  160  and  172  of sacrificial material are hard baked at 250 degrees Celsius for six hours in a controlled atmosphere. The sacrificial material  172  shrinks to 1.0 micron.  
         [0141]     It is of importance to note that this step results in the formation of deposition zones  178  for the titanium aluminum nitride of the thermal actuator  30 . Further, deposition zones  180  for the nozzle chamber wall  62 , in particular the ink sealing structure  78 , are provided. Still further, deposition zones  182  for the contacts  102  for the test switch arrangement  100  are provided.  
         [0142]     In  FIGS. 26 and 27 , reference numeral  184  generally indicates the structure  170  with a layer of titanium aluminum nitride deposited thereon. With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0143]     In this stage, initially, approximately 50 Angstroms of titanium aluminum alloy at approximately 200 degrees Celsius are sputtered onto the structure  170  in an argon atmosphere. Thereafter, a nitrogen gas supply is provided and 5000 Angstroms of titanium aluminum is sputtered with the result that titanium aluminum nitride is deposited on the initial titanium aluminum metallic layer.  
         [0144]     The initial titanium aluminum metallic layer is essential to inhibit the formation of non-conductive aluminum nitride at the resulting aluminum/titanium aluminum nitride interface.  
         [0145]     The titanium aluminum is sputtered from a Ti 0.8  Al 0.2  alloy target in a nitrogen atmosphere.  
         [0146]     Titanium nitride can also be used for this step, although titanium aluminum nitride is the preferred material.  
         [0147]     Possible new CMOS copper barrier materials such as titanium aluminum silicon nitride have potential due to their amorphous nanocomposite nature. In  FIGS. 26 and 27 , the layer of titanium aluminum nitride is indicated with reference numeral  186 .  
         [0148]     The deposition thickness can vary by up to 5 percent.  
         [0149]     In FIGS.  28  to  30 , reference numeral  188  generally indicates the structure  184  with the titanium aluminum nitride layer  186  etched down to a preceding resist layer. With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0150]     At this stage, approximately 1 micron of a positive resist material is spun onto the layer  186 .  
         [0151]     A mask  190  in  FIG. 30  is used together with a photolithographic process to image the positive resist material. The resist material is then developed and undergoes a soft bake process.  
         [0152]     The photolithographic process is a 0.5 micron or better stepper process. The mask bias is +0.2 micron for the top features only. The alignment of the mask  180  is +/−0.25 micron.  
         [0153]     The titanium aluminum nitride layer  186  is then etched to a depth of approximately 1.5 micron. A wet stripping process is then used to remove the resist. This ensures that the sacrificial material is not removed. A brief clean with oxygen plasma can also be carried out. This can remove sacrificial material so should be limited to 0.2 micron or less.  
         [0154]     The result of this process is shown in  FIGS. 28 and 29 . As can be seen, this process forms the anchor portions  32  and the actuator arms  48  together with the bridge portion  50  of the thermal actuator  30 . Further, this process forms the titanium aluminum nitride nozzle chamber wall  62 . Still further, the result of this process is the formation of the test switch contacts  102 .  
         [0155]     In FIGS.  31  to  33 , reference numeral  192  generally indicates the structure  188  with a fourth layer  194  of sacrificial resist material positioned on the structure  188 . With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0156]     In this step, approximately 4.7 microns (+/−0.25 microns) of the sacrificial material  194  is spun onto the structure  188 .  
         [0157]     A mask  198  shown in  FIG. 33  is then used together with a photolithographic process to generate an image on the sacrificial material  194 . The sacrificial material  194  is a positive resist material and the image generated can be deduced from the mask  198 .  
         [0158]     The photolithographic process is a 0.5 micron stepper or better process. The mask bias is +0.2 microns. The alignment is +/−0.15 microns.  
         [0159]     The image is then developed to provide the structure as can be seen in  FIGS. 31 and 32 . As can be seen in these drawings, the development of the sacrificial material  194  provides deposition zones  200  for a titanium layer that defines the titanium layer  44  of the vias  42  and which serves to fix the anchor portions  32  of the thermal actuator  30  to the silicon nitride layer  26 . The sacrificial material  194  also defines a deposition zone  202  for the titanium layer  44  of the mounting formation  94 . Still further, the sacrificial material  194  defines a deposition zone  204  for the titanium of the complementary nozzle chamber walls  76 . Still further, the sacrificial material  194  defines deposition zones  206  for the test switch arrangement  100 .  
         [0160]     Once the sacrificial material  194  has been developed, the material  194  is cured with deep ultraviolet radiation. Thereafter, the sacrificial material  194  is hard baked at approximately 250 degrees Celsius in a controlled atmosphere for six hours. The resist material  194  subsequently shrinks to approximately 4 microns in thickness.  
         [0161]     In  FIGS. 34 and 35 , reference numeral  208  generally indicates the structure  192  with a layer  210  of titanium deposited thereon.  
         [0162]     At this stage, approximately 0.5 micron of titanium is sputtered on to the structure  192  at approximately 200 degrees Celsius in an argon atmosphere.  
         [0163]     It is important to note that the mechanical properties of this layer are not important. Instead of titanium, the material can be almost any inert malleable metal that is preferably highly conductive. Platinum or gold can be used in conjunction with a lift-off process. However, the use of gold will prevent subsequent steps being performed in the CMOS fabrication. Ruthenium should not be used as it oxidizes in subsequent oxygen plasma etch processes which are used for the removal of sacrificial materials.  
         [0164]     The deposition thickness can vary by  30 % from  0 . 5  micron and remain adequate. A deposition thickness of 0.25 micron should be achieved in any holes.  
         [0165]     In FIGS.  36  to  38 , reference numeral  212  generally indicates the structure  208  with the layer  210  of titanium etched down to the sacrificial layer  194 .  
         [0166]     At this stage, approximately 1 micron of resist material is spun on to the layer  210 . A mask  214  shown in  FIG. 38  is then used together with a photolithographic process to form an image on the layer  210 .  
         [0167]     The resist material is a positive resist material. It follows that the image can be deduced from the mask  214 . It should be noted that all vertical geometry is masked. It follows that there are no etches of sidewalls.  
         [0168]     The photolithographic process is a 1.0 micron stepper process or better. Further, the mask bias is +0.3 micron and the alignment of the mask is +/−0.25 micron.  
         [0169]     The resist material is developed and undergoes a soft bake process. The titanium layer  210  is etched down to the preceding sacrificial layer  194 . The sacrificial layer  194  was hard baked. This hard baking process inhibits the sacrificial layer  194  from being etched together with the titanium layer  210 .  
         [0170]     The etching process is planar and the lithographic process is therefore not critical.  
         [0171]     The resist material is then removed with a wet stripping process. This ensures that the sacrificial material is not also removed. Thereafter, the front side of the structure is cleaned in oxygen plasma, if necessary. It should be noted that oxygen plasma cleaning would strip the resist material. It follows that the oxygen plasma stripping or cleaning should be limited to 0.2 micron or less.  
         [0172]     The result of this process can clearly be seen in  FIGS. 36 and 37 . In particular, the deposition zones  200 ,  202 ,  204 ,  206  are now each covered with a layer of titanium, the purpose of which has been described earlier in this specification.  
         [0173]     In  FIGS. 39 and 40 , reference numeral  216  generally indicates the structure  212  with a layer  218  of silicon nitride deposited thereon. With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0174]     At this stage, the layer  218  of low temperature silicon nitride having a thickness of approximately 1.5 microns is deposited through ICP chemical vapor deposition (CVD) on the structure  212  at approximately 200° C.  
         [0175]     Any suitably strong, chemically inert dielectric material could be used instead. The material properties of this layer are not especially important. The silicon nitride does not need to be densified. It follows that high temperature deposition and annealing are not required. Furthermore, this deposition process should be approximately conformal but this is not particularly critical. Still further, any keyholes that may occur are acceptable.  
         [0176]     In FIGS.  41  to  43 , reference numeral  220  generally indicates the structure  216  with a nozzle rim  222  etched into the layer  218 . With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0177]     In this step, approximately 1 micron of resist material is spun on to the structure  216 . A mask  224  in  FIG. 43  is used together with a photolithographic process to form an image of the nozzle rim  222  on the resist material.  
         [0178]     The photolithographic process is a 1.0 micron stepper process or better. Further, the mask bias is +0.2 microns and the alignment is +/−0.25 microns.  
         [0179]     The resist material is developed and undergoes a soft bake process. The resist material is a positive  10  resist material and it follows that the resultant image can be easily deduced from the mask  224 .  
         [0180]     The layer  218  of silicon nitride is then etched to a depth of 0.6 micron +/−0.2 micron so that a recess  226  to be positioned about the nozzle rim  212  is formed.  
         [0181]     It will be appreciated that this process is an initial stage in the formation of the roof member  74  as described earlier.  
         [0182]     The resist material is wet or dry stripped.  
         [0183]     In FIGS.  44  to  46 , reference numeral  228  generally indicates the structure  220  subsequent to the layer  218  of silicon nitride being subjected to a further etching process. With reference to the preceding figures, like reference numerals refer to like parts, unless otherwise specified.  
         [0184]     At this stage, approximately 1.0 micron of resist material is spun onto the structure  220 . A mask  229  shown in  FIG. 46  is used together with a photolithographic process to form an image on the layer  218 .  
         [0185]     The resist material is a positive resist material. It follows that the image can easily be deduced from the mask  229 .  
         [0186]     The photolithographic process is a 0.5 micron stepper process or better. Further, the mask bias is +0.2 micron and the alignment is +/−0.15 micron.  
         [0187]     The image is then developed and undergoes a soft bake process. Subsequently, a timed etch of the silicon nitride takes place to a nominal depth of approximately 1.5 microns.  
         [0188]     The result of this process is clearly indicated in  FIGS. 44 and 45 . As can be seen, this process results in the sandwiching effect created with the anchor portions  32  of the thermal actuator  30 , as described earlier in the specification. Furthermore, the silicon nitride of the mounting formation  94  is formed. Still further, this process results in the formation of the roof member  74  and the extended portion  104  of the roof structure  72 . Still further, development of the image results in the creation of the ink ejection port  88 .  
         [0189]     It is to be noted that alignment with the previous etch is important.  
         [0190]     At this stage, it is not necessary to strip the resist material.  
         [0191]     In  FIG. 47  to  49 , reference numeral  230  generally indicates the stage of  FIG. 44  in which the wafer substrate  114  is thinned and subjected to a back etching process.  
         [0192]     During this step, 5 microns (+/−2 microns) of resist  232  are spun on to a front side  234  of the structure of  FIG. 44 . This serves to protect the front side  234  during a subsequent grinding operation.  
         [0193]     A back side  236  of the CMOS wafer substrate  114  is then coarsely ground until the wafer  114  reaches a thickness of approximately 260 microns. The back side  236  is then finely ground until the wafer  114  reaches a thickness of approximately 220 microns. The depth of the grinding operations depends on the original thickness of the wafer  114 .  
         [0194]     After the grinding operations, the back side  236  is subjected to a plasma thinning process that serves to thin the wafer  114  further to approximately 200 microns. An apparatus referred to as a Tru-Sce TE-200INT or equivalent can carry out the plasma thinning process.  
         [0195]     The plasma thinning serves to remove any damaged regions on the back side  236  of the wafer  114  that may have been caused by the grinding operations. The resultant smooth finish serves to improve the strength of the printhead chip  12  by inhibiting breakage due to crack propagation.  
         [0196]     At this stage, approximately  4  microns of resist material is spun on to the back side  236  of the wafer  114  after the thinning process.  
         [0197]     A mask  238  shown in  FIG. 49  is used to pattern the resist material. The mask bias is zero microns. A photolithographic process using a suitable backside mask aligner is then carried out on the back side  236  of the wafer  114 . The alignment is +/−2 microns. The resultant image is then developed and softbaked. A 190 micron, deep reactive ion etch (DRIE) is carried out on the back side  236 . This is done using a suitable apparatus such as an Alcatel 601E or a Surface Technology Systems ASE or equivalent.  
         [0198]     This etch creates side walls which are oriented at 90 degrees +/−0.5 degrees relative to the back side  236 . This etch also serves to dice the wafer. Still further, this etch serves to expose the sacrificial material positioned in the ink inlet channel  22 .  
         [0199]     In  FIGS. 50 and 51 , reference numeral  240  generally indicates the structure  230  subjected to an oxygen plasma etch from the back side  236 .  
         [0200]     In this step, an oxygen plasma etch is carried out to a depth of approximately 25 microns into the ink inlet channel  22  to clear the sacrificial material in the ink inlet channel  22  and a portion of the sacrificial material positioned in the nozzle chamber  75 .  
         [0201]     Etch depth is preferably 25 microns +/−10 microns. It should be noted that a substantial amount of over etch would not cause significant problems. The reason for this is that this will simply meet with a subsequent front side plasma etch.  
         [0202]     Applicant recommends that the equipment for the oxygen plasma etch be a Tepla 300 Autoload PC or equivalent. This provides a substantially damage-free “soft” microwave plasma etch at a relatively slow rate being 100 to 140 nanometers per minute. However, this equipment is capable of etching  25  wafers at once in a relatively low cost piece of equipment.  
         [0203]     The oxygen should be substantially pure. The temperature should not exceed 140 degrees Celsius due to a thermally bonded glass handle wafer. The time taken for this step is approximately 2.5 hours. The process rate is approximately 10 wafers per hour.  
         [0204]     In  FIGS. 52 and 53 , reference numeral  242  generally indicates the structure  240  subsequent to a front side oxygen plasma etch being carried out on the structure  240 .  
         [0205]     During this step, the structure  240  is subjected to an oxygen plasma etch from the front side  234  to a depth of 20 microns +/−5 microns. Substantial over etch is not a problem, since it simply meets with the previous etch from the back side  236 . It should be noted that this etch releases the MEMS devices and so should be carried out just before guard wafer bonding steps to minimize contamination.  
         [0206]     The Applicant recommends that an apparatus for this step be a Tepla 300 Autoload PC or equivalent. This provides a substantially damage-free “soft” microwave plasma etch at a relatively slow rate of between 100 and 140 nanometers per minute. The slow rate is countered by the fact that up to 25 wafers can be etched at once in a relatively low cost piece of equipment.  
         [0207]     The oxygen should be substantially pure. The temperature should not exceed 160 degrees Celsius. The process takes about two hours and the process rate is approximately 12.5 wafers per hour.  
         [0208]     During testing, the nozzle arrangement  10  was actuated with approximately 130 nanojoules for a duration of approximately 0.8 microseconds.  
         [0209]     It should be noted that the test switch arrangement  100  does not quite close under normal operation.  
         [0210]     However, when the nozzle arrangement  10  is operated without ink or with a more energetic pulse, the test switch arrangement  100  closes.  
         [0211]     It was found that the ejection of ink occurred approximately 4 microseconds after the start of an actuation pulse. Drop release is caused by the active return of the actuator to the quiescent position as the actuator cools rapidly.  
         [0212]     Turning to  FIGS. 54 and 55 , there is shown an alternative embodiment of the invention in which reference numerals used in other Figures are used to indicate like features. It will be appreciated that  FIGS. 54 and 55  are schematic in nature, in order to illustrate the operation of the embodiment in its simplest form, and are not intended to represent actual structural details, including the specifics of construction type and materials choice. Those skilled in the art will be able to determine appropriate construction techniques and material choices by referring to the main embodiment and other construction techniques described in the cross-referenced documents.  
         [0213]     The nozzle arrangement  250  of  FIGS. 54 and 55  differs from the main embodiment in that the roof structure  72  is fixed in position relative to the substrate  14 . The thermal actuator  30  is attached to a dynamic structure  252  that includes an operative end  254  that is enclosed within the nozzle chamber  75 .  
         [0214]     In operation, the operative end  254  of the dynamic structure  252  moves up (rather than down, as in the earlier-described embodiment) relative to the substrate  14 , which causes an increase in fluid pressure in the region between the operative end  254  and the roof portion  72 . Whilst there is a gap  256  between an edge  258  of the operative end  254  and the walls of the nozzle chamber  75 , this is considerably smaller in area than the ink ejection port  88 . Accordingly, whilst there is some back-leakage of ink past the operative end  254  through the gap  256  during actuation, considerably more ink is caused to bulge out of the ink ejection port  88 , as shown in  FIG. 55 .  
         [0215]     As drive current through the active portions  28 . 1  is stopped, the operative end  254  stops moving towards the roof portion, then begins to move back towards the quiescent position shown in  FIG. 54 . This causes a bulging, thinning, and breaking of the ink extending from the nozzle as shown in  FIG. 5A , such that an ink droplet continues to move away from the ink ejection port  88 .  
         [0216]     Refill takes place in a similar way to that described in the main embodiment, and the nozzle arrangement is then ready to fire again.  
         [0217]     Although the invention has been described with reference to a number of specific embodiments, it will be appreciated by those skilled in the art that the invention can be embodied in many other forms.