Patent Publication Number: US-6986202-B2

Title: Method of fabricating a micro-electromechanical fluid ejection device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Application is a Continuation Application of U.S. Ser. No. 10/728,887, filed on Dec. 8, 2003, now Issued U.S. Pat. No. 6,824,252, which is a Continuation Application of U.S. Ser. No. 10/309,080, filed on Dec. 4, 2002, now Issued U.S. Pat. No. 6,682,176, which is a Continuation-in-Part Application of U.S. Ser. No. 09/113,122, filed on Jul. 10, 1998, now Issued U.S. Pat. No. 6,557,977. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to micro-electromechanical fluid ejection devices. More particularly, the invention relates to a method of fabricating a micro-electromechanical fluid ejection device having enhanced actuator strength. 
     BACKGROUND OF THE INVENTION 
     Many different types of printing have been invented, a large number of which are presently in use. The known forms of printers have a variety of methods for marking the print media with relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc. 
     In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature. 
     Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207–220 (1988). 
     Ink Jet printers themselves come in many different types. The utilisation of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electrostatic ink jet printing. 
     U.S. Pat. No. 3,596,275 by Sweet also discloses a process of continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al) 
     Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, by Stemme in U.S. Pat. No. 3,747,120 (1972) which discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 which discloses a piezoelectric push mode actuation of the ink jet stream and by Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element. 
     Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and by Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned reference ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture in communication with the confined space onto a relevant print media Manufacturers such as Canon and Hewlett Packard manufacture printing devices utilizing the electrothermal actuator. 
     As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high-speed operation, safe and continuous long-term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction, operation, durability and consumables. 
     In the construction of any inkjet printing system, there are a considerable number of important factors which must be traded off against one another especially as large scale printheads are constructed, especially those of a pagewidth type. A number of these factors are outlined in the following paragraphs. 
     Firstly, inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon the standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, gallium arsenide etc. Hence, it is desirable, in any MEMS construction, to utilize well-proven semi-conductor fabrication techniques that do not require the utilization of any “exotic” processes or materials. Of course, a certain degree of trade off will be undertaken in that if the use of the exotic material far outweighs its disadvantages then it may become desirable to utilize the material anyway. 
     With a large array of ink ejection nozzles, it is desirable to provide for a highly automated form of manufacturing which results in an inexpensive production of multiple printhead devices. 
     Preferably, the device constructed utilizes a low amount of energy in the ejection of ink. The utilization of a low amount of energy is particularly important when a large pagewidth full color printhead is constructed having a large array of individual print ejection mechanisms with each ejection mechanism, in the worst case, being fired in a rapid sequence. 
     In the parent application, namely U.S. application Ser. No. 09/113,122 there is disclosed a printhead chip having a plurality of nozzle arrangements. These nozzle arrangements each include an actuator. The actuator has two pairs of actuating arms, each pair comprising an active actuating arm and a passive actuating arm. The active actuating arms are configured so that when heated upon receipt of an electrical signal, they deform and drive an ink displacement mechanism so that ink can be ejected from the respective nozzle chambers. The passive actuating arms serve to provide resilient flexibility and stability to the actuator. 
     The Applicant has found that it is desirable that the actuator has a certain configuration to avoid buckling of the actuator when the active actuating arms are deformed to displace the actuator. While avoiding buckling, this configuration must also maintain efficiency of the actuator. This configuration is the subject of this invention. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided a method of fabricating a micro-electromechanical fluid ejection device that comprises the steps of: 
     forming a first layer of a sacrificial material on a substrate incorporating a drive circuitry layer; 
     forming a first electrically conducting layer, a first structural layer and a second electrically conducting layer on the sacrificial material, with the first structural layer interposed between the electrically conducting layers, the sacrificial material being formed so that the first electrically conducting layer defines a heating circuit connected to the drive circuitry, and the electrically conducting layers and the first structural layer define a fluid ejecting member connected to an actuator arm that is displaceable on heating and subsequent expansion of the first electrically conducting layer; 
     forming a second layer of sacrificial material on the second electrically conducting layer; 
     forming a second structural layer on the second layer of sacrificial material, the sacrificial material being formed so that the second structural layer defines a nozzle chamber structure, with the fluid ejecting member positioned in the nozzle chamber structure; and 
     removing the sacrificial material so that the nozzle chamber structure defines a nozzle chamber and a fluid ejection port in fluid communication with the nozzle chamber. 
     The method may include the step of etching the substrate to form a fluid inlet channel in fluid communication with the nozzle chamber. 
     The second electrically conducting layer may be formed in substantially the same manner as the first electrically conducting layer. 
     The step of forming the first electrically conducting layer, the first structural layer and the second electrically conducting layer may include the steps of depositing the first electrically conducting layer, the first structural layer and the second electrically conducting layer and etching the electrically conducting layers and the first structural layer in a single operation. 
     The first sacrificial layer may be deposited so that, when the first electrically conducting layer is formed, a break is formed between the actuator arm and the fluid ejecting member so that the fluid ejecting member is electrically isolated. 
     The step of forming the second structural layer may include the step of forming a nozzle rim positioned about the fluid ejection port. 
     The second layer of sacrificial material may be formed so that the second structural layer defines a post for anchoring the actuator to the substrate. 
     According to a second aspect of the invention, there is provided a micro-electromechanical fluid ejection device that comprises 
     a substrate that defines a fluid inlet channel and incorporates a wafer and CMOS layers positioned on the wafer; 
     a nozzle chamber structure that is positioned on the substrate to define a nozzle chamber in fluid communication with the fluid inlet channel and a fluid ejection port in fluid communication with the nozzle chamber; 
     an actuator that is connected to the CMOS layers and operatively positioned with respect to the nozzle chamber, the actuator being displaceable on receipt of an electrical signal from the CMOS layers to act on fluid in the nozzle chamber to eject fluid from the fluid ejection port; and 
     a nozzle guard that is mounted on the substrate to be spaced from and cover the nozzle chamber structure, the nozzle guard including a body member that defines a passage that is aligned with the fluid ejection port so that fluid ejected from the fluid ejection port passes through the passage. 
     The nozzle guard may include support members that are fast with the substrate to support the body member above the nozzle chamber structure. 
     The support members may define air inlet openings to permit air to be pumped into a region between the nozzle chamber structure and the body member and to exit through the passage. 
     The actuator may be elongate and may be connected at one end to the CMOS layers. An opposite end of the actuator may be displaceable towards and away from the substrate on receipt of an electrical signal from the CMOS layers. The nozzle chamber structure may include a nozzle that is connected to said opposite end of the actuator. The nozzle may have a crown portion and a skirt portion that depends from the crown portion, the crown portion defining the fluid ejection port and the skirt portion being positioned so that the nozzle and the wall define the nozzle chamber. A volume of the nozzle chamber may thus be reduced and subsequently enlarged as the nozzle is driven towards and away from the nozzle chamber by the actuator to eject fluid from the fluid ejection port. 
     An edge of the skirt portion may be positioned adjacent an edge of the wall such that, when the nozzle chamber is filled with liquid, a meniscus is pinned by the edges of the skirt portion and the wall to define a fluidic seal that inhibits the egress of liquid from between the wall and the skirt as liquid is ejected from the fluid ejection port. 
     The crown portion may include a rim that defines the fluid ejection port. The rim may provide an anchor point for a meniscus that is formed in the fluid ejection port when the chamber is filled with liquid. 
     According to a third aspect of the invention, there is provided a micro-electromechanical fluid ejection device which comprises 
     a substrate that defines a plurality of fluid inlet channels and incorporates a wafer and CMOS layers positioned on the wafer; 
     nozzle chamber structures that are positioned on the substrate to define nozzle chambers in fluid communication with respective fluid inlet channels and fluid ejection ports in fluid communication with respective nozzle chambers; 
     actuators that are connected to the CMOS layers and operatively positioned with respect to respective nozzle chambers, the actuators being displaceable on receipt of an electrical signal from the CMOS layers to act on fluid in the respective nozzle chambers to eject fluid from the fluid ejection ports; and 
     a nozzle guard that is mounted on the substrate to be spaced from and cover the nozzle chamber structures, the nozzle guard including a body member that defines passages that are aligned with respective fluid ejection ports so that fluid ejected from the fluid ejection ports passes through the passages. 
     In general, there is disclosed herein an ink jet nozzle assembly including a nozzle chamber and a nozzle, the chamber including a movable portion and an actuating arm connected to or formed integrally with the movable portion and functioning in use to move said movable portion selectively to eject ink from the chamber via said nozzle, the actuating arm having portions with equivalent thermal expansion characteristics so as to avoid differential thermal expansion in response to changes in ambient temperature. 
     Preferably the actuating arm is formed of materials having equivalent thermal expansion characteristics and a current is passed through only a portion of the actuating arm to effect said movement. 
     Preferably said nozzle chamber has an inlet in fluid communication with an ink reservoir. The nozzle chamber may include a fixed portion configured with said movable portion such that relative movement in an ejection phase reduces an effective volume of the chamber, and alternate relative movement in a refill phase enlarges the effective volume of the chamber; 
     Portions of the actuating arms may be spaced apart and are adapted for selective differential thermal expansion upon heating so as to effect said relative movement. 
     The inlet may be positioned and dimensioned relative to the nozzle such that ink is ejected preferentially from the chamber through said nozzle in droplet form in the ejection phase, and ink is alternately drawn preferentially into the chamber from the reservoir through the inlet in the refill phase. 
     Preferably, said movable portion includes the nozzle and the fixed portion is mounted on a substrate. 
     Preferably the actuating arm effectively extends between the movable portion and the substrate. 
     Preferably the fixed portion includes the nozzle mounted on a substrate and the movable portion includes an ejection paddle. 
     Preferably the actuating arm is located substantially within the chamber. 
     Alternatively the actuating arm is located substantially outside the chamber. 
     Preferably the fixed portion includes a slotted sidewall in the chamber through which the actuating arm is connected to the movable portion. 
     Preferably the actuating arm has two portions that are of substantially the same cross-sectional profile relative to one another. 
     Alternatively the portions of the actuating arm are of different cross-sectional profiles relative to one another. 
     Preferably the portions are of substantially the same material composition relative to one another. 
     Alternatively the portions are of different material composition relative to one another. 
     Preferably the portions are substantially parallel to one another. 
     Alternatively the portions are substantially non-parallel to one another. 
     Preferably one portion is adapted to be heated to a higher temperature than the other portion in order to effect thermal actuation. 
     Preferably the respective portions are formed from multiple layers of different material compositions disposed such that thermal expansion or contraction in one portion due to the ambient temperature fluctuations is balanced by a substantially corresponding thermal expansion or contraction in the other portion. 
     Preferably the assembly is manufactured using micro-electro-mechanical-systems (MEMS) techniques. 
     Preferably an electric current is passed through one said portion arm and not the other said portion in use. 
     According to a fourth aspect of the invention, there is provided an ink jet printhead chip that comprises
         a substrate;   a plurality of nozzle arrangements positioned on the substrate, each nozzle arrangement comprising
           nozzle chamber walls that define a nozzle chamber and an ink ejection port in fluid communication with the nozzle chamber;   an actuator that is connected to the substrate and is displaceable with respect to the substrate upon receipt of a control signal, the actuator being operatively arranged with respect to the nozzle chamber to eject ink from the ink ejection port on displacement of the actuator; wherein   the actuator includes an actuating arm that has at least one active portion that is configured to be displaced upon receipt of the control signal and at least-one corresponding passive portion, the, or each, active portion being spaced from its corresponding passive portion in a plane that spans the substrate, so that spacing between the, or each, active portion and its corresponding passive portion is greater than one percent of a length of the actuating arm and less than twenty percent of the length of the actuating arm.   
               

     The actuator may include at least two pairs of corresponding active and passive portions. 
     Each active portion may be in the form of an elongate active beam and each passive portion may be in the form of an elongate passive beam. 
     The spacing between each active beam and its associated passive beam may be greater than five percent of the length of the actuating arm and less than ten percent of the length of the actuating arm. 
     The actuator may include an ink ejecting mechanism that is operatively positioned with respect to the nozzle chamber. An end of the actuating arm may be anchored to the substrate and an opposed end of the actuating arm may be connected to the ink ejecting mechanism so that displacement of the actuating arm results in the ink ejecting mechanism ejecting ink from the ink ejection port. 
     The invention extends to an ink jet printhead, which comprises at least one ink jet printhead chip as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Notwithstanding any other forms, which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIGS. 1–3  illustrate the operational principles of the preferred embodiment; 
         FIG. 4  is a side perspective view of a single nozzle arrangement of the preferred embodiment; 
         FIG. 5  illustrates a sectional side view of a single nozzle arrangement; 
         FIGS. 6 and 7  illustrate operational principles of the preferred embodiment; 
         FIGS. 8–15  illustrate the manufacturing steps in the construction of the preferred embodiment; 
         FIG. 16  illustrates a top plan view of a single nozzle; 
         FIG. 17  illustrates a portion of a single color printhead device; 
         FIG. 18  illustrates a portion of a three-color printhead device; 
         FIG. 19  provides a legend of the materials indicated in  FIGS. 20 to 29 ; 
         FIG. 20  to  FIG. 29  illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle; 
         FIG. 30  shows a three dimensional, schematic view of a nozzle assembly for an ink jet printhead in accordance with another embodiment of the invention; 
         FIGS. 31 to 33  show a three dimensional, schematic illustration of an operation of the nozzle assembly of  FIG. 30 ; 
         FIG. 34  shows a three dimensional view of a nozzle array constituting an ink jet printhead; 
         FIG. 35  shows, on an enlarged scale, part of the array of  FIG. 34 ; 
         FIG. 36  shows a three dimensional view of an ink jet printhead including a nozzle guard; 
         FIGS. 37   a  to  37   r  show three-dimensional views of steps in the manufacture of a nozzle assembly of an ink jet printhead; 
         FIGS. 38   a  to  38   r  show sectional side views of the manufacturing steps; 
         FIGS. 39   a  to  39   k  show layouts of masks used in various steps in the manufacturing process; 
         FIGS. 40   a  to  40   c  show three dimensional views of an operation of the nozzle assembly manufactured according to the method of  FIGS. 37 and 38 ; and 
         FIGS. 41   a  to  41   c  show sectional side views of an operation of the nozzle assembly manufactured according to the method of  FIGS. 37 and 38 . 
     
    
    
     DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS 
     In the preferred embodiment, there is provided a nozzle chamber having ink within it and a thermal actuator device interconnected to an ink ejecting mechanism in the form of a paddle, the thermal actuator device being actuated so as to eject ink from the nozzle chamber. The preferred embodiment includes a particular thermal actuator structure which includes an actuator arm in the form of a tapered heater structure arm for providing positional heating of a conductive heater layer row. The actuator arm is connected to the paddle through a slotted wall in the nozzle chamber. The actuator arm has a mating shape so as to mate substantially with the surfaces of the slot in the nozzle chamber wall. 
     Turning initially to  FIGS. 1–3 , there is provided schematic illustrations of the basic operation of the device. A nozzle chamber  1  is provided filled with ink  2  by means of an ink inlet channel  3  which can be etched through a wafer substrate on which the nozzle chamber  1  rests. The nozzle chamber  1  includes an ink ejection nozzle or aperture  4  around which an ink meniscus forms. 
     Inside the nozzle chamber  1  is a paddle type device  7  which is connected to an actuator arm  8  through a slot in the wall of the nozzle chamber  1 . The actuator arm  8  includes a heater means  9  located adjacent to a post end portion  10  of the actuator arm. The post  10  is fixed to a substrate. 
     When it is desired to eject a drop from the nozzle chamber, as illustrated in  FIG. 2 , the heater means  9  is heated so as to undergo thermal expansion. Preferably, the heater means itself or the other portions of the actuator arm  8  are built from materials having a high bend efficiency where the bend efficiency is defined as 
         bend   ⁢           ⁢   efficiency     =         Young   &#39;     ⁢   s   ⁢           ⁢   Modulus   ×     (     Coefficient   ⁢           ⁢   of   ⁢           ⁢   thermal   ⁢           ⁢   Expansion     )         Density   ×   Specific   ⁢           ⁢   Heat   ⁢           ⁢   Capacity           
 
     A suitable material for the heater elements is a copper nickel alloy which can be formed so as to bend a glass material. 
     The heater means is ideally located adjacent the post end portion  10  such that the effects of activation are magnified at the paddle end  7  such that small thermal expansions near post  10  result in large movements of the paddle end. The heating  9  causes a general increase in pressure around the ink meniscus  5  which expands, as illustrated in  FIG. 2 , in a rapid manner. The heater current is pulsed and ink is ejected out of the nozzle  4  in addition to flowing in from the ink channel  3 . Subsequently, the paddle  7  is deactivated to again return to its quiescent position. The deactivation causes a general reflux of the ink into the nozzle chamber. The forward momentum of the ink outside the nozzle rim and the corresponding backflow results in a general necking and breaking off of a drop  12  which proceeds to the print media. The collapsed meniscus  5  results in a general sucking of ink into the nozzle chamber  1  via the in flow channel  3 . In time, the nozzle chamber is refilled such that the position in  FIG. 1  is again reached and the nozzle chamber is subsequently ready for the ejection of another drop of ink. 
     Turning now to  FIG. 4 , there is illustrated a single nozzle arrangement  20  of the preferred embodiment. The arrangement includes an actuator arm  21  which includes a bottom layer  22  which is constructed from a conductive material such as a copper nickel alloy (hereinafter called cupronickel) or titanium nitride (TiN). The layer  22 , as will become more apparent hereinafter includes a tapered end portion near the end post  24 . The tapering of the layer  22  near this end means that any conductive resistive heating occurs near the post portion  24 . 
     The layer  22  is connected to the lower CMOS layers  26  which are formed in the standard manner on a silicon substrate surface  27 . The actuator arm  21  is connected to an ejection paddle which is located within a nozzle chamber  28 . The nozzle chamber  28  includes an ink ejection nozzle  29  from which ink is ejected and includes a convoluted slot arrangement  30  which is constructed such that the actuator arm  21  is able to move up and down while causing minimal pressure fluctuations in the area of the nozzle chamber  28  around the slot  30 . 
       FIG. 5  illustrates a sectional view through a single nozzle.  FIG. 5  illustrates more clearly the internal structure of the nozzle chamber which includes the paddle  32  attached to the actuator arm  21  having face  33 . Importantly, the actuator arm  21  includes, as noted previously, a bottom conductive layer  22 . Additionally, a top layer  25  is also provided. 
     The utilization of a second layer  25  of the same material as the first layer  22  allows for more accurate control of the actuator position as will be described with reference to  FIGS. 6 and 7 . In  FIG. 6 , there is illustrated the example where a high Young&#39;s Modulus material  40  is deposited utilizing standard semiconductor deposition techniques and on top of which is further deposited a second layer  41  having a much lower Young&#39;s Modulus. Unfortunately, the deposition is likely to occur at a high temperature. Upon cooling, the two layers are likely to have different coefficients of thermal expansion and different Young&#39;s Moduli. Hence, in ambient room temperature, the thermal stresses are likely to cause bending of the two layers of material as shown at  42 . 
     By utilizing a second deposition of the material having a high Young&#39;s Modulus, the situation in  FIG. 7  is likely to result wherein the material  41  is sandwiched between the two layers  40 . Upon cooling, the two layers  40  are kept in tension with one another so as to result in a more planar structure  45  regardless of the operating temperature. This principle is utilized in the deposition of the two layers  22 ,  25  of  FIGS. 4–5 . 
     Turning again to  FIGS. 4 and 5 , one important attribute of the preferred embodiments includes the slotted arrangement  30 . The slotted arrangement results in the actuator arm  21  moving up and down thereby causing the paddle  32  to also move up and down resulting in the ejection of ink. The slotted arrangement  30  results in minimum ink outflow through the actuator arm connection and also results in minimal pressure increases in this area. The face  33  of the actuator arm is extended out so as to form an extended interconnect with the paddle surface thereby providing for better attachment. The face  33  is connected to a block portion  36  which is provided to provide a high degree of rigidity. The actuator arm  21  and the wall of the nozzle chamber  28  have a generally corrugated nature so as to reduce any flow of ink through the slot  30 . The exterior surface of the nozzle chamber adjacent the block portion  36  has a rim eg.  38  so to minimize wicking of ink outside of the nozzle chamber. A pit  37  is also provided for this purpose. The pit  37  is formed in the lower CMOS layers  26 . An ink supply channel  39  is provided by means of back etching through the wafer to the back surface of the nozzle. 
     Turning to  FIGS. 8–15  there will now be described fabrication steps utilized in the construction of a single nozzle in accordance with the preferred embodiment. 
     The fabrication uses standard micro-electromechanical techniques. For a general introduction to a micro-electromechanical systems (MEMS) reference is made to standard proceedings in this field including the proceeding of the SPIE (International Society for Optical Engineering) including volumes 2642 and 2882 which contain the proceedings of recent advances and conferences in this field. 
     1. The preferred embodiment starts with a double sided polished wafer complete with, say, a 0.2 μm 1 poly 2 metal CMOS process providing for all the electrical interconnects necessary to drive the inkjet nozzle. 
     2. As shown in  FIG. 8 , the CMOS wafer  26  is etched at  50  down to the silicon layer  27 . The etching includes etching down to an aluminum CMOS layer  51 ,  52 . 
     3. Next, as illustrated in  FIG. 9 , a 1 μm layer of sacrificial material  55  is deposited. The sacrificial material can be aluminum or photosensitive polyimide. 
     4. The sacrificial material is etched in the case of aluminum or exposed and developed in the case of polyimide in the area of the nozzle rim  56  and including a dished paddle area  57 . 
     5. Next, a 1 μm layer of heater material  60  (cupronickel or TiN) is deposited. 
     6. A 3.4 μm layer of PECVD glass  61  is then deposited. 
     7. A second layer  62  equivalent to the first layer  60  is then deposited. 
     8. All three layers  60 – 62  are then etched utilizing the same mask. The utilization of a single mask substantially reduces the complexity in the processing steps involved in creation of the actuator paddle structure and the resulting structure is as illustrated in  FIG. 10 . Importantly, a break  63  is provided so as to ensure electrical isolation of the heater portion from the paddle portion. 
     9. Next, as illustrated in  FIG. 11 , a 10 μm layer of sacrificial material  70  is deposited. 
     10. The deposited layer is etched (or just developed if polyimide) utilizing a fourth mask which includes nozzle rim etchant holes  71 , block portion holes  72  and post portion  73 . 
     11. Next a 10 μm layer of PECVD glass is deposited so as to form the nozzle rim  71 , arm portions  72  and post portions  73 . 
     12. The glass layer is then planarized utilizing chemical mechanical planarization (CMP) with the resulting structure as illustrated in  FIG. 11 . 
     13. Next, a 3 μm layer of PECVD glass is deposited. 
     14. The deposited glass is then etched as shown in  FIG. 12 , to a depth of approximately 1 μm so as to form nozzle rim portion  81  and actuator interconnect portion  82 . 
     15. Next, as illustrated in  FIG. 13 , the glass layer is etched utilizing a 6th mask so as to form final nozzle rim portion  81  and actuator guide portion  82 . 
     16. Next, as illustrated in  FIG. 14 , the ink supply channel is back etched  85  from the back of the wafer utilizing a 7th mask. The etch can be performed utilizing a high precision deep silicon trench etcher such as the STS Advanced Silicon Etcher (ASE). This step can also be utilized to nearly completely dice the wafer. 
     17. Next, as illustrated in  FIG. 15  the sacrificial material can be stripped or dissolved to also complete dicing of the wafer in accordance with requirements. 
     18. Next, the printheads can be individually mounted on attached molded plastic ink channels to supply ink to the ink supply channels. 
     19. The electrical control circuitry and power supply can then be bonded to an etch of the printhead with a TAB film. 
     20. Generally, if necessary, the surface of the printhead is then hydrophobized so as to ensure minimal wicking of the ink along external surfaces. Subsequent testing can determine operational characteristics. 
     Importantly, as shown in the plan view of  FIG. 16 , the heater element has a tapered portion adjacent the post  73  so as to ensure maximum heating occurs near the post. 
     Of course, different forms of inkjet printhead structures can be formed. For example, there is illustrated in  FIG. 17 , a portion of a single color printhead having two spaced apart rows  90 ,  91 , with the two rows being interleaved so as to provide for a complete line of ink to be ejected in two stages. Preferably, a guide rail  92  is provided for proper alignment of a TAB film with bond pads  93 . A second protective barrier  94  can also preferably be provided. Preferably, as will become more apparent with reference to the description of  FIG. 18  adjacent actuator arms are interleaved and reversed. 
     Turning now to  FIG. 18 , there is illustrated a full color printhead arrangement which includes three series of inkjet nozzles  95 ,  96 ,  97  one each devoted to a separate color. Again, guide rails  98 ,  99  are provided in addition to bond pads, eg.  100 . In  FIG. 18 , there is illustrated a general plan of the layout of a portion of a full color printhead which clearly illustrates the interleaved nature of the actuator arms. 
     The presently disclosed ink jet printing technology is potentially suited to a wide range of printing system including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers high speed pagewidth printers, notebook computers with inbuilt pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic “minilabs”, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays. 
     One alternative form of detailed manufacturing process which can be used to fabricate monolithic ink jet printheads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps: 
     1. Using a double sided polished wafer  27 , complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, 2 metal CMOS process to form layer  26 . Relevant features of the wafer at this step are shown in  FIG. 20 . For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle.  FIG. 19  is a key to representations of various materials in these manufacturing diagrams, and those of other cross-referenced inkjet configurations. 
     2. Etch oxide down to silicon or aluminum using Mask  1 . This mask defines the nozzle chamber, the surface anti-wicking notch  37 , and the heater contacts  110 . This step is shown in  FIG. 21 . 
     3. Deposit 1 micron of sacrificial material  55  (e.g. aluminum or photosensitive polyimide) 
     4. Etch (if aluminum) or develop (if photosensitive polyimide) the sacrificial layer using Mask  2 . This mask defines the nozzle chamber walls  112  and the actuator anchor point. This step is shown in  FIG. 22 . 
     5. Deposit 1 micron of heater material  60  (e.g. cupronickel or TiN). If cupronickel, then deposition can consist of three steps—a thin anti-corrosion layer of, for example, TiN, followed by a seed layer, followed by electroplating of the 1 micron of cupronickel. 
     6. Deposit 3.4 microns of PECVD glass  61 . 
     7. Deposit a layer  62  identical to step 5. 
     8. Etch both layers of heater material, and glass layer, using Mask  3 . This mask defines the actuator, paddle, and nozzle chamber walls. This step is shown in  FIG. 23 . 
     9. Wafer probe. All electrical connections are complete at this point, bond pads are accessible, and the chips are not yet separated. 
     10. Deposit 10 microns of sacrificial material  70 . 
     11. Etch or develop sacrificial material using Mask  4 . This mask defines the nozzle chamber wall  112 . This step is shown in  FIG. 24 . 
     12. Deposit 3 microns of PECVD glass  113 . 
     13. Etch to a depth of (approx.) 1 micron using Mask  5 . This mask defines the nozzle rim  81 . This step is shown in  FIG. 25 . 
     14. Etch down to the sacrificial layer using Mask  6 . This mask defines the roof  114  of the nozzle chamber, and the nozzle itself. This step is shown in  FIG. 26 . 
     15. Back-etch completely through the silicon wafer (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask  7 . This mask defines the ink inlets  30  which are etched through the wafer. The wafer is also diced by this etch. This step is shown in  FIG. 27 . 
     16. Etch the sacrificial material. The nozzle chambers are cleared, the actuators freed, and the chips are separated by this etch. This step is shown in  FIG. 28 . 
     17. Mount the printheads in their packaging, which may be a molded plastic former incorporating ink channels which supply the appropriate color ink to the ink inlets at the back of the wafer. 
     18. Connect the printheads to their interconnect systems. For a low profile connection with minimum disruption of airflow, TAB may be used. Wire bonding may also be used if the printer is to be operated with sufficient clearance to the paper. 
     19. Hydrophobize the front surface of the printheads. 
     20. Fill the completed printheads with ink  115  and test them. A filled nozzle is shown in  FIG. 29 . 
     Referring now to  FIG. 30  of the drawings, a nozzle assembly, in accordance with a further embodiment of the invention is designated generally by the reference numeral  110 . An ink jet printhead has a plurality of nozzle assemblies  110  arranged in an array  114  ( FIGS. 34 and 35 ) on a silicon substrate  116 . The array  114  will be described in greater detail below. 
     The assembly  110  includes a silicon substrate or wafer  116  on which a dielectric layer  118  is deposited. A CMOS passivation layer  120  is deposited on the dielectric layer  118 . 
     Each nozzle assembly  110  includes a nozzle  122  defining a nozzle opening  124 , a connecting member in the form of a lever arm  126  and an actuator  128 . The lever arm  126  connects the actuator  128  to the nozzle  122 . 
     As shown in greater detail in  FIGS. 31 to 33  of the drawings, the nozzle  122  comprises a crown portion  130  with a skirt portion  132  depending from the crown portion  130 . The skirt portion  132  forms part of a peripheral wall of a nozzle chamber  134  ( FIGS. 31 to 33  of the drawings). The nozzle opening  124  is in fluid communication with the nozzle chamber  134 . It is to be noted that the nozzle opening  124  is surrounded by a raised rim  136  which “pins” a meniscus  138  ( FIG. 31 ) of a body of ink  140  in the nozzle chamber  134 . 
     An ink inlet aperture  142  (shown most clearly in  FIG. 35  of the drawing) is defined in a floor  146  of the nozzle chamber  134 . The aperture  142  is in fluid communication with an ink inlet channel  148  defined through the substrate  116 . 
     A wall portion  150  bounds the aperture  142  and extends upwardly from the floor portion  146 . The skirt portion  132 , as indicated above, of the nozzle  122  defines a first part of a peripheral wall of the nozzle chamber  134  and the wall portion  150  defines a second part of the peripheral wall of the nozzle chamber  134 . 
     The wall  150  has an inwardly directed lip  152  at its free end which serves as a fluidic seal which inhibits the escape of ink when the nozzle  122  is displaced, as will be described in greater detail below. It will be appreciated that, due to the viscosity of the ink  140  and the small dimensions of the spacing between the lip  152  and the skirt portion  132 , the inwardly directed lip  152  and surface tension function as a seal for inhibiting the escape of ink from the nozzle chamber  134 . 
     The actuator  128  is a thermal bend actuator and is connected to an anchor  154  extending upwardly from the substrate  116  or, more particularly, from the CMOS passivation layer  120 . The anchor  154  is mounted on conductive pads  156  which form an electrical connection with the actuator  128 . 
     The actuator  128  comprises an actuator arm in the form of a pair of active beams  158  arranged above a pair of passive beams  160 . In a preferred embodiment, both beams  158  and  160  are of, or include, a conductive ceramic material such as titanium nitride (TiN). 
     The beams  158  and  160  have their first ends anchored to the anchor  154  and their opposed ends connected to the arm  126 . When a current is caused to flow through the active beams  158  thermal expansion of the beams  158  results. As the passive beams  160 , through which there is no current flow, do not expand at the same rate, a bending moment is created causing the arm  126  and, hence, the nozzle  122  to be displaced downwardly towards the substrate  116  as shown in  FIG. 32  of the drawings. This causes an ejection of ink through the nozzle opening  124  as shown at  162  in  FIG. 32  of the drawings. Thus, the nozzle  122  and the arm  126  define an ink ejecting mechanism. When the source of heat is removed from the active beams  158 , i.e. by stopping current flow, the nozzle  122  returns to its quiescent position as shown in  FIG. 33  of the drawings. When the nozzle  122  returns to its quiescent position, an ink droplet  164  is formed as a result of the breaking of an ink droplet neck as illustrated at  166  in  FIG. 33  of the drawings. The ink droplet  164  then travels on to the print media such as a sheet of paper. As a result of the formation of the ink droplet  164 , a “negative” meniscus is formed as shown at  168  in  FIG. 33  of the drawings. This “negative” meniscus  168  results in an inflow of ink  140  into the nozzle chamber  134  such that a new meniscus  138  ( FIG. 31 ) is formed in readiness for the next ink drop ejection from the nozzle assembly  110 . 
     Each active beam  158  corresponds with one passive beam  160  to form two pairs of beams comprising an active beam  158  and a corresponding passive beam  160 . Each active beam  158  is spaced from its corresponding passive beam  160  in a plane that is substantially parallel to the substrate. The spacing between each active beam  158  and its respective passive beam  160  is suitably between 1 percent and 20 percent of the length of the beams. Preferably the spacing is between 5 percent and 10 percent of the length of the beams. The Applicant has found that this configuration provides the best protection against mutual buckling while maintaining efficiency of operation. In particular, Applicant has found that if the spacing is less than 1 percent of the length of the beams there is an unacceptable risk of mutual buckling and if the spacing is greater than 20 percent of the length of the beams the efficiency of the actuators  128  is compromised. 
     Referring now to  FIGS. 34 and 35  of the drawings, the nozzle array  114  is described in greater detail. The array  114  is for a four-color printhead. Accordingly, the array  114  includes four groups  170  of nozzle assemblies, one for each color. Each group  170  has its nozzle assemblies  110  arranged in two rows  172  and  174 . One of the groups  170  is shown in greater detail in  FIG. 35  of the drawings. 
     To facilitate close packing of the nozzle assemblies  110  in the rows  172  and  174 , the nozzle assemblies  110  in the row  174  are offset or staggered with respect to the nozzle assemblies  10  in the row  172 . Also, the nozzle assemblies  110  in the row  172  are spaced apart sufficiently far from each other to enable the lever arms  126  of the nozzle assemblies  10  in the row  174  to pass between adjacent nozzles  122  of the assemblies  110  in the row  172 . It is to be noted that each nozzle assembly  110  is substantially dumbbell shaped so that the nozzles  122  in the row  172  nest between the nozzles  122  and the actuators  128  of adjacent nozzle assemblies  110  in the row  174 . 
     Further, to facilitate close packing of the nozzles  122  in the rows  172  and  174 , each nozzle  122  is substantially hexagonally shaped. 
     It will be appreciated by those skilled in the art that, when the nozzles  122  are displaced towards the substrate  116 , in use, due to the nozzle opening  124  being at a slight angle with respect to the nozzle chamber  134  ink is ejected slightly off the perpendicular. It is an advantage of the arrangement shown in  FIGS. 34 and 35  of the drawings that the actuators  128  of the nozzle assemblies  10  in the rows  172  and  174  extend in the same direction to one side of the rows  172  and  174 . Hence, the ink droplets ejected from the nozzles  122  in the row  172  and the ink droplets ejected from the nozzles  122  in the row  174  are parallel to one another resulting in an improved print quality. 
     Also, as shown in  FIG. 34  of the drawings, the substrate  116  has bond pads  176  arranged thereon which provide the electrical connections, via the pads  156 , to the actuators  128  of the nozzle assemblies  110 . These electrical connections are formed via the CMOS layer (not shown). 
     Referring to  FIG. 36  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  180  is mounted on the substrate  116  of the array  114 . The nozzle guard  180  includes a body member  182  having a plurality of passages  184  defined therethrough. The passages  184  are in register with the nozzle openings  124  of the nozzle assemblies  110  of the array  114  such that, when ink is ejected from any one of the nozzle openings  124 , the ink passes through the associated passage  184  before striking the print media. 
     The body member  182  is mounted in spaced relationship relative to the nozzle assemblies  110  by limbs or struts  186 . One of the struts  186  has air inlet openings  188  defined therein. 
     In use, when the array  114  is in operation, air is charged through the inlet openings  188  to be forced through the passages  184  together with ink travelling through the passages  184 . 
     The ink is not entrained in the air as the air is charged through the passages  184  at a different velocity from that of the ink droplets  164 . For example, the ink droplets  164  are ejected from the nozzles  122  at a velocity of approximately 3 m/s. The air is charged through the passages  184  at a velocity of approximately 1 m/s. 
     The purpose of the air is to maintain the passages  184  clear of foreign particles. A danger exists that these foreign particles, such as dust particles, could fall onto the nozzle assemblies  110  adversely affecting their operation. With the provision of the air inlet openings  88  in the nozzle guard  180  this problem is, to a large extent, obviated. 
     Referring now to  FIGS. 37 to 39  of the drawings, a process for manufacturing the nozzle assemblies  110  is described. 
     Starting with the silicon substrate or wafer  116 , the dielectric layer  118  is deposited on a surface of the wafer  116 . The dielectric layer  118  is in the form of approximately 1.5 microns of CVD oxide. Resist is spun on to the layer  118  and the layer  118  is exposed to mask  200  and is subsequently developed. 
     After being developed, the layer  118  is plasma etched down to the silicon layer  116 . The resist is then stripped and the layer  118  is cleaned. This step defines the ink inlet aperture  142 . 
     In  FIG. 37   b  of the drawings, approximately 0.8 microns of aluminum  202  is deposited on the layer  118 . Resist is spun on and the aluminum  202  is exposed to mask  204  and developed. The aluminum  202  is plasma etched down to the oxide layer  118 , the resist is stripped and the device is cleaned. This step provides the bond pads and interconnects to the ink jet actuator  128 . 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  120 . Resist is spun on and the layer  120  is exposed to mask  206  whereafter it is developed. After development, the nitride is plasma etched down to the aluminum layer  202  and the silicon layer  116  in the region of the inlet aperture  142 . The resist is stripped and the device cleaned. 
     A layer  208  of a sacrificial material is spun on to the layer  120 . The layer  208  is 6 microns of photo-sensitive polyimide or approximately 4 μm of high temperature resist. The layer  208  is softbaked and is then exposed to mask  210  whereafter it is developed. The layer  208  is then hardbaked at 400° C. for one hour where the layer  208  is comprised of polyimide or at greater than 300° C. where the layer  208  is high temperature resist. It is to be noted in the drawings that the pattern-dependent distortion of the polyimide layer  208  caused by shrinkage is taken into account in the design of the mask  210 . 
     In the next step, shown in  FIG. 37   e  of the drawings, a second sacrificial layer  212  is applied. The layer  212  is either 2 μm of photosensitive polyimide, which is spun on, or approximately 1.3 μm of high temperature resist. The layer  212  is softbaked and exposed to mask  214 . After exposure to the mask  214 , the layer  212  is developed. In the case of the layer  212  being polyimide, the layer  212  is hardbaked at 400° C. for approximately one hour. Where the layer  212  is resist, it is hardbaked at greater than 300° C. for approximately one hour. 
     A 0.2 micron multi-layer metal layer  216  is then deposited. Part of this layer  216  forms the passive beam  160  of the actuator  128 . 
     The layer  216  is formed by sputtering 1,000 Å of titanium nitride (TiN) at around 300° C. followed by sputtering 50 Å of tantalum nitride (TaN). A further 1,000 Å of TiN is sputtered on followed by 50 Å of TaN and a further 1,000 Å of TiN. 
     Other materials which can be used instead of TiN are TiB 2 , MoSi 2  or (Ti, Al)N. 
     The layer  216  is then exposed to mask  218 , developed and plasma etched down to the layer  212  whereafter resist, applied for the layer  216 , is wet stripped taking care not to remove the cured layers  208  or  212 . 
     A third sacrificial layer  220  is applied by spinning on 4 μm of photosensitive polyimide or approximately 2.6 μm high temperature resist. The layer  220  is softbaked whereafter it is exposed to mask  222 . The exposed layer is then developed followed by hardbaking. In the case of polyimide, the layer  220  is hardbaked at 400° C. for approximately one hour or at greater than 300° C. where the layer  220  comprises resist. 
     A second multi-layer metal layer  224  is applied to the layer  220 . The constituents of the layer  224  are the same as the layer  216  and are applied in the same manner. It will be appreciated that both layers  216  and  224  are electrically conductive layers. 
     The layer  224  is exposed to mask  226  and is then developed. The layer  224  is plasma etched down to the polyimide or resist layer  220  whereafter resist applied for the layer  224  is wet stripped taking care not to remove the cured layers  208 ,  212  or  220 . It will be noted that the remaining part of the layer  224  defines the active beam  158  of the actuator  128 . 
     A fourth sacrificial layer  228  is applied by spinning on 4 μm of photosensitive polyimide or approximately 2.6 μm of high temperature resist. The layer  228  is softbaked, exposed to the mask  230  and is then developed to leave the island portions as shown in  FIG. 9   k  of the drawings. The remaining portions of the layer  228  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  FIG. 371  of the drawing a high Young&#39;s modulus dielectric layer  232  is deposited. The layer  232  is constituted by approximately 1 μm of silicon nitride or aluminum oxide. The layer  232  is deposited at a temperature below the hardbaked temperature of the sacrificial layers  208 ,  212 ,  220 ,  228 . The primary characteristics required for this dielectric layer  232  are a high elastic modulus, chemical inertness and good adhesion to TiN. 
     A fifth sacrificial layer  234  is applied by spinning on 2 μm of photosensitive polyimide or approximately 1.31 μm of high temperature resist. The layer  234  is softbaked, exposed to mask  236  and developed. The remaining portion of the layer  234  is then hardbaked at 400° C. for one hour in the case of the polyimide or at greater than 300° C. for the resist. 
     The dielectric layer  232  is plasma etched down to the sacrificial layer  228  taking care not to remove any of the sacrificial layer  234 . 
     This step defines the nozzle opening  124 , the lever arm  126  and the anchor  154  of the nozzle assembly  110 . 
     A high Young&#39;s modulus dielectric layer  238  is deposited. This layer  238  is formed by depositing 0.2 μm of silicon nitride or aluminum nitride at a temperature below the hardbaked temperature of the sacrificial layers  208 ,  212 ,  220  and  228 . 
     Then, as shown in  FIG. 37   p  of the drawings, the layer  238  is anisotropically plasma etched to a depth of 0.35 microns. This etch is intended to clear the dielectric from the entire surface except the side walls of the dielectric layer  232  and the sacrificial layer  234 . This step creates the nozzle rim  136  around the nozzle opening  124  which “pins” the meniscus of ink, as described above. 
     An ultraviolet (UV) release tape  240  is applied. 4 μm of resist is spun on to a rear of the silicon wafer  116 . The wafer  116  is exposed to mask  242  to back etch the wafer  116  to define the ink inlet channel  148 . The resist is then stripped from the wafer  116 . 
     A further UV release tape (not shown) is applied to a rear of the wafer  16  and the tape  240  is removed. The sacrificial layers  208 ,  212 ,  220 ,  228  and  234  are stripped in oxygen plasma to provide the final nozzle assembly  110  as shown in  FIGS. 37   r  and  38   r  of the drawings. For ease of reference, the reference numerals illustrated in these two drawings are the same as those in  FIG. 30  of the drawings to indicate the relevant parts of the nozzle assembly  110 .  FIGS. 40 and 41  show the operation of the nozzle assembly  110 , manufactured in accordance with the process described above with reference to  FIGS. 37 and 38 , and these figures correspond to  FIGS. 31 to 34  of the drawings. 
     It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present 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 to be illustrative and not restrictive.