# Patent

## Title
Printhead unit cell having rimmed nozzle plate

## Abstract

A unit cell of a printhead is provided having a multi-layer substrate defining an ink inlet, one or more side walls extending from the substrate around the ink inlet, a nozzle plate supported by the side walls to define a chamber in fluid communication with the ink inlet, where the nozzle plate defines an aperture through which ink in the chamber can be ejected, and a looped and elongate heater element suspended within the chamber, which can be heated so that bubbles are generated in ink within the chamber and ink is ejected from the aperture. The nozzle plate defines a protruding rim bounding the aperture.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of Ser. No. 12/017,771 filed on Jan. 22, 2008, now issued U.S. Pat. No. 7,469,997, which is a continuation application of U.S. patent application Ser. No. 11/097,266 filed on Apr. 4, 2005, now issued U.S. Pat. No. 7,344,226, all of which is herein incorporated by reference.
CO-PENDING APPLICATIONS
The following application has been filed by the Applicant simultaneously with U.S. Pat. No. 7,344,226:

    
    
        U.S. Pat. No. 7,328,976
    
    


The disclosure of this co-pending application are incorporated herein by reference.
CROSS REFERENCES TO RELATED APPLICATIONS
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.

















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FIELD OF THE INVENTION
The present invention relates to the field of inkjet printers and, discloses an inkjet printing system using printheads manufactured with microelectro-mechanical systems (MEMS) techniques. 
BACKGROUND OF THE INVENTION
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous inkjet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also 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, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the inkjet stream and 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 Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the  electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
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 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, galium arsenide etc. Hence, it is desirable, in any MEMS constructions, to utilize well proven semi-conductor fabrication techniques which do not require any “exotic” processes or materials. Of course, a certain degree of trade off will be undertaken in that if the advantages of using the exotic material far out weighs its disadvantages then it may become desirable to utilize the material anyway. However, if it is possible to achieve the same, or similar, properties using more common materials, the problems of exotic materials can be avoided.
A desirable characteristic of inkjet printheads would be a hydrophobic nozzle (front) face, preferably in combination with hydrophilic nozzle chambers and ink supply channels. This combination is optimal for ink ejection. Moreover, a hydrophobic front face minimizes the propensity for ink to flood across the front face of the printhead. With a hydrophobic front face, the aqueous inkjet ink is less likely to flood sideways out of the nozzle openings and more likely to form spherical, ejectable microdroplets.
However, whilst hydrophobic front faces and hydrophilic ink chambers are desirable, there is a major problem in fabricating such printheads by MEMS techniques. The final stage of MEMS printhead fabrication is typically ashing of photoresist using an oxygen plasma. However, any organic, hydrophobic material deposited onto the front face will typically be removed by the ashing process to leave a hydrophilic surface. Accordingly, the deposition of hydrophobic material needs to  occur after ashing. However, a problem with post-ashing deposition of hydrophobic materials is that the hydrophobic material will be deposited inside nozzle chambers as well as on the front face of the printhead. With no photoresist to protect the nozzle chambers, the nozzle chamber walls become hydrophobized, which is highly undesirable in terms of generating a positive ink pressure biased towards the nozzle chambers. This is a conundrum, which has to date not been addressed in printhead fabrication.
Accordingly, it would be desirable to provide a printhead fabrication process, in which the resultant printhead chip has improved surface characteristics, without comprising the surface characteristics of nozzle chambers. It would further be desirable to provide a printhead fabrication process, in which the resultant printhead chip has a hydrophobic front face in combination with hydrophilic nozzle chambers.
SUMMARY OF THE INVENTION
In a first aspect, there is provided a printhead comprising a plurality of nozzles formed on a substrate, each nozzle comprising a nozzle chamber, a nozzle opening defined in a roof of the nozzle chamber and an actuator for ejecting ink through the nozzle opening, wherein at least part of an ink ejection face of the printhead is hydrophobic relative to the inside surfaces of each nozzle chamber.
In a second aspect, there is provided a method of hydrophobizing an ink ejection face of a printhead, whilst avoiding hydrophobizing nozzle chambers and/or ink supply channels, the method comprising the steps of:
(a) filling nozzle chambers on the printhead with a liquid; and
(b) depositing a hydrophobizing material onto the ink ejection face of the printhead.



BRIEF DESCRIPTION OF THE DRAWINGS
Notwithstanding any other forms that 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:
FIG. 1 is a schematic cross-sectional view through an ink chamber of a unit cell of a printhead according to an embodiment using a bubble forming heater element;
FIG. 2 is a schematic cross-sectional view through the ink chamber FIG. 1, at another stage of operation; 
FIG. 3 is a schematic cross-sectional view through the ink chamber FIG. 1, at yet another stage of operation;
FIG. 4 is a schematic cross-sectional view through the ink chamber FIG. 1, at yet a further stage of operation; and
FIG. 5 is a diagrammatic cross-sectional view through a unit cell of a printhead in accordance with an embodiment of the invention showing the collapse of a vapor bubble.
FIG. 6 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 7 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 6.
FIG. 8 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 9 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 8.
FIG. 10 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 11 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 10.
FIG. 12 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 13 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 14 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 13. 
FIGS. 15 to 25 are schematic perspective views of the unit cell shown in FIGS. 13 and 14, at various successive stages in the production process of the printhead.
FIG. 26 shows partially cut away schematic perspective views of the unit cell of FIG. 25.
FIG. 27 shows the unit cell of FIG. 25 primed with a fluid.
FIG. 28 shows the unit cell of FIG. 27 with a hydrophobic coating on the nozzle plate



DESCRIPTION OF OPTIONAL EMBODIMENTS
Bubble Forming Heater Element Actuator
With reference to FIGS. 1 to 4, the unit cell 1 of a printhead according to an embodiment of the invention comprises a nozzle plate 2 with nozzles 3 therein, the nozzles having nozzle rims 4, and apertures 5 extending through the nozzle plate. The nozzle plate 2 is plasma etched from a silicon nitride structure which is deposited, by way of chemical vapor deposition (CVD), over a sacrificial material which is subsequently etched.
The printhead also includes, with respect to each nozzle 3, side walls 6 on which the nozzle plate is supported, a chamber 7 defined by the walls and the nozzle plate 2, a multi-layer substrate 8 and an inlet passage 9 extending through the multi-layer substrate to the far side (not shown) of the substrate. A looped, elongate heater element 10 is suspended within the chamber 7, so that the element is in the form of a suspended beam. The printhead as shown is a microelectromechanical system (MEMS) structure, which is formed by a lithographic process which is described in more detail below.
When the printhead is in use, ink 11 from a reservoir (not shown) enters the chamber 7 via the inlet passage 9, so that the chamber fills to the level as shown in FIG. 1. Thereafter, the heater element 10 is heated for somewhat less than 1 microsecond, so that the heating is in the form of a thermal pulse. It will be appreciated that the heater element 10 is in thermal contact  with the ink 11 in the chamber 7 so that when the element is heated, this causes the generation of vapor bubbles 12 in the ink. Accordingly, the ink 11 constitutes a bubble forming liquid. FIG. 1 shows the formation of a bubble 12 approximately 1 microsecond after generation of the thermal pulse, that is, when the bubble has just nucleated on the heater elements 10. It will be appreciated that, as the heat is applied in the form of a pulse, all the energy necessary to generate the bubble 12 is to be supplied within that short time.
When the element 10 is heated as described above, the bubble 12 forms along the length of the element, this bubble appearing, in the cross-sectional view of FIG. 1, as four bubble portions, one for each of the element portions shown in cross section.
The bubble 12, once generated, causes an increase in pressure within the chamber 7, which in turn causes the ejection of a drop 16 of the ink 11 through the nozzle 3. The rim 4 assists in directing the drop 16 as it is ejected, so as to minimize the chance of drop misdirection.
The reason that there is only one nozzle 3 and chamber 7 per inlet passage 9 is so that the pressure wave generated within the chamber, on heating of the element 10 and forming of a bubble 12, does not affect adjacent chambers and their corresponding nozzles. The pressure wave generated within the chamber creates significant stresses in the chamber wall. Forming the chamber from an amorphous ceramic such as silicon nitride, silicon dioxide (glass) or silicon oxynitride, gives the chamber walls high strength while avoiding the use of material with a crystal structure. Crystalline defects can act as stress concentration points and therefore potential areas of weakness and ultimately failure.
FIGS. 2 and 3 show the unit cell 1 at two successive later stages of operation of the printhead. It can be seen that the bubble 12 generates further, and hence grows, with the resultant advancement of ink 11 through the nozzle 3. The shape of the bubble 12 as it grows, as shown in FIG. 3, is determined by a combination of the inertial dynamics and the surface tension of the ink 11. The surface tension tends to minimize the surface area of the bubble 12 so that, by the time a certain amount of liquid has evaporated, the bubble is essentially disk-shaped.
The increase in pressure within the chamber 7 not only pushes ink 11 out through the nozzle 3, but also pushes some ink back through the inlet passage 9. However, the inlet passage 9 is approximately 200 to 300 microns in length, and is only approximately 16 microns in diameter. Hence there is a substantial viscous drag. As a result, the predominant effect of the  pressure rise in the chamber 7 is to force ink out through the nozzle 3 as an ejected drop 16, rather than back through the inlet passage 9.
Turning now to FIG. 4, the printhead is shown at a still further successive stage of operation, in which the ink drop 16 that is being ejected is shown during its “necking phase” before the drop breaks off. At this stage, the bubble 12 has already reached its maximum size and has then begun to collapse towards the point of collapse 17, as reflected in more detail in FIG. 21.
The collapsing of the bubble 12 towards the point of collapse 17 causes some ink 11 to be drawn from within the nozzle 3 (from the sides 18 of the drop), and some to be drawn from the inlet passage 9, towards the point of collapse. Most of the ink 11 drawn in this manner is drawn from the nozzle 3, forming an annular neck 19 at the base of the drop 16 prior to its breaking off.
The drop 16 requires a certain amount of momentum to overcome surface tension forces, in order to break off. As ink 11 is drawn from the nozzle 3 by the collapse of the bubble 12, the diameter of the neck 19 reduces thereby reducing the amount of total surface tension holding the drop, so that the momentum of the drop as it is ejected out of the nozzle is sufficient to allow the drop to break off.
When the drop 16 breaks off, cavitation forces are caused as reflected by the arrows 20, as the bubble 12 collapses to the point of collapse 17. It will be noted that there are no solid surfaces in the vicinity of the point of collapse 17 on which the cavitation can have an effect.
Features and Advantages of Further Embodiments
FIGS. 6 to 29 show further embodiments of unit cells 1 for thermal inkjet printheads, each embodiment having its own particular functional advantages. These advantages will be discussed in detail below, with reference to each individual embodiment. For consistency, the same reference numerals are used in FIGS. 6 to 29 to indicate corresponding components.
Referring to FIGS. 6 and 7, the unit cell 1 shown has the chamber 7, ink supply passage 32 and the nozzle rim 4 positioned mid way along the length of the unit cell 1. As best seen in FIG. 7, the drive circuitry 22 is partially on one side of the chamber 7 with the remainder on the opposing side of the chamber. The drive circuitry 22 controls the operation of the heater 14  through vias in the integrated circuit metallisation layers of the interconnect 23. The interconnect 23 has a raised metal layer on its top surface. Passivation layer 24 is formed in top of the interconnect 23 but leaves areas of the raised metal layer exposed. Electrodes 15 of the heater 14 contact the exposed metal areas to supply power to the element 10.
Alternatively, the drive circuitry 22 for one unit cell is not on opposing sides of the heater element that it controls. All the drive circuitry 22 for the heater 14 of one unit cell is in a single, undivided area that is offset from the heater. That is, the drive circuitry 22 is partially overlaid by one of the electrodes 15 of the heater 14 that it is controlling, and partially overlaid by one or more of the heater electrodes 15 from adjacent unit cells. In this situation, the center of the drive circuitry 22 is less than 200 microns from the center of the associate nozzle aperture 5. In most Memjet printheads of this type, the offset is less than 100 microns and in many cases less than 50 microns, preferably less than 30 microns.
Configuring the nozzle components so that there is significant overlap between the electrodes and the drive circuitry provides a compact design with high nozzle density (nozzles per unit area of the nozzle plate 2). This also improves the efficiency of the printhead by shortening the length of the conductors from the circuitry to the electrodes. The shorter conductors have less resistance and therefore dissipate less energy.
The high degree of overlap between the electrodes 15 and the drive circuitry 22 also allows more vias between the heater material and the CMOS metalization layers of the interconnect 23. As best shown in FIGS. 14 and 15, the passivation layer 24 has an array of vias to establish an electrical connection with the heater 14. More vias lowers the resistance between the heater electrodes 15 and the interconnect layer 23 which reduces power losses. However, the passivation layer 24 and electrodes 15 may also be provided without vias in order to simplify the fabrication process.
In FIGS. 8 and 9, the unit cell 1 is the same as that of FIGS. 6 and 7 apart from the heater element 10. The heater element 10 has a bubble nucleation section 158 with a smaller cross section than the remainder of the element. The bubble nucleation section 158 has a greater resistance and heats to a temperature above the boiling point of the ink before the remainder of the element 10. The gas bubble nucleates at this region and subsequently grows to surround the rest of the element 10. By controlling the bubble nucleation and growth, the trajectory of the ejected drop is more predictable. 
The heater element 10 is configured to accommodate thermal expansion in a specific manner. As heater elements expand, they will deform to relieve the strain. Elements such as that shown in FIGS. 6 and 7 will bow out of the plane of lamination because its thickness is the thinnest cross sectional dimension and therefore has the least bending resistance. Repeated bending of the element can lead to the formation of cracks, especially at sharp corners, which can ultimately lead to failure. The heater element 10 shown in FIGS. 8 and 9 is configured so that the thermal expansion is relieved by rotation of the bubble nucleation section 158, and slightly splaying the sections leading to the electrodes 15, in preference to bowing out of the plane of lamination. The geometry of the element is such that miniscule bending within the plane of lamination is sufficient to relieve the strain of thermal expansion, and such bending occurs in preference to bowing. This gives the heater element greater longevity and reliability by minimizing bend regions, which are prone to oxidation and cracking.
Referring to FIGS. 10 and 11, the heater element 10 used in this unit cell 1 has a serpentine or ‘double omega’ shape. This configuration keeps the gas bubble centered on the axis of the nozzle. A single omega is a simple geometric shape which is beneficial from a fabrication perspective. However the gap 159 between the ends of the heater element means that the heating of the ink in the chamber is slightly asymmetrical. As a result, the gas bubble is slightly skewed to the side opposite the gap 159. This can in turn affect the trajectory of the ejected drop. The double omega shape provides the heater element with the gap 160 to compensate for the gap 159 so that the symmetry and position of the bubble within the chamber is better controlled and the ejected drop trajectory is more reliable.
FIG. 12 shows a heater element 10 with a single omega shape. As discussed above, the simplicity of this shape has significant advantages during lithographic fabrication. It can be a single current path that is relatively wide and therefore less affected by any inherent inaccuracies in the deposition of the heater material. The inherent inaccuracies of the equipment used to deposit the heater material result in variations in the dimensions of the element. However, these tolerances are fixed values so the resulting variations in the dimensions of a relatively wide component are proportionally less than the variations for a thinner component. It will be appreciated that proportionally large changes of components dimensions will have a greater effect on their intended function. Therefore the performance characteristics of a relatively wide heater element are more reliable than a thinner one. 
The omega shape directs current flow around the axis of the nozzle aperture 5. This gives good bubble alignment with the aperture for better ejection of drops while ensuring that the bubble collapse point is not on the heater element 10. As discussed above, this avoids problems caused by cavitation.
Referring to FIGS. 13 to 26, another embodiment of the unit cell 1 is shown together with several stages of the etching and deposition fabrication process. In this embodiment, the heater element 10 is suspended from opposing sides of the chamber. This allows it to be symmetrical about two planes that intersect along the axis of the nozzle aperture 5. This configuration provides a drop trajectory along the axis of the nozzle aperture 5 while avoiding the cavitation problems discussed above.
Fabrication Process
In the interests of brevity, the fabrication stages have been shown for the unit cell of FIG. 13 only (see FIGS. 15 to 25). It will be appreciated that the other unit cells will use the same fabrication stages with different masking.
Referring to FIG. 15, there is shown the starting point for fabrication of the thermal inkjet nozzle shown in FIG. 13. CMOS processing of a silicon wafer provides a silicon substrate 21 having drive circuitry 22, and an interlayer dielectric (“interconnect”) 23. The interconnect 23 comprises four metal layers, which together form a seal ring for the inlet passage 9 to be etched through the interconnect. The top metal layer 26, which forms an upper portion of the seal ring, can be seen in FIG. 15. The metal seal ring prevents ink moisture from seeping into the interconnect 23 when the inlet passage 9 is filled with ink.
A passivation layer 24 is deposited onto the top metal layer 26 by plasma-enhanced chemical vapour deposition (PECVD). After deposition of the passivation layer 24, it is etched to define a circular recess, which forms parts of the inlet passage 9. At the same as etching the recess, a plurality of vias 50 are also etched, which allow electrical connection through the passivation layer 24 to the top metal layer 26. The etch pattern is defined by a layer of patterned photoresist (not shown), which is removed by O2 ashing after the etch. 
Referring to FIG. 16, in the next fabrication sequence, a layer of photoresist is spun onto the passivation later 24. The photoresist is exposed and developed to define a circular opening. With the patterned photoresist 51 in place, the dielectric interconnect 23 is etched as far as the silicon substrate 21 using a suitable oxide-etching gas chemistry (e.g. O2/C4F8). Etching through the silicon substrate is continued down to about 20 microns to define a front ink hole 52, using a suitable silicon-etching gas chemistry (e.g. ‘Bosch etch’). The same photoresist mask 51 can be used for both etching steps. FIG. 17 shows the unit cell after etching the front ink hole 52 and removal of the photoresist 51.
Referring to FIG. 18, in the next stage of fabrication, the front ink hole 52 is plugged with photoresist to provide a front plug 53. At the same time, a layer of photoresist is deposited over the passivation layer 24. This layer of photoresist is exposed and developed to define a first sacrificial scaffold 54 over the front plug 53, and scaffolding tracks 35 around the perimeter of the unit cell. The first sacrificial scaffold 54 is used for subsequent deposition of heater material 38 thereon and is therefore formed with a planar upper surface to avoid any buckling in the heater element (see heater element 10 in FIG. 13). The first sacrificial scaffold 54 is UV cured and hardbaked to prevent reflow of the photoresist during subsequent high-temperature deposition onto its upper surface.
Importantly, the first sacrificial scaffold 54 has sloped or angled side faces 55. These angled side faces 55 are formed by adjusting the focusing in the exposure tool (e.g. stepper) when exposing the photoresist. The sloped side faces 55 advantageously allow heater material 38 to be deposited substantially evenly over the first sacrificial scaffold 54.
Referring to FIG. 19, the next stage of fabrication deposits the heater material 38 over the first sacrificial scaffold 54, the passivation layer 24 and the perimeter scaffolding tracks 35. The heater material 38 is typically a monolayer of TiAlN. However, the heater material 38 may alternatively comprise TiAlN sandwiched between upper and lower passivating materials, such as tantalum or tantalum nitride. Passivating layers on the heater element 10 minimize corrosion of the and improve heater longevity.
Referring to FIG. 20, the heater material 38 is subsequently etched down to the first sacrificial scaffold 54 to define the heater element 10. At the same time, contact electrodes 15 are defined on either side of the heater element 10. The electrodes 15 are in contact with the top metal layer 26 and so provide electrical connection between the CMOS and the heater element  10. The sloped side faces of the first sacrificial scaffold 54 ensure good electrical connection between the heater element 10 and the electrodes 15, since the heater material is deposited with sufficient thickness around the scaffold 54. Any thin areas of heater material (due to insufficient side face deposition) would increase resistivity and affect heater performance.
Adjacent unit cells are electrically insulated from each other by virtue of grooves etched around the perimeter of each unit cell. The grooves are etched at the same time as defining the heater element 10.
Referring to FIG. 21, in the subsequent step a second sacrificial scaffold 39 of photoresist is deposited over the heater material. The second sacrificial scaffold 39 is exposed and developed to define sidewalls for the cylindrical nozzle chamber and perimeter sidewalls for each unit cell. The second sacrificial scaffold 39 is also UV cured and hardbaked to prevent any reflow of the photoresist during subsequent high-temperature deposition of the silicon nitride roof material.
Referring to FIG. 22, silicon nitride is deposited onto the second sacrificial scaffold 39 by plasma enhanced chemical vapour deposition. The silicon nitride forms a roof 44 over each unit cell, which is the nozzle plate 2 for a row of nozzles. Chamber sidewalls 6 and unit cell sidewalls 56 are also formed by deposition of silicon nitride.
Referring to FIG. 23, the nozzle rim 4 is etched partially through the roof 44, by placing a suitably patterned photoresist mask over the roof, etching for a controlled period of time and removing the photoresist by ashing.
Referring to FIG. 24, the nozzle aperture 5 is etched through the roof 24 down to the second sacrificial scaffold 39. Again, the etch is performed by placing a suitably patterned photoresist mask over the roof, etching down to the scaffold 39 and removing the photoresist mask.
With the nozzle structure now fully formed on a frontside of the silicon substrate 21, an ink supply channel 32 is etched from the backside of the substrate 21, which meets with the front plug 53. 
Referring to FIG. 25, after formation of the ink supply channel 32, the first and second sacrificial scaffolds of photoresist, together with the front plug 53 are ashed off using an O2 plasma. Accordingly, fluid connection is made from the ink supply channel 32 through to the nozzle aperture 5.
It should be noted that a portion of photoresist, on either side of the nozzle chamber sidewalls 6, remains encapsulated by the roof 44, the unit cell sidewalls 56 and the chamber sidewalls 6. This portion of photoresist is sealed from the O2 ashing plasma and, therefore, remains intact after fabrication of the printhead. This encapsulated photoresist advantageously provides additional robustness for the printhead by supporting the nozzle plate 2. Hence, the printhead has a robust nozzle plate spanning continuously over rows of nozzles, and being supported by solid blocks of hardened photoresist, in addition to support walls.
Hydrophobic Coating of Front Face
Referring to FIG. 24, it can been seen that a hydrophobic material may be deposited onto the roof 44 at this stage by, for example, chemical vapour deposition. The whole of the front face of the printhead may be coated with hydrophobic material. Alternatively, predetermined regions of the roof 44 (e.g. regions surrounding each nozzle aperture 5) may be coated. However, referring to FIG. 25, the final stage of printhead fabrication involves ashing off the photoresist, which occupies the nozzle chambers. Since hydrophobic coating materials are generally organic in nature, the ashing process will remove the hydrophobic coating on the roof 44 as well as the photoresist 39 in the nozzle chambers. Hence, a hydrophobic coating step at this stage would ultimately have no effect on the hydrophobicity of the roof 44.
Referring to FIG. 25, it can be seen that a hydrophobic material may be deposited onto the roof 44 at this stage by, for example, chemical vapour deposition. However, the CVD process will deposit the hydrophobic material both onto the roof 44, onto nozzle chamber sidewalls, onto the heater element 10 and inside ink supply channels 32. A hydrophobic coating inside the nozzle chambers and ink supply channels would be highly undesirable in terms of creating a positive ink pressure biased towards the nozzle chambers. A hydrophobic coating on the heater element 10 would be equally undesirable in terms of kogation during printing.
Referring to FIG. 27, there is shown a process for depositing a hydrophobic material onto the roof 44, which eliminates the aforementioned selectivity problems. Before deposition of the hydrophobic material, the printhead is primed with a liquid, which fills the ink supply channels 32 and nozzle chamber up to the rim 4. The liquid is preferably ink so that the hydrophobic deposition step can be incorporated into the overall printer manufacturing process.  Once primed with ink 60, the front face of the printhead, including the roof 44, is coated with a hydrophobic material 61 by chemical vapour deposition (see FIG. 28). The hydrophobic material 61 cannot be deposited inside the nozzle chamber, because the ink 60 effectively seals the nozzle aperture 5 from the vapour. Hence, the ink 60 protects the nozzle chamber and allows selective deposition of the hydrophobic material 61 onto the roof 44. Accordingly, the final printhead has a hydrophobic front face in combination with hydrophilic nozzle chambers and ink supply channels.
The choice of hydrophobic material is not critical. Any hydrophobic compound, which can adhere to the roof 44 by either covalent bonding, ionic bonding, chemisorption or adsorption may be used. The choice of hydrophobic material will depend on the material forming the roof 44 and also the liquid used to prime the nozzles.
Typically, the roof 44 is formed from silicon nitride, silicon oxide or silicon oxynitride. In this case, the hydrophobic material is typically a compound, which can form covalent bonds with the oxygen or nitrogen atoms exposed on the surface of the roof Examples of suitable compounds are silyl chlorides (including monochlorides, dichlorides, trichlorides) having at least one hydrophobic group. The hydrophobic group is typically a C1-20 alkyl group, optionally substituted with a plurality of fluorine atoms. The hydrophobic group may be perfluorinated, partially fluorinated or non-fluorinated. Examples of suitable hydrophobic compounds include: trimethylsilyl chloride, dimethylsilyl dichloride, methylsilyl trichloride, triethylsilyl chloride, octyldimethylsilyl chloride, perfluorooctyldimethylsilyl chloride, perfluorooctylsilyl trichloride, perfluorooctylchlorosilane etc.
Typically, the nozzles are primed with an inkjet ink. In this case, the hydrophobic material is typically a compound, which does not polymerise in aqueous solution and form a skin across the nozzle aperture 5. Examples of non-polymerizable hydrophobic compounds include: trimethylsilyl chloride, triethylsilyl chloride, perfluorooctyldimethylsilyl chloride, perfluorooctylchlorosilane etc.
Whilst silyl chlorides have been exemplified as hydrophobizing compounds hereinabove, it will be appreciated that the present invention may be used in conjunction with any hydrophobizing compound, which can be deposited by CVD or another suitable deposition process.
Other Embodiments
The invention has been described above with reference to printheads using bubble forming heater elements. However, it 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 trade mark 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.
It will be appreciated by ordinary workers in this field that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the 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.
Ink Jet Technologies
The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used.
The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. In conventional thermal inkjet printheads, this leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.
The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.
Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital  color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:
low power (less than 10 Watts)
high resolution capability (1,600 dpi or more)
photographic quality output
low manufacturing cost
small size (pagewidth times minimum cross section)
high speed (<2 seconds per page).
All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.
The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.
For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.
Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.
Tables of Prop-on-Demand Ink Jets 
Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.
The following tables form the axes of an eleven dimensional table of inkjet types.
Actuator mechanism (18 types)
Basic operation mode (7 types)
Auxiliary mechanism (8 types)
Actuator amplification or modification method (17 types)
Actuator motion (19 types)
Nozzle refill method (4 types)
Method of restricting back-flow through inlet (10 types)
Nozzle clearing method (9 types)
Nozzle plate construction (9 types)
prop ejection direction (5 types)
Ink type (7 types)
The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of inkjet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 above which matches the docket numbers in the table under the heading Cross References to Related Applications.
Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.
Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, print technology may be listed more than once in a table, where it shares characteristics with more than one entry. 
Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.
The information associated with the aforementioned 11 dimensional matrix are set out in the following tables. 










ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS)












Description
Advantages
Disadvantages
Examples















Thermal
An electrothermal
Large force
High power
Canon


bubble
heater heats the
generated
Ink carrier
Bubblejet 1979



ink to above
Simple
limited to water
Endo et al GB



boiling point,
construction
Low
patent 2,007,162



transferring
No moving
efficiency
Xerox heater-



significant heat to
parts
High
in-pit 1990



the aqueous ink. A
Fast operation
temperatures
Hawkins et al



bubble nucleates
Small chip
required
U.S. Pat. No. 4,899,181



and quickly forms,
area required for
High
Hewlett-



expelling the ink.
actuator
mechanical
Packard TIJ



The efficiency of

stress
1982 Vaught et



the process is low,

Unusual
al U.S. Pat. No.



with typically less

materials
4,490,728



than 0.05% of the

required



electrical energy

Large drive



being transformed

transistors



into kinetic energy

Cavitation



of the drop.

causes actuator





failure





Kogation





reduces bubble





formation





Large print





heads are





difficult to





fabricate


Piezoelectric
A piezoelectric
Low power
Very large
Kyser et al



crystal such as
consumption
area required for
U.S. Pat. No. 3,946,398



lead lanthanum
Many ink
actuator
Zoltan U.S. Pat. No.



zirconate (PZT) is
types can be
Difficult to
3,683,212



electrically
used
integrate with
1973 Stemme



activated, and
Fast operation
electronics
U.S. Pat. No. 3,747,120



either expands,
High
High voltage
Epson Stylus



shears, or bends to
efficiency
drive transistors
Tektronix



apply pressure to

required
IJ04



the ink, ejecting

Full



drops.

pagewidth print





heads





impractical due





to actuator size





Requires





electrical poling





in high field





strengths during





manufacture


Electro-
An electric field is
Low power
Low
Seiko Epson,


strictive
used to activate
consumption
maximum strain
Usui et all JP



electrostriction in
Many ink
(approx. 0.01%)
253401/96



relaxor materials
types can be
Large area
IJ04



such as lead
used
required for



lanthanum
Low thermal
actuator due to



zirconate titanate
expansion
low strain



(PLZT) or lead
Electric field
Response



magnesium
strength required
speed is



niobate (PMN).
(approx. 3.5 V/μm)
marginal (~10 μs)




can be
High voltage




generated
drive transistors




without
required




difficulty
Full




Does not
pagewidth print




require electrical
heads




poling
impractical due





to actuator size


Ferroelectric
An electric field is
Low power
Difficult to
IJ04



used to induce a
consumption
integrate with



phase transition
Many ink
electronics



between the
types can be
Unusual



antiferroelectric
used
materials such as



(AFE) and
Fast operation
PLZSnT are



ferroelectric (FE)
(<1 μs)
required



phase. Perovskite
Relatively
Actuators



materials such as
high longitudinal
require a large



tin modified lead
strain
area



lanthanum
High



zirconate titanate
efficiency



(PLZSnT) exhibit
Electric field



large strains of up
strength of



to 1% associated
around 3 V/μm



with the AFE to
can be readily



FE phase
provided



transition.


Electrostatic
Conductive plates
Low power
Difficult to
IJ02, IJ04


plates
are separated by a
consumption
operate



compressible or
Many ink
electrostatic



fluid dielectric
types can be
devices in an



(usually air). Upon
used
aqueous



application of a
Fast operation
environment



voltage, the plates

The



attract each other

electrostatic



and displace ink,

actuator will



causing drop

normally need to



ejection. The

be separated



conductive plates

from the ink



may be in a comb

Very large



or honeycomb

area required to



structure, or

achieve high



stacked to increase

forces



the surface area

High voltage



and therefore the

drive transistors



force.

may be required





Full





pagewidth print





heads are not





competitive due





to actuator size


Electrostatic
A strong electric
Low current
High voltage
1989 Saito et


pull
field is applied to
consumption
required
al, U.S. Pat. No.


on ink
the ink, whereupon
Low
May be
4,799,068



electrostatic
temperature
damaged by
1989 Miura et



attraction

sparks due to air
al, U.S. Pat. No.



accelerates the ink

breakdown
4,810,954



towards the print

Required field
Tone-jet



medium.

strength





increases as the





drop size





decreases





High voltage





drive transistors





required





Electrostatic





field attracts dust


Permanent
An electromagnet
Low power
Complex
IJ07, IJ10


magnet
directly attracts a
consumption
fabrication


electro-
permanent magnet,
Many ink
Permanent


magnetic
displacing ink and
types can be
magnetic



causing drop
used
material such as



ejection. Rare
Fast operation
Neodymium Iron



earth magnets with
High
Boron (NdFeB)



a field strength
efficiency
required.



around 1 Tesla can
Easy
High local



be used. Examples
extension from
currents required



are: Samarium
single nozzles to
Copper



Cobalt (SaCo) and
pagewidth print
metalization



magnetic materials
heads
should be used



in the neodymium

for long



iron boron family

electromigration



(NdFeB,

lifetime and low



NdDyFeBNb,

resistivity



NdDyFeB, etc)

Pigmented





inks are usually





infeasible





Operating





temperature





limited to the





Curie





temperature





(around 540 K)


Soft
A solenoid
Low power
Complex
IJ01, IJ05,


magnetic
induced a
consumption
fabrication
IJ08, IJ10, IJ12,


core
magnetic field in a
Many ink
Materials not
IJ14, IJ15, IJ17


electro-
soft magnetic core
types can be
usually present


magnetic
or yoke fabricated
used
in a CMOS fab



from a ferrous
Fast operation
such as NiFe,



material such as
High
CoNiFe, or CoFe



electroplated iron
efficiency
are required



alloys such as
Easy
High local



CoNiFe [1], CoFe,
extension from
currents required



or NiFe alloys,
single nozzles to
Copper



Typically, the soft
pagewidth print
metalization



magnetic material
heads
should be used



is in two parts,

for long



which are

electromigration



normally held

lifetime and low



apart by a spring.

resistivity



When the solenoid

Electroplating



is actuated, the two

is required



parts attract,

High



displacing the ink.

saturation flux





density is





required (2.0-2.1





T is achievable





with CoNiFe





[1])


Lorenz
The Lorenz force
Low power
Force acts as a
IJ06, IJ11,


force
acting on a current
consumption
twisting motion
IJ13, IJ16



carrying wire in a
Many ink
Typically,



magnetic field is
types can be
only a quarter of



utilized.
used
the solenoid



This allows the
Fast operation
length provides



magnetic field to
High
force in a useful



be supplied
efficiency
direction



externally to the
Easy
High local



print head, for
extension from
currents required



example with rare
single nozzles to
Copper



earth permanent
pagewidth print
metalization



magnets.
heads
should be used



Only the current

for long



carrying wire need

electromigration



be fabricated on

lifetime and low



the print-head,

resistivity



simplifying

Pigmented



materials

inks are usually



requirements.

infeasible


Magneto-
The actuator uses
Many ink
Force acts as a
Fischenbeck,


striction
the giant
types can be
twisting motion
U.S. Pat. No. 4,032,929



magnetostrictive
used
Unusual
IJ25



effect of materials
Fast operation
materials such as



such as Terfenol-D
Easy
Terfenol-D are



(an alloy of
extension from
required



terbium,
single nozzles to
High local



dysprosium and
pagewidth print
currents required



iron developed at
heads
Copper



the Naval
High force is
metalization



Ordnance
available
should be used



Laboratory, hence

for long



Ter-Fe-NOL). For

electromigration



best efficiency, the

lifetime and low



actuator should be

resistivity



pre-stressed to

Pre-stressing



approx. 8 MPa.

may be required


Surface
Ink under positive
Low power
Requires
Silverbrook,


tension
pressure is held in
consumption
supplementary
EP 0771 658 A2


reduction
a nozzle by surface
Simple
force to effect
and related



tension. The
construction
drop separation
patent



surface tension of
No unusual
Requires
applications



the ink is reduced
materials
special ink



below the bubble
required in
surfactants



threshold, causing
fabrication
Speed may be



the ink to egress
High
limited by



from the nozzle.
efficiency
surfactant




Easy
properties




extension from




single nozzles to




pagewidth print




heads


Viscosity
The ink viscosity
Simple
Requires
Silverbrook,


reduction
is locally reduced
construction
supplementary
EP 0771 658 A2



to select which
No unusual
force to effect
and related



drops are to be
materials
drop separation
patent



ejected. A
required in
Requires
applications



viscosity reduction
fabrication
special ink



can be achieved
Easy
viscosity



electrothermally
extension from
properties



with most inks, but
single nozzles to
High speed is



special inks can be
pagewidth print
difficult to



engineered for a
heads
achieve



100:1 viscosity

Requires



reduction.

oscillating ink





pressure





A high





temperature





difference





(typically 80





degrees) is





required


Acoustic
An acoustic wave
Can operate
Complex
1993



is generated and
without a nozzle
drive circuitry
Hadimioglu et



focussed upon the
plate
Complex
al, EUP 550,192



drop ejection

fabrication
1993 Elrod et



region.

Low
al, EUP 572,220





efficiency





Poor control





of drop position





Poor control





of drop volume


Thermo-
An actuator which
Low power
Efficient
IJ03, IJ09,


elastic
relies upon
consumption
aqueous
IJ17, IJ18, IJ19,


bend
differential
Many ink
operation
IJ20, IJ21, IJ22,


actuator
thermal expansion
types can be
requires a
IJ23, IJ24, IJ27,



upon Joule heating
used
thermal insulator
IJ28, IJ29, IJ30,



is used.
Simple planar
on the hot side
IJ31, IJ32, IJ33,




fabrication
Corrosion
IJ34, IJ35, IJ36,




Small chip
prevention can
IJ37, IJ38, IJ39,




area required for
be difficult
IJ40, IJ41




each actuator
Pigmented




Fast operation
inks may be




High
infeasible, as




efficiency
pigment particles




CMOS
may jam the




compatible
bend actuator




voltages and




currents




Standard




MEMS




processes can be




used




Easy




extension from




single nozzles to




pagewidth print




heads


High CTE
A material with a
High force
Requires
IJ09, IJ17,


thermo-
very high
can be generated
special material
IJ18, IJ20, IJ21,


elastic
coefficient of
Three
(e.g. PTFE)
IJ22, IJ23, IJ24,


actuator
thermal expansion
methods of
Requires a
IJ27, IJ28, IJ29,



(CTE) such as
PTFE deposition
PTFE deposition
IJ30, IJ31, IJ42,



polytetrafluoroethylene
are under
process, which is
IJ43, IJ44



(PTFE) is
development:
not yet standard



used. As high CTE
chemical vapor
in ULSI fabs



materials are
deposition
PTFE



usually non-
(CVD), spin
deposition



conductive, a
coating, and
cannot be



heater fabricated
evaporation
followed with



from a conductive
PTFE is a
high temperature



material is
candidate for
(above 350° C.)



incorporated. A 50 μm
low dielectric
processing



long PTFE
constant
Pigmented



bend actuator with
insulation in
inks may be



polysilicon heater
ULSI
infeasible, as



and 15 mW power
Very low
pigment particles



input can provide
power
may jam the



180 μN force and
consumption
bend actuator



10 μm deflection.
Many ink



Actuator motions
types can be



include:
used



Bend
Simple planar



Push
fabrication



Buckle
Small chip



Rotate
area required for




each actuator




Fast operation




High




efficiency




CMOS




compatible




voltages and




currents




Easy




extension from




single nozzles to




pagewidth print




heads


Conductive
A polymer with a
High force
Requires
IJ24


polymer
high coefficient of
can be generated
special materials


thermo-
thermal expansion
Very low
development


elastic
(such as PTFE) is
power
(High CTE


actuator
doped with
consumption
conductive



conducting
Many ink
polymer)



substances to
types can be
Requires a



increase its
used
PTFE deposition



conductivity to
Simple planar
process, which is



about 3 orders of
fabrication
not yet standard



magnitude below
Small chip
in ULSI fabs



that of copper. The
area required for
PTFE



conducting
each actuator
deposition



polymer expands
Fast operation
cannot be



when resistively
High
followed with



heated.
efficiency
high temperature



Examples of
CMOS
(above 350° C.)



conducting
compatible
processing



dopants include:
voltages and
Evaporation



Carbon nanotubes
currents
and CVD



Metal fibers
Easy
deposition



Conductive
extension from
techniques



polymers such as
single nozzles to
cannot be used



doped
pagewidth print
Pigmented



polythiophene
heads
inks may be



Carbon granules

infeasible, as





pigment particles





may jam the





bend actuator


Shape
A shape memory
High force is
Fatigue limits
IJ26


memory
alloy such as TiNi
available
maximum


alloy
(also known as
(stresses of
number of cycles



Nitinol - Nickel
hundreds of
Low strain



Titanium alloy
MPa)
(1%) is required



developed at the
Large strain is
to extend fatigue



Naval Ordnance
available (more
resistance



Laboratory) is
than 3%)
Cycle rate



thermally switched
High
limited by heat



between its weak
corrosion
removal



martensitic state
resistance
Requires



and its high
Simple
unusual



stiffness austenic
construction
materials (TiNi)



state. The shape of
Easy
The latent



the actuator in its
extension from
heat of



martensitic state is
single nozzles to
transformation



deformed relative
pagewidth print
must be



to the austenic
heads
provided



shape. The shape
Low voltage
High current



change causes
operation
operation



ejection of a drop.

Requires pre-





stressing to





distort the





martensitic state


Linear
Linear magnetic
Linear
Requires
IJ12


Magnetic
actuators include
Magnetic
unusual


Actuator
the Linear
actuators can be
semiconductor



Induction Actuator
constructed with
materials such as



(LIA), Linear
high thrust, long
soft magnetic



Permanent Magnet
travel, and high
alloys (e.g.



Synchronous
efficiency using
CoNiFe)



Actuator
planar
Some varieties



(LPMSA), Linear
semiconductor
also require



Reluctance
fabrication
permanent



Synchronous
techniques
magnetic



Actuator (LRSA),
Long actuator
materials such as



Linear Switched
travel is
Neodymium iron



Reluctance
available
boron (NdFeB)



Actuator (LSRA),
Medium force
Requires



and the Linear
is available
complex multi-



Stepper Actuator
Low voltage
phase drive



(LSA).
operation
circuitry





High current





operation



















BASIC OPERATION MODE












Description
Advantages
Disadvantages
Examples















Actuator
This is the
Simple
Drop
Thermal ink


directly
simplest mode of
operation
repetition rate is
jet


pushes
operation: the
No external
usually limited
Piezoelectric


ink
actuator directly
fields required
to around 10 kHz.
ink jet



supplies sufficient
Satellite drops
However,
IJ01, IJ02,



kinetic energy to
can be avoided if
this is not
IJ03, IJ04, IJ05,



expel the drop.
drop velocity is
fundamental to
IJ06, IJ07, IJ09,



The drop must
less than 4 m/s
the method, but
IJ11, IJ12, IJ14,



have a sufficient
Can be
is related to the
IJ16, IJ20, IJ22,



velocity to
efficient,
refill method
IJ23, IJ24, IJ25,



overcome the
depending upon
normally used
IJ26, IJ27, IJ28,



surface tension.
the actuator used
All of the drop
IJ29, IJ30, IJ31,





kinetic energy
IJ32, IJ33, IJ34,





must be
IJ35, IJ36, IJ37,





provided by the
IJ38, IJ39, IJ40,





actuator
IJ41, IJ42, IJ43,





Satellite drops
IJ44





usually form if





drop velocity is





greater than 4.5 m/s


Proximity
The drops to be
Very simple
Requires close
Silverbrook,



printed are
print head
proximity
EP 0771 658 A2



selected by some
fabrication can
between the
and related



manner (e.g.
be used
print head and
patent



thermally induced
The drop
the print media
applications



surface tension
selection means
or transfer roller



reduction of
does not need to
May require



pressurized ink).
provide the
two print heads



Selected drops are
energy required
printing alternate



separated from the
to separate the
rows of the



ink in the nozzle
drop from the
image



by contact with the
nozzle
Monolithic



print medium or a

color print heads



transfer roller.

are difficult


Electrostatic
The drops to be
Very simple
Requires very
Silverbrook,


pull
printed are
print head
high electrostatic
EP 0771 658 A2


on ink
selected by some
fabrication can
field
and related



manner (e.g.
be used
Electrostatic
patent



thermally induced
The drop
field for small
applications



surface tension
selection means
nozzle sizes is
Tone-Jet



reduction of
does not need to
above air



pressurized ink).
provide the
breakdown



Selected drops are
energy required
Electrostatic



separated from the
to separate the
field may attract



ink in the nozzle
drop from the
dust



by a strong electric
nozzle



field.


Magnetic
The drops to be
Very simple
Requires
Silverbrook,


pull on
printed are
print head
magnetic ink
EP 0771 658 A2


ink
selected by some
fabrication can
Ink colors
and related



manner (e.g.
be used
other than black
patent



thermally induced
The drop
are difficult
applications



surface tension
selection means
Requires very



reduction of
does not need to
high magnetic



pressurized ink).
provide the
fields



Selected drops are
energy required



separated from the
to separate the



ink in the nozzle
drop from the



by a strong
nozzle



magnetic field



acting on the



magnetic ink.


Shutter
The actuator
High speed
Moving parts
IJ13, IJ17,



moves a shutter to
(>50 kHz)
are required
IJ21



block ink flow to
operation can be
Requires ink



the nozzle. The ink
achieved due to
pressure



pressure is pulsed
reduced refill
modulator



at a multiple of the
time
Friction and



drop ejection
Drop timing
wear must be



frequency.
can be very
considered




accurate
Stiction is




The actuator
possible




energy can be




very low


Shuttered
The actuator
Actuators with
Moving parts
IJ08, IJ15,


grill
moves a shutter to
small travel can
are required
IJ18, IJ19



block ink flow
be used
Requires ink



through a grill to
Actuators with
pressure



the nozzle. The
small force can
modulator



shutter movement
be used
Friction and



need only be equal
High speed
wear must be



to the width of the
(>50 kHz)
considered



grill holes.
operation can be
Stiction is




achieved
possible


Pulsed
A pulsed magnetic
Extremely low
Requires an
IJ10


magnetic
field attracts an
energy operation
external pulsed


pull on
‘ink pusher’ at the
is possible
magnetic field


ink
drop ejection
No heat
Requires


pusher
frequency. An
dissipation
special materials



actuator controls a
problems
for both the



catch, which

actuator and the



prevents the ink

ink pusher



pusher from

Complex



moving when a

construction



drop is not to be



ejected.



















AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES)












Description
Advantages
Disadvantages
Examples





None
The actuator
Simplicity of
Drop ejection
Most ink jets,



directly fires the
construction
energy must be
including



ink drop, and there
Simplicity of
supplied by
piezoelectric and



is no external field
operation
individual nozzle
thermal bubble.



or other
Small physical
actuator
IJ01, IJ02,



mechanism
size

IJ03, IJ04, IJ05,



required.


IJ07, IJ09, IJ11,






IJ12, IJ14, IJ20,






IJ22, IJ23, IJ24,






IJ25, IJ26, IJ27,






IJ28, IJ29, IJ30,






IJ31, IJ32, IJ33,






IJ34, IJ35, IJ36,






IJ37, IJ38, IJ39,






IJ40, IJ41, IJ42,






IJ43, IJ44


Oscillating
The ink pressure
Oscillating ink
Requires
Silverbrook,


ink
oscillates,
pressure can
external ink
EP 0771 658 A2


pressure
providing much of
provide a refill
pressure
and related


(including
the drop ejection
pulse, allowing
oscillator
patent


acoustic
energy. The
higher operating
Ink pressure
applications


stimulation)
actuator selects
speed
phase and
IJ08, IJ13,



which drops are to
The actuators
amplitude must
IJ15, IJ17, IJ18,



be fired by
may operate
be carefully
IJ19, IJ21



selectively
with much lower
controlled



blocking or
energy
Acoustic



enabling nozzles.
Acoustic
reflections in the



The ink pressure
lenses can be
ink chamber



oscillation may be
used to focus the
must be



achieved by
sound on the
designed for



vibrating the print
nozzles



head, or preferably



by an actuator in



the ink supply.


Media
The print head is
Low power
Precision
Silverbrook,


proximity
placed in close
High accuracy
assembly
EP 0771 658 A2



proximity to the
Simple print
required
and related



print medium.
head
Paper fibers
patent



Selected drops
construction
may cause
applications



protrude from the

problems



print head further

Cannot print



than unselected

on rough



drops, and contact

substrates



the print medium.



The drop soaks



into the medium



fast enough to



cause drop



separation.


Transfer
Drops are printed
High accuracy
Bulky
Silverbrook,


roller
to a transfer roller
Wide range of
Expensive
EP 0771 658 A2



instead of straight
print substrates
Complex
and related



to the print
can be used
construction
patent



medium. A
Ink can be

applications



transfer roller can
dried on the

Tektronix hot



also be used for
transfer roller

melt



proximity drop


piezoelectric ink



separation.


jet






Any of the IJ






series


Electrostatic
An electric field is
Low power
Field strength
Silverbrook,



used to accelerate
Simple print
required for
EP 0771 658 A2



selected drops
head
separation of
and related



towards the print
construction
small drops is
patent



medium.

near or above air
applications





breakdown
Tone-Jet


Direct
A magnetic field is
Low power
Requires
Silverbrook,


magnetic
used to accelerate
Simple print
magnetic ink
EP 0771 658 A2


field
selected drops of
head
Requires
and related



magnetic ink
construction
strong magnetic
patent



towards the print

field
applications



medium.


Cross
The print head is
Does not
Requires
IJ06, IJ16


magnetic
placed in a
require magnetic
external magnet


field
constant magnetic
materials to be
Current



field. The Lorenz
integrated in the
densities may be



force in a current
print head
high, resulting in



carrying wire is
manufacturing
electromigration



used to move the
process
problems



actuator.


Pulsed
A pulsed magnetic
Very low
Complex print
IJ10


magnetic
field is used to
power operation
head


field
cyclically attract a
is possible
construction



paddle, which
Small print
Magnetic



pushes on the ink.
head size
materials



A small actuator

required in print



moves a catch,

head



which selectively



prevents the



paddle from



moving.



















ACTUATOR AMPLIFICATION OR MODIFICATION METHOD












Description
Advantages
Disadvantages
Examples















None
No actuator
Operational
Many actuator
Thermal



mechanical
simplicity
mechanisms
Bubble Ink jet



amplification is

have insufficient
IJ01, IJ02,



used. The actuator

travel, or
IJ06, IJ07, IJ16,



directly drives the

insufficient
IJ25, IJ26



drop ejection

force, to



process.

efficiently drive





the drop ejection





process


Differential
An actuator
Provides
High stresses
Piezoelectric


expansion
material expands
greater travel in
are involved
IJ03, IJ09,


bend
more on one side
a reduced print
Care must be
IJ17, IJ18, IJ19,


actuator
than on the other.
head area
taken that the
IJ20, IJ21, IJ22,



The expansion

materials do not
IJ23, IJ24, IJ27,



may be thermal,

delaminate
IJ29, IJ30, IJ31,



piezoelectric,

Residual bend
IJ32, IJ33, IJ34,



magnetostrictive,

resulting from
IJ35, IJ36, IJ37,



or other

high temperature
IJ38, IJ39, IJ42,



mechanism. The

or high stress
IJ43, IJ44



bend actuator

during formation



converts a high



force low travel



actuator



mechanism to high



travel, lower force



mechanism.


Transient
A trilayer bend
Very good
High stresses
IJ40, IJ41


bend
actuator where the
temperature
are involved


actuator
two outside layers
stability
Care must be



are identical. This
High speed, as
taken that the



cancels bend due
a new drop can
materials do not



to ambient
be fired before
delaminate



temperature and
heat dissipates



residual stress. The
Cancels



actuator only
residual stress of



responds to
formation



transient heating of



one side or the



other.


Reverse
The actuator loads
Better
Fabrication
IJ05, IJ11


spring
a spring. When the
coupling to the
complexity



actuator is turned
ink
High stress in



off, the spring

the spring



releases. This can



reverse the



force/distance



curve of the



actuator to make it



compatible with



the force/time



requirements of



the drop ejection.


Actuator
A series of thin
Increased
Increased
Some


stack
actuators are
travel
fabrication
piezoelectric ink



stacked. This can
Reduced drive
complexity
jets



be appropriate
voltage
Increased
IJ04



where actuators

possibility of



require high

short circuits due



electric field

to pinholes



strength, such as



electrostatic and



piezoelectric



actuators.


Multiple
Multiple smaller
Increases the
Actuator
IJ12, IJ13,


actuators
actuators are used
force available
forces may not
IJ18, IJ20, IJ22,



simultaneously to
from an actuator
add linearly,
IJ28, IJ42, IJ43



move the ink. Each
Multiple
reducing



actuator need
actuators can be
efficiency



provide only a
positioned to



portion of the
control ink flow



force required.
accurately


Linear
A linear spring is
Matches low
Requires print
IJ15


Spring
used to transform a
travel actuator
head area for the



motion with small
with higher
spring



travel and high
travel



force into a longer
requirements



travel, lower force
Non-contact



motion.
method of




motion




transformation


Coiled
A bend actuator is
Increases
Generally
IJ17, IJ21,


actuator
coiled to provide
travel
restricted to
IJ34, IJ35



greater travel in a
Reduces chip
planar



reduced chip area.
area
implementations




Planar
due to extreme




implementations
fabrication




are relatively
difficulty in




easy to fabricate.
other





orientations.


Flexure
A bend actuator
Simple means
Care must be
IJ10, IJ19,


bend
has a small region
of increasing
taken not to
IJ33


actuator
near the fixture
travel of a bend
exceed the



point, which flexes
actuator
elastic limit in



much more readily

the flexure area



than the remainder

Stress



of the actuator.

distribution is



The actuator

very uneven



flexing is

Difficult to



effectively

accurately model



converted from an

with finite



even coiling to an

element analysis



angular bend,



resulting in greater



travel of the



actuator tip.


Catch
The actuator
Very low
Complex
IJ10



controls a small
actuator energy
construction



catch. The catch
Very small
Requires



either enables or
actuator size
external force



disables movement

Unsuitable for



of an ink pusher

pigmented inks



that is controlled



in a bulk manner.


Gears
Gears can be used
Low force,
Moving parts
IJ13



to increase travel
low travel
are required



at the expense of
actuators can be
Several



duration. Circular
used
actuator cycles



gears, rack and
Can be
are required



pinion, ratchets,
fabricated using
More complex



and other gearing
standard surface
drive electronics



methods can be
MEMS
Complex



used.
processes
construction





Friction,





friction, and





wear are





possible


Buckle
A buckle plate can
Very fast
Must stay
S. Hirata et al,


plate
be used to change
movement
within elastic
“An Ink-jet



a slow actuator
achievable
limits of the
Head Using



into a fast motion.

materials for
Diaphragm



It can also convert

long device life
Microactuator”,



a high force, low

High stresses
Proc. IEEE



travel actuator into

involved
MEMS, February



a high travel,

Generally
1996, pp 418-423.



medium force

high power
IJ18, IJ27



motion.

requirement


Tapered
A tapered
Linearizes the
Complex
IJ14


magnetic
magnetic pole can
magnetic
construction


pole
increase travel at
force/distance



the expense of
curve



force.


Lever
A lever and
Matches low
High stress
IJ32, IJ36,



fulcrum is used to
travel actuator
around the
IJ37



transform a motion
with higher
fulcrum



with small travel
travel



and high force into
requirements



a motion with
Fulcrum area



longer travel and
has no linear



lower force. The
movement, and



lever can also
can be used for a



reverse the
fluid seal



direction of travel.


Rotary
The actuator is
High
Complex
IJ28


impeller
connected to a
mechanical
construction



rotary impeller. A
advantage
Unsuitable for



small angular
The ratio of
pigmented inks



deflection of the
force to travel of



actuator results in
the actuator can



a rotation of the
be matched to



impeller vanes,
the nozzle



which push the ink
requirements by



against stationary
varying the



vanes and out of
number of



the nozzle.
impeller vanes


Acoustic
A refractive or
No moving
Large area
1993


lens
diffractive (e.g.
parts
required
Hadimioglu et



zone plate)

Only relevant
al, EUP 550,192



acoustic lens is

for acoustic ink
1993 Elrod et



used to concentrate

jets
al, EUP 572,220



sound waves.


Sharp
A sharp point is
Simple
Difficult to
Tone-jet


conductive
used to concentrate
construction
fabricate using


point
an electrostatic

standard VLSI



field.

processes for a





surface ejecting





ink-jet





Only relevant





for electrostatic





ink jets



















ACTUATOR MOTION












Description
Advantages
Disadvantages
Examples















Volume
The volume of the
Simple
High energy is
Hewlett-


expansion
actuator changes,
construction in
typically
Packard Thermal



pushing the ink in
the case of
required to
Ink jet



all directions.
thermal ink jet
achieve volume
Canon





expansion. This
Bubblejet





leads to thermal





stress, cavitation,





and kogation in





thermal ink jet





implementations


Linear,
The actuator
Efficient
High
IJ01, IJ02,


normal to
moves in a
coupling to ink
fabrication
IJ04, IJ07, IJ11,


chip
direction normal to
drops ejected
complexity may
IJ14


surface
the print head
normal to the
be required to



surface. The
surface
achieve



nozzle is typically

perpendicular



in the line of

motion



movement.


Parallel to
The actuator
Suitable for
Fabrication
IJ12, IJ13,


chip
moves parallel to
planar
complexity
IJ15, IJ33,, IJ34,


surface
the print head
fabrication
Friction
IJ35, IJ36



surface. Drop

Stiction



ejection may still



be normal to the



surface.


Membrane
An actuator with a
The effective
Fabrication
1982 Howkins


push
high force but
area of the
complexity
U.S. Pat. No. 4,459,601



small area is used
actuator
Actuator size



to push a stiff
becomes the
Difficulty of



membrane that is
membrane area
integration in a



in contact with the

VLSI process



ink.


Rotary
The actuator
Rotary levers
Device
IJ05, IJ08,



causes the rotation
may be used to
complexity
IJ13, IJ28



of some element,
increase travel
May have



such a grill or
Small chip
friction at a pivot



impeller
area
point




requirements


Bend
The actuator bends
A very small
Requires the
1970 Kyser et



when energized.
change in
actuator to be
al U.S. Pat. No.



This may be due to
dimensions can
made from at
3,946,398



differential
be converted to a
least two distinct
1973 Stemme



thermal expansion,
large motion.
layers, or to have
U.S. Pat. No. 3,747,120



piezoelectric

a thermal
IJ03, IJ09,



expansion,

difference across
IJ10, IJ19, IJ23,



magnetostriction,

the actuator
IJ24, IJ25, IJ29,



or other form of


IJ30, IJ31, IJ33,



relative


IJ34, IJ35



dimensional



change.


Swivel
The actuator
Allows
Inefficient
IJ06



swivels around a
operation where
coupling to the



central pivot. This
the net linear
ink motion



motion is suitable
force on the



where there are
paddle is zero



opposite forces
Small chip



applied to opposite
area



sides of the paddle,
requirements



e.g. Lorenz force.


Straighten
The actuator is
Can be used
Requires
IJ26, IJ32



normally bent, and
with shape
careful balance



straightens when
memory alloys
of stresses to



energized.
where the
ensure that the




austenic phase is
quiescent bend is




planar
accurate


Double
The actuator bends
One actuator
Difficult to
IJ36, IJ37,


bend
in one direction
can be used to
make the drops
IJ38



when one element
power two
ejected by both



is energized, and
nozzles.
bend directions



bends the other
Reduced chip
identical.



way when another
size.
A small



element is
Not sensitive
efficiency loss



energized.
to ambient
compared to




temperature
equivalent single





bend actuators.


Shear
Energizing the
Can increase
Not readily
1985 Fishbeck



actuator causes a
the effective
applicable to
U.S. Pat. No. 4,584,590



shear motion in the
travel of
other actuator



actuator material.
piezoelectric
mechanisms




actuators


Radial
The actuator
Relatively
High force
1970 Zoltan


constriction
squeezes an ink
easy to fabricate
required
U.S. Pat. No. 3,683,212



reservoir, forcing
single nozzles
Inefficient



ink from a
from glass
Difficult to



constricted nozzle.
tubing as
integrate with




macroscopic
VLSI processes




structures


Coil/
A coiled actuator
Easy to
Difficult to
IJ17, IJ21,


uncoil
uncoils or coils
fabricate as a
fabricate for
IJ34, IJ35



more tightly. The
planar VLSI
non-planar



motion of the free
process
devices



end of the actuator
Small area
Poor out-of-



ejects the ink.
required,
plane stiffness




therefore low




cost


Bow
The actuator bows
Can increase
Maximum
IJ16, IJ18,



(or buckles) in the
the speed of
travel is
IJ27



middle when
travel
constrained



energized.
Mechanically
High force




rigid
required


Push-Pull
Two actuators
The structure
Not readily
IJ18



control a shutter.
is pinned at both
suitable for ink



One actuator pulls
ends, so has a
jets which



the shutter, and the
high out-of-
directly push the



other pushes it.
plane rigidity
ink


Curl
A set of actuators
Good fluid
Design
IJ20, IJ42


inwards
curl inwards to
flow to the
complexity



reduce the volume
region behind



of ink that they
the actuator



enclose.
increases




efficiency


Curl
A set of actuators
Relatively
Relatively
IJ43


outwards
curl outwards,
simple
large chip area



pressurizing ink in
construction



a chamber



surrounding the



actuators, and



expelling ink from



a nozzle in the



chamber.


Iris
Multiple vanes
High
High
IJ22



enclose a volume
efficiency
fabrication



of ink. These
Small chip
complexity



simultaneously
area
Not suitable



rotate, reducing

for pigmented



the volume

inks



between the vanes.


Acoustic
The actuator
The actuator
Large area
1993


vibration
vibrates at a high
can be
required for
Hadimioglu et



frequency.
physically
efficient
al, EUP 550,192




distant from the
operation at
1993 Elrod et




ink
useful
al, EUP 572,220





frequencies





Acoustic





coupling and





crosstalk





Complex





drive circuitry





Poor control





of drop volume





and position


None
In various ink jet
No moving
Various other
Silverbrook,



designs the
parts
tradeoffs are
EP 0771 658 A2



actuator does not

required to
and related



move.

eliminate
patent





moving parts
applications






Tone-jet



















NOZZLE REFILL METHOD












Description
Advantages
Disadvantages
Examples















Surface
This is the normal
Fabrication
Low speed
Thermal ink


tension
way that ink jets
simplicity
Surface
jet



are refilled. After
Operational
tension force
Piezoelectric



the actuator is
simplicity
relatively small
ink jet



energized, it

compared to
IJ01-IJ07,



typically returns

actuator force
IJ10-IJ14, IJ16,



rapidly to its

Long refill
IJ20, IJ22-IJ45



normal position.

time usually



This rapid return

dominates the



sucks in air

total repetition



through the nozzle

rate



opening. The ink



surface tension at



the nozzle then



exerts a small



force restoring the



meniscus to a



minimum area.



This force refills



the nozzle.


Shuttered
Ink to the nozzle
High speed
Requires
IJ08, IJ13,


oscillating
chamber is
Low actuator
common ink
IJ15, IJ17, IJ18,


ink
provided at a
energy, as the
pressure
IJ19, IJ21


pressure
pressure that
actuator need
oscillator



oscillates at twice
only open or
May not be



the drop ejection
close the shutter,
suitable for



frequency. When a
instead of
pigmented inks



drop is to be
ejecting the ink



ejected, the shutter
drop



is opened for 3



half cycles: drop



ejection, actuator



return, and refill.



The shutter is then



closed to prevent



the nozzle



chamber emptying



during the next



negative pressure



cycle.


Refill
After the main
High speed, as
Requires two
IJ09


actuator
actuator has
the nozzle is
independent



ejected a drop a
actively refilled
actuators per



second (refill)

nozzle



actuator is



energized. The



refill actuator



pushes ink into the



nozzle chamber.



The refill actuator



returns slowly, to



prevent its return



from emptying the



chamber again.


Positive
The ink is held a
High refill
Surface spill
Silverbrook,


ink
slight positive
rate, therefore a
must be
EP 0771 658 A2


pressure
pressure. After the
high drop
prevented
and related



ink drop is ejected,
repetition rate is
Highly
patent



the nozzle
possible
hydrophobic
applications



chamber fills

print head
Alternative



quickly as surface

surfaces are
for:, IJ01-IJ07,



tension and ink

required
IJ10-IJ14, IJ16,



pressure both


IJ20, IJ22-IJ45



operate to refill the



nozzle.



















METHOD OF RESTRICTING BACK-FLOW THROUGH INLET












Description
Advantages
Disadvantages
Examples















Long inlet
The ink inlet
Design
Restricts refill
Thermal ink


channel
channel to the
simplicity
rate
jet



nozzle chamber is
Operational
May result in
Piezoelectric



made long and
simplicity
a relatively large
ink jet



relatively narrow,
Reduces
chip area
IJ42, IJ43



relying on viscous
crosstalk
Only partially



drag to reduce

effective



inlet back-flow.


Positive
The ink is under a
Drop selection
Requires a
Silverbrook,


ink
positive pressure,
and separation
method (such as
EP 0771 658 A2


pressure
so that in the
forces can be
a nozzle rim or
and related



quiescent state
reduced
effective
patent



some of the ink
Fast refill time
hydrophobizing,
applications



drop already

or both) to
Possible



protrudes from the

prevent flooding
operation of the



nozzle.

of the ejection
following: IJ01-IJ07,



This reduces the

surface of the
IJ09-IJ12,



pressure in the

print head.
IJ14, IJ16, IJ20,



nozzle chamber


IJ22,, IJ23-IJ34,



which is required


IJ36-IJ41, IJ44



to eject a certain



volume of ink. The



reduction in



chamber pressure



results in a



reduction in ink



pushed out through



the inlet.


Baffle
One or more
The refill rate
Design
HP Thermal



baffles are placed
is not as
complexity
Ink Jet



in the inlet ink
restricted as the
May increase
Tektronix



flow. When the
long inlet
fabrication
piezoelectric ink



actuator is
method.
complexity (e.g.
jet



energized, the
Reduces
Tektronix hot



rapid ink
crosstalk
melt



movement creates

Piezoelectric



eddies which

print heads).



restrict the flow



through the inlet.



The slower refill



process is



unrestricted, and



does not result in



eddies.


Flexible
In this method
Significantly
Not applicable
Canon


flap
recently disclosed
reduces back-
to most ink jet


restricts
by Canon, the
flow for edge-
configurations


inlet
expanding actuator
shooter thermal
Increased



(bubble) pushes on
ink jet devices
fabrication



a flexible flap that

complexity



restricts the inlet.

Inelastic





deformation of





polymer flap





results in creep





over extended





use


Inlet filter
A filter is located
Additional
Restricts refill
IJ04, IJ12,



between the ink
advantage of ink
rate
IJ24, IJ27, IJ29,



inlet and the
filtration
May result in
IJ30



nozzle chamber.
Ink filter may
complex



The filter has a
be fabricated
construction



multitude of small
with no



holes or slots,
additional



restricting ink
process steps



flow. The filter



also removes



particles which



may block the



nozzle.


Small
The ink inlet
Design
Restricts refill
IJ02, IJ37,


inlet
channel to the
simplicity
rate
IJ44


compared
nozzle chamber

May result in


to nozzle
has a substantially

a relatively large



smaller cross

chip area



section than that of

Only partially



the nozzle,

effective



resulting in easier



ink egress out of



the nozzle than out



of the inlet.


Inlet
A secondary
Increases
Requires
IJ09


shutter
actuator controls
speed of the ink-
separate refill



the position of a
jet print head
actuator and



shutter, closing off
operation
drive circuit



the ink inlet when



the main actuator



is energized.


The inlet
The method avoids
Back-flow
Requires
IJ01, IJ03,


is located
the problem of
problem is
careful design to
IJ05, IJ06, IJ07,


behind
inlet back-flow by
eliminated
minimize the
IJ10, IJ11, IJ14,


the ink-
arranging the ink-

negative
IJ16, IJ22, IJ23,


pushing
pushing surface of

pressure behind
IJ25, IJ28, IJ31,


surface
the actuator

the paddle
IJ32, IJ33, IJ34,



between the inlet


IJ35, IJ36, IJ39,



and the nozzle.


IJ40, IJ41


Part of
The actuator and a
Significant
Small increase
IJ07, IJ20,


the
wall of the ink
reductions in
in fabrication
IJ26, IJ38


actuator
chamber are
back-flow can be
complexity


moves to
arranged so that
achieved


shut off
the motion of the
Compact


the inlet
actuator closes off
designs possible



the inlet.


Nozzle
In some
Ink back-flow
None related
Silverbrook,


actuator
configurations of
problem is
to ink back-flow
EP 0771 658 A2


does not
ink jet, there is no
eliminated
on actuation
and related


result in
expansion or


patent


ink back-
movement of an


applications


flow
actuator which


Valve-jet



may cause ink


Tone-jet



back-flow through



the inlet.



















NOZZLE CLEARING METHOD












Description
Advantages
Disadvantages
Examples















Normal
All of the nozzles
No added
May not be
Most ink jet


nozzle
are fired
complexity on
sufficient to
systems


firing
periodically,
the print head
displace dried
IJ01, IJ02,



before the ink has

ink
IJ03, IJ04, IJ05,



a chance to dry.


IJ06, IJ07, IJ09,



When not in use


IJ10, IJ11, IJ12,



the nozzles are


IJ14, IJ16, IJ20,



sealed (capped)


IJ22, IJ23, IJ24,



against air.


IJ25, IJ26, IJ27,



The nozzle firing


IJ28, IJ29, IJ30,



is usually


IJ31, IJ32, IJ33,



performed during a


IJ34, IJ36, IJ37,



special clearing


IJ38, IJ39, IJ40,,



cycle, after first


IJ41, IJ42, IJ43,



moving the print


IJ44,, IJ45



head to a cleaning



station.


Extra
In systems which
Can be highly
Requires
Silverbrook,


power to
heat the ink, but do
effective if the
higher drive
EP 0771 658 A2


ink heater
not boil it under
heater is
voltage for
and related



normal situations,
adjacent to the
clearing
patent



nozzle clearing can
nozzle
May require
applications



be achieved by

larger drive



over-powering the

transistors



heater and boiling



ink at the nozzle.


Rapid
The actuator is
Does not
Effectiveness
May be used


succession
fired in rapid
require extra
depends
with: IJ01, IJ02,


of
succession. In
drive circuits on
substantially
IJ03, IJ04, IJ05,


actuator
some
the print head
upon the
IJ06, IJ07, IJ09,


pulses
configurations, this
Can be readily
configuration of
IJ10, IJ11, IJ14,



may cause heat
controlled and
the ink jet nozzle
IJ16, IJ20, IJ22,



build-up at the
initiated by

IJ23, IJ24, IJ25,



nozzle which boils
digital logic

IJ27, IJ28, IJ29,



the ink, clearing


IJ30, IJ31, IJ32,



the nozzle. In other


IJ33, IJ34, IJ36,



situations, it may


IJ37, IJ38, IJ39,



cause sufficient


IJ40, IJ41, IJ42,



vibrations to


IJ43, IJ44, IJ45



dislodge clogged



nozzles.


Extra
Where an actuator
A simple
Not suitable
May be used


power to
is not normally
solution where
where there is a
with: IJ03, IJ09,


ink
driven to the limit
applicable
hard limit to
IJ16, IJ20, IJ23,


pushing
of its motion,

actuator
IJ24, IJ25, IJ27,


actuator
nozzle clearing

movement
IJ29, IJ30, IJ31,



may be assisted by


IJ32, IJ39, IJ40,



providing an


IJ41, IJ42, IJ43,



enhanced drive


IJ44, IJ45



signal to the



actuator.


Acoustic
An ultrasonic
A high nozzle
High
IJ08, IJ13,


resonance
wave is applied to
clearing
implementation
IJ15, IJ17, IJ18,



the ink chamber.
capability can be
cost if system
IJ19, IJ21



This wave is of an
achieved
does not already



appropriate
May be
include an



amplitude and
implemented at
acoustic actuator



frequency to cause
very low cost in



sufficient force at
systems which



the nozzle to clear
already include



blockages. This is
acoustic



easiest to achieve
actuators



if the ultrasonic



wave is at a



resonant frequency



of the ink cavity.


Nozzle
A microfabricated
Can clear
Accurate
Silverbrook,


clearing
plate is pushed
severely clogged
mechanical
EP 0771 658 A2


plate
against the
nozzles
alignment is
and related



nozzles. The plate

required
patent



has a post for

Moving parts
applications



every nozzle. A

are required



post moves

There is risk



through each

of damage to the



nozzle, displacing

nozzles



dried ink.

Accurate





fabrication is





required


Ink
The pressure of the
May be
Requires
May be used


pressure
ink is temporarily
effective where
pressure pump
with all IJ series


pulse
increased so that
other methods
or other pressure
ink jets



ink streams from
cannot be used
actuator



all of the nozzles.

Expensive



This may be used

Wasteful of



in conjunction

ink



with actuator



energizing.


Print
A flexible ‘blade’
Effective for
Difficult to
Many ink jet


head
is wiped across the
planar print head
use if print head
systems


wiper
print head surface.
surfaces
surface is non-



The blade is
Low cost
planar or very



usually fabricated

fragile



from a flexible

Requires



polymer, e.g.

mechanical parts



rubber or synthetic

Blade can



elastomer.

wear out in high





volume print





systems


Separate
A separate heater
Can be
Fabrication
Can be used


ink
is provided at the
effective where
complexity
with many IJ


boiling
nozzle although
other nozzle

series ink jets


heater
the normal drop e-
clearing methods



ection mechanism
cannot be used



does not require it.
Can be



The heaters do not
implemented at



require individual
no additional



drive circuits, as
cost in some ink



many nozzles can
jet



be cleared
configurations



simultaneously,



and no imaging is



required.



















NOZZLE PLATE CONSTRUCTION












Description
Advantages
Disadvantages
Examples















Electroformed
A nozzle plate is
Fabrication
High
Hewlett


nickel
separately
simplicity
temperatures and
Packard Thermal



fabricated from

pressures are
Ink jet



electroformed

required to bond



nickel, and bonded

nozzle plate



to the print head

Minimum



chip.

thickness





constraints





Differential





thermal





expansion


Laser
Individual nozzle
No masks
Each hole
Canon


ablated or
holes are ablated
required
must be
Bubblejet


drilled
by an intense UV
Can be quite
individually
1988 Sercel et


polymer
laser in a nozzle
fast
formed
al., SPIE, Vol.



plate, which is
Some control
Special
998 Excimer



typically a
over nozzle
equipment
Beam



polymer such as
profile is
required
Applications, pp.



polyimide or
possible
Slow where
76-83



polysulphone
Equipment
there are many
1993




required is
thousands of
Watanabe et al.,




relatively low
nozzles per print
U.S. Pat. No. 5,208,604




cost
head





May produce





thin burrs at exit





holes


Silicon
A separate nozzle
High accuracy
Two part
K. Bean,


micromachined
plate is
is attainable
construction
IEEE



micromachined

High cost
Transactions on



from single crystal

Requires
Electron



silicon, and

precision
Devices, Vol.



bonded to the print

alignment
ED-25, No. 10,



head wafer.

Nozzles may
1978, pp 1185-1195





be clogged by
Xerox 1990





adhesive
Hawkins et al.,






U.S. Pat. No. 4,899,181


Glass
Fine glass
No expensive
Very small
1970 Zoltan


capillaries
capillaries are
equipment
nozzle sizes are
U.S. Pat. No. 3,683,212



drawn from glass
required
difficult to form



tubing. This
Simple to
Not suited for



method has been
make single
mass production



used for making
nozzles



individual nozzles,



but is difficult to



use for bulk



manufacturing of



print heads with



thousands of



nozzles.


Monolithic,
The nozzle plate is
High accuracy
Requires
Silverbrook,


surface
deposited as a
(<1 μm)
sacrificial layer
EP 0771 658 A2


micromachined
layer using
Monolithic
under the nozzle
and related


using
standard VLSI
Low cost
plate to form the
patent


VLSI
deposition
Existing
nozzle chamber
applications


litho-
techniques.
processes can be
Surface may
IJ01, IJ02,


graphic
Nozzles are etched
used
be fragile to the
IJ04, IJ11, IJ12,


processes
in the nozzle plate

touch
IJ17, IJ18, IJ20,



using VLSI


IJ22, IJ24, IJ27,



lithography and


IJ28, IJ29, IJ30,



etching.


IJ31, IJ32, IJ33,






IJ34, IJ36, IJ37,






IJ38, IJ39, IJ40,






IJ41, IJ42, IJ43,






IJ44


Monolithic,
The nozzle plate is
High accuracy
Requires long
IJ03, IJ05,


etched
a buried etch stop
(<1 μm)
etch times
IJ06, IJ07, IJ08,


through
in the wafer.
Monolithic
Requires a
IJ09, IJ10, IJ13,


substrate
Nozzle chambers
Low cost
support wafer
IJ14, IJ15, IJ16,



are etched in the
No differential

IJ19, IJ21, IJ23,



front of the wafer,
expansion

IJ25, IJ26



and the wafer is



thinned from the



back side. Nozzles



are then etched in



the etch stop layer.


No nozzle
Various methods
No nozzles to
Difficult to
Ricoh 1995


plate
have been tried to
become clogged
control drop
Sekiya et al U.S. Pat. No.



eliminate the

position
5,412,413



nozzles entirely, to

accurately
1993



prevent nozzle

Crosstalk
Hadimioglu et al



clogging. These

problems
EUP 550,192



include thermal


1993 Elrod et



bubble


al EUP 572,220



mechanisms and



acoustic lens



mechanisms


Trough
Each drop ejector
Reduced
Drop firing
IJ35



has a trough
manufacturing
direction is



through which a
complexity
sensitive to



paddle moves.
Monolithic
wicking.



There is no nozzle



plate.


Nozzle slit
The elimination of
No nozzles to
Difficult to
1989 Saito et


instead of
nozzle holes and
become clogged
control drop
al U.S. Pat. No.


individual
replacement by a

position
4,799,068


nozzles
slit encompassing

accurately



many actuator

Crosstalk



positions reduces

problems



nozzle clogging,



but increases



crosstalk due to



ink surface waves



















DROP EJECTION DIRECTION












Description
Advantages
Disadvantages
Examples















Edge
Ink flow is along
Simple
Nozzles
Canon


(‘edge
the surface of the
construction
limited to edge
Bubblejet 1979


shooter’)
chip, and ink drops
No silicon
High
Endo et al GB



are ejected from
etching required
resolution is
patent 2,007,162



the chip edge.
Good heat
difficult
Xerox heater-




sinking via
Fast color
in-pit 1990




substrate
printing requires
Hawkins et al




Mechanically
one print head
U.S. Pat. No. 4,899,181




strong
per color
Tone-jet




Ease of chip




handing


Surface
Ink flow is along
No bulk
Maximum ink
Hewlett-


(‘roof
the surface of the
silicon etching
flow is severely
Packard TIJ


shooter’)
chip, and ink drops
required
restricted
1982 Vaught et



are ejected from
Silicon can

al U.S. Pat. No.



the chip surface,
make an

4,490,728



normal to the
effective heat

IJ02, IJ11,



plane of the chip.
sink

IJ12, IJ20, IJ22




Mechanical




strength


Through
Ink flow is through
High ink flow
Requires bulk
Silverbrook,


chip,
the chip, and ink
Suitable for
silicon etching
EP 0771 658 A2


forward
drops are ejected
pagewidth print

and related


(‘up
from the front
heads

patent


shooter’)
surface of the chip.
High nozzle

applications




packing density

IJ04, IJ17,




therefore low

IJ18, IJ24, IJ27-IJ45




manufacturing




cost


Through
Ink flow is through
High ink flow
Requires
IJ01, IJ03,


chip,
the chip, and ink
Suitable for
wafer thinning
IJ05, IJ06, IJ07,


reverse
drops are ejected
pagewidth print
Requires
IJ08, IJ09, IJ10,


(‘down
from the rear
heads
special handling
IJ13, IJ14, IJ15,


shooter’)
surface of the chip.
High nozzle
during
IJ16, IJ19, IJ21,




packing density
manufacture
IJ23, IJ25, IJ26




therefore low




manufacturing




cost


Through
Ink flow is through
Suitable for
Pagewidth
Epson Stylus


actuator
the actuator, which
piezoelectric
print heads
Tektronix hot



is not fabricated as
print heads
require several
melt



part of the same

thousand
piezoelectric ink



substrate as the

connections to
jets



drive transistors.

drive circuits





Cannot be





manufactured in





standard CMOS





fabs





Complex





assembly





required



















INK TYPE












Description
Advantages
Disadvantages
Examples















Aqueous,
Water based ink
Environmentally
Slow drying
Most existing


dye
which typically
friendly
Corrosive
ink jets



contains: water,
No odor
Bleeds on
All IJ series



dye, surfactant,

paper
ink jets



humectant, and

May
Silverbrook,



biocide.

strikethrough
EP 0771 658 A2



Modern ink dyes

Cockles paper
and related



have high water-


patent



fastness, light


applications



fastness


Aqueous,
Water based ink
Environmentally
Slow drying
IJ02, IJ04,


pigment
which typically
friendly
Corrosive
IJ21, IJ26, IJ27,



contains: water,
No odor
Pigment may
IJ30



pigment,
Reduced bleed
clog nozzles
Silverbrook,



surfactant,
Reduced
Pigment may
EP 0771 658 A2



humectant, and
wicking
clog actuator
and related



biocide.
Reduced
mechanisms
patent



Pigments have an
strikethrough
Cockles paper
applications



advantage in


Piezoelectric



reduced bleed,


ink-jets



wicking and


Thermal ink



strikethrough.


jets (with






significant






restrictions)


Methyl
MEK is a highly
Very fast
Odorous
All IJ series


Ethyl
volatile solvent
drying
Flammable
ink jets


Ketone
used for industrial
Prints on


(MEK)
printing on
various



difficult surfaces
substrates such



such as aluminum
as metals and



cans.
plastics


Alcohol
Alcohol based inks
Fast drying
Slight odor
All IJ series


(ethanol,
can be used where
Operates at
Flammable
ink jets


2-butanol,
the printer must
sub-freezing


and
operate at
temperatures


others)
temperatures
Reduced



below the freezing
paper cockle



point of water. An
Low cost



example of this is



in-camera



consumer



photographic



printing.


Phase
The ink is solid at
No drying
High viscosity
Tektronix hot


change
room temperature,
time-ink
Printed ink
melt


(hot melt)
and is melted in
instantly freezes
typically has a
piezoelectric ink



the print head
on the print
‘waxy’ feel
jets



before jetting. Hot
medium
Printed pages
1989 Nowak



melt inks are
Almost any
may ‘block’
U.S. Pat. No. 4,820,346



usually wax based,
print medium
Ink
All IJ series



with a melting
can be used
temperature may
ink jets



point around 80° C.
No paper
be above the



After jetting
cockle occurs
curie point of



the ink freezes
No wicking
permanent



almost instantly
occurs
magnets



upon contacting
No bleed
Ink heaters



the print medium
occurs
consume power



or a transfer roller.
No
Long warm-




strikethrough
up time




occurs


Oil
Oil based inks are
High
High
All IJ series



extensively used in
solubility
viscosity: this is
ink jets



offset printing.
medium for
a significant



They have
some dyes
limitation for use



advantages in
Does not
in ink jets, which



improved
cockle paper
usually require a



characteristics on
Does not wick
low viscosity.



paper (especially
through paper
Some short



no wicking or

chain and multi-



cockle). Oil

branched oils



soluble dies and

have a



pigments are

sufficiently low



required.

viscosity.





Slow drying


Microemulsion
A microemulsion
Stops ink
Viscosity
All IJ series



is a stable, self
bleed
higher than
ink jets



forming emulsion
High dye
water



of oil, water, and
solubility
Cost is



surfactant. The
Water, oil,
slightly higher



characteristic drop
and amphiphilic
than water based



size is less than
soluble dies can
ink



100 nm, and is
be used
High



determined by the
Can stabilize
surfactant



preferred curvature
pigment
concentration



of the surfactant.
suspensions
required (around





5%)

## Claims

1. A unit cell of a printhead, the unit cell comprising:
a multi-layer substrate defining an ink inlet;
one or more side walls extending from the substrate around the ink inlet;
a nozzle plate supported by the side walls to define a chamber in fluid communication with the ink inlet, the nozzle plate defining an aperture through which ink in the chamber can be ejected; and
a looped and elongate heater element suspended within the chamber, and which can be heated so that bubbles are generated in ink within the chamber and ink is ejected from the aperture,
wherein the nozzle plate defines a protruding rim bounding the aperture.

2. A unit cell as claimed in claim 1, wherein the heater element is configured so that the bubbles merge to form a single elongate bubble extending transverse to the side walls.

3. A unit cell as claimed in claim 1, wherein the nozzle plate further defines a well in which the rim is located.

4. A unit cell as claimed in claim 3, wherein the well has an endless wall surrounding the rim that is corrugated.