# Patent

## Title
Inkjet printhead having isolated nozzles

## Abstract

A printhead suitable for minimizing cross-contamination between nozzles is provided. The printhead comprises a substrate, which includes a plurality of nozzles for ejecting ink droplets onto a print medium. Each nozzle has a nozzle aperture, which is defined in an ink ejection surface of the substrate. The printhead also comprises a plurality of formations on the ink ejection surface. The surface formations are configured to isolate each nozzle from at least one adjacent nozzle, and typically take the form of enclosures surrounding each nozzle.

## Background
CO-PENDING APPLICATIONS
The following applications have been filed by the Applicant simultaneously with the present application:
















11/084237
11/084240










The disclosures of these co-pending applications 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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Some applications have been listed by docket numbers. These will be replaced when application numbers are known.

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 inkjet 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 ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, 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 ink jet 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.
A problem with inkjet printheads, and especially inkjet printheads having a high nozzle density, is that ink can flood across the printhead surface contaminating adjacent nozzles. This is undesirable because it results in reduced print quality. Moreover, cross-contamination of ink across the printhead surface can potentially result in electrolysis and accelerated corrosion of nozzle actuators.
Previous attempts to minimize ink flooding across the printhead surface typically involve coating the printhead with a hydrophobic material. However, hydrophobic coatings have only had limited success in minimizing the extent of flooding.
A further problem with inkjet printheads, especially inkjet printheads having senstitive MEMS nozzles formed on an ink ejection surface of the printhead, is that the nozzle structures can become damaged by cleaning the printhead surface. Typically, printheads are wiped regularly to remove particles of paper dust or paper fibers, which build up on the ink ejection surface. When a wiping mechanism comes into contact with nozzle structures on the printhead surface, there is an obvious risk of damaging the nozzles.
It would be desirable to provide a printhead, which minimizes cross-contamination by ink flooding between adjacent nozzles. It would be further desirable to provide a printhead, which allows regular cleaning of the printhead surface by a wiping mechanism without risk of damaging nozzle structures on the printhead.
SUMMARY OF THE INVENTION
In a first aspect, there is provided a printhead comprising:
a substrate including a plurality of nozzles for ejecting ink droplets onto a print medium, each nozzle having a nozzle aperture defined in an ink ejection surface of the substrate; and
a plurality of formations on the ink ejection surface, the surface formations being configured to isolate each nozzle from at least one adjacent nozzle.
In a second aspect, there is provided a method of operating a printhead, whilst minimizing cross-contamination of ink between adjacent nozzles, the method comprising the steps of:
(a) providing a printhead comprising:
a substrate including a plurality of nozzles for ejecting ink droplets onto a print medium, each nozzles having a nozzle aperture defined in an ink ejection surface of the substrate; and
a plurality of formations on the ink ejection surface, the surface formations being configured to isolate each nozzle from at least one adjacent nozzle; and
(b) printing onto a print medium using said printhead.
In a third aspect, there is provided a method of fabricating a printhead having isolated nozzles, the method comprising the steps of:
(a) providing a substrate, the substrate including a plurality of nozzles for ejecting ink droplets onto a print medium, each nozzle having a nozzle aperture defined in an ink ejection surface of the substrate;
(b) depositing a layer of photoresist over the ink ejection surface;
(c) defining recesses in the photoresist, each recess revealing a portion of the ink ejection surface surrounding a respective nozzle aperture;
(d) depositing a roof material over the photoresist and into the recesses;
(e) etching the roof material to define a nozzle enclosure around each nozzle aperture, each nozzle enclosure having an opening defined in a roof and sidewalls extending from the roof to the ink ejection surface; and
(f) removing the photoresist.
Optionally, the formations have a hydrophobic surface. Inkjet inks are typically aqueous-based inks and hydrophobic formations will repel any flooded ink. Hence, hydrophobic formations minimize as far as possible any cross-contamination of ink by acting as a physical barrier and by intermolecular repulsive forces. Moreover, hydrophobic formations promote ingestion of any flooded ink back into respective nozzle chambers and ink supply channels. Since nozzle chambers are typically hydrophilic, ink will tend to be drawn back into the nozzle and away from a surrounding hydrophobic formation.
Optionally, the formations are arranged in a plurality of nozzle enclosures, each nozzle enclosure comprising sidewalls surrounding a respective nozzle, the sidewalls forming a seal with the ink ejection surface. Hence, each nozzle is isolated from its adjacent nozzles by a nozzle enclosure.
Optionally, each nozzle enclosure further comprises a roof spaced apart from the respective nozzle, the roof having a roof opening aligned with a respective nozzle opening for allowing ejected ink droplets to pass therethrough onto the print medium. Hence, each nozzle enclosure may typically take the form of a cap, which covers or encapsulates an individual nozzle on the ink ejection surface. The roof not only provides additional containment of any flooded ink, it also provides further protection of each nozzle from, for example, the potentially damaging effects of paper dust, paper fibers or wiping.
Typically, the sidewalls extend from a perimeter region of each roof to the ink ejection surface. Sidewalls of adjacent nozzle enclosures are usually spaced apart across the ink ejection surface.
Optionally, the printhead is an inkjet printhead, such as a pagewidth inkjet printhead. Optionally, the printhead has a nozzle density, which is sufficient to print at up to 1600 dpi. The present invention is particularly beneficial for printheads having a high nozzle density, because high density printheads are especially prone to flooding between adjacent nozzles.



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.
FIGS. 7 to 20 are schematic perspective views of the unit cell shown in FIG. 6, at various successive stages in the fabrication process of the printhead.



DESCRIPTION OF OPTIONAL EMBODIMENTS
Bubble Forming Heater Element Actuator
With reference to FIGS. 1 to 4, the unit cell 1 of one of the Applicant's printheads is shown. The unit cell 1 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.
Advantages of Nozzle Enclosures
Referring to FIG. 6, an embodiment of the unit cell 1 according to the invention is shown. The aperture 5 is surrounded by a nozzle enclosure 60, which isolates adjacent apertures on the printhead. The nozzle enclosure 60 has a roof 61 and sidewalls 62, which extend from the roof to the nozzle plate 2 and form a seal therewith. An opening 63 is defined in the roof 61, which allows ink droplets (not shown) to pass through the nozzle enclosure and onto a print medium (not shown).
The nozzle enclosure 60 minimize cross-contamination between adjacent apertures 5 by containing any flooded ink in the immediate vicinity of each nozzle. Flooding of ink from each nozzle may be caused by a variety of reasons, such as nozzle misfires or pressure fluctuations in ink supply channels. The nozzle enclosure may be formed from or coated with a hydrophobic material during the fabrication process, which further minimizes the risk of cross-contamination.
A further advantage of the printhead according to the invention is that it allows the nozzle plate 2 of the printhead to be wiped without risk of damaging the sensitive nozzle structures. Typically, inkjet printheads are cleaned by a wiping mechanism as part of a warm-up cycle. The nozzle enclosures 60 provide a protective barrier between the nozzles and the wiping mechanism (not shown).
Fabrication Process
In the interests of brevity, the fabrication stages have been shown for the unit cell of FIG. 6 only (see FIGS. 7 to 20). It will be appreciated that the other unit cells will use the same fabrication stages with different masking.
Referring to FIG. 7, 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. 7. 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. 8, 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. 9 shows the unit cell after etching the front ink hole 52 and removal of the photoresist 51.
Referring to FIG. 10, 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. 10). 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. 11, 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. 12, 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. 13, 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. 14, 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. 15, 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. 16, 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.
Referring to FIG. 17, in the next stage a third sacrificial scaffold 64 is deposited over the roof 44. The third sacrificial scaffold 64 is exposed and developed to define sidewalls for the cylindrical nozzle enclosure over each aperture 5. The third sacrificial scaffold 64 is also UV cured and hardbaked to prevent any reflow of the photoresist during subsequent high-temperature deposition of the nozzle enclosure material.
Referring to FIG. 18, silicon nitride is deposited onto the third sacrificial scaffold 64 by plasma enhanced chemical vapour deposition. The silicon nitride forms an enclosure roof 61 over each aperture 5. Enclosure sidewalls 62 are also formed by deposition of silicon nitride. Whilst silicon nitride is deposited in the embodiment shown, the enclosure roof 61 may equally be formed from silicon oxide, silicon oxynitride etc. Optionally, a layer of hydrophobic material (e.g. fluoropolymer) is deposited onto the enclosure roof 61 after deposition. This extra deposition step may be performed at any stage after deposition (e.g. after etching or after ashing).
Referring to FIG. 19, the nozzle enclosure 60 is formed by etching through the enclosure roof layer 61. The enclosure opening 63 is defined by this etch. In addition, the enclosure roof material which is located outside the enclosure sidewalls 62 is removed. The etch pattern is defined by standard photoresist masking.
With the nozzle structure, including nozzle enclosure 60, 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. 20, after formation of the ink supply channel 32, the first, second and 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 and the nozzle enclosure opening 63.
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.
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. However presently popular ink jet printing technologies are unlikely to be suitable.
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 Drop-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 ink jet 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)
Drop ejection direction (5 types)
Ink type (7 types)
The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet 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.
















Description
Advantages
Disadvantages
Examples
















ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS)











Thermal
An electrothermal
Large force
High power
Canon Bubblejet


bubble
heater heats the ink to
generated
Ink carrier
1979 Endo et al GB



above boiling point,
Simple
limited to water
patent 2,007,162



transferring significant
construction
Low efficiency
Xerox heater-in-



heat to the aqueous
No moving parts
High
pit 1990 Hawkins et



ink. A bubble
Fast operation
temperatures
al U.S. Pat. No. 4,899,181



nucleates and quickly
Small chip area
required
Hewlett-Packard



forms, expelling the
required for actuator
High mechanical
TIJ 1982 Vaught et



ink.

stress
al U.S. Pat. No. 4,490,728



The efficiency of the

Unusual



process is low, with

materials required



typically less than

Large drive



0.05% of the electrical

transistors



energy being

Cavitation causes



transformed into

actuator failure



kinetic energy of the

Kogation reduces



drop.

bubble formation





Large print heads





are difficult to





fabricate


Piezoelectric
A piezoelectric crystal
Low power
Very large area
Kyser et al U.S. Pat. No.



such as lead
consumption
required for actuator
3,946,398



lanthanum zirconate
Many ink types
Difficult to
Zoltan U.S. Pat. No.



(PZT) is electrically
can be used
integrate with
3,683,212



activated, and either
Fast operation
electronics
1973 Stemme



expands, shears, or
High efficiency
High voltage
U.S. Pat. No. 3,747,120



bends to apply

drive transistors
Epson Stylus



pressure to the ink,

required
Tektronix



ejecting drops.

Full pagewidth
IJ04





print heads





impractical due to





actuator size





Requires





electrical poling in





high field strengths





during manufacture


Electrostrictive
An electric field is
Low power
Low maximum
Seiko Epson,



used to activate
consumption
strain (approx.
Usui et all JP



electrostriction in
Many ink types
0.01%)
253401/96



relaxor materials such
can be used
Large area
IJ04



as lead lanthanum
Low thermal
required for actuator



zirconate titanate
expansion
due to low strain



(PLZT) or lead
Electric field
Response speed



magnesium niobate
strength required
is marginal (~10 μs)



(PMN).
(approx. 3.5 V/μm)
High voltage




can be generated
drive transistors




without difficulty
required




Does not require
Full pagewidth




electrical poling
print heads





impractical due to





actuator size


Ferroelectric
An electric field is
Low power
Difficult to
IJ04



used to induce a phase
consumption
integrate with



transition between the
Many ink types
electronics



antiferroelectric (AFE)
can be used
Unusual



and ferroelectric (FE)
Fast operation
materials such as



phase. Perovskite
(<1 μs)
PLZSnT are



materials such as tin
Relatively high
required



modified lead
longitudinal strain
Actuators require



lanthanum zirconate
High efficiency
a large area



titanate (PLZSnT)
Electric field



exhibit large strains of
strength of around 3 V/μm



up to 1% associated
can be readily



with the AFE to FE
provided



phase transition.


Electrostatic
Conductive plates are
Low power
Difficult to
IJ02, IJ04


plates
separated by a
consumption
operate electrostatic



compressible or fluid
Many ink types
devices in an



dielectric (usually air).
can be used
aqueous



Upon application of a
Fast operation
environment



voltage, the plates

The electrostatic



attract each other and

actuator will



displace ink, causing

normally need to be



drop ejection. The

separated from the



conductive plates may

ink



be in a comb or

Very large area



honeycomb structure,

required to achieve



or stacked to increase

high forces



the surface area and

High voltage



therefore the force.

drive transistors





may be required





Full pagewidth





print heads are not





competitive due to





actuator size


Electrostatic
A strong electric field
Low current
High voltage
1989 Saito et al,


pull
is applied to the ink,
consumption
required
U.S. Pat. No. 4,799,068


on ink
whereupon
Low temperature
May be damaged
1989 Miura et al,



electrostatic attraction

by sparks due to air
U.S. Pat. No. 4,810,954



accelerates the ink

breakdown
Tone-jet



towards the print

Required field



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


electromagnetic
permanent magnet,
Many ink types
Permanent



displacing ink and
can be used
magnetic material



causing drop ejection.
Fast operation
such as Neodymium



Rare earth magnets
High efficiency
Iron Boron (NdFeB)



with a field strength
Easy extension
required.



around 1 Tesla can be
from single nozzles
High local



used. Examples are:
to pagewidth print
currents required



Samarium Cobalt
heads
Copper



(SaCo) and magnetic

metalization should



materials in the

be used for long



neodymium iron boron

electromigration



family (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 induced a
Low power
Complex
IJ01, IJ05, IJ08,


magnetic
magnetic field in a soft
consumption
fabrication
IJ10, IJ12, IJ14,


core electromagnetic
magnetic core or yoke
Many ink types
Materials not
IJ15, IJ17



fabricated from a
can be used
usually present in a



ferrous material such
Fast operation
CMOS fab such as



as electroplated iron
High efficiency
NiFe, CoNiFe, or



alloys such as CoNiFe
Easy extension
CoFe are required



[1], CoFe, or NiFe
from single nozzles
High local



alloys. Typically, the
to pagewidth print
currents required



soft magnetic material
heads
Copper



is in two parts, which

metalization should



are normally held

be used for long



apart by a spring.

electromigration



When the solenoid is

lifetime and low



actuated, the two parts

resistivity



attract, displacing the

Electroplating is



ink.

required





High 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, IJ13,


force
acting on a current
consumption
twisting motion
IJ16



carrying wire in a
Many ink types
Typically, only a



magnetic field is
can be used
quarter of the



utilized.
Fast operation
solenoid length



This allows the
High efficiency
provides force in a



magnetic field to be
Easy extension
useful direction



supplied externally to
from single nozzles
High local



the print head, for
to pagewidth print
currents required



example with rare
heads
Copper



earth permanent

metalization should



magnets.

be used for long



Only the current

electromigration



carrying wire need be

lifetime and low



fabricated on the print-

resistivity



head, simplifying

Pigmented inks



materials

are usually



requirements.

infeasible


Magnetostriction
The actuator uses the
Many ink types
Force acts as a
Fischenbeck,



giant magnetostrictive
can be used
twisting motion
U.S. Pat. No. 4,032,929



effect of materials
Fast operation
Unusual
IJ25



such as Terfenol-D (an
Easy extension
materials such as



alloy of terbium,
from single nozzles
Terfenol-D are



dysprosium and iron
to pagewidth print
required



developed at the Naval
heads
High local



Ordnance Laboratory,
High force is
currents required



hence Ter-Fe-NOL).
available
Copper



For best efficiency, the

metalization should



actuator should be pre-

be used for long



stressed to approx. 8 MPa.

electromigration





lifetime and low





resistivity





Pre-stressing





may be required


Surface
Ink under positive
Low power
Requires
Silverbrook, EP


tension
pressure is held in a
consumption
supplementary force
0771 658 A2 and


reduction
nozzle by surface
Simple
to effect drop
related patent



tension. The surface
construction
separation
applications



tension of the ink is
No unusual
Requires special



reduced below the
materials required in
ink surfactants



bubble threshold,
fabrication
Speed may be



causing the ink to
High efficiency
limited by surfactant



egress from the
Easy extension
properties



nozzle.
from single nozzles




to pagewidth print




heads


Viscosity
The ink viscosity is
Simple
Requires
Silverbrook, EP


reduction
locally reduced to
construction
supplementary force
0771 658 A2 and



select which drops are
No unusual
to effect drop
related patent



to be ejected. A
materials required in
separation
applications



viscosity reduction can
fabrication
Requires special



be achieved
Easy extension
ink viscosity



electrothermally with
from single nozzles
properties



most inks, but special
to pagewidth print
High speed is



inks can be engineered
heads
difficult to achieve



for a 100:1 viscosity

Requires



reduction.

oscillating ink





pressure





A high





temperature





difference (typically





80 degrees) is





required


Acoustic
An acoustic wave is
Can operate
Complex drive
1993 Hadimioglu



generated and
without a nozzle
circuitry
et al, EUP 550,192



focussed upon the
plate
Complex
1993 Elrod et al,



drop ejection region.

fabrication
EUP 572,220





Low efficiency





Poor control of





drop position





Poor control of





drop volume


Thermo-
An actuator which
Low power
Efficient aqueous
IJ03, IJ09, IJ17,


elastic bend
relies upon differential
consumption
operation requires a
IJ18, IJ19, IJ20,


actuator
thermal expansion
Many ink types
thermal insulator on
IJ21, IJ22, IJ23,



upon Joule heating is
can be used
the hot side
IJ24, IJ27, IJ28,



used.
Simple planar
Corrosion
IJ29, IJ30, IJ31,




fabrication
prevention can be
IJ32, IJ33, IJ34,




Small chip area
difficult
IJ35, IJ36, IJ37,




required for each
Pigmented inks
IJ38, IJ39, IJ40,




actuator
may be infeasible,
IJ41




Fast operation
as pigment particles




High efficiency
may jam the bend




CMOS
actuator




compatible voltages




and currents




Standard MEMS




processes can be




used




Easy extension




from single nozzles




to pagewidth print




heads


High CTE
A material with a very
High force can
Requires special
IJ09, IJ17, IJ18,


thermo-
high coefficient of
be generated
material (e.g. PTFE)
IJ20, IJ21, IJ22,


elastic
thermal expansion
Three methods of
Requires a PTFE
IJ23, IJ24, IJ27,


actuator
(CTE) such as
PTFE deposition are
deposition process,
IJ28, IJ29, IJ30,



polytetrafluoroethylene
under development:
which is not yet
IJ31, IJ42, IJ43,



(PTFE) is used. As
chemical vapor
standard in ULSI
IJ44



high CTE materials
deposition (CVD),
fabs



are usually non-
spin coating, and
PTFE deposition



conductive, a heater
evaporation
cannot be followed



fabricated from a
PTFE is a
with high



conductive material is
candidate for low
temperature (above



incorporated. A 50 μm
dielectric constant
350° C.) processing



long PTFE bend
insulation in ULSI
Pigmented inks



actuator with
Very low power
may be infeasible,



polysilicon heater and
consumption
as pigment particles



15 mW power input
Many ink types
may jam the bend



can provide 180 μN
can be used
actuator



force and 10 μm
Simple planar



deflection. Actuator
fabrication



motions include:
Small chip area



Bend
required for each



Push
actuator



Buckle
Fast operation



Rotate
High efficiency




CMOS




compatible voltages




and currents




Easy extension




from single nozzles




to pagewidth print




heads


Conduct-ive
A polymer with a high
High force can
Requires special
IJ24


polymer
coefficient of thermal
be generated
materials


thermo-
expansion (such as
Very low power
development (High


elastic
PTFE) is doped with
consumption
CTE conductive


actuator
conducting substances
Many ink types
polymer)



to increase its
can be used
Requires a PTFE



conductivity to about 3
Simple planar
deposition process,



orders of magnitude
fabrication
which is not yet



below that of copper.
Small chip area
standard in ULSI



The conducting
required for each
fabs



polymer expands
actuator
PTFE deposition



when resistively
Fast operation
cannot be followed



heated.
High efficiency
with high



Examples of
CMOS
temperature (above



conducting dopants
compatible voltages
350° C.) processing



include:
and currents
Evaporation and



Carbon nanotubes
Easy extension
CVD deposition



Metal fibers
from single nozzles
techniques cannot



Conductive polymers
to pagewidth print
be used



such as doped
heads
Pigmented inks



polythiophene

may be infeasible,



Carbon granules

as pigment particles





may jam the bend





actuator


Shape
A shape memory alloy
High force is
Fatigue limits
IJ26


memory
such as TiNi (also
available (stresses
maximum number


alloy
known as Nitinol —
of hundreds of MPa)
of cycles



Nickel Titanium alloy
Large strain is
Low strain (1%)



developed at the Naval
available (more than
is required to extend



Ordnance Laboratory)
3%)
fatigue resistance



is thermally switched
High corrosion
Cycle rate



between its weak
resistance
limited by heat



martensitic state and
Simple
removal



its high stiffness
construction
Requires unusual



austenic state. The
Easy extension
materials (TiNi)



shape of the actuator
from single nozzles
The latent heat of



in its martensitic state
to pagewidth print
transformation must



is deformed relative to
heads
be provided



the austenic shape.
Low voltage
High current



The shape change
operation
operation



causes ejection of a

Requires pre-



drop.

stressing to distort





the martensitic state


Linear
Linear magnetic
Linear Magnetic
Requires unusual
IJ12


Magnetic
actuators include the
actuators can be
semiconductor


Actuator
Linear Induction
constructed with
materials such as



Actuator (LIA), Linear
high thrust, long
soft magnetic alloys



Permanent Magnet
travel, and high
(e.g. CoNiFe)



Synchronous Actuator
efficiency using
Some varieties



(LPMSA), Linear
planar
also require



Reluctance
semiconductor
permanent magnetic



Synchronous Actuator
fabrication
materials such as



(LRSA), Linear
techniques
Neodymium iron



Switched Reluctance
Long actuator
boron (NdFeB)



Actuator (LSRA), and
travel is available
Requires



the Linear Stepper
Medium force is
complex multiphase



Actuator (LSA).
available
drive circuitry




Low voltage
High current




operation
operation







BASIC OPERATION MODE











Actuator
This is the simplest
Simple operation
Drop repetition
Thermal ink jet


directly
mode of operation: the
No external
rate is usually
Piezoelectric ink


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



supplies sufficient
Satellite drops
However, this
IJ01, IJ02, IJ03,



kinetic energy to expel
can be avoided if
is not fundamental
IJ04, IJ05, IJ06,



the drop. The drop
drop velocity is less
to the method, but is
IJ07, IJ09, IJ11,



must have a sufficient
than 4 m/s
related to the refill
IJ12, IJ14, IJ16,



velocity to overcome
Can be efficient,
method normally
IJ20, IJ22, IJ23,



the surface tension.
depending upon the
used
IJ24, IJ25, IJ26,




actuator used
All of the drop
IJ27, IJ28, IJ29,





kinetic energy must
IJ30, IJ31, IJ32,





be provided by the
IJ33, IJ34, IJ35,





actuator
IJ36, IJ37, IJ38,





Satellite drops
IJ39, IJ40, IJ41,





usually form if drop
IJ42, IJ43, IJ44





velocity is greater





than 4.5 m/s



















BASIC OPERATION MODE












Description
Advantages
Disadvantages
Examples















Proximity
The drops to be
Very simple print
Requires close
Silverbrook, EP



printed are selected by
head fabrication can
proximity between
0771 658 A2 and



some manner (e.g.
be used
the print head and
related patent



thermally induced
The drop
the print media or
applications



surface tension
selection means
transfer roller



reduction of
does not need to
May require two



pressurized ink).
provide the energy
print heads printing



Selected drops are
required to separate
alternate rows of the



separated from the ink
the drop from the
image



in the nozzle by
nozzle
Monolithic color



contact with the print

print heads are



medium or a transfer

difficult



roller.


Electrostatic
The drops to be
Very simple print
Requires very
Silverbrook, EP


pull
printed are selected by
head fabrication can
high electrostatic
0771 658 A2 and


on ink
some manner (e.g.
be used
field
related patent



thermally induced
The drop
Electrostatic field
applications



surface tension
selection means
for small nozzle
Tone-Jet



reduction of
does not need to
sizes is above air



pressurized ink).
provide the energy
breakdown



Selected drops are
required to separate
Electrostatic field



separated from the ink
the drop from the
may attract dust



in the nozzle by a
nozzle



strong electric field.


Magnetic
The drops to be
Very simple print
Requires
Silverbrook, EP


pull on ink
printed are selected by
head fabrication can
magnetic ink
0771 658 A2 and



some manner (e.g.
be used
Ink colors other
related patent



thermally induced
The drop
than black are
applications



surface tension
selection means
difficult



reduction of
does not need to
Requires very



pressurized ink).
provide the energy
high magnetic fields



Selected drops are
required to separate



separated from the ink
the drop from the



in the nozzle by a
nozzle



strong magnetic field



acting on the magnetic



ink.


Shutter
The actuator moves a
High speed (>50 kHz)
Moving parts are
IJ13, IJ17, IJ21



shutter to block ink
operation can
required



flow to the nozzle. The
be achieved due to
Requires ink



ink pressure is pulsed
reduced refill time
pressure modulator



at a multiple of the
Drop timing can
Friction and wear



drop ejection
be very accurate
must be considered



frequency.
The actuator
Stiction is




energy can be very
possible




low


Shuttered
The actuator moves a
Actuators with
Moving parts are
IJ08, IJ15, IJ18,


grill
shutter to block ink
small travel can be
required
IJ19



flow through a grill to
used
Requires ink



the nozzle. The shutter
Actuators with
pressure modulator



movement need only
small force can be
Friction and wear



be equal to the width
used
must be considered



of the grill holes.
High speed (>50 kHz)
Stiction is




operation can
possible




be achieved


Pulsed
A pulsed magnetic
Extremely low
Requires an
IJ10


magnetic
field attracts an ‘ink
energy operation is
external pulsed


pull on ink
pusher’ at the drop
possible
magnetic field


pusher
ejection frequency. An
No heat
Requires special



actuator controls a
dissipation
materials for both



catch, which prevents
problems
the actuator and the



the ink pusher from

ink pusher



moving when a drop is

Complex



not to be ejected.

construction



















AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES)












Description
Advantages
Disadvantages
Examples















None
The actuator directly
Simplicity of
Drop ejection
Most ink jets,



fires the ink drop, and
construction
energy must be
including



there is no external
Simplicity of
supplied by
piezoelectric and



field or other
operation
individual nozzle
thermal bubble.



mechanism required.
Small physical
actuator
IJ01, IJ02, IJ03,




size

IJ04, IJ05, 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 external
Silverbrook, EP


ink pressure
oscillates, providing
pressure can provide
ink pressure
0771 658 A2 and


(including
much of the drop
a refill pulse,
oscillator
related patent


acoustic
ejection energy. The
allowing higher
Ink pressure
applications


stimulation)
actuator selects which
operating speed
phase and amplitude
IJ08, IJ13, IJ15,



drops are to be fired
The actuators
must be carefully
IJ17, IJ18, IJ19,



by selectively
may operate with
controlled
IJ21



blocking or enabling
much lower energy
Acoustic



nozzles. The ink
Acoustic lenses
reflections in the ink



pressure oscillation
can be used to focus
chamber must be



may be achieved by
the 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, EP


proximity
placed in close
High accuracy
assembly required
0771 658 A2 and



proximity to the print
Simple print head
Paper fibers may
related patent



medium. Selected
construction
cause problems
applications



drops protrude from

Cannot print on



the print head further

rough substrates



than unselected drops,



and contact the print



medium. The drop



soaks into the medium



fast enough to cause



drop separation.


Transfer
Drops are printed to a
High accuracy
Bulky
Silverbrook, EP


roller
transfer roller instead
Wide range of
Expensive
0771 658 A2 and



of straight to the print
print substrates can
Complex
related patent



medium. A transfer
be used
construction
applications



roller can also be used
Ink can be dried

Tektronix hot



for proximity drop
on the transfer roller

melt piezoelectric



separation.


ink jet






Any of the IJ






series


Electrostatic
An electric field is
Low power
Field strength
Silverbrook, EP



used to accelerate
Simple print head
required for
0771 658 A2 and



selected drops towards
construction
separation of small
related patent



the print medium.

drops is near or
applications





above air
Tone-Jet





breakdown


Direct
A magnetic field is
Low power
Requires
Silverbrook, EP


magnetic
used to accelerate
Simple print head
magnetic ink
0771 658 A2 and


field
selected drops of
construction
Requires strong
related patent



magnetic ink towards

magnetic field
applications



the print medium.


Cross
The print head is
Does not require
Requires external
IJ06, IJ16


magnetic
placed in a constant
magnetic materials
magnet


field
magnetic field. The
to be integrated in
Current densities



Lorenz force in a
the print head
may be high,



current carrying wire
manufacturing
resulting in



is used to move the
process
electromigration



actuator.

problems


Pulsed
A pulsed magnetic
Very low power
Complex print
IJ10


magnetic
field is used to
operation is possible
head construction


field
cyclically attract a
Small print head
Magnetic



paddle, which pushes
size
materials required in



on the ink. A small

print head



actuator moves a



catch, which



selectively prevents



the paddle from



moving.



















ACTUATOR AMPLIFICATION OR MODIFICATION METHOD












Description
Advantages
Disadvantages
Examples















None
No actuator
Operational
Many actuator
Thermal Bubble



mechanical
simplicity
mechanisms have
Ink jet



amplification is used.

insufficient travel,
IJ01, IJ02, IJ06,



The actuator directly

or insufficient force,
IJ07, IJ16, IJ25,



drives the drop

to efficiently drive
IJ26



ejection process.

the drop ejection





process


Differential
An actuator material
Provides greater
High stresses are
Piezoelectric


expansion
expands more on one
travel in a reduced
involved
IJ03, IJ09, IJ17,


bend
side than on the other.
print head area
Care must be
IJ18, IJ19, IJ20,


actuator
The expansion may be

taken that the
IJ21, IJ22, IJ23,



thermal, piezoelectric,

materials do not
IJ24, IJ27, IJ29,



magnetostrictive, or

delaminate
IJ30, IJ31, IJ32,



other mechanism. The

Residual bend
IJ33, IJ34, IJ35,



bend actuator converts

resulting from high
IJ36, IJ37, IJ38,



a high force low travel

temperature or high
IJ39, IJ42, IJ43,



actuator mechanism to

stress during
IJ44



high travel, lower

formation



force mechanism.


Transient
A trilayer bend
Very good
High stresses are
IJ40, IJ41


bend
actuator where the two
temperature stability
involved


actuator
outside layers are
High speed, as a
Care must be



identical. This cancels
new drop can be
taken that the



bend due to ambient
fired before heat
materials do not



temperature and
dissipates
delaminate



residual stress. The
Cancels residual



actuator only responds
stress of formation



to transient heating of



one side or the other.


Reverse
The actuator loads a
Better coupling
Fabrication
IJ05, IJ11


spring
spring. When the
to the ink
complexity



actuator is turned off,

High stress in the



the spring releases.

spring



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 travel
Increased
Some


stack
actuators are stacked.
Reduced drive
fabrication
piezoelectric ink jets



This can be
voltage
complexity
IJ04



appropriate where

Increased



actuators require high

possibility of short



electric field strength,

circuits due to



such as electrostatic

pinholes



and piezoelectric



actuators.


Multiple
Multiple smaller
Increases the
Actuator forces
IJ12, IJ13, IJ18,


actuators
actuators are used
force available from
may not add
IJ20, IJ22, IJ28,



simultaneously to
an actuator
linearly, reducing
IJ42, IJ43



move the ink. Each
Multiple
efficiency



actuator need provide
actuators can be



only a portion of the
positioned to control



force required.
ink flow accurately


Linear
A linear spring is used
Matches low
Requires print
IJ15


Spring
to transform a motion
travel actuator with
head area for the



with small travel and
higher travel
spring



high force into a
requirements



longer travel, lower
Non-contact



force motion.
method of motion




transformation


Coiled
A bend actuator is
Increases travel
Generally
IJ17, IJ21, IJ34,


actuator
coiled to provide
Reduces chip
restricted to planar
IJ35



greater travel in a
area
implementations



reduced chip area.
Planar
due to extreme




implementations are
fabrication difficulty




relatively easy to
in other orientations.




fabricate.


Flexure
A bend actuator has a
Simple means of
Care must be
IJ10, IJ19, IJ33


bend
small region near the
increasing travel of
taken not to exceed


actuator
fixture point, which
a bend actuator
the elastic limit in



flexes much more

the flexure area



readily than the

Stress



remainder of the

distribution is very



actuator. The actuator

uneven



flexing is effectively

Difficult to



converted from an

accurately model



even coiling to an

with finite element



angular bend, resulting

analysis



in greater travel of the



actuator tip.


Catch
The actuator controls a
Very low
Complex
IJ10



small catch. The catch
actuator energy
construction



either enables or
Very small
Requires external



disables movement of
actuator size
force



an ink pusher that is

Unsuitable for



controlled in a bulk

pigmented inks



manner.


Gears
Gears can be used to
Low force, low
Moving parts are
IJ13



increase travel at the
travel actuators can
required



expense of duration.
be used
Several actuator



Circular gears, rack
Can be fabricated
cycles are required



and pinion, ratchets,
using standard
More complex



and other gearing
surface MEMS
drive electronics



methods can be used.
processes
Complex





construction





Friction, friction,





and wear are





possible


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



used to change a slow
movement
elastic limits of the
“An Ink-jet Head



actuator into a fast
achievable
materials for long
Using Diaphragm



motion. It can also

device life
Microactuator”,



convert a high force,

High stresses
Proc. IEEE MEMS,



low travel actuator

involved
February 1996, pp 418–423.



into a high travel,

Generally high
IJ18, IJ27



medium force motion.

power requirement


Tapered
A tapered magnetic
Linearizes the
Complex
IJ14


magnetic
pole can increase
magnetic
construction


pole
travel at the expense
force/distance curve



of force.


Lever
A lever and fulcrum is
Matches low
High stress
IJ32, IJ36, IJ37



used to transform a
travel actuator with
around the fulcrum



motion with small
higher travel



travel and high force
requirements



into a motion with
Fulcrum area has



longer travel and
no linear movement,



lower force. The lever
and can be used for



can also reverse the
a fluid seal



direction of travel.


Rotary
The actuator is
High mechanical
Complex
IJ28


impeller
connected to a rotary
advantage
construction



impeller. A small
The ratio of force
Unsuitable for



angular deflection of
to travel of the
pigmented inks



the actuator results in
actuator can be



a rotation of the
matched to the



impeller vanes, which
nozzle requirements



push the ink against
by varying the



stationary vanes and
number of impeller



out of the nozzle.
vanes


Acoustic
A refractive or
No moving parts
Large area
1993 Hadimioglu


lens
diffractive (e.g. zone

required
et al, EUP 550,192



plate) acoustic lens is

Only relevant for
1993 Elrod et al,



used to concentrate

acoustic ink jets
EUP 572,220



sound waves.


Sharp
A sharp point is used
Simple
Difficult to
Tone-jet


conductive
to concentrate an
construction
fabricate using


point
electrostatic field.

standard VLSI





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-Packard


expansion
actuator changes,
construction in the
typically required to
Thermal Ink jet



pushing the ink in all
case of thermal ink
achieve volume
Canon Bubblejet



directions.
jet
expansion. This





leads to thermal





stress, cavitation,





and kogation in





thermal ink jet





implementations


Linear,
The actuator moves in
Efficient
High fabrication
IJ01, IJ02, IJ04,


normal to
a direction normal to
coupling to ink
complexity may be
IJ07, IJ11, IJ14


chip surface
the print head surface.
drops ejected
required to achieve



The nozzle is typically
normal to the
perpendicular



in the line of
surface
motion



movement.


Parallel to
The actuator moves
Suitable for
Fabrication
IJ12, IJ13, IJ15,


chip surface
parallel to the print
planar fabrication
complexity
IJ33, IJ34, IJ35,



head surface. Drop

Friction
IJ36



ejection may still be

Stiction



normal to the surface.


Membrane
An actuator with a
The effective
Fabrication
1982 Howkins


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



area is used to push a
becomes the
Actuator size



stiff membrane that is
membrane area
Difficulty of



in contact with the ink.

integration in a





VLSI process


Rotary
The actuator causes
Rotary levers
Device
IJ05, IJ08, IJ13,



the rotation of some
may be used to
complexity
IJ28



element, such a grill or
increase travel
May have



impeller
Small chip area
friction at a pivot




requirements
point


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



when energized. This
change in
actuator to be made
U.S. Pat. No. 3,946,398



may be due to
dimensions can be
from at least two
1973 Stemme



differential thermal
converted to a large
distinct layers, or to
U.S. Pat. No. 3,747,120



expansion,
motion.
have a thermal
IJ03, IJ09, IJ10,



piezoelectric

difference across the
IJ19, IJ23, IJ24,



expansion,

actuator
IJ25, IJ29, IJ30,



magnetostriction, or


IJ31, IJ33, IJ34,



other form of relative


IJ35



dimensional change.


Swivel
The actuator swivels
Allows operation
Inefficient
IJ06



around a central pivot.
where the net linear
coupling to the ink



This motion is suitable
force on the paddle
motion



where there are
is zero



opposite forces
Small chip area



applied to opposite
requirements



sides of the paddle,



e.g. Lorenz force.


Straighten
The actuator is
Can be used with
Requires careful
IJ26, IJ32



normally bent, and
shape memory
balance of stresses



straightens when
alloys where the
to ensure that the



energized.
austenic phase is
quiescent bend is




planar
accurate


Double
The actuator bends in
One actuator can
Difficult to make
IJ36, IJ37, IJ38


bend
one direction when
be used to power
the drops ejected by



one element is
two nozzles.
both bend directions



energized, and bends
Reduced chip
identical.



the other way when
size.
A small



another element is
Not sensitive to
efficiency loss



energized.
ambient temperature
compared to





equivalent single





bend actuators.


Shear
Energizing the
Can increase the
Not readily
1985 Fishbeck



actuator causes a shear
effective travel of
applicable to other
U.S. Pat. No. 4,584,590



motion in the actuator
piezoelectric
actuator



material.
actuators
mechanisms


Radial constriction
The actuator squeezes
Relatively easy
High force
1970 Zoltan U.S. Pat. No.



an ink reservoir,
to fabricate single
required
3,683,212



forcing ink from a
nozzles from glass
Inefficient



constricted nozzle.
tubing as
Difficult to




macroscopic
integrate with VLSI




structures
processes


Coil/uncoil
A coiled actuator
Easy to fabricate
Difficult to
IJ17, IJ21, IJ34,



uncoils or coils more
as a planar VLSI
fabricate for non-
IJ35



tightly. The motion of
process
planar devices



the free end of the
Small area
Poor out-of-plane



actuator ejects the ink.
required, therefore
stiffness




low cost


Bow
The actuator bows (or
Can increase the
Maximum travel
IJ16, IJ18, IJ27



buckles) in the middle
speed of travel
is constrained



when energized.
Mechanically
High force




rigid
required


Push-Pull
Two actuators control
The structure is
Not readily
IJ18



a shutter. One actuator
pinned at both ends,
suitable for ink jets



pulls the shutter, and
so has a high out-of-
which directly push



the other pushes it.
plane rigidity
the ink


Curl
A set of actuators curl
Good fluid flow
Design
IJ20, IJ42


inwards
inwards to reduce the
to the region behind
complexity



volume of ink that
the actuator



they enclose.
increases efficiency


Curl
A set of actuators curl
Relatively simple
Relatively large
IJ43


outwards
outwards, pressurizing
construction
chip area



ink in a chamber



surrounding the



actuators, and



expelling ink from a



nozzle in the chamber.


Iris
Multiple vanes enclose
High efficiency
High fabrication
IJ22



a volume of ink. These
Small chip area
complexity



simultaneously rotate,

Not suitable for



reducing the volume

pigmented inks



between the vanes.


Acoustic
The actuator vibrates
The actuator can
Large area
1993 Hadimioglu


vibration
at a high frequency.
be physically distant
required for
et al, EUP 550,192




from the ink
efficient operation
1993 Elrod et al,





at useful frequencies
EUP 572,220





Acoustic





coupling and





crosstalk





Complex drive





circuitry





Poor control of





drop volume and





position


None
In various ink jet
No moving parts
Various other
Silverbrook, EP



designs the actuator

tradeoffs are
0771 658 A2 and



does not move.

required to
related patent





eliminate moving
applications





parts
Tone-jet



















NOZZLE REFILL METHOD












Description
Advantages
Disadvantages
Examples















Surface
This is the normal way
Fabrication
Low speed
Thermal ink jet


tension
that ink jets are
simplicity
Surface tension
Piezoelectric ink



refilled. After the
Operational
force relatively
jet



actuator is energized,
simplicity
small compared to
IJ01–IJ07, IJ10–IJ14,



it typically returns

actuator force
IJ16, IJ20,



rapidly to its normal

Long refill time
IJ22–IJ45



position. This rapid

usually dominates



return sucks in air

the 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, IJ15,


oscillating
chamber is provided at
Low actuator
common ink
IJ17, IJ18, IJ19,


ink pressure
a pressure that
energy, as the
pressure oscillator
IJ21



oscillates at twice the
actuator need only
May not be



drop ejection
open or close the
suitable for



frequency. When a
shutter, instead of
pigmented inks



drop is to be ejected,
ejecting the ink drop



the shutter 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 ejected a
the nozzle is
independent



drop a second (refill)
actively refilled
actuators per 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 ink
The ink is held a slight
High refill rate,
Surface spill
Silverbrook, EP


pressure
positive pressure.
therefore a high
must be prevented
0771 658 A2 and



After the ink drop is
drop repetition rate
Highly
related patent



ejected, the nozzle
is possible
hydrophobic print
applications



chamber fills quickly

head surfaces are
Alternative for:,



as surface tension and

required
IJ01–IJ07, IJ10–IJ14,



ink pressure both


IJ16, IJ20, IJ22–IJ45



operate to refill the



nozzle.



















METHOD OF RESTRICTING BACK-FLOW THROUGH INLET












Description
Advantages
Disadvantages
Examples















Long inlet
The ink inlet channel
Design simplicity
Restricts refill
Thermal ink jet


channel
to the nozzle chamber
Operational
rate
Piezoelectric ink



is made long and
simplicity
May result in a
jet



relatively narrow,
Reduces
relatively large chip
IJ42, IJ43



relying on viscous
crosstalk
area



drag to reduce inlet

Only partially



back-flow.

effective


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


pressure
positive pressure, so
and separation
method (such as a
0771 658 A2 and



that in the quiescent
forces can be
nozzle rim or
related patent



state some of the ink
reduced
effective
applications



drop already protrudes
Fast refill time
hydrophobizing, or
Possible



from the nozzle.

both) to prevent
operation of the



This reduces the

flooding of the
following: IJ01–IJ07,



pressure in the nozzle

ejection surface of
IJ09–IJ12,



chamber which is

the print head.
IJ14, IJ16, IJ20,



required to eject a


IJ22, IJ23–IJ34,



certain volume of ink.


IJ36–IJ41, IJ44



The reduction in



chamber pressure



results in a reduction



in ink pushed out



through the inlet.


Baffle
One or more baffles
The refill rate is
Design
HP Thermal Ink



are placed in the inlet
not as restricted as
complexity
Jet



ink flow. When the
the long inlet
May increase
Tektronix



actuator is energized,
method.
fabrication
piezoelectric ink jet



the rapid ink
Reduces
complexity (e.g.



movement creates
crosstalk
Tektronix hot melt



eddies which restrict

Piezoelectric print



the flow through the

heads).



inlet. The slower refill



process is unrestricted,



and does not result in



eddies.


Flexible flap
In this method recently
Significantly
Not applicable to
Canon


restricts
disclosed by Canon,
reduces back-flow
most ink jet


inlet
the expanding actuator
for edge-shooter
configurations



(bubble) pushes on a
thermal ink jet
Increased



flexible flap that
devices
fabrication



restricts the inlet.

complexity





Inelastic





deformation of





polymer flap results





in creep over





extended use


Inlet filter
A filter is located
Additional
Restricts refill
IJ04, IJ12, IJ24,



between the ink inlet
advantage of ink
rate
IJ27, IJ29, IJ30



and the nozzle
filtration
May result in



chamber. The filter
Ink filter may be
complex



has a multitude of
fabricated with no
construction



small holes or slots,
additional process



restricting ink flow.
steps



The filter also removes



particles which may



block the nozzle.


Small inlet
The ink inlet channel
Design simplicity
Restricts refill
IJ02, IJ37, IJ44


compared
to the nozzle chamber

rate


to nozzle
has a substantially

May result in a



smaller cross section

relatively large chip



than that of the nozzle,

area



resulting in easier ink

Only partially



egress out of the

effective



nozzle than out of the



inlet.


Inlet shutter
A secondary actuator
Increases speed
Requires separate
IJ09



controls the position of
of the ink-jet print
refill actuator and



a shutter, closing off
head operation
drive circuit



the ink inlet when the



main actuator is



energized.


The inlet is
The method avoids the
Back-flow
Requires careful
IJ01, IJ03, 1J05,


located
problem of inlet back-
problem is
design to minimize
IJ06, IJ07, IJ10,


behind the
flow by arranging the
eliminated
the negative
IJ11, IJ14, IJ16,


ink-pushing
ink-pushing surface of

pressure behind the
IJ22, IJ23, IJ25,


surface
the actuator between

paddle
IJ28, IJ31, IJ32,



the inlet and the


IJ33, IJ34, IJ35,



nozzle.


IJ36, IJ39, IJ40,






IJ41


Part of the
The actuator and a
Significant
Small increase in
IJ07, IJ20, IJ26,


actuator
wall of the ink
reductions in back-
fabrication
IJ38


moves to
chamber are arranged
flow can be
complexity


shut off the
so that the motion of
achieved


inlet
the actuator closes off
Compact designs



the inlet.
possible


Nozzle
In some configurations
Ink back-flow
None related to
Silverbrook, EP


actuator
of ink jet, there is no
problem is
ink back-flow on
0771 658 A2 and


does not
expansion or
eliminated
actuation
related patent


result in ink
movement of an


applications


back-flow
actuator which may


Valve-jet



cause ink back-flow


Tone-jet



through the inlet.

























Description
Advantages
Disadvantages
Examples
















NOZZLE CLEARING METHOD











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


nozzle firing
fired periodically,
complexity on the
sufficient to
systems



before the ink has a
print head
displace dried ink
IJ01, IJ02, IJ03,



chance to dry. When


IJ04, IJ05, IJ06,



not in use the nozzles


IJ07, IJ09, IJ10,



are sealed (capped)


IJ11, IJ12, IJ14,



against air.


IJ16, IJ20, IJ22,



The nozzle firing is


IJ23, IJ24, IJ25,



usually performed


IJ26, IJ27, IJ28,



during a special


IJ29, IJ30, IJ31,



clearing cycle, after


IJ32, IJ33, IJ34,



first moving the print


IJ36, IJ37, IJ38,



head to a cleaning


IJ39, IJ40, IJ41,



station.


IJ42, IJ43, IJ44,






IJ45


Extra
In systems which heat
Can be highly
Requires higher
Silverbrook, EP


power to
the ink, but do not boil
effective if the
drive voltage for
0771 658 A2 and


ink heater
it under normal
heater is adjacent to
clearing
related patent



situations, nozzle
the nozzle
May require
applications



clearing can be

larger drive



achieved by over-

transistors



powering the heater



and boiling ink at the



nozzle.


Rapid
The actuator is fired in
Does not require
Effectiveness
May be used


success-ion
rapid succession. In
extra drive circuits
depends
with: IJ01, IJ02,


of actuator
some configurations,
on the print head
substantially upon
IJ03, IJ04, IJ05,


pulses
this may cause heat
Can be readily
the configuration of
IJ06, IJ07, IJ09,



build-up at the nozzle
controlled and
the ink jet nozzle
IJ10, IJ11, IJ14,



which boils the ink,
initiated by digital

IJ16, IJ20, IJ22,



clearing the nozzle. In
logic

IJ23, IJ24, IJ25,



other situations, it may


IJ27, IJ28, IJ29,



cause sufficient


IJ30, IJ31, IJ32,



vibrations to dislodge


IJ33, IJ34, IJ36,



clogged nozzles.


IJ37, IJ38, IJ39,






IJ40, IJ41, IJ42,






IJ43, IJ44, IJ45


Extra
Where an actuator is
A simple
Not suitable
May be used


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


ink pushing
the limit of its motion,
applicable
hard limit to
IJ16, IJ20, IJ23,


actuator
nozzle clearing may be

actuator movement
IJ24, IJ25, IJ27,



assisted by providing


IJ29, IJ30, IJ31,



an enhanced drive


IJ32, IJ39, IJ40,



signal to the actuator.


IJ41, IJ42, IJ43,






IJ44, IJ45


Acoustic
An ultrasonic wave is
A high nozzle
High
IJ08, IJ13, IJ15,


resonance
applied to the ink
clearing capability
implementation cost
IJ17, IJ18, IJ19,



chamber. This wave is
can be achieved
if system does not
IJ21



of an appropriate
May be
already include an



amplitude and
implemented at very
acoustic actuator



frequency to cause
low cost in systems



sufficient force at the
which already



nozzle to clear
include acoustic



blockages. This is
actuators



easiest to achieve if



the ultrasonic wave is



at a resonant



frequency of the ink



cavity.


Nozzle
A microfabricated
Can clear
Accurate
Silverbrook, EP


clearing
plate is pushed against
severely clogged
mechanical
0771 658 A2 and


plate
the nozzles. The plate
nozzles
alignment is
related patent



has a post for every

required
applications



nozzle. A post moves

Moving parts are



through each nozzle,

required



displacing dried ink.

There is risk of





damage to the





nozzles





Accurate





fabrication is





required


Ink
The pressure of the ink
May be effective
Requires
May be used


pressure
is temporarily
where other
pressure pump or
with all IJ series ink


pulse
increased so that ink
methods cannot be
other pressure
jets



streams from all of the
used
actuator



nozzles. This may be

Expensive



used in conjunction

Wasteful of ink



with actuator



energizing.


Print head
A flexible ‘blade’ is
Effective for
Difficult to use if
Many ink jet


wiper
wiped across the print
planar print head
print head surface is
systems



head surface. The
surfaces
non-planar or very



blade is usually
Low cost
fragile



fabricated from a

Requires



flexible polymer, e.g.

mechanical parts



rubber or synthetic

Blade can wear



elastomer.

out in high volume





print systems


Separate
A separate heater is
Can be effective
Fabrication
Can be used with


ink boiling
provided at the nozzle
where other nozzle
complexity
many IJ series ink


heater
although the normal
clearing methods

jets



drop e-ection
cannot be used



mechanism does not
Can be



require it. The heaters
implemented at no



do not require
additional cost in



individual drive
some ink jet



circuits, as many
configurations



nozzles can be cleared



simultaneously, and no



imaging is required.







NOZZLE PLATE CONSTRUCTION











Electroformed
A nozzle plate is
Fabrication
High
Hewlett Packard


nickel
separately fabricated
simplicity
temperatures and
Thermal Ink jet



from electroformed

pressures are



nickel, and bonded to

required to bond



the print head chip.

nozzle plate





Minimum





thickness constraints





Differential





thermal expansion


Laser
Individual nozzle
No masks
Each hole must
Canon Bubblejet


ablated or
holes are ablated by an
required
be individually
1988 Sercel et


drilled
intense UV laser in a
Can be quite fast
formed
al., SPIE, Vol. 998


polymer
nozzle plate, which is
Some control
Special
Excimer Beam



typically a polymer
over nozzle profile
equipment required
Applications, pp.



such as polyimide or
is possible
Slow where there
76–83



polysulphone
Equipment
are many thousands
1993 Watanabe




required is relatively
of nozzles per print
et al., U.S. Pat. No.




low cost
head
5,208,604





May produce thin





burrs at exit holes


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


micromachined
plate is
attainable
construction
Transactions on



micromachined from

High cost
Electron Devices,



single crystal silicon,

Requires
Vol. ED-25, No. 10,



and bonded to the

precision alignment
1978, pp 1185–1195



print head wafer.

Nozzles may be
Xerox 1990





clogged by adhesive
Hawkins et al., U.S. Pat. No.






4,899,181


Glass
Fine glass capillaries
No expensive
Very small
1970 Zoltan U.S. Pat. No.


capillaries
are drawn from glass
equipment required
nozzle sizes are
3,683,212



tubing. This method
Simple to make
difficult to form



has been used for
single nozzles
Not suited for



making individual

mass production



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, EP


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


micromachined
using standard VLSI
Monolithic
under the nozzle
related patent


using VLSI
deposition techniques.
Low cost
plate to form the
applications


lithographic
Nozzles are etched in
Existing
nozzle chamber
IJ01, IJ02, IJ04,


processes
the nozzle plate using
processes can be
Surface may be
IJ11, IJ12, IJ17,



VLSI lithography and
used
fragile to the touch
IJ18, IJ20, IJ22,



etching.


IJ24, IJ27, IJ28,






IJ29, IJ30, IJ31,






IJ32, IJ33, IJ34,






IJ36, IJ37, IJ38,






IJ39, IJ40, IJ41,






IJ42, IJ43, IJ44


Monolithic,
The nozzle plate is a
High accuracy
Requires long
IJ03, IJ05, IJ06,


etched
buried etch stop in the
(<1 μm)
etch times
IJ07, IJ08, IJ09,


through
wafer. Nozzle
Monolithic
Requires a
IJ10, IJ13, IJ14,


substrate
chambers are etched in
Low cost
support wafer
IJ15, IJ16, IJ19,



the front of the wafer,
No differential

IJ21, IJ23, IJ25,



and the wafer is
expansion

IJ26



thinned from the back



side. Nozzles are then



etched in the etch stop



layer.


No nozzle
Various methods have
No nozzles to
Difficult to
Ricoh 1995


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



the nozzles entirely, to

position accurately
5,412,413



prevent nozzle

Crosstalk
1993 Hadimioglu



clogging. These

problems
et al EUP 550,192



include thermal bubble


1993 Elrod et al



mechanisms and


EUP 572,220



acoustic lens



mechanisms


Trough
Each drop ejector has
Reduced
Drop firing
IJ35



a trough through
manufacturing
direction is sensitive



which a paddle moves.
complexity
to wicking.



There is no nozzle
Monolithic



plate.


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


instead of
nozzle holes and
become clogged
control drop
U.S. Pat. No. 4,799,068


individual
replacement by a slit

position accurately


nozzles
encompassing many

Crosstalk



actuator positions

problems



reduces nozzle



clogging, but increases



crosstalk due to ink



surface waves



















DROP EJECTION DIRECTION












Description
Advantages
Disadvantages
Examples















Edge
Ink flow is along the
Simple
Nozzles limited
Canon Bubblejet


(‘edge
surface of the chip,
construction
to edge
1979 Endo et al GB


shooter’)
and ink drops are
No silicon
High resolution
patent 2,007,162



ejected from the chip
etching required
is difficult
Xerox heater-in-



edge.
Good heat
Fast color
pit 1990 Hawkins et




sinking via substrate
printing requires
al U.S. Pat. No. 4,899,181




Mechanically
one print head per
Tone-jet




strong
color




Ease of chip




handing


Surface
Ink flow is along the
No bulk silicon
Maximum ink
Hewlett-Packard


(‘roof
surface of the chip,
etching required
flow is severely
TIJ 1982 Vaught et


shooter’)
and ink drops are
Silicon can make
restricted
al U.S. Pat. No. 4,490,728



ejected from the chip
an effective heat

IJ02, IJ11, IJ12,



surface, normal to the
sink

IJ20, IJ22



plane of the chip.
Mechanical




strength


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


chip,
chip, and ink drops are
Suitable for
silicon etching
0771 658 A2 and


forward
ejected from the front
pagewidth print

related patent


(‘up
surface of the chip.
heads

applications


shooter’)

High nozzle

IJ04, IJ17, IJ18,




packing density

IJ24, IJ27–IJ45




therefore low




manufacturing cost


Through
Ink flow is through the
High ink flow
Requires wafer
IJ01, IJ03, IJ05,


chip,
chip, and ink drops are
Suitable for
thinning
IJ06, IJ07, IJ08,


reverse
ejected from the rear
pagewidth print
Requires special
IJ09, IJ10, IJ13,


(‘down
surface of the chip.
heads
handling during
IJ14, IJ15, IJ16,


shooter’)

High nozzle
manufacture
IJ19, IJ21, IJ23,




packing density

IJ25, IJ26




therefore low




manufacturing cost


Through
Ink flow is through the
Suitable for
Pagewidth print
Epson Stylus


actuator
actuator, which is not
piezoelectric print
heads require
Tektronix hot



fabricated as part of
heads
several thousand
melt piezoelectric



the same substrate as

connections to drive
ink jets



the drive transistors.

circuits





Cannot be





manufactured in





standard CMOS





fabs





Complex





assembly required



















INK TYPE












Description
Advantages
Disadvantages
Examples















Aqueous,
Water based ink which
Environmentally
Slow drying
Most existing ink


dye
typically contains:
friendly
Corrosive
jets



water, dye, surfactant,
No odor
Bleeds on paper
All IJ series ink



humectant, and

May
jets



biocide.

strikethrough
Silverbrook, EP



Modern ink dyes have

Cockles paper
0771 658 A2 and



high water-fastness,


related patent



light fastness


applications


Aqueous,
Water based ink which
Environmentally
Slow drying
IJ02, IJ04, IJ21,


pigment
typically contains:
friendly
Corrosive
IJ26, IJ27, IJ30



water, pigment,
No odor
Pigment may
Silverbrook, EP



surfactant, humectant,
Reduced bleed
clog nozzles
0771 658 A2 and



and biocide.
Reduced wicking
Pigment may
related patent



Pigments have an
Reduced
clog actuator
applications



advantage in reduced
strikethrough
mechanisms
Piezoelectric ink-



bleed, wicking and

Cockles paper
jets



strikethrough.


Thermal ink jets






(with significant






restrictions)


Methyl
MEK is a highly
Very fast drying
Odorous
All IJ series ink


Ethyl
volatile solvent used
Prints on various
Flammable
jets


Ketone
for industrial printing
substrates such as


(MEK)
on difficult surfaces
metals and plastics



such as aluminum



cans.


Alcohol
Alcohol based inks
Fast drying
Slight odor
All IJ series ink


(ethanol, 2-
can be used where the
Operates at sub-
Flammable
jets


butanol,
printer must operate at
freezing


and others)
temperatures below
temperatures



the freezing point of
Reduced paper



water. An example of
cockle



this is in-camera
Low cost



consumer



photographic printing.


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


change
room temperature, and
ink instantly freezes
Printed ink
melt piezoelectric


(hot melt)
is melted in the print
on the print medium
typically has a
ink jets



head before jetting.
Almost any print
‘waxy’ feel
1989 Nowak



Hot melt inks are
medium can be used
Printed pages
U.S. Pat. No. 4,820,346



usually wax based,
No paper cockle
may ‘block’
All IJ series ink



with a melting point
occurs
Ink temperature
jets



around 80° C. After
No wicking
may be above the



jetting the ink freezes
occurs
curie point of



almost instantly upon
No bleed occurs
permanent magnets



contacting the print
No strikethrough
Ink heaters



medium or a transfer
occurs
consume power



roller.

Long warm-up





time


Oil
Oil based inks are
High solubility
High viscosity:
All IJ series ink



extensively used in
medium for some
this is a significant
jets



offset printing. They
dyes
limitation for use in



have advantages in
Does not cockle
ink jets, which



improved
paper
usually require a



characteristics on
Does not wick
low viscosity. Some



paper (especially no
through paper
short chain and



wicking or cockle).

multi-branched oils



Oil soluble dies and

have a sufficiently



pigments are required.

low viscosity.





Slow drying


Microemulsion
A microemulsion is a
Stops ink bleed
Viscosity higher
All IJ series ink



stable, self forming
High dye
than water
jets



emulsion of oil, water,
solubility
Cost is slightly



and surfactant. The
Water, oil, and
higher than water



characteristic drop size
amphiphilic soluble
based ink



is less than 100 nm,
dies can be used
High surfactant



and is determined by
Can stabilize
concentration



the preferred curvature
pigment
required (around



of the surfactant.
suspensions
5%)

## Claims

1. A printhead comprising:
a substrate including a plurality of nozzles for ejecting ink droplets onto a print medium, each nozzle having a nozzle aperture defined in an ink ejection surface of the substrate; and
a plurality of formations on the ink ejection surface, the surface formations being configured to isolate each nozzle from at least one adjacent nozzle.

wherein the surface formations are configured in a plurality of nozzle enclosures, each nozzle enclosure comprising sidewalls surrounding a respective nozzle, the sidewalls forming a seal with the ink ejection surface, thereby isolating each nozzle from a least one adjacent nozzle.

2. The printhead of claim 1, wherein the surface formations each have a hydrophobic surface.

3. The printhead of claim 1, wherein each nozzle enclosure further comprises a roof spaced apart from the respective nozzle aperture, the roof having a roof opening aligned with its respective nozzle aperture, thereby allowing ejected ink droplets to pass therethrough onto the print medium.

4. The printhead of claim 3, wherein the sidewalls extend from each roof to the ink ejection surface.

5. The printhead of claim 4, wherein the sidewalls extend from a perimeter region of each roof.

6. The printhead of claim 1, which is a pagewidth inkjet printhead.

7. The printhead of claim 1, wherein the printhead has a nozzle density sufficient to print at up to 1600 dpi.

8. A printer comprising the printhead according to claim 1.

9. A method of printing from the printhead of claim 1, whilst minimizing cross-contamination of ink between adjacent nozzles, the method comprising the steps of:
(a) providing a printhead comprising:
a substrate including a plurality of nozzles for ejecting ink droplets onto a print medium, each nozzle having a nozzle aperture defined in an ink ejection surface of the substrate; and
a plurality of formations on the ink ejection surface, the surface formations being configured to isolate each nozzle from at least one adjacent nozzle; and

(b) printing onto a print medium using said printhead,
wherein the surface formations are configured in a plurality of nozzle enclosures, each nozzle enclosure comprising sidewalls surrounding a respective nozzle, the sidewalls forming a seal with the ink ejection surface, thereby isolating each nozzle from a least one adjacent nozzle.

10. A method of fabricating the printhead of claim 1, having isolated nozzles, the method comprising the steps of:
(a) providing a substrate, the substrate including a plurality of nozzles for ejecting ink droplets onto a print medium, each nozzle having a nozzle aperture defined in an ink ejection surface of the substrate;
(b) depositing a layer of photoresist over the ink ejection surface;
(c) defining recesses in the photoresist, each recess revealing a portion of the ink ejection surface surrounding a respective nozzle aperture;
(d) depositing a roof material over the photoresist and into the recesses;
(e) etching the roof material to define a nozzle enclosure around each nozzle aperture, each nozzle enclosure having an opening defined in a roof and sidewalls extending from the roof to the ink ejection surface; and
(f) removing the photoresist,

wherein said sidewalls surround a respective nozzle, the sidewalls forming a seal with the ink ejection surface, thereby isolating each nozzle from at least one adjacent nozzle.