(en)A nozzle arrangement for use in an integrated circuit device is provided. The nozzle arrangement comprises a wafer substrate, a nozzle chamber wall disposed on the substrate, which with a roof wall defines a nozzle chamber, the roof wall forming an ejection port that is in fluid communication with the nozzle chamber, an inlet channel which extends through the substrate to the nozzle chamber, a thermal actuator having an actuating arm that extends through an opening in the nozzle chamber wall into the nozzle chamber for ejection of fluid from the ejection port, and a sealing structure depending from the actuating arm within the nozzle chamber wall opening. The sealing structure, nozzle chamber wall and roof wall are complementarily configured so as to form fluidic seals therebetween within the nozzle chamber wall opening.

1.ApplicationNumber: US-49004106-A
1.PublishNumber: US-7802871-B2
2.Date Publish: 20100928
3.Inventor: SILVERBROOK KIA

4.Inventor Harmonized: SILVERBROOK KIA(AU)

5.Country: US
6.Claims:
(en)A nozzle arrangement for use in an integrated circuit device is provided. The nozzle arrangement comprises a wafer substrate, a nozzle chamber wall disposed on the substrate, which with a roof wall defines a nozzle chamber, the roof wall forming an ejection port that is in fluid communication with the nozzle chamber, an inlet channel which extends through the substrate to the nozzle chamber, a thermal actuator having an actuating arm that extends through an opening in the nozzle chamber wall into the nozzle chamber for ejection of fluid from the ejection port, and a sealing structure depending from the actuating arm within the nozzle chamber wall opening. The sealing structure, nozzle chamber wall and roof wall are complementarily configured so as to form fluidic seals therebetween within the nozzle chamber wall opening.

7.Description:
(en)CROSS REFERENCES TO RELATED APPLICATIONS
The present application is a Continuation of U.S. application Ser. No. 10/728,970 filed on Dec. 8, 2003, which is a Continuation In Part of U.S. application Ser. No. 10/160,273 filed on Jun. 4, 2002, now issued as U.S. Pat. No. 6,746,105, which is a Continuation of U.S. application Ser. No. 09/112,767 filed on Jul. 10, 1998, now issued as U.S. Pat. No. 6,416,167.
The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their U.S. patent application serial numbers (USSN) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.









CROSS-



REFERENCED
U.S. PATENT/PATENT

AUSTRALIAN
APPLICATION (CLAIMING

PROVISIONAL
RIGHT OF PRIORITY

PATENT
FROM AUSTRALIAN
DOCKET

APPLICATION NO.
PROVISIONAL APPLICATION)
NO.



PO7991
6,750,901
ART01US

PO8505
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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
FIELD OF THE INVENTION
The present invention relates to the field of inkjet printers and, discloses an inkjet printing system using printheads manufactured with microelectro-mechanical systems (MEMS) techniques.
BACKGROUND OF THE INVENTION
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electrostatic 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.
In the construction of any inkjet printing system, there are a considerable number of important factors which must be traded off against one another especially as large scale printheads are constructed, especially those of a pagewidth type. A number of these factors are outlined in the following paragraphs.
Firstly, inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, galium arsenide etc. Hence, it is desirable, in any MEMS constructions, to utilize well proven semi-conductor fabrication techniques which do not require any “exotic” processes or materials. Of course, a certain degree of trade off will be undertaken in that if the advantages of using the exotic material far out weighs its disadvantages then it may become desirable to utilize the material anyway. However, if it is possible to achieve the same, or similar, properties using more common materials, the problems of exotic materials can be avoided.
With a large array of ink ejection nozzles, it is desirable to provide for a highly automated form of manufacturing which results in an inexpensive production of multiple printhead devices.
Preferably, the device constructed utilizes a low amount of energy in the ejection of ink. The utilization of a low amount of energy is particularly important when a large pagewidth full color printhead is constructed having a large array of individual print ejection mechanism with each ejection mechanisms, in the worst case, being fired in a rapid sequence.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ink ejection nozzle arrangement suitable for incorporation into an inkjet printhead arrangement for the ejection of ink on demand from a nozzle chamber in an efficient and reliable manner.
According to a first aspect, the present invention provides an ink jet printhead comprising:
a plurality of nozzles;
a bubble forming chamber corresponding to each of the nozzles respectively, the bubble forming chambers adapted to contain a bubble forming liquid; and,
at least one heater element disposed in each of the bubble forming chambers respectively, the heater elements configured for thermal contact with the bubble forming liquid; such that,
heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein, the bubble forming chamber is at least partially formed by an amorphous ceramic material.
Amorphous ceramic material provides the bubble forming chamber with high strength. The non-crystalline structure avoids any points of weakness due to crystalline defects. These defects can act as stress concentration areas and are prone to failure.
According to a second aspect, the present invention provides a printer system which incorporates a printhead, the printhead comprising:
a plurality of nozzles;
a bubble forming chamber corresponding to each of the nozzles respectively, the bubble forming chambers adapted to contain a bubble forming liquid; and,
at least one heater element disposed in each of the bubble forming chambers respectively, the heater elements configured for thermal contact with the bubble forming liquid; such that,
heating the heater element to a temperature above the boiling point of the bubble forming liquid forms a gas bubble that causes the ejection of a drop of an ejectable liquid through the nozzle corresponding to that heater element; wherein,
the bubble forming chamber is at least partially formed by an amorphous ceramic material.
According to a third aspect, the present invention provides a method of ejecting drops of an ejectable liquid from a printhead, the printhead comprising a plurality of nozzles;
a chamber corresponding to each of the nozzles respectively, the chambers adapted to contain an ejectable liquid; and,
at least one droplet ejection actuator associated with each of the chambers respectively; wherein, the chamber is at least partially formed by an amorphous ceramic material;
the method comprising the steps of:
placing the ejectable liquid into contact with the drop ejection actuator; and actuating the droplet ejection actuator such that a droplet of an ejectable liquid is ejected through the corresponding nozzle.
Preferably, the amorphous ceramic material is silicon nitride. In another form, the amorphous ceramic material is silicon dioxide. In yet another embodiment, the amorphous ceramic material is silicon oxynitride.
Preferably, the thermal actuator units are interconnected at a first end to a substrate and at a second end to a rigid strut member. The rigid strut member can, in turn, be interconnected to the arm having one end attached to the paddle vane. The thermal actuator units can operate upon conductive heating along a conductive trace and the conductive heating can include the generation of a substantial portion of the heat in the area adjacent the first end. The conductive heating trace can include a thinned cross-section adjacent the first end. The heating layers of the thermal actuator units can comprise substantially either a copper nickel alloy or titanium nitride. The paddle can be constructed from a similar conductive material to portions of the thermal actuator units however it is conductively insulated therefrom.
Preferably, the thermal actuator units are constructed from multiple layers utilizing a single mask to etch the multiple layers.
The nozzle chamber can include an actuator access port in a second surface of the chamber. The access port can comprise a slot in a corner of the chamber and the actuator is able to move in an arc through the slot. The actuator can include an end portion that mates substantially with a wall of the chamber at substantially right angles to the paddle vane. The paddle vane can include a depressed portion substantially opposite the fluid ejection port.
In accordance with a further aspect of the present invention, there is provided a thermal actuator including a series of lever arms attached at one end to a substrate, the thermal actuator being operational as a result of conductive heating of a conductive trace, the conductive trace including a thinned cross-section substantially adjacent the attachment to the substrate.



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:
FIGS. 1-3 illustrate the basic operational principles of a preferred embodiment using a thermal bend actuator;
FIG. 4 illustrates a three dimensional view of a single ink jet nozzle arrangement constructed in accordance with the preferred embodiment of FIG. 1 ;
FIG. 5 illustrates an array of the nozzle arrangements of FIG. 4 ;
FIG. 6 shows a table to be used with reference to FIGS. 7 to 16 ;
FIGS. 7 to 16 show various stages in the manufacture of the ink jet nozzle arrangement of FIG. 4 ;
FIG. 17 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. 18 is a schematic cross-sectional view through the ink chamber FIG. 17 , at another stage of operation;
FIG. 19 is a schematic cross-sectional view through the ink chamber FIG. 17 , at yet another stage of operation;
FIG. 20 is a schematic cross-sectional view through the ink chamber FIG. 17 , at yet a further stage of operation; and
FIG. 21 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. 22 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 23 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 22 .
FIG. 24 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 25 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 24 .
FIG. 26 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 27 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 26 .
FIG. 28 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 29 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 30 is a schematic, partially cut away, exploded perspective view of the unit cell of FIG. 29 .
FIGS. 31 to 41 are schematic perspective views of the unit cell shown in FIGS. 29 and 30 , at various successive stages in the production process of the printhead.
FIGS. 42 and 43 show schematic, partially cut away, schematic perspective views of two variations of the unit cell of FIGS. 29 to 41 .
FIG. 44 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.
FIG. 45 is a schematic, partially cut away, perspective view of a further embodiment of a unit cell of a printhead.



DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS
Thermal Bend Actuator
In one preferred embodiment, there is provided a nozzle arrangement having a nozzle chamber containing ink and a thermal bend actuator connected to a paddle positioned within the chamber. The thermal actuator device is actuated so as to eject ink from the nozzle chamber. The preferred embodiment includes a particular thermal bend actuator which includes a series of tapered portions for providing conductive heating of a conductive trace. The actuator is connected to the paddle via an arm received through a slotted wall of the nozzle chamber. The actuator arm has a mating shape so as to mate substantially with the surfaces of the slot in the nozzle chamber wall.
Turning initially to FIG. 1-3 , there is provided schematic illustrations of the basic operation of a nozzle arrangement of the invention. A nozzle chamber 1 is provided filled with ink 2 by means of an ink inlet channel 3 which can be etched through a wafer substrate on which the nozzle chamber 1 rests. The nozzle chamber 1 further includes an ink ejection port 4 around which an ink meniscus forms.
Inside the nozzle chamber 1 is a paddle type device 7 which is interconnected to an actuator 8 through a slot in the wall of the nozzle chamber 1 . The actuator 8 includes a heater means eg. 9 located adjacent to an end portion of a post 10 . The post 10 is fixed to a substrate.
When it is desired to eject a drop from the nozzle chamber 1 , as illustrated in FIG. 2 , the heater means 9 is heated so as to undergo thermal expansion. Preferably, the heater means 9 itself or the other portions of the actuator 8 are built from materials having a high bend efficiency where the bend efficiency is defined as





bend
⁢



⁢
efficiency

=



Young
'

⁢
s
⁢



⁢
Modulus
×

(

Coefficient
⁢



⁢
of
⁢



⁢
thermal
⁢



⁢
Expansion

)



Density
×
Specific
⁢



⁢
Heat
⁢



⁢
Capacity






A suitable material for the heater elements is a copper nickel alloy which can be formed so as to bend a glass material.
The heater means 9 is ideally located adjacent the end portion of the post 10 such that the effects of activation are magnified at the paddle end 7 such that small thermal expansions near the post 10 result in large movements of the paddle end.
The heater means 9 and consequential paddle movement causes a general increase in pressure around the ink meniscus 5 which expands, as illustrated in FIG. 2 , in a rapid manner. The heater current is pulsed and ink is ejected out of the port 4 in addition to flowing in from the ink channel 3 .
Subsequently, the paddle 7 is deactivated to again return to its quiescent position. The deactivation causes a general reflow of the ink into the nozzle chamber. The forward momentum of the ink outside the nozzle rim and the corresponding backflow results in a general necking and breaking off of the drop 12 which proceeds to the print media. The collapsed meniscus 5 results in a general sucking of ink into the nozzle chamber 2 via the ink flow channel 3 . In time, the nozzle chamber 1 is refilled such that the position in FIG. 1 is again reached and the nozzle chamber is subsequently ready for the ejection of another drop of ink.
FIG. 4 illustrates a side perspective view of the nozzle arrangement FIG. 5 illustrates sectional view through an array of nozzle arrangement of FIG. 4 . In these figures, the numbering of elements previously introduced has been retained.
Firstly, the actuator 8 includes a series of tapered actuator units e.g. 15 which comprise an upper glass portion (amorphous silicon dioxide) 16 formed on top of a titanium nitride layer 17 . Alternatively a copper nickel alloy layer (hereinafter called cupronickel) can be utilized which will have a higher bend efficiency where bend efficiency is defined as:





bend
⁢



⁢
efficiency

=



Young
'

⁢
s
⁢



⁢
Modulus
×

(

Coefficient
⁢



⁢
of
⁢



⁢
thermal
⁢



⁢
Expansion

)



Density
×
Specific
⁢



⁢
Heat
⁢



⁢
Capacity






The titanium nitride layer 17 is in a tapered form and, as such, resistive heating takes place near an end portion of the post 10 . Adjacent titanium nitride/glass portions 15 are interconnected at a block portion 19 which also provides a mechanical structural support for the actuator 8 .
The heater means 9 ideally includes a plurality of the tapered actuator unit 15 which are elongate and spaced apart such that, upon heating, the bending force exhibited along the axis of the actuator 8 is maximized. Slots are defined between adjacent tapered units 15 and allow for slight differential operation of each actuator 8 with respect to adjacent actuators 8 .
The block portion 19 is interconnected to an arm 20 . The arm 20 is in turn connected to the paddle 7 inside the nozzle chamber 1 by means of a slot e.g. 22 formed in the side of the nozzle chamber 1 . The slot 22 is designed generally to mate with the surfaces of the arm 20 so as to minimize opportunities for the outflow of ink around the arm 20 . The ink is held generally within the nozzle chamber 1 via surface tension effects around the slot 22 .
When it is desired to actuate the arm 20 , a conductive current is passed through the titanium nitride layer 17 via vias within the block portion 19 connecting to a lower CMOS layer 6 which provides the necessary power and control circuitry for the nozzle arrangement. The conductive current results in heating of the nitride layer 17 adjacent to the post 10 which results in a general upward bending of the arm 20 and consequential ejection of ink out of the nozzle 4 . The ejected drop is printed on a page in the usual manner for an inkjet printer as previously described.
An array of nozzle arrangements can be formed so as to create a single printhead. For example, in FIG. 5 there is illustrated a partly sectioned various array view which comprises multiple ink ejection nozzle arrangements of FIG. 4 laid out in interleaved lines so as to form a printhead array. Of course, different types of arrays can be formulated including full color arrays etc.
The construction of the printhead system described can proceed utilizing standard MEMS techniques through suitable modification of the steps as set out in U.S. Pat. No. 6,243,113 entitled “Image Creation Method and Apparatus (IJ 41)” to the present applicant, the contents of which are fully incorporated by cross reference.
Fabrication of the ink jet nozzle arrangement is indicated in FIGS. 7 to 16 . The preferred embodiment achieves a particular balance between utilization of the standard semi-conductor processing material such as titanium nitride and glass in a MEMS process. The use of glass, or indeed any amorphous ceramic, to form the chamber is particularly beneficial. The pressure transients within the chamber can exert significant stresses on the chamber wall. Amorphous ceramics are relatively inexpensive and high strength, but also have a non-crystalline structure. Defects in a crystal structure can act as stress concentration points that are prone to failure in the cyclical loading environment of the nozzle chambers.
Obviously the skilled person may make other choices of materials and design features where the economics are justified. For example, a copper nickel alloy of 50% copper and 50% nickel may be more advantageously deployed as the conductive heating compound as it is likely to have higher levels of bend efficiency. Also, other design structures may be employed where it is not necessary to provide for such a simple form of manufacture.
Bubble Forming Heater Element Actuator
The present invention is also applicable to printheads using bubble forming heater elements. FIGS. 17 to 20 show a nozzle of this type. While the fabrication of nozzles of this type is described below, the nozzles, ejection actuators, associated drive circuitry and ink supply passages is formed on and through a wafer using lithographically masked etching techniques described in great detail in U.S. Ser. No. 10/302,274. In the interests of brevity, the disclosure of the '274 application is incorporated herein in it entirety.
With reference to FIGS. 17 to 20 , the unit cell 1 of a printhead according to an embodiment of the invention comprises a nozzle plate 2 with nozzles 3 therein, the nozzles having nozzle rims 4 , and apertures 5 extending through the nozzle plate. The nozzle plate 2 is plasma etched from a silicon nitride structure which is deposited, by way of chemical vapor deposition (CVD), over a sacrificial material which is subsequently etched.
The printhead also includes, with respect to each nozzle 3 , side walls 6 on which the nozzle plate is supported, a chamber 7 defined by the walls and the nozzle plate 2 , a multi-layer substrate 8 and an inlet passage 9 extending through the multi-layer substrate to the far side (not shown) of the substrate. A looped, elongate heater element 10 is suspended within the chamber 7 , so that the element is in the form of a suspended beam. The printhead as shown is a microelectromechanical system (MEMS) structure, which is formed by a lithographic process which is described in more detail below.
When the printhead is in use, ink 11 from a reservoir (not shown) enters the chamber 7 via the inlet passage 9 , so that the chamber fills to the level as shown in FIG. 17 . 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. 17 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. 17 , 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. As discussed above in relation to the previous embodiment, 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. 18 and 19 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. 20 , the printhead is shown at a still further successive stage of operation, in which the ink drop 16 that is being ejected is shown during its “necking phase” before the drop breaks off. At this stage, the bubble 12 has already reached its maximum size and has then begun to collapse towards the point of collapse 17 , as reflected in more detail in FIG. 21 .
The collapsing of the bubble 12 towards the point of collapse 17 causes some ink 11 to be drawn from within the nozzle 3 (from the sides 18 of the drop), and some to be drawn from the inlet passage 9 , towards the point of collapse. Most of the ink 11 drawn in this manner is drawn from the nozzle 3 , forming an annular neck 19 at the base of the drop 16 prior to its breaking off.
The drop 16 requires a certain amount of momentum to overcome surface tension forces, in order to break off. As ink 11 is drawn from the nozzle 3 by the collapse of the bubble 12 , the diameter of the neck 19 reduces thereby reducing the amount of total surface tension holding the drop, so that the momentum of the drop as it is ejected out of the nozzle is sufficient to allow the drop to break off.
When the drop 16 breaks off, cavitation forces are caused as reflected by the arrows 20 , as the bubble 12 collapses to the point of collapse 17 . It will be noted that there are no solid surfaces in the vicinity of the point of collapse 17 on which the cavitation can have an effect.
Features and Advantages of Further Embodiments
FIGS. 22 to 45 show further embodiments of unit cells 1 for thermal inkjet printheads, each embodiment having its own particular functional advantages. These advantages will be discussed in detail below, with reference to each individual embodiment. However, the basic construction of each embodiment is best shown in FIGS. 23 , 25 , 27 and 30 . The manufacturing process is substantially the same as that described above in relation to FIGS. 6 to 31 of the above referenced U.S. Ser. No. 10/302,274 (incorporated herein by cross reference). For consistency, the same reference numerals are used in FIGS. 22 to 45 to indicate corresponding components. In the interests of brevity, the fabrication stages have been shown for the unit cell of FIG. 29 only (see FIGS. 31 to 41 ). It will be appreciated that the other unit cells will use the same fabrication stages with different masking. Again, the deposition of successive layers shown in FIGS. 31 to 41 need not be described in detail below given that the lithographic process largely corresponds to that shown in FIGS. 6 to 31 in U.S. Ser. No. 10/302,274.
Referring to FIGS. 22 and 23 , the unit cell 1 shown has the chamber 7 , ink supply passage 32 and the nozzle rim 4 positioned mid way along the length of the unit cell 1 . As best seen in FIG. 23 , the drive circuitry is partially on one side of the chamber 7 with the remainder on the opposing side of the chamber. The drive circuitry 22 controls the operation of the heater 14 through vias in the integrated circuit metallisation layers of the interconnect 23 . The interconnect 23 has a raised metal layer on its top surface. Passivation layer 24 is formed in top of the interconnect 23 but leaves areas of the raised metal layer exposed. Electrodes 15 of the heater 14 contact the exposed metal areas to supply power to the element 10 .
Alternatively, the drive circuitry 22 for one unit cell is not on opposing sides of the heater element that it controls. All the drive circuitry 22 for the heater 14 of one unit cell is in a single, undivided area that is offset from the heater. That is, the drive circuitry 22 is partially overlaid by one of the electrodes 15 of the heater 14 that it is controlling, and partially overlaid by one or more of the heater electrodes 15 from adjacent unit cells. In this situation, the center of the drive circuitry 22 is less than 200 microns from the center of the associate nozzle aperture 5 . In most Memjet printheads of this type, the offset is less than 100 microns and in many cases less than 50 microns, preferably less than 30 microns.
Configuring the nozzle components so that there is significant overlap between the electrodes and the drive circuitry provides a compact design with high nozzle density (nozzles per unit area of the nozzle plate 2 ). This also improves the efficiency of the printhead by shortening the length of the conductors from the circuitry to the electrodes. The shorter conductors have less resistance and therefore dissipate less energy.
The high degree of overlap between the electrodes 15 and the drive circuitry 22 also allows more vias between the heater material and the CMOS metalization layers of the interconnect 23 . As best shown in FIGS. 30 and 31 , the passivation layer 24 has an array of vias to establish an electrical connection with the heater 14 . More vias lowers the resistance between the heater electrodes 15 and the interconnect layer 23 which reduces power losses.
In FIGS. 24 and 25 , the unit cell 1 is the same as that of FIGS. 22 and 23 apart from the heater element 10 . The heater element 10 has a bubble nucleation section 158 with a smaller cross section than the remainder of the element. The bubble nucleation section 158 has a greater resistance and heats to a temperature above the boiling point of the ink before the remainder of the element 10 . The gas bubble nucleates at this region and subsequently grows to surround the rest of the element 10 . By controlling the bubble nucleation and growth, the trajectory of the ejected drop is more predictable.
The heater element 10 is configured to accommodate thermal expansion in a specific manner. As heater elements expand, they will deform to relieve the strain. Elements such as that shown in FIGS. 22 and 23 will bow out of the plane of lamination because its thickness is the thinnest cross sectional dimension and therefore has the least bending resistance. Repeated bending of the element can lead to the formation of cracks, especially at sharp comers, which can ultimately lead to failure. The heater element 10 shown in FIGS. 24 and 25 is configured so that the thermal expansion is relieved by rotation of the bubble nucleation section 158 , and slightly splaying the sections leading to the electrodes 15 , in preference to bowing out of the plane of lamination. The geometry of the element is such that miniscule bending within the plane of lamination is sufficient to relieve the strain of thermal expansion, and such bending occurs in preference to bowing. This gives the heater element greater longevity and reliability by minimizing bend regions, which are prone to oxidation and cracking.
Referring to FIGS. 26 and 27 , the heater element 10 used in this unit cell 1 has a serpentine or ‘double omega’ shape. This configuration keeps the gas bubble centered on the axis of the nozzle. A single omega is a simple geometric shape which is beneficial from a fabrication perspective. However the gap 159 between the ends of the heater element means that the heating of the ink in the chamber is slightly asymmetrical. As a result, the gas bubble is slightly skewed to the side opposite the gap 159 . This can in turn affect the trajectory of the ejected drop. The double omega shape provides the heater element with the gap 160 to compensate for the gap 159 so that the symmetry and position of the bubble within the chamber is better controlled and the ejected drop trajectory is more reliable.
FIG. 28 shows a heater element 10 with a single omega shape. As discussed above, the simplicity of this shape has significant advantages during lithographic fabrication. It can be a single current path that is relatively wide and therefore less affected by any inherent inaccuracies in the deposition of the heater material. The inherent inaccuracies of the equipment used to deposit the heater material result in variations in the dimensions of the element. However, these tolerances are fixed values so the resulting variations in the dimensions of a relatively wide component are proportionally less than the variations for a thinner component. It will be appreciated that proportionally large changes of components dimensions will have a greater effect on their intended function. Therefore the performance characteristics of a relatively wide heater element are more reliable than a thinner one.
The omega shape directs current flow around the axis of the nozzle aperture 5 . This gives good bubble alignment with the aperture for better ejection of drops while ensuring that the bubble collapse point is not on the heater element 10 . As discussed above, this avoids problems caused by cavitation.
Referring to FIGS. 29 to 42 , another embodiment of the unit cell 1 is shown together with several stages of the etching and deposition fabrication process. In this embodiment, the heater element 10 is suspended from opposing sides of the chamber. This allows it to be symmetrical about two planes that intersect along the axis of the nozzle aperture 5 . This configuration provides a drop trajectory along the axis of the nozzle aperture 5 while avoiding the cavitation problems discussed above. FIGS. 43 and 44 show other variations of this type of heater element 10 .
FIG. 44 shows a unit cell 1 that has the nozzle aperture 5 and the heater element 10 offset from the center of the nozzle chamber 7 . Consequently, the nozzle chamber 7 is larger than the previous embodiments. The heater 14 has two different electrodes 15 with the right hand electrode 15 extending well into the nozzle chamber 7 to support one side of the heater element 10 . This reduces the area of the vias contacting the electrodes which can increase the electrode resistance and therefore the power losses. However, laterally offsetting the heater element from the ink inlet 31 increases the fluidic drag retarding flow back through the inlet 31 and ink supply passage 32 . The fluidic drag through the nozzle aperture 5 comparatively much smaller so little energy is lost to a reverse flow of ink through the inlet when a gas bubble form on the element 10 . The unit cell 1 shown in FIG. 45 also has a relatively large chamber 7 which again reduces the surface area of the electrodes in contact with the vias leading to the interconnect layer 23 . However, the larger chamber 7 allows several heater elements 10 offset from the nozzle aperture 5 . The arrangement shown uses two heater elements 10 ; one on either side of the chamber 7 . Other designs use three or more elements in the chamber. Gas bubbles nucleate from opposing sides of the nozzle aperture and converge to form a single bubble. The bubble formed is symmetrical about at least one plane extending along the nozzle axis. This enhances the control of the symmetry and position of the bubble within the chamber 7 and therefore the ejected drop trajectory is more reliable.
Other Embodiments
The invention has been described above with reference to printheads using thermal bend actuators and 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 inkjet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 above which matches the docket numbers in the table under the heading Cross References to Related Applications.
Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.
Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, print technology may be listed more than once in a table, where it shares characteristics with more than one entry.
Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.
The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.







ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS)








Description
Advantages
Disadvantages
Examples










Thermal
An electrothermal
Large force
High power
Canon 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

Thermoelastic
An actuator which
Low power
Efficient aqueous
IJ03, IJ09, IJ17,

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,

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

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


(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

thermoelastic
expansion (such as
Very low power
development (High

actuator
PTFE) is doped with
consumption
CTE conductive


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








































































































































































































































































































































































Description
Advantages
Disadvantages
Examples








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

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)







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


an ink reservoir,
to fabricate single
required
U.S. Pat. No. 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, IJ05,

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.























































































































NOZZLE CLEARING METHOD








Description
Advantages
Disadvantages
Examples










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








Description
Advantages
Disadvantages
Examples










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%)