In piezoelectric inkjet printheads, ink or other fluid is typically ejected in the form of drops. The fluid travels from various fluid chambers, through various nozzles, onto a substrate. The fluid is ejected by movement of a piezoelectric element. The fluid chamber has a wall that consists of a piezoelectric actuator, typically a membrane that is connected to the piezoelectric element. The fluid is moved towards the nozzle by vibration movement of the membrane actuated by the piezoelectric element.
At present, piezoelectric actuators of the unimorph type comprise a flexible membrane that is integrated with or attached to a piezoelectric layer. When the actuator has a relatively small thickness, e.g. between 1 and 10 micron, such as with thin film piezoceramic and thin membrane layers, the maximum width it may span over the fluid chamber is usually at most between 50-100 micron or less. At larger spans, the actuator is unsuitable to achieve a desired frequency and/or pressure. Therefore, the fluid chamber usually has an elongate shape, so that the maximum width is between about 50-100 micron or less, while its length is significantly larger, e.g. between 0.5 mm-2 mm.
It is an object of the invention to provide for an alternative piezoelectric method and device.
For the purpose of illustration, certain embodiments of the present invention will now be described with reference to the accompanying diagrammatic drawings, in which:
In the following detailed description, reference is made to the accompanying drawings. The embodiments in the description and drawings should be considered illustrative and are not to be considered as limited to the specific embodiment of element described. For illustrative purposes, the scale and relative dimensions are not as they would be in practice.
The indicated views in the drawings should not be considered as limiting for the orientation of the element or device. For example, a top view could also represent a bottom view, or a side view, etc., depending on the orientation of the respective element(s). However, multiple views of a single embodiment may indicate the relative relationships and relative orientation of the shown features. Accordingly, a top wall may be regarded as a bottom wall, and vice versa, depending on the orientation and use of the device, while the relationships between the bottom and top wall with respect to each other and with respect to the device may be preserved. The same principle may account for other features, e.g. a length or width of a feature may be chosen in any consistent manner.
Multiple embodiments may be derived from the following description through modification, combination or variation of certain elements. Furthermore, embodiments or elements that may not be specifically disclosed in this disclosure may be derived from the description and drawings.
The unit 1 may comprise an actuator 9. The actuator 9 may comprise a thin film actuator 9. The actuator 9 may function as a wall of the fluid chamber 2, for example as a bottom or a top wall of the fluid chamber 2, hereafter referred to as the actuator wall. The actuator 9 may comprise a membrane 10 and at least one piezoceramic element 11. The piezoceramic element 11 may comprise a thin film piezoceramic element 11. Both the membrane 10 and the piezoceramic element 11 may comprise thin film material. The thin film piezoceramic element 11 may comprise deposited or deposited and sintered piezoceramic material. The membrane 10 may form the wall of the fluid chamber 2. In an embodiment, one actuator 9 may comprise one membrane 10 extending along one fluid chamber 2, the actuator 9 comprising multiple piezoceramic elements 11A, 11B extending along the same fluid chamber 2.
The piezoceramic material may be patterned onto the membrane 10. A “patterned” piezoceramic element 11 may be understood as the piezoceramic element 11 comprising at least one interruption 12 above the fluid chamber 2. For example, the actuator 9 may comprise parts of a membrane 10 that are not covered by piezoceramic material between other parts of the same membrane 10 that are covered by piezoceramic material. Another patterned piezoceramic element 11 may comprise multiple piezoceramic elements 11A, 11B that are provided on one actuator 9. The exemplary piezoceramic element 11 of
The unit 1 may comprise a support element 13. As shown, the unit 1 may comprise multiple support elements 13. The support elements 13 may be arranged for preventing a supported portion 14 of the actuator 9 from movement in a main direction of actuation movement M of the actuator 9. The support element 13 may be connected to a printhead unit portion that extends approximately opposite to the actuator 9. The support element 13 may be connected to a rigid portion of the printhead. The printhead portion to which the support element 13 is connected may for example comprise part of a chamber wall 3 that is opposite to the actuator wall 4, for example a bottom or top wall 3 or 4 of the fluid chamber 2, depending on which one comprises the actuator wall. The support element 13 may allow for a thin film actuator 9 to extend over the entire fluid chamber 2; whereas, without the support element 13 the actuator 9 would be two or more times thicker.
The supported portion 14 may comprise a portion of the membrane 10 that is connected to the support element 13. The support element 13 may support the actuator 9 in the direction of actuation movement M, so that the supported portion 14 and the support element 13 may remain relatively static while surrounding parts of the actuator 9 may be vibrated by actuation of the piezoceramic element 11. For example, in the example of
The fluid chamber 2 may comprise at least one inlet 15 for letting fluid into the fluid chamber 2. The inlet 15 may for example be provided in either of the chamber walls 3, 4, 5A-D. In the drawing the inlet is provided in the side wall 5B. The inlet 15 and outlet 6 may be provided at opposite positions in the volume of the chamber so that fluid sweeps through all points in the volume. For example, the inlet 15 and the outlet 6 may be provided in or near opposite walls 3, 4 and/or in or near opposite side walls 5A, 5B or 5C, 5D. In the shown embodiment, the outlet 6 extends in the top wall 3, near a respective side wall 5A, and the inlet 15 extends in an opposite side wall 5B, near the bottom wall 4. In an embodiment, one or more support elements 13 may extend between the outlet 6 and the inlet 15. The respective support element 13 may extend in the fluid chamber 2, i.e. between or within the at least one side wall 5A-D.
The support element 13 may comprise a post. The post may be substantially cylindrical, and/or may have a substantially rounded, for example circular or elliptical, circumferential wall. Amongst others, a post shape may be desirable to maximize the area of the moving portion of the actuator. The unit 1 may comprise an array of posts.
The cross sectional lateral thickness C of the support element 13 may, for example, be between approximately 5 and approximately 30 micron, for example 10 to 15 micron. An exemplary cross sectional thickness C of the depicted support element 13 may be approximately 15 micron. The minimal cross-sectional thickness may be determined by the depth of the chamber 5, the type of etch process, and non-uniformity in the cross-sectional thickness C that allows adequate flow.
The actuator 9 may comprise two independently controllable piezoceramic elements 11A, 11B. For example, an independently controllable piezoceramic element 11A, 11B may extend on one side of a respective support element 13.
Use of the support element 13 may allow the span of the thin film actuator 9 to be increased with respect to conventional printhead units having an actuator of the same thickness. If needed, a conventional elongate shape of the fluid chamber 2 may be avoided by using the support element 13. Instead, more space efficient chamber shapes may be achieved. In an embodiment, the basic shape of the fluid chamber 2, as seen from a top view, may for example be approximately circular, square, hexagonal, any cyclic polygon, or the like. Of course, such shapes may be slightly modified, for example corners may be rounded and/or clipped, or lengths may be slightly longer than widths. For example, advantageous shapes may include elliptical, rhomboidal, and/or rectangular shapes, as seen from top view. In an embodiment, the length of the fluid chamber 2 may be between approximately one and three times the width of the fluid chamber 2. Here, the length L and width W may be regarded as the distances between opposite side walls 5A-D in two perpendicular directions, in a plane parallel to a top or bottom wall of the unit 1. The height H of the chamber 2 may refer to the distance between a bottom and top wall 3 and 4 of the chamber 2.
A distance D between adjacent support elements 13 may be between 20 and 90 microns, for example between 30 and 80 microns. For example, the distance between adjacent support elements may be approximately 55 micron. The minimal distance may be determined by the depth of the chamber 5, the type of etch process, and/or the opening size between the adjacent support elements 13 that may allow for adequate flow. Like-wise, a distance between a support element 13 and a side wall may be between 20 and 90 microns, for example 55 micron. In an embodiment, the actuator 9 may span the entire fluid chamber 2 over a distance of at least approximately 115 micron in two perpendicular directions, for example at least approximately 150 micron. Said distance may be the distance between opposite side wall portions 5A, 5B or 5C, 5D. One or more support elements 13 may support the actuator 9 so as to obtain a relatively wide span. The support elements 13 may be arranged to reduce the maximum unsupported span of the actuator 9, i.e. between support elements 13 and/or between a support element 13 and a wall 5A-D, by at least half of the width of the chamber 2.
The thickness T of the piezoceramic element 11 may be approximately 5 micron or less, for example approximately 3 micron or less, for example 1.5 micron or less. The thickness T of the piezoceramic element 11 may for example be approximately 0.5 micron. The thickness of the actuator 9 may for example be 10 micron or less, for example between approximately 1 and approximately 10 micron, for example between approximately 2.5 and approximately 5.5 microns. The support element 13 may allow for relatively thin actuators 9 spanning relatively wide fluid chambers 2. The total span of the actuator 9 over the fluid chamber 2 between opposite side wall portions may be at least 150 micron or more in two perpendicular directions, while the thickness of the actuator 9 may be 5 micron or less, for example 1.5 micron or less. The total span may be much higher, for example depending on the arrangement and number of support elements 13 that is used in the unit 1.
If a support element 13 supports the actuator 9 approximately in the middle between side wall portions of a fluid chamber 2, or in the middle between two support elements 13, a thickness of the actuator 9 may be reduced approximately 2.5 times while achieving the same displacement of the actuator 9 in the direction of actuation movement M. In other words, by decreasing an unsupported actuator span to one half of the original unsupported span, the thickness of the actuator may be reduced approximately 2.5 times for a similar displacement. Furthermore, by decreasing an unsupported actuator span to one half, the thickness of the actuator may be reduced approximately 2 times without loss of pressure. Therefore, by selectively placing support elements 13 the dimensions of the fluid chamber 2 may be chosen relatively freely.
Formulas may be used for estimating a level of stress σ and a maximum displacement ymax at the center of a rectangular membrane 10. In below formulas, a uniform load is applied across the whole surface of the rectangular membrane 10. This situation may for example correspond to a rectangular actuator 9 having a piezoceramic element 11 applying a load across substantially the whole surface of the membrane 10, and clamped by four side walls 5A-D. An indication of the maximum displacement ymax of the membrane 10 at the center of the membrane 10 may be obtained through equation
wherein α represents a constant factor indicated below, E represents the modulus of elasticity, t represents the thickness of the membrane, b represents the width of the membrane 10 between the side walls 5C-D and q represents the applied pressure across the surface. For identical conditions, an indication of the stress σ in the membrane 10 at the center of the membrane 10 may be obtained through equation
wherein β2 is a constant. The following table may be used for retrieving the constant factors α and β2, and a represents the length of the membrane 10 between the side walls 5A-B.
When for the same chamber 2 and an equal actuator 9, a row of support elements 13 is positioned along the center-line of the membrane 9, i.e. in the middle between respective sidewalls 5C-D, the resulting change in thickness t, stress σ and/or displacement ymax may be estimated by decreasing the value of b by one half of its value without support elements 13. A resulting change in maximum pressure may correspond to the change in stress σ.
The theoretical situation sketched above corresponds to a membrane 10 that is composed out of one layer. When applying multiple layer actuators 9, the values of constants such as E, α and β2 may change. However, the exponents for thickness t and width b may be close enough to estimate a general impact of placing support elements 13. Therefore, a general impact of placing support elements 13 in relation to total actuator 9 thickness and spans may be estimated using these formulas. For example, when support elements 13 are taken into account, the following formulas may be used:
(b2/b1)4=(t2/t1)3
wherein t1 and b1 are the initial thickness and width of the membrane 10, and b2 is a width of the span between bisecting support elements 13 and the respective side wall 5, wherein
b2=(1−ε)b1/2
wherein ε is the width of the support element 13 indicated in the form of a percentage of the width of the entire chamber 2. For example, for ε=0, t2≈t1/2.5 and for ε=0.14, t2≈t1/3. Hence, if a single row of support elements 13 bisects the chamber and the width of the support element 13 is included, having a width of approximately 14% of the total chamber width, the thickness of the actuator 9 may be reduced at least 3 times for a similar displacement ymax, and the thickness t may be reduced at least 2.3 times without loss of pressure.
To achieve approximately the same displacement and pressure after inserting the support elements 13 and reducing the thickness of the actuator 9, the patterning of the piezoelectric element 11 and other geometrical factors may be adjusted. Furthermore, instead of, or in addition to above formulas, actual values may be calculated through finite element analysis models and/or experiments.
A method of producing a unit 1 may comprise patterning thin film piezoceramic material on a membrane 10. For example thin film piezoceramic material may be deposited on the membrane 10 and afterwards sintered. Amongst others, deposition of the piezoceramic material may be performed by sputtering, sol gel coating, aerosol impingement, or the like. In another embodiment, a thin film piezoceramic element may be patterned by etching a substrate comprising piezoceramic material, for example using a photolithographic method.
The resulting actuator 9 may have a thickness of 5 micron or less, for example 3 micron or less, or for example 1.5 micron or less. The fluid chamber 2 may be lithographically manufactured, or otherwise, by illuminating and etching a wafer. The surrounding parts of the wafer may form the side walls 5A-D. For example, the lithographically processed wafer may comprise the side walls 5A-D and the support elements 13. The thin film actuator 9 may be connected to the wafer, such as the side walls 5A-D, for example after the fluid chamber 2 and the support elements 13 were etched. The support element 13 may extend between the at least one side wall 5A-D of the chamber 2, so that the support element 13 supports the thin film actuator 9 after connection with the wafer portion.
A method of shooting a fluid drop by piezoelectric actuation using the unit 1 may comprise the following. In response to an actuation of the piezoceramic element 11, the membrane 10 may be vibrated. The vibrations generate transient pressure pulses in the fluid inside the chamber 2, which may cause fluid to flow in the direction of the outlet 6, and one or more drops to shoot from the nozzle 7. The membrane 10 may be supported by at least one fluid chamber wall 5A-D and at least one support element 13 so that the membrane deflects on at least two sides next to the respective support element 13, at least as seen from a top view. Deflection in the actuator 9 is inhibited where it is attached to the respective support element 13, e.g. at the supported portion 14, at least in the direction of movement M. The fluid in the fluid chamber 2 may flow along the respective support element 13 as a response to the vibration on the at least two sides of the support element 13, in the direction of the outlet 6, and a fluid drop may be ejected from the respective outlet 6.
In
In
The interruption 12 and the support element 13 may conveniently allow a driving interconnect electrode 16 to be placed onto the supported portion 14. The interruption 12 may prevent that the interconnect electrode 16 needs to be placed onto the piezoceramic element 11. By placing the interconnect electrode 16 onto the supported portion 14, which is kept relatively static by the support element 13, vibration of the interconnect electrode 16 may be prevented and a relatively stress-free attachment may be achieved. As shown in
As is known in the art, an actuator 9 may comprise at least two electrodes (not shown) connected to a piezoelectric element, with a voltage between the electrodes. An embodiment may have electrodes on opposing surfaces of the piezoceramic element 11. The respective electrodes on the plane at the interface between the respective piezoceramic elements 11 and the membrane 10, hereafter called “inside electrodes”, may form part of the same layer and may have the same voltage with respect to the ground. In fact, the inside electrode layer may be maintained at ground potential. When the piezoceramic element 11 comprises patterned piezoceramic elements 11A, 11B, an interface conductive layer, which may extend between the electrodes and the piezoceramic elements 11, may be continuous, so that each inside electrode may be electrically connected to the respective piezoceramic elements 11A, 11B via the interface conductive layer. The opposite electrodes, i.e. on the outside of the piezoceramic element 11, opposite to the membrane 10, may be connected to the interconnect electrode 16 via conductive thin film strips. In a method of manufacturing, the conductive thin film strips may be added after the piezoceramic element 11 is patterned to the membrane 10. To avoid an extra processing step, the inside electrode may be continuous. In an embodiment where each of the piezoceramic elements 11A, 11B are independently controlled, a conductive film may extends from each separate interconnect electrode 16 associated with each outside electrode.
In other embodiments, two electrodes may be provided in the same plane and/or on the outside surface of the piezoceramic element 11. Multiple electrodes may be provided and interdigitated with every other electrode having the same voltage, and connected to corresponding patterned piezoceramic elements 11A, 11B.
In
The actuator 9 may comprise an interruption 12 at the supported portion 14. The actuator 9 may comprise a substantially circular shaped piezoceramic element 11. The interruption 12 may be provided approximately in a middle portion of the piezoceramic element 11. The piezoceramic element 11 may be arranged next to the support element 13 and next to the side wall 5, between the support element 13 and the side wall 5, as seen from a top view.
At portions of the membrane 10 that are relatively close to the support element 13, or that are close to a respective side wall 5, vibration may be impeded. Therefore, the piezoceramic element 11 may be arranged at a distance from the respective support element 13 and/or at a distance from the respective side wall 5, as seen from a top view. For example, such distance may be at least 1 micron, or at least 5 micron, or at least 10 micron.
In
In
The actuator 9 may have a thickness of approximately 2.5 micron. The distance D between adjacent support elements 13 and the distance between the support element 13 and the side wall 5 may for example be approximately 55 micron, or for example at least between 30 and 80 micron. The shown pattern of the piezoceramic element 11 may allow a relatively uniform displacement and stiffness of the actuator 9, also where spans are not exactly the same as said distance D. The shown example, having an actuator thickness of approximately 2.5 micron, and a distance D between support elements 13, and support elements 13 and side walls 5, of approximately 55 micron, may result in a maximum displaced volume of fluid of approximately 3.3 picoliters per deflection of the actuator 9 into the outlet 6.
The dividing interruption 12D may extend over at least one of the supported portions 14. The dividing interruption 12D may comprise an opening extending laterally over the width of the membrane 10, in the middle of the membrane 10, at least as seen from a top view.
In an embodiment, the separate, independently controllable piezoceramic elements 11G, 11H may be non-simultaneously actuated so as to achieve better fluid flow.
Advantageously, the patterning of the respective piezoceramic elements 11 may be adapted to achieve maximum deflection. The thickness of the membrane 10 and/or the thickness of the piezoceramic element 11 may be adapted to achieve a desired fluid pressure. This may apply to every actuator 9 within this disclosure. Every design may be optimized to achieve the largest possible displacement with a pressure that meets the flow speed desired at the outlet.
Although it may be advantageous to provide for interruptions 12 at supported portions 14, as described above, in certain embodiments the piezoceramic element 11 may extend over the supported portion 14 and the support element 13 or the sidewalls 5A-D without interruption. Furthermore, the invention does not exclude the use of elongate fluid chamber shapes.
Although in this description, a unit 1 for an inkjet printhead is described, in other embodiments, the unit 1 may comprise any type of piezoelectric actuator, for example other than a piezoelectric inkjet printhead unit. For example, the fluid may comprise a liquid and/or gas. The unit 1 may be part of a MEMS (micro electro mechanical system) device that moves fluid, wherein the MEMS device may for example form part of a lab on a chip. In other embodiments, the unit 1 may comprise a speaker or tone generating device for displacing air. In again another embodiment, the unit 1 may comprise a device for moving a component, for example controlling the position of tips in an atomic force microscope.
In a first aspect, a piezoelectric unit 1 is provided, comprising (i) a fluid chamber 2, (ii) a fluid outlet 6, (iii) an actuator 9. The unit 1 may comprise a thin film piezoceramic element 11 and a membrane 10, acting as a wall 4 of the fluid chamber 2, and (iv) a support element 13 arranged for preventing a supported portion 14 of the actuator 9 from movement in a main direction of actuation movement M of the actuator 9, while allowing such actuation movement M on at least two sides of the supported portion 14, wherein the support element 13 may be connected to a unit portion 4, 17 that may extend approximately opposite to the actuator.
In a second aspect, a method of ejecting a fluid drop by piezoelectric actuation may be provided. The method may comprise (i) actuating a piezoceramic element 11, (ii) vibrating a membrane 10 that is supported by at least one fluid chamber wall 5, 5A-D and at least one support element 13 so that the membrane 10 deflects on at least two sides next to the respective support element 13 and deflection in the membrane 10 is inhibited at the portion 14 where it is attached to the respective support element 13, (iii) fluid in the fluid chamber 2 flowing along the respective support element 13 as a response to the vibration on the at least two sides of the support element 13, in the direction of an outlet 6 that opens into the chamber 2, and (iv) a fluid drop ejecting from the respective outlet 6 by the vibration.
In a third aspect, a method of producing a piezoelectric unit 1 may be provided. The method may comprise (i) creating a thin film actuator 9 by patterning piezoceramic material on a membrane 10, wherein the actuator 9 may have a thickness t of approximately 5 micron or less, and (ii) connecting the actuator 9 to a wafer, wherein the wafer may comprise a fluid chamber wall 5, 5A-D and a support element 13, the support element 13 extending between at least one side wall 5 of the chamber 2, as seen from a direction perpendicular to the surface of the actuator 9 after connection, so that the support element 13 and the wall 5 may support the thin film actuator 9 after connection with the wafer.
The above description is not intended to be exhaustive or to limit the invention to the embodiments disclosed. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality, while a reference to a certain number of elements does not exclude the possibility of having more elements. A single unit may fulfil the functions of several items recited in the disclosure, and several items recited in the disclosure may fulfil the function of one unit.
The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Multiple alternatives, equivalents, variations and combinations may be made without departing from the scope of the invention.
Number | Name | Date | Kind |
---|---|---|---|
7159966 | Taira | Jan 2007 | B2 |
7240996 | Kobayashi et al. | Jul 2007 | B2 |
20060077237 | Shin et al. | Apr 2006 | A1 |
20070236541 | Wijshoff | Oct 2007 | A1 |
20090073242 | Xu et al. | Mar 2009 | A1 |
Number | Date | Country |
---|---|---|
2007268962 | Oct 2007 | JP |
20030050477 | Jun 2003 | KR |
Entry |
---|
International Search Report for Application No. PCT/US2010/054700. Report issued Jul. 28, 2011. |
Number | Date | Country | |
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20110102516 A1 | May 2011 | US |