PIEZOELECTRIC PRINTING DEVICE WITH OUTER SURFACE ELECTRODE LAYER

Abstract

A piezoelectric printing device includes a substrate and a piezoelectric plate. A pair of staggered rows of drop ejectors is disposed along a row direction on the substrate. Each drop ejector includes a nozzle in fluid communication with a pressure chamber that is bounded by side walls. The piezoelectric plate has a first surface that is proximate to the pressure chambers. An electrode layer is disposed on an opposing outer second surface of the piezoelectric plate. The electrode layer includes a signal line corresponding to each drop ejector in the pair of staggered rows, and at least one common ground bus connected to ground traces that are aligned over the side walls of each pressure chamber. Each signal line leads to a corresponding signal input pad that is disposed between the staggered rows. The common ground bus extends along the row direction and leads to a ground return pad.

Claims

1. A piezoelectric printing device comprising: a substrate including: a first side; and a second side that is opposite to the first side; at least one pair of staggered rows of drop ejectors disposed on the substrate, each row being aligned along a row direction, each drop ejector including: a pressure chamber having a width W along the row direction disposed in the substrate on the first side of the substrate, the pressure chamber being bounded by a first side wall and a second side wall; and a nozzle in fluidic communication with the pressure chamber, the nozzle being disposed in a nozzle layer on the second side of the substrate; a piezoelectric plate having a thickness T between a first surface that is proximate to the pressure chambers and an outer second surface opposite to the first surface; an electrode layer disposed on the second surface of the piezoelectric plate, wherein the electrode layer includes: a signal line corresponding to each drop ejector in the at least one pair of staggered rows of drop ejectors, each signal line leading to a corresponding signal input pad that is disposed between the staggered rows of drop ejectors in the at least one pair of staggered rows of drop ejectors; and at least one common ground bus connected to ground traces that are aligned over the first side wall and the second side wall of each pressure chamber, wherein the at least one common ground bus extends along the row direction and leads to at least one ground return pad.

2. The piezoelectric printing device of claim 1, wherein the at least one common ground bus is disposed between the signal input pads of the first staggered row of drop ejectors and the signal input pads of the second staggered row of drop ejectors in the at least one pair of staggered rows of drop ejectors.

3. The piezoelectric printing device of claim 1, wherein the signal input pads of the at least one pair of staggered rows of drop ejectors are disposed proximate to a first end of the corresponding pressure chambers and the at least one common ground bus is disposed proximate to a second end of the corresponding pressure chambers opposite to the first end.

4. The piezoelectric printing device of claim 1, wherein the first row in the at least one pair of staggered rows of drop ejectors and the second row in the at least one pair of staggered rows of drop ejectors are spaced apart from each other along a first direction perpendicular to the row direction.

5. The piezoelectric printing device of claim 1, wherein the nozzle is disposed near a first end of the pressure chamber that is proximate to the signal input pad.

6. The piezoelectric printing device of claim 5, wherein each drop ejector further includes an ink inlet that is in fluidic communication with the pressure chamber, and wherein the ink inlet is disposed near a second end of the pressure chamber opposite the first end.

7. The piezoelectric printing device of claim 1, wherein the piezoelectric plate is poled along a direction that is perpendicular to the first surface of the piezoelectric plate.

8. The piezoelectric printing device of claim 1, wherein the nozzles of the first staggered row of drop ejectors are proximate to the nozzles of the second staggered row of drop ejectors, and wherein the pressure chambers of the first staggered row of drop ejectors and the pressure chambers of the second staggered row of drop ejectors extend in opposite directions from the respective nozzles.

9. The piezoelectric printing device of claim 1, wherein T is less than 0.5W.

10. The piezoelectric printing device of claim 9, wherein T is less than 0.3W.

11. The piezoelectric printing device of claim 1, wherein a distance between a signal line and an adjacent ground trace is greater than 0.1W.

12. The piezoelectric printing device of claim 1, wherein a width of a signal line is greater than 0.1W.

13. The piezoelectric printing device of claim 1, wherein a distance between a signal line and an adjacent ground trace is greater than 0.5T and less than 2T.

14. The piezoelectric printing device of claim 1, wherein a width of a signal line is greater than 0.2T.

15. The piezoelectric printing device of claim 1, wherein each signal line is disposed over a corresponding pressure chamber and extends in a direction perpendicular to the row direction.

16. The piezoelectric printing device of claim 15, wherein each signal line is disposed over a center of the corresponding pressure chamber.

17. The piezoelectric printing device of claim 1, wherein the ground traces are disposed midway between corresponding pressure chambers and extend in a direction perpendicular to the row direction.

18. The piezoelectric printing device of claim 1, wherein the ground traces have a width that is greater than a width of the side walls of the pressure chambers.

19. The piezoelectric printing device of claim 1, further comprising a masking layer disposed over the electrode layer, wherein the masking layer includes windows over the signal input pads and over the at least one ground return pad.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows an exploded perspective view of a prior art piezoelectric drop ejector array configuration;

[0017] FIG. 2 shows a cross-section of a single drop ejector of the type shown in FIG. 1;

[0018] FIG. 3 shows a cross-section of a portion of a piezoelectric plate and a corresponding portion of a substrate;

[0019] FIG. 4A shows a top view of three drop ejectors in a substrate;

[0020] FIG. 4B shows a top view of electrical lines on a piezoelectric plate corresponding to the drop ejectors shown in FIG. 4A;

[0021] FIG. 5 shows a top view of a single drop ejector and its corresponding electrical lines;

[0022] FIG. 6 shows a top view of a portion of a piezoelectric printing device according to an embodiment;

[0023] FIG. 7 shows a top view of a masking layer with windows; and

[0024] FIG. 8 shows a top view of a portion of a piezoelectric printing device according to another embodiment.

[0025] It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The invention is inclusive of combinations of the embodiments described herein. References to “a particular embodiment” and the like refer to features that are present in at least one embodiment of the invention. Separate references to “an embodiment” or “particular embodiments” or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. The use of singular or plural in referring to the “method” or “methods” and the like is not limiting. It should be noted that, unless otherwise explicitly noted or required by context, the word “or” is used in this disclosure in a non-exclusive sense. Words such as “over”, “under”, “above” or “below” are intended to describe positional relationships of features that are in different planes, but it is understood that a feature of a device that is “above” another feature of the device in one orientation would be “below” that feature if the device is turned upside down.

[0027] FIG. 3 shows a cross-section of a piezoelectric plate 210 and a corresponding portion of a substrate 100 through dashed line 3-3 of FIG. 6. Piezoelectric plate 210 has a thickness T. Substrate 100 includes a pair of pressure chambers 111 and 112, which extend outwardly from a central region. Each pressure chamber 111 and 112 includes a channel 130 that leads to a nozzle 132 disposed in a nozzle layer 330. A bonding layer 270 is disposed on a first surface 211 of the piezoelectric plate 210. The bonding layer 270 can be a polymer adhesive, for example. Bonding layer 270 joins piezoelectric plate 210 to the first side 101 of substrate 100 in the assembled piezoelectric printing device 10 (FIG. 6). An electrode layer 220 is disposed on outer second surface 212 piezoelectric plate 210. Electrode layer 220 includes signal lines 251 on outer second surface 212 of the piezoelectric plate 210 that extend over pressure chambers 111 and 112 in the assembled device. Signal lines 251 lead to corresponding signal input pads 255. Electrode layer 220 also includes at least one common ground bus 264.

[0028] FIG. 4A shows a top view of a row of three drop ejectors 150 formed on a substrate 100 (FIG. 3) each drop ejector 150 including a pressure chamber 110 and a nozzle 132. Nozzles 132 (as well as drop ejectors 150) are aligned along a row direction 51 and the centers of adjacent nozzles are spaced at a pitch p. Pressure chambers 110 have a width W along the row direction 51 and are bounded by side walls 161 and 162, each having a wall width s, such that W+s=p. In order to provide sufficiently large area of the pressure chamber 110, it is advantageous to have W greater than 0.8 p in many embodiments. In other words, typically s is less than 0.2 p. The nozzle 132 is disposed near a first end 115 of the pressure chamber 110. In the example shown in FIG. 4A, ink enters the pressure chamber 110 from ink groove 120 (connected to an ink inlet port 230 as in FIGS. 1 and 2), through ink inlet 121, through filter 146 and through restrictor 145 near second end 116 of pressure chamber 110 opposite the first end 115. Ink groove 120 provides ink to a plurality of pressure chambers 110. In other examples described below, ink enters ink inlets 121 directly from an edge of the substrate 100. Filter 146 can include pillars similar to the pillars 141 shown in prior art FIG. 1. Restrictor 145 provides flow impedance (as does filter 146) to help limit the flow of ink toward inlet 121 when a drop of ink is being ejected from pressure chamber 110, thereby directing more of the pressure of the deflecting piezoelectric plate to propelling the drop of ink.

[0029] FIG. 4B shows a top view of electrical lines corresponding to the drop ejectors 150 shown in FIG. 4A. The electrical lines are provided as part of an electrode layer 220 disposed on outer second surface 212 piezoelectric plate 210 (FIG. 3). Widths and spacings of electrical lines are configured for efficient driving of the piezoelectric plate 210. FIG. 5 shows a top view of a single drop ejector 150 (dashed lines) that is disposed in a substrate 100 below the corresponding electrical lines disposed on the piezoelectric plate 210 in order to show spatial relationships. A signal line 251 is disposed over each corresponding pressure chamber 110 and extends in a direction 52 that is perpendicular to the row direction 51. In the example shown in FIG. 5, signal line 251 is disposed over a center of the corresponding pressure chamber 110. Each signal line leads to a corresponding signal input pad 255. Nozzle 132 is disposed near a first end 115 of the pressure chamber 110 proximate to the signal input pad 255. With reference to FIGS. 4A and 4B, signal line 251 has a width b that is greater than 0.1 times the width W of the pressure chamber 110. Signal line width b is also greater than 0.2 times the thickness T of the piezoelectric plate 210 (FIG. 3). Ground traces 261 are aligned over the first side wall 161 and the second side wall 162. Ground traces are typically disposed midway between corresponding pressure chambers 110 and extend in a direction 52 that is perpendicular to row direction 51. Ground trace 261 has a width c that is greater than the width s of side walls 161 and 162 in many embodiments. A distance d between a signal line 251 and an adjacent ground trace 261 is typically greater than 0.1 W. A distance d between a signal line 251 and an adjacent ground trace 261 is typically greater than 0.5 T and less than 2T.

[0030] FIG. 6 shows a top view of a portion of a piezoelectric printing device 10 according to an embodiment of the invention. A pair of staggered rows 181 and 182 of drop ejectors 150 (similar to those described above with reference to FIGS. 4A, 4B and 5) is disposed on the substrate 100 (FIG. 3). Each row is aligned along row direction 51. First row 181 and second row 182 are spaced apart from each other along a direction 52 that is perpendicular to row direction 51. Each drop ejector 150 in first row 181 includes a pressure chamber 111 and each drop ejector in second row 182 includes a pressure chamber 112 that is disposed on a first side 101 of the substrate 100. In the example shown in FIG. 6, ink is fed into the ink inlets 121 of each drop ejector 150 directly from the edges of substrate 100 that extend along row direction 51. The pressure chambers 111 and 112 are bounded a first side wall 161 and a second side wall 162. Each drop ejector also includes a nozzle 132 that is in fluidic communication with the corresponding pressure chamber 111 or 112. The nozzles 132 are disposed in a nozzle layer 330 on a second side 102 of the substrate 100. An electrode layer 220 disposed on an outer second surface 212 of a piezoelectric plate 210 (FIG. 3) includes a signal line 251 corresponding to each drop ejector 150 in each of the staggered rows 181 and 182 of drop ejectors 150. Each signal line 251 leads to a corresponding signal input pad 255 that is disposed between the staggered rows 181 and 182 of drop ejectors 150. The electrode layer 220 also includes at least one common ground bus 264 that is connected to ground traces 261 that are aligned over the first and second side walls 161 and 162 of each pressure chamber. The common ground bus 264 extends along the row direction 51 and leads to a ground return pad 265. In the example shown in FIG. 6, the common ground bus 264 is disposed between the signal input pads 255 of the first staggered row 181 of drop ejectors 150 and the signal input pads 255 of the second staggered row 182 of drop ejectors 150. The configuration of signal input pads 255 and ground return pad 265 is advantageous for providing electrical interconnection from piezoelectric printing device 10 in a compact region to a printhead package (not shown).

[0031] The nozzles 132 in row 181 are spaced at pitch p, and the nozzles 132 in row 182 are also spaced at pitch p. The two rows are offset by a distance p/2 along the row direction 51. As a result, if a recording medium (not shown) is moved relative to piezoelectric printing device 10 along direction 52, ejecting ink drops by the drop ejectors in row 181 at a suitable timing relative to ejecting ink drops by the drop ejectors in row 182 can print a composite row of dots on the recording medium with a dot spacing of p/2. It is preferable to have a small printing region on the piezoelectric printing device 10, i.e. a relatively short distance between the nozzles 132 in row 181 and the nozzles 132 in row 182 along direction 52. In order to accomplish this, the drop ejectors 150 in rows 181 and 182 are oppositely oriented, such that the nozzles 132 of the first staggered row 181 are proximate to the nozzles 132 of the second row, and such that the pressure chambers 111 of the first row 181 and the pressure chambers 112 of the second row 182 extend in opposite directions along direction 52 from their respective nozzles 132. The printing region can be further reduced on the piezoelectric printing device 10 in the embodiment shown below in FIG. 8.

[0032] As shown in the top view of FIG. 7, in order to provide more reliable electrical interconnection without shorts, an electrically insulating masking layer 280 can be disposed over the electrode layer 220, such that the masking layer 280 includes windows 281 over the signal input pads 255 and a window 282 over the ground return pad 265 in order to expose the pads for electrical interconnection.

[0033] FIG. 8 shows a top view of a portion of a piezoelectric printing device 10 according to another embodiment of the invention. The configuration shown in FIG. 8 is similar to that shown in FIG. 6, except for the positions of the common ground bus 264 and the ground return pad 265. In the embodiment shown in FIG. 8, a first common ground bus 264 is disposed proximate to the second end 116 of the corresponding pressure chambers 110 in first row 181, and a second common ground bus 266 is disposed proximate to the second end 116 of the corresponding pressure chambers 110 in second row 182. The signal input pads 255 are disposed proximate to the first ends 115 of the pressure chambers 110 in both rows 181 and 182, as they were in the FIG. 6 embodiment. First common ground bus 264 leads to a first ground return pad 265, and second common ground bus 266 leads to a second ground return pad 267. The same electrically insulating masking layer 280 shown in FIG. 7 can be used for exposing the pads for electrical interconnection. In other embodiments (not shown) ground return pads 265 and 267 can be extended further toward the center so that they merge into a single ground return pad.

[0034] The drop ejectors 150 and electrical lines described above with reference to FIGS. 3, 4A, 4B, 5, 6 and 8 are well suited for a piezoelectric plate 210 that is configured to cause local deflection of the piezoelectric plate 210 into one or more pressure chambers 110 when a voltage pulse is applied to the electrodes corresponding to those pressure chambers 110 in order to eject a drop of ink. For such applications, the piezoelectric plate 210 is poled along a direction that is normal to first surface 211. For efficient deflection of the piezoelectric plate 210 of thickness T into a pressure chamber 110 having a width W, it is advantageous for T to be less than 0.5W, and in some embodiments for T to be less than 0.3W.

[0035] In an exemplary embodiment, the pitch p in each row is 0.01 inch, so that the nozzles 132 in each row are disposed at 100 nozzles per inch and a composite row of dots can be printed at 200 dots per inch by the pair of rows. For a pitch p=0.01 inch=254 microns a chamber width W can be 224 microns and a side wall width s can be 30 microns, so that s is less than 0.2p as described above with reference to FIG. 4A. It is advantageous for a discrete piezoelectric plate 210 to have a thickness of around 50 microns, so that it is not too fragile. In such an example, T˜0.22W. It can be seen from FIGS. 4A and 4B that nozzle pitch p is equal to the width b of signal line 251 plus the width c of ground trace 261 plus twice the distance d between signal line 251 and ground trace 261, i.e. p=b+c+2d. In an example, width b of signal line 251 is 90 microns, width c of ground trace 261 is 90 microns and distance d is 37 microns. For the example where W=224 microns and d=37 microns, the distance d between a signal line 251 and an adjacent ground trace 261 is greater than 0.1W. In addition in this example, the width b of signal line 251 is greater than 0.1W. Further, for a thickness T of the piezoelectric plate 210 of 50 microns, the distance d=37 microns between a signal line 251 and an adjacent ground trace 261 is greater than 0.5T and less than 2T, and the width b of a signal line 251 is greater than 0.2T.

[0036] In the embodiments described above there has been a single pair of staggered rows 181 and 182 of drop ejectors 150. In other embodiments (not shown) there can be additional pairs of staggered rows of drop ejectors that can be used to provide higher printing resolution or increased ink coverage, or can eject different types of ink (such as different colors of ink) for each pair of staggered rows, or can eject different ranges of drop sizes for each pair of staggered rows.

[0037] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.