Droplet deposition head

Abstract

A droplet deposition head having a fluid chamber connected to a droplet ejection nozzle and to a reservoir for the fluid, and a piezoelectric actuator element formed at least in part by a fluid chamber wall having an electrode thereon, which element is displaceable in response to a drive voltage to generate a pressure in the chamber to eject a droplet of fluid from the chamber through the nozzle wherein the electrode is provided with a passivation coating which comprises, at least in part, a laminate comprising an inorganic insulating layer nearest to or contacting the electrode and an organic insulating layer overlying the inorganic insulating layer wherein defects in the insulating layers tend to be misaligned at the interface there between and wherein the inorganic insulating layer has thickness less than or equal to 500 nm and the organic insulating layer has a thickness less than 3 m.

Claims

1. A droplet deposition head comprising: a fluid chamber connected to a droplet ejection nozzle and to a reservoir for the fluid, and a piezoelectric actuator element formed at least in part by a fluid chamber wall comprising an electrode thereon, wherein the piezoelectric actuator element is displaceable in response to a drive voltage to thereby generate a pressure in the chamber to eject a droplet of fluid from the chamber through the nozzle, wherein: the electrode is provided with a passivation coating which comprises, at least in part, a laminate comprising an inorganic insulating layer nearest to the electrode and an organic insulating layer overlying the inorganic insulating layer, defects in the inorganic and organic insulating layers are substantially misaligned at the interface between the inorganic and organic insulating layers, and the inorganic insulating layer has thickness less than or equal to 500 nm and the organic insulating layer has a thickness less than 3 m.

2. A droplet deposition head according to claim 1, wherein the inorganic insulating layer has thickness less than or equal to 100 nm and the organic insulating layer has thickness less than or equal to 1.5 m.

3. A droplet deposition head according to claim 1, wherein the laminate comprises more than one inorganic insulating layer and more than one organic insulating layer and at least one organic insulating layer is disposed between two inorganic insulating layers.

4. A droplet deposition head according to claim 3, wherein the laminate comprises two inorganic insulating layers and two organic insulating layers.

5. A droplet deposition head according to claim 3, wherein the laminate has a top insulating layer which is an organic insulating layer.

6. A droplet deposition head according to claim 5, wherein the top insulating layer comprises an aperture.

7. A droplet deposition head according to claim 1, wherein the passivation coating comprises an electroless metal layer disposed within or on the laminate.

8. A droplet deposition head according to claim 1, wherein the passivation coating comprises a buffer or seed layer provided on the electrode.

9. A droplet deposition apparatus comprising: the droplet deposition head according to claim 1, wherein the passivation coating comprises a layer of an electroless metal on an inorganic insulating layer and an organic insulating layer on the electroless metal layer.

10. A method for the manufacture of a droplet deposition head comprising: providing a fluid chamber connected to a droplet ejection nozzle and to a reservoir for the fluid, providing a piezoelectric actuator element formed at least in part by a fluid chamber wall having an electrode thereon, wherein the piezoelectric actuator element is displaceable in response to a drive voltage to thereby generate a pressure in the fluid chamber to eject a droplet of fluid from the fluid chamber through the nozzle, forming a passivation coating on the electrode by depositing an inorganic insulating layer of thickness less than 500 nm on or over an electrode using a first deposition technique at a temperature less than or equal to 150 C., and depositing an organic insulating layer of thickness less than 3 m over the inorganic insulating layer using a second deposition technique at a temperature less than or equal to 150 C. which is a different technique to that of the first deposition technique.

11. A method according to claim 10, wherein the depositing of the inorganic insulating layer employs atomic layer deposition at a temperature equal to or below 110 C.

12. A method according to claim 11, wherein the depositing of the organic insulating layer employs plasma enhanced chemical vapor deposition at a temperature equal to or below 110 C.

13. A method according to claim 10, wherein the depositing of the organic insulating layer comprises depositing to a thickness of 1.0 m or 1.2 m or 1.5 m.

14. A method according to claim 10, wherein the forming of the passivation coating comprises depositing more than one inorganic insulating layer and more than one organic insulating layer so that at least one organic insulating layer is disposed between two inorganic insulating layers.

15. A method according to claim 14, wherein the forming of the passivation coating comprises depositing an inorganic insulating layer as a top insulating layer.

16. A method according to claim 14, wherein the forming of the passivation coating comprises depositing an organic insulating layer as a top insulating layer.

17. A method according to claim 10, wherein the forming of the passivation coating comprises depositing a layer of an electroless metal on the top insulating layer.

18. A method according to claim 10, wherein the forming of the passivation coating comprises depositing a layer of an electroless metal on an inorganic insulating layer and depositing an organic insulating layer on the electroless metal layer.

19. A method according to claim 10, wherein the forming of the passivation coating comprises depositing a buffer or seed layer on to the electrode.

20. A method according to claim 10, which is a method for the manufacture of an inkjet printhead.

Description

(1) Embodiments will now be described in some detail with reference to the Examples and to the accompanying Drawings in which:

(2) FIG. 1 shows a droplet deposition head which may be adapted by a passivation coating to a droplet deposition head according to one embodiment;

(3) FIG. 2 shows a cyclic firing in the droplet deposition head shown in FIG. 1;

(4) FIGS. 3 (a) and (b) and FIG. 4 show another droplet deposition head which may be adapted by a passivation coating to a droplet deposition head according to another embodiment;

(5) FIGS. 5 a) to c) show passivation coatings according to several embodiments of the present disclosure;

(6) FIGS. 6 a) to c) show passivation coatings according to several other embodiments of the present disclosure;

(7) FIGS. 7 a) to c) show passivating coatings according to further embodiments of the present disclosure; and

(8) FIGS. 8 a) and b) are graphs plotting the current voltage response of single HfO.sub.2 layers of different thickness on a nickel electrode.

(9) Referring now to FIGS. 1 to 4, two droplet deposition heads which are discussed in detail above comprise electrodes layers which are in contact with fluid and may be adapted to droplet deposition heads according to the present disclosure by applying a passivation coating as described below in relation to FIGS. 5 to 8.

(10) FIG. 5 is a schematic showing parts of several piezoelectric actuator elements, generally designated 10, in droplet deposition heads according to three embodiments of the present disclosure.

(11) The piezoelectric actuator elements comprise a nickel electrode 12 which contacts a piezoceramic body 11 comprising lead zirconate titanate or other suitable piezoelectric material.

(12) The piezoelectric actuator elements are each provided with a passivation coating, generally designated 13, which is a laminate of insulating layers of amorphous HfO.sub.2 14 and insulating layers of parylene C, 15.

(13) The insulating layers of each laminate alternate so that a bottom insulating layer is a HfO.sub.2 layer 14 which contacts the electrode 12 and the top insulating layer is a HfO.sub.2 layer 14 which is exposed to ink.

(14) The number of alternating insulating layers varies depending upon the balance between optimal protection from penetration of ink and optimal utilisation of available space.

(15) FIG. 5 a) shows a laminate of two HfO.sub.2 layers 14 and one parylene layer 15, FIG. 5 b) a laminate of four HfO.sub.2 layers 14 and three parylene layers 15 and FIG. 5 c) a laminate of five HfO.sub.2 layers 14 and four parylene layers 15.

(16) In all these laminates, the thickness of each HfO.sub.2 layer 14 is 45 nm and the thickness of the parylene layer 15 may be 1.0 m, 1.2 m or 1.5 m.

(17) FIG. 6 is a schematic showing parts of several piezoelectric actuator elements, generally designated 10, in inkjet printheads according to three other embodiments of the present invention.

(18) The piezoelectric actuator elements comprise a nickel electrode 12 which contacts a piezoceramic body 11 comprising lead zirconate titanate or other suitable piezoelectric material.

(19) The piezoelectric actuator elements are each provided with a passivation coating, generally designated 13, which is a laminate of insulating layers of amorphous HfO.sub.2 14 and insulating layers of parylene C, 15.

(20) The insulating layers of each laminate alternate so that a bottom insulating layer is a HfO.sub.2 layer 14 which contacts the electrode 12 and the top insulating layer is a parylene layer 15 which is exposed to a fluid such as an ink.

(21) The number of alternating insulating layers varies depending upon the balance between optimal protection from penetration of the ink and optimal utilisation of available space.

(22) FIG. 6 a) shows a laminate of one HfO.sub.2 layer 14 and one parylene layer 15, FIG. 6 b) a laminate of two HfO.sub.2 layers 14 and two parylene layers 15 and FIG. 6 c) a laminate of four HfO.sub.2 layers 14 and four parylene layers 15.

(23) In all these laminates, the thickness of each HfO.sub.2 layer 14 is 45 nm and the thickness of the parylene layer 15 may be 1.0 m, 1.2 m or 1.5 m.

(24) FIG. 7 a) shows a part of a piezoelectric actuator element in a droplet deposition head according to another embodiment of the present disclosure. In this embodiment, the passivation coating comprises a laminate similar to those shown in FIG. 6. However, the number of the HfO.sub.2 layers 14 is three and the number of the parylene layers 15 is three.

(25) In this part, the top parylene layer 15 shows laser damage which exposes an underlying HfO.sub.2 layer 14 to ink. The laminate, however, still provides an extended pathway for migration of ionic species to the electrode 12.

(26) FIG. 7 b) shows part of a piezoelectric actuator element in a droplet deposition head according to another embodiment of the present disclosure. In this embodiment, the laminate is similar to that shown in FIG. 6 b) but includes a layer of electroless nickel 16 under the top parylene layer 15. The electroless nickel layer 16 acts as a light barrier to protect the underlying parylene layers from laser ablation during the laser cutting of the nozzles in the nozzle plate in the manufacture of the droplet deposition head.

(27) FIG. 7 c) shows part of a piezoelectric actuator element in a droplet deposition head according to still another embodiment of the present disclosure. In this embodiment, the laminate is similar to that shown in FIG. 5 b) but includes a layer of electroless nickel 17 on the top HfO.sub.2 layer 14. The electroless nickel layer 17 provides that the laminate acts as a Faraday buffer which shields the fluid chamber against the electric field generated when the printhead is operated.

EXAMPLE 1

(28) A laminate of two HfO.sub.2 layers and two parylene C layers (similar to FIG. 5 b)) was prepared on a nickel electrode deposited by electroless plating on a lead zirconate titanate substrate.

(29) The substrate was pre-treated with an oxygen plasma generated by plasma ashing (Metroline M4L Plasma Asher; PVA Tepla America) of a helium-oxygen mixture (He 50 sccm; O.sub.2 150 sccm) at 400 W and 500 mTorr for 2 minutes.

(30) An HfO.sub.2 layer of 45 nm thickness was formed on the nickel electrode using a thermal atomic disposition system (ALD-150LE, Kurt J. Lesker Company) through cycles (362) of alternate exposure of the substrate (heated to 110 C.) to tetrakis(ethylmethyl)amino hafnium (TDMAH, 0.15, 10 seconds) and water (0.06, 20 seconds).

(31) A silane coating (A-174) was applied to the HfO.sub.2 layer using a chemical vapour deposition system (YES 1224P, Yield Engineering Systems Inc.) at 110 C., chamber pressure 0.8 Torr and exposure time 5 minutes.

(32) A parylene polymer layer of thickness about 1.2 m was formed on the coated HfO.sub.2 layer using a plasma enhanced chemical vapour deposition system (SCS Labcoater 2, Speciality Coating Systems Inc.) through exposure (at room temperature) of the substrate at chamber pressure 25 mTorr and to a parylene vapour obtained by vaporisation of parylene C at 690 C.

(33) A second HfO.sub.2 layer of thickness 45 nm was formed on the parylene layer using the same atomic layer deposition system and process conditions as for the first HfO.sub.2 layer. After repeating the silane coating process for this HfO.sub.2 layer, a second parylene polymer layer of thickness about 1.2 m was formed on the second HfO.sub.2 layer using the same plasma enhanced chemical vapour deposition system and process conditions as for the first parylene polymer layer.

(34) Current voltage tests (IVT) were made on the substrate using an impedance measurement system (Keithley Picoammeter 6487) coupled to an electrochemical cell comprising the substrate and a graphite counter electrode in which portions of the laminate are exposed through O-rings of diameter 10 mm to MIMIC ink (an aqueous model fluid comprising nominal 70 v/v % water, water mixable co-solvents and 1 g/L electrolyte).

(35) The leakage current of the laminate was determined to be less than 210.sup.9 A at applied voltages ranging from 0 to 60Vviz. at least an order of magnitude less than existing passivation coatings.

(36) The impedance of the laminate was determined by electrical impedance spectroscopy (EIS, Voltalab PGZ402; the cell including a working electrode, a graphite counter electrode and a Ag/AgCl reference electrode) at low frequency (e.g., 10.sup.1 Hz to 10.sup.4 Hz) to be at least an order of magnitude higher than these prior art passivation coatings. Further, the impedance was the same before and after the current voltage tests.

EXAMPLE 2

(37) The breakdown voltages of single HfO.sub.2 layers formed at different thickness (22 nm and 45 nm) on a similar nickel electrodelead zirconate titanate substrate by atomic layer deposition at 110 C. using the same atomic layer deposition system was examined by the aforementioned electrochemical cell (three O-rings).

(38) As may be seen in FIG. 8, an IVT graph (a) for the 22 nm HfO.sub.2 layer shows that the leakage current density and breakdown voltage is different at each location of exposureand as low as 1.36 MV/cm. This and an inability to measure I-V more than 50% due to shorting suggest that the layer is not uniform.

(39) The IVT graph (b) for the 45 nm HfO.sub.2 layer shows that the leakage current density is the same at each location of exposure and as high as 4.89 MV/cm. The 45 nm HfO.sub.2 layer is uniform and has more suitable electrical properties for forming a barrier layer against ink penetration.

(40) The present disclosure provides a droplet deposition head having an improved passivation coating for the chamber walls and/or electrodes.

(41) The multilayer passivation coating is highly resistant to field assisted penetration of ionic species and has lower thickness as compared to passivation coatings employed in prior art droplet deposition heads.

(42) The multilayer passivation coating can show a good adhesion on the electrode and an adhesion between its layers which is sufficiently robust to mechanical stresses induced by distortion of the piezoceramic body when the droplet deposition head is operated.

(43) The droplet deposition head can be used with a wider variety of fluids than those presently used. The fluids may be found within a broader pH range (from 3 to 10) and have higher ion conductivity (by two orders of magnitude) than those presently used.

(44) The present disclosures provide, in particular, an inkjet printhead which has an increased operational lifetime as compared to prior art inkjet printheads.

(45) Although embodiments have been described in relation to EP 0 364 136 B1 and EP 1 885 561 B1, other embodiments are possible which are not described here. The droplet deposition head may, for example, have a configuration which is different to those described in detail here and the passivation coating may include an inorganic material and/or organic material other than described in detail here.

(46) Unless otherwise indicated a reference to a particular range of values (for example, layer thickness) includes the mentioned starting and finishing values.

(47) Note further that it is the accompanying claims which point out the limits of the presently claimed invention. A reference in the accompanying claims to a droplet deposition head having a piezoelectric actuator element and a fluid chamber includes a reference to a plurality of such elements and chambers. Further, a reference to a fluid chamber wall having an electrode thereon includes a reference to two fluid chamber walls each having an electrode thereon.