Multilayered Piezoelectric Thin Film Element

Abstract

A piezoelectric thin film element having a first electrode, a second electrode and a piezoelectric thin film between the electrodes, wherein the thin film comprises a laminate having two or more piezoelectric thin film layers and wherein a first thin film layer is doped by one or more dopants and a second film layer is doped by one or more dopants and wherein at least one dopant of the second thin film layer is different from the dopant or dopants of the first thin film layer.

Claims

1. A piezoelectric thin film element having a first electrode, a second electrode and a piezoelectric thin film between the electrodes, wherein the thin film comprises a laminate having two or more piezoelectric thin film layers and wherein a first thin film layer is doped by one or more dopants and a second thin film layer is doped by one or more dopants and wherein at least one dopant of the second thin film layer is different from the dopant or dopants of the first thin film layer.

2. A piezoelectric thin film element according to claim 1, in which the dopants are selected from the group of dopant types consisting of donor dopants, acceptor dopants and isovalent dopants.

3. A piezoelectric thin film element according to claim 1, in which the thin film layers comprise a crystal or crystallites based on metal oxides which have a perovskite crystal structure (ABO.sub.3).

4. A piezoelectric thin film element according to claim 3, in which the dopants occupy the same or different co-ordination sites (A-site or B-site) in the perovskite crystal structure.

5. A piezoelectric thin film element according to claim 1, in which the laminate further comprises one or more thin film layers which are undoped.

6. A piezoelectric thin film element according to claim 1, in which the laminate comprises one or more further thin film layers which are doped by one or more dopants which are the same as or different to the dopant or dopants of the first thin film layer and/or the dopants of the second thin film layer.

7. A piezoelectric thin film element according to claim 1, in which the first thin film layer is singly doped by a first dopant and the second thin film layer is singly doped by a second dopant.

8. A piezoelectric thin film element according to claim 7, in which the first dopant and the second dopant are of the same dopant type or of a different dopant type.

9. A piezoelectric thin film element according to claim 7, in which the laminate comprises one or more further thin film layers which are singly doped by dopants of the same or different dopant type.

10. A piezoelectric thin film element according to claim 7, in which the laminate comprises two or more thin film layers which are alternately doped by dopants of a first dopant type or by a dopant of a first dopant type and a dopant of a second dopant type.

11. A piezoelectric thin film element according to claim 10, in which any two adjacent thin film layers are alternately doped by a dopant of the first dopant type and a dopant of the second dopant type.

12. A piezoelectric thin film element according to claim 10, in which any one thin film layer which is doped is adjacent a thin film layer which is undoped or doped and any two sequential thin film layers which are doped, are alternately doped by a dopant of the first dopant type and a dopant of the second dopant type.

13. A piezoelectric thin film element according to claim 10, in which the laminate comprises a first series of adjacent thin film layers which are doped by a dopant of the first dopant type and a second series of adjacent thin film layers which are doped by a dopant of the second dopant type.

14. A piezoelectric thin film element according to claim 10, in which similarly doped thin film layers define a gradient in dopant concentration across thin film layers.

15. A piezoelectric thin film according to claim 14, in which the dopant concentration increases or decreases from the first electrode to the second electrode.

16. A piezoelectric thin film element according to claim 14, in which the dopant concentration increases from the first electrode and decreases to the second electrode.

17. A piezoelectric thin film element according to claim 1, in which one or more thin film layers define a gradient in dopant concentration within the thin film layer.

18. A method for manufacturing a piezoelectric thin film element having a first electrode, a second electrode and a piezoelectric thin film between the electrodes, which method comprises a first step of forming a piezoelectric thin film layer on an electrode and one or more further steps of forming a piezoelectric thin film layer on the thin film layer whereby to form a laminate comprising a plurality of piezoelectric thin film layers wherein a first thin film layer is doped by one or more dopants and a second film layer is doped by one or more dopants and wherein at least one dopant of the second thin film layer is different from the dopant or dopants of the first thin film layer.

19. (canceled)

20. A method according to claim 18, in which the dopants are selected from the group of dopant types consisting of donor dopants, acceptor dopants and isovalent dopants.

21. A method according to claim 18, in which the thin film layers comprise a crystal or crystallites based on metal oxides which have a perovskite crystal structure (ABO.sub.3).

22.-24. (canceled)

25. A method according to claim 18, in which the first and further steps form a laminate in which the first thin film layer is singly doped by a first dopant and the second thin film layer is singly doped by a second dopant.

26.-34. (canceled)

35. An actuator for a printhead, which actuator comprises a piezoelectric element according to claim 1.

36. A printhead, comprising the actuator of claim 35.

37. An ink-jet printer, comprising the printhead of claim 36.

Description

[0105] The present invention is disclosed in more detail as follows and with reference to certain non-limiting embodiments and the accompanying Drawings in which:

[0106] FIG. 1 is a graph showing a depth profile obtained by X-ray photoelectron spectroscopy of a 1 μm PZT film disposed on a platinum electrode over a silicon dioxide substrate provided with a zinc tin oxide adhesion layer (PZT/Pt/ZTO/SiO.sub.2);

[0107] FIG. 2 is a scheme illustrating in section view one embodiment of the method of the present invention;

[0108] FIG. 3 is a section view illustrating one embodiment of the piezoelectric thin film element of the present invention;

[0109] FIG. 4 is a section view illustrating another embodiment of the piezoelectric thin film element of the present invention;

[0110] FIG. 5 is a section illustrating a further embodiment of the piezoelectric thin film element of the present invention; and

[0111] FIG. 6 is a section view illustrating still another embodiment of the piezoelectric thin film element of the present invention;

[0112] FIG. 7 is a section view illustrating still another embodiment of the piezoelectric thin film element of the present invention;

[0113] FIG. 8 is a section view illustrating still another embodiment of the piezoelectric thin film element of the present invention;

[0114] FIG. 9 is a section view illustrating an embodiment of the piezoelectric thin film element of the present invention and a graph showing a gradient in dopant concentration across the layers;

[0115] FIG. 10 is a section view illustrating another embodiment of the piezoelectric thin film element of the present invention and a graph showing another gradient in dopant concentration across the layers; and

[0116] FIG. 11 is a section view of a drop ejector portion of an ink-jet printhead showing use of one embodiment of the piezoelectric thin film of the present invention as an actuator.

[0117] FIG. 1 shows a graph reporting the result of an X-ray photoelectron spectroscopy experiment examining the depth profile of the concentration of elements within a PZT thin film of 1 μm on a platinum electrode provided on a glass substrate. The thin film is formed by depositing a precursor layer and annealing the precursor layer by heating from below the electrode and repeating these steps to form a laminate of six crystallised thin film layers.

[0118] The graph plots the elemental composition in the thin film against sputter time (increasing depth of penetration of incident radiation).

[0119] As may be seen, the Ti.sup.4+ concentration and the Zr.sup.4+ concentration within the thin film follows a profile (circled) which is consistent with faster crystallisation of lead titanate as compared to lead zirconate and is repeated throughout the film in a number corresponding to the number of crystallised thin layers.

[0120] The graph shows not just six distinct crystallisations but also that the Ti.sup.4+ concentration and the Zr.sup.4+ concentration within a first crystallised thin film layer is unaltered by repeated annealing to form subsequent crystallised thin film layers.

[0121] In other words, there is no migration of Ti.sup.4+ or Zr.sup.4+ between layers during the formation of one or more crystallised thin film layers on an already formed crystallised thin film layer.

[0122] Referring now to FIG. 2, there is shown a scheme illustrating a method for manufacturing a piezoelectric thin film element 10 according to one embodiment of the present invention.

[0123] A sol-gel layer comprising appropriate amounts of PZT and acceptor dopant precursor is provided to an upper surface of an electrode 11 (for example, of lanthanum niobate) provided on a silicon substrate by spin coating. The sol-gel layer is dried by heating the substrate and sol-gel layer to a temperature of between 120° C. and 150° C. After cooling, the dried layer is pyrolised by heating the substrate and dried layer to a temperature of about 350° C. to provide an amorphous precursor layer 12a.

[0124] The spin coating, drying and pyrolysis are repeated so as to provide further amorphous precursor layers 12b and 12c on the substrate.

[0125] After cooling, the substrate and the three precursor layers are heated rapidly to a temperature of about 700° C. by placing the substrate on or above a hot plate. The below substrate heating anneals the three precursor layers into a first thin film layer 13 comprising crystallites of PZT doped by an acceptor dopant (A, for example, Mn.sup.2+ at the B-site).

[0126] After cooling, a sol-gel layer comprising appropriate amounts of PZT and donor dopant precursor is provided to the thin film layer 13 on the substrate and dried and pyrolised as before to provide a precursor layer 14a on the thin film layer.

[0127] The spin coating, drying and pyrolysis are repeated so as to provide further amorphous precursor layers 14b and 14c on the substrate.

[0128] The substrate and its layers are again rapidly heated to a temperature of about 700° C. by placing the substrate on or above a hot plate. The below substrate heating anneals the precursor layers into a second thin film layer 15 comprising crystallites of PZT doped by a donor dopant (D, for example Nb.sup.5+, at the B-site or La.sup.3+ at the A-site).

[0129] A sol-gel layer comprising appropriate amounts of PZT and donor dopant precursor is provided to the thin film layer 15 by spin-coating, drying and pyrolysis in the same way it is applied to the electrode. The precursor layers are annealed into a thin film layer 16 comprising crystallites of PZT doped by an acceptor dopant (A, for example, Mn.sup.2+ at the B-site).

[0130] The cycle can be repeated for so as to provide a laminate of desired thickness (for example, 1 μm) comprising alternately doped PZT thin film layers (sixteen for example). Of course, the process may use a sol-gel solution without a dopant precursor so that the laminate includes one or more undoped thin film layers of crystallites of PZT.

[0131] Finally an electrode (not shown in FIGS. 2 to 10, for example of gold metal) is formed by sputtering (for example) on to the top thin film layer.

[0132] In this embodiment, the first thin film and the third thin film layer may be doped by an acceptor dopant (A, for example, Mn.sup.2+, at the B-site) and the second thin film layer may be doped by a donor dopant (D, for example Nb.sup.5+, at the B-site or La.sup.3+ at the A-site).

[0133] In another embodiment (not shown), the first thin film layer is undoped, the second thin film layer is doped by a donor dopant (D, for example Nb.sup.5+, at the B-site or La.sup.3+ at the A-site) and the third thin film layer is doped by an acceptor dopant (A, for example, Mn.sup.2+, at the B-site).

[0134] FIG. 3 shows an embodiment of the present invention having four thin film layers. The first thin film layer 13 and the fourth thin film layer 17 are undoped whilst the second thin film layer 15 is doped by an acceptor dopant (A, for example, Mn.sup.2+, at the B-site) and the third thin film layer 16 is doped by a donor dopant (D, for example Nb.sup.5+, at the B-site or La.sup.3+ at the A-site).

[0135] FIG. 4 shows an embodiment of the present invention also having four thin film layers. The first thin film layer 13 and the second thin film layer 15 are doped by acceptor dopants (A, for example, Mn.sup.2+, at the B-site) whilst the third thin film layer 16 and the fourth thin film layer 17 are doped by donor dopants (D, for example Nb.sup.5+ at the B-site or La.sup.3+ at the A-site).

[0136] FIG. 5 shows an embodiment of the present invention having seven thin film layers. The thin film layers 13 to 20 are alternately doped by donor dopant and acceptor dopant. In particular, the first, third, fifth and seventh thin film layers 13, 16, 18, 20 are doped by an acceptor dopant (A, for example, Mn.sup.2+, at the B-site) and the second, fourth and sixth thin film layers 15, 17, 19 are doped by a donor dopant (D, for example Nb.sup.5+ at the B-site or La.sup.3+ at the A-site).

[0137] FIG. 6 shows an embodiment of the present invention also having seven thin film layers. The thin film layers include a series of layers which are similarly doped. The first thin film layer 13 and the fourth and seventh thin film layers 17, 20 are undoped whilst the second and third thin film layers 15, 16 are doped by an acceptor dopant (A, for example, Mn.sup.2+, at the B-site) and the fifth and sixth thin film layers 18, 19 are doped by a donor dopant (D, for example Nb.sup.5+, at the B-site or La.sup.3+ at the A-site).

[0138] FIG. 7 shows an embodiment of the present invention also having seven thin film layers. The thin film layers are alternately doped with donor dopant and acceptor dopant. In particular, the first, third and sixth thin film layers 14, 16, 19 are doped by an acceptor dopant (A, for example, Mn.sup.2+, at the B-site). The second, fifth and seventh thin film layers 15, 18, 20 are doped by a donor dopant (D, for example Nb.sup.5+, at the B-site or La.sup.3+ at the A-site) whilst the fourth thin film layer 17 is doped by compensating dopants comprising a combination of acceptor and donor dopants (A and D, for example, Mg.sup.2+ and Sb.sup.5+ in molar ratio 1:2 or Ni.sup.2+ and Nb.sup.5+ in molar ratio 1:2 or Mg.sup.2+ and W.sup.6+ in molar ratio 1:1).

[0139] FIG. 8 shows an embodiment of the present invention also having seven thin film layers. In this embodiment, the thin film layers are alternately doped but have an intervening undoped layer. In particular, the first thin film layer 13 and the fifth thin film layer 18 are doped by an acceptor dopant, the third and seventh thin film layers 16, 20 are doped by a donor dopant and the second, fourth and sixth thin film layers 15, 17, 19 are undoped.

[0140] FIG. 9 shows a similar embodiment to that shown in FIG. 5. In this embodiment, however, the concentration of dopant in each thin film layer doped by an acceptor dopant differs and increases toward the seventh layer (A.sub.1 to A.sub.4). The concentration of dopant in each thin film layer doped by a donor dopant increases toward the seventh layer (D.sub.1 to D.sub.3). The accompanying graph (ordinate axis 0.5 mole % increments) particularly points out acceptor and donor dopant concentrations which increase from 0.5 mole % to 2.0 mole % or from 0. 5 mole % to 1.5 mole %.

[0141] FIG. 10 also shows a similar embodiment to that shown in FIG. 5. In this embodiment, however, the concentration of dopant in each thin film layer doped by the acceptor dopant differs and increases towards the seventh layer. The concentration of dopant in each thin film layer doped by the donor dopant decreases to toward the seventh layer (D.sub.1 to D.sub.3). The accompanying graph (ordinate axis 0.5 mole % increments) particularly points out acceptor dopant concentrations (A.sub.1 to A.sub.3) which increase from 0.5 mole % to 2.0 mole % and donor dopant concentrations which decrease from 1.5 mole % to 0.5 mole %.

[0142] FIG. 11 shows a section view of an ink-jet printhead 21 according to one embodiment of the present invention. A piezoelectric thin film element 10 comprising first and second electrodes 11 and 22 having a piezoelectric thin film comprising a laminate of seven thin film layers interposed between the electrodes is provided to a diaphragm 23 on top of a pressure chamber 24, provided with a nozzle plate 25.

[0143] The pressure chamber 24 may comprise a silicon single crystal of thickness about 200 pm and the diaphragm may comprise a thin film comprising one or more of silicon dioxide, zirconium oxide, tantalum oxide, and silicon nitride or aluminium oxide.

[0144] A buffer layer 26 of ultra-thin titanium film or chromium film (about 10 nm thickness) is interposed between the diaphragm and the first electrode.

[0145] In use, a predetermined drive voltage is applied between the first and second electrodes by a signal from a control circuit. The voltage causes the piezoelectric thin film element 10 to deform so deflecting the diaphragm 23 into the pressure chamber 24 and changing its volume. A sufficient increase in pressure within the pressure chamber causes ink droplets to be ejected from the nozzle.

[0146] The present invention has been described in detail with reference to certain embodiments which are illustrated by the drawings. However, it will be understood that other embodiments not described in detail or illustrated by the drawings are also included within the scope of the present invention.

[0147] It will be appreciated that similar alternate arrangements are possible in singly doped thin film layers doped by two different donor dopants or by two different acceptor dopants (for example, doping at the A-site and the B-site) or by a plurality of donor dopants including different dopants or by a plurality of different acceptor dopants including different dopants.

[0148] It will also be appreciated that the first thin film layer and the second thin film layer may be triply doped or doped by four or more dopants. And that laminates comprising any reasonable combination of thin film layers which are undoped, singly doped and triply doped or doped by four or more dopants are possible.