A PIEZOELECTRIC THIN FILM ELEMENT

Abstract

A piezoelectric thin film element comprising a first electrode, a second electrode and one or more piezoelectric thin films there between wherein the first electrode is a platinum metal electrode having an average grain size greater than 50 nm and wherein a piezoelectric thin film adjacent the platinum metal electrode comprises a laminate having a plurality of piezoelectric thin film layers wherein a piezoelectric thin film layer contacting the platinum metal electrode comprises lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3 where 0<x?0.60 and has a degree of pseudo cubic {100} orientation greater than or equal to 90%.

Claims

1-15. (canceled)

16. A piezoelectric thin film element comprising: a first electrode, the first electrode being a platinum metal electrode having an average grain size greater than 50 nm; a second electrode; and one or more piezoelectric thin films there between, wherein the one or more piezoelectric thin films comprise a piezoelectric thin film adjacent the platinum metal electrode, the piezoelectric thin film comprising a laminate having a plurality of piezoelectric layers, and the plurality of piezoelectric layers comprise a piezoelectric layer contacting the platinum metal electrode, the piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, and having a degree of pseudo cubic {100} orientation greater than or equal to 90%.

17. The piezoelectric thin film element of claim 16, wherein the piezoelectric layer has a composition at or about PbZr.sub.xTi.sub.1-xO.sub.3 where 0<x?0.40.

18. The piezoelectric thin film element of claim 16, wherein the piezoelectric layer has a composition at or about PbZr.sub.xTi.sub.1-xO.sub.3 where 0.40?x?0.60.

19. The piezoelectric thin film element of claim 16, wherein the piezoelectric layer is doped by one or more of a donor dopant, an acceptor dopant, or an isovalent dopant.

20. The piezoelectric thin film element of claim 17, wherein the piezoelectric layer is doped by one or more of a donor dopant, an acceptor dopant, or an isovalent dopant.

21. The piezoelectric thin film element of claim 18, wherein the piezoelectric layer is doped by one or more of a donor dopant, an acceptor dopant, or an isovalent dopant.

22. The piezoelectric thin film element of claim 16, wherein the piezoelectric layer is a first piezoelectric layer; and the plurality of piezoelectric layers comprise at least a second piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, formed on the first piezoelectric layer.

23. A piezoelectric thin film element according to claim 17, wherein the piezoelectric layer is a first piezoelectric layer; the plurality of piezoelectric layers comprises at least one piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, formed on the first piezoelectric layer.

24. A piezoelectric thin film element according to claim 18, wherein the piezoelectric layer is a first piezoelectric layer; the plurality of piezoelectric layers comprises at least a second piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, formed on the first piezoelectric layer.

25. A method for manufacturing a piezoelectric thin film element comprising: forming a platinum metal electrode on a substrate heated to a predetermined temperature at or above 450? C.; forming a piezoelectric thin film comprising a laminate of piezoelectric layers on the platinum metal electrode; and forming a top electrode, wherein the forming of the piezoelectric thin film comprises forming a piezoelectric layer contacting the platinum metal electrode by a chemical solution deposition, the chemical solution deposition employing a solution having a predetermined excess lead content between 10 mol % and 40 mol %, and the piezoelectric layer comprises lead zirconate titanate of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3 where 0<x?0.60 and has a degree of pseudo cubic {100} orientation greater than or equal to 90%.

26. The method of claim 25, wherein the forming of the piezoelectric layer employs a solution having a predetermined excess lead content between 10 mol % and 40 mol %, and the piezoelectric layer comprises lead zirconate titanate of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3 where 0<x?0.40.

27. The method of claim 25, wherein the chemical solution deposition employs a solution having a predetermined excess lead content between 12 mol % and 20 mol %.

28. The method of claim 25, wherein the chemical solution deposition employs a solution providing one or more of a donor dopant, an acceptor dopant, or an isovalent dopant in the piezoelectric layer.

29. The method of claim 26, wherein the chemical solution deposition employs a solution providing one or more of a donor dopant, an acceptor dopant, or an isovalent dopant in the piezoelectric layer.

30. The method of claim 27, wherein the chemical solution deposition employs a solution providing one or more of a donor dopant, an acceptor dopant, or an isovalent dopant in the piezoelectric layer.

31. The method of claim 25, wherein the piezoelectric layer is a first piezoelectric layer; the forming of the piezoelectric thin film further comprises forming at least a second piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, on the first piezoelectric layer by a chemical solution deposition; and the second piezoelectric layer has a degree of pseudo cubic {100} orientation greater than or equal to 90%.

32. The method of claim 26, wherein the piezoelectric layer is a first piezoelectric layer; the forming of the piezoelectric thin film further comprises forming at least a second piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, on the first piezoelectric layer by a chemical solution deposition; and the second piezoelectric layer has a degree of pseudo cubic {100} orientation greater than or equal to 90%.

33. The method of claim 27, wherein the piezoelectric layer is a first piezoelectric layer; the forming of the piezoelectric thin film further comprises forming at least a second piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, on the first piezoelectric layer by a chemical solution deposition; and the second piezoelectric layer has a degree of pseudo cubic {100} orientation greater than or equal to 90%.

34. A printhead for droplet deposition coupled to a control circuit comprising: a first electrode comprising platinum having an average grain size greater than 50 nm; a second electrode; and piezoelectric thin films between the first electrode and the second electrode, wherein the control circuit is configured to apply a drive voltage between the first electrode and the second electrode, which causes the piezoelectric thin films to deform, the piezoelectric thin films comprise a laminate having a plurality of piezoelectric layers, and the plurality of piezoelectric layers comprise a piezoelectric layer contacting the platinum metal electrode, the piezoelectric layer comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.xTi.sub.1-xO.sub.3, where 0<x?0.60, and having a degree of pseudo cubic {100} orientation greater than or equal to 90%.

35. The printhead of claim 34, further comprising: an adhesion layer in contact with the first electrode; a membrane in contact with the adhesion layer; a pressure chamber in contact with the membrane; and a nozzle plate in contact with the pressure chamber, wherein the pressure chamber comprises silicon single crystal; and the membrane comprises a dielectric thin film.

Description

[0113] FIG. 1 shows a scanning electron microscope (SEM) image of a platinum electrode obtained by sputtering platinum metal onto a silicon substrate held at room temperature;

[0114] FIG. 2 shows a scanning electron microscope (SEM) image of a platinum electrode obtained by sputtering platinum metal onto a silicon substrate heated from below to 500? C.;

[0115] FIGS. 3 (a) and (b) show two embodiments of a piezoelectric thin film element according to the present disclosure;

[0116] FIG. 4 show X-ray diffraction patterns for piezoelectric thin films comprising doped and undoped lead zirconate titanate (PZT) of composition at or about PbZr.sub.0.52Ti.sub.0.48O.sub.3 which are deposited onto a high-temperature deposited platinum electrode;

[0117] FIG. 5 shows X-ray diffraction patterns for piezoelectric thin films comprising doped lead zirconate titanate (PZT) of composition at or about PbZr.sub.0.52Ti.sub.0.48O.sub.3 which are deposited onto a high-temperature deposited platinum electrode to varying degrees of thickness; and

[0118] FIG. 6 shows one embodiment of a piezoelectric actuator according to the present disclosure.

[0119] Referring now to FIG. 1, a SEM image shows the microstructure of a platinum electrode deposited on to a silicon substrate by sputtering platinum metal. The silicon substrate is held at room temperature (RT) throughout the process. As may be seen, the platinum electrode has a very fine grain sizewhich is determined to be about 20 nm to 30 nm.

[0120] The SEM image of FIG. 2 shows the microstructure of a platinum electrode deposited on to a silicon substrate provided by sputtering platinum metal under similar conditions to those described in U.S. Pat. No. 6,682,722 B1 (see Example 1 below). The silicon substrate is held at a temperature of 500? C. throughout the process. As may be seen, the platinum electrode has a larger lateral grain size as compared to that shown in SEM image of FIG. 1which is determined to be about 200 nm.

[0121] The texture for each of the platinum electrodes was determined by peak-force tapping mode atomic force microscopy (AFM) analysis of surface roughness R using a Bruker Dimension Icon AFM apparatus in open-loop mode and by rocking curve X-ray diffraction (XRD) measurements using Phillips Pro MRD 4-Circle XRD apparatus.

[0122] AFM images were collected using a Bruker ScanAsyst-Air probe (an uncoated, etched silicon tip on a nitride lever) using Bruker NanoScope software (v 8.1.5).

[0123] The XRD measurements determined the full width at half maximum (FWHM) from the rocking curve obtained for the platinum 111 peak identified in a 2? scan. The scan axis was omega and the range about 4? with step size 0.01? at frequency 0.5 Hz.

TABLE-US-00001 TABLE 1 Pt on substrate (sputtered Pt on substrate at RT) (sputtered at 500? C.) R.sub.max (Z range)/nm 11.9 11.3 R.sub.q (root mean square)/nm 0.95 1.23 R.sub.a (arithmetic average)/nm 0.75 0.97 Pt 111 rocking curve FWHM/? 4.7 1.5

[0124] Table 1 shows the Pt 111 rocking curve FWHM and roughness (R) data and that the platinum electrode deposited on the heated silicon substrate has a much higher quality of crystallinity as compared to that deposited on a silicon substrate held at room temperature.

[0125] Referring now to FIG. 3 (a), a piezoelectric thin film element 10 according to one embodiment of the present disclosure comprises a platinum metal electrode 11 deposited by sputtering on a silicon substrate provided with a TiO.sub.x adhesion layer (not shown) which is heated from below to a temperature above 450? C.

[0126] A PZT thin film (12) provided on the electrode comprises a laminate of three PZT thin film layers (13, 14 and 15) of composition at or about PbZr.sub.0.52Ti.sub.0.48O.sub.3. A top electrode (shown in FIG. 5 as 26) provided on the laminate is formed, for example, by sputtering platinum, iridium or ruthenium and/or by reactive sputtering of iridium dioxide.

[0127] The PZT thin film layer contacting the platinum electrode (13; shown with hash lines) is formed by a sol-gel deposition in which the sol-gel solution has a predetermined excess lead content greater than 10 mol % and has a degree of pseudo cubic {100} orientation equal to or greater than 90%. The overlying PZT thin film layers (14 and 15) are also formed by a sol-gel process in which the sol-gel solution has a predetermined excess lead content equal to 10 mol % and have a degree of pseudo cubic {100} orientation similar to or identical to that of the PZT thin film layer (13).

[0128] FIG. 3 (b) shows a piezoelectric thin film element which differs from that shown in FIG. 3 (a) in that the laminate comprises five PZT thin film layers which are formed by a hybrid process.

[0129] The PZT thin film layer contacting the platinum electrode (13, shown with hash lines) is formed by a sol-gel deposition in which the sol-gel solution has a predetermined excess lead content greater than 10 mol % and has a degree of pseudo cubic {100} orientation greater than or equal to 90%. The overlying PZT thin film layers (16 to 19) are formed by metallo-organic chemical vapour deposition (employing similar annealing steps) and have a degree of pseudo cubic {100} orientation similar or identical to that of the PZT thin film (13).

[0130] Referring now to FIG. 4, an X-ray diffraction pattern (a) of a piezoelectric thin film layer comprising lead zirconate titanate (PZT) of composition at PbZr.sub.0.52Ti.sub.0.48O.sub.3 deposited onto a high-temperature deposited platinum electrode by a sol-gel deposition using a 15 wt % sol-gel solution with lead excess of 10 mol % (a Pb.sub.1.10Zr.sub.0.52Ti.sub.0.48O.sub.3 solution) shows only 100 and 200 diffraction peaks (the peaks marked * are due to platinum electrode/silicon substrate).

[0131] An X-ray diffraction pattern (b) of a PZT thin film layer of composition about PbZr.sub.0.52Ti.sub.0.48O.sub.3 which has been deposited onto a high temperature deposited platinum electrode by a sol-gel process using a 15 wt % sol-gel solution with lead excess of 10 mol % and 1 mol % of a manganese dopant compound (a Pb.sub.1.10Mn.sub.0.01(Zr.sub.0.52Ti.sub.0.48)O.sub.3 solution) also shows only 100 and 200 diffraction peaks.

[0132] An X-ray diffraction pattern (c) of a PZT thin film layer of composition about PbZr.sub.0.52Ti.sub.0.48O.sub.3 which has been deposited onto a high temperature deposited platinum electrode by a sol-gel process using a 15 wt % sol-gel solution with a lead excess of 13 mol % and 1 mol % manganese dopant compound (a Pb.sub.1.13Mn.sub.0.01(Zr.sub.0.52Ti.sub.0.48)O.sub.3 solution) also shows only 100 and 200 diffraction peaks.

[0133] However, as may be seen, the intensity of the 100 and 200 diffraction peaks in the doped PZT thin film layer is much larger when the excess lead content of the sol-gel solution is 13 mol % as compared to 10 mol %.

[0134] The excess lead content of the sol-gel solution is, therefore, critical to crystallinity and initiation of pseudo cubic {100} orientation in the piezoelectric thin film layer.

[0135] Referring now to FIG. 5, X-ray diffraction patterns are shown for PZT thin film layers comprising lead zirconate titanate (PZT) of composition at or about PbZr.sub.0.52Ti.sub.0.48O.sub.3 deposited onto a high-temperature deposited platinum electrode. The PZT thin film layers are deposited by spin coating a 12 wt % sol-gel solution with excess lead content of 14 mol % and 2 mol % niobium dopant compound (a Pb.sub.1.14Nb.sub.0.02(Zr.sub.0.52Ti.sub.0.48)O.sub.3 solution) at four different spin rates during 30 seconds.

[0136] The different spin rates (from top to bottom: (a) 3000 rpm, (b) 4000 rpm, (c) 5000 rpm and (d) 6000 rpm) lead to piezoelectric thin film layers of different thickness (45 to 80 nm from (d) to (a)).

[0137] As may be seen, the intensity of the 100 and 200 diffraction peaks is large in each diffraction pattern and of comparable size (the peaks marked * are due to platinum electrode/silicon substrate).

[0138] In other words, there is no direct dependency between the thickness of the piezoelectric thin film layer which is deposited on the high temperature deposited platinum electrode and the degree of pseudo cubic {100} orientation in that thin film layer. Piezoelectric thin film layers having high pseudo cubic {100} orientation can be obtained across a wide range of thicknesses.

EXAMPLE 1

Formation of PZT Thin Film Orientation-Controlling Layers on HT-Pt

[0139] A platinum electrode was deposited by RF magnetron sputtering (at 500 W DC cathode power during about 1 minute) of a platinum target (99.99% pure) of diameter 250 nm and thickness 4 mm under an argon atmosphere (50 sccm flow rate) on to silicon substrates (target-substrate distance 50 mm) heated from below to a temperature of 450? C. and 500? C. The deposition rate was 11.8 ?/s and the chamber pressure was 3.8 mTorr.

[0140] Sol-gel solutions of concentration about 12 wt % of lead zirconate titanate precursor compounds having different mol % excess lead content and different mol % dopant concentrations were deposited on to the electrode by spin coating at 3500 rpm for 45 seconds.

[0141] The coatings were dried and pyrolyzed at 200? C. during 150 seconds and annealed at 700? C. for 1 minute using a rapid thermal heating (RTA) apparatus (with 2 SLPM O.sub.2 flow and 10? C./second temperature ramp). The final coatings had a composition at or about PbZr.sub.0.52Ti.sub.0.48O.sub.3 and thickness of 60 nm.

[0142] The degree of pseudo cubic {100} orientation of the resultant piezoelectric thin film layers was determined by X-ray crystallography inspecting the relative intensities of the 100 diffraction peaks as compared to other diffraction peaks and evaluated in terms of Lotgering factor LF.sub.100.

[0143] Table 2 summarises the results as compared with coatings of similar thickness formed on a platinum electrode deposited at room temperature. These coatings were formed under similar conditions and at similar thicknesses (except that pyrolysis was carried out at 100? for 60 seconds followed by 300? C. for 240 seconds). The degree of {100} orientation of the coatings on the high-temperature deposited platinum electrodes was in general excellent and compared well to those coatings formed on the room temperature platinum electrode.

TABLE-US-00002 TABLE 2 Degree of {100} Orientation Pt on Pt on Pt on 12 wt % Solution substrate substrate substrate Lead Excess; Dopant (sputtered (sputtered (sputtered concentration at RT) at 450? C.) at 500? C.) 10 mol % Pb; undoped E E E 12 mol % Pb; undoped E E or M B 12 mol % Pb; 1 mol % Mn.sup.2+ B M E 14 mol % Pb; 2 mol % Nb.sup.5+ E E E *10 mol % Pb; 1.1 mol % La.sup.3+ E E E *15 wt % solution (E = excellent, a Lotgering factor LF.sub.100 greater than or equal to 0.98; M = mixture, a Lotgering Factor LF.sub.100 is between 0.50 and 0.80; B = random orientation or poor crystallinity).

[0144] FIG. 6 shows a part section view of an actuator (20) in an inkjet printhead according to one embodiment of the present disclosure. The construction of the actuator and the inkjet printhead is conventional except that the piezoelectric thin film element according to the present disclosure is used. In this embodiment, the piezoelectric thin film element of FIG. 3 (a) is provided to a membrane (21) on top of a pressure chamber (22), provided with a nozzle plate (23).

[0145] The pressure chamber (22) may comprise a silicon single crystal of thickness about 70 ?m and the membrane (21) may comprise a thin film comprising one or more of silicon dioxide, zirconium oxide, tantalum oxide, silicon, silicon nitride or aluminium oxide and the like.

[0146] A titanium oxide adhesion layer (24) of thickness about 20 nm is interposed between the membrane (21) and the platinum metal electrode (11).

[0147] In use, a predetermined drive voltage is applied between the electrodes (11 and 26) by a signal from a control circuit. The voltage causes the piezoelectric thin film element to deform so deflecting the membrane (21) into the pressure chamber (22) and changing its volume. A sufficient increase in pressure within the pressure chamber (22) causes fluid droplets to be ejected from the nozzle (25).

[0148] The present disclosure provides a simple and economic way to control pseudo cubic {100} orientation in a piezoelectric thin film element comprising piezoelectric thin films provided on a high-temperature deposited platinum electrode.

[0149] In particular, the PZT thin film orientation-controlling layer can be simply obtained by chemical solution deposition from a solution obtained from existing commercially available sol-gel solutions (12 wt %, 15 wt % and 25 wt %)without the need to limit its thickness.

[0150] The present disclosure provides a method which avoids the use of lead titanate as a seed layer and minimises current leakage and capacitance effects associated with very large excess lead content (lead titanate requires up to 40 mol % excess lead content) which can lead to degradation of the performance of the piezoelectric element.

[0151] The use of a PZT thin film layer which is directly formed on the platinum electrode as an orientation-controlling layer and does not require control of thickness may also provide a more efficient manufacture of the piezoelectric element by minimizing the number of solutions to be used.

[0152] The solution employed for forming the PZT thin film layer contacting the platinum electrode may also be used in forming one or more other PZT thin film layer of the laminate.

[0153] The present disclosure provides a detailed description of certain embodiments of the piezoelectric thin film element. Note that other embodiments will be apparent to those skilled in the art which are not described in detail here.

[0154] Note also that a reference to a particular range of values (for example, average grain size) includes the starting and finishing values.

[0155] Note further that it is the accompanying claims which particularly point out an invention in the present disclosure and the scope of protection which is sought.