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Title:
THIN FILM STACK
Document Type and Number:
WIPO Patent Application WO/2014/116208
Kind Code:
A1
Abstract:
A thin film stack has a first layer including silicon dioxide, a second layer directly on the first layer that includes a blend of zinc oxide and silicon dioxide; and a third layer including tin oxide.

Inventors:
ABBOTT JR JAMES ELMER (US)
MARDILOVICH PETER (US)
STICKLE WILLIAM F (US)
Application Number:
PCT/US2013/022638
Publication Date:
July 31, 2014
Filing Date:
January 23, 2013
Export Citation:
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Assignee:
HEWLETT PACKARD DEVELOPMENT CO (US)
International Classes:
B32B7/02; B32B15/00; B32B27/00
Foreign References:
KR100971135B12010-07-20
KR101115074B12012-03-13
US20120012840A12012-01-19
JPH08203841A1996-08-09
Other References:
XU, X. ET AL.: "Formation mechanism of Zn2Si04 crystal and amorphous Si02 in Zn0/Si system", JOURNAL OF PHYSICS: CONDENSED MATTER., vol. 15, no. 40, 2003, pages L607 - L613
Attorney, Agent or Firm:
BRUSH, Robert M. et al. (Intellectual Property Administration3404 E. Harmony Road,Mail Stop 3, Fort Collins Colorado, US)
Download PDF:
Claims:
CLAIMS

What is Claimed is:

1. A thin film stack, comprising:

a first layer including silicon dioxide;

a second layer directly on the first layer, the second layer including a blend of zinc oxide and silicon dioxide; and

a third layer including tin oxide.

2. The thin film stack of claim 1 , wherein the third layer is directly on the second layer.

3. The thin film stack of claim 1 , further comprising a fourth layer including a blend of zinc oxide and tin oxide, wherein the fourth layer is between the second and third layers.

4. The thin film stack of claim 1 , further comprising a metal layer on the third layer.

5. The thin film stack of claim 3, further comprising a metal layer on the third layer.

6. The thin film stack of claim 4, further comprising a piezoelectric layer on the metal layer.

7. The thin film stack of claim 5, further comprising a piezoelectric layer on the metal layer.

8. The thin film stack of claim 6, wherein the thin film stack is an actuator for fluid ejection device.

9. A method, comprising:

providing a first layer including silicon dioxide;

depositing a blend of zinc oxide and tin oxide (ZTO) on the first layer;

heating the first layer and the ZTO to form a second layer including a blend of zinc oxide and silicon dioxide, and a third layer including tin oxide.

10. The method of claim 9, wherein heating the first layer and the ZTO includes forming a fourth layer including a blend of ZTO and tin oxide, wherein the fourth layer is between the second and third layers.

13. The method of claim 9, wherein heating the first layer and the ZTO includes heating to at least 500°C.

14. The method of claim 9, further comprising:

depositing a metal layer on the third layer; and

depositing a piezoelectric layer on the metal layer.

Description:
THIN FILM STACK

Background

[0001]Thin films are known in the micro and nanoelectronics industry for the fabrication of sensors, actuators, transistors, etc. In many applications, metal and non-metal films are layered to form a stack.

[0002] For example, piezoelectric devices, such as piezoelectric inkjet printheads or sensors, can be prepared by stacking various piezoelectric materials, other films, and metals, e.g., conductors and/or electrodes, in specific configurations for piezoelectric actuation or piezoelectric sensing. In the case of a piezoelectric printhead, piezoelectric actuation on or in an ink chamber can be used to eject or jet fluids therefrom. One such piezoelectric material is lead zirconate titanate, or "PZT," which can be grown or otherwise applied on the surface of a metal electrode.

Brief Description of the Drawings

[0003] Figures 1A-1 D are block diagrams illustrating examples of thin film stacks.

[0004] Figure 2 is a flow diagram illustrating a method for creating thin film stacks.

[0005] Figures 3A-3G are charts illustrating X-ray photoelectron spectroscopy (XPS) analyses of thin film components mixing and segregation. [0006] Figure 4 is a chart illustrating results of an X-ray diffraction (XRD) characterization of annealed ZTO on a silicon dioxide substrate.

[0007] Figure 5 is a schematic view illustrating a portion of an example inkjet printhead.

[0008] Figure 6 is a block diagram illustrating example thin film stack layers of the inkjet printhead of Figure 5.

[0009] Figure 7 is a block diagram illustrating further example thin film stack layers of the inkjet printhead of Figure 5.

[0010] Figure 8 is a chart illustrating an atomic force microscopy (AFM) analysis of surface roughness.

[0011] Figures 9A-9D are charts illustrating depth profile data from an XPS analysis of a piezoelectric thin film stack.

[0012] Figure 10 illustrates transverse piezoelectric coefficient for an example of a disclosed device.

Detailed Description

[0013] In the following detailed description, reference is made to the

accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples. In this regard, directional terminology, such as "top," "bottom," "front," "back," etc., is used with reference to the orientation of the Figure(s) being described. Because the various components can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other versions may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. It is to be understood that features of the various examples described herein may be combined with each other, unless specifically noted otherwise. [0014] Thin film structures are employed in many applications. Adhesion between various materials in thin film stacks, including the adherence of metals to non-metal films, present challenges, particularly in environments where high temperatures, piezoelectric vibration, and certain migrating elements or compounds may be present in nearby layers.

[0015] The piezoelectric printhead is an example of such a device that can be prepared or used under some of these conditions. In the case of a piezoelectric printhead, piezoelectric actuation on or in an ink chamber can be used to eject or jet fluids therefrom. One such piezoelectric material is lead zirconate titanate, or "PZT," which can be grown or otherwise applied on the surface of a metal electrode, such as platinum, ruthenium, palladium, and iridium, as well as some conductive and non-conductive oxides, such as lrO 2 , SrRuO 3 , ZrO 2 , etc.

[0016]The appropriate adhesion of the metal electrode (which upon completion, can have PZT or another piezoelectric material applied to one side thereof) to an underlying layer can be provided by an adhesion layer including a blend of zinc oxide and tin oxide. The adhesion of many noble metal electrodes and other metals (e.g., copper) that do not adhere well to other materials, such as especially non-metallic surfaces, oxide surfaces, or polymers, may not be strong enough without the presence of an adhesive layer. Furthermore, even if adhesion is acceptable by using other types of adhesive materials, there can be other drawbacks with some of these other known adhesive materials that are used in thin film stacks. In piezoelectric printheads, for example, various layers of metal and non-metal films are stacked and adhered together; and high temperatures, piezoelectric actuation, and migration of lead or other materials can be common from layer to layer. Lead ion migration through metal electrodes can undermine the function of the device over time. Furthermore, known adhesive layers tend to underperform when exposed to very high manufacturing temperatures.

[0017] In accordance with aspects of the present disclosure, a thermally annealed blend of zinc oxide and tin oxide (ZTO) on a silicon dioxide SiO 2 substrate provides a precisely controllable process for engineering the ZTO film. In general, ZTO is deposited on a first layer including silicon dioxide, and the first layer and the ZTO are heated in an annealing process. Aspects of the resulting thin film structures can be controlled by varying the anneal time and temperature, for example, resulting in various constructions including a thin film stack having a first layer including silicon dioxide, a second layer directly on the first layer including a blend of zinc oxide and silicon dioxide, and a third layer including a blend of zinc oxide and tin oxide.

[0018] It is noted that when referring to "tin oxide," this term can include any of various blends of oxidized tin, including blends of stannous oxide and stannic oxide, e.g., SnO, SnO 2 , respectively. Furthermore, because there are multiple forms of tin oxide, when referring to the atomic % (at%) of the blends of zinc oxide and tin oxide (e.g., "ZnSnO 3 " or "ZTO"), this percentage can be

determined based on the total atomic percentage of each respective element, i.e. zinc, tin, and oxygen. For example, if a composition includes 100 at% ZTO (with essentially no dopant), then there could be about 20 at% zinc, about 20 at% tin, and about 60 at% oxygen. If there is dopant present (anything other than zinc, tin, and oxygen), then the percentages of each of these elements would decrease accordingly. On the other hand, when determining the relative atomic percentage of the zinc oxide and the tin oxide relative to one another, the metal oxide can form the basis of the atomic percentage (or molecular percentage of the oxide compound). Thus, in accordance with the present disclosure, atomic percentages can be calculated not only for individual elements, but also for metal oxides, taking into account both the metal content and the oxygen content. This can also be referred to as "molecular percent" but for consistency, atomic percent is used herein throughout and the context will determine whether the percentage is based on the individual element or on the small molecule.

[0019] Figures 1A-1 D are block diagrams illustrating examples of various thin film structures, and Figure 2 is a flow diagram illustrating an example of a process for forming such structures. In each of the various embodiments described herein, whether discussing the thin film stack device or related methods, there may be some common features of each of these embodiments that further characterize options in accordance with principles discussed herein. Thus, any discussion of the thin film stack or method, either alone or in combination, is also applicable to the other embodiments not specifically mentioned. For example, a discussion of the various layers in the context of the thin film stack is also applicable to the related method, and vice versa.

[0020] In Figure 1A, a first structure 1 is illustrated, wherein a first layer 10 including a silicon dioxide substrate is provided (block 20 of Figure 2). A ZTO blend 12 (xZnO:ySnO 2 ; x and y are both positive) is deposited on the substrate 10 in block 22 of Figure 2. Block 24 represents an annealing process in which the first layer 10 and the ZTO 12 are heated to form various layers, as represented by block 26. In some examples, the annealing 24 was performed in air or a nitrogen/oxygen (N 2 /O 2 ) mixture that mimics the air composition in a furnace or in a rapid thermal processing (RTP) system. The anneal duration varied from 30 seconds when using RTP, to 60 minutes in a furnace in some examples. Suitable ramp rates range from about 5 to 200°C/s for RTP and from about 1 to 20°C/min for furnace.

[0021] As the ZTO 12 and the first layer 10 are heated, the ZTO begins to mix with the silicon dioxide substrate 10 such that the zinc begins to segregate from the tin in the ZTO blend 12. Zinc oxide is "absorbed" by silicon dioxide, or in other words, the silicon dioxide reacts with the zinc oxide "extracted" from the ZTO, to form a second layer 14 that includes a blend of zinc oxide and silicon dioxide in Figure 1 B. Thus, the amount of zinc oxide x in the ZTO blend 12 in Figure 1A is reduced by an amount δι, (δ 1 is positive and less than x), so that the ZTO 12' becomes (x- 5i)ZnO:ySnO 2 in Figure 1 B.

[0022] As the anneal process 24 continues, the zinc from the ZTO 12' continues to be absorbed by the silicon dioxide so that the amount of zinc in the ZTO is further reduced by an amount <¾, (<¾ ' s greater than δι and less than x) in Figure 1 C. The outcome of such "absorption" - mixing of zinc oxide and silicon dioxide - is tin oxide segregation. The tin oxide is "pushed" out from the ZTO to the surface. The thin film stack 3 shown in Figure 1C thus includes a third layer 16 including tin oxide, such that the thin film stack 3 includes the substrate first layer 10, the second layer 14, the tin oxide third layer 16 with a ZTO

((x-¾)ZnO:ySnO 2 ) fourth layer 12" thereunder.

[0023] Figure 1 D illustrates a still further structure 4 after further annealing, where the ZTO fourth layer 12" has been completely incorporated into the tin oxide third layer 16, which is situated directly on the second layer 14. Thus, as illustrated in Figures 1A-1 D and Figure 2, the composition of the thin film stack can be adjusted as desired by controlling the annealing process 24.

[0024] In one example, ZTO with a zinc to tin oxide ratio of 2:1 (Zn 2 SnO 4 ) was deposited on the substrate 10. The film started to crystallize above 600°C. When the temperatures of anneal were increased to 700°C and greater, the Zn 2+ of the ZTO began to interact with the SiO 2 substrate 10, making a Zn 2 SiO 4 second layer 14. The tin oxide segregated from the ZTO, so that after anneal at about 1000°C, the surface of the film (third layer 16) was observed to be a crystalline tin oxide (SnO) with a Zn 2 SiO 4 underlayer 14.

[0025] Figures 3A - 3G illustrate the mixing and segmenting of the components shown in the thin film stacks of Figures 1A-1 D using X-ray photoelectron spectroscopy (XPS). Specimens were analyzed using a PHI Quantera

Scanning ESCA. The spectrometer uses a monochromatic aluminum x-ray source with a photon energy of 1486.6eV. The samples were cleaved from larger samples so as to avoid fingerprints and analyzed without further preparation. The areas of interest were determined from a secondary electron image generated by the scanning photon beam and the analysis was performed using a 20pm photon beam placed on the area of interest.

[0026] A low spectral resolution survey spectrum was acquired from each area of interest on the sample. Higher spectral resolution data were acquired from the detected elements to determine the surface chemistry and composition. The data were charge corrected to carbon 1s at 284.8eV. The data were reduced using a non-linear least squares method to determine the chemical states to determine the organic and inorganic oxygen species. Quantification calculations were made using established sensitivity factors (bracketed values) and the reported values should be regarded as semi-quantitative. It should be noted that the analysis is of only the first 7 nm of the surface.

[0027] The sputter depth profiles were acquired by alternately sputtering and acquiring spectral data. The samples were sputtered using an Ar+ ion beam with a sputter rate of about 5 nm/min relative to Si0 2 with a 2kV beam. The Y- axis is the atomic percentage of an element, and the X-axis is the sputter time (how long the sample was bombarded by Ar, how much was removed in prior analyses). The sputter time is proportional to the depth of the films, such that "0" represents the sample surface and as the times get longer deeper portions of the sample were analyzed.

[0028] The charts for "As Deposited", 500°C and 600°C (Figures 3A-3C) show that after about 10 minutes sputtering time, the Si0 2 layer was reached (Si content was zero before about 10 minutes sputter time and is close to 33% after 10 min as would be expected for pure SiO 2 . The 800°C chart (Figure 3E) shows that Zn and Si are self penetrates - Zn goes in the Si0 2 layer and Sn is not present in the portion of the ZnO:Si0 2 blend. The situation is even more pronounced after the 900°C anneal shown in Figure 3F. After the 1000°C anneal (Figure 3G) the top portion of the film (up to 3 minutes of sputtering) has mainly tin oxide.

[0029] Figure 4 illustrates results of an X-ray diffraction (XRD) characterization of ZTO (Zn 2 Si0 4 ) on Si0 2 , showing that the analyzed films are "amorphous" - in that there is no clear crystallinity, there is no long-range order that would normally be detected by XRD up to 600°C. After 700X the system is more and more crystalline and after 900 and 1000°C a blend of tin oxide (Sn0 2 or possibly an SnO 2 and SnO blend) could be detected.

[0030] The disclosed process thus demonstrates the ability to precisely control the layer composition of the doped zinc oxide film to modulate the film

properties as a dielectric, semiconductor, conductor, barrier layer for lead diffusivity, and adhesion layer for precious metals.

[0031] Figure 5 is a schematic view of a portion of an inkjet printhead 100, with expanded views of a thin film stack 101 in Figures 6 and 7 provided to illustrate example thin film stacks employed in the illustrated inkjet printhead 100.

Though an inkjet printhead is shown in Figure 5 with various specific layers, it is understood that this is not intended to limit the scope of the present disclosure. This is provided to show examples of various thin film stacks that can be used in various devices, such as piezoelectric actuators or sensors.

[0032] In Figure 5, a silicon support is fabricated to include multiple ink chambers 112 for receiving and jetting ink therefrom. It is noted that often, ink chambers or other areas where ink may contact the printhead can be coated with any of a number of protective coatings. Those coatings are not shown, but it is understood that such a coating may be used for protective purposes without departing from the scope of the present disclosure. For example, tantalum or tantalum oxide coatings, such as Ta 2 0 5 , are often used for this purpose. Other support material(s) can be used alternatively or in addition to the mentioned silicon support and optional protective coatings. Thus, the term "support" typically includes structures comprising semi-conductive materials such as silicon wafer, either alone or in assemblies comprising other materials applied thereto. Metallic supports can also be used, including metallic materials with an insulating material applied thereto. Certain specific materials that can be used for the support material include silicon, glass, gallium arsenide, silicon on sapphire (SOS), germanium, germanium silicon, diamond, silicon on insulator (SOI) material, selective implantation of oxygen (SIMOX) substrates, or other similar materials. Furthermore, the substrate described herein can actually be the support material, particularly when the support material inherently includes an oxidized surface. However, in many typical examples, a separate membrane of oxidized material is applied to the support and acts as the substrate.

[0033] In Figure 5, the printhead 100 includes a substrate 10, an adhesive layer 116, a first metal electrode 118, a piezoelectric layer 120, a second metal electrode 122, and a passivation layer 124. Some typical printheads could additionally include further layers, including other insulating, semi-conducing, conducting, or protective layers that are not shown. However, one skilled in the art would recognize other layers that could optionally be used, or optionally omitted from the illustrated structure. [0034] In the system shown, the first metal electrode 1 18 and the second metal electrode 122 are used to generate an electric field with respect to the piezoelectric layer 120, and as the piezoelectric layer is actuated, the thin film stack bends into an appropriate ink chamber 12, causing inkjetting to occur. The substrate layer 10 can be the support material with an oxide layer inherently present on its surface, but is typically prepared as an oxide membrane applied to the support material, e.g., Si0 2 , Zr0 2 , HfO 2 , Ta 2 O 5 , Al 2 0 3 , SrTiO 3 , etc. These membranes can be applied as multiple layers, and/or be prepared using multiple materials in a common layer. Thus, the materials are typically applied as one or more layer to the silicon or other support material as described above. When the substrate is in the form of a thin film or membrane, the substrate can be formed at a thickness from 10 A to 10 pm, for example. In an example piezoelectric actuator device, the thickness of this substrate, e.g., oxidized membrane, can be approximately the same thickness as piezoelectric layer, e.g., at a 1 :2 to 2:1 thickness ratio of substrate layer to piezoelectric layer, and both layers can be about 50 nm or greater.

[0035]The metal electrodes 118, 122 can be applied at a thickness from about 5 nm to 5 microns, though thicknesses outside this range can also be used. Materials that can be used, particularly for electrodes, typically include noble metals or other metals or alloys, including but not limited to, platinum, copper, gold, ruthenium, iridium, silver, nickel molybdenum, rhodium, and palladium. In other examples, oxides of these or other metals can also be used, such as Ir0 2 or SrRu0 3 , if the adhesive properties of the adhesion layers of the present disclosure would be beneficial for use. Platinum is of particular interest as a metal that benefits from the adhesive layers of the present disclosure because its surface does not become readily oxidized. Metal electrodes (or metals applied for another purpose, such as for conductive layers or traces) can be deposited using any technique known in the art, such as sputtering,

evaporation, growing the metal on a substrate, plasma deposition,

electroplating, etc.

[0036] In the printhead 100 illustrated in Figure 5, a passivation layer 124 is shown, which can be formed of any suitable material, including, but not limited to wet or dry process silicon dioxide, aluminum oxide (e.g., Al 2 0 3 ), silicon carbide, silicon nitride, tetraethylorthosilicate-based oxides, borophosphosilicate glass, phosphosilicate glass, or borosilicate glass, Hf0 2 , Zr0 2 , or the like.

Suitable thicknesses for this layer can be from 10nm to 1 pm, though

thicknesses outside of this range can also be used.

[0037] Figures 6 and 7 illustrate examples of the thin film stack 101 , with additional aspects of the adhesion layer 116 illustrated. In some example thin film stacks 101 , the adhesion layer 116 results from the process illustrated in Figure 2, including the annealing process 24 prior to depositing the subsequent layers of the thin film stack.

[0038] In Figure 6, the adhesion layer 116 is similar to that shown in Figure 1C. Thus, the first layer 10 is a substrate including silicon dioxide, the second layer 14 includes a blend of zinc oxide and silicon dioxide, the third layer 16 includes tin oxide, and the ZTO fourth layer 12" is between the second and third layers. The first metal layer 118 (platinum, for example) is deposited on the tin oxide layer 16, and the piezoelectric layer 120 (PZT in Figure 6) is deposited on the first metal layer 118.

[0039] Figure 7 illustrates a thin film stack 101 in which the adhesion layer 116 is similar to that shown in Figure 1 D. The adhesion layer 116 includes the second layer 14 with the zinc oxide and silicon dioxide blend situated on the substrate 10, and the third layer 16 that includes tin oxide. The first metal layer 118 (platinum, for example) is deposited on the tin oxide layer 16, and the piezoelectric layer 120 (PZT in Figure 7) is deposited on the first metal layer 118.

[0040]The adhesion layer 116 disclosed herein promotes uniform mechanical performance and provides acceptable barrier properties to lead and other impurities that may migrate through the adjacent electrode. Thus, the adhesive layer 116 of the present disclosure provides reliable adhesion between many noble and other metallic materials, including platinum, copper, gold, ruthenium, and iridium. Furthermore, acceptable adhesion to non-metallic materials can also be achieved, making it a good adhesive to use between metallic and non- metallic layers or surfaces.

[0041] Generally, as processing temperatures are increased, the surface roughness can increase as well. However, with the adhesive layers of the present disclosure comprising annealed blends of zinc oxide and tin oxide, the surface roughness, even with very high annealing temperatures, e.g. 1000 °C or more, can be low enough to still be effective for processing and use. Figure 8 is a chart illustrating an atomic force microscopy (AFM) analysis of surface roughness for ZTO (Zn 2 Sn0 4 ) on a silicon dioxide substrate. For example, when annealed at 1000 C° for one hour, a 6 nm RMS roughness was observed and an even lower roughness was observed, down to 1 nm, when the material was annealed for a shorter time using Rapid Thermal Processing (RTP).

[0042] A suitable material for the piezoelectric layer 120 that can be used includes, as mentioned, lead zirconium titanate (PZT). In general, with respect to PZT, the general formula can be Pb(Zr 1-x Ti x )O 3 , where x is from 0.1 to 0.9. However, it is notable that different dopants can be used, such as La, Nb, etc. Thus, other materials for the piezoelectric layer can also be used, including lead lanthanum zirconium titanate (PLZT, or La doped PZT), lead niobium zirconium titanate (PNZT, or Nb doped PZT), and PMN-PT (Pb(Mg,Nb)0 3 -PbTi0 3 ). Lead- free piezoelectric layers may also be used, examples of which include LiNb0 3 , BCTZ [Ba(Tio.8Zr 0 . 2 )0 3 -(Ba 0 .7Cao .3 )Ti0 3 ], tungsten bronze structured

ferroelectrics (TBSF), BNT-BT [(Bio.5Nao.5)Ti0 3 -BaTi0 3 ], BT [BaTi0 3 ], AIN, AIN doped with Sc, and ternary compositions in the BKT-BNT-BZT [(Bi 0 .5K 0.5 )TiO 3 - (Bio .5 Nao .5 )TiO 3 -Bi(Zno.5Tio.5)0 3 ] system, a specific example of which includes 0.4(Bio.5Ko.5)Ti0 3 -0.5(Bio. 5 Nao.5)Ti0 3 -0.1 Bi(Zno. 5 Tio.5)0 3 ). Other suitable piezoelectric materials can be used for the piezoelectric layer, or combinations of materials or multiple layers can likewise be used in accordance with examples of the present disclosure.

[0043] In piezoelectric systems in particular, the metal electrodes 118, 122 selected for use should be those which can effectively cause appropriate movement of the piezoelectric materials, such as those used in the piezoelectric layer 120. This is particularly true with respect to the metal electrode 1 18, which is in direct contact with the adhesive layer 1 16. As PZT contains lead, and lead cations are migratory though other metals under the proper conditions, there can be problems associated with lead migrating into and through the metal electrode, e.g., lead migrates fairly readily through platinum when a titanium oxide adhesive layer is applied to the opposite side of the metal electrode. This is believed to occur because after annealing platinum and titanium oxide during the manufacturing process, especially at high temperatures, lead cations will diffuse into or through the platinum (preferably along the Pt grain boundaries) and into the titanium oxide, forming lead titanate (PbTi0 3 ). Thus, in accordance with examples of the present disclosure, by using an annealed blend of zinc oxide and tin oxide, decreased migration of lead cations through the metal layer.

[0044] Figures 9A-9D are charts illustrating depth profile data from XPS analysis of a piezoelectric thin film stack. More specifically, the analyzed thin film stack was essentially as illustrated in Figure 7, wherein 120 PZT was deposited on a platinum layer 1 18, with an adhesion layer 1 16 between the metal layer 118 and the Si0 2 substrate 10. The adhesion layer 1 16 included a 50 nm ZTO layer annealed at 800°C, resulting in a tin oxide layer 16 and a layer 14 having a zinc oxide and silicon dioxide blend.

[0045] In one example, the stack of the PZT layer 120, first platinum electrode 118 and the annealed ZTO-based adhesion layer 1 16 were analyzed by XPS down to the silicon dioxide layer 0 to determine whether lead diffused through the metal electrode and the adhesion layer. The sample was thus analyzed for the presence of platinum and PZT related ingredients (Pb, Zr, Ti and O), in addition to the materials of the adhesion layer and substrate (Zn, Sn, Si and O). With the annealed ZTO adhesion layer, the lead diffusivity was negligible - less than 0.5 atomic% in the illustrated analysis. For comparison, a similar analysis was performed using a device with a "typical" titanium oxide adhesive layer, wherein about 3 atomic% of lead was diffused through the metal electrode.

[0046] Figure 10 illustrates hysteresis loops for an example structure having a PZT piezoelectric layer deposited on a platinum electrode, with an annealed ZTO adhesion layer 1 16 in accordance with the present disclosure (1 μιη PZT, 100 nm Pt, 50 nm ZTO preliminary annealed at 800 and 1000 °C in the illustrated example). PZT was deposited by a sol-gel approach with a pyrolysis step at 350 °C and sintering at 700 °C in one example. Transverse

piezoelectric coefficient, e31 ,f, for these samples was measured using AixACCT 4PB (four point bender) and values 10.1 , 10,7 and 10,9 C/m 2 were observed for PZT deposited on Pt/ZTO with ZTO as deposited and annealed at 800 and 1000 °C respectively.

[0047] With respect to the various layers described herein, any of a number of deposition methods or techniques can be used. For example, as mentioned, a PZT layer can be grown on or otherwise applied to the surface of a metal in some examples. Deposition techniques that can be used for depositing piezoelectric material or other layers on top of one another include sol-gel deposition, physical vapor deposition (PVD), pulsed laser deposition (PLD), atomic layer deposition (ALD), Metal Organic CVD (MOCVD), etc. Metal can be deposited, for example, by sputtering or other known deposition methods.

Semi-conductive, non-conductive, or passivation layers can be deposited by plasma enhanced chemical vapor deposition (PECVD), a low pressure chemical vapor deposition (LPCVD), an atmosphere pressure chemical vapor deposition (APCVD), atomic layer deposition (ALD), sputter deposition, evaporation, thermal oxidation, or other known methods. Any combination of these or other methods can be used.

[0048]Aithough specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof