Electromechanical responsive film, stacked arrangement and methods of forming the same

Abstract

Various embodiments may relate to an electromechanical responsive film. The electromechanical responsive film may include potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (K1-xNax)yNbO3z. x may be any value selected from a range from 0.4 to 0.8. y may be any value selected from a range from 0.61 to 0.65. z may be any value selected from a range from 0 to 0.96. The film may have a (001)-oriented or (100)- oriented perovskite crystalline structure.

Description

ELECTROMECHANICAL RESPONSIVE FILM, STACKED ARRANGEMENT AND METHODS OF FORMING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application No.10202404096V filed December 27, 2024, the contents of it being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] Various embodiments of this disclosure may relate to an electromechanical responsive film. Various embodiments of this disclosure may relate to a stacked arrangement. Various embodiments of this disclosure may relate to a method of forming an electromechanical responsive film. Various embodiments of this disclosure may relate to a method of forming a stacked arrangement.BACKGROUND

[0003] Microelectromechanical systems (MEMS) are made up of miniaturized microelectromechanical sensors and actuators, and thin films with large electromechanical response, e.g., high performance piezoelectric properties, are in high demand. Currently, piezoelectric thin films with large electromechanical response, represented by large piezoelectric coefficient, are typically lead-based solid solutions, e.g. Pb(Zr1–xTix)O3(lead zirconate titanate or PZT) materials having ~60 wt% of lead, which is a toxic element. However, the existence of lead in these materials raises environmental concerns. Thereare international legislative regulations, such as Restriction of Hazardous Substances (RoHS) regulations which restrict the usage of lead in electrical and electronics equipment in Europe, and J-Moss regulations (a Japanese version RoHS). Though lead in piezoelectric materials is currently exempted, it is unknown when the exemption will be extended till. Therefore, there is a pressing need to develop lead-free materials with high piezoelectric performance as replacement Among lead-free materials, alkali niobate-based lead-free piezoceramic is promising as it has achieved a large d33of 416 pCN-1, which is close to PZT’s value of 490 pCN'1. Giant effective piezoelectric coefficient d33of 1098 pmV-1has been achieved at 1 kHz in nonstoichiometric potassium sodium niobate (KNN) epitaxial thin film grown on niobium-doped strontium titanate (Nb-doped SrTiO3) single crystal substrate with the lattice matching perovskite structure, which is around 4 times compared to that of the state-of-the-art PZT thin film. However, the single crystal substrates with the lattice matching perovskite structures are expensive and incompatible with the current main-stream silicon-based semiconductor and micro-electromechanical system (MEMS) manufacturing processes. Hence, considering the industry scalability, cost and circuit integration compatibility, high performance lead-free piezoelectric polycrystalline thin films over silicon (Si) substrate are highly sought.SUMMARY

[0004] Various embodiments may relate to an electromechanical responsive film. The electromechanical responsive film may include potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (K1-xNax)yNbO3z. x may be any value selected from a range from 0.4 to 0.8. y may be any value selected from a range from 0.61 to 0.65. z may be any value selected from a range from 0 to 0.96. The film may have a (OOl)-oriented or (100)-oriented perovskite crystalline structure.

[0005] Various embodiments may relate to a stacked arrangement. The stacked arrangement may include a (lOO)-oriented substrate. The stacked arrangement may include a (lOO)-oriented zirconium (Zr)-based intermediate layer on or over the (lOO)-oriented substrate The stacked arrangement may also include a (lOO)-oriented electrode layer on the (lOO)-oriented zirconium (Zr)-based intermediate layer. The stacked arrangement may include an electromechanical responsive film as described herein on the (100)-oriented electrode layer. The stacked arrangement may further include a further electrode layer on the electromechanical responsive film.

[0006] Various embodiments may relate to a method of forming an electromechanical responsive film. The method may include using magnetron co-sputtering of two targets to form the film including potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (Ki.xNax)yNbO3z. x may be any value selected from a range from 0.4 to 0.8. y may be any value selected from a range from 0.61 to 0.65. z may be any value selected from a range from 0 to 0.96. The film may have a (OOl)-oriented or (lOO)-oriented perovskite crystalline structure.

[0007] Various embodiments may relate to a method of forming a stacked arrangement. The method may include forming a (lOO)-oriented zirconium (Zr)-based intermediate layer on or over a (lOO)-oriented substrate. The method may also include forming a (lOO)-oriented electrode layer on the (lOO)-oriented zirconium (Zr)-based intermediate layer. The method may further include forming an electromechanical responsive film as described herein on the (100) -oriented electrode layer. The method may additionally include forming a further electrode layer on the electromechanical responsive film.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings.FIG. 1 shows a general illustration of an electromechanical responsive fdm according to various embodiments.FIG. 2 shows a stacked arrangement according to various embodiments.FIG. 3 shows a general illustration of a method of forming an electromechanical responsive film according to various embodiments.FIG. 4 shows a general illustration of a method of forming a stacked arrangement according to various embodiments.FIG. 5A shows a schematic of a multilayer stack according to various embodiments.FIG. 5B is a table showing the crystal lattice symmetry and lattice constants of potassium sodium niobate (KNN) film, platinum layer, zirconium nitride (ZrN) layer, zirconium dioxide (ZrO2) layer and silicon layer according to various embodiments.FIG. 5C shows a schematic illustrating an (OOl)-oriented or (lOO)-oriented electromechanical responsive film / (lOO)-oriented platinum (Pt) electrode layer / (lOO)-oriented zirconium nitride (ZrN) layer / (lOO)-oriented silicon (Si) substrate stacked arrangement according to various embodimentsFIG. 5D shows a schematic illustrating an (OOl)-oriented or (lOO)-oriented electromechanical responsive film / (lOO)-oriented platinum (Pt) electrode layer / (lOO)-oriented zirconium dioxide (ZrO2) layer / (100)-oriented silicon (Si) substrate stacked arrangement according to various embodiments.FIG. 6A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) XRD image of a (OOl)-oriented potassium sodium niobate KNN (001) / platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments. FIG. 6B shows X-ray Photoelectron Spectroscopy (XPS) compositional data of a (OOl)-oriented or (lOO)-oriented electromechanical responsive film on a platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments.FIG. 6C shows a three dimensional (3D) plot of displacement (in meters or m) as a function of X position (in millimeters or mm) and Y position (in millimeters or mm) illustrating the surface displacement profile of the (OOl)-oriented or (lOO)-oriented electromechanical responsive film on a platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments.FIG. 6D shows a plot of intensity (counts) as a function of depth (in nanometers or nm) illustrating Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis for the (OOl)-oriented or (lOO)-oriented potassium sodium niobate KNN (001) or KNN (100) / platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments.FIG. 7A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) XRD image of a (OOl)-oriented or (lOO)-oriented potassium sodium niobate KNN (001) or KNN (100) / platinum Pt (100) / zirconium dioxide ZrO2(100) / silicon Si (100) stack according to various embodiments.FIG. 7B shows X-ray Photoelectron Spectroscopy (XPS) compositional data of a (OOl)-oriented or (lOO)-oriented electromechanical responsive film on a platinum Pt (100) / zirconium dioxide ZrO2(100) / silicon Si (100) stack according to various embodiments.FIG. 7C shows a plot of intensity (counts) as a function of depth (in nanometers or nm) illustrating Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis for the (OOl)-oriented or (lOO)-oriented potassium sodium niobate KNN (001) or KNN (100) / platinum Pt (100) / zirconium dioxide ZrO2(100) / silicon Si (100) stack according to various embodiments.FIG. 8A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) image of a potassium sodium niobate KNN / platinum Pt / titanium dioxide (TiO2) / silicon dioxide (SiO2) / silicon Si (100) stack.FIG. 8B shows X-ray Photoelectron Spectroscopy (XPS) compositional data of an electromechanical responsive film with low level (001) orientation or (100) orientation on a platinum Pt / titanium dioxide (TiO2) / silicon dioxide (SiO2) / silicon Si (100) stack.FIG. 9A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) image of a potassium sodium niobate KNN / platinum Pt / titanium dioxide (TiO2) / silicon dioxide (SiO2) / silicon Si (100) stack by single target magnetron sputtering.FIG. 9B shows X-ray Photoelectron Spectroscopy (XPS) compositional data of an electromechanical responsive film with low level (001) orientation or (100) orientation on a platinum Pt / titanium dioxide (TiO2) / silicon dioxide (SiO2) / silicon Si (100) stack by single target magnetron sputtering.DESCRIPTION

[0009] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the artto practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0010] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0011] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0012] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e.g. within 10% of the specified value.

[0013] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0014] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0015] By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0016] Embodiments described in the context of one of the films / stacked arrangements are analogously valid for the other films / stacked arrangements, embodiments described in the context of a method are analogously valid for a film / stacked arrangement, and vice versa.

[0017] FIG. 1 shows a general illustration of an electromechanical responsive film 102 according to various embodiments. The electromechanical responsive film 102 may include potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (K1-xNax)yNbO3z. x may be any value selected from a range from 0.4 to 0.8. y may be any value selected from a range from 0.61 to 0.65. z may be any value selected from a range from 0 to 0.96. The film 102 may have a (OOl)-oriented or (lOO)-oriented perovskite crystalline structure.

[0018] In other words, the film 102 may have an oxygen (O) content 3z times that of niobium (Nb), where 0 < z < 0.96 The ratio of potassium (K) to sodium (Na) may be 1-x: x, where 0.4 < x < 0.8. The ratio of Ki-xNaxmay be y times that of niobium (Nb), where 0.61 < y < 0.65. Due to the pseudo-cubic phase of the film 102, the (001) orientation may be taken to be equivalent to the (100) orientation.

[0019] In one example, x may be about 0.79, y may be about 0.65 and z may be about 0.68. In another example, x may be about 0.45, y may be about 061 and z may be about 0.96.

[0020] The film 102 may be suitable to be formed over a suitable silicon substrate, and may have a large electromechanical response. The film 102 may be a thin film with (OOl)-oriented or (100) oriented perovskite crystalline structure. The film 102 may alternatively be referred to as an electromechanical thin film, a KNN electromechanical thin film, or simply a KNN film. The film 102 may have any suitable thickness, e g., any thickness selected from a range from 100 nm to 2000 nm, such as 150 nm to 300 nm, e.g., about 200 nm or about 240 nm.

[0021] For avoidable of doubt, FIG 1 is intended to provide a general illustration of the film 102, and is not intended to limit, for instance, the dimensions, size, orientation, shape etc. of the film 102.

[0022] In various embodiments, the electromechanical response may be extraordinarily large. In various embodiments, an effective longitudinal piezoelectric strain coefficient (d*33,r) of the film 102 may be greater than 1000 pm V-1at 1 kHz.

[0023] In various embodiments, the effective longitudinal piezoelectric strain coefficient of the film 102 may be greater than 1477 pm V-1at 1 kHz.

[0024] In various embodiments, the film 102 may have an orientation coefficient of about 1.0, (i.e., about 100%).

[0025] FIG. 2 shows a stacked arrangement according to various embodiments. The stacked arrangement may include a (lOO)-oriented substrate 204. The stacked arrangement may include a (lOO)-oriented zirconium (Zr)-based intermediate layer 206 on or over the (lOO)-oriented substrate 204. The stacked arrangement may also include a (lOO)-oriented electrode layer 208 on the (lOO)-oriented zirconium (Zr)-based intermediate layer 206. The stacked arrangement may include an electromechanical responsive film 202 (e.g., the film 102 shown in FIG. 1) on the (lOO)-oriented electrode layer 208. The stacked arrangement may further include a further electrode layer 210 on the electromechanical responsive film 202.

[0026] In other words, the stacked arrangement may include an electromechanical responsive film 202 between a (lOO)-oriented electrode layer 208 and a further electrode layer 210. The stacked arrangement may also include a (lOO)-oriented zirconium (Zr)-based intermediate layer 206 between a (lOO)-oriented substrate 204 and the (lOO)-oriented electrode layer 208. The stacked arrangement may alternatively be referred to as a multilayer stack.

[0027] For avoidable of doubt, FIG. 2 is intended to provide a general illustration of features of the stacked arrangements, and is not intended to limit, for instance, the dimensions, size, orientation, shape etc. of the various features.

[0028] In various embodiments, the (lOO)-oriented electrode layer 208 may be a platinum layer. The (lOO)-oriented electrode layer 208 may be referred to as a bottom electrode layer or(lOO)-oriented bottom electrode layer. Conversely, the further electrode layer 210 may be referred to as a top electrode layer.

[0029] The (lOO)-oriented substrate 204 may be a silicon substrate.

[0030] In various embodiments, the (lOO)-oriented zirconium (Zr)-based intermediate layer 206 may include a zirconium compound. In various embodiments, the (lOO)-oriented zirconium (Zr)-based intermediate layer 206 may include zirconium nitride (ZrN) (i.e., the zirconium compound may be ZrN). In various other embodiments, the (lOO)-oriented zirconium (Zr)-based intermediate layer 206 may include zirconium dioxide (ZrO2) (i.e., the zirconium compound may be ZrO2). The inclusion of the (lOO)-oriented zirconium (Zr)-based intermediate layer 206 may allow for the formation of the overlying (lOO)-oriented electrode layer 208. The electromechanical responsive film 202 may then be formed on the (100)-oriented electrode layer 208. The electromechanical responsive film 202 may be a polycrystalline perovskite film having a (OOl)-oriented or (lOO)-oriented perovskite crystalline structure with nonstoichiometric composition, and may be able to exhibit a large electromechanical response due to lattice defects present in the electromechanical responsive film 202.

[0031] In various embodiments, the further electrode layer may include gold, platinum or silver.

[0032] FIG. 3 shows a general illustration of a method of forming an electromechanical responsive film according to various embodiments. The method may include, in 302, using magnetron co-sputtering of two targets to form the film including potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (K1-xNax)yNbO3z. x may be any value selected from a range from 0.4 to 0.8. y may be any value selected from a range from 0.61 to 0.65. z may be any value selected from a range from 0 to 0.96. The film may have a (OOl)-oriented or (lOO)-oriented perovskite crystalline structure.

[0033] In other words, the method may involve magnetron co-sputtering using two targets to form the film. The film formed may be film 102 as illustrated in FIG. 1.

[0034] In various embodiments, a first target of the two targets may include a material including K, Nb and O, e.g., a material having a formula KaNbbO3. In various embodiments, a second target of the two targets may include a material including Na, Nb and O, e.g., a material having a formula NacNbbO3. Each of a, b and c may be any positive real number.

[0035] In various embodiments, the material of the first target is K1.05NbO3. The material of the second target may be Na1.05NbO3. Different radio frequency powers may be provided to the first target and to the second target.

[0036] In various embodiments, the magnetron co-sputtering may be radio frequency (RF) co-sputtering carried out in a mixture of suitable gases, e.g., oxygen and argon.

[0037] In various embodiments, the magnetron co-sputtering may be carried out at a temperature above room temperature, i.e., 20 °C. In various embodiments, the temperature may be preferably equal to or above 500 °C, such as 600°C to 700 °C).

[0038] In various embodiments, the magnetron co-sputtering may be carried out at any suitable pressure, e.g., a pressure selected from a range from 20 mTorr to 30 mTorr, e.g., 24 mTorr to 30 mTorr.

[0039] FIG. 4 shows a general illustration of a method of forming a stacked arrangement according to various embodiments. The method may include, in 402, forming a (lOO)-oriented zirconium (Zr)-based intermediate layer on or over a (lOO)-oriented substrate. The method may also include, in 404, forming a (100)-oriented electrode layer on the (lOO)-oriented zirconium (Zr)-based intermediate layer. The method may further include, in 406, forming an electromechanical responsive film as described herein on the (lOO)-oriented electrode layer. The method may additionally include, in 408, forming a further electrode layer on the electromechanical responsive film.

[0040] In other words, the method may include forming an electromechanical responsive film between a (lOO)-oriented electrode layer and a further electrode layer. The method may also include forming a (lOO)-oriented zirconium (Zr)-based intermediate layer between a (100) -oriented substrate and the (lOO)-oriented electrode layer.

[0041] In various embodiments, the (lOO)-oriented substrate may be a silicon substrate.

[0042] In various embodiments, the (lOO)-oriented electrode layer may be formed via sputtering.

[0043] In various embodiments, the (lOO)-oriented zirconium (Zr)-based intermediate layer may be formed via sputtering. In various embodiments, the (lOO)-oriented zirconium (Zr)-based intermediate layer may include a zirconium compound. In various embodiments, the (100)-oriented zirconium (Zr)-based intermediate layer may include zirconium nitride (ZrN) (i.e., the zirconium compound may be ZrN). In various other embodiments, the (lOO)-oriented zirconium (Zr)-based intermediate layer may include zirconium dioxide (ZrO?) (i.e., the zirconium compound may be ZrO2). The (lOO)-oriented substrate may be cleaned to remove contaminants and native oxide (i.e., silicon oxide) before the zirconium compound is deposited onto the (lOO)-oriented substrate, which may be heated to a suitable temperature (e.g., a temperature selected from 350 °C to 400 °C, e.g., 380 °C).

[0044] In various embodiments, the (lOO)-oriented electrode layer may be a platinum layer. Platinum may be deposited onto the underlying (lOO)-oriented zirconium (Zr)-based intermediate layer to form the (lOO)-oriented platinum layer, which may be heated to a suitable temperature (e g., a temperature selected from 500 °C to 550 °C, e.g., 530 °C). The (100)-oriented electrode layer may be a bottom electrode layer formed after forming the (100)-oriented zirconium (Zr)-based intermediate layer. The electromechanical responsive film may be formed after forming the (lOO)-oriented electrode layer. The further electrode layer may be formed after forming the electromechanical responsive film.

[0045] Various embodiments may relate to an electromechanical thin film with (001)-oriented or (lOO)-oriented perovskite crystalline structure and large electromechanical response formed over silicon. The thin film may include a KNN-based oxide, i.e., may contain the elements potassium (K), sodium (Na), niobium (Nb) and oxygen (O). Various embodiments may relate to a stacked arrangement (i.e., multilayer stack) including a top electrode layer, the (OOl)-oriented or (lOO)-oriented KNN electromechanical thin film, a bottom platinum (Pt) electrode layer with (lOO)-orientation, and an intermediate layer of Zr compound, and a (100)-oriented silicon substrate. Various embodiments may relate to a method for fabricating the electromechanical thin film.

[0046] FIG. 5A shows a schematic of a multilayer stack according to various embodiments. The multilayer stack may include a top electrode layer 510 (e g. gold), an electromechanical responsive film 502 with (OOl)-oriented or (lOO)-oriented perovskite crystalline structure, a (100)- oriented Pt bottom electrode layer 508, an intermediate layer 506 of Zr compound, and a (lOO)-oriented silicon substrate 504. The electromechanical responsive film 502 may be a potassium sodium niobate (KNN) film that has a compositional formula as (Ki-xNax)yNbO3z, wherein 0.4 < x < 0.8, 0.61 < y < 0.65 and z < 0.96. Other than the specific elemental composition range, the structural orientation of KNN film may affect or contribute to a large electromechanical response The intermediate layer 506 of Zr compound may be a ZrO2 or ZrN layer. FIG. 5B is a table showing the crystal lattice symmetry and lattice constants of potassium sodium niobate (KNN) film, platinum layer, zirconium nitride (ZrN) layer, zirconium dioxide (ZrOj layer and silicon layer according to various embodiments. The lattice symmetry of KNN, Pt, ZrN and Si may be similar and all may be pseudo-cubic (for KNN) or cubic. The lattice constants of KNN, Pt, and ZrN may be similar.

[0047] KNN possesses a pseudo-cubic ABO3 perovskite structure with unit cell parameters a, b and c are very close to one another. Normal X-ray diffraction (XRD) may not distinguish(100) or (001) orientations. Therefore, the (100) orientation in many publications and prior art may include the (001) orientation for the crystalline pseudo-cubic phase. Further studies show that the inter-atom distances in the plane perpendicular to <100> direction between ZrN and (lOO)-oriented Si may be close to each other. These conditions may lead to a highly-textured (OOl)-oriented or (lOO)-oriented KNN film 502 grown on or over Pt (100) / ZrN (100) / Si (100), giving a high electromechanical response ZrO2may have a ditetragonal dipyramidal structure, which may form pyramids along the lattice constant of the upper layer, giving a single texture form of that upper layer material, hence subsequent Pt bottom electrode layer 508 may also be (lOO)-oriented, leading to a (OOl)-oriented or (lOO)-oriented KNN film 502 forming on the Pt (100) bottom electrode layer 508. Overall, the Pt bottom electrode layer 508 on Zr compound film 506, either ZrN or ZrO2, may have a cubic crystal structure with (100) orientation in accordance with the orientation of the Si (100) substrate, and the KNN film 502 may have a pseudo-cubic crystal structure in accordance with the orientation of the Pt (100) bottom electrode layer 508. FIG. 5C shows a schematic illustrating an (OOl)-oriented or (lOO)-oriented electromechanical responsive film / (lOO)-oriented platinum (Pt) electrode layer / (lOO)-oriented zirconium nitride (ZrN) layer / (100)-oriented silicon (Si) substrate stacked arrangement according to various embodiments. FIG. 5D shows a schematic illustrating an (OOl)-oriented or (lOO)-oriented electromechanical responsive film / (lOO)-oriented platinum (Pt) electrode layer / (lOO)-oriented zirconium dioxide (ZrO2) layer / (100)-oriented silicon (Si) substrate stacked arrangement according to various embodiments.

[0048] One fabrication method of the electromechanical responsive film 502 may include co-sputtering of 2 targets to deposit the (OO l)-oriented or (lOO)-oriented KNN film 502 over Pt (100) / ZrN (100) / Si (100) or Pt (100) / ZrO2 (100) / Si (100), by controlling the film growth parameters, such as substrate temperature, gas pressure, gas flow, distance between target and substrate and sputtering power.

[0049] Example 1

[0050] Example 1 relates to a stack including a top electrode layer (gold or Au), a (001)-oriented or (lOO)-oriented electromechanical responsive film with perovskite structure and elements: potassium (K), sodium (Na), niobium (Nb) and oxygen (O) (KNN film), a bottom electrode layer of (lOO)-oriented-Pt, an intermediate layer of zirconium (Zr) compound (i.e., zirconium nitride (ZrN), and a (lOO)-oriented silicon (Si) substrate. The electromechanical responsive KNN film has a thickness of -200 nm and is fabricated using magnetron cosputtering. In order to obtain the KNN(001) or KNN(100) film on a Pt (100) / ZrN ( 100) / Si (100) substrate, a Pt (100) / ZrN (100) / Si (100) stack is prepared first. The silicon substrate is first cleaned using acetone, ethanol, dilute hydrofluoric acid (HF) (5%) and subsequently rinsed in de-ionized water to remove surface contamination and native oxide. The cleaned Si (100) substrate is heated up to 380 °C and a ZrN(100) layer is deposited in an argon-nitrogen ambience. Next, the ZrN (100) / Si (100) sample is heated up to 530 °C for Pt (100) deposition in an argon ambience. After obtaining the Pt (100) / ZrN ( 100) / Si (100) stack, the Pt (100) / ZrN (100) / Si (100) stack is first heated up to 600 °C in a vacuum chamber and the KNN film is deposited by co-sputtering of two targets with composition K1.05NbO3and Na1.05NbO3. The radio frequency (RF) powers for the co-sputtering are 105 W and 90 W respectively in an argonoxygen ambience. The argon flow rate is 20 seem and the oxygen flow rate is 6 seem at an operating pressure of 27 mTorr. Deposition time is 90 min. Finally, the substrate is cooled down at a rate of 10 °C / min in an argon-oxygen ambience.

[0051] FIG. 6 A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 29 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) XRD image of a (001)- or (lOO)-oriented potassium sodium niobate KNN (001) / platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments. The full width at half maximum (FWHM) of the (001) or (100) peak for KNNis 0.353°. To quantify crystal lattice orientation, an orientation coefficient is defined as the ratio of the intensity of XRD peaks for the lattice planes with the specified orientation over the sum of the XRD intensity for all the planes of the film (as in the formula for KNN (001): orientation coefficient = - - ^J™w(°01)+J™iV(002) -, jm an(jn mayany2.1 KNN Cool) +1KNN (002) +1KNN (Imn) suitable positive integers). A higher value of orientation coefficient represents a higher crystal orientation in the film. The (OOl)-oriented or (lOO)-oriented KNN film deposited on Pt (100) / ZrN (100) / Si (100) apparently shows an orientation coefficient of 1.0.

[0052] FIG. 6B shows X-ray Photoelectron Spectroscopy (XPS) (XPS) compositional data of a (OOl)-oriented or (lOO)-oriented electromechanical responsive film on a platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments. The elemental composition of the film surface has (K+Na)ZNb ratio of 0.65, OZNb ratio is 2.05 and OZ(K+Na) is 3.14. According to the proposed KNN formula as (Ki.xNax)yNbO3z, wherein 0.4 < x < 0.8, 0.61 < y< 0.65 and z < 0.96, this high electromechanical responsive (001)- or (lOO)-oriented KNN film has x = 0.79, y = 0.65 and z = 0.68, giving film composition of (Ko.21Nao.79)o.65Nb03x0.68.

[0053] The electromechanical response may be characterized with a laser scanning vibrometer, which may measure the surface displacement due to the mechanical strain induced by the applied electrical field, as shown in FIG. 6C. FIG. 6C shows a three dimensional (3D) plot of displacement (in meters or m) as a function of X position (in millimeters or mm) and Y position (in millimeters or mm) illustrating the surface displacement profile of the (001)-oriented or (lOO)-oriented electromechanical responsive film on a platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments. The effective piezoelectric strain coefficient d*33,r of the (Ko.2iNao.79)o.65Nb03xo.68 film is greater than 1000 pmV1, up to -1477 pmV1under 115 kVcm'1field at 1 kHz.

[0054] To examine the compositional distribution in the KNN (001) / Pt (100) / ZrN (100) / Si (100) stack, a Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) may be performed with depth profiling, with results shown in FIG 6D. FIG 6D shows a plot of intensity (counts) as a function of depth (in nanometers or nm) illustrating Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis for the (OOl)-oriented or (lOO)-oriented potassium sodium niobate KNN (001) or KNN (100) / platinum Pt (100) / zirconium nitride ZrN (100) / silicon Si (100) stack according to various embodiments. Due to the different elements involved in the stack, the depth is converted from the sputtering time using the standard silicon dioxide SiO2erosion calibration rate and selected elements are presented. This can give a relative diffusion behavior of the different elements between the films. From the compositional depth profile, it is evident that Na, K and Nb diffuse into the Pt (100) / ZrN (100) / Si (100) stack. Such diffusion may cause loss of elements in the KNN(001) or KNN(100) film, nonstoichiometric chemical composition, and thus more lattice defects in the KNN film. The existence of large number of lattice defects may potentially result in the extraordinarily large electromechanical response. To quantify the diffusion behavior of Na, K and Nb in the stack, the depth to reach one order lower intensity of an element may be recorded as diffusion depth. The diffusion depth into Pt(lOO) is 78.3 nm for Na, 87.1 nm for K, and 60.4 nm for Nb. The result may partially explain for much lower K and Na than Nb in the KNN (001) film, as described by the formula: (Ki.xNax)yNbO3z, wherein 0.4< x < 0.8, 0.61 < y< 0.65 and z < 0.96.

[0055] Example 2

[0056] Example 2 relates to a stack including a top electrode layer (gold or Au), a (001 )- or (lOO)-oriented electromechanical responsive film with perovskite structure and elements: potassium (K), sodium (Na), niobium (Nb) and oxygen (O) (KNN film), a bottom electrode layer of (lOO)-oriented Pt, an intermediate layer of (lOO)-oriented ZrCh, and a (100)- oriented silicon substrate. The electromechanical responsive KNN film is -240 nm in thickness. It isfabricated using magnetron co-sputtering. To fabricate the stack of KNN (001) or KNN (100) / Pt (100) / ZrO2 (100) / Si (100), the silicon substrate is first cleaned using acetone, ethanol, dilute hydrofluoric (HF) acid and deionized (DI) water to remove surface contamination and native oxide. Then, ZrChQOO) film is formed on the substrate via deposition. The deposited ZrCT may form pyramids, giving the ZrCh film a (100) orientation / texture form. As such, the subsequent bottom electrode layer of Pt is also (lOO)-oriented. FIG. 7A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) XRD image of a (OOl)-oriented or (lOO)-oriented potassium sodium niobate KNN (001) or KNN (100) / platinum Pt (100) / zirconium dioxide ZrCh (100) / silicon Si (100) stack according to various embodiments. FIG.7A shows the (100) (same direction as (200) and (400)) orientations of Pt, Z1O2 and Si. Then, the Pt (100) / ZrC>2 ( 100) / Si (100) stack is heated up to 600 °C and the KNN (001) or KNN (100) film is deposited by co-sputtering of two targets with composition Ki.osNbCh and Na1.05NbO3in a vacuum chamber with RF power of 105 W and 90 W respectively in an argon-oxygen ambience. The argon flow rate is 20 seem and the oxygen flow rate is 6 seem at an operating pressure of 27 mTorr. Deposition time is 90 min. Finally, the substrate is cooled down at a rate of 10 °C / min in an argon-oxygen ambience. The FWHM of the KNN (001) peak is 0.399°. To quantify crystal lattice orientation extent, an orientation coefficient is defined as the ratio between the intensity of XRD peaks for the lattice planes with the specified orientation over the sum of the XRD intensity for all the planes of the film (as in the formula for KNN (001): orientation coefficient - - - ^J™'v(°01)+J™'v(002) -,m W1(jn mayanysuitable positive integers). The (OOl)-oriented or (lOO)-oriented KNN film on Pt (100) / ZrO2 (100) / Si (100) has an orientation coefficient of 1.0, showing (001) or (100) plane of the KNN crystalline structure is highly oriented.

[0057] FIG. 7B shows X-ray Photoelectron Spectroscopy (XPS) (XPS) compositional data of a (OO l)-oriented or (lOO)-oriented electromechanical responsive film on a platinum Pt (100) / zirconium dioxide ZrO2(100) / silicon Si (100) stack according to various embodiments. The elemental composition of the film surface has (K+Na) / Nb ratio of 0.61, O / Nb ratio is 2.88 and O / (K+Na) is 4.73. According to the proposed KNN formula as (Ki.xNax)yNbO3z, wherein 0.4 < x < 0.8, 0.61 < y< 0.65 and z < 0.96, this high electromechanical responsive (001)- or (100)-oriented KNN film has x = 0.45, y = 0.61 and z = 0.96, giving film composition of (Ko.55Nao.45)o.6iNb03xQ.96. The KNN (OOl)-oriented or (lOO)-oriented film exhibits a large effective piezoelectric strain coefficient d*33,f greater than 1000 pm / V, up to -1155 pm / V under 100 kV cm'1field at 1 kHz.

[0058] To examine the composition distributions in the KNN (001) or KNN (100) / Pt (100) / ZrO2(100) / Si (100) stack, a Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) is performed by depth profiling, with results shown in FIG. 7C. FIG. 7C shows a plot of intensity (counts) as a function of depth (in nanometers or nm) illustrating Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) depth profile analysis for the (OOl)-oriented or (lOO)-oriented potassium sodium niobate KNN (001) or KNN (100) / platinum Pt (100) / zirconium dioxide ZrCb (100) / silicon Si (100) stack according to various embodiments. Due to the different elements involved in the stack, the depth is converted from the sputtering time using the standard SiO2erosion calibration rate and selected elements are presented. This can provide a relative diffusion behavior of the different elements between the films. From the compositional depth profile, it is evident that Na, K and Nb diffuse into the Pt (100) / ZrO2 (100) / Si (100) stack. Such diffusion may cause loss of elements in the KNN (001) or KNN (100) film, nonstoichiometric chemical composition, and thus more lattice defects in the KNN film. The existence of large number of lattice defects may potentially result in an extraordinarily large electromechanical response. To quantify the diffusion behavior of Na, K and Nb in the stack,the depth to reach one order lower intensity of an element may be recorded as diffusion depth. The diffusion depth into Pt (100) is 26.3 nm for Na, 23.9 nm for K, and 21.0 nm for Nb. The result may partially explain for much lower K and Na than Nb in the KNN (001) or (100) fdm, as described by the formula: (Ki-xNax)yNbO3z, wherein 0.4< x < 0.8, 0.61 < y< 0.65 and z < 0.96.

[0059] Example 3

[0060] Example 3 relates to a stack including a top electrode layer (gold or Au), an electromechanical responsive film with perovskite structure and elements: potassium (K), sodium (Na), niobium (Nb) and oxygen (O) (KNN film), a bottom electrode layer of platinum (Pt) having various orientations (Pt (111), Pt (100) (same orientation with (200)), Pt (220) and Pt (222)), an intermediate titanium dioxide (TiO2) layer, a silicon dioxide (SiO2) film, and a (lOO)-oriented silicon substrate. The KNN film in the stack is fabricated using magnetron sputtering, with a thickness of -397 nm. The stack of Pt / TiO2 / SiO2 / Si (100) is first cleaned with acetone, ethanol and DI water to remove surface contaminants. Then, the Pt / TiO2 / SiO2 / Si (100) stack is heated up to 700 °C and the KNN film is deposited by co-sputtering of two targets with composition K1.05NbO3and Na1.05NbO3in a vacuum chamber with RF power of 120 W and 75 W respectively in an argon-oxygen ambience. The argon flow rate is 20 seem and the oxygen flow rate is 4 seem at an operating pressure of 24 mTorr. Deposition time is 300 min. Finally, the stack is cooled down at a rate of 10 °C / min in an argon-oxygen ambience. FIG. 8A shows (left) a plot of intensity (in arbitrary units or a.u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) image of a potassium sodium niobate KNN / platinum Pt / titanium dioxide (TiO2) / silicon dioxide (SiO2) / silicon Si (100) stack. The FWHM of KNN (001) peak is 0.472°. To quantify crystal lattice orientation, an orientation coefficient is defined as the ratio between the intensity of XRD peaks for the lattice planes with the specified orientation over the sum of the XRD intensity for all theplanes of the film (as in the formula for KNN (001): orientation coefficient — - W -,mand nmay beany suitable positive integers). The KNN filmLl KNN (001)+l KNN (002)+1KNN(lmn)on Pt / TiO₂ / SiO₂ / Si (100) has a smaller orientation coefficient for (001) or (100) plane of 0.38. A smaller orientation coefficient represents a lower level of (001) or (100) plane orientation.

[0061] FIG. 8B shows X-ray Photoelectron Spectroscopy (XPS) compositional data of an electromechanical responsive film with low level (001) orientation or (100) orientation on a platinum Pt / titanium dioxide (TiO₂) / silicon dioxide (SiO₂) / silicon Si (100) stack. The (K+Na) / Nb ratio is 0.73, O / Nb ratio is 2.84 and O / (K+Na) is 3.90. The electromechanical responsive film has x = 0.53, y = 0.73 and z = 0.95, giving a film composition of (K₀.₄₇Na₀.₅₃)₀.₇₃NbO₃×₀.₉₅. Accordingly, the electromechanical film of Example 3 does not fulfil the formula (K₁₋ₓNaₓ)ᵧNbO₃z, wherein 0.4 ≤ x ≤ 0.8, 0.61 ≤ y≤ 0.65 and z ≤ 0.96. The effective piezoelectric strain coefficient d*₃₃,f is much lower than 1000 pm / V, up to ~456 pm / V at 3.5 V under 100 kV cm⁻¹ field at 1 kHz.

[0062] Example 4

[0063] Example 4 relates to a stack including a top electrode layer (gold or Au), an electromechanical responsive film with perovskite structure and elements: potassium (K), sodium (Na), niobium (Nb) and oxygen (O) (KNN film), a bottom electrode layer of platinum (Pt) having various orientations (Pt (111), Pt (100) (same orientation with (200)), Pt (220) and Pt (222)), an intermediate titanium dioxide (TiO2) layer, a silicon dioxide (SiO2) film, and a (lOO)-oriented silicon substrate. The KNN film in the stack is fabricated using magnetron sputtering, with a thickness of -353 nm. Before deposition, the stack of Pt / TiO2 / SiO2 / Si (100) is first cleaned with acetone, ethanol and DI water to remove surface contaminants. Then, the Pt / TiO2 / SiO2 / Si (100) stack is heated up to 650 °C and the KNN film is deposited in a vacuum chamber by sputtering a single target with composition of Ko.ssNao.ssNbOs target with RF power of 120 W in an argon-oxygen ambience. The argon flow rate is 20 seem and the oxygenflow rate is 4 seem at an operating pressure of 24 mTorr. Deposition time is 900 min. Finally, the film is cooled down at a rate of 10 °C / min in an argon-oxygen ambience. FIG. 9A shows (left) a plot of intensity (in arbitrary units or a u.) as a function of angle 20 (in degrees or deg) illustrating the X-ray diffraction (XRD) pattern and (right) a two-dimensional (2D) image of a potassium sodium niobate KNN / platinum Pt / titanium dioxide (TiO2) / silicon dioxide (SiO2) / silicon Si (100) stack by single target magnetron sputtering. The FWHM of KNN (001) or KNN (100) XRD peak is 0.490°. To quantify crystal lattice orientation, an orientation coefficient is defined as the ratio between the intensity of XRD peaks for the lattice planes with the specified orientation over the sum of the XRD intensity for all the planes of the film (as in the formula for (100) orientation: orientation coefficient — - - - (o o i ) + (o o 2 ) + (Im) I, m and n may be any suitable positive integers). The KNN film on Pt / TiO2 / SiO2 / Si (100) has a smaller orientation coefficient for (001) or (100) plane of 0.54. A smaller orientation coefficient represents a lower level of (001) or (100) plane orientation.

[0064] FIG. 9B shows X-ray Photoelectron Spectroscopy (XPS) compositional data of an electromechanical responsive film with low level (001) orientation or (100) orientation on a platinum Pt / titanium dioxide (TiO₂) / silicon dioxide (SiO₂) / silicon Si (100) stack by single target magnetron sputtering. The (K+Na) / Nb ratio is 0.82, O / Nb ratio is 3.15 and O / (K+Na) is 3.84. The electromechanical responsive film has x = 0.42, y = 0.82 and z = 1.05, giving a film composition of (K₀.₅₈Na₀.₄₂)₀.₈₂NbO₃×₁.₀₅. Accordingly, the electromechanical film of Example 4 does not fulfil the formula (K₁₋ₓNaₓ)ᵧNbO₃z, wherein 0.4 ≤ x ≤ 0.8, 0.61 ≤ y≤ 0.65 and z ≤ 0.96. The effective piezoelectric strain coefficient d*₃₃,f is much lower than 1000 pm / V, up to ~403 pm / V at 5 V under 70 kV cm⁻¹ field at 1 kHz.

[0065] Various embodiments may have high scalability and repeatability. The lead-free KNN thin film may be fabricated by scalable magnetron co-sputtering method with high repeatability over silicon, which is suitable for mass production and industry application.1Various embodiments may have high performance properties, e g., large effective piezoelectric coefficient d*₃₃,f of >1000 pmV⁻¹ at 1 kHz, even larger than lead-based PZT over silicon. Various embodiments may have wide applications in various micro-electromechanical systems (MEMS), electromechanical sensors, actuators and transducers to replace piezoelectric PZT thin films containing hazardous lead in the market.

Claims

Claims1. An electromechanical responsive film comprising:potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (K₁₋ₓNaₓ)ᵧNbO₃z,wherein x is any value selected from a range from 0.4 to 0.8;wherein y is any value selected from a range from 0.61 to 0.65;wherein z is any value selected from a range from 0 to 0.96; andwherein the film has a (OOl)-oriented or (lOO)-oriented perovskite crystalline structure.

2. The electromechanical responsive film according to claim 1,wherein an effective longitudinal piezoelectric strain coefficient of the film is greater than 1000 pm V-1at 1 kHz.

3. The electromechanical responsive film according to claim 2,wherein the effective longitudinal piezoelectric strain coefficient of the film is greater than 1477 pm V-1at 1 kHz.

4. The electromechanical responsive film according to any one of claims 1 to 3,wherein the film has an orientation coefficient of about 1.0.

5. The electromechanical responsive film according to any one of claims 1 to 4,wherein x is 0.79, y is 0.65 and z is 0.68.

6. The electromechanical responsive film according to any one of claims 1 to 4,wherein x is 0.45, y is 0.61 and z is 0.96.

7. A stacked arrangement comprising:a (lOO)-oriented substrate;a (lOO)-oriented zirconium (Zr)-based intermediate layer over the (lOO)-oriented substrate;a (lOO)-oriented electrode layer on the (lOO)-oriented zirconium (Zr)-based intermediate layer;an electromechanical responsive film according to any one of claims 1 to 6 on the (lOO)-oriented electrode layer; anda further electrode layer on the electromechanical responsive film.

8. The stacked arrangement according to claim 7,wherein the (lOO)-oriented electrode layer is a platinum layer; and wherein the (lOO)-oriented substrate is a silicon substrate.

9. The stacked arrangement according to claim 7 or claim 8,wherein the (lOO)-oriented zirconium (Zr)-based intermediate layer comprises zirconium nitride (ZrN).

10. The stacked arrangement according to claim 7 or claim 8,wherein the (100)-oriented zirconium (Zr)-based intermediate layer comprises zirconium dioxide (ZrO₂).

11. The stacked arrangement according to any one of claims 7 to 10,wherein the further electrode layer comprises gold, platinum or silver.

12. A method of forming an electromechanical responsive film, the method comprising: using magnetron co-sputtering of two targets to form the film including potassium (K), sodium (Na), niobium (Nb) and oxygen (O) such that the film has a formula (Ki-xNax)yNbO3Z;wherein x is any value selected from a range from 0.4 to 0.8;wherein y is any value selected from a range from 0.61 to 0.65;wherein z is any value selected from a range from 0 to 0.96; andwherein the film has a (OOl)-oriented or (lOO)-oriented perovskite crystalline structure.

13. The method according to statement 12,wherein a first target of the two targets has a material having a formula KₐNbᵇO₃; wherein a second target of the two targets has a material having a formula NaᶜNbᵇO₃;wherein each of a, b and c is any positive real number.

14. The method according to statement 13,wherein the material of the first target is Ki.osNbCh; andwherein the material of the second target is Na1.05NbO3.

15. The method according to any one of statements 12 to 14,wherein the magnetron co-sputtering is radio frequency (RF) co-sputtering carried out in a mixture of oxygen and argon.

16. The method according to any one of statements 12 to 15,wherein the magnetron co-sputtering is carried out at a temperature above room temperature.

17. The method according to statement 16,wherein the temperature is equal to or above 600 °C.

18. The method according to any one of statements 12 to 17,wherein the magnetron co-sputtering is carried out at a pressure selected from a range from 24 mTorr to 30 mTorr.

19. A method of forming a stacked arrangement, the method comprising:forming a (lOO)-oriented zirconium (Zr)-based intermediate layer over a (100)- oriented substrate;forming a (lOO)-oriented electrode layer on the (lOO)-oriented zirconium (Zr)- based intermediate layer;forming an electromechanical responsive film according to any one of claims 1 to 6 on the (lOO)-oriented electrode layer; andforming a further electrode layer on the electromechanical responsive film.

20. The method according to statement 19,wherein the (lOO)-oriented electrode layer is a platinum layer; and wherein the (lOO)-oriented substrate is a silicon substrate.

21. The method according to statement 1 or statement 20,wherein the (lOO)-oriented electrode layer is formed via sputtering.

22. The method according to any one of statements 19 to 21,wherein the (lOO)-oriented zirconium (Zr)-based intermediate layer is formed via sputtering.

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