Piezoelectric ink formulation, piezoelectric device and related methods

Abstract

There is provided a piezoelectric ink formulation for preparation of a piezoelectric device, the formulation comprising: (i) perovskite-based powder, (ii) optionally a dispersing agent; (iii) optionally a sintering agent; (iv) a binding agent; (v) optionally lead oxide; and (vi) a solvent. Also provided are a method of preparing a piezoelectric device and said piezoelectric device for providing haptic feedback.

Description

[0001] PIEZOELECTRIC INK FORMULATION, PIEZOELECTRIC DEVICE AND RELATED METHODS TECHNICAL FIELD

[0002] The present disclosure relates broadly to a piezoelectric ink formulation and a piezoelectric device. The present disclosure also relates broadly to a method of preparing said piezoelectric device.

[0003] BACKGROUND

[0004] In the rapidly evolving field of haptics and user interfaces, the demand for effective and versatile haptic feedback systems is of paramount importance.

[0005] However, current technologies used to generate haptic feedback, e.g., eccentric rotary mass (ERM) and linear resonant actuators (LRAs)-based electromagnetic haptic actuators face significant limitations that hinder their performance and applicability in various consumer markets.

[0006] One of the primary challenges with existing ERM technology is the inability to achieve / produce a random combination of frequencies and amplitudes. This limitation severely restricts the diversity of vibration waveforms that can be generated, resulting in a lack of nuanced tactile feedback that modern applications require. Similarly, LRAs operate only within a narrow frequency range, and they suffer from issues such as residual vibrations, making them less effective for applications demanding a broad spectrum of haptic sensations.

[0007] In addition to the aforementioned performance issues, the large size of electromagnetic haptic actuators leads to slower response speeds and higher energy consumption. Such inefficiencies are particularly detrimental in larger display panels, where the performance of these actuators are compromised. For example, while ERMs and LRAs may be effective for small size display panels like mobile phone, their performance are compromised when used for large display panels. Currently, manufacturers aiming to create compact, energy-efficient devices face challenges due to complex equipment design and limited deformability of existing actuator technologies.

[0008] Furthermore, surface haptics that provide complex tactile sensations for contacts through squeeze-film effect and propagation of Lamb Waves on the plane requires vibrations in ultrasonic frequencies. Due to human perception threshold, 1 pm out-of-plane displacements under frequency above 20 kHz are usually required for surface haptics. However, the ultrasonic frequency vibration of such a range of amplitudes is difficult to obtain using existing technologies ERM and LRA.

[0009] InternalAnother critical issue lies in the complex manufacturing processes associated with piezoelectric actuators. Compared with traditional ERMs and LRAs, piezoelectric actuators have wider operating frequency range and high acceleration rates, allowing the piezoelectric actuators to generate vibration both in low frequency (< 1kHz) and high frequency (> 20kHz). However, current fabrication processes for producing piezoelectric materials involve complicated steps such as bulk production, dicing, and bonding, limit its wide adoption in consumer market-focused applications, as such processing complexity hinders design flexibility and increases costs. Moreover, attempts to fabricate piezoelectric ceramics directly on glass encounter substantial hurdles due to long sintering and cooling times (which could extend for days). This not only complicates industrial scalability in manufacturing but also raises energy consumption concerns.

[0010] In view of the above, there is a need to address or at least ameliorate the above-mentioned problems. In particular, there is a need for a piezoelectric ink formulation, a piezoelectric device, and a method of preparing said piezoelectric device that seek to address at least one of the above problems.

[0011] SUMMARY

[0012] In one aspect, there is provided a piezoelectric ink formulation for preparation of a piezoelectric device, the formulation comprising:

[0013] (i) perovskite-based powder, (iv) a binding agent;

[0014] (ii) optionally a dispersing agent; (v) optionally lead oxide; and

[0015] (iii) optionally a sintering agent; (vi) a solvent.

[0016] In one embodiment, the formulation comprises from 50 wt% to 80 wt%, preferably 55 wt% to 78 wt%, more preferably 60 wt% to 75 wt% of the perovskite-based powder. In one embodiment, the formulation comprises no more than 3 wt%, preferably no more than 2 wt%, more preferably no more than 1 wt% of the dispersing agent. In one embodiment, the formulation comprises no more than 5 wt%, preferably no more than 4 wt%, more preferably no more than 3 wt% of the sintering agent. In one embodiment, the formulation comprises from 0.1 wt% to 5 wt%, preferably 0.5 wt% to 4.5 wt%, more preferably 1 wt% to 4 wt% of the binding agent. In one embodiment, the formulation comprises no more than 5 wt% of the lead oxide. In one embodiment, the formulation comprises from 5 wt% to 60 wt% of the solvent. In one embodiment, the formulation has a viscosity falling in the range of from 500 mPa s to 10,000 mPa s. In one embodiment, the perovskite-based powder comprises oxygen and two or more metals selected from the group consisting of titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zirconium

[0017] Internal(Zr), niobium (Nb), lead (Pb), and combinations thereof. In one embodiment, the perovskite-based powder comprises lead zirconate titanate. In one embodiment, the dispersing agent comprises one or more surfactants selected from the group consisting of non-ionic surfactant, anionic surfactant, cationic surfactant, amphoteric surfactant, natural surfactant and combinations thereof. In one embodiment, the sintering agent comprises one or more compounds selected from the group consisting of boron compounds, lithium compounds, copper compounds, calcium compounds, magnesium compounds, aluminum compounds, sodium compounds, potassium compounds and combinations thereof. In one embodiment, the solvent comprises one or more organic solvents selected from the group consisting of organic acids, alcohols, ketones, and combinations thereof.

[0018] In one embodiment, the binding agent comprises one or more polymers selected from the group consisting of poly(meth)acrylates, polyacrylates, polymethacrylates, polyvinyl, polyurethane, polyalkylene glycol, cellulose, polyacrylic acid and combinations thereof.

[0019] In one aspect, there is provided a method of preparing a piezoelectric device, the method comprising:

[0020] (a) printing a piezoelectric ink formulation as disclosed herein on a substrate;

[0021] (b) sintering the piezoelectric ink formulation printed on the substrate; and

[0022] (c) poling the piezoelectric ink formulation printed on the substrate.

[0023] In one embodiment, sintering is completed in no more than 30 minutes.

[0024] In one embodiment, sintering is performed at a temperature falling in the range of from 500°C to l,500°C. In one embodiment, sintering is performed at a temperature ramp rate falling in the range of from 5°C / s to 150°C / s and / or with a dwell time falling in the range of from 5 s to 500 s. In one embodiment, sintering is performed in the presence of a thermal shield that is located on a side of the substrate that is devoid of the printed piezoelectric ink formulation. In one embodiment, sintering is performed in the presence of a heating element that has a resistance falling in the range of from 0.5 ohms to 15 ohms. In one embodiment, printing the piezoelectric ink formulation comprises printing the piezoelectric ink formulation to obtain a printed layer having a thickness falling in the range of from 5 pm to 5,000 pm. In one embodiment, the method further comprises, prior to printing the piezoelectric ink formulation, depositing an electrode on the substrate. In one embodiment, the method further comprises, prior to printing the piezoelectric ink formulation: providing the piezoelectric ink formulation; and milling said formulation to obtain a viscosity falling in the range of from 500 mPa- s to 10,000 mPa s. In one aspect, there is provided a piezoelectric device for providing haptic feedback, wherein the piezoelectric device comprises a substrate with a piezoelectric ink formulation as disclosed herein printed thereon.

[0025] InternalIn one embodiment, the piezoelectric device is one of an human-machine interface (HMI) device, haptics device, touch sensor device, on-display force sensor device, and gaming haptics device.

[0026] DEFINITIONS

[0027] The use of “a”, “an” or “the” is intended to mean “one or more” unless it is described specifically to the contrary. The terms “first”, “second” and the like are used to refer to parts / components of the respective figures. These terms are not intended to be limiting or limited to a specific part / component. Rather, the terms should be read with the respective figures and the meanings ascribed accordingly.

[0028] The term “particle” as used herein broadly refers to a discrete entity or a discrete body. The particle described herein can include an organic, an inorganic, a composite particle or a biological particle. The particle used described herein may also be a macro-particle that is formed by an aggregate of a plurality of sub-particles or a fragment of a small object. The particle of the present disclosure may be spherical, substantially spherical, or non- spherical, such as irregularly shaped particles or ellipsoidally shaped particles. The term “size” when used to refer to the particle broadly refers to the largest dimension of the particle. For example, the term “size” when used in the context of nanoparticle can refer to the diameter of the nanoparticle although it is not limited as such. In various embodiments, when the particle is substantially spherical, the term “size” can refer to the diameter of the particle; or when the particle is substantially non-spherical, the term “size” can refer to the largest length of the particle.

[0029] The term "nano" as used herein is to be interpreted broadly to include dimensions in a nanoscale, z.e., less than about 1000 nm, about 1 nm to less than about 1000 nm, about 1 nm to about 900 nm, about 1 nm to about 800 nm, about 1 nm to about 700 nm, about 1 nm to about 600 nm, about 1 nm to about 500 nm, about 1 nm to about 400 nm, about 1 nm to about 300 nm, about 1 nm to about 200 nm, or from about 1 nm to about 100 nm. Accordingly, the term “nanostructures”, “nanoparticles”, “nanomaterials” and the like as used herein may include structures that have at least one dimension in the range of no more than said range. The term “nanostructures”, “nanoparticles”, “nanomaterials” and the like as used herein may include structures that have at least one dimension that is no more than about 1,000 nm, no more than about 950 nm, no more than about 900 nm, no more than about 850 nm, no more than about 800 nm, no more than about 750 nm, no more than about 700 nm, no more than about 650 nm, no more than about 600 nm, no more than about 550 nm, no more than about 500 nm, no more than about

[0030] Internal450 nm, no more than about 400 nm, no more than about 350 nm, no more than about 300 nm, no more than about 250 nm, no more than about 200 nm, no more than about 150 nm, no more about 100 nm, no more than about 90 nm, no more than about 80 nm, no more than about 70 nm, no more than about 60 nm, no more than about 50 nm, no more than about 40 nm, no more than about 30 nm, no more than about 20 nm, or no more than about 10 nm.

[0031] The term "micro" as used herein is to be interpreted broadly to include dimensions from about 1 micron to about 1000 microns, from about 1 micron to less than about 1000 microns, from about 1 micron to about 900 microns, from about 1 micron to about 800 microns, from about 1 micron to about 700 microns, from about 1 micron to about 600 microns, from about 1 micron to about 500 microns, from about 1 micron to about 400 microns, from about 1 micron to about 300 microns, from about 1 micron to about 200 microns, from about 1 micron to about 100 microns, or from about 1 micron to about 5 microns.

[0032] The terms "coupled" or "connected" as used in this description are intended to cover both directly connected or connected through one or more intermediate means, unless otherwise stated. The terms "associated with", “related to” and the like used herein when referring to two elements refers to a broad relationship between the two elements. The relationship includes, but is not limited to a physical, a chemical or a biological relationship. For example, when element A is associated with element B, elements A and B may be directly or indirectly attached to each other or element A may contain element B or vice versa. The term "adjacent" used herein when referring to two elements refers to one element being in close proximity to another element and may be but is not limited to the elements contacting each other or may further include the elements being separated by one or more further elements disposed therebetween. The terms “configured to (perform a task / action)”, “configured for (performing a task / action)” and the like as used in this description include being programmable, programmed, connectable, wired or otherwise constructed to have the ability to perform the task / action when arranged or installed as described herein. The terms “configured to (perform a task / action)”, “configured for (performing a task / action)” and the like are intended to cover “when in use, the task / action is performed”, e.g. specifically to and / or specifically configured to and / or specifically arranged to and / or specifically adapted to do or perform a task / action. The term "and / or", e.g., "X and / or Y" is understood to mean either "X and Y" or "X or Y" and should be taken to provide explicit support for both meanings or for either meaning. Further, in the description herein, the word “substantially” whenever used is understood to include, but not restricted to, "entirely" or “completely” and the like. In addition, terms such as "comprising", "comprise", and the like whenever used, are intended

[0033] Internalto be non-restricting descriptive language in that they broadly include elements / components recited after such terms, in addition to other components not explicitly recited. For example, when “comprising” is used, reference to a “one” feature is also intended to be a reference to “at least one” of that feature. Terms such as “consisting”, “consist”, and the like, may in the appropriate context, be considered as a subset of terms such as "comprising", "comprise", and the like. Therefore, in embodiments disclosed herein using the terms such as "comprising", "comprise", and the like, it will be appreciated that these embodiments provide teaching for corresponding embodiments using terms such as “consisting”, “consist”, and the like. Further, terms such as "about", "approximately" and the like whenever used, typically means a reasonable variation, for example a variation of + / - 5% of the disclosed value, or a variance of 4% of the disclosed value, or a variance of 3% of the disclosed value, a variance of 2% of the disclosed value or a variance of 1% of the disclosed value.

[0034] Furthermore, in the description herein, certain values may be disclosed in a range. The values showing the end points of a range are intended to illustrate a preferred range. Whenever a range has been described, it is intended that the range covers and teaches all possible sub-ranges as well as individual numerical values within that range. That is, the end points of a range should not be interpreted as inflexible limitations. For example, a description of a range of 1% to 5% is intended to have specifically disclosed sub-ranges 1% to 2%, 1% to 3%, 1% to 4%, 2% to 3% etc., as well as individually, values within that range such as 1%, 2%, 3%, 4% and 5%. It is to be appreciated that the individual numerical values within the range also include integers, fractions and decimals. Furthermore, whenever a range has been described, it is also intended that the range covers and teaches values of up to 2 additional decimal places or significant figures (where appropriate) from the shown numerical end points. For example, a description of a range of 1% to 5% is intended to have specifically disclosed the ranges 1.00% to 5.00% and also 1.0% to 5.0% and all their intermediate values (such as 1.01%, 1.02% ... 4.98%, 4.99%, 5.00% and 1.1%, 1.2% ... 4.8%, 4.9%, 5.0% etc.,) spanning the ranges. The intention of the above specific disclosure is applicable to any depth / breadth of a range. Additionally, when describing some embodiments, the disclosure may have disclosed a method and / or process as a particular sequence of steps. However, unless otherwise required, it will be appreciated that the method or process should not be limited to the particular sequence of steps disclosed. Other sequences of steps may be possible. The particular order of the steps disclosed herein should not be construed as undue limitations. Unless otherwise required, a method and / or process disclosed herein should not be limited to the steps being carried out in the order written. The sequence of steps may be varied and still remain within

[0035] Internalthe scope of the disclosure. Furthermore, it will be appreciated that while the present disclosure provides embodiments having one or more of the features / characteristics discussed herein, one or more of these features / characteristics may also be disclaimed in other alternative embodiments and the present disclosure provides support for such disclaimers and these associated alternative embodiments. It will also be appreciated that where priority is claimed to an earlier application, the full contents of the earlier application is also taken to form part of the present disclosure and may serve as support for embodiments disclosed herein.

[0036] DESCRIPTION OF EMBODIMENTS

[0037] Exemplary, non-limiting embodiments of a piezoelectric ink formulation for preparation of a piezoelectric device, a piezoelectric device for providing haptic feedback, a method of preparing said piezoelectric device and a system for preparing said piezoelectric device are disclosed hereinafter.

[0038] PIEZOELECTRIC INK FORMULATION

[0039] There is provided a formulation that is suitable for use in preparation of a piezoelectric device. The formulation may be in the form of a slurry, paste, mixture, blend or composition comprising one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more components. Advantageously, in various embodiments, the formulation is designed / configured to be printable or capable of being printed. For example, the formulation may be printed directly onto a surface of a substrate. In various embodiments, the design of the formulation allows embodiments of said formulation to flow and / or adhere / bond well and effectively to a surface to be printed (e.g., printing surface). Advantageously, in various embodiments therefore, the design of the formulation allows for embodiments of the formulation to be used as an ink formulation or printing formulation.

[0040] Advantageously, in various embodiments, the formulation is also designed / configured to substantially retain or capable of substantially retain its structure after being subjected to one or more of the following processes: printing, sintering and polarization. It will be appreciated that most conventional formulations are not expected to withstand sintering and / or polarization processes, as these processes are typically conducted at high temperatures and the components (e.g., lead) present in conventional formulations tend to evaporate easily under such conditions. Advantageously, in various embodiments therefore, the design of the formulation allows for embodiments of the formulation to be formulated into (part of) a device, e.g., an actuator.

[0041] InternalIn various embodiments, the formulation comprises perovskite-based powder. In various embodiments, the perovskite-based powder possesses piezoelectric property, piezomechanical property and / or demonstrates piezoelectric response / behaviour. Advantageously, in various embodiments, the presence of perovskite-based powder equips the formulation with or imparts the ability to be piezoelectric.

[0042] In various embodiments, the perovskite-based powder comprises a perovskite structure. The perovskite-based powder may comprise a ceramic material or an inorganic material. In various embodiments, the perovskite-based powder comprises oxygen element and two or more different metal elements in its chemical structure. For example, the perovskite-based powder may comprise oxygen and two or more, three or more, four or more, five or more, six or more, or seven or more different metals. In various embodiments, the metal is selected from lead (Pb), zirconium (Zr), titanium (Ti), niobium (Nb), nickel (Ni), manganese (Mn), cobalt (Co), the like, and combinations thereof. In various embodiments, the perovskite-based powder comprises PZT. In various embodiments, the PZT powder comprises Pb, Zr, Ti, Nb, Ni, Mn, Co and O.

[0043] In various embodiments, the perovskite-based powder comprises a perovskite structure represented by general formula (I):

[0044] ABOz (I)

[0045] wherein

[0046] A comprises one metal;

[0047] B comprises one or more metal(s);

[0048] O is oxygen; and

[0049] z = 3.

[0050] In various embodiments, A = lead (Pb) atom. In various embodiments, B comprises a mixture of zirconium (Zr) and titanium (Ti) atoms. In such embodiments, the perovskite-based powder comprises a perovskite structure represented by general formula (II):

[0051] Pb(ZrxTii.x)O3(II)

[0052] wherein

[0053] x is from 0 to 1 and denotes the fraction of zirconium (Zr) in (II).

[0054] In various embodiments, the oxygen atoms form part of the oxide ions (O2) that combine with the lead, zirconium, and titanium cations to form the crystal lattice of the perovskite structure.

[0055] In various embodiments, the perovskite-based powder comprises lead zirconate titanate. In various embodiments, the perovskite-based powder comprises a soft piezo material selected from APC 850, APC 854, APC 855, the like, or combinations thereof. In various embodiments, the

[0056] Internalperovskite-based powder comprises a hard piezo material selected from APC 840, APC 841 and APC 880, the like, or combinations thereof.

[0057] In various embodiments, the formulation comprises from about 50 wt% to about 80 wt%, preferably about 55 wt% to about 78 wt%, more preferably about 60 wt% to about 75 wt% of the perovskite-based powder. In various embodiments, the formulation comprises from about 50 wt% to about 80 wt%, from about 51 wt% to about 79 wt%, from about 52 wt% to about 78 wt%, from about 53 wt% to about 77 wt%, from about 54 wt% to about 76 wt%, from about 55 wt% to about 75 wt%, from about 56 wt% to about 74 wt%, from about 57 wt% to about 73 wt%, from about 58 wt% to about 72 wt%, from about 59 wt% to about 71 wt%, from about 60 wt% to about 70 wt%, from about 61 wt% to about 69 wt%, from about 62 wt% to about 68 wt%, from about 63 wt% to about 67 wt%, from about 64 wt% to about 66 wt%, or about 65 wt% of the perovskitebased powder.

[0058] In various embodiments, the formulation comprises a dispersing agent (or dispersant). Advantageously, in various embodiments, the presence of a dispersing agent (or dispersant) equips the formulation with or imparts the ability to improve dispersion of various components present in the formulation and enhance stability by preventing particle aggregation and / or agglomeration. The dispersant agent may comprise a surfactant. In various embodiments, the surfactant comprises hydrophilic group(s) and lipophilic group(s). Advantageously, the presence of hydrophilic group(s) and lipophilic group(s) in the surfactant aids in the stabilization of the particles and / or components present in the formulation.

[0059] In various embodiments, the dispersing agent comprises one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more surfactants selected from the group consisting of neutral / non-ionic surfactant, ionic surfactant (e.g., anionic surfactant, cationic surfactant), amphoteric surfactant, natural surfactant or biosurfactant and combinations thereof.

[0060] In various embodiments, the dispersing agent comprises non-ionic surfactants. In various embodiments, the surfactant has a hydrophilic-lipophilic balance (HLB) of from about 7.0 to about 20.0, from about 8.0 to about 19.0, from about 9.0 to about 18.0, from about 10.0 to about 17.0, from about 11.0 to about 16.0, from about 12.0 to about 15.0, or from about 13.0 to about 14.0. It will be appreciated that various surfactants having a HLB of from about 7.0 to about 20.0 may be used in embodiments of the formulation disclosed herein. For example, the surfactant may comprise Triton X-100 having a HLB = 13.5. Without being bound by theory, it is believed that hydrophilic-lipophilic balance (HLB) and / or orientation of hydrophilic and lipophilic groups in

[0061] Internalthe surfactant may advantageously help / aid in stabilizing particles. HLB value is an arbitrary scale between 0 and 20 which measures the size and strength of the polar portion relative to the nonpolar portion of the non-ionic surfactant molecule, where 0 is completely lipophilic and 20 is completely hydrophilic. In various embodiments, the dispersing agent comprises a neutral surfactant having polyethylene glycol) (PEG) chains. In various embodiments, the dispersing agent comprises octylphenol ethoxylates. For example, the surfactant may be octylphenol polyethoxylated surfactants (e.g., members of the Triton family including Triton™ X-100, Triton™ X-114), polyoxyethylene surfactant (e.g., Brij® L23), poloxamers (e.g., poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (or Pol oxamer 188)), poly(ethylene glycol )-b-poly(s-caprolactone) (PEG-b-PCL)) or combinations thereof. In various embodiments, the surfactant comprises a neutral surfactant having both polyethylene glycol) chains and fatty acid ester chains. For example, the surfactant comprises polysorbate surfactants (e.g., members of the Tween family including Tween 20 and Tween 80). It will also be appreciated that various surfactants having a structure and / or hydrophilic-lipophilic balance (HLB) similar / close to that of Triton X-100 may be used in embodiments of the formulation disclosed herein.

[0062] In various embodiments, the dispersing agent comprises anionic surfactants. The anionic surfactants may be selected from sodium salts, phosphate esters, alkyl sulfates, aryl ethoxy sulfates, the like, or combinations thereof. It will also be appreciated that various surfactants having a structure similar / close to that of phosphate esters may be used in embodiments of the formulation disclosed herein.

[0063] In various embodiments, the dispersing agent comprises natural surfactants or biosurfactants. The natural surfactants may be selected from saponin, rhamnolipids, sophorolipids, fish oil, the like, or combinations thereof. It will also be appreciated that various surfactants having a structure similar / close to that of fish oil may be used in embodiments of the formulation disclosed herein.

[0064] In various embodiments, the piezoelectric ink formulation comprises no more than about 3 wt%, preferably no more than about 2 wt%, more preferably no more than about 1 wt% of the dispersing agent. In various embodiments, the piezoelectric ink formulation comprises no more than about 3 wt%, no more than about 2.9 wt%, no more than about 2.8 wt%, no more than about 2.7 wt%, no more than about 2.6 wt%, no more than about 2.5 wt%, no more than about 2.4 wt%, no more than about 2.3 wt%, no more than about 2.2 wt%, no more than about 2.1 wt%, no more than about 2 wt%, no more than about 1.9 wt%, no more than about 1.8 wt%, no more than about

[0065] Internal1.7 wt%, no more than about 1.6 wt%, no more than about 1.5 wt%, no more than about 1.4 wt%, no more than about 1.3 wt%, no more than about 1.2 wt%, no more than about 1.1 wt%, or no more than about 1 wt% of the dispersing agent. In various embodiments, the piezoelectric ink formulation comprises from about or more than about 0 wt% to about 3 wt%, from about 0.01 wt% to about 3 wt%, from about 0.1 wt% to about 2.9 wt%, from about 0.2 wt% to about 2.8 wt%, from about 0.3 wt% to about 2.7 wt%, from about 0.4 wt% to about 2.6 wt%, from about 0.5 wt% to about 2.5 wt%, from about 0.6 wt% to about 2.4 wt%, from about 0.7 wt% to about 2.3 wt%, from about 0.8 wt% to about 2.2 wt%, from about 0.9 wt% to about 2.1 wt%, from about 1 wt% to about 2 wt%, from about 1.1 wt% to about 1.9 wt%, from about 1.2 wt% to about 1.8 wt%, from about 1.3 wt% to about 1.7 wt%, from about 1.4 wt% to about 1.6 wt%, or about 1.5 wt% of the dispersing agent. In various embodiments, the dispersing agent (or di spersant / surf actant) is added in an amount that is no more than about 3 wt% to ensure stability of the formulation. It will be appreciated that, in various embodiments, having too much dispersing agent (or dispersant / surfactant) can destabilize the formulation.

[0066] In various embodiments, the formulation comprises a sintering agent (or sintering aid). Advantageously, in various embodiments, the presence of a sintering agent (or sintering aid) equips the formulation with or imparts the ability to promote sintering and densification, which consequently increases the structure integrity of the final sintered product.

[0067] In various embodiments, the sintering agent comprises one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more compounds selected from the group consisting of boron compounds, lithium compounds, copper compounds, calcium compounds, magnesium compounds, aluminum compounds, sodium compounds, potassium compounds and combinations thereof. In various embodiments, the sintering agent comprises oxides (e.g., metal oxides), carbonates (e.g., metal carbonates), borates (e.g., metal borates) and / or . For example, the sintering agent may be selected from LiB (lithium borate), CuO (copper oxide), lithium carbonate (I^CCh), boron oxide (B2O3), magnesium oxide (MgO), calcium oxide (CaO), calcium carbonate (CaCCh), aluminum oxide (AI2O3), sodium oxide (Na2O), sodium carbonate (TsfeCCh), potassium oxide (K2O), the like, or combinations thereof. It will be appreciated that various sintering agents that effectively aids in sintering and / or helps promote densification may be used in embodiments of the formulation disclosed herein.

[0068] In various embodiments, the piezoelectric ink formulation comprises no more than about 5 wt%, preferably no more than about 4 wt%, more preferably no more than about 3 wt% of the sintering agent. In various embodiments, the piezoelectric ink formulation comprises no more than

[0069] Internalabout 5 wt%, no more than about 4.9 wt%, no more than about 4.8 wt%, no more than about 4.7 wt%, no more than about 4.6 wt%, no more than about 4.5 wt%, no more than about 4.4 wt%, no more than about 4.3 wt%, no more than about 4.2 wt%, no more than about 4.1 wt%, no more than about 4 wt%, no more than about 3.9 wt%, no more than about 3.8 wt%, no more than about 3.7 wt%, no more than about 3.6 wt%, no more than about 3.5 wt%, no more than about 3.4 wt%, no more than about 3.3 wt%, no more than about 3.2 wt%, no more than about 3.1 wt%, or no more than about 3 wt% of the sintering agent. In various embodiments, the piezoelectric ink formulation comprises from about 0.01 wt% to about 5 wt%, from about 0.1 wt% to about 5 wt%, from about 0.1 wt% to about 4.9 wt%, from about 0.2 wt% to about 4.8 wt%, from about 0.3 wt% to about 4.7 wt%, from about 0.4 wt% to about 4.6 wt%, from about 0.5 wt% to about 4.5 wt%, from about 0.6 wt% to about 4.4 wt%, from about 0.7 wt% to about 4.3 wt%, from about 0.8 wt% to about 4.2 wt%, from about 0.9 wt% to about 4.1 wt%, from about 1 wt% to about 4 wt%, from about 1.1 wt% to about 3.9 wt%, from about 1.2 wt% to about 3.8 wt%, from about 1.3 wt% to about 3.7 wt%, from about 1.4 wt% to about 3.6 wt%, from about 1.5 wt% to about 3.5 wt%, from about 1.6 wt% to about 3.4 wt%, from about 1.7 wt% to about 3.3 wt%, from about 1.8 wt% to about 3.2 wt%, from about 1.9 wt% to about 3.1 wt%, from about 2 wt% to about 3 wt%, from about 2.1 wt% to about 2.9 wt%, from about 2.2 wt% to about 2.8 wt%, from about 2.3 wt% to about 2.7 wt%, from about 2.4 wt% to about 2.6 wt%, or about 2.5 wt% of the sintering agent.

[0070] In various embodiments, the piezoelectric ink formulation comprises a binding agent (or binder). Advantageously, in various embodiments, the presence of a binding agent (or binder) equips the formulation with or imparts the ability to enhance / promote adhesion between particles in the formulation and / or adhesion to the surfaces to be printed.

[0071] In various embodiments, the binding agent comprises one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more polymers selected from poly(meth)acrylates, polyacrylates, polymethacrylates, polyvinyl, polyurethane, polyalkylene glycol, cellulose, polyacrylic acid, the like, or combinations thereof. The binding agent may comprise polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), polybutyl methacrylate (PBMA), polyhexyl methacrylate (PHMA), polyisobutyl methacrylate (PIBMA), poly(2-hydroxyethyl methacrylate) (PHEMA), polystyrene-co-methyl methacrylate (PS-co-MMA), poly(methyl methacrylate-co-butyl methacrylate) (PMMA-co-BMA), poly(methyl methacrylate-co-ethyl methacrylate) (PMMA-co-EMA), polyvinyl butyral, polybutyral resin (PBR), polybutyral acetate (PBA), the like, or combinations thereof.

[0072] InternalIn various embodiments, the piezoelectric ink formulation comprises from about 0.1 wt% to about 5 wt%, preferably about 0.5 wt% to about 4.5 wt%, more preferably about 1 wt% to about 4 wt% of the binding agent. In various embodiments, the piezoelectric ink formulation comprises from about 0.1 wt% to about 5 wt%, from about 0.1 wt% to about 4.9 wt%, from about 0.2 wt% to about 4.8 wt%, from about 0.3 wt% to about 4.7 wt%, from about 0.4 wt% to about 4.6 wt%, from about 0.5 wt% to about 4.5 wt%, from about 0.6 wt% to about 4.4 wt%, from about 0.7 wt% to about 4.3 wt%, from about 0.8 wt% to about 4.2 wt%, from about 0.9 wt% to about 4.1 wt%, from about 1 wt% to about 4 wt%, from about 1.1 wt% to about 3.9 wt%, from about 1.2 wt% to about 3.8 wt%, from about 1.3 wt% to about 3.7 wt%, from about 1.4 wt% to about 3.6 wt%, from about 1.5 wt% to about 3.5 wt%, from about 1.6 wt% to about 3.4 wt%, from about 1.7 wt% to about 3.3 wt%, from about 1.8 wt% to about 3.2 wt%, from about 1.9 wt% to about 3.1 wt%, from about 2 wt% to about 3 wt%, from about 2.1 wt% to about 2.9 wt%, from about 2.2 wt% to about 2.8 wt%, from about 2.3 wt% to about 2.7 wt%, from about 2.4 wt% to about 2.6 wt%, or about 2.5 wt% of the binding agent.

[0073] In various embodiments, the piezoelectric ink formulation comprises lead oxide. The lead oxide may be present in the form of lead oxide (PbO) and / or lead dioxide (PbCh). In various embodiments, the lead oxide is present in excess.

[0074] In various embodiments, the piezoelectric ink formulation comprises no more than about 5 wt%, no more than about 4.9 wt%, no more than about 4.8 wt%, no more than about 4.7 wt%, no more than about 4.6 wt%, no more than about 4.5 wt%, no more than about 4.4 wt%, no more than about 4.3 wt%, no more than about 4.2 wt%, no more than about 4.1 wt%, no more than about 4 wt%, no more than about 3.9 wt%, no more than about 3.8 wt%, no more than about 3.7 wt%, no more than about 3.6 wt%, no more than about 3.5 wt%, no more than about 3.4 wt%, no more than about 3.3 wt%, no more than about 3.2 wt%, no more than about 3.1 wt%, or no more than about 3 wt% of the lead oxide. In various embodiments, the piezoelectric ink formulation comprises from about or more than about 0 wt% to about 5 wt%, preferably 0.01 wt% to 5 wt%, more preferably about 0.5 wt% to about 4 wt%, even more preferably about 1 wt% to about 3 wt% of the lead oxide. In various embodiments, the piezoelectric ink formulation comprises from about 0 wt% to about 5 wt%, from about 0.1 wt% to about 4.9 wt%, from about 0.2 wt% to about 4.8 wt%, from about 0.3 wt% to about 4.7 wt%, from about 0.4 wt% to about 4.6 wt%, from about 0.5 wt% to about 4.5 wt%, from about 0.6 wt% to about 4.4 wt%, from about 0.7 wt% to about 4.3 wt%, from about 0.8 wt% to about 4.2 wt%, from about 0.9 wt% to about 4.1 wt%, from about 1 wt% to about 4 wt%, from about 1.1 wt% to about 3.9 wt%, from about 1.2 wt% to about 3.8 wt%,

[0075] Internalfrom about 1.3 wt% to about 3.7 wt%, from about 1.4 wt% to about 3.6 wt%, from about 1.5 wt% to about 3.5 wt%, from about 1.6 wt% to about 3.4 wt%, from about 1.7 wt% to about 3.3 wt%, from about 1.8 wt% to about 3.2 wt%, from about 1.9 wt% to about 3.1 wt%, from about 2 wt% to about 3 wt%, from about 2.1 wt% to about 2.9 wt%, from about 2.2 wt% to about 2.8 wt%, from about 2.3 wt% to about 2.7 wt%, from about 2.4 wt% to about 2.6 wt%, or about 2.5 wt% of the lead oxide.

[0076] In various embodiments, the piezoelectric ink formulation comprises a solvent. In various embodiments, any solvent that effectively serves as a medium to contain the components of the formulation may be used in embodiments of the formulation disclosed herein. In various embodiments, the solvent comprises one or more, two or more, three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more organic solvents selected from the group consisting of organic acids, alcohols, ketones, and combinations thereof. The solvent may be selected from acetic acid, formic acid, citric acid, lactic acid, propionic acid, ethanol, isopropyl alcohol, methanol, butanol, propylene alcohol, benzyl alcohol, phenethyl alcohol, toluene, eugenol, dipropylene glycol, terpineol, methyl ethyl ketone, the like, azeotropic mixture / combination thereof, or combinations thereof.

[0077] In various embodiments, the formulation comprises from about 50 wt% to about 80 wt% of the perovskite-based powder, no more than about 3 wt% of the dispersing agent, no more than about 5 wt% of the sintering agent, from about 0.1 wt% to about 5 wt% of the binding agent, from about 0 wt% to about 5 wt% of the lead oxide, the remainder being a solvent. In various embodiments therefore, the solvent makes up the remainder of the piezoelectric ink formulation. In various embodiments, the piezoelectric ink formulation comprises from about 5 wt% to about 60 wt%, from about 6 wt% to about 59 wt%, from about 7 wt% to about 58 wt%, from about 8 wt% to about 57 wt%, from about 9 wt% to about 56 wt%, from about 10 wt% to about 55 wt%, from about 11 wt% to about 54 wt%, from about 12 wt% to about 53 wt%, from about 13 wt% to about 52 wt%, from about 14 wt% to about 51 wt%, from about 15 wt% to about 50 wt%, from about 16 wt% to about 49 wt%, from about 17 wt% to about 48 wt%, from about 18 wt% to about 47 wt%, from about 19 wt% to about 46 wt%, from about 20 wt% to about 45 wt%, from about 21 wt% to about 44 wt%, from about 22 wt% to about 43 wt%, from about 23 wt% to about 42 wt%, from about 24 wt% to about 41 wt%, from about 25 wt% to about 40 wt%, from about 26 wt% to about 39 wt%, from about 27 wt% to about 38 wt%, from about 28 wt% to about 37 wt%, from about 29 wt% to about 36 wt%, from about 30 wt% to about 35 wt%, from about 31 wt% to

[0078] Internalabout 34 wt%, from about 32 wt% to about 33 wt%, about 32.5 wt% or from about 2 wt% to about 49.9 wt% of the solvent.

[0079] In various embodiments, the piezoelectric ink formulation comprises / consists essentially of / consists of:

[0080] (i) perovskite-based powder,

[0081] (ii) optionally a dispersing agent;

[0082] (iii) optionally a sintering agent;

[0083] (iv) a binding agent;

[0084] (v) optionally lead oxide; and

[0085] (vi) a solvent.

[0086] In various embodiments, the formulation has a viscosity falling in the range of from about 500 mPa- s to about 10,000 mPa s. In various embodiments, the formulation has a viscosity falling in the range of from about 500 mPa- s to about 10,000 mPa s, from about 600 mPa- s to about 9,500 mPa s, from about 700 mPa s to about 9,000 mPa s, from about 800 mPa- s to about 8,500 mPa s, from about 900 mPa s to about 8,000 mPa s, from about 1,000 mPa s to about 7,500 mPa s, from about 1,500 mPa s to about 7,000 mPa s, from about 2,000 mPa s to about 6,500 mPa s, from about 2,500 mPa s to about 6,000 mPa s, from about 3,000 mPa s to about 5,500 mPa s, from about 3,500 mPa s to about 5,000 mPa s, from about 4,000 mPa- s to about 4,500 mPa s, or about 4,250 mPa s. Advantageously, in various embodiments, the formulation is designed / configured to have a viscosity falling in the range of from about 500 mPa- s to about 10,000 mPa- s, which allows embodiments of said formulation to flow and / or adhere / bond well and effectively to a surface to be printed (e.g., printing surface).

[0087] In various embodiments, the piezoelectric ink formulation comprises particles having an average particle size (or diameter) falling in the range of from about 0.05 pm (or 50 nm) to about 5 pm. In various embodiments, the piezoelectric ink formulation comprises particles having an average particle size (or diameter) falling in the range of from about 50 nm to about 5 pm, from about 100 nm to about 4.9 pm, from about 150 nm to about 4.8 pm, from about 200 nm to about 4.7 pm, from about 250 nm to about 4.6 pm, from about 300 nm to about 4.5 pm, from about 350 nm to about 4.4 pm, from about 400 nm to about 4.3 pm, from about 450 nm to about 4.2 pm, from about 500 nm to about 4.1 pm, from about 550 nm to about 4 pm, from about 600 nm to about 3.9 pm, from about 650 nm to about 3.8 pm, from about 700 nm to about 3.7 pm, from about 750 nm to about 3.6 pm, from about 800 nm to about 3.5 pm, from about 850 nm to about 3.4 pm, from about 900 nm to about 3.3 pm, from about 950 nm to about 3.2 pm, from about

[0088] Internal1,000 nm (or 1 pm) to about 3.1 pm, from about 1.1 pm to about 3 pm, from about 1.2 pm to about 2.9 pm, from about 1.3 pm to about 2.8 pm, from about 1.4 pm to about 2.7 pm, from about 1.5 pm to about 2.6 pm, from about 1.6 pm to about 2.5 pm, from about 1.7 pm to about 2.4 pm, from about 1.8 pm to about 2.3 pm, from about 1.9 pm to about 2.2 pm, or from about 2.0 pm to about 2.1 pm.

[0089] In various embodiments, the piezoelectric ink formulation is substantially devoid of a photopolymer, e.g., photocurable resin.

[0090] METHOD OF PREPARING A PIEZOELECTRIC DEVICE

[0091] There is provided a method of preparing a piezoelectric device, the method comprising: (a) printing a piezoelectric ink formulation as disclosed herein on a substrate; and

[0092] (b) sintering the piezoelectric ink formulation printed on the substrate.

[0093] In various embodiments, the printing step (a) comprises two-dimensional printing, three-dimensional printing or a combination thereof. In various embodiments, the printing step (a) is performed via inkjet printing, binder jet printing, the like or combinations thereof. In some embodiments, the method comprises printing and sintering of a PZT ink formulation on a glass substrate.

[0094] In various embodiments, the formulation is printed on a surface of the substrate. The formulation may be printed on any suitable substrate. For example, the substrate may be glass, ceramic, metal, the like, or combinations thereof. In various embodiments, the substrate is one that is substantially resistant to heat. In various embodiments, the substrate is thermally stable and / or capable of resisting chemical and / or physical (e.g., structural) changes at a high temperature of at least about 500°C, preferably at least about l,000°C, more preferably at least about l,500°C. In various embodiments, the substrate is thermally stable and / or capable of resisting chemical and / or physical (e.g., structural) changes at a high temperature of at least about 500°C, at least about 600°C, at least about 700°C, at least about 800°C, at least about 900°C, at least about l,000°C, at least about l,100°C, at least about l,200°C, at least about l,300°C, at least about l,400°C, or at least about l,500°C.

[0095] In various embodiments, the formulation is printed on a surface of the substrate via a layer-by-layer method. That is, in various embodiments, after a first layer of formulation is printed on the substrate, the printing process is repeated with a subsequent layer. In various embodiments, the printing process is repeated and several layers are printed until the required final thickness or structure is achieved. In various embodiments, the formulation is printed to obtain a printed layer having a thickness falling in the range of from about 5 pm to about 5,000 pm. In various

[0096] Internalembodiments, the formulation is printed to obtain a printed layer having a thickness falling in the range of from about 5 pm to about 5,000 pm, from about 10 pm to about 4,500 pm, from about 15 pm to about 4,000 pm, from about 20 pm to about 3,500 pm, from about 25 pm to about 3,000 pm, from about 30 pm to about 2,500 pm, from about 35 pm to about 2,000 pm, from about 40 pm to about 1,500 pm, from about 45 pm to about 1,000 pm, from about 50 pm to about 900 pm, from about 55 pm to about 800 pm, from about 60 pm to about 700 pm, from about 65 pm to about 600 pm, from about 70 pm to about 500 pm, from about 75 pm to about 400 pm, from about 80 pm to about 300 pm, from about 85 pm to about 200 pm, from about 90 pm to about 100 pm, or about 95 pm.

[0097] In various embodiments, the method further comprises, after printing step (a) and / or prior to sintering step (b), a step of degassing the printed formulation. In various embodiments, degassing is carried out to remove trapped air bubbles and / or gases which may otherwise interfere with the printing process. The degassing step may be carried out under vacuum (e.g., placing in a vacuum chamber), reduced pressure and / or heating.

[0098] In various embodiments, the piezoelectric ink formulation printed on the substrate is subjected to sintering. In various embodiments, the piezoelectric ink formulation printed on the substrate is subjected to poling (or polarization). In various embodiments, poling comprises polarization of dipoles when an electric field is applied to align dipoles in the structure of the printed formulation, thereby activating the piezoelectric effect in said printed formulation. In various embodiments, sintering and poling / polarization are carried out simultaneously or concurrently.

[0099] Advantageously, in various embodiments, the sintering step comprises ultrafast, ultrarapid or high speed sintering. That is, in various embodiments, the sintering step comprises heating and / or cooling cycles that are ultrafast, ultrarapid or high speed. In various embodiments, the sintering step comprises ultrafast sintering (UFS) where the ceramic densifies. In various embodiments, the sintering occurs viaPoy Joule heating. In various embodiments, the sintering step (or heating and / or cooling) is completed in no more than about 30 minutes, no more than about 25 minutes, no more than about 20 minutes, no more than about 15 minutes, no more than about 14 minutes, no more than about 13 minutes, no more than about 12 minutes, no more than about 11 minutes, no more than about 10 minutes, no more than about 9 minutes, no more than about 8 minutes, no more than about 7 minutes, no more than about 6 minutes, no more than about 5 minutes (or 300 seconds), no more than about 4.5 minutes (or 270 seconds), no more than about 4 minutes (or 240 seconds), no more than about 3.5 minutes (or 210 seconds), no more than about

[0100] Internal3 minutes (or 180 seconds), no more than about 2.5 minutes (or 150 seconds), no more than about 2 minutes (or 120 seconds), no more than about 1.5 minutes (or 90 seconds), no more than about 1 minute (or 60 seconds), no more than about 55 seconds, no more than about 50 seconds, no more than about 45 seconds, no more than about 40 seconds, no more than about 35 seconds, no more than about 30 seconds, no more than about 25 seconds, no more than about 20 seconds, no more than about 15 seconds, no more than about 10 seconds, or no more than about 5 seconds. In various embodiments, the sintering step (or heating and / or cooling) is completed over a time period of from about 5 seconds to 30 minutes, from about 6 seconds to about 30 minutes, from about 7 seconds to about 30 minutes, from about 8 seconds to about 25 minutes, from about 9 seconds to about 20 minutes, from about 10 seconds to about 15 minutes, from about 15 seconds to about 14 minutes, from about 20 seconds to about 13 minutes, from about 25 seconds to about 12 minutes, from about 30 seconds to about 11 minutes, from about 35 seconds to about 10 minutes, from about 40 seconds to about 9 minutes, from about 45 seconds to about 8 minutes, from about 50 seconds to about 7 minutes, from about 55 seconds to about 6 minutes, from about 1 minute (or 60 seconds) to about 5 minutes (or 300 seconds), from about 1.5 minutes (or 90 seconds) to about 4.5 minutes (or 270 seconds), from about 2 minutes (or 120 seconds) to about 4 minutes (or 240 seconds), from about 2.5 minutes (or 150 seconds) to about 3.5 minutes (or 210 seconds), or about 3 minutes (or 180 seconds).

[0101] In various embodiments, the step of sintering is performed at a temperature falling in the range of from about 500°C to about l,500°C. In various embodiments, the step of sintering is performed at a temperature falling in the range of from about 500°C to about l,500°C, from about 600°C to about l,400°C, from about 700°C to about l,300°C, from about 800°C to about l,200°C, from about 900°C to about l,100°C, or about l,000°C.

[0102] In various embodiments, the heating profile of the sintering step is executed either as a single step ramp-up or multiple steps with varying ramp-up rates. In various embodiments, the step of sintering comprises a single step ramp-up where the printed formulation is supplied with heat at a constant rate until the desired sintering temperature is reached. In various embodiments, a single step ramp-up comprises a constant / uniform temperature increase. In various embodiments, the step of sintering comprises multiple steps ramp-up where the printed formulation is supplied with heat at different rates over several stages. In various embodiments, the step of sintering is performed at a temperature ramp rate falling in the range of from about 5°C / s to about 150°C / s. In various embodiments, the step of sintering is performed at a temperature ramp rate falling in the range of from about 5°C / s to about 150°C / s, from about 10°C / s to about 145°C / s, from about

[0103] Internal15°C / s to about 140°C / s, from about 20°C / s to about 135°C / s, from about 25°C / s to about 130°C / s, from about 30°C / s to about 125°C / s, from about 35°C / s to about 120°C / s, from about 40°C / s to about 115°C / s, from about 45°C / s to about 110°C / s, from about 50°C / s to about 105°C / s, from about 55°C / s to about 100°C / s, from about 60°C / s to about 95°C / s, from about 65°C / s to about 90°C / s, from about 70°C / s to about 85°C / s, or from about 75°C / s to about 80°C / s. In various embodiments, the step of sintering is performed with a dwell time falling in the range of from about 5 s to about 500 s. In various embodiments, the step of sintering is performed with a dwell time falling in the range of from about 5 seconds to about 500 seconds, from about 10 seconds to about 450 seconds, from about 15 seconds to about 400 seconds, from about 20 seconds to about 350 seconds, from about 25 seconds to about 300 seconds, from about 30 seconds to about 250 seconds, from about 35 seconds to about 200 seconds, from about 40 seconds to about 150 seconds, from about 45 seconds to about 145 seconds, from about 50 seconds to about 140 seconds, from about 55 seconds to about 135 seconds, from about 60 seconds to about 130 seconds, from about 65 seconds to about 125 seconds, from about 70 seconds to about 120 seconds, from about 75 seconds to about 115 seconds, from about 80 seconds to about 110 seconds, from about 85 seconds to about 105 seconds, from about 90 seconds to about 100 seconds, or about 95 seconds.

[0104] In various embodiments, the step of sintering is performed in the presence of a thermal shield. The thermal shield may comprise carbon (e.g., carbon fiber), graphite, alumina, zirconia, tungsten, molybdenum, ceramic (e.g., ceramic wool, ceramic board, ceramic blanket), the like, or combinations thereof. For example, the thermal shield may be a carbon felt thermal shield. In various embodiments, the thermal shield is designed / configured to be located / positioned on or in contact with a side / surface of the substrate that is devoid of the piezoelectric ink formulation. Advantageously, in various embodiments, the presence of a thermal shield helps maintain the desired heating / temperature profile and / or control heat distribution within the sintering system. By controlling heat distribution, embodiments of the method disclosed herein prevents / minimizes overheating and ensures that only the desired surface (i.e. surface printed with the piezoelectric ink formulation) of the substrate reaches the sintering temperatures. In various embodiments, the presence of a thermal shield also helps minimize heat loss to the environment, allowing for more efficient energy use and reducing the time required to achieve the desired sintering temperature.

[0105] In various embodiments, the step of sintering is performed in the presence of a heating element. The heating element may comprise graphite, molybdenum, silicon carbide (SiC), tungsten, the like, or combinations thereof. In various embodiments, the heating element is substantially devoid of an amorphous structure / form / compound. In various embodiments, the

[0106] Internalheating element comprises a crystalline structure / form / compound. For example, the heating element may be crystalline graphite or a structure / compound with a predominantly graphitic structure. In various embodiments, the step of sintering is performed in the presence of a heating element that has a resistance falling in the range of from about 0.5 ohms to about 15 ohms, from about 0.6 ohms to about 14 ohms, from about 0.7 ohms to about 13 ohms, from about 0.8 ohms to about 12 ohms, from about 0.9 ohms to about 11 ohms, from about 1 ohms to about 10 ohms, from about 1.5 ohms to about 9.5 ohms, from about 2 ohms to about 9 ohms, from about 2.5 ohms to about 8.5 ohms, from about 3 ohms to about 8 ohms, from about 3.5 ohms to about 7.5 ohms, from about 4 ohms to about 7 ohms, from about 4.5 ohms to about 6.5 ohms, from about 5 ohms to about 6 ohms, or about 5.5 ohms.

[0107] In various embodiments, the step of sintering comprises directional Joule heating. Advantageously, in various embodiments, the step of sintering comprises controlling heat generation and directing the heat along a particular path or region, allowing uniform thermal profile to be achieved across the material. In various embodiments, the heating element is designed / configured to be positioned in an orientation such that the heating element faces a surface / side of the substrate that is printed with the piezoelectric ink formulation. Even more advantageously, in various embodiments, by orienting the heating element towards the surface / side printed with the formulation, embodiments of the method disclosed herein ensures that only the desired surface (i.e. surface printed with the piezoelectric ink formulation) of the substrate reaches the sintering temperatures, therefore significantly reducing the thermal impact reaching the surface of the substrate that is devoid of the piezoelectric ink formulation, and consequently reducing / eliminating / minimizing the risk of delamination and warping of the substrate. In various embodiments, the heating element is designed / configured to be located / positioned on or in contact with a surface / side of the substrate with the piezoelectric ink formulation printed thereon. In other embodiments, the heating element is designed / configured to be in proximity to the surface / side of the substrate with the piezoelectric ink formulation printed thereon. For example, the heating element is located / positioned a distance away or spaced apart from a surface / side of the substrate with the piezoelectric ink formulation printed thereon. In such embodiments, the distance between heating element and the surface / side of the substrate with the piezoelectric ink formulation printed thereon is from about 0.1 mm to about 5 mm. In various embodiments, the distance between heating element and the surface / side of the substrate with the piezoelectric ink formulation printed thereon is from about 0.1 mm to about 5 mm, from about 0.1 mm to about 4.9 mm, from about 0.2 mm to about 4.8 mm, from about 0.3 mm to about 4.7 mm,

[0108] Internalfrom about 0.4 mm to about 4.6 mm, from about 0.5 mm to about 4.5 mm, from about 0.6 mm to about 4.4 mm, from about 0.7 mm to about 4.3 mm, from about 0.8 mm to about 4.2 mm, from about 0.9 mm to about 4.1 mm, from about 1 mm to about 4 mm, from about 1.1 mm to about 3.9 mm, from about 1.2 mm to about 3.8 mm, from about 1.3 mm to about 3.7 mm, from about 1.4 mm to about 3.6 mm, from about 1.5 mm to about 3.5 mm, from about 1.6 mm to about 3.4 mm, from about 1.7 mm to about 3.3 mm, from about 1.8 mm to about 3.2 mm, from about 1.9 mm to about 3.1 mm, from about 2 mm to about 3 mm, from about 2.1 mm to about 2.9 mm, from about 2.2 mm to about 2.8 mm, from about 2.3 mm to about 2.7 mm, from about 2.4 mm to about 2.6 mm, or about 2.5 mm. In such embodiments, the heating element may still be closer / nearer to the surface / side of the substrate with the piezoelectric ink formulation printed thereon as compared to the surface / side of the substrate that is substantially devoid of the piezoelectric ink formulation printed thereon (e.g. the side opposite to the that having the ink formulation printed thereon).

[0109] Advantageously, in various embodiments, the method is substantially devoid of delamination or peeling of the formulation during and / or after sintering. Advantageously, in various embodiments, the method is also substantially devoid of warping of substrate(s) during and / or after sintering. Advantageously, in various embodiments, issues such as warping of glass and delamination of printed PZT are overcome by carefully controlled and specially designed conditions / parameters in UHS (e.g., temperature and / or dwell time).

[0110] In various embodiments, the step of sintering comprises densification. Advantageously, in various embodiments, the step of sintering allows embodiments of the printed formulation to come into contact and bond, thereby decreasing the surface area and / or increasing compactness to obtain a highly dense printed layer. In various embodiments, the printed formulation is sintered to obtain a printed layer having a density that is no more about 7.2 gram per cubic centimetre (gm / cc). In various embodiments, the printed formulation is sintered to obtain a printed layer having a high density falling in the range of from about 6.7 gm / cc to about 7.2 gm / cc. In various embodiments, by carefully controlling the sintering parameters, the printed formulation is sintered to obtain a printed layer having a density of about 6.7 gm / cc, about 6.8 gm / cc, about 6.9 gm / cc, about 7 gm / cc, about 7.1 gm / cc, or about 7.2 gm / cc.

[0111] Advantageously, by carrying out the sintering (and / or polarization) step with the carefully designed / controlled conditions described above, embodiments of the method disclosed herein have significantly reduced / shortened the total amount of time required for sintering as compared to conventional processes. In various embodiments, the method disclosed herein is cost effective, energy saving and / or has a high production efficiency. Advantageously, by reducing / shortening

[0112] Internalthe sintering time, embodiments of the method disclosed herein reduces the exposure of the substrate to high temperatures, and consequently minimizes the risk of causing significant thermal stress or damage to the substrate, such as delamination or warping.

[0113] In various embodiments, the method further comprising, prior to printing the piezoelectric ink formulation, depositing an electrode on the substrate. In various embodiments, the electrode is deposited on / at a surface / side of the substrate that is devoid of the printed piezoelectric ink formulation. The deposition of the electrode may be performed via DC sputtering, screen printing, chemical vapor deposition, atomic layer deposition, air-jetting, ink-jetting, the like or combinations thereof.

[0114] In various embodiments, the method further comprising, prior to printing the piezoelectric ink formulation, providing the piezoelectric ink formulation i.e. containing the components described above.

[0115] In various embodiments, the method further comprising, prior to printing the piezoelectric ink formulation milling, grinding, and / or pulverizing said formulation to obtain a viscosity falling in the range of from 500 mPas to 10,000 mPa s, from about 600 mPa s to about 9,500 mPa s, from about 700 mPa s to about 9,000 mPa s, from about 800 mPa s to about 8,500 mPa s, from about 900 mPa s to about 8,000 mPa s, from about 1,000 mPa s to about 7,500 mPa s, from about 1,500 mPa s to about 7,000 mPa s, from about 2,000 mPa s to about 6,500 mPa s, from about 2,500 mPa s to about 6,000 mPa s, from about 3,000 mPa s to about 5,500 mPa s, from about 3,500 mPa- s to about 5,000 mPa s, from about 4,000 mPa- s to about 4,500 mPa s, or about 4,250 mPa s.

[0116] Advantageously, embodiments of the disclosed method employ methods that are simple, straightforward and scalable. Embodiments of the disclosed methods do not involve the more complex, costlier and less scalable steps of dicing and bonding. Instead, embodiments of the methods disclosed herein are capable of printing and sintering piezoelectric ink formulations directly on substrates (e.g., glass substrates).

[0117] SYSTEM FOR PREPARING A PIEZOELETRIC DEVICE

[0118] There is provided a system for preparing a piezoelectric device, the system comprising: a first electrode;

[0119] a second electrode;

[0120] a heating element;

[0121] a substrate for a piezoelectric ink formulation to be printed thereon; and

[0122] a thermal shield.

[0123] InternalIn various embodiments, the system further comprises a printer or a print nozzle for printing the piezoelectric ink formulation onto the substrate.

[0124] The system may comprise one or more, two or more, three or more, or four or more first electrode(s). The system may comprise one or more, two or more, three or more, or four or more second electrode(s). The first electrode(s) and / or second electrode(s) may be provided in pairs. For example, the system may comprise a pair of first electrodes and / or a pair of second electrodes. The first electrode(s) may be provided in the form of plate(s) (e.g., metallic plate(s)). The second electrode(s) may be provided in the form of block(s) (e.g., non-metallic block(s)). The first electrode(s) and second electrode(s) may each comprise graphite, molybdenum, silicon carbide (SiC), tungsten, the like, or combinations thereof. For example, the first electrode may be a copper electrode or copper plate while the second electrode may be a graphite electrode or graphite block.

[0125] In various embodiments, the first electrode(s) and second electrode(s) are connected to a power supply which provides / supplies electric current to the setup.

[0126] In various embodiments, the system comprises a heating element. In various embodiments, the heating element is coupled to the first and second electrodes which supply an electric current to the heating element for heating. In various embodiments, the heating element is designed / configured to be positioned in an orientation such that the heating element faces a surface / side of the substrate that is printed with the piezoelectric ink formulation. Advantageously, in various embodiments, by orienting the heating element towards the surface / side printed with the formulation, embodiments of the system disclosed herein ensures that only the desired surface (i.e. surface printed with the piezoelectric ink formulation) of the substrate reaches the sintering temperatures, therefore significantly reducing the thermal impact reaching the surface of the substrate that is devoid of the piezoelectric ink formulation, and consequently reducing / eliminating / minimizing the risk of delamination and warping of the substrate. In various embodiments, the heating element is designed / configured to be located / positioned on or in contact with a surface / side of the substrate with the piezoelectric ink formulation printed thereon. In other embodiments, the heating element is designed / configured to be located / positioned in proximity to a surface / side of the substrate with the piezoelectric ink formulation printed thereon, e.g. a distance away or spaced apart from a surface / side of the substrate with the piezoelectric ink formulation printed thereon. In such embodiments, the distance between heating element and the surface / side of the substrate with the piezoelectric ink formulation printed thereon is from about 0.1 mm to about 3 mm, from about 0.1 mm to about 2.9 mm, from about 0.2 mm to about 2.8 mm, from about 0.3 mm to about 2.7 mm, from about 0.4 mm to about 2.6 mm, from about 0.5 mm to about 2.5

[0127] Internalmm, from about 0.6 mm to about 2.4 mm, from about 0.7 mm to about 2.3 mm, from about 0.8 mm to about 2.2 mm, from about 0.9 mm to about 2.1 mm, from about 1 mm to about 2 mm, from about 1.1 mm to about 1.9 mm, from about 1.2 mm to about 1.8 mm, from about 1.3 mm to about 1.7 mm, from about 1.4 mm to about 1.6 mm, or about 1.5 mm.

[0128] In various embodiments, the system comprises a thermal shield, which is designed / configured to be located / positioned on or in contact with a side / surface of the substrate that is devoid of the piezoelectric ink formulation. Advantageously, in various embodiments, the presence of a thermal shield helps maintain the desired heating / temperature profile and / or control heat distribution within the sintering system. By controlling heat distribution, embodiments of the system disclosed herein prevents / minimizes overheating and ensures that only the desired surface (i.e. surface printed with the piezoelectric ink formulation) of the substrate reaches the sintering temperatures. In various embodiments, the presence of a thermal shield also helps minimize heat loss to the environment, allowing for more efficient energy use and reducing the time required to achieve the desired sintering temperature.

[0129] PIEZOELETRIC DEVICE

[0130] There is provided a piezoelectric device for providing haptic feedback, wherein the piezoelectric device comprises a substrate with a piezoelectric ink formulation as disclosed herein printed thereon.

[0131] Advantageously, the piezoelectric device designed in accordance with various embodiments disclosed herein exhibits higher piezoelectric properties than conventional printed substrates. Even more advantageously, in various embodiments, the piezoelectric device possess high, excellent and outstanding piezoelectric properties, making embodiments of the piezoelectric device suitable / useful / desirable for actuator applications, e.g., in human-machine interface (HMI), haptics, touch sensors, on-display force sensors and gaming haptics etc.

[0132] In various embodiments, the piezoelectric device may be used in one or more of the following applications: human-machine interface (HMI), haptics, touch sensors, on-display force sensors, and gaming haptics.

[0133] In various embodiments, the piezoelectric device may be used in a human-machine interface (HMI) system or device, e.g., for user interaction such as smartphones, cars, industrial machines and healthcare devices etc. In various embodiments, the piezoelectric device may be used in a haptics system or device, e.g., in technologies providing tactile feedback such as smartphones, virtual reality (VR), augmented reality (AR), automotive, healthcare and gaming etc. In various embodiments, the piezoelectric device may be used in a touch sensor system or device,

[0134] Internale.g., used in inputs based on physical touch or proximity such as mobile devices, kiosks, automotive, and consumer electronics etc. In various embodiments, the piezoelectric device may be used in an on-display force sensor system or device, e.g., in pressure-sensitive touchscreens providing advanced functionality such as smartphones, interactive displays, gaming and wearables etc. In various embodiments, the piezoelectric device may be used in a gaming haptics system or device, e.g., used in tactile feedback in gaming systems to enhance immersion such as game controllers, VR / AR, and simulation systems etc.

[0135] In various embodiments, the piezoelectric device designed in accordance with various embodiments disclosed herein exhibits / possesses high piezoelectricity (e.g., high piezoelectric coefficient / response). In various embodiments, the piezoelectric device designed in accordance with various embodiments disclosed herein has a high piezoelectric coefficient (d33) of from about 180 pC / N to about 250 pC / N, from about 185 pC / N to about 245 pC / N, from about 190 pC / N to about 240 pC / N, from about 195 pC / N to about 235 pC / N, from about 200 pC / N to about 230 pC / N, from about 205 pC / N to about 225 pC / N, from about 210 pC / N to about 220 pC / N, or about 215 pC / N. In various embodiments, the piezoelectric device designed in accordance with various embodiments disclosed herein has a high piezoelectric coefficient (d31) of from about 20 pC / N to about 40 pC / N, from about 21 pC / N to about 39 pC / N, from about 22 pC / N to about 38 pC / N, from about 23 pC / N to about 37 pC / N, from about 24 pC / N to about 36 pC / N, from about 25 pC / N to about 35 pC / N, from about 26 pC / N to about 34 pC / N, from about 27 pC / N to about 33 pC / N, from about 28 pC / N to about 32 pC / N, from about 29 pC / N to about 31 pC / N, or about 30 pC / N.

[0136] BRIEF DESCRIPTION OF FIGURES FIG. l is a schematic flowchart for illustrating a method of preparing a piezoelectric device in accordance with various embodiments disclosed herein.

[0137] FIG. 2 is a schematic block diagram of a setup for illustrating ultrafast high-temperature sintering (UHS) in accordance with various embodiments disclosed herein.

[0138] FIG. 3 is a temperature versus time (or temperature-time) graph showing a heating profile of a UHS experiment in accordance with various embodiments.

[0139] FIG. 4 is a power versus time (or power-time) graph showing a heating profile of a UHS experiment in accordance with various embodiments.

[0140] InternalDETAILED DESCRIPTION OF FIGURES

[0141] FIG. 1 is a schematic flowchart 100 for illustrating a method of preparing a piezoelectric device in accordance with various embodiments disclosed herein. At step 102, a piezoelectric ink formulation is printed on a substrate (e.g., on a surface of the substrate). In various embodiments, step 102 may comprise additional steps such as degassing and / or drying the piezoelectric ink formulation that has been printed on the substrate. At step 104, the piezoelectric ink formulation printed on the substrate is subjected to sintering (e.g., ultrafast high-temperature sintering (UHS)) to obtain a piezoelectric device in accordance with various embodiments disclosed herein.

[0142] In various embodiments, any one of steps 106, 108 and 110 is / are optional.

[0143] In certain embodiments, prior to steps 102 and / or 104, the method further comprises a step 106 of depositing an electrode on the substrate (e.g., glass substrate). The step 106 of depositing an electrode on the substrate may also be carried out after steps 102 and / or 104.

[0144] In certain embodiments, prior to steps 102 and / or 104, the method further comprises a step 108 of providing a piezoelectric ink formulation to be printed on the substrate for preparing a piezoelectric device in accordance with various embodiments disclosed herein.

[0145] In certain embodiments, prior to steps 102 and / or 104, the method further comprises a step 110 of milling the piezoelectric ink formulation to obtain a viscosity falling in the range of from about 500 mPa- s to about 10,000 mPa s.

[0146] FIG. 2 is a schematic block diagram of a setup 200 for illustrating ultrafast high-temperature sintering (UHS) in accordance with various embodiments disclosed herein. In various embodiments, the sintering step 104 (as shown in FIG. 1) is carried out using the setup 200.

[0147] The setup 200 comprises first electrodes 202a and 202b. The first electrodes may be provided in the form of plates (e.g., metallic plates). The setup 200 also comprises second electrodes 204a and 204b. The second electrodes may be provided in the form of blocks (e.g., non-metallic blocks). It will be appreciated that although not shown in the figure, when in use, the first electrodes and second electrodes are connected to a power supply which provides / supplies electric current to the setup. In the figure, the first electrodes are shown in pairs (e.g., 202a and 202b) but it will be appreciated that, practically, there may be a single first electrode or a plurality of (or several) first electrodes. Likewise, in the figure, the second electrodes are shown in pairs (e.g., 204a and 204b) but it will be appreciated that, practically, there may be a single second electrode or a plurality of (or several) second electrodes. The setup 200 also comprises a heating element 206 which may be in contact with or spaced apart from a substrate 208 with a piezoelectric ink formulation printed thereon. The setup 200 also comprises a thermal shield 210 that is placed in

[0148] Internalcontact with a surface of the substrate 208 that is devoid of the printed piezoelectric ink formulation. When in use, the setup 200 facilitates the flow of electric current, allowing for Joule heating during the sintering process.

[0149] FIG. 3 is a temperature versus time (or temperature-time) graph showing a heating profile of a UHS experiment in accordance with various embodiments. The heating profile shows a rapid change in temperature over time, allowing a high temperature of about 1,500 °C to be reached in about 40 seconds to 30 minutes. As shown, the heating and cooling process is completed quickly in about 60 seconds to about 3,600 seconds.

[0150] FIG. 4 is a power versus time (or power-time) graph showing a heating profile of a UHS experiment in accordance with various embodiments. The heating profile shows a rapid change in power over time, allowing a high power of about 160 watts to be reached in about 40 seconds. As shown, the heating and cooling process is completed quickly in about 100 seconds to 30 minutes.

[0151] EXAMPLES

[0152] Example embodiments of the disclosure will be better understood and readily apparent to one of ordinary skill in the art from the following examples, tables and if applicable, in conjunction with the figures. It should be appreciated that other modifications related to structural, and / or chemical changes may be made without deviating from the scope of the invention. Example embodiments are not necessarily mutually exclusive as some may be combined with one or more embodiments to form new example embodiments. The example embodiments should not be construed as limiting the scope of the disclosure.

[0153] The following examples describe the development of a printable ink formulation of piezoelectric ceramic ink that is designed to be printed and sintered on glass substrates. Advantageously, such an approach offers a unique method to generate a variety of tactile sensations while also enabling the sensing of pressure. By allowing direct printing on display panels, embodiments of the method disclosed herein offer increased and / or added design flexibility, opening new possibilities e.g, for interactive touch interfaces and customizable user experiences in product designs.

[0154] Additionally, embodiments of the method disclosed herein eliminates the need for complex procedures such as dicing and bonding process of thin strips of piezoelectric ceramics. This reduces both the manufacturing cost and complexity of production, thereby streamlining the creation of piezoelectric devices / components.

[0155] InternalFurthermore, the method designed in accordance with various embodiments disclosed herein has shown that the sintering time required was shortened from days to a matter of a few minutes, and energy consumption was reduced, thereby increasing overall production efficiency, making the method a sustainable and cost-effective one.

[0156] Creating PZT-based actuators for haptic feedback involves the following main steps: PZT ink preparation, bottom electrode deposition, PZT ink printing, and sintering and polarization.

[0157] Example 1: PZT Paste Preparation and Deposition

[0158] The PZT ink is formulated using APC 841 powder (60-75 wt% solid loading), dispersants (0-1 wt% of Triton-X 100 / Phosphate Ester / Menhaden Fish Oil), sintering aids (0-3 wt% of LiB / CuO), solvents (acetic acid, ethanol, or benzyl alcohol), excess PbO, and binders (PMMA (1-3wt%) / PVB (0.25-lwt%)), then milled to achieve the desired viscosity (1000-5000 mPas). The bottom electrode is deposited on a high-temperature-resistant glass substrate either by screen printing or DC sputtering (20 to 100 pm). The PZT ink with varying thicknesses (40-1000 pm) is then printed onto the glass substrate deposited with electrode, degassed, and dried. Finally, the printed layer undergoes sintering and polarization to complete the actuator.

[0159] Example 2: Sintering and Polarization

[0160] Ultrafast field-assisted sintering technologies (FAST) have been investigated as a possible alternative conventional sintering methods of piezoelectric ceramic materials, which are both timeconsuming and energy-consuming. Ultrafast high-temperature sintering (UHS) involves the passing of an electric current through a carbon felt strip to generate Joule heating to densify ceramic green bodies over a very short period.

[0161] In this example, UHS sintering of PZT ceramic as piezoelectric ceramic was demonstrated on glass substrates for automotive applications. Advantageously, it is shown that the PZT ink designed in accordance with various embodiments disclosed herein is suitable for use in UHS method despite its element lead (Pb) being easy to evaporate. It will be appreciated that conventional PZT coatings on glass substrates often result in delamination and glass substrates often become warped at high temperatures required for the densification of PZT. On the other hand, the UHS method designed in accordance with various embodiments disclosed herein obviates these issues as excessive heating of glass substrates is eliminated from embodiments of the method. In this example, this form of sintering is obtained by adapting UHS with a directional j oule heating setup. By placing the PZT coated surface facing towards the carbon heating elements,

[0162] Internalas well as significantly shortening the time required for the sintering of the PZT, only the PZT ceramic layers are exposed to an appropriate heating temperature. This reduces / minimizes exposure of the substrate to high temperatures, and consequently reduces the thermal impact on the substrate. Through this method, the densification of the PZT ceramic is achieved with minimal delamination or warping of the glass substrate.

[0163] Each UHS experiment was conducted with the inventors’ in-house UHS setup as devised and developed by the inventors, which comprises specially designed copper plates and graphite blocks (FIG. 2) connected to a power supply. The temperature of the heating elements is measured with an infrared (IR) thermometer that is capable of measuring a temperature of up to 3000 °C.

[0164] To ensure a fast and successful densification of PZT coating on glass substrate without causing warping or delamination, the following features are employed in the setup:

[0165] (a) The space between PZT coating and carbon felt is at least 0 mm - 2.0 mm wide.

[0166] (b) A thermal shield is placed on the other side of the glass substrate without PZT coating. (c) The UHS temperature is kept at 800 °C - 1200 °C and the dwell time is 10 s - 300 s. The ramp rate is controlled in a range of 20 °C / s -130 °C / s.

[0167] (d) UHS heating profile can be a single step or multiple steps of ramp up.

[0168] (e) The heating element can be various carbon felts with major phases of graphite The heating element is not amorphous to reduce carbon contamination caused by evaporation of carbon. Other heating element materials can also be used, such as molybdenum, tungsten M0S2, and the like. The resistance of heating elements is kept at 1.0 Q - 10.0 Q.

[0169] With this procedure, highly dense PZT layers are manufactured on glass substrates with piezoelectric properties that are better than the ones reported in the literature by any other alternative sintering approaches.

[0170] It will be appreciated by a person skilled in the art that other variations and / or modifications may be made to the embodiments disclosed herein without departing from the spirit or scope of the disclosure as broadly described. For example, in the description herein, features of different exemplary embodiments may be mixed, combined, interchanged, incorporated, adopted, modified, included etc. or the like across different exemplary embodiments. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

[0171] Internal

Claims

CLAIMS1. A piezoelectric ink formulation for preparation of a piezoelectric device, the formulation comprising:(i) perovskite-based powder,(ii) optionally a dispersing agent;(iii) optionally a sintering agent;(iv) a binding agent;(v) optionally lead oxide; and(vi) a solvent.

2. The formulation of claim 1, wherein the formulation comprises from 50 wt% to 80 wt%, preferably 55 wt% to 78 wt%, more preferably 60 wt% to 75 wt% of the perovskite-based powder.

3. The formulation of claim 1 or claim 2, wherein the formulation comprises no more than 3 wt%, preferably no more than 2 wt%, more preferably no more than 1 wt% of the dispersing agent.

4. The formulation of any one of claims 1 to 3, wherein the formulation comprises no more than 5 wt%, preferably no more than 4 wt%, more preferably no more than 3 wt% of the sintering agent.

5. The formulation of any one of claims 1 to 6, wherein the formulation comprises from 0.1 wt% to 5 wt%, preferably 0.5 wt% to 4.5 wt%, more preferably 1 wt% to 4 wt% of the binding agent.

6. The formulation of any one of claims 1 to 5, wherein the formulation comprises no more than 5 wt% of the lead oxide.

7. The formulation of any one of claims 1 to 4, wherein the formulation comprises from 5 wt% to 60 wt% of the solvent.

8. The formulation of any one of claims 1 to 7, wherein the formulation has a viscosity falling in the range of from 500 mPa s to 10,000 mPa s.

9. The formulation of any one of claims 1 to 8, wherein the perovskite-based powder comprises oxygen and two or more metals selected from the group consisting of titanium (Ti), manganese (Mn), cobalt (Co), nickel (Ni), zirconium (Zr), niobium (Nb), lead (Pb), and combinations thereof.Internal10. The formulation of claim 9, wherein the perovskite-based powder comprises lead zirconate titanate.11 . The formulation of any one of claims 1 to 10, wherein the dispersing agent comprises one or more surfactants selected from the group consisting of non-ionic surfactant, anionic surfactant, cationic surfactant, amphoteric surfactant, natural surfactant and combinations thereof.

12. The formulation of any one of claims 1 to 11, wherein the sintering agent comprises one or more compounds selected from the group consisting of boron compounds, lithium compounds, copper compounds, calcium compounds, magnesium compounds, aluminum compounds, sodium compounds, potassium compounds and combinations thereof.

13. The formulation of any one of claims 1 to 12, wherein the solvent comprises one or more organic solvents selected from the group consisting of organic acids, alcohols, ketones, and combinations thereof.

14. The formulation of any one of claims 1 to 13, wherein the binding agent comprises one or more polymers selected from the group consisting of poly(meth)acrylates, polyacrylates, polymethacrylates, polyvinyl, polyurethane, polyalkylene glycol, cellulose, polyacrylic acid and combinations thereof.

15. A method of preparing a piezoelectric device, the method comprising:(a) printing a piezoelectric ink formulation of any one of claims 1 to 14 on a substrate;(b) sintering the piezoelectric ink formulation printed on the substrate; and(c) poling the piezoelectric ink formulation printed on the substrate.

16. The method of claim 15, wherein sintering is completed in no more than 30 minutes.

17. The method of any one of claims 15 to 16, wherein sintering is performed at a temperature falling in the range of from 500°C to l,500°C.Internal18. The method of any one of claims 15 to 17, wherein sintering is performed at a temperature ramp rate falling in the range of from 5°C / s to 150°C / s and / or with a dwell time falling in the range of from 5 s to 500 s.

19. The method of any one of claims 15 to 18, wherein sintering is performed in the presence of a thermal shield that is located on a side of the substrate that is devoid of the printed piezoelectric ink formulation.

20. The method of any one of claims 15 to 19, wherein sintering is performed in the presence of a heating element that has a resistance falling in the range of from 0.5 ohms to 15 ohms.

21. The method of any one of claims 15 to 20, wherein printing the piezoelectric ink formulation comprises printing the piezoelectric ink formulation to obtain a printed layer having a thickness falling in the range of from 5 pm to 5,000 pm.

22. The method of any one of claims 15 to 21, further comprising, prior to printing the piezoelectric ink formulation, depositing an electrode on the substrate.

23. The method of any one of claims 15 to 22, further comprising, prior to printing the piezoelectric ink formulation:providing the piezoelectric ink formulation; andmilling said formulation to obtain a viscosity falling in the range of from 500 mPa- s to 10,000 mPa s.

24. A piezoelectric device for providing haptic feedback, wherein the piezoelectric device comprises a substrate with a piezoelectric ink formulation of any one of claims 1 to 14 printed thereon.

25. The piezoelectric device of claim 24, wherein the piezoelectric device is one of an humanmachine interface (HMI) device, haptics device, touch sensor device, on-display force sensor device, and gaming haptics device.Internal

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