Lead zirconate titanate film material with ultrahigh piezoelectric coefficient, preparation method and application thereof

Abstract

The present invention discloses a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, a preparation method thereof, and an application thereof, and belongs to the field of electronic material development and thin film material technology. The present invention adopts a sol-gel spin coating method and realizes the preparation of the lead zirconate titanate film material by controlling the number of annealing times. The piezoelectric film material provided by the present invention can be directly deposited on a metal Pt-coated Si substrate without introducing an additional buffer layer or doping any elements. The annealing time is short, the preparation process is simple, and all the required raw materials are cheap and easily available. In particular, it has high orientation, low coercive voltage, and excellent ferroelectric and piezoelectric properties. It is suitable for the preparation of large-size (2-4 inch) wafers and shows great application potential in the field of piezoelectric microelectromechanical systems (MEMS) devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic material development and thin film materials, and particularly relates to a lead zirconate titanate film material with an ultrahigh piezoelectric coefficient, a preparation method thereof, and an application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Piezoelectric materials are materials that develop a voltage between their two end surfaces when subjected to pressure. This phenomenon encompasses both the direct piezoelectric effect (electric charge generated by mechanical stress) and the inverse piezoelectric effect (electric field-induced deformation). As a class of functional materials that enable the conversion of mechanical energy into electrical energy, piezoelectric materials are widely used in microelectromechanical systems (MEMS), such as sensors, transducers, large-displacement actuators, and energy harvesters. Lead zirconate titanate (PZT), a representative perovskite-type piezoelectric material, is formed by the solid solution of lead zirconate (PbZrO₃) and lead titanate (PbTiO₃). Its composition exhibits optimal piezoelectric and electromechanical coupling properties near the morphotropic phase boundary (MPB, Zr / Ti ~ 52 / 48). Combined with its high Curie temperature, PZT has become a core material for current piezoelectric devices. While environmentally friendly, lead-free piezoelectric materials (such as potassium sodium niobate) have been extensively researched, PZT has yet to be replaced due to its unparalleled high-voltage electrical activity and reliability. Among them, lead zirconate titanate film has become the core material of miniaturized electronic devices due to its miniaturization, low power consumption and high response speed, such as high-precision displacement actuators, micro-nano sensors and flexible electronic devices.

[0004] Currently, the mainstream preparation methods for lead zirconate titanate thin films include sol-gel, magnetron sputtering, and pulsed laser deposition (PLD). Although physical vapor deposition techniques (PLD and magnetron sputtering) can produce high-quality single-crystalline thin films, they are subject to high equipment costs, low deposition rates, and stringent requirements for target material composition uniformity. Furthermore, the long, high-temperature deposition process can easily cause the volatilization of lead elements in the thin film material and deviations in composition, which can easily lead to the generation of impurities and defects. This leads to high leakage loss, high coercive electric field, and low compressive strength, significantly compromising the material's piezoelectric performance and stability. Researchers typically improve and enhance the piezoelectric properties of lead zirconate titanate films by introducing a buffer layer or by doping with multiple elements during the preparation process. However, these improvement methods have significant drawbacks: the use of buffer layers such as PbO or LaNiO3 significantly increases the number of preparation steps and increases the process complexity; although doping elements (such as La, Mn, etc.) can enhance the piezoelectric response, they may increase the leakage current or lower the Curie temperature, making it difficult to coordinately optimize parameters such as the piezoelectric coefficient and dielectric loss, thus making the large-scale industrial application of lead zirconate titanate films face huge challenges.

[0005] The membrane material disclosed in the prior art without adding a buffer layer has a transverse piezoelectric coefficient of (111) oriented PZT thin film of 8~9 C / m 2 , or increase the buffer layer film material, the (100) / (001) oriented PZT film transverse piezoelectric coefficient is usually 8~15 C / m 2 However, regardless of whether a buffer layer is added, the film material preparation process often has drawbacks such as complex preparation process, high cost, and long time. In addition, the prepared film material does not have ultra-high piezoelectric coefficient, low operating voltage and low dielectric loss, and is not suitable for the preparation of wafer-scale lead zirconate titanate films, which is not conducive to industrial scale-up.

[0006] Therefore, as MEMS devices develop towards high integration and low drive voltage, the development of wafer-scale lead zirconate titanate films with ultra-high piezoelectric coefficients, low operating voltage, and low dielectric loss has become an urgent need. A low-cost, simple, short-annealing, and scalable lead zirconate titanate film preparation process is urgently needed to overcome the current technological bottleneck. Summary of the Invention

[0007] To address the shortcomings of the prior art, the present invention aims to provide a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, its preparation method, and its application. This invention utilizes a sol-gel spin coating method and, by controlling the number of annealing steps, can directly deposit a lead zirconate titanate film (PZT film) onto a Pt-coated Si substrate. This film, without the need for an additional buffer layer or doping, features a short annealing time (only a few minutes), a simple preparation process, and readily available, inexpensive raw materials. The material exhibits significant advantages, including high orientation, low coercive voltage, and excellent ferroelectric and piezoelectric properties. It is suitable for the preparation of large-scale (2-4 inch) wafers and exhibits significant potential for application in piezoelectric microelectromechanical systems (MEMS) devices.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] In a first aspect, the present invention provides a method for preparing a lead zirconate titanate film material having an ultrahigh piezoelectric coefficient, comprising the following steps:

[0010] a) forming a conductive layer on a substrate, wherein the substrate is a Pt / Ti / SiO2 / Si matrix or a Pt / Ti / Si matrix;

[0011] b) preparing a lead zirconate titanate precursor solution by a sol-gel method, and forming a precursor film on the conductive layer by a spin coating method;

[0012] c) drying and pyrolyzing the precursor film;

[0013] d) repeating steps b) and c) to form a multilayer precursor film, and then performing a rapid thermal annealing treatment, wherein the rapid thermal annealing is performed in an oxygen atmosphere at 550-750° C. for 3-10 minutes; wherein steps b) and c) are repeated 5-8 times to form the multilayer precursor film;

[0014] e) repeating steps b) to d) until the desired film thickness is reached to obtain a lead zirconate titanate film material;

[0015] In step e), steps b) to d) are repeated until the desired film thickness is reached, with one rapid thermal annealing treatment being considered as one cycle, and 2 to 4 cycles are repeated.

[0016] In one or more embodiments, in step a), the substrate is a Si substrate and a Ti layer and a bottom electrode Pt layer are sequentially supported on the Si substrate.

[0017] The Si substrate is Si or Si with a SiO2 oxide layer.

[0018] The thickness of the Si substrate is 0.2~1 mm, preferably 0.4~0.6 mm. The most common Si thickness sold on the market is 0.5 mm.

[0019] The thickness of the Ti layer is 30-80 nm. If the Ti layer is too thin, the bonding strength between the Si substrate and the Pt layer will be affected, causing the Pt electrode to fall off easily.

[0020] The thickness of the bottom electrode Pt layer is 100~300nm. Too thin a Pt layer will weaken the (111) orientation of the PZT film, while thickening the Pt layer will have no effect on the film performance and will increase the economic cost.

[0021] Furthermore, the substrate is a Pt / Ti / SiO2 / Si matrix or a Pt / Ti / Si matrix.

[0022] Furthermore, in step a), the substrate may be a common commercially available product or a Ti layer and a bottom electrode Pt layer may be deposited on a Si substrate in sequence by magnetron sputtering.

[0023] The Ti layer is a connecting layer between the Si substrate and the Pt bottom electrode to increase the adhesion between the two.

[0024] The specific steps of sequentially depositing the Ti layer and the bottom electrode Pt layer on the Si substrate by magnetron sputtering are as follows:

[0025] Place the Si substrate in the magnetron sputtering chamber and evacuate the chamber until the pressure is less than 2×10 -4Pa; introduce argon gas with an argon flow rate of 20~60 sccm, modulate the chamber pressure to 0.1~1.0 Pa, heat up at a rate of 5~10 ℃ / min to 200~400 ℃, adjust the magnetron sputtering power to 50~100 W, and successively sputter-deposit the Ti layer and the bottom electrode Pt layer to the desired thickness.

[0026] In one or more embodiments, in step b), the process conditions of the spin coating method are: low speed of 600-1000 rpm, spin coating time of 9-15 s, high speed of 2000-5500 rpm, spin coating time of 15-35 s.

[0027] In one or more embodiments, in step c), the drying temperature is 150-300° C. (preferably 200-250° C.), and the drying time is 2-5 min.

[0028] In step c), the pyrolysis temperature is 350-500°C (preferably 400-500°C), and the pyrolysis time is 2-10 min (preferably 2-5 min).

[0029] In one or more embodiments, in step d), the annealing temperature is 650-750° C., and the annealing time is 4-6 min.

[0030] Generally speaking, a moderate drying temperature can fully and thoroughly evaporate the moisture in the PZT wet film, shorten the drying time, and improve production efficiency; if the pyrolysis temperature is too low, the organic matter in the wet film cannot be completely decomposed, and if the temperature is too high, the film will crack; if the annealing temperature is too low, the PZT film cannot be crystallized, and if it is too high, its performance will be seriously degraded.

[0031] In one or more embodiments, in step d), steps b) and c) are repeated 5-8 times to form a multilayer precursor film. The number of repetitions provided here is a process for preliminary screening and optimization. If the number of repetitions is too small, the number of annealing times will be too large, resulting in excessive volatilization of Pb in the PZT film and serious degradation of its performance; otherwise, it will lead to Figure 6 The PZT film shown is cracked and its performance cannot be tested.

[0032] In one or more embodiments, in step e), steps b) to d) are repeated until a desired film thickness is reached, with one rapid thermal annealing process being considered as one cycle, and the process is repeated 2 to 4 times.

[0033] The number of annealing times is crucial for the preparation of membrane materials. If only one annealing is performed, the membrane material may crack. Figure 6However, if the annealing times are too many, the Pb in the PZT film will volatilize excessively, causing its composition to deviate from the stoichiometric ratio; at the same time, multiple annealing will cause the film to produce impurities, resulting in serious degradation of the film performance.

[0034] In one or more embodiments, in step e), the lead zirconate titanate film material is Pb(Zr x Ti 1-x )O3, wherein 0.4≤x≤0.6, preferably 0.5≤x≤0.55. The lead zirconate titanate film material is preferably Pb(Zr 0.52 Ti 0.48 )O3.

[0035] The thickness of the lead zirconate titanate film material is 0.5-1.5 μm, which is the best thickness for the present invention.

[0036] In one or more embodiments, in step b), the lead zirconate titanate precursor solution is prepared as follows: the contents of the three raw materials Pb, Zr, and Ti required to prepare the solution are calculated separately according to the stoichiometric ratio; ethylene glycol methyl ether and glacial acetic acid are uniformly mixed in a volume ratio of (1.1-1.3):1, and then the weighed Pb raw material is added and stirred at room temperature until the Pb raw material is completely dissolved; then an appropriate volume (the volume here depends on the concentration and volume of the prepared precursor solution and there is no fixed range) of acetylacetone is added and stirred evenly, followed by the weighed Ti and Zr raw materials being added in sequence and thoroughly stirred and mixed evenly; finally, an appropriate amount of ethylene glycol methyl ether is added (the required volume depends on the concentration and volume of the final precursor solution, so there is no need to determine a fixed value) to adjust the precursor solution, stirred at room temperature, and allowed to stand for aging.

[0037] Among them, ethylene glycol methyl ether is used as a solvent and is also used to adjust the concentration of the precursor solution; glacial acetic acid is used as a solvent; and acetylacetone is used as a stabilizer for the precursor solution to prevent it from precipitating.

[0038] Preferably, the concentration of the precursor solution is 0.1 to 0.4 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or 0.4 mol / L, preferably 0.1 to 0.2 mol / L. Stir at room temperature for 6 to 12 hours and allow to stand for 24 to 72 hours.

[0039] During the preparation of the lead zirconate titanate precursor solution, the molar content of the Pb element is 5-20% excess, such as 5% excess, 9% excess, 10% excess, 11% excess, 15% excess, 20% excess, preferably 5-15% excess, more preferably 9-11% excess, and most preferably 10% excess. The purpose of the excess is to supplement the volatility loss of the Pb element during the heat treatment of the lead zirconate titanate film. As in Example 1, the molar content of the Pb element is 10% excess, which means that the obtained lead zirconate titanate precursor material should be Pb 1.1 (Zr x Ti 1-x )O3, but in the actual preparation process, due to the loss of Pb element, the final prepared material is Pb(Zr x Ti 1-x )O3.

[0040] In one or more embodiments, the method further includes step f): depositing a top electrode Pt layer on the lead zirconate titanate film material obtained in step e) by magnetron sputtering.

[0041] Furthermore, the thickness of the top electrode Pt layer is 10~30 nm.

[0042] Furthermore, in step f), the conditions for magnetron sputtering are: the sputtering atmosphere is argon, the argon flow rate is 30-60 sccm, the sputtering pressure is 0.1-1.0 Pa, the sputtering power is 50-100 W, the sputtering deposition time is 1-10 min (preferably 1-5 min), and the deposition temperature is room temperature.

[0043] In one or more embodiments, a buffer layer is added between step a) and step b); the buffer layer is an oxide buffer layer, and the oxide buffer layer includes a PbO or LaNiO3 buffer layer. The thickness of the buffer layer is about 200 nm.

[0044] The specific steps are: using oxide ceramic as a sputtering target, using a radio frequency magnetron sputtering method to sputter and deposit a buffer layer, the sputtering atmosphere is argon and oxygen, the argon flow rate is adjusted to 20~60 sccm (preferably 50-60 sccm), the oxygen flow rate is adjusted to 20~60 sccm (preferably 10-20 sccm), the sputtering pressure is 0.5-1.5 Pa (preferably 1.2), the sputtering power is set to 50~100 W (preferably 55 W), and the sputtering time is 20-40 min (preferably 25 min).

[0045] In a second aspect, the present invention provides a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, which is prepared by the above-mentioned preparation method.

[0046] The lead zirconate titanate film material is a large-size (2-4 inches) and highly uniform wafer film material.

[0047] Pb(Zr 0.52 Ti 0.48 )O3 film material is directly grown on the bottom electrode without introducing any buffer layer, Pb(Zr 0.52 Ti 0.48 )O3 film material shows (111) preferred orientation growth.

[0048] When the buffer layer is introduced, Pb(Zr 0.52 Ti 0.48 )O3 film material presents an excellent (001) growth orientation.

[0049] In a third aspect, the present invention provides an application of the above-mentioned lead zirconate titanate film material with an ultra-high piezoelectric coefficient in a piezoelectric microelectromechanical system (MEMS). Preferably, the piezoelectric microelectromechanical system includes a sensor, an actuator, a transducer, and a resonator.

[0050] In a fourth aspect, the present invention provides a prototype device of a sensor, comprising a substrate and a lead zirconate titanate piezoelectric film material and a top electrode sequentially deposited on the substrate;

[0051] Or, it includes a substrate and a lead zirconate titanate piezoelectric film material, a buffer layer and a top electrode deposited in sequence on the substrate.

[0052] One or more of the above technical solutions have the following advantages or beneficial effects:

[0053] (1) The present invention adopts a sol-gel spin coating method and controls the number of annealing times to achieve the preparation of lead zirconate titanate piezoelectric films. This preparation method is simple and does not require expensive and complex high vacuum deposition equipment (such as magnetron sputtering and PLD), resulting in low investment and maintenance costs. At the same time, the raw materials and reagents required for preparing the lead zirconate titanate film material provided by the present invention are all commercially available and very inexpensive, which has significant economic advantages over the sputtering targets and expensive single crystal oxide substrates required for preparing the lead zirconate titanate film material by physical vapor deposition methods such as magnetron sputtering and PLD.

[0054] (2) The precursor components required for preparing the lead zirconate titanate film material provided by the present invention can be precisely controlled to achieve molecular-level uniformity and reduce component segregation, thereby ensuring that the prepared lead zirconate titanate film material has uniform composition, excellent stoichiometric ratio, and uniform film material performance.

[0055] (3) The ultra-high piezoelectric coefficient lead zirconate titanate film material provided by the present invention can be directly deposited on a Si substrate coated with a Pt bottom electrode without the need for additional oxide buffer layers such as lanthanum nickelate and strontium ruthenate. It is not doped with any elements, and the preparation method and process are simpler. It is suitable for the preparation of large-size (2-4 inches) and highly uniform wafer film materials, which is convenient for industrial promotion and large-scale production.

[0056] (4) The ultra-high piezoelectric coefficient lead zirconate titanate film material provided by the present invention has a short annealing time (only a few minutes) and does not require a long high-temperature deposition process (magnetron sputtering, PLD and other methods usually have a high-temperature deposition time of several hours to more than ten hours). It can effectively inhibit the volatilization of lead elements and composition deviation in the film caused by long-term heat treatment, avoid the generation of defects such as impurities and oxygen vacancies, and reduce the leakage current and loss of the film material.

[0057] (5) The lead zirconate titanate film material directly deposited on the Si substrate of the Pt electrode provided by the present invention has high orientation, low coercive voltage (<5V), high dielectric constant (2000-2200) and low leakage current density (<2x10 -5 A / cm 2 ) and dielectric loss (<0.09), especially high saturation polarization intensity (80-120 μC / cm 2 ), high remnant polarization intensity (40-65 μC / cm 2 ) and ultra-high transverse piezoelectric coefficient (8-13 C / m 2 ). Therefore, the preparation method provided by the present invention can achieve the same technical effect as adding a buffer layer on the basis of no buffer layer and no doping of any elements, and is also better than the film material without adding a buffer layer in the prior art (the lateral piezoelectric coefficient of the (111) oriented PZT film is generally reported to be 8~9 C / m 2 ) has better technical effects, and more importantly, the preparation method of the present invention has the advantages of simpler process, lower cost and shorter annealing time.

[0058] (6) When the preparation method provided by the present invention is used to prepare the lead zirconate titanate film material by adding a buffer layer, the average transverse piezoelectric coefficient e 31,f 16.5 C / m 2 , the highest transverse piezoelectric coefficient e 31,f Up to 17.6 C / m 2 , while having a lower leakage current density (<8x10 -6 A / cm 2 ) and dielectric loss (<0.07), and its dielectric constant is 1700-2100. Compared with the membrane material with added buffer layer in the existing technology (the existing report (100) / (001) oriented PZT film lateral piezoelectric coefficient is usually 8~15 C / m2 ) has better technical effects, and the preparation method of the present invention has the advantages of simpler process, lower cost and shorter annealing time. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0060] Figure 1 XRD patterns of the lead zirconate titanate film materials obtained in Example 1 and Example 11 of the present invention and the corresponding pole figures of the lead zirconate titanate films, wherein (a1) and (a2) are the XRD patterns of the lead zirconate titanate film materials obtained in Example 1 and Example 11, respectively, and (b1) and (b2) are the pole figures of the lead zirconate titanate film materials obtained in Example 1 and Example 11, respectively;

[0061] Figure 2 Surface and cross-sectional scanning electron micrographs of the lead zirconate titanate film material prepared in Example 1 of the present invention;

[0062] Figure 3 The hysteresis loop and polarization reversal current density curve of the lead zirconate titanate film material prepared in Example 1 of the present invention;

[0063] Figure 4 Graphs showing the leakage current density and dielectric frequency of the lead zirconate titanate film materials obtained in Examples 1 and 11 of the present invention, wherein (a) is a graph showing the leakage current density and (b) is a graph showing the dielectric frequency.

[0064] Figure 5 Schematic diagram of a transverse piezoelectric testing device, the tip displacement and transverse piezoelectric coefficient of a cantilever beam made of a lead zirconate titanate film material, and a physical image of a lead zirconate titanate film wafer, wherein (a) is a schematic diagram of a transverse piezoelectric testing device, (b) is the tip displacement and transverse piezoelectric coefficient of a cantilever beam made of a lead zirconate titanate film material obtained in Examples 1, 10, and 11 of the present invention, and (c) is a physical image of a 2-inch lead zirconate titanate film wafer obtained in Example 2;

[0065] Figure 6 This is a physical picture of the lead zirconate titanate film material prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0066] The raw materials required for the lead zirconate titanate film material provided by the present invention are all commercially available products, and are cheap and easily available.

[0067] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0068] Example 1

[0069] A method for preparing a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, comprising the following steps:

[0070] (1) Substrate treatment and bottom electrode preparation

[0071] A semiconductor Si wafer or Si with a SiO2 oxide layer was used as the substrate (size: 20×20×0.5 mm). After ultrasonic cleaning with anhydrous ethanol and drying with high-purity nitrogen, the Si wafer was placed in the sample holder of the magnetron sputtering chamber. The chamber was evacuated to a pressure below 2×10 -4 Pa; argon gas was introduced with a flow rate of 40 sccm, the Si wafer was heated to 300 °C at a heating rate of 5 °C / min, and the chamber pressure was adjusted to 0.3 Pa; a metal Ti layer and a metal Pt electrode layer were sequentially deposited on the Si substrate using radio frequency magnetron sputtering technology, the sputtering power was adjusted to 55 W, and the deposition time was controlled to 5 min and 15 min, respectively, where Pt was the bottom electrode layer, and the Ti layer was used to enhance the bonding strength between the Si substrate and the Pt electrode layer.

[0072] The lead zirconate titanate precursor is synthesized based on Pb(Zr 0.52 Ti 0.48 )O3 stoichiometric ratios were used to calculate the required contents of Pb, Zr, and Ti for synthesizing the precursor sol, with a 10% molar excess of Pb. Ethylene glycol methyl ether and glacial acetic acid were uniformly mixed at a volume ratio of 1.25:1, followed by the weighed Pb raw material and stirring at room temperature until the Pb raw material was completely dissolved. An appropriate volume of acetylacetone was then added and stirred until uniformly dissolved. The weighed Ti and Zr raw materials were then added in sequence and thoroughly mixed. Finally, an appropriate amount of ethylene glycol methyl ether was added to adjust the precursor solution concentration to 0.2 mol / L. The solution was stirred at room temperature for 6 hours and allowed to age for 24 hours before use. The Pb raw material used was lead acetate trihydrate, the Ti raw material was tetrabutyl titanate, and the Zr raw material was zirconium n-propoxide. Ethylene glycol methyl ether and glacial acetic acid served as solvents, and acetylacetone was used as a stabilizer.

[0073] Preparation of lead zirconate titanate thin material The lead zirconate titanate thin material is prepared by a spin coating method: first, the lead zirconate titanate precursor synthesized in step (2) is added to the substrate in step (1) through a syringe, and then a crystallized lead zirconate titanate thin material is obtained through a spin coating, drying, pyrolysis, and annealing process. Each spin coating, drying, and pyrolysis are performed once and annealed as a cycle. This cycle is repeated 3 times to obtain a lead zirconate titanate film material of the required thickness. Among them, the spin coating process is: low speed of 800 rpm, spin coating time of 12 s; high speed of 3500 rpm, spin coating time of 30 s. The drying, pyrolysis, and annealing processes are: drying temperature of 230 ° C, drying time of 3 min; pyrolysis temperature of 450 ° C, pyrolysis time of 3 min; annealing temperature of 700 ° C, annealing time of 5 min, and the annealing atmosphere is oxygen.

[0074] Preparation of the top electrode: A thin layer of metal Pt was sputtered onto the surface of the lead zirconate titanate film prepared in step (3) using magnetron sputtering as the top electrode. The sputtering atmosphere was argon with a flow rate of 40 sccm, a sputtering pressure of 0.3 Pa, a sputtering power of 55 W, and a deposition time of 1 min. The sample was removed after sputtering was completed.

[0075] Cantilever beam preparation The lead zirconate titanate film sample prepared in step (4) was cut into cantilever beams of 20 mm (length) × 3 mm (width) for piezoelectric performance testing.

[0076] Example 2

[0077] The difference from Example 1 is that the size of the Si substrate used in step (1) is a 2-inch wafer, and the other steps and process parameters are the same as those in Example 1. The performance test shows that the performance of the lead zirconate titanate film prepared in this example is shown in Table 1.

[0078] Example 3

[0079] The difference from Example 1 is that in the process of synthesizing the lead zirconate titanate precursor sol in step (2), the molar content of the Pb element is 5%, 15%, or 20% in excess, and the other steps and process parameters are the same as those in Example 1. The saturation polarization, remnant polarization, and transverse piezoelectric coefficient of the lead zirconate titanate film containing 20% ​​excess Pb element prepared in this embodiment are 96 μC / cm 2 , 47 μC / cm 2 、10.1 C / m 2 .

[0080] Example 4

[0081] The difference from Example 1 is that the concentration of the lead zirconate titanate precursor sol in step (2) is 0.1 mol / L, 0.3 mol / L or 0.4 mol / L, and the other steps and process parameters are the same as those in Example 1. According to the performance test, the saturation polarization, remnant polarization and transverse piezoelectric coefficient of the lead zirconate titanate film prepared in this embodiment with a precursor sol concentration of 0.4 mol / L are 98 μC / cm 2 , 48 μC / cm 2 , 11.2 C / m 2 .

[0082] Example 5

[0083] The difference from Example 1 is that in step (3), one cycle is formed by performing annealing once every six times of spin coating, drying, and pyrolysis, and this cycle is repeated three or four times. The other steps and process parameters are the same as those in Example 1. According to the performance test, the saturation polarization, residual polarization, and transverse piezoelectric coefficient of the lead zirconate titanate film obtained by repeating the cycle four times in this embodiment are 118 μC / cm 2 、61μC / cm 2 , 12.2 C / m 2 .

[0084] Example 6

[0085] The difference from Example 1 is that in step (3), the spin coating process is as follows: low speed is 600 rpm, spin coating time is 15 s; high speed is 5000 rpm, spin coating time is 20 s, and other steps and process parameters are the same as Example 1. According to the performance test, the saturation polarization, remnant polarization and transverse piezoelectric coefficient of the lead zirconate titanate film prepared in this embodiment are 101 μC / cm 2 , 47μC / cm 2 、10.5 C / m 2 .

[0086] Example 7

[0087] The difference from Example 1 is that in step (3), the drying, pyrolysis and annealing processes are as follows: drying temperature 150°C, drying time 3 min; pyrolysis temperature 350°C, pyrolysis time 5 min; annealing temperature 600°C, annealing time 8 min. The other steps and process parameters are the same as those in Example 1. According to the performance test, the saturation polarization, remanent polarization and transverse piezoelectric coefficient of the lead zirconate titanate film prepared in this embodiment are 81 μC / cm 2 , 40 μC / cm 2 、8.6 C / m 2 .

[0088] Example 8

[0089] The difference from Example 1 is that the sputtering deposition time of the top electrode Pt thin layer in step (4) is 2 min or 3 min, and the other steps and process parameters are the same as those in Example 1. Performance testing shows that the piezoelectric coefficient of the lead zirconate titanate film prepared in this example is almost the same as that in Example 1.

[0090] Example 9

[0091] The difference from Example 1 is that the width of the cantilever beam of the lead zirconate titanate film sample cut in step (5) is 2 mm or 4 mm, and the other steps and process parameters are the same as those in Example 1. Performance testing shows that the piezoelectric coefficient of the lead zirconate titanate film prepared in this example is almost the same as that in Example 1.

[0092] Example 10

[0093] The difference from Example 1 is that a commercially available Pt / Ti / SiO2 / Si matrix product (Hefei Anjing Crystal Materials Co., Ltd., size: 20×20×0.5 mm) is used in step (1). Other steps and process parameters except step (1) are the same as those in Example 1. The piezoelectric properties of the lead zirconate titanate film prepared in this example are as follows: Figure 5 As shown in (b) in .

[0094] Example 11

[0095] The difference from Example 1 is that the preparation of a buffer layer is added between step (2) and step (3), that is, after the Pt electrode is sputtered and deposited in step (1), the lanthanum nickelate buffer layer is sputtered and deposited using a RF magnetron sputtering method with lanthanum nickelate oxide ceramic as the sputtering target. The sputtering atmosphere is argon and oxygen, the argon flow rate is adjusted to 60 sccm, the oxygen flow rate is adjusted to 15 sccm, the sputtering pressure is 1.2 Pa, the sputtering power is set to 55 W, and the sputtering time is 25 min. The other steps and process parameters are the same as those in Example 1. After performance testing, the piezoelectric properties of the lead zirconate titanate film prepared in this embodiment are as follows: Figure 5 As shown in (b) in .

[0096] Comparative Example 1

[0097] The difference from Example 1 is that in step (3), a lead zirconate titanate film of the desired thickness is obtained through spin coating, drying, and pyrolysis processes, and the film material is finally annealed once. The other steps and process parameters are the same as those in Example 1.

[0098] Figure 1The XRD patterns and pole figures of the lead zirconate titanate film materials prepared in Example 1 and Example 11, respectively. From the XRD pattern combined with the corresponding pole figure, it can be seen that the lead zirconate titanate film material prepared in Example 1 is well crystallized without any impurities, especially showing a strong (111) preferred orientation growth, and almost no diffraction peaks of other orientations can be detected. In comparison, due to the induction effect of the buffer layer, the grain growth orientation of the lead zirconate titanate film material in Example 11 changes, showing an excellent (001) growth orientation, and no diffraction peaks of other orientations are detected. It should be noted that the lead zirconate titanate film prepared on the commercially available Pt / Ti / SiO2 / Si substrate product in Example 10 has an XRD pattern consistent with that of the lead zirconate titanate film material in Example 1. Figure 2 The surface and cross-sectional scanning electron micrographs of the lead zirconate titanate film prepared in Example 1 show uniform and dense grains on the surface, and the cross-sectional view shows that the lead zirconate titanate film layer is approximately 882 nm.

[0099] Performance tests show that the lead zirconate titanate film materials prepared in Examples 1 to 11 have excellent performance.

[0100] Figure 3 It shows that the lead zirconate titanate film prepared in Example 1 has a high polarization strength (saturation polarization strength value is as high as 113μC / cm 2 , the residual polarization intensity is 55 μC / cm 2 ) and breakdown voltage (≥125 V), and its polarization reversal current curve shows two obvious reversal current peaks.

[0101] Figure 4 The leakage current density and dielectric frequency curves of the lead zirconate titanate films prepared in Example 1 and Example 11 show that the lead zirconate titanate film prepared in Example 1 has a high dielectric constant (~2100), a low leakage current density (<2x10 -5 A / cm 2 ) and dielectric loss (<0.09); while adding a buffer layer to prepare the lead zirconate titanate film material showed a lower leakage current density (<8x10 -6 A / cm 2 ) and dielectric loss (<0.07), and its dielectric constant is 1700-2100.

[0102] Figure 5 (a) is a schematic diagram of the transverse piezoelectric test device; Figure 5 (b) shows the tip displacement and transverse piezoelectric coefficient of the cantilever beam of the lead zirconate titanate film prepared in Example 1, Example 10, and Example 11. It can be seen that the prepared lead zirconate titanate film exhibits a large cantilever tip displacement and increases approximately linearly with the applied voltage. The transverse piezoelectric coefficient shows good stability within the applied voltage range (4-15 V). Among them, the average transverse piezoelectric coefficient e of the lead zirconate titanate film prepared in Example 1 is 31,f~12.2C / m 2 , and the maximum e 31,f Up to 12.9 C / m 2 , which is the highest transverse piezoelectric coefficient of the lead zirconate titanate film reported so far directly on the Si substrate of the Pt electrode. In Example 10, the piezoelectric coefficient of the lead zirconate titanate film obtained by using the commercially available Pt / Ti / SiO2 / Si finished product as the substrate is almost the same as that of the lead zirconate titanate film in Example 1. In the same voltage range, the average transverse piezoelectric coefficient of the lead zirconate titanate film obtained in Example 11 is 31,f 16.5 C / m 2 , the highest e 31,f Up to 17.6 C / m 2 It can be seen that compared with the lead zirconate titanate film with a lanthanum nickelate buffer layer in Example 11, the lateral piezoelectric coefficient of the lead zirconate titanate film without a buffer layer prepared in Example 1 or Example 10 of the present invention is not much different, but the preparation method and process are simpler. Figure 5 (c) is a photo of a 2-inch lead zirconate titanate film wafer produced in Example 2. Performance testing was conducted on this 2-inch wafer-level lead zirconate titanate film. The test areas marked in the figure are, from top to bottom, Area 1, Area 2, Area 3, Area 4, and Area 5. The test results are shown in Table 1. This shows that the 2-inch wafer-level lead zirconate titanate film produced by the present invention has excellent electrical and lateral piezoelectric properties, making it suitable for the preparation of large-size (2-4 inches), highly uniform wafer-level film materials, facilitating industrial promotion and large-scale production.

[0103] Figure 6 This is a photo of the lead zirconate titanate film material produced in Comparative Example 1. The image shows that even after only one annealing step, the lead zirconate titanate film material cracks. Therefore, the number of annealing steps is crucial for the successful production of the film material.

[0104] Table 1 Properties of the 2-inch lead zirconate titanate film prepared in Example 2

[0105]

[0106] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, characterized in that: The following steps are involved: a) forming a conductive layer on a substrate, wherein the substrate is a Pt / Ti / SiO2 / Si matrix or a Pt / Ti / Si matrix; b) preparing a lead zirconate titanate precursor solution by a sol-gel method, and forming a precursor film on the conductive layer by a spin coating method; c) drying and pyrolyzing the precursor film; d) repeating steps b) and c) to form a multilayer precursor film, and then performing a rapid thermal annealing treatment, wherein the rapid thermal annealing is performed in an oxygen atmosphere at 550-750° C. for 3-10 minutes; wherein steps b) and c) are repeated 5-8 times to form a multilayer precursor film; e) repeating steps b) to d) until the desired film thickness is reached to obtain a lead zirconate titanate film material; In step a), the substrate is a Si substrate and a Ti layer and a bottom electrode Pt layer are sequentially loaded on the Si substrate; the Si substrate is Si or Si with a SiO2 oxide layer; In step b), the preparation method of lead zirconate titanate precursor solution is as follows: 0.52 Ti 0.48 ) O3 stoichiometric ratio respectively calculates the contents of three kinds of raw materials of Pb, Zr and Ti required for synthesizing its precursor sol, ethylene glycol monomethyl ether and glacial acetic acid are uniformly mixed in a volume ratio of (1.1-1.3): 1, then Pb raw material is added, and stirred until the Pb raw material is completely dissolved; then acetylacetone is added and stirred, followed by sequentially adding Ti and Zr raw materials, and fully stirring and mixing; finally, ethylene glycol monomethyl ether is added to adjust the concentration of the precursor solution, stirred at room temperature, and allowed to stand for aging; In step b), the process conditions of the spin coating method are: low speed of 600-1000 rpm, spin coating time of 9-15 s, high speed of 2000-5500 rpm, spin coating time of 15-35 s; In step c), the drying temperature is 150-300°C and the drying time is 2-5 minutes; In step c), the pyrolysis temperature is 350-500°C and the pyrolysis time is 2-10 min; In step e), steps b) to d) are repeated until the desired film thickness is reached, with one rapid thermal annealing treatment being considered as one cycle, and the process is repeated 2 to 4 times.

2. The preparation method according to claim 1, characterized in that The thickness of the Si substrate is 0.2~1 mm; the thickness of the Ti layer is 30~80 nm; the thickness of the bottom electrode Pt layer is 100~300 nm; and the thickness of the lead zirconate titanate film material is 0.5~1.5 μm.

3. The preparation method according to claim 2, characterized in that In step a), a Ti layer and a bottom electrode Pt layer are deposited on a Si substrate in sequence by magnetron sputtering. The specific steps are as follows: Place the Si substrate in the magnetron sputtering chamber and evacuate the chamber until the pressure is less than 2×10 -4 Pa; introduce argon gas with a flow rate of 20-60 sccm, modulate the chamber pressure by 0.1-1.0 Pa, increase the temperature to 200-400 °C at a heating rate of 5-10 °C / min, adjust the magnetron sputtering power to 50-100 W, and successively sputter-deposit a Ti layer and a bottom electrode Pt layer to the desired thickness; In step e), the lead zirconate titanate film material is Pb(Zr 0.52 Ti 0.48 )O3.

4. The preparation method according to claim 1, characterized in that The precursor solution concentration is 0.1-0.4 mol / L, stirred at room temperature for 6-12 h, and aged for 24-72 h. During the preparation of the lead zirconate titanate precursor solution, the molar content of the Pb element is in excess of 5-20%.

5. The preparation method according to claim 1, characterized in that The method further comprises the step f): depositing a top electrode Pt layer on the lead zirconate titanate film material obtained in step e) by magnetron sputtering; The thickness of the top electrode Pt layer is 10~30 nm; In step f), the magnetron sputtering conditions are as follows: the sputtering atmosphere is argon, the argon flow rate is 30-60 sccm, the sputtering pressure is 0.1-1.0 Pa, the sputtering power is 50-100 W, and the deposition temperature is room temperature.

6. The preparation method according to claim 1 or 5, characterized in that The method further comprises adding a buffer layer between step a) and step b); the buffer layer is an oxide buffer layer.

7. A lead zirconate titanate film material with ultra-high piezoelectric coefficient, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. The lead zirconate titanate film material according to claim 7, characterized in that: The lead zirconate titanate film material is a 2-4 inch wafer film material.

9. Use of the lead zirconate titanate film material with ultra-high piezoelectric coefficient according to claim 7 or 8 in a piezoelectric micro-electromechanical system.

10. A prototype device of a sensor, characterized in that: The lead zirconate titanate film material with an ultrahigh piezoelectric coefficient as claimed in claim 7 or 8 is used as a piezoelectric film, comprising a substrate and the lead zirconate titanate piezoelectric film material and a top electrode sequentially deposited on the substrate; Or, it includes a substrate and a lead zirconate titanate piezoelectric film material, a buffer layer and a top electrode deposited in sequence on the substrate.

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