Lead zirconate titanate film material with ultrahigh piezoelectric coefficient as well as preparation method and application of lead zirconate titanate film material

Abstract

The invention discloses a lead zirconate titanate film material with an ultrahigh voltage coefficient as well as a preparation method and application of the lead zirconate titanate film material, and belongs to the technical field of electronic material development and film materials. The preparation of the lead zirconate titanate film material is realized by adopting a sol-gel spin-coating method and controlling the annealing times. The piezoelectric film material provided by the invention can be directly deposited on a Si substrate coated with metal Pt, does not need to introduce an additional buffer layer or dope any element, is short in annealing time and simple in preparation process, all required raw materials are cheap and easy to obtain, and the piezoelectric film material particularly has high orientation degree, low coercive voltage and excellent ferroelectric and piezoelectric properties, is suitable for preparing large-size (2-4 inches) wafers, and has a wide application prospect. And huge application potential is shown in the field of piezoelectric micro-electro-mechanical system (MEMS) devices.

Description

Technical Field

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

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or any form of implication that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Piezoelectric materials refer to materials that generate voltage across their two end faces when subjected to pressure, including the direct piezoelectric effect (mechanical stress generates charge) and the inverse piezoelectric effect (electric field induces deformation). As a type of functional material for realizing the mutual conversion of mechanical energy and electrical energy, piezoelectric materials have a wide range of applications in microelectromechanical systems (MEMS) fields such as sensors, transducers, large-displacement actuators, and energy harvesters. Lead zirconate titanate (PZT), as a most representative perovskite-type piezoelectric material, is formed by the solid solution of lead zirconate (PbZrO3) and lead titanate (PbTiO3). Its components exhibit optimal piezoelectric and electromechanical coupling properties near the morphotropic phase boundary (MPB, Zr / Ti~52 / 48). Coupled with its relatively high Curie temperature, it has become the core material of current piezoelectric devices. Although environmentally friendly lead-free piezoelectric materials (such as sodium potassium niobate) have been widely studied, lead zirconate titanate has not been replaced due to its incomparable high piezoelectric activity and reliability. Among them, lead zirconate titanate thin films, due to their characteristics of miniaturization, low power consumption, and high response speed, have become the core materials of miniaturized electronic devices, such as high-precision displacement drivers, micro-nano sensors, and flexible electronic devices.

[0004] Currently, the mainstream preparation methods of lead zirconate titanate thin films include sol-gel method, magnetron sputtering, and pulsed laser deposition (PLD). Although physical vapor deposition techniques (PLD and magnetron sputtering) can prepare high-quality single-crystal thin films, they have high equipment costs, low deposition rates, and strict requirements for the uniformity of target material composition. In addition, the long-time high-temperature deposition process is prone to lead element volatilization and composition deviation of the thin film material, and is prone to generating impurity phases and defects, resulting in large leakage conductance losses, high coercive electric fields, and low breakdown voltage strengths, greatly reducing the piezoelectric performance and stability of the material. Researchers usually introduce buffer layers or perform doping with various elements during the preparation of lead zirconate titanate thin films to improve and enhance their piezoelectric performance. However, these improvement methods have significant drawbacks: using buffer layers such as PbO or LaNiO3 significantly increases the preparation steps and the process complexity; although doping elements (such as La, Mn, etc.) can improve the piezoelectric response, they may increase the leakage current or lower the Curie temperature, making it difficult to optimize parameters such as piezoelectric coefficient and dielectric loss synergistically, thus posing a huge challenge to the large-scale industrial application of lead zirconate titanate films.

[0005] In the prior art, for the film material without a buffer layer, the transverse piezoelectric coefficient of the (111)-oriented PZT film is usually 8 - 9 C / m 2 , or for the film material with a buffer layer added, the transverse piezoelectric coefficient of the (100) / (001)-oriented PZT film is usually 8 - 15 C / m 2 . However, regardless of whether a buffer layer is added or not, most of the preparation processes of the prepared film materials have drawbacks such as complex preparation processes, high costs, and long time, and the prepared film materials do not have ultra-high piezoelectric coefficients, low operating voltages, and low dielectric losses, and are not suitable for preparing lead zirconate titanate films of wafer-level size, which is not conducive to industrial scale-up.

[0006] Therefore, with the development of MEMS devices towards high integration and low drive voltage, the development of wafer-level size lead zirconate titanate films with both ultra-high piezoelectric coefficients, low operating voltages, and low dielectric losses has become an urgent need. There is an urgent need to develop a preparation process for lead zirconate titanate films with low cost, simple process, short annealing time, and scalability to break through the bottleneck of the existing technology. Summary of the Invention

[0007] To solve the deficiencies of the prior art, the purpose of the present invention is to provide a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, its preparation method, and application. The present invention adopts the sol-gel spin coating method, and by controlling the number of annealing times, a lead zirconate titanate film (PZT film) can be directly deposited on a Si substrate coated with metal Pt, which can have a short annealing time (only a few minutes), a simple preparation process, and all the required raw materials are cheap and easily available without introducing an additional buffer layer or doping any elements. In particular, it has advantages such as high orientation degree, low coercive voltage, and excellent ferroelectric and piezoelectric properties, and is suitable for preparing large-sized (2 - 4 inches) wafers, showing great application potential in the field of piezoelectric microelectromechanical system (MEMS) devices.

[0008] To achieve the above purpose, the technical solution of the present invention is as follows: In the first aspect, the present invention provides a preparation method for a lead zirconate titanate film material with an ultra-high piezoelectric coefficient, including the following steps: a) Form a conductive layer on a substrate, and the substrate is a Pt / Ti / SiO2 / Si substrate or a Pt / Ti / Si substrate; b) Prepare a lead zirconate titanate precursor solution by the sol-gel method, and form a precursor film on the conductive layer by the spin coating method; c) Perform drying and pyrolysis treatment on the precursor film; d) Repeat steps b) and c) to form a multi-layer precursor film, and then perform a rapid thermal annealing treatment once. The rapid thermal annealing is carried out in an oxygen atmosphere at 550 - 750 °C for 3 - 10 min; wherein, in repeating steps b) and c) to form a multi-layer precursor film, the number of repetitions is 5 - 8 times; e) Repeat steps b) to d) until the desired film thickness is reached to obtain a lead zirconate titanate film material; In step e), in repeating steps b) to d) until the desired film thickness is reached, taking one rapid thermal annealing treatment as a cycle, repeat 2 - 4 cycles.

[0009] In one or more embodiments, in step a), the substrate is a Si substrate and a Ti layer and a bottom electrode Pt layer sequentially loaded on the Si substrate.

[0010] The Si substrate is Si or Si with a SiO2 oxide layer.

[0011] The thickness of the Si substrate is 0.2 - 1 mm, preferably 0.4 - 0.6 mm, and the most common thickness of Si sold on the market is 0.5 mm.

[0012] The thickness of the Ti layer is 30 - 80 nm. If the Ti layer is too thin, it will affect the bonding force between the Si substrate and the Pt layer, resulting in easy detachment of the Pt electrode.

[0013] The thickness of the bottom electrode Pt layer is 100 - 300 nm. If the Pt layer is too thin, the (111) orientation of the PZT thin film becomes weak, while increasing the thickness of the Pt layer has no effect on the film properties and will increase the economic cost.

[0014] Further, the substrate is a Pt / Ti / SiO2 / Si substrate or a Pt / Ti / Si substrate.

[0015] Further, in step a), the substrate can be a common commercially available product or the Ti layer and the bottom electrode Pt layer are sequentially deposited on the Si substrate by magnetron sputtering.

[0016] The Ti layer is a connection layer between the Si substrate and the Pt bottom electrode to increase the adhesion between the two.

[0017] 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: Put the Si substrate into the magnetron sputtering chamber and evacuate to a chamber pressure lower than 2×10 -4Pa; Argon is introduced with an argon flow rate of 20 - 60 sccm, the chamber pressure is modulated to 0.1 - 1.0 Pa, the heating rate is 5 - 10 °C / min, heated to 200 - 400 °C, and the magnetron sputtering power is adjusted to 50 - 100 W. Then, the Ti layer and the bottom electrode Pt layer are sputter - deposited to the required thickness.

[0018] In one or more embodiments, in step b), the process conditions of the spin - coating method are: the low rotation speed is 600 - 1000 rpm, the spin - coating time is 9 - 15 s, the high rotation speed is 2000 - 5500 rpm, and the spin - coating time is 15 - 35 s.

[0019] 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.

[0020] 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).

[0021] In one or more embodiments, in step d), the annealing temperature is 650 - 750 °C, and the annealing time is 4 - 6 min.

[0022] 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 it is too high, the film will crack; if the annealing temperature is too low, the PZT thin film cannot be crystallized, and if it is too high, its performance will seriously degrade.

[0023] In one or more embodiments, in step d), when repeating steps b) and c) to form a multi - layer precursor film, the number of repetitions is 5 - 8 times. The number of repetitions provided here is a process optimized by previous screening. If the number of repetitions is small, the number of annealing times will be too many, resulting in serious volatilization of Pb in the PZT thin film and significant degradation of its performance; conversely, it will cause cracking of the PZT film as shown in Figure 6 and the performance cannot be tested.

[0024] In one or more embodiments, in step e), when repeating steps b) to d) until the required film thickness is reached, taking one rapid thermal annealing treatment as a cycle, repeat 2 - 4 cycles.

[0025] The number of annealing times is crucial for the preparation of the film material. If only one annealing is performed, it will instead cause the film material to crack, as shown in Figure 6As shown. If the number of annealing times is too many, it will cause excessive volatilization of Pb in the PZT thin film, resulting in the deviation of its composition from the stoichiometric ratio; at the same time, multiple annealing will cause the generation of impurity phases in the thin film, resulting in serious degradation of the thin film performance.

[0026] In one or more embodiments, in step e), the lead zirconate titanate film material is Pb(Zr x Ti 1-x )O3, where 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.

[0027] The thickness of the lead zirconate titanate film material is 0.5 - 1.5 μm. For the present invention, this thickness has the best performance.

[0028] In one or more embodiments, in step b), the preparation method of the lead zirconate titanate precursor solution: calculate the contents of the three raw materials of Pb, Zr, and Ti required for preparing the solution according to the stoichiometric ratio; uniformly mix ethylene glycol monomethyl ether and glacial acetic acid at a volume ratio of (1.1 - 1.3):1, then add the weighed Pb raw material, and stir at room temperature until the Pb raw material is completely dissolved; then add an appropriate volume (the volume here depends on the concentration and volume of the prepared precursor solution and has no fixed range) of acetylacetone and stir evenly, then successively add the weighed Ti and Zr raw materials, and stir and mix evenly; finally, add an appropriate amount of ethylene glycol monomethyl ether (the required volume depends on the concentration and volume of the final precursor solution, so no fixed value needs to be determined) to adjust the precursor solution, stir at room temperature, and stand for aging.

[0029] Among them, ethylene glycol monomethyl 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; acetylacetone is used as a stabilizer for the precursor solution to prevent it from generating precipitation.

[0030] Preferably, the concentration of the precursor solution is 0.1 - 0.4 mol / L, such as it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, preferably 0.1 - 0.2 mol / L. Stir at room temperature for 6 - 12 h and stand for aging for 24 - 72 h.

[0031] During the preparation of the lead zirconate titanate precursor solution, the molar content of Pb element is 5-20% in excess, such as 5% in excess, 9% in excess, 10% in excess, 11% in excess, 15% in excess, 20% in excess. It is preferably 5-15% in excess, more preferably 9-11% in excess, and most preferably 10% in excess. The purpose of the excess is to supplement the volatile loss of Pb element during the heat treatment of the lead zirconate titanate thin film. In Example 1, if the molar content of Pb element is 10% in excess, it means that the obtained lead zirconate titanate precursor material should be Pb 1.1 (Zr x Ti 1-x )O3. However, in the actual preparation process, due to the loss of Pb element, the finally prepared material is Pb(Zr x Ti 1-x )O3.

[0032] In one or more embodiments, it further includes step f): depositing a top electrode Pt layer on the lead zirconate titanate film material obtained in step e) by magnetron sputtering.

[0033] Furthermore, the thickness of the top electrode Pt layer is 10-30 nm.

[0034] Furthermore, in step f), the conditions of 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.

[0035] In one or more embodiments, it further includes adding a buffer layer 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 ~200 nm.

[0036] The specific steps are as follows: using an oxide ceramic as the sputtering target, sputtering and depositing the buffer layer by radio frequency magnetron sputtering. 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).

[0037] In the second aspect, the present invention provides a lead zirconate titanate film material with a super high piezoelectric coefficient, which is prepared by the above preparation method.

[0038] The lead zirconate titanate film material is a large-sized (2-4 inches), highly uniform wafer film material.

[0039] When the Pb(Zr 0.52 Ti 0.48 )O3 film material is directly grown on the bottom electrode without introducing any buffer layer, the Pb(Zr 0.52 Ti 0.48 )O3 film material shows (111) preferred orientation growth.

[0040] When a buffer layer is introduced, the Pb(Zr 0.52 Ti 0.48 )O3 film material shows excellent (001) growth orientation.

[0041] Thirdly, the present invention provides an application of the above-mentioned lead zirconate titanate film material with ultra-high piezoelectric coefficient in piezoelectric microelectromechanical systems (MEMS). Preferably, the piezoelectric microelectromechanical system includes sensors, actuators, transducers, and resonators.

[0042] Fourthly, the present invention provides a prototype device of a sensor, including a substrate and a 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 sequentially deposited on the substrate.

[0043] One or some of the above technical solutions have the following advantages or beneficial effects: (1) The present invention uses the sol-gel spin coating method and by controlling the number of annealing times, realizes the preparation of the lead zirconate titanate piezoelectric film. This preparation method is simple and does not require high-vacuum deposition equipment (such as magnetron sputtering, PLD) that is expensive and complex to operate, with lower investment and maintenance costs. At the same time, the raw material reagents required for preparing the lead zirconate titanate film material provided by the present invention are all commercially available and very cheap, and have a more significant economic advantage than 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.

[0044] (2) The precursor components required for preparing the lead zirconate titanate film material provided by the present invention can be precisely regulated, molecular-level uniformity can be achieved, and component segregation can be reduced, thereby ensuring that the prepared lead zirconate titanate film material has uniform composition, excellent stoichiometry, and uniform film material properties.

[0045] (3) The lead zirconate titanate film material with ultra-high piezoelectric coefficient provided by the present invention can be directly deposited on the Si substrate coated with the Pt bottom electrode without the need to additionally introduce oxide buffer layers such as lanthanum nickelate and strontium ruthenate, and without doping any elements. The preparation method and process are simpler, suitable for preparing large-sized (2-4 inches), highly uniform wafer film materials, and facilitating industrial promotion and large-scale production.

[0046] (4) The lead zirconate titanate film material with a high piezoelectric coefficient provided by the present invention has a short annealing time (only a few minutes) and does not require a long high-temperature deposition process (the high-temperature deposition time of methods such as magnetron sputtering and PLD is usually several hours to more than ten hours). It can effectively inhibit the volatilization of lead elements in the film and the deviation of composition caused by long-term heat treatment, avoid the generation of defects such as secondary phases and oxygen vacancies, and reduce the leakage current and loss of the film material.

[0047] (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 degree, low coercive voltage (<5 V), high dielectric constant (2000 - 2200), and low leakage current density (<2x10 -5 A / cm 2 ) and excellent dielectric loss (<0.09) properties. In particular, it has a high saturation polarization intensity (80 - 120 μC / cm 2 ), a high remanent polarization intensity (40 - 65 μC / cm 2 ), and an ultra-high transverse piezoelectric coefficient (8 - 13 C / m 2 ). Therefore, through the preparation method provided by the present invention, on the basis of no buffer layer and no doping of any elements, the technical effect equivalent to that of adding a buffer layer can be achieved, and it also has better technical effects than the film materials without adding a buffer layer in the prior art (the reported transverse piezoelectric coefficient of (111)-oriented PZT thin films is usually 8 - 9 C / m 2 ). Importantly, the preparation method of the present invention has the advantages of simpler process, lower cost, and shorter annealing time.

[0048] (6) When using the preparation method provided by the present invention to prepare the lead zirconate titanate film material by adding a buffer layer, the average transverse piezoelectric coefficient e 31,f is 16.5 C / m 2 , and the highest transverse piezoelectric coefficient e 31,f can reach 17.6 C / m 2 . At the same time, it has 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 film materials with buffer layers added in the prior art (the reported transverse piezoelectric coefficient of (100) / (001)-oriented PZT thin films is usually 8 - 15 C / m 2 ), it has better technical effects, and the preparation method of the present invention has the advantages of simpler process, lower cost, and shorter annealing time. Description of the Drawings

[0049] The accompanying drawings of the specification, which form a part of the present invention, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0050] Figure 1 XRD diagrams of the lead zirconate titanate film materials prepared in Example 1 and Example 11 of the present invention and the pole figures of the corresponding lead zirconate titanate films, wherein (a1) and (a2) are the XRD diagrams of the lead zirconate titanate film materials prepared in Example 1 and Example 11 respectively, and (b1) and (b2) are the pole figures of the lead zirconate titanate film materials prepared in Example 1 and Example 11 respectively; Figure 2 Surface and cross-section scanning electron microscope images of the lead zirconate titanate film material prepared in Example 1 of the present invention; Figure 3 Electric hysteresis loop and polarization reversal current density curve of the lead zirconate titanate film material prepared in Example 1 of the present invention; Figure 4 Leakage current density and dielectric frequency curve diagrams of the lead zirconate titanate film materials prepared in Example 1 and Example 11 of the present invention, wherein (a) is the leakage current density diagram and (b) is the dielectric frequency curve diagram; Figure 5 Schematic diagram of a transverse piezoelectric test device, tip displacement and transverse piezoelectric coefficient of a lead zirconate titanate film material cantilever beam, and a physical diagram of a lead zirconate titanate film wafer, wherein (a) is the schematic diagram of the transverse piezoelectric test device, (b) is the tip displacement and transverse piezoelectric coefficient of the lead zirconate titanate film material cantilever beams prepared in Example 1, Example 10, and Example 11 of the present invention, and (c) is the physical diagram of a 2-inch lead zirconate titanate film wafer prepared in Example 2; Figure 6 Physical diagram of the lead zirconate titanate film material prepared in Comparative Example 1 of the present invention. Detailed Description of the Invention

[0051] All raw materials required for the lead zirconate titanate film material provided by the present invention are commercially available products and are inexpensive and easily available.

[0052] 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.

[0053] Example 1 A preparation method of a lead zirconate titanate film material with a super high piezoelectric coefficient, the specific steps are as follows: (1) Substrate treatment and bottom electrode preparation Using a semiconductor Si wafer or Si with an SiO2 oxide layer as the substrate (size: 20×20×0.5 mm), ultrasonic cleaning is carried out with anhydrous ethanol, and then dried with high-purity nitrogen. After that, the Si wafer is placed in the sample holder of the magnetron sputtering chamber. The vacuum is pumped until the chamber pressure is lower than 2×10 -4 Pa; argon is introduced, and the argon flow rate is 40 sccm. The Si wafer is heated to 300 °C at a heating rate of 5 °C / min, and the chamber pressure is adjusted to 0.3 Pa; using radio frequency magnetron sputtering technology, a metal Ti layer and a metal Pt electrode layer are sequentially deposited on the Si substrate. The sputtering power is adjusted to 55 W, and the deposition times are controlled to be 5 min and 15 min respectively. Among them, Pt is the bottom electrode layer, and the Ti layer is used to enhance the bonding force between the Si substrate and the Pt electrode layer.

[0054] The synthesis of lead zirconate titanate precursor is based on the chemical stoichiometry of Pb(Zr 0.52 Ti 0.48 )O3 to calculate the contents of three raw materials, Pb, Zr, and Ti, required for synthesizing its precursor sol. The molar content of Pb element is in excess by 10%. Ethylene glycol monomethyl ether and glacial acetic acid are uniformly mixed at a volume ratio of 1.25∶1, and then the weighed Pb raw material is added. Stir at room temperature until the Pb raw material is completely dissolved; then add an appropriate volume of acetylacetone and stir evenly. Then, the weighed Ti and Zr raw materials are added in sequence and stirred and mixed evenly; finally, an appropriate amount of ethylene glycol monomethyl ether is added to adjust the concentration of the precursor solution to 0.2 mol / L, and stir at room temperature for 6 h, and stand for aging for 24 h for standby. Among them, the selected Pb raw material is lead acetate trihydrate, the Ti raw material is tetrabutyl titanate, the Zr raw material is zirconium n-propoxide, ethylene glycol monomethyl ether and glacial acetic acid are used as solvents, and acetylacetone is used as a stabilizer.

[0055] The preparation of lead zirconate titanate thin material: The lead zirconate titanate precursor synthesized in step (2) is first dropped onto the substrate in step (1) through a syringe, and then a crystallized lead zirconate titanate thin material is obtained through the processes of spin coating, drying, pyrolysis, and annealing. Annealing is carried out once every 8 times of spin coating, drying, and pyrolysis as a cycle, and this cycle is repeated 3 times to obtain a lead zirconate titanate film material with the required thickness. Among them, the spin coating process is: the low rotation speed is 800 rpm, and the spin coating time is 12 s; the high rotation speed is 3500 rpm, and the spin coating time is 30 s. The drying, pyrolysis, and annealing processes are: the drying temperature is 230 °C, and the drying time is 3 min; the pyrolysis temperature is 450 °C, and the pyrolysis time is 3 min; the annealing temperature is 700 °C, and the annealing time is 5 min, and the annealing atmosphere is oxygen.

[0056] Top electrode preparation: A thin layer of metal Pt was sputter - deposited on the surface of the lead zirconate titanate film obtained in step (3) by magnetron sputtering to serve 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. After sputtering, the sample was taken out.

[0057] Cantilever beam preparation: The lead zirconate titanate film sample obtained in step (4) was cut into cantilever beams with a size of 20 mm (length) × 3 mm (width) for piezoelectric performance testing.

[0058] Example 2 Different from Example 1, the size of the Si substrate used in step (1) was a 2 - inch wafer, and the other steps and process parameters were the same as those in Example 1. Through performance testing, the performance of the lead zirconate titanate film prepared in this example is shown in Table 1.

[0059] Example 3 Different from Example 1, during the synthesis of the lead zirconate titanate precursor sol in step (2), the molar content of Pb element was in excess by 5% or 15% or 20%. The other steps and process parameters were the same as those in Example 1. The saturation polarization, remanent polarization, and transverse piezoelectric coefficient of the lead zirconate titanate film with 20% excess Pb element prepared in this example were 96 μC / cm 2 、47 μC / cm 2 、10.1 C / m 2 .

[0060] Example 4 Different from Example 1, the concentration of the lead zirconate titanate precursor sol synthesized in step (2) was 0.1 mol / L or 0.3 mol / L or 0.4 mol / L. The other steps and process parameters were the same as those in Example 1. Through performance testing, the saturation polarization, remanent polarization, and transverse piezoelectric coefficient of the lead zirconate titanate film prepared with a precursor sol concentration of 0.4 mol / L in this example were 98 μC / cm 2 、48 μC / cm 2 、11.2 C / m 2 .

[0061] Example 5 Different from Example 1, in step (3), annealing was carried out once every 6 times of spin - coating, drying, and pyrolysis as a cycle, and this cycle was repeated 3 times or 4 times. The other steps and process parameters were the same as those in Example 1. Through performance testing, the saturation polarization, remanent polarization, and transverse piezoelectric coefficient of the lead zirconate titanate film obtained with 4 repeated cycles in this example were 118 μC / cm 2 、61 μC / cm 2 、12.2 C / m 2 .

[0062] Example 6 Different from Example 1, in step (3), the spin coating process is as follows: the low rotation speed is 600 rpm, and the spin coating time is 15 s; the high rotation speed is 5000 rpm, and the spin coating time is 20 s. Other steps and process parameters are the same as those in Example 1. After performance testing, the saturation polarization, remanent polarization and transverse piezoelectric coefficient of the lead zirconate titanate film prepared in this example are 101 μC / cm 2 , 47 μC / cm 2 , 10.5 C / m 2 .

[0063] Example 7 Different from Example 1, in step (3), the drying, pyrolysis and annealing processes are as follows: the drying temperature is 150 °C, and the drying time is 3 min; the pyrolysis temperature is 350 °C, and the pyrolysis time is 5 min; the annealing temperature is 600 °C, and the annealing time is 8 min. Other steps and process parameters are the same as those in Example 1. After performance testing, the saturation polarization, remanent polarization and transverse piezoelectric coefficient of the lead zirconate titanate film prepared in this example are 81 μC / cm 2 , 40 μC / cm 2 , 8.6 C / m 2 .

[0064] Example 8 Different from Example 1, in step (4), the sputtering deposition time of the top electrode Pt thin layer is 2 min or 3 min. Other steps and process parameters are the same as those in Example 1. After performance testing, the piezoelectric coefficient of the lead zirconate titanate film prepared in this example is almost the same as that in Example 1.

[0065] Example 9 Different from Example 1, in step (5), the width of the cantilever beam of the lead zirconate titanate film sample cut is 2 mm or 4 mm. Other steps and process parameters are the same as those in Example 1. After performance testing, the piezoelectric coefficient of the lead zirconate titanate film prepared in this example is almost the same as that in Example 1.

[0066] Example 10 Different from Example 1, in step (1), a commercially available Pt / Ti / SiO2 / Si substrate finished product (Hefei Anjing Crystal Materials Co., Ltd., size: 20×20×0.5 mm) is used. Other steps and process parameters except step (1) are the same as those in Example 1. After performance testing, the piezoelectric properties of the lead zirconate titanate film prepared in this example are as shown in (b) of Figure 5 .

[0067] Example 11 Different from Example 1, the preparation of a buffer layer is added between step (2) and step (3). That is, after sputter-depositing the Pt electrode in step (1), lanthanum nickelate oxide ceramic is used as the sputtering target, and the lanthanum nickelate buffer layer is sputter-deposited by radio frequency magnetron sputtering. 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. 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 example are as Figure 5 shown in (b) of

[0068] Comparative Example 1 Different from Example 1, in step (3), after spin coating, drying, and pyrolysis processes, a lead zirconate titanate film with the required thickness is obtained, and finally the film material is annealed once. Other steps and process parameters are the same as those in Example 1.

[0069] Figure 1 The XRD patterns and pole figures of the lead zirconate titanate film materials prepared in Example 1 and Example 11 are shown 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 impurity phases. In particular, it shows a strong (111) preferred orientation growth, and almost no diffraction peaks of other orientations can be detected. In contrast, due to the induction effect of the buffer layer in the lead zirconate titanate film material in Example 11, the grain growth orientation 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 finished product in Example 10 has the same XRD pattern as the lead zirconate titanate film material in Example 1. Figure 2 The surface and cross-sectional scanning electron microscope images of the lead zirconate titanate film prepared in Example 1 are shown. Uniform and dense grains can be observed on the surface. It can be seen from the cross-section that the lead zirconate titanate film layer is ~882 nm.

[0070] After performance testing, the lead zirconate titanate film materials prepared in Examples 1 to 11 have excellent properties.

[0071] Figure 3 It is shown that the lead zirconate titanate film prepared in Example 1 has a high polarization intensity (the saturated polarization intensity value is as high as 113 μC / cm 2 , and the remanent polarization intensity value is 55 μC / cm 2 ) and a breakdown voltage resistance (≥125 V). Its polarization reversal current curve shows two obvious reversal current peaks.

[0072] Figure 4Leakage current density and dielectric frequency curves of the lead zirconate titanate films prepared in Example 1 and Example 11 indicate 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 a dielectric loss (<0.09); while the lead zirconate titanate film material prepared by adding a buffer layer exhibits a lower leakage current density (<8x10 -6 A / cm 2 ) and a dielectric loss (<0.07), and its dielectric constant is 1700 - 2100.

[0073] Figure 5 In (a) of is a schematic diagram of the lateral piezoelectric test device; Figure 5 In (b) of Figure 5 are the tip displacements and lateral piezoelectric coefficients of the lead zirconate titanate film cantilevers prepared in Example 1, Example 10, and Example 11. It can be seen that the prepared lead zirconate titanate film exhibits a large tip displacement of the cantilever and approximately linearly increases with the applied voltage, and the lateral piezoelectric coefficient shows good stability within the applied voltage range (4 - 15 V). Among them, the average lateral piezoelectric coefficient e 31,f ~12.2 C / m 2 of the lead zirconate titanate film prepared in Example 1, and the maximum e 31,f is up to 12.9 C / m 2 , which is the lead zirconate titanate film with the highest lateral piezoelectric coefficient reported so far directly obtained on the Si substrate with Pt electrodes. In Example 10, the lead zirconate titanate film obtained by using a commercially available Pt / Ti / SiO2 / Si finished product as the substrate has almost no difference in piezoelectric coefficient from the lead zirconate titanate film in Example 1. Within the same voltage range, the average lateral piezoelectric coefficient e 31,f of the lead zirconate titanate film prepared in Example 11 is 16.5 C / m 2 , and the highest e 31,f can reach 17.6 C / m 2 . Thus, it can be seen that compared with the lead zirconate titanate film with a lanthanum nickelate buffer layer in Example 11, the lateral piezoelectric coefficients of the lead zirconate titanate films without a buffer layer prepared in Example 1 or Example 10 of the present invention are not much different, but the preparation methods and processes are simpler. Figure 5 In (c) of Figure 5 is a physical picture of the 2-inch lead zirconate titanate film wafer prepared in Example 2, and the performance of this 2-inch wafer-level lead zirconate titanate film is tested. The test areas marked in the figure are Region 1, Region 2, Region 3, Region 4, and Region 5 from top to bottom in sequence, and the test results are shown in Table 1. From this, it can be seen that the 2-inch wafer-level lead zirconate titanate film prepared by the present invention has excellent electrical properties and lateral piezoelectric properties, is suitable for preparing large-size (2 - 4 inches), high-uniformity wafer-level film materials, and is convenient for industrial promotion and large-scale production.

[0074] Figure 6 It is a physical picture of the lead zirconate titanate film material obtained in Comparative Example 1. It can be seen from the figure that when annealing is carried out only once, the prepared lead zirconate titanate film material will crack. Therefore, the number of annealing times is very important for the successful preparation of the film material.

[0075] Table 1 Performance of the 2-inch lead zirconate titanate film obtained in Example 2

[0076] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a lead zirconate titanate film material with a high piezoelectric coefficient, characterized in that, It includes the following steps: a) Form a conductive layer on a substrate, where the substrate is a Pt / Ti / SiO2 / Si substrate or a Pt / Ti / Si substrate; b) Prepare a lead zirconate titanate precursor solution by the sol-gel method, and form a precursor film on the conductive layer by spin coating; c) Dry and pyrolyze the precursor film; d) Repeat steps b) and c) to form a multi-layer precursor film, and then perform a rapid thermal annealing treatment. The rapid thermal annealing is carried out in an oxygen atmosphere at 550 - 750 °C for 3 - 10 min; among them, when repeating steps b) and c) to form a multi-layer precursor film, the number of repetitions is 5 - 8 times; e) Repeat steps b) to d) until the desired film thickness is reached to obtain a lead zirconate titanate film material; In step e), when repeating steps b) to d) until the desired film thickness is reached, taking one rapid thermal annealing treatment as a cycle, repeat 2 - 4 cycles.

2. The preparation method according to claim 1, wherein, In step a), the substrate is a Si substrate and a Ti layer and a bottom electrode Pt layer sequentially loaded on the Si substrate; The Si substrate is Si or Si with a SiO2 oxide layer; 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; Or, in step b), the process conditions of the spin coating method are: the low rotation speed is 600 - 1000 rpm, the spin coating time is 9 - 15 s, the high rotation speed is 2000 - 5500 rpm, and the spin coating time is 15 - 35 s; Or, in step c), the drying temperature is 150 - 300 °C and the drying time is 2 - 5 min; In step c), the pyrolysis temperature is 350 - 500 °C and the pyrolysis time is 2 - 10 min; In step e), the lead zirconate titanate film material is Pb(Zr x Ti 1-x )O3, where 0.4 ≤ x ≤ 0.6; the thickness of the lead zirconate titanate film material is 0.5 - 1.5 μm.

3. The preparation method according to claim 2, wherein, In step a), the substrate is deposited with a Ti layer and a bottom electrode Pt layer on the Si substrate by magnetron sputtering. The specific steps are: Place the Si substrate into a magnetron sputtering chamber and evacuate the chamber until the chamber pressure is lower than 2×10 -4 Pa; introduce argon gas with a flow rate of 20 - 60 sccm, modulate the chamber pressure to 0.1 - 1.0 Pa, with a heating rate of 5 - 10 °C / min, heat up to 200 - 400 °C, adjust the magnetron sputtering power to 50 - 100 W, and successively sputter-deposit the Ti layer and the bottom electrode Pt layer to the required 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, In step b), the preparation method of the lead zirconate titanate precursor solution: According to the stoichiometric ratio of Pb(Zr 0.52 Ti 0.48 )O3, calculate the contents of the three raw materials of Pb, Zr, and Ti required to synthesize its precursor sol respectively. Uniformly mix ethylene glycol monomethyl ether and glacial acetic acid at a volume ratio of (1.1 - 1.3):1, then add the Pb raw material and stir until the Pb raw material is completely dissolved; then add acetylacetone and stir evenly, and then add the Ti and Zr raw materials in sequence and stir well to mix evenly; finally, add ethylene glycol monomethyl ether to adjust the precursor solution, stir at room temperature, and let it stand for aging; The concentration of the precursor solution is 0.1 - 0.4 mol / L, stirred at room temperature for 6 - 12 h, and left to age for 24 - 72 h; During the preparation of the lead zirconate titanate precursor solution, the molar content of the Pb element is 5 - 20% in excess.

5. The preparation method according to claim 1, characterized in that, It further includes step f): deposit 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 conditions of 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, and the deposition temperature is room temperature.

6. The preparation method according to claim 1 or 5, characterized in that, It further includes 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 a high piezoelectric coefficient, characterized in that, Prepared by the preparation method described in any one of claims 1 - 6.

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

9. Application of the lead zirconate titanate film material with a super high piezoelectric coefficient described in claim 7 or 8 in a piezoelectric microelectromechanical system.

10. A prototype device of a sensor, characterized in that, Using the lead zirconate titanate film material with a high piezoelectric coefficient described in claim 7 or 8 as the piezoelectric film, comprising a substrate and a lead zirconate titanate piezoelectric film material and a top electrode sequentially deposited on the substrate; Or, comprising a substrate and a lead zirconate titanate piezoelectric film material, a buffer layer and a top electrode sequentially deposited on the substrate.

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