Multilayer orientation induction layer structure, piezoelectric film and preparation method of piezoelectric film

Abstract

The invention discloses a multi-layer orientation induction layer structure, a piezoelectric film and a preparation method of the piezoelectric film, the multi-layer orientation induction layer structure specifically comprises at least one group of laminated units stacked in sequence, and each laminated unit comprises a ZnO orientation induction layer and a ZnO piezoelectric layer deposited on the ZnO orientation induction layer; the electrode layer covers the upper end face of the multi-layer orientation induction layer structure, and the substrate is arranged on the lower end face of the multi-layer orientation induction layer structure and used for bearing the insulating layer. According to the invention, ZnO homogeneous with the piezoelectric layer is used as an orientation induction layer, the step-by-step fine regulation and control of the crystal growth process are realized through multi-layer iterative deposition, the problem of new interface lattice mismatch caused by a heterogeneous interface is effectively avoided, the preferred orientation trend of the ZnO piezoelectric layer along the c-axis (002) direction is strengthened, the scattering of a crystal boundary and crystal defects to carriers is effectively reduced, and the performance of the piezoelectric device is improved. The dielectric loss and the leakage current density are reduced, and the breakdown field strength and the device reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric thin film preparation technology, and more specifically, to a multilayer orientation-inducing layer structure, a piezoelectric thin film, and a method for preparing a piezoelectric thin film. Background Technology

[0002] Zinc oxide (ZnO), as a group II-VI wide bandgap semiconductor material, possesses excellent piezoelectric properties, dielectric properties, and chemical stability, and is widely used in piezoelectric ultrasonic sensors, transducers, and microelectromechanical systems (MEMS). The piezoelectric properties of ZnO are highly dependent on its crystal structure, especially the degree of preferred orientation along the c-axis (002). Highly c-axis oriented ZnO films can achieve maximum ion displacement polarization under the action of an electric field, thus exhibiting higher piezoelectric and dielectric constants.

[0003] Currently, to prepare high-quality c-axis oriented ZnO thin films on heterogeneous substrates such as silicon and alloys, buffer layers, such as AlN, MgO, and SiO2, are typically introduced. While these buffer layers can partially improve the nucleation and growth behavior of ZnO, the differences in lattice constants and coefficients of thermal expansion between the buffer layer and ZnO easily lead to interface and lattice mismatch problems, resulting in high defect density and residual stress. These interface defects become charge traps and scattering centers, thereby degrading the dielectric properties of the film, manifested as increased dielectric loss, increased leakage current, and weakened uniformity and reliability of the piezoelectric response.

[0004] Furthermore, for cutting-edge applications such as aero-engine monitoring and high-temperature environment sensing, traditional technical solutions suffer from the following problems: On the one hand, while the commonly used SiO2 insulating layer has good insulation performance, its mechanical strength and thermal conductivity are low. Under continuous high temperature and high mechanical vibration loads, it is prone to performance degradation or failure, making it difficult to meet the long-term reliability requirements under extreme conditions. On the other hand, although Cr, Ti, and other materials are easy to adhere to as electrode materials, their electrical conductivity is relatively low, and their high-temperature oxidation resistance is poor. After oxidation, the electrical conductivity drops sharply, leading to sensor signal distortion or even loss of function.

[0005] In view of this, the present invention proposes a method that uses ZnO, which is homogeneous with the piezoelectric layer, as an orientation induction layer, and achieves step-by-step fine control of the crystal growth process through multi-layer iterative deposition, which effectively improves the piezoelectric performance and reliability of the piezoelectric thin film under high temperature and harsh environment. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a multilayer orientation-inducing layer structure, a piezoelectric thin film, and a method for preparing the piezoelectric thin film. In this invention, the multilayer orientation-inducing layer structure includes:

[0007] At least one set of stacked units are stacked sequentially. Each stacked unit includes a ZnO orientation-inducing layer and a ZnO piezoelectric layer deposited on the ZnO orientation-inducing layer. The ZnO orientation-inducing layer is used to regulate the crystal growth orientation of the ZnO piezoelectric layer so that it maintains a continuous c-axis (002) preferred orientation.

[0008] Furthermore, in the technical solution of the present invention, the number of stacked units is 1-4 groups, the thickness of the ZnO orientation-inducing layer is 50-350nm, and the thickness of the ZnO piezoelectric layer is 1-4μm.

[0009] A piezoelectric thin film, comprising:

[0010] The aforementioned multi-layer orientation-inducing layer structure;

[0011] An electrode layer covering the upper surface of the multilayer orientation-inducing layer structure;

[0012] An insulating layer disposed on the lower end face of the multilayer orientation-inducing layer structure;

[0013] And a substrate for supporting the insulating layer.

[0014] Furthermore, in the technical solution of the present invention, the electrode layer is made of Ag or Au and has a thickness of 100-300 nm.

[0015] Furthermore, in the technical solution of the present invention, the substrate is single-crystal silicon or an alloy block with a surface roughness of 0.1-0.16 μm.

[0016] Furthermore, in the technical solution of the present invention, the insulating layer is made of Si3N4 or SiC and has a thickness of 100-300nm.

[0017] A piezoelectric thin film preparation process includes the following steps:

[0018] ① Pre-treat the substrate;

[0019] ② Deposit an insulating layer on the pretreated substrate surface;

[0020] ③ A ZnO orientation-induced layer is deposited on the insulating layer by radio frequency magnetron sputtering;

[0021] ④ A ZnO piezoelectric layer is deposited on the ZnO orientation-induced layer by radio frequency magnetron sputtering;

[0022] ⑤ Deposit an electrode layer on the topmost ZnO piezoelectric layer.

[0023] Furthermore, in the technical solution of the present invention, the steps of depositing a ZnO orientation-inducing layer and depositing a ZnO piezoelectric layer are repeated n times, where n is 0-3, to obtain a multilayer structure with 1-4 sets of stacked units.

[0024] Furthermore, in the technical solution of the present invention, the process parameters for depositing the ZnO orientation-induced layer include: target-substrate distance 60-65 mm, sputtering pressure 1.0-3.0 Pa, power 40-70 W, and sputtering time 1-2.5 hours;

[0025] The process parameters for depositing ZnO piezoelectric layers include: RF power 200-300 W, target-substrate distance 60-65 mm, sputtering pressure 0.5-1.5 Pa, and sputtering time 4-8 hours.

[0026] Effective gain:

[0027] In the technical solution of this invention, ZnO, which is homogeneous with the piezoelectric layer, is used as the orientation induction layer. Through multi-layer iterative deposition, the crystal growth process is precisely controlled in stages. This effectively avoids the lattice mismatch problem caused by the heterogeneous interface. Each ZnO induction layer serves as a "seed template" for subsequent growth: the first induction layer mainly overcomes the lattice mismatch with the substrate; subsequent induction layers correct and reguide potential lattice defects and orientation deviations in the underlying layers, gradually constructing a highly ordered, well-integrity textured template structure. This multi-layer architecture significantly reduces the adverse effects of interface trap state concentration and local polarization charge, suppresses the interference of random spontaneous polarization on the overall piezoelectric performance, and thus strengthens the preferred orientation trend of the ZnO piezoelectric layer along the c-axis (002) direction.

[0028] Furthermore, the ZnO-induced layer effectively reduces the free wave height (FWHM) of the (002) crystal plane of the piezoelectric thin film, thereby improving the crystallinity of zinc oxide. When an external electric field is applied, the highly c-axis oriented Zn inside the thin film... 2+ and O 2- Synergistic displacement polarization along the polar axis enhances both the dielectric constant and piezoelectric response. Simultaneously, the highly ordered grain arrangement effectively reduces the scattering of charge carriers by grain boundaries and crystal defects, lowering dielectric loss and leakage current density, and improving breakdown field strength and device reliability.

[0029] Finally, Si3N4 or SiC is used to replace the conventional SiO2 insulating layer. Utilizing the material's high hardness and excellent thermal conductivity, the mechanical strength and heat dissipation performance of the thin film are significantly enhanced, enabling it to withstand harsh environments with high vibration and ultra-high temperatures, such as those found in aero-engines. The electrode layer is made of Ag or Au, whose high conductivity and resistance to high-temperature oxidation ensure the accuracy and long-term stability of signal transmission in high-temperature environments.

[0030] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0031] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the structure of the piezoelectric thin film (ZnO M-OIL-1) with a single-layer orientation-inducing layer of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the piezoelectric thin film (ZnO M-OIL-2) with a double-layer orientation-inducing layer according to the present invention;

[0034] Figure 3 This is a schematic diagram of the structure of the piezoelectric thin film (ZnO M-OIL-4) with four orientation-inducing layers of the present invention;

[0035] Figure 4 XRD patterns (a) and orientation analysis diagrams (b) of embodiments 1-3 of the present invention are shown.

[0036] Figure 5 This is the XRD pattern of Comparative Example 1 of the present invention;

[0037] Figure 6 This is a TEM image of the ZnO piezoelectric thin film in Experimental Example 2 of the present invention;

[0038] Figure 7 This is a high-resolution transmission electron microscope image of Embodiment 1 of the present invention;

[0039] Figure 8 The images show the surface morphology and cross-sectional structure of the ZnO piezoelectric thin films in Experimental Examples 1-3 of this invention, as shown in the SEM images.

[0040] Figure 9 The diagram shows the composition of the ZnO piezoelectric thin film and the Zn / O ratio for Experimental Examples 1-3 of this invention.

[0041] Figure 10 The figures show the nanoindentation test results of ZnO piezoelectric thin films in Experimental Examples 1-3 of this invention;

[0042] Figure 11 The piezoelectric response diagrams of the ZnO piezoelectric thin film PFM in Experimental Examples 1-3 of this invention are shown.

[0043] Figure 12 The diagrams show the amplitude probability density distribution, phase probability density distribution, and the relationship between bias voltage and displacement / phase of the ZnO piezoelectric thin film PFM in Experimental Examples 1 and 3 of the present invention.

[0044] Figure 13This is the PFM probability density diagram of Comparative Example 1 of the present invention;

[0045] Figure 14 XPS images of ZnO piezoelectric thin films from Experimental Examples 1 and 3 of this invention;

[0046] Figure 15 The valence band photoelectron spectroscopy and ultraviolet-visible absorption spectra of ZnO piezoelectric thin films in Experimental Examples 1 and 3 of the present invention are shown below.

[0047] Figure 16 This is a flowchart illustrating the preparation process of the ZnO piezoelectric thin film according to the present invention.

[0048] The structure consists of 1 substrate, 2 insulating layer, 3 ZnO orientation-inducing layer, 4 ZnO piezoelectric layer, and 5 electrode layer. Detailed Implementation

[0049] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0050] This invention proposes a multilayer orientation-inducing layer structure, comprising:

[0051] At least one set of stacked units are stacked sequentially. Each stacked unit includes a ZnO orientation-inducing layer and a ZnO piezoelectric layer deposited thereon. The orientation-inducing layer is used to regulate the crystal growth orientation of the ZnO piezoelectric layer so that it maintains a continuous c-axis (002) preferred orientation.

[0052] Specifically, the ZnO orientation-induced layer is prepared by magnetron sputtering with a thickness of 50-350 nm; the ZnO piezoelectric layer is deposited on the upper surface of the ZnO orientation-induced layer by magnetron sputtering with a thickness of 1-4 μm and has strong c-axis (002) orientation growth characteristics.

[0053] In this embodiment, the number of stacked units is 1-4 groups, and the preferred number of stacked units is 2 groups.

[0054] It is understandable that there is a significant difference in lattice constant between the ZnO piezoelectric layer and common substrates such as silicon and alloys, and direct deposition would lead to high interfacial stress and numerous defects. The pre-sputtered ZnO orientation-inducing layer, as a buffer layer, has lattice parameters between the substrate and the ZnO dielectric layer, which can gradually transition lattice distortion and reduce dislocation density. Moreover, the surface of the pre-sputtered ZnO orientation-inducing layer has a high density of (002) crystal plane exposure sites, and the subsequently deposited ZnO atoms preferentially grow epitaxially along these sites to form a consistent c-axis arrangement. The subsequent orientation-inducing layer plays a role in grain reguiding and adjustment during the growth process, effectively correcting possible local orientation deviations and defects in the underlying layer, forming a more complete and stable texture template. Furthermore, by setting multiple sets of orientation-inducing layers, staged and multi-level grain orientation control can be achieved, further strengthening the preferred orientation trend of the ZnO dielectric layer.

[0055] It should be noted that the wurtzite structure of ZnO has a polar c-axis, exhibiting spontaneous polarization along the (002) direction. The surface energy densities of different crystal planes, such as (002), (110), and (100), are 99, 123, and 209 eV / nm, respectively. 2 The (002) crystal plane is the most thermodynamically stable because it has the lowest surface energy. When the thin film is highly oriented along the c-axis (002), the grains are highly ordered and there are few grain boundaries, which reduces carrier scattering and interface trap states, thereby reducing dielectric loss. However, multi-oriented mixed thin films have high grain boundary density and are prone to forming defects such as oxygen vacancies and zinc interstitials. These defects act as charge traps, increasing leakage current and dielectric loss.

[0056] When an electric field is applied along the c-axis, Zn 2+ and O 2- Maximum displacement polarization occurs in the tetrahedral coordination structure, resulting in a strong dielectric response; while non-polar surfaces such as (103) have low polarization efficiency due to the large angle between the atomic displacement direction and the electric field.

[0057] Another aspect of the present invention proposes a piezoelectric thin film having a multilayer orientation-inducing layer structure, such as Figures 1 to 3 As shown, it includes:

[0058] The above-mentioned multi-layer orientation-inducing layer structure;

[0059] Electrode layer 5 covering the upper end face of the multilayer orientation-inducing layer structure;

[0060] Insulating layer 2 is disposed on the lower end face of the multilayer orientation-inducing layer structure;

[0061] And a substrate 1 for supporting the insulation layer.

[0062] In this embodiment, the multilayer orientation-inducing layer structure includes several sets of overlapping ZnO orientation-inducing layers 3 and ZnO piezoelectric layers 4. The electrode layer 5 material is deposited on the upper surface of the topmost ZnO piezoelectric layer 4 by magnetron sputtering. The material is Ag or Au, and the thickness is 100-300 nm. The substrate 1 is a single crystal silicon or an alloy block. In this embodiment, the single crystal silicon is selected from Putian Antaike Optoelectronics, and the model is 11N high-purity single-polished silicon wafer. It can also be other commercially available or self-made single crystal silicon wafers with a surface roughness Ra<1nm. In this embodiment, the alloy block is specifically GH2132 alloy with a surface roughness of 0.1-0.16 μm. In other embodiments, it can also be an alloy block of other components with a surface roughness of 0.1-0.16 μm. The insulating layer 2 material is either Si3N4 or SiC. It is deposited on the upper surface of the substrate by magnetron sputtering, and the thickness of the insulating layer 2 is 100-300 nm.

[0063] Understandably, compared to common SiO2 insulating layers, Si3N4 and SiC have a hardness of over 2000 HV, which gives them higher mechanical strength and hardness, enabling piezoelectric films to have higher mechanical load-bearing capacity. In addition, Si3N4 and SiC have extremely high thermal conductivity, making them more suitable for applications in high-temperature environments such as aero-engines.

[0064] This invention also proposes a process for preparing piezoelectric thin films with the above-mentioned multilayer orientation-induced layer structure, comprising the following steps:

[0065] ① Pre-treat the substrate;

[0066] Specifically, the substrate is placed in an alcohol solution for ultrasonic cleaning for 25-35 minutes, then the substrate surface is wiped clean with acetone, dried at 55-65℃ for 30-40 minutes, the substrate is mounted on the sample holder, and the substrate and target are plasma cleaned for 15-25 minutes.

[0067] Furthermore, the plasma cleaning is specifically argon plasma cleaning, with parameters set to a bias voltage of -250 to -450V and a duty cycle of 70% to 95%. The preferred plasma cleaning parameters are a bias voltage of -300V and a duty cycle of 70%.

[0068] ② An insulating layer is deposited on the substrate surface. The material is Si3N4 or SiC, and the thickness is 100-300 nm.

[0069] Specifically, the insulating layer is deposited on the substrate surface by radio frequency magnetron sputtering with a sputtering power of 50-200 W, a sputtering time of 30-60 min, an argon atmosphere, and a gas flow rate of 50-200 sccm.

[0070] Furthermore, the preferred RF magnetron sputtering process parameters for the Si3N4 insulating layer are: gas flow rate of 50 sccm, target-substrate distance of 60 mm, stage rotation speed of 15 r / min, and vacuum degree of 1.5 × 10⁻⁶. -4 Pa, RF power sputtering power 50 W, sputtering pressure 1.0 Pa, duty cycle 70%, bias voltage -50 V, deposition time 30 min, insulating layer thickness 100 nm.

[0071] ③ A ZnO orientation-induced layer was deposited on the insulating layer by radio frequency magnetron sputtering. The deposition parameters were: target-substrate distance 60-65 mm, sputtering pressure 1.0-3.0 Pa, power 40-70 W, and sputtering time 1-2.5 hours.

[0072] Specifically, the vacuum level of RF magnetron sputtering is 1.5 × 10⁻⁶. -4 -3×10 -4 Pa, sample stage rotation speed is 8-15 r / min, RF power supply bias is -10 to -50 V, duty cycle is 70% to 80%, sputtering atmosphere is argon, gas flow rate is 50-100 sccm.

[0073] Furthermore, the preferred RF magnetron sputtering process parameters for the ZnO orientation-induced layer are: gas flow rate 50 sccm, target-substrate distance 60 mm, and vacuum degree 1.5 × 10⁻⁶. -4 The parameters were: Pa, stage rotation speed 15 r / min, RF power supply bias -50 V, duty cycle 70%, sputtering pressure 1.0 Pa, sputtering power 50 W, deposition time 2 hours, and ZnO orientation-induced layer thickness 350 nm.

[0074] It is understandable that the orientation induction layer material is ZnO with the same composition as the piezoelectric layer. The nanoscale thickness and uniform and dense buffer layer have a higher bonding strength with the substrate, reduce the lattice mismatch between the substrate and the ZnO piezoelectric film, reduce the defect density and dislocation density in the film, improve the crystal quality of the film, and facilitate the orientation growth of the ZnO piezoelectric layer.

[0075] ④ A ZnO piezoelectric layer is deposited on the orientation-induced layer prepared in step ③ by radio frequency magnetron sputtering. The deposition parameters are: radio frequency power 200-300 W, target-substrate distance 60-65 mm, sputtering pressure 0.5-1.5 Pa, and sputtering time 4-8 hours.

[0076] Specifically, the deposition conditions were: a background vacuum of 1×10⁻⁶. -4 -3×10 -4Pa, sample stage rotation speed 5-20 r / min, bias voltage -10 to -50 V, duty cycle 70% to 95%, sputtering atmosphere is argon, gas flow rate 50-200 sccm.

[0077] Furthermore, the preferred RF magnetron sputtering process parameters for the ZnO piezoelectric layer are: gas flow rate 50 sccm, target-substrate distance 60 mm, and vacuum degree 1.5 × 10⁻⁶. -4 The parameters were: Pa, stage rotation speed 15 r / min, RF power supply bias -50 V, duty cycle 70%, sputtering pressure 1.0 Pa, sputtering power 200 W, deposition time 8 hours, and ZnO piezoelectric layer thickness 4 μm.

[0078] It should be added that steps ③ and ④ are repeated n times, where n is 0-3, to obtain a multi-layer structure with 1-4 sets of stacked units.

[0079] It should be noted that in this embodiment, the equipment used in steps ③ and ④ is the Pudi Vacuum PD600 multi-functional magnetron multi-arc coating machine, and the ZnO target material used is selected from Zhongnuo New Materials with a purity of 99.99%.

[0080] ⑤ Deposit an electrode layer on the ZnO piezoelectric layer, the material being Ag or Au, with a thickness of 100-300 nm;

[0081] Specifically, the electrode layer is deposited on the upper surface of the top ZnO piezoelectric layer by DC magnetron sputtering. The deposition power is 50-200 W, the deposition time is 30-60 min, the thickness is 100-300 nm, the sputtering atmosphere is argon, and the gas flow rate is 50-200 sccm.

[0082] Furthermore, the preferred DC magnetron sputtering process parameters for the electrode layer are: gas flow rate of 50 sccm, sputtering pressure of 1.0 Pa, duty cycle of 70%, and vacuum degree of 1.5 × 10⁻⁶. -4 Pa, sample stage rotation speed 15 r / min, bias voltage -50 V, sputtering power 50 W, deposition time 30 min, electrode layer thickness 100 nm.

[0083] It is understandable that Ag or Au electrode layers have higher conductivity than traditional metal electrodes such as Cr and Ti. Ag and Au have conductivity as high as 107 S / m, which is an order of magnitude higher than Cr and Ti. They also have high-temperature oxidation resistance, which prevents the electrodes from losing their conductivity after oxidation in high-temperature environments, thus limiting the application of piezoelectric thin films with multi-layer orientation-induced layer structures at high temperatures.

[0084] It should be noted that in this embodiment, the Au electrode layer sputtering target is selected from Suzhou Zhongzhina Semiconductor Technology Co., Ltd., model Au1, and the Ag electrode layer sputtering target is selected from Dongguan Dingwei New Materials Co., Ltd., model high-purity silver target (99.99%–99.999%).

[0085] To further understand the present invention, the following description, in conjunction with embodiments, illustrates a piezoelectric thin film with a multilayer orientation-induced layer structure provided by the present invention. The scope of protection of the present invention is not limited by the following embodiments.

[0086] Experimental Example 1

[0087] (1) Substrate pretreatment:

[0088] The substrate, a single-crystal silicon with Ra < 1 nm, was ultrasonically cleaned in an anhydrous ethanol solution with a volume concentration of 99.5% for 25 min. Then, the substrate surface was wiped clean with acetone with a volume concentration of 99.5% and dried at 65°C for 30 min. The substrate was then mounted on the sample holder of a vacuum PD600 multi-functional magnetron multi-arc coating machine, and the substrate and Si3N4 target were cleaned by argon plasma. The cleaning parameters were set as follows: bias voltage -300 V, duty cycle 70%, and cleaning time 20 min.

[0089] (2) Insulating layer deposition:

[0090] High-purity argon gas was introduced into the equipment at a flow rate of 50 sccm. The target-substrate distance was adjusted to 60 mm, the sample stage rotation speed was 15 r / min, and the vacuum degree was 1.5 × 10⁻⁶. -4 Pa, select RF power supply, set sputtering power to 50 W, sputtering pressure to 1.0 Pa, duty cycle to 70%, bias voltage to -50 V, deposit Si3N4 insulating layer on substrate, deposition time to 30 min, insulating layer thickness to 100 nm.

[0091] (3) ZnO orientation-induced layer deposition:

[0092] The target material was replaced with a high-purity ZnO target, and the inner cavity was cleaned with argon gas at a flow rate of 50 sccm, reducing the vacuum level to 1.5 × 10⁻⁶. -4 Pa, the sample stage rotation speed remained constant, the RF power supply was selected with a bias voltage of -50 V, a duty cycle of 70%, a sputtering pressure of 1.0 Pa, and a sputtering power of 50 W, and a ZnO orientation-induced layer was deposited on the upper end face of the Si3N4 insulating layer for 2 hours. The thickness of the ZnO orientation-induced layer was 350 nm.

[0093] (4) Deposition of ZnO piezoelectric layer:

[0094] The sputtering power was increased to 200W, while other parameters remained unchanged. A ZnO piezoelectric layer was deposited on the upper surface of the ZnO orientation-induced layer for 8 hours, and the thickness of the ZnO piezoelectric layer was 4μm.

[0095] (5) Repeat steps (3) and (4) in sequence, repeating once.

[0096] (6) Electrode layer deposition:

[0097] The target was replaced with an Ag target, and the inner cavity was purged with argon gas at a flow rate of 50 sccm. A DC power supply was selected, with a sputtering pressure of 1.0 Pa, a duty cycle of 70%, and a vacuum level of 1.5 × 10⁻⁶. -4 At Pa, with a sample stage rotation speed of 15 r / min, a bias voltage of -50 V, and a sputtering power of 50 W, an electrode layer was deposited on the upper surface of the top ZnO piezoelectric layer for 30 min. The electrode layer thickness was 100 nm, resulting in a ZnO piezoelectric thin film (ZnO M-OIL-2) with a structure of insulating layer + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + electrode layer.

[0098] Experimental Example 2

[0099] Steps (1) to (4) are the same as steps (1) to (4) in Experiment Example 1;

[0100] (5) Electrode layer deposition: Replace the target material with an Ag target, clean the inner cavity with argon gas at a flow rate of 50 sccm, select a DC power supply, sputtering pressure of 1.0 Pa, duty cycle of 70%, and vacuum degree of 1.5 × 10⁻⁶. -4 Pa, sample stage rotation speed 15 r / min, bias voltage -50 V, sputtering power 50 W, an electrode layer was deposited on the top surface of the ZnO piezoelectric layer for 30 min, and the electrode layer thickness was 100 nm, resulting in a ZnO piezoelectric thin film (ZnO M-OIL-1) with the structure of insulating layer + ZnO orientation induction layer film + ZnO piezoelectric thin film + electrode layer.

[0101] Experimental Example 3

[0102] Steps (1) to (4) are the same as those in Experiment Example 1.

[0103] (5) Repeat steps (3) and (4) in sequence, for a total of 3 repetitions;

[0104] (6) Electrode layer deposition;

[0105] The target was replaced with an Ag target, and the inner cavity was purged with argon gas at a flow rate of 50 sccm. A DC power supply was selected, with a sputtering pressure of 1.0 Pa, a duty cycle of 70%, and a vacuum level of 1.5 × 10⁻⁶. -4 At Pa, with a sample stage rotation speed of 15 r / min, a bias voltage of -50 V, and a sputtering power of 50 W, an electrode layer was deposited on the top surface of the ZnO piezoelectric layer for 30 min. The electrode layer thickness was 100 nm, resulting in a ZnO piezoelectric thin film (ZnO M-OIL-4) with the structure of insulating layer + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + electrode layer.

[0106] Experiment Example 4

[0107] (1) Substrate pretreatment:

[0108] The GH2132 alloy substrate was ultrasonically cleaned in an anhydrous ethanol solution with a volume concentration of 99.5% for 35 min. Then, the substrate surface was wiped clean with acetone with a volume concentration of 99.5% and dried at 55°C for 40 min. The substrate was then mounted on the sample holder of a vacuum PD600 multi-functional magnetron multi-arc coating machine, and the substrate and Si3N4 target were cleaned by argon plasma. The cleaning parameters were set as follows: bias voltage -250 V, duty cycle 90%, and cleaning time 25 min.

[0109] (2) Insulating layer deposition:

[0110] High-purity argon gas was introduced into the equipment at a flow rate of 200 sccm. The target-substrate distance was adjusted to 65 mm, the sample stage rotation speed was 15 r / min, and the vacuum degree was 1.5 × 10⁻⁶. -4 Pa, select RF power supply, set sputtering power to 50 W, sputtering pressure to 1.0 Pa, duty cycle to 70%, bias voltage to -50 V, deposit Si3N4 insulating layer on substrate, deposition time to 60 min, insulating layer thickness to 300 nm.

[0111] (3) ZnO orientation-induced layer deposition:

[0112] The target material was replaced with a high-purity ZnO target, and the inner cavity was cleaned with argon gas at a flow rate of 100 sccm. The vacuum level was then reduced to 3 × 10⁻⁶. -4 Pa, the sample stage rotation speed remained constant, the RF power supply was selected with a bias voltage of -30 V, a duty cycle of 80%, a sputtering pressure of 3.0 Pa, and a sputtering power of 70 W, and a ZnO orientation-induced layer was deposited on the upper end face of the Si3N4 insulating layer for 1 hour. The thickness of the ZnO orientation-induced layer was 200 nm.

[0113] (4) Deposition of ZnO piezoelectric layer:

[0114] The sputtering power was increased to 300W, the sputtering pressure was 0.5Pa and the other parameters remained unchanged. A ZnO piezoelectric layer was deposited on the upper surface of the ZnO orientation-induced layer. The deposition time was 4 hours and the thickness of the ZnO piezoelectric layer was 1.2μm.

[0115] (5) Repeat steps (3) and (4) in sequence, repeating once.

[0116] (6) Electrode layer deposition;

[0117] The target was replaced with an Au target, and the inner cavity was purged with argon gas at a flow rate of 200 sccm. A DC power supply was selected, with a sputtering pressure of 1.0 Pa, a duty cycle of 70%, and a vacuum level of 1.5 × 10⁻⁶. -4 At Pa, with a sample stage rotation speed of 15 r / min, a bias voltage of -50 V, and a sputtering power of 200 W, an electrode layer was deposited on the upper surface of the top ZnO piezoelectric layer. The deposition time was 60 min, and the electrode layer thickness was 300 nm, resulting in a piezoelectric thin film with a structure of insulating layer + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + electrode layer.

[0118] Experimental Example 5

[0119] (1) Substrate pretreatment:

[0120] The substrate, a single-crystal silicon with Ra < 1 nm, was ultrasonically cleaned in an anhydrous ethanol solution with a volume concentration of 99.5% for 35 min. Then, the substrate surface was wiped clean with acetone with a volume concentration of 99.5% and dried at 55°C for 40 min. The substrate was then mounted on the sample holder of a vacuum PD600 multi-functional magnetron multi-arc coating machine, and the substrate and SiC target were cleaned by argon plasma. The cleaning parameters were set as follows: bias voltage -450 V, duty cycle 70%, and cleaning time 25 min.

[0121] (2) Insulating layer deposition:

[0122] High-purity argon gas was introduced into the equipment at a flow rate of 100 sccm. The target-substrate distance was adjusted to 62 mm, the sample stage rotation speed was 5 r / min, and the vacuum degree was 1.5 × 10⁻⁶. -4 Pa, select RF power supply, set sputtering power to 40 W, sputtering pressure to 1.0 Pa, duty cycle to 70%, bias voltage to -50 V, deposit SiC insulating layer on substrate, deposition time to 40 min, insulating layer thickness to 200 nm.

[0123] (3) ZnO orientation-induced layer deposition:

[0124] The target material was replaced with a high-purity ZnO target, and the inner cavity was cleaned with argon gas at a flow rate of 50 sccm, reducing the vacuum level to 1.5 × 10⁻⁶. -4 Pa, the sample stage rotation speed remained constant, the RF power supply was selected with a bias voltage of -10 V, a duty cycle of 70%, a sputtering pressure of 1.0 Pa, and a sputtering power of 40 W, and a ZnO orientation-induced layer was deposited on the upper end face of the SiC insulating layer for 2.5 hours, with a ZnO orientation-induced layer thickness of 300 nm.

[0125] (4) Deposition of ZnO piezoelectric layer:

[0126] The sputtering power was increased to 300W, the sputtering pressure was 0.5Pa, and the other parameters remained unchanged. A ZnO piezoelectric layer was deposited on the upper surface of the ZnO orientation-induced layer for 4 hours. The thickness of the ZnO piezoelectric layer was 2μm.

[0127] (5) Repeat steps (3) and (4) in sequence, repeating once.

[0128] (6) Electrode layer deposition;

[0129] The target was replaced with an Au target, and the inner cavity was purged with argon gas at a flow rate of 100 sccm. A DC power supply was selected, the sputtering pressure was 1.0 Pa, the duty cycle was 70%, and the vacuum degree was 1.5 × 10⁻⁶. -4 At Pa, with a sample stage rotation speed of 15 r / min, a bias voltage of -50 V, and a sputtering power of 100 W, an electrode layer was deposited on the upper surface of the top ZnO piezoelectric layer for 40 min. The electrode layer thickness was 200 nm, resulting in a piezoelectric thin film with a structure of insulating layer + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + ZnO orientation-inducing layer film + ZnO piezoelectric thin film + electrode layer.

[0130] Comparative Example 1

[0131] Steps (1) and (2) are the same as steps (1) and (2) in Experiment Example 1;

[0132] Step (3) is the same as step (4) in Experiment Example 1 (5);

[0133] (4) Electrode layer deposition:

[0134] The target was replaced with an Ag target, and the inner cavity was cleaned with argon gas at a flow rate of 50 sccm. A DC power supply was selected, with a sputtering pressure of 1.0 Pa, a duty cycle of 70%, a vacuum of 1.5 × 10⁻⁴ Pa, a sample stage rotation speed of 15 r / min, a bias voltage of -50 V, and a sputtering power of 50 W. An electrode layer was deposited on the top surface of the ZnO piezoelectric layer for 30 min, with an electrode layer thickness of 100 nm, resulting in a piezoelectric thin film with an insulating layer + ZnO piezoelectric thin film + electrode layer structure.

[0135] Test example:

[0136] The crystal structure and orientation of the ZnO piezoelectric thin films prepared in Experimental Examples 1-3 and Comparative Example 1 were analyzed using a Rigaku SmartLab 9kW system equipped with a GI-XRD instrument. Specific results are shown in [Figure number missing]. Figure 4 and Figure 5 ;

[0137] High-resolution transmission electron microscopy (HR-TEM) was used to perform high-resolution transmission electron microscopy analysis on the surface morphology and cross-section of the ZnO piezoelectric thin film in Experimental Example 2, as well as the intermediate orientation-inducing layer portion of the double-layer orientation-inducing layer thin film in Example 1. Specific results are shown in [link to HR-TEM]. Figure 6 and Figure 7 ;

[0138] The surface morphology and cross-section of the ZnO piezoelectric films prepared in Examples 1-3 were characterized using a scanning electron microscope (SEM) model RISE-CLARA. Specific results are shown in [Figure 1]. Figure 8 ;

[0139] Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to analyze the ZnO piezoelectric thin films prepared in Examples 1-3. Specific results are shown in [Figure 1]. Figure 9 ;

[0140] A nanoindenter (Bruker TI750 model) was used to perform load-depth curve analysis and elastic modulus histogram analysis on the ZnO piezoelectric films prepared in Examples 1-3. Specific results are shown in […]. Figure 10 ;

[0141] The piezoelectric properties of the ZnO piezoelectric thin films prepared in Examples 1-3 and Comparative Example 1 were characterized using a piezoelectric power microscope (PFM) with a Jupiter XR instrument. Specific results are shown in [Figure number missing]. Figures 11 to 13 ;

[0142] An X-ray photoelectron spectrometer (Axis-Ultra Dld-600W) was used to characterize Experiments 1 and 3 using X-ray photoelectron spectroscopy and valence band photoelectron spectroscopy. Specific results are shown in [link to results]. Figure 14 and Figure 15 .

[0143] Data Analysis:

[0144] Please see Figure 4 and Figure 5 ,like Figure 5 As shown, without a ZnO orientation-inducing layer, the ZnO film is predominantly (103) oriented, with a very weak c-axis preference; combined with Figure 4 As shown in (a), with the increase of the number of ZnO orientation-induced layers, the diffraction peak intensity of the (002) crystal plane initially increases slightly, while the diffraction peak intensity of the (103) crystal plane gradually increases. Figure 4 As shown in (b), with the increase of the induced layer, the I(002) / I(103) ratio first increases and then decreases, with the ZnO M-OIL-2 sample having the highest ratio. This indicates that when the number of ZnO orientation induced layers is 2, the piezoelectric film exhibits the strongest c-axis preferred orientation. Moreover, in Figure 4 The FWHM value of the (002) crystal plane in (b) indicates that the ZnOM-OIL-2 sample has good crystal quality.

[0145] Please see Figure 6 and Figure 7 , Figure 6 The top three images show the cross-sectional structure of the material, revealing the electrode layer, stacked units, and substrate. The stacked units exhibit a columnar crystal structure, a common feature in electronic devices that contributes to improved device performance and stability. The bottom four images show the distribution of Zn, O, and Si elements. In TEM mode, a clear columnar crystal structure is visible, with Zn and O elements uniformly distributed, indicating a homogeneous chemical composition of the stacked unit material. The deposition of the orientation-induced layer contributes to the stability and consistency of the ZnO piezoelectric film's performance.

[0146] Furthermore, such as Figure 7 As shown, obvious grain boundaries and lattice fringes with different arrangements were observed in the middle orientation-inducing layer of ZnO M-OIL-2, but all showed the same interplanar spacing, revealing that different grains exhibited strong preferred orientations. All grains were stacked along the (002) crystal plane, and the artificially designed "texture template" macroscopically induced (002) preference. Compared with the single-layer orientation-inducing layer film of M-OIL-1, the interfacial stress regulation and high orientation driving force of the second orientation-inducing layer film make the "texture template" more perfect and stable, reducing grain disorder and orientation dispersion. The orientation anisotropy of the "texture template" is stronger and the texture coefficient is higher.

[0147] Please see Figure 8 As shown in Figures (a, b, c), the film exhibits a uniform and dense cauliflower structure and nanoscale grain size. As shown in Figures (d, e, f), the piezoelectric film interface has a clear and dense columnar crystal structure, the orientation-induced layer and the rapid deposition layer are densely bonded, and the interface is clearly visible.

[0148] Please see Figure 9 Figures (a, b, c) represent the percentages of Zn and O atoms in the multilayer orientation-induced layer structures of Experiments 2, 1, and 3, respectively. The comparison shows that the compressive stress generated by the multi-orientation-induced layer forces oxygen atoms to diffuse laterally, preventing local oxygen enrichment or deficiency, and stabilizing the Zn / O ratio at 61.3:38.7, as shown in figure b. The multilayer orientation-induced layer can optimize interfacial stress, change the oxygen diffusion rate, avoid the disordered distribution of oxygen defects, and thus regulate the oxygen supply, maintaining a stable Zn and O ratio in the film.

[0149] Please see Figure 10 As shown in Figure (a), the three load-depth curves exhibit similar trends, indicating that the mechanical response of the ZnO piezoelectric films prepared in Experiments 1-3 is consistent in the depth direction. The curve curvature of the sample in Example 1 is moderate, indicating that ZnO M-OIL-2 has a moderate change in indentation depth and relatively moderate hardness under the same load, and the mechanical response is the most stable. As shown in Figure (b), the elastic modulus increases with the increase of the number of M-OIL layers, which suppresses the generation of dislocations and defects, thereby improving the rigidity of the film. However, a high elastic modulus has a stronger ability to resist plastic deformation, which will affect the energy conversion efficiency.

[0150] Please see Figures 11 to 15 ZnO M-OIL-1, ZnO M-OIL-2, and ZnO M-OIL-4 all exhibit differences in amplitude and phase, and the phase shows a single piezoelectric domain. From Figure 11It can be seen that there are significant differences in the surface morphology of ZnO films with different numbers of induced layers. The PFM height image of ZnO M-OIL-1 shows a significant change in surface height, indicating that the surface roughness of this sample is relatively high. In contrast, the PFM height images of ZnO M-OIL-2 and ZnO M-OIL-4 have more uniform color, indicating that their surface roughness is lower, which is beneficial to reducing energy loss under mechanical stress and thus enhancing the piezoelectric effect. From the PFM amplitude images, it can be seen that the amplitude image of ZnO M-OIL-1 sample has obvious amplitude changes, indicating that its hardness and elasticity distribution is relatively uneven. In contrast, the PFM amplitude images of ZnO M-OIL-2 and ZnO M-OIL-4 are more uniform, indicating that their surface hardness and elasticity distribution are more consistent, ensuring that the material produces a consistent charge response under mechanical stress, which helps to improve the piezoelectric properties of the material. The PFM phase images show significant phase changes in ZnO M-OIL-1, indicating different crystal orientations or domain structures on the sample surface. This inhomogeneity suggests the possible presence of multiple crystal orientations or domain structures within the material, thus affecting its piezoelectric properties. In contrast, the PFM phase images of ZnO M-OIL-2 and ZnO M-OIL-4 exhibit more uniform color distribution, indicating more consistent crystal orientations and more uniform domain distribution. In conclusion, ZnO piezoelectric films with more than one induced layer number exhibit more stable piezoelectric properties.

[0151] For further details, please refer to Figure 12 and Figure 13 ,like Figure 12 As shown in the upper left PFM amplitude probability density distribution diagram, ZnO M-OIL-2 exhibits a higher central peak value (79.19 Pm) compared to ZnO M-OIL-4 (17.07 Pm), indicating that ZnO M-OIL-2 has the best piezoelectric response amplitude. The upper right phase probability density distribution histogram shows that the phase distribution of ZnO M-OIL-2 shows a larger proportion of Zn polarity and a smaller proportion of bias domains, indicating that the orientation of Zn polarity is more unified. ZnO M-OIL-2 exhibits higher piezoelectric amplitude and piezoelectric coefficient, and its piezoelectric performance is superior. Meanwhile, the lower left and lower right bias voltage, displacement, and phase relationship diagrams show that both ZnO M-OIL-2 and ZnO M-OIL-4 have the ability to polarize 180°, but the phase change of ZnO M-OIL-2 is more significant.

[0152] Furthermore, such as Figure 13 As shown, the thin film without a deposited ZnO induced layer has a very weak c-axis preference, resulting in a very low piezoelectric center amplitude and weak piezoelectric response.

[0153] Please see Figure 14and Figure 15 ,like Figure 14 As shown, the binding energy peaks of Zn 2p occur at approximately 1020 eV (Zn 2p3 / 2) and 1045 eV (Zn 2p1 / 2), corresponding to Zn 2+ The characteristic binding energy indicates that Zn is mainly present in the sample as Zn. 2+ It exists in the form of O; the binding energy peak of O 1s occurs at approximately 530 eV, corresponding to O 2- The characteristic binding energy of ZnO M-OIL-4 shows an OV-related peak compared to ZnO M-OIL-2, indicating that excessive ZnO-induced layers lead to lattice mismatch and increased interfacial stress, affecting the crystal structure and properties of the material, resulting in more oxygen vacancy defects and reducing the piezoelectric properties of the material.

[0154] Furthermore, Figure 15 The results show that the valence band position of the ZnO M-OIL-2 sample is EVB=2.62eV, while that of the ZnO M-OIL-4 sample is EVB=3.39eV. This indicates that the Fermi level of ZnO M-OIL-2 shifts to a lower energy state, which helps reduce excited electron-hole pairs and thus enhances piezoelectric stability. The optical band gap of the ZnO M-OIL-2 sample is Eg=2.86eV, while that of the ZnO M-OIL-4 sample is Eg=2.81eV. The wider optical band gap of ZnO M-OIL-2 helps reduce electron-hole recombination caused by photoexcitation and improves the stability of piezoelectric properties.

[0155] In summary, this invention provides a multilayer orientation-induced layer structure, a piezoelectric thin film, and a method for preparing a piezoelectric thin film. By designing a "homogeneous multilayer, stepwise optimization" overall architecture, selecting material systems for extreme working conditions, and implementing precise and coordinated process control, a high-performance ZnO piezoelectric thin film with high crystal quality, excellent piezoelectric properties, high reliability, and suitability for high-temperature environments is prepared.

[0156] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multilayer orientation-inducing layer structure, characterized in that, include: At least one set of stacked units stacked sequentially, the stacked unit including a ZnO orientation-inducing layer and a ZnO piezoelectric layer formed on the upper surface of the ZnO orientation-inducing layer, the ZnO orientation-inducing layer being used to control the ZnO piezoelectric layer crystal to maintain a continuous c-axis (002) preferred orientation.

2. The multilayer orientation-inducing layer structure according to claim 1, characterized in that, The thickness of the ZnO orientation-inducing layer is 50-350 nm; the thickness of the ZnO piezoelectric layer is 1-4 μm.

3. A piezoelectric thin film, characterized in that, include: Base (1); An insulating layer (2) is formed on the upper end face of the substrate (1); The multilayer orientation-inducing layer structure according to any one of claims 1-2 is formed on the upper end face of the insulating layer (2); The electrode layer (5) is formed on top of the multilayer orientation-inducing layer structure.

4. The piezoelectric thin film according to claim 3, characterized in that, The preferred number of stacked units is 2 groups.

5. The piezoelectric thin film according to claim 3, characterized in that, The insulating layer is made of Si3N4 or SiC and has a thickness of 100-300 nm.

6. A piezoelectric thin film preparation process according to any one of claims 3-5, characterized in that, Includes the following steps: ① Place the substrate in an alcohol solution and ultrasonically clean it for 25-35 minutes. Then wipe the substrate surface with acetone and dry it at 55-65℃ for 30-40 minutes. Install the substrate on the sample holder and perform plasma cleaning on the substrate and target for 15-25 minutes. Specifically, plasma cleaning is argon plasma cleaning, with parameters set to a bias voltage of -250 to -450 V and a duty cycle of 70% to 95%. ② The insulating layer is deposited on the substrate surface by radio frequency magnetron sputtering, with a sputtering power of 50-200 W, a sputtering time of 30-60 min, an argon atmosphere, and a gas flow rate of 50-200 sccm; ③ A ZnO orientation-induced layer is deposited on the insulating layer by radio frequency magnetron sputtering; ④ A ZnO piezoelectric layer is deposited on the ZnO orientation-induced layer by radio frequency magnetron sputtering; ⑤ An electrode layer was deposited on the upper surface of the top ZnO piezoelectric layer by DC magnetron sputtering. The sputtering power was 50-200 W, the deposition time was 30-60 min, the thickness was 100-300 nm, the sputtering atmosphere was argon, and the gas flow rate was 50-200 sccm.

7. The piezoelectric thin film preparation process according to claim 6, characterized in that, Also includes: The steps of depositing the ZnO orientation-induced layer and depositing the ZnO piezoelectric layer are repeated n times in sequence, where n is 0-3, to obtain a multilayer structure with 1-4 sets of stacked units.

8. The preparation process according to claim 6 or 7, characterized in that: The process parameters for depositing the ZnO orientation-induced layer include: RF power 40-70 W, target-substrate distance 60-65 mm, sputtering pressure 1.0-3.0 Pa, and sputtering time 1-2.5 hours; The process parameters for depositing the ZnO piezoelectric layer include: RF power 200-300 W, target-substrate distance 60-65 mm, sputtering pressure 0.5-1.5 Pa, and sputtering time 4-8 hours.

9. The preparation process according to claim 8, characterized in that: The process parameters for depositing the ZnO orientation-induced layer also include: a base vacuum of 1.5 × 10⁻⁶. -4 -3×10 -4 Pa, sample stage rotation speed is 8-15 r / min, RF power supply bias is -10 to -50 V, duty cycle is 70% to 80%, sputtering atmosphere is argon, gas flow rate is 50-100 sccm; The process parameters for depositing the ZnO orientation-induced layer also include: a base vacuum of 1×10⁻⁶. -4 -3×10 -4 Pa, sample stage rotation speed 5-20 r / min, bias voltage -10 to -50 V, duty cycle 70% to 95%, sputtering atmosphere is argon, gas flow rate 50-200 sccm.

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