High-entropy hafnium-based ferroelectric film and preparation method and application thereof

Abstract

The invention discloses a high-entropy hafnium-based ferroelectric film and a preparation method and application thereof, and the preparation method comprises the following steps: dispersing a hafnium source, a zirconium source, a lanthanum source, a vanadium source and a yttrium source in a solvent, heating, stirring, and aging to obtain sol; spin-coating the sol on a cleaned substrate, and then carrying out pre-annealing to obtain a pre-annealed film; and carrying out annealing crystallization on the pre-annealed film to obtain the high-entropy hafnium-based ferroelectric film. The hafnium-based ferroelectric film containing five metal elements is adopted, and the ferroelectric film is prepared by matching a sol-gel method with parameter adjustment, so that the grain refinement process, the mechanical property enhancement and the entropy stabilization effect are facilitated, and the obtained high-entropy hafnium-based ferroelectric film is low in leakage current.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic technology, and in particular to a high-entropy hafnium-based ferroelectric thin film and a preparation method and application thereof. Background Art

[0002] An attractive property of HfO2 (hafnium dioxide) is the pyroelectric effect, which is related to the temperature-dependent change in ferroelectric polarization. Slight temperature changes between polar materials cause the strength of the spontaneous polarization to change, resulting in a large temporary surface charge, which in turn generates electricity—the so-called pyroelectric effect. The pyroelectric effect is the primary method for sensing temporal photon illumination and is widely used in practical sensing applications such as infrared detection and thermal imaging. Infrared photons thermally interact with ferroelectric materials by modulating the effective surface polarization, resulting in an electrical response.

[0003] Relatively little research has been conducted on HfO2-based devices that effectively utilize the thermophotoelectric effect to generate electrical responses and their well-controlled modulation with applied electric pulses. Related technologies use divalent and trivalent dopants to induce ferroelectricity in hafnium oxide. However, these dopants introduce a large number of oxygen vacancies while inducing ferroelectricity. While oxygen vacancies are highly effective in inducing ferroelectricity, they are a double-edged sword. While effectively stabilizing the polar phase, oxygen vacancies can also cause local structural field inhomogeneities and severe lattice distortion, hindering domain wall inversion and, in turn, the polarization response of the device, resulting in poor ferroelectric performance in ferroelectric thin film materials.

[0004] Therefore, it is necessary to provide a solution for improving the ferroelectric properties of ferroelectric thin film materials. Summary of the Invention

[0005] In view of this, the present application provides a high-entropy hafnium-based ferroelectric thin film and a preparation method and application thereof, which are used to solve the problem of how to improve the ferroelectric properties of ferroelectric thin film materials.

[0006] In order to achieve the above technical objectives, this application adopts the following technical solutions: In a first aspect, the present application provides a method for preparing a high-entropy hafnium-based ferroelectric thin film, comprising the following steps: Dispersing a hafnium source, a zirconium source, a lanthanum source, a vanadium source, and a yttrium source in a solvent, heating and stirring, and then aging to obtain a sol; Spin-coating the sol on a cleaned substrate, and then pre-annealing to obtain a pre-annealed film; The pre-annealed film is annealed and crystallized to obtain a high-entropy hafnium-based ferroelectric film.

[0007] Preferably, the hafnium source includes hafnium acetylacetonate, the zirconium source includes zirconium acetylacetonate, the lanthanum source includes lanthanum acetylacetonate, the vanadium source includes vanadium acetylacetonate, and the yttrium source includes yttrium acetylacetonate; and the solvent includes one or more of acetic acid, acetylacetone, and propionic acid.

[0008] Preferably, the usage ratio of the hafnium source, zirconium source, lanthanum source, vanadium source, yttrium source and solvent is 1 g: 0.5-0.8 g: 0.01-0.02 g: 0.02 g: 0.01-0.2 g: 20 mL.

[0009] Preferably, the heating and stirring temperature is 80-200° C., and the time is 2-5 hours; the aging time is 1-7 days, and the aging temperature is -10~80° C.

[0010] Preferably, the substrate is a p-type silicon wafer; the thickness of the substrate is 0.5-1 mm and the area is 1-2 cm 2 .

[0011] Preferably, the spin coating speed is 3000-4000 rpm / min; the pre-annealing temperature is 150-300° C., and the pre-annealing time is 1-5 min.

[0012] Preferably, the method further comprises repeating spin coating and pre-annealing of the sol before annealing and crystallization of the pre-annealed film, and the thickness of the pre-annealed film before annealing and crystallization is 60-70 nm.

[0013] Preferably, the annealing crystallization process is: heating to 500-800° C. at a heating rate of 8-10° C. / s and keeping the temperature for 2-10 minutes; the annealing crystallization atmosphere is air.

[0014] In a second aspect, the present application provides a high-entropy hafnium-based ferroelectric thin film.

[0015] In a third aspect, the present application provides an application of a high-entropy hafnium-based ferroelectric thin film in the preparation of a photodetector.

[0016] The beneficial effects of the present application are as follows: the present application adopts a hafnium-based ferroelectric film containing five metal elements, and utilizes a sol-gel method with parameter adjustment to prepare the ferroelectric film, which is beneficial to the grain refinement process, mechanical property enhancement and entropy stabilization effect, and the resulting high-entropy hafnium-based ferroelectric film has low leakage current. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 TEM image of a high-entropy hafnium-based ferroelectric thin film sample; Figure 2 This is the Raman spectrum of the high entropy hafnium-based ferroelectric thin film sample; Figure 3 This is the full XPS spectrum of the high entropy hafnium-based ferroelectric thin film sample; Figure 4 XPS graph of high entropy hafnium-based ferroelectric thin film sample: (a) Hf 4f; (b) Zr 3d; (c) O 1s; (d) Y3d; (e) La 3d; (f) V 2p; Figure 5 (a) PV curve of the high-entropy hafnium-based ferroelectric thin film sample, with a remanent polarization value of 49.26 μC cm 2 (b) JV curve, leakage current density is 1.719×10 -10 A / cm 2 ; Figure 6 PV curves of high entropy hafnium-based ferroelectric thin films at different annealing temperatures of 500℃, 600℃, and 700℃; Figure 7 This is the process flow chart of this application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] High-entropy ferroelectrics are solid solutions of five or more metallic elements in equimolar or near-equimolar ratios at a specific site in their crystal structure. Increasing polarization configuration disorder in ferroelectrics has been shown to enhance performance and can be directly achieved in high-entropy ferroelectrics. First-principles calculations show that increased entropy broadens the statistical distribution of the polarization vector, thereby enhancing polarization flexibility and broadening the range of polarization amplitudes and angles. This allows different polarization states to exhibit similar free energies, and enhances polarization instability under external stimuli. The resulting polarization structure supports the tunable high performance of high-entropy ferroelectrics. Furthermore, high-entropy strategies facilitate grain refinement, mechanical property enhancement, and entropy stabilization, providing opportunities for designing high-entropy ferroelectrics with novel polarization structures and superior performance. Furthermore, hafnium-based thin films are significantly thinner than traditional ferroelectric materials, enabling device miniaturization at the nanoscale while maintaining excellent ferroelectric properties, such as high remnant polarization and low coercive field, within this thickness range. This feature ensures excellent electrical performance while reducing the device size, and has broad application potential in fields such as photoelectric detection devices, high-density integration and non-volatile memory.

[0020] Based on this, this application was created.

[0021] like Figure 7 As shown, the present application provides a method for preparing a high-entropy hafnium-based ferroelectric thin film, comprising the following steps: Dispersing a hafnium source, a zirconium source, a lanthanum source, a vanadium source, and a yttrium source in a solvent, heating and stirring, and then aging to obtain a sol; Spin-coating the sol on a cleaned substrate, and then pre-annealing to obtain a pre-annealed film; The pre-annealed film is annealed and crystallized to obtain a high-entropy hafnium-based ferroelectric film.

[0022] The preparation method of the present application has the following advantages: In terms of raw materials, first of all, the present application uses a five-metal high-entropy component, which is more conducive to inducing phase transition, improving the crystallinity of the ferroelectric thin film system, and reducing the grain size compared to single-phase or dual-phase components, which is very effective in reducing the leakage current of the ferroelectric thin film; the reason is that the zero-electric-field dipole entropy of the high-entropy component system is higher than that of the low-entropy component. By reaching a low-entropy state when the electric field E=E0 and adjusting to a high-entropy state when the electric field E=0, the electrocaloric effect can be greatly enhanced, indicating that the zero-electric-field dipole entropy change of the system can provide the energy driving force required for the phase transition. When the dipole entropy increases, the free energy of the system may decrease, making the new phase more stable, thereby inducing a phase transition; Secondly, the raw materials of the present application include pentavalent doping elements such as vanadium, which can not only obtain a lower ferroelectric phase O phase energy than divalent and trivalent dopants, but also make it easier to obtain an orthorhombic phase during the phase transition process. In addition, the content of oxygen vacancies can be controlled to reduce, and the lattice dislocation and defects can be reduced, thereby reducing the leakage current of the ferroelectric film. The principle is that divalent and trivalent dopants with ionic radii ranging from 54 to 135 pm induce ferroelectricity in hafnium oxide, but divalent and trivalent dopants introduce a large number of oxygen vacancies while inducing ferroelectricity. Although oxygen vacancies have an excellent effect in inducing ferroelectricity, it is still a double-edged sword. While effectively stabilizing the polar phase, oxygen vacancies will cause local structural / field inhomogeneities and severe lattice distortion, thereby hindering domain wall inversion and thus hindering the polarization response of the device. Co-doping with pentavalent metals can overcome the above defects. From the method, the method of the present application is a sol-gel method, which is simple to operate, has a short experimental cycle, low raw material cost, low experimental equipment, and a simple experimental environment. The experiments are all carried out at room temperature and atmosphere, and the doping concentration can be flexibly and simply regulated. The film thickness is regulated by regulating the concentration of the precursor sol, the speed of the slurry dispersing machine, and the number of spin-coated layers. The ferroelectric phase content is regulated by annealing at different temperatures and atmospheres, and the defects of physical vapor deposition (PVD) and chemical vapor deposition (CVD) can be overcome. As known to those skilled in the art, PVD is a technology that uses physical methods to vaporize the surface of a material source into gaseous atoms, molecules, or partially ionized into ions under vacuum conditions, and deposits a thin film having some special functions on the surface of a substrate through a low-pressure gas process. However, this method has high requirements for vacuum degree, a low coating speed, and a small control degree of the component ratio for multi-component compounds, resulting in uneven film formation and poor quality. CVD is a process in which reactants undergo a chemical reaction in a gaseous state, generating a solid substance that is deposited on a heated solid substrate, thereby producing a solid material. However, this method suffers from a relatively low deposition rate. In many cases, the reaction sources involved in the deposition and the residual gases after the reaction are flammable, explosive, or toxic, necessitating measures to prevent environmental pollution and often requiring corrosion resistance from the equipment. The present application utilizes a sol-gel method to prepare high-entropy hafnium-based ferroelectric thin films, which overcomes these drawbacks.

[0023] In some embodiments, the hafnium source includes hafnium acetylacetonate, the zirconium source includes zirconium acetylacetonate, the lanthanum source includes lanthanum acetylacetonate, the vanadium source includes vanadium acetylacetonate, and the yttrium source includes yttrium acetylacetonate; and the solvent includes one or more of acetic acid, acetylacetone, and propionic acid.

[0024] In this embodiment, hafnium acetylacetonate can be dissolved to form a colloid, acetylacetonate is completely dissolved in the solvent, and a metal source is introduced to obtain a sol containing the target metal. The selected raw materials are conducive to the formation of the sol, and the metal elements in the sol can coexist and be evenly distributed.

[0025] In some embodiments, the ratio of the hafnium source, the zirconium source, the lanthanum source, the vanadium source, the yttrium source to the solvent is 1 g: 0.5-0.8 g: 0.01-0.02 g: 0.02 g: 0.01-0.2 g: 20 mL.

[0026] In this embodiment, by adjusting the amount of each raw material, on the one hand, the content of pentavalent vanadium element is adjusted to 0.02-0.2%, which is conducive to obtaining a lower ferroelectric phase O phase energy, and the orthorhombic phase is easier to obtain and more stable during the phase transition process, and the high entropy strategy is beneficial to the grain refinement process, mechanical property enhancement and entropy stabilization effect; on the other hand, lanthanum and tantalum co-doping is achieved.

[0027] In some embodiments, the heating and stirring temperature is 80-200° C., the time is 2-5 h, and the aging time is 1-7 d.

[0028] In some embodiments, the substrate is a p-type silicon wafer; the thickness of the substrate is 0.5-1 mm and the area is 1-2 cm 2 .

[0029] In this embodiment, the p-type silicon wafer is also cleaned. The cleaning steps are as follows: the p-type silicon wafer is first ultrasonically cleaned with acetone, then ultrasonically cleaned with alcohol, and then ultrasonically cleaned with deionized water to remove impurities on the substrate, and finally blown dry with nitrogen to obtain a clean substrate. The advantage of choosing a p-type silicon wafer as a substrate is that it has good conductivity.

[0030] In some embodiments, the spin coating speed is 3000-4000 rpm / min; the pre-annealing temperature is 150-300° C., and the pre-annealing time is 1-5 min.

[0031] In this embodiment, the pre-annealing step is beneficial for volatilizing the organic matter in the colloid, thereby removing the organic matter in the film.

[0032] In some embodiments, the method further includes repeating spin coating and pre-annealing of the sol before annealing and crystallization of the pre-annealed film, and the thickness of the pre-annealed film before annealing and crystallization is 60-70 nm.

[0033] In this embodiment, repeated spin coating and pre-annealing steps facilitate obtaining a pre-annealed film of the target thickness. The repetitive process involves performing pre-annealing after each spin coating layer, and repeating the spin coating and pre-annealing steps until the desired pre-annealed film thickness is achieved. The film thickness is controlled by adjusting the spin coater speed and the number of spin-coated layers to achieve optimal ferroelectric performance. Hafnium-based films, because their thickness is significantly lower than that of traditional ferroelectric materials, enable device miniaturization at the nanoscale while maintaining good ferroelectric performance within this thickness range.

[0034] In some embodiments, the annealing crystallization process is: heating to 500-800° C. at a heating rate of 8-10° C. / s and keeping the temperature for 2-10 minutes; the annealing crystallization atmosphere is air.

[0035] In this embodiment, annealing at a specific temperature is beneficial to the crystallization of the film, thereby obtaining a polycrystalline high-entropy hafnium-based ferroelectric film containing an O phase; wherein, too high or too low a heating rate or annealing temperature is not conducive to the improvement of the ferroelectric performance, because at a lower annealing temperature and cooling rate, the proportion of the monoclinic m phase will increase, and the stabilization of the orthorhombic o phase requires a higher annealing rate; while high-temperature annealing improves the ferroelectric properties, it inadvertently forms an interface layer and increases the interface state density, but too high an annealing temperature will increase the content of the monoclinic m phase, thereby reducing the ferroelectric performance.

[0036] The present application provides a high-entropy hafnium-based ferroelectric thin film.

[0037] The present application provides an application of a high-entropy hafnium-based ferroelectric thin film in the preparation of a photodetector.

[0038] The present invention is further described below through specific examples.

[0039] Example 1 A method for preparing a high-entropy hafnium-based ferroelectric thin film comprises the following steps: S1. Dissolve 1 g of hafnium acetylacetonate, 0.8 g of zirconium acetylacetonate, 0.02 g of lanthanum acetylacetonate, 0.02 g of vanadium acetylacetonate, and 0.02 g of yttrium acetylacetonate in 20 ml of acetic acid. Heat and stir at 80°C for 2 h, and age for 1 day to obtain a sol. S2. The thickness is 0.5mm and the area is 1cm 2 The p-type silicon wafer was first ultrasonically cleaned with acetone for 15 minutes, then ultrasonically cleaned with alcohol for 10 minutes, and then ultrasonically cleaned with deionized water for 10 minutes. The cleaned substrate was placed in the center of a spin coater and the sol was spin-coated on the cleaned substrate at 3000 rpm / min. The substrate was then pre-annealed at 150°C for 1 minute. The spin coating-pre-annealing step was repeated 5 times to obtain a pre-annealed film. S3. In an air atmosphere, the pre-annealed film is heated to 600°C at a heating rate of 8°C / s for annealing, and kept at this temperature for 2 minutes to crystallize the film, thereby obtaining a polycrystalline high-entropy hafnium-based ferroelectric film containing an O phase.

[0040] Example 2 A method for preparing a high-entropy hafnium-based ferroelectric thin film is the same as that of Example 1 except that the annealing temperature is 500°C.

[0041] Example 3 A method for preparing a high-entropy hafnium-based ferroelectric thin film is the same as that of Example 1 except that the annealing temperature is 700°C.

[0042] Testing and Evaluation The TEM image of the high entropy hafnium-based ferroelectric thin film sample in Test Example 1, where HEHZO represents high entropy hafnium-based ferroelectric thin film, is shown in FIG. Figure 1 As shown; The Raman spectrum of the high entropy hafnium-based ferroelectric thin film sample of Example 1 was tested, and the results were as follows: Figure 2 As shown, Figure 2In the figure, m\o\t represent m\o\t phases, and Si represents silicon substrate. It is worth noting that since the film is deposited at a relatively low temperature, it is not fully crystallized and does not have perfect crystal symmetry. The phonon function is spatially restricted, which may cause the shape and frequency of the Raman line to change. Therefore, the peak intensity and position in the Raman spectrum may show differences. The XPS spectrum of the high entropy hafnium-based ferroelectric thin film sample of Example 1 was tested, and the results were as follows: Figure 3 As shown; The XPS graph of the high entropy hafnium-based ferroelectric thin film sample of Example 1 was tested, and the results were as follows: Figure 4 As shown, Figure 4 (a) is the XPS graph of Hf 4f; Figure 4 (b) is the XPS graph of Zr 3d; Figure 4 (c) is the XPS graph of O 1s; Figure 4 (d) is the XPS graph of Y3d; Figure 4 (e) is the XPS graph of La 3d; Figure 4 (f) is the XPS graph of V 2p.

[0043] The PV curve of the high entropy hafnium-based ferroelectric thin film sample of Example 1 was tested, and the results were as follows: Figure 5 As shown in (a), the remanent polarization value is 49.26 μC cm 2 ; JV curve of the high entropy hafnium-based ferroelectric thin film sample of Example 1, the results are as follows Figure 5 As shown in (b), the leakage current density is 1.719×10 -10 A / cm 2 .

[0044] Figure 6 The PV curves of high entropy hafnium-based ferroelectric thin films annealed at 500℃, 600℃, and 700℃ are shown below: the remnant polarization value after annealing at 500℃ is 30.83 μC cm 2 The remanent polarization value after annealing at 600℃ is 49.26 μC cm 2 The remanent polarization value after annealing at 700℃ is 50.35 μC cm 2 .

[0045] The above results show that the present application adopts a hafnium-based ferroelectric film containing five metal elements and uses a sol-gel method with parameter adjustment to prepare the ferroelectric film, which is beneficial to the grain refinement process, mechanical property enhancement and entropy stabilization effect, and the obtained high-entropy hafnium-based ferroelectric film has low leakage current.

[0046] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a high-entropy hafnium-based ferroelectric thin film, characterized in that: The following steps are involved: Dispersing a hafnium source, a zirconium source, a lanthanum source, a vanadium source, and a yttrium source in a solvent, heating and stirring, and then aging to obtain a sol; Spin-coating the sol on a cleaned substrate, and then pre-annealing to obtain a pre-annealed film; The pre-annealed film is annealed and crystallized to obtain a high-entropy hafnium-based ferroelectric film.

2. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 1, wherein: The hafnium source includes hafnium acetylacetonate, the zirconium source includes zirconium acetylacetonate, the lanthanum source includes lanthanum acetylacetonate, the vanadium source includes vanadium acetylacetonate, and the yttrium source includes yttrium acetylacetonate; the solvent includes one or more of acetic acid, acetylacetone, and propionic acid.

3. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 2, wherein: The usage ratio of the hafnium source, zirconium source, lanthanum source, vanadium source, yttrium source and solvent is 1g:0.5-0.8g:0.01-0.02g:0.02g:0.01-0.2g:20mL.

4. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 1, wherein: The heating and stirring temperature is 80-200° C., and the time is 2-5 hours; the aging time is 1-7 days, and the aging temperature is -10~80° C.

5. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 1, wherein: The substrate is a p-type silicon wafer; the thickness of the substrate is 0.5-1 mm and the area is 1-2 cm 2 .

6. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 1, wherein: The spin coating speed is 3000-4000 rpm / min; the pre-annealing temperature is 150-300° C., and the pre-annealing time is 1-5 min.

7. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 1, wherein: The method further includes repeating spin coating and pre-annealing of the sol before annealing and crystallization of the pre-annealing film, and the thickness of the pre-annealing film before annealing and crystallization is 60-70 nm.

8. The method for preparing a high-entropy hafnium-based ferroelectric thin film according to claim 1, wherein: The annealing crystallization process is: heating to 500-800° C. at a heating rate of 8-10° C. / s and keeping the temperature for 2-10 minutes; the atmosphere of the annealing crystallization is air.

9. A high-entropy hafnium-based ferroelectric thin film obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the high-entropy hafnium-based ferroelectric thin film according to claim 9 in preparing a photodetector.

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