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

Abstract

The application 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 and stirring, and then aging to obtain a sol; coating the sol on a cleaned substrate, and then performing pre-annealing to obtain a pre-annealed film; and performing annealing crystallization on the pre-annealed film to obtain the high-entropy hafnium-based ferroelectric film; the application adopts the hafnium-based ferroelectric film containing five metal elements, and utilizes a sol-gel method to prepare the ferroelectric film by adjusting parameters, so that the crystal grain refining process, the mechanical property enhancement and the entropy stabilization effect are facilitated, and the obtained high-entropy hafnium-based ferroelectric film has low leakage current.

Description

TECHNICAL FIELD

[0001] The present application 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

[0002] One attractive property of HfO2 (hafnium dioxide) is the pyroelectric effect, which is related to the change of ferroelectric polarization with temperature. A small change in temperature between polar materials will change the strength of the spontaneous polarization, resulting in a large number of temporary surface charges, and in turn, an electric - the so-called pyroelectric effect. The pyroelectric effect is the main way to perceive time photon illumination, and is widely used in practical sensing applications such as infrared detection and thermal imaging. Infrared photons interact with ferroelectric materials through modulated effective surface polarization, and in turn, an electric response is generated.

[0003] There are relatively few studies on the effective use of the pyroelectric effect to generate an electric response based on HfO2 devices and good control modulation with applied electric pulses. In related technologies, divalent and trivalent dopants are used to induce ferroelectricity in hafnium oxide, but the divalent and trivalent dopants will introduce a large number of oxygen vacancies while inducing ferroelectricity. Although oxygen vacancies have excellent effects in inducing ferroelectricity, they are still a double-edged sword. While effectively stabilizing the polar phase, oxygen vacancies will cause local structural field inhomogeneity, severe lattice distortion, and hinder domain wall reversal, and in turn, hinder the polarization response of the device, resulting in poor ferroelectric performance of the ferroelectric thin film material.

[0004] Therefore, it is necessary to provide a scheme for improving the ferroelectric performance of the ferroelectric thin film material. SUMMARY

[0005] In view of the above, 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 performance of the ferroelectric thin film material.

[0006] To achieve the above technical purposes, the present application adopts the following technical scheme:

[0007] In a first aspect, the present application provides a preparation method of a high-entropy hafnium-based ferroelectric thin film, comprising the following steps:

[0008] Disperse hafnium source, zirconium source, lanthanum source, vanadium source, and yttrium source in a solvent, heat and stir, and then age to obtain a sol;

[0009] Spin coat the sol on a cleaned substrate, and then perform pre-annealing to obtain a pre-annealed thin film;

[0010] Anneal and crystallize the pre-annealed thin film to obtain the high-entropy hafnium-based ferroelectric thin film.

[0011] Preferably, the hafnium source includes acetylacetone hafnium, the zirconium source includes acetylacetone zirconium, the lanthanum source includes acetylacetone lanthanum, the vanadium source includes acetylacetone vanadium, and the yttrium source includes acetylacetone yttrium; the solvent includes one or more of acetic acid, acetylacetone, and propionic acid.

[0012] Preferably, the ratio of the hafnium source, the zirconium source, the lanthanum source, the vanadium source, the yttrium source, and the solvent is 1g:0.5-0.8g:0.01-0.02g:0.02g:0.01-0.2g:20mL.

[0013] Preferably, the temperature of the heating and stirring is 80-200℃, and the time is 2-5h; the time of the aging is 1-7d, and the temperature of the aging is -10~80℃.

[0014] Preferably, the substrate is a p-type silicon wafer; the thickness of the substrate is 0.5-1mm, and the area is 1-2cm 2 .

[0015] Preferably, the rotation speed of the spin coating is 3000-4000rpm / min; the temperature of the pre-annealing is 150-300℃, and the time of the pre-annealing is 1-5min.

[0016] Preferably, the method further includes, before the pre-annealed thin film is annealed and crystallized, repeatedly performing the spin coating and the pre-annealing of the sol, and the thickness of the pre-annealed thin film before the annealing and crystallization is 60-70nm.

[0017] Preferably, the annealing and crystallization process includes heating at a temperature increasing rate of 8-10℃ / s to 500-800℃, and maintaining the temperature for 2-10min; the annealing and crystallization atmosphere is air.

[0018] In a second aspect, the application provides a high-entropy hafnium-based ferroelectric thin film.

[0019] In a third aspect, the application provides a use of a high-entropy hafnium-based ferroelectric thin film in preparing a photodetector.

[0020] The application has the following beneficial effects: the application uses a hafnium-based ferroelectric thin film containing five metal elements, and uses a sol-gel method to prepare the ferroelectric thin film by adjusting parameters, which is beneficial to the grain refinement process, the enhancement of mechanical properties, and the entropy stabilization effect, and the obtained high-entropy hafnium-based ferroelectric thin film has low leakage current. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a TEM image of a high-entropy hafnium-based ferroelectric thin film sample;

[0022] Figure 2 FIG. 3 is a Raman spectrum of a high-entropy hafnium-based ferroelectric thin film sample;

[0023] Figure 3 FIG. 5 is an XPS full spectrum of a high-entropy hafnium-based ferroelectric thin film sample;

[0024] Figure 4 XPS spectra of the high-entropy hafnium-based ferroelectric thin film sample: (a) Hf 4f; (b) Zr 3d; (c) O 1s; (d) Y 3d; (e) La 3d; (f) V 2p;

[0025] Figure 5 (a) P-V curve of the high-entropy hafnium-based ferroelectric thin film sample, and the remanent polarization value is 49.26 μC cm 2 ; (b) J-V curve, and the leakage current density is 1.719 x 10 -10 A / cm 2 ;

[0026] Figure 6 P-V curves of the high-entropy hafnium-based ferroelectric thin film samples with different annealing temperatures of 500℃, 600℃ and 700℃;

[0027] Figure 7 A process flow diagram of the present application. DETAILED DESCRIPTION

[0028] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0029] The high-entropy ferroelectric material refers to a solid solution compound formed by five or more metal elements at an equal molar ratio or an approximate equal molar ratio at a certain site in the crystal structure of the material. The increase in the polarization configuration disorder in the ferroelectric body has been proved to be beneficial to the performance improvement, and can be directly realized in the high-entropy ferroelectric body. The first principle calculation shows that the increase in the entropy expands the statistical distribution of the polarization vector, thereby enhancing the flexibility of the polarization, making the amplitude and angle range of the polarization wider, so that different polarization states exhibit similar free energy, and the polarization instability under external stimulation is enhanced, thereby generating a polarization structure supporting the adjustable high performance of the high-entropy ferroelectric material, and the high-entropy strategy is beneficial to the grain refinement process, the mechanical property enhancement and the entropy stabilization effect, providing an opportunity for designing a high-entropy ferroelectric body with a novel polarization structure and excellent performance. Secondly, the thickness of the hafnium-based thin film is significantly lower than that of the traditional ferroelectric material, which can realize the miniaturization of the device at the nanoscale, and at the same time, the hafnium-based thin film can still maintain good ferroelectric properties, such as high remanent polarization and low coercive field, in the thickness range. This feature enables the device to be miniaturized while ensuring excellent electrical properties, thereby providing a broad application potential in the fields of optoelectronic detection devices, high-density integration and non-volatile memories.

[0030] Based on this, the present application is established.

[0031] As Figure 7 The application provides a preparation method of a high-entropy hafnium-based ferroelectric film, which comprises the following steps:

[0032] The hafnium source, the zirconium source, the lanthanum source, the vanadium source and the yttrium source are dispersed in a solvent, and after heating and stirring, aging is performed to obtain a sol;

[0033] The sol is spin-coated on a cleaned substrate, and then pre-annealing is performed to obtain a pre-annealing film;

[0034] The pre-annealing film is annealed and crystallized to obtain the high-entropy hafnium-based ferroelectric film.

[0035] The preparation method has the following advantages:

[0036] In terms of raw materials, first, the application uses a five-metal high-entropy component, which is more conducive to inducing phase transition, improving the crystallinity of the ferroelectric film system and reducing the grain size compared with single-phase or double-phase components, which is very effective in reducing the leakage current of the ferroelectric 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, and by reaching the low-entropy state at the electric field E=E0 and adjusting to the high-entropy state at the electric field E=0, the electric clamping effect can be greatly enhanced, indicating that the change in the zero electric field dipole entropy of the system can provide the energy driving force required for phase transition, and when the dipole entropy increases, the free energy of the system may decrease, making the new phase state more stable, thereby inducing phase transition;

[0037] Secondly, the raw materials of the application include a pentavalent dopant element such as vanadium, which can not only obtain a lower ferroelectric phase O phase energy, but also more easily obtain an orthorhombic phase during phase transition, and can control and reduce the content of oxygen vacancies, reduce lattice dislocation and defects, thereby reducing the leakage current of the ferroelectric film; the principle is that divalent and trivalent dopants with an ionic radius of 54 to 135 pm induce ferroelectricity in hafnium oxide, but divalent and trivalent dopants induce ferroelectricity while introducing a large number of oxygen vacancies, although oxygen vacancies have excellent effect in inducing ferroelectricity, but it is still a double-edged sword, which effectively stabilizes the polar phase while causing local structure / field inhomogeneity, serious lattice distortion, thereby hindering the domain wall reversal, and further hindering the polarization response of the device, and the co-doping of the pentavalent metal can overcome the above defects;

[0038] In terms of methods, the method of the present application is a sol-gel method, which is simple to operate, short in experimental period, low in raw material cost, low in experimental equipment, and simple in required experimental environment. The experiment is realized at room temperature and in the atmosphere, the doping concentration can be flexibly and simply regulated, the film thickness can be regulated by regulating the precursor sol concentration, the rotation speed of the homogenizing machine and the number of spin coating layers, the ferroelectric phase content can be 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 by those skilled in the art, PVD is a technology for depositing a thin film with certain special functions on a substrate surface by using a physical method to vaporize the surface of a material source into gaseous atoms, molecules or partially ionized ions under vacuum conditions, and through a low-pressure gas process, but this method has higher requirements for vacuum degree, lower plating speed, smaller control degree of component proportion for multi-component compounds, uneven film formation and poor quality. CVD is a process technology for generating solid materials by depositing solid substances on the surface of a heated solid substrate through chemical reactions of reactants in a gaseous state, but the deposition rate of this method is not high, and in many cases, the reaction source participating in the deposition and the residual gas after the reaction are flammable, explosive or toxic, so measures need to be taken to prevent environmental pollution, and the equipment often has corrosion resistance requirements. The use of the sol-gel method to prepare high-entropy hafnium-based ferroelectric films can overcome the above-mentioned defects.

[0039] 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.

[0040] In this embodiment, the hafnium acetylacetonate can be dissolved to form a colloid, the acetylacetonate salt is completely dissolved in the solvent, the metal source is introduced to obtain a sol containing target metals, the selected raw materials are conducive to the formation of the sol, and each metal element in the sol coexists and is uniformly distributed.

[0041] In some embodiments, the amount ratio of the hafnium source, the zirconium source, the lanthanum source, the vanadium source, the yttrium source and the solvent is 1g: 0.5-0.8g: 0.01-0.02g: 0.02g: 0.01-0.2g: 20mL.

[0042] In this embodiment, by adjusting the amount of each raw material, on the one hand, the content ratio of the pentavalent vanadium element is 0.02-0.2%, which is conducive to obtaining a lower ferroelectric phase O phase, the orthorhombic phase is more easily obtained in the phase transition process, is more stable, and the high-entropy strategy is conducive to the grain refinement process, the enhancement of mechanical properties and the entropy stabilization effect; on the other hand, lanthanum and tantalum co-doping is realized.

[0043] In some embodiments, the temperature of heating and stirring is 80-200℃, and the time is 2-5h; the aging time is 1-7d.

[0044] In some embodiments, the substrate is a p-type silicon wafer; the thickness of the substrate is 0.5-1mm, and the area is 1-2cm 2 .

[0045] In this embodiment, the p-type silicon wafer is also cleaned, and the cleaning process is as follows: the p-type silicon wafer is first cleaned with acetone by ultrasonic cleaning, then cleaned with alcohol by ultrasonic cleaning, and then cleaned with deionized water by ultrasonic cleaning to remove impurities on the substrate, and finally dried with nitrogen to obtain a clean substrate; the advantage of selecting a p-type silicon wafer as the substrate is that it has good electrical conductivity.

[0046] In some embodiments, the rotation speed of the spin coating is 3000-4000rpm / min; the pre-annealing temperature is 150-300℃, and the pre-annealing time is 1-5min.

[0047] In this embodiment, the pre-annealing step is beneficial to the volatilization of organic matter in the colloid, thereby removing the organic matter in the film.

[0048] In some embodiments, the process of spin coating and pre-annealing of the sol is repeated before the pre-annealed film is annealed and crystallized, and the thickness of the pre-annealed film before annealing and crystallization is 60-70nm.

[0049] In this embodiment, by repeating the spin coating and pre-annealing steps, a pre-annealed film with a target thickness is obtained, wherein the process of repeating is that for each layer of film spin coated, pre-annealing is performed once, and the spin coating and pre-annealing steps are repeated until a pre-annealed film with the desired thickness is obtained; the film thickness is adjusted by adjusting the rotation speed of the spin coater and the number of spin coating layers to obtain the best ferroelectric performance. The hafnium-based film has a thickness significantly lower than that of traditional ferroelectric materials, which can realize the miniaturization of devices at the nanoscale, and still maintains good ferroelectric performance in this thickness range.

[0050] In some embodiments, the process of annealing and crystallization is as follows: heating at a temperature increasing rate of 8-10℃ / s to 500-800℃, and maintaining for 2-10min; the annealing and crystallization atmosphere is air.

[0051] In this embodiment, by annealing at a specific temperature, the film is crystallized to obtain a polycrystalline high-entropy hafnium-based ferroelectric film containing an O phase; a too high or too low temperature increasing rate or annealing temperature is not conducive to the improvement of ferroelectric performance, because at a lower annealing temperature and cooling rate, the proportion of monoclinic m phase increases, and a higher annealing rate is required for the stability of the orthorhombic o phase; high-temperature annealing improves the ferroelectric performance, but inadvertently forms an interface layer, increasing the interface state density, but a too high annealing temperature increases the content of monoclinic m phase, thereby reducing the ferroelectric performance.

[0052] The application provides a high-entropy hafnium-based ferroelectric film.

[0053] The application provides an application of the high-entropy hafnium-based ferroelectric film in preparation of a photoelectric detector.

[0054] The application is further described below through specific examples.

[0055] Example 1

[0056] A preparation method of a high-entropy hafnium-based ferroelectric film comprises the following steps:

[0057] S1. 1 g of acetylacetone hafnium, 0.8 g of acetylacetone zirconium, 0.02 g of acetylacetone lanthanum, 0.02 g of acetylacetone vanadium and 0.02 g of acetylacetone yttrium are dissolved in 20 ml of acetic acid, heated and stirred at 80 ℃ for 2 h, and then aged for 1 d to obtain a sol;

[0058] S2. A p-type silicon wafer with a thickness of 0.5 mm and an area of 1 cm 2 is first cleaned by ultrasonic cleaning with acetone for 15 min, then cleaned by ultrasonic cleaning with alcohol for 10 min, and then cleaned by ultrasonic cleaning with deionized water for 10 min; the cleaned substrate is placed in the center of a spin coater, and the sol is spin-coated on the cleaned substrate under the condition of 3000 rpm / min; then, pre-annealing is performed at 150 ℃ for 1 min; the spin-coating-pre-annealing step is repeated 5 times to obtain a pre-annealed film;

[0059] S3. The pre-annealed film is heated to 600 ℃ at a heating rate of 8 ℃ / s under an air atmosphere, and annealed for 2 min to crystallize the film, so as to obtain a polycrystalline high-entropy hafnium-based ferroelectric film containing an O phase.

[0060] Example 2

[0061] A preparation method of a high-entropy hafnium-based ferroelectric film, and other contents are the same as those in example 1, except that the annealing temperature is 500 ℃.

[0062] Example 3

[0063] A preparation method of a high-entropy hafnium-based ferroelectric film, and other contents are the same as those in example 1, except that the annealing temperature is 700 ℃.

[0064] Testing and evaluation

[0065] TEM images of the high-entropy hafnium-based ferroelectric film sample in example 1 are tested, wherein HEHZO represents the high-entropy hafnium-based ferroelectric film, and the results are shown in Figure 1 .

[0066] Raman spectra of the high-entropy hafnium-based ferroelectric film sample in example 1 are tested, and the results are shown in Figure 2 . 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.

[0067] 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;

[0068] 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.

[0069] 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 .

[0070] 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 .

[0071] 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.

[0072] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

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; the amount ratio of the hafnium source, zirconium source, lanthanum source, vanadium source, yttrium source to the solvent is 1g:0.5-0.8g:0.01-0.02g:0.02g:0.01-0.2g:20mL; 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 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.

4. 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 .

5. 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.

6. 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.

7. 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.

8. A high-entropy hafnium-based ferroelectric thin film obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the high-entropy hafnium-based ferroelectric thin film according to claim 8 in the preparation of a photodetector.

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