A La-doped hafnium oxide-based ferroelectric thin film, capacitor and preparation method thereof

Abstract

The present invention discloses a La-doped hafnium oxide-based ferroelectric thin film, a capacitor and a preparation method thereof. The La-doped hafnium oxide-based ferroelectric thin film has a single (111)-oriented orthorhombic phase structure. The preparation method is to epitaxially grow a buffer layer with consistent orientation on a (111)-oriented perovskite substrate first, and then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer to obtain the La-doped hafnium oxide-based ferroelectric thin film. The thickness of the thin film is precisely controlled to optimize the performance of the La-doped hafnium oxide-based ferroelectric thin film and meet the requirements of electronic devices for high-performance ferroelectric thin films. The laser pulse deposition epitaxial La-doped hafnium oxide-based ferroelectric thin film proposed by the present invention has high purity and good film-forming uniformity; at the same time, the operation process is simple, the energy consumption is low, there is no pollution and it is easy to realize industrialization.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductors, and particularly relates to a La-doped hafnium oxide-based ferroelectric thin film, a capacitor and a preparation method thereof. Background Art

[0002] With the accelerating evolution of the semiconductor industry towards high integration and low power consumption, the massive storage requirements driven by artificial intelligence and big data pose stringent requirements on the CMOS compatibility and three-dimensional integration capabilities of storage devices. Ferroelectric memories have become a research hotspot due to their advantages such as non-volatility, high-speed read and write, and low power consumption. However, the compatibility issues between traditional ferroelectric materials and complementary metal oxide semiconductor (CMOS) processes restrict their applications. HfO2-based thin films have high-K characteristics and are used as dielectric materials. Since the first report of Si:HfO2 ferroelectric thin films in 2011, hafnium oxide-based ferroelectrics have attracted much attention due to their compatibility with CMOS processes, and many breakthroughs have been made in their applications in semiconductor electronic devices such as ferroelectric random access memories (FeRAMs), ferroelectric field effect transistors (FeFETs), and ferroelectric tunnel junctions (FTJs).

[0003] In recent years, epitaxial growth technology has provided a key path for optimizing the performance of HfO2-based ferroelectric thin films: the metastable orthorhombic phase of the thin films can be precisely regulated through heteroepitaxial strain engineering, significantly improving its polarization stability. The research focus has shifted from polycrystalline thin films to single-crystalline epitaxial systems. Currently, the mainstream research focuses on Zr element-doped hafnium oxide-based ferroelectric thin films. However, such thin films generally have some problems that need to be solved urgently: firstly, there is a serious polarization fatigue dilemma. As the number of uses increases, the polarization performance of the material deteriorates rapidly, which greatly shortens the service life of the material and limits the long-term stable operation of related devices; secondly, taking the traditional HZO (zirconium-doped hafnium oxide) system as an example, its coercive field is relatively high, which leads to more energy consumption during the operation of the device to achieve polarization reversal, resulting in higher energy consumption. Therefore, exploring new doping systems to reduce the coercive field and energy consumption has become an urgent task; thirdly, in terms of substrate selection, the current mainstream research mostly uses perovskite (001) and (110) orientation substrates, and the research on (111) orientation perovskite substrates is still in its infancy. Although the exploration of (111) orientation substrates has been carried out, the experimental results show that the quality of the grown ferroelectric hafnium oxide-based thin films is poor, multiple crystal systems appear in the thin films, it is difficult to obtain high-quality thin films with a single (111) orientation, and there is still a polarization fatigue dilemma. At the same time, due to the difficulty in precisely controlling the growth conditions, different doping elements and concentrations will cause the lattice constant of the ferroelectric hafnium oxide thin film to be mismatched with the (111) orientation perovskite substrate, thereby affecting the growth quality and orientation consistency of the thin film. Summary of the Invention

[0004] Objectives of the Invention: The first objective of the present invention is to provide a La-doped hafnium oxide-based ferroelectric thin film with high remanent polarization, low coercive field, and good anti-fatigue performance, epitaxially grown on a (111)-oriented perovskite substrate; the second objective of the present invention is to provide a preparation method for this thin film, precisely controlling the thickness of the thin film to optimize the performance of the La-doped hafnium oxide-based ferroelectric thin film and meet the requirements of electronic devices for high-performance ferroelectric thin films; the third objective of the present invention is to provide a La-doped hafnium oxide-based ferroelectric thin film capacitor and its preparation method.

[0005] Technical Solution: The La-doped hafnium oxide-based ferroelectric thin film described in the present invention has a single (111)-oriented orthorhombic phase structure.

[0006] Preferably, the La doping concentration of the La-doped hafnium oxide-based is 2 - 8 at%.

[0007] More preferably, the La doping concentration of the La-doped hafnium oxide-based is 5 at%.

[0008] Preferably, the thickness of the La-doped hafnium oxide-based ferroelectric thin film is 10nm - 20nm.

[0009] The La-doped hafnium oxide-based ferroelectric thin film capacitor described in the present invention includes a buffer layer, a La-doped hafnium oxide-based ferroelectric thin film, and a metal top electrode; the buffer layer is on the bottom, the La-doped hafnium oxide-based ferroelectric thin film is on the buffer layer, and the metal top electrode is on the La-doped hafnium oxide-based ferroelectric thin film.

[0010] More preferably, the metal top electrode is a Pt top electrode, an Au top electrode, or an Ag top electrode.

[0011] More preferably, the metal top electrode is a Pt top electrode.

[0012] Preferably, the buffer layer is La (1-x) A x MnO3, where 0 < x < 1 and A is a divalent metal ion.

[0013] More preferably, A is Sr, Ca, or Ba.

[0014] More preferably, the buffer layer is La 0.67 Sr 0.33 MnO3 (LSMO) or La 0.67 Ca 0.33 MnO3 (LCMO).

[0015] Preferably, the thickness of the buffer layer is 15 - 20nm, and the thickness of the metal top electrode is 30 - 50nm.

[0016] More preferably, the thickness of the metal top electrode is 40nm.

[0017] The preparation method of the La-doped hafnium oxide-based ferroelectric thin film described in the present invention is to epitaxially grow a buffer layer with consistent orientation on a (111)-oriented perovskite substrate, and then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer to obtain the La-doped hafnium oxide-based ferroelectric thin film.

[0018] Preferably, the (111)-oriented perovskite substrate includes SrTiO3, GdScO3 or LaAlO3.

[0019] More preferably, the (111)-oriented perovskite substrate is SrTiO3.

[0020] More preferably, the thickness of the (111)-oriented perovskite substrate is 0.3 - 0.7 mm.

[0021] More preferably, the thickness of the (111)-oriented perovskite substrate is 0.5 mm.

[0022] Preferably, the buffer layer is La (1-x) A x MnO3, where 0 < x < 1, and A is a divalent metal ion.

[0023] More preferably, A is Sr, Ca or Ba.

[0024] More preferably, the buffer layer is La 0.67 Sr 0.33 MnO3 (LSMO) or La 0.67 Ca 0.33 MnO3 (LCMO).

[0025] Preferably, the preparation method of the La-doped hafnium oxide-based ferroelectric thin film described in the present invention includes the following steps:

[0026] (1) Firing the La-doped hafnium oxide-based target and the buffer layer target by the solid-phase reaction method, and placing the targets in the target chamber in the growth cavity of the laser pulse deposition instrument;

[0027] (2) Fixing the (111)-oriented perovskite substrate wafer on the sample stage, putting the sample stage into the sample introduction chamber, evacuating the growth cavity and the sample introduction chamber, and then sending the sample stage from the sample introduction chamber into the growth cavity;

[0028] (3) Heating the (111)-oriented perovskite substrate wafer to 720 - 780 °C, and using a baffle to separate the target from the wafer; when the temperature reaches 320 - 380 °C, introducing O2 to make the air pressure in the growth cavity reach 3 - 7 mtorr;

[0029] (4) Pre-sputtering the La-doped hafnium oxide-based target and the buffer layer target;

[0030] After the pre-sputtering is completed, open the baffle. After the temperature is heated to 720 - 780 °C, increase the O₂ flow rate to make the pressure in the growth chamber reach 90 - 110 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 2500 - 3500 pulses; after the sputtering is completed, raise the temperature to 750 - 810 °C and deposit a La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 2000 - 4000 pulses; after the deposition is completed, cool the sample to room temperature, and maintain the O₂ pressure at 90 - 110 mtorr during the cooling process; obtain a La-doped hafnium oxide-based ferroelectric thin film.

[0031] Further preferably, the method for preparing the La-doped hafnium oxide-based ferroelectric thin film of the present invention includes the following steps:

[0032] (1) Fire a La-doped hafnium oxide-based target and a buffer layer target by the solid-phase reaction method, and place the targets in the target chamber in the growth chamber of the laser pulse deposition instrument;

[0033] (2) Fix a (111)-oriented perovskite substrate wafer on the sample stage, place the sample stage in the sample introduction chamber, evacuate the growth chamber and the sample introduction chamber, and then send the sample stage from the sample introduction chamber into the growth chamber;

[0034] (3) Heat the (111)-oriented perovskite substrate wafer to 720 - 780 °C at a rate of 3 - 7 °C / min, and use a baffle to separate the target from the substrate; when the temperature reaches 320 - 380 °C, introduce O₂ to make the pressure in the growth chamber reach 3 - 7 mtorr;

[0035] (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target;

[0036] (5) After the pre-sputtering is completed, open the baffle. After the temperature is heated to 720 - 780 °C, increase the O₂ flow rate to make the pressure in the growth chamber reach 90 - 110 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 2500 - 3500 pulses; after the sputtering is completed, raise the temperature to 750 - 810 °C at a rate of 3 - 7 °C / min and deposit a La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 2000 - 4000 pulses; after the deposition is completed, cool the sample to room temperature at a rate of 3 - 7 °C / min, and maintain the O₂ pressure at 90 - 110 mtorr during the cooling process; obtain a La-doped hafnium oxide-based ferroelectric thin film.

[0037] Further preferably, the method for preparing the La-doped hafnium oxide-based ferroelectric thin film of the present invention includes the following steps:

[0038] (1) Fire a La-doped hafnium oxide-based target and a buffer layer target by the solid-phase reaction method, and place the targets in the target chamber in the growth chamber of the laser pulse deposition instrument;

[0039] (2) Fix the (111)-oriented perovskite substrate on the sample stage, place the sample stage into the sample introduction chamber, and evacuate the growth chamber and the sample introduction chamber to 5×10 -6 mbar. Then, send the sample stage from the sample introduction chamber into the growth chamber;

[0040] (3) Heat the (111)-oriented perovskite substrate to 750 °C at a rate of 5 °C / min, and use a baffle to separate the target from the substrate. When the temperature reaches 350 °C, introduce O2 to make the pressure in the growth chamber reach 5 mtorr;

[0041] (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target;

[0042] (5) After the pre-sputtering is completed, open the baffle. After the temperature is heated to 750 °C, increase the amount of O2 introduced to make the pressure in the growth chamber reach 100 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 3000 pulses. After the sputtering is completed, heat the sample to 780 °C at a rate of 5 °C / min, deposit the La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 3000 pulses. After the deposition is completed, cool the sample to room temperature at a rate of 5 °C / min, and maintain the O2 pressure at 100 mtorr during the cooling process. Obtain the La-doped hafnium oxide-based ferroelectric thin film.

[0043] Further preferably, before fixing the (111)-oriented perovskite substrate on the sample stage in step (2), it needs to be cleaned, and the (111)-oriented perovskite substrate is ultrasonically cleaned with absolute ethanol.

[0044] Further preferably, after cooling to room temperature in step (5), cut off the O2 supply. After the molecular pump in the growth chamber pumps out the residual O2, connect the growth chamber and the sample introduction chamber, take out the sample stage to the sample introduction chamber, cut off the channel between the growth chamber and the sample introduction chamber, and break the vacuum in the sample introduction chamber to take out the sample stage.

[0045] The preparation method of the La-doped hafnium oxide-based ferroelectric thin film capacitor of the present invention is to first epitaxially grow a buffer layer with the same orientation on the (111)-oriented perovskite substrate, then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer, cover a mask plate on the surface of the La-doped hafnium oxide-based ferroelectric thin film layer, and magnetron sputter a metal target to form a metal top electrode, thereby obtaining the La-doped hafnium oxide-based ferroelectric thin film capacitor.

[0046] Further preferably, the sputtering time is 8 - 12 min.

[0047] Further preferably, the sputtering time is 10 min.

[0048] Principle of the invention: An (111)-oriented La-doped hafnium oxide-based HfO2 thin film HLO is epitaxially grown on a (111)-oriented perovskite substrate, clarifying that the growth orientation of the thin film on this substrate is controlled by surface energy. Moreover, appropriate La doping can significantly reduce the nucleation barrier and domain wall mobility, thereby reducing the coercive field. It is also found that there is a rhombic distortion in the HLO thin film, which originates from the flexoelectric effect caused by the doping of La element, can stabilize the metastable ferroelectric orthorhombic phase, prevent the transformation from the orthorhombic phase to the monoclinic phase, and combined with a lower coercive field, thus optimizing the fatigue performance and enhancing the service life.

[0049] Advantages: Compared with the prior art, the present invention has the following remarkable advantages: The present invention epitaxially grows an (111)-oriented La-doped hafnium oxide-based thin film HLO on a (111)-oriented perovskite substrate, which usefully supplements the experimental growth conditions and methods in the related field. The HLO thin film with an appropriate thickness exhibits good ferroelectric properties. The remanent polarization of the 10-nm thin film can reach 13 μC / cm², and the coercive field is 2.1 MV / cm; the remanent polarization of the 15-nm thin film is 11 μC / cm², and the coercive field is 1.9 MV / cm; the remanent polarization of the 20-nm thin film is 10 μC / cm², and the coercive field is 1.7 MV / cm, all of which are smaller than those of the HZO thin film with the same thickness. In terms of fatigue performance, the 10-nm, 15-nm, and 20-nm thick HLO films can still maintain more than 80%, 74%, and 68% of the remanent polarization after 10 9 cycles, which is significantly better than the HZO thin film with the same thickness. The lower coercive field and more excellent fatigue performance have a positive impact on reducing energy consumption, saving costs, and improving the service life of devices in ferroelectric memories. The laser pulse deposition epitaxial HLO ferroelectric thin film proposed by the present invention has high purity and good film-forming uniformity; at the same time, the operation process is simple, the energy consumption is low, there is no pollution, and it is easy to realize industrialization. Description of the drawings

[0050] Figure 1 It is the operation flow chart of the preparation method of Embodiment 1 of the present invention.

[0051] Figure 2 It is the preparation flow chart of the La-doped hafnium oxide-based ferroelectric capacitor of Embodiment 1 of the present invention.

[0052] Figure 3 It is the schematic diagram of the target sintering temperature of Embodiment 1 of the present invention.

[0053] Figure 4 It is the XRD q-2q pattern of the La-doped hafnium oxide-based ferroelectric thin film of Embodiment 1 of the present invention.

[0054] Figure 5 It is the XRD q-2q pattern of the {111} diffraction of the La-doped hafnium oxide-based ferroelectric thin film of Embodiment 1 of the present invention.

[0055] Figure 6 This is the AFM morphology diagram of the La-doped hafnium oxide-based ferroelectric thin film in Example 1 of the present invention.

[0056] Figure 7 This is the ferroelectric hysteresis loop of the La-doped hafnium oxide-based ferroelectric thin film in Example 1 of the present invention.

[0057] Figure 8 This is the leakage current curve of the La-doped hafnium oxide-based ferroelectric thin film in Example 1 of the present invention.

[0058] Figure 9 This is the fatigue durability cycle diagram of the La-doped hafnium oxide-based ferroelectric thin film in Example 1 of the present invention.

[0059] Figure 10 This is the polarization state diagram of the La-doped hafnium oxide-based ferroelectric thin film in Example 1 of the present invention under different cycle periods. Detailed implementation manners

[0060] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0061] Example 1

[0062] Example 1 provides a method for preparing a La-doped HfO2 ferroelectric thin film and its capacitor on a (111)-oriented SrTiO3 substrate as shown in Figure 1-2 The following steps are specifically included:

[0063] In the first step, a 5% La:HfO2 target and a La 0.67 Sr 0.33 MO3 target are fired by the solid-phase reaction method, and the targets are placed in the target chamber in the growth chamber.

[0064] Specifically, for the firing of the target by the solid-phase reaction method in the first step, first, the calculation and weighing of the powder raw materials are carried out, then the raw materials are ground and mixed. After sufficient grinding and mixing, the powder is pre-sintered for 11 hours (including heating and cooling), and then the pre-sintered powder is pressed into a tablet. The formed target is sintered again for 19 hours (including heating and cooling). The specific method is as follows:

[0065] A1. Calculate the powder dosage. The raw materials selected are HfO2 and La2O3 powders with a purity of 99.99%. According to the target total mass of 15 g and the atomic ratio Hf:La = 19:1, the dosages of the two powders are calculated in advance.

[0066] A2. Weigh the powder, clean a clean area on the desktop, prepare an analytical balance, and weigh the powder for the first time according to about 20% more than the required mass. Place the weighed powder in an oven and keep it at 150 °C for 2 hours to dry the moisture in the powder and prevent unnecessary side reactions in subsequent reactions. After drying, conduct a second measurement and weigh the two powders according to the calculated required mass.

[0067] A3. Grinding: Pour the accurately weighed powder into a mortar and grind it for 5 hours to ensure that the larger particles in the powder are ground into fine small particles and are fully mixed together, thereby increasing the contact area of the reaction and improving the reaction efficiency.

[0068] A4. Pour the ground powder into a corundum crucible. After covering the crucible, place it in a box-type muffle furnace and perform pre-sintering according to the Figure 3 shown pre-sintering heating and cooling steps. On the one hand, pre-sintering the powder can preliminarily connect the powder particles, facilitate atomic diffusion, and promote the formation of the corresponding HLO solid solution during final sintering. On the other hand, it can effectively remove gases such as moisture and carbon dioxide in the raw materials, reduce the volume shrinkage of the target during final sintering, and play a positive role in preventing the target from cracking and getting damp.

[0069] A5. Powder tablet forming: Pour the pre-sintered powder into a mortar and grind it for half an hour. After the powder returns to the state of uniformly mixed small particles, put it into a cylindrical tablet die with a diameter of 25 mm, and use a manual powder press to press it into a cylindrical target. The manual powder press is pressurized to 20 MPa (no binder is added and the pressure required for the HLO target is relatively large), and the pressure holding time is 10 min. The powder tablet forming is considered successful if there is no obvious looseness.

[0070] A6. Target sintering: Place the formed target in a crucible and put it in a box-type muffle furnace, and perform final sintering according to the Figure 3 steps. During the sintering process, it is necessary to control the heating rate and cooling rate to avoid cracking or generating defects in the green body due to thermal stress.

[0071] The second step: Clean the (111)-oriented SrTiO3 substrate. Ultrasonically clean the (111)-oriented SrTiO3 substrate with absolute ethanol.

[0072] Specifically, the specific cleaning method in the second step is to ultrasonically clean with 60 ml of absolute ethanol for 15 min, rinse with absolute ethanol for 15 s, and dry with a nitrogen gun to remove surface impurities and dirt.

[0073] The method of ultrasonically cleaning the SrTiO3 substrate with absolute ethanol is as follows:

[0074] A1. Preparation work: Ensure good ventilation in the operation area and wear appropriate personal protective equipment such as gloves and goggles.

[0075] A2, Preparation of the cleaning chamber: Select a suitable ultrasonic cleaning machine chamber to ensure that it can accommodate the SrTiO3 substrate to be cleaned and the substrate can be completely covered by the liquid. According to the instructions in the operation manual, preheat the cleaning chamber to a temperature suitable for the characteristics of the substrate and contaminants to ensure the best cleaning effect.

[0076] A3, Solution preparation: Pour high-purity anhydrous ethanol into the cleaning chamber. Due to its high purity, it can ensure the cleaning effect and the safety of the substrate.

[0077] A4, Substrate placement: Check and ensure that the surface of the SrTiO3 substrate is clean and intact, and then place it in the cleaning chamber.

[0078] A5, Ultrasonic cleaning: Start the ultrasonic cleaning machine, set the cleaning time to about 15 minutes, and the ultrasonic power can be adjusted appropriately according to the actual situation. Use the ultrasonic oscillation to remove the contaminants on the surface of the substrate.

[0079] A6, Post-cleaning treatment: After cleaning, stop the ultrasonic cleaning machine, take out the substrate, rinse it with pure anhydrous ethanol to remove the residual cleaning agent, and then use a nitrogen gun to generate a drying air flow to dry it thoroughly to make the substrate completely dry.

[0080] In the third step, take out the SrTiO3 substrate, stick it on the sample stage of the laser pulse deposition instrument, and place the sample stage in the sample loading chamber. Evacuate the growth chamber and the sample loading chamber to 5×10 -6 mbar, and then send the sample stage from the sample loading chamber into the growth chamber.

[0081] It should be noted that the used (111)-oriented SrTiO3 substrate, namely strontium titanate, is a compound with a perovskite structure (ABO3 type), where the A site is Sr²⁺ ions and the B site is Ti 4 ⁺ ions. It has a series of excellent physical properties, including high dielectric constant, low dielectric loss, good optical properties, and thermal stability, etc. For cubic SrTiO3, the (111) orientation means that during the crystal growth process, the crystal grows and arranges along the direction of the (111) crystal plane in crystallography, making the surface of the substrate parallel to the (111) crystal plane. The SrTiO3 in the example is a product obtained by processes such as cutting, grinding, and polishing of a single crystal. It has a complete crystal structure, a relatively high dielectric constant itself, a flat surface, and shows good chemical stability in common chemical environments, being able to withstand a certain degree of acid-base corrosion, ensuring that the performance of the substrate will not be significantly affected by chemical factors during various preparation and application processes.

[0082] The sample stage is used to hold the substrate. The sample stage is part of the laser pulse deposition instrument and appears as an alloy carrier plate with a square ceramic piece in the center. On one side of the ceramic piece, the SrTiO3 substrate is pasted, and on the other side, it is used to receive the laser for heating. The sample stage is placed on a specially adapted sample rod in the sample introduction chamber. Subsequently, the sample introduction chamber is closed, and the molecular pump connected to the sample introduction chamber is turned on to evacuate the air. At the same time, the channel between the sample introduction chamber and the growth chamber is kept closed, and the growth chamber always maintains a vacuum degree of 5×10 -6 mbar during non-deposition time. When the vacuum degree of the sample introduction chamber reaches 5×10 -6 mbar, the channel between the sample introduction chamber and the growth chamber is opened, and the sample stage is sent into the growth chamber through the sample rod and fixed on the device in the growth chamber that holds the sample stage. Subsequently, the sample rod is retracted, and the channel between the sample introduction chamber and the growth chamber is closed.

[0083] In the fourth step, the SrTiO3 substrate is heated to 750 °C at a rate of 5 °C / min, and a baffle is used to separate the target from the substrate. When the temperature reaches 350 °C, the reaction gas O2 is introduced to make the pressure in the growth chamber reach 5 mtorr.

[0084] Specifically, when heating the SrTiO3 substrate in the fourth step, the substrate is heated by laser. By adjusting the laser power emitted by the laser, the laser energy is increased, and the laser is focused on the back of the ceramic piece of the sample stage. By heating the ceramic piece on the sample stage, the heat is conducted to the substrate, thereby achieving the heating purpose. Infrared rays are simultaneously emitted on the ceramic piece to detect the temperature for temperature monitoring. The purpose of using a baffle to separate the target from the substrate is to prevent the plume flow generated by sputtering from reaching the substrate during the pre-sputtering process and affecting the normal deposition.

[0085] Furthermore, SrTiO3 may undergo crystal phase transformation at different temperatures. Heating to 750 °C at a rate of 5 °C / min can, to a certain extent, avoid unwanted phase transformation of the substrate. If the heating rate is too fast, it may cause excessive internal stress in the substrate, trigger phase transformation, and affect the performance of the substrate and its bonding with the thin film; while too slow heating rate will affect the production efficiency.

[0086] It should be noted that O2, abbreviated as oxygen, is the gaseous form of the oxygen element in the periodic table under normal temperature and pressure. Oxygen is a colorless, odorless, and tasteless gas that exists widely in nature. It is the second largest component in the air, accounting for about 21%, second only to nitrogen. During the heating stage of the laser pulse deposition of ferroelectric thin films, introducing oxygen mainly has the following effects:

[0087] Cleaning the substrate: At high temperatures, oxygen can react with impurities such as hydrocarbons on the substrate surface to form volatile substances such as carbon dioxide and water, achieving a cleaning effect. At the same time, it can also slightly etch the substrate surface to remove unevenness and defects, making the substrate surface smoother and facilitating the uniform growth of the ferroelectric film in the subsequent process.

[0088] Optimizing the substrate state: Oxygen can change the chemical state and physical properties of the substrate surface, making the atomic arrangement more orderly and the surface energy more appropriate. For example, an oxide layer is formed on the surface of the metal substrate to stabilize the surface, enhance the lattice matching and chemical bonding with the ferroelectric film, and improve the bonding force between the two. In addition, by adjusting the active sites on the substrate surface, the adsorption and reaction of the ferroelectric film precursor are in the best state.

[0089] Pre-reaction and formation of a buffer layer: Oxygen will pre-react with the elements or impurities in the ferroelectric material to oxidize low-valent metal ions to high-valent states and adjust the chemical composition. The reaction may also generate a buffer layer on the substrate surface to relieve the lattice mismatch and thermal stress between the film and the substrate, reduce the internal stress of the film, and improve the stability.

[0090] Creating a suitable atmosphere: Establish an oxygen-rich environment in the chamber in advance to provide stable conditions for the chemical reactions during deposition, ensuring that the chemical composition and crystal structure of the film meet the standards.

[0091] In the fifth step, set the laser power density of the laser in the laser pulse deposition instrument to 1.5 - 2 J / cm², the repetition frequency to 2 Hz. First, pre-sputter the HLO target for 2000 pulses, and then pre-sputter the LSMO target for 2000 pulses.

[0092] Among them, pulsed laser deposition (PLD) is a vacuum thin-film growth technology. It uses high-power laser pulses to bombard the target, melting, evaporating, and ionizing the materials from the surface of the target. This "ablation" will generate an instantaneous and highly luminous plasma plume flow. The plume rapidly expands away from the surface. Place the substrate for depositing the growth material in the appropriate position in advance, so that the plume reaches the substrate for deposition growth to form a film. Its advantages include the ability to precisely control the composition, accurately transfer the target composition to the film, ensure the accuracy of complex chemical compositions and stoichiometry, and can also prepare high-quality films with good crystallinity, high flatness, and strong bonding force with the substrate. Moreover, the applicable material range is extremely wide, covering almost all materials such as metals, semiconductors, ceramics, and polymers. At the same time, it is easy to realize the preparation of multi-layer films and heterostructures, providing strong support for the research and development of new materials and devices.

[0093] A laser power density of 1.5 - 2 J / cm² can provide just the right amount of energy for the target material. If the energy is too low, the target material cannot be fully evaporated and ionized to form a high-quality plasma plume, which will lead to a slow deposition rate and difficulty in film growth. If the energy is too high, the target material may be over-evaporated and sputtered, causing damage to the surface of the target material. It will also make the particles in the plasma plume have too high energy, which may damage the structure and properties of the film when depositing on the substrate surface.

[0094] The repetition frequency of 2 Hz is to control the deposition rate, thereby improving the film quality. 2 Hz means that there are 2 laser pulses acting on the target material per second. Acting together with the power density, it can accurately control the sputtering amount and deposition amount of the target material per unit time, enabling the film to grow at an appropriate rate. Too slow a deposition rate will affect the experimental efficiency, while too fast a rate may lead to problems such as uneven film growth and poor crystallization quality.

[0095] Pre-sputtering is the preparatory work before the formal growth sputtering. By using high-energy ions or plasma generated by laser pulses, etc., it can clean the surface of the target material, remove pollutants such as dust, impurities, and oxide layers that may be adsorbed during the installation process, enabling the target material to participate in the subsequent film deposition process with a clean surface, thus avoiding the incorporation of impurities into the film and ensuring the purity and quality of the film. It can also activate the surface of the target material, making the atoms on the surface of the target material in a more active state. This is because the input of energy during the pre-sputtering process breaks the relatively stable state of the atoms on the surface of the target material, increasing the activity of the surface atoms. The activated surface of the target material is more conducive to reacting or combining with the particles in the plasma during the formal deposition, thereby improving the deposition efficiency and quality of the film and helping the film to grow and crystallize better. Pre-sputtering also plays a role in stabilizing the sputtering process. Pre-sputtering makes the interaction process between the laser and the target material tend to be stable, making the generation and transmission processes of the plasma more stable. In this way, when depositing the film formally later, it can ensure that the sputtered particles have relatively consistent energy and quantity, thereby improving the uniformity and consistency of film growth and being conducive to obtaining a film with stable quality.

[0096] First pre-sputtering the HLO target material and then pre-sputtering the LSMO target material is to keep the change in the growth environment as small as possible. Since the formal growth process is to first grow the LSMO electrode buffer layer, continuously pre-sputtering the LSMO target material together with the LSMO electrode buffer layer is conducive to the relative stability of the deposition environment.

[0097] Step 6: After the pre-sputtering is completed, open the baffle. After the temperature is heated to 750 °C, increase the O2 flow rate to make the pressure in the growth chamber reach 100 mtorr. First, deposit the LSMO layer on the substrate, and set the number of sputtering pulses to 3000 pulses. After the sputtering is completed, heat it to 780 °C at a rate of 5 °C / min, and then deposit the HLO layer, setting the number of sputtering pulses to 2000 pulses. After the deposition is completed, cool the sample to room temperature at a rate of 5 °C / min. During the cooling process, the O2 pressure is kept constant at 100 mtorr. After cooling to room temperature, cut off the O2 supply. After the molecular pump in the growth chamber pumps out the residual O2, connect the growth chamber to the sample loading chamber, take out the sample stage to the sample loading chamber. After cutting off the channel between the growth chamber and the sample loading chamber, break the vacuum in the sample loading chamber and take out the sample stage.

[0098] Specifically, growing LSMO at 750 °C is because LSMO has a perovskite structure. At a temperature of about 750 °C, atoms have enough energy for diffusion and rearrangement, which is beneficial to the formation of a complete and ordered perovskite crystal structure. This temperature can promote the arrangement of atoms such as lanthanum (La), strontium (Sr), manganese (Mn), and oxygen (O) in LSMO at specific lattice positions, thereby obtaining good crystallization quality and electrical properties.

[0099] Furthermore, growing HLO at 780 °C is because hafnium oxide exists in multiple crystal phases, and different crystal phases correspond to different physical properties. At about 780 °C, it is beneficial for hafnium oxide to form a ferroelectric crystal phase, such as the orthorhombic phase or the tetragonal phase. This crystal phase transformation is crucial for realizing the ferroelectric properties of the hafnium oxide thin film, enabling the film to have good polarization characteristics and a hysteresis loop.

[0100] Still further, introducing O2 to 100 mtorr during the deposition process can first stabilize the stoichiometry of the thin film. During the deposition process, introducing oxygen helps to ensure that the metal elements La, Sr, Mn in the LSMO electrode buffer layer, and the metal element Hf in the ferroelectric HLO thin film reach the correct stoichiometry with oxygen. If the oxygen supply is insufficient, oxygen vacancies may appear in the electrode buffer layer and the HLO thin film, causing the chemical composition of the HLO thin film to deviate from the ideal, thereby affecting its ferroelectric properties. Secondly, a suitable oxygen atmosphere is crucial for the formation of a good crystal structure of the ferroelectric thin film. Oxygen participates in the chemical reactions during the deposition process, helping the atoms to arrange according to a specific lattice structure and promoting the formation of a ferroelectric phase with good crystallinity. In particular, the La element is a variable valence element, and there are La 2+ and La 3+ in two valence states in the crystal structure. If the oxygen is insufficient, too much La 2+ is likely to affect the crystal structure, leading to the transformation of the ferroelectric phase to a non-ferroelectric phase.

[0101] Further, the growth times of the LSMO electrode buffer layer and the HLO thin film are set to control their film thicknesses. The thickness of the HLO thin film obtained in this way is about 10 nm.

[0102] After the deposition is completed, the sample is cooled to room temperature at a rate of 5 °C / min. Firstly, this is to stabilize the crystal structure: slow cooling helps the crystal structures of the thin film and the substrate to maintain the specific phase and orientation formed during the deposition process. Cooling at a rate of 5 °C / min allows atoms to have sufficient time for relaxation and adjustment, maintaining the formed crystal structure during the cooling process and avoiding crystal structure distortion or phase transformation caused by rapid cooling, thereby ensuring that the material has the expected physical and chemical properties. Secondly, this is to reduce stress-induced phase transformation: rapid cooling may generate large thermal stresses inside the sample, and these stresses may induce unexpected phase transformations in the crystal structure. When cooling slowly, the thermal stresses can be released more evenly, reducing the possibility of stress-induced phase transformation and making the crystal structure of the sample more stable. Finally, this is to prevent the thin film from detaching from the substrate or generating additional stresses: The HLO thin film and the STO substrate have different thermal expansion coefficients. During the cooling process, if the cooling rate is too fast, the stress generated by the thermal expansion difference between the two may exceed the interfacial bonding force, resulting in the thin film detaching from the substrate. Slow cooling allows more time for the thin film and the substrate to adapt to the thermal expansion difference, reducing the interfacial stress and ensuring good bonding between the thin film and the substrate.

[0103] Step 7: Cover the surface of the sample with a circular mask plate with a diameter of 30 μm, fix it on the magnetron sputtering sample stage, place the sample stage into the sputtering chamber, and pump the background vacuum to 5×10 -5 torr, sputter the Pt target for 10 min to sputter a circular top electrode on the surface of the sample as the metal top electrode of the capacitor, and test the ferroelectric properties of the thin film with a ferroelectric tester.

[0104] It should be noted that magnetron sputtering is a type of physical vapor deposition (PVD) technology. This technology forms a thin film by converting solid materials into gaseous atoms or molecules and depositing them on the surface of the substrate to be coated. After the sample is fixed, the sample stage is carefully placed into the sputtering chamber.

[0105] The sputtering chamber is the core equipment of magnetron sputtering, mainly composed of components such as a vacuum chamber, a target, a substrate holder, and a sputtering source. To ensure the quality of the thin film, the background vacuum of the sputtering chamber needs to be pumped to 5×10 -5torr. Among them, the vacuum chamber plays a crucial sealing role, which can prevent the reaction of the film during the formation process with air or impurities. The gas inside it is extracted by the pumping system to maintain a low-pressure environment; the target material is selected as Pt, which is the raw material for forming the film and will release atoms under the bombardment of high-energy particles; the substrate holder is used to carry the sample, and this sample will be the substrate for the subsequent film formation; the sputtering source activates the target material in a specific way to prompt it to release atoms.

[0106] When the sputtering chamber reaches the required vacuum degree, start sputtering the Pt target for a duration of 10 min. During the sputtering process, the sputtering source works, enabling the target material to release Pt particles. These particles are deposited on the surface of the sample in the form of a sputtering current in the vacuum environment, gradually forming a circular top electrode, which will serve as the metal top electrode of the capacitor.

[0107] Specifically, in the seventh step, the formed thickness of the circular top electrode is 40 nm and the diameter is 30 μm.

[0108] In Example 1, a circular mask plate with a diameter of 30 μm is covered on the surface of the sample, and Pt with a sputtering thickness of 40 nm and a diameter of 30 μm is sputtered as the circular top electrode. Subsequently, the Pt / HLO / LSMO / STO capacitor structure with a Pt top electrode and an LSMO bottom electrode is processed. According to Figure 2 the steps shown, expose the bottom electrode, cover and smear the exposed part with silver paste, and then use a heating table to heat at 70 °C for 5 min to bake dry the ethanol in the silver paste.

[0109] After completing the steps as Figure 2 shown, use a ferroelectric tester to test the ferroelectric properties of the film.

[0110] The XRD q-2q pattern of the sample is as Figure 4 shown. The diffraction peak of the (111) plane of the HLO orthorhombic phase is observed at 2q = 29.7 °, and no monoclinic phase characteristic peak appears, indicating that the film is mainly orthorhombic. The XRD q-2q pattern of the {111} diffraction of the sample is as Figure 5 shown. The 2q angle in the out-of-plane (111) direction is less than that of the in-plane {111} plane, indicating that the out-of-plane lattice constant is larger than the in-plane one, and the HLO film shows a rhombic deformation. The AFM topography of the sample is as Figure 6 shown. Observe the surface topography of the film, select an area of 3×3 μm², and the root mean square roughness is less than 120 pm, with a high surface quality. The hysteresis loop measured by the ferroelectric tester is as Figure 7 shown, and the remanent polarization P r is 13 mC / cm², and the coercive field E c is about 2.1 MV / cm. The current density existing in the film is as Figure 8 shown, and the current is at 10-6 A / cm -2 Magnitude. Fatigue durability tests were carried out as Figure 9 shown. A triangular cyclic pulse with an amplitude of 5 V (more than 1.5 times the coercive force field) was used. After 10 9 cycle periods, more than 80% of the initial polarization was maintained. The polarization state diagrams at different cycle periods are as Figure 10 shown.

[0111] Example 2

[0112] First, a buffer layer (La 0.67 Sr 0.33 MnO3) with a consistent orientation was epitaxially grown on a (111)-oriented SrTiO3 substrate. Then, a La-doped hafnium oxide-based ferroelectric thin film layer was epitaxially grown on the surface of the buffer layer to obtain a La-doped hafnium oxide-based ferroelectric thin film. The La doping concentration of the La-doped hafnium oxide-based was 5 at%. The thickness of the La-doped hafnium oxide-based ferroelectric thin film was 15 nm. A Pt top electrode was further prepared to obtain a capacitor structure, and ferroelectric tests and XRD tests were carried out. The XRD results showed that the HLO had an obvious orthorhombic phase of (111), and the remanent polarization P r was about 11 mC / cm², and the coercive field E c was about 1.9 MV / cm. A triangular cyclic pulse with an amplitude of 5 V (more than 1.5 times the coercive force field) was used. After 10 9 cycle periods, about 74% of the initial polarization was maintained.

[0113] Example 3

[0114] First, a buffer layer (La 0.67 Ca 0.33 MnO3 (LCMO)) with a consistent orientation was epitaxially grown on a (111)-oriented GdScO3 substrate. Then, a La-doped hafnium oxide-based ferroelectric thin film layer was epitaxially grown on the surface of the buffer layer to obtain a La-doped hafnium oxide-based ferroelectric thin film. The La doping concentration of the La-doped hafnium oxide-based was 2 at%. The thickness of the La-doped hafnium oxide-based ferroelectric thin film was 10 nm. The specific experimental steps were as follows:

[0115] (1) The La-doped hafnium oxide-based target and the buffer layer target were fired by the solid-phase reaction method, and the targets were placed in the target chamber in the growth chamber of the pulsed laser deposition instrument;

[0116] (2) The (111)-oriented perovskite substrate wafer was fixed on the sample stage, and the sample stage was placed in the sample introduction chamber. After evacuating the growth chamber and the sample introduction chamber, the sample stage was sent from the sample introduction chamber into the growth chamber;

[0117] (3) Heat the (111)-oriented perovskite substrate wafer to 720 °C, and use a baffle to separate the target from the substrate; when the temperature reaches 320 °C, introduce O2 to make the pressure in the growth chamber reach 3 mtorr;

[0118] (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target;

[0119] (5) After the pre-sputtering is completed, open the baffle. After the temperature is heated to 720 °C, increase the amount of O2 introduced to make the pressure in the growth chamber reach 90 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 2500 pulse; after the sputtering is completed, raise the temperature to 750 °C and deposit a La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 3000 pulse; after the deposition is completed, cool the sample to room temperature, and maintain the O2 pressure at 90 mtorr during the cooling process; obtain a La-doped hafnium oxide-based ferroelectric thin film.

[0120] Further prepare an Au top electrode to obtain a capacitor structure, and perform ferroelectric testing and XRD testing. The XRD results show that HLO has an obvious orthorhombic phase of (111), and the remanent polarization P r is about 9 mC / cm², and the coercive field E c is about 2.5 MV / cm. Using a triangular cyclic pulse with an amplitude of 5 V (more than 1.5 times the coercive force field), after 10 9 cycle periods, about 63% of the initial polarization is maintained.

[0121] Example 4

[0122] First, epitaxially grow a buffer layer (La 0.5 Sr 0.5 MnO3) with the same orientation on a (111)-oriented LaAlO3 substrate, and then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer to obtain a La-doped hafnium oxide-based ferroelectric thin film. The La doping concentration of the La-doped hafnium oxide-based is 8 at%. The thickness of the La-doped hafnium oxide-based ferroelectric thin film is 20 nm. The specific experimental steps are as follows:

[0123] (1) Use the solid-phase reaction method to fire the La-doped hafnium oxide-based target and the buffer layer target, and place the targets in the target chamber in the growth chamber of the pulsed laser deposition instrument;

[0124] (2) Fix the (111)-oriented perovskite substrate wafer on the sample stage, place the sample stage in the sample introduction chamber, evacuate the growth chamber and the sample introduction chamber, and then send the sample stage from the sample introduction chamber into the growth chamber;

[0125] (3) Heat the (111)-oriented perovskite substrate to 780 °C, and use a baffle to separate the target from the substrate; when the temperature reaches 380 °C, introduce O2 to make the pressure in the growth chamber reach 7 mtorr;

[0126] (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target;

[0127] (5) After the pre-sputtering is completed, open the baffle. After the temperature is heated to 780 °C, increase the amount of O2 introduced to make the pressure in the growth chamber reach 110 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 3500 pulse; after the sputtering is completed, heat up to 810 °C and deposit the La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 4000 pulse; after the deposition is completed, cool the sample to room temperature, and maintain the O2 pressure at 110 mtorr during the cooling process; obtain the La-doped hafnium oxide-based ferroelectric thin film.

[0128] Further prepare an Ag top electrode to obtain a capacitor structure, and perform ferroelectric testing and XRD testing. Its XRD results show that HLO has an obvious orthorhombic monoclinic phase of (111), and the remanent polarization P r is about 14 mC / cm², and the coercive field E c is about 2.8 MV / cm. Using a triangular cyclic pulse with an amplitude of 6 V (more than 1.5 times the coercive force field), after 10 9 cycle periods, about 59% of the initial polarization is maintained.

[0129] Example 5

[0130] First, epitaxially grow a buffer layer (La 0.67 Sr 0.33 MnO3) with the same orientation on a (111)-oriented SrTiO3 substrate, and then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer to obtain the La-doped hafnium oxide-based ferroelectric thin film. The La doping concentration of the La-doped hafnium oxide-based is 2 at%. The thickness of the La-doped hafnium oxide-based ferroelectric thin film is 20 nm. The specific experimental steps are as follows:

[0131] (1) Use the solid-phase reaction method to sinter the La-doped hafnium oxide-based target and the buffer layer target, and place the target in the target chamber in the growth chamber of the laser pulse deposition instrument;

[0132] (2) Fix the (111)-oriented perovskite substrate on the sample stage, place the sample stage in the sample introduction chamber, evacuate the growth chamber and the sample introduction chamber, and then send the sample stage from the sample introduction chamber into the growth chamber;

[0133] (3) Heat the (111)-oriented perovskite substrate to 750 °C and separate the target from the substrate using a baffle; when the temperature reaches 350 °C, introduce O2 to make the pressure in the growth chamber reach 5 mtorr;

[0134] (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target;

[0135] (5) After the pre-sputtering is completed, open the baffle. After the temperature is heated to 750 °C, increase the amount of O2 introduced to make the pressure in the growth chamber reach 100 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 3000 pulse; after the sputtering is completed, heat up to 780 °C and deposit a La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 4000 pulse; after the deposition is completed, cool the sample to room temperature, and maintain the O2 pressure at 100 mtorr during the cooling process; obtain a La-doped hafnium oxide-based ferroelectric thin film.

[0136] And cover the Pt electrode on it according to the process and device of Example 1, prepare a capacitor structure, and perform ferroelectric testing and XRD testing. Obtain an HLO ferroelectric thin film with a thickness of about 20 nm, which shows an orthorhombic phase of HLO (111) in the XRD result, and the remanent polarization P r is 10 mC / cm², and the coercive field E c is about 2.5 MV / cm. Using a triangular cyclic pulse with an amplitude of 6 V (more than 1.5 times the coercive force field), after 10 9 cycle periods, maintain about 60% of the initial polarization.

[0137] Example 6

[0138] Clean the SrTiO3 (111)-oriented substrate according to the method of Example 1, perform pre-sputtering on the target, and during the thin film growth stage, grow a buffer layer of La 0.67 Sr 0.33 MnO3 with the same 3000 pulse of growth sputtering, and sputter-grow the HLO layer for 4000 pulse to obtain a La-doped hafnium oxide-based ferroelectric thin film. The La doping concentration of the La-doped hafnium oxide-based is 5 at%. The thickness of the La-doped hafnium oxide-based ferroelectric thin film is 20 nm. The specific steps are as follows:

[0139] (1) Burn the La-doped hafnium oxide-based target and the buffer layer target by the solid-phase reaction method, and place the target in the target chamber in the growth chamber of the laser pulse deposition instrument;

[0140] (2) Fix the cleaned (111)-oriented perovskite substrate on the sample stage, place the sample stage in the sample introduction chamber, and evacuate the growth chamber and the sample introduction chamber to 5×10 -6After mbar, the sample stage is sent from the sample loading chamber into the growth chamber;

[0141] (3) Heat the (111)-oriented perovskite substrate to 750 °C at a rate of 5 °C / min, and use a baffle to separate the target from the substrate; when the temperature reaches 350 °C, introduce O2 to make the pressure in the growth chamber reach 5 mtorr;

[0142] (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target;

[0143] (5) After the pre-sputtering is completed, open the baffle. After the temperature is heated to 750 °C, increase the amount of O2 introduced to make the pressure in the growth chamber reach 100 mtorr. First, deposit a buffer layer on the substrate, and set the number of sputtering pulses to 3000 pulse; after the sputtering is completed, heat it to 780 °C at a rate of 5 °C / min, deposit the La-doped hafnium oxide-based thin film layer, and set the number of sputtering pulses to 4000 pulse; after the deposition is completed, cool the sample to room temperature at a rate of 5 °C / min, and maintain the O2 pressure at 100 mtorr during the cooling process; obtain the La-doped hafnium oxide-based ferroelectric thin film.

[0144] Cover the Pt electrode on the HLO thin film according to the process and device of Example 1, prepare a capacitor structure, and perform ferroelectric testing and XRD testing. Finally, obtain an HLO thin film with a thickness of about 20 nm, which shows that the HLO is an orthorhombic phase of (111) in the XRD result, and the remanent polarization P r is about 10 mC / cm², and the coercive field E c is about 1.7 MV / cm. Using a triangular cyclic pulse with an amplitude of 5 V (more than 1.5 times the coercive force field), after 10 9 cycle periods, maintain about 68% of the initial polarization.

[0145] Comparative Example 1

[0146] Prepare the Hf 0.5 Zr 0.5 O2 target according to the method of Example 1. Clean the SrTiO3 (111)-oriented substrate according to the method of Example 1, perform pre-sputtering on the target, and maintain the same growth conditions during the thin film growth stage. Grow and sputter the La 0.67 Sr 0.33MnO3, sputter-grow the HZO layer for 2000 pulses. Cover the Pt electrode on the HZO thin film according to the process and device of Example 1 to prepare a capacitor structure, and perform ferroelectric testing and XRD testing. An HZO ferroelectric thin film with a thickness of about 10 nm is obtained. In the XRD results, the HZO phase is not observed. Through reciprocal space scanning and scanning transmission electron microscopy (STEM) analysis, it can be found that HZO does not have a pure orientation, but an inclined epitaxy, and there are three crystals with different angles relative to the plane normal direction. Its remanent polarization P r is about 14 mC / cm², and the coercive field E c is about 3.8 MV / cm. After 10 9 cycle periods, about 20% of the initial polarization is maintained.

[0147] Comparative Example 2

[0148] Clean the SrTiO3 (001)-oriented substrate according to the method of Example 1, pre-sputter the target. In the thin film growth stage, maintain the same growth conditions, and grow and sputter La 0.67 Sr 0.33 MnO3 for 2000 pulses on the HLO layer. Cover the Pt electrode on the HLO thin film according to the process and device of Example 1 to prepare a capacitor structure, and perform ferroelectric testing and XRD testing. Finally, an HLO thin film with a thickness of about 10 nm is obtained. In the XRD results, it shows that HLO has an orthorhombic phase of (111) and a monoclinic phase of (-111). The remanent polarization P r is about 14 mC / cm², and the coercive field E c is about 4 MV / cm. Using a triangular cyclic pulse with an amplitude of 7 V (more than 1.5 times the coercive force field), after 10 9 cycle periods, about 18% of the initial polarization is maintained.

Claims

1. A La-doped hafnium oxide-based ferroelectric thin film, characterized in that, The La-doped hafnium oxide-based ferroelectric thin film has a single (111)-oriented orthorhombic phase structure; the La doping concentration of the La-doped hafnium oxide-based is 2-8 at%; the preparation method of the La-doped hafnium oxide-based ferroelectric thin film is to epitaxially grow a buffer layer with consistent orientation on a (111)-oriented perovskite substrate first, and then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer to obtain the La-doped hafnium oxide-based ferroelectric thin film.

2. The HfO₂-based ferroelectric thin film doped with La according to claim 1, characterized in that, The thickness of the La-doped hafnium oxide-based ferroelectric thin film is 10nm - 20nm.

3. A La-doped hafnium oxide-based ferroelectric thin film capacitor, characterized in that, It includes a buffer layer, a La-doped hafnium oxide-based ferroelectric thin film, and a metal top electrode; the La-doped hafnium oxide-based ferroelectric thin film is on the buffer layer, and the metal top electrode is on the La-doped hafnium oxide-based ferroelectric thin film; the La-doped hafnium oxide-based ferroelectric thin film is the La-doped hafnium oxide-based ferroelectric thin film described in Claim 1.

4. The La-doped hafnium oxide-based ferroelectric thin film capacitor according to claim 3, wherein The buffer layer is La (1-x) A x MnO3, where 0 < x < 1, and A is a divalent metal ion.

5. The hafnium oxide-based ferroelectric thin film capacitor doped with La according to claim 3, wherein The thickness of the buffer layer is 15 - 20nm, and the thickness of the metal top electrode is 30 - 50nm.

6. The hafnium oxide-based ferroelectric thin film doped with La according to claim 1, wherein The (111)-oriented perovskite substrate includes SrTiO3, GdScO3, or LaAlO3.

7. The HfO₂-based ferroelectric thin film doped with La according to claim 1, characterized in that, The preparation method specifically includes the following steps: (1) Fire the La-doped hafnium oxide-based target and the buffer layer target by the solid-phase reaction method, and place the targets in the target chamber of the growth chamber of the laser pulse deposition instrument. (2) Fix the (111)-oriented perovskite substrate wafer on the sample stage, put the sample stage into the sample introduction chamber, evacuate the growth chamber and the sample introduction chamber, and then send the sample stage from the sample introduction chamber into the growth chamber. (3) Heat the (111)-oriented perovskite substrate wafer to 720 - 780°C, and use a baffle to separate the target from the wafer; when the temperature reaches 320 - 380°C, introduce O2 to make the pressure in the growth chamber reach 3 - 7mtorr. (4) Perform pre-sputtering on the La-doped hafnium oxide-based target and the buffer layer target. (5) After the pre-sputtering is completed, open the baffle. After heating the temperature to 720 - 780°C, increase the O2 introduction amount to make the pressure in the growth chamber reach 90 - 110mtorr. First deposit the buffer layer on the substrate, and set the number of sputtering times to 2500 - 3500pulse; after the sputtering is completed, heat up to 750 - 810°C and deposit the La-doped hafnium oxide-based thin film layer, and set the number of sputtering times to 2000 - 4000pulse; after the deposition is completed, cool the sample to room temperature, and maintain the O2 pressure at 90 - 110mtorr during the cooling process; obtain the La-doped hafnium oxide-based ferroelectric thin film.

8. The preparation method of the La-doped hafnium oxide-based ferroelectric thin film capacitor according to claim 3, characterized in that, First epitaxially grow a buffer layer with consistent orientation on a (111)-oriented perovskite substrate, then epitaxially grow a La-doped hafnium oxide-based ferroelectric thin film layer on the surface of the buffer layer, cover a mask plate on the surface of the La-doped hafnium oxide-based ferroelectric thin film layer, magnetron sputter a metal target to form a metal top electrode, and obtain a La-doped hafnium oxide-based ferroelectric thin film capacitor.

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