Gradient diffusion doped ferroelectric film and preparation method thereof

Abstract

The invention discloses a gradient diffusion doped ferroelectric film and a preparation method thereof. The preparation method comprises the following steps: selecting a substrate and depositing a film layer on the substrate; preparing a ferroelectric film on the substrate on which the film layer is deposited by using a chemical method; and performing high-energy crystallization treatment on the ferroelectric film to obtain the gradient doped ferroelectric film. According to the invention, a means of preparing the film through a chemical method is combined with a characteristic of diffusing film particles through continuous action of a high-energy crystallization method, so that the element gradient doped ferroelectric film with strong ferroelectric property and high polarization switching speed is effectively prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ferroelectric information devices, and particularly relates to a gradient diffusion doped ferroelectric thin film and a preparation method thereof. BACKGROUND

[0002] The artificial intelligence era has put forward huge demands for information devices with high speed, low power consumption and high recognition accuracy. Among emerging information devices, ferroelectric information devices stand out due to their unique ferroelectricity, low power consumption, high speed and stability. However, it is challenging to make ferroelectric thin films have both super strong ferroelectricity and extremely fast polarization reversal speed.

[0003] To make ferroelectric thin films have high content of ferroelectric phase or fast polarization reversal speed, previous researchers have made various attempts such as introducing doping elements (silicon, aluminum, zirconium, etc.), adjusting film thickness, adjusting stress, optimizing annealing temperature, etc. Hao et al. prepared a gradient zirconium-doped hafnium oxide ferroelectric thin film to improve the polarization reversal speed. However, no obvious enhancement of ferroelectricity was observed in this system. Zhou et al. prepared a lanthanum and tantalum double-doped hafnium oxide ferroelectric thin film to achieve a super-thin hafnium oxide ferroelectric thin film with strong ferroelectricity and fast polarization reversal. However, this system still faces the problem of low ferroelectric polarization intensity, which seriously limits the overall improvement of the performance of ferroelectric information devices. Therefore, the technology for simultaneously improving ferroelectricity and polarization reversal speed still needs to be improved and developed.

[0004] The strong ferroelectric performance of ferroelectric thin films can effectively improve the storage performance, enhance the logic operation ability, improve the sensor performance and optimize the performance of optoelectronic devices for ferroelectric information devices. However, the residual polarization value of most ferroelectric capacitors is in the range of 20−25 µC / cm 2 To improve the ferroelectric performance, doping elements are introduced, the film thickness is adjusted, the stress is adjusted, and the annealing temperature is optimized. As for the polarization reversal speed of ferroelectric thin films in ferroelectric information devices, its fast reversal can effectively improve the read-write speed of memory devices, improve the operation efficiency of logic devices and promote the integration and miniaturization of devices. The common ways to improve the polarization reversal speed include single-element doping, gradient doping of elements and different annealing temperatures. However, the polarization reversal speed of these methods is basically in the microsecond level and the ferroelectric performance has not been significantly improved. There is also a method of using double-element co-doping to improve the polarization reversal speed, which is lower than the microsecond level but has poor ferroelectric performance. SUMMARY

[0005] To solve the above problems in the prior art, the application provides a gradient diffusion doped ferroelectric thin film and a preparation method thereof. The technical problems to be solved by the application are solved by the following technical solutions. One aspect of the present application provides a method for preparing a gradient diffusion doped ferroelectric thin film, comprising: S1: selecting a substrate and depositing a thin film layer on the substrate; S2: preparing a ferroelectric thin film on the substrate with the thin film layer deposited thereon by a chemical method; S3: performing high-energy crystallization treatment on the ferroelectric thin film to obtain a gradient diffusion doped ferroelectric thin film with a distorted electric effect.

[0006] In one embodiment of the present application, the thin film layer is a metal layer, a metal oxide layer or a semiconductor layer, and has a thickness of 5-100 nm.

[0007] In one embodiment of the present application, the chemical method in S2 includes sol-gel method, chemical vapor deposition or electrochemical deposition method.

[0008] In one embodiment of the present application, the material of the thin film layer is ZnO, the chemical method in S2 is sol-gel method, and S2 comprises: S2.1: preparing HfCeO x a precursor solution; S2.2: spin-coating the HfCeO x a precursor solution on the substrate at a preset rotation speed for a predetermined time; S2.3: sequentially performing a drying process and a pyrolysis process on the sample with the HfCeO x a precursor solution spin-coated thereon; S2.4: repeating the spin-coating-drying-pyrolysis process of steps S2.2 and S2.3 until a ferroelectric thin film with a desired thickness is obtained.

[0009] In one embodiment of the present application, S2.3 comprises: drying the sample with the HfCeO x a precursor solution spin-coated thereon in an air atmosphere at a temperature of 150-200℃ for 60-300s, and then pyrolyzing the sample in an air atmosphere at a temperature of 300-400℃ for 60-300s.

[0010] In one embodiment of the present application, S3 comprises: adopting a rapid annealing process to anneal the substrate with the ferroelectric thin film prepared thereon at a first temperature for a third preset time and at a second temperature for a fourth preset time to form a gradient diffusion doped ferroelectric thin film, wherein the first temperature is less than the second temperature.

[0011] Another aspect of the present application provides a gradient diffusion doped ferroelectric thin film prepared by the method according to any one of the above embodiments.

[0012] Compared with the prior art, the present application has the following advantages: In view of the problem that the ferroelectric phase content and polarization switching speed of the ferroelectric thin film are difficult to be simultaneously improved and maintained at a high level in the prior art, the present application provides a preparation method of a gradient diffusion doped ferroelectric thin film, which combines the means of preparing the thin film by a chemical method with the characteristics of the high-energy crystallization method for continuously acting on the thin film particles to diffuse, so as to effectively prepare the element gradient diffusion doped ferroelectric thin film with strong ferroelectric performance and fast polarization switching speed. Moreover, it is proved by the phase field simulation that the element gradient doped ferroelectric thin film with strong ferroelectric performance and fast polarization switching speed is caused by the distorted electric effect generated in the thin film.

[0013] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flow chart of a preparation method of a gradient diffusion doped ferroelectric thin film provided by an embodiment of the present application; Figure 2 is a schematic diagram of a chemical reaction and a pyrolysis process provided by an embodiment of the present application; Figure 3 is an HfCeO x ferroelectric thin film and a gradient Zn doped HfCeO x ferroelectric thin film prepared by the preparation method of the present embodiment P - E curve comparison; Figure 4 is an HfCeO x ferroelectric thin film and a gradient Zn doped HfCeO x thin film prepared by the preparation method of the present embodiment Figure 5 is a simplified schematic diagram of a gradient doping distribution mode discussed in a phase field model; Figure 6 is a polarization switching speed curve of an HfO2-based ferroelectric thin film simulated by the present embodiment P - E curve; Figure 7 is a schematic diagram of a ferroelectric phase distribution of an HfO2-based thin film simulated by the present embodiment Figure 8 is a schematic diagram of a strain gradient of an HfO2-based ferroelectric thin film in a thickness direction ε 11,2 simulated by the present embodiment. DETAILED DESCRIPTION

[0015] In order to further clarify the technical means and effects taken by the present application to achieve the predetermined object, the gradient diffusion doped ferroelectric thin film and the preparation method thereof according to the present application are described in detail below in combination with the drawings and specific embodiments.

[0016] The foregoing and other technical contents, features and effects of the present application can be clearly presented in the following detailed description of specific embodiments in combination with the drawings. Through the description of specific embodiments, the technical means and effects taken by the present application to achieve the predetermined object can be more deeply and specifically understood. However, the accompanying drawings are provided for reference and illustration only, and are not intended to limit the technical solutions of the present application.

[0017] It should be noted that, in this document, relational terms such as first and second and the like can only be used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations exist in any such actual relationship or order. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a list of elements does not necessarily include only those elements in the list, but can include other elements not expressly listed or included. Without more limitations, the element defined by the sentence "comprising a" does not exclude the presence of additional identical elements in the process, method, article or apparatus including the element.

[0018] Embodiment one Please refer to Figure 1 , Figure 1 The present application provides a preparation method flow chart of a gradient diffusion doped ferroelectric thin film, which improves the ferroelectric phase content and polarization switching speed of the thin film by changing the lattice distortion inside the thin film. The preparation method specifically includes: S1: selecting a substrate and depositing a thin film layer on the substrate.

[0019] The selected substrate includes but is not limited to a silicon wafer, a platinum sheet, a mica substrate, etc. The prepared thin film layer includes but is not limited to a metal layer, a metal oxide layer and a semiconductor layer, etc. The elements contained in the substance of the thin film layer include but are not limited to Al, Si, Zr, Y, etc. The thickness is several nanometers to tens of nanometers.

[0020] In this embodiment, the selected substrate is heavily doped P-type Si(100) (p +a metal oxide layer on the surface of the selected substrate. The metal oxide layer includes but is not limited to zinc oxide, tungsten oxide, silicon oxide, etc. Preferably, the metal oxide of the embodiment is zinc oxide, and the thickness is about 20 nm. In other embodiments, the process for preparing the thin film layer includes but is not limited to atomic layer deposition technology, magnetron sputtering technology, sol-gel method, chemical vapor deposition technology, etc.

[0021] S2: preparing a ferroelectric thin film on the thin film layer by a chemical method.

[0022] The step S2 of the embodiment includes: S2.1: preparing a HfCeO x precursor solution.

[0023] Specifically, the mass of the two solutes of hafnium acetylacetonate and cerium nitrate required for preparing the solution is calculated according to the mole percentage; a predetermined amount of hafnium acetylacetonate is dissolved in an acetic acid solution and placed on a magnetic stirrer for stirring until completely dissolved to obtain solution A; cerium nitrate and a certain amount of acetylacetone are added to the solution A to obtain solution B, which is magnetically stirred for 20 minutes until completely dissolved; solution B is heated in a water bath for 40 minutes, and the thin film precursor solution C is obtained after stirring for 6 hours by using a magnetic stirrer; then, the thin film precursor solution C is filtered to obtain the HfCeO x precursor solution, wherein the doping amount of cerium (Ce) is 15%, and the concentration is 0.1-0.3 mol / L.

[0024] S2.2: spin-coating the HfCeO x precursor solution on the substrate at a preset rotation speed for a predetermined time.

[0025] Specifically, the HfCeO x precursor solution is spin-coated on the substrate at a first rotation speed for a first predetermined time, and then spin-coated at a second rotation speed for a second predetermined time, wherein the first rotation speed is less than the second rotation speed, and preferably, the first predetermined time is 10-40 s, and the second predetermined time is 20-60 s; the first rotation speed is 300-800 r / min, and the second rotation speed is 3000-5000 r / min.

[0026] S2.3: sequentially performing a drying process and a pyrolysis process on the sample spin-coated with the HfCeO x precursor solution.

[0027] Specifically, the sample spin-coated with the HfCeO xThe sample of the precursor solution is dried at a temperature of 150-200 ℃ for 60-300 s in an air atmosphere; and then pyrolysis treatment is performed at a temperature of 300-400 ℃ for 60-300 s in an air atmosphere, and the pyrolysis treatment is to remove the organic matter in the solution.

[0028] S2.4: Repeat the spin-drying-pyrolysis process of steps S2.2 and S2.3 until the ferroelectric thin film with a desired thickness is obtained.

[0029] In this embodiment, the HfCeO x The precursor solution is used to form the ferroelectric thin film by repeating the spin-drying-pyrolysis process. In the pyrolysis process, the ZnO and HfCeO x The precursor solution undergoes the following chemical reaction: ZnO + 2HNO3= Zn (NO3)2+ H2O, as shown in the following formula: Figure 2 The thickness of the prepared ferroelectric thin film is as low as several nanometers and as high as microns.

[0030] S3: Perform high-energy crystallization treatment on the ferroelectric thin film to obtain a gradient-doped ferroelectric thin film with a perturbed electric effect.

[0031] Specifically, the substrate with the prepared ferroelectric thin film is annealed at a first temperature for a third preset time and then annealed at a second temperature for a fourth preset time by using a rapid annealing process to form the gradient-doped ferroelectric thin film, wherein the first temperature is less than the second temperature.

[0032] In this embodiment, the substrate with the prepared ferroelectric thin film is pre-annealed at 400 ℃ for 300 s and then high-temperature annealed at 800 ℃ for 400 s by using a rapid thermal annealing process to form the gradient-doped ferroelectric thin film. In this step, the ferroelectric thin film is crystallized by the method of high-energy crystallization (i.e., high-temperature annealing) and the depth of the element diffusion of the thin film layer is controlled. The time of the high-energy continuous action controls the depth of the element diffusion of the thin film layer, and the element diffusion can be controlled to any depth by controlling the time of the continuous annealing.

[0033] In other embodiments of the present application, the diffusion of the ferroelectric thin film and the element diffusion of the thin film layer can also be realized by the method of high-energy crystallization such as laser or particle beam irradiation.

[0034] Embodiment Two Based on the embodiment one, the present embodiment provides a specific preparation method of the gradient-diffusion-doped ferroelectric thin film, comprising: Step 1: Prepare a ZnO thin film on the upper surface of a p + -Si substrate by using a magnetron sputtering process, thereby obtaining a ZnO / p + -Si substrate.

[0035] Step 2: Calculate the mass of the two solutes, hafnium acetylacetonate and cerium nitrate, required for preparing the solution according to the mole percentage. Dissolve a predetermined amount of hafnium acetylacetonate in acetic acid solution and place it on a magnetic stirrer to stir until completely dissolved to obtain solution A; add cerium nitrate and acetylacetone to the above solution A to obtain solution B, and stir for 20 minutes by magnetic stirring until completely dissolved; heat solution B in a water bath for 40 minutes, and obtain thin film precursor solution C after stirring for 6 hours by magnetic stirrer; then filter the thin film precursor solution C to obtain a ferroelectric thin film precursor solution (i.e. HfCeO x precursor solution) with a cerium doping amount of 15% and a concentration of 0.1 mol / L.

[0036] Step 3: Spin-coat the above HfCeO x precursor solution on the ZnO / p + -Si substrate by the method of spin-coating at a lower speed and a higher speed, specifically, first spin-coat at a speed of 500 rpm for 15 s, and then spin-coat at a speed of 4000 rpm for 30 s.

[0037] Step 4: Perform a drying process and a pyrolysis process on the ZnO / p x -Si substrate on which the HfCeO + precursor solution has been spin-coated. Specifically, the drying process is to dry at 180 ℃ for 180 s in an air atmosphere, and the pyrolysis process is to pyrolysis treatment at 350 ℃ for 180 s in an air atmosphere, and repeat the spin-coating, drying and pyrolysis 5 times.

[0038] Due to the reaction of ZnO with nitric acid, the drying process at 180 ℃ for 180 s and the air pyrolysis process at 350 ℃ for 180 s result in the initial diffusion doping of Zn. After repeated spin-coating and drying-pyrolysis processes, a Zn initial diffusion doped HfCeO x thin film with a thickness of about 85 nm is obtained.

[0039] Step 5: Anneal at a high temperature of 800 ℃ for 400 s in an N2 atmosphere by a rapid annealing furnace to obtain a Zn element gradient doped HfCeO x crystalline thin film (ferroelectric thin film).

[0040] Finally, in order to perform electrical characterization, a MFM capacitor structure with a Pt top point electrode is sputtered on the Zn gradient diffusion doped HfCeO x (Zn:HCO) thin film by using a direct current small ion sputtering instrument, and the radius of the electrode circle point is 60 µm.

[0041] Please refer to Figure 3 , Figure 3 , which is an undoped HfCeO xFerroelectric thin films and Zn:HCO prepared using the method of this embodiment under annealing conditions at 800 °C P – E Curve, from Figure 3 It can be observed that, under saturated electric field conditions, the ferroelectric properties of the Zn:HCO thin film prepared by this invention are improved by about 40%.

[0042] Please see Figure 4 , Figure 4 It is undoped HfCeO x The polarization reversal rate curves of the ferroelectric thin film and the Zn:HCO thin film prepared using the method of this embodiment are shown below. Figure 4 It can be observed that, under the same electric field conditions, the polarization reversal speed of the Zn:HCO thin film prepared by this invention is significantly improved.

[0043] To address the challenge of simultaneously controlling ferroelectricity and polarization reversal characteristics, this embodiment proposes a gradient diffusion-doped ferroelectric thin film and its preparation method, leveraging the combined effects of chemical thin film preparation and high-energy crystallization to achieve particle diffusion. This method effectively prepares ferroelectric thin films with both strong ferroelectric properties and rapid polarization switching speed.

[0044] The effects of three different Zn distribution patterns on the ferroelectric properties of HfO2-based ferroelectric thin films were analyzed using the established phase-field model. These three distribution patterns included undoped Zn, uniformly doped Zn, and gradient-doped Zn. Based on experimental observations, the gradient doping distribution mode discussed in the phase-field model was simplified to... Figure 5 The pattern shown (where x2 represents film thickness) uses different colors to represent different doping concentrations. To align with experimental doping concentrations and facilitate calculations, the doping concentrations are divided into three layers from bottom to top: 6.4%, 3.2%, and 0%. Notably, under both uniform and gradient distributions, the average Zn concentration in the film remains constant at 3.2%.

[0045] Based on the model, this embodiment simulates as follows: Figure 6 The HfO2-based ferroelectric thin films shown are undoped Zn, uniformly doped Zn, and gradient-doped Zn. P – E The curves revealed that the HfO2-based ferroelectric thin film with 3.2% Zn gradient doping exhibited the highest remanent polarization, reaching 25.54 μC / cm. 2 This indicates that Zn gradient doping results in superior macroscopic electrical properties of HfO2 ferroelectric films compared to uniformly doped and undoped Zn-based films. (See also: [link to relevant documentation]). Figure 7 , Figure 7are schematic diagrams of ferroelectric phase distribution of HfO2-based ferroelectric thin films with undoped Zn, uniformly doped Zn and gradiently doped Zn, wherein (a) is undoped, (b) is uniformly doped, (c) is gradiently doped, and (d) is a statistical diagram of ferroelectric phase content in (a)-(c).

[0046] In order to explore the effect of Zn gradient distribution on the ferroelectric phase of the thin film, it is assumed that the strain gradient introduced by the gradient distribution of Zn atoms in the thin film promotes the formation of the polarization phase in the thin film. Figure 7 (a)-(c) show that the blue area is the polarization area, which is the ferroelectric phase, and the gray area is the non-ferroelectric phase. Figure 7 (d) counts the volume fraction of the ferroelectric phase under three conditions. In the undoped and uniformly doped Zn HfO2 thin film, the proportion of the ferroelectric phase is 45.29% and 55.06% respectively. The volume fraction of the ferroelectric phase in the doped thin film increases significantly, and the distribution of the ferroelectric phase is obviously more uniform. Zn doping has a significant promoting effect on the formation of the ferroelectric phase of the HfO2-based thin film. The volume fraction of the ferroelectric phase in the gradiently doped Zn HfO2-based ferroelectric thin film increases to 67.70%, indicating that gradient doping has a great promoting effect on the enhancement of the ferroelectricity of the HfO2-based thin film.

[0047] Figure 8 are strain gradients of the simulated Zn uniformly distributed thin film and the Zn gradiently distributed thin film respectively ε 11,2 , wherein (a) is Zn uniformly doped, and (b) is Zn gradiently doped. ε 11,2 , wherein (a) is Zn uniformly doped, and (b) is Zn gradiently doped. It can be seen that there is a large and uniform strain gradient in the gradiently doped thin film, while the strain gradient in the uniformly doped thin film is small. The existence of the strain gradient promotes the generation of the ferroelectric phase through the flexoelectric effect, thereby improving the ferroelectric performance of the thin film.

[0048] In order to solve the problem that the existing technology cannot simultaneously improve the ferroelectric phase content and the polarization switching speed of the ferroelectric thin film and keep them at a high level, the present application provides a gradient diffusion doped ferroelectric thin film and a preparation method thereof. The present application combines the means of preparing the thin film by chemical method with the characteristics of the continuous action of high-energy crystallization method to effectively prepare an element gradiently doped ferroelectric thin film with strong ferroelectric performance and fast polarization switching speed. Moreover, the present application uses phase field simulation to confirm that the element gradiently doped ferroelectric thin film with strong ferroelectric performance and fast polarization switching speed is due to the flexoelectric effect generated in the thin film.

[0049] In several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the above-described device embodiments are merely illustrative, for example, the division of the modules is only a logical function division, and actual implementation can have another division manner, for example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0050] In addition, each function module in each embodiment of the present application can be integrated into a processing module, or each module can exist physically alone, or two or more modules can be integrated into one module. The integrated module can be realized in the form of hardware or in the form of a hardware plus software function module.

[0051] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application should not be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, several simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A method for preparing a gradient-diffusion doped ferroelectric thin film, characterized in that, The method comprises the following steps: S1: selecting a substrate and depositing a thin film layer on the substrate; S2: preparing a ferroelectric thin film on the substrate with the thin film layer deposited thereon by using a chemical method; S3: performing high-energy crystallization treatment on the ferroelectric thin film to obtain a gradient-doped ferroelectric thin film with a distorted electric effect.

2. The method for preparing gradient diffusion-doped ferroelectric thin films according to claim 1, characterized in that, The thin film layer is a metal layer, a metal oxide layer or a semiconductor layer, and has a thickness of 5-100 nm.

3. The method for preparing gradient diffusion-doped ferroelectric thin films according to claim 1, characterized in that, The chemical method in S2 comprises a sol-gel method, a chemical vapor deposition method or an electrochemical deposition method.

4. The method for preparing gradient diffusion-doped ferroelectric thin films according to claim 1, characterized in that, The material of the thin film layer is ZnO, the chemical method in S2 is a sol-gel method, and S2 comprises the following steps: S2.1: Preparation of HfCeO x precursor solution; S2.2: depositing said HfCeO x The precursor solution is spin-coated on the substrate at a preset rotation speed for a predetermined time. S2.3: spin coating the HfCeO x The sample of the precursor solution is subjected to a drying process and a pyrolysis process in this order; S2.4: repeating the spin-coating-drying-pyrolysis process of steps S2.2 and S2.3 until a ferroelectric thin film with a desired thickness is obtained.

5. The method for preparing gradient diffusion-doped ferroelectric thin films according to claim 4, characterized in that, S2.3 comprises the following steps: spin-coated with the HfCeO x A sample of the precursor solution was dried under air atmosphere at a temperature of 150-200 °C for 60-300 s; followed by pyrolysis treatment under air atmosphere at a temperature of 300-400 °C for 60-300 s.

6. The method for preparing gradient diffusion-doped ferroelectric thin films according to claim 1, characterized in that, S3 comprises the following steps: The substrate with the prepared ferroelectric thin film is annealed at a first temperature for a third preset time and then annealed at a second temperature for a fourth preset time by using a rapid annealing process to form a gradient-doped ferroelectric thin film, wherein the first temperature is less than the second temperature.

7. A graded-diffusion-doped ferroelectric thin film, characterized in that, The method is prepared by using any one of claims 1-6.

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