PVDF ferroelectric film, preparation method thereof and ferroelectric device

Abstract

The application relates to the technical field of PVDF ferroelectric film preparation, and particularly provides a PVDF ferroelectric film, a preparation method thereof and a ferroelectric device. The method comprises the following steps: preparing an initial PVDF film; placing the initial PVDF film on a moving platform; controlling a femtosecond laser to generate a downward laser beam, and controlling the moving platform to drive the initial PVDF film to move below the femtosecond laser, so as to scan the initial PVDF film by the laser beam and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film. The method can effectively overcome the limitation that micro-area regulation and control is difficult to implement, and effectively avoid the problems of introducing additional mechanical stress, high-voltage breakdown risk or nanometer impurities.

Description

Technical Field

[0001] This application relates to the field of PVDF ferroelectric thin film preparation technology, and more specifically, to a PVDF ferroelectric thin film, its preparation method, and ferroelectric devices. Background Technology

[0002] Polyvinylidene fluoride (PVDF) and its copolymers exhibit broad application prospects in sensors, actuators, energy harvesters, and non-volatile memories due to their excellent flexibility, biocompatibility, and low acoustic impedance. The ferroelectricity of PVDF primarily stems from the β-crystalline phase formed by the ordered arrangement of -CF2- dipoles in its molecular chains. Therefore, efficiently and precisely inducing and optimizing the β-crystalline phase in PVDF films is crucial for preparing high-performance PVDF ferroelectric films.

[0003] Currently, the main methods for inducing and optimizing the β phase in PVDF films include mechanical stretching, high-voltage electric field polarization, and nanocomposite modification. Mechanical stretching involves unidirectional or bidirectional stretching of the α-phase film at a specific temperature, causing the molecular chains to align and transform into the β phase. This method is complex, difficult to control locally in micro-regions, and may introduce internal stress and defects into the film, affecting its mechanical properties and stability. High-voltage electric field polarization applies an extremely high DC electric field to the film at high temperatures, causing dipoles to align along the electric field direction. This method requires sophisticated equipment, carries a risk of breakdown, and is difficult to achieve complex patterned polarization, limiting its application in microelectronic devices. Nanocomposite modification promotes β-phase nucleation by adding nanofillers. This method may introduce impurities, affecting the purity and uniformity of the material, and consequently impacting the electrical properties and long-term stability of the PVDF ferroelectric film.

[0004] The existing techniques used in the preparation of PVDF ferroelectric thin films generally suffer from problems such as complex processes, difficulty in achieving precise local control, and easy introduction of defects or impurities. This leads to unstable performance of the prepared PVDF ferroelectric thin films, making it difficult to meet the demands of high-performance, miniaturized ferroelectric devices. Therefore, developing a novel preparation method that can precisely control the polarization process of PVDF thin films, effectively induce β-phase formation, and simultaneously avoid introducing defects and impurities is of great significance for promoting the application of PVDF ferroelectric materials.

[0005] There is currently no effective technical solution to the above problems. Summary of the Invention

[0006] The purpose of this application is to provide a PVDF ferroelectric thin film, its preparation method, and ferroelectric devices, which can effectively overcome the limitations of micro-region control and effectively avoid the problems of introducing additional mechanical stress, high-voltage breakdown risk, or nano-impurities.

[0007] In a first aspect, this application provides a method for preparing PVDF ferroelectric thin films, which includes the following steps:

[0008] S1. Preparation of initial PVDF film;

[0009] S2. Place the initial PVDF film on the moving platform;

[0010] S3. Control the femtosecond laser to generate a downward laser beam, and control the moving platform to drive the initial PVDF film to move below the femtosecond laser, so as to use the laser beam to scan the initial PVDF film and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film.

[0011] Step S3 includes:

[0012] S31. Obtain the initial PVDF film thickness, crystal phase content, and surface morphology information;

[0013] S32. Determine the operating parameters of the femtosecond laser and the moving speed of the moving platform based on the thickness information, crystal phase content and surface morphology information;

[0014] S33. Control the femtosecond laser to operate according to the operating parameters so that the femtosecond laser produces a downward laser beam;

[0015] S34. Control the moving platform to drive the initial PVDF film to move below the femtosecond laser according to the moving speed, so as to use the laser beam to scan the initial PVDF film and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film.

[0016] This application provides a method for preparing PVDF ferroelectric thin films. By introducing femtosecond laser scanning technology, the method achieves non-thermal and filler-free modification and polarization of PVDF thin films. Specifically, this method can precisely induce the dipole orientation in the PVDF molecular chain without causing thermal damage or adding nanofillers, thereby promoting the formation of the β-crystal phase. Therefore, this method can effectively overcome the limitations of micro-region control and effectively avoid the introduction of additional mechanical stress, high-voltage breakdown risk, or nano-impurities, thus ensuring the purity and stability of the PVDF ferroelectric thin film. Consequently, the PVDF ferroelectric thin film can meet the requirements of high-performance, miniaturized ferroelectric devices.

[0017] Optionally, step S3 further includes the step:

[0018] A1. During the scanning of the initial PVDF film using a laser beam, monitor the modification state and surface temperature of the initial PVDF film.

[0019] A2. Adjust the operating parameters of the femtosecond laser and the moving speed of the moving platform according to the modified state and surface temperature to scan the initial PVDF film without ablating it.

[0020] This technical solution effectively avoids film ablation problems caused by discrepancies between preset parameters and actual conditions by dynamically adjusting the operating parameters of the femtosecond laser and the moving speed of the platform based on real-time monitoring of the modification state and surface temperature during laser scanning. This significantly improves the yield and quality stability of PVDF ferroelectric thin films. Furthermore, this solution reduces the stringent requirements for initial operating parameters and moving speed settings, effectively enhancing the robustness and adaptability of the ferroelectric thin film fabrication process.

[0021] Optionally, step A2 includes:

[0022] A21. Obtain the deviation of the modified state based on the change curve of the modified state and the preset modified state;

[0023] A22. Under the premise that the surface temperature is less than the preset ablation critical point threshold, generate the operating parameter compensation factor and the moving speed compensation factor according to the modified state deviation and the preset adjustment rules.

[0024] A23. The operating parameters of the femtosecond laser are compensated according to the operating parameter compensation factor, and the moving speed of the moving platform is compensated according to the moving speed compensation factor, so as to scan the initial PVDF film without ablation of the initial PVDF film.

[0025] Optionally, step S32 includes:

[0026] S321. Based on the thickness information, crystal phase content, and surface morphology information, query the pre-built database or lookup table of mapping relationships between thickness information, crystal phase content, surface morphology, femtosecond laser parameters, and thin film moving speed to determine the operating parameters of the femtosecond laser and the moving speed of the moving platform.

[0027] Optionally, the operating parameters include laser beam wavelength, laser beam pulse width, laser beam frequency, and laser beam single pulse energy.

[0028] Secondly, this application also provides a PVDF ferroelectric thin film, which is prepared by the PVDF ferroelectric thin film preparation method provided in the first aspect above.

[0029] Thirdly, this application also provides a ferroelectric device comprising the PVDF ferroelectric thin film provided in the second aspect above.

[0030] As can be seen from the above, the PVDF ferroelectric thin film, its preparation method, and the ferroelectric device provided in this application achieve non-thermal and filler-free modification and polarization of the PVDF thin film by introducing femtosecond laser scanning technology. That is, this application can accurately induce the dipole orientation in the PVDF molecular chain without causing thermal damage and without adding nanofillers to promote the formation of the β crystal phase. Therefore, this application can effectively overcome the limitations of difficult micro-area control and effectively avoid the problems of introducing additional mechanical stress, high voltage breakdown risk, or nano-impurities, thereby ensuring the purity and stability of the PVDF ferroelectric thin film. In this way, the PVDF ferroelectric thin film can meet the requirements of high-performance and miniaturized ferroelectric devices. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating a method for preparing a PVDF ferroelectric thin film, as provided in an embodiment of this application. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0033] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] Firstly, such as Figure 1 As shown, this application provides a method for preparing PVDF ferroelectric thin films, which includes the following steps:

[0035] S1. Preparation of initial PVDF film;

[0036] S2. Place the initial PVDF film on the moving platform;

[0037] S3. Control the femtosecond laser to generate a downward laser beam, and control the moving platform to drive the initial PVDF film to move below the femtosecond laser, so as to use the laser beam to scan the initial PVDF film and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film.

[0038] Step S3 includes:

[0039] S31. Obtain the initial PVDF film thickness, crystal phase content, and surface morphology information;

[0040] S32. Determine the operating parameters of the femtosecond laser and the moving speed of the moving platform based on the thickness information, crystal phase content and surface morphology information;

[0041] S33. Control the femtosecond laser to operate according to the operating parameters so that the femtosecond laser produces a downward laser beam;

[0042] S34. Control the moving platform to drive the initial PVDF film to move below the femtosecond laser according to the moving speed, so as to use the laser beam to scan the initial PVDF film and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film.

[0043] This application achieves precise local modification and polarization of PVDF thin films by introducing femtosecond laser scanning technology, effectively overcoming the limitations of traditional methods in terms of process complexity, control precision and material purity, and providing a new approach for preparing high-performance and miniaturized PVDF ferroelectric thin films.

[0044] To better understand the PVDF ferroelectric thin film preparation method proposed in this application, the following describes some key terms and implementation environments. PVDF (polyvinylidene fluoride) in this embodiment is a semi-crystalline polymer, whose ferroelectricity mainly originates from the β-phase formed by the ordered arrangement of -CF2- dipoles in the molecular chain. The initial PVDF thin film in this embodiment refers to the original PVDF thin film without any polarization treatment, and the crystal phase of this initial PVDF thin film is mainly α-phase. The femtosecond laser in this embodiment is a device capable of generating ultrashort pulse lasers; the pulse width of the laser beam generated by the femtosecond laser can reach femtoseconds (10^6). -15The laser beam generated by the femtosecond laser has extremely high peak power and extremely short duration, and can be used for non-thermal processing of materials, i.e., precise modification of materials without causing thermal damage. It should be understood that the femtosecond laser in this embodiment is an existing device, and its specific structure and working principle will not be discussed in detail here. The moving platform in this embodiment is a device for carrying and precisely moving the initial PVDF film to ensure that the initial PVDF film can be scanned below the femtosecond laser along a preset path and speed. Since the energy in the laser beam generated by the femtosecond laser can induce the orientation of dipoles in the PVDF molecular chain, promoting the transformation from the α-phase to the β-phase, thereby endowing the PVDF film with ferroelectric properties, this embodiment can form a PVDF ferroelectric film (a PVDF film with ferroelectric properties) by scanning the initial PVDF film with the laser beam and modifying and polarizing the initial PVDF film.

[0045] The PVDF ferroelectric thin film preparation method of this application includes the following core steps: In step S1, the initial PVDF thin film can be prepared by any of the following methods: 1. Solution casting: PVDF resin is dissolved in a suitable solvent to form a uniform PVDF solution, and then the solution is cast onto a flat substrate, and the initial PVDF thin film is formed by solvent evaporation; 2. Melt extrusion: PVDF resin is melted at high temperature and a continuous initial PVDF thin film is formed by extrusion die; 3. Spin coating: PVDF solution is dropped onto a rotating substrate, and the solution is spread uniformly by centrifugal force to form an initial PVDF thin film; 4. Solution casting: A PVDF solution of a certain concentration is injected and cast onto an endless metal strip at a certain speed, the solvent is removed by heating to solidify it, and then it is peeled off from the carrier to obtain the initial PVDF thin film. In step S2, the initial PVDF film is placed on a moving platform, which is an electrically controlled precision displacement platform. The moving platform can fix the initial PVDF film placed on it, for example, by using a vacuum chuck to fix the initial PVDF film on the moving platform, so as to ensure that the initial PVDF film will not be displaced relative to the moving platform during subsequent movement. In step S3, the femtosecond laser is controlled to generate a downward-facing laser beam, and the moving platform is controlled to drive the initial PVDF film to move below the femtosecond laser. This allows the laser beam to scan the initial PVDF film and modify and polarize it, thereby forming a PVDF ferroelectric film. Specifically, in this embodiment, the femtosecond laser generates a downward-facing laser beam by setting its output port downwards. The moving platform in this embodiment can achieve precise movement of the initial PVDF film through its own drive system (e.g., a stepper motor or a servo motor). It should be understood that the operator can preset the moving path and speed of the moving platform to perform linear or patterned scanning of the initial PVDF film below the femtosecond laser. For example, the moving platform can be set to move at a constant speed along the X-axis so that the initial PVDF film passes under the femtosecond laser, thereby achieving uniform modification and polarization of the entire PVDF film area. Step S31 comprehensively understands the physical properties of the initial PVDF film by acquiring its thickness information, crystal phase content, and surface morphology information. Specifically, the thickness information in this embodiment can be obtained using existing contact or non-contact thickness gauges, the crystal phase content can be obtained using existing X-ray diffraction (XRD) or Fourier transform infrared spectroscopy (FTIR) techniques, and the surface morphology information can be obtained using existing atomic force microscopy (AFM) or scanning electron microscopy (SEM) equipment.Step S32 determines the operating parameters of the femtosecond laser and the moving speed of the moving platform based on the acquired thickness, crystal phase content, and surface morphology information. In other words, step S32 is equivalent to selecting the most suitable laser processing conditions based on the specific characteristics of the thin film. For example, for thicker films or films with specific crystal phase contents, the laser energy or scanning speed needs to be adjusted to ensure uniform and sufficient modification; for films with irregular surface morphology, a finer scanning path or a lower moving speed is needed to avoid localized overheating or underprocessing. Subsequently, in step S33, the femtosecond laser is controlled to operate according to the determined operating parameters to generate a downward-facing laser beam. Precise control of the operating parameters is crucial for achieving the desired thin film modification. Finally, in step S34, the moving platform is controlled to drive the initial PVDF film to move below the femtosecond laser at a determined moving speed. Thus, this embodiment can use the laser beam to scan the initial PVDF film and cause the scanned initial PVDF film to undergo modified polarization, ultimately forming a PVDF ferroelectric film with excellent ferroelectric properties. This embodiment can ensure the uniform distribution of laser energy on the film surface and the duration of action by precisely controlling the moving speed, thereby avoiding the problems of overscanning or underscanning.

[0046] This application presents a method for preparing PVDF ferroelectric thin films, aiming to address the problems of complex processes, difficulty in achieving precise local control, and easy introduction of defects or impurities in traditional PVDF ferroelectric thin film preparation methods. By introducing femtosecond laser scanning technology, this application can achieve precise local modification and polarization of PVDF thin films, effectively inducing the formation of the β-phase while avoiding the introduction of defects and impurities. Specifically, after preparing the initial PVDF thin film, it is placed on a moving platform. Subsequently, a femtosecond laser is controlled to generate a downward-facing laser beam, and the moving platform is controlled to drive the initial PVDF thin film to move below the femtosecond laser. During this process, the laser beam scans the initial PVDF thin film. The ultrashort pulse and high peak power of the laser beam can interact with the PVDF molecular chains, inducing the orientation of molecular dipoles, thereby promoting the transformation of the α-phase to the β-phase, and achieving the modified polarization of the PVDF thin film. This non-thermal and painless processing method avoids the risks of film ablation or breakdown that may be caused by traditional high-voltage electric field polarization methods, the internal stress and defects that may be introduced by traditional mechanical stretching methods, and the potential impact on material purity and uniformity that may be caused by traditional nanocomposite modification methods. This application achieves precise control over the operating parameters of the femtosecond laser and the moving speed of the platform, enabling precise regulation of the modification area and degree of PVDF thin films. This allows for the fabrication of patterned PVDF ferroelectric thin films with specific ferroelectric properties. Therefore, the method of this application effectively solves the problems of complex processes, difficulty in achieving precise local control, and easy introduction of defects or impurities in existing technologies, providing reliable technical support for the fabrication of high-performance, miniaturized ferroelectric devices. Furthermore, this embodiment obtains the thickness, crystal phase content, and surface morphology information of the initial PVDF thin film before laser scanning modification, thus comprehensively understanding the film's physical properties. Given that these properties may differ among different initial PVDF thin films, using fixed laser operating parameters and moving speed would make it difficult to guarantee the consistency and optimization of the modification effect. It is precisely because of obtaining this key information that the operating parameters of the femtosecond laser and the moving speed of the platform can be specifically determined based on these specific film characteristics. This parameter adaptive adjustment mechanism based on the properties of PVDF thin films ensures that the interaction between laser energy and the thin film material is optimal, effectively avoiding problems such as insufficient modification or film damage caused by parameter mismatch. Because this embodiment can dynamically adjust the operating parameters of the femtosecond laser and the moving speed of the platform according to the actual characteristics of the initial PVDF thin film, it can effectively improve the accuracy and controllability of the PVDF ferroelectric thin film preparation process. This effectively avoids problems such as uneven PVDF film modification, low efficiency, or film ablation caused by mismatch between the operating parameters of the femtosecond laser and the moving speed of the platform and the characteristics of the initial PVDF thin film, thereby effectively improving the production yield of PVDF ferroelectric thin films.

[0047] This application provides a method for preparing PVDF ferroelectric thin films. By introducing femtosecond laser scanning technology, the method achieves non-thermal and filler-free modification and polarization of PVDF thin films. Specifically, this method can precisely induce the dipole orientation in the PVDF molecular chain without causing thermal damage or adding nanofillers, thereby promoting the formation of the β-crystal phase. Therefore, this method can effectively overcome the limitations of micro-region control and effectively avoid the introduction of additional mechanical stress, high-voltage breakdown risk, or nano-impurities, thus ensuring the purity and stability of the PVDF ferroelectric thin film. Consequently, the PVDF ferroelectric thin film can meet the requirements of high-performance, miniaturized ferroelectric devices.

[0048] In some preferred embodiments, step S3 further includes the step:

[0049] A1. During the scanning of the initial PVDF film using a laser beam, monitor the modification state and surface temperature of the initial PVDF film.

[0050] A2. Adjust the operating parameters of the femtosecond laser and the moving speed of the moving platform according to the modified state and surface temperature to scan the initial PVDF film without ablating it.

[0051] The modified state in step A1 refers to the changes in the internal crystal phase structure (especially the β phase content) and polarization of the PVDF film during laser scanning. Specifically, the crystal phase transformation and polarization of the film can be monitored in real time using techniques such as in-situ Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), or X-ray diffraction (XRD). For example, the modified state can be quantified by monitoring the intensity change of the β phase characteristic peak at a specific wavenumber. The surface temperature in step A1 can be measured using existing temperature sensors.

[0052] This embodiment introduces a real-time monitoring mechanism during laser scanning to dynamically perceive the modification process of the initial PVDF film and potential ablation risks. Specifically, monitoring the modification state allows the system to understand the polarization degree and structural changes of the film, while monitoring the surface temperature provides timely warnings of potential material damage. Based on this real-time feedback information, the system can intelligently adjust the operating parameters of the femtosecond laser and the movement speed of the moving platform. For example, when insufficient modification is detected, the laser energy can be appropriately increased or the movement speed reduced; when the surface temperature approaches the preset ablation critical point, the laser energy can be rapidly reduced or the movement speed increased, thereby preventing the film from being overheated or damaged. This closed-loop control mechanism ensures precise application of laser energy, keeping the film in an optimal modification state throughout the scanning process while effectively avoiding ablation. Therefore, this embodiment effectively avoids the film ablation problem caused by discrepancies between preset parameters and actual conditions by dynamically adjusting the operating parameters of the femtosecond laser and the moving speed of the moving platform based on real-time monitoring of the modification state and surface temperature during laser scanning. This effectively improves the yield and quality stability of PVDF ferroelectric thin films. Furthermore, this embodiment reduces the stringent requirements for initial operating parameters and moving speed settings, effectively improving the robustness and adaptability of the ferroelectric thin film fabrication process.

[0053] In some preferred embodiments, step A2 includes:

[0054] A21. Obtain the deviation of the modified state based on the change curve of the modified state and the preset modified state;

[0055] A22. Under the premise that the surface temperature is less than the preset ablation critical point threshold, generate the operating parameter compensation factor and the moving speed compensation factor according to the modified state deviation and the preset adjustment rules.

[0056] A23. The operating parameters of the femtosecond laser are compensated according to the operating parameter compensation factor, and the moving speed of the moving platform is compensated according to the moving speed compensation factor, so as to scan the initial PVDF film without ablation of the initial PVDF film.

[0057] The preset modified state change curve in step A21 refers to the preset trajectory of the PVDF film's modified state changing with time or scanning progress under ideal or desired laser scanning conditions. This preset modified state change curve can be established using prior experimental data, theoretical models, or simulations. It should be understood that pre-constructing the modified state change curve is existing technology, and its workflow will not be discussed in detail here. The modified state deviation in step A21 refers to the difference between the real-time monitored modified state and the preset modified state change curve. In this embodiment, the modified state deviation can be obtained by calculating the absolute or relative difference between the real-time monitored value and the corresponding point of the preset modified state change curve. For example, if the β-phase content of the preset modified state change curve at a certain moment is X, and the actual monitored value is Y, then the deviation is YX. The preset ablation critical point threshold in step A22 refers to the upper limit of the temperature at which the PVDF film begins to ablate or suffer irreversible damage under laser irradiation. In this embodiment, the preset ablation critical point threshold can be determined experimentally. For example, by conducting laser irradiation experiments on the PVDF film at different temperatures, the lowest temperature at which ablation marks begin to appear can be determined as the threshold. The preset adjustment rule in step A22 refers to the logic or algorithm for determining the operating parameter compensation factor and the moving speed compensation factor based on the modification state deviation and surface temperature. Specifically, it can employ existing PID control algorithms or fuzzy control algorithms. For example, when the modification state deviation is positive (over-modification), the rule can be set to decrease the laser energy or increase the moving speed; when the deviation is negative (under-modification), the rule can be set to increase the laser energy or decrease the moving speed. In this embodiment, the operating parameter compensation factor refers to the correction amount used to adjust the operating parameters of the femtosecond laser. Specifically, it can be a multiplicative factor or an additive factor. For example, if the laser energy needs to be reduced by 10%, the compensation factor is 0.9. In this embodiment, the moving speed compensation factor refers to the correction amount used to adjust the moving speed of the moving platform. Specifically, it can be a multiplicative factor or an additive factor. For example, if the moving speed needs to be increased by 5%, the compensation factor is 1.05.

[0058] This embodiment achieves closed-loop control of the laser scanning process by real-time monitoring of the modification state and surface temperature, and dynamic adjustments based on preset curves, thresholds, and rules. This control mechanism combines feedback on the modification effect with prevention of film damage, ensuring effective modification and polarization of the PVDF film without ablation. For example, when a large deviation in the modification state is detected (insufficient modification), the system generates corresponding compensation factors according to preset adjustment rules, increasing laser energy or decreasing the moving speed to optimize the subsequent modification and polarization process. Simultaneously, if the surface temperature approaches the ablation critical point threshold, the system adjusts the operating parameter compensation factor to reduce the temperature and the moving speed compensation factor to reduce the moving speed, thereby avoiding film damage and ensuring scanning results. This dynamic adjustment mechanism allows the laser scanning process to adapt to the microscopic inhomogeneities of the film material or changes in the external environment, resulting in more uniform and higher-performance PVDF ferroelectric films.

[0059] This embodiment aims to achieve effective scanning and modified polarization of the initial PVDF film without ablation by finely adjusting the laser operating parameters and the moving platform speed. First, during the scanning of the initial PVDF film using the laser beam, the modification state and surface temperature of the initial PVDF film are monitored in real time. Monitoring the modification state provides real-time feedback on the internal phase transformation and polarization degree of the film, while monitoring the surface temperature prevents overheating and ablation. Second, the real-time monitored modification state is compared with a preset modification state change curve to obtain the modification state deviation. This step quantifies the gap between the current modification effect and the ideal effect, providing a precise basis for subsequent parameter adjustments. For example, if the actual modification speed is slower than the preset curve, a negative deviation will occur, indicating that the laser effect needs to be enhanced. Furthermore, ensuring that the surface temperature is below the preset ablation critical point threshold, operating parameter compensation factors and moving speed compensation factors are generated based on the obtained modification state deviation and preset adjustment rules. This step is crucial, combining feedback on the modification effect with prevention of film damage to ensure the effectiveness and safety of the adjustment. Through preset adjustment rules, the modification state deviation can be translated into specific parameter adjustment amounts, thereby achieving intelligent parameter control. For example, when the modification state deviation is negative, the adjustment rule may indicate increasing the laser single-pulse energy or decreasing the moving speed; when the deviation is positive, it may indicate decreasing the laser energy or increasing the moving speed. Simultaneously, if the surface temperature approaches the ablation critical point, the system will reduce the operating parameter compensation factor to lower the temperature and the moving speed compensation factor to lower the moving speed, effectively scanning the PVDF film while avoiding film damage. Finally, the operating parameters of the femtosecond laser are compensated according to the generated operating parameter compensation factor, and the moving speed of the moving platform is compensated according to the moving speed compensation factor. This step applies the calculated adjustment amounts to the actual equipment control, thereby dynamically optimizing the laser scanning process. This real-time feedback and compensation mechanism ensures that the laser beam scan of the initial PVDF film is always optimal, effectively promoting the modified polarization of the film while avoiding film ablation due to overheating or improper energy, thus producing high-performance PVDF ferroelectric films. Compared to existing technologies, which often suffer from complex processes, difficulty in achieving precise local control, and susceptibility to introducing defects or impurities, this approach, through the introduction of a real-time monitoring and dynamic adjustment mechanism, achieves precise control over the polarization process of the PVDF film, effectively inducing the formation of the β-phase while avoiding the introduction of defects and impurities, thereby improving the performance stability and uniformity of the PVDF ferroelectric film.

[0060] As a preferred embodiment, the specific implementation of this application is as follows: First, an initial PVDF film with a thickness of 50 micrometers is prepared and placed on a moving platform. The initial operating parameters of the femtosecond laser are set as follows: laser beam wavelength 1030 nm, laser beam pulse width 290 fs, laser beam frequency 100 Hz, and laser beam single pulse energy 5 μJ. The initial moving speed of the moving platform is set to 0.5 mm / s. During laser scanning, the β-phase content of the film is monitored in real time as the modified state using an in-situ Raman spectrometer, and the surface temperature of the film is monitored in real time using an infrared thermal imager. The preset modified state change curve is set to a linear increase in β-phase content to 80% during the scanning process, and the preset ablation critical point threshold is set to 150°C. When the monitored β-phase content of the film is lower than the β-phase content at the corresponding moment of the preset modified state change curve, the modified state deviation is calculated. For example, if the actual β-phase content is 5% lower than the β-phase content at the corresponding moment of the preset modified state change curve, then according to the preset adjustment rules (e.g., PID control algorithm), an operating parameter compensation factor and a moving speed compensation factor are generated. Specifically, if the modification is insufficient, a compensation factor is generated that increases the laser single pulse energy by 0.5 μJ, and a compensation factor that decreases the moving speed by 0.05 mm / s is generated.

[0061] Simultaneously, if the monitored film surface temperature approaches 140°C (below the ablation critical threshold of 150°C), the system reduces the operating parameter compensation factor to lower the temperature and the moving speed compensation factor to lower the moving speed. For example, the system generates an operating parameter compensation factor that reduces the laser single-pulse energy by 0.2 μJ and a moving speed compensation factor that reduces the moving speed by 0.1 mm / s to reduce the film temperature and moving speed, thereby ensuring scanning effect while avoiding film ablation. Finally, based on the generated compensation factors, the single-pulse energy of the femtosecond laser and the moving speed of the moving platform are dynamically adjusted. For example, if the laser single-pulse energy increases by 0.5 μJ, the new single-pulse energy becomes 5.5 μJ; if the moving speed decreases by 0.1 mm / s, the new moving speed becomes 0.4 mm / s. Through this real-time feedback and adjustment, the optimal modification polarization effect of the PVDF film is ensured without ablation.

[0062] In some preferred embodiments, step S32 includes:

[0063] S321. Based on the thickness information, crystal phase content, and surface morphology information, query the pre-built database or lookup table of mapping relationships between thickness information, crystal phase content, surface morphology, femtosecond laser parameters, and thin film moving speed to determine the operating parameters of the femtosecond laser and the moving speed of the moving platform.

[0064] The mapping database or lookup table in this embodiment refers to a collection that stores a large amount of experimental data or simulation results. Both the mapping database and the lookup table record the correlation between the thickness information, crystal phase content, and surface morphology of different PVDF films and the corresponding optimal femtosecond laser operating parameters and the moving platform speed. This embodiment can pre-construct the mapping database or lookup table by obtaining the correlation between the thickness information, crystal phase content, and surface morphology of multiple PVDF films and the corresponding optimal femtosecond laser operating parameters and the moving platform speed through a large number of experiments and simulations before preparing the PVDF ferroelectric film, and by integrating all the correlations.

[0065] This embodiment simplifies and standardizes the determination of femtosecond laser operating parameters and moving platform speed by introducing a pre-built mapping database or lookup table. Specifically, after obtaining the initial PVDF film thickness, crystal phase content, and surface morphology information, the system can directly query the database or lookup table to quickly match the optimal operating parameters and moving speed corresponding to the current film characteristics. This data-driven determination method avoids the complex calculations, manual experience judgments, or trial-and-error processes that may exist in traditional methods, thereby effectively improving the efficiency and accuracy of parameter determination.

[0066] In some preferred embodiments, it is assumed that the initial PVDF film has a thickness of 50 micrometers, a crystalline phase content (e.g., β phase content) of 80%, and a surface roughness (e.g., Ra value) of 5 nanometers. Before fabrication begins, the system first acquires this information. Subsequently, the system automatically queries a pre-built mapping database based on this information. This database may store entries such as: when the thickness is 50 micrometers, the crystalline phase content is 80%, and the surface morphology is 5 nanometers, the corresponding optimal femtosecond laser operating parameters are: laser beam wavelength 1030 nm, laser beam pulse width 290 fs, laser beam frequency 100 Hz, laser beam single pulse energy 5 μJ, and moving platform speed 0.3 mm / s. By matching these input parameters, the system directly extracts the preset optimal operating parameters and moving speed from the database and applies them to the control of the femtosecond laser and moving platform, thereby achieving efficient and precise fabrication of PVDF ferroelectric thin films.

[0067] In some preferred embodiments, the operating parameters include laser beam wavelength, laser beam pulse width, laser beam frequency, and laser beam single-pulse energy. In this embodiment, the laser beam wavelength refers to the wavelength of the laser beam emitted by the femtosecond laser, which determines the energy and penetration depth of the interaction between the laser and the PVDF film. The laser beam pulse width in this embodiment refers to the duration of each laser pulse, which affects the temporal concentration of laser energy and thus the instantaneous intensity of the interaction with the PVDF film. The laser beam frequency in this embodiment refers to the number of laser pulses per unit time, which determines the cumulative energy input to the PVDF film and the scanning efficiency during laser scanning. The laser beam single-pulse energy in this embodiment refers to the energy carried by each laser pulse, which directly affects the modification and polarization effect of the laser on the PVDF film.

[0068] As can be seen from the above, the PVDF ferroelectric thin film preparation method provided in this application achieves non-thermal and filler-free modification and polarization of the PVDF thin film by introducing femtosecond laser scanning technology. That is, this application can accurately induce the dipole orientation in the PVDF molecular chain without causing thermal damage and without adding nanofillers, so as to promote the formation of the β crystal phase. Therefore, this application can effectively overcome the limitations of difficult micro-area control and effectively avoid the problems of introducing additional mechanical stress, high voltage breakdown risk or nano-impurities, thereby ensuring the purity and stability of the PVDF ferroelectric thin film. In this way, the PVDF ferroelectric thin film can meet the needs of high-performance and miniaturized ferroelectric devices.

[0069] Secondly, this application also provides a PVDF ferroelectric thin film, which is prepared by the PVDF ferroelectric thin film preparation method provided in the first aspect above.

[0070] The PVDF ferroelectric thin film provided in this embodiment is made by the PVDF ferroelectric thin film preparation method provided in the first aspect above. The principle of the PVDF ferroelectric thin film provided in this embodiment is the same as that of the PVDF ferroelectric thin film preparation method provided in the first aspect above, and will not be discussed in detail here.

[0071] Thirdly, this application also provides a ferroelectric device comprising the PVDF ferroelectric thin film provided in the second aspect above.

[0072] As can be seen from the above, the PVDF ferroelectric thin film, its preparation method, and the ferroelectric device provided in this application achieve non-thermal and filler-free modification and polarization of the PVDF thin film by introducing femtosecond laser scanning technology. That is, this application can accurately induce the dipole orientation in the PVDF molecular chain without causing thermal damage and without adding nanofillers to promote the formation of the β crystal phase. Therefore, this application can effectively overcome the limitations of difficult micro-area control and effectively avoid the problems of introducing additional mechanical stress, high voltage breakdown risk, or nano-impurities, thereby ensuring the purity and stability of the PVDF ferroelectric thin film. In this way, the PVDF ferroelectric thin film can meet the requirements of high-performance and miniaturized ferroelectric devices.

[0073] In the embodiments provided in this application, it should be understood that relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0074] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing PVDF ferroelectric thin films, characterized in that, The method for preparing the PVDF ferroelectric thin film includes the following steps: S1. Prepare an initial PVDF film; the initial PVDF film is a raw PVDF film that has not undergone any polarization treatment; S2. Place the initial PVDF film on the mobile platform; S3. Without adding nanofillers to the initial PVDF film, control the femtosecond laser to generate a downward laser beam, and control the moving platform to drive the initial PVDF film to move below the femtosecond laser, so as to use the laser beam to scan the initial PVDF film and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film. Step S3 includes: S31. Obtain the thickness information, crystal phase content and surface morphology information of the initial PVDF film; S32. Determine the operating parameters of the femtosecond laser and the moving speed of the moving platform based on the thickness information, the crystal phase content, and the surface morphology information; the operating parameters include the laser beam wavelength, laser beam pulse width, laser beam frequency, and laser beam single pulse energy. S33. Without adding nanofillers to the initial PVDF film, the femtosecond laser is controlled to operate according to the operating parameters so that the femtosecond laser generates a downward laser beam. The moving platform is controlled to drive the initial PVDF film to move below the femtosecond laser at the moving speed so as to use the laser beam to scan the initial PVDF film and modify and polarize the scanned initial PVDF film, thereby forming a PVDF ferroelectric film. Specifically, the modified polarization promotes the transformation of the α-crystal phase to the β-crystal phase of the initial PVDF film; Step S3 also includes the following steps: A1. During the scanning of the initial PVDF film using the laser beam, the modification state and surface temperature of the initial PVDF film are monitored. A2. Adjust the operating parameters of the femtosecond laser and the moving speed of the moving platform according to the modified state and the surface temperature, so as to scan the initial PVDF film without ablating the initial PVDF film; Step A2 includes: A21. Obtain the deviation of the modified state based on the modified state and the preset modified state change curve; A22. Under the premise that the surface temperature is less than the preset ablation critical point threshold, generate the operating parameter compensation factor and the moving speed compensation factor according to the modified state deviation and the preset adjustment rule. A23. The operating parameters of the femtosecond laser are compensated according to the operating parameter compensation factor, and the moving speed of the moving platform is compensated according to the moving speed compensation factor, so as to scan the initial PVDF film without ablating the initial PVDF film.

2. The method for preparing PVDF ferroelectric thin films according to claim 1, characterized in that, Step S32 includes: S321. Based on the thickness information, the crystal phase content, and the surface morphology information, query a pre-built database or lookup table of mapping relationships between thickness information, crystal phase content, surface morphology, femtosecond laser parameters, and thin film moving speed to determine the operating parameters of the femtosecond laser and the moving speed of the moving platform.

3. A PVDF ferroelectric thin film, characterized in that, The PVDF ferroelectric thin film is prepared by the PVDF ferroelectric thin film preparation method according to any one of claims 1-2.

4. A ferroelectric device, characterized in that, The ferroelectric device includes the PVDF ferroelectric thin film as described in claim 3.

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