A device and method for detecting the ferroelectric direction of a thin film under stress

Abstract

The present invention discloses a device for detecting the ferroelectric direction of a thin film under stress, which mainly consists of the following modules: an excitation light module: used for the polarization initialization, regulation, and stray light filtering of the incident fundamental frequency light. It includes an excitation light source - a femtosecond pulsed laser, which is used to generate an incident excitation light beam with a suitable frequency; it includes a polarizer, which is used for the polarization initialization of the incident light; it includes a lens A, which is used to focus the incident laser on the sample to be measured; it includes a rotatable half-wave plate controlled by electricity, which is used for the polarization regulation of the incident light. The present invention utilizes nonlinear optical detection to detect the ferroelectric direction of a thin film under stress, and provides a corresponding test system and method, which not only overcomes the problems of high sensitivity to the environment and difficult sample preparation process in the existing measurement technology, but also solves the problems that the sample is damaged during the measurement and cannot be further studied, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of ferroelectric direction measurement, and particularly to a device and method for detecting the ferroelectric direction of a thin film under stress. Background Art

[0002] Due to their unique dielectric properties and ferroelectric domain structures, ferroelectric thin film materials have broad application prospects in the fields of information storage, sensors, optoelectronic devices, etc. Stress, as a common influencing factor and regulation means, has an important impact on the performance and stability of thin films and their devices. Accurately measuring the ferroelectric direction under stress is crucial for realizing high-performance devices.

[0003] Currently, traditional methods for measuring the ferroelectric direction include transmission electron microscopy (TEM), X-ray diffraction (XRD), and piezoresponse force microscopy (PFM), etc. However, these methods not only require complex sample preparation processes and expensive experimental equipment, but also highly depend on the equipment parameters and sample preparation processes for the test results. In addition, they have high requirements for the size and thickness of the thin film, and there is a risk that the sample will be damaged and cannot be used again. More importantly, these integrated devices cannot be coupled with stress application devices to detect the ferroelectric direction of thin films under stress.

[0004] Second harmonic generation (SHG) technology, as a non-destructive and highly sensitive measurement means, is an important tool for detecting the ferroelectric direction of thin films under stress. Second harmonic generation is a non-linear optical process in which the frequency of the incident light wave is doubled to generate a second harmonic signal. For ferroelectric materials, their non-centrosymmetric structures endow them with the ability to generate second harmonics. When the polarization direction of the incident light matches the polarization direction of the ferroelectric material, the intensity of the second harmonic signal reaches the maximum value. Therefore, by measuring the intensity and phase of the second harmonic signal, the ferroelectric direction of the ferroelectric material can be determined. In addition, the SHG measurement system can be better compatible with various stress application devices to assist in studying the dynamic process of the change in the ferroelectric direction of thin films under stress.

[0005] In recent years, methods for detecting the ferroelectric domain distribution of thin films using the second harmonic method have gradually emerged. For example, in the patent "A System and Method for Measuring the Domain Orientation of Ferroelectric Films Using Optical Second Harmonics" in 2017 (CN 107144550 A), the detection of the ferroelectric domain distribution in the thin film is achieved by rotating the sample and the polarization of the incident light. Although this technology overcomes problems such as complex sample preparation processes and the destructiveness of measurements on samples, since it rotates the sample through a rotating stage, during the measurement process, it is necessary to require that the center of the sample to be measured (i.e., the measurement position) is strictly located at the center of the optical path and the rotating displacement stage. Once the measurement position is slightly offset from the center, it will cause it to deviate from the optical path during the rotation of the sample, resulting in the need to re-adjust the sample position for each measured angle. In addition, there are also significant challenges during the coupling process of the rotating displacement stage with the stress application device. Once the applied stress causes the sample to deviate from the center of the displacement stage, the sample position needs to be re-adjusted. The entire measurement process is complex to adjust and has a high degree of limitation. Summary of the Invention

[0006] In order to solve the problems mentioned in the above background technology, the present invention provides a device and method for detecting the ferroelectric direction of a thin film under stress.

[0007] In order to solve the problems of difficult measurement of the ferroelectric direction of thin films under stress, destructiveness, environmental sensitivity, and high complexity and limitation in measurement. The present invention provides a device and method for using nonlinear optical technology to detect the ferroelectric direction of a thin film under stress. Specifically, the second harmonic generation technology is used to establish a device for measuring the ferroelectric direction of a thin film under stress. Its basic principle is as follows:

[0008] When a laser with a sufficiently high electric field strength (generally higher than 100 kV / cm) irradiates a dielectric material, the strong electric field will affect the relative positions of atoms and the motion states of electrons in the dielectric, causing nonlinear polarization of the dielectric, and then causing changes in the incident light frequency and energy transfer. Among them, second harmonic generation is a second-order nonlinear optical phenomenon, and the polarization generated by it satisfies with the incident light electric field:

[0009] ,

[0010] wherein is the second-order nonlinear susceptibility tensor. The polarization generated by the second-order nonlinear process will correspondingly radiate a signal light of the second harmonic with a frequency twice that of the incident light frequency, which is the second harmonic generation process. It should be noted that the second harmonic is only generated in materials with broken centrosymmetry. Ferroelectric thin films are a typical non-centrosymmetric material, and the intensity of their second harmonic strongly depends on the angle between the polarization direction of the incident light and the ferroelectric polarization direction. By changing the angle size, the polarization-dependent SHG intensity change can be obtained, and then the ferroelectric direction in the thin film can be calculated.

[0011] A device for detecting the ferroelectric direction of a thin film under stress proposed by the present invention mainly consists of the following modules:

[0012] Excitation light module: used for polarization initialization, regulation and stray light filtering of the incident fundamental light. It includes an excitation light source - a femtosecond pulsed laser for generating an incident excitation light beam with a suitable frequency; a polarizer for initializing the polarization of the incident light; a lens A for focusing the incident laser on the sample to be measured; an electrically controlled rotatable half-wave plate for regulating the polarization of the incident light; a filter A, which is a band-pass filter, selects the corresponding central wavelength and band-pass width according to the frequency of the incident light, and is used to filter the stray frequency light generated by the optical elements in the excitation light module to ensure that only the light with the incident laser frequency irradiates on the sample.

[0013] Imaging module: includes a white light source, an imaging CCD, a push-pull beam splitter and an objective lens, and is used to realize the imaging of the surface of the sample to be measured. The push-pull beam splitter and the objective lens are located on the optical path system during imaging and can be pulled away from the optical path system after observing the sample.

[0014] Pressure module: compatible with various sample mounting and pressure application modules, used for applying stress to the sample; includes a displacement stage for finely adjusting the measurement position of the sample;

[0015] Signal receiving module: used for collecting the second harmonic signal of the sample. It includes a filter B, which is a band-pass filter with the central wavelength based on the second harmonic wavelength of the sample (usually half of the incident light wavelength) as the band-pass filter, and is used to filter the incident light and only pass the second harmonic signal light; includes a lens B for converting the second harmonic generated at the focal point of the sample into parallel light; includes an electrically controlled rotatable Glan-Taylor prism for realizing the selection of the polarization of the detected signal light. Includes a lens C for focusing the second harmonic signal on the detector. Includes a detector for completing the detection of the second harmonic signal intensity.

[0016] The present invention also discloses a method for detecting the ferroelectric direction of a thin film under stress, including the following steps:

[0017] S1: After transferring the sample onto a flexible substrate capable of applying stress and installing it on a stress application device, install the device on the displacement stage in the stress module. During the installation process, pay attention to making the edges of the device as parallel as possible to the horizontal direction of the optical path in the laboratory. Adjust the optical system, observe the sample to be measured through the imaging system, find the required measurement area, focus the incident light on the measurement area of the sample to be measured, and focus the signal light on the detector sensing window.

[0018] S2: Use the motion controller to make the initial position of the fast axis of the half-wave plate and the initial position of the optical axis of the Glan-Taylor prism parallel to the laboratory horizontal direction. Link the controller and the detector, and let the half-wave plate and the Glan-Taylor prism rotate simultaneously at an angle of (1 / 2) and respectively, detect the SHG intensity at each angle, and thus obtain the change in SHG intensity under different polarizations. This process has the same effect as rotating the sample, which is equivalent to fixing the polarization of the incident light and the outgoing light, rotating the sample at an angle of and performing SHG measurement, so that the dependence relationship between the SHG intensity and the ferroelectric polarization direction in the sample can be established. This operation avoids the problem caused by the sample deviating from the optical path center due to the sample not being at the center of the rotating stage during the rotation of the sample.

[0019] S3: To apply stress to the thin film to be measured, it can be achieved by stretching the film or changing the shape of the sample. At the same time, observe the morphological changes of the sample under each stress with the help of the imaging module. By measuring the change in SHG intensity with the angle under each stress, the dynamic process of the ferroelectric direction evolution under stress can be obtained.

[0020] Data analysis method: According to the above, the device of the present invention realizes the rotation of the optical path by rotating the polarization of the incident light and the signal light at an angle of simultaneously, replacing the rotation of the sample at an angle of , and the dependence relationship between the SHG intensity and the angle can be established. The following introduces the formula for the dependence relationship between and the angle :

[0021] For the measurement system, there are currently known the laboratory coordinate system ( ), the sample coordinate system ( ), and the crystal coordinate system ( ). According to the above, as a second-order nonlinear optical phenomenon, second harmonic generation will generate the corresponding polarization intensity . Among them, the incident optical field is expressed in the laboratory coordinate system, where and are the electric field components along the horizontal and vertical directions of the laboratory, respectively. Since the light is incident perpendicular to the sample surface, thus . And the second-order nonlinear coefficient is expressed in the crystal lattice coordinate system. It is a third-order tensor element with 27 elements. Since the frequencies of the two incident lights are the same, thus . At this time the components of are simplified to 18.

[0022]

[0023] Therefore, in order to describe the dependence relationship between the SHG intensity and the angle , it is necessary to transform the second-order nonlinear coefficient from the crystal lattice coordinate system to the laboratory coordinate system . Since the second-order nonlinear polarization coefficient tensor is usually known in the crystal coordinate system as , it is necessary to first transform it from the crystal coordinate system to the sample coordinate system and then to the laboratory coordinate system. The transformation matrix can be expressed as: , where is the transformation from the crystal lattice coordinate system to the sample coordinate system, is the transformation from the sample coordinate system to the laboratory coordinate system. By using the transformation matrix , the second-order nonlinear coefficient in the laboratory coordinate system can be expressed as:

[0024]

[0025] In the laboratory coordinate system, the electric field component of the incident light can be expressed as , then the second-order nonlinear polarization generated in the thin film can be expressed as:

[0026]

[0027] The intensity of the second harmonic light radiated by the polarization intensity is then . Since the polarization direction of the incident light is parallel to the polarization direction of the signal light, the dependence relationship between the SHG intensity and the angle can be expressed as:

[0028]

[0029] where and are Fresnel factors. By measuring the Converting from the lattice coordinate system to the laboratory coordinate system, the SHG intensity under different stresses can be fitted through the above equations. and the angle variation, where the angle corresponding to the maximum value to a certain extent reflects the main direction of the in-plane ferroelectric direction of the thin film.

[0030] In addition, the total SHG intensity can be obtained as:

[0031]

[0032] where is the proportion of the in-plane direction ferroelectric polarization.

[0033] The device of the present invention can quickly, accurately, and non-destructively analyze the influence of stress on the ferroelectric direction of the thin film. By using nonlinear optical technology, it avoids the complexity, time-consuming, destructiveness, and environmental sensitivity in traditional methods, and provides a reliable means for detecting the ferroelectric direction of the thin film under stress.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. The present invention uses nonlinear optical detection of the ferroelectric direction of the thin film under stress and provides a corresponding test system and method, which not only overcomes the problems of high environmental sensitivity and difficult sample preparation process in existing measurement technologies, but also solves the problem that the sample is damaged during the measurement and cannot be further studied.

[0036] 2. The system of the present invention can overcome the requirement that the sample must be placed on a rotating table and can adapt to the application of various stress conditions. In addition, it overcomes the requirement that the sample measurement position must be placed at the center of the rotating table and the problems of inconsistent measurement positions caused by rotation, reduces the sample placement requirements, and can more accurately achieve in-situ detection by rotating the optical path instead of rotating the sample.

[0037] 3. The device and method of the present invention are a highly sensitive and non-destructive means for detecting the ferroelectric direction of the thin film under stress, and are of great significance for in-depth study of the dynamic process of the ferroelectric direction change of the thin film under stress. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1 Schematic diagram of the structure of the thin-film ferroelectric direction detection device under stress of the present invention;

[0040] Figure 2 Schematic diagram of the self-made stress application sample holder in Example 3 of the present invention;

[0041] Figure 3 Schematic diagram of the evolution of the surface morphology of the 40-nm-thick BFO thin film with stress in Example 3 of the present invention;

[0042] Figure 4 Schematic diagram of the evolution of the SHG intensity map of the 40-nm-thick BFO thin film under different polarizations with stress in Example 3 of the present invention (where and respectively represent the magnitudes of the stresses applied in the x and y directions and )

[0043] Figure 5 In (a)-(c) are respectively , , The evolution of the second harmonic intensity of the BFO thin film with the rotation angle under stress, where and respectively represent the magnitudes of the stresses applied in the x and y directions, the black circles are experimental data, and the red curve is the fitting result using the formula in Example 4. (d) is the evolution process of the ferroelectric polarization direction with stress obtained using the fitting result;

[0044] In the figure: 1 excitation light module, 11 excitation light source, 12 polarizer, 13 lens A, 14 half-wave plate, 15 filter A, 2 imaging module, 21 white light source, 22 imaging CCD, 23 beam splitter, 24 objective lens, 3 pressure module, 4 signal receiving module, 41 filter B, 42 lens B, 43 Glan-Taylor prism, 44 lens C, 45 detector, 46 stress application sample holder, 47 displacement stage. Detailed implementation manners

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0046] Example 1

[0047] Referring to Figure 1 , a device for detecting the ferroelectric direction of a thin film under stress includes an excitation light module 1, an imaging module 2, a pressure module 3, and a signal receiving module 4; the excitation light module 1, the imaging module 2, the pressure module 3, and the signal receiving module 4 work together to achieve non-contact and high-precision detection of the ferroelectric direction of the thin film under stress;

[0048] The excitation light module 1 is used to generate incident light with a specific frequency and energy, precisely regulate its polarization, and filter out stray light to ensure that the incident light meets the requirements for detecting the ferroelectric direction of the thin film;

[0049] The imaging module 2 is used to perform high-resolution imaging of the sample surface to assist in determining the measurement area and to monitor in real time the changes in the surface topography of the sample under stress, which are associated with the evolution of the ferroelectric direction;

[0050] The pressure module 3 includes a stress-applying sample holder 46, and four displacement stages 47 are installed on the stress-applying sample holder 46. The stretching of the sample is achieved by moving the displacement stages 47, so as to apply a controllable biaxial stress to the sample, and the measurement position of the sample can be finely adjusted during the stress application process to maintain the stability of the sample position, so as to accurately study the relationship between stress and ferroelectric direction;

[0051] The signal receiving module 4 is used to efficiently and accurately collect the second harmonic signals generated by the sample under the action of stress and incident light, and this signal is the key basis for determining the ferroelectric direction.

[0052] Among them, the excitation light module 1 includes an excitation light source, a polarizer 12, a lens A 13, a polarization regulation element, and a filter A 15, and the excitation light source can generate high-energy incident light.

[0053] Among them, the imaging module 2 includes an illumination light source, an imaging CCD 22, a beam splitting element, and an objective lens 24, and the imaging element has high resolution and high sensitivity.

[0054] Among them, the signal receiving module 4 includes a filter B 41, a lens B 42, a polarization selection element, a focusing element, and a detection element, and the detection element can accurately detect second harmonic signals of different intensities.

[0055] Among them, the excitation light source is a femtosecond pulsed laser 11, and it can generate laser with high intensity and a specific frequency range.

[0056] Among them, the polarization regulation element is a rotatable half-wave plate 14 controlled by electricity.

[0057] Among them, the illumination light source is a white light source 21, and the beam splitting element is a push-pull beam splitter 23.

[0058] Among them, the polarization selection element is a rotatable Glan-Taylor prism 43 controlled by electricity, the focusing element is a lens C44, and the detection element is a high-performance detector 45.

[0059] Example 2

[0060] A method for detecting the ferroelectric direction of a thin film under stress includes the following steps:

[0061] S1: Transfer the sample to a flexible substrate capable of applying stress, then mount it on a stress application device, and install the device on the displacement stage (47) in the stress module. During the installation process, make the side line of the device as parallel as possible to the horizontal direction of the optical path in the laboratory;

[0062] S2: Adjust the optical system, observe the sample to be measured through the imaging system, find the required measurement area, focus the incident light on the measurement area of the sample to be measured, and focus the signal light on the detector sensing window;

[0063] S3: Through the motion controller, make the initial position of the fast axis of the half-wave plate and the initial position of the optical axis of the Glan-Taylor prism parallel to the laboratory horizontal direction. Link the controller and the detector, and let the half-wave plate and the Glan-Taylor prism rotate simultaneously at an angle of (1 / 2) and respectively. Detect the SHG intensity at each angle, and then obtain the change of the SHG intensity under different polarizations, and establish the dependence relationship between the SHG intensity and the ferroelectric polarization direction in the sample. This operation avoids the problem that the sample deviates from the optical path center due to the sample not being at the center of the rotating table when the sample is rotated;

[0064] S4: For applying stress to the thin film to be measured, it can be achieved by stretching the thin film or changing the shape of the sample. At the same time, with the help of the imaging module, observe the morphological changes of the sample under each stress, and measure the change of the SHG intensity with the angle under each stress to obtain the kinetic process of the ferroelectric direction evolution under stress.

[0065] Example 3

[0066] An example of a device for detecting the ferroelectric direction of a thin film under stress stretching and its use method.

[0067] In this example, the sample to be measured is a 40-nm-thick BiFeO3 (BFO) thin film. Transfer the BFO thin film to be measured to the stress application sample holder 46. In this example, the stress application sample holder 46 is a self-assembled stress stretching device. By fixing four displacement stages 47 on a bracket, the stretching of the sample is realized by the movement of the displacement stages 47. The physical diagram is as Figure 2As shown. It should be noted that when installing the film, the bottom edge of the sample should be kept parallel to the horizontal direction of the laboratory (i.e., the horizontal direction of the incident light) as much as possible.

[0068] In this embodiment, the central wavelength of the excitation light source 11 used is 800 nm, the repetition frequency is 80 MHz, and the pulse width is 35 fs. The excitation light power is attenuated to 10 mW through an attenuation sheet. The optical path system is adjusted so that the fundamental frequency light of 800 nm passes through the center of optical elements such as the polarizer 12, the lens A 13, the half-wave plate 14, and the filter A 15 with a 10-nm bandpass centered at 800 nm in sequence and is focused on the sample to be measured. Among them, the direction of the polarizer 12 is set horizontally to ensure that the incident fundamental frequency light is horizontally polarized light. The half-wave plate 14 is installed on an electric rotating stage, and its initial angle and rotation can be accurately controlled through a motion controller. The half-wave plate 14 in this embodiment is a true zero-order wave plate at 800 nm, which can avoid changing the excitation light power during the rotation of the wave plate. The filter A 15 at 800 nm can remove stray light of other bands generated in front of the sample, and only allow the incident light of 800 nm to pass through. By moving the slidable beam splitter 23 and the objective lens 24, the light is made to pass through the center of the light passing aperture of the objective lens 24, and the surface of the sample and the position irradiated by the light spot can be observed through the imaging CCD 22. By moving the sample stage, the 800-nm incident light is irradiated on the sample to be measured.

[0069] The second harmonic signal of 400 nm and the fundamental frequency light signal of 800 nm generated by the sample will be incident on the filter B 41 with a 10-nm bandpass centered at 400 nm. Subsequently, the 800-nm fundamental frequency light is filtered out, and only the signal light of 400 nm becomes horizontal light after passing through the lens B 42, and then passes through the center of the Glan-Taylor prism 43 and the lens C 44 and is focused on the photomultiplier tube detector 45. Among them, the Glan-Taylor prism 43 is installed on an electric rotating stage, and its angle initialization and rotation can be controlled through a motion controller.

[0070] The initial angles of the half-wave plate 14 and the Glan-Taylor prism 43 are set to be horizontal through the motion controller. The detector and the motion controller are linked, and the half-wave plate 14 in the excitation light module 1 and the Glan-Taylor prism 43 in the signal collection module 4 are rotated simultaneously (ensuring that the rotation angle of the Glan-Taylor prism 43 is twice the rotation angle of the half-wave plate 14 . This process is equivalent to rotating the sample at an angle while fixing the polarization of the incident light and the outgoing light, so that the SHG intensity under different polarizations can be obtained.

[0071] Then, by pulling the four displacement stages 47 on the sample holder, tensile stress in the horizontal and vertical directions can be applied respectively (the stress part can be changed to other devices that can apply stress. If the stress part is an automated device, it can also be linked with the detector and the motion control module). By moving the imaging module 2, the surface morphology of the sample can be observed in real time under each stress. The surface morphology of the 40 nm thick BFO film in this embodiment changes with the stress in the horizontal and vertical directions as shown in FIG. Figure 3 By linking the detector and the motion controller, the evolution of the polarization-dependent SHG intensity map with stress can be obtained, as shown in Figure 4 As shown in the figure, the direction of the arrows shows the change of ferroelectric direction under stress.

[0072] Example 4

[0073] An embodiment of detecting and analyzing the ferroelectric direction distribution through SHG intensity results with different polarizations under stress.

[0074] This embodiment is a method for analyzing the change of ferroelectric direction by using the evolution of SHG intensity in 40 nm thick BFO measured by the device in Example 3 with stress.

[0075] According to the initial polarization angles of the incident fundamental frequency light and the signal light, the measurement configuration is divided into parallel and perpendicular configurations. Among them, for the parallel configuration, the measured SHG signal intensity under different polarizations is It can be expressed by the following equation:

[0076]

[0077]

[0078] in is the rotation angle of the Glan-Taylor prism, and The SHG intensity diagrams under different pressures in Example 3 are fitted using this equation to obtain the Fresnel factors under different stresses. With Angle Changes. Figure 5 The red curves in (a)-(c) show , , Second harmonic intensity of BFO film under stress Evolution with rotation angle. In the absence of stress, The angle corresponding to the maximum value of (( Figure 5(a)), which to a certain extent reflects the main in-plane direction of the ferroelectric polarization in the sample without stress application. By fitting, the evolution of the in-plane ferroelectric direction of the thin film with the applied stress can be obtained, as shown in Figure 5 (d).

[0079] In addition, the total SHG intensity can be obtained as follows:

[0080]

[0081] where is the proportion of the ferroelectric polarization in the in-plane direction. To a certain extent, it reflects the proportion of the ferroelectric polarization in different in-plane directions in the material.

[0082] In summary, by analyzing the SHG intensities measured under different stresses in the device of the present invention, the direction distribution and corresponding proportion of the in-plane projection of the ferroelectric polarization in the measured sample can be obtained.

[0083] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0084] In the present invention, unless otherwise clearly defined and limited, the terms "set", "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0085] The control mode of the present invention is automatically controlled by a controller. The control circuit of the controller can be realized by simple programming of those skilled in the art. The provision of the power supply also belongs to the common knowledge in the art, and the present invention mainly aims to protect mechanical devices, so the control mode and circuit connection of the present invention will not be further explained in detail.

[0086] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A device for detecting the ferroelectric direction of a thin film under stress, characterized in that It includes an excitation light module (1), an imaging module (2), a pressure module (3), and a signal receiving module (4); the excitation light module (1), imaging module (2), pressure module (3), and signal receiving module (4) work together to achieve non-contact and high-precision detection of the ferroelectric direction of the thin film under stress; The excitation light module (1) is used to generate incident light with a specific frequency and energy, precisely control its polarization, and filter stray light to ensure that the incident light meets the requirements for detecting the ferroelectric direction of the thin film; The imaging module (2) is used to perform high-resolution imaging of the sample surface to assist in determining the measurement area and to monitor in real time the changes in the sample surface topography under stress, which are associated with the evolution of the ferroelectric direction; The pressure module (3) includes a stress-applying sample holder (46), and four displacement stages (47) are mounted on the stress-applying sample holder (46). The stretching of the sample is achieved by moving the displacement stages (47), thereby applying a controllable biaxial stress to the sample, and the measurement position of the sample can be finely adjusted during the stress application process to maintain the stability of the sample position, so as to accurately study the relationship between stress and ferroelectric direction; The signal receiving module (4) is used to efficiently and accurately collect the second harmonic signals generated by the sample under the action of stress and incident light. This signal is the key basis for determining the ferroelectric direction. The signal receiving module (4) includes a polarization selection element, and the polarization selection element is a motor-controlled rotatable Glan-Taylor prism (43) for screening the polarization direction of the second harmonic signals, establishing the dependence relationship between the SHG intensity and the ferroelectric polarization direction, and avoiding the measurement position shift caused by rotating the sample.

2. The thin-film ferroelectric direction detection device under stress according to claim 1, wherein: The excitation light module (1) includes an excitation light source, a polarizer (12), a lens A (13), a polarization control element, and a filter A (15), and the excitation light source can generate high-energy incident light.

3. The thin-film ferroelectric direction detection device under stress according to claim 1, wherein: The imaging module (2) includes an illumination light source, an imaging CCD (22), a beam splitting element, and an objective lens (24), and the imaging element has high resolution and high sensitivity.

4. The thin-film ferroelectric direction detection device under stress according to claim 1, characterized in that: The signal receiving module (4) includes a filter B (41), a lens B (42), a focusing element, and a detection element, and the detection element can accurately detect second harmonic signals with different intensities.

5. The stress - induced thin - film ferroelectric direction detection device according to claim 2, characterized in that: The excitation light source is a femtosecond pulsed laser (11), and it can generate laser with high intensity and a specific frequency range.

6. The thin-film ferroelectric direction detection device under stress according to claim 2, characterized in that: The polarization control element is a motor-controlled rotatable half-wave plate (14).

7. The thin-film ferroelectric direction detection device under stress according to claim 3, characterized in that: The illumination light source is a white light source (21), and the beam splitting element is a push-pull beam splitter (23).

8. A device for detecting the ferroelectric direction of a thin film under stress according to claim 4, characterized in that: The focusing element is a lens C (44), and the detection element is a high-performance detector (45).

9. A method for detecting the ferroelectric direction of a thin film under stress, which is realized by a device for detecting the ferroelectric direction of a thin film under stress according to any one of claims 1-8, characterized in that, It includes the following steps: S1: Transfer the sample to a flexible stress-applying substrate, then mount it on a stress-applying device, and install the device on the displacement stage (47) in the stress module. During the installation process, make the side line of the device as parallel as possible to the horizontal direction of the optical path in the laboratory; S2: Adjust the optical system, observe the sample to be measured through the imaging system, find the required measurement area, focus the incident light on the measurement area of the sample to be measured, and focus the signal light on the detector sensing window; S3: Through the motion controller, make the starting position of the fast axis of the half-wave plate and the starting position of the optical axis of the Glan-Taylor prism parallel to the laboratory horizontal direction, link the controller and the detector, and let the half-wave plate and the Glan-Taylor prism rotate simultaneously at an angle of 1 / 2 and respectively, detect the SHG intensity at each angle, and then obtain the change of SHG intensity under different polarizations, establish the dependence relationship between the SHG intensity and the ferroelectric polarization direction in the sample. This operation avoids the problem that the sample deviates from the optical path center due to the sample position not being at the center of the rotating table when the sample is rotated; S4: Applying stress to the thin film to be measured can be achieved by stretching the film or changing the shape of the sample. At the same time, with the help of the imaging module, observe the morphological changes of the sample under each stress, and measure the change of the SHG intensity with the angle under each stress to obtain the dynamic process of the ferroelectric direction evolution under stress.

Images