Multi-physical-quantity microscopic imaging device and method based on microwave S21 parameters
By combining vector network analyzer and atomic force microscope to measure microwave S21 parameters, the problem of difficulty in measuring the internal structure and properties of the materials in the prior art is solved, and high-quality multi-physical quantities microscopy is achieved.
Patent Information
- Application Number
- CN202510411274.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-02
- Publication Date
- 2025-06-20
AI Technical Summary
Existing microscopic imaging techniques are difficult to effectively measure the internal structure and properties of materials, resulting in poor imaging quality.
Using a multi-physical quantum microscope based on microwave S21 parameters, a vector network analyzer is combined with an atomic force microscope to measure the S21 parameters of the sample, and a variety of physical information such as the surface morphology, internal structure, defects and electrical properties of the material are obtained.
It improves the quality and accuracy of microscopic imaging, can better study the internal properties and structure of the material, and provides richer physical information.
Smart Images
Figure CN120177831A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of microscopic imaging technology, and specifically to a multi-physical quantity microscopic imaging device and method based on microwave S21 parameters. Background Art
[0002] Traditional microscopic imaging methods can only image the surface topography of materials and cannot meet the needs of studying the internal structure of materials. An atomic force microscope mainly obtains the surface information of materials by detecting the intermolecular force (the weak repulsive or attractive force between the atoms at the tip of the probe and the atoms on the surface of the sample). It can be used to study the microscopic topography, surface thickness, roughness, and mechanical properties of the material surface, and plays an important role in the preparation, characterization, and application of nanomaterials, and has a wide range of applications in the fields of semiconductors, nanomaterials, chemical engineering, biology, etc. The scanning microwave microscope combines microwave scanning technology, integrates the microwave signal path on the atomic force microscope, and can quantitatively obtain various electrical properties of materials, such as complex impedance (resistance and capacitance), dielectric constant, conductivity, etc. by collecting and analyzing the characteristic information of microwave signals and combining physical models. It has a nanoscale spatial resolution, can accurately obtain the microwave information on the surface of the sample; can perform non-invasive measurements on the sample without damaging the sample; due to the strong microwave penetration ability, it is applicable to a variety of materials including semiconductors, metals, insulators, and various buried structures, and can analyze the subsurface of the sample, with very wide applications.
[0003] Using the microwave S11 parameter for scanning microwave imaging can obtain the internal structure information of materials, but the S11 parameter can only reflect the relationship between the incident signal and the reflected signal, as well as the impedance matching degree and reflection loss of the port. For the transmission characteristics such as attenuation, phase change, and time delay of the signal during transmission in the transmission line, and the loss of the signal during transmission, the S11 parameter cannot directly give.
[0004] The S21 parameter represents the forward transmission coefficient and can directly reflect the loss situation of the signal during transmission. That is, when port 2 is matched, it represents the forward transmission coefficient from port 1 to port 2, and can directly reflect the transmission characteristics such as the amplitude attenuation and phase change of the signal when passing through the sample during the process of the signal transmitting from port 1 to port 2. When designing and analyzing a radio frequency system, the S21 parameter can be used to evaluate the matching degree between different parts of the system and to analyze the transmission characteristics of the signal between multiple transmission line segments, which is particularly important for signal integrity analysis in complex systems. Therefore, the S21 signal focuses on describing the attenuation or amplification of the signal during transmission and the performance of the entire transmission path, is more complete and in-depth than the S11 signal, and can obtain richer physical information.
[0005] In this context, according to the imaging requirements of various material properties, a multi-physical quantity microscopic imaging device and method based on microwave S21 parameters are developed for broader applications. Summary of the Invention
[0006] The present invention provides a multi-physical quantity microscopic imaging device and method based on microwave S21 parameters to solve the problems of low current microscopic imaging quality, lack of internal structure information of materials, and difficulty in efficiently measuring the properties and internal structures of materials.
[0007] The present invention is implemented as follows: The present invention provides a multi-physical quantity microscopic imaging device based on microwave S21 parameters, including an atomic force microscope on which a sample is placed. The atomic force microscope uses the tapping mode. The output end of the position deflection detector of the atomic force microscope is connected to the input end of a preamplifier, and the output end of the preamplifier is connected to a lock-in amplifier. The lock-in amplifier is connected to a PID controller connected to the sample stage. The lock-in amplifier is connected to a computer through an analog-to-digital converter. The cantilever beam of the atomic force microscope is connected to the microwave transmitting port of a vector network analyzer through a coaxial cable, and the sample is connected to the microwave receiving port of the vector network analyzer through a coaxial cable. The output end of the vector network analyzer is connected to the analog-to-digital converter through digital signal processing, and the analog-to-digital converter is connected to the computer. The computer is respectively connected to the sample stage and the vector network analyzer.
[0008] During implementation, it includes an atomic force microscope (AFM) on which a sample is placed. The atomic force microscope includes a sample stage. The sample stage is an XYZ scanning stage using a piezoelectric ceramic tube. The sample is placed on the sample stage as the target object to be detected. Above the sample stage, there is a laser beam emitter as the laser source. The laser beam emitter emits a laser beam that is directed at the back of the cantilever beam and is reflected into the position deflection detector. The tip of the cantilever beam is fixed with a probe, which can scan the sample. The probe is accurately positioned at a suitable position above the sample. A spring-shaped cantilever beam is used to support the tip of the probe, and the cantilever beam is installed through a probe holder. The probe is a metal conductive probe with a tip radius less than 20 nm. An elastic cantilever system is used as a force sensor. As the interaction force changes, the cantilever beam will produce a small bend. During the process of the probe scanning the sample surface, the interaction between the tip of the probe and the sample will generate attractive and repulsive forces. As the tip of the probe and the sample approach each other, the attractive force will deflect the cantilever beam towards the sample. When the tip of the probe touches the sample, the repulsive force will deflect the cantilever beam away from the sample. These interaction forces contain the topographical characteristics of the sample surface.
[0009] The atomic force microscope (AFM) adopts the tapping mode. The position deflection detector is connected to the pre-feedback amplifier circuit. The output end of the position deflection detector of the atomic force microscope is connected to the input end of the pre-amplifier. The output end of the pre-amplifier is connected to the lock-in amplifier. The lock-in amplifier is connected to the PID controller connected to the sample stage. The lock-in amplifier is connected to the computer through the analog-to-digital converter. The output signal of the lock-in amplifier is connected to the oscillator. The oscillator is controlled to be connected to the cantilever beam and returns the signal to the lock-in amplifier.
[0010] The two ports port 1 and port 2 of the vector network analyzer are respectively the microwave transmitting port and the microwave receiving port. The cantilever beam of the atomic force microscope is connected to the microwave transmitting port of the vector network analyzer through a coaxial cable. The sample is connected to the microwave receiving port of the vector network analyzer through a coaxial cable. The output end of the vector network analyzer is connected to the analog-to-digital converter through digital signal processing. The analog-to-digital converter is connected to the computer. The computer is respectively connected to the sample stage and the vector network analyzer.
[0011] The present invention also provides a multi-physical quantity microscopic imaging method based on the microwave S21 parameter, including the following steps: a. Use the atomic force microscope (AFM) to perform topographic imaging Install the sample on the sample stage. The sample stage controls the movement of the sample in the x, y, and z directions. Use the probe to scan the surface of the sample. Use the piezoelectric ceramic block as the excitation source. Drive the probe to vibrate by applying an alternating voltage. Drive the probe to scan on the surface of the sample. Through the scanning frequency response, obtain the resonance peak of the probe. Make the probe vibrate at a frequency lower than this resonance peak, that is, make the probe vibrate in a state lower than the natural frequency to keep its amplitude constant. When the surface topography of the sample changes, the oscillating tip of the probe will collide with the sample, and the amplitude of the probe changes, causing the deflection of the cantilever beam.
[0012] Use the laser beam emitter to emit laser light and irradiate it on the cantilever beam equipped with the probe. The laser is reflected into the position deflection detector. The deflection detector collects the position of the transformed reflected light beam and adjusts the laser position to make the laser irradiate the center of the position deflection detector. When the probe tip interacts with the surface of the sample, the cantilever beam deflects, that is, different bending degrees of the cantilever beam cause the deflection of the laser beam. The slight deflection will change the position of the reflected light beam, and the position of the reflected light changes accordingly. The position deflection detector detects the change in the laser position, converts the optical signal into an electrical signal, and transmits the electrical signal to the pre-feedback amplifier circuit for processing. Specifically, the pre-amplifier in the pre-feedback amplifier circuit enhances the gain and filters and purifies the current signal to improve the signal-to-noise ratio and stability of the signal. The processed signal is transmitted to the lock-in amplifier. Inside the lock-in amplifier, using the phase discrimination unit in the phase-locked loop technology, the signal to be measured is compared with the reference signal in terms of phase, and the amplitude offset ΔA of the signal is accurately calculated, which is used as the feedback adjustment.
[0013] b, PID controller feedback regulation The feedback loop of the atomic force microscope maintains a preset point determined by the instrument. The adjustment method is the amplitude modulation (AM) mode. The amplitude change value ΔA is used as the feedback quantity to control the deflection of the cantilever. The PID controller dynamically adjusts the displacement of the sample stage Z-axis through the amplitude offset information ΔA to keep the distance between the sample and the probe constant.
[0014] c, S21 parameter acquisition On the basis of scanning the sample surface using an atomic force microscope (AFM), turn on the vector network analyzer. Connect the microwave emission port of the vector network analyzer to the cantilever of the atomic force microscope through a coaxial cable, and connect the microwave receiving port of the vector network analyzer to the sample through a coaxial cable. The excitation source of the vector network analyzer generates an excitation signal, which is emitted from the microwave emission port and transmitted to the probe through the coaxial cable. The probe acts as a microwave probe. The incident wave interacts with the sample at the tip and is transmitted in the sample. The output signal is transmitted back to the vector network analyzer through the coaxial cable and received by the microwave receiving port. The data acquisition card in the vector network analyzer stores the signals before and after the microwave interaction, and measures the S21 parameter of the sample; the digital signal processing and analog-to-digital converter convert and store the S21 parameter information and send it to the computer.
[0015] Specifically, in the vector network analyzer, the transmitted signal and the excitation signal are respectively mixed with the local oscillator signal through a mixer to convert the high-frequency signal into an intermediate-frequency signal; then they enter the measurement receiver and the reference receiver respectively, compare the amplitude and phase information of the transmitted signal and the reference signal, and obtain the S21 parameter of the measured sample, thus realizing the information acquisition of a single point of the sample.
[0016] d, Synchronous scanning and imaging Scan the sample line by line and ensure that the data synchronization can achieve the purpose of quickly detecting the surface structure field; whenever a line scan is completed, a curve will be generated on the display screen of the vector network analyzer, and this curve directly maps the field distribution characteristics corresponding to the sample topography; after the interaction between the probe and the sample is converted into an electrical signal, it is transmitted to the computer after analog-to-digital conversion to form the original data of the sample topography; at the same time, the vector network analyzer records the transmitted signals of each point in each line one by one, which is presented in the form of the S21 parameter (forward transmission coefficient). Through the vector network calculation, the amplitude, phase, real part, and imaginary part information of the S21 signal can be obtained, which carries local analytical information about the measured sample; use LabVIEW software to write a control program for data storage and extraction, and set the parameters of the vector network analyzer to make the data recording time consistent with the scanning period of the atomic force microscope, thus ensuring the synchronous acquisition of data.
[0017] The computer combines the extracted sample stage (X, Y) coordinate information with the obtained facial features and S21 raw data, uses Matlab software for data processing, demodulates the information, and plots the corresponding grayscale image, enabling simultaneous imaging of topography and S21; For each complete scan over a set area, an image is stored once.
[0018] e. Subsequent image processing and multi - physical quantity calculation Use Gwyddion software for image processing, process and analyze the original data image obtained from the scan, perform noise filtering, image enhancement, and baseline calibration operations on the image to improve the image quality; The computer converts the parsed information in S21 into sample material properties through a physical model. The sample material properties include dielectric constant, conductivity, permeability, impurity concentration, etc., which can reflect the internal defects and subsurface structures in different regions of the sample, as well as its electromagnetic properties, and have broad application prospects.
[0019] Compared with the prior art, the present invention has the following beneficial effects: A multi - physical quantity microscopic imaging device and method based on microwave S21 parameters provided by the present invention rely on the LabVIEW platform. By combining a vector network analyzer (VNA) with an atomic force microscope (AFM), microwaves are loaded onto the probe of the atomic force microscope (AFM). After the microwaves interact with the material, the microwave signal coupled with the material information is transmitted back to the VNA. By measuring and analyzing the microwave S21 parameters, various physical information such as the surface topography, internal structure, defects, and electrical properties of the measured sample can be obtained. This method can improve the imaging quality. By analyzing the loss situation inside the sample, information such as the dielectric constant, conductivity, permeability, and internal defects of the material can be further calculated, thereby better studying the internal properties of the material. Brief description of the drawings
[0020] Figure 1 It represents the structural schematic diagram of the present invention.
[0021] Figure 2 It represents the schematic diagram of line - by - line scanning in the present invention.
[0022] Figure 3 It represents the schematic diagram of the working process of the present invention.
[0023] Figure 4 It represents the schematic diagram of the interdigital electrode scanning of the present invention.
[0024] In the figure: 1 - laser beam emitter, 2 - position deflection detector, 3 - probe, 4 - sample, 5 - cantilever beam, 6 - probe holder, 7 - oscillator, 8 - sample stage, 9 - PID controller, 10 - preamplifier, 11 - lock-in amplifier, 12 - computer, 13 - analog-to-digital converter, 14 - digital signal processing, 15 - mixer, 16 - local oscillator signal, 17 - excitation source, 18 - measurement receiver, 19 - reference receiver, 20 - vector network analyzer, 21 - microwave transmitting port, 22 - microwave receiving port. Specific embodiments
[0025] The specific embodiments of the present invention will be described in detail below.
[0026] A multi-physical quantity microscopic imaging device and method based on microwave S21 parameter, as Figures 1 to 4 shown, includes an atomic force microscope (AFM) with a sample 4 placed thereon, and an AFM scanning imaging system is used in cooperation. The atomic force microscope includes a sample stage 8, and the sample stage 8 is an XYZ scanning stage using a piezoelectric ceramic tube. The sample 4 is placed on the sample stage 8 as the target object to be detected. Above the sample stage 8, there is a laser beam emitter 1 as the laser source. The laser beam emitter 1 emits a laser beam that is directed at the back of the cantilever beam 5 and is reflected into the position deflection detector 2. A probe 3 capable of scanning the sample 4 is fixed on the cantilever beam 5. The probe 3 is accurately positioned at a suitable position above the sample 4. A spring-shaped cantilever beam 5 is used to support the probe tip, and the cantilever beam 5 is installed through a probe holder 6; the probe 3 is a metal conductive probe with a tip radius less than 20 nm. An elastic cantilever system is used as a force sensor. As the interaction force changes, the cantilever beam will produce a small bend. During the process of the probe 3 scanning the surface of the sample 4, the interaction between the tip of the probe 3 and the sample 4 will generate an attractive force or a repulsive force. When the tip of the probe 3 and the sample 4 approach each other, the attractive force will deflect the cantilever beam 5 towards the sample 4. When the tip of the probe 3 contacts the sample 4, the repulsive force will deflect the cantilever beam 5 away from the sample 4; the interaction force contains the topographical characteristics of the sample surface.
[0027] The atomic force microscope (AFM) adopts the tapping mode. The position deflection detector 2 is connected to a pre-feedback amplification circuit. The output end of the position deflection detector 2 of the atomic force microscope is connected to the input end of the preamplifier 10. The output end of the preamplifier 10 is connected to the lock-in amplifier 11. The lock-in amplifier 11 is connected to the PID controller 9 connected to the sample stage 8. The lock-in amplifier 11 is connected to the computer 12 through the analog-to-digital converter 13; the output signal of the lock-in amplifier 11 is connected to the oscillator 7. The oscillator 7 controls and connects to the cantilever beam 5. The oscillator 7 controls the vibration deflection of the cantilever beam 5 to keep the cantilever beam 5 in a relatively stable position and returns the signal to the lock-in amplifier 11.
[0028] The two ports, port 1 and port 2, of the vector network analyzer are respectively the microwave transmitting port 21 and the microwave receiving port 22. The cantilever beam 5 of the atomic force microscope is connected to the microwave transmitting port 21 of the vector network analyzer 20 through a coaxial cable, and the sample 4 is connected to the microwave receiving port 22 of the vector network analyzer 20 through a coaxial cable. That is, connect the probe cantilever beam 5 to port 1 and the sample 4 to port 2. Apply microwave loading through the vector network analyzer 20, convert and store the microwave S-parameters using the digital signal processing 14 and the analog-to-digital converter 13, and store the signals before and after the action on the sample in the computer 12. That is, the output end of the vector network analyzer 20 is connected to the analog-to-digital converter 13 through the digital signal processing 14, the analog-to-digital converter 13 is connected to the computer 12, and the obtained parameter information is processed and converted into image information. The computer 12 is respectively connected to the sample stage 8 and the vector network analyzer 20.
[0029] The present invention also provides a multi-physical quantity microscopic imaging method based on the microwave S21 parameter, including the following steps: a. Use an atomic force microscope (AFM) for topography imaging Check the zero calibration of the input channel of the control system. During the calibration operation, first completely block the laser light path inside the probe with an opaque paper sheet, and perform system automatic calibration on the IN0 zero value, IN1B zero value, and IN1D zero value in the A / D channel zero adjustment to ensure that they are within their respective ranges. If it exceeds the range interval, it may be due to abnormal instrument status. Check whether the instrument wiring is correct, restart the software and the control box, and correct again to check the situation; perform spot detection.
[0030] Remove the opaque card, install the cantilever beam with the probe 3 fixed on the probe holder 6, move the sample stage 8 to the rightmost side, start spot detection, and adjust the position of the laser 1 slightly to make the laser spot hit the front end of the probe cantilever beam 5 correctly. When the laser spot accurately hits the probe cantilever 5, a clear diffraction spot will appear on the white sticker on the left side of the probe, and the red dot in the "Spot Detection" window is at the center of the cross frame, and the energy value reaches the maximum. Stop detection and close the window.
[0031] Install the sample 4 on the sample stage 8, move the sample stage 8 to the middle, ensure that the sample 4 is under the probe 3, and the sample stage 8 controls the movement of the sample 4 in the x, y, and z directions; use the tapping-mode AFM to scan the surface of the sample 4 with the probe 3, search for the resonance peak, and set the imaging range; control the motor to approach the probe 3 close to the sample 4, set the distance parameter between the tip and the sample according to the scanning range, first step single-step, and then "automatically approach" until the probe 3 approaches the sample 4 to reach the working interval and the motor automatically stops.
[0032] A piezoelectric ceramic block is used as an excitation source. By applying an alternating voltage, the probe is driven to vibrate, and the probe is driven to scan the surface of the sample. Through the scanning frequency response, the resonance peak of the probe 3 is obtained, and the probe 3 vibrates at a frequency lower than this resonance peak, that is, the probe vibrates in a state lower than its natural frequency, so that its amplitude is constant. When the surface topography of the sample 4 changes, the oscillating tip of the probe 3 will collide with the sample, and the amplitude of the probe 3 changes, causing the deflection of the cantilever beam 5.
[0033] A laser beam emitter 1 emits a laser beam and irradiates it on the cantilever beam 5 equipped with the probe 3. The laser is reflected into the position deflection detector 2. The deflection detector 2 collects the position of the changing reflected beam, and adjusts the laser position so that the laser irradiates the center of the position deflection detector 2. When the tip of the probe 3 interacts with the surface of the sample 4, the cantilever beam 5 deflects, that is, different bending degrees of the cantilever beam 5 cause the deflection of the laser beam. The slight deflection will change the position of the reflected beam, and the position of the reflected light will change accordingly. The position deflection detector 2 converts the optical signal into an electrical signal by detecting the change in the laser position, and the electrical signal is transmitted to the pre-feedback amplifier circuit for processing, and image scanning is performed. During the scanning process, the scanning range and display range can be gradually changed according to the undulation of the sample surface. After the scanning is completed, the probe is withdrawn, and the topography image of the sample surface can be obtained. Specifically, the preamplifier 10 in the pre-feedback amplifier circuit enhances the gain and filters and purifies the current signal to improve the signal-to-noise ratio and stability of the signal. The processed signal is transmitted to the lock-in amplifier 11. Inside the lock-in amplifier 11, the phase comparison unit in the phase-locked loop technology is used to compare the phase of the signal to be measured with the reference signal, and the amplitude offset ΔA of the signal is accurately calculated, which is used as the feedback adjustment.
[0034] b, PID controller feedback adjustment The feedback loop of the atomic force microscope maintains a preset point determined by the instrument. The adjustment method is the amplitude modulation (AM) mode. The amplitude change value ΔA is used as the feedback quantity to control the deflection of the cantilever. The PID controller 9 dynamically adjusts the displacement of the Z-axis of the sample stage 8 through the amplitude offset information ΔA to keep the distance between the sample 4 and the probe 3 constant.
[0035] c, S21 parameter acquisition On the basis of scanning the surface of the sample using an atomic force microscope (AFM), the vector network analyzer 20 is turned on. The microwave emission port 21 of the vector network analyzer 20 is connected to the cantilever beam 5 of the atomic force microscope, and the microwave receiving port 22 of the vector network analyzer 20 is connected to the sample 4 through a coaxial cable. The excitation source 17 of the vector network analyzer 20 generates an excitation signal, which is emitted from the microwave emission port 1. The signal is transmitted through the coaxial cable to the tip of the probe 3. The probe 3 serves as a microwave probe. The incident wave interacts with the sample at the tip and is transmitted in the sample 4. The output signal is transmitted back to the microwave receiving end at port 2 through the coaxial cable.
[0036] The data acquisition card in the vector network analyzer 20 stores the signals before and after the microwave action to obtain the S21 parameter of the sample 4. Specifically, in the vector network analyzer 20, the transmitted signal and the excitation signal are respectively mixed with the local oscillator signal by the mixer 15 to convert the high-frequency signal into an intermediate-frequency signal. Then they enter the measurement receiver and the reference receiver respectively. In the measurement receivers A and B and the reference receivers R1 and R2, the amplitudes and phase information of the transmitted signal and the reference signal are compared to obtain the S21 parameter of the measured sample, thus realizing the information acquisition of a single point of the sample. The S21 parameter carries local analytical information about the sample.
[0037] The digital signal processing 14 and the analog-to-digital converter 13 convert and store the S21 parameter information and send it to the computer 12.
[0038] d. Synchronous scanning and imaging The software control part of the scanning microwave imaging system mainly includes control software and image processing software. The control software uses the LabVIEW platform to control various parameter settings of the VNA and AFM. Its main function is to achieve data synchronization and comprehensive regulation among various modules. The image processing software mainly uses the Gwyddion software to process and analyze the original data obtained by scanning; uses the matlab software for data processing, demodulates the information and draws the corresponding grayscale image.
[0039] The interaction between the probe 3 and the sample 4 is converted into an electrical signal. The electrical signal is transmitted to the computer after analog-to-digital conversion 13 to form the original data of the sample morphology. At the same time, the vector network analyzer 20 records the transmitted signals of each point in each row one by one, which is presented in the form of the S21 parameter (forward transmission coefficient). Through vector network calculation, the amplitude, phase, real part, and imaginary part information of the S21 signal can be obtained. The S21 parameter carries local analytical information of the measured sample. A control program is written using the LabVIEW software to store and extract data and set the parameters of the vector network analyzer 20 to make the data recording time consistent with the scanning period of the atomic force microscope, thus ensuring the synchronous acquisition of data.
[0040] The computer combines the extracted sample stage 8 (X, Y) coordinate information with the obtained appearance and S21 raw data, uses Matlab software for data processing, demodulates the information and plots the corresponding grayscale image, so as to perform simultaneous imaging of topography and S21; For each complete scan over the set area, an image is stored once.
[0041] e, subsequent image processing and multi-physical quantity calculation Use Gwyddion software for image processing, process and analyze the raw data map obtained by scanning, and perform noise filtering, image enhancement, and baseline calibration operations on the image to improve the image quality; the computer 12 converts the parsed information in S21 into sample material properties through a physical model. The sample material properties include dielectric constant, resistivity, magnetic permeability, etc., which can reflect the internal defects and subsurface structures in different regions of the sample, as well as the electromagnetic properties, and have broad application prospects.
[0042] The scope of protection required by the present invention is not limited to the above specific embodiments. Moreover, for those skilled in the art, the present invention can have various deformations and modifications. Any modifications, improvements, and equivalent replacements made within the concept and principle of the present invention should be included within the protection scope of the present invention.
Claims
1. A multi-physical quantity microscopic imaging device based on microwave S21 parameters, characterized in that: The invention comprises an atomic force microscope on which a sample (4) is placed, the atomic force microscope adopts a tapping mode, the output end of a position deflection detector (2) of the atomic force microscope is connected to the input end of a preamplifier (10), the output end of the preamplifier (10) is connected to a lock-in amplifier (11), the lock-in amplifier (11) is connected to a PID controller (9) connected to a sample stage (8), and the lock-in amplifier (11) is connected to a computer (12) via an analog-to-digital converter (13); The cantilever beam (5) of the atomic force microscope is connected to a microwave transmitting port (21) of a vector network analyzer (20) via a coaxial cable, the sample (4) is connected to a microwave receiving port (22) of the vector network analyzer (20) via a coaxial cable, the output end of the vector network analyzer (20) is connected to an analog-to-digital converter (13) via a digital signal processor (14), the analog-to-digital converter (13) is connected to a computer (12), and the computer (12) is respectively connected to a sample stage (8) and a vector network analyzer (20).
2. The multi-physical quantity microscopic imaging device based on microwave S21 parameters according to claim 1, characterized in that: The output signal of the phase-locked amplifier (11) is connected to the oscillator (7), and the oscillator (7) controls the cantilever beam (5) and returns the signal to the phase-locked amplifier (11).
3. The multi-physical quantity microscopic imaging device based on microwave S21 parameters according to claim 1, characterized in that: The atomic force microscope comprises a sample stage (8), a laser beam emitter (1) is arranged above the sample stage (8), the laser beam emitter (1) emits a laser beam directly toward the back of a cantilever beam (5), and the laser beam is reflected into a position deflection detector (2), and a probe (3) is fixed on the cantilever beam (5) to scan a sample (4).
4. The multi-physical quantity microscopic imaging device based on microwave S21 parameters according to claim 1, characterized in that: The two ports port 1 and port 2 of the vector network analyzer (20) are respectively a microwave transmission port (21) and a microwave receiving port (22).
5. The multi-physical quantity microscopic imaging device based on microwave S21 parameters according to claim 1, characterized in that: The probe (3) is a metal conductive probe with a needle tip radius of less than 20 nm.
6. A multi-physical quantity microscopic imaging method based on microwave S21 parameters, characterized in that: The following steps are involved: a, Topography imaging using atomic force microscopy The sample (4) is mounted on a sample stage (8), the sample stage (8) controls the movement of the sample (4) in the x, y, and z directions, a probe (3) is used to scan the surface of the sample (4), a piezoelectric ceramic block is used as an excitation source, an AC voltage is applied to drive the probe to vibrate, a resonance peak of the probe (3) is obtained by scanning the frequency response, and the probe (3) is vibrated at a frequency lower than the resonance peak. When the surface morphology of the sample (4) changes, the oscillating tip of the probe (3) collides with the sample, the amplitude of the probe (3) changes, and the cantilever beam (5) is deflected; A laser beam emitter (1) is used to emit laser light onto a cantilever beam (5) equipped with a probe (3), and the laser light is reflected into a position deflection detector (2). The position of the laser light is adjusted so that the laser light is irradiated onto the center of the position deflection detector (2); The position deflection detector (2) detects the change in the laser position and converts the optical signal into an electrical signal. The electrical signal is transmitted to the pre-feedback amplifier circuit for processing and then to the phase-locked amplifier (11) to compare the phase of the measured signal with the reference signal and accurately calculate the amplitude offset ΔA of the signal, which is used as feedback regulation. b. PID controller feedback adjustment The feedback loop of the atomic force microscope maintains a preset point determined by the instrument, and the adjustment mode is an amplitude adjustment mode, and the amplitude change value ΔA is used as a feedback amount to control the deflection of the cantilever. The PID controller (9) dynamically adjusts the displacement of the Z axis of the sample stage (8) through the amplitude offset information ΔA to make the distance between the sample (4) and the probe (3) constant; c. S21 parameter collection On the basis of scanning the sample surface using an atomic force microscope, the vector network analyzer (20) is turned on, the microwave transmitting port (21) of the vector network analyzer (20) is connected to the cantilever beam (5) of the atomic force microscope via a coaxial cable, the microwave receiving port (22) of the vector network analyzer (20) is connected to the sample (4) via a coaxial cable, the excitation source (17) of the vector network analyzer (20) generates an excitation signal, which is emitted from the microwave transmitting port (21) and transmitted to the probe (3) via the coaxial cable. The probe (3) acts as a microwave probe, and the incident wave interacts with the sample (4) at the tip and is transmitted in the sample (4). The output signal is transmitted back to the vector network analyzer (20) via the coaxial cable and is received by the microwave receiving port (22). The data acquisition card in the vector network analyzer (20) stores the signals before and after the microwave action, and measures the S21 parameter of the sample (4); the digital signal processing (14) and the analog-to-digital converter (13) convert and store the S21 parameter information, and transmit it to the computer (12); d, Synchronous scanning and imaging Scanning the sample (4) line by line to complete simultaneous imaging of the morphology and microwave of the sample (4); after the interaction between the probe (3) and the sample (4) is converted into an electrical signal, it is transmitted to a computer after analog-to-digital conversion (13) to form raw data of the sample morphology; at the same time, the vector network analyzer (20) records the transmission signal of each point in each line one by one, and presents it in the form of S21 parameters. After vector network calculation, the amplitude, phase, real part and imaginary part information of the S21 signal can be obtained; using LabVIEW software to write a control program to store and extract data, and to realize parameter setting of the vector network analyzer (20) so that its data recording time is consistent with the scanning period of the atomic force microscope, thereby ensuring synchronous data collection; The computer combines the extracted (X, Y) coordinate information of the sample stage (8) with the acquired morphology and S21 raw data, uses MATLAB software to process the data, demodulates the information and draws a corresponding grayscale image, so that the morphology and S21 can be imaged simultaneously; each time a complete scan is performed on a set area, an image is stored; e. Subsequent image processing and multi-physics calculation Use Gwyddion software to process and analyze the raw data obtained by scanning, and perform noise filtering, image enhancement, and baseline calibration on the image to improve the image quality; The computer (12) converts the analytical information in S21 into sample material properties through a physical model.
7. The multi-physical quantity microscopic imaging method based on microwave S21 parameters according to claim 6, characterized in that: In step a, the preamplifier (10) in the pre-feedback amplifier circuit performs gain enhancement and filtering purification on the current signal, and the processed signal is transmitted to the phase-locked amplifier (11). Inside the phase-locked amplifier (11), a phase detection unit in the phase-locked loop technology is used to perform phase comparison between the signal to be measured and the reference signal, and the amplitude offset ΔA is calculated.
8. The multi-physical quantity microscopic imaging method based on microwave S21 parameters according to claim 6, characterized in that: In step c, in the vector network analyzer (20), the transmission signal and the excitation signal are mixed with the local oscillator signal (16) through the mixer (15) to convert the high-frequency signal into an intermediate-frequency signal; then they enter the measurement receiver (18) and the reference receiver (19) respectively to compare the amplitude and phase information of the transmission signal and the reference signal to obtain the S21 parameter of the sample under test, thereby realizing the information collection of a single point of the sample.
9. The multi-physical quantity microscopic imaging method based on microwave S21 parameters according to claim 6, characterized in that: In step e, the sample material properties include dielectric constant, electrical conductivity, magnetic permeability, internal defects, subsurface structure, and impurity concentration.