Dielectric constant measuring system and dielectric constant measuring method

Abstract

The invention discloses a dielectric constant measuring system and a dielectric constant measuring method, an arbitrary waveform generator (AWG) is integrated to an SNDM system, waveform diversification and polarization field intensity enhancement are realized, a polarization sequence can be customized according to material characteristics through the arbitrary waveform output by the AWG, and polarization driving flexibility is greatly improved; meanwhile, a manual or electronic SPDT change-over switch and a Bias-T overlay network are adopted, so that polarization writing and dielectric imaging are rapidly switched in the same area, and repositioning and wiring are avoided; the measurement process time can be shortened by about 70%, and the data acquisition efficiency can be remarkably improved in a high-throughput experiment; meanwhile, the measuring system can remarkably improve the detection speed, the service life of the probe and the multi-material applicability, meanwhile, the thermal disturbance effect is restrained, and a reliable solution is provided for accurate characterization of nano electronic devices.

Description

Technical Field

[0001] This invention relates to the field of dielectric constant testing technology, specifically to a dielectric constant measurement system and a dielectric constant measurement method. Background Technology

[0002] Scanning nonlinear dielectric microscopy (SNDM) is a highly sensitive and high-resolution tool for characterizing nanoscale dielectric materials. It adopts the principle of nonlinear dielectric response detection, which excites the second or higher harmonic signals of the material by applying a high-frequency electric field and combines it with lock-in amplification technology to achieve sub-nanometer resolution. This technology is widely used in fields such as domain structure observation of ferroelectric materials and carrier distribution analysis of semiconductor devices.

[0003] Traditional SNDM technology employs the following techniques: 1. High-frequency LC oscillator design: By optimizing the capacitive coupling between the probe and sample, the detection sensitivity is increased to 10⁻⁶. 22 F / √Hz; 2. Non-contact probe (NC-SNDM): Utilizing the cantilever resonance characteristics of atomic force microscopy (AFM) probes to reduce mechanical contact damage; 3. Time-resolved SNDM (tr-SNDM): Achieving nanosecond-level transient capacitance detection through femtosecond laser synchronous triggering technology; It is evident that traditional SNDM systems mostly use microwave frequency bands (1-10GHz) for signal processing, and their bandwidth limitations result in insufficient real-time data acquisition speed, making it difficult to capture ultrafast dynamic processes. Secondly, metal probes are prone to oxidation and wear under prolonged high-frequency electric fields, significantly shortening probe lifespan and affecting measurement stability. In addition, existing systems have low detection sensitivity for low dielectric constant materials (such as two-dimensional semiconductors and organic ferroelectrics), making it difficult to achieve accurate quantitative analysis.

[0004] Traditional SNDM technology leads to the following technical problems: (1) Insufficient signal bandwidth: The signal processing capability of microwave band is limited, making it difficult to support GHz-level real-time imaging and restricting ultrafast process research; (2) Short probe life: Metal probes are prone to oxidation and wear under high-frequency electric fields, and their lifespan is usually less than 200 hours, resulting in increased maintenance costs; (3) Difficulty in detecting low dielectric materials: The signal-to-noise ratio for two-dimensional materials (such as MoS2) is less than 5dB, making it difficult to accurately analyze the carrier distribution; (4) Significant impact of thermal disturbance: Local temperature rise leads to a decrease in the stability of ferroelectric domains, and the long-term measurement error can reach more than 10%. Moreover, as nanoelectronic devices develop towards higher frequencies and smaller sizes, the limitations of traditional SNDM in terms of signal processing speed, probe stability and multi-material adaptability are gradually becoming apparent.

[0005] Meanwhile, due to insufficient flexibility in waveform application during testing, traditional SNDM can only output high-frequency small-signal biases with fixed frequency and amplitude, making it difficult to provide sufficient polarization electric field amplitude or diverse waveforms. This fails to meet the requirements for precise polarization control of ferroelectric thin films with different thicknesses, compositions, and geometries. Consequently, the measurement mode switching efficiency is low. Existing solutions require manual or frequent replacement of the bias source to switch between polarization writing and dielectric imaging modes, resulting in cumbersome experimental procedures, long switching times, and difficulty in achieving real-time multiple measurements in the same area.

[0006] Based on this, the purpose of this invention is to address the shortcomings of the prior art by providing a dielectric constant measurement system and method. This aims to overcome the technical bottlenecks of traditional SNDM (Single-Site Diode Detector). By integrating an arbitrary waveform generator (AWG) into the SNDM system, waveform diversification and enhanced polarization field intensity are achieved. The arbitrary waveform output by the AWG allows for customized polarization sequences based on material properties, significantly improving the flexibility of polarization driving. Simultaneously, the use of a manual or electronic SPDT (Special Spatial Dimensioning Device) switch and a Bias-T (Bias-T) overlay network enables rapid switching between polarization writing and dielectric imaging within the same region, avoiding repositioning and wiring. The measurement process time is reduced by approximately 70%, significantly improving data acquisition efficiency in high-throughput experiments. This provides a reliable solution for the precise characterization of nanoelectronic devices. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a dielectric constant measurement system and method to solve the limitations of traditional SNDM in terms of signal processing speed, probe stability, and adaptability to multiple materials, as well as the problems of insufficient waveform application flexibility and low measurement mode switching efficiency.

[0008] Specifically, the technical problem to be solved by the present invention is to address the shortcomings of the prior art. In a first aspect, the present invention provides a dielectric constant measurement system, comprising: a probe module, a low-frequency signal module, a frequency modulation demodulator, and a lock-in amplifier; the probe module includes a probe, one end of which forms a small capacitance C with the upper surface of the sample to be tested. s The low-frequency signal module applies a low-frequency signal to the lower surface of the sample under test. The probe module consists of an LC resonant circuit and a signal amplifier connected in series, with the other end of the probe connected to the LC resonant circuit in the probe module. The output of the signal amplifier in the probe module is connected to the frequency demodulator. The output of the frequency demodulator is connected to the lock-in amplifier. The low-frequency signal module includes a low-frequency signal generator and an arbitrary waveform generator (AWG). The low-frequency signal from the low-frequency signal generator is used as a modulation signal for the high-frequency signal and applied to the sample under test. The arbitrary waveform generator outputs a programmable high voltage / arbitrary waveform to drive the polarization of the sample under test.

[0009] In one embodiment of the dielectric constant measurement system according to the present invention, the low-frequency signal module further includes a switching switch, which switches between a low-frequency signal generator being connected to the sample under test and an arbitrary waveform generator being connected to the sample under test by manual operation or control signal.

[0010] In one embodiment of the dielectric constant measurement system according to the present invention, the low-frequency signal module further includes a Bias-T circuit, which is connected to a low-frequency signal generator, an arbitrary waveform generator, and a switching switch, respectively, and superimposes the high-frequency imaging signal generated by the arbitrary waveform generator and the low-frequency / high-voltage polarization signal generated by the low-frequency signal generator at the bottom electrode of the sample to be tested.

[0011] In one embodiment of the dielectric constant measurement system according to the present invention, the frequency demodulator demodulates the frequency signal modulated by the probe module, removes the high-frequency carrier signal, inputs the demodulated signal into the lock-in amplifier, and uses the frequency of the low-frequency signal applied to the sample under test as the reference frequency for detection, separating and amplifying to generate a high signal-to-noise ratio signal; in another embodiment of the dielectric constant measurement system according to the present invention, a digital pulse generator is used to replace the arbitrary waveform generator.

[0012] In one embodiment of the dielectric constant measurement system according to the present invention, the switching switch is a manual SPDT switch or a solid-state multiplex RF switch.

[0013] In one embodiment of the dielectric constant measurement system according to the present invention, the switching switch is a dual bias circuit parallel structure: two bias paths are introduced at the bottom electrode of the sample to be tested, one bias path is an AWG path and the other bias path is a low frequency signal path, which are connected in parallel through an independent circuit breaker or electronic relay, and one path is disconnected in the measurement mode to realize the signal switching function.

[0014] In one embodiment of the dielectric constant measurement system according to the present invention, the low-frequency signal module is a waveform control module based on FPGA / SoC: it integrates multi-channel DAC and timing logic using FPGA or high-performance SoC (System on Chip) to realize arbitrary waveform generation and synchronous triggering functions, and directly outputs to the bottom electrode of the sample under test.

[0015] In one embodiment of the dielectric constant measurement system according to the present invention, the probe is a gallium nitride (GaN) probe.

[0016] In one embodiment of a dielectric constant measurement system according to the present invention, the surface of the probe has a diamond coating.

[0017] In one embodiment of the dielectric constant measurement system according to the present invention, an oxide film is formed on the surface of the probe, which can directly form a MOS structure with the sample to be tested.

[0018] In one embodiment of the dielectric constant measurement system according to the present invention, the frequency of the high-frequency radio frequency signal generated by the LC resonant circuit is 0.5 GHz to 3.0 GHz.

[0019] In one embodiment of the dielectric constant measurement system according to the present invention, the signal amplifier is a negative feedback amplifier.

[0020] In one embodiment of the dielectric constant measurement system according to the present invention, a high signal-to-noise ratio signal is used as the output signal. The output signal can be used for the observation of strong dielectric polarization distribution, the ultra-high sensitivity measurement of charge distribution and impurity distribution in semiconductor devices, and the visualization of atomic bipolar torque using a non-contact SNDM (scanning nonlinear dielectric microscope).

[0021] Secondly, the present invention provides a dielectric constant measurement method, which is implemented using a dielectric constant measurement system as described above. The probe is installed at the end of the cantilever beam. When the probe approaches the sample surface, it generates interatomic forces, which control the movement of the sample under test in the x and y directions to achieve scanning. The laser irradiates the back of the cantilever beam and is then reflected onto a four-quadrant photodetector to detect the minute bending or deflection of the cantilever.

[0022] In one embodiment of the dielectric constant measurement method according to the present invention, a high-frequency small signal is applied to the probe end, and the bottom electrode of the sample to be tested is grounded; a tiny MOS structure is formed between the probe and the sample; the nonlinear dielectric response of the ferroelectric material causes the capacitance to be slightly modulated with the bias voltage, and the signal generated by the above-mentioned slight modulation is extracted by a frequency demodulator and a lock-in amplifier; at each scanning point, the amplitude R or phase θ output by the lock-in amplifier is acquired, and the scanning position is saved one-to-one with the corresponding signal value; the two-dimensional signal intensity matrix is ​​mapped into a grayscale image or a pseudo-color image using software.

[0023] Compared with the prior art, the positive effects of the present invention are as follows: The dielectric constant measurement system proposed in this invention integrates an arbitrary waveform generator (AWG) into the SNDM system, which has the following significant advantages compared with the prior art: waveform diversification and enhanced polarization field intensity: The present invention outputs arbitrary waveforms (square wave, pulse, triangular wave, frequency sweep, etc.) through the AWG, and the polarization sequence can be customized according to the material properties, which greatly improves the flexibility of polarization driving.

[0024] Seamless switching and improved measurement efficiency: The use of manual or electronic SPDT switching and Bias-T overlay network enables rapid switching between polarization writing and dielectric imaging in the same area, avoiding repositioning and wiring.

[0025] The measurement process time is reduced by about 70%, and data acquisition efficiency can be significantly improved in high-throughput experiments.

[0026] Meanwhile, the dielectric constant measurement method proposed in this invention breaks through the resolution and sensitivity limits of traditional characterization methods by combining high-frequency nonlinear dielectric response detection with atomic-level probe technology: It employs gallium nitride (GaN) probes with diamond coatings to extend probe lifespan and expand signal processing bandwidth, achieving stronger real-time data acquisition capabilities; the GaN probe has a lifespan exceeding 1000 hours, significantly improved compared to the traditional Pt probe (200 hours); addressing the problem of localized sample heating caused by high-frequency electric fields, leading to polarization state drift in ferroelectric materials, this invention uses laser pulses to locally heat the sample, increasing the nonlinear dielectric constant to 1000 times that of room temperature, simultaneously triggering signal acquisition and avoiding thermal disturbance accumulation; millimeter-wave signal processing enables imaging speeds of up to 3Gbps, 30 times faster than traditional SNDM (100Mbps); to improve detection sensitivity for low dielectric constant materials (such as two-dimensional semiconductors), an oxide film is formed on the probe surface, directly forming a MOS structure with the sample under test, resulting in a wider measurement range and greater ease of use. Attached Figure Description

[0027] Figure 1 This is a block diagram of the SNDM system structure in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram illustrating the measurement of nonlinear dielectric constant in an embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram illustrating the dielectric polarization measurement principle in an embodiment of the present invention.

[0030] Figure 4 This is a measurement example diagram of the probe in an embodiment of the present invention.

[0031] Figure 5 This is a flowchart of the SNDM system in an embodiment of the present invention.

[0032] Figure 6 This is a flowchart illustrating the operation of the improved low-frequency signal module in an embodiment of the present invention.

[0033] Figure 7 The image shows the SNDM measurement results when VPP=5mV in an embodiment of the present invention.

[0034] Figure 8 This is a graph showing the SNDM measurement results when VPP=10mV in an embodiment of the present invention.

[0035] Figure 9 This is a graph showing the SNDM measurement results when VPP=50mV in an embodiment of the present invention.

[0036] Figure 10 This is a graph showing the SNDM measurement results when VPP=200mV in an embodiment of the present invention.

[0037] Figure 11 The graph shows the measurement results obtained by the AFM method.

[0038] Figure 12 This is a comparison chart of the measurement results obtained by the AFM method and the ferroelectric polarization distribution measurement results of the SNDM in the embodiments of the present invention. Detailed Implementation

[0039] Hereinafter, exemplary embodiments according to this application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments of this application. It should be understood that this application is not limited to the exemplary embodiments described herein.

[0040] It is understood that the term "a" should be understood as "at least one" or "one or more," meaning that in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple. The term "a" should not be construed as a limitation on the quantity. "Multiple" means two or more.

[0041] While ordinal numbers such as “first,” “second,” etc., will be used to describe various components, there is no limitation on which components are used herein. The term is used only to distinguish one component from another. For example, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component, without departing from the teachings of this application. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0042] The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting. As used herein, the singular form also includes the plural form, unless the context clearly indicates otherwise. It will also be understood that the terms “comprising” and / or “having” as used in this specification specify the presence of the described features, numbers, operations, components, elements or combinations thereof, without excluding the presence or addition of one or more other features, numbers, operations, components, elements or combinations thereof.

[0043] The following combination Figures 1-12 The present invention will be further described with reference to specific embodiments.

[0044] Scanning nonlinear dielectric microscopy (SNDM) is a highly sensitive and high-resolution tool for characterizing nanoscale dielectric materials, and it has important applications in fields such as ferroelectric domain observation and semiconductor carrier distribution analysis.

[0045] SNDM (Single-Nano Response Dielectric Dynamics) technology, based on the principle of nonlinear dielectric response detection, excites the second or higher harmonic signals of materials by applying a high-frequency electric field, and achieves sub-nanometer resolution by combining lock-in amplification technology. This technology is widely used in fields such as domain structure observation of ferroelectric materials and carrier distribution analysis of semiconductor devices. Since its inception, SNDM has been widely applied to semiconductor doping distribution analysis and polarization domain imaging research of ferroelectric / dielectric materials. With the development of applications such as ferroelectric memory, logic devices, and microelectromechanical systems (MEMS), the demand for research on the local polarization dynamics, switching behavior, and fatigue performance of ferroelectric materials is increasing. Traditional electrical testing often only obtains large-area average characteristics, while SNDM can obtain local dielectric responses at the nanoscale, filling the blind spots of macroscopic electrical testing. However, for the polarization characteristics of ferroelectric materials, its polarization control capabilities are limited; it can only apply a single-frequency, low-frequency signal, and cannot perform strong electric field driving or flexible polarization writing operations on ferroelectric materials.

[0046] The existing technology employs the following approach: 1. Fixed bias method: Most SNDM systems use the internal bias source of a lock-in amplifier to output a small-amplitude sinusoidal signal applied to the probe. This method is only suitable for measuring the nonlinear dielectric response of ferroelectric materials and cannot provide a sufficient polarization electric field to achieve domain flipping.

[0047] 2. Applying polarization voltage via external DC power supply: When polarization writing is required, the operator usually temporarily disconnects the bias circuit and connects a high-voltage DC source, applying it to the sample via a manual switch. This method involves cumbersome wiring, and the measurement and polarization steps are separated, making dynamic switching or synchronous measurement impossible.

[0048] As can be seen from the above analysis, several key issues still need to be addressed in the existing technology. First, the waveform application flexibility is insufficient. Traditional SNDM can only output high-frequency, small-signal biases with fixed frequency and amplitude, making it difficult to provide sufficient polarization electric field amplitude or diverse waveforms, thus failing to meet the requirements for precise polarization control of ferroelectric thin films with different thicknesses, compositions, and geometries. Second, the measurement mode switching efficiency is low. Existing schemes require manual or frequent replacement of the bias source to switch between polarization writing and dielectric imaging modes, resulting in cumbersome experimental procedures, long switching times, and difficulty in achieving real-time multiple measurements in the same area.

[0049] In other words, although existing SNDM technology can achieve dielectric imaging at the nanoscale, it still has many shortcomings in polarization control and dynamic measurement of ferroelectric materials: limited polarization capability: traditional SNDM can only output small-amplitude high-frequency signals at a fixed frequency, which is difficult to provide sufficient polarization electric field and cannot effectively realize the flipping and control of ferroelectric domains; cumbersome testing procedures: applying polarization voltage requires manual switching of external DC power supply, the experimental operation is complicated, and polarization and measurement cannot be performed simultaneously; limited waveform types: most systems do not have the ability to output arbitrary waveforms, which cannot meet the research needs of different polarization modes (such as pulse, square wave, frequency sweep, etc.); poor system stability: most of them are built by researchers themselves, lacking standardized design, resulting in poor system stability and repeatability, which affects the reliability of measurement.

[0050] In view of the above, the purpose of this invention is to address the shortcomings of the prior art by providing an improved dielectric constant measurement system, specifically as follows: Figure 1 shows a structural block diagram of a dielectric constant measurement system according to this invention, including: a probe module, a low-frequency signal module, a frequency modulation demodulator, and a lock-in amplifier; wherein, "SNDM data" in the figure refers to scanning nonlinear dielectric microscopy data, and "Ref." refers to a reference signal; the probe module includes a probe, one end of which forms a small capacitance C with the upper surface of the sample to be tested. s The low-frequency signal module applies a low-frequency signal to the lower surface of the sample to be tested; the probe module consists of an LC resonant circuit and a signal amplifier connected in series, and the other end of the probe is connected to the LC resonant circuit in the probe module; the output of the signal amplifier in the probe module is connected to the frequency demodulator; the output of the frequency demodulator is connected to the lock-in amplifier.

[0051] like Figure 5 As shown, the low-frequency signal module includes a low-frequency signal generator and an arbitrary waveform generator (AWG). The low-frequency signal of the low-frequency signal generator is used as a modulation signal for the high-frequency signal and applied to the sample under test. The arbitrary waveform generator outputs a programmable high voltage / arbitrary waveform to drive the polarization of the sample under test.

[0052] like Figure 6 As shown, the low-frequency signal module also includes a switching switch, which switches between a low-frequency signal generator connected to the sample under test and an arbitrary waveform generator connected to the sample under test via manual operation or control signal; wherein, “AWG” in the figure is an arbitrary waveform generator; “Bias-T” is a bias device (BiasTee), which is a three-port network device.

[0053] The low-frequency signal module also includes a Bias-T circuit, which is connected to a low-frequency signal generator, an arbitrary waveform generator, and a switching switch, respectively. The high-frequency imaging signal generated by the arbitrary waveform generator is superimposed on the low-frequency / high-voltage polarization signal generated by the low-frequency signal generator at the bottom electrode of the sample to be tested.

[0054] The frequency demodulator demodulates the frequency signal modulated by the probe module, removes the high-frequency carrier signal, inputs the demodulated signal into the lock-in amplifier, and uses the frequency of the low-frequency signal applied to the sample under test as the reference frequency for detection, separating and amplifying to generate a high signal-to-noise ratio signal.

[0055] Among them, the probe module is the AFM probe module: used to scan the sample surface and acquire morphology signals.

[0056] The frequency modulation demodulator is the frequency modulation demodulation unit: the radio frequency signal output by the demodulation probe module.

[0057] Lock-in amplifier: Using the low-frequency signal generator under the sample as the reference frequency, it separates and amplifies the output signal of the frequency modulation and demodulation.

[0058] The low-frequency signal generator is a low-frequency signal source: it acts as a modulation signal for the high-frequency signal and is applied to the sample under test.

[0059] Arbitrary waveform generator (AWG): Outputs programmable high voltage / arbitrary waveform to drive the polarization of ferroelectric materials.

[0060] Switch: Switches between the low-frequency signal source and the AWG to the sample bottom electrode by manual operation or control signal.

[0061] Bias-T circuit: superimposes high-frequency imaging signals with low-frequency / high-voltage polarization signals at the bottom electrode of the sample.

[0062] like Figure 4 As shown, the probe is mounted at the end of a very flexible cantilever beam. When the probe approaches the sample surface, it generates interatomic forces. The movement of the sample in the x and y directions is controlled to achieve scanning. The laser shines on the back of the cantilever beam and is then reflected onto a four-quadrant photodetector to detect the minute bending or deflection of the cantilever.

[0063] A high-frequency small signal is applied to the probe tip, and the sample bottom electrode is grounded; a tiny MOS structure is formed between the probe and the sample; the nonlinear dielectric response of the ferroelectric material causes the capacitance to be slightly modulated with the bias voltage; these signals are extracted by a frequency modulation demodulator and a lock-in amplifier. At each scan point, the output R (amplitude) or θ (phase) of the lock-in amplifier is acquired, and the scan position (x, y) is saved one-to-one with the corresponding signal value; the two-dimensional signal intensity matrix is ​​mapped to a grayscale image or pseudo-color image using software (such as LabVIEW, Gwyddion, IgorPro, WSxM).

[0064] The measurement steps include: 1. When the sample being tested is a ferroelectric material, if you want to change its polarization state, you can connect the AWG to the sample substrate electrode via a switch, design a waveform to coordinate with the probe scanning to achieve the desired sample state. After completion, connect the substrate back to the low-frequency signal source via a switch to start the test.

[0065] 2. Probe-sample capacitive coupling: A tiny capacitor C is formed between the probe and the sample surface. s Its value is affected by the sample's dielectric constant, polarization state, and carrier distribution. A low-frequency signal with frequency ω is applied to the sample from its back side. m The system generates high-frequency radio frequency signals (0.5GHz~3.0GHz) through an LC resonant circuit (L is the inductor, C0 is the reference capacitor). When C s When a small shift occurs due to changes in sample properties (such as polarization reversal or carrier migration), the nonlinear dielectric response of the sample causes a frequency shift in the circuit.

[0066] 3. Signal Modulation and Amplification: The frequency modulation demodulator demodulates the modulated frequency signal, removes the high-frequency carrier signal, and inputs the demodulated signal into the amplifier. Using the frequency of the signal applied to the sample as a reference frequency, the signal is detected, separated, and amplified to generate a high signal-to-noise ratio signal.

[0067] 4. For example Figure 2 , Figure 3 As shown, the output signal can be used for observing strong dielectric polarization distribution, ultra-high sensitivity measurement of charge and impurity distribution in semiconductor devices, and visualization of atomic bipolar torque using non-contact SNDM (scanning nonlinear dielectric microscopy). In the figure, "P"... s "This represents the spontaneous polarization intensity. It employs the principle of dielectric polarization measurement, and the following is the formula for capacitance as a function of an alternating electric field:" ΔC - Change in alternating capacitance; C s - Static capacitance formed between the probe and the sample; ε - Nonlinear dielectric constant; E P - The intensity of the applied electric field; ω P - The angular frequency of the applied low-frequency signal.

[0068] Compared with existing technologies, the advantages of this invention are: 1. AWG direct-coupled bottom electrode structure: The output terminal of the arbitrary waveform generator (AWG) is directly connected to the sample substrate electrode via a manual or electronic switching switch, giving the SNDM system the ability to apply programmable polarized waveforms. The coupling method between the AWG and the bottom electrode, the type of switching switch, and the design of the connection interface are specifically selected according to the actual application.

[0069] 2. Superimposing Low-Frequency Imaging and Polarization Signals: A Bias-T network is placed at the intersection of the AWG and the high-frequency small-signal path to achieve seamless superimposition and switching of low-frequency / high-voltage polarization signals and high-frequency imaging signals. Two switching methods are provided: manual SPDT and electronic RF switch (relay or solid-state switch), enabling rapid switching between the polarization source and the imaging source. The specific Bias-T circuit parameters, topology, and superimposition method are selected based on the actual application.

[0070] Alternative solutions that can also be used to achieve the purpose of this invention include, but are not limited to: 1. A digital pulse generator replacing an arbitrary waveform generator (AWG).

[0071] A dedicated pulse generator with programmable digital output and high voltage drive capability is used to replace the general-purpose AWG to achieve pulse polarization control of the bottom electrode.

[0072] Alternative approach: Design of waveform generator type and its output interface.

[0073] 2. Solid-state multi-channel RF switch replaces manual SPDT.

[0074] A semiconductor-based (GaAs / CMOS) RF switch matrix is ​​used to achieve fast, contactless switching between the polarization source and the measurement source through control signals.

[0075] Alternative approach: Electronic switch structure and control logic.

[0076] 3. Parallel structure of dual bias circuits.

[0077] Two bias paths (AWG path and small signal path) are introduced at the bottom electrode and connected in parallel through an independent circuit breaker or electronic relay. One path is disconnected in measurement mode to achieve the same signal switching function.

[0078] Alternative approach: Parallel switch and bias circuit configuration.

[0079] 4. Waveform control module based on FPGA / SoC.

[0080] Integrate multi-channel DAC and timing logic using FPGA or high-performance SoC (System on Chip) to achieve arbitrary waveform generation and synchronous triggering functions, and directly output to the bottom electrode.

[0081] Alternative point: An integrated implementation solution for waveform generation and synchronous triggering.

[0082] Example: As Figures 7-10 Shown is a case of specific measurement, a case of measuring the ferroelectric polarization distribution using a dielectric constant measurement system and a dielectric constant measurement method in the present invention; Test material: BTO material (barium titanate).

[0083] 1. Mechanical integration of the probe head and AFM.

[0084] Select a metal tip probe with a ring-shaped ground electrode (length 225 µm, 75 kHz, 2.8 N / m).

[0085] Install it on the AFM scanning head and set the force feedback parameters in contact or intermittent contact mode.

[0086] 2. Build an LC resonance circuit.

[0087] Connect a variable inductor L in series with a fixed capacitor C0 and tune it to 1 GHz.

[0088] Connect the probe-sample capacitance C s in parallel to the circuit.

[0089] 3. Bias and harmonic excitation.

[0090] Apply a DC bias voltage V_dc (5 V) to determine the operating point.

[0091] Superimpose a small-signal AC bias voltage V_ac (5 mV < VPP < 2 V, 10 kHz) to drive the nonlinear response.

[0092] 4. Signal demodulation and acquisition.

[0093] Use a lock-in amplifier to access the reference low-frequency excitation source and the output signal to be frequency-modulated and demodulated.

[0094] FPGA / MCU performs real-time sampling and outputs frequency offset and phase data.

[0095] 5. Master control software and scanning control.

[0096] Run the scanning path planning module on the PC side to generate X–Y–Z control instructions.

[0097] PID adjusts the Z-axis force control parameters to ensure that the probe slides with a constant force.

[0098] Data buffering, parallel display of the original harmonic amplitude curve.

[0099] 6. Image reconstruction and quantification.

[0100] For 3ω P The signal undergoes bandpass filtering and phase correction to map the ε3 intensity.

[0101] Based on the standard calibration curve, the grayscale values ​​are converted to absolute ε3 units.

[0102] Supports image domain recognition and statistical interfaces.

[0103] 7. Calibration and verification.

[0104] The dC / dV response was calibrated using a linear dielectric standard sample.

[0105] The accuracy of third harmonic imaging was verified using a ferroelectric thin film with a known ε3.

[0106] Regularly check the loop Q value and probe grounding integrity.

[0107] Figure 7 , Figure 8 , Figure 9 , Figure 10 The results were obtained at VPP = 5mV, 10mV, 50mV, and 200mV, respectively. The measured voltage was obtained by processing the original signal frequency through a lock-in amplifier, and the frequency change was obtained by the capacitance formed by the sample. Therefore, its ferroelectricity can be measured. The specific calculation process is as follows: ;in The frequency is GHz. After FM demodulation, the following is obtained: ;in, This represents the change in capacitance formed by the probe and the sample; after processing with lock-in detection, we obtain: .

[0108] The overall calculation and processing flow is as follows: .

[0109] Figure 11 This is a morphology image; that is, an image obtained by AFM (atomic force microscopy) testing, which can only obtain the surface morphology of the material. Figure 12 This is a comparison diagram of the morphology obtained by the AFM method and the ferroelectric polarization distribution measurement results of SNDM (scanning nonlinear dielectric microscopy) in the embodiments of the present invention.

[0110] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0111] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0112] It should be understood that in this invention, "at least one (item)" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0113] It should also be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0114] The steps of the methods or algorithms described in conjunction with the embodiments disclosed in this invention can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0115] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in this invention may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A dielectric constant measurement system, comprising: Probe module, low-frequency signal module, frequency modulation demodulator and lock-in amplifier; The probe module includes a probe, one end of which forms a small capacitance C with the upper surface of the sample to be tested. s The low-frequency signal module applies a low-frequency signal to the lower surface of the sample under test; the probe module consists of an LC resonant circuit and a signal amplifier connected in series, with the other end of the probe connected to the LC resonant circuit in the probe module; the output of the signal amplifier in the probe module is connected to the frequency modulation demodulator; the output of the frequency modulation demodulator is connected to the lock-in amplifier; the low-frequency signal module includes a low-frequency signal generator and an arbitrary waveform generator (AWG), wherein the signal emitted by the low-frequency signal generator is used as a modulation signal for a high-frequency signal and applied to the sample under test; the arbitrary waveform generator outputs a programmable high voltage / arbitrary waveform to drive the polarization of the sample under test.

2. The dielectric constant measurement system as described in claim 1, characterized in that, The low-frequency signal module also includes a switching switch, which switches between a low-frequency signal generator being connected to the sample under test and an arbitrary waveform generator being connected to the sample under test by manual operation or control signal.

3. The dielectric constant measurement system as described in claim 2, characterized in that, The low-frequency signal module also includes a Bias-T circuit, which is connected to a low-frequency signal generator, an arbitrary waveform generator, and a switching switch, respectively. The high-frequency imaging signal generated by the arbitrary waveform generator is superimposed on the low-frequency / high-voltage polarization signal generated by the low-frequency signal generator at the bottom electrode of the sample to be tested.

4. The dielectric constant measurement system as described in claim 1, characterized in that, The frequency demodulator demodulates the frequency signal modulated by the probe module, removes the high-frequency carrier signal, inputs the demodulated signal into the lock-in amplifier, and uses the frequency of the low-frequency signal applied to the sample under test as the reference frequency for detection, separating and amplifying to generate a high signal-to-noise ratio signal.

5. The dielectric constant measurement system as described in claim 2, characterized in that, The arbitrary waveform generator is replaced with a digital pulse generator.

6. The dielectric constant measurement system as described in claim 3, characterized in that, The switching switch is a manual SPDT switch or a solid-state multi-channel RF switch.

7. The dielectric constant measurement system as described in claim 3, characterized in that, The switching switch is a dual-bias circuit in parallel structure: two bias paths are introduced at the bottom electrode of the sample to be tested. One bias path is the AWG path, and the other bias path is the low-frequency signal path. They are connected in parallel through an independent circuit breaker or electronic relay, and one path is disconnected in measurement mode to achieve the signal switching function.

8. The dielectric constant measurement system as described in claim 3, characterized in that, The low-frequency signal module is a waveform control module based on FPGA / SoC: it integrates multi-channel DAC and timing logic using FPGA or high-performance SoC (System on Chip) to realize arbitrary waveform generation and synchronous triggering functions, and directly outputs to the bottom electrode of the sample under test.

9. A method for measuring dielectric constant, wherein the method is implemented using a dielectric constant measurement system as described in any one of claims 1-8, characterized in that, The probe is installed at the end of the cantilever beam. When the probe approaches the sample surface, it generates interatomic forces, which control the movement of the sample under test in the x and y directions to achieve scanning. The laser shines on the back of the cantilever beam and is then reflected onto the four-quadrant photodetector to detect the minute bending or deflection of the cantilever.

10. The dielectric constant measurement method as described in claim 9, characterized in that, A high-frequency small signal is applied to the probe tip, and the bottom electrode of the sample to be tested is grounded; a tiny MOS structure is formed between the probe and the sample; the nonlinear dielectric response of the ferroelectric material causes the capacitance to be slightly modulated with the bias voltage, and the signal generated by the above tiny modulation is extracted by a frequency demodulator and a lock-in amplifier; at each scanning point, the amplitude R or phase θ output by the lock-in amplifier is acquired, and the scanning position is saved one by one with the corresponding signal value; the two-dimensional signal intensity matrix is ​​mapped into a grayscale image or a pseudo-color image using software.

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