A dielectric constant measurement system and a dielectric constant measurement method

Abstract

The application discloses a kind of dielectric constant measurement system and dielectric constant measurement method, by arbitrary waveform generator (AWG) integrated to SNDM system, waveform diversification and polarization field intensity enhancement are realized, and polarization sequence can be defined according to material characteristics by arbitrary waveform output by AWG, greatly improve polarization drive flexibility;Manual or electronic SPDT switch and Bias-T superposition network are used simultaneously, so that polarization write and dielectric imaging are rapidly switched in the same area, to avoid repositioning and wiring;Measurement process time can be shortened by about 70%, and data acquisition efficiency can be significantly improved in high-throughput experiment;Meanwhile, the measurement system of the application can significantly improve detection speed, probe life and multi-material applicability, while suppressing thermal disturbance effect, to provide reliable solution for accurate characterization of nano electronic devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material dielectric constant testing, and particularly relates to a dielectric constant measurement system and a dielectric constant measurement method. BACKGROUND

[0002] As a kind of high sensitivity, high resolution nanoscale dielectric material characterization tool, scanning nonlinear dielectric microscope (SNDM) adopts the detection principle based on nonlinear dielectric response, and through the application of high frequency electric field to stimulate the second or high harmonic signal of the material, combined with the lock-in amplification technology to realize the sub-nanometer resolution, which is widely used in the field of ferroelectric material domain structure observation, semiconductor device carrier distribution analysis, etc.

[0003] The traditional SNDM technical scheme adopts the following technologies: 1. High frequency LC oscillator design: through optimizing the capacitive coupling between the probe and the sample, the detection sensitivity is improved to 10- 22 F / √Hz; 2. Non-contact probe (NC-SNDM): using the cantilever resonance characteristics of the atomic force microscope (AFM) probe, the mechanical contact damage is reduced; 3. Time-resolved SNDM (tr-SNDM): through the femtosecond laser synchronous triggering technology, the nanosecond transient capacitance detection is realized; it can be seen that the traditional SNDM system mostly uses microwave frequency band (1-10GHz) for signal processing, and the bandwidth limitation leads to insufficient real-time data acquisition speed, which is difficult to capture the ultrafast dynamics process. Secondly, the metal probe is easy to be oxidized and worn under the action of long time high frequency electric field, which significantly shortens the service life of the probe and affects the measurement stability. In addition, the detection sensitivity of the existing system for low dielectric constant materials (such as two-dimensional semiconductor, organic ferroelectric) is low, and it is difficult to realize accurate quantitative analysis.

[0004] The traditional SNDM technical scheme leads to the following technical problems: (1) insufficient signal bandwidth: the signal processing capability of the microwave frequency band is limited, which is difficult to support GHz level real-time imaging, and restricts the ultrafast process research; (2) short service life of the probe: the metal probe is easy to be oxidized and worn under the action of high frequency electric field, and the service life is usually less than 200 hours, which leads to increased maintenance cost; (3) difficulty in detecting low dielectric materials: the signal-to-noise ratio of two-dimensional materials (such as MoS2) is less than 5dB, which makes it difficult to accurately analyze the carrier distribution; (4) significant influence of thermal disturbance: local temperature rise leads to the decrease of ferroelectric domain stability, and the long-term measurement error can be more than 10%; moreover, with the development of nanoelectronic devices to higher frequency and smaller size, the limitations of traditional SNDM in signal processing speed, probe stability and multi-material adaptability are gradually highlighted.

[0005] Meanwhile, due to the insufficient flexibility of waveform application during the test, the traditional SNDM can only output a high-frequency small signal bias with fixed frequency and amplitude, and it is difficult to provide sufficient polarization field amplitude or diversified waveforms, and it is unable to meet the fine polarization regulation requirements of ferroelectric thin films with different thickness, composition and geometric structure. Therefore, the measurement mode switching efficiency is low, and the existing scheme needs to manually or frequently change the bias source to switch between the polarization writing and dielectric imaging modes, which causes a tedious experimental process and a long switching time, and it is difficult to realize real-time multiple measurements in the same area.

[0006] Therefore, the purpose of the present application is to overcome the deficiencies of the prior art, and to provide a dielectric constant measurement system and a dielectric constant measurement method, which break through the technical bottleneck of the traditional SNDM, integrate an arbitrary waveform generator (AWG) into the SNDM system, realize waveform diversification and polarization field intensity enhancement, and greatly improve the polarization driving flexibility through the arbitrary waveform output by the AWG, which can define the polarization sequence according to the material properties. At the same time, the manual or electronic SPDT switching switch and the Bias-T superposition network are used to quickly switch the polarization writing and dielectric imaging in the same area, avoiding repositioning and wiring. The measurement process time is shortened by about 70%, and the data acquisition efficiency can be significantly improved in high-throughput experiments. It provides a reliable solution for the accurate characterization of nanoelectronic devices. SUMMARY

[0007] In view of the defects in the prior art, the purpose of the present application is to provide a dielectric constant measurement system and a dielectric constant measurement method to solve the limitations of the traditional SNDM in signal processing speed, probe stability and multi-material adaptability, 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 application is to overcome the deficiencies of the prior art. In a first aspect, the present application provides a dielectric constant measurement system, comprising: a probe module, a low-frequency signal module, a frequency modulation demodulator and a phase-locked amplifier; the probe module comprises a probe, and a micro-capacitor C s is formed between one end of the probe and the upper surface of a sample to be tested; the low-frequency signal module applies a low-frequency signal to the lower surface of the sample to be tested; the probe module is connected in series by an LC resonant circuit and a signal amplifier, and the other end of the probe is connected to the LC resonant circuit in the probe module; the output end of the signal amplifier in the probe module is connected to the frequency modulation demodulator; the output end of the frequency modulation demodulator is connected to the phase-locked amplifier; the low-frequency signal module comprises a low-frequency signal generator and an arbitrary waveform generator (AWG), wherein the low-frequency signal of the low-frequency signal generator is used as a modulation signal of a high-frequency signal and is applied to the sample to be tested; the arbitrary waveform generator outputs a programmable high-voltage / arbitrary waveform to drive the polarization of the sample to be tested.

[0009] In an embodiment of the dielectric constant measurement system according to the present application, the low-frequency signal module further comprises a switching switch, which is switched between a state of connection between the low-frequency signal generator and the sample to be tested and a state of connection between the arbitrary waveform generator and the sample to be tested by manual operation or a control signal.

[0010] In an embodiment of the dielectric constant measurement system according to the present application, the low-frequency signal module further comprises a Bias-T circuit, which is connected with the low-frequency signal generator and the arbitrary waveform generator and the 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 an embodiment of the dielectric constant measurement system according to the present application, the frequency signal modulated by the probe module is demodulated by the frequency modulation demodulator to remove the high-frequency carrier signal, and the demodulated signal is input into the phase-locked amplifier, and the frequency of the low-frequency signal applied to the sample to be tested is taken as a reference frequency for detection, separation and amplification to generate a high signal-to-noise ratio signal; in an embodiment of the dielectric constant measurement system according to the present application, the arbitrary waveform generator is replaced by a digital pulse generator.

[0012] In an embodiment of the dielectric constant measurement system according to the present application, the switching switch is a manual SPDT switch or a solid-state multi-path radio frequency switch.

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

[0014] In an embodiment of the dielectric constant measurement system according to the present application, the low-frequency signal module is a waveform control module based on FPGA / SoC: a multi-channel DAC and timing logic are integrated by using FPGA or high-performance SoC (System on Chip) to realize the functions of arbitrary waveform generation and synchronous triggering, and are directly output to the bottom electrode of the sample to be tested.

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

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

[0017] In an embodiment of the dielectric constant measurement system according to the present application, the surface of the probe is formed with an oxide film, capable of directly forming a MOS structure with the sample to be tested.

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

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

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

[0021] In a second aspect, the present application provides a dielectric constant measurement method, which is implemented by using the dielectric constant measurement system as described above. The probe is installed at the end of the cantilever beam. When the probe approaches the surface of the sample, interatomic forces are generated. The movement of the sample to be tested in the x and y directions is controlled to achieve scanning. The laser is irradiated on the back of the cantilever beam and then reflected onto the four-quadrant photodetector for detecting the slight bending or deflection of the cantilever.

[0022] In an embodiment of the dielectric constant measurement method according to the present application, a high-frequency small signal is applied to the end of the probe, and the bottom electrode of the sample to be tested is grounded. A slight MOS structure is formed between the probe and the sample. The nonlinear dielectric response of the ferroelectric material causes slight modulation of the capacitance with the bias voltage. The signal generated by the above slight modulation is extracted through a frequency modulation demodulator and a lock-in amplifier. At each scanning point, the amplitude R or phase θ output by the lock-in amplifier is collected, and the scanning position and the corresponding signal value are saved one by one. 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 application are as follows. The dielectric constant measurement system according to the present application integrates an arbitrary waveform generator (AWG) into the SNDM system, which has the following significant advantages compared with the prior art: waveform diversification and polarization field intensity enhancement. The present application outputs arbitrary waveforms (square wave, pulse, triangular wave, sweep, etc.) through the AWG, and can define the polarization sequence according to the material properties, greatly improving the flexibility of polarization driving.

[0024] Seamless switching and measurement efficiency improvement: using manual or electronic SPDT switch and Bias-T superposition network, the polarization writing and dielectric imaging are quickly switched in the same area, avoiding repositioning and wiring.

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

[0026] Meanwhile, the dielectric constant measurement method provided by the application breaks through the resolution and sensitivity limit of traditional characterization methods by combining high-frequency nonlinear dielectric response detection and atomic-level probe technology: a gallium nitride (GaN) probe and a diamond coating are used to prolong the service life of the probe, and the signal processing bandwidth is expanded to realize stronger real-time data acquisition capability; the GaN probe has a service life of more than 1000 hours, which is significantly improved compared with the traditional Pt probe (200 hours); in order to solve the problem that the local heating of the sample caused by the high-frequency electric field may cause the polarization state of the ferroelectric material to drift, the application uses laser pulse to locally heat the sample, which improves the nonlinear dielectric constant to 1000 times of room temperature, and synchronously triggers signal acquisition to avoid heat disturbance accumulation; the use of millimeter wave signal processing makes the imaging speed reach 3Gbps, which is 30 times higher than the traditional SNDM (100Mbps); in order to improve the detection sensitivity of low dielectric constant materials (such as two-dimensional semiconductors), an oxide film is formed on the surface of the probe to form a MOS structure directly with the sample to be measured, which has a wider measurement material range and is more convenient to use. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The SNDM system structure diagram in the embodiment of the application.

[0028] Figure 2 The schematic diagram of measuring nonlinear dielectric constant in the embodiment of the application.

[0029] Figure 3 The dielectric polarization measurement principle diagram in the embodiment of the application.

[0030] Figure 4 The measurement example diagram of the probe in the embodiment of the application.

[0031] Figure 5 The working flowchart of the SNDM system in the embodiment of the application.

[0032] Figure 6 The working flowchart of the improved low-frequency signal module in the embodiment of the application.

[0033] Figure 7 The SNDM measurement result diagram when VPP=5mV in the embodiment of the application.

[0034] Figure 8 SNDM measurement result graph for VPP=10mV in the embodiment of the present application.

[0035] Figure 9 SNDM measurement result graph for VPP=50mV in the embodiment of the present application.

[0036] Figure 10 SNDM measurement result graph for VPP=200mV in the embodiment of the present application.

[0037] Figure 11 Measurement result graph obtained by AFM method test.

[0038] Figure 12 Comparison graph of measurement result obtained by AFM method test and ferroelectric polarization distribution measurement result of SNDM in the embodiment of the present application. DETAILED DESCRIPTION

[0039] Hereinafter, example embodiments according to the present application will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and thus should not be used to limit the whole embodiments of the present application, and it should be understood that the present application is not limited by the example embodiments described herein.

[0040] It can be understood that the term "one" should be understood as "at least one" or "one or more", that is, in an embodiment, the number of one element can be one, and in another embodiment, the number of the element can be multiple, and the term "one" cannot be understood as a limitation on the number. "Multiple" means greater than or equal to two.

[0041] Although ordinal numbers such as "first", "second" and the like will be used to describe various components, they are not limited to those components. The terms are used only to distinguish one component from another. For example, a first component can be referred to as a second component, and similarly, a second component can also be referred to as a first component without departing from the teachings of the present application. The term "and / or" as used herein includes any and all combinations of one or more associated listed items.

[0042] The terms used herein are only for the purpose of describing various embodiments and are not intended to limit. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. In addition, it will be understood that the terms "include" and / or "have" when used in the specification designate the presence of stated features, numbers, operations, components, elements or combinations thereof, and do not exclude the presence or addition of one or more other features, numbers, operations, components, elements or combinations thereof.

[0043] The present application will be further described below in conjunction with the specific embodiments. Figures 1-12 with the specific embodiments.

[0044] Scanning nonlinear dielectric microscopy (SNDM) is a high-sensitivity and high-resolution nanoscale dielectric material characterization tool, which has important applications in ferroelectric domain observation, semiconductor carrier distribution analysis, etc.

[0045] SNDM technology is based on the principle of nonlinear dielectric response detection, which excites the second or higher harmonic signal of the material by applying a high-frequency electric field, and realizes sub-nanometer resolution combined with lock-in amplification technology. This technology is widely used in the fields of ferroelectric material domain structure observation, semiconductor device carrier distribution analysis, etc. Since its inception, SNDM has been widely used in semiconductor doping distribution analysis and ferroelectric / dielectric material polarization domain imaging research. With the development of ferroelectric storage, logic devices and micro-electro-mechanical systems (MEMS) applications, the demand for research on the local polarization dynamics, switching behavior and fatigue performance of ferroelectric materials is increasing. Traditional electrical testing can only obtain average characteristics on a large scale, while SNDM can obtain local dielectric response on a nanoscale, making up for the blind spot of macroscopic electrical testing. However, for the polarization characteristics of ferroelectric materials, its function in polarization control is limited, and it can only apply a small high-frequency signal of a single frequency, and cannot perform strong electric field driving and flexible polarization write operation on ferroelectric materials.

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

[0047] 2. External DC power supply to apply polarization voltage: When polarization writing is needed, the operator usually temporarily disconnects the bias circuit, connects a direct-current high-voltage source, and applies it to the sample through a manual switch. This type of wiring is complicated, and the measurement and polarization steps are separate, and cannot realize dynamic switching or synchronous measurement.

[0048] As can be seen from the above analysis, there are still several key problems in the prior art that need to be solved. First, the waveform application flexibility is insufficient, and the traditional SNDM can only output a high-frequency small signal bias of fixed frequency and amplitude, which is difficult to provide sufficient polarization electric field amplitude or diversified waveforms, and cannot meet the fine polarization control requirements of ferroelectric thin films of different thickness, composition and geometric structure. Second, the measurement mode switching efficiency is low, and the existing scheme needs to manually or frequently change the bias source to switch between polarization writing and dielectric imaging modes, resulting in a complicated experimental process, long switching time, and difficulty in realizing real-time multiple measurements in the same area.

[0049] That is, although existing SNDM technology can achieve dielectric imaging at the nanoscale, there are still many deficiencies in the polarization control and dynamic measurement of ferroelectric materials: limited polarization capability: traditional SNDM can only output small high-frequency signals of fixed frequency, which is difficult to provide sufficient polarization electric field, and cannot effectively realize the flipping and regulation of ferroelectric domains; complex test process: the application of polarization voltage needs to rely on manual switching of external DC power supply, and the experimental operation is complex, and the polarization and measurement cannot be carried out synchronously; single waveform type: most systems do not have arbitrary waveform output capability, which cannot meet the research needs of different polarization modes (such as pulse, square wave, sweep, etc.); poor system stability: most of them are built by researchers themselves, lack of standardized design, poor system stability and repeatability, affecting the reliability of measurement.

[0050] Therefore, the purpose of the present application is to overcome the deficiencies of the prior art, and to provide an improved dielectric constant measurement system, as follows: as shown in FIG. 1, a structure block diagram of a dielectric constant measurement system in the present application, comprising: a probe module, a low-frequency signal module, a frequency modulation demodulator and a phase-locked amplifier; wherein "SNDM data" in the figure is scanning nonlinear dielectric microscope data, and "Ref." is a reference signal; the probe module comprises a probe, and a micro-capacitor C s is formed between one end of the probe and the upper surface of the sample to be tested; the low-frequency signal module applies a low-frequency signal to the lower surface of the sample to be tested; the probe module is connected in series by an LC resonant circuit and a signal amplifier, and the other end of the probe is connected to the LC resonant circuit in the probe module; the output end of the signal amplifier in the probe module is connected to the frequency modulation demodulator; the output end of the frequency modulation demodulator is connected to the phase-locked amplifier.

[0051] As shown in FIG. 1, the low-frequency signal module comprises a low-frequency signal generator and an arbitrary waveform generator (AWG), wherein the low-frequency signal of the low-frequency signal generator is used as a modulation signal of the high-frequency signal and is applied to the sample to be tested; the arbitrary waveform generator outputs a programmable high-voltage / arbitrary waveform to drive the polarization of the sample to be tested. Figure 5 As shown in FIG. 1, the low-frequency signal module further comprises a switching switch, which is switched between the connection state of the low-frequency signal generator and the sample to be tested and the connection state of the arbitrary waveform generator and the sample to be tested by manual operation or control signal; wherein "AWG" in the figure is an arbitrary waveform generator; "Bias-T" is a bias tee, which is a three-port network device.

[0052] Figure 6 As shown in FIG. 1, the low-frequency signal module further comprises a switching switch, which is switched between the connection state of the low-frequency signal generator and the sample to be tested and the connection state of the arbitrary waveform generator and the sample to be tested by manual operation or control signal; wherein "AWG" in the figure is an arbitrary waveform generator; "Bias-T" is a bias tee, which is a three-port network device.

[0053] ​The low frequency signal module further comprises a Bias-T circuit, which is connected with the low frequency signal generator and the arbitrary waveform generator and the switching switch respectively, and the high frequency imaging signal generated by the arbitrary waveform generator is superimposed with 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 modulated demodulator demodulates the frequency signal modulated by the probe module, removes the high frequency carrier signal, inputs the demodulated signal into the phase-locked amplifier, and takes the frequency of the low frequency signal applied to the sample to be tested as the reference frequency for detection, separation and amplification to generate a high signal-to-noise ratio signal.

[0055] The probe module is an AFM probe module: used for scanning the surface of the sample and collecting topographic signals.

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

[0057] The phase-locked amplifier: taking the low frequency signal generator under the sample as the reference frequency, separating and amplifying the output signal of the frequency demodulation.

[0058] The low frequency signal generator is a low frequency signal source: as a modulation signal of the high frequency signal, applied to the sample to be tested.

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

[0060] The switching switch: through manual control or control signal, switching between the low frequency signal source and the AWG to the bottom electrode of the sample.

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

[0062] As shown in Figure 4 The probe is mounted at the end of a very soft cantilever beam, and when the probe approaches the surface of the sample, interatomic forces will be generated; the movement of the sample in the x and y directions is controlled to realize scanning; the laser is irradiated on the back of the cantilever beam and then reflected to the four-quadrant photodetector for detecting the slight bending or deflection of the cantilever.

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

[0064] The measurement steps include: 1. When the measured sample is a ferroelectric material, if the polarization state of the sample is to be changed, the AWG can be connected to the sample substrate electrode through a switch, and the waveform is designed to cooperate with the scanning of the probe to achieve the desired planned state of the sample. After completion, the substrate is connected back to the low-frequency signal source through the switch, and the test can be started.

[0065] 2. Probe-sample capacitance coupling: a small capacitance C s is formed between the probe and the sample surface, which is affected by the dielectric constant, polarization state, and carrier distribution of the sample. A low-frequency signal is applied to the back of the sample, and the frequency is ω m . The system generates a high-frequency radio frequency signal (0.5 GHz-3.0 GHz) through an LC resonant circuit (L is inductance, and C0 is a reference capacitance). When C s is slightly offset due to changes in sample characteristics (such as polarization reversal or carrier migration), the nonlinear dielectric response of the sample causes the frequency in the circuit to shift.

[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. The signal frequency applied to the sample is used as a reference frequency for detection, and a high signal-to-noise ratio signal is separated and amplified.

[0067] 4. As shown in Figure 2 , Figure 3 , the output signal can be used for observation of the polarization distribution of strong dielectric, ultra-high sensitivity measurement of charge distribution and impurity distribution in semiconductor devices, and visualization of atomic dipole torque using non-contact SNDM (scanning nonlinear dielectric microscope), wherein “P s ” in the figure is the spontaneous polarization strength. It uses the dielectric polarization measurement principle, and the formula for the change of capacitance with alternating electric field is as follows: ; ΔC- alternating capacitance change; C s - the static value of the capacitance formed by the probe and the sample; ε- nonlinear dielectric constant; E P - applied electric field strength; ω P - the angular frequency of the applied low-frequency signal.

[0068] Compared with the prior art, the positive effects of the present application are: 1. AWG direct coupling bottom electrode structure: the output end of an arbitrary waveform generator (AWG) is directly connected with the sample substrate electrode through a manual or electronic switching switch, and the SNDM system is endowed with programmable polarization waveform application capability. According to the actual application occasion, the coupling mode of the AWG and the bottom electrode, the type of the switching switch and the design of the connection interface are specifically selected and designed.

[0069] 2. Superimposed low-frequency imaging and polarization signal: a Bias-T network is arranged at the intersection of the AWG and the high-frequency small signal path, and the seamless superposition and switching of the low-frequency / high-voltage polarization signal and the high-frequency imaging signal are realized. Two switching modes of manual SPDT and electronic radio frequency switch (relay or solid-state switch) are provided, and the rapid switching of the polarization source and the imaging source is realized. According to the actual application occasion, the Bias-T circuit parameters, the topological structure and the superposition method are specifically selected and designed.

[0070] Alternative solutions that can also be used to achieve the purpose of the present application include but are not limited to: 1. Digital pulse generator instead of arbitrary waveform generator (AWG).

[0071] A dedicated pulse generator (Pulse Generator) with programmable digital output and high-voltage driving capability is used to replace the general AWG, and the pulse polarization control of the bottom electrode is completed.

[0072] Replacement point: design of waveform generator type and its output interface.

[0073] 2. Solid-state multi-channel radio frequency switch instead of manual SPDT.

[0074] A semiconductor (GaAs / CMOS) radio frequency switch matrix is adopted, and the rapid non-contact switching of the polarization source and the measurement source is realized through a control signal.

[0075] Replacement point: electronic switch structure and control logic.

[0076] 3. Double bias circuit parallel structure.

[0077] Two groups of bias paths (AWG path and small signal path) are introduced at the bottom electrode, which are connected in parallel through independent circuit breakers or electronic relays, and one path is disconnected in the measurement mode, realizing the same signal switching function.

[0078] Replacement point: parallel switch and bias circuit configuration.

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

[0080] The arbitrary waveform generation and synchronous triggering function are realized by integrating multi-channel DAC and timing logic of FPGA or high-performance SoC (System on Chip), and the function is directly output to the bottom electrode.

[0081] Alternative point: integrated implementation scheme of waveform generation and synchronous triggering.

[0082] Embodiment: as Figures 7-10 As shown in the following figure, a case of measuring ferroelectric polarization distribution by using a dielectric constant measurement system and a dielectric constant measurement method in the application is shown; test material: BTO material (barium titanate).

[0083] 1. Probe head and AFM mechanical integration.

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

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

[0086] 2. LC resonant circuit construction.

[0087] Series trimming inductance L and fixed capacitance C0 are tuned to 1GHz.

[0088] The probe-sample capacitance C s is connected in parallel to the circuit.

[0089] 3. Bias and harmonic excitation.

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

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

[0092] 4. Signal demodulation and acquisition.

[0093] Use a phase-locked amplifier to access the reference low-frequency excitation source and the frequency-demodulated output signal.

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

[0095] 5. Master 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 constant force sliding of the probe.

[0098] Data buffering and parallel display of original harmonic amplitude curves.

[0099] 6. Image reconstruction and quantification.

[0100] 3ω P signal is band-pass filtered and phase corrected to map ε3 intensity.

[0101] Based on the calibration curve, the gray value is converted into absolute ε3 units.

[0102] Support image domain recognition and statistical interface.

[0103] 7. Calibration and verification.

[0104] Calibrate dC / dV response using linear dielectric standard sample.

[0105] Verify the third harmonic imaging accuracy with ferroelectric thin film with known ε3.

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

[0107] Figure 7 , Figure 8 , Figure 9 , Figure 10 The results measured at VPP=5mV, 10mV, 50mV, and 200mV, respectively, are obtained from the original signal frequency processed by a lock-in amplifier, and the frequency change is obtained from the sample formed capacitor, so that the ferroelectricity can be measured, and the specific calculation process is as follows: ; wherein The frequency is GHz, After FM demodulation processing, we get: ; wherein, The capacitance change amount of the capacitor formed by the probe and the sample; after lock-in detection processing, we get: .

[0108] The overall calculation process is as follows: .

[0109] Figure 11 is a topographic map; that is, an image obtained by AFM (atomic force microscope) testing, which can only obtain the surface morphology of the material; Figure 12 is a comparison chart of the topographic map obtained by the AFM method and the ferroelectric polarization distribution measurement result of the SNDM (scanning nonlinear dielectric microscope) in the embodiment of the application.

[0110] Finally, it should be noted that the above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Although the present application 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 replacements to some technical features, without departing from the spirit and principles of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0111] It should be noted that the embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between embodiments can be mutually referred to. For the system or device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0112] It should be understood that in the present application, “at least one” refers to one or more, and “multiple” refers to two or more. “And / or” is used to describe the association between the associated objects, which means that there can be three relationships, for example, “A and / or B” can mean that there are three cases of only A, only B, and A and B at the same time, wherein A and B can be singular or plural. The character “ / ” generally represents an “or” relationship between the front and rear associated objects. “At least one of the following” or similar expressions means any combination of these items, including any combination of single item or multiple items. For example, at least one of a, b or c, can mean a, b, c, “a and b”, “a and c”, “b and c”, or “a and b and c”, wherein a, b, and c can be single or multiple.

[0113] It should also be noted that in the present application, relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms “include”, “contain” or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement “including a…” does not exclude the presence of another identical element in the process, method, article or device including the 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 permittivity measurement system, comprising: Probe module, low frequency signal module, frequency modulation demodulator and phase lock amplifier; The probe module comprises a probe, one end of which forms a minute 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 is connected in series with an LC resonant circuit and a signal amplifier, and the other end of the probe is connected to the LC resonant circuit in the probe module; The output end of the signal amplifier in the probe module is connected to the frequency modulation demodulator, and the output end of the frequency modulation demodulator is connected to the phase lock amplifier; The low frequency signal module includes a low frequency signal generator, wherein the signal generated by the low frequency signal generator is used as a modulation signal of a high frequency signal and is applied to the sample to be tested; An arbitrary waveform generator is further included, which outputs a programmable arbitrary high voltage waveform signal to drive the polarization of the sample to be tested; A switching switch is further included, which is switched between the connection state of the low frequency signal generator and the sample to be tested and the connection state of the arbitrary waveform generator and the sample to be tested through manual operation or control signal; A Bias-T circuit is further included, which is connected with the low frequency signal generator and the arbitrary waveform generator and the 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.

2. A dielectric constant measurement system as claimed in claim 1, wherein, The frequency signal modulated by the probe module is demodulated by the frequency modulation demodulator, the high frequency carrier signal is removed, the demodulated signal is input into the phase lock amplifier, and the frequency of the low frequency signal applied to the sample to be tested is used as a reference frequency for detection, separation and amplification to generate a high signal-to-noise ratio signal.

3. A dielectric constant measurement system as claimed in claim 1, wherein, The arbitrary waveform generator is replaced by a digital pulse generator.

4. A dielectric constant measurement system as claimed in claim 1, wherein, The switching switch is a manual SPDT switch or a solid-state multi-path radio frequency switch.

5. A dielectric constant measuring system as defined in claim 1, wherein, The switching switch is a double bias circuit parallel structure: two groups of bias paths are introduced at the bottom electrode of the sample to be tested, one group of bias paths is an AWG path, and the other group of bias paths is a low frequency signal path, which are connected in parallel through independent circuit breakers or electronic relays, and one path is disconnected in the measurement mode to realize the signal switching function.

6. A dielectric constant measurement system as in claim 1, wherein, The arbitrary waveform generator uses a waveform control module based on FPGA or high-performance SoC: a multi-channel DAC and timing logic are integrated by using FPGA or high-performance SoC to realize arbitrary waveform generation and synchronous trigger function, and the output is directly output to the bottom electrode of the sample to be tested.

7. A method of measuring the dielectric constant, using a system for measuring the dielectric constant according to any one of claims 1 to 6, characterized in that, The probe is installed at the end of the cantilever beam, and when the probe approaches the surface of the sample, atomic interaction force is generated to control the movement of the sample to be tested in the x and y directions, realize scanning, and the laser is irradiated on the back of the cantilever beam and then reflected on the four-quadrant photodetector for detecting the slight bending or deflection of the cantilever.

8. A method of measuring dielectric constant as claimed in claim 7, wherein, A high frequency small signal is applied to the probe end, and the bottom electrode of the sample to be tested is grounded; a small MOS structure is formed between the probe and the sample; the nonlinear dielectric response of the ferroelectric material causes a small modulation of the capacitance with the bias voltage, and the signal generated by the above small modulation is extracted through a frequency modulation demodulator and a lock-in amplifier; at each scanning point, the amplitude R or the phase θ output by the lock-in amplifier is collected, and the scanning position and the corresponding signal value are saved one by one; a two-dimensional signal strength matrix is mapped into a gray scale image or a pseudo-color image by using software.

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