An in-situ ac voltage shg system and method of characterizing intrinsic ferroelectric switching thereof

Abstract

The application discloses an in-situ AC voltage SHG system and a method for characterizing intrinsic ferroelectric flipping thereof, and belongs to the technical field of solid-state dielectric application.The application utilizes a chopper to generate periodic light as a carrier signal, generates an AC voltage signal by an arbitrary signal generator, and uses the SHG signal generated when the AC voltage signal acts on a sample as a modulation signal, so that amplitude modulation of an optical signal is realized, and the modulated optical signal is converted into an electrical signal by a PMT photodetector.The photoelectric signal of the PMT photodetector is input into a digital lock-in amplifier together with the carrier signal and is demodulated and output.The application of the AC voltage and the demodulation output of the PMT photoelectric signal are performed simultaneously, and are realized by a trigger signal generated by an AWG.Compared with the static voltage SHG system for characterizing intrinsic ferroelectric flipping, the method of the application can test polarization flipping of a sample with a larger leakage current, reduces test time, and reduces or eliminates the influence of external conditions on test results.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state dielectric applications, in particular to an in-situ AC voltage SHG system and a method for characterizing intrinsic ferroelectric switching thereof. BACKGROUND

[0002] Ferroelectric materials are a class of functional materials with spontaneous polarization properties. They have stable spontaneous polarization and switchable polarization characteristics under an applied electric field, and have broad application prospects in non-volatile ferroelectric memory, pyroelectric infrared detectors, ferroelectric tunnel junctions, field effect transistors, etc. Ferroelectric polarization strength is an important parameter of ferroelectric materials, which has a direct impact on the performance of ferroelectric devices, and the hysteresis loop obtained by changing the external electric field can be used as an important basis for whether a material has ferroelectricity. Generally, ferroelectric materials are characterized by macroscopic ferroelectric polarization through a ferroelectric analyzer to establish a curve relationship between macroscopic ferroelectric polarization and applied voltage, which has the advantages of simple operation, convenience, and speed, etc. However, it is affected by leakage current during testing. Ferroelectric materials can also be characterized by the ferroelectric polarization performance of a small area using a piezoelectric force microscope (PFM), which tests the domain switching state of ferroelectric materials under different regions and voltages, has the advantages of real-time testing and high resolution, etc. However, it is affected by the static force of the probe tip during testing. The optical second harmonic generation (SHG) detection technology is a non-contact, non-destructive all-optical detection technology, which is not disturbed by factors such as static force and leakage current, and is easy to obtain intrinsic polarization information of ferroelectric samples. At the same time, SHG technology has high sensitivity and unique advantages in the detection of weak polarization signal domain structure.

[0003] The prior art CN 117664925 A discloses a static voltage SHG test method. The static voltage SHG test technology applies a stable voltage while testing the SHG signal, and tests the change of the SHG signal with voltage. Compared with macroscopic hysteresis loop testing, the static voltage SHG test technology can eliminate the influence of leakage current factors during testing, and obtain the change of intrinsic ferroelectric polarization with electric field. However, it takes several minutes to tens of minutes to test one voltage cycle using the static voltage SHG test technology. The long testing time makes it more likely for external conditions to affect the energy, position and focusing state of the laser, which in turn causes abnormal jumping and poor repeatability of the test data points. In addition, the ferroelectric material switching time is extremely short, and the test method of applying a static voltage cannot accurately represent the polarization characteristics of the ferroelectric material itself.

[0004] Therefore, how to realize the rapid test of the SHG signal under the in-situ electric field, reduce or eliminate the influence of external conditions, and better characterize the polarization characteristics of the ferroelectric material is an urgent technical problem for the person skilled in the art to solve when using the SHG to test the ferroelectric device. SUMMARY

[0005] Therefore, in order to better characterize the polarization characteristics of the ferroelectric material, the application provides an in-situ alternating voltage SHG system for improving the test speed and a method for characterizing the intrinsic ferroelectric flip.

[0006] The application utilizes the periodic light generated by the chopper as the carrier signal, generates the alternating voltage signal by the arbitrary signal generator (AWG), takes the SHG signal generated by the sample as the modulation signal, realizes the amplitude modulation of the optical signal, and converts the modulated optical signal into an electrical signal by the PMT photodetector (PMT). The photoelectric signal of the PMT photodetector and the carrier signal are input into the digital lock-in amplifier at the same time and are demodulated and output. The application of the alternating voltage and the demodulation output of the PMT photoelectric signal are performed at the same time, and are realized by the trigger signal generated by the AWG. Compared with the static voltage test, the method can complete the test within 300 ms.

[0007] To achieve the above object, the application adopts the following technical scheme:

[0008] An in-situ alternating voltage SHG system, comprising a femtosecond laser, a variable attenuator, a chopper, a Glan prism, a half-wave plate, a long-wave pass filter, a light splitting prism, an objective lens, a sample, a probe, a lens, a band-pass filter, a PMT photodetector, a control system, an arbitrary signal generator and a digital lock-in amplifier;

[0009] The Glan prism comprises a first Glan prism and a second Glan prism.

[0010] The light entrance side of the light splitting prism is sequentially provided with the femtosecond laser, the variable attenuator, the chopper, the first Glan prism, the half-wave plate and the long-wave pass filter from far to near.

[0011] The objective lens is arranged on the first light splitting light exit side of the light splitting prism, and the lens, the second Glan prism, the band-pass filter and the PMT photodetector are sequentially arranged on the second light splitting light exit side of the light splitting prism from near to far, the first light splitting light exit side is perpendicular to the light entrance side of the light splitting prism in a clockwise direction by 90°, and the second light splitting light exit side is opposite to the direction of the first light splitting light exit side.

[0012] The sample is vertically arranged at the bottom of the objective lens, the top of the probe is connected with the sample, and the probe is electrically connected with the arbitrary signal generator.

[0013] The chopper is electrically connected with the digital phase-locked amplifier, and the PMT photoelectric detector is electrically connected with the digital phase-locked amplifier;

[0014] The arbitrary signal generator and the digital phase-locked amplifier are respectively electrically connected with the control system, and a trigger signal output end of the arbitrary signal generator is electrically connected with a trigger signal input end of the digital phase-locked generator.

[0015] Further, the in-situ AC voltage SHG system further comprises a mirror;

[0016] The mirror comprises a first mirror and a second mirror;

[0017] The first mirror is arranged between the variable attenuator and the chopper, the chopper is located at the left side of the variable attenuator and is obliquely below, and the first mirror is used for refracting the laser passing through the variable attenuator by 90° and making the laser pass through the chopper;

[0018] The second mirror is arranged between the first Glan prism and the half-wave plate, the half-wave plate is located at the right side of the first Glan prism and is obliquely below, and the second mirror is used for refracting the laser passing through the first Glan prism by 90° and making the laser pass through the half-wave plate.

[0019] Further, the sample is a ferroelectric thin film sample or a transistor device sample;

[0020] The ferroelectric thin film sample comprises, from bottom to top, a substrate, a bottom electrode, a ferroelectric layer and a top electrode, and the transistor device sample comprises, from bottom to top, a substrate, a bottom electrode, a gate dielectric layer, a channel layer and a top electrode;

[0021] The probe is provided with two, and the two probes are respectively connected with the top electrode and the bottom electrode of the sample.

[0022] The application further provides a method for characterizing intrinsic ferroelectric flipping by using the in-situ AC voltage SHG system.

[0023] (1) preparing a ferroelectric thin film or a transistor device;

[0024] (2) connecting lines, connecting a TTL signal of the chopper and an output signal of the PMT to two input ends of a digital phase-locked amplifier respectively, connecting an output end of the AWG to the probe, and connecting a trigger signal output end of the AWG to a trigger signal input end of the digital phase-locked generator;

[0025] (3) setting a waveform, a frequency, an amplitude and a trigger signal of a pulse signal in the AWG;

[0026] (4) setting the demodulation parameters in the digital lock-in amplifier and the triggering mode of signal acquisition;

[0027] (5) connecting two probes to the top electrode and the bottom electrode of the sample respectively; vertically applying pulsed laser to the sample by the femtosecond laser, and focusing the pulsed laser on the surface of the ferroelectric thin film sample or the channel beside the top electrode of the transistor device through the electrode by the objective lens;

[0028] (6) applying an alternating voltage to the sample and sending a trigger signal to control the lock-in amplifier to acquire data, completing the test of the device and obtaining the curve of the SHG signal of the ferroelectric layer changing with the applied electric field.

[0029] In the scheme of the present application, the electric field application and data acquisition are carried out simultaneously, and the whole test can be completed within 300 ms. The trigger signal control of the present application simultaneously carries out the voltage application and signal acquisition, the present application adopts a vertical optical path, and the generated SHG signal completely comes from the in-plane signal of the sample, and the substrate, the bottom electrode and the top electrode will not generate SHG signal.

[0030] Further, the laser wavelength of the femtosecond laser is 800 nm.

[0031] Further, the model of the AWG used in the present application is Zurich UHF-AWG 600MHz, and the model of the digital lock-in amplifier is Zurich HF2Li 50MHz.

[0032] Further, the alternating voltage is a triangular wave voltage.

[0033] Preferably, in the above step (3), the waveform, phase, direct current bias, amplitude, frequency and trigger signal of the voltage signal in the AWG are set, the phase, direct current bias and amplitude correspond to the voltage required to be applied to the sample, the out-of-range selection selects the applied voltage amplifier, the frequency is related to the chopping frequency and the demodulation parameter tc, one cycle time is set to more than 300 ms, the trigger signal is set by market or trigger command, the alternating voltage starts and ends to 1, and the other time is set to 0.

[0034] Preferably, in the above step (4), the demodulation parameters in the digital lock-in amplifier and the triggering mode of signal acquisition are set, wherein the demodulation parameter setting is related to noise, sample signal and the like, the filter order is set to 3-4 orders, and 1-2 orders can be selected for particularly strong signal, and the parameter tc is 2-10 carrier cycles; the triggering mode of signal acquisition is set to the trigger signal input port name such as DIO, DIO1 and the like in the DAQ module

[0035] Further, the ferroelectric layer is PbZr 0.2 Ti 0.8 O3 ferroelectric material.

[0036] Further, the preparation method of the ferroelectric thin film sample is:

[0037] A bottom electrode is deposited on the substrate by laser pulse deposition, then a ferroelectric thin film is deposited on the bottom electrode, and then a top electrode is deposited on the ferroelectric thin film by a mask, thereby obtaining the ferroelectric thin film sample.

[0038] The transistor device sample is a negative capacitance transistor device, and the preparation method of the transistor device sample is:

[0039] A bottom electrode is deposited on the substrate by laser pulse deposition, then a gate dielectric layer composed of a dielectric layer and a ferroelectric thin film is deposited on the bottom electrode, then a two-dimensional material is transferred as a channel layer above the gate dielectric layer, and a top electrode is prepared on the channel layer by photolithography and evaporation, thereby obtaining the transistor sample.

[0040] Further, the bottom electrode is SRO, the deposition conditions are that the temperature is 690 DEG C, the oxygen pressure is 80 mTorr, the laser energy is 380 mJ, and the focal length is 10.

[0041] Further, the ferroelectric thin film is PZT, the deposition temperature is 600 DEG C, the oxygen pressure is 200 mTorr, the laser energy is 340 mJ, and the focal length is -10.

[0042] The structure of the gate dielectric layer is STO / PZT / STO, the deposition temperature is 600 DEG C, the oxygen pressure is 200 mTorr, the laser energy is 340 mJ, and the focal length is -10.

[0043] Preferably, the PZT is oriented as (001) or (111).

[0044] Further, the top electrode is ITO, the deposition temperature is 400 DEG C, the oxygen pressure is 5 mTorr, the laser energy is 330 mJ, and the focal length is 10.

[0045] Further, the channel layer is two-dimensional MoS2.

[0046] The present application has the advantages that the present application solves the problems of long time and large external influence in electrostatic voltage SHG testing, and can better characterize the polarization characteristics of ferroelectric materials, and the present application can be used for in-situ optical second harmonic generation of intrinsic ferroelectric flip under alternating voltage. The method of the present application is a supplement to the fast testing direction of in-situ electrostatic voltage SHG testing technology, reduces the influence of external conditions on the test results (such as laser point drift, sample damage caused by long time irradiation, etc.), improves the test efficiency, and better characterizes the polarization characteristics of ferroelectric materials. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 Damage map of sample irradiated by laser for long time and laser spot moving map before and after test;

[0048] Figure 2 Sample structure map in the present application;

[0049] Figure Figure 2 In the figure, the structure of each label is as follows: 01 - substrate, 02 - bottom electrode, 03 - dielectric layer, 04 - ferroelectric layer, 05 - channel layer, 06 - top electrode.

[0050] Figure 3 Traditional macroscopic polarization test map of ferroelectric thin film sample in the embodiment of the present application;

[0051] Figure 4 In-situ AC voltage SHG system structure schematic diagram of applied electric field in the present application;

[0052] Figure Figure 4 In the figure, the structure of each label is as follows:

[0053] 1 - femtosecond laser, 2 - variable attenuator, 3 - reflector, 4 - chopper, 5 - Glan prism, 6 - half-wave plate, 7 - long-wave pass filter, 8 - beam splitter prism, 9 - objective lens, 10 - sample, 11 - probe, 12 - lens, 13 - band-pass filter, 14 - PMT photodetector, 15 - control system, 16 - arbitrary signal generator, 17 - digital lock-in amplifier.

[0054] Figure 5 In-situ electrostatic voltage SHG test result map of ferroelectric thin film sample with different orientations in the embodiment of the present application;

[0055] Figure 6 In-situ AC voltage SHG test result map of ferroelectric thin film sample with different orientations in the embodiment of the present application;

[0056] Figure 7 In-situ electrostatic voltage and AC voltage test result map of negative capacitance transistor sample in the embodiment of the present application. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0058] In the description of the present application, it needs to be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0059] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified and limited.

[0060] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixed connection, or detachable connection, or integral; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0061] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include the direct contact of the first and second features, or can include the contact of the first and second features through another feature between them. Moreover, the "upper", "upper" and "upper" of the first feature to the second feature include the vertical of the first feature above and oblique above the second feature, or only indicate that the horizontal height of the first feature is higher than that of the second feature. The "below", "below" and "below" of the first feature to the second feature include the vertical of the first feature below and oblique below the second feature, or only indicate that the horizontal height of the first feature is less than that of the second feature.

[0062] An in-situ AC voltage SHG system, characterized in that the in-situ AC voltage SHG system comprises a femtosecond laser 1, a variable attenuator 2, a chopper 4, a Glan prism 5, a half-wave plate 6, a long-wave pass filter 7, a beam splitter prism 8, an objective lens 9, a sample 10, a probe 11, a lens 12, a band-pass filter 13, a PMT photodetector 14, a control system 15, an arbitrary signal generator 16 and a digital lock-in amplifier 17;

[0063] The Glan prism 5 comprises a first Glan prism and a second Glan prism.

[0064] The light entrance side of the light splitting prism 8 is sequentially provided with the femtosecond laser 1, the variable attenuator 2, the chopper 4, the first Glan prism 5, the half-wave plate 6 and the long-wave pass filter 7 from far to near;

[0065] The objective lens 9 is arranged on the first light splitting and light emitting side of the light splitting prism 8, the lens 12, the second Glan prism 5, the band pass filter 13 and the PMT photodetector 14 are sequentially arranged on the second light splitting and light emitting side of the light splitting prism 8 from near to far, the first light splitting and light emitting side is perpendicular to the light entrance side of the light splitting prism 8 in a clockwise direction by 90°, and the second light splitting and light emitting side is opposite to the direction of the first light splitting and light emitting side;

[0066] The sample 10 is vertically arranged at the bottom of the objective lens 9, the probe 11 is connected to the sample at the top, and the probe 11 is electrically connected to the arbitrary signal generator 16;

[0067] The chopper 4 is electrically connected to the digital lock-in amplifier 17, and the PMT photodetector 14 is electrically connected to the digital lock-in amplifier 17;

[0068] The arbitrary signal generator 16 and the digital lock-in amplifier 17 are respectively electrically connected to the control system 15, and the trigger signal output end of the arbitrary signal generator 16 is electrically connected to the trigger signal input end of the digital lock-in generator 17.

[0069] In some embodiments, the in-situ AC voltage SHG system further comprises a mirror 3;

[0070] The mirror 3 comprises a first mirror and a second mirror;

[0071] The first mirror is arranged between the variable attenuator 2 and the chopper 4, the chopper 4 is located obliquely below the left side of the variable attenuator 2, and the first mirror is used to refract the laser passing through the variable attenuator 2 by 90° and make it pass through the chopper 4;

[0072] The second mirror is arranged between the first Glan prism 5 and the half-wave plate 6, the half-wave plate 6 is located obliquely below the right side of the first Glan prism 5, and the second mirror is used to refract the laser passing through the first Glan prism 5 by 90° and make it pass through the half-wave plate 6.

[0073] In some embodiments, the sample 10 is a ferroelectric thin film sample or a transistor device sample;

[0074] The ferroelectric thin film sample comprises a substrate 01, a bottom electrode 02, a ferroelectric layer 04 and a top electrode 06 from bottom to top, and the transistor device sample comprises a substrate 01, a bottom electrode 02, a gate dielectric layer (composed of a dielectric layer 03 and a ferroelectric layer 04), a channel layer 05 and a top electrode 06 from bottom to top;

[0075] Two probes 11 are provided, and the two probes 11 are connected with the top electrode 06 and the bottom electrode 01 of the sample 10 respectively.

[0076] In the embodiment of the present application, the PbZr 0.2 Ti 0.8 O3(PZT) ferroelectric thin film and a negative capacitance transistor device comprising a (001)-oriented PZT ferroelectric layer are taken as examples to illustrate the method for in-situ optical second harmonic generation characterization of the polarization of the ferroelectric thin film and the device under the pulse electric field, and the test under the static voltage is compared.

[0077] Embodiment 1

[0078] A preparation method of a ferroelectric thin film sample, and the preferred embodiment of the ferroelectric thin film of the present application is PZT.

[0079] As Figure 2 As shown in (a) of Fig. 1, it is a schematic diagram of a ferroelectric thin film sample for in-situ SHG test in the embodiment 1 of the present application, and the ferroelectric thin film sample comprises a substrate 01, a bottom electrode 02, a ferroelectric layer 04 and a top electrode 06.

[0080] Figure 4 It is a light path diagram of the SHG system and a connection mode of the characterization system of the present application, a laser with a wavelength of 800 nm is emitted from a femtosecond laser (1), the laser energy is adjusted through a variable attenuator (2), the laser is changed into a periodic light with a frequency of 1000 Hz through an optical chopper (4), the laser is screened as p-polarization (the horizontally polarized light is defined as p-polarization) through a Glan prism (5), then the polarization direction of the incident light is changed through a half-wave plate (6), the laser below 700 nm is filtered through a long-wave pass filter (7), then the laser is focused on the sample (10) through an objective lens (9) through a depolarization prism (8), a second harmonic signal of 400 nm is excited, and then the 800 nm fundamental frequency light reflected by the sample surface returns to the prism, and the laser is focused through a lens (12), the polarization direction of the signal to be extracted is selected through the Glan prism (5), then the 800 nm fundamental frequency light is filtered through a band-pass filter (13), and the influence of other wavebands of the laser on the final signal is avoided, and the remaining second harmonic signal of 400 nm is detected by a PMT photodetector (14).

[0081] The parameter setting and data reading of the digital phase-locked amplifier and the AWG are controlled by the labone program in the control system (15). The voltage signal is generated by the AWG (16), and two probes are connected by a BNC-to-alligator clip line. One probe is placed on the top electrode (for the ferroelectric thin film sample) or the electrode beside the channel (for the negative capacitor device sample) irradiated by the laser, and the probe cannot block the laser spot. The other end of the probe is connected to the silver paste led out from the bottom electrode. The AWG generates a trigger signal at the same time as generating the voltage signal, which is transmitted to the digital phase-locked amplifier (17) for synchronous signal acquisition, so as to ensure that the SHG signal is detected in situ while the electric field is applied, thereby reflecting the polarization information of the ferroelectric thin film or device.

[0082] The preparation method of the ferroelectric thin film sample comprises the following steps:

[0083] A SrRuO3(SRO) bottom electrode is first deposited on a (001)-oriented SrTiO3(STO) substrate by a laser pulse deposition method (PLD), and the preparation parameters of the SRO bottom electrode are as follows: a temperature of 690℃, an oxygen pressure of 80mTorr, a laser energy of 380mJ, a focal length of 10, and a thickness of 25nm. Then, a PZT ferroelectric thin film is deposited on the SRO bottom electrode, and the deposition parameters of the PZT ferroelectric thin film are as follows: a temperature of 600℃, an oxygen pressure of 200mTorr, a laser energy of 340mJ, a focal length of -10, and a thickness of 140nm. Finally, an indium tin oxide (ITO) transparent top electrode with a diameter of 100μm is deposited on the surface of the PZT thin film using a metal mask plate, and the deposition temperature of the ITO transparent electrode is 400℃, the oxygen pressure is 5mTorr, the laser energy is 330mJ, the focal length is 10, and the thickness is 200nm.

[0084] This embodiment is described by taking PZT as the ferroelectric thin film sample, but the ferroelectric thin film sample used in the embodiment can also be other ferroelectric materials such as barium titanate (BTO) and lead titanate (PTO); meanwhile, the in-situ AC voltage SHG system can be used to measure the ferroelectric thin film sample, and a better SHG flip loop can be obtained to realize the characterization of the intrinsic ferroelectric flip under voltage.

[0085] Embodiment 2

[0086] A preparation method of a ferroelectric thin film sample, which is different from that of embodiment 1, is that a (111)-oriented PZT thin film is prepared by using a (111)-oriented STO substrate.

[0087] Embodiment 3

[0088] Fabrication method of PZT negative capacitance transistor device sample: First, an SRO bottom gate electrode was deposited on a (001) oriented STO substrate using pulsed laser deposition (PLD). The fabrication parameters of the SRO bottom gate electrode were as follows: temperature 690℃, oxygen pressure 80mTorr, laser energy 380mJ, focal length 10, and thickness 25nm. Then, an STO / PZT / STO gate dielectric layer was fabricated on the SRO bottom gate electrode. The fabrication parameters of the STO / PZT / STO gate dielectric layer were as follows: temperature 600℃, oxygen pressure 200mTorr, laser energy 340mJ, focal length -10, and thickness 160nm. Then, a 3nm thick MoS2 was transferred on the STO / PZT / STO gate dielectric layer using a two-dimensional transfer stage. Finally, Ti / Au source and drain electrodes were fabricated on the MoS2 using micro-nano fabrication and electron beam evaporation.

[0089] This embodiment uses Ti / Au source / drain electrodes for illustration, but other conductive materials such as ITO, graphene, and other transparent conductive materials can also be selected. Furthermore, this embodiment uses a negative capacitance transistor device for illustration, but other gate dielectric layer transistor structures can also be selected, such as gate dielectric layers with different ratios of STO / PZT, pure PZT, etc. Simultaneously, in-situ AC voltage SHG system can be used to measure the device, obtaining a good SHG curve and characterizing intrinsic ferroelectric reversal under voltage. In this invention, because the two-dimensional stacked structure of graphene and MoS2 is more easily ablated by laser, it is suitable for samples that require only low laser energy for testing.

[0090] Example 4

[0091] The difference from Example 1 is that the (001) oriented PZT thin film sample was tested using a conventional polarization measurement method to characterize polarization reversal.

[0092] Example 5

[0093] The difference from Example 1 is that the (111) oriented PZT thin film sample was tested using a conventional polarization measurement method to characterize polarization reversal.

[0094] Figure 3 These are the traditional macroscopic polarization test results from Examples 4 and 5, in which... Figure 3 (a) and Figure 3 (c) is the result of the macroscopic hysteresis loop test. Figure 3 (b) and Figure 3 (d) shows the leakage current test results. It can be seen that the two PZT ferroelectric thin film samples have serious leakage current and cannot be effectively polarized by conventional polarization.

[0095] Example 6

[0096] The difference from Example 1 is that the intrinsic ferroelectric switching is characterized by an in-situ static voltage SHG test system. That is, a fixed DC voltage is applied by a voltage source, the SHG signal of the sample is tested, and then the DC voltage value is changed for cyclic testing, with a voltage change step of 0.2V, and the voltage changes are 0V~6V~-6V~0V.

[0097] Example 7

[0098] The difference from Example 2 is that the intrinsic ferroelectric switching is characterized by an in-situ static voltage SHG test system. That is, a fixed DC voltage is applied by a voltage source, the SHG signal of the sample is tested, and then the DC voltage value is changed for cyclic testing, with a voltage change step of 0.4V, and the voltage changes are 0V~10V~-10V~0V.

[0099] Figure 5 The figure is the static voltage test result of the ferroelectric thin film sample in the embodiment of the application, wherein, Figure 5 (a) of FIG. 1 is a curve of the SHG signal intensity of the (001)-oriented PZT ferroelectric thin film sample (i.e., Example 6) with the applied voltage, and it can be seen that in the case of a large leakage current, the intrinsic ferroelectric polarization of the ferroelectric thin film can still be characterized by the in-situ static voltage SHG test system.

[0100] Figure 5 (b) of FIG. 1 is a curve of the SHG signal intensity of the (111)-oriented PZT ferroelectric thin film sample (i.e., Example 7) with the applied voltage, and the sample can also characterize the intrinsic ferroelectric polarization in the case of a large leakage current.

[0101] However, it is found in actual use that this static voltage test method requires too long a time (10 to 20 min), and is easily affected by external conditions during testing, resulting in jumping points and overall signal intensity decline. In addition, long-time testing results in a large difference in signal between before and after sample testing, which can be alleviated by multiple cycles, but at a large time cost. And since the testing is carried out under quasi-static conditions, the hysteresis of the curve obtained is small, and the difference with the actual use of the device is large.

[0102] Example 8

[0103] A method for characterizing intrinsic ferroelectric switching by an in-situ alternating voltage SHG test system, comprising the following steps:

[0104] S1, a layer of SrRuO3(SRO) bottom electrode is deposited on a SrTiO3(STO) substrate with an orientation of (001) by a laser pulse deposition method (PLD), and the preparation parameters of the SRO bottom electrode are as follows: a temperature of 690 DEG C, an oxygen pressure of 80 mTorr, a laser energy of 380 mJ, a focal length of 10, and a thickness of 25 nm; then a PZT ferroelectric film is deposited on the SRO bottom electrode, and the preparation parameters of the PZT ferroelectric film are as follows: a temperature of 600 DEG C, an oxygen pressure of 200 mTorr, a laser energy of 340 mJ, a focal length of -10, a thickness of 140 nm, and finally a transparent top electrode of indium tin oxide (ITO) with a diameter of 100 μm is deposited on the surface of the PZT film using a metal mask, and the deposition temperature of the ITO transparent electrode is 400 DEG C, the oxygen pressure is 5 mTorr, the laser energy is 330 mJ, the focal length is 10, and the thickness is 200 nm.

[0105] S2, the TTL signal of the chopper and the photoelectric output signal of the PMT are respectively connected to two input ends of a digital lock-in amplifier; the output end of the AWG is connected to the probe; and the trigger signal output end of the AWG is connected to the DIO 1 signal input end of the digital lock-in generator;

[0106] S3, a period of triangular wave voltage is output by the AWG, the amplitude is 6V, there is no direct current offset, there is no phase offset, the sampling point is 64000Sa, and the sampling frequency is 219.72kSa / s. A trigger signal is generated by the marker command at the same time when the triangular wave is output by the AWG, and is used to trigger the synchronous signal collection of the digital lock-in amplifier;

[0107] S4, the demodulation parameters of the digital lock-in amplifier are 4-order filtering, the filtering parameter tc is 5.082ms, the sampling frequency is 14.39kSa / s, and the trigger mode is changed to DIO 1 signal triggering;

[0108] S5, two probes are respectively connected to the top electrode and the bottom electrode of the sample; the pulsed laser is vertically applied to the sample along the optical path, the laser power is 15mW, and the pulsed laser is focused on the surface of the ferroelectric film through the transparent electrode by the objective lens;

[0109] S6, the triangular wave voltage is applied to the gate and the substrate by the AWG, a trigger signal is sent to control the data collection of the lock-in amplifier, the testing of the device is completed, and the curve of the SHG signal of the ferroelectric layer changing with the applied electric field is obtained. The time lag is t=3.9tc, the sampling point corresponding to the triangular wave voltage is calculated according to the sampling frequency of the digital lock-in amplifier, and the curve of the SHG signal intensity changing with the voltage is obtained.

[0110] Figure 6(a) shows the in-situ AC voltage SHG test results of Embodiment 8 of the present invention. Compared with the static voltage test results (Example 6), the two have the same trend and shape, but the hysteresis effect is quite different. In addition, the curve is smoother, the hysteresis effect is better, and it is closer to the actual working state of the device. Moreover, the test time is faster, and a large number of tests can be performed in a short time, reducing the influence of external factors on the test.

[0111] Similarly, based on the ferroelectric thin film sample prepared in Example 2, Example 9 was set up.

[0112] Example 9

[0113] A method for characterizing intrinsic ferroelectric reversal using an in-situ AC voltage SHG test system differs from Example 8 in that the ferroelectric thin film is (111) oriented and has an amplitude of 10V.

[0114] Figure 6 (b) shows the test results of Example 9. Compared with the test results of Example 7, the hysteresis effect is better, which can better reflect the ferroelectric layering reversal effect. The test is faster and less affected by external factors.

[0115] To test the effectiveness of this characterization method in devices, Examples 10 and 11 were set up based on Example 3, where static voltage and AC voltage were applied respectively to characterize the SHG signal strength.

[0116] Example 10

[0117] The intrinsic ferroelectric reversal of the ferroelectric layer of the negative capacitance transistor was characterized by an in-situ static voltage SHG signal testing system. Compared with Example 6, the laser focusing position was changed to the channel next to the top electrode, starting from -2V with a step size of 0.02V, while other conditions remained unchanged.

[0118] Figure 7 (a) shows the test results of this embodiment. The test curves show that the curves are nearly parallel under negative voltage and exhibit a flipping phenomenon under positive voltage, which is consistent with the ferroelectric layering state of this negative capacitance transistor device as a function of voltage. However, negative capacitance transistor testing requires a smaller step size, so it takes more than twice the time of normal ferroelectric thin film testing, and is more susceptible to external influences. As shown in the figure, the jump point causes the SHG signal strength after the jump point to shift downwards overall, affecting the analysis of the actual curve shape.

[0119] Example 11

[0120] The intrinsic ferroelectric reversal of the ferroelectric layer of the negative capacitance transistor was characterized using an in-situ AC voltage SHG signal testing system. Compared to Example 8, the difference lies in changing the laser focusing position to the channel next to the top electrode, changing the amplitude to 2V, and starting the phase from -2V.

[0121] Figure 7 (b) is the test result of the present example, the test curve is basically similar to that of example 10, but is smoother, there is a ferroelectric polarization hysteresis phenomenon at the positive voltage, and no flip phenomenon occurs at the negative voltage. Moreover, in the positive voltage part, the rising and falling lines have smaller slope changes compared with example 10, and there is a small amount of hysteresis.

[0122] Examples 6-7 and examples 8-9 show that the ferroelectric thin film sample is prone to various problems in the in-situ static voltage test SHG signal, and the in-situ alternating voltage proposed in the present application can eliminate or reduce the influence of external conditions on the test result. Examples 10 and 11 show that not only ferroelectric thin film samples, but also ferroelectric devices can be tested by this method.

[0123] In summary, the present application provides a method for characterizing intrinsic ferroelectric flip using an in-situ alternating voltage SHG system, which can be applied to ferroelectric thin films and transistor devices, is a supplement to the static voltage SHG test method, can eliminate or reduce external problems caused by long-term testing; the method is suitable for ferroelectric material systems and can be used for rapid characterization of a large number of ferroelectric devices. The present application has important significance for in-depth understanding of ferroelectric materials, exploring intrinsic polarization of ferroelectric devices, and promoting the use of ferroelectric negative capacitor devices.

[0124] Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. An in-situ AC voltage SHG system, characterized by, The in-situ AC voltage SHG system comprises a femtosecond laser, a variable attenuator, a chopper, a Glan prism, a half-wave plate, a long-wave pass filter, a light splitting prism, an objective lens, a sample, a probe, a lens, a band pass filter, a PMT photodetector, a control system, an arbitrary signal generator and a digital lock-in amplifier; The Glan prism comprises a first Glan prism and a second Glan prism; The light entrance side of the light splitting prism is sequentially provided with the femtosecond laser, the variable attenuator, the chopper, the first Glan prism, the half-wave plate and the long-wave pass filter from far to near; The objective lens is arranged on the first light splitting light exit side of the light splitting prism, and the lens, the second Glan prism, the band pass filter and the PMT photodetector are sequentially arranged on the second light splitting light exit side of the light splitting prism from near to far, the first light splitting light exit side is 90° in the clockwise direction along the light entrance side of the light splitting prism, and the second light splitting light exit side is opposite to the direction of the first light splitting light exit side; The sample is vertically arranged at the bottom of the objective lens, the top of the probe is connected with the sample, and the probe is electrically connected with the arbitrary signal generator; The chopper is electrically connected with the digital lock-in amplifier, and the PMT photodetector is electrically connected with the digital lock-in amplifier; The arbitrary signal generator and the digital lock-in amplifier are respectively electrically connected with the control system, and the trigger signal output end of the arbitrary signal generator is electrically connected with the trigger signal input end of the digital lock-in amplifier; The system further comprises a mirror; The mirror comprises a first mirror and a second mirror; The first mirror is arranged between the variable attenuator and the chopper, the chopper is located obliquely below the left side of the variable attenuator, and the first mirror is used for refracting the laser passing through the variable attenuator by 90° and making the laser pass through the chopper; The second mirror is arranged between the first Glan prism and the half-wave plate, the half-wave plate is located obliquely below the right side of the first Glan prism, and the second mirror is used for refracting the laser passing through the first Glan prism by 90° and making the laser pass through the half-wave plate; The sample is a ferroelectric thin film sample or a transistor device sample; The ferroelectric thin film sample comprises a substrate, a bottom electrode, a ferroelectric layer and a top electrode from bottom to top, and the transistor device sample comprises a substrate, a bottom electrode, a gate dielectric layer, a channel layer and a top electrode from bottom to top; The probe is provided with two, and the two probes are respectively connected with the top electrode and the bottom electrode of the sample.

2. A method of characterizing intrinsic ferroelectric switching using the in-situ AC voltage SHG system of claim 1, wherein, The method comprises the following steps: The sample is vertically irradiated with pulsed laser by the femtosecond laser, the pulsed laser is focused on the surface of the ferroelectric thin film sample or the channel beside the top electrode of the transistor device sample through the objective lens, then an AC voltage is applied to the sample, a trigger signal is sent to control the digital lock-in amplifier to collect data, the testing of the device is completed, and the curve of the SHG signal of the ferroelectric layer changing with the applied electric field is obtained.

3. The method of characterizing intrinsic ferroelectric switching with an in situ AC voltage SHG system of claim 2, wherein, The AC voltage is a triangular wave voltage.

4. The method of characterizing intrinsic ferroelectric switching with an in situ AC voltage SHG system of claim 2, wherein, The ferroelectric layer is a PbZr 0.2 Ti 0.8 O3 ferroelectric material.

5. The method of characterizing intrinsic ferroelectric switching with an in situ AC voltage SHG system of claim 2, wherein, The preparation method of the transistor device sample is A bottom electrode is deposited on a substrate by laser pulse deposition, then a gate dielectric layer composed of a dielectric layer and a ferroelectric thin film is deposited on the bottom electrode, and then a two-dimensional material is transferred on the gate dielectric layer as a channel layer, a top electrode is prepared on the channel layer by photolithography and evaporation, and a transistor sample is obtained.

6. The method of characterizing intrinsic ferroelectric switching with an in situ AC voltage SHG system of claim 5, wherein, The bottom electrode is SRO, the deposition conditions are that the temperature is 690 DEG C, the oxygen pressure is 80 mTorr, and the laser energy is 380 mJ.

7. The method of characterizing intrinsic ferroelectric switching with an in situ AC voltage SHG system of claim 5, wherein, The structure of the gate dielectric layer is STO / PZT / STO, the deposition temperature is 600 DEG C, the oxygen pressure is 200 mTorr, and the laser energy is 340 mJ.

8. The method of characterizing intrinsic ferroelectric switching with an in situ AC voltage SHG system of claim 5, wherein, The channel layer is a two-dimensional MoS2.

Images