Method for rapidly detecting microdefects of ferroelectric crystal material based on backward voltage pulse

Abstract

The invention relates to a method for rapidly detecting microdefects of a ferroelectric crystal material based on reverse voltage pulses, which comprises the following steps of: preparing the ferroelectric crystal material to be detected, connecting an aluminum electrode on a + Z surface of the ferroelectric crystal material to be detected with a negative electrode of an external electric field, connecting an evaporation transparent indium tin oxide conductive layer on a-Z surface of the ferroelectric crystal material to be detected with a positive electrode of the external electric field, and placing in silicone oil; voltage pulse is applied, the condition of the to-be-detected ferroelectric crystal material is observed through the real-time monitoring device, the to-be-detected ferroelectric crystal material with point defects can be excited by reverse voltage and has contrast display in the real-time monitoring device, and the to-be-detected ferroelectric crystal material without point defects has no phenomenon in the real-time monitoring device after being excited by the reverse voltage. By adopting the method for detecting the microdefect of the ferroelectric crystal material by applying the reverse pulse, the quality of the wafer can be quickly detected in a lossless manner, and a high-quality ferroelectric crystal can be developed and guaranteed for subsequent crystal devices.

Description

Technical Field

[0001] This invention relates to a method for rapid detection of microscopic defects in ferroelectric crystal materials based on reverse voltage pulses, belonging to the field of defect detection technology. Background Technology

[0002] Ferroelectric crystals, due to their spontaneous polarization and high dielectric constant, are widely used in non-volatile storage, actuators, energy harvesting, and microelectromechanical systems (MEMS). Microscopic defects in these materials (such as oxygen vacancies, metal ion vacancies, and acceptor / donor defects generated by impurity doping) have a decisive impact on domain wall motion, polarization reversal dynamics, and electrical reliability, leading to phenomena such as fatigue, aging, imprinting, leakage current, and switching asymmetry. Therefore, accurate characterization of microscopic defects is crucial for optimizing the performance of ferroelectric devices.

[0003] Existing detection methods mainly include: transmission electron microscopy / energy dispersive spectroscopy, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and other spectroscopic techniques. These methods can provide structural or valence state information of defects, but current detection techniques are mostly destructive and have problems such as complex sample preparation and limited spatial / bulk representativeness. Scanning probe techniques (such as piezoelectric response force microscopy (PFM) and scanning nonlinear dielectric microscopy (SNDM)) have high spatial resolution, but they are easily affected by probe-sample coupling and electro-deformation coupling, making it difficult to quantitatively separate the contribution of defects. Dielectric / impedance spectroscopy and pyroelectric current methods can characterize relaxation and trap release processes, but the superposition of response signals from different processes leads to non-unique analytical models. Hysteresis loop, switching current and IV characteristic tests are convenient to operate, but factors such as interface barriers, leakage current and parasitic capacitance often mask the intrinsic information dominated by point defects, and the sensitivity to weak defects is insufficient. Especially under external electric field driving, the internal bias voltage, space charge, and domain wall pinning effect generated by defect dipoles and migratable ions can affect polarization reversal on sub-millisecond to second timescales. Traditional steady-state or quasi-steady-state measurements are difficult to analyze such rapid and reversible dynamic processes. Therefore, there is an urgent need for a time-domain, electrical, non-destructive method that can be implemented under device operating conditions to selectively excite and read defect-related depolarization, re-switching, and trap recombination signals during the transient process of polarization reversal, thereby improving the sensitivity and quantification of point defect distribution and migration activation energy. In addition, existing pulse testing methods mostly focus on forward-driven switches, which do not pay enough attention to the re-switching and de-trapping behavior induced by reverse voltage pulses and lack a unified evaluation index.

[0004] In addition, existing detection methods have the following technical problems. First, structural / valence state spectroscopy often requires complex sample preparation and even destructive testing, resulting in strong locality and difficulty in reflecting the overall statistical characteristics of device operating conditions and bulk / interface. Second, the testing conditions are harsh, requiring vacuum, thin films, special electrodes, or complex calibration, which limits the testing window and is not conducive to in-situ evaluation. Third, probe-based and electrical measurements are easily affected by multiple factors such as probe-sample coupling, interface barriers, parasitic capacitance, and domain wall motion.

[0005] Therefore, there is an urgent need for a new detection method that has high detection sensitivity, high repeatability, strong comparability, fast detection speed, requires no complicated sample preparation, is non-destructive, and can be implemented under device operating conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for rapid detection of microscopic defects in ferroelectric crystal materials based on reverse voltage pulses. This method solves the problems of low detection accuracy and unstable response signals in the characterization of microscopic defects in ferroelectric crystal materials. As a result, it enables more accurate and efficient detection of the distribution and characteristics of microscopic defects, achieves non-destructive and efficient detection of the quality of ferroelectric functional crystals, ensures the demand for high-quality crystal materials for high-quality ferroelectric functional devices, and expands the application scenarios and fields of ferroelectric functional crystal materials.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A method for rapid detection of microscopic defects in ferroelectric crystal materials based on reverse voltage pulses includes the following steps: S1. Preparation of ferroelectric crystal materials with electrode patterns A uniform aluminum electrode is deposited on the +Z plane of the ferroelectric crystal material; Photoresist was spin-coated onto the +Z side of the ferroelectric crystal material with aluminum electrodes deposited on it. The ferroelectric crystal material with electrode patterns on the +Z side is obtained by sequentially performing ultraviolet lithography, development, baking, metal etching, and photoresist removal on the surface of the spin-coated photoresist. S2. A transparent indium tin oxide conductive layer is deposited on the -Z side of the ferroelectric crystal material with electrode patterns on the +Z side to obtain the ferroelectric crystal material to be tested. S3, Apply reverse voltage pulse to detect defect The aluminum electrode on the +Z side of the ferroelectric crystal material to be tested is connected to the negative electrode of the applied electric field, and the vapor-deposited transparent indium tin oxide conductive layer on the -Z side is connected to the positive electrode of the applied electric field. Then, it is placed in silicone oil, a voltage pulse is applied, and the condition of the ferroelectric crystal material to be tested is observed through a real-time monitoring device. Ferroelectric crystal materials to be tested with point defects will be excited by the reverse voltage and will be displayed with contrast in the real-time monitoring device. Ferroelectric crystal materials to be tested without point defects will not show any phenomenon in the real-time monitoring device after being excited by the reverse voltage.

[0008] According to a preferred embodiment of the present invention, in step S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium tantalate niobate, lithium niobate film, lithium tantalate film, or potassium tantalate niobate film.

[0009] More preferably, in step S1, the ferroelectric crystal material is lithium niobate.

[0010] According to a preferred embodiment of the present invention, in step S1, the thickness of the aluminum electrode is 80-150 nm.

[0011] According to a preferred embodiment of the present invention, in step S1, spin-coating photoresist results in metal strips on the surface of the ferroelectric crystal material, wherein the metal strips are regular stripes or irregular patterns.

[0012] According to a preferred embodiment of the present invention, in step S2, the thickness of the indium tin oxide conductive layer is 150-160 nm.

[0013] According to a preferred embodiment of the present invention, in step S3, the temperature of the silicone oil is 180-200°C.

[0014] Most preferably, in step S3, the temperature of the silicone oil is 190°C.

[0015] According to a preferred embodiment of the present invention, in step S3, the applied voltage is 1100-1300V and the pulse width is 400-600ms.

[0016] More preferably, in step S3, the applied voltage is 1200V and the pulse width is 500ms.

[0017] According to a preferred embodiment of the present invention, in step S3, the real-time monitoring device includes a white light source, polarizer 1, polarizer 2, and an imaging system. The light from the white light source passes through polarizer 1 and then through the ferroelectric crystal material to be tested. Due to domain inversion at point defects, the optical properties of the ferroelectric crystal material change, and these changes are captured by the imaging system. Therefore, the real-time monitoring system can observe the phenomenon of point defects being excited by reverse voltage pulses in real time and determine the crystal quality accordingly.

[0018] According to a preferred embodiment of the present invention, the imaging system is a CCD camera.

[0019] This invention provides a method for rapid detection of microscopic defects in ferroelectric crystal materials based on reverse voltage pulses. By introducing reverse voltage pulses, it achieves accurate analysis of the defect response behavior of ferroelectric crystal materials under different bias conditions, thereby overcoming the shortcomings of existing detection methods in terms of sensitivity and reproducibility.

[0020] This invention provides a method for rapid detection of microscopic defects in ferroelectric crystal materials based on reverse voltage pulses. This method is not only applicable to ferroelectric crystal defect research under laboratory conditions, but also provides a reliable basis for rapid screening and evaluation in actual device production and quality control.

[0021] This invention uses ferroelectric crystal materials to apply reverse voltage pulses and observes the crystal condition through a real-time monitoring device. Wafers with point defects are excited by the reverse voltage and are displayed with contrast in the real-time monitoring device, while wafers without point defects show no phenomenon in the real-time monitoring device after being excited by the reverse voltage.

[0022] Compared with the prior art, the present invention brings the following beneficial technical effects. 1. Significantly improved detection sensitivity: By applying a reverse voltage pulse during the detection process, this invention can effectively excite the response behavior of point defects in the crystal, making weak defect signals stand out from the overall dielectric or hysteresis changes, thereby improving the resolution of subtle defects compared to conventional constant voltage testing methods.

[0023] 2. Improved data stability and repeatability: The controllable pulse parameters (such as amplitude, width, and frequency) of this invention make the detection conditions easier to standardize, reducing interference caused by external factors such as temperature fluctuations and electrostatic noise in traditional methods, thereby obtaining detection results with high repeatability and strong comparability.

[0024] 3. Wider range of applications: This method is not only applicable to the typical ferroelectric crystal material lithium niobate, but can also be extended to other ferroelectric or related functional crystals such as potassium niobate and barium titanate, thus possessing strong versatility and extensibility.

[0025] 4. Higher practical application value: Due to the simple structure and fast detection speed of the detection device, this method can be used for basic research on ferroelectric crystal defects at the scientific research level, and is also applicable to quality control and failure analysis of crystal devices in the production process, which significantly improves the practical value at the application level. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the real-time monitoring device of the present invention.

[0027] Figure 2 The diagram shows the waveform of the reverse voltage pulse applied in the embodiment.

[0028] Figure 3 A structural diagram of lithium niobate with a slight defect detected by applying a reverse voltage pulse in Embodiment 1 of the present invention.

[0029] Figure 4 The diagram shows the structure of lithium niobate without point defects detected by applying a reverse voltage pulse in Embodiment 1 of the present invention.

[0030] Figure 5 The image shows the results of testing lithium niobate with point defects and lithium niobate without point defects using the existing periodic polarization method. Detailed Implementation

[0031] This invention proposes a method for detecting point defects in ferroelectric crystal materials using reverse voltage pulses. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be further described below with reference to specific embodiments.

[0032] In the description of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone.

[0033] All the raw materials mentioned in this invention can be purchased through commercial channels.

[0034] The main technical concept of this invention is as follows: the invention utilizes a reverse electric field pulse to excite point defects and generates a comparison signal through real-time monitoring. By utilizing the local response of point defects under the action of an electric field, the quality of crystals can be directly compared and detected. This can quickly and accurately distinguish between crystals with and without point defects, thereby effectively improving detection efficiency, ensuring the high-quality preparation of ferroelectric crystals such as PPLN, and providing a reliable material basis for the application of nonlinear optical devices.

[0035] A method for rapid detection of microscopic defects in ferroelectric crystal materials based on reverse voltage pulses includes the following steps: S1. Preparation of ferroelectric crystal materials with electrode patterns A uniform aluminum electrode is deposited on the +Z plane of the ferroelectric crystal material; Photoresist was spin-coated onto the +Z side of the ferroelectric crystal material with aluminum electrodes deposited on it. The ferroelectric crystal material with electrode patterns on the +Z side is obtained by sequentially performing ultraviolet lithography, development, baking, metal etching, and photoresist removal on the surface of the spin-coated photoresist. S2. A transparent indium tin oxide conductive layer is deposited on the -Z side of the ferroelectric crystal material with electrode patterns on the +Z side to obtain the ferroelectric crystal material to be tested. S3, Apply reverse voltage pulse to detect defect The aluminum electrode on the +Z side of the ferroelectric crystal material to be tested is connected to the negative electrode of the applied electric field, and the vapor-deposited transparent indium tin oxide conductive layer on the -Z side is connected to the positive electrode of the applied electric field. Then, it is placed in silicone oil, a voltage pulse is applied, and the condition of the ferroelectric crystal material to be tested is observed through a real-time monitoring device. Ferroelectric crystal materials to be tested with point defects will be excited by the reverse voltage and will be displayed with contrast in the real-time monitoring device. Ferroelectric crystal materials to be tested without point defects will not show any phenomenon in the real-time monitoring device after being excited by the reverse voltage.

[0036] In this embodiment, the real-time monitoring device includes a white light source, polarizer 1, polarizer 2, and an imaging system. The light from the white light source passes through polarizer 1 and then through the ferroelectric crystal material to be tested. Due to domain inversion at point defects, the optical properties of the ferroelectric crystal material to be tested are altered. These changes are captured by the imaging system, which is a CCD camera.

[0037] The present invention will now be described in detail with reference to specific embodiments.

[0038] Example 1: A method for rapid detection of microscopic defects in lithium niobate based on reverse voltage pulses includes the following steps: S1. Preparation of ferroelectric crystal materials with electrode patterns (1) Using ferroelectric crystal material as raw material, a uniform conductive electrode is deposited on its +Z surface; preferably, the ferroelectric crystal material is lithium niobate, lithium tantalate or potassium tantalate niobate, or a thin film of lithium niobate, lithium tantalate or potassium tantalate niobate.

[0039] (2) Spin-coating photoresist onto the surface of the ferroelectric crystal material on which the conductive electrode is deposited. The purpose of this step is to create metal strips on the surface of the ferroelectric crystal material. These metal strips can be regular stripes or other patterns.

[0040] (3) The ferroelectric crystal material with electrode pattern is obtained by sequentially photolithography, development, baking, metal etching and photoresist removal on the surface of the spin-coated photoresist.

[0041] S2. An indium tin oxide conductive layer is deposited on the -Z side of the ferroelectric crystal material with electrode patterns on the +Z side to obtain the ferroelectric crystal material to be tested. S3, Apply reverse voltage pulse to detect defect The aluminum electrode on the +Z side of the ferroelectric crystal material to be tested is connected to the negative electrode of the applied electric field, and the vapor-deposited transparent indium tin oxide conductive layer on the -Z side is connected to the positive electrode of the applied electric field. Then, it is placed in silicone oil at 190°C, and a 1200V voltage pulse is applied. The condition of the ferroelectric crystal material to be tested is observed through a real-time monitoring device. Ferroelectric crystal materials to be tested with point defects will be excited by the reverse voltage and will be displayed with contrast in the real-time monitoring device. Ferroelectric crystal materials to be tested without point defects will not show any phenomenon in the real-time monitoring device after being excited by the reverse voltage.

[0042] Figure 3 To detect the results of lithium niobate with some defects, the following method was used: Figure 3 As can be seen from Figure ②, after processing with a voltage pulse with a width of 500ms, the point defects of lithium niobate are excited by reverse voltage and are clearly displayed with contrast in the real-time monitoring device. Figure 4 To obtain the structural diagram of lithium niobate without point defects, through... Figure 4 As can be seen from Figure ②, after processing with a voltage pulse with a width of 500ms, no phenomenon was observed in the real-time monitoring device.

[0043] Example 2: The method described in the same way as in Example 1, except that: The ferroelectric crystal material is lithium tantalate.

[0044] Example 3: The method described in the same way as in Example 1, except that: The ferroelectric crystal material is potassium tantalate niobate.

[0045] Example 4: The method described in the same way as in Example 1, except that: The ferroelectric crystal material is a thin film of lithium niobate.

[0046] Example 5: The method described in the same way as in Example 1, except that: The ferroelectric crystal material is a thin film of lithium tantalate.

[0047] Example 6: The method described in the same way as in Example 1, except that: The ferroelectric crystal material is a thin film of potassium tantalate niobate.

[0048] Experimental example: Using lithium niobate with some defects and lithium niobate without defects, similar to that in Example 1, without reverse voltage pulse treatment, and following the normal periodic polarization process, the detection results are shown in [Figure 1]. Figure 5 Both images are magnified 50x. The left image shows a defective lithium niobate after periodic polarization, revealing numerous hexagonal defects that severely disrupt the periodic domain structure. The right image shows a defect-free lithium niobate after periodic polarization, exhibiting a uniform periodic structure and better polarization quality. The color difference between the two images is due to the fact that during periodic polarization, after applying an external voltage, we typically use HF acid etching to remove the surface electrodes and deeply etch the crystal to observe the domain structure. The left image shows a slightly longer etching time than the right image, resulting in deeper etching of the periodic structure.

[0049] Through with Figure 3 , Figure 4 As can be seen from the comparison, the detection method of this invention is basically the same as the existing periodic polarization detection method.

[0050] Those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of protection of the claims of this application.

Claims

1. A method for detecting micro-defects of ferroelectric crystal material based on reverse voltage pulse, comprising the following steps: S1, preparing a ferroelectric crystal material with electrode pattern evaporating uniform aluminum electrode on the +Z surface of the ferroelectric crystal material; spin-coating photoresist on the +Z surface of the ferroelectric crystal material with aluminum electrode; on the surface of the ferroelectric crystal material with spin-coated photoresist, sequentially passing through UV lithography, development, baking, etching metal, and removing photoresist to obtain the ferroelectric crystal material with electrode pattern on the +Z surface; S2, evaporating transparent indium tin oxide conductive layer on the -Z surface of the ferroelectric crystal material with electrode pattern on the +Z surface to obtain the ferroelectric crystal material to be detected; S3, applying reverse voltage pulse to detect defects connecting the aluminum electrode on the +Z surface of the ferroelectric crystal material to be detected to the negative electrode of the applied electric field, connecting the evaporated transparent indium tin oxide conductive layer on the -Z surface to the positive electrode of the applied electric field, then placing in silicone oil, applying voltage pulse, and observing the ferroelectric crystal material to be detected by real-time monitoring device, the ferroelectric crystal material to be detected with point defects will be excited by reverse voltage and have contrast display in the real-time monitoring device, and the ferroelectric crystal material to be detected without point defects will have no phenomenon in the real-time monitoring device after being excited by reverse voltage.

2. The method of claim 1, wherein, In step S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium tantalum niobate, lithium niobate thin film, lithium tantalate thin film, or potassium tantalum niobate thin film.

3. The method of claim 1, wherein, In step S1, the ferroelectric crystal material is lithium niobate.

4. The method of claim 1, wherein, In step S1, the thickness of the aluminum electrode is 80-150 nm.

5. The method of claim 1, wherein, In step S1, spin-coating photoresist makes the surface of the ferroelectric crystal material have metal strips, and the metal strips are regular strips or irregular patterns.

6. The method of claim 1, wherein, In step S2, the thickness of the indium tin oxide conductive layer is 150-160 nm.

7. The method of claim 1, wherein, In step S3, the temperature of the silicone oil is 180-200℃, and preferably, in step S3, the temperature of the silicone oil is 190℃.

8. The method of claim 1, wherein, In step S3, the applied voltage is 1100-1300V, and the pulse width is 400-600 ms.

9. The method of claim 1, wherein, In step S3, the applied voltage is 1200V, and the pulse width is 500 ms.

10. The method of claim 1, wherein, In step S3, the real-time monitoring device comprises a white light source, a polarizer 1, a polarizer 2, and an imaging system, the light of the white light source passes through the polarizer 1, penetrates the ferroelectric crystal material to be detected, the domain inversion at the point defects of the ferroelectric crystal material to be detected changes the optical properties of the crystal, and these changes are captured by the imaging system; therefore, the real-time monitoring system can observe the phenomenon that the point defects are excited by reverse voltage pulse in real time, and the quality of the crystal is judged accordingly, and the imaging system is a CCD camera.

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