Ferroelectric crystal with uniform domain structure, method for periodic polarization and application

Abstract

The application discloses a ferroelectric crystal with a uniform domain structure, a period polarization method and application, and relates to the technical field of nonlinear optical crystal materials and laser technology. The method comprises the following steps: evaporating a layer of uniform metal electrode on the front surface of a ferroelectric crystal material, and evaporating a layer of uniform transparent electrode on the back surface of the ferroelectric crystal material; spin-coating photoresist on the surface of the ferroelectric crystal material with the evaporated electrode, and then sequentially performing photoetching, developing, baking, etching and removing the photoresist to obtain the ferroelectric crystal material carrying the metal electrode pattern; exciting the polarization reverse direction of the ferroelectric crystal material carrying the metal electrode pattern through a reverse voltage or an electron beam focusing method to construct domain nucleus sites; and performing period polarization on the obtained ferroelectric crystal material through an external electric field. The application can quickly prepare high-quality period polarization ferroelectric crystal materials with a large light transmission size, and the increase of the aperture of the period polarization ferroelectric crystal can widen the application scenarios and fields of the period polarization ferroelectric crystal materials.

Description

Technical Field

[0001] This invention relates to the fields of nonlinear optical crystal materials and laser technology, specifically to a ferroelectric crystal with a uniform domain structure, a periodic polarization method, and its applications. Background Technology

[0002] Quasi-phase matching (QPM) technology compensates for phase mismatch in light waves caused by refractive index dispersion by periodically controlling the nonlinear polarizability of a crystal, thereby improving the efficiency of nonlinear optical frequency conversion. Periodically inverted ferroelectric crystals are important materials for nonlinear frequency doubling, sum-frequency generation, difference-frequency generation, and optical parametric oscillation applications, and are widely used in laser, aerospace, quantum communication, and military fields.

[0003] Current technologies for preparing periodically polarized ferroelectric materials mainly involve applying an external electric field. This involves annealing and polarizing the native ferroelectric crystal, followed by cutting, polishing, and wafer fabrication. Conductive electrodes are then deposited onto the wafer using micro / nano-fabrication photolithography. Finally, a voltage with a specific waveform is applied to achieve periodic reversal of the ferroelectric domains. While polarization methods for thin-film (less than 1 mm) ferroelectric crystals are relatively mature, limitations in the crystal's resistance to optical damage necessitate the use of nonlinear crystals with large apertures to achieve higher power mid-infrared lasers, meeting the needs of research, industry, and defense. However, due to the crystal's high coercive field and the lateral expansion of reversed domains caused by prolonged pressure application, achieving periodic electric field polarization in thick-film ferroelectric crystals is difficult. Simply increasing the polarization voltage results in significant lateral expansion of the domain structure, making it difficult to obtain a uniform domain structure. Summary of the Invention

[0004] One of the objectives of this invention is to provide a periodic polarization method for ferroelectric crystals with uniform domain structures. This method overcomes the limitations of preparing thick (1-10 mm) ferroelectric crystal materials using external electric field polarization methods by optimizing the process, thereby achieving rapid polarization of the periodic polarization inversion domains of periodically polarized inverted ferroelectric crystal materials, improving the quality of the inversion domains, and expanding the application scenarios and fields of periodically polarized ferroelectric crystal materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a periodic polarization method for a ferroelectric crystal with a uniform domain structure, comprising the following steps in sequence: S1, selecting a ferroelectric crystal material with a thickness of 0.1μm to 10mm, depositing a uniform metal electrode on the front side of the ferroelectric crystal material, and depositing a uniform transparent electrode on the back side of the ferroelectric crystal material.

[0006] S2. Spin-coat photoresist onto the surface of the ferroelectric crystal material of the vapor-deposited electrode; sequentially perform photolithography, development, baking, etching and photoresist removal on the surface of the spin-coated ferroelectric crystal material to obtain a ferroelectric crystal material carrying a metal electrode pattern.

[0007] S3. The polarization of the ferroelectric crystal material carrying the metal electrode pattern is excited in the opposite direction by reverse voltage or electron beam focusing method to construct domain nucleation sites, which are then used in the polarization activation process.

[0008] S4. Periodically polarize the ferroelectric crystal material obtained in step S3 by applying an external electric field, and remove the electrodes on both sides of the obtained ferroelectric crystal material to obtain a ferroelectric crystal with a uniform domain structure.

[0009] In the above-mentioned periodic polarization method for a ferroelectric crystal with a uniform domain structure, in step S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate, or potassium titanyl arsenate, or a thin film of lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate, or potassium titanyl arsenate.

[0010] The above-mentioned periodic polarization method for a ferroelectric crystal with a uniform domain structure uses lithium niobate as the ferroelectric crystal material.

[0011] In the above-mentioned periodic polarization method for a ferroelectric crystal with a uniform domain structure, in step S1, the metal electrode is an aluminum electrode and the transparent electrode is an indium tin oxide electrode.

[0012] In the above-mentioned periodic polarization method for a ferroelectric crystal with a uniform domain structure, in step S2, during photolithography, the metal electrode not covered by the photoresist is baked at a temperature of 50-70°C for 10-30 minutes, and during development, it is baked at a temperature of 50-70°C for 20-40 minutes; during the etching process, phosphoric acid is used to remove the metal electrode not covered by the photoresist through phosphoric acid etching, and the photoresist is removed by acetone.

[0013] The periodic polarization method of the above-mentioned ferroelectric crystal with uniform domain structure has a specific periodic polarization of 28 μm.

[0014] Another object of the present invention is to provide a ferroelectric crystal with a uniform domain structure as described above, which is prepared by the periodic polarization method of the ferroelectric crystal with a uniform domain structure described above.

[0015] The ferroelectric crystal with a uniform domain structure described above is wherein the ferroelectric domains are arranged in a regular strip or pattern shape.

[0016] Another object of the present invention is to provide the application of the above-described ferroelectric crystal with uniform domain structure in nonlinear frequency conversion crystal devices.

[0017] Compared with the prior art, the present invention brings the following beneficial technical effects: (1) The present invention proposes a periodic polarization method for ferroelectric crystals with uniform domain structure. It excites the polarization reverse direction of ferroelectric crystal material carrying metal electrode pattern by reverse voltage or electron beam focusing method to construct domain nucleation sites for polarization activation. Then, the domain structure of the ferroelectric crystal material in the target polarization direction is controlled by an external electric field, thereby achieving rapid polarization and obtaining a periodic polarized ferroelectric crystal with uniform domain structure.

[0018] (2) The present invention can quickly prepare high-quality periodically polarized ferroelectric crystal materials with large light transmission size. The increase in the aperture of the periodically polarized ferroelectric crystal can broaden the application scenarios and fields of periodically polarized ferroelectric crystal materials.

[0019] (3) The method of the present invention is particularly applicable to thick-sized (0.1μm~10mm) ferroelectric crystal materials, overcoming the technical defects of the prior art in which it is difficult to achieve periodic electric field polarization for thick-sized ferroelectric crystal materials. The present invention can adjust the direction and polarization period of the domain structure according to actual needs, and has the ability to stably control the domain structure in non-target directions and obtain periodically polarized ferroelectric crystals, and can realize a high-efficiency nonlinear frequency conversion process. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of reverse domain nucleation excitation of ferroelectric crystal material according to Embodiment 1 of the present invention.

[0021] Figure 2 This refers to the domain nucleus structure generated by activation via reverse voltage or electron beam focusing.

[0022] Figure 3 This is a schematic diagram of the normal polarization process.

[0023] Figure 4 This is a schematic diagram of the polarization process after the reverse domain nucleus is activated. Detailed Implementation

[0024] This invention proposes a ferroelectric crystal with a uniform domain structure, a periodic polarization method, and its application. 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.

[0025] The main technical concept of this invention lies in the preparation of a periodically polarized ferroelectric crystal by assisting external field polarization on the basis of the original polarization electric field. The external field serves to construct ferroelectric domain nuclei that can activate the polarization. The ferroelectric crystal is cut along a certain axis. A periodic electrode is deposited on the front side of the ferroelectric crystal along this axis, and a conductive layer is deposited on the negative side. A voltage is applied to the front side along this axis to form the original polarization electric field, while the negative side is grounded. This causes the ferroelectric domains under the periodic electrodes to reverse. Simultaneously, an external field is applied along other axes of the ferroelectric crystal to generate activated polarized ferroelectric domain nuclei. In this invention, the external field is preferably a reverse voltage or an electron beam focusing method.

[0026] In this paper, the domains can be arranged in regular stripes or in a pattern, depending on the shape of the polarization electrode. The ferroelectric crystal materials used in this paper are lithium niobate, lithium tantalate, potassium titanyl phosphate, rubidium titanyl phosphate, or potassium titanyl arsenate, or their thin films.

[0027] Appendix Figure 1 The +z plane represents the front side of the ferroelectric crystal material, and the -z plane represents the back side.

[0028] The present invention will be further described below with reference to specific embodiments.

[0029] Example 1: The ferroelectric crystal material in this example is lithium niobate.

[0030] A periodic polarization method for a lithium niobate crystal with a uniform domain structure includes the following steps: S1, selecting a lithium niobate crystal material with a thickness of 100 μm, the light transmission direction of the lithium niobate crystal being the x-direction, the polarization period being 28 μm, and designing a 28 μm periodic electrode mask.

[0031] A uniform aluminum electrode is deposited on the front side of the lithium niobate crystal material, and a uniform indium tin oxide electrode is deposited on the back side of the lithium niobate crystal material.

[0032] S2. Spin-coat photoresist onto the surface of the lithium niobate crystal material with the vapor-deposited electrode. The lithium niobate crystal material with the spin-coated photoresist then undergoes photolithography, development, baking, etching, and photoresist removal sequentially to obtain a lithium niobate crystal material carrying a metal electrode pattern. During photolithography, the material is baked at 60°C for 20 minutes, and during development, it is baked at 60°C for 30 minutes. Phosphoric acid is used during etching to remove the metal electrodes not covered by the photoresist, and acetone is used to remove the photoresist.

[0033] S3. The polarization of the lithium niobate crystal material carrying the metal electrode pattern is excited in the opposite direction by a reverse voltage to construct domain nucleation sites, which are then used in the polarization activation process. For example... Figure 1As shown, under real-time monitoring, domain nuclei structures were observed on the surface of the lithium niobate crystals and were stably controlled. The specific domain nuclei structure is as follows: Figure 2 As shown.

[0034] S4. Periodically polarize the lithium niobate crystal material obtained in step S3 by applying an external electric field, and remove the electrodes on both sides of the obtained lithium niobate crystal material to obtain a lithium niobate crystal with a uniform domain structure, such as... Figure 4 As shown.

[0035] Example 2: The ferroelectric crystal material in this example is lithium tantalate.

[0036] A periodic polarization method for a lithium tantalate crystal with a uniform domain structure includes the following steps: S1, selecting a lithium tantalate crystal material with a thickness of 10 mm, the light transmission direction of the lithium tantalate crystal being the x-direction, the polarization period being 28 μm, and designing a 28 μm periodic electrode mask.

[0037] A uniform aluminum electrode is deposited on the front side of the lithium tantalate crystal material, and a uniform indium tin oxide electrode is deposited on the back side of the lithium tantalate crystal material.

[0038] S2. Spin-coat photoresist onto the surface of the lithium tantalate crystal material with the vapor-deposited electrode. The lithium tantalate crystal material with the spin-coated photoresist then undergoes photolithography, development, baking, etching, and photoresist removal sequentially to obtain a lithium tantalate crystal material carrying a metal electrode pattern. During photolithography, the material is baked at 50°C for 10 minutes, and during development, it is baked at 50°C for 20 minutes. Phosphoric acid is used during etching to remove the metal electrodes not covered by the photoresist, and acetone is used to remove the photoresist.

[0039] S3. The polarization of the lithium tantalate crystal material carrying the metal electrode pattern is excited in the opposite direction by a reverse voltage to construct domain nucleation sites, which are then used in the polarization activation process.

[0040] S4. Periodically polarize the lithium tantalate crystal material obtained in step S3 by applying an external electric field, and remove the electrodes on both sides of the obtained lithium tantalate crystal material to obtain a lithium tantalate crystal with a uniform domain structure.

[0041] Example 3: The ferroelectric crystal material in this example is potassium titanium oxyphosphate.

[0042] A periodic polarization method for a potassium titanate oxyphosphate crystal with a uniform domain structure includes the following steps: S1, selecting a potassium titanate oxyphosphate crystal material with a thickness of 5 mm, the light transmission direction of the potassium titanate oxyphosphate crystal being the x-direction, the polarization period being 28 μm, and designing a 28 μm periodic electrode mask.

[0043] A uniform aluminum electrode is deposited on the front side of the potassium titanate phosphate crystal material, and a uniform indium tin oxide electrode is deposited on the back side of the potassium titanate phosphate crystal material.

[0044] S2. Spin-coat photoresist onto the surface of the potassium titanium oxide phosphate crystal material of the vapor-deposited electrode. The surface of the spin-coated potassium titanium oxide phosphate crystal material is then subjected to photolithography, development, baking, etching, and photoresist removal sequentially to obtain a potassium titanium oxide phosphate crystal material carrying a metal electrode pattern. During photolithography, the material is baked at 70℃ for 30 minutes, and during development, it is baked at 70℃ for 40 minutes. Phosphoric acid is used in the etching process to remove the metal electrodes not covered by the photoresist, and acetone is used to remove the photoresist.

[0045] S3. The polarization reverse direction of potassium titanate oxyphosphate crystal material carrying metal electrode patterns is excited by electron beam focusing to construct domain nucleation sites, which are then used in the polarization activation process.

[0046] S4. Periodically polarize the potassium titanate oxyphosphate crystal material obtained in step S3 by applying an external electric field, and remove the electrodes on both sides of the obtained potassium titanate oxyphosphate crystal material to obtain a potassium titanate oxyphosphate crystal with a uniform domain structure.

[0047] The ferroelectric crystals prepared in Examples 1 to 3 above can be used as one-dimensional quasi-phase-matched optical parametric crystal devices with wavelengths from 1.064 μm to 5 μm.

[0048] Comparative Example 1: The ferroelectric crystal material in this comparative example is lithium niobate.

[0049] A polarization method for lithium niobate crystals includes the following steps: S1, selecting a lithium niobate crystal material with a thickness of 100 μm, wherein the light transmission direction of the lithium niobate crystal is the x-direction and the polarization period is 28 μm, and designing a 28 μm period electrode mask.

[0050] A uniform aluminum electrode is deposited on the front side of the lithium niobate crystal material, and a uniform indium tin oxide electrode is deposited on the back side of the lithium niobate crystal material.

[0051] S2. Spin-coat photoresist onto the surface of the lithium niobate crystal material with the vapor-deposited electrode. The lithium niobate crystal material with the spin-coated photoresist then undergoes photolithography, development, baking, etching, and photoresist removal sequentially to obtain a lithium niobate crystal material carrying a metal electrode pattern. During photolithography, the material is baked at 60°C for 20 minutes, and during development, it is baked at 60°C for 30 minutes. Phosphoric acid is used during etching to remove the metal electrodes not covered by the photoresist, and acetone is used to remove the photoresist.

[0052] S3. The lithium niobate crystal material obtained in step S2 is polarized by applying an external electric field, and the electrodes on both sides of the obtained lithium niobate crystal material are removed to obtain lithium niobate crystal, such as... Figure 3 As shown.

[0053] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0054] 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 periodic polarization of a ferroelectric crystal with a uniform domain structure, characterized in that, The steps are as follows: S1. Select a ferroelectric crystal material with a thickness of 0.1μm to 10mm, deposit a uniform metal electrode on the front side of the ferroelectric crystal material, and deposit a uniform transparent electrode on the back side of the ferroelectric crystal material. S2. Spin-coat photoresist onto the ferroelectric crystal material surface of the vapor-deposited electrode; The ferroelectric crystal material with a metal electrode pattern is obtained by sequentially performing photolithography, development, baking, etching and photoresist removal on the surface of the spin-coated photoresist. S3. Excite the polarization in the reverse direction of the ferroelectric crystal material carrying the metal electrode pattern by reverse voltage or electron beam focusing method to construct domain nucleation sites and use them for the polarization activation process. S4. Periodically polarize the ferroelectric crystal material obtained in step S3 by applying an external electric field, and remove the electrodes on both sides of the obtained ferroelectric crystal material to obtain a ferroelectric crystal with a uniform domain structure; In step S1, the ferroelectric crystal material is lithium niobate, lithium tantalate, potassium titanate phosphate, rubidium titanate phosphate, or potassium titanate arsenate, or a thin film of lithium niobate, lithium tantalate, potassium titanate phosphate, rubidium titanate phosphate, or potassium titanate arsenate; In step S1, the metal electrode is an aluminum electrode, and the transparent electrode is an indium tin oxide electrode; In step S2, during photolithography, the electrode is baked at 50-70°C for 10-30 minutes, and during development, it is baked at 50-70°C for 20-40 minutes. During etching, phosphoric acid is used to remove the metal electrodes not covered by the photoresist, and acetone is used to remove the photoresist.

2. The periodic polarization method for a ferroelectric crystal with a uniform domain structure according to claim 1, characterized in that: The ferroelectric crystal material is lithium niobate.

3. The periodic polarization method for a ferroelectric crystal with a uniform domain structure according to claim 1, characterized in that: The periodic polarization is specifically 28 μm.

4. A ferroelectric crystal with a uniform domain structure, characterized in that, It is prepared by the periodic polarization method according to any one of claims 1 to 3 of a ferroelectric crystal with a uniform domain structure.

5. A ferroelectric crystal with a uniform domain structure according to claim 4, characterized in that: The ferroelectric domains in the ferroelectric crystal are arranged in a regular strip or pattern shape.

6. The application of the ferroelectric crystal with a uniform domain structure according to claim 4 in nonlinear frequency conversion crystal devices.

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