Method for preparing ferroelectric crystal optical superlattice by using pyroelectric effect, superlattice and application

Abstract

The application discloses a method for preparing a ferroelectric crystal optical superlattice by using a pyroelectric effect, a superlattice and application, and belongs to the field of electronic and optical devices. The method comprises the following steps: preparing a ferroelectric crystal material carrying an electrode pattern; heating the ferroelectric crystal material carrying the electrode pattern, and the heating temperature is 50-200 DEG C; in the temperature range, the ferroelectric crystal material carrying the electrode pattern is excited in the reverse direction of polarization by using the pyroelectric property of the ferroelectric crystal material itself; then, an annealing step is performed, and the annealing rate is 50-150 DEG C / h; after 1-10 times of heating and annealing cycles, the superlattice is obtained. The application breaks through the limitation of the external electric field polarization method for different electrode structures by creating a new polarization process, realizes the preparation of different superlattice crystals based on various structure electrodes, and further expands the application scenarios and application fields of the ferroelectric crystal material.

Description

Technical Field

[0001] This invention belongs to the field of electronic and optical devices, and relates to nonlinear optical crystal material technology and laser technology. Specifically, it relates to a method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, the superlattice, and its applications. Background Technology

[0002] Ferroelectric crystal optical superlattices are nonlinear optical materials based on quasi-phase-matching technology. By engineering ferroelectric domains to fabricate optical superlattices with different microstructures, efficient and flexible nonlinear frequency conversion and multidimensional manipulation of the optical field can be achieved. The basic building block of an optical superlattice consists of a pair of positive and negative domains. For example, in ferroelectric crystals such as lithium niobate and lithium tantalate, the spontaneous polarization directions of the positive and negative domains are parallel and antiparallel to the z-axis of the crystal, respectively. Repeating such basic building blocks forms a one-dimensional periodic optical superlattice. Arranging two sets of building blocks according to a certain pattern constitutes a two-element quasi-periodic optical superlattice. The microstructures of optical superlattices can provide a rich variety of reciprocal lattice vectors, compensating for wave vector mismatch caused by material dispersion during nonlinear optical parametric processes, thus achieving high nonlinear frequency conversion efficiency. Currently, it has shown great potential in optical shaping, laser sources, and quantum communication.

[0003] The existing technology for preparing optical superlattices mainly involves applying an external electric field to anneal and polarize the native lithium niobate crystal, then cutting and polishing it into a wafer. Conductive electrodes are then deposited on the wafer using micro-nano processing photolithography technology. Finally, a voltage with a special waveform is applied to achieve the periodic reversal of the ferroelectric domains of the wafer.

[0004] The existing fabrication methods described above have the following technical problems. First, the process involves pressurization at high temperatures, which makes it difficult to precisely control the growth and fabrication of domain structures. Furthermore, pressurization at high temperatures can limit the production of two-dimensional optical superlattice materials due to electrode structure limitations. Second, the electrodes constructed for two-dimensional optical superlattices cannot be fully connected in a circuit, so the external electric field polarization scheme cannot meet the requirements for fabricating all types of optical superlattices.

[0005] This shows that the existing technology needs further improvement. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect. By creating a novel polarization process, this invention overcomes the limitations of external electric field polarization methods on different electrode structures, enabling the preparation of different superlattice crystals based on various electrode structures, and further expanding the application scenarios and fields of ferroelectric crystal materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, comprising the following steps: S1, preparing a ferroelectric crystal material carrying an electrode pattern: using the ferroelectric crystal material as raw material, uniformly conductive electrodes are deposited on its front and back sides respectively; photoresist is spin-coated on the surface of the ferroelectric crystal material with the conductive electrodes deposited; the surface of the ferroelectric crystal material with the spin-coated photoresist is sequentially subjected to photolithography, development, baking, metal etching and photoresist removal to obtain a ferroelectric crystal material carrying an electrode pattern.

[0008] S2, Heating-annealing: The ferroelectric crystal material carrying the electrode pattern is heated to a temperature of 50-200℃. Within this temperature range, the ferroelectric crystal material carrying the electrode pattern is excited in the opposite polarization direction by utilizing its own pyroelectric properties. When the heating time is 300 s, the annealing step is performed at a rate of 50-150℃ / h.

[0009] S3. Repeat S2 1 to 10 times to obtain a ferroelectric crystal optical superlattice.

[0010] In the above-mentioned method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, in S1, the ferroelectric crystal material is a thin film of lithium niobate, lithium tantalate, potassium tantalate niobate, or any one of them.

[0011] The above-mentioned method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect uses lithium niobate as the ferroelectric crystal material.

[0012] In the above-mentioned method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, in step S2, the heating temperature is 200°C and the annealing rate is 100°C / h.

[0013] The above-mentioned method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect involves cycling S2 10 times.

[0014] Another object of the present invention is to provide a ferroelectric crystal optical superlattice, which is prepared by the above-described method for preparing a ferroelectric crystal optical superlattice using the pyroelectric effect.

[0015] The aforementioned ferroelectric crystal optical superlattice is a two-dimensional structure.

[0016] Another object of the present invention is to provide the application of the above-mentioned ferroelectric crystal optical superlattice in nonlinear frequency conversion crystal devices.

[0017] The principle of fabricating ferroelectric crystal optical superlattices using the pyroelectric effect in this invention is as follows: The phenomenon of spontaneous polarization intensity changes in polar crystals due to changes in external temperature is called the pyroelectric effect. Crystals possessing this property are referred to as pyroelectricity. A fundamental characteristic of ferroelectric crystals is their pyroelectric effect, which can be generated without the addition of an external electric field. A certain pyroelectric effect occurs when the external temperature changes. Below their Curie temperature, ferroelectric crystals spontaneously exhibit asymmetry in certain directions due to the lack of lattice vibration modes, resulting in a certain degree of phase transition. If pyroelectric heating is applied, the dipoles within the material lose their orientation due to thermal vibration, and their spontaneous polarization level decreases, leading to a reduction in the number of free charges bound to the material surface. If the crystal is in an open-circuit state, the free charges remain on the electrode surface, generating a potential in the material, thus constructing a built-in electric field within the crystal. Crystal polarization is achieved by applying a high voltage to the crystal using an external electric field. Therefore, the pyroelectric effect can be used to fabricate ferroelectric crystal optical superlattices.

[0018] This invention selects lithium niobate, lithium tantalate, or potassium tantalate niobate as the ferroelectric crystal material, or as a thin film of lithium niobate, lithium tantalate, or potassium tantalate niobate. When the ferroelectric crystal material is heated to 50-200°C, it releases an electric charge. The pyroelectric properties of the ferroelectric crystal material are used to excite its polarization in the opposite direction. Combined with an annealing process, with the annealing rate controlled at 50-150°C / h, domain structure inversion of the electrode patterned portion can be achieved.

[0019] Compared with the prior art, the present invention brings the following beneficial technical effects: (1) In terms of raw material selection, the ferroelectric crystal material lithium niobate and the like selected in the present invention have pyroelectric properties. After being heated to a certain temperature, they can release charges themselves, eliminating the need for additional pressure process steps in the prior art; in addition, by tightly combining the heating-annealing process, domain structure inversion of the part with electrode pattern can be achieved. Compared with the external electric field polarization in the prior art, the present invention does not require an external electric field. By utilizing the pyroelectric properties of the crystal itself and combining it with metal electrodes, an optical superlattice crystal material consistent with the electrode design can be obtained.

[0020] (2) By means of the polarized electrode structure of the present invention, the limitation of not being able to obtain two-dimensional optical superlattice materials due to the limitation of electrode structure in the preparation of optical superlattice materials by using an external electric field can be solved, and the preparation of different superlattice crystals based on various electrode structures can be realized, thus expanding the application scenarios and fields of ferroelectric crystal materials. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the fabrication process of a ferroelectric crystal optical superlattice according to the present invention.

[0022] Figure 2 This is a diagram of the reverse domain structure of lithium niobate obtained by pyroelectric effect in an embodiment of the present invention.

[0023] Figure 3 The domain nucleus distribution of the lithium niobate crystal optical superlattice prepared in Examples 1 to 4 is shown, where (a) corresponds to Example 2, (b) corresponds to Example 3, (c) corresponds to Example 4, and (d) corresponds to Example 1.

[0024] Figure 4 The domain nucleus distribution of the lithium niobate crystal fiber superlattice prepared in Examples 1, 10, 11 and 12 is shown, where (e) corresponds to Example 10, (f) corresponds to Example 11, (g) corresponds to Example 12 and (h) corresponds to Example 1. Detailed Implementation

[0025] This invention proposes a method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, the superlattice itself, and its applications. 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.

[0026] 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.

[0027] All of the raw materials mentioned above in this invention can be purchased through commercial channels.

[0028] The main technical concept of this invention is to change the existing process for preparing optical superlattices. This is mainly reflected in eliminating the original pressurization step and, through the selection of ferroelectric crystal materials and the combination of heating-annealing processes, realizing the preparation of different superlattice crystals based on various electrode structures.

[0029] This invention discloses a method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, such as... Figure 1 As shown, the process includes the following steps: Step 1: Prepare a ferroelectric crystal material carrying an electrode pattern: (1) Using the ferroelectric crystal material as raw material, uniform conductive electrodes are deposited on its front and back sides respectively; 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.

[0030] (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.

[0031] (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.

[0032] Step 2, Heating-annealing: The ferroelectric crystal material with electrode patterns is heated to a temperature of 50-200℃. Within this temperature range, the ferroelectric crystal material with electrode patterns is excited in the opposite polarization direction by utilizing its own pyroelectric properties. When the heating time is 300 s, the annealing step is performed at a rate of 50-150℃ / h.

[0033] The third step is to repeat the second step 1 to 10 times to obtain the ferroelectric crystal optical superlattice.

[0034] As a further preferred embodiment, in the above-mentioned method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, the ferroelectric crystal material is lithium niobate.

[0035] As a further preferred embodiment, in the above-mentioned method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect, the heating temperature is 200℃, the annealing rate is 100℃ / h, and the number of annealing cycles is 10.

[0036] The present invention will now be described in detail with reference to specific embodiments.

[0037] Example 1: The ferroelectric crystal material in this example is lithium niobate.

[0038] The specific steps are as follows: Step 1: Prepare ferroelectric crystal material with electrode pattern: (1) Evaporate uniform conductive electrodes on both sides of lithium niobate. (2) Spin-coat photoresist on the surface of the lithium niobate crystal material with the conductive electrodes. (3) Sequentially perform photolithography, development, baking, metal etching and photoresist removal on the surface of the lithium niobate crystal material with the spin-coated photoresist to obtain the lithium niobate crystal material with electrode pattern.

[0039] Step 2, Heating-annealing: The lithium niobate crystal material with electrode patterns is heated to 200℃. At this temperature, the ferroelectric crystal material with electrode patterns is excited in the opposite polarization direction by its own pyroelectric properties. When the heating time is 300 s, the annealing step is carried out at a rate of 100℃ / h for 10 min to bring it to room temperature.

[0040] The third step is to repeat the second step ten times to obtain the lithium niobate crystal optical superlattice.

[0041] Figure 2 This is a diagram of the inverted domain structure of the lithium niobate crystal optical superlattice prepared in this embodiment.

[0042] Example 2: The difference from Example 1 is that the heating temperature in this example is 25°C.

[0043] Example 3: The difference from Example 1 is that the heating temperature in this example is 100°C.

[0044] Example 4: The difference from Example 1 is that the heating temperature in this example is 150°C.

[0045] The domain nucleus distribution of the lithium niobate crystal optical superlattices prepared in Examples 1 to 4 was observed, such as... Figure 3 As shown in (a), (b), (c), and (d), the optimal domain distribution is obtained when the heating temperature is 200℃. When the heating temperature continues to increase, such as to 250℃, the threshold of the pyroelectric effect of the crystal will be reached, and there will be no better effect. Furthermore, with the increase of temperature, the thermal stress inside the crystal will cause dislocations and slip line defects in the crystal lattice, which can easily lead to crystal breakage.

[0046] Example 5: The difference from Example 1 is that the ferroelectric crystal material in this example is lithium tantalate.

[0047] Example 6: The difference from Example 1 is that the ferroelectric crystal material in this example is potassium tantalate niobate.

[0048] Example 7: The difference from Example 1 is that the ferroelectric crystal material in this example is a thin film of lithium niobate.

[0049] Example 8: The difference from Example 1 is that the ferroelectric crystal material in this example is a thin film of lithium tantalate.

[0050] Example 9: The difference from Example 1 is that the ferroelectric crystal material in this example is a thin film of potassium tantalate niobate.

[0051] Example 10: The difference from Example 1 is that in the third step of this example, the annealing cycle is repeated once to obtain the lithium niobate crystal optical superlattice.

[0052] Example 11: The difference from Example 1 is that in the third step of this example, the annealing cycle is repeated three times to obtain the lithium niobate crystal optical superlattice.

[0053] Example 12: The difference from Example 1 is that in the third step of this example, the annealing cycle is repeated five times to obtain the lithium niobate crystal optical superlattice.

[0054] The domain nucleus distribution of the lithium niobate crystal fiber superlattices prepared in Examples 1, 10, 11, and 12 above was analyzed, such as... Figure 4 As shown, Figure 4(e) corresponds to Example 10, (f) corresponds to Example 11, (g) corresponds to Example 12, and (h) corresponds to Example 1. Figure 4 It was found that the best results were achieved when the number of cycles in Example 1 was 10. When the number of cycles continued to increase, such as to 15 cycles, thermal stress would cause dislocations and slip line defects to be generated inside the crystal lattice, leading to crystal fracture.

[0055] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0056] 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 preparing ferroelectric crystal optical superlattices using the pyroelectric effect, characterized in that, Includes the following steps: S1. Preparation of ferroelectric crystal materials carrying electrode patterns Using ferroelectric crystal material as raw material, uniform conductive electrodes are deposited on both the front and back sides. Photoresist is spin-coated onto the surface of a ferroelectric crystal material on which a conductive electrode is deposited by vapor deposition; The ferroelectric crystal material with electrode pattern is obtained by sequentially performing photolithography, development, baking, metal etching and photoresist removal on the surface of the spin-coated photoresist. S2, Heating-annealing The ferroelectric crystal material with electrode patterns is heated to a temperature of 50–200°C. Within this temperature range, the ferroelectric crystal material with electrode patterns is excited in the opposite polarization direction by utilizing its own pyroelectric properties. When the heating time is 300s, an annealing step is performed at a rate of 50–150°C / h. S3. Repeat S2 1 to 10 times to obtain a ferroelectric crystal optical superlattice; In S1, the ferroelectric crystal material is a thin film of lithium niobate, lithium tantalate, potassium tantalate niobate, or any one of them.

2. The method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect according to claim 1, characterized in that: The ferroelectric crystal material is lithium niobate.

3. The method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect according to claim 1, characterized in that: In S2, the heating temperature is 200℃ and the annealing rate is 100℃ / h.

4. The method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect according to claim 1, characterized in that: In S3, S2 is looped 10 times.

5. A ferroelectric crystal optical superlattice, characterized in that, It is prepared by the method for preparing ferroelectric crystal optical superlattices using the pyroelectric effect as described in any one of claims 1 to 4.

6. The ferroelectric crystal optical superlattice according to claim 5, characterized in that: The ferroelectric crystal optical superlattice is a two-dimensional structure.

7. An application of a ferroelectric crystal optical superlattice, characterized in that, The application described is the application of the ferroelectric crystal optical superlattice of claim 5 in a nonlinear frequency conversion crystal device.

Images