Periodically polarized film preparation method

Abstract

The invention relates to the technical field of semiconductor elements, and provides a periodically polarized thin film preparation method, which comprises the following steps: providing a substrate layer; forming an isolation layer on the substrate layer, and adjusting the oxygen content of the isolation layer; forming a thin film layer and bonding the thin film layer with the isolation layer; periodically arranged metal electrodes are formed on the surface of the side, away from the isolation layer, of the thin film layer, so that a thin film structure with the periodically arranged metal electrodes is obtained; and carrying out temperature change treatment on the film structure with the metal electrode to obtain the periodically polarized film with the periodic reversal domain structure. The preparation method provided by the invention is simple and convenient to operate and low in cost, and can inhibit the transverse broadening effect of the inversion domain.

Description

Technical Field

[0001] This application relates to the field of semiconductor device technology, and in particular to a method for preparing a periodically polarized thin film and a periodically polarized thin film. Background Technology

[0002] Periodically polarized thin films are core materials in photonic integrated devices and are widely used in optical communication and information processing as well as in the fields of sensors and detectors.

[0003] Currently, the mainstream method for preparing periodically polarized thin films is the external electric field method. This method requires the fabrication of periodic metal electrodes on the surface of the thin film using photolithography, and the application of high voltage to the electrodes through an external circuit. This high voltage electric field drives Li⁺ ions across the oxygen plane to achieve polarization reversal.

[0004] However, the above method requires the use of equipment such as a signal generator, high-voltage amplifier, and oscilloscope, which is costly and complex to operate. Furthermore, high voltage can easily cause lateral widening of the inversion domains, making it difficult to precisely control the duty cycle and thus affecting the phase matching accuracy. Summary of the Invention

[0005] This application provides a solution to the problems in related technologies where achieving polarization reversal of thin film structures via an external electric field method is costly, complex to operate, and prone to causing lateral broadening of reversed domains, affecting phase matching accuracy.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] This application provides a method for preparing a periodically polarized thin film, comprising: providing a substrate layer; forming an isolation layer on the substrate layer and adjusting the oxygen content of the isolation layer; forming a thin film layer and bonding the thin film layer to the isolation layer; forming periodically arranged metal electrodes on the side surface of the thin film layer away from the isolation layer to obtain a thin film structure with periodically arranged metal electrodes; and subjecting the thin film structure with metal electrodes to a temperature change treatment to obtain a periodically polarized thin film with a periodically reversed domain structure.

[0008] As an optional implementation, forming an isolation layer on a substrate and adjusting the oxygen content of the isolation layer includes adjusting the oxygen content of the isolation layer formed on the substrate by thermal oxidation or plasma-enhanced chemical vapor deposition.

[0009] As an optional implementation, when the oxygen content of the isolation layer formed on the substrate is adjusted by plasma-enhanced chemical vapor deposition, the flow ratio of the reactant gas to nitrous oxide in the plasma-enhanced chemical vapor deposition process is greater than or equal to 20:80 and less than or equal to 80:20.

[0010] As an optional implementation, the periodic reverse domain structure includes a plurality of alternately arranged reverse domain regions and non-reverse domain regions; wherein the sum of the widths of a group of adjacent reverse domain regions and non-reverse domain regions is the polarization period, and the polarization period is greater than or equal to 1 μm and less than or equal to 20 μm.

[0011] As an optional implementation, applying a temperature change treatment to a thin film structure with metal electrodes includes: heating the thin film structure and raising the temperature of the thin film layer from room temperature to a preset temperature within a first time; maintaining the thin film layer at the preset temperature for a second time to make the surface of the thin film layer electrically neutral; and cooling the thin film structure and lowering the temperature of the thin film layer from the preset temperature to room temperature within a third time.

[0012] As an optional implementation, the preset temperature is greater than or equal to 100°C and less than or equal to 300°C; and / or, the cooling rate of the thin film layer in the third time period is greater than or equal to 1°C / min and less than or equal to 10°C / min; and / or, the heating rate of the thin film layer in the first time period is greater than or equal to 1°C / min and less than or equal to 10°C / min.

[0013] As an optional implementation, forming a thin film layer and bonding the thin film layer to an isolation layer includes: providing a ferroelectric crystal wafer and performing ion implantation on the ferroelectric crystal wafer to form an implanted wafer; the implanted wafer includes a residual mass layer, an implanted layer, and a thin film layer stacked together; and bonding the thin film layer and the isolation layer to form a bond.

[0014] As an optional implementation, before forming periodically arranged metal electrodes on the side of the thin film layer away from the isolation layer, the method further includes: heat-treating the bond to remove the implanted layer and the residual layer, and obtaining a thin film structure; the thin film structure includes a thin film layer, an isolation layer and a thin film layer stacked sequentially.

[0015] As an optional implementation, forming periodically arranged metal electrodes on the side surface of the thin film layer away from the isolation layer includes: forming a periodically arranged photoresist pattern on the side surface of the thin film layer away from the isolation layer; depositing metal on the surface of the thin film layer with the photoresist pattern; and stripping the photoresist pattern and the metal covering the photoresist pattern to obtain a thin film structure with periodically arranged metal electrodes.

[0016] As an optional implementation, before obtaining a periodically polarized thin film with a periodic reverse domain structure after subjecting the thin film structure with metal electrodes to a temperature change treatment, the method further includes: removing the metal electrodes formed on the surface of the thin film layer opposite to the isolation layer.

[0017] The method for preparing a periodically polarized thin film provided in this application includes: providing a substrate layer; forming an isolation layer on the substrate layer and adjusting the oxygen content of the isolation layer; forming a thin film layer and bonding the thin film layer to the isolation layer; forming periodically arranged metal electrodes on the surface of the thin film layer away from the isolation layer to obtain a thin film structure with periodically arranged metal electrodes; and subjecting the thin film structure with metal electrodes to a temperature change treatment to obtain a periodically polarized thin film with a periodic reverse domain structure.

[0018] At room temperature, the spontaneous polarization of a thin film structure generates a space charge field, which attracts free charges on the surface to compensate, thereby achieving a steady-state charge balance and making the thin film structure macroscopically electrically neutral. However, when subjected to temperature changes (such as heating or cooling), the spontaneous polarization intensity inside the thin film layer changes with the temperature. For example, the spontaneous polarization intensity (Ps) of the thin film layer decreases when heated and increases when cooled.

[0019] At this point, the original free charge compensation system on the surface of the thin film layer will become unbalanced, resulting in residual bound charges on the surface of the thin film layer that have not been fully compensated, generating a pyroelectric field.

[0020] The presence of periodic metal electrodes provides the thin film layer with a high density of transferable free charges, which can rapidly form a strong potential difference when heated or cooled, thereby generating a pyroelectric field of a certain intensity. When the intensity of the generated pyroelectric field is greater than the coercive field of the thin film layer and opposite to the spontaneous polarization direction of the thin film layer, the pyroelectric field can drive the spontaneous polarization direction of the corresponding region to reverse.

[0021] The region without the metal electrode covering relies solely on a small number of free ions in the environment for compensation, resulting in minimal charge change during heating or cooling. This insufficient charge difference prevents the formation of a sufficiently strong potential difference, thus maintaining the original polarization direction in this region. Therefore, the above method enables the fabrication of periodically polarized thin films with a periodic reverse domain structure.

[0022] This application utilizes a pyroelectric field generated by temperature changes to replace an external high-voltage electric field, thus eliminating the need for an external circuit to provide a polarization reversal voltage. Instead, it only requires utilizing the inherent pyroelectric properties of ferroelectric crystals and generating a pyroelectric field through temperature changes to achieve polarization reversal.

[0023] Compared to the externally applied electric field polarization method, the pyroelectric field in the fabrication of periodically polarized thin films via the pyroelectric effect exists only between the upper and lower surfaces of the film layer. In this case, since the pyroelectric field directly polarizes a film layer with a thickness ≤1 μm, only a voltage of tens of volts is required to achieve polarization reversal. Furthermore, the lower polarization reversal voltage can suppress the lateral broadening effect of the reverse domains, thereby enabling the fabrication of submicron periodic reverse domain structures. This allows for use in spontaneous parametric down-conversion processes for reverse propagation, generating narrow-linewidth quantum entangled light sources.

[0024] Meanwhile, the preparation process does not require signal generators, high-voltage amplifiers, oscilloscopes, or other equipment, nor does it require connecting the polarization electrode to an external circuit. It only requires temperature control equipment to regulate the temperature of the thin film structure, which is simple to operate and reduces production costs.

[0025] Furthermore, the preparation method provided in this application offers a high degree of freedom in adjusting the intensity of the pyroelectric field. By adjusting the oxygen content of the isolation layer, the isolation layer can be made to have different conductivity properties, thereby enabling the change and adjustment of the dissipation of pyroelectric charge, so as to finely adjust the pyroelectric field, achieve precise control of the domain structure, and improve the consistency of thin film performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram illustrating the principle of periodically polarized lithium niobate crystal using an external electric field method.

[0028] Figure 2 A process flow diagram of a method for preparing a periodically polarized thin film provided in this application embodiment;

[0029] Figure 3 A schematic diagram illustrating the formation of a lithium niobate single-crystal thin film provided in an embodiment of this application;

[0030] Figure 4 This is a schematic diagram of the temperature change processing provided in an embodiment of this application;

[0031] Figure 5 For ferroelectric lithium niobate crystals in Figure 4 A schematic diagram illustrating the principle of the internal pyroelectric effect under temperature change processing;

[0032] Figure 6 for Figure 5The temperature change curve corresponding to the temperature change processing provided in the document;

[0033] Figure 7 Another temperature change curve provided for an embodiment of this application;

[0034] Figure 8 This is a schematic diagram illustrating the formation of another lithium niobate single-crystal thin film provided in an embodiment of this application.

[0035] Explanation of reference numerals in the attached figures:

[0036] 100 - Support structure; 110 - Substrate layer; 120 - Isolation layer; 130 - Capture layer;

[0037] 200 - Ferroelectric crystal wafer; 210 - Thin film layer; 220 - Implanted layer; 230 - Residual mass layer. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0039] Electromagnetic waves profoundly influence modern society, finding wide application in areas such as information transmission, television broadcasting, mobile telecommunications, and Wi-Fi data access. Electromagnetic waves in the tens of gigahertz (GHz) range can be generated using electronic oscillators, corresponding to radio waves and microwave bands; millimeter waves and terahertz (THz) waves can be generated using resonant tunnel diodes, with frequencies ranging from tens of GHz to several THz; and even higher optical frequencies can be generated using solid-state and gas lasers, reaching frequencies on the picohertz scale.

[0040] However, these methods typically rely on fixed energy levels of specific materials, resulting in limited spectral coverage and often narrow spectral bandwidth. To overcome this limitation, scientists have proposed the "Nonlinear Frequency Mixing" method. This involves multi-wave mixing of optical frequencies using nonlinear optical effects to unlock previously unavailable electromagnetic frequencies as needed.

[0041] Phase matching is a core prerequisite and necessary condition for achieving high-efficiency nonlinear mixing. Methods for achieving phase matching include birefringence phase matching (BPM), mode phase matching (MPM), cyclic phase matching (CPM), and quasi-phase matching (QPM). Quasi-phase matching is widely used because it has no requirements on the direction of light transmission, polarization direction, or wavelength (theoretically, there are no matching limitations for any wavelength of light within the crystal's transmission range). It also provides a new approach to achieving phase matching for some crystals with excellent nonlinear properties but no birefringence (such as lithium tantalate).

[0042] Taking lithium niobate as an example of a nonlinear mixing material, periodic polarization is the most common and effective method for achieving quasi-phase matching on lithium niobate crystals.

[0043] In existing technologies, the external electric field polarization method is the most mainstream preparation technique for periodically polarized lithium niobate crystals or thin films. Figure 1 The principle of periodically polarized lithium niobate crystals using an external electric field method is demonstrated.

[0044] There are two polarization directions in lithium niobate crystals, due to Li + The position of the ion relative to the oxygen plane determines its polarization. When Li+ ions shift upwards along the +z direction towards the oxygen plane, it is called "upward polarization," while when they shift downwards along the -z direction towards the oxygen plane, it is called "downward polarization." Figure 1 As shown in (a), the spontaneous polarization direction of the single-domain lithium niobate crystal is along the +z direction of the crystal, i.e., "upward polarization".

[0045] When an external electric field higher than the crystal coercivity is applied to a single-domain lithium niobate crystal, for example, by applying a high-voltage electric field to the single-domain lithium niobate crystal through electrodes, Li can be made to... + When ions overcome the potential energy barrier of the oxygen plane and cross it to reach another stable state on the oxygen plane, Li can... + Ions "downward polarization," achieving polarization reversal, such as... Figure 1 As shown in (b) of the diagram.

[0046] The process flow for realizing periodically polarized lithium niobate crystals using the external electric field method includes the following steps:

[0047] First, periodic metal electrodes are fabricated on the upper surface (+z plane) of the z-cut lithium niobate crystal using processes such as ultraviolet lithography, electrode deposition, and lift-off. A fully covered electrode is similarly fabricated on the lower surface (-z plane) by metal deposition.

[0048] Then, a circuit is formed by connecting the upper and lower surface electrodes with wires, and external devices are connected. For example, a waveform generator can be connected to edit the required polarization voltage waveform, a high-voltage amplifier can be connected to amplify the polarization voltage, and a dual-channel oscilloscope can be connected to monitor the amplified polarization voltage signal and the current signal during the periodic polarization process in real time. Finally, periodic polarization is achieved by applying an external high voltage.

[0049] Compared to bulk dielectric lithium niobate crystals, the lithium niobate layer thickness in thin-film lithium niobate (TFLN) films is typically ≤1μm. Under the same coercive field, if the upper and lower electrodes are directly applied to the upper and lower surfaces of the lithium niobate film layer, the polarization reversal voltage of TFLN can be reduced from several kilovolts to tens of volts. This reduces the need for high-voltage amplifiers during periodic polarization, making operation more convenient and reducing equipment costs.

[0050] However, in practice, it is difficult to directly apply a voltage signal to the lower surface of the lithium niobate thin film. This requires adding a metal electrode to the lower surface of the lithium niobate layer and partially exposing it through a special process to allow connection to external circuits via wires. However, this not only increases the complexity of the process but also severely affects the yield of the TFLN thin film and disrupts the high refractive index contrast between the silicon dioxide and lithium niobate layers, making it impossible to form a strongly constrained optical waveguide structure.

[0051] Therefore, when using the external electric field method to periodically polarize TFLN thin films, the lower electrode is usually placed on the back side of the silicon substrate. Due to the influence of the silicon dioxide layer, the silicon substrate, and the bonding interface, the required inversion voltage is still as high as several hundred volts or even thousands of volts. This not only requires a high-voltage amplifier to amplify the voltage signal, increasing the cost and process complexity, but also the high polarization voltage may lead to a severe lateral broadening effect of the inversion domains, which is not conducive to the precise control of the duty cycle of the inversion domains.

[0052] In view of this, embodiments of this application provide a method for preparing a periodically polarized thin film, comprising: providing a substrate layer; forming an isolation layer on the substrate layer and adjusting the oxygen content of the isolation layer; forming a thin film layer and bonding the thin film layer to the isolation layer; forming periodically arranged metal electrodes on the surface of the thin film layer away from the isolation layer to obtain a thin film structure having periodically arranged metal electrodes; and subjecting the thin film structure having metal electrodes to a temperature change treatment to obtain a periodically polarized thin film having a periodically reversed domain structure.

[0053] At room temperature, the spontaneous polarization of a thin film structure generates a space charge field, which attracts free charges on the surface to compensate, thereby achieving a steady-state charge balance and making the thin film structure macroscopically electrically neutral. However, when subjected to temperature changes (such as heating or cooling), the spontaneous polarization intensity inside the thin film layer changes with the temperature. For example, the spontaneous polarization intensity (Ps) of the thin film layer decreases when heated and increases when cooled.

[0054] At this point, the original free charge compensation system on the surface of the thin film layer will become unbalanced, resulting in residual bound charges on the surface of the thin film layer that have not been fully compensated, generating a pyroelectric field.

[0055] The presence of periodic metal electrodes provides the thin film layer with a high density of transferable free charges, which can rapidly form a strong potential difference when heated or cooled, thereby generating a pyroelectric field of a certain intensity. When the intensity of the generated pyroelectric field is greater than the coercive field of the thin film layer and opposite to the spontaneous polarization direction of the thin film layer, the pyroelectric field can drive the spontaneous polarization direction of the corresponding region to reverse.

[0056] The region without the metal electrode covering relies solely on a small number of free ions in the environment for compensation, resulting in minimal charge change during heating or cooling. This insufficient charge difference prevents the formation of a sufficiently strong potential difference, thus maintaining the original polarization direction in this region. Therefore, the above method enables the fabrication of periodically polarized thin films with a periodic reverse domain structure.

[0057] This application utilizes a pyroelectric field generated by temperature changes to replace an external high-voltage electric field, thus eliminating the need for an external circuit to provide a polarization reversal voltage. Instead, it only requires utilizing the inherent pyroelectric properties of ferroelectric crystals and generating a pyroelectric field through temperature changes to achieve polarization reversal.

[0058] Compared to the externally applied electric field polarization method, the pyroelectric field in the fabrication of periodically polarized thin films via the pyroelectric effect exists only between the upper and lower surfaces of the film layer. In this case, since the pyroelectric field directly polarizes a film layer with a thickness ≤1 μm, only a voltage of tens of volts is required to achieve polarization reversal. Furthermore, the lower polarization reversal voltage can suppress the lateral broadening effect of the reverse domains, thereby enabling the fabrication of submicron periodic reverse domain structures. This allows for use in spontaneous parametric down-conversion processes for reverse propagation, generating narrow-linewidth quantum entangled light sources.

[0059] Meanwhile, the preparation process does not require signal generators, high-voltage amplifiers, oscilloscopes, or other equipment, nor does it require connecting the polarization electrode to an external circuit. It only requires temperature control equipment to regulate the temperature of the thin film structure, which is simple to operate and reduces production costs.

[0060] Furthermore, the preparation method provided in this application offers a high degree of freedom in adjusting the intensity of the pyroelectric field. By adjusting the oxygen content of the isolation layer, the isolation layer can be made to have different conductivity properties, thereby enabling the change and adjustment of the dissipation of pyroelectric charge, so as to finely adjust the pyroelectric field, achieve precise control of the domain structure, and improve the consistency of thin film performance.

[0061] The contents of this application will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can have a clearer and more detailed understanding of the contents of this application.

[0062] Figure 2 This is a process flow diagram of a method for preparing a periodically polarized thin film, provided in an embodiment of this application. Figure 3 This is a schematic diagram illustrating the formation of a lithium niobate single-crystal thin film according to an embodiment of this application.

[0063] Reference Figure 2 and Figure 3 As shown in the embodiment of this application, a method for preparing a periodically polarized thin film includes:

[0064] S100 provides a substrate layer.

[0065] The substrate layer 110 can be any one of a silicon (Si) substrate, a single-crystal alumina substrate, and a magnesium oxide (MgO) substrate. A silicon substrate is preferred.

[0066] S200: An isolation layer is formed on the substrate, and the oxygen content of the isolation layer is adjusted.

[0067] For example, the isolation layer 120 may be a silicon dioxide layer. It is understood that, as... Figure 3 As shown, the isolation layer 120 can be directly deposited on top of the substrate layer 110. In this case, the isolation layer 120 and the substrate layer 110 form a support structure 100. Alternatively, a functional structure can be provided between the substrate layer 110 and the isolation layer 120, and the isolation layer 120 can be formed on the substrate layer 110 through the functional structure. In this case, the isolation layer, the functional structure, and the substrate layer 110 together form a support structure. No specific limitations are made here.

[0068] By controlling the oxygen content of the isolation layer 120 (silicon dioxide layer), the conductivity of the isolation layer 120 can be adjusted, thereby controlling and changing the intensity of the pyroelectric field (described later) by adjusting the charge dissipation rate.

[0069] S300, forming a thin film layer and bonding the thin film layer to the isolation layer.

[0070] For example, the thin film layer 210 can be obtained by ion implantation of a ferroelectric crystal wafer 200. In this way, the formed thin film layer 210 is a ferroelectric material, serving as a carrier for spontaneous polarization and providing a material basis for polarization reversal. For example, the thin film layer 210 can be a lithium niobate thin film layer, a lithium tantalate thin film layer, a lead zirconate titanate thin film layer, etc., without specific limitations. For example, the thickness of the thin film layer 210 can be ≤1 μm.

[0071] Bonding the isolation layer 120 to the thin film layer 210 not only provides mechanical support for the extremely thin thin film layer 210 through the support structure 100 formed by the isolation layer 120 and the substrate layer 110, preventing warping, deformation, and cracking of the thin film layer 210 due to thermal expansion and contraction during temperature changes, but also achieves uniform heat conduction, allowing temperature changes to be transmitted synchronously and uniformly throughout the thin film layer 210, avoiding uneven electric field distribution caused by local temperature gradients, and ensuring the consistency of the domain structure.

[0072] S400. A periodically arranged metal electrode is formed on the surface of the thin film layer away from the isolation layer to obtain a thin film structure with a periodically arranged metal electrode.

[0073] By placing a metal electrode (not shown) on the upper surface of the thin film layer 210, the metal electrode can quickly accumulate or release free charges when the temperature changes, thereby forming a pyroelectric field with a certain intensity within the thin film layer 210.

[0074] The period, width, and spacing of the metal electrodes determine the spatial distribution period of the pyroelectric field, thus affecting the period and duty cycle range of the inverted domain structure. Understandably, the periodic arrangement of the metal electrodes can be adjusted according to the specific fabrication requirements of the periodically polarized thin film; therefore, no limitations are imposed here.

[0075] S500: Apply temperature change treatment to a thin film structure with metal electrodes to obtain a periodically polarized thin film with a periodic reverse domain structure.

[0076] Understandably, the thin film structure with metal electrodes can be placed on a temperature-controlled device such as a heating plate or a hot-cold stage. The heating plate or hot-cold stage contacts the bottom of the substrate layer 110, with the upper surface of the thin film layer 210 facing upwards and exposed to the air atmosphere. The heating plate or hot-cold stage allows for precise and uniform control of the temperature change of the thin film structure, causing a controllable abrupt change in the spontaneous polarization intensity of the thin film layer 210. This disrupts the charge balance, deposits residual bound charges, and forms a pyroelectric field.

[0077] At room temperature, the spontaneous polarization of the thin film structure generates a space charge field, which attracts free charges on the surface of the thin film layer 210 to compensate for the polarization, thereby achieving a steady-state charge balance and making the thin film structure macroscopically electrically neutral. However, when subjected to temperature changes (such as heating or cooling), the spontaneous polarization intensity inside the thin film layer 210 changes with the temperature. For example, the spontaneous polarization intensity Ps of the thin film layer 210 decreases when heated and increases when cooled.

[0078] At this point, the original free charge compensation system on the surface of the thin film layer 210 will become unbalanced, resulting in residual bound charges on the surface of the thin film layer 210 that are not fully compensated, thus generating a pyroelectric field. The presence of the periodic metal electrode provides the thin film layer 210 with a high density of transferable free charges, which can quickly form a strong potential difference when heated or cooled, thereby generating a pyroelectric field of a certain intensity.

[0079] When the electric field intensity in the region below the metal electrode exceeds the coercive field of the thin film structure at this temperature and is opposite to the initial spontaneous polarization direction of the thin film layer 210, the spontaneous polarization direction in that region can be reversed. Meanwhile, the electric field intensity in the region not covered by the metal electrode is lower than the coercive field, and the polarization direction remains in its initial state. Thus, a periodic reversed domain structure can be formed within the thin film layer 210.

[0080] In the above preparation method, the pyroelectric field generated by temperature change replaces the traditional externally applied high voltage electric field. Therefore, it is not necessary to provide polarization reversal voltage by external circuit. Instead, it is only necessary to utilize the inherent pyroelectric properties of ferroelectric crystals and generate a pyroelectric field by temperature change to achieve polarization reversal.

[0081] Compared to the externally applied electric field polarization method, in the fabrication of periodically polarized thin films via the pyroelectric effect, the pyroelectric field exists only between the upper and lower surfaces of the thin film layer 210. In this case, since the pyroelectric field directly polarizes the thin film layer 210 with a thickness ≤1μm, only a voltage of tens of volts is required to achieve polarization reversal. Furthermore, the lower polarization reversal voltage can suppress the lateral broadening effect of the reverse domains, thereby enabling the fabrication of submicron periodic reverse domain structures. This allows for use in the spontaneous parametric down-conversion process of reverse propagation, generating narrow-linewidth quantum entangled light sources.

[0082] Meanwhile, the preparation process does not require signal generators, high-voltage amplifiers, oscilloscopes, or other equipment, nor does it require connecting the polarization electrode to an external circuit. It only requires temperature control equipment to regulate the temperature of the thin film structure, which is simple to operate and reduces production costs.

[0083] Furthermore, the preparation method provided in this application offers a high degree of freedom in adjusting the intensity of the pyroelectric field. By adjusting the oxygen content of the isolation layer 120, the isolation layer 120 can be made to have different conductivity properties, thereby enabling the change and adjustment of the dissipation of pyroelectric charge, and thus allowing for fine-tuning of the pyroelectric field.

[0084] For example, the high oxygen content isolation layer 120 can form a high barrier to block the bound charges of the thin film layer 210, making it almost impossible for the charges to be transported to the substrate layer 110 and accumulate at the interface between the thin film layer 210 and the isolation layer 120. At this time, the charge accumulation density can reach the maximum value.

[0085] When the oxygen content of the isolation layer 120 is low, its resistivity decreases significantly. At this time, the bound charges generated by the thin film layer 210 can quickly flow through the isolation layer 120 to the substrate layer 110, and the amount of interface charge accumulation is greatly reduced, thereby enabling control over the reduction of the pyroelectric field strength.

[0086] It should be noted that the above preparation method is applicable at least to lithium niobate single crystal thin films and lithium tantalate single crystal thin films with a film layer thickness ≤ 1 μm, as well as all tangential directions except X-cut and Y-cut, such as Z, Y36, Y42, Y64, Y128, etc.

[0087] In one implementation, step S200, forming an isolation layer on the substrate and adjusting the oxygen content of the isolation layer, may include:

[0088] The oxygen content of the isolation layer 120 formed on the substrate 110 is adjusted by thermal oxidation method or plasma-enhanced chemical vapor deposition (PECVD).

[0089] Among these methods, thermal oxidation allows for the control of the oxygen content of the isolation layer 120 by adjusting parameters such as oxidation temperature, time, and atmosphere. Plasma-enhanced chemical vapor deposition allows for the deposition of isolation layers 120 with different oxygen contents on the substrate layer 110 by adjusting parameters such as the reactant gas ratio (e.g., SiH4:N2O), radio frequency power, and cavity pressure. Thus, isolation layers 120 with different oxygen contents can be flexibly prepared using various processes.

[0090] The resistivity of SiO2 layers prepared by thermal oxidation can reach 1E18 Ω·cm, while that prepared by PECVD (SiH4:N2O = 40:60) can reach 1E17 Ω·cm. Furthermore, as the SiH4 flux ratio increases, the oxygen content of the SiO2 layer gradually decreases, leading to improved conductivity. This improved conductivity of the SiO2 layer accelerates the charge dissipation rate on the lower surface of the lithium niobate layer, resulting in different pyroelectric field strengths.

[0091] For example, when the oxygen content of the isolation layer formed on the substrate is adjusted by plasma-enhanced chemical vapor deposition,

[0092] In plasma-enhanced chemical vapor deposition (PECVD) processes, the flow ratio of the reactive gas (SiH4) to nitrous oxide (N2O) is greater than or equal to 20:80 and less than or equal to 80:20.

[0093] For example, the flow ratio of the reactant gas (SiH4) to nitrous oxide (N2O) can be 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, or any combination of the above.

[0094] The above-mentioned flow ratio range can cover the full range of controllable conductivity of the isolation layer 120, adapting to the diverse needs of pyroelectric fields.

[0095] Figure 4 This is a schematic diagram of the temperature change processing provided in an embodiment of this application. Figure 5 For ferroelectric lithium niobate crystals in Figure 4 A schematic diagram illustrating the principle of the internal pyroelectric effect under temperature change processing is provided. Figure 6 for Figure 4 The temperature change curve provided in the software corresponds to the temperature change processing.

[0096] in, Figure 5 (a) in the diagram corresponds to the internal changes of a ferroelectric lithium niobate crystal at room temperature; Figure 5 (b) in the diagram represents the internal changes of the ferroelectric lithium niobate crystal under heated conditions. Figure 5 (c) in the diagram corresponds to the internal changes of the ferroelectric lithium niobate crystal under isothermal conditions; Figure 5 (d) in the diagram corresponds to the internal changes of the ferroelectric lithium niobate crystal under cooling conditions. It can be understood that the pyroelectric effect occurring inside the lithium niobate single crystal thin film can be inferred by referring to the principle of pyroelectric effect inside the ferroelectric lithium niobate crystal.

[0097] Reference Figure 4 As shown, in S500, applying a temperature change treatment to a thin film structure with metal electrodes may include:

[0098] S501. The thin film structure is heated, and the temperature of the thin film layer is raised from room temperature to the preset temperature within the first time.

[0099] Reference Figure 5 As shown, at room temperature, inside the ferroelectric lithium niobate crystal, Li + Ions and Nb 5+ The ions all exhibit a certain degree of displacement along the z-axis. Among them, Li... + The ion left the common face of the oxygen octahedron, Nb 5+ When ions leave the center of the oxygen octahedron, the symmetry on the z-axis is broken, the centers of positive and negative charges no longer overlap, an electric dipole moment is generated, and spontaneous polarization is formed.

[0100] This spontaneous polarization generates a space charge field, attracting free charges on the surface to compensate, thus resulting in overall electrical neutrality, such as... Figure 5 As shown in (a) of the diagram.

[0101] When the thin film structure is heated, the thermal energy of the ions increases, and Li + Ions and Nb 5+ Ions migrate towards the adjacent oxygen plane and the center of the oxygen octahedron, respectively, reducing the spontaneous polarization of the crystal and weakening the positive charge of the +z plane. This results in an excess of negative charge for charge balance, making the crystal planes negatively charged. Figure 5 As shown in (b) above. However, at this time, the direction of the generated pyroelectric field is the same as the spontaneous polarization direction of the lithium niobate crystal, and it cannot cause polarization reversal.

[0102] For example, as one implementation method, the above process can be carried out by... Figure 6 The heating curve L1 shown is achieved. At t=0, the initial temperature of the thin film structure is room temperature RT. At this time, the thin film structure can be continuously heated by a heating plate or a hot-cold stage to raise the temperature of the thin film layer 210 from room temperature RT to a preset temperature T0 within the first time period (0-t1 interval). At this time, the heating rate of the thin film layer 210 within the first time period is (T0-RT) / t1. The preset temperature T0 can be set as needed and is not limited here.

[0103] Since there are periodic metal electrodes on the surface of the thin film layer 210, and metal is a good conductor, excess compensation charge will be quickly transferred to the metal electrode in contact with it, thereby accumulating negative charge when heated, and the potential becomes negative.

[0104] It should be noted that the heating process can be continuous (as shown in L1) or segmented. No specific form of heating process is specified here.

[0105] S502. The thin film layer is kept at a preset temperature for a second time to make the surface of the thin film layer electrically neutral.

[0106] When the temperature is raised to a preset temperature T0 and kept constant, the surface free charges attracted by the space charge field will respond to the changes in spontaneous polarization inside the crystal, and eventually return to electrical neutrality on the crystal surface, such as... Figure 5 As shown in (c) in the figure.

[0107] This process can be achieved through Figure 6 The isothermal curve L2 shown is achieved. During the second time period (corresponding to the interval t1 to t2), the thin film layer 210 is kept at a constant temperature T0 to allow the surface of the thin film layer 210 to regain electrical neutrality. The isothermal time (t2-t1) here needs to be greater than the response time of the surface free charges to avoid the residual pyroelectric field partially compensating for the pyroelectric field generated during cooling, which would be in the opposite direction and thus reduce the strength of the pyroelectric field used for polarization reversal. During the isothermal process, a multimeter can be used to detect the potential difference between the upper surface of the TFLN thin film and the heating plate. When the potential difference drops to 0, it can be considered that the TFLN thin film as a whole has regained electrical neutrality.

[0108] S503. Cool the thin film structure and reduce the temperature of the thin film layer from the preset temperature to room temperature within a third time period.

[0109] When the thin film structure is cooled, the thermal energy of the ions decreases, and Li + Ions and Nb 5+ The ions are further away from the oxygen plane and the center of the oxygen octahedron, which enhances the spontaneous polarization of the crystal, and the +z plane exhibits positive charge, such as... Figure 5 As shown in (d) in the figure.

[0110] During cooling, the periodic metal electrodes on the surface of thin film layer 210 accumulate positive charges, causing their potential to become positive and thus generating a pyroelectric field with the -z plane of the crystal. The direction of this pyroelectric field is opposite to the spontaneous polarization direction of the lithium niobate crystal. During cooling, polarization reversal occurs when the intensity of the pyroelectric field exceeds the coercive field of the lithium niobate crystal.

[0111] This process can be achieved through Figure 6 The cooling curve L3 shown is achieved. During the third time period (corresponding to the interval t2 to t3), the thin film layer 210 cools back from the preset temperature T0 to room temperature RT. At this time, the cooling rate of the thin film layer 210 during the third time period is (T0-RT) / (t3-t2). During this process, a pyroelectric field with the opposite polarization direction to the spontaneous polarization direction of the lithium niobate crystal and a field strength greater than the coercive field can be generated in the thin film layer 210 to drive polarization reversal in the region below the metal electrode.

[0112] In this way, through the combined temperature change treatment of heating, isothermal and cooling, the region corresponding to the metal electrode in the thin film layer 210 can achieve polarization reversal during the cooling process, while the part not covered by the metal electrode still maintains the original polarization direction, thereby obtaining a periodically polarized thin film with a periodic reverse domain structure at room temperature.

[0113] In one embodiment, the periodic inverted domain structure may include a plurality of alternately arranged inverted domain regions and non-inverted domain regions. The sum of the widths of a set of adjacent inverted domain regions and non-inverted domain regions constitutes the polarization period, which is greater than or equal to 1 μm and less than or equal to 20 μm.

[0114] For example, the polarization period can be 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, or any combination of both, to meet the polarization period requirements of practical nonlinear optical mixing designs.

[0115] As one implementation method, the preset temperature can be greater than or equal to 100°C and less than or equal to 300°C.

[0116] For example, the preset temperature T0 can be 100℃, 120℃, 150℃, 180℃, 200℃, 220℃, 250℃, 280℃, 300℃, or any range of both. This setting balances the polarization reversal voltage and the maximum operating temperature of the thin film.

[0117] It is understandable that changing the preset temperature T0 can adjust the amount of temperature change, as well as the intensity of the pyroelectric field, thus determining the magnitude of the pyroelectric voltage.

[0118] Since this application can adjust the conductivity of the isolation layer 120 by adjusting the oxygen content of the isolation layer 120, thereby adjusting the charge dissipation rate, the preset temperature T0 and the cooling rate can be kept constant, and different pyroelectric field strengths can be obtained by only using the oxygen content of the isolation layer 120 as a variable.

[0119] For example, the heating rate and cooling rate can both be set to 5℃ / min, the second time period (constant temperature time) can be set to 2hrs, and the preset temperature T0 can be set to 200℃, and temperature change processing can be performed on it.

[0120] Understandably, depending on different design requirements, the oxygen content and temperature change of the isolation layer 120 can also be adjusted simultaneously, and no limitation is made here.

[0121] In one embodiment, the cooling rate of the thin film layer 210 during the third time period can be greater than or equal to 1°C / min and less than or equal to 10°C / min.

[0122] For example, the cooling rate of the thin film layer 210 during the third time period can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any combination of the above.

[0123] Similarly, the heating rate of the thin film layer 210 during the first time period can be greater than or equal to 1 °C / min and less than or equal to 10 °C / min.

[0124] For example, the heating rate of the thin film layer 210 during the first time period can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, or any combination of the above.

[0125] It is understandable that, since TFLN film is a composite multilayer material, each layer has a different coefficient of thermal expansion. If drastic temperature changes are used, large stress or strain may be generated. Therefore, by setting the heating and cooling rates within a reasonable range, the film structure can be prevented from cracking during the heating and cooling process.

[0126] Furthermore, the polarization reversal process occurs in the third time period (corresponding to the interval from t2 to t3). By extending the cooling time, i.e. reducing the cooling rate, the dissipation of pyroelectric charge to the surrounding environment can also be increased, thereby reducing the intensity of the pyroelectric field and achieving regulation of the intensity of the pyroelectric field.

[0127] Similarly, since this application can adjust the conductivity of the isolation layer 120 by adjusting the oxygen content of the isolation layer 120, and consequently adjust the ability of pyroelectric charge to dissipate to the surrounding environment, different pyroelectric field strengths can be obtained by maintaining the same cooling rate and using only the oxygen content of the isolation layer 120 as a variable.

[0128] Understandably, depending on different design requirements, the oxygen content and cooling rate of the isolation layer 120 can be adjusted simultaneously, or the oxygen content, temperature change, and cooling rate of the isolation layer 120 can be adjusted simultaneously, and no limitation is made here.

[0129] Figure 7 Another temperature change curve provided for an embodiment of this application.

[0130] In another embodiment, S501, heating the thin film structure and raising the temperature of the thin film layer from room temperature to a preset temperature within a first time period, may include:

[0131] The temperature of the thin film layer is increased from room temperature to a preset temperature through a stepwise heating curve. The stepwise heating curve includes n heating segments and n-1 isothermal segments.

[0132] The isothermal segment is connected between two adjacent heating segments. The sum of the heating duration of each heating segment and the isothermal duration of each isothermal segment constitutes the first time period. The sum of the temperature differences of each heating segment is the difference between the preset temperature and the room temperature.

[0133] Heating can be achieved through gradual, step-by-step heating. For example, refer to... Figure 7 As shown, n can be equal to 3, and the segmented heating curve can include 3 heating segments and 2 isothermal segments. An isothermal segment is placed between two adjacent heating segments to allow the thin film layer 210 to respond to polarization abrupt changes caused by heating. Similarly, the potential difference between the upper surface of the thin film layer 210 and the heating plate can be measured using a multimeter. When the potential difference drops to 0, it can be considered that the thin film layer 210 has returned to electrical neutrality overall.

[0134] The sum of the temperature differences in each heating segment is the temperature change T0 - RT. For example, Figure 7 The temperature difference in the first heating segment is A1, the temperature difference in the second heating segment is A2, and the temperature difference in the third heating segment is A3. A1 + A2 + A3 = T0 - RT. The heating duration of each heating segment and the isothermal duration of each isothermal segment constitute the first time period.

[0135] It should be noted that during the segmented heating process, the temperature difference between each heating segment can be the same or different, and the heating rate of each segment can be the same or different, which can be set according to specific needs. Furthermore, the number of heating segments can be reasonably set according to the temperature change, as long as n is an integer greater than 1.

[0136] At this point, the first time period corresponds to the interval 0-t1'. The second time period corresponds to the interval t1'-t2. The third time period still corresponds to the interval t2-t3. It is understandable that... Figure 6 Compared to continuous heating processes, due to Figure 7 The step-by-step heating process used in the process, when Figure 6 and Figure 7 When the same heating rate is used, Figure 7 The value of t1' in the equation is clearly greater than 1 / 2. Figure 6 The t1 value is given. Since the overall temperature change T0-RT has not changed, the t2 values ​​for both remain the same, thus not affecting the subsequent third time period.

[0137] Because the thermal expansion coefficients of the thin film layer 210, the isolation layer 120, and the substrate layer 110 are significantly different, continuous rapid heating may cause a sharp accumulation of interfacial stress, leading to problems such as cracking of the thin film layer 210 or peeling off from the isolation layer 120.

[0138] By employing a segmented heating method, the isothermal period between adjacent heating segments allows the thermal expansion of each layer to gradually reach equilibrium, releasing interfacial stress and ensuring the integrity of the thin film structure. Simultaneously, this design also reduces the duration of the second time period, decomposing the original isothermal response time into the preceding heating process, thus preventing the second time period from becoming excessively long when temperature changes are significant.

[0139] Continue to refer to Figure 3 As shown, in one embodiment, step S300, forming a thin film layer and bonding the thin film layer to the isolation layer, may include:

[0140] A ferroelectric crystal wafer is provided, and ion implantation is performed on the ferroelectric crystal wafer to form an implanted wafer. The implanted wafer may include a residual mass layer, an implanted layer, and a thin film layer stacked together. The bonding thin film layer and the isolation layer form a bond.

[0141] Reference Figure 3 As shown, at this time, the upper surface of the thin film layer 210 is covered by the implanted layer 220 and the residual layer 230. The lower surface of the thin film layer 210 can be bonded to the upper surface of the insulating layer 120. It should be noted that the ion implantation method is not limited here, and any ion implantation method in the prior art can be used to perform ion implantation on the ferroelectric crystal wafer 200. Furthermore, the implanted ions can be any ions that can generate gas through heat treatment, such as hydrogen ions, helium ions, nitrogen ions, oxygen ions, or argon ions.

[0142] Furthermore, this application can use any bonding method in the prior art to achieve the bonding of the thin film layer 210 and the isolation layer 120. For example, the process surfaces of the thin film layer 210 and the isolation layer 120 can be surface activated, and then the two activated surfaces can be bonded to obtain a bonded body.

[0143] As one implementation, before forming periodically arranged metal electrodes on the surface of the thin film layer away from the insulating layer, the fabrication method further includes:

[0144] The bond is subjected to heat treatment to remove the implanted layer and residual mass layer, resulting in a thin film structure. The thin film structure comprises a thin film layer, an isolation layer, and a substrate layer stacked sequentially.

[0145] For example, a thin film structure can be obtained by removing the implanted layer 220 and the residual mass layer 230 through annealing. The bond body is subjected to annealing heat treatment, and the heat treatment process can be in the range of 180℃-600℃ for 1-100 hours. During the heat treatment, bubbles are formed in the implanted layer 220, for example, H ions form hydrogen gas, He ions form helium gas, etc. As the heat treatment progresses, the bubbles in the implanted layer 220 merge together, and finally the implanted layer 220 cracks, separating the residual mass layer 230 from the thin film layer 210, thereby peeling the residual mass layer 230 off the bond body and forming the thin film layer 210 on the top surface of the treated substrate.

[0146] In other embodiments, reference is made to Figure 8 As shown, a trapping layer 130 can be formed between the substrate layer 110 and the isolation layer 120 to reduce the radio frequency loss of the thin film.

[0147] At this time, a trapping layer 130 can be formed on top of the substrate layer 110, and an isolation layer 120 can be deposited on top of the trapping layer 130 to obtain the support structure 100. At this time, the support structure 100 includes the isolation layer 120, the trapping layer 130 and the substrate layer 110 stacked together.

[0148] The material of the trapping layer 130 can be selected from at least one of polycrystalline silicon, amorphous silicon, or polycrystalline germanium. The trapping layer 130 can be formed by depositing polycrystalline silicon, depositing amorphous silicon, depositing polycrystalline germanium, etching the substrate layer 110, or implanting the substrate layer 110 to generate implantation damage.

[0149] The thin film layer 210 is then bonded to the isolation layer 120 to form a bonded body, and the implantation layer 220 and the residual layer 230 are removed by annealing and peeling to obtain the thin film structure.

[0150] Because the trapping layer 130 has a certain density of lattice defects, it can trap the charge carriers existing between the isolation layer 120 and the substrate layer 110, and prevent these charge carriers from causing the charge carriers to accumulate at the interface between the isolation layer 120 and the substrate layer 110, thereby reducing the radio frequency loss of the thin film.

[0151] It is understood that the provided ferroelectric crystal wafer 200 can be a single crystal wafer, a single crystal doped wafer, or a bonded combination of single crystal wafers and single crystal doped wafers.

[0152] When the ferroelectric crystal wafer 200 is a bond between a single crystal wafer and a single crystal doped wafer, for example, a lithium niobate single crystal wafer and a lithium niobate doped wafer arranged in parallel can be bonded to prepare a composite TFLN thin film, and the formation process can refer to the above process.

[0153] In one implementation, S400, forming periodically arranged metal electrodes on the surface of the thin film layer away from the insulating layer, may include:

[0154] S401. A periodically arranged photoresist pattern is formed on the surface of the thin film layer away from the isolation layer.

[0155] For example, a layer of positive ultraviolet photoresist can be coated on the upper surface of the cleaned thin film layer 210 using a spin coater. The thickness of the photoresist is generally greater than 1 μm, and the thickness of the photoresist is at least 1.5 times the thickness of the metal electrode.

[0156] Pre-baking the UV photoresist using a heating plate or oven evaporates the organic solvent components, allowing the photoresist to cure. The pre-baking temperature and time are set according to different photoresists.

[0157] A photomask with a periodically arranged pattern is provided. The sample is exposed using an ultraviolet lithography machine. Ultraviolet light shines through the transparent window on the photomask onto the photoresist, causing the photoresist to denature and thus be dissolved by the developer during the subsequent development process. The photoresist that is not exposed to ultraviolet light due to the pattern on the photomask is retained after development.

[0158] High-temperature baking is used to harden the patterned photoresist formed after development, so that the photoresist can adhere more firmly to the wafer surface and enhance the photoresist's resistance to etching. The hardening temperature is usually slightly higher than the pre-baking temperature.

[0159] S402, Deposit metal on the surface of a thin film layer with a photoresist pattern.

[0160] A metal electrode is deposited on the surface of a periodically arranged photoresist pattern using methods such as electron beam evaporation and magnetron sputtering.

[0161] S403. Strip the photoresist pattern and the metal covering the photoresist pattern to obtain a thin film structure with periodically arranged metal electrodes.

[0162] Metal electrode liftoff is performed using specialized resist removers such as acetone and NMP. The metal deposited on the photoresist surface is removed as the photoresist dissolves, while the metal electrode directly deposited on the surface of thin film layer 210 is retained, thus forming a periodic metal electrode pattern consistent with the pattern on the photomask.

[0163] In some embodiments, the material of the metal electrode can be any one of Au, Al, Cr, and Ti. This allows the metal electrode to have good electrical conductivity.

[0164] The thickness of the metal electrode can be greater than or equal to 100 nm and less than or equal to 1000 nm. For example, the thickness of the metal electrode can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or any combination of both. This ensures the conductivity of the metal electrode.

[0165] Considering the potential lateral broadening effect of reversed domains, the width of the metal electrode can be set to 40%~50% of the polarization period, that is, the width of the metal electrode is greater than or equal to 0.4μm and less than or equal to 10μm.

[0166] In some embodiments, before obtaining a periodically polarized thin film with a periodic reverse domain structure after subjecting the thin film structure with metal electrodes to a temperature change treatment, the preparation method further includes:

[0167] Remove the metal electrode formed on the surface of the thin film layer away from the isolation layer.

[0168] After the inverted domain structure is formed within the thin film layer 210, the metal electrode can be removed using wet etching technology to obtain a periodically polarized thin film. The inverted domain structure can be non-destructively inspected using piezoelectric microscopy (PFM).

[0169] It should be noted that the embodiments referred to in the specification, such as "one embodiment," "embodiment," "exemplary embodiment," and "some embodiments," may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0170] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "one" can be understood to convey either singular or plural usage.

[0171] It should be readily understood that the terms “on,” “above,” and “on top of” in this application should be interpreted in the broadest possible sense, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on something” but also “on something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0172] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90° or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0173] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a periodically polarized thin film, characterized in that, include: Provide a substrate layer; An isolation layer is formed on the substrate layer, and the oxygen content of the isolation layer is adjusted. A thin film layer is formed and the thin film layer is bonded to the isolation layer; A periodically arranged metal electrode is formed on the surface of the thin film layer away from the insulating layer to obtain a thin film structure with a periodically arranged metal electrode. By subjecting the thin film structure with the metal electrode to a temperature change treatment, a periodically polarized thin film with a periodic reverse domain structure is obtained.

2. The method for preparing periodically polarized thin films according to claim 1, characterized in that, Forming an isolation layer on the substrate and adjusting the oxygen content of the isolation layer includes: The oxygen content of the isolation layer formed on the substrate is adjusted by thermal oxidation or plasma-enhanced chemical vapor deposition.

3. The method for preparing periodically polarized thin films according to claim 2, characterized in that, When the oxygen content of the isolation layer formed on the substrate is adjusted by plasma-enhanced chemical vapor deposition... In plasma-enhanced chemical vapor deposition (PECVD) processes, the flow ratio of reactant gas to nitrous oxide is greater than or equal to 20:80 and less than or equal to 80:

20.

4. The method for preparing periodically polarized thin films according to claim 1, characterized in that, The periodic reverse domain structure includes multiple alternately arranged reverse domain regions and non-reverse domain regions; The sum of the widths of a group of adjacent inverted domain regions and non-inverted domain regions is the polarization period, which is greater than or equal to 1 μm and less than or equal to 20 μm.

5. The method for preparing periodically polarized thin films according to claim 1, characterized in that, The temperature change treatment applied to the thin film structure having the metal electrode includes: The thin film structure is heated, and the temperature of the thin film layer is raised from room temperature to a preset temperature within a first time. The thin film layer is held at the preset temperature for a second time to make the surface of the thin film layer electrically neutral. The thin film structure is cooled down, and the temperature of the thin film layer is reduced from a preset temperature to room temperature within a third time period.

6. The method for preparing periodically polarized thin films according to claim 5, characterized in that, The preset temperature is greater than or equal to 100℃ and less than or equal to 300℃; and / or, The cooling rate of the thin film layer during the third time period is greater than or equal to 1°C / min and less than or equal to 10°C / min; and / or, The heating rate of the thin film layer during the first time period is greater than or equal to 1°C / min and less than or equal to 10°C / min.

7. The method for preparing periodically polarized thin films according to claim 1, characterized in that, Forming a thin film layer and bonding the thin film layer to the isolation layer includes: A ferroelectric crystal wafer is provided, and the ferroelectric crystal wafer is ion implanted to form an implanted wafer; the implanted wafer includes a residual mass layer, an implanted layer, and a thin film layer stacked together. The thin film layer and the isolation layer are bonded to form a bonded body.

8. The method for preparing periodically polarized thin films according to claim 7, characterized in that, Before forming periodically arranged metal electrodes on the surface of the thin film layer opposite to the insulating layer, the method further includes: The bond is subjected to heat treatment to remove the implantation layer and the residual material layer, and a thin film structure is obtained; the thin film structure includes the thin film layer, the isolation layer and the substrate layer stacked in sequence.

9. The method for preparing periodically polarized thin films according to claim 8, characterized in that, A periodically arranged metal electrode is formed on the surface of the thin film layer opposite to the insulating layer, comprising: A periodically arranged photoresist pattern is formed on the surface of the thin film layer opposite to the isolation layer; Metal is deposited on the surface of the thin film layer having the photoresist pattern; The photoresist pattern and the metal covering the photoresist pattern are stripped to obtain a thin film structure with periodically arranged metal electrodes.

10. The method for preparing periodically polarized thin films according to claim 1, characterized in that, Before obtaining a periodically polarized thin film with a periodic reverse domain structure after subjecting the thin film structure having the metal electrode to a temperature change treatment, the method further includes: Remove the metal electrode formed on the surface of the thin film layer opposite to the insulating layer.

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