Temperature field structure for growth of X-cut lithium niobate crystal

Abstract

The utility model discloses a thermal field structure for X-cut lithium niobate crystal growth, the X-axis is defined to extend upwards, the thermal field structure comprises a thermal insulation structure and a crucible, both the thermal insulation structure and the crucible are elliptical cylinders with open upper ends and closed lower ends, when the thermal field structure is used, the crucible is placed in the thermal insulation structure, the central axes of the crucible and the thermal insulation structure coincide, and the central axes of the crucible and the thermal insulation structure coincide. The heat preservation structure is provided with a long axis a1 and a short axis b1, the crucible is provided with a long axis a2 and a short axis b2, the long axis of the heat preservation structure and the long axis of the crucible both extend in the Y-axis direction, the short axis of the heat preservation structure and the short axis of the crucible both extend in the Z-axis direction, and the grown lithium niobate crystal is an elliptic cylinder. According to the utility model, the problem that the crystal is easy to crack in the prior art is solved, and the success rate of the growth of the X-axis lithium niobate crystal is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of crystal growth, in particular to a temperature field structure for growing X-cut lithium niobate crystals. Background Art

[0002] Lithium niobate crystals have attracted widespread attention from researchers due to their excellent electro-optical effect, virtually unlimited intrinsic modulation bandwidth, low optical insertion loss, low transmission power consumption, and excellent device stability. Integrated optical circuits based on lithium niobate single crystal thin films have surpassed the key performance parameters of traditional titanium diffusion and proton exchange waveguides, such as transmission loss and optical confinement. Scientists have already achieved various active and passive integrated optoelectronic devices with ultra-low transmission loss, ultra-low half-wave voltage, and ultra-compact size in the laboratory.

[0003] Lithium niobate single crystal thin film is peeled off from lithium niobate wafer. Lithium niobate crystal belongs to the trigonal system. The largest component γ in the electro-optic coefficient matrix is 33 ~30.9 pm / V@632 nm, to achieve on-chip integration of lithium niobate, an X-axis wafer is required, waveguide coplanar electrodes are used, and an electric field is applied along the Z axis of the crystal to utilize the electro-optic effect γ 33 weight; on the other hand, the preparation of integrated chips requires semiconductor micromachining technology. The current mainstream semiconductor production line is 8 inches, so the 8-inch X-axis lithium niobate crystal is the cornerstone of the integrated optoelectronic chip industry chain.

[0004] However, the X-axis is not a rotationally symmetric axis, and the growth rates of each crystal plane on the growth interface vary, making it the most challenging direction to grow. For a long time, China has only been able to provide a small number of 3-inch and 4-inch X-axis lithium niobate crystals, and some still use the technical route of horizontally hollowing out small X-axis crystal rods from large Z-axis crystals. Especially as crystal size increases, the horizontal hollowing technology becomes increasingly unfeasible. Therefore, breakthroughs in key technologies for the industrialization of large-scale X-axis lithium niobate crystals are a key foundation for building an integrated optoelectronic chip industry chain.

[0005] The growth of X-axis lithium niobate crystals is carried out in a temperature field structure, which includes a crucible and an insulation structure. The insulation structure and crucible of the existing temperature field structure are cylindrical, and a small hole is opened on one side of the insulation structure to observe the growth situation. At the same time, crystal rotation or crucible rotation and pulling are applied. This is to increase forced convection and ensure the uniformity of the entire temperature gradient distribution. The obtained lithium niobate crystal is cylindrical.

[0006] Since existing temperature field structures are most commonly used to grow Z-axis lithium niobate crystals, and lithium niobate crystals grown along the Z-axis are isotropic, meaning that the various properties and growth rates along the X-axis and Y-axis directions are not much different, a completely symmetrical insulation structure provides an isotropic temperature distribution, which is very consistent with the characteristics of Z-axis crystals, thus significantly improving crystal quality. However, using existing temperature field structures to grow X-axis lithium niobate crystals, due to the different growth rates of X-axis lithium niobate crystals in different directions, the traditional cylindrical symmetrical insulation structure and crucible are no longer suitable for X-axis crystal growth. When pulling lithium niobate crystals along the X-axis, due to the large difference in growth rates between the Z-axis and Y-axis directions, anisotropic nucleation and twinning are very likely to occur during the growth process. This is also accompanied by high thermal stress and crystal cracking, resulting in an extremely low crystal growth success rate and difficulty in industrial production. Utility Model Content

[0007] The embodiment of the utility model provides a temperature field structure for growing X-cut lithium niobate crystals to solve the technical problem in the prior art that X-axis lithium niobate crystals grown are prone to anisotropic nucleation, twinning, and crystal cracking, resulting in a low success rate of crystal growth.

[0008] The present invention provides a temperature field structure for growing X-cut lithium niobate crystals:

[0009] A temperature field structure for growing an X-cut lithium niobate crystal, the temperature field structure being used for growing an X-axis lithium niobate crystal, wherein the X-axis is defined to extend upward, the temperature field structure comprising a heat preservation structure (1) and a crucible (2), the heat preservation structure (1) and the crucible (2) both being elliptical cylinders with an open upper end and a closed lower end, and when in use, the crucible (2) is placed in the heat preservation structure (1), the central axes of the crucible (2) and the heat preservation structure (1) coincide, the heat preservation structure (1) having a major axis a1 and a minor axis b1, the crucible (2) having a major axis a2 and a minor axis b2, the major axis of the heat preservation structure (1) and the major axis of the crucible (2) both extending in the Y-axis direction, and the minor axis of the heat preservation structure (1) and the minor axis of the crucible (2) both extending in the Z-axis direction, so that the grown lithium niobate crystal is an elliptical cylinder.

[0010] Furthermore, the ratio of the major axis a1 to the minor axis b1 of the heat-insulating structure (1) is equal to the ratio of the major axis a2 to the minor axis b2 of the crucible (2).

[0011] Furthermore, the ratio of the major axis a1 to the minor axis b1 of the thermal insulation structure (1) is d, and 1.1≤d≤1.5.

[0012] Furthermore, the difference between the long axis of the heat-insulating structure (1) and the long axis of the crucible (2) is a=a1-a2, 2cm≤a≤5cm.

[0013] Furthermore, the thermal insulation structure (1) comprises an elliptical cylinder and a cylinder bottom connected to the lower end of the cylinder, the cylinder comprising a quartz layer (11), a thermal insulation cotton layer (12) and a corundum layer (13), and the cylinder bottom comprising a thermal insulation cotton layer (12) and a zircon sand layer (14).

[0014] Furthermore, the quartz layer (11), the thermal insulation cotton layer (12), and the corundum layer (13) of the cylinder are sequentially arranged from the outside of the cylinder to the inside of the cylinder, and the cylinder bottom includes two layers of thermal insulation cotton layers (12) and two layers of zircon sand layers (14), the lowermost layer of the cylinder bottom is the thermal insulation cotton layer (12), and the uppermost layer is the zircon sand layer (14), and the thermal insulation cotton layer (12) and the zircon sand layer (14) of the cylinder bottom are alternately arranged.

[0015] The beneficial effects of the present invention are as follows: the present invention takes into account the growth habits of X-axis lithium niobate crystals and designs a temperature field structure suitable for the growth of X-axis crystals. By setting the heat preservation structure and the crucible in the temperature field structure as elliptical cylindrical structures, and allowing the long axes of the heat preservation structure and the crucible to extend along the Y-axis growth direction of the lithium niobate crystal, and the short axes to extend along the Z-axis growth direction of the lithium niobate crystal, the larger long axis and the smaller short axis can respectively match the faster growth rate of the lithium niobate crystal on the Y-axis and the slower growth rate on the Z-axis, so that the grown X-axis lithium niobate crystals grow naturally without being squeezed, and the grown lithium niobate crystals are in the shape of an elliptical cylinder. The internal density distribution of the lithium niobate crystals in the elliptical cylinder shape is uniform, and anisotropic nucleation and twinning phenomena are not likely to occur. At the same time, the crystals are not likely to crack, thereby improving the success rate of crystal growth.

[0016] In addition, the utility model formulates the major and minor axis ratio parameters of the elliptical insulation structure and the crucible structure according to the characteristics of lithium niobate crystal growth, ensuring the stable growth of the X-axis crystal under controllable conditions as much as possible, reducing the possibility of anisotropic nucleation of the X-axis crystal, reducing the risk of polycrystal and cracking, and improving the yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 This is a top view of a temperature field structure for growing an X-cut lithium niobate crystal in one embodiment of the present invention;

[0019] Figure 2This is an AA cross-sectional schematic diagram of a temperature field structure for growing an X-cut lithium niobate crystal in one embodiment of the present invention;

[0020] In the figure: 1. Insulation structure; 11. Quartz layer; 12. Insulation cotton layer; 13. Corundum layer; 14. Zirconium sand layer; 2. Crucible; 3. Lithium niobate crystal. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0022] In the description of the present invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0023] In the description of this utility model, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0024] Embodiment 1 of the utility model of a temperature field structure for growing X-cut lithium niobate crystals, such as Figures 1 to 2As shown, this temperature field structure is used to grow X-axis lithium niobate crystals, with the X-axis extending upward. The lithium niobate crystal 3 grown using this temperature field structure is an elliptical cylinder. The temperature field structure includes a heat-insulating structure 1 and a crucible 2. Both the heat-insulating structure 1 and the crucible 2 are elliptical cylinders with an open upper end and a closed lower end. During use, the crucible 2 is placed within the heat-insulating structure 1, with the central axes of the crucible 2 and the heat-insulating structure 1 coinciding. The heat-insulating structure 1 has a major axis a1 and a minor axis b1, and the crucible 2 has a major axis a2 and a minor axis b2. The major axes of the heat-insulating structure 1 and the crucible 2 both extend along the Y-axis, and the minor axes of the heat-insulating structure 1 and the crucible 2 both extend along the Z-axis.

[0025] like Figure 1 and Figure 2 As shown, the thermal insulation structure 1 includes an elliptical cylinder and a cylinder bottom connected to the lower end of the cylinder, and the cylinder bottom is an ellipse with the same size as the cross-section of the cylinder. The cylinder includes a quartz layer 11, a thermal insulation cotton layer 12 and a corundum layer 13, and the cylinder bottom includes a thermal insulation cotton layer 12 and a zircon sand layer 14. Specifically, the quartz layer 11, the thermal insulation cotton layer 12 and the corundum layer 13 of the cylinder are arranged in sequence from the outside of the cylinder to the inside of the cylinder, and the cylinder bottom includes two layers of thermal insulation cotton layers 12 and two layers of zircon sand layers 14. The bottom layer of the cylinder bottom is the thermal insulation cotton layer 12, and the top layer is the zircon sand layer 14. The thermal insulation cotton layer 12 and the zircon sand layer 14 of the cylinder bottom are arranged alternately. In other embodiments of the present utility model, the thermal insulation structure 1 can be set with the number of layers, as well as the material and thickness of each layer of the structure according to actual needs.

[0026] The crucible 2 is a platinum crucible 2. The structure of the crucible 2 differs from that of conventional platinum crucibles 2 only in its cross-sectional shape: the prior art crucibles 2 are cylindrical, while the present invention has an elliptical cylindrical crucible 2. The crucible 2 comprises an annular crucible body and a bottom connected to the lower end of the annular crucible body. In the present invention, the cross-sectional shape of the annular crucible body is elliptical.

[0027] In this embodiment, the ratio of the major axis a1 to the minor axis b1 of the heat preservation structure 1 is equal to the ratio of the major axis a2 to the minor axis b2 of the crucible 2. The ratio of the major axis a1 to the minor axis b1 of the heat preservation structure 1 is d, and 1.1≤d≤1.5. For the X-axis lithium niobate crystal growth method, d=1.2 is preferred. Of course, in other embodiments, a reasonable value of d can be set according to the growth conditions of lithium niobate crystals under different growth environments. The growth rate of the X-axis lithium niobate crystal along the Y axis is V Y , the growth rate along the Z axis is V z ,d=V Y :V Z .

[0028] In this embodiment, the difference a between the long axis of the heat-insulating structure 1 and the long axis of the crucible 2 is a1-a2, 2cm≤a≤5cm. In other embodiments, the required difference a can be set according to the growth conditions of the lithium niobate crystal.

[0029] The utility model discloses an X-cut lithium niobate crystal growth method. The growth method adopts the above-mentioned temperature field structure for growing X-cut lithium niobate crystals. The X-axis lithium niobate crystal grown by this growth method is an elliptical cylinder, the central axis of the elliptical cylinder extending along the X-axis, and the cross-section of the elliptical cylinder lithium niobate crystal perpendicular to the X-axis is an ellipse, with the major axis of the ellipse being a and the minor axis being b. That is, the major axis of the elliptical cylinder lithium niobate crystal is a, and the minor axis is b. Here, the X-axis is defined as extending upward.

[0030] The heat field structure used in the method includes a heat-insulating structure 1 and a crucible 2. The heat-insulating structure 1 and the crucible 2 are both elliptical cylinders with an open upper end and a closed lower end. When in use, the crucible 2 is placed in the heat-insulating structure 1, and the central axes of the crucible 2 and the heat-insulating structure 1 coincide with each other. The heat-insulating structure 1 has a major axis a1 and a minor axis b1, and the crucible 2 has a major axis a2 and a minor axis b2. The major axis of the heat-insulating structure 1 and the major axis of the crucible 2 both extend along the Y-axis direction, and the minor axis of the heat-insulating structure 1 and the minor axis of the crucible 2 both extend along the Z-axis direction. The lithium niobate crystal grown by the X-cut lithium niobate crystal growth method is an elliptical cylinder.

[0031] In this method, the ratio of the long axis a1 to the short axis b1 of the heat-insulating structure 1 is equal to the ratio of the long axis a2 to the short axis b2 of the crucible 2. The ratio of the long axis a1 to the short axis b1 of the heat-insulating structure 1 is d, and 1.1≤d≤1.5. For the X-axis lithium niobate crystal growth method, d=1.2 is preferred. Of course, in other embodiments, a reasonable value of d can be set according to the growth conditions of the lithium niobate crystal under different growth environments. The growth rate of the X-axis lithium niobate crystal along the Y axis is V Y , the growth rate along the Z axis is V z ,d=V Y :V Z .

[0032] In this method, the heat-insulating structure 1 comprises an elliptical cylinder and a cylinder bottom connected to the lower end of the cylinder, wherein the cylinder bottom is an elliptical shape having the same size as the cross section of the cylinder. Figures 1 to 2As shown, the cylinder includes a quartz layer 11, a thermal insulation cotton layer 12 and a corundum layer 13, and the cylinder bottom includes a thermal insulation cotton layer 12 and a zircon sand layer 14. Specifically, the quartz layer 11, the thermal insulation cotton layer 12 and the corundum layer 13 of the cylinder are arranged in sequence from the outside of the cylinder to the inside of the cylinder, and the cylinder bottom includes two layers of thermal insulation cotton layers 12 and two layers of zircon sand layers 14. The bottom layer of the cylinder bottom is the thermal insulation cotton layer 12, and the top layer is the zircon sand layer 14. The thermal insulation cotton layer 12 and the zircon sand layer 14 of the cylinder bottom are arranged alternately. In other embodiments of the present invention, the thermal insulation structure 1 can be set according to actual needs to set the number of layers, as well as the material and thickness of each layer structure.

[0033] The crucible 2 is a platinum crucible 2. The structure of the crucible 2 differs from that of conventional platinum crucibles 2 only in its cross-sectional shape: the prior art crucibles 2 are cylindrical, while the present invention has an elliptical cylindrical crucible 2. The crucible 2 comprises an annular crucible body and a bottom connected to the lower end of the annular crucible body. In the present invention, the cross-sectional shape of the annular crucible body is elliptical.

[0034] The present invention adopts the pulling method to grow X-axis lithium niobate crystal, that is, the lithium niobate crystal is pulled along the X-axis direction. During the crystal growth process, the pulling speed of the crystal along the X-axis is V t , 0.2mm / h ≤ Vt ≤ 1mm / h. Furthermore, during the lithium niobate crystal growth process, neither the crucible 2 nor the lithium niobate crystal rotates, and the crystal is observed from directly above the temperature field structure. The temperature field structure of this utility model is highly consistent around the periphery, ensuring a stable internal temperature distribution and providing a stable and favorable condition for crystal growth.

[0035] In this embodiment, the X-cut lithium niobate crystal growth method of the present invention further includes an automatic control program for the equal diameter stage. The automatic control program for the equal diameter stage is prior art. In the prior art, the diameter of the lithium niobate crystal to be grown can be set in the control program. In the present invention, the diameter R of the lithium niobate crystal is set, R= , a represents the major axis of the elliptical cylinder of lithium niobate crystal, and b represents the minor axis of the elliptical cylinder of lithium niobate crystal.

[0036] The utility model discloses an X-cut lithium niobate crystal growth method, which takes into account the growth habits of X-axis lithium niobate crystals and designs a temperature field structure suitable for X-axis crystal growth. Specifically, the heat preservation structure 1 and the crucible 2 in the temperature field structure are both configured as elliptical cylindrical structures, and the long axes of the heat preservation structure 1 and the crucible 2 extend along the Y-axis growth direction of the lithium niobate crystal, and the short axes extend along the Z-axis growth direction of the lithium niobate crystal. In this way, the larger long axis and the smaller short axis can respectively match the faster growth rate of the lithium niobate crystal on the Y-axis and the slower growth rate on the Z-axis. Therefore, the grown X-axis lithium niobate crystal grows naturally without being squeezed, and the grown lithium niobate crystal has an elliptical cylindrical shape. The internal density distribution of the lithium niobate crystal in the elliptical cylindrical shape is uniform.

[0037] In addition, the utility model formulates the major and minor axis ratio parameters of the elliptical insulation structure 1 and the crucible 2 structure according to the characteristics of lithium niobate crystal growth, ensuring the stable growth of the X-axis crystal under controllable conditions as much as possible, reducing the possibility of anisotropic nucleation of the X-axis crystal, reducing the risk of polycrystal and cracking, and improving the yield.

[0038] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A temperature field structure for growing X-cut lithium niobate crystals, characterized in that: The temperature field structure is used to grow X-axis lithium niobate crystals, and the X-axis is defined to extend upward. The temperature field structure includes a heat preservation structure (1) and a crucible (2). The heat preservation structure (1) and the crucible (2) are both elliptical cylinders with an open upper end and a closed lower end. When in use, the crucible (2) is placed in the heat preservation structure (1). The central axes of the crucible (2) and the heat preservation structure (1) coincide. The heat preservation structure (1) has a long axis a1 and a short axis b1, and the crucible (2) has a long axis a2 and a short axis b2. The long axis of the heat preservation structure (1) and the long axis of the crucible (2) both extend in the Y-axis direction, and the short axis of the heat preservation structure (1) and the short axis of the crucible (2) both extend in the Z-axis direction, so that the grown lithium niobate crystal is an elliptical cylinder.

2. The temperature field structure for growing X-cut lithium niobate crystals according to claim 1, characterized in that: The ratio of the major axis a1 to the minor axis b1 of the heat-insulating structure (1) is equal to the ratio of the major axis a2 to the minor axis b2 of the crucible (2).

3. The temperature field structure for growing X-cut lithium niobate crystals according to claim 2, characterized in that: The ratio of the major axis a1 to the minor axis b1 of the thermal insulation structure (1) is d, and 1.1≤d≤1.

5.

4. The temperature field structure for growing X-cut lithium niobate crystals according to any one of claims 1 to 3, characterized in that: The difference between the long axis of the heat-insulating structure (1) and the long axis of the crucible (2) is a=a1-a2, 2cm≤a≤5cm.

5. The temperature field structure for growing X-cut lithium niobate crystals according to any one of claims 1 to 3, characterized in that: The thermal insulation structure (1) comprises an elliptical cylinder and a cylinder bottom connected to the lower end of the cylinder, the cylinder comprising a quartz layer (11), a thermal insulation cotton layer (12) and a corundum layer (13), and the cylinder bottom comprising a thermal insulation cotton layer (12) and a zircon sand layer (14).

6. The temperature field structure for growing X-cut lithium niobate crystals according to claim 5, characterized in that: The quartz layer (11), the thermal insulation cotton layer (12) and the corundum layer (13) of the cylinder are sequentially arranged from the outside of the cylinder to the inside of the cylinder, and the cylinder bottom comprises two layers of thermal insulation cotton layers (12) and two layers of zircon sand layers (14), the lowermost layer of the cylinder bottom is the thermal insulation cotton layer (12), and the uppermost layer is the zircon sand layer (14), and the thermal insulation cotton layer (12) and the zircon sand layer (14) of the cylinder bottom are alternately arranged.

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