Refractive index gradient type cladding of thin film lithium niobate modulator and preparation method of refractive index gradient type cladding

Abstract

The invention relates to a refractive index gradient type cladding of a thin film lithium niobate modulator and a preparation method, and belongs to the technical field of thermal management and stability enhancement of photonic devices. The cladding structure of the invention adopts a multi-layer stacking design of an inner layer, a conductive buffer layer and a high thermal conductivity outer layer, and alternately uses layer combinations of Al O, AZO, AlN and the like; and the heat conductivity or the electric conductivity is in exponential type / step type jump. A high-conductivity buffer layer is adopted in a region close to an electrode, a high-thermal-conductivity outer layer material is adopted in a region far away from a waveguide region, a non-uniform regulation and control structure is constructed, directional heat release and non-uniform voltage distribution optimization are achieved, and the structure is suitable for a thermal-electric coupling asymmetric regulation and control scene; by controlling the deposition rate and the annealing gradient and regulating and controlling the grain size and stress distribution, a continuous thermal diffusion channel and an electric field buffer slope are formed between the layers, the preparation process is simple, heat flow conduction is stable, the method is suitable for a heat-dominated stability optimization scene, and the light field shielding or thermal field focusing capacity of a specific area is enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photonic device thermal management and stability enhancement, in particular to a refractive index gradient type cladding of a thin film lithium niobate modulator and a preparation method thereof, and more particularly to a gradient type upper cladding structure for suppressing low frequency DC drift and enhancing device thermal stability. BACKGROUND

[0002] Thin film lithium niobate (TFLN) modulators have excellent electro-optical conversion performance and are widely used in key fields such as high-speed optical communication, fiber-optic gyroscopes, and quantum information processing. However, under low-frequency DC bias conditions, the device usually exhibits significant long-term optical phase drift, which severely restricts the stability and reliability of the system. Research shows that this drift problem is not only related to charge traps and interface polarization, but also subject to the thermal dissipation capacity of the device. Existing technologies usually use a single material (such as SiO2) as the upper cladding, which has low thermal conductivity and slow heat dissipation, leading to severe heat accumulation in the device and exacerbating the charge drift problem. Therefore, there is an urgent need to develop a high-efficiency, composite gradient structure cladding. SUMMARY

[0003] In view of the above problems, the present application provides a refractive index gradient type cladding of a thin film lithium niobate modulator and a preparation method thereof. The cladding structure of the present application is designed by stacking multiple layers of a conforming inner layer, a conductive buffer layer, and a high thermal conductivity outer layer. The thermal conductivity or electrical conductivity of the layers is exponentially / stepwise changed by using combinations of Al O , AZO, AlN, etc. The present application uses a high-conductivity buffer layer near the electrode region and a high-thermal-conductivity outer layer material away from the waveguide region to construct a non-uniform regulation structure, achieving directional heat release and non-uniform voltage distribution optimization. This structure is suitable for thermal-electric coupling asymmetric regulation scenarios. By controlling the deposition rate and annealing gradient, the present application regulates the grain size and stress distribution to provide continuous heat diffusion channels and electric field buffer slopes between layers. The preparation process is simple, the heat flow is stable, and it is suitable for thermal-dominant stability optimization scenarios, enhancing the light field shielding or thermal field focusing ability of specific regions.

[0004] The present application provides a refractive index gradient type cladding of a thin film lithium niobate modulator, which comprises:

[0005] a conforming inner layer 1, a conductive buffer layer 2, and a high thermal conductivity outer layer 3 connected in sequence from bottom to top along the x direction;

[0006] The conforming inner layer 1 is used to coat the upper surface of the ridge waveguide 4 of the thin film lithium niobate; and the conforming inner layer 1 is also connected to the electrode structure 5.

[0007] The conductive buffer layer 2 is made of aluminum-doped zinc oxide material.

[0008] The refractive index gradient type of the conductive buffer layer in the refractive index gradient type cladding layer is linear gradient or nonlinear gradient.

[0009] Optionally, the electrode structure 5 is a coplanar capacitive electrode structure or a double-sided capacitive electrode structure.

[0010] Optionally, when the electrode structure is a coplanar capacitive electrode structure, the conductive buffer layer 2 is attached to the upper surface of the inner layer 1;

[0011] When the electrode structure is a double-sided capacitive electrode structure, the conductive buffer layer 2 is attached to the upper surface of the inner layer 1 and the surface of the electrode structure 5.

[0012] Optionally, when the gradient type is linear gradient, the thickness ratio of the inner layer 1, the conductive buffer layer 2 and the high-thermal-conductivity outer layer 3 is 0.8-1.2:0.8-1.2:1.8-2.2.

[0013] Optionally, when the gradient type is linear gradient, the doping concentration of aluminum in the conductive buffer layer changes smoothly along the x direction;

[0014] When the gradient type is nonlinear, the conductive buffer layer includes a first refractive index layer 2-1, a second refractive index layer 2-2 and a third refractive index layer 2-3 distributed in sequence along the x direction.

[0015] Optionally, the doping concentration ratio of aluminum in the first refractive index layer, the second refractive index layer and the third refractive index layer is 0.3-0.8:1.5-3:4-6.

[0016] Optionally, the doping concentration of the first refractive index layer, the second refractive index layer and the third refractive index layer changes along the x direction in the form of step, exponential or hyperbolic.

[0017] Optionally, when the electrode structure is a coplanar capacitive electrode structure, the inner layer 1 covers the surface of the electrode structure;

[0018] When the electrode structure is a double-sided capacitive electrode structure, the inner layer 1 covers the surface of the electrode structure and the upper part of the ridge waveguide 4 of the thin film lithium niobate.

[0019] Optionally, the refractive index ratio of the inner layer, the conductive buffer layer and the high-thermal-conductivity outer layer is 1.8-2.1:1.9-2.0:2.1-2.4.

[0020] The second object of the present application is to provide a preparation method of a refractive index gradient type cladding layer of a thin film lithium niobate modulator, comprising:

[0021] Step one, select an indium tin oxide target and fix it on the target position of a direct current magnetron sputtering system;

[0022] Place the thin film lithium niobate device wafer on the sample stage, and preheat for the first time;

[0023] After the sputtering cavity is vacuumed, introduce the first working gas;

[0024] Turn on the direct current sputtering power, sputter the indium tin oxide target material onto the thin film lithium niobate device wafer to deposit the inner layer 1, until the first target etching depth is reached, and then anneal to obtain the thin film lithium niobate device wafer after the first sputtering;

[0025] In step two, the zinc oxide target material and the aluminum oxide target material are respectively selected and installed in the multi-target co-sputtering system;

[0026] Adjust the doping concentration of aluminum in the aluminum oxide target material;

[0027] Introduce the second working gas;

[0028] Apply radio frequency power to the zinc oxide target material and direct current power to the aluminum oxide target material to deposit the conductive buffer layer 2 on the upper surface of the thin film lithium niobate device wafer after the first sputtering, until the second target etching depth is reached, to form the conductive buffer layer, and obtain the thin film lithium niobate device wafer after the second sputtering;

[0029] In step three, the high-purity aluminum nitride ceramic target material is selected and installed in the radio frequency sputtering target position;

[0030] The thin film lithium niobate device wafer after the second sputtering is preheated for the second time;

[0031] The sputtering cavity is vacuumed, and the third working gas is introduced;

[0032] Turn on the radio frequency power to deposit the high-purity aluminum nitride ceramic target on the upper surface of the thin film lithium niobate device wafer after the second sputtering, until the third target etching depth is reached, cool to room temperature in vacuum, and slowly recover to atmospheric pressure to complete the high-thermal-conductivity outer layer sputtering and the preparation of the refractive index gradient type cladding.

[0033] Compared with the prior art, the present application has at least the following beneficial effects:

[0034] (1) The present application significantly improves the heat dissipation capacity: the three-layer gradient structure establishes a longitudinal heat diffusion path, and the heat response time is shortened from dozens of seconds in the traditional structure to <5 seconds;

[0035] (2) The present application reduces the drift amplitude: effectively inhibits the charge migration and interface polarization phenomena caused by heat accumulation; the present application effectively inhibits charge drift and interface polarization: the electric field buffering effect of the conductive buffer layer and the interface inhibition function of the matching layer synergistically reduce the low-frequency phase drift amplitude;

[0036] (3) The present application enhances the long-term thermal stability of the device: the gradient structure realizes coordinated matching among the thermal, electrical and stress fields, and significantly suppresses the structural warping and functional degradation caused by material interface mismatch;

[0037] (4) The present application has strong process compatibility: the materials and deposition processes used can be seamlessly integrated into the existing TFLN device production process; each layer can be prepared by using conventional processes such as magnetron sputtering or PECVD, and can be seamlessly integrated into the existing TFLN device manufacturing process;

[0038] (5) The present application has wide applicability: it can be widely applied to integrated photon systems with high requirements for long-term stability, including fiber-optic gyroscopes and quantum communication chips. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of this specification, illustrate embodiments of the present application and together with the description serve to explain the principles of the present application.

[0040] Figure 1 A schematic diagram of a comparison chart of the thermal conductivity distribution of the linear and nonlinear refractive index gradient cladding of the thin-film lithium niobate modulator in the embodiments of the present application;

[0041] Figure 2 A structural schematic diagram of the refractive index gradient cladding of the thin-film lithium niobate modulator in the embodiments of the present application;

[0042] Figure 3 A flowchart of the preparation method of the refractive index gradient cladding of the thin-film lithium niobate modulator in the embodiments of the present application;

[0043] Figure 4 A structural schematic diagram of the nonlinear refractive index gradient cladding of the thin-film lithium niobate modulator in the embodiments of the present application;

[0044] Figure 5 A schematic diagram of the refractive index gradient of the thin-film lithium niobate modulator in the embodiments of the present application;

[0045] Figure 6 A schematic diagram of the first nonlinear refractive index gradient cladding of the coplanar electrode structure in the embodiments of the present application;

[0046] Figure 7 A schematic diagram of the second nonlinear refractive index gradient cladding of the coplanar electrode structure in the embodiments of the present application.

[0047] REFERENCE NUMERALS:

[0048] The inner layer 1, the conductive buffer layer 2, the high-thermal-conductivity outer layer 3, the ridge waveguide 4 of the thin-film lithium niobate, the electrode structure 5, the first refractive index layer 2-1, the second refractive index layer 2-2, the third refractive index layer 2-3, the first layer 2-11, the second layer 2-12, the third layer 2-22, the fourth layer 2-21, the fifth layer 2-31, the sixth layer 2-32, the lithium niobate ridge layer 4-1, the lithium niobate thin layer 4-2, the first electrode 5-1, the second electrode 5-2, and the bottom layer 6. DETAILED DESCRIPTION

[0049] In order to enable a more clearly understanding of the above-mentioned objects, features and advantages of the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict. In addition, the present application can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0050] One specific embodiment of the present application, as Figures 1-7 , discloses a refractive index gradient cladding of a thin-film lithium niobate modulator and a preparation method, and the specific implementation steps are as follows:

[0051] The present application provides a refractive index gradient cladding of a thin-film lithium niobate modulator, comprising: an inner layer 1, a conductive buffer layer 2 and a high-thermal-conductivity outer layer 3 connected in sequence from bottom to top along the x direction. Figure 2 , the direction perpendicular to the thin-film lithium niobate waveguide layer is the x direction, and the in-plane direction is the z direction and the y direction.

[0052] Optionally, the refractive index gradient type in the refractive index gradient cladding is a linear gradient or a nonlinear gradient; different thermal conductivity, electrical conductivity or refractive index distribution control is achieved, so as to enhance the shielding or conduction characteristics of a specific region.

[0053] It can be understood that the refractive indices of the inner layer 1, the conductive buffer layer 2 and the high-thermal-conductivity outer layer 3 are distributed in a linear gradient or a nonlinear gradient along the x direction.

[0054] Optionally, the refractive index gradient type of the conductive buffer layer in the refractive index gradient cladding is a linear gradient or a nonlinear gradient.

[0055] Optionally, when the gradient type is a linear gradient, the thickness ratio of the inner layer 1, the conductive buffer layer 2 and the high-thermal-conductivity outer layer 3 along the x direction is: 0.8-1.2:0.8-1.2:1.8-2.2.

[0056] Further, the thickness ratio of the conforming inner layer 1, the conductive buffer layer 2 and the high-thermal-conductivity outer layer 3 is 1:1:2; the thermal conductivity gradually transitions from 12-20 W / m·K of the conforming inner layer to 180 W / m·K of the high-thermal-conductivity outer layer, forming a continuous and smooth thermal-conductivity gradient distribution.

[0057] Optionally, the material of the conductive buffer layer 2 is aluminum-doped zinc oxide (AZO) material, wherein the doping concentration of aluminum (Al) is 0.3-6%.

[0058] It can be understood that the aluminum-doped zinc oxide (AZO) material is obtained by doping aluminum (Al) into zinc oxide (ZnO).

[0059] Further, when the gradient type is a linear gradient, the doping concentration of aluminum (Al) in the conductive buffer layer changes smoothly and continuously along the x direction, without clear layering and obvious interfaces.

[0060] Optionally, when the gradient type is nonlinear, the conductive buffer layer is designed in layers according to the doping concentration of aluminum (Al), including a first refractive index layer 2-1, a second refractive index layer 2-2 and a third refractive index layer 2-3 distributed along the x direction in turn.

[0061] Optionally, the thickness of the first refractive index layer 2-1 is 5-100 nm, and the doping concentration of aluminum (Al) is 0.3-0.8%.

[0062] The thickness of the second refractive index layer 2-2 is 50-100 nm, and the doping concentration of aluminum (Al) is 1.5-3%.

[0063] The thickness of the third refractive index layer 2-3 is 50-100 nm, and the doping concentration of aluminum (Al) is 4-6%.

[0064] Further, the doping concentrations of aluminum (Al) in the first refractive index layer 2-1, the second refractive index layer 2-2 and the third refractive index layer 2-3 are 0.5%, 2% and 5%, respectively.

[0065] Optionally, the doping concentrations of aluminum (Al) in the first refractive index layer, the second refractive index layer and the third refractive index layer change in a step, exponential or hyperbolic manner along the x direction, with clear layering and obvious interfaces within the layers.

[0066] For example, when the electrode structure is a double-sided capacitive electrode structure, the structure of the first refractive index layer 2-1 can be a T-shaped or rectangular structure.

[0067] The structure of the second refractive index layer 2-2 is a T-shaped or rectangular structure.

[0068] The third refractive index layer 2-3 is coated on the upper surface of the conforming inner layer and filled to the level of the upper surface of the conforming inner layer 1.

[0069] Optionally, the first refractive index layer 2-1 comprises a first layer 2-11 and a second layer 2-12, the second layer 2-12 is connected with the first layer at 90° along the x direction, and the second layer 2-12 is arranged at the middle position of the first layer 2-11;

[0070] The second refractive index layer 2-2 comprises a third layer 2-22 and a fourth layer 2-21, the fourth layer 2-21 is connected with the third layer 2-22 at 90° along the x direction, and the fourth layer 2-21 is arranged at the middle position of the third layer 2-22;

[0071] The third refractive index layer comprises a fifth layer 2-31 and a sixth layer 2-32; the fifth layer and the sixth layer are arranged on both sides of the lithium niobate ridge waveguide.

[0072] Optionally, the thickness ratio of the first layer 2-11, the second layer 2-12, the third layer 2-22, the fourth layer 2-21 and the fifth layer 2-31 along the x direction is: 1-5:5-19:5-19:1-5:5-19;

[0073] Optionally, the thickness ratio of the first layer 2-11 and the second layer 2-12 along the x direction is: 1-5:5-19;

[0074] The thickness ratio of the third layer 2-22 and the fourth layer 2-21 along the x direction is: 5-19:1-5;

[0075] The thickness of the fifth layer 2-31 and the sixth layer 2-32 along the x direction is 25-95nm;

[0076] For example, the thickness of the first layer along the x direction is 5-25nm;

[0077] The thickness of the second layer along the x direction is 25-95nm

[0078] The thickness of the fourth layer along the x direction is 5-25nm;

[0079] The thickness of the third layer along the x direction is 25-95nm;

[0080] Optionally, along the y direction, the width ratio of the first layer 2-11, the second layer 2-12, the third layer 2-22, the fourth layer 2-21 and the fifth layer 2-31 is: 80-200:1-4:5-10:1-4:1.636-8.765;

[0081] Optionally, along the y direction, the width of the first layer is 80-200um; the width of the second layer is 1-4um;

[0082] The width of the third layer is 5-10um; the width of the fourth layer is 1-4um;

[0083] The width of the fifth layer and the sixth layer is 1.636-8.765um;

[0084] Further, the width of the second layer and the fourth layer is 3.5um; the width of the third layer is 6.5um;

[0085] Further, along the x direction, the maximum thickness of the first refractive layer is 30-100nm, and the minimum thickness is 5-25nm;

[0086] Along the x direction, the maximum thickness of the second refractive layer is 30-95nm, and the minimum thickness is 5-25nm.

[0087] For example, when the electrode structure is a coplanar capacitive electrode structure, the structure of the first refractive layer 2-1 is an open-upward and / or open-downward T-shaped structure, a T-shaped structure or a rectangular structure;

[0088] The structure of the second refractive layer 2-2 is an open-upward and / or open-downward T-shaped structure, a T-shaped structure or a rectangular structure;

[0089] The third refractive layer 2-3 is coated on the upper surface of the inner adhesion layer, is arranged between the second refractive layer and the inner adhesion layer 1, and has a uniform thickness, and the shape is determined according to the inner adhesion layer.

[0090] It can be understood that the first refractive layer, the second refractive layer and the third refractive layer are coated on the upper part of the inner adhesion layer one by one in thickness.

[0091] In the present application, the non-uniform distribution of the refractive index of the inner adhesion layer 1, the conductive buffer layer 2 and the high-thermal-conductivity outer layer 3 realizes efficient transmission or regulation of optical signals through the alternating action of refraction and total reflection.

[0092] Optionally, the inner adhesion layer 1 is used to coat the upper surface of the ridge waveguide 4 of the thin film lithium niobate; the inner adhesion layer 1 is also connected to the electrode structure 5; optionally, the electrode structure 5 is arranged on the upper surface of the ridge waveguide 4 of the thin film lithium niobate; the ridge waveguide 4 of the thin film lithium niobate is arranged on the upper surface of the bottom layer 6;

[0093] Optionally, when the electrode structure is a double-sided capacitive electrode structure, the first refractive layer is arranged on the upper surface of the electrode structure;

[0094] When the electrode structure is a coplanar capacitive electrode structure, the third refractive layer is arranged on the upper surface of the inner adhesion layer;

[0095] Optionally, the ridge waveguide 4 of the thin film lithium niobate includes a lithium niobate ridge layer 4-1 and a lithium niobate thin layer 4-2; the lithium niobate ridge layer 4-1 is arranged at the middle position of the lithium niobate thin layer 4-2; the lithium niobate ridge layer and the lithium niobate thin layer are integrally formed;

[0096] Optionally, the electrode structure 5 includes an electrode one 5-1 and an electrode two 5-2;

[0097] The electrode one 5-1 and the electrode two 5-2 are respectively arranged in parallel and symmetrically along the x direction on the upper surface of the ridge waveguide of the thin film lithium niobate, located on the two sides away from the lithium niobate ridge layer 4-1, so that a polygonal groove is formed between the electrode structure and the thin film lithium niobate ridge waveguide for partially or completely filling the inner layer and the conductive buffer layer;

[0098] Optionally, the inner layer 1 and the conductive buffer layer 2 are arranged on the upper part of the lithium niobate ridge layer 4-1, and between the electrode one 5-1 and the electrode two 5-2.

[0099] Optionally, the wafer thickness of the ridge waveguide 4 of the thin film lithium niobate is 600 nm;

[0100] The thickness of the lithium niobate ridge layer 4-1 is 100-500 nm, and the thickness of the lithium niobate thin layer 4-2 is 100-500 nm;

[0101] Optionally, the internal angle α of the lithium niobate ridge layer 4-1 is 70-80°, the waveguide width along the y direction is 1.2-3 um, and the waveguide width along the y direction is 1.235-3.364 um;

[0102] Optionally, under the incident light of 1550 nm, the refractive index of ordinary light is 2.211; the refractive index of extraordinary light is 2.138;

[0103] Further, the thickness of the lithium niobate ridge layer is 300 nm, and the thickness of the lithium niobate thin layer is 300 nm;

[0104] Further, the internal angle α of the lithium niobate ridge layer 4-1 is 74°, the waveguide width along the y direction is 1.5 um, and the waveguide width along the y direction is 1.844 um.

[0105] Optionally, the electrode structure 5 is a coplanar capacitive electrode structure or a double capacitive electrode structure;

[0106] Optionally, the spacing of the electrode one 5-1 and the electrode two 5-2 along the y direction on the upper surface of the lithium niobate thin layer 4-2 is 5-10 um, and the thickness of the electrode is 0.8-1.2 um;

[0107] Further, the spacing between the electrode 5-1 and the electrode 5-2 along the y direction on the surface of the lithium niobate thin layer 4-2 is 8.5 um, and the thickness of the electrode is 1.0 um.

[0108] In an embodiment of the present application, when the electrode structure is a coplanar capacitive electrode structure, the fitting inner layer 1 completely covers the surface of the electrode structure 5, improves the surface charge inhibition and uniformity, and is suitable for long-term high-precision stable applications.

[0109] For example, when the electrode structure is a coplanar capacitive electrode structure, the refractive index gradient type cladding layer is applied in an optical fiber gyroscope, a precision phase modulator, or a quantum communication chip.

[0110] The electrode structure of the present application can be a coplanar capacitive electrode structure, which is suitable for scenarios with high requirements for uniformity of device surface electric field distribution, for scenarios that need to comprehensively inhibit device surface charge accumulation and interface trap effect, and for scenarios that need to strictly control the interface Schottky barrier and the interface electric field under low frequency bias conditions.

[0111] In an embodiment of the present application, when the electrode structure is a double-sided capacitive electrode structure, the fitting inner layer 1 partially covers the surface of the electrode structure 5, improves the longitudinal electric field strength and modulation efficiency, and is suitable for high-efficiency and high-bandwidth application scenarios.

[0112] For example, when the electrode structure is a double-sided capacitive electrode structure, the refractive index gradient type cladding layer is applied in a high-speed optical communication modulator, a high-bandwidth on-chip integrated photonic device, or a silicon-based heterogeneous integrated electro-optical chip.

[0113] The electrode structure of the present application can be a double-sided capacitive electrode structure, which is suitable for scenarios with high requirements for the strength of the vertically superimposed electric field inside the device, for scenarios that need to optimize the electro-optical overlap efficiency and reduce the driving voltage for high-efficiency modulation, and for high-speed communication scenarios that have strict requirements for both the longitudinal electric field of the device and the transverse optical mode field distribution.

[0114] Optionally, the thickness of the fitting inner layer 1 along the x direction is 50-150 nm, and the stable thermal conductivity of the fitting inner layer is >10 W / mK.

[0115] Further, the thickness of the fitting inner layer 1 along the x direction is 100 nm.

[0116] Optionally, the material of the fitting inner layer is indium tin oxide (ITO) or aluminum nitride (AlN), which is used to improve the thermal fitting and electric field uniformity of the ridge waveguide interface of the thin film lithium niobate.

[0117] Optionally, the refractive index of the fitting inner layer is 1.8-2.1, and the relative dielectric constant of the fitting inner layer is 5-9.

[0118] Further, the refractive index of the fitting inner layer is 1.95; the relative dielectric constant of the fitting inner layer is 7, so as to realize the optimized matching of the light, electricity and heat three field coupling performance, improve the device stability and modulation efficiency, and adapt to the interface buffer demand under various electrode structures.

[0119] In the application, the fitting inner layer 1 is closely fitted with the surface of the ridge waveguide of the thin film lithium niobate, has good thermal-electric contact performance, can effectively inhibit the accumulation of Schottky barrier and trap charge, and improves the low frequency stability of the device.

[0120] Optionally, the fitting inner layer comprises a fitting ridge layer 1-1 and a fitting thin layer 1-2.

[0121] The fitting ridge layer 1-1 is coated on the surface of the lithium niobate ridge layer 4-1; the fitting thin layer 1-2 is coated on the upper surface of the lithium niobate thin layer 4-2; optionally, the conductive buffer layer 2 is coated on the upper surface of the fitting inner layer 1.

[0122] In an embodiment of the application, referring to Figure 6 When the electrode structure is a coplanar capacitance electrode structure, the conductive buffer layer 2 completely coats the upper surface of the fitting inner layer 1; the shape of the conductive buffer layer is set according to the shape of the fitting inner layer.

[0123] When the electrode structure is a double-sided capacitance electrode structure, referring to Figure 2 , the conductive buffer layer 2 is coated on the upper surface of the fitting inner layer 1 and the surface of the electrode structure 5.

[0124] Optionally, the conductive buffer layer has a maximum thickness of 100-300 nm in the x direction.

[0125] Further, the conductive buffer layer has a maximum thickness of 200 nm in the x direction.

[0126] Optionally, the conductive buffer layer is an aluminum-doped zinc oxide (AZO) conductive buffer layer.

[0127] Optionally, the conductivity of the conductive buffer layer is 10 -4 -10 -2 S / m, which can buffer the thermal gradient and adjust the electric field distribution.

[0128] The refractive index of the conductive buffer layer is 1.9-2.0; the relative dielectric constant is 9-12.

[0129] Further, the conductivity of the conductive buffer layer is 5×10 -3 S / m; the refractive index of the conductive buffer layer is 1.95; the relative dielectric constant is 10.5.

[0130] Optionally, when the gradient type is a linear gradient, the doping concentration of Al inside the conductive buffer layer 2 is smoothly transitioned from 0.5% to 5%;

[0131] The conductive buffer layer achieves dynamic balance between thermal conductivity and electrical conductivity, alleviates electrode peak effect through controllable conductive channels, smooths electric field distribution, and reduces interface polarization phenomena while maintaining optical transparency.

[0132] It can be understood that the refractive index gradient type cladding layer of the thin film lithium niobate modulator is a waveguide cladding layer.

[0133] Optionally, the high thermal conductivity outer layer 3 is wrapped on the upper surface of the conductive buffer layer 2, and the high thermal conductivity outer layer has excellent longitudinal heat diffusion capacity, can quickly conduct the heat generated during operation, reduce the temperature rise of the waveguide region, prevent charge migration and refractive index disturbance caused by temperature gradient, and is used for quickly conducting and releasing heat and reducing heat accumulation inside the device.

[0134] In the present application, the high thermal conductivity outer layer, the conductive buffer layer and the conforming inner layer form a functional gradient of "heat conduction + buffer + conforming", and the three layers cooperatively form a thermal-electric-field coupling regulation channel to suppress thermal-induced drift under low frequency bias, improve the long-term thermal stability and modulation precision of the thin film lithium niobate modulator, further improve the thermal-electric synergistic regulation ability, realize rapid and stable temperature, and further significantly suppress the thermal-induced charge drift.

[0135] Optionally, the thickness of the high thermal conductivity outer layer 3 is 1.5-2.5 μm, and the material of the high thermal conductivity outer layer is aluminum nitride AlN, polycrystalline diamond, nanocrystalline diamond or diamond-like carbon material.

[0136] Further, the thickness of the high thermal conductivity outer layer 3 is 2.0 μm.

[0137] The refractive index of the high thermal conductivity outer layer is 2.1-2.4; and the relative dielectric constant is 5.5-8.5.

[0138] Further, the refractive index of the high thermal conductivity outer layer is 2.2; and the relative dielectric constant is 7.0.

[0139] Optionally, the refractive index gradient type cladding layer forms a center-symmetric structural layout on the cross section with the electrode mechanism, which not only has mirror symmetry in the appearance of the modulator, but also realizes functional symmetry in the distribution of thermal field, electric field and stress field, thereby further improving the long-term operation stability and bias fault tolerance ability of the modulator.

[0140] Optionally, the width of the conforming inner layer 1, the conductive buffer layer 2 and the high thermal conductivity outer layer 3 along the y direction is 80-200 μm.

[0141] Further, the width of the inner bonding layer 1, the conductive buffer layer 2 and the high-thermal-conductivity outer layer 3 along the y direction is 120 um.

[0142] The cladding structure of the application is designed by stacking the inner bonding layer, the conductive buffer layer and the high-thermal-conductivity outer layer. O The layers such as Al, AZO, AlN and the like are combined to make the thermal conductivity or the electrical conductivity jump exponentially or in steps.

[0143] The application adopts the high-conductive buffer layer near the electrode area and uses the high-thermal-conductivity outer layer material far from the waveguide area to construct a non-uniform regulation structure, realizes directional heat release and non-uniform voltage distribution optimization, and is suitable for the thermal-electric coupling asymmetric regulation scene, especially suitable for the case where there is a local electric field peak or a heat source concentration area in the device, such as an on-chip integrated driving circuit / thermal sensitive photonic device.

[0144] When the cladding of the application is connected with the coplanar capacitive electrode structure, the third refractive index layer is tightly attached to the inner bonding layer, located between the electrode and the waveguide, directly participates in the interface electric field regulation, plays a role in interface polarization suppression and electric field homogenization; the second refractive index layer serves as an intermediate transition area, buffers the thermal gradient, gradually improves the electrical conductivity and the thermal conductivity, and forms an intermediate transition channel; the first refractive index layer is arranged at the uppermost part, close to the environment / high-thermal-conductivity layer, provides a rapid charge discharge and a thermal conduction path, plays a shielding role, and reduces the influence of the electrode electric field peak under thermal excitation.

[0145] When the cladding of the application is connected with the double-sided capacitive electrode structure, the inner bonding layer and the conductive buffer layer are embedded in the polygonal groove between the electrode one and the electrode two, and the distribution form of the three refractive index layers is: each refractive index layer forms an asymmetric ring around the lithium niobate ridge waveguide side wall; the cross-sectional gradient causes the electric field to be regulated in the x direction and the y direction at the same time; it is especially suitable for high-speed modulation scenes with high requirements for electric-optical overlap and vertical electric field optimization.

[0146] The application provides a cladding collaborative design scheme suitable for coplanar electrode structures and double capacitive electrode structures. For the coplanar electrode structure, the bonding layer and the buffer layer cover the top area of the electrode, are suitable for scenes with high requirements for surface electric field uniformity and need to comprehensively suppress surface polarization, and can be a fiber gyroscope; for the double capacitive structure, the bonding layer is partially embedded in the groove instead of covering the top of the electrode, retains a longitudinal electric field enhancement path, and is suitable for the requirements of modulation efficiency and bandwidth of high-speed communication devices.

[0147] Another object of the application is to provide a preparation method of the refractive index gradient type cladding of the thin film lithium niobate modulator, comprising:

[0148] Step one, select a high-purity indium tin oxide target material, and fix it on the target position of a direct current magnetron sputtering system;

[0149] Clean the thin film lithium niobate device wafer and fix it in the center of the sample stage for the first preheating;

[0150] After the sputtering cavity is vacuumed, introduce the first working gas;

[0151] Turn on the direct current sputtering power, sputter the indium tin oxide target material on the thin film lithium niobate device wafer to deposit the inner layer 1, until the first target etching depth is reached, and then anneal to obtain the thin film lithium niobate device wafer after the first sputtering;

[0152] Optionally, the chemical composition of the indium tin oxide target material is indium oxide In O and tin oxide SnO ; the mass ratio of indium oxide In O and tin oxide SnO is 90:10; the purity of the indium tin oxide target material is ≥99.99%;

[0153] Optionally, the temperature of the first preheating is 50-80℃;

[0154] Optionally, the indium tin oxide target material is a 2-inch or 4-inch circular sheet;

[0155] Optionally, the TFLN device wafer is cleaned using the standard RCA cleaning process;

[0156] Optionally, the vacuum degree of the sputtering cavity is less than 5×10 -5 Pa;

[0157] Optionally, the first working gas is high-purity Ar gas, the working pressure is 0.5-1.0 Pa, and the single gas atmosphere is maintained;

[0158] Optionally, the power of the direct current sputtering power is 100-150 W; the deposition rate of the deposited inner layer 1 is 5-10 nm / min, and the first target etching depth is 50-150 nm;

[0159] Further, the first target etching depth is about 100 nm.

[0160] Optionally, the annealing temperature is 200-500℃, and the annealing time is 30-60 minutes, which is used to improve the film layer density and thermal conductivity, and improve the adhesion performance of the thin film lithium niobate interface.

[0161] Further, the annealing temperature is 300℃.

[0162] Step two, respectively select high-purity zinc oxide ZnO target material and aluminum oxide Al O Target material is installed in a multi-target co-sputtering system;

[0163] Adjusting the aluminum oxide Al O The doping concentration of Al in the target material;

[0164] Introducing a second working gas;

[0165] The RF power is applied to the ZnO target, and the Al O The DC power is applied to the target, and the conductive buffer layer 2 is deposited on the upper surface of the thin film lithium niobate device wafer after the first sputtering until the second target etching depth is reached, forming a conductive buffer layer, and obtaining the thin film lithium niobate device wafer after the second sputtering;

[0166] Optionally, the aluminum oxide Al O The sputtering power of the target material and the sputtering power of the ZnO target, and the aluminum oxide Al O The doping concentration of Al in the target material;

[0167] The doping concentration of Al is 0.3-6%;

[0168] Further, when the gradient type is linear, the doping concentration of Al is 0.5-5%, and the coating is performed along the x direction on the upper surface of the inner layer, and the doping concentration of Al gradually decreases from large to small;

[0169] When the gradient type is nonlinear, the doping concentration of aluminum Al in the first refractive layer 2-1 is 0.5-0.8%;

[0170] The doping concentration of aluminum Al in the second refractive layer 2-2 is 2-3%;

[0171] The doping concentration of aluminum Al in the third refractive layer 2-3 is 4-5%.

[0172] Optionally, the expression of the doping concentration of Al is:

[0173]

[0174] Optionally, the second working gas is a mixed working gas, which includes Ar and O ;

[0175] Further, the volume ratio of Ar:O is 10-20:1, and the total pressure is 0.5-1.0 Pa, which is used to cooperatively control the redox state in the AZO film forming process.

[0176] Optionally, the radio frequency (RF) power is 150-200 W, and the direct current (DC) power is 10-50 W.

[0177] Optionally, the deposition rate of the conductive buffer layer is 8-15 nm / min, and the second target etching depth is 100-300 nm, so that the conductive buffer layer has certain electrical conductivity and does not cause obvious optical loss.

[0178] Optionally, the method further comprises: performing heat treatment on the conductive buffer layer to stabilize the electrical parameter.

[0179] Further, the heat treatment is performed at a temperature of 200-250 DEG C for 15-30 min.

[0180] In one embodiment of the application, when the gradient type is nonlinear, the Al content of the first refractive index layer 2-1, the second refractive index layer 2-2 and the third refractive index layer 2-3 is 0-0.5%, 0.5-1% and 1-2% respectively. O The power ratio of the target material is 4-5:10-15:20-25.

[0181] For example, the specific steps for preparing the first refractive index layer include:

[0182] AZO and 0.5% Al doping: ZnO target, RF power 150-200 W, Al O The power of the target material is 8-10 W, and the deposition thickness is 50-100 nm.

[0183] The specific steps for preparing the second refractive index layer include:

[0184] AZO and 2% Al doping: Al O The power of the target material is 20-30 W, and the deposition thickness is 50-100 nm.

[0185] The specific steps for preparing the third refractive index layer include:

[0186] AZO and 5% Al doping: Al O The power of the target material is 40-50 W, and the deposition thickness is 50-100 nm.

[0187] Step three, a high-purity aluminum nitride (AlN) ceramic target is selected and installed in a radio frequency (RF) sputtering target position;

[0188] The lithium niobate wafer after the second sputtering is preheated again;

[0189] The sputtering cavity is vacuumized, and a third working gas is introduced;

[0190] Turn on the RF power supply and deposit a high-purity AlN ceramic target on the upper surface of the thin-film lithium niobate device wafer after the second sputtering until the third target etching depth is reached. Cool to room temperature in vacuum and slowly restore to atmospheric pressure to complete the sputtering of the high thermal conductivity outer layer and complete the fabrication of the refractive index gradient cladding.

[0191] Optionally, the purity of the high-purity aluminum nitride (AlN) ceramic target is ≥99.99%.

[0192] Optionally, the second preheating temperature is 150-200℃ to reduce thermal stress differences.

[0193] Optionally, the third working gas is high-purity Ar and high-purity N. Gas; high-purity Ar gas and N gas The volume ratio of the gases is Ar:N =5:1;

[0194] The high-purity Ar gas and high-purity N The purity of the gas is ≥99.99%;

[0195] Optionally, a vacuum of 5×10 -5 The total air pressure is maintained at 0.8-1.2 Pa below Pa.

[0196] Optionally, the RF power supply has a power of 100-200W, a deposition rate of 10-20nm / min, and a third target etching thickness of 1.5-2.5μm.

[0197] In this invention, each layer of material is prepared using either PECVD or magnetron sputtering processes according to its physical properties.

[0198] In this invention, the refractive index gradient cladding is customized and optimized through etching depth, doping concentration and material combination to achieve the integrated design goal of "parameter gradient - functional continuity - physical compatibility".

[0199] The refractive index gradient cladding described in this invention has high integration and practical feasibility in terms of structural design, material selection, process parameters and thermoelectric behavior control, significantly improving the response stability of TFLN modulators under low-frequency bias conditions, and providing a solid foundation for high-precision photonic systems.

[0200] This invention proposes a multi-layer gradient cladding structure, which effectively improves the thermal response speed and electric field stability of the TFLN modulator under low-frequency bias conditions through a layer-by-layer design of thermal-electric functions.

[0201] The materials selected for each layer of this invention are material systems with continuous thermal-electric properties; in terms of process, by controlling the deposition rate and annealing gradient, the grain size and stress distribution are adjusted to enable continuous thermal diffusion channels and electric field buffer slopes between each layer.

[0202] The preparation process of the cladding structure in the application is simple, the heat flow conduction is stable, is suitable for a heat dominant type stability optimization scene, and includes applications with strict requirements on device surface temperature rise and response time, namely high-speed modulators and fiber gyroscope front ends.

[0203] The application adopts a multi-step deposition + intermediate annealing strategy, controls crystal structure and stress distribution of each section, and enhances light field shielding / heat field focusing capability of specific regions.

[0204] Embodiment one

[0205] The cladding three-layer structure is in turn: 1) the outer layer of heat-conducting material is aluminum nitride (AlN), with a thickness of about 2.0 microns and a thermal conductivity of about 180 W / m·K; 2) the intermediate buffer layer is aluminum-doped zinc oxide (AZO), with a thickness of 200 nm and a doping concentration controlled at 5%, and an electrical conductivity of about 10-3 S / m; and 3) the inner layer of bonding material is indium tin oxide (ITO), with a thickness of 100 nm and a thermal conductivity of more than 12 W / m·K.

[0206] The three-layer material is in turn deposited on the waveguide area of the TFLN modulator by using a magnetron sputtering process, and the deposition temperature is controlled at 100-150 DEG C to ensure that the bonding between the layers is dense, and there are no obvious stress cracks or delamination.

[0207] The device is subjected to thermal stability testing under a ±5V direct current bias condition, the phase drift is measured, and the thermal response process is monitored in combination with infrared thermal imaging.

[0208] The test results show that the drift amplitude of the three-layer gradient cladding sample is significantly reduced to about 2.9pi (test duration of 1000s), the thermal response time is shortened from about 28s of the traditional structure to less than 5s, the device surface temperature rise is reduced by about 12 DEG C, and the thermal field distribution is more uniform. The surface roughness Ra is maintained within 2nm, verifying that the structure has excellent thermal stability and processing compatibility.

[0209] The synergistic mechanism of the three-layer structure is further analyzed: the outer layer of AlN provides a rapid heat diffusion channel; the intermediate AZO adjusts the electric field slope and buffers the heat flow; and the bonding layer of ITO improves the interface matching and suppresses the trap state excitation. The three together constitute a dynamic multi-physical steady-state platform, realizing stable and low-drift modulation behavior.

[0210] In addition, the thickness and doping of each functional layer are optimized and designed. The AZO layer doping concentration adjustment range is 0.5%-5%, when the leakage needs to be suppressed, the low concentration (about 0.5-1.0%) is selected, when the electric field peak needs to be dispersed, it can be increased to about 2-3%, and when the charge discharge channel needs to be guided, 4-5% can be selected.

[0211] The thickness of the inner layer is suggested to be controlled in the range of 50-150 nm, which can ensure excellent thermal-electric coupling and avoid disturbance to the optical mode field. The actual measurement shows that the optimized structure can enhance the thermal drift suppression by more than 40% and reduce the peak value of the interface electric field by 35% without affecting the modulation efficiency.

[0212] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A refractive index gradient type cladding of a thin film lithium niobate modulator, characterized by, The application relates to a ridge waveguide lithium niobate film device, which comprises the following parts in sequence from bottom to top along the x direction: a fitting inner layer (1), a conductive buffer layer (2) and a high-thermal-conductivity outer layer (3). The fitting inner layer (1) is used for covering the upper surface of a ridge waveguide (4) of a thin-film lithium niobate device; the fitting inner layer (1) is also connected with an electrode structure (5). The conductive buffer layer (2) is made of an aluminum-doped zinc oxide material. The refractive index gradient type of the conductive buffer layer in the refractive index gradient cladding layer is linear gradient or nonlinear gradient. The electrode structure (5) is a coplanar capacitance electrode structure or a double-sided capacitance electrode structure.

2. The thin-film lithium niobate modulator refractive index gradient type cladding according to claim 1, characterized by, When the electrode structure is the coplanar capacitance electrode structure, the conductive buffer layer (2) covers the upper surface of the fitting inner layer (1).

3. The refractive index gradient type cladding of the thin film lithium niobate modulator according to claim 2, characterized by, When the electrode structure is the double-sided capacitance electrode structure, the conductive buffer layer (2) covers the upper surface of the fitting inner layer (1) and the surface of the electrode structure (5). When the gradient type is linear gradient, the thickness ratio of the fitting inner layer (1), the conductive buffer layer (2) and the high-thermal-conductivity outer layer (3) is 1:1.5-3:4-6.

4. The refractive index gradient type cladding of the thin film lithium niobate modulator according to claim 1, characterized by, When the gradient type is linear gradient, the doping concentration of aluminum in the conductive buffer layer changes continuously and smoothly along the x direction. 0.8-1.2:0.8-1.2:1.8-2.2。 5. The thin-film lithium niobate modulator refractive index gradient cladding of claim 1, wherein, When the gradient type is nonlinear, the conductive buffer layer comprises a first refractive index layer (2-1), a second refractive index layer (2-2) and a third refractive index layer (2-3) which are sequentially distributed along the x direction. The doping concentration ratio of aluminum in the first refractive index layer, the second refractive index layer and the third refractive index layer is 0.3-0.8:1.5-3:4-6.

6. The thin-film lithium niobate modulator refractive index gradient type cladding according to claim 5, characterized by The doping concentration of the first refractive index layer, the second refractive index layer and the third refractive index layer changes in the form of step, exponential or hyperbolic along the x direction.

7. The thin-film lithium niobate modulator of claim 5, wherein, When the electrode structure is the coplanar capacitance electrode structure, the fitting inner layer (1) covers the surface of the electrode structure.

8. The refractive index gradient type cladding of the thin film lithium niobate modulator according to claim 2, characterized by, When the electrode structure is the double-sided capacitance electrode structure, the fitting inner layer (1) covers the surface of the electrode structure and the upper part of the ridge waveguide (4) of the thin-film lithium niobate device. The refractive index ratio of the fitting inner layer, the conductive buffer layer and the high-thermal-conductivity outer layer is 1.8-2.1:1.9-2.0:2.1-2.

4.

9. The thin-film lithium niobate modulator of claim 7, wherein, The application further relates to a preparation method of the ridge waveguide lithium niobate film device.

10. A method of fabricating a refractive index gradient type cladding of a thin film lithium niobate modulator, characterized by, In step one, an indium tin oxide target is selected and fixed on a target position of a direct-current magnetron sputtering system; A thin-film lithium niobate device wafer is placed on a sample table and preheated for the first time; After the sputtering cavity is vacuumized, a first working gas is introduced; A direct-current sputtering power source is started, the indium tin oxide target is sputtered on the thin-film lithium niobate device wafer, the fitting inner layer (1) is deposited, until a first target etching depth is reached, annealing treatment is carried out, and a thin-film lithium niobate device wafer after the first sputtering is obtained; In step two, a zinc oxide target and an aluminum oxide target are selected and installed in a multi-target co-sputtering system; The doping concentration of aluminum in the aluminum oxide target is adjusted; A second working gas is introduced; Radio frequency power is applied to the zinc oxide target, direct-current power is applied to the aluminum oxide target, the conductive buffer layer (2) is deposited on the upper surface of the thin-film lithium niobate device wafer after the first sputtering, until a second target etching depth is reached, the conductive buffer layer is formed, and a thin-film lithium niobate device wafer after the second sputtering is obtained; In step three, a high-purity aluminum nitride ceramic target is selected and installed in a radio frequency sputtering target position. ​ The thin film lithium niobate device wafer after the second sputtering is preheated for the second time; The sputtering cavity is vacuumed and the third working gas is introduced; The radio frequency power source is turned on, the high-purity aluminum nitride ceramic target is deposited on the upper surface of the thin film lithium niobate device wafer after the second sputtering until the third target etching depth is reached, and the vacuum is cooled to room temperature and slowly restored to atmospheric pressure, the high-thermal-conductivity outer layer sputtering is completed, and the refractive index gradient type cladding is prepared.

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