Lithium niobate-silicon nitride waveguide structure, preparation method and optical gyroscope

Abstract

The lithium niobate-silicon nitride waveguide structure comprises a silicon substrate layer, a first silicon oxide isolation layer, a second silicon oxide isolation layer, a lithium niobate thin film layer and a silicon oxide dielectric layer which are stacked in sequence, the second silicon oxide isolation layer is wrapped with a silicon nitride layer; the thickness of the second silicon oxide isolation layer between the silicon nitride layer and the lithium niobate thin film layer is 50 + / -10nm; the thickness of the silicon nitride layer is 400 + / -10nm, and the thickness of the lithium niobate film layer is 600 + / -50nm; the silicon oxide dielectric layer is provided with at least two electrodes which are arranged at intervals. According to the lithium niobate-silicon nitride waveguide structure, the preparation method and the optical gyroscope provided by the invention, on the basis of the advantages of silicon nitride and lithium niobate materials, an ultra-low-loss silicon nitride waveguide, an ultra-high-Q-value micro-ring resonator and a high-modulation-rate lithium niobate modulator are obtained at the same time through a lithium niobate and silicon nitride hybrid integration method; and thus, the overall performance of the resonant integrated optical gyroscope is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-speed optical modulation chips in the optical communication waveband, and particularly relates to a lithium niobate-silicon nitride waveguide structure, a preparation method and an optical gyroscope. BACKGROUND

[0002] The resonant integrated optical gyroscope (RIOG) has the performance advantages of high precision and high sensitivity, but the current integrated optical gyroscope is faced with many problems such as high waveguide transmission loss, low modulation frequency, and large noise.

[0003] The silicon nitride (SiN) waveguide has low transmission loss and low nonlinear effect, and has good stability, which is an ideal material platform for the waveguide ring resonator, a key sensing unit of the resonant integrated optical gyroscope. However, the disadvantage of the silicon nitride material platform is that the low nonlinear effect and the absence of a significant Pockels effect cannot realize the design of a high-modulation-frequency modulator, which greatly affects the reading of signals by the resonant integrated optical gyroscope, and the lithium niobate (LN) material is a mainstream platform for realizing a high-speed electro-optic modulator.

[0004] The existing resonant integrated optical gyroscope design scheme is partly based on a pure silicon nitride platform, which has extremely low loss but is often incompatible with mainstream process platforms, and the modulator adopts an external commercial modulator to modulate signals without truly integrating on-chip; and partly uses a pure lithium niobate method for integration, but the lithium niobate process is complex, and the waveguide loss is much greater than that of the silicon nitride platform, resulting in that the theoretical precision of the resonant integrated optical gyroscope cannot reach the level of the silicon nitride platform. SUMMARY

[0005] The application provides a lithium niobate-silicon nitride waveguide structure, a preparation method and an optical gyroscope, which are based on the advantages of silicon nitride and lithium niobate materials, and simultaneously obtain an ultra-low-loss silicon nitride waveguide, an ultra-high-Q micro-ring resonator and a high-modulation-rate lithium niobate modulator through a lithium niobate and silicon nitride hybrid integration method, thereby improving the overall performance of the resonant integrated optical gyroscope.

[0006] Other purposes and advantages of the application can be further understood from the technical features disclosed in the application.

[0007] To achieve one or part or all of the above purposes or other purposes, the application provides a lithium niobate-silicon nitride waveguide structure, a preparation method and an optical gyroscope.

[0008] A lithium niobate-silicon nitride waveguide structure includes a silicon substrate layer, a first silicon oxide isolation layer, a second silicon oxide isolation layer, a lithium niobate thin film layer, and a silicon oxide dielectric layer stacked sequentially.

[0009] The second silicon oxide insulating layer is encapsulated with a silicon nitride layer;

[0010] The thickness of the second silicon oxide isolation layer between the silicon nitride layer and the lithium niobate thin film layer is 50±10nm;

[0011] The thickness of the silicon nitride layer is 400±10nm, and the thickness of the lithium niobate thin film layer is 600±50nm.

[0012] The silicon oxide dielectric layer has at least two electrodes spaced apart.

[0013] A method for fabricating a lithium niobate-silicon nitride waveguide structure includes:

[0014] A first silicon oxide isolation layer and a silicon nitride layer are sequentially deposited on the silicon substrate to complete the fabrication of the silicon nitride waveguide;

[0015] Silicon oxide is deposited on the silicon nitride waveguide to encapsulate the silicon nitride layer until a second silicon oxide isolation layer is formed as a bonding contact layer, thus completing the fabrication of the silicon nitride wafer;

[0016] The silicon nitride wafer and the lithium niobate wafer are wafer bonded together to obtain a lithium niobate thin film layer.

[0017] A silicon oxide dielectric layer is deposited on the lithium niobate thin film layer, and the silicon oxide dielectric layer has at least two spaced electrodes.

[0018] The specific fabrication process of the silicon nitride waveguide is as follows:

[0019] A first silicon oxide isolation layer is deposited on the silicon substrate, and a silicon nitride layer is deposited by chemical vapor deposition. The silicon nitride waveguide is obtained by photolithography and etching.

[0020] The lithium niobate wafer bonded to the silicon nitride wafer includes a silicon substrate layer, a third silicon oxide isolation layer, and a lithium niobate thin film layer stacked sequentially.

[0021] The silicon nitride wafer and the lithium niobate wafer are bonded together using a smart-cut process.

[0022] The specific process of obtaining the lithium niobate thin film layer after wafer bonding of the silicon nitride wafer and the lithium niobate wafer is as follows:

[0023] The lithium niobate wafer was removed using an ion implantation process, and a lithium niobate thin film with a thickness of 600±50 nm was obtained by chemical mechanical polishing and annealing.

[0024] The ion implantation includes the implantation of hydrogen ions and / or helium ions.

[0025] An optical gyroscope, based on the above-mentioned lithium niobate-silicon nitride waveguide structure, includes: an incident unit, a modulation unit, and a coupling unit;

[0026] The incident unit uses a silicon nitride waveguide as a substrate to receive and transmit incident light signals;

[0027] The modulation unit uses a lithium niobate-silicon nitride waveguide as a substrate to modulate the incident light signal and generate a modulated light signal.

[0028] The coupling unit uses a silicon nitride waveguide as a substrate to receive the modulated optical signal and couple it to a microring resonator.

[0029] The incident unit is equipped with a Y-branch and a circulator based on a silicon nitride waveguide.

[0030] The Y-branch is connected to the light source via a silicon nitride waveguide. The incident light signal output from the light source is transmitted along the silicon nitride waveguide, passes through the Y-branch and the circulator (two passive devices) in sequence, and then enters the modulation unit.

[0031] Each circulator is connected to a detector, and the silicon nitride waveguide has a thickness of 400±10nm. The optical signal is transmitted only inside the silicon nitride waveguide.

[0032] The modulation unit uses a lithium niobate-silicon nitride waveguide as its substrate. The incident optical signal is transmitted into the hybrid waveguide of lithium niobate and silicon nitride and is modulated by a lithium niobate modulator to generate a modulated optical signal.

[0033] The modulated optical signal enters the coupling unit, and the modulated optical signal is transmitted along the silicon nitride waveguide and coupled to the multimode silicon nitride microring resonator.

[0034] The lithium niobate-silicon nitride waveguide has a thickness of 600±50nm and a silicon nitride waveguide thickness of 400±10nm. A second silicon oxide isolation layer with a thickness of 50±10nm is disposed between the two waveguides.

[0035] Compared with the prior art, the beneficial effects of the present invention mainly include:

[0036] This application provides a lithium niobate-silicon nitride waveguide structure, a fabrication method, and an optical gyroscope. Based on the advantages of silicon nitride and lithium niobate materials, by using a hybrid integration method of lithium niobate and silicon nitride, an ultra-low loss silicon nitride waveguide, an ultra-high Q value microring resonator, and a high modulation rate lithium niobate modulator are obtained simultaneously, thereby improving the overall performance of the resonant integrated optical gyroscope.

[0037] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the cross-section of the lithium niobate-silicon nitride waveguide provided in Embodiment 1 of this application.

[0040] Figure 2 This is a flowchart illustrating steps s1 and s2 of the method for fabricating the lithium niobate-silicon nitride waveguide structure provided in Embodiment 2 of this application.

[0041] Figure 3 The diagram shown is a flowchart of step s3 of the method for fabricating a lithium niobate-silicon nitride waveguide structure provided in Embodiment 2 of this application.

[0042] Figure 4 The diagram shown is a flowchart of step s4 of the method for fabricating a lithium niobate-silicon nitride waveguide structure provided in Embodiment 2 of this application.

[0043] Figure 5 This is a schematic diagram of the optical gyroscope structure provided in Embodiment 3 of this application. Detailed Implementation

[0044] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the present invention.

[0045] This application provides a lithium niobate-silicon nitride waveguide structure, a fabrication method, and an optical gyroscope. Based on the advantages of silicon nitride and lithium niobate materials, by using a hybrid integration method of lithium niobate and silicon nitride, an ultra-low loss silicon nitride waveguide, an ultra-high Q value microring resonator, and a high modulation rate lithium niobate modulator are obtained simultaneously, thereby improving the overall performance of the resonant integrated optical gyroscope.

[0046] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0047] Example 1

[0048] Figure 1 The diagram shown is a schematic cross-section of the lithium niobate-silicon nitride waveguide provided in Embodiment 1 of this application.

[0049] like Figure 1 As shown, a lithium niobate-silicon nitride waveguide structure includes:

[0050] A silicon substrate layer 1, a first silicon oxide isolation layer 21, a second silicon oxide isolation layer 22, a lithium niobate thin film layer 3, and a silicon oxide dielectric layer 4 are sequentially stacked.

[0051] The second silicon oxide isolation layer 22 encapsulates the silicon nitride layer 2;

[0052] The thickness of the second silicon oxide isolation layer 22 between the silicon nitride layer 2 and the lithium niobate thin film layer 3 is 50±10nm;

[0053] The thickness of silicon nitride layer 2 is 400±10nm, and the thickness of lithium niobate thin film layer 3 is 600±50nm;

[0054] The silicon oxide dielectric layer 4 has at least two electrodes 41 spaced apart.

[0055] A method for fabricating a lithium niobate-silicon nitride waveguide structure includes:

[0056] Figure 2 The diagram shown is a flowchart of steps s1 and s2 of the method for fabricating a lithium niobate-silicon nitride waveguide structure provided in Embodiment 2 of this application.

[0057] like Figure 2 As shown, step s1:

[0058] A first silicon oxide isolation layer 21 is deposited on a silicon substrate 1, and a silicon nitride layer 2 is deposited on the first silicon oxide isolation layer 21 by chemical vapor deposition. The silicon nitride waveguide is obtained by photolithography and etching.

[0059] Step s2:

[0060] A silicon oxide layer 2 is deposited on the silicon nitride waveguide to encapsulate the silicon nitride until a second silicon oxide isolation layer 22 is formed as a bonding contact layer, thus completing the fabrication of the silicon nitride wafer;

[0061] Figure 3The diagram shown is a flowchart of step s3 of the method for fabricating a lithium niobate-silicon nitride waveguide structure provided in Embodiment 2 of this application.

[0062] like Figure 3 As shown, step s3:

[0063] Lithium niobate wafers are fabricated, and silicon nitride wafers and lithium niobate wafers are bonded together using a smart-cut process;

[0064] The lithium niobate wafer was stripped using an ion implantation process, and a lithium niobate thin film layer with a thickness of 600±50nm was obtained by chemical mechanical polishing and annealing.

[0065] Figure 4 The diagram shown is a flowchart of step s4 of the method for fabricating a lithium niobate-silicon nitride waveguide structure provided in Embodiment 2 of this application.

[0066] like Figure 4 As shown, step s4:

[0067] A silicon oxide dielectric layer 4 is deposited on a lithium niobate thin film layer 3, and the silicon oxide dielectric layer 4 has at least two spaced electrodes 41.

[0068] In a preferred embodiment of the present invention, the wafer bonding in this embodiment adopts a smart-cut process, which can effectively reduce the grinding time of the chemical mechanical polishing process.

[0069] In a preferred embodiment of the present invention, the lithium niobate wafer includes a silicon substrate layer 31, a third silicon oxide isolation layer 32, and a lithium niobate thin film layer 3, which are sequentially stacked. Figure 3 As shown.

[0070] The fabrication process of lithium niobate wafers includes:

[0071] A third silicon oxide isolation layer 32 is deposited on the silicon substrate layer 31, and a lithium niobate thin film layer 3 is deposited on the third silicon oxide isolation layer 32.

[0072] In a preferred embodiment of the present invention, ion implantation in this embodiment includes implantation of hydrogen ions and / or helium ions.

[0073] Ion implantation involves accelerating impurity ions in a vacuum at low temperature (voltage ≥ 105V for Si) to achieve high kinetic energy, allowing them to directly enter the semiconductor. However, this process also introduces lattice defects, necessitating post-implantation annealing at low temperature or laser annealing to eliminate these defects. The impurity concentration distribution after ion implantation typically exhibits a Gaussian distribution, with the highest concentration not at the surface but at a certain depth within the surface. Ion implantation allows for precise control of the total impurity dose, depth distribution, and surface uniformity. Furthermore, it is a low-temperature process (preventing re-diffusion of existing impurities) and enables self-alignment techniques (to reduce capacitance effects).

[0074] Figure 5 The diagram shown is a schematic diagram of the optical gyroscope structure provided in Embodiment 3 of this application.

[0075] like Figure 5 As shown, an optical gyroscope using the above-mentioned lithium niobate-silicon nitride waveguide structure includes:

[0076] Incident unit 11, modulation unit 12 and coupling unit 13;

[0077] Incident unit 11 uses a silicon nitride waveguide as its substrate to receive and transmit incident light signals. Incident unit 11, also using a silicon nitride waveguide as its substrate, includes a Y-splitter b and a circulator c. The Y-splitter b is connected to light source a via the silicon nitride waveguide. The incident light signal output from light source a is transmitted along the silicon nitride waveguide, passing sequentially through the Y-splitter b and circulator c (both passive devices), before entering modulation unit 12. Circulator c is connected to detector d. The silicon nitride waveguide has a thickness of 400±10 nm, and the light signal is transmitted only within the silicon nitride waveguide.

[0078] The modulation unit 12 uses a lithium niobate-silicon nitride waveguide as its substrate. The incident light signal is transmitted into the hybrid waveguide of lithium niobate and silicon nitride, and the incident light signal is modulated by the lithium niobate modulator f to generate a modulated light signal. The lithium niobate waveguide in the lithium niobate-silicon nitride waveguide has a thickness of 600±50nm, the silicon nitride waveguide has a thickness of 400±10nm, and a second silicon oxide isolation layer 22 with a thickness of 50±10nm is provided between the two waveguides.

[0079] The modulated optical signal enters the coupling unit 13, and the modulated optical signal is transmitted along the silicon nitride waveguide and coupled to the multimode silicon nitride microring resonator e.

[0080] This application provides a lithium niobate-silicon nitride waveguide structure, a fabrication method, and an optical gyroscope. Based on the advantages of silicon nitride and lithium niobate materials, by using a hybrid integration method of lithium niobate and silicon nitride, an ultra-low loss silicon nitride waveguide, an ultra-high Q value microring resonator, and a high modulation rate lithium niobate modulator are obtained simultaneously, thereby improving the overall performance of the resonant integrated optical gyroscope.

[0081] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, specific embodiments have been described above. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims can be performed in a different order than that shown in the embodiments and still achieve the desired result. Additionally, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0082] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the device embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0083] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0084] The common English terms or letters used in this invention for clarity of description are for illustrative purposes only and are not limiting interpretations or specific uses. They should not be used to limit the scope of protection of this invention based on their possible Chinese translations or specific letters.

[0085] It should also be noted that in this article, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

Claims

1. A lithium niobate-silicon nitride waveguide structure, characterized in that, It includes a silicon substrate layer (1), a first silicon oxide isolation layer (21), a second silicon oxide isolation layer (22), a lithium niobate thin film layer (3), and a silicon oxide dielectric layer (4) stacked sequentially. The second silicon oxide isolation layer (22) is wrapped with a silicon nitride layer (2); The thickness of the second silicon oxide isolation layer (22) between the silicon nitride layer (2) and the lithium niobate thin film layer (3) is 50±10nm; The silicon nitride layer (2) has a thickness of 400±10nm, and the lithium niobate thin film layer (3) has a thickness of 600±50nm; The silicon oxide dielectric layer (4) has at least two electrodes (41) spaced apart.

2. A method for fabricating a lithium niobate-silicon nitride waveguide structure, characterized in that, include: A first silicon oxide isolation layer (21) and a silicon nitride layer (2) are sequentially deposited on the silicon substrate layer (1) to complete the fabrication of the silicon nitride waveguide; Silicon oxide is deposited on the silicon nitride waveguide to encapsulate the silicon nitride layer (2) until a second silicon oxide isolation layer (22) is formed as a bonding contact layer, thus completing the fabrication of the silicon nitride wafer; The silicon nitride wafer and the lithium niobate wafer are wafer bonded to obtain a lithium niobate thin film layer (3); A silicon oxide dielectric layer (4) is deposited on the lithium niobate thin film layer (3), and the silicon oxide dielectric layer (4) has at least two spaced electrodes (41).

3. The method for fabricating a lithium niobate-silicon nitride waveguide structure according to claim 2, characterized in that, The specific fabrication process of the silicon nitride waveguide is as follows: A first silicon oxide isolation layer (21) is deposited on the silicon substrate layer (1), and a silicon nitride layer (2) is deposited by chemical vapor deposition. The silicon nitride waveguide is obtained by photolithography and etching.

4. The method for fabricating a lithium niobate-silicon nitride waveguide structure according to claim 3, characterized in that, The lithium niobate wafer bonded to the silicon nitride wafer includes a silicon substrate layer (31), a third silicon oxide isolation layer (32), and a lithium niobate thin film layer (3) stacked sequentially.

5. The method for fabricating a lithium niobate-silicon nitride waveguide structure according to claim 4, characterized in that, The silicon nitride wafer and the lithium niobate wafer are bonded together using a smart-cut process.

6. The method for fabricating a lithium niobate-silicon nitride waveguide structure according to claim 5, characterized in that, The specific process of obtaining the lithium niobate thin film layer (3) after wafer bonding of the silicon nitride wafer and the lithium niobate wafer is as follows: The lithium niobate wafer was stripped using an ion implantation process, and a lithium niobate thin film layer with a thickness of 600±50 nm was obtained by chemical mechanical polishing and annealing (3).

7. The method for fabricating a lithium niobate-silicon nitride waveguide structure according to claim 6, characterized in that, The ion implantation includes the implantation of hydrogen ions and / or helium ions.

8. An optical gyroscope, based on the lithium niobate-silicon nitride waveguide structure of claim 1, characterized in that, include: Incident unit (11), modulation unit (12) and coupling unit (13); The incident unit (11) uses a silicon nitride waveguide as a substrate to receive and transmit incident light signals; The modulation unit (12) modulates the incident light signal using a lithium niobate-silicon nitride waveguide as a substrate to generate a modulated light signal. The coupling unit (13) is based on a silicon nitride waveguide, receives the modulated optical signal and couples it to the microring resonator (e).

9. An optical gyroscope according to claim 8, characterized in that, The incident unit (11) is equipped with a Y-branch (b) and a circulator (c) on a silicon nitride waveguide substrate; The Y-branch (b) is connected to the light source (a) via a silicon nitride waveguide. The incident light signal output from the light source (a) is transmitted along the silicon nitride waveguide and passes through the two passive devices, the Y-branch (b) and the circulator (c), before entering the modulation unit (12). Each circulator (c) is connected to a detector (d). The silicon nitride waveguide has a thickness of 400±10nm, and the optical signal is transmitted only inside the silicon nitride waveguide.

10. An optical gyroscope according to claim 9, characterized in that, The modulation unit (12) is based on a lithium niobate-silicon nitride waveguide. The incident light signal is transmitted into the mixed waveguide of lithium niobate and silicon nitride and is modulated by the lithium niobate modulator (f) to generate a modulated light signal. The modulated optical signal enters the coupling unit (13), the modulated optical signal is transmitted along the silicon nitride waveguide, and coupled to the multimode silicon nitride microring resonator (e); The lithium niobate-silicon nitride waveguide has a thickness of 600±50nm and a silicon nitride waveguide thickness of 400±10nm. A second silicon oxide isolation layer (22) is provided between the two waveguides. The thickness of the second silicon oxide isolation layer (22) between the silicon nitride layer (2) and the lithium niobate thin film layer (3) is 50±10nm.

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