A heterogeneously integrated gyro chip and a method of manufacturing the same

Abstract

The application relates to a hetero-integrated gyro chip and a preparation method thereof, wherein a waveguide pattern of the gyro chip is prepared based on silicon nitride and thin film lithium niobate, and the waveguide pattern comprises an end face coupler, a polarizer, two 1x2 MMIs of a 3 dB beam splitter, an interlayer coupler, a Mach-Zehnder type thin film lithium niobate waveguide structure and ground-signal-ground electrodes, and an ultrathin silicon nitride waveguide ring; the Mach-Zehnder type thin film lithium niobate waveguide structure comprises two phase modulators; the phase modulators are driven in a push-pull mode and are coupled in and out of the ultrathin silicon nitride waveguide ring in clockwise and counterclockwise modes; the gyro chip comprises an on-chip SLD light source and an on-chip detector which are integrated on the edge of the waveguide structure through end face packaging. The gyro chip is prepared based on a hetero-integration scheme of thin film lithium niobate and silicon nitride, the integration degree is greatly improved, the area and volume of traditional components are reduced, wafer-level preparation with low cost can be realized, and the gyro chip has the characteristics of full integration and compactness.

Description

Technical Field

[0001] This invention belongs to the field of integrated optics and inertial sensing technology, and specifically relates to a heterogeneous integrated gyroscope chip and its fabrication method. Background Technology

[0002] As a core component of high-performance inertial navigation systems, the integration and miniaturization of optical gyroscopes are current development trends. While traditional fiber optic gyroscopes are technologically mature, they suffer from large size, high cost, and difficulty in mass production. Integrated optical gyroscope solutions integrate optical components onto a chip, significantly reducing size, weight, and power consumption. However, pure silicon photonics integration solutions suffer from high power consumption, nonlinear effects, high insertion loss, and high waveguide loop loss. Pure thin-film lithium niobate integration solutions suffer from high cost and incomplete integration of reciprocal waveguides, modulation, and sensing loops.

[0003] Invention patent CN119717127A discloses an on-chip integrated photonic chip gyroscope, which uses a BCB micro-transfer integration process to fabricate an active-passive heterogeneous integrated chip. However, this process suffers from problems such as high alignment accuracy requirements, difficulty in controlling the thickness of the BCB material, poor flatness, and poor thermomechanical properties, leading to reliability issues during transfer. Invention patent CN118654657A discloses a fully integrated optical gyroscope containing a thin-film lithium niobate multifunctional chip, which suffers from high manufacturing costs and difficulty in controlling the low loss and high polarization of the waveguide ring.

[0004] Therefore, there is an urgent need to provide a new integration solution to address the problems existing in current integrated optical gyroscope solutions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a heterogeneous integrated gyroscope chip and its fabrication method, so as to solve the problems of high cost, incomplete integration of reciprocal waveguide, modulation and sensing loop and other units in the existing integration scheme.

[0006] This invention provides a heterogeneously integrated gyroscope chip whose waveguide pattern is based on silicon nitride (SiN) and thin-film lithium niobate (LN). It includes an end-face coupler, a polarizer, two 1x2 MMI 3 dB beamsplitters, an interlayer coupler, a Mach-Zehnder type thin-film lithium niobate waveguide structure, a ground-signal-ground electrode, and an ultrathin silicon nitride waveguide ring. The Mach-Zehnder type thin-film lithium niobate waveguide structure includes two phase modulators. The phase modulators are driven in a push-pull manner and coupled into and out of the ultrathin silicon nitride waveguide ring in a clockwise and counterclockwise manner. The gyroscope chip also includes an on-chip SLD light source and an on-chip detector integrated into the edge of the waveguide structure via end-face packaging.

[0007] The optical signal generated by the on-chip SLD light source enters the waveguide through the end-face coupler, is polarized by the polarizer, and then splits into two paths by two 3 dB beam splitters and an interlayer coupler. These paths enter the thin-film lithium niobate phase modulation region, and after conversion by the interlayer coupler, the optical signal enters the ultrathin silicon nitride waveguide ring for transmission. The clockwise and counterclockwise optical paths then return along their original paths, and the light intensity is obtained by the on-chip detector. Due to the Sagnac effect of double-beam interference in the clockwise and counterclockwise optical paths within the ultrathin silicon nitride waveguide ring, a phase difference occurs, which can ultimately be demodulated to obtain the magnitude of the rotational angular velocity.

[0008] Preferably, the interlayer coupler is an inverted conical structure with upper and lower layers, enabling flexible switching of the optical mode field between silicon nitride waveguide and lithium niobate waveguide.

[0009] Preferably, the ground-signal-ground electrode is an AlCu metal electrode.

[0010] The present invention also provides a method for fabricating the above-mentioned heterogeneous integrated gyroscope chip, comprising the following steps:

[0011] The waveguide structure of the gyroscope chip, from bottom to top, includes a silicon substrate, a silicon oxide buried layer, a silicon nitride waveguide, a silicon oxide buffer layer, a Mach-Zehnder type thin-film lithium niobate waveguide structure, a titanium nitride heater, an AlCu metal electrode, and a silicon oxide upper cladding.

[0012] S1. Thermally deposit a silicon oxide buried layer on a silicon substrate;

[0013] S2. A silicon nitride layer is deposited on a silicon oxide buried layer by low-pressure vapor deposition. After photolithography and dry etching, a silicon nitride waveguide is formed, and then an end coupler, a polarizer, two 3 dB beam splitters, and an ultrathin silicon nitride waveguide ring are constructed.

[0014] S3. Continue to deposit a silicon oxide buffer layer, and after chemical mechanical polishing, directly bond the thin film lithium niobate wafer, remove the silicon substrate, and then form a Mach-Zehnder type thin film lithium niobate waveguide structure, including two phase modulators, through photolithography and dry etching.

[0015] S4. The lithium niobate film with a thickness of 400-600 nm described in step S3 is etched to 100-500 nm, and then a cladding layer is deposited on silicon oxide. Subsequently, it is thinned to 1 μm by grinding and polishing. Titanium nitride heater and AlCu metal electrode are prepared on the flat silicon oxide by sputtering and dry etching.

[0016] S5. Using CMOS-compatible technology, an inverted conical interlayer coupler of silicon nitride-lithium niobate upper and lower layers is fabricated to achieve flexible switching of optical mode field between silicon nitride waveguide and lithium niobate waveguide;

[0017] S6. The on-chip light source and on-chip detector are end-face packaged and integrated into the edge of the waveguide structure to obtain the gyroscope chip.

[0018] Preferably, in step S2, the ultrathin silicon nitride waveguide ring is a single-layer structure with a thickness of 40-80 nm and a width of 3-4 μm, forming a low-loss, high-polarity-maintaining sensitive waveguide ring.

[0019] Preferably, the thickness of the silicon oxide buffer layer in step S3 is 150-200 nm.

[0020] Preferably, in step S3, the lithium niobate waveguide has a line width of 1-1.6 μm.

[0021] Preferably, the electrode spacing of the AlCu metal electrodes in step S4 is 3-5 μm, resulting in higher modulation efficiency.

[0022] The heterogeneous integration of ultrathin silicon nitride and thin-film lithium niobate in this invention exhibits unique advantages, providing an ideal solution for realizing high-performance, miniaturized optical gyroscope chips. In the heterogeneous integrated chip, the advantages of ultrathin silicon nitride and thin-film lithium niobate are complementary. Thin-film lithium niobate possesses excellent electro-optic effects, enabling efficient phase modulation; while silicon nitride waveguides exhibit low transmission loss, making them ideal for use as waveguide rings over ultra-long distances. Using mature CMOS-compatible processes, inverted conical interlayer couplers are fabricated between the upper and lower layers to achieve flexible switching of the optical mode field between the silicon nitride waveguide and the lithium niobate waveguide.

[0023] Furthermore, integrating the light source and detector into the chip assembly is a crucial step in realizing a practical gyroscope system. The light source couples the optical signal into the on-chip waveguide via a lens and an on-chip end-face coupler, while the surface-receiving detector is aligned and coupled to the on-chip end-face coupler via an edge-fitting method, constructing a complete miniaturized optical gyroscope system. This integration scheme not only reduces size but also significantly improves the stability of the integrated optical gyroscope system, laying the foundation for next-generation inertial navigation technology.

[0024] Beneficial effects

[0025] This invention combines the advantages of ultrathin silicon nitride and lithium niobate films. While maintaining high efficiency in phase modulation, it also features full integration and compactness, and possesses wafer-level fabrication and large-scale integration capabilities based on mature silicon-based optoelectronic devices. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the gyroscope chip and its components based on the heterogeneous integration of thin-film lithium niobate and silicon nitride in this invention.

[0027] Figure 2 This is a schematic diagram of the waveguide cross-section based on the heterogeneous integration scheme of thin-film lithium niobate and silicon nitride in this invention.

[0028] Figure 3This is a schematic diagram of the silicon nitride waveguide in this invention.

[0029] Figure 4 This is a waveguide mode field simulation diagram of the ultrathin silicon nitride scheme in an embodiment of the present invention. Detailed Implementation

[0030] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] Example

[0032] This embodiment provides a gyroscope chip based on heterogeneous integration of thin-film lithium niobate and silicon nitride, the structure of which is as follows: Figure 1 As shown, it includes an end-face coupler, a polarizer, two 1x2 MMI 3 dB beam splitters, and an inter-layer coupler ( Figure 1 (Not shown) A Mach-Zehnder type thin-film lithium niobate waveguide structure and a ground-signal-ground electrode, and an ultrathin silicon nitride waveguide ring; the Mach-Zehnder type thin-film lithium niobate waveguide structure includes two phase modulators; the phase modulators are driven by a push-pull method and coupled into and out of the ultrathin silicon nitride waveguide ring in a clockwise and counterclockwise manner; the gyroscope chip also includes an on-chip SLD light source and an on-chip detector integrated through end-face packaging; the interlayer coupler is an inverted conical structure of upper and lower layers, realizing flexible conversion of optical mode field between silicon nitride waveguide and lithium niobate waveguide;

[0033] The optical signal generated by the on-chip SLD light source enters the waveguide through the end-face coupler, is polarized by the polarizer, and then splits into two paths by two 3 dB beam splitters and an interlayer coupler. These paths enter the thin-film lithium niobate phase modulation region, and after conversion by the interlayer coupler, the optical signal enters the ultrathin silicon nitride waveguide ring for transmission. The clockwise and counterclockwise optical paths then return along their original paths, and the light intensity is obtained by the on-chip detector. Due to the Sagnac effect of double-beam interference in the clockwise and counterclockwise optical paths within the ultrathin silicon nitride waveguide ring, a phase difference occurs, which can ultimately be demodulated to obtain the magnitude of the rotational angular velocity.

[0034] The heterogeneously integrated gyroscope chip described above is fabricated using the following method:

[0035] The waveguide structure cross-section of the gyroscope chip is as follows: Figure 2 As shown, from bottom to top, it includes a silicon substrate, a silicon oxide buried layer, a silicon nitride waveguide, a silicon oxide buffer layer, a Mach-Zehnder type thin-film lithium niobate waveguide structure, a titanium nitride heater, an AlCu metal electrode, and a silicon oxide upper cladding.

[0036] S1. Thermally deposit a silicon oxide buried layer on a silicon substrate;

[0037] S2. A silicon nitride layer is deposited on a silicon oxide buried layer using low-pressure vapor deposition, and a silicon nitride waveguide is formed by photolithography and dry etching, such as... Figure 3 As shown, an end-face coupler, a polarizer, two 3 dB beam splitters, and an ultrathin silicon nitride waveguide ring are then constructed; the ultrathin silicon nitride waveguide ring is 80 nm thick and 4 μm wide, forming a low-loss, high-polarity-maintaining sensitive waveguide ring.

[0038] S3. Continue to deposit a 200 nm silicon oxide buffer layer, and after chemical mechanical polishing, directly bond the thin film lithium niobate wafer, remove the silicon substrate, and then form a Mach-Zehnder type thin film lithium niobate waveguide structure by photolithography and dry etching, including two phase modulators, with a lithium niobate waveguide line width of 1.5 μm;

[0039] S4. The lithium niobate film described in step S3 has a thickness of 400 nm. After etching 250 nm, a silicon oxide cladding layer is deposited on top of the lithium niobate film. Then, it is thinned to 1 μm thickness by chemical mechanical polishing. Titanium nitride heater and AlCu metal electrode are prepared on the flat silicon oxide by sputtering and dry etching. The electrode spacing is 4 μm, resulting in high modulation efficiency.

[0040] S5. Using CMOS-compatible technology, an inverted conical interlayer coupler of silicon nitride-lithium niobate upper and lower layers is fabricated to achieve flexible switching of optical mode field between silicon nitride waveguide and lithium niobate waveguide;

[0041] S6. The on-chip light source and on-chip detector (on-chip PD) are end-face packaged and integrated on the edge of the waveguide structure to obtain the gyroscope chip.

[0042] The waveguide mode field simulation diagram based on the thin-film lithium niobate and silicon nitride heterogeneous integration scheme in this embodiment is as follows: Figure 4 As shown, most of the mode field energy leaks into the silicon oxide layer to achieve low-loss transmission, and the effective refractive index of the mode field is 1.468.

[0043] This invention integrates a reciprocal waveguide unit, a phase modulation unit, and a waveguide ring sensing unit onto a single chip using a thin-film lithium niobate and silicon nitride heterogeneous integration scheme. The on-chip light source and detector are then end-face packaged to form a gyroscope assembly. Compared to traditional solutions, this approach significantly improves integration density, reduces the area and volume of traditional components, enables low-cost wafer-level fabrication, and features full integration and compactness.

Claims

1. A heterogeneously integrated gyroscope chip, characterized in that, The waveguide pattern of the gyroscope chip is based on silicon nitride and thin-film lithium niobate, and includes an end-face coupler, a polarizer, two 1x2MMI 3 dB beam splitters, an interlayer coupler, a Mach-Zehnder type thin-film lithium niobate waveguide structure, a ground-signal-ground electrode, and an ultrathin silicon nitride waveguide ring; the Mach-Zehnder type thin-film lithium niobate waveguide structure includes two phase modulators; the phase modulators are driven by a push-pull method and coupled into and out of the ultrathin silicon nitride waveguide ring in a clockwise and counterclockwise manner; the gyroscope chip includes an on-chip SLD light source and an on-chip detector integrated into the edge of the waveguide structure through end-face packaging.

2. The heterogeneously integrated gyroscope chip according to claim 1, characterized in that, The interlayer coupler is an inverted conical structure with upper and lower layers, enabling flexible switching of the optical mode field between silicon nitride waveguides and lithium niobate waveguides.

3. The heterogeneously integrated gyroscope chip according to claim 1, characterized in that, The ground-signal-ground electrode is an AlCu metal electrode.

4. A method for fabricating a heterogeneous integrated gyroscope chip as described in claim 1, comprising the following steps: The waveguide structure of the gyroscope chip, from bottom to top, includes a silicon substrate, a silicon oxide buried layer, a silicon nitride waveguide, a silicon oxide buffer layer, a Mach-Zehnder type thin-film lithium niobate waveguide structure, a titanium nitride heater, an AlCu metal electrode, and a silicon oxide upper cladding. S1. Thermally deposit a silicon oxide buried layer on a silicon substrate; S2. A silicon nitride layer is deposited on a silicon oxide buried layer by low-pressure vapor deposition, and a silicon nitride waveguide is formed by photolithography and dry etching. Then, an end coupler, a polarizer, two 3 dB beam splitters, and an ultrathin silicon nitride waveguide ring are constructed. S3. Continue to deposit a silicon oxide buffer layer, and after chemical mechanical polishing, directly bond the thin film lithium niobate wafer, remove the silicon substrate, and then form a Mach-Zehnder type thin film lithium niobate waveguide structure, including two phase modulators, through photolithography and dry etching. S4. The lithium niobate film with a thickness of 400-600 nm described in step S3 is etched to 100-500 nm, and then a cladding layer is deposited on silicon oxide. Subsequently, it is thinned to 1 μm by grinding and polishing. Titanium nitride heater and AlCu metal electrode are prepared on the flat silicon oxide by sputtering and dry etching. S5. A silicon nitride-lithium niobate bilayer inverted cone structure interlayer coupler was fabricated using a CMOS-compatible process; S6. The on-chip light source and on-chip detector are end-face packaged and integrated into the edge of the waveguide structure to obtain the gyroscope chip.

5. The preparation method according to claim 4, characterized in that, In step S2, the ultrathin silicon nitride waveguide ring is a single-layer structure with a thickness of 40-80 nm and a width of 3-4 μm.

6. The preparation method according to claim 4, characterized in that, The thickness of the silicon oxide buffer layer in step S3 is 150-200 nm.

7. The preparation method according to claim 4, characterized in that, In step S3, the lithium niobate waveguide has a line width of 1-1.6 μm.

8. The preparation method according to claim 4, characterized in that, In step S4, the electrode spacing of the AlCu metal electrodes is 3-5 μm.

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