Multilayer nitride acousto-optic coupling structure and preparation method thereof

Abstract

The invention discloses a multilayer nitride acousto-optic coupling structure and a preparation method thereof, and mainly solves the problem of poor modulation efficiency caused by limitation of piezoelectric films and optical waveguide materials in the prior art. Comprising the following steps: forming a SiO2 layer on Si through a PECVD (Plasma Enhanced Chemical Vapor Deposition) or thermal oxidation process, preparing an AlN layer on the SiO2 layer by adopting a magnetron sputtering or bonding process, growing a doped AlN layer on the AlN layer by adopting magnetron sputtering, and depositing a metal IDT layer on the doped AlN layer by adopting EBE (Electron Beam Enhancement); coating photoresist for multiple times and photoetching, and forming a bilaterally symmetrical piezoelectric layer in the middle of the AlN-doped layer; an optical transmission device is manufactured in the middle of the AlN layer, and the optical transmission device and the AlN films on the two sides jointly serve as a waveguide layer; and depositing a nitride protection layer on the upper surface of the modulation region by using an atomic layer deposition (ALD) process to complete the preparation of the modulator. The process is simple, the cost is low, the piezoelectric coefficient can be improved, lattice matching can be improved, and the modulation efficiency can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microelectronic devices, further relates to the technical field of acousto-optic modulators, and in particular to a multilayer nitride acousto-optic coupling structure and a preparation method thereof, which can be used in the fields of optical communication, spectral analysis and optical signal processing. BACKGROUND

[0002] With the continuous development of microelectronic technology, the size of transistors in chips is getting smaller and smaller, the speed of a single transistor is getting faster and faster, and the integration level is getting higher and higher, so that the computing speed of each module is greatly improved, and the communication rate requirement between each module in the chip is also increasing. At present, in the timing management of high-end chips, the delay of interconnection lines accounts for more than 60% of the total delay of the chip, and the interconnection line has become the biggest factor restricting the speed of the chip. Due to the parasitic effect of the line, the delay of the traditional electrical interconnection cannot be avoided, and the adjacent lines will generate crosstalk when transmitting high-speed signals, which affects the signal quality, so there is an urgent need for a new type of interconnection form with high bandwidth, low delay and weak interference in the industry.

[0003] Optical communication is undoubtedly the best candidate for new communication methods. Electronics has the characteristics of easy storage and easy calculation, while photons have the characteristics of high frequency and low loss, so the integration of microelectronic and optoelectronic devices on a chip is the inevitable development direction of future chips. Microelectronic devices are responsible for storage and calculation, and optoelectronic devices are responsible for electrical-optical conversion and optical interconnection. The core device for realizing on-chip optical interconnection is the modulator, which is responsible for converting electrical signals into optical signals. Modulators are mainly divided into electro-optic modulators and acousto-optic modulators. The working principle of the acousto-optic modulator is to convert electrical signals into acoustic signals, and then convert acoustic signals into optical signals. Compared with electro-optic modulators, acousto-optic modulators have the advantages of high signal-to-noise ratio, low starting threshold and can only be driven by specific frequencies, and are expected to replace electro-optic modulators in some application scenarios.

[0004] An acousto-optic modulator is an optoelectronic device that converts high-speed electrical signals into optical signals, mainly composed of an interdigital transducer (IDT), a piezoelectric film and an optical waveguide. In a typical thin-film acousto-optic modulator structure, the piezoelectric film and the optical waveguide material form the core functional area; the piezoelectric film is responsible for converting radio frequency electrical signals into mechanical acoustic waves, while the optical waveguide restricts the propagation path of the optical field and enhances the interaction intensity of light and sound. The piezoelectric coefficient of the piezoelectric film determines the conversion efficiency of electrical energy to mechanical energy, and the bandgap of the optical waveguide material affects the optical loss and the compatibility of the working waveband. As can be seen, the piezoelectric coefficient of the piezoelectric film and the bandgap of the optical waveguide material are two factors that seriously restrict the modulation efficiency of the acousto-optic modulator. In most current research, the piezoelectric film and the optical waveguide are mainly prepared from the same material, such as lithium niobate (LN) and aluminum nitride (AlN).

[0005] In the prior art, the piezoelectric film of the acousto-optic modulator is mainly prepared by LN and AlN materials, and the waveguide is mainly prepared by LN and Si materials. For example, the preparation scheme proposed in Shi H, Huang C, Yu L, et al. Intramodal acousto-optics scattering of optopiezomechanical device on aluminum nitride [J]. Journal of Lightwave Technology, 2023, 41 (19): 6348-6355. The piezoelectric film and the optical waveguide are both prepared by AlN material, and a cavity is etched below the piezoelectric film to form a suspended acousto-optic modulator structure. This design uses a compact IDT to reduce the number of interdigital electrodes, successfully verifies the microwave-mechanical wave conversion capability, and finally realizes acousto-optic modulation. In Cai L, Mahmoud A, Khan M, et al. Acoustooptical modulation of thin film lithium niobate waveguide devices [J]. Photonics Research, 2019, 7 (9): 1003-1013. The piezoelectric film, interferometer and resonator are all prepared by LN material, and the optical waveguide adopts a ridge waveguide structure. The interdigital electrodes are arranged with reflective gratings in front and back to reflect the scattered surface acoustic waves back to improve the utilization efficiency of the surface acoustic waves and complete efficient modulation. In the patent document with publication number CN113419364A, the piezoelectric film and the waveguide are both prepared by lithium niobate material, and a groove is etched on the top of the waveguide to solve the problem of weak interaction between the traditional regular strip waveguide and the surface acoustic wave. The above-mentioned groove can enhance the elastic deformation degree of the waveguide excited by the surface acoustic wave and improve the acousto-optic modulation efficiency. However, for the piezoelectric film, the biggest defect of LN material is that it cannot be deposited at low temperature, so it does not have CMOS process compatibility and is expensive. For the optical waveguide, the biggest defect of Si material is that the band gap is narrow, only 1.12eV at room temperature, and when a high-power laser is input, a huge loss will be generated due to the two-photon absorption effect (TPA), so the light spectrum range is small. LN material still does not have CMOS process compatibility.

[0006] For the piezoelectric film, its piezoelectric coefficient d 33Especially important, piezoelectric coefficient represents the conversion efficiency between electrical signal and acoustic signal. The piezoelectric coefficient of AlN is lower than that of TFLN, but the polycrystalline AlN film with performance close to single crystal can be deposited at low temperature (350℃) by magnetron sputtering process, and the AlScN film prepared by element doping (such as scandium element Sc) has a relatively high piezoelectric coefficient, which is 3-5 times higher than that of AlN film; the preparation methods of AlN and AlScN are compatible with CMOS process, so in terms of piezoelectric film, AlScN has more advantages than AlN. For optical waveguide, the refractive index and band gap are particularly important, the refractive index represents the ability to bind photons, and the band gap represents the ability to carry optical energy. The large band gap of AlN makes it work in the mid-infrared, near-infrared and even visible light bands when used as a waveguide, avoiding optical energy loss caused by light-induced birefringence and two-photon absorption (TPA) effects; compared with AlScN, AlN has fewer crystal structure defects, and AlScN has more crystal defects, so its ability to limit light modes is inferior to AlN; therefore, in terms of optical waveguide, AlN has more advantages. Therefore, it is urgent to study an integrated solution that can comprehensively consider the respective advantages of AlScN and AlN materials. SUMMARY

[0007] The present application aims at the deficiencies of the prior art, and provides a multilayer nitride acousto-optic coupling structure and a preparation method thereof. The present application aims at solving the problem of poor modulation efficiency caused by the restriction of piezoelectric film and optical waveguide material in the prior art. The AlScN&AlN composite structure acousto-optic modulator based on silicon substrate designed in the present application comprises AlScN as a piezoelectric film and AlN as an optical waveguide; through the processes of layer-by-layer growth and etching of AlN and AlScN, the piezoelectric film and optical waveguide structure are formed, the sound field and light field are well coupled, and the high-speed modulation of signals is completed. The present application has the advantages of simple process and low cost, can improve the piezoelectric coefficient, improve the lattice matching, and improve the modulation efficiency.

[0008] To achieve the above-mentioned purpose, the technical scheme of the present application comprises the following:

[0009] A multilayer nitride acousto-optic coupling structure comprises, from bottom to top, a Si substrate 1, a SiO2 layer 2 and a modulation region 3.

[0010] The modulation region 3 is composed of a metal IDT layer 31, a piezoelectric layer 32 and a waveguide layer 33; the piezoelectric layer 32 and the waveguide layer 33 form a composite structure;

[0011] The waveguide layer 33 comprises AlN films uniformly distributed on both sides and an optical transmission device in the middle, the device being used to limit the transmission of light waves; the piezoelectric layer 32 is distributed symmetrically on the upper surface of the AlN films of the waveguide layer 33; and the metal IDT layer 31 is located on the upper surface of the piezoelectric layer 32;

[0012] The piezoelectric layer 32 adopts a doped AlN film, the doping element is scandium Sc, and the doping ratio is 5% to 45%, which is used to improve the piezoelectric coefficient of the piezoelectric layer (32).

[0013] Further, the above-mentioned metal IDT layer 31 is used to load a radio frequency electrical signal to the electrode, so that the piezoelectric layer 32 generates a reverse piezoelectric effect; the piezoelectric layer 32 generates a surface acoustic wave by using the material reverse piezoelectric effect, and transmits the surface acoustic wave to the waveguide layer; the waveguide layer 33 uses the photoelastic effect to complete the modulation of the laser in the waveguide by periodically changing the refractive index of the material generated by the surface acoustic wave.

[0014] Further, the above-mentioned metal IDT layer 31 is made of a metal material, which at least includes aluminum Al, copper Cu, silver Ag, and gold Au; the interdigital period of the IDT is greater than the width of the waveguide.

[0015] Further, the above-mentioned metal IDT layer 31 is symmetrically distributed on both sides of the piezoelectric layer 32, forming a double interdigital transducer structure.

[0016] A preparation method of a high-speed acousto-optic modulator, comprising the following steps:

[0017] S1. Pre-treating a Si wafer to obtain a Si substrate 1 with impurities removed from the surface;

[0018] S2. Forming a SiO2 layer 2 on the Si substrate 1 by a plasma enhanced chemical vapor deposition (PECVD) or a thermal oxidation process;

[0019] S3. Preparing a c-axis oriented AlN layer on the SiO2 layer by a magnetron sputtering or a bonding process;

[0020] S4. Growing a c-axis oriented doped AlN layer on the AlN layer by a magnetron sputtering;

[0021] S5. Coating a photoresist on the doped AlN layer and performing photolithography, depositing a metal electrode by an electron beam evaporation (EBE), and removing the photoresist to obtain a metal IDT layer 31;

[0022] S6. Coating a photoresist and performing photolithography, removing the middle part of the doped AlN layer by a strong oxidizing etching liquid to form a piezoelectric layer 32 symmetrically distributed on the left and right sides, which is used to expose the lower AlN layer, and removing the photoresist;

[0023] S7. Forming an optical transmission device in the middle of the AlN layer, which is used as a waveguide layer 33 together with the AlN films on both sides of the device; the metal IDT layer 31, the piezoelectric layer 32, and the waveguide layer 33 constitute a modulation region 3;

[0024] S8. Depositing a nitride protective layer on the surface of the modulation region 3 by an atomic layer deposition (ALD) process, and completing the preparation of the acousto-optic modulator.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] Firstly, the present application considers that AlScN has high sound speed and high piezoelectric coefficient, and AlN has less lattice defects and larger band gap, so AlScN is selected as the piezoelectric thin film material and AlN is selected as the optical waveguide material; the integrated acousto-optic modulator has higher modulation efficiency than the LN acousto-optic modulator.

[0027] Secondly, the preparation processes of AlN and AlScN used in the present application are compatible with CMOS process, and when etching the top AlScN thin film by wet etching, the two have different selectivity to strong oxidizing etchants such as piranha solution (a mixture of concentrated sulfuric acid and hydrogen peroxide), so that the etching of AlScN thin film has higher fault tolerance, and the lower AlN thin film will not be damaged in a short time, so that large-scale integration can be quickly realized in the background of the highly mature CMOS process; at the same time, since the production and manufacturing technology of LNOI wafer is the same as the traditional SOI wafer manufacturing method, and is mainly realized based on "Smart-cut", which mainly includes five steps: ion implantation, substrate preparation, thin film bonding, annealing and stripping, and CMP planarization; while AlN wafer can be prepared by magnetron sputtering, chemical vapor deposition and other methods, the process is relatively simple, so for the same size wafer, the price of LN is several times that of AlN; the present application significantly simplifies the process steps and reduces the production cost.

[0028] Thirdly, since Sc exists in the form of substitutional impurity in AlN, the lattice matching degree at the interface of AlScN and AlN is high, and when the two are integrated together, stress will not be generated due to lattice mismatch, which will affect the device performance.

[0029] Fourthly, the present application covers nitride on the piezoelectric thin film and the optical waveguide, so as to protect the two from "oxygen pollution"; the AlScN and AlN composite structure is realized by using dielectric loading to avoid damage caused by etching; at the same time, double-channel modulation is adopted to increase the number of channels and improve the communication efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the acousto-optic modulator in the present application;

[0031] Figure 2 It is a schematic diagram of the structure of the modulation region in the present application;

[0032] Figure 3 It is a process flow chart of the preparation of the acousto-optic modulator in the present application;

[0033] Figure 4 It is a simulation diagram of the optical mode in the straight waveguide in the present application;

[0034] Figure 5 is a simulation diagram of a PCNBC first-order light mode in the application;

[0035] Figure 6 is a structural schematic diagram of a ridge waveguide modulator provided in Example Three in the application;

[0036] Figure 7 is a structural schematic diagram of a nitride-covered strip waveguide modulator provided in Example Four in the application;

[0037] Figure 8 is a structural schematic diagram of a nitride-covered ridge waveguide modulator provided in Example Four in the application;

[0038] Figure 9 is a structural schematic diagram of a straight waveguide modulator realized in a dielectric loading structure provided in Example Five in the application;

[0039] Figure 10 is a structural schematic diagram of a straight waveguide double-channel modulator provided in Example Six in the application;

[0040] Figure 11 is a structural schematic diagram of a Mach-Zehnder interferometer (MZI) modulator provided in Example Seven in the application;

[0041] Figure 12 is a structural schematic diagram of a micro-ring resonator (MRR) modulator provided in Example Seven in the application;

[0042] Figure 13 is a structural schematic diagram of a photonic crystal nanobeam cavity (PCNBC) modulator provided in Example Seven in the application;

[0043] Figure 14 is a structural schematic diagram of a cavity modulator with an IDT lower SiO2 layer provided in Example Eight in the application;

[0044] Figure 15 is a structural schematic diagram of a cavity modulator with a ridge waveguide lower SiO2 layer provided in Example Nine in the application;

[0045] Figure 16 is a structural schematic diagram of a cavity modulator with an IDT and a ridge waveguide lower SiO2 layer provided in Example Ten in the application;

[0046] Figure 17 is a structural schematic diagram of a cavity modulator with an IDT and a ridge waveguide lower SiO2 layer and a Si layer provided in Example Eleven in the application; DETAILED DESCRIPTION

[0047] The application will be further described below with reference to the accompanying drawings.

[0048] Embodiment One: refer to the attached Figures 1-2 The present application provides a high-speed acousto-optic modulator, the overall structure as shown in Figure 1 from bottom to top in turn comprising: Si substrate 1, SiO2 layer 2 and modulation region 3; the modulation region 3 is composed of metal IDT layer 31, piezoelectric layer 32 and waveguide layer 33, as shown in Figure 3 ; wherein the piezoelectric layer 32 and the waveguide layer 33 form a composite structure; the waveguide layer 33 contains AlN film uniformly distributed on both sides and the middle optical transmission device, which is used to limit the transmission of light waves; the piezoelectric layer 32 is on the surface of the AlN film of the waveguide layer 33, and is symmetrically distributed on the left and right; the metal IDT layer 31 is located on the upper surface of the piezoelectric layer 32, which can be on one side or symmetrically distributed on both sides, which is determined according to the type of optical transmission device; the piezoelectric layer 32 adopts doped AlN film, which is used to improve the lattice matching degree at the interface between the piezoelectric layer 32 and the waveguide layer 33. In this embodiment, the piezoelectric layer 32 adopts doped AlN film, wherein the doping element is preferably scandium Sc, and the doping element exists in the form of substitutional impurity in the crystal, replaces Al atoms, and the doping ratio is 5% to 45%.

[0049] The metal IDT layer 31 in the above embodiment is made of a metal material, which at least includes aluminum Al, copper Cu, silver Ag, gold Au, etc.; the IDT layer is used to load radio frequency electrical signals to the electrode, so that the piezoelectric layer 32 generates inverse piezoelectric effect; the piezoelectric layer 32 generates acoustic surface wave by using the material inverse piezoelectric effect, and transmits the acoustic surface wave to the waveguide layer; the waveguide layer 33 utilizes the photoelastic effect to complete the modulation of the laser in the waveguide by periodically changing the refractive index of the material through the acoustic surface.

[0050] In the structure provided in this embodiment, AlScN is preferably used as the piezoelectric layer, and AlN is preferably used as the waveguide layer, which respectively utilizes the high piezoelectric coefficient of AlScN and the large band gap of AlN to improve the modulation efficiency; and the AlN wafer preparation process is relatively simple and low in cost. Since Sc exists in the form of substitutional impurity in AlN, the lattice matching degree at the interface between AlScN and AlN is high, and no stress is generated at the contact surface to cause structural deformation. And the composite structure of AlScN on the top and AlN on the bottom can utilize the different characteristics of the etchant selection ratio of the two in the preparation process to improve the process tolerance, without causing unexpected damage to the underlying AlN, the preparation process is compatible with CMOS process, simplifying the process steps, which is conducive to rapid large-scale production.

[0051] Embodiment Two: refer to the attached Figure 3 The present application provides a preparation method of a high-speed acousto-optic modulator, which specifically comprises the following steps:

[0052] Step 1. Pre-treat the Si wafer to obtain a Si substrate 1 with surface impurities removed;

[0053] Step 2. Form a SiO2 layer 2 on the Si substrate 1 by a plasma enhanced chemical vapor deposition (PECVD) or thermal oxidation process;

[0054] Step 3. Prepare a c-axis oriented AlN layer on the SiO2 layer using a magnetron sputtering or bonding process;

[0055] Step 4. Grow a c-axis oriented doped AlN layer on the AlN layer using a magnetron sputtering process;

[0056] Step 5. Apply photoresist and perform photolithography on the doped AlN layer, deposit a metal electrode using electron beam evaporation (EBE), remove the photoresist, and obtain a metal IDT layer 31;

[0057] Step 6. Apply photoresist and perform photolithography, remove the middle part of the doped AlN layer using a strong oxidizing etching solution to form a left-right symmetric piezoelectric layer 32 for exposing the underlying AlN, and remove the photoresist;

[0058] Step 7. Form an optical transmission device in the middle of the AlN layer, which together with the AlN thin film on both sides serves as a waveguide layer 33; the metal IDT layer 31, piezoelectric layer 32, and waveguide layer 33 constitute a modulation region 3; the optical transmission device formed in this step of the embodiment is used to constrain the optical mode and can be a waveguide structure, or can be replaced by a Mach-Zehnder interferometer (MZI), a micro-ring resonator (MRR) structure, or a photonic crystal nanobeam cavity (PCNBC) structure.

[0059] Step 8. Deposit a nitride protective layer on the surface of the modulation region 3 using an atomic layer deposition (ALD) process to complete the preparation of the acousto-optic modulator; in this embodiment, the nitride deposited on the modulation region 3 is used to protect the waveguide layer 33 from oxygen element erosion, and the nitride selected here is preferably any one of silicon nitride (Si3N4), gallium nitride (GaN), boron nitride (BN), or phosphorus nitride (P3N5).

[0060] Embodiment Three: Refer to Fig. 3, the high-speed acousto-optic modulator of the embodiment is prepared using the same overall process as Embodiment Two, and the optical transmission device formed in the middle of the AlN layer is a ridge waveguide structure, which is implemented as follows: Figure 6

[0061] ​In step 8 of the above process, dry etching is used to form the AlN waveguide. This allows for control of the etching depth, eliminating the need to completely etch the AlN to expose the underlying SiO2 layer. A certain thickness of AlN is retained to form a ridge waveguide. In this structure, surface acoustic waves (SAWs) propagate through the AlScN film, the AlN film, and air at extreme distances to the waveguide to modulate the optical carrier. However, some SAWs still leak into the SiO2 substrate within the AlN film. Therefore, the ridge waveguide structure proposed in this embodiment allows SAWs to propagate along the planar region of the ridge waveguide. Furthermore, since the optical mode is distributed in both the strip and planar regions of the ridge waveguide, this portion of SAWs can also modulate the optical carrier, increasing the acousto-optic overlap area.

[0062] Example 4: Refer to Appendix Figure 7 , 8 The fabrication method of the high-speed acousto-optic modulator proposed in this embodiment is the same as that in Embodiment 2, except that the nitride-covered modulator structure is as follows:

[0063] In the appendix Figure 2 The AlScN and AlN materials are protected by a nitride film, such as silicon nitride (Si3N4), gallium nitride (GaN), boron nitride (BN), or phosphorus nitride (P3N5), which are low-loss dielectrics. Because Sc and Al atoms have a strong affinity for oxygen, oxygen in the air, at the material interface, and in the SiO2 substrate can replace nitrogen atoms in the AlScN and AlN materials, disrupting the crystal lattice and affecting the piezoelectric coefficient of the AlScN film and the photoelastic effect of the AlN film, thus impacting the modulation efficiency of the acousto-optic modulator. Therefore, a nitride coating is used to isolate the AlScN from the air. (See attached image.) Figure 8 As shown, with the attached Figure 7 Similarly, ridge waveguides also need to be protected by nitride coatings, including materials such as Si3N4, GaN, BN, and P3N5.

[0064] Example 5: Refer to Appendix Figure 9 The fabrication method of the high-speed acousto-optic modulator proposed in this embodiment is the same as that in Embodiment 2. The specific method of realizing the modulator structure by dielectric loading is given below:

[0065] The light energy is limited in the waveguide by means of medium loading. Since the refractive index of the medium is lower than that of AlN, the light field is still limited in the composite structure of SiO2-AlN-medium, which constitutes a composite waveguide. The etching error of traditional ICP, RIE and other etching processes will cause the roughness of the side of the waveguide, greatly weakening the limitation of the waveguide on the light field. The advantage of this structure is that the etching of the AlN film to form the waveguide is avoided, and the composite waveguide structure of SiO2-AlN-medium is formed by means of medium loading, so that the limitation of the AlN waveguide on the light field will not be affected by the introduction of the side wall roughness and lattice damage.

[0066] The medium loading processing steps are similar to those of Example Two. In step 8, an atomic layer deposition (ALD) process is used to deposit a medium material with the same width as the waveguide on the AlN layer to form a composite waveguide structure. The remaining process steps are the same.

[0067] Example Six: Refer to the accompanying drawings Figure 10 The preparation method of the high-speed acousto-optic modulator proposed in this embodiment realizes the same overall steps as in Example Two. The specific implementation of the modulator obtained by taking the waveguide structure as the light transmission device is as follows:

[0068] Reflection gratings are designed before and after the IDT for reflecting the surface acoustic wave, improving the utilization rate of the surface acoustic wave, and thus improving the modulation efficiency. Two pairs of interdigital electrode structures are used to modulate the light mode in the waveguide. Specifically, two pairs of interdigital transducers with different periods are arranged on both sides of the waveguide to generate corresponding frequency surface acoustic waves. At this time, the output laser of the modulator is the superposition of the modulation results of two different frequency radio frequency signals.

[0069] The demodulation signals of the corresponding frequencies can be obtained through the following three steps:

[0070] Step One. Convert the optical signal into an electrical signal through a detector. At this time, the electrical signal is the superposition of the different frequency electrical signals of the two pairs of interdigital transducers:

[0071] Step Two. Convert the time domain signal to the frequency domain by using fast Fourier transform (FFT) to separate the different frequency signals.

[0072] Step Three. Perform inverse fast Fourier transform (IFFT) on the spectrum regions corresponding to the two different frequency radio frequency signals, respectively, to restore the two groups of signals to the time domain, and finally obtain two groups of separated different frequency radio frequency signals.

[0073] Thus, two channels are obtained, that is, the modulation and demodulation process of two communication frequencies can be realized on one straight waveguide acousto-optic modulator, so that the communication rate is improved to twice that of a single channel.

[0074] Example Seven: Refer to the accompanying drawings Figures 11-13The preparation method of the high-speed acousto-optic modulator provided in the embodiment, the overall implementation steps are the same as those of Embodiment Two, and the implementation mode of preparing the modulator by using a Mach-Zehnder interferometer (MZI), a micro-ring resonator (MRR), or a photonic crystal nanobeam cavity (PCNBC) as an optical transmission device is given:

[0075] The Figure 10 The straight waveguide modulator cannot realize the interference and resonance of optical energy, and thus the optical energy density is low. Figure 11 The Mach-Zehnder interferometer (MZI), the Figure 12 The micro-ring resonator (MRR), or the photonic crystal nanobeam cavity (PCNBC) in the Figure 13 The Mach-Zehnder interferometer, the micro-ring resonator, and the photonic crystal nanobeam resonant cavity can all be used as the laser carrier of the acousto-optic modulator provided in the embodiment, and thus the structure has great development potential.

[0076] Embodiment Eight: Refer to Figure 14 The high-speed acousto-optic modulator provided in the embodiment is based on Embodiment Three, the SiO2 waveguide layer is hollowed out to form a cavity directly below the IDT, so as to limit the downward leakage of sound waves, reduce the divergence of sound waves, and improve the utilization rate of sound waves.

[0077] Embodiment Nine: Refer to Figure 15 The high-speed acousto-optic modulator provided in the embodiment is based on Embodiment Three, the SiO2 waveguide layer is hollowed out to form a cavity directly below the ridge waveguide. The air in the cavity and the ridge waveguide form a larger refractive index difference, and the optical mode in the waveguide is better constrained.

[0078] Embodiment Ten: Refer to Figure 16 The high-speed acousto-optic modulator provided in the embodiment is based on Embodiment Three, the SiO2 layer is hollowed out to form a cavity below the waveguide layer. In this way, the downward leakage of sound waves is limited, the utilization rate of sound waves is improved, the air in the cavity can form a larger refractive index difference with the AlN ridge waveguide to better constrain the optical mode in the waveguide, and the cavity can also increase the deformation degree of the waveguide under the action of sound waves. Stronger deformation will produce a larger periodic refractive index change amplitude, and the action efficiency of sound waves on the waveguide is improved.

[0079] Embodiment Eleven: Refer to Figure 17 The high-speed acousto-optic modulator provided in the embodiment is based on Embodiment Three, and the SiO2 layer and the Si substrate layer are hollowed out by using a bottom silicon etching process. The same effect as that of Embodiment Ten is achieved, in addition, the cavity helps to release the stress between different layers and prevent the device from deforming.

[0080] The high-speed acousto-optic modulator structure provided by the application replaces the traditional AlN and LN materials with AlScN to improve the piezoelectric coefficient and reduce the cost; the optical waveguide replaces the traditional Si and LN materials with AlN to increase the band gap and expand the light spectrum; and both the AlScN piezoelectric film and the AlN film can be deposited at low temperature, so that the acousto-optic modulator provided by the application has COMS process compatibility, significantly reducing the process difficulty. The technical scheme can effectively improve the modulation efficiency, reduce the chip cost and increase the number of channels, provides a key basic solution for on-chip integrated acousto-optic modulators, and has important application prospects.

[0081] The effect of the application will be further described below in combination with a simulation experiment.

[0082] 1. Simulation conditions:

[0083] The simulation experiment of the application is carried out in the COMSOL Multiphysics 6.2 environment of finite element analysis software.

[0084] 2. Simulation content:

[0085] The wave optics module, electromagnetic wave and frequency domain physical field in the software are used to simulate the light mode distribution in the straight waveguide and PCNBC by using the mode analysis function, and the results are shown in Figure 4 and 5 .

[0086] 3. Simulation result analysis:

[0087] Figure 4 The result graph of the light mode in the straight waveguide, from which it can be seen that the light mode is well limited in the waveguide;

[0088] Figure 5 The first-order light mode result graph in the PCNBC, from which it can be seen that the first-order light mode of the PCNBC has a resonance center, and the light energy is well limited in the cavity at the resonance center. Compared with the existing waveguide structure, the PCNBC can realize the distribution of extremely high light energy density in the cavity, greatly improving the modulation efficiency.

[0089] It should be noted that the user information (including but not limited to user equipment information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or authorized by all parties, and the collection, use and processing of related data need to comply with relevant national and regional laws, regulations and standards, and provide corresponding operation entrances for users to choose authorization or refusal.

[0090] The simulation analysis proves the correctness and effectiveness of the method provided by the application.

[0091] The portions of the application that are not specifically recited are within the common general knowledge of a person skilled in the art.

[0092] The above description is only preferred embodiments of the present application, not to limit the present application. Obviously, for those skilled in the art, based on the content and principles of the present application, various modifications and changes in form and details can be made without departing from the principles and structures of the present application. However, these modifications and changes based on the idea of the present application are still within the protection scope of the claims of the present application.

Claims

1. A multilayer nitride acousto-optic coupling structure, characterized by, From bottom to top, it includes Si substrate (1), SiO2 layer (2) and modulation region (3) in sequence. The modulation region (3) is composed of metal IDT layer (31), piezoelectric layer (32) and waveguide layer (33); wherein the piezoelectric layer (32) and the waveguide layer (33) form a multilayer structure. The waveguide layer (33) contains AlN thin films uniformly distributed on both sides and an optical transmission device located in the middle part, which is used to constrain the optical field; the piezoelectric layer (32) is on the upper surface of the AlN thin films of the waveguide layer (33) and is symmetrically distributed on the left and right; the metal IDT layer (31) is on the upper surface of the piezoelectric layer (32). The piezoelectric layer (32) adopts doped AlN thin film, the doping element is scandium Sc, and the doping ratio is 5% to 45%, which is used to improve the piezoelectric coefficient of the piezoelectric layer (32).

2. The structure of claim 1, wherein: The metal IDT layer (31) is used to load radio frequency electrical signals onto the electrode, effectively utilizing the inverse piezoelectric effect of the piezoelectric layer (32); the piezoelectric layer (32) generates surface acoustic waves by utilizing the inverse piezoelectric effect of the material, and transmits the surface acoustic waves to the waveguide layer; the waveguide layer (33) utilizes the photoelastic effect to complete the modulation of the optical field in the waveguide by periodically changing the refractive index of the material through the acoustic surface.

3. The structure of claim 1, wherein: The metal IDT layer (31) is made of metal materials, which at least include aluminum Al, copper Cu, silver Ag and gold Au; the interdigital period of the IDT is greater than the width of the waveguide.

4. The structure of claim 1, wherein: The metal IDT layer (31) is symmetrically distributed on both sides of the piezoelectric layer (32), forming a double interdigital transducer structure.

5. A method for fabricating a multilayer nitride acousto-optic coupling structure, characterized in that, The method comprises the following steps: S1. Pre-treating the Si wafer to obtain the Si substrate (1) with impurities removed from the surface; S2. Forming the SiO2 layer (2) on the Si substrate (1) by plasma enhanced chemical vapor deposition PECVD or thermal oxidation process; S3. Growing the c-axis oriented AlN layer on the polished SiO2 layer by magnetron sputtering or metal organic chemical vapor deposition MOCVD; S4. Growing the c-axis oriented doped AlN layer on the AlN layer by magnetron sputtering; S5. Coating photoresist on the doped AlN layer and performing photolithography, depositing metal electrodes by electron beam evaporation EBE, and removing the photoresist to obtain the metal IDT layer (31); S6. Coating photoresist and performing photolithography, removing the middle part of the doped AlN layer by strong oxidizing etching liquid wet method to form the piezoelectric layer (32) symmetrically distributed on the left and right, for exposing the lower AlN, and removing the photoresist; S7. Forming the optical transmission device in the middle part of the AlN layer, which together with the AlN thin films on both sides of the device serves as the waveguide layer (33); the metal IDT layer (31), the piezoelectric layer (32) and the waveguide layer (33) constitute the modulation region (3); S8. Depositing the nitride protective layer on the upper surface of the modulation region (3) by atomic layer deposition ALD process, to complete the preparation of the acousto-optic modulator.

6. The structure of claim 5, wherein: The SiO2 layer (2) in step S2 comprises an air cavity (21) between the modulation region (3) and the Si substrate (1) for realizing the suspended structure; the air cavity overlaps with the metal IDT layer (31) of the modulation region (3), or overlaps with the optical transmission device in the waveguide layer (33), or overlaps with both.

7. The method of claim 5, wherein: The optical transmission device in step S7 comprises a strip waveguide, a ridge waveguide, a Mach-Zehnder interferometer (MZI), a micro-ring resonator (MRR) structure and a photonic crystal nanobeam cavity (PCNBC) structure.

8. The method of claim 7, wherein: The optical transmission device is obtained by coating a photoresist on the doped AlN layer, etching the AlN layer in the middle part by using a Cl2-based dry etching method after photoetching, and finally removing the photoresist.

9. The method of claim 7, wherein: The optical transmission device is formed by using a dielectric loading method, and a composite optical transmission device structure is formed by covering the waveguide layer (33) with a dielectric having the same width as the optical transmission device.

10. The method of claim 5, wherein: The nitride deposited on the modulation region (3) in step S9 is used for protecting the waveguide layer (33) from oxygen elements, and the nitride comprises silicon nitride Si3N4, gallium nitride GaN, boron nitride BN and phosphorus nitride P3N5.

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