Aluminum nitride waveguide structure based on nitride layered coating and preparation method thereof

Abstract

The application discloses an aluminum nitride waveguide structure based on nitride layered coating and a preparation method thereof, and mainly solves the problem of poor long-term working stability of an electro-optical modulator caused by oxygen permeation in the prior art. The scheme comprises the following steps: designing a waveguide modulation area composed of a top electrode, two bottom electrodes, a nitride coated waveguide structure, an oxide cover layer and an oxide buried layer on a silicon substrate; wherein the nitride coated waveguide structure is located on the upper surface of the buried layer, the cover layer covers the waveguide structure; the top electrode is located directly above the waveguide structure and is in close contact with the upper surface of the cover layer; and the two bottom electrodes are respectively located on the left and right sides of the waveguide. The application realizes basic protection by preparing a base nitride layer, and realizes full-wrapping oxygen barrier on the top of the waveguide functional layer, so as to isolate the pollution of oxygen elements to the material; the performance degradation phenomenon of an electro-optical modulator based on an AlN waveguide and other optoelectronic devices can be avoided, and the electro-optical modulation efficiency and reliability of the device are effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon-based photonic integrated circuits, further relates to a composite optical waveguide structure, in particular to an aluminum nitride waveguide structure based on nitride layered coating and a preparation method thereof. The application can be used for the manufacture of Mach-Zehnder (MZ) modulators, micro-ring modulators, nanobeam resonator modulators and the like. BACKGROUND

[0002] As one of the core technologies in the field of modern communication, optical communication technology has been widely used in global communication network infrastructure construction due to its high-speed transmission, large capacity, low loss and strong anti-interference ability. In an optical communication system, an electro-optic modulator, as a key functional device, realizes efficient conversion of electrical signals to optical signals by controlling the phase of the optical carrier signal, thereby supporting long-distance and high-speed transmission of information. With the rapid development of emerging technologies such as 5G, cloud computing and big data, especially the rise of generative artificial intelligence (AI) and large model AI technology, intelligent infrastructure is gradually taking shape, leading to explosive growth in computing power demand. In this context, as a core device of high-speed interconnection technology, the electro-optic modulator has become a fundamental guarantee for computing power improvement and data center expansion.

[0003] With the progress of material science, electro-optic modulators have gradually developed from the first generation of semiconductor material silicon to new polarization material systems including lithium niobate (LiNbO3) and aluminum nitride (AlN). Although the intrinsic electro-optic coefficient of AlN (~6pm / V) is smaller than that of LiNbO3 (~30pm / V), it has a larger band gap (~6.2eV) and is not affected by photorefractive effects or two-photon absorption loss in the mid-infrared, near-infrared, and even visible light bands. In addition, AlN can be prepared by low-temperature thin film deposition processes such as magnetron sputtering, and does not introduce contaminant elements that cannot be tolerated on the CMOS process line, thus enabling compatibility with existing COMS back-end processes. These lay the foundation for batch production and widespread application of AlN electro-optic modulators. According to different working principles, AlN electro-optic modulator structures can be divided into traditional Mach-Zehnder interferometers, new micro-ring resonators, and photonic crystal microcavities. The resonant structure has a compact size, high quality factor, and strong photon confinement capability, which can significantly reduce the driving power of the device and improve the modulation rate, adapting to future higher-performance optical communication system scenarios.

[0004] The optical waveguide structure is composed of a low refractive index material wrapping a high refractive index material. The principle is that when light propagates from a high refractive index material to a low refractive index material, total reflection occurs, which can ensure that light does not escape from the waveguide. In the field of silicon-based optoelectronics, SiO2 is a low refractive index medium material and can form a stable optical field confinement structure with high refractive index waveguide material, so it is usually selected as a waveguide cover layer. In Y. Sun, W. Shin, D. A. Laleyan, P. Wang, A. Pandey, X. Liu, Y. Wu, M. Soltani, and Z. Mi, Ultrahigh Q microring resonators using a single-crystal aluminum-nitride-on-sapphire platform. Optics letters, 2019, 44(23): 5679-5682, metal electrodes are arranged on both sides of the AlN optical waveguide to apply an electric field for modulating the electro-optic effect of the AlN optical waveguide. The waveguide cover layer is selected as silicon dioxide. Although this scheme of directly using SiO2 as the AlN waveguide cover layer can form an optical field confinement structure and prevent light leakage to some extent, it still has the following shortcomings: first, the cover of the electro-optic modulator is an oxide, which will cause the degradation and failure of the oxygenophilic AlN-based waveguide electro-optic properties; Al and Sc have a strong affinity for oxygen, and the oxygen elements in silicon dioxide will gradually replace the nitrogen atoms in the wurtzite crystal structure with the assistance of an electric field or temperature. This "oxygen contamination" will cause the refractive index of the waveguide material to decrease and the electro-optic performance to degrade, ultimately affecting the overall performance of the electro-optic modulator; second, because the electrodes are arranged far from the AlN waveguide, it will also cause insufficient electric field strength and excessive device operating voltage.

[0005] On the one hand, the electro-optic modulator structure requires the electrodes to be as close as possible to the AlN waveguide, which can maximize the conversion of the applied voltage into the electric field strength loaded on the waveguide and improve the electro-optic tuning efficiency; on the other hand, the metal electrodes will have a strong absorption effect on the optical field. In order to avoid the loss of optical energy, the electrodes cannot be too close to the waveguide. Therefore, an improved scheme is urgently needed to balance the above two contradictory situations and further improve the electro-optic modulation efficiency. SUMMARY

[0006] The present application aims at the deficiencies of the prior art, and provides an aluminum nitride waveguide structure based on nitride layered coating and a preparation method thereof, which is used to solve the problem of poor long-term working stability of an electro-optical modulator caused by the oxide of Al or Sc formed by the penetration of oxygen into the polycrystalline AlN / AlScN interface in the prior art. The present application realizes the protection of the base layer and the upper layer of the AlN waveguide by physical vapor deposition (PVD), chemical vapor deposition (CVD), pulsed laser deposition (PLD) and atomic layer deposition (ALD) processes, realizes full-wrapping oxygen barrier, effectively isolates the pollution of oxygen elements to the AlN-based waveguide material, avoids the performance degradation of the electro-optical modulator based on the AlN waveguide, and provides an effective improvement scheme for a large-scale integrated long-life and high-reliability optoelectronic chip on a chip.

[0007] The basic idea of the present application is to build a double-layer silicon nitride protection system with oxygen barrier ability and optical adaptability on the surface of the AlN waveguide through multiple thin film deposition processes; the structure realizes full-morphology packaging of the waveguide core under low temperature conditions, effectively isolates the penetration and damage of external oxygen elements to the AlN waveguide, and forms a low refractive index through material component regulation, thereby maintaining efficient constraint of the optical field while avoiding the mode leakage problem caused by the traditional thick coating layer. The structure effectively isolates oxygen elements, prevents the influence of "oxygen pollution" on the aluminum nitride and aluminum scandium nitride electro-optical modulator, and further maintains the excellent electro-optical performance, breaks through the technical barrier of long-term stable operation of the aluminum nitride and aluminum scandium nitride electro-optical modulator in a complex environment, and ensures the electro-optical modulation efficiency and device reliability of the electro-optical modulator.

[0008] I. Technical principle

[0009] The AlN-based waveguide is located above the Si substrate, and the oxygen barrier protection is realized by building a multi-layer nitride packaging layer such as common low-loss silicon nitride (SiN), gallium nitride (GaN), boron nitride (BN), phosphorus nitride (P3N5) and the like on the surface of the AlN waveguide. The nitride wrapping layer is composed of a dense base layer formed by a thin film deposition process and an upper coating layer. By adjusting the material components to form optical properties matched with the AlN waveguide, and the simultaneously deposited nitride thin film is extremely thin, so it neither affects the restriction of the waveguide to the transmission optical field, nor effectively isolates the invasion of oxygen elements. The electrodes are arranged on the upper side and the lower side of the AlN-based waveguide, and the electric field is consistent with the c-axis direction after power-on, thereby effectively utilizing the electro-optical tuning function of AlN.

[0010] As Figure 1 and Figure 2As shown, the AlN-based waveguide material itself, due to its large bandgap, exhibits properties similar to those of an insulator. Furthermore, it has the largest electro-optic coefficient in the c-axis direction. By providing electrode structures on both the upper and lower sides of the waveguide, electric field lines along the c-axis can be obtained, maximizing the electro-optical properties of the AlN-based waveguide. As the core structure of the present invention, the nitride wrapping layer mainly serves the following functions:

[0011] a) A composite waveguide structure is formed based on a layered nitride cladding structure and an AlN-based waveguide. By adjusting the nitrogen content of the nitride layer, a larger refractive index difference with the AlN waveguide is formed. By controlling the thickness of the nitride cladding layer to around 10nm, the light field energy is still confined to the AlN-based waveguide structure.

[0012] b) As a ceramic material with excellent oxidation resistance, silicon nitride can effectively slow down and block the penetration path of oxygen into AlN grain boundaries, preventing changes in the crystal structure at the interface and within the AlN-based waveguide material, which could affect its electro-optical performance. At the same time, the low-temperature deposition process avoids thermal damage to the AlN waveguide and electrode interface in a high-temperature environment, thereby ensuring the long-term stability and reliability of the optoelectronic modulator.

[0013] On the one hand, the silicon nitride coating is controlled to approximately 10nm, effectively isolating the AlN-based waveguide from oxygen. On the other hand, the thinner nitride coating does not significantly affect the optical field transmission mode of the AlN-based waveguide, and the optical field energy can still be confined within the AlN-based waveguide. When a voltage is applied to the top electrode above the optical waveguide and the bottom electrodes below it, electric field lines are formed along the c-axis (the y-axis in the figure) and pass through the optical waveguide. Based on the Pockels effect, the refractive index of the AlN-based waveguide is effectively adjusted, thereby achieving precise electrical modulation. This has important application potential in modulators such as MZIs, microring resonators, and photonic crystal microcavities.

[0014] 2. Device Structure

[0015] Reference Figures 4-6 According to the above principle, the present invention proposes an aluminum nitride waveguide structure based on nitride layered coating, which includes, from bottom to top: a silicon substrate 1 and a waveguide modulation region 2;

[0016] The waveguide modulation region 2 includes a top electrode 21, two bottom electrodes, a nitride-clad waveguide structure 24, an oxide cap layer 25, and an oxide buried layer 26; wherein the nitride-clad waveguide structure 24 is located on the upper surface of the oxide buried layer 26, and the oxide cap layer 25 covers the nitride-clad waveguide structure 24;

[0017] The nitride-clad waveguide structure 24 includes a nitride cap layer 241, a waveguide 242, and a nitride bottom layer 243. The waveguide 242 is located in the middle of the upper surface of the nitride bottom layer 243, and the nitride cap layer 241 covers the waveguide 242 and the nitride bottom layer 243.

[0018] The top electrode 21 is located in the middle position just above the nitride-coated waveguide structure 24 and is in close contact with the upper surface of the oxide cap layer 25 ; the two bottom electrodes include a first bottom electrode 22 and a second bottom electrode 23 , which are respectively located on the left and right sides of the waveguide 242 .

[0019] Furthermore, the materials of the nitride cap layer 241 and the nitride bottom layer 243 are any low-loss nitride, including silicon nitride, gallium nitride, boron nitride, and phosphorus nitride; and the thickness thereof ranges from 1 to 50 nm.

[0020] Furthermore, the waveguide 242 is any one of aluminum nitride and doped aluminum nitride; the doping element in the doped aluminum nitride is scandium Sc, and the chemical formula is Al 1-x Sc x N, where x represents the occupied ratio, and the value range of x is 0 to 50%.

[0021] Furthermore, the oxide capping layer 25 and the oxide buried layer 26 are electrically insulating materials, including silicon oxide and aluminum oxide.

[0022] Furthermore, the longitudinal position structures of the above-mentioned two bottom electrodes are the same; the bottom electrode includes a bottom electrode metal plating, a conductive channel and a lower electrode, and its longitudinal position structure is specifically as follows: the bottom electrode metal plating is located in the middle of the upper surface of the oxide cap layer 25; the lower electrode is embedded in the oxide buried layer 26, and its upper surface is in contact with the lower surface of the nitride-coated waveguide structure 24; the conductive channel is embedded in and passes through the oxide cap layer 25 and the nitride-coated waveguide structure 24, and its upper and lower surfaces are in contact with the bottom electrode metal plating and the lower electrode respectively.

[0023] Furthermore, the waveguide modulation region 2 changes the refractive index of the waveguide 242 by applying an electrical signal between the top electrode 21 and the two bottom electrodes, thereby realizing a phase modulation function.

[0024] At the same time, the present invention also proposes a method for preparing an aluminum nitride waveguide structure based on nitride layer coating, which grows nitride by physical vapor deposition (PVD), chemical vapor deposition (CVD), pulsed laser deposition (PLD), and atomic layer deposition (ALD) processes to achieve base layer protection of the AlN waveguide, and then deposits a thin nitride layer by PVD, CVD, PLD, or ALD processes to achieve upper layer protection of the AlN waveguide; the method specifically includes the following steps:

[0025] S1. Growing a buried oxide layer 26 on the silicon substrate 1 as a base layer for providing support and optical confinement structure;

[0026] S2 by photolithography and patterning process to form a lower electrode on the buried oxide layer 26;

[0027] S3. Depositing a dense nitride base layer, ie, a nitride bottom layer 243, on the upper surface of the buried oxide layer 26 by PVD, CVD, PLD or ALD.

[0028] S4. Growing an aluminum nitride layer or a doped aluminum nitride layer on the nitride bottom layer 243, and forming a waveguide 242 for optical signal transmission and electro-optical modulation by a patterning process;

[0029] S5. According to the three-dimensional morphology of the waveguide, a nitride cap layer 241 is grown on the surface of the nitride bottom layer 243 and the waveguide 242 by any one of PVD, CVD, PLD or ALD processes to complete the preparation of the nitride-coated waveguide structure 24;

[0030] S6. Growing an oxide cap layer 25 on the nitride-clad waveguide structure 24 by CVD;

[0031] S7. The oxide cap layer 25 is planarized by a chemical mechanical polishing (CMP) process, and its minimum thickness is greater than 0;

[0032] S8. The oxide cap layer 25, the nitride cap layer 241 and the nitride bottom layer 243 are sequentially etched on both sides of the electro-optical modulation waveguide 242 until a through hole is formed on the surface of the lower electrode. Then, the surface extraction of the bottom electrode 22 and the bottom electrode 23 and the preparation of the top electrode 21 are achieved at one time through the metal tape stripping process.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] First, since the present invention achieves base layer protection of the AlN waveguide by depositing nitride through the PVD process, an AlN-based material thin film is grown on the nitride thin layer, and a rectangular waveguide structure is etched to form a rectangular waveguide structure. Then, a nitride thin layer suitable for complex topological structures is deposited through the PECVD or ALD process to cover the AlN-based waveguide, thereby effectively isolating oxygen elements and preventing the influence of "oxygen contamination" on the AlN-based waveguide electro-optical modulator, thereby ensuring the stability and reliability of the electro-optical modulation waveguide structure.

[0035] Second, during the preparation process of the present invention, the temperature of the PVD, PECVD and ALD processes is less than 400°C throughout, avoiding damage to the AlN waveguide and degradation of the electrode interface caused by high temperature. At the same time, the nitrogen content of the SiN layer can be regulated by deposition process parameters (such as gas ratio and energy input) to form a controllable refractive index difference with the AlN waveguide core, thereby suppressing mode leakage and reducing oxygen permeability.

[0036] Third, since the present invention uses a PVD process to deposit the base nitride and only uses a PECVD or ALD process for the upper cladding layer, the overall process cost generated during the preparation can be significantly reduced.

[0037] Fourth, the process compatibility of the present invention is strong, and its structure can be manufactured using CMOS standard processing technology, has mass production characteristics, can be used to prepare nonlinear optoelectronic devices with large-scale integration on chip, and is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the technical solution principle of the present invention;

[0039] Figure 2 This is the electric field distribution diagram of the AlN waveguide structure with a nitride oxygen barrier layer of the present invention;

[0040] Figure 3 Figures 1 and 2 are comparative analysis diagrams of the optical field modes of nitride-wrapped waveguides with different thicknesses provided by an embodiment of the present invention; (a) to (d) are optical field simulation diagrams of the AlN waveguide structure with a nitride oxygen barrier layer when there is no silicon nitride coating, the silicon nitride thickness is 10 nm, the silicon nitride thickness is 20 nm, and the silicon nitride thickness is 30 nm, respectively.

[0041] Figure 4 It is a schematic diagram of the overall structure of the present invention;

[0042] Figure 5 Schematic diagram of the waveguide region structure in the present invention;

[0043] Figure 6 Schematic diagram of the structure of the layered nitride encapsulated region in the present invention;

[0044] Figure 7 Schematic diagram of the bottom electrode structure of the present invention;

[0045] Figure 8 Schematic diagram of the aluminum nitride waveguide structure with nitride layer coating provided in Example 3 of the present invention;

[0046] Figure 9 Schematic diagram of the aluminum nitride waveguide structure with nitride layer coating provided in the fourth embodiment of the present invention;

[0047] Figure 10Schematic diagram of a Mach-Zehnder (MZ) modulator constructed based on the waveguide structure of the present invention;

[0048] Figure 11 Schematic diagram of the structure of a micro-ring modulator constructed based on the waveguide structure of the present invention;

[0049] Figure 12 It is a structural schematic diagram of a one-dimensional nanobeam microcavity modulator constructed based on the waveguide structure of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings.

[0051] Example 1: Refer to the attached Figures 4-7 The present invention proposes an aluminum nitride waveguide structure based on nitride layered coating, which comprises, from bottom to top: a silicon substrate 1 and a waveguide modulation region 2;

[0052] The waveguide modulation region 2 includes a top electrode 21, two bottom electrodes, a nitride-clad waveguide structure 24, an oxide cap layer 25, and an oxide buried layer 26; wherein the nitride-clad waveguide structure 24 is located on the upper surface of the oxide buried layer 26, and the oxide cap layer 25 covers the nitride-clad waveguide structure 24;

[0053] The nitride-clad waveguide structure 24 includes a nitride cap layer 241, a waveguide 242, and a nitride bottom layer 243. The waveguide 242 is located in the middle of the upper surface of the nitride bottom layer 243, and the nitride cap layer 241 covers the waveguide 242 and the nitride bottom layer 243.

[0054] The top electrode 21 is located in the middle position just above the nitride-coated waveguide structure 24 and is in close contact with the upper surface of the oxide cap layer 25 ; the two bottom electrodes include a first bottom electrode 22 and a second bottom electrode 23 , which are respectively located on the left and right sides of the waveguide 242 .

[0055] Furthermore, the materials of the nitride cap layer 241 and the nitride bottom layer 243 are any low-loss nitride, including silicon nitride, gallium nitride, boron nitride, and phosphorus nitride; and the thickness thereof ranges from 1 to 50 nm.

[0056] Furthermore, the waveguide 242 is any one of aluminum nitride and doped aluminum nitride; the doping element in the doped aluminum nitride is scandium Sc, and the chemical formula is Al 1-x Sc x N, where x represents the occupied ratio, and the value range of x is 0 to 50%.

[0057] Furthermore, the oxide capping layer 25 and the oxide buried layer 26 are electrically insulating materials, including silicon oxide and aluminum oxide.

[0058] Furthermore, the longitudinal position structures of the above-mentioned two bottom electrodes are the same; the bottom electrode includes a bottom electrode metal plating, a conductive channel and a lower electrode, and its longitudinal position structure is specifically as follows: the bottom electrode metal plating is located in the middle of the upper surface of the oxide cap layer 25; the lower electrode is embedded in the oxide buried layer 26, and its upper surface is in contact with the lower surface of the nitride-coated waveguide structure 24; the conductive channel is embedded in and passes through the oxide cap layer 25 and the nitride-coated waveguide structure 24, and its upper and lower surfaces are in contact with the bottom electrode metal plating and the lower electrode respectively.

[0059] Furthermore, the waveguide modulation region 2 changes the refractive index of the waveguide 242 by applying an electrical signal between the top electrode 21 and the two bottom electrodes, thereby realizing a phase modulation function.

[0060] Example 2: Reference Figures 1-7 The present invention also proposes a method for preparing an aluminum nitride waveguide structure based on nitride layer coating, wherein nitride is grown by physical vapor deposition (PVD), chemical vapor deposition (CVD), pulsed laser deposition (PLD), and atomic layer deposition (ALD) processes to achieve base layer protection of the AlN waveguide, and then a thin nitride layer is deposited by PVD, CVD, PLD, or ALD processes to achieve upper layer protection of the AlN waveguide; the method specifically comprises the following steps:

[0061] Step S1. Growing a buried oxide layer 26 on the silicon substrate 1 as a base layer for providing support and optical confinement structure;

[0062] Step S2. forming a lower electrode on the buried oxide layer 26 by photolithography and patterning processes;

[0063] Step S3: Deposit a dense nitride base layer, i.e., nitride bottom layer 243, on the upper surface of the buried oxide layer 26 by any of PVD, CVD, PLD, or ALD processes to ensure optical field confinement and prevent oxygen intrusion. In this embodiment, the nitride base layer is preferably deposited by physical vapor deposition (PVD).

[0064] Step S4. Growing an aluminum nitride layer or a doped aluminum nitride layer on the nitride bottom layer 243, and forming a waveguide 242 for optical signal transmission and electro-optical modulation through a patterning process for optical signal transmission and electro-optical modulation.

[0065] Step S5. In view of the three-dimensional morphology of the waveguide, a nitride capping layer 241 is grown on the surface of the nitride bottom layer 243 and the waveguide 242 by any one of PVD, CVD, PLD or ALD processes to complete the preparation of the nitride-coated waveguide structure 24. In this embodiment, in this step, the plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) process is preferably used to grow the nitride capping layer, which provides an effective oxygen isolation function without affecting the waveguide light field confinement effect, thereby preventing oxygen elements from penetrating into the interior of the waveguide.

[0066] In this embodiment, the PVD, CVD, PLD, and ALD processes mentioned in step S3 and the current step S5 all regulate the nitrogen content of the nitride layer through deposition process parameters to form a controllable refractive index difference with the AlN waveguide core; the process parameters involved include gas ratio, energy input, etc.

[0067] Step S6: growing an oxide capping layer 25 on the nitride-clad waveguide structure 24 by CVD to provide additional optical confinement for the waveguide and ensure the overall structural stability of the waveguide.

[0068] Step S7. Planarizing the oxide cap layer 25 by a chemical mechanical polishing (CMP) process, wherein the minimum thickness of the oxide cap layer 25 is greater than 0;

[0069] Step S8. The oxide cap layer 25, the nitride cap layer 241 and the nitride bottom layer 243 are sequentially etched on both sides of the electro-optical modulation waveguide 242 until a through hole is formed on the surface of the lower electrode. Then, through the metal tape stripping process, the surface lead-out of the bottom electrode 22 and the bottom electrode 23 and the preparation of the top electrode 21 are achieved at one time to realize the electric field control of the electro-optical modulation.

[0070] Example 3: Reference Figure 8The aluminum nitride waveguide structure based on nitride layered coating provided in this embodiment includes a silicon substrate 1 and a waveguide modulation region 2. The waveguide modulation region 2 is located on the upper part of the silicon substrate 1, and is used to limit the transmitted light field, provide oxygen isolation function for the waveguide, and realize electro-optical modulation of the light field. The waveguide modulation region 2 includes a top electrode 21, a first bottom electrode 22, a second bottom electrode 23, a nitride-coated waveguide structure 24, and an oxide buried layer 26. The nitride-coated waveguide structure 24 is located on the upper surface of the oxide buried layer 26 and is in close contact with the oxide buried layer 26; the top electrode 21 is located in the middle position directly above the waveguide 242 and is in close contact with the upper surface of the nitride-coated waveguide structure 24; the two bottom electrodes include a first bottom electrode 22 and a second bottom electrode 23, which are respectively located on the left and right sides of the waveguide 242. The nitride-clad waveguide structure 24 includes a nitride cap layer 241, a waveguide 242, and a nitride bottom layer 243. The waveguide 242 is located in the middle of the upper surface of the nitride bottom layer 243, and the nitride cap layer 241 covers the waveguide 242 and the nitride bottom layer 243. The top electrode 21, the first bottom electrode 22, and the second bottom electrode 23 are all graphene electrodes, formed by transferring graphene grown by chemical vapor deposition. The high carrier mobility and electric field enhancement effect of the graphene electrodes significantly improve the electro-optical modulation response rate. At the same time, their low light absorption characteristics effectively reduce the interaction loss between the light field and the electrodes.

[0071] Example 4: Reference Figure 9 The aluminum nitride waveguide structure based on nitride layered coating provided in this embodiment includes a silicon substrate 1 and a waveguide modulation region 2. The waveguide modulation region 2 is located on the upper part of the silicon substrate 1, and is used to limit the transmitted light field, provide oxygen isolation function for the waveguide, and realize electro-optical modulation of the light field. The waveguide modulation region 2 includes a top electrode 21, a first bottom electrode 22, a second bottom electrode 23, a nitride-coated waveguide structure 24, an oxide capping layer 25 and an oxide buried layer 26. The nitride-coated waveguide structure 24 is located on the upper surface of the oxide buried layer 26, and the oxide capping layer 25 covers the nitride-coated waveguide structure 24; the top electrode 21 is located in the middle position directly above the waveguide 242 and is in close contact with the upper surface of the oxide capping layer 25; the two bottom electrodes include a first bottom electrode 22 and a second bottom electrode 23, which are respectively located on the left and right sides of the waveguide 242. The top electrode 21 comprises a metal coating 211 and an indium tin oxide (ITO) electrode 212. The metal coating 211 is located on top of the ITO electrode 212, which is in close contact with the oxide capping layer 25. ITO's low k value in the near-infrared band effectively reduces optical transmission damage while maintaining high conductivity. The first and second bottom electrodes 22 and 23 are made of either ITO plus a metal coating or simply metal, and are in close contact with the oxide capping layer 25.

[0072] The effects of the present invention will be further described below in conjunction with simulation experiments.

[0073] 1. Simulation conditions:

[0074] The simulation of the present invention adopts finite element software, and the geometric structure of the present invention is modeled and simulated by selecting the electromagnetic wave frequency domain (ewfd) physical field and the electrostatic (es) physical field in the wave optics module.

[0075] 2. Simulation content:

[0076] In the simulation of the electric field distribution of the waveguide structure, the thickness of the silicon nitride coating is set to 50nm, the height of the aluminum nitride waveguide is 300nm and the width is 500nm, and the electrode height is 50nm and the width is 600nm. The top electrode is located 325nm above the waveguide, and the center of the bottom electrode is 800nm ​​away from the center of the waveguide. The rest is filled with silicon oxide material. By calling the electromagnetic wave frequency domain and electrostatic physics field, the distribution of the electric field strength in the structure is analyzed, as shown in the figure below. Figure 2 shown.

[0077] In the simulation of the optical field mode of nitride-wrapped waveguides with different thicknesses, the aluminum nitride waveguide has a height of 300nm and a width of 500nm. The thickness of the silicon nitride coating is set to 0nm, 10nm, 20nm and 30nm respectively, and the rest is filled with silicon oxide material. By calling the electromagnetic wave frequency domain physical field, the optical field mode and limitation factor in the structure are analyzed, such as Figure 3 shown.

[0078] 3. Analysis of simulation results:

[0079] Figure 2 This is the electric field distribution diagram of the AlN waveguide structure with a nitride oxygen barrier layer of the present invention. It can be seen that this type of electrode arrangement can achieve efficient electric field loading along the c-axis orientation direction of the aluminum nitride material, greatly improving the performance of the aluminum nitride electro-optic modulator;

[0080] Figure 3 This is a comparative analysis diagram of the light field modes of nitride-wrapped waveguides with different thicknesses provided by an embodiment of the present invention; (a)-(d) are light field simulation diagrams of the AlN waveguide structure with a nitride oxygen isolation layer when there is no silicon nitride coating, the silicon nitride thickness is 10nm, the silicon nitride thickness is 20nm, and the silicon nitride thickness is 30nm, respectively. It can be seen that while providing an effective oxygen isolation function, the thin layer of nitride coating basically does not affect the limiting effect of the waveguide on the transmitted light field.

[0081] The present invention addresses the technical problem of AlN-based optical waveguide materials being susceptible to oxygen corrosion, leading to degradation of electro-optical performance. The proposed waveguide structure first forms a dense nitride base layer on the surface of the AlN waveguide substrate through physical vapor deposition (PVD), providing a low-cost basic oxygen barrier. Based on the three-dimensional morphology of the waveguide, a plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) process is further used to construct an upper cladding layer on the AlN waveguide surface. This structure effectively isolates oxygen by coating the AlN optical waveguide with a SiN layer through a thin film deposition process, preventing "oxygen contamination" from affecting aluminum nitride and aluminum-scandium-nitride electro-optical modulators, thereby maintaining their excellent electro-optical performance. Furthermore, to address the thermal expansion mismatch between the AlN and silicon-based substrate interfaces that may be caused by traditional high-temperature deposition processes, the present invention significantly reduces interfacial thermal stress through a low-temperature process system that combines PVD and PECVD / ALD. Furthermore, by adjusting the Si / N stoichiometric ratio and increasing the proportion of nitrogen-containing precursor atmosphere, the refractive index of the SiN cladding layer is reduced to approximately 1.8, creating a larger refractive index difference with AlN. At the same time, the extremely thin SiN layer does not affect the waveguide's confinement of the light field. This composite waveguide structure provides a key foundational solution for large-scale on-chip integration of nonlinear optoelectronic devices and has significant application prospects.

[0082] In commercial applications, based on the aluminum nitride waveguide structure based on nitride layered coating proposed in this embodiment, the electro-optic modulator manufactured by changing the shape of the AlN-based material waveguide has huge development space in the fields of micro-ring modulator, Mach-Zehnder MZ modulator, nano-beam resonant cavity modulator. Figure 10 As shown in the figure, it is a top view and a cross-sectional view of the Mach-Zehnder MZ modulator. The electro-optical modulator performs phase modulation through the MZ double-arm waveguide, which can realize the conversion of the output optical signal between "0" and "1", thereby changing the intensity of the output optical mode. Figure 11 and Figure 12 The following are top views and cross-sectional views of a microring modulator and a nanobeam resonant cavity modulator, respectively. By locally enhancing the light field, these devices significantly improve the electro-optical interaction intensity and achieve a more compact design.

[0083] Parts of the present invention that are not described in detail belong to common knowledge among those skilled in the art.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, for professionals in this field, after understanding the content and principles of the present invention, they may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. An aluminum nitride waveguide structure based on nitride layered cladding, characterized in that: From bottom to top, it includes: silicon substrate (1) and waveguide modulation area (2); The waveguide modulation region (2) comprises a top electrode (21), two bottom electrodes, a nitride-coated waveguide structure (24), an oxide capping layer (25), and an oxide buried layer (26); wherein the nitride-coated waveguide structure (24) is located on the upper surface of the oxide buried layer (26), and the oxide capping layer (25) covers the nitride-coated waveguide structure (24); The nitride-coated waveguide structure (24) comprises a nitride cap layer (241), a waveguide (242), and a nitride bottom layer (243), wherein the waveguide (242) is located in the middle of the upper surface of the nitride bottom layer (243), and the nitride cap layer (241) covers the waveguide (242) and the nitride bottom layer (243); The top electrode (21) is located in the middle position directly above the nitride-coated waveguide structure (24) and is in close contact with the upper surface of the oxide cap layer (25); the two bottom electrodes include a first bottom electrode (22) and a second bottom electrode (23), which are respectively located on the left and right sides of the waveguide (242).

2. The nitride layered aluminum nitride waveguide structure according to claim 1, wherein: The materials of the nitride cap layer (241) and the nitride bottom layer (243) are any low-loss nitride, including silicon nitride, gallium nitride, boron nitride, and phosphorus nitride; and their thickness ranges from 1 to 50 nm.

3. The nitride layered aluminum nitride waveguide structure according to claim 1, wherein: The waveguide (242) is any one of aluminum nitride and doped aluminum nitride.

4. The nitride layered aluminum nitride waveguide structure according to claim 3, wherein: The doping element in the doped aluminum nitride is scandium (Sc), and its chemical formula is Al 1-x Sc x N, where x represents the occupied ratio, and the value range of x is 0 to 50%.

5. The nitride layered aluminum nitride waveguide structure according to claim 1, wherein: The oxide cap layer (25) and the oxide buried layer (26) are electrically insulating materials, including silicon oxide and aluminum oxide.

6. The nitride layered aluminum nitride waveguide structure according to claim 1, wherein: The longitudinal position structures of the two bottom electrodes are the same.

7. The nitride layered aluminum nitride waveguide structure according to claim 6, characterized in that: The bottom electrode comprises a bottom electrode metal plating layer, a conductive channel and a lower electrode, and its longitudinal position structure is specifically as follows: the bottom electrode metal plating layer is located in the middle of the upper surface of the oxide cap layer (25); the lower electrode is embedded in the oxide buried layer (26), and its upper surface contacts the lower surface of the nitride-coated waveguide structure (24); the conductive channel is embedded in and penetrates the oxide cap layer (25) and the nitride-coated waveguide structure (24), and its upper and lower surfaces contact the bottom electrode metal plating layer and the lower electrode respectively.

8. The nitride layered aluminum nitride waveguide structure according to claim 1, wherein: The waveguide modulation region (2) changes the refractive index of the waveguide (242) by applying an electrical signal between the top electrode (21) and the two bottom electrodes, thereby realizing a phase modulation function.

9. A method for preparing an aluminum nitride waveguide structure based on nitride layered coating according to claim 1, characterized in that: The base layer protection of the AlN waveguide is achieved by growing nitride through physical vapor deposition (PVD), chemical vapor deposition (CVD), pulsed laser deposition (PLD), and atomic layer deposition (ALD) processes, and then a thin layer of nitride is deposited through PVD, CVD, PLD, or ALD processes to achieve the upper layer protection of the AlN waveguide. The specific steps include: S1. Growing a buried oxide layer (26) on a silicon substrate (1) as a base layer for providing support and optical confinement structure; S2. forming a lower electrode on the buried oxide layer (26) by photolithography and patterning processes; S3. Depositing a dense nitride base layer, ie, a nitride bottom layer (243), on the upper surface of the buried oxide layer (26) by any one of PVD, CVD, PLD or ALD processes; S4. Growing an aluminum nitride layer or a doped aluminum nitride layer on the nitride bottom layer (243), and forming a waveguide (242) for optical signal transmission and electro-optical modulation by a patterning process; S5. Based on the three-dimensional morphology of the waveguide, a nitride capping layer (241) is grown on the surface of the nitride bottom layer (243) and the waveguide (242) by any one of PVD, CVD, PLD or ALD processes to complete the preparation of the nitride-coated waveguide structure (24); S6. Growing an oxide cap layer (25) on the nitride-clad waveguide structure (24) by CVD; S7. The oxide cap layer (25) is planarized by a chemical mechanical polishing (CMP) process, and its minimum thickness is greater than 0; S8. The oxide cap layer (25), the nitride cap layer (241) and the nitride bottom layer (243) are sequentially etched on both sides of the electro-optical modulation waveguide (242) until a through hole is formed on the surface of the lower electrode. Then, the surface extraction of the bottom electrode (22) and the bottom electrode (23) and the preparation of the top electrode (21) are achieved at one time through a metal tape stripping process.

10. The method according to claim 9, characterized in that: The PVD, CVD, PLD and ALD processes in steps S3 and S5 are to control the nitrogen content of the nitride layer by means of deposition process parameters to form a controllable refractive index difference with the AlN waveguide core; The process parameters include gas ratio and energy input.

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