Lithium niobate modulator chip with multi-layer electrode structure and preparation method of lithium niobate modulator chip

Abstract

The invention provides a lithium niobate modulator chip with a multi-layer electrode structure and a preparation method thereof, and relates to the technical field of quantum communication and optical fiber communication, the lithium niobate modulator chip with the multi-layer electrode structure comprises a substrate wafer, a plurality of optical waveguides and a plurality of electrodes; the substrate wafer comprises a three-layer structure of silicon, silicon oxide and a lithium niobate film; the optical waveguides are parallel to one another, the middle electrode of each optical waveguide is a live wire, and the electrodes on two sides are ground wires; the electrode is formed by alternately distributing a plurality of electrode layers and a plurality of dielectric layers; the input end and the output end of the traveling wave electrode each comprise a live wire bonding pad and a ground wire bonding pad, the live wire bonding pads and the ground wire bonding pads are of a stacked structure, and each layer of bonding pad is connected to a radio frequency lead pin and a terminal load through an independent gold wire. According to the invention, the multi-layer electrode structure is adopted, so that the usage amount of gold is saved, the production cost of the modulator is reduced, and the mass production capability of a modulator chip is improved; and by reducing the half-wave voltage length product, the power consumption of the device is reduced.

Description

Technical Field

[0001] The present invention provides a lithium niobate modulator chip with a multi-layer electrode structure and a preparation method thereof, and relates to technical fields such as quantum communication and optical fiber communication. Background Art

[0002] In quantum communication systems, lithium niobate modulators are a key electro-optical conversion device that can modulate the phase and intensity of optical signals. Figure 1 The quantum system built uses multiple lithium niobate phase modulators (PM) and lithium niobate intensity modulators (AM) to realize a long-distance quantum key distribution system.

[0003] The lithium niobate modulator used in the above system needs to meet the requirements of large bandwidth and low power consumption at the same time. For this purpose, a traveling wave electrode design structure is usually used, such as Figure 2 、 Figure 3 As shown, the gold electrode thickness is 20-30um, and the optical waveguide structure is an MZ structure (the MZI modulator uses two parallel optical waveguides) or a dual-parallel MZ structure (the QPSK modulator uses four parallel optical waveguides), which is suitable for intensity modulators. Considering that the thickness of the gold film prepared by the electron beam evaporation process usually does not exceed 1um, the realization of a 20-30um gold electrode requires the use of an unconventional electroplating process, which is extremely difficult and restricts the mass production capacity of the modulator chip. In addition, the thick gold process also significantly increases the cost of the modulator. As mentioned above, in the traditional design, in order to meet the phase velocity matching and reduce the half-wave voltage at the same time, the design of the modulator is mainly based on thick gold electrodes. Usually, the electrode thickness exceeds 20um. It is an unconventional process and is extremely difficult to implement, which restricts the mass production capacity of the modulator. At the same time, the thick gold process also increases the production cost of the modulator, which is not conducive to the promotion and application of the modulator.

[0004] In the prior art, patent document CN116626922A discloses a thin-film lithium niobate electro-optical modulator with internal electrodes. The two layers of electrodes in this patent are electrically connected and in contact with each other, but are realized through two evaporation processes. They are functionally equivalent to one layer of electrode, and there is no dielectric layer between the two layers of electrodes. For external signal access, the two layers of electrodes share a common pad, and the maximum electrode thickness is only 2μm.

[0005] The present invention proposes a lithium niobate modulator chip with a multilayer electrode structure. Compared to patent document CN116626922A, the multilayer electrodes of the present invention are separated by a dielectric layer, which can be silicon oxide, silicon oxynitride, aluminum oxide, or silicon nitride. Each electrode layer is insulated and connected to the same signal input terminal via multilayer pads to achieve the same potential. The electrodes and dielectric layers are arranged alternately, and can have multiple layers, not just two. The pads of the present invention are stacked, with each electrode layer having a separate pad. Furthermore, the present invention can achieve an equivalent electrode thickness of over 20 μm. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention proposes a lithium niobate modulator chip with a multi-layer electrode structure, comprising: a substrate wafer, a plurality of optical waveguides, and a plurality of traveling wave electrodes;

[0007] The substrate wafer includes silicon, silicon oxide, and lithium niobate thin film;

[0008] The plurality of optical waveguides are parallel to each other; the plurality of traveling wave electrodes include a live wire and a ground wire, the live wire is located in the middle of the plurality of optical waveguides, and the ground wire is located at both ends of the plurality of optical waveguides;

[0009] Each traveling wave electrode is formed by alternatingly distributing multiple electrode layers and multiple dielectric layers.

[0010] In a preferred embodiment, the substrate wafer is a lithium niobate thin film wafer or a lithium niobate bulk material wafer.

[0011] In a preferred embodiment, the multiple dielectric layers are made of different dielectric materials, and the dielectric material is any one of silicon oxide, silicon oxynitride dielectric layer, aluminum oxide or silicon nitride.

[0012] In a preferred embodiment, the live pad and the ground pad are a stacked pad structure, and the input and output ends of each layer of pads are connected to the RF pin and the terminal load respectively through independent bonding gold wires to ensure signal phase synchronization of different electrode layers.

[0013] The present invention also provides a method for preparing a lithium niobate modulator chip having a multi-layer electrode structure, which is used to prepare the lithium niobate modulator chip having the multi-layer electrode structure, comprising:

[0014] First, multiple parallel optical waveguides are etched on a substrate wafer;

[0015] Then, a plurality of traveling wave electrodes are prepared, wherein the plurality of traveling wave electrodes include a live wire and a ground wire, wherein the live wire is located in the middle of the plurality of optical waveguides and the ground wire is located at both ends of the plurality of optical waveguides;

[0016] Each traveling wave electrode is prepared by an electron beam evaporation process to prepare an electrode layer, and a plasma enhanced chemical vapor deposition process to prepare a dielectric layer; the electron beam evaporation process and the plasma enhanced chemical vapor deposition process are used to alternately prepare the electrode layer and the dielectric layer, and finally a multi-layer electrode structure is prepared in which multiple electrode layers and multiple dielectric layers are alternately distributed.

[0017] In a preferred embodiment, the thickness of each electrode layer prepared by the electron beam evaporation process is 1um, and the thickness of each dielectric layer prepared by the plasma enhanced chemical vapor deposition process is 5um. Repeating three times obtains a thick electrode with an equivalent thickness of 18um; repeating 4 times obtains a thick electrode with an equivalent thickness of 24um.

[0018] In a preferred embodiment, at the pad position, stacked pads are formed through multiple etching steps, and each layer of pads is connected to the RF pin and the terminal load respectively using gold wire bonding.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] Existing lithium niobate modulators use a thick gold electrode design, which means that the electrodes cannot be manufactured using conventional semiconductor processes. This makes the process difficult, and mass production efficiency is low and the cost is high. The lithium niobate modulator chip in the present invention uses a multi-layer electrode structure, with each electrode layer no thicker than 1 μm. It can be manufactured using conventional semiconductor processes and is easy to mass produce. At the same time, the multi-layer electrode structure also saves gold usage, reduces the production cost of the modulator, and improves the mass production capability of the modulator chip. Moreover, by optimizing structural parameters, the present invention can also reduce the half-wave voltage-length product, thereby reducing the power consumption of the device.

[0021] The multilayer electrode of the present invention can use silicon oxide medium and metal electrode alternately distributed, or can use other mediums such as silicon oxide medium, aluminum oxide, silicon nitride, etc. to achieve a thicker equivalent electrode thickness; the multilayer electrode can also use different mediums alternately distributed, such as using silicon oxide as the first layer of medium and using silicon oxide medium as the second layer of medium to achieve a modulation effect equivalent to that of a thick gold electrode.

[0022] The multilayer electrode of the present invention adopts a stacked pad structure at the input and output pads, and realizes electrical interconnection through gold wire bonding. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a framework diagram of the long-distance quantum key distribution system;

[0025] Figure 2 This is a front view of the electrode structure of a lithium niobate modulator in the prior art;

[0026] Figure 3 for Figure 2 sectional view of

[0027] Figure 4 This is a cross-sectional view of the lithium niobate modulator chip of the present invention;

[0028] Figure 5 This is a schematic diagram of the three-dimensional structure of the lithium niobate modulator chip of the present invention;

[0029] Figure 6 is a schematic diagram of the through-hole structure;

[0030] Figure 7 This is a schematic diagram of the FireWire pad;

[0031] Figure 8 For contrasting structure. DETAILED DESCRIPTION

[0032] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] In the drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the various components in the system, the connection relationship of the various parts in the device is shown, which only clearly distinguishes the relative position relationship between the various components, and does not constitute a limitation on the signal transmission direction, connection sequence and structural size, size and shape of each part within the component or structure.

[0034] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0035] Example 1

[0036] In order to reduce the process difficulty of manufacturing lithium niobate modulator electrodes and at the same time reduce the cost of the modulator, this embodiment proposes a method for preparing a lithium niobate modulator chip with a multi-layer electrode structure. By changing the preparation method of the electrode, the difficulty of the electrode manufacturing process is reduced, the production cost of the modulator is reduced, and the application of the modulator product is facilitated.

[0037] The cross-sectional view of the lithium niobate modulator chip with the multi-layer electrode structure of the present invention is as follows: Figure 4 As shown, the three-dimensional structure is Figure 5 shown.

[0038] like Figure 4 As shown, the lithium niobate modulator chip with a multi-layer electrode structure includes: a substrate wafer, an optical waveguide, and a traveling wave electrode.

[0039] The substrate wafer includes a silicon substrate, silicon oxide, and a lithium niobate thin film; the substrate wafer is a lithium niobate thin film wafer or a lithium niobate bulk material wafer.

[0040] Two optical waveguides are arranged in parallel (preferably Mach-Zehnder MZ optical waveguide branches), the traveling wave electrode in the middle of the optical waveguide is the live wire, and the traveling wave electrodes on both sides are the ground wires.

[0041] The electrode structure adopts a multi-layer design. In this embodiment, three electrode layers and three dielectric layers are alternately distributed to increase the thickness of the equivalent electrode. Preferably, the electrode layer is a gold electrode layer.

[0042] The electrode layer is prepared using electron beam evaporation technology, which can produce a single layer of electrode layer with a thickness of 1 μm. The dielectric layer is prepared using PECVD technology.

[0043] In a preferred embodiment, the dielectric material may be silicon oxide, such as Figure 4 As shown; other dielectric materials may also be used, such as silicon oxide nitride dielectric layer, aluminum oxide, silicon nitride, etc. The dielectric layer may be made of one material or two or more materials at the same time, such as silicon oxide for the first dielectric layer and silicon oxide nitride for the second dielectric layer.

[0044] Considering the differences in dielectric layer preparation processes, dielectric layers formed from different dielectric materials can achieve different thicknesses. For example, a silicon oxide dielectric layer prepared using PECVD can achieve a thickness of 1 μm, while a silicon oxide nitride (SiON) dielectric layer prepared using PECVD can achieve a thickness of 4-6 μm.

[0045] The preparation process of the lithium niobate modulator chip in this embodiment is as follows: first, an optical waveguide is etched on the wafer, and then a multilayer electrode is prepared. That is, 1 μm gold electrodes are prepared by electron beam evaporation process, and 1 μm silicon oxide is prepared by PECVD process. Repeating this three times can achieve Figure 4The electrode structure shown; the wafer in the present invention can be a lithium niobate thin film wafer, such as Figure 4 As shown, it can also be a lithium niobate material wafer.

[0046] In a preferred embodiment, a lithium niobate modulator chip is prepared using a silicon oxynitride medium, and the process sequence is as follows: first, multiple optical waveguides are etched on a wafer, and then a multi-layer electrode structure is prepared.

[0047] When preparing a multi-layer electrode structure, an evaporation process is used to prepare a 1um thick gold electrode; then a 5um thick silicon oxide nitrogen dielectric layer is prepared using PECVD; the above process is repeated three times to prepare an 18um thick electrode with three electrode layers and three dielectric layers alternatingly distributed; the above process is repeated four times to prepare a 24um thick electrode with four electrode layers and four dielectric layers alternatingly distributed.

[0048] like Figure 5 As shown, the substrate wafer can be a lithium niobate thin film wafer or a lithium niobate bulk material wafer, the input end of the traveling wave electrode includes a live wire pad and a ground wire pad, and the output end also includes a live wire pad and a ground wire pad.

[0049] In order to realize the input and output of traveling wave electrode signals, you can use Figure 6 The through-hole structure shown is that a through-hole is made on the input pad to connect the multi-layer electrodes together; through the pad, it is connected to the RF pin on the tube shell using gold wire bonding; the same through-hole is also made at the output end to connect the multi-layer electrode to the terminal load.

[0050] Example 2

[0051] This embodiment proposes a method for designing electrical interconnection of pads. Through semiconductor technology, the pads of the multi-layer electrodes are etched out separately to form a terraced distribution of pads, such as Figure 7 As shown. Each layer of pads is connected to the RF pins and terminal loads through gold wire bonding. With through-hole technology, the RF signal first reaches the top pad, then the middle pad, and then the bottom pad. The RF signals between different layers need to be delayed to ensure phase synchronization of electrodes on different layers. With a multi-layer pad design, pads on different layers are directly connected to the RF pins through gold wires. There is no problem of signals arriving in sequence, and no need to add delay compensation, which can ensure phase synchronization of electrodes on different layers. Compared with through-hole technology, this design does not need to consider the delay and synchronization requirements between electrodes on different layers.

[0052] The pad design of the present invention is prepared using multiple photolithography processes. The top pad is first etched with a pattern, followed by photolithography and etching of the second pad; and then photolithography and etching of the bottom pad.

[0053] Example 3

[0054] To test the modulation effect of the multilayer electrode on the optical waveguide, a simulation of the multilayer electrode was conducted. For comparison, in addition to the traditional design structure ⑦ (the single-layer live wire and ground wire structure in the prior art), a total of 6 multilayer electrode structures of the present invention (each electrode structure uses a different number of gold electrode layers for the live wire and ground wire) were simulated. Figure 8 shown.

[0055] Figure 8 In the figure, the dark blue is the gold electrode layer, the white is the silicon oxide dielectric layer, and the oblique line is lithium niobate:

[0056] ①: Two layers of ground wire and one layer of live wire;

[0057] ②: Both the ground wire and the live wire are double-layered;

[0058] ③: Two layers of live wire and one layer of ground wire;

[0059] ④: Both the live wire and the ground wire are three-layer;

[0060] ⑤: Three layers of live wire and two layers of ground wire;

[0061] ⑥: Three layers of live wire and one layer of ground wire;

[0062] ⑦: Traditional design, the live wire and ground wire are both on the same layer.

[0063] in, Figure 8 The electrode structure No. ④ in the Figure 4 The three-layer electrode and three-layer dielectric structure shown in FIG. 1 is used to perform the simulation of the half-wave voltage-length product of the structure, as shown in Table 1.

[0064] Table 1 Simulation results of three-layer electrode and three-layer dielectric structure

[0065]

[0066] The conventional design structure ⑦, using a single layer of ground and live wires, achieved a photoelectric overlap integral of 0.553 and a half-wave voltage-length product of 2.25. The present invention's design ②, with a two-layer structure of live and ground wires, achieved a photoelectric overlap integral of 0.5934 and a half-wave voltage-length product of 2.10. Compared to the single-layer design, the half-wave voltage is reduced by 6.7%.

[0067] The above design is for simple comparison and has not been optimized. By optimizing the structural design, including optimizing the thickness of each electrode and dielectric layer, optimizing the dielectric layer material selection, electrode spacing, waveguide width, height and other design parameters, a lower half-wave voltage-length product can be achieved, which can more effectively reduce the half-wave voltage and device power consumption.

[0068] The above simulation results show that the use of a multi-layer electrode structure can reduce the half-wave voltage-length product to a certain extent, thereby reducing the power consumption of the lithium niobate modulator; and the present invention does not require the use of unconventional electroplating processes, and only uses conventional semiconductor processes (including PECVD, electron beam evaporation and other deposition processes) to prepare the modulator electrodes, which reduces the process difficulty and production cost of the modulator chip and improves the mass production capacity of the lithium niobate modulator chip.

[0069] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, database or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processor involved in the various embodiments provided herein may be, but are not limited to, a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, and the like.

[0070] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0071] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A lithium niobate modulator chip with a multi-layer electrode structure, characterized in that: include: A substrate wafer, a plurality of optical waveguides, and a plurality of traveling wave electrodes; The substrate wafer includes silicon, silicon oxide, and lithium niobate thin film; The multiple optical waveguides are parallel to each other; The plurality of traveling wave electrodes include a live wire and a ground wire, wherein the live wire is located in the middle of the plurality of optical waveguides and the ground wire is located at both ends of the plurality of optical waveguides; Each traveling wave electrode is formed by alternatingly distributing multiple electrode layers and multiple dielectric layers.

2. The lithium niobate modulator chip with a multi-layer electrode structure according to claim 1, characterized in that: The substrate wafer is a lithium niobate thin film wafer or a lithium niobate bulk material wafer.

3. The lithium niobate modulator chip with a multi-layer electrode structure according to claim 1, characterized in that: The multi-layer dielectric layer is made of different dielectric materials, and the dielectric material is any one of silicon oxide, silicon oxynitride dielectric layer, aluminum oxide or silicon nitride.

4. The lithium niobate modulator chip with a multi-layer electrode structure according to claim 1, characterized in that: The live pad and ground pad are stacked pad structures. The input and output ends of each layer of pads are connected to the RF pin and terminal load respectively through independent bonding gold wires to ensure signal phase synchronization of different electrode layers.

5. A method for preparing a lithium niobate modulator chip with a multi-layer electrode structure, characterized in that: A lithium niobate modulator chip for preparing the multilayer electrode structure according to any one of claims 1 to 4, comprising: First, multiple parallel optical waveguides are etched on a substrate wafer; Then, a plurality of traveling wave electrodes are prepared, wherein the plurality of traveling wave electrodes include a live wire and a ground wire, wherein the live wire is located in the middle of the plurality of optical waveguides and the ground wire is located at both ends of the plurality of optical waveguides; Each traveling wave electrode is prepared by an electron beam evaporation process to prepare an electrode layer, and a plasma enhanced chemical vapor deposition process to prepare a dielectric layer; the electron beam evaporation process and the plasma enhanced chemical vapor deposition process are used to alternately prepare the electrode layer and the dielectric layer, and finally a multi-layer electrode structure is prepared in which multiple electrode layers and multiple dielectric layers are alternately distributed.

6. The method for preparing a lithium niobate modulator chip with a multi-layer electrode structure according to claim 5, characterized in that: The thickness of each electrode layer prepared by electron beam evaporation process is 1um, and the thickness of each dielectric layer prepared by plasma enhanced chemical vapor deposition process is 5um. Repeating three times will obtain a thick electrode with an equivalent thickness of 18um; repeating 4 times will obtain a thick electrode with an equivalent thickness of 24um.

7. The method for preparing a lithium niobate modulator chip with a multi-layer electrode structure according to claim 5, characterized in that: At the pad position, stacked pads are formed after multiple etchings, and each layer of pads is connected to the RF pin and terminal load using gold wire bonding.

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