Lithium tantalate on silicon hybrid waveguide and its preparation method

Abstract

A silicon-based lithium tantalate hybrid waveguide and its manufacturing method. The hybrid waveguide sequentially includes, from top to bottom: an amorphous silicon layer, a thin film silicon oxide layer for preventing black dot impurities from appearing during the deposition of amorphous silicon and affecting the waveguide transmission effect, a lithium tantalate layer for transmitting the TE mode, a silicon oxide buried layer, and a silicon substrate. Among them: the amorphous silicon layer, the thin film silicon oxide layer, and the lithium tantalate layer are deposited to form a hierarchical structure, serving as the structural layer for light propagation in the waveguide structure. The present invention realizes a hybrid waveguide structure of heterogeneous integration of silicon and lithium tantalate through deposition and etching techniques on an LTO wafer. The light field will leak into the lithium tantalate layer of the waveguide during propagation, thereby realizing the localization of light in the lithium tantalate layer. Through the above process, a material with excellent properties, lithium tantalate, can be introduced into the integrated optical waveguide, achieving a breakthrough in traditional silicon-based optical waveguides.

Description

Technical Field

[0001] The present invention relates to a technology in the field of integrated optoelectronics, specifically a silicon-based lithium tantalate hybrid waveguide and a preparation method thereof. Background Art

[0002] With the rapid development of information industry technology, optoelectronic integration technology is playing a huge role. In an integrated optical circuit, in order to reduce the size of a chip and improve the performance of devices on the chip, it is necessary to design an integrated optical waveguide with strong mode field confinement, low transmission loss and meeting the design purpose. The integrated optical waveguide is a dielectric device that guides an optical field to propagate therein through total internal reflection generated by a large refractive index difference of a material. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides a silicon-based lithium tantalate hybrid waveguide and a preparation method thereof. A hybrid waveguide structure with heterogeneous integration of silicon and lithium tantalate is realized on an LTO wafer through deposition and etching technologies. The optical field will leak into the lithium tantalate layer of the waveguide during propagation, thereby realizing the localization of light in the lithium tantalate layer. Through the above process, a material with excellent properties, lithium tantalate, can be introduced into the integrated optical waveguide to achieve a breakthrough in traditional silicon-based optical waveguides.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a silicon-based lithium tantalate hybrid waveguide, which successively includes from top to bottom: an amorphous silicon layer, a thin film silicon oxide layer for preventing black dot impurities from appearing during the deposition of amorphous silicon and affecting the waveguide transmission effect, a lithium tantalate layer for transmitting the TE mode, a silicon oxide buried layer, and a silicon substrate, wherein: the amorphous silicon layer, the thin film silicon oxide layer, and the lithium tantalate layer are deposited to form a hierarchical structure, serving as a structural layer for light propagation in the waveguide structure.

[0006] The refractive index distribution of the silicon-based lithium tantalate hybrid waveguide is as follows: the refractive index of silicon material n1≈3.42, the refractive index of lithium tantalate material n2≈2.176, and the refractive index of silicon oxide material n3≈1.45.

[0007] The thickness of the amorphous silicon layer fluctuates around 100 nm according to actual situations such as process level, and the amorphous silicon layer should not be too thick to prevent part of the optical field from detaching from the lithium tantalate layer.

[0008] The thickness of the thin film silicon oxide layer is changed according to actual needs. The change in the thickness of the lithium tantalate layer leads to a change in the ratio of the optical mode field localized in the lithium tantalate layer. Specifically: the proportion of the TE mode localized in the lithium tantalate layer is positively correlated with the thickness of the lithium tantalate; preferably, when the thickness is 600 nm, the proportion of the optical mode field localized in the aluminum nitride layer is 50.7%.

[0009] The present invention relates to a method for preparing the above-mentioned silicon-based lithium tantalate hybrid waveguide, which is obtained by using a CMOS-compatible process on an LTO wafer, and specifically includes:

[0010] Step 1: Deposit a 20-nm-thick silicon oxide film on the LTO wafer by plasma-enhanced chemical vapor deposition (PECVD) to form a four-layer structure from top to bottom: silicon oxide - lithium tantalate - silicon oxide - silicon substrate.

[0011] The LTO wafer includes a lithium tantalate layer, a silicon oxide layer, and a silicon layer from bottom to top, wherein: the thickness of the lithium tantalate layer is 600 nm.

[0012] Step 2: Deposit 100-nm-thick amorphous silicon on the prepared four-layer structure by plasma-enhanced chemical vapor deposition (PECVD).

[0013] Step 3: Use EBL electron beam lithography technology to define the waveguide structure on the photoresist;

[0014] Step 4: Through plasma etching (ICP-RIE), etch 100 nm in total to form a 100-nm-thick amorphous silicon waveguide structure.

[0015] Step 5: Deposit a 1-μm-thick silicon oxide cladding layer by plasma-enhanced chemical vapor deposition to finally obtain a silicon-based lithium tantalate hybrid waveguide.

[0016] Technical effects

[0017] By preparing an optical waveguide structure for the heterogeneous integration of lithium tantalate and silicon, the present invention localizes part of the light in lithium tantalate, providing a case and direction for the research of new materials in the optoelectronic field. Description of the drawings

[0018] Figure 1 It is a flowchart of the present invention;

[0019] Figure 2 It is a three-dimensional view and a partial cross-sectional view (silicon - silicon oxide - lithium tantalate) of the silicon-based lithium tantalate hybrid waveguide prepared in the embodiment;

[0020] Figure 3 It is a simulation spectrogram of the embodiment;

[0021] Figure 4 It is a function diagram of the percentage value of light localization in the lithium tantalate layer varying with its thickness in the embodiment;

[0022] Figure 5 It is a transmission spectrogram of the photonic device prepared from the waveguide obtained by experimental testing;

[0023] Figure 6It is the transmission spectrum diagram of the above-mentioned photon device under different applied bias voltages. Detailed implementation manners

[0024] As Figure 1 shown, this embodiment relates to a silicon-based aluminum nitride hybrid waveguide and its implementation method, including:

[0025] Step 1) Deposit a layer of silicon dioxide film with a thickness of 20 nm on an LTO wafer by plasma-enhanced chemical vapor deposition (PECVD).

[0026] Step 2) Deposit a 100-nm-thick amorphous silicon layer on the prepared silicon dioxide film layer by plasma-enhanced chemical vapor deposition (PECVD).

[0027] Step 3) Use EBL electron beam lithography technology to define the waveguide structure on the photoresist.

[0028] Step 4) Through plasma etching (ICP-RIE), etch 100 nm completely to form a 100-nm-thick top amorphous silicon waveguide structure.

[0029] Step 5) Use plasma-enhanced chemical vapor deposition to deposit a 1-μm-thick SiO2 cladding layer on the amorphous silicon waveguide structure and the amorphous silicon layer, and finally obtain a hybrid waveguide structure with a core structure of silicon-silicon dioxide-lithium tantalate for light propagation.

[0030] The hybrid waveguide prepared by the above method in this embodiment, from top to bottom, successively includes: a silicon layer, a thin film silicon dioxide layer, a lithium tantalate layer, a silicon dioxide buried layer, and a silicon substrate. As Figure 2 shown, the structural layers for light propagation in this hybrid waveguide include: an amorphous silicon layer, a silicon dioxide layer, and a lithium tantalate layer, that is Figure 1 the top three layers from top to bottom in []. Among them: the thickness of the silicon layer is 100 nm, the thickness of the silicon dioxide thin film is set to 20 nm to prevent black dots from appearing when depositing amorphous silicon directly on lithium tantalate. The thickness of lithium tantalate can be adjusted according to actual use conditions. In this embodiment, it is preferably 600 nm.

[0031] Through waveguide simulation by Mode Solution software and experimental preparation of a device based on the optical waveguide structure shown in the present invention, the obtained results are: light is partially localized in the lithium tantalate layer, and the specific numerical ratio under the above parameters is 0.507 (simulation). On the device based on the above waveguide, the material characteristics of lithium tantalate can be used to adjust the device (the experimental results show that the Pockels effect of lithium tantalate can be used to adjust the waveguide refractive index, so as to realize the electrical tuning of the wavelength).

[0032] AsFigure 6 As shown, a photonic device is fabricated using the waveguide, and the projection spectrum of the device is wavelength-tuned by using the Pockels effect of the lithium tantalate crystal. The experimental results show that the wavelength center shifts under different bias voltages (±70V). The experimental results show that the hybrid waveguide can indeed electro-tune the photonic device by using the electro-optic effect (Pockels effect) of the lithium tantalate crystal.

[0033] By simulating the calculator to calculate the percentage of the localized light of aluminum nitride in the hybrid waveguide, it is proved that its mode field can be effectively localized in the waveguide. Among them, the TE fundamental mode is localized in the above-mentioned hybrid lithium tantalate layer at a ratio of 50.7%. By continuously changing the simulated thickness of lithium tantalate, the calculated result of the light localization ratio also changes accordingly. Specifically, it increases with the increase of the thickness of aluminum nitride, as Figure 4 shown.

[0034] Compared with the prior art, the present invention integrates a lithium tantalate crystal and silicon, realizing that part of the light is localized in the lithium tantalate layer when propagating in the waveguide, and it can be used for the preparation of optical devices. On it, the special properties of lithium tantalate, such as electro-optic properties, can be utilized to make its application superior to and more convenient than the devices prepared by traditional waveguides (such as electro-tuning) in some aspects, as Figure 6 shown.

[0035] The optical waveguide device with a three-layer structure of amorphous silicon - silicon oxide - lithium tantalate prepared by the present invention. The excellent properties of the lithium tantalate material can overcome some limitations of traditional silicon and are compatible with the microelectronic CMOS process. The optical waveguide obtained by the novel structure and materials provided by the present invention can not only effectively transmit light, but also introduce the excellent piezoelectric and electro-optic and other properties and material characteristics of lithium tantalate, and the specific thickness of the lithium tantalate layer can be changed to achieve different light localization ratios, and it can be applied to different scenarios by changing the thickness of the lithium tantalate layer.

[0036] The above specific embodiments can be locally adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific embodiments. All implementation schemes within its scope are subject to the constraints of the present invention.

Claims

1. A silicon-based lithium tantalate hybrid waveguide, characterized in that, From top to bottom, it successively includes: an amorphous silicon layer, a thin film silicon oxide layer for preventing black dot impurities from appearing during the deposition of amorphous silicon and affecting the waveguide transmission effect, a lithium tantalate layer for transmitting the TE mode, a silicon oxide buried layer, and a silicon substrate, where: the amorphous silicon layer, the thin film silicon oxide layer, and the lithium tantalate layer are deposited to form a hierarchical structure, serving as the structural layer for light propagation in the waveguide structure; The refractive index distribution of the silicon-based lithium tantalate hybrid waveguide is as follows: the refractive index of silicon material n1≈3.42, the refractive index of lithium tantalate material n2≈2.176, and the refractive index of silicon oxide material n3≈1.

45.

2. The lithium tantalate on silicon hybrid waveguide according to claim 1, wherein The thickness of the amorphous silicon layer is 100 nm.

3. The lithium tantalate on silicon hybrid waveguide according to claim 1, characterized in that, The proportion of the TE mode localized in the lithium tantalate layer is positively correlated with the thickness of the lithium tantalate; when the thickness is 600 nm, the proportion of the optical mode field localized in the aluminum nitride layer is 50.7%.

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