Experimental study on chemical mechanical polishing of LNOI surfaces

In recent years, lithium niobate (LiNbO3) has been widely used in optical fiber communication, quantum communication, fiber optic gyroscopes and microwave photonics as an important photonic material. Lithium niobate on insulator (LNOI) has attracted much attention as an emerging photonic integrated material. Compared with traditional lithium niobate crystal materials, LNOI materials have the ability to realize miniaturized photonic devices with higher efficiency and lower energy consumption, thus showing great potential in the design and manufacture of photonic devices. However, due to the high hardness and inactive chemical properties of LNOI materials, the traditional semiconductor process cannot process its nanostructures, which limits the optimization of the key performance indicators of the device, thus hindering the further development of high-quality and miniaturized LNOI optoelectronic functional devices. In the preparation process of the LNOI waveguide, the sidewall of the ridge waveguide formed by etching is often not flat enough, which may lead to an increase in light scattering loss. To solve this problem, surface polishing technology, especially chemical mechanical polishing (CMP), has become an important method. Polishing the surface of the LNOI device by CMP can reduce the roughness of the waveguide sidewall after etching, improve the performance and power transmission efficiency of the device, and ensure that the sidewall surface is flat and smooth to achieve the minimum optical coupling loss and maximum power transmission.