Aluminum Nitride Waveguides with 0.12 dB/cm Propagation Loss Around the Telecommunication C-Band

Aluminum nitride (AlN) is a promising material for photonic waveguides, offering a broad transparency range from ultraviolet (UV) to mid-infrared wavelengths due to a wide bandgap of more than 6.0 eV [1]. The AlN platform has similar optical properties to SiN, such as refractive index and extinction coefficient, enabling the fabrication of low-loss optical devices in telecommunication bands. Unlike SiN, AlN exhibits both second and third-order optical nonlinearity due to its centrosymmetric crystal structure. In addition, AlN has higher optical power handling capabilities due to reduced two-photon absorption. These properties make it a promising candidate for integrated photonics in linear and nonlinear applications. Moreover, its compatibility with CMOS processes further enables scalable production of such devices [2], [3]. This study presents the fabrication and optical characterization of sputtered AlN photonic waveguides. A 190 nm thick AlN film was deposited on a thermally grown 4.5 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu\mathrm{m}$</tex> silicon dioxide (SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) substrate by magnetron sputtering at 700°C with a low base pressure of 1 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times 10^{-8}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3\times 10^{-8}$</tex> mbar to minimize oxygen in the chamber. This controlled environment improves the quality of the films by reducing the extinction coefficient [4].