Enhancing the electro-optic response of a sputtered aluminum nitride-on-insulator (AlNOI) platform via high-temperature annealing

Aluminum nitride-on-insulator (AlNOI) is a promising platform for integrated photonics owing to its wide bandgap and second-order nonlinearity, enabling carrier-free electro-optic modulation. This work focuses on AlNOI racetrack resonator-based electro-optic modulators operating at telecom wavelengths, designed and fabricated from reactively sputtered AlN thin films. The study is based on a direct comparison between as-deposited reference devices and those optimized via high-temperature cyclic annealing. The electro-optic analysis reveals that for c -axis misorientations below 10°, the geometric impact remains minor. The macroscopic performance enhancement observed after annealing is therefore primarily attributed to microstructural healing and increased resistivity, which together optimize the electric field distribution. Notably, this material transformation significantly attenuates the static electric-field screening phenomena (charge trapping, leakage) that typically hinder the low-frequency response. Consequently, the DC electro-optic tuning efficiency increases by 138%, reaching 0.798 pm/V for annealed films. From these measurements, the macroscopic Pockels coefficient r 13 , the second-order nonlinear susceptibility χ (2) , and the V π . L figure of merit are extracted. To the best of our knowledge, these values establish the state of the art for the macroscopic DC/low-frequency electro-optic response of AlN, without relying on field-enhancement strategies based on III-N heterostructures or ferroelectricity. Ultimately, high-temperature cyclic annealing represents a compelling approach for unlocking the macroscopic electro-optic potential of AlN and positions the annealed AlNOI platform as a highly competitive, engineered photonic substrate compatible with front-end-of-line (FEOL) integration for wafer-scale photonic integrated circuits.