Enhancing the Reliability of Nanostructured Optical Devices via Nano-trench Filling

Nanostructured optical devices, such as form-birefringent waveplates and polarizers, offer compact, high-performance functionality but suffer from reliability challenges due to environmental exposure. Without protective trench filling, the nanoscale gratings are directly exposed to air and humidity, leading to cavity formation, index drift, and optical degradation over time. We investigated the use of atomic layer deposition (ALD) to conformally fill the nano-trenches and encapsulate the structures, thereby preventing environmental infiltration and stabilizing optical properties. Cross-sectional analysis confirmed complete trench burial with uniform, pinhole-free films. Accelerated aging and GR-1221 reliability tests—including 2000-hour high- and low-temperature exposure, 500-hour 85°C/85% RH humidity testing, and 15-cycle thermal shock—showed no physical damage and negligible changes in transmission (<0.3%) or retardation (<0.5°). The ALD-filled devices demonstrated a marked improvement in lifetime and optical stability compared to unfilled structures. This study establishes atomic layer deposition trench filling as a scalable, material-agnostic method to achieve long-term environmental reliability in nanostructured optical components for industrial applications.