Humidity-resilient room-temperature NO₂ sensing enabled by epitaxial single-crystalline Bi₂WO₆ ultrathin films

The development of embedded and distributed artificial olfaction systems requires gas sensors that combine low-power operation, miniaturization, environmental robustness, and scalable fabrication. Here, we demonstrate that epitaxial single-crystalline Bi₂WO₆ (BWO) ultrathin films can simultaneously achieve room-temperature NO₂ sensing, high selectivity, and strong humidity resilience, which is a combination rarely reported for perovskite oxide thin films. By decoupling the effects of thickness and crystalline quality, sensor responses are correlated with key morphological parameters via a quantitative transduction model. The optimized BWO-12 device (12-nm-thick single-crystalline film) achieves room-temperature NO₂ sensing performance with high selectivity, rapid response/recovery (24/71 s at 10 ppm), a low detection limit of 27 ppb, and minimal variation under humidity (<5% variation up to 86% RH). The devices demonstrate long-term stability over 8 months with aging and high device-to-device reproducibility (∼7.5% variation). Density functional theory calculations reveal strong adsorption and charge transfer for NO₂ relative to water, providing mechanistic insight into the high selectivity and humidity tolerance. The observations are consistent with classical sensing models and demonstrate that, through precise epitaxial growth and nanoscale morphology engineering, single-crystalline Aurivillius-phase perovskites are a promising materials platform for the development of energy-efficient artificial olfactory systems in robotics and distributed environmental monitoring.