Bottom-up strategy to develop ultrathin active layers by atomic layer deposition for room temperature hydrogen sensors

Inhalt:
The European Union is currently facing significant challenges related to climate change and the depletion of fossil fuels, both of which are exacerbated by regional and global geopolitical conflicts. Therefore, transitioning toward an independent renewable energy system based on new energy vectors such as synthetic fuels or hydrogen (H2) is urgently needed. Main efforts have been focused on direct energy conversion and storage systems, but a mass transition also requires the development of auxiliary components, such as highly sensitive hydrogen gas sensors integrated into mass devices that operate at ambient conditions. Recent advances in nanostructured metal oxide thin films have been reported, highlighting the simplicity of their fabrication processes and their compatibility with integrated circuits. However, the novel miniaturized devices usually require expensive noble metals or elevated operation temperatures (>250 degC) to achieve high sensitivity and short response/recovery times, which results in increased costs or higher power consumption, the latter, inducing poor long-term stability. To overcome these problems and create a new generation of metal oxide active films compatible with complementary metal-oxide semiconductor technology (CMOS), the Cottbus Innovationscampus Elektronik und Mikrosensorik (iCampmus) was established at the end of 2019, focusing on the development of integrated sensor solutions by combining a multidisciplinary dual approach based on applied science supported by basic research focused on materials optimization. This strategy encompasses various work areas for sensor development, including sensor architecture, deposition strategy of the active layer, sensing mechanism, and rapid testing under controlled environments. Here, we report the outcomes of this bottom-up approach in the active layer development and optimization for the case of cerium oxide (CeOx) layers grown by atomic layer deposition (ALD), particularly showing how the operando and in-situ characterization and control of the layer growth can help to understand the cross-interaction between film and substrate and its influence on sensor performance.