High-Performance, Transparent Thin Film Hydrogen Gas Sensor Using 2D Electron Gas at Interface of Oxide Thin Film Heterostructure Grown by Atomic Layer Deposition

Abstract

A high-performance, transparent, and extremely thin (<15 nm) hydrogen (H-2) gas sensor is developed using 2D electron gas (2DEG) at the interface of an Al2O3/TiO2 thin film heterostructure grown by atomic layer deposition (ALD), without using an epitaxial layer or a single crystalline substrate. Palladium nanoparticles (approximate to 2 nm in thickness) are used on the surface of the Al2O3/TiO2 thin film heterostructure to detect H-2. This extremely thin gas sensor can be fabricated on general substrates such as a quartz, enabling its practical application. Interestingly, the electron density of the Al2O3/TiO2 thin film heterostructure can be tailored using ALD process temperature in contrast to 2DEG at the epitaxial interfaces of the oxide heterostructures such as LaAlO3/SrTiO3. This tunability provides the optimal electron density for H-2 detection. The Pd/Al2O3/TiO2 sensor detects H-2 gas quickly with a short response time of <30 s at 300 K which outperforms conventional H-2 gas sensors, indicating that heating modules are not required for the rapid detection of H-2. A wide bandgap (>3.2 eV) with the extremely thin film thickness allows for a transparent sensor (transmittance of 83% in the visible spectrum) and this fabrication scheme enables the development of flexible gas sensors.