Using ultrathin double-layer gas-permeable capping metal to form sensitive low-power gas sensors

In this work, we investigated a simple, sensitive, and low-powered ammonia (NH3) gas sensor using a thin bi-layered metal capped on an organic semiconductor chemoresistor to deliver a sensitive response to NH3 (ppb level) at room temperature. An optimized thin bi-layered Al/Ag metal (2 nm/10 nm) successfully forms a gas-permeable structure to realize ppb-regime gas sensing better than other single-layered thin Ag, Al, or Au (12 nm) metal electrodes. The performance of the simple metal-capped gas sensor is greatly dependent on the surface roughness of the thin metal electrodes, and the very rough thin bi-layered metal Al/Ag (2 nm/10 nm) allows high gas penetration. The optimized device exhibits more than 10% response to 100 ppb NH3 at only 0.5 V. The simple, low-cost, highly sensitive, and low-powered gas sensors are promising for Internet of things applications.