On-substrate fabrication of a self-activated nanostructured ZnO gas sensor.

Gaining rational control over bottom-up device fabrication processes is necessary to achieve high-performance devices and overcome technical obstacles. Among these is the need for activation of metal oxide gas sensors (GSs) by an external heating source, which limits their miniaturization and integration. A well-controlled, seedless, and position-selective hydrothermal method to fabricate high-performance self-activated zinc oxide (ZnO) nano-needle (ZNN) GSs directly on a substrate was developed. The morphology and position of the grown ZnO nanostructures were controlled by tuning the substrate coating and growth reaction parameters such as the growth solution concentration and the growth time, as well as introducing capping agents to the growth solution during the growth process. Furthermore, the efficiency of the fabricated device structure was improved and subsequently enhanced its performance substantially. Compared to other fabricated nanostructured ZnO GSs, the on-substrate fabricated bridging ZNN (BZNN) GS demonstrated superior sensitivity and self-activation, which were attributed to the reduction in the sensing material dimensions and ultrahigh surface-to-volume ratio, as well as the unique device structure with direct contact between ZnO and Au electrodes. This work paves the way for low cost, large scale, low temperature, seedless and position-selective fabrication of high-performance self-activated nanostructured ZnO GSs on flexible and transparent substrates.