The study of E-nose based on metal oxide semiconductor

Abstract

Electronic nose (E-nose) is an artificial olfactory system which imitating olfactory system of living or-ganisms like human or insects, has been gradually studied due to its large potentiality on various areas like food industry or diagnosis of disease. Especially, E-nose based on metal oxide semiconductor is widely stud-ied due to its advantages like easy fabrication, low cost and high sensitivity on many harmful, environmen-tal, explosive and toxic gases. However, still they have some limitations like high working temperature due to their activation energy barrier. To achieve high sensitivity and resolution, working temperature above 200℃ was usually required in many studies. Therefore, enhancing sensitivity in room temperature is one of the chal-lenges for metal oxide semiconductor-based E-nose. In the present study, highly sensitive E-nose under room temperature were designed using IGZO and ZnO. Thin film transistor system was chosen as a base design of E-nose. IGZO and ZnO layer has deposited by sputter and annealed under 300℃ for 1 hour. Gas response of E-nose was measured by shift of transfer curve and two terminal real time resistance measurement. IPA gas was applied on device by N2 gas which has low chemical reactivity. IGZO shows significantly high gas response compares to ZnO due to its difference in physical-chemical structures. And due to their amorphous state, both IGZO and ZnO TFT show poor recov-ery characteristics under room temperature. They showed significantly enhanced recovery characteristic un-der 90℃ which is not appropriate for most of organic materials. To solve the problems, ZnO nanowire junction-based E-nose was prepared by hydro-thermal synthesiz-ing process. ZnCl and HMTA was used as solution for synthesizing. Solution changing period and synthesiz-ing time was controlled to fabricate various structure of nanowires. They show better gas response than ZnO TFT due to its significantly increased surface to volume ratio. Additionally, they show highly enhanced re-covery characteristic due to their crystal structure. As density of nanowires increase, recovery characteristic of nanowires was weakened. As length of nanowires increases, number of junctions increased, and it leads to enhancement in gas sensitivity. ZnO nanowires shows high sensitivity on Isopropyl alcohol and DI water. Al-so, they show excellent sensitivity on ethyl butyrate, eugenol and decanal which are odorants smells like fruity, clove and orange. E-nose based on ZnO nanowire junction has many advantages such like eco-friendly, bio-compatibility, low working temperature, high sensitivity on various gas and smells, and en-hanced recovery characteristic. Therefore, this E-nose device can be applied to various field such as bio-material enhanced E-nose, wearable E-nose or in implantable type of E-nose.