Effects of Postdeposition Annealing Ambience on NO2 Gas Sensing Performance in Si-Based FET-Type Gas Sensor

We investigate the effects of postdeposition annealing (PDA) ambience on the nitrogen dioxide (NO₂) gas sensing performance in the Si-based field-effect transistor (FET)-type gas sensor having an indium–gallium–zinc oxide (IGZO) as a sensing material. After the IGZO thin films are deposited, the sensors are postannealed in vacuum and atmospheric ambiences. The content of oxygen vacancy in IGZO films varies depending on the PDA ambience, which changes the electrical properties and NO₂ gas sensing performance of the sensors. The sensor postannealed in a vacuum ambience has more oxygen vacancy, which acts as an electrical donor, than that in an atmospheric ambience. Thus, the former has a larger coupling ratio and transconductance of the FET transducer. Also, the oxygen vacancy produces negatively charged oxygen species, increasing the response to NO₂. Due to a larger response to NO₂ gas and low noise, the sensor postannealed in a vacuum shows excellent signal-to-noise ratio (SNR) and limit-of-detection performances.