Effects of O ₂ /Ar flow ratio on the alcohol sensitivity of tin oxide film

The aim of this study is to find the effects of oxygen flow rate during manufacturing on the sensitivity of SnO ₂ (tin oxide) thin films to ethanol (C ₂ H ₅ OH). In this study, an RF sputtering process was employed to fabricate the SnO ₂ thin films. The SnO ₂ was deposited on gold electrode silicon microchips. A target composed of SnO ₂ doped with 1 at.% Li was used with a working pressure of 3 mTorr. The RF power was fixed at 150 W. The reaction gas was a mixture of argon and oxygen. The total flow rate was constant at 50 sccm with the O ₂ /Ar ratio varying from 0.2 to 0.8. An annealing heat treatment was employed at 400 °C for 1 h to stabilize the properties of the films. The sensitivity of the film to ethanol was tested by placing the micro-reactor device on a hot plate, heated to 300 °C, and measuring the variation of electrical resistivity of the film with and without the presence of ethanol. The results show that an O ₂ /Ar flow ratio of 0.2 produces films with the highest ethanol sensitivity. Before heat treating, the ethanol sensitivity was 126. After heat treating at 400 °C for 1 h, the sensitivity decreased to 104. © 2005 Elsevier B.V. All rights reserved.