The electrical and gas sensing properties of both doped and undoped ZnO thin films are investigated in a dark chamber. The electrical measurements were carried out in ambient air, in vacuum and under nitrogen (N₂) flow at the room temperature and also in the temperature range of 290−425 K. The effect of volatile organic compounds such as alcohol and acetic acid on electrical conductivity of thin films was investigated. Clear, homogeneous and stable ZnO solution was prepared by sol-gel synthesis using zinc acetate (ZnAc) precursor. Methanol was selected as a solvent and acetyl acetone was used as chelating agents. In order to improve adhesion of ZnO on the interdigital transducer (IDT), triethanolamine was used in the solution. Yttrium 2, 4 pentanedionate was used as the dopant. ZnO and ZnO doped with 1-5 wt% Y thin films were coated on the IDT using Spin coater Model P6700 Series and preheating at 250 °C for 2 min after each coating. After that all films were post-annealed at 600 °C for 30 min. The IDT consisted of 10 interdigital pairs of gold fingers, evaporated on microscope slides in a UNIVEX 450 coater system with a thickness of 150 nm, 100 μm wide and spaced 100 μm from the next finger. The dc and ac conductivity measurements were carried out on the thin films using Keithley 6517A Electrometer/High-Resistance Meter and Agilent 4294A Precision Impedance Analyzer, respectively. The effect of the VOCs vapors on the conductivity of the thin films was measured in a home made chamber and dry nitrogen was used as carrier gas at the room temperature. It was found that the conductivity of doped ZnO increased approximately 5 times than the case of undoped ZnO. This conductivity increase of the thin films depends on the concentration of VOCs which is between 500ppm-5000ppm. The details of the conduction and sensing mechanism of the samples will be discussed.

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