Thickness dependency of sol-gel derived ZnO thin films on gas sensing behaviors

ZnO thin films were fabricated by a sol-gel method using Zn(CH3COO)2·2H2O as starting material in order to prepare an acetone gas sensor. A homogeneous and stable solution was prepared by dissolving the zinc acetate in a solution of ethanol and monoethanolamine. The sol-gel solution is coated on alumina substrates with various thicknesses by spin coating technique and heat treated to grow crystalline ZnO thin films. The effect of thickness on physical and electrical properties of as deposited ZnO thin films has been studied. The as deposited ZnO thin films were characterized by X-ray diffraction spectroscopy, field emission scanning electron microscopy and atomic force microscopy. The root mean square surface roughness factors increase with thickness of the films and found 3.9, 6.6, 9.0, and 11.28 nm for 80-, 220-, 450- and 620-nm-thin films respectively. The activation energies of the films are calculated from the resistance temperature characteristics. The sensitivities of the ZnO films towards the acetone gas were determined at an operating temperature of 200 °C. The sensitivity towards acetone vapor is strongly depending on surface morphology of the ZnO thin films.