The isotropic nature of the sensing elements decides the overall sensing performance of metal oxide gas/chemical sensors. Even a minimum deviation in the morphological and electrical characteristics of the sensing surface will lead to a nonuniform sensing performance, which in turn results in undesired figure of merits. With this background, the inhomogeneity of plasma discharge due to the racetrack effect of the magnetic field orbit in the planar magnetron and its significant influence on the formation of nanostructured ZnO thin films with desired uniformity has been investigated. The effect of the intensity of plasma discharges on the structural studies was a change in crystallite size from 11 to 35 nm. Anisotropic characteristics of the film influenced the mobility of carriers (10 and 220 cm(2) V(-1) s(-1)) by populating the carrier concentration (2.13 × 10(11) and 3.87 × 10(7) cm(-2)) in the nanostructures. Furthermore, the influence of this anisotropic surface of the obtained film on the room-temperature ethanol-sensing behavior is reported. The first observation of the racetrack effect on the sensing gradient of the sputter-deposited ZnO thin film has brought out the challenge in preparing an isotropic sensing element without anisotropy.
Keywords: ethanol sensing; nanostructured ZnO; plasma discharges; rf-magnetron sputtering; room temperature; thin film.