High-sensitivity fractal SnO2 sensors with optimized operating temperature for ethanol detection

Purpose Sensitivity and detection limit are the core indicators of gas sensors. This paper aims to present a method to prepare SnO2 gas sensors with the desired fractal dimension. By adjusting the annealing temperature gradient and optimizing the working temperature, the sensor can achieve optimal sensitivity and detection limit toward ethanol. Design/methodology/approach The fractal analysis method is based on fractal geometry theory, which quantitatively characterizes the complexity of the surface morphology of films through parameters such as fractal dimension and associates their microstructure with gas-sensing properties. In this paper, SnO2 sensors were annealed at temperatures ranging from 450°C to 550°C with a temperature gradient of 25°C. The heating temperature was controlled by adjusting the heating voltage from 4.9 to 5.5 V with a gradient of 0.1 V, and ethanol gas-sensing tests were carried out at different heating voltages. By calculating parameters including fractal dimension, porosity, average particle size and average pore diameter of the film scanning electron microscopy images, the correlation among annealing temperature, gas-sensing properties and fractal dimension was investigated. Findings The experimental results show that as the annealing temperature increases, the fractal dimension of the film is proportional to the sensitivity of the gas sensor. The sensor annealed at 475°C has the most favorable fractal box dimension and gas-sensing properties. The optimal heating voltage for sensors annealed at all temperatures is 5.3 V, but a higher fractal dimension of the sensor corresponds to a greater optimized sensitivity. The SnO2 fractal sensor annealed at 475°C exhibited the best sensitivity (the response of the sensor to 25 ppm ethanol reached 3.8162) and detection limit (0.9894 ppm) through heating temperature optimization. Originality/value This paper investigates the relationship among annealing temperature, fractal structure, ethanol gas-sensing performance and operating temperature of SnO2 sensors. Furthermore, a method is proposed to obtain SnO2 gas sensors with optimal sensitivity, detection limit and desired fractal dimension by adjusting the annealing temperature gradient and optimizing the operating temperature. This research can theoretically be extended to other gases and metal oxide semiconductor materials in the future.