High temperature operable low humidity (10 to 20%RH) sensor using spin coated SnO2 thin films

The paper presents Tin oxide (SnO₂) based low cost, high temperature operable resistive type low humidity (10-20%RH) sensor. SnO₂ thin films were prepared by spin coating 50 μl of synthesized (SnCl₂) solution on alumina substrate (1.44 cm²). Material characterization of the synthesized material was carried out using UV-Visible, SEM and XRD. To get films of higher thickness they were coated from 1 to 4 layers and annealed in the furnace at an optimized temperature of 550°C for ~1 hour. Obtained SnO₂ thin films were tested for change in resistance w.r.t. humidity from 10 to 20% RH at 200°C and 300°C to be used in boilers. Samples have low hysteresis (~12%) with recovery time of about ~10 sec. They have shown good repeatability (5%). The sensitivity of tested films was found to increase with respect to number of SnO₂ layers. Sensitivity of 2 layered film operating at 200°C is 146 Ω/%RH and that of 4 layered film is 314 Ω/%RH, likewise at 300 °C the sensitivity of the films are 165 Ω/%RH and 323 Ω/%RH respectively.