Influence of nanoscale TiO2 film thickness on gas sensing properties of capacitor-like Pt/TiO2/Pt sensing structure

Due to the combustible and explosive nature of hydrogen, it is important to keep its safety during the production, storage, transportation and utilization. To this context, new type of sensors based on TiO₂ nano-films with 100, 50 and 30 nm thickness and capacitor-like sandwiched Pt/TiO₂/Pt structure were fabricated to monitor the hydrogen leakage. The gas sensing tests indicate that sensing performance improved with the decrease of TiO₂ film thickness thus the sensors with 30 nm thick TiO₂ film show higher performance in terms of response (6.16 × 10⁴ to 1000 ppm H₂) and response time (25.2 s). Moreover, tests also prove that humidity shows a negative effect on the performance. To investigate the sensing mechanism, temperature dependent resistance (R-T) and voltage dependent current (I-V) measurements was performed. The structure and surface topography of the TiO₂ film is characterized by the GIXRD and AFM, respectively. In addition, the elemental depth profile of the sensor was studied by the XPS, about 0.9 at.% Pt element was clearly observed in the middle region of the annealed TiO₂ layer. Based on the hydrogen diffusion, sensing mechanism of the presented structures is discussed.