Hydrogen Gas Sensor Based on Nanocrystalline SnO₂ Thin Film Grown on Bare Si Substrates

In this paper, high-quality nanocrystalline SnO₂ thin film was grown on bare Si (100) substrates by a sol-gel method. A metal-semiconductor-metal gas sensor was fabricated using nanocrystalline SnO₂ thin film and palladium (Pd) metal. The contact between Pd and nanocrystalline SnO₂ film is tunable. Ohmic barrier contact was formed without addition of glycerin, while Schottky contact formed by adding glycerin. Two kinds of sensor devices with Schottky contact were fabricated (Device 1: 8 h, 500 °C; Device 2: 10 h, 400 °C). The room temperature sensitivity for hydrogen (H₂) was 120 and 95 % in 1000 ppm H₂, and the low power consumption was 65 and 86 µW for two devices, respectively. At higher temperature of 125 °C, the sensitivity was increased to 195 and 160 %, respectively. The sensing measurements were repeatable at various temperatures (room temperature, 75, 125 °C) for over 50 min. It was found that Device 1 has better sensitivity than Device 2 due to its better crystallinity. These findings indicate that the sensors fabricated on bare Si by adding glycerin to the sol solution have strong ability to detect H₂ gas under different concentrations and temperatures.