Electrical Properties of the MOS Capacitor Hydrogen Sensor Based on the Ni/SiO₂/Si Structure

The MOS capacitors with the Ni/SiO₂/Si structure for detection of hydrogen gas have been fabricated. The influence of trapped charges on the flat-band voltage (V _FB) and performance of the MOS capacitor sensor has been investigated at 130 °C. The MOS sensors were fabricated on n-type Si 〈400〉 (0.2 cm) substrate with oxide film thicknesses of 37, 50, 63 and 73 nm. The Nickel gate of 100 nm was deposited on the oxide film by electron gun method. Results indicate the trapped charges in the oxide film causes a shift in the V _FB. The measured V _FB for the oxide film thicknesses of 37 and 73 nm is 1.4 and 2.5 V, respectively. The total trapped charges in the oxide film were measured using the Bias Thermal Stress (BTS) technique. With increase of the oxide film thickness from 37 to 73 nm the measured total trapped charges is increased from 59.4 to 66.9 (10^–9 C cm^–2). Results show, when sensors exposer to the 4000 ppm hydrogen concentration the response (R%) with increase the oxide film thickness is decreased. The main reason for this behavior is related to the decrease of the trap states in the Ni/SiO₂ interface. The highest response observed at the bias voltage of 0.51 V for the oxide thickness of 37 nm and is 58.2%. Experimental results demonstrate that the MOS sensors are sensitive to the trapped charges in the oxide film, which can be used for response and V _FB studies.