Field effect transistor type NO2 sensor combined with NaNO2 auxiliary phase

A field effect transistor (FET) sensor for NO2 was fabricated by depositing an NaNO2 layer together with an Au electrode over the gate area. The NaNO2-attached FET exhibited almost ideal FET behavior at 180°C in air. The threshold voltage was found to shift up ward in a well controlled manner with increasing NO2 concentration of the atmosphere. Under the condition of a fixed source-drain voltage (3.0 V), the gate-source voltage (VGS) necessary to keep the drain current at a small constant value (200 μA) was found to increase linearly with an increase in the logarithm of NO2 concentration in the range from 500 ppb to 10 ppm. The times of 90% response and recovery to switching-on and -off 500 ppb NO2 were about 2 and 4 min, respectively. The NO2 sensitivity was hardly or only slightly affected by variations in the concentrations of coexistent O2, CO2 or H2O.