Behavior of toxic gas sensor based on conducting polypyrrole

A sensor for two types of ammonia (NH₃) and carbon monoxide (CO) is fabricated on silicon substrate by using the drop-coating method and the sensor performance is investigated. Polypyrrole, an electro-conductive plastic, is used as the sensing material of the gas sensor. The gas sensor functions to maintain a constant gate voltage in a state that facilitates measurement of the conductivity of the gate, source, and drain having a source electrode and the drain electrode of a field effect transistor channel between the structures. The sensor exhibits an increase/decrease of the resistance upon exposure to a low concentration of NH₃ and CO gas. This approach can be applied for highly sensitive room-temperature sensing of CO and NH₃ at sub-ppm concentrations and for the development of very low-power devices. The synthesized conducting polypyrrole was characterized via field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FTIR). The electronic transport properties of the sensors are measured in a field effect transistor geometry under ambient conditions. The sensing properties of the conducting polypyrrole gas sensor at sub-ppm gas concentrations are described.