Highly selective ZnO gas sensor based on MOSFET having a horizontal floating-gate

A metal-oxide-semiconductor field-effect transistor (MOSFET)-based gas sensor having a floating gate (FG) is fabricated and its sensing property is characterized. The gas sensor has 10 nm thick ZnO as a sensing layer prepared by atomic layer deposition (ALD). The FG, the sensing layer and the control gate (CG) are formed horizontally so that diverse sensing materials can be applied to the structure of the sensor without contamination. The gas-sensing performance of the sensor is investigated for seven target gases. Drain currents in NO2 and H2S ambiences are changed by 176% and 58%, respectively, for given NO2 (20 ppm) and H2S (20 ppm) concentrations. Whereas the changes of drain current for NH3, SO2, CO2, CH4 and C3H8 gases are less than 5%. Response and recovery times for NO2 are 90 s and 580 s, respectively, at 180 °C. The responses with working temperature and gas concentration are also studied. The sensing mechanisms for NO2 and H2S gases are explained.