Effects of oxygen gas in the sputtering process of the WO3 sensing layer on NO2 sensing characteristics of the FET-type gas sensor

Abstract

This paper investigates the effect of oxygen gas in the sputtering process of the WO3 sensing layer. The WO3 sensing layer is deposited on the Si FET-type gas sensor platform having horizontal floating-gate (FG) interdigitated with control-gate (CG) by using the DC magnetron sputtering method. When exposed to the NO2 gas, the drain current of the FET-type gas sensor with the WO3 sensing layer increases since the NO2 gas is known as an oxidizing gas. In this work, NO2 sensing characteristics of the gas sensors with the WO3 sensing layer deposited under three different sputtering conditions are compared. The flow rate of argon gas in total sputtering gas is fixed at 30 sccm, and the flow rate of oxygen gas is changed (0, 1, and 3 sccm). NO2 response of the gas sensor with WO3 sensing layer deposited using the oxygen gas with the argon gas in the sputtering process is higher than that of the gas sensor with WO3 sensing layer deposited using only argon gas. As the ratio of oxygen gas in the total sputtering gas increases, the response of the gas sensor increases since the size of the grain is reduced and the number of W = O bonds at the grain boundary increases. Therefore, NO2 response of the FET-type gas sensor with the WO3 sensing layer deposited at an oxygen flow rate of 3 sccm in the sputtering process is the largest. The optimized FET-type gas sensor has excellent selectivity for NO2 target gas.