Low-Temperature Ammonia Gas Sensor Based on NiO/ZnO Heterojunction Nanosheet on MEMS Devices

Abstract

A double layered nanosheet structure of NiO over ZnO incorporated on Micro electro mechanical system (MEMS) device consisting of heater electrodes and sensing electrodes were investigated for gas sensing characteristics of Ammonia (NH3) gas. This process was achieved by combining 2 different deposition processes which are hydrothermal for ZnO and sputtering for NiO. From the synthesized samples, a series of different structural and morphological properties were analyzed such as X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM) and Energy dispersive spectroscopy (EDS). Sensing properties of ammonia gas are investigated with two different thicknesses of NiO and at different temperatures in order to find the best possible sensing response properties. The inspection of NiO/ZnO loaded samples sensing properties with ammonia gas ranging from 2.25 ppm to 18 ppm, revealed that 20 nm thickness of NiO with ZnO at 35 °C is the optimal sensing condition for the study. 18 ppm of ammonia gas recorded 55.8% sensing response at 35 °C with a response time of 8 s. Selectivity of the NiO/ZnO sensor is tested with 6 different gases such as CO, H2, H2S, NO2, SO2 and NH3, sensor demonstrated good selectivity for ammonia gas and showed excellent repeatability property.