Double-Layered NiO/SnO ₂ Sensor for Improved SO ₂ Gas Sensing with MEMS Microheater Device

Abstract

Micro Electro mechanical systems (MEMS) sensor is fabricated for testing low concentration gas sensing of sulphur dioxide (SO 2 ) with sensing layers of single layer tin oxide (SnO 2 ) and double layered heterojunction structure of nickel oxide and tin oxide (NiO/SnO 2 ). NiO and SnO 2 structures are deposited with RF sputtering and the elemental composition were identified with structural properties such as X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy Dispersive X-ray Analysis (EDX) analysis. Sensing results proved that NiO/SnO 2 double layered sensor had better sensing characteristics than single layered SnO 2 sensor due to the formation of p-n junctions. At 400 ppb of SO 2 gas concentration, NiO/SnO 2 sensor has maximum sensing response of 20% is recorded and at 2000 ppb, 30% sensing response is recoded. The optimal temperature of the sensor is 250 °C (∼63 mW). Selectivity of the sensor is tested with 5 different gases such as VOC, pyruvate, CO, NH 3 , SO 2 and the sensor has high and better response with SO 2 gas.