TiO2-based nitrogen dioxide gas sensor with transparent ordered micro-hollow bump structure prepared by 3D heterogeneous integration technology

Abstract

This study produces the TiO2 membrane for a transparent ordered micro-hollow-bump (TOMHB) structure using a micro electro mechanical system (MEMS) and 3D heterogeneous integration (HI). The SEM image shows that the diameter and depth of each MHB are 12.5 μm and 8.5 μm. The TEM image shows that a 70 nm-thick TiO2 membrane is uniformly coated onto the MHB using atomic layer deposition (ALD). For NO2 gas sensing, the TiO2 TOMHB gas sensor is measured with and without UV irradiation at a working temperature for the sensor of room temperature, and a measurement time from NO2 injection to exhaust of about 5 min. Without UV irradiation, the gas response is good but the response time is slow and difficult-recoverable. With UV irradiation, the TiO2 TOMHB gas sensor has a fast response and recovery time. Four consecutive stability experiments show that the sensor response has an average value of 9.5 % for NO2 4.25 ppm. The average response time is 7 s and the average recovery time is 144 s. In addition, the TiO2 TOMHB gas sensor is a good selective for NO2 gas. These results show that the TiO2 TOMHB NO2 gas sensor has good stability, reproducibility and selectivity.