Double-Phase Ga-Doped In₂O₃ Nanospheres and Their Self-Assembled Monolayer Film for Ultrasensitive HCHO MEMS Gas...

In the sensing field, the electronic structure of sensing materials has a great influence on the properties of the sensors. Here, by Ga doping pure rhombohedral In₂O₃ (h-In₂O₃), the double-phase In₂O₃ (cubic/rhombohedral In₂O₃, c/h-In₂O₃) porous nanospheres are obtained. And then Micro Electromechanical System (MEMS) gas sensors based on monolayer film are further fabricated by self-assembling the above nanospheres. The 5% Ga-doped In₂O₃ sensors exhibit excellent HCHO sensing performance with a high-response (110.6@100 ppm), rapid response/recovery time (5.2/18.4 s) and low limit of detection (50 ppb) at an operating temperature of 180 °C. The 5% Ga-doped In₂O₃ sensors also show high consistency (fluctuations of only 8.3%). Besides, a handheld device is developed to enable real-time monitoring and early warning of indoor HCHO at ppb-level. Based on experimental results and DFT theoretical calculation, the enhanced sensing mechanism is revealed, which is correlated with the optimization of electronic band structure by Ga doping and the appearance of double-phase heterostructures caused by Ga doping. Therefore, the relationship between electronic structure and gas sensing properties has also been established. This work significantly introduces a novel approach for the mass production of MEMS gas sensors, ensuring high sensitivity, repeatability and consistency.