ZnO-Nanorod-Based Ammonia Gas Sensors With Underlying Pt/Cr Interdigitated Electrodes

ZnO-nanorod-based resistor-type ammonia gas sensors with underlying Pt/Cr interdigitated electrodes have been fabricated and investigated. The response is improved by reducing the electrode spacing d. Experimentally, a high response of 80.6 is found when d is reduced to 2 μm under exposure to a 1000-ppm NH₃ /air gas at 300 ^°C. A lower detection limit of 10-ppm NH₃/air at 300 ^°C is also obtained. This device possesses response and recovery times of <; 3 min even at low ammonia concentrations (10 ppm). The enhanced ammonia-sensing capability with reducing electrode spacing d could be attributed to the formation of more ZnO grain boundaries. A simple cross-linked structure model is presented to interpret the ammonia-gas-sensing performance, and a good correlation between theory and experiment is demonstrated.