Study On The Preparation And Properties Of Gas Sensors Based On AZO Thin Films

Many public places need to detect accurately and permanent monitoring for explosivegas, to lower human health risks and safeguard public safety. The largest barrier to achieveenvironmental control often lies at the interface between the system and the environment to bemonitored, i.e. the sensor. Significant progress in achieving environmental control andinstrumentation will be impossible without sensors. Among many sensitive materials, AZOgas sensor comes to the fore due to its excellent gas-sensitivity and highly stability. Oxygenphysical or chemical adsorbed from the air plays the role of electron acceptor state on AZOgrain surface. At specific working temperature, target gas on the sensor surface reductionreaction occurs with adsorbing oxygen, causing that the coverage on some parts of the surfacedecreases, which led to the surface resistance decreases. AZO films exhibit sensing properties.To herein, radio sputtering method is used for preparing AZO thin films which has highlygas sensitivity and low operating temperature. Considering that sputtering thin films haveuniform-sized grain, fewer impurities, and the film is not easy to detach from the substrate. Itis convenient to realize the control of deposition conditions. By performing differentexperiments, this thesis uses XRD, Four-probe tester, Atomic Force Microscope, and otheradvanced analytical tools for films.Then using static gas sensing testing system to analyze the effect of the RF sputteringpower, working pressure, the substrate sputtering temperature and post-annealing conditionsto the surface morphology, the microstructure, electrical and gas sensing properties of thefilms for ethanol, nitrogen dioxide and ammonia, and found some rules effecting AZO filmsand the optimal parameters of some preparing conditions was generalized. Target-substratedistance is6cm, argon flue of45sccm, sputtering power of110W, the substrate temperature of300℃. For the optimum preparing parameters of AZO sensing film, the sensitivity reaches92%and68%, the optimal working temperature reduced to250℃and200℃for ethanoland nitrogen dioxide, respectively. After that, the post thermal processed was used for films,working temperature, response and recovery time and the sensitivity of the superficialprocessed AZO thin films have been improved with varying degree.Preparing different thickness Ti onto the AZO thin film surface prepared at the optimalparameters to improve the selectivity for ammonia, then the sensing film was heat-treated tomodify the surface of AZO films. The addition of Ti contributed to improve the sensitivityand low the best working temperature and the selectivity is also much better. When thethickness of added Ti was20nm, the sensitivity improved to99.2%for50ppm NH3and theoptimum operating temperature is140℃. The selectivity is also improved for ammonia.