Effect of metal oxide sensing layers on the distinct detection of ammonia using surface acoustic wave (SAW) sensors

In the present work, SAW sensors coated with various metal oxides as sensitive layer have been exploited for distinct detection of ammonia. Thin films of different metal oxides (ZnO, SnO2, TeO2 and TiO2) of same thickness (40 nm) were deposited under optimized parameters using rf sputtering technique for selective detection of liquor ammonia. As deposited ZnO thin film was highly c-axis oriented, whereas SnO2 thin film was polycrystalline. However the coatings of TiO2 and TeO2 thin films were amorphous. SAW sensor coated with ZnO film (ZnO/SAW) was found to be highly sensitive towards liquor ammonia as compared to other metal oxide coated SAW sensors. Effect of the thickness of ZnO sensing layer (20-80 nm) has been studied on the sensing response characteristics. Mass loading and elastic loading are identified as the major contributions towards the response of SAW sensor for ammonia and their contributions were evaluated by fitting with the theory.