NH₃-Sensing Mechanism Using Surface Acoustic Wave Sensor with AlO(OH) Film

In this study, AlO(OH) (boehmite) film was deposited onto a surface acoustic wave (SAW) resonator using a combined sol-gel and spin-coating technology, and prepared and used as a sensitive layer for a high-performance ammonia sensor. The prepared AlO(OH) film has a mesoporous structure and a good affinity to NH₃ (ammonia gas) molecules, and thus can selectively adsorb and react with NH₃. When exposed to ammonia gases, the SAW sensor shows an initial positive response of the frequency shift, and then a slight decrease of the frequency responses. The sensing mechanism of the NH₃ sensor is based on the competition between mass-loading and elastic-loading effects. The sensor operated at room temperature shows a positive response of 1540 Hz to 10 ppm NH₃, with excellent sensitivity, selectivity and stability.