A room-temperature SAW methane sensor with Cryptophane-A film

Methane is an important but dangerous industrial gas. Compared with existing methane gas sensors, Surface Acoustic Wave (SAW) sensor exhibits many unique advantages like smaller size, fast response and room temperature operation. Thanks to the good affinity to methane molecules, the Cryptophane-A (CrypA) was chosen as the sensitive interface coated onto the SAW device surface for methane sensing operating at room temperature. Moreover, a 300MHz two-port SAW resonator with low insertion loss (~3dB) and high quality factor (~2500) were developed, and acted as the feedback element of a differential oscillation structure. To improve the sensor performance, the CrypA coating method was optimized, that is, an gas experiment was conducted, in which, CrypA was deposited on the sensing SAW resonators via drop-coating and spin-coating, respectively. The experimental results indicated that drop-coating method achieved much larger response (~1 kHz) over the spin-coating (~200Hz) because of the larger roughness. Satisfactory sensitivity and detection limit were observed in the gas experiments.