An integrated passive impedance-loaded SAW sensor

Abstract An integrated passive impedance-loaded SAW H 2 S sensor working at room temperature has been presented in this paper. The sensor consists of a SAW transponder with delay line structure and a resistive H 2 S sensor as an impedance-loaded sensor. The SAW delay line was fabricated on a 128° LiNbO 3 substrate and its center frequency is 233 MHz. The resistive sensor composed of the nano-crystalline SnO 2 film and aluminum electrodes was also fabricated on the same substrate. The gas sensing properties of the resistive H 2 S sensor have been tested separately. In order to maximize the sensitivity of the whole sensor, the resistance of the impedance-loaded sensor was adjusted to match the output impedance of the SAW interdigital transducer (IDT) by changing the resistivity of the Sb-doped SnO 2 nano-crystalline films and optimizing the electrode structure. The variation in the return loss magnitude was increased to 2.51 dB. Finally, the impedance-loaded SAW sensor was configured and measured wirelessly for various H 2 S concentrations at room temperature. The measurement results show that the proposed H 2 S sensor not only has good repeatability and high sensitivity but also is capable of passive wireless detection at room temperature.