A novel 440 MHz wireless SAW microsensor integrated with pressure-temperature sensors and ID tag

This paper presents the development of a 440 MHz range surface acoustic wave (SAW)-based microsensor integrated with pressure - temperature sensors and ID tag. Two piezoelectric substrates were bonded, in which a similar to 150 mu m air gap was structured by metal poles. The pressure sensor was placed on the top substrate, whereas the ID tag and temperature sensor were located on the bottom substrate. Coupling of modes (COM) modeling was used to find optimal design parameters. Using the extracted optimal design parameters, the SAW device was fabricated. In wireless device testing using a network analyzer, sharp reflection peaks with high S/N ratio, small signal attenuation and small spurious peaks were observed in the time domain. All the reflection peaks were well matched with the predicted values from the simulation. With 10 mW RF power from the network analyzer, a similar to 1 m readout distance was observed. Depending on applied external pressure, the phase shifts of the reflection peaks were linearly varied. The evaluated sensitivity was about similar to 2.9 degrees kPa(-1). Eight sharp ON reflection peaks were observed for the ID tag. The temperature sensor was characterized from 20 degrees C to 200 degrees C. A large phase shift per unit temperature change was observed.