GHz AlN-based multiple mode SAW temperature sensor fabricated on PEN substrate

Polymeric based surface acoustic wave (SAW) devices represent one of the most interesting platform for the development of wireless passive sensors for IoT and smart packaging applications. An important feature to be addressed in order to develop a compact and conformable wireless SAW sensor is the increase of the working frequency which allows an easy antenna integration and miniaturization. In this work, we present a disposable polymeric SAW temperature sensor device working in the GHz range, based on aluminum nitride (AlN) and built on a 125 μm thick film of polyethylene naphthalate. The flexible device has been compared to the same SAW device fabricated onto silicon substrates. The polymeric based SAW device shows three operating wave modes corresponding to the Rayleigh, Love, and Lamb, highlighting that the Lamb mode exhibits a resonance frequency as high as 1.325 GHz, corresponding to a phase wave velocity of 10,600 m/s, an electromechanical coupling of 2.91 % and Q factor of 109. Temperature coefficient of frequency (TCF) values of 149, 109, 53 ppm/°C have been calculated for the Rayleigh, Love and Lamb waves, respectively. The different behavior of the three SAW modes let us envision the development of a multiple sensing platforms based on different modes in the same device (e.g. temperature, microbiological contamination, light exposure).