Wireless temperature sensing using a passive RFID tag with film bulk acoustic resonator

The lifetime of active RFID tag is limited by the equipped battery capacity. A passive RFID tag which gathers power via inductive coupling from RF power for temperature sensing was proposed to extend the lifetime of the tag. An oscillator with film bulk acoustic resonator (FBAR) lies at the heart of the tag. A four-layered FBAR with Al/AlN/SiN_X/Au composite structure was fabricated. The oscillation frequency of the oscillator varies with the temperature linearly. The temperature can be detected easily by measuring the shift of oscillation frequency. The measured phase noise of the oscillator is -75 dBc/Hz at 10 kHz offset. A linear temperature sensitivity of -34.5 ppm/degC in the temperature range from 10 and 80degC at 2.48 GHz is achieved.