Perhaps one simply use inductive loop coupled to temperature sensitive piezo resonator e.g. https://www.fcd-tech.com/quartz-crystals/piezoelectric-sensors/piezoelectric-temperature-sensor

Thanks Nikolay..can u little elaborate..it further...tag is designed at 860 to 960 MHz..Where's resonator frequency is mentioned in KHz..

I thought about near field tags (which indeed are not actually RF tags). In case of 860..960MHz one may think about using RF rectifier driving low frequency micropower on tag oscillator. That oscillator may modulate impedance switch connected to the antenna therefore communicating (retromodulation communication) the low frequency which contains temperature information. The t freq dependant oscillator can be made using t dependant piezocrystall or even simply thermistor.