Radio Frequency Temperature Transducers Based on Insulator-Metal Phase Transition in VO2 and Ge-Doped VO2 ALD Thin Films

The need for new accurate temperature monitoring is becoming high, especially with the proliferation of IoT monitoring and biological applications. In this work, we report the design, fabrication and electrical characterization results of a new type of resonant RF sensors that can be used as RF temperature tags, exploiting the high temperature sensitivity of reversible insulator-metal transition in VO
2
. We have explored split-ring resonator transducers on 40 nm thick undoped VO
2
and on 2.3% Ge-doped VO
2
ALD thin films below coplanar waveguide (CPW). The temperature sensing principle is based on the non-linear dielectric constant variation of VO
2
around its transition temperature. We demonstrate two regions with very contrasted temperature sensitivities in insulator-phase and near-transition temperature. For the Ge-doped VO
2
resonator, the experimental temperature sensitivity is higher than for the VO
2
resonator, reaching 6.9 MHz/°C between 25 and 78°C and a record high value of 463 MHz/°C between 78 and 95°C, respectively. This shows that doping plays an important role in controlling both transition temperature and temperature sensitivity.