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 VO2. We have explored split-ring resonator transducers on 40 nm thick undoped VO2 and on 2.3% Ge-doped VO2 ALD thin films below coplanar waveguide (CPW). The temperature sensing principle is based on the non-linear dielectric constant variation of VO2 around its transition temperature. We demonstrate two regions with very contrasted temperature sensitivities in insulator-phase and near-transition temperature. For the Ge-doped VO2 resonator, the experimental temperature sensitivity is higher than for the VO2 resonator, reaching 6.9 MHz/degrees C between 25 and 78 degrees C and a record high value of 463 MHz/degrees C between 78 and 95 degrees C, respectively. This shows that doping plays an important role in controlling both transition temperature and temperature sensitivity.POWERLABNANOLA

3D Smith charts scattering parameters frequency-dependent orientation analysis and complex-scalar multi-parameter characterization applied to Peano reconfigurable vanadium dioxide inductors

Recently, the field of Metal-Insulator-Transition (MIT) materials has emerged as an unconventional solution for novel energy efficient electronic functions, such as steep slope subthermionic switches, neuromorphic hardware, reconfigurable radiofrequency functions, new types of sensors, terahertz and optoelectronic devices. Employing radiofrequency (RF) electronic circuits with a MIT material like vanadium Dioxide, VO2, requires appropriate characterization tools and fabrication processes. In this work, we develop and use 3D Smith charts for devices and circuits having complex frequency dependences, like the ones resulting using MIT materials. The novel foundation of a 3D Smith chart involves here the geometrical fundamental notions of oriented curvature and variable homothety in order to clarify first theoretical inconsistencies in Foster and Non Foster circuits, where the driving point impedances exhibit mixed clockwise and counter-clockwise frequency dependent (oriented) paths on the Smith chart as frequency increases. We show here the unique visualization capability of a 3D Smith chart, which allows to quantify orientation over variable frequency. The new 3D Smith chart is applied as a joint complex-scalar 3D multi-parameter modelling and characterization environment for reconfigurable RF design exploiting Metal-Insulator-Transition (MIT) materials. We report fabricated inductors with record quality factors using VO2 phase transition to program multiple tuning states, operating in the range 4 GHz to 10 GHz