PhD in materials engineering (M/F) – Control of the structure of thin films with tunable permittivity for a microwave sensor used to assess air quality

This research project aims to develop and optimize thin-film dielectric materials with a tunable low relative permittivity (between 2 and 4) and a low loss tangent in the 1–10 GHz microwave band. The materials studied will primarily be HMDSO-based films prepared by plasma processes, as well as ZnO/SiO₂ nanocomposites obtained by co-sputtering.

These materials will be integrated into microwave resonant structures to create sensitive, selective gas sensors compatible with microfabrication technologies. The ultimate goal is to demonstrate the feasibility of a high-performance resonant sensor, operating at room temperature, designed for the detection of gases of environmental interest.

Films derived from organosilicon precursors such as HMDSO were initially studied for passivation, encapsulation, and low-permittivity dielectric applications in the field of microelectronics. Research conducted at PCM has shown that thin films deposited by PECVD from HMDSO exhibit a wide range of relative permittivity (typically between 2 and 6), which can be finely tuned depending on plasma parameters and the incorporated oxygen content.

Furthermore, studies have demonstrated the low dielectric losses of “HMDSO” films in the microwave range, with loss tangents compatible with resonant applications up to several gigahertz. The low electrical conductivity, combined with good film homogeneity, allows for the maintenance of high quality factors, an essential condition for the precise detection of permittivity variations induced by gas adsorption.

This approach paves the way for a deeper understanding of gas-material interaction mechanisms in the microwave range—which remain largely unexplored—while targeting the detection of environmentally relevant gases such as NO₂, NH₃, O₃, or certain volatile organic compounds. It will be complemented by a comparative study with reference materials in the ZnO/SiO₂ system, such that the permittivity is modulated relative to a layer of ZnO alone.

This research project aims to develop and optimize thin-film dielectric materials with a tunable low relative permittivity (between 2 and 4) and a low loss tangent in the 1–10 GHz microwave band. The materials studied will primarily be HMDSO-based films prepared by plasma processes, as well as ZnO/SiO₂ nanocomposites obtained by co-sputtering.