Co-conception matériaux hyperfréquences : étude et réalisation de couches minces accordables de BST en vue d’une application réseau réflecteur

摘要

Nowadays, wireless systems have to be able to adapt to different environments and standards, requiring reconfigurable microwave devices in order to dynamically vary their characteristics. Among all possible technological solutions to achieve this reconfigurability, agile materials, more specifically ferroelectrics, have an increasing interest. The major advantages compared to other technologies are a low bias current and the absence of moving parts.This manuscript presents the optimization and characterization of BaSrTiO (BST) ferroelectric thin films elaborated by chemical solution deposition. The complex permittivity was measured as a function of frequency, temperature, DC and AC fields. The fundamental study by impedance spectroscopy allows describing the relations between the structural microscopic properties (doping, grain size, defects, etc.) and the different permittivity contributions, including domain wall motion. This also helps to better understand the origin of the tunability and the dielectric losses in the material.The developed thin films were used for the realization of reconfigurable reflectarray cells, optimized by parametric studies. Two cell versions having increasing complexity and performance have been designed, realized and measured. Cell modeling also helped to develop an equivalent circuit, suitable for fast and efficient optimization of dimensions. The results indicate that the BST is a valuable candidate for this kind of application.