Tunable ferroelectric materials for RF- Microwave applications: high frequency properties and integration in frequency-agile devices
Résumé
Ferroelectric (FE) thin film capacitors can be a convenient technology for tuning microwave devices. The high
agility of ferroelectric materials with an applied DC bias is presented to be employed for tunable systems. Existing
reconfiguration solutions are based on varactor diodes, Micro-Electro-Mechanical systems (MEMS), PIN diodes, field
effect transistors (FET) or on the introduction of tunable ferroelectric materials. Among these, PIN diodes present only
two possible states (On/Off) and, like the FETs devices, have high power consumption. Varactor diodes present high
capacitance tunability but have a very low power handling capability (although they are widely referenced for
frequency tunable antennas). In this framework, two solutions with low power consumption are emerging for the
conception of reconfigurable circuits: MEMS and ferroelectric materials. The potential of ferroelectric materials is
evaluated within practical devices to meet the current requirements for highly reconfigurable, integrated, efficient and
low power-consuming systems. In this context, the integration of agile capacitors based on ferroelectric materials within compact devices to be
reconfigurable will be presented. Indeed, the high agility these materials with an applied DC bias voltage and their
reasonable loss tangent values can be employed to develop tunable systems. Particularly, reconfigurable filters, phase
shifters and frequency agile antennas based on different ferroelectric materials will be discussed. The characterization
of their dielectric properties at RF frequencies will be presented followed by their integration inside the devices.
Reconfigurable components could present either a 2D-shape, i.e. interdigital capacitors or a 3D-shape as the Metal-
Ferroelectric-Metal tunable components. Designs and performances of the devices incorporating these two kinds of
ferroelctric-based components will be presented and detailed.