The design and realisation of miniature RFID tags are nowadays subjects of innovation and drivers of many R&D works, both at the industrial and academic levels. These types of developments focus mainly on the miniaturisation of the antenna, which is the bulkiest part of an RFID tag. These structures can be obtained by modifying the geometry of the antenna or by using materials with specific dielectric properties. Indeed, the use of materials with high dielectric permittivity (er) and low losses (tan(d)) will allow to obtain an antenna with reduced physical dimensions, while having performances adapted to the targeted application. The use of high dielectric permittivity materials, such as BaTiO3 based materials, has allowed to reduce the dimensions of the antennas by more than 75% compared to conventional antennas used for RFID tags.

The objective of this study is to select and develop ceramic materials with high dielectric permittivity. The existence of high dielectric permittivity is intrinsically linked to the polar character of ceramic compounds. In return, the permittivity has generally a strong temperature dependence. This is the challenge of this project, as the miniaturisation of the antenna makes the RFID tag more sensitive to variations in the dielectric permittivity. Therefore, the dielectric properties of the ceramic material must also be thermally stable between -60°C and 100°C for microwave operating range (GHz). Finally, in order to optimise the energy gain of the RFID tag, the selected materials must also have low dielectric losses.

Initially, a literature review targeted materials with high dielectric permittivity values (?r > 200), low dielectric loss values (tan(d) » 5.10-3) and the most stable thermal evolution possible. The most relevant compositions were synthesised by the conventional solid route from suitable precursors. The resulting powders were sintered and the dielectric properties of the obtained ceramics were measured, as well as their temperature evolution. The most promising compositions were characterised in the microwave domain to confirm the relevance of the selected materials. The synthesis and the sintering of the most interesting compositions was then optimised to improve the microstructure of the ceramics, in order to exploit the full potential of these compositions and ensure reproducibility of their properties.