High efficiencY PiezoElectRiC leAd-free Materials (comPosites and textured ceramics) for UltraSound applications – HYPERCAMPUS

Piezoelectric ceramics have been in commercial use for several decades and they have always witnessed a tremendous growth rate. Nowadays, these materials are integrated in a wide range of devices and in particular in ultrasonic applications. Since the discovery in the 50’s of lead-zirconate-titanate (PZT), derived compositions have been developed to optimize the efficiency of this material. Thanks to use of dopants/additives and efficient production processes, PZT-based compositions are the dominant piezoceramics since their electroacoustic properties are high. This increasing success of PZT is associated to health and environmental problems because PZT contains lead. As a consequence, the European Union in 2003 and also many countries in the world included PZTs in their legislation as hazardous substances to be substituted by safer materials. Their objective is to protect human health and environment. The European regulations will be reviewed every four years, and whenever a viable replacement to hazardous substances exists, the exemptions will be cancelled.

We propose through this HYPERCAMPUS project that a complementary French Consortium sets up a research axis from the development and optimisation of high efficiency piezoelectric lead-free materials to the manufacturing of several demonstrators for underwater, NDT and medical imaging applications (with centre frequencies between 500kHz and 20 MHz for the ultrasonic transducers). This Consortium is composed of six partners with four public laboratories (François-Rabelais University of Tours (U930), University of Limoges (SPCTS), Chimie-ParisTech (LCMCP), Institut d’Electronique de Microélectronique et de Nanotechnologie (IEMN)) and two companies (Thales Research & Technology, VERMON SA).

The scientific and technical objectives, which concern mainly experimental developments, are multiple, to cover requirements of several applications, but with the same goal: obtaining
high efficiency lead-free piezoelectric materials. The development of these materials will be declined in three forms. First the fabrication of dense and reproducible lead-free KNN-based ceramics will be performed. Secondly lead-free textured ceramics by TGG method will also be developed with high expected degree of texturation. Two basic compositions will be studied (barium titanate (BaTiO3) and KNN (K1-xNaxNbO3) based ceramics with corresponding single crystal templates). Third, the fabrication of 1-3 piezocomposites with lead-free single crystals (KNN) using a new fabrication process (lamination method) will allow obtaining large area and homogeneous properties. This fabrication process will be favoured as opposed to the classical dice and fill method.

With these different new materials, several prototypes will be designed and manufactured. Single and multi-element ultrasonic transducers (HF linear array and 2D array) will be fabricated. The new generations of lead-free piezoelectric materials (ceramic, textured and piezocomposites) will have performance at least equivalent to that of lead-based materials to confirm the possible replacement of the lead-based materials by new lead-free materials developed in the project. Specific numerical models (for composite materials and demonstrators) will be developed and will support the optimization of piezoelectric materials and transducer prototypes.

For the two industrial partners, HYPERCAMPUS expected results are essential for future activities. For the first industrial, control the lead-free piezoceramic production is the opportunity to remain in a leading position among few major actors in sonar applications. Moreover, the second industrial has to be at the early stage of the lead-free materials development to remain competitive in case of the non prolongation of the exemption. With the HYPERCAMPUS project, one can imagine that a new generation of green arrays will be commercialized and will supplant the current state of art devices.