Lead free ferroelectric films deposited by sol-gel for electronic applications

Lead in electronic components is prohibited by the RoHS directive since july 2006. Nevertheless, there are some exceptions for example PbZrXTi1-XO3 (PZT) materials because they present exceptional piezoelectric properties. PZT is used as sensors and actuators in numerous applications such in sonar, echography, alarm, etc…Up to now, neither in ceramic form nor in film form, it have been surpassed by lead free materials. At present, many studies are devoted to find a substitute to PZT as it will be probably banned in five years or so. Our work is in this objective and concerns the study of the electrical properties at low frequency, from DC to 1MHz, of ferroelectric films with thickness inferior or equal to 1ìm. The starting material is BaTiO3 in which Ba is exchanged by Sr at different levels and also doped with various cations (monovalent, divalent, trivalent…). This permits us to improve the dielectric and ferroelectric properties: for example to decrease the losses and to increase the tunability. Another method to optimize the electrical properties is to study the annealing conditions: very high temperature applied a short time (950°C@15mn) should be favoured. This leads to both higher dielectric constant and polarization. The pyroelectric and piezoelectric coefficients have also been improved but as concerns the piezoelectric performance, our lead free films are still inferior to the PZT one. Further optimization is needed.