Printed Lead-free piezoelectric ceramic energy harvesters: towards greener processing with high performance – PLAYER-ONE

Today’s electronic based technologies require electrical power, preferably supplied in-situ to achieve self-powered autonomous devices. Advances in wireless technologies and the reduction of the power consumption of integrated circuits have enabled different solutions to power these systems. Harvesting mechanical energy of ambient vibrations (<500Hz) can supply a reasonable amount of energy, typically hundreds of µW. This solution proposed to supply autonomous electronic devices with energy, or even to complete their primary power source, presents indeed a double interest: important density of the mechanical energy source (about 300µW.cm-3) and simplicity of the electromechanic conversion by direct piezoelectric effect. To reach this objective, the design, the choice of materials (active material, electrode and passive substrate) and the process will definitely prefigure the global electromechanical performances in terms of frequency, acceleration and power density required when considering the above mentioned application. Current research in this field tends to reduce manufacturing costs and to replace the silicon substrate, traditionally used for MEMS, by flexible substrates. One of the current research challenges lies in the integration of new lead-free active materials in these MEMS.
In a context of energy consumption reduction and durability, PLAYER-ONE aims at developing devices based on lead-free inorganic piezoelectric materials dedicated to vibratory energy recovery. Our approach combines modeling to design, and advanced processes to develop efficient and durable piezoelectric energy harvesters at low temperature. We are targeting the highly promising (K,Na)NbO3 (KNN) material for the next generation of lead-free piezoelectric materials. The considered MEMS harvester will be a 3D cantilever-like structure, formed by a thick lead-free piezoelectric KNN layer sandwiched between 2 electrode layers; the whole will be deposited by the additive screen printing technique on a flexible substrate with an optimized geometry and co-sintered by the SPS (Spark Plasma Sintering) sintering technique under specific low temperature conditions (<900°C). SPS allows to sinter within short times (< 5min) thanks to the combination of pressure and pulsed current and has been proven to efficiently sinter piezoelectric ceramics. The simple, versatile and low-cost screen printing technique will enable thick layers (10-100µm) of various dimensions and will bridge the gap between thin films and ceramics to maximize the recovered power. The process of manufacturing a multilayer sintered energy harvester in one step is fully original but also ambitious since it is necessary to solve the problems related to the chemistry and the microstructure (volatility of alkalis, density, size of grains and grain boundaries, interfaces, etc). The optimizations in terms of material properties, global structure and reliability will be carried out on the basis of numerical simulations and advanced characterizations (microstructure and interfaces, dielectrics and electromechanics). For the simulations, the vibration energy harvesting performances will be optimized by maximizing the electromechanical coupling coefficient k2 and the mechanical quality factor Q (i.e. the inverse of the mechanical losses). Our consortium will pool its resources and complementary know-how (chemistry, material science, electronics, microsystems, modeling and reliability) to meet the challenge.