Over the past four decades, energy microsources based on piezoelectric energy harvesting have been intensively studied for applications in autonomous sensor systems. The research is triggered by the quest for replacing standard lead-based piezoelectric ceramics with environmentally friendly lead-free materials and potential deployment of energy-harvesting microsystems in internet of things, internet of health, “place and leave” sensors in infrastructures and agriculture monitoring. Moreover, futher system miniaturization and co-integration of functions are required in line with a desired possibility to increase the harvested power density per material volume. Thus, further research efforts are necessary to develop more sustainable materials/systems with high-performance. This paper gives a comprehensive overview on the processing and functional testing the lead-free bulk materials and thin films and discuss their potential in the applications in the stress- and strain-driven piezoelectric energy harvesting. This includes the methodology of estimation of the substrate clamping and orientation/texture effects in the thin films, and identification of orientations offering high figure of merit. The ability to control film orientation of different lead-free materials is reviewed and the expected piezoelectric performances are compared with the ones reported in literature.

Surface acoustic wave delay lines with operational frequency of 2.5 GHz have been designed to measure the acousto-electronic transport of carriers in graphene transferred onto YX128°-LiNbO3 piezoelectric substrate. The monolayer of graphene on LiNbO3 presented sheet resistance in the range of 733 to 1230 Ω/□ and ohmic contact resistance with gold of 1880 to 5200 Ωµm. The measurements with different interaction lengths on graphene bars have allowed to extract carrier absorption and mobility parameters from acousto-electric current. Graphene presented higher acousto-electronic interaction in the GHz range than previously reported values in the range of 100s MHz with carrier absorption losses of 109 m-1 and a mobility for acoustically generated charges of 101 cm2/Vs.