Alkaline niobates and tantalates for electroactive devices

Lead-free piezoelectric materials are actively investigated for energy harvesting, sensor and high-frequency acoustic wave devices. In this manuscript, different architectures and microfabrication processes based on lead-free LiNbO₃ and KTa1-xNb_xO₃ crystals single crystals are investigated.

In a first part, energy harvester of LiNbO₃ on silicon substrate is fabricated by using wafer bonding and polishing. The transducers attained one of the highest power densities (965 µW/cm²/g²) compared to Pb and Pb-free vibrational harvesting devices. Then, the scalability of the LiNbO₃/Si to MEMS technology devices is investigated with LiNbO₃ and silicon etching. The etching of LiNbO₃ have been performed by implementing a pulsed mode reactive ion etching by using Ar/SF₆ gas. Accelerometric sensor has been demonstrated.

In a second part, our interest moved toward flexible metallic substrates. A big step has been achieved by developing Au-Au bonding of LiNbO₃ to metal substrates. The performances of bimorph beam of LiNbO₃-stainless steel-LiNbO₃ attained 209.7 µW/cm²/g² at 39.3 Hz.

Finally, we investigate alternative lead-free piezoelectric materials of KTa1-xNb_xO₃ crystals, for SAW devices application. First, structural and microstructural characterization of the crystal was carried out followed by fabrication and characterization of one-port SAW resonator. An electrotechnical coupling of 80 % was achieved while 49 % was obtained for KNbO₃ resonators.

alkaline niobates and tantalates, piezoelectric energy harvesting, saw resonators, microfabrication

Confidential thesis until 15/07/2034.