Structural characterisation of BaTiO_3 thin films deposited on SrRuO_3/YSZ buffered silicon substrates and silicon microcantilevers

摘要

We report on the progress towards an all epitaxial oxide layer technology on silicon substrates for epitaxial piezoelectric microelectromechanical systems. (101)-oriented epitaxial tetragonal BaTiO_3 (BTO) thin films were deposited at two different oxygen pressures, 5.10~(-2) mbar and 5.10~(-3) mbar, on SrRuO_3/Yttria-stabilized zirconia (YSZ) buffered silicon substrates by pulsed laser deposition. The YSZ layer full (001) orientation allowed the further growth of a fully (HO)-oriented conductive SrRuO_3 electrode as shown by X-ray diffraction. The tetragonal structure of the BTO films, which is a prerequisite for the piezoelectric effect, was identified by Raman spectroscopy. In the BTO film deposited at 5.10~(-2) mbar strain was mostly localized inside the BTO grains whereas at 5.10~(-3) mbar, it was localized at the grain boundaries. The BTO/SRO/YSZ layers were finally deposited on Si microcantilevers at an O_2 pressure of 5.10~(-3) mbar. The strain level was low enough to evaluate the BTO Young modulus. Transmission electron microscopy (TEM) was used to investigate the epitaxial quality of the layers and their epitaxial relationship on plain silicon wafers as well as on released microcantilevers, thanks to Focused-Ion-Beam TEM lamella preparation.