TEM observation of ferroelectric films grown on silicon using Y₂O₃ buffer layer

Ferroelectric films grown on Si substrates using Y₂O₃ buffer layers were investigated by cross-sectional high-resolution transmission electron microscopy (HRTEM). It was found that no interfacial SiO₂ layer was formed when an Y₂O₃ layer was grown by molecular beam epitaxy (MBE) on a Si(111) substrate at 600°C, while that a SiO₂ layer was formed on a Si(100) substrate under the same growth conditions. Then, ferroelectric YMnO₃, SrBi₂Ta₂O₉(SBT), and Pb(Zr,Ti)O₃(PZT) films were deposited on the Y₂O₃/Si structures and cross-sections were observed. It was found that the interfacial SiO₂ layer about 5 to 6 nm in the thickness was formed even on a Si(111) substrate after deposition of the ferroelectric film. It was also found that polygrains in PZT film were much smaller than those in SBT, although both films were formed by the same sol-gel driven method.