Effects of ferroelectric/metal interface on the electric properties of PMN-PT thin films epitaxially grown on Si substrates

Lead magnesium niobate-lead titanate 0.72Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ (PMN-PT) ferroelectric thin films were deposited on SrRuO₃ (SRO), SrTiO₃, and TiN-buffered Si substrates by pulsed laser deposition. X-ray diffraction θ–2θ and Phi scans reveal that PMN-PT films were epitaxially grown on Si substrates. Pt, Al, and Gd metals were employed as top electrodes to investigate the ferroelectric and dielectric properties of these metal/PMN-PT/SRO capacitors. It was found that the coercive field (E _C) of the Gd(or Al)/PMN-PT/SRO capacitor is 4.5 times larger than that of the Pt/PMN-PT/SRO capacitor while the permittivity for the former is only ~27 % of that for the latter, which is analyzed using the model for metal-ferroelectric-metal heterostructures with Schottky contacts. Compared with the Pt/PMN-PT/SRO capacitor, the higher E _C and lower permittivity of the Gd(or Al)/PMN-PT/SRO capacitor are attributed to the stronger space charge field at the Gd(or Al)/PMN-PT interface. The capacitance–voltage characteristics of the metal/PMN-PT/SRO capacitors were also discussed.