Ferroelectric properties influenced by the formation of oxygen vacancy layers within PbTiO₃ multilayer thin films

The imprint phenomenon, in which the ferroelectric hysteresis loop of ferroelectric thin films moves in one direction, is caused by an internal electric field generated by an imbalance of internal charges. This internal electric field formed in the ferroelectric thin films can be generated from the imbalance of defects caused by using two different electrodes or heat treatment. In this study, we investigated the imprinted ferroelectric hysteresis loops occurring in PbTiO₃ (PTO) multilayer thin films composed of oxygen-deficient PbTiO_3-δ (DPTO) layers combined with PTO thin films. To form PTO multilayer thin films on Nb-doped SrTiO₃ substrates by a pulsed laser deposition method, a normal PTO layer and an oxygen-deficient DPTO layer were mixed and deposited where the oxygen-deficient DPTO layer was deposited by a PbTiO_3-δ target. PTO capacitors with configurations of PTO/DPTO and DPTO/PTO exhibited implanted ferroelectric hysteretic loops moving left and right, respectively. In particular, the PTO capacitor of the DPTO/PTO/DPTO structure exhibited imprinted ferroelectric hysteresis loops spreading in both directions. The results provide an opportunity for free control of the imprint direction of the PTO multilayer films by controlling the position of the oxygen-vacancy DPTO layer applying ferroelectric hysteresis loops.