Pulsed Laser Deposition And Electrical Properties Of Heterostructural BFO/BCZT Films

With the development of microelectronics,ferroelectric materials are demanded to be thin-filmed in applications to electronic devices and integrated circuits.BiFeO₃?BFO?thin films have great theoretical remanent polarization,which have potential applications in nonvolatile memory,but their practical performance is largely diminished by the exist of leakage current.In order to reduce the leakage current and improve the remanent polarization of BFO thin films,in this study,on the one hand,pulsed laser deposition?PLD?technique was applied and the preparation processes were optimized to prepare high-quality BFO films.On the other hand,BCZT thin films with low leakage and high dielectric constant were laminated to block the leakage current.Phase-pure epitaial BFO thin films were deposited on SrTiO₃?111?substrate by PLD technique.Among the process parameters,the substrate temperature?Tsub?and O2partial pressure(P_O2)mainly influence the crystallinity and composition of the films,while the pulsed laser energy density?D_L?mainly influences the crystallinity and orientation.The processing parameters were optimized at T_sub=650?,D_L=1.5 J/cm²and P_O2=12.5 Pa,where the BFO thin films excellent ferroelectric properties,with remanent polarization 2P_r=133.3?C/cm² and leakage current density of 4×10^-7 A/cm²?E=100 kV/cm?.The study of leakage mechanism of BFO thin films indicates that,at high electric field intensity,Pool-Frenkel emission dominates the leakage behavior of the BFO films with hybrid phase,while phase-pure BFO films follow the space charge limited current?SCLC?mechanism?Epitaxial BCZT thin films were deposited on SrTiO₃?111?substrate by PLD technique.Among the processing parameters,pulsed laser density mainly influences the crystallinity,while substrate temperature and O₂ partial pressure influences both crystallinity and strain state of the films.The BCZT films deposited at Tsub=600?,DL=1.5 J/cm² and P_O2=15 Pa exhibited lowest in-plane compressive strain and smallest in grain size,with highest dielectric constant,lowest dielectric loss??_r=559,tan?=0.037?,and the leakage current density as low as 9×10^-8 A/cm²?E=100 kV/cm?.The leakage behavior of the films follows ohmic conduction mechanism at low electric field intensity and SCLC mechanism at high electric field intensity.On the basis of the optimized PLD preparation processes of single layered BFO and BCZT films,heterostructural films of different structures,BCZT/BFO,BFO/BCZT and BCZT/BFO/BCZT,were constructed by varying deposition sequences,which showed large effects on the strain state of different layers.The BFO/BCZT films exhibited highest remanent polarization and lowest coercive electric field?2Pr=133.3?C/cm²,E_c=206 kV/cm?,and the leakage current density decreases by an order of magnitude compared with that of single-layer BFO films.The structures of BFO/BCZT and BZCT/BFO/BCZT show the optimization of the leakage performance of BFO thin films,the leakage behavior of which conforms to the SCLC mechanism at low field intensity and the Schottky emission mechanism at high field intensity.