Microstructure and ferroelectric properties of low-fatigue epitaxial, all (001)-oriented (Bi,La)_(4)Ti_(3)O_(12)/Pb(Zr_(0.4)Ti_(0.6))O_(3)/(Bi,La)_(4)Ti_(3)O_(12) trilayered thin films on (001) SrTiO_(3) substrates

摘要

(Bi,La)_(4)Ti_(3)O_(12)(BLT)/Pb(Zr,Ti)O_(3)(PZT)/(Bi,La)_(4)Ti_(3)O_(12) trilayered ferroelectric thin films were epitaxially grown by pulsed laser deposition onto (001) SrTiO_(3) (STO) substrates with and without SrRuO_(3) (SRO) bottom electrodes. From x-ray pole figures and electron-diffraction patterns, the epitaxial relationships between BLT, PZT, SRO, and STO were identified to be BLT(001)PZT(001)SRO(001)SrTiO_(3)(001); BLT110PZT100SRO100SrTiO_(3)100. Cross-sectional transmission electron microscopy investigations revealed that 90 deg ferroelectric domain boundaries lying on {110} planes are present in the PZT layer, with an average domain width of 20 nm and an average spacing of 120 nm. These long 90 deg ferroelectric domains, as a rule having nucleated at the bottom of the PZT layer, extend to the top of the latter. The thin films have sharp BLT/PZT interfaces and a very flat surface. The remanent polarization and coercive field were determined as 13.9 (mu)C/cm~(2) and 72.9 kV/cm, respectively, indicating that the epitaxial, all (001)-oriented trilayered thin films have rather good ferroelectric properties, although single epitaxial (001)-oriented BLT films are usually not favored for application due to their very poor ferroelectric properties. The thin films showed a high fatigue resistance at least up to 10~(10) switching pulse cycles, confirming that such a trilayered structure effectively shows the fatigue-free behavior of BLT.