Fabrication of Lead-Free (Na0.5K0.5)NbO3--BaZrO3--(Bi0.5Li0.5)TiO3 Ferroelectric Thin Films on (111)Pt/Ti/SiO2/(100)Si Substrate by Pulsed Laser Deposition

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0.92(Na0.5K0.5)NbO3--0.06BaZrO3--0.02(Bi0.5Li0.5)TiO3 (NKN--BZ--BLT) thin films were fabricated on a (111)Pt/Ti/SiO2/(100)Si substrate by pulsed laser deposition (PLD). The quality of the NKN--BZ--BLT thin films was improved by introducing an NKN--BZ--BLT buffer layer, which was deposited at a high substrate temperature of 850 °C. An X-ray diffraction pattern (XRD) showed that the 100\text{pt preferential-oriented NKN--BZ--BLT thin films [on the basis of a pseudotetragonal perovskite (pt) structure] were obtained without and with buffer layers. From the rocking curves, the crystallinity of the film was slightly improved by introducing the buffer layer. SEM images showed that the grain size was increased and cracks were eliminated by introducing the buffer layer. The dielectric constant of the films was comparable to that of NKN--BZ--BLT ceramics. The $P$--$E$ hysteresis loops showed that the remanent polarization and spontaneous polarization of the films increased with the increase in the thickness of the buffer layer. The NKN--BZ--BLT film with a 0.8-μm-thick buffer layer exhibited a remanent polarization of 6.7 μC/cm2 and a spontaneous polarization of 28.0 μC/cm2. This improvement of the ferroelectric properties would be due to the relaxation of the tensile stress in the presence of the buffer layer.
2011-09-25