Enhanced ferroelectric properties of Hf-doped bismuth titanate thin films on STO (111) substrates

Abstract

Bi4 Ti3 O12 (BIT) and Hf-doped BIT (BTH) thin films have been fabricated on (111) SrTiO3 substrates with SrRuO3 bottom electrodes by pulsed laser deposition, respectively. X-ray photoelectron spectroscopy investigation revealed that Hf doping would strengthen the oxygen covalent bond to B -site ions, which could consolidate the BO6 octahedral structure in BTH. As confirmed by x-ray diffraction scans, including θ-2θ and scans, both films were highly (104) oriented and showed triple-twin situation. Compared to the BIT films, the BTH films have significantly enhanced electrical properties with 3 times larger remanent polarization (2 Pr =45.7 μC/ cm2), 0.7 times smaller coercive field (2 Ec =184 kV/cm), and better fatigue endurance (11.4% degradation). The difference of ionic radius and the strengthened covalency in BO6 octahedral structure are supposed to be the two aspects resulting in the enhancement of 2 Pr value. The improved fatigue properties could be believed to result from the high activation energies of oxygen vacancy caused by Hf doping. © 2008 American Institute of Physics.