Low Temperature Crystallization of Bismuth Layer-Structured Ferroelectric Thin Films Using Lead Titanate Sol-Gel Templating Technique and Their Electrical Properties

摘要

The crystal structure and electrical properties of lead titanate (PbTiO_3: PT) sol-gel network templated bismuth layer-structured ferroelectric (BLSF) thin films were systematically investigated as a function of the doping amount of lead titanate sol-gel solution and annealing temperature. The starting solutions of lead titanate sol-gel templated BLSF were prepared by adding lead titanate sol-gel solution to BLSF solutions such as strontium bismuth tantalate (SrBi_2Ta_2O_9: SBT), bismuth titanate (Bi_4Ti_3O_(12): BiT) and lanthanum-doped bismuth titanate ((Bi,La)_4Ti_3O_(12): BLT). These solutions were spin-coated on platinized silicon wafers and pyrolized on a hot plate, then crystallized at 550°C ― 738°C by RTA (Rapid Thermal Annealing). The crystallized films with sputtered platinum top electrodes were post-annealed for electrical property measurements. In the case of SBT-PT, it was found that the added lead titanate so-gel network has no remarkable effect on lowering the BLSF (m=2) crystallization temperature but rather enhances the pyrochlore phase. In the case of BiT-PT, the bismuth layered-structure was confirmed at the temperature down to 550°C as the amount of lead titanate sol-gel network is increased. The major layered-structure, however, was not desired m=3, but unexpected m (e.g m=4 or higher). In the case of BLT-PT, lowering the BLSF (m=3) crystallization temperature down to 638°C was finally achieved within proper amount of lead titanate sol-gel network without drastic drop of ferroelectricity. A 2Pr of 32 μC/cm~2 was obtained in 0.96BLT-0.04PT thin film.