SrTiO3 ve BaSrTiO3 ince filmlerin düşük sıcaklıkta depolanması, karakterizasyonu ve uygulamaları

Among the several perovskite ferroelectric oxides, SrTiO3 (STO) and BaSrTiO3 (BST) thin films have attracted significant attention due to their potential applications in oxide-based electronics. However, reliability and performance of STO and BST thin films depend usually on the precise knowledge of microstructure, as well as optical and electrical properties. STO and BST thin films were deposited at room-temperature on Si (100), UV-grade fused silica, quartz substrates and TiO2 nanofibers by radio frequency (RF) magnetron sputtering using different plasma power, oxygen mixing ratios (OMRs) and deposition pressure levels. As-deposited thin films showed amorphous-like nanocrystalline microstructure almost independent of the deposition conditions. Influence of post-deposition annealing at various temperatures of RF sputtered STO thin films were also investigated. All films were found to be highly transparent (>75%) in the visible region, and both STO and BST films exhibited well defined main absorption edges: the calculated indirect and direct band gaps for STO films were in the range of 2.32 to 4.55 eV. The refractive index of the STO films increased with OMR and post-deposition annealing for 3 mTorr deposition for STO, BST and STO annealing study. However, there is no correlation for 5 mTorr deposition. The refractive indices of BST films were in the range of 1.90-2.07 at 550 nm depending on their deposition conditions. The optical band gap of the BST films were calculated the ranging in 3.60 to 4.30 eV. Electrical dielectric constant values of the STO thin films were extracted from frequency or voltage dependent capacitance measurements using micro-fabricated Ag/STO/p-Si device structures. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 μC/cm2 charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). Post-deposition annealing at 800°C for 1 h resulted in polycrystalline BST thin films with increased refractive indices and dielectric constants, along with reduced optical transmission values. Frequency dependent dielectric constants were found to be in the range of 46-72, and the observed leakage current was very small, less than 1 μA. Our experimental results show that these low temperature grown STO and BST films have the potential for various electrical applications.