| Popis: |
Ferroelectric materials, such as BaTiO3 (BTO), Pb(Zr,Ti)O3 (PZT), SrBi2Ta2O9 (SBT), and LiNbO3 (LNO), are a category of materials with reorientable spontaneous polarization, a sub-category of pyroelectric materials. Because of their high dielectric constant, large polarization, and high breakdown voltage, ferroelectric materials have a wide range of applications, including infrared (IR) detectors for security systems and navigation, high density capacitors, high-density dynamic random access memory (DRAM), non-volatile ferroelectric random access memory (FRAM), and high frequency devices such as varactors, frequency multipliers, delay lines, filters, oscillators, resonators and tunable microwave devices (Tagantsev, et al., 2003; Cole, et al., 2000; Bao, et al., 2008; Gevorgian, et al., 2001; Dawber, et al., 2005). Among these ferroelectric materials, BTO based films with Sr dopant, namely Ba1-xSrxTiO3 (BST) are the most investigated one for various applications, especially for electric field response (or tunable) components and devices because of its high dielectric constant, reasonable dielectric loss, high tunability, and large breakdown strength. The Curie temperature Tc can be easily adjusted by controlling the Ba to Sr ratio. Studies have revealed that the electrical properties of BST films are influenced by the deposition and postdeposition process, stoichiometry, electrodes, microstructure, thickness, surface roughness, oxygen vacancies in films, and film homogeneity. The composition of the BST film such as the (Ba+Sr)/Ti ratio plays a critical role in determining its electrical properties (Y. H. Xu, 1991; Takeuchi, et al., 1998; Im, et al., 2000). Both the dielectric constant and loss increased with increasing (Ba+Sr)/Ti ratio. The lowest loss tangent (0.0047) and the best figure of merit were achieved with a (Ba+Sr)/Ti ratio of 0.73, but tunability was diminished (Im, et al., 2000). nGimat has also optimized the elemental ratios to achieve some of the highest figures of merit in tunable devices using the enhancements thus optimized. It has also been reported that dopants influence the electrical properties of BST thin films, but all dopants negatively affect at least one of the desired properties of the solicitation (Copel, et al., 1998 and Chung, et al., 2008). Copel and coworkers (Copel, et al., 1998) investigated the effect of Mn on electrical properties of BST thin films and found that leakage current was improved by introducing Mn. This was attributed to the acceptor Mn |
