Pst Ceramics And Thin Film Materials Research

Ferroelectric materials are attractive for applications in tunable microwave devices, such as electrically tunable resonators, tunable filters and phase shifters. Barium strontium titanate (BST) and its doped series have intensively been investigated up to date. Recently, Cross et al. have found that lead strontium titanate (Pb_xSr_1-xTiO₃)(PST) ceramic has both high tunability (70%) and quite low dielectric loss (＜0.1%), and its figure of merit (FOM) could reach quite high (700). In addition, the PST films have lower crystallization temperature than BST. Thus, PST could become a very perspective material for tunable devices applications.PST (x=0.2-0.8) ceramics were fabricated by the conventional processing method and the effect of the Pb content on the microstructure and dielectric properties were studied. The optimized composition, excess Pb content and the process condition were selected to sinter the ceramics target. Then PST30 thin film were prepared by RF magnetron sputtering system, and the effect of deposite substrates, temperature, power and the annealing temperature were investigated. The following are the results.The lattice structure of the PST ceramics is changed from cubic to tetragonal phase at 45 at% Pb content. Therefore, the well-behaved hysteresis loops can be observed for the PST ceramics with Pb content higher than 45 at%. The values of the coercive electric field (E_c) and remnant polarization (P_r) increase with Pb/Sr ratio. The sintered temperature decreases with inreasing the Pb/Sr ratio. Sintered at the same temperature, the grain size and the density increase with the Pb/Sr ratio. The Curie temperature(T_c), which is always higher than the Weiss temperature(T₀), increases linearly with the increase of the Pb content. It is found that the PST ceramics show the similar Curie-Wiess constant. Complete perovskite structure as well as suplus Pb₃O₄ phase has been found in PST ceramics at 900℃. Abnormal hysteresis loops are observed due to both the superfluous Pb and the Pb vacancies.PST30 ceramics with 3 mol% excess Pb is a good target composition for phase shifter. The PST30 targets have fabricated at 1250℃for 2 hours.The PST thin films have been prepared by radio frequence (RF) magnetron sputtering under the optimized conditions. The depositions were performed by sputtering a PST target at 400℃of substrate temperature. The RF power is 100W, and the sputtering gas was composed of a mixture of oxygen and nitrogen with the ratio of 1:6. And then, the annealing was performed at various tempertures. The results show that the tunability is measured to be about 32.46% for the films annealed at 650℃.The thin films have been grown on (100) LaAlO₃ (LAO) single crystal and Platinized silicon (Pt/Ti/SiO₂/Si) substrates. These results reveal that the films on LAO are a polycrystalline structure with a preferential (100) orientation, while no preferred orientation has been observed in the films Platinized silicon. The thin films on LAO substrates have the bigger grain size and higher tunability.