Medium Shift The Phase Used In Ferroelectric Thin Films Optimization Study

The ferroelectric thin films used for dielectric phase shifter must have a large relative dielectric constant, strong dielectric nonlinearity, small dielectric loss and low leakage current. In this paper, some works were done to optimize the properties of BST thin films, including the annealing temperature, orientation and composition gradient. BZT thin films were prepared by rf-magnetron sputtering system. And Effects of O₂/Ar and Zr/Ti on the properties BZT thin films were investigated. At last, the temperature character and fatigue of BST, BZT thin films were tested. The following results are obtained:1. BZT thin films deposited on the different substrates can bear the different annealing temperature (900℃-Al₂O₃ substrate, 1100℃-LaAlO₃ substrate, 1200℃-MgO substrate). The substrate lattice constants and thermal expansion coefficients are the main factors to influence the annealing temperature. High temperature is good for the dielectric nonlinearity of BST films.2. (110)-oriented BST has stronger ferroelectric properties than (100)-oriented BST thin films. (110)-oriented BST with smaller tgδhas larger relative dielectric constant and tunability.3. BST thin films with composition gradient have lower tunability and dielectric loss than single-layer structure. Ba_0.5Sr_0.5TiO₃/Ba_0.6Sr_0.4TiO₃ have better properties than Ba_0.6Sr_0.4 TiO₃/Ba_0.5Sr_0.5TiO₃.4. BZT thin films were prepared by rf-magnetron sputtering. BZT thin films are crystallized, no pinholes, dense and uniform. BZT thin films have slim hysteresis loop and low leakage current. When E=400kV/cm, the tunability is 15%, tgδis 0.016. After halving thickness (E=800kV/cm), the tunability is increased to 33.5%, tgδis 0.021.5. With the increase of O₂/Ar, the preferred orientation of BZT thin films changes from (l00) to (111) direction. The grain size, RMS, relative dielectric constant and tunability become larger with the increase of the O₂/Ar ratio. The ferroelectric properties also have been enhanced. 6. Compared BaZr_0.1Ti_0.9O₃ to BaZr_0.2Ti_0.8O₃, it is found that the ferroelectric properties, relative dielectric constant and the tunability increase with reducing the Zr⁴⁺. The tunability is increased to 60.5% when E=800kV/cm.7. From -30℃to 130℃, the relative dielectric constant of BST and BZT thin films increase slowly with the temperature. There is no Curie point in this temperature rang. From -50℃to 150℃, the curves are relatively flat at 1MHz. It is also found that the dielectric nonlinearity of BST, BZT thin films is difficult to fatigue.