Microwave Tuner Barium Strontium Titanate Thin Films And Their New Doping Film Series Performance

Barium strontium titanate (BST) films show extensive applications in phase shifter, filter, oscillator, etc, Owing to excellent dielectric and tunable properties. Sol-gel method is the most popular and practical one to prepare BST films. However, BST films prepared by Sol-gel exhibit serious surface cracks, loose structures and shrinkage cavities, resulting in preventing the BST films from applying. Therefore, this thesis centres on the studies of BST film preparation by modified Sol-gel method and the film composite doping with Cerium (Ce) and Yttrium (Y). The as-prepared BST films are characterized by XRD, SEM, AFM and XPS. The dielectric properties of the films are measured. BST films with satisfied dielectric properties have been obtained by optimizing process conditions. Also, the relationships among the Sol-gel method, film composition, film structure, and film properties have been found and discussed.A proper amount of polyvinyl pyrrolidone (PVP) has been added to BST precursor Sol, and smooth and compact BST films have been obtained, solving the serious crack problem of BST films prepared by normal Sol-gel method. Also, it has been found that the effect by PVP on BST films is closely associated with PVP content, seed layer prepared by pre-annealing, annealing conditions, film thickness, etc. Optimized BST films with 45.1% dielectric tunability and 0.0187 dielectric loss tangent value at 40V bias have been gained.On the other hand, a serious of BST films composited doped with Ce and Y have been prepared by modified Sol-gel method. It has been shown that the compositely doped BST films can simultaneously exhibit high dielectric tunability and low dielectric loss tangent. XPS shows the compositely doped films significantly decrease the surface non-perovskite structure. BST films alternately doped with 1mol% Ce and Y, respectively,show 56.9% dielectric tunability, 0.0241 dielectric loss tangent, and 23.6 FOM value which is defined as the ratio of dielectric tunability/ dielectric loss tangent; while BST films simultaneously doped with 1mol% Ce and Y, respectively, present 49.4%, 0.0255 and 19.4. Additionally, the compositely doped BST films display high voltage-resistance and good tangent-voltage properties.