Neo-pentoxide precursor synthesis, solution preparation, and electronic properties of (Ba,Sr)TiO3 thin films derived from a solution route

We have recently isolated the neo-pentoxide (HOCH2CMe3, ONp) derivatives of Ba, Sr, and Ti as Ba-4(ONp)(8)(HONp)(6)(py)(2), Sr-5(O)(ONp)(8)(Solv)(5) (Solv = solvent), and Ti-2(ONp)(8), respectively. The combination of these precursors were found to be readily soluble in a wide range of solvents and thus were excellent candidates for preparation of barium strontium titanate ((Ba,Sr)TiO3 or BST) thin films using spin-cast deposition techniques. The highest quality BST films for this system were generated from ternary mixtures dissolved in either pyridine or pyridine/toluene. By in situ VT-GIXRD analysis it was determined that the perovskite phase of BST was readily formed at 650 degrees C. The electronic properties of films crystallized at 700 degrees C indicated that the thin films (300 nm) possessed a dielectric constant of 120 (tan delta = 0.03) with a tunability of 29% at +/- 10 V. 300 nm films (700 degrees C) which had been generated from a standard BST solution modified with a novel tridentate ligand, had a higher dielectric constant of 180 and a tunability of 35% at +/- 10 V. The collective characteristics of these precursors offer an attractive alternative to the more complex, less stable sol-gel precursors currently in use.