Deposition of ferroelectric BST thin films by sol gel route in view of electronic applications

We report on the deposition of Ba0.7Sr0.3TiO3 thin films, BST (70/30), by a sol-gel process. After deposition by spin coating, the film is annealed at 750degreesC, one hour in air. BST films have been deposited on (111) silicon substrates (bare and platinum coated) and on (0001) sapphire. X-Ray diffration patterns show that the films are polycristalline with perovskite structure and free of secondary phase. From SEM images, we infer that the film surface is smooth, the grain size is about 50 nm and the thickness of the BST layer is 300 nm. Electrical characterizations are mainly presented on BST deposited on platinized silicon. The dielectric constant Er is about 400 at 10 kHz and slightly decreases with frequency. The leakage current density is low: typically 10 nA/cm(2) at +5 Volts. At ambient temperature, the existence of an hysterisis cycle attest that a BST (70/30) film is in the ferroelectric state. As concerns the dissipation factor, the lower value has been obtained with a BST film deposited on sapphire: tgdelta = 0.014 at 100 kHz.