Influence of sputter deposition parameters on the properties of tunable barium strontium titanate thin films for microwave applications

Barium strontium titanate (BST) thin films are studied with respect to their application as tunable dielectric at microwave frequencies. BST thin films are deposited by means of radio-frequency magnetron sputtering on platinized Si substrates. The substrate to target distance during sputter deposition is varied and the effect on structure, topology, composition and electronic properties is monitored using X-ray diffraction, atomic force microscopy, Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. These findings are related to the dielectric measurements, which are carried out at 1 MHz and in the microwave range up to 8 GHz using metal-insulator-metal structures with Pt electrodes. For further device evaluation, leakage current measurements are carried out. Changing the process parameter strongly affects the composition of the films. The results emphasize the possibility for enhancing the microwave properties by fine-tuning of the chosen process parameter.