Evaluation of Ta2O5 as a buffer layer film for integration of microwave tunable Ba1−xSrxTiO3 based thin films with silicon substrates

Successful integration of Ba1−xSrxTiO3 (BST) based thin films with affordable Si substrates has a potential significant commercial impact as the demand for high-frequency tunable devices intensifies. This work evaluates the material properties of postdeposition annealed Ta2O5 thin films fabricated via the metalorganic solution technique for use as a passive buffer layer between BST and Si. The microstructure, surface morphology, and interfacial properties of the Ta2O5 film deposited on n+-Si and PtSi substrates was evaluated via field-emission scanning electron microscopy, Rutherford backscattering spectrometry, Auger electron spectroscopy, and atomic force microscopy. The presence of a transition interaction zone between the Ta2O5 film and Si substrate was detected after annealing at temperatures >600 °C. The width of the interaction zone increased with increasing annealing temperature reaching a maximum of 29 nm at 750 °C. The width of the interaction zone was also found to be dependent on the Ta2O5 film microstructure. The Ta2O5 film was typified by a smooth; fine grain, crack/pinhole free surface morphology. The presence of the interfacial layer had no appreciable effect on the microstructure of the film or surface morphology. The narrowness of the interaction zone with respect to the overall film thickness combined with the fact that the interfacial layer did not seriously deteriorate the dielectric properties of the Ta2O5 film suggests Ta2O5 to be a favorable candidate buffer layer enabling the integration of BST with Si substrates.