Integration of Ba1-xSrxTiO3-based active thin films with silicon-compatible materials and process science protocols to enable affordable on-the-move communications technologies -: art. no. 024507

Integration of Ba1-xSrxTiO3- (BST) based thin films with affordable Si substrates has a potentially significant commercial impact as the demand for high-frequency tunable devices intensifies. Utilizing a coplanar device design we have monolithically integrated, optimized, and fabricated a high-performance composite bilayer heterostructure, Si/Ta2O5/BST, whereby the base layer film Ta2O5 serves as a passive buffer layer to allow integration of BST active thin films with affordable Si substrates. Optimization of this design configuration was achieved by evaluating two heterostructure processing protocols: (1) a single-anneal and (2) a dual-anneal process protocol. The reliability susceptibility, i.e., the nonabrupt defect-laden bilayer film interface, of the single-anneal protocol deemed it inappropriate for the fabrication of this monolithic heterostructure design. In contrast, the defect-free, structurally abrupt bilayer and buffer layer film-substrate interfaces suggest the dual anneal process to be an excellent method for realizing monolithic integration of BST with affordable Si substrates. This work suggests that the coefficient of thermal expansion mismatch between the Ta2O5 buffer and the BST thin films in the coplanar device design serves to enhance the dielectric tunability of the device. Realization of this materials integration technology serves to promote broadscale implementation of affordable tunable microwave devices across a variety of advanced communications platforms.