Ultra-high tunability in polycrystalline Ba_1-xSr _xTiO₃ thin films

Ba_0.7Sr_0.3TiO₃ thin polycrystalline films with an ultra-high capacitance tunability approaching 5:1 at 175kV/cm were made possible by a flux-assisted synthesis approach. In this process, a small volume fraction of a low melting temperature glass is added during low-temperature sputter deposition. Subsequent annealing activates the liquid phase, which in turn provides the mass transport needed to approach full density, to increase grain size, and to improve crystallinity, and, in so doing, achieves a stronger non-linear dielectric response. Ba_0.7Sr_0.3TiO₃ films with 0%, 1%, 4%, and 7% BaO-3B₂O₃ flux exhibited grain sizes of 25nm, 28nm, 48nm, and 56nm, and dielectric tunabilities of 25%, 33%, 64%, and 80% respectively. These values represent substantial improvements when compared to conventionally processed tunable dielectric films.