Ultra-high tunability in polycrystalline Ba1−xSrxTiO3 thin films

Abstract

Ba0.7Sr0.3TiO3 thin polycrystalline films with an ultra-high capacitance tunability approaching 5:1 at 175 kV/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. Ba0.7Sr0.3TiO3 films with 0%, 1%, 4%, and 7% BaO-3B2O3 flux exhibited grain sizes of 25 nm, 28 nm, 48 nm, and 56 nm, and dielectric tunabilities of 25%, 33%, 64%, and 80% respectively. These values represent substantial improvements when compared to conventionally processed tunable dielectric films.