Sputtering pressure dependent composition and dielectric properties in Bi_1.5MgNb_1.5O₇ thin films deposited at room temperature by RF magnetron sputtering

Bismuth magnesium niobate (Bi_1.5MgNb_1.5O₇, BMN) thin films with cubic pyrochlore phase and a highly [111] orientation were deposited by radio frequency magnetron sputtering at different pressures and crystallized at 700 C in oxygen atmosphere. For low temperature deposition, the sputtering pressure has significant influence on the surface roughness and composition of the BMN thin film. The film deposited at 4.0 Pa has the closest stoichiometric composition and a lowest surface roughness, which exhibits large dielectric constant and low dielectric loss (158 and 0.0046 at 1 MHz, respectively). The dielectric tunability and the figure of merit (FOM) value are 16.4 % and 36 at a dc bias field of 0.8 MV/cm. The relative large dielectric constant, low dielectric loss, and high FOM value suggest that BMN thin films have potential application for tunable microwave device.