Cubic Pyrochlore Structure Bzn Thin Film Preparation And Dielectric Tunability Study

Bismuth zinc niobates with the pyrochlore structure have recently attracted interest for high permittivity, low loss, low temperature coefficient in tunable microwave device applications. In this work, BZN thin films have been deposited by RF magnetron sputtering. The effect of sputtering parameters on microstructure of BZN thin films have been investigated. Microstructures, dielectric properties, and tunable properties of BZN films were studied systematically. Enhanced dielectric tunable properties were obtained by adopting the method of excessive Zn in the target. The results are summarized as follows:1. The round plate Bi_1.5Zn_1.0Nb_1.5O₇ ceramic targets were prepared with traditional sintering technology. X-ray powder diffraction showed the single cubic pyrochlore phase in the targets. The relative density is 92.6%.2. Thin films were deposited by rf sputtering in Pt/Si(100) substrates. Based on the study of deposition parameters, the optimized deposition parameters were: an Ar/O2 flow ratio of 85/15, an overall gas pressure of 4Pa, the temperature of substrates of 600℃, and an ex situ 30 min post-deposition annealing at 750°C to crystallize the films. X-ray powder diffraction demonstrated only the cubic pyrochlore phase. The average size of crystallite is 170nm with a smooth surface of RMS =7.494nm.3. By the method to add excessive ZnO in the targets, a stoichiometric Bi_1.5Zn_1.0Nb_1.5O₇ films were deposited. This films showed a relatively low permittivity, but lower dielectric losses, and a larger electric field tunability of the dielectric constant.4. The role of radio- frequency (rf) magnetron sputtering deposition parameters and postdeposition annealing process in optimizing the dielectric properties of Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) films have been investigated. BZN films exhibited the permittivities up to162, and dielectric loss tangent less than 0.002. A maximum applied bias field of 1.3MV/cm resulted in a～21.7% tunability of the dielectric constant. The permittivity and losses were almost independent of the measurement frequency over a wide frequency range (10 Hz–1MHz).