CD With Bzn Study On Preparation And Properties Of Thin Films

Bismuth zinc niobates with the cubic pyrochlore structure have been paid more and more attention for very low losses and large tunabilities in tunable microwave device applications .So it is important and valuable to systematically study the preparation and the dielectric properties of BZN thin films. In this paper, Cd-doped BZCN thin films have been deposited by RF magnetron sputtering,and microstructures, dielectric properties, and tunable properties of Cd-doped BZN thin films were studied systematically.(1)The round plate BZCN (Bi_1.5Zn_0.9Cd_0.1Nb_1.5O₇,Bi_1.5Zn_0.8Cd_0.2Nb_1.5O₇,Bi_1.5Zn_0.7Cd_0.3Nb_1.5O₇,Bi_1.5ZnNb_1.5O₇) ceramic targets were prepared with traditional sintering technology. Dense BZCN ceramic targets were prepared with pressing pressure 200MP, sintered at 1100℃for 3h. The XRD spectrum is consistent with the standard PDF cards of BZN powders. The SEM photos suggested smooth surface topography without cracks. The relative density is up to 90%.(2)BZCN thin films were deposited on Pt(111)/TiO₂/SiO₂/Si substrates by RF magnetron sputtering. The effects of deposition temperature, the total gas pressure, O₂/ Ar flow ratio on the surface morphology and crystallization of BZCN thin films were systematically studied. The optimized deposition parameters were: an O₂/ Ar flow ratio of 1/5, the total gas pressure of 4Pa, the temperature of substrates of 600℃, and annealed at 700°C to crystallize the thin films. X-ray powder diffraction detected only the cubic pyrochlore phase. The size of crystallite is 45-80nm, the surface is smooth, RMS =1.86nm.(3)The Au/BZCN/Pt flat capacitors were ready-made for properties tests. The BZCN thin films sputtered with the substrate tempetature of 600℃and annealed at 700℃showed a voltage tunability of 11.8%, dielectric loss lower than 0.004 and the relative dielectric constant is about 183 at a dc bias field of 1.33MV/cm under measurement frequency of 100 kHz. The permittivity and losses were independent of the measurement frequency(1K–100KHz). After post-annealling, the voltage tunability raised to 18.4%, but the dielectric loss raised too.(4)We deposed Bi_1.5Zn_1-xCd_xNb_1.5O₇(x=0,0.1,0.2,0.3) thin films at the same deposition condition, and the dielectric properties of the thin films.were examined With increasing the content of Cd, the tunability inceased.