Passive coplanar isolator with barium ferrite thin films

The development of integrated devices combining a ferrite is a major focus of current research. Barium hexaferrite (BaFe₁₂O₁₉ or BaM), which exhibits a high anisotropy field and high coercive force are deposited on alumina substrate using an RF sputtering system. After deposition BaM films are amorphous and a post deposition thermal annealing is needed to obtain magnetic properties. The saturation magnetization and coercive force was about 500 mT and 330 kA/m. After that, coplanar lines were made with BaM thin films on alumina substrates and with gold conductor. The transmission coefficients of a barium ferrite coplanar isolator are measured up to 55 GHz. The measurements of transmission parameters S₁₂ and S₂₁ was performed by a 65 GHz vector network analyzer and a probing system. First experimental results showed an isolation of 3.3 dB/cm at 50 GHz.