C-axis oriented barium ferrite thin/thick films for microwave applications

Because of their good chemical stability and high uniaxial anisotropies, highly c-axis oriented hexagonal M-type ferrites (or BaM) have provoked much interest in recent years for their applications in the microwave devices. In current technology, microwave ferrite devices use bulk BaM under an external magnetic field bias to control the microwave propagation in the circulator. Our goal was set to fabricate a self-biased microwave circulator, which does not require an external magnetic field; therefore, the self-biased circulator will be much lighter and smaller in size. To develop the future generation of microwave devices that can be fully integrated into a chip, and functional in the GHz range, excellent c-axis orientation with high coercivity, good squareness and thickness of at least 100 micrometers or more are required so that BaM films can be self-biased.;We have used RF sputtering to grow BaM thin and thick films on different substrates. We have grown BaM thin films using external and in-situ annealing. The c-axis orientation of the films was not of high quality. With the in-situ method, MS value has increased up to 82% of the bulk value, however the c-axis orientation did not improve much. Excellent c-axis orientation has been obtained by developing the alternating temperature multilayered method. Using this method, we grew the anti ferromagnetic phase (alpha-Fe2O3) and used it as a pinning layer to grow BaM thin films on Al2O3 (0001) without any seed layer. The c-axis and magnetic parameters are consistent with our mathematical micro-magnetic model.;Liquid Phase Epitaxy (LPE) method has proven to be the most effective way to grow thick BaM films; these thick films have excellent c-axis orientation and single crystal structure with about 10 Oe coercivites, however, single crystal BaM films can not be self-biased. We have developed the vacuum LPE and the reflow method to grow up to 0.5 mm polycrystalline thick films. Our new method uses no seed layer which greatly simplifies the fabrication process. The effect of BaM thin film seed layer on the growth and magnetic properties of the thick films has been briefly studied.