Evaluation of Exchange-Biased Magnetic Materials for High Density GHz Toroidal Integrated Inductors

Abstract

We evaluated the interest of exchanged-biased magnetic materials for integrated toroidal inductors with operating frequency above 1GHz. Exchange-biased magnetic materials enable designers to use closed magnetic cores up to 5GHz, which lead to very high inductance densities. We used simple considerations about DC resistance and gyromagnetic losses in order to estimate the upper limitations of such devices in terms of quality factor. These estimations were used in order to optimize the properties of toroidal magnetic core at 2GHz operating frequency. We used physical parameters based on experimental data for Fe₆₅Co₃₅ ferromagnetic layers coupled with NiMn, NiO or IrMn antiferromagnetic layers. We found that (Fe₆₅Co₃₅/IrMn) multilayers provide the best trade-off for integration and that quality factor limitations can be overcome by the use of thick (≥1μm) multilayer cores. Also, an important issue for high quality factor is to lower the damping parameter (≤0.01). Inductance densities of optimized devices were also calculated and were found to be in most cases higher than for air-core spiral inductors. These results may orientate material developments in order to meet the requirements for future high density microwave inductive devices fabrication.