Abstract:
Recent advances in mobile electronic devices demand the integration of more functions and a further decrease in the overall device size. Device miniaturization and compact design, therefore, have become important factors. Radio frequency (RF) passive devices, including antennas and inductors, are key components in mobile telecommunication systems. The interaction of magnetization dynamics with electromagnetic waves in the RF devices allows electromagnetic radiation, wave propagation, and RF signal processing. Ferrites possess both frequency-dependent permeability and permittivity. Thus, miniaturization and electromagnetic scaling of antennas and inductors can be realized with the magnetic and dielectric properties of ferrites. In addition, the unique features of ferrites, such as high electrical resistivity, excellent chemical stability, and mechanical hardness, provide a low eddy current loss at high frequencies and a variety of applications in power and microwave systems. In designing ferrite passive devices, the frequency-dependent permeability and magnetic loss of ferrites play important roles in device form factor and efficiency. This dissertation focuses on the magnetic loss mechanism of ferrites, miniaturization, and performance improvement of RF antennas and inductors. In this dissertation, the effectiveness of small relative permeability in improvement of gigahertz (GHz) antenna performance is investigated. In addition, the magnetic loss reduction of ferrites is described using a different approach from material processing aspects. Both the relative permeability higher than unity and the low-magnetic loss of ferrites are presented with a small direct current (DC) magnetic field, therefore, antenna miniaturization and gain improvement are achieved. A high-isolation multi-input multi-output (MIMO) antenna array design is demonstrated with miniature ferrite antenna elements for long-term evolution (LTE) mobile technology. Furthermore, micron-thick ferrite film deposition process is developed using DC magnetron sputtering for high inductance and quality-factor ferrite inductors. The measured and simulated results suggest that high resistivity and large magnetic-anisotropy ferrites in combination with high-efficiency RF device design can lead to the development of compact high-performance antennas and inductors.
