Ferrite-Piezoelectric Heterostructures for Microwave and Millimeter Devices: Recent Advances and Future Possibilities

There have been considerable interests in recent years in ferrite-ferroelectric composites for dual magnetic- and electric field tunable microwave and mm-wave devices such as resonators, filters, and phase shifters. Low-loss spinel and hexagonal ferrites are used in high frequency devices and the tuning in general is with a magnetic field H. When the ferrite is replaced by a ferrite-ferroelectric composite, however, the piezoelectric strain due to an electric field E applied to the ferroelectric will manifest as an induced anisotropy in the ferrite and facilitate E-tuning of the device. This review focuses on recent efforts on voltage tunable ferrite filters. A related phenomenon of importance is the nature of magneto-dielectric resonance in ferrites and its potential for low-loss H-tunable dielectric resonators, filters, isolators, and phase shifters for the frequency range 18–110 GHz. Potential avenues for enhancing the E-tuning of ferrite devices are also addressed.