Novel microwave magnetic and magnetoelectric composite materials and devices

Abstract

Bulk microwave magnetic materials and devices have been widely used in different RF/microwave devices such as inductors, filters, circulars, isolators, and phase shifters. With the even increasing level of integration of RFIC and MMIC, there is an urgent need for new microwave magnetic thin film materials and new integrated RF/microwave magnetic devices. In this thesis, we have addressed these needs in three different areas: (1) exchange biased ferromagnetic/antiferromagnetic multilayer thin films with enhanced anisotropy fields, (2) magneto-electric heterostructures and devices, and (3) metamaterial multilayers for FMR enhancement, tunability, and plane wave absorption. Metallic soft magnetic thin films have been demonstrated to have high saturation magnetization, large permeability and relatively high self-biased ferromagnetic resonance (FMR) frequencies, showing great promise for applications in integrated RF and microwave magnetic devices. One problem for these metallic magnetic films is however their relatively low anisotropy fields that are typically in the range of 10~30 Oe, which severely limit their application frequency range. In this work, we investigated the exchange coupled ferromagnetic/anti-ferromagnetic/ferromagnetic CoFe/PtMn/CoFe multilayer films. These CoFe/PtMn/CoFe multilayer films showed a significantly enhanced anisotropy field of 160 Oe, which was 5~10 times of that of the FeCo films. In addition, a narrow FMR linewidth of 45 Oe at X-band was achieved in the CoFe/PtMn/CoFe trilayer. The exchange coupling in the ferromagnetic/anti-ferromagnetic/ferromagnetic trilayers leads to a significantly enhanced anisotropy field that is crucial for the application of metallic magnetic films in integrated magnetic RF/microwave devices. The magnetoelectric coupling of novel YIG/PZT, FeCoB/PZT and FeGaB/PZT multiferroic heterostructures were investigated at DC and at microwave frequencies. An electrostatically tunable band-reject filter device was demonstrated, which had a peak attenuation of greater than 50 dB, 40dB rejection band of 10 MHz, and pass band insertion loss of < 5 dB at ~4.6 GHz. Metamaterial wave absorbers were designed and simulated in HFSS. It involves utilizing a multilayer structure that isolates the electric coupling from the magnetic coupling to absorb radiation from an incident electromagnetic plane wave. The absorber achieved a maximum absorptivity of 46 percent, at ~4GHz.