Microwave applications of soft ferrites

The development and current status of microwave ferrite technology is reviewed in this paper. An introduction to the physics and fundamentals of key ferrite devices is provided, followed by a historical account of the development of ferrimagnetic spinel and garnet (YIG) materials. Key ferrite components, i.e., circulators and isolators, phase shifters, tunable filters, and nonlinear devices are also discussed separately.

Ferrite devices and materials

Lorentz reciprocity is a fundamental characteristic of the vast majority of electronic and photonic structures. However, non-reciprocal components such as isolators, circulators and gyrators enable new applications ranging from radio frequencies to optical frequencies, including full-duplex wireless communication and on-chip all-optical information processing. Such components today dominantly rely on the phenomenon of Faraday rotation in magneto-optic materials. However, they are typically bulky, expensive and not suitable for insertion in a conventional integrated circuit. Here we demonstrate magnetic-free linear passive non-reciprocity based on the concept of staggered commutation. Commutation is a form of parametric modulation with very high modulation ratio. We observe that staggered commutation enables time-reversal symmetry breaking within very small dimensions (λ/1,250 × λ/1,250 in our device), resulting in a miniature radio-frequency circulator that exhibits reduced implementation complexity, very low loss, strong non-reciprocity, significantly enhanced linearity and real-time reconfigurability, and is integrated in a conventional complementary metal-oxide-semiconductor integrated circuit for the first time.

Magnetic-free non-reciprocity based on staggered commutation

Highly oriented films of BaFe12O19 have been deposited onto MgO (111) substrates by pulsed laser ablation deposition. In contrast to epitaxial BaFe12O19 films grown on Al2O3 (001) substrates, these films experience an in-plane biaxial compressive stress, and do not crack or delaminate to thicknesses of at least 28 μm. X-ray diffraction, magnetometry, torque magnetometry, and ferrimagnetic resonance results all indicate excellent c-axis orientation normal to the film plane, and magnetic properties comparable to bulk values. The thickness and properties of these films approach those required for applications in low-loss self-biased nonreciprocal microwave devices.

https://repository.library.northeastern.edu/files/neu:330589/fulltext.pdf

Growth and characterization of thick oriented barium hexaferrite films on MgO (111) substrates

It is widely recognized that as electronic systems’ operating frequency shifts to microwave and millimeter wave bands, the integration of ferrite passive devices with semiconductor solid state active devices holds significant advantages in improved miniaturization, bandwidth, speed, power and production costs, among others. Traditionally, ferrites have been employed in discrete bulk form, despite attempts to integrate ferrite as films within microwave integrated circuits. Technical barriers remain centric to the incompatibility between ferrite and semiconductor materials and their processing protocols. In this review, we present past and present efforts at ferrite integration with semiconductor platforms with the aim to identify the most promising paths to realizing the complete integration of on-chip ferrite and semiconductor devices, assemblies and systems.

Ferrite film growth on semiconductor substrates towards microwave and millimeter wave integrated circuits

We have calculated the S-parameters and losses in ferrite-film-junction circulators using a new effective-field theory assuming TEM-like propagation. Conductivity loss dominates the dielectric and magnetic losses in Y-junction circulators fabricated on ferrite films with thicknesses less than 200 /spl mu/m. It is plausible to fabricate Y-junction thin-film circulator at X-band with insertion loss less than 0.5 dB if the film thickness is larger than 100 /spl mu/m. The quality of the conductor plane is important in reducing the overall insertion loss of the thin-film-junction circulator.

Theory and experiment of thin-film junction circulator

Production of truly monolithic microwave integrated circuits that incorporate ferrite passive control elements has been hindered by the material property mismatches between ferrites and semiconductors. In this work, monolithic Y-junction circulators were fabricated by bonding 100-/spl mu/m-thick single-crystal yttrium iron garnet films to silicon at 195/spl deg/C, and then removing the gadolinium gallium garnet substrate. S-parameter measurements on the circulator and matching microstrip circuit yield an isolation of 20 dB over a 1 GHz bandwidth at 9 GHz, with a minimum insertion loss near 1 dB. Improvements in circuit design and fabrication techniques may yield monolithic circulators that are fully compatible with large-scale semiconductor manufacturing methods.

A monolithic single-crystal yttrium iron garnet/silicon X-band circulator

We have analytically formulated the problem that a ferrite circulator junction is biased by a nonuniform magnetic field. Interport impedances of the junction can, therefore, be solved numerically. Nonuniform-bias field will reduce the transmission bandwidth, and the circulation condition is apt to be altered if the bias field shows nonuniformity near the center of the junction. Our calculation compares very well with measurements.

Influence of nonuniform magnetic field on a ferrite junction circulator

http://ieeexplore.ieee.org/iel3/4676/13086/00597459.pdf

A Monolithically Integrated Single-Crystal Yttrium Iron Garnet/ Silicon X-Band Circulator

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Papers

Theory and experiment of thin-film junction circulator

A monolithic single-crystal yttrium iron garnet/silicon X-band circulator

Influence of nonuniform magnetic field on a ferrite junction circulator

A Monolithically Integrated Single-Crystal Yttrium Iron Garnet/ Silicon X-Band Circulator