The development of passive devices using a ferrite is a major focus of current research for electronic applications in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which has a large resistivity and high permeability at high frequencies are indeed of great interest for microwave device applications. In this work we developed an integrated and self-biased coplanar isolator using BaM sputtered films. BaM films, 1-36 mum thick, were deposited under optimized conditions by radio frequency magnetron sputtering on alumina substrates. The films were crystallized using a 800degC thermal annealing. Isolators were then realized using patterning of coplanar waveguides (CPW) with standard lift-off technique. The slots and the central width were 300 mum wide and gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film's thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate), the CPW metallic thickness and the polarizing field. As standard design, the CPW were deposited on the top of the magnetic film. At the remanent magnetization (no polarizing field applied), the transmission coefficients then showed a non reciprocal effect, which reached 5.4 dB per cm of line length at 50 GHz for a 26.5 mum thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate after a selective etching of the BaM film, we measured that the non reciprocal effect reached higher values for lower BaM thicknesses than for the first design and that the insertion losses also decreased. The interaction between the field lines created by the conductors and the magnetic film was indeed favored in the second case. Finally, we show the tunability of the isolator with the polarizing field.

Feasibility of an Integrated Self Biased Coplanar Isolator With Barium Ferrite Films

Development of millimeter wave integrated circulator based on barium ferrite

Influence of substrate temperature on the texture of barium ferrite film by magnetron sputtering

This paper reports a study of Co–Ti equiatomic co-substitution of M-type hexagonal barium ferrites Ba(CoTi)xFe12−2xO19, with the objective to adjust coercivity to meet different application requirements. The ferrites, with x = 0.00−1.30, all exhibited the single-phase M-type barium ferrite structure. At x = 1.30, the saturation magnetization (MS) decreased by 27.7% to 47.5 Am2 kg−1 and the coercivity (HC) decreased from 4047 to 171 Oe, providing a wide control range of coercivity. Complex magnetic permeability (μ' and μ'') was measured to be μ'max = 25 and μ''max = 1.5 (at 10 MHz). The value of μ' is much higher than that of un-doped barium ferrite (x = 0.00). Co–Ti substitution reduced the coercivity whilst increased magnetic permeability. These improvements in magnetic properties are attributed to Co and Ti occupancies at different sites in the barium ferrite crystalline structure. Substitution is preferred at 4f2, 2b and 2a sites at x < 0.50, but 2a and 4f1 sites at x < 1.15. In addition, the bulk density (ρ) of the sintered compound was found to increase with increasing Co–Ti substitution.

https://iopscience.iop.org/article/10.1088/2053-1591/2/4/046104/pdf

Co–Ti co-substitution of M-type hexagonal barium ferrite

Ce-substituted BaFe12O19 (BaCexFe12−xO19, x = 0, 0.01, 0.03, 0.05) was prepared by citrate sol–gel method. The thermal decomposition process of precursor was investigated by TG-DSC. The phase composition of the BaCexFe12−xO19 was characterized by X-ray powder diffraction analysis (XRD) which reveals that the BaCexFe12−xO19 crystallizes in a hexagonal structure. The lattice parameter of BaCexFe12−xO19 increases slightly when Ce was substituted into BaFe12O19. The average crystallite size calculated from the XRD line broadening is about 30–33 nm and no intermediate phases are detected in the XRD patterns. The transmission electron microscope (TEM) analysis indicates that the particles of samples obtained are the rod-like morphology.

Sol–gel synthesis of Ce-substituted BaFe12O19

Ferrites have magnetic properties suitable for electronic applications, especially in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), are of great interest for microwave device applications because of their large resistivity and high permeability at high frequencies. BaM films, 1–10 μm thick, were deposited under optimized conditions by RF magnetron sputtering on alumina and silicon substrates. After deposition, films were amorphous and needed a post-deposition annealing at 800 °C to crystallize and to present magnetic properties. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that BaM films deposited on alumina and silicon substrates presented a good crystallization, a smooth surface and no cracks. Ba, Fe and O depth profiles obtained by secondary ion mass spectroscopy (SIMS) showed that the films have a good in-depth uniformity. The film residual stress was evaluated using curvature measurements. Whatever the substrate type, the films are in compression after deposition. Upon annealing and crystallization, a tensile stress adds up in relation with crystalline arrangements. Finally, regarding the magnetic properties measured using a vibrating sample magnetometer (VSM), the optimized saturation magnetization of such films reached 500 mT and the coercive force 325 kA/m. These values are close to that of the bulk BaM.

E. Mery

Papers

Properties of barium ferrite sputtered films