Ba‐Hexaferrite Films for Next Generation Microwave Devices

Abstract

Next generation magnetic microwave devices require ferrite films to be thick ͑Ͼ300 m͒, self-biased ͑high remanent magnetization͒, and low loss in the microwave and millimeter wave bands. Here we examine recent advances in the processing of thick Ba-hexaferrite ͑M-type͒ films using pulsed laser deposition ͑PLD͒, liquid-phase epitaxy, and screen printing. These techniques are compared and contrasted as to their suitability for microwave materials processing and industrial production. Recent advances include the PLD growth of BaM on wide-band-gap semiconductor substrates and the development of thick, self-biased, low-loss BaM films by screen printing. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2165145͔ INTRODUCTIONDriven by radar electronics and wireless technologies, the next generation of magnetic microwave devices ͑isola-tors, filters, phase shifters, and circulators and related components͒ will be planar, self-biased, and low loss, and operate well beyond the performance metrics of today's devices. Self-biasing is an important property that eliminates the need for a biasing field that is provided by a comparatively large permanent magnet. The elimination of this magnet is an essential step in making these devices smaller and planar. Integration with semiconductor devices continues to be a desirable property that requires ferrite fabrication techniques to be compatible with complementary metal-oxide semiconductor ͑CMOS͒ processing. This is a difficult task considering that most ferrite fabrication techniques require temperatures Ͼ900°C to produce high-quality films.In order to achieve these goals, magnetic materials must possess high saturation magnetization ͑4M s ͒, high remanent magnetization ͑M r ͒, adjustable magnetic anisotropy fields ͑H A ͒, low microwave losses ͓i.e., low ferromagnetic resonance ͑FMR͒ linewidths ⌬H FMR ͔, and for many applications, have the easy axis of magnetization perpendicular to the film plane ͑i.e., perpendicular magnetic anisotropy͒. In physical terms, the films should be thick ͑Ͼ300 m͒, dense ͑low levels of porosity that are responsible for added microwave loss͒, and pure phase. For many applications the microstructure should possess a strong crystallographic orientation, although true epitaxy is not required.In this paper, we focus on recent advances made in the processing of Ba hexaferrite films for applications in microwave and millimeter-wave devices, with special emphasis on circulator devices. We will compare and contrast different film processing technologies including pulsed laser deposition ͑PLD͒, liquid-phase epitaxy ͑LPE͒, and screen printing.Ba ͑M-type͒ hexaferrite ͑henceforth BaM͒ has the magnetoplumbite structure and a stoichiometry of BaFe 12 O 19 . This structure has 32 atoms/ f.u. and 64 atoms in a single unit cell ͑see Fig. 1͒. One property of this compound that is of particular value in microwave device design is the strong uniaxial anisotropy with the easy direction being along the c axis ͑H A ϳ 17 000 Oe͒.1,2 The high magnetic anisotropy field can b...

Structure and Magnetism of Ba-Hexaferrite Films Grown on Single Crystal 6-H SiC With Graduated Interfacial MgO Buffer Layers

“…The magnetic hysteresis loop squareness (i.e., Sq ) approached 0.7. High Sq values are required, and highly desirable, for self-biased ferrite device applications [6]. For the highest quality films, we measured this squareness as low as 0.2.…”

Negative Permeability-Based Electrically Small Antennas

“…The negative permeability materials offer a better promise in this regard. In fact, one can use a self-biased hexaferrite in gigahertz spectrum and operates above the material resonance to provide desired negative permeability [5]. Hence, it will be of practical importance if one can design a small antenna utilizing MNG materials.…”

“…It can provide more radiation to the outside region and help to create wideband small antenna [3]; however, the major challenge is to achieve a low-loss weak-frequency-dispersive magnetic material at a desired frequency. In contrast to the electric property, it is very hard to establish magnetic polarization in a natural medium at high-frequency spectrum, although, a lot of research is Manuscript currently in the progress to accomplish this importance [5]. Artificially, the magnetism can be created by embedding resonant loop circuits inside a dielectric material [4].…”

Effects of magnetic pre-alignment of nano-powders on formation of high textured barium hexa-ferrite quasi-single crystals via a magnetic forming and liquid participation sintering route

“…M-type barium hexa-ferrite (BaM) with narrow ferromagnetic resonance (FMR) line-width is a potential gyromagnetic material for radar electronics, wireless devices and monolithic microwave integrated circuits due to its large uniaxial magneto-crystalline anisotropy ( $17 kOe) which can partially or totally replace the required external static magnetic field and establish self-biasing [1][2][3]. As well known as one of the conventional low cost permanent magnets, BaM poly-crystals are easy to be fabricated, but their FMR line-widths are too large to satisfy the practical utilization.…”