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Ultra-compact wireless implantable medical devices are in great demand for healthcare applications, in particular for neural recording and stimulation. Current implantable technologies based on miniaturized micro-coils suffer from low wireless power transfer efficiency (PTE) and are not always compliant with the specific absorption rate imposed by the Federal Communications Commission. Moreover, current implantable devices are reliant on differential recording of voltage or current across space and require direct contact between electrode and tissue. Here, we show an ultra-compact dual-band smart nanoelectromechanical systems magnetoelectric (ME) antenna with a size of 250 × 174 µm2 that can efficiently perform wireless energy harvesting and sense ultra-small magnetic fields. The proposed ME antenna has a wireless PTE 1–2 orders of magnitude higher than any other reported miniaturized micro-coil, allowing the wireless IMDs to be compliant with the SAR limit. Furthermore, the antenna’s magnetic field detectivity of 300–500 pT allows the IMDs to record neural magnetic fields.

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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...