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Size reduction for spiral inductors is investigated. We reveal bidirectional ferromagnetic inductors with an /spl sim/30% to 135% increase in L over the air-core value. This is advantageously realized by using single deposition. The realization uses above-IC techniques and high-magnetization FeHfN laminated films. We also report a quality factor of /spl sim/10 at 1.5 GHz, which is mitigated while realizing high FMR frequency (up to 6 GHz). This leads to considerations on nonmagnetic excess losses. Finally, a surface reduction of 25% to 50% for conventional spirals is demonstrated.

Significant size reduction for RF spiral inductors is shown possible with using high magnetization (4 π Ms) ferromagnetic material. High 4 π Ms (-19kG) is suitable for realizing high ferromagnetic resonance frequencies FMR (-6GHz) and significant L-enhancements thanks to a high permeability. However, increasing the natural resistivity of FeHfN (-102 μ Ohm.cm) would be also advantageous for a better confinement of the magnetic flux and reducing the series-capacitance with the inductor. Indeed, with a very high resistivity (typically= 103 μ Ohm.cm), the magnetic materials can be almost in contact to the metal traces, therefore reducing the gap between the spiral and the magnetic planes. In a first part, we detail the optimization of FeHfN single layer films and the realization of ferromagnetic spiral inductors integrating this film as a laminated material. The results point out 30% to 130% increase in L over the air-core value which leads to a surface reduction of 25% to 50%. In a second part, we investigate the possibility of coincorporation of oxygen and nitrogen in FeHf films in order to raise the resistivity and to retain a high magnetization. It is shown that nitrogenation and oxidation processes act separately with opposed effects on the microstructures of the films (grain size, lattice parameter.) but combine advantageously. However, the expected compromise with 4 π Ms above-10kg and a resistivity of-103μΩ. cm has not been found yet. Finally, it is concluded that the dual N2-O2-reactive process with FeHf material is promising but requires further investigations.

“ Proximity effects” could be the superior mechanism responsible for lowering the quality factor (Q) of ferromagnetic spiral inductors, apart from ferromagnetic resonance considerations. In this paper, a model extraction from previous measurements is described. In particular, the extracted series resistance Rs is discussed with regards to skin depth and current crowding contributions in the metal traces. Comparing air-core and ferromagnetic spirals, it is shown that“ proximity effects” are enhanced with magnetic materials leading to a much stiffer increase in Rs with frequency (f2 instead of √ f). This points out Q being naturally always lowered at the same frequency with ferromagnetic spirals, even if an adequate high FMR is realized. Thus, it is necessary to reconsider the design of spirals when using magnetic materials and some solutions are suggested at the end of this paper.

The paper investigates the characteristics of microwave transmission in coplanar waveguides (CPWs) fabricated on various silicon carbide substrates. Propagation constant and characteristic impedance measurements were performed at frequencies from 0.1 to 10 GHz. Different propagation modes are observed as a function of frequency and substrate resistivity. In the case of the low-loss structure, a quasi-TEM equivalent circuit model was developed from the available process parameters, taking into account the effects of electromagnetic fields in CPW structures.

Soft ferromagnetic zero-magnetostrictive Co Nb Zr thin films have been dynamically deposited by dc planar magnetron sputtering onto continuously transported substrates. No magnetic field has been applied to the films during deposition. The films reveal a well-defined in plane uniaxial anisotropy with an easy axis aligned along the direction of substrate motion. As a result, an anisotropy field of 75 Oe and a ferromagnetic resonance frequency of 2.6 GHz have been measured. The study of the relationship between magnetic properties and film thickness points out a critical thickness around 0.3 μm, above which the films exhibit a stripe-domain-like behavior which is detrimental for the high frequency use. The thermal stability of the films is found to be usual as regular amorphous core materials (stable up to 300°C). Additionally, it is shown that the films do not suffer from rotatable magnetic anisotropy usually observed inconventional statically deposited films under magneticfield. Finally, a different origin of the magnetic anisotropyis suggested in dynamically deposited films.

Silicon carbide materials offer specific advantages to MESFET applications. However, to put them to good use requires to apply higher drain voltages than in GaAs devices. Therefore, in spite of the high thermal conductivity of the SiC substrates, this leads to a large power dissipation and a substantial increase in the local temperature. Depending on the device configuration, this self-heating can induce a negative differential conductance at very low frequency near dc regime. A simple analytical model is proposed, which yields a reasonable fit of the MESFET static characteristics. Further experimental evidence for such effects is also given, which corroborates the predictions of the model.

We report the observation of random telegraph signals (RTS) occurring in the forward regime of silicon carbide Schottky diodes. RTS noise is attributed to the modulation of the conductivity either by the trapping/detrapping of a single electron or by the switching of a bistable defect, in the neighbourhood of a localized current path. Noise measurement is therefore a convenient and non-destructive method for assessing the defectivity of SiC power diodes.

This work describes magnetically confined inductors using coplanar waveguide (CPW) lines. The fabrication uses antiferromagnetic exchange coupled iron-cobalt films with high ferromagnetic resonance frequency (5 to 7 GHz). A first type of inductors uses sandwiched lines and exhibits a linear density of inductance of 0.9 nHmiddotmm-1. A second type includes magnetic flanges and indicates 1.15 nHmiddotmm -1. The influence of the flanges contributes to 30% increase of the intrinsic coupling with the line. The measured inductance (L) and quality factor (Q) perfectly agree with theoretical permeability considerations. With meanders, we show L of ~3 nH which competes standard spiral inductors. We also demonstrate that Q only depends on the intrinsic values of the reference line (Q0) and the magnetic material (Qmat). Therefore, Q-optimization is possible at high frequency. We indicate a typical maximum of ~10 at 5 GHz

Ferromagnetic spiral inductors were fabricated using thick copper technology. 30% increase in L is shown over the air core value. However, we observe a large restriction in Q when frequency is beyond 1 GHz. This strongly contrasts with the high ferromagnetic resonance (FMR) frequency measured at 6 GHz. Also still increasing the FMR up to 10 GHz using multipatterning do not improve Q. The highlight is on excess losses not originating from magnetic losses (/spl mu/'') and the Joule effect. Additionally, when comparing multiturn inductor to single strip inductor, proximity effect or current crowding is shown responsible.

Two-port coplanar ferromagnetic inductors using solid magnetic planes were fabricated on silicon. L, R, and Q measurements are presented. Cutoff frequencies exceed 10 GHz, indicating no capacitance limitation. The increase in L over the air-core value is /spl sim/15%, and the quality factor Q is of /spl sim/10 up to 1.5 GHz. The inductance scales with HA-alignment and spiral excitation ratio. Agreement with High-Frequency Structure Simulator simulations including ferromagnetic resonance led to a better understanding in terms of L and Q. Current increase in L is limited by the film thickness (0.2 /spl mu/m). Thicker films (0.5-1 /spl mu/m) would lead to larger gain over L (23% to 31%) with similar Q (/spl sim/10). The restriction in Q from the air-core inductor consists in magnetic losses but not only. Another contribution would come from anomalous ohmic losses from the spiral itself enhanced by the proximity of the magnetic planes.

We used a simple method based on fast magnetostatic computations in order to analyse proximity effects in integrated devices with high permeability magnetic material. This method was applied to various micro-inductors and showed good agreement with experiment. These results enlighten the importance of the proximity effect contribution on the total losses of integrated magnetic devices and demonstrated the interest of this simple method for quality factor optimization.

The main issue for 100% amplification with spirals using single deposition step process has been successfully achieved in this paper, with the use of high magnetization feHfN film as a core material. This allows combining shape anisotropy, solid magnetic plane design, high permeability and high FMR, being thought the most efficient and low cost solution for inductance enhancement and scaling down inductor dimensions.

Significant inductance enhancement over the air-core value using appropriate ferromagnetic thin film as flux amplifier is now possible that would allow RF designers to scale-down the air-core spirals. It was observed that by using high-Q air-core inductors with thick Cu metal trace, the integration of magnetic films results in lower Q. This paper examines the origin of the excess losses with respect to the air-core ones when associating high magnetization film with thick Cu spiral inductors. Results indicate that the origin of the anomalous losses is related to the multi-turn planar geometry. The basic mechanism behind current crowding directly depends on the amplitude of the B-field of adjacent turns in the inductor penetrating a trace normal to its surface.

This paper investigates the high frequency (HF) characterization of spiral inductors on various Si substrates. Some of them were chemically anodized in order to form a thick porous Si layer, which provides a low substrate loss and greatly enhanced inductor quality factor. The HF performance and behavior of these inductors have been analyzed by modeling and parameter extraction in order to compare all the substrates.

SiC power MESFETs are studied for applications to power amplification in the microwave domain. A small-signal model is explained. It provides the intrinsic bias-dependent parameters of the devices, such as G/sub m/, C/sub gs/, C/sub ds/, C/sub gd/, and the current gain cut-off frequency f/sub T/. It is shown that f/sub T/ and G/sub m/ decrease with the drain to source bias V/sub DS/, because of self-heating effects. The model also includes temperature dependence and is in good agreement with experiments. This is a first step to non-linear modelling of SiC MESFETs.