Fabrication and characterization of a planar interleaved micro-transformer with magnetic core

This paper presents the design, the fabrication and the characterization of a planar interleaved micro-transformer with an Yttrium Iron Garnet (YIG) core. The design of this micro-transformer and the manufacturing steps are presented. HFSS software is used for the conception and the simulation of the interleaved magnetic micro-transformer. It is composed of two identical windings. A bottom magnetic core is used to improve the integrated transformer performances. To form the windings, we have used a surface micromachining process. We have also used a negative photoresist (SU-8) as an insulating layer and as support for the fabrication of a bridge to connect the central end of the coils to the ground shield. The micro-transformer have been characterized with impedance meter up to 100 MHz, and completed to 1 GHz using vector network analyzer.     

Consequence of the Pulling Solution Ageing on the Properties of Tin Oxide Layers Elaborated by the Sol-Gel Dip-Coating Technique

In the sol-gel technology, either for bulk or thin films, the stability in time of the solutions is a major factor to control. An evolution of the solution may influence strongly the properties of the elaborated material (thickness, cracks, refractive index, conductivity, etc.), and cases have been reported where solutions had to be stored in a dry and cold place to prevent any hydrolysis-condensation reaction, and so any consequent gelation.This paper evaluates the influence of the solution aging on the properties of undoped SnO₂ layers obtained by sol-gel dip-coating (SGDC). Results are given in relation with storage conditions and for experiences conducted over several months.The evolution of the solution viscosity is first followed, and the corresponding properties for the layers are presented: optical reflection and transmission, optical gap, conductivity, morphology... The importance of the interaction with water is discussed.     

Influence of Elaboration Parameters on the Properties of Tin Oxide Films Obtained by the Sol-Gel Process

The influence of elaboration parameters during the sol-gel process is studied for tin oxide films deposition. The Dip Coating Sol-Gel route can be divided into three elaboration stages: the pulling phase and the drying and densification steps. During the pulling phase, the relative humidity ratio and the withdrawal speed are found to influence the film morphology and the film thickness respectively. Then, we show how a correct control of the sample drying is able to eliminate cracks. The densification step (temperature and duration), leading to the final network, is considered in details, and resulting effects on physical properties are presented: crytallinity, optical behaviour, atomic density, stoichiometry, electrical conductivity etc... We show through these results the specificity of the tin oxide elaborated with our procedure     

Extended X-Ray Absorption Fine Structure Study of Arsenic in HgCdTe

Extended x-ray absorption fine structure (EXAFS) experiments using the As K-edge have been carried out at the European Synchrotron Radiation Facility on two molecular beam epitaxy (MBE) grown arsenic-doped HgCdTe samples. Arsenic (As) is provided by a radio-frequency plasma cell and was incorporated to a level of a few 10¹⁸ at·cm⁻³. Both samples were analyzed as grown and after a high-temperature anneal (410°C/1 h) under saturated mercury pressure. The EXAFS signature of as-grown and annealed samples are strikingly different, indicating a drastic change in the environment of the As atom. In any case, the EXAFS signal originates from at least two different contributions and is found to be dominated by As clusters. The other contribution for as-grown samples comes from tellurium neighbors indicating that As incorporates partially in the (Cd,Hg) site.     

Frequency characterization of thin soft magnetic material layers used in spiral inductors

The paper details the characterization of thin magnetic materials layers, particularly soft materials, with respect to their behaviour in frequency (from 10 MHz to 1 GHz). The proposed method is suitable for any soft but insulating magnetic material; Yttrium Iron Garnet (YIG) is used as an example. The principle is based on a comparison between simulations for different values of the permeability and measurement values versus frequency of planar inductor structures; an experimental validation is proposed as well. Thin magnetic material is first deposited on an alumina substrate using RF sputtering technique; a planar spiral winding of copper is then deposited on the magnetic material by the same technique. The effective permeability versus frequency is obtained by comparing two samples of spiral windings with and without magnetic material. Network analyser measurements on samples of various geometrical dimensions and of different thicknesses are necessary to determine the effective magnetic permeability; we have obtained a relative effective permeability of about 30 for seven turns spiral inductor of a 17 μm YIG film.