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法国图卢兹第三大学博士生招生，有奖学金
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PhD position available, October 2019 Study of charge trapping phenomena in thin films used in capacitors by space charge and photo-stimulated discharge measurements. Contact: Laurent Boudou, LAPLACE, – laurent.boudou@laplace.univ-tlse.fr, +33 (0)5 61 55 73 26 Laurent Berquez, LAPLACE, – laurent.berquez@laplace.univ-tlse.fr, +33 (0)5 61 55 84 10 Abstract: With the growing of polymer capacitor market (essentially BoPP: Biaxially Oriented Polypropylene), having applications in the field of electronics or energy storage, the interest of studying charge generation, transport and trapping in thin dielectric films increased over the past decades. Indeed, this is a field where the electrical constraints are strong, close to the intrinsic limits of the materials. Charge trapping in the bulk of materials, that induces local electrical field enhancement, represents a weakness. Therefore, the nature and properties of traps need to be identified. Among the experimental methods used for charge trapping study, those that allow to access to the energy level distribution are not numerous. The most used ones are probably the TSD (Thermally Stimulated Discharge) and PSD (Photo-Stimulated Discharge) methods. PSD method, that consists in measuring the discharge current under monochromatic light scanning in the UV-visible wavelength range, is well adapted to estimate charge trap energy level in transparent or semi-transparent materials [1]. Its advantage, when compared to TSD method that needs temperature ramp, is to probe deeper charge traps without any thermal effect that can affect the material microstructure and the charge stability. However, the interpretation of the PSD data is sometimes difficult, actually the recorded PSD current can originate from charge detrapping, but also from photoconduction effect, photoelectric effect or distorted by dipolar relaxations. In order to dissociate charge detrapping phenomena from other mechanisms at play when PSD spectra is recorded, a coupling between PSD and space charge methods is aimed in this project. Space charge measurements allow to access to charge density and position within the sample. The FLIMM (Focused Light Intensity Modulation Method) will be preferred, because well adapted to the study of thin films (few μm), with a good spatial resolution near the metal/dielectric interfaces and the possibility to scan charge density in the 3 dimensions, that represents a real advantage to study electrical field enhancement due to the use of fingered electrode for PSD measurement. The main objectives of the study are: To couple PSD and FLIMM measurements with the aim to dissociate the different mechanism at play To study the influence of several parameters (electrical field, temperature, electrode structure, material…) on the PSD signature in order to improve our understanding of charge transport and trapping phenomena in thin dielectrics and evaluate the trap level distribution for the tested materials. To identify chemical species acting as traps by complementary technics. The PhD work will be performed in the “Solid Dielectrics and Reliability” group, from LAPLACE laboratory (www.laplace.univ-tlse.fr), in Toulouse, France. Keywords: thin films, space charge, Photo-Stimulated Discharge Duration: 3 years, starting on October 1st, 2019. Salary ≈2000�/1650� rough/net per month Expected profile: Candidate having a Master degree in Materials Science or Electrical Engineering with preference for experimental research. Good English is required. Objectivity, autonomy and team oriented skills are highly demanded. Email: boqiao1988@gmail.com |
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