Manganites are well known in the oxide community, especially La2/3Sr1/3MnO3 (LSMO) for its magnetic behavior above room temperature. In these materials, electrical conduction is due to several phenomena such as double exchange or polaronic conduction that give rise to a modulation of the material’s resistivity with the temperature. Measuring the resistance of a device can thus be a way to measure its temperature and was notably used to design bolometers working at room temperature, thanks to its high Temperature Coefficient of Resistance (TCR) close to the ferromagnetic transition. For suspended microdevices, dependence on the background gaz pressure is also observed. This phenomenon relates to the Pirani effect where the surrounding gas cools down the heated device because the local thermal conductivity depends on ambient gas pressure. Close to the ferromagnetic transition, the TCR of LSMO is almost a decade higher than Platinum making this material a good candidate for sensor application at room temperature. Additionally, the high chemical stability of manganites and their very low intrinsic electrical noise level are other arguments to use them in this field. Micro-pirani sensors were fabricated thanks to the integration of LSMO on Si with STO and YSZ buffer following by MEMS technology processes. Such oxide-based sensors exhibit sensitivity 10 times better and power consumption reduced by a factor of 100 with respect to a metallic sensor with the same geometry.

Les oxydes sont des matériaux complexes possédant une physique riche et toujours au centre de nombreuses recherches. Parmi ces oxydes, les manganites ont retenu notre attention car ils présentent une transition métal-isolant abrupte en température, générant un très fort coefficient en température en conditions d’environnement standards. L’objectif de ce travail est de démontrer que ce fort coefficient peut être exploité pour l’amélioration des performances des jauges de pression de type Pirani qui subissent un certain essoufflement dans leur développement. La voie menant à l’aboutissement d’une telle jauge à base d’oxydes pose en revanche un certain nombre de limites technologiques à lever et auxquelles nous avons répondu. La première de ces limites concerne l’intégration des oxydes monocristallins sur silicium, que nous avons reproduite et étendue au cas des substrats de type SOI et GaAs. Nos procédés proposent de passer par deux techniques, l’épitaxie par jets moléculaire et l’ablation laser, pour assurer une croissance optimale de nos films sur ces substrats et d’assurer la reproductibilité de leur réponse en température, notamment la position de leur température de transition en accord avec l’état de l’art. L’épitaxie de ces oxydes génère un niveau de contrainte non négligeable qui n’a jamais été mesuré. En concevant divers dispositifs autosupportés, et en s’appuyant sur les considérations théoriques et des modélisations par éléments finis, nous avons pu quantifier la relaxation de cette contrainte importante et assurer près de 100% de reproductibilité des systèmes suspendus. Ces mêmes systèmes nous permettent de caractériser pour la première fois le facteur de jauge des manganites monocristallines par l’application d’une contrainte contrôlée par nanoindentation. Il est également démontré qu’ils constituent des jauges de pression Pirani à la sensibilité accrue de deux ordres de grandeur pour une consommation en puissance réduite. Des solutions permettant d’améliorer l’ensemble des aspects de ces jauges sont étudiées.

The highly temperature-dependent resistivity of the La2/3Sr1/3MnO3 (LSMO) manganite is taken as an advantage in a pressure sensor design based on the Pirani effect. Thin epitaxial films are grown on silicon substrate thanks to a SrTiO3 buffer layer that allows the fabrication of freestanding bridges by means of clean-room processes. The devices are then heated by Joule effect and their temperature modulated by heat transfer through the surrounding gas. The higher the current flowing in the bridge, the larger the resistance variation with pressure is, due to the Pirani effect. The heating current and device geometry are tuned in order to stay in a monotonous regime, avoiding the change of sign of the LSMO temperature coefficient. A sensitivity increased by a factor of 3 and a power consumption reduced by 5 orders of magnitude are measured by comparing oxide devices with conventional metallic ones of same geometry.

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Ferroelectric epitaxial Pb(Zr, Ti)O3(PZT) layers were grown by pulsed laser deposition on SrTiO3/GaAs templates fabricated by molecular beam epitaxy. The templates present an excellent structural quality and the SrTiO3/GaAs is abrupt at the atomic scale. The PZT layers contain a- and c- domains, as shown by X-Ray diffraction analyses. Piezoresponse force microscopy experiments and macroscopic electrical characterizations indicate that PZT is ferroelectric. A relative dielectric permittivity of 164 is extracted from these measurements.

Ferroelectric epitaxial Pb(Zr,Ti)O3 (PZT) layers were grown by pulsed laser deposition on SrTiO3/GaAs templates fabricated by molecular beam epitaxy. The templates present an excellent structural quality and the SrTiO3/GaAs is abrupt at the atomic scale thanks to surface Ti pre-treatment. The PZT layers contain a- and c- domains, as shown by X-Ray diffraction analyses. Piezoforce microscopy experiments and macroscopic electrical characterizations indicate that PZT is ferroelectric. A relative dielectric permittivity of 164 is extracted from these measurements.

We report the study of the wavelength dependence in the NIR range (1.3 μm-1.63 μm), of the Pockels effect in strained silicon. The measured second order nonlinear optical susceptibilities varied from Xxxy(2) = 74 ± 25 pm/V to Xxxy(2) = 221 ±34 pm/V, at λ = 1300 nm and λ = 1630 nm respectively.

We investigate the influence of the wavelength, within the 1.3μm-1.63μm range, on the second-order optical nonlinearity in silicon waveguides strained by a silicon nitride (Si₃N ₄) overlayer. The effective second-order optical susceptibility χxxy(2)¯ evolutions have been determined for 3 different waveguide widths 385 nm, 435 nm and 465 nm and it showed higher values for longer wavelengths and narrower waveguides. For wWG = 385 nm and λ = 1630 nm, we demonstrated χxxy(2)¯ as high as 336 ± 30 pm/V. An explanation based on the strain distribution within the waveguide and its overlap with optical mode is then given to justify the obtained results.

Ferroelectric epitaxial Pb(Zr,Ti)O3 (PZT) layers were grown by pulsed laser deposition on SrTiO3/GaAs templates fabricated by molecular beam epitaxy. The templates present an excellent structural quality and the SrTiO3/GaAs is abrupt at the atomic scale. The PZT layers contain a- and c-domains, as shown by X-Ray diffraction analyses. Piezoforce microscopy experiments and macroscopic electrical characterizations indicate that PZT is ferroelectric. A relative dielectric permittivity of 164 is extracted from these measurements.

Using heterostructures that combine a large-polarization ferroelectric (BiFeO3) and a high-temperature superconductor (YBa2Cu3O(7-δ)), we demonstrate the modulation of the superconducting condensate at the nanoscale via ferroelectric field effects. Through this mechanism, a nanoscale pattern of normal regions that mimics the ferroelectric domain structure can be created in the superconductor. This yields an energy landscape for magnetic flux quanta and, in turn, couples the local ferroelectric polarization to the local magnetic induction. We show that this form of magnetoelectric coupling, together with the possibility to reversibly design the ferroelectric domain structure, allows the electrostatic manipulation of magnetic flux quanta.