Combined strain and composition-induced effects in the metal-insulator transition of epitaxial VO 2 films

International audienceThe role of epitaxial strain, thermal strain, and bulk (strain-free) lattice parameter in the metal-insulator transition (MIT) and the structural phase transition (SPT) of VO2 is investigated for the case epitaxial films grown on (001)-oriented TiO2 substrates. Temperature-resolved X-ray reciprocal space mapping has been used to determine the absolute state of strain as well as the bulk lattice parameters of VO2 at 100 • C. For the thinnest film (15 nm), the state of strain is dominated by the film/substrate lattice mismatch yielding an in-plane tensile strain which, in turn, shifts both the MIT and the SPT towards lower temperatures. Conversely, for the thickest film (100 nm), the epitaxial strain is relaxed, so that state of strain is dominated by the VO2/TiO2 thermal expansion mismatch which is responsible for a compressive in-plane strain. In all cases a swelling of the strain-free VO2 unit-cell is observed which indicates the presence of interfacial oxygen vacancies and/or Ti diffusion into the VO2 films. The presence of oxygen vacancies stabilize the metallic rutile phase and counterbalances the action of thermal strain on the MIT and the SPT and degrade the electric properties for the thinnest film. For the thickest film the resistivity ratio is 6.4 × 10 4

(Z EDP Sciences, Les Ulis

Optimisation des paramètres de dépôt de DLC par ablation laser U. V. de carbone vitreu

ZnOGaAs acoustic biosensors: focus on ZnO thin film characterization

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ZnO-GaAs acoustic biosensors: Focus on ZnO thin film characterization

International audienceWe have been developing biosensors based on acoustic waves transduction for the detection of bacterial pathogens in complex biological media. The biosensor’s architecture consists of a GaAs membrane produced by clean room microfabrication techniques on which is deposited a thin layer of piezoelectric ZnO. In the present work, we focus on the structural, topographical and electrical characterization of ZnO layers deposited on GaAs substrates under different conditions. Keywords—piezoelectric zinc oxide thin film; X-ray diffraction; Raman spectroscopy; atomic force microscopy; impedance measurement

ZnOGaAs acoustic biosensors: focus on ZnO thin film characterization

International audienc

Sub-Hundred nanosecond reconfiguration capabilities of Nanogap RF MEMS Switched capacitor

International audienc

Nanogap MEMS micro-relay with 70 ns swithing speed

International audienceThis paper presents Micro-electro-mechanical relays for very fast switching applications. Prototype relays have been fabricated tested and demonstrated reconfiguration capabilities as fast as 70 ns with a 300 ns additional settling time once electrical contact is fully stabilized. Such switching speed has been previously demonstrated on capacitive RF-MEMS switches, but this is the first time that such a fast mechanical switching is reported on relays, i.e. ohmic contact switches. The ability to open or close a contact at such speed can lead to many applications such as ultra low power electromechanical computing, or harsh environment electronics

Applications of Vanadium Dioxide (V02)-loaded Electrically Small Resonators in the Design of Tunable Filters

International audienc

Role of thermal strain in the metal-insulator and structural phase transition of epitaxial VO 2 films

International audienceThe metal-insulator switching characteristics of VO2 play a crucial role in the performances of VO2-based devices. In this work we study high-quality (010)-oriented epitaxial films grown on (001) sapphire substrates by means of electron-beam evaporation and investigate the role of interface defects and thermal strain on the parallel evolution of the metal-insulator transition (MIT) and structural phase transition (SPT) between the monoclinic (insulator) and rutile (metal) phases. It is demonstrated that the highly-mismatched VO2/Al2O3 interface promotes a domain-matching epitaxial growth process where the film grows in a strain-relaxed state and the lattice distortions are confined at the interface in regions with limited spatial extent. Upon cooling down from the growth temperature, tensile strain is stored in the films as a consequence of the thermal expansion mismatch between VO2 and Al2O3. The thinnest film exhibit the highest level of tensile strain in the interfacial plane resulting in a shift of both the MIT and the SPT temperatures towards higher values, pointing to a stabilization of the monoclinic / insulating phase. Concomitantly, the electrical switching characteristics are altered (lower resistivity ratio and broader transition) as result of the presence of structural defects located at the interface. The SPT exhibits a similar evolution with, additionally, a broader hysteresis due to the formation of an intermediate, strain-stabilized, phase in the M1-R transition. Films with thickness ranging between 100-300 nm undergo a partial strain relaxation and exhibit the best performances, with a sharp (10 • C temperature range) and narrow (hysteresis < 4 • C) MIT extending over more than four orders of magnitude in resistivity (6 × 10 4)

Intégration des films de VO2 à transitions de phase pour la réalisation d'un filtre accordable passe-bande en technologie SSR

National audienc