Thermal conductivity reduction in thermoelectric nanowires

Comunicación presentada en la 12th European Conference on Thermoelectricity (ECT2014), celebrada en Madrid del 24 al 26 de septiembre de 2014.Peer Reviewe

Joule Expansion Imaging Techniques on Microlectronic Devices

We have studied the electrically induced off-plane surface displacement on two microelectronic devices using Scanning Joule Expansion Microscopy (SJEM). We present the experimental method and surface displacement results. We show that they can be successfully compared with surface displacement images obtained using an optical interferometry method. We also present thermal images using Scanning Thermal Microscopy (SThM) technique to underline that SJEM is more adapted to higher frequency measurements, which should improve the spatial resolution.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Nanoscale Measurement of Thermal Conductivity of Organic and Inorganic Nanowires embedded in a matrix

Póster presentado en la 12th European Conference on Thermoelectricity (ECT2014), celebrada en Madrid del 24 al 26 de septiembre de 2014.In this abstract, we present thermal conductivity measurements of inorganic and organic nanowires. These measurements have been carried out with a Scanning Thermal Microscope (SThM) working in 3¿ mode. This technique has been proved to be a successful method to evaluate the thermal conductivity of single nanowires without the need of removing the matrix at which they are embedded. On the one hand, regarding inorganic nanowires, a thermal conductivity of 1.37±0.20W/m·K have been determined for nanowires made of Bi2Te3 with 350nm diameter [1]. On the other hand, measurements of the thermal conductivity of polymeric nanowires made of P3HT embedded in a matrix have been studied in dependence with the diameter of the nanowire. In this work, a reduction of the thermal conductivity of the nanowire is observed as its diameter becomes lower, which can be correlated with its different polymer crystalline orientations [2]. The thermal conductivity of the nanowires varies drastically from 2.29±0.15W/m·K to 0.5±0.24W/m·K when the diameter of the P3HT nanowire is reduced from 350nm to 120nm [2]. Moreover, a finite element model with COMSOL was also developed to validate the results of the thermal conductivity of the nanowires obtained from the analysis of the 3¿ signal of the thermal probe and the use of the effective medium theory. The 3¿-SThM technique is a powerful technique to determine the thermal properties of individual nanowires and study how this property changes in comparison to bulk structures or as a dependence of its diameter size, among others.Peer Reviewe

Temperature measurement of sub-micrometric ICs by scanning thermal microscopy

Surface temperature measurements were performed with a Scanning Thermal Microscope mounted with a thermoresistive wire probe of micrometrSurface temperature measurements were performed with a Scanning Thermal Microscope mounted with a thermoresistive wire probe of micrometric size. A CMOS device was designed with arrays of resistive lines 0.35µm in width. The array periods are 0.8 µm and 10µm to study the spatial resolution of the SThM. Integrated Circuits with passivation layers of micrometric and nanometric thicknesses were tested. To enhance signal-to-noise ratio, the resistive lines were heated with an AC current. The passivation layer of nanometric thickness allows us to distinguish the lines when the array period is 10μm. The results raise the difficulties of the SThM measurement due to the design and the topography of ICs on one hand and the size of the thermal probe on the other hand.ic size. A CMOS device was designed with arrays of resistive lines 0.35µm in width. The array periods are 0.8 µm and 10µm to study the spatial resolution of the SThM. Integrated Circuits with passivation layers of micrometric and nanometric thicknesses were tested. To enhance signal-to-noise ratio, the resistive lines were heated with an AC current. The passivation layer of nanometric thickness allows us to distinguish the lines when the array period is 10μm. The results raise the difficulties of the SThM measurement due to the design and the topography of ICs on one hand and the size of the thermal probe on the other hand

Precise control of thermal conductivity at the nanoscale through individual phonon-scattering barriers

International audienceThe ability to precisely control the thermal conductivity (κ) of a material is fundamental in the development of on-chip heat management or energy conversion applications. Nanostructuring permits a marked reduction of κ of single-crystalline materials, as recently demonstrated for silicon nanowires. However, silicon-based nanostructured materials with extremely low κ are not limited to nanowires. By engineering a set of individual phonon-scattering nanodot barriers we have accurately tailored the thermal conductivity of a single-crystalline SiGe material in spatially defined regions as short as ∼15 nm. Single-barrier thermal resistances between 2 and 4×10−9 m2 K W−1 were attained, resulting in a room-temperature κ down to about 0.9 W m−1 K−1, in multilayered structures with as little as five barriers. Such low thermal conductivity is compatible with a totally diffuse mismatch model for the barriers, and it is well below the amorphous limit. The results are in agreement with atomistic Green’s function simulations

Imagerie thermique et thermoélastique de circuits intégrés (application à l'analyse de défaillances)

Ce travail décrit le développement d'une instrumentation en mesures thermiques et thermoélastiques pour l'analyse de défaillance sur circuits intégrés, il comporte trois parties: la première partie concerne des mesures interférométriques effectuées avec deux interférométries, homodyne et hétérodyne. Ces interféromètres seront appliqués pour la détéction de points chauds sur des circuits défaillants. La deuxième partie concerne des mesures thermiques effectuées en thermoréflectance. deux bancs de mesure ont été développés : le premier s'applique pour l'imagerie face avant. Le deuxième entièrement original, conerne l'imagerie large champ face arrière qui utilise une porte optique temporelle. La dernière partie concerne le développement d'une nouvelle approche pour les mesures de température et déplacement enutilisant la microscopie à balayage laser, avec une étude de résolution et sensibilité.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Développement d'un dispositif pompe-sonde hétérodyne (application à l'imagerie en acoustique picoseconde)

L' acoustique picoseconde permet l'étude de structures aux dimensions sub-microniques grâce à l'utilisation d'ultrasons dont le contenu spectral peut s' étendre au-delà du THz. La génération et la détection de ces ondes sont rendues possibles par l'association de lasers impulsionnels femtosecondes à dispositifs de type pompe-sonde. Ce manuscrit de thèse décrit la mise en place d'une expérience d' imagerie opto-acoustique avec une résolution spatiale submicronique. L' utilisation combinée d'un échantillonnage optique hétérodyne et de cavités lasers à bas taux de répétition (50 MHz) permet de gagner plusieurs ordres de grandeur sur les temps d'acquisition et de disposer d'une très bonne résolution spectrale. Le manuscrit s'articule autour de trois parties. Dans un premier temps les deux cavités laser aux taux de répértition légèrement différents permettant l'échantillonnage otpique hétérdodyne sont présentées. Puis l'architecture et les performances du système d'asservissement de leur taux de répétion sont décrites. Dans la seconde partie du manuscrit, l'implémentation de cette double cavité dans une expérience pompre-sonde est détaillée et la possibilité de détecter des ondes acoustiques sub-THz avec une résolution de 50 MHz est démontrée. Enfin, dans le dernier chapitre, la puissance de cette expérience pour réaliser de l'imagerie ultra-rapide est illustrée au travers de deux exemples : l'étude d'ondes acoustiques de surface GHz dont la dispersion est induite par la présence d'une couche nanométrique et la détection d'hétérogénéités élastiques submicroniquesAcoustice waves in the Gifahertz or Terahertz frequency range allow the mechanical characterization of submicronic structures. The generation and the detection of these waves can be performed with the use of femtosecond lasers combined with pump-probe setups. This report describes the settingèup of an opto-acoustic imaging experiment with a submicronic spatial resolution.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

High speed heterodyne infrared thermography applied to thermal diffusivity identification

We have combined InfraRed thermography and thermal wave techniques to perform microscale, ultrafast (microsecond) temperature field measurements. The method is based on an IR camera coupled to a microscope and synchronized to the heat source by means of phase locked function generators. The principle is based on electronic stroboscopic sampling where the low IR camera acquisition frequency facq (25 Hz) undersamples a high frequency thermal wave. This technique permits the measurement of the emissive thermal response at a (microsecond) short time scale (microsecond) with the full frame mode of the IR camera with a spatial thermal resolution of 7 μm. Then it becomes possible to study 3D transient heat transfer in heterogeneous and high thermal conductive thin layers. Thus it is possible for the first time in our knowledge to achieve temperature field measurements in heterogeneous media within a wide range of time domains. The IR camera is now a suitable instrument for multiscale thermal analysis