Carbon nanotubes and silver flakes filled epoxy resin for new hybrid conductive adhesives

Combining conductive micro and nanofillers is a new way to improve electrical conductivity. Micrometric silver flakes and nanometric carbon nanotubes (CNTs) exhibit high electrical conductivity. A new type of hybrid conductive adhesives filled with silver flakes and carbon nanotubes (DWCNTs or MWCNTs) were investigated. High electrical conductivity is measured as well as improved mechanical properties at room temperature. Small agglomerates and free MWCNTs dispersed in the silver/epoxy composites improve the electrical conductivity and a synergistic effect between MWCNTs and micro sized silver flakes is observed in hybrid composites. Glassy and rubbery storage moduli of the hybrid composites increase with increasing silver loading at fixed CNTs volume fraction. High value of the storage modulus, measured in DWCNTs/μAg hybrid composites at rubbery state, is caused by strong agglomeration of DWCNTs bundles. The electrical and mechanical properties are consistent with the morphologies of the hybrid composites characterized by SEM

Thermo-mechanical analysis of GaAs devices under temperature-humidity-bias testing

International audienceAccelerated life tests on microelectronic devices are needed to estimate their degradation under severe environment. THB (Temperature Humidity Bias) [1] at 85°C and 85%RH (relative humidity) is commonly used for reliability studies. Empirical acceleration laws, used for THB test take into account the temperature change (from 22°C to 85°C), but they do not quantify its impact of the corresponding thermo-elastic stress which it adds to the residual stress in the die and of possible microstructure changes. The aim of this work is to determine the thermo-mechanical stresses induced in the active layer of a Gallium Arsenide (GaAs) chip by the THB test. They are due to the mismatch in Coefficients of Thermal Expansion (CTE) between the stack of thin film materials used as metallurgic interconnection and the intermediate dielectric layers above the active area of the chip. To estimate this stress, fist layers thicknesses measurement have been made with various techniques; second few configurations have been used to simulate heating and finally " complete " 2D Finite Element Analysis (FEA) has been performed. Elastic and thermo-physical materials data come from the literature. The results indicate compression of metal gate (Ti/Al/Au) and tensile stress concentration in the SiNx passivation layer. The outcomes is compared with THB test results from [2] and suggests that stress induced by heating must be considered to explain failure during THB test

Silver oxalate-based solders: New materials for high thermal conductivity microjoining

Micrometric oxalate powders can be decomposed starting from temperatures as low as 90°C, leading to the formation of temporary nanometric grains of metallic silver with a high propensity for sintering. The decomposition being highly exothermic, this additional energy favours the sintering, i.e. the soldering, process. Solders processed at 300°C and very low pressure (<0.5 MPa) displayed a thermal conductivity close to 100 W m-1 K-1, making silver oxalate very promising for safe, moderate temperature and very low pressure bonding

ImPAC Lyon : évaluer l'impact environnemental et thermique de l'exploitation des aquifères superficiels pour la climatisation

Face au fort développement de la géothermie de très basse énergie, des questions sont posées quant à son influence sur l'intégrité des aquifères exploités. La présente étude a eu pour objectif d'appréhender les incidences thermiques, physico-chimiques et microbiologiques d'une exploitation de très basse énergie, destinée à la climatisation, sur l'aquifère des alluvions du Rhône, à Lyon. Il s'agit d'une étude expérimentale qui repose sur un volet d'observations in situ et sur un ensemble de simulations en laboratoire

Spatial qualification tests for highly selective compact micro machined band pass planar filters

International audienc

Validation of simulation platform for modeling of RF MEMS contacts

International audienceFor the DC contact RF MEMS, it has been identified that most of the limitations are related to the quality and the repeatability of the contact that drive the RF performances and the reliability. In order to propose new generation of RF MEMS devices, it is important to get a deeper insight on the physic of contact in order to choose appropriate materials. As part of our study on the electrical contacts of RF MEMS micro switches, the need of multiphysics software offering a well developed solver to simulate many mechanical contact problems coupled with other physics, with a reduced time of calculation and good accuracy on the results is under investigation. As a first step, we need to validate the results of the numerical platforms existing in our laboratory. To do so, a static Hertz contact problem is simulated using ANSYS 10 and COMSOL 3.3 and we compared the results of the simulation with the analytical model. The second step consists of comparing the capabilities of each software to model interaction between objects and solve a variety of contact problems. Then we compare the facilities for the user to fit the contact parameters in the model in order to obtain an accurate solution of our problem. This study permits us to choose the software the most efficient for our application. The accuracy of ANSYS, the various methods available to solve the wide variety of contact problems and with a minimum effort from the user, makes of ANSYS's solver an excellent candidate to be used in our project. Especially, the real topography of the contact surfaces can be included in finite element simulations

Micro-Relais MEMS RF aux temps de commutation de 200ns

National audienc

Impact of The Surface Roughness Description on the electrical contact resistance of ohmic switches under low actuation forces

International audienceAt the present time, the insertion of radio frequency microelectromechanical switches into real architecture requires reduced actuation voltages, reduced dimensions, and better control of the electrical and electromechanical behavior that gives more importance to surface effects, their understanding, and modeling. The use of such devices requires the development of methods for estimating the contact performances as a function of surface roughness, contact materials, and contact topologies. With increase in computation capabilities, the rough surface topography can be implemented in the finite element model but implies long calculation times or even calculation overloading if a high definition of the roughness is desired. To reduce these limitations, assumptions on the microgeometry are required. This paper treats, by use of finite element modeling, the influence of the definition of roughness of contacting switch members on the electrical contact resistance of resistive switches, and investigates the error introduced by using a minimum defined atomic force microscope sampling interval of 10 nm. The present numerical analysis is implemented for switch test structures

DC CONTACT RF MEMS SWITCHES WITH LOW ACTUATION VOLTAGE

Capacitive RF MEMS switches demonstrate that it is difficult to obtain a perfect capacitive contact for a low actuation voltage. Architectures of MEMS switches with resistive contact are then developed. The objective is to minimize the contact resistance to obtain the best RF performances while keeping a low actuation voltage. First set of results have shown that good RF performances, with contact resistance lower than 1.3O, can be obtained with a 30V actuation voltage and with a 6µm gap height. With cantilever height around 1.5µm it will be then possible to obtain enough contact force with 6V applied voltage