Frédéric Courtade

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.

Colloidal Solutions of Organic Conductive Nanoparticles

Although molecular metals have been known for decades, their insolubility, low vapor pressure, and synthesis routes have prevented them from being integrated into electronic devices. We have prepared stable colloidal solutions of the organic metal TTF-TCNQ that overcome such difficulties. The solutions contain well-dispersed nanoparticles stabilized by long alkyl chain amines. They afford soluble powders by evaporation and homogeneous thin films by drop-casting. Powders and films show room temperature conductivities in the 0.01-0.1 S cm(-1) range.

Sub-hundred nanosecond electrostatic actuated RF MEMS switched capacitors

This paper presents a new mechanical architecture for RF MEMS components that are able to achieve reconfiguration faster than conventional MEMS switches. For most MEMS switches, the electrical switching speed is generally limited to a few microseconds, inherently restricted by the delay required to mechanically move their mobile membrane up and down. By using a proper mechanical design and the structural material fabrication process, this paper will show miniature bridges that are able to exhibit mechanical resonance frequencies over 10 MHz range to be compared to the few tens of kHz for conventional RF MEMS switches. As a result, the switching speed of these miniature components is greatly improved and reaches 50 to 100 ns. Such performance has been achieved using composite micro-beams based on the multilayer material assembly of alumina/aluminum/alumina. To our knowledge, this is the fastest switching speed reported for RF MEMS components so far.

Impact of the Surface Roughness Description on the Electrical Contact Resistance of Ohmic Switches Under Low Actuation Forces

At 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.

Validation of bending tests by nanoindentation for micro-contact analysis of MEMS switches

Research on contact characterization for microelectromechanical system (MEMS) switches has been driven by the necessity to reach a high-reliability level for micro-switch applications. One of the main failures observed during cycling of the devices is the increase of the electrical contact resistance. The key issue is the electromechanical behaviour of the materials used at the contact interface where the current flows through. Metal contact switches have a large and complex set of failure mechanisms according to the current level. This paper demonstrates the validity of a new methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate the micro-scale contact physics. Dedicated validation tests and modelling are performed to assess the introduced methodology by analyzing the gold contact interface with 5 µm2 square bumps at various current levels. Contact temperature rise is measured, which affects the mechanical properties of the contact materials and modifies the contact topology. In addition, the data provide a better understanding of micro-contact behaviour related to the impact of current at low- to medium-power levels.

Thermal and topological characterization of Au, Ru and Au/Ru based MEMS contacts using nanoindenter

This paper reports the comparisons between several pairs of contact materials for micro switches. This study is done with a new methodology using a commercial nanoindenter coupled with electrical stimulation of test vehicles specially designed. The stability of the contact resistance, when the contact force increases, is studied for contact pairs of soft (Au/Au contact), harder (Ru/Ru contact) and mixed material configuration (Au/Ru contact). An enhanced stability of the bimetallic contact Au/Ru was demonstrated considering the sensitivity to power increase, and related topological modifications of the contact surfaces.

Characterization of gold/gold, gold/ruthenium, and ruthenium/ruthenium ohmic contacts in MEMS switches improved by a novel methodology

Comparisons between several pairs of contact materials are done with a new methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate microscale contact physics. Experimental measurements are obtained to characterize the response of a 5-µm2-square contact bump under electromechanical stress with increased applied current. The data provide a better understanding of microcontact behavior related to the impact of current at low- to medium-power levels. Contact temperature rise is observed, leading to shifts of the mechanical properties of contact materials and modifications of the contact surface. The stability of the contact resistance, when the contact force increases, is studied for contact pairs of soft (Au/Au contact), harder (Ru/Ru contact), and mixed material configuration (Au/Ru contact). An enhanced stability of the bimetallic contact Au/Ru is demonstrated, considering sensitivity to power increase related to creep effects and topological modifications of the contact surfaces. These results are compared to previous ones and discussed in a theoretical way by considering the temperature distribution around the hottest area at the contact interface.

Characterization of Au/Au, Au/Ru, and Ru/Ru ohmic contacts in MEMS switches improved by a novel methodology

Comparisons between several pairs of contact materials have been done with a new methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate the micro-scale contact physics. Experimental measurements are obtained to characterize the response of a 5 μm2 square contact bump under electromechanical stress with increased applied current. The data provide a better understanding of micro-contact behaviour related to the impact of current at low- to medium-power levels. Contact temperature rise is observed, leading to shifts of the mechanical properties of contact materials and modifications of the contact surface. The stability of the contact resistance, when the contact force increases, is studied for contact pairs of soft (Au/Au contact), harder (Ru/Ru contact) and mixed material configuration (Au/Ru contact). An enhanced stability of the bimetallic contact Au/Ru is demonstrated considering sensitivity to power increase, related to creep effects and topological modifications of the contact surfaces. These results are compared to previous ones and discussed in a theoretical way by considering the temperature distribution around the hottest area at the contact interface.

Nanogap MEMS micro-relay with 70 ns switching speed

This 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.

Junction delineation and EBIC on FIB cross section

Abstract This paper presents a sample preparation study on a FIB based X-section. It shows that wet etching is a simple and reproducible solution for the decoration of both implanted and deposited layers. The methodology is applicable on bare or packaged dice. Results with EBIC on FIB cross-sections were also obtained. A specific double FIB box method was developed and characterized to improve spatial resolution of EBIC.