Jean-Michel Desmarres

Experimental setup and realization of thin film specimens for microtensile tests

This paper describes a microtensile test system and the design as the realization of the samples dedicated to the tensile experiments. Two different technologies for the development of miniaturized specimens are detailed: self-standing tensile samples sustained by silicon frames and metal on polymer specimens obtained by laser cutting. The design of the samples has been optimized by means of finite element simulations. Aluminum beams with very large length on thickness ratio have been released from their silicon substrate using a standard etching process. Stress/strain curves are derived from experimental force/displacement values and discussed in terms of Youngs modulus values and critical parameters (flow and rupture stresses).

Electromechanical study of polyurethane films with carbon black nanoparticles for MEMS actuators

Pure polyurethane and nanocomposite carbon black (CB) polyurethane solutions were deposited by spin-coating on a silicon substrate using gold as the adhesion layer and electrode. Different test structures were achieved for electrical and mechanical characterizations. The incorporation of CB nanoparticles in the polyurethane matrix has a significant influence on the dielectric permittivity of the material with an increase of about one third of its value. The Youngs modulus of PU and nanocomposite PU films was determined by different characterization methods. Nanoindentation experiments have pointed out a Youngs modulus gradient through the film thickness. By performing mechanical tests (tensile, bulge, point deflection) on freestanding films, an average Youngs modulus value of about 30 MPa was found as well as a residual stress value of about 0.4 MPa. However, no influence of the presence of the nanoparticles was found. Finally, several MEMS actuators were realized and characterized. At their fundamental resonance frequency, the actuation of the nanocomposite membranes is more efficient than that of pure polyurethane. However, the time constant of the material seems to provide a major barrier for the development of high-frequency PU-based micro-actuators.

Methodology to analyze failure mechanisms of ohmic contacts on MEMS switches

This paper demonstrates the efficiency of a new methodology using a commercial nanoindenter coupling with electrical measurement on test vehicles specially designed to investigate the micro contact reliability. This study examines the response of gold contacts with 5 μm2 square bumps under various levels of current flowing through contact asperities. Contact temperature rising is observed leading to shifts of the mechanical properties of contact material, modifications of the contact topology and a diminution of the time dependence creep effect. The data provides a better understanding of micro-scale contact physics especially failure mechanisms due to the heating of the contact on MEMS switches.

Micro-tensile tests on micromachined metal on polymer specimens: Elasticity, plasticity and rupture

This study is focused on the mechanical characterization of materials used in microelectronic and micro- electromechanical systems (MEMS) devices. In order to determine their mechanical parameters, a new deformation bench test with suitable micromachined specimens have been developed. Uniaxial tensile tests were performed on ldquolow costrdquo specimens, consisting in electroplated thin copper films and structures, deposited on a polimide type substrate. Moreover, a cyclic mechanical actuation via piezoelectric actuators was tested on the same deformation bench. These experiments validate the device for performing dynamic characterization of materials, and reliability studies of different microstructures.

MEMS Reliability: Accurate Measurements of Beam Stiffness Using Nanoindentation Techniques

Bending tests on suspended parts of MicroElectroMechanical System (MEMS) can be achieved thanks to nanoindentation techniques. The paper presents the main difficulties met when performing such a test, and shows how they can be reduced by experimental ways. An application is realized on gold bridges, with a validation of some theoretical assumptions.Copyright

Quantification of the pile-up effect for improving inverse mechanical analysis by means of nanoindentation

This paper deals with the identification of elastic-plastic material properties by means of nanoindentation. A dimensional analysis leads to the identification of a specific parameter based on the estimation of the pile-up effect This parameter may be used in an inverse analysis. Theoretical aspects and experimental issues are discussed.

A comparative study of microscratch and microtensile adhesion tests for nickel coatings on various substrates

The present paper first focuses on discussing application ranges for the scratch test and the microtensile test. For that purpose, both have been implemented on the same nickel coating plated on several substrates, in particular a PCB, which are expected to have different adhesion behaviors. Afterward, correlations are highlighted between these two types of adhesion tests.