Jérémie Dhennin

A new method for the hermeticity testing of wafer-level packaging

Until now, the determination of microelectronic packages hermeticity has been related to the MIL-STD-883 method 1014 which is based on the helium leak detection method. But this method is no longer suited for small packages due to the resolution limit of the apparatus. Indeed, leaks induced by nonhermetic MEMS packages are often one order of magnitude smaller than the resolution of the helium leak tester. Consequently, characterization of MEMS packages requires new methodologies to measure hermeticity accurately. Two methods will be investigated in the context of this study: the membrane deflection measurement, when exposed to different pressures, using optical profilometry, and the measurement of the variation of gas concentration in a sealed silicon cavity by Fourier transform infrared spectroscopy (FTIR). The calculated leak rates are compared for samples where the standard fine leak test gave no results. The values obtained for the leak rates with the optical test and FTIR test for the same sample are identical, showing the relevance of these two methods. FTIR spectroscopy is a promising method which enhances standard detection limits. It can be used as a reliable process quality control tool.

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.

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.

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.

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.

A new method for hermeticity testing of wafer-level packaging

Until now, the determination of the hermeticity of microelectronic packages is related to the MIL-STD-883 method 1014 which is based on the He leak detection method. But this method is no more suited for small packages due to the resolution limit of the apparatus used conventionally. Indeed the minimum detectable leak rate is of the order of 5.10-11 atm.cm3.s-1. Leaks induced by non hermetic MEMS packages are often one order of magnitude smaller. So, the sensitivity of the He leak detector method is too low and this method can not be applied anymore. The MEMS packages produced with wafer level encapsulation techniques, require new methodologies to measure hermeticity appropriately and accurately. The purpose of this paper is to present the development of alternative methods for testing the hermeticity of MEMS micro-cavities. Two methods will be investigated in the context of this study: The membrane deflection measurement exposed to different pressures, using optical profilometry, and the measurement of the variation of gas concentration in a sealed silicon cavity by Fourier-transform infrared spectroscopy (FT-IR). The calculated leak rates are compared for samples where standard fine leak test gave no results. The values obtained for the leak rates within optical test and FT-IR test for the same sample are identical, showing the relevance of these two methods.

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

Comparative study of RF MEMS micro-contact materials

A systematic comparison between several pairs of contact materials based on an innovative methodology early developed at NOVA MEMS is hereby presented. The technique exploits a commercial nanoindenter coupled with electrical measurements, and test vehicles specially designed to investigate the underlying physics driving the surface-related failure modes. The study provides a comprehensive understanding of micro-contact behavior with respect to the impact of low-to-medium levels of electrical current. The decrease of the contact resistance, when the contact force increases, is measured for contact pairs of soft material (Au/Au contact), harder materials (Ru/Ru and Rh/Rh contacts), and mixed configuration (Au/Ru and Au/Ni contacts). The contact temperatures have been calculated and compared with the theoretical values of softening temperature for each couple of contact materials. No softening behavior has been observed for mixed contact at the theoretical softening temperature of both materials. The enhanced resilience of the bimetallic contacts Au/Ru and Au/Ni is demonstrated.