Spectroscopic analysis of material transfer phenomena in MEMS switches

Material transfer in electrical contacts is a degradation mechanism that has been recently highlighted in Micro Electro-Mechanical Switches and which leads to their failure by contact sticking. However the physical mechanism of material transfer at micrometer and lower scale still remains insufficiently addressed. This paper deals with optical spectroscopy analysis used as a new and original approach to study material transfer in MEMS switches designed with a contact gap smaller than 6μm. Light emission in MEMS switches has been measured by a photomultiplier at contact opening and closure. The light emission has been exactly localized at contact spots of the switch. Spectra of the emitted light within the wavelength of 200nm to 800nm have also been realized on an experimental setup which reproduces contact cycles. Results prove that whatever the metallic contact material used, only metallic plasma is produced whereas oxygen and nitrogen wavelengths are never observed. The presence (or the absence) of the anodic metallic material in the plasma is also revealed by spectra. Moreover a theoretical model of metallic plasma spectra is simulated and adjusted to our results to extract the physical properties of the plasma by assuming Local Thermodynamic Equilibrium (LTE) conditions. The excitation temperature of the plasma is found to be around 7600K. These new results contribute to a better understanding of the degradation of MEMS switches electrical contacts under hot switching conditions.