Contact resistance evolution of highly cycled, lightly loaded micro-contacts

Abstract

Reliable microelectromechanical systems (MEMS) switches are critical for developing high performance radio frequency circuits like phase shifters. Engineers have attempted to improve reliability and lifecycle performance using novel contact metals, unique mechanical designs and packaging. Various test fixtures including: MEMS devices, atomic force microscopes (AFM) and nanoindentors have been used to collect resistance and contact force data. AFM and nanoindentor test fixtures allow direct contact force measurements but are severely limited by low resonance sensors, and therefore low data collection rates. This paper reports the contact resistance evolution results and fabrication of thin film, sputtered and evaporated gold, micro-contacts dynamically tested up to 3kHz. The upper contact support structure consists of a gold surface micromachined, fix-fix beam designed with sufficient restoring force to overcome adhesion. The hemisphere-upper and planar-lower contacts are mated with a calibrated, external load resulting in approximately 100μN of contact force and are cycled in excess of 106 times or until failure. Contact resistance is measured, in-situ, using a cross-bar configuration and the entire apparatus is isolated from external vibration and housed in an enclosure to minimize contamination due to ambient environment. Additionally, contact cycling and data collection are automated using a computer and LabVIEW. Results include contact resistance measurements of 6 and 8 μm radius contact bumps and lifetime testing up to 323.6 million cycles.