Interrelationship Between Hardness and Resistivity of Metal Alloy Films as Contact Materials in MEMS Switches

This study presents a basic step towards the selection methodology of electric contact materials for microelectromechanical systems (MEMS) metal contact switches. This involves the interrelationship between the two important parameters, resistivity and hardness, since they provide the guidelines and assessment of the contact resistance, wear, deformation, and adhesion characteristics of MEMS switches. For this purpose, thin film alloys of three noble metals; platinum (Pt), rhodium (Rh) and ruthenium (Ru) with gold (Au) were investigated. The interrelationship between resistivity and hardness was established for three amounts of alloying of these metals with gold. Thin films of gold (Au), platinum (Pt), ruthenium (Rh), and rhodium (Ru) were also characterized to obtain their baseline data for comparison. All films were deposited on silicon substrates. When Ru, Rh, and Pt are alloyed with Au, their hardness generally decreases but resistivity increases. This decrease or increase was, in general, dependent upon the amount of alloying.