Investigation of contact resistance evolution of Ir, Pt, W, Ni, Cr, Ti, Cu and Al over repeated hot-contact switching for NEMS switches

This article reports on the evolution of contact resistance (R_c) of metal contacts over 100,000 cycles. A contact-mode atomic force microscope connected to a current versus voltage (I-V) measurement system was used and successive I-V measurements between a Cr-coated AFM conducting tip and Ir, Pt, W, Ni, Cr, Ti, Cu or Al thin-film metals on silicon nitride coated silicon in a nitrogen ambient were carried out. Adhesion forces between the samples and the conducting AFM tip was also measured. The best cyclic I-V performers were Ir, Pt, W & Ti. The trend in changing R_c seen in Ir, Pt and W are similar and can be attributed to factors such as their high Young´s modulus, high melting temperatures and high density and low adhesion forces. Ti yeilded the best I-V behavior where contact resistance improved slightly as a function of cycling. A relationship between adhesion forces and defect generation in the contact region is observed and the results of both sets of experiments are detailed here.