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

Abstract

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 Crcoated 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.

Review: Electrostatically actuated nanobeam-based nanoelectromechanical switches – materials solutions and operational conditions

“…The reliability of various metals as electrode materials has been examined both theoretically [ 144 ] and experimentally [ 63 , 145 – 152 ] using mechanical [ 145 – 146 ], electrical [ 145 – 146 ] or coupled electromechanical [ 63 , 147 – 152 ] testing experiments. The materials properties such as hardness, wear resistance, melting point, conductivity and oxidation characteristics should be considered for each particular application.…”

“…Other noble metals such as Ir and Pt are attractive due to their high Young’s modulus and oxidation resistance in ambient environment. Under I ( V ) cycling with a Cr-coated AFM tip, both materials exhibited relatively low initial contact resistances in comparison with Ni and Cr [ 145 ]. Adhesion forces were measured to be more than four times higher for the Ir/Si contact than for Pt/Si [ 145 ].…”

“…Under I ( V ) cycling with a Cr-coated AFM tip, both materials exhibited relatively low initial contact resistances in comparison with Ni and Cr [ 145 ]. Adhesion forces were measured to be more than four times higher for the Ir/Si contact than for Pt/Si [ 145 ]. The electromechanical cycling of Pt/Pt contacts for 10 9 cycles in ambient air showed more than three orders of magnitude increase of contact resistance accompanied by only a moderate 12% increase of adhesion force and no signs of wear-related degradation [ 63 ].…”

“…The use of W as the contact material in NEM switches is advantageous due to the high hardness of the metal, high Young’s modulus and high melting and boiling points. A W/Cr contact demonstrated the lowest adhesion force, compared to other metals (e.g., Pt and Ni) [ 145 ]. However, for a W contact material, relatively large changes in contact resistance [ 146 ] and degradation of the on state current during cycling [ 49 ] have been reported, which has been attributed to the impact of its native oxide [ 49 , 146 ].…”

Back-end-of-the-line MEMS switches for power management, ESD and security

“…13 shows the I-Vs of the 100 nm gap device. The evolution of the contact resistance in the thin film for platinum has been studied in [27] and the results are summarized in Fig. 13.…”