Nanoscale Ruthenium Coatings of MEMS Switches Contacts
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1249-F08-09
Nanoscale Ruthenium Coatings of MEMS Switches Contacts Sergey M. Karabanov1, Andrey S. Karabanov2, Dmitriy V. Suvorov1, Benoit Grappe3, Caroline Coutier3, Henry Sibuet4, Boris N. Sazhin1and Anatoliy A. Krutilin1 1 Ryazan Metal Instrumentation Plant JSC, 51 B Novaya St., Ryazan, 390029, Russia. 2 Solar Energy Ltd., 51 B Novaya St., Ryazan, 390029, Russia. 3 Schneider Electric Industries, 37 Quai Paul Louis Merlin, Grenoble, 38000, France. 4 CEA-Leti, 17 rue des Martyrs, Grenoble, 38000, France. ABSTRACT The paper reports the tests results of ruthenium contacts coatings of magnetically controlled MEMS switches. During the tests the contact resistance was measured and the lifetime of MEMS switches was evaluated. After testing the analysis of the form and contact surface structure using SEM-method was carried out. The experiment results showed that the application of ruthenium nanolayers as the contact coating at slight increase of the contact resistance improves the lifetime of MEMS switches considerably. INTRODUCTION Nowadays the increase of the lifetime [2] of all MEMS switch types (RF MEMS relays, magnetically controlled on-off MEMS switches [1]) is the most actual problem. The work resource and operating characteristics, first of all, contact resistance, of any switching unit, the basis of the construction of which is a dry contact, are determined by the contact coating properties. This is true for MEMS switches too. The paper presents the results of the study of the operating characteristics of magnetically controlled MEMS switches with two types of contact coatings with the thickness of up to 100 nm: ruthenium and gold. THEORY AND EXPERIMENT Electrical MEMS switch contacts are made by sputtering of a thin metal layer using PVD technology. This method allows to obtain a high degree of chemical purity and coating smoothness, and to provide almost an ideal surface condition. Due to these coating properties MEMS switches have a very low contact resistance at a small contact pressure force. Contact material selection Commonly used materials for the contact coating are gold, ruthenium, tungsten, and molybdenum. The experimental investigation has shown that the use of gold as the MEMS switch contact material allows to obtain a very low contact resistance: 0,25 ohm at the contact pressure force of 100 µN (at 10 µА and 1 mV). The use of more solid metals such as ruthenium, tungsten, and molybdenum as contact coating materials allows to minimize the problem of the contact sticking. So, the study of MEMS switches with ruthenium contact coating has shown that the switch operates without the contact
sticking, and the contact resistance increases slightly (up to 0,4 ohm at 100 µNn contact pressure force). The use of tungsten and molybdenum as the MEMS switch contact coating also eliminates sticking at operation, but the contact resistance increases significantly (up to 7 ohm at the contact pressure force of 100 µN, current of 10 µА, and voltage of 1 mV) as the result of the contact surface oxidation during the p
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