A Ruthenium-Based Multimetal-Contact RF MEMS Switch With a Corrugated Diaphragm

Abstract

This paper presents a ruthenium metal-contact RF microelectromechanical system switch based on a corrugated silicon oxide/silicon nitride diaphragm. The corrugations are designed to substantially reduce the influence of the fabricationinduced stress in the membrane, resulting in a highly insensitive design to process parameter variations. Furthermore, a novel multilayer metal-contact concept, comprising a 50-nm chromium/ 50-nm ruthenium/500-nm gold/50-nm ruthenium structure, is introduced to improve the contact reliability by having a hard-metal surface of ruthenium without substantial compromise in the contact and transmission-line resistances, which is shown by theoretical analysis of the contact physics and confirmed by measurement results. The contact resistance of the novel metallization stack is investigated for different contact pressures and is compared to pure-gold contacts. The contact reliability is investigated for different dc signal currents. At a measurement current of 1.6 mA, the Ru-Au-Ru contacts have an average lifetime of about 100 million cycles, whereas the Au-Au contacts reach 24 million cycles only. For larger signal currents, the metal contacts have proven to be more robust over the Au-Au contacts by a factor of ten. The measured pull-in voltage is reduced significantly from 61 V for flat diaphragm to 36 V for corrugated diaphragm with the introduction of corrugation. The measured RF isolation with a nominal contact separation of 5 µm is better than −30 dB up to 4 GHz and still −21 dB at 15 GHz, whereas the insertion loss of the fully packaged switch including its transmission line is about −0.7 dB up to 4 GHz and −2.8 dB at 15 GHz.[ 2007-0271]Index Terms-Contact metal, contact resistance, corrugated membrane, RF microelectromechanical system (MEMS) switch, wafer-level packaging.

Research Status and Development Trend of MEMS Switches: A Review

“…Soft metals, such as gold, are suitable for reducing contact resistance, but their contact surfaces are prone to microwelding. Ke et al [58] coated Au contacts with Ru to investigate placing harder materials on top of softer materials for a lifetime enhancement. Yang et al [59] showed Au-Ni alloy contacts resist material transfer better than Au-Au contacts.…”

Reviews on Corrugated Diaphragms in Miniature Fiber-Optic Pressure Sensors

“…CDs have been studied for quite a long time and were first widely used in capacitive pressure sensors and RF MEMS switches [41,42,[44][45][46][52][53][54][55][56]. Introducing the corrugated structure into the fiber-optic sensor can significantly improve the performance of sensors.…”

RF-MEMS switches for a full control of the propagating modes in uniplanar microwave circuits and their application to reconfigurable multimodal microwave filters

“…A solution to this problem is the use of RF-MEMS switched capacitors to obtain precise frequency shifts (Pothier et al 2005;Nadaud et al 2016). The fabrication residual stress can be reduced either by improving the geometry and the structural switch design (Mahameed et al 2010;Philippine et al 2013;Patel et al 2012;Zaireie et al 2013;Yang et al 2015), since these determine their stiffness and therefore actuation voltage and reliability, or utilizing particular materials, and therefore a special dedicated fabrication process (Palego et al 2009, Ke et al 2013, Sterner et al 2008. In (Patel et al 2012) a crab-leg beam geometry is used to achieve a highly reliable switch, but with a high actuation voltage (80-90 V).…”