High performance RF MEMS series contact switch — Process considerations and device performance

In this paper we present a detailed discussion of the processing considerations and device RF performance for a surface micromachined MEMS (microelectromechanical systems) electrostatic RF switch. As with any MEMS device, process is a critical part of the technology development. Processing considerations in the successful fabrication of RF MEMS switches consist of many areas such as surface planarization, reliable contact formation, film stress and uniformity control. In this paper, we will discuss each of these areas and their impact on the device´s mechanical integrity. Device planarization and smooth contact metal surface formation were realized through special lift-off and polyimide coating processes. Experiments indicated that devices fabricated without the planarization process and standard contact formation method were prone to stiction and early failures. Optimized processes were developed to fabricate planarized surfaces prior to mechanical layer deposition and form round-cornered and smooth-surface contact dimples. A process was also developed to deposit a very low stress SiON film using a low temperature PECVD deposition technique to improve device stability and reliability. The fabricated switch has a pull-in voltage of 20 V-25 V. The switch closing time is in the range of 10 mus -15 mus with a driving voltage of 50 V to 60 V. Excellent performance such as <0.3dB insertion loss and >25 dB rejection up to 40 GHz has been realized.