INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY VOL. 1 , NO. 1 , JUNE 2006 IJMOT-2006-4-21 © 2006 ISRAMT Microwave Phase Shifter with Electromagnetic Signal Coupling in Silicon Bulk Technology Stefan Leidich 1 *, Sebastian Voigt 1 , Steffen Kurth 2 , Karla Hiller 1 , Thomas Gessner 1,2 1 Chemnitz University of Technology, Center for Microtechnologies, Chemnitz, 09107, Germany 2 Fraunhofer IZM, Dept. Multi Device Integration, Chemnitz, 09126, Germany Tel: +49 371 531 35500; E-mail: stefan.leidich@zfm.tu-chemnitz.de Abstract- This contribution presents a Distributed MEMS Transmission Line (DMTL) phase shifter for the 24 GHz ISM band fabricated in silicon bulk technology. Using this technology enables the suspension of all capacitive loads on one movable plate and therefore allows wide range analog and homogeneous tuning. To avoid commonly used metallic feed-throughs for signal connection, an electromagnetic signal coupler guides the microwave signal non-galvanically from printed circuit board level, through the chip substrate into the MEMS device. The first available prototypes of the phase shifter are characterized to provide 50°/dB loss normalized differential phase shift at 24 GHz. The achievable normalized insertion loss of the coupling structure has been determined with 0.13 - 0.17 dB. Index Terms- RF-MEMS, phase shifter, coupler, coplanar waveguide. I. INTRODUCTION Many microwave and millimeter-wave circuits using micro electro mechanical system (MEMS) devices have demonstrated outstanding RF performance and low DC power consumption. Within regards to mechanic actuation, the majority of proposed RF-MEMS are digitally actuated devices. The fabrication of analog adjustable components like Distributed MEMS Transmission Line (DMTL) phase shifters requires several equal, tunable capacitances loading a transmission line [1, 2]. Using surface technology for the fabrication of variable capacitors seems to be difficult, since the tuning ratio is limited to low numbers [3] and the mechanical characteristics of commonly used double-clamped beams strongly depend on residual stress and Young’s modulus of thin films [2]. It can be shown that differences between individual loads result in local impedance variations and cause higher reflection losses. Recent publications on analog tunable MEMS capacitors in configurations much different from switches using polycrystalline silicon have demonstrated high tuning range with very low actuation voltage [4]. Because of long signal lines made of polycrystalline silicon partly covered with gold the quality factors and the self resonance frequencies of these devices are comparably low. The focus of this work is to demonstrate the capabilities of silicon bulk technology for the fabrication of analog tunable DMTL phase shifters. In a second part of the paper an impedance matched electromagnetic signal coupler is described. The coupler connects the MEMS phase shifter to the printed circuit board non-galvanically and therefore avoids technologically challenging metallic feed- throughs used for signal connection of packaged devices [5]. II. DMTL PHASE SHIFTER IN SILICON BULK TECHNOLOGY For the design of analog DMTL phase shifters the silicon bulk technology offers advantages compared to surface technologies. The capability of etching structures into the single crystalline silicon, in contrast to the limitation of solely depositing and structuring thin films, allows the fabrication of actually 3-dimensional structures. This enables the design of actuation mechanisms that commonly suspend all capacitive loads and therefore minimize capacitance variations between the individual elements. Further on, the 1