Markus Ulm

Design considerations and technology assessment of phased-array antenna systems with RF MEMS for automotive radar applications

Planar array antennas are attractive for use in future automotive radar systems due to their flexibility in design and control of radar beams. The complexity and cost of a radar front-end phased array can be decreased by applying a beam-steering/switching concept, which reduces the number of parallel RF and baseband signal paths. RF-microelectromechanical systems (MEMS) subsystems are employed because of their excellent RF properties and potential low-cost manufacturability. We present design considerations for prototypical automotive applications of RF-MEMS-based automotive radar front-ends using phased-array antennas based on phase shifters or a Rotman lens. The single RF-MEMS switch is optimized with respect to its RF and thermomechanical behavior taking into account automotive requirements. The respective RF-MEMS subsystems, i.e., phase shifters and single-pole-multiple-throw switching networks are presented in conjunction with packaging and mounting approaches. We evaluate two different wafer-level packaging technologies using glass-frit sealing or polymer sealing. Finally, functional packaged devices are demonstrated: a glass-frit-sealed and flip-chip-mounted RF-MEMS switch and a benzocyclobutene-packaged single-pole-quadruple-throw switch network.

Vertical Silicon K-Band CPW Through-Wafer Interconnects

With the increase in production volume of RF devices (e.g. for automotive applications), packaging and interconnection become more and more important. Furthermore, new system concepts such as chip-on-chip or RF-MEMS demand new packaging strategies. This paper presents a vertical silicon micromachined RF CPW through-wafer feedthrough with excellent performance in the K-band. In particular, the feed through demonstrates an insertion loss of 0.16dB and a return loss of 20dB at 25GHz. Alumped element model was developed and was evaluated with measurements.

Millimeter-wave microelectromechanical (MEMS) switches for automotive surround sensing systems

In recent years, great advances have been made in the field of silicon millimeter-wave integrated circuits (SIMMWIC) as well as In microsystems technology. These developments jointly allow the preparation of micromechanical capacitive switches, which exhibit excellent RF properties far into the millimeter-wave frequency range. This paper presents coplanar bridge and longitudinal switches and discusses their applicability for automotive surround sensing systems. It comprises a detailed review of RF properties in addition to an short introduction to the systems background. Furthermore, aspects are treated which are important for the application, such as thermal and mechanical properties, reliability aspects and packaging and mounting technologies.

K-band capacitive MEMS-switches

In this paper single-pole single-throw K-band microelectro-mechanical capacitive switches are discussed, exhibiting low insertion losses (<0.3 dB@21 GHz) and good isolation (34 dB@21 GHz). Depending on the respective geometry, an electromechanical characterization yields actuation voltages from 16 to 33 V and switching times around 10 /spl mu/s. Furthermore, resonance frequencies above 50 kHz have been measured. The switches are integrated in coplanar transmission lines on high resistivity silicon substrates. In order to be compatible with present semiconductor device technology, the fabrication process mainly employs copper and aluminum metallisations.

Monolithic integration of RF-MEMS and semiconductor devices for the K-band

In this paper a process for complete monolithic integration of semiconductor devices and radio-frequency micro-electro-mechanical systems (RF-MEMS) on a single substrate is presented. Our attempt was to combine RF-Schottky-Diodes to form sub-harmonic mixer and RF-MEMS-phaseshifters on a single chip. The diodes were etched from a molecular beam epitaxy grown silicon stack using two mesa etching steps. Nickel forms a nickel-silicon alloy (nickel silicide) during a rapid thermal processing step acting as Schottky-metallisation. On this stack, the RF-MEMS-fabrication starts with its metallisation layers as a back-end process. To insulate the relatively high actuation voltage (20-40 V) from the RF circuitry, a new concept for bias decoupling is presented. To demonstrate the functionality of the semiconductor integration approach, a mixer for 24 GHz has been designed in coplanar waveguide technology, the local oscillator frequency is at 12 GHz. Fabricated within the same run, switched line phaseshifters are used to show the MEMS capabilities. First tests of diodes revealed good results in their DC- and RF characteristics, the conversion loss of the subharmonic zero biased mixer reached 20 dB for 6 dBm power of the local oscillator. Fabricated teststructures of the phaseshifters achieved good results showing that transmission losses lower than 3 dB at a phaseshift of 180° can be reached.

Scalability of Capacitive RF MEMS Switches

MEMS capacitive shunt switches have attracted large interest in various microwave or mm-wave applications, such as low power communication systems or phased arrayed antennas [1,2,3]. Two types of RF MEMS switches are discussed with respect to their impedance matching, scalability in frequency and related mechanical limitations. As a result, a W-band MEMS switch with a measured insertion loss of 33 dB at 94 GHz is presented.

Planar Phased-Array Antenna Systems forW-Band Automotive Radar Sensors with Beam Steering Based on RF MEMS

Future automotive radar systems can be realized using planar array antennas, which offer a flexible design and control of radar beams. In addition, the complexity and cost of the automotive radar front-end antenna system can be reduced. RF-MEMS subsystems are employed for beam steering in phased array systems due to their excellent RF properties and potential low-cost manufacturability. We present design considerations for prototypical automotive applications of RF-MEMS based automotive radar front-end systems using phased array antennas based on phase shifters or a Rotman lens. The design of a planar antenna using series-fed antenna columns is described, in which analytical models for the patches and also full 3D EM simulations are used. An optimization procedure of the elevation pattern is proposed. In azimuth, the beam forming is either based on phase shifters or on a Rotman lens. We present designs for shortto-medium and long-range applications. Beam steering in a phased array antenna is realized with RF-MEMS systems, which are based on membrane shunt switches. The single RF-MEMS switches are optimized with respect to their RF and thermomechanical behaviour taking into account automotive requirements. Further, coplanar passive components, such as 90° bends and T-junctions are optimized separately. Using these switches and passive components, single-bit stub-loaded-line and switched-line phase shifters for 45° and, respectively, 90° or 180° phase shift are demonstrated with very good phase accuracy. For beam switching of a Rotman lens, we further present single-polemultiple-throw RF-MEMS switching networks. We evaluate two different packaging technologies using glass-frit sealing or polymer sealing. We finally demonstrate functional packaged devices: a glass-frit-sealed and flipchip-mounted RF-MEMS switch and a BCB-packagd SP4T switching network. Index Terms – RF-MEMS Switches, Phase Shifters, Packaging, Phased-Array Antennas, Beam-Steering, W-Band Radar Planar Phased-Array Antenna Systems for W-Band Automotive Radar Sensors with Beam Steering Based on RF MEMS Fig. 1: Concepts for beam steering with RF-MEMS-based planar

Mikromechanische (MEMS) Schalter für Millimeterwellen-Systeme in KFZ-Rundumsichtanwendungen

In recent years, great advances have been made in the field of silicon millimeter-wave integrated circuits (SIMMWIC) as well as in microsystems technology. These developments jointly allow the preparation of micromechanical capacitive switches, which exhibit excellent RF properties far into the millimeter-wave frequency range. This paper presents coplanar bridge and longitudinal switches and discusses their applicability for automotive surround sensing system. It comprises a detailed review of RF properties in addition to an introduction to the systems background. Further, aspects are treated which are important for the application, as mechanical properties, reliability, and packaging and mounting technologies. Finally, the potential for further systems integration will be shown. Für die Dokumentation Mikromechanik / Schalter / Millimeterwelle / Radar / Integration