RF MEMS High-Impedance Tuneable Metamaterials for Millimeter-Wave Beam Steering

This paper presents the design, fabrication and evaluation of RF MEMS analog tuneable metamaterial high-impedance surfaces (HIS). These miniaturized structures are designed for W-band beam steering applications and are intended to replace a large multi-component subsystem by a single chip. Furthermore, the MEMS tuneable microwave metamaterials of this paper present a new class of microsystems interacting with microwaves, by uniquely combining the functionality of the microwave structures with the tuning MEMS actuators in one and the same distributed surface elements. A high-impedance surface array with 200 times 52 elements and a pitch of 350 m has been successfully fabricated and evaluated. The device features monocrystalline silicon membranes which are transfer-bonded on a multi-wafer silicon-glass substrate. The measured pull-in voltage is 15.9 V. Microwave measurements from 70 GHz to 114 GHz confirm the frequency selective nature of the surface. The fabricated devices showed a resonance frequency of 111.3 GHz to 111.8 GHz with losses ranging from -18 dB to -23 dB at the resonance and from -5 dB to -7 dB outside the resonance, which is worse than theoretically predicted but mainly attributed to imperfections in the design and fabrication of the first prototypes.