THz MEMS — Micromachining enabling new solutions at millimeter and submillimeter frequencies

Since RF MEMS switches appeared more than 20 years ago, micromechanics has been attracting huge attention for enabling near-ideal microwave devices. MEMS switches and MEMS-switch based circuits have been through different development stages and are currently proving themselves commercially, among others for mobile-phone antenna tuners. However, micromachining can do much more than “just” two-dimensional MEMS switches for planar transmission-line technology: Three-dimensional micromachining allows for new microwave devices with unprecedented performance, and has the potential to become an enabling technology for volume-manufacturable, reconfigurable submillimeter-wave and THz systems. This paper provides an overview of 3D silicon micromachining capability and examples of innovative microwave devices enabled by this technique, including W-band phase shifters, tuneable capacitors and couplers, and near-ideal V-band waveguide switches based on MEMS-tuneable surfaces. Then, the state of the art of micromachined waveguide systems up to 2.9 THz is given, including single components such as micromachined-waveguide filters up to 1 THz, but also very complex systems such as a 340 GHz 8-pixel imaging radar. Finally, the potential of MEMS-tuneable micromachined-waveguide systems is outlined, given the examples of recent work at KTH on THz MEMS devices operating at 500-750 GHz, including a 3.3 bit MEMS phase shifter and a waveguide switch.