THz MEMS — Micromachining enabling new solutions at millimeter and submillimeter-wave frequencies (invited paper)

Since RF MEMS switches appeared more than 20 years ago, micromachining and micromechanics have been receiving large 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-tuner switched-capacitor banks. However, micromachining can do much more than just two-dimensional MEMS switches for planar transmission-line technology: Three-dimensional, deep-silicon 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 recent achievements of innovative microwave devices and systems enabled by micromachining high up into the THz spectrum are given, including the first MEMS-reconfigurable submillimeter-wave devices. Highlights of devices presented are a 3.3 bit MEMS phase shifter and a low-insertion loss / high-isolation MEMS waveguide switch operating at 500-750 GHz, and a micromachined technology for multi-pole, multi-transmission zero filers which enables multi-mode resonators with Q factors of 800 at 270 GHz. Furthermore, a technology is shown for very low loss micromachined waveguides with only 0.02 dB/mm loss at 200-300 GHz, which has enabled ultra-low loss waveguide components such as couplers and power combiners/splitters.