THz Frequency Control Circuits
The 0.1 - 1 THz band is still a fairly new region for the industry as well as academic societies to explore. Yet the great potential for future high-speed communication attracts increasing interest in the THz circuits $\&$ electronics research and development. In the THz band, the micro-machined transmission line technique provides an ultra-wideband signal path with high linearity, a low loss that could be easily integrated with other circuits.
This research is focused on developing high-performance THz DC contact RF-MEMS switches and THz graphene detectors. In the THz switch development, a THz MEMS switch design process adaptable to different dielectric constant environments is presented. The challenges and solutions associated with mm-wave / THz switch design, modeling, fabrication, and test are explored and discussed. To prove this process, THz MEMS switches are realized on both quartz and silicon substrate and tested in the 140 - 750 GHz frequency band. The results agree with the design expectations well. In the graphene detector development, detectors are demonstrated based on the photo-thermoelectric effect with a measured performance from 140 to 500 GHz. Epitaxial graphene is realized by sublimating silicon from the surface of a silicon carbide wafer in a chemical vapor deposition reactor. Following etching, a variety of metals are used to realize the drain contacts including gold, nickel, chromium, and ytterbium. Three different graphene channel lengths are also included in the comparison. The measurement suggests the drain contact metal and graphene channel length both impact the detection performance. Among all combinations, the detector with 25 $\mu$m graphene channel and ytterbium drain metal has the highest responsivity of 19 V/W under 180 GHz incident radiation with a calculated NEP of 2.4 nW/. In the end, a CMOS based MEMS switch is proposed to integrate MEMS switch with the commercial CMOS manufacturing through a post-CMOS process. Potential methods to improve the graphene detector’s performance is also proposed.