THz Frequency Control Circuits
Abstract: The terahertz (THz) band (0.1-1 THz) remains a difficult region to access within the electromagnetic spectrum. For a long time, technological limitations have made the manufacturing of high frequency electronic devices costly. Meanwhile, applications of the THz spectrum have mostly concentrated in certain specialized fields: in medical imaging, THz radiation is considered a safer replacement of X-rays due to lower photon-energies and lower damage to tissues and DNA; in security surveillance and screening, THz radiation can penetrate fabrics and plastics, to remotely uncover concealed weapons on a person;in astronomy, THz spectroscopy could provides important sources of information for chemistry and biochemistry.On the other hand, since the vast majority of commercial applications are based on only a few GHz, the industry has not been motivated to push forward the exploration in THz domain.
Nowadays, however, the upcoming 5G and future generation communication systems are calling for higher speed and wider communication bandwidths. This demand makes the utilization of higher frequency bands a must. According to the 2018 report The Latest Update On 5G From IEEE Communication Society,the planned 5G wireless channels will reach up to ~60 GHz. As a result, the industry is now having an increased interest in accessing the THz frequency band, leading to a new concentration on developing THz frequency control circuits.
One of the challenges of THz frequency control circuits is to realize a THz switch. The traditional transistor based switching circuit has relatively high parasitic resistance (in Ohm level) and parasitic capacitance (in pF level.) In the THz band, such parasitics are no longer negligible due to their role in generating significant impedance mismatch and dramatic drop in both insertion loss and isolation. This thesis proposes a silicon substrate based RF-MEMS switch design that could realize high performance (insertion loss smaller than 2.7 dB and isolation better than 17 dB) up to 750 GHz. In addition, to make this technique compatible with more substrates and fabrication processes, while maintaining high performance and reliability, a quartz based RF MEMS switch is also proposed.
To apply the advanced MEMS switch performance in commercial electronics, an idea to integrate a high frequency RF-MEMS design with CMOS fabrication process is proposed in order to realize a future RF MEMS switch that is more compatible with conventional electronic devices and costs less.
In addition to the RF MEMS switch, efforts have been made to realize RF signal detection circuits at THz frequencies by combining coplanar waveguide structure and graphene. In this way, a wide band THz detector could be realized and be very compatible with other surface micro-machined THz circuits.
These investigations will provide solutions for development in aspects of THz switching and detection. Based upon these solutions, higher performance and more reliable THz frequency control circuits could be realized, and ultimately benefit the whole communication industry.