Integrated diode circuits for greater than 1 THz

by Schoenthal, Gerhard Siegbert.

The terahertz frequency band, spanning from roughly 100 GHz to 10 THz, forms the transition from electronics to photonics. This band is often referred to as the “terahertz technology gap” because it lacks typical microwave and optical components. The deficit of terahertz devices makes it difficult to conduct important scientific measurements that are exclusive to this band in fields such as radio astronomy and chemical spectroscopy. In addition, a number of scientific, military and commercial applications will become more practical when a suitable terahertz technology is developed. UVa’s Applied Electrophysics Laboratory has extended non-linear microwave diode technology into the terahertz region. Initial success was achieved with whiskercontacted diodes and then discrete planar Schottky diodes soldered onto quartz circuits. Work at UVa and the Jet Propulsion Laboratory succeeded in integrating this diode technology onto low dielectric substrates, thereby producing more practical components with greater yield and improved performance. However, the development of circuit integration technologies for greater than 1 THz and the development of broadly tunable sources of terahertz power remain as major research goals. Meeting these critical needs is the primary motivation for this research. To achieve this goal and demonstrate a useful prototype for one of our sponsors, this research project has focused on the development of a Sideband Generator at 1.6 THz. This component allows use of a fixed narrow band source as a tunable power source for terahertz spectroscopy and compact range radar. To prove the new fabrication and circuit v technologies, initial devices were fabricated and tested at 200 and 600 GHz. These circuits included non–ohmic cathodes, air-bridged fingers, oxideless anode formation, and improved quartz integration processes. The excellent performance of these components validated these new concepts. The prototype process was then further optimized to produce a substantially increased yield and to maintain excellent performance at 1.6 THz. The successful fabrication of integrated 1.6 THz SBG circuits establishes the viability of the new processes for terahertz applications. Additionally, this new technology can also be applied to other components, such as mixers, multipliers, and direct detectors thereby helping to close the terahertz technology gap. vi