Over the last few years, the development of transistor technologies with maximum frequency of oscillation, fMAX, beyond 1 THz has driven amplifier operating frequencies into the sub-millimeter-wave range. Work in the 460-to-500-GHz range, for example, recently centered on a high-electron-mobility-transistor (HEMT) amplifier with 11.4-dB packaged gain, a noise figure of 11.7 dB, and a 16.1-dB gain amplifier measured on-wafer at 460 GHz. An examination of the different facets that enable such performance was recently conducted by Northrop Grumman Corp.'s William Deal, X.B. Mei, Kevin M.K.H. Leong, Vesna Radisic, S. Sarkozy, and Richard Lai.
The researchers focus specifically on terahertz monolithic integrated circuits using indium-phosphide (InP) HEMT. They conclude that three-terminal transistors are becoming viable circuit technology at frequencies approaching 1 THz for low-noise amplification, power amplification, and frequency conversion. Thanks to the HEMT process, all of these functions can be integrated as multiple functions on a single chip. See "THz Monolithic Integrated Circuits Using InP High Electron Mobility Transistors," IEEE Transactions On Terahertz Science And Technology, Sept. 2011, p. 25.