A 220–300 GHz Twin-FET Detector for Rotational Spectroscopy of Gas Mixtures

In this paper, a twin-FET (field effect transistor) THz detector monolithically integrated with a dual-feed antenna is presented. The antenna-detector configuration can be extended for 'N' FET elements to relax the input impedance requirement for the detector readout circuitry while maintaining good responsivity. A dual-feed octagonal slot antenna is used to couple THz radiation and provide differential excitation to the twin-FET detector. The multi-feed antenna-FET detector interface can be designed for an arbitrary phase excitation of one or more FET elements. Fabricated in Global Foundries 22nm FD-SOI process, the proposed detector covers a measured frequency range from 220 GHz to 300 GHz. Such bandwidth is sufficiently wide to capture reliable spectral information for distinguishing a number of gases in a mixture. The absorption spectra of pure methanol, chloromethane and acetonitrile are measured using a rotational spectroscopy setup incorporating the twin-FET detector. Detection of a small concentration of acetonitrile, at 4 Torr pressure, is demonstrated in a binary mixture with predominantly chloromethane. Detection of ethanol and methanol in their binary mixture is also demonstrated at 4 Torr pressure. This is a significant step towards the development of all-electronic THz spectroscopy for the detection of volatile organic compounds (VOCs) in the presence of contaminants with a strong THz absorption signature at >1 Torr pressure.