Circuit techniques for plasma wave FET based integrated terahertz receivers

Abstract

The mostly under-utilized spectrum in the mm-wave and THz frequency ranges is expected to enable disruptive applications in extreme wide bandwidth (XWB) communications, imaging and spectroscopy. With the ongoing scaling of device channel size and consequently device fT/fmax, nanoscale technologies enable the integration of transceiver systems at such frequency range. However, the challenge remains in realizing circuit blocks operating far above the unity gain frequency (fT) with acceptable conversion gain and noise performance. Unlike traditional detection/receiver architectures based on frequency down-converters, plasma-wave THz detection is limited by the technology’s fT and thus, can be considered a low power, low form factor, and fully integrable alternative to conventional receiver architectures. This thesis presents the design considerations, analysis, and measurement results for plasma wave field effect transistor (FET) based THz detection systems.

The fabricated systems are characterized for narrow and wide band THz detection. In CMOS technology, the E-shaped patch antenna coupled FET, achieves 2X better responsivity than the stacked half wave coupled system; with a 1.5X bigger aperture area. With on-chip amplification and under open drain bias mode, the responsivity is measured as 10 and 4 V/W for E-shaped and half wave coupled system; while maintaining a minimum signal to noise ratio of 40 dB over a 3 dB bandwidth of 10 GHz. In the current driven mode, the response increases to 100 and 20 V/W with a corresponding decrease in bandwidth to 3.5 GHz due to the increased channel resistance of the detector. In general, the HEMT detectors in InGaAs/GaAs technology achieve better responsivity than the Si FETs. The absolute responsivity of the patch, dipole and bow-tie antenna coupled HEMT detector is measured as 15, 30, and 30 V/W respectively at the open drain mode. Effect of substrate thinning and external lens has also been characterized and the results show ∼ 13X improvement. An wide band on chip amplifier is also included with the dipole and patch antenna coupled detectors for high modulation frequency characterization. The detection systemachieve ∼ 3 V/W responsivity in the open drain mode with a detection bandwidth of 8 GHz. The results presented in this thesis show the great promise of low cost and small size modules integrated in standard semiconductor technologies for applications in imaging and wide band communications at THz frequency range.

The basic system architecture of a plasma wave FET based THz detection system consists of an on chip antenna, a FET detector, and a base band amplifier. The design analysis and simulation results of several on chip antennas (E-shaped patch, stacked E-shaped patch, stacked half wave patch, rectangular patch, dipole and bow-tie) in CMOS and GaAs technologies are presented. Wide band amplifiers employing inductive peaking and active feedback techniques are designed in 130 nm CMOS and GaAs technology.