670-GHz Cascode Circuits Based on InGaAs Metamorphic High-Electron-Mobility Transistors

Abstract

This article reports on the development of high-gain cascode amplifier circuits in the frequency range around 670 GHz. The cascode circuits are based on a 35-nm metamorphic high-electron-mobility transistor (mHEMT) technology. Up to date, only common-source transistors have been used in HEMT-based amplifier circuits above 600 GHz. For this reason, prospects and design considerations of cascode devices operating at this THz frequency band are evaluated. The design and implementation of high-gain six-stage cascode amplifier circuits is described, achieving up to 30 dB of measured gain at 670 GHz and a small-signal gain of at least 25 dB over the frequency range from 630 to 690 GHz. The gain benefit of cascode devices is demonstrated with up to 5 dB of gain per cascode stage at 670 GHz. This corresponds to the highest reported gain per stage for HEMT-based WR-1.5 circuits.

High-Gain 670-GHz Amplifier Circuits in InGaAs-on-Insulator HEMT Technology

“…Table I, furthermore, shows a comparison of high-gain TMIC amplifier results around 670 GHz, based on different III-V transistor technologies. In comparison to similar 670-GHz cascode circuits in our standard 35-nm mHEMT technology [9], which is processed on GaAs substrate, less amplification per cascode stage is achieved. Thus, with NF values around 11 dB, the simulated noise figure is slightly above the 35-nm mHEMT simulation results reported in [9].…”

“…In comparison to similar 670-GHz cascode circuits in our standard 35-nm mHEMT technology [9], which is processed on GaAs substrate, less amplification per cascode stage is achieved. Thus, with NF values around 11 dB, the simulated noise figure is slightly above the 35-nm mHEMT simulation results reported in [9]. However, with gain levels in excess of 30 dB, state-of-the-art small-signal gain is achieved in this frequency range.…”

“…The chip photographs of two TMIC amplifiers with six and nine gain stages-which have been designed for the frequency range around 670 GHz, based on the design considerations discussed in [9]-are depicted in Figs. 2 and 3, respectively.…”

“…4 Besides the different transistor-finger width and number of stages, the main difference between the two TMIC amplifiers is the length of the TFMSL interconnection, which is connecting the CS and CG transistors in the cascode configuration. The length-or series inductance L MSL -of this transmission line, significantly the maximum achievable (stable) gain of the cascode configuration at sub-mmwave frequencies, as discussed for the THz cascode devices in [9] and [10]. To compensate the de-tuning of the respective source and load impedances between the CS and CG devices with increasing frequency, a transmission line with a length of at least 20 μm is required at 670 GHz.…”