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

Laurenz John,Hermann Massler,Axel Tessmann,Arnulf Leuther

doi:10.1109/tthz.2021.3136335

Abstract

This article reports 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 (HEMT) technology. Till 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 terahertz 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.

Highlights

O VER the last decade, III-V high-electron-mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) technologies have demonstrated active devices with power-gain cutoff frequencies exceeding 1 THz [1]–[3]
While a low noise figure is crucial for such applications, the main focus of this work is on design considerations that enable high levels of gain with THz monolithic integrated circuits (TMICs) based on metamorphic high-electron-mobility transistor (mHEMT) devices in cascode configuration
Prior to the work described in this article, only amplifier topologies based on CS devices have been reported in HEMT technologies at frequencies above 560 GHz

Summary

INTRODUCTION

O VER the last decade, III-V high-electron-mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) technologies have demonstrated active devices with power-gain cutoff frequencies (fmax) exceeding 1 THz [1]–[3]. In the frequency bands above 460 GHz, only CS based mHEMT TMICs have been implemented up to date These CS circuits have demonstrated gain with mHEMT devices at circuit level up the frequency range above 800 GHz in [9]. While a low noise figure is crucial for such applications, the main focus of this work is on design considerations that enable high levels of gain with TMICs based on mHEMT devices in cascode configuration. To this end, the benefits and limitations of the cascode configuration at THz frequencies above 500 GHz are discussed. A detailed description of the BEOL and possible layer sequences for thin-film wiring—including the corresponding transmission-line characteristics—are given in [12]

EVALUATION OF DEVICE CONFIGURATIONS

Cascode Design Considerations

CASCODE TMIC DESIGN—FIRST DESIGN CYCLE

Ω 100 Ω

CASCODE TMIC DESIGN—SECOND DESIGN CYCLE

DISCUSSION AND CONCLUSION