Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

The 2016 terahertz science and technology roadmap

This article presents a compact 150-GHz transmitter with 12-dBm $P_{\mathrm{ sat}}$ and 17-dB conversion gain. This $D$ -band transmitter is composed of a frequency doubler, a micromixer, a two-stage $g_{m}$ -boosting power amplifier (PA), and an on-chip dielectric resonate (DR) antenna. At sub-terahertz, the output power and the gain are the limiting factors for the transmitter’s performance. In this work, $g_{m}$ -boosting topology is implemented to achieve the 17-dB gain by taking advantage of the base inductor without sacrificing the PA’s stability. The output power of the 150-GHz PA is enhanced by the proposed phase compensation method. In this proposed method, an auxiliary inductor is added for adjusting the phase difference to decrease the introduced loss from power combining and matching networks. The imbalance at the LO port is also reduced by the proposed capacitor and the resistor compensation method. From 140 to 160 GHz, the transmitter delivers more than 8-dBm output power, with the maximum $P_{\mathrm{ sat}}$ of 12 dBm at 148 GHz. This transmitter exhibits a conversion gain of 17 dB and an output 1-dB compression point ( ${\mathrm{ OP}}_{1~{\mathrm{ dB}}}$ ) of 11.4 dBm. The transmitter exhibits the highest output power, the highest ${\mathrm{ OP}}_{1~{\mathrm{ dB}}}$ , competitive conversion gain, and bandwidth among any silicon-based transmitters in $D$ -band, to the best of our knowledge.

A 150-GHz Transmitter With 12-dBm Peak Output Power Using 130-nm SiGe:C BiCMOS Process

This article presents an ultra-low-power silicon germanium heterojunction bipolar transistor (SiGe HBT) amplifier operating at 200 GHz. The amplifier consists of three cascaded gain-cell stages and was implemented in an experimental 130-nm SiGe HBT technology with peak $f_{{\textrm {T}}}/f_{\text {max}}$ of 460/600 GHz. In order to achieve the demonstrated extremely low dc power dissipation, the circuit was designed with transistors operating at forward-biased base–collector junction voltage ( $V_{\text {BC}}$ ). With 1.3-V supply voltage ( $V_{\text {BC}}\approx 0.2$ V), this amplifier exhibits a peak gain of 23.5 dB at 180 and 205 GHz with 34-GHz 3-dB bandwidth (BW) from 173 to 207 GHz, consuming 3.2-mW static dc power. Even with a supply voltage of 0.7 V ( $V_{\text {BC}} \approx 0.5$ V), this amplifier still operates with a peak gain of 18.3 dB at 175 GHz, dissipating an extremely low dc power of 1.73 mW. Compared with the previously reported low-power amplifiers operating around 200 GHz, this article achieves the highest linear gain relative to the dc power consumption with an improvement factor of ten, as well as highly competitive performances in terms of noise figure and 3-dB BW.

3.2-mW Ultra-Low-Power 173–207-GHz Amplifier With 130-nm SiGe HBTs Operating in Saturation

This letter presents a 230-GHz high-gain amplifier implemented in a 0.13- $\mu \text{m}$ SiGe BiCMOS technology. The amplifier consists of a single-ended cascode (CC) stage for noise optimization and two differential CC stages for power capacity consideration. A symmetrical peripheral interconnection with self-shielded bypass capacitors for gm-boosting technique realization is employed to overcome the low inherent gain. The noise components of CC transistors are investigated and a parallel-inductor-based noise reduction technique is adopted to improve the noise figure (NF). The proposed amplifier provides a measured gain of 21.8-dB at 232 GHz with a 3-dB bandwidth of 35 GHz and a simulated NF of 10.5 dB at 230 GHz. The measured output power and maximum power-added efficiency (PAE) at 225 GHz is 3.5 dBm and 2.9%, respectively. The amplifier occupies a small area of 0.154 mm2 and consumes a moderate power of 66 mW. Remarkable performances including gain, NF, bandwidth, and output power enable the amplifier to be adopted as either a low noise amplifier (LNA) or a driver amplifier in the sub-terahertz (sub-THz) receivers.

A 230-GHz SiGe Amplifier With 21.8-dB Gain and 3-dBm Output Power for Sub-THz Receivers

A 220-GHz power amplifier (PA) with high gain, high output power, and high efficiency for a 220-GHz transceiver system is presented in this letter. At terahertz (THz) and sub-terahertz (sub-THz) bands, the maximum available gain/maximum stable gain (MAG/MSG) of the device degrades rapidly, which increases the difficulty of high-gain and high-efficiency PA design. In this letter, the gm-boosting technique is analyzed and used in differential cascode (CC) topology to boost the gain of the single stage. Metal–oxide–metal (MOM) capacitors are used to reduce the insertion losses of the matching networks, therefore enhancing the gain and efficiency. The proposed PA exhibits a measured gain of 22.5 dB at 225 GHz with a 3-dB bandwidth of 35 GHz from 204 to 239 GHz. The measured OP1dB of 6.0 dBm and the peak power added efficiency (PAE) of 2.96% are achieved at 215 GHz. The measured $P_{\mathrm {sat}}$ is larger than 9 dBm from 200 to 216 GHz. The PA occupies a small area of 0.162 mm2 with a compact core area of 0.069 mm2. The power consumption of the chip is 245 mW. From the aspect of overall performances, including gain, output power, efficiency, and chip area, this work exhibits one of the best performances in silicon-based PAs at sub-THz bands. Besides, to the best of our knowledge, the proposed PA exhibits the highest efficiency in silicon-based implementations beyond 210 GHz.

A 220-GHz Power Amplifier With 22.5-dB Gain and 9-dBm P sat in 130-nm SiGe

This letter presents a 97-GHz downconversion mixer in a 130-nm SiGe HBT technology. For achieving the demonstrated ultralow dc power consumption, the mixer was designed with transistors operating in saturation using an accurate compact model. With 0.7-V supply voltage and −5-dBm local oscillator pumping power, this mixer achieves a double-sideband conversion gain (CG) of 6.6 ± 3 dB over the RF frequency range from 91 to 100 GHz, consuming 12-mW static dc power. With the supply voltage further reduced to 0.5 V, this mixer still works with a maximum upper-sideband CG of 5.2 dB from 94 to 100 GHz, with only 8-mW static power consumption.

12-mW 97-GHz Low-Power Downconversion Mixer With 0.7-V Supply Voltage

A 190-GHz mixer-based down-conversion receiver realized in a 130-nm SiGe BiCMOS technology featuring high-speed heterojunction bipolar transistors (HBTs) with ( $f_{\text {T}}$ , $f_{\text {max}}$ ) = (300, 500) GHz is presented. The core part of the receiver consists of a low-noise amplifier (LNA), an active tunable fundamental mixer, an intermediate frequency (IF) buffer amplifier (BA), and an active inverse balun. A wideband, high conversion gain (CG) local oscillator (LO) chain is integrated to make the receiver suitable for applications requiring tunable LO, which contains a multiplier with a multiplication factor of 12 ( $\times 12$ ) and a driver amplifier. To exploit the best possible performance with ultralow dc power consumption ( $P_{\text {dc}}$ ), the mixer and LNA transistors operate at forward-biased base–collector junction voltage ( $V_{\text {BC}}$ ). With a fixed IF frequency at 1 GHz, this receiver exhibits a peak CG of 49 dB with a 14-dB tuning range and a minimum single-sideband noise figure (NF) of 16.5 dB, consuming only 29-mW static dc power for the core part and 171 mW overall, including the LO chain. Within the CG tuning range, this receiver achieves a 6-dB RF bandwidth (BW) from 25 to 32 GHz. Compared with previously reported receivers at similar frequencies, the highest CG and the lowest $P_{\text {dc}}$ with highly competitive performance in terms of BW, CG tuning range, 1-dB output compression point, and NF have been achieved.

LO Chain (×12) Integrated 190-GHz Low-Power SiGe Receiver With 49-dB Conversion Gain and 171-mW DC Power Consumption

Many different methods have been proposed in the literature for the extraction of the thermal resistance of heterojunction bipolar transistors (HBTs). This review presents a detailed evaluation and discussion of several widely used methods. Special emphasis is put on a generalized analysis of the underlying assumptions, suitable operating point range, and necessary measurement effort of each method. The accuracy of each method is determined by applying it to data based on circuit simulations of advanced SiGe and III-V HBT technologies. Experimental data from those technologies are used to highlight practical issues. A guideline for the selection of the most suitable method in practice is also given.

Methods for Extracting the Temperature- and Power-Dependent Thermal Resistance for SiGe and III-V HBTs From DC Measurements: A Review and Comparison Across Technologies

The temperature dependence of series resistance components in SiGe:C HBTs was measured from 4.3 to 423 K. A physics-based description as well as various widely used analytical formulations for modeling the temperature dependence of sheet and contact resistances were compared with the measured data. The standard two-parameter power law model only covers a limited temperature range, while three-parameter models exhibit good accuracy over the entire measured temperature range, and a four-parameter physics-based model shows excellent accuracy. This is the first demonstration for modeling the various sheet resistances from 4.3 to 423 K.

Xiaodi Jin

Papers

3.2-mW Ultra-Low-Power 173–207-GHz Amplifier With 130-nm SiGe HBTs Operating in Saturation

12-mW 97-GHz Low-Power Downconversion Mixer With 0.7-V Supply Voltage

LO Chain (×12) Integrated 190-GHz Low-Power SiGe Receiver With 49-dB Conversion Gain and 171-mW DC Power Consumption

Methods for Extracting the Temperature- and Power-Dependent Thermal Resistance for SiGe and III-V HBTs From DC Measurements: A Review and Comparison Across Technologies

Modeling the temperature dependence of sheet and contact resistances in SiGe:C HBTs from 4.3 to 423 K