Terahertz Monolithic Integrated Circuit Research Articles

Systematic Study and Review of InP‐based Tera‐Hertz‐ICs Fabrication Process Technology for Beyond 5G/6G Wireless Communication Networks

Next‐generation “Beyond 5G (B5G)/6G” wireless network systems have been researched and developed for meeting the rapid growth of mobile traffic. A high‐yield fabrication process of InP‐based transistors and tera‐hertz monolithic integrated circuits with 300 GHz operation is reported, which is a candidate frequency for “Beyond 5G/6G” network systems. The main focus is on a high‐yield and reproductive fabrication process of InP‐based high electron mobility transistors (HEMTs) while revisiting previous studies. The DC and radio frequency characteristics of fabricated InP‐HEMTs from the viewpoint of integrating circuits are described. Then, high‐frequency performances of ft = 280 GHz and fmax = 860 GHz in the bias conditions of Vgs/Vds = 0.2/1.1 V with good uniformity are obtained. Finally, InP‐based 300 GHz‐band mixer and power amplifiers are introduced, to which a backside process is also applied for ensuring their stability and enhancing output power.

(Invited) III-V Integration on Silicon for Resource-Efficient Sensor-Technology

This work deals with the wafer-level integration of advanced group III-V devices and integrated circuits on silicon substrate for RF-sensor integration, such as radar functions a very high frequencies beyond 300 GHz [1]. The aim is to achieve both performance improvements on device level, co-integration with digital functions, and advanced integration to achieve a greener usage of material critical to the environment. Submillimeter-Wave frequency bands beyond 300 GHz allow for broadband transmit and receive windows, serviceable to both communications and radar-based applications—increasing data rates and imaging resolutions, respectively. On the other hand, CMOS co-integration is called for by the data acquisition- and other mixed-mode- and fast digital functions. As examples of the integration schemes Terahertz Monolithic Integrated Circuit amplifiers (TMICs) are implemented in an advanced transferred-substrate InGaAs-channel HEMT technology with 20-nm gate length on silicon. The inverted III-V HEMT heterostructure is grown by molecular beam epitaxy (MBE) on 100-mm semi-isolating GaAs wafers and transferred to silicon substrates by using a SiO2-based wafer bond process with subsequent wafer thinning and removal of the GaAs substrate. Thus, only a 100-nm-thick III-V heterostructure layer is remaining on the Si substrate. This advanced transferred-substrate technology also offers the implementation of HEMT devices with backside gate [2,3] to achieve better sub-threshold slope, or field plates to increase both channel confinement and higher breakdown voltages. The 20-nm InGaAs-OI HEMT technology features typical values for the OFF-state breakdown voltage of 5 V and and maximum drain-current density of 1200 mA/mm, respectively. A maximum transconductance of 2400 mS/mm is achieved. The expected cutoff frequency values fT and fmax are above 500 GHz and 1 THz, respectively [4]. A fully passivated back-end-of-line (BEOL) process is used, including three metal layers (MET1–MET3). A NiCr 50 Ohm sq thin-film-resistor layer, as well as an SiN layer for the implementation of MIM capacitors between MET2 andMET3. S-parameter characteristics of a six-stage and nine-stage TMIC amplifiers in the frequency band from 620 to 730 GHz are given as examples. During the on-wafer characterization, the HEMT devices in cascode configuration have been biased at VD= 2 V (1 V drain–source voltage per device) and a current of 350 mA/mm. The measured small-signal gain of the six-stage cascode TMIC amplifier is in the range of 22–25 dB over the frequency range from 670 to above 700 GHz. This corresponds to 4 dB of gain per cascode stage around the 670-GHz frequency range. A nine-stage TMIC amplifier, on the other hand, achieves at least 30 dB of measured gain from 660 to about 700 GHz. This again corresponds to a gain per stage below 4 dB. Such results prove both the advancements in integration as well as state-of-the-art circuit performance co-integrated on silicon.

High-Efficiency GaN/SiC Doubler Terahertz Monolithic Integrated Circuit at 175 GHz

A high-power, high-efficiency, 175 GHz frequency doubler terahertz monolithic integrated circuit (TMIC) in continuous wave (CW) mode has been fabricated using planar gallium nitride (GaN) Schottky barrier diodes (SBDs) on a SiC substrate. Heat dissipation is improved by adopting a high thermal conductivity SiC substrate. At room temperature, the GaN doubler has an output power exceeding 110 mW at 164 GHz to 181 GHz with an efficiency of 11 % to 20.6 % in CW mode. A 242 mW maximum output power with 20.2 % efficiency is obtained at 175 GHz. The results imply that a GaN-based monolithic integrated frequency doubler provides a viable means of obtaining high output power and high efficiency in CW mode.

Terahertz monolithic integrated narrow-band filter based on the silicon carbide substrate

This paper presented a narrow-band terahertz integrated cavity filter based on the silicon carbide (SiC) substrate. By introducing two metalized via-holes in a rectangular integrated cavity, an integrated coupling cavity was built, on the one hand, to operate as a coupling structure; on the other hand, to control the direct coupling between input and output feeding lines, further to control the frequency of the transmission zero. This novel approach was thoroughly investigated with attention paid to the position of the via-holes. Based on this approach, a terahertz narrow-band filter was realized on the semi-insulating SiC substrate, demonstrated good filtering performance, especially the stopband rejection characteristic, and established the groundwork for the production of the terahertz monolithic integrated circuit.

Collector Series-Resistor to Stabilize a Broadband 400 GHz Common-Base Amplifier

The indium phosphide (InP) 130 nm double-heterojunction bipolar transistor (DHBT) offers milliwatts of output power and high signal amplification in the lower end of the terahertz frequency band when the transistor is used in a common-base configuration. Instrumentation can directly benefit from this technology by enabling the development of novel broadband sources or synthesizers that rely on our ability to amplify the signal over enormous bandwidths. However, the design of high gain and stable amplifiers presents many obstacles and limitations as we increase the bandwidth and the carrier frequency. Here, we show that adding a series resistor at the collector terminal of the common-base transistor prevents instabilities in the terahertz monolithic integrated circuit amplifier and increases its fractional bandwidth. Adopting this technique, we report a state-of-the-art broadband common-base amplifier that exhibits a minimum small-signal gain of 18.9 dB from 325 to 477 GHz. This amplifier presents the highest fractional bandwidth and gain above 300 GHz. Our work demonstrates the feasibility of high-performance amplifiers that address the need of future terahertz electronic systems.

Terahertz Monolithic Integrated Cavity Filter Based on Cyclic Etched SiC Via-Holes

This article presents a terahertz integrated cavity bandpass filter based on cyclic etched silicon carbon (SiC) via-holes. Solutions are discussed in detail, including design, fabrication, and optimization. The fabrication procedures of the integrated filters are specially optimized, which are fully compatible with that of the common terahertz monolithic integrated circuit. The cyclic via-hole etching technique based on inductively coupled plasma (ICP) is proposed, which achieves via-holes with a controllable inclination on SiC substrate. Measurements show that the insertion loss of the cavity integrated filter is only 1.55 dB at 185 GHz, with a relative bandwidth of 9.7%. Two transmission zeros are introduced by the over-moded technique, achieving the out-of-band suppression of the filter higher than 40 dB. Compared with the traditional terahertz cavity filters, the integrated cavity on SiC substrate provides similar electric performances and better integration but with the one-thousandth of the volume.

Integrated Dipole Antenna With Bandwidth Enhancement for Terahertz Waveguide-to-CPWG Transition

In this letter, a broadband waveguide-to-coplanar waveguide with ground transition for large-chip-width substrate operating within terahertz frequencies is demonstrated. This transition adopts an integrated dipole antenna with coupling branches and disks topology. This compact transition reduces parasitic effects by wire bonding and is suitable for direct integration with terahertz monolithic integrated circuits, and it enables low energy conversion loss over a wide frequency band. The transition was fabricated on a 970 μm wide substrate by the 50 μm thick InP technology and designed for WR-4.3 standard waveguide (546 μm width). The measured results show that the bandwidth with 1 dB insertion loss per antenna is as wide as 80 GHz, and the in-band return loss is better than 10 dB.

Optimization of terahertz monolithic integrated frequency multiplier based on trap-assisted physics model of THz Schottky barrier varactor

The optimization of high power terahertz monolithic integrated circuit (TMIC) is systemically studied based on the physical model of the Schottky barrier varactor (SBV) with interface defects and tunneling effect. An ultra-thin dielectric layer is added to describe the extra tunneling effect and the damping of thermionic emission current induced by the interface defects. Power consumption of the dielectric layer results in the decrease of capacitance modulation ration (Cmax/Cmin), and thus leads to poor nonlinear C–V characteristics. The proposed Schottky metal-brim (SMB) terminal structure could improve the capacitance modulation ration by reducing the influence of the interface charge and eliminating the fringing capacitance effect. Finally, a 215 GHz tripler TMIC is fabricated based on the SMB terminal structure. The output power is above 5 mW at 210–218 GHz and the maximum could exceed 10 mW at 216 GHz, which could be widely used in terahertz imaging, radiometers, and so on. This paper also provides theoretical support for the SMB structure to optimize the TMIC performance.

GaAs metamorphic high electron mobility transistors for future deep space-biomedical-millitary and communication system applications: A review

Following the introduction of metamorphic high electron mobility transistors (MHEMTs) 30 years back, there has been a rapid growth in their use in advanced MMIC (monolithic microwave integrated circuit) and TMIC (Terahertz monolithic integrated circuit) applications in sub-millimetre wave (S-MMW) and terahertz (THz) frequency regime. Undoubtedly, they are capable of making a great impact in applications such as deep space, cryogenic, biomedical instrumentation, military, high speed communication networks etc, in the years to come. This review article not only studies the progress of depletion mode (D-Mode), enhancement mode (E-Mode) type MHEMTs in the last 30 years, extensively but also critically and systematically analyzes the fabrication challenges, reliability issues and their use in cryogenic fields. Yet another highlight is that the work also carefully examines the utility of MHEMTs in deep space, biomedical, scientific, military, communication areas and so forth.

180 to 240 GHz broadband, EM‐based power amplifier using 0.5‐μm InP DHBT technology

AbstractThis paper reports a power amplifier (PA) terahertz monolithic integrated circuit (TMIC) from 180 to 240 GHz. This amplifier is fabricated from a 0.5‐μm indium phosphide double heterojunction bipolar transistor (InP DHBT) technology, jointly with a thin‐film microstrip wiring environment. Furthermore, an electromagnetic (EM) simulation method is proposed for the parameter extraction of InP DHBTs and amplifier design. This five‐stage amplifier has >6.1 dB S21 gain from 180 to 240 GHz, peaks 10.4 dB S21 gain at 210 GHz. At 213 GHz operation, the saturated output power is 5.8 dBm with 7.3 dB large‐signal gain, and this amplifier occupies 2.52 mm2 including pads.

A 220-GHz InP DHBT Power Amplifier With Integrated Planar Spatial Power Combiner

In this letter, we present a research on the application possibility of the integrated planar spatial (IPS) combiner in terahertz monolithic integrated circuits (TMICs). The IPS combiner has several attractive characters, such as low loss and good port-to-port isolation. Measured insertion loss of the back-to-back four-way IPS combiner prototype is less than 1.65 dB from 220 to 260 GHz. Then, the IPS power combiner is applied to a four-way six-stage common-emitter InP double heterojunction bipolar transistor amplifier based on a 0.5- $\mu \text{m}$ process. With the help of the IPS combiner and the compact circuit design, this letter greatly improves the output power and output power density compared with other TMICs of the same InP HBT technology. The output power density per unit emitter length (output stage) is 0.51 mW/ $\mu $ m, which is at the same level of amplifiers based on the 0.25- $\mu \text{m}$ InP HBT technology.

Transferred-Substrate InP/GaAsSb Heterojunction Bipolar Transistor Technology With <inline-formula> <tex-math notation="LaTeX">${f}_{\text{max}}$ </tex-math> </inline-formula> ~ 0.53 THz

We report on the realization mymargin of transferred-substrate InP/GaAsSb double heterostructure bipolar transistors in a terahertz monolithic integrated circuit process. Transistors with 0.4- $\mu \text{m}$ -wide single emitters reached unilateral gain cutoff frequencies of around 530 GHz with simultaneous current gain cutoff frequencies above 350 GHz. Extrinsic collector capacitance is effectively reduced in the transfer-substrate process. In combination with the high collector breakdown voltage in the InP/GaAsSb heterobipolar transistor structure of 5 V, this process is amenable to analog power applications at millimeter (mm-wave) and sub-mm-wave frequencies. We demonstrate reliable extraction procedures for unilateral gain and current gain cutoff frequencies.

Substrate Integrated Waveguide Structural Transmission Line and Filter on Silicon Carbide Substrate

Substrate integrated waveguide (SIW) structural transmission line (TL) and filter are designed and fabricated on semi-insulating silicon carbide (SiC) substrates for operation at the low end of $H$ -band. The via-holes as the sidewall of SIW are achieved by using a fine dry-etching technique, where the radius and the via–via distance of the via-hole row are determined according to the transmission characteristics and the fabrication process. Measurements show that SIW-based TLs have the attenuation constant of as low as 0.45 dB/mm at 220 GHz, a third of that for TLs on grounded coplanar waveguide, and SIW-structural filters have the minimum insertion loss of <1 dB at the center frequency of 183 GHz with a bandwidth of 5.3 %. It illustrates the availability of passive device fabrications on SiC substrate, and paves the way for the forthcoming terahertz monolithic integrated circuits based on wide bandgap semiconductors.

InP HBT Technologies for THz Integrated Circuits

Highly scaled indium phosphide (InP) heterojunction bipolar transistor (HBT) technologies have been demonstrated with maximum frequencies of oscillation ( $f_{\max}$ ) of >1 THz and circuit operation has been extended into the lower end of the terahertz (THz) frequency band. InP HBTs offer high radio-frequency (RF) output power density, millivolt (mV) threshold uniformity, and high levels of integration. Integration with multilevel thin-film wiring permits the realization of compact and complex THz monolithic integrated circuits (TMICs). Circuit results reported from InP HBT technologies include: 200-mW power amplifiers at 210 GHz, 670-GHz amplifiers and fundamental oscillators, and fully integrated 600-GHz transmitter circuits. We review the state of the art in THz-capable InP HBT devices and integrated circuit (IC) technologies. Challenges in extending transistor bandwidth and in circuit design at THz frequencies will also be addressed.

A G-band terahertz monolithic integrated amplifier in 0.5-μm InP double heterojunction bipolar transistor technology**Project supported by the National Natural Science Foundation of China (Grant No. 61501091) and the Fundamental Research Funds for the Central Universities of Ministry of Education of China (Grant Nos. ZYGX2014J003 and ZYGX2013J020).

Design and characterization of a G-band (140–220 GHz) terahertz monolithic integrated circuit (TMIC) amplifier in eight-stage common-emitter topology are performed based on the 0.5-μm InGaAs/InP double heterojunction bipolar transistor (DHBT). An inverted microstrip line is implemented to avoid a parasitic mode between the ground plane and the InP substrate. The on-wafer measurement results show that peak gains are 20 dB at 140 GHz and more than 15-dB gain at 140–190 GHz respectively. The saturation output powers are −2.688 dBm at 210 GHz and −2.88 dBm at 220 GHz, respectively. It is the first report on an amplifier operating at the G-band based on 0.5-μm InP DHBT technology. Compared with the hybrid integrated circuit of vacuum electronic devices, the monolithic integrated circuit has the advantage of reliability and consistency. This TMIC demonstrates the feasibility of the 0.5-μm InGaAs/InP DHBT amplifier in G-band frequencies applications.

First Demonstration of Amplification at 1 THz Using 25-nm InP High Electron Mobility Transistor Process

We report the first ever terahertz monolithic integrated circuit amplifier based on 25-nm InP high electron mobility transistor (HEMT) process demonstrating amplification at 1 THz (1000 GHz) with 9-dB measured gain at 1 THz. This milestone was achieved with a 25-nm InP HEMT transistor, which exhibits 3.5-dB maximum available gain at 1 and 1.5 THz projected $f_{\mathrm {\mathbf {MAX}}}$ .

Power Amplification at 0.65 THz Using InP HEMTs

In this paper, progress toward developing solid-state power-amplifier modules at 0.65 THz is reported. This work is enabled by a >;1 THz fMAX InP HEMT transistor with a 30-nm gate and an integrated circuit process specifically tailored for circuits operating at frequencies approaching 1 THz. The building block of the reported amplifier modules is an eight-stage terahertz monolithic integrated circuit (TMIC) amplifier. The first six stages of the TMIC use 20- transistors, while the final two output stages rely on two power-combined 20-μm transistors to increase the output power. For operation at 0.65 THz, the TMIC also relies on integrated electromagnetic transitions for direct coupling with the WR1.5 waveguide of the amplifier package. Two modules are reported, with the first module containing a single TMIC and demonstrating a peak saturated output power of 1.7 mW at 640 GHz with a measured small-signal gain ≥10 dB from 629 to 638 GHz. The second module features two power-combined TMICs to increase output power. This is done using a waveguide Y-junction as both the combiner and splitter. In test, this power-combined module reached a peak output power of 3 mW at 650 GHz and measured small-signal gain ≥10 dB from 625 to 640 GHz.

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Following the introduction of metamorphic high electron mobility transistors (MHEMTs) 30 years back, there has been a rapid growth in their use in advanced MMIC (monolithic microwave integrated circuit) and TMIC (Terahertz monolithic integrated circuit) applications in sub-millimetre wave (S-MMW) and terahertz (THz) frequency regime. Undoubtedly, they are capable of making a great impact in applications such as deep space, cryogenic, biomedical instrumentation, military, high speed communication networks etc, in the years to come. This review article not only studies the progress of depletion mode (D-Mode), enhancement mode (E-Mode) type MHEMTs in the last 30 years, extensively but also critically and systematically analyzes the fabrication challenges, reliability issues and their use in cryogenic fields. Yet another highlight is that the work also carefully examines the utility of MHEMTs in deep space, biomedical, scientific, military, communication areas and so forth.