http://www.acsu.buffalo.edu/~jmjornet/papers/2014/j1.pdf

Full length article: Terahertz band: Next frontier for wireless communications

The field of terahertz integrated technology has undergone significant development in the past ten years. This has included work on different substrate technologies such as III–V semiconductors and silicon, work on field-effect transistor devices and heterojunction bipolar devices, and work on both fully electronic and hybrid electronic–photonic systems. While approaches in electronic and photonics can often seem distinct, techniques have blended in the terahertz frequency range and many emerging systems can be classified as photonics-inspired or hybrid. Here, we review the development of terahertz integrated electronic and hybrid electronic–photonic systems, examining, in particular, advances that deliver important functionalities for applications in communication, sensing and imaging. Many of the advances in integrated systems have emerged, not from improvements in single devices, but rather from new architectures that are multifunctional and reconfigurable and break the trade-offs of classical approaches to electronic system design. We thus focus on these approaches to capture the diversity of techniques and methodologies in the field. This Review Article examines the development of terahertz integrated electronic and hybrid electronic–photonic systems, considering, in particular, advances that deliver important functionalities for applications in communication, sensing and imaging.

Terahertz integrated electronic and hybrid electronic–photonic systems

A 1 k-pixel camera chip for active terahertz video recording at room-temperature has been fully integrated in a 65-nm CMOS bulk process technology. The 32 × 32 pixel array consists of 1024 differential on-chip ring antennas coupled to NMOS direct detectors operated well-beyond their cutoff frequency based on the principle of distributed resistive self-mixing. It includes row and column select and integrate-and-dump circuitry capable of capturing terahertz videos up to 500 fps. The camera chip has been packaged together with a 41.7-dBi silicon lens (measured at 856 GHz) in a 5 × 5 × 3 cm3 camera module. It is designed for continuous-wave illumination (no lock-in technique required). In this video-mode the camera operates up to 500 fps. At 856 GHz it achieves a responsivity Rv of about 115 kV/W (incl. a 5-dB VGA gain) and a total noise equivalent power (NEPtotal) of about 12 nW integrated over its 500-kHz video bandwidth. At a 5-kHz chopping frequency (non-video mode) a single pixel can provide a maximum responsivity Rv of 140 kV/W (incl. a 5-dB VGA gain) and a minimum noise equivalent power ( NEP) of 100 pW/√Hz at 856 GHz. The wide-band antenna and pixel design achieves a 3-dB bandwidth of at least 790-960 GHz.

A 1 k-Pixel Video Camera for 0.7–1.1 Terahertz Imaging Applications in 65-nm CMOS

Terahertz (THz) science and technology have greatly progressed over the past two decades to a point where the THz region of the electromagnetic spectrum is now a mature research area with many fundamental and practical applications. Furthermore, THz imaging is positioned to play a key role in many industrial applications, as THz technology is steadily shifting from university-grade instrumentation to commercial systems. In this context, the objective of this review is to discuss recent advances in THz imaging with an emphasis on the modalities that could enable real-time high-resolution imaging. To this end, we first discuss several key imaging modalities developed over the years: THz transmission, reflection, and conductivity imaging; THz pulsed imaging; THz computed tomography; and THz near-field imaging. Then, we discuss several enabling technologies for real-time THz imaging within the time-domain spectroscopy paradigm: fast optical delay lines, photoconductive antenna arrays, and electro-optic sampling with cameras. Next, we discuss the advances in THz cameras, particularly THz thermal cameras and THz field-effect transistor cameras. Finally, we overview the most recent techniques that enable fast THz imaging with single-pixel detectors: mechanical beam-steering, compressive sensing, spectral encoding, and fast Fourier optics. We believe that this critical and comprehensive review of enabling hardware, instrumentation, algorithms, and potential applications in real-time high-resolution THz imaging can serve a diverse community of fundamental and applied scientists.

Toward real-time terahertz imaging

Herein, we focus on convergent 6G communication, localization and sensing systems by identifying key technology enablers, discussing their underlying challenges, implementation issues, and recommending potential solutions. Moreover, we discuss exciting new opportunities for integrated localization and sensing applications, which will disrupt traditional design principles and revolutionize the way we live, interact with our environment, and do business. Regarding potential enabling technologies, 6G will continue to develop towards even higher frequency ranges, wider bandwidths, and massive antenna arrays. In turn, this will enable sensing solutions with very fine range, Doppler, and angular resolutions, as well as localization to cm-level degree of accuracy. Besides, new materials, device types, and reconfigurable surfaces will allow network operators to reshape and control the electromagnetic response of the environment. At the same time, machine learning and artificial intelligence will leverage the unprecedented availability of data and computing resources to tackle the biggest and hardest problems in wireless communication systems. As a result, 6G will be truly intelligent wireless systems that will provide not only ubiquitous communication but also empower high accuracy localization and high-resolution sensing services. They will become the catalyst for this revolution by bringing about a unique new set of features and service capabilities, where localization and sensing will coexist with communication, continuously sharing the available resources in time, frequency, and space. This work concludes by highlighting foundational research challenges, as well as implications and opportunities related to privacy, security, and trust.

/pdf/convergent-communication-sensing-and-localization-in-6g-h2pm0nrgkq.pdf

Convergent Communication, Sensing and Localization in 6G Systems: An Overview of Technologies, Opportunities and Challenges

Future submillimeter-wave and THz (300GHz-3THz) imaging applications will require low-cost portable systems
operating at room-temperature with a video-rate speed and capable of delivering acceptable sensitivity at the very low-power
consumption levels to become attractive for truly commercial applications. In particular, CMOS technologies are
of interest due to their high integration level offered at a high yield that is capable of massive cost reduction of currently
existing THz systems. It has been recently demonstrated that CMOS direct detectors achieve the performance
comparable or even superior to the today's existing classical THz devices for active imaging operating at room-temperature. So far, however, only single pixels have been used, allowing only a raster-scan operation. To address this
obstacle, we present the very initial work on a 1k-pixel camera chip with a completely integrated readout circuitry and
with a full video-rate capability at a power consumption of 2.5μW/pixel. The chip is fully compliant with an industrial
bulk CMOS technology and it is intended for active imaging applications. It exhibits a pixel pitch of 80μm, defined by a
novel on-chip wire ring antenna, and is designed to accommodate silicon hyper-hemispherical lens for a wide operation
bandwidth of at least 0.7-1.1 THz.

Real-time video rate imaging with a 1k-pixel THz CMOS focal plane array

This paper reports on the status of some of the research activities conducted at the University of Wuppertal that are related to the development of low-cost highly-integrated electronic detectors and sources in state-of-the-art core silicon technologies, both CMOS and SiGe HBT, for active imaging applications beyond 300 GHz.

http://ieeexplore.ieee.org/iel7/6526699/6546197/06546578.pdf

Toward room-temperature all-silicon integrated THz active imaging

This paper reports on the design of broadband lens-integrated differentially driven wire ring on-chip antennas for THz direct detectors in a state-of-the-art SiGe HBT technology. The antenna provides wideband detector operation on a high-permittivity substrate at least within the measured 650-1028 GHz, high radiation efficiency at THz frequencies on a bulk silicon substrate, layout fully compatible with silicon design rules, rotationally symmetric Gaussian radiation patterns with a -20 dB sidelobe level.

Lens-integrated on-chip antennas for THz direct detectors in SiGe HBT technology

This paper presents a 90–100 GHz heterodyne radiometer module based on a CMOS receiver system-on-chip (SoC). The SoC contains a frequency synthesizer, downconverter, RF&IF amplification, as well as a wide range of auto-leveling and calibration, and LO stabilization functions. To provide low-noise operation the CMOS SoC is packaged within a waveguide block and mated with an InP MMIC based LNA pre-amplifier. The complete module delivers noise performance below 400°K and is capable of less than 0.5K NEΔT with an integration time of 50 ms. The entire radiometer instrument consumes 257mW of power and weighs only 334 grams.

R. Al Hadi

Papers

A 1 k-Pixel Video Camera for 0.7–1.1 Terahertz Imaging Applications in 65-nm CMOS

Real-time video rate imaging with a 1k-pixel THz CMOS focal plane array

Toward room-temperature all-silicon integrated THz active imaging

Lens-integrated on-chip antennas for THz direct detectors in SiGe HBT technology

A W-Band 65nm CMOS/InP-hybrid radiometer & passive imager