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

Summary Terahertz (THz) electromagnetic spectrum ranging from 0.1THz to 10THz has become critical for sixth generation (6G) applications, such as high-speed communication, fingerprint chemical sensing, non-destructive biosensing, and bioimaging. However, the limited response of naturally existing materials THz waves has induced a gap in the electromagnetic spectrum, where a lack of THz functional devices using natural materials has occurred in this gap. Metamaterials, artificially composed structures that can engineer the electromagnetic properties to manipulate the waves, have enabled the development of many THz devices, known as “metadevices”. Besides, the tunability of THz metadevices can be achieved by tunable structures using microelectromechanical system (MEMS) technologies, as well as tunable materials including phase change materials (PCMs), electro-optical materials (EOMs), and thermo-optical materials (TOMs). Leveraging various tuning mechanisms together with metamaterials, tremendous research works have demonstrated reconfigurable functional THz devices, playing an important role to fill the THz gap toward the 6G applications. This review introduces reconfigurable metadevices from fundamental principles of metamaterial resonant system to the design mechanisms of functional THz metamaterial devices and their related applications. Moreover, we provide perspectives on the future development of THz photonic devices for state-of-the-art applications.

http://www.cell.com/article/S2589004222000694/pdf

Reconfigurable terahertz metamaterials: From fundamental principles to advanced 6G applications

The ability to sense terahertz waves in a chip-scale technology operable at room temperature has potential for transformative applications in chemical sensing, biomedical imaging, spectroscopy and security. However, terahertz sensors are typically limited in their responsivity to a narrow slice of the incident field properties including frequency, angle of incidence and polarization. Sensor fusions across these field properties can revolutionize THz sensing allowing robustness, versatility and real-time imaging. Here, we present an approach that incorporates frequency, pattern and polarization programmability into a miniaturized chip-scale THz sensor. Through direct programming of a continuous electromagnetic interface at deep subwavelength scales, we demonstrate the ability to program the sensor across the spectrum (0.1–1.0 THz), angle of incidence and polarization simultaneously in a single chip implemented in an industry standard 65-nm CMOS process. The methodology is compatible with other technology substrates that can allow extension of such programmability into other spectral regions. Chip-scale, room-temperature terahertz sensing can potentially enable many applications, but remains restricted in terms of spectrum, angle of incidence and polarization. Here the authors report a methodology for a CMOS-based, programmable THz sensor surface that allows dynamic adaption in all three properties.

/pdf/programmable-terahertz-chip-scale-sensing-interface-with-30o7tc27ma.pdf

Programmable terahertz chip-scale sensing interface with direct digital reconfiguration at sub-wavelength scales.

This paper discusses advances related to the integration of future mobile electronic THz systems. Without claiming to provide a comprehensive review of this surging research area, the authors gathered research on selected topics that are expected to be of relevance for the future exploration of components for practical mobile THz imaging and sensing applications. First, a brief technology review of integrated mobile THz components is given. Advances in III-V technology, silicon technology, and resonant-tunneling diodes (RTD) are discussed. Based on an RTD source and a SiGe-HBT direct detector, low-cost and compact computed tomography is presented for volumetric continuous-wave imaging at around 300 GHz. Moreover, aspects of system integration of mobile THz MIMO radars are discussed. Thereby, a novel phase-locked loop concept utilizing a high-stability yttrium-iron-garnet-tuned oscillator to synthesize ultra-stable reference mmWave signals is shown, and an adaptive self-interference cancellation algorithm for THz MIMO in the digital domain based on Kalman filter theory is proposed.

Toward Mobile Integrated Electronic Systems at THz Frequencies

As wireless networks move to millimetre-wave (mm-wave) and terahertz (THz) frequencies for 5G communications and beyond, ensuring security and resilience to eavesdropper attacks has become increasingly important. Traditional encryption methods are challenging to scale for high-bandwidth, ultralow-latency applications. An alternative approach is to use physical-layer techniques that rely on the physics of signal propagation to incorporate security features without the need for an explicit key exchange. Ensuring security through the use of directional, narrow-beam-like features of mm-wave/THz signals has proven to be vulnerable to passive eavesdroppers. Here we report a space-time modulation approach that ensures security by enforcing loss of information through selective spectral aliasing towards the direction of eavesdroppers, even though the channel can be physically static. This is achieved by using custom-designed spatio-temporal transmitter arrays realized in silicon chips with packaged antennas operating in the 71–76 GHz range. We also analytically and experimentally demonstrate the resilience of our links against distributed and synchronized eavesdropper attacks in the mm-wave band. Directional 5G communication channels can be made secure at the physical layer by using a time-modulation approach that enforces the fundamental loss of information through selective spectral aliasing towards the direction of unwanted listeners.

Secure space–time-modulated millimetre-wave wireless links that are resilient to distributed eavesdropper attacks

An integrated THz imager is proposed with an actively reconfigurable electromagnetic interface that can engineer the surface reception properties to reconfigure its sensitivity and aperture for three incident field properties, namely frequency, polarization and incident angle. The chip realized in a 65 nm CMOS process achieves upto 15x enhancement in responsivity and NEP across 0.1-0.99 THz and enables a programmable and versatile THz interface for hyperspectral, multi-angle and multi-polarization imaging.

A Programmable Active THz Electromagnetic Surface on-Chip for Multi-functional Imaging

In this paper, we present a method to miniaturize THz spectroscopic receivers into chip-scale systems by eliminating traditional spectrum analysis components such as wideband tunable THz sources, frequency multipliers, nonlinear mixing and amplifiers. This is achieved by extracting incident THz spectral signatures from the current distribution impressed on the surface of an on-chip antenna under the THz field incidence. A log-periodic tooth antenna is converted from a classical single port antenna into a massively multi-port structure with 84 detectors that sense the 2D current distribution. This method converts THz spectroscopy into a linear estimation problem and we apply robust estimation techniques such as LASSO, typically used in machine learning, to extract spectral signatures with noisy detectors with high sensitivity. The paper presents analytical and experimental results for the single chip operating at room temperature across 0.04-0.99 THz with 10 MHz accuracy in spectrum estimation of THz tones. The presented examples demonstrates that through a co-design approach of THz electromagnetics and electronics, such as by combining deep sub-wavelength near-field sensing and regression analyses, can enable a new class of THz chip-scale sensory systems.

Wide-band THz Spectroscope in Silicon THz Combining Sub-wavelength Near-field Sensing and Robust Regression Analysis

In modern systems-on-chips, several hardware protocols are used for communication and interaction among different modules. These protocols are complex and need to be implemented correctly for correct operation of the system-on-chip. Therefore, protocol verification has received significant attention. However, this verification is often limited to checking high-level properties on a protocol specification or an implementation. Verifying these properties directly on an implementation faces scalability challenges due to its size and design complexity. Further, even after some high-level properties are verified, there is no guarantee that an implementation fully complies with a given specification, even if the same properties have also been checked on the specification. We address these challenges and gaps by adding a layer of component specifications, one for each component in the protocol implementation, and specifying and verifying the interactions at the interfaces between each pair of communicating components. We use the recently proposed formal model termed Instruction-Level Abstraction (ILA) as a component specification, which includes an interface specification for the interactions in composing different components. The use of ILA models as component specifications allows us to decompose the complete verification task into two sub-tasks: checking that the composition of ILAs is sequentially equivalent to a verified formal protocol specification, and checking that the protocol implementation is a refinement of the ILA composition. This check requires that each component implementation is a refinement of its ILA specification and includes interface checks guaranteeing that components interact with each other as specified. We have applied the proposed ILA-based methodology for protocol verification to several third-party design case studies. These include an AXI on-chip communication protocol, an off-chip communication protocol, and a cache coherence protocol. For each system, we successfully detected bugs in the implementation, and show that the full formal verification can be completed in reasonable time and effort. 

SoC Protocol Implementation Verification Using Instruction-Level Abstraction (ILA) Specifications

Hierarchical Formal Verification of Hardware

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