The development of high quality passive components for sub-millimetre wave applications

Advances in transistors with cut-off frequencies >400GHz have fuelled interest in security, imaging and telecommunications applications operating well above 100GHz. However, further development of passive networks has become vital in developing such systems, as traditional coplanar waveguide (CPW) transmission lines, the most fundamental passive component, exhibit high losses in the millimetre and sub-millimetre wave regime. This work investigates novel, practical, low loss, transmission lines for frequencies above 100GHz and high-Q passive components composed of these lines. At these frequencies, transmission line losses are primarily due to the influence of the waveguide substrate. We therefore focus on structures which elevate transmission line traces above the substrate using air-bridge technology. Thorough analysis is performed on a range of elevated structures, and analytic / semi-analytic formulae for component figures of merit obtained. These, along with comprehensive 2 and 3D simulations are used to design discrete lines and distributed passive networks, with a focus on the 140-320 GHz frequency range. Innovative fabrication and detailed characterisation of the components are also carried out. The key result is the development of a novel MMIC compatible transmission line structure, Elevated-Grounded CPW, with a relatively simple fabrication process. EGCPW provides high substrate isolation, resulting in a low losses and high-quality passive networks. 50Ω EGCPW transmission line shows an insertion loss of 2.5dB/mm at 320GHz, 2.5dB/mm less than CPW. EGCPW passive networks, including resonators and filters, show higher performance than both conventional CPW and other forms of elevated CPW. 30-80% improvements in quality factor are shown, and an EGCPW band-pass filter with the centre frequency of 220GHz shows a 12% reduction in bandwidth and 4.5dB reduced in-band loss compared with its CPW counterpart. Due to the superior performance of MMIC-compatible EGCPW, as well as its ability to support a wide range of characteristic impedances, this structure is suggested as a candidate for widespread use in sub-millimetre wave circuits in order to increase efficiency and reduce losses

Vidutinių dažnių 5G belaidžių tinklų galios stiprintuvų tyrimas

This dissertation addresses the problems of ensuring efficient radio fre-quency transmission for 5G wireless networks. Taking into account, that the next generation 5G wireless network structure will be heterogeneous, the device density and their mobility will increase and massive MIMO connectivity capability will be widespread, the main investigated problem is formulated – increasing the efficiency of portable mid-band 5G wireless network CMOS power amplifier with impedance matching networks. The dissertation consists of four parts including the introduction, 3 chapters, conclusions, references and 3 annexes. The investigated problem, importance and purpose of the thesis, the ob-ject of the research methodology, as well as the scientific novelty are de-fined in the introduction. Practical significance of the obtained results, defended state-ments and the structure of the dissertation are also included. The first chapter presents an extensive literature analysis. Latest ad-vances in the structure of the modern wireless network and the importance of the power amplifier in the radio frequency transmission chain are de-scribed in detail. The latter is followed by different power amplifier archi-tectures, parameters and their improvement techniques. Reported imped-ance matching network design methods are also discussed. Chapter 1 is concluded distinguishing the possible research vectors and defining the problems raised in this dissertation. The second chapter is focused around improving the accuracy of de-signing lumped impedance matching network. The proposed methodology of estimating lumped inductor and capacitor parasitic parameters is dis-cussed in detail provi-ding complete mathematical expressions, including a summary and conclusions. The third chapter presents simulation results for the designed radio fre-quency power amplifiers. Two variations of Doherty power amplifier archi-tectures are presented in the second part, covering the full step-by-step de-sign and simulation process. The latter chapter is concluded by comparing simulation and measurement results for all designed radio frequency power amplifiers. General conclusions are followed by an extensive list of references and a list of 5 publications by the author on the topic of the dissertation. 5 papers, focusing on the subject of the discussed dissertation, have been published: three papers are included in the Clarivate Analytics Web of Sci-ence database with a citation index, one paper is included in Clarivate Ana-lytics Web of Science database Conference Proceedings, and one paper has been published in unreferred international conference preceedings. The au-thor has also made 9 presentations at 9 scientific conferences at a national and international level.Dissertatio

Design and characterisation of millimetre wave planar Gunn diodes and integrated circuits

Heterojunction planar Gunn devices were first demonstrated by Khalid et al in 2007. This new design of Gunn device, or transferred electron device, was based on the well-established material system of GaAs as the oscillation media. The design did not only breakthrough the frequency record of GaAs for conventional Gunn devices, but also has several advantages over conventional Gunn devices, such as the possibility of making multiple oscillators on a single chip and compatibility with monolithic integrated circuits. However, these devices faced the challenge of producing high enough RF power for practical applications and circuit technology for integration. This thesis describes systematic work on the design and characterisations of planar Gunn diodes and the associated millimetre-wave circuits for RF signal power enhancement. Focus has been put on improving the design of planar Gunn diodes and developing high performance integrated millimetre-wave circuits for combining multiple Gunn diodes. Improvement of device design has been proved to be one of the key methods to increase the signal power. By introducing additional δ-doping layers, electron concentration in the channel increases and better Gunn domain formation is achieved, therefore higher RF power and frequency are produced. Combining multiple channels in the vertical direction within devices is another effective way to increase the output signal power as well as DC-to-RF conversion efficiency. In addition, an alternative material system, i.e. In0.23Ga0.77As, has also been studied for this purpose. Planar passive components, such as resonators, couplers, low pass filters (LPFs), and power combiners with high performance over 100 GHz have been developed. These components can be smoothly integrated with planar Gunn diodes for compact planar Gunn oscillators, and therefore contribute to RF power enhancement. In addition, several new measurement techniques for characterising oscillators and passive devices have also been developed during this work and will be included in this thesis

Reconfigurable electronics based on metal-insulator transition:steep-slope switches and high frequency functions enabled by Vanadium Dioxide

The vast majority of disruptive innovations in science and technology has been originated from the discovery of a new material or the way its properties have been exploited to create novel devices and systems. New advanced nanomaterials will have a lasting impact over the next decades, providing breakthroughs in all scientific domains addressing the main challenges faced by the world today, including energy efficiency, sustainability, climate and health. The electronics industry relied over the last decades on the miniaturization process based on the scaling laws of complementary metal-oxide semiconductors (CMOS). As this process is approaching fundamental limitations, new materials or physical principles must be exploited to replace or supplement CMOS technology. The aim of the work in this thesis is to propose the abrupt metal-insulator transition in functional oxides as a physical phenomenon enabling new classes of Beyond CMOS devices. In order to provide an experimental validation of the proposed designs, vanadium dioxide (VO2) has been selected among functional oxides exhibiting a metal-insulator transition, due to the possibility to operate at room temperature and the high contrast between the electrical properties of its two structural phases. A CMOS-compatible sputtering process for uniform large scale deposition of stoichiometric polycrystalline VO2 has been optimized, enabling high yield and low variability for the devices presented in the rest of the thesis. The high quality of the film has been confirmed by several electrical and structural characterization techniques. The first class of devices based on the MIT in VO2 presented in this work is the steep-slope electronic switch. A quantitative study of the slope of the electrically induced MIT (E-MIT) in 2-terminal VO2 switches is reported, including its dependence on temperature. Moreover, the switches present excellent ON-state conduction independently of temperature, suggesting MIT VO2 switches as promising candidates for steep-slope, highly conductive, temperature stable electronic switches. A novel design for the shape of the electrodes used in VO2 switches has been proposed, targeting a reduction in the actuation voltage necessary to induce the E-MIT. The electrothermal simulations addressing this effect have been validated by measurements. The potential of the MIT in VO2 for reconfigurable electronics in the microwave frequency range has been expressed by the design, fabrication and characterization of low-loss, highly reliable, broadband VO2 radio-frequency (RF) switches, novel VO2 tunable capacitors and RF tunable filters. The newly proposed tunable capacitors overcome the frequency limitations of conventional VO2 RF switches, enabling filters working at a higher frequency range than the current state-of-the-art. An alternative actuation method for the tunable capacitors has been proposed by integrating microheaters for local heating of the VO2 region, and the design tradeoffs have been discussed by coupled electrothermal and electromagnetic simulations. The last device presented in this work operates in the terahertz (THz) range; the MIT in VO2 has been exploited to demonstrate for the first time the operation of a modulated scatterer (MST) working at THz frequencies. The proposed MST is the first THz device whose working principle is based on the actuation of a single VO2 junction, in contrast to commonly employed VO2 metasurfaces

High Bit Rate Wireless and Fiber-Based Terahertz Communication

RÉSUMÉ Dans le spectre électromagnétique, la bande des térahertz s’étend de 100 GHz à 10 THz (longueurs d’onde de 3 mm à 30 μm). Des décennies auparavant, le spectre des THz était connu sous le nom de « gap térahertz » en raison de l’indisponibilité de sources et détecteurs efficaces à ces fréquences. Depuis quelques années, la science a évolué pour faire migrer la technologie THz des laboratoires aux produits commerciaux. Il existe plusieurs applications des ondes THz en imagerie, spectroscopie et communications. Dans cette thèse, nous nous intéressons aux communications THz à travers deux objectifs. Le premier objectif est de développer une source THz de haute performance dédiée aux communications et basée sur les technologies optiques avec des produits commerciaux uniquement. Le second objectif est de démontrer l’utilisation de fibres optiques afin de renforcer la robustesse des communications THz sans fil. Nous débutons cette thèse avec une revue de la littérature scientifique sur le sujet de la communications THz sans fil et filaire. D’abord, nous discutons des deux méthodes communément utilisées (électronique et optique) pour démontrer des liens de communications THz avec leurs avantages et inconvénients. Nous présentons par la suite la possibilité d’utiliser un système de spectroscopie THz pour des applications en communications avec des modifications mineures au montage. Nous présentons ensuite plusieurs applications gourmandes en bande passante qui pourraient bénéficier du spectre THz, incluant la diffusion en continu (streaming) de flux vidéo aux résolutions HD et 4K non compressés. Ensuite, nous discutons de la motivation d’utiliser de longues fibres THz et notamment du fait qu’elles ne sont pas destinées à remplacer les fibres optiques conventionnelles de l’infrarouge, mais plutôt à augmenter la robustesse des liens THz sans fil. En particulier, les fibres THz peuvent être utilisées pour garantir le lien de communication dans des environnements géométriques complexes ou difficile à atteindre, ainsi que pour immuniser le lien THz aux attaques de sécurité. Plusieurs designs de fibres et guides d’onde précédemment démontrées dans la littérature sont discutés avec, entre autres, leurs méthodes de fabrication respectives. Nous discutons ensuite de la possibilité d’utiliser un simple guide d’onde diélectrique et sous-longueur d’onde pour transmettre l’information à un débit de l’ordre de plusieurs Gbps sur une distance de quelques mètres.----------ABSTRACT The Terahertz (THz) spectral range spans from 100 GHz to 10 THz (wavelength: 3 mm to 30 μm) in the electromagnetic spectrum. Decades ago, the THz spectral range is often named as ‘THz gap’ due to the non-availability of efficient THz sources and detectors. In the recent years, the science has evolved in bringing the THz technology from lab scale to commercial products. There are several potential applications of THz frequency band such as imaging, spectroscopy and communication. In this thesis, we focus on THz communications by addressing two objectives. The first objective is to develop a high-performance photonics-based THz communication system using all commercially available components. The second objective is to demonstrate the THz-fiber based communications, which can be used to increase the reliability of THz wireless links. We begin this thesis with a scientific literature review on the subject of THz wireless and fiber-based communications. First, the two different methodologies (all electronics based and photonics-based THz system) that is commonly used in the demonstration of THz communications is discussed along with their advantages and challenges. We then present the flexibility of photonics-based THz system where it is possible to switch it with minor modifications for THz spectroscopic studies and THz communication applications. Several bandwidth hungry applications that demands the use of THz spectrum for next generation communications is detailed. This includes the streaming of uncompressed HD/4K and beyond high-resolution videos, where the THz spectrum can be beneficial. Next, the motivation of using long THz fibers is discussed and we convince the readers that the THz fibers are not meant to replace the fibers in the optical-infrared region but to increase the reliability of THz wireless links. Particularly, the THz fibers can be used to provide connectivity in complex geometrical environments, secure communications and signal delivery to hard-to-reach areas. Several novel fiber/waveguide designs along with their fabrication technologies from the literature are presented. We then show that a simple solid core dielectric subwavelength fiber can be used to transmit the information in the order of several Gbps to a distance of a few meters

Enhancing Digital Controllability in Wideband RF Transceiver Front-Ends for FTTx Applications

Enhancing the digital controllability of wideband RF transceiver front-ends helps in widening the range of operating conditions and applications in which such systems can be employed. Technology limitations and design challenges often constrain the extensive adoption of digital controllability in RF front-ends. This work focuses on three major aspects associated with the design and implementation of a digitally controllable RF transceiver front-end for enhanced digital control. Firstly, the influence of the choice of semiconductor technology for a system-on-chip integration of digital gain control circuits are investigated. The digital control of gain is achieved by utilizing step attenuators that consist of cascaded switched attenuation stages. A design methodology is presented to evaluate the influence of the chosen technology on the performance of the three conventionally used switched attenuator topologies for desired attenuation levels, and the constraints that the technology suitable for high amplification places on the attenuator performance are examined. Secondly, a novel approach to the integrated implementation of gain slope equalization is presented, and the suitability of the proposed approach for integration within the RF front-end is verified. Thirdly, a sensitivity-aware implementation of a peak power detector is presented. The increased employment of digital gain control also increases the requirements on the sensitivity of the power detector employed for adaptive power and gain control. The design, implementation, and measurement results of a state-of-the-art wideband power detector with high sensitivity and large dynamic range are presented. The design is optimized to provide a large offset cancellation range, and the influence of offset cancellation circuits on the sensitivity of the power detector is studied. Moreover, design considerations for high sensitivity performance of the power detector are investigated, and the noise contributions from individual sub-circuits are evaluated. Finally, a wideband RF transceiver front-end is realized using a commercially available SiGe BiCMOS technology to demonstrate the enhancements in the digital controllability of the system. The RF front-end has a bandwidth of 500 MHz to 2.5 GHz, an input dynamic range of 20 dB, a digital gain control range larger than 30 dB, a digital gain slope equalization range from 1.49 dB/GHz to 3.78 dB/GHz, and employs a power detector with a sensitivity of -56 dBm and dynamic range of 64 dB. The digital control in the RF front-end is implemented using an on-chip serial-parallel-interface (SPI) that is controlled by an external micro-controller. A prototype implementation of the RF front-end system is presented as part of an RFIC intended for use in optical transceiver modules for fiber-to-the-x applications

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)