A Novel Genetic Algorithm Based Method for Measuring Complex Permittivity of Dielectric, Lossy and Multilayered Materials with Thin Features Using Open-Ended Coaxial Probe

M.S

Design of new radiating systems and phase shifters for 5G communications at millimeter-wave frequencies

With the arrival of the new generation of communications, known as 5G, the systems that constitute it must offer better performance in terms of data speed, latency and connection density than the previous generation of communications. For 5G, an allocation of the frequency ranges that will support future wireless communications has been established. This allocation is formed by a range of frequencies corresponding to bands below 6 GHz and the other range of frequencies includes bands above 24 GHz. In the latter frequency range, which includes part of the millimeter-wave frequency band (from 30 GHz to 300 GHz), the development of new radio frequency (RF) components is necessary because their design and manufacture is a technological challenge. As the frequency that supports wireless communications increases, propagation losses also increase. Therefore, these losses must be compensated by the radiating systems in 5G to make these communications possible. The RF devices that make up these new systems must provide high antenna gain, be power efficient and offer spatial reconfigurability of the radiated signal. In this thesis, the main objective is the design of both guided and radiating RF devices to provide design solutions for future 5G systems at millimeter-wave frequencies. In particular, the contributions made have been to the design of phase shifters and antenna arrays. To improve efficiency at millimeter-wave frequencies, these devices have been designed in waveguide technology. Phase shifters are essential RF devices to control the phase shift of the electromagnetic wave that will be radiated to a certain spatial direction by an antenna array. The design of beamforming networks requires the implementation of phase shifters that produce a fixed or variable phase shift value. However, the design and fabrication of these devices at millimeter-wave frequencies is a complex task. In this thesis, four designs of waveguide phase shifters that produce both fixed and variable phase shift are presented. For phase shifters that provide a fixed phase shift, the value of this phase shift along the frequency is tuned in a desired manner by using periodic structures with higher symmetries. These types of configurations provide both flexibility in the design process and improved electromagnetic performance such as greater operating bandwidth. All the phase shifters have been implemented in gap-waveguide technology to demonstrate its effectiveness in these devices for millimeter-wave frequencies. Regarding the radiating systems, two feeding strategies have been considered in the design process. First, the design of a 70 GHz centered antenna array implemented in gap-waveguide technology combined with the use of separate waveguides in E-plane is proposed. In this design, the feed is guided through a waveguide corporate-feed network. Second, the design of a reflectarray whose unit cells are formed using three-dimensional geometries is presented. In this case, the feeding is done in free space by radiation from a source antenna. In the previous designs, the fabrication of the prototypes was done by 3D printing based on stereolithography. Finally, using unit cells with three-dimensional geometries, the design of radiating devices with more complex functionalities such as reflection/transmission with high directivity and reconfiguration of the reflected radiation by means of graphene structures are proposed.Con la llegada de la nueva generación de comunicaciones, denominada 5G, los sistemas que la conforman deben ofrecer unas mejores prestaciones en términos de velocidad de datos, latencia y densidad de conexiones respecto a la generación de comunicaciones anterior. Para 5G se ha establecido una asignación de los rangos de frecuencia que van a soportar las futuras comunicaciones inalámbricas. Esta asignación se compone por un rango de frecuencias correspondiente a las bandas por debajo de los 6 GHz y el otro rango de frecuencias engloba a las bandas por encima de los 24 GHz. En este ´ultimo rango de frecuencias, en el cual están incluidas parte de la banda de las frecuencias milimétricas (desde 30 GHz a 300 GHz), es necesario el desarrollo de nuevos componentes de radiofrecuencia (RF) ya que su diseño y fabricación supone un reto tecnológico. Al aumentar la frecuencia que soporta las comunicaciones inalámbricas, las pérdidas por propagación también aumentan. Es por ello por lo que estas pérdidas deben ser compensadas por los sistemas radiantes en 5G para que las comunicaciones sean posibles. Los dispositivos de RF que componen estos nuevos sistemas deben proporcionar una alta ganancia de antena, ser eficientes en términos de potencia y ofrecer reconfigurabilidad espacial de la señal radiada. En esta tesis, el objetivo principal es el diseño de dispositivos de RF tanto guiados como radiantes para ofrecer soluciones de diseño a los futuros sistemas 5G en frecuencias milimétricas. De manera particular, las contribuciones realizadas han sido al diseño de desfasadores y agrupaciones de antenas. Para mejorar la eficiencia en frecuencias milimétricas, estos dispositivos han sido diseñados en tecnología en guía de ondas. Los desfasadores son dispositivos RF esenciales para controlar el desfase de la onda electromagnética que será radiada hacia una cierta dirección espacial por una agrupación de antenas. Las redes de beamforming tienen la necesidad de implementar en su diseño desfasadores que producen un valor de desfase fijo o variable. Sin embargo, el diseño y fabricación de estos dispositivos en frecuencias milimétricas resulta una tarea de alta dificultad. En esta tesis se presenta cuatro diseños de desfasadores en guía de onda que producen un desfase tanto fijo como variable. Para los desfasadores que proporcionan un desfase fijo, el valor de este desfase a lo largo de la frecuencia es ajustado de manera deseada mediante el uso de estructuras periódicas con simetrías superiores. Este tipo de configuraciones proporcionan tanto flexibilidad en el proceso de diseño como una mejora de las características electromagnéticas como puede ser un mayor ancho de banda de operación. Todos los desfasadores realizados han sido implementados en tecnología gap waveguide para demostrar su efectividad en estos dispositivos para frecuencias milimétricas. Respecto a los sistemas radiantes, se han considerado dos estrategias de alimentación en el proceso diseño. En primer lugar, se propone el diseño de un array centrado a 70 GHz implementado en tecnología gap waveguide combinado con el uso de guías de onda separadas en plano E. En este diseño, la alimentación es guiada a través de una red de alimentación corporativa en guía de onda. En segundo lugar, se presenta el diseño de un reflectarray cuyas celdas unitarias son formadas mediante geometrías tridimensionales. En este caso, la alimentación se hace en el espacio libre mediante la radiación de una antena fuente. En los anteriores diseños, la fabricación de los prototipos se realizó mediante impresión 3D basado en estereolitografía. Finalmente, a través del uso de celdas unitarias con geometrías tridimensionales, se proponen el diseño de dispositivos radiantes con funcionalidades más complejas como la reflexión/transmisión con alta directividad y la reconfiguración de la radiación reflejada mediante estructuras con grafeno.Tesis Univ. Granada

BiCMOS Millimetre-wave low-noise amplifier

Abstract: Please refer to full text to view abstract.D.Phil. (Electrical and Electronic Engineering

Engineering Metamaterials

A couple of decades have passed since the advent of electromagnetic metamaterials. Although the research on artificial microwave materials dates back to the middle of the 20th century, the most prominent development in the electromagnetics of artificial media has happened in the new millennium. In the last decade, the electromagnetics of one-, two-, and three-dimensional metamaterials acquired robust characterization and design tools. Novel fabrication techniques have been developed. Many exotic effects involving metamaterials and metasurfaces, which initially belonged in a scientist’s lab, are now well understood by practicing engineers. Therefore, it is the right time for the metamaterial concepts to become a designer’s tools of choice in the landscape of electronics, microwaves, and photonics. Answering such a demand, the book “Engineering Metamaterials” focuses on the theory and applications of electromagnetic metamaterials, metasurfaces, and metamaterial transmission lines as the building blocks of present-day and future electronic, photonic, and microwave devices

Waveplates based on metasurfaces in the THz range

Los platos de onda basados en metasuperficies son componentes clave en electromagnetismo, ya que permiten un control total de la polarización de las ondas electromagnéticas con la ventaja de presentar estructuras más compactas que los platos de onda convencionales. Además, la aplicación del principio de Pancharatnam Berry (PB) a los platos de media onda (HWP) basados en metasuperficies, permite la manipulación de frentes de onda junto con la conversión de la polarización de las ondas incidentes circularmente polarizadas, simplemente girando los meta-átomos que componen la metasuperficie. Para lograr altos niveles de eficiencia de transmisión con platos de onda basados en metasuperficies, generalmente se requieren diseños multicapa. Esto implica estructuras voluminosas y complica el proceso de fabricación, restando importancia a la ventaja de utilizar metasuperficies. El propósito de esta tesis realizada en la Universidad Pública de Navarra y en L’École Polytechnique Fédérale de Lausanne, Suiza (EPFL) es ofrecer una ventaja tecnológica tanto para el control de polarización como para la manipulación del frente de onda y contribuir al desarrollo de dispositivos basados en metamasuperficies, incluyendo su fabricación y verificación experimental. Los resultados incluyen lo siguiente: Un plato de media onda operando en transmisión, ultradelgado y basado en una metasuperficie en zigzag de dos capas que opera en la parte baja del espectro del THz con un 90% de eficiencia de transmisión, que se demuestra numérica y experimentalmente. Se lleva a cabo un análisis detallado de la robustez del dispositivo con respecto a los desalineamientos de las capas mediante el diseño y la fabricación de dos dispositivos adicionales con el máximo desalineamiento entre capas en ambas direcciones transversales. Una metalente ultradelgada y compacta basada en el principio Pancharatnam Berry con solo dos capas alcanzando un 90% de eficiencia de transmisión, enfocando el frente de onda de una onda incidente polarizada circularmente y convirtiendo su polarización. La estructura es estudiada semi-analítica y numéricamente y medida experimentalmente, comprobándose un excelente comportamiento como HWP PB metalente a 87 GHz. Una aplicación de ingeniería de frentes de onda para la manipulación de los mismos se demuestra numéricamente en el rango de ondas milimétricas mediante la integración de la metalente en un sistema de antena-metalente, que se estudia semi-analíticamente y se corrobora experimentalmente. El sistema convierte la polarización de las ondas polarizadas circularmente, logrando un incremento de la directividad de antena de 17 dB a ⁓35 dB a 87 GHz con un AR inferior a 0.5 dB. Finalmente, se presentan dos configuraciones extra del sistema para trabajar entre los extremos del rango de frecuencia comprendido entre 75 GHz y 105 GHz, con directividades ⁓32 dB y AR < 3 dB.Transmissive waveplates based on metasurfaces are key components in electromagnetism, as they allow for a full control of the electromagnetic wave polarization with the advantage of presenting structures more compact than conventional waveplates. Moreover, applying the Pancharatnam Berry (PB) principle to half-wave plate (HWP) metasurfaces allows the manipulation of wavefronts along with the conversion of the handedness of circularly polarized incident waves by simply rotating the meta-atoms that compose the metasurface. For achieving high levels of transmission efficiency with transmissive waveplates based on metasurfaces, multiple layer designs are usually required. It implies bulky structures and complicates the fabrication process, downplaying the aim of the use of metasurfaces. The purpose of this thesis performed at the Public University of Navarre and at École Polytechnique Fédérale de Lausanne (EPFL) is to offer a technological advantage both for polarization controlling as wavefront manipulation and contribute to the development of metasurface-based devices, including their fabrication and experimental verification. The results include the following: An ultrathin transmissive half-wave plate based on a bi-layered zigzag metasurface operating at the lower-frequency edge of the THz spectrum with a 90% of transmission efficiency, which is numerically and experimentally demonstrated. A detailed analysis of the device robustness with respect to layer misalignments is carried out by designing and fabricating two additional devices with the maximum possible shift between layers along both transverse directions. A compact ultrathin metalens based on the Pancharatnam Berry principle with only two layers with a 90% of transmission efficiency, focusing the wavefront of a circularly polarized incident wave and converting its handedness. The structure is semi-analytically and numerically studied and experimentally measured, verifying an excellent behavior as HWP PB metalens at 87 GHz. A wavefront engineering application for wavefront manipulation is numerically demonstrated in the millimeter-wave range by the integration of the metalens in an antenna-metalens system, which is semi-analytically studied and experimentally corroborated. The system converts the handedness of circular polarized waves, achieving an increment of the antenna directivity from17 dB to ⁓35 dB at 87 GHz with an AR lesser than 0.5 dB. Finally, two extra system configurations are presented to work around the frequency range extremes comprised between 75 GHz and 105 GHz, with directivities ⁓32 dB and AR < 3 dB.Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011)Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011

Design and Analysis of Low-power Millimeter-Wave SiGe BiCMOS Circuits with Application to Network Measurement Systems

Interest in millimeter (mm-) wave frequencies covering the spectrum of 30-300 GHz has been steadily increasing. Advantages such as larger absolute bandwidth and smaller form-factor have made this frequency region attractive for numerous applications, including high-speed wireless communication, sensing, material science, health, automotive radar, and space exploration. Continuous development of silicon-germanium heterojunction bipolar transistor (SiGe HBT) and associated BiCMOS technology has achieved transistors with fT/fmax of 505/720 GHz and integration with 55 nm CMOS. Such accomplishment and predictions of beyond THz performance have made SiGe BiCMOS technology the most competitive candidate for addressing the aforementioned applications. Especially for mobile applications, a critical demand for future mm-wave applications will be low DC power consumption (Pdc), which requires a substantial reduction of supply voltage and current. Conventionally, reducing the supply voltage will lead to HBTs operating close to or in the saturation region, which is typically avoided in mm-wave circuits due to expectated performance degradation and often inaccurate models. However, due to only moderate speed reduction at the forward-biased base-collector voltage (VBC) up to 0.5 V and the accuracy of the compact model HICUM/L2 also in saturation, low-power mm-wave circuits with SiGe HBTs operating in saturation offer intriguing benefits, which have been explored in this thesis based on 130 nm SiGe BiCMOS technologies: • Different low-power mm-wave circuit blocks are discussed in detail, including low-noise amplifiers (LNAs), down-conversion mixers, and various frequency multipliers covering a wide frequency range from V-band (50-75 GHz) to G-band (140-220 GHz). • Aiming at realizing a better trade-off between Pdc and RF performance, a drastic decrease in supply voltage is realized with forward-biased VBC, forcing transistors of the circuits to operate in saturation. • Discussions contain the theoretical analysis of the key figure of merits (FoMs), topology and bias selection, device sizing, and performance enhancement techniques. • A 173-207 GHz low-power amplifier with 23 dB gain and 3.2 mW Pdc, and a 72-108 GHz low-power tunable amplifier with 10-23 dB gain and 4-21 mW Pdc were designed. • A 97 GHz low-power down-conversion mixer was presented with 9.6 dB conversion gain (CG) and 12 mW Pdc. • For multipliers, a 56-66 GHz low-power frequency quadrupler with -3.6 dB peak CG and 12 mW Pdc, and a 172-201 GHz low-power frequency tripler with -4 dB peak CG and 10.5 mW Pdc were realized. By cascading these two circuits, also a 176-193 GHz low-power ×12 multiplier was designed, achieving -11 dBm output power with only 26 mW Pdc. • An integrated 190 GHz low-power receiver was designed as one receiving channel of a G-band frequency extender specifically for a VNA-based measurement system. Another goal of this receiver is to explore the lowest possible Pdc while keeping its highly competitive RF performance for general applications requiring a wide LO tuning range. Apart from the low-power design method of circuit blocks, the careful analysis and distribution of the receiver FoMs are also applied for further reduction of the overall Pdc. Along this line, this receiver achieved a peak CG of 49 dB with a 14 dB tunning range, consuming only 29 mW static Pdc for the core part and 171 mW overall Pdc, including the LO chain. • All designs presented in this thesis were fabricated and characterized on-wafer. Thanks to the accurate compact model HICUM/L2, first-pass access was achieved for all circuits, and simulation results show excellent agreement with measurements. • Compared with recently published work, most of the designs in this thesis show extremely low Pdc with highly competitive key FoMs regarding gain, bandwidth, and noise figure. • The observed excellent measurement-simulation agreement enables the sensitivity analysis of each design for obtaining a deeper insight into the impact of transistor-related physical effects on critical circuit performance parameters. Such studies provide meaningful feedback for process improvement and modeling development.:Table of Contents Kurzfassung . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii 1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 List of symbols and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Technology 7 2.1 Fabrication Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 SiGe HBT performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.2 B11HFC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.3 SG13G2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.4 SG13D7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Commonly Used Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.1 Grounded-sidewall-shielded microstrip line . . . . . . . . . . . . . . . . . . 12 2.2.2 Zero-impedance Transmission Line . . . . . . . . . . . . . . . . . . . . . . 15 2.2.3 Balun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.2.3.1 Active Balun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.2.3.2 Passive Balun . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3 Low-power Low-noise Amplifiers 25 3.1 173-207 GHz Ultra-low-power Amplifier . . . . . . . . . . . . . . . . . . . . . . . 25 3.1.1 Topology Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.1.2 Bias Dependency of the Small-signal Performance . . . . . . . . . . . . . 27 3.1.2.1 Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.1.2.2 Bias vs Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.1.2.3 Bias vs Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 3.1.2.4 Bias vs Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 3.1.3 Bias selection and Device sizing . . . . . . . . . . . . . . . . . . . . . . . . 36 3.1.3.1 Bias Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.1.3.2 Device Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.1.4 Performance Enhancement Technologies . . . . . . . . . . . . . . . . . . . 41 3.1.4.1 Gm-boosting Inductors . . . . . . . . . . . . . . . . . . . . . . . 41 3.1.4.2 Stability Enhancement . . . . . . . . . . . . . . . . . . . . . . . 43 3.1.4.3 Noise Improvement . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.1.5 Circuit Realization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.1.5.1 Layout Scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.1.5.2 Inductors Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.1.5.3 Dual-band Matching Network . . . . . . . . . . . . . . . . . . . 48 3.1.5.4 Circuit Implementation . . . . . . . . . . . . . . . . . . . . . . . 50 3.1.6 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.1.6.1 Measurement Setup . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.1.6.2 Measurement Results . . . . . . . . . . . . . . . . . . . . . . . . 51 3.1.6.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 3.2 72-108 GHz Low-Power Tunable Amplifier . . . . . . . . . . . . . . . . . . . . . . 55 3.2.1 Configuration, Sizing, and Bias Tuning Range . . . . . . . . . . . . . . . . 55 3.2.2 Regional Matching Network . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.2.2.1 Impedance Variation . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.2.2.2 Regional Matching Network Design . . . . . . . . . . . . . . . . 60 3.2.3 Circuit Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.2.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.2.4.1 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3.2.4.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 4 Low-power Down-conversion Mixers 73 4.1 97 GHz Low-power Down-conversion Mixer . . . . . . . . . . . . . . . . . . . . . 74 4.1.1 Mixer Design and Implementation . . . . . . . . . . . . . . . . . . . . . . 74 4.1.1.1 Mixer Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.1.1.2 Bias Selection and Device Sizing . . . . . . . . . . . . . . . . . . 77 4.1.1.3 Mixer Implementation . . . . . . . . . . . . . . . . . . . . . . . . 79 4.1.2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.1.2.1 Measurement Results . . . . . . . . . . . . . . . . . . . . . . . . 80 4.1.2.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.2 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5 Low-power Multipliers 87 5.1 General Design Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.2 56-66 GHz Low-power Frequency Quadrupler . . . . . . . . . . . . . . . . . . . . 89 5.3 172-201 GHz Low-power Frequency Tripler . . . . . . . . . . . . . . . . . . . . . 93 5.4 176-193 GHz Low-power ×12 Frequency Multiplier . . . . . . . . . . . . . . . . . 96 5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 6 Low-power Receivers 101 6.1 Receiver Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 6.2 LO Chain (×12) Integrated 190 GHz Low-Power Receiver . . . . . . . . . . . . . 104 6.2.1 Receiver Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 6.2.2 Low-power Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 6.2.3 Building Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.2.3.1 LNA and LO DA . . . . . . . . . . . . . . . . . . . . . . . . . . 108 6.2.3.2 Tunable Mixer and IF BA . . . . . . . . . . . . . . . . . . . . . 111 6.2.3.3 65 GHz (V-band) Quadrupler . . . . . . . . . . . . . . . . . . . 116 6.2.3.4 G-band Tripler . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6.2.4 Receiver Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . 123 6.2.5 Measurement Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 6.2.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 6.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 7 Conclusions 133 7.1 Summaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 7.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Bibliography 135 List of Figures 149 List of Tables 157 A Derivation of the Gm 159 A.1 Gm of standard cascode stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 A.2 Gm of cascode stage with Lcas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 A.3 Gm of cascode stage with Lb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 B Derivation of Yin in the stability analysis 163 C Derivation of Zin and Zout 165 C.1 Zin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 C.2 Zout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 D Derivation of the cascaded oP1dB 169 E Table of element values for the designed circuits 17

Impact of adjacent dielectrics on the high-frequency performance of graphene field-effect transistors

Transistors operating at high frequencies are the basic building blocks of millimeter wave communication and sensor systems. The high velocity and mobility of carriers in graphene can open ways for development of ultra-fast group IV transistors with similar or even better performance than that achieved with III-V based semiconductors. However, the progress of high-speed graphene transistors has been hampered by limitations associated with fabrication, influence of adjacent materials and self-heating effects.This thesis work presents results of the comprehensive analysis of the influence of material imperfections, self-heating and limitations of the charge carrier velocity, imposed by adjacent dielectrics, on the transit frequency, fT, and the maximum frequency of oscillation, fmax, of graphene field-effect transistors (GFETs). The analysis allowed for better understanding and developing a strategy for addressing the limitations.In particular, it was shown that the GFET high-frequency performance can be enhanced by utilizing the gate and substrate dielectric materials with higher optical phonon (OP) energy, allowing for higher saturation velocity and, hence, higher fT and fmax. This approach was experimentally verified by demonstration of enhancement in the fT and fmax in GFETs with graphene channel encapsulated by the Al2O3 layers. As a further step, GFETs on diamond, material with highest OP energy and thermal conductivity, were introduced, developed and fabricated, showing the extrinsic fmax up to 50 GHz, at the gate length of 0.5 \ub5m, which is highest reported so far among the best published graphene and semiconductor counterparts.The main achievements of this thesis work are as follows: (i) comprehensive study of correlations between graphene-dielectric material quality, small-signal equivalent circuit parameters and high-frequency performance of the GFETs; (ii) experimental verification of the concept of improving the GFET high- frequency performance via selection of adjacent dielectric materials with high OP energy; (iii) introducing the diamond as a most promising dielectric material for high-frequency GFETs; (iv) development of technology and demonstration of fully integrated X and Ku band GFET IC amplifiers with state-of-the art performance.In conclusion, the routes of future development depicted in this thesis work may allow for enhancing the high-frequency performance of GFETs up to the level or even higher than that of the modern III-V semiconductor counterparts

Manufacture and Investigation of Organic Composite Polymer Based Films for Advanced Flexible Solar Cells

Modern society has created big challenges in the area of sustainable supply of energy to satisfy the needs of growing population and to account for depleting fossil fuel resources. The Irish Government has set targets for the energy sector by 2020, with 33% of electricity to be generated from renewable sources. Organic photovoltaic devices offer several advantages over expensive silicon solar cells, including deposition of ultra-thin films by spin-coating, printing and spray-coating. This in turn provides for the exciting possibility to make lightweight, flexible solar cells for a broad range of existing and emerging applications for security, military and medicine. This research project was inspired by the current drive into finding alternative technologies and materials for the design and manufacture of advanced solar cells. The primary objective was to tailor the properties of Poly3Hexylthiophene: PhenylC60 Buturic Acid Methyl Esther composite (P3HT:PCBM) thin films for flexible organic solar cells performance. The extensive experimental work was conducted to reveal the effect of the solar irradiation and thermal annealing on the dielectric, optical and electrical properties of P3HT:PCBM thin films. A common degradation pattern was demonstrated in the films after UV exposure whereby the optical absorbance and the resistivity were shown to be inversely proportionate. These two correlating techniques showed similar patterns after exposure. It was also shown that annealing the structure after deposition increased the absorbance in the thin film and the quantum efficiency of the final prototype device was related to film morphology. The dielectric properties of these films were studied using a novel microwave spectroscopy technique and it is believed to be the first report on the application of this novel technique to photovoltaic materials characterisation. To examine the dielectric properties of the P3HT:PCBM films using microwave spectroscopy, two types of Electro Magnetic (EM) wave sensors were fabricated, one on a Rogers substrate with Cu patterns and a second on a flexible substrate with Ag patterns. Both types of EM sensors exhibited shifts in resonant peak frequencies and amplitude during exposure to solar irradiation. All other experimental parameters and environmental conditions were kept constant. Therefore it is reasonable to conclude that the proposed method of microwave spectroscopy is a reliable tool to trace the changes in the properties of the materials caused by solar irradiation. The optical properties of the P3HT:PCBM films displayed a decrease in absorbance after 40mins solar simulator irradiation and then an increase in absorbance from 40 min to 20hrs. The electrical properties of P3HT:PCBM films showed a resistance decrease as the films were illuminated by a solar simulator from 0 to 40 min, and a subsequent increase in resistance up to 20hrs. In addition, a bespoke solar cell on flexible Polyethylene terephthalate (PET) was constructed and tested. It exhibited a fill factor and an efficiency of 0.3238 and 0.49% respectively. Although the performance is poor compared to reported state of the art for organic solar cells, the work demonstrates that operational devices can be manufactured under non-optimised laboratory conditions