Design of 300 ghz combined doubler/subharmonic mixer based on schottky diodes with integrated mmic based local oscillator

In this paper the design and experimental characterization of a combined doublersubharmonic mixer based on Schottky diodes which uses a 75 GHz MMIC based local oscillator is presented. This solution integrates in the same substrate the doubler and the mixer, which share the same metallic packaging with the local oscillator. The prototype has been fabricated and measured. For characterization, the Y-Factor technique has been used and the prototype yields a best conversion loss and equivalent noise temperature of 11 dB and 1976 K, respectively, at 305 GHz. This performance is close to the state of the art, and shows the potential of this approach, which allows a significant reduction in terms of size and volume.This research was funded by the Spanish MINECO, Project No. TEC2016-76997-C3-1-R, and by the Spanish State Research Agency, Project No. PID2019-109984RB-C43/AEI/10.13039/501100011033

Nanodevices for Microwave and Millimeter Wave Applications

The microwave and millimeter wave frequency range is nowadays widely exploited in a large variety of fields including (wireless) communications, security, radar, spectroscopy, but also astronomy and biomedical, to name a few. This Special Issue focuses on the interaction between the nanoscale dimensions and centimeter to millimeter wavelengths. This interaction has been proven to be efficient for the design and fabrication of devices showing enhanced performance. Novel contributions are welcome in the field of devices based on nanoscaled geometries and materials. Applications cover, but not are limited to, electronics, sensors, signal processing, imaging and metrology, all exploiting nanoscale/nanotechnology at microwave and millimeter waves. Contributions can take the form of short communications, regular or review papers

GaN Schottky diodes for signal generation and control

The aim of this work is to explore the potential of GaN Schottky diodes for high fre- quency signal generation and control, with emphasis on their power handling capability. GaN Schottky diodes are expected to provide superior power handling capability due to the wide band-gap of GaN. Theoretical analysis has been performed analytically and numerically. Devices have been fabricated and their performance has been evaluated experimentally. Demonstration of monolithic integrated circuits utilizing the realized devices was also made. The diode figure of merits e.g. Cj0, Rs , Vbr , have been considered with respect to power handling and harmonic generation to permit evaluation of the diode design requirements for satisfying specific circuit needs. Numerical simulation allowed the prediction of device performance for specific geometry and material properties. Simulation results have shown that GaN Schottky diodes have a power handling capability at least 2 times higher than their GaAs counterparts, while maintaining acceptable losses. Several fabrication technology approaches have been studied and implemented for real- izing GaN-based Schottky diodes. Their key steps include dry etching, metal contacts, as well as interconnects. The surface treatment before metal deposition necessary for good quality Schottky contacts has been thoroughly studied. Three means of intercon- nect methods were demonstrated for on-wafer tests. They allowed rapid evaluation of the electrical characteristics of the diodes and set up the basis for the development of monolithic integrated circuits. High frequency small-signal measurements have been performed for the GaN Schot- tky diodes. The obtained S-parameters were used to extract equivalent circuit models. A parameter extraction procedure was established to de-embed the pad parasitics, and obtaining information about their intrinsic elements permitting in this way diode opti- mization. The large-signal characteristics of the fabricated diodes were measured on-wafer using a large-signal network analyzer. This novel characterization method provided immediate information about diode features such as power handling, loss etc. The time-domain waveforms of the diodes were obtained under various operating conditions allowing a better insight into the diode operation. Large-signal models of the diodes have been obtained by considering the extracted small- signal equivalent circuit characteristics and the large-signal measurement results. GaN- based circuits using diodes have been studied. They include a frequency doubler and an analog phase shifter. Consideration of their large-signal characteristics was possible using the extracted diode large-signal models. Doublers made with this technology are expected to provide an output power of 10 dBm at 94 GHz. MMIC phase shifters were designed, fabricated and characterized. They showed a phase tuning (∆φ) of 45◦ and 6-7 dB insertion loss in the 32-38 GHz range

Two-Dimensional Electronics - Prospects and Challenges

During the past 10 years, two-dimensional materials have found incredible attention in the scientific community. The first two-dimensional material studied in detail was graphene, and many groups explored its potential for electronic applications. Meanwhile, researchers have extended their work to two-dimensional materials beyond graphene. At present, several hundred of these materials are known and part of them is considered to be useful for electronic applications. Rapid progress has been made in research concerning two-dimensional electronics, and a variety of transistors of different two-dimensional materials, including graphene, transition metal dichalcogenides, e.g., MoS2 and WS2, and phosphorene, have been reported. Other areas where two-dimensional materials are considered promising are sensors, transparent electrodes, or displays, to name just a few. This Special Issue of Electronics is devoted to all aspects of two-dimensional materials for electronic applications, including material preparation and analysis, device fabrication and characterization, device physics, modeling and simulation, and circuits. The devices of interest include, but are not limited to transistors (both field-effect transistors and alternative transistor concepts), sensors, optoelectronics devices, MEMS and NEMS, and displays

Sistemas eficientes de transmissão de energia sem-fios e identificação por radiofrequência

Doutoramento em Engenharia EletrotécnicaIn the IoT context, where billions of connected objects are expected to be ubiquitously deployed worldwide, the frequent battery maintenance of ubiquitous wireless nodes is undesirable or even impossible. In these scenarios, passive-backscatter radios will certainly play a crucial role due to their low cost, low complexity and battery-free operation. However, as passive-backscatter devices are chiefly limited by the WPT link, its efficiency optimization has been a major research concern over the years, gaining even more emphasis in the IoT context. Wireless power transfer has traditionally been carried out using CW signals, and the efficiency improvement has commonly been achieved through circuit design optimization. This thesis explores a fundamentally different approach, in which the optimization is focused on the powering waveforms, rather than the circuits. It is demonstrated through theoretical analysis, simulations and measurements that, given their greater ability to overcome the built-in voltage of rectifying devices, high PAPR multi-sine (MS) signals are capable of more efficiently exciting energy harvesting circuits when compared to CWs. By using optimal MS signals to excite rectifying devices, remarkable RF-DC conversion efficiency gains of up to 15 dB with respect to CW signals were obtained. In order to show the effectiveness of this approach to improve the communication range of passive-backscatter systems, a MS front-end was integrated in a commercial RFID reader and a significant range extension of 25% was observed. Furthermore, a software-defined radio RFID reader, compliant with ISO18000-6C standard and with MS capability, was constructed from scratch. By interrogating passive RFID transponders with MS waveforms, a transponder sensitivity improvement higher than 3 dB was obtained for optimal MS signals. Since the amplification and transmission of high PAPR signals is critical, this work also proposes efficient MS transmitting architectures based on space power combining techniques. This thesis also addresses other not less important issues, namely self-jamming in passive RFID readers, which is the second limiting factor of passive-backscatter systems. A suitable self-jamming suppression scheme was first used for CW signals and then extended to MS signals, yielding a CW isolation up to 50 dB and a MS isolation up 60 dB. Finally, a battery-less remote control system was developed and integrated in a commercial TV device with the purpose of demonstrating a practical application of wireless power transfer and passive-backscatter concepts. This allowed battery-free control of four basic functionalities of the TV (CH+,CH-,VOL+,VOL-).No contexto da internet das coisas (IoT), onde são esperados bilhões de objetos conectados espalhados pelo planeta de forma ubíqua, torna-se impraticável uma frequente manutenção e troca de baterias dos dispositivos sem fios ubíquos. Nestes cenários, os sistemas radio backscatter passivos terão um papel preponderante dado o seu baixo custo, baixa complexidade e não necessidade de baterias nos nós móveis. Uma vez que a transmissão de energia sem fios é o principal aspeto limitativo nestes sistemas, a sua otimização tem sido um tema central de investigação, ganhando ainda mais ênfase no contexto IoT. Tradicionalmente, a transferência de energia sem-fios é feita através de sinais CW e a maximização da eficiência é conseguida através da otimização dos circuitos recetores. Neste trabalho explora-se uma abordagem fundamentalmente diferente, em que a otimização foca-se nas formas de onda em vez dos circuitos. Demonstra-se, teoricamente e através de simulações e medidas que, devido à sua maior capacidade em superar a barreira de potencial intrínseca dos dispositivos retificadores, os sinais multi-seno (MS) de elevado PAPR são capazes de excitar os circuitos de colheita de energia de forma mais eficiente quando comparados com o sinal CW tradicional. Usando sinais MS ótimos em circuitos retificadores, foram verificadas experimentalmente melhorias de eficiência de conversão RF-DC notáveis de até 15 dB relativamente ao sinal CW. A fim de mostrar a eficácia desta abordagem na melhoria da distância de comunicação de sistemas backscatter passivos, integrou-se um front-end MS num leitor RFID comercial e observou-se um aumento significativo de 25% na distância de leitura. Além disso, desenvolveu-se de raiz um leitor RFID baseado em software rádio, compatível com o protocolo ISO18000-6C e capaz de gerar sinais MS, com os quais interrogou-se transponders passivos, obtendo-se ganhos de sensibilidade dos transponders maiores que 3 dB. Uma vez que a amplificação de sinais de elevado PAPR é uma operação crítica, propôs-se também novas arquiteturas eficientes de transmissão baseadas na combinação de sinais em espaço livre. Esta tese aborda também outros aspetos não menos importantes, como o self-jamming em leitores RFID passivos, tido como o segundo fator limitativo neste tipo de sistemas. Estudou-se técnicas de cancelamento de self-jamming CW e estendeu-se o conceito a sinais MS, tendo-se obtido isolamentos entre o transmissor e o recetor de até 50 dB no primeiro caso e de até 60 dB no segundo. Finalmente, com o objetivo de demonstrar uma aplicação prática dos conceitos de transmissão de energia sem fios e comunicação backscatter, desenvolveu-se um sistema de controlo remoto sem pilhas, cujo protótipo foi integrado num televisor comercial a fim de controlar quatro funcionalidades básicas (CH+,CH-,VOL+,VOL-)

Energy Harvesting for Tire Pressure Monitoring Systems

Tire pressure monitoring systems (TPMSs) predict over- and underinflated tires, and warn the driver in critical situations. Today, battery powered TPMSs suffer from limited energy. New sensor features such as friction determination or aquaplaning detection require even more energy and would significantly decrease the TPMS lifetime. Harvesting electrical energy inside the tire of a vehicle has been considered as a promising alternative to overcome the limited lifetime of a battery. However, it is a real challenge to design a system, that generates electrical energy at low velocities while being robust at 200 km/h where radial accelerations up to 20000 m/s2 occur. This work focusses on developing different electromechanical energy transducers that meet the high requirements of the automotive sector. Different approaches are addressed on how the change of acceleration and strain within the tire can be used to provide mechanical energy to the energy harvester. The energy harvester converts the mechanical energy into electrical energy. In this thesis, piezoelectric and electromagnetic transducers are discussed in depth, modelled as electromechanical networks. Since the transducers provide energy in the form of an AC voltage, but sensors require a DC voltage, various common interface circuits are compared, using LTspice and applying method of the stochastic signal analysis. Furthermore, a buck-boost converter concept for the electromagnetic energy harvester is optimized and improved. Experiments on a tire test rig validate the theoretically determined output and confirm that well designed energy harvesters in the tire can generate much more energy than required by an TPMS not only at high velocities but also at velocities as low as 20 km/h

Development of Ultrathin Niobium Nitride and Niobium Titanium Nitride Films for THz Hot-Electron Bolometers

The main focus of this work is the development of ultrathin NbN and NbTiN films. A reproducible and reliable deposition process for ultrathin NbN and NbTiN films for the use in phonon-cooled HEB devices was established. The ultrathin films were deposited on silicon (Si) substrates and on 2µm Si3N4 membranes by DC reactive magnetron sputtering. A method for the precise control of the nitrogen partial pressure by monitoring the target voltage has been introduced to deposit high quality, ultrathin NbN (3-4nm, Tc=8.5 K) and NbTiN (4-5nm, Tc=8K) films. Substrate heating of at least 600°C during the deposition is essential for the fabrication of ultrathin NbN and NbTiN films on Si substrates and Si3N4 membranes. The fabrication process required for HEB devices to be used in a quasi-optical mixer was developed. The ultrathin film was patterned by electron beam lithography (EBL), resulting in bolometer devices that measure areas of about 0.4 µm x 4 µm. The nature of the contact determines the interface transparency between the bolometer and the contact structure. Different cleaning processes have been performed and the influence on the contact resistance has been instigated. A better interface transparency gives less RF losses and could improve the HEB sensitivity and local oscillator (LO) requirement. A better control of the interface transparency also leads to a better reproducibility in values of the normal state resistance of the HEB devices. Heterodyne measurements were performed at 0.8 THz and 1.6 THz. For the NbTiN HEB devices, the double sideband (DSB) receiver noise temperature at 0.8 THz was found to be 2500 K for at 1.2 GHz IF. The main problem with HEB mixers is the limitation in the IF bandwidth. The measured noise bandwidth was about 1.5 GHz. The DSB receiver noise temperature at 1.6 THz LO frequency measured at Chalmers University, Sweden, was found to be 1600 K at 1.5 GHz IF. This result shows that the noise of these NbTiN HEB devices is comparable with the NbN HEB mixers fabricated at the Chalmers University. For the NbN HEB devices the DSB receiver noise temperature Trec was 1344 K at 0.8 THz with an absorbed LO power of 55 nW, estimated using the isothermal method. This receiver noise temperature is higher than the state-of-the-art receiver noise temperature at this frequency. This is possibly due to the losses in the optics. It was not possible to determine the noise bandwidth of this device, because the noise temperature did not increase by the factor of two in the bandwidth of the isolator. But the noise bandwidth is estimated to be about than 1.8 GHz. Although the true bandwidth of the NbTiN and NbN HEB devices could only be measured with an appropriate IF system, the combination of these results show that NbTiN is possibly inferior in bandwidth to NbN used for the HEB fabrication

Etude du bruit aux basses fréquences dans les transistors à haute mobilité électronique à base de Nitrure de Gallium

Ce mémoire a pour thème l'étude du bruit de fond aux basses fréquences des transistors microondes de type HEMT sur Nitrure de Gallium (GaN). Le premier chapitre est consacré à la présentation de cette filière technologique. Après une description des propriétés physiques du matériau GaN, le fonctionnement et la fabrication des HEMTs sont détaillés, pour finir sur les performances de ces composants et leurs applications. Le deuxième chapitre décrit les cinq technologies étudiées, ainsi qu'une comparaison de leurs caractéristiques électriques statiques. Le troisième chapitre se rapporte aux mesures de bruit basses fréquences associé au courant de drain. Les mesures sont réalisées en régime ohmique, pour permettre l'extraction du paramètre de Hooge (αH). Pour les deux meilleures technologies étudiées, αH est de l'ordre de 10-4, valeur comparable à celle obtenue pour des filières plus matures, telle que GaAs. L'étude du bruit BF mesuré entre drain et source est ensuite réalisée en fonction de la polarisation du composant, ce qui permet de localiser et de modéliser les sources de bruit prédominantes. Enfin, l'évolution du bruit BF associé au courant de drain en fonction de la température permet d'extraire la signature des pièges profonds. Le quatrième chapitre détaille l'évolution du bruit associé au courant de grille en fonction de la polarisation, et à la corrélation entre le bruit de drain et le bruit de grille. Pour les composants présentant un courant de fuite de grille important, des valeurs proches de 1 indiquent la contribution du bruit du circuit d'entrée au bruit mesuré sur le drain.This report deals with the study of low frequency electrical noise in microwave HEMT, based on Gallium Nitride (GaN). The first chapter details the presentation of GaN HEMTs technology. After a description of GaN physical properties, the fabrication and the operation of HEMTs are described. Finally, a summary of the electrical performances and of the potential applications of those devices is given. The second chapter presents the five technologies under study, and a comparison between the electric static parameters of each technology. The third chapter deals with the LF drain current noise measurements. Measurements are performed in the ohmic regime, which allows the extraction of the Hooge parameter (αH). For the two technologies under study presenting the lowest noise levels, αH is in the range of 10-4, which is comparable to those of mature GaAs technologies. Then, the study of low frequency drain current noise is performed versus the bias of the devices, to locale and model the main noise sources. Then, the evolution of the LF drain current noise versus temperature leads to the extraction of deep level signatures. The last chapter is focused on the low frequency gate current noise analysis versus the bias of HEMTs, and on the correlation between drain and gate noise. For devices presenting high gate leakage current, values of the coherence function close to 1 show the contribution of the input circuit noise on the measured drain noise