Biennial Scientific Report 2007-2008 : Volume 1: Advanced Materials Research

nicht vorhande

Covering THz Gap using photomixers techonologies: arrays and new antenna topologies

Mención Internacional en el título de doctorEl objetivo de esta tesis es el diseño y construcción de generadores de señal de terahercios basados en fotomezcladores de bajo coste y que funcionen a temperatura ambiente. Como se explica en la introducción, existen muchas aplicaciones potenciales a frecuencias comprendidas entre los 100 GHz y 1.000 GHz. Propuestas en el campo de la seguridad, radioastronomía y medicina, entre otros, han sido consideradas y evaluadas. Algunas de ellas han comenzado a ser explotadas comercialmente, por ejemplo, en la detección de armas y explosivos ocultos en puestos de control y seguridad. No obstante, todavía existe un nicho, el de la electrónica de consumo (comunicaciones, entretenimiento, etc), en el que las frecuencias de esta banda no son utilizadas por su alto coste. En una primera parte, se analizan distintos tipos de antenas planares que son especialmente atractivas para ser integradas con dispositivos fotomezcladores generadores de terahercios. El efecto de los sustratos semiconductores en sus propiedades de radiación es analizado en profundidad. Así mismo, se estudian las principales familias de dispositivos fotomezcladores. A continuación, se propone el uso de antenas dieléctricas combinadas con este tipo de fuentes. Con esto, se pretende evitar el uso de lentes dieléctricas de alto costo sin reducir drásticamente la cantidad de potencia de terahercios radiada por la fuente. Se propone un diseño de antena dieléctrica que permitiría aprovechar el ancho de banda de este tipo de generadores, comenzando en los 50-60 GHz hasta por encima del terahercio. Este tipo de antenas dieléctricas ofrece la posibilidad de combinar varios generadores a fin de cumplir dos objetivos: incrementar la potencia disponible y escanear electrónicamente en uno o dos planos. Se propone el uso de nanotubos de carbono para la realización de desfasadores controlados electrónicamente, componente imprescidible para arrays de escaneo electrónico. Finalmente, se estudia la capacidad de este tipo de antenas de actuar como acoplos de campo cercano en resonadores. Como ejemplo de aplicación, se propone su uso en un receptor de terahercios cuya sensibilidad, no limitada por el ruido térmico, llega al límite cuántico, esto es, la detección de fotones de terahercios.The objective of this thesis is the design and manufacturing of roomtemperature cost-affordable terahertz sources based on photomixing. As explained in the preface, there are many potential applications for frequencies between 100 GHz and 1 THz. Many of them, specially in the fields of security, radioastronomy, and medicine have been deeply studied and evaluated. Some of them have led to already available commercial products, e.g. in hidden weapons and explosives detection in security controls. Nevertheless, there are many consumer-oriented applications related with communication and entertainment industry that cannot be implemented because of the actual costs of terahertz systems. Firstly, some planar antenna topologies appealing for photomixing sources are shown. The effect of the semiconductor substrates on its radiation properties is theoretically analyzed. Also, the main families of terahertz photomixing sources are described. Secondly, the use of dielectric antennas in combination with photomixing sources is proposed. This allows to reduce costs without a drastic decrement of the radiated power. An utra-wideband design that could allow us to take advantage of the photomixers bandwidth (from 50-60 GHz up to beyond the terahertz) is presented. Thirdly, the combination of many sources in array configurations is proposed. It allows us to accomplish two objectives: increasing the available terahertz power and 1D or 2D beam steering. A novel phase shifter made of carbon nanotubes is presented, since such component is critical for the development of a electronically steerable array. Finally, the use of this family of dielectric antennas as a near field coupler for dielectric resonators is studied. A room temperature photoncounting teraherz receiver is proposed as an example of application. This receiver is limited only by a quantum limit, which gives the theoretical maximum achievable sensitivity for a receiver.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Zoya Popovic.- Secretario: Luis Emilio García Castillo.- Vocal: Cyril Luxe

Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz

The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks

Bolometers

Infrared Detectors and technologies are very important for a wide range of applications, not only for Military but also for various civilian applications. Comparatively fast bolometers can provide large quantities of low cost devices opening up a new era in infrared technologies. This book deals with various aspects of bolometer developments. It covers bolometer material aspects, different types of bolometers, performance limitations, applications and future trends. The chapters in this book will be useful for senior researchers as well as beginning graduate students

Studies of an Electrically Conducting Organic Material: Tetrathiafulvalene-7,7,8,8-Tetracyanoquinodimethane

This thesis aims to investigate the electrical properties of the organic charge transfer complex Tetrathiafulvalene-7,7,8,8-Tetracyanoquinodimethane, TTF-TCNQ. This is done through two different experimental techniques: Hall characterization and terahertz measurements. Before performing the experiments, suitable devices for these techniques were designed and produced. The layer of TTF-TCNQ was evaporated by physical vapour deposition on an insulating contact of parylene-N and on metallic chromium. According to these results the most promising layer sequence is TTF-TCNQ deposited on top of parylene-N. The adhesive skills of TTF-TCNQ deposited on different materials was also tested using the standardized adhesion test ASTM D3359-97. Two types of electrical devices were produced, Hall devices and terahertz devices. A third sample was also produced in order to image the material of interest using a scanning electron microscope and to measure the film thickness of the polycrystalline TTF-TCNQ layer and of parylene-N. The electric measurements provided the charge carrier concentrations, the sheet carrier density and the conductivity of TTF-TCNQ. The charge carrier densities were high but the measured conductivity was very low. This indicates that the measurement techniques used here may not be very suitable for the both hole and electron conducting TTF-TCNQ material, as the effect of the oppositely charged charge carriers cancel each other out. Also, polycrystalline TTF-TCNQ, which was used here, seems to have a much lower mobility than single crystalline TTF-TCNQ. When working with the type of one-dimensional conductivity observed in TTF-TCNQ it is therefore important to grow single crystalline TTF-TCNQ when very high conductivities are desired. The thesis provides an idea of charge carrier transport in molecular materials, electrical measurement techniques and how to produce a suitable device for examining TTF-TCNQ using terahertz measurements and Hall characterization