Hall Sensors for Extreme Temperatures

We report on the preparation of the first complete extreme temperature Hall sensor. This means that the extreme-temperature magnetic sensitive semiconductor structure is built-in an extreme-temperature package especially designed for that purpose. The working temperature range of the sensor extends from −270 °C to +300 °C. The extreme-temperature Hall-sensor active element is a heavily n-doped InSb layer epitaxially grown on GaAs. The magnetic sensitivity of the sensor is ca. 100 mV/T and its temperature coefficient is less than 0.04 %/K. This sensor may find applications in the car, aircraft, spacecraft, military and oil and gas industries

Fabrication and Characterization of Metal-Loaded Mixed Metal Oxides Gas Sensors for the Detection of Hazardous Gases

This study concerns gas sensors that may protect individuals by detecting hazardous gases that may be generated in hot spaces (≥50°C) with residues of organic waste. We investigated the responses and selectivities of the sensors to different kinds of hazardous gases such as acetaldehyde, toluene and hydrogen sulfide. We also investigated operating temperatures and catalysts for the sensors. The thick film semiconductor sensors that detected some hazardous gases were prepared using nano-sized sensing material powders (SnO2, WO3, ZnO) that were prepared through sol-gel and precipitation methods. The nano-sized sensing materials were blended with various amounts of metal oxides (SnO2, ZnO, WO3) and coated with transition metals (Pt, Pd, Ru, Au, Ag, Cu and In). The metal oxide thick films were fabricated on an Al2O3 plate with a Ni-Cr heater and a Pt electrode through a screen-printing method. Morphologies, compositions, phases, surface areas and particle sizes of sensor compounds were examined by SEM, EDS, XRD and BET analysis. The investigated response to the various hazardous vapors was expressed as the value of Ra/Rg, where Ra and Rg are the resistance of the sensor material in the air and in hazardous gas, respectively

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

Non-silicon Microfabricated Nanostructured Chemical Sensors For Electric Nose Application

A systematic investigation has been performed for Electric Nose , a system that can identify gas samples and detect their concentrations by combining sensor array and data processing technologies. Non-silicon based microfabricatition has been developed for micro-electro-mechanical-system (MEMS) based gas sensors. Novel sensors have been designed, fabricated and tested. Nanocrystalline semiconductor metal oxide (SMO) materials include SnO2, WO3 and In2O3 have been studied for gas sensing applications. Different doping material such as copper, silver, platinum and indium are studied in order to achieve better selectivity for different targeting toxic gases including hydrogen, carbon monoxide, hydrogen sulfide etc. Fundamental issues like sensitivity, selectivity, stability, temperature influence, humidity influence, thermal characterization, drifting problem etc. of SMO gas sensors have been intensively investigated. A novel approach to improve temperature stability of SMO (including tin oxide) gas sensors by applying a temperature feedback control circuit has been developed. The feedback temperature controller that is compatible with MEMS sensor fabrication has been invented and applied to gas sensor array system. Significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient conditions. Single walled carbon nanotube (SWNT) has been studied to improve SnO2 gas sensing property in terms of sensitivity, response time and recovery time. Three times of better sensitivity has been achieved experimentally. The feasibility of using TSK Fuzzy neural network algorithm for Electric Nose has been exploited during the research. A training process of using TSK Fuzzy neural network with input/output pairs from individual gas sensor cell has been developed. This will make electric nose smart enough to measure gas concentrations in a gas mixture. The model has been proven valid by gas experimental results conducted

Recent Developments in R.F. Magnetron Sputtered Thin Films For pH Sensing Applications - An Overview

pH sensors are widely used in chemical and biological applications. Metal oxides-based pH sensors have many attractive features including insolubility, stability, mechanical strength, electrocatalyst and manufacturing technology. Various metal oxide thin films prepared by radio frequency (R.F.) magnetron sputtering have attractive features, including high pH sensitivity, fast response, high resolution, good stability and reversibility as well as potential for measuring pH under conditions that are not favourable for the commonly used glass electrodes-based pH sensors. In addition, thin film pH sensors prepared by R.F. magnetron sputtering offer many advantages, such as ease of packaging, low cost through the use of standard microfabrication processes, iniaturisation, capability of measuring pH at high temperatures, ruggedness and disposability. In this paper, recent development of R.F. magnetron sputtered thin films for pH sensing applications are reviewed

Performance optimization of metal oxides for gas sensing: the case of WO3 and SnO2

Electrical gas sensors based on semiconducting metal oxides are now used in a wide range of applications and provided by many companies. They attracted the attention of many users and scientists due to the low cost, flexibility of production, ease of use, long-term stability and large number of detectable gases. The rising demand for gas sensors for a wide range of applications has highlighted not only the capabilities of these devices, but also their limits. Although common metal oxides, such as SnO2, TiO2, WO3 and ZnO, are catalytically active, different strategies are required to improve their selectivity and sensitivity. The quest for highly selective and high-performance gas sensors encouraged research into new sensing materials. Two approaches were used in this thesis to enhance the sensing capabilities of metal oxide-based thick films for detection of ethanol and hydrogen, i.e., two analytes of widespread interest for several applications. The first strategy aimed to control the size and shape of WO3 nanostructured powders used to produce thick films. WO3 nanoflakes have been synthetized through a simple and time effective solvothermal method. Two-dimensional (2D) WO3 was evaluated as most promising for the optimization of active surface area and film porosity for ethanol sensing. The second approach tuned the chemical composition and structure of SnO2 through substitution of Sn sites with Ti and Nb in different contents. Ti, Nb and Sn have similar ionic radii and bimetallic oxide solid solution of (Sn,Ti)xO2 and (Ti,Nb)xO2 have been claimed to enhance the sensing properties of single oxides, although some limitations remain. Nevertheless, the large number of compositional and structural combinations that these materials offer, makes it possible still unexplored possibilities. Indeed, what emerged from this work was that the incorporation of Nb in (Sn,Ti)xO2 offer a number of advantages, including increased film conductance and structural stability, as well as improved sensitivity to some gases, i.e. ethanol and hydrogen. Moreover, humidity (a common interferent) had a negligible influence on the baseline conductance of the (Sn,Ti,Nb)xO2 solid solution. While the reactions between the target gas and the surface of WO3 are well documented in the literature, those that occur over (Sn,Ti,Nb)xO2 are unknown due to the new chemical nature of the material. Therefore, operando Diffuse Reflectance Infrared Fourier Transform (DRIFT)-spectroscopy was employed to explore the interactions between ethanol, hydrogen and water vapour with the surface of the most promising (Sn,Ti,Nb)xO2 sensors while they were in operation.I sensori elettrici a base di ossidi metallici semiconduttori sono ad oggi ampiamente usati in numerose applicazioni e venduti da diverse compagnie. Hanno attratto l’attenzione di molti utilizzatori e scienziati grazie al loro basso costo, adattabilità di produzione, facilità di utilizzo, stabilità a lungo termine e largo numero di gas rilevabili. La crescente domanda per sensori di gas in applicazioni diversificate ha portato alla luce non solo le capacità di questi sensori, ma anche i loro limiti. Nonostante i comuni ossidi metallici, come SnO2, TiO2, WO3 e ZnO, siano cataliticamente attivi, diverse strategie devono essere adottate per migliorare la loro selettività e sensibilità. La richiesta di sensori di gas altamente performanti e selettivi ha incoraggiato la ricerca verso nuovi materiali sensibili. In questa tesi sono stati usati due approcci per ottimizzare film spessi a base di ossidi metallici per il rilevamento di etanolo ed idrogeno, ovvero due analiti di interesse diffuso per molte applicazioni. La prima strategia aveva l’obiettivo di controllare dimensione e forma di polveri nanostrutturate a base di WO3 usate per produrre film spessi. Nano lamine di WO3 sono state sintetizzate con un metodo solvotermale semplice e veloce. Il WO3 bidimensionale (2D) è stato considerato come il più promettente per ottimizzare la superficie attiva e la porosità del film verso il rilevamento di etanolo. Il secondo approccio ha modificato la struttura e composizione chimica dell’SnO2 tramite sostituzione di siti Sn con Ti e Nb, in diverse concentrazioni. Ti, Nb e Sn hanno raggi ionici simili e soluzioni solide di ossidi bimetallici come (Sn,Ti)xO2 and (Ti,Nb)xO2 hanno dimostrato di migliorare le proprietà di rilevamento dei singoli ossidi metallici, anche se rimangono alcune limitazioni. Ciononostante, l’ampio numero di combinazioni composizionali e strutturali che questi materiali offrono consentono ancora possibilità inesplorate. Ad esempio, dal lavoro di tesi è emerso che l’aggiunta di Nb in (Sn,Ti)xO2 offre diversi vantaggi, tra cui una maggiore conduttanza del film e stabilità strutturale, nonché una migliore sensibilità verso alcuni gas, come etanolo ed idrogeno. Inoltre, l’umidità (un comune interferente) ha un’influenza trascurabile sulla conduttanza della soluzione solida di (Sn,Ti,Nb)xO2. Mentre le reazioni tra i gas target e la superficie del WO3 sono documentate nella letterature, quelle che avvengono su (Sn,Ti,Nb)xO2 sono sconosciute a causa della nuova composizione chimica del materiale. Quindi, è stata impiegata la spettroscopia DRIFT (Diffuse Reflectance Infrared Fourier Transform) operando per investigare le interazioni tra etanolo, idrogeno e vapore acqueo con la superficie dei sensori (Sn,Ti,Nb)xO2 più promettenti mentre erano in funzione

Investigation of direct integrated optics modulators

Direct optical modulation techniques applicable to integrated optical data preprocessors were studied. Emphasis was placed on the analysis and fabrication of a field effect type modulator. A series of computer modeling studies were performed to determine the effects of semiconductor cladding on the fields of propagating waves in planar dielectric waveguides. These studies predicted that changes in the propagation characteristics of waveguides clad with silicon and gallium arsenide could be made large enough to be useful in modulators. These effects are dependent on the complex permittivity and thickness of the cladding. Since the conductivity of the cladding can be changed by the photon generation of hole-electron pairs, incoherent light may be used as the input to modulate a coherent light beam. Waveguides were fabricated and silicon claddings were applied to verify the theoretical predictions