This dissertation focuses on an uncooled Mid-Wave Infra-Red (MWIR) detector was developed by doping an n-type 4H-SiC with Ga using the laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide, a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 µm. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the semiconductor. This process modifies the electron density, which changes the refraction index and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam such as a He-Ne laser. This capability of measuring the detector response remotely makes it a wireless optical detector. The variation of refraction index was calculated as a function of absorbed irradiance based on the reflectance data for the as-received and doped samples. A distinct change was observed for the refraction index of the doped sample, indicating that the detector is suitable for applications at 4.21 µm wavelength. The Ga dopant energy level in the substrate was confirmed by optical absorption spectroscopy. Secondary ion mass spectroscopy (SIMS) of the doped samples revealed an enhancement in the solid solubility of Ga in the substrate when doping is carried out by increasing the number of laser scans. Higher dopant concentration increases the number of holes in the dopant energy level, enabling photoexcitation of more electrons from the valence band by the incident MWIR photons. The detector performance improves as the dopant concentration increases from 1.15×1019 to 6.25×1020 cm-3. The detectivity of the optical photodetector is found to be 1.07×1010 cm·Hz1/2/W for the case of doping with 4 laser passes. The noise mechanisms in the probe laser, silicon carbide MWIR detector and laser power meter affect the performance of the detector such as the responsivity, noise equivalent temperature difference (NETD) and detectivity. For the MWIR wavelength 4.21 and 4.63 µm, the experimental detectivity of the optical photodetector of this study is found to be 1.07×1010 cm·Hz1/2/W, while the theoretical value is 2.39×1010 cm·Hz1/2/W. The values of NETD are found to be 404.03 and 15.48 mK based on experimental data for an MWIR radiation source of temperature 25°C and theoretical calculation respectively. The doped SiC also has a capability of gas detection since gas emission spectra are in infrared range. Similarly, the sensor is based on the semiconductor optics principle, i.e., an energy gap is created in a semiconductor by doping it with an appropriate dopant to ensure that the energy gap matches with an emission spectral line of the gas of interest. Specifically four sensors have been fabricated by laser doping four quadrants of a 6H-SiC substrate with Ga, Al, Sc and P atoms to detect CO2, NO, CO and NO2 gases respectively. The photons, which are emitted by the gas, excite the electrons in the doped sample and consequently change the electron density in various energy states. This phenomenon affects the refraction index of the semiconductor and, therefore, the reflectivity of the semiconductor is altered by the gas. The optical response of this semiconductor sensor is the reflected power of a probe beam, which is a He-Ne laser beam in this study. The CO2, NO, CO and NO2 gases change the refraction indices of Ga-, Al-, Sc- and Al-doped 6H-SiC, respectively, more prominently than the other gases tested in this study. Hence these doped 6H-SiC samples can be used as CO2, NO, CO and NO2 gas sensors respectively.

This thesis reports the fabrication and characterization of long wavelength infrared mercury cadmium telluride (Hg1-xCdxTe) photodiodes and 128x128 focal plane arrays grown on lattice matched cadmium zinc telluride (Cd1-yZnyTe) substrates by metal organic vapor phase epitaxy (MOVPE). The dark current modeling of 33x33 mm2 Hg1-xCdxTe photodiodes has shown the dark current is dominated by trap assisted tunneling under small reverse bias voltages typically used to bias these detectors. The dominant dark current mechanisms under high reverse bias and low forward bias are band&ndash / to&ndash / band tunneling and generation&ndash / recombination, respectively. The photodiodes have yielded a peak 77 K detectivity of 3.2x1010 cm&amp / #8730 / Hz/W with a cut-off wavelength (50%) of 10.92 mm. It has also been found that the 1/f noise current of the detectors at 1 Hz is related to the trap-assisted tunneling current through the empirical relation in=&amp / #945 / TAT(ITAT)&amp / #946 / with &amp / #945 / TAT=7.0 x 10-5 and &amp / #946 / =0.65. In the course of the focal plane array (FPA) fabrication process development work, ohmic contact formation on p-type Hg1-xCdxTe and mesa wet etch were studied in detail. Contacts with chromium, gold, platinum and copper on p-type Hg1-xCdxTe resulted in bad ohmic contacts, which did not seem to improve with annealing. On the other hand a HgTe cap layer on p-type Hg1-xCdxTe resulted in good ohmic contact with acceptably low resistance. Among the etchants studied for mesa etching of the diode structures, Br2/HBr solution yielded the best performance. After developing all of the steps of FPA processing, 128x128 Hg1-xCdxTe FPAs were successfully fabricated and tested in a thermal imager. While thermal imaging was performed with the FPAs, high nonuniformity of the material and low R0A product of the pixels did not allow high sensitivity imaging.

abstract: InAs/InAsSb type-II superlattices (T2SLs) can be considered as potential alternatives for conventional HgCdTe photodetectors due to improved uniformity, lower manufacturing costs with larger substrates, and possibly better device performance. This dissertation presents a comprehensive study on the structural, optical and electrical properties of InAs/InAsSb T2SLs grown by Molecular Beam Epitaxy. The effects of different growth conditions on the structural quality were thoroughly investigated. Lattice-matched condition was successfully achieved and material of exceptional quality was demonstrated. After growth optimization had been achieved, structural defects could hardly be detected, so different characterization techniques, including etch-pit-density (EPD) measurements, cathodoluminescence (CL) imaging and X-ray topography (XRT), were explored, in attempting to gain better knowledge of the sparsely distributed defects. EPD revealed the distribution of dislocation-associated pits across the wafer. Unfortunately, the lack of contrast in images obtained by CL imaging and XRT indicated their inability to provide any quantitative information about defect density in these InAs/InAsSb T2SLs. The nBn photodetectors based on mid-wave infrared (MWIR) and long-wave infrared (LWIR) InAs/InAsSb T2SLs were fabricated. The significant difference in Ga composition in the barrier layer coupled with different dark current behavior, suggested the possibility of different types of band alignment between the barrier layers and the absorbers. A positive charge density of 1.8 × 1017/cm3 in the barrier of MWIR nBn photodetector, as determined by electron holography, confirmed the presence of a potential well in its valence band, thus identifying type-II alignment. In contrast, the LWIR nBn photodetector was shown to have type-I alignment because no sign of positive charge was detected in its barrier. Capacitance-voltage measurements were performed to investigate the temperature dependence of carrier densities in a metal-oxide-semiconductor (MOS) structure based on MWIR InAs/InAsSb T2SLs, and a nBn structure based on LWIR InAs/InAsSb T2SLs. No carrier freeze-out was observed in either sample, indicating very shallow donor levels. The decrease in carrier density when temperature increased was attributed to the increased density of holes that had been thermally excited from localized states near the oxide/semiconductor interface in the MOS sample. No deep-level traps were revealed in deep-level transient spectroscopy temperature scans. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2015

Orientador: Ioshiaki Doi / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-20T21:32:16Z (GMT). No. of bitstreams: 1 Neli_RobertoRibeiro_D.pdf: 20995056 bytes, checksum: 0072f9af377dc8c222632b4d9608b5b0 (MD5) Previous issue date: 2012 / Resumo: Este trabalho tem como objetivo a fabricação e caracterização de sensores térmicos descritos como bolométricos, que são dedicados a detecção da radiação infravermelha distante. Estes sensores são construídos a partir de técnicas de microfabricação, utilizando filmes finos seletivos a corrosão úmida. Estas microestruturas mecânicas são formadas sobre laminas de silício a partir de um ataque químico úmido sobre a superfície da mesma. Como estas estruturas são obtidas utilizando-se técnicas convencionais de fabricação de circuitos integrados, torna-se possível a integração monolítica de circuitos eletrônicos e dispositivos mecânicos, permitindo o desenvolvimento de microssistemas integrados. O ouro poroso ou "ouro negro" foi estudado e caracterizado, sendo utilizado como absorvedor de radiação e apresentou neste trabalho índices de absorção superiores a 80%. Foi desenvolvido também um processo para integrar este filme ao dispositivo. O silício policristalino, submetido a dopagem de boro, foi desenvolvido para se obter valores de TCR próximos a -2%K-1 e resistências abaixo de 1k'ômega'. Finalmente, foram desenvolvidos os layouts, fabricadas e testadas as microestruturas de diversas geometrias, como pontes, vigas, membranas, espiras, entre outras. Os dispositivos bolométricos testados apresentaram TCR de -2,54%K-1 , um tempo de resposta de aproximadamente 2 ms, uma responsividade de 0,35 V/W e uma detectividade específica de 6,04.109 mHz1/2W-1, quando submetido a uma radiação de 0,85 THz / Abstract: This work has as a main goal the fabrication and characterization of thermal sensors, described as bolometrics, which are dedicated to detection of far infrared radiation. These sensors are fabricated using microfabrication techniques and the thin films are selectives to wet etching. These mechanical microstructures are formed on silicon wafers using a surface wet etching. As these structures are obtained using conventional techniques for CI's manufacturing, it becomes possible perform a monolithic integration of electronics and mechanical devices, allowing the integrated microsystems development. The porous gold or "gold black" used as a radiation absorber, was studied and characterized, and this study showed absorption index greater than 80%. Was developed a process to integrate this film to device. The doped polycrystalline silicon was performed to obtain TCR values near to -2% K-1 and resistance less than 1k'omega'. Finally, the layouts are designed, performed and tested the microstructure of various geometries such as bridges, beams, membranes, coils, among others. The devices tested presented TCR about -2.54% K-1, a response time of approximately 2 ms, responsivity about 0.35 V / W and specific detectivity about 6.04x109 mHz1/2W-1 when subjected to a 0,85 THz radiation / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

The potential imaging performance of infrared (IR) detectors is dependent on the noise level in the detector pixels. Noise measurements at pixel level can therefore provide basic understanding of the intrinsic limitations of detectors. Accurate noise studies with measurements at different biases and with high frequency resolution can however consume a lot of time; therefore, automation of this process is necessary. In this thesis, automation of a noise measurement setup has been implemented. The noise measurement system that has been automated has proven to work for automatically acquiring noise spectra from long wavelength infrared detectors of different types, such as Quantum Well Infrared Photodetectors (QWIPs) and Type II-superlattice (T2SL) detectors. The results of these studies have been used to calculate the noise gain of the detectors. It also has been key to determine discrepancies between different QWIP fabrication batches and helped to clarify the differences in performance of the detectors from those batches. Regarding T2SL, noise measurements on detectors with big differences in dark current have been carried out. Finally, a study of the impact of pixel shape in T2sL noise has been conducted. / Bildkvaliteten hos bildgenererande infraröda (IR) detektorer påverkas av brusnivån i de enskilda pixlarna i detektormatrisen. Brusmätningar på pixelnivå kan därför ge en grundläggande förståelse för vad som begränsar detektorns prestanda. Noggranna studier av bruset, med mätningar vid olika spänningar och med hög frekvensupplösning kan dock vara väldigt tidskrävande, varför automatisering av dessa mätningar är nödvändigt.I detta examensarbete har automatisering av en brusmätuppställning för IR-detektorer utförts.Automatiseringen av brusmätsystemet har fungerat tillfredsställande och har använts för att mäta brus i olika sorters långvågiga IR-detektorer, såsom kvantbrunnsbaserade IR-detektorer (QWIP= Quantum well infrared photodetector) och typ-II supergitterbaserade IR-detektorer (T2SL = Type II superlattice).Resultaten av dessa studier har använts för att beräkna brusförstärkningsfaktorn i dessa detektorer. Studier av brusspektra från olika tillverkningsbatcher av QWIPar har varit en avgörande faktor för att förstå varför detektorprestanda varierar mellan olika batcher. För T2SL-baserade IRdetektorer har studier utförts för att avgöra inverkan av pixelformen, pixelstorlek och mörkerströmsnivå på brusnivån i dessa detektorer.

High sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current theory, and efforts to maximize signal to noise ratio are shown and evaluated. Most notably, presented are the experimental results and analysis from the integration of two different absorptive coatings: a patterned gold black film and a plasmonic resonant structure. Infrared-absorbing gold black was selectively patterned onto the active surfaces of the detector. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves gold black's near unity absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. Infrared responsivity is improved 70% for mid-wave IR and 22% for long-wave IR. The increase in the thermal time constant caused by the additional mass of gold black is a modest 15%. However, this film is sensitive to thermal processing; experimental results indicate a decrease in absorptance upon device heating. Sub-wavelength resonant structures designed for long-wave infrared (LWIR) absorption have also been investigated. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 ?m LWIR wavelength band, a broader range than can be achieved using the usual resonance quarter-wave cavity engineered into the air-bridge structures. Experimental measurements show an increase in responsivity of 96% for mid-wave IR and 48% for long-wave IR, while thermal response time only increases by 16% due to the increased heat capacity. The resonant structures are not as susceptible to thermal processing as are the gold black films. This work suggests that plasmonic resonant structures can be an ideal method to improve detector performance for microbolometers.

Ce travail traite des aides optroniques aux déplacements des non-voyants. Préalablement à ce travail, deux « détecteurs de passage » ont été développés au Laboratoire Aimé Cotton le « Tom Pouce » et le « Télétact ». Le « Tom Pouce » est simple d’utilisation mais présente des limitations pour détecter les passages étroits à des distances supérieures à trois mètres ainsi que pour éviter les poteaux fins. Le « Télétact » permet de gérer l’ensemble des situations mais le nombre d’utilisateurs est limité par l’effort cognitif important que demande son utilisation ainsi que sa fragilité.Le but principal de cette thèse est d’améliorer les capteurs ainsi que leur façon de représenter l’espace afin d’avoir un dispositif facile d’utilisation détectant tous les passages.Dans un premier temps, l’hypothèse que la forme de la zone de protection idéale devrait être d’aspect cylindrique est émise. La réalisation approchée de cette forme à partir de capteurs infrarouges est analysée théoriquement et validée expérimentalement. Deux dispositifs le « Tom Pouce II » et le « Minitact » utilisant ce concept ont été proposés à des non-voyants et ont reçu un accueil favorable. Dans un second temps, les capteurs laser télémétriques du « Télétact » ont été revus afin d’améliorer leurs performances permettant entre autres une moindre sensibilité aux contraintes mécaniques. Une nouvelle forme d’association des capteurs infrarouges et laser permet de gérer l’ensemble des configurations de passages, y compris en chicane, avec une interface tactile ayant seulement trois niveaux d’alerte correspondant à trois zones de protection (moins de 2 mètres de profondeur sur 10 cm de large, entre 2 et 6 mètres sur plus de 50 cm de large, plus de 6m de profondeur et 1m de large ) avec un effort cognitif très réduit par rapport au « Télétact » initial utilisant 32 sons différents. Des outils pour pouvoir analyser objectivement les performances des dispositifs dans des environnements contrôlés ont été mis au point afin de pouvoir ajuster finement les formes des zones de protection. Un dernier point concerne les possibilités d’identification des obstacles, l’imagerie est explorée mais s’avère immature, actuellement seules les « astuces d’utilisation » des capteurs sont opérationnelles. / This work deals with optical electronic travel aids for visually impaired people. Initially, two devices allowing the detection of an unrestricted path were developed at the Aime Cotton Laboratory: the "Tom Pouce" and the "Télétact". The "Tom Pouce" is simple to use but presents limitations for detecting narrow passages at distances over three meters as well as avoiding fine posts. The "Télétact" allows users to manage every situation but the number of users is restricted due to the cognitive effort required.The main purpose of this thesis is to improve the sensors as well as the way the spatial information is transmitted to the user to allow the safe detection of all passages with reduced cognitive effort.First, the hypothesis is that the ideal protection zone could be a cylindrical shape. The approached realization of the cylindrical shape with infrared sensors is theoretically analyzed and experimentally tested. Two devices,"Tom Pouce II" and "Minitact”, using this concept were proposed to visually impaired people already using the “Tom Pouce I”. They greatly appreciated the improvement.Second, the laser telemetric laser sensors of the «Télétact» were modified to improve their performance and to reduce the sensitivity of mechanical constraints during daily use. The association of infrared sensors and laser telemetric sensors allowed the management of all kinds of passages, including chicanes, with a tactile interface having only three levels of alert corresponding to three zones of protection (less than 2 meters deep and 10 cm wide, between 2 and 6 meters deep and about 50 cm wide, and more than 6m deep and 1m wide). The cognitive effort is greatly reduced compared to the initial "Télétact" , which used 32 different sounds.Third, tools to objectively analyze the performance of the implemented devices in controlled environments were developed to finely adjust the shape of the protection zones.The last point dealt with the possibilities of identification of obstacles, imagery is explored but it is proved to be premature. Nowadays only tricks of the trade are effectively working.

Ce travail se consacrera à l’étude des performances électro-optiques sur des détecteurs infrarouges à base de photodiodes. Les performances étudiées seront le rendement quantique qui étudie la capacité de conversion de la diode et la fonction de transfert de modulation qui quantifie la capacité du détecteur à échantillonner les fréquences spatiales. La problématique sera de comprendre les phénomènes impactant ces performances pour permettre leur optimisation et ainsi réduire le temps de développement d’un nouveau produit. Deux moyens sont mis à disposition pour répondre à cette problématique : la mesure et la simulation par éléments finis.Après avoir présenté ces performances électro-optiques, ainsi que leur place dans le Marché de l’infrarouge, des mesures et des simulations de rendement quantique et de FTM seront réalisées pour mettre en avant les phénomènes responsables des performances actuelles. Des technologies plus avancées seront également étudiées par simulation pour rechercher les meilleurs candidats pour les petits pas pixels. / The purpose of this thesis is to evaluate the electro-optical performances of infrared detectors based on photodiodes. The performances studied are the quantum efficiency and the modulation transfer function. The problematic is to understand which phenomenon impacts these performances for reducing the development time. In order to answer this problematic, this study is made through measurements and numerical simulations.Firstly, electro-optical performances are discussed with their link to the infrared market. Then, measurements and numerical computations are made in order to explain the reasons of the actual values. Finally, by computation, advance technologies are analyzed and compared for the modulation transfer function.

abstract: Current hybrid vehicle and/or Fuel Cell Vehicle (FCV) use both FC and an electric system. The sequence of the electric power train with the FC system is intended to achieve both better fuel economies than the conventional vehicles and higher performance. Current hybrids use regenerative braking technology, which converts the vehicles kinetic energy into electric energy instead of wasting it. A hybrid vehicle is much more fuel efficient than conventional Internal Combustion (IC) engine and has less environmental impact The new hybrid vehicle technology with it's advanced with configurations (i.e. Mechanical intricacy, advanced driving modes etc) inflict an intrusion with the existing Thermal Management System (TMS) of the conventional vehicles. This leaves for the opportunity for now thermal management issues which needed to be addressed. Till date, there has not been complete literature on thermal management issued of FC vehicles. The primary focus of this dissertation is on providing better cooling strategy for the advanced power trains. One of the cooling strategies discussed here is the thermo-electric modules. The 3D Thermal modeling of the FC stack utilizes a Finite Differencing heat approach method augmented with empirical boundary conditions is employed to develop 3D thermal model for the integration of thermoelectric modules with Proton Exchange Membrane fuel cell stack. Hardware-in-Loop was designed under pre-defined drive cycle to obtain fuel cell performance parameters along with anode and cathode gas flow-rates and surface temperatures. The FC model, combined experimental and finite differencing nodal net work simulation modeling approach which implemented heat generation across the stack to depict the chemical composition process. The structural and temporal temperature contours obtained from this model are in compliance with the actual recordings obtained from the infrared detector and thermocouples. The Thermography detectors were set-up through dual band thermography to neutralize the emissivity and to give several dynamic ranges to achieve accurate temperature measurements. The thermocouples network was installed to provide a reference signal. The model is harmonized with thermo-electric modules with a modeling strategy, which enables optimize better temporal profile across the stack. This study presents the improvement of a 3D thermal model for proton exchange membrane fuel cell stack along with the interfaced thermo-electric module. The model provided a virtual environment using a model-based design approach to assist the design engineers to manipulate the design correction earlier in the process and eliminate the need for costly and time consuming prototypes. / Dissertation/Thesis / Masters Thesis Technology 2014

Main goal of this thesis is evaluation of the available SON and sacrificial layer technologies from the perspective of temperature sensor design. Based on the findings, a series of detector architectures is proposed. The work is subdivided into two major parts, with the first one targeting the process characterization. Good command of the selected technology, awareness of its dependencies and limitations, is essential and has to be examined prior to any MEMS design. Pressure related topics are of particular interest, since this criterion, among others, highly influences the performance of thermal systems. Knowledge of the critical parameters is applied in the second half, where the actual IR sensor design is considered. Process characterization, required for thermal insulation estimations, is not the only link between the two physics fields. Discussed IR detectors are highly inspired by the developed pressure sensing solutions. This resulted in either similar operation principles being applied, or even the same fabricated structures being adapted for new use.:List of abbreviations List of Figures List of Tables Acknowledgements 1 Introduction 1.1 Motivation and organization of the work 1.2 Microstructure fabrication methods 1.2.1 Surface micromachining 1.2.2 Bulk micromachining 1.2.3 SOI and SON structuring 2 Pressure sensor for process characterization applications 2.1 Motivation 2.2 Pirani gauge approach 2.2.1 Principles of operation and state of the art 2.2.2 Modelling 2.2.2.1 Setup 2.2.2.2 Results 2.2.3 Processing 2.2.4 Measurement 2.2.4.1 Setup 2.2.4.2 Results 2.2.5 Application 2.2.5.1 Outgassing characterization 2.2.5.2 Reliability investigation 2.2.5.3 Thermal emitter for IR spectroscopy 2.2.5.4 Active pressure sensor 2.3 Capacitive sensor approach 2.3.1 Principles of operation and state of the art 2.3.2 Surface channel approach 2.3.3 SON channel approach 2.3.4 Application 2.3.4.1 MEMS dynamic characterization 2.3.4.2 Differential capacitive pressure sensor 2.4 Summary and overview of results 3 Temperature sensor for IR applications 3.1 Motivation 3.2 Resistive sensor approach 3.2.1 Principles of operation 3.2.2 Modelling 3.2.3 Measurement 3.3 Capacitive sensor approach 3.3.1 Principles of operation 3.3.2 Modelling 3.3.2.1 Setup 3.3.2.2 Results 3.3.3 Processing 3.4 Junction - based approach 3.4.1 State of the art 3.4.2 Thermal insulation design 3.4.2.1 Overview 3.4.2.2 Processing 3.4.2.3 Thermal performance 3.4.3 Detector design 3.4.3.1 Diode sensing solution 3.4.3.2 Bipolar Junction Transistor sensing solution 3.4.3.3 Junction Field Effect Transistor sensing solution 3.5 Summary and overview of results 4 Conclusion Bibliography