集積化AlGaN/GaNイオン感応性電界効果トランジスタに関する研究

AlGaN/GaN heterostructure ion-sensitive field-effect transistors (ISFETs) can provide high sensitivity and fast response due to the high electron mobility and high electron density providing by the two-dimensional electron gas (2DEG) generated at the AlGaN/GaN heterostructure interface. My research mainly focuses on the investigation of the integrated AlGaN/GaN ISFETs for pH sensing. To achieve high performance on AlGaN/GaN ISFET pH sensor, we fabricated sensors with different Al composition (25%, and 35%). We compared the characteristics of the sensors with 25% and 35% Al composition. The pH sensor with Al composition (35%) in the barrier layer with a 16 nm transition layer of 25% Al composition shows better surface sensitivity (SV) of 56.01 mV/pH, which is higher than that of the sensor with 25% Al composition (53.94 mV /pH), but worse current sensitivity SA (-0.095 mA/pH Vs -0.102 mA/pH). In addition, threshold voltage increases from approximately -1.6 V to approximately -0.8 V when measured in alkaline solution for 5 times, along with a decreasing output current. High-resolution SEM photos show that there are high density hexagonal pits with the size of approximately 100 nm on the device surface, presenting the etching effect along the dislocations during alkaline sensing. The X-ray photoelectron spectroscopy (XPS) demonstrates that the intensity of the Ga3d and Al2p spectra decreases after pH sensing measurement, implying the variation of chemical component occurs in the upper AlGaN thin layer. Many voids with a size of approximately 100 nm were observed from the transmission electron microscope (TEM) pictures, which are comparable with that of the scanning electron microscope (SEM). Combining with the energy dispersive X-ray spectroscopy (EDX), the degradation in electrical performance can be attributed to the transformation of AlGaN into oxide as well as the followed alkaline solution dissolve. To avoid the reaction of surface Al with solution, a 3 nm GaN cap layer was added. To reduce the barrier layer thickness, a recessed gate with a length of 2 μm and a depth of about 14 nm was formed. The current sensitivity of the AlGaN/GaN ISFET pH sensors has been improved by 61%, from 52.25 to 84.39 μA/pH, by the recessed-gate structure and ammoniate water treatment. A pH meter system based on the GaN pH sensor was constructed and evaluated. GaN-based ISFET can measure the pH value of the solutions with similar circuit, whether in the linear region or the saturation region. The measurement is stable and repeatable. The small current in the linear region can make the measurement stable and fast, but the resolution is a bit low. High resolution can be obtained in the saturation region, but the measurement is unstable due to excessive current. The Schottky barrier diode (SBD) based on GaN can be used for temperature sensing, and the temperature sensitivity can be improved by different structure design. A recessed anode AlGaN/GaN SBD is suitable to integrate with GaN-based power device for temperature sensor application. The temperature dependent forward voltage at a fixed current shows good linearity, resulting in a sensitivity of approximately 1.0 mV/K. The p-NiO guard ring can suppress the electric field at the anode/GaN interface and field crowding at the anode edge effectively, which enhances the breakdown voltage to approximately -250 V. Using the same material, we can design an integrated device sensor based on GaN to measure temperature and pH simultaneously, which will solve the measurement deviation of pH sensor at different temperatures

Chemical Bionics - a novel design approach using ion sensitive field effect transistors

In the late 1980s Carver Mead introduced Neuromorphic engineering in which various aspects of the neural systems of the body were modelled using VLSI1 circuits. As a result most bio-inspired systems to date concentrate on modelling the electrical behaviour of neural systems such as the eyes, ears and brain. The reality is however that biological systems rely on chemical as well as electrical principles in order to function. This thesis introduces chemical bionics in which the chemically-dependent physiology of specific cells in the body is implemented for the development of novel bio-inspired therapeutic devices. The glucose dependent pancreatic beta cell is shown to be one such cell, that is designed and fabricated to form the first silicon metabolic cell. By replicating the bursting behaviour of biological beta cells, which respond to changes in blood glucose, a bio-inspired prosthetic for glucose homeostasis of Type I diabetes is demonstrated. To compliment this, research to further develop the Ion Sensitive Field Effect Transistor (ISFET) on unmodified CMOS is also presented for use as a monolithic sensor for chemical bionic systems. Problems arising by using the native passivation of CMOS as a sensing surface are described and methods of compensation are presented. A model for the operation of the device in weak inversion is also proposed for exploitation of its physical primitives to make novel monolithic solutions. Functional implementations in various technologies is also detailed to allow future implementations chemical bionic circuits. Finally the ISFET integrate and fire neuron, which is the first of its kind, is presented to be used as a chemical based building block for many existing neuromorphic circuits. As an example of this a chemical imager is described for spatio-temporal monitoring of chemical species and an acid base discriminator for monitoring changes in concentration around a fixed threshold is also proposed

Graphene inspired sensing devices

Graphene’s exciting characteristics such as high mechanical strength, tuneable electrical prop- erties, high thermal conductivity, elasticity, large surface-to-volume ratio, make it unique and attractive for a plethora of applications including gas and liquid sensing. Adsorption, the phys- ical bonding of molecules on solid surfaces, has huge impact on the electronic properties of graphene. We use this to develop gas sensing devices with faster response time by suspending graphene over large area (cm^2) on silicon nanowire arrays (SiNWAs). These are fabricated by two-step metal-assisted chemical etching (MACE) and using a home-developed polymer-assisted graphene transfer (PAGT) process. The advantage of suspending graphene is the removal of diffusion-limited access to the adsorption sites at the interface between graphene and its support. By modifying the Langmuir adsorption model and fitting the experimental response curves, we find faster response times for both ammonia and acetone vapours. The use of suspended graphene improved the overall response, based on speed and amplitude of response, by up to 750% on average. This device could find applications in biomedical breath analysis for diseases such lung cancer, asthma, kidney failure and more. Taking advantage of the mechanical strength of graphene and using the developed PAGT process, we transfer it on commercial (CMOS) Ion-Sensitive Field-Effect Transistor (ISFET) arrays. The deposition of graphene on the top sensing layer reduces drift that results from the surface modification during exposure to electrolyte while improving the overall performance by up to about 10^13 % and indicates that the ISFET can operate with metallic sensing membrane and not only with insulating materials as confirmed by depositing Au on the gate surface. Post- processing of the ISFET top surface by reactive ion plasma etching, proved that the physical location of trapped charge lies within the device structure. The process improved its overall performance by about 105 %. The post-processing of the ISFET could be applied for sensor performance in any of its applications including pH sensing for DNA sequencing and glucose monitoring.Open Acces

Developing ultrasensitive and CMOS compatible ISFETs in the BEOL of industrial UTBB FDSOI transistors

Le marché des capteurs a récemment connu une croissance spectaculaire alimentée par l'application remarquable de capteurs dans l'électronique de consommation, l'industrie de l'automatisation, les appareils portables, le secteur automobile et l'internet des objets de plus en plus adopté. La technologie avancée des complementary metal oxide semiconductor (CMOS), les technologies de nano et de micro-fabrication et les plateformes de synthèse de matériaux innovantes sont également des moteurs du développement incroyable de l'industrie des capteurs. Ces progrès ont permis la réalisation de capteurs dotés de nombreuses caractéristiques telles que la précision accrue, les dimensions miniaturisées, l’intégrabilité, la production de masse, le coût très réduit et le temps de réponse rapide. Les ion-sensitive field-effect transistors (ISFETs) sont des capteurs à l'état solide (bio) chimiques, destinés à la détection des ions H+ (pH), Na+ et K+. Malgré cela, la commercialisation des ISFETs est encore à ses balbutiements, après près de cinq décennies de recherche et développement. Cela est dû principalement à la sensibilité limitée, à la controverse sur l'utilisation de l'électrode de référence pour le fonctionnement des ISFETs et à des problèmes de stabilité. Dans cette thèse, les ISFETs ultrasensibles et compatibles CMOS sont intégrés dans le BEOL des transistors UTBB FDSOI standard. Un circuit diviseur capacitif est utilisé pour polariser la grille d’avant afin d'assurer des performances stables du capteur. En exploitant la fonction d’amplification intrinsèque fournie par les transistors UTBB FDSOI, nous avons présenté des ISFET ultra sensibles. L'amplification découle du fort couplage électrostatique entre la grille avant et la grille arrière du FDSOI et des capacités asymétriques des deux grilles. Un changement de tension au niveau de la grille avant apparaît sur la grille arrière sous la forme d'un décalage amplifié de la tension. L'amplification, représentée par le facteur de couplage (γ), est égale au rapport de la capacité de l'oxyde de grille et de la capacité de le buried oxide (BOX). Par conséquent, en fonctionnalisant la détection du pH sur la grille avant pour les dispositifs FDSOI, la modification du potentiel de surface sur la grille avant est détectée par la grille arrière et amplifiée du facteur de couplage (γ), donnant lieu à un capteur chimique à l'état solide à sensibilité ultra-élevée. L'intégration de la fonctionnalité de détection a été réalisée en back end of line (BEOL), ce qui offre les avantages d'une fiabilité et d'une durée de vie accrues du capteur, d'une compatibilité avec le processus CMOS standard et d'une possibilité d'intégration d'un circuit diviseur capacitif. Le fonctionnement des MOSFETs, sans une polarisation appropriée de la grille avant, les rend vulnérables aux effets de grilles flottantes indésirables. Le circuit diviseur capacitif résout ce problème en polarisant la grille avant tout enmaintenant la fonctionnalité de détection sur la même grille par un couplage capacitif au métal commun du BEOL. Par conséquent, le potentiel au niveau du métal BEOL est une somme pondérée du potentiel de surface au niveau de la grille de détection et de la polarisation appliquée au niveau de la grille de contrôle. Le capteur proposé est modélisé et simulé à l'aide de TCAD-Sentaurus. Un modèle mathématique complet a été développé. Il fournit la réponse du capteur en fonction du pH de la solution (entrée du capteur) et des paramètres de conception du circuit diviseur capacitif et du transistor UTBB FDSOI. Dans ce cas, des résultats cohérents ont été obtenus des travaux de modélisation et de simulation, avec une sensibilité attendue de 780 mV / pH correspondant à un film de détection ayant une réponse de Nernst. La modélisation et la simulation du capteur proposé ont également été validées par une fabrication et une caractérisation du capteur de pH à grille étendue avec validation de son concept. Ces capteurs ont été développés par un traitement séparé du composant de détection de pH, qui est connecté électriquement au transistor uniquement lors de la caractérisation du capteur. Ceci permet une réalisation plus rapide et plus simple du capteur sans avoir besoin de masques et de motifs par lithographie. Les capteurs à grille étendue ont présenté une sensibilité de 475 mV/pH, ce qui est supérieur aux ISFET de faible puissance de l'état de l’art. Enfin, l’intégration de la fonctionnalité de détection directement dans le BEOL des dispositifs FDSOI UTBB a été poursuivie. Une sensibilité expérimentale de 730 mV/pH a été obtenue, ce qui confirme le modèle mathématique et la réponse simulée. Cette valeur est 12 fois supérieure à la limite de Nernst et supérieure aux capteurs de l'état de l’art. Les capteurs sont également évalués pour la stabilité, la résolution, l'hystérésis et la dérive dans lesquels d'excellentes performances sont démontrées. Une nouvelle architecture de détection du pH est également démontrée avec succès, dans laquelle la détection est fonctionnalisée au niveau de la diode de protection de la grille plutôt que de la grille avant des dispositifs UTBB FDSOI. La commutation de courant abrupte, aussi basse que 9 mV/decade, pourrait potentiellement augmenter la sensibilité de polarisation fixée à 6,6 decade/pH. Nous avons démontré expérimentalement une sensibilité de 1,25 decade/pH supérieure à la sensibilité reportée à l’état de l’art.Abstract: The sensor market has recently seen a dramatic growth fueled by the remarkable application of sensors in the consumer electronics, automation industry, wearable devices, the automotive sector, and in the increasingly adopted internet of things (IoT). The advanced complementary metal oxide semiconductor (CMOS) technology, the nano and micro fabrication technologies, and the innovative material synthesis platforms are also driving forces for the incredible development of the sensor industry. These technological advancements have enabled realization of sensors with characteristic features of increased accuracy, miniaturized dimension, integrability, volume production, highly reduced cost, and fast response time. Ion-sensitive field-effect transistors (ISFETs) are solid state (bio)chemical sensors, for pH (H+), Na+, K+ ion detection, that are equipped with the promise of the highly aspired features of CMOS devices. Despite this, the commercialization of ISFETs is still at the stage of infancy after nearly five decades of research and development. This is due mainly to the limited sensitivity, the controversy over the use of the reference electrode for ISFET operation, and because of stability issues. In this thesis, ultrasensitive and CMOS compatible ISFETs are integrated in the back end of line (BEOL) of standard UTBB FDSOI transistors. A capacitive divider circuit is employed for biasing the front gate for stable performance of the sensor. Exploiting the intrinsic amplification feature provided by UTBB FDSOI transistors, we demonstrated ultrahigh sensitive ISFETs. The amplification arises from the strong electrostatic coupling between the front gate and the back gate of the FDSOI, and the asymmetric capacitances of the two gates. A change in voltage at the front gate appears at the back gate as an amplified shift in voltage. The amplification, referred to as the coupling factor (γ), is equal to the ratio of the gate oxide capacitance and the buried oxide (BOX) capacitance. Therefore, functionalizing the pH sensing at the front gate of FDSOI devices, the change in surface potential at the front gate is detected at the back gate amplified by the coupling factor (γ), giving rise to an ultrahigh-sensitive solid state chemical sensor. Integration of the sensing functionality was made in the BEOL which gives the benefits of increased reliability and life time of the sensor, compatibility with the standard CMOS process, and possibility for embedding a capacitive divider circuit. Operation of the MOSFETs without a proper front gate bias makes them vulnerable for undesired floating body effects. The capacitive divider circuit addresses these issues by biasing the front gate simultaneously with the sensing functionality at the same gate through capacitive coupling to a common BEOL metal. Therefore, the potential at the BEOL metal would be a weighted sum of the surface potential at the sensing gate and the applied bias at the control gate. The proposed sensor is modeled and simulated using TCAD-Sentaurus. A complete mathematical model is developed which provides the output of the sensor as a function of the solution pH (input to the sensor), and the design parameters of the capacitive divider circuit and the UTBB FDSOI transistor. In that case, consistent results have been obtained from the modeling and simulation works, with an expected sensitivity of 780 mV/pH corresponding to a sensing film having Nernst response. The modeling and simulation of the proposed sensor was further validated by a proof of concept extended gate pH sensor fabrication and characterization. These sensors were developed by a separated processing of just the pH sensing component, which is electrically connected to the transistor only during characterization of the sensor. This provides faster and simpler realization of the sensor without the need for masks and patterning by lithography. The extended gate sensors showed 475 mV/pH sensitivity which is superior to state of the art low power ISFETs. Finally, integration of the sensing functionality directly in the BEOL of the UTBB FDSOI devices was pursued. An experimental sensitivity of 730 mV/pH is obtained which is consistent with the mathematical model and the simulated response. This is more than 12-times higher than the Nernst limit, and superior to state of the art sensors. Sensors are also evaluated for stability, resolution, hysteresis, and drift in which excellent performances are demonstrated. A novel pH sensing architecture is also successfully demonstrated in which the detection is functionalized at the gate protection diode rather than the front gate of UTBB FDSOI devices. The abrupt current switching, as low as 9 mV/decade, has the potential to increase the fixed bias sensitivity to 6.6 decade/pH. We experimentally demonstrated a sensitivity of 1.25 decade/pH which is superior to the state of the art sensitivity

Investigation and development of titanium nitride solid-state potentiometric pH sensor

The measurement of pH value is crucial parameter in various fields like, drinking water monitoring, food preparation, biomedical and environmental applications. The most common device for pH sensing is the conventional pH glass electrode. While glass electrodes have several advantages, such as Nernstian sensitivity, superior ion selectivity, excellent stability, and extensive operating range, they have several key disadvantages. pH glass electrodes need to be stored in buffer solutions, they are fragile and have limited size and shape, making them impractical for some applications, such as being potentially used as miniature pH sensors for capsule endoscopy and ambulatory esophageal pH monitoring. To address these issues of limitations of glass electrodes, various metal oxides have been investigated and proposed as potential electrode materials for the development of pH sensors. Solid metal sensors offer unique features such as insolubility, stability, mechanical strength, and possibility of miniaturization. However, the main drawback of the metal oxide pH sensors is the interference caused by oxidizing and reducing agents present in some sample solutions. To reduce the redox interference, metal nitride solid sensors were investigated in this project with the potential for the development of high-sensitivity pH sensing electrodes. Metal nitrides are refractory, have high melting points and interstitial defects, and, at room temperature, they are chemically stable and resist hydrolysis caused by weak acids. There are many reports on different metal nitrides electrodes in literature, of which several have been previously investigated for use as pH sensors. Here, specifically, thin films of titanium nitride (TiN) were manufactured using radio frequency magnetron sputtering. The effect of sputtering parameters (e.g., thickness, sputter power, gas composition) were investigated to optimize the materials for use as pH sensor. Additionally, the underlining mechanism governing the pH sensitivity of these metal nitrides was investigated by examining the pH sensing properties (i.e., sensitivity, hysteresis, and drift) and the effect of redox agents. The successfully optimized material was then used to construct and demonstrate the concept of a solid-state pH sensor using an appropriate reference electrode. The solid-state TiN sensor paves the way for future development of a miniaturised pH sensor capsule for biomedical applications or lab-on-a-chip pH sensor for environmental and industrial applications. Expending the realms of pH monitoring, currently limited by the glass pH electrode

Solid State Circuits Technologies

The evolution of solid-state circuit technology has a long history within a relatively short period of time. This technology has lead to the modern information society that connects us and tools, a large market, and many types of products and applications. The solid-state circuit technology continuously evolves via breakthroughs and improvements every year. This book is devoted to review and present novel approaches for some of the main issues involved in this exciting and vigorous technology. The book is composed of 22 chapters, written by authors coming from 30 different institutions located in 12 different countries throughout the Americas, Asia and Europe. Thus, reflecting the wide international contribution to the book. The broad range of subjects presented in the book offers a general overview of the main issues in modern solid-state circuit technology. Furthermore, the book offers an in depth analysis on specific subjects for specialists. We believe the book is of great scientific and educational value for many readers. I am profoundly indebted to the support provided by all of those involved in the work. First and foremost I would like to acknowledge and thank the authors who worked hard and generously agreed to share their results and knowledge. Second I would like to express my gratitude to the Intech team that invited me to edit the book and give me their full support and a fruitful experience while working together to combine this book

Nitric oxide an pH measurement with AlGaN/GaN based ISFETs

This thesis deals with the optimization of aluminum-gallium nitride/gallium nitride (AlGaN/GaN) ion sensitive field effect transistors (ISFETs), including the material parameters associated with fabrication, and the implementation of these optimized sensors for the detection of nitric oxide (NO), specifically aimed at biological detection. As the sensors will be used in fluidic environments, requirements regarding the chemical and mechanical stability of passivation can be quite demanding. It was demonstrated that polyimide exhibits the best passivation properties for these transistors in comparison to the well-known ‘hard passivation’ materials Si3N4 or SiO2. In order to employ polyimide as the insulation, a unique ECR (Electron Cyclotron Resonance) plasma process was developed to enable patterning while protecting the active sensor area of each of the AlGaN/GaN devices. This active area is the so-called two-dimensional electron gas (2DEG), which is spontaneously formed between AlGaN and GaN. The ECR plasma step delivers the essential anisotropic polyimide etching to insulate each ISFET with no measureable damage to the 2DEG. Furthermore, it was demonstrated that a contamination free surface was attained through the use of this fabrication process, providing good device functionality from the initial measurement-state of the ISFET, without the need of the additional cleaning procedures. A number of new technological processes were developed involving AlGaN/GaN ISFET gate area functionalization to enable NO measurement. A complete analysis of the sensor performance based on these functionalization methods showed tungsten trioxide and graphene functionalization techniques to be the most useful and compatible. These experiments also verify NO sensitivity in the presence of known interfering substances. Additionally, the possibility to make simultaneous pH and NO measurements was demonstrated via a suitable reduction of pH sensitivity of the functionalized transistors. Preliminary biocompatibility tests were demonstrated using L929 (mouse fibroblast) cells. Finally, a miniaturized AlGaN/GaN ISFET array was developed. A sensor size reduction and pitch size of 10 µm x 10 µm and 100 µm x 100 µm, respectively, was employed to improve precision for in vitro cell culture or tissue related experiments. With both the large-scale devices, as well as those miniaturized for the ISFET array, sensitivities of up to 57.0 mV/pH (values extremely near the theoretical Nernstian limit of 58.2 mV/pH at 20 °C) could be achieved. By combining the sensors with this achieved pH sensitivity and the NO sensors in the small-scale ISFET arrays, future work could enable simultaneous NO and pH measurement on a single chip across a local gradient in physiological applications.Diese Arbeit befasst sich mit der Optimierung von Aluminium-Gallium-Nitrid/Gallium-Nitrid (AlGaN/GaN) -Ionen-sensitiven-Feldeffekttransistoren (ISFETs), einschließlich der zur Prozessierung notwendigen Materialparameter, so wie die Implementierung dieser optimierten Sensoren zur Detektion von Stichstoffmonoxid (NO), im Speziellen für biologische Anwendungen. Durch den angestrebten Einsatz der Transistoren in Flüssigkeiten werden an die chemische und mechanische Stabilität der Passivierung hohe Anforderungen gestellt. Im Vergleich mit den bekannten 'harten' Passivierungsmaterialien wie Si3N4 oder SiO2 konnte gezeigt werden, dass Polyimid die besten Isolationseigenschaften aufweist. Um Polyimid als Passivierung einzusetzen, musste aber ein neuartiger ECR (Electron Cyclotron Resonance) Plasmaprozess entwickelt werden, der einerseits die AlGaN/GaN-Elemente strukturiert und gleichzeitig den aktiven Sensorbereich schützt. Dabei handelt es sich um das sogenannte zweidimensionale Elektronengas (2DEG), das sich spontan zwischen der AlGaN- und GaN-Schicht ausbildet. Der ECR Plasmaschritt ermöglicht das notwendige anisotrope Ätzen zur Isolierung der ISFETs gegeneinander ohne eine messbare Degeneration des 2DEG. Dieser Prozess hinterlässt eine kontaminationsfreie Oberfläche und somit sofort messbare ISFETs, was vorher benötigte Reinigungsschritte überflüssig macht. Um die Detektion von NO zu erlauben, wurde eine Reihe neuer technologischer Prozesse entwickelt, wie etwa die entsprechende Gate-Funktionalisierung der AlGaN/GaN-ISFETs. Wolframtrioxid und Graphen stellten sich bei der vollständigen Analyse des Sensorverhaltens als die Besten der untersuchten Funktionalisierungen heraus. Beim Nachweis der NO-Sensitivität gegenüber bekannten störenden Substanzen, konnte über die Verringerung der pH-Sensitivität des funktionalisierten Transistors, eine gleichzeitige Messung des pH-Wertes und NO durchgeführt werden. Mit Hilfe von L929-Zellen (Maus-Fibroblasten) wurden darüber hinaus die ersten Tests zur Biokompatibilität des Systems durchgeführt. Um die Genauigkeit für in vitro Zellkulturen oder Gewebe-basierte Experimente zu erhöhen, wurde ein miniaturisiertes AlGaN/GaN-ISFET-Array entwickelt, mit einer Miniaturisierung und einem Pitch von 10 mm x 10 mm bzw. 100 mm x 100 mm. Mit einzelnen Sensoren wie auch den miniaturisierten Arrays kann eine Sensitivität von bis zu 57.0 mV/pH (nahe am theoretischen Nernst'schen Verhalten mit 58.2 mV/pH bei 20 °C) erreicht werden. Die Kombination von miniaturisierten Arrays und der Verringerung der pH-Sensitivität könnte in zukünftigen Arbeiten eine simultane NO- sowie pH-Messung auf einem Chip über einen lokalen Gradienten physiologischer Anwendungen ermöglichen

Silicon nanowire : fabrication, characterisation and application

PhD ThesisThis thesis focuses on the fabrication considerations and the characterisation of silicon nanowires and their integration into chemical sensors. One aim is to optimize a top-down fabrication process for silicon nanowires, in particular the methods that use optical lithography, wet etching and thermal oxidation. The main concerns here are to achieve a reproducible and high yield fabrication process and to obtain a controllable structure. Extensive work was carried out to study the parameters that affect the repeatability of the process. The properties of silicon nitride films, the oxidation method and the characteristics of the anisotropic etchant were found to be key parameters affecting the reproducibility of the process. Several silicon nitride films were deposited under various conditions and their optical properties were tested before and after thermal oxidation. It was found that the oxynitride thickness depends on the refractive index of the nitride film: the lower the refractive index, the thinner the oxynitride. Then an etching process was developed to selectively etch the oxidised silicon nitride over silicon dioxide. The etching process included two steps: firstly ion milling to remove the oxynitride film and secondly using boiling phosphoric acid to strip the silicon nitride film. Nitride-rich silicon nitride films exhibited higher etching selectivity over silicon dioxide compared with silicon-rich silicon nitride. Based on the etch selectivity, oxynitride thickness, and silicon dioxide thickness the maximum thickness of silicon nitride film that can be used to act as a mask during the fabrication of silicon nanowires was determined. The impact of oxidation method on the reliability of the process was studied, and SOI and bulk silicon samples were oxidised at the same temperature and time using lamp-based RTP radiation and also a furnace with resistive heating. The results showed that the SOI sample is colder than the bare silicon sample when both were heated using the lamp-based RTP. This effect was considered during the fabrication of silicon nanowires to obtain a reliable process. Comprehensive experimental measurements were carried out to compare the characteristics of Tetra-Methyl Ammonium Hydroxide (TMAH) and Potassium Hydroxide (KOH) etching to optimise the fabrication process. The use of TMAH was found to lead to a more reliable process. ii Another aim of the project was to characterise the fabricated devices, and for this the contact properties and the electrical properties of the silicon nanowires needed to be evaluated. Extensive electrical measurements were carried out to study the thermal stability and ohmic contact formation for the silicon nanowire. Three metallization schemes were studied: Al/Ti, Al/W/Ti and Al/Ti/AlOx. All these exhibited ohmic contact to the nanowires. However, Al/Ti/Si and Al/W/Ti/Si were found to be unstable after 425 °C RTP annealing. Al/Ti/AlOx/Si withstood this level of temperature but the contact resistance was about ten times higher than that of Al/W/Ti. The electrical resistivity of the silicon nanowires was then studied; it was found that the measured electrical resistivity decreases with the nanowire thickness. Several models were then developed to explain the apparent increase in resistivity. It was suggested it can be largely attributed to the reduction of the conductive area of the nanowire due to interface traps. Finally, a silicon nanowire sensor was designed and fabricated, and this sensor was used to detect the changes in pH. The preliminary results showed that the sensor detected the change of pH in the buffer solution. However, reliability and yield were low, which was assumed to be due to the large parasitic current between the source/drain and the buffer solution.For a scholarship to pursue my postgraduate studies, I am grateful to Damascus University in Syria

Label-free detection of biomolecules with Ta2O5-based field effect devices

Dissertação para obtenção do Grau de Doutor em Nanotecnologias e NanociênciasInternational Iberian Nanotechnology Laboratory (INL

DNA Logic-A novel approach to semiconductor based genetics

In the coming years, genetic test results will be increasingly used as indicators that influence medical decision-making. With chronic disease on the rise and the continuing global spread of infectious disease, novel instruments able to detect relevant mutations in a point-of-care setting are being developed to facilitate this increased demand in personalized health care. However, diagnosis for such demand often requires laboratory facilities and skilled personnel, meaning that diagnostic tests are restricted by time and access. This thesis presents a novel configuration for Ion sensitive Field Effect Transistors (ISFETs) to be used as a threshold detector during nucleic acid base pairs match. ISFET-based inverters are used as reaction threshold detectors to convey the chemical reaction level to a logic output once a threshold has been reached. Using this method, novel DNA logic functions are derived for nucleotides allowing local digital computations. The thesis also presents business models that enable such technology to be utilised in point of care applications, and experiment as results and business models given for an HIV point of care example are proposed