Academic literature on the topic 'CNTFETs'

In this paper, we report the wafer-scale fabrication of carbon nanotube field-effect transistors (CNTFETs) with the dielectrophoresis (DEP) method. Semiconducting carbon nanotubes (CNTs) were positioned as the active channel material in the fabrication of carbon nanotube field-effect transistors (CNTFETs) with dielectrophoresis (DEP). The drain-source current (IDS) was measured as a function of the drain-source voltage (VDS) and gate-source voltage (VGS) from each CNTFET on the fabricated wafer. The IDS on/off ratio was derived for each CNTFET. It was found that 87% of the fabricated CNTFETs was functional, and that among the functional CNTFETs, 30% of the CNTFETs had an IDS on/off ratio larger than 20 while 70% of the CNTFETs had an IDS on/off ratio lower than 20. The highest IDS on/off ratio was about 490. The DEP-based positioning of carbon nanotubes is simple and effective, and the DEP-based device fabrication steps are compatible with Si technology processes and could lead to the wafer-scale fabrication of CNT electronic devices.

This paper discusses the device physics of carbon nanotube field-effect transistors (CNTFETs). After reviewing the status of device technology, we use results of our numerical simulations to discuss the physics of CNTFETs emphasizing the similarities and differences with traditional FETs. The discussion shows that our understanding of CNTFET device physics has matured to the point where experiments can be explained and device designs optimized. The paper concludes with some thoughts on challenges and opportunities for CNTFET electronics.

Recently, carbon nanotube field-effect transistors (CNTFETs) have attracted wide attention as promising candidates for components in the next generation of electronic devices. In particular CNTFET-based RF devices and circuits show superior performance to those built with silicon FETs since they are able to obtain higher power-gain and cut-off frequency at lower power dissipation. The aim of this paper is to present a compact, design-oriented model of CNTFETs that is able to ease the development of a complete amplifier. As a case study, the detailed design of a high-gain CNTFET-based broadband inductorless LNA is presented.

The excellent performance and radiation-hardness potential of carbon nanotube (CNT) field effect transistors (CNTFETs) have attracted wide attention. However, top-gate structure CNTFETs, which are often used to make high-performance devices, have not been studied enough. In this paper, the total ionizing dose (TID) effect of the top-gate structure CNTFETs and the influence of the substrate on top-gate during irradiation are studied. The parameter degradation caused by the irradiation- and radiation-damage mechanisms of the top-gate P-type CNTFET were obtained by performing a Co-60 γ-ray irradiation test. The results indicate that the transfer curves of the top-gate P-type CNTFETs shift negatively, the threshold voltage and the transconductance decrease when TID increases, and the subthreshold swing decreases first and then increases with the increase in TID. The back-gate transistor is constructed by using the substrate as a back-gate, and the influence of back-gate bias on the characteristics of the top-gate transistor is tested. We also test the influence of TID irradiation on the characteristics of back-gate transistors, and reveal the effect of trapped charge introduced by radiation on the characteristics of top-gate transistors. In addition, the CNTFETs that we used have obvious hysteresis characteristics. After irradiation, the radiation-induced trapped charges generated in oxide and the OH groups generated by ionization of the CNT adsorbates aggravate the hysteresis characteristics of CNTFET, and the hysteresis window increases with the increase in TID.

We present the compact unified charge control model (UCCM) for carbon nanotube field-effect transistors (CNTFETs) to enable the accurate simulation of the DC characteristics and plasmonic terahertz (THz) response in the CNTFETs. Accounting for the ambipolar nature of the carrier transport (n-type and p-type conductivity at positive and negative gate biases, respectively), we use n-type and p-type CNTFET non-linear equivalent circuits connected in parallel, representing the ambipolar conduction in the CNTFETs. This allows us to present a realistic non-linear model that is valid across the entire voltage range and is therefore suitable for the CNTFET design. The important feature of the model is that explicit equations for gate bias, current, mobility, and capacitance with smoothing parameters accurately describe the device operation near the transition from above- to below-threshold regimes, with scalability in device geometry. The DC performance in the proposed compact CNTFET model is validated by the comparison between the SPICE simulation and the experimental DC characteristics. The simulated THz response resulted from the validated CNTFET model is found to be in good agreement with the analytically calculated response and also reveals the bias and power dependent sub-THz response and relatively wide dynamic range for detection that could be suitable for THz detectors. The operation of CNTFET spectrometers in the THz frequency range is further demonstrated using the present model. The simulation exhibits that the CNT-based spectrometers can cover a broad THz frequency band from 0.1 to 3.08 THz. The model that has been incorporated into the circuit simulators enables the accurate assessment of DC performance and THz operation. Therefore, it can be used for the design and performance estimation of the CNTFETs and their integrated circuits operating in the THz regime.

We compare the pH sensing performance of non-functionalized carbon nanotubes (CNT) field-effect transistors (p-CNTFET) and CNTFET functionalized with a conjugated polyfluorene polymer (labeled FF-UR) bearing urea-based moieties (f-CNTFET). The devices are electrolyte-gated, PMMA-passivated, 5 µm-channel FETs with unsorted, inkjet-printed single-walled CNT. In phosphate (PBS) and borate (BBS) buffer solutions, the p-CNTFETs exhibit a p-type operation while f-CNTFETs exhibit p-type behavior in BBS and ambipolarity in PBS. The sensitivity to pH is evaluated by measuring the drain current at a gate and drain voltage of −0.8 V. In PBS, p-CNTFETs show a linear, reversible pH response between pH 3 and pH 9 with a sensitivity of 26 ± 2.2%/pH unit; while f-CNTFETs have a much stronger, reversible pH response (373%/pH unit), but only over the range of pH 7 to pH 9. In BBS, both p-CNTFET and f-CNTFET show a linear pH response between pH 5 and 9, with sensitivities of 56%/pH and 96%/pH, respectively. Analysis of the I–V curves as a function of pH suggests that the increased pH sensitivity of f-CNTFET is consistent with interactions of FF-UR with phosphate ions in PBS and boric acid in BBS, with the ratio and charge of the complexed species depending on pH. The complexation affects the efficiency of electrolyte gating and the surface charge around the CNT, both of which modify the I–V response of the CNTFET, leading to the observed current sensitivity as a function of pH. The performances of p-CNTFET in PBS are comparable to the best results in the literature, while the performances of the f-CNTFET far exceed the current state-of-the-art by a factor of four in BBS and more than 10 over a limited range of pH in BBS. This is the first time that a functionalization other than carboxylate moieties has significantly improved the state-of-the-art of pH sensing with CNTFET or CNT chemistors. On the other hand, this study also highlights the challenge of transferring this performance to a real water matrix, where many different species may compete for interactions with FF-UR.

Based on artificial neural network (ANN), a new method of modeling carbon nanotube field effect transistors (CNTFETs) is developed. This paper presents two ANN CNTFET models, including P-type CNTFET (PCNTFET) and N-type CNTFET (NCNTFET). In order to describe the devices more accurately, a segmentation voltage of the voltage between gate and source is defined for each type of CNTFET to segment the workspace of CNTFET. With the smooth connection by a quasi-Fermi function for, the two segmented networks of CNTFET are integrated into a whole device model and implemented by Verilog-A. To validate the ANN CNTFET models, quantitative test with different device intrinsic parameters are done. Furthermore, a complementary CNTFET inverter is designed using these NCNTFET and PCNTFET ANN models. The performances of the inverter show that our models are both efficient and accurate for simulation of nanometer scale circuits.

Carbon Nanotube Field Effect Transistor (CNTFET) is one of the promising devices for future nanoscale technologies. In this paper, we have studied the drain characteristics of MOSFET-like CNTFETs for different device parameters like, channel length, diameter of CNT, and number of tubes. It is shown that these device parameters can be used to make important design decisions while designing nanoelectronic circuits. A buffer and ring oscillator circuits are designed using the MOSFET-like CNTFET and propagation delay, power, and power-delay-product (PDP) values are calculated and compared with the CMOS based designs. Also, the CNTFET technology based SRAM cell is compared with CMOS technology based SRAM in term of power consumption. We have shown that CNTFET can exhibit better performance in the nanoscale regime as compared to its CMOS counterparts.

Due to the difficulties associated with scaling of silicon transistors, various technologies beyond binary logic processing are actively being investigated. Ternary logic circuit implementation with carbon nanotube field effect transistors (CNTFETs) and resistive random access memory (RRAM) integration is considered as a possible technology option. CNTFETs are currently being preferred for implementing ternary circuits due to their desirable multiple threshold voltage and geometry-dependent properties, whereas the RRAM is used due to its multilevel cell capability which enables storage of multiple resistance states within a single cell. This article presents the 2-trit arithmetic logic unit (ALU) design using CNTFETs and RRAM as the design elements. The proposed ALU incorporates a transmission gate block, a function select block, and various ternary function processing modules. The ALU design optimization is achieved by introducing a controlled ternary adder–subtractor module instead of separate adder and subtractor circuits. The simulations are analyzed and validated using Synopsis HSPICE simulation software with standard 32 nm CNTFET technology under different operating conditions (supply voltages) to test the robustness of the designs. The simulation results indicate that the proposed CNTFET-RRAM integration enables the compact circuit realization with good robustness. Moreover, due to the addition of RRAM as circuit element, the proposed ALU has the advantage of non-volatility.

In this paper we propose a procedure for the study of CNTFETs as memory devices. In particular we analyze the design of a 6-T SRAM, in order to evaluate the writing and reading times, in single and double supplies, the static noise margin, the static power consumption and the power-delay product. For these goals, we use a CNTFET model, already proposed by us. Then we apply the same procedure using the Stanford model in order to compare the obtained results. At last we apply the proposed analysis for the design of a 6-T SRAM in CMOS technology, showing the improvements obtained with CNTFET technology.

Downscaling of the contact length Lc of a side-contacted carbon nanotube field-effect transistor (CNTFET) is challenging because of the rapidly increasing contact resistance as Lc falls below 20–50 nm. If in agreement with existing experimental results, theoretical work might answer the question, which metals yield the lowest CNT–metal contact resistance and what physical mechanisms govern the geometry dependence of the contact resistance. However, at the scale of 10 nm, parameter-free models of electron transport become computationally prohibitively expensive. In our work we used a dedicated combination of the Green function formalism and density functional theory to perform an overall ab initio simulation of extended CNT–metal contacts of an arbitrary length (including infinite), a previously not achievable level of simulations. We provide a systematic and comprehensive discussion of metal–CNT contact properties as a function of the metal type and the contact length. We have found and been able to explain very uncommon relations between chemical, physical and electrical properties observed in CNT–metal contacts. The calculated electrical characteristics are in reasonable quantitative agreement and exhibit similar trends as the latest experimental data in terms of: (i) contact resistance for Lc = ∞, (ii) scaling of contact resistance Rc(Lc); (iii) metal-defined polarity of a CNTFET. Our results can guide technology development and contact material selection for downscaling the length of side-contacts below 10 nm.

Downscaling of the contact length Lc of a side-contacted carbon nanotube field-effect transistor (CNTFET) is challenging because of the rapidly increasing contact resistance as Lc falls below 20–50 nm. If in agreement with existing experimental results, theoretical work might answer the question, which metals yield the lowest CNT–metal contact resistance and what physical mechanisms govern the geometry dependence of the contact resistance. However, at the scale of 10 nm, parameter-free models of electron transport become computationally prohibitively expensive. In our work we used a dedicated combination of the Green function formalism and density functional theory to perform an overall ab initio simulation of extended CNT–metal contacts of an arbitrary length (including infinite), a previously not achievable level of simulations. We provide a systematic and comprehensive discussion of metal–CNT contact properties as a function of the metal type and the contact length. We have found and been able to explain very uncommon relations between chemical, physical and electrical properties observed in CNT–metal contacts. The calculated electrical characteristics are in reasonable quantitative agreement and exhibit similar trends as the latest experimental data in terms of: (i) contact resistance for Lc = ∞, (ii) scaling of contact resistance Rc(Lc); (iii) metal-defined polarity of a CNTFET. Our results can guide technology development and contact material selection for downscaling the length of side-contacts below 10 nm.

Microorganisms are present in a variety of sources, including food, water, animals, environment as well as the human body. They can be harmless or harmful. The latter is also called pathogenic and their detection is extremely important due to health and safety reasons.

It is well known that food contaminated with bacteria can produce a number of foodborne diseases. As a consequence, thousands of euros are invested each year in medical treatments trying to keep the population healthy. There are more than 250 known foodborne diseases. For example, outbreaks of salmonellosis have increased in many countries in the last decades being Salmonella Infantis one of the most important etiological agents associated with this enteric disease. Moreover, due to the wide distribution of the microorganisms, they can also contaminate foods in the field as well as during the storage stage. In that sense, filamentous fungi are one of the etiological agents responsible for most post-harvest food spoilage producing quality losses and economic devaluation.

On the other hand, the invasive fungal infections due to yeast have risen considerably in recent years. Candidiasis is the so-called disease produced by Candida albicans. This is an opportunistic infection that affects immunocompromised patients requiring costly treatment with advanced medicine.

Several methods have been proposed so far to detect pathogenic microorganisms. Conventional culture is highly selective and sensitive but they also require several days to yield the results. To simplify and automate the identification of both bacteria and fungi rapid biochemical kits have been developed. Although the results obtained with these kits are comparable to the traditional biochemical tests they also need 1 or 2 days to obtain results. Enzyme-linked immunosorbent assays (ELISA) can be applied for the direct identification of pathogenic microorganisms in real samples. This immuno-based method has been widely used in both food and the medical sector with high sensitivity. Nevertheless, the main disadvantage of this method is that it can also be time-consuming because a pre-enrichment of the sample is often required in order to achieve low limits of detection. As a consequence, many researchers have addressed their efforts towards the development of alternative methods to allow the rapid detection of pathogens.

Molecular biology-based methods, specifically polymerase chain reaction (PCR) and real-time PCR are nowadays the most common tools used for pathogen detection. They are highly sensitive and allow the quantification of the target. In addition, microarray platforms of DNA have been developed in order to analyse hundreds of targets simultaneously. However, this technique is costly and reagent-consuming.

The introduction of biosensors has brought new alternatives in pathogenic detection. Biosensors are the most used tools in pathogenic detection after PCR, culture methods and ELISA. They provide rapid results after the sample has been taken. However, their real application lies in achieving selectivities and sensitivities comparable to the established methods and at low cost.

Since carbon nanotubes (CNTs) were discovered by Iijima, many papers have reported their unique electronic and optical properties which, together with their size, make these nanostructures interesting materials in the development of biosensing platforms. Their very high capacity for charge transfer between heterogeneous phases makes them suitable as components in electrochemical sensors. The electrical conductivity of the CNTs is highly sensitive to changes in their chemical environment and, as a result, they have been successfully applied in the study of molecular recognition processes.

An approach for the direct electrical detection of biomolecules integrates CNTs as transducer elements within a field-effect transistor (FET) configuration. The main advantages of this kind of configuration lies in that the conducting channel is usually located on the surface of the substrate and as a result, they are extremely sensitive to any change in the surrounding environment. Moreover, CNTFET devices can operate at room temperature and in ambient conditions.
At the beginning of this research (2006) electrochemical CNTFETs based on single walled carbon nanotubes had not been applied to detect bacteria or fungi. Only the interaction between CNTs and bacteria had been explored, but without sensing purposes. Therefore, this thesis reports the first CNTFET devices applied to the detection of pathogenic microorganisms. First, the background and the introduction containing the state of the art are presented covering relevant investigations made in the last years. Next, the main analytical methods are described. These descriptions involve detailed information of all procedures, analytical tools and materials used throughout this research work.

In the following chapters, the application of the CNTFETs for the determination of bacteria, yeast and moulds is presented throughout the scientific articles published along the development of the thesis. Briefly, the first device developed was applied to the detection of Salmonella Infantis in a simple matrix (0.85 % saline solution) and it was proven for first time, that this kind of sensor was able to detect, at least, 100 cfu/mL of the bacteria in just one hour with high selectivity. Subsequently, we enlarged the application field to other types of microorganisms: Candida albicans. In this study we improved not only the detection limit of the devices to 50 cfu/mL but also we proved the selectivity of the CNTFETs against possible interference that can be present in real samples like serum proteins. Finally, the devices were applied to the detection of the mould Aspegillus flavus in real samples. In this assay the response time was 30 minutes and a high sensitivity (10 µg of A. flavus / 25 g of rice) was obtained.

As the final chapters, general conclusions extracted from the overall work and annexes are reported. It can be stated that nanomaterials displaying extraordinary properties like carbon nanotubes can be combined with biological entities to obtain highly sensitive and selective biosensors able to detect bacteria, yeasts and moulds in a very short time. In future work, other performance parameters such as, long term stability, robustness and reusability must be studied further and contrasted with standard methods before thinking of the commercialization of the devices.
Los microorganismos están presentes en una gran variedad de orígenes, incluyendo alimentos, agua, animales, medio ambiente también como en el propio cuerpo humano. Estos pueden ser beneficiosos o perjudiciales. Los microorganismos perjudiciales reciben el nombre de patógenos y su detección es de gran importancia por razones de salud y seguridad.

Es bien conocido que los alimentos contaminados con bacterias pueden producir cierto número de enfermedades. Como consecuencia de esto, miles de euros se invierten cada año en tratamientos médicos para mantener la salud de la población. Existen más de 250 enfermedades transmitidas por alimentos. En las últimas décadas se ha incrementado por ejemplo, la incidencia de brotes de salmonelosis en muchos países, siendo Salmonella Infantis uno de los agentes etiológicos más importantes asociados con la producción de esta enfermedad entérica. Debido a la amplia distribución de los microorganismos, estos pueden llegar también a contaminar alimentos durante su cultivo como durante la fase de almacenamiento. En este sentido, los hongos filamentosos son en gran parte los agentes etiológicos responsables del deterioro de alimentos después de la cosecha produciendo pérdidas en la calidad y devaluación económica.

Por otra parte, las infecciones fúngicas invasivas producidas por levaduras han aumentado considerablemente en los últimos años. Candidiasis, es la enfermedad producida por Candida albicans. Esta es una de las infecciones más comunes que afectan pacientes inmunocomprometidos requiriendo tratamientos de elevado coste.

Se han propuesto varios métodos hasta la fecha para la detección de microorganismos patógenos. El cultivo es el método de referencia utilizado para la detección y cuantificación de bacterias. Tiene la ventaja de ser altamente selectivo y sensible pero tiene el inconveniente de requerir varios días para obtener un resultado. Para simplificar y automatizar la identificación de bacterias y hongos se han desarrollado kits bioquímicos rápidos. Aunque los resultados obtenidos usando esta clase de kits son comparables a las pruebas bioquímicas tradicionales, también 1 o 2 días son requeridos para la obtención de resultados. El enzimoinmunoensayo ("Enzyme Linked Immunosorbent Assay", ELISA) es un método immunológico de gran sensibilidad que se utiliza ampliamente para detectar y cuantificar microorganismos patógenos, tanto en el sector médico como en el alimentario. Sin embargo, su principal desventaja es que a veces el tiempo de análisis puede aumentar considerablemente, específicamente cuando se realizan etapas de pre-enriquecimiento de la muestra para disminuir el límite de detección. Como consecuencia, muchos investigadores han dirigido sus esfuerzos hacia el desarrollo de métodos más rápidos.

Los métodos basados en el uso de la biología molecular, específicamente la reacción en cadena de la polimerasa (PCR) y la PCR en tiempo real, son hoy en día las herramientas más comúnmente usadas para la detección de patógenos. Estas técnicas son altamente sensibles y permiten la cuantificación del patógeno. Adicionalmente, se han desarrollado chips con plataformas de DNA para analizar cientos de patógenos simultáneamente. Sin embargo, esta técnica es costosa y requiere el uso de muchos reactivos.

La introducción de los biosensores ha contribuído a generar nuevas alternativas para la detección de patógenos. Los biosensores son las herramientas más usadas en la detección de patógenos después de la PCR, los métodos convencionales y el ELISA. Tienen la ventaja de proporcionar respuestas rápidas entre la toma de muestra y la obtención de los resultados. No obstante, el reto para su aplicación en muestras reales radica en alcanzar selectividades y sensibilidades comparables a los métodos convencionales ya establecidos y a un costo económico reducido.

Desde que Iijima descubrió los nanotubos de carbono (CNTs) se han publicado numerosos trabajos sobre sus excelentes propiedades electrónicas y ópticas, las cuales, en conjunción con su tamaño, hacen de estas nanoestructuras materiales interesantes en el desarrollo de plataformas de biodetección. Los CNTs presentan una gran capacidad de transferencia de carga entre estructuras heterogéneas. Ello les confiere una gran utilidad en la elaboración de sensores de tipo electroquímico. Su conductividad eléctrica varía de forma muy acusada con cambios en su ambiente químico y, como resultado, se han aplicado con éxito en el estudio de procesos de reconocimiento molecular.

Una metodología para la detección directa de biomoléculas integra los CNTs como elementos transductores dentro de una configuración de transistor de efecto campo (FET). Las principales ventajas de esta clase de configuraciones radican en que el canal conductor se localiza sobre la superficie del substrato y, como resultado, es altamente sensible a cualquier cambio en el medio ambiente. Además, los CNTFETs pueden operar a temperatura y, humedad ambientales.

Al inicio de esta tesis (2006), todavía no se habían aplicado los CNTFETs basados en nanotubos de carbono monocapa a la detección de bacterias y hongos. Sólo se había estudiado la interacción entre los CNTs y bacterias, pero sin el objetivo de detección. Por tanto, esta tesis aporta los primeros CNTFETs aplicados a la detección de microorganismos patógenos. En primer lugar, se presentan los antecedentes y la introducción, donde se realiza una revisión crítica y actualizada de los métodos e investigaciones más relevantes para detectar microorganismos patógenos. Posteriormente, se incluye un capítulo con la información detallada de todos los procedimientos experimentales, herramientas analíticas y materiales utilizados a lo largo del trabajo de investigación.

En los siguientes capítulos, se presenta la aplicación de CNTFETs en la determinación de bacterias, mohos y levaduras mediante artículos científicos publicados a lo largo del desarrollo de la tesis. Brevemente, el primer dispositivo desarrollado se aplicó a la detección de Salmonella Infantis en una matriz simple (solución salina 0.85 %) y se comprobó por primera vez que esta clase de sensores eran capaces de detectar al menos 100 ufc/mL de la bacteria en tan solo una hora con alta selectividad. Seguidamente, se amplió el campo de aplicación a otro tipo de microorganismo, Candida albicans. En este estudio, se mejoró no sólo el límite de detección de los dispositivos a 50 ufc/mL sino que también se mejoró la selectividad de los CNTFETs frente a posibles interferentes que pueden estar presentes en muestras reales, tales como proteínas séricas. Finalmente, se aplicaron los dispositivos a la detección del moho Aspergillus flavus en muestras reales. En este ensayo, el tiempo de respuesta fue de 30 minutos y se obtuvo una buena sensiblidad (10 µg de A. flavus / 25 g de arroz).



Como parte final de la tesis, se presentan las conclusiones generales extraídas a lo largo del trabajo completo junto con los anexos. Puede concluirse que, gracias a las propiedades únicas de los nanotubos de carbono, dichos nanomateriales pueden combinarse con entidades biológicas (como los anticuerpos) para obtener biosensores altamente sensibles y selectivos capaces de detectar bacterias, levaduras y mohos en un tiempo de análisis muy reducido. Como trabajo futuro, se deberán estudiar otros parámetros de calidad de los dispositivos tales como la estabilidad a lo largo del tiempo, la robustez o su reutilización con el fin de contrastarlos con los métodos estándar antes de poder iniciar la comercialización de este tipo de sensores.

Parmi les nouveaux nano-dispositifs, les CNTFETs sont des candidats prometteurs. Mais les circuits à base de nanotubes auront une probabilité élevée de défectuosité lors de la fabrication et une assez grande dispersion des caractéristiques. Dans ce contexte, cette thèse étudie l'implantation de portes logiques élémentaires à base de CNTFETs. Une comparaison précise de plusieurs structures logiques montre les avantages de la structure complémentaire pour les applications futures. L'influence des variations paramétriques sur les caractéristiques des CNTFETs et des portes logiques complémentaires est ensuite analysée. Une étude synthétique des défauts et fautes transitoires spécifiques aux circuits à base de CNTFETs est présentée. Enfin, une structure logique redondante est proposée pour réduire l'effet des dispersions paramétriques et pour améliorer le rendement de fabrication en tolérant certains défauts
Amongst novel nanodevices, CNTFETs are promising candidates. But circuits based on CNTFETs will have a high probability of manufacturing defects and large characteristic dispersions. In this context, this thesis studies the implementation of CNTFET-based elementary logic gates. A precise comparison of several logic structures shows the advantages of the complementary structure for future applications. The influence of parametric variations on the CNTFET and complementary logic gate characteristics is then analyzed. A synthetic study is presented on the specific defects and transient faults in CNTFET-based circuits. Finally, a redundant logic structure is proposed to reduce the effect of parametric dispersions and to improve the manufacturing yield by tolerating some defects

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2013.
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Neste projeto foram desenvolvidos e simulados circuitos `a base de nano tubos de carbono(CNT) de efeito de campo (FET). Esses circuitos tiveram como propósito analisar a viabilidade da substituição da tecnologia CMOS pela tecnologia CNTFET para o padrão Bluetooth em 2,4 GHz . As simulações dos circuitos foram realizadas com um modelo compacto para CNTFETs, denominado TCAM. Os elementos passivos dos circuitos foram selecionados da biblioteca da tecnologia CMOS 0,35 μm. A plataforma profissional Cadence, que possui um módulo destinado a simulações chamado de Spectre, foi utilizada para o projeto e para a simulação dos circuitos.Para a realização desse estudo, foram projetados os principais componentes/blocos do padrão Bluetooth: o amplificador fonte comum, o oscilador LC tanque e o misturador Célula de Gilbert. Para cada circuito projetado, os seguintes parâmetros característicos do CNTFET foram analisados: i) densidade de tubos, ii) número de dedos em paralelo,iii) porcentagem de nano tubos metálicos e iv) largura da porta. O impacto da presença de nano tubos metálicos no canal dos CNTFETs, que degrada o sinal e limita o uso dessa tecnologia no desempenho de circuitos analógicos, foi estudado com maior detalhe. Pode-se concluir que a complexidade do circuito está diretamente relacionada à tolerância a presença de nano tubos metálicos.A influência do layout do CNTFET multi-tubos e multi-dedos na performance do circuito pode ser demonstrada mais claramente pelo amplificador fonte comum. A largura da porta altera o número de tubos paralelos que conectam a fonte com o dreno e portanto, muda o ponto de operação DC. O aumento do número de dedos do transistor e benéfico para desempenho AC em altas freqüências, pois a impedância da porta é reduzida. Os parâmetros do layout e da tecnologia precisam ser selecionados com cuidado para o sucesso de projetos de circuitos mais complexos. A parte ativa do oscilador investigada gera uma resistência negativa, na qual e essencial para manter um sinal não atenuado. O número de dedos do transistor mostrou ser o parâmetro essencial para obter a magnitude requerida da resistência negativa. Para o projeto do misturado, todos os parâmetros tiveram que ser otimizados para atingir o ganho necessário para funcionamento. Depois da otimização dos parâmetros, todos os componentes Bluetooth aqui investigados puderam ser projetados com sucesso empregando a plataforma da tecnologia CNTFET. No entanto, os circuitos complexos requerem uma tecnologia CNTFET quase-ideal e não disponível atualmente. Uma possível solução a este problema seria odesing de novas arquiteturas dos circuitos. _______________________________________________________________________________________ ABSTRACT
This project presents the development and simulation of integrated circuits based oncarbon nanotube (CNT) field-effect transistors (FETs). These circuits were aimed toanalyze the feasibility of replacing CMOS by CNTFET technology for devices fulfillingthe Bluetooth standard at 2.4 GHz. The circuit simulations were performed witha compact model for CNTFETs, called TCAM. The passive circuit elements wereselected from the CMOS 0.35 μm library. The professional platform Cadence, whichhas a simulation module called Spectre, was used for circuit design and simulation.To perform this study, we designed some Bluetooth standard main components/blocks:a common-source amplifier, an LC tank oscillator and a Gilbert cell mixer. For eachdesigned circuit, the following CNTFET parameters were analyzed: density of tubes,number of fingers in parallel, the percentage of metallic nanotubes and gate width. Itcan be concluded that the complexity of the circuit is directly related to the toleranceto the presence of metallic nanotubes.The influence of the layout of a multi-tube multi-finger CNTFET on circuit performancecould be most clearly demonstrated for the common-source amplifier. The gatewidth alters the number of parallel tubes connecting source and drain and thereforeshifts the DC bias point. An increasing number of transistor fingers is beneficial forthe high frequency AC performance since the gate impedance is reduced.The layout and technology parameters had to be chosen with care for the successfuldesign of more complex circuits. The active part of the investigated oscillator createsa negative resistance which is essential for maintaining a non-attenuated signal. Thenumber of transistor fingers proved to be the essential parameter to obtain the requiredmagnitude of the negative resistance. For the mixer design all parameters had to beoptimised to achieve the necessary gain.After parameter optimisation, all Bluetooth components investigated here could be designed successfully employing a CNTFET technology platform. However, complexcircuits require a quasi-ideal CNTFET technology not available today. A possibleresort would be the invention of new system architectures.

Depuis quelques années, les explosifs artisanaux à base de peroxyde sont fréquemment utilisés dans les actes de terrorisme. Leur simplicité de conception ne les rend pas moins inoffensifs car ils sont tout aussi puissants que ceux à base de TNT (trinitrotoluène). Au regard des enjeux majeurs de la sécurité globale et en particulier de la protection du citoyen, il devient nécessaire de bénéficier d'instruments de détection fiables. C'est dans ce cadre que s'inscrit ce travail de thèse qui vise à développer un capteur intégré, sensible et sélectif aux traces d'explosifs, notamment ceux à base de peroxyde. Ce nez électronique est constitué d'une matrice de transistors à nanotubes de carbone (CNTFET) et d'une électronique et traitement des données. Après une brève introduction relative aux CNTFET pour la détection gazeuse, nous présentons les bases de l'élaboration d'une modélisation électrique du capteur. Cette modélisation a pour but, à terme, de permettre aux concepteurs decircuits intégrés de bénéficier d'un support de simulation des CNTFET, nécessaire à la mise en oeuvre de l'électronique de contrôle et de conditionnement des signaux. Nous détaillerons également ce qui constitue selon nous l'étape fondamentale précédant l'élaboration d'un modèle compact prédictif basé sur la physique, c'est à dire la compréhension topologique du réseau de nanotubes. Nous détaillerons alors différentes probabilités de contacts entre nanotubes. Nous présentons ensuite,l'élaboration de l'électronique permettant le contrôle des potentiels appliqués aux CNTFET et le conditionnement des signaux électriques. Ce conditionnement a pour objectif d'acheminer les réponses électriques du capteur vers des architectures de traitement de données utilisées pour la détection des différents gaz cibles. L'électronique intégrée en technologie CMOS HV (haute tension) est alimentée par pile basse tension. Des pompes de charge, élévateurs de tension, générant ces hautes tensions ont été étudiées, modélisées et réalisées. Nous proposons également dans ce manuscrit une nouvelle architecture de pompe de charge qui constitue, dans certaines plages d'utilisation, une alternative intéressante aux pompes de charge les plus performantes utilisées jusqu'à présent
For the last few years, improvised peroxide based explosives are frequently used in acts of terrorism. Their simple design does not make them less threatening than those based on TNT because they are equally as powerful as those based on TNT (trinitrotoluene). In view of the major issues of the overall safety and, in particular, the citizens' protection, it becomes necessary to enjoy reliable detection instruments. Such is the background of this PhD work which aims to develop a built-in sensor,sensitive and selective to traces of explosives, especially those based on peroxide. This electronic nose is made up of a network of carbon nanotube field-effect transistors (CNTFET), and data processing hardware. After a brief introduction relating to CNTFETs for gaseous detection, we will provide the basis for the elaboration of an electronic modeling of the sensor. This modeling aims, at the end, to allow designers of integrated circuits to benefit from a simulation support of CNTFETs, required to the implementation of control and signal conditioning electronics. We will also detail what are the fundamental steps mandatory before the development of a predictive compact model based on physics, which means the topological understanding of the nanotubes network. Then, we will describe different probabilities of contacts between nanotubes. Later, we will introduce the elaboration of the electronics allowing the control of the voltages applied to the CNTFETs and the electrical signals conditioning. The objective of this conditioning is to carry electrical responses from the sensor to data processing architectures used for the detection of the different target gasses. High Voltage CMOS integrated electronics are powered by low-voltage batteries. Charge pumps and voltage boosters which generate these high voltages, have been investigated, modeled and carried out. We also provide in this dissertation a new charge pump architecture which offers, in some ranges of application, an interesting alternative to the most efficient charge pumps used until now

La poursuite de la loi de Moore nécessite l'exploration et l'utilisation de composants nouveaux pouvant compléter ou remplacer le transistor CMOS dans les systèmes sur puce dans les années à venir. Dans ce contexte, l'émergence de nanocomposants offre l'opportunité d'inventer de nouvelles structures de circuit, d'élaborer des techniques non-conventionnelles de conception et par conséquent de repenser le paradigme de conception des architectures. Le principal objectif de cette thèse est de proposer de nouvelles structures de circuits (portes logiques élémentaires et reconfigurables) exploitant la propriété d'ambivalence des transistors à base de nanotube de carbone (CNTFET) double grille, et d'en évaluer les performances par rapport aux circuits à base de composants CMOS. Autour de ce composant, nous avons développé une famille de cellules dynamiquement reconfigurables. Grâce à un modèle comportemental, dérivé d'un modèle compact existant, nous avons démontré une consommation de ces cellules d'environ 2nW à 4GHz, se comparant ainsi très favorablement aux circuits CMOS conventionnels (look-up tables – LUTs – à m-bit à base de MUX). Puis, dans le but d'utiliser aux mieux ces cellules de très petites tailles, nous avons développé une architecture matricielle qui permet l'intégration de plusieurs cellules identiques et la réalisation d'un large panel de fonctions logiques, ainsi qu'une méthode de transposition de graphes logiques sur l'architecture. Cette méthode permet l'exploration de plusieurs topologies d'interconnexion et d'en évaluer le taux de réussite de transposition de fonctions logiques sur la matrice dans le cas idéal ainsi que dans le cas d'un fonctionnement dégradé, incluant un ou plusieurs défauts au niveau des cellules physiques
The pursuit of Moore’s Law has pointed to significant future intrinsic device hurdles and requires the use and exploration of novel devices to complement or even replace the CMOS transistor in systems on chip within the next decade and before silicon based technology will reach its limits. In this context, the emergence of nanodevices offers the opportunity to invent new circuits, and to develop unconventional design and therefore to rethink the paradigm of design architectures. The main objective of this thesis is to propose new structures circuits (basic reconfigurable logic gates) based on the ambivalence characteristic of double gate CNTFET (carbon nanotube field effect transistor), and evaluate the performance with reports to circuits based on CMOS components. Using double gate CNTFET, we have developed a family of dynamically reconfigurable logic cells. Thanks to a behavioral model, derived from an existing compact model, we have estimated elementary performance metrics and compared those to conventional CMOS based circuits (MUX based m-bit look-up tables). The simulation results demonstrated significant power savings for comparable speeds (2nW at 4GHz). Then, in order to use these very small cells more efficiently, we have developed a matrix architecture that allows integration of several identical cells and realization of a wide range of logic functions. We also developed a method to map function graphs representing complex logical functions to such matrices. This method allows us to compare several interconnection topologies and evaluate the success rate of the function mapping on the matrix in the ideal case as well as in the case of one or more interconnection failures

Orientadores: Peter Jürgen Tatsch, José Alexandre Diniz
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Este trabalho teve como objetivo o desenvolvimento de materiais e métodos avançados de fabricação de sensores químicos/bioquímicos. Utilizando equipamentos disponíveis no Centro de Componentes Semicondutores da UNICAMP, foram desenvolvidos e caracterizados filmes finos de alta constante dielétrica e filmes metálicos. Os materiais desenvolvidos foram empregados na fabricação de sensores baseados em transistores de efeito de campo sensíveis a íons (ISFET) e em dispositivos de efeito de campo que incorporam nanoestruturas de carbono como elemento funcional [grafeno (GraFET) e nanotubos de carbono (CNTFET)]. A aplicação dos materiais como camada sensível, dielétrico de porta e eletrodos, assim como a utilização de nanoestruturas, tem por objetivo aumentar a sensibilidade e a biocompatibilidade dos dispositivos, construir dispositivos robustos que possam ser empregados em ambientes agressivos e obter sensores com resposta linear e estável com o tempo e temperatura. Foram fabricados, caracterizados e encapsulados ISFET's com camada sensível constituída por filmes finos de nitreto de silício (SiNx)/nitreto de alumínio (AlN) e com eletrodos formados por filmes metálicos de alumínio. Filmes finos de óxido de titânio (TiOx) e óxido de tântalo (TaOx), cujas características são de interesse para aplicação como filme sensível em determinadas aplicações, também foram estudados. Os filmes foram obtidos pelas técnicas de deposição química em fase vapor (LPCVD), sputtering dc e oxidação térmica rápida (RTO). Foram desenvolvidas técnicas de fabricação de dispositivos de efeito de campo baseados em grafeno e nanotubos de carbono, utilizando como dielétrico de porta os filmes finos desenvolvidos para formar a camada sensível dos ISFET's. Entretanto, os eletrodos foram construídos empregando-se filmes finos de nitreto de tântalo (TaN) depositados por sputtering dc. Filmes sensíveis de SiNx são quimicamente estáveis e tornam os sensores robustos com sensibilidade em tensão próxima ao limite de Nernst (59 mV/pH). Entretanto, a grande sensibilidade em tensão obtida (50 mV/pH) não é transformada em alta sensibilidade em corrente (1,35 ?A/pH), devido ao baixo valor de transcondutância observado (19 ?S). Por outro lado, quando se utiliza AlN depositado a temperatura ambiente, tem-se um baixo valor de sensibilidade em tensão (20 mV/pH) que é transformado em uma alta sensibilidade em corrente (28 ?A/pH), em razão da alta transcondutância dos dispositivos (329 ?S). GraFET's e CNTFET's demonstraram a modulação da corrente entre os eletrodos de fonte e dreno pela ação do campo elétrico perpendicular, aplicado com o auxílio do eletrodo de porta. Entretanto, o efeito de campo observado é ambipolar, ou seja, existem dois regimes possíveis de operação dos dispositivos, um regime dominado pelo transporte de lacunas e outro dominado pelo transporte de elétrons. A característica ambipolar possibilita a detecção de moléculas carregadas positiva e negativamente, enquanto que o baixo coeficiente de temperatura do filme de TaN possibilita a utilização dos dispositivos em processos realizados em altas temperaturas
Abstract: The main aim of this work is the development of advanced materials and methods for the fabrication of chemical/biochemical sensors. By using equipments available in the Center of Semiconductor Components of UNICAMP, high dielectric constant thin films and metallic films have been developed and characterized. The materials developed were employed in the fabrication of sensors based on ion-sensitive field effect transistors (ISFET) and in field-effect devices incorporating carbon nanostructures as functional elements [Graphene (GraFET) and carbon nanotubes (CNTFET)]. The application of these materials as sensitive layer, gate dielectric and electrodes, as well as the use of nanostructures, aims to increase the sensitivity and biocompatibility of the devices, to build robust devices that can be used in harsh environments and obtain sensors with linear and stable response over time and temperature. ISFET's with sensitive layer consisting of thin films of silicon nitride (SiNx)/aluminum nitride (AlN) and with electrodes formed by aluminum metallic films were fabricated, characterized and packaged. Thin films of titanium oxide (TiOx) and tantalum oxide (TaOx), whose characteristics are interesting in certain applications, were also studied. The films were obtained by chemical deposition techniques in vapor phase (LPCVD), dc sputtering and rapid thermal oxidation (RTO). Techniques have been developed for manufacturing field effect devices based on graphene and carbon nanotubes, the thin films developed to form the ISFET's sensitive layer were used as gate dielectric. However, the electrodes were built by using thin film of tantalum nitride (TaN) deposited by dc sputtering. SiNx sensitive films are chemically stable and make sensors robust with sensitivity in voltage near to the Nernst limit (59 mV/pH). However, the great sensitivity in voltage (50 mV/pH) is not transformed into high current sensitivity (1.35 ?A/pH), due to the low value of transconductance (19 ?S). On the other hand, when AlN deposited at room temperature is used, a low voltage sensitivity value is obtained (20 mV/pH) that is transformed into a high sensitivity in current (28 ?A/pH), due to high transconductance of the devices (329 ?S). GraFETs and CNTFETs demonstrated the current modulation between the source and drain electrodes by the action of perpendicular electric field, applied with the aid of the gate electrode. However, the field effect observed is ambipolar, in other words, there are two possible operation regime, a regime dominated by the transport of holes and another dominated by transport of electrons. The ambipolar feature enables the detection of positively and negatively charged molecules, while the low temperature coefficient of TaN film allows the use of devices in processes carried out at high temperatures
Doutorado
Eletrônica, Microeletrônica e Optoeletrônica
Doutor em Engenharia Elétrica

The Schottky barrier, contact resistance and carrier mobility in carbon nanotube (CNT) field-effect transistors (FETs) are discussed in detail in this thesis. Novel extraction methods and definitions are proposed for these parameters. A technology comparison with other emerging transistor technologies and a performance projection study are also presented. A Schottky barrier height extraction method for CNTFETs considering one-dimensional (1D) conditions is developed. The methodology is applied to simulation and experimental data of CNTFETs feasible for manufacturing. Y-function-based methods (YFMs) have been applied to simulation and experimental data in order to extract a contact resistance for CNTFETs. Both extraction methods are more efficient and accurate than other conventional approaches. Practical mobility expressions are derived for CNTFETs covering the ballistic as well as the non-ballistic transport regime which enable a straightforward evaluation of the transport in CNTs. They have been applied to simulation and experimental data of devices with different channel lengths and Schottky barrier heights. A comparison of fabricated emerging transistors based on similar criteria for various application scenarios reveals CNTFETs as promising candidates to compete with Si-based technologies in low-power static and dynamic applications. A performance projection study is suggested for specific applications in terms of the studied design parameters.

В статье рассмотрены нанотранзисторы и основные свойства нанотрубок. Представлен обзор CNTFET транзисторов и основные особенности технологии их изготовления. Полевые транзисторы из углеродных нанотрубок (CNTFET) являются перспективными наноразмерными устройствами для реализации высокопроизводительных схем с очень плотной и низкой мощностью. Проводящий канал CNTFET представляет собой углеродную нанотрубку. The article deals with nanotransistors and the main properties of nanotubes. An overview of CNTFET transistors and the main features of their manufacturing technology is presented. Carbon nanotube field effect transistors (CNTFETs) are promising nanoscale devices for implementing high-performance circuits with very dense and low power. The CNTFET conducting channel is a carbon nanotube.