Miniaturized Transistors, Volume II

In this book, we aim to address the ever-advancing progress in microelectronic device scaling. Complementary Metal-Oxide-Semiconductor (CMOS) devices continue to endure miniaturization, irrespective of the seeming physical limitations, helped by advancing fabrication techniques. We observe that miniaturization does not always refer to the latest technology node for digital transistors. Rather, by applying novel materials and device geometries, a significant reduction in the size of microelectronic devices for a broad set of applications can be achieved. The achievements made in the scaling of devices for applications beyond digital logic (e.g., high power, optoelectronics, and sensors) are taking the forefront in microelectronic miniaturization. Furthermore, all these achievements are assisted by improvements in the simulation and modeling of the involved materials and device structures. In particular, process and device technology computer-aided design (TCAD) has become indispensable in the design cycle of novel devices and technologies. It is our sincere hope that the results provided in this Special Issue prove useful to scientists and engineers who find themselves at the forefront of this rapidly evolving and broadening field. Now, more than ever, it is essential to look for solutions to find the next disrupting technologies which will allow for transistor miniaturization well beyond silicon’s physical limits and the current state-of-the-art. This requires a broad attack, including studies of novel and innovative designs as well as emerging materials which are becoming more application-specific than ever before

On improvements in metal oxide based flexible transistors through systematic evaluation of material properties

Thin-film metal oxide (MOx) semiconductors have opened the way to a new generation of electronics based on their unique properties. With mobilities, mu, of up to 80 cm2V-1s-1, metal oxides do not rival crystalline silicon (mu~1000 cm2V-1s-1) for complex applications. But such oxides do have three unique characteristics driving great interest: their mobilities persist in the amorphous form, contrary to the thousandfold drop seen in silicon; they are transparent; and they can be processed at, or near, room temperature. Most work on MOx semiconductors, in particular indium gallium zinc oxide (IGZO), has focused on display applications, where MOx thin-film transistors (TFTs) are used to drive individual pixels, reducing power consumption by blocking less light than alternatives, and allowing smaller pixels due to reduced TFT sizes. Such work has seen great advances in IGZO, but has generally not considered the thermal budget during production. By utilising the low temperature processing possible with MOx, a new world of applications becomes possible: flexible electronics. This work aims to improve the characteristics of TFTs based on amorphous IGZO (a-IGZO) through detailed study of the thin-film structure in relation to functional performance, looking at the material structure of three critical layers in an a-IGZO TFT. A study of optimisation of a dielectric layer of Al2O3, deposited by atomic layer deposition (ALD), is presented. This dielectric, between the a-IGZO and the gate electrode, shows a three-layer substructure in what has previously been regarded as a single homogeneous layer. A study of the insulating Al2O3 buffer layer below the a-IGZO compared the properties of Al2O3 deposited by ALD and sputtering. Sputtered material has a more complex structure than ALD, consisting of multiple sublayers that correlate with the sputtering process. The structure of the two materials is discussed, and the impact on device performance considered. A detailed systematic study of the effects of annealing of a-IGZO shows a strong dependence of the density on both time and temperature. A two mechanism model is proposed which consists of structural relaxation of the amorphous material followed by absorption of oxygen from the environment. Finally, investigation of the influence of the buffer material on the a-IGZO, and the structure of this interface showed little difference in the growth of the a-IGZO, but did reveal some changes in the interface, while a systematic study of annealing effects on the a-IGZO-dielectric interface showed some interesting changes in this structure, both of which are likely to significantly impact the operational characteristics of TFT devices

Non-volatile organic memory devices: from design to applications

The research activity described in the attached dissertation focused on the development, fabrication and characterization of new non-volatile memory elements based on organic technology. During the last few decades, organic materials based devices have attracted considerable interest due to their great potential for future electronic systems. Low fabrication costs, high mechanical flexibility and versatility of the chemical structure, good scalability and easy processing are the unique advantages of organic electronics. As memory devices are essential elements of any kind of electronic system, the development of organic memory devices is fundamental in order to extend the application of organic materials to different electronic circuits. Research on organic electronic memories is currently at a rapid growth stage, since it is recognized that they may be an alternative or supplementary to the conventional memory technologies. Despite considerable progress in the advancement of novel memory technologies in recent years, some challenging tasks still need to be resolved. The Ph.D. research activity of this thesis is related to the still -opened challenges in the organic memories technologies. In particular, it focused mainly on the study, development, fabrication and characterization of new non-volatile organic memory elements based on resistive switching. The activity has been carried out in the frame of the European project “HYbrid organic/inorganic Memory Elements for integration of electronic and photonic Circuitry” (HYMEC), which involved the University of Cagliari during the last three years. The project goal was to realize new hybrid inorganic/organic resistive memory devices with functionality far beyond the state of the art. A complementary activity on transistor-based organic memory devices has been also carried out and described in this thesis. As regards resistive memory devices, the research activity included design, fabrication and testing of a novel non-volatile memory device based on the combination of an air-stable organic semiconductor and metal nanoparticles. This topic required the development of technology and procedures for easy and reliable production of devices as well as the definition of measurement protocols. The proposed structure was thoroughly characterized by morphological techniques, which allowed to interpret the resistive switching mechanisms in terms of formation and rupture of metallic filaments inside the organic layer assisted by the metal NPs. The obtained performances are the best reported so far in literature, and, to our knowledge, the statistics analysis is the largest ever reported for organic-based resistive memories. The developed technology was then successfully applied on flexible plastic substrates. The definition of technological processes for the reliable fabrication of high performance printed organic memory devices was also carried out: this work clearly demonstrates the real possibility of fabricating high performance printed memory elements. A significant effort was also devoted to the development of basic memory/sensor systems entirely fabricated on plastic substrates. The suitability of organic non-volatile memory devices for the detection and the storage of external parameters was demonstrated. The results definitely demonstrated the feasibility of the proposed technology for the fabrication of systems including organic memories for their final application in different industrial processes, including e-textile and smart packaging. As regards transistor memory devices, highly flexible Organic Field-Effect Transistor (OFET)-based memory elements with excellent mechanical stability and high retention time were developed. As main innovation with respect to the state of the art, low voltage operation of the OFET-based memory was investigated. Such an activity was also related to the development of reliable measurement procedure

Inorganic micro/nanostructures-based high-performance flexible electronics for electronic skin application

Electronics in the future will be printed on diverse substrates, benefiting several emerging applications such as electronic skin (e-skin) for robotics/prosthetics, flexible displays, flexible/conformable biosensors, large area electronics, and implantable devices. For such applications, electronics based on inorganic micro/nanostructures (IMNSs) from high mobility materials such as single crystal silicon and compound semiconductors in the form of ultrathin chips, membranes, nanoribbons (NRs), nanowires (NWs) etc., offer promising high-performance solutions compared to conventional organic materials. This thesis presents an investigation of the various forms of IMNSs for high-performance electronics. Active components (from Silicon) and sensor components (from indium tin oxide (ITO), vanadium pentaoxide (V2O5), and zinc oxide (ZnO)) were realised based on the IMNS for application in artificial tactile skin for prosthetics/robotics. Inspired by human tactile sensing, a capacitive-piezoelectric tandem architecture was realised with indium tin oxide (ITO) on a flexible polymer sheet for achieving static (upto 0.25 kPa-1 sensitivity) and dynamic (2.28 kPa-1 sensitivity) tactile sensing. These passive tactile sensors were interfaced in extended gate mode with flexible high-performance metal oxide semiconductor field effect transistors (MOSFETs) fabricated through a scalable process. The developed process enabled wafer scale transfer of ultrathin chips (UTCs) of silicon with various devices (ultrathin chip resistive samples, metal oxide semiconductor (MOS) capacitors and n‐channel MOSFETs) on flexible substrates up to 4″ diameter. The devices were capable of bending upto 1.437 mm radius of curvature and exhibited surface mobility above 330 cm2/V-s, on-to-off current ratios above 4.32 decades, and a subthreshold slope above 0.98 V/decade, under various bending conditions. While UTCs are useful for realizing high-density high-performance micro-electronics on small areas, high-performance electronics on large area flexible substrates along with low-cost fabrication techniques are also important for realizing e-skin. In this regard, two other IMNS forms are investigated in this thesis, namely, NWs and NRs. The controlled selective source/drain doping needed to obtain transistors from such structure remains a bottleneck during post transfer printing. An attractive solution to address this challenge based on junctionless FETs (JLFETs), is investigated in this thesis via technology computer-aided design (TCAD) simulation and practical fabrication. The TCAD optimization implies a current of 3.36 mA for a 15 μm channel length, 40 μm channel width with an on-to-off ratio of 4.02x 107. Similar to the NRs, NWs are also suitable for realizing high performance e-skin. NWs of various sizes, distribution and length have been fabricated using various nano-patterning methods followed by metal assisted chemical etching (MACE). Synthesis of Si NWs of diameter as low as 10 nm and of aspect ratio more than 200:1 was achieved. Apart from Si NWs, V2O5 and ZnO NWs were also explored for sensor applications. Two approaches were investigated for printing NWs on flexible substrates namely (i) contact printing and (ii) large-area dielectrophoresis (DEP) assisted transfer printing. Both approaches were used to realize electronic layers with high NW density. The former approach resulted in 7 NWs/μm for bottom-up ZnO and 3 NWs/μm for top-down Si NWs while the latter approach resulted in 7 NWs/μm with simultaneous assembly on 30x30 electrode patterns in a 3 cm x 3 cm area. The contact-printing system was used to fabricate ZnO and Si NW-based ultraviolet (UV) photodetectors (PDs) with a Wheatstone bridge (WB) configuration. The assembled V2O5 NWs were used to realize temperature sensors with sensitivity of 0.03% /K. The sensor arrays are suitable for tactile e-skin application. While the above focuses on realizing conventional sensing and addressing elements for e-skin, processing of a large amount of data from e-skin has remained a challenge, especially in the case of large area skin. A Neural NW Field Effect Transistors (υ-NWFETs) based hardware-implementable neural network (HNN) approach for tactile data processing in e-skin is presented in the final part of this thesis. The concept is evaluated by interfacing with a fabricated kirigami-inspired e-skin. Apart from e-skin for prosthetics and robotics, the presented research will also be useful for obtaining high performance flexible circuits needed in many futuristic flexible electronics applications such as smart surgical tools, biosensors, implantable electronics/electroceuticals and flexible mobile phones

Printed and drawn flexible electronics based on cellulose nanocomposites

Sustainability, flexibility, and low-power consumption are key features to meet the growing re- quirements of simplicity and multifunctionality of low-cost, disposable/recyclable smart electronic -of- -based composites hold po- tential to fulfill such demands when explored as substrate and/or electrolyte-gate, or as active channel layer on printed transistors and integrated circuits based on ionic responses (iontronics). In this work, a new generation of reusable, healable and recyclable regenerated cellulose hydro- gels with high ionic conductivity and conformability, capable of being provided in the form of stick- ers, are demonstrated. These hydrogels are obtained from a simple, fast, low-cost, and environ- mental-friendly aqueous alkali salt/urea dissolution method of native cellulose, combined with eration and simultaneous ion incorporation with acetic acid. Their electrochemical properties can be also merged with the mechanical robustness, thermal resistance, transparency, and smooth- - strate. Beyond gate dielectrics, a water-based screen-printable ink, composed of CMC binder and com- mercial zinc oxide (ZnO) semiconducting nanoparticles, was formulated. The ink enables the printing of relatively smooth and densely packed films on office paper with semiconducting func- tionality at room temperature. The rather use of porous ZnO nanoplates is beneficial to form per- colative pathways at lower contents of functional material, at the cost of rougher surfaces. The engineered cellulose composites are successfully integrated into flexible, recyclable, low- voltage (<3.5 V), printed electrolyte-gated office paper or on the ionically modified nanopaper. Ubiquitous calligraphy accessories are used -the- out on the target substrate, where are already printed the devices. Such concept paves the way for a worldwide boom of creativity, where we can freely create personal electronic kits, while having fun at it and without generating waste.Sustentabilidade, flexibilidade e baixo consumo energético são características chave para atender aos crescentes requisitos de simplicidade e multifuncionalidade de sistemas eletrónicos inteligentes de baixo custo, das- Compósitos à base de celulose têm potencial para atender a tais necessidades quando explora- dos como substrato e/ou porta-de-eletrólito ou como camada de canal ativo em transístores impressos e circuitos integrados baseados em respostas iónicas (iontronics). Neste trabalho, é demonstrada uma nova geração de hidrogéis reutilizáveis, reparáveis e recicláveis baseados em celulose regenerada, que apresentam alta condução iónica e conformabilidade, podendo ser fornecidos na forma de adesivos. Estes hidrogéis são obtidos a partir de um método simples, rápido, barato e amigo do ambiente que permite a dissolução de celulose nativa em soluções aquosas com mistura de sal alcalino e ureia, combinado com carboximetil celulose (CMC) para melhorar a sua robustez, seguido da regeneração e simultâneo enriquecimento iónico com ácido acético. As suas propriedades eletroquímicas podem ser combinadas com a inbase de celulose micro/nanofibrilada para obter um substrato eletrolítico semelhante a papel. Para além de portas-dielétricas, foi formulada uma tinta aquosa compatível com serigrafia, composta por CMC como espessante e nanopartículas semicondutoras de ZnO. A tinta permite a impressão de filmes pouco rugosos e densamente percolados sobre papel de escritório, e com funcionalidade semicondutora à temperatura ambiente. O uso alternativo de nanoplacas porosas de ZnO é benéfico para criar caminhos percolativos com menores teores de material funcional, apesar de se obter filmes rugosos. Os compósitos à base celulose foram integrados com sucesso em transístores e portas lógicas porta-eletrolítica, os quais foram impressos em papel de escritório ou no "nanopapel" iconicamente modificado. Acessórios de caligrafia permitem a fácil e rápida padronização de pistas condutoras/resistivas, desenhando-as no substrato alvo, onde estão impressos os dispositivos. Este conceito despoleta um mundo criativo, onde é possível criar livremente kits eletrónicos customizados de forma divertida e sem gerar resíduos

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

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

Wearable Nano-Based Gas Sensors for Environmental Monitoring and Encountered Challenges in Optimization

With a rising emphasis on public safety and quality of life, there is an urgent need to ensure optimal air quality, both indoors and outdoors. Detecting toxic gaseous compounds plays a pivotal role in shaping our sustainable future. This review aims to elucidate the advancements in smart wearable (nano)sensors for monitoring harmful gaseous pollutants, such as ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), ozone (O3), hydrocarbons (CxHy), and hydrogen fluoride (HF). Differentiating this review from its predecessors, we shed light on the challenges faced in enhancing sensor performance and offer a deep dive into the evolution of sensing materials, wearable substrates, electrodes, and types of sensors. Noteworthy materials for robust detection systems encompass 2D nanostructures, carbon nanomaterials, conducting polymers, nanohybrids, and metal oxide semiconductors. A dedicated section dissects the significance of circuit integration, miniaturization, real-time sensing, repeatability, reusability, power efficiency, gas-sensitive material deposition, selectivity, sensitivity, stability, and response/recovery time, pinpointing gaps in the current knowledge and offering avenues for further research. To conclude, we provide insights and suggestions for the prospective trajectory of smart wearable nanosensors in addressing the extant challenges