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This dissertation, "Multi-terminal Nano-electronic Device Simulations With Atomistic Details" by Siu-kong, Koo, 顧兆光, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Miniaturization of electronics is an unstoppable trend in the semiconductor industry. Moore's Law has been the driving force to the advancement of the industry for half a century; and will continue to be the indicator for technology developments. As the feature size of an electronic device is reducing to the nano-scale level, quantum mechanics and atomistic details will become more and more important. In addition, simulations on devices with two or more terminals, such as transistors or junctions, are essential for design of electronics. Thus, Quantum mechanics based method with atomistic details for simulations of nano-electronic devices with two or more terminals is proposed and demonstrated. Similar studies can be found in the literature. However, most work was focusing on static / steady state problems, only few had looked into the dynamics. On the other hand, most methods being used in previous work can only handle two-terminal devices, while those few methods which can be applied for multi-terminal devices can only deal with steady state problems. Therefore, there is a research gap lies in multi-terminal time-dependent device simulations; and this gap will be filled by the work in this thesis. Quantum mechanics based method for open system has been used to simulate the electrical response through nano-electronic devices. Nearest neighbor tight binding models and carbon based models are the systems of interests. The core part of the structures of the systems of interest is a hexagonal ring. This is essentially a benzene ring based structure in our studies. Several situations for electrodes connecting the benzene ring at para- and metapositions are considered. Two-terminal cases and three-terminal cases for the mentioned systems have been studied. The third terminal in the three-terminal case is basically being viewed as a probe to the corresponding two-terminal case. For all the cases, steady state currents have been calculated; and currentvoltage curves of the systems have been obtained. Transient currents have also been calculated, so that dynamic responses of the systems are revealed. Different magnitudes of bias voltages have been applied to the systems. Linear response of the currents through the devices with respect to the bias voltage is observed for most cases. The para-position case can be taken as a reference to the meta-position case, due to simple structure and well-behaved responses. Interesting electric responses from the meta-position case is observed. The possibility for the meta-position system to be used as a transistor or other devices is briefly discussed. DOI: 10.5353/th_b5312347 Subjects: Nanoelectromechanical systems
Computational nanoelectronics is an emerging multi-disciplinary field covering condensed matter physics, applied mathematics, computer science, and electronic engineering. In recent decades, a few state-of-the-art software packages have been developed to carry out first-principle atomistic device simulations. Nevertheless those packages are either black boxes (commercial codes) or accessible only to very limited users (private research codes). The purpose of this book is to open one of the commercial black boxes, and to demonstrate the complete procedure from theoretical derivation, to numerical implementation, all the way to device simulation. Meanwhile the affiliated source code constitutes an open platform for new researchers. This is the first book of its kind. We hope the book will make a modest contribution to the field of computational nanoelectronics.
"Computational nanoelectronics is an emerging multi-disciplinary field covering condensed matter physics, applied mathematics, computer science, and electronic engineering. In recent decades, a few state-of-the-art software packages have been developed to carry out first-principle atomistic device simulations. Nevertheless those packages are either black boxes (commercial codes) or accessible only to very limited users (private research codes). The purpose of this book is to open one of the commercial black boxes, and to demonstrate the complete procedure from theoretical derivation, to numerical implementation, all the way to device simulation. Meanwhile the affiliated source code constitutes an open platform for new researchers. This is the first book of its kind. We hope the book will make a modest contribution to the field of computational nanoelectronics"--
Nanoelectronic Device Applications Handbook gives a comprehensive snapshot of the state of the art in nanodevices for nanoelectronics applications. Combining breadth and depth, the book includes 68 chapters on topics that range from nano-scaled complementary metal–oxide–semiconductor (CMOS) devices through recent developments in nano capacitors and AlGaAs/GaAs devices. The contributors are world-renowned experts from academia and industry from around the globe. The handbook explores current research into potentially disruptive technologies for a post-CMOS world. These include: Nanoscale advances in current MOSFET/CMOS technology Nano capacitors for applications such as electronics packaging and humidity sensors Single electron transistors and other electron tunneling devices Quantum cellular automata and nanomagnetic logic Memristors as switching devices and for memory Graphene preparation, properties, and devices Carbon nanotubes (CNTs), both single CNT and random network Other CNT applications such as terahertz, sensors, interconnects, and capacitors Nano system architectures for reliability Nanowire device fabrication and applications Nanowire transistors Nanodevices for spintronics The book closes with a call for a new generation of simulation tools to handle nanoscale mechanisms in realistic nanodevice geometries. This timely handbook offers a wealth of insights into the application of nanoelectronics. It is an invaluable reference and source of ideas for anyone working in the rapidly expanding field of nanoelectronics.
While theories based on classical physics have been very successful in helping experimentalists design microelectronic devices, new approaches based on quantum mechanics are required to accurately model nanoscale transistors and to predict their characteristics even before they are fabricated. Advanced Nanoelectronics provides research information on advanced nanoelectronics concepts, with a focus on modeling and simulation. Featuring contributions by researchers actively engaged in nanoelectronics research, it develops and applies analytical formulations to investigate nanoscale devices. The book begins by introducing the basic ideas related to quantum theory that are needed to better understand nanoscale structures found in nanoelectronics, including graphenes, carbon nanotubes, and quantum wells, dots, and wires. It goes on to highlight some of the key concepts required to understand nanotransistors. These concepts are then applied to the carbon nanotube field effect transistor (CNTFET). Several chapters cover graphene, an unzipped form of CNT that is the recently discovered allotrope of carbon that has gained a tremendous amount of scientific and technological interest. The book discusses the development of the graphene nanoribbon field effect transistor (GNRFET) and its use as a possible replacement to overcome the CNT chirality challenge. It also examines silicon nanowire (SiNW) as a new candidate for achieving the downscaling of devices. The text describes the modeling and fabrication of SiNW, including a new top-down fabrication technique. Strained technology, which changes the properties of device materials rather than changing the device geometry, is also discussed. The book ends with a look at the technical and economic challenges that face the commercialization of nanoelectronics and what universities, industries, and government can do to lower the barriers. A useful resource for professionals, researchers, and scientists, this work brings together state-of-the-art technical and scientific information on important topics in advanced nanoelectronics.
The unique electrical and optical properties of two-dimensional (2D) materials has spurred intense research interest towards development of nanoelectronic devices utilizing these novel materials. The atomically thin form of 2D materials translates to excellent electrostatic gate control even at nanoscale channel length dimensions, near-ideal two-dimensional carrier behavior, and perhaps conventional and novel devices applications. Monolayer transition metal dichalcogenides (TMDs) are novel, gapped 2D materials. Toward device applications, I consider MoS2 layers on dielectrics, in particular in this work, the effect of vacancies on the electronic structure. In density-functional-theory (DFT) simulations, the effects of near-interface oxygen vacancies in the oxide slab, and Mo or S vacancies in the MoS2 layer are considered. Band structures and atom-projected densities of states for each system and with differing oxide terminations were calculated, as well as those for the defect-free MoS2-dielectrics system and for isolated dielectric layers for reference. Among the results, I find that with O-vacancies, both the HfO2-MoS2 and the Al2O3-MoS2 systems appear metallic due to doping of the oxide slab followed by electron transfer into the MoS2, in manner analogous to modulation doping. The n-type doping of monolayer MoS2 by high-k oxides with O-vacancies is confirmed through collaborative experimental work in which back-gated monolayer MoS2 FETs encapsulated by oxygen deficient high-k oxides have been characterized. Van der Waal’s heterostructures allow for novel devices such as two-dimensional-to-two-dimensional tunnel devices, exemplified by interlayer tunnel FETs. These devices employ channel/tunnel-barrier/channel geometries. However, during layer-by-layer exfoliation of these multi-layer materials, rotational misalignment is the norm and may substantially affect device characteristics. In this work, by using density functional theory methods, I consider a reduction in tunneling due to weakened coupling across the rotationally misaligned interface between the channel layers and the tunnel barrier. As a prototypical system, I simulate the effects of rotational misalignment of the tunnel barrier layer between aligned channel layers in a graphene/hBN/graphene system. Rotational misalignment between the channel layers and the tunnel barrier in this van der Waal’s heterostructure can significantly reduce coupling between the channels by reducing, specifically, coupling across the interface between the channels and the tunnel barrier. This weakened coupling in graphene/hBN/graphene with hBN misalignment may be relevant to all such van der Waal’s heterostructures. TMDs are viable alternatives to graphene and hBN as channel and tunnel barrier layers, respectively, for improved performance in interlayer tunnel FET device structures. In particular, I used DFT simulations to study the bilayer-graphene/WSe2/bilayer-graphene heterostructure as well as single and multilayer ReS2-layer systems. Significant roadblocks to the widespread use of TMDs for nanoelectronic devices are the large contact resistance and absence of reliable doping techniques. Hence, I studied substitutional doping of, and evaluated various metal contacts to MoS2 by computing the density of states for the systems. Metal contacts that pin the Fermi level within the desired band are optimal for device applications. My simulation results suggest that monolayer (ML) MoS2 can be doped n-type or p-type by substituting for an S atom in the supercell with a group-17 Cl atom or a group-15 P atom, respectively. My simulations also suggest that Sc and Ti would serve as excellent contacts to n-type ML MoS2 due to the strong bonding and large number of states near the Fermi level. But the theoretical expectations are tempered by the material characteristics, i.e., the extremely reactive nature of Sc and the oxidation prone nature of Ti atoms. I also studied commonly used Ag and Au metal contacts to ML MoS2, which exhibited medium strength bonding to MoS2 and an apparent pinning of the Fermi level nearer to the nominal MoS2 conduction band edge
This dissertation, "Efficiency Enhancement for Nanoelectronic Transport Simulations" by Jun, Huang, 黃俊, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Continual technology innovations make it possible to fabricate electronic devices on the order of 10nm. In this nanoscale regime, quantum physics becomes critically important, like energy quantization effects of the narrow channel and the leakage currents due to tunneling. It has also been utilized to build novel devices, such as the band-to-band tunneling field-effect transistors (FETs). Therefore, it presages accurate quantum transport simulations, which not only allow quantitative understanding of the device performances but also provide physical insight and guidelines for device optimizations. However, quantum transport simulations usually require solving repeatedly the Green's function or the wave function of the whole device region with open boundary treatment, which are computationally cumbersome. Moreover, to overcome the short-channel effects, modern devices usually employ multi-gate structures that are three-dimensional, making the computation very challenging. It is the major target of this thesis to enhance the simulation efficiency by proposing several fast numerical algorithms. The other target is to apply these algorithms to study the physics and performances of some emerging electronic devices. First, an efficient method is implemented for real space simulations with the effective mass approximation. Based on the wave function approach, asymptotic waveform evaluation combined with a complex frequency hopping algorithm is successfully adopted to characterize electron conduction over a wide energy range. Good accuracy and efficiency are demonstrated by simulating several n-type multi-gate silicon FETs. This technique is valid for arbitrary potential distribution and device geometry, making it a powerful tool for studying n-type silicon nanowire (SiNW) FETs in the presence of charged impurity and surface roughness scattering. Second, a model order reduction (MOR) method is proposed for multiband simulation of nanowire structures. Employing three- or six-band k.p Hamiltonian, the non-equilibrium Green's function (NEGF) equations are projected into a much smaller subspace constructed by sampling the Bloch modes of each cross-section layer. Together with special sampling schemes and Krylov subspace methods for solving the eigenmodes, large cross-section p-type SiNW FETs can be simulated. A novel device, junctionless FET, is then investigated. It is found that its doping density, channel orientation, and channel size need to be carefully optimized in order to outperform the classical inversion-mode FET. With a spurious band elimination process, the MOR method is subsequently extended to the eight-band k.p model, allowing simulation of band-to-band tunneling devices. In particular, tunneling FETs with indium arsenide (InAs) nanowire channel are studied, considering different channel orientations and configurations with source pockets. Results suggest that source pocket has no significant impact on the performances of the nanowire device due to its good electrostatic integrity. At last, improvements are made for open boundary treatment in atomistic simulations. The trick is to condense the Hamiltonian matrix of the periodic leads before calculating the surface Green's function. It is very useful for treating leads with long unit cells. DOI: 10.5353/th_b5153685 Subjects: Nanoelectronics - Mathematical methods
Presents technologies and key concepts to produce suitable smart materials and intelligent structures for sensing, information and communication technology, biomedical applications (drug delivery, hyperthermia therapy), self-healing, flexible memories and construction technologies. Novel developments of environmental friendly, cost-effective and scalable production processes are discussed by experts in the field.
ABSTRACT: Electronic devices, gas sensors, micro- and nano- electromechanical systems and catalytic devices are usually composed of multifunctional nano-scaled structures. Inherent to these complex nanostructures are heterogeneous interfaces such as, for example, metal/metal oxide, semiconductor/metal oxide, and metal oxide/gaseous molecule interfaces. These heterogeneous interfaces play a crucial role in the applications of nanostructures. With recent advancements in technology, these nanostructures have shrunk to dimensions less than tens of nanometers and contain less than hundreds of billions of atoms. It has also recently become routine to model and simulate these multi-million-atom nanostructures with heterogeneous interfaces at the atomistic level using molecular dynamics (MD) simulations. The capability to simulate atoms interacting with each other in these multifunctional nanostructures has made probing, understanding and engineering the atomic-level properties of materials possible.