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Master Class in nanoscale physics and devices |
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Monday, 6 October, 2014 AG 66
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9– 10:30am : Murali Kota and Aniruddha Konar, IBM
Quantum Effects in Nanodevices
The revolution in information and micro/nano electronics technology has been possible due to the continuously shrinking transistor. The size of the transistor has shrunk by more than 5 orders of magnitude in 5 decades! Can this scaling continue and how small can devices shrink to? These are some of the questions of interest to the nanoelectronics community. As the devices enter nanoscale dimensions, many quantum effects start to dominate and these effects become important to design next generation devices. In the first part of the lecture, we will address challenges associated with scaling of transistors to nanoscale dimensions. We will then discuss the effects of quantum (size and potential dependent) confinement, tunneling of various forms (direct, trap-assisted and band to band tunneling), work function engineering, and reliability of nanodevices and related phenomena. In the 2nd part of the lecture, carrier transport mechanism will be discussed for both Front-end of the line (FEOL) and in the back-end of the line (BEOL) of a chip. Starting from Drude's classical theory of transport, we will go through the semi-classical formalism of diffusive carrier transport in devices. All possible disordered-limited scattering mechanisms in nano-devices will be discussed in a colloquial manner. For simple examples, we will work out impurity scattering in nanowires and graphene in detail, We will point out failure of Ohm's law /semi-classical transport in the BEOL line, particularly in via, where semi-classical treatment of transport does not hold in state-of -the art technology. As a remedy of this, we will talk about "Landauer" quantum transport and a simple way to estimate interface resistance of small length conductor. Useful reading:
11-12:30pm Victor Zhirnov, Semiconductor Research Corporation and North Carolina State University, USA
Fundamental Limits of Charge Based Computing We will examine the physics of extreme scaling of information processing devices and systems, with a focus on energy minimization and also discuss the materials and architectural implications on system scaling. The fundamental limiting factors for electronic information processors are: 1) the tunneling limit on the minimal size due to small mass of electrons, 2) excessive energy consumption in metal wires used for rigid interconnect systems, and 3) heat generation in a small volume. There are also proposals for alternative future information processing technologies based on information carriers other than electrons, however their potential for using in practical systems remains unclear. The primary objective of this study is to explore the connection of device physics from the viewpoint of the Boltzmann-Heisenberg limits and the parameters of the digital circuits implemented from these devices. The central question addressed in this talk is: What is the smallest volume of matter needed for a memory or logic device? The scaling limits of electron-based devices, such as transistors are shown to be~5-7 nm due to quantum-mechanical tunneling. Smaller devices can be made, if information-bearing particles are used whose mass is greater than the mass of an electron. Therefore the new principles for logic and memory devices, scalable to ~1 nm, could be based on ‘moving atoms’ instead of ‘moving electrons’; for example using nanoinonic structures. We will also consider an abstraction of a Minimal Turing Machine built from the limiting devices and circuits, thus address the Turing-Heisenberg Rapprochement. The analysis suggests a possible limit to computational performance similar to the Carnot efficiency limit for heat engines. Finally, the living cell will be considered in the context of information processing. The essential parameters of the logic and memory hardware of biological processors and implications for the minimum-energy computing systems will be discussed.
Useful reading:
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Lunch 12:45-1:30pm Lab visits 1:30-2:30pm
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2:30-4:00pm Nicola Marzari, EPFL Electrical and thermal transport from first-principles I'll give a brief overview of the state-of-the art in calculating electrical and thermal transport from first-principles quantum-mechanical simulations, either in the semi-classical or in the fully quantum regime, and will discuss in detail two case studies. The first is based on constructing the electronic structure of complex nanostructures using maximally localized Wannier functions, while the second is based on determining thermal or electrical conductivities from the Boltzmann transport equation, using carrier lifetimes determined from density-functional perturbation theory.
4:30-6:00pm Sadasivan (Sadas) Shankar, Computational Materials Design Currently, development of materials from concept to product is both capital- and time-intensive. Computational Materials Design is one of the techniques starting to get used to accelerate designing materials from atoms or condensed matter that when synthesized exhibits targeted properties at the systems level. As one of the earliest proponents and adopters of using Materials Design in the industry for bringing materials to prototyping faster, we have identified several gaps that are being addressed. This involves development and application of theory, simulations, and experiments. Although there is enormous potential for using computer-based design in materials and chemistry, we demonstrate both the challenges and the opportunities to cross the last mile from theory to real time applications. We will also touch upon President’s Materials Genome initiative, consistent with our own earlier efforts, which was launched nationwide to get materials to manufacturing faster. References
Useful links:
http://www.ted.com/pages/intel_sadasivan_shankar
http://media.quantum-espresso.org/santa_barbara_2009_07/slides-exercices/QESB09_Shankar_keynote.pdf
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7-8pm Dinner
8:30pm departure |
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Master Class in nanoscale physics and devices |
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Tuesday, 7 October, 2014 AG 66 |
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9-10:30am
R. Vijayaraghavan, TIFR Superconducting quantum electrical circuits
I will introduce the idea of quantum mechanical electrical circuits and how one can build 'artificial atoms' with quantized energy levels using superconducting circuits. I will also discuss how one manipulates the quantum levels using microwave frequency signals and discuss microwave engineering strategies to protect these quantum levels from decaying.
References:
11-12:30pm
Subhasish Mitra, Stanford Carbon Nanotube Robust Digital VLSI Carbon Nanotube Field Effect Transistors (CNFETs) are excellent candidates for building highly energy-efficient future electronic systems. Unfortunately, carbon nanotubes (CNTs) are subject to substantial inherent imperfections that pose major obstacles to the design of robust and very large-scale CNFET digital systems:
A combination of design and processing techniques overcomes these challenges by creating robust CNFET digital systems that are immune to these inherent imperfections. This imperfection-immune paradigm enabled the first experimental demonstration of the carbon nanotube computer, and, more generally, arbitrary digital systems that can be built using CNFETs. Monolithically-integrated three-dimensional CNFET digital systems will also be discussed. This research was performed at Stanford University in collaboration with Prof. H.-S. Philip Wong and several graduate students. References: M. Shulaker, G. Hills, N. Patil, H. Wei, H. Chen, H.-S.P. Wong and S. Mitra, “Carbon Nanotube Computer,” Nature vol 501, pg 526 (2013). J. Zhang, L. Wei, N. Patil, A. Lin, H. Wei, H.-S.P. Wong and S. Mitra, “Carbon Nanotube Robust Digital VLSI,” Keynote Paper, IEEE TRANSACTIONS ON COMPUTER-AIDED DESIGN OF INTEGRATED CIRCUITS AND SYSTEMS, VOL. 31, PG 453 (2012).
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Lunch 12:45-1:30pm Lab visits 1:30-2:30pm
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Manu Jaiswal IIT Madras 2:30-4pm Graphene: Physics and Devices Speaker: Manu Jaiswal, IIT Madras Graphene, a two-dimensional honeycomb network of carbon atoms, is unique in many ways. The initial part of my talk will provide an overview of the most interesting physical properties of graphene. The quasi-particle charge carriers in the background of a 2D honeycomb behave as relativistic massless Fermions obeying the Dirac equation. This relativistic aspect of the carriers together with the pseudospin makes graphene a unique electronic material. Carriers can propagate through potential barriers of arbitrary height and width, without getting scattered. These unique electronic properties also lead to the anomalous quantum hall effect in graphene. Furthermore, the optical transmission of graphene is no less interesting – it is entirely determined by fundamental constants of nature. In the later part of my talk, the extent to which these properties can be translated to real applications will be discussed. Some of these applications, such as those related to sensors, will likely be realized soon and I will share my research work in this direction. There are many other, perhaps more intriguing phenomena, which can potentially lead to a paradigm shift in technological applications in the distant future. These phenomena include long-distance transport of carriers mediated through virtual states as well as the idea of graphene origami analogous to paper origami. These ideas are mainly at a nascent stage of development. I will share some of my recent works in both these directions. Reading:
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4:30-6:30pm
Public Lecture at Homi Bhabha Auditorium Stuart Parkin, IBM / Max Planck The spin on electronics High Tea
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6:30-8pm Erik Bakkers, TU Eindhoven Towards light emission from hexagonal silicon Light emission from silicon is a long standing goal in semiconductor industry. It would facilitate the integration of optical functionalities of which optical data transfer is the most important. Si in the cubic crystal has a direct band gap and efforts so far have not been successful to obtain light emission from Si. We now focus on silicon and germanium with the hexagonal band structure. It is expected from band structure calculations that hexagonal SiGe compounds will have a direct band gap. During this talk, fabrication strategies of hexagonal materials will be discussed. It will be shown that nanowires are a promising platform to obtain precise control of the crystal structure and composition.
Reading:
Dinner 8pm-9pm
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