Limits on Fundamental Limits to Computation

An indispensable part of our lives, computing has also become essential to industries and governments. Steady improvements in computer hardware have been supported by periodic doubling of transistor densities in integrated circuits over the last fifty years. Such Moore scaling now requires increasingly heroic efforts, stimulating research in alternative hardware and stirring controversy. To help evaluate emerging technologies and enrich our understanding of integrated-circuit scaling, we review fundamental limits to computation: in manufacturing, energy, physical space, design and verification effort, and algorithms. To outline what is achievable in principle and in practice, we recall how some limits were circumvented, compare loose and tight limits. We also point out that engineering difficulties encountered by emerging technologies may indicate yet-unknown limits.Comment: 15 pages, 4 figures, 1 tabl

Circuit-level modelling and simulation of carbon nanotube devices

The growing academic interest in carbon nanotubes (CNTs) as a promising novel class of electronic materials has led to significant progress in the understanding of CNT physics including ballistic and non-ballistic electron transport characteristics. Together with the increasing amount of theoretical analysis and experimental studies into the properties of CNT transistors, the need for corresponding modelling techniques has also grown rapidly. This research is focused on the electron transport characteristics of CNT transistors, with the aim to develop efficient techniquesto model and simulate CNT devices for logic circuit analysis.The contributions of this research can be summarised as follows. Firstly, to accelerate the evaluation of the equations that model a CNT transistor, while maintaining high modelling accuracy, three efficient numerical techniques based on piece-wise linear, quadratic polynomial and cubic spline approximation have been developed. The numerical approximation simplifies the solution of the CNT transistor’s self-consistent voltage such that the calculation of the drain-source current is accelerated by at least two orders of magnitude. The numerical approach eliminates complicated calculations in the modelling process and facilitates the development of fast and efficient CNT transistor models for circuit simulation.Secondly, non-ballistic CNT transistors have been considered, and extended circuit-level models which can capture both ballistic and non-ballistic electron transport phenomena, including elastic scattering, phonon scattering, strain and tunnelling effects, have been developed. A salient feature of the developed models is their ability to incorporate both ballistic and non-ballistic transport mechanisms without a significant computational cost. The developed models have been extensively validated against reported transport theories of CNT transistors and experimental results.Thirdly, the proposed carbon nanotube transistor models have been implemented on several platforms. The underlying algorithms have been developed and tested in MATLAB, behaviourallevel models in VHDL-AMS, and improved circuit-level models have been implemented in two versions of the SPICE simulator. As the final contribution of this work, parameter variation analysis has been carried out in SPICE3 to study the performance of the proposed circuit-level CNT transistor models in logic circuit analysis. Typical circuits, including inverters and adders, have been analysed to determine the dependence of the circuit’s correct operation on CNT parameter variation

New Logic Synthesis As Nanotechnology Enabler (invited paper)

Nanoelectronics comprises a variety of devices whose electrical properties are more complex as compared to CMOS, thus enabling new computational paradigms. The potentially large space for innovation has to be explored in the search for technologies that can support large-scale and high- performance circuit design. Within this space, we analyze a set of emerging technologies characterized by a similar computational abstraction at the design level, i.e., a binary comparator or a majority voter. We demonstrate that new logic synthesis techniques, natively supporting this abstraction, are the technology enablers. We describe models and data-structures for logic design using emerging technologies and we show results of applying new synthesis algorithms and tools. We conclude that new logic synthesis methods are required to both evaluate emerging technologies and to achieve the best results in terms of area, power and performance

Designing Universal Logic Module FPGA Architectures for Use With Ambipolar Transistor Technology

Recent publications show a rise of ambipolar transistor technology research and associated implementations of multi-function logic cells in these technologies. Special properties of these technologies enable implementations of Universal Logic Modules (ULMs) using few transistors, which draws renewed interest to use such ULMs as basic logic blocks for FPGA architectures. Unlike N-input Lookup Tables (LUTs), most ULMs only implement a fixed subset of the possible Boolean functions. In this work, we first adapt the Verilog-to-Routing (VTR) 8.0 toolflow to target such reduced-function ULM primitives. We then modify VTR\u27s flagship 40nm architecture to use an ULM primitive instead of LUTs, modeling the double-gate carbon nanotube FET 8-function logic gate CNT-DR8F published by Liu et al. Using VTR\u27s extensive benchmark framework, we analyze effects caused by the limited set of function offered by these primitives. To counter some of the observed effects, we present various clustered architectures, where multiple ULM cells are combined in a logic block. We conclude with an analysis of various parameters which affect performance of the different implementations

VLSI Design

This book provides some recent advances in design nanometer VLSI chips. The selected topics try to present some open problems and challenges with important topics ranging from design tools, new post-silicon devices, GPU-based parallel computing, emerging 3D integration, and antenna design. The book consists of two parts, with chapters such as: VLSI design for multi-sensor smart systems on a chip, Three-dimensional integrated circuits design for thousand-core processors, Parallel symbolic analysis of large analog circuits on GPU platforms, Algorithms for CAD tools VLSI design, A multilevel memetic algorithm for large SAT-encoded problems, etc

Self-Checking Ripple-Carry Adder with Ambipolar Silicon Nanowire FET

For the rapid adoption of new and aggressive technologies such as ambipolar Silicon NanoWire (SiNW), addressing fault-tolerance is necessary. Traditionally, transient fault detection implies large hardware overhead or performance decrease compared to permanent fault detection. In this paper, we focus on on-line testing and its application to ambipolar SiNW. We demonstrate on self - checking ripple - carry adder how ambipolar design style can help reduce the hardware overhead. When compared with equivalent CMOS process, ambipolar SiNW design shows a reduction in area of at least 56% (28%) with a decreased delay of 62% (6%) for Static (Transmission Gate) design style

Vertically-Stacked Silicon Nanowire Transistors with Controllable Polarity: a Robustness Study

Vertically-stacked Silicon NanoWire FETs (SiN- WFETs) with gate-all-around control are the natural and most advanced extension of FinFETs. At advanced technology nodes, due to Schottky contacts at channel interfaces, devices show an ambipolar behavior, i.e., the device exhibits n- and p-type charac- teristics simultaneously. This property, when controlled by an independent Double-Gate (DG) structure, can be exploited for logic computation, as it provides intrinsic XOR operation. Elec- trostatic doping of the transistor suppresses the need for dopant implantation at the source and drain regions, which potentially leads to a larger process variations immunity of the devices. In this paper, we propose a novel method based on Technology Computer-Aided Design (TCAD) simulations, enabling the predic- tion of emerging devices variability. This method is used within our DG-SiNWFET framework and shows that devices, whose polarity is controlled electrostatically, present better immunity to variations for some of their parameters, such as the off-current with 16× less standard deviation

Advanced System on a Chip Design Based on Controllable-Polarity FETs (invited paper)

Field-Effect Transistors (FETs) with on-line controllable-polarity are promising candidates to support next generation System-on-Chip (SoC). Thanks to their enhanced functionality, controllable-polarity FETs enable a superior design of critical components in a SoC, such as processing units and memories, while also providing native solutions to control power consumption. In this paper, we present the efficient design of a SoC core with controllable-polarity FET. Processing units are speeded-up at the datapath level, as arithmetic operations require fewer physical resources than in standard CMOS. Power consumption is decreased via embedded power-gating techniques and tunable high-performance/low-power devices operation. Memory cells are made smaller by merging the access interface with the storage circuitry. We foresee the advantages deriving from these techniques, by evaluating their impact on the design of SoC for a contemporary telecommunication application. Using a 22-nm vertically-stacked silicon nanowire technology, a coarse-grain evaluation at the block level estimates a delay and power reduction of 20% and 19% respectively, at a cost of a moderate area overhead of 15%, with respect to a state-of-art FinFET technology

Top-Down Fabrication of Gate-All-Around Vertically-Stacked Silicon Nanowire FETs with Controllable Polarity

Asthe currentMOSFET scaling trend is facing strong limitations, technologies exploiting novel degrees of freedom at physical and architecture level are promising candidates to enable the continuation of Moore's predictions. In this paper, we report on the fabrication of novel ambipolar Silicon nanowire (SiNW) Schottky-barrier (SB) FET transistors featuring two independent gate-all-around electrodes and vertically stacked SiNW channels. A top-down approach was employed for the nanowire fabrication, using an e-beam lithography defined design pattern. In these transistors, one gate electrode enables the dynamic configuration of the device polarity (n- or p-type) by electrostatic doping of the channel in proximity of the source and drain SBs. The other gate electrode, acting on the center region of the channel switches ON or OFF the device. Measurement results on silicon show I-on/I-off > 10(6) and subthreshold slopes approaching the thermal limit, SS approximate to 64 mV/dec (70 mV/dec) for p(n)-type operation in the same physical device. Finally, we show that the XOR logic operation is embedded in the device characteristic, and we demonstrate for the first time a fully functional two-transistor XOR gate