DESIGN, MODELING, OPTIMIZATION, AND BENCHMARKING OF INTERCONNECTS AND SCALING TECHNOLOGIES AND THEIR CIRCUIT AND SYSTEM LEVEL IMPACT

This research focuses on the future of integrated circuit (IC) scaling technologies at the device and back end of line (BEOL) level. This work includes high level modeling of different technologies and quantifying potential performance gains on a circuit and system level. From the device side, this research looks at the scaling challenges and the future scaling drivers for conventional charge-based devices implemented at the 7nm technology node and beyond. It examines the system-level performance of stacking device logic in addition to tunneling field effect transistors (TFET) and their potential as beyond-CMOS devices. Finally, this research models and benchmarks BEOL scaling challenges and evaluates proposed technological advancements such as metal barrier scaling for copper interconnects and replacing local interconnects with ruthenium. Potential impact on performance, power, and area of these interconnect technologies is quantified for fully placed and routed circuits.Ph.D

Network-on-Chip Synchronization

Technology scaling has enabled the number of cores within a System on Chip (SoC) to increase significantly. Globally Asynchronous Locally Synchronous (GALS) systems using Dynamic Voltage and Frequency Scaling (DVFS) operate each of these cores on distinct and dynamic clock domains. The main communication method between these cores is increasingly more likely to be a Network-on-Chip (NoC). Typically, the interfaces between these clock domains experience multi-cycle synchronization latencies due to their use of “brute-force” synchronizers. This dissertation aims to improve the performance of NoCs and thereby SoCs as a whole by reducing this synchronization latency. First, a survey of NoC improvement techniques is presented. One such improvement technique: a multi-layer NoC, has been successfully simulated. Given how one of the most commonly used techniques is DVFS, a thorough analysis and simulation of brute-force synchronizer circuits in both current and future process technologies is presented. Unfortunately, a multi-cycle latency is unavoidable when using brute-force synchronizers, so predictive synchronizers which require only a single cycle of latency have been proposed. To demonstrate the impact of these predictive synchronizer circuits at a high level, multi-core system simulations incorporating these circuits have been completed. Multiple forms of GALS NoC configurations have been simulated, including multi-synchronous, NoC-synchronous, and single-synchronizer. Speedup on the SPLASH benchmark suite was measured to directly quantify the performance benefit of predictive synchronizers in a full system. Additionally, Mean Time Between Failures (MTBF) has been calculated for each NoC synchronizer configuration to determine the reliability benefit possible when using predictive synchronizers

A hierarchical optimization engine for nanoelectronic systems using emerging device and interconnect technologies

A fast and efficient hierarchical optimization engine was developed to benchmark and optimize various emerging device and interconnect technologies and system-level innovations at the early design stage. As the semiconductor industry approaches sub-20nm technology nodes, both devices and interconnects are facing severe physical challenges. Many novel device and interconnect concepts and system integration techniques are proposed in the past decade to reinforce or even replace the conventional Si CMOS technology and Cu interconnects. To efficiently benchmark and optimize these emerging technologies, a validated system-level design methodology is developed based on the compact models from all hierarchies, starting from the bottom material-level, to the device- and interconnect-level, and to the top system-level models. Multiple design parameters across all hierarchies are co-optimized simultaneously to maximize the overall chip throughput instead of just the intrinsic delay or energy dissipation of the device or interconnect itself. This optimization is performed under various constraints such as the power dissipation, maximum temperature, die size area, power delivery noise, and yield. For the device benchmarking, novel graphen PN junction devices and InAs nanowire FETs are investigated for both high-performance and low-power applications. For the interconnect benchmarking, a novel local interconnect structure and hybrid Al-Cu interconnect architecture are proposed, and emerging multi-layer graphene interconnects are also investigated, and compared with the conventional Cu interconnects. For the system-level analyses, the benefits of the systems implemented with 3D integration and heterogeneous integration are analyzed. In addition, the impact of the power delivery noise and process variation for both devices and interconnects are quantified on the overall chip throughput.Ph.D

Design and Characterization of Standard Cell Library using FinFETs

The processors and digital circuits designed today contain billions of transistors on a small piece of silicon. As devices are becoming smaller, slimmer, faster, and more efficient, the transistors also have to keep up with the demands and needs of the daily user. Unfortunately, the CMOS technology has reached its limit and cannot be used to scale down due to the transistor\u27s breakdown caused by short channel effects. An alternative solution to this is the FinFET transistor technology, where the gate of the transistor is a three dimensional fin that surrounds the transistor and prevents the breakdown caused by scaling and short channel effects. FinFET devices are reported to have excellent control over short channel effects, high On/Off Ratio, extremely low gate leakage current and relative immunization over gate edge line roughness. Sub 20 nm node size is perceived to be the limit of scaling the CMOS transistors, but FinFETs can be scaled down further because of its unique design. Due to these advantages, the VLSI industry has now shifted to FinFET in implementation of their designs. However, these transistors have not been completely opened to academia. Analyzing and observing the effects of these devices can be pivotal in gaining an in-depth understanding of them. This thesis explores the implementation of FinFETs using a standard cell library designed using these transistors. The FinFET package file used to design these cells is a 15nm FinFET technology file developed by NCSU in collaboration with Cadence and Mentor Graphics. Post design, the cells were characterized, the results were analyzed and compared with cells designed using CMOS transistors at different node sizes to understand and extrapolate conclusions on FinFET devices

Near-Threshold Computing: Past, Present, and Future.

Transistor threshold voltages have stagnated in recent years, deviating from constant-voltage scaling theory and directly limiting supply voltage scaling. To overcome the resulting energy and power dissipation barriers, energy efficiency can be improved through aggressive voltage scaling, and there has been increased interest in operating at near-threshold computing (NTC) supply voltages. In this region sizable energy gains are achieved with moderate performance loss, some of which can be regained through parallelism. This thesis first provides a methodical definition of how near to threshold is "near threshold" and continues with an in-depth examination of NTC across past, present, and future CMOS technologies. By systematically defining near-threshold, the trends and tradeoffs are analyzed, lending insight in how best to design and optimize near-threshold systems. NTC works best for technologies that feature good circuit delay scalability, therefore technologies without strong short-channel effects. Early planar technologies (prior to 90nm or so) featured good circuit scalability (8x energy gains), but lacked area in which to add cores for parallelization. Recent planar nodes (32nm – 20nm) feature more area for cores but suffer from poor delay scalability, and so are not well-suited for NTC (4x energy gains). The switch to FinFET CMOS technology allows for a return to strong voltage scalability (8x gain), reversing trends seen in planar technologies, while dark silicon has created an opportunity to add cores for parallelization. Improved FinFET voltage scalability even allows for latency reduction of a single task, as long as the task is sufficiently parallelizable (< 10% serial code). Finally, we will look at a technique for fast voltage boosting, called Shortstop, in which a core's operating voltage is raised in 10s of cycles. Shortstop can be used to quickly respond to single-threaded performance demands of a near-threshold system by leveraging the innate parasitic inductance of a dedicated dirty supply rail, further improving energy efficiency. The technique is demonstrated in a wirebond implementation and is able to boost a core up to 1.8x faster than a header-based approach, while reducing supply droop by 2-7x. An improved flip-chip architecture is also proposed.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113600/1/npfet_1.pd

Design for Reliability and Low Power in Emerging Technologies

Die fortlaufende Verkleinerung von Transistor-Strukturgrößen ist einer der wichtigsten Antreiber für das Wachstum in der Halbleitertechnologiebranche. Seit Jahrzehnten erhöhen sich sowohl Integrationsdichte als auch Komplexität von Schaltkreisen und zeigen damit einen fortlaufenden Trend, der sich über alle modernen Fertigungsgrößen erstreckt. Bislang ging das Verkleinern von Transistoren mit einer Verringerung der Versorgungsspannung einher, was zu einer Reduktion der Leistungsaufnahme führte und damit eine gleichbleibenden Leistungsdichte sicherstellte. Doch mit dem Beginn von Strukturgrößen im Nanometerbreich verlangsamte sich die fortlaufende Skalierung. Viele Schwierigkeiten, sowie das Erreichen von physikalischen Grenzen in der Fertigung und Nicht-Idealitäten beim Skalieren der Versorgungsspannung, führten zu einer Zunahme der Leistungsdichte und, damit einhergehend, zu erschwerten Problemen bei der Sicherstellung der Zuverlässigkeit. Dazu zählen, unter anderem, Alterungseffekte in Transistoren sowie übermäßige Hitzeentwicklung, nicht zuletzt durch stärkeres Auftreten von Selbsterhitzungseffekten innerhalb der Transistoren. Damit solche Probleme die Zuverlässigkeit eines Schaltkreises nicht gefährden, werden die internen Signallaufzeiten üblicherweise sehr pessimistisch kalkuliert. Durch den so entstandenen zeitlichen Sicherheitsabstand wird die korrekte Funktionalität des Schaltkreises sichergestellt, allerdings auf Kosten der Performance. Alternativ kann die Zuverlässigkeit des Schaltkreises auch durch andere Techniken erhöht werden, wie zum Beispiel durch Null-Temperatur-Koeffizienten oder Approximate Computing. Wenngleich diese Techniken einen Großteil des üblichen zeitlichen Sicherheitsabstandes einsparen können, bergen sie dennoch weitere Konsequenzen und Kompromisse. Bleibende Herausforderungen bei der Skalierung von CMOS Technologien führen außerdem zu einem verstärkten Fokus auf vielversprechende Zukunftstechnologien. Ein Beispiel dafür ist der Negative Capacitance Field-Effect Transistor (NCFET), der eine beachtenswerte Leistungssteigerung gegenüber herkömmlichen FinFET Transistoren aufweist und diese in Zukunft ersetzen könnte. Des Weiteren setzen Entwickler von Schaltkreisen vermehrt auf komplexe, parallele Strukturen statt auf höhere Taktfrequenzen. Diese komplexen Modelle benötigen moderne Power-Management Techniken in allen Aspekten des Designs. Mit dem Auftreten von neuartigen Transistortechnologien (wie zum Beispiel NCFET) müssen diese Power-Management Techniken neu bewertet werden, da sich Abhängigkeiten und Verhältnismäßigkeiten ändern. Diese Arbeit präsentiert neue Herangehensweisen, sowohl zur Analyse als auch zur Modellierung der Zuverlässigkeit von Schaltkreisen, um zuvor genannte Herausforderungen auf mehreren Designebenen anzugehen. Diese Herangehensweisen unterteilen sich in konventionelle Techniken ((a), (b), (c) und (d)) und unkonventionelle Techniken ((e) und (f)), wie folgt: $\textbf{(a)}$ Analyse von Leistungszunahmen in Zusammenhang mit der Maximierung von Leistungseffizienz beim Betrieb nahe der Transistor Schwellspannung, insbesondere am optimalen Leistungspunkt. Das genaue Ermitteln eines solchen optimalen Leistungspunkts ist eine besondere Herausforderung bei Multicore Designs, da dieser sich mit den jeweiligen Optimierungszielsetzungen und der Arbeitsbelastung verschiebt. $\textbf{(b)}$ Aufzeigen versteckter Interdependenzen zwischen Alterungseffekten bei Transistoren und Schwankungen in der Versorgungsspannung durch „IR-drops“. Eine neuartige Technik wird vorgestellt, die sowohl Über- als auch Unterschätzungen bei der Ermittlung des zeitlichen Sicherheitsabstands vermeidet und folglich den kleinsten, dennoch ausreichenden Sicherheitsabstand ermittelt. $\textbf{(c)}$ Eindämmung von Alterungseffekten bei Transistoren durch „Graceful Approximation“, eine Technik zur Erhöhung der Taktfrequenz bei Bedarf. Der durch Alterungseffekte bedingte zeitlich Sicherheitsabstand wird durch Approximate Computing Techniken ersetzt. Des Weiteren wird Quantisierung verwendet um ausreichend Genauigkeit bei den Berechnungen zu gewährleisten. $\textbf{(d)}$ Eindämmung von temperaturabhängigen Verschlechterungen der Signallaufzeit durch den Betrieb nahe des Null-Temperatur Koeffizienten (N-ZTC). Der Betrieb bei N-ZTC minimiert temperaturbedingte Abweichungen der Performance und der Leistungsaufnahme. Qualitative und quantitative Vergleiche gegenüber dem traditionellen zeitlichen Sicherheitsabstand werden präsentiert. $\textbf{(e)}$ Modellierung von Power-Management Techniken für NCFET-basierte Prozessoren. Die NCFET Technologie hat einzigartige Eigenschaften, durch die herkömmliche Verfahren zur Spannungs- und Frequenzskalierungen zur Laufzeit (DVS/DVFS) suboptimale Ergebnisse erzielen. Dies erfordert NCFET-spezifische Power-Management Techniken, die in dieser Arbeit vorgestellt werden. $\textbf{(f)}$ Vorstellung eines neuartigen heterogenen Multicore Designs in NCFET Technologie. Das Design beinhaltet identische Kerne; Heterogenität entsteht durch die Anwendung der individuellen, optimalen Konfiguration der Kerne. Amdahls Gesetz wird erweitert, um neue system- und anwendungsspezifische Parameter abzudecken und die Vorzüge des neuen Designs aufzuzeigen. Die Auswertungen der vorgestellten Techniken werden mithilfe von Implementierungen und Simulationen auf Schaltkreisebene (gate-level) durchgeführt. Des Weiteren werden Simulatoren auf Systemebene (system-level) verwendet, um Multicore Designs zu implementieren und zu simulieren. Zur Validierung und Bewertung der Effektivität gegenüber dem Stand der Technik werden analytische, gate-level und system-level Simulationen herangezogen, die sowohl synthetische als auch reale Anwendungen betrachten

A COMPARATIVE STUDY OF RELIABILITY FOR FINFET

The continuous downscaling of CMOS technologies over the last few decades resulted in higher Integrated Circuit (IC) density and performance. The emergence of FinFET technology has brought with it the same reliability issues as standard CMOS with the addition of a new prominent degradation mechanism. The same mechanisms still exist as for previous CMOS devices, including Bias Temperature Instability (BTI), Hot Carrier Degradation (HCD), Electro-migration (EM), and Body Effects. A new and equally important reliability issue for FinFET is the Self -heating, which is a crucial complication since thermal time-constant is generally much longer than the transistor switching times. FinFET technology is the newest technological paradigm that has emerged in the past decade, as downscaling reached beyond 20 nm, which happens also to be the estimated mean free path of electrons at room temperature in silicon. As such, the reliability physics of FinFET was modified in order to fit the newly developed transistor technology. This paper highlights the roles and impacts of these various effects and aging mechanisms on FinFET transistors compared to planar transistors on the basic approach of the physics of failure mechanisms to fit to a comprehensive aging model

Multiple-valued logic: technology and circuit implementation

Title from PDF of title page, viewed March 1, 2023Dissertation advisors: Masud H. Chowdhury and Yugyung LeeVitaIncludes bibliographical references (pages 91-107)Dissertation (Ph.D.)--Department of Computer Science and Electrical Engineering. University of Missouri--Kansas City, 2021Computing technologies are currently based on the binary logic/number system, which is dependent on the simple on and off switching mechanism of the prevailing transistors. With the exponential increase of data processing and storage needs, there is a strong push to move to a higher radix logic/number system that can eradicate or lessen many limitations of the binary system. Anticipated saturation of Moore's law and the necessity to increase information density and processing speed in the future micro and nanoelectronic circuits and systems provide a strong background and motivation for the beyond-binary logic system. During this project, different technologies for Multiple-Valued-Logic (MVL) devices and the associated prospects and constraints are discussed. The feasibility of the MVL system in real-world applications rests on resolving two major challenges: (i) development of an efficient mathematical approach to implement the MVL logic using available technologies and (ii) availability of effective synthesis techniques. The main part of this project can be divided into two categories: (i) proposing different novel and efficient design for various logic and arithmetic circuits such as inverter, NAND, NOR, adder, multiplexer etc. (ii) proposing different fast and efficient design for various sequential and memory circuits. For the operation of the device, two of the very promising emerging technologies are used: Graphene Nanoribbon Field Effect Transistor (GNRFET) and Carbon Nano Tube Field Effect Transistor (CNTFET). A comparative analysis of the proposed designs and several state-of-the-art designs are also given in all the cases in terms of delay, total power, and power-delay-product (PDP). The simulation and analysis are performed using the H-SPICE tool with a GNRFET model available on the Nanohub website and CNTFET model available from Standford University website.Introduction -- Fundamentals and scope of multiple valued logic -- Technological aspect of multiple valued logic circuit -- Ternary logic gates using Graphene Nano Ribbon Field Effect Transistor (GNRFET) -- Ternary arithmetic circuits using Graphene Nano Ribbon Field Effect Transistor (GNRFET) -- Ternary sequential circuits using Graphene Nano Ribbon Field Effect Transistor (GNRFET) -- Ternary memory circuits using Carbon Nano Tube Field Effect Transistor (CNTFET) -- Conclusions & future wor