Nanoscale Memristive Devices for Memory and Logic Applications.

As the building block of semiconductor electronics, field effect transistor (FET), approaches the sub 100 nm regime, a number of fundamental and practical issues start to emerge such as short channel effects that prevent the FET from operating properly and sub-threshold slope non-scaling that leads to increased power dissipation. In terms of nonvolatile memory, it is generally believed that transistor based Flash memory will approach the end of scaling within about a decade. As a result, novel, non-FET based devices and architectures will likely be needed to satisfy the growing demands for high performance memory and logic electronics applications. In this thesis, we present studies on nanoscale resistance switching devices (memristive devices). The device shows excellent resistance switching properties such as fast switching time ( 10^6), good data retention (> 6 years) and programming endurance (> 10^5). The studies suggest that the nonvolatile resistance switching in a nanoscale a-Si resistive switch is caused by the formation of a single conductive filament within 10 nm range near the bottom electrode. New functionalities, such as multi-bit switching with partially formed filaments, can be obtained by controlling the resistance switching process through current programming. As digital memory devices, the devices are ideally suited in the crossbar architecture which offers ultra-high density and intrinsic defect tolerance capability. As an example, a high-density (2 Gbits/cm^2) 1kb crossbar memory was demonstrated with excellent uniformity, high yield (> 92%) and ON/OFF ratio (> 10^3), proving its promising aspects for memory and reconfigurable logic applications. Furthermore, we demonstrated that properly designed devices can exhibit controlled analog switching behavior and function as flux controlled memristor devices. The analog memristors can be used in biology-inspired neuromorphic circuits in which signal processing efficiency orders of magnitude higher than conventional digital computer systems can be reached. As a prototype illustration, we showed Spike Timing Dependent Plasticity (STDP), one of the key learning rules in biological system, can be realized by CMOS neurons and nanoscale memristor synapses.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75835/1/josung_1.pd

실리콘 기반의 전하 트랩 메모리를 이용한 시냅스의 가소성 및 학습 기능 구현

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 8. 이종호.The development of an energy efficient and highly integrated electronic synapse is an important step in the effort to mimic the adaptive learning and memory in a biological neural network. Recently, several types of two-terminal memristors have been proposed to emulate biologically inspired synaptic functions using various components such as atomic switches, phase-change memory (PCM), and resistive switching devices. However, these two terminal devices require one select device per cell in a cell array to imitate a synapse-neuron network. Moreover, they need to be improved in terms of reliability, repeatability and processing complexity. In this thesis, we propose a new silicon-based charge trap memory device with an Al2O3/HfO2/Si3N4 (A/H/N) gate stack to realize the imitation of memory features in a biological synapse. In a fabricated capacitor having the proposed gate stack, short-term plasticity (STP) and long-term potentiation (LTP) properties with their transition are demonstrated, which are similar to the behavior of biological synapses. A single charge trapping layer (Si3N4) on silicon interface induces fast charge loss by trap-assisted tunneling (TAT) or direct tunneling. In addition, there is no remarkable pulse interval dependence when repeated input pulses are applied, in which the pulse amplitude and width are same. However, more frequent input pulses leads to larger current changes with longer retention property when HfO2 layer is inserted on Si3N4 layer as a second charge trapping layer. It is originated from the deep trap level (ET) in HfO2 layer leading to a transition into long-term memory. Lastly, we proposed a pair of pre- and post-synaptic spike scheme for the synaptic device and STDP property was demonstrated from experimental data. This suggested architecture has remarkable advantages, including high uniformity over a large area, excellent reliability, the use of CMOS-compatible materials, and easy integration with CMOS circuits.Chapter 1. Introduction 1 1.1 Motivation 1 1.2 Major factors influencing retention properties 2 1.3 Si3N4 and HfO2 for charge trap layers 5 1.4 Design of gate stack for synaptic device 7 1.5 Thesis organization 9 Chapter 2. Al2O3/HfO2/Si3N4 (A/H/N) gate stack 11 2.1 Introduction 11 2.2 Fabrication process for a capacitor 12 2.3 Measurement setup 14 2.4 C-V characteristics 15 2.5 Transient properties with C-t measurements 20 Chapter 3. Analysis of charge trapping and retention mechanism 30 3.1 Introduction 30 3.2 Measurement and discussion 31 Chapter 4. Synaptic characteristics in a FET device 41 4.1 Fabrication process of a FET device 41 4.2 Characteristics of SiO2/Si3N4 (O/N) stack 44 4.3 Scaling of Al2O3/HfO2/Si3N4 (A/H/N) stack 54 4.4 Spike-timing-dependent plasticity (STDP) 65 Chapter 5. Conclusions 70 Appendix. Spatial trap distribution near silicon interface 71 3.1 Introduction 71 3.2 Measurement results and discussion. 75 Bibliography 80 List of Publication 92 Abstract in Korean 94Docto

Synaptic weight modification and storage in hardware neural networks

In 2011 the International Technology Roadmap for Semiconductors, ITRS 2011, outlined how the semiconductor industry should proceed to pursue Moore’s Law past the 18nm generation. It envisioned a concept of ‘More than Moore’, in which existing semiconductor technologies can be exploited to enable the fabrication of diverse systems and in particular systems which integrate non-digital and biologically based functionality. A rapid expansion and growing interest in the fields of microbiology, electrophysiology, and computational neuroscience occurred. This activity has provided significant understanding and insight into the function and structure of the human brain leading to the creation of systems which mimic the operation of the biological nervous system. As the systems expand a need for small area, low power devices which replicate the important biological features of neural networks has been established to implement large scale networks. In this thesis work is presented which focuses on the modification and storage of synaptic weights in hardware neural networks. Test devices were incorporated on 3 chip runs; each chip was fabricated in a 0.35μm process from Austria MicroSystems (AMS) and used for parameter extraction, in accordance with the theoretical analysis presented. A compact circuit is presented which can implement STDP, and has advantages over current implementations in that the critical timing window for synaptic modification is implemented within the circuit. The duration of the critical timing window is set by the subthreshold current controlled by the voltage, Vleak, applied to transistor Mleak in the circuit. A physical model to predict the time window for plasticity to occur is formulated and the effects of process variations on the window is analysed. The STDP circuit is implemented using two dedicated circuit blocks, one for potentiation and one for depression where each block consists of 4 transistors and a polysilicon capacitor, and an area of 980µm2. SpectreS simulations of the back-annotated layout of the circuit and experimental results indicate that STDP with biologically plausible critical timing windows over the range 10µs to 100ms can be implemented. Theoretical analysis using parameters extracted from MOS test devices is used to describe the operation of each device and circuit presented. Simulation results and results obtained from fabricated devices confirm the validity of these designs and approaches. Both the WP and WD circuits have a power consumption of approximately 2.4mW, during a weight update. If no weight update occurs the resting currents within the device are in the nA range, thus each circuit has a power consumption of approximately 1µW. A floating gate, FG, device fabricated using a standard CMOS process is presented. This device is to be integrated with both the WP and WD STDP circuits. The FG device is designed to store negative charge on a FG to represent the synaptic weight of the associated synapse. Charge is added or removed from the FG via Fowler-Nordheim tunnelling. This thesis outlines the design criteria and theoretical operation of this device. A model of the charge storage characteristics is presented and verified using HFCV and PCV experimental results. Limited precision weights, LPW, and its potential use in hardware neural networks is also considered. LPW offers a potential solution in the quest to design a compact FG device for use with CTS. The algorithms presented in this thesis show that LPW allows for a reduction in the synaptic weight storage device while permitting the network to function as intended

Synthesis and analysis of nonlinear, analog, ultra low power, Bernoulli cell based CytoMimetic circuits for biocomputation

A novel class of analog BioElectronics is introduced for the systematic implementation of ultra-low power microelectronic circuits, able to compute nonlinear biological dynamics. This class of circuits is termed ``CytoMimetic Circuits'', in an attempt to highlight their actual function, which is mimicking biological responses, as observed experimentally. Inspired by the ingenious Bernoulli Cell Formalism (BCF), which was originally formulated for the modular synthesis and analysis of linear, time-invariant, high-dynamic range, logarithmic filters, a new, modified mathematical framework has been conceived, termed Nonlinear Bernoulli Cell Formalism (NBCF), which forms the core mathematical framework, characterising the operation of CytoMimetic circuits. The proposed nonlinear, transistor-level mathematical formulation exploits the striking similarities existing between the NBCF and coupled ordinary differential equations, typically appearing in models of naturally encountered biochemical systems. The resulting continuous-time, continuous-value, low-power CytoMimetic electronic circuits succeed in simulating with good accuracy cellular and molecular dynamics and found to be in very good agreement with their biological counterparts. They usually occupy an area of a fraction of a square millimetre, while consuming between hundreds of nanowatts and few tenths of microwatts of power. The systematic nature of the NBCF led to the transformation of a wide variety of biochemical reactions into nonlinear Log-domain circuits, which span a large area of different biological model types. Moreover, a detailed analysis of the robustness and performance of the proposed circuit class is also included in this thesis. The robustness examination has been conducted via post-layout simulations of an indicative CytoMimetic circuit and also by providing fabrication-related variability simulations, obtained by means of analog Monte Carlo statistical analysis for each one of the proposed circuit topologies. Furthermore, a detailed mathematical analysis that is carefully addressing the effect of process-parameters and MOSFET geometric properties upon subthreshold translinear circuits has been conducted for the fundamental translinear blocks, CytoMimetic topologies are comprised of. Finally, an interesting sub-category of Neuromorphic circuits, the ``Log-Domain Silicon Synapses'' is presented and representative circuits are thoroughly analysed by a novel, generalised BC operator framework. This leads to the conclusion that the BC operator consists the heart of such Log-domain circuits, therefore, allows the establishment of a general class of BC-based silicon synaptic circuits, which includes most of the synaptic circuits, implemented so far in Log-domain.Open Acces

The 1992 4th NASA SERC Symposium on VLSI Design

Papers from the fourth annual NASA Symposium on VLSI Design, co-sponsored by the IEEE, are presented. Each year this symposium is organized by the NASA Space Engineering Research Center (SERC) at the University of Idaho and is held in conjunction with a quarterly meeting of the NASA Data System Technology Working Group (DSTWG). One task of the DSTWG is to develop new electronic technologies that will meet next generation electronic data system needs. The symposium provides insights into developments in VLSI and digital systems which can be used to increase data systems performance. The NASA SERC is proud to offer, at its fourth symposium on VLSI design, presentations by an outstanding set of individuals from national laboratories, the electronics industry, and universities. These speakers share insights into next generation advances that will serve as a basis for future VLSI design

Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14

Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Microbiology for Allied Health Students

This open textbook is a remix of Openstax Microbiology, CC-BY 4.0, and created through an Affordable Learning Georgia Round Six Textbook Transformation Grant. The textbook has the following supplemental materials within this repository: This is a collection of instructional materials for the following open textbook and lab manual: Microbiology for Allied Health Students Lab Manual Microbiology for Allied Health Students Instructional Materials Authors\u27 Description: Microbiology for Allied Health Students is designed to cover the scope and sequence requirements for the single semester Microbiology course for non-majors and allied health students. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of Microbiology for Allied Health Students make the material interesting and accessible to students while maintaining the career-application focus and scientific rigor inherent in the subject matter. The scope and sequence of Microbiology for Allied Health Students has been developed and vetted with input from numerous instructors at institutions across the U.S. It is designed to meet the needs of most microbiology courses allied health students. With these objectives in mind, the content of this textbook has been arranged in a logical progression from fundamental to more advanced concepts. The opening chapters present an overview of the discipline, with individual chapters focusing on cellular biology as well as each of the different types of microorganisms and the various means by which we can control and combat microbial growth. The focus turns to microbial pathogenicity, emphasizing how interactions between microbes and the human immune system contribute to human health and disease. The last several chapters of the text provide a survey of medical microbiology, presenting the characteristics of microbial diseases organized by body system. Accessible files with optical character recognition (OCR) and auto-tagging provided by the Center for Inclusive Design and Innovation.https://oer.galileo.usg.edu/biology-textbooks/1015/thumbnail.jp

Spacelab Science Results Study

Beginning with OSTA-1 in November 1981 and ending with Neurolab in March 1998, a total of 36 Shuttle missions carried various Spacelab components such as the Spacelab module, pallet, instrument pointing system, or mission peculiar experiment support structure. The experiments carried out during these flights included astrophysics, solar physics, plasma physics, atmospheric science, Earth observations, and a wide range of microgravity experiments in life sciences, biotechnology, materials science, and fluid physics which includes combustion and critical point phenomena. In all, some 764 experiments were conducted by investigators from the U.S., Europe, and Japan. The purpose of this Spacelab Science Results Study is to document the contributions made in each of the major research areas by giving a brief synopsis of the more significant experiments and an extensive list of the publications that were produced. We have also endeavored to show how these results impacted the existing body of knowledge, where they have spawned new fields, and if appropriate, where the knowledge they produced has been applied