Study of organic molecules and nano-particle/polymer composites for flash memory and switch applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 205-218).Organic materials exhibit fascinating optical and electronic properties which motivate their hybridization with traditional silicon-based electronics in order to achieve novel functionalities and address scaling challenges of these devices. The application of organic molecules and nano-particle/polymer composites for flash memory and switch applications is studied in this dissertation. Facilitating data storage on individual small molecules as the approach the limits in miniaturization for ultra-high density and low power consumption media may enable orders of magnitude increase in data storage capabilities. A floating gate consisting of a thin film of molecules would provide the advantage of a uniform set of identical nano-structured charge storage elements with high molecular area densities which can result in a several-fold higher density of charge-storage sites as compared to quantum dot (QD) memory and even SONOS devices. Additionally, the discrete charge storage in such nano-segmented floating gate designs limits the impact of any tunnel oxide defects to the charge stored in the proximity of the defect site. The charge retention properties of molecular films was investigated in this dissertation by injecting charges via a biased conductive atomic force microscopy (AFM) tip into molecules comprising the thin films. The Kelvin force microscopy (KFM) results revealed minimal changes in the spatial extent of the charge trapping over time after initial injection. Fabricated memory capacitors show a device durability over 105 program/erase cycles and hysteresis window of up to 12.8 V, corresponding to stored charge densities as high as 5.4x 1013 cm-2, suggesting the potential use of organic molecules in high storage capacity memory cells. Also, these results demonstrate that charge storage properties of the molecular trapping layer can be engineered by rearranging molecules and their a-orbital overlaps via addition of dopant molecules. Finally, the design, fabrication, testing and evaluation of a MEMS switch that employs viscoelastic organic polymers doped with nano-particles as the active material is presented in this dissertation. The conductivity of the nano-composite changes 10,000-fold as it is mechanically compressed. In this demonstration the compressive squeeze is applied with electric actuation. Since squeezing initiates the switching behavior, the device is referred to as a "squitch". The squitch is essentially a new type of FET that is compatible with large area processing with printing or photolithography, on rigid or flexible substrates and can exhibit large on-to-off conduction ratio.by Sarah Paydavosi.Ph.D

Organic molecular floating gate memories

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 42-45).Flash memory devices dominate the non-volatile memory market, with device structures that utilize charge storage in polysilicon floating gates imbedded in insulating silicon oxide films'. As demands for high storage density, high chip memory capacity, and decreasing process costs continue to mount, conventional flash memory has found it challenging to continue scaling and it may reach fundamental scaling limits because of the minimum tunnel oxide thickness and poor charge retention due to defects in the tunneling oxide, necessitating modification in the implementation of the flash memory technology . In this study nano-segmented floating gate memories consisting of a uniform set of identical organic dye molecules were fabricated and evaluated for potential use as programmable charge storage and charge retention elements in a future flash memory technology. Viability of molecular thin films to serve as an energetically-uniform set of ~1nm in size charge- retaining sites is tested on a series of molecular materials, the best performing of which are thermally evaporated thin films of 3,4,9,10- perylenetetracarboxylic bis-benzimidazole (PTCBI). The initial results show device durability over 105 program/erase cycles, with hysteresis window of up to 3.3V, corresponding to charge storage density as high as 5 x 1012 cm2. Data shows that charge retention is improved for molecular films with lower carrier mobility, which for the first time experimentally confirms in a coherent material set that inhibiting charge transport by nano-segmented floating-gate structures benefits the memory retention. These results show a first step towards a possible approach to miniaturization of non-volatile memory by using molecules as segmented charge storage elements in the floating gate flash memory technology.by Sarah Paydavosi.S.M

Modeling the impact of substrate depletion in FDSOI MOSFETs

In this work, we have modeled the impact of substrate depletion in fully-depleted silicon-on-insulator (FDSOI) transistor and have extensively verified the model for both NMOS and PMOS with geometrical and temperature scaling. The model has an accurate behavior for C–V and I–V characteristics and preserves the smooth behavior of the high order derivatives. Model validation is done at 50 nm technology node with state of the art FDSOI transistors provided by Low-power Electronics Association and Project (LEAP) and excellent agreement with the experimental data is achieved after parameter extraction.6 page(s

FinFET modeling for IC simulation and design : using the BSIM-CMG standard

This book is the first to explain FinFET modeling for IC simulation and the industry standard - BSIM-CMG - describing the rush in demand for advancing the technology from planar to 3D architecture, as now enabled by the approved industry standard. The book gives a strong foundation on the physics and operation of FinFET, details aspects of the BSIM-CMG model such as surface potential, charge and current calculations, and includes a dedicated chapter on parameter extraction procedures, providing a step-by-step approach for the efficient extraction of model parameters. With this book you will learn: • Why you should use FinFET • The physics and operation of FinFET • Details of the FinFET standard model (BSIM-CMG) • Parameter extraction in BSIM-CMG • FinFET circuit design and simulation • Authored by the lead inventor and developer of FinFET, and developers of the BSIM-CM standard model, providing an experts' insight into the specifications of the standard • The first book on the industry-standard FinFET model - BSIM-CMG.Front Cover; FinFET Modeling for IC Simulation and Design: Using the BSIM-CMG Standard; Copyright; Contents; Author Biographies; Preface; Chapter 1:FinFET-From device concept to standard compact model; 1.1 The root cause of short-channel effects in the twenty-first century MOSFETs; 1.2 The thin-body MOSFET concept; 1.3 The FinFET and a new scaling path for MOSFETs; 1.4 Ultra-thin-body FET; 1.5 FinFET compact model-the bridge between FinFET technology and IC design; 1.6 A brief history of the first standard compact model, BSIM; 1.7 Core and real-device models. 1.8 The industry standard FinFET compact modelReferences; Chapter 2: Compact models for analog and RF applications; 2.1 Introduction; 2.2 Important Compact Model Metrics; 2.3 Analog Metrics; 2.3.1 Quiescent Operating Point; 2.3.2 Geometric Scalability; 2.3.3 Variability Model; 2.3.4 Intrinsic Voltage Gain; 2.3.5 Speed: Unity Gain Frequency; 2.3.6 Noise; 2.3.7 Linearity and Symmetry; Harmonic distortion; Gain compression; Memory effects; Intermodulation distortion; 2.3.8 Symmetry; 2.4 RF Metrics; 2.4.1 Two-Port Parameters; 2.4.2 The Need for Speed. The maximum unity power gain frequency (fmax) Mason's unilateral gain U; 2.4.3 Non-Quasi-Static Model; 2.4.4 Noise; Minimum achievable noise figure (Fmin); Simple model for FET noise; Phase noise; Phase noise derivation: Lorentzian spectrum; Phase noise and flicker noise; 2.4.5 Linearity; Memory effects; Other distortion metrics; 2.5 Conclusion; References; Chapter 3:Core model for FinFETs; 3.1 Core Model for Double-Gate FinFETs; 3.2 Unified FinFET Compact Model; Chapter 3 Appendix: Explicit surface potential model; 3A.1 Continuous Starting Function. 3A.2 Quartic Modified Iteration: Implementation and EvaluationReferences; Chapter 4:Channel current and real device effects; 4.1 Introduction; 4.2 Threshold Voltage Roll-Off; 4.3 Subthreshold Slope Degradation; 4.4 Quantum Mechanical Vth Correction; 4.5 Vertical-Field Mobility Degradation; 4.6 Drain Saturation Voltage, Vdsat; 4.6.1 Extrinsic Case (RDSMOD=1 and 2); 4.6.2 Intrinsic Case (RDSMOD = 0); 4.7 Velocity Saturation Model; 4.8 Quantum Mechanical Effects; 4.8.1 Effective Width Model; 4.8.2 Effective Oxide Thickness/Effective Capacitance; 4.8.3 Charge Centroid Calculation for Accumulation. 4.9 Lateral Nonuniform Doping Model4.10 Body Effect Model for a Bulk FinFET (BULKMOD=1); 4.11 Output Resistance Model; 4.11.1 Channel-Length Modulation; 4.11.2 Drain-Induced Barrier Lowering; 4.12 Channel Current; References; Chapter 5:Leakage currents; 5.1 Weak-Inversion Current; 5.2 Gate-Induced Source and Drain Leakages; 5.2.1 GIDL/GISL Current Formulation in BSIM-CMG; 5.3 Gate Oxide Tunneling; 5.3.1 Gate Oxide Tunneling Formulation in BSIM-CMG; 5.3.2 Gate-to-Body Tunneling Current in Depletion/Inversion; 5.3.3 Gate-to-Body Tunneling Current in Accumulation.292 page(s