On the relationship between carrier mobility and velocity in sub-50 mm MOSFETs via calibrated Monte Carlo simulation

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, June 2004."May 2004."Includes bibliographical references (leaves 38-39).Subsequent to accurate 2D inverse modeling in the regime sensitive to electrostatics of industrial sub-50 nm NMOSFETs, a 2D full-band Monte Carlo device simulator was calibrated in the regime sensitive to transport parameters. The relationship between electron mobility and high-electric-field velocity at the source-channel potential energy barrier was investigated. The results show a strong correlation, as was demonstrated previously experimentally. Moreover, further proof is provided that the velocity at which carriers are injected from the source region in modem NMOSFET's is only about half of the limiting thermal velocity.by Osama Munir Nayfeh.S.M

Flexible Supercapacitor Sheets Based on Hybrid Nanocomposite Materials

Nanomaterials with quasi-zero, one and two dimensionalities, including silicon nanoparticles, carbon nanotubes, titanium oxide particles and graphene flakes, have been incorporated into the conducting polymer polyaniline to form nanocomposite materials for making flexible supercapacitor sheets. Characterization of the capacitor sheets showed that the inclusion of the nanomaterials in polyaniline has significantly improved the energy and power capabilities of the capacitor. In particular, a specific capacitance of 477.1 F/g has been obtained. The important properties of carbon nanotubes of improving the charge storage and reducing the resistance of the nanocomposite material and hence to enhance the power capability of the capacitor sheets have been studied. Stacks of capacitor sheets have been used to power a LED lamp to demonstrate the potential of the nanocomposite-based capacitor sheet in illumination applications

Flexible Supercapacitor Sheets Based on Hybrid Nanocomposite Materials

Nanomaterials with quasi-zero, one and two dimensionalities, including silicon nanoparticles, carbon nanotubes, titanium oxide particles and graphene flakes, have been incorporated into the conducting polymer polyaniline to form nanocomposite materials for making flexible supercapacitor sheets. Characterization of the capacitor sheets showed that the inclusion of the nanomaterials in polyaniline has significantly improved the energy and power capabilities of the capacitor. In particular, a specific capacitance of 477.1 F/g has been obtained. The important properties of carbon nanotubes of improving the charge storage and reducing the resistance of the nanocomposite material and hence to enhance the power capability of the capacitor sheets have been studied. Stacks of capacitor sheets have been used to power a LED lamp to demonstrate the potential of the nanocomposite-based capacitor sheet in illumination applications

Nonvolatile memory devices with colloidal, 1.0 nm silicon nanoparticles : principles of operation, fabrication, measurements, and analysis

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (leaves 101-105).Silicon nanoparticles are candidate charge trapping and storage elements for future high density, low-voltage nonvolatile memory devices. Most previous works have studied nanoparticles of larger than 5 nm size and exhibited bulk-like trapping characteristics. Technologically viable and competitive future devices, however, will require nanoparticles of sub 3-nm dimensions; a zero-dimensional regime where significant changes to silicon electronic structure occur. In this thesis, the physical processes involved in charge based nonvolatile memory device operation with colloidal mono-disperse 1.0 nm silicon nanoparticles embedded in a metal-oxide-semiconductor (MOS) gate stack is studied for the first time. Spin-coating was used to uniformly deliver the nanoparticle colloid across 150 mm wafers with density control over a thin tunneling oxide. Material characterization via spectroscopic ellipsometry, atomic force microscopy and transmission electron microscopy showed that across wafer sub-monolayer coverage with low-levels of agglomeration was achieved with nanoparticles so positioned possibly due to solvent-mediated self-assembly effects, and that the intrinsic nanoparticle crystallinity was intact after complete device processing. MOS capacitors with Si nanoparticles embedded in their dielectric exhibit strong endurance and well-behaved impedance (capacitance-voltage) characteristics with persistent hysteresis and only 53 mV standard deviation across wafer. Measurements showed that successive dilution of the nanoparticle colloid correlated directly with a decreased measured hysteresis and similarly fabricated zero-nanoparticle control devices exhibited a negligible hysteresis. Systems with 1.0 nm nanoparticles exhibited pure hole storage.(cont.) Energy band analysis was used to understand the nature of charging, hole-type versus electron-type and pure hole-type charging was shown to occur due to the characteristics of ultra-small silicon nanoparticles: large energy gap, large charging energy, and consequently small electron affinity. The retention time behavior of the 1.0 nm nanoparticle device was shown to be reduced due to a reduced valence band-offset with SiO2, however the programming time is shown to be dramatically reduced over that of conventional bulk devices. Quantum mechanical tunneling calculations were used to explore and predict routes for increasing the retention behavior by modulating the tunneling distance and experimental devices based on these calculations were fabricated in the SiO2 system to study experimentally directly these dependencies.by Osama M. Nayfeh.Ph.D

A Silicon Nanoparticle-based Polymeric Nano-composite Material for Glucose Sensing

A novel non-enzyme glucose sensing material has been prepared by incorporating ultrasmall (1–3 nm) silicon nanoparticles in polyaniline, a conducting polymer, as a nano-composite material (NCM). When deposited on electrodes, the composite material with three-dimensional loading of the nanoparticles showed a significantly enhanced amperometric response to glucose, compared to the nanoparticles deposited on bare electrodes and electrodes immobilized with the enzyme, glucose oxidase. The linear range of the glucose response of NCM electrodes covered both the hypo- and hyper-glycaemic glucose levels. The sensitivity of the NCM electrodes was 2.5 μA cm−2 mM−1. The NCM electrodes’ selectivity for glucose against interfering agents was achieved by covering the composite material with a Nafion membrane. The glucose response of Nafion–NCM electrodes was characterized with single 1 μl drops of glucose-solution, showing a sensitivity of 2.2 μA cm−2 mM−1. The NCM electrode’s long-term in vitro glucose response appeared to be reasonably stable over a period of 40 days

A Hybrid Biofuel Cell Based on Electrooxidation of Glucose Using Ultra-Small Silicon Nanoparticles

The ultra-small silicon nanoparticle was shown to be an electrocatalyst for the electrooxidation of glucose. The oxidation appeared to be a first order reaction which involves the transfer of 1 electron. The oxidation potential showed a low onset of −0.4V vs. Ag/AgCl (−0.62V vs. RHE). The particle was used as the anode catalyst of a prototype hybrid biofuel cell, which operated on glucose and hydrogen peroxide. The output power of the hybrid cell showed a dependence on the enzymes used as the cathode catalyst. The power density was optimized to 3.7μW/cm2 when horseradish peroxidase was replaced by microperoxidase-11 (MP-11). Comparing the output power of the hybrid cell to that of a biofuel cell indicates enhanced cell performance due to the fast reaction kinetics of the particle. The long-term stability of the hybrid cell was characterized by monitoring the cell voltage for 5 days. It appeared to that the robustness of the silicon particle resulted in more cell stability compared to the long-term performance of a biofuel cell

A Hybrid Biofuel Cell Based on Electrooxidation of Glucose Using Ultra-Small Silicon Nanoparticles

The ultra-small silicon nanoparticle was shown to be an electrocatalyst for the electrooxidation of glucose. The oxidation appeared to be a first order reaction which involves the transfer of 1 electron. The oxidation potential showed a low onset of −0.4V vs. Ag/AgCl (−0.62V vs. RHE). The particle was used as the anode catalyst of a prototype hybrid biofuel cell, which operated on glucose and hydrogen peroxide. The output power of the hybrid cell showed a dependence on the enzymes used as the cathode catalyst. The power density was optimized to 3.7μW/cm2 when horseradish peroxidase was replaced by microperoxidase-11 (MP-11). Comparing the output power of the hybrid cell to that of a biofuel cell indicates enhanced cell performance due to the fast reaction kinetics of the particle. The long-term stability of the hybrid cell was characterized by monitoring the cell voltage for 5 days. It appeared to that the robustness of the silicon particle resulted in more cell stability compared to the long-term performance of a biofuel cell

Fluorescent Si Nanoparticle-Based Electrode for Sensing Biomedical Substances

We have been studying the miniaturization of silicon crystals and the transition from the solid state to the atomistic state. We demonstrated the existence of “sweet spots” in cluster size in the range 1–3nm that have enhanced chemical, structural, and photo stability. The particles are produced by an electrochemical etching process as dispersion in liquid, and they are reconstituted in films, patterns, alloys, or spread on chips to produce super chips. Unlike bulk, these Si nanoparticle configurations have a spectacular ability to glow in distinct RGB colors. In this paper we describe an electrode sensor built by decorating metal or heavily doped silicon electrode with nanoparticles. We demonstrated amperometric response of the electrode to glucose and compared the response to that of heavily doped silicon wafer decorated with GOx. The all silicon electrode shows improved sensitivity, selectivity and stability. Light induced modulation of the response allows phase sensitive detection. The device is suitable for miniaturization, which may enable in vivo use

Investigation of the electron transport and electrostatics of nanoscale strained Si/Si/Ge heterostructure MOSFETs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 125-138).This thesis presents work aimed at investigating the possible benefit of strained-Si/SiGe heterostructure MOSFETs designed for nanoscale (sub-50-nm) gate lengths with the aid of device fabrication and electrical measurements combined with computer simulation. MOSFET devices fabricated on bulk-Si material are scaled in order to achieve gains in performance and integration. However, as device dimensions continue to scale, physical constraints are being reached that may limit continued scaling and/or the gains in performance from scaling. In order to continue the benefits of scaling, a possible solution is to change to a strained-Si/SiGe material system where enhanced electron mobility of 1.7-2X has been demonstrated for long-channel n-type devices. The electron mobility enhancement observed for long channel length devices may not be the same for devices with nanoscale gate length. In particular, increased channel doping, which is required to control short-channel effects can result in degraded transport characteristics. In this work, the impact of high channel doping on mobility enhancements in strained-Si n-MOSFETs is investigated experimentally. Increased channel doping will increase Coulomb scattering interactions increasing its influence on the overall mobility. Electron transport models were calibrated using experimental data for both strained and un-strained Si devices for various channel doping concentrations. The transport models were then used to investigate, by computer simulation, the performance enhancement of nanoscale strained Si devices for equivalent off-current.by Hasan M. Nayfeh.Ph.D