Effect of high-k materials in the control dielectric stack of nanocrystal memories

In this paper we studied program/erase characteristics by FN tunneling in Si nanocrystal memories. Starting from a very good agreement between experimental data and simulations in the case of a memory cell with a thin tunnel oxide, Silicon dots as medium for charge storage, and a CVD silicon dioxide used as control dielectric, we present estimated values of the charge trapping when a high-k material is present in the control dielectric. We then show preliminary results of nanocrystal memories with control dielectric containing high-k materials. ©2004 IEEE.

Compact instrumentation for radiation tolerance test of flash memories in space environment

Aim of this work is the description of a test equipment, designed to be integrated on board of a microsatellite, able to investigate the radiation tolerance of non-volatile memory arrays in a real flight experiment. An FPGA-based design was adopted to preserve a high flexibility degree. Besides standard Program/Read/Erase functions, additional features such as failure data screening and latch-up protection have been implemented. The instrument development phase generated, as a by-product, a non-rad-hard version of the instrument that allowed performing in-situ experiments using 60Co and 10 MeV Boron irradiation facilities on Ground. Preliminary measurement results are reported to show the i…

Ionizing radiation effects on Non Volatile Read Only Memory cells

Threshold voltage (V-th) and drain-source current (I-DS) behaviour of nitride read only memories (NROM) were studied both in situ during irradiation or after irradiation with photons and ions. V-th loss fluctuations are well explained by the same Weibull statistics regardless of the irradiation species and total dose. Results of drain current measurements in-situ during irradiation with photons and ions reveal a step-like increase of I-DS with the total irradiation dose. A brief physical explanation is also provided.

Nanocrystal metal-oxide-semiconductor memories obtained by chemical vapor deposition of Si nanocrystals

We have realized nanocrystal memories by using silicon quantum dots embedded in silicon dioxide. The Si dots with the size of few nanometers have been obtained by chemical vapor deposition on very thin tunnel oxides and subsequently coated with a deposited SiO2 control dielectric. A range of temperatures in which we can adequately control a nucleation process, that gives rise to nanocrystal densities of ∼3×1011 cm−2 with good uniformity on the wafer, has been defined. The memory effects are observed in metal-oxide-semiconductor capacitors or field effect transistors by significant and reversible flat band or threshold voltage shifts between written and erased states that can be achieved by …

EDEME GENERALIZZATO, IPOTONIA E IPERECCITABILITA' ALLA NASCITA IN NEONATO A TERMINE CON GALATTOSIALIDOSI:APPROCCIO CLINICO E DIAGNOSTICO

Nanocrystal MOS with silicon-rich oxide

By electrical measurements we investigate the charge trapping and the charge transport in MOS capacitors in which the gate oxide has been replaced with a silicon rich oxide (SRO) film sandwiched between two thin SiO2 layers.

Nanocrystal memories for FLASH device applications

Nanocrystals memory cells, in which the conventional polysilicon floating gate is replaced by an array of silicon nanocrystals, have been fabricated and characterized. Single cells and cell arrays of 1 Mb and 10 k have been realized by using a conventional 0.15 μm FLASH technology. Si nanocrystals are deposited on top of tunnel oxide by chemical vapor deposition. Properties of the memory cell have been investigated both for NAND and NOR applications in terms of program/erase window and programming times. Suitable program/erase threshold voltage window can be achieved with fast voltage pulses by adequate choice of tunnel and control dielectric. The feasibility of dual bit storage is also pro…

Aracnodattilia contrattuale congenita (ACC) presentazione clinica in epoca neonatale.

L’obesità nella Sindrome di Down: analisi di 320 soggetti in età evolutiva

Memory effects in MOS capacitors with silicon rich oxide insulators

ABSTRACTTo form crystalline Si dots embedded in SiO2, we have deposited thin films of silicon rich oxide (SRO) by plasma-enhanced chemical vapor deposition of SiH4 and O2. Then the materials wereannealed in N2 ambient at temperatures between 950 and 1100 °C. Under such processing, the supersaturation of Si in the amorphous SRO film produces the formation of crystalline Si dots embedded in SiO2. The narrow dot size distributions, analyzed by transmission electron microscopy, are characterized by average grain radii and standard deviations down to about 1 nm. The memory function of such structures has been investigated in metal-oxidesemiconductor (MOS) capacitors with a SRO film sandwiched be…

Improvement of the P/E window in nanocrystal memories by the use of high-k materials in the control dielectric

Abstract In this paper nanocrystals memories program curves are shown and their saturation points (steady state condition) can be observed. We present a model that relates the voltage shift at the steady state ( Δ V T ss ) to the gate program voltage (VG). Starting from a good agreement between experimental data and simulations for nanocrystals memory cells with a conventional dielectric structure (SiO2), we present the estimated values of the Δ V T ss vs VG for different control stacks. Our investigation shows an improvement if a material with a high dielectric constant and a small conduction band-offset with respect to the SiO2, is placed between two SiO2 layers when the first of them is …

Memory effects in MOS capacitors with silicon quantum dots

To form crystalline Si dots embedded in SiO2, we have deposited thin films of silicon-rich oxide (SRO) by plasma-enhanced chemical vapor deposition of SiH4 and O2. Then the materials have been annealed in N2 ambient at temperatures between 950°C and 1100°C. Under such processing, the supersaturation of Si in the amorphous SRO film produces the formation of crystalline Si dots embedded in SiO2. The narrow dot size distributions, analyzed by transmission electron microscopy, are characterized by average grain radii and standard deviations down to about 1 nm. The memory functions of such structures has been investigated in MOS capacitors with a SRO film sandwiched between two thin SiO2 layers …

Electrical and structural characterization of metal-oxide-semiconductor capacitors with silicon rich oxide

Metal-oxide-semiconductor capacitors in which the gate oxide has been replaced with a silicon rich oxide (SRO) film sandwiched between two thin SiO2 layers are presented and investigated by transmission electron microscopy and electrical measurements. The grain size distribution and the amount of crystallized silicon remaining in SRO after annealing have been studied by transmission electron microscopy, whereas the charge trapping and the charge transport through the dots in the SRO layer have been extensively investigated by electrical measurements. Furthermore, a model, which explains the electrical behavior of such SRO capacitors, is presented and discussed. © 2001 American Institute of …

Nanostructured electrodes for hydrogen production in alkaline electrolyzer

Abstract Ever-widespread employment of renewable energy sources, such as wind and sun, request the simultaneous use of effective energy storage systems owing to the intermittent and unpredictable energy generation by these sources. The most reliable storage systems currently under investigation are batteries and electrochemical cells for hydrogen production from water splitting. Both systems store chemical energy which can be converted on demand. The low power density is the weakness of the batteries while the high production cost limits currently the wide use of hydrogen from electrochemical water splitting. In this work, attention was focused on the use of nanostructured Ni as a cathode f…

Thin-Film Photovoltaics 2014

The interest toward alternative energy sources to fossil fuels (still the most convenient in terms of efficiency and cost) is current. Initiatives that seek to convert wind, geothermal energy, hydropower, marine, solar thermal energy, and photovoltaics or derived from biomass energy into other forms continue to involve several research groups. For example, the transfer from solar energy into electricity, which in turn can be used for water splitting and for the subsequent production of hydrogen, seems a major challenge to provide a sustainable contribution to the “Earth system” together with the realization of devices having high conversion efficiencies, low environmental impact, and low pr…

Location of holes in silicon-rich oxide as memory states

The induced changes of the flatband voltage by the location of holes in a silicon-rich oxide (SRO) film sandwiched between two thin SiO 2 layers [used as gate dielectric in a metal-oxide-semiconductor (MOS) capacitor] can be used as the two states of a memory cell. The principle of operation is based on holes permanently trapped in the SRO layer and reversibly moved up and down, close to the metal and the semiconductor, in order to obtain the two logic states of the memory. The concept has been verified by suitable experiments on MOS structures. The device exhibits an excellent endurance behavior and, due to the low mobility of the holes at low field in the SRO layer, a much longer refresh …

Investigation of recovery mechanisms in dye sensitized solar cells

Abstract We study the spontaneous recovery phenomenon displayed by solar cells sensitized with a ruthenium complex-based dye N719, which manifests with the increase over the time (from several minutes up to some days) of the short circuit current density J sc and the open circuit voltage V oc , during cell illumination. Under dark conditions the current decreases over time after the application of forward bias voltages. We investigate the effects of temperature and electrolyte composition by means of current–voltage measurements and electrochemical impedance spectroscopy, both under dark and illumination conditions. The main result is that the recovery of the performances depends on the cha…

Displaced persons: i diritti degli uomini o le prerogative degli Stati?

Peculiar aspects of nanocrystal memory cells: Data and extrapolations

Nanocrystal memory cell are a promising candidate for the scaling of nonvolatile memories in which the conventional floating gate is replaced by an array of nanocrystals. The aim of this paper is to present the results of a thorough investigation of the possibilities and the limitations of such new memory cell. In particular, we focus on devices characterized by a very thin tunnel oxide layer and by silicon nanocrystals formed by chemical vapor deposition. The direct tunneling of the electrons through the tunnel oxide, their storage into the silicon nanocrystals, and furthermore, retention, endurance, and drain turn-on effects, well-known issues for nonvolatile memories, are all investigate…

Design and development of a fNIRS system prototype based on SiPM detectors

Functional Near Infrared Spectroscopy (fNIRS) uses near infrared sources and detectors to measure changes in absorption due to neurovascular dynamics in response to brain activation. The use of Silicon Photomultipliers (SiPMs) in a fNIRS system has been estimated potentially able to increase the spatial resolution. Dedicated SiPM sensors have been designed and fabricated by using an optimized process. Electrical and optical characterizations are presented. The design and implementation of a portable fNIRS embedded system, hosting up to 64 IR-LED sources and 128 SiPM sensors, has been carried out. The system has been based on a scalable architecture whose elementary leaf is a flexible board …

Electrical characterization of deoxyribonucleic acid hybridization in metal-oxide-semiconductor-like structures

In this work, metal-oxide-semiconductor (MOS)-like sensors in which deoxyribonucleic acid (DNA) strands are covalently immobilized either on Si oxide or on a gold surface were electrically characterized. Si oxide fabrication process allowed us to have a surface insensitive to the solution pH. A significant shift in the flat band voltage was measured after single strand DNA immobilization (+0.47 +/- 0.04 V) and after the complementary strand binding (+0.07 +/- 0.02 V). The results show that DNA sensing can be performed using a MOS structure which can be easily integrated in a more complex design, thus avoiding the problems related to the integration of micro-electrochemical cells.

Reduction of thermal damage in ultrathin gate oxides after intrinsic dielectric breakdown

We have compared the thermal damage in ultrathin gate SiO2 layers of 5.6 and 3 nm thickness after intrinsic dielectric breakdown due to constant voltage Fowler-Nordheim stress. The power dissipated through the metal-oxide-semiconductor capacitor during the breakdown transient, measured with high time resolution, strongly decreases with oxide thickness. This is reflected in a noticeable reduction of the thermal damage found in the structure after breakdown. The effect can be explained as the consequence of the lower amount of defects present in the oxide at the breakdown instant and of the occurrence of a softer breakdown in the initial spot. The present data allow us to estimate the power t…

Electrical characterization of highefficiency bifacial silicon solar cells

This work presents a preliminary study on the electrical characterization of high efficiency bifacial solar cells. An opening discussion on the state-of-the-art of such advanced technology is initially proposed and the experimental characterization of some prototypes is described. From this analysis, it can be stated that the bifacial silicon solar cells can be a very promising technology with high electrical performances and efficiency.

Multi-bit storage through Si nanocrystals embedded in SiO2

We have realized Si nanocrystal memory cells in which the Si dots have been deposited by CVD on SiO2 and then covered by a CVD control oxide. In this paper, we report a study on the potential of these cells for dual bit storage. © 2004 Elsevier B.V. All rights reserved.

Memory effects in MOS devices based on Si quantum dots

Silicon quantum dots have been deposited on top of a 3-nm tunnel oxide by Low Pressure Chemical Vapour Deposition (LPCVD) and coated with a 7-nm Chemical Vapour Deposited (CVD) oxide. This stack was then incorporated in Metal-Oxide-Semiconductor structure and used as floating gate of a memory cell. The presence of 3 nm of tunnel oxides allows the injection of the charge by direct tunnel (DT) using low voltages for both program and erase operations. The charge stored in the quantum dots is able to produce a well-detectable flat band shift in the capacitors or, equivalently, a threshold voltage shift in the transistors. Furthermore, due to the presence of SiO 2 between the grains, the lateral…

SOCIETA' DELL'INFORMAZIONE E COMPETENZA DELLE REGIONI. IL CORECOM SICILIA

La normativa delle tossicodipendenze e l'azione preventiva della scuola

La neurofibromatosi 1 in età evolutiva: contributo casistico e revisione clinica

How far will Silicon nanocrystals push the scaling limits of NVMs technologies?

For the first time, memory devices with optimized high density (2E12#/cm/sup 2/) LPCVD Si nanocrystals have been reproducibly achieved and studied on an extensive statistical basis (from single cell up to 1 Mb test-array) under different programming conditions. An original experimental and theoretical analysis of the threshold voltage shift distribution shows that Si nanocrystals have serious potential to push the scaling of NOR and NAND flash at least to the 35 nm and 65 nm nodes, respectively.

Memory effects in single-electron nanostructures

We investigate the memory function at room temperature in devices based on quantum dots. By Low Pressure Chemical Vapour Deposition (LPCVD) we deposited Si dots embedded in SiO2. On these devices flat band voltage shifts were well detected at low write voltages for write times of the order of milliseconds, and furthermore, a plateau in the flat band voltage shift, maybe consequence of Coulomb blockdale, was observed.

Effects of partial self-ordering of Si dots formed by chemical vapor deposition on the threshold voltage window distribution of Si nanocrystal memories

We study the role that the denuded zone around Si nanocrystals obtained by chemical vapor deposition plays on the fluctuations of the dot surface coverage. In fact, the capture mechanism of the silicon adatoms in the proximity of existing dots restricts the number of possible nucleation sites, the final dot size, and the dot position, thus driving the process toward partial self-order. We numerically evaluate the relative dispersion of surface coverage for several gate areas and compare the results to the fully random case. The coverage dispersion is related to the fluctuations from bit to bit of the threshold voltage window (Δ Vth) distribution of nanocrystal memories. The evaluations, com…

Obesità nella sindrome di Down: analisi di 320 soggetti in età evolutiva

UN EDEMA MOLTO SOSPETTO IN UN NEONATO IPOTONICO

Localized charge storage in nanocrystal memories: Feasibility of a multi-bit cell

We have realized Si nanocrystal memory cells in which the Si dots have been deposited by chemical vapor deposition (CVD) on the tunnel oxide and then covered by a CVD control oxide. In this paper we report a study on the potential of this type of cells for multi-bit storage. In particular, the possibilities offered by these devices from the point of view of program/erase mechanisms, endurance, and charge retention are shown and discussed.

LONG GAP ESOPHAGEAL ATRESIA AND ASSOCIATED ANOMALIES ATRESIA ESOFAGEA “LONG GAP” ED ANOMALIE ASSOCIATE

Patients with long gap esophageal atresia are often managed with gastrostomy and tube drainage of the proximal pouch, despite the high risk of aspiration and nosocomial infections. Long gap esophageal atresia has been reported in the presence of congenital anomalies, most often within the spectrum of the VACTERL association. We report on three preterm newborns in whom the association of long gap esophageal atresia, prematurity and congenital anomalies led to a significant reduction of the patients' life span, amplifying many clinical problems. Patients with long gap esophageal atresia are often managed with gastrostomy and tube drainage of the proximal pouch, despite the high risk of aspira…

Threshold Voltage Variability of NROM Memories After Exposure to Ionizing Radiation

Threshold voltage (V-th) behavior of nitride readonly memories (NROMs) was studied after irradiation with photons (gamma-and X-rays), light and heavy ions. Both programmed and nonprogrammed single cells were investigated. The data suggest that two main physical phenomena are contributing to V-th variation and that the V-th loss and the variability can be modeled by a Weibull statistics with a shape parameter k similar to 2.2 regardless of the irradiation species and total dose. The same peculiarities were found in large memory arrays, confirming the results from single-cell studies but with significantly larger statistics. Hence, once the irradiation dose is known, the V-th loss distributio…

CY5 fluorescence measured with silicon photomultipliers

This paper presents an efficient optical biosensor set up for a low-level light detection, using fluorescent dyes and a novel Si-based detector. Fluorescence emitted by a traditional fluorophore, CY5, widely used as optical label in DNA microarrays, was detected using a 25 pixels Silicon photomultiplier (SiPM), a device formed by avalanche diodes operating in Geiger mode, in parallel connections. We measured the fluorescence current in different deposition (fluorophore concentration; solvent; salt concentration) and operation (angle of analysis, optical laser power, device gain) conditions. The characterization of DNA samples labeled with CY5 is also reported to demonstrate the detector pot…

Programming options for nanocrystal MOS memories

Nanocrystal memories represent a promising candidate for the scaling of FLASH memories. In these devices, the charge is not stored in a continuous floating gate but in a discontinuous layer composed by numerous discrete silicon quantum dots well separated one from the other.The nanocrystals of radius of few nanometers are realized by chemical vapor deposition (CVD) of silicon on the tunnel oxide of 2.8 nm of thickness. These islands have been coated with a control oxide of 7 nm formed by CVD and incorporated in Metal-Oxide-Semiconductor structure. The devices are programmed and erased by tunnelling using low voltages and fast times. In addition, the programming can be easily achieved also b…

Nanocrystal MOS memories obtained by LPCVD deposition of Si nanograins

We have realized silicon quantum dots embedded in SiO2 which act as nano-floating gates of MOS memories. The dots with nanometer sizes have been deposited by LPCVD on a 3nm tunnel oxide. Two processes at a fixed pressure have been explored by varying the temperature. SiH4 with a N2 carrier gas have been used in the former case, SiH4 and H2 have been used in the latter. In both cases a nanocrystalline silicon layer is obtained, with nanocrystals a density higher than 1011 cm-2. The process with H2 carrier gas is more controllable and leads to the formation of nanocrystals with a more regular shape. In both cases the density of grains is able to originate detectable threshold shifts in the me…

Radiation tolerance of NROM embedded products

Radiation tolerance of NROM memories is demonstrated at the level of industrial 4 Mbit memory embedded modules, specifically not designed for operation in radiation harsh environments. The memory fabricated in 0.18 um technology remains fully functional after total ionization doses exceeding 100 krad. The tests were performed by irradiating with γ-rays (60Co source) and 10 MeV 11B ions in active (during programming/erase and read-out) and passive (no bias) modes. Comprehensive statistics were obtained by using large memory arrays and comparison of the data with the parameters of irradiated single cells allowed deep understanding of the physical phenomena in the irradiated NROM devices for b…

Improvement of DSSC performance by voltage stress application

Dye-sensitized solar cells (DSSCs) are promising third generation photovoltaic devices given their potential low cost and high efficiency. Some factors still affect DSSCs performance, such structure of electrodes, electrolyte compositions, nature of the sensitizers, power conversion efficiency, long-term stability, etc. In this work we discuss the effect of electrical stresses, which allow to improve DSSC performance. We have investigated the outcomes of forward and reverse DC bias stress as a function of time, voltage, and illumination level in the DSSCs sensitized with the N719, Ruthenium complex based dye. We demonstrate that all the major solar cell parameters, i.e., open circuit voltag…