2,203 research outputs found
A Complementary Resistive Switch-based Crossbar Array Adder
Redox-based resistive switching devices (ReRAM) are an emerging class of
non-volatile storage elements suited for nanoscale memory applications. In
terms of logic operations, ReRAM devices were suggested to be used as
programmable interconnects, large-scale look-up tables or for sequential logic
operations. However, without additional selector devices these approaches are
not suited for use in large scale nanocrossbar memory arrays, which is the
preferred architecture for ReRAM devices due to the minimum area consumption.
To overcome this issue for the sequential logic approach, we recently
introduced a novel concept, which is suited for passive crossbar arrays using
complementary resistive switches (CRSs). CRS cells offer two high resistive
storage states, and thus, parasitic sneak currents are efficiently avoided.
However, until now the CRS-based logic-in-memory approach was only shown to be
able to perform basic Boolean logic operations using a single CRS cell. In this
paper, we introduce two multi-bit adder schemes using the CRS-based
logic-in-memory approach. We proof the concepts by means of SPICE simulations
using a dynamical memristive device model of a ReRAM cell. Finally, we show the
advantages of our novel adder concept in terms of step count and number of
devices in comparison to a recently published adder approach, which applies the
conventional ReRAM-based sequential logic concept introduced by Borghetti et
al.Comment: 12 pages, accepted for IEEE Journal on Emerging and Selected Topics
in Circuits and Systems (JETCAS), issue on Computing in Emerging Technologie
Resistive Switching Assisted by Noise
We extend results by Stotland and Di Ventra on the phenomenon of resistive
switching aided by noise. We further the analysis of the mechanism underlying
the beneficial role of noise and study the EPIR (Electrical Pulse Induced
Resistance) ratio dependence with noise power. In the case of internal noise we
find an optimal range where the EPIR ratio is both maximized and independent of
the preceding resistive state. However, when external noise is considered no
beneficial effect is observed.Comment: To be published in "Theory and Applications of Nonlinear Dynamics:
Model and Design of Complex Systems", Proceedings of ICAND 2012 (Springer,
2013
Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties
Ferroelectric and dielectric properties of polydomain (twinned)
single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a
nonlinear thermodynamic theory, which has been developed recently for epitaxial
ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3
(PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit
strain-temperature" phase diagrams are calculated and compared with each other.
It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar
to the diagram of PbTiO3 films. They consist of only four different stability
ranges, which correspond to the paraelectric phase, single-domain tetragonal
ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at
x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of
stable polarization states, involving at least one monoclinic polydomain state.
Using the developed phase diagrams, the mean out-of-plane polarization of a
poled PZT film is calculated as a function of the misfit strain and
composition. Theoretical results are compared with the measured remanent
polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane
dielectric response of PZT films on the misfit strain in the heterostructure is
also reported.Comment: 23 pages, 4 figure
Resistive switching effects on the spatial distribution of phases in metal-complex oxide interfaces
In order to determine the key parameters that control the resistive switching
mechanism in metal-complex oxides interfaces, we have studied the electrical
properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different
oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the
surface of a YBCO ceramic sample. By analyzing the IV characteristics of the
contact interfaces and the temperature dependence of their resistance, we
inferred that ion migration may generate or cancel conducting filaments, which
modify the resistance near the interface, in accordance with the predictions of
a recent model.Comment: 3 pages, 5 figures, to be published in Physica B. Corresponding
author: C. Acha ([email protected]
Applicability of Well-Established Memristive Models for Simulations of Resistive Switching Devices
Highly accurate and predictive models of resistive switching devices are
needed to enable future memory and logic design. Widely used is the memristive
modeling approach considering resistive switches as dynamical systems. Here we
introduce three evaluation criteria for memristor models, checking for
plausibility of the I-V characteristics, the presence of a sufficiently
non-linearity of the switching kinetics, and the feasibility of predicting the
behavior of two anti-serially connected devices correctly. We analyzed two
classes of models: the first class comprises common linear memristor models and
the second class widely used non-linear memristive models. The linear memristor
models are based on Strukovs initial memristor model extended by different
window functions, while the non-linear models include Picketts physics-based
memristor model and models derived thereof. This study reveals lacking
predictivity of the first class of models, independent of the applied window
function. Only the physics-based model is able to fulfill most of the basic
evaluation criteria.Comment: 9 pages; accepted for IEEE TCAS-
Characterization of the Active Site of Acetylcholinesterases by Application of Sterically Modified Acetylcholine Homologues
Our aim was to find steric limitations for the model of the
active site of acetylcholinesterase and cho1inesterase. For thi<s purpose
we used homologues of acetylcholine with hydrocarbon chains
of increasing size at the cationic head. Catalysis of hydrolysis
ceased for both enzymes, when the methyl groups of the cationic
head of acetylcholine were substituted by three n-propyl groups.
With data already documented in the literature and our additional
experiments, under the same conditions, we were able to present
models of the active sites for both enzymes
DISTRIBUTION AND KINETICS OF 14C-VECURONIUM IN RATS AND MICE
The distribution and kinetics of 14C-vecuronium were studied in rats and mice. 14C-Vecuronium accumulated rapidly in the liver. Both unchanged and metabolized vecuronium were excreted with the bile into the intestines and stomach. Reabsorption in the gut was probably responsible for an enterohepatic increase in radioactivity in the liver after one hour. Excretion through the kidneys increased continuously from low values after the initial peak. Binding in compartments with acid mucopolysaccharides such as cartilage, connective tissue etc., was less important. Bloodbrain barrier and placenta were permeable only to a small degre
Coercive field of ultrathin PbZr0.52Ti0.48O3 epitaxial films
The polarization reversal in single-crystalline ferroelectric films has been investigated experimentally and theoretically. The hysteresis loops were measured for Pb(Zr0.52Ti0.48)O-3 films with thicknesses ranging from 8 to 250 nm. These films were grown epitaxially on SrRuO3 bottom electrodes deposited on SrTiO3 substrates. The measurements using Pt top electrodes showed that the coercive field E-c increases drastically as the film becomes thinner, reaching values as high as E(c)approximate to1200 kV/cm. To understand this observation, we calculated the thermodynamic coercive field E-th of a ferroelectric film as a function of the misfit strain S-m in an epitaxial system and showed that E-th strongly depends on S-m. However, the coercive field of ultrathin films, when measured at high frequencies, exceeds the calculated thermodynamic limit. Since this is impossible for an intrinsic coercive field E-c, we conclude that measurements give an apparent E-c rather than the intrinsic one. An enormous increase of apparent coercive field in ultrathin films may be explained by the presence of a conductive nonferroelectric interface layer. (C) 2003 American Institute of Physics
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