Insights on the variability of Cu filament formation in the SiO2 electrolyte of quantized-conductance conductive bridge random access memory devices

Conductive bridge random access memory devices such as Cu/SiO2/W are promising candidates for applications in neuromorphic computing due to their fast, low-voltage switching, multiple-conductance states, scalability, low off-current, and full compatibility with advanced Si CMOS technologies. The conductance states, which can be quantized, originate from the formation of a Cu filament in the SiO2 electrolyte due to cation-migration-based electrochemical processes. A major challenge related to the filamentary nature is the strong variability of the voltage required to switch the device to its conducting state. Here, based on a statistical analysis of more than hundred fifty Cu/SiO2/W devices, we point to the key role of the activation energy distribution for copper ion diffusion in the amorphous SiO2. The cycle-to-cycle variability is modeled well when considering the theoretical energy landscape for Cu diffusion paths to grow the filament. Perspectives of this work point to developing strategies to narrow the distribution of activation energies in amorphous SiO2

Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

For contacting boron emitters by screen-printing metal pastes, up to now, it has been necessary to add a small amount of Al to the Ag paste to facilitate a reasonable contact resistivity. With the addition of Al to the Ag paste, deep Ag/Al spikes appear, which can be deep enough to penetrate the emitter and, therefore, affect the emitter and space charge region, and, finally, affect the performance of the solar cell. In this paper, a transmission electron microscopy (TEM) analysis of these Ag/Al spikes is presented. The crystalline nature of the Ag/Al spikes is revealed for different surface structures of the crystalline Si wafer and different Al contents in the screen-printing paste. This result is confirmed by X-ray diffraction measurements of etched-back contacts. Additionally, TEM energy-dispersive X-ray spectroscopy facilitates the examination of the Si-rich inclusions found in the Ag/Al spikes. They prove to be multicrystalline Si precipitates with at least 99 at% Si. The observations help to understand the contact formation process of Al containing Ag screen-printing pastes and support the previously presented model.publishe

CURLED POLARIZATION NANODOMAINS IN (BaTiO3/SrTiO3) EPITAXIAL SUPERLATTICES ON SILICON

The discovery of exotic polarization textures in low-dimensional SrTiO3-PbTiO3 heterostructures grown on DyScO3 has sparked tremendous interest in nanoscale ferroelectric superlattices [1-3]. The unusual rotational polarization patterns in these heterostructures lead to emergent properties such as negative capacitance effect and chirality [4-6]. To make use of these novel functionalities in electronic devices, the integration of polar textures on a silicon platform is necessary. Here, we fabricated BaTiO3-SrTiO3 superlattices on silicon by molecular beam epitaxy and studied their crystalline structure and polarization pattern

Correction to Understanding Anomalous Gas-Phase Peak Shifts in Dip-and-Pull Ambient Pressure XPS Experiments.

[This corrects the article DOI: 10.1021/acs.jpcc.4c00113.]

ZnO@TiO2 Core Shell Nanorod Arrays with Tailored Structural, Electrical, and Optical Properties for Photovoltaic Application

ZnO has prominent electron transport and optical properties, beneficial for photovoltaic application, but its surface is prone to the formation of defects. To overcome this problem, we deposited nanostructured TiO2 thin film on ZnO nanorods to form a stable shell. ZnO nanorods synthesized by wet-chemistry are single crystals. Three different procedures for deposition of TiO2 were applied. The influence of preparation methods and parameters on the structure, morphology, electrical and optical properties were studied. Nanostructured TiO2 shells show different morphologies dependent on deposition methods: (1) separated nanoparticles (by pulsed laser deposition (PLD) in Ar), (2) a layer with nonhomogeneous thickness (by PLD in vacuum or DC reactive magnetron sputtering), and (3) a homogenous thin layer along the nanorods (by chemical deposition). Based on the structural study, we chose the preparation parameters to obtain an anatase structure of the TiO2 shell. Impedance spectroscopy shows pure electron conductivity that was considerably better in all the ZnO@TiO2 than in bare ZnO nanorods or TiO2 layers. The best conductivity among the studied samples and the lowest activation energy was observed for the sample with a chemically deposited TiO2 shell. Higher transparency in the visible part of spectrum was achieved for the sample with a homogenous TiO2 layer along the nanorods, then in the samples with a layer of varying thickness

Complexions at the Electrolyte/Electrode Interface in Solid Oxide Cells

Rapid deactivation presently limits a wide spread use of high-temperature solid oxide cells (SOCs) as otherwise highly efficient chemical energy converters. With deactivation triggered by the ongoing conversion reactions, an atomic-scale understanding of the active triple-phase boundary (TPB) between electrolyte, electrode and gas phase is essential to increase cell performance. Here we use a multi-method approach comprising transmission electron microscopy and first-principles calculations and molecular simulations to untangle the atomic arrangement of the prototypical SOC interface between a lanthanum strontium manganite (LSM) anode and an yttria-stabilized zirconia (YSZ) electrolyte. We identify an interlayer of self-limited width with partial amorphization and strong compositional gradient, thus exhibiting the characteristics of a complexion that is stabilized by the confinement between two bulk phases. This offers a new perspective to understand the function of SOCs at the atomic scale. Moreover, it opens up a hitherto unrealized design space to tune the conversion efficiency

Nanocrystal formation in silicon oxy-nitride films for photovoltaic applications: Optical and electrical properties

Thin films of nanocrystalline SiOxNy are studied in view of their application in silicon heterojunction (SHJ) solar cells. In particular, the formation of the nanocrystals and their effects on the electrical and optical properties of the films are investigated. The role of the oxygen content on the properties of the layers is clarified as well. The obtained layers show very high conductivity (44 S/cm), low activation energy (1.85 meV) and high Tauc gap (2.5 eV), promising features for their application in photovoltaics